Frequent interruptions of sedentary time modulates contraction- and insulin-stimulated glucose uptake pathways in muscle: Ancillary analysis from randomized clinical trials.

Epidemiological studies have observed associations between frequent interruptions of sitting time with physical activity bouts and beneficial metabolic outcomes, even in individuals who regularly exercise. Frequent interruptions to prolonged sitting reduce postprandial plasma glucose. Here we studied potential skeletal muscle mechanisms accounting for this improved control of glycemia in overweight adults under conditions of one day uninterrupted sitting and sitting interrupted with light-intensity or moderate-intensity walking every 20-min (n = 8); and, after three days of either uninterrupted sitting or light-intensity walking interruptions (n = 5). Contraction- and insulin-mediated glucose uptake signaling pathways as well as changes in oxidative phosphorylation proteins were examined. We showed that 1) both interventions reduce postprandial glucose concentration, 2) acute interruptions to sitting over one day stimulate the contraction-mediated glucose uptake pathway, 3) both acute interruptions to sitting with moderate-intensity activity over one day and light-intensity activity over three days induce a transition to modulation of the insulin-signaling pathway, in association with increased capacity for glucose transport. Only the moderate-intensity interruptions resulted in greater capacity for glycogen synthesis and likely for ATP production. These observations contribute to a mechanistic explanation of improved postprandial glucose metabolism with regular interruptions to sitting time, a promising preventive strategy for metabolic diseases.

Reduced UCP-1 content in in vitro differentiated beige/brite adipocytes derived from preadipocytes of human subcutaneous white adipose tissues in obesity.

INTRODUCTION: Brown adipose tissue (BAT) is a potential therapeutic target to reverse obesity. The purpose of this study was to determine whether primary precursor cells isolated from human adult subcutaneous white adipose tissue (WAT) can be induced to differentiate in-vitro into adipocytes that express key markers of brown or beige adipose, and whether the expression level of such markers differs between lean and obese young adult males. METHODS: Adipogenic precursor cells were isolated from lean and obese individuals from subcutaneous abdominal WAT biopsies. Cells were grown to confluence, differentiated for 2.5 weeks then harvested for measurement of gene expression and UCP1 protein. RESULTS: There was no difference between groups with respect to differentiation into adipocytes, as indicated by oil red-O staining, rates of lipolysis, and expression of adipogenic genes (FABP4, PPARG). WAT genes (HOXC9, RB1) were expressed equally in the two groups. Post differentiation, the beige adipose specific genes CITED1 and CD137 were significantly increased in both groups, but classic BAT markers ZIC1 and LHX8 decreased significantly. Cell lines from both groups also equally increased post-differentiation expression of the thermogenic-responsive gene PPARGC1A (PGC-1α). UCP1 gene expression was undetectable prior to differentiation, however after differentiation both gene expression and protein content were increased in both groups and were significantly greater in cultures from lean compared with obese individuals (p<0.05). CONCLUSION: Human subcutaneous WAT cells can be induced to attain BAT characteristics, but this capacity is reduced in WAT cells from obese individuals.

Potential vascular mechanisms of ramipril induced increases in walking ability in patients with intermittent claudication.

RATIONALE: We recently reported that ramipril more than doubled maximum walking times in patients with peripheral artery disease with intermittent claudication. OBJECTIVE: Our aim was to conduct exploratory analyses of the effects of ramipril therapy on circulating biomarkers of angiogenesis/arteriogenesis, thrombosis, inflammation, and leukocyte adhesion in patients with intermittent claudication. METHODS AND RESULTS: One hundred sixty-five patients with intermittent claudication (mean, 65.3 [SD, 6.7] years) were administered ramipril 10 mg per day (n=82) or matching placebo (n=83) for 24 weeks in a randomized, double-blind study. Plasma biomarkers of angiogenesis/arteriogenesis (vascular endothelial growth factor-A, fibroblast growth factor-2), thrombosis (D-dimer, von Willebrand factor, thrombin-antithrombin III), inflammation (high-sensitivity C-reactive protein, osteopontin), and leukocyte adhesion (soluble vascular cell adhesion molecule-1, soluble intracellular adhesion molecule-1) were measured at baseline and 24 weeks. Relative to placebo, ramipril was associated with increases in vascular endothelial growth factor-A by 38% (95% confidence interval [CI], 34%-42%) and fibroblast growth factor-2 by 64% (95% CI, 44-85%; P<0.001 for both), and reductions in D-dimer by 24% (95% CI, -30% to -18%), von Willebrand factor by 22% (95% CI, -35% to -9%), thrombin-antithrombin III by 16% (95% CI, -19% to -13%), high-sensitivity C-reactive protein by 13% (95% CI, -14% to -9%), osteopontin by 12% (95% CI, -14% to -10%), soluble vascular cell adhesion molecule-1 by 14% (95% CI, -18% to -10%), and soluble intracellular adhesion molecule-1 by 15% (95% CI, -17% to -13%; all P<0.001). With the exception of von Willebrand factor, all the above changes correlated significantly with the change in maximum walking time (P=0.02-0.001) in the group treated with ramipril. CONCLUSIONS: Ramipril is associated with an increase in the biomarkers of angiogenesis/arteriogenesis and reduction in the markers of thrombosis, inflammation, and leukocyte adhesion. This study informs strategies to improve mobility in patients with intermittent claudication. CLINICAL TRIAL REGISTRATION INFORMATION URL: http://clinicaltrials.gov. Unique identifier: NCT00681226.

Skeletal muscle insulin resistance associated with cholesterol-induced activation of macrophages is prevented by high density lipoprotein.

BACKGROUND: Emerging evidence suggests that high density lipoprotein (HDL) may modulate glucose metabolism through multiple mechanisms including pancreatic insulin secretion as well as insulin-independent glucose uptake into muscle. We hypothesized that HDL may also increase skeletal muscle insulin sensitivity via cholesterol removal and anti-inflammatory actions in macrophages associated with excess adiposity and ectopic lipid deposition. METHODS: Human primary and THP-1 macrophages were treated with vehicle (PBS) or acetylated low density lipoprotein (acLDL) with or without HDL for 18 hours. Treatments were then removed, and macrophages were incubated with fresh media for 4 hours. This conditioned media was then applied to primary human skeletal myotubes derived from vastus lateralis biopsies taken from patients with type 2 diabetes to examine insulin-stimulated glucose uptake. RESULTS: Conditioned media from acLDL-treated primary and THP-1 macrophages reduced insulin-stimulated glucose uptake in primary human skeletal myotubes compared with vehicle (primary macrophages, 168±21% of basal uptake to 104±19%; THP-1 macrophages, 142±8% of basal uptake to 108±6%; P<0.05). This was restored by co-treatment of macrophages with HDL. While acLDL increased total intracellular cholesterol content, phosphorylation of c-jun N-terminal kinase and secretion of pro- and anti-inflammatory cytokines from macrophages, none were altered by co-incubation with HDL. Insulin-stimulated Akt phosphorylation in human skeletal myotubes exposed to conditioned media was unaltered by either treatment condition. CONCLUSION: Inhibition of insulin-stimulated glucose uptake in primary human skeletal myotubes by conditioned media from macrophages pre-incubated with acLDL was restored by co-treatment with HDL. However, these actions were not linked to modulation of common pro- or anti-inflammatory mediators or insulin signaling via Akt.

Sex steroids modulate human aortic smooth muscle cell matrix protein deposition and matrix metalloproteinase expression.

Large artery stiffening increases cardiovascular risk and promotes isolated systolic hypertension which is more prevalent in elderly women than men. Variation in sex steroid levels between males and females and throughout life may modulate arterial stiffness. We hypothesized that sex steroids directly influence expression of important structural proteins which determine arterial biomechanical properties. Human aortic smooth muscle cells were incubated with physiological concentrations of 17beta-estradiol, progesterone, 17beta-estradiol and progesterone, or testosterone for 4 weeks. Collagen, elastin, and fibrillin-1 deposition was examined (histochemistry/immunohistochemistry). Gene and protein expression of 2 important matrix metalloproteinases (MMPs), MMPs 2 and 3, regulating matrix turnover was assessed. All sex steroids reduced collagen deposition relative to control (100%). However, the reduction was greater with female sex steroids than testosterone (control, 100%; 17beta-estradiol plus progesterone, 20+/-2%; testosterone 74+/-12%, P<0.001). Female sex steroids increased elastin deposition compared with control (control, 100%; 17beta-estradiol, 540+/-60%; progesterone, 290+/-40%; 17beta-estradiol plus progesterone, 400+/-80%, all P<0.01). The elastin/collagen ratio was >11-fold higher in the presence of 17beta-estradiol and progesterone compared with testosterone. Fibrillin-1 deposition was doubled in the presence of female sex steroids (17beta-estradiol plus progesterone) compared with testosterone (P<0.01). MMP-2 gene and protein expression was unaffected by any sex steroid. Testosterone increased both gene and protein expression of MMP-3 relative to both control and female sex steroids (P<0.01). This may contribute to degradation of elastic matrix proteins. In conclusion, female sex steroids promote an elastic matrix profile, which likely contributes to variation in large artery stiffness observed between sexes and with changes in hormonal status across the lifespan.