Impact of B-Ring Substitution and Acylation with Hydroxy Cinnamic Acids on the Inhibition of Porcine α-Amylase by Anthocyanin-3-Glycosides

Abstract

An inhibitory effect on α-amylase and α-glucosidase is postulated for polyphenols. Thus, ingestion of those secondary plant metabolites might reduce postprandial blood glucose level (hyperglycemia), which is a major risk factor for diabetes mellitus type II. In addition to a previous study investigating structure−effect relationships of different phenolic structures, the effect of anthocyanins is studied in detail here, by applying an α-amylase activity assay, on the basis of the conversion of 2-chloro-4-nitrophenyl-4-O-ß-galactopyranosyl maltoside (GalG2CNP) and detection of CNP release by UV/Vis spectroscopy and isothermal titration calorimetry (ITC). All anthocyanin-3-glucosides showed a mixed inhibition with a strong competitive proportion, Kic < 134 µM and Kiu < 270 µM; however, the impact of the B-ring substitution was not statistically significant. UV/Vis detection failed to examine the inhibitory effect of acylated cyanidins isolated from black carrot (Daucus carota ssp. Sativus var. Autrorubens Alef.). However, ITC measurements reveal a much stronger inhibitory effect compared to the cyanidin-3-glucoside. Our results support the hypothesis that anthocyanins are efficient α-amylase inhibitors and an additional acylation with a cinnamic acid boosts the observed effect. Therefore, an increased consumption of vegetables containing acylated anthocyanin derivatives might help to prevent hyperglycemia.

Acylated anthocyanins: A review on their bioavailability and effects on postprandial carbohydrate metabolism and inflammation

“…Comparison of different anthocyanin glucosides shows inhibition of pancreatic α-amylase from pigs with nonsignificant differences (glucosides of pelargonidin > malvidin > cyanidin > delphinidin > peonidin); petunidin glucoside was not studied. Interestingly, anthocyanins acylated with hydroxycinnamic acids, originating from black carrots, inhibited pancreatic α-amylase even more than nonacylated ones (Kaeswurm et al, 2020). Purple maize extract containing both acylated and nonacylated anthocyanins inhibited pancreatic α-amylase in vitro (Zhang et al, 2019).…”

Primary and Phenolic Metabolites Analyses, In Vitro Health-Relevant Bioactivity and Physical Characteristics of Purple Corn (Zea mays L.) Grown at Two Andean Geographical Locations

“…Moreover, a high correlation between the total anthocyanin contents and the α-amylase inhibitory activity was found in cob samples (r = 0.8386, r = 0.8822, and r = 0.8639 at 10, 12.5, and 25 mg of sample dose, respectively). Acylated anthocyanins isolated from black carrots have shown stronger inhibition of the pancreatic α-amylase enzyme compared to anthocyanin-3-glucosides [55]. Purple corn anthocyanin composition also includes acylated forms, which could explain its α-amylase inhibitory potential [3].…”

Phenolic Metabolites in the Urine and Plasma of Healthy Men After Acute Intake of Purple Potato Extract Rich in Methoxysubstituted Monoacylated Anthocyanins

“…Considering the earlier reported beneficial health effects of purple potatoes [ 7 ] and the PPE [ 8 ] on human carbohydrate metabolism, acylated anthocyanins may inhibit pancreatic α‐amylase [ 43 ] and intestinal maltase [ 44 ] as detected in vitro. More bioavailable phenolic metabolites may contribute to these health effects; for example, protocatechuic acid has insulin‐like properties [ 45,46 ] and other phenolic metabolites may modulate carbohydrate metabolism by inhibiting salivary α‐amylase, enhancing the intestinal uptake of glucose and downregulating sugar transporters as detected in vitro.…”