Lidan Sun

Structure–activity relationships of a snake cathelicidin-related peptide, BF-15

Cathelicidin-BF15 (BF-15) is a 15-mer peptide derived from Cathelicidin-BF (BF-30), which is found in the venom of the snake Bungarus fasciatus and exhibits broad antimicrobial activity. Since BF-15 retains most part of the antimicrobial activity of BF-30 but has significantly reduced haemolytic activity and a much shorter sequence length (and less cost), it is a particularly attractive template around which to design novel antimicrobial peptides. However, the structure-activity relationship of it is still unknown. We designed and synthesized a series of C-terminal amidated analogs of BF-15 based on its amphipathic α-helix structure. And we characterized their antimicrobial potency and haemolytic activity. We identified the amidated BF-15 (analog B1) with potent antimicrobial activity against several antibiotic-resistant bacteria (MICs between 1 and 64 μg/mL, 2-16-folds higher than BF-30) and much lower haemolytic activity. The subsequent circular dichroism study results showed a typical α-helix pattern of analog B1 and the content of the α-helix structure of it increased significantly comparing with BF-30, which indicates the peptide sequence of BF-15 may provide a major contribution to the α-helix content of the whole BF-30 sequence. The peptide induced chaotic membrane morphology and cell debris as determined by electron microscopy. This suggests that the antimicrobial activity of B1 is based on cytoplasmic membrane permeability. Taken together, our results suggested that peptide B1 should be considered as an excellent candidate for developing therapeutic drugs.

Design, Synthesis, and Biological Activity of Novel Dicoumarol Glucagon-like Peptide 1 Conjugates

Twelve novel dicoumarol glucagon-like peptide 1 (GLP-1) conjugates were designed, synthesized, and tested for biological activity. All derivatives retained receptor activation efficacy, and exhibited improved albumin affinity and in vitro stability in rat plasma. The in vivo elimination half-lives of 13c and 13 l (22.07 and 18.78 h, respectively) were much longer than those of the GLP-1 receptor agonists exendin-4 (2.82 h) and liraglutide (12.53 h). The prolonged in vivo antidiabetic effects of 13c and 13 l on db/db mice were confirmed by the hypoglycemic efficacy test and the multiple intraperitoneal glucose tolerance test. Importantly, a once daily administration of 13c to db/db mice for 7 weeks provided long-term beneficial effects by lowering glycated hemoglobin (HbA1c) levels to 5.05%, which was lower than with liraglutide treatment (5.41%). These results suggest that 13c is a promising long-lasting GLP-1 mimetic that may be suitable for clinical use following further research.

Novel fatty chain-modified glucagon-like peptide-1 conjugates with enhanced stability and prolonged in vivo activity

A series of fatty chain conjugates of glucagon-like peptide-1(GLP-1) were designed and synthesized. First, eleven cysteine modified peptides (1-11) were prepared using Gly8-GLP-1(7-36)-NH2 peptide as a starting point. Peptides 1, 6, 9, and 11 which showed comparable GLP-1 receptor activate potency and glucose-lowering effect in vivo with Gly8-GLP-1(7-36)-NH2 were selected for second step modifications to yield conjugates 12-23. All conjugates retained significant GLP-1 receptor activate potency and more importantly exerted enhanced albumin-binding properties and in vitro plasma stability. The protracted antidiabetic effects of the most stable compound 14 were further confirmed by both multiple intraperitoneal glucose tolerance test and hypoglycemic efficacies test in vivo. Furthermore, once daily injection of compound 14 to db/db mice achieved long-term beneficial effects on HbA1c lowering and glucose tolerance. Our results suggest that compound 14 is a promising type 2 antidiabetic agent deserving further investigation.

Novel coumarin modified GLP-1 derivatives with enhanced plasma stability and prolonged in vivo glucose-lowering ability.

The short biological half‐life limits the therapeutic use of glucagon‐like peptide‐1 (GLP‐1) and chemical modification to improve the interaction of peptides with serum albumin represents an effective strategy to develop long‐acting peptide analogues. Coumarin, a natural product, is known to bind tightly to plasma proteins and possesses many biological activities. Therefore, we designed and synthesized a series of coumarin‐modified GLP‐1 derivatives, hypothesizing that conjugation with coumarin would retain the therapeutic effects and prolong the biological half‐life of the conjugates.

Site-specific fatty chain-modified exenatide analogs with balanced glucoregulatory activity and prolonged in vivo activity

The therapeutic utility of exenatide (Ex-4) is limited due to short plasma half-life of 2.4h and thus numerous approaches have been used to obtain a longer action time. However, such strategies often attend to one thing and lose another. The study aimed to identify a candidate with balanced glucoregulatory activity and prolonged in vivo activity. A series of fatty chain conjugates of Ex-4 were designed and synthesized. First, thirteen cysteine modified peptides (1-13) were prepared. Peptides 1, 10, and 13 showed improved glucagon-like peptide-1 (GLP-1) receptor activate potency and were thus selected for second step modifications to yield conjugates I-1-I-9. All conjugates retained significant GLP-1 receptor activate potency and more importantly exerted enhanced albumin-binding properties and in vitro plasma stability. The protracted antidiabetic effects of the most stable I-3 were further confirmed by both multiple intraperitoneal glucose tolerance test and hypoglycemic efficacies test in vivo. Furthermore, once daily injection of I-3 to streptozotocin (STZ) induced diabetic mice achieved long-term beneficial effects on hemoglobin A1C (HbA1C) lowering and glucose tolerance. Once daily injection of I-3 to diet induced obesity (DIO) mice also achieved favorable effects on food intake, body weight, and blood chemistry. Our results suggested that I-3 was a promising agent deserving further investigation to treat obesity patients with diabetes.

Coumaglutide, a novel long-acting GLP-1 analog, inhibits β-cell apoptosis in vitro and invokes sustained glycemic control in vivo

Glucagon-like peptide-1 (GLP-1) is a potential candidate for the treatment of type 2 diabetes. However, native GLP-1 is not suitable for therapy of diabetes due to its short half-life (t1/2=2 min). Our recent discovery of the novel long-acting GLP-1 analog, coumaglutide, elicits favorable hypoglycemic effects. The present study was aimed at determining the protection effect of β-cell from apoptosis and in vivo pharmacologic properties of coumaglutide in diabetic mice. To determine the protective effect of coumaglutide on INS-1 cell viability and apoptosis, cells were exposed to 1 μM streptozotocin (STZ) and coumaglutide for 24 h. Moreover, STZ-induced diabetic mice were treated daily with coumaglutide for 20 days and a range of pharmacologic parameters, including hemoglobin A1c (HbA1C), intraperitoneal glucose tolerance, food intake and body weight were assessed before and after the treatment. As with other glucagon-like peptide-1 receptor agonizts, coumaglutide was able to protect β-cell from apoptosis in vitro and induce a durable restoration of glycemic control (normalization of both HbA1C and improvement of intraperitoneal glucose tolerance) in diabetic mice. It can be concluded that coumaglutide retains native GLP-1 activities and thus may serve as a promising hypoglycemic drug candidate.

Novel Pentapeptide GLP-1 (32–36) Amide Inhibits β-Cell Apoptosis In Vitro and Improves Glucose Disposal in Streptozotocin-Induced Diabetic Mice

We proposed that a pentapeptide, LVKGR amide, GLP‐1 (32–36) amide, derived from the gluco‐incretin hormone, glucagon‐like peptide‐1 (GLP‐1), might possess favorable actions against diabetes. Therefore, GLP‐1 (32–36) amide was synthesized and the effects of it were examined in INS‐1 cell and streptozotocin‐induced diabetic mice model. To determine the protective effects of GLP‐1 (32–36) amide on INS‐1 cell viability and apoptosis, cells were exposed to 1 μm streptozotocin (STZ) and GLP‐1 (32–36) amide for 24 h. Results showed that GLP‐1 (32–36) amide treatment decreased apoptosis rate and significantly retained cell viability compared with saline‐treated controls. Then, GLP‐1 (32–36) amide was administered intraperitoneally to streptozotocin‐induced diabetic mice with normal mice used as control. Body weight, energy intake, plasma glucose, and histopathology of the pancreas were assessed. Results showed that GLP‐1 (32–36) amide protected β‐cell viability and apoptosis against STZ‐induced toxicity, inhibited weight gain, and relieved symptoms of polydipsia. Moreover, GLP‐1 pentapeptide‐treated mice showed a slight trend toward reduced glucose excursions in intraperitoneal glucose tolerance test at the end of the experiment. GLP‐1 (32–36) amide exerted favorable protective actions in streptozotocin‐induced diabetic mice. The peptide curtailed weight gain and alleviates symptoms of polydipsia. These findings suggested the probable utility of GLP‐1 (32–36) amide, a peptide mimetic derived there from GLP‐1, for adjuvant treatment of diabetes.

Virtual screening for cholesterol absorption inhibitors.

BACKGROUND Cholesterol, derived from two different sources of endogenous synthesis and diet, is essential for the growth and maintenance of mammalian cells. However, elevated level of serum cholesterol is among the associated risk factors for the coronary heart disease. Statins can reduce endogenous sterol synthesis by inhibiting HMG-CoA reductase, whereas cholesterol absorption inhibitors, such as ezetimibe, can block cholesterol uptake from dietary sources by blocking Niemann- Pick C1-like 1 (NPC1L1). OBJECTIVE The present review focuses on the main research progress of cholesterol absorption inhibitors, the structure of NPC1L1 and discovery of novel chemical entities by virtual screening. CONCLUSION Studies on the structure-activity relationship reveal that azetidinone is important to maintain activity in azetidinone derivatives and the novel heterocyclic compounds with replacement of β-lactam scaffold by oxazolidinone also show similar activity as ezetimibe. Moreover, virtual screening is a computer-aided molecular design tool to propose novel cholesterol absorption inhibitors.

Biological activity studies of the novel glucagon-like peptide-1 derivative HJ07.

AIM To identify the glucose lowering ability and chronic treatment effects of a novel coumarin-glucagon-like peptide-1 (GLP-1) conjugate HJ07. METHOD A receptor activation experiment was performed in HEK 293 cells and the glucose lowering ability was evaluated with hypoglycemic duration and glucose stabilizing tests. Chronic treatment was performed by daily injection of exendin-4, saline, and HJ07. Body weight and HbA1c were measured every week, and an intraperitoneal glucose tolerance test was performed before treatment and after treatment. RESULTS HJ07 showed well-preserved receptor activation efficacy. The hypoglycemic duration test showed that HJ07 possessed a long-acting, glucose-lowering effect and the glucose stabilizing test showed that the antihyperglycemic activity of HJ07 was still evident at a predetermined time (12 h) prior to the glucose challenge (0 h). The long time glucose-lowering effect of HJ07 was better than native GLP-1 and exendin-4. Furthermore, once daily injection of HJ07 to db/db mice achieved long-term beneficial effects on HbA1c lowering and glucose tolerance. CONCLUSION The biological activity results of HJ07 suggest that HJ07 is a potential long-acting agent for the treatment of type 2 diabetes.

Novel fatty acid chain modified GLP-1 derivatives with prolonged in vivo glucose-lowering ability and balanced glucoregulatory activity

Glucagon-like peptide-1 is a potent hypoglycemic hormone with beneficial properties for the treatment of diabetes. However, its half-life is short because the rapid metabolic degradation. This study aims to prolong the half-life of glucagon-like peptide-1 through conjugation with the fatty acid side chain which helps the conjugates to interact with the albumin. Firstly, we chose two optimized polypeptide chains which have tremendous hypoglycemic effect named Cys17-Gly8-GLP-1(7-36)-NH2 and Cys37-Gly8-GLP-1(7-37)-NH2, and various fatty acid chains were modified. All conjugates preserved relatively strong GLP-1R activation and I-6 behaved best in glucose-lowering ability. The prolonged antidiabetic effects of I-6 were further confirmed by hypoglycemic efficacy test in vivo. Meanwhile, once daily injection of I-6 to diabetic mice achieved long-term beneficial effects on glucose tolerance, body weight and blood chemistry. It is concluded that I-6 is a promising agent for further investigation of its potential to treat obese patients with diabetes.