Exenatide-loaded PLGA microspheres with improved glycemic control: In vitro bioactivity and in vivo pharmacokinetic profiles after subcutaneous administration to SD rats

A subcutaneous exenatide delivery system was developed and characterized in vitro and in vivo. The results clearly showed that the exenatide loaded PLGA microspheres prepared by using a non-aqueous processing medium had low burst release and high drug encapsulation efficiency. Exenatide loaded in the microspheres preserved its bioactivity. The pharmacokinetics parameters were determined after subcutaneous administration of microspheres to SD rats. The plasma concentration of the single dose of the sustained-release microspheres attained C_max of 108.19 ± 14.92 ng/ml at t_max of 1.33 ± 0.58 h and the t_1/2 was 120.65 ± 44.18 h. There was a linear correlation between the in vitro and in vivo release behavior (R² = 0.888). Exenatide loaded microspheres may prove to have great potential for clinical use.     

Biological activity of AC3174, a peptide analog of exendin-4

Exenatide, the active ingredient of BYETTA (exenatide injection), is an incretin mimetic that has been developed for the treatment of patients with type 2 diabetes. Exenatide binds to and activates the known GLP-1 receptor with a potency comparable to that of the mammalian incretin GLP-1(7-36), thereby acting as a glucoregulatory agent. AC3174 is an analog of exenatide with leucine substituted for methionine at position 14, [Leu(14)]exendin-4. The purpose of these studies was to evaluate the glucoregulatory activity and pharmacokinetics of AC3174. In RINm5f cell membranes, the potency of AC3174 for the displacement of [(125)I]GLP-1 and activation of adenylate cyclase was similar to that of exenatide and GLP-1. In vivo, AC3174, administered as a single IP injection, significantly decreased plasma glucose concentration and glucose excursion following the administration of an oral glucose challenge in both non-diabetic (C57BL/6) and diabetic db/db mice (P<0.05 vs. vehicle-treated). The magnitude of glucose lowering of AC3174 was comparable to exenatide. The ED(50) values of AC3174 for glucose lowering (60 minute post-dose) were 1.2 microg/kg in db/db mice and 1.3 microg/kg in C57BL/6 mice. AC3174 has insulinotropic activity in vivo. Administration of AC3174 resulted in a 4-fold increase in insulin concentrations in normal mice following an IP glucose challenge. AC3174 was also shown to inhibit food intake and decrease gastric emptying in rodent models. AC3174 was stable in human plasma (>90% of parent peptide was present after 5 h of incubation). In rats, the in vivo half-life of AC3174 was 42-43 min following SC administration. In summary, AC3174 is an analog of exenatide that binds to the GLP-1 receptor in vitro and shares many of the biological and glucoregulatory activities of exenatide and GLP-1 in vivo.     

Circulating isoflavonoid levels in CD-1 mice: effect of oral versus subcutaneous delivery and frequency of administration

The CD-1 mouse is a commonly used animal model to understand the biological effects of early-life exposure to soy isoflavones in infants. Most studies using CD-1 mice have administered isoflavones by daily subcutaneous injection, while infants receive oral feeds every few hours. The study objectives were to compare the total serum levels of genistein (GEN), daidzein (DAI) and the DAI metabolites equol and O-desmethyl-angolensin (O-DMA), after subcutaneous injection and oral dosing and to determine if frequency of oral administration results in different circulating levels of isoflavones using the CD-1 mouse model. From postnatal days 1 to 5, pups randomly received corn oil or soy isoflavones (total daily dose, 0.010 mg DAI+0.025 mg GEN) by subcutaneous injection once a day, orally once a day or orally every 4 hours. On postnatal day 5, 1 h posttreatment, mice were killed and serum was collected. Mice treated with soy isoflavones had higher (P<.05) serum GEN (female: 1895–3391 ng/ml and male: 483–578 ng/ml) and DAI (female: 850–1580 ng/ml and male: 248–322 ng/ml) concentrations versus control (5–20 ng/ml) mice, regardless of route or frequency of administration, and were similar among dosing strategies. Total serum concentrations of GEN and DAI were higher (P<.05) among females (GEN: 2714 ± 393 ng/ml and DAI: 1205 ± 164 ng/ml) than males (GEN: 521 ± 439 ng/ml and DAI: 288 ± 184 ng/ml) across treatment groups. Serum equol and O-DMA concentrations were negligible (<3 ng/ml) across groups. In conclusion, different routes of delivery and frequency of administration resulted in similar total serum levels of GEN, DAI¸ equol or O-DMA.     

Improved Glucose Control and Reduced Body Weight in Rodents with Dual Mechanism of Action Peptide Hybrids

Combination therapy is being increasingly used as a treatment paradigm for metabolic diseases such as diabetes and obesity. In the peptide therapeutics realm, recent work has highlighted the therapeutic potential of chimeric peptides that act on two distinct receptors, thereby harnessing parallel complementary mechanisms to induce additive or synergistic benefit compared to monotherapy. Here, we extend this hypothesis by linking a known anti-diabetic peptide with an anti-obesity peptide into a novel peptide hybrid, which we termed a phybrid. We report on the synthesis and biological activity of two such phybrids (AC164204 and AC164209), comprised of a glucagon-like peptide-1 receptor (GLP1-R) agonist, and exenatide analog, AC3082, covalently linked to a second generation amylin analog, davalintide. Both molecules acted as full agonists at their cognate receptors in vitro, albeit with reduced potency at the calcitonin receptor indicating slightly perturbed amylin agonism. In obese diabetic Lep^ob/Lep ^ob mice sustained infusion of AC164204 and AC164209 reduced glucose and glycated haemoglobin (Hb_A1c) equivalently but induced greater weight loss relative to exenatide administration alone. Weight loss was similar to that induced by combined administration of exenatide and davalintide. In diet-induced obese rats, both phybrids dose-dependently reduced food intake and body weight to a greater extent than exenatide or davalintide alone, and equal to co-infusion of exenatide and davalintide. Phybrid-mediated and exenatide + davalintide-mediated weight loss was associated with reduced adiposity and preservation of lean mass. These data are the first to provide in vivo proof-of-concept for multi-pathway targeting in metabolic disease via a peptide hybrid, demonstrating that this approach is as effective as co-administration of individual peptides.     

Eudragit S100 entrapped insulin microspheres for oral delivery

The purpose of this research was to investigate whether Eudragit S100 microspheres have the potential to serve as an oral carrier for peptide drugs like insulin. Microspheres were prepared using water-in oil-in water emulsion solvent evaporation technique with polysorbate 20 as a dispersing agent in the internal aqueous phase and polyvinyl alcohol (PVA)/polyvinyl pyrrolidone as a stabilizer in the external aqueous phase. The use of smaller internal aqueous-phase volume (50 μL) and external aqueous-phase volume (25 mL) containing PVA in the manufacturing process resulted in maximum encapsulation efficiency (81.8%±0.9%). PVA-stabilized microspheres having maximum drug encapsulation released 2.5% insulin at pH 1.0 in 2 hours. In phosphate buffer (pH 7.4), microspheres showed an initial burst release of 22% in 1 hour with an additional 28% release in the next 5 hours. The smaller the volumes of internal and external aqueous phase, the lower the initial burst release. The release of drug from microspheres followed Higuchi kinetics. Scanning electron microscopy of PVA-stabilized microspheres demonstrated spherical particles with smooth surface, and laser diffractometry revealed a mena particle size of 32.51±20 μm. Oral administration of PVA stabilized microspheres in normal albino rabbits (equivalent to 6.6 IU insulin/kg of animal weight) demonstrated a 24% reduction in blood glucose level, with maximum plasma glucose reduction of 76±3.0% in 2 hours and effect continuing up to 6 hours. The area under the percentage glucose reduction-time curve was 93.75%. Thus, our results indicate that Eudragit S100 microspheres on oral administration can protect insulin from proteolytic degradation in the gastrointestinal tract and produce hypoglycemic effect.     

A Novel Peptide with Similar Pharmacology to Exenatide in Rodents as GLP-1 Receptor Agonist

The prevalence of type-2 diabetes is rapidly increasing. Currently, exenatide is the first medicine which mimics incretin. However, it requires subcutaneous injection twice a day, an inconvenient way for patients. In this study, we identified a novel peptide with similar pharmacology to exenatide in rodents as GLP-1 receptor agonist which consists of 17 amino acids (17P). It promotes Ins-1 cell proliferation and insulin secretion and lowers blood glucose of diabetic rats. 17P was synthetized by solid-phase peptide synthesis. Interactions between GLP-1 receptor and 17P were studied by Bio-layer interferometry. Ins-1 cell proliferation was studied by MTT assay. ELISA was used to study Ins-1 cell insulin secretion. In vivo tests were performed with male Wistar rats. We used high fat diet and STZ injection to induce a type-2 diabetic rats model. Then, those rats were randomized to different test groups, and administered exenatide, 17P and saline water injection, to evaluate different responses. Based on HPLC (high performance liquid chromatography) and MS (mass spectrometry), 17P synthesis was successful. Bio-layer interferometry data showed a close interaction between GLP-1 receptor and 17P. 17P treatment of Ins-1 cells for 24 h could promote cell proliferation and insulin secretion in a dose-dependent manner. Administration of 17P in HF-STZ male Wistar rats demonstrated that 17P could lower the level of blood glucose and stabilize the body weight of the diabetic rats. All 17P treatments were similar to treatment with exenatide. In vitro and in vivo studies demonstrated that 17P could relieve symptoms of type-2 diabetes. Therefore, 17P could be developed as a promising type-2 diabetes therapeutic drug.     

Day-long subcutaneous infusion of exenatide lowers glycemia in patients with type 2 diabetes.

Exenatide (exendin-4) is an incretin mimetic with potential antidiabetic activity. This study examined the effects of a continuous subcutaneous (SC) infusion of exenatide (0.2, 0.4, 0.6, or 0.8 microg/kg/day) or placebo (PBO) on glycemic control over 23 h intervals. Twelve subjects with type 2 diabetes treated with metformin and/or diet received 10 infusions (4 exenatide, 6 PBO) on consecutive days. Exenatide was given in a dose-increasing design with at least one placebo infusion between each exenatide infusion, and with meals and a snack provided during the first 14 h of infusion. Plasma exenatide concentrations were dose-proportional. Plasma glucose (4-23 h) was lower in all exenatide arms compared to placebo (p<0.0001). The change in insulin/glucagon ratio and amylin concentrations from pre-infusion to post-infusion was increased (p<0.005, p<0.05, respectively) in the combined exenatide arms, but remained unchanged in the placebo groups. Nausea and vomiting were the most common treatment emergent adverse events. Exenatide infusion also appeared to have positive effects on beta-cell and alpha-cell function as measured by proinsulin/insulin ratios and mean glucagon concentrations. In summary, exenatide lowered plasma glucose during both prandial and fasting states when delivered as a continuous SC infusion over twenty-three hours, suggesting that exenatide can provide day-long glycemic control in patients with type 2 diabetes.     

Physiological analysis of various types of osmotic diuresis

Efficacy of drugs reduced proximal reabsorption was compared in experiments with female Wistar rats. Urine flow rate for the 1st h of experiment was enhanced after polyethylene glycol-400 (PEG) and 6% Na2SO4 infusion by over 30-fold, exenatide--40-fold, glycerol--11-fold as compared with the control. The maximal values of Na+ excretion were observed during Na2SO4 and exenatide administration (280 +/- 31 micromol/h vs. 3.2 +/- 0.6 Imol/h/100 g bw). The highest K+ excretion was revealed in experiments with glycerol administration (41 +/- 5 micromol/h vs. 7 +/- 2 micromol/h/100 g bw), Mg2+ --after exenatide injection (5.3 +/- 1.3 micromol/h vs. 0.16 +/- 0.03 micromol/ h/100 g bw). Diuretic effects were additive after combined administration of maximal doses of exenatide and PEG which suggests a different mechanism of action of solutes filtrated (PEG) to the proximal nephron segment and generated due to Na+/HW-exchange inhibition (exenatide). Osmotic diuretics differ by potency, mechanism of diuretic action and selectivity of ion excretion).     

Glucagon-like peptide 1 and its derivatives in the treatment of diabetes

Glucagon-like peptide 1 (GLP-1) was discovered as an insulinotropic gut hormone, suggesting a physiological role as an incretin hormone, i.e., being responsible, in part, for the higher insulin secretory response after oral as compared to intravenous glucose administration. This difference, the incretin effect, is partially lost in patients with Type 2 diabetes. The actions of GLP-1 include (a) a stimulation of insulin secretion in a glucose-dependent manner, (b) a suppression of glucagon, (c) a reduction in appetite and food intake, (d) a deceleration of gastric emptying, (e) a stimulation of beta-cell neogenesis, growth and differentiation in animal and tissue culture experiments, and (f) an in vitro inhibition of beta-cell apoptosis induced by different toxins. Intravenous GLP-1 can normalize and subcutaneous GLP-1 can significantly lower plasma glucose in the majority of patients with Type 2 diabetes. GLP-1 itself, however, is inactivated rapidly in vivo and thus does not appear to be useful as a therapeutic agent in the long-term treatment of Type 2 diabetes. Other agents acting on GLP-1 receptors have been found (like exendin-4) or developed as GLP-1 derivatives (like liraglutide or GLP-1/CJC-1131). Clinical trials with exenatide (two injections per day) and liraglutide (one injection per day) have shown reductions in glucose concentrations and HbA1c by more than 1%, associated with moderate weight loss (2-3 kg), but also some nausea and, rarely, vomiting. It is hoped that this new class of drugs interacting with the GLP-1 or other incretin receptors, the so-called "incretin mimetics", will broaden our armamentarium of antidiabetic medications in the nearest future.     

A fusion protein derived from plants holds promising potential as a new oral therapy for type 2 diabetes

The incretin hormone glucagon‐like peptide‐1 (GLP‐1) is recognized as a promising candidate for the treatment of type 2 diabetes (T2D), with one of its mimetics, exenatide (synthetic exendin‐4) having already been licensed for clinical use. We seek to further improve the therapeutic efficacy of exendin‐4 (Ex‐4) using innovative fusion protein technology. Here, we report the production in plants a fusion protein containing Ex‐4 coupled with human transferrin (Ex‐4‐Tf) and its characterization. We demonstrated that plant‐made Ex‐4‐Tf retained the activity of both proteins. In particular, the fusion protein stimulated insulin release from pancreatic β‐cells, promoted β‐cell proliferation, stimulated differentiation of pancreatic precursor cells into insulin‐producing cells, retained the ability to internalize into human intestinal cells and resisted stomach acid and proteolytic enzymes. Importantly, oral administration of partially purified Ex‐4‐Tf significantly improved glucose tolerance, whereas commercial Ex‐4 administered by the same oral route failed to show any significant improvement in glucose tolerance in mice. Furthermore, intraperitoneal (IP) injection of Ex‐4‐Tf showed a beneficial effect in mice similar to IP‐injected Ex‐4. We also showed that plants provide a robust system for the expression of Ex‐4‐Tf, producing up to 37 μg prEx‐4‐Tf/g fresh leaf weight in transgenic tobacco and 137 μg prEx‐4‐Tf/g freshweight in transiently transformed leaves of N. benthamiana. These results indicate that Ex‐4‐Tf holds substantial promise as a new oral therapy for type 2 diabetes. The production of prEx‐4‐Tf in plants may offer a convenient and cost‐effective method to deliver the antidiabetic medicine in partially processed plant food products.     

Management of Hyperglycemia with the Administration of Intravenous Exenatide to Patients in the Cardiac Intensive Care Unit

ObjectiveTo evaluate the feasibility, effectiveness, and safety of intravenous exenatide to control hyperglycemia in the cardiac intensive care unit (CICU).MethodsA prospective, single-center, open-label, nonrandomized pilot study. Forty patients admitted to the CICU with glucose levels of 140 to 400 mg/dL received intravenous exenatide as a bolus followed by a fixed dose infusion for up to 48 hours. Exenatide effectiveness was benchmarked to two historical insulin infusion cohorts, one (INT) with a target glucose of 90 to 119 mg/dL (n = 84) and the other (MOD) with a target of 100 to 140 mg/dL (n = 71).ResultsMedian admission glucose values were 185.5 mg/dL (161.0, 215.5), 259.0 mg/dL (206.0, 343.0), and 189.5 mg/dL (163.5, 245.0) in the exenatide, MOD, and INT groups, respectively (P<.001). Steady state glucose values were similar between the exenatide (132.0 mg/dL [110.0, 157.0]) and the MOD groups (127.0 mg/dL [105.0, P = .15), but lower in the INT group (105.0 mg/dL [92.0, 128.0], P<.001 for exenatide versus INT). Median (IQR) time to steady state was 2.0 hours (1.5, 5.0) in the exenatide group compared to 12.0 hours (7.0, 15.0) in the MOD group (P<.001) and 3.0 hours (1.0, 5.0) in the INT group (P = .80 for exenatide versus INT). Exenatide was discontinued in 3 patients after failure to achieve glycemic control. No episodes of severe hypoglycemia (<50 mg/dL) occurred in patients who received exenatide. Nausea was reported by 16 patients and vomiting by 2 patients.ConclusionIntravenous exenatide is effective in lowering glucose levels in CICU patients, but its use may be limited by nausea. (Endocr Pract. 2013;19:81-90)     

Plasmodium berghei: the antimalarial action of artemisinin and sodium artelinate in vivo and in vitro, studied by flow cytometry

Sodium artelinate, a new water-soluble and relatively stable derivative of artemisinin, and its parent compound were tested for their antimalarial action. Experiments were done in vitro with synchronous cultures of Plasmodium berghei. The inhibition of growth by different concentrations of sodium artelinate and artemisinin was determined using flow cytometry. In vivo testing was done by subcutaneous injection of each drug in mice infected with P. berghei. Sodium artelinate, being stable in aqueous solution, was also administered orally to infected mice by its addition to their drinking water. Comparison of the parent compound and the derivative showed that sodium artelinate was slightly less active than artemisinin both in culture and in vivo. However, after oral administration of sodium artelinate, parasites were cleared from the blood with one-half to one-tenth of the dose used in the experiments with subcutaneous injection. The number of mice which were cured by oral administration of sodium artelinate was greater than after subcutaneous injection, even with a total oral dose lower than the injected dose.     

Diurnal Glucose Patterns of Exenatide Once Weekly: A 1-Year Study Using Continuous Glucose Monitoring with Ambulatory Glucose Profile Analysis

ObjectiveTo use continuous glucose monitoring (CGM) to characterize diurnal glucose patterns produced by a novel formulation of exenatide consisting of biodegradable polymeric microspheres that entrap exenatide and provide extended release enabling once-weekly administration.MethodsWe performed a subgroup analysis of patients with type 2 diabetes who participated in a multicenter trial (DURATION-1: Effects of Exenatide Long- Acting Release on Glucose Control and Safety in Subjects With Type 2 Diabetes Mellitus) comparing once-weekly with twice-daily formulations of exenatide. We are the only center to use CGM with ambulatory glucose profile (AGP) analysis to characterize glucose exposure, variability, and stability in participants assigned to exenatide once weekly.ResultsSeven of the 303 patients in the larger study population were included in the subgroup analysis. Mean age (57.6 ± 7 years), weight (102 ± 17 kg), body mass index (34 ± 3 kg/m²), and duration of diabetes (5 ± 2 years) were comparable to characteristics of the larger study population. At 30 weeks and 52 weeks, participants treated with exenatide once weekly had a mean reduction in hemoglobin A_1c level of 1.3 ± 0.3% and 1.0 ± 0.3%, respectively (P < .05). CGM analysis revealed a significant (P < .01) decrease in diurnal glucose exposure for 4 participants during nocturnal and daytime periods. Excess glucose exposure (compared with reference values) decreased in 6 of 7 participants, as did glucose variability. Glucose stability improved in 5 participants. The percentage of glucose values less than 70 mg/dL initially increased during the first half of the study then decreased to baseline levels by study end.ConclusionsIndividual glucose profiles revealed that changes in hemoglobin A_1c did not consistently parallel alterations in glucose exposure, variability, and stability. AGPs provided a visual representation of improved glucose responses to exenatide once weekly. (Endocr Pract. 2009;15:326-334)     

H-Pro-[3H]Leu-Gly-NH2: Plasma Profile and Brain Uptake Following Subcutaneous Injection in the Rat

Following subcutaneous injection of the tripeptide H-Pro-[3H]Leu-Gly-NH2 ([3H]PLG) in rats, the profile of intact peptide and its radioactively labeled metabolites was examined both in plasma and in brain tissue. [3H]PLG and metabolites were determined in trichloroacetic acid extracts by reverse-phase paired-ion HPLC. Maximal plasma levels of unmetabolized PLG were reached 6-8 min after administration, after which they decreased with an elimination half-life of 20 min. The uptake of [3H]PLG in the brain ranged from 0.0013% to 0.0017% of the administered dose per g tissue at 6-30 min following subcutaneous injection. After comparing these results with our previous findings with intravenous injection of [3H]PLG, it seemed likely that the subcutaneous route of administration might be more effective in eliciting CNS effects of PLG than the intravenous route of administration. The metabolite profiles in plasma and brain point to an initial cleavage of PLG at the NH2-terminal side and a very rapid degradation of the peptide intermediate H-Leu-Gly-NH2.     

Greater Combined Reductions in Hba1C ≥1.0% and Weight ≥5.0% with Semaglutide Versus Comparators in type 2 Diabetes

Objective: Semaglutide is a glucagon-like peptide 1 (GLP-1) analog for the once-weekly treatment of type 2 diabetes (T2D). In the global SUSTAIN clinical trial program, semaglutide demonstrated superior glycated hemoglobin (HbA_1c) and body weight reductions versus comparators. This post hoc analysis compared the proportion of patients achieving combined reductions in glycemia and body weight versus comparators.Methods: A total of 5,119 subjects with T2D in the phase 3 SUSTAIN 1 through 5 and 7 trials, from 33 countries, were included in this post hoc analysis. Subjects received subcutaneous semaglutide 0.5 or 1.0 mg, placebo or active comparator (sitagliptin 100 mg, exenatide extended release 2.0 mg, insulin glargine, dulaglutide 0.75 or 1.5 mg). The main endpoint was a composite of ≥1.0% HbA_1c reduction and ≥5.0% weight loss at end of treatment.Results: Significantly greater proportions of subjects achieved the composite endpoint with semaglutide 0.5 (25 to 38%) and 1.0 mg (38 to 59%) versus comparators (2 to 23%). More subjects treated with semaglutide versus comparators achieved ≥1.0% HbA_1c reductions (58 to 77% and 75 to 83% for semaglutide 0.5 and 1.0 mg versus 12 to 68%) and ≥5.0% weight loss (37 to 46%, 45 to 66% versus 4 to 30%). Proportions of subjects achieving targets were significantly higher with semaglutide 1.0 versus 0.5 mg in four of five trials. Semaglutide was well tolerated, with a safety profile similar to other GLP-1 receptor agonists.Conclusion: Significantly more subjects achieved both ≥1.0% HbA_1c reduction and ≥5.0% weight loss with once-weekly subcutaneous semaglutide treatment versus comparators in the SUSTAIN trials. A dose-dependent effect was observed with semaglutide.Abbreviations: AE = adverse event; CV = cardiovascular; ER = extended release; GLP-1 = glucagon-like peptide 1; GLP-1 RA = glucagon-like peptide 1 receptor agonist; HbA_1c = glycated hemoglobin; OAD = oral antidiabetic drug; sc = subcutaneous; T2D = type 2 diabetes     

Comparison of three subcutaneous modes of prostaglandin F2α administration for pregnancy termination in the hamster

Dose response relationships for pregnancy termination in hamsters following administration of prostaglandin F_2α (PGF_2α by three subcutaneous methods were determined in 526 hamsters. The median effective dose (ED₅₀) for PGF_2α given as a single subcutaneous injection in 500 μl of saline was 22.2 μg. Administration of the prostaglandin with an Alzet® osmotic minipump (subcutaneous insertion for 24 hours) required 1.35 times more PGF_2α (ED₅₀ = 30.0 μg). The least effective method of prenancy termination in the hamster involved administration of PGF_2α by a single subcutaneous injection in 20.4 μl of saline (the same volume delivered by the minipump in 24 hours); the ED₅₀ for this method of administration was 41.3 μg of PGF_2α.     

Novel antimicrobial peptides isolated from the skin secretions of Hainan odorous frog, Odorrana hainanensis

Intraperitoneal (i.p.) administration of the synthetic agonist of the glucagon like peptide-1 (GLP-1) receptor exenatide reduces food intake. Here, we evaluated possible peripheral pathways for this reduction. Exenatide (0.5 μg/kg, i.p.) was given to three, overnight food-deprived, groups of rats: total subdiaphragmatic vagotomy (VGX, severs the vagus nerve), celiaco-mesenteric ganglionectomy (CMGX, severs the splanchnic nerve) and combined VGX/CMGX. Following the injection, meal sizes (MSs) and intermeal intervals (IMIs) were determined for a total of 120 min. We found that exenatide reduced the sizes of the first two meals but failed to prolong the IMI between them, that VGX attenuated the reduction of the first MS, and that VGX, CMGX and combined VGX/CMGX attenuated the reduction of the second MS by exenatide. Therefore, the vagus nerve appears necessary for the reduction of the first MS by exenatide, whereas both nerves appear necessary for the reduction of the second MS by this peptide.     

抗生素缓控释给药系统——载药微球的研究与开发

利用具良好生物相容性和生物可降解性的聚合物制得的微球作为一种新型药物载体, 具有良好的缓控释作用,并具有一定的靶向性,可用于口服和注射,在药学领域和临床上有着广阔的应用前景。综述近年来各种抗生素缓控释微球制剂的研究与开发。     

Stimulation of somatotropin secretion following peripheral administration of the tripeptide, syndyphalin 33 in sheep, pigs and rats

In the present study, a simple tripeptide alkylamine, syndyphalin 33 (SD33, Tyr-DMet (O)-Gly-methylphenethylamide) was shown to stimulate somatotropin (GH) secretion in sheep, hogs and rats following peripheral administration. Intravenous (i.v.) administration of SD33 at doses of 0.05, 0.1 and 0.2 mumol/kg stimulated a significant increase in circulating GH levels in sheep within 5 minutes post-injection. This response was not attenuated following repeated i.v. injections of SD33 (0.05 /mmol/kg) administered at 2 hour intervals. In addition, plasma GH levels were significantly stimulated following either subcutaneous (s.c.) or oral administration of SD33 in hogs and rats. Subcutaneous administration of SD33 at doses of 0.5, 1.0 and 2.0 mumol/kg stimulated a significant increase in plasma GH concentrations within 30 minutes of injection in both species. Oral administration of SD33 at 1.0, 10 or 100 mumol/kg in rats resulted in a significant elevation in plasma GH levels which peaked at 30 minutes post-gavage. In the pig, circulating GH levels were significantly increased within 30 minutes post-ingestion and remained elevated for at least 2 hours at the 2.0 mumol/kg dose level. The ability of naloxone to block SD33-stimulated GH secretion suggests that this peptide acts via mu opiate receptors.     

Immunogenicity of chloroplast-derived HIV-1 p24 and a p24-Nef fusion protein following subcutaneous and oral administration in mice

High-level expression of foreign proteins in chloroplasts of transplastomic plants provides excellent opportunities for the development of oral vaccines against a range of debilitating or fatal diseases. The HIV-1 capsid protein p24 and a fusion of p24 with the negative regulatory protein Nef (p24-Nef) accumulate to ～4% and ～40% of the total soluble protein of leaves of transplastomic tobacco (Nicotiana tabacum L.) plants. This study has investigated the immunogenicity in mice of these two HIV-1 proteins, using cholera toxin B subunit as an adjuvant. Subcutaneous immunization with purified chloroplast-derived p24 elicited a strong antigen-specific serum IgG response, comparable to that produced by Escherichia coli-derived p24. Oral administration of a partially purified preparation of chloroplast-derived p24-Nef fusion protein, used as a booster after subcutaneous injection with either p24 or Nef, also elicited strong antigen-specific serum IgG responses. Both IgG1 and IgG2a subtypes, associated with cell-mediated Th1 and humoral Th2 responses, respectively, were found in sera after subcutaneous and oral administration. These results indicate that chloroplast-derived HIV-1 p24-Nef is a promising candidate as a component of a subunit vaccine delivered by oral boosting, after subcutaneous priming by injection of p24 and/or Nef.