Clinical and Preclinical Evidence for Gut Microbiome Mechanisms in Substance Use Disorders

Colony-stimulating factor 2 (CSF2) as a gut microbiome dependent immune factor that alters molecular and behavioral responses to cocaine in male mice

Cocaine use disorder is a condition that leads to tremendous morbidity and mortality for which there are currently no FDA-approved pharmacotherapies. Previous research has demonstrated an important role for the resident population of bacteria of the large intestine, collectively dubbed the gut microbiome, in modulating brain and behavior in models of cocaine and other substance use disorders. Importantly, previous work has repeatedly shown that depletion of the gut microbiome leads to increased cocaine taking and seeking behaviors in multiple models. While the precise mechanism of these gut-brain signaling pathways in models of cocaine use is not fully clear, and intriguing possibility is through gut microbiome influences on innate immune system function. In this manuscript we identify the cytokine colony stimulating factor 2 (CSF2) as an immune factor that is increased by cocaine in a gut microbiome dependent manner. Peripherally injected CSF2 crosses the blood-brain barrier into the nucleus accumbens, a brain region central to behavioral responses to cocaine. Treatment with peripheral CSF2 reduces acute and sensitized locomotor responses to cocaine as well as reducing cocaine place preference at high doses. On a molecular level, we find that peripheral injections of CSF2 alter the transcriptional response to both acute and repeated cocaine in the nucleus accumbens. Finally, treatment of microbiome depleted mice with CSF2 reverses the behavioral effects of microbiome depletion on the conditioned place preference assay. Taken together, this work identifies an innate immune factor that represents a novel gut-brain signaling cascade in models of cocaine use and lays the foundations for further translational work targeting this pathway.

Role of gut microbiota in regulating immune checkpoint inhibitor therapy for glioblastoma

Glioblastoma (GBM) is a highly malignant, invasive, and poorly prognosed brain tumor. Unfortunately, active comprehensive treatment does not significantly prolong patient survival. With the deepening of research, it has been found that gut microbiota plays a certain role in GBM, and can directly or indirectly affect the efficacy of immune checkpoint inhibitors (ICIs) in various ways. (1) The metabolites produced by gut microbiota directly affect the host's immune homeostasis, and these metabolites can affect the function and distribution of immune cells, promote or inhibit inflammatory responses, affect the phenotype, angiogenesis, inflammatory response, and immune cell infiltration of GBM cells, thereby affecting the effectiveness of ICIs. (2) Some members of the gut microbiota may reverse T cell function inhibition, increase T cell anti-tumor activity, and ultimately improve the efficacy of ICIs by targeting specific immunosuppressive metabolites and cytokines. (3) Some members of the gut microbiota directly participate in the metabolic process of drugs, which can degrade, transform, or produce metabolites, affecting the effective concentration and bioavailability of drugs. Optimizing the structure of the gut microbiota may help improve the efficacy of ICIs. (4) The gut microbiota can also regulate immune cell function and inflammatory status in the brain through gut brain axis communication, indirectly affecting the progression of GBM and the therapeutic response to ICIs. (5) Given the importance of gut microbiota for ICI therapy, researchers have begun exploring the use of fecal microbiota transplantation (FMT) to transplant healthy or optimized gut microbiota to GBM patients, in order to improve their immune status and enhance their response to ICI therapy. Preliminary studies suggest that FMT may enhance the efficacy of ICI therapy in some patients. In summary, gut microbiota plays a crucial role in regulating ICIs in GBM, and with a deeper understanding of the relationship between gut microbiota and tumor immunity, it is expected to develop more precise and effective personalized ICI therapy strategies for GBM, in order to improve patient prognosis.