MEFV sequence variants and amyloidosis: still an enigmatic question

Review of eprodisate for the treatment of renal disease in AA amyloidosis

Secondary (AA) amyloidosis is a multisystem disorder complicating chronic infections or inflammatory diseases. It is characterized by extracellular deposit of fibrils composed of fragments of serum amyloid A (SAA), an acute phase reactant protein. The kidney is the most frequent organ involved, manifesting as progressive proteinuria and renal impairment. Attenuation of the level of circulating SAA protein by treating the underlying inflammatory condition remains the primary strategy in treating AA amyloidosis. However, at times, achieving adequate control of protein production can prove difficult. In addition, relapse of renal function often occurs rapidly following any subsequent inflammatory stimulus in patients with existing amyloidosis. Recently there has been an interest in finding other potential strategies targeting amyloid deposits themselves. Eprodisate is a sulfonated molecule with a structure similar to heparan sulfate. It competitively binds to the glycosaminoglycan-binding sites on SAA and inhibits fibril polymerization and amyloid deposition. Recent randomized clinical trial showed that it may slow down progressive renal failure in patients with AA amyloidosis. However confirmatory studies are needed and results of a second Phase III study are eagerly awaited to clarify whether or not eprodisate has a place in treating renal amyloid disease.

Increased susceptibility of serum amyloid A 1.1 to degradation by MMP-1: potential explanation for higher risk of type AA amyloidosis

OBJECTIVE

Genetic polymorphisms in serum amyloid A (SAA) have been shown to substantially influence the risk of developing type AA amyloidosis. Recently, a role for MMP-1 has been suggested in the pathogenesis of AA amyloidosis. Therefore, we investigated if the SAA1 isotypes are differentially degraded by MMP-1.

METHODS

Degradation of different SAA isotypes by MMP-1 was assessed by immunoblotting. MALDI-TOF mass spectrometry was used to identify degradation fragments.

RESULTS

We found that SAA1.5 is more resistant to degradation by MMP-1 than SAA1.1. This difference is caused by the capacity of MMP-1 to cleave at the site of the polymorphism at position 57.

CONCLUSION

These results may explain the higher risk of amyloidosis in patients with a SAA1.1/1.1 genotype vs SAA1.5/1.5 or SAA1.1/1.5 genotype. In addition, the impaired degradation of SAA1.5 by MMP-1 could also explain the higher serum SAA concentrations in persons with a SAA1.5 genotype.

Expression of ASC in renal tissues of familial mediterranean fever patients with amyloidosis: postulating a role for ASC in AA type amyloid deposition

Familial Mediterranean fever (FMF) is characterized by recurrent attacks of fever and serositis; in some cases, ensuing amyloidosis results in kidney damage. Treatment with colchicine reduces the frequency and severity of FMF attacks and prevents amyloidosis, although the mechanisms behind these effects are unknown. Pyrin, the protein product of the MEFV gene, interacts with ASC, a key molecule in apoptotic and inflammatory processes. ASC forms intracellular speck-like aggregates that presage cell death. Here we show that cell death after ASC speck formation is much slower in nonmyeloid cells than in myeloid cells. Additionally, we demonstrate that colchicine prevents speck formation and show that specks can survive in the extracellular space after cell death. Because we also found that ASC is expressed in renal glomeruli of patients with FMF but not in those of control patients, we posit that high local ASC expression may result in speck formation and that specks from dying cells may persist in the extracellular space where they have the potential (perhaps in association with pyrin) to nucleate amyloid. The fact that speck formation requires an intact microtubule network as shown here could potentially account for the ability of prophylactic colchicine to prevent or reverse amyloidosis in patients with FMF.

Country as the primary risk factor for renal amyloidosis in familial Mediterranean fever

OBJECTIVE

Familial Mediterranean fever (FMF), the prototype of autoinflammatory disorders, is caused by recessive mutations in the MEFV gene. Some FMF patients develop renal amyloidosis, a potentially fatal condition. This complication has mainly been associated with the M694V mutation, although the different study designs, small numbers of patients, and/or evaluation of few or no covariables calls this association into question. The aim of this study was to examine the controversial issue of amyloidosis susceptibility in FMF by determining the relative contributions of MEFV and numerous epidemiologic factors to the risk of renal amyloidosis.

METHODS

Online questionnaires were completed at the MetaFMF database by patients at 35 centers in 14 countries. Using a standardized mode of data collection, we retrieved crude initial data from over half of the genetically confirmed FMF patients referred worldwide until May 2003 (2,482 cases, including 260 patients who developed renal amyloidosis).

RESULTS

Amyloid nephropathy was present in 11.4% of the cases. In the total study population, country of recruitment was the leading risk factor for this manifestation (odds ratio 3.2 [95% confidence interval 1.8-5.9]), followed by M694V homozygosity, proband status, and disease duration. Differing results were found when countries were stratified.

CONCLUSION

Country of recruitment, rather than MEFV genotype, is the key risk factor for renal amyloidosis in FMF. This risk, which parallels infant mortality rates, indicates a possible environmental origin of amyloidosis susceptibility. The patient's country should be considered in addition to MEFV genotype as an indication for prophylactic colchicine, a treatment suggested for asymptomatic individuals who are incidentally discovered to be M694V homozygous.