Obesity increases neuropathic pain via the AMPK-ERK-NOX4 pathway in rats.

This study focused on the relationship between extracellular-regulated kinase (ERK) and obesity-induced increases in neuropathic pain. We fed rats a high-fat diet to establish the obesity model, and rats were given surgery to establish the chronic compression of the dorsal root ganglia (CCD) model. U0126 was applied to inhibit ERK, and metformin or 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) was applied to cause AMP-activated protein kinase (AMPK) activation. Paw withdrawal mechanical threshold (PWMT) were calculated to indicate the level of neuropathic pain. The data indicated that compared with normal CCD rats, the PWMT of obese CCD rats were decreased, accompanied with an increase of ERK phosphorylation, NAD(P)H oxidase 4 (NOX4) protein expression, oxidative stress and inflammatory level in the L4 to L5 spinal cord and dorsal root ganglia (DRG). Administration of U0126 could partially elevate the PWMT and reduce the protein expression of NOX4 and the above pathological changes in obese CCD rats. In vitro, ERK phosphorylation, NOX4 protein expression increased significantly in DRG neurons under the stimulation of palmitic acid (PA), accompanied with increased secretion of inflammatory factors, oxidative stress and apoptosis level, while U0126 partially attenuated the PA-induced upregulation of NOX4 and other pathological changes. In the rescue experiment, overexpression of NOX4 abolished the above protective effect of U0126 on DRG neurons in high-fat environment. Next, we explore upstream mechanisms. Metformin gavage significantly reduced neuropathic pain in obese CCD rats. For the mechanisms, activating AMPK with metformin (obese CCD rats) or AICAR (DRG neurons in a high-fat environment) not only inhibited the ERK-NOX4 pathway, but also improved oxidative stress and inflammation caused by high-fat. In conclusion, the AMPK-ERK-NOX4 pathway may has a pivotal role in mediating obesity-induced increases in neuropathic pain.

Vitamin B6 inhibits macrophage activation to prevent lipopolysaccharide-induced acute pneumonia in mice.

Macrophage activation participates in the pathogenesis of pulmonary inflammation. As a coenzyme, vitamin B6 (VitB6) is mainly involved in the metabolism of amino acids, nucleic acids, glycogen and lipids. We have previously reported that activation of AMP-activated protein kinase (AMPK) produces anti-inflammatory effects both in vitro and in vivo. Whether VitB6 via AMPK activation prevents pulmonary inflammation remains unknown. The model of acute pneumonia was induced by injecting mice with lipopolysaccharide (LPS). The inflammation was determined by measuring the levels of interleukin-1 beta (IL-1ß), IL-6 and tumour necrosis factor alpha (TNF-α) using real time PCR, ELISA and immunohistochemistry. Exposure of cultured primary macrophages to VitB6 increased AMP-activated protein kinase (AMPK) Thr172 phosphorylation in a time/dose-dependent manner, which was inhibited by compound C. VitB6 downregulated the inflammatory gene expressions including IL-1ß, IL-6 and TNF-α in macrophages challenged with LPS. These effects of VitB6 were mirrored by AMPK activator 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR). However, VitB6 was unable to inhibit LPS-induced macrophage activation if AMPK was in deficient through siRNA-mediated approaches. Further, the anti-inflammatory effects produced by VitB6 or AICAR in LPS-treated macrophages were abolished in DOK3 gene knockout (DOK3-/- ) macrophages, but were enhanced in macrophages if DOK3 was overexpressed. In vivo studies indicated that administration of VitB6 remarkably inhibited LPS-induced both systemic inflammation and acute pneumonia in wild-type mice, but not in DOK3-/- mice. VitB6 prevents LPS-induced acute pulmonary inflammation in mice via the inhibition of macrophage activation.