1
DISSERTATION ON
TO ESTIMATE THE CORRELATION BETWEEN
SERUM SIALIC ACID LEVELS WITH
MICROALBUMINURIA AND GLYCATED HEMOGLOBIN
IN DIABETIC NEPHROPATHY PATIENTS
Dissertation submitted to
TAMILNADU Dr.M.G.R MEDICAL UNIVERSITY
In partial fulfillment of the requirement
for the award of degree of
MD BRANCH -XIII
IN
BIO-CHEMISTRY
KARPAGA VINAYAGA INSTITUTE OF MEDICAL SCIENCES
AND RESEARCH CENTRE
MADHURANTHAGAM.
THE TAMIL NADU DR. M.G.R. MEDICAL UNIVERSITY, CHENNAI,
TAMILNADU.
2
CERTIFICATE
This is to certify that Dr.K.PIRUTHIVIRAJAN, a Post Graduate student
in the Department of Bio-Chemistry has carried out the work titled “TO
ESTIMATE THE CORRELATION BETWEEN SERUM SIALIC ACID
LEVELS WITH MICROALBUMINURIA AND GLYCATED
HEMOGLOBIN IN DIABETIC NEPHROPATHY PATIENTS” under the
guidance of Dr.ARUNA KUMARI, Professor and Head, Dept. of
Bio-Chemistry, towards the partial fulfilment of regulations laid down by the
Tamilnadu Dr.M.G.R Medical University, Chennai, Tamilnadu, India, for the
award of Doctor of Medicine (M.D.,) in Bio-Chemistry.
Dr .A.R. Chakravarthy.MD, DGO,
Dean,
Karpaga Vinayaga Institute of Medical Sciences and Research Centre
Madurantagam Tk,
Kancheepuram Dist-603308 Tamilnadu, India.
Prof. Dr.ARUNA KUMARI.,M.D., PROFESSOR AND HEAD
DEPARTMENT OF BIO-CHEMISTRY Karpaga Vinayaga Institute of Medical Sciencesand Research Centre
Madurantagam Tk,
3
DECLARATION
I declare that the dissertation entitled “TO ESTIMATE THE
CORRELATION BETWEEN SERUM SIALIC ACID LEVELS WITH
MICROALBUMINURIA AND GLYCATED HEMOGLOBIN IN
DIABETIC NEPHROPATHY PATIENTS” submitted by me for the Degree
of M.D is the record work carried out by me during the period of January 2014
to March 2015 under the guidance of Dr.ARUNA KUMARI.M.D.,
PROFESSOR and H.O.D of Bio-Chemistry, Karpaga Vinayaga Institute of
Medical Sciences and Research Centre and has not formed the basis of any
Degree ,Diploma, Fellowship, titles in this or any other University or other
similar Institutions of Higher learning.
Signature of the candidate
Place: Dr.K.PIRUTHIVIRAJAN
Date:
Signature of the guide
Dr.ARUNA KUMARI.MD.,
H.O.D & Professor
Karpaga Vinayaga Institute of medical Sciences and Research Centre,
4
ACKNOWLEDGEMENT
My heartfelt gratitude and sincere thanks to
Dr. R. Annamalai.MS.MCh.,(Ortho) Managing Director, Karpaga Vinayaga
Institute of Medical Sciences for his valuable support and guidance in helping
me with all available resources..
I wish to thank Dr.A.R.Chakravarthy.MD.DGO., Dean Karpaga
Vinayaga Institute of Medical Sciences and Research Centre for providing me all
the facilities to conduct this study.
I express my sincere thanks to my esteemed guide Dr.ARUNA
KUMARI,M.D., Professor and Head in the Department of Bio-Chemistry,
Karpaga Vinayaga Institute of Medical Sciences and Research Centre for her
encouragement and valuable guidance in the topic given from time to time for
the successful completion of this study.
I am also thankful to Dr.D.PREM KUMAR.MS., Medical
Superintendent, Dr.S.SWETHA,M.D., and Dr.KATHEEJA,M.D., Assistant
Professors in the Department of Bio-Chemistry, Karpaga Vinayaga Institute of
Medical Sciences and Research Centre for their kind guidance and
encouragement during the course of this study.
I am extremely thankful to Mr.Saravanan.,M.Sc., Department of
Bio-Chemistry, Karpaga Vinagaya Institute of Medical Sciences and Research
5
I convey my valuable thanks to all the Post Graduate colleagues of
Department of Bio-Chemistry for their greatest support and co-operation in
completing my dissertation.
I also thank my technical staffs and nontechnical staffs of department of
Bio-Chemistry and the Central Lab for their excellent help in laboratory work.
Finally, I am deeply indebted to my parents, my wife Dr.P.KALAI
SELVI , my daughter NIVEDHITHA PIRUTHIVIRAJAN and my son
K.P.ESHWAANTH KEERTHI for their support, encouragement and sacrifice
during the study period.
6
TABLE OF CONTENTS
S.
NO.
TITLE
PAGE
NO.
1. INTRODUCTION 01
2. AIMS AND OBJECTIVES 04
3. REVIEW OF LITERATURE 05
4. MATERIALS AND METHODS 46
5. RESULTS 52
6. DISCUSSION 67
7. SUMMARY 72
8. CONCLUSION 75
9. ANNEXURES
7
INTRODUCTION
“Diabetes mellitus” is the major healthcare problem occurring all over the
world. “Diabetes mellitus”, the most common endocrine disease is represented
by “metabolic abnormalities” due to relative or absolute deficiency of insulin and
or insulin resistance resulting in “hyperglycemia” and associated with “micro
and macrovascular complications”.1
Diabetes is not an epidemic anymore but has turned into pandemic for the
whole world.2 The universal survey reported that diabetes is disturbing nearly
10% of the inhabitants.3 According to the “World Health Organization (WHO)”
projections, the predominance of diabetes is likely to augment by 35% by the
year 2025.4 India has a elevated predominance of diabetes and the numbers are
increasing.5
“Diabetes mellitus” presents with characteristic symptoms such as
“polydipsia, polyuria, polyphagia, weight loss and the long-term effects include
progressive development of microvascular complications, particularly in the eye
and kidney, and an increased frequency of macrovascular disease such as
peripheral vascular and coronary heart disease”.6 “Diabetes mellitus” is the most
important reason of “End Stage Renal Disease (ESRD)”. It is responsible for
30-40 % of all ESRD. Even though “Type 1 and Type 2 DM” lead to ESRD, most
of the patients are those with “Type 2 DM”7
“Diabetic renal disease” is categorized by an augment in the “flow of
8
pressure” and decrease in the rate of filtration in the “glomerulus” most
important ultimately to “End Stage Renal Disease”.7 “Reactive oxygen species
(ROS)” increase is caused by “Hyperglycemia”. “Poly ADP-ribose polymerase
(PARP)” is activated by stand breaks in DNA. Decreased
“glyceraldhyde-3-phosphate dehydrogenase (GAPDH)”, activity causes augmented “polyol
pathway flux, intracellular advanced glycation end product formation, activation
of protein kinase C and hexosamine pathway flux”.8,9 These pathways in
combination, finally results in high renal albumin permeability and extracellular
matrix growth, resulting in “proteinuria, glomerulosclerosis and tubular
interstitial fibrosis”.10
“Serum sialic acid” is a recently recognized possible risk factor for the
rise of “macro and microvascular complications of diabetes”.11 “Serum sialic
acid” is a part of “glycoprotein” such as acute phase proteins which are increased
in diabetes. The possible mechanism linked with the function of sialic acid is to
maintain the “negative charge of renal glomerular basement membrane”. Due to
increased “vascular permeability” there is shedding of “vascular endothelial
sialic acid into circulation”.12
“Microalbuminuria” is the earliest manifestation of “diabetic
nephropathy” and it is the predictor of incipient nephropathy in diabetic patients.
“Glycated haemoglobin” is a standard measure of severity of diabetes mellitus
and gives an idea about long term “glycemic control”. “Microalbuminuria” arise
from the amplified passage of albumin throughout the “glomerular filtration”
9
due to “renal disease” is more frequent in diabetics than in non diabetics.7 If
obvious nephropathy is present, progression cannot be stopped, only delayed.
Susceptible tests for “microalbuminuria” are needed to avoid the initial
stages of injury by forceful control of “hyperglycemia and hypertension”.
Several studies have demonstrated increased “serum sialic acid levels in diabetic
nephropathy patients” when compared to controls.11
Thus, the present study was intended to explore the role of “serum sialic
acid” as a dangerous factor in the progress of “diabetic nephropathy” and to
associate the clinical relationship of “serum sialic acid with glycated
haemoglobin and the indicator of diabetic nephropathy such as
10
AIM OF THE STUDY
-
To estimate the serum sialic acid levels in diabetic nephropathy
patients.
-
To know the correlation between serum sialic acid and
microalbuminuria in diabetic nephropathy patients.
-
To know the correlation between serum sialic acid and glycated
11
REVIEW OF LITERATURE
HISTORICAL REVIEW OF DIABETES MELLITUS:
The clinical characteristics of diabetes were depicted 3000 years prior by
the customary Egyptians. The expression "diabetes" was first authored by
Araetus of Cappodocia (81-133 AD). “United Nations organization” presented a
“clinical portrayal of the infection”, detecting the “increased urine flow, thirst,
appetite and weight reduction”, highlights which are immediately identifiable
now a days.The sweet taste of urine in “polyuric diabetics”, which congregated
ants was observed during the 5th and 6th century AD by “ancient Indians (Susruta
and Charuka)” and these descriptions even mention 2 varieties of diabetes, one in
older (adult onset), obese individuals and another in thin and younger subjects
and this division predated the modem classification into “type 2 and type 1
diabetes”. Later, Thomas Willis rediscovered the sweetness of diabetic urine in
1675.14
In 1776, Matthew Dobson in the UK made the vital scrutiny, confirmed
that the sweetness in both urine and serum was due to sugar, and suggested that
diabetes is a common disease. “Cotunnius, who described the parting of a clot in
heated diabetic urine, first discovered the presence of proteinuria in a diabetic
patient in 1764”.15
In 1797, an effort at treatment began on the “origin of glycosuria and
polyuria”, John Rollo executed a detailed metabolic study of a “plump diabetic”,
and he showed that the degree of “glycosuria” depended upon the type of food
12
presumably those in an advanced stage of type 1 diabetes and he also observed
cataracts in diabetics”.15
In 1857, “an important milestone in the history of diabetes was the
establishment of the role of the liver in glycogenesis and the concept that
diabetes was due to excess glucose production,” which was discovered by
Claude Bernard, and he also demonstrated links between the central nervous
system dysfunction and the diabetic state.16
In 1869, Paul Langerhans was the first to describe, pancreatic clusters of
cells in teased preparations of pancreas which are now known as the "Islets of
Langerhans" and “the role of the pancreas in the pathogenesis of diabetes” was
confirmed by Mering and Minkowski in1889. Consequently, this discovery
constituted the basis of insulin isolation and its clinical use by Banting and Best
in 1921.
The difficulties of diabetes influencing the eyes, to be specific “Diabetic
retinopathy”, had been depicted before the revelation of insulin but it was a rarity
because few diabetics lived long enough to develop “retinopathy and
glomerulosclerosis”, which gradually progressed to “renal failure and death and
this condition” was named the "Kimmelstiel-Wilson" nodules after its American
and British co-discoverers in 1936. Moreover, with longer survival of diabetic
subjects, consequences influencing the peripheral and later the autonomic,
“sensory system and gestational diabetes were portrayed”. On the other hand, at
present, “diabetes mellitus” contains a “heterogeneous” gathering of complex
13
“varied consequences and hyperglycaemia” which is the cardinal element of
these conditions and has accordingly been utilized to characterize diabetes .16
“Diabetes mellitus (DM)” is a collection of “metabolic syndrome with
hyperglycemia”. “It is associated with abnormalities in carbohydrate, fat, and
protein metabolism and results in chronic complications including
micro-vascular, macro-micro-vascular, and neuropathic disorders”.
The economic burden of DM, including direct restorative and treatment
costs and additionally backhanded expenses ascribed to inability and mortality
have expanded considerably. “DM is the leading cause of blindness in adults
aged 20 to 74 years, and the leading contributor to development of end stage
renal disease”. It likewise represents roughly 82,000 lower limb removals
annually.17 “The cardiovascular event is responsible for two-thirds of deaths in
individuals with type 2 DM. Although efforts to control hyperglycemia and
associated symptoms are important, the major challenges in optimally managing
the patient with DM are targeted at reducing or preventing complications, and
improving life expectancy and quality of life.”
Research and drug advancement endeavours in the course of recent
decades have given significant data that applies specifically to enhance the
results in patients with DM and have expanded the “therapeutic
14
Characterization of Diabetes:
Diabetes is a metabolic disorder characterized by resistance to the action
of insulin, insufficient insulin secretion, or both.18 The clinical indication of these
issue is “hyperglycemia”. The dominant part of diabetic patients are
characterized into one of two general classifications: “type 1 diabetes caused by
an absolute deficiency of insulin, or type 2 diabetes defined by the presence of
insulin resistance with an inadequate compensatory increase in insulin
secretion”. Females who generate diabetes due to the “stress of pregnancy” are
classified as having “gestational diabetes”. Finally, uncommon types of diabetes
“caused by infections, drugs, endocrinopathies, pancreatic destruction, and
known genetic defects”.
Type 1 Diabetes:
Occurs due to autoimmune destruction of the β-cells of the pancreas.
Markers of “immune destruction of the B-cell” are available at the time of
diagnosis in 90% of people and “incorporate islet cell antibodies, antibodies to
glutamic acid decarboxylase and antibodies to insulin”. In spite of the fact that
this type of diabetes normally happens in children and adolescents, it can happen
at any age. More young people ordinarily have a “rapid rate of β-cell destruction
and present with ketoacidosis”, whereas “adults often maintain sufficient insulin
secretion to prevent ketoacidosis for many years, which is often referred to as
15
Type 2 Diabetes:
It is described by insulin resistance and a relative absence of insulin
secretion, with progressive lower insulin secretion after some time. Most people
with “type 2 diabetes” show abdominal obesity, which itself cause insulin
resistance. Furthermore, “hypertension, dyslipidemia and increased Plasminogen
Activator Inhibitor Type 1 (PAI-1) levels” are regularly present in these people.
This “clustering of abnormalities” is referred to as the “insulin resistance
syndrome or the metabolic syndrome”. Because of these abnormalities, “patients
with type 2 diabetes” are at increased risk of “developing macrovascular
complications”. “Type 2 diabetes” has a strong “genetic predisposition” and is
more common in all ethnic groups other than those of “European ancestry”. At
this point the genetic cause of most cases of “type 2 diabetes” is not well
defined.20
Gestational diabetes mellitus: (GDM)
“GDM is characterized as glucose intolerance first recognized during
pregnancy. Gestational diabetes complicates approximately 7% of all
pregnancies.”
Other particular types of diabetes (Genetic imperfections):
“Maturity-onset diabetes” of youth is described by impaired insulin
secretion with minimal or no insulin resistance. Patients typically exhibit “mild
hyperglycemia” at an early age. The ailment is acquired in an “autosomal
dominant pattern” with no less than six distinctive loci recognized to date.
16
hyperglycemia” and is acquired in an autosomal dominant pattern. Also, the
generation of mutant insulin molecules has been distinguished in a couple of
families and results in gentle “glucose intolerance”. A few hereditary changes
have been portrayed in the “insulin receptor” and are connected with “insulin
resistance”.
“Type A insulin resistance” alludes to the “clinical disorder of acanthosis
nigricans, virilization in ladies, polycystic ovaries, and hyperinsulinemia”.
Conversely, “type B insulin resistance” is brought on via auto antibodies to the
insulin receptor.
“Leprechaunism is a pediatric syndrome” with specific facial features and
severe insulin resistance because of a defect in the insulin receptor gene. 21
Prevalence:
The worldwide commonness of diabetes in 2008 was assessed to be 10%
in grown-ups matured >25 years. The predominance of diabetes was most
noteworthy in “Eastern Mediterranean Region and the Region of Americas (11%
for both genders)”. The lower economic nations over the world demonstrated
predominance of 8%.
In India, the results of prevalence showed that 37.7 million people of
diabetes were present among which 21.4 were in urban area and 16.3 in rural
area. The total mortality due to diabetes was 1.09 lakh and around 2.2 million
17
Epidemiology:
Typical “type 1 DM is an autoimmune disorder” developing in childhood
or early adulthood, although some latent forms do occur. “Type 1 DM” accounts
for 5% to 10% of all cases of DM and is likely initiated by the exposure of a
genetically susceptible individual to an environmental agent.23 “Candidate genes
and environmental factors” are reportedly prevalent in the general population,
but “development of B-cell autoimmunity” occurs in less than 10% of the
“genetically susceptible population” and progresses to “type 1 DM” in less than
1% of the population.24
The pervasiveness of “type 2 DM” is expanding. There is likely one
individual undiscovered for each three persons as of now determined to have the
sickness. “Multiple risk factors” for the advancement of “type 2 DM” have been
recognized, including family history (i.e., folks or kin with diabetes); over
weight (i.e., ≥20% over perfect body weight, or body mass list [BMI] ≥25
kg/m2); “habitual physical inactivity; race or ethnicity; previously identified
impaired glucose tolerance or impaired fasting glucose, hypertension (≥140/90
mm Hg in adults); high-density lipoprotein (HDL) cholesterol ≤35 mg/dL and/or
a triglyceride level ≥250 mg/dL; history of gestational DM or delivery of a baby
weighing >4 kg (9 lb); history of vascular disease; presence of acanthosis
nigricans and polycystic ovary disease”.25
Most instances of “type 2 DM” do not have an understood reason.
18
in the United States.27 Most females will come back to “normoglycemia”, yet
30% of them tend to have “type 2 DM” later in their life.
Pathogenesis of Type 1 Diabetes Mellitus:
Type 1 DM is portrayed by a lack of pancreatic β-cell function. What is
clear are four primary components: “(1) a long preclinical period marked by the
presence of immune markers when β-cell destruction is thought to occur; (2)
hyperglycemia when 80% to 90% of β-cells are destroyed; (3) transient
remission (the so-called honeymoon phase); and (4) established disease with
associated risks for complications and death. Unknown is whether there is one or
more inciting factors (e.g., cow’s milk, or viral, dietary, or other environmental
exposure) that initiate the autoimmune process”.20
The immune system procedure is interceded by “macrophages” and “T
lymphocytes” with “auto antibodies to different β-cell antigens” that circulate in
the body. The most normally recognized immune response connected with “type
1 DM” is the islet cell counter acting agent. The test for islet “cell immune
response”, is hard to institutionalize crosswise over research facilities. Other all
the more promptly measured circulating antibodies incorporate insulin auto
antibodies, antibodies coordinated against “glutamic acid decarboxylase”, insulin
antibodies against islet “tyrosine phosphatise”, and a few others. More than 90%
of recently determined persons to have “type 1 DM” have some of these
antibodies, as will 3.5% to 4% of unaffected first-degree relatives. “Preclinical
β-cell autoimmunity” goes before the determination of “type 1 DM” by up to 9 to
19
persons”, or can advance to failure of the “B-cells” in others. These antibodies
are by and large considered as markers of sickness instead of “β-cell
destruction”. They have been utilized to recognize people at risk for “type 1
DM” in assessing illness avoidance strategies.
Other non pancreatic immune system issue are connected with “type 1
DM”, most often “Hashimoto's thyroiditis”, yet the degree of organ contribution
can extend from no different organs to “polyglandular failure”.28 Other applicant
quality areas have been recognized on a few different chromosomes also. Since
twin studies don't demonstrate 100% concordance, ecological agents like
infection, chemicals, and diet are more likely to contribute to the disease.
“Annihilation of pancreatic β-cell function causes hyperglycemia” in view of an
outright lack of “both insulin and amylin”.29 Insulin brings down blood glucose
by a mixture of components including: incitement of tissue glucose uptake,
concealment of glucose generation by the liver, and decrease of free unsaturated
fat discharge from fat cells.30
The decrease of free unsaturated fats assumes a critical part in glucose
homeostasis. Enhanced levels of free unsaturated fats restrain the uptake of
glucose by muscle and induces hepatic gluconeogenesis.31 Amylin, a
glucoregulatory peptide hormone co-discharged with insulin, assumes a part in
slowing so as to “bring down blood glucose gastric emptying, supressing
glucagon yield cells, and expanding satiety from pancreatic β-cell.”32 In type 1
20
Pathogenesis of Type 2 Diabetes Mellitus:
Normal Insulin Action:
During Fasting, 75% of aggregate “body glucose transfer happens in non–
insulin dependent tissues: the cerebrum and splanchnic tissues (liver and
gastrointestinal tissues)”.33 Actually, brain glucose uptake happens at the same
rate amid bolstered and fasting periods and is not modified in type 2 diabetes.
The rest of the 25% of glucose uptake happens in muscle, which is reliant on
insulin.34 In the fasting state more or less 85% of glucose is received from the
liver, and the remaining sum is delivered by the kidney.33-35
Glucagon, delivered by pancreatic β-cells, is discharged in the fasting
state to restrict the activity of insulin and invigorate hepatic glucose creation. In
this way, glucagons forestall hypoglycemia or restores normoglycemia if
hypoglycemia has occurred.36
In the fed state, starch ingestion builds the plasma glucose focus and
invigorates insulin discharge from the pancreatic β-cells. The resultant
hyperinsulinemia decreases hepatic glucose and increases glucose uptake by the
tissues in the periphery.37 “The majority (~80%–85%) of glucose that is taken up
by peripheral tissues is disposed in muscle, with only a small amount (~4%–5%)
being metabolized by adipocytes. In the fed state, glucagon is suppressed. 36”
“Although fat tissue is responsible for only a small amount of total body
glucose disposal, it plays a very important role in the maintenance of total body
glucose homeostasis. Small increments in the plasma insulin concentration exert
21
fatty acid (FFA) level. The decline in plasma FFA concentration results in
increased glucose uptake in muscle38 and reduces hepatic glucose production.39
Thus a decrease in the plasma FFA concentration lowers plasma glucose by both
decreasing its production and enhancing the uptake in muscle.40,41”
“Type 2 diabetic individuals are characterized by (a) defects in insulin
secretion; and (b) insulin resistance involving muscle, liver, and the adipocyte.
Insulin resistance is present even in lean type 2 diabetic individuals.”
(a)Impaired insulin secretion:
“The pancreas in people with a cell is able to adjust its secretion of insulin to
maintain normal functioning β- normal glucose tolerance. Thus, in non-diabetic
individuals, insulin is increased in proportion to the severity of the insulin
resistance, and glucose tolerance remains normal.”
“Impaired insulin secretion is a uniform finding in type 2 diabetic patients
and the evolution of β-cell dysfunction has been well characterized in diverse
ethnic populations. As the FPG concentration increases from 80 to 140 mg/dl,
the fasting plasma insulin concentration increases progressively, peaking at a
value that is 2- to 2.5- fold greater than in normal weight nondiabetic controls.
When the FPG cell is unable to maintain its elevated concentration exceeds 140
mg/dL, the β- rate of insulin secretion, and the fasting insulin concentration
declines precipitously. This decrease in fasting insulin leads to an increase in
hepatic glucose production overnight, which results in an elevated FPG
concentration.42 In the type 2 diabetic patient, decreased postprandial insulin
22
stimulus for insulin secretion from gut hormones. The role gut hormones play in
insulin secretion is best shown by comparing the insulin response to an oral
glucose load versus an isoglycemic intravenous glucose infusion.”43
“In nondiabetic control individuals, 73% more insulin is released in response
to an oral glucose load compared to the same amount of glucose given
intravenously. This increased insulin secretion in response to an oral glucose
stimulus is referred to as the incretin effect and suggests that gut derived
hormones when stimulated by glucose lead to an increase in pancreatic insulin
secretion. In type 2 diabetic patients this incretin effect is blunted, with the
increase in insulin secretion to only 50% of that seen in nondiabetic control
individuals.43 It is now known that two hormones, glucagon-like peptide-1
(GLP-1) and glucose-dependent insulin-releasing peptide (GIP), are responsible for
more than 90% of the increased insulin secretion seen in response to an oral
glucose load. In patients with type 2 diabetes GLP- 1 levels are reduced whereas
GIP levels are increased.44 GLP-1 is secreted from the L-cells in the distal
intestinal mucosa in response to mixed meals. Because GLP-1 levels increase
within minutes of food ingestion, neural signals initiated by food entry in the
proximal gastrointestinal tract must simulate GLP-1 secretion.45 The
insulinotropic action of GLP-1 is glucose-dependent, and for GLP-1 to enhance
insulin secretion, glucose concentrations must be higher than 90 mg/dL.”44
“In addition to stimulating insulin secretion, GLP-1 suppresses glucagon
secretion, slows gastric emptying and reduces food intake by increasing satiety.
23
secreted by K-cells in the intestine and like GLP, increase insulin secretion. 46
However, GIP has no effect on glucagon secretion, gastric motility, or satiety.” 47
(a)Site of insulin resistance in type 2 diabetes:
Liver:
“In type 2 diabetic subjects with mild to moderate fasting hyperglycemia
(140 to 200 mg/dl, 7.8 to 11.1 mmol/l) basal hepatic glucose production is
increased by ~0.5 mg/kg per minute. Consequently, during the overnight
sleeping hours the liver of an 80-kg diabetic individual with modest fasting
hyperglycemia adds an additional 35 g of glucose to the systemic circulation.
This increase in fasting hepatic glucose production is the cause of fasting
hyperglycemia.”33
“Following glucose ingestion, insulin is secreted into the portal vein and
carried to the liver, where it suppresses glucagon secretion and reduces hepatic
glucose output. Type 2 diabetic patients fail to suppress glucagon in response to
a meal and can even have a paradoxical rise in glucagon levels.48,49 Thus, hepatic
insulin resistance and hyperglucagonemia result in continued production of
glucose by the liver. Therefore, type 2 diabetic patients have two sources of
glucose in the postprandial state, one from the diet and one from continued
glucose production from the liver. These sources of glucose in combination with
a shortened gastric emptying time can result in marked hyperglycemia.”
Peripheral (Muscle):
“Muscle is the major site of glucose disposal in man, and approximately
24
physiologic increase in plasma insulin concentration, muscle glucose uptake
increases linearly, reaching a plateau value of 10 mg/kg per minute. In contrast,
in lean type 2 diabetic subjects, the onset of insulin action is delayed for ~40
minutes, and the ability of insulin to stimulate leg glucose uptake is reduced by
50%. Therefore the primary site of insulin resistance in type 2 diabetic subjects
resides in muscle tissue.”33
Peripheral (Adipocyte):
In obese nondiabetic and diabetic humans, basal plasma FFA levels are
increased and fail to suppress normally after glucose ingestion. FFAs are stored
as triglycerides in adipocytes and serve as an important energy source during
conditions of fasting. Insulin is a potent inhibitor of lipolysis, and restrains the
release of FFAs from the adipocyte by inhibiting the hormone-sensitive lipase
enzyme. It is now recognized that chronically elevated plasma FFA
concentrations can lead to insulin resistance in muscle and liver, 33,38,40,50 and
impair insulin secretion.51,52 In addition to FFAs that circulate in plasma in
increased amounts, type 2 diabetic and obese nondiabetic individuals have
increased stores of triglycerides in muscle53,54 and liver 55,56 and the increased fat
content correlates closely with the presence of insulin resistance in these tissues.
In summary, insulin resistance involving both muscle and liver are characteristic
features of the glucose intolerance in type 2 diabetic individuals. In the basal
state, the liver represents a major site of insulin resistance, and this is reflected
by overproduction of glucose. This accelerated rate of hepatic glucose output is
25
individuals. In the fed state, both decreased muscle glucose uptake and impaired
suppression of hepatic glucose production contribute to the insulin resistance. In
obese individuals and in the majority (>80%) of type 2 diabetic subjects, there is
an expanded fat cell mass, and the adipocytes are resistant to the antilipolytic
effects of insulin. Most obese and diabetic individuals are characterized by
expanded visceral adiposity, which is especially refractory to insulin effects and
results in a high lipolytic rate. Not surprisingly, both type 2 diabetes and obesity
are characterized by an elevation in the mean 24-hour plasma FFA concentration.
Elevated plasma FFA levels, as well as increased triglyceride/fatty acyl
coenzyme A (CoA) content in muscle, liver, and β- cells, lead to the
development of muscle/hepatic insulin resistance and impaired insulin secretion.
Cellular Mechanisms of Insulin Resistance:
“Weight gain leads to insulin resistance, and obese nondiabetic
individuals have the same degree of insulin resistance as lean type 2 diabetic
patients.57 In 1,146 nondiabetic, normotensive individuals, Ferrannini and
associates showed a progressive loss of insulin sensitivity when the BMI
increased from 18 kg/m2 to 38 kg/m2.58 The increase in insulin resistance with
weight gain is directly related to the amount of visceral adipose tissue.59,60 The
term visceral adipose tissue (VAT) refers to fat cells located within the
abdominal cavity and includes omental, mesenteric, retroperitoneal, and
perinephric adipose tissue. Visceral adipose tissue represents 20% of fat in men
and 6% of fat in women. This fat tissue has been shown to have a higher rate of
26
These fatty acids are released into the portal circulation and drain into the liver,
where they stimulate the production of very low density lipoproteins and
decrease insulin sensitivity in peripheral tissues.59 VAT also produces a number
of cytokines that cause insulin resistance. These factors drain into the portal
circulation and reduce insulin sensitivity in peripheral tissues.61 The fat cell also
has the capability of producing at least one hormone that improves insulin
sensitivity: adiponectin. This factor is made in decreasing amounts as an
individual becomes more obese.62,63 In animal models, adiponectin decreases
hepatic glucose production and increases fatty acid oxidation in muscle.”64,65
SIGNS AND SYMPTOMS:
“The classical symptoms of diabetes are polyuria (frequent urination),
polydipsia (increased thirst) and polyphagia (increased hunger).66 Symptoms
may develop rapidly (weeks or months) in type 1 diabetes while in type 2
diabetes they usually develop much more slowly and may be subtle or absent.
Prolonged high blood glucose can cause glucose absorption in the lens of the
eye, which leads to changes in its shape, resulting in vision changes. Blurred
vision is a common complaint leading to a diabetes diagnosis; type 1 should
always be suspected in cases of rapid vision change, whereas with type 2
changes is generally more gradual, but should still be suspected. A number of
skin rashes can occur in diabetes that is collectively known as diabetic
27
COMPLICATIONS:
“All forms of diabetes increase the risk of long-term complications. These
typically develop after many years (10–20 years), but may be the first symptom
in those who have otherwise not received a diagnosis before that time. The major
long-term complications relate to damage to blood vessels. Diabetes doubles the
risk of cardiovascular disease.”67
The main "macrovascular" diseases (related to atherosclerosis of larger
arteries) are ischemic heart disease (angina and myocardial infarction), stroke
and peripheral vascular disease. “Diabetes also causes "microvascular"
complications - damage to the small blood vessels.68 Diabetic retinopathy, which
affects blood vessel formation in the retina of the eye, can lead to visual
symptoms, reduced vision, and potentially blindness. Diabetic nephropathy, the
impact of diabetes on the kidneys, can lead to scarring changes in the kidney
tissue, loss of small or progressively larger amounts of protein in the urine, and
eventually chronic kidney disease requiring dialysis. Diabetic neuropathy is the
impact of diabetes on the nervous system, most commonly causing numbness,
tingling and pain in the feet and also increasing the risk of skin damage due to
altered sensation. Together with vascular disease in the legs, neuropathy
contributes to the risk of diabetes-related foot problems (such as diabetic foot
ulcers) that can be difficult to treat and occasionally require amputation.”69
DIABETIC NEPHROPATHY
“The commonest of the systemic disease involving the kidney is diabetes
28
with diabetes nephropathy has proved to be an important consequence of
mortality. Diabetic nephropathy plays a significant role as one cause of end stage
renal failure in the western world.”
“Diabetic nephropathy is a clinical syndrome characterized by persistent
albuminuria, arterial blood pressure elevation, a relentless decline in glomerular
filtration rate (GFR), and an associated high risk of cardiovascular morbidity and
mortality.70 This major life-threatening complication develops in approximately
35% of subjects with type 1 diabetes. The prevalence in type 2 diabetes is higher
than type 1; this form of diabetes now contributes to at least 50% of those with
diabetic nephropathy who develop end stage renal disease (ESRD) and requires
dialysis or transplantation for survival.”71
Natural history of Diabetic Nephropathy:
“The natural history of diabetic nephropathy has been relatively well
defined in type 1 diabetics. In type 2 diabetics, the process remains unclear with
regard to the time of onset of disease or the presence of other factors such as
hypertension, age or race. However, clinical investigators have been able to
classify the development of ESRD based on the onset and duration of the
disease.”
“The classifications of ESRD were introduced by Mogensen et al, (1993) and
divided into five stages as described below. 72
Stage 1, at the onset of the diabetes, there is glomerular hyperfiltration
29
hypertension associated with high blood glucose concentrations. At this
stage urinary albumin excretion may be normal or slightly elevated.
Stage II is a silent phase that follows hyperfiltration and is associated with
subtle morphological changes including thickening of the glomerular
basement membrane (GBM), glomerular hypertrophy, mesangial
expansion, and modest expansion of the tubulointerstitium.
Stage III develops after 7-15 years, with diabetic patients or incipient
nephropathy this can be detected clinically by the presence of
microalbuminuria. Abnormal urinary albumin excretion cannot be
detected by conventional or dipstick methods (semi-quantitative) but are
measurable using sensitive techniques such as quantitative immunoassay.
Stage IV is characterised by the presence of overt nephropathy, with
dipstick-positive proteinuria. GFR falls steadily, by about 12ml/min. year,
and clinically, measurement of plasma creatinine and microalbuminuria
are used to monitor renal function and to indicate the decline of GFR.
Hypertension when present in patients at this stage is usually associated
with the presence of >500 mg urinary total protein/24 h. However,
histological glomerular lesions, found in most long-term diabetics with
nephropathy, may include thickened glomerular capillaries, mesangial
expansion, intercapillary nodules of glomerulosclerosis of the afferent and
efferent arterioles and the presence of glomerular microanueurysms. The
mesangial cells of one or more of the glomerular segments produce
30
as Kimmelstiel-Wilson nodules. The development of oedema is one of the
earliest clinical features of renal impairment, often associated with
anaemia and a rather non-specific decline in general health.
Stage V is end stage renal failure, with the presence of severe mesangial
expansion, uraemia, hypertension, and serum creatinine concentration of
more than 400 gmol/1.”
STRUCTURAL, FUNCTIONAL, BIOCHEMICAL AND
PHYSIOLOGICAL ASPECTS OF THE KIDNEY:
“The kidneys play a major role in the homeostatic mechanisms of the
human body and reduced renal function strongly correlates with increasing
patient’s morbidity and motility. The kidneys form a paired organ system,
located in the retroperitoneal space, and demonstrate exquisite heterogeneity
which consist of three main areas namely the cortex, the medulla and the inner
medulla or papilla. The kidneys have both sympathetic and parasympathetic
nervous supply whose function appears to be predominantly associated with
vasomotor activity. Each kidney receives its blood supply from a single renal
artery derived from the abdominal aorta, with the venous return along a renal
vein that emerges into the vena cava. The renal artery divides into posterior and
anterior elements, which then divide into interlobar, arcuate, interlobular, and
ultimately into the afferent arterioles, which expand into the highly specialised
capillary bed that form the glomerulus. These capillaries then rejoin to form the
afferent arteriole, which then forms the capillary plexuses as well as the
31
of the nephron, the proximal and distal tubules, the loop of Henle, and collecting
duct, providing oxygen and nutrients and removing ions, molecules, and water
which are reabsorbed by the nephron.”
NEPHRON:
“The functional unit of the kidney is the nephron and each kidney has
been reported to contain between I and 1.5 million nephrons. There are at least
three types of nephrons, which include the superficial, midcortical and
juxtamedullary types. Each nephron consists of a glomerulus and Bowman's
capsule, which is next to the proximal tubule (PT) and the following section is
the loop of Henle, which leads into the renal medulla.”
At the junction of the inner and outer medulla, the loop becomes thicker
before leading to the distal tubule (DT) and collecting tubule (CT). This section
of the nephron then merges with those of other nephrons to form the renal pelvis
and ultimately the ureter.
GLOMERULUS:
“The glomerulus consists of a turft of blood capillaries, which is in close
contact with Bowmans's capsule. This close alliance enables the ultrafiltration of
plasma through three layers of cells which together act as a selective permeable
barrier. Glomerular structure and permeability are maintained by the glomerular
mesangial cells, thereby altering the glomerular capillary surface area available
for filtration. The glomerular basement membrane (GBM) is approximately 300
nm thick in adult humans and consists of three distinct electron-dense layers such
32
lamina densa consists of mainly type IV collagen embedded in a matrix of
glucoprotein and proteoglycans. This forms the main size discriminant barrier to
protein passage into the tubular lumen. The other two layers of the GBM are rich
in negatively charged polyanionic glucoprotein such as heparin sulphate
proteoglycans (HSP). The epithelial cells lining Bowmans's capsule are known
as podocytes and have a large number of extensions or foot processes that are
embedded in the GBM. The foot processes from adjacent podocytes are
interdigitated to form filtration slits, which are covered by highly hydrated
anionic mucopolysaccharide that is rich in sialic acid.”
“Consequently, the resulting structure is relatively impermeable to most
proteins above 60 kD, but passage of proteins is also modulated by their charge
and shape i.e. charge and size selectivity. The final cellular component of the
glomerulus is the mesangial cells (MC), which are embedded in an extra cellular
matrix (ECM) between the capillaries and play a critical role in the modulation
of glomerular blood flow and filtration by contraction and relaxation. MC are of
mesenchymal origin and contain contractile elements which express receptors to
many different hormones and cytokines, including angiotensin II, insulin-like
growth factor 1 (IGF-1), tumour necrosis factor, inteleukin-1, transforming
growth factor beta (TGF-ß) and advanced glycation end products (AGES). The
mesangial matrix, although developmentally and morphologically distinct from
the GBM, is composed of essentially the same components, i. e. collagen type
33
PROXIMAL TUBULE (PT)
“The proximal tubular region of the nephron consists of the proximal
convoluted tubule, and a straight segment, also known as the pars recta. Three
distinct cell types from the epithelial lining of these proximal structures and the
S1, S2 and S3 regions are separated on the basis of their morphological and
functional characteristics. The S1 segment, composed of S1-type cells, makes up
the beginning and middle portion of the convoluted proximal tubule and are
generally columnar with abundant microvilli on the luminal surface, thereby
increasing the surface area for reabsorption from tubular fluid by 40 fold. A well
developed phagolysosomal system, a large endocytotic apparatus of numerous
apical vacuoles and numerous mitochondria are also present in this segment. The
S2 segment forms the remaining portion of the proximal convoluted tubule and
the initial portion of the straight segment. S2 cells have fewer microvilli and
mitochondria than Si cells and they also contain the majority of the PT
lysosomes. Finally, the remaining portion of the pars recta is the S3 segment
which consists of the end of the straight portion and the beginning of the thin
descending loop Henle. Cells in this region have few microvilli and
mitochondria. The Si and S2 segments perform the majority of the solute and
fluid reabsorption coupled largely to sodium reabsorption. Large basolateral
membrane (BLM) interdigitations are found within the PT providing a large
surface area for Na+/K+ transport, which maintains the osmotic gradients
34
LOOP OF HENLE AND DISTAL TUBULE (DT)
“The loop of Henle is divided into the descending and ascending limbs.
These limbs form a hairpin loop, which either extend deeply into
(juxtramedullary) or reach only just into the medulla (cortical). The terminal
segment of the distal tubule is the convoluted part. Each segment of the loop of
Henle and the subsequent distal section has different permeability properties,
allowing the production of concentrated urine, as well as controlling intra and
extracellular osmolality and pH. Part of the distal tubule is especially close to the
glomerulus and the afferent and the efferent arterioles. Specialised cells, called
the macula densa, which are in this area respond to the sodium and chloride
composition of tubular fluid in order to maintain water and electrolyte
homeostasis (i.e. tubuloglomerulo feed back).”
FILTRATION, REABSORPTION AND SECRETION:
Glomerular filtration is a passive process dependent on the pressure
within the glomerular capillary network which in turn depends on the surface
area and intrinsic permeability of the glomerulus. The hydrostatic and oncotic
pressure gradients across the capillary walls are determined by both flow and
resistance. In the normally functioning kidney, molecules of > 50 A° are not
filtered due to size, shape or charge, whilst molecules < 40 A° are freely
permeable. These include glucose, amino acids, urea, Na+ and K+ ions. The
filtrate entering the nephron is isotonic with, and of similar composition to,
plasma except for the presence of large molecular weight proteins, which remain
35
Approximately 60-70% of the filtrate volume (water, sodium, and urea) is
reabsorbed in the PT whilst some ions and molecules are actively secreted
further down the nephron to maintain blood ionic concentration and volume. The
sodium concentration in the PT cell effects levels of energy generation and Na+
ions enter passively down an electrical gradient (-70mV) and are then actively
transported across the BLM via Na+-K+- ATPase and Na+-H+-ATPase activity
which allows the reabsorption and secretion of other solutes such as Cl", K+, H+
ions, to balance the Na+ ion movement.
RENAL BLOOD FLOW (RBF) AND GLOMERULAR FILTRATION
RATE (GFR)
“According to the myogenic theory, increased tension of the afferent
arterioles, brought about by an increase in perfusion pressure, causes automatic
contraction of the smooth muscle fibres in the vessel wall, thereby increasing the
resistance to flow and so keeping the flow constant in spite of the increase in
perfusion pressure. Tubulo-glomerular feedback (TGF) mechanisms are also
involved in supporting this process. TGF is a mechanism in which changes in DT
fluid composition are detected by the macula densa and, as a consequence, alter
the vascular elements of the glomeruli, thereby affecting single nephron GFR,
RBF and GFR are also under hormonal and nervous control. An intact renin
angiotensin aldosterone system (RAAS) is required for the normal regulation of
36
Measurement of GFR
“GFR is considered to be the most reliable measure of the glomerular
functional capacity of the kidneys and is often thought of as indicative of the
number of functioning nephrons. An estimate of the GFR can be made by
measuring the urinary excretion of a substance which is completely filtered from
the blood by the glomeruli and which is not secreted, reabsorbed or metabolised
by the renal tubules. Experimentally, inulin has been found to meet these
requirements. However, measurement of creatinine clearance is commonly used
method for estimation of the GFR in the routine clinical laboratory.”
U= urinary creatinine concentration (μmol/1),
V= urine flow rate [ml/min or (1/24 h)/1.44m2)]
P= plasma creatinine concentration (µmol/1)
Structural and functional changes in diabetic kidney
Nephromegaly was first described in diabetes more than a century ago
and is an early feature of both experimental and human diabetes.73 In animals,
nephromegaly occurs within four days of diabetes onset and most type 1
diabetics have large kidneys at diagnosis. Consequently, this enlargement is
mostly due to a combination of tubular hypertrophy and hyperplasia and
interstitial expansion, and is probably a response to increased glucose and fluid
37
1% of total kidney volume, so their contribution to whole organ enlargement is
significant.74
Glomerular enlargement has been a recognised feature of diabetes, and is
present both in early and later stages of the disease.75 Early glomerular
enlargement in experimental diabetes is the result of an increase in capillary
filtration surface area caused by an increase in capillary length, or number, or
both. In experimental diabetes, early glomerular enlargement coincides with
increased glomerular filtration.76 This, so-called hyperfiltration has been
proposed as an important pathophysiological factor for diabetic
glomerulopathy.77 Glomerular enlargement has therefore been considered as a
factor predisposing the subject to progression of glomerulopathy, perhaps by an
increase in capillary wall radius in response to raised intraglomerular pressure,
thus leading to increased capillary wall tension.74
Furthermore, the end result of diabetic glomerulopathy is a globally
sclerosed, non-functioning glomerulus. Such glomeruli can appear either as
relatively acellular, eosinophilic globes, which ultimately hyalinize and become
reabsorbed or as collapsed structures with an irregular crenated basement
membrane. The former appearance is consistent with an internal glomerular
obliteration by mesangial expansion, the latter more with ischaemia. These
interpretations are supported by reported positive correlations of percentage of
globally sclerosed glomeruli with mesangial expansion and afferent arteriolar
38
GBM thickening can be demonstrated in most diabetic subjects,
irrespective of the severity of their nephropathy, although those with heavier
proteinuria tend to have thicker membranes. It is thus not as specific a sign of
renal complication as the diffuse mesangial lesion, although those subjects with
nephropathy tend to have thicker GBMs than age and diabetes duration matched
subjects with normal renal function. Most of the increase in matrix is due to type
IV collagen accumulation. There is, however, a net loss of proteoglycan, which
is also dispersed throughout the thicker membranes. This loss is probably to
result in a loss of negative electrostatic charge and thus permit the passage of
positively charged proteins such as albumin.74
The Kimmelstiel-Wilson nodule is more specific for diabetic
nephropathy but occurs in only 20-70% of diabetics who demonstrate the diffuse
lesion. Furthermore, there are no obvious changes in endothelial or epithelial
cells in glomerulopathy, except that there is a widening of podocyte foot
processes. This development may be a ubiquitous response to increased protein
passage across the GBM, as its observed in other proteinuric states.74
A tubulo-interstitium compartment is also a major feature of diabetic
nephropathy and an important predictor of renal dysfunction. Renal enlargement
in diabetic animals is due to an initial tubular cell hyperplasia and subsequently
to cell hypertrophy. These changes are associated with alteration in expression of
growth factors such as TGF-ß and can be prevented by appropriate insulin
therapy. Tubular basement membrane (TBM) probably has a similar composition
39
has still not been widely studied. Diabetics develop TBM thickening about two
to three times the value observed in their non-diabetic siblings.79 Furthermore,
macromolecular penetration of the interstitial space may activate fibrosis and
would be further facilitated by disruption of the TBM. AGES also have been
demonstrated to increase pore size in bovine TBM, which may also result in
increased protein permeation.80
Clinical and biochemical aspects of diabetic nephropathy
Diagnosis of diabetic nephropathy
“The diagnosis of diabetic nephropathy is only definitively made by renal
biopsy, but this is rarely necessary clinically where the diagnosis is based on
both the clinical and biochemical abnormalities demonstrated the kidney, such as
the presence of proteinuria, development of a progressive rise in blood pressure,
and a progressive and relentless decline in renal function towards end stage renal
failure. Elevations of urinary albumin excretion are used to define both the
diagnosis of diabetic nephropathy and it progression. An increase in albumin
excretion is taken as the hallmark of diabetic nephropathy.”81
MICROALBUMINURIA
“Microalbuminuria is one of the earliest signs of renal insult in diabetes
and is currently the main focus of attention, as it is also associated with increased
risk of morbidity and premature death from cardiovascular disease.82 The
presence of microproteinuria in general, or microalbuminuria in particular,
reflects loss of charge selectivity and an increase in capillary permeability in the
40
failure (overt nephropathy) in diabetes mellitus; its presence here is termed
incipient nephropathy.”
Microalbuminuria, defined as an increased urinary albumin excretion
detectable only by sensitive immunoassay expressed either by time or with
reference to creatinine concentration, has been used for many years as a predictor
of incipient nephropathy in diabetics.81 The gold standard of microalbuminuria
measurement is based on the excretion rate of albumin in a timed urine
collection, while for more rapid estimations the urinary albumin concentration in
an early morning mid stream specimen of urine may be used. In order to correct
for variations in body fluid balance, the latter is normally referenced against the
41
Table: 1 Classification of Albuminuria:74
Normalbuminuria
Microalbuminuri
a
Macroalbuminuri
a
Albumin excretion rate
(mg/24h)
< 30 30-300 >300
Albumin excretion rate
(μg/min)
< 20 20-200 >200
Albumin concentration
(mg/L)
< 20 20-200 >200
ACR(mg/g creatinine) < 30 30-300 >300
ACR(mg/mmol
creatinine)
<3.5 3.5-35 >35
“Microalbuminuria may initially be transient in nature, but may become
persistent and result in the patient progressing to end stage renal failure if left
untreated. Indeed, microalbuminuria may progress to ESRD in 7-10 years after
onset of diabetes.83 In subjects with type 1 diabetes, about 80% of who develop
persistent microalbuminuria if left untreated, develop overt nephropathy within
10-15 years, accompanied by hypertension. This may eventually lead to end
stage renal failure within a further 10-20 years without appropriate therapeutic
42
develop microalbuminuria and overt nephropathy shortly after the diagnosis of
diabetes is probably because diabetes has been present for many years before the
diagnosis was made. However, overall 20-40% of type 2 diabetics with
microalbuminuria progress to overt nephropathy which ultimately may lead to
ESRD.”84
Pathophsiyology
“The intimate relationship between low-level albumin excretion and
vascular permeability makes UAE highly sensitivity to the presence of any
inflammatory process, including cardiovascular disease.82 Almost all filtered
albumin is reabsorbed by the proximal tubule via a high-affinity, low-capacity
endocytotic mechanism. Since tubular mechanisms for albumin reabsorption are
near saturation, urinary albumin excretion would increase following any increase
in tubular load. Glomerular permeability to albumin is dependent on endothelial
charge selectivity as well as size selectivity. The negative charge conferred on
the glomerular membrane by its constituent glycoproteins plays a role in
restricting the permeability of anionic proteins. Loss of glomerular charge
selectivity has been found in both diabetic and non-diabetic subjects with
microalbuminuria. However, the mechanisms underlying microalbuminuria still
remain to be fully elucidated.”85
SCREENING
“Annual screening for microalbuminuria will allow the identification of
those diabetics with either nephropathy or at risk of developing nephropathy. A
43
diabetes. Conversely, microalbuminuria rarely occurs with short duration of type
1 diabetes or before puberty and therefore, screening should begin with puberty
and after 5 years disease duration. If the urinalysis is positive for protein, a
quantitative measure is frequently helpful in the development of a treatment
regime.”
Screening for microalbuminuria can be performed by three methods: 1)
measurement of the albumin to creatinine ratio in a random spot urine collection;
2) 24h collection with creatinine, allowing the simultaneous measurement of
creatinine clearance; and 3) timed (e. g. 4h or overnight) collection.83
TREATMENT OF DIABETIC NEPHROPATHY
Effective of glycemic control
The DCCT, the UKPDS, the Stockholm and Intervention Study have
demonstrated definitively that intensive diabetes therapy can significantly reduce
the risk of the development of microalbuminuria and overt nephropathy in
subjects with diabetes. However, an improvement in renal function, which is
already restricted, can be attained by limiting maintaining blood glucose
concentrations close to reference values (mean HbA1c 6.5%) and intensified
blood pressure treatment.
Control of blood pressure and antihypertensive agent
Both systolic and diastolic hypertension significantly accelerates the
progression of diabetic nephropathy, and aggressive antihypertensive
management is able to greatly decrease the rate of decline of GFR. According to
44
Prevention, Detection, Evaluation, and Treatment of High Blood Pressure, blood
pressure levels above 135/85 mm Hg in a diabetic is abnormal. Treatment should
be directed at lowering the systolic level to about 100 to 110 mm Hg. The
positive response to antihypertensive treatment coupled with the concept that
often there is a progressive deterioration of renal function regardless of the
underlying etiology gave rise to the idea that haemodynamic factors may be
critical in furthering the depletion in GFR. In this hypothesis, damage to
glomeruli causes changes in the microcirculation that result in hyperfiltration
occurring in the remaining glomuruli with increased intraglomerular pressure
and increased sensitivity to angiotension II; the single nephron hyperfiltration
with intraglomerular hypertension is in itself damaging. Initially, Angiotensin
Converting Enzyme (ACE) inhibitors can reduce the degree of microalbuminuria
and can reduce the rate of progression of diabetic nephropathy to a greater
degree in both type 1 and type 2 diabetics. 75,83
Protein Restriction
“Dietary protein restriction has been demonstrated to decrease
albuminuria and reduce the rate of deterioration glomerular function in various
renal diseases. Both animal and human studies have demonstrated that restriction
of dietary protein intake also reduces diabetic intraglomerular pressure and
retards the progression of renal disease and diabetic nephropathy. The consensus
is to prescribe a protein intake of approximately the adult recommended dietary
allowance (RDA) of 0.8 g/kg/day (approximately 10% of daily calories) in the
45
GFR begins to decline, further restriction to 0.6 g/kg/day may prove useful in
slowing any further decline of GFR.”83
Renal replacement therapy (RRT)
“RRT consists of haemodialysis, continuous ambulatory peritoneal
dialysis (CAPD) and renal transplantation. Renal transplantation is the treatment
of choice for those under 60 years of age and should be considered when the
serum creatinine concentration reaches about 500-800 μmol/l.”74
SIALIC ACID
“Sialic acids are small aminosaccharides. They consist of a neuraminic
acid backbone with one or multiple O- or N-linked side chains, the most
abundant derivative in humans being Nacetylneuraminic acid (Figure 1).”
N- acetylneuraminic acid
“Sialic acids are numerous in many human tissues and fluids. In serum,
sialic acids are mostly bound to the carbohydrate chains of glycoproteins and
glycolipids.86 Sialic acid residues are located in the terminal ends of
carbohydrate chains of many glycoproteins, for instance immunoglobulins
and peptide hormones, and when the terminal sialic acid is removed by
neuraminidase of the vascular endothelium, a galactose molecule is
revealed. Specific receptors on hepatocytes recognize these asialoglyco-proteins
