Key words

Amyloidosis is an inherited or acquired sys-temic storage disease in which a pathologic, amor-phous substance produced as a result of abnormal protein metabolism and resistant to proteolysis is deposited in the extracellular space of various tis-sues (intracellular deposits occur rarely), which leads to the destruction of normal tissue archi-tecture and disturbs its function. The disease may

affect one organ or several organs simultaneously and is always fatal [1–3].

So far, 27 proteins which may initiate the pro-cess of formation of abnormal forms of amyloido-sis have been identified. The proteins are heteroge-neous and unrelated, they are characterized by the ability to assume more than one conformation and forming amyloid deposits of a typical, common

Lidia Usnarska-Zubkiewicz

_{, Jadwiga Hołojda}

_{, Kazimierz Kuliczkowski}

AL Amyloidosis (Amyloidosis Antibody Light).

Part 1. Definition, Classification, Amyloid Structure,

Development and Etiopathogenesis of AL Amyloidosis

Amyloidoza AL (

amyloidosis antibody light

). Część I. Definicja,

podział, budowa i rozwój amyloidu, etiopatogeneza amyloidozy AL

1 _{Departament of Hematology, Blood Neoplasms and Bone Marrow Transplantation,}

Wroclaw Medical University, Poland

2 _{Hematology Department of District Specialist Hospital of Legnica, Poland}

Abstract

Amyloidosis is an inherited or acquired systemic storage disease in which a pathologic, amorphous substance pro-duced as a result of abnormal protein metabolism and resistant to proteolysis is deposited in the extracellular space of various tissues (intracellular deposits occur rarely). This leads to the destruction of normal tissue architecture and disturbs its function. The development of amyloidosis is associated with the transformation of the α-spiral con-formation of fibrous protein into a stratified, parallel, folded spatial β-concon-formation. The transition of the fibrous proteins conformation and their tissue localization causes resistance of the fibers to proteolytic processes as a result of a limited access of the protein converting enzymes. In this paper we show the actual classification of amyloidosis and up-to-date knowledge about the amyloid structure, development and etiopathogenesis of AL amyloidosis (Adv Clin Exp Med 2011, 20, 5, 647–652).

Key words: amyloidosis AL, classification, amyloid structure, etiopathogenesis.

Streszczenie

Amyloidoza (skrobiawica) jest wrodzoną lub nabytą układową chorobą spichrzeniową, w przebiegu której dochodzi do gromadzenia się w przestrzeni pozakomórkowej różnych tkanek (rzadko wewnątrzkomórkowo), patologicznej, amorficznej substancji, która powstaje na skutek nieprawidłowego metabolizmu białek i jest oporna na proteolizę. Prowadzi to do zniszczenia normalnej architektoniki tkanek i zakłócenia ich funkcji. Rozwój amyloidozy jest związany z przekształceniem α-spiralnej konformacji włókien białkowych w warstwową, równoległą, pofałdowaną, przestrzenną β-konformację. Zmiana konformacji włókien białkowych i ich tkankowe umiejscowienie powoduje oporność włókien na procesy proteolityczne w wyniku ograniczonego dostępu enzymów rozkładających białka. W pracy przedstawiono aktualny podział amyloidozy oraz obecny stan wiedzy na temat rozwoju, budowy i etiopa-togenezy amyloidozy z łańcuchów lekkich (Adv Clin Exp Med 2011, 20, 5, 647–652).

Słowa kluczowe: amyloidoza AL, klasyfikacja, struktura amyloidu, etiopatogeneza.

Adv Clin Exp Med 2011, 20, 5, 647–652 ISSN 1230-025X

REvIEW

structure. The kind of protein deposit determines the type of amyloidosis [3, 4].

Classification of

Amyloidosis

The names of the individual types of amyloido-sis start with the letter A (symbolic term for amyloid fibrils), followed by an abbreviation of the protein forming the deposits [5]. The first classification of amyloidosis, which distinguished primary and sec-ondary amyloidosis, was presented in 1971.

In AL amyloidosis (amyloidosis antibody light), the amyloid deposits consist of monoclo-nal immunoglobulin light chains, most commonly of the λ class, vI subclass, which are a product of a neoplastic plasma cell clone. Depending on the number of plasma cells in the bone marrow, the level of monoclonal protein in the serum and/or urine and the presence of osteolytic changes, we can diagnose AL, or AL in the course of multiple myeloma and other monoclonal gammapathies. Kyle et al. demonstrated that 85% of patients di-agnosed with AL amyloidosis meet the criteria of various forms of plasma cell dyscrasia, while the remaining 15% lack clinical symptoms of plasma cell clonal growth [3]. According to Abraham et al., all patients with AL amyloidosis reveal mono-clonal gammapathy on the basis of a serum free light chain evaluation [6]. AL amyloidosis affects organs originating from the mesoderm tissue (the heart, digestive tract, peripheral nervous system, skin and tongue).

Secondary amyloidosis (AA) is associated with chronic inflammatory diseases. In this reactive form of amyloidosis, amyloid A protein deposits form in the organs originating from the parenchymal tissue (the kidneys, spleen and adrenal glands) [7].

In 1998, Saeger and Röcken divided amyloido-sis into 27 types depending on the kind of protein precursors. In 2002, Wastermark and colleagues presented a classification of amyloidosis includ-ing the inheritance type and disease syndromes or organ involvement which occur in its course (Table 1) [4, 5, 8, 9].

Structure of Amyloid

and Development of

Amyloidosis AL

In normal conditions, plasma cells and B lym-phocytes produce one of five types of heavy chains together with κ or λ light chains, with the num-ber of light chains exceeding the numnum-ber of heavy

chains by about 40%. Moreover, the synthesis of kappa chains, which are monomers with a mass of 25 kDa, is twice as big as that of lambda chains, which are chain dimers with a mass of 50 kDa, but kappa monomers are 2–3 times more quickly filtered by the kidneys than lambda chain dimers [10]. In healthy individuals, the number of plas-mocytes producing light chains does not exceed 4%, and the λ to κ ratio is 2 : 3. In patients suffering from AL amyloidosis, about 5–10% of plasma cells in the bone marrow produce excessive amounts of immunoglobulin light chains, and in the amyloid fibril, the λ to κ or κ to λ ratios are 2 : 1 and 3 : 1, respectively [11, 12].

AL amyloidosis from λ light chains is the most common type, the next most prevalent being AL from kappa chains, while heavy chain AH amyloi-dosis is extremely rare and only a few cases have been reported worldwide.

The development of amyloidosis is associated with the transformation of the α-spiral conforma-tion of fibrous protein into a stratified, parallel, folded spatial β-conformation. The transition of the fibrous proteins conformation and their tissue localization causes resistance of the fibers to prote-olytic processes as a result of a limited access of the protein converting enzymes. Amyloid fibrils are of various lengths and widths and do not break read-ily. Amyloid fibrils precursor monomers contain N--terminal fragments of proteins, they join together hydrostatically and form filaments, coil in 4–6 ele-ment bundles and form amyloid fibrils [13].

Immunoglobulin germ line genes have been demonstrated to play an important role in the development of amyloidosis in specific organs. Comenzo et al. proved that λ chain overproduc-tion, which is associated with a significant vλ6a gene overexpression, predisposes a person to the development of renal amyloidosis, while excessive expression of the vλ3r, vλ1c and vλ2a2 genes pro-motes the development of multi-organ amyloido-sis, and especially cardiac amyloidosis [14]. More-over, it was demonstrated that the λvI subtype of a light chain forms amyloid more readily than other chains [15]. A similar relationship concerns kappa light chains, for which the rearrangement of the vκI and vκIv genes more often conditions the development of AL amyloidosis [12, 15, 16].

of amyloidogenic fibrils, combining immediately with specific domains or their precursor proteins, as well as protect and stabilize the fibrils against degradation [18, 19].

The SAP, also referred to as P-pentraxine, is a globular protein with a pentagonal structure, con-stant sedimentation 9.5S and molecular mass 254 Da, and it occurs in all types of amyloid. The protein is synthesized and catabolized in the liver, and its half-life is 24 hours [3]. The primary function of SAP is to bind amyloid fibrils (the process is calcium-depen-dent), which may constitute additional protection for the fibrils against proteolysis. The glycoprotein

character of SAP is probably responsible for a posi-tive PAS reaction of amyloid deposits [20].

Etiopathogenesis

of Amyloidosis and

Amyloidogenic Mechanisms

The most important factor in the develop-ment of amyloidosis is the formation of amyloid fibrils mainly in the extracellular matrix, and very rarely, intracellularly, e.g. in pathological plasma Table 1. Classification of amyloidosis according to Wastermark, Saeger, Schonland, Skotnicki [4, 5, 8, 9]

Tabela 1. Podział amyloidozy wg Wastermark, Saeger, Schonland, Skotnickiego [4, 5, 8, 9] Amyloid

proteins (Białko amy-loidowe)

Precursor

(Prekursor) Distribution(Umiejscowienie) Type(Typ) Syndrome or involved tissues(Zespół lub zajęte tkanki)

β Aβ protein precursor local acquired sporadic Alzheimer disease, ageing local inherited prototype inherited cerebral angiopathy

– Dutch type amyloidosis

AprP prion protein local acquired sporadic (iatrogenic) CJD, new-variant CJD (alimentary?)

local inherited familial CJD, GSSD, FFI Abri Abpi protein precursor local or systemic? inherited British dementia family

Acys C cystatin systemic inherited Island inherited cerebral amyloid angiopathy Aβ2M beta2-microglobulin systemic acquired chronic hemodialysis

AL immunoglobulin light

chains systemic or local acquired myeloma-associated primary amyloidosis AA serum A amyloid systemic acquired secondary amyloidosis in reaction to

chronic infection or inflammation, includ-ing inherited periodic fever syndrome (FMF, TRAPS, HIDS, FCU and MWS)

ATTR transthyretin systemic inherited prototype FAP systemic acquired senile heart, vessels AapoAI A-I Apolipoprotein systemic inherited liver, kidneys, heart AApoAII A-II Apolipoprotein systemic inherited kidneys, heart

Agel gelsolin systemic inherited inherited systemic amyloidosis finnish type Alys lysozyme systemic inherited kidneys, liver, spleen

Afib Aα fibrynogen chain systemic inherited kidneys

CJD – Creutzfeldt-Jakob disease; GSSD – Gerstmann-Sträussler-Scheinker disease; FFI – fatal familial insomnia; FMF – fatal familial fever; TRAPS – tumor necrosis factor receptor associated periodic syndrome; HIDS – tumor necrosis factor receptor-associated periodic syndrome; FCU – familial cold urticaria; MWS – Muckle-Wells syndrome; FAP – familial amy-loidotic polyneuropathy.

cells. The process in which the precursor proteins are transformed into fibrils has a multi-factorial character and differs with different amyloid types. Buxbaum presented 4 basic mechanisms of amy-loidogenesis [21].

1. Overproduction and disturbed elimination of unchanged molecules, which, having achieved high concentration, reveal a tendency to abnormal breaking and formation of higher order spatial conformations, as in the case of b₂ -microglobu-lin, atrial natriuretic factor (ANF) and islet amy-loid polypeptides (AIPP) [22]. The molecules do not require supporting processes to form fibrils, although partial proteolysis may increase their capability of fibrilogenesis. It is probably a basic mechanism in the development of amyloidosis in plasma cell dyscrasias.

2. A normal molecule does not have amyloido-genic properties, however abnormal proteolysis leads to transformation of a protein precursor, e.g. amyloid β-AP and release of amyloidogenic protein fragments, as in the case of Alzheimer disease [23].

3. Insufficient proteolysis leads to the forma-tion of amyloidogenic fragments, e.g. in the case of increased production and insufficient degrada-tion of a specific protein. This type of producdegrada-tion is responsible for the development of AA amyloi-dosis and participates in the development of AL amyloidosis.

4. It occurs in prion infections, which consti-tute a template for abnormal breaking of a protein molecule. This type amyloidosis develops in infec-tions.

The tendency to fibrilogenesis and develop-ment of amyloidosis is a derivative of the genetic predispositions and factors affecting micro-envi-ronment and protein precursors.

Genetic predispositions include: 1) gene mu-tations, which lead to the production of “wild” analogues of proteins, 2) the polymorphism of co-factors (e.g. E apolipoproteins) and proteins (e.g. serum A protein), 3) the inheritance of dis-eases which lead to the accumulation of precursor proteins, e.g. presanilin – a mutation in familial Alzheimer disease, 4) inborn diseases, which are associated with chronic inflammation and deposi-tion of precursor proteins.

Contrarily to other plasma cell dyscrasias, the light chain lambda isotope is more common in AL amyloidosis, which points to the presence of the vλ germ line gene, with excessive expression of vλ 6a and vλ 3r [16, 24]. Moreover, it has been demonstrated that the rearrangement of the vκI and vκIv genes occurs more often in AL

amyloi-dosis [15]. Perhaps the presence of the germ line genes increases the tendency of the light chains to assume various molecular conformations. It has been shown that amino acid exchange occurs in the light chains that were formed as a result of gene mutations, which decreases their thermostabil-ity and promotes fibril formation [25]. Common chromosome aberrations in AL amyloidosis in-clude: chromosome 18 monosomy, trisomy of nu-merous chromosomes, t(11;14)(q13;q23) and dele-tion (13q14) [26, 27]. Bryce reported that, among 56 patients with light chain amyloidosis, 70% had abnormal cIg-FISH, with the most common ab-normalities being t(11;14) [39%], t(14;16) [2%]. and del13/del13q [30%]. [28]. The risk of death for patients with the t(11;14) translocation was the highest, 2.1 (CI 1.04-6.4), independent of therapy. It is important to note that patients with t(11;14) had the lowest levels of clonal plasma cells, and those with del13 had the highest. The levels of cir-culating immunoglobulin free light chains among patients with AL vary greatly too, but even patients with very low levels can have very advanced amy-loidosis. According to Poshusta et al., the location of mutations rather than the amount of free light chains in circulation determines its amyloidogenic propensity, as in patients with different levels of secreted light chains there are significant differ-ences in the location of mutations. This is espe-cially true for patients with very low levels of light chains and advanced amyloid deposition [29]. On the other hand, the data gathered by Solomon et al. has shown that the spleens of 12/26 patients with amyloidosis also contain plasma cells, producing a monoclonal light chain identical to the amyloid, which indicated that the spleen may be another source of amyloidogenic light chains [30].

Conclusions

Most cases of AL amyloidosis are associated with a mature plasma cell clone, but part of them have “dangerous small” clones and do not meet the criteria for multiple myeloma. The clonal plasma cells produce abnormal monoclonal immunoglobu-lin light chains, the precursor proteins for amyloid fibrils. The tendency to fibrilogenesis and the devel-opment of amyloidosis is a derivative of a genetic predisposition and factors affecting the micro-en-vironment and protein precursors. In AL amyloi-dosis, the light chain lambda isotope is more

com-mon, which points to the presence of the vλ germ line gene, with excessive expression of vλ 6a and vλ 3r. Moreover, it has been demonstrated that the rearrangement of the vκI and vκIv genes occurs more often in AL amyloidosis. Patients with differ-ent levels of secreted light chains have distinct dif-ferences in the location of mutations, which rather than the amount of free light chains in circulation, may determine its amyloidogenic propensity. Envi-ronmental conditions promoting amyloid forma-tion include: low pH, elevated temperature, insuf-ficient proteolysis, metal ions, and high local levels of amyloidogenic protein precursors.

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Address for correspondence:

Department of Hematology, Blood Neoplasms and Bone Marrow Transplantation Wroclaw Medical University

Pasteura 4 50-367 Wrocław Poland

E-mail: [email protected]

Tel. +48 71 784 25 96, +48 600 642 881

Conflict of interest: None declared