Black Bean (Phaseolus Vulgaris L.) Protein Hydrolysates Reduce Acute Postprandial Glucose Levels in Prediabetes and Normal Glucose Tolerance Adults

Introduction Prediabetes is an intermediate state of hyperglycemia characterized by impaired fasting glucose (fasting plasma glucose levels of 100-125 mg/dL), glucose tolerance (a 2 h post-load plasma glucose levels of 140-199 mg/dL), or glycated hemoglobin A1c (HbA1c) of 5.7-6.4%. Subjects with prediabetes have a relatively high risk of developing cardiovascular disease and type 2 diabetes (T2D). Therefore, treating prediabetes is essential for delaying the progression of this disease. Current treatment of prediabetes focuses on weight loss, lifestyle modifications (diet and exercise), and the use of pharmacological agents, such as biguanides (metformin), sulfonylureas, α-amylase and α-glucosidase inhibitors, and incretin-based treatments. Moreover, those drugs could generate side effects, such as low blood sugar levels, weight modifications, atherosclerotic cardiovascular disease, congestive heart failure, and renal disease, among others. In recent years, natural alternatives with low or null adverse effects have been investigated for diabetes treatment. In this sense, functional ingredients and foods designed to help patients achieve glucose level goals are important in preventing or treating prediabetes and T2D.

Food proteins have been widely studied as a source of bioactive peptides, which are specific protein fragments that positively affect physiological functions and human health. Food proteins' bioactivity depends on the bioaccessibility and bioavailability of their peptides. Small bioactive peptides (<1,000-200 Da) present important characteristics such as high biological potential, low toxicity, low or null allergenicity, high structural diversity, and small size (relative to antibodies). These properties allow bioactive peptides to be applied as therapeutic agents against several diseases, including prediabetes and T2D.

Proteins from black beans (Phaseolus vulgaris L.) have been studied as a source of bioactive peptides. Enzymatic hydrolysis is the most popular method to generate bioactive peptides from common beans and other pulses' parental protein sequences.

Numerous in vitro studies have demonstrated that black bean protein hydrolysates (BPH) and bioactive peptides have hypoglycemic or antidiabetic effects. BPH generated with Alcalase® inhibited the in vitro activity of dipeptidyl peptidase-IV (DPP-IV), whose biological function is to inactivate glucagon-like peptide-1 (GLP-1). Also, it inhibited the enzymes α-amylase and α-glucosidase, which are involved in the starch breaking-down process. Moreover, it has been reported that BPH could reduce the expression and translocation of glucose transporters in the plasmatic membrane, such as glucose transporter-2 (GLUT2) and sodium-dependent glucose cotransporter (SGLT1). Besides, in vivo, experiments have demonstrated the efficacy of BPH reducing reduced postprandial glucose in non-hyperglycemic (16.9-24.5%) and hyperglycemic (22.7-47.7%) Wistar rats. The results of in vivo and in vitro experimental models demonstrated the potential of BPH to inhibit digestive enzymes and block gastrointestinal glucose transporters (involved in regulating postprandial blood glucose). Also, bioactive peptides from hard-to-cook beans increased glucose-simulated insulin secretion (57%) from iNS-1E insulinoma cells.

As the evidence shows, bioactive peptides from BPH may exert antidiabetic effects through several mechanisms. All the studies showing the antidiabetic potential of BPH and bioactive peptides have been performed using in silico, biochemical assays, in vitro, and in vivo studies. However, clinical trials are needed to validate the black bean protein hydrolysates' hypoglycemic effect. Therefore, this study aimed to evaluate the acute effect of BPH on glucose and insulin levels in adults with normal glucose tolerance or prediabetes.