Cognitive and hippocampal synaptic profiles in monosodium glutamate-induced obese mice

Reconsideration of the health effects of monosodium glutamate: from bench to bedside evidence

Monosodium glutamate (MSG) is a food additive that enhances the palatability of foods, thus its frequent use both domestically and industrially. Based on the dose-factor, frequency, and duration of exposure, MSG may provoke adverse health outcomes both in animals and humans. The present report aims at providing a comprehensive analysis of the scientifically proven untoward health effects of MSG. To achieve our aim, we adopted the PRISMA guidelines and checklist and searched four databases (Scopus, Web of Science, PubMed, and Google Scholar) from 2014 to 2024. Retrieved research papers were critically appraised for quality using the ARRIVE and Joanna Briggs (JB) checklists and data analysis was conducted via the narrative synthesis method. Our analysis reveals that though MSG is generally considered safe at low doses; however, high doses and repeated exposure to MSG are associated with embryotoxicity and teratogenicity, obesity, cardiotoxicity, hepatotoxicity, kidney toxicity, neurotoxicity, endothelial dysfunction, reproductive toxicities, alteration of lipid, and glucose metabolism. Thus, chronic exposure to MSG may be of human pathological importance. The findings of the present narrative synthesis provide a rationale for informed decisions on the use and labeling of this widely used food additive.

Cognitive Impairment and Synaptic Dysfunction in Cardiovascular Disorders: The New Frontiers of the Heart-Brain Axis

Within the central nervous system, synaptic plasticity, fundamental to processes like learning and memory, is largely driven by activity-dependent changes in synaptic strength. This plasticity often manifests as long-term potentiation (LTP) and long-term depression (LTD), which are bidirectional modulations of synaptic efficacy. Strong epidemiological and experimental evidence show that the heart-brain axis could be severely compromised by both neurological and cardiovascular disorders. Particularly, cardiovascular disorders, such as heart failure, hypertension, obesity, diabetes and insulin resistance, and arrhythmias, may lead to cognitive impairment, a condition known as cardiogenic dementia. Herein, we review the available knowledge on the synaptic and molecular mechanisms by which cardiogenic dementia may arise and describe how LTP and/or LTD induction and maintenance may be compromised in the CA1 region of the hippocampus by heart failure, metabolic syndrome, and arrhythmias. We also discuss the emerging evidence that endothelial dysfunction may contribute to directly altering hippocampal LTP by impairing the synaptically induced activation of the endothelial nitric oxide synthase. A better understanding of how CV disorders impact on the proper function of central synapses will shed novel light on the molecular underpinnings of cardiogenic dementia, thereby providing a new perspective for more specific pharmacological treatments.

High-fat diet induced hippocampal CREB dysfunction, cognitive impairment and depression-like behaviors via downregulation of interleukin-2 in the mice

BACKGROUND

Inhibition of hippocampal CREB signaling contributed to obesity-induced cognitive impairment. But, the potential mechanism by which obesity inhibits hippocampal CREB signaling is not clear. The aim of this study was to explore whether interleukin-2 played a intermediary role in this pathogenic effect in a high-fat diet model.

METHODS

C57BL/6J interleukin-2^+/+ wild-type and interleukin-2^-/- knockout mice were fed a standard diet or high-fat diet for 12 weeks. After that, cognitive function was assessed by Morris water maze and Y maze. Depression-like behaviors were determined using sucrose preference test and tail suspension test. Expression of p-CREB and interleukin-2 in peripheral blood mononuclear cells and hippocampus was measured using western blotting and qRT-PCR.

RESULTS

In the interleukin-2^+/+ wild-type mice, a high-fat diet inhibited the expression of interleukin-2 and p-CREB both in the peripheral blood mononuclear cells and hippocampus. The high-fat diet also caused cognitive impairment and depression-like behaviors in these mice. In the interleukin-2^-/- knockout mice, there was no significant depression of interleukin-2. A high-fat diet can only aggravate the p-CREB signaling dysfunction in the peripheral blood mononuclear cells, but not in the hippocampus. Meanwhile, the high-fat diet can not cause the cognitive impairment and depression-like behaviors in these mice.

CONCLUSIONS

A high-fat diet induced hippocampal CREB dysfunction, cognitive impairment and depression-like behaviors partly through downregulation of interleukin-2 in the mice.