Effect of cyclosporin A or tacrolimus on the function of blood-brain barrier cells.

Recently, it has been reported that continuous treatment with cyclosporin A or tacrolimus induces encephalopathy in transplant patients. The mechanism of immunosuppressant-induced encephalopathy is unclear. We investigated the cytotoxicity to brain capillary endothelial cells and the effect of these two drugs on P-glycoprotein function using mouse brain capillary endothelial (MBEC4) cells. The transcellular transport of [3H]sucrose was significantly increased and the cellular viability, based on 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromide (MTT) assay and trypan blue exclusion test, was decreased by cyclosporin A (approximately 50% at 5 microM; P<0.005), while tacrolimus showed a much smaller effect. These findings indicate that the toxicity of cyclosporin A was greater than that of tacrolimus. The uptake of [3H]vincristine, a substrate of P-glycoprotein, was increased by these two drugs. The expression of P-glycoprotein in MBEC4 cells was reduced, but there was no effect on mdr1b mRNA levels. The decrease in the expression of P-glycoprotein may be due to the inhibition of the turnover of P-glycoprotein, which involves translation. In conclusion, the direct cytotoxic effect on the brain capillary endothelial cells and the inhibition of P-glycoprotein may be partly involved in the occurrence of immunosuppressant-induced encephalopathy.