Sambucus nigra (elder) has been documented as a traditional treatment of diabetes. In the present study, an aqueous extract of elder (AEE, 1 g/L) significantly increased 2-deoxy-glucose transport, glucose oxidation and glycogenesis of mouse abdominal muscle in the absence of added insulin (2 x 2 factorial design). in acute 20-min tests, 0.25-1 g/L AEE evoked a stepwise stimulation of insulin secretion from clonal pancreatic beta-cells. The insulin releasing effect of AEE (0.5 g/L) was significantly potentiated by 16.7 mmol/L of glucose and significantly reduced by 0.5 mmol/L of diazoxide. AEE did not further enhance insulin secretion in cells stimulated by 10 mmol/L of L-alanine, 1 mmol/L of 3-isobutyl-1-methylxanthine or a depolarizing concentration of KCl (25 mmol/L). Prior exposure of clonal pancreatic beta-cells to AEE did not alter subsequent stimulation of insulin secretion induced by 10 mmol/L of L-alanine, thereby precluding a detrimental effect on cell viability. The insulinotropic action of AEE was partially dependent upon use of heat during extract preparation. Activity of AEE was heat-stable, acetone-insoluble and unaltered by prolonged exposure to acid/alkali (0.1 mol/L of HCl and NaOH). However, activity was significantly decreased 41% by dialysis to remove components with molecular mass <2000 Da. Sequential extraction with solvents revealed activity in both methanol and water fractions, indicating a cumulative effect of more than one extract constituent. Known constituents of elder, including lectin, rutin and the lipophilic triterpenoid (lupeol) and sterol (beta-sitosterol), did not stimulate insulin secretion. The results demonstrate the presence of insulin-releasing and insulin-like activity in the traditional antidiabetic plant, Sambucus nigra.

A novel insulin-secreting cell line (BRIN-BD11) was established after electrofusion of RINm5F cells with New England Deaconess Hospital rat pancreatic islet cells. Wells of cell fusion mixture with insulin output 5-10 times greater than parent RINm5F cells were subcultured with eventual establishment of clones, including BRIN-BD11. Morphological studies established that these cells grow as monolayers with epithelioid characteristics, maintaining stability in tissue culture for > 50 passages. Culture of these cells for 24 h at 5.6-33.3 mmol/l glucose revealed a 1.8- to 2.0-fold increase of insulin output compared with 1.4 mmol/l glucose. Dynamic insulin release was recorded in response to 16.7 mmol/l glucose, resulting in a rapid threefold insulin secretory peak followed by a sustained output slightly above basal. In acute 20-min tests, 4.2-16.7 mmol/l glucose evoked a stepwise two- to three-fold stimulation of insulin release. 3-Isobutyl-1-methylxanthine (1 mmol/l) served to increase basal and glucose-stimulated insulin release, shifting the threshold from 4.4 to 1.1 mmol/l glucose. Stimulation of insulin secretion with 16.7 mmol/l glucose was abolished by mannoheptulose or diazoxide (15 or 0.5 mmol/l). In contrast, glyceraldehyde (10 mmol/l) and 25 mmol/l K+ evoked 1.7- to 9.0-fold insulin responses. L-Alanine (10 mmol/l) evoked a twofold secretory response, which was potentiated 1.4-fold by increasing the Ca2+ concentration from 1.28 to 7.68 mmol/l. Forskolin (25 mumol/l) and phorbol 12-myristate 13-acetate (10 nmol/l) both increased insulin secretion in the presence of L-alanine (1.4- and 1.8-fold, respectively). Western blotting confirmed that BRIN-BD11 cells expressed the GLUT2 glucose transporter. This, coupled with a high glucokinase/hexokinase ratio in the cells, confirms an intact glucose sensing mechanism. High-performance liquid chromatography analysis demonstrated that insulin was the major product secreted under stimulatory conditions. Collectively, these data indicate that the BRIN-BD11 cell line represents an important stable glucose-responsive insulin-secreting beta-cell line for future studies.

A B S T R A C TThe aim of this study was to design a controlled release vehicle for insulin to preserve its stability and biological activity during fabrication and release. A modified, double emulsion, solvent evaporation, technique using homogenisation force optimised entrapment efficiency of insulin into biodegradable nanoparticles (NP) prepared from poly (DL-lactic-co-glycolic acid) (PLGA) and its PEGylated diblock copolymers. Formulation parameters (type of polymer and its concentration, stabiliser concentration and volume of internal aqueous phase) and physicochemical characteristics (size, zeta potential, encapsulation efficiency, in vitro release profiles and in vitro stability) were investigated. In vivo insulin sensitivity was tested by diet-induced type II diabetic mice. Bioactivity of insulin was studied using Swiss TO mice with streptozotocin-induced type I diabetic profile. Insulin-loaded NP were spherical and negatively charged with an average diameter of 200-400 nm. Insulin encapsulation efficiency increased significantly with increasing ratio of co-polymeric PEG. The internal aqueous phase volume had a significant impact on encapsulation efficiency, initial burst release and NP size. Optimised insulin NP formulated from 10% PEG-PLGA retained insulin integrity in vitro, insulin sensitivity in vivo and induced a sustained hypoglycaemic effect from 3 h to 6 days in type I diabetic mice..

Aims/hypothesis Abnormal cannabidiol (Abn-CBD) and AS-1269574 are potent selective agonists for GPR55 and GPR119, respectively. The present study evaluated the actions and ability of these small-molecule agonists to counteract experimental diabetes in mice. Methods Diabetes was induced in NIH Swiss mice by five consecutive daily intraperitoneal injections of 40 mg/(kg body weight) streptozotocin. Diabetic mice received daily oral administration of Abn-CBD or AS-1269574 (0.1 μmol/kg) or saline vehicle (0.9% wt/vol. NaCl) over 28 days. Body weight, food intake, fluid intake, plasma glucose, insulin, glucose tolerance, insulin release, lipid profile and pancreatic morphology were examined. Mechanism of action of agonists was assessed in acute studies using incretin-receptor-knockout mice. Results Abn-CBD and AS-1269574 decreased plasma glucose (20-26%, p < 0.05) and increased circulating insulin (47-48%, p < 0.05) by 10-28 days, compared with saline-treated diabetic controls. Food intake and polydipsia were reduced by both agonists (21-23%, p < 0.05 and 33-35%, p < 0.01, respectively). After 28 days of treatment, plasma glucagon concentrations were reduced (p < 0.01) and glucose tolerance was enhanced by 19-44% by Abn-CBD (p < 0.05 or p < 0.001) and AS-1269574 (p < 0.05 to p < 0.001). Plasma insulin responses were improved (p < 0.01) and insulin resistance was decreased (p < 0.05 or p < 0.01) in both Abn-CBD-and AS-1269574-treated groups. Triacylglycerols were decreased by 19% with Abn-CBD (p < 0.05) and 32% with AS-1269574 (p < 0.01) while total cholesterol was reduced by 17% (p < 0.01) and 15% (p < 0.05), respectively. Both agonists enhanced beta cell proliferation (p < 0.001) although islet area was unchanged. Acute studies in Gipr-and Glp1r-knockout mice revealed an important role for the glucagon-like peptide 1 (GLP-1) receptor in the actions of both agonists, with the glucose-lowering effects of Abn-CBD also partly mediated through the glucosedependent insulinotropic peptide (GIP) receptor. Conclusions/interpretation These data highlight the potential for fatty acid G-protein-coupled receptor-based therapies as novel insulinotropic and glucose-lowering agents acting partly through the activation of incretin receptors.

1 The cyclic nucleotide phosphodiesterases (PDEs) present in an insulin secreting cell line, BRIN ± BD11, were characterized using calcium/calmodulin, IGF-1, isoenzyme-selective PDE inhibitors and RT ± PCR. 2 Calmodulin activated cyclic AMP or cyclic GMP PDE activity in pellet and was 3 fold (P=0.002) more potent in activating cyclic nucleotide hydrolysis in pellet compared with supernatant fractions. 3 The PDE1/PDE5 inhibitor zaprinast inhibited both cyclic AMP and cyclic GMP PDE activity in both pellet and supernatant fractions of cell homogenates by a maximum of around 25% (IC 50 1 ± 5 mM), while rolipram (PDE4 selective) inhibited only cyclic AMP hydrolysis. 4 The PDE3-selective inhibitors Org 9935 (0.02 ± 10 mM) and siguazodan (0.1 ± 10 mM) inhibited cyclic AMP PDE activity in the pellet but not the supernatant fractions of cell homogenates, with a maximum inhibition of about 30%. IGF-1 (2 ± 7.5 ng ml 71) potently augmented this PDE activity. 5 RT ± PCR using speci®c primers for PDE3B, but not for PDE3A, ampli®ed, from BRIN ± BD11 cell total RNA, a 351 base pair product that was 497% homologous with rat adipose tissue PDE3B. 6 IBMX, Org 9935, siguazodan and rolipram (1 ± 50 mM), but not zaprinast, each augmented glucose-induced insulin secretion in the presence of 16.7 mM but not 1 mM glucose. 7 These ®ndings, in a clonal insulin secreting cell line, are consistent with an important role for PDE3B in regulating the pool of cyclic AMP relevant to the modulation of glucose-induced insulin secretion.

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The glycation of immunoreactive insulin (IRI) was assessed in extracts of pancreas and islets from control and hyperglycemic animal models. Glycated and nonglycated IRI were separated by affinity chromatography and quantified by radioimmunoassay. Hydrocortisone-treated Wistar rats (80 mg x kg-1 x day-1 and obese hyperglycemic (ob/ob) mice showed significant increases in plasma glucose (P < 0.001), percentage glycated hemoglobin (P < 0.001), plasma IRI (P < 0.01), and total pancreatic IRI content (P < 0.01), compared with their respective controls. These diabetic groups also demonstrated significant increases (P < 0.05) in the percentage of glycated pancreatic IRI above the controls. Streptozotocin-treated (200 mg/kg) Swiss TO mice exhibited significant increases in plasma glucose (P < 0.001), glycated hemoglobin (P < 0.001), and percentage glycated pancreatic IRI (P < 0.05), compared with untreated controls, despite a marked decrease in both plasma IRI (P < 0.001) and total pancreatic IRI content (P < 0.001). Significant elevations in the percentage of glycated IRI were also observed in islets isolated from obese hyperglycemic (ob/ob) mice (P < 0.001), compared with islets from lean controls, and when lean mouse islets were cultured in hyperglycemic media for 24 h (33.3 vs. 5.6 mmol/l D-glucose; P < 0.001). The contribution of glycated plus nonglycated insulin and proinsulin to the total IRI was estimated in lean and obese mouse pancreatic extracts following high-performance liquid chromatography separation. The contribution of proinsulin to the total IRI was approximately 10%. Proinsulin represented 27-28% of the total glycated IRI. These data indicate that the glycation of insulin and proinsulin occurs within the pancreatic islets and is elevated in both insulin-deficient and insulin-resistant diabetic animal models.

Characteristics of cellular insulin glycation were examined in the pancreatic B-cell line, BRIN-BD11. The extent of insulin glycation increased stepwise during 72 h of culture at 5.6-33.3 mmol/l glucose, attaining levels up to 27%. Glycation of insulin at 33.3 mmol/l glucose was rapid, reaching maximal values within 2 h, and not readily reversible during 2 to 24 h of subsequent exposure to 5.6 mmol/l glucose. Glycated insulin was readily secreted by BRIN-BD11 cells upon active stimulation with glucose and other secretagogues. Cellular insulin glycation was decreased by 66-80% by inhibitors of protein glycation, vitamin C, aminoguanidine or acetylsalicylic acid. Modulation of insulin-secretory activity of BRIN-BD11 cells by co-culture at high glucose with diazoxide. L-alanine or glibenclamide indicated that long-term stimulation of secretion was associated with a decrease in the extent of insulin glycation. Glycation of insulin in vitro was substantially less extensive than in BRIN-BD11 cells, although glucose-6-phosphate and glyceraldehyde-3-phosphate were 1.4- to 2.0-fold more reactive than glucose per se. These observations indicate that insulin is readily glycated and secreted from insulin-secreting cells under hyperglycaemic conditions in culture.