Babich, H. and E. Borenfreund. Cytotoxic and Morphological Effects of Phenylpropanolamine, Caffeine, Nicotine, and Some of their Metabolites Studied In Vitro. Toxic. in Vitro 1992. 6(6): 493-502. [Reprinted with permission from Elsevier Science].

caffeine - 58-08-2; phenylpropanolamine hydrochloride - 4345-16-8; theophylline - 5967-84-0; nicotinic acid - 59-67-6; nicotine - 54-11-5; nicotinamide - 98-92-0; cotinine - 486-56-6

The neutral red cytotoxicity assay was used in vitro to evaluate the potencies of phenylpropanolamine (PPA), nicotine, caffeine, some of their metabolites, and related chemicals. The human cell types used as targets included fibroblast (HFF), melanoma (SK-Mel/27), and hepatoma (HepG2) cell lines and early passage endothelial (ENDO) cells and keratinocytes (NHEK). For all of these cells, nicotine was more cytotoxic than cotinine, its major metabolite. In turn, cotinine was more cytotoxic than chemically related compounds such as nicotinic acid and nicotinamide. Nicotine, but neither cotinine, nicotinic acid, nor nicotinamide, induced cytoplasmic vacuolization in all the cell types tested. Except for the ENDO cells, caffeine and its metabolite, theophylline, showed approximately equivalent cytotoxic potencies. However, for the ENDO cells, caffeine was more cytotoxic than theophylline. Furthermore, the ENDO cells were 2-3 times more sensitive to caffeine and theophylline than were the other cell types. The phenylpropanolamine induced cytoplasmic vacuolization only in the ENDO cells. Combinations of caffeine + PPA interacted synergistically in their cytotoxicity towards the HepG2 cells; a similar synergistic interaction was not noted with the ENDO cells.