Potential new treatments for type 2 diabetes

The Role of Grifola frondosa Polysaccharide in Preventing Skeletal Muscle Atrophy in Type 2 Diabetes Mellitus

Type 2 diabetes mellitus (T2DM) is a burgeoning public health challenge worldwide. Individuals with T2DM are at increased risk for skeletal muscle atrophy, a serious complication that significantly compromises quality of life and for which effective prevention measures are currently inadequate. Emerging evidence indicates that systemic and local inflammation stemming from the compromised intestinal barrier is one of the crucial mechanisms contributing to skeletal muscle atrophy in T2DM patients. Notably, natural plant polysaccharides were found to be capable of enhancing intestinal barrier function and mitigating secondary inflammation in some diseases. Herein, we hypothesized that Grifola frondosa polysaccharide (GFP), one of the major plant polysaccharides, could prevent skeletal muscle atrophy in T2DM via regulating intestinal barrier function and inhibiting systemic and local inflammation. Using a well-established T2DM rat model, we demonstrated that GFP was able to not only prevent hyperglycemia and insulin resistance but also repair intestinal mucosal barrier damage and subsequent inflammation, thereby alleviating the skeletal muscle atrophy in the T2DM rat model. Additionally, the binding free energy analysis and molecular docking of monosaccharides constituting GFP were further expanded for related targets to uncover more potential mechanisms. These results provide a novel preventative and therapeutic strategy for T2DM patients.

A Review on CRISPR-Mediated Epigenome Editing: A Future Directive for Therapeutic Management of Cancer

Abstract:

Recent studies have shed light on the role of epigenetic marks in certain diseases like cancer, type II diabetes mellitus (T2DM), obesity, and cardiovascular dysfunction, to name a few. Epigenetic marks like DNA methylation and histone acetylation are randomly altered in the disease state. It has been seen that methylation of DNA and histones can result in down-regulation of gene expression, whereas histone acetylation, ubiquitination, and phosphorylation are linked to enhanced expression of genes. How can we precisely target such epigenetic aberrations to prevent the advent of diseases? The answer lies in the amalgamation of the efficient genome editing technique, CRISPR, with certain effector molecules that can alter the status of epigenetic marks as well as employ certain transcriptional activators or repressors. In this review, we have discussed the rationale of epigenetic editing as a therapeutic strategy and how CRISPR-Cas9 technology coupled with epigenetic effector tags can efficiently edit epigenetic targets. In the later part, we have discussed how certain epigenetic effectors are tagged with dCas9 to elicit epigenetic changes in cancer. Increased interest in exploring the epigenetic background of cancer and non-communicable diseases like type II diabetes mellitus and obesity accompanied with technological breakthroughs has made it possible to perform large-scale epigenome studies.

Comparison of efficacy and safety of gabapentin and duloxetine in painful diabetic peripheral neuropathy: A systematic review and meta-analysis of randomised controlled trials

BACKGROUND

In patients with diabetes mellitus, painful diabetic peripheral neuropathy (PDPN) is a frequent complication and can cause poor quality of life. We compared the efficacy and safety of duloxetine with those of gabapentin in patients with PDPN through a systematic review and meta-analysis of randomised controlled trials.

MATERIALS AND METHODS

PubMed, Embase and the Cochrane Library were searched for eligible studies published from database inception to January 2021. Visual Analogue Scale (VAS), sleep interference score, Clinical Global Impression of Change (CGIC), Patient Global Impression of Change (PGIC), Diabetic Neuropathy Symptom (DNS) score, Diabetic Neuropathic Examination (DNE) score, Neuropathic Disability Score (NDS) and side effects were used to compare duloxetine and gabapentin in patients with PDPN.

RESULTS

Three eligible randomised controlled trials involving 290 patients were included. No significant differences were observed between patients receiving duloxetine and gabapentin with respect to VAS (mean change difference = -1.23, 95% CI, -6.09 to 3.62; P = .62), sleep interference score (mean change difference = 0.42, 95% CI, -0.15 to 1.00; P = .15), CGIC (mean difference = 0.04, 95% CI, -0.11 to 0.20; P = .60), PGIC (mean difference= 0.24, 95% CI, -0.13 to 0.60; P = .21), DNS (mean change difference = 0.14, 95% CI, -0.35 to 0.63; P = .58), DNE (mean change difference = 0.26, 95% CI, -0.35 to 0.86; P = .41) and NDS (mean change difference = 0.30, 95% CI, -0.02 to 0.63; P = .07).

CONCLUSIONS

No significant differences were observed in the efficacy of duloxetine and gabapentin when treating patients with PDPN.

Effect of SGLT inhibitors on weight and lipid metabolism at 24 weeks of treatment in patients with diabetes mellitus: A systematic review and network meta-analysis

BACKGROUND

The goals of improving quality of life and increasing longevity are receiving growing amounts of attention. Body weight and lipid metabolism are closely related to various complications of diabetes. The aim of this study was to rank SGLT inhibitors according to their efficacy with regard to weight and evaluate the effect of SGLT inhibitors on lipid metabolism at 24 weeks of treatment.

METHODS

The Web of Science, PubMed, Cochrane Library, Embase, and Clinical Trials databases were electronically searched to collect randomized controlled trials involving patients with type 2 diabetes mellitus through June 2020. Two researchers independently screened and evaluated the selected studies and extracted the outcome indexes. ADDIS 1.16.5 and STATA 16 software were used to perform the network meta-analysis and draw the plots.

RESULTS

Ultimately, 36 studies were selected and included in this study. We found that all SGLT inhibitors were effective at reducing weight; canagliflozin was the most effective. SGLT inhibitors and placebo were not associated with significantly different serum cholesterol levels. SGLT inhibitors lowered serum triglyceride levels and increased serum high-density and low-density lipoprotein cholesterol levels. SGLT inhibitors also reduced the level of alanine aminotransferase.

CONCLUSIONS

SGLT inhibitors can bring about weight loss in patients with T2DM and can also improve lipid metabolism. Therefore, patients with hyperlipidemia who have been unsuccessful at losing weight should consider taking SGLT inhibitors. In addition, SGLT inhibitors are hepatoprotective and appear to be safe for patients with mild to moderate liver dysfunction.

TRIAL REGISTRATION

CRD42020198516.

Long non-coding RNA MEG3 promotes fibrosis and inflammatory response in diabetic nephropathy via miR-181a/Egr-1/TLR4 axis

Long non-coding RNAs (lncRNAs) play vital roles in diabetic nephropathy (DN). This research aimed to study the potential role and underlying molecular mechanisms of long non-coding RNA MEG3 in DN. We found that MEG3 was upregulated in DN in vivo and in vitro and could enhance cell fibrosis and inflammatory response in DN. MEG3 functioned as an endogenous sponge for miR-181a in mesangial cells (MCs) via direct targeting and in an Ago2-dependent manner. MiR-181a inhibition promoted MC fibrosis and inflammatory response. In addition, Egr-1 was confirmed as a target gene of miR-181a. Further investigations verified that MEG3 promotes fibrosis and inflammatory response via the miR-181a/Egr-1/TLR4 axis in vitro and in vivo. These results provide new insights into the regulation between MEG3 and the miR-181a/Egr-1/TLR4 signaling pathway during DN progression.

In Silico Computations of Selective Phytochemicals as Potential Inhibitors Against Major Biological Targets of Diabetes Mellitus

BACKGROUND

In the past few years, several developments have been made to understand and control the complications and harmful side-effects associated with the disorder diabetes mellitus (DM). Many new steps have been taken in a better understanding of the pathophysiology of the disease. With the advancement in the field of medical sciences, various novel therapies have been developed to efficiently control the pathological effects of diabetes mellitus. Recently, phytochemicals possessing various medicinal properties have opened up a new vast range of opportunities to design novel therapeutic drugs against diabetes mellitus.

OBJECTIVE

The present study aims to identify and screen phytochemicals as potent and novel inhibitors against diabetes mellitus.

METHODS

Three major biological targets of diabetes mellitus named Cytochrome P450, glycogen synthase kinase and PPARγ are targeted using phytochemicals by performing pharmacological properties prediction, molecular docking and density functional theory studies.

RESULTS

Out of 108 phytochemicals, 20, 12 and 3 phytochemicals showed higher binding affinity values as compared to chemically synthesized drugs against cytochrome P450, glycogen synthase kinase and PPARγ, respectively.

CONCLUSION

The screened phytochemicals have strong inhibitory potential against diabetes mellitus and in future, these compounds, holding immense potential, can be considered as candidate drugs for treating diabetes mellitus.

Variation in the metabolites and α-glucosidase inhibitory activity of Cosmos caudatus at different growth stages

BACKGROUND

Cosmos caudatus is an annual plant known for its medicinal value in treating several health conditions, such as high blood pressure, arthritis, and diabetes mellitus. The α-glucosidase inhibitory activity and total phenolic content of the leaf aqueous ethanolic extracts of the plant at different growth stages (6, 8. 10, 12 and 14 weeks) were determined in an effort to ascertain the best time to harvest the plant for maximum medicinal quality with respect to its glucose-lowering effects.

METHODS

The aqueous ethanolic leaf extracts of C. caudatus were characterized by NMR and LC-MS/MS. The total phenolic content and α-glucosidase inhibitory activity were evaluated by the Folin-Ciocalteu method and α-glucosidase inhibitory assay, respectively. The statistical significance of the results was evaluated using one-way ANOVA with Duncan's post hoc test, and correlation among the different activities was performed by Pearson's correlation test. NMR spectroscopy along with multivariate data analysis was used to identify the metabolites correlated with total phenolic content and α-glucosidase inhibitory activity of the C. caudatus leaf extracts.

RESULTS

It was found that the α-glucosidase inhibitory activity and total phenolic content of the optimized ethanol:water (80:20) leaf extract of the plant increased significantly as the plant matured, reaching a maximum at the 10th week. The IC50 value for α-glucosidase inhibitory activity (39.18 μg mL- 1) at the 10th week showed greater potency than the positive standard, quercetin (110.50 μg mL- 1). Through an 1H NMR-based metabolomics approach, the 10-week-old samples were shown to be correlated with a high total phenolic content and α-glucosidase inhibitory activity. From the partial least squares biplot, rutin and flavonoid glycosides, consisting of quercetin 3-O-arabinofuranoside, quercetin 3-O-rhamnoside, quercetin 3-O-glucoside, and quercetin 3-O-xyloside, were identified as the major bioactive metabolites. The metabolites were identified by NMR spectroscopy (J-resolve, HSQC and HMBC experiments) and further supported by dereplication via LC-MS/MS.

CONCLUSION

For high phytomedicinal quality, the 10th week is recommended as the best time to harvest C. caudatus leaves with respect to its glucose lowering potential.

Cycloaddition reactions for antiviral compounds

Prominent in the current stage of drug development, antiviral compounds can be efficiently prepared through cycloaddition reactions. The chapter reports the use of classical Diels–Alder and their hetero version for the design and synthesis of compounds that were tested for their antiviral activities against a variety of viruses. Furthermore, 1,3-dipolar cycloaddition reactions of selected 1,3-dipoles, such as azides, nitrones, and nitrile oxides, are reviewed in the light of their application in the preparation of key intermediates for antiviral synthesis. A few examples of [2+2] cycloaddition reactions are also presented. The products obtained from these pericyclic reaction approaches were all tested for their activities in terms of blocking the virus replication, and the relevant biological data are highlighted.

Preparation, Optimization and In vitro Evaluation of Glipizide Nanoparticles Integrated with Eudragit RS-100

BACKGROUND

Solubility is an important criterion for drug efficacy, independent of the route of administration. It also poses a major challenge for pharmaceutical industries, which are developing new pharmaceutical products, since 40% of the active substances being identified are either insoluble or poorly soluble in aqueous media.

OBJECTIVE

The objective of this study was to develop nanoformulation of glipizide drugloaded nanoparticles providing controlled release formulation.

METHOD

Nanoparticles were prepared by the solvent evaporation method. Eudragit RS100, a nonbiodegradable polymer with varying ratios was used for making the formulation. The effect of key formulation variables on the particle size and entrapment efficiency and drug loading of nanoparticles were studied by using factorial design.

RESULTS

DSC thermograms indicate that glipizide was dispersed in an amorphous state in the polymer. TEM study indicates that the nanoparticles were in spherical shape. The mean diameter was dependent on the presence of the amount of Eudragit RS100 and viscosity of the organic phase. The in vitro study showed that the cumulative drug release was from 69.52-81.44 % in 10 hrs at pH 6.8 in phosphate buffer respectively.

CONCLUSION

The developed NPs could reduce dose frequency, decrease side effects, and improve patient compliance. Using factorial design, maximum entrapment efficiency with minimum particle size could be achieved with a few experiments.

Intrinsic and Antipsychotic Drug-Induced Metabolic Dysfunction in Schizophrenia

For decades, there have been observations demonstrating significant metabolic disturbances in people with schizophrenia including clinically relevant weight gain, hypertension, and disturbances in glucose and lipid homeostasis. Many of these findings pre-date the use of antipsychotic drugs (APDs) which on their own are also strongly associated with metabolic side effects. The combination of APD-induced metabolic changes and common adverse environmental factors associated with schizophrenia have made it difficult to determine the specific contributions of each to the overall metabolic picture. Data from drug-naïve patients, both from the pre-APD era and more recently, suggest that there may be an intrinsic metabolic risk associated with schizophrenia. Nevertheless, these findings remain controversial due to significant clinical variability in both psychiatric and metabolic symptoms throughout patients' disease courses. Here, we provide an extensive review of classic and more recent literature describing the metabolic phenotype associated with schizophrenia. We also suggest potential mechanistic links between signaling pathways associated with schizophrenia and metabolic dysfunction. We propose that, beyond its symptomatology in the central nervous system, schizophrenia is also characterized by pathophysiology in other organ systems directly related to metabolic control.

Instant coffee extract with high chlorogenic acids content inhibits hepatic G-6-Pase in vitro, but does not reduce the glycaemia

Coffee is the main source of chlorogenic acid in the human diet, and it contains several chlorogenic acid isomers, of which the 5-caffeoylquinic acid (5-CQA) is the predominant isomer. Because there are no available data about the action of chlorogenic acids from instant coffee on hepatic glucose-6-phosphatase (G-6-Pase) activity and blood glucose levels, these effects were investigated in rats. The changes on G-6-Pase activity and liver glucose output induced by 5-CQA were also investigated. Instant coffee extract with high chlorogenic acids content (37.8%) inhibited (p < 0.05) the G-6-Pase activity of the hepatocyte microsomal fraction in a dose-dependent way (up to 53), but IV administration of this extract did not change the glycaemia (p > 0.05). Similarly, 5-CQA (1 mM) reduced (p < 0.05) the activity of microsomal G-6-Pase by about 40%, but had no effect (p > 0.05) on glucose output arising from glycogenolysis in liver perfusion. It was concluded that instant coffee extract with high content of chlorogenic acids inhibited hepatic G-6-Pase in vitro, but failed to reduce the glycaemia probably because the coffee chlorogenic acids did not reach enough levels within the hepatocytes to inhibit the G-6-Pase and reduce the liver glucose output.

Hypoglycemic effect of Rhizophora mucronata in streptozotocin induced diabetic rats

Rhizophora mucronata, plant of Mangroove family, found on the coastal region of India and used in treatment of various diseases. Different parts of plants are used in treatment of diabetes as folkloric medicine. The present study was designed to evaluate the hypoglycemic effect of hydro-alcoholic extract of R. mucronata. Streptozotocin (STZ)-induced diabetic rats were treated with RME (100 mg/kg and 200 mg/kg) and glibenclamide (0.5 mg/kg). Blood glucose levels were evaluated for the acute and sub-acute studies and body weight of rats were also monitored. All the treatments showed the highly significant (p<0.01) hypoglycemic effect in both the acute and the sub-acute studies. RME and glibenclamide treated rats were maintained the body weight during the study period while as the body weight of diabetic rats had gone down. The result of this study scientifically proved the hypoglycemic folkloric use of leaves of R. mucronata in treatment of diabetes.

Ragaglitazar: The Pharmacokinetics, Pharmacodynamics, and Tolerability of a Novel Dual PPARα and γ Agonist in Healthy Subjects and Patients with Type 2 Diabetes

Ragaglitazar is a novel dual peroxisome proliferator-activated receptor (PPAR) alpha and gamma agonist intended to restore insulin sensitivity and correct diabetic dyslipidemia. These studies assessed single-dose pharmacokinetics and tolerability of ragaglitazar in healthy subjects, as well as multiple-dose pharmacokinetics, pharmacodynamics, and tolerability of ragaglitazar in healthy subjects and in patients with type 2 diabetes. Healthy subjects received a single oral dose (1-120 mg), and healthy subjects and type 2 diabetic patients received a loading dose and thereafter once-daily doses (0.5-16 mg) of ragaglitazar for 6 and 20 days, respectively. Ragaglitazar was rapidly absorbed (tmax: 1.5-1.7 h), with mean AUC0-24 h and Cmax proportional to dose after single and multiple dosing; t1/2 was 80 hours following a single dose and 104 hours in healthy subjects and 122 hours in patients after multiple dosing. Administration of 4 mg ragaglitazar to patients (n = 4) for 21 days resulted in mean decreases from baseline in fasting levels of plasma glucose (18%), C-peptide (18%), fructosamine (6%), triglycerides (36%), free fatty acids (49%), total cholesterol (11%), low-density lipoprotein (LDL) cholesterol (21%), and very low-density lipoprotein (VLDL) cholesterol (15%), as well as an increase in high-density lipoprotein (HDL) cholesterol (33%). Overall, ragaglitazar was well tolerated; with multiple dosing, there was a higher incidence of adverse events for patients that, at the highest dose level (16 mg), included peripheral edema and anemia.

Effect of Rebaudioside A, a diterpenoid on glucose homeostasis in STZ-induced diabetic rats

Rebaudioside A (Reb A), a major constituent of Stevia rebaudiana, was recently proposed as an insulinotropic agent. The aim of this investigation was to evaluate the antihyperglycemic effect of Reb A on the activities of hepatic enzymes of carbohydrate metabolism in streptozotocin (STZ)-induced diabetic rats. Diabetes was induced in adult male Albino Wistar rats, weighing 180-200 g, by a single intraperitoneal injection at a dose of STZ (40 mg/kg body weight). Diabetic rats showed significant (P<0.05) increase in the levels of plasma glucose and glycosylated hemoglobin and significant (P<0.05) decrease in the levels of plasma insulin and hemoglobin. Activities of gluconeogenic enzymes such as glucose-6-phosphatase and fructose-1,6-bisphosphatase were significantly (P<0.05) increased while hexokinase and glucose-6-phosphate dehydrogenase were significantly (P<0.05) decreased in the liver along with glycogen. Oral treatment with Reb A to diabetic rats significantly (P<0.05) decreased blood glucose and reversed these hepatic carbohydrate metabolizing enzymes in a significant manner. Histopathology changes of pancreas confirmed the protective effects of Reb A in diabetic rats. Thus, the results show that Reb A possesses an antihyperglycemic activity and provide evidence for its traditional usage in the control of diabetes.

Effects of garlic extract treatment in normal and streptozotocin diabetic rats infected with Candida albicans

The anti-candidial effect of garlic extract (Allium sativum L.) was investigated in normal and streptozotocin-induced diabetic rats. Diabetes was induced after a single intraperitoneal injection of streptozotocin (60 mg/kg). Rats were divided into six groups with fifteen rats in each group: (1) Normal control rats (2) Control rats + C. albicans (3) Control rats + garlic extract + C. albicans (4) Diabetic control rats (5) Diabetic rats + C. albicans (6) Diabetic rats + garlic extract + C. albicans. The concerned groups were inoculated with C.albicans on the 15 th day. At the end of one month experiment, fasted rats were killed by cervical decapitation. Blood was collected for estimation of glucose and C. albicans concentrations were estimated in liver and kidneys homogenates. A significant increase was observed in serum glucose levels in diabetic rats. A loss of bodyweight, polydipsia and polyphagia were observed in diabetic rats. Administration of alcoholic extract of garlic (0.25 g/kg body weight) reduced the hyperglycemia, polydipsia, polyphagia and associated weight loss of streptozotocin-treated rats. Administration of garlic extract significantly reduced C. albicans concentrations in liver and kidneys homogenates in infected control and diabetic rats. It is concluded that garlic extract improves candidia infection in diabetic rats.

Overnight hypoxic exposure and glucagon-like peptide-1 and leptin levels in humans

Altitude exposure has been associated with loss of appetite and weight loss in healthy humans; however, the endocrine factors that contribute to these changes remain unclear. Leptin and glucagon-like peptide-1 (GLP-1) are peptide hormones that contribute to the regulation of appetite. Leptin increases with hypoxia; however, the influence of hypoxia on GLP-1 has not been studied in animals or humans to date. We sought to determine the influence of normobaric hypoxia on plasma leptin and GLP-1 levels in 25 healthy humans. Subjects ingested a control meal during normoxia and after 17 h of exposure to normobaric hypoxia (fraction of inspired oxygen of 12.5%, simulating approximately 4100 m). Plasma leptin was assessed before the meal, and GLP-1 was assessed premeal, at 20 min postmeal, and at 40 min postmeal. We found that hypoxia caused a significant elevation in plasma leptin levels (normoxia, 4.9 +/- 0.8 pg.mL-1; hypoxia, 7.7 +/- 1.5 pg.mL-1; p < 0.05; range, -16% to 190%), no change in the average GLP-1 response to hypoxia, and only a small trend toward an increase in GLP-1 levels 40 min postmeal (fasting, 15.7 +/- 0.9 vs 15.9 +/- 0.7 pmol.L-1; 20 min postmeal, 21.7 +/- 0.9 vs 21.8 +/- 1.2 pmol.L-1; 40 min postmeal, 19.5 +/- 1.2 vs. 21.0 +/- 1.2 pmol.L-1 for normoxia and hypoxia, respectively; p > 0.05 normoxia vs hypoxia). There was a correlation between SaO2 and leptin after the 17 h exposure (r = 0.45; p < 0.05), but no relation between SaO2 and GLP-1. These data confirm that leptin increases with hypoxic exposure in humans. Further study is needed to determine the influence of hypoxia and altitude on GLP-1 levels.

Oxidative stress in the testis of hyperglycemic rabbits treated with repaglinide

In the present study, the induction of oxidative stress was examined in the testis of alloxan-induced diabetic rabbits. In addition, the protective effect of repaglinide, an oral anti-diabetic, at a dose of 1 mg daily was studied after four and eight weeks of the treatment. For these purposes, the levels of superoxide dismutase (Cu,Zn-SOD), catalase (CAT), glutathione peroxidase (GSH-Px), glutathione reductase (GSSG-R), glutathione (GSH), ascorbic acid (AA), lipid peroxidation products (LPO) and protein carbonyl groups (PCG) were quantified. Hyperglycemia resulted in significant increases in the antioxidative enzymes, Cu, Zn-SOD, CAT, GSH-Px, and GSSG-R after four and eight weeks, respectively. There was also an increase in GSH level, and a decrease in the level of AA. These effects were accompanied by an elevation in testicular LPO levels and PCG levels. Repaglinide was found to normalize the activity of GSSG-R and levels of GSH and AA, and blunted the increased lipid peroxidation, however no decrease in PCG levels were observed. In conclusion, some oxidative changes provoked in the testis of rabbits by hyperglycemia, were found to be reduced with repaglinide treatment at therapeutic dose.

Synthesis, biological evaluation and molecular modeling studies of arylidene-thiazolidinediones with potential hypoglycemic and hypolipidemic activities

New arylidene-thiazolidinediones (ATZDs) were synthesized and evaluated in the alloxan-induced hyperglycemia mice model. The molecular target taken into consideration is the nuclear PPAR-gamma whose crystallographic structure is available on the PDB database as 2PRG. Thus the hypoglycemic and hypolipidemic activities of compounds were compared with the result of their docking after removal of the co-crystallized ligand present in the 2PRG structure. Molecular modeling studies were carried out using the Autodock 3.0.5 and ADT 1.1 programs.

Preclinical pharmacokinetics and interspecies scaling of ragaglitazar, a novel biliary excreted PPAR dual activator

Allometric scaling has been used as an effective tool for the prediction of human pharmacokinetic parameters. Allometry has been a useful approach for the analysis of compounds that are eliminated unchanged in the urine and/or exhibit similar metabolic patterns across species. However, it has been a challenging issue to correctly predict human pharmacokinetic parameters for drugs that are eliminated intact and/or as conjugates in the bile. Ragaglitazar is a novel, non-thiazolidinedione peroxisome proliferator-activated receptor (PPAR) alpha- and gamma-agonist. In our investigation, preclinical pharmacokinetic data on ragaglitazar were gathered for several animal species (mice, rats, rabbits and dogs). Ragaglitazar when administered orally has shown a low clearance rate (Cl/F; < 5% of hepatic blood flow) in mice, rats and rabbits and a moderately high Cl/F in dogs (> 15% of hepatic blood flow). A qualitative estimation of rat bile has unequivocally confirmed the elimination of ragaglitazar in the bile. The human pharmacokinetic data are also indicative of the involvement of enterohepatic biliary recycling. In order to predict key parameters such as Cl/F and volume of distribution (V/F), simple allometry was the approach adopted at the onset. Although V/F scaled adequately, it failed to accurately predict human Cl/F. Therefore, standard correction factors such as maximum life span potential (MLP) and brain weight were also included. Although such modifications improved the linearity (r2 > 0.9), they failed to predict the investigated values. Further incorporation of correction factors particularly relevant to biliary excreted drugs improved the prediction of these values. Interestingly, the exclusion of dog data from the interspecies scaling considerably improved the prediction of both Cl/F and V/F.

Calpains and their multiple roles in diabetes mellitus

Type 2 diabetes mellitus (T2DM) can lead to death without treatment and it has been predicted that the condition will affect 215 million people worldwide by 2010. T2DM is a multifactorial disorder whose precise genetic causes and biochemical defects have not been fully elucidated, but at both levels, calpains appear to play a role. Positional cloning studies mapped T2DM susceptibility to CAPN10, the gene encoding the intracellular cysteine protease, calpain 10. Further studies have shown a number of noncoding polymorphisms in CAPN10 to be functionally associated with T2DM while the identification of coding polymorphisms, suggested that mutant calpain 10 proteins may also contribute to the disease. Here we review recent studies, which in addition to the latter enzyme, have linked calpain 5, calpain 3, and its splice variants, calpain 2 and calpain 1 to T2DM-related metabolic pathways along with T2DM-associated phenotypes, such as obesity and impaired insulin secretion, and T2DM-related complications, such as epithelial dysfunction and diabetic cataract.

Antioxidative and anti-inflammatory effects of repaglinide in plasma of diabetic animals

Oxidative stress, defined as an imbalance between the production of reactive oxygen species (ROS) and antioxidant defense, is considered to be an important pathogenic factor in diabetes mellitus and its complications. In diabetic state, ROS might also be implicated in promoting a state of systemic inflammation. Recently, it was demonstrated that antioxidant therapy could be used to stop the initiation and propagation of this inflammatory response. Repaglinide is a new oral antidiabetic agent with a possible antioxidant activity. Therefore, in the present study, a possible therapeutic value of repaglinide in ameliorating the oxidative and inflammatory processes was tested in diabetic animals. In the study, the levels of total antioxidant status (TAS), ascorbic acid (AA), protein carbonyl groups (PCG) and interleukin-6 (IL-6) were determined in plasma of diabetic rabbits after 4 and 8 weeks of repaglinide treatment (1mg daily). Ex vivo analysis revealed that there were significant differences in these markers between hyperglycemic and control animals (P<0.05). Some of these parameters were ameliorated by repaglinide treatment. In diabetic rabbits treated with repaglinide, protein oxidation was diminished by 17.8% after 8 weeks of experiment. The level of AA in plasma of diabetic treated animals was higher than in non-treated diabetic groups (by 9.4 and 22.6% after 4 and 8 weeks, respectively). In diabetic treated animals, the TAS level was also significantly increased (by 23.6 and 16.7%). However, in diabetic rabbits, repaglinide did not affect the concentration of IL-6.

Nigella sativa seed extracts enhance glucose-induced insulin release from rat-isolated Langerhans islets

Nigella sativa L. 'Black cumin' (Ranunculaceae) is one of the plants commonly used in Moroccan folk medicine for treatment of various ailments including diabetes mellitus. The present study was undertaken to investigate the effect of different N. sativa seed extracts on insulin secretion. Different fractions of the seed were prepared: the defatted fraction (HR II), which was divided into two subfractions: the first (HR III) containing acidic and neutral compounds and the second (HR IV) containing basic compounds. The insulin secretory effects of these extracts were evaluated individually at different concentrations (0.01, 0.1, 1 and 5 mg/mL), in vitro in isolated rat pancreatic islets in the presence of 8.3 mmol/L glucose. The results show that addition of the defatted whole extract or of the basic subfraction of the seed in the incubation medium significantly increased glucose-induced insulin release from the islets. In the case of the acidic and neutral subfraction, the stimulatory effect was observed only for the higher concentration (5 mg/mL). However, a clear concentration-dependent increase in insulin release from isolated pancreatic islets was observed for the basic subfraction. Our data show that the antidiabetic properties of N. sativa seeds may be, at least partly, mediated by stimulated insulin release, and that the basic subfraction largely contributes to this stimulatory effect. Further phytochemical studies are underway in order to isolate the pharmacological compound(s) responsible for the insulinotropic effect of N. sativa seeds.

Epidemiology of diabetic retinopathy and macular oedema: a systematic review

AIMS

To systematically review the literature on the prevalence and incidence of diabetic retinopathy (DR) and macular oedema (MO).

METHODS

A search of the bibliographic databases (Medline, Embase, CINAHL) was conducted up to October 2001. Selected relevant studies were scrutinized and included in the review.

RESULTS

A total of 359 studies were included. The studies were reported in nearly 100 different journals and in over 50 countries. The majority of the studies were US-based, with large studies such as the Wisconsin Epidemiologic Study of Diabetic Retinopathy dominating the literature. The studies were quite dated and highly heterogeneous in nature in terms of patient selection with variable inclusion criteria (age range, gender, diabetes duration and type, ethnicity, comorbidity, and DR status, assessment, and classification).

CONCLUSIONS

There are inconsistencies between epidemiological studies, and differences in study methods may contribute to conflicting reports of prevalence and incidence of DR and MO in diabetic populations. As new therapies for DR and its associated complications emerge, the need to capture and monitor new epidemiological data becomes increasingly important to be able to assess the impact and effectiveness of these therapies. Robust, longitudinal capture of patient data is, therefore, essential to evaluate the impact of current practice on the epidemiology of diabetic eye complications.

Effect of chromium picolinate on histopathological alterations in STZ and neonatal STZ diabetic rats

Earlier studies from our laboratory have indicated insulin sensitizing action of chromium picolinate as the mechanism of its anti-diabetic activity in experimental models of type I and type II diabetes. In the present investigation, we have evaluated the effects of chronic administration of chromium picolinate on the functional and histological alterations of streptozotocin (STZ)-induced diabetes in rats. Type I diabetes was induced by intravenous injection of STZ (40 mg/kg) in adult rats, whereas, type II diabetes was induced by intraperitoneal injection of STZ (90 mg/kg) in 2-day old rat pups which in adulthood develop abnormalities resembling type II diabetes. Chromium picolinate was administered at 8 microg/ml in drinking water for 6 weeks and was found to improve glucose tolerance and increase insulin sensitivity of STZ-diabetic rats. This treatment decrease elevated serum creatinine and urea levels as well as elevated serum levels of hepatic enzymes of both groups of diabetic rats. Histopathological studies of kidney and liver show decrease in the intensity and incidence of vacuolations, cellular infiltration and hypertrophy of STZ and nSTZ (neonatal STZ) diabetic rats. Chronic treatment with chromium picolinate however, did not alter the normal function or morphology of control rats. Chronic chromium picolinate at the therapeutic doses that improved glucose tolerance, was observed to have no hepatotoxic or nephrotoxic potential. It was rather found to improve renal and hepatic function and to reduce abnormalities associated with STZ-diabetes. Chromium picolinate could play an important role in the long term management of diabetes mellitus.

Diabetes control and complications: the role of glycated haemoglobin, 25 years on

The long-term complications of diabetes have major consequences for individual subjects and growing healthcare delivery and cost implications for society. Evidence for the benefits of good glycaemic control, as monitored by glycated haemoglobin measurements, has been developed in the 25 years since they were introduced to the point where HbA(1c) assays play central roles in patient management, clinical guidance and audit, and clinical trial design. In this review this evidence is examined and three classes of uncertainty identified that diminish confidence in the effectiveness of these roles for HbA(1c). 1 Analytical variability between different methods for HbA(1c) has restricted the application of clinical targets and this problem has recently been addressed by reference method standardization. There are two approaches to this which result in different HbA(1c) values and this discrepancy needs to be resolved. 2 Biological variability in HbA(1c) values between individuals also restricts its predictive role when applied to populations. The correlations between HbA(1c) measurements and various components of glycaemia (overall, fasting, postprandial) are still uncertain and differences in protein glycation and de-glycation are greater between subjects than often thought. The influence of variability in erythrocyte life span is an area where research is needed, especially in diabetic subjects. 3 Clinical variability is the most important and complex area of uncertainty. A predictive link between HbA(1c) and clinical outcomes is not as clear-cut as often stated. The correlation with the development of microvascular disease is well established in Type 1 diabetes, but in Type 2 subjects (90% of those with diabetes) the evidence that HbA(1c) monitoring is of value in predicting or preventing macrovascular disease is not strong, although it is the major cause of morbidity and early death in this group. It is recommended that, as a matter of urgency, these issues be examined, particularly within the context of self-care in diabetes.

Fluoropyrrolidine amides as dipeptidyl peptidase IV inhibitors

Amides derived from fluorinated pyrrolidines and 4-substituted cyclohexylglycine analogues have been prepared and evaluated as inhibitors of dipeptidyl dipeptidase IV (DP-IV). Analogues which incorporated (S)-3-fluoropyrrolidine showed good selectivity for DP-IV over quiescent cell proline dipeptidase (QPP). Compound 48 had good pharmacokinetic properties and was orally active in an oral glucose tolerance test in lean mice.

Effect of cogent db, a herbal drug, on plasma insulin and hepatic enzymes of glucose metabolism in experimental diabetes

AIMS

The present study was designed to investigate the effect of cogent db, a polyherbal drug on blood glucose, plasma insulin and the activities of hepatic glucose metabolic enzymes in alloxan-induced diabetic rats.

METHODS

Male Wistar rats body weight of 180-200 g (six normal and 18 diabetic rats) were used in this study. The rats were divided into four groups after the induction of alloxan diabetes. In the experiment, six rats were used in each group: Group 1, normal rats given 2 ml of saline; Group 2, diabetic control rats given 2 ml of saline; Group 3, diabetic rats given aqueous solution of cogent db (0.45 g/body kg weight); and Group 4, diabetic rats given aqueous solution of glibenclamide (600 micro g/kg body weight). The treatment was given for 40 days. After the treatment, fasting blood glucose, plasma insulin, urine sugar and the activities of hepatic glucose metabolic enzymes were determined in normal and experimental animals.

RESULTS

Treatment with cogent db resulted in a significant reduction in blood glucose and the activities of glucose-6-phosphatase and fructose-1,6-bisphosphatase in the liver, whereas the level of plasma insulin and hepatic hexokinase activity were significantly increased in alloxan-diabetic rats.

CONCLUSIONS

The present investigation suggests that cogent db controls the blood glucose level by increasing glycolysis and decreasing gluconeogenesis with a lower demand of pancreatic insulin than in untreated rats. This is possible because it regulates the activities of hepatic glucose metabolic enzymes.

Superoxide anion-dependent Raf/MEK/ERK activation by peroxisome proliferator activated receptor gamma agonists 15-deoxy-delta(12,14)-prostaglandin J(2), ciglitazone, and GW1929

In this study, we examined the signaling pathways for extracellular signal-related protein kinase (ERK) activation by three structurally different peroxisome proliferator activated receptor-gamma (PPARgamma) agonists. In murine C2C12 myoblasts, treatment with 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)), ciglitazone, and GW1929 leads to ERK1/2 phosphorylation in a time- and concentration-dependent manner. Consistent with ERK phosphorylation, mitogen activated protein/ERK kinase (MEK) phosphorylation as well as Raf-1 kinase activity are also accordingly stimulated, while the constitutive Ser259 phosphorylation of Raf-1 is decreased. The ERK phosphorylation induced by PPARgamma agonists is not blocked by the PKC inhibitors GF109203X and Ro31-8220, the PI3K inhibitor wortmannin, the Ras inhibitor FPTI, the negative mutant of Ras, or the PPARgamma antagonist bisphenol A diglycidil ether. Expression of PPARgamma2 without DNA binding domain or with a nonphosphorylatable mutant (S112A) fails to change ERK phosphorylation by 15d-PGJ(2). On the contrary, the ERK phosphorylation by PPARgamma agonists is inhibited by the MEK inhibitor PD98059, GSH, and permeable SOD mimetic MnTBAP. Chemiluminescence study reveals that these three PPARgamma agonists are able to induce superoxide anion production, with an efficacy similar to their action on ERK phosphorylation. Consistent with this notion, we also show that superoxide anion donor 2,3-dimethoxy-1,4-naphoquinone elicits ERK phosphorylation. In this study, we for the first time demonstrate a novel mechanism, independent of Ras activation but initiated by superoxide anion production, for PPARgamma agonists to trigger the Raf-MEK-ERK1/2 signaling pathway.

Desensitization of insulin secretion

Desensitization of insulin secretion describes a reversible state of decreased secretory responsiveness of the pancreatic beta-cell, induced by a prolonged exposure to a multitude of stimuli. These include the main physiological stimulator, glucose, but also other nutrients like free fatty acids and practically all pharmacological stimulators acting by depolarization and Ca2+ influx into the beta-cell. Desensitization of insulin secretion appears to be an important step in the manifestation of type 2 diabetes and in the secondary failure of oral antidiabetic treatment. In this commentary, the basic concepts and the controversial issues in the field will be outlined. With regard to glucose-induced desensitization, two fundamentally opposing concepts have emerged. The first is that desensitization is the consequence of functional changes in the beta-cell that impair glucose-recognition. The second is that long-term increased secretory activity leads to a depletion of releasable insulin, often in spite of increased insulin synthesis. The latter concept is more appropriately termed beta-cell exhaustion. The same dichotomy applies to the desensitization evoked by pharmacological stimuli: again the relative contributions of a decreased insulin content versus alterations in signal transduction are in dispute. The action of tolbutamide on beta-cells may be an example of desensitization caused by a lack of releasable insulin since the signaling mechanisms are nearly unchanged, whereas the action of phentolamine, an imidazoline, induces a strong desensitization without reducing insulin content or secretory granules, apparently by abolishing Ca2+ influx. With pharmacological agents it seems that both, alterations in signal transduction and decreased availability of releasable insulin, can contribute to the desensitized state of the beta-cell, the relative contribution being variable depending upon the exact nature of the secretory stimulus.

Future therapies

New and improved therapies are required for type 1 and type 2 diabetic patients to assist the return of glucose homeostasis to as near normal as possible. More intensive use of existing therapies is proving beneficial, while potential new agents are progressing in development. These include agents to improve and partially mimic insulin action, such as peroxisome proliferator-activated receptor-gamma (PPARgamma) agonists, stimulants of intracellular insulin signalling intermediates, and inhibitors of substances that deactivate insulin receptor tyrosine kinase activity. Novel agents to enhance nutrient-stimulated insulin release and promote the replication and neogenesis of beta-cells are emerging, along with new agents to combat obesity and dyslipidaemia. Gene therapy approaches to replace defective or destroyed beta-cells are feasible future options for both type 1 and type 2 diabetes.

Toxicological consequences of altered peroxisome proliferator-activated receptor gamma (PPARgamma) expression in the liver: insights from models of obesity and type 2 diabetes

The pivotal role of peroxisome proliferator-activated receptor gamma (PPARgamma) in the liver, although important for the regulation of genes involved in glucose and lipid metabolism, has generally not been fully appreciated. This may be due to the fact that PPARgamma, in contrast to PPARalpha or PPARdelta, is not abundantly expressed in liver under normal conditions. However, recent findings have revealed that in several murine models of obesity and type 2 diabetes mellitus (T2DM), PPARgamma mRNA and receptor protein are highly up-regulated in the liver, and that the receptor causes increased transcriptional activity as demonstrated by the activation of PPARgamma-responsive genes in the liver. Prolonged treatment of obese and diabetic mice, but not of lean control mice, with the selective PPARgamma ligands and activators, thiazolidinediones (TZDs), including troglitazone, rosiglitazone, or pioglitazone, has resulted in the development of severe hepatic centrilobular steatosis. In contrast to these effects in hepatocytes, TZD-mediated effects on Kupffer cells (down-regulation of proinflammatory cytokines) seem to be PPARgamma-independent. In view of the findings that sustained hepatic steatosis can lead to steatohepatitis and/or fibrosis and that troglitazone (but not the other TZDs) has been associated with rare but serious hepatotoxicity in patients, further insight into PPARgamma-mediated versus non-PPARgamma-mediated effects of TZDs is desirable. It is concluded that liver-specific effects associated with TZD antidiabetics may become relevant under conditions of selective PPARgamma up-regulation in the liver. Therefore, receptor expression in human liver tissue of obese and T2DM patients should deserve increased consideration in the future.

Insulinotropic meglitinide analogues

The loss of early-phase insulin secretion is an important and early event in the natural history of type 2 diabetes. Because a normal pattern of insulin secretion is essential for the effective control of postprandial metabolism, a rational basis for the development of agents that target early-phase insulin release exists. Conventional oral hypoglycaemic agents do not target, or adequately control, postprandial glycaemia. The emergence of new classes of oral agent with a more specific mode of action provides, for the first time, an opportunity to restore early-phase insulin release. One such drug class is the meglitinide analogues (repaglinide, nateglinide, and mitiglinide). These drugs are ideally suited for combination use with metformin. They could also prove effective in combination with a thiazolidinedione, a drug class that targets insulin resistance. Exogenous insulin is frequently required in the late management of type 2 diabetes. However, one hope for newer combinations of diabetic drugs is that the functional life of the beta cell can be extended, thereby delaying the need for insulin injections.

New pharmacologic agents for diabetes

New agents are being developed to address the underlying endocrinopathies and metabolic disturbances of type 2 diabetes. Stimulants of the nuclear peroxisome proliferator-activated receptor gamma (PPAR gamma) are being identified to selectively improve insulin actions, and dual agonists of PPAR gamma and PPAR alpha are being evaluated for enhanced control of hyperglycemia and dyslipidemia. Novel activators of insulin receptor phosphorylation and inhibitors of receptor dephosphorylation are offering encouraging leads for new agents. Analogues of glucagon-like peptide-1 that increase glucose-induced insulin secretion may additionally increase beta-cell neogenesis from progenitor duct cells. The amylin analogue pramlintide, which suppresses glucagon secretion and reduces weight, is advancing in clinical trial. Direct stimulants of glucose utilization and partial inhibitors of gluconeogenesis are providing useful new drug templates. Thus, new pharmacologic approaches are emerging to treat the multiple lesions of type 2 diabetes.