Since iron has been implicated as a potential nephrotoxin, we examined the effect of iron on several aspects of cultured renal tubular epithelial cell biology. We found that exposure to 10(-4) M of either the ferrous or ferric form of iron impaired healing of denuded areas made within confluent monolayers of LLC-PK1 cells. This impairment required 30 to 80 hours of exposure to iron to occur and was also seen in another renal tubular epithelial cell line (MDCK cells). To delineate the potential mechanism(s) of this impairment, we examined the expression of a key integrin subunit involved in cell-matrix adhesion. Exposure of LLC-PK1 cells to 10(-4) M ferric citrate for 72 hours significantly decreased expression of the beta 1 integrin subunit as determined by flow cytometry. To determine if iron impairs another process that occurs at the basolateral surface, the effects of 72 hours of exposure to iron on adenylate cyclase activity were examined. Both ferric and ferrous citrate significantly enhanced vasopressin- and forskolin-stimulated adenylate cyclase activity. To examine if iron can regulate proliferation, the effect of iron on 3H-thymidine uptake was measured. We found that ferric citrate diminished proliferation and this decrease required the presence of either serum or transferrin. To ascertain if iron affected ultrastructure, we used transmission electron microscopy and found that iron accumulation within cells was much more apparent with ferric than ferrous citrate. Ferric iron induced mild-to-moderate cytopathic changes. These results indicate that iron is capable of inducing multiple changes in renal tubular epithelial function. The effect of iron to impair wound healing may be related to diminished expression of the beta 1 integrin subunit and perhaps to impaired proliferation.

Local release of mitogenic and chemotactic signals during angioplasty-induced vascular injury may initiate restenosis. We investigated whether mechanical injury to vascular smooth muscle cells (VSMC) results in the release of biologically active peptide growth factors. Monolayers of bovine SMC cultures were mechanically injured by cell scraping. Conditioned medium (CM) from control and injured SMC cultures was collected, and the mitogenic activity was measured by [3H]thymidine incorporation in recipient SMC cultures. Mitogenic activity from injured CM was detected within 15 min after injury. When the CM from injured cells was removed 15 min after injury and replaced with serum-free media, there was no detectable mitogenic activity in the replacement CM assessed 1-6 days postinjury. Suramin, a nonspecific peptide growth factor antagonist, significantly inhibited the mitogenic activity of injured CM. Basic fibroblast growth factor (bFGF), platelet-derived growth factor (PDGF A chain), and epidermal growth factor (EGF) were detected in CM from injured cells by immunoblot analysis. The mitogenic activity of injured CM was significantly inhibited with neutralizing antibodies to bFGF (34%), PDGF-AA (32%), PDGF-BB (25%), and EGF (25%). A neutralizing antibody to transforming growth factor (TGF)-beta had no effect. In conclusion, bFGF, PDGF, and EGF are immediately released from mechanically injured VSMC. VSMC likely contain preformed, biologically active growth factors that are efficiently released from the cell cytoplasm following mechanical injury. Conditioned medium from injured VSMC is highly mitogenic, and this activity is probably due to multiple growth factors interacting synergistically.

Risk of type 1 diabetes at 3 years is high for initially multiple and single Ab+ IT and multiple Ab+ NT. Genetic predisposition, age, and male sex are significant risk factors for development of Ab+ in twins.

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