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)

Novel carbohydrate-triazole derivatives as potential α-glucosidase inhibitors

A series of novel pyrano[2, 3-d]trizaole compounds were synthesized and their α-glucosidase inhibitory activities were evaluated by in vitro enzyme assay. The experimental data demonstrated that compound 10f showed up to 10-fold higher inhibition (IC₅₀74.0 ± 1.3 μmol·L^-1) than acarbose. The molecular docking revealed that compound 10f could bind to α-glucosidase via the hydrophobic, π-π stacking, and hydrogen bonding interactions. The results may benefit further structural modifications to find new and potent α-glucosidase inhibitors.

Risk of liver injury after α-glucosidase inhibitor therapy in advanced chronic kidney disease patients

Although α-glucosidase inhibitors (AGIs) are commonly used for controlling postprandial blood glucose, AGIs-induced liver injuries have been reported. However, the relationship between AGIs and liver injuries in advanced chronic kidney disease (CKD) patients remains unexplored. In this nationwide case-control study, we recruited 1765 advanced diabetic CKD patients, who received AGIs therapy from January 1, 2000 to December 31, 2010 as the study sample and 5295 matched controls. Recent and former AGIs users were defined as patients who received the AGIs prescription for 30–60 d and 30–210 d before the event of liver injury. The risk of AGIs-induced liver injury was examined using time-dependent Cox proportional hazards model. Liver injury occurred in 3.9% of patients in the study group and 3.3% of patients in the control group. AGIs use did not increase the risk of liver injury in advanced CKD patients (P = 0.19). The stratified analysis indicated no increased risk of liver injury in all AGIs-using subgroups (all P > 0.05). The available evidence supports extending the use of AGIs without increasing the risk of liver injury in patients with advanced CKD. Additional randomized controlled trials are warranted to confirm our results.

Antiobesity effects and improvement of insulin sensitivity by 1-deoxynojirimycin in animal models

The alpha-glucosidase inhibitor 1-deoxynojirimycin (DNJ) is one of the simplest naturally occurring carbohydrate mimics, with promising biological activity in vivo. Although there is considerable interest in the pharmacological effects of DNJ, the antidiabetic effects of DNJ in type 2 diabetes mellitus have received little attention. In this work, DNJ was isolated from the silkworm (Bombyx mori), and its antidiabetic effects were evaluated in Otsuka Long-Evans Tokushima Fatty (OLETF) rats, an established animal model of human type 2 diabetes mellitus, and in control Long-Evans Tokushima Otsuka (LETO) rats. DNJ treatment showed significant antidiabetic effects in OLETF rats, with significant improvements in fasting blood glucose levels and glucose tolerance and, especially, increased insulin sensitivity. Furthermore, there was significant loss of body weight in both groups. DNJ also showed significant antihyperglycemic effects in streptozotocin- and high-fat-diet-induced hyperglycemic rats. Its efficacy and dose profiles were better than those of acarbose, a typical alpha-glucosidase inhibitor in clinical use. Furthermore, a substantial fraction of DNJ was absorbed into the bloodstream within a few minutes of oral administration. DNJ was also detected in the urine. These findings suggest that its postprandial hypoglycemic effect in the gastrointestinal tract is a possible but insufficient mechanism of action underlying the antidiabetic effects of DNJ. Its antiobesity effect and improvement of insulin sensitivity are other possible antidiabetic effects of DNJ.

Rapid diagnosis of late-onset Pompe disease by fluorometric assay of alpha-glucosidase activities in dried blood spots

The enzymatic defect in Pompe disease is insufficient lysosomal acid alpha-glucosidase (GAA) activity which leads to lysosomal glycogen accumulation. We recently introduced a simple and reliable method to measure GAA activity in dried blood spots using Acarbose, a highly selective alpha-glucosidase inhibitor, to eliminate isoenzyme interference. Here we demonstrate that this method efficiently detects late-onset Pompe patients who are frequently misdiagnosed by conventional methods due to residual GAA activity in other tissue types.

Inhibition of glycogen breakdown by imino sugars in vitro and in vivo

The imino sugar N-butyldeoxynojirimycin (NB-DNJ) is a glucose analogue which inhibits the glycoprotein N-glycan processing enzymes alpha-glucosidases I and II and the ceramide glucosyltransferase that catalyses the first step of glycosphingolipid biosynthesis. This and other N-alkylated DNJ compounds have the potential to inhibit other glucosidase, including acid alpha-glucosidase and alpha-1,6-glucosidase, enzymes involved in glycogen breakdown. We have investigated the effect of NB-DNJ and N-nonyldeoxynojirimycin (NN-DNJ) on glycogen catabolism. Both NB-DNJ and NN-DNJ were potent inhibitors of acid alpha-glucosidase and alpha-1,6-glucosidase in vitro. NB-DNJ and NN-DNJ inhibited liver glycogen breakdown in vivo in fasting mice. Inhibition of glycogen catabolism occurred in the cytosol and lysosomes. The liver glycogen breakdown inhibition was only induced at high doses of NB-DNJ, whereas NN-DNJ caused glycogen accumulation at lower doses. The in vivo effect of NB-DNJ on liver glycogen was transient as there was no inhibition of breakdown after 90 days of treatment. The inhibition by NN-DNJ, was more pronounced, reached a plateau at 50 days and then remained unchanged. Increased glycogen was also observed in skeletal muscle in NB-DNJ- and NN-DNJ-treated mice. Since the effects on glycogen metabolism by NB-DNJ are transient and only occur at high concentrations, it is not predicted that glycogen breakdown will be impaired in patients receiving NB-DNJ therapy. NN-DNJ is the prototype of long alkyl chain derivatives of DNJ that are entering pre-clinical development as potential hepatitis B/hepatitis C (HBV/HCV) therapeutics. Depending on the dose of these compounds used, there is the potential for glycogen catabolism to be partially impaired in experimental animals and man.

Lysosomal dysfunction in muscle with special reference to glycogen storage disease type II

The importance of proper lysosomal activity in cell and tissue homeostasis is underlined by "experiments of nature", i.e. genetic defects in one of the at least 40 lysosomal enzymes/proteins present in the human cell. The complete lack of 1-4 alpha-glucosidase (glycogen storage disease type II (GSD II) or Pompe disease) is life-threatening. Patients suffering from GSD II commonly die before the age of 2 years because of cardiorespiratory insufficiency. Striated muscle cells appear to be particularly vulnerable in GSD II. The high cytoplasmic glycogen content in muscle cells most likely gives rise to a high rate of glycogen engulfment by the lysosomes. The polysaccharides become subsequently trapped in these organelles when 1-4 alpha-glucosidase activity is absent. During the course of the disease, muscle wasting occurs. It is hypothesised that the gradual loss of muscle mass is caused by a combination of disuse atrophy and lipofuscine-mediated apoptosis of myocytes. Moreover, we hypothesise that in the remaining skeletal muscle cells, longitudinal transmission of force is hampered by swollen lysosomes, clustering of non-contractile material and focal regions with degraded contractile proteins, which results in muscle weakness.

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.

Disposition of glycosidase inhibitors in the isolated perfused rat liver: hepatobiliary and subcellular concentration gradients of 1-deoxymannojirimycin and N-methyl-1-deoxynojirimycin

The hepatic disposition of two glycosidase inhibitors was studied in the isolated perfused rat liver and after subcellular fractionation. The mannosidase inhibitor 1-deoxymannojirimycin (dMM) and the glucosidase inhibitor N-methyl-1-deoxynojirimycin (MedNM) exhibited minimal binding to albumin and reached liver concentrations that approximately equaled their medium concentrations, after 30 min (MedNM) or 90 min (dMM). Within 2 hr 0.5% of the dose of MedNM and 2.9% of dMM were excreted in bile. No metabolites were found for MedNM, whereas minor (bio)degradation was inferred for dMM. After subcellular fractionation, dMM and MedNM were found predominantly in the cytosolic fraction. Compared to the other particulate fractions, MedNM was elevated in the microsomal fraction, and both compounds were slightly enriched in the lysosomal fraction. We conclude that dMM and MedNM will likely inhibit liver enzymes when sufficiently high plasma levels are reached.