Abstract
BackgroundHomocysteine and pro-inflammatory mediators such as cyclooxygenase-2 (COX-2) have been linked to vascular dysfunction and risks of cardiovascular diseases. Fulvic acid (FA), a class of compounds of humic substances, possesses various pharmacological properties. However, the effect of FA on inflammatory responses of the monocytes remains unclear. We investigated the regulatory effect of FA on homocysteine-induced COX-2 expression in human monocytes.MethodsPeripheral blood monocytes and U937 cells were used for all experiments. Real-time PCR and ELISA assay were used to analyze the COX-2 mRNA expression and PGE2 secretion, respectively. Specific inhibitors were used to investigate the mechanism of homocysteine-mediating COX-2 mRNA expression and PGE2 secretion. Luciferase assay, transcription factor ELISA, and chromatin immunoprecipitation were used to determine the role of nuclear factor-κB in FA-mediated inhibition of homocysteine effect on monocytes.ResultsThe results show that pretreating monocytes with FA inhibited the homocysteine-induced COX-2 expression in a dose-dependent manner. Stimulation of U937 monocytes with homocysteine induced rapid increases in the phosphorylation of ERK and JNK; the inhibitor for ERK and JNK attenuated the homocysteine-induced nuclear factor-κB activation and COX-2 expression. Transcription factor ELISA and chromatin immunoprecipitation assays showed that FA blocked the homocysteine-induced increases in the binding activity and in vivo promoter binding of nuclear factor-κB in monocytes.ConclusionsOur findings provide a molecular mechanism by which FA inhibits homocysteine-induced COX-2 expression in monocytes, and a basis for using FA in pharmaceutical therapy against inflammation.
Highlights
Homocysteine and pro-inflammatory mediators such as cyclooxygenase-2 (COX-2) have been linked to vascular dysfunction and risks of cardiovascular diseases
Our findings provide a molecular mechanism by which Fulvic acid (FA) inhibits homocysteine-induced COX-2 expression in monocytes, and a basis for using FA in pharmaceutical therapy against inflammation
Cytotoxic effect of FA on human monocytes To examine the effect of FA on the viability of monocytes, human primary monocytes and U937 cells were treated with FA at a concentration of 0.5, 1, 5, or 10 μg/mL for 24 h, and the MTT assay was performed
Summary
Homocysteine and pro-inflammatory mediators such as cyclooxygenase-2 (COX-2) have been linked to vascular dysfunction and risks of cardiovascular diseases. We investigated the regulatory effect of FA on homocysteine-induced COX-2 expression in human monocytes. FA has been reported recently to have nutraceutical properties and physiological action on the human body. It is one of the most interesting naturally occurring phytochemicals with its neuroprotective effect [2,3]. The FA extracted from peat had an antioxidant activity and an inhibitory effect on chemical mediator release in basophils [6]. These results imply that the FA may possess a predominant role in their biological activity. There are a number of studies on the effect of FA on cellular and biological functions, the detailed mechanisms underlying the regulatory effect of FA remain unclear
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