Iron in skin of mice with three etiologies of systemic iron overload

Abstract

In human hemochromatosis, tissue toxicity is a function of tissue iron levels. Despite reports of skin toxicity in hemochromatosis, little is known about iron levels in skin of individuals with systemic iron overload. We measured skin iron and studied skin histology in three mouse models of systemic iron overload: mice with a deletion of the hemochromatosis (Hfe) gene, mice fed a high iron diet, and mice given parenteral injections of iron. In Hfe(-/-) mice, iron content in the epidermis and dermis was unexpectedly the same as in Hfe(+/+) mice, and there were no histological abnormalities detected after 30 wk. A high iron diet produced increased iron in the epidermis of both normal and Hfe(-/-) animals; a high diet increased iron in the dermis only in Hfe(-/-) mice. Increased skin iron was not associated with other histological changes, even after 19 wk. Parenteral administration of iron produced increased iron in the epidermis and dermis, and gave the skin a bronze hue. These results show that the amount and distribution of iron in the skin depends on the etiology of iron overload. It appears that neither Hfe deletion nor elevated skin iron alone can account for cutaneous manifestations reportedly seen in humans with hereditary hemochromatosis.

Figure 1. Iron content changes over time in skin, but is unaffected by genotype

Iron was measured (μg per g dry weight) in the epidermis and hair, harvested at various times and from various locations of 129/Sv Hfe^−/− (solid square or bar) and 129/Sv Hfe^+/+ (open diamond or bar) mice. Each point represents mean + SEM of eight to 13 female animals. Last panel shows 30 wk measurements from additional tissues and dermis from ventral (V), tail (T), dorsal (D), and ear (E) skin.

Figure 2. Supplemental dietary iron increases iron in the epidermis, dermis, hair, and liver in 129/Sv Hfe^−/− and 129/Sv Hfe^+/+ mice

Animals were maintained for 5 wk on a normal diet containing 0.226 g per kg iron (open bars) or on a diet containing 20.226 g per kg iron (closed bars). Iron measurements in the epidermis, dermis, and hair and liver are means ± SEM from five female animals.

Figure 3. Ferritin increases in the epidermis of 129/Sv Hfe^−/− mice maintained on a high iron diet

Protein extracts from the epidermis of 129/Sv Hfe^−/− mice fed on a normal basal diet (lo) or on a high iron diet (hi) were analyzed for 21 kDa mouse ferritin by western blot. Cross-reacting 28 kDa band on this blot serves as internal loading control.

Figure 4. Parenteral injections of iron increase iron in the dermis and epidermis of SKH/129/Sv Hfe^−/− mice

Iron was measured in tissues of SKH/129/Sv Hfe^−/− mice that had received biweekly injections of iron dextran for 2 wk. Data are from groups of five female animals ± SEM saline (□); 0.1 mg ; 1 mg ; 5 mg (■).

Figure 5. Gross and histological appearance of SKH/129/Sv Hfe^−/− mice with iron overload from parentral injections

(A) The hairless, hereditary hemochromatosis mouse on the right was given biweekly injections of 5 mg iron dextran for 2 wk. The littermate on the left was injected with saline. (B) Skin sections from ears were stained with H&E, Perl's iron or Fontana Masson. Blue granules of iron are visible only in the dermis of mice receiving iron injections. Scale bar=250 μm.