Effect of cyclosporin A on rat smooth-muscle cell proliferation

Cyclosporin A (CsA) is a potent immunosuppressive agent that has significantly improved graft survival in organ- and bone-marrow-transplant recipients. However, in the context of graft transplantation, CsA has been suggested to potentiate vascular disease by stimulating smooth-muscle cell (SMC) proliferation. As previous studies on the effect of CsA on smooth-muscle proliferation have afforded conflicting results, we conducted an in vitro study of the effect of two concentrations of CsA--10(-6) M (corresponding to the maximal concentration in patients) and 10(-7) M (corresponding to trough concentrations)--on cultured rat SMC proliferation, as assessed by [3H]thymidine incorporation into DNA and measuring cell number by a colorimetric method based on the quantitative staining of cell nuclei. In the presence of 0.5% fetal calf serum (FCS), 10(-6) M CsA induced an increase in [3H]thymidine incorporation into DNA (from 614.44 +/- 67.76 to 1,472.6 +/- 177.63 cpm/well; p < 0.05) with no increase in the number of cells. A cytotoxic effect for this dose was ruled out owing to the absence of significant levels of lactate dehydrogenase (LDH) activity in the supernatant. CsA, 10(-7) M, induced an increase in both [3H]thymidine incorporation into DNA (from 614.44 +/- 67.76 to 1,220.91 +/- 145.59 cpm/well) and cell number (82.49 +/- 6.16 to 165.79 +/- 10.48 cells x 10[3]; p < 0.05). In the presence of 10% FCS, the highest CsA concentration increased [3H]thymidine incorporation to 2,115.91 +/- 224.06 cpm/well, with no significant changes in cell number. However, the lowest CsA concentration increased both [3H]thymidine incorporation (to 3.752.58 +/- 525.06 cpm/well) and cell number (to 181.27 +/- 14.2 cells x 10[3]). These findings suggest that the proliferative effect of CsA on SMCs is variable and that it depends on the concentration of the drug, in support of the discordant results reported previously.