Passive
Heymann nephritis (PHN) is a model of human
membranous nephropathy that is characterized by formation of granular subepithelial immune deposits in the glomerular capillary wall which results in complement activation. This is causally related to damage of the filtration barrier and subsequent
proteinuria. The local accumulation of injurious
reactive oxygen species (ROS) is a major effector mechanism in PHN. ROS 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-hydroxynonenal-lysine adducts in glomeruli of PHN rats by immunofluorescence microscopy, using specific
monoclonal antibodies. By immunogold electron microscopy, MDA adducts were localized to cytoplasmic vesicles and cell membranes of glomerular epithelial cells, to the glomerular basement membrane (GBM), and also to immune deposits.
Type IV collagen was specifically identified as being modified by MDA adducts, using a variety of techniques.
Collagenase pretreatment of GBM extracts indicated that the NC-1 domain of
type IV collagen was a site of adduct formation. When LPO was inhibited by pretreatment of PHN rats with the
antioxidant probucol,
proteinuria was reduced by approximately 85%, and glomerular immunostaining for dialdehyde adducts was markedly reduced, even though the formation of immune deposits was not affected. By contrast, lowering of the serum
cholesterol levels had no influence on the development of
proteinuria. These findings are consistent with the premise that ROS-induced glomerular injury in PHN involves LPO and that this results not only in damage of cell membranes but in modification of
type IV collagen in the GBM as well. The close temporal correlation of the occurrence of LPO with
proteinuria and the ability of
probucol to inhibit
proteinuria support a causal role for LPO in the the alteration of the glomerular permselectivity which results in
proteinuria.