Abstract. Photooxidation products of biogenic volatile organic compounds, mainly isoprene and monoterpenes, are significant sources of atmospheric particulate matter in forested regions. The objectives of this study were to examine time trends and diurnal variations of polar organic tracers for the photooxidation of isoprene and α-pinene to investigate whether they are linked with meteorological parameters or trace gases and to estimate their regional carbon contributions. PM2.5 (particulate matter with an aerodynamic diameter <2.5 μm) aerosol samples were collected from forests in eastern China and compared with data from forested sites in Europe and America. Aerosol sampling was conducted at four sites located along a gradient of ecological succession in four different regions of China, i.e. Changbai Mountain Nature Reserve (boreal-temperate), Chongming National Forest Park (temperate), Dinghu Mountain Nature Reserve (subtropical) and Jianfengling Nature Reserve (tropical) during summer periods when the meteorological conditions are believed to be favorable for photochemical processes. Fifty PM2.5 samples were collected; seventeen organic compounds, organic carbon (OC), elemental carbon and trace gases were measured. Results indicate that the concentration trends of the secondary organic compounds reflected those of the trace gases and meteorological parameters. The 24-h average concentrations of isoprene oxidation products, α-pinene oxidation products, sugars and sugar alcohols vary systematically along gradients of ecological succession, except malic acid which may have both biogenic and anthropogenic sources. The maximum carbon contribution of isoprene and α-pinene oxidation products to the OC was 2.4% (293 ng/m3, Changbai day-time) and 0.3% (41.3 ng/m3, Changbai night-time), respectively.
Sulforaphane (SFN) is a dietary component with multiple bioactivities; however, its role in obesity-related metabolic derangement remains unclear. Here, the effect of SFN on the glucose intolerance of obese mice and the underlying mechanism were determined. C57B/6J male mice were randomly divided into two groups, having free access to water and a normal-fat diet (ND, n = 6) or a high-fat diet (HFD, n = 33) for 8 weeks; thereafter twelve mice having the greatest weight gain among the HFD-fed mice were considered as obese mice. These obese mice were randomly divided into two groups and treated orally for 6 weeks with or without SFN (100 μmol per kg bw, 3 times per week). During this period the animals were continuously maintained on a ND or a HFD. Blood glucose and serum insulin were examined; then glucose tolerance and insulin resistance were evaluated. In addition, the expression of insulin signaling pathway-related genes in the muscle was determined. Our data showed that the obese mice presented a marked insulin resistance and glucose intolerance as compared to the control group, while SFN treatment exerted a prominently protective effect. In addition, the SFN-treated obese mice had a significantly increased insulin receptor substrate 1 (IRS-1) protein level (P < 0.05), markedly elevated Akt activation, as well as dramatically enhanced phosphorylation of PDK-1 (P < 0.05) when compared with the SFN-untreated obese mice. Moreover, the SFN-treated obese mice exhibited a significantly enhanced translocation of GLUT4 (P < 0.05) to the plasma membrane in the muscle compared to the obese mice without SFN treatment. In conclusion, our results support the notion that SFN acts as a promising agent to improve glucose tolerance through the up-regulation of insulin signaling mainly involving the IRS-1/Akt/GLUT4 pathway in the muscle.
Adipose tissue is functionally composed of brown adipose tissue and white adipose tissue. The unique thermogenic capacity of brown adipose tissue results from expression of uncoupling protein 1 in the mitochondrial inner membrane. On the basis of recent findings that adult humans have functionally active brown adipose tissue, it is now recognized as playing a much more important role in human metabolism than was previously thought. More importantly, brown-like adipocytes can be recruited in white adipose tissue upon environmental stimulation and pharmacologic treatment, and this change is associated with increased energy expenditure, contributing to a lean and healthy phenotype. Thus, the promotion of brown-like adipocyte development in white adipose tissue offers novel possibilities for the development of therapeutic strategies to combat obesity and related metabolic diseases. In this review, we summarize recent advances in understanding the molecular mechanisms involved in the recruitment of brown-like adipocyte in white adipose tissue.
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