Alpha glucosidase inhibition in the treatment of non-insulin-dependent diabetes mellitus

Effects of alpha-glucosidase-inhibiting drugs on acute postprandial glucose and insulin responses: a systematic review and meta-analysis

Background/objectives

Despite considerable literature supporting the potential health benefits of reducing postprandial glucose (PPG), and insulin (PPI) exposures, the size of a clinically relevant reduction is currently unknown. We performed a systematic review and meta-analysis to quantify effects of alpha-glucosidase-inhibiting (AGI) drugs on acute PPG and PPI responses.

Methods

We searched EMBASE and MEDLINE until March 13, 2018 for controlled studies using AGI drugs together with a standardized carbohydrate load or mixed meal. The mean incremental PPG and PPI levels were calculated as outcomes. Meta-analyses, stratified by diabetes state, were performed by using random effects models.

Results

The 66 included publications comprised 127 drug-control comparisons for PPG, and 106 for PPI, mostly testing acarbose or miglitol. The absolute effects on PPG were larger among individuals with diabetes (−1.5 mmol/l mean PPG [95% CI −1.9, −1.1] by acarbose, and −1.6 [−1.9, −1.4] by miglitol) as compared to individuals without diabetes (−0.4 [95% CI −0.5, −0.3] by acarbose, and −0.6 [−0.8, −0.4] by miglitol). Relative reductions in PPG by both drugs were similar for diabetic and non-diabetic individuals (43−54%). Acarbose and miglitol also significantly reduced mean PPI, with absolute and relative reductions being largest among individuals without diabetes.

Conclusions

The present meta-analyses provide quantitative estimates of reductions of PPG and PPI responses by AGI drugs in diabetes and non-diabetic individuals. These data can serve as benchmarks for clinically relevant reductions in PPG and PPI via drug or diet and lifestyle interventions.

The Addition of Xanthan Gum to Enteral Nutrition Suppresses Postprandial Glycemia in Humans

The semi-solidified nutrition supplemented with soluble dietary fiber, xanthan gum (XG), inhibited postprandial glycemia in rats. The purpose of the present study is to examine whether XG exerts the same effects in humans. Subjects fasted for 12 h and then ingested the enteral nutrient, Meibalance with or without XG at 9 AM. Blood glucose levels were measured 0, 20, 40, 60, and 120 min after its ingestion. Postprandial blood glucose levels were lower in the XG group than in the control group. At 20 min, postprandial blood glucose levels were significantly lower in the XG group (84±5.3 mg/dL) than in the control group (107±7.8 mg/dL) (p<0.05). A significant difference was also observed in ΔAUC between the two groups. These results demonstrate that XG exerts inhibitory effects on glucose excursion in humans.

Miglitol: a review of its therapeutic potential in type 2 diabetes mellitus

Miglitol, the first pseudomonosaccharide alpha-glucosidase inhibitor, smooths postprandial peak plasma glucose levels and thus improves glycaemic control, which is reflected in a reduced glycosylated haemoglobin (HbA1c) level. This oral antihyperglycaemic agent is indicated for the treatment of patients with type 2 diabetes mellitus. Miglitol is generally well tolerated and, unlike the sulphonylurea agents, is not associated with bodyweight gain or hypoglycaemia when administered as monotherapy. The drug is systemically absorbed but is not metabolised and is rapidly excreted via the kidneys. Clinical trials with miglitol (usually 50 or 100 mg 3 times daily) in patients with type 2 diabetes mellitus consistently demonstrated a significant improvement in glycaemic control for periods of 6 to 12 months. There were also marked reductions in postprandial serum insulin levels, although miglitol generally had no effect on fasting insulin levels. In comparative studies miglitol had similar efficacy to acarbose, but at lower therapeutic doses (50 and 100 mg 3 times daily, respectively). In addition, although sulphonylurea agents provided superior reductions in HbA1c levels, miglitol provided similar or superior reductions in fasting and postprandial plasma glucose levels. In combination with other oral antidiabetic agents or insulin, miglitol improved glycaemic control in patients in whom metabolic control was suboptimal despite dietary and pharmacological intervention. Most adverse events associated with miglitol treatment involve disturbances of the gastrointestinal tract (most common effects are flatulence, abdominal pain and diarrhoea). These symptoms are usually dose dependent, mild to moderate in severity, occur at the onset of treatment, decline with time and resolve promptly on discontinuation of the drug or with dosage adjustment. As monotherapy, miglitol is not associated with hypoglycaemia, but concomitant use with other oral antidiabetic agents may necessitate dosage adjustment of the other agents. Miglitol had no significant effects on renal, cardiovascular, respiratory or haematological parameters in long term studies. No dosage adjustments are required in elderly patients, in those with hepatic impairment or in those with mild to moderate renal insufficiency.

CONCLUSIONS

In long term, well designed trials miglitol reduces fasting and postprandial plasma glucose levels, thus improving glycaemic control, which is reflected in a reduced HbA1c level in patients with type 2 diabetes mellitus. Most adverse events associated with miglitol involve disturbances of the gastrointestinal tract. This agent is a useful first-line therapy in patients with type 2 diabetes mellitus insufficiently controlled by diet alone and as second-line or as adjuvant therapy in those insufficiently controlled with diet and sulphonylurea agents. Miglitol may prove particularly beneficial in elderly patients and those with hepatic impairment or mild to moderate renal impairment, in whom other oral antidiabetic agents are contraindicated or need to be used with caution.

Comparative tolerability profiles of oral antidiabetic agents

The sulphonylureas and the biguanides are widely used as adjuncts to dietary measures in the treatment of non-insulin-dependent (type 2) diabetes mellitus (NIDDM). Adverse effect profiles differ markedly between the sulphonylureas and biguanides, reflecting differences in chemical structure and mode of action. Sulphonylureas are generally well tolerated, although pharmacokinetic differences between these agents have important clinical implications. The main adverse effect associated with sulphonylureas is hypoglycaemia. This effect is a predictable consequence of the principal pharmacological effect of these drugs, i.e. sensitisation of the islet beta-cell to glucose, resulting in enhanced endogenous insulin secretion. Sulphonylurea-induced suppression of hepatic glucose production may cause profound and protracted hypoglycaemia, especially in elderly patients, in individuals with intercurrent illnesses and reduced caloric intake, or when taken in combination with other compounds with hypoglycaemic potential, e.g. alcohol (ethanol). Sulphonylureas with a longer duration of action, notably chlorpropamide and glibenclamide (glyburide), are more liable to induce serious hypoglycaemia, particularly when drug elimination is reduced by renal impairment. Other drugs such as salicylates may potentiate the actions of sulphonylureas, thereby increasing the risk of hypoglycaemia. Biguanide therapy is associated with alterations in lactate homeostasis which under certain clinical circumstances may result in fatal lactic acidosis. Phenformin is associated with a markedly greater risk of lactic acidosis than metformin. Phenformin has been withdrawn in many countries for this reason. All biguanides must be avoided in patients with renal impairment, hepatic dysfunction and cardiac failure--conditions where drug accumulation or disordered lactate metabolism may predispose to lactic acidosis. Phenformin should not be given to individuals who exhibit a severe, genetically conferred hepatic defect of hydroxylation which impedes metabolism of this drug. Less seriously, the biguanides are associated with a relatively high incidence of gastrointestinal adverse effects which limit compliance. Acarbose, a competitive inhibitor of intestinal alpha-glucosidases, has recently been introduced. In contrast to the sulphonylureas and biguanides, acarbose has not been associated with life-threatening adverse effects. This reflects the low systemic absorption of the drug and, predictably, its principal unwanted effects are gastrointestinal disturbances resulting from iatrogenic carbohydrate malabsorption.

An evaluation of the potential side-effects of alpha-glucosidase inhibitors used for the management of diabetes mellitus

Orally taken alpha-glucosidase inhibitors are used for the management of diabetes mellitus. These drugs can prevent the postprandial rise of the blood glucose level by inhibiting the enzymatic digestion of carbohydrates in the intestinal lumen. Non-absorbable inhibitors such as acarbose are expected to function exclusively in the intestine, but absorbable inhibitors such as miglitol may exert an inhibitory effect on non-intestinal alpha-glucosidases present in the various cell types of the body. The potential side-effects of absorbable inhibitors are evaluated in this literature review. It is concluded that there is little risk of inducing unwanted side-effects when miglitol is taken in an oral dose of approximately 1 mg kg-1 body weight. The use of absorbable inhibitors is, however, not advised in case of kidney dysfunction.

Ca2+ deficiency, selective alpha-glucosidehydrolase inhibition, and insulin secretion

We investigated the relation between activities of islet glycogenolytic alpha-glucosidehydrolases and insulin secretion induced by glucose and 3-isobutyl-1-methylxanthine (IBMX) by means of suppressing 1) insulin release (Ca2+ deficiency) and 2) islet alpha-glucosidehydrolase activity (selective inhibition by the deoxynojirimycin derivative miglitol). Additionally, the in vivo insulin response to both secretagogues was examined. We observed that, similar to glucose-induced insulin release, islet glycogenolytic hydrolases (acid amyloglucosidase, acid alpha-glucosidase) were highly Ca2+ dependent. Acid phosphatase, N-acetyl-beta-D-glucosaminidase, or neutral alpha-glucosidase (endoplasmic reticulum) was not influenced by Ca2+ deficiency. In Ca2+ deficiency IBMX-induced insulin release was unaffected and was accompanied by reduced activities of islet alpha-glucosidehydrolases. Miglitol strongly inhibited glucose-induced insulin release concomitant with a marked suppression of islet alpha-glucosidehydrolase activities. Direct addition of miglitol to islet homogenates suppressed acid amyloglucosidase [half-maximal effective concentration (EC50) approximately 10(-6) M] and acid alpha-glucosidase. Acid phosphatase and N-acetyl-beta-D-glucosaminidase were unaffected. The miglitol-induced inhibition of glucose-stimulated insulin release was dose dependent (EC50 approximately 10(-6) M) and displayed a remarkable parallelism with the inhibition curve for acid amyloglucosidase. The in vivo insulin secretory response to glucose was markedly reduced in dystrophic mice (low amyloglucosidase), whereas the response to IBMX was unaffected. In summary, islet glycogenolytic hydrolases are Ca2+ dependent, and acid amyloglucosidase is directly involved in the multifactorial process of glucose-induced insulin release. In contrast the mechanisms of IBMX-stimulated insulin secretion operate independently of these enzymes. The effects of miglitol, a drug currently used in diabetes therapy, deserves further investigation.

Dietary therapy in NIDDM

Clearly the dietary treatment of the NIDDM patient remains an act of faith bearing in mind the poor compliance of the patient to dietary advice, and the lack of long-term studies confirming the efficacy of diets (old or new) in the prevention of diabetic vascular complications. Few of the newer recommended diets seem to have been tested in the hurly-burly of the busy, understaffed diabetic clinic. Perhaps another major hurdle has been the attitude of patients and doctors in failing to regard diet therapy as a form of treatment, akin to tablets. The phrase 'I eat my diet, doctor, then I have my usual meal' sums up the problem. There needs to be a change in attitude to diet by both doctors and patients so that the dietary changes suggested should be eating habits which would become second nature to patients--the so called 'healthy eating'--more fibre, less refined carbohydrate, less total and saturated fat and more polyunsaturated fats. It seems difficult for a majority of NIDDM patients to add onto 'healthy eating' calorie restriction to achieve weight loss. This difficulty also applies to non-diabetic obese subjects with similar poor results. One cannot help but feel that NIDDM patients should benefit from the general change in attitude of the general population towards nutrition, but reinforced education concerning diet goals for NIDDM patients is an urgent requirement and needs closer examination by the diabetic health care team as to how it may be delivered to the individual NIDDM patients. Perhaps dietitians in particular should become more critical in their approach to diet strategies and should investigate and report on the results of this treatment.