Serum Protein Carbonyl Level Is Higher in AL Amyloidosis Patients Versus Healthy Controls – Evidence of Systemic Oxidative Stress

Background: Light chain AL amyloidosis (AL) is a plasma cell dyscrasia that is associated with high morbidity and mortality especially in the setting of cardiac involvement. The disease arises from clonal production of immunoglobulin light chains that are deposited in various tissues causing multiorgan injury. The mechanism behind the tissue injury is not known. Biopsy of colon tissue suggests oxidative stress surrounding amyloid fibrils with oxidized lipids and proteins. Animal cardiomyocyte studies also suggest oxidative stress following acute exposure to AL light chains. Protein carbonyls are established markers of oxidative stress and are products of protein oxidation. Aim: The aim of the study is to compare protein carbonyl level between AL subjects and healthy controls. Methods: Sera from 23 subjects with biopsy-proven AL undergoing workup at 1 institution and 9 healthy subjects were collected. Protein carbonyl were measured using enzyme-linked immunosorbent assay method, derivatising with dinitrophenylhydrazine (DNP) and measuring bound DNP colourimetrically (450 nM absorbance) (Biocell PC Test, Biocell Corp., Papatoetoe, NZ). Results: AL subjects were 60±11 years old (57% female) while healthy subjects were 54±2 years old (p=NS) with 44% females. Biopsy was positive for amyloid in kidneys (n=12), GI tract (n=5), bone marrow (n=2), hip bone, axillary mass, fat pad and cardiac tissue (1 each). 65% involved lamda light chains. There was significantly increased protein carbonyl in AL subjects versus controls (see figure). There was no difference in protein carbonyl level between AL with lambda versus kappa light chain (0.2±0.23 vs. 0.1±0.13 nmol/mg protein). Conclusion: Serum protein carbonyl is increased in AL amyloid subjects compared to healthy controls. This suggests systemic oxidative stress in AL and may be important in the pathophysiology of the disease.