Gut Microbiota Influences Postoperative Cognitive Dysfunction through Indole-3-Propionic Acid
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In up to 26% surgical patients, subtle yet persistent deficits in learning and memory occur postoperatively, referred to as postoperative cognitive dysfunction (POCD). POCD has become a serious public health concern as it is associated with worse clinical outcomes including increased mortality. The pathogenesis underlying POCD remains unclear. Both modifiable and non-modifiable factors may contribute to POCD. To date, studies on POCD have primarily focused on direct influences of surgery and anesthesia on the central nervous system, which have identified age and genetics as major risk factors in POCD. Unfortunately, these are non-modifiable factors and difficult to be translated into clinical treatment. As such, there is an urgent need to identify modifiable factors underlying POCD. Among many modifiable factors, dietary influences and gut microbiota have been implicated in many neurological diseases with inflammatory features. Whether gut microbiota influences POCD has yet to be examined. In our preliminary studies, we observed a previously unrecognized role for gut microbiota in the development of POCD in mice post femoral artery exposure under isoflurane anesthesia. Specifically, we found: 1) mice with normal gut microbiota did not develop POCD while mice with gut dysbiosis developed POCD; 2) oral ampicillin treatment led to a status of gut dysbiosis, characterized by gut microbiota community structure changes and a dramatic decrease of indoles, particularly indoxyl-3-sulfate (IS) and indole-3-propionic acid (IPA); 3) oral administration of IPA, but not IS, deterred the POCD development; 4) mice with POCD displayed increased oxidation and impaired mitochondria function in the hippocampus, suggested by an enhanced production of reactive oxygen species (ROS), decreased production of NADH, and decreased protein levels of NDUFS4 (a critical mitochondria complex I component), when compared with mice without POCD; and 5) oral administration of IPA decreased ROS generation, increased NADH production and NDUFS4 protein levels in the hippocampus of ampicillin-treated mice. Based on these preliminary findings, we hypothesize that gut microbiota has a key influence on the development of POCD through IPA. In the research program proposed in this grant, we will examine the hypothesis by addressing three key questions: 1) Does the observed effect of gut dysbiosis on POCD represent an epiphenomenon or a ‘permissive’ effect? 2) What are the mechanisms underlying the IPA’s protective role in POCD? and 3) Can we develop a strategy based on gut microbiota and metabolites to prevent and treat POCD? This grant is built on our novel preliminary findings and our established research platform that combines cutting-edge metagenomics and metabolomics with immunological and neurobehavioral assays. Successful execution of this proposal will establish a novel conceptual framework linking modifiable factors such as diet and gut microbiota with POCD, and lead to new therapeutic strategies.
