Amyloid in hereditary amyloid polyneuropathy is related to prealbumin

Complement in autoimmune inflammatory myopathies, the role of myositis-associated antibodies, COVID-19 associations, and muscle amyloid deposits

INTRODUCTION

The inflammatory myopathies (IM) have now evolved into distinct subsets requiring clarification about their immunopathogenesis to guide applications of targeted therapies.

AREAS COVERED

Immunohistopathologic criteria of IM with a focus on complement, anti-complement therapeutics, and other biologic immunotherapies. The COVID19-triggered muscle autoimmunity along with the correct interpretation of muscle amyloid deposits is discussed.

EXPERT OPINION

The IM, unjustifiably referred as idiopathic, comprise Dermatomyositis (DM), Necrotizing Autoimmune Myositis (NAM), Anti-synthetase syndrome-overlap myositis (Anti-SS-OM), and Inclusion-Body-Myositis (IBM). In DM, complement activation with MAC-mediated endomysial microvascular destruction and perifascicular atrophy is the fundamental process, while innate immunity activation factors, INF1 and MxA, sense and secondarily enhance inflammation. Complement participates in muscle fiber necrosis from any cause and may facilitate muscle-fiber necrosis in NAM but seems unlikely that myositis-associated antibodies participate in complement-fixing. Accordingly, anti-complement therapeutics should be prioritized for DM. SARS-CoV-2 can potentially trigger muscle autoimmunity, but systematic studies are needed as the reported autopsy findings are not clinically relevant. In IBM, tiny amyloid deposits within muscle fibers are enhanced by inflammatory mediators contributing to myodegeneration; in contrast, spotty amyloid deposits in the endomysial connective tissue do not represent 'amyloid myopathy' but only have diagnostic value for amyloidosis due to any cause.

Transthyretin Pro55, a variant associated with early-onset, aggressive, diffuse amyloidosis with cardiac and neurologic involvement

Mutations in the protein transthyretin cause amyloidosis involving the heart, peripheral nerves, and other organs. A family from West Virginia developed an unusually aggressive form of widespread transthyretin amyloidosis. Single-strand conformation polymorphism analysis revealed a variant in the transthyretin gene, which was found on sequencing to be a T----C transversion at position 2 of codon 55, corresponding to a Leu----Pro substitution. The variant sequence was confirmed by restriction analysis and polymerase chain reaction (PCR)-primer introduced restriction analysis.

Chemical heterogeneity of amyloid in the carpal tunnel syndrome

140 biopsies from 108 patients afflicted with the carpal tunnel syndrome were studied, 27 of whom showed deposition of amyloid, in 6 of them to such an extent that the amyloid was considered significant in the pathogenesis of the carpal tunnel syndrome. Morphologically, vessels and ligaments were affected and especially the peritendinous structures. As it was always part of generalized amyloidosis, the amyloid in the carpal tunnel consisted immunohistologically of amyloid A in three cases (including one case with simultaneous amyloid deposition of the AA- and the AB-type), of amyloid A kappa in one case, of amyloid of prealbumin origin in seventeen cases and of AB-amyloid in eight cases. We also described for the first time the manifestation of generalized senile amyloidosis (ASs) in the carpal tunnel. Deposition of amyloid of beta-2-microglobulin type (AB) in the carpal tunnel was particularly frequent and massive.

Chronic idiopathic ataxic neuropathy

Fifteen patients with chronic sensory ataxia caused by a large-fiber sensory neuropathy were studied and followed up for a period of 17.4 years (range, 4 to 41). When first seen, they had distal paresthesias and sensory ataxia of slow onset and progression, areflexia, normal strength, and a profound loss of proprioceptive and kinesthetic sensation extending up to the most proximal joints. Needle electromyogram and motor-nerve conduction velocity findings were normal in most of the patients and sensory potentials were absent in all. Nerve biopsy showed severe loss of the large myelinated fibers. Nine patients had a serum monoclonal or polyclonal gammopathy (3 with IgM kappa, 1 with IgA kappa, and 5 with a polyclonal increase of IgG, IgA, or IgM), and 8 had elevated cerebrospinal fluid gamma globulin levels in spite of low normal total cerebrospinal fluid protein levels. No circulating antibodies to ganglionic neurons were found. Therapy with immunosuppressants or plasmapheresis was unsuccessful. All patients are disabled and their conditions have continued to worsen without signs of malignancy or systemic illness during a mean follow-up period of 17.4 years. Chronic idiopathic ataxic neuropathy is a proprioceptive neuropathy, clinically indistinguishable from the one associated with carcinoma or pyridoxine abuse due to involvement of the dorsal root ganglia, and could represent a distinct form of an indolent, slowly progressive sensory neuronopathy (ganglionopathy). Although immunopathological mechanisms may play a role, especially in patients with an associated paraproteinemia, the resistance of such patients to therapy, the progressive course, and the resemblance of this disorder to other toxic neuronopathies associated with pyridoxine abuse or doxorubicin administration suggest a possible toxic etiopathogenesis.

Characterization of amyloid deposits in biopsies of 15 with "sporadic" (non-familial or plasma cell dyscrasia amyloid polyneuropathy

Review of the clinical and laboratory findings of 39 patients with amyloid polyneuropathy (AP) showed 12 cases to be hereditary and 12 to be associated with plasma cell dyscrasia (PCD). The remaining 15, termed "sporadic" AP, had neuropathy clinically indistinguishable from the other two groups but without a clinicopathologically identified PCD or positive family history. In an attempt to identify the type of amyloid in "sporadic" AP, the immunoreactivity of amyloid deposits was investigated using specific antisera raised against the following different chemical types of amyloid fibril proteins: variable regions of amyloid light chains kappa (A kappa) and lambda (A lambda), amyloid protein AA, and prealbumin. It was found that the amyloid in "sporadic" AP had A lambda antigenic determinants in ten cases, A kappa in one and prealbumin in three; in one case, the A lambda nature of amyloid was confirmed biochemically on the extracted amyloid fibrills. Thus, the most common type of AP in our population appears to be the "sporadic" form. In "sporadic" AP, the amyloid is most commonly of immunoglobulin light chain origin, even in the absence of overt PCD, and it can be rapidly categorized immunocytochemically to determine therapeutic directions or provide genetic guidance.

Familial amyloid polyneuropathy

Amyloid fibrils were isolated from the myocardium of two patients with familial amyloid polyneuropathy. The solubilized amyloid fibril whole protein shared immunologic determinants with normal human serum prealbumin (transthyretin), but revealed subtle differences on immunoelectrophoresis and radial immunodiffusion. On sodium dodecyl sulfate-polyacrylamide gel electrophoresis, amyloid fibril whole protein was resolved into numerous bands that reacted with antitransthyretin on immunoblots. The whole protein also contained peptide fragments of fibronectin, but was devoid of amyloid P protein. An antiserum raised against the whole protein was suitable for immunocytochemistry of amyloid in paraffin sections. In contrast, commercial antitransthyretin, raised against the intact tetrameric protein failed to react with tissue amyloid. Immunochemical and immunocytochemical results support the concept that familial amyloid polyneuropathy with cardiomyopathy is due to infiltration of susceptible tissues by an anomalous transthyretin.

Family studies of the genetic abnormality in transthyretin (prealbumin) in Portuguese patients with familial amyloidotic polyneuropathy

Amyloid deposits in several heredofamilial forms of amyloidosis are chemically related to transthyretin (TTR, the protein usually referred to as prealbumin). A genetically abnormal TTR may be involved. Studies were conducted on TTR isolated from sera of patients with familial amyloidotic polyneuropathy (FAP), and on amyloid fibril protein (AFp) isolated from tissues of two Portuguese patients who died with FAP. AFp, purified by affinity chromatography on retinol-binding protein (RBP), resembled plasma TTR in forming a stable tetrameric structure, and in its binding affinities for both thyroxine and RBP. Purified AFp was found to comprise a TTR variant with a methionine for valine substitution at position 30. This conclusion was based upon studies that included: (i) comparative peptide mapping by reverse-phase high-performance liquid chromatography after trypsin digestion; (ii) cyanogen bromide (CNBr) cleavage studies; and (iii) amino acid microsequence analysis of selected tryptic and CNBr peptides. The variant TTR was also found to be present in serum samples from FAP patients, along with larger amounts of normal TTR. An effective, small-scale procedure was developed to determine whether or not the variant TTR was present in the plasma of an individual subject. This procedure involved isolation of TTR by affinity chromatography on RBP, followed by CNBr cleavage, and analysis for the presence of specific aberrant CNBr peptides. Studies with six kindreds, including 21 asymptomatic children of 6 patients with FAP, showed that the "abnormal" TTR can be detected and used as a preclinical marker of the disease in affected children of patients with FAP. It is likely that the variant TTR represents a point mutation within the TTR structural gene, and that the normal and mutant genes act as co-dominant alleles at a single locus in FAP. The distribution of the mutant TTR within the six families was consistent with the autosomal dominant mode of inheritance of FAP. The mutant TTR apparently selectively deposits in tissues as the amyloid characteristic of the disease.

Clinical value of immunohistochemistry with AF-antibody in the diagnosis of familial amyloid neuropathy

Peripheral polyneuropathy associated with recurrent diarrhoea and orthostatic hypotension was observed in two unrelated German kinships and two sporadic cases. Congo red staining and polarization microscopy of biopsy specimens revealed amyloid deposits. Immunohistochemical investigation using the indirect immunoperoxidase staining with antisera to several purified amyloid fibril proteins showed a positive reaction with an antiserum to the prealbumin-related AF-amyloid in the families and one of the sporadic cases and with an antiserum to the immunoglobulin light chain amyloid (A lambda) in the other sporadic case. Therefore, the amyloid of the families and one of the sporadic cases was identified as the prealbumin-related AF amyloid, while the amyloid of the other sporadic case was of immunoglobulin origin. It is concluded that immunohistochemistry with antisera to the different amyloid proteins is useful in the differential diagnosis of amyloid neuropathy.

Lack of evidence for protein AA reactivity in amyloid deposits of lattice corneal dystrophy and amyloid corneal degeneration

Amyloid fibrils occurring in primary and myeloma-associated (AL), secondary (AA), and certain neuropathic hereditary forms of systemic amyloidosis can be distinguished biochemically or immunohistologically as being composed of immunoglobulin light chain, protein AA, or prealbumin respectively. All types of systemic and several localized forms of amyloidosis contain amyloid P component (protein AP). We studied formalin-fixed tissue from eight cases of lattice corneal dystrophy by the immunoperoxidase method using antisera to proteins AA and AP, to normal serum prealbumin and prealbumin isolated from a case of hereditary amyloidosis, and to light-chain determinants; additional cases were examined by indirect immunofluorescence of fresh-frozen material. We found weak (1:10 dilution) staining with anti-AP, but no reactivity with other antisera. Congo red staining was resistant to pretreatment of sections with potassium permanganate, a characteristic of non-AA amyloid. Two-dimensional gels of solubilized proteins from frozen tissue from two cases of lattice corneal dystrophy resembled those obtained from normal human cornea. Western blots of two cases of polymorphous amyloid degeneration and solubilized protein from normal cornea did not react with radioactive iodine-labeled anti-AA or anti-AP with purified protein AP and unfixed protein AA amyloid tissue as controls. We were unable to corroborate the presence of protein AA in the amyloid deposits of lattice corneal dystrophy. Although staining with antiserum to protein AP was demonstrable, the molecular configuration of this protein in stromal deposits remains to be defined.

Amyloid fibril protein in familial amyloidotic polyneuropathy, Portuguese type. Definition of molecular abnormality in transthyretin (prealbumin)

Amyloid fibril protein in patients with familial amyloidotic polyneuropathy is known to be chemically related to transthyretin (TTR), the plasma protein that is usually referred to as prealbumin. A genetically abnormal TTR may be involved in this disease. Studies were conducted on amyloid fibril protein (AFp) isolated from tissues of two Portuguese patients who died with familial amyloidosis, and on TTR isolated from sera of patients with this disease. AFp, purified by affinity chromatography on retinol-binding protein linked to Sepharose, resembled plasma TTR in forming a stable tetrameric structure, and in its binding affinities for both thyroxine and retinol-binding protein. The structural studies included: (a) comparative peptide mappings by reverse-phase high performance liquid chromatography (HPLC) after trypsin digestion; (b) cyanogen bromide cleavage studies; and (c) amino acid microsequence analysis of selected tryptic and CNBr peptides. On the basis of the known amino acid sequence of TTR, comparative tryptic peptide maps showed the presence of a single aberrant tryptic peptide (peptide 4, residues 22-34) in AFp as compared with TTR. This aberrant peptide contained a methionine residue, not present in normal tryptic peptide 4. CNBr cleavage of AFp produced two extra peptide fragments, which were demonstrated, respectively, by HPLC analysis and by sodium dodecyl sulfate-gel electrophoresis. Sequence analyses indicated the presence of a methionine-for-valine substitution at position 30 in AFp as compared with TTR. Thus, the purified amyloid fibril protein comprised a TTR variant with a methionine-forvaline substitution at position 30. A single nucleotide change in a possible codon for valine 30 could explain the substitution. The variant TTR was also present in the TTR isolated from the pooled sera of amyloidoses patients, together with larger (four- to six-fold) amounts of the normal TTR. Thus, in these patients, the variant TTR was circulating in plasma, along with larger amounts of normal TTR. We suggest that the variant TTR represents the specific biochemical cause of the disease, and that this abnormal form of TTR selectively deposits in tissues as the amyloid characteristic of the disease.

Paraproteins in the spinal fluid of patients with paraproteinemic polyneuropathies

High-resolution agarose gel electrophoresis, combined with immunofixation electrophoresis, was used to detect and identify immunoglobulins in the cerebrospinal fluid of six patients with paraproteinemic polyneuropathy. In four patients with serum IgM kappa monoclonal protein, we found a discrete band in the cerebrospinal fluid identified also as IgM kappa; one patient with serum IgG kappa had an IgG kappa cerebrospinal fluid band, and one patient with serum IgA kappa had an IgA kappa monoclonal band in the cerebrospinal fluid. The permeability of the blood-cerebrospinal fluid barrier was increased 3 to 10 times in all these patients. The findings indicate that in patients with paraproteinemic polyneuropathy, the increased permeability of the blood-cerebrospinal fluid barrier results in influx of serum proteins into the cerebrospinal fluid, including high-molecular-weight IgM. Because monoclonal IgM, unlike monoclonal IgG and IgA, is not found in the cerebrospinal fluid of neurologically intact patients, its presence in the cerebrospinal fluid of patients with paraproteinemias should lead the physician to suspect neurological involvement and can be of diagnostic value.

Prealbumin and retinol binding protein serum concentrations in the Indiana type hereditary amyloidosis

Serum prealbumin and retinol binding protein (RBP) concentrations were determined for 68 members of a kindred in Indiana with a familial type of systemic amyloidosis. Immunohistochemical studies on rectal and muscle biopsy material from individuals with this type of amyloidosis revealed staining of amyloid deposits with anti-prealbumin. Both the serum prealbumin and RBP concentrations were significantly depressed in 9 patients with amyloidosis when compared with normal controls and unaffected kin. In addition, the mean RBP serum concentration of 21 offspring of the patients with amyloidosis was significantly depressed. A more significant finding was that on the basis of the serum RBP concentrations, the offspring could be divided into 2 distinct groups. One group represented approximately 50% of the children and had serum prealbumin and RBP concentrations not significantly different from their afflicted parents. The second group had serum prealbumin and RBP concentrations not significantly different from those of normal controls and non-affected kin. These findings show that prealbumin and RBP serum concentrations are depressed in patients with the Indiana type of hereditary amyloidosis and that these serum abnormalities may be present long before development of clinical disease. They suggest that individuals with this genetic abnormality may be identified prior to clinical expression of the disease.

Familial amyloid polyneuropathy with marked hypertrophy of the peripheral nerves

Autopsy findings in a 40-year-old male with heredofamilial amyloidosis and polyneuropathy are reported. He had been suffering from progressive autonomic as well as sensorimotor dysfunctions. Prominent amyloid deposit was found in the kidney, heart, thyroid, and testis, and less in the interstitium and small vessels of almost all organs. The peripheral nerves, some showing prominent hypertrophy, were most severely involved by amyloid deposit in a form of stellate mass, which ultrastructurally consisted of radially arranged amyloid filaments. In the hypertrophied nerves and ganglia, in addition to amyloid, massive accumulation of acid mucopolysaccharide (AMPS) was seen filling up the interstitial space, which was the cause of hypertrophy. Ultrastructurally, AMPS was seen as finely granular substance. An extracted amyloid from the kidney showed 8 nm filament on negative staining and was estimated of having a molecular weight of 14,000.

The isolation and amino acid composition of senile plaque core protein

A new method has been developed for the isolation of intact senile (neuritic) plaque cores from post-mortem brains of patients with Alzheimer's disease. The plaque cores were found to be insoluble in various protein denaturants. The amino acid composition of the plaque core protein does not resemble that of any known form of amyloid.