TETRAHYDROCANNABINOL INHIBITION OF MACROPHAGE NITRIC-OXIDE PRODUCTION

Delta(9)-Tetrahydrocannabinol (THC) inhibited nitric oxide (NO.), prod uction by mouse peritoneal macrophages activated by bacterial endotoxi n lipopolysaccharide (LPS) and interferon-gamma (IFN)-gamma). Inhibiti on of NO. production was noted at THC concentrations as low as 0.5 mu g/mL, and was nearly total at 7 mu g/mL. Inhibition was greatest if TH C was added 1-4 hr before induction of nitric oxide synthase (NOS) by LPS and IFN-gamma, and declined with time after addition of the induci ng agents. This suggested that an early step such as NOS gene transcri ption or NOS synthesis, rather than NOS activity, was affected by THC. Steady-state levels of mRNA for NOS were not affected by THC. In cont rast, protein synthesis was inhibited as indicated by immunoblotting. NOS activity was also decreased in the cytosol of cells pretreated wit h THC. Addition of excess cofactors did not restore activity. Inhibiti on of NO. production was greater at low levels of IFN-gamma, indicatin g the ability of the cytokine to overcome inhibition. The effectivenes s of various THC analogues, in decreasing order of potency, was Delta( 8)-THC > Delta(9)-THC > cannabidiol greater than or equal to 11-OH-THC > cannabinol. The presumably inactive stereoisomer, (+)Delta(9)-THC, and the endogenous ligand for cannabinoid receptors, anandamide, were weakly inhibitory. Inhibition may be mediated by a process that depend s partly on stereoselective receptors and partly on a nonselective pro cess. LPS, IFN-gamma, hormone receptor agonists, and forskolin increas ed macrophage cyclic AMP levels. THC inhibited this increase, indicati ng functional cannabinoid receptors. Addition of 8-bromocyclic AMP inc reased NO. 2-fold, and partially restored NO. production that had been inhibited by THC. This occurred only under conditions of limited NOS induction, suggesting that the effect of THC on cyclic AMP was respons ible for only a small portion of the inhibition of NO. production.