Microbial α-Glucosidase Inhibitors: Chemistry, Biochemistry, and Therapeutic Potential

Synthesis,Antidiabetic and Antitubercular Evaluation of Quinoline-pyrazolopyrimidine hybrids and Quinoline-4-Arylamines

Two libraries of quinoline-based hybrids 1-(7-chloroquinolin-4-yl)-1H-pyrazolo[3,4-d]pyrimidin-4-amine and 7-chloro-N-phenylquinolin-4-amine were synthesized and evaluated for their α-glucosidase inhibitory and antioxidant properties. Compounds with 4-methylpiperidine and para-trifluoromethoxy groups, respectively, showed the most promising α-glucosidase inhibition activity with IC50 =46.70 and 40.84 μM, compared to the reference inhibitor, acarbose (IC50 =51.73 μM). Structure-activity relationship analysis suggested that the cyclic secondary amine pendants and para-phenyl substituents account for the variable enzyme inhibition. Antioxidant profiling further revealed that compounds with an N-methylpiperazine and N-ethylpiperazine ring, respectively, have good DPPH scavenging abilities with IC50 =0.18, 0.58 and 0.93 mM, as compared to ascorbic acid (IC50 =0.05 mM), while the best DPPH scavenger is NO2 -substituted compound (IC50 =0.08 mM). Also, compound with N-(2-hydroxyethyl)piperazine moiety emerged as the best NO radical scavenger with IC50 =0.28 mM. Molecular docking studies showed that the present compounds are orthosteric inhibitors with their quinoline, pyrimidine, and 4-amino units as crucial pharmacophores furnishing α-glucosidase binding at the catalytic site. Taken together, these compounds exhibit dual potentials; i. e., potent α-glucosidase inhibitors and excellent free radical scavengers. Hence, they may serve as structural templates in the search for agents to manage Type 2 diabetes mellitus. Finally, in preliminary assays investigating the anti-tubercular potential of these compounds, two pyrazolopyrimidine series compounds and a 7-chloro-N-phenylquinolin-4-amine hybrid showed sub-10 μM whole-cell activities against Mycobacterium tuberculosis.

Synthesis of hydroxymethyl analogues of mannostatin A and their evaluation as inhibitors of GH38 α-mannosidases

Analogues of mannostatin A were synthesised and evaluated as inhibitors of GH38 α-mannosidases. Different regioselectivity of aziridine opening with sodium methanethiolate was observed and investigated by quantum mechanics calculations.

Inhibitory effects against α-glucosidase and α-amylase of the flavonoids-rich extract from Scutellaria baicalensis shoots and interpretation of structure-activity relationship of its eight flavonoids by a refined assign-score method

A flavonoids-rich extract of Scutellaria baicalensis shoots and its eight high content flavonoids were investigated for their inhibitory effects against α-glucosidase and α-amylase. Results show that abilities of the extract in inhibiting the two enzymes were obviously higher than those of acarbose. Moreover, inhibitory abilities of all the eight individual flavonoids against the two enzymes show exactly a same order (i.e., apigenin > baicalein > scutellarin > chrysin > apigenin-7-O-glucuronide > baicalin > chrysin-7-O-glucuronide > isocarthamidin-7-O-glucuronide), and their structure-activity relationship could be well-interpretated by the refined assign-score method. Furthermore, based on the inhibitory abilities and their contents in the extract, it was found that the eight flavonoids made predominant contributions, among which baicalein and scutellarin played roles as preliminary contributors, to overall inhibitory effects of the extract against the two enzymes. Beyond these, contributions of the eight flavonoids to the overall enzyme inhibitory activity were compared with those to the overall antioxidant activity characterized in our recent study, and it could be inferred that within the basic flavonoid structure the hydroxyl on C-4' of ring B was more effective than that on C-6 of ring A in enzyme inhibitory activities while they behaved inversely in antioxidant activities; scutellarin and apigenin contributed more to the overall enzyme inhibitory activity, and baicalin and scutellarin, to the overall antioxidant activity of the extract; and flavonoids of the extract, apart from directly inhibiting enzymes, might also be conducive to curing type 2 diabetes via scavenging various free radicals caused by increased oxidative stresses.

Safety and efficacy of acarbose in the treatment of Type 2 diabetes: data from a 5-year surveillance study

This 5-year surveillance study assessed the tolerability and safety of acarbose in patients with diabetes. A total of 2035 patients were enrolled of whom 1954 were classified as having Type 2 diabetes. The study was open with no control group. Physicians had sole control of the acarbose doses prescribed. Fasting blood glucose levels, 2-h postprandial glucose levels, HbA(1) or HbA(1c) and other clinical parameters, such as lipids and liver enzyme levels, were also assessed as measures of efficacy and safety. One-third of the patients received acarbose as monotherapy and two-thirds in combination with other glucose-lowering treatment. The concomitant diseases were also assessed. Doses of acarbose were low in the majority of the patients and well tolerated. The incidence of acarbose-associated side effects was 4.7%. No sustained adverse changes in laboratory measures occurred. Over the 5 years, HbA(1) and glycated haemoglobin (HbA(1c)) decreased by 2.4 and 1.8% points, respectively, and the mean fasting glucose and 2-h postprandial glucose decreased by 2.7 and 3.4 mmol/l. Mean body weight was reduced by 0.9 kg. The results suggest that when used in long-term day-to-day management of diabetes, acarbose is well tolerated and can improve glycaemic control as monotherapy, as well as in combination therapy. In a high-risk patient group acarbose proved to be a safe drug.

Efficacy and safety of acarbose in the treatment of Type 1 diabetes mellitus: a placebo-controlled, double-blind, multicentre study

AIMS

The aim of the study was to evaluate the efficacy and safety of acarbose in patients with Type 1 diabetes mellitus (DM).

METHODS

A multicentre double-blind, randomized, placebo-controlled study was performed. After a 6-week run-in, 121 patients were randomized to acarbose or placebo and to high- or low-fibre diet for 24 weeks. Acarbose dose was 50 mg t.d.s. for the first 2 weeks and 100 mg t.d.s. for the subsequent weeks.

RESULTS

At the end of 24 weeks of treatment the intention to treat analysis showed that acarbose compared with placebo decreased 2 h postprandial plasma glucose levels (12.23 +/- 0.83 vs. 14.93 +/- 0.87 mmol/l; F = 6.1, P < 0.02) (least square means +/- SEM). No significant effect of acarbose was recorded on HbA1c or on the number of hypoglycaemic episodes. The effect of acarbose on blood glucose control was not influenced by the amount of carbohydrate and/or fibre intake. The incidence of adverse events were 75% and 39% in acarbose and placebo groups, respectively; they were mild and confined to the gastrointestinal tract.

CONCLUSIONS

The use of acarbose in combination with insulin reduces postprandial plasma glucose levels in Type 1 diabetic patients who are not satisfactorily controlled with insulin alone but without significant effect on HbA1c.

Bioactive agents from natural sources: trends in discovery and application

About 30% of the worldwide sales of drugs are based on natural products. Though recombinant proteins and peptides account for increasing sales rates, the superiority of low-molecular mass compounds in human diseases therapy remains undisputed mainly due to more favorable compliance and bioavailability properties. In the past, new therapeutic approaches often derived from natural products. Numerous examples from medicine impressively demonstrate the innovative potential of natural compounds and their impact on progress in drug discovery and development. However, natural products are currently undergoing a phase of reduced attention in drug discovery because of the enormous effort which is necessary to isolate the active principles and to elucidate their structures. To meet the demand of several hundred thousands of test samples that have to be submitted to high-throughput screening (HTS) new strategies in natural product chemistry are necessary in order to compete successfully with combinatorial chemistry. Today, pharmaceutical companies have to spend approximately US $350 million to develop a new drug. Currently, approaches to improve and accelerate the joint drug discovery and development process are expected to arise mainly from innovation in drug target elucidation and lead finding. Breakthroughs in molecular biology, cell biology, and genetic engineering in the 1980 s gave access to understanding diseases on the molecular or on the gene level. Subsequently, constructing novel target directed screening assay systems of promising therapeutic significance, automation, and miniaturization resulted in HTS approaches changing the industrial drug discovery process drastically. Furthermore, elucidation of the human genome will provide access to a dramatically increased number of new potential drug targets that have to be evaluated for drug discovery. HTS enables the testing of an increasing number of samples. Therefore, new concepts to generate large compound collections with improved structural diversity are desirable.

The role of acarbose in the treatment of non-insulin-dependent diabetes mellitus

Acarbose is the first of a new class of antidiabetic agents, the alpha-glucosidase inhibitors. Acarbose has proven effectiveness as a first-line drug in type 2 diabetes insufficiently controlled by diet alone. In addition to providing short-term glycemic control, acarbose also reduces HbA1c levels. This effect is greatest when therapy is initiated early in the disease and when baseline HbA1c levels are high. Depending on the baseline HbA1c value, therapeutic doses of acarbose lead to a HbA1c reduction of 0.5%-1.2%. Acarbose may be safely combined with all oral hypoglycemic agents, and has been found to have utility as an adjunct to sulfonylurea and metformin therapy. It also improves control of insulin-treated type 2 diabetes and enables a reduction of exogenous insulin requirements of up to 30%. Acarbose also has beneficial effects on the coronary risk factors, e.g. postprandial triglyceride levels, elevated cholesterol, and hyperinsulinemia. The early phase of acarbose therapy may be associated with side effects such as meteorism, flatulence, and diarrhea. These result from the local effect of the drug and decline with time. To date, there have been no reports of systemic toxicity. Acarbose does not cause hypoglycemias or weight gain.

Efficacy and safety of acarbose in the treatment of type 2 diabetes: data from a 2-year surveillance study

This 2-year surveillance study assessed the tolerability and safety of acarbose in patients with diabetes. A total of 2035 patients were enrolled; approximately 95% were classified as having Type 2 diabetes. The study was open with no control groups. Physicians had sole control of the acarbose doses prescribed. Doses of acarbose were generally low, and hence well-tolerated. The incidence of acarbose-associated adverse effects and withdrawals was 7.5 and 2.5%, respectively. No sustained adverse changes in laboratory parameters occurred. Fasting blood glucose levels, 1- and 2-h postprandial glucose levels, HbA1c or HbA1, and other clinical parameters, such as blood cell counts and liver enzyme levels were also assessed as measures of efficacy and safety. Over the 2 years the mean fasting blood glucose level decreased by 2.39 mmol/l in patients with Type 2 diabetes, while mean 1- and 2-h postprandial blood glucose levels both decreased by 3.56 mmol/l. HbA1 and HbA1c decreased by 2.0 and 1.1 percentage points, respectively. These results suggest that when used in long-term day-to-day management of diabetes, acarbose is well tolerated and can improve glycaemic control.

The effect of the timing and the administration of acarbose on postprandial hyperglycaemia

To clarify the optimum timing for ingestion of acarbose, a 100 mg dose of this oral hypoglycaemic agent was administered 30 min before, at the beginning, and 15 min after ingestion of a test meal, and the effects of the drug on blood glucose rises were compared with increases observed after a control meal (no drug). Twenty-four patients with Type 2 diabetes were included in a randomized, open, cross-over study. The smallest increases in blood glucose (p < 0.001) occurred when acarbose was taken at the beginning and 15 min after starting the test meal (3.3 +/- 1.6 mmol l-1 and 3.3 +/- 1.4 mmol l-1). The increase in blood glucose levels when acarbose was taken 30 min before the test meal was significantly higher (4.2 +/- 1.8 mmol l-1) and it was at its maximum following the control meal (5.2 +/- 1.7 mmol l-1). Similar results were observed when the effects of acarbose on insulin and C-peptide levels were measured. It is recommended that patients should be instructed to take acarbose with their first mouthful of food.

Lysosomal storage of glycogen as a sequel of alpha-glucosidase inhibition by the absorbed deoxynojirimycin derivative emiglitate (BAYo1248). A drug-induced pattern of hepatic glycogen storage mimicking Pompe's disease (glycogenosis type II)

Effects of the two absorbable alpha-glucosidase inhibitors miglitol (BAYm1099) and emiglitate (BAYo1248) on hepatic and muscular glycogen concentrations were investigated in the rat after 3, 7, and 28 days. Both compounds were (orally) administered at very high doses (5-50-500 mg/kg b.wt.). In a second experiment, glycogen storage after oral administration of acarbose (1000 mg/kg b.wt.) was studied after 7 days. In a third protocol, hepatic glycogen concentrations were investigated in the fed rat after 7 days of either inhibitor at the respective highest dosage. In fasted rats, emiglitate induced a significant, dose-dependent increase of hepatic glycogen concentrations, which--at the dose of 500 mg/kg b.wt.--were present after 3, 7, and 28 days, but resulted in a significant increase of the liver weight after 28 days only. Light and electron microscopy proved that the increase in hepatic glycogen was due to lysosomal storage of glycogen only. Emiglitate in the amount of 5 mg/kg b.wt. did not induce significant changes either of glycogen concentrations or at the EM-level. While emiglitate also increased hepatic glycogen at a dosage of 50 mg/kg b.wt., miglitol led to significant storage of hepatic glycogen after 3, 7, or 28 days at the highest dose only. With miglitol (500 mg/kg b.wt.), only insignificant lysosomal storage of glycogen could be detected by electron and light microscopy, and liver weight was essentially unaffected. Both compounds displayed a dose-dependent tendency towards higher glycogen concentrations in the soleus muscle, which was significant with the highest dosage of either inhibitor. At an oral dose of o.i.d. 1000 mg/kg b.wt., the almost unabsorbable alpha-glucosidase inhibitor acarbose induced significantly increased glycogen concentrations both in the liver and in the soleus muscle after 7 days. With respect to an enormous enlargement of the lysosomes (EM) and in the absence of cytoplasmatic alpha-glycogen, this accumulation of glycogen must be attributed to lysosomal storage. In fed rats, all alpha-glucosidase inhibitors investigated significantly decreased postprandial hepatic glycogen concentrations (emiglitate greater than miglitol greater than acarbose), thereby reflecting the modulation of absorption. It is concluded that in the rat acarbose at approximately 1000 x ED50 may penetrate the intestinal mucosa at amounts significant enough to induce lysosomal storage of glycogen. Miglitol may cause some hepatocellular, lysosomal glycogen storage at a dose of 500 mg/kg b.wt., but no glycogen storage could be proven up to 100 x ED50 over 28 days.(ABSTRACT TRUNCATED AT 400 WORDS)