In vitro palmitate treatment of myotubes from postmenopausal women leads to ceramide accumulation, inflammation and affected insulin signaling

Impact of Lipids on Insulin Resistance: Insights from Human and Animal Studies

Insulin resistance (IR) is a complex pathological condition central to metabolic diseases such as type 2 diabetes mellitus (T2DM), cardiovascular disease, non-alcoholic fatty liver disease, and polycystic ovary syndrome (PCOS). This review evaluates the impact of lipids on insulin resistance (IR) by analyzing findings from human and animal studies. The articles were searched on the PubMed database using two keywords: (1) "Role of Lipids AND Insulin Resistance AND Humans" and (2) "Role of Lipids AND Insulin Resistance AND Animal Models". Studies in humans revealed that elevated levels of free fatty acids (FFAs) and triglycerides (TGs) are closely associated with reduced insulin sensitivity, and interventions like metformin and omega-3 fatty acids show potential benefits. In animal models, high-fat diets disrupt insulin signaling and increase inflammation, with lipid mediators such as diacylglycerol (DAG) and ceramides playing significant roles. DAG activates protein kinase C, which eventually impairs insulin signaling, while ceramides inhibit Akt/PKB, further contributing to IR. Understanding these mechanisms is crucial for developing effective prevention and treatment strategies for IR-related diseases.

The impact of EPA and DHA on ceramide lipotoxicity in the metabolic syndrome

The metabolic syndrome (MetS) is a cluster of cardiovascular risk factors including obesity, insulin resistance (IR) and dyslipidaemia. Consumption of a high-fat diet (HFD) enriched in SFA leads to the accumulation of ceramide (Cer), the central molecule in sphingolipid metabolism. Elevations in plasma and tissue Cer are found in obese individuals, and there is evidence to suggest that Cer lipotoxicity contributes to the MetS. EPA and DHA have shown to improve MetS parameters including IR, inflammation and hypertriacylglycerolaemia; however, whether these improvements are related to Cer is currently unknown. This review examines the potential of EPA and DHA to improve Cer lipotoxicity and MetS parameters including IR, inflammation and dyslipidaemia in vitro and in vivo. Current evidence from cell culture and animal studies indicates that EPA and DHA attenuate palmitate- or HFD-induced Cer lipotoxicity and IR, whereas evidence in humans is greatly lacking. Overall, there is intriguing potential for EPA and DHA to improve Cer lipotoxicity and related MetS parameters, but more research is warranted.

Brown Adipose Tissue: A Metabolic Regulator in a Hypothalamic Cross Talk?

Since the discovery of functionally competent, energy-consuming brown adipose tissue (BAT) in adult humans, much effort has been devoted to exploring this tissue as a means for increasing energy expenditure to counteract obesity. However, despite promising effects on metabolic rate and insulin sensitivity, no convincing evidence for weight-loss effects of cold-activated human BAT exists to date. Indeed, increasing energy expenditure would naturally induce compensatory feedback mechanisms to defend body weight. Interestingly, BAT is regulated by multiple interactions with the hypothalamus from regions overlapping with centers for feeding behavior and metabolic control. Therefore, in the further exploration of BAT as a potential source of novel drug targets, we discuss the hypothalamic orchestration of BAT activity and the relatively unexplored BAT feedback mechanisms on neuronal regulation. With a holistic view on hypothalamic-BAT interactions, we aim to raise ideas and provide a new perspective on this circuit and highlight its clinical relevance.

Sphingolipids in Obesity and Correlated Co-Morbidities: The Contribution of Gender, Age and Environment

This paper reviews our present knowledge on the contribution of ceramide (Cer), sphingomyelin (SM), dihydroceramide (DhCer) and sphingosine-1-phosphate (S1P) in obesity and related co-morbidities. Specifically, in this paper, we address the role of acyl chain composition in bodily fluids for monitoring obesity in males and females, in aging persons and in situations of environmental hypoxia adaptation. After a brief introduction on sphingolipid synthesis and compartmentalization, the node of detection methods has been critically revised as the node of the use of animal models. The latter do not recapitulate the human condition, making it difficult to compare levels of sphingolipids found in animal tissues and human bodily fluids, and thus, to find definitive conclusions. In human subjects, the search for putative biomarkers has to be performed on easily accessible material, such as serum. The serum “sphingolipidome” profile indicates that attention should be focused on specific acyl chains associated with obesity, per se, since total Cer and SM levels coupled with dyslipidemia and vitamin D deficiency can be confounding factors. Furthermore, exposure to hypoxia indicates a relationship between dyslipidemia, obesity, oxygen level and aerobic/anaerobic metabolism, thus, opening new research avenues in the role of sphingolipids.

Metabolic control and sex: A focus on inflammatory-linked mediators

Men and women have many differing biological and physiological characteristics. Thus, it is no surprise that the control of metabolic processes and the mechanisms underlying metabolic-related diseases have sex-specific components. There is a clear metabolic sexual dimorphism in that up until midlife, men have a far greater likelihood of acquiring cardio-metabolic disease than women. Following menopause, however, this difference is reduced, suggestive of a protective role of the female sex hormones. Inflammatory processes have been implicated in the pathogenesis of cardio-metabolic disease with human studies correlating metabolic disease acquisition or risk with levels of various inflammatory markers. Rodent studies employing genetic modifications or novel pharmacological approaches have provided mechanistic insight into the role of these inflammatory mediators. Sex differences impact inflammatory processes and the subsequent biological response. As a consequence, this may affect how inflammation alters metabolic processes between the sexes. Recently, some of our work in the field of inflammatory genes and metabolic control identified a sexual dimorphism in a preclinical model and caused us to question the frequency and scale of such findings in the literature. This review concentrates on inflammatory-related signalling in relation to obesity, insulin resistance, and type 2 diabetes and highlights the differences observed between males and females. Differences in the activation and signalling of various inflammatory genes and proteins present another reason why studying both male and female patients or animals is important in the context of understanding and finding therapeutics for metabolic-related disease. LINKED ARTICLES: This article is part of a themed section on The Importance of Sex Differences in Pharmacology Research. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.21/issuetoc.

Characteristics of Glucose Metabolism in Underweight Japanese Women

Context

Japanese women have substantially lower body mass index (BMI) than women in other developed countries. The BMI of Japanese women has steadily decreased over time. However, glucose metabolism in underweight Japanese women has not been fully characterized.

Objective

The aim of this study was to investigate glucose metabolism and the physical characteristics of underweight Japanese women.

Design and Participants

We recruited 31 young (20 to 29 years of age) and 30 postmenopausal (50 to 65 years of age) underweight women. We also recruited young normal-weight women (n = 13) and postmenopausal normal-weight women (n = 10) to serve as references. We administered an oral glucose tolerance test (OGTT) and evaluated intramyocellular lipid (IMCL) levels and body composition using ¹H-magnetic resonance spectroscopy and dual-energy X-ray absorptiometry, respectively.

Results

Young underweight women had similar glucose tolerance as young normal-weight women. However, postmenopausal underweight women had a higher area under the curve (AUC) for glucose during OGTT than postmenopausal normal-weight women. In postmenopausal underweight women, 2-hour glucose levels during OGTT were negatively correlated with lean body mass (r = −0.55, P < 0.01) and insulinogenic index (r = −0.42, P = 0.02) and were positively correlated with IMCL levels (r = 0.40, P = 0.03). Compared with young underweight women, postmenopausal underweight women had a higher AUC for glucose during OGTT and a lower insulinogenic index and AUC for insulin during OGTT.

Conclusions

Postmenopausal underweight women had more impaired glucose tolerance than young underweight women. In postmenopausal underweight women, the degree of glucose tolerance impairment was associated with decreased lean body mass, increased IMCL accumulation, and impaired insulin secretion.

Anti-diabetic effects and mechanisms of action of a Chinese herbal medicine preparation JQ-R in vitro and in diabetic KKAy mice

Refined-JQ (JQ-R) is a mixture of refined extracts from Coptis chinensis (Ranunculaceae), Astragalus membranaceus (Leguminosae) and Lonicera japonica (Caprifoliaceae), the three major herbs of JinQi-JiangTang tablet, a traditional Chinese medicine (TCM) formula. The mechanisms by which JQ-R regulates glucose metabolism and improves insulin sensitivity were studied in type 2 diabetic KK^Ay mice and insulin-resistant L6 myotubes. To investigate the mechanisms by which JQ-R improves insulin sensitivity, a model of insulin-resistant cells induced with palmitic acid (PA) was established in L6 myotubes. Glucose uptake and expression of factors involved in insulin signaling, stress, and inflammatory pathways were detected by immunoblotting. JQ-R showed beneficial effects on glucose homeostasis and insulin resistance in a euglycemic clamp experiment and decreased fasting insulin levels in diabetic KK^Ay mice. JQ-R also improved the plasma lipid profiles. JQ-R directly increased the activity of superoxide dismutase (SOD) and decreased malondialdehyde (MDA) as well as inducible nitric oxide synthase (iNOS) levels in insulin-resistant L6 cells, and elevated the insulin-stimulated glucose uptake with upregulated phosphorylation of AKT. The phosphorylation levels of nuclear factor kappa B (NF-κB p65), inhibitor of NF-κB (IκB α), c-Jun N-terminal kinase (JNK1/2) and extracellular-signal-regulated kinases (ERK1/2) were also changed after JQ-R treatment compared with the control group. Together these findings suggest that JQ-R improved glucose and lipid metabolism in diabetic KK^Ay mice. JQ-R directly enhanced insulin-stimulated glucose uptake in insulin-resistant myotubes with improved insulin signalling and inflammatory response and oxidative stress. JQ-R could be a candidate to achieve improved glucose metabolism and insulin sensitivity in type 2 diabetes mellitus.

Concurrent Training Promoted Sustained Anti-atherogenic Benefits in the Fasting Plasma Triacylglycerolemia of Postmenopausal Women at 1-Year Follow-up

Rossi, FE, Diniz, TA, Fortaleza, ACS, Neves, LM, Picolo, MR, Monteiro, PA, Buonani, C, Lira, FS, and Freitas, IF Jr. Concurrent training promoted sustained anti-atherogenic benefits in the fasting plasma triacylglycerolemia of postmenopausal women at 1-year follow-up. J Strength Cond Res 32(12): 3573-3582, 2018-The aim of this study was to compare the effects of aerobic and concurrent training (aerobic plus strength training) on the lipid profiles of normotriacylglycerolemic and hypertriacylglycerolemic postmenopausal women and to verify whether the benefits of aerobic and concurrent training were sustained after 1 year. Total cholesterol, high-density lipoprotein cholesterol (HDL-c), low-density lipoprotein cholesterol, triacylglycerol (TAG), and glucose were assessed in 46 normotriacylglycerolemic (TAG < 150 mg·dl) postmenopausal women divided into 3 groups: aerobic training, concurrent training (CT), and a control group. For CT group, hypertriacylglycerolemic postmenopausal women were recruited (TAG ≥ 150 mg·dl, n = 14). Total daily caloric consumption and free-living physical activity were evaluated by dietary questionnaires and accelerometer, respectively, and fat mass by DXA. In 16 weeks, CT was effective in increasing HDL-c (normotriacylglycerolemic: pre = 57.1 ± 17.3 mg·dl × post = 64.3 ± 16.1 mg·dl p = 0.020 and hypertriacylglycerolemic: pre = 44.7 ± 9.6 mg·dl × post = 50.3 ± 15.3 mg·dl; p = 0.012) and reducing the atherogenic index in normotriacylglycerolemic (pre = 3.6 ± 0.9 mg·dl × post = 3.0 ± 0.6 mg·dl; p = 0.003) and hypertriacylglycerolemic (pre = 5.2 ± 1.1 mg·dl × post = 4.7 ± 1.2 mg·dl; p = 0.018) postmenopausal women. In addition, the effects were sustained at the 1-year follow-up only among the hypertriacylglycerolemic postmenopausal women. The anti-atherogenic status in normotriacylglycerolemic and hypertriacylglycerolemic postmenopausal women was changed by CT but without significant differences between groups. Furthermore, these benefits are sustained at the 1-year follow-up among the hypertriacylglycerolemic subjects.

Fenofibrate improves high-fat diet-induced and palmitate-induced endoplasmic reticulum stress and inflammation in skeletal muscle

AIMS

Fenofibrate (FF) is commonly used clinically as a lipid-lowering drug, but whether it participates in endoplasmic reticulum (ER) stress and decreases inflammation in skeletal muscle is still unknown. The aim of this study is to determine whether FF treatment reduces insulin resistance (IR) by alleviating ER stress and downstream inflammation in skeletal muscle tissues and cells.

MAIN METHODS

Female SD rats were randomly divided into groups receiving the standard chow diet (SCD), a high-fat diet (HFD), or HFD plus FF (HFD+FF). The rats in the latter two groups were subjected to a standard HFD for 20weeks, then the HFD+FF rats were administered FF (30mg/kg once daily via gavage) for another 8weeks. Whole-body IR, expression of peroxisome proliferator-activated receptor α (PPARα), ER stress-related genes, and inflammatory genes in the soleus muscle were assessed. The differentiated C2C12 myotubes were treated with palmitic acid or pretreated with fenofibric acid or 4-phenylbutyric acid (4-PBA), etomoxir, and the expression of ER stress, beta-oxidation-related genes, inflammatory genes, Toll-like receptor 4 (TLR4), and insulin-signaling-related molecules were determined.

KEY FINDINGS

Eight weeks of FF treatment attenuated HFD-induced IR by decreased tribbles 3 (TRB3) expression, ER stress and inflammation in skeletal muscle. FA pretreatment markedly inverted the PA-induced expression of TLR4 and downstream inflammatory genes, activated ER stress, improved β-oxidation and insulin signaling in differentiated myotube cells.

SIGNIFICANCE

FF treatment significantly improved HFD-induced IR in skeletal muscle and PA-induced IR in myotube cells, which may be related to reduced ER stress-induced inflammation.

Sphingolipids in High Fat Diet and Obesity-Related Diseases

Nutrient oversupply associated with a high fat diet (HFD) significantly alters cellular metabolism, and specifically including sphingolipid metabolism. Sphingolipids are emerging as bioactive lipids that play key roles in regulating functions, in addition to their traditional roles as membrane structure. HFD enhances de novo sphingolipid synthesis and turnover of sphingolipids via the salvage pathway, resulting in the generation of ceramide, and more specifically long chain ceramide species. Additionally, HFD elevates sphingomyelin and sphingosine-1 phosphate (S1P) levels in several tissues including liver, skeletal muscle, adipose tissue, and cardiovascular tissues. HFD-stimulated sphingolipid generation contributes to systemic insulin resistance, dysregulated lipid accumulation, and cytokine expression and secretion from skeletal muscle and adipose tissues, exacerbating obesity-related conditions. Furthermore, altered sphingolipid levels, particularly ceramide and sphingomyelin, are involved in obesity-induced endothelial dysfunction and atherosclerosis. In this review, HFD-mediated sphingolipid metabolism and its impact on HFD-induced biology and pathobiology will be discussed.

Relationship between moderate-to-vigorous physical activity, abdominal fat and immunometabolic markers in postmenopausal women

OBJECTS

To assess the burden of levels of physical activity, non-esterified fatty acids (NEFA), triacylglycerol and abdominal fat on the immunometabolic profile of postmenopausal women.

STUDY DESIGN

Forty-nine postmenopausal women [mean age 59.43 (standard deviation 5.61) years] who did not undertake regular physical exercise participated in this study. Body composition was assessed using dual-energy X-ray absorptiometry, and levels of NEFA, tumour necrosis factor-α, adiponectin, insulin and triacylglycerol were assessed using fasting blood samples. The level of physical activity was assessed using an accelerometer (Actigraph GTX3x), and reported as counts/min, time spent undertaking sedentary activities and time spent undertaking moderate-to-vigorous physical activity (MVPA). The following conditions were considered to be risk factors: (i) sedentary lifestyle (<150min of MVPA per week); (ii) high level (above median) of abdominal fat; and (iii) hypertriacylglycerolaemia (<150mg/dl of triacylglycerol).

RESULTS

In comparison with active women, sedentary women had higher levels of body fat (%) (p=0.041) and NEFA (p=0.064). Women with higher levels of abdominal fat had impaired insulin resistance (HOMA-IR) (p=0.016) and spent more time undertaking sedentary activities (p=0.043). Moreover, the women with two risk factors or more had high levels of NEFA and HOMA-IR (p<0.05), as well as an eight-fold higher risk of a high level of NEFA, independent of age (p<0.05). No significant relationship was found between levels of physical activity, abdominal fat, tumour necrosis factor-α and adiponectin (p>0.05).

CONCLUSION

Postmenopausal women with a combination of hypertriacylglycerolaemia, a high level of abdominal fat and a sedentary lifestyle are more likely to have metabolic disturbances.