Immunolocalization of lipid peroxidation/advanced glycation end products in amyloid A amyloidosis.

Chronic inflammation, superimposed by amyloid fibril deposition, is believed to trigger the cascade of oxidative stress response in the affected organs and tissues. We examined immunohistochemically the distribution of 4-hydroxy-2-nonenal (HNE) and N(epsilon)-(carboxymethyl)lysine (CML), markers of lipid peroxidation and advance glycation end products (AGE), respectively, in spleen sections and peritoneal macrophages (MPhi) from mice before and during AA amyloidosis. With time, both HNE and CML immunoreactivities increased significantly in MPhi and splenic reticuloendothelial cells, known to be associated with the clearance of serum amyloid A, the precursor of AA fibrils. HNE and CML were localized to the plasma membrane and the cytoplasmic compartment of MPhi and HNE only at the nuclear membrane. These markers were also colocalized bound to AA fibrils infiltrating the splenic sinus walls. Our results reinforce the notion that oxidative stress is an integral component of amyloidotic tissues. Both lipid peroxidation and AGE have been implicated in protein modification and amyloid fibril formation. The significance of HNE and CML associated with the monocytoid cells and implicated in SAA clearance and AA fibril formation, is discussed with the pathogenesis of AA fibrils.

Heme-oxygenase-1 response, a marker of oxidative stress, in a mouse model of AA amyloidosis.

Expression of heme-oxygenase-1 (HO-1), an important marker of oxidative stress, has been studied extensively in the context of Alzheimer's disease. Evidence of HO-1 expression during AA amyloidosis is, at best, sketchy. We present comparative data on HO-1 response in alveolar hydatid cyst (AHC) infected amyloid sensitive (C57BL/6) and amyloid resistant (CE/J) mouse strains. Histochemical and peroxidase-immunoperoxidase methods were used to monitor serum amyloid A (SAA) and AA fibril deposition and HO-1 expression in hepato-splenic reticuloendothelial (RE) cells of the AHC-infected mice prior and during AA fibril deposition. Based on the cumulative data, we conclude that HO-1 expression corresponded closely with tissue deposition of SAA, but was unrelated to AA fibril deposition. To ascertain whether SAA deposition might act as the trigger for HO-1 expression in the RE cells, macrophages were incubated for up to 72 h with SAA-containing mouse serum. The SAA-treated macrophages, although negative for HO-1 protein, demonstrated SAA in the cell extracts and immunocytochemically in the vacuolar compartments, indicating macrophage-mediated endocytosis and trafficking of SAA. In sum, these results exclude SAA and AA fibrils as the primary triggers in the induction of HO-1 expression in RE cells; the potential role of inflammatory cytokines in HO-1 response need to be investigated further.