α‐glucosidase, α‐amylase inhibitory potential and antioxidant activity of fragrant black rice (Thai coloured rice)

Gamma Irradiation and Exogenous Proline Enhanced the Growth, 2AP Content, and Inhibitory Effects of Selected Bioactive Compounds against α-Glucosidase and α-Amylase in Thai Rice

Exogenous proline can improve the growth, aroma intensities, and bioactive compounds of rice. This study evaluated the effects of gamma irradiation under proline conditions on the 2-acetyl-1-pyrroline (2AP), phenolic, and flavonoid contents of rice. Moreover, the bioactive compounds of gamma-irradiated rice under proline conditions that inhibited α-glucosidase and α-amylase were evaluated by in silico study. A low gamma dose (40 Gy) induced the highest rice growth under 5 mM proline concentration. The highest 2AP content was stimulated at a gamma dose of 5－100 Gy under 10 mM proline concentration. At 500 and 1,000 Gy gamma dose, the highest flavonoid and phenolic contents of rice were stimulated. 1-(2-Hydroxy-5-methylphenyl)-ethanone, which had the highest binding affinity (-7.9 kcal/mol) against α-glucosidase, was obtained at 500 and 1,000 Gy gamma dose under 5 and 10 mM proline concentrations. Meanwhile, 6-amino-1,3,5-triazine-2,4(1H,3H)-dione, which had the highest binding affinity (-6.3 kcal/mol) against α-amylase, was obtained under 10 mM proline concentration in non-gamma-irradiated rice. The results indicate that using a combination of gamma irradiation and exogenous proline is suitable for producing new rice varieties. Moreover, the bioactive compounds that were obtained in new rice varieties exhibited health benefits, especially for diabetes mellitus treatment (inhibition of α-glucosidase and α-amylase).

Drug repurposing for diabetes mellitus: In silico and in vitro investigation of DrugBank database for α-glucosidase inhibitors

The process of developing novel compounds/drugs is arduous, time-intensive, and financially burdensome, characterized by a notably low success rate and relatively high attrition rates. To alleviate these challenges, compound/drug repositioning strategies are employed to predict potential therapeutic effects for DrugBank-approved compounds across various diseases. In this study, we devised a computational and enzyme inhibitory mechanistic approach to identify promising compounds from the pool of DrugBank-approved substances targeting Diabetes Mellitus (DM). Molecular docking analyses were employed to validate the binding interaction patterns and conformations of the screened compounds within the active site of α-glucosidase. Notably, Asp352 and Glu277 participated in interactions within the α-glucosidase-ligand complexes, mediated by conventional hydrogen bonding and van der Waals forces, respectively. The stability of the docked complexes (α-glucosidase-compounds) was scrutinized through Molecular Dynamics (MD) simulations. Subsequent in vitro analyses assessed the therapeutic potential of the repositioned compounds against α-glucosidase. Kinetic studies revealed that "Forodesine" exhibited a lower IC50 (0.24 ± 0.04 mM) compared to the control, and its inhibitory pattern corresponds to that of competitive inhibitors. In-depth in silico secondary structure content analysis detailed the interactions between Forodesine and α-glucosidase, unveiling significant alterations in enzyme conformation upon binding, impacting its catalytic activity. Overall, our findings underscore the potential of Forodesine as a promising candidate for DM treatment through α-glucosidase inhibition. Further validation through in vitro and in vivo studies is imperative to confirm the therapeutic benefits of Forodesine in conformational diseases such as DM.

The Potential of Crude and Partially Purified Black Rice Bran Extracts Obtained by Ultrasound-Assisted Extraction: Anti-Glycemic, Cytotoxicity, Cytoprotective, and Antitumoral Effects

Recovering anthocyanins from black rice bran is a way of valuing this byproduct, by obtaining an extract with biological potential. The objective of this study was to recover anthocyanins using ultrasound-assisted extraction. Some of the extract was partially purified, and both (crude and partially purified) extracts were evaluated for their anthocyanin content, antioxidant activity, antidiabetic and antitumoral activities, cytotoxicity, and oxidative stress. An increase in the laboratory scale was also achieved, making possible to increase the extraction volume up to 20 times without significantly changing the content of anthocyanins (1.85 mg C3G/g DW). It was found that the purified sample presented a 4.2 times higher value of total anthocyanins compared to the crude sample. The best IC50 values for the purified sample were verified by DPPH and ABTS (0.76 and 0.33 mg/mL). The best results for antidiabetic activity were obtained for the partially purified sample: 0.82 µM C3G for α-glucosidase and 12.5 µM C3G for α-amylase. The extracts demonstrated protection (~70%) when subjected to the oxidative stress of L929 cells. An antitumoral effect of 25-30% for both extracts was found in A459 cells. The crude and partially purified extracts of black rice have antidiabetic and anticancer effects and more studies are needed to explore their potential.

Metabolomics approach to identify key volatile aromas in Thai colored rice cultivars

In addition to white jasmine rice, Thailand has many native-colored rice varieties with numerous health benefits and the potential to become a global economic crop. However, the chemical characteristics of aromatic substances in native-colored rice are still mostly unknown. This study aimed to identify the key volatile aroma compounds and the biosynthetic pathways possibly involved in their formation in Thai native-colored rice varieties, and thus leading to the search for potential genetic markers for breeding colored rice with better aromatic properties. Twenty-three rice varieties in four categories: aromatic white, aromatic black, non-aromatic black, and non-aromatic red, were investigated (n=10 per variety). Seed husks were removed before the analysis of rice volatile aromas by static headspace gas chromatography-mass spectrometry. Untargeted metabolomics approach was used to discover the key volatile compounds in colored rice. Forty-eight compounds were detected. Thirty-eight of the 48 compounds significantly differed among groups at p<0.05, 28 of which at p<0.0001, with the non-aromatic black and red rice containing much lower content of most volatile constituents than the aromatic black and white rice. Focusing on the aromatic black rice, the samples appeared to contain high level of both compound groups of aldehydes (3-methylbutanal, 2-methylbutanal, 2-methylpropanal, pentanal, hexanal) and alcohols (butane-2,3-diol, pentan-1-ol, hexan-1-ol). Biosynthetically, these distinctive black-rice volatile compounds were proposed to be formed from the metabolic degradation of branched-chain amino acids (L-leucine, L-isoleucine and L-valine) and polyunsaturated fatty acids (linoleic acid and α-linolenic acid), involving the branched-chain aminotransferases and keto-acid decarboxylases and the 9-lipoxygonases and 13-lipoxygeases, respectively. The proposed degradative pathways of amino acids and fatty acids were well agreed with the profiles key volatile compounds detected in the Thai native-colored rice varieties.

Inhibitory potential of phenolic compounds of Thai colored rice (Oryza sativa L.) against α-glucosidase and α-amylase through in vitro and in silico studies

BACKGROUND

This study investigated the inhibitory efficiency of phenolic compounds content methyl vanillate, syringic acid and vanillic acid against α-glucosidase and α-amylase. The phenolic compound contents of 10 Thai colored rice cultivars were also determined, and the relationship between the inhibitory efficiency of colored rice extract with methyl vanillate, syringic acid and vanillic acid was evaluated.

RESULTS

The results revealed that the inhibition efficiency of methyl vanillate, syringic acid and vanillic acid was higher against α-glucosidase than against α-amylase. Inhibitory activity of vanillic acid against α-glucosidase and α-amylase was highest, with IC₅₀ of 0.100 ± 0.01 and 0.130 ± 0.02 mmol L^-1 , respectively. Docking study showed strong binding by three hydrogen bonds and four hydrogen bonds between vanillic acid with the amino acid in the binding site of α-glucosidase and α-amylase, respectively. Inhibition modes of these phenolic compounds were defined as a mixed type inhibition against α-glucosidase. Highest phenolic compound contents of methyl vanillate, syringic acid and vanillic acid were obtained from methanol extracts of all rice cultivars. The methanol extracts of all colored rice cultivars such as Khao Leum Pua also showed the highest inhibition potential against α-glucosidase and α-amylase. The results indicated that these phenolic compound contents were closely related to the inhibition potential of colored rice extracts against α-glucosidase and α-amylase.

CONCLUSION

Our results suggest that rice, especially colored rice cultivars, has the source of phenolic compounds. Moreover, the phenolic compounds had the greatest source of natural inhibitor against α-glucosidase and α-amylase. © 2022 Society of Chemical Industry.

Antidiabetic Activity of Extract Combination of Orthosiphon aristatus and Oryza sativa L. var glutinosa

Traditionally and scientifically, research has shown that Orthosiphon aristatus and Oryza sativa L. var. glutinosa have antidiabetic activity. The combination of two medicinal plants can increase their biological activity. This study aimed to determine the antidiabetic activity of O. aristatus and O. sativa L. var. glutinosa on single and combined extracts. Phytochemical screening of the single extract was done qualitatively. The α-glucosidase inhibitory method was used as an antidiabetic activity. The results showed that every extract contained alkaloids, steroids/triterpenoids, flavonoids, tannins, quinones, and coumarins. A single extract of O. sativa L. var glutinosa, O. aristatus, and their combinations (1:1, 1:2, and 2:1) had an α-glucosidase enzyme inhibitory activity with an IC50 value of 67.82, 80.93, 73.81, 88.72, and 61.51 µg/ml, respectively. The combination shows that the ratio of 1:1 was nearly additive, 1:2 was slight to moderate antagonism, and 2:1 was moderate to slight synergism. The combination of 96% ethanol extract of O. sativa L. var. glutinosa and O. aristatus in a ratio of 2:1 was the most effective in increasing its inhibitory activity.

Evaluation of Cyanide Content, Volatile Compounds Profile, and Biological Properties of Fresh and Boiled Sliced Thai Bamboo Shoot (Dendrocalamus asper Back.)

This study evaluated the cyanide content, bio-active compounds profile, volatile compounds profile, and biological activity of fresh and boiled sliced bamboo. Cyanide was only detected in fresh bamboo shoots, at a content of 140.40±5.34 mg/kg. Furthermore, the fresh bamboo shoots extracts had free radical scavenging properties, as demonstrated by ABTS･⁺ and DPPH･ assays, and contained phytochemical compounds, such as flavonoid, terpenoid, and reducing sugar. Indeed, the total phenolic and flavonoid contents were 12.12±0.12 mg gallic acid equivalent/dw and 1.60±0.11 mg quercetin equivalent/dw, respectively. In addition, these extracts demonstrated inhibitory activity against α-glucosidase (61.30±0.45%), α-amylase (37.00±1.82%), and tyrosinase (26.57±0.57%). Some volatile compounds, such as 2-methoxyphenol and 2-pentylfuran, show α-glucosidase inhibitory activity, and these compounds exerted α-amylase inhibitory activity in the fresh sliced bamboo shoots. The major volatile compound 4-methylphenol (68.15%), which exerts tyrosinase inhibitory activity, was also detected in fresh sliced bamboo shoots. The boiled sliced bamboo shoots extracts also contained bio-active compounds and exhibited biological activity similar to those in the fresh sliced bamboo shoots extracts. However, the boiling process and sliced technique reduced the bio-active compounds and biological properties as well as some of volatile compounds.