Systemic amyloidosis in transgenic mice carrying the human mutant transthyretin (Met30) gene. Pathologic similarity to human familial amyloidotic polyneuropathy, type I.

To analyze the pathologic processes of amyloid deposition in type I familial amyloidotic polyneuropathy (FAP), mice were made transgenic by introducing the human mutant transthyretin (TTR) gene. In these transgenic mice, amyloid deposition started in the gastrointestinal tract, cardiovascular system, and kidneys 6 months after birth and extended to various other organs and tissues with advancing age. At age 24 months, the pattern of amyloid deposition was similar to that observed in human autopsy cases of FAP, except for its absence in the choroid plexus and in the peripheral and autonomic nervous systems. Amyloid deposition was shown to be composed of human mutant TTR and, in addition, mouse serum amyloid P component. These results clearly indicate that human variant TTR produced in transgenic mice deposits is a major component of amyloid fibrils in various organs and tissues. Thus this animal model is useful for analyzing how amyloid deposition initiates and proceeds in FAP.     

Effect of serum amyloid P component level on transthyretin-derived amyloid deposition in a transgenic mouse model of familial amyloidotic polyneuropathy.

To elucidate the pathogenesis of amyloid deposition associated with familial amyloidotic polyneuropathy (FAP), we developed several transgenic mouse lines carrying the human mutant transthyretin (TTR) gene. We found that human TTR and mouse serum amyloid P component (SAP) are deposited as amyloid in tissues of these mouse lines. Because SAP is a major acute-phase reactant in mice, we asked whether repeated injections of Escherichia coli lipopolysaccharide (LPS) would enhance the amyloid deposition in one of these transgenic mouse lines. During the course of repeated LPS injections, serum levels of SAP in the transgenic mice remained between severalfold to about 50-fold higher than seen in the absence of stimulation. As no significant difference was detected in the onset, progression, and tissue distribution of TTR-derived amyloid (ATTR) deposition between the LPS-stimulated and unstimulated transgenic mice, the induction of SAP synthesis by acute inflammation probably does not affect the onset and extent of ATTR deposition.     

4'-Iodo-4'-deoxydoxorubicin disrupts the fibrillar structure of transthyretin amyloid

Transthyretin (TTR) is a tetrameric protein synthesized mainly by the liver and the choroid plexus, from where it is secreted into the plasma and the cerebrospinal fluid, respectively. Some forms of polyneuropathy, vitreopathy, and cardiomyopathy are caused by the deposition of normal and/or mutant TTR molecules in the form of amyloid fibrils. Familial amyloidotic polyneuropathy is the most common form of TTR amyloidosis related to the V30M variant. It is still unclear the process by which soluble proteins deposit as amyloid. The treatment of amyloid-related disorders might attempt the stabilization of the soluble protein precursor to retard or inhibit its deposition as amyloid; or aim at the resorption of the deposited amyloid. The anthracycline 4'-iodo-4'-deoxydoxorubicin (I-DOX) has been shown to reduce the amyloid load in immunoglobulin light-chain amyloidosis. We investigated 1) whether I-DOX has affinity for TTR amyloid in tissues, 2) determined the I-DOX binding constants to TTR synthetic fibrils, and 3) determined the nature of the effect of I-DOX on TTR fibrils. We report that 1) I-DOX co-localizes with amyloid deposits in tissue sections of patients with familial amyloidotic polyneuropathy; 2) I-DOX strongly interacts with TTR amyloid fibrils and presents two binding sites with k(d) of 1.5 x 10(-11) mol/L and 5.6 x 10(-10) mol/L, respectively; and 3) I-DOX disrupts the fibrillar structure of TTR amyloid into amorphous material, as assessed by electron microscopy but does not solubilize the fibrils as confirmed by filter assays. These data support the hypothesis that I-DOX and less toxic derivatives can prove efficient in the treatment of TTR-related amyloidosis.     

Amyloid and nonfibrillar deposits in mice transgenic for wild-type human transthyretin: a possible model for senile systemic amyloidosis

The human serum protein transthyretin (TTR) is highly fibrillogenic in vitro and is the fibril precursor in both autosomal dominant (familial amyloidotic polyneuropathy [FAP] and familial amyloidotic cardiomyopathy [FAC]) and sporadic (senile systemic amyloidosis [SSA]) forms of human cardiac amyloidosis. We have produced mouse strains transgenic for either wild-type or mutant (TTRLeu55Pro) human TTR genes. Eighty-four percent of C57BI/6xDBA/2 mice older than 18 months, transgenic for the wild-type human TTR gene, develop TTR deposits that occur primarily in heart and kidney. In most of the animals, the deposits are nonfibrillar and non-Congophilic, but 20% of animals older than 18 months that bear the transgene have human TTR cardiac amyloid deposits identical to the lesions seen in SSA. Amino terminal amino acid sequence analysis and mass spectrometry of the major component extracted from amyloid and nonamyloid deposits revealed that both were intact human TTR monomers with no evidence of proteolysis or codeposition of murine TTR. This is the first instance in which the proteins from amyloid and nonfibrillar deposits in the same or syngeneic animals have been shown to be identical by sequence analysis. It is also the first time in any form of amyloidosis that nonfibrillar deposits have been shown to systematically occur temporally before the appearance of fibrils derived from the same precursor in the same tissues. These findings suggest, but do not prove, that the nonamyloid deposits represent a precursor of the fibril. The differences in the ultrastructure and binding properties of the deposits, despite the identical sizes and amino terminal amino acid sequences of the TTR and the dissociation of deposition and fibril formation, provide evidence that in vivo factors, perhaps associated with aging, impact on both systemic precursor deposition and amyloid fibril formation.     

Concurrent cardiac transthyretin and brain β amyloid accumulation among the older adults: The Hisayama study

Previous studies have revealed risk for cognitive impairment in cardiovascular diseases. We investigated the relationship between degenerative changes of the brain and heart, with reference to Alzheimer's disease (AD) pathologies, cardiac transthyretin amyloid (ATTR) deposition, and cardiac fibrosis. A total of 240 consecutive autopsy cases of a Japanese population-based study were examined. β amyloid (Aβ) of senile plaques, phosphorylated tau protein of neurofibrillary tangles, and ATTR in the hearts were immunohistochemically detected and graded according to the NIH-AA guideline for AD pathology and as Tanskanen reported, respectively. Cerebral amyloid angiopathy (CAA) was graded according to the Vonsattel scale. Cardiac fibrosis was detected by picrosirius red staining, followed by image analysis. Cardiac ATTR deposition occurred after age 75 years and increased in an age-dependent manner. ATTR deposition was more common, and of higher grades, in the dementia cases. We subdivided the cases into two age groups: ≤90 years old (n = 173) and >90 years old (n = 67), which was the mean and median age at death of the AD cases. When adjusted for age and sex, TTR deposition grades correlated with Aβ phase score (A2–3), the Consortium to Establish a Registry for AD score (sparse to frequent), and high Braak stage (V–VI) only in those aged ≤90 years at death. No significant correlation was observed between the cardiac ATTR deposition and CAA stages, or between cardiac fibrosis and AD pathologies. Collectively, AD brain pathology correlated with cardiac TTR deposition among the older adults ≤90 years.     

Intervertebral disc amyloidosis: histochemical, immunohistochemical and ultrastructural observations

Intervertebral discs selected at random from autopsies and surgical operations on herniated discs were examined for evidence of amyloid deposition. Amyloid deposits were detected in 53 (81.5%) of 65 autopsy cases. Discs from subjects over 50 years of age revealed a significantly high incidence of amyloid deposition. Among herniated discs, amyloid deposits were documented in 49 (75.4%) of 65 surgical specimens. The incidence of amyloid deposition in intervertebral discs increased with advancing age. Intervertebral disc amyloidosis consisted of amyloid deposits of three morphological types: linear amyloid deposits around the degenerating chondrocytes (perichondrocyte type), and nodular or band-like deposits in the annulus fibrosus (annulus fibrosus type) and nucleus pulposus (nucleus pulposus type). We suspect that the precursor protein of perichondrocyte type amyloid is derived from chondrocytes, and those of annulus fibrosus type and nucleus pulposus types are derived from the blood. The amyloid deposits were resistant to treatment with potassium permanganate. Immunohistochemically, the amyloid deposits reacted with antibody against amyloid P-component, but not with antibodies against AA, A k , Aλ, transthyretin or β₂-microglobulin. Ultrastructurally, the amyloid deposits were composed of 10 nm-wide nonbranching fibrils. The amyloid in herniated discs had the same biochemical and immunohistochemical properties as those found in autopsy cases. The immunohistochemical characteristics of the amyloid deposits suggest that it derives from an, as yet, unknown precursor protein.     

Secondary (AA) amyloidosis in cystic fibrosis. A report of three cases

The authors report the pathologic features of three cases of amyloidosis associated with cystic fibrosis. Renal biopsy led to the diagnosis (case 1) or suspicion (case 2) of amyloidosis in patients who were 23 and 21 years old, respectively. The third patient died at age 22 years, and amyloidosis was not discovered until autopsy. Immunohistochemical staining and potassium-permanganate pretreatment of histologic sections in all three cases provided evidence that the amyloid seen in these patients is of the secondary (AA) type. Congo red staining in each case and electron microscopy in case 1 confirmed the initial diagnosis of amyloidosis. A markedly elevated serum amyloid A protein (160 micrograms/mL; normal less than 1 microgram/mL) in case 1 indicated the presence of large quantities of the precursor protein from which the AA fibrils of secondary amyloid are derived. The kidneys, spleen, and liver contained amyloid deposits in autopsy material from all three cases. Involvement of other organs by amyloid was variable. Review of autopsy material in Boston from 23 additional cystic fibrosis patients with long-term survival did not reveal any evidence of amyloidosis. It appears that secondary amyloidosis is emerging as a significant, although rare, complication of cystic fibrosis as greater numbers of these patients survive into adulthood.     

Transthyretin binds amyloid beta peptides, Abeta1-42 and Abeta1-40 to form complex in the autopsied human kidney - possible role of transthyretin for abeta sequestration

The deposition of amyloid beta protein (Abeta), a proteolytic cleavage product of amyloid precursor protein (APP), is an invariable pathological feature of the Alzheimer's disease brain, while APP gene is widely expressed in all neuronal and non-neuronal tissues with the highest levels of expression in the brain, and kidney. To understand the role transthyretin (TTR) plays in the sequestration mechanism of Abeta in the kidney, we have investigated interactions of TTR with Abeta1-40 and Abeta1-42 molecules by an immunoprecipitation method, in vitro binding studies, and overlay assay. These in vivo and in vitro biochemical experiments showed that TTR bound Abeta1-42 preferentially, and Abeta1-40 only to a limited extent, to form TTR-monomer and -dimer-Abeta complexes in the normal human kidney. We provide new evidence supporting the hypothesis that TTR, an Abeta binding protein, plays an important role in the sequestration of Abeta and prevents amyloid formation in the kidney.     

Familial amyloidotic polyneuropathy (ATTR Ser50Ile): the first autopsy case report

We report an autopsy case of a pedigree of familial amyloidotic polyneuropathy (FAP) with a mutation of isoleucine-50 transthyretin (ATTR Ser50Ile). A 47-year-old man started developing severe diarrhea and weight loss at age 41 years, followed by urinary incontinence, autonomic-nervous-system abnormalities and serious heart failure; the diagnosis of FAP (ATTR Ser50Ile) was made on the basis of genetic, histochemical and immunohistochemical analysis. Six years after the initial symptoms, he died of septic shock. Autopsy revealed suppurative peritonitis, perforation of the sigmoid colon and marked systemic amyloid deposition. The total amount of amyloid deposited in the heart was greatly increased and was much lower in the thyroid gland and kidneys compared with amyloid deposits in ordinary FAP (ATTR Val30Met). Amyloid deposition in peripheral vessel walls was prominent, particularly in lymphatics and veins. His elder sister, 54 years old, started to develop orthostatic hypotension at age 49 years, followed by dysesthesia, diarrhea and severe congestive heart failure. Endomyocardial biopsy revealed severe TTR–amyloid deposition; ultrastructural examination demonstrated that amyloid fibrils were deposited disproportionately and extended radially around microvessels. These characteristic patterns of systemic amyloid deposition and distinct clinical manifestations, especially in the cardiovascular system, are considered to be a characteristic feature of ATTR Ser50Ile amyloidosis. Received: 31 August 1999 / Accepted: 19 October 1999     

Chain reaction of amyloid fibril formation with induction of basement membrane in familial amyloidotic polyneuropathy

Familial amyloidotic polyneuropathy (FAP) is characterized by extracellular deposition of amyloid fibrils caused by a point mutation in the transthyretin (TTR) gene. Despite data from a number of in vitro studies of TTR amyloidogenesis, many questions, including where and how these fibrils form in vivo and what is the impact of amyloid deposition on tissues, remain unanswered. Here, we analysed the relationship between amyloid fibril formation and micro‐environmental changes by using autopsy cardiac tissues from 11 patients with FAP and a smooth muscle cell line. Ultrastructural studies of cardiomyocytes and vascular smooth muscle cells showed that amyloid fibrils formed first at the basement membrane and that amorphous non‐fibrillar TTR deposits and premature fibrils predominated during the early stage of amyloid deposition. Immunohistochemical analyses revealed that expression of major components of the basement membrane, such as collagen IV, laminin, and fibronectin, increased in parallel with the accumulation of TTR amyloid fibrils. In vitro studies with a vascular smooth muscle cell line revealed that synthetic TTR aggregates increased expression of these basement membrane components. Serum levels of collagen IV in FAP patients were significantly higher than those in healthy controls. Our data thus indicate that TTR amyloid fibrils formed first at the basement membrane and that expression of basement membrane components that was induced by amyloid deposition contributed to further amyloid deposition. This chain reaction may have important implications for FAP pathogenesis. Copyright © 2009 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.     

Analysis of amyloid deposition in a transgenic mouse model of homozygous familial amyloidotic polyneuropathy.

Amyloid fibrils derived from the Japanese, Portuguese, and Swedish types of familial amyloidotic polyneuropathy all consist of a variant transthyretin (TTR) with a substitution of methionine for valine at position 30 (TTR Met 30). In an attempt to establish an animal model of TTR Met-30-associated homozygous familial amyloidotic polyneuropathy and to study the structural and functional properties of human TTR Met 30, we generated a mouse line carrying a null mutation at the endogenous ttr locus (ttr-/-) and the human mutant ttr gene (6.0-hMet 30) as a transgene. In these mice, human TTR Met-30-derived amyloid deposits were first observed in the esophagus and stomach when the mice were 11 months of age. With advancing age, amyloid deposits extended to various other tissues. Because no significant difference was detected in the onset, progression, and tissue distribution of amyloid deposition between the ttr-/- and ttr+/+ transgenic mice expressing 6.0-hMet 30, endogenous normal mouse TTR probably does not affect the deposition of human TTR Met-30-derived amyloid in mice. TTR is a tetramer composed of four identical subunits that binds thyroxine (T4) and plasma retinol-binding protein. The introduction of 6.0-hMet 30 into the ttr-/- mice significantly increased their depressed serum levels of T4 and retinol-binding protein, suggesting that human TTR Met 30 binds T4 and retinol-binding protein in vivo. The T4-binding ability of human TTR Met 30 was confirmed by the analysis of T4-binding proteins in the sera of ttr-/- transgenic mice expressing 6.0-hMet 30. The T4-binding studies also demonstrated the presence of hybrid tetramers between mouse and human TTR subunits in the ttr+/+ transgenic mice expressing 6.0-hMet 30.     

Familial amyloidotic polyneuropathy type 1 in Kumamoto, Japan: a clinicopathologic, histochemical, immunohistochemical, and ultrastructural study

Seventeen autopsy and five biopsy cases of familial amyloidotic polyneuropathy were examined clinicopathologically, histochemically, immunohistochemically, and ultrastructurally. In the autopsy cases, amyloid deposits were predominant in the peripheral nerve tissues, autonomic nervous system, choroid plexus, cardiovascular system, and kidneys. Amyloid involvements in the anterior and posterior roots of the spinal cord, spinal ganglia, thyroid, and gastrointestinal tract were also frequent. In the cardiac conduction system, amyloid deposition was prominent in the sinoatrial node and in limbs of the intraventricular bundle. In the sural nerve biopsy, besides amyloid deposits, degenerative changes of nerve fibers and Schwann cells were detected ultrastructurally, and the morphometric analysis showed a marked reduction in the number of myelinated fibers which correlated with the clinical stage. Amyloid deposits were resistant to pretreatment with potassium permanganate in Congo red staining, and transthyretin was confirmed immunohistochemically as a major component of amyloid deposits, along with the presence of serum amyloid P-component. Besides the amyloid deposits, transthyretin was proven in the liver cells, epithelial cells of the choroid plexus, and pancreatic islet A cells, suggesting that the transthyretin produced by these cells is secreted, transferred into tissues, and deposited in situ as the major component of amyloid in this disorder.     

Amyloid A gastrointestinal amyloidosis associated with idiopathic retroperitoneal fibrosis. Report of a rare autopsy case and review of the literature

We report a rare autopsy case of secondary gastrointestinal amyloid A (AA) amyloidosis associated with idiopathic retroperitoneal fibrosis (IRF) in a 67-year-old woman. Masses were identified around the aorta and inferior vena cava in her abdomen. Histologically, plasma cell infiltration was observed within fibrotic areas. Because no specific cause for the inflammatory mass was apparent, we diagnosed it as IRF. Steroid therapy, which usually reduces IRF masses, proved ineffective, and malabsorption syndrome developed 4 years later. On autopsy, amyloid protein was present systemically in the vascular walls of several organs, and deposition was highest in the gastrointestinal mucosa. Amyloid protein was identified as AA type, strongly suggesting that the amyloidosis was secondarily induced by IRF. To our knowledge, only 2 other cases of IRF-associated amyloidosis have been reported. Two of the 3 patients of these cases were women who showed resistance to steroid therapy.     

Evidence of the presence of amyloid substance in the blood of familial amyloidotic polyneuropathy patients with ATTR Val30Met mutation

Transthyretin (TTR) is a major amyloid fibril protein found in patients with familial amyloidotic polynuropathy (FAP) and senile systemic amyloidosis (SSA). Mainly synthesized in the live, TTR is transferred in the form of tetramer bound with thyroxine, retinol-binding protein (RBP) and lipoprotein in the blood. The aim of this study was to demonstrate the presence of amyloid substances in the blood by investigated the hemocoelom amyloid in different tissue sections from autopsies such as brain, kidney, heart and aorta arch tissue. Congo red staining was employed following by application of polarized light examination, to verify the presence of amyloid deposition in the tissues. Immunohistochemical staining was then performed to identify the specific type of amyloid deposition. Matrix-assisted laser desorption-ionization/time of flight mass spectrometry (MALDI-TOF/MS) was also used to analyze TTR mutation in FAP patients. All subjects were FAP ATTR Val30Met patients. In FAP patients, TTR amyloid deposition was found mainly in the tunica intima of the aortic arch. Interestingly, amyloid substance was found in the blood of FAP patient. Our results suggest that amyloid substance was present in the blood of FAP ATTR Val30Met patients.     

Lmmunohistochemical classification of 140 autopsy cases with systemic amyloidosis

One hundred and forty autopsy cases of systemic amyloid-osis were examined using the potassium permanganate method for distinction of amyloid A protein from other amyloid proteins and an immunohistochemical technique. Of those cases, amyloid proteins were identified in 121 cases. There were 68 cases of amyloid A-related (AA) amyloidosis and these were the most common type among the cases (56.2%). There were 39 cases of immunoglobulin light chain-related (AL) amyloidosis (32.2%), six cases of β₂-microglobulin-related (Aβ2M) amyloidosis (5%), and five cases of transthyretin-related (ATTR) amyloidosis (4.1%). Minute areas of amyloid deposits in four cases with AA were resistant to potassium permanganate pretreatment. In Aβ2M amyloidosis amyloid deposits were either resistant or sensitive to potassium permanganate pretreatment, from case to case. The coexistence of two different amyloid proteins was seen in three cases: one case had ATTR and Ax types, and two cases had Aβ2M and AA types. Some discrepancies were seen between the immunohistochemical typing and clinical classification of amyloidosis referred to in the Annual of the Pathological Autopsy Cases in Japan, for example, one case of AA type in myeloma-associated amyloidosis and one case of AL type in secondary amyloidosis. From the present results, the importance of the immunohistochemical method in classifying amyloidosis is stressed.     

Deposition and passage of transthyretin through the blood-nerve barrier in recipients of familial amyloid polyneuropathy livers

Familial amyloid polyneuropathy (FAP) is characterized by deposition of mutated transthyretin (TTR) in the peripheral nervous system. Prior to amyloid fibrils, nonfibrillar TTR aggregates are deposited inducing oxidative stress with increased nitration (3-NT). As the major source of TTR is the liver, liver transplantation (LT) is used to halt FAP. Given the shortage of liver donors, domino LT (DLT) using FAP livers is performed. The correlation between TTR deposition in the skin and nerve was tested in biopsies from normal individuals, asymptomatic carriers (FAP 0) and FAP patients; in FAP 0, nonfibrillar TTR was observed both in the skin and nerve in the same individuals; in patients, amyloid was detected in both tissues. The occurrence of amyloidosis in recipients of FAP livers was evaluated 1-7 years after DLT: TTR deposition occurred in the skin 3 years after transplantation either as amyloid or aggregates; in one of the recipients, fibrillar TTR was present in the epineurium 6 years after DLT. Deposits were scarce and 3-NT immunostaining was irrelevant. Nerve biopsies from DLT recipients had no FAP-related neuropathy. Our findings suggest that TTR amyloid formation occurs faster than predicted and that TTR of liver origin can cross the blood-nerve barrier. Recipients of FAP livers should be under surveillance for TTR deposition and tissue damage.     

Pathogenesis and therapy for transthyretin related amyloidosis

Transthyretin (TTR) is a beta-sheet rich protein whose plasma half life is 1.9 days. It behaves as a tetramer and binds to retinol binding protein (RBP) and thyroxin in plasma. Since TTR is a tryptophan-rich-protein, the protein is used as a useful marker protein for nutrition supporting team (NST). However, TTR is also an anti-acute phase protein, and its concentration is influenced by various conditions, such as inflammation and infection. Mutated forms of TTR are the precursor protein of familial amyloidotic polyneuropathy (FAP). Since plasma TTR is predominantly synthesized by the liver, liver transplantation has been performed as an effective therapy for FAP. However, the surgery has several problems, so we must develop novel essential therapies for FAP. Single stranded oligonucleotides (SSOs) or short interference RNA (SiRNA) is a promising option for an essential therapy for FAP. In mutated TTR, instability of tetrameric form of TTR occurs, resulting in misfolding of TTR molecule, which lead to amyloid fibril formation. Since mutated TTR exposes criptic epitopes on the surface of TTR molecule, induction of an antibody for the epitopes was thought to be effective. We synthesized ATTR Y78P, a spontaneously misfolded TTR, and injected it to amyloid laden transgenic mice having human ATTR V30M to induce the antibody for amyloid fibrils. As we expected, amyloid deposition was significantly reduced by the injection of ATTR Y78P to the mice. These therapies may become novel strategies for essential FAP therapy instead of liver transplantation.     

Application to transthyretin analysis

Transthyretin (TTR) is the precursor protein of familial amyloidotic polyneuropathy (FAP) and senile systemic amyloidosis (SSA). TTR-related FAP is a hereditary amyloidosis induced by mutated TTR. The most common type of FAP is FAP amyloidogenic TTR (ATTR) Val30Met: TTR substitution of methionine for valine at position 30 of the TTR sequence. In this type of FAP, amyloid deposition causes organ failure including peripheral neuropathy, autonomic disorders, gastrointestinal symptoms, and cardiac and renal failure. In Japan, it is well known that Kumamoto and Nagano are the two major foci of FAP, but recently, FAP has been found throughout Japan. In addition, various different types of mutations in the TTR gene and phenotypes of FAP have also been documented. Medical care for FAP is becoming more important. Detection of mutant TTR is indispensable to diagnose the disease in order to treat FAP. We have developed a method for detecting mutant TTR in serum and cerebrospinal fluid by means of mass spectrometry to screen for variant TTR in FAP patients. In this article, we reviewed the general characteristics of TTR and clinical features of FAP, and described the identification of mutant TTR using surface-enhanced laser desorption/ionization time-of-flight (SELDI-TOF) mass spectrometry (MS). In addition, we analyzed TTR modifications and protein profiles in serum samples of Japanese and Swedish patients using SELDI-TOF-MS to look for a key protein(s) as a trigger of FAP.     

The pathogenesis and biochemistry of amyloidosis

The transformation of serum proteins into Congo red-sensitive fibrillar material is requisite for the onset and progression of amyloid disease. All the mechanisms which lead to the disease itself have not been elucidated, but our knowledge has increased significantly. It is apparent that in all types of amyloid fibrils, three common features are displayed by the major protein constituents. These are that the fibril protein has a serum precursor, a high degree of anti-parallel beta-sheet conformation and a distinctive ultrastructure on electron microscopy. In the AL and AA forms of amyloidosis, the putative precursors appear to undergo limited degradation to form the protein component of amyloid fibrils. It has been suggested that there may be certain primary structural characteristics inherent in precursor molecules which make them amyloidogenic, thus predisposing them to amyloid fibril formation. This would include certain subtypes of immunoglobulin light chains, possibly kappa I and lambda VI, in the AL type of amyloidosis and one of the polymorphic SAA species, SAA2, which has been identified as the predominating isotype found in AA amyloid fibrils. In AH amyloidosis, the mechanism of amyloid fibril formation appears to be simply a concentration phenomenon where elevated concentrations of B2-M are not handled normally and amyloid deposition is the result. Amyloidogenesis in the hereditary form of systemic amyloidosis may involve other factors in addition to the presence of a variant precursor prealbumin as indicated by the delayed onset of the disease. It is evident that the elucidation of the mechanism(s) which governs the onset and progression of the amyloidoses will allow future regulation and treatment of these all too often complex disorders.     

Immunization in familial amyloidotic polyneuropathy: counteracting deposition by immunization with a Y78F TTR mutant

The mechanism of amyloid formation in familial amyloidotic polyneuropathy (FAP), a hereditary disorder associated with mutant transthyretin (TTR), is still unknown. It is generally believed that altered conformations exposing cryptic regions are intermediary steps in this mechanism. A TTR mutant--Y78F (transthyretin mutant with phenylalanine replacing tyrosine at position 78)--designed to destabilize the native structure has been shown to expose a cryptic epitope recognized by a monoclonal antibody that reacts only with highly amyloidogenic mutants presenting the amyloid fold or with amyloid fibrils. To test whether TTR deposition in FAP can be counteracted by antibodies for cryptic epitopes, we immunized with TTR Y78F, transgenic mice carrying the most common FAP-associated TTR mutant--V30M (transthyretin mutant with methionine replacing valine at position 30)--at selected ages that present normally with either nonfibrillar or TTR amyloid deposition. Compared to age-matched control nonimmunized mice, Y78F-immunized mice had a significant reduction in TTR deposition usually found in this strain, in particular in stomach and intestine; by contrast, animals immunized with V30M did not show differences in deposition in comparison with nonimmunized mice. Immunohistochemical analyses of tissues revealed that immunization with Y78F lead to infiltration by lymphocytes and macrophages at common deposition sites, but not in tissues such as liver, choroid plexus, and Langerhans islets, in which TTR is produced. These results suggest that Y78F induced production of an antibody that reacts specifically with deposits and leads to an immune response effective in removing/preventing TTR deposition. Therefore, TTR immunization with selected TTR mutants has potential application in immune therapy for FAP.