To explore the pathogenesis of nontransfusional iron overload in iron- loading anemia, we examined features of external iron exchange, internal iron kinetics, and tissue iron burden in adult mice with inherited gene-deletion beta-thalassemia. Mice homozygous for beta- thalassemia display moderate anemia, reticulocytosis, and shortened red cell survival, whereas heterozygous carriers appear hematologically normal. Quantitative iron determination revealed that iron content and concentration in liver, spleen, and kidney, but not heart, were far higher (P less than .01) in 15-to 35-week old homozygous thalassemic mice than in age-matched normal and heterozygous controls; of these tissues, iron content increased with age only in kidneys (P = .01) of homozygous affected mice. Although plasma iron levels were only minimally elevated in homozygotes, plasma iron turnover was threefold greater (P less than .001) than that seen in heterozygote controls. Nevertheless hyperabsorption of enteric radioiron, discernible among homozygous thalassemic mice as late as 6 to 8 weeks after birth, was not observed in older mice, additionally, thalassemic and control mice at 18 to 34 weeks showed comparable iron excretion after intravenous radioiron. We conclude that adult mice with beta-thalassemia regain balanced external iron exchange, despite substantial tissue iron excess and accelerated internal iron transit.
Because clinical disorders of spontaneous iron overload have no experimental counterpart, we studied iron distribution (atomic absorption analysis) and intestinal absorption (59Fe) in mice with hereditary alpha-thalassemia. Mice heterozygous for a radiation-induced alpha-Hb gene deletion exhibit a mild hemolytic anemia, like the human condition, with microcytosis, reticulocytosis, splenomegaly, and chemical evidence of defective alpha-chain synthesis. Quantitative iron determination showed that total iron content in spleen, liver, and kidney, but not heart or lung, of adult alpha-thalassemic mice was greater (P less than .05) than that in unaffected littermates. Iron concentration was also increased in liver (P less than .001), spleen (P = .025), kidney (P = .058), and heart (P = .010); in general, the greater the iron concentration in liver, the greater that in spleen (r = .39, P = .009), kidney (r = .70, P less than .001), and heart (r = .46, P less than .001). In mice examined 8 months postoperatively, splenectomy, as compared to sham operation, significantly raised iron content in extrasplenic tissues, but did not affect total body iron. At 10–11 weeks of age, but no longer at 12–14 weeks, thalassemic mice showed higher rates of iron absorption than age-matched controls. Thus, alpha-thalassemic mice display an early occurring iron absorption defect, leading to a modest, sustained, nonprogressive iron overload, and thereby represent a valuable model for exploring disorders of iron homeostasis.
Because clinical disorders of spontaneous iron overload have no experimental counterpart, we studied iron distribution (atomic absorption analysis) and intestinal absorption (59Fe) in mice with hereditary alpha-thalassemia. Mice heterozygous for a radiation-induced alpha-Hb gene deletion exhibit a mild hemolytic anemia, like the human condition, with microcytosis, reticulocytosis, splenomegaly, and chemical evidence of defective alpha-chain synthesis. Quantitative iron determination showed that total iron content in spleen, liver, and kidney, but not heart or lung, of adult alpha-thalassemic mice was greater (P less than .05) than that in unaffected littermates. Iron concentration was also increased in liver (P less than .001), spleen (P = .025), kidney (P = .058), and heart (P = .010); in general, the greater the iron concentration in liver, the greater that in spleen (r = .39, P = .009), kidney (r = .70, P less than .001), and heart (r = .46, P less than .001). In mice examined 8 months postoperatively, splenectomy, as compared to sham operation, significantly raised iron content in extrasplenic tissues, but did not affect total body iron. At 10–11 weeks of age, but no longer at 12–14 weeks, thalassemic mice showed higher rates of iron absorption than age-matched controls. Thus, alpha-thalassemic mice display an early occurring iron absorption defect, leading to a modest, sustained, nonprogressive iron overload, and thereby represent a valuable model for exploring disorders of iron homeostasis.
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