Nitric oxide and energy production in articular chondrocytes

Abstract

Addition of human, recombinant interleukin-1β (hrIL-1β) to cultures of lapine articular chondrocytes provoked a delayed increase in the production of both nitric oxide (NO) and lactate. These two phenomena followed a similar time course and shared a parallel dose-response sensitivity to hrIL-1β. A causal relationship is suggested by the ability of N-monomethyl-L-arginine (NMA), an inhibitor of NO synthase, to blunt the glycolytic response to hrIL-1β. Furthermore, addition of S-nitroso-N-acetylpenicillamine (SNAP), which spontaneously generates NO in culture, increased lactate production to the same degree as IL-1. However, 8-Br-cGMP and isobutylmethylxanthine (IBMX) had no effect either in the presence or absence of IL-1. Even under standard, aerobic, cell culture conditions, chondrocytes consumed little oxygen, either in the presence or absence of IL-1 or NMA. Furthermore, cyanide at concentrations up to 100 μM had no effect upon NO synthesis or lactate production. Thus, the increases in glycolysis under study were not secondary to reduced mitochondrial activity. Although cells treated with IL-1 had increased rates of glycolysis, their concentrations of ATP fell below those of untreated chondrocytes in a time-dependent, but NMA-independent, manner. Transforming growth factor-β (TGF-β) and synovial cytokines (CAF) also increased lactate production. However, TGF-β failed to induce NO, and its effect on glycolysis was independent of NMA. Furthermore, cells treated with TGF-β were not depleted in ATP. These data are consistent with hypotheses that rates of proteoglycan synthesis are, in part, regulated by the intracellular concentration of ATP or by changes in pericellular pH. These two possibilities are not mutually exclusive.