Inhibition of lipopolysaccharide‐induced inducible nitric oxide synthase and cyclooxygenase‐2 gene expression by 5‐aminoimidazole‐4‐carboxamide riboside is independent of AMP‐activated protein kinase

Abstract

Recent studies suggest AMP-activated protein kinase (AMPK), an enzyme involved in energy homeostasis, might be a novel signaling pathway in regulating inflammatory response, but the precise intracellular mechanisms are not fully understood. In this study, we have demonstrated that 5-aminoimidazole-4-carboxamide riboside (AICAR), an activator of AMPK, inhibited lipopolysaccharide (LPS)-induced protein expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) in macrophages and microglial cells at the gene transcription level. Data obtained from electrophoretic mobility shift assay (EMSA) and promoter activity assay have further confirmed the ability of AICAR to block LPS-mediated NF-kappaB, AP-1, CREB, and C/EBPbeta activation. However, AICAR did not affect LPS-mediated IKK, ERK, and p38 activation. Regardless of the ability of AICAR to activate AMPK, the inhibitory effects of AICAR on iNOS and COX-2 expression were not associated with AMPK. An adenosine kinase inhibitor 5'-iodotubercidin, which effectively abolished AMPK activation caused by AICAR, did not reverse the anti-inflammatory effect of AICAR. Moreover, another AMPK activator metformin was not able to mimic the effects of AICAR. Direct addition of AICAR in EMSA assay interrupted binding of NF-kappaB, CREB, and C/EBPbeta to specific DNA elements. Taken together, this study demonstrates that the anti-inflammatory effects of AICAR against LPS-induced iNOS and COX-2 gene transcription are not associated with AMPK activation, but might be resulting from the direct interference with DNA binding to transcription factors.

AMP-activated Kinase (AMPK) Promotes Innate Immunity and Antiviral Defense through Modulation of Stimulator of Interferon Genes (STING) Signaling

“…There are published examples of AMPK-independent roles for both of these compounds (63,64), stressing the importance of using genetic models to corroborate pharmacologic data. Even after taking this caveat into account, the genetic evidence for the role of AMPK is also not always clear-cut, sometimes even when the same pathways are being scrutinized.…”

Metformin, an Antidiabetic Agent, Suppresses the Production of Tumor Necrosis Factor and Tissue Factor by Inhibiting Early Growth Response Factor-1 Expression in Human Monocytes in Vitro

“…Isoda et al (2006) reported that metformin reduces high-glucose induced proinflammatory signaling independent of AMPK activation in human saphenous vein endothelial cells. Another AMPK activator, 5-aminoimidazole-4-carboxamide riboside, was shown to exhibit anti-inflammatory effects independent of the activation of AMPK in RAW264.7 cells stimulated with LPS (Jhun et al, 2004;Kuo et al, 2008). These observations indicate that the inhibitory effects of metformin on the production of TNF and TF in LPS-or oxLDL-stimulated monocytes might be independent of its activation of AMPK.…”

Identification of Yeast and Human 5-Aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAr) Transporters

“…Although many effects of AICAR are at least partially dependent on AMPK, in many cases the effects of AICAR are AMPKindependent (11)(12)(13)(14)(15), suggesting the existence of additional AICAR targets. Interestingly, in yeast the AMPK homolog named Snf1 appears unaffected by AICAR (16).…”