Current Enzyme Inhibition - Volume 19, Issue 3, 2023

Enzyme inhibitors are an important therapeutic agent in drug discovery, as they can be used to manipulate biochemical pathways to treat a wide range of diseases. Current strategies for enzyme inhibition involve the use of small molecule inhibitors, natural products, or peptide-based inhibitors. These inhibitors can be used to target and modulate the activity of enzymes, which in turn can affect the progression of a particular disease. The future of enzyme inhibitor-based drug discovery lies in the development of more selective and potent inhibitors, as well as the ability to target enzymes that are involved in multiple pathways. Additionally, there is significant potential for the use of enzyme inhibitors in combination with other therapeutic strategies, such as gene therapy. Finally, the development of novel computational strategies for the design and optimization of enzyme inhibitor-based drugs is an exciting area of research. Such strategies could lead to the discovery of new and more effective inhibitors, which would facilitate the development of improved treatments for a variety of diseases. Hence, this review focuses on some techniques for the discovery of enzyme inhibitors and their applications as various therapeutic agents.

Cytochrome P450 enzymes are the main drug-metabolizing enzyme, and their activity is influenced by numerous factors, including several plants’ constituents. Herbal products mediated induction or inhibition of cytochrome P450 leads to a change in drug metabolism and consequently, drug bioavailability, safety, therapeutic efficacy, and herb-drug interaction. Since herbal preparations are commonly used either alone or concomitantly with conventional drugs, understanding the interactions of plant constituents with cytochrome P450 is crucial. Therefore, this review highlighted plants with significant inhibition, induction, or modulatory /contradictory effects on human and animal cytochrome P450 enzymes. An extensive literature search was conducted on PubMed, ScienceDirect, and Google Scholar databases to identify relevant literature. About sixty medicinal plants with significant interaction with cytochrome P450 isoforms were summarized with their common uses and affected cytochrome P450 enzyme isoforms. Besides, representative examples of plant constituents and other factors contributing to plant-induced cytochrome P450 modulation and possible herb-drug interactions were also discussed in this review.

Background: Enhanced aldose reductase activity results in increased accumulation of sorbitol. Therefore, inhibition of aldose reductase is an effective strategy to prevent or delay certain diabetic complications. Methods: Various extracts of the leaves of B. orellanawere tested for their inhibitory activity on the aldose reductase. Ethyl acetate extract that showed maximum inhibition was further fractionated and the inhibitor was identified as isoscutellarein by spectroscopic methods. IC50 of recombinant human aldose reductase by isoscutellarein was found to be 14 μM and the mode of inhibition was uncompetitive with a decrease in both Km and Vmax. Isoscutellarein was bound to the active site of aldose reductase (3RX3), namely to Ala-299, Leu-300, Leu-301, His-110 and Tyr-48. Results: Docking results exhibited a binding energy of -9.15 kJ/mol. Conclusion: The incubation of red blood cells with high glucose concentrations mimicking hyperglycemic conditions promoted sorbitol accumulation, which was effectively inhibited by isoscutellarein. Further, xylose-induced opacity of the lens was effectively inhibited by isoscutellarein.

Background: Inhibition of certain specific glutathione S-transferase isozymes is associated with the efficacy of chemotherapy in the treatment of cancer patients. Objective: We aimed to determine whether ascorbic acid, which can be used as a drug and antioxidant food supplement, is a glutathione S-transferase isozyme inhibitor. Methods: For this purpose, glutathione S-transferase was first purified from human erythrocytes and the in vitro effect of ascorbic acid on enzyme activity was investigated. Then, kinetic studies were performed to evaluate the inhibition potential of ascorbic acid, which was determined to be an inhibitor of the enzyme. Results: The enzyme was purified 1286-fold with a yield of 81% and specific activity of 18.00 U/mg protein. The effects of ascorbic acid were tested on the in vitro enzyme activity of glutathione Stransferase and detected to be an inhibitor for the enzyme with 10 mM of IC50 value. Ki constants and inhibition type were also determined for the enzyme. Conclusion: This finding indicates that ascorbic acid can be an effective inhibitor of some GST isozymes increased in cancer cells. Abundant ascorbic acid intake may prevent cancer formation by strengthening the antioxidant defense system, on the other hand, it may increase the effectiveness of cancer treatment by inhibiting the chemotherapy-resistant GST enzyme.

Background: The growing occurrence of complications associated with diabetes calls for the unending exploration of natural products for more efficient therapeutic substances. The polyol pathway is a foundational scheme involved in the development of diabetic complications. Retarding the activities of enzymes in the polyol pathway is, therefore, a potent method of managing these complications. Objective: This work assessed the ability of four non-leafy vegetables, namely Daucus carotaLinn. (carrot), Abelmoschus esculentus(L.) Moench (okra), Allium cepaLinn. (onion), and Lycopersicon esculentum Mill. (tomato), to inhibit the activities of aldose reductase and sorbitol dehydrogenase. Methods: The vegetables’ ability was evaluated by incubating the vegetables with suitable enzymes and substrates. Sample(s) with the lowest inhibitory concentration (IC50) was utilized to determine the mechanism of action of the enzymes by constructing the Lineweaver-Burk graph. Results: Results showed that the aqueous extract of carrot exhibited the lowest IC50 value for the inhibition of both aldose reductase (135.17 μg/mL) and sorbitol dehydrogenase (14.64 μg/mL), respectively. The double reciprocal plot also showed that the aqueous extract of carrot inhibited both aldose reductase and sorbitol dehydrogenase in an uncompetitive fashion. Conclusion: Aqueous extract of carrot successfully retarded the action of polyol pathway enzymes, which may result in the recovery of diabetic complications. This activity may due to the availability of phytochemicals, including carotenoids and phenylacetylenes.

Background: Oxidative stress is implicated in many neurodegenerative disorders, such as Alzheimer’s disease. As an alternative, Punica granatumpeels are widely used in the treatment of several ailments. To date, this is the first study on the anti-acetyl/butyrylcholinesterase effects of diethyl ether extract from Algerian pomegranate peels. Objective: This research aimed to evaluate the content of total phenolics, flavonoids, flavonols, and tannins in Punica granatumpeel crude extract and its fraction diethyl ether, as well as to assess its antioxidant and neuroprotective activities. Methods: The total phenolic, flavonoid, flavonol, and tannin contents in the extracts were evaluated using spectrophotometric methods. The inhibitory effects on acetyl/butyrylcholinesterase were assessed using the in vitromodels. In addition, several methods were used to investigate the antioxidant capacity of extracts, including 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-azino-bis(3-ethylbenzothiazoline- 6-sulfonate) (ABTS) free radicals scavenging, phenanthroline, reducing power and cupric ion reducing antioxidant capacity (CUPRAC) assays. Results: Phytochemical analysis revealed that the diethyl ether extract recorded the highest content of total phenolics, flavonoids, flavonols, and tannins with values of 643.3 ± 9.96 μgGAE/mg, 78.97 ± 9.97 μgQE/mg, 31.32 ± 1.79 μgQE/mg and 96.6 ± 13.65 μgTAE/mg, respectively. Moreover, the diethyl ether extract exhibited the strongest activity in the DPPH scavenging assay (IC50=3.36 ± 0.11 μg/mL), ABTS scavenging assay (IC50=1.46 ± 0.10 μg/mL), CUPRAC assay (CA0.5=3.62 ± 0.36 μg/mL), phenanthroline assay (CA0.5=1.04 ± 0.10 μg/mL), reducing power assay (CA0.5=4.14 ± 0.32 μg/mL), antiacetylcholinesterase assay (IC50=114.86 ± 13.66μg/mL), and anti-butyrylcholinesterase assay (IC50=147.00 ± 10.41 μg/mL). Conclusion: The present study has shown the extracts from Punica granatumpeel to be a rich source of bioactive compounds, potent antioxidants, and cholinesterase inhibitors. They could be considered as natural agents that can be used in anti-neurodegenerative pharmaceutical formulations.

Background: The primary goal of researchers interested in the field of oncology continues to be the development of a new anti-cancer medicine with minimal side effects. Due to their minimal toxicity and impressive performance, natural source-mediated anti-cancer treatments are attracting a lot of attention. Objective: The purpose of the current work was to extract and purify resveratrol from local Leguminosae, such as peanut, beans, cowpea, lupine, fava bean, and soybean, and then assess its cyclooxygenase- 2 (COX-2) inhibition. The aim was then to evaluate the anticancer potential of extracted resveratrol individually or combined with doxorubicin against Ehrlich ascites carcinoma (EAC) model. Methods: Resveratrol was extracted and purified using a silica gel column. The inhibition study of extracted resveratrol was conducted against COX-2 in vitro. Then, the anti-proliferation impact of resveratrol alone or combined with doxorubicin was evaluated against the previously established EAC model. Apoptotic/anti-apoptotic genes and cell cycle arrest were investigated. Results: After being extracted from peanuts, resveratrol inhibited COX-2 in vitrocompetitively with an inhibition constant (Ki) of 0.545 μM, which is extremely close to the theoretically predicted value (0.48 μM) from molecular docking. Further, resveratrol obviously inhibited COX-2 in vivo. Importantly, resveratrol was able to cause apoptosis by upregulating Bax and downregulating the anti-apoptotic gene Bcl-2, either by itself or in combination with doxorubicin. Additionally, resveratrol's ability to stop the cell cycle is evidence of its COX-2-inhibiting antiproliferative properties. Conclusion: Resveratrol exhibits anticancer potential via inhibition of COX-2, and it could be appropriate for combinational therapy in vivo.