Nicotinamide is a potent inhibitor of proinflammatory cytokines

Abstract

The present study investigates the modulating effects of nicotinamide on the cytokine response to endotoxin. In an in vitro model of endotoxaemia, human whole blood was stimulated for two hours with endotoxin at 1 ng/ml, achieving high levels of the proinflammatory cytokines IL-1 beta, IL-6, IL-8 and TNF alpha. When coincubating whole blood, endotoxin and the vitamin B3 derivative nicotinamide, all four cytokines measured were inhibited in a dose dependent manner. Inhibition was observed already at a nicotinamide concentration of 2 mmol/l. At a concentration of 40 mmol/l, the IL-1 beta, IL-6 and TNF alpha responses were reduced by more than 95% and the IL-8 levels reduced by 85%. Endotoxin stimulation activates poly(ADP-ribose)polymerase (PARP), a nuclear DNA repair enzyme. It has been hypothesized that the anti-inflammatory properties of nicotinamide are due to PARP inhibition. In the present study, the endotoxin induced PARP activation was dose dependently decreased with 4-40 mmol/l nicotinamide or 4-100 micro mol/l 6(5H) phenanthridinone, a specific PARP inhibitor. 6(5H)phenanthridinone however, failed to inhibit the proinflammatory cytokines. Thus, the mechanism behind the cytokine inhibition in our model seems not to be due to PARP inhibition. In conclusion, the present study could not only confirm previous reports of a down-regulatory effect on TNFalpha, but demonstrates that nicotinamide is a potent modulator of several proinflammatory cytokines. These findings demonstrate that nicotinamide has a potent immunomodulatory effect in vitro, and may have great potential for treatment of human inflammatory disease.

Fig. 1

(a) IL-6, (b) TNFα,(c) IL-1β and (d) IL-8 responses to a two hour incubation of whole blood with 1 ng/ml endotoxin at 37°C with 5% CO₂. A dose dependent down-regulation by 2–100 mmol/l nicotinamide is observed. Box plots are shown with 5th & 95th percentiles. *statistically significant P < 0·05 compared to initial levels.

Fig. 2

PARP activity was inhibited by nicotinamide. PARP activity induced by 1 ng/ml endotoxin was set to 100%. Arrows indicate samples incubated for two hours without endotoxin or nicotinamide. …… negative control for each experiment. • and ○ symbolize the two healthy volunteers.

Fig. 3

IL-1β, IL-6, IL-8 and TNFα responses to 1 ng/ml endotoxin in whole blood, into which different amounts of the specific PARP inhibitor 6(5H)phenanthridinone had been added to five different tubes. n= 2, each line represents one healthy volunteer. Left y-axis: □ TNFα, ○ IL-8, ▪ IL-6; right side y-axis • IL-1β.