Is there a role for alpha-glucosidase inhibitors in the prevention of type 2 diabetes mellitus?

Effect of the addition of sitagliptin and miglitol on insulin-treated type 2 diabetes

INTRODUCTION

To examine the efficacy of sitagliptin and miglitol when added to ongoing insulin treatment in a patient with type 2 diabetes who had undergone partial gastrectomy.

METHODS

Continuous glucose monitoring (CGM) was performed and either sitagliptin or miglitol, or both, were added to fixed-dose insulin therapy. Blood was drawn at 0, 30, 60, and 120 min after breakfast, and C-peptide, glucagon, glucagon-like peptide (GLP)-1, and glucose-dependent insulinotropic peptide (GIP) were measured.

RESULTS

CGM showed that compared to insulin alone, the addition of either sitagliptin or miglitol, or both, to insulin achieved better glucose control. Compared to insulin alone, early postprandial increments in plasma C-peptide levels and suppressed glucagon levels were observed when sitagliptin was added. Glucagon suppression was even more prominent when both sitagliptin and miglitol were added. Compared to insulin alone, GLP-1 levels were higher during the early postprandial stage when sitagliptin or miglitol was added and even higher when both were added. GIP levels decreased when sitagliptin or miglitol, or both, were added to insulin therapy.

CONCLUSION

The authors showed that the addition of sitagliptin or miglitol, or both, was effective in this insulin-treated patient with diabetes who had undergone gastrectomy.

Potential new approaches to modifying intestinal GLP-1 secretion in patients with type 2 diabetes mellitus: focus on bile acid sequestrants

Type 2 diabetes mellitus is associated with a progressive decline in insulin-producing pancreatic β-cells, an increase in hepatic glucose production, and a decrease in insulin sensitivity. The incretin hormones glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) stimulate glucose-induced insulin secretion; however, in patients with type 2 diabetes, the incretin system is impaired by loss of the insulinotropic effects of GIP as well as a possible reduction in secretion of GLP-1. Agents that modify GLP-1 secretion may have a role in the management of type 2 diabetes. The currently available incretin-based therapies, GLP-1 receptor agonists (incretin mimetics) and dipeptidyl peptidase-4 (DPP-4) inhibitors (CD26 antigen inhibitors) [incretin enhancers], are safe and effective in the treatment of type 2 diabetes. However, they may be unable to halt the progression of type 2 diabetes, perhaps because they do not increase secretion of endogenous GLP-1. Therapies that directly target intestinal L cells to stimulate secretion of endogenous GLP-1 could possibly prove more effective than treatment with GLP-1 receptor agonists and DPP-4 inhibitors. Potential new approaches to modifying intestinal GLP-1 secretion in patients with type 2 diabetes include G-protein-coupled receptor (GPCR) agonists, α-glucosidase inhibitors, peroxisome proliferator-activated receptor (PPAR) agonists, metformin, bile acid mimetics and bile acid sequestrants. Both the GPCR agonist AR231453 and the novel bile acid mimetic INT-777 have been shown to stimulate GLP-1 release, leading to increased insulin secretion and improved glucose tolerance in mice. Similarly, a study in insulin-resistant rats demonstrated that the bile acid sequestrant colesevelam increased GLP-1 secretion and improved glucose levels and insulin resistance. In addition, the bile acid sequestrant colestimide (colestilan) has been shown to increase GLP-1 secretion and decrease glucose levels in patients with type 2 diabetes; these results suggest that the glucose-lowering effects of bile acid sequestrants may be partly due to their ability to increase endogenous GLP-1 levels. Evidence suggests that GPCR agonists, α-glucosidase inhibitors, PPAR agonists, metformin, bile acid mimetics and bile acid sequestrants may represent a new approach to management of type 2 diabetes via modification of endogenous GLP-1 secretion.

Preventive pharmacotherapy in type 2 diabetes mellitus

Over the last few decades certain demographic changes have been observed worldwide, which have led to an increase in the prevalence of chronic non-communicable diseases. Type 2 diabetes mellitus and associated cardiovascular disease are major contributors to this disease burden leading to rising morbidity and mortality. It is worrisome to see that type 2 diabetes with its micro- and macrovascular complications is occurring in younger populations where it was hitherto unseen. Prevention appears to be an important strategy to reduce the burden of disease. Along with inculcating healthy lifestyle habits across populations, it may be suitable to use preventive pharmacotherapy in those with pre-diabetes and / or other risk factors like obesity, hypertension, and on the like. Metformin, alpha glucosidase inhibitors like acarbose, miglitol, and voglibose, and pioglitazone have all been used with success. The issues of compliance and adverse effects during long-term use have tempered the use of these drugs. The best approach would be to motivate the patient for effective lifestyle changes, and pharmacological management if the lifestyle changes are not successful in achieving their goals.

A pilot study of the efficacy of miglitol and sitagliptin for type 2 diabetes with a continuous glucose monitoring system and incretin-related markers

Background

Glucose fluctuations including robust postprandial hyperglycemia are a risk for promoting atherosclerosis and diabetic complications. The α-glucosidase inhibitors and the dipeptidyl peptidase-4 (DPP-4) inhibitors have been found to effectively decrease postprandial hyperglycemia independently. Therefore, glycemic control with the combination of these drugs is warranted.

Methods

Continuous glucose monitoring (CGM) was performed for 3 patients with type 2 diabetes and 1 control subject from the beginning to the end of the study. Medications were not administered to any of the subjects on the first day of the study. From the second day to the end of study (days 2-5), the subjects received miglitol (150 mg per day) and on days 4 and 5, sitagliptin (50 mg per day) was added to the treatment regimen. On the first, third, and fifth days of the study, blood was drawn at 0, 30, 60, 120, 180, and 240 min after breakfast for measurements of serum insulin, 1,5-anhydroglucitol (1,5-AG), plasma glucagon, glucagon-like peptide-1 (GLP-1), and glucose-dependent insulinotropic peptide (GIP).

Results

Measurements of CGM and 1,5-AG levels showed that miglitol attenuated the escalation and fluctuation of glucose levels, and this was even more pronounced with the combination of miglitol and sitagliptin. The patterns of insulin secretion and glucagon secretion with miglitol alone or with a combination of miglitol and sitagliptin were various in the study subjects. Miglitol alone enhanced the release of GLP-1 in 1 patient with type 2 diabetes and the control subject, whereas the combination of miglitol and sitagliptin increased GLP-1 levels to varying degrees in all the subjects. Except for 1 subject, none of the subjects showed any change in GIP levels after the addition of sitagliptin, compared to the administration of miglitol alone.

Conclusions

In conclusion, CGM measurements revealed that a combination of the α-GI miglitol and the DPP-4 inhibitor sitagliptin effectively reduced postprandial glucose fluctuation and stabilized blood glucose levels. Completely different response patterns of insulin, glucagon, GLP-1, and GIP were observed among the study subjects with either medication alone or in combination, suggesting that individual hormone-dependent glycemic responses to the α-GI and DPP-4 inhibitors are complicated and multifactorial.

Incretin therapy--present and future

Although newer treatments for type 2 diabetes (T2D) patients have produced continual improvements in outcome, a large and growing population with prediabetes remains under-treated. In the last few years, incretin-based therapies have become an important treatment option for patients with T2D. There are two classes of incretin agents: the dipeptidyl peptidase-4 (DPP-4) inhibitors and the glucagon like peptide 1 (GLP-1) receptor agonists. The ultimate goal of agents within both of these classes is to increase GLP-1 signaling, which results in augmented glucose-induced insulin secretion, inhibition of glucagon secretion, and decreased appetite. This should result in improved regulation of glucose homeostasis. GLP-1 receptor agonists enable patients to achieve significant weight loss. In contrast, DPP-4 inhibitors result in a less dramatic increase in GLP-1 levels; therefore, they are weight neutral. Incretin therapies are currently recommended for use early in the treatment algorithm for T2D patients whose disease is not manageable by diet and exercise alone, but the potential for these agents may be farther reaching. Current studies are evaluating the potential benefits of combining incretin therapies with basal insulin to provide continuous glucose control before and after meals. In addition, these agents may be promising for patients with prediabetes since they effectively reduce glycosylated hemoglobin levels and fasting plasma glucose levels, enable weight control, and have the potential to preserve β-cell function. Clearly, all of these properties are desirable for patients with prediabetes.

Novel tripeptides with α-glucosidase inhibitory activity isolated from silk cocoon hydrolysate

Active compounds with antidiabetic potential were isolated from silk peptide E5K6 by consecutive ultrafiltration and gel filtration using Biogel P-2 and RS-HPLC using a YMC-Pack Pro C18 column. The highest α-glucosidase inhibitory activity of silk peptide E5K6 resulted from fractions with MW <1 kDa. The activities of gel-filtered fractions from silk peptide E5K6 of <1 kDa were assayed in vitro, demonstrating that the fourth peak (F4) had the highest α-glucosidase inhibitory activity (IC(50) = 37.1 mg/mL). F4 of silk peptide E5K6 was separated by HPLC into two peaks. Moreover, the purified compounds were identified as Gly-Glu-Tyr (GEY, MW = 367 Da) and Gly-Tyr-Gly (GYG, MW = 295 Da) according to amino acid sequences, and their α-glucosidase inhibitory activities (IC(50)) were 2.7 and 1.5 mg/mL, respectively.

Coffee polyphenols modulate whole-body substrate oxidation and suppress postprandial hyperglycaemia, hyperinsulinaemia and hyperlipidaemia

Postprandial energy metabolism, including postprandial hyperglycaemia, hyperinsulinaemia and hyperlipidaemia, is related to the risk for developing obesity and CVD. In the present study, we examined the effects of polyphenols purified from coffee (coffee polyphenols (CPP)) on postprandial carbohydrate and lipid metabolism, and whole-body substrate oxidation in C57BL/6J mice. In mice that co-ingested CPP with a lipid-carbohydrate (sucrose or starch)-mixed emulsion, the respiratory quotient determined by indirect calorimetry was significantly lower than that in control mice, whereas there was no difference in VO2 (energy expenditure), indicating that CPP modulates postprandial energy partitioning. CPP also suppressed postprandial increases in plasma glucose, insulin, glucose-dependent insulinotropic polypeptide and TAG levels. Inhibition experiments on digestive enzymes revealed that CPP inhibits maltase and sucrase, and, to a lesser extent, pancreatic lipase in a concentration-dependent manner. Among the nine kinds of polyphenols (caffeoyl quinic acids (CQA), di-CQA, feruloyl quinic acids (FQA)) contained in CPP, di-CQA showed more potent inhibitory activity than CQA or FQA on these digestive enzymes, suggesting a predominant role of di-CQA in the regulation of postprandial energy metabolism. These results suggest that CPP modulates whole-body substrate oxidation by suppressing postprandial hyperglycaemia and hyperinsulinaemia, and these effects are mediated by inhibiting digestive enzymes.

Oral anti-diabetic drugs for the prevention of Type 2 diabetes

AIM

To determine the comparative efficacy of oral anti-diabetic drugs in preventing the development of Type 2 diabetes.

METHODS

A systematic literature search of MEDLINE, EMBASE and Cochrane CENTRAL was conducted for randomized controlled trials evaluating oral anti-diabetic drugs in patients at high risk for developing Type 2 diabetes. Mixed-treatment comparison meta-analysis methods were used to evaluate the relative risks and risk differences of developing Type 2 diabetes, along with associated 95% credible intervals.

RESULTS

Overall, 20 trials (n = 23 230 participants) were included. Upon mixed-treatment comparison meta-analysis, thiazolidinediones, alpha-glucosidase inhibitors and biguanides significantly reduced the relative risk of developing diabetes by 64, 40 and 27%, respectively, compared with control. Sulphonylureas and glinides showed no significant effect. Moreover, thiazolidinediones significantly reduced the relative risk of diabetes by 50% compared with biguanides and trended towards a 40% risk reduction vs. alpha-glucosidase inhibitors [relative risk 0.60 (95% credible intervals 0.34-1.02)]. None of the results were appreciably altered upon subgroup or sensitivity analyses. When evaluating risk differences compared with control, thiazolidinediones (-9%, number needed to treat = 11), alpha-glucosidase inhibitors (-7%, number needed to treat = 14) and biguanides (-7%, number needed to treat = 14) continued to show significant benefit.

CONCLUSIONS

Of the oral anti-diabetic drugs evaluated to prevent Type 2 diabetes, thiazolidinediones were associated with the greatest risk reduction compared with control and associated with greater risk reduction than biguanides. Alpha-glucosidase inhibitors and biguanides performed similarly, and better than control, while sulphonylureas and glinides provided no significant benefit.

Comparison of 1-deoxynojirimycin and aqueous mulberry leaf extract with emphasis on postprandial hypoglycemic effects: in vivo and in vitro studies

Carbohydrate digestion by α-glucosidase and subsequent glucose uptake at the brush border are critical for postprandial blood glucose control. Any specific inhibitors are useful as hyperglycemia modulating agents. In this study, it was postulated that an array of active components in mulberry leaf extract (MLE) may provide higher potency in inhibiting intestinal glucose absorption compared to the single component 1-deoxynojirimycin (DNJ), which is recognized as a promising inhibitor of intestinal glucose absorption. Both MLE and DNJ were active in inhibiting α-glucosidase. However, in Caco-2 cells, only MLE showed significant inhibition of 2-deoxyglucose uptake, whereas DNJ was ineffective. For glucose loading, co-administration of MLE resulted in potent inhibitions of glucose responses compared to those by DNJ in Sprague Dawley (SD) rats, but this was not found for maltose loading. These novel findings add evidence that the unabsorbed phytochemicals in MLE compete with glucose for intestinal glucose transporters, but DNJ itself does not. We also evaluated the timing of MLE consumption. By administering MLE for 30 min before glucose loading, the incremental area under the curve (IAUC) was significantly lowered in the rats, as compared to a simultaneously administered group. Similarly, cellular glucose uptake was significantly reduced in Caco-2 cells following pretreatment.

Changes in α-glucosidase activities along the jejunal-ileal axis of normal rats by the α-glucosidase inhibitor miglitol

Miglitol, an α-glucosidase inhibitor that inhibits postprandial hyperglycemia by delaying carbohydrate digestion and absorption along the jejunal-ileal axis, has recently been approved for use in patients with type 2 diabetes mellitus. Miglitol treatment may lead to increased α-glucosidase activities toward the ileum because carbohydrate flow toward the ileum increases. However, it is not yet known if miglitol treatment alters the α-glucosidase activities along the jejunal-ileal axis. In this study, we examined the effects of miglitol supplementation for 3 or 7 days on α-glucosidase activities along the jejunal-ileal axis of Wistar rats. Supplementation with miglitol for 3 or 7 days in rats increased tissue weights of the lower jejunum and ileum, but did not alter tissue weights of the upper jejunum and cecum or the contents of the cecum. Furthermore, supplementation with miglitol for 7 days reduced the activities of isomaltase and maltase in the upper jejunum and increased the activities of sucrase, isomaltase, and maltase in the lower jejunum and ileum. These results suggest that the delay in carbohydrate digestion and absorption along the jejunal-ileal axis by miglitol supplementation in rats is associated with increased α-glucosidase activities toward the ileum.

New glucosidase inhibitors from an ayurvedic herbal treatment for type 2 diabetes: structures and inhibition of human intestinal maltase-glucoamylase with compounds from Salacia reticulata

An approach to controlling blood glucose levels in individuals with type 2 diabetes is to target alpha-amylases and intestinal glucosidases using alpha-glucosidase inhibitors acarbose and miglitol. One of the intestinal glucosidases targeted is the N-terminal catalytic domain of maltase-glucoamylase (ntMGAM), one of the four intestinal glycoside hydrolase 31 enzyme activities responsible for the hydrolysis of terminal starch products into glucose. Here we present the X-ray crystallographic studies of ntMGAM in complex with a new class of alpha-glucosidase inhibitors derived from natural extracts of Salacia reticulata, a plant used traditionally in Ayuverdic medicine for the treatment of type 2 diabetes. Included in these extracts are the active compounds salacinol, kotalanol, and de-O-sulfonated kotalanol. This study reveals that de-O-sulfonated kotalanol is the most potent ntMGAM inhibitor reported to date (K(i) = 0.03 microM), some 2000-fold better than the compounds currently used in the clinic, and highlights the potential of the salacinol class of inhibitors as future drug candidates.

Combination treatment with alogliptin and voglibose increases active GLP-1 circulation, prevents the development of diabetes and preserves pancreatic beta-cells in prediabetic db/db mice

AIM

Alogliptin, a dipeptidyl peptidase-4 (DPP-4) inhibitor, and voglibose, an alpha-glucosidase inhibitor, have different but complementary mechanisms of action on glucagon-like peptide-1 (GLP-1) regulation and glucose-lowering effects. The present study evaluated the chronic effects of combination treatment with alogliptin and voglibose in prediabetic db/db mice.

METHODS

Alogliptin (0.03%) and voglibose (0.001%) alone or in combination were administered in the diet to prediabetic db/db mice.

RESULTS

After 3 weeks, voglibose treatment increased GLP-1 secretion (voglibose alone, 1.6-fold; alogliptin plus voglibose, 1.5-fold), while it decreased plasma glucose-dependent insulinotropic polypeptide (GIP) (voglibose alone, -30%; alogliptin plus voglibose, -29%). Alogliptin, voglibose and combination treatment decreased plasma DPP-4 activity by 72, 15 and additively by 80%, respectively, and increased plasma active GLP-1 levels by 4.5-, 1.8- and synergistically by 9.1-fold respectively. Combination treatment increased plasma insulin by 3.6-fold (alogliptin alone, 1.3-fold; voglibose alone, 1.8-fold), decreased plasma glucagon by 30% (alogliptin alone, 11%; voglibose alone, 8%), and prevented the development of diabetes, much more effectively than either agent alone. After 4 weeks, alogliptin, voglibose and combination treatment increased pancreatic insulin content by 1.6-, 3.4- and synergistically by 8.5-fold respectively. Furthermore, combination treatment resulted in an increased expression of insulin, pancreatic and duodenal homeobox 1 (PDX1) and glucose transporter 2 (GLUT2), and maintenance of normal beta/alpha-cell distribution in the pancreatic islet.

CONCLUSIONS

Chronic treatment with alogliptin in combination with voglibose concurrently increased active GLP-1 circulation, increased insulin secretion, decreased glucagon secretion, prevented the onset of the disease, and preserved pancreatic beta-cells and islet structure in prediabetic db/db mice.

Treatment of type 2 diabetes mellitus with orally administered agents: advances in combination therapy

OBJECTIVE

To discuss the effects and clinical benefit provided by combining various orally administered antidiabetic drugs (OADs) for the treatment of type 2 diabetes and to examine the advantages of single-tablet combinations with respect to targeting hyperglycemia and adherence.

METHODS

A review of randomized controlled trials that studied OAD combinations for the treatment of type 2 diabetes was conducted by using search terms in PubMed.

RESULTS

Reported data have documented that OAD combination therapies have additional benefits over monotherapy in terms of glycemic efficacy. Results from randomized controlled trials on a range of OAD combinations have demonstrated differences in safety and efficacy. The use of single-tablet OAD combinations has been shown to improve adherence in patients.

CONCLUSION

The development of single-tablet OAD combinations that can address all aspects of glycemia with a favorable tolerability profile has the potential to help patients manage their glycemic control more effectively and to minimize the risk of long-term diabetes-related complications. In addition, single-tablet combinations of agents offer improved convenience for patients as well as potential cost benefits. Thus, they represent an important treatment option for type 2 diabetes.

Capillary electrophoresis as a screening tool for alpha amylase inhibitors in plant extracts

Capillary electrophoresis (CE) method was developed for screening plant extract for potential alpha amylase (AA) inhibitory activity. The method was validated against a well established UV method. Overall, the proposed method was shown able to detect plants with significant alpha amylase inhibitory activity but not those with rather clinically insignificant activities. Fifty plant species were screened using both the proposed CE method and the UV method and seven plant species were found to possess significant AA inhibitory activities. Two plant species were proved to have alpha amylase inhibitory activity for the first time.

Aqueous extract of Abutilon indicum Sweet inhibits glucose absorption and stimulates insulin secretion in rodents

The objective of this study was to evaluate the antidiabetic effects of the aqueous extract derived from the Thai Abutilon indicum Sweet plant and to explore its effects on intestinal glucose absorption and insulin secretion. The authors hypothesized that the plasma glucose level could be reduced through the inhibition of glucose absorption and/or the enhancement of insulin secretion. Administration of the extract (0.5 and 1 g/kg body weight) in an oral glucose tolerance test led to a significant reduction in plasma glucose levels in 30 minutes after the administration in moderately diabetic rats, as compared with untreated rats (P < .05), and this was at a faster rate than the use of an antidiabetic drug, glibenclamide. The inhibition of glucose absorption through the small intestine was investigated using an everted intestinal sac. The results showed that the extract at concentrations of 0.156 to 5 mg/mL caused a reduction of glucose absorption in a dose response manner. The maximum response was noted at a dose of 2.5 mg/mL. The promotion of the extract on insulin secretion was confirmed by incubating beta cell of pancreatic islets and INS-1E insulinoma cells with the extract at 1 to 1000 microg/mL. These observations suggest that the aqueous extract from the A indicum plant has antidiabetic properties, which inhibited glucose absorption and stimulated insulin secretion. Phytochemical screening also revealed that the extract contained alkaloids, flavonoids, tannins, glycosides, and saponins that could account for the observed pharmacologic effects of the plant extract.

The potential of cinnamon to reduce blood glucose levels in patients with type 2 diabetes and insulin resistance

AIM

Cinnamon has a long history as an antidiabetic spice, but trials involving cinnamon supplementation have produced contrasting results. The aim of this review was to examine the results of randomized controlled clinical trials of cinnamon and evaluate the therapeutic potential amongst patients with diabetes and insulin-resistant patients, particularly the ability to reduce blood glucose levels and inhibit protein glycation.

METHODS

A systematic electronic literature search using the medical subject headings 'cinnamon' and 'blood glucose' was carried out to include randomized, placebo-controlled in vivo clinical trials using Cinnamomum verum or Cinnamomum cassia conducted between January 2003 and July 2008.

RESULTS

Five type 2 diabetic and three non-diabetic studies (total N = 311) were eligible. Two of the diabetic studies illustrated significant fasting blood glucose (FBG) reductions of 18-29% and 10.3% (p < 0.05), supported by one non-diabetic trial reporting an 8.4% FBG reduction (p < 0.01) vs. placebo, and another illustrating significant reductions in glucose response using oral glucose tolerance tests (p < 0.05). Three diabetic studies reported no significant results.

CONCLUSIONS

Whilst definitive conclusions cannot be drawn regarding the use of cinnamon as an antidiabetic therapy, it does possess antihyperglycaemic properties and potential to reduce postprandial blood glucose levels. Further research is required to confirm a possible correlation between baseline FBG and blood glucose reduction and to assess the potential to reduce pathogenic diabetic complications with cinnamon supplementation.

Voglibose for prevention of type 2 diabetes mellitus: a randomised, double-blind trial in Japanese individuals with impaired glucose tolerance

BACKGROUND

The increased prevalence of type 2 diabetes mellitus is a major concern for health providers. We therefore assessed whether voglibose, an alpha-glucosidase inhibitor, could prevent the development of type 2 diabetes in high-risk Japanese individuals with impaired glucose tolerance.

METHODS

1780 eligible patients on a standard diet and taking regular exercise with impaired glucose tolerance were randomly assigned to oral voglibose 0.2 mg three times a day (n=897) or placebo (n=883) in a multicentre, double-blind, parallel group trial. Treatment was continued until participants developed type 2 diabetes (primary endpoint) or normoglycaemia (secondary endpoint), or for a minimum of 3 years, subject to the findings of an interim analysis. Analysis was by full analysis set. This trial is registered with the University Hospital Medical Information Network (UMIN) clinical trials registry, number UMIN 000001109.

FINDINGS

In the interim analysis, voglibose was better than placebo (p=0.0026) in individuals treated for an average of 48.1 weeks (SD 36.3). Patients treated with voglibose had a lower risk of progression to type 2 diabetes than did those on placebo (50 of 897 vs 106 of 881; hazard ratio 0.595, 95% CI 0.433-0.818; p=0.0014). More people in the voglibose group achieved normoglycaemia than did those in the placebo group (599 of 897 vs 454 of 881; 1.539, 1.357-1.746; p<0.0001). 810 (90%) of 897 patients in the voglibose group had adverse events versus 750 (85%) of 881 in the placebo group. Serious adverse events (all one each) in the voglibose group were cholecystitis, colonic polyp, rectal neoplasm, inguinal hernia, liver dysfunction, and subarachnoid haemorrhage, and in the placebo group were cerebral infarction and cholecystitis.

INTERPRETATION

Voglibose, in addition to lifestyle modification, can reduce the development of type 2 diabetes in high-risk Japanese individuals with impaired glucose tolerance.

FUNDING

Takeda.

Chronic administration of voglibose, an alpha-glucosidase inhibitor, increases active glucagon-like peptide-1 levels by increasing its secretion and decreasing dipeptidyl peptidase-4 activity in ob/ob mice

Administration of an alpha-glucosidase inhibitor, voglibose, increases the secretion of glucagon-like peptide (GLP)-1, a key modulator of pancreatic islet hormone secretion and glucose homeostasis. In the present study, novel mechanisms by which voglibose increases active GLP-1 circulation were evaluated. Voglibose (0.001 and 0.005%) was administered in the diet to ob/ob mice for 1 day or 3 to 4 weeks to determine effects on incretin profiles and plasma activity of dipeptidyl peptidase-4 (DPP-4), an enzyme responsible for GLP-1 degradation. Voglibose showed no direct inhibitory effect against DPP-4 in vitro (DPP-4 inhibitor alogliptin, IC(50) < 10 nM). Likewise, 1-day treatment with voglibose did not change plasma DPP-4 activity; however, it increased plasma active GLP-1 by 1.6- to 3.4-fold. After chronic treatment, voglibose stimulated GLP-1 secretion, as evidenced by the 1.3- to 1.5-fold increase in plasma active plus inactive amidated GLP-1 levels. Plasma DPP-4 activity was decreased unexpectedly by 40 to 51%, resulting from reduced plasma DPP-4 concentrations in voglibose-treated mice. Voglibose increased GLP-1 content by 1.5- to 1.6-fold and 1.4- to 1.6-fold in the lower intestine and colon, respectively. The increased GLP-1 content in the colon was associated with elevated expression of gut glucagon gene. Chronic treatment with voglibose resulted in 1.9- to 4.1-fold increase in active GLP-1 circulation, which was higher than 1-day treatment. A similar treatment with pioglitazone (0.03%), an insulin sensitizer, did not affect plasma DPP-4 activity or GLP-1 levels. These results suggest that increased GLP-1 secretion, decreased DPP-4 activity, and increased gut GLP-1 content may have contributed to increased active GLP-1 circulation after chronic treatment with voglibose in a glucose control-independent manner in ob/ob mice.

Microarray based analysis of temperature and oxidative stress induced messenger RNA in Schistosoma mansoni

The body's defense against schistosome infection can take many forms. For example, upon developing acute schistosomiasis, patients often have fever coinciding with larval maturation, migration and early oviposition. As the infection becomes established, the parasite comes under oxidative stress generated by the host immune system. The most common treatment for schistosomiasis is the anti-helminthic drug praziquantel. Its effectiveness, however, is limited due to its inability to kill schistosomes 2-4 weeks post-infection. Clearly there is a need for new anti-schistosomal drugs. We hypothesize that gene products expressed as part of a protective response against heat and/or oxidative stress are potential therapeutic targets for future drug development. Using a 12,166 element oligonucleotide microarray to characterize Schistosoma mansoni genes induced by heat and oxidative stress we found that 1878 S. mansoni elements were significantly induced by heat stress. These included previously reported heat-shock genes expressing homologs of HSP40, HSP70 and HSP86. One thousand and one elements were induced by oxidative stress including those expressing homologs of superoxide dismutase, glutathione peroxidase and aldehyde dehydrogenase. Seventy-two elements were common to both stressors and could potentially be exploited in the development of novel anti-schistosomal therapeutics.

Orlistat in the prevention of diabetes in the obese patient

There has been an increase in the concern about preventing type 2 diabetes mellitus (T2DM), a disease with great and increasing prevalence. The prevalence of obesity, physical inactivity, Western processed diet, important risk factors for the development of T2DM, are also rising. Free fatty acids are increased in obesity and reduce insulin clearance and increase hepatic glucose production. Implementation of a healthy lifestyle has been show to slow the progression of impaired glucose tolerance to T2DM. Orlistat is an inhibitor of lipase activity, with proved efficacy in body weight reduction and long-term management of obesity and more favorable effects on carbohydrate metabolism and it was prospectively shown in XENDOS study that orlistat promoted long-term weight loss and prevented T2DM onset in obese individuals with normal and impaired glucose tolerance at baseline over four years. This benefit could be associated to the weight loss itself, to the limited absorption of lipids and reduction of plasma free fatty acids, to increased production of incretins or to modulation of secretion of cytokines by adipocytes, all effects secondary to orlistat treatment. A proposed strategy is to identify subjects at highest risk to receive a drug intervention, using lifestyle interventions alone at the community level.

Effects of miglitol, an alpha-glucosidase inhibitor, on glycaemic status and histopathological changes in islets in non-obese, non-insulin-dependent diabetic Goto-Kakizaki rats

Miglitol, a 1-deoxynojirimycin derivative, is an alpha-glucosidase inhibitor. In the present study, the effects of acute (single-dose) and chronic (8-week) oral administration of miglitol in Goto-Kakizaki (GK) rats, an animal model of type 2 diabetes, were investigated. Dose-dependent decreases in incremental blood glucose concentrations integrated over a period of 2 h (deltaAUC0-2 h) for values of blood glucose after sucrose-loading in miglitol-treated GK rats were observed following an acute oral administration of miglitol (1, 3 or 10 mg/kg body weight). At 10 mg/kg, the deltaAUC0-2 h of blood glucose was decreased by 45 % compared with the control group. Following the oral administration of miglitol in a dietary mixture (10 mg, 20 mg or 40 mg miglitol/100 g control diet) for 8 weeks, the ratio of HbA1c at 8 weeks compared with 0 weeks in GK rats treated with 40 mg miglitol/100 g control diet miglitol was significantly decreased compared with control GK rats without changes in body weight. In oral glucose tolerance testing, miglitol caused a slight decrease in the deltaAUC0-2 h of plasma glucose concentration. In addition, miglitol treatment slightly inhibited the reduction in beta-cell mass, and lessened the irregular contours and fibrosis of the islets in GK rats. These results indicate that miglitol ameliorates the hyperglycaemic state of GK rats and the impaired function of the pancreatic islets, as well as preventing the degeneration of islets in GK rats.

Thioglycosides as inhibitors of hSGLT1 and hSGLT2: potential therapeutic agents for the control of hyperglycemia in diabetes

The treatment of diabetes has been mainly focused on maintaining normal blood glucose concentrations. Insulin and hypoglycemic agents have been used as standard therapeutic strategies. However, these are characterized by limited efficacy and adverse side effects, making the development of new therapeutic alternatives mandatory. Inhibition of glucose reabsorption in the kidney, mediated by SGLT1 or SGLT2, represents a promising therapeutic approach. Therefore, the aim of the present study was to evaluate the effect of thioglycosides on human SGLT1 and SGLT2. For this purpose, stably transfected Chinese hamster ovary (CHO) cells expressing human SGLT1 and SGLT2 were used. The inhibitory effect of thioglycosides was assessed in transport studies and membrane potential measurements, using alpha-methyl-glucoside uptake and fluorescence resonance energy transfer, respectively. We found that some thioglycosides inhibited hSGLT more strongly than phlorizin. Specifically, thioglycoside I (phenyl-1'-thio-beta-D-glucopyranoside) inhibited hSGLT2 stronger than hSGLT1 and to a larger extent than phlorizin. Thioglycoside VII (2-hydroxymethyl-phenyl-1'-thio-beta-D-galacto-pyranoside) had a pronounced inhibitory effect on hSGLT1 but not on hSGLT2. Kinetic studies confirmed the inhibitory effect of these thioglycosides on hSGLT1 or hSGLT2, demonstrating competitive inhibition as the mechanism of action. Therefore, these thioglycosides represent promising therapeutic agents for the control of hyperglycemia in patients with diabetes.

Antidiabetic agents in subjects with mild dysglycaemia: prevention or early treatment of type 2 diabetes?

Besides lifestyle, various pharmacological treatments have proven their efficacy to reduce the incidence of type 2 diabetes in high-risk individuals, especially in those with impaired glucose tolerance (IGT) and/or impaired fasting glucose (IFG). Major placebo-controlled clinical trials demonstrated favourable effects of various glucose-lowering drugs generally used for the treatment of type 2 diabetes, i.e. metformin, acarbose and thiazolidinediones (glitazones). These trials showed a lower rate of progression to overt diabetes and a higher regression rate to a normal glucose status with active treatment as compared to placebo after a follow up of several years. Ongoing trials should confirm such a favourable effect with those drugs and may demonstrate a similar protective effect with other pharmacological approaches such as glinides or even basal insulin regimen. However, the reported favourable effects were generally observed while the subjects were still on treatment, and partially vanished after a rather short period of wash-out of several weeks. Therefore, the distinction between a true preventing effect and simply a masking effect is difficult with glucose-lowering drugs. In addition, as type 2 diabetes is a progressive disease, it is still questionable whether the effect corresponds to a prevention effect or only to a postponing of the development of the disease. Owing to the pathophysiology of the disease, the only way to block the progression of type 2 diabetes is probably to avoid the progressive loss of beta-cell function and/or mass. Whatsoever, these data obtained in large clinical trials bring further argument to support early treatment of diabetes, even at a prediabetic state, in order to stop the vicious circle leading to an inevitable deterioration of glycaemia in predisposed subjects.

Non-alcoholic steatohepatitis in children

Non-alcoholic steatohepatitis (NASH) is an important liver disease in children; it can cause cirrhosis in children. The disease mechanism involves hepatic insulin resistance with hyperinsulinemia and changes in certain adipocytokines and inflammatory mediators. The differential diagnosis of childhood NASH includes metabolic disorders, drug hepatotoxicity, and alcoholic hepatitis in adolescent patients. The histologic features in childhood NASH often differ from those in adults who have NASH. Treatment is gradual weight loss through changes in food intake patterns and increased levels of physical activity; the role of drug treatment of NASH in children is an area of ongoing research.

Comparative safety of newer oral antidiabetic drugs

Oral antidiabetic agents were introduced into clinical practice during the 1950s. Biguanides and sulfonylureas are still used extensively today and their safety and tolerability profiles are well defined. Developments and refinements within these classes have included the introduction of second- and third-generation sulfonylureas, the introduction of modified-release preparations, and the emergence of fixed-dose preparations with metformin and with novel drugs. The latter include the thiazolidinediones, agents with a putative genomic mechanism of action that have been under intense scrutiny since the emergence of severe hepatotoxicity with troglitazone. Recent concerns about thiazolidinediones have centred on the issue of oedema and the risk of precipitating heart failure in vulnerable patients. Only prolonged exposure will determine the long-term safety of thiazolidinediones. Rapid-acting non-sulfonylurea secretagogues appear to be effective and perhaps safer than sulfonylureas in some groups of patients with certain comorbidities (e.g., those with renal impairment). alpha-Glucosidase inhibitors have an excellent safety record and acarbose has been shown to retard the progression from impaired glucose tolerance to Type 2 diabetes. However, their use is limited by tolerability issues.

Antidiabetic activity of lipophilic (-)-epigallocatechin-3-gallate derivative under its role of alpha-glucosidase inhibition

(-)-Epigallocatechin-3-gallate (EGCG), a component of catechins, has been shown to reduce blood glucose levels. In the present study, we investigated the antidiabetic activity and its mechanism of lipophilic EGCG derivative (L-EGCGd) in streptozotocin (STZ)-induced diabetic rats. L-EGCGd was chemically modified from traditional hydrophilic EGCG. After 30 days treatment, plasma levels of glucose were significantly reduced by 40.5+/-7.0% and 17.0+/-2.8% in groups administered 50 or 25 mg kg(-1)d(-1) L-EGCGd, respectively, as compared with that in the diabetic control group. Lipid metabolites, such as total cholesterol (TC), triglyceride (TG) and low-density lipoprotein cholesterol (LDLC) were effectively attenuated by L-EGCGd administration, but plasma HDLC levels did not change significantly. The oral glucose tolerance test (OGTT) greatly revealed the improved ability of glucose tolerance with treatment of L-EGCGd. L-EGCGd only retarded the postprandial rise in blood glucose with sucrose loading but not glucose loading. And activity of alpha-glucosidase was inhibited by 50% at the concentration of 246.6 microg ml(-1) L-EGCGd. As a result, we first demonstrated that the purified form of compound L-EGCGd possessed the hypoglycemic effect under its role of alpha-glucosidase inhibition, and therefore should be possibly accepted as an alternative oral medication protecting patients against postprandial hyperglycemic toxicity on the treatment of diabetes and its complications.

A review of the economic evidence for acarbose in the prevention of diabetes and cardiovascular events in individuals with impaired glucose tolerance

The highly prevalent, prediabetic condition of impaired glucose tolerance (IGT) confers a high risk for type 2 diabetes mellitus (T2DM) and cardiovascular disease (CVD). There is an emerging body of cost-effectiveness literature in the management of IGT. For acarbose, an alpha-glucosidase inhibitor, economic analyses have been conducted for Spain, Germany, Sweden and Canada. In Spain, acarbose was more effective and less costly (dominant) compared with placebo. In Germany, the cost per patient free of diabetes was under Pounds 800; acarbose was dominant for those at high risk for T2DM, CVD or both, and a similar outcome in the Swedish study. In Canada, acarbose was dominant compared with no intervention and very cost-effective compared with metformin [C Dollars 1798/life years gained (LYG)]. The particularly cost-effective outcomes or cost savings delivered by acarbose for IGT subjects at high risk for T2DM and/or CVD render an IGT-intervention program prioritised to such high-risk individuals an economically attractive strategy.

Inhibition of recombinant human maltase glucoamylase by salacinol and derivatives

Inhibitors targeting pancreatic alpha-amylase and intestinal alpha-glucosidases delay glucose production following digestion and are currently used in the treatment of Type II diabetes. Maltase-glucoamylase (MGA), a family 31 glycoside hydrolase, is an alpha-glucosidase anchored in the membrane of small intestinal epithelial cells responsible for the final step of mammalian starch digestion leading to the release of glucose. This paper reports the production and purification of active human recombinant MGA amino terminal catalytic domain (MGAnt) from two different eukaryotic cell culture systems. MGAnt overexpressed in Drosophila cells was of quality and quantity suitable for kinetic and inhibition studies as well as future structural studies. Inhibition of MGAnt was tested with a group of prospective alpha-glucosidase inhibitors modeled after salacinol, a naturally occurring alpha-glucosidase inhibitor, and acarbose, a currently prescribed antidiabetic agent. Four synthetic inhibitors that bind and inhibit MGAnt activity better than acarbose, and at comparable levels to salacinol, were found. The inhibitors are derivatives of salacinol that contain either a selenium atom in place of sulfur in the five-membered ring, or a longer polyhydroxylated, sulfated chain than salacinol. Six-membered ring derivatives of salacinol and compounds modeled after miglitol were much less effective as MGAnt inhibitors. These results provide information on the inhibitory profile of MGAnt that will guide the development of new compounds having antidiabetic activity.

Effect of inhibition of alpha-glucosidase on age-related glucose intolerance and pancreatic atrophy in rats

Oral administration of alpha-glucosidase inhibitor reduces postprandial serum glucose and insulin concentrations; thus, alpha-glucosidase inhibitor is used for the treatment of diabetes mellitus worldwide. In our study, we have evaluated the effect of alpha-glucosidase inhibitor, acarbose, on age-related glucose intolerance and pancreatic atrophy in the Long-Evans Tokushima Otsuka (LETO) rat. The first group of rats received a standard rat diet (control). The second group received a diet containing acarbose (150 mg/100 g food) from 12 to 28 weeks and then switched to a standard rat diet until 72 weeks of age (A12-28W). The third group was administered the same diet containing acarbose from 12 to 72 weeks of age (A12-72W). Fasting serum glucose and insulin concentrations gradually increased with increasing age in the control group, but these increases were completely prevented (A12-72W) or delayed (A12-28W) by acarbose treatment. In addition, acarbose treatment prevented the deterioration in insulin resistance with increasing age. At 72 weeks of age, pancreatic wet weight and DNA content in the A12-72W group were significantly higher than those in the control group. Although most islets were enlarged, and some portions of pancreatic tissue contained fatty and connective tissue in the control group, these alterations were mild in the A12-28W group and remained minimal in the A12-72W group. Our study suggests that acarbose is useful in the prevention of age-related glucose intolerance and pancreatic atrophy.

Synthesis of New Nitrogen Analogues of Salacinol and Deoxynojirimycin and Their Evaluation as Glycosidase Inhibitors

The synthesis of two enantiomerically pure iminosugars, analogues of 1-L-deoxynojirimycin (l-DNJ) and 1-D-deoxymannojirimycin (DMJ), was achieved using cyclic sulfate substituted isoxazoline derivatives. The piperidine ring was formed via the reduction of an isoxazoline into an amine which underwent a spontaneous intramolecular cyclization by reaction with the cyclic sulfate moiety. The nucleophilic attack of these two trisubstituted piperidines and morpholine on L- and D-erythritol-1,3-cyclic sulfates gave six new nitrogen analogues of salacinol. The inhibitory properties of the synthesized salacinol analogues were evaluated on several commercial glycosidases.

A chlorogenic acid-induced increase in GLP-1 production may mediate the impact of heavy coffee consumption on diabetes risk

Recent prospective epidemiology links heavy coffee consumption to a substantial reduction in risk for type 2 diabetes. Yet there is no evidence that coffee improves insulin sensitivity and, at least in acute studies, caffeine has a negative impact in this regard. Thus, it is reasonable to suspect that coffee influences the risk for beta cell "failure" that precipitates diabetes in subjects who are already insulin resistant. Indeed, there is recent evidence that coffee increases production of the incretin hormone glucagon-like peptide-1 (GLP-1), possibly owing to an inhibitory effect of chlorogenic acid (CGA -- the chief polyphenol in coffee) on glucose absorption. GLP-1 acts on beta cells, via cAMP-dependent mechanisms, to promote the synthesis and activity of the transcription factor IDX-1, crucial for maintaining the responsiveness of beta cells to an increase in plasma glucose. Conversely, the "glucolipotoxicity" thought to initiate and sustain beta cell dysfunction in diabetics can suppress expression of this transcription factor. The increased production of GLP-1 associated with frequent coffee consumption could thus be expected to counteract the adverse impact of chronic free fatty acid overexposure on beta cell function in overweight insulin resistant subjects. CGA's putative impact on glucose absorption may reflect the ability of this compound to inhibit glucose-6-phosphate translocase 1, now known to play a role in intestinal glucose transport. Delayed glucose absorption may itself protect beta cells by limiting postprandial hyperglycemia -- though, owing to countervailing effects of caffeine on plasma glucose, and a paucity of relevant research studies, it is still unclear whether coffee ingestion blunts the postprandial rise in plasma glucose. More generally, diets high in "lente carbohydrate", or administration of nutraceuticals/pharmaceuticals which slow the absorption of dietary carbohydrate, should help preserve efficient beta cell function by boosting GLP-1 production, as well as by blunting the glucotoxic impact of postprandial hyperglycemia on beta cell function.

Metabolic syndrome therapy: prevention of vascular injury by antidiabetic agents

More than 65 million Americans are currently obese. Type 2 diabetes mellitus, frequently seen in obese subjects, affects 17 million adults in the United States, with a continuous and alarmingly increasing rate. To prevent development of diabetes in those who are at high risk, it is recommended to optimize meal planning and enhance physical activity to make sustained weight reduction possible. In addition to lifestyle changes, various oral antidiabetic agents are available, with diverse mechanisms of action. Some target defective insulin secretion (sulphonylureas, benzoic acid derivatives) or glucose absorption (glycosidase inhibitors), whereas others target insulin resistance (metformin, thiazolidinediones). Patients with metabolic syndrome and diabetes have an increased risk for cardiovascular disease linked to a higher prevalence of hypertension, dyslipidemia, microalbuminuria, and altered hemostasis--parameters that may be modified by antidiabetic agents. In this article, we review the oral agents used to treat type 2 diabetes and the metabolic syndrome, and their effects on vascular tissue.

Ageing and metabolism: drug discovery opportunities

There has recently been significant progress in our understanding of the mechanisms that regulate ageing, and it has been shown that changes in single genes can dramatically extend lifespan and increase resistance to many diseases. Furthermore, many of these genes belong to evolutionarily conserved pathways that also control energy metabolism. In this review, we describe the shared molecular machinery that regulates ageing and energy metabolism. Although drugs to slow ageing face severe regulatory hurdles, it is likely that an understanding of ageing pathways will help to identify novel drug targets to treat metabolic disorders and other age-related diseases.

Oral antidiabetic agents: current role in type 2 diabetes mellitus

Type 2 diabetes mellitus is a progressive and complex disorder that is difficult to treat effectively in the long term. The majority of patients are overweight or obese at diagnosis and will be unable to achieve or sustain near normoglycaemia without oral antidiabetic agents; a sizeable proportion of patients will eventually require insulin therapy to maintain long-term glycaemic control, either as monotherapy or in conjunction with oral antidiabetic therapy. The frequent need for escalating therapy is held to reflect progressive loss of islet beta-cell function, usually in the presence of obesity-related insulin resistance. Today's clinicians are presented with an extensive range of oral antidiabetic drugs for type 2 diabetes. The main classes are heterogeneous in their modes of action, safety profiles and tolerability. These main classes include agents that stimulate insulin secretion (sulphonylureas and rapid-acting secretagogues), reduce hepatic glucose production (biguanides), delay digestion and absorption of intestinal carbohydrate (alpha-glucosidase inhibitors) or improve insulin action (thiazolidinediones). The UKPDS (United Kingdom Prospective Diabetes Study) demonstrated the benefits of intensified glycaemic control on microvascular complications in newly diagnosed patients with type 2 diabetes. However, the picture was less clearcut with regard to macrovascular disease, with neither sulphonylureas nor insulin significantly reducing cardiovascular events. The impact of oral antidiabetic agents on atherosclerosis--beyond expected effects on glycaemic control--is an increasingly important consideration. In the UKPDS, overweight and obese patients randomised to initial monotherapy with metformin experienced significant reductions in myocardial infarction and diabetes-related deaths. Metformin does not promote weight gain and has beneficial effects on several cardiovascular risk factors. Accordingly, metformin is widely regarded as the drug of choice for most patients with type 2 diabetes. Concern about cardiovascular safety of sulphonylureas has largely dissipated with generally reassuring results from clinical trials, including the UKPDS. Encouragingly, the recent Steno-2 Study showed that intensive target-driven, multifactorial approach to management, based around a sulphonylurea, reduced the risk of both micro- and macrovascular complications in high-risk patients. Theoretical advantages of selectively targeting postprandial hyperglycaemia require confirmation in clinical trials of drugs with preferential effects on this facet of hyperglycaemia are currently in progress. The insulin-sensitising thiazolidinedione class of antidiabetic agents has potentially advantageous effects on multiple components of the metabolic syndrome; the results of clinical trials with cardiovascular endpoints are awaited. The selection of initial monotherapy is based on a clinical and biochemical assessment of the patient, safety considerations being paramount. In some circumstances, for example pregnancy or severe hepatic or renal impairment, insulin may be the treatment of choice when nonpharmacological measures prove inadequate. Insulin is also required for metabolic decompensation, that is, incipient or actual diabetic ketoacidosis, or non-ketotic hyperosmolar hyperglycaemia. Certain comorbidities, for example presentation with myocardial infarction during other acute intercurrent illness, may make insulin the best option. Oral antidiabetic agents should be initiated at a low dose and titrated up according to glycaemic response, as judged by measurement of glycosylated haemoglobin (HbA1c) concentration, supplemented in some patients by self monitoring of capillary blood glucose. The average glucose-lowering effect of the major classes of oral antidiabetic agents is broadly similar (averaging a 1-2% reduction in HbA1c), alpha-glucosidase inhibitors being rather less effective. Tailoring the treatment to the individual patient is an important principle. Doses are gradually titrated up according to response. However, the maximal glucose-lowering action for sulphonylureas is usually attained at appreciably lower doses (approximately 50%) than the manufacturers' recommended daily maximum. Combinations of certain agents, for example a secretagogue plus a biguanide or a thiazolidinedione, are logical and widely used, and combination preparations are now available in some countries. While the benefits of metformin added to a sulphonylurea were initially less favourable in the UKPDS, longer-term data have allayed concern. When considering long-term therapy, issues such as tolerability and convenience are important additional considerations. Neither sulphonylureas nor biguanides are able to appreciably alter the rate of progression of hyperglycaemia in patients with type 2 diabetes. Preliminary data suggesting that thiazolidinediones may provide better long-term glycaemic stability are currently being tested in clinical trials; current evidence, while encouraging, is not conclusive. Delayed progression from glucose intolerance to type 2 diabetes in high-risk individuals with glucose intolerance has been demonstrated with troglitazone, metformin and acarbose. However, intensive lifestyle intervention can be more effective than drug therapy, at least in the setting of interventional clinical trials. No antidiabetic drugs are presently licensed for use in prediabetic individuals.

Nutraceutical resources for diabetes prevention--an update

There is considerable need for safe agents that can reduce risk for diabetes in at-risk subjects. Although certain drugs--including metformin, acarbose, and orlistat--have shown diabetes-preventive activity in large randomized studies, nutraceuticals have potential in this regard as well. Natural agents which slow carbohydrate absorption may mimic the protective effect of acarbose; these include: soluble fiber--most notably glucomannan; chlorogenic acid--likely responsible for reduction in diabetes risk associated with heavy coffee intake; and legume-derived alpha-amylase inhibitors. There does not appear to be a natural lipase inhibitor functionally equivalent to orlistat, although there are poorly documented claims for Cassia nomame extracts. Metformin's efficacy reflects activation of AMP-activated kinase; there is preliminary evidence that certain compounds in barley malt have similar activity, without the side effects associated with metformin. In supraphysiological concentrations, biotin directly activates soluble guanylate cyclase; this implies that, at some sufficient intake, biotin should exert effects on beta cells, the liver, and skeletal muscle that favor good glucose tolerance and maintenance of effective beta cell function. Good magnesium status is associated with reduced diabetes risk and superior insulin sensitivity in recent epidemiology; ample intakes of chromium picolinate appear to promote insulin sensitivity in many individuals and improve glycemic control in some diabetics; calcium/vitamin D may help preserve insulin sensitivity by preventing secondary hyperparathyroidism. Although conjugated linoleic acid--like thiazolidinediones, a PPAR-gamma agonist--has not aided insulin sensitivity in clinical trials, the natural rexinoid phytanic acid exerts thiazolidinedione-like effect in animals and cell cultures, and merits clinical examination. Other natural agents with the potential to treat and possibly prevent diabetes include extracts of bitter melon and of cinnamon. Nutraceuticals featuring meaningful doses of combinations of these agents would likely have substantial diabetes-preventive efficacy, and presumably could be marketed legally as aids to good glucose tolerance and insulin sensitivity.

Prevention of type 2 diabetes mellitus through inhibition of the Renin-Angiotensin system

Type 2 diabetes mellitus is becoming a major health problem associated with excess morbidity and mortality. As the prevalence of type 2 diabetes is rapidly increasing, prevention of the disease should be considered as a key objective in the near future. Besides lifestyle changes, various pharmacological treatments have proven their efficacy in placebo-controlled clinical trials, including antidiabetic drugs such as metformin, acarbose and troglitazone, or antiobesity agents such as orlistat. Arterial hypertension, a clinical entity in which insulin resistance is common, is strongly associated with type 2 diabetes and may precede the disease by several years. While antihypertensive agents such as diuretics or beta-adrenoceptor antagonists may worsen insulin resistance and impair glucose tolerance, newer antihypertensive agents exert neutral or even slightly positive metabolic effects. Numerous clinical trials have investigated the effects of ACE inhibitors or angiotensin II receptor antagonists (ARAs) on insulin sensitivity in hypertensive patients, with or without diabetes, with no consistent results. Almost half of the studies with ACE inhibitors in hypertensive nondiabetic individuals demonstrated a slight but significant increase in insulin sensitivity as assessed by insulin-stimulated glucose disposal during a euglycaemic hyperinsulinaemic clamp, while the other half failed to reveal any significant change. The effects of ARAs on insulin sensitivity are neutral in most studies. Mechanisms of improvement of glucose tolerance and insulin sensitivity through the inhibition of the renin-angiotensin system (RAS) are complex. They may include improvement of blood flow and microcirculation in skeletal muscles and, thereby, enhancement of insulin and glucose delivery to the insulin-sensitive tissues, facilitating insulin signalling at the cellular level and improvement of insulin secretion by the beta cells. Six recent large-scale clinical studies reported a remarkably consistent reduction in the incidence of type 2 diabetes in hypertensive patients treated with either ACE inhibitors or ARAs for 3-6 years, compared with a thiazide diuretic, beta-adrenoceptor antagonist, the calcium channel antagonist amlodipine or even placebo. The relative risk reduction averaged 14% (p = 0.034) in the CAPPP (Captopril Prevention Project) with captopril compared with a thiazide or beta1-adrenoceptor antagonist, 34% (p < 0.001) in the HOPE (Heart Outcomes Prevention Evaluation) study with ramipril compared with placebo, 30% (p < 0.001) in the ALLHAT (Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial) with lisinopril compared with chlortalidone, 25% (p < 0.001) in the LIFE (Losartan Intervention For Endpoint reduction in hypertension study) with losartan compared with atenolol, and 25% (p = 0.09) in the SCOPE (Study on Cognition and Prognosis in the Elderly) with candesartan cilexetil compared with placebo, and 23% (p < 0.0001) in the VALUE (Valsartan Antihypertensive Long-term Use Evaluation) trial with valsartan compared with amlodipine. All these studies considered the development of diabetes as a secondary endpoint, except the HOPE trial where it was a post hoc analysis. These encouraging observations led to the initiation of two large, prospective, placebo-controlled randomised clinical trials whose primary outcome is the prevention of type 2 diabetes: the DREAM (Diabetes REduction Approaches with ramipril and rosiglitazone Medications) trial with the ACE inhibitor ramipril and the NAVIGATOR (Nateglinide And Valsartan in Impaired Glucose Tolerance Outcomes Research) trial with the ARA valsartan. Finally, ONTARGET (ONgoing Telmisartan Alone and in combination with Ramipril Global Endpoint Trial) will also investigate as a secondary endpoint whether it is possible to prevent the development of type 2 diabetes by blocking the RAS with either an ACE inhibitor or an ARA or a combination of both. Thus, the recent consistent observations of a 14-34% reduction of the development of diabetes in hypertensive patients receiving ACE inhibitors or ARAs are exciting. From a theoretical point of view, they emphasise that there are many aspects of the pathogenesis, prevention and treatment of type 2 diabetes that still need to be uncovered. From a practical point of view, they may offer a new strategy to reduce the ongoing epidemic and burden of type 2 diabetes.

Natural products to drugs: natural product derived compounds in clinical trials

Natural product and natural product-derived compounds that are being evaluated in clinical trials or in registration (current 31 December 2004) have been reviewed. Natural product derived drugs launched in the United States of America, Europe and Japan since 1998 and new natural product templates discovered since 1990 are discussed.