Abstract
Diabetes mellitus is a chronic disease that is becoming a serious global health problem. Diabetes has been considered to be one of the major risks of cataract and retinopathy. Synthetic and natural product inhibitors of carbohydrate degrading enzymes are able to reduce type 2 diabetes and its complications. For a long time, potatoes have been portrayed as unhealthy for diabetic patients by some nutritionist due to their high starch content. However, purple and red potato cultivars have received considerable attention from consumers because they have high levels of polyphenolic compounds that have potent antioxidant activities. In this study, we screened the total phenolics (TP) and total anthocyanins (TA) and analyzed the phenolic and anthocyanin compounds in selected potato cultivars and advanced selections with distinct flesh colors (purple, red, yellow and white). Purple and red potato cultivars had higher levels of TP and TA than tubers with other flesh colors. Chlorogenic acid is the predominant phenolic acid, and major anthocyanin is composed of the derivatives of petunidin, peonidin, malvidin and pelargonidin. We tested the potential inhibitory effect of potato extracts on the activities of α-amylase and α-glucosidase, which were targeted to develop antidiabetic therapeutic agents. We also measured inhibitory effect of potato extracts on aldose reductase (AR) which is a key enzyme that has been a major drug target for the development of therapies to treat diabetic complications. Purple flesh tubers extract showed the most effective inhibition of α-amylase, α-glucosidase, and aldose reductase with IC50 values 25, 42, and 32 μg/ml, respectively. Kinetic studies showed that anthocyanins are noncompetitive inhibitors of these enzymes, whereas phenolic acids behaved as mixed inhibitors for α-amylase and α-glucosidase and noncompetitive inhibitors for AR. This study supports the development of a positive and healthful image of potatoes, which is an important issue for consumers.
Highlights
Diabetes mellitus (DM) is a chronic disease and is characterized by abnormal glucose tolerance and insulin resistance [1]
Selected potato tubers were evaluated for phenolics and anthocyanin as previous earlier reports had suggested that phenolics and anthocyanins are some of the major compound groups that constitute potato tubers and they impart extra health benefits
We measured total phenolics (TP) and total anthocyanins (TA) in these extracts and the results are shown in Fig 3 (S1 Table)
Summary
Diabetes mellitus (DM) is a chronic disease and is characterized by abnormal glucose tolerance and insulin resistance [1]. Sugars in blood originates from the hydrolysis of carbohydrates and is catalyzed by digestive enzymes, such as α-glucosidase and α- amylase. Α- amylase is an enzyme that is secreted by the pancreas and salivary glands that can hydrolyze starches and oligosaccharide into simple sugars. Inhibition of these enzymes can retard carbohydrate digestion, causing a reduction in the rate of glucose absorption into the blood. Inhibition of these enzyme activities in digestive organs is considered to be a therapeutic approach for managing diabetes [4,5,6]. Aldose reductase has been an attractive drug target in the clinical management of these diabetic complications [8,9,10]
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