Natural Products and Extracts as Xantine Oxidase Inhibitors - A Hope for Gout Disease?

Xanthine oxidase (EC 1.17.3.2) (XO) is one of the main enzymatic sources that create reactive oxygen species (ROS) in the living system. It is a dehydrogenase enzyme that performs electron transfer to nicotinamide adenine dinucleotide (NAD+), while oxidizing hypoxanthin, which is an intermediate compound in purine catabolism, first to xanthine and then to uric acid. XO turns into an oxidant enzyme that oxidizes thiol groups under certain stress conditions in the tissue. The last metabolic step, in which hypoxanthin turns into uric acid, is catalyzed by XO. Uric acid, considered a waste product, can cause kidney stones and gouty-type arthritis as it is crystallized, when present in high concentrations. Thus, XO inhibitors are one of the drug classes used against gout, a purine metabolism disease that causes urate crystal storage in the joint and its surroundings caused by hyperuricemia. Urate-lowering therapy includes XO inhibitors that reduce uric acid production as well as uricosuric drugs that increase urea excretion. Current drugs that obstruct uric acid synthesis through XO inhibition are allopurinol, febuxostat, and uricase. However, since the side effects, safety and tolerability problems of some current gout medications still exist, intensive research is ongoing to look for new, effective, and safer XO inhibitors of natural or synthetic origins for the treatment of the disease. In the present review, we aimed to assess in detail XO inhibitory capacities of pure natural compounds along with the extracts from plants and other natural sources via screening Pubmed, Web of Science (WoS), Scopus, and Google Academic. The data pointed out to the fact that natural products, particularly phenolics such as flavonoids (quercetin, apigenin, and scutellarein), tannins (agrimoniin and ellagitannin), chalcones (melanoxethin), triterpenes (ginsenoside Rd and ursolic acid), stilbenes (resveratrol and piceatannol), alkaloids (berberin and palmatin) have a great potential for new XO inhibitors capable of use against gout disease. In addition, not only plants but other biological sources such as microfungi, macrofungi, lichens, insects (silk worms, ants, etc) seem to be the promising sources of novel XO inhibitors.

Spiro Heterocyclic Compounds as Potential Anti-Alzheimer Agents (Part 2): Their Metal Chelation Capacity, POM Analyses and DFT Studies.

BACKGROUND: One of the best methods to treat Alzheimer disease (AD) is through the effective use of cholinesterase inhibitors as vital drugs due to the identification of acetylcholine deficit in the AD patients. OBJECTIVE: The present study aims the investigation of spiro heterocyclic compounds as potential AD agents supported by their metal chelation capacity, POM analyses and DFT studies, respectively. METHODS: The cholinesterase inhibition and metal chelation ability were performed on ELISA microtiter assay. Whereas, the B3LYP method with 6-31+G(d,p) basis set was implemented to study HOMOLUMO energy calculations. The pharmacokinetic properties of the synthesized molecules were studied through Petra, Osiris and Molinspiration (POM). RESULTS: The six spiro (1-6) skeletons were tested for their inhibitory potential and metal-chelation capacity. Our findings revealed that the tested spiro skeletons exerted none or lower than 50% inhibition against both cholinesterases, while compound 4 proved to be the most active molecule with 57.21±0.89% of inhibition toward BChE. The spiro molecule 3 exhibited the highest metal-chelation capacity (9.12±5.26%). Molecular docking model for the most active molecule exhibited promising bindings with AChE and BChE's active site pertained to hydrophobic hydrogen bonds and positive ionizable interactions. The POM analyses gave the information about the flexibility at the site of coordination of spiro compounds (1-6). CONCLUSION: The screening of spirocompounds (1-6) against cholinesterases revealed that some of them show considerable potential to inhibit AChE and BChE. Herein, we propose that the spiro molecules after further derivatization could serve interesting AD inhibitor drugs.

Inhibition of Melanogenesis by Some Well-Known Polyphenolics: A Review.

Melanogenesis is simply defined as the production of melanin in melanosomes by melanocytes through a complex process. Melanin, a pigment derived from L-tyrosine, comes into two forms, namely eumelanin (brownish to black) and pheomelanin (red to yellow). Melanin synthesis starts via the hydroxylation of L-tyrosine to L-3,4-Dihydroxyphenylalanine (DOPA) catalyzed by the enzyme known as Tyrosinase (TYR), which triggers further conversion reaction to DOPAquinone and then to DOPAchrome. Additionally, this process is also related to two more proteins, i.e., oxygenase TYR-related Protein 1 (TYRP1), and Dopachrome Tautomerase TYRP2 (or DCT). However, TYR located in the melanosomal membrane still stands as the key enzyme to initiate the whole process of melanogenesis. Due to some deficits, melanogenesis may emerge as hypo- or hyperpigmentation in the skin. High production of melanin in melanocytes leads to hyperpigmentation- related skin disorders, including freckles, melasma, melanoma, etc., that may cause displeasure in personal appearance and reduce quality of life. Consequently, several melanogenesis inhibitors of synthetic and natural origins have been developed up to date, though most of them have been reported with serious side effects. For this reason, extensive research is still going on to find novel and more effective melanogenesis inhibitors with less side effects. In this sense, particularly flavonoids, catechins, and stilbenes from plants have been a hope to discover new inhibitors which gain significant attention from scientists. In this review, promising natural products effective in melanogenesis inhibition will be scrutinized.