Alterations in renal heme biosynthesis during metal nephrotoxicity.

The regulation of the heme biosynthetic pathway in the kidney by various metals has been reviewed. In addition, a study on the effects of lead on renal heme biosynthesis after acute treatment of rats has been reported. Chronic low-level lead exposure in rats results in relatively small effects on renal heme biosynthetic pathway enzymes. After acute treatment of rats with lead, no effects on ALAD or UROS and mild, transitory effects on ALAS and ferrochelatase are observed. The intracellular binding of lead within intranuclear inclusion bodies in the proximal tubule cells and to high-affinity cytosolic lead-binding proteins probably protects sensitive subcellular systems, such as the heme pathway, from lead toxicity. Chronic exposure to methyl mercury results in increased urinary excretion of uro- and coproporphyrins in rats, mediated via inhibition of ferrochelatase and UROS and stimulation of ALAS. A tissue-specific inhibition of ALAD occurs in the kidney after treatment of rats with indium. Acute treatment of rats with nickel, platinum, tin, antimony, bismuth, and cobalt results in induction of heme oxygenase, followed by decreased microsomal heme content and ALAS stimulation in the kidney.