Gut Microbial Metabolite Short-Chain Fatt Acids Partially Reverse Surgery and Anesthesia-Induced Behavior Deficits in C57BL/6J Mice

Postoperative delirium after cardiac surgery associated with perioperative gut microbiota dysbiosis: Evidence from human and antibiotic-treated mouse model

BACKGROUND

Research links gut microbiota to postoperative delirium (POD) through the gut-brain axis. However, changes in gut microbiota and fecal short-chain fatty acids (SCFAs) in POD patients during the perioperative period and their association with POD are unclear.

METHODS

We conducted a nested case-control study among patients undergoing off-pump coronary artery bypass grafting, focusing on POD as the main outcome. POD patients were matched 1:1 with non-POD patients based on sociodemographic characteristics, health, and diet. Fecal samples were collected pre- and post-surgery to assess gut microbiota and SCFAs changes. Postoperative fecal samples were transplanted into antibiotic-treated mice to evaluate delirium-like behavior and neuroinflammation.

RESULTS

Out of 120 patients, 60 were matched. Before surgery, gut microbiota in both groups was similar. After surgery, POD patients had lower alpha diversity and distinct microbiota compared to non-POD patients. LEfSe analysis showed POD was linked to increased opportunistic pathogens (Enterococcus) and decreased SCFAs producers (Bacteroides, Ruminococcus, etc.). SCFAs were significantly reduced in POD patients and negatively correlated with delirium severity and plasma inflammation. Mice receiving fecal transplants from POD patients exhibited delirium-like behavior and neuroinflammation.

CONCLUSIONS

Postoperative delirium is associated with gut microbiota dysbiosis, marked by an increase in opportunistic pathogens and a decrease in SCFA-producing genera.

REGISTRATION

Chinese Clinical Trial Registry ChiCTR2300070477.

Short chain fatty acids mediates complement C1q pathway alleviation of perioperative neurocognitive disorders

Perioperative neurocognitive disorders (PND) is one of the most common postoperative complications, which can lead to a harmful impact on self-dependence, longer hospital stays, increased medical costs, morbidity, and mortality amongst older adults. Microglia can modulate synapse elimination involved in the complement component protein 1q (C1q) pathway to induce cognitive dysfunction, which is significantly improved by short chain fatty acids (SCFAs) treatment. Here we investigate the effects of SCFAs treatment on PND via mediating C1q complement pathway. High-throughput sequencing of 16S rDNA from fecal samples of male SD rats was applied to assess the changes in gut microbiota. Fecal microbiota transplantation (FMT) was performed to investigate whether gut microbiota from PND rats could alter cognitive impairment. The blood from the rat tail vein was collected to measure the SCFAs concentrations. Hippocampal and brain tissue samples were obtained to perform Western blots, Golgi and immunofluorescence staining. Primary microglia treated with SCFAs or Histone deacetylase inhibitor were cultured to measure microglial activation states and the expression of acetylated histone. The 16S rDNA sequencing results showed that PND rats had the significant changes in the species diversity of the gut microbiota and the metabolite of specifc species. Gut microbiota from PND rats could alter spatial learning and memory, and meanwhile, the changed SCFAs concentrations in plasma were involved. The synapse elimination in PND rats was strikingly reversed by SCFAs treatment involved in modulation complement C1q via suppressing neuroinflammation. This suggests that a link between gut microbiota dysbiosis and cognitive function impairment is involved in synapse elimination via mediating complement C1q pathway. SCFAs treatment can alleviate PND, the mechanisms of which may be associated with regulating complement C1q pathway.

Alterations in gut microbiota and metabolites contribute to postoperative sleep disturbances

BACKGROUND

The composition of the intestinal flora and the resulting metabolites affect patients' sleep after surgery.

METHODS

We intended to elucidate the mechanisms by which disordered intestinal flora modulate the pathophysiology of postoperative sleep disturbances in hosts. In this study, we explored the impacts of anesthesia, surgery, and postoperative sleep duration on the fecal microbiota and metabolites of individuals classified postprocedurally as poor sleepers (PS) and good sleepers (GS), as diagnosed by the bispectral index. We also performed fecal microbiota transplantation in pseudo-germ-free (PGF) rats and applied Western blotting, immunohistochemistry, and gut permeability analyses to identify the potential mechanism of its effect.

RESULTS

Research finding shows the PS group had significantly higher postoperative stool levels of the metabolites tryptophan and kynurenine than the GS group. PGF rats that received gut microbiota from PSs exhibited less rapid eye movement (REM) sleep than those that received GS microbiota (GS-PGF: 11.4% ± 1.6%, PS-PGF: 4.8% ± 2.0%, p < 0.001). Measurement of 5-hydroxytryptophan (5-HTP) levels in the stool, serum, and prefrontal cortex (PFC) indicated that altered 5-HTP levels, including reduced levels in the PFC, caused sleep loss in PGF rats transplanted with PS gut flora. Through the brain-gut axis, the inactivity of tryptophan hydroxylase 1 (TPH1) and TPH2 in the colon and PFC, respectively, caused a loss of REM sleep in PGF rats and decreased the 5-HTP level in the PFC.

CONCLUSIONS

These findings indicate that postoperative gut dysbiosis and defective 5-HTP metabolism may cause postoperative sleep disturbances. Clinicians and sleep researchers may gain new insights from this study.

SCFAs Supplementation Rescues Anxiety- and Depression-like Phenotypes Generated by Fecal Engraftment of Treatment-Resistant Depression Rats

Alteration of gut microbiota and microbial metabolites such as short-chain fatty acids (SCFAs) coexisted with stress-generated brain disorders, including depression. Herein, we investigated the effect of SCFAs in a treatment-resistant depression (TRD) model of rat. Rats were exposed to chronic-unpredictable mild stress (CUMS) and repeated adrenocorticotropic hormone (ACTH) injections to generate a TRD-like phenotype. The cecal contents of these animals were engrafted into healthy-recipient rats and allowed to colonize for 4 weeks (TRD-FMT group). Blood, brain, colon, fecal, and cecal samples were collected for molecular studies. Rats exposed to CUMS + ACTH showed TRD-like phenotypes in sucrose-preference (SPT), forced swim (FST), and elevated plus maze (EPM) tests. The TRD-FMT group also exhibited anxiety- and depression-like behaviors. Administration of SCFAs (acetate, propionate, and butyrate at 67.5, 25, and 40 mM, respectively) for 7 days exerted robust antidepressant and antianxiety effects by restoring the levels of SCFAs in plasma and fecal samples, and proinflammatory cytokines (TNF-α and IL-6), serotonin, GABA, norepinephrine, and dopamine in the hippocampus and/or frontal cortex of TRD and TRD-FMT animals. SCFAs treatment elevated the expression of free-fatty acid receptors 2/3, BDNF, doublecortin, and zonula-occludens, and reduced the elevated plasma levels of kynurenine and quinolinic acid and increased mucus-producing goblet cells in TRD and TRD-FMT animals. In 16S sequencing results, decreased microbial diversity in TRD rats corresponds with differences in the genus of Faecalibacterium, Anaerostipes, Allobaculum, Blautia, Peptococcus, Rombustia, Ruminococcaceae_UCG-014, Ruminococcaceae_UCG-002, Solobacterium, Subdolibacterium, and Eubacterium ventriosum. SCFAs may impart beneficial effects via modulation of tryptophan metabolism, inflammation, neurotransmitters, and microbiota-gut-brain axis in TRD rats.

Surgery-induced gut microbial dysbiosis promotes cognitive impairment via regulation of intestinal function and the metabolite palmitic amide

BACKGROUND

Perioperative neurocognitive disorders (PND) are the most common postoperative complications with few therapeutic options. Gut microbial dysbiosis is associated with neurological diseases; however, the mechanisms by which the microbiota regulates postoperative gastrointestinal and cognitive function are incompletely understood.

METHODS

Behavioral testing, MiSeq 16S rRNA gene sequencing, non-target metabolism, intestinal permeability detection, protein assays, and immunofluorescence staining were employed to discern the impacts of surgery on microbial profiles, intestinal barriers, serum metabolism, and the brain. Interventions in mice included fecal microbiota transplantation, the anti-inflammatory agent dexamethasone, Lactobacillus supplementation, indole propionic acid supplementation, and palmitic amide administration.

RESULTS

Surgery-induced cognitive impairment occurs predominantly in aged mice, and surgery-induced alterations in the microbiota composition profile exacerbate intestinal barrier disruption in aged mice. These adverse effects can be mitigated by transferring microbiota from young donors or by bolstering the intestinal barrier function using dexamethasone, Lactobacillus, or indole propionic acid. Moreover, microbiota composition profiles can be restored by transplanting feces from young mice to aged surgical mice, improving neuropathology and cognitive function, and these effects coincide with increased intestinal permeability. Metabolomic screening identified alterations in metabolites in mouse serum after surgery, especially the increase in palmitic amide. Palmitic amide levels in serum and brain can be decreased by transplanting feces from young mice to aged surgical mice. Oral palmitic amide exacerbates cognitive impairment and neuropathological changes in mice.

CONCLUSIONS

Gut microbial dysbiosis in mice after surgery is a key mechanism leading to cognition dysfunction, which disrupts the intestinal barrier and metabolic abnormalities, resulting in neuroinflammation and dendritic spine loss. Intestinal barrier damage and high level of palmitic amide in old mice may be the cause of high incidence of PND in the elderly. Preoperative microbiota regulation and intestinal barrier restoration may be of therapeutic benefit in preventing PND. Video Abstract.

Gut microbiota in perioperative neurocognitive disorders: current evidence and future directions

Perioperative neurocognitive disorders (PND) is a common surgical anesthesia complication characterized by impairment of memory, attention, language understanding and social ability, which can lead to a decline in the quality of life of patients, prolong the hospitalization period and increase the mortality rate. PND has a high incidence rate, which has a great impact on postoperative recovery and quality of life of patients, and has caused a heavy economic burden to society and families. In recent years, PND has become an important public health problem. The high risk population of PND is more prone to gut microbiota imbalance, and gut microbiota may also affect the inflammatory response of the central nervous system through the microbiota-gut-brain axis. Meanwhile, Neuroinflammation and immune activation are important mechanisms of PND. Regulating gut microbiota through probiotics or fecal bacteria transplantation can significantly reduce neuroinflammation, reduce the abnormal activation of immune system and prevent the occurrence of PND. This review summarizes the research progress of gut microbiota and PND, providing basis for the prevention and treatment of PND.

The microbiota-gut- hippocampus axis

Introduction

It is well known that the intestinal bacteria substantially affect physiological processes in many body organs. Especially, through a bidirectional communication called as gut-microbiota-brain axis, the gut microbiota deeply influences development and function of the nervous system. Hippocampus, as a part of medial temporal lobe, is known to be involved in cognition, emotion, and anxiety. Growing evidence indicates that the hippocampus is a target of the gut microbiota. We used a broad search linking the hippocampus with the gut microbiota and probiotics.

Methods

All experimental studies and clinical trials published until end of 2021 were reviewed. Influence of the gut microbiota on the behavioral, electrophysiological, biochemical and histological aspects of the hippocampus were evaluated in this review.

Results

The effect of disrupted gut microbiota and probiotic supplements on the microbiota-hippocampus link is also considered. Studies show that a healthy gut microbiota is necessary for normal hippocampus dependent learning and memory and synaptic plasticity. The known current mechanisms are production and modulation of neurotrophins, neurotransmitters and receptors, regulation of intracellular molecular processes, normalizing the inflammatory/anti-inflammatory and oxidative/antioxidant factors, and histological stability of the hippocampus. Activity of the hippocampal neuronal circuits as well as behavioral functions of the hippocampus positively respond to different mixtures of probiotic bacteria.

Discussion

Growing evidence from animal researches indicate a close association between the hippocampus with the gut microbiota and probiotic bacteria as well. However, human studies and clinical trials verifying such a link are scant. Since the most of papers on this topic have been published over the past 3 years, intensive future research awaits.

Activation of TREM2 attenuates neuroinflammation via PI3K/Akt signaling pathway to improve postoperative cognitive dysfunction in mice

Postoperative cognitive dysfunction (POCD) is a common postoperative complication involving the central nervous system, but the underlying mechanism is not well understood. Neuroinflammation secondary to surgery and anesthesia is strongly correlated with POCD. A key aspect of neuroinflammation is microglia activation. Triggering receptor expressed on myeloid cells (TREM)2, which is highly expressed in microglia, is an innate immune receptor that modulates microglia function. In this study we investigated the role of TREM2 in cognitive impairment and microglia-mediated neuroinflammation using a mouse model of POCD and in vitro systems. We found that hippocampus-dependent learning and memory were impaired in POCD mice, which was accompanied by activation of microglia and downregulation of TREM2. Pretreatment with the TREM2 agonist heat shock protein (HSP)60 inhibited surgery-induced microglia activation and alleviated postoperative cognitive impairment. In BV2 microglial cells, the phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 significantly reversed the attenuation of TREM2 activation on lipopolysaccharide (LPS)-induced neuroinflammation and abrogated the protective effect of activated TREM2 against LPS-induced neuronal injury in a microglia/neuron coculture system. Accordingly, the beneficial effects of TREM2 activation on cognitive function were reversed by preoperative administration of LY294002 in the POCD mouse model. These results demonstrate that TREM2 is involved in the regulation of the inflammatory response mediated by microglia and cognitive impairment following surgery. Activation of TREM2 can attenuate neuroinflammation by modulating PI3K/protein kinase B (Akt) signaling, thereby alleviating postoperative learning and memory deficits.

Gut-Brain Axis: Possible Role of Gut Microbiota in Perioperative Neurocognitive Disorders

Aging is becoming a severe social phenomenon globally, and the improvements in health care and increased health awareness among the elderly have led to a dramatic increase in the number of surgical procedures. Because of the degenerative changes in the brain structure and function in the elderly, the incidence of perioperative neurocognitive disorders (PND) is much higher in elderly patients than in young people following anesthesia/surgery. PND is attracting more and more attention, though the exact mechanisms remain unknown. A growing body of evidence has shown that the gut microbiota is likely involved. Recent studies have indicated that the gut microbiota may affect postoperative cognitive function via the gut-brain axis. Nonetheless, understanding of the mechanistic associations between the gut microbiota and the brain during PND progression remains very limited. In this review, we begin by providing an overview of the latest progress concerning the gut-brain axis and PND, and then we summarize the influence of perioperative factors on the gut microbiota. Next, we review the literature on the relationship between gut microbiota and PND and discuss how gut microbiota affects cognitive function during the perioperative period. Finally, we explore effective early interventions for PND to provide new ideas for related clinical research.

Research Progress on the Role of Inflammatory Mechanisms in the Development of Postoperative Cognitive Dysfunction

Postoperative cognitive dysfunction (POCD), as one of the common postoperative complications, mainly occurs after surgery and anesthesia, especially in the elderly. It refers to cognitive function changes such as decreased learning and memory ability and inability to concentrate. In severe cases, there could be personality changes and a decline in social behavior. At present, a great deal of research had been carried out on POCD, but its specific mechanism remains unclear. The release of peripheral inflammation-related factors, the degradation and destruction of the blood-brain barrier, the occurrence of central inflammation, and the neuronal apoptosis and synaptic loss could be promoted by neuroinflammation indicating that inflammatory mechanisms may play key roles in the occurrence of POCD.

Neuroprotective Potential of Non-Digestible Oligosaccharides: An Overview of Experimental Evidence

Non-digestible oligosaccharides (NDOs) from dietary sources have the potential as prebiotics for neuroprotection. Globally, diverse populations suffering from one or the other forms of neurodegenerative disorders are on the rise, and NDOs have the potential as supportive complementary therapeutic options against these oxidative-linked disorders. Elevated levels of free radicals cause oxidative damage to biological molecules like proteins, lipids, and nucleic acids associated with various neurological disorders. Therefore, investigating the therapeutic or prophylactic potential of prebiotic bioactive molecules such as NDOs as supplements for brain and cognitive health has merits. Few prebiotic NDOs have shown promise as persuasive therapeutic solutions to counter oxidative stress by neutralizing free radicals directly or indirectly. Furthermore, they are also known to modulate through brain-derived neurotrophic factors through direct and indirect mechanisms conferring neuroprotective and neuromodulating benefits. Specifically, NDOs such as fructo-oligosaccharides, xylo-oligosaccharides, isomalto-oligosaccharides, manno-oligosaccharides, pectic-oligosaccharides, and similar oligosaccharides positively influence the overall health via various mechanisms. Increasing evidence has suggested that the beneficial role of such prebiotic NDOs is not only directed towards the colon but also distal organs including the brain. Despite the wide applications of these classes of NDOs as health supplements, there is limited understanding of the possible role of these NDOs as neuroprotective therapeutics. This review provides important insights into prebiotic NDOs, their source, and production with special emphasis on existing direct and indirect evidence of their therapeutic potential in neuroprotection.