Isoflurane aggravates peripheral and central insulin resistance in high-fat diet/streptozocin-induced type 2 diabetic mice

PPARα agonist fenofibrate prevents postoperative cognitive dysfunction by enhancing fatty acid oxidation in mice

Background

Due to high rates of incidence and disability, postoperative cognitive dysfunction (POCD) currently receives a lot of clinical attention. Disturbance of fatty acid oxidation is a potential pathophysiological manifestation underlying POCD. Peroxisome proliferator-activated receptor α (PPARα) is a significant transcription factor of fatty acid oxidation that facilitates the transfer of fatty acids into the mitochondria for oxidation. The potential role of PPARα intervention in POCD warrants consideration.

Objective

The present study is aimed to investigate whether PPARα agonist fenofibrate (FF) could protect long-term isoflurane anesthesia-induced POCD model and to explore the potential underlying function of fatty acid oxidation in the process.

Methods

We established the POCD model via 6 h long-term isoflurane anesthesia in vivo with C57BL/6J mice and in vitro with N2a cells. Cells and mice were pretreated with PPARα agonist FF before anesthesia, after which fatty acid oxidation and cognitive function were assessed. The level of fatty acid oxidation-related proteins was determined using western blotting. The contextual fear conditioning test was utilized to evaluate mice's learning and memory.

Results

Our results showed that 6 h long-term isoflurane anesthesia induced contextual memory damage in mice, accompanied by decreases of fatty acid oxidation-related proteins (peroxisome proliferator-activated receptor γ coactivator 1α, carnitine palmitoyltransferase 1A, and PPARα) both in the hippocampus of POCD mice and in N2a cells. In the N2a cell model, pretreatment of PPARα agonist FF led to the upregulation of fatty acid oxidation-related proteins. In vivo results showed that preconditioned FF reached similar effects. More crucially, FF has been shown to reduce cognitive damage in mice after long-term isoflurane anesthesia. Additionally, our data showed that after blocking fatty acid oxidation by Etomoxir, FF failed to protect cognitive function from long-term isoflurane anesthesia.

Conclusions

Pretreatment of PPARα agonist FF can protect against long-term isoflurane anesthesia-induced POCD by enhancing fatty acid oxidation.

Insulin signaling in the central nervous system, a possible pathophysiological mechanism of anesthesia-induced delayed neurocognitive recovery/postoperative neurocognitive disorder: a narrative review

INTRODUCTION

Impairment in neurocognitive functions ranges between delayed neurocognitive recovery (DNR) and postoperative neurocognitive disorders (pNCD). Incidence varies from 11% after noncardiac surgery to 60% after cardiac surgery.

AREAS COVERED

Insulin receptors (IRs) signaling pathway in the central nervous system (CNS) could be a possible pathophysiological mechanism of anesthesia-induced DNR/pNCD and perioperative intranasal insulin administration could be a preventive approach. This hypothesis is supported by the following evidence: effects of IRs-CNS signaling pathway on neuromodulation; higher incidence of DNR/pNCD in patients with insulin resistance; neurotoxicity of IRs signaling pathways after anesthetic exposure; improvement of neurocognitive impairment after insulin exposure. This narrative review was conducted after a literature search of PubMed, EMBASE and SCOPUS online medical data performed in May 2022.

EXPERT OPINION

Perioperative intranasal insulin is shown to be protective and future studies should address: the role of insulin as a neuromodulator; its integration into neuroprotection approaches; patient populations that might benefit from this approach; a well-defined protocol of intranasal insulin administration in a perioperative background and other disciplines; and possible collateral effects.

Aronia melanocarpa Anthocyanin Extracts Improve Hepatic Structure and Function in High-Fat Diet-/Streptozotocin-Induced T2DM Mice

Anthocyanins can prevent and ameliorate type 2 diabetes mellitus (T2DM), but its mechanism of action has not been fully established. IKK/NF-κB and JAK/Stat pathways have multiple effects, triggering T2DM. Liver abnormalities in individuals with T2DM are detrimental to glycemic control. We determined whether anthocyanins could improve the liver of individuals with T2DM using IKK/NF-κB and JAK/Stat. We established a T2DM mouse model using a high-fat diet and streptozotocin and then performed Aronia melanocarpa anthocyanin extracts' (AMAEs') administration for 5 weeks. AMAEs improved blood glucose and hyperinsulinemia of T2DM mice. In the liver of AMAE-administered T2DM mice, ROS, IKKβ/NF-κB p65, and JAK2/Stat3/5B signalings were down-regulated, thereby reducing the suppressor of cytokine signaling 3 (SOCS3), iNOS, and inflammatory mediators. AMAE-improved hyperinsulinemia also down-regulated SOCS3 by decreasing p-Stat5B in hepatocytes. AMAEs enhanced glucose uptake and conversion and decreased hepatocyte enlargement and inflammatory cells in the liver of T2DM mice. These indicated that AMAEs could alleviate oxidative stress, insulin resistance, inflammation, and tissue damage in the liver of T2DM mice through inhibiting NF-κB p65 and Stat3/5B.

Electroacupuncture at Bilateral ST36 Acupoints: Inducing the Hypoglycemic Effect through Enhancing Insulin Signal Proteins in a Streptozotocin-Induced Rat Model during Isoflurane Anesthesia

In rats with 2-deoxy-2-(3-(methyl-3-nitrosoureido)-d-glucopyranose streptozotocin- (STZ-) induced insulin-dependent diabetes (IDDM), continuous 15 Hz electrical stimulation at bilateral ST36 acupoints for 30 and 60 minutes has been shown to prevent hyperglycemia. We hypothesized that the mechanism of action in STZ-induced IDDM rats is that electrical stimulation at bilateral ST36 acupoints is effective in improving insulin receptor substrate type 1 (IRS-1) and glucose transporter type 4 (GLUT4) protein expressions associated with counteracting both plasma glucose and free fatty acid (FFA) levels during isoflurane anesthesia. In this study, twenty-six healthy male Wistar rats, weighing 250–350 g and aged 8–10 weeks were tested. Rats in the experimental electroacupuncture (EA) group (n = 13) received 15 Hz electrical stimulation at bilateral ST 36 acupoints for 30 and 60 minutes. Rats in the control group (n = 13) were handled but not subjected to the stimulation treatment. In both IDDM and normal Wistar rats, we observed a negative change in plasma glucose levels when rats were given the EA treatment, but a positive change in plasma glucose without EA treatment relative to baseline. Within the IDDM group, a negative change in FFA levels was observed when rats were given the EA treatment, while a positive change in the FFA level was shown without the EA treatment. In the expressed protein signals, we found a significant elevation in both GLUT4 and IRS-1 proteins in the IDDM group treated by EA. Moreover, we found a significant mean difference between GLUT4 and IRS-1 protein expression levels relative to β-actin. Our findings suggested that EA at bilateral ST36 acupoints could serve as an effective strategy for lowering plasma glucose by decreasing free fatty acid levels and improving the expression of IRS-1 and GLUT4 proteins in a STZ-IDDM rat model during isoflurane anesthesia.

Amelioration of Hippocampal Insulin Resistance Reduces Tau Hyperphosphorylation and Cognitive Decline Induced by Isoflurane in Mice

General anesthetics can induce cognitive impairments and increase the risk of Alzheimer’s disease (AD). However, the underlying mechanisms are still unknown. Our previous studies shown that long-term isoflurane exposure induced peripheral and central insulin resistance (IR) in adult mice and aggravated IR in type 2 diabetes mellitus (T2DM) mice. Clinical and preclinical studies revealed an association between impaired insulin signaling and tau pathology in AD and other tauopathies. We investigated if alleviation of hippocampal IR by the antidiabetic agent metformin could reduce tau hyperphosphorylation and cognitive decline induced by isoflurane in mice. The effects of prolonged (6 h) isoflurane anesthesia on hippocampal IR, hippocampal tau hyperphosphorylation, and hippocampus-dependent cognitive function were evaluated in wild type (WT) adult mice and the high-fat diet plus streptozotocin (HFD/STZ) mouse model of T2DM. Here we shown that isoflurane and HFD/STZ dramatically and synergistically induced hippocampal IR and fear memory impairment. Metformin pretreatment strongly ameliorated hippocampal IR and cognitive dysfunction caused by isoflurane in WT mice, but was less effective in T2DM mice. Isoflurane also induced hippocampal tau hyperphosphorylation and metformin reversed this effect. In addition, isoflurane significantly increased blood glucose levels in both adult and T2DM mice, and metformin reversed this effect as well. Administration of 25% glucose to metformin-pretreated mice induced hyperglycemia, but surprisingly did not reverse the benefits of metformin on hippocampal insulin signaling and fear memory following isoflurane anesthesia. Our findings show hippocampal IR and tau hyperphosphorylation contribute to acute isoflurane-induced cognitive dysfunction. Brief metformin treatment can mitigate these effects through a mechanism independent of glycemic control. Future studies are needed to investigate whether long-term metformin treatment can also prevent T2DM-induced hippocampal IR and cognitive decline.

The Effects of Erchen Decoction on Gut Microbiota and Lipid Metabolism Disorders in Zucker Diabetic Fatty Rats

Obesity is a chronic metabolic disease caused by genetic and environmental factors that has become a serious global health problem. There is evidence that gut microbiota is closely related to the occurrence and development of obesity. Erchen Decoction (ECD), a traditional Chinese medicine, has been widely used for clinical treatment and basic research of obesity and related metabolic diseases in recent years. It can significantly improve insulin resistance (IR) and lipid metabolism disorders. However, there is no microbiological study on its metabolic regulation. In this study, we investigated the effects of ECD on obesity, especially lipid metabolism and the composition and function of gut microbiota in Zucker diabetic fatty (ZDF) rats, and explored the correlation between the biomarkers of gut microbiota and metabolite and host phenotype. The results showed that ECD could reduce body weight, improve IR and lipid metabolism, and reduce the concentration of free fatty acids (FFA) released from white adipose tissue (WAT) due to excessive lipolysis by interfering with the insulin receptor substrate 1 (IRS1)/protein kinase B (AKT)/protein kinase A (PKA)/hormone-sensitive triglyceride lipase (HSL) signaling pathway in ZDF rats. Additionally, ECD gradually adjusted the overall structure of changed gut microbiota, reversed the relative abundance of six genera, and changed the function of gut microbiota by reducing the content of propionic acid, a metabolite of gut microbiota, in ZDF rats. A potentially close relationship between biomarkers, especially Prevotella, Blautia, and Holdemania, propionic acid and host phenotypes were demonstrated through correlation analysis. The results suggested that the beneficial effects of ECD on obesity, especially lipid metabolism disorders, are related to the regulation of gut microbiota in ZDF rats. This provides a basis for further research on the mechanism and clinical application of ECD to improve obesity via gut microbiota.

Irisin treatment lowers levels of phosphorylated tau in the hippocampus of pre-symptomatic female but not male htau mice

AIMS

Irisin is a hormone cleaved from fibronectin type-III domain-containing protein 5 in response to exercise and may be therapeutic in Alzheimer's disease (AD). Irisin is shown to repair damage caused by midlife cardiometabolic risk factors for AD (i.e., diabetes mellitus; hypertension), prevent neural amyloid beta aggregation and reduce neuroinflammation. However, there are no investigations of irisin's effect on AD-associated tauopathy in the brain. This study begins to address this gap in knowledge.

METHODS

Transgenic htau mice that selectively develop age-related tauopathy were treated with recombinant irisin (100 µg/kg weekly i.p.) beginning at a pre-symptomatic age (4 months) to determine if irisin could prevent emergence of early neuropathology. One month later, mice were sacrificed to collect brain tissue and serum. Protein levels of ptau (serine 202), inflammatory cytokine tumour necrosis factor alpha (TNFα) and FNDC5 were quantified using capillary-based western blotting (Wes).

RESULTS

Our data show that irisin treatment significantly reduced ptau and TNFα in the hippocampus and serum of female htau mice compared to vehicle-treated controls. Irisin treatment did not alter ptau levels in male htau hippocampus and appeared to enhance both neural and systemic TNFα levels.

CONCLUSIONS

This study provides the first evidence that enhancing the endogenous hormone irisin may be therapeutic against emerging neuropathology in a tauopathy-selective AD model. This is important because there are currently no disease-modifying therapeutics available for AD, and few agents in development address the multiple disease targets irisin appears to-making irisin an intriguing therapeutic candidate for further investigation.

Venlafaxine Attenuated the Cognitive and Memory Deficit in Mice Exposed to Isoflurane Alone

Post-operative cognitive dysfunction (POCD) is a common complication during the post-operative period. It affects the recovery time of the patient after surgery and the stay time in hospital, which causes a great deal of burden to patients and families emotionally and financially. However, there is no specific and effective treatment available for this disorder. Recent study indicated exposure to general anesthetics contributed to POCD by triggering gamma-amino butyric acid type A (GABA_A) receptors hyperactivities that persisted even the anesthetic compounds have been eliminated. Here, we investigated the antidepressant, venlafaxine (VLX), in a mouse model of POCD and studied whether VLX attenuated the cognitive dysfunction of mice exposed to general anesthetic, isoflurane (ISO). We found that ISO significantly induced an increased surface expression of the GABA_A receptor subunit, α5, in the hippocampus of the mice. However, VLX treatment reduced the increase in α5 subunit expression. Meanwhile, we found the expression levels of interleukin (IL)-1β, tumor necrosis factor alpha (TNF-α), and IL-6 in the brains of mice exposed to ISO were significantly increased. However, VLX could prevent the increase in these cytokines. We also investigated the memory deficit of these mice by using a Y maze behavioral test. Mice with ISO exposure showed decreased alternation performance that could be prevented by the VLX treatment. Collectively, our results here are in line with the previous findings that α5 subunit plays an important role of the formation of POCD, but VLX may be a promising candidate compound for the treatment of POCD.

Diet-induced rodent models of obesity-related metabolic disorders-A guide to a translational perspective

Diet is a critical element determining human health and diseases, and unbalanced food habits are major risk factors for the development of obesity and related metabolic disorders. Despite technological and pharmacological advances, as well as intensification of awareness campaigns, the prevalence of metabolic disorders worldwide is still increasing. Thus, novel therapeutic approaches with increased efficacy are urgently required, which often depends on cellular and molecular investigations using robust animal models. In the absence of perfect rodent models, those induced by excessive consumption of fat and sugars better replicate the key aspects that are the root causes of human metabolic diseases. However, the results obtained using these models cannot be directly compared, particularly because of the use of different dietary protocols, and animal species and strains, among other confounding factors. This review article revisits diet-induced models of obesity and related metabolic disorders, namely, metabolic syndrome, prediabetes, diabetes and nonalcoholic fatty liver disease. A critical analysis focused on the main pathophysiological features of rodent models, as opposed to the criteria defined for humans, is provided as a practical guide with a translational perspective for the establishment of animal models of obesity-related metabolic diseases.

Propofol Improved Glucose Tolerance Associated with Increased FGF-21 and GLP-1 Production in Male Sprague-Dawley Rats

Anesthetics, particularly volatile anesthetics, have been shown to impair glucose metabolism and cause hyperglycemia, closely linking them with mortality and morbidity as related to surgery. Beyond being an anesthetic used for general anesthesia and sedation, intravenous hypnotic propofol displays an effect on glucose metabolism. To extend the scope of propofol studies, its effects on glucose metabolism were evaluated in male Sprague-Dawley rats of various ages. Unlike chloral hydrate and isoflurane, propofol had little effect on basal glucose levels in rats at 2 months of age, although it did reduce chloral hydrate- and isoflurane-induced hyperglycemia. Propofol reduced postload glucose levels after either intraperitoneal or oral administration of glucose in both 7- and 12-month-old rats, but not those at 2 months of age. These improved effects regarding propofol on glucose metabolism were accompanied by an increase in insulin, fibroblast growth factor-21 (FGF-21), and glucagon-like peptide-1 (GLP-1) secretion. Additionally, an increase in hepatic FGF-21 expression, GLP-1 signaling, and FGF-21 signaling, along with a decrease in endoplasmic reticulum (ER) stress, were noted in propofol-treated rats at 7 months of age. Current findings imply that propofol may turn into insulin-sensitizing molecules during situations of existing insulin resistance, which involve FGF-21, GLP-1, and ER stress.