Dipeptidyl peptidase 4 inhibitor sitagliptin protected against dextran sulfate sodium-induced experimental colitis by potentiating the action of GLP-2.

Dipeptidyl peptidase 4 (DPP4), a ubiquitously expressed protease that cleaves off the N-terminal dipeptide from proline and alanine on the penultimate position, has important roles in many physiological processes. In the present study, experimental colitis was induced in mice receiving 3% dextran sulfate sodium (DSS) in drinking water. We found that mice with DSS-induced colitis had significantly increased intestinal DPP activity and decreased serum DPP activity, suggesting a probable correlation of DPP4 with experimental colitis. Then, we investigated whether sitagliptin, a specific DPP4 inhibitor could protect against DSS-induced colitis. We showed that oral administration of single dose of sitagliptin (30 mg/kg) on D7 remarkably inhibited DPP enzyme activity in both serum and intestine of DSS-induced colitic mice. Repeated administration of sitagliptin (10, 30 mg/kg, bid, from D0 to D8) significantly ameliorated DSS-induced colitis, including reduction of disease activity index (DAI) and body weight loss, improvement of histological score and colon length. Sitagliptin administration dose-dependently increased plasma concentrations of active form of GLP-1 and colonic expression of GLP-2R. Co-administration of GLP-2R antagonist GLP-23-33 (500 µg/kg, bid, sc) abolished the protective effects of sitagliptin in DSS-induced colitic mice. Moreover, sitagliptin administration significantly decreased the ratio of apoptotic cells and increased the ratio of proliferative cells in colon epithelium of DSS-induced colitic mice, and this effect was also blocked by GLP-23-33. Taken together, our results demonstrate that sitagliptin could attenuate DSS-induced experimental colitis and the effects can be attributed to the enhancement of GLP-2 action and the subsequent protective effects on intestinal barrier by inhibiting epithelial cells apoptosis and promoting their proliferation. These findings suggest sitagliptin as a novel therapeutic approach for the treatment of ulcerative colitis.

OL3, a novel low-absorbed TGR5 agonist with reduced side effects, lowered blood glucose via dual actions on TGR5 activation and DPP-4 inhibition.

AIM: TGR5 agonists stimulate intestinal glucagon-like peptide-1 (GLP-1) release, but systemic exposure causes unwanted side effects, such as gallbladder filling. In the present study, linagliptin, a DPP-4 inhibitor with a large molecular weight and polarity, and MN6, a previously described TGR5 agonist, were linked to produce OL3, a novel low-absorbed TGR5 agonist with reduced side-effects and dual function in lowering blood glucose by activation of TGR5 and inhibition of DPP-4. METHODS: TGR5 activation was assayed in HEK293 cells stably expressing human or mouse TGR5 and a CRE-driven luciferase gene. DPP-4 inhibition was assessed based on the rate of hydrolysis of a surrogate substrate. GLP-1 secretion was measured in human enteroendocrine NCI-H716 cells. OL3 permeability was tested in Caco-2 cells. Acute glucose-lowering effects of OL3 were evaluated in ICR and diabetic ob/ob mice. RESULTS: OL3 activated human and mouse TGR5 with an EC50 of 86.24 and 17.36 nmol/L, respectively, and stimulated GLP-1 secretion in human enteroendocrine NCI-H716 cells (3-30 µmol/L). OL3 inhibited human and mouse DPP-4 with IC50 values of 18.44 and 69.98 µmol/L, respectively. Low permeability of OL3 was observed in Caco-2 cells. In ICR mice treated orally with OL3 (150 mg/kg), the serum OL3 concentration was 101.10 ng/mL at 1 h, and decreased to 13.38 ng/mL at 5.5 h post dose, confirming the low absorption of OL3 in vivo. In ICR mice and ob/ob mice, oral administration of OL3 significantly lowered the blood glucose levels, which was a synergic effect of activating TGR5 that stimulated GLP-1 secretion in the intestine and inhibiting DPP-4 that cleaved GLP-1 in the plasma. In ICR mice, oral administration of OL3 did not cause gallbladder filling. CONCLUSION: OL3 is a low-absorbed TGR5 agonist that lowers blood glucose without inducing gallbladder filling. This study presents a new strategy in the development of potent TGR5 agonists in treating type 2 diabetes, which target to the intestine to avoid systemic side effects.

Intestinally-targeted TGR5 agonists equipped with quaternary ammonium have an improved hypoglycemic effect and reduced gallbladder filling effect.

TGR5 activation of enteroendocrine cells increases glucagon-like peptide 1 (GLP-1) release, which maintains glycemic homeostasis. However, TGR5 activation in the gallbladder and heart is associated with severe side effects. Therefore, intestinally-targeted TGR5 agonists were suggested as potential hypoglycemic agents with minimal side effects. However, until now no such compounds with robust glucose-lowering effects were reported, especially in diabetic animal models. Herein, we identify a TGR5 agonist, 26a, which was proven to be intestinally-targeted through pharmacokinetic studies. 26a was used as a tool drug to verify the intestinally-targeted strategy. 26a displayed a robust and long-lasting hypoglycemic effect in ob/ob mice (once a day dosing (QD) and 18-day treatment) owing to sustained stimulation of GLP-1 secretion, which suggested that robust hypoglycemic effect could be achieved with activation of TGR5 in intestine alone. However, the gallbladder filling effect of 26a was rather complicated. Although the gallbladder filling effect of 26a was decreased in mice after once a day dosing, this side effect was still not eliminated. To solve the problem above, several research strategies were raised for further optimization.

Yhhu4488, a novel GPR40 agonist, promotes GLP-1 secretion and exerts anti-diabetic effect in rodent models.

G protein-coupled receptor 40 (GPR40) is predominantly expressed in pancreatic ß-cells and activated by long-chain fatty acids. GPR40 has drawn considerable interest as a potential therapeutic target for type 2 diabetes mellitus (T2DM) due to its important role in enhancing glucose-stimulated insulin secretion (GSIS). Encouragingly, GPR40 is also proven to be highly expressed in glucagon-like peptide-1 (GLP-1)-producing enteroendocrine cells afterwards, which opens a potential role of GPR40 in enhancing GLP-1 secretion to exert additional anti-diabetic efficacy. In the present study, we discovered a novel GPR40 agonist, yhhu4488, which is structurally different from other reported GPR40 agonists. Yhhu4488 showed potent agonist activity with EC50 of 49.96 nM, 70.83 nM and 58.68 nM in HEK293 cells stably expressing human, rat and mouse GPR40, respectively. Yhhu4488 stimulated GLP-1 secretion from fetal rat intestinal cells (FRIC) via triggering endogenous calcium store mobilization and extracellular calcium influx. The effect of yhhu4488 on GLP-1 secretion was further confirmed in type 2 diabetic db/db mice. Yhhu4488 exhibited satisfactory potency in in vivo studies. Single administration of yhhu4488 improved glucose tolerance in SD rats. Chronic administration of yhhu4488 effectively decreased fasting blood glucose level, improved ß-cell function and lipid homeostasis in type 2 diabetic ob/ob mice. Taken together, yhhu4488 is a novel GPR40 agonist that enhances GLP-1 secretion, improves metabolic control and ß-cell function, suggesting its promising potential for the treatment of type 2 diabetes.

Emodin, an 11ß-hydroxysteroid dehydrogenase type 1 inhibitor, regulates adipocyte function in vitro and exerts anti-diabetic effect in ob/ob mice.

AIM: Emodin (1,3,8-trihydroxy-6-methylanthraquinone) is a potent and selective inhibitor of 11ß-hydroxysteroid dehydrogenase type 1 (11ß-HSD1) with the ability to ameliorate metabolic disorders in diet-induced obese mice. In the present study, we investigated the effects of emodin on adipocyte function and the underlying mechanisms in vitro, and its anti-diabetic effects in ob/ob mice. METHODS: 3T3-L1 adipocytes were used for in vitro studies. 11ß-HSD1A activity was evaluated with a scintillation proximity assay. The adipogenesis, glucose uptake, lipolysis and adiponectin secretion were investigated in 3T3-L1 adipocytes treated with emodin in the presence of active (corticosterone) or inactive glucocorticoid (11-dehydrocorticosterone). For in vivo studies, ob/ob mice were administered emodin (25 and 50 mg·kg⁻¹·d⁻¹, ip) for 26 d. On the last day of administration, the serum was collected and the mesenteric and perirenal fat were dissected for analyses. RESULTS: Emodin inhibited the 11ß-HSD1 activity in 3T3-L1 adipocytes in concentration- and time-dependent manners (the IC50 values were 7.237 and 4.204 µmol/L, respectively, after 1 and 24 h treatment. In 3T3-L1 adipocytes, emodin (30 µmol/L) suppressed 11-dehydrocorticosterone-induced adipogenesis without affecting corticosterone-induced adipogenesis; emodin (3 µmol/L) reduced 11-dehydrocorticosterone-stimulated lipolysis, but had no effect on corticosterone-induced lipolysis. Moreover, emodin (3 µmol/L) partly reversed the impaired insulin-stimulated glucose uptake and adiponectin secretion induced by 11-dehydrocorticosterone but not those induced by corticosterone. In ob/ob mice, long-term emodin administration decreased 11ß-HSD1 activity in mesenteric adipose tissues, lowered non-fasting and fasting blood glucose levels, and improved glucose tolerance. CONCLUSION: Emodin improves the inactive glucocorticoid-induced adipose tissue dysfunction by selective inhibition on 11ß-HSD1 in adipocyte in vitro and improves glycemic control in ob/ob mice.

Bioactive compounds from Peperomia pellucida.

Five new compounds (1-5), including two secolignans, two tetrahydrofuran lignans, and one highly methoxylated dihydronaphthalenone, were isolated from the whole plant of Peperomia pellucida. These compounds were accompanied by the known peperomins A, B, C, and E, 7,8-trans-8,8'-trans-7',8'-cis-7,7'-bis(5-methoxy-3,4-methylenedioxyphenyl)-8-acetoxymethyl-8'-hydroxymethyltetrahydrofuran, 7,8-trans-8,8'-trans-7',8'-cis-7-(5-methoxy-3,4-methylenedioxyphenyl)-7'-(4-hydroxy-3,5-dimethoxyphenyl)-8,8'-diacetoxymethyltetrahydrofuran, sesamin, and isoswertisin. New structures were elucidated mainly by NMR and MS techniques, and anticancer activities evaluated in HL-60, MCF-7, and HeLa cell lines. Compound 1 and peperomin E show growth inhibitory effects on the three cancer cell lines with IC(50) values ranging between 1.4 and 9.1 and between 1.8 and 11.1 microM, respectively. Compound 2 has a weak suppressive activity on HL-60 cells (IC(50) = 10.8 microM), while 7,8-trans-8,8'-trans-7',8'-cis-7,7'-bis(5-methoxy-3,4-methylenedioxyphenyl)-8-acetoxymethyl-8'-hydroxymethyltetrahydrofuran exhibits estrogen-like properties (EC(50) = 3.1 microM) in CV-1 cells transfected with human estrogen receptor (ERalpha).