Peroxisome proliferator-activated receptor-γ mediates the anti-inflammatory effect of 3-hydroxy-4-pyridinecarboxylic acid derivatives: Synthesis and biological evaluation

Seven 3-hydroxy-4-pyridinecarboxylic acid derivatives (HPs), aza-analogues of salicylic acid and structurally close to other potent inflammatory pyridine compounds such as aminopyridinylmethanols and aminopyridinamines, were synthesized, and their anti-inflammatory activity was evaluated. The synthesis was performed by adopting a general procedure involving an intramolecular Diels-Alder cycloaddition of oxazoles with acrylic acid to form various substituted pyridinic acids. The newly synthesized HPs did not exhibit cytotoxic activity on human monocytes-derived macrophages at concentrations up to 102 M. Anti-inflammatory activity of the compounds was screened in vitro by evaluating the capability to inhibit cytokines release from lipopolysaccharide (LPS) stimulated human macrophages. 3-hydroxy-1-methyl-4-pyridinecarboxylic acid (24) was found to be the most active HP. At 10 M concentration, HP 24 reduced LPS-induced and nuclear factor-kB activation and cyclooxygenase-2 expression, while increased intracellular reactive oxygen species generation and peroxisome proliferator-activated receptor (PPAR-γ) mRNA transcript level. Indeed, pre-treatment of LPS-exposed human macrophages with PPAR-γ specific antagonist completely prevented HP 24-induced TNF- and IL8 down-regulation, demonstrating that the PPARγ pathway is mandatory for the HP 24 anti-inflammatory effect. Finally, daily treatment with HP 24 ameliorated the outcome of DSS-induced colitis in mice, significantly reducing colonic MPO activity and IL-1 tissue levels.