Single-dose acarbose decreased glucose-dependent insulinotropic peptide and glucagon levels in Chinese patients with newly diagnosed type 2 diabetes mellitus after a mixed meal

Structure-function relationships in (poly)phenol-enzyme binding: Direct inhibition of human salivary and pancreatic α-amylases

(Poly)phenols inhibit α-amylase by directly binding to the enzyme and/or by forming starch-polyphenol complexes. Conventional methods using starch as the substrate measure inhibition from both mechanisms, whereas the use of shorter oligosaccharides as substrates exclusively measures the direct interaction of (poly)phenols with the enzyme. In this study, using a chromatography-based method and a short oligosaccharide as the substrate, we investigated the detailed structural prerequisites for the direct inhibition of human salivary and pancreatic α-amylases by over 50 (poly)phenols from the (poly)phenol groups: flavonols, flavones, flavanones, flavan-3-ols, polymethoxyflavones, isoflavones, anthocyanidins and phenolic acids. Despite being structurally very similar (97% sequence homology), human salivary and pancreatic α-amylases were inhibited to different extents by the tested (poly)phenols. The most potent human salivary α-amylase inhibitors were luteolin and pelargonidin, while the methoxylated anthocyanidins, peonidin and petunidin, significantly blocked pancreatic enzyme activity. B-ring methoxylation of anthocyanidins increased inhibition against both human α-amylases while hydroxyl groups at C3 and B3' acted antagonistically in human salivary inhibition. C4 carbonyl reduction, or the positive charge on the flavonoid structure, was the key structural feature for human pancreatic inhibition. B-ring glycosylation did not affect salivary enzyme inhibition, but increased pancreatic enzyme inhibition when compared to its corresponding aglycone. Overall, our findings indicate that the efficacy of interaction with human α-amylase is mainly influenced by the type and placement of functional groups rather than the number of hydroxyl groups and molecular weight.

Effects of Polyphenols on Glucose-Induced Metabolic Changes in Healthy Human Subjects and on Glucose Transporters

Dietary polyphenols interact with glucose transporters in the small intestine and modulate glucose uptake after food or beverage consumption. This review assesses the transporter interaction in vitro and how this translates to an effect in healthy volunteers consuming glucose. As examples, the apple polyphenol phlorizin inhibits sodium-glucose linked transporter-1; in the intestinal lumen, it is converted to phloretin, a strong inhibitor of glucose transporter-2 (GLUT2), by the brush border digestive enzyme lactase. Consequently, an apple extract rich in phlorizin attenuates blood glucose and insulin in healthy volunteers after a glucose challenge. On the other hand, the olive phenolic, oleuropein, inhibits GLUT2, but the strength of the inhibition is not enough to modulate blood glucose after a glucose challenge in healthy volunteers. Multiple metabolic effects and oxidative stresses after glucose consumption include insulin, incretin hormones, fatty acids, amino acids, and protein markers. However, apart from acute postprandial effects on glucose, insulin, and some incretin hormones, very little is known about the acute effects of polyphenols on these glucose-induced secondary effects. In summary, attenuation of the effect of a glucose challenge in vivo is only observed when polyphenols are strong inhibitors of glucose transporters.

The effect of additional acarbose on metformin-associated artificially high 18F-Fluorodeoxyglucose uptake in positron emission tomography/computed tomography

AIM

Metformin causes diffuse and intense fluorodeoxyglucose (FDG) uptake more frequently in the colon and less frequently in the small intestine. In this study, we aimed to investigate the effect of simultaneous use of acarbose and metformin on FDG uptake in positron emission tomography/computed tomography (PET/CT), which has not been investigated previously.

METHODS

Totally 145 patients with a median age of 65 years (range: 18-80 years), who underwent FDG PET/CT in the Department of Nuclear Medicine of Erciyes University Medical School between 2018 and 2021, were involved in the study. The patients undergoing PET/CT were categorized as metformin plus acarbose users (group MA), metformin users (group M), and control subjects without diabetes (group C). The maximum and mean standard uptake values (SUVmax and SUVmean) of FDG uptake of the all intestine segments were measured separately.

RESULTS

The number of participants in each group was 35, 51 and 59 in group MA, group M and group C, respectively. The FDG uptake of all intestine was significantly higher in group MA and group M than in group C. The FDG uptake of ascending, transverse, descending, and sigmoid colon was significantly lower in group MA than in group M. The FDG uptake of the small intestine was not different between group MA and group M. The FDG uptake of the rectum was lower in group MA than group M and it was significant for SUVmean, but not significant for SUVmax.

CONCLUSION

The addition of acarbose to metformin therapy decreased SUV and artificially high FDG uptake in the colon and may be an alternative recommendation to discontinuing metformin in patients going to PET/CT imaging.

Postprandial Reactive Hypoglycemia

Reactive hypoglycemia (RH) is the condition of postprandially hypoglycemia occurring 2-5 hours after food intake. RH is clinically seen in three different forms as follows: idiopathic RH (at 180 min), alimentary (within 120 min), and late RH (at 240–300 min). When the first-phase insulin response decreases, firstly, blood glucose starts to rise after the meal. This leads to late but excessive secretion of the second-phase insulin secretion. Thus, late reactive hypoglycemia occurs. Elevated insulin levels also cause down-regulation of the insulin post-receptor on the muscle and fat cells, thus decreasing insulin sensitivity. The cause of the increase in insulin sensitivity in IRH at 3 h is not completely clear. However, there is a decrease in insulin sensitivity in late reactive hypoglycaemia at 4 or 5 hours. Thus, patients with hypoglycemia at 4 or 5 h who have a family history of diabetes and obesity may be more susceptible to diabetes than patients with hypoglycemia at 3 h. We believe that some cases with normal glucose tolerance in OGTT should be considered as prediabetes at <55 or 60 mg/dl after 4-5 hours after OGTT. Metformin and AGI therapy may be recommended if there is late RH with IFG. Also Metformin, AGİ, TZD, DPP-IVInhibitors, GLP1RA therapy may be recommended if there is late RH with IGT. As a result, postprandial RH (<55 or 60 mg/dl), especially after 4 hours may predict diabetes. Therefore, people with RH along with weight gain and with diabetes history in the family will benefit from a lifestyle modification as well as the appropriate antidiabetic approach in the prevention of diabetes.

Augmented GLP-1 Secretion as Seen After Gastric Bypass May Be Obtained by Delaying Carbohydrate Digestion

CONTEXT

Exaggerated postprandial glucagon-like peptide-1 (GLP-1) secretion seems important for weight loss and diabetes remission after Roux-en-Y gastric bypass (RYGB) and may result from carbohydrate absorption in the distal small intestine.

OBJECTIVE

To investigate distal [GLP-1; peptide YY (PYY)] and proximal [glucose-dependent insulinotropic polypeptide (GIP)] gut hormone secretion in response to carbohydrates hydrolyzed at different rates. We hypothesized that slow digestion restricts proximal absorption, facilitating distal delivery of carbohydrates and thereby enhanced GLP-1 secretion in unoperated individuals, whereas this may not apply after RYGB.

DESIGN

Single-blinded, randomized, crossover study.

SETTING

Hvidovre Hospital, Hvidovre, Denmark.

PARTICIPANTS

Ten RYGB-operated patients and 10 unoperated matched subjects.

INTERVENTIONS

Four separate days with ingestion of different carbohydrate loads, either rapidly/proximally digested (glucose plus fructose; sucrose) or slowly/distally digested (isomaltulose; sucrose plus acarbose).

MAIN OUTCOME MEASURES

GLP-1 secretion (area under the curve above baseline). Secondary outcomes included PYY and GIP.

RESULTS

Isomaltulose enhanced secretion of GLP-1 nearly threefold (P = 0.02) and PYY ninefold (P = 0.08) compared with sucrose in unoperated subjects but had a modest effect after RYGB. Acarbose failed to increase sucrose induced GLP-1 secretion in unoperated subjects and diminished the responses by 50% after RYGB (P = 0.03). In both groups, GIP secretion was reduced by isomaltulose and even more so by sucrose plus acarbose when compared with sucrose intake.

CONCLUSIONS

GLP-1 secretion depends on the rate of carbohydrate digestion, but in a different manner after RYGB. Enhanced GLP-1 secretion is central after RYGB, but it may also be obtained in unoperated individuals by delaying hydrolysis of carbohydrates, pushing their digestion and absorption distally in the small intestine.