Ascorbic acid-based inhibitors of alpha-amylases

Ascorbic acid as serine protease inhibitor in lung cancer cell line and human serum albumin

Serine proteases (SPs) are distributed among all living cells accounting for almost one-third of all proteases. Dysregulation of SPs during inflammation and/or infection can result in devastating consequences, such as skin and lung inflammation, neuroinflammation, arthritis, as well as metastasis of cancerous cells. Such activities are tightly regulated by various inhibitors known as serine protease inhibitors (SERPIN). The thermodynamic investigations previously revealed that L-ascorbic acid binds to trypsin more firmly than pepsin and the binding force of L-ascorbic acid is driven by hydrogen bonds and van der Waals forces. However, the physiochemical effects of such interaction on trypsin and/or pepsin have not yet been reported. Ascorbic acid, also known as vitamin C, is one of the essential nutrients and most common food supplements, fortificants, and preservatives. The aim of this study was to explore the inhibitory effects of ascorbic acid on serine proteases at various concentrations on the in-vitro digestion and/or hydrolysis of intercellular matrix of cell monolayer and human serum albumin (HSA). The inhibitory effects of ascorbic on trypsin are investigated by qualitative and quantitative analysis using SDS-PAGE imaging and NIH densitometric software. Upon the addition of ascorbic acid in both indicator systems, the detachment and/or dissociation of cell monolayer and the digestion of HSA were inhibited in the presence of EDTA-Trypsin. The inhibitory effect of ascorbic acid on the digestion of intercellular matrix and/or hydrolysis of HSA showed a dose-dependent trend until it reached the maximum extent of inhibition. At an equal concentration (2.5mg/mL) ascorbic acid and EDTA-Trypsin exhibited the most potent inhibitory effect on the in vitro digestion of protein either in the form of intercellular matrix in cell monolayer and/or HSA respectively. Overall, our results based on two indicator systems strongly indicate that ascorbic acid may function as a serine protease inhibitor (SERPIN) beyond other important functions.

Stability and bioaccessibility of micronutrients and phytochemicals present in processed leek and Brussels sprouts during static in vitro digestion

Vegetables are frequently processed before consumption. However, vegetable functionalization continues beyond ingestion as the human digestive tract exposes vegetable products to various conditions (e.g. elevated temperature, pH alterations, enzymes, electrolytes, mechanical disintegration) which can affect the stability of micronutrients and phytochemicals. Besides the extent to which these compounds withstand the challenges posed by digestive conditions, it is equally important to consider their accessibility for potential absorption by the body. Therefore, this study investigated the impact of static in vitro digestion on the stability (i.e. concentration) and bioaccessibility of vitamin C, vitamin K1, glucosinolates, S-alk(en)yl-l-cysteine sulfoxides (ACSOs) and carotenoids in Brussels sprouts (Brassica oleracea var. gemmifera) and leek (Allium ampeloprasum var. porrum). Water-soluble compounds, glucosinolates and ACSOs, remained stable during digestion while vitamin C decreased by >48%. However, all water-soluble compounds were completely bioaccessible. Lipid-soluble compounds were also stable during digestion but were only bioaccessible for 26-81%.

Highly stable and versatile α-amylase from Anoxybacillus vranjensis ST4 suitable for various applications

α-Amylase from the thermophilic bacterial strain Anoxybacillus vranjensis ST4 (AVA) was cloned into the pMALc5HisEk expression vector and successfully expressed and purified from the Escherichia coli ER2523 host strain. AVA belongs to the GH13_5 subfamily of glycoside hydrolases and has 7 conserved sequence regions (CSRs) distributed in three distinct domains (A, B, C). In addition, there is a starch binding domain (SBD) from the CBM20 family of carbohydrate binding modules (CBMs). AVA is a monomer of 66 kDa that achieves maximum activity at 60-80 °C and is active and stable over a wide pH range (4.0-9.0). AVA retained 50 % of its activity after 31 h of incubation at 60 °C and was resistant to a large number of denaturing agents. It hydrolyzed starch granules very efficiently, releasing maltose, maltotriose and maltopentaose as the main products. The hydrolysis rates of raw corn, wheat, horseradish, and potato starch, at a concentration of 10 %, were 87.8, 85.9, 93.0, and 58 %, respectively, at pH 8.5 over a 3 h period. This study showed that the high level of expression as well as the properties of this highly stable and versatile enzyme show all the prerequisites for successful application in industry.

The impact of ascorbic acid (E 300) on digestion of different nutrients using In Vitro digestion model.. [DOI: 10.21203/rs.3.rs-3108018/v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Ascorbic acid is a very common antioxidant food additive and vitamin supplement which is used by human on daily basis. Especially during corona virus pandemic because it is included in COVID-19 treatment guidelines. During this study the physicochemical properties as well as cytotoxicity, antioxidant activity and anti-diabetic activity were determined. Moreover, the effect of ascorbic acid on the digestibility of different nutrients including proteins, and fats were evaluated using INFOGEST in vitro digestion model. The structural analysis of ascorbic acid reveals that it has a monoclinic crystal structure with particle size in the nanoscale (41.496 ± 12.96 nm ). Cytotoxicity and antioxidant activity measurements proved that ascorbic acid is a powerful antioxidant with high safety profile. Moreover, it stimulates cell growth and proliferation at a dose dependent manner (12.5, 25, 50,100, and 200 mM). Ascorbic acid showed to have a low inhibition effect on alpha glucosidase enzyme, even at high concentrations (22.1% at 1800 ppm ). Digestibility measurements demonstrates that it has a positive effect on proteins and fats digestibility with a concentration dependent manner.

Inhibitory Effect of Ascorbic Acid on in vitro Enzymatic Digestion of Raw and Cooked Starches

Ascorbic acid, also known as vitamin C, was previously reported to inhibit the activity of pancreatic α-amylase, the primary digestive enzyme for starch. A major implication of such inhibition is a slowed rate of starch digestion into glucose, which thereby reduces postprandial hyperglycemia. The aim of this study was to explore the inhibitory effects of ascorbic acid at various concentrations on the in vitro digestion of high amylose maize starch (HAMS) and potato starch (PS) in both raw and cooked conditions. Resistant starch (RS) content, defined as the starch that remained after 4 h of simulated in vitro enzymatic digestion, was measured for the starch samples. Upon the addition of ascorbic acid, the RS contents increased in both raw and cooked starches. Cooking significantly reduced the RS contents as compared to raw starches, and less increase in RS was observed with the addition of ascorbic acid. The inhibitory effect of ascorbic acid on the digestion of raw starches showed a dose-dependent trend until it reached the maximum extent of inhibition. At the concentrations of 12.5 and 18.75 mg/mL, ascorbic acid exhibited the most potent inhibitory effect on the in vitro starch digestion in raw and cooked conditions, respectively. Overall, our results strongly indicate that ascorbic acid may function as a glycemic modulatory agent beyond other important functions, and its effects persist upon cooking with certain concentrations applied.

Nutritional influences on enzyme activities in saliva of Asian and African elephants

Asian and African elephants show morphological adaptations to their ecological niche including the oral cavity. Variety and preferences of forage plants differ between both herbivorous elephant species. Diet can affect salivary enzymes. Asian elephants were shown to have a higher salivary amylase activity than African elephants. Species-specific differences were presumed to be influenced by feeding during collection procedure. This study aimed to determine the influence of feeding on enzyme activities in saliva of both elephant species to differentiate from species-specific effects. Additionally, season and housing conditions on salivary enzyme activities in non-fed elephants of both species were investigated. Salivary amylase (sAA), lysozyme (sLYS) and peroxidase (sPOD) activity were measured photometrically or fluorometrically. Results of this study reinforce previous observations of higher basic sAA activity in Asian elephants compared to African elephants. Salivary LYS and sPOD activity showed neither species-specific nor housing-specific differences. Independent from season, most elephants of both species revealed a lack of or low sPOD activity. Feeding caused a temporary decrease of sAA, sLYS and sPOD activity in both elephant species kept in four of eight tested zoos. Furthermore, sAA activity in Asian elephants was higher and sLYS activity lower in Spring than in Autumn. This study summarizes that sAA and sLYS are components of Asian and African elephant saliva in an active conformation in contrast to sPOD. Diet varying between season and zoos might influence sAA and sLYS activities primarily in Asian elephants but temporary low effects suggest sufficient buffer capacity of elephant saliva of both species.

Morphology and Characteristics of Starch Nanoparticles Self-Assembled via a Rapid Ultrasonication Method for Peppermint Oil Encapsulation

Starch nanoparticles (SNPs) and peppermint oil (PO)-loaded SNPs were fabricated via an ultrasonic bottom-up approach using short linear glucan debranched from waxy maize starch. The effects of the glucan concentration, ultrasonic irradiation time, and chain length on the SNPs' characteristics were investigated. Under the optimal conditions, i.e., short linear glucan concentration of 5% and ultrasonication time of 8-10 min, SNPs were successfully prepared. The as-prepared SNPs showed good uniformity and an almost perfect spherical shape, with diameters of 150-200 nm. The PO-loaded SNPs also exhibited regular shapes, with sizes of approximately 200 nm. The loading capacity, encapsulation efficiency, and yield of PO-loaded SNPs were ∼25.5%, ∼87.7%, and ∼93.2%, respectively. After encapsulation, PO possessed enhanced stability against thermal treatment (80 °C). The pseudo-first-order kinetics model accurately described the slow-release properties of PO from SNPs. This new approach of fabricating SNPs is rapid, high yield, and nontoxic, showing great potential in the encapsulation and sustained release of labile essential oils or other lipids.

Does diet influence salivary enzyme activities in elephant species?

Asian elephants (Elephas maximus) and African elephants (Loxodonta africana) are herbivore generalists; however, Asian elephants might ingest a higher proportion of grasses than Africans. Although some studies have investigated nutrition-specific morphological adaptations of the two species, broader studies on salivary enzymes in both elephant species are lacking. This study focuses on the comparison of salivary enzymes activity profiles in the two elephant species; these enzymes are relevant for protective and digestive functions in humans. We aimed to determine whether salivary amylase (sAA), lysozyme (sLYS), and peroxidase (sPOD) activities have changed in a species-specific pattern during evolutionary separation of the elephant genera. Saliva samples of 14 Asian and eight African elephants were collected in three German zoos. Results show that sAA and sLYS are salivary components of both elephant species in an active conformation. In contrast, little to no sPOD activity was determined in any elephant sample. Furthermore, sAA activity was significantly higher in Asian compared with African elephants. sLYS and sPOD showed no species-specific differences. The time of food provision until sample collection affected only sAA activity. In summary, the results suggest several possible factors modulating the activity of the mammal-typical enzymes, such as sAA, sLYS, and sPOD, e.g., nutrition and sampling procedure, which have to be considered when analyzing differences in saliva composition of animal species.

Imino sugars and glycosyl hydrolases: historical context, current aspects, emerging trends

Forty years of discoveries and research on imino sugars, which are carbohydrate analogues having a basic nitrogen atom instead of oxygen in the sugar ring and, acting as potent glycosidase inhibitors, have made considerable impact on our contemporary understanding of glycosidases. Imino sugars have helped to elucidate the catalytic machinery of glycosidases and have refined our methods and concepts of utilizing them. A number of new aspects have emerged for employing imino sugars as pharmaceutical compounds, based on their profound effects on metabolic activities in which glycosidases are involved. From the digestion of starch to the fight against viral infections, from research into malignant diseases to potential improvements in hereditary storage disorders, glycosidase action and inhibition are essential issues. This account aims at combining general developments with a focus on some niches where imino sugars have become useful tools for glycochemistry and glycobiology.

The novel C-5 aryl, alkenyl, and alkynyl substituted uracil derivatives of L-ascorbic acid: synthesis, cytostatic, and antiviral activity evaluations

The novel C-5 substituted uracil derivatives of l-ascorbic acid were synthesized by coupling of 5-iodouracil-4,5-didehydro-5,6-dideoxy-l-ascorbic acid with unsaturated stannanes under Stille reaction conditions. The new compounds were evaluated for their antitumoral and antiviral activities. Among all compounds evaluated the 5-propynyl substituted uracil derivative of l-ascorbic acid (7) exhibited the most pronounced cytostatic activities against all examined tumor cell lines (IC(50): 0.2-0.78 microM). However, this compound was also cytotoxic to human normal fibroblasts WI 38. The 5-(phenylethynyl)uracil-2,3-di-O-benzylated l-ascorbic acid derivative (4) exhibited an albeit slight (IC(50): 55-108 microM), but selective inhibitory effect toward all tumor cell lines except for cervical carcinoma (HeLa), pancreatic carcinoma (MiaPaCa-2), laryngeal carcinoma (Hep-2), and colon carcinoma (SW 620), and no cytotoxicity to normal human fibroblast (WI 38). Compound 7 showed some, not highly specific, inhibitory potential against vesicular stomatitis virus, Coxsackie B4 virus, and Sindbis viruses (EC(50): 1.6 microM).

The novel pyrimidine and purine derivatives of l-ascorbic acid: synthesis, one- and two-dimensional 1H and 13C NMR study, cytostatic and antiviral evaluation

The syntheses of the novel C-5 substituted pyrimidine derivatives of l-ascorbic acid containing free hydroxy groups at C-2' (6-10) or C-2' and C-3' (11-15) positions of the lactone ring are described. Debenzylation of the 6-chloro- and 6-(N-pyrrolyl)purine derivatives of 2,3-O,O-dibenzyl-l-ascorbic acid (16 and 17) gave the new compounds containing hydroxy groups at C-2' (18) and C-2' and C-3' (19 and 20). Z- and E-configuration of the C4'C5' double bond and position of the lactone ring of the compounds 6-9 were deduced from their one- and two-dimensional (1)H and (13)C NMR spectra and connectivities in NOESY and HMBC spectra. Compounds 15 and 18 showed the best inhibitory activities of all evaluated compounds in the series. The compound 15 containing 5-(trifluoromethyl)uracil showed marked inhibitory activity against all human malignant cell lines (IC(50): 5.6-12.8 microM) except on human T-lymphocytes. Besides, this compound influenced the cell cycle by increasing the cell population in G2/M phase and induced apoptosis in SW 620 and MiaPaCa-2 cells. The compound 18 containing 6-chloropurine ring expressed the most pronounced inhibitory activities against HeLa (IC(50): 6.8 microM) and MiaPaCa-2 cells (IC(50): 6.5 microM). The compound 20 with 6-(N-pyrrolyl)purine moiety showed the best differential inhibitory effect against MCF-7 cells (IC(50): 35.9 microM).

Prediction of potential toxicity and side effect protein targets of a small molecule by a ligand-protein inverse docking approach

Determination of potential drug toxicity and side effect in early stages of drug development is important in reducing the cost and time of drug discovery. In this work, we explore a computer method for predicting potential toxicity and side effect protein targets of a small molecule. A ligand-protein inverse docking approach is used for computer-automated search of a protein cavity database to identify protein targets. This database is developed from protein 3D structures in the protein data bank (PDB). Docking is conducted by a procedure involving multiple conformer shape-matching alignment of a molecule to a cavity followed by molecular-mechanics torsion optimization and energy minimization on both the molecule and the protein residues at the binding region. Potential protein targets are selected by evaluation of molecular mechanics energy and, while applicable, further analysis of its binding competitiveness against other ligands that bind to the same receptor site in at least one PDB entry. Our results on several drugs show that 83% of the experimentally known toxicity and side effect targets for these drugs are predicted. The computer search successfully predicted 38 and missed five experimentally confirmed or implicated protein targets with available structure and in which binding involves no covalent bond. There are additional 30 predicted targets yet to be validated experimentally. Application of this computer approach can potentially facilitate the prediction of toxicity and side effect of a drug or drug lead.

A novel class of inhibitors for steroid 5alpha-reductase: synthesis and evaluation of umbelliferone derivatives

A series of umbelliferone derivatives was prepared and their 5alpha-reductase type 1 inhibitory activities were evaluated in cell culture systems. Our studies have identified a new series of potent 5alpha-reductase type 1 inhibitors and provided the basis for further development for the treatment of human endocrine disorders associated with overproduction of DHT by 5alpha-reductase type 1. The preliminary structure-activity relationship was described to elucidate the essential structural requirements.

Kinetic characterisation of ene-diol-based inhibitors of alpha-amylase

A kinetic analysis of the inhibition of malt alpha-amylase by compounds based on ascorbic acid has shown the mode of inhibition to be competitive for the parent compound, but more complex for its derivatives. We have further simplified the ascorbic acid ene-diol pharmacophore by demonstrating that dihydroxyfumaric acid is also a good inhibitor of malt alpha-amylase.