Biochemical basis for mouse resistance to hyaline droplet nephropathy: lack of relevance of the alpha 2u-globulin protein superfamily in this male rat-specific syndrome.
It is well-established that binding of a chemical to alpha 2u-globulin is the rate-limiting step in the development of male rat-specific hyaline droplet nephropathy. Mice synthesize mouse urinary protein (MUP), a protein which is very similar to alpha 2u-globulin, but this protein does not render the mouse sensitive to a similar renal toxicity. Therefore, the purpose of the present study was to determine the biochemical basis for mouse resistance to hyaline droplet nephropathy. Male Fischer 344 rats and B6C3F1 mice excreted 12.24 +/- 0.60 and 14.88 +/- 0.99 mg of alpha 2u-globulin and MUP daily, indicating that quantitative differences in protein excretion were not involved in the species specificity of the nephropathy. With d-limonene as a model hyaline droplet inducing agent, both rat and mouse liver microsomes oxidized the terpene to its 1,2-epoxide (the metabolite that binds reversibly to alpha 2u-globulin in vivo), demonstrating that metabolic differences do not determine the mouse resistance to this lesion. In spite of the formation of the epoxide intermediate, no binding of [14C]d-limonene equivalents to mouse kidney proteins was observed. In contrast, about 40% of the d-limonene equivalents in male rat kidney was reversibly bound to renal proteins. The renal reabsorption of alpha 2u-globulin and MUP was markedly different, as rats reabsorbed about 60% of the total filtered load of alpha 2u-globulin, but MUP was not reabsorbed by the mouse kidney. Given the absence of MUP in mouse kidney, in vitro equilibrium saturation binding studies were also conducted to determine whether MUP could bind the epoxide metabolite. alpha 2u-Globulin bound [14C]d-limonene-1,2-oxide with an apparent Kd of 4 x 10(-7) M. However, under identical experimental conditions, MUP failed to bind the epoxide. These data indicate that two major biochemical differences between alpha 2u-globulin and MUP contribute to mouse resistance to hyaline droplet nephropathy. Under both in vivo and in vitro conditions, MUP does not bind d-limonene-1,2-oxide, the rate-limiting step in the development of the nephropathy. However, even if MUP did bind the epoxide, the fact that it is not reabsorbed into the mouse kidney precludes its involvement in a syndrome involving renal protein overload. Finally, the absence of an interaction between d-limonene, a model hyaline droplet inducer, and the protein most similar to alpha 2u-globulin suggests that no other protein in the alpha 2u-globulin superfamily is likely to cause hyaline droplet nephropathy in other species.
Lehman-McKeeman
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Human & Environmental Safety Division, Miami Valley Laboratories, Procter & Gamble Company, Cincinnati, Ohio 45239.
Caudill
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D000510:Alpha-Globulins / Q000378:metabolism* / Q000652:urine; D000818:Animals; D000081005:Cyclohexane Monoterpenes; D005260:Female; D006818:Hyalin; D007113:Immunity, Innate; D007668:Kidney / Q000378:metabolism; D007674:Kidney Diseases / Q000276:immunology / Q000378:metabolism*; D008297:Male; D051379:Mice; D039821:Monoterpenes; D011506:Proteins; D051381:Rats; D011916:Rats, Inbred F344; D012737:Sex Factors; D013045:Species Specificity; D013729:Terpenes / Q000378:metabolism
D000510:Alpha-Globulins; D000081005:Cyclohexane Monoterpenes; D039821:Monoterpenes; D011506:Proteins; D013729:Terpenes; C025500:alpha(2)-microglobulin; C035737:major urinary proteins; C028940:limonene-1,2-epoxide