Inhibitory effect of porphyrins on the proliferation of mouse spleen lymphocytes in vitro

The influence of various porphyrins (deuteroporphyrin IX, mesoporphyrin IX, protoporphyrin IX, hematoporphyrin) and two related compounds (hemin, biliverdin) on the spontaneous proliferation of mouse spleen lymphocytes has been estimated in vitro by the 3H-thymidine uptake assay. It has been found that porphyrins (endogenous ligands for the mitochondrial benzodiazepine receptor) produce a concentration-dependent inhibition of 3H-thymidine incorporation into the DNA of these cells. Metalloporphyrin-hemin has been observed to evoke a weak inhibitory effect, in a high concentration (10(-4)M), whereas biliverdin, a porphyrins degradation product, was inactive in the same experimental conditions. Those findings indicate that endogenous porphyrins, presumably acting through the mitochondrial benzodiazepine receptor, could regulate the proliferation of mouse spleen lymphocytes in vitro.