METHODS: In this study, the chronotherapeutic effect of fisetin on ammonium chloride (AC)-induced hyperammonaemic rats was investigated, to ascertain the time point at which the maximum drug effect is achieved. The anti-hyperammonaemic potential of fisetin (50mg/kg b.w. oral) was analysed when administered to AC treated (100mg/kg b.w. i.p.) rats at 06:00, 12:00, 18:00 and 00:00h. Amelioration of pathophysiological conditions by fisetin at different time points was measured by analysing the levels of expression of liver urea cycle enzymes (carbamoyl phosphate synthetase-I (CPS-I), ornithine transcarbamoylase (OTC) and argininosuccinate synthetase (ASS)), nuclear transcription factor kappaB (NF-κB p65), brain glutamine synthetase (GS) and inducible nitric oxide synthase (iNOS) by Western blot analysis.
RESULTS: Fisetin increased the expression of CPS-I, OTC, ASS and GS and decreased iNOS and NF-κB p65 in hyperammonaemic rats. Fisetin administration at 00:00h showed more significant effects on the expression of liver and brain markers, compared with other time points.
CONCLUSIONS: Fisetin could exhibit anti-hyperammonaemic effect owing to its anti-oxidant and cytoprotective influences. The temporal variation in the effect of fisetin could be due to the (i) chronopharmacological, chronopharmacokinetic properties of fisetin and (ii) modulations in the endogenous circadian rhythms of urea cycle enzymes, brain markers, redox enzymes and renal clearance during hyperammonaemia by fisetin. However, future studies in these lines are necessitated.
METHODOLOGY/PRINCIPAL FINDINGS: Four ligands (1-4) and their respective nickel-containing complexes (5-8) were synthesized and characterized. The compounds synthesized were tested for their effects on NF-κB nuclear translocation, pro-inflammatory cytokines secretion and NF-κB transactivation activity. The active compound was further evaluated on its ability to suppress carrageenan-induced acute inflammation in vivo. A potential binding target of the active compound was also predicted by molecular docking analysis.
CONCLUSIONS/SIGNIFICANCE: Among all synthesized compounds tested, we found that complex [Ni(H2L1)(PPh3)]Cl (5) (complex 5), potently inhibited IκBα degradation and NF-κB p65 nuclear translocation in LPS-stimulated RAW264.7 cells as well as TNFα-stimulated HeLa S3 cells. In addition, complex 5 significantly down-regulated LPS- or TNFα-induced transcription of NF-κB target genes, including genes that encode the pro-inflammatory cytokines TNFα, IFNβ and IL6. Luciferase reporter assays confirmed that complex 5 inhibited the transactivation activity of NF-κB. Furthermore, the anti-inflammatory effect of complex 5 was also supported by its suppressive effect on carrageenan-induced paw edema formation in wild type C57BL/6 mice. Interestingly, molecular docking study showed that complex 5 potentially interact with the active site of IKKβ. Taken together, we suggest complex 5 as a novel NF-κB inhibitor with potent anti-inflammatory effects.