Brain Insulin Resistance at the Crossroads of Metabolic and Cognitive Disorders in Humans

The brain has traditionally thought to be insensitive to insulin, primarily because insulin does not stimulate glucose uptake/metabolism in the brain (as it does in classic insulin sensitive tissues such as muscle, liver and fat). However, over the past 20 years, research in this field has identified unique actions of insulin in the brain. There is accumulating evidence that insulin crosses into the brain and regulates central nervous system functions such as feeding, depression and cognitive behavior. Additionally, insulin acts in the brain to regulate systemic functions such as hepatic glucose production, lipolysis, lipogenesis, reproductive competence and the sympathoadrenal response to hypoglycemia. Decrements in brain insulin action (or brain insulin resistance) can be observed in obesity, type 2 diabetes (T2DM), aging and Alzheimer's disease (AD), indicating a possible link between metabolic and cognitive health. Here, we describe recent findings on the pleiotropic actions of insulin in the brain and highlight the precise sites, specific neuronal population and roles for supportive astrocytic cells through which insulin acts in the brain. In addition, we also discuss how boosting brain insulin action could be a therapeutic option for people at an increased risk of developing metabolic and cognitive diseases such as AD and T2DM. Overall, this perspective article serves to highlight some of these key scientific findings, identify unresolved issues, and indicate future directions of research in this field that would serve to improve the lives of people with metabolic and cognitive dysfunctions.

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Empagliflozin Improves Insulin Sensitivity of the Hypothalamus in Humans With Prediabetes: A Randomized, Double-Blind, Placebo-Controlled, Phase 2 Trial

10.2337/figshare.16652713 ◽

2021 ◽

Author(s):

Stephanie Kullmann ◽

Julia Hummel ◽

Robert Wagner ◽

Corinna Dannecker ◽

Andreas Vosseler ◽

...

Keyword(s):

Insulin Resistance ◽

Insulin Sensitivity ◽

Insulin Action ◽

Sglt2 Inhibitors ◽

Whole Body ◽

Double Blind ◽

Double Blind Placebo ◽

Brain Insulin ◽

Sglt2 Inhibition ◽

Brain Insulin Resistance

Objective: Insulin action in the human brain reduces food intake, improves whole-body insulin sensitivity, and modulates body fat mass and its’ distribution. Obesity and type 2 diabetes are often associated with brain insulin resistance, resulting in impaired brain-derived modulation of peripheral metabolism. So far, no pharmacological treatment for brain insulin resistance has been established. Since SGLT2 inhibitors lowers glucose levels and modulate energy metabolism, we hypothesized that SGLT2 inhibition may be a pharmacological approach to reverse brain insulin resistance. Research Design and Methods: In this randomized, double-blind, placebo-controlled clinical trial, 40 patients (mean ± SD; age: 60 ± 9 years; BMI: 31.5 ± 3.8 kg/m²) with prediabetes were randomized to receive 25 mg empagliflozin qd or placebo. Before and after 8 weeks of treatment, brain insulin sensitivity was assessed by functional MRI combined with intranasal administration of insulin to the brain. Results: We identified a significant interaction between time and treatment in the hypothalamic response to insulin. Post hoc analyses revealed that only empagliflozin treated patients experienced increased hypothalamic insulin responsiveness. Hypothalamic insulin action significantly mediated empagliflozin-induced decrease in fasting glucose and liver fat. Conclusions: Our results corroborate insulin resistance of the hypothalamus in humans with prediabetes. Treatment with empagliflozin for 8 weeks was able to restore hypothalamic insulin sensitivity; a favorable response that could contribute to the beneficial effects of SGLT2 inhibitors. Our findings position SGLT2 inhibition as the first pharmacological approach to reverse brain insulin resistance, with potential benefits for adiposity and whole-body metabolism.

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Empagliflozin Improves Insulin Sensitivity of the Hypothalamus in Humans With Prediabetes: A Randomized, Double-Blind, Placebo-Controlled, Phase 2 Trial

10.2337/figshare.16652713.v1 ◽

2021 ◽

Author(s):

Stephanie Kullmann ◽

Julia Hummel ◽

Robert Wagner ◽

Corinna Dannecker ◽

Andreas Vosseler ◽

...

Keyword(s):

Insulin Resistance ◽

Insulin Sensitivity ◽

Insulin Action ◽

Sglt2 Inhibitors ◽

Whole Body ◽

Double Blind ◽

Double Blind Placebo ◽

Brain Insulin ◽

Sglt2 Inhibition ◽

Brain Insulin Resistance

Objective: Insulin action in the human brain reduces food intake, improves whole-body insulin sensitivity, and modulates body fat mass and its’ distribution. Obesity and type 2 diabetes are often associated with brain insulin resistance, resulting in impaired brain-derived modulation of peripheral metabolism. So far, no pharmacological treatment for brain insulin resistance has been established. Since SGLT2 inhibitors lowers glucose levels and modulate energy metabolism, we hypothesized that SGLT2 inhibition may be a pharmacological approach to reverse brain insulin resistance. Research Design and Methods: In this randomized, double-blind, placebo-controlled clinical trial, 40 patients (mean ± SD; age: 60 ± 9 years; BMI: 31.5 ± 3.8 kg/m²) with prediabetes were randomized to receive 25 mg empagliflozin qd or placebo. Before and after 8 weeks of treatment, brain insulin sensitivity was assessed by functional MRI combined with intranasal administration of insulin to the brain. Results: We identified a significant interaction between time and treatment in the hypothalamic response to insulin. Post hoc analyses revealed that only empagliflozin treated patients experienced increased hypothalamic insulin responsiveness. Hypothalamic insulin action significantly mediated empagliflozin-induced decrease in fasting glucose and liver fat. Conclusions: Our results corroborate insulin resistance of the hypothalamus in humans with prediabetes. Treatment with empagliflozin for 8 weeks was able to restore hypothalamic insulin sensitivity; a favorable response that could contribute to the beneficial effects of SGLT2 inhibitors. Our findings position SGLT2 inhibition as the first pharmacological approach to reverse brain insulin resistance, with potential benefits for adiposity and whole-body metabolism.

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γ-PGA-Rich Chungkookjang, Short-Term Fermented Soybeans: Prevents Memory Impairment by Modulating Brain Insulin Sensitivity, Neuro-Inflammation, and the Gut–Microbiome–Brain Axis

Foods ◽

10.3390/foods10020221 ◽

2021 ◽

Vol 10 (2) ◽

pp. 221

Author(s):

Do-Youn Jeong ◽

Myeong Seon Ryu ◽

Hee-Jong Yang ◽

Sunmin Park

Keyword(s):

Insulin Resistance ◽

Insulin Sensitivity ◽

Gut Microbiome ◽

Memory Impairment ◽

Memory Function ◽

Bacillus Species ◽

Fermented Foods ◽

Short Term ◽

Brain Insulin ◽

Brain Insulin Resistance

Fermented soybean paste is an indigenous food for use in cooking in East and Southeast Asia. Korea developed and used its traditional fermented foods two thousand years ago. Chungkookjang has unique characteristics such as short-term fermentation (24–72 h) without salt, and fermentation mostly with Bacilli. Traditionally fermented chungkookjang (TFC) is whole cooked soybeans that are fermented predominantly by Bacillus species. However, Bacillus species are different in the environment according to the regions and seasons due to the specific bacteria. Bacillus species differently contribute to the bioactive components of chungkookjang, resulting in different functionalities. In this review, we evaluated the production process of poly-γ-glutamic acid (γ-PGA)-rich chungkookjang fermented with specific Bacillus species and their effects on memory function through the modulation of brain insulin resistance, neuroinflammation, and the gut–microbiome–brain axis. Bacillus species were isolated from the TFC made in Sunchang, Korea, and they included Bacillus (B.) subtilis, B. licheniformis, and B. amyloliquefaciens. Chungkookjang contains isoflavone aglycans, peptides, dietary fiber, γ-PGA, and Bacillus species. Chungkookjangs made with B. licheniformis and B. amyloliquefaciens have higher contents of γ-PGA, and they are more effective for improving glucose metabolism and memory function. Chungkookjang has better efficacy for reducing inflammation and oxidative stress than other fermented soy foods. Insulin sensitivity is improved, not only in systemic organs such as the liver and adipose tissues, but also in the brain. Chungkookjang intake prevents and alleviates memory impairment induced by Alzheimer’s disease and cerebral ischemia. This review suggests that the intake of chungkookjang (20–30 g/day) rich in γ-PGA acts as a synbiotic in humans and promotes memory function by suppressing brain insulin resistance and neuroinflammation and by modulating the gut–microbiome–brain axis.

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