tin-mesoporphyrin and Anemia--Hypochromic

Long-term treatment with the heme oxygenase inhibitor tin-mesoporphyrin produces an iron deficiency anemia in rats analogous to that we reported in patients with the Crigler-Najjar type I syndrome receiving prolonged treatment with the inhibitor to ameliorate severe jaundice [Pediatrics 1992; 89: 175-182]. A dose- and time-dependent inhibition of intestinal heme oxygenase is produced by tin-mesoporphyrin which is independent of iron status of the animal. Tin-mesoporphyrin inhibits the intestinal enzyme whether administered orally or parenterally. Enzyme inhibition by either route results in diminished uptake of 59Fe from radiolabelled heme in the gut. Since tin-mesoporphyrin stimulates excretion of unmetabolized heme into bile its ability to inhibit intestinal heme oxygenase and to decrease heme-iron absorption in the gut probably accounts in part for the iron deficiency produced by the agent. The availability of an orally active agent which inhibits heme oxygenase and heme-iron absorption in the intestine may prove useful for experimental and therapeutic studies in diseases of iron metabolism.

Topics: Anemia, Hypochromic; Animals; Dose-Response Relationship, Drug; Heme; Heme Oxygenase (Decyclizing); Intestinal Absorption; Intestines; Iron; Male; Metalloporphyrins; Rats; Rats, Sprague-Dawley; Time Factors

The heme oxygenase inhibitor tin (Sn4+)-mesoporphyrin, administered to two 17-year-old Crigler-Najjar type I patients during a 400-day study to lower plasma bilirubin levels, also produced changes, beginning approximately 50 days after initiation of treatment, in hematological and iron metabolism indices consistent with the development of iron deficiency anemia. These indices were responsive to iron supplementation and reverted to normal after termination of inhibitor treatment. Tin-mesoporphyrin enhances biliary heme excretion and inhibits intestinal heme oxygenase when administered orally or parenterally; the changes in blood indices could thus reflect, in part, blockade of heme catabolism and therefore of uptake of heme-derived iron, by intestinal epithelium. This action of the inhibitor suggests that such agents may facilitate studies involving aberrant metabolism of heme-derived iron in humans and that they merit further investigation with respect to their potential value in enhancing iron disposal in certain disorders such as those related, for example, to transfusion-induced iron overload states.

Topics: Adolescent; Anemia, Hypochromic; Crigler-Najjar Syndrome; Hematologic Tests; Heme Oxygenase (Decyclizing); Hemoglobins; Humans; Iron; Male; Metalloporphyrins