Gut microbiota in chronic pain: Novel insights into mechanisms and promising therapeutic strategies.

Chronic pain remains one of the world's most persistent and unsolved clinical challenges that severely affect patients' quality of life. Presently, considering that the mechanisms underlying chronic pain are not fully understood, there is a lack of effective drugs and interventions to treat chronic pain in clinical practice. Therefore, exploring the pathogenic mechanism of chronic pain and establishing potential targets are the keys to treating chronic pain. Substantial evidence has indicated that gut microbiota plays a crucial role in modulating chronic pain, which has opened up a new frontier for investigating the pathogenesis of chronic pain. The gut microbiota is a pivotal junction point between the neuroimmune-endocrine and the microbiome-gut-brain axes that could directly or indirectly affect chronic pain. Different signaling molecules (such as metabolites, neuromodulators, neuropeptides, and neurotransmitters) from the gut microbiota regulate the progress of chronic pain by modulating the peripheral and central sensitization by targeting the corresponding receptors. Furthermore, gut microbiota dysbiosis is associated with the progress of different chronic pain disorders, such as visceral pain, neuropathic pain, inflammatory pain, migraine, and fibromyalgia. Therefore, the present review attempted to systematically summarize the action of the gut microbiota toward regulating the pathological mechanisms of chronic pain and discussed the beneficial effects of probiotics supplementation or fecal microbiota transplantation (FMT) to restore the gut microbiota in chronic pain patients so as to provide a new strategy for targeting the gut microbiota for alleviating chronic pain issues.

Nrf2-Dependent Protective Effect of Paeoniflorin on α-Naphthalene Isothiocyanate-Induced Hepatic Injury.

The pathological mechanism of cholestatic hepatic injury is associated with oxidative stress, hepatocyte inflammation, and dysregulation of hepatocyte transporters. Paeonia lactiflora Pall. and its compound can improve hepatic microcirculation, dilate bile duct, and promote bile flow, which is advantageous to ameliorate liver damage. Paeoniflorin (PEA), as the main efficacy component of Paeonia lactiflora Pall., has multiple pharmacological effects. PEA improves liver injury, but it remains obscure whether the protective action on [Formula: see text]-naphthalene isothiocyanate (ANIT)-induced cholestatic liver injury is dependent on the NF-E2 p45-related Factor 2 (Nrf2) signaling pathway. In this study, C57BL/6 mice were administrated with 80 mg⋅kg[Formula: see text]⋅d[Formula: see text] ANIT followed by PEA (75, 150, and 300 mg⋅kg[Formula: see text]⋅d[Formula: see text]) orally for 10 days, respectively. Tissue histology and liver function were detected, including serum enzymes, gallbladder (GB) weight, phenobarbital-induced sleeping time (PEN-induced ST), hepatic uridine di-phosphoglucuronosyltransferase (UDPG-T), malondialdehyde (MDA), and glutathione (GSH). The expressions of protein Nrf2, sodium taurocholate cotransporting polypeptide (Ntcp), and NADPH oxidase 4 (Nox4) were evaluated. Nrf2 plasmid or siRNA-Nrf2 transfection on LO2 cells and Nrf2-/- mice were used to explore the liver protective mechanism of PEA. Compared to ANIT-treated mice, PEA decreased serum levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), total bilirubin (TBIL), direct bilirubin (DBIL), total bile acid (TBA), and phenobarbital-induced sleeping time. The bile secretion, hepatic UDPG-T, MDA, GSH, and liver histology were improved. The expressions of protein Nrf2 and Ntcp in liver tissues increased, but Nox4 decreased. After Nrf2 plasmid or small interfering RNA (siRNA)-Nrf2 transfection, the protective effects of PEA on LO2 cells were, respectively, strengthened or weakened. Moreover, PEA had no significant effects on ANIT-treated Nrf2-/- mice. Our results suggest that Nrf2 is essential for PEA protective effects on ANIT-induced liver injury.