Dipeptidyl peptidase-4 (DPP-4) inhibitory activity and glucagon-like peptide (GLP-1) secretion in arsenically safe pigmented red rice (Oryza sativa L.) and its product.

Inhibition of DPP-4 and stimulation of GLP-1 secretion are therapeutic strategies for controlling glycaemia in type 2 diabetes. The present study assessed the DPP-4 inhibitory activity and GLP-1 secretory action of pigmented and non-pigmented rice (Oryza sativa L.), along with an extruded food product. Cereal-based extruded food products, with or without passion fruit powder, were prepared from red rice using a twin extruder. Optimal extrusion conditions were determined using a CCD of response surface methodology resulting in optimal conditions to be 97.5 °C, a screw speed of 250 rpm, feed moisture of 25.2% and addition of 11.25% passion fruit powder. Samples were sequentially extracted in n-hexane, ethanol (50%) and water. Ethanol/water (50:50) extracts of rice bran significantly inhibited DPP-4 activity by 70.48 ± 1.06%, comparing favourably with RR (42.55 ± 0.84%), PRR (35.91 ± 1.27%) and PA (29.14 ± 1.23%). DPP-4 inhibitory activity was retained in both extruded products albeit at reduced levels. GLP-1 secretion was stimulated mostly by extruded products extracted with n-hexane or ethanol which upregulated basal secretion by 6.1-fold and 4.2-fold, respectively. ICP-MS results showed that extruded food items have a lower arsenic content. In conclusion, there are potential opportunities for the nutraceuticals and functional food products using pigmented red rice. Supplementary Information: The online version contains supplementary material available at 10.1007/s13197-022-05444-x.

Assessment of antidiabetic potential and phytochemical profiling of Rhazya stricta root extracts.

BACKGROUND: Diabetes mellitus is a chronic disease characterized by hyperglycemia that may occur due to genetic, environmental or lifestyle factors. Natural remedies have been used to treat diabetes since long and many antidiabetic compounds of varied efficacies have been isolated from medicinal plants. Rhazya stricta has been used for decades for the treatment of diabetes mellitus and associated ailments. Considering the folkloric use of R. stricta against diabetes, it was aimed to investigate the effectiveness of its root extracts against diabetes through in vitro assays and in vivo studies using animal model along with phytochemical profiling through GCMS. METHODS: Various fractions of Rhazya stricta obtained through column chromatography were evaluated for a variety of assays including α-glucosidase, Dipeptidyl peptidase-IV (DPP-IV), ß-secretase and Glucagon-like peptide-1 (GLP-1) secretion studies. For the in vivo studies the alloxan-induced diabetic mice were treated with root extracts and blood glucose levels, HbA1C, and other biochemical markers along with the histological study of the liver were done. The phytochemical identification was performed using an Agilent 7890B GC coupled to a 7010 Triple Quadrupole (MS/MS) system. GraphPad Prism software version 5.01 was used for statistical analysis. RESULTS: Majority of the extract fractions showed excellent results against diabetes by inhibiting enzymes DPP-IV (Up to 61%) and ß-secretase (Up to 83%) with IC50s 979 µg/ml and 169 µg/ml respectively with increase in the GLP1 secretion. The results of in vivo studies indicated a marked reduction in blood glucose and HbA1c levels along with positive effects on other parameters like lipid profile, liver functions and renal functions of extract-treated mice as compared to control. The histological examination of the liver demonstrated hepatoprotective effects against diabetes led changes and various classes of phytochemicals were also identified through GCMS in different fractions. CONCLUSION: The results revealed strong antidiabetic activity of R. stricta root with the potential to protect body organs against diabetic changes. Moreover, a variety of phytochemicals has also been identified through GCMS that might be responsible for the antidiabetic potential of Rhazya stricta root.

The Health Promoting Bioactivities of Lactuca sativa can be Enhanced by Genetic Modulation of Plant Secondary Metabolites.

Plant secondary metabolites are protective dietary constituents and rol genes evidently increase the synthesis of these versatile phytochemicals. This study subjected a globally important vegetable, lettuce (Lactuca sativa) to a combination of untargeted metabolomics (LC-QTof-MS) and in vitro bioactivity assays. Specifically, we examined the differences between untransformed cultured lettuce (UnT), lettuce transformed with either rolABC (RA) or rolC (RC) and commercially grown (COM) lettuce. Of the 5333 metabolite features aligned, deconvoluted and quantified 3637, 1792 and 3737 significantly differed in RA, RC and COM, respectively, compared with UnT. In all cases the number of downregulated metabolites exceeded the number increased. In vitro bioactivity assays showed that RA and RC (but not COM) significantly improved the ability of L. sativa to inhibit α-glucosidase, inhibit dipeptidyl peptidase-4 (DPP-4) and stimulate GLP-1 secretion. We putatively identified 76 lettuce metabolites (sesquiterpene lactones, non-phenolic and phenolic compounds) some of which were altered by several thousand percent in RA and RC. Ferulic acid levels increased 3033-9777%, aminooxononanoic acid increased 1141-1803% and 2,3,5,4'tetrahydroxystilbene-2-O-ß-d-glucoside increased 40,272-48,008%. Compound activities were confirmed using commercially obtained standards. In conclusion, rol gene transformation significantly alters the metabolome of L.sativa and enhances its antidiabetic properties. There is considerable potential to exploit rol genes to modulate secondary metabolite production for the development of novel functional foods. This investigation serves as a new paradigm whereby genetic manipulation, metabolomic analysis and bioactivity techniques can be combined to enable the discovery of novel natural bioactives and determine the functional significance of plant metabolites.

Metabolically-inactive glucagon-like peptide-1(9-36)amide confers selective protective actions against post-myocardial infarction remodelling.

BACKGROUND: Glucagon-like peptide-1 (GLP-1) therapies are routinely used for glycaemic control in diabetes and their emerging cardiovascular actions have been a major recent research focus. In addition to GLP-1 receptor activation, the metabolically-inactive breakdown product, GLP-1(9-36)amide, also appears to exert notable cardiovascular effects, including protection against acute cardiac ischaemia. Here, we specifically studied the influence of GLP-1(9-36)amide on chronic post-myocardial infarction (MI) remodelling, which is a major driver of heart failure progression. METHODS: Adult female C57BL/6 J mice were subjected to permanent coronary artery ligation or sham surgery prior to continuous infusion with GLP-1(9-36)amide or vehicle control for 4 weeks. RESULTS: Infarct size was similar between groups with no effect of GLP-1(9-36)amide on MI-induced cardiac hypertrophy, although modest reduction of in vitro phenylephrine-induced H9c2 cardiomyoblast hypertrophy was observed. Whilst echocardiographic systolic dysfunction post-MI remained unchanged, diastolic dysfunction (decreased mitral valve E/A ratio, increased E wave deceleration rate) was improved by GLP-1(9-36)amide treatment. This was associated with modulation of genes related to extracellular matrix turnover (MMP-2, MMP-9, TIMP-2), although interstitial fibrosis and pro-fibrotic gene expression were unaltered by GLP-1(9-36)amide. Cardiac macrophage infiltration was also reduced by GLP-1(9-36)amide together with pro-inflammatory cytokine expression (IL-1ß, IL-6, MCP-1), whilst in vitro studies using RAW264.7 macrophages revealed global potentiation of basal pro-inflammatory and tissue protective cytokines (e.g. IL-1ß, TNF-α, IL-10, Fizz1) in the presence of GLP-1(9-36)amide versus exendin-4. CONCLUSIONS: These data suggest that GLP-1(9-36)amide confers selective protection against post-MI remodelling via preferential preservation of diastolic function, most likely due to modulation of infiltrating macrophages, indicating that this often overlooked GLP-1 breakdown product may exert significant actions in this setting which should be considered in the context of GLP-1 therapy in patients with cardiovascular disease.

Naturally-occurring TGR5 agonists modulating glucagon-like peptide-1 biosynthesis and secretion.

Selective GLP-1 secretagogues represent a novel potential therapy for type 2 diabetes mellitus. This study examined the GLP-1 secretory activity of the ethnomedicinal plant, Fagonia cretica, which is postulated to possess anti-diabetic activity. After extraction and fractionation extracts and purified compounds were tested for GLP-1 and GIP secretory activity in pGIP/neo STC-1 cells. Intracellular levels of incretin hormones and their gene expression were also determined. Crude F. cretica extracts stimulated both GLP-1 and GIP secretion, increased cellular hormone content, and upregulated gene expression of proglucagon, GIP and prohormone convertase. However, ethyl acetate partitioning significantly enriched GLP-1 secretory activity and this fraction underwent bioactivity-guided fractionation. Three isolated compounds were potent and selective GLP-1 secretagogues: quinovic acid (QA) and two QA derivatives, QA-3ß-O-ß-D-glycopyranoside and QA-3ß-O-ß-D-glucopyranosyl-(28→1)-ß-D-glucopyranosyl ester. All QA compounds activated the TGR5 receptor and increased intracellular incretin levels and gene expression. QA derivatives were more potent GLP-1 secretagogues than QA. This is the first time that QA and its naturally-occurring derivatives have been shown to activate TGR5 and stimulate GLP-1 secretion. These data provide a plausible mechanism for the ethnomedicinal use of F. cretica and may assist in the ongoing development of selective GLP-1 agonists.

Whey proteins have beneficial effects on intestinal enteroendocrine cells stimulating cell growth and increasing the production and secretion of incretin hormones.

Whey protein has been indicated to curb diet-induced obesity, glucose intolerance and delay the onset of type 2 diabetes mellitus. Here the effects of intact crude whey, intact individual whey proteins and beta-lactoglobulin hydrolysates on an enteroendocrine (EE) cell model were examined. STC-1 pGIP/neo cells were incubated with several concentrations of yogurt whey (YW), cheese whey (CW), beta-lactoglobulin (BLG), alpha-lactalbumin (ALA) and bovine serum albumin (BSA). The findings demonstrate that BLG stimulates EE cell proliferation, and also GLP-1 secretion (an effect which is lost following hydrolysis with chymotrypsin or trypsin). ALA is a highly potent GLP-1 secretagogue which also increases the intracellular levels of GLP-1. Conversely, whey proteins and hydrolysates had little impact on GIP secretion. This appears to be the first investigation of the effects of the three major proteins of YW and CW on EE cells. The anti-diabetic potential of whey proteins should be further investigated.

Exendin-4 protects against post-myocardial infarction remodelling via specific actions on inflammation and the extracellular matrix.

Glucagon-like peptide-1 (GLP-1) is an insulin-releasing hormone clinically exploited for glycaemic control in diabetes, which also confers acute cardioprotection and benefits in experimental/clinical heart failure. We specifically investigated the role of the GLP-1 mimetic, exendin-4, in post-myocardial infarction (MI) remodelling, which is a key contributor to heart failure. Adult female normoglycaemic mice underwent coronary artery ligation/sham surgery prior to infusion with exendin-4/vehicle for 4 weeks. Metabolic parameters and infarct sizes were comparable between groups. Exendin-4 protected against cardiac dysfunction and chamber dilatation post-MI and improved survival. Furthermore, exendin-4 modestly decreased cardiomyocyte hypertrophy/apoptosis but markedly attenuated interstitial fibrosis and myocardial inflammation post-MI. This was associated with altered extracellular matrix (procollagen IαI/IIIαI, connective tissue growth factor, fibronectin, TGF-ß3) and inflammatory (IL-10, IL-1ß, IL-6) gene expression in exendin-4-treated mice, together with modulation of both Akt/GSK-3ß and Smad2/3 signalling. Exendin-4 also altered macrophage response gene expression in the absence of direct actions on cardiac fibroblast differentiation, suggesting cardioprotective effects occurring secondary to modulation of inflammation. Our findings indicate that exendin-4 protects against post-MI remodelling via preferential actions on inflammation and the extracellular matrix independently of its established actions on glycaemic control, thereby suggesting that selective targeting of GLP-1 signalling may be required to realise its clear therapeutic potential for post-MI heart failure.

Plants Fagonia cretica L. and Hedera nepalensis K. Koch contain natural compounds with potent dipeptidyl peptidase-4 (DPP-4) inhibitory activity.

ETHNOPHARMACOLOGICAL RELEVANCE: The two plants investigated here (Fagonia cretica L. and Hedera nepalensis K. Koch) have been previously reported as natural folk medicines for the treatment of diabetes but until now no scientific investigation of potential anti-diabetic effects has been reported. MATERIALS AND METHODS: In vitro inhibitory effect of the two tested plants and their five isolated compounds on the dipeptidyl peptidase 4 (DPP-4) was studied for the assessment of anti-diabetic activity. RESULTS: A crude extract of Fagonia cretica possessed good inhibitory activity (IC50 value: 38.1 µg/ml) which was also present in its n-hexane (FCN), ethyl acetate (FCE) or aqueous (FCA) fractions. A crude extract of Hedera nepalensis (HNC) possessed even higher inhibitory activity (IC50 value: 17.2 µg/ml) and this activity was largely retained when further fractionated in either ethyl acetate (HNE; IC50: 34.4 µg/ml) or n-hexane (HNN; 34.2 µg/ml). Bioactivity guided isolation led to the identification of four known compounds (isolated for the first time) from Fagonia cretica: quinovic acid (1), quinovic acid-3ß-O-ß-D-glycopyranoside (2), quinovic acid-3ß-O-ß-D-glucopyranosyl-(28→1)-ß-D-glucopyranosyl ester (3), and stigmasterol (4) all of which inhibited DPP-4 activity (IC50: 30.7, 57.9, 23.5 and >100 µM, respectively). The fifth DPP-4 inhibitor, the triterpenoid lupeol (5) was identified in Hedera nepalensis (IC50: 31.6 µM). CONCLUSION: The experimental study revealed that Fagonia cretica and Hedera nepalensis contain compounds with significant DPP-4 inhibitory activity which should be further investigated for their anti-diabetic potential.

Lactobacillus strains isolated from infant faeces possess potent inhibitory activity against intestinal alpha- and beta-glucosidases suggesting anti-diabetic potential.

PURPOSE: Inhibitors of intestinal alpha-glucosidases are used therapeutically to treat type 2 diabetes mellitus. Bacteria such as Actinoplanes sp. naturally produce potent alpha-glucosidase inhibitor compounds, including the most widely available drug acarbose. It is not known whether lactic acid bacteria (LAB) colonising the human gut possess inhibitory potential against glucosidases. Hence, the study was undertaken to screen LABs having inherent alpha- and beta-glucosidase inhibitory potential. METHODS: This study isolated, screened, identified and extracted Lactobacillus strains (Lb1-15) from human infant faecal samples determining their inhibitory activity against intestinal maltase, sucrase, lactase and amylase. Lactobacillus reference strains (Ref1-7), a Gram positive control (Ctrl1) and two Gram negative controls (Ctrl2-3), were also analysed to compare activity. RESULTS: Faecal isolates were identified by DNA sequencing, with the majority identified as unique strains of Lactobacillus plantarum. Some strains (L. plantarum, L. fermentum, L. casei and L. rhamnosus) had potent and broad spectrum inhibitory activities (up to 89%; p < 0.001; 500 mg/ml wet weight) comparable to acarbose (up to 88%; p < 0.001; 30 mg/ml). Inhibitory activity was concentration-dependent and was freely available in the supernatant, and was not present in other bacterial genera (Bifidobacterium bifidum and Escherichia coli or Salmonella typhimurium). Interestingly, the potency and spectrum of inhibitory activity across strains of a single species (L. plantarum) differed substantially. Some Lactobacillus extracts had broader spectrum activities than acarbose, effectively inhibiting beta-glucosidase activity (lactase) as well as alpha-glucosidase activities (maltase, sucrase and amylase). Anti-diabetic potential was indicated by the fact that oral gavage with a L. rhamnosus extract (1 g/kg) was able to reduce glucose excursions (Area under curve; 22%; p < 0.05) in rats during a carbohydrate challenge (starch; 2 g/kg). CONCLUSION: These results definitively demonstrate that Lactobacillus strains present in the human gut have alpha- and beta-glucosidase inhibitory activities and can reduce blood glucose responses in vivo. Although the potential use of LAB such as Lactobacillus as a dietary supplement, medicinal food or biotherapeutic for diabetes is uncertain, such an approach might offer advantages over drug therapies in terms of broader spectrum activities and fewer unpleasant side effects. Further characterisation of this bioactivity is warranted, and chronic studies should be undertaken in appropriate animal models or diabetic subjects.

Examining acute and chronic effects of short- and long-chain fatty acids on peptide YY (PYY) gene expression, cellular storage and secretion in STC-1 cells.

PURPOSE: Peptide YY (PYY) is a gastrointestinal hormone with physiological actions regulating appetite and energy homoeostasis. The cellular mechanisms by which nutrients stimulate PYY secretion from intestinal enteroendocrine cells are still being elucidated. METHODS: This study comprehensively evaluated the suitability of intestinal STC-1 cells as an in vitro model of PYY secretion. PYY concentrations (both intracellular and in culture media) with other intestinal peptides (CCK, GLP-1 and GIP) demonstrated that PYY is a prominent product of STC-1 cells. Furthermore, acute and chronic PYY responses to 15 short (SCFAs)- and long-chain (LCFAs) dietary fatty acids were measured alongside parameters for DNA synthesis, cell viability and cytotoxicity. RESULTS: We found STC-1 cells to be reliable secretors of PYY constitutively releasing PYY into cell culture media (but not into non-stimulatory buffer). We demonstrate for the first time that STC-1 cells produce PYY mRNA transcripts; that STC-1 cells produce specific time- and concentration-dependent PYY secretory responses to valeric acid; that linoleic acid and conjugated linoleic acid 9,11 (CLA 9,11) are potent PYY secretagogues; and that chronic exposure of SCFAs and LCFAs can be detrimental to STC-1 cells. CONCLUSIONS: Our studies demonstrate the potential usefulness of STC-1 cells as an in vitro model for investigating nutrient-stimulated PYY secretion in an acute setting. Furthermore, our discovery that CLA directly stimulates L-cells to secrete PYY indicates another possible mechanism contributing to the observed effects of dietary CLA on weight loss.