Sulfur compounds isolated from garlic exert anti-inflammatory properties. We recently isolated thiacremonone, a novel sulfur compound from garlic. Here, we investigated the anti-inflammatory and arthritis properties of thiacremonone through inhibition of NF-kappaB since NF-kappaB is known to be a target molecule of sulfur compounds and an implicated transcription factor regulating inflammatory response genes.
The anti-inflammatory and arthritis effects of thiacremone in in vivo were investigated in 12-O-tetradecanoylphorbol-13-acetate-induced ear edema, carrageenan and mycobacterium butyricum-induced inflammatory and arthritis models. Lipopolysaccharide-induced nitric oxide (NO) production was determined by Griess method. The DNA binding activity of NF-kappaB was investigated by electrophoretic mobility shift assay. NF-kappaB and inducible nitric oxide synthetase (iNOS) transcriptional activity was determined by luciferase assay. Expression of iNOS and cyclooxygenase-2 (COX-2) was determined by western blot.
The results showed that topical application of thiacremonone (1 or 2 microg/ear) suppressed the 12-O-tetradecanoylphorbol-13-acetate-induced (1 microg/ear) ear edema. Thiacremonone (1-10 mg/kg) administered directly into the plantar surface of hind paw also suppressed the carrageenan (1.5 mg/paw) and mycobacterium butyricum (2 mg/paw)-induced inflammatory and arthritic responses as well as expression of iNOS and COX-2, in addition to NF-kappaB DNA-binding activity. In further in vitro study, thiacremonone (2.5-10 microg/ml) inhibited lipopolysaccharide (LPS, 1 microg/ml)-induced nitric oxide (NO) production, and NF-kappaB transcriptional and DNA binding activity in a dose dependent manner. The inhibition of NO by thiacremonone was consistent with the inhibitory effect on LPS-induced inducible nitric oxide synthase (iNOS) and COX-2 expression, as well as iNOS transcriptional activity. Moreover, thiacremonone inhibited LPS-induced p50 and p65 nuclear translocation, resulting in an inhibition of the DNA binding activity of the NF-kappaB. These inhibitory effects on NF-kappaB activity and NO generation were suppressed by reducing agents dithiothreitol (DTT) and glutathione, and were abrogated in p50 (C62S)-mutant cells, suggesting that the sulfhydryl group of NF-kappaB molecules may be a target of thiacremonone.
The present results suggested that thiacremonone exerted its anti-inflammatory and anti-arthritic properties through the inhibition of NF-kappaB activation via interaction with the sulfhydryl group of NF-kappaB molecules, and thus could be a useful agent for the treatment of inflammatory and arthritic diseases.