Occupational hydrocarbon exposure and renal histopathology

Occupational hydrocarbon exposure and chronic nephropathy

This review aims at discussing the questions raised by the hydrocarbon-related chronic nephropathy and its possible consequence, the hydrocarbon-related chronic renal failure. It has been attempted to adopt the point of view of the clinician. Therefore, the most important part of the review is devoted to a presentation and an analysis of the available data on humans. The main features of the available studies on human subjects are presented, their conclusions discussed in the light of the possible methodological flaws, and practical conclusions drawn. After a discussion of the main difficulties encountered for selecting the suitable exposure indicator, the studies are discussed in order of decreasing quality of the study design (cohort, case-control, cross-sectional studies, and the case reports). It is concluded that a great deal of controversies about chronic hydrocarbon-related nephropathy is explained by differences in the study design and that hydrocarbon-induced nephropathy is probably more than a mere hypothesis, although a causal relationship has not yet been proven. Finally, some practical consequences for dealing with a hydrocarbon-exposed patient diagnosed with a kidney disease and the need for further research are discussed.

The role of lysosomes in hyaline droplet nephropathy induced by a variety of pharmacological agents in the male rat

The male rat is prone to hyaline droplet formation in renal proximal tubular cells. Several unrelated pharmaceutical agents exacerbate the formation and accumulation of these droplets. Where the loading of the proximal tubular cells is marked it gives rise to increased cell turnover and a hyaline droplet nephropathy develops. Cytochemical procedures, have confirmed that this accumulation of hyaline droplets represents an increase in the size and number of secondary lysosomes involved in protein uptake and metabolism. This predisposition of the male rat to develop hyaline droplet nephropathy relates to (1) the large amounts of the low-molecular-weight protein alpha 2U globulin in the glomerular filtrate, (2) the resistance of the globulin to proteolysis, and (3) the low protease activity in the proximal tubule lysosomes. The current data would suggest that the pharmacological agents, which cause the nephropathy, exert their effect by reducing the proteolytic breakdown of alpha 2U globulin in the proximal tubule lysosomes. This results in the overloading of a system which is already operating near maximal load. Female rats, and all other species excrete only small amounts of alpha 2U globulin or similar proteins, which are more easily hydrolyzed. Thus it is argued that the type of hyaline droplet nephropathy induced by these pharmacological agents is unique to the male rat and of little relevance to man.

A comparison of male rat and human urinary proteins: implications for human resistance to hyaline droplet nephropathy

alpha 2u-Globulin (alpha G), the major urinary protein of sexually mature male rats, is a key determinant of susceptibility to hyaline droplet nephropathy (HDN) induced by a variety of hydrocarbons in male rats. Arguments against extrapolating renal toxicity and carcinogenicity data for HDN-inducing toxicants from male rats to risk assessment for humans rely on the observation that humans do not express alpha G. Yet, human serum and urine are known to contain proteins coded for by the same gene family that also controls alpha G synthesis in the rat. Therefore, to understand some of the quantitative and qualitative differences between proteins of human and male rat urine which confer apparent resistance to HDN in humans, urinary proteins of male F344 rats (ca. 3 months old) and normal human males were compared by cation exchange, gel filtration, SDS-PAGE, and partially identified by Western blotting. We observed that (1) the protein content of human urine is only 1% that of male rat urine; (2) human urinary proteins, recovered by (NH4)2SO4 precipitation followed by dialysis, are primarily of high (greater than or equal to 75 kDa) molecular weight (MW) with minor components of 12-66 kDa; (3) male rat urine has little high-MW protein, but is rich in alpha G (18.5 kDa); (4) at pH 5, the most cationic fraction of human urinary protein constituted only about 4% of the total while the analogous fraction of rat urine, containing alpha G, contained 26% of total urinary protein; and (5) cationic (at pH 5.0) human urinary proteins included small amounts of proteins, e.g., alpha 1-acid glycoprotein, and alpha 1-microglobulin, which are products of the gene family coding for alpha G in rat. Thus, although humans excrete trace amounts of proteins similar to alpha G, the very low protein content of human urine, the relatively small proportion of cationic to total proteins, and the high MW of the most abundant human urinary proteins form a biological basis for suggesting that humans are not at risk for the type of fuel and solvent hydrocarbon-induced nephropathy, and the sequelae of such nephropathy, observed in male rats.

Leupeptin-mediated alteration of renal phagolysosomes: similarity to hyaline droplet nephropathy of male rats exposed to unleaded gasoline

alpha 2u-Globulin, a protein of hepatic origin found in the urine of male rats, is accumulated in the kidney cortex during exposure to unleaded gasoline and has been implicated in the development of fuel hydrocarbon-induced nephropathy and renal neoplasia. The principal morphological feature of gasoline-induced nephropathy is accumulation of hyaline droplets (enlarged secondary lysosomes or phagolysosomes) in epithelial cells of the proximal convoluted tubule S1 and S2 segments. Inhibition of cathepsin B (a major lysosomal peptidase) by treatment of male rats with leupeptin causes rapid accumulation of phagolysosomes and alpha 2u-globulin in the kidney very similar to gasoline exposure. Further, the renal cortical subcellular distribution of alpha 2u-globulin, determined with an electron microscopic immunochemical method, is almost totally confined to phagolysosomes following administration of either gasoline or leupeptin. These results, taken together, indicate that the mechanism of nephrotoxicity of gasoline involves inhibition of renal phagolysosomal proteolysis.