EFFECT OF CYCLOSPORINE-A ON RAT SMOOTH-MUSCLE CELL-PROLIFERATION

Cyclosporin A (CsA) is a potent immunosuppressive agent that has signi ficantly 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-mu scle cell (SMC) proliferation. As previous studies on the effect of Cs A on smooth-muscle proliferation have afforded conflicting results, we conducted an in vitro study of the effect of two concentrations of Cs A-10(-6) M (corresponding to the maximal concentration in patients) an d 10(-7) M (corresponding to trough concentrations)-on cultured rat SM C proliferation, as assessed by [H-3]thymidine incorporation into DNA and measuring cell number by a colorimetric method based on the quanti tative staining of cell nuclei. In the presence of 0.5% fetal calf ser um (FCS), 10(-6) M CsA induced an increase in [H-3]thymidine incorpora tion 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 f or 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 [H-3]thymidine incorporation into DNA (from 614.44 +/- 67.76 to 1,220.91 +/- 145.59 cpm/well) and cell numb er (82.39 +/- 6.16 to 165.79 +/- 10.48 cells x 10(3); p < 0.05). In th e presence of 10% FCS, the highest CsA concentration increased [H-3]th ymidine incorporation to 2,115.91 +/- 224.06 cpm/well, with no signifi cant changes in cell number. However, the lowest CsA concentration inc reased both [H-3]thymidine incorporation (to 3,752.58 +/- 525.06 cpm/w ell) and cell number (to 181.27 +/- 14.2 cells x 10(3)). These finding s 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 d iscordant results reported previously.