Skeletal muscle ceramides do not contribute to physical-inactivity-induced insulin resistance

Physical inactivity increases the risk to develop type 2 diabetes, a disease characterized by a state of insulin resistance. By promoting inflammatory state, ceramides are especially recognized to alter insulin sensitivity in skeletal muscle. The present study was designed to analyze, in mice, whether muscle ceramides contribute to physical-inactivity-induced insulin resistance. For this purpose, we used the wheel lock model to induce a sudden reduction of physical activity, in combination with myriocin treatment, an inhibitor of de novo ceramide synthesis. Mice were assigned to 3 experimental groups: voluntary wheel access group (Active), a wheel lock group (Inactive), and wheel lock group treated with myriocin (Inactive-Myr). We observed that 10 days of physical inactivity induces hyperinsulinemia and increases basal insulin resistance (HOMA-IR). The muscle ceramide content was not modified by physical inactivity and myriocin. Thus, muscle ceramides do not play a role in physical-inactivity-induced insulin resistance. In skeletal muscle, insulin-stimulated protein kinase B phosphorylation and inflammatory pathway were not affected by physical inactivity, whereas a reduction of glucose transporter type 4 content was observed. Based on these results, physical-inactivity-induced insulin resistance seems related to a reduction in glucose transporter type 4 content rather than defects in insulin signaling. We observed in inactive mice that myriocin treatment improves glucose tolerance, insulin-stimulated protein kinase B, adenosine-monophosphate-activated protein kinase activation, and glucose transporter type 4 content in skeletal muscle. Such effects occur regardless of changes in muscle ceramide content. These findings open promising research perspectives to identify new mechanisms of action for myriocin on insulin sensitivity and glucose metabolism.

Assessing the Levels of L-Carnitine and Total Antioxidant Capacity in Adults With Newly Diagnosed and Long-Standing Type 2 Diabetes

OBJECTIVES

This study is essentially a correlative study that examines the potential of reduced levels of L-carnitine (LC) when combined with the pathophysiology of type 2 diabetes. The aim of the study was to assess the levels of LC, total antioxidant capacity (TAOC), fasting blood sugar (FBS), triglycerides and cholesterol in people with newly diagnosed and long-standing type 2 diabetes and in healthy controls.

METHODS

The study was done in 90 adult subjects, including 30 with newly diagnosed diabetes, 30 with long-standing type 2 diabetes and 30 healthy controls. Plasma samples were used to assay the biochemical parameters.

RESULTS

In this study, both groups (newly diagnosed and long-standing type 2 diabetes) were significantly different in baseline characteristics, such as age, height, weight, body mass index, FBS, cholesterol and triglycerides, compared to the healthy controls. Plasma LC levels in patients with newly diagnosed and long-standing type 2 diabetes were significantly lower than in healthy controls (p<0.001). Also, the mean plasma TAOC level in the patients with newly diagnosed and long-standing type 2 diabetes was slightly lower than in the healthy controls. Nevertheless, TAOC levels were not significantly different across all the groups (p=0.87). The plasma LC levels were significantly positive when compared to the plasma TAOC levels (r=0.516), which means that an increase in LC levels is associated with an increase in TAOC levels. However, a negative correlation was observed between LC levels and FBS (r=-0.387), triglycerides (-0.159) and body mass indexes (r=-0.068). This means that a decrease in LC levels is associated with increases in FBS, triglyceride and body mass index levels.

CONCLUSIONS

According to the effects of reduced LC levels on the metabolic profiles of patients with long-standing type 2 diabetes, setting the LC content value to prevent diabetes through the use of effective drugs or nutrition containing LC can be useful in managing diabetes.

The effect of exercise intensity and excess postexercise oxygen consumption on postprandial blood lipids in physically inactive men

Reductions in postprandial lipemia have been observed following aerobic exercise of sufficient energy expenditure. Increased excess postexercise oxygen consumption (EPOC) has been documented when comparing high- versus low-intensity exercise. The contribution of EPOC energy expenditure to alterations in postprandial lipemia has not been determined. The purpose of this study was to evaluate the effects of low- and high-intensity exercise on postprandial lipemia in healthy, sedentary, overweight and obese men (age, 43 ± 10 years; peak oxygen consumption, 31.1 ± 7.5 mL·kg^-1·min^-1; body mass index, 31.8 ± 4.5 kg/m²) and to determine the contribution of EPOC to reductions in postprandial lipemia. Participants completed 4 conditions: nonexercise control, low-intensity exercise at 40%-50% oxygen uptake reserve (LI), high-intensity exercise at 70%-80% oxygen uptake reserve (HI), and HI plus EPOC re-feeding (HI+EERM), where the difference in EPOC energy expenditure between LI and HI was re-fed in the form of a sports nutrition bar (Premier Nutrition Corp., Emeryville, Calif., USA). Two hours following exercise participants ingested a high-fat (1010 kcals, 99 g sat fat) test meal. Blood samples were obtained before exercise, before the test meal, and at 2, 4, and 6 h postprandially. Triglyceride incremental area under the curve was significantly reduced following LI, HI, and HI+EERM when compared with nonexercise control (p < 0.05) with no differences between the exercise conditions (p > 0.05). In conclusions, prior LI and HI exercise equally attenuated postprandial triglyceride responses to the test meal. The extra energy expended during EPOC does not contribute significantly to exercise energy expenditure or to reductions in postprandial lipemia in overweight men.

Dietary intake and cardiometabolic biomarkers in relation to insulin resistance and hypertension in a middle-aged and elderly population in Beijing, China

This study investigated the relationships of dietary intake and cardiometabolic biomarkers with insulin resistance and hypertension in rural middle-aged and elderly people in China. One hundred and eight middle-aged and elderly adults were recruited in Zhangfang village in May 2014. We measured blood pressure, anthropometric parameters, and biochemical indexes, including high-sensitivity C-reactive protein (hsCRP), soluble intercellular adhesion molecule-1 (sICAM-1), glucose, insulin, and blood lipids. Homeostasis model assessment of insulin resistance index (HOMA-IR) was assessed on the basis of fasting glucose and insulin. We recorded participant demographic characteristics, dietary intake, and lifestyle using questionnaires. Hypertensive participants had higher levels of triglycerides (TG), hsCRP, sICAM-1, body fat percentage (BF%), arm muscle circumference (AMC) and HOMA-IR than nonhypertensive individuals. Hypertensive participants had higher carbohydrate intake but lower intakes of protein and fat. Carbohydrate intake was positively correlated with hsCRP, sICAM-1, TG, BF%, and HOMA-IR, and was negatively correlated with AMC. Protein and fat intakes were negatively correlated with hsCRP and sICAM-1. Protein intake was also significantly negatively correlated with TG and HOMA-IR, and positively correlated with AMC. HOMA-IR was positively correlated with hsCRP, sICAM-1, TG and BF%, and negatively correlated with AMC. Multivariable linear regression indicated that TG, sICAM-1, and hsCRP were significantly associated with HOMA-IR. In conclusion, in a rural Chinese population, high intake of carbohydrate and low intake of fat and protein were associated with insulin resistance and hypertension, possibly by increasing inflammatory factors such as sICAM-1 and hsCRP, increasing BF% and increasing the level of plasma TG.

Adaptations to excess choline in insulin resistant and Pcyt2 deficient skeletal muscle

It was hypothesized that choline supplementation in insulin resistant (IR) CTP:phosphoethanolamine cytidylyltransferase deficient (Pcyt2^+/-) mice would ameliorate muscle function by remodeling glucose and fatty acid (FA) metabolism. Pcyt2^+/- mice either received no treatment or were allowed access to 2 mg/mL choline in drinking water for 4 weeks. Skeletal muscle was harvested from choline treated and untreated mice. Lipid analysis and metabolic gene expression and signaling pathways were compared between untreated Pcyt2^+/- mice, treated Pcyt2^+/- mice, and Pcyt2^+/+ mice. The major positive effect of choline supplementation on IR muscle was the reduction of glucose utilization for FA and triglyceride (TAG) synthesis and increased muscle glucose storage as glycogen. Choline reduced the expression of genes for FA and TAG formation (Scd1, Fas, Srebp1c, Dgat1/2), upregulated the genes for FA oxidation (Cpt1, Pparα, Pgc1α), and had minor effects on phospholipid and lipolysis genes. Pcyt2^+/- muscle had reduced insulin signaling (IRS1), autophagy (LC3), and choline transport (CTL1) proteins that were restored by choline treatment. Additionally, choline activated AMPK and Akt while inhibiting mTORC1 phosphorylation. These data established that choline supplementation could restore muscle glucose metabolism by reducing lipogenesis and improving mitochondrial and intracellular signaling for protein and energy metabolism in insulin resistant Pcyt2 deficient mice.

Metabolic syndrome in people with a long-standing spinal cord injury: associations with physical activity and capacity

This study investigated (i) the prevalence of the metabolic syndrome (MetS) in people with a long-standing spinal cord injury (SCI); (ii) whether personal or lesion characteristics are determinants of the MetS; and (iii) the association with physical activity or peak aerobic capacity on the MetS. In a cross-sectional study, persons with SCI (N = 223; time since injury of ≥10 years) were tested. The individual components of the MetS were assessed together with the physical activity measured by the Physical Activity Scale for Individuals with Physical Disabilities (PASIPD), while peak aerobic capacity was tested during a graded wheelchair exercise test on a treadmill. Thirty-nine percent of the participants had MetS. In a multivariate logistic regression analyses and after performing a backward regression analysis, only age and education were significant determinants of the MetS. A 10-year increase in age leads to a 1.5 times more chance to have the MetS. Furthermore, people with a low education will multiply the relative risk of MetS compared with people with high education by almost 2. With and without correcting for confounders, no significant relationship was found between PASIPD or peak aerobic capacity and the MetS. It can be concluded that the prevalence of the MetS is high (39%) in people with a long-standing SCI but is comparable to the general Dutch population. Older people and those with a lower education level are most at risk for the MetS. Physical activity and peak aerobic fitness were not related to the MetS in this group with a long-standing SCI.

Cholesterol ester transfer protein polymorphism rs5882 is associated with triglyceride-lowering in response to plant sterol consumption

Recent work suggests that plant sterol (PS) consumption may lower triglyceride (TG) concentrations; however, human clinical trial evidence is inconsistent. We associated SNP r5882 in cholesteryl ester transfer protein with changes in TG concentrations following PS consumption (2 g/day for 4 weeks) in a dual-centre, single-blind, randomized, crossover trial. TG concentrations were lowered in homozygotes for the minor G-allele of rs5882 (-0.46 ± 0.13 mmol/L, p = 0.002, n = 10); there was no effect in the A-allele carriers.

Diabetic dyslipidemia: from evolving pathophysiological insight to emerging therapeutic targets

Diabetic dyslipidemia is characterized by hepatic very low density lipoprotein (VLDL) and intestinal chylomicron overproduction, reduced high density lipoprotein cholesterol (HDL-C) level, increased propensity of small dense LDL (sdLDL) and increased postprandial lipemia. This dyslipidemic profile is also strongly linked to other features of the metabolic syndrome. Diabetic dyslipidemia is a well-recognized risk factor for atherosclerotic cardiovascular diseases. Currently, statins remain the first line therapy primarily through reducing the atherogenic LDL. Clinical trials on other lipid modifying agents were met with variable success in selective patient populations. Emerging new insights into the pathophysiology of lipid metabolism, in general, and diabetic dyslipidemia, in particular, have opened up potentially novel therapeutic strategies to further reduce the risk associated with diabetic dyslipidemia and insulin resistant state.