Vitamin D mitigates diabetes-associated metabolic and cognitive dysfunction by modulating gut microbiota and colonic cannabinoid receptor 1

Progress in the Pathogenesis of Diabetic Encephalopathy: The Key Role of Neuroinflammation

Diabetic encephalopathy (DE) is a severe complication that occurs in the central nervous system (CNS) and leads to cognitive impairment. DE involves various pathophysiological processes, and its pathogenesis is still unclear. This review summarised current research on the pathogenesis of diabetic encephalopathy, which involves neuroinflammation, oxidative stress, iron homoeostasis, blood-brain barrier disruption, altered gut microbiota, insulin resistance, etc. Among these pathological mechanisms, neuroinflammation has been focused on. This paper summarises some of the molecular mechanisms involved in neuroinflammation, including the Mammalian Target of Rapamycin (mTOR), Lipocalin-2 (LCN-2), Pyroptosis, Advanced Glycosylation End Products (AGEs), and some common pro-inflammatory factors. In addition, we discuss recent advances in the study of potential therapeutic targets for the treatment of DE against neuroinflammation. The current research on the pathogenesis of DE is progressing slowly, and more research is needed in the future. Further study of neuroinflammation as a mechanism is conducive to the discovery of more effective treatments for DE in the future.

Vitamin D3 improves glucose metabolism and attenuates inflammation in prediabetic human and mice

Prediabetes is a crucial stage for prevention and treatment of diabetes, and vitamin D (VD) has been found to be linked to the development of prediabetes and diabetes. Thus, we aimed to identify the effect of VD supplementation on glucose metabolism in prediabetic participants and mice. A 1:1 paired design of randomized, placebo-controlled trial with 1600 IU/day VD3 or placebo was administered to individuals with prediabetes, two-way repeated-measures ANCOVA was used to analyze glycolipid and inflammatory factors. A high-fat diet induced prediabetic KKay mice were utilized to evaluate the effects of VD3 with 16 weeks supplementation. Generalized estimation equation, one way ANOVA were used to analyze continuous monitoring indexes and terminal indexes, respectively. Exercise capacity, skeletal muscle pathological features and relevant proteins were examined. The clinical results showed that VD3 could improve insulin secretion and decrease inflammation. Results of KKay mice exhibited that VD3 not only ameliorate glycolipid metabolism and inflammatory indicators, but also regulated pathological changes of skeletal muscle and exercise capacity. Mechanistically, our results demonstrated that VD3 could inhibit the TLR4/NFκB and activate PI3K/AKT signaling pathway. Collectively, the study indicated that VD3 exerts its beneficial effects by inhibiting TLR4/NFκB to decrease inflammatory response, and activating PI3K/AKT signaling pathway to regulate glucose homeostasis.

Decreased vitamin D bio-availability with altered DNA methylation of its metabolism genes in association with the metabolic disorders among the school-aged children with degree I, II, and III obesity

Obesity is strongly associated with disturbances of vitamin D (VD) metabolites in the animal models. However, the related epidemiological evidence is still controversial, especially the different degrees of obesity children. Hence, in this present representative case-control study, 106 obesity school-age children aged 7-12 years were included and divided into different subgroups as degree I (the age- and sex-specific BMI≥95th percentile, n=45), II (BMI ≥120% percentile, n=34) and III (BMI ≥140% percentile, n=27) obesity groups across the ranges of body mass index (BMI). While the age- and sex-matched subjects without obesity were as the control group. Notably, it was significantly different of body composition, anthropological and clinical characteristics among the above four subgroups with the dose-response relationships (P<.05). Moreover, comparing with the control group, the serum VD concentrations were higher, VD metabolites like 25(OH)D, 25(OH)D3 and 1,25(OH)2D, and related hydroxylases as CYP27A1, CYP2R1 and CYP27B1 were lower in the degree I, II, and III obesity subgroups (P<.05), which were more disorder with the anthropological and clinical characteristics as the obesity was worsen in a BMI-independent manner (P<.05). However, there was a significant increase of CYP27B1 in the degree III obesity group than those in the degree I and II obesity subgroups. Furthermore, the methylation patterns on the genome-wide (Methylation/Hydroxymethylation) and VD metabolism genes (CYP27A1, CYP2R1 and CYP27B1) were negatively correlated with the worse obesity and their related expressions (P<.05). In summary, these results indicated that obesity could affect the homeostasis of VD metabolism related genes such as CYP27A1, CYP2R1, CYP27B1 and etc through abnormal DNA methylation, resulting in the disorders of VD related metabolites to decrease VD bio-availability with the BMI-independent manner. In turn, the lower levels of VD metabolites would affect the liver function to exacerbate the progression of obesity, as the Degree II and III obesity subgroups.

Idiopathic chronic intestinal pseudo-obstruction syndrome is strongly associated with low serum levels of vitamin D

Idiopathic chronic intestinal pseudo-obstruction (CIPO) is associated with intestinal inflammation and malabsorption and may cause serum vitamin D deficiency. We aimed to assess whether there is an association between idiopathic CIPO and serum levels of 25-hydroxy-vitamin D. Consecutive patients with confirmed diagnosis of idiopathic CIPO were prospectively enrolled and matched with healthy controls by gender, age, and BMI. Median serum level of 25-hydroxy-vitamin D of patients with CIPO was compared with that of healthy subjects using the Wilcoxon signed-rank test for matched samples. A total of 35 patients with CIPO and 35 matched healthy subjects were enrolled. All patients with CIPO had a 25-hydroxy-vitamin D deficiency with serum levels <12 ng/ml. The median serum level of vitamin D was significantly lower in patients with CIPO than in healthy controls (5.7 vs. 29.7 ng/ml, P  < 0.0001). Serum level of vitamin D was not associated with gender ( P  = 0.27), age ( P  = 0.22), BMI ( P  = 0.95), high (>10 000 × ml) WBC count ( P  = 0.08), or high (>5 mg/l) C-reactive protein ( P  = 0.87) among patients with CIPO. CIPO seems to be strongly associated with low serum levels of 25-hydroxy-vitamin D.

Diabetes and vitamin D: The effect of insulin sensitivity and gut microbial health

Current global estimation suggests that about 10% of adults worldwide have diabetes, thus, various strategies are needed to address the issue, including dietary factors such as vitamin D. Various studies have suggested an inverse associations between vitamin D and the risks and pathogenesis of all forms of diabetes (type 1, type 2 and gestational diabetes). The underlying mechanism is not fully understood; however, the expression of vitamin D receptors in pancreatic beta cells suggests an important physiological role for vitamin D in beta cell function. Vitamin D deficiency may impair blood glucose control and decrease insulin sensitivity by reducing insulin secretion from beta cells. Many studies suggest that vitamin D intervention may be beneficial; however, there is inconclusive evidence of the effectiveness of vitamin D supplementation on reducing the risks or managing the pathogenesis of all forms of diabetes. Part of the pathogenesis of vitamin D for reducing diabetes is thought to be related to its impact on gut microbiota profile, via the suggested prebiotic properties of vitamin D.

The role of vitamin D in depression and anxiety disorders: a review of the literature

BACKGROUND

Prevalence of mental health disorders continue to increase worldwide. Over the past decades, suboptimal vitamin D (VD) levels and gut dysbiosis have been associated with neurological dysfunction and psychiatric disorders.

METHODS

In this review, we examined the available literature on VD and mental health disorders, particularly depression and anxiety, in both clinical and pre-clinical studies.

RESULTS

Our extensive review failed to find a link between VD deficiency, depression, and anxiety-related behavior in preclinical animal models. However, strong evidence suggests that VD supplementation may alleviate symptoms in chronically stressed rodents, with some promising evidence from clinical studies. Further, fecal microbiota transplantations suggest a potential role of gut microbiota in neuropsychiatric disorders, although the underlying mechanisms remain to be fully elucidated. It has been postulated that serotonin, primarily produced by gut bacteria, may be a crucial factor. Hence, whether VD has the ability to impact gut microbiota and modulate serotonin synthesis warrants further investigation.

CONCLUSIONS

Taken together, literature has suggested that VD may serve as a key regulator in the gut-brain axis to modulate gut microbiota and alleviate symptoms of depression and anxiety. The inconsistent results of VD supplementation in clinical studies, particularly among VD deficient participants, suggests that current intake recommendations may need to be re-evaluated for individuals at-risk (i.e. prior to diagnosis) of developing depression and/or anxiety.

Gut-brain communication mediates the impact of dietary lipids on cognitive capacity

Cognitive impairment, as a prevalent symptom of nervous system disorders, poses one of the most challenging aspects in the management of brain diseases. Lipids present in the cell membranes of all neurons within the brain and dietary lipids can regulate the cognition and memory function. In recent years, the advancements in gut microbiome research have enabled the exploration of dietary lipids targeting the gut-brain axis as a strategy for regulating cognition. This present review provides an in-depth overview of how lipids modulate cognition via the gut-brain axis depending on metabolic, immune, neural and endocrine pathways. It also comprehensively analyzes the effects of diverse lipids on the gut microbiota and intestinal barrier function, thereby affecting the central nervous system and cognitive capacity. Moreover, comparative analysis of the positive and negative effects is presented between beneficial and detrimental lipids. The former encompass monounsaturated fatty acids, short-chain fatty acids, omega-3 polyunsaturated fatty acids, phospholipids, phytosterols, fungal sterols and bioactive lipid-soluble vitamins, as well as lipid-derived gut metabolites, whereas the latter (detrimental lipids) include medium- or long-chain fatty acids, excessive proportions of n-6 polyunsaturated fatty acids, industrial trans fatty acids, and zoosterols. To sum up, the focus of this review is on how gut-brain communication mediates the impact of dietary lipids on cognitive capacity, providing a novel theoretical foundation for promoting brain cognitive health and scientific lipid consumption patterns.

Vitamin D3 supplementation shapes the composition of gut microbiota and improves some obesity parameters induced by high-fat diet in mice

PURPOSE

Individuals with vitamin D (VD) insufficiency have a greater tendency to develop obesity and have increased systemic inflammation. Gut microbiota are involved in the regulation of host inflammation and energy metabolism, which plays a role in the pathogenesis of obesity. Thus, we aimed to evaluate the effects of different doses of VD3 on body weight, serum lipids, inflammatory factors, and intestinal barrier function in obese mice and to explore the regulatory effect of VD3 on gut microbiota in obese mice.

METHODS

Male C57BL/6 J mice received a normal chow diet (NCD, 10% fat) or high-fat diet (HFD, 60% fat) to induce obesity within 10 weeks. Then, HFD mice were supplemented with 5650, 8475, or 11,300 IU VD3/kg diet for 8 weeks. Finally, 16 s rRNA analysis was performed to analyze gut microbiota composition in cecal contents. In addition, body weight, serum lipids, inflammatory factors, and intestinal barrier function were analyzed.

RESULTS

VD3 supplementation reduced body weight and the levels of TG, TC, HDL-C, TNF-α, IL-1β and LPS, and increased ZO-1 in HFD-fed mice. Moreover, it increased α-diversity, reduced F/B ratio and altered microbiota composition by increasing relative abundance of Bacteroidetes, Proteobacteria, Desulfovibrio, Dehalobacterium, Odoribacter, and Parabacteroides and reducing relative abundance of Firmicutes and Ruminococcus. There were significant differences between HFD and NCD groups in several metabolic pathways, including endotoxin biosynthesis, tricarboxylic acid cycle, lipid synthesis and metabolism, and glycolysis.

CONCLUSIONS

Low, medium, and high doses of VD3 inhibited weight gain, reduced levels of blood lipids and inflammatory factors, and improved endotoxemia and gut barrier function in obese mice. It also increased the α-diversity of gut microbiota in obese mice and reduced the relative abundance of some intestinal pathogenic bacteria, increased the relative abundance of some beneficial bacteria, and corrected the intestinal flora disorder of obese mice, with the low- and high-dose groups showing better effects than the medium-dose group.

Nutrition at the Intersection between Gut Microbiota Eubiosis and Effective Management of Type 2 Diabetes

Nutrition is one of the most influential environmental factors in both taxonomical shifts in gut microbiota as well as in the development of type 2 diabetes mellitus (T2DM). Emerging evidence has shown that the effects of nutrition on both these parameters is not mutually exclusive and that changes in gut microbiota and related metabolites such as short-chain fatty acids (SCFAs) and branched-chain amino acids (BCAAs) may influence systemic inflammation and signaling pathways that contribute to pathophysiological processes associated with T2DM. With this background, our review highlights the effects of macronutrients, carbohydrates, proteins, and lipids, as well as micronutrients, vitamins, and minerals, on T2DM, specifically through their alterations in gut microbiota and the metabolites they produce. Additionally, we describe the influences of common food groups, which incorporate varying combinations of these macronutrients and micronutrients, on both microbiota and metabolic parameters in the context of diabetes mellitus. Overall, nutrition is one of the first line modifiable therapies in the management of T2DM and a better understanding of the mechanisms by which gut microbiota influence its pathophysiology provides opportunities for optimizing dietary interventions.

Emerging mechanisms by which endocannabinoids and their derivatives modulate bacterial populations within the gut microbiome

Bioactive lipids such as endocannabinoids serve as important modulators of host health and disease through their effects on various host functions including central metabolism, gut physiology, and immunity. Furthermore, changes to the gut microbiome caused by external factors such as diet or by disease development have been associated with altered endocannabinoid tone and disease outcomes. These observations suggest the existence of reciprocal relationships between host lipid signaling networks and bacterial populations that reside within the gut. Indeed, endocannabinoids and their congeners such as N-acylethanolamides have been recently shown to alter bacterial growth, functions, physiology, and behaviors, therefore introducing putative mechanisms by which these bioactive lipids directly modulate the gut microbiome. Moreover, these potential interactions add another layer of complexity to the regulation of host health and disease pathogenesis that may be mediated by endocannabinoids and their derivatives. This mini review will summarize recent literature that exemplifies how N-acylethanolamides and monoacylglycerols including endocannabinoids can impact bacterial populations in vitro and within the gut microbiome. We also highlight exciting preclinical studies that have engineered gut bacteria to synthesize host N-acylethanolamides or their precursors as potential strategies to treat diseases that are in part driven by aberrant lipid signaling, including obesity and inflammatory bowel diseases.

Gut microbiota regulation of inflammatory cytokines and microRNAs in diabetes-associated cognitive dysfunction

Type 2 diabetes mellitus (T2DM) has a major comorbidity known as diabetes-associated cognitive dysfunction (DACD). Studies have demonstrated that the gut microbiota is crucial in mediating the cognitive abnormalities that occur in diabetic individuals. Additionally, changes in dietary fatty acid intake levels, inflammatory cytokines, and microRNAs (miRs) have an effect on cognitive performance. However, further studies are needed to identify the link between gut microbiota and cognition in T2DM patients and the role that the above indicators play in this process. In order to provide a new rationale for the treatment of cognitive dysfunction in diabetes, this study was conducted in the middle-aged and elderly Beijing population to examine the differences in gut microbiota between DACD and T2DM patients as well as to further explore the role of erythrocyte membrane fatty acids, inflammatory cytokines, and miRs in gut microbiota-mediated cognitive impairment. According to the results, the abundance of norank_f_Eubacterium_coprostanoligenes_group, Acidaminococcus, Enterorhabdus, and norank_f_Clostridium_methylpentosum_group was higher in DACD patients compared to T2DM patients at the genus level. Compared with T2DM patients, plasma interleukin-12 (IL-12) concentrations were significantly higher in DACD patients than in T2DM patients, and IL-12 was significantly positively correlated with norank_f_Eubacterium_coprostanoligenes_group. In addition, plasma miR-142-5p was significantly positively correlated with Enterorhabdus and norank_f_Eubacterium_coprostanoligenes_group. We therefore hypothesize that cognitive impairment in T2DM patients is associated with altered gut microbial composition and that the effect of microbiota on cognition may be mediated through IL-12 and miR-142-5p. KEY POINTS: • Type 2 diabetes with or without cognitive impairment differs in gut microbiota. • Differential genera of gut microbiota were associated with inflammatory cytokines. • Differential genera of gut microbiota were associated with plasma microRNAs.

Vitamin D3 affects the gut microbiota in an LPS-stimulated systemic inflammation mouse model

Although gut dysbiosis contributes to systemic inflammation, the counteractive effect of systemic inflammation on gut microbiota is unknown. Vitamin D may exert anti-inflammatory effects against systemic inflammation, but its regulation of the gut microbiota is poorly understood. In this study, mice were intraperitoneally injected with lipopolysaccharide (LPS) to create a systemic inflammation model and received vitamin D3 treatment orally for 18 continuous days. Then, body weight, morphological changes in the colon epithelium, and gut microbiota (n = 3) were evaluated. We verified that LPS stimulation caused inflammatory changes in the colon epithelium, which could be obviously attenuated by vitamin D3 treatment (10 μg/kg/day) in mice. Then, 16S rRNA gene sequencing of the gut microbiota first revealed that LPS stimulation induced a large number of operational taxonomic units, and vitamin D3 treatment reduced the number. In addition, vitamin D3 had distinctive effects on the community structure of the gut microbiota, which was obviously changed after LPS stimulation. However, neither LPS nor vitamin D3 affected the alpha and beta diversity of the gut microbiota. Furthermore, statistical analysis of differential microorganisms showed that the relative abundance of microorganisms in the phylum Spirochaetes decreased, the family Micrococcaceae increased, the genus [Eubacterium]_brachy_group decreased, the genus Pseudarthrobacter increased, and the species Clostridiales_bacterium_CIEAF_020 decreased under LPS stimulation, but vitamin D3 treatment significantly reversed the LPS-induced changes in the relative abundance of these microorganisms. In conclusion, vitamin D3 treatment affected the gut microbiota and alleviated inflammatory changes in the colon epithelium in the LPS-stimulated systemic inflammation mouse model.

Effect of Vitamin D on the Proliferation and Barrier of Atrophic Vaginal Epithelial Cells

Atrophic vaginitis is very common in postmenopausal women due to declining estrogen levels. Vitamin D plays an important role in promoting epithelial cell proliferation, migration and adhesion. We established a rat model of ovariectomy (OVX) induced atrophic vaginitis with the aim of investigating the effects of Vitamin D supplementation on the vaginal epithelial barrier. The results showed that ovariectomised rats had significantly higher vaginal pH, reduced Lactobacillus, significantly lower uterine and vaginal weights, and lower vaginal epithelial PCNA, occludin, and E-cadherin mRNA expression compared with sham-operated rats. Vitamin D supplementation could reduce the vaginal pH, promote the proliferation and keratinization of vaginal epithelial cells, enhance the expression of PCNA mRNA in vaginal tissues, and improve the vaginal and uterine atrophy. Vitamin D can also increase the expression of E-cadherin and occludin proteins in vaginal tissues, maintain the integrity of the vaginal epithelium, increase the number of Lactobacillus, and reduce pathogenic bacterial infections. In vitro experiments demonstrated that 1,25(OH)2D3 could promote the proliferation and migration of VK2/E6E7 vaginal epithelial cells and increase the expression of E-cadherin protein. In conclusion, we demonstrated that Vitamin D can regulate the expression of vaginal epithelial tight junction proteins, promotes cell proliferation, and improves vaginal atrophy due to estrogen deficiency.

Vitamin D is a potential treatment for the management of gastrointestinal mucositis

PURPOSE OF THE REVIEW

Gastrointestinal mucositis (GM) is a severe side effect of cancer treatments, negatively impacting the patient's quality of life, and has limited treatment. GM consists of complex biological processes involving apoptosis and inflammation, leading to damage and ulceration of the gastrointestinal system. Recently, vitamin D has been shown to have multiple roles in the gut, including immunomodulation, epithelial barrier regulation and microbiome regulation. Hence, this review aims to put forth vitamin D as a potential therapeutic due to its protective role in the intestine.

RECENT FINDINGS

Recent studies have shown that vitamin D can reduce intestinal inflammation by reducing NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells) activation. Vitamin D also targets and maintains the intestinal epithelial barrier via the tight junction protein expression and the inhibition of microbiome translocation. Significant evidence also suggests that vitamin D exerts multiple therapeutic effects through binding to vitamin D receptors (VDRs), and the downregulation of VDR has been associated with the severity of the disease. Additionally, vitamin D deficiency is reported in cancer patients.

SUMMARY

There is a dire need for effective treatment for GM, and recent animal and human studies show that vitamin D may be a potential therapy to prevent or treat GM.

Rosa canina L. improves learning and memory-associated cognitive impairment by regulating glucose levels and reducing hippocampal insulin resistance in high-fat diet/streptozotocin-induced diabetic rats

ETHNOPHARMACOLOGICAL RELEVANCE

Recent studies claim that Type-2 diabetes mellitus (T2DM) and Alzheimer's disease (AD) overlap in several common pathological pathways which from neuronal damage to impaired memory performance. It is known that the use of Rosa canina L. (R. canina) as medicine in folk medicine dates back to ancient times and is used in the treatment of nervous diseases in Persian medicine. However, the effect of R. canina on diabetes-related cognitive decline and memory impairment has not yet been studied.

AIM OF THE STUDY

We evaluated the impact of T2DM on AD-like alterations and examined the molecular mechanism of a possible effect of R. canina on cognitive alterations in diabetic rats.

MATERIALS&METHODS

R. canina ethanol extract was obtained by maceration method. This study was performed with male Spraque-Dawley rats fed with a high-fat diet (HFD) for 8 weeks, low-dose streptozotocin (STZ; 35 mg/kg IP) injection for 4 weeks, and R. canina (250 mg/kg; per oral) and metformin (400 mg/kg; per oral) administration for 4 weeks. The weight and blood glucose of rats were measured weekly. To evaluate glucose tolerance area under the curve (AUC) was calculated by performing an oral glucose tolerance test. Then the rats were subjected to behavioural tests, and their hippocampus and cortex tissues were obtained for biochemical and morphological analyses.

RESULTS

R. canina could manage glucose responsiveness by reducing post-prandial blood glucose levels, preventing weight loss, and raising serum insulin levels in T2DM-induced rats. Behavioural tests showed that R. canina significantly improves diabetes-related cognitive decline in recall and long-term memory. Treatment with R. canina significantly reversed HFD/STZ-induced increases in insulin, amyloid-β, amyloid precursor protein levels, and acetylcholinesterase activity in the prefrontal cortex and hippocampus. Furthermore, histological analyzes revealed the protection of R. canina against neuronal disruption in the cortical and hippocampal CA3 region caused by chronic hyperglycemia.

CONCLUSION

Analyzed collectively, these results suggest that R. canina can correct T2DM-related cognitive decline may be attributed to insulin pathway modulation, prevention of amyloid deposition, and increased cholinergic transmission.

Vitamin D, Gut Microbiota, and Cardiometabolic Diseases-A Possible Three-Way Axis

Metabolic syndrome (MetSyn) is a precursor for several cardiometabolic diseases such as obesity, type-2 diabetes mellitus (T2DM), and cardiovascular diseases. Emerging evidence suggests that vitamin D deficiency links to cardiometabolic diseases through microbiota. A combination of poor vitamin D status and dysbiosis may contribute to the progression of cardiometabolic diseases. Therefore, in this review, we present the relationship among vitamin D, microbiota, and cardiometabolic diseases with a focus on MetSyn. We searched major databases for reports on vitamin D, microbiota, and MetSyn until June 2022. We reviewed 13 reports on the relation between vitamin D and MetSyn (6 randomized controlled and 7 cross-sectional studies) and 6 reports on the effect of vitamin D on the gut microbiome. Adequate vitamin D status has a beneficial effect on gut microbiota, therefore preventing the progression of MetSyn. Further, well-controlled studies are needed for a better understanding of the mechanisms of action involving vitamin D and microbiota in the pathogenesis of cardiometabolic diseases.

Paroxetine effects in adult male rat colon: Focus on gut steroidogenesis and microbiota

Paroxetine, a selective serotonin reuptake inhibitor (SSRI), is prescribed to treat psychiatric disorders, although an off-label SSRI use is also for functional gastrointestinal disorders. The mutual correlation between serotonin and peripheral sex steroids has been reported, however little attention to sex steroids synthesized by gut, has been given so far. Indeed, whether SSRIs, may also influence the gut steroid production, immediately after treatment and/or after suspension, is still unclear. The finding that gut possesses steroidogenic capability is of particular relevance, also for the existence of the gut-microbiota-brain axis, where gut microbiota represents a key orchestrator. On this basis, adult male rats were treated daily for two weeks with paroxetine or vehicle and, 24 h after treatment and at 1 month of withdrawal, steroid environment and gut microbiota were evaluated. Results obtained reveal that paroxetine significantly affects steroid levels, only in the colon but not in plasma. In particular, steroid modifications observed immediately after treatment are not overlap with those detected at withdrawal. Additionally, paroxetine treatment and its withdrawal impact gut microbiota populations differently. Altogether, these results suggest a biphasic effect of the drug treatment in the gut both on steroidogenesis and microbiota.

The Role of Vitamin D in Stroke Prevention and the Effects of Its Supplementation for Post-Stroke Rehabilitation: A Narrative Review

Hypovitaminosis D is a serious public health problem, representing an independent factor in mortality among the general population. Vitamin D deficiency may affect up to one billion people worldwide. Recently, the potential association between vitamin D levels and stroke has gained increasing attention. Many studies suggest that maintaining normal serum vitamin D levels is associated with improvement of the cardiovascular system and a reduction in stroke risk. As a neurosteroid, vitamin D influences brain development and function and immunomodulation and affects brain neuroplasticity. It supports many processes that maintain homeostasis in the body. As stroke is the second most common cause of death worldwide, more studies are needed to confirm the positive effects of vitamin D supplementation, its dosage at different stages of the disease, method of determination, and effect on stroke onset and recovery. Many studies on stroke survivors indicate that serum vitamin D levels only offer insignificant benefits and are not beneficial to recovery. This review article aims to highlight recent publications that have examined the potential of vitamin D supplementation to improve rehabilitation outcomes in stroke survivors. Particular attention has been paid to stroke prevention.

Cross sectional determinants of VO2 max in free living Iranians: Potential role of metabolic syndrome components and vitamin D status

BACKGROUND AND AIMS

The purpose of the study was to evaluate the determinants of cardiorespiratory fitness (CRF) in Iranian adults and the potential contribution of vitamin D status.

METHODS

In this cross-sectional study 264 cases (116 men and 147 women aged 18-70 years old were participated. Maximal oxygen consumption (VO_{2 max}) was measured by the Bruce protocol utilizing treadmill exercise testing. Anthropometric data, body composition and fasting blood glucose and lipid concentrations were measured. Serum levels of 25-hydroxyvitamin D (25(OH)D) and 1,25-dihydroxyvitamin D (1,25(OH)₂D) were assessed using enzyme-linked immunosorbent assay. Stepwise linear regression analysis was applied to determine significant predictors of VO2 peak. We tested non-linear (quadratic and cubic terms) versus linear association of adjusted (for determinants) VO2 max and vitamin D levels.

RESULTS

Multiple regression results showed that fat free mass, HDL-C and physical activity, waist circumference, age and sex were determinants of VO_{2 peak}. All of these explained the 65.3% of VO2 peak. There was a non-linear cubic association (R² = 0.03, p = 0.046) between serum 25(OH)D and adjusted VO2 peak in which 25(OH)D in people with a high 25(OH)D levels (>60 nmol/L), had better fitness and those with serum 25(OH) less than 20 nmol/L. We found no linear and non-linear associations between serum 1,25(OH)₂ D and adjusted VO_{2 max}.

CONCLUSIONS

Our results showed that waist circumference and HDL-C, as components of metabolic syndrome, contribute ∼2% to the variance in VO_{2 max}. Moreover, high concentrations of 25(OH)D but not 1,25(OH)₂ D may make additional contributions to CRF.

The Role of Gut Microbiota—Gut—Brain Axis in Perioperative Neurocognitive Dysfunction

With the aging of the world population and advances in medical and health technology, more and more elderly patients are undergoing anesthesia and surgery, and perioperative neurocognitive dysfunction (PND) is receiving increasing attention. The latest definition of PND, published simultaneously in November 2018 in 6 leading journals in the field of anesthesiology, clarifies that PND includes preoperatively cognitive impairment, postoperative delirium, delayed neurocognitive recovery, and postoperative cognitive dysfunction and meets the diagnostic criteria for neurocognitive impairment in the Diagnostic and Statistical Manual of Mental Disorders -fifth edition (DSM-5). The time frame for PND includes preoperatively and within 12 months postoperatively. Recent studies have shown that gut microbiota regulates central nervous function and behavior through the gut microbiota - gut - brain axis, but the role of the axis in the pathogenesis of PND remains unclear. Therefore, this article reviews the mechanism of the role of gut microbiota-gut-brain axis in PND, so as to help explore reasonable early treatment strategies.

Metabolites of Gut Microbiota and Possible Implication in Development of Diabetes Mellitus

Diabetes mellitus is characterized by having a disorder of glucose metabolism. The types of diabetes mellitus include type 1 diabetes mellitus, type 2 diabetes mellitus, gestational diabetes mellitus, and other specific types of diabetes mellitus. Many risk factors contribute to diabetes mellitus mainly including genetics, environment, obesity, and diet. In the recent years, gut microbiota has been shown to be linked to the development of diabetes. It has been reported that the gut microbiota composition of diabetic patients is different from that of healthy people. Although the mechanism behind the abnormality remains to be explored, most hypotheses focus on the inflammation response and leaky gut in relation to the changes in production of endotoxins and metabolites derived from the intestinal flora. Consequently, the above-mentioned abnormalities trigger a series of metabolic changes, gradually leading to development of hyperglycemia, insulin resistance, and diabetes. This review is (i) to summarize the differences in gut microbiota between diabetic patients and healthy people, (ii) to discuss the underlying mechanism(s) by which how lipopolysaccharide, diet, and metabolites of the gut microbiota affect diabetes, and (iii) to provide a new insight in the prevention and treatment of diabetes.