A role for gut microbiota in early-life stress-induced widespread muscle pain in the adult rat

Gut Microbiota: A Modulator and Therapeutic Target for Chronic Pain

Chronic pain is a prevalent condition, impacting nearly one-fifth of the global population. Despite the availability of various clinical treatments, each comes with inherent limitations, and few offer a complete cure, resulting in a significant social and economic burden. Therefore, it is important to determine the pathogenesis and causes of chronic pain. Numerous studies have shown a close link between the intestinal microflora and chronic pain. The gut microbiota can exert their effects on chronic pain through both central and peripheral mechanisms and is able to communicate with the brain through its own components or metabolites. They also can regulate chronic pain by affecting pro- and anti-inflammatory cells. This review is aimed at reviewing the connection between gut flora and different types of chronic pain, including visceral pain, neuropathic pain, inflammatory pain, musculoskeletal pain, migraine, and chronic cancer pain; exploring the central and peripheral mechanisms of the influence of gut flora on chronic pain; and attempting to provide novel treatment options for chronic pain, that is, the gut microbiota can be regulated by probiotics, fecal microbial transplantation, and natural products to treat chronic pain. By examining the intricate relationship between gut flora and chronic pain, the review sought to pave the way for new treatment strategies that target the gut microbiota, offering hope for more effective pain management.

Rodent Diets Incorporated with Live Biotherapeutic Products (LBPs): An Innovative Dosing Strategy to Support Preclinical Animal Studies on LBP Intervention

Currently, the administration of live biotherapeutic products (LBPs) in animal-based pre-clinical studies is achieved via oral gavage or voluntary consumption through the water supply. Oral gavage provides the most accurate and precise dosing for the administration of LBPs to laboratory animals; however, it induces stress responses and is labor-intensive, especially when long-term dosing is needed, placing a significant burden on both lab personnel and the subject animals. On the other hand, voluntary LBP consumption through water supply requires less effort and reduces animal stress, but still puts challenges concerning uncontrolled dosing, variations in LBP viability during the dosing period, uneven dosing due to sedimentation of LBPs, and the need for frequent refreshments due to stability and viability concerns in an aqueous environment. To address these problems, we developed lyophilized rodent diet pellets incorporated with stabilized Bioengineered Probiotic Yeast Medicines (BioPYM™), with customizable pellet size, robust mechanical strength, low friability, uniform BioPYM distribution, and proved stability for 10 weeks at 4 to 8°C storage, ensuring easy handling and more reliable dosing. Optimal cell viability preservation in dry diets was achieved through optimization of lyoprotectant and blending methods. Pharmacokinetic studies of the shedding of live BioPYM cells and their therapeutic payloads revealed the effective delivery of therapeutic agents targeting rodent gastrointestinal system. Overall, BioPYM-diet pellets represent an improved method for the delivery of LBP, and provide convenient and precise dosing. In addition, this method improves laboratory animal welfare and decreases laboratory workload.

Microbiome contributions to pain: a review of the preclinical literature

ABSTRACT

Over the past 2 decades, the microbiome has received increasing attention for the role that it plays in health and disease. Historically, the gut microbiome was of particular interest to pain scientists studying nociplastic visceral pain conditions given the anatomical juxtaposition of these microorganisms and the neuroimmune networks that drive pain in such diseases. More recently, microbiomes both inside and across the surface of the body have been recognized for driving sensory symptoms in a broader set of diseases. Microbiomes have never been a more popular topic in pain research, but to date, there has not been a systematic review of the preclinical microbiome pain literature. In this article, we identified all animal studies in which both the microbiome was manipulated and pain behaviors were measured. Our analysis included 303 unique experiments across 97 articles. Microbiome manipulation methods and behavioral outcomes were recorded for each experiment so that field-wide trends could be quantified and reported. This review specifically details the animal species, injury models, behavior measures, and microbiome manipulations used in preclinical pain research. From this analysis, we were also able to conclude how manipulations of the microbiome alter pain thresholds in naïve animals and persistent pain intensity and duration in cutaneous and visceral pain models. This review summarizes by identifying existing gaps in the literature and providing recommendations for how to best plan, implement, and interpret data collected in preclinical microbiome pain experiments.

Dysbiosis is associated with the behavioral phenotype observed in the triple-hit Wisket rat model of schizophrenia

Comorbidities between gastrointestinal diseases and psychiatric disorders have been widely reported, with the gut-brain axis implicated as a potential biological basis. Thus, dysbiosis may play an important role in the etiology of schizophrenia, which is barely detected. Triple-hit Wisket model rats exhibit various schizophrenia-like behavioral phenotypes. The present study aimed to compare the diversity and abundance of gut microbiota in Wisket model and control rats; furthermore, to correlate the microbial taxonomic profiles to indices of behavioral change. Tail-flick and Ambitus tests were used to assess acute heat pain sensitivity, and record exploration and locomotor activity along with motivation in young adult, control and Wisket model rats. Fecal microbiota composition was profiled by deep sequencing of bacterial 16S rRNA, and it was correlated to behavioral phenotype. Wisket rats exhibited significantly decreased pain sensitivity, lower locomotor activity and exploration, and impaired motivation compared with controls. No significant differences were observed in bacterial alpha diversity between the groups; however, clear differences in community structure were observed. Wisket rats showed decreases in several genera of Firmicutes and Saccharimonas, and increases in Bacteriodetes and Helicobacter phyla compared with controls. Correlation analysis revealed significant associations between the microbiota profile and the behavioral phenotype. This is the first demonstration that fecal microbiota composition is markedly altered in a triple-hit schizophrenia rat model, suggesting the contribution of the microbiota-gut-brain axis in the development of the schizophrenia-like behavioral phenotype. Thus targeting the gut microbiota may be a novel approach to treat such impairments.

Probiotic and high-fat diet: effects on pain assessment, body composition, and cytokines in male and female adolescent and adult rats

Obesity in adolescence is increasing in frequency and is associated with elevated proinflammatory cytokines and chronic pain in a sex-dependent manner. Dietary probiotics may mitigate these detrimental effects of obesity. Using a Long-Evans adolescent and adult rat model of overweight (high-fat diet (HFD) - 45% kcal from fat from weaning), we determined the effect of a single-strain dietary probiotic [Lactiplantibacillus plantarum 299v (Lp299v) from weaning] on the theoretically increased neuropathic injury-induced pain phenotype and inflammatory cytokines. We found that although HFD increased fat mass, it did not markedly affect pain phenotype, particularly in adolescence, but there were subtle differences in pain in adult male versus female rats. The combination of HFD and Lp299v augmented the increase in leptin in adolescent females. There were many noninteracting main effects of age, diet, and probiotic on an array of cytokines and adipokines with adults being higher than adolescents, HFD higher than the control diet, and a decrease with probiotic compared with placebo. Of particular interest were the probiotic-induced increases in IL12p70 in female adolescents on an HFD. We conclude that a more striking pain phenotype could require a higher and longer duration caloric diet or a different etiology of pain. A major strength of our study was that a single-strain probiotic had a wide range of inhibiting effects on most proinflammatory cytokines. The positive effect of the probiotic on leptin in female adolescent rats is intriguing and worthy of exploration.NEW & NOTEWORTHY A single-strain probiotic (Lp299v) had a wide range of inhibiting effects on most proinflammatory cytokines (especially IL12p70) measured in this high-fat diet rat model of mild obesity. The positive effect of probiotic on leptin in female adolescent rats is intriguing and worthy of exploration.

Pathology of pain and its implications for therapeutic interventions

Pain is estimated to affect more than 20% of the global population, imposing incalculable health and economic burdens. Effective pain management is crucial for individuals suffering from pain. However, the current methods for pain assessment and treatment fall short of clinical needs. Benefiting from advances in neuroscience and biotechnology, the neuronal circuits and molecular mechanisms critically involved in pain modulation have been elucidated. These research achievements have incited progress in identifying new diagnostic and therapeutic targets. In this review, we first introduce fundamental knowledge about pain, setting the stage for the subsequent contents. The review next delves into the molecular mechanisms underlying pain disorders, including gene mutation, epigenetic modification, posttranslational modification, inflammasome, signaling pathways and microbiota. To better present a comprehensive view of pain research, two prominent issues, sexual dimorphism and pain comorbidities, are discussed in detail based on current findings. The status quo of pain evaluation and manipulation is summarized. A series of improved and innovative pain management strategies, such as gene therapy, monoclonal antibody, brain-computer interface and microbial intervention, are making strides towards clinical application. We highlight existing limitations and future directions for enhancing the quality of preclinical and clinical research. Efforts to decipher the complexities of pain pathology will be instrumental in translating scientific discoveries into clinical practice, thereby improving pain management from bench to bedside.

Opioid-induced dysbiosis of maternal gut microbiota during gestation alters offspring gut microbiota and pain sensitivity

There has been a rapid increase in neonates born with a history of prenatal opioid exposure. How prenatal opioid exposure affects pain sensitivity in offspring is of interest, as this may perpetuate the opioid epidemic. While few studies have reported hypersensitivity to thermal pain, potential mechanisms have not been described. This study posits that alterations in the gut microbiome may underly hypersensitivity to pain in prenatally methadone-exposed 3-week-old male offspring, which were generated using a mouse model of prenatal methadone exposure. Fecal samples collected from dams and their offspring were subjected to 16s rRNA sequencing. Thermal and mechanical pain were assessed using the tail flick and Von Frey assays. Transcriptomic changes in whole brain samples of opioid or saline-exposed offspring were investigated using RNA-sequencing, and midbrain sections from these animals were subjected to qPCR profiling of genes related to neuropathic and inflammatory pain pathways. Prenatal methadone exposure increased sensitivity to thermal and mechanical pain and elevated serum levels of IL-17a. Taxonomical analysis revealed that prenatal methadone exposure resulted in significant alterations in fecal gut microbiota composition, including depletion of Lactobacillus, Bifidobacterium, and Lachnospiracea sp and increased relative abundance of Akkermansia, Clostridium sensu stricto 1, and Lachnoclostridium. Supplementation of the probiotic VSL#3 in dams rescued hypersensitivity to thermal and mechanical pain in prenatally methadone-exposed offspring. Similarly, cross-fostering prenatally methadone-exposed offspring to control dams also attenuated hypersensitivity to thermal pain in opioid-exposed offspring. Modulation of the maternal and neonatal gut microbiome with probiotics resulted in transcriptional changes in genes related to neuropathic and immune-related signaling in whole brain and midbrain samples of prenatally methadone-exposed offspring. Together, our work provides compelling evidence of the gut-brain-axis in mediating pain sensitivity in prenatally opioid-exposed offspring.

Folic acid attenuates chronic visceral pain by reducing clostridiales abundance and hydrogen sulfide production

Irritable bowel syndrome (IBS) related chronic visceral pain affects 20% of people worldwide. The treatment options are very limited. Although the scholarly reviews have appraised the potential effects of the intestinal microbiota on intestinal motility and sensation, the exact mechanism of intestinal microbiota in IBS-like chronic visceral pain remains largely unclear. The purpose of this study is to investigate whether Folic Acid (FA) attenuated visceral pain and its possible mechanisms. Chronic visceral hyperalgesia was induced in rats by neonatal colonic inflammation (NCI). 16S rDNA analysis of fecal samples from human subjects and rats was performed. Patch clamp recording was used to determine synaptic transmission of colonic-related spinal dorsal horn. Alpha diversity of intestinal flora was increased in patients with IBS, as well as the obviously increased abundance of Clostridiales order (a main bacteria producing hydrogen sulfide). The hydrogen sulfide content was positive correlation with visceral pain score in patients with IBS. Consistently, NCI increased Clostridiales frequency and hydrogen sulfide content in feces of adult rats. Notably, the concentration of FA was markedly decreased in peripheral blood of IBS patients compared with non-IBS human subjects. FA supplement alleviated chronic visceral pain and normalized the Clostridiales frequency in NCI rats. In addition, FA supplement significantly reduced the frequency of sEPSCs of neurons in the spinal dorsal horn of NCI rats. Folic Acid treatment attenuated chronic visceral pain of NCI rats through reducing hydrogen sulfide production from Clostridiales in intestine.

Enriched environment alleviates adolescent visceral pain, anxiety- and depression-like behaviors induced by neonatal maternal separation

BACKGROUND

Neonatal maternal separation (NMS), a major kind of early life stress, increases the risk of visceral pain, anxiety- and depression-like behaviors in adulthood. An enriched environment (EE) has been shown to successfully rescue the brain from various early life psychological stressors. Therefore, this study aimed to investigate whether NMS induces visceral pain, anxiety- and depression-like behaviors in adolescents and to evaluate the impact of EE in infancy on these symptoms.

METHODS

Male C57BL/6 J mice that had been subjected to NMS were used in this study. The visceral pain threshold test (PTT), open field test (OFT), and sucrose preference test (SPT) were conducted to evaluate visceral pain, anxiety- and depression-like behaviors in mice, respectively. An enzyme linked immunosorbent assay (ELISA) for tumor necrosis factor-α (TNF-α), interleukin-1β, (IL-1β), and interleukin-10 (IL-10) was performed to assess neuroinflammatory responses. Then, the effects of EE (free-turning running wheels, pipes, stairs, and various colored ocean balls, etc.) on NMS-induced behaviors and neuroinflammatory factors were examined.

RESULTS

The impacts of NMS included adolescent visceral pain, anxiety- and depression-like behaviors. The medial prefrontal cortex (mPFC), basolateral amygdala (BLA), and paraventricular nucleus (PVN) were biased towards pro-inflammatory features. Further, EE alleviated adolescent visceral pain, anxiety- and depression-like behaviors. The application of EE up-regulated the expression of IL-10, and down-regulated the expression of IL-1β and TNF-α in mPFC, BLA, and PVN.

CONCLUSIONS

The effects of NMS include adolescent visceral pain, anxiety- and depression-like behaviors, accompanied by an imbalance of neuroinflammation. Intervention with EE in pediatric mice relieved these symptoms by reducing neuroinflammation in the central nervous system.

Microbiota and Pain: Save Your Gut Feeling

Recently, a growing body of evidence has emerged regarding the interplay between microbiota and the nervous system. This relationship has been associated with several pathological conditions and also with the onset and regulation of pain. Dysregulation of the axis leads to a huge variety of diseases such as visceral hypersensitivity, stress-induced hyperalgesia, allodynia, inflammatory pain and functional disorders. In pain management, probiotics have shown promising results. This narrative review describes the peripheral and central mechanisms underlying pain processing and regulation, highlighting the role of the gut-brain axis in the modulation of pain. We summarized the main findings in regard to the stress impact on microbiota’s composition and its influence on pain perception. We also focused on the relationship between gut microbiota and both visceral and inflammatory pain and we provided a summary of the main evidence regarding the mechanistic effects and probiotics use.

MafK accelerates Salmonella mucosal infection through caspase-3 activation

Gastrointestinal homeostasis is critical for maintaining host health, and is affected by many factors. A recent report showed that Musculoaponeurotic fibrosarcoma K (MafK) expression is increased in patients that have ulcerative colitis (UC). Even so, MafK’s significance in sustaining intestinal homeostasis has not been investigated. In this research, MafK overexpressing transgenic (MafK Tg) mice were found to be more susceptible to infection with Salmonella on the mucosa than the wild-type (WT) mice. Following Salmonella oral infection, MafK Tg mice suffered higher mortality and a lot more weight loss, damage to the intestines, and inflammation in the intestines than WT mice. MafK Tg mice were also unable to control Salmonella colonization and dissemination. In vivo data showed that increased MafK expression promoted epithelial cell apoptosis which was further confirmed by in vitro data. The rapid cleavage of caspase-3 in epithelial cells contributed to Salmonella dissemination and inflammation initiation. This study reveals that MafK participates in Salmonella pathogenesis acceleration by increasing caspase-3 activation.