PROTEINURIA IN PASSIVE HEYMANN NEPHRITIS IS ASSOCIATED WITH LIPID-PEROXIDATION AND FORMATION OF ADDUCTS ON TYPE-IV COLLAGEN

Passive Heymann nephritis (PHN) is a model of human membranous nephrop athy that is characterized by formation of granular subepithelial immu ne deposits in the glomerular capillary wall which results in compleme nt activation. This is causally related to damage of the filtration ba rrier and subsequent proteinuria. The local accumulation of injurious reactive oxygen species (ROS) is a major effector mechanism in PHN. RO S may induce tissue damage by initiating lipid peroxidation (LPO). In turn, this leads to adduct formation between breakdown products of LPO with structural proteins, such as formation of malondialdehyde (MDA) or 4-hydroxynonenal-lysine adducts. To examine the role of LPO in the development of proteinuria we have localized MDA and 4-hydroxynoneal-l ysine adducts in glomeruli of PHN rats by immunofluoresence microscopy , using specific monoclonal antibodies. By immunogold electron microsc opy, MDA adducts were localized to cytoplasmic vesicles and cell membr anes of glomerular epithelial cells, to the glomerular basement membra ne (GBM), and also to immune deposits. Type IV collagen was specifical ly identified as being modified by MDA adducts, using a variety of tec hniques. Collagenase pretreatment of GBM extracts indicated that the N C-1 domain of type IV collagen was a site of adduct formation. When LP O was inhibited by pretreatment of PHN rats with the antioxidant probu col, proteinuria was reduced by similar to 85%, and glomerular immunos taining for dialdehyde adducts was markedly reduced, even though the f ormation of immune deposits was not affected. By contrast, lowering of the serum cholesterol levels had no influence on the development of p roteinuria. These findings are consistent with the premise that ROS-in duced glomerular injury in PHN involves LPO and that this results not only in damage of cell membranes but in modification of type IV collag en in the GBM as well. The close temporal correlation of the occurrenc e of LPO with proteinuria and the ability of probucol to inhibit prote inuria support a causal role for LPO in the the alteration of the glom erular permselectivity which results in proteinuria.