Zaid O. Ibraheem
1,
Munavvar A. Sattar
1, Nor A. Abdullah
2, Mohammed H. Abdulla
1,
Hassaan A. Rathore
1, Tan Y. Chia
1, Fiaz Uldin
1, Edward J. Johns
3The Effect of Acute Experimental Nephrotoxicity
on the Progression of Metabolic and Cardiovascular
Abnormalities in a Rat Model of Saturated
Free Fatty Acid-Induced Metabolic Syndrome
Wpływ ostrej doświadczalnej nefrotoksyczności na rozwój
zaburzeń metabolicznych i układu krążenia w modelu szczurzym
zespołu metabolicznego wywołanego przez nasycone
wolne kwasy tłuszczowe
1 School of Pharmaceutical Sciences, Universiti Sains Malaysia, Penang, Malaysia
2 Department of Pharmacology, Faculty of Medicine, Universiti Malaya, Kuala Lumpur, Malaysia 3 Department of Physiology, Aras Windle, University College Cork, Ireland
Abstract
Background. Metabolic syndrome is a constellation of biomedical disorders characterized by glucose intolerance, hyperlipidemia and hypertension.
Objectives. The study evaluates the impact of acute experimental gentamin-induced nephrotoxicity on the meta-bolic and cardiovascular parameters in a rat model of metameta-bolic syndrome induced by saturated free fatty acids (SAFFAs).
Material and Methods. Sprague-Dawley rats weighing 200 gm were divided into four groups. The control group was fed with standard rodent chow for 8 weeks; Group H was fed an experimental ad libitum high-fat for the same period; Group HG was fed the same diet as Group H, and was injected intraperitoneally with 80 mg/kg/day of gentamicin during the last 24 days of the feeding period; Group G was fed standard rodent chow and injected with gentamicin as described above. Oral-glucose-tolerance-tests (OGTT) and lipid profiles were performed to assess metabolic function. Serum creatinine and absolute excretion of sodium were measured to assess renal function. At the end, the rats underwent a surgical procedure to measure arterial pressure and arterial stiffness.
Results. Glucose intolerance, hyperlipidemia, hypertension and higher stiffness were observed in Group H. In Group HG, co-administration of gentamicin along with the high-fat diet deteriorated glucose tolerance without having a high impact on the lipid profile. Arterial pressure was reduced while the stiffness remained comparable to that of group H. Greater nephrotoxicity was observed in renal failure rats fed with the high-fat diet.
Conclusions. Gentamicin did not have a strong impact on the progression of SAFFA-induced metabolic and car-diovascular abnormalities. However, the high-fat diet along with gentamicin worsened nephrotoxicity (Adv Clin Exp Med 2011, 20, 6, 667–676).
Key words: nephrotoxicity, metabolic syndrome, glucose intolerance, creatinine clearance, arterial stiffness.
Streszczenie
Wprowadzenie. Zespół metaboliczny jest zbiorem biomedycznych zaburzeń charakteryzujących się nietolerancją glukozy, hiperlipidemią i nadciśnieniem.
Cel pracy. W badaniu oceniono wpływ ostrej doświadczalnej nefrotoksyczności wywołanej przez gentamycynę na wskaźniki metaboliczne i układu krążenia w modelu szczurzym zespołu metabolicznego wywołanego przez nasy-cone wolne kwasy tłuszczowe (SAFFAs).
Materiał i metody. Szczury szczepu Sprague-Dawley o wadze 200 g podzielono na cztery grupy. Grupie kontrolnej podawano standardowy pokarm dla gryzoni przez 8 tygodni, w grupie H wprowadzono doświadczalny pokarm ad libitum o dużej zawartości tłuszczu w tym samym czasie; grupa HG była karmiona tym samym pokarmem co grupa H.
Adv Clin Exp Med 2011, 20, 6, 667–676 ISSN 1230-025X
ORIGINAL PAPERS
Metabolic syndrome is a constellation of bio-medical disorders characterized by glucose intol-erance, hyperlipidemia and high blood pressure. Ingestion of high amounts of saturated free fatty acids (SAFFAs) is one of the factors that can pro-voke metabolic syndrome [1].
Gentamicin is an aminoglycoside antibiotic widely used in the clinical practice to treat vari-ous bacterial infections, in spite of its unavoidable side effects. It is well known as a nephrotoxic, oc-ulo-toxic and vestibule-toxic drug [2]. Moreover, it has been found that gentamicin interferes with the metabolic pathways related to lipid homeo-stasis [3].
Arterial stiffness is one of the prognostic pa-rameters for cardiovascular abnormalities. It re-flects changes that occur in the arterial wall in association with various pathophysiological condi-tions, and is closely related to the cushioning func-tions of the artery (the ability of the artery to dis-tend and recoil after each ventricular systole. The ground substance of the arterial wall is made up mainly of elastin and collagen. The elastin/colla-gen ratio is balanced to maintain arterial function. Various pathophysiological conditions disturb this balance, leading to more collagen and less elastin production, resulting in higher arterial stiffness, as in diabetes mellitus, hypertension and senility [4].
The current study aimed to find the impact of gentamicin administration on the progression of metabolic and cardiovascular abnormalities in a rat model of SAFFA-induced metabolic syndrome.
Material and Methods
Animals and Diet
Male Sprague-Dawley rats weighing 200 gm, obtained from the Universiti Sains Malaysia animal house, were used in the study. They were housed in the animal transit room with four animals per cage at room temperature with a 12:12-h light-dark
cycle. All the procedures were performed accord-ing to the Universiti Sains Malaysia Animal Eth-ics Committee guidelines for the use of animals in research.
Before the start of the experiment, the rats were given a one-week habituation period, during which they were fed with standard commercial ro-dent chow. The rats were divided into four groups of 10 animals each: the control group was fed with standard rodent chow for 8 weeks; Group H was fed a high-fat diet rich in palm kernel oil (40% of the calories as fat) for 8 weeks; Group HG was fed the same diet as Group H, and was injected intra-peritoneally with 80 mg/kg/day of gentamicin sul-phate (Nova chemicals) during the last 24 days of the feeding period; and Group G was fed standard chow and injected with gentamicin as described above. The experimental diet was formulated to supply equal quantities of all nutrients as a per-centage of energy with the exception of fat and car-bohydrates (Table 1). It was stored in a refrigera-tor at 4°C after being prepared and was given daily to the animals. A mixture of palm kernel oil and palm oil was the main source of fat. The oil (from Moi Foods Malaysia Sdn Bhd) was composed of 55% saturated free fatty acids and 45% unsaturated free fatty acids. Cholesterol and cholic acid were added to induce hypercholesterolemia. Cholic acid has a hypercholesterolemic effect by inhibiting 17α-hydroxylase enzyme, a key enzyme for hepatic metabolism of cholesterol into bile acids [5].
Monitoring the Animals
Body weight and food intake (corrected for spillage) were monitored continuously during the treatment period. On days 34, 50 and 58 of the high-fat diet feeding period (which corresponds to days 0, 16 and 24 of the gentamicin treatment period), 24-hr urine samples and fasting tail-vein serum samples were obtained. Oral glucose toler-ance tests (OGTTs) were performed on days 34 and 58 of the treatment period. One day after the
Szczurom z grupy HG wstrzykiwano dootrzewnowo gentamycynę w dawce 80 mg/kg/dzień przez ostatnie 24 dni okresu karmienia. Grupie G podawano standardowy pokarm dla gryzoni i zastrzyk gentamycyny, jak opisano powy-żej. Aby ocenić funkcje metaboliczne, przeprowadzono doustny test tolerancjiglukozy i ocenę profilu lipidowego. Stężenie kreatyniny w surowicy i bezwzględne wydalanie sodu zmierzono w celu oceny czynności nerek. Na koniec szczury poddano zabiegowi chirurgicznemu, aby zmierzyć ciśnienie tętnicze i sztywność tętnic.
Wyniki. W grupie H zaobserwowano nietolerancję glukozy, hiperlipidemię, nadciśnienie tętnicze i większą sztyw-ność naczyń. W grupie HG jednoczesne podawanie gentamycyny wraz z wysokotłuszczową dietą pogorszyło tole-rancję glukozy, ale nie miało dużego wpływu na profil lipidowy. Ciśnienie tętnicze zmniejszyło się, a sztywność pozostała porównywalna z grupą H. Większą nefrotoksyczność zaobserwowano u szczurów z niewydolnością nerek karmionych dietą o dużej zawartości tłuszczu.
Wnioski. Gentamycyna nie miała silnego wpływu na rozwój zaburzeń metabolicznych i krążenia wywołanych przez nasycone wolne kwasy tłuszczowe. Dieta z dużą zawartością tłuszczu wraz z gentamycyną pogłębiła nefrotoksycz-ność (Adv Clin Exp Med 2011, 20, 6, 667–676).
treatment period ended, the rats were subjected to the acute study described below.
Oral Glucose Tolerance Tests
On days 34 and 58 the animals were fasted for 12 hours: All food was removed and the sawdust in the cages was changed to ensure there were no remaining food pellets. Then 5 gm/kg of glucose was given orally by gastric gavage. Blood glucose in mmol/l was measured in the blood obtained from the tail vein using a glucose meter (ACCU-CHEK®
Advantage Blood Glucose Monitoring System, Roche Diagnostics Corporation, Indianapolis, USA) at 0, 30, 60, 120 and 180 minutes after glu-cose administration. The gluglu-cose tolerance curve and the area under the curve (AUC) were deter-mined for each group [6].
Serum and Urine
Biochemical Analyses
Serum and urine samples were collected to measure creatinine in serum and sodium in urine. Creatinine was measured using the Jaffe reaction (picric acid test), while sodium was measured us-ing a flame photometer (Jenway PFP7). Absolute excretion of sodium was calculated using the con-ventional equations. Serum triglyceride and
cho-lesterol were measured using an auto-analyzer (Chemwell Biochemistry Analyzer, Spain).
Acute Study
Each rat was fasted for 12–14 hours, with free access to drinking water. It was anaesthetized us-ing sodium pentobarbital (Nembutal®, CEVA,
France) intraperitoneally at a dose of 60 mg/kg. The neck and abdominal regions were shaved with a hair clipper (WAHL Clipper Corporation, USA). A small area of the skin around the ventral neck region was cut and a blunt incision was made to separate the muscles of the neck. The trachea was exposed and a tracheotomy performed. A PP250 endotracheal cannula (Portex, UK) was inserted into the trachea to facilitate the animal’s breath-ing. The tracheal tube was periodically checked for mucus accumulation. The jugular vein was isolated and cannulated using a PP50 cannula (Portex, UK) for supplementary anesthesia and fluid administra-tion. The right carotid artery was catheterized using a PP50 cannula (Portex, UK) and the cannula was pushed up to the level of the aortic arch and con-nected to the transducer. After that the animal was left to stabilize for 30–60 minutes with continuous monitoring of the blood pressure and pulse wave. The blood pressure readings were done at a sam-pling rate of 0.4 KHz (LabChart 7Pro, ADInstru-ments, Australia). To ensure prominent and stable
Table 1. Composition of the experimental diet in comparison to the standard rodent-chow diet
Tabela 1. Skład doświadczalnego pokarmu dla gryzoni w porównaniu ze standardowym pokarmem dla gryzoni
Constituents
(Składniki) Standard chow diet (Standardowy pokarm dla gryzoni) Experimental diet (Doświadczalny pokarm dla gryzoni)
Wt (g) percent of total calories Wt (g) percent of total calories
Protein (Białko) 0.22 0.88 0.22 0.88
Carbohydrates (Węglowodany) 0.47 1.88 0.122 0.49
Fat (Tłuszcze) 0.03 0.27 0.181 1.66
Cholesterol – – 0.01 –
Cholic acid (Kwas cholowy) – – 0.0025 –
Calcium (Wapń) 0.012 – 0.012 –
Phosphate (Fosforany) 0.012 – 0.012 –
Sodium (Sód) 0.021 – 0.021 –
Potassium (Potas) 0.007 – 0.007 –
Fiber (Włókno) 0.05 0.03
Ash (Popiół) 0.08 0.05
Moisture (Woda) 0.13 0.13
waves, the presence of air bubbles in the transduc-er, clots at the tip of the cannula and the animals’ stability were regularly checked. A midline ventral abdominal incision was made and the abdomen was opened using an electrocautery knife (Model HDCS, Rimmer Brothers, UK). The abdominal or-gans were moved to the right side with cotton wool and the aorta was exposed. The left iliac artery was isolated and a PP50 cannula (Portex, UK) was pushed up to the abdominal aorta just proximal to the iliac bifurcation. Both the carotid and iliac cannulae were connected to a pressure transducer (P23 ID Gould, Statham Instruments, Nottingham, UK), which was connected to a computerized data acquisition system (PowerLab, ADInstruments,
Australia). The pulse wave velocity (PWV) was calculated from both the propagation time and the propagation distance. The propagation time was calculated by analyzing both the proximal and distal wave fronts using the diastolic phase center method (DPC) as described in Figure 1. The β in-dex is calculated to evaluate the participation of diastolic pressure in increasing arterial stiffness. It can be calculated using the following formula [7]:
2.2X(PWV)2
B index = DBP .
Data Analysis
Results were expressed as mean ± SEM (stan-dard error of mean). A one-way ANOVA followed by Tukey’s test was used for statistical analysis at a 95% confidence level using SPSS Student Version 16 software (IBM).
Results
Metabolic Data
(Body Weight, Food Uptake
and Urine Flow Rate)
No differences were noted in the results ofthe weekly increment of body weight and food uptake between the groups fed with the high-fat diet and the control group (Figures 2 & 3). Throughout the high-fat diet feeding period the urine flow rate in those groups declined noticeably, but not to a sta-tistically significant degree as compared to the con-trol animals (Table 2).
Gentamicin co-administration along with the standard rodent chow did not produce any change in food uptake and body weight in comparison to
BP (mmHg)
100 120 140
IL
-BP (mmHg)
100 110 120 130 140 150
9:07.6 9:07.65 9:07.7 9: 07.75 9:07.8 9:07.85 9:07.9 9:07.95
Time difference between the DPC points of both the proximal and distal waves
DPC of the proximal wave
DPC of the distal wave Aortic arch
wave front
Iliac artery wave front
Fig. 1. (a) Measurement of the diastolic phase center (DPC) for a wave. The DPC is the average point between two points that lie 1 mm Hg above the deepest points in both the upstroke and downstroke limbs of the pulse wave; (b) measurement of the pulse wave velocity from both the carotid and iliac artery wave fronts
Ryc. 1. (a) Pomiar środka fazy rozkurczowej (DPC) dla fali. DPC jest średnią między dwoma punktami, które leżą 1 mm Hg powyżej najgłębszych punktów fali zarówno podczas wznoszenia, jak i opadania czoła fali impulsowej; (b) pomiar prędkości fali impulsowej z czoła fali tętnicy szyjnej i biodrowej
a
the controls. On the other hand, its co-adminis-tration with the experimental high-fat diet mark-edly reduced these parameters, but not to a statisti-cally significant degree as compared to the control group (Figures 2 & 3). The urine flow rate was significantly increased throughout the gentamicin treatment period under the two feeding protocols (Table 2).
Metabolic Syndrome Assessment
Lipid Profile
Serum triglyceride increased markedly in renal failure rats and non-renal failure rats fed with the high-fat diet, with no significant difference between the two groups. Cholesterol levels increased after the high-fat diet. Gentamicin co-administration along with the high-fat diet raised serum cholesterol slightly in comparison to Group H (Table 3).
Fig. 2. Percent of weekly change in body weight for all the treated groups throughout the treatment period. Results are expressed in mean ± SEM. * indicates statistical significance in comparison to the control (p < 0.05); # indicates statistical significance in comparison to Group H (p < 0.05); ¤ indicates statistical significance in comparison to Group HG (p < 0.05); § indicates statistical significance in comparison to Group G (p < 0.05)
Ryc. 2. Odsetek tygodniowej zmiany masy ciała dla wszystkich grup przez cały okres leczenia. Wyniki są wyrażone jako średnia ± SEM. * oznacza istotność statystyczną w porównaniu z grupą kontrolną (p < 0,05); # oznacza istotność statystyczną w porównaniu z grupą H (p < 0,05); ¤ oznacza istotność statystyczną w porównaniu z grupą HG (p < 0,05); § oznacza istotność statystyczną w porównaniu z grupą G (p < 0,05)
Oral Glucose Tolerance Test
Impairment of glucose tolerance was seen in rats fed with the high-fat diet. This was obvious from the upward shifting of the glucose tolerance curve and the increment of the area under the curve (AUC) for this group in comparison with the control group (Table 3 and Figure 3). After gentamicin co-administration, this increment was higher, and reached statistical sig-nificance (Table 3, Figures 4 and 5).
Obesity Index
Thehigh-fat diet increased visceral fat accumula-tion in Group H, as seen in the results of the obesity index (Table 3). In Group HG, gentamicin co-admin-istration along with the high-fat diet reduced visceral fat accumulation in comparison to Group H.
Table 2. Renal function study on days 0, 16 and 24 of the gentamicin treatment period, which corresponded to the 34th,
50th and 58th days of the ad libitum high-fat diet feeding period. Results are expressed in mean ± SEM. * indicates statistical
significance in comparison to the control (p < 0.05); # indicates statistical significance in comparison to Group H (p < 0.05); ¤ indicates statistical significance in comparison to Group HG (p < 0.05); § indicates statistical significance in comparison to Group G (p < 0.05)
Tabela 2. Badanie czynności nerek w dniach 0, 16 i 24 leczenia gentamycyną, które odpowiadały dniom 34, 50 i 58
karmie-nia szczurów wysokotłuszczową dietą ad libitum. Wyniki są wyrażone jako średnia ± SEM. * oznacza istotność statystyczną
w porównaniu z grupą kontrolną (p < 0,05); # oznacza istotność statystyczną w porównaniu z grupą H (p < 0,05); ¤ oznacza istotność statystyczną w porównaniu z grupą HG (p < 0,05); § oznacza istotność statystyczną w porównaniu z grupą G (p < 0,05)
Parameter (Wskaźnik) Time (Czas) Control
(Grupa kontrolna) H HG G
UFR
µl/min/100 gm B.W d0d16
d24
2.18 ± 0.2 2.19 ± 0.18¤,§
2.06 ± 0.13¤,§
2.10 ± 0.1 1.42 ± 0.10¤,§
1.35 ± 0.08¤,§
1.74 ± 0.12* 5.29 ± 0.50*,#
4.75 ± 0.76*,#
–
4.40 ± 0.60* 4.17 ± 0.27* Abs. Na+ excretion
X 10-3
mmol/hr
d0 d16 d24
17 ± 1.60#,§
16 ± 1.50§
18 ± 1.70§
15 ± 1.00* 10 ± 0.80§
10 ± 0.90§
19 ± 1.10* 45 ± 4.20*,#
40 ± 6.20*,#
–
36 ± 4.70*,#
36 ± 2.80#
Ser cr.
µmol/l d0d16
d24
77 ± 5.1 80 ± 3.7§,¤
90 ± 5.8§,¤
68 ± 4.1 71 ± 3.6§,¤
71 ± 3.8§,¤
78.6 ± 4 292 ± 35*,#
274 ± 37*,#
–
203 ± 17*,#
182 ± 12*,#,§
Table 3. Metabolic syndrome assessment study, including obesity index, lipid profile and AUC of the OGTT at the specified time. * indicates statistical significance in comparison to the control (p < 0.05); # indicates statistical significance in compari-son to Group H (p < 0.05); ¤ indicates statistical significance in comparicompari-son to Group HG (p < 0.05); § indicates statistical significance in comparison to Group G (p < 0.05)
Tabela 3. Ocena zespołu metabolicznego, w tym wskaźnik otyłości, profil lipidowy i pole pod krzywą OGTT w określonym czasie. * oznacza istotność statystyczną w porównaniu z grupą kontrolną (p < 0,05); # oznacza istotność statystyczną w porównaniu z grupą H (p < 0,05); ¤ oznacza istotność statystyczną w porównaniu z grupą HG (p < 0,05); § oznacza istotność statystyczną w porównaniu z grupą G (p < 0,05)
Parameter (Wskaźnik) Control (Grupa kontrolna) H HG G
Obesity index (Wskaźnik otyłości)
1.97±0.10# 2.95 ± 0.22*,§,¤ 2.04 ± 0.21# 2 ± 0.36#
AUC
mmol/L.min time
week 0 1320 ± 47 1322 ± 45 1267 ± 41 1302 ± 28
week 4 1347 ± 42 1401 ± 64 1364 ± 90 1323 ± 34
week 8 1431 ± 55 1600 ± 86 1716 ± 124¤ 1412 ± 38
Cholesterol
mmol/l day 16 1.14 ± 0.017 1.35 ± 0.028 1.62 ± 0.119 1.29 ± 0.137
day 24 1.19 ± 0.016#, ¤ 1.46 ± 0.03* 1.59 ± 0.13* 1.3 ± 0.116
Triglyceride
mmol/l day 16 0.42 ± 0.008 0.054 ± 0.012 0.62 ± 0.036 0.4 ± 0.108
Cardiovascular Parameters
Unlike the other treated groups, Group H showed significantly higher blood pressure parameters (DBP – diastolic blood pressure, SBP – systolic blood pres-sure and MAP – mean arterial prespres-sure) (p < 0.05) in comparison to the control group (Table 4). Eight weeks on the high-fat diet increased arte-rial stiffness, as is evident from the PWV results for Group H, which were significantly raised at the end of the treatment period (p < 0.05) in comparison to the control group. The β index was not affected in Group H in comparison to the control.
In Group HG, blood pressure dropped in com-parison with Group H after gentamicin treatment. Gentamicin co-administration along with the high-fat diet during the last 24 days of the feeding period significantly raised the PWV in comparison to the control (p < 0.05); there were no differences in this parameter in comparison to the group given the high-fat diet alone. In Group HG, the β index showed some increase in comparison to the con-trol and Group H (Table 4).
Fig. 5. Oral glucose tolerance curve for Group HG on days 0, 34 and 58 of the high-fat diet treatment. Days 34 and 58 correspond to days 0 and 24 of gentamicin treatment period. Glucose level was measured at 0, 15, 30, 60, 120 and 180 minutes after giving the rats 5 g/kg (BW) of glucose orally. All data are expressed as mean ± SEM. * indicates p < 0.05 in comparison to week 0
Ryc. 5. Krzywa cukrowa w grupie HG w dniach 0, 34 i 58 podczas stosowania diety o dużej zawartości tłuszczu. Dni 34 i 58 odpowiadają dniom 0 i 24 leczenia gentamycyną. Stężenie glukozy mierzono 0, 15, 30, 60, 120 i 180 minut po podaniu szczurom 5 g/kg (BW) glukozy doustnie. Wszystkie dane przedstawiono jako średnią ± SEM. * oznacza p < 0,05 w porównaniu z tygodniem 0 badania
Fig. 4. Oral glucose tolerance curve for all the treated groups at the end of the treatment period. Glucose level was measured at 0, 15, 30, 60, 120 and 180 minutes after giving 5 g/kg (BW) of glucose orally
Renal Function
In Groups HG and G, renal function was re-duced after gentamicin treatment. The decline was more pronounced when gentamicin was given to the rats fed with the high-fat diet, as seen in the serum creatinine results and the absolute excretion of sodium (Table 2). The high-fat diet did not have a nephrotoxic effect, as serum creatinine did not increase. Higher renal handling of sodium was ob-served in Group H,which indicates higher tubular re-absorptive function (Table 2).
Discussion
The International Diabetes Federation (IDF) defines metabolic syndrome as central obesity along with one or two of the following disorders: hyperlipidemia (increased lipid profile), dyslipi-demia (changes in the lipoprotein content), hyper-tension and impairment of glucose tolerance [8].
According to this definition, present results confirmed the presence of metabolic syndrome af-ter the experimental high-fat diet feeding. SAFFAs induce many changes to induce metabolic disorders. Hyperinsulinemia [9] occurs due to the direct effect of SAFFAs on the β-cells of the islets of Langerhanz and due to the release of some gastrointestinal pep-tides that have a stimulatory effect on insulin secre-tion after ingesting high amounts of SAFFAs [10]. Hyperinsulinemia down-regulates insulin receptors and suppresses cellular uptake of both glucose and potassium [11]. SAFFAs directly induce insulin re-sistance in muscles and hepatocytes by increasing interference with the activity of insulin receptor substrate-1 (IRS-1). IRS-1 is crucial for glycogen synthesis and glucose uptake [12].
On the other hand, SAFFA ingestion results in visceral obesity [13]. Visceral fat does not act merely as an energy storage site, but also as an endocrine gland, secreting some inflammatory
cy-tokines, such as tumor necrotic factor-α, interleu-kin-1, interleukin-8 and interleukin-6; acute phase proteins, such as C-reactive protein; and chemot-actic factors, such as macrophage chemotchemot-actic fac-tor-1 (MCP). These inflammatory cytokines have a negative impact on glucose tolerance. They can directly interfere with IRS-1 activity. Insulin-me-diated glucose uptake occurs in muscles, and he-patocytes and adipocytes are insulin target sites. The development of glucose tolerance in response to SAFFAs is more frequent in muscles and hepa-tocytes in comparison to adipose tissue [14].
Recent studies have stated that SAFFAs act on a specific type of immune system-related re-ceptors called toll-like rere-ceptors (TLRs). TLRs are expressed in many body cells as immune cells, he-patocytes and myocytes. Their activation triggers a cascade of sequential reactions resulting in the activation of genes related to the synthesis of in-flammatory cytokines mentioned above [15].
The hypertensive effect of SAFFAs is attribut-ed to the metabolic abnormalities inducattribut-ed by their ingestion [16]. First, hyperinsulinemia plays a role. Insulin activates the catecholaminergic system [17], triggers vascular smooth-muscle proliferation [18] and renal handling of fluid [18, 19]. On the other hand, the accumulation of visceral adipose tissue induces hypertension [20]. The compressive effect of visceral fat on renal tissue results in overactiv-ity of the renin-angiotensin system and water and sodium retention [20]. Furthermore, increased electrolyte handling after hyperinsulinemia raises the effective circulatory volume (ECV), which may increase diastolic pressure and mean arterial pres-sure. It has been found that SAFFAs trigger elec-trolyte handling by increasing the expression of thiazide sensitive Na+-K+-Cl co-transporters in the ascending limb of the loop of Henle and Na+ channels in renal tubules [20].
The higher glucose intolerance observed in the current study after the co-administration of
gen-Table 4. Acute study parameters at the end of the treatment period. * indicates statistical significance in comparison to the control (p < 0.05); # indicates statistical significance in comparison to Group H (p < 0.05); ¤ indicates statistical significance in comparison to Group HG (p < 0.05)
Tabela 4. Ocena parametrów ciężkości pod koniec leczenia. * oznacza istotność statystyczną w porównaniu z grupą kontrolną (p < 0,05); # oznacza istotność statystyczną w porównaniu z grupą H (p < 0,05); ¤ oznacza istotność statystyczną w porównaniu z grupą HG (p < 0,05)
Parameter (Wskaźnik) Control (Grupa kontrolna) H HG G
MAP (mmHg) 109 ± 2.4# 128 ± 3.5* 118 ± 2.9 109 ± 3.4
DBP (mmHg) 98 ± 2.2 115 ± 3.3* 106 ± 3.1 96 ± 2.8
SBP (mmHg) 129 ± 2.1 152 ± 4.1 118 ± 2.9 109 ± 3.4
PWV (m/s) 4.7 ± 0.072# § 5.6 ± 0.243* 5.7 ± 0.265* 4.77 ± 0.1
tamicin along with the high-fat diet may be attrib-uted to the biochemical abnormalities associated with renal failure. A previous study declared that muscular cachexia and a decrease in glucose uptake in muscles occur after hyperuremia due to the sim-ulation of a protease pathway in the muscles [21]. The hyperlipidemic effect of gentamicin has been noted in previous studies [3], and has been attrib-uted to the aptitude of gentamicin to form a layer around low-density lipoprotein (LDL), rendering it insusceptible to the lipoprotein lipase enzyme. On the other hand, gentamicin-induced nephrotoxic-ity is characterized by glomerular damage, which leads to the loss of low-molecular weight proteins as albumin. These proteins are required for main-taining lipid profile homeostasis [3]. The results of the present study did not show any change in the triglyceride profile, while there was a slight change in cholesterol level. This may be due to the hyperlipidemic effect of gentamicin being vitiated by a decrease in food uptake. Moreover, there was a decline in the weekly increment in body weight in the group that was given gentamicin. This phe-nomenon may be due to fluid loss or to the bio-chemical changes that accompany renal failure, which trigger anorexia and cachexia [21].
Arterial stiffness parameters, which are prog-nostic parameters for cardiovascular abnormali-ties [22], included a higher PWV for Group H, and a comparable increase in Group HG. Gener-ally, hypertension or overactivation of the rennin-angiotensin system triggers arterial remodeling. In arterial remodeling, biochemical changes occur in the wall of the blood vessel, characterized by an in-crease in its collagen content and a reduction of its elastin content. When the collagen/elastin ratio rises, the arteriolar conduit system experiences in-creased stiffness [4]. At the same time, oxidative stress, hyperlipidemia and inflammatory cytokines increase stiffness by repressing the endothelial function. The endothelium plays an important role in maintaining proper arterial function. Endothe-lial cells generate a cluster of biological products that maintain vascular tone, hinder coagulation and trigger more elastin synthesis in the arterial wall. Disruption of arteriolar function diminishes
these activities, resulting in higher blood pressure and arterial stiffness [4].
In spite of Group HG having lower blood pres-sure than Group H and a comparable lipid profile, the PWV of the two groups was similar. This sug-gests the role of biochemical changes associated with renal failure in increasing arterial stiffness. This is evident from results of the β index calcu-lations, which were higher for Group HG. Previ-ous studies have confirmed overactivation of the renin-angiotensin-aldosteron system (RAAS) in renal failure [23]. RAAS overactivation induces ar-terial remodeling through vascular smooth muscle proliferation, by stimulating fibroblasts to release more collagen and by triggering the pro-oxidant pathway in the endothelium [23].
In addition to gentamicin altering the pro-gression of saturated fat-induced metabolic and cardiovascular abnormalities, saturated fat also worsened the progression of gentamicin-induced renal failure. This may be attributed to an increase in the preparedness of mitochondria to unleash more free radicals after long-term ingestion of saturated fats [24]. On the other hand, gentami-cin exerts a daunting effect on the mitochondrial membrane, resulting in an increase in the release of free radicals [2].
Overall, gentamicin co-administration along with the high-fat diet slightly worsened the meta-bolic syndrome without any obvious deterioration in cardiovascular parameters. On the other hand, the progression of renal failure was more severe after the high-fat diet.
The authors concluded that feeding behav-ior has significant impact on the progression of drug-induced toxicity. Long-term ingestion of saturated fats deteriorates the body’s ability to cope with the toxic effect of xenobiotics. It is well known that the long-term ingestion of saturated fats adversely affects metabolic and cardiovascu-lar functions. The progression of these adverse ef-fects is affected by the co-administration of drugs. Further studies are required to show the adverse effect of this combination on metabolic and car-diovascular functions.
Acknowledgements
The School of Pharmaceutical Sciences of the Universiti Sains Malaysiais gratefully acknowledged for providing financial support. The authors also thank the USM Advance Medical and Dental Institute for technical support in the experiment.
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Address for correspondence:
Zaid O. Ibraheem
School of Pharmaceutical Sciences University Sains Malaysia 11800 Minden
Penang, Malaysia
E-mail: [email protected]
Conflict of interest: None declared
