Decreased microglial activation through gut-brain axis by prebiotics, probiotics, or synbiotics effectively restored cognitive function in obese-insulin resistant rats

Prospecting prebiotics, innovative evaluation methods, and their health applications: a review

Prebiotics are necessary natural and synthetic food ingredients that help in the growth and development of gut microflora. There is a complex relationship between gut dysbiosis and microbes, so alteration in both probiotics and prebiotics can reduce illness of gut, which further plays a decisive role in human health. The prebiotic efficiency can be validated using various in vitro and in vivo experiments, and this gives an important insight to this field. This review focuses on these aspects including the standardized assessment of prebiotics and its metabolic products for customary applications. This review has also summarized the mechanism of their beneficial actions such as immunomodulation, nutrient absorption, pathogen inhibition, etc., and its significance in human nutrition. In addition to this, some fascinating applications of prebiotics in health-related disorders have also discussed, with current challenges in this facet.

Testosterone deprivation intensifies cognitive decline in obese male rats via glial hyperactivity, increased oxidative stress, and apoptosis in both hippocampus and cortex

AIM

The study hypothesized that testosterone deprivation aggravates cognitive decline in obesity through increasing oxidative stress, glial activation, and apoptosis.

METHODS

Male Wistar rats (n = 24) were fed with either normal-diet (ND) or high-fat diet (HFD) for 24 weeks. At week 13, ND-fed rats and HFD-fed rats were randomly assigned to two subgroups to receive either a sham-operation or bilateral-orchiectomy (ORX). Rats were evaluated for metabolic parameters and cognition at 4, 8, and 12 weeks after the operation. At the end of protocol, the reactive oxygen species (ROS), glial morphology, and cell apoptosis were determined in hippocampus and cortex.

RESULTS

Both HFD-fed groups developed obese-insulin resistance, but ND-fed rats did not. HFD-fed rats with sham-operation showed cognitive decline, when compared to ND-fed rats with sham-operation at all time points. At 4- and 8-week after ORX, the cognitive impairment of ND-fed rats and both HFD-fed groups was not different. However, 12-week after ORX, cognitive decline and of glial hyperactivity of HFD-fed rats had the greatest increase among all groups. Hippocampal ROS levels and apoptotic cells in both HFD-fed groups were equally increased, but the cortical ROS levels and apoptotic cells of HFD-fed rats with ORX were the highest ones.

CONCLUSIONS

These findings suggest that testosterone deprivation aggravates cognitive decline in obesity via increasing oxidative stress, glial activity and apoptosis.

The presence of elevated circulating trimethylamine N-oxide exaggerates postoperative cognitive dysfunction in aged rats

Surgical trauma can cause brain oxidative stress and neuroinflammation, leading to postoperative cognitive dysfunction (POCD), especially in the elderly. Additionally, the pre-existing risk factors may enhance POCD. Gut microbiota-derived metabolite trimethylamine N-oxide (TMAO) has recently been shown to contribute to the pathogenesis of many diseases by increasing oxidative stress and inflammation in the peripheral tissues. Here we examined whether the presence of elevated circulating TMAO would influence surgery-induced cognitive decline. Aged rats were treated with vehicle or TMAO for 3 weeks. After two weeks of treatment, these rats underwent sham-operation or laparotomy. One week after surgery, rats underwent laparotomy exhibited hippocampal-dependent cognitive dysfunction as evidenced by reduced contextual freezing time, which was associated with elevated plasma proinflammatory cytokine levels, increased microglia-mediated neuroinflammation and reactive oxygen species (ROS) production in the hippocampus. Treatment with TMAO, which elevated plasma TMAO before and 1 week after surgery, further increased microglia-mediated neuroinflammation and ROS production in the hippocampus, resulting in exaggerated cognitive dysfunction in laparotomy group but not in sham-operation group. Moreover, TMAO treatment decreased expression of antioxidant enzyme methionine sulfoxide reductase (Msr) A in both groups. The results suggest that the presence of elevated circulating TMAO downregulates antioxidant enzyme MsrA in the hippocampus, which may increase the susceptibility to surgery-induced oxidative stress, contributing to exaggerations of neuroinflammation and cognitive decline in aged rats following surgery. Interventions to reduce circulating TMAO in the perioperative period may be a novel strategy to prevent the exaggeration of cognitive decline in elderly patients with high circulating TMAO.

Juvenile Rats Show Altered Gut Microbiota After Exposure to Isoflurane as Neonates

Inhaled anesthetic agents may be neurotoxic to the developing brain of a neonatal rodent. Isoflurane is a commonly used volatile anesthetic agent for maintenance of general anesthesia in various types of surgery. Neonatal exposure to isoflurane has been implicated in long-term neurocognitive dysfunction in children. The mechanisms of isoflurane-induced neurotoxicity have not been fully elucidated. Disruption of gut microbiota is currently attracting considerable interest as a vital pathogeny of some neurologic disorders. In the rat model, it is unknown whether neonatal exposure to isoflurane impacts the gut microbiota composition of juvenile animals. In the present study, postnatal 7-day-old male rats were exposed to 1 minimum alveolar concentration isoflurane for 4 h. Non-anesthetized rats served as controls. The fecal microbiomes of rats were observed using 16S RNA sequencing technique on postnatal day 42. Results indicated that composition of gut microbiota of isoflurane-exposed rats was different from controls. Several bacteria taxa in isoflurane-exposed rats were different from those of controls at various taxonomic levels. In particular, the abundance of Firmicutes, Proteobacteria, Clostridia, Clostridiales, and Lachnospiraceae were significantly increased in exposed rats and the abundance of Bacteroidetes, Actinobacteria, Bacteroidia and Bacteroidaceae were significantly decreased compared to controls. These results may offer new insights into the pathogenesis of isoflurane-induced neurotoxicity.

The intestinal microbiome and its relevance for functionality in older persons

PURPOSE OF REVIEW

This article summarizes the advances of research on the role of the intestinal microbiota in influencing sarcopenia, frailty, and cognitive dysfunction in older individuals, and thus its relevance for healthy active ageing.

RECENT FINDINGS

Age-related alterations of intestinal microbiota composition may negatively influence muscle protein synthesis and function by promoting chronic systemic inflammation, insulin resistance, oxidative stress, and reducing nutrient bioavailability. However, this 'gut-muscle axis' hypothesis is not supported by human data to date. Some observational studies have instead demonstrated that, in older individuals, frailty and Alzheimer-type dementia are associated with fecal microbiota dysbiosis, that is, reduced biodiversity and overexpression of pathobionts. The main possible mechanisms of the 'gut-brain axis' in cognitive function modulation include effects on neurotransmission, neuroinflammation, and amyloid deposition. Conversely, longevity in good health may be associated with the maintenance of a fecal microbiota composition similar to that of healthy young adults. However, the role of gut microbiota as an independent modulator of frailty and cognition still remains uncertain, being influenced by several physiological factors, including diet and exercise.

SUMMARY

The intestinal microbiome composition represents a possible determinant of functional performance in older people, and a promising target for antiaging therapeutic interventions.

Effects of prebiotic galacto-oligosaccharide on postoperative cognitive dysfunction and neuroinflammation through targeting of the gut-brain axis

Background

Surgery-induced neuroinflammation plays an important role in postoperative cognitive dysfunction (POCD). Gut microbiota is a key regulator of neurological inflammation. Nurturing with prebiotics is an effective microbiota manipulation that can regulate host immunity and cognition. The aim of the present study was to test whether administration of the prebiotic Bimuno® (galactooligosaccharide (B-GOS) mixture) could ameliorate POCD and attenuate surgery-induced neuroinflammation through the microbiota-brain-axis.

Methods

Adult rats undergoing abdominal surgery under isoflurane anesthesia were fed with water or prebiotic B-GOS supplementation (15 g/L) for 3 weeks. Novel objective recognition task was employed for testing cognitive changes on postoperative day three. Expression of microglial marker Iba-1 in the hippocampus was assessed by immunohistochemical staining. Expression levels of phenotypic gene markers of activated microglia (M1: iNOS, CD68, CD32; M2: Ym1, CD206, and SOCS3) in hippocampus were determined by quantitative polymerase chain reaction (qPCR). Inflammatory cytokines in the hippocampus were assessed using enzyme-linked immunosorbent assay (ELISA). Feces were collected for microbial community analysis.

Results

Rats exhibited an impairment in novel objective recognition 3 days after surgery compared with control rats (P < .01). In the hippocampus, expressions of Iba-1 and M1 markers of surgical rats were significantly upregulated. Similarly, expressions of SOCS3 and CD206 in the hippocampus were upregulated. Additionally, increasing levels of IL-6 and IL-4 were evident in the hippocampus. Administration of B-GOS significantly alleviated cognitive decline induced by surgery (P < .01). B-GOS-fed rats showed a significantly downregulated activation of microglia and expressions of M1-related genes and SOCS3 and IL-6. While there was no significant difference in expressions of CD206 and Ym1 and IL-4 between the surgical and B-GOS groups. Analysis of gut microbiome found that administration of B-GOS induced a significant change beta diversity of the gut microbiome and proliferation of Bifidobacterium and other potentially anti-inflammatory microbes.

Conclusions

Administration of B-GOS has a beneficial effect on regulating neuroinflammatory and cognitive impairment in a rat model of abdominal surgery and was associated with the manipulation of gut microbiota.

Cross-species examination of single- and multi-strain probiotic treatment effects on neuropsychiatric outcomes

Interest in elucidating gut-brain-behavior mechanisms and advancing neuropsychiatric disorder treatments has led to a recent proliferation of probiotic trials. Yet, a considerable gap remains in our knowledge of probiotic efficacy across populations and experimental contexts. We conducted a cross-species examination of single- and multi-strain combinations of established probiotics. Forty-eight human (seven infant/child, thirty-six young/middle-aged adult, five older adult) and fifty-eight non-human (twenty-five rat, twenty-seven mouse, five zebrafish, one quail) investigations met the inclusion/exclusion criteria. Heterogeneity of probiotic strains, substrains, and study methodologies limited our ability to conduct meta-analyses. Human trials detected variations in anxiety, depression, or emotional regulation (single-strain 55.6%; multi-strain 50.0%) and cognition or social functioning post-probiotic intake (single-strain 25.9%; multi-strain 31.5%). For the non-human studies, single- (60.5%) and multi-strain (45.0%) combinations modified stress, anxiety, or depression behaviors in addition to altering social or cognitive performance (single-strain 57.9%; multi-strain 85.0%). Rigorous trials that confirm existing findings, investigate additional probiotic strain/substrain combinations, and test novel experimental paradigms, are necessary to develop future probiotic treatments that successfully target specific neuropsychiatric outcomes.

Microbial treatment: the potential application for Parkinson's disease

Alterations in the composition of the intestinal flora are associated with the pathophysiology of Parkinson's disease (PD). More importantly, the possible cause-effect links between gut flora and PD pathogenesis have been identified using PD animal models. Recent studies have found that probiotics improve the symptoms associated with constipation in PD patients. In addition, fecal microbiota transplantation (FMT) was recently shown to provide a protective effect against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced neurotoxicity in mice. Effective microbial therapy for PD includes probiotics and FMT. Therefore, microbial therapy may be a useful and novel approach for treatment of PD. In this review, I discuss the use of microbial treatment in PD.

Purple Corn Extract as Anti-allodynic Treatment for Trigeminal Pain: Role of Microglia

Natural products have attracted interest in the search for new and effective analgesics and coadjuvant approaches to several types of pain. It is in fact well known that many of their active ingredients, such as anthocyanins (ACNs) and polyphenols, can exert potent anti-inflammatory actions. Nevertheless, their potential beneficial effects in orofacial painful syndromes have not been assessed yet. Here, we have evaluated the preventive effect of an ACN-enriched purple corn extract against the development of orofacial allodynia, in comparison with isogenic yellow corn extract containing only polyphenols. Orofacial allodynia developed following induction of temporomandibular joint (TMJ) inflammation in male rats, due to the injection of Complete Freund’s Adjuvant (CFA), and was evaluated by von Frey filaments. Animals drank purple or yellow corn extracts or water starting from 11 days before induction of inflammation and up to the end of the experiment 3 days later. To highlight possible additive and/or synergic actions, some animals also received the anti-inflammatory drug acetyl salicylic acid (ASA). In parallel with the evaluation of allodynia, we have focused our attention on the activation of microglia cells in the central nervous system (CNS), as it is well-known that they significantly contribute to neuronal sensitization and pain. Our data demonstrate that purple corn extract is as effective as ASA in preventing the development of orofacial allodynia, and only partial additive effect is observed when the two agents are co-administered. Yellow corn exerted no effect. Multiple mechanisms are possibly involved in the action of purple corn, including reduction of trigeminal macrophage infiltration and the shift of microglia cell polarization to an anti-inflammatory phenotype. In fact, in rats receiving yellow corn or water microglia cells show thick, short cell processes typical of activated cells. Conversely, thinner and longer microglia cell processes are observed in the brainstem of animals drinking purple corn extract; shape changes are accompanied by a reduction in the expression of pro-inflammatory molecules and increased production of anti-inflammatory mediators. Administration of purple corn extracts therefore represents a possible low-cost and easy way to reduce trigeminal-associated pain in various pathological conditions also thanks to the modulation of microglia reactivity.

Current Perspectives and Mechanisms of Relationship between Intestinal Microbiota Dysfunction and Dementia: A Review

BACKGROUND

Accumulating data suggest a crucial role of the intestinal microbiota in the development and progression of neurodegenerative diseases. More recently, emerging reports have revealed an association between intestinal microbiota dysfunctions and dementia, a debilitating multifactorial disorder, characterized by progressive deterioration of cognition and behavior that interferes with the social and professional life of the sufferer. However, the mechanisms of this association are not fully understood.

SUMMARY

In this review, I discuss recent data that suggest mechanisms of cross-talk between intestinal microbiota dysfunction and the brain that underlie the development of dementia. Potential therapeutic options for dementia are also discussed. The pleiotropic signaling of the metabolic products of the intestinal microbiota together with their specific roles in the maintenance of both the intestinal and blood-brain barriers as well as regulation of local, distant, and circulating immunocytes, and enteric, visceral, and central neural functions are integral to a healthy gut and brain.

KEY MESSAGES

Research investigating the effect of intestinal microbiota dysfunctions on brain health should focus on multiple interrelated systems involving local and central neuroendocrine, immunocyte, and neural signaling of microbial products and transmitters and neurohumoral cells that not only maintain intestinal, but also blood brain-barrier integrity. The change in intestinal microbiome/dysbiome repertoire is crucial to the development of dementia.

Gut microbiota, cognitive frailty and dementia in older individuals: a systematic review

Cognitive frailty, defined as the coexistence of mild cognitive impairment symptoms and physical frailty phenotype in older persons, is increasingly considered the main geriatric condition predisposing to dementia. Recent studies have demonstrated that gut microbiota may be involved in frailty physiopathology by promoting chronic inflammation and anabolic resistance. The contribution of gut microbiota to the development of cognitive impairment and dementia is less defined, even though the concept of "gut-brain axis" has been well demonstrated for other neuropsychiatric disorders. The aim of this systematic review was to summarize the current state-of-the-art literature on the gut microbiota alterations associated with cognitive frailty, mild cognitive impairment and dementia and elucidate the effects of pre- or probiotic administration on cognitive symptom modulation in animal models of aging and human beings. We identified 47 papers with original data (31 from animal studies and 16 from human studies) suitable for inclusion according to our aims. We concluded that several observational and intervention studies performed in animal models of dementia (mainly Alzheimer's disease) support the concept of a gut-brain regulation of cognitive symptoms. Modulation of vagal activity and bacterial synthesis of substances active on host neural metabolism, inflammation and amyloid deposition are the main mechanisms involved in this physiopathologic link. Conversely, there is a substantial lack of human data, both from observational and intervention studies, preventing to formulate any clinical recommendation on this topic. Gut microbiota modulation of cognitive function represents, however, a promising area of research for identifying novel preventive and treatment strategies against dementia.

Probiotic Lactobacillus paracasei HII01 protects rats against obese-insulin resistance-induced kidney injury and impaired renal organic anion transporter 3 function

The relationship between gut dysbiosis and obesity is currently acknowledged to be a health topic which causes low-grade systemic inflammation and insulin resistance and may damage the kidney. Organic anion transporter 3 (Oat3) has been shown as a transporter responsible for renal handling of gut microbiota products which are involved in the progression of metabolic disorder. The present study investigated the effect of probiotic supplementation on kidney function, renal Oat3 function, inflammation, endoplasmic reticulum (ER) stress, and apoptosis in obese, insulin-resistant rats. After 12 weeks of being provided with either a normal or a high-fat diet (HF), rats were divided into normal diet (ND); ND treated with probiotics (NDL); HF; and HF treated with probiotic (HFL). Lactobacillus paracasei HII01 1 × 108 colony forming unit (CFU)/ml was administered to the rats daily by oral gavage for 12 weeks. Obese rats showed significant increases in serum lipopolysaccharide (LPS), plasma lipid profiles, and insulin resistance. Renal Oat 3 function was decreased along with kidney dysfunction in HF-fed rats. Obese rats also demonstrated the increases in inflammation, ER stress, apoptosis, and gluconeogenesis in the kidneys. These alterations were improved by Lactobacillus paracasei HII01 treatment. In conclusion, probiotic supplementation alleviated kidney inflammation, ER stress, and apoptosis, leading to improved kidney function and renal Oat3 function in obese rats. These benefits involve the attenuation of hyperlipidemia, systemic inflammation, and insulin resistance. The present study also suggested the idea of remote sensing and signaling system between gut and kidney by which probiotic might facilitate renal handling of gut microbiota products through the improvement of Oat3 function.

Both oophorectomy and obesity impaired solely hippocampal-dependent memory via increased hippocampal dysfunction

Our previous study demonstrated that obesity aggravated peripheral insulin resistance and brain dysfunction in the ovariectomized condition. Conversely, the effect of obesity followed by oophorectomy on brain oxidative stress, brain apoptosis, synaptic function and cognitive function, particularly in hippocampal-dependent and hippocampal-independent memory, has not been investigated. Our hypothesis was that oophorectomy aggravated metabolic impairment, brain dysfunction and cognitive impairment in obese rats. Thirty-two female rats were fed with either a normal diet (ND, n = 16) or a high-fat diet (HFD, n = 16) for a total of 20 weeks. At week 13, rats in each group were subdivided into sham and ovariectomized subgroups (n = 8/subgroup). At week 20, all rats were tested for hippocampal-dependent and hippocampal-independent memory by using Morris water maze test (MWM) and Novel objective recognition (NOR) tests, respectively. We found that the obese-insulin resistant condition occurred in sham-HFD-fed rats (HFS), ovariectomized-ND-fed rats (NDO), and ovariectomized-HFD-fed rats (HFO). Increased hippocampal oxidative stress level, increased hippocampal apoptosis, increased hippocampal synaptic dysfunction, decreased hippocampal estrogen level and impaired hippocampal-dependent memory were observed in HFS, NDO, and HFO rats. However, the hippocampal-independent memory, cortical estrogen levels, cortical ROS production, and cortical apoptosis showed no significant difference between groups. These findings suggested that oophorectomy and obesity exclusively impaired hippocampal-dependent memory, possibly via increased hippocampal dysfunction. Nonetheless, oophorectomy did not aggravate these deleterious effects under conditions of obesity.

Lactobacillus paracasei PS23 Delays Progression of Age-Related Cognitive Decline in Senescence Accelerated Mouse Prone 8 (SAMP8) Mice

Probiotic supplements are potential therapeutic agents for age-related disorders due to their antioxidant and anti-inflammatory properties. However, the effect of probiotics on age-related brain dysfunction remains unclear. To investigate the effects of Lactobacillus paracasei PS23 (LPPS23) on the progression of age-related cognitive decline, male and female senescence-accelerated mouse prone 8 (SAMP8) mice were divided into two groups (n = 6 each): the control and PS23 groups. From the age of 16 weeks, these groups were given saline and LPPS23, respectively, because SAMP8 mice start aging rapidly after four months of age. After 12 weeks of treatment, we evaluated the effect of LPPS23 by analyzing their appearance, behavior, neural monoamines, anti-oxidative enzymes, and inflammatory cytokines. The PS23 group showed lower scores of senescence and less serious anxiety-like behaviors and memory impairment compared to the control group. The control mice also showed lower levels of neural monoamines in the striatum, hippocampus, and serum. Moreover, LPPS23 induced the anti-oxidative enzymes superoxide dismutase (SOD) and glutathione peroxidase (GPx). Higher levels of tumor necrosis factor (TNF)-α and monocyte chemotactic protein-1 (MCP1) and lower levels of interleukin (IL)-10 indicated that LPPS23 modulated the inflammation. Our results suggest that LPPS23 supplements could delay age-related cognitive decline, possibly by preventing oxidation and inflammation and modulating gut–brain axis communication.

The In Ovo Feeding Administration (Gallus Gallus)-An Emerging In Vivo Approach to Assess Bioactive Compounds with Potential Nutritional Benefits

In recent years, the in ovo feeding in fertilized broiler (Gallus gallus) eggs approach was further developed and currently is widely applied in the evaluation process of the effects of functional foods (primarily plant origin compounds) on the functionality of the intestinal brush border membrane, as well as potential prebiotic properties and interactions with the intestinal microbial populations. This review collates the information of potential nutrients and their effects on the mineral absorption, gut development, brush border membrane functionality, and immune system. In addition, the advantages and limitations of the in ovo feeding method in the assessment of potential prebiotic effects of plant origin compounds is discussed.