The Modulatory Action of Vitamin D on the Renin-Angiotensin System and the Determination of Hepatic Insulin Resistance.

Vitamin D deficiency or hypovitaminosis D is associated with increased risks of insulin resistance, type 2 diabetes mellitus (T2DM) and its related non-alcoholic fatty liver disease (NAFLD). Meanwhile, inappropriate over-activation of the renin-angiotensin system (RAS) in the liver leads to the hepatic dysfunction and increased risk of T2DM, such as abnormalities in lipid and glucose metabolism. Our previous findings have shown that calcitriol, an active metabolite of vitamin D, reduces hepatic triglyceride accumulation and glucose output in diabetic db/db mice and human hepatocellular cell HepG2 cells under insulin-resistant conditions. Notwithstanding the existence of this evidence, the protective action of vitamin D in the modulation of overexpressed RAS-induced metabolic abnormalities in the liver under insulin resistance remains to be elusive and investigated. Herein, we have reported the potential interaction between vitamin D and RAS; and its beneficial effects on the expression and function of the RAS components in HepG2 cells and primary hepatocytes under insulin-resistance states. Our study findings suggest that hormonal vitamin D (calcitriol) has modulatory action on the inappropriate upregulation of the hepatic RAS under insulin-resistant conditions. If confirmed, vitamin D supplementation might provide a nutraceutical potential as a cost-effective approach for the management of hepatic metabolic dysfunction as observed in T2DM and related NAFLD.

GPR120 protects lipotoxicity-induced pancreatic ß-cell dysfunction through regulation of PDX1 expression and inhibition of islet inflammation.

G-protein coupled receptor 120 (GPR120) has been shown to act as an omega-3 unsaturated fatty acid sensor and is involved in insulin secretion. However, the underlying mechanism in pancreatic ß cells remains unclear. To explore the potential link between GPR120 and ß-cell function, its agonists docosahexaenoic acid (DHA) and GSK137647A were used in palmitic acid (PA)-induced pancreatic ß-cell dysfunction, coupled with GPR120 knockdown (KD) in MIN6 cells and GPR120 knockout (KO) mice to identify the underlying signaling pathways. In vitro and ex vivo treatments of MIN6 cells and islets isolated from wild-type (WT) mice with DHA and GSK137647A restored pancreatic duodenal homeobox-1 (PDX1) expression levels and ß-cell function via inhibiting PA-induced elevation of proinflammatory chemokines and activation of nuclear factor κB, c-Jun amino (N)-terminal kinases1/2 and p38MAPK signaling pathways. On the contrary, these GPR120 agonism-mediated protective effects were abolished in GPR120 KD cells and islets isolated from GPR120 KO mice. Furthermore, GPR120 KO mice displayed glucose intolerance and insulin resistance relative to WT littermates, and ß-cell functional related genes were decreased while inflammation was exacerbated in islets with increased macrophages in pancreas from GPR120 KO mice. DHA and GSK137647A supplementation ameliorated glucose tolerance and insulin sensitivity, as well as improved Pdx1 expression and islet inflammation in diet-induced obese WT mice, but not in GPR120 KO mice. These findings indicate that GPR120 activation is protective against lipotoxicity-induced pancreatic ß-cell dysfunction, via the mediation of PDX1 expression and inhibition of islet inflammation, and that GPR120 activation may serve as a preventative and therapeutic target for obesity and diabetes.

Exploring brusatol as a new anti-pancreatic cancer adjuvant: biological evaluation and mechanistic studies.

Pancreatic cancer is highly resistant to chemotherapeutic agents and is known to have a poor prognosis. The development of new therapeutic entities is badly needed for this deadly malignancy. In this study, we demonstrated for the first time that brusatol, a natural quassinoid isolated from a Chinese herbal medicine named Bruceae Fructus, possessed potent cytotoxic effect against different pancreatic adenocarcinoma cell lines. Its anti-pancreatic cancer effect was comparable to that of the first-line chemotherapeutic agents such as gemcitabine and 5-fluorouracil, with a more favorable safety profile. In addition, brusatol showed a synergistic anti-proliferative effect toward PANC-1 and Capan-2 cell lines when combined with gemcitabine or 5-fluorouracil. The results of flow cytometry suggested that brusatol combination treatment with gemcitabine or 5-fluorouracil was able to cause cell cycle arrest at G2/M phase, and accentuate apoptosis in PANC-1 cells. Moreover, brusatol deactivated gemcitabine/5-fluorouracil-induced NF-κB activation. Western blot analysis and qRT-PCR results showed that brusatol significantly down-regulated the expression of vimentin and Twist, and markedly stimulated the expression of E-cadherin, the key regulatory factors of the epithelial-mesenchymal transition process. Furthermore, treatment with combination of brusatol and gemcitabine or 5-fluorouracil significantly reduced in vivo tumor growth when compared with treatment of either brusatol or gemcitabine/5-fluorouracil alone. Taken together, these results have amply demonstrated that brusatol is a potent anti-pancreatic cancer natural compound, and the synergistic anti-pancreatic cancer effects of brusatol and gemcitabine/5-fluorouracil observed both in vitro and in vivo are associated with the suppression of epithelial-mesenchymal transition process, indicating that brusatol is a promising adjunct to the current chemotherapeutic regimen.

The Effects of Empagliflozin, an SGLT2 Inhibitor, on Pancreatic ß-Cell Mass and Glucose Homeostasis in Type 1 Diabetes.

The novel sodium glucose co-transporter 2 (SGLT2) inhibitor empagliflozin has recently been reported to improve glycemic control in streptozotocin-induced type 1 diabetic rats in an insulin-independent manner, via an increase in urinary glucose output. We investigated the potential of empagliflozin to recover insulin pathways in type 1 diabetes by improving pancreatic ß-cell mass. Blood glucose homeostasis was assessed by an intraperitoneal glucose tolerance test. Serum insulin levels and insulin mRNA expression were determined using commercial insulin ELISA kits and real-time quantitative polymerase chain reaction, respectively. Immunohistochemistry was used to investigate ß-cell areas, ß-cell proliferation, apoptosis of pancreatic ß-cells, and reactive oxygen species production in the pancreatic ß-cells. Results showed that glucose tolerance was significantly improved in streptozotocin-induced type 1 diabetic mice treated with empagliflozin. Empagliflozin-treated mice also showed an increase in insulin mRNA expression. Higher serum insulin levels were detected in mice treated with empagliflozin compared with the vehicle group. Immunohistochemistry indicated that ß-cell area/total pancreatic area and the expression of cell proliferation marker Ki-67 (co-stained with insulin) were significantly enhanced by empagliflozin treatment. These effects were due, probably, to a reduction in apoptosis and reactive oxygen species in the pancreatic ß-cells. Taken together, the results of this study indicate that empagliflozin may have a beneficial effect on preserving ß-cell regeneration, thus improving blood glucose homeostasis in type 1 diabetes mellitus, probably via the protection of pancreatic ß-cell from glucotoxicity-induced oxidative stress.

Involvement of the Niacin Receptor GPR109a in the LocalControl of Glucose Uptake in Small Intestine of Type 2Diabetic Mice.

Niacin is a popular nutritional supplement known to reduce the risk of cardiovascular diseases by enhancing high-density lipoprotein levels. Despite such health benefits, niacin impairs fasting blood glucose. In type 2 diabetes (T2DM), an increase in jejunal glucose transport has been well documented; however, this is intriguingly decreased during niacin deficient state. In this regard, the role of the niacin receptor GPR109a in T2DM jejunal glucose transport remains unknown. Therefore, the effects of diabetes and high-glucose conditions on GPR109a expression were studied using jejunal enterocytes of 10-week-old m+/db and db/db mice, as well as Caco-2 cells cultured in 5.6 or 25.2 mM glucose concentrations. Expression of the target genes and proteins were quantified using real-time polymerase chain reaction (RT-PCR) and Western blotting. Glucose uptake in Caco-2 cells and everted mouse jejunum was measured using liquid scintillation counting. 10-week T2DM increased mRNA and protein expression levels of GPR109a in jejunum by 195.0% and 75.9%, respectively, as compared with the respective m+/db control; high-glucose concentrations increased mRNA and protein expression of GPR109a in Caco-2 cells by 130.2% and 69.0%, respectively, which was also confirmed by immunohistochemistry. In conclusion, the enhanced GPR109a expression in jejunal enterocytes of T2DM mice and high-glucose treated Caco-2 cells suggests that GPR109a is involved in elevating intestinal glucose transport observed in diabetes.

Niacin-induced hyperglycemia is partially mediated via niacin receptor GPR109a in pancreatic islets.

The widely used lipid-lowering drug niacin is reported to induce hyperglycemia during chronic and high-dose treatments, but the mechanism is poorly understood. Recently, the niacin receptor [G-protein-coupled receptor, (GPR) 109a], has been localized to islet cells while its potential role therein remains unclear. We, therefore, aimed at investigating how GPR109a regulates islet beta-cell function and its downstream signaling using high-fat diet-induced obese mice and INS-1E beta cells. Eight-week niacin treatment elevated blood glucose concentration in obese mice with increased areas under the curve at oral glucose and intraperitoneal insulin tolerance tests. Additionally, niacin treatment significantly decreased glucose-stimulated insulin secretion (GSIS) but induced peroxisome proliferator-activated receptor gamma (Pparg) and GPR109a expression in isolated pancreatic islets; concomitantly, reactive oxygen species (ROS) were transiently increased, with decreases in GSIS, intracellular cyclic adenosine monophosphate (cAMP) accumulation and mitochondrial membrane potential (ΔΨm), but with increased expression of uncoupling protein 2 (Ucp2), Pparg and Gpr109a in INS-1E cells. Corroborating these findings, the decreases in GSIS, ΔΨm and cAMP production and increases in ROS, Pparg and GPR109a expression were abolished in INS-1E cells by GPR109a knockdown. Our data indicate that niacin-induced pancreatic islet dysfunction is probably modulated through activation of the islet beta-cell GPR109a-induced ROS-PPARγ-UCP2 pathways.

Use of herbal medicines and natural products: an alternative approach to overcoming the apoptotic resistance of pancreatic cancer.

Pancreatic cancer has a poor prognosis with a 5-year survival rate of <5%. It does not respond well to either chemotherapy or radiotherapy, due partly to apoptotic resistance (AR) of the cancer cells. AR has been attributed to certain genetic abnormalities or defects in apoptotic signaling pathways. In pancreatic cancer, significant mutations of K-ras and p53, constitutive activation of NFκB, over-expression of heat shock proteins (Hsp90, Hsp70), histone deacetylase (HDACs) and the activities of other proteins (COX-2, Nrf2 and bcl-2 family members) are closely linked with resistance to apoptosis and invasion. AR has also been associated with aberrant signaling of MAPK, PI3K-AKT, JAK/STAT, SHH, Notch, and Wnt/ß-catenin pathways. Strategies targeting these signaling molecules and pathways provide an alternative for overcoming AR in pancreatic cancer. The use of herbal medicines or natural products (HM/NPs) alone or in combination with conventional anti-cancer agents has been shown to produce beneficial effects through actions upon multiple molecular pathways involved in AR. The current standard first-line chemotherapeutic agents for pancreatic cancer are gemcitabine (Gem) or Gem-containing combinations; however, the efficacy is dissatisfied and this limitation is largely attributed to AR. Meanwhile, emerging data have pointed to a combination of HM/NPs that may augment the sensitivity of pancreatic cancer cells to Gem. Greater understanding of how these compounds affect the molecular mechanisms of apoptosis may propel development of HM/NPs as anti-cancer agents and/or adjuvant therapies forward. In this review, we give a critical appraisal of the use of HM/NPs alone and in combination with anti-cancer drugs. We also discuss the potential regulatory mechanisms whereby AR is involved in these protective pathways.

Involvement of the mitochondrial pathway in bruceine D-induced apoptosis in Capan-2 human pancreatic adenocarcinoma cells.

The fruit of Brucea javanica L. is a common herb used in Chinese medicine for the treatment of a variety of cancers. Our research group has previously identified bruceine D (BD), a quassinoid found abundantly in B. javanica, to have potent cytotoxic effect on a number of pancreatic cancer cell lines, including Panc-1, SW1990 and Capan-1 cells. In the present study, we showed that BD was also able to inhibit the growth of the Capan-2 human pancreatic adenocarcinoma cell line, but it exerted only modest cytotoxicity on the WRL68 human hepatocyte cell line and a human pancreatic progenitor cell line. The antiproliferative effects of BD were comparable to those exhibited by camptothecin and gemcitabine in our culture system. We found a dose-dependent decrease of the mitochondrial membrane potential in BD-treated Capan-2 cells as measured by the JC-1 assay. BD exposure was able to attenuate the expression of Bcl-2 protein in Capan-2 cells as detected by western blot analysis. In addition, the expression of both caspase 9 and caspase 3 in BD-treated Capan-2 cells was significantly accentuated. Moreover, BD was capable of inducing the fragmentation of genomic DNA in Capan-2 cells as evidenced by Hoechst staining. Cell cycle analysis demonstrated that BD could increase the percentage of Capan-2 cells in the subG1 phase in a dose-related manner. An increase in the apoptosis of Capan-2 cells was also observed by Annexin V and PI staining. These results unequivocally indicate that BD induces cytotoxicity in Capan-2 cells via the induction of cellular apoptosis involving the mitochondrial pathway.

Brucea javanica fruit induces cytotoxicity and apoptosis in pancreatic adenocarcinoma cell lines.

Brucea javanica fruit is thought to have anticancer properties in Chinese medicine and its extract has been shown to possess antiproliferative and pro-apoptotic activities on human carcinoma cells. In the present study we demonstrated for the first time that Fructus Bruceae extract exhibited cytotoxic effects on the three pancreatic adenocarcinoma cell lines, PANC-1, SW1990 and CAPAN-1; the effects were comparable to those exhibited by camptothecin in our culture system. In addition, Fructus Bruceae extract induced fragmentation of genomic DNA, as evidenced by Hoechst staining and the cell death detection ELISA(PLUS) assay. Western blot analysis further showed down-regulation of pro-caspase 3 protein expression, indicating that the observed cytotoxic effects of the extract were associated with induction of apoptosis. These findings are not only significant in the development of traditional Chinese medicine as an alternative treatment for pancreatic cancer, but also in the elucidation of the potential mechanism(s) of Fructus Bruceae extract in cancer therapy.