Petroleum hydrocarbon toxicity in vitro: effect of n-alkanes,benzene and toluene on pulmonary alveolar macrophages and lysosomal enzymes of the lung

The in vitro effects of straight chain alkanes (nC₆-nC₁₀), benzene and toluene on pulmonary alveolar macrophages (PAM) of rats and rabbits was studied. The concentrations used ranged from 0.02 to 1.0 mM. All hydrocarbons used in the study were cytotoxic to isolated cultured PAM cells in a dose-dependent manner. The LC₅₀ for these hydrocarbons towards rat PAM cells was estimated to be 1.0 mM for nC₈, 2 mM for nC₇, 5 mM for nC₉ and 10 mM for nC₆, nC₁₀, benzene and toluene. Rabbit PAM cells were more sensitive to the hydrocarbons, resulting in an LC₅₀ half that for rat PAM cells. Hydrocarbons also caused extracellular release of the lysosomal enzymes cathepsin D (EC 3.4.23.5) and cathepsin B (EC 3.4.22.1) in a manner corresponding with cell damage. There was more cathepsin D activity released from cells than cathepsin B. In addition, hydrocarbons also caused the release of cathepsin B and D from isolated lysosomes, and there was 10–15% more enzyme activity released in the culture medium of lysosomes exposed to concentrations of 0.5 and 1.0 mM compared to PAM cell cultures of either rats or rabbits. Hydrocarbons also caused loss of cell respiration and stimulated a dose-dependent and a time-dependent increase in lipid peroxidation. The two alkanes nC₇ and nC₈ caused the greatest increase in lipid peroxidation and the greatest loss of cell respiration. The results indicate that there is a relationship between chain length of alkanes and their cytotoxicity to PAM cells. The results also demonstrate a good correlation between decreased cell viability, increased lysosomal enzyme release, decreased cell respiration and increased lipid peroxidation in response to the hydrocarbons.