Chronic oleoylethanolamide treatment attenuates diabetes-induced mice encephalopathy by triggering peroxisome proliferator-activated receptor alpha in the hippocampus

Preliminary characterization of Ramaria botrytoides polysaccharide RB-P1-1 and analysis of its hypoglycemic effects by altering the gut microbiota and metabolites in mice with type 2 diabetes mellitus

Gut microbiota has a symbiotic relationship with the host and is closely linked to the development of type 2 diabetes mellitus (T2DM). Polysaccharides are natural bioactive compounds with beneficial effects on T2DM; however, the mechanisms underlying their effects remain unclear. This study investigated the hypoglycemic effects of a purified polysaccharide, RB-P1-1, from Ramaria botrytoides and assessed its association with gut microbiota and metabolite changes using 16S rDNA sequencing and liquid chromatography-mass spectrometry, respectively. Hypoglycemic effects were evaluated after microbial community restoration via fecal microbiota transplantation. RB-P1-1 significantly improved hyperglycemia profiles and reshaped gut microbiota, increasing the abundance of Alistipes, Bacteroides, Ruminococcus, Odoribacter, Akkermansia, and Turicibacter. RB-P1-1 modulated microbiota metabolites associated with hypoglycemic effects, including pyridoxamine, L-histidine, quercetin, 3-phosphonopropionic acid, oleoylethanolamide, 3-ketocholanic acid, 4-phenylbutyric acid, LysoPC(P-16:0/0:0), LysoPC(18:2), and short-chain fatty acids, and altered various metabolic pathways involved in T2DM development. Gut microbiota that showed altered abundance were correlated with metabolites that showed altered concentration. Gut microbiota isolated from the RB-P1-1-treated group alleviated the symptoms associated with T2DM. These results suggest RB-P1-1 is an effective active ingredient in the treatment of T2DM by modulating gut microbiota and metabolites.

The Alteration of Proteomic Profiles in Hippocampus of Type 2 Diabetic Mice Associated With Cognitive Impairment

Clinical and experimental studies have demonstrated that type 2 diabetes mellitus (T2DM) affects the brain structure and function, in particular the hippocampus, leading to cognitive impairments. However, the molecular mechanisms underlying cognitive deficits induced by T2DM are not fully understood. In this study, we aimed to investigate the effects of T2DM on behavior, the proteome profile in the hippocampus, and the potential molecular pathways involved in the development of cognitive dysfunction in T2DM mice. We found that the diabetic mice exhibited cognitive impairment in the novel object location recognition test and the novel object recognition test. The proteomic analysis revealed that various molecular pathways were involved in this context. These included the upregulation of proteins in the protein synthesis and folding pathway (EIF5A, RSP24, and PPIB), endocytosis and cellular trafficking (VPS24, SNX12, and ARP2/3), cannabinoid receptor interacting (CRIP1), ubiquitination (SKP1), and oxidative stress response (NUDT3). Downregulated proteins were related to mitochondria function (ANT1), neuronal development (ELP1), protein glycosylation (RPN2), and endocytosis (VPS4). Our study shows that T2DM mice exhibit neurocognitive impairment, which is linked to the dysregulation of hippocampal proteins involved in various molecular pathways. These findings contribute to a better understanding of the pathophysiology of T2DM-related cognitive impairment and may identify molecular targets for drug development to treat T2DM-associated cognitive impairment conditions.

Relationship between sex, APOE genotype, endocannabinoids and cognitive change in older adults with metabolic syndrome during a 3-year Mediterranean diet intervention

BACKGROUND

The Mediterranean diet (MedDiet) has demonstrated efficacy in preventing age-related cognitive decline and modulating plasma concentrations of endocannabinoids (eCBs) and N-acylethanolamines (NAEs, or eCB-like compounds), which are lipid mediators involved in multiple neurological disorders and metabolic processes. Hypothesizing that eCBs and NAEs will be biomarkers of a MedDiet intervention and will be related to the cognitive response, we investigated this relationship according to sex and apolipoprotein E (APOE) genotype, which may affect eCBs and cognitive performance.

METHODS

This was a prospective cohort study of 102 participants (53.9% women, 18.8% APOE-ɛ4 carriers, aged 65.6 ± 4.5 years) from the PREDIMED-Plus-Cognition substudy, who were recruited at the Hospital del Mar Research Institute (Barcelona). All of them presented metabolic syndrome plus overweight/obesity (inclusion criteria of the PREDIMED-Plus) and normal cognitive performance at baseline (inclusion criteria of this substudy). A comprehensive battery of neuropsychological tests was administered at baseline and after 1 and 3 years. Plasma concentrations of eCBs and NAEs, including 2-arachidonoylglycerol (2-AG), anandamide (AEA), oleoylethanolamide (OEA), palmitoylethanolamide (PEA), and N-docosahexaenoylethanolamine (DHEA), were also monitored. Baseline cognition, cognitive changes, and the association between eCBs/NAEs and cognition were evaluated according to gender (crude models), sex (adjusted models), and APOE genotype.

RESULTS

At baseline, men had better executive function and global cognition than women (the effect size of gender differences was - 0.49, p = 0.015; and - 0.42, p = 0.036); however, these differences became nonsignificant in models of sex differences. After 3 years of MedDiet intervention, participants exhibited modest improvements in memory and global cognition. However, greater memory changes were observed in men than in women (Cohen's d of 0.40 vs. 0.25; p = 0.017). In men and APOE-ε4 carriers, 2-AG concentrations were inversely associated with baseline cognition and cognitive changes, while in women, cognitive changes were positively linked to changes in DHEA and the DHEA/AEA ratio. In men, changes in the OEA/AEA and OEA/PEA ratios were positively associated with cognitive changes.

CONCLUSIONS

The MedDiet improved participants' cognitive performance but the effect size was small and negatively influenced by female sex. Changes in 2-AG, DHEA, the OEA/AEA, the OEA/PEA and the DHEA/AEA ratios were associated with cognitive changes in a sex- and APOE-dependent fashion. These results support the modulation of the endocannabinoid system as a potential therapeutic approach to prevent cognitive decline in at-risk populations.

TRIAL REGISTRATION

ISRCTN89898870.

Therapeutic effects of a walnut-derived peptide on NLRP3 inflammasome activation, synaptic plasticity, and cognitive dysfunction in T2DM mice

NLRP3 inflammasome activation plays a key role in the development of diabetes-induced cognitive impairment. However, strategies to inhibit NLRP3 inflammasome activation remain elusive. Herein, we evaluated the impact of a walnut-derived peptide, TWLPLPR (TW-7), on cognitive impairment in high-fat diet/streptozotocin-induced type 2 diabetes mellitus (T2DM) mice and explored its underlying mechanisms in high glucose-induced HT-22 cells. In the Morris water maze test, TW-7 alleviated cognitive deficits in mice; this was confirmed at the level of synaptic structure and dendritic spine density in the mouse hippocampus using transmission electron microscopy and Golgi staining. TW-7 increased the expression of synaptic plasticity-related proteins and suppressed the NEK7/NLRP3 inflammatory pathway, as determined by western blotting and immunofluorescence analysis. The mechanism of action of TW-7 was verified in an HT-22 cell model of high glucose-induced insulin resistance. Collectively, TW-7 could regulate T2DM neuroinflammation and synaptic function-induced cognitive impairment by inhibiting NLRP3 inflammasome activation and improving synaptic plasticity.

A systematic review of preclinical studies exploring the role of insulin signalling in executive function and memory

Beside its involvement in somatic dysfunctions, altered insulin signalling constitutes a risk factor for the development of mental disorders like Alzheimer's disease and obsessive-compulsive disorder. While insulin-related somatic and mental disorders are often comorbid, the fundamental mechanisms underlying this association are still elusive. Studies conducted in rodent models appear well suited to help decipher these mechanisms. Specifically, these models are apt to prospective studies in which causative mechanisms can be manipulated via multiple tools (e.g., genetically engineered models and environmental interventions), and experimentally dissociated to control for potential confounding factors. Here, we provide a narrative synthesis of preclinical studies investigating the association between hyperglycaemia - as a proxy of insulin-related metabolic dysfunctions - and impairments in working and spatial memory, and attention. Ultimately, this review will advance our knowledge on the role of glucose metabolism in the comorbidity between somatic and mental illnesses.

Lipin2 ameliorates diabetic encephalopathy via suppressing JNK/ERK-mediated NLRP3 inflammasome overactivation

OBJECTIVES

Diabetic encephalopathy (DE) is a common complication of diabetes in the central nervous system, which can cause cognitive dysfunction in patients. However, its pathophysiological mechanism has not been elucidated, and thus effective prevention and treatment methods are still lacking.Previous studies reported that neuroinflammation involved in the central neuropathy, while lipin2 plays an important role in inflammatory response.Therefore, we aimed to investigate the effects of lipin2 on regulating inflammatory response in the pathogenesis of DE.

METHODS

BV2 cells were treated with high glucose and infected with lipin2 overexpression or knockdown virus to observe the cell viability. Then, we constructed a mouse model of DE, and constructed a lipin2 knockdown or overexpression model by injecting lentivirus into the brain with stereotaxis. The expression of lipin2 in inflammatory bodies and related inflammatory factor signaling pathway-related proteins were examined by western blot and quantitative real-time PCR. Morris water maze was used to evaluate the spatial learning and memory of mice.

RESULTS

High glucose decreased the expression of lipin2 in BV2 cells, while overexpression of lipin2 in BV2 cells significantly suppressed the inflammatory response and apoptosis induced by high glucose. Meanwhile, the expression of lipin2 was down-regulated in the hippocampus in a DE mice model. Up-regulation of lipin2 in the hippocampus of DE mice inhibited JNK/ERK signaling pathway, reduced NLRP3 inflammasome-mediated inflammatory response, down-regulated IL-1/TNF-α expression, and improved synaptic plasticity and cognitive dysfunction in mice. Conversely, knockdown of lipin2 increased NLRP3 inflammasome overactivation, caused neuronal abnormalities and cognitive impairment in mice.

CONCLUSIONS

Lipin2 may play a neuroprotective role in DE by inhibiting JNK/ERK-mediated NLRP3 inflammasome overactivation and subsequent inflammatory responses. It may be a potential therapeutic target for DE therapy.

Improved glycemic status, insulin resistance and inflammation after receiving oral oleoylethanolamide supplement in people with prediabetes: a randomized controlled trial

BACKGROUND

The anti-inflammatory properties of cannabinoids have been shown. This study was conducted to assess effect of oleoylethanolamide (OEA) supplementation on glycemic status, insulin resistance (IR) and inflammatory factor in pre-diabetic individuals.

METHODS

This double-blind randomized clinical trial was done at Qazvin University of Medical Sciences in which 46 pre-diabetic patients were divided into two equal groups and received one 125 mg OEA capsule in the intervention group (23 subjects) and 125 mg capsule containing wheat flour in placebo group daily for 8 weeks. After collecting demographic information, at the beginning and end of the study, the questionnaires of physical activity, 24-hour food recall were completed and blood glucose (BG), plasma insulin level, IR, hemoglobin A₁c (HbA₁c), and C-reactive protein (CRP) were measured. Statistical analysis was performed using SPSS software.

RESULTS

At the beginning and end of the study, there was no significant difference between the two groups in terms of anthropometric indices, food intake and physical activity (P > 0.05). At the end of the study, consumption of OEA significantly reduced BS, insulin, IR, HbA₁c, and CRP (P < 0.05). No significant change was observed in mentioned biochemical factors in placebo group (P > 0.05).

CONCLUSIONS

Given that OEA supplementation improved the glycemic status, IR and reduced the inflammatory factor, use of this supplement can be introduced as a useful supplement to control pre-diabetes status.

TRIAL REGISTRATION

The protocol of this clinical trial is registered with the Iranian Registry of Clinical Trials ( http://www.IRCT.IR , identifier: IRCT20141025019669N16).

Matrine alleviates spatial learning and memory impairment in diabetic mice by inhibiting endoplasmic reticulum stress and through modulation of PK2/PKRs pathway

Clinical and epidemiological studies indicate that diabetic cognitive impairment often occurs in diabetes mellitus patients. Matrine (Mat), an active component of Sophora flavescens Ait root extracts, has widely pharmacological activities including anti-tumor, anti-diabetes, cardioprotective and neuroprotective effects. The present study was designed to elucidate the possibly neuroprotective effects of Mat against diabetic spatial learning and memory impairment caused by high-fat diet and streptozotocin injection in mice. The results showed that Mat treatment significantly ameliorated fasting blood glucose level, impaired glucose tolerance, and lipid metabolism disorder in diabetic mice. In addition, diabetic mice exhibited spatial learning and memory impairment in the Morris water maze test, which could be attenuated by Mat treatment. Moreover, administration of Mat remarkably alleviated histological damage in diabetic hippocampus. Also, further investigations showed that Mat treatment abated endoplasmic reticulum stress induced hippocampal ultra-structure injury as evidenced by increasing the numbers of rough endoplasmic reticulum and mitochondria, as well as down-regulating endoplasmic reticulum stress related protein levels (GRP78, CHOP, ATF6 and Caspase-12). Furthermore, administration of Mat enhanced hippocampal protein expressions of PK2, PKR1 and PKR2, which decreased significantly in diabetic mice. Collectively, these findings suggested that Mat could ameliorate diabetes-induced spatial learning and memory impairment, possibly by alleviating ER stress, and partly through modulation of PK2/PKRs pathway.

Protective effect of quercetin against the metabolic dysfunction of glucose and lipids and its associated learning and memory impairments in NAFLD rats

BACKGROUND

Quercetin (QUE) is a flavonol reported with anti-inflammatory and antioxidant activities, and previous results from the group of this study have demonstrated its neuroprotective effect against lipopolysaccharide-induced neuropsychiatric injuries. However, little is known about its potential effect on neuropsychiatric injuries induced or accompanied by metabolic dysfunction of glucose and lipids.

METHODS

A nonalcoholic fatty liver disease (NAFLD) rat model was induced via a high-fat diet (HFD), and glucolipid parameters and liver function were measured. Behavioral performance was observed via the open field test (OFT) and the Morris water maze (MWM). The plasma levels of triggering receptor expressed on myeloid cells-1 (TREM1) and TREM2 were measured via enzyme-linked immunosorbent assay (ELISA). The protein expression levels of Synapsin-1 (Syn-1), Synaptatogmin-1 (Syt-1), TREM1 and TREM2 in the hippocampus were detected using western blotting. Morphological changes in the liver and hippocampus were detected by HE and Oil red or silver staining.

RESULTS

Compared with the control rats, HFD-induced NAFLD model rats presented significant metabolic dysfunction, hepatocyte steatosis, and impaired learning and memory ability, as indicated by the increased plasma concentrations of total cholesterol (TC) and triglyceride (TG), the impaired glucose tolerance, the accumulated fat droplets and balloon-like changes in the liver, and the increased escaping latency but decreased duration in the target quadrant in the Morris water maze. All these changes were reversed in QUE-treated rats. Moreover, apart from improving the morphological injuries in the hippocampus, treatment with QUE could increase the decreased plasma concentration and hippocampal protein expression of TREM1 in NAFLD rats and increase the decreased expression of Syn-1 and Syt-1 in the hippocampus.

CONCLUSIONS

These results suggested the therapeutic potential of QUE against NAFLD-associated impairment of learning and memory, and the mechanism might involve regulating the metabolic dysfunction of glucose and lipids and balancing the protein expression of synaptic plasticity markers and TREM1/2 in the hippocampus.

A Duet Between Histamine and Oleoylethanolamide in the Control of Homeostatic and Cognitive Processes

In ballet, a pas de deux (in French it means "step of two") is a duet in which the two dancers perform ballet steps together. The suite of dances shares a common theme of partnership. How could we better describe the fine interplay between oleoylethanolamide (OEA) and histamine, two phylogenetically ancient molecules controlling metabolic, homeostatic and cognitive processes? Contrary to the pas de deux though, the two dancers presumably never embrace each other as a dancing pair but execute their "virtuoso solo" constantly exchanging interoceptive messages presumably via vagal afferents, the blood stream, the neuroenteric system. With one exception, which is in the control of liver ketogenesis, as in hepatocytes, OEA biosynthesis strictly depends on the activation of histaminergic H₁ receptors. In this review, we recapitulate our main findings that evidence the interplay of histamine and OEA in the control of food consumption and eating behaviour, in the consolidation of emotional memory and mood, and finally, in the synthesis of ketone bodies. We will also summarise some of the putative underlying mechanisms for each scenario.

Cerebellar and cortical TLR4 activation and behavioral impairments in Wernicke-Korsakoff Syndrome: Pharmacological effects of oleoylethanolamide

Wernicke-Korsakoff Syndrome (WKS) is a neuropsychiatric disorder whose etiology is a thiamine deficiency (TD), with alcoholism being the main underlying cause. Previous evidence suggests the presence of initial neuroinflammation and oxidative/nitrosative stress in the physiopathology, although the specific molecular mechanisms underlying TD-induced brain damage and behavioral disabilities are unknown. We explored the specific role of the innate immune receptor TLR4 in three murine models of WKS, based on the combination of a thiamine-deficient diet and pyrithiamine injections (0.25 mg/kg, i.p.) over time. The Symptomatic Model (SM) allowed us to describe the complete neurological/neurobehavioral symptomatology over 16 days of TD. Animals showed an upregulation of the TLR4 signaling pathway both in the frontal cortex (FC) and cerebellum and clear motor impairments related with cerebellar dysfunction. However, in the Pre-Symptomatic Model (PSM), 12 days of TD induced the TLR4 pathway upregulation in the FC, which correlated with disinhibited-like behavior, but not in the cerebellum, and no motor impairments. In addition, we tested the effects of the biolipid oleoylethanolamide (OEA, 10 mg/kg, i.p., once daily, starting before any symptom of the pathology is manifested) through the Glucose-Precipitated Model (GPM), which was generated by glucose loading (5 g/kg, i.v., last day) in thiamine-deficient animals to accelerate damage. Pretreatment with OEA prevented the TLR4-induced signature in the FC, as well as an underlying incipient memory disability and disinhibited-like behavior. This study suggests a key role for TLR4 in TD-induced neuroinflammation in the FC and cerebellum, and it reveals different vulnerability of these brain regions in WKS over time. Pre-treatment with OEA counteracts TD-induced TLR4-associated neuroinflammation and may serve as co-adjuvant therapy to prevent WKS-induced neurobehavioral alterations.

Effects of diabetes on apoptosis and mitosis in rat hippocampus

Diabetes contributes to neurological dysfunction including peripheral nerve diseases, stroke and dementia. We investigated the effects of diabetes on apoptosis and mitosis in the hippocampal CA1 region. Rats were given diabetes by injection of streptozotocin (STZ). The mass and blood glucose levels of the rats were measured until day 7 of the experiment. The loss of mass index was approximately 10%, and the diabetogenic index was approximately 330% between nondiabetic and diabetic groups. We investigated caspase-3, caspase-7 and Ki 67 levels immunohistochemically for mitotic activity, the TUNEL method for apoptosis and GFAP for astrocyte cell density in the hippocampal CA1 region. We found that apoptotic cells and the number of astrocytes and mitotic activity in the diabetic group were increased significantly compared to controls. Diabetes stimulates apoptosis and promotes cell proliferation in the hippocampal CA1 region, which may impair its homeostasis and function.

Oleoylethanolamide Increases Glycogen Synthesis and Inhibits Hepatic Gluconeogenesis via the LKB1/AMPK Pathway in Type 2 Diabetic Model

Oleoylethanolamide (OEA) is an endogenous peroxisome proliferator-activated receptor α (PPARα) agonist that acts on the peripheral control of energy metabolism. However, its therapeutic potential and related mechanisms in hepatic glucose metabolism under type 2 diabetes mellitus (T2DM) are not clear. Here, OEA treatment markedly improved glucose homeostasis in a PPARα-independent manner. OEA efficiently promoted glycogen synthesis and suppressed gluconeogenesis in mouse primary hepatocytes and liver tissue. OEA enhanced hepatic glycogen synthesis and inhibited gluconeogenesis via liver kinase B1 (LKB1)/5' AMP-activated protein kinase (AMPK) signaling pathways. PPARα was not involved in the roles of OEA in the LKB1/AMPK pathways. We found that OEA exerts its antidiabetic effect by increasing glycogenesis and decreasing gluconeogenesis via the LKB1/AMPK pathway. The ability of OEA to control hepatic LKB1/AMPK pathways may serve as a novel therapeutic approach for the treatment of T2DM. SIGNIFICANCE STATEMENT: Oleoylethanolamide (OEA) exerted a potent antihyperglycemic effect in a peroxisome proliferator-activated receptor α-independent manner. OEA played an antihyperglycemic role primarily via regulation of hepatic glycogen synthesis and gluconeogenesis. The main molecular mechanism of OEA in regulating liver glycometabolism is activating the liver kinase B1/5' AMP-activated protein kinase signaling pathways.

Oleoylethanolamide supplementation in obese patients newly diagnosed with non-alcoholic fatty liver disease: Effects on metabolic parameters, anthropometric indices, and expression of PPAR-α, UCP1, and UCP2 genes

The effects of oleoylethanolamide (OEA) on NAFLD are yet to be examined in human. The objective of the present study was to examine the effects of OEA supplementation along with weight loss intervention on the expression of PPAR-α, uncoupling proteins 1and 2 (UCP1 and UCP2) genes in the peripheral blood mononuclear cells (PBMCs), metabolic parameters, and anthropometric indices among obese patients with NAFLD. In this triple-blind placebo-controlled randomized clinical trial, 76 obese patients newly diagnosed with NAFLD were randomly allocated into either OEA or placebo group along with calorie-restricted diets for 12 weeks. At pre-and post-intervention phase, mRNA expression levels of PPAR-α, UCP1, and UCP2 genes in the PBMCs, serum levels of metabolic parameters as well as diet and appetite sensations were assessed. There was a significant increase in the expression levels of PPAR-α, UCP1, and UCP2 genes in the PBMCs, compared to the placebo at the endpoint. A significant decrease in the anthropometric indices, energy and carbohydrate intakes, glycemic parameters, except for hemoglobin A1c concentration was also observed in the OEA group, compared to the placebo group. OEA treatment significantly resulted in decreased serum levels of triglyceride (TG), alanine aminotransferase (ALT), aspartate aminotransferase (AST), ALT/AST, increased serum levels of high-density lipoprotein cholesterol (HDL-C), and improved appetite sensations. Importantly, a significant improvement in TG, ALT, AST, ALT/AST, HDL-C levels as well as appetite sensations by OEA were under the influence of body mass index (BMI). Although liver steatosis severity was significantly reduced in both groups, the between-group differences did not reach statistical significance (P = 0.061). In conclusion, the present study, for the first time, revealed that OEA supplementation significantly improved anthropometric and metabolic risk factors related to NAFLD.