HEME OXYGENASE IS INDUCED IN NEPHROTOXIC NEPHRITIS AND HEMIN, A STIMULATOR OF HEME OXYGENASE SYNTHESIS, AMELIORATES DISEASE

Heme oxygenase (HO) catalyses degradation of heme to biliverdin, iron and carbon monoxide (CO). Two isoforms exist, a constitutive form and an inducible form (HO-1). Induction of HO-1 may have protective effect s in inflammation. We studied heterologous (HNTN) and accelerated (ANT N) nephrotoxic nephritis in Lewis rats. Hemin. an inducer of HO-1. (30 mu mol/kg) was administered 18 hours before induction of nephritis an d 72 hours later in ANTN. HO-1 was not detected immunohistochemically in normal glomeruli but was present in HNTN and ANTN in cells with the morphology of macrophages. HO-1 induction was confirmed by RT-PCR. In normal rats hemin induced glomerular HO-1 mRNA at 18 hours. In HNTN h emin markedly reduced proteinuria at 24 hours (10 +/- 4 mg/24 hr; cont rol 54 +/- 16; P < 0.05), neutrophil infiltration at two hours (29.8 /- 1.8 vs. 22.3 +/- 1.5 neutrophils/glomerulus, P < 0.05), and glomeru lar macrophage number at two hours (2.1 +/- 0.1 vs. 3.1 +/- 0.4 cells/ glomerulus, P < 0.05). In ANTN proteinuria was reduced al dal; 1 and d ay 4 (36 +/- 11 vs. 60 +/- 15 and 35 +/- 7 vs. 86 +/- 9 mg protein/24 hr, respectively, P < 0.001), glomerular thrombi were reduced by hemin at day 1 and 4 (1.5 +/- 2.7 vs. 3.7 +/- 0.2 and 1.3 +/- 0.01 vs. 2.9 +/- 0.02, respectively. P < 0.001) and glomerular macrophage infiltrat ion was reduced on day 4 (11.2 +/- 0.8 cells/glom; control 15.9 +/- 0. 8, P < 0.01). Possible mechanisms by which HO-1 ameliorates disease in clude anti-complement or anti-oxidant effects of bilirubin and vasodil ator and anti-platelet effects of carbon monoxide.