Sex differences in serotonin-hypothalamic connections underpin a diminished sense of emotional well-being with increasing body weight

BACKGROUND/OBJECTIVES

The neurobiological mechanisms linking obesity to emotional distress related to weight remain largely unknown.

PARTICIPANTS/METHODS

Here we combined positron emission tomography, using the serotonin transporter (5-HTT) radiotracer [(11)C]-3-amino-4-(2-dimethylaminomethylphenylsulfanyl)-benzonitrile, with functional connectivity magnetic resonance imaging, the Beck Depression Inventory (BDI-II) and the Impact of Weight on Quality of Life-Lite questionnaire (IWQOL-Lite) to investigate the role of central serotonin in the severity of depression (BDI-II), as well as in the loss of emotional well-being with body weight (IWQOL-Lite).

RESULTS

In a group of lean to morbidly obese individuals (n=28), we found sex differences in the 5-HTT availability-related connectivity of the hypothalamus. Males (n=11) presented a strengthened connectivity to the lateral orbitofrontal cortex, whereas in females (n=17) we found strengethened projections to the ventral striatum. Both regions are known as reward regions involved in mediating the emotional response to food. Their resting-state activity correlated positively to the body mass index (BMI) and IWQOL-Lite scores, suggesting that each region in both sexes also underpins a diminished sense of emotional well-being with body weight. Contrarily to males, we found that in females also the BDI-II positively correlated with the BMI and by trend with the activity in ventral striatum, suggesting that in females an increased body weight may convey to other mood dimensions than those weight-related ones included in the IWQOL-Lite.

CONCLUSIONS

This study suggests sex differences in serotonin-hypothalamic connections to brain regions of the reward circuitry underpinning a diminished sense of emotional well-being with an increasing body weight.

Obesogenic memory can confer long-term increases in adipose tissue but not liver inflammation and insulin resistance after weight loss

Objective

Obesity represents a major risk factor for the development of type 2 diabetes mellitus, atherosclerosis and certain cancer entities. Treatment of obesity is hindered by the long-term maintenance of initially reduced body weight, and it remains unclear whether all pathologies associated with obesity are fully reversible even upon successfully maintained weight loss.

Methods

We compared high fat diet-fed, weight reduced and lean mice in terms of body weight development, adipose tissue and liver insulin sensitivity as well as inflammatory gene expression. Moreover, we assessed similar parameters in a human cohort before and after bariatric surgery.

Results

Compared to lean animals, mice that demonstrated successful weight reduction showed increased weight gain following exposure to ad libitum control diet. However, pair-feeding weight-reduced mice with lean controls efficiently stabilized body weight, indicating that hyperphagia was the predominant cause for the observed weight regain. Additionally, whereas glucose tolerance improved rapidly after weight loss, systemic insulin resistance was retained and ameliorated only upon prolonged pair-feeding. Weight loss enhanced insulin action and resolved pro-inflammatory gene expression exclusively in the liver, whereas visceral adipose tissue displayed no significant improvement of metabolic and inflammatory parameters compared to obese mice. Similarly, bariatric surgery in humans (n = 55) resulted in massive weight reduction, improved hepatic inflammation and systemic glucose homeostasis, while adipose tissue inflammation remained unaffected and adipocyte-autonomous insulin action only exhibit minor improvements in a subgroup of patients (42%).

Conclusions

These results demonstrate that although sustained weight loss improves systemic glucose homeostasis, primarily through improved inflammation and insulin action in liver, a remarkable obesogenic memory can confer long-term increases in adipose tissue inflammation and insulin resistance in mice as well as in a significant subpopulation of obese patients.

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Upon weight loss in mice liver insulin sensitivity rapidly improves.

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Upon weight loss in mice fat retains metabolic inflammation and insulin resistance.

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Weight gain upon successful weight reduction in mice is driven by increased food intake.

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A proportion of human subjects undergoing bariatric surgery retain AT-inflammation.

Autophagy in adipose tissue of patients with obesity and type 2 diabetes

BACKGROUND

Pathophysiology of obesity is closely associated with enhanced autophagy in adipose tissue (AT). Autophagic process can promote survival or activate cell death. Therefore, we examine the occurrence of autophagy in AT of type 2 diabetes (T2D) patients in comparison to obese and lean individuals without diabetes.

METHODOLOGY/PRINCIPAL FINDINGS

Numerous autophagosomes accumulated within adipocytes were visualized by electron transmission microscopy and by immunofluorescence staining for autophagy marker LC3 in obese and T2D patients. Increased autophagy was demonstrated by higher LC3-II/LC3-I ratio, up-regulated expression of LC3 and Atg5 mRNA, along with decreased p62 and mTOR protein levels. Increased autophagy occurred together with AT inflammation.

CONCLUSIONS

Our data suggest fat depot-related differences in autophagy regulation. In subcutaneous AT, increased autophagy is accompanied by increased markers of apoptosis in patients with obesity independently of T2D. In contrast, in visceral AT only in T2D patients increased autophagy was related to higher markers of apoptosis.

[Pharmacological therapy versus bariatric surgery for patients with obesity and type 2 diabetes]

There is strong epidemiological evidence for an association between increased body weight and a higher incidence of type 2 diabetes. Moreover, reduction in body weight may delay the onset of type 2 diabetes. The basic therapy of type 2 diabetes includes lifestyle modifications, such as education, nutritional advice, increased physical activity, non-smoking and strategies to cope with stress. If lifestyle modifications are not successful, antidiabetic pharmacotherapy is stepwise intensified to achieve individual therapeutic targets; however, pharmacological treatment of type 2 diabetes frequently fails to prevent the progress of the disease and the manifestation of diabetes complications. Sustained weight reduction belongs to the individual treatment targets for patients with obesity and type 2 diabetes. Because conservative weight reduction strategies are frequently not successful, bariatric surgery has emerged as an effective treatment particularly for those patients with obesity-associated type 2 diabetes in whom a glycosylated hemoglobin (HbA1c) target < 7.5% could not be achieved with pharmacological therapy. Bariatric surgery should no longer be considered as the last option for patients with obesity-associated type 2 diabetes.

Circulating angiopoietin-like protein 8 is independently associated with fasting plasma glucose and type 2 diabetes mellitus

OBJECTIVE

Angiopoietin-like protein 8 (Angptl8) has recently been introduced as a novel adipokine/hepatokine that promotes pancreatic β-cell proliferation and improves glucose tolerance in mouse models of insulin resistance. However, regulation of Angptl8 in human type 2 diabetes mellitus (T2DM) and renal dysfunction has not been determined.

RESEARCH DESIGN AND METHODS

Serum Angptl8 levels were quantified by ELISA in 62 patients with T2DM as compared with 58 nondiabetic subjects in vivo. Within both groups, about half of the patients were on chronic hemodialysis or had an estimated glomerular filtration rate above 50 mL/min/1.73 m(2). Furthermore, we investigated the effect of insulin and differentiation on Angptl8 mRNA expression in 3T3-L1 adipocytes in vitro.

RESULTS

Median [interquartile range] serum Angptl8 levels were higher in patients with T2DM (1.19 [0.37] μg/L) as compared with nondiabetic subjects (1.03 [0.47] μg/L) (P = .005). Furthermore, the adipokine/hepatokine was significantly higher in women (1.21 [0.47] μg/L) as compared with men (1.05 [0.44] μg/L]) (P = .013). In multivariate analysis, fasting glucose and T2DM but not renal function remained independent and positive predictors of circulating Angptl8 even after adjustment for markers of obesity, lipid status, and inflammation (P < .05). Furthermore, Angptl8 mRNA expression was induced by insulin and during adipogenesis in 3T3-L1 adipocytes in vitro.

CONCLUSIONS

Circulating Angptl8 is positively and independently associated with T2DM and fasting glucose in vivo. Furthermore, Angptl8 mRNA expression is induced by insulin and during adipogenesis in 3T3-L1 adipocytes in vitro.

[Insulin or surgery? : the perspective of a diabetologist]

Obesity significantly increases the risk of developing type 2 diabetes by a factor of up to 9. Medical treatment of type 2 diabetes with lifestyle and pharmacological interventions frequently fails to prevent the progress of the disease and the manifestation of diabetes complications. In recent years bariatric metabolic surgery has emerged as an effective treatment for patients with obesity and type 2 diabetes. Compared to medical treatment alone, metabolic surgery has been shown to be more effective in reducing mortality, improving hyperglycemia, hypertension and dyslipidemia in randomized clinical trials among patients with obesity and type 2 diabetes. However, surgery also has the risk for acute perioperative complications, long-term micronutrient deficiencies and psychological problems. Weighing these risks against the benefits of significant weight loss and improved glycemic control, metabolic surgery seems to be a promising treatment option for obesity-associated type 2 diabetes. However, current guidelines and treatment algorithms for the treatment of type 2 diabetes either ignore or underestimate the potential of metabolic surgery. In my opinion, metabolic surgery should be considered earlier in the treatment of type 2 diabetes and obesity and no longer be considered as the last therapeutic option for patients with obesity-associated type 2 diabetes.