In this work, the effect of oxidation pretreatment on the enzymatic hydrolysis of cellulose in tobacco stems was evaluated. A comparison was made between the effect of H2O2 pretreatment and conventional alkali pretreatment on the weight loss of cellulose, lignins and hemicelluloses of tobacco stems. The effects of H2O2 concentration, pretreatment time and temperature on the enzymatic hydrolysis of tobacco stems were investigated. This pretreatment could give a higher recovery of cellulose and better removal of lignin and hemicellulose than alkali‐only pretreatment. Compared with the untreated stems, the yield of reducing sugar pretreated by H2O2 pretreatment (pH 11.5, 0.6% H2O2) for 9 h at 60C increased 347.2%. The results of scanning electron microscope and X‐ray diffraction analysis also showed that the structural and crystalline properties of the tobacco stems were changed by pretreatment, and they were in favor of the following enzymatic hydrolysis. The optimal pretreatment conditions were 60C of temperature, 0.6% of H2O2 concentration and 9 h of time, which were calculated by orthogonal experiments. PRACTICAL APPLICATIONS Pretreatment on lignocellulosic materials to disrupt the recalcitrant structure is helpful for their bioconversion into low‐molecular weight substances. The tobacco stems were pretreated by H2O2 oxidation before subjecting to enzymatic hydrolysis by cellulase in this work. This pretreatment was confirmed effectively to improve the recovery of celllulose, and helpful to remove lignin and hemicellulose. Moreover, the yield of reducing sugar produced by cellulase hydrolysis was apparently improved. These results were helpful for the extensive development of tobacco stems.

No abstract

Islet inflammation is the hallmark of all types of diabetes mellitus (DM). 1,2 Accumulated evidence indicates that chronic islet inflammation exerts a strong role in pancreatic β-cell dysfunction, including impaired insulin secretion function and diminished mass of islet β-cells. 3 IL-1β has been identified as a main inflammatory mediator of eliciting islet β-cell injury in diabetes, 4 and animal studies and clinical trials blocking IL-1β signalling pathway have proved to ameliorate β-cell function and improve glucose homeostasis in DM, 5,6 yet the mechanism by which IL-1β impairs islet β-cell biology is not completely understood.

Calcium/calmodulin-dependent serine protein kinase (CASK) is involved in the secretion of insulin vesicles in pancreatic β-cells. The current study revealed a new in vivo role of CASK in glucose homeostasis during the progression of type 2 diabetes mellitus (T2DM). A Cre-loxP system was used to specifically delete the Cask gene in mouse β-cells (βCASKKO), and glucose metabolism was evaluated in βCASKKO mice fed a normal chow diet (ND) or a high-fat diet (HFD). ND-fed mice exhibited impaired insulin secretion in response to glucose stimulation. Transmission electron microscopy showed significantly reduced numbers of insulin granules at or near the cell membrane in the islets of βCASKKO mice. By contrast, HFD-fed βCASKKO mice showed reduced blood glucose and a partial relief of hyperinsulinemia and insulin resistance when compared with HFD-fed wild-type mice. The IRS1/PI3K/AKT signaling pathway was upregulated in the adipose tissue of HFD-fed βCASKKO mice. These results indicated that knockout of the Cask gene in β-cells had a diverse effect on glucose homeostasis; it reduced insulin secretion in ND-fed mice but improved insulin sensitivity in HFD-fed mice. Therefore, CASK appears to function in insulin secretion and contributes to hyperinsulinemia and insulin resistance during the development of obesity-related T2DM.

Peroxisome proliferator-activated receptor-γ (PPAR-γ) is expressed in pancreatic β cells and is involved in insulin secretion. However, the precise mechanisms remain unclear. Calcium/calmodulin-dependent serine protein kinase (CASK), which plays a vital role in the anchoring of insulin granules on pancreatic β cell membrane, is probably a downstream of the transcription factor PPAR-γ. The aim of the present study was to investigate the correlation among PPAR-γ, CASK and insulin secretion. We found that rosiglitazone (RSG) had a positive effect on the expression of CASK and PPAR-γ in INS-1 cells as shown by real-time polymerase chain reaction (PCR) and western blot analysis, but did not change the cellular location of CASK as shown by immunofluorescence assay. Knockdown of PPAR-γ significantly attenuated the mRNA and protein expression levels of CASK. ChIP-qPCR and luciferase assays showed that PPAR-γ bound with the Cask promoter, and promoter activity of Cask was elevated by RSG. RSG significantly enhanced the insulin secretion with potassium stimulation, but did not alter the insulin content as shown by potassium-stimulated insulin secretion assay. In addition, with RSG pretreatment, knockdown of Cask did not significantly affect the PPAR-γ activation-mediated insulin secretion. Moreover, electron microscopy demonstrated that with RSG pretreatment, silence of Cask did not change the number of vesicles anchored on the cell membranes compared with those in siCask-treated cells. Overall, the present study identifies that CASK is one of the PPAR-γ downstream targets and PPAR-γ exerts a positive effect on the expression of CASK in INS-1 cells. PPAR-γ activation increases insulin secretion independent of the upregulation of CASK.