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.

Altered gut microbiome drives heightened pain sensitivity in a murine model of metastatic triple-negative breast cancer.

The microbiota residing in the gut environment is essential for host homeostasis. Increasing evidence suggests that microbial perturbation (dysbiosis) regulates cancer initiation and progression at local and distant sites. Here, we have identified microbial dysbiosis with the depletion of commensal bacteria as a host-intrinsic factor associated with metastatic dissemination to the bone. Using a mouse model of triple-negative mammary cancer, we demonstrate that a pre-established disruption of microbial homeostasis using an antibiotic cocktail increases tumor growth, enhanced circulating tumor cells, and subsequent dissemination to the bone. We found that the presence of pathogenic bacteria and loss of commensal bacteria in an antibiotic-induced gut environment is associated with sustained inflammation. Increased secretion of G-CSF and MMP-9 in intestinal tissues, followed by increased neutrophil infiltration and severe systemic inflammation in tumor-bearing mice, indicates the direct consequence of a dysbiotic microbiome. Increased neutrophil infiltration to the bone metastatic niche facilitates extravasation and transendothelial migration of tumor cells. It provides a novel, pre-established, and favorable environment to form an immunosuppressive pre-metastatic niche. The presence of tumor cells in immunosuppressive metastatic tumor niche disrupts the balance between osteoblasts and osteoclasts, promotes osteoclast differentiation, and remodels the bone structure. Excessive bone resorption by osteoclasts causes bone degradation and ultimately causes extreme pain in a bone metastatic mouse model. In clinical settings, bone metastasis is associated with intractable severe pain that severely compromises the quality of life in these patients.