Faculty Bibliography

Type 2 diabetes (T2D) is a chronic metabolic disorder in which insulin resistance and impaired insulin secretion result in altered metabolite balance, specifically elevated levels of circulating glucose and succinate, which increases the risk of many pathologies, including periodontitis. Succinate, a tricarboxylic acid (TCA) cycle intermediate, can be produced and metabolized by both host cells and host microbiota, where elevated levels serve as an inflammation and pathogen threat signal through activating the succinate G protein-coupled receptor, SUCNR1. Modulating succinate-induced SUCNR1 signaling remains a promising therapeutic approach for pathologies resulting in elevated levels of succinate, such as T2D and periodontitis. Here, we demonstrate hyperglycemia and elevated intracellular succinate in a T2D mouse model and determine gut microbiome composition. Drawing on previous work demonstrating the ability of a novel SUCNR1 antagonist, compound 7a, to block inflammation and alleviate dysbiosis in a mouse model, we examined if compound 7a has an impact on the growth and virulence gene expression of bacterial and fungal human microbiota in vitro, and if 7a could reduce bone loss in a periodontitis-induced mouse model. T2D mice harbored a significantly different gut microbiome, suggesting the altered metabolite profile of T2D causes shifts in host-microbial community structure, with enrichment in succinate producers and consumers and mucin-degrading bacteria. Bacterial and fungal cultures showed that 7a did not influence growth or virulence gene expression, suggesting the therapeutic effects of 7a are a direct result of 7a interacting with host cells and that alterations in microbial community structure are driven by reduced host SUCNR1 signaling. This work further suggests that targeting SUCNR1 signaling is a promising therapeutic approach in metabolic, inflammatory, or immune disorders with elevated succinate levels.

The gastrointestinal ecosystem has received the most attention when examining the contributions of the human microbiome to health and disease. This concentration of effort is logical due to the overwhelming abundance of microbes in the gut coupled with the relative ease of sampling compared with other organs. However, the intestines are intimately connected to multiple extraintestinal organs, providing an opportunity for homeostatic microbial colonisation and pathogenesis in organs traditionally thought to be sterile or only transiently harbouring microbiota. These habitats are challenging to sample, and their low microbial biomass among large amounts of host tissue can make study challenging. Nevertheless, recent findings have shown that many extraintestinal organs that are intimately linked to the gut harbour stable microbiomes, which are colonised from the gut in selective manners and have highlighted not just the influence of the bacteriome but that of the mycobiome and virome on oncogenesis and health.

Background: Neoadjuvant therapy is now a standard strategy for localized PDAC, and this preoperative window provides an excellent opportunity in which to test novel therapeutic approaches. Trials using IO in PDAC have largely been unsuccessful, and immune tolerance is implicated as a major mechanism of IO resistance. The gut and tumor microbiome have emerged as key modulators of response to both IO and chemotherapy. High tumor microbial diversity has been linked to longer survival in PDAC, and gut microbiota may have the ability to colonize pancreatic tumors. There is preclinical evidence that endogenous microbiota promotes the immunosuppressive tumor microenvironment characteristic of PDAC through stimulation of pro-tumor regulatory T cells and myeloid-derived suppressor cells at the expense of anti-tumor activated CD4⁺ and CD8⁺ T cells. Further, preclinical data show that ablation of the gut microbiota may induce T cell activation, improve immune surveillance, and increase sensitivity to IO. We hypothesize that ablative antibiotics (abx) will activate tumor infiltrating T cells and enhance IO activity in PDAC.
Method(s): This is a multi-center, single-arm, open-label pilot study of pre-operative chemotherapy followed by abx and pembrolizumab to evaluate overall immune response to abx + IO. Eligible patients will have histologically confirmed, resectable PDAC, without probiotic consumption or use of immunosuppressive agents. Patients will be enrolled at diagnosis after undergoing a baseline biopsy. They will then receive mFOLFIRINOX every 2 weeks for 5 cycles. After completion of chemotherapy, ciprofloxacin 500 mg PO BID and metronidazole 500 mg PO TID will be administered for 21 days, and pembrolizumab 200 mg IV x1 will be given 7 days after initiation of abx. Patients will then undergo surgical resection and adjuvant therapy at the investigators' discretion. On-treatment biopsy will be obtained prior to cycle 5 of mFOLFIRINOX. Blood and stool will be collected at baseline, during mFOLFIRINOX therapy, before and after pembrolizumab administration, and postoperatively. The primary endpoint is the overall immune response, which will be measured as activation of one or more of the T cell markers HLA-DR, CD38, CD25, Ki67, and CD69, defined as an increase in expression level of at least 20% from the on-treatment specimen to the surgical specimen, before and after abx + IO. Key secondary endpoints will be the evaluation of adverse events, R0 resection rate, histologic regression score, objective response rate, and overall survival rate. Correlative studies will be carried out to evaluate immune and microbiome changes in the blood and tissue following abx and pembrolizumab. These findings will be correlated with clinical endpoints. The target study accrual is 25 patients

Nonalcoholic fatty liver disease (NAFLD) is the most common liver disease in the United States and the world; with no Food and Drug Administration-approved pharmacological treatment available, it remains an area of unmet medical need. In nonalcoholic steatohepatitis (NASH), the most important predictor of clinical outcome is the fibrosis stage. Moreover, the Food and Drug Administration recommends that clinical trials for drugs to treat this disease include patients with fibrosis stage 2 or greater. Therefore, when using animal models for investigating the pathophysiology of NAFLD and for the preclinical evaluation of new drugs, it is important that the animals develop substantial fibrosis. The aim of this study was to develop a mouse model of NAFLD that replicated the disease in humans, including obesity and progressive liver fibrosis. Agouti yellow mutant mice, which have hyperphagia, were fed a Western diet and water containing high-fructose corn syrup for 16 weeks. Mice became obese and developed glucose intolerance. Their gut microbiota showed dysbiosis with changes that replicate some of the changes described in humans with NASH. They developed NASH with activity scores of 5-6 and fibrosis, which was stage 1 after 16 weeks, and stage 3 after 12 months. Changes in liver gene expression assessed by gene-set enrichment analysis showed 90% similarity with changes in human patients with NASH. Conclusion: Ay mice, when fed a Western diet similar to that consumed by humans, develop obesity and NASH with liver histology, including fibrosis, and gene expression changes that are highly similar to the disease in humans.

Distinct fungal communities or "mycobiomes" have been found in individual tumor types and are known to contribute to carcinogenesis. Two new studies present a comprehensive picture of the tumor-associated mycobiomes from a variety of human cancers. These studies reveal that fungi, although in low abundance, are ubiquitous across all major human cancers and that specific mycobiome types can be predictive of survival.

Periodontal disease (PD) is one of the most common inflammatory diseases in humans and is initiated by an oral microbial dysbiosis that stimulates inflammation and bone loss. Here, we report an abnormal elevation of succinate in the subgingival plaque of subjects with severe PD. Succinate activates succinate receptor-1 (SUCNR1) and stimulates inflammation. We detected SUCNR1 expression in the human and mouse periodontium and hypothesize that succinate activates SUCNR1 to accelerate periodontitis through the inflammatory response. Administration of exogenous succinate enhanced periodontal disease, whereas SUCNR1 knockout mice were protected from inflammation, oral dysbiosis, and subsequent periodontal bone loss in two different models of periodontitis. Therapeutic studies demonstrated that a SUCNR1 antagonist inhibited inflammatory events and osteoclastogenesis in vitro and reduced periodontal bone loss in vivo. Our study reveals succinate's effect on periodontitis pathogenesis and provides a topical treatment for this disease.

Cannabinoid receptor 2 (CB2) is of interest as a much-needed target for the treatment or prevention of several neurogenerative diseases. However, CB2 agonists, particularly phytocannabinoids, have been ascribed antimicrobial properties and are associated with the induction of microbiome compositional fluxes. When developing novel CB2 therapeutics, CB2 engagement and antimicrobial functions should both be considered. This review summarizes those cannabinoids and cannabis-informed molecules and preparations (CIMPs) that show promise as microbicidal agents, with a particular focus on the most recent developments. CIMP-microbe interactions and anti-microbial mechanisms are discussed, while the major knowledge gaps and barriers to translation are presented. Further research into CIMPs may proffer novel direct or adjunctive strategies to augment the currently available antimicrobial armory. The clinical promise of CIMPs as antimicrobials, however, remains unrealized. Nevertheless, the microbicidal effects ascribed to several CB2 receptor-agonists should be considered when designing therapeutic approaches for neurocognitive and other disorders, particularly in cases where such regimens are to be long-term. To this end, the potential development of CB2 agonists lacking antimicrobial properties is also discussed.

The gut microbiome shapes local and systemic immunity. The liver is presumed to be a protected sterile site. As such, a hepatic microbiome has not been examined. Here, we showed a liver microbiome in mice and humans that is distinct from the gut and is enriched in Proteobacteria. It undergoes dynamic alterations with age and is influenced by the environment and host physiology. Fecal microbial transfer experiments revealed that the liver microbiome is populated from the gut in a highly selective manner. Hepatic immunity is dependent on the microbiome, specifically Bacteroidetes species. Targeting Bacteroidetes with oral antibiotics reduced hepatic immune cells by ~90%, prevented APC maturation, and mitigated adaptive immunity. Mechanistically, our findings are consistent with presentation of Bacteroidetes-derived glycosphingolipids to NKT cells promoting CCL5 signaling, which drives hepatic leukocyte expansion and activation, among other possible host-microbe interactions. Collectively, we reveal a microbial - glycosphingolipid - NKT - CCL5 axis that underlies hepatic immunity.