Lactic acidosis increases tumor necrosis factor secretion and transcription in vitro

Lactic acid has been shown to affect numerous biologic processes. We investigated the role of lactic acidosis as a signal for the production of TNF by macrophages in vitro. Male F344 rats were administered thioglycolate media intraperitoneally. Macrophages were recovered 7 days later, cultured for 24 hr in complete media (CM), or CM with L-lactic acid (5, 10, or 15 mM), or with endotoxin (LPS) (10 micrograms/ml). TNF levels were measured in the supernatants. Female C57BL/6 mice were similarly treated, and macrophages were harvested and cultured in CM or CM containing lactic acid (15 mM), or LPS (10 micrograms/ml). RNA was extracted after 24 hr, separated by electrophoresis, and transferred to nitrocellulose. Human 32P-cDNA TNF and actin probes were used to determine relative TNF gene expression. Gel densitometry was used to calculate the TNF expression index (EI) in lactic acid and LPS treated cells as described. pH levels of the supernatant indicated that increasing concentrations of lactic acid caused increasing acidosis. Trypan blue exclusion demonstrated that lactic acidosis did not reduce cell viability. LPS significantly increased secretion of TNF relative to control (P less than 0.001). Each concentration of lactic acid significantly increased TNF secretion (P less than 0.05), but not in a dose-dependent manner. TNF gene transcription was elevated in macrophages cultured with lactic acid and LPS relative to control (EI = 1.13 and 1.18, respectively). This suggests that lactic acid concentration can regulate TNF secretion at the level of transcription, and is consistent with the hypothesis that local levels of lactic acid (lactic acidosis) may be a regulator of cytokine secretion.