Insulin-Induced Recurrent Hypoglycemia Up-Regulates Glucose Metabolism in the Brain Cortex of Chemically Induced Diabetic Rats

Disturbed hippocampal histidine metabolism contributes to cognitive impairment induced by recurrent nonsevere hypoglycemia in diabetes

Hypoglycemia is a common adverse reaction to glucose-lowering treatment. Diabetes mellitus (DM) combined with recurrent nonsevere hypoglycemia (RH) can accelerate cognitive decline. Currently, the metabolic pattern changes in cognition-related brain regions caused by this combined effect of DM and RH (DR) remain unclear. In this study, we first characterized the metabolic profiles of the hippocampus in mice exposed to DR using non-targeted metabolomic platforms. Our results showed that DR induced a unique metabolic pattern in the hippocampus, and several significant differences in metabolite levels belonging to the histidine metabolism pathway were discovered. Based on these findings, in the follow-up experiment, we found that histidine treatment could attenuate the cognitive impairment and rescue the neuronal and synaptic damage induced by DR in the hippocampus, which are closely related to ameliorated mitochondrial injury. These findings provide new insights into the metabolic mechanisms of the hippocampus in the progression of DR, and l-histidine supplementation may be a potential metabolic therapy in the future.

Cognitive dysfunction in diabetes: abnormal glucose metabolic regulation in the brain

Cognitive dysfunction is increasingly recognized as a complication and comorbidity of diabetes, supported by evidence of abnormal brain structure and function. Although few mechanistic metabolic studies have shown clear pathophysiological links between diabetes and cognitive dysfunction, there are several plausible ways in which this connection may occur. Since, brain functions require a constant supply of glucose as an energy source, the brain may be more susceptible to abnormalities in glucose metabolism. Glucose metabolic abnormalities under diabetic conditions may play an important role in cognitive dysfunction by affecting glucose transport and reducing glucose metabolism. These changes, along with oxidative stress, inflammation, mitochondrial dysfunction, and other factors, can affect synaptic transmission, neural plasticity, and ultimately lead to impaired neuronal and cognitive function. Insulin signal triggers intracellular signal transduction that regulates glucose transport and metabolism. Insulin resistance, one hallmark of diabetes, has also been linked with impaired cerebral glucose metabolism in the brain. In this review, we conclude that glucose metabolic abnormalities play a critical role in the pathophysiological alterations underlying diabetic cognitive dysfunction (DCD), which is associated with multiple pathogenic factors such as oxidative stress, mitochondrial dysfunction, inflammation, and others. Brain insulin resistance is highly emphasized and characterized as an important pathogenic mechanism in the DCD.

Impairment of Mitochondrial Respiration in Metabolic Diseases: An Overview

Mitochondrial dysfunction has emerged as a central pathomechanism in the setting of obesity and diabetes mellitus, linking these intertwined pathologies that share insulin resistance as a common denominator. High-resolution respirometry (HRR) is a state-of-the-art research method currently used to study mitochondrial respiration and its impairment in health and disease. Tissue samples, cells or isolated mitochondria are exposed to various substrate-uncoupler-inhibitor-titration protocols, which allows the measurement and calculation of several parameters of mitochondrial respiration. In this review, we discuss the alterations of mitochondrial bioenergetics in the main dysfunctional organs that contribute to the development of the obese and diabetic phenotypes in both animal models and human subjects. Herein we review data regarding the impairment of oxidative phosphorylation as integrated mitochondrial function assessed by means of HRR. We acknowledge the critical role of this method in determining the alterations in oxidative phosphorylation occurring in the early stages of metabolic pathologies. We conclude that there is a mutual two-way relationship between mitochondrial dysfunction and insulin insensitivity that characterizes these diseases.