Reducing insulin via conditional partial gene ablation in adults reverses diet-induced weight gain

Early exposure to a cholinergic receptor blocking agent mitigates adult obesity and protects pancreatic islet function in male rats

We tested the hypothesis that attenuation of the circulating insulin level in rats during early life can provide sustained protection against diet-induced obesity and metabolic dysfunction in adulthood. Male Wistar rats received intraperitoneal scopolamine butylbromide (SB) during the first 12 days of suckling, whereas control rats received 0.9% saline injections. The animals were weaned on day 21 and fed a normal chow diet. At 60 days of age, the control and SB groups were fed a normal chow diet (ND; 4.5% fat) or a high-fat diet (HF; 35% fat) until 90 days of age to induce obesity and metabolic dysfunction. Insulin secretion, food intake, and body weight were measured. Pancreatic islet function, autonomic nervous system function, and glucose homeostasis were evaluated at 90 days of age. During lactation, the plasma insulin concentration was significantly lower in the SB groups than in the control group. SB rats also exhibited reduced body weight. The HF diet resulted in obesity, glucose intolerance, insulin resistance, disruption of insulin secretion, and vagal hyperactivity in adult control rats. Remarkably, SB-treated rats fed the HF diet showed attenuated body weight and adiposity and did not develop diet-induced glucose/insulin imbalance. In addition, vagal activity and adequate pancreatic islet insulin secretion were preserved. Offspring exposed to SB during early life are provided with long-lasting protection against obesity and metabolic complications induced by an HF diet. An attenuated circulating insulin level in early life may have far-reaching consequences on metabolic programming.NEW & NOTEWORTHY High insulin levels during early life may lead to the late development of obesity and diabetes. We investigated whether attenuation of insulin levels by using an antimuscarinic agent could prevent diet-induced obesity and diabetes. Rats' early exposure to an antimuscarinic agent reduced insulin levels during the lactation period and promoted protection against obesity and metabolic dysfunctions. Independent of the programming mechanisms, insulin levels during early life may be a defining factor of health or diseases later in life.

Loss of MER Tyrosine Kinase Attenuates Adipocyte Hypertrophy and Leads to Enhanced Thermogenesis in Mice Exposed to High-Fat Diet

Obesity is characterized by low-grade inflammation that originates predominantly from the expanding visceral adipose tissue, in which adipocytes respond to lipid overload with hypertrophy, and consequently die by apoptosis. Recruited adipose tissue macrophages (ATMs) take up the excess lipids and remove the dead cells; however, long-term exposure to high concentrations of lipids alters their phenotype to M1-like ATMs that produce pro-inflammatory cytokines and resistin leading to insulin resistance and other obesity-related pathologies. Mer tyrosine kinase is expressed by macrophages and by being an efferocytosis receptor, and by suppressing inflammation, we hypothesized that it might play a protective role against obesity. To our surprise, however, the loss of Mer protected mice against high-fat diet (HFD)-induced obesity. We report in this paper that Mer is also expressed by adipocytes of both white and brown adipose tissues, and while its activity facilitates adipocyte lipid storage both in vitro and in vivo in mice exposed to HFD, it simultaneously attenuates thermogenesis in the brown adipose tissue contributing to its 'whitening'. Our data indicate that Mer is one of the adipocyte tyrosine kinase receptors, the activity of which contributes to the metabolic decision about the fate of excess lipids favoring their storage within the body.

Pancreatic β-Cell TRAPδ Deficiency Reduces Insulin Production but Improves Insulin Sensitivity

The translocon-associated protein-δ (TRAPδ) plays a role in insulin biosynthesis within pancreatic β-cells. However, its pathophysiological significance in maintaining islet β-cell function and glucose homeostasis remains unclear. In this study, we generated a mouse model featuring pancreatic β-cell-specific deletion of TRAPδ (TRAPδ βKO). Our findings revealed that TRAPδ βKO resulted in decreased circulating insulin levels in mice fed either a normal chow diet or a high-fat diet. Multiple independent experiments established that although TRAPδ deletion reduced insulin content in the islets, it had no discernible effect on insulin gene expression, the insulin to proinsulin ratio, or the expression and glycosylation of the prohormone enzymes involved in proinsulin processing. These data suggest that TRAPδ does not play a pivotal role in the transcription of the insulin gene or proinsulin processing. However, untranslocated preproinsulin levels were significantly increased when islets were treated with a proteasomal inhibitor, suggesting that TRAPδ deficiency may hinder preproinsulin translocation, resulting in a rapid degradation of untranslocated preproinsulin that accounts for the decreased insulin production. Remarkably, despite the moderate decrease in circulating insulin levels in TRAPδ βKO mice, their glucose levels remained unaffected, indicating the presence of compensatory mechanisms that help maintain glucose homeostasis. Insulin tolerance tests further revealed improved insulin sensitivity, accompanied by upregulation of phosphorylated AKT in the peripheral tissues of TRAPδ βKO mice. Collectively, these data highlight the important role of TRAPδ in insulin biosynthesis and β-cell function. The moderate reduction in circulating insulin appears to promote insulin sensitivity in insulin target tissues.

ARTICLE HIGHLIGHTS

Trapped fat: Obesity pathogenesis as an intrinsic disorder in metabolic fuel partitioning

Our understanding of the pathophysiology of obesity remains at best incomplete despite a century of research. During this time, two alternative perspectives have helped shape thinking about the etiology of the disorder. The currently prevailing view holds that excessive fat accumulation results because energy intake exceeds energy expenditure, with excessive food consumption being the primary cause of the imbalance. The other perspective attributes the initiating cause of obesity to intrinsic metabolic defects that shift fuel partitioning from pathways for mobilization and oxidation to those for synthesis and storage. The resulting reduction in fuel oxidation and trapping of energy in adipose tissue drives a compensatory increase in energy intake and, under some conditions, a decrease in expenditure. This theory of obesity pathogenesis has historically garnered relatively less attention despite its pedigree. Here, we present an updated comprehensive formulation of the fuel partitioning theory, focused on evidence gathered over the last 80 years from major animal models of obesity showing a redirection of fuel fluxes from oxidation to storage and accumulation of excess body fat with energy intake equal to or even less than that of lean animals. The aim is to inform current discussions about the etiology of obesity and by so doing, help lay new foundations for the design of more efficacious approaches to obesity research, treatment and prevention.

Mechanism of Acupuncture in Treating Obesity: Advances and Prospects

Obesity is a common metabolic syndrome that causes a significant burden on individuals and society. Conventional therapies include lifestyle interventions, bariatric surgery, and pharmacological therapies, which are not effective and have a high risk of adverse events. Acupuncture is an effective alternative for obesity, it modulates the hypothalamus, sympathetic activity and parasympathetic activity, obesity-related hormones (leptin, ghrelin, insulin, and CCK), the brain-gut axis, inflammatory status, adipose tissue browning, muscle blood flow, hypoxia, and reactive oxygen species (ROS) to influence metabolism, eating behavior, motivation, cognition, and the reward system. However, hypothalamic regulation by acupuncture should be further demonstrated in human studies using novel techniques, such as functional MRI (fMRI), positron emission tomography (PET), electroencephalogram (EEG), and magnetoencephalography (MEG). Moreover, a longer follow-up phase of clinical trials is required to detect the long-term effects of acupuncture. Also, future studies should investigate the optimal acupuncture therapeutic option for obesity. This review aims to consolidate the recent improvements in the mechanism of acupuncture for obesity as well as discuss the future research prospects and potential of acupuncture for obesity.

Both early and late maternal age at childbirth is associated with increasing odds of central obesity in offspring

OBJECTIVE

Despite studies on offspring obesity and delayed parenthood, little attention has been paid to the central obesity of offspring. The purpose of this study was to test the hypothesis that maternal age at childbirth (MAC) was associated with central obesity in offspring among the adult population, and fasting insulin may play a role in this association as a mediating factor.

METHODS

A total of 423 adults (mean age 37.9 years, 37.1% female) were included. Information about maternal variables and other confounders was collected by face-to-face interview. Waist circumference and insulin were determined through physical measurements and biochemical examinations. Logistic regression model and restricted cubic spline model were used to analyze the relationship between MAC and central obesity of offspring. The mediating effect of fasting insulin levels on association between MAC and offspring waist circumference was also analyzed.

RESULTS

There was a nonlinear relationship between MAC and central obesity in offspring. Compared with subjects with MAC 27-32 years, those with MAC 21-26 years (OR = 1.814, 95% CI: 1.129-2.915) and MAC ≥33 years (OR = 3.337, 95% CI: 1.638-6.798) had higher odds to develop central obesity. Offspring fasting insulin was also higher in MAC 21-26 years and MAC ≥33 years compared with those with MAC 27-32 years. Taking the group MAC 27-32 years as reference, the mediating effect of fasting insulin levels on the waist circumference was 20.6% and 12.4% for MAC 21-26 years and ≥ 33 years, respectively.

CONCLUSION

MAC 27-32 years has the lowest odds of central obesity in offspring. Fasting insulin levels may have a partial mediating effect on the association between MAC and central obesity.

Inhibition of AXL receptor tyrosine kinase enhances brown adipose tissue functionality in mice

The current obesity epidemic and high prevalence of metabolic diseases necessitate efficacious and safe treatments. Brown adipose tissue in this context is a promising target with the potential to increase energy expenditure, however no pharmacological treatments activating brown adipose tissue are currently available. Here, we identify AXL receptor tyrosine kinase as a regulator of adipose function. Pharmacological and genetic inhibition of AXL enhance thermogenic capacity of brown and white adipocytes, in vitro and in vivo. Mechanistically, these effects are mediated through inhibition of PI3K/AKT/PDE signaling pathway, resulting in induction of nuclear FOXO1 localization and increased intracellular cAMP levels via PDE3/4 inhibition and subsequent stimulation of the PKA-ATF2 pathway. In line with this, both constitutive Axl deletion as well as inducible adipocyte-specific Axl deletion protect animals from diet-induced obesity concomitant with increases in energy expenditure. Based on these data, we propose AXL receptor as a target for the treatment of obesity.

Body Fat Distribution, Fasting Insulin Levels, and Insulin Secretion: A Bidirectional Mendelian Randomization Study

CONTEXT

Hyperinsulinemia and adiposity are associated with one another, but the directionality of this relation is debated.

OBJECTIVE

Here, we tested the direction of the causal effects of fasting insulin (FI) levels and body fat accumulation/distribution using 2-sample bidirectional Mendelian randomization (MR).

METHODS

We included summary statistics from large-scale genome-wide association studies for body mass index (BMI, n = 806 834), waist to hip ratio adjusted for BMI (WHRadjBMI, n = 694 649), abdominal subcutaneous, visceral and gluteofemoral adipose tissue (n = 38 965), FI levels (n = 98 210), pancreatic islets gene expression (n = 420), and hypothalamus gene expression (n = 155). We used inverse variance-weighted and robust MR methods that relied on statistically and biologically driven genetic instruments.

RESULTS

Both BMI and WHRadjBMI were positively associated with FI. Results were consistent across all robust MR methods and when variants mapped to the hypothalamus (presumably associated with food behavior) were included. In multivariable MR analyses, when waist circumference and BMI were mutually adjusted, the direct effect of waist circumference on FI was 2.43 times larger than the effect of BMI on FI. FI was not associated with adiposity. By contrast, using genetic instruments mapped to gene expression in pancreatic islets (presumably more specific to insulin secretion), insulin was positively associated with BMI and abdominal subcutaneous and gluteofemoral adipose tissue, but not with visceral adipose tissue.

CONCLUSION

Although these results will need to be supported by experimental investigations, results of this MR study suggest that abdominal adiposity may be a key determinant of circulating insulin levels. Alternatively, insulin secretion may promote peripheral adipose tissue accumulation.

Effects of short-term endurance and strength exercise in the molecular regulation of skeletal muscle in hyperinsulinemic and hyperglycemic Slc2a4+/- mice

OBJECTIVE

Intriguingly, hyperinsulinemia, and hyperglycemia can predispose insulin resistance, obesity, and type 2 diabetes, leading to metabolic disturbances. Conversely, physical exercise stimulates skeletal muscle glucose uptake, improving whole-body glucose homeostasis. Therefore, we investigated the impact of short-term physical activity in a mouse model (Slc2a4+/-) that spontaneously develops hyperinsulinemia and hyperglycemia even when fed on a chow diet.

METHODS

Slc2a4+/- mice were used, that performed 5 days of endurance or strength exercise training. Further analysis included physiological tests (GTT and ITT), skeletal muscle glucose uptake, skeletal muscle RNA-sequencing, mitochondrial function, and experiments with C2C12 cell line.

RESULTS

When Slc2a4+/- mice were submitted to the endurance or strength training protocol, improvements were observed in the skeletal muscle glucose uptake and glucose metabolism, associated with broad transcriptomic modulation, that was, in part, related to mitochondrial adaptations. The endurance training, but not the strength protocol, was effective in improving skeletal muscle mitochondrial activity and unfolded protein response markers (UPRmt). Moreover, experiments with C2C12 cells indicated that insulin or glucose levels could contribute to these mitochondrial adaptations in skeletal muscle.

CONCLUSIONS

Both short-term exercise protocols were efficient in whole-body glucose homeostasis and insulin resistance. While endurance exercise plays an important role in transcriptome and mitochondrial activity, strength exercise mostly affects post-translational mechanisms and protein synthesis in skeletal muscle. Thus, the performance of both types of physical exercise proved to be a very effective way to mitigate the impacts of hyperglycemia and hyperinsulinemia in the Slc2a4+/- mouse model.

Impact of a Low-Insulin-Stimulating Bread on Weight Development-A Real Life Randomised Controlled Trial

The impact on body weight development is usually analysed by comparing different diet types. Our approach was to change only one component, namely bread, common to most diets. In a single-centre triple-blind randomised controlled trial the effects of two different breads on body weight were analyzed without further lifestyle modification. Overweight adult volunteers (n = 80) were randomised 1:1 to exchange previously consumed breads for either a rye bread from milled whole grain (control) or a medium-carbohydrate, low-insulin-stimulating bread (intervention). Pre-tests demonstrated that the two bread types strongly differed in the glucose and insulin response elicited, but had similar energy content, texture and taste. The primary endpoint was the estimated treatment difference (ETD) in change of body weight after 3 months of treatment. Whereas body weight remained unchanged in the control group (-0.1 ± 2.0 kg), significant weight reduction was observed in the intervention group (-1.8 ± 2.9 kg), with an ETD of -1.7 ± 0.2 kg (p = 0.007), that was more pronounced in participants ≥ 55 years (-2.6 ± 3.3 kg), paralleled by significant reductions in body mass index and hip circumference. Moreover, in the intervention group, the percentage of participants with significant weight loss (≥1 kg) was twice as high as in the control group (p < 0.001). No other statistically significant changes in clinical or lifestyle parameters were noted. Simply exchanging a common insulinogenic bread for a low-insulin-stimulating bread demonstrates potential to induce weight loss in overweight persons, especially those at older age.

GC-Globulin/Vitamin D-Binding Protein Is Required for Pancreatic α-Cell Adaptation to Metabolic Stress

GC-globulin (GC), or vitamin D-binding protein, is a multifunctional protein involved in the transport of circulating vitamin 25(OH)D and fatty acids, as well as actin scavenging. In the pancreatic islets, the gene encoding GC, GC/Gc, is highly localized to glucagon-secreting α-cells. Despite this, the role of GC in α-cell function is poorly understood. We previously showed that GC is essential for α-cell morphology, electrical activity, and glucagon secretion. We now show that loss of GC exacerbates α-cell failure during metabolic stress. High-fat diet-fed GC-/- mice have basal hyperglucagonemia, which is associated with decreased α-cell size, impaired glucagon secretion and Ca2+ fluxes, and changes in glucose-dependent F-actin remodelling. Impairments in glucagon secretion can be rescued using exogenous GC to replenish α-cell GC levels, increase glucagon granule area, and restore the F-actin cytoskeleton. Lastly, GC levels decrease in α-cells of donors with type 2 diabetes, which is associated with changes in α-cell mass, morphology, and glucagon expression. Together, these data demonstrate an important role for GC in α-cell adaptation to metabolic stress.

Declining muscle NAD+ in a hyperandrogenism PCOS mouse model: Possible role in metabolic dysregulation

Polycystic ovary syndrome (PCOS) is a common endocrine disorder, defined by reproductive and endocrine abnormalities, with metabolic dysregulation including obesity, insulin resistance and hepatic steatosis. Recently, it was found that skeletal muscle insulin sensitivity could be improved in obese, post-menopausal, pre-diabetic women through treatment with nicotinamide mononucleotide (NMN), a precursor to the prominent redox cofactor nicotinamide adenine dinucleotide (NAD+). Given that PCOS patients have a similar endocrine profile to these patients, we hypothesised that declining NAD levels in muscle might play a role in the pathogenesis of the metabolic syndrome associated with PCOS, and that this could be normalized through NMN treatment. Here, we tested the impact of NMN treatment on the metabolic syndrome of the dihydrotestosterone (DHT) induced mouse model of PCOS. We observed lower NAD levels in the muscle of PCOS mice, which was normalized by NMN treatment. PCOS mice were hyperinsulinaemic, resulting in increased adiposity and hepatic lipid deposition. Strikingly, NMN treatment completely normalized these aspects of metabolic dysfunction. We propose that addressing the decline in skeletal muscle NAD levels associated with PCOS can normalize insulin sensitivity, preventing compensatory hyperinsulinaemia, which drives obesity and hepatic lipid deposition, though we cannot discount an impact of NMN on other tissues to mediate these effects. These findings support further investigation into NMN treatment as a new therapy for normalizing the aberrant metabolic features of PCOS.

Weight Cycling Impairs Pancreatic Insulin Secretion but Does Not Perturb Whole-Body Insulin Action in Mice With Diet-Induced Obesity

In the setting of obesity and insulin resistance, glycemia is controlled in part by β-cell compensation and subsequent hyperinsulinemia. Weight loss improves glycemia and decreases hyperinsulinemia, whereas weight cycling worsens glycemic control. The mechanisms responsible for weight cycling-induced deterioration in glucose homeostasis are poorly understood. Thus, we aimed to pinpoint the main regulatory junctions at which weight cycling alters glucose homeostasis in mice. Using in vivo and ex vivo procedures we show that despite having worsened glucose tolerance, weight-cycled mice do not manifest impaired whole-body insulin action. Instead, weight cycling reduces insulin secretory capacity in vivo during clamped hyperglycemia and ex vivo in perifused islets. Islets from weight-cycled mice have reduced expression of factors essential for β-cell function (Mafa, Pdx1, Nkx6.1, Ucn3) and lower islet insulin content, compared with those from obese mice, suggesting inadequate transcriptional and posttranscriptional response to repeated nutrient overload. Collectively, these data support a model in which pancreatic plasticity is challenged in the face of large fluctuations in body weight resulting in a mismatch between glycemia and insulin secretion in mice.

Competing paradigms of obesity pathogenesis: energy balance versus carbohydrate-insulin models

The obesity pandemic continues unabated despite a persistent public health campaign to decrease energy intake (“eat less”) and increase energy expenditure (“move more”). One explanation for this failure is that the current approach, based on the notion of energy balance, has not been adequately embraced by the public. Another possibility is that this approach rests on an erroneous paradigm. A new formulation of the energy balance model (EBM), like prior versions, considers overeating (energy intake > expenditure) the primary cause of obesity, incorporating an emphasis on “complex endocrine, metabolic, and nervous system signals” that control food intake below conscious level. This model attributes rising obesity prevalence to inexpensive, convenient, energy-dense, “ultra-processed” foods high in fat and sugar. An alternative view, the carbohydrate-insulin model (CIM), proposes that hormonal responses to highly processed carbohydrates shift energy partitioning toward deposition in adipose tissue, leaving fewer calories available for the body’s metabolic needs. Thus, increasing adiposity causes overeating to compensate for the sequestered calories. Here, we highlight robust contrasts in how the EBM and CIM view obesity pathophysiology and consider deficiencies in the EBM that impede paradigm testing and refinement. Rectifying these deficiencies should assume priority, as a constructive paradigm clash is needed to resolve long-standing scientific controversies and inform the design of new models to guide prevention and treatment. Nevertheless, public health action need not await resolution of this debate, as both models target processed carbohydrates as major drivers of obesity.

The energy balance model of obesity: beyond calories in, calories out

A recent Perspective article described the "carbohydrate-insulin model (CIM)" of obesity, asserting that it "better reflects knowledge on the biology of weight control" as compared with what was described as the "dominant energy balance model (EBM)," which fails to consider "biological mechanisms that promote weight gain." Unfortunately, the Perspective conflated and confused the principle of energy balance, a law of physics that is agnostic as to obesity mechanisms, with the EBM as a theoretical model of obesity that is firmly based on biology. In doing so, the authors presented a false choice between the CIM and a caricature of the EBM that does not reflect modern obesity science. Here, we present a more accurate description of the EBM where the brain is the primary organ responsible for body weight regulation operating mainly below our conscious awareness via complex endocrine, metabolic, and nervous system signals to control food intake in response to the body's dynamic energy needs as well as environmental influences. We also describe the recent history of the CIM and show how the latest "most comprehensive formulation" abandons a formerly central feature that required fat accumulation in adipose tissue to be the primary driver of positive energy balance. As such, the new CIM can be considered a special case of the more comprehensive EBM but with a narrower focus on diets high in glycemic load as the primary factor responsible for common obesity. We review data from a wide variety of studies that address the validity of each model and demonstrate that the EBM is a more robust theory of obesity than the CIM.

The energy balance model of obesity: beyond calories in, calories out

A recent Perspective article described the "carbohydrate-insulin model (CIM)" of obesity, asserting that it "better reflects knowledge on the biology of weight control" as compared with what was described as the "dominant energy balance model (EBM)," which fails to consider "biological mechanisms that promote weight gain." Unfortunately, the Perspective conflated and confused the principle of energy balance, a law of physics that is agnostic as to obesity mechanisms, with the EBM as a theoretical model of obesity that is firmly based on biology. In doing so, the authors presented a false choice between the CIM and a caricature of the EBM that does not reflect modern obesity science. Here, we present a more accurate description of the EBM where the brain is the primary organ responsible for body weight regulation operating mainly below our conscious awareness via complex endocrine, metabolic, and nervous system signals to control food intake in response to the body's dynamic energy needs as well as environmental influences. We also describe the recent history of the CIM and show how the latest "most comprehensive formulation" abandons a formerly central feature that required fat accumulation in adipose tissue to be the primary driver of positive energy balance. As such, the new CIM can be considered a special case of the more comprehensive EBM but with a narrower focus on diets high in glycemic load as the primary factor responsible for common obesity. We review data from a wide variety of studies that address the validity of each model and demonstrate that the EBM is a more robust theory of obesity than the CIM.

Human and mouse muscle transcriptomic analyses identify insulin receptor mRNA downregulation in hyperinsulinemia-associated insulin resistance

Hyperinsulinemia is commonly viewed as a compensatory response to insulin resistance, yet studies have demonstrated that chronically elevated insulin may also drive insulin resistance. The molecular mechanisms underpinning this potentially cyclic process remain poorly defined, especially on a transcriptome-wide level. Transcriptomic meta-analysis in >450 human samples demonstrated that fasting insulin reliably and negatively correlated with INSR mRNA in skeletal muscle. To establish causality and study the direct effects of prolonged exposure to excess insulin in muscle cells, we incubated C2C12 myotubes with elevated insulin for 16 h, followed by 6 h of serum starvation, and established that acute AKT and ERK signaling were attenuated in this model of in vitro hyperinsulinemia. Global RNA-sequencing of cells both before and after nutrient withdrawal highlighted genes in the insulin receptor (INSR) signaling, FOXO signaling, and glucose metabolism pathways indicative of 'hyperinsulinemia' and 'starvation' programs. Consistently, we observed that hyperinsulinemia led to a substantial reduction in Insr gene expression, and subsequently a reduced surface INSR and total INSR protein, both in vitro and in vivo. Bioinformatic modeling combined with RNAi identified SIN3A as a negative regulator of Insr mRNA (and JUND, MAX, and MXI as positive regulators of Irs2 mRNA). Together, our analysis identifies mechanisms which may explain the cyclic processes underlying hyperinsulinemia-induced insulin resistance in muscle, a process directly relevant to the etiology and disease progression of type 2 diabetes.

The carbohydrate-insulin model: a physiological perspective on the obesity pandemic

According to a commonly held view, the obesity pandemic is caused by overconsumption of modern, highly palatable, energy-dense processed foods, exacerbated by a sedentary lifestyle. However, obesity rates remain at historic highs, despite a persistent focus on eating less and moving more, as guided by the energy balance model (EBM). This public health failure may arise from a fundamental limitation of the EBM itself. Conceptualizing obesity as a disorder of energy balance restates a principle of physics without considering the biological mechanisms that promote weight gain. An alternative paradigm, the carbohydrate-insulin model (CIM), proposes a reversal of causal direction. According to the CIM, increasing fat deposition in the body-resulting from the hormonal responses to a high-glycemic-load diet-drives positive energy balance. The CIM provides a conceptual framework with testable hypotheses for how various modifiable factors influence energy balance and fat storage. Rigorous research is needed to compare the validity of these 2 models, which have substantially different implications for obesity management, and to generate new models that best encompass the evidence.

On the causal relationships between hyperinsulinaemia, insulin resistance, obesity and dysglycaemia in type 2 diabetes

Hundreds of millions of people are affected by hyperinsulinaemia, insulin resistance, obesity and the dysglycaemia that mark a common progression from metabolic health to type 2 diabetes. Although the relative contribution of these features and the order in which they appear may differ between individuals, the common clustering and seemingly progressive nature of type 2 diabetes aetiology has guided research and clinical practice in this area for decades. At the same time, lively debate around the causal relationships between these features has continued, as new data from human trials and highly controlled animal studies are presented. This 'For debate' article was prompted by the review in Diabetologia by Esser, Utzschneider and Kahn ( https://doi.org/10.1007/s00125-020-05245-x ), with the purpose of reviewing established and emerging data that provide insight into the relative contributions of hyperinsulinaemia and impaired glucose-stimulated insulin secretion in progressive stages between health, obesity and diabetes. It is concluded that these beta cell defects are not mutually exclusive and that they are both important, but at different stages.

Chop/Ddit3 depletion in β cells alleviates ER stress and corrects hepatic steatosis in mice

Type 2 diabetes (T2D) is a metabolic disorder characterized by hyperglycemia, hyperinsulinemia, and insulin resistance (IR). During the early phase of T2D, insulin synthesis and secretion by pancreatic β cells is enhanced, which can lead to proinsulin misfolding that aggravates endoplasmic reticulum (ER) protein homeostasis in β cells. Moreover, increased circulating insulin may contribute to fatty liver disease. Medical interventions aimed at alleviating ER stress in β cells while maintaining optimal insulin secretion are therefore an attractive therapeutic strategy for T2D. Previously, we demonstrated that germline Chop gene deletion preserved β cells in high-fat diet (HFD)-fed mice and in leptin receptor-deficient db/db mice. In the current study, we further investigated whether targeting Chop/Ddit3 specifically in murine β cells conferred therapeutic benefits. First, we showed that Chop deletion in β cells alleviated β cell ER stress and delayed glucose-stimulated insulin secretion (GSIS) in HFD-fed mice. Second, β cell-specific Chop deletion prevented liver steatosis and hepatomegaly in aged HFD-fed mice without affecting basal glucose homeostasis. Third, we provide mechanistic evidence that Chop depletion reduces ER Ca²⁺ buffering capacity and modulates glucose-induced islet Ca²⁺ oscillations, leading to transcriptional changes of ER chaperone profile ("ER remodeling"). Last, we demonstrated that a GLP1-conjugated Chop antisense oligonucleotide strategy recapitulated the reduction in liver triglycerides and pancreatic insulin content. In summary, our results demonstrate that Chop depletion in β cells provides a therapeutic strategy to alleviate dysregulated insulin secretion and consequent fatty liver disease in T2D.

Therapeutic opportunities for pancreatic β-cell ER stress in diabetes mellitus

Diabetes mellitus is characterized by the failure of insulin-secreting pancreatic β-cells (or β-cell death) due to either autoimmunity (type 1 diabetes mellitus) or failure to compensate for insulin resistance (type 2 diabetes mellitus; T2DM). In addition, mutations of critical genes cause monogenic diabetes. The endoplasmic reticulum (ER) is the primary site for proinsulin folding; therefore, ER proteostasis is crucial for both β-cell function and survival under physiological and pathophysiological challenges. Importantly, the ER is also the major intracellular Ca²⁺ storage organelle, generating Ca²⁺ signals that contribute to insulin secretion. ER stress is associated with the pathogenesis of diabetes mellitus. In this Review, we summarize the mutations in monogenic diabetes that play causal roles in promoting ER stress in β-cells. Furthermore, we discuss the possible mechanisms responsible for ER proteostasis imbalance with a focus on T2DM, in which both genetics and environment are considered important in promoting ER stress in β-cells. We also suggest that controlled insulin secretion from β-cells might reduce the progression of a key aspect of the metabolic syndrome, namely nonalcoholic fatty liver disease. Finally, we evaluate potential therapeutic approaches to treat T2DM, including the optimization and protection of functional β-cell mass in individuals with T2DM.

Insulin action at a molecular level - 100 years of progress

The discovery of insulin 100 years ago and its application to the treatment of human disease in the years since have marked a major turning point in the history of medicine. The availability of purified insulin allowed for the establishment of its physiological role in the regulation of blood glucose and ketones, the determination of its amino acid sequence, and the solving of its structure. Over the last 50 years, the function of insulin has been applied into the discovery of the insulin receptor and its signaling cascade to reveal the role of impaired insulin signaling-or resistance-in the progression of type 2 diabetes. It has also become clear that insulin signaling can impact not only classical insulin-sensitive tissues, but all tissues of the body, and that in many of these tissues the insulin signaling cascade regulates unexpected physiological functions. Despite these remarkable advances, much remains to be learned about both insulin signaling and how to use this molecular knowledge to advance the treatment of type 2 diabetes and other insulin-resistant states.

Hyperinsulinemia in Obesity, Inflammation, and Cancer

The relative insufficiency of insulin secretion and/or insulin action causes diabetes. However, obesity and type 2 diabetes mellitus can be associated with an absolute increase in circulating insulin, a state known as hyperinsulinemia. Studies are beginning to elucidate the cause-effect relationships between hyperinsulinemia and numerous consequences of metabolic dysfunctions. Here, we review recent evidence demonstrating that hyperinsulinemia may play a role in inflammation, aging and development of cancers. In this review, we will focus on the consequences and mechanisms of excess insulin production and action, placing recent findings that have challenged dogma in the context of the existing body of literature. Where relevant, we elaborate on the role of specific signal transduction components in the actions of insulin and consequences of chronic hyperinsulinemia. By discussing the involvement of hyperinsulinemia in various metabolic and other chronic diseases, we may identify more effective therapeutics or lifestyle interventions for preventing or treating obesity, diabetes and cancer. We also seek to identify pertinent questions that are ripe for future investigation.

A New Hypothesis for Type 1 Diabetes Risk: The At-Risk Allele at rs3842753 Associates With Increased Beta-cell INS Messenger RNA in a Meta-Analysis of Single-Cell RNA-Sequencing Data

OBJECTIVES

Type 1 diabetes is characterized by the autoimmune destruction of insulin-secreting beta cells. Genetic variants upstream at the insulin (INS) locus contribute to ∼10% of type 1 diabetes heritable risk. Previous studies showed an association between rs3842753 C/C genotype and type 1 diabetes susceptibility, but the molecular mechanisms remain unclear. To date, no large-scale studies have looked at the effect of genetic variation at rs3842753 on INS mRNA at the single-cell level.

METHODS

We aligned all human islet single-cell RNA sequencing data sets available to us in year 2020 to the reference genome GRCh38.98 and genotyped rs3842753, integrating 2,315 β cells and 1,223 β-like cells from 13 A/A protected donors, 23 A/C heterozygous donors and 35 C/C at-risk donors, including adults without diabetes and with type 2 diabetes.

RESULTS

INS expression mean and variance were significantly higher in single β cells from females compared with males. On comparing across β cells and β-like cells, we found that rs3842753 C‒containing cells (either homozygous or heterozygous) had the highest INS expression. We also found that β cells with the rs3842753 C allele had significantly higher endoplasmic reticulum stress marker gene expression compared with the A/A homozygous genotype.

CONCLUSIONS

These findings support the emerging concept that inherited risk of type 1 diabetes may be associated with inborn, persistent elevated insulin production, which may lead to β-cell endoplasmic reticulum stress and fragility.

Bidirectional temporal relationship between obesity and hyperinsulinemia: longitudinal observation from a Chinese cohort

INTRODUCTION

Although obesity and hyperinsulinemia are closely intercorrelated, their temporal sequence is still uncertain. This study aims to investigate the temporal relationship patterns between obesity measures and hyperinsulinemia in Chinese adults.

RESEARCH DESIGN AND METHODS

The longitudinal cohort consisted of 2493 participants (860 males and 1633 female, mean age 56.71 years at follow-up) for whom measurements of obesity and hyperinsulinemia measures were collected twice between 2011 and 2014, with an average follow-up time of 3 years. Cross-lagged panel analysis was used to examine the temporal relationship between obesity measures (body mass index (BMI); waist circumference (WC); hip circumference (HC); waist-to-hip ratio (WHR)) and hyperinsulinemia (insulin, homeostasis model assessment of insulin resistance (HOMA-IR), or homeostasis model assessment of beta cell function (HOMA-%β)).

RESULTS

After the adjustment of age, sex, smoking, drinking and follow-up years, in the BMI-insulin model, the path coefficient (β₂=0.229; p<0.001) of baseline BMI to follow-up insulin was significantly greater than the path coefficient (β₁=0.073; p<0.001) of baseline insulin to follow-up BMI (p<0.001 for β₂>β₁). In the WHR-insulin model, the path coefficient (β₁=0.152; p<0.001) of baseline insulin to follow-up WHR was significantly greater than the path coefficient (β₂=0.077; p<0.001) of baseline WHR to follow-up insulin (p=0.007 for β₁>β₂). In the WC/HC-insulin model, the path coefficients of baseline insulin to follow-up WC or HC (β_1s) were also greater than the path coefficients of baseline WC or HC to follow-up insulin (β_2s), but the difference between β_1s and β_2s were not significant. The similar temporal patterns were founded between obesity measures with HOMA-IR or HOMA-%β.

CONCLUSIONS

These findings indicate that there is a bidirectional relationship between obesity and hyperinsulinemia, and abdominal obesity measures are more sensitive to hyperinsulinemia measures than BMI.

Driver versus navigator causation in biology: the case of insulin and fasting glucose

BACKGROUND

In biomedicine, inferring causal relation from experimental intervention or perturbation is believed to be a more reliable approach than inferring causation from cross-sectional correlation. However, we point out here that even in interventional inference there are logical traps. In homeostatic systems, causality in a steady state can be qualitatively different from that in a perturbed state. On a broader scale there is a need to differentiate driver causality from navigator causality. A driver is essential for reaching a destination but may not have any role in deciding the destination. A navigator on the other hand has a role in deciding the destination and the path but may not be able to drive the system to the destination. The failure to differentiate between types of causalities is likely to have resulted into many misinterpretations in physiology and biomedicine.

METHODS

We illustrate this by critically re-examining a specific case of the causal role of insulin in glucose homeostasis using five different approaches (1) Systematic review of tissue specific insulin receptor knock-outs, (2) Systematic review of insulin suppression and insulin enhancement experiments, (3) Differentiating steady state and post-meal state glucose levels in streptozotocin treated rats in primary experiments, (4) Mathematical and theoretical considerations and (5) Glucose-insulin relationship in human epidemiological data.

RESULTS

All the approaches converge on the inference that although insulin action hastens the return to a steady state after a glucose load, there is no evidence that insulin action determines the steady state level of glucose. Insulin, unlike the popular belief in medicine, appears to be a driver but not a navigator for steady state glucose level. It is quite likely therefore that the current line of clinical action in the field of type 2 diabetes has limited success largely because it is based on a misinterpretation of glucose-insulin relationship. The insulin-glucose example suggests that we may have to carefully re-examine causal inferences from perturbation experiments and set up revised norms for experimental design for causal inference.

Adipose depot-specific upregulation of Ucp1 or mitochondrial oxidative complex proteins are early consequences of genetic insulin reduction in mice

Hyperinsulinemia plays a causal role in adipose tissue expansion. Mice with reduced insulin have increased energy expenditure, but the mechanisms remained unclear. Here we investigated the effects of genetically reducing insulin production on uncoupling and oxidative mitochondrial proteins in liver, skeletal muscle, white adipose tissue (WAT), and brown adipose tissue (BAT). Male Ins1^+/+ or Ins1^+/- littermates were fed either a low-fat diet (LFD) or a high-fat diet (HFD) for 4 wk, starting at 8 wk of age. Replicating our previous observations, HFD increased fasting hyperinsulinemia, and Ins1^+/- mice had significantly lower circulating insulin compared with Ins1^+/+ littermates. Fasting glucose and body weight were not different between genotypes. We did not observe robust significant differences in liver or skeletal muscle. In mesenteric WAT, Ins1^+/- mice had reduced Ndufb8 and Sdhb, while Ucp1 was increased in the context of HFD. HFD alone had a dramatic inhibitory effect on Pparg abundance. In inguinal WAT, Ins1^+/- mice exhibited significant increases in oxidative complex proteins, independent of diet, without affecting Ucp1, Pparg, or Prdm16:Pparg association. In BAT, lowered insulin increased Sdhb protein levels that had been reduced by HFD. Ucp1 protein, Prdm16:Pparg association, and Sirt3 abundance were all increased in the absence of diet-induced hyperinsulinemia. Our data show that reducing insulin upregulates oxidative proteins in inguinal WAT without affecting Ucp1, whereas in mesenteric WAT and BAT, reducing insulin upregulates Ucp1 in the context of HFD. Preventing hyperinsulinemia has early depot-specific effects on adipose tissue metabolism and helps explain the increased energy expenditure previously reported in Ins1^+/- mice.

Insulin: too much of a good thing is bad

BACKGROUND

Insulin shares a limited physiological concentration range with other endocrine hormones. Not only too low, but also too high systemic insulin levels are detrimental for body functions.

MAIN BODY

The physiological function and clinical relevance of insulin are usually seen in association with its role in maintaining glucose homeostasis. However, insulin is an anabolic hormone which stimulates a large number of cellular responses. Not only too low, but also excess insulin concentrations are detrimental to the physiological balance. Although the glucoregulatory activity of insulin is mitigated during hyperinsulinemia by dampening the efficiency of insulin signaling ("insulin resistance"), this is not the case for most other hormonal actions of insulin, including the promotion of protein synthesis, de novo lipogenesis, and cell proliferation; the inhibition of lipolysis, of autophagy-dependent cellular turnover, and of nuclear factor E2-related factor-2 (Nrf2)-dependent antioxidative; and other defense mechanisms. Hence, there is no general insulin resistance but selective impairment of insulin signaling which causes less glucose uptake from the blood and reduced activation of endothelial NO synthase (eNOS). Because of the largely unrestricted insulin signaling, hyperinsulinemia increases the risk of obesity, type 2 diabetes, and cardiovascular disease and decreases health span and life expectancy. In epidemiological studies, high-dose insulin therapy is associated with an increased risk of cardiovascular disease. Randomized controlled trials of insulin treatment did not observe any effect on disease risk, but these trials only studied low insulin doses up to 40 IU/day. Proof for a causal link between elevated insulin levels and cardiovascular disease risk comes from Mendelian randomization studies comparing individuals with genetically controlled low or high insulin production.

CONCLUSIONS

The detrimental actions of prolonged high insulin concentrations, seen also in cell culture, argue in favor of a lifestyle that limits circadian insulin levels. The health risks associated with hyperinsulinemia may have implications for treatment regimens used in type 2 diabetes.

RIPK2 Dictates Insulin Responses to Tyrosine Kinase Inhibitors in Obese Male Mice

Tyrosine kinase inhibitors (TKIs) used in cancer are also being investigated in diabetes. TKIs can improve blood glucose control in diabetic cancer patients, but the specific kinases that alter blood glucose or insulin are not clear. We sought to define the role of Receptor Interacting Serine/Threonine Kinase 2 (RIPK2) in mouse models of insulin resistance. We tested the TKI gefitinib, which inhibits RIPK2 activity, in wild-type (WT), Nod1-/-, Nod2-/-, and Ripk2-/- mice fed an obesogenic high-fat diet. Gefitinib lowered blood glucose during a glucose tolerance test (GTT) in a nucleotide-binding oligomerization domain (NOD)-RIPK2-independent manner in all obese mice. However, gefitinib lowered glucose-stimulated insulin secretion only in obese Ripk2-/- mice. Gefitinib had no effect on insulin secretion in obese WT, Nod1-/-, or Nod2-/- mice. Hence, genetic deletion of Ripk2 promoted the insulin-sensitizing potential of gefitinib, since this TKI lowered both blood glucose and insulin only in Ripk2-/- mice. Gefitinib did not alter the inflammatory profile of pancreas, adipose, liver, or muscle tissues in obese Ripk2-/- mice compared with obese WT mice. We also tested imatinib, a TKI that does not inhibit RIPK2 activity, in obese WT mice. Imatinib lowered blood glucose during a GTT, consistent with TKIs lowering blood glucose independently of RIPK2. However, imatinib increased glucose-stimulated insulin secretion during the glucose challenge. These data show that multiple TKIs lower blood glucose, where actions of TKIs on RIPK2 dictate divergent insulin responses, independent of tissue inflammation. Our data show that RIPK2 limits the insulin sensitizing effect of gefitinib, whereas imatinib increased insulin secretion.

Partial impairment of insulin receptor expression mimics fasting to prevent diet-induced fatty liver disease

Excessive insulin signaling through the insulin receptor (IR) may play a role in the pathogenesis of diet-induced metabolic disease, including obesity and type 2 diabetes. Here we investigate whether heterozygous impairment of insulin receptor (IR) expression limited to peripheral, i.e. non-CNS, tissues of adult mice impacts the development of high-fat diet-induced metabolic deterioration. While exhibiting some features of insulin resistance, PerIRKO^+/− mice display a hepatic energy deficit accompanied by induction of energy-sensing AMPK, mitochondrial biogenesis, PPARα, unexpectedly leading to protection from, and reversal of hepatic lipid accumulation (steatosis hepatis, NAFLD). Consistently, and unlike in control mice, the PPARα activator fenofibrate fails to further affect hepatic lipid accumulation in PerIRKO^+/− mice. Taken together, and opposing previously established diabetogenic features of insulin resistance, incomplete impairment of insulin signaling may mimic central aspects of calorie restriction to limit hepatic lipid accumulation during conditions of metabolic stress.

Hyper-insulinemia associated with excess calorie intake may cause metabolic dysfunction. Here the authors report that mice with partially reduced insulin receptor expression in peripheral tissues are protected from and experience reversal of fatty liver disease.

Intravascular Follistatin gene delivery improves glycemic control in a mouse model of type 2 diabetes

Type 2 diabetes (T2D) manifests from inadequate glucose control due to insulin resistance, hypoinsulinemia, and deteriorating pancreatic β-cell function. The pro-inflammatory factor Activin has been implicated as a positive correlate of severity in T2D patients, and as a negative regulator of glucose uptake by skeletal muscle, and of pancreatic β-cell phenotype in mice. Accordingly, we sought to determine whether intervention with the Activin antagonist Follistatin can ameliorate the diabetic pathology. Here, we report that an intravenous Follistatin gene delivery intervention with tropism for striated muscle reduced the serum concentrations of Activin B and improved glycemic control in the db/db mouse model of T2D. Treatment reversed the hyperglycemic progression with a corresponding reduction in the percentage of glycated-hemoglobin to levels similar to lean, healthy mice. Follistatin gene delivery promoted insulinemia and abundance of insulin-positive pancreatic β-cells, even when treatment was administered to mice with advanced diabetes, supporting a mechanism for improved glycemic control associated with maintenance of functional β-cells. Our data demonstrate that single-dose intravascular Follistatin gene delivery can ameliorate the diabetic progression and improve prognostic markers of disease. These findings are consistent with other observations of Activin-mediated mechanisms exerting deleterious effects in models of obesity and diabetes, and suggest that interventions that attenuate Activin signaling could help further understanding of T2D and the development of novel T2D therapeutics.

Mitochondrial Proton Leak Regulated by Cyclophilin D Elevates Insulin Secretion in Islets at Nonstimulatory Glucose Levels

Fasting hyperinsulinemia precedes the development of type 2 diabetes. However, it is unclear whether fasting insulin hypersecretion is a primary driver of insulin resistance or a consequence of the progressive increase in fasting glycemia induced by insulin resistance in the prediabetic state. Herein, we have discovered a mechanism that specifically regulates non-glucose-stimulated insulin secretion (NGSIS) in pancreatic islets that is activated by nonesterified free fatty acids, the major fuel used by β-cells during fasting. We show that the mitochondrial permeability transition pore regulator cyclophilin D (CypD) promotes NGSIS, but not glucose-stimulated insulin secretion, by increasing mitochondrial proton leak. Islets from prediabetic obese mice show significantly higher CypD-dependent proton leak and NGSIS compared with lean mice. Proton leak-mediated NGSIS is conserved in human islets and is stimulated by exposure to nonesterified free fatty acids at concentrations observed in obese subjects. Mechanistically, proton leak activates islet NGSIS independently of mitochondrial ATP synthesis but ultimately requires closure of the KATP channel. In summary, we have described a novel nonesterified free fatty acid-stimulated pathway that selectively drives pancreatic islet NGSIS, which may be therapeutically exploited as an alternative way to halt fasting hyperinsulinemia and the progression of type 2 diabetes.

The carbohydrate-insulin model does not explain the impact of varying dietary macronutrients on the body weight and adiposity of mice

Objectives

The carbohydrate-insulin model (CIM) predicts that increases in fasting and post-prandial insulin in response to dietary carbohydrates stimulate energy intake and lower energy expenditures, leading to positive energy balance and weight gain. The objective of the present study was to directly test the CIM's predictions using C57BL/6 mice.

Methods

Diets were designed by altering dietary carbohydrates with either fixed protein or fat content and were fed to C57BL/6 mice acutely or chronically for 12 weeks. The body weight, body composition, food intake, and energy expenditures of the mice were measured. Their fasting and post-prandial glucose and insulin levels were also measured. RNA-seq was performed on RNA from the hypothalamus and subcutaneous white adipose tissue. Pathway analysis was conducted using IPA.

Results

Only the post-prandial insulin and fasting glucose levels followed the CIM's predictions. The lipolysis and leptin signaling pathways in the sWAT were inhibited in relation to the elevated fasting insulin, supporting the CIM's predicted impact of high insulin. However, because higher fasting insulin was unrelated to carbohydrate intake, the overall pattern did not support the model. Moreover, the hypothalamic hunger pathways were inhibited in relation to the increased fasting insulin, and the energy intake was not increased. The browning pathway in the sWAT was inhibited at higher insulin levels, but the daily energy expenditure was not altered.

Conclusions

Two of the predictions were partially supported (and hence also partially not supported) and the other three predictions were not supported. We conclude that the CIM does not explain the impact of dietary macronutrients on adiposity in mice.

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Higher fasting insulin related to inhibited lipolysis and leptin pathways in sWAT, supporting CIM.

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Higher fasting insulin related to inhibited hypothalamic hunger pathway, contrasting CIM.

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Fasting insulin decreased with higher dietary carbohydrate, overall contrasting CIM.

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Higher dietary carbohydrate did not lead to greater EI/adiposity, or lowered EE.

Immune Cells Gate White Adipose Tissue Expansion

The immune system plays a critical role in white adipose tissue (WAT) energy homeostasis and, by extension, whole-body metabolism. Substantial evidence from mouse and human studies firmly establishes that insulin sensitivity deteriorates as a result of subclinical inflammation in the adipose tissue of individuals with diabetes. However, the relationship between adipose tissue expandability and immune cell infiltration remains a complex problem important for understanding the pathogenesis of obesity. Notably, a large body of work challenges the idea that all immune responses are deleterious to WAT function. This review highlights recent advances that describe how immune cells and adipocytes coordinately enable WAT expansion and regulation of energy homeostasis.

Assessment of the effects of repeated doses of potassium iodide intake during pregnancy on male and female rat offspring using metabolomics and lipidomics

Preparedness for nuclear accident responsiveness includes interventions to protect pregnancies against prolonged exposure to radioactive iodine. The aim of this study was to investigate a new design consisting of repeated administration of potassium iodide (KI, 1 mg/kg) for 8 days in late pregnancy gestational day 9-16 (GD9-GD16) in rats. The later-life effects of this early-life iodine thyroid blocking (ITB) strategy were assessed in offspring two months afterbirth. Functional behavioral tests including forced swimming test (FST) and rotarod test (RRT) in rats of both genders showed lower FST performance in KI-treated females and lower RRT performance in KI-treated male pups. This performance decline was associated with metabolic disruptions in cortex involving amino acid metabolism, tyrosine metabolism, as well as docosahexaenoic acid (DHA) lipids and signaling lipids in males and females. Beyond these behavior-associated metabolic changes, a portion of the captured metabolome (17-25%) and lipidome (3.7-7.35%) remained sensitive to in utero KI prophylactic treatment in both cortex and plasma of post-weaning rats, with some gender-related variance. Only part of these disruptions was attributed to lower levels of TSH and T4 (males only). The KI-induced metabolic shifts involved a broad spectrum of functions encompassing metabolic and cell homeostasis and cell signaling functions. Irrespective Regardless of gender and tissues, the predominant effects of KI affected neurotransmitters, amino acid metabolism, and omega-3 DHA metabolism. Taken together, data demonstrated that repeated daily KI administration at 1 mg/kg/day for 8 days during late pregnancy failed to protect the mother-fetus against nuclear accident radiation. Abbreviations: CV-ANOVA: Cross-validation analysis of variance; DHA: Docosahexaenoic acid; FST: Forced swimming test; FT3: plasma free triiodothyronine; FT4: plasma free thyroxine; GD: Gestational day; ITB: Iodine thyroid blocking; KI: potassium iodide; LC/MS: Liquid chromatography coupled with mass spectrometry; MTBE: Methyl tert-butyl ether; m/z: mass-to-charge ratio; PLS-DA: Partial least squares-discriminant analysis; PRIODAC: Repeated stable iodide prophylaxis in accidental radioactive releases; RRT: Rotarod test; TSH: Thyroid-stimulating hormone; VIP: Variable importance in projection.

Insulin translates unfavourable lifestyle into obesity

Lifestyle factors conferring increased diabetes risk are associated with elevated basal insulin levels (hyperinsulinaemia). The latter predicts later obesity in children and adolescents.A causal role of hyperinsulinaemia for adipose tissue growth is probable because pharmacological reduction of insulin secretion lowers body weight in people who are obese. Genetic inactivation of insulin gene alleles in mice also lowers their systemic insulin levels and prevents or ameliorates high-fat diet-induced obesity. Hyperinsulinaemia causes weight gain because of a physiological property of insulin. Insulin levels that are on the high side of normal, or which are slightly elevated, are sufficient to suppress lipolysis and promote lipogenesis in adipocytes. The effect of insulin on glucose transport or hepatic glucose production requires six or two times higher hormone levels, respectively.It seems justified to suggest a lifestyle that avoids high insulin levels in order to limit anabolic fat tissue activity.

Mild Suppression of Hyperinsulinemia to Treat Obesity and Insulin Resistance

Insulin plays roles in lipid uptake, lipolysis, and lipogenesis, in addition to controlling blood glucose levels. Excessive circulating insulin is associated with adipose tissue expansion and obesity, yet a causal role for hyperinsulinemia in the development of mammalian obesity has proven controversial, with many researchers suggesting it as a consequence of insulin resistance. Recently, evidence that specifically reducing hyperinsulinemia can prevent and reverse obesity in animal models has been presented. Our experiments, and others in this field, question the current dogma that hyperinsulinemia is a response to obesity and/or insulin resistance. In this review, we discuss preclinical evidence in the context of the broader literature and speculate on the possibility of clinical translation of alternative approaches for treating obesity.