Of tyrosinase inhibitors

A large number and diverse classes of compounds have been reported to possess tyrosinase inhibitory activities to various extents from the millimo-lar to nanomolar concentration ranges. From our laboratory we have also reported a large variety of tyrosinase inhibitors and for some of them we have performed molecular modeling as well. Among them there are several alkaloids, and nitrogen-containing molecules are also present. 

Poma A et al, Effect of tyrosinase inhibitors on Tuber borchii mycelium growth in vitro, FEMS Microbiol Lett 180 69-75, 1999. 

PIH after a peel with 70% unbuffered glycolic acid neutralization with a sodium bicarbonate solution as soon as erythema appeared. There is no visible frosting. Postoperative developments were normal. On the 8th day, the patient consulted the doctor about the appearance of PIH 3 days before (a). Treatment consisted of tyrosinase inhibitors, topical antioxidants, sun avoidance and protection, (b) The patient after 5 weeks, (c) After 8 weeks. The hyperpigmentation has improved significantly. A telephone call revealed that the problem has cleared up completely after 3 months. 

Casanola-Martm, G.M., Marrero-Ponce, Y, Khan, M. T.H., Ather, A., Sultan, S., Torrens, F. and Rotondo, R. (2007b) TOMOCOMD-CARDD descriptors-based virtual screening of tyrosinase inhibitors evaluation of different classification model combinations using bond-based linear indices. Bioorg. Med. Chem., 15, 1483—1503. 

Tyrosinase inhibition may be a potential approach to prevent and control the enzymatic browning reactions and improve the quality and nutritional value of food products [20]. Tyrosinase also plays a major key role in the developmental and defensive functions of insects. Tyrosinase is involved in melanogenesis, wound healing, parasite encapsulation, and sclerotization in insects [21-23]. For these reasons, in recent years the development of tyrosinase inhibitors has become an active alternative approach to control insect pests [20]. Additionally, it is now well-recognized that tyrosinase inhibitors are important for their potential applications in medical and cosmetic products [24-26]. 

In the next sections some of the promising classes of tyrosinase inhibitors are discussed with especial emphasis on heterocyclic origin a few of them may not be heterocyclic but their inhibition pattern and chemistry is highly interesting. 

TableS. Melanin Formation Inhibitory Activity of Tyrosinase Inhibitors on Melanoma Cells...

Oxidative conversion of dopa into M. is catalysed by the enzyme Tyrosinase (EC 1.14.18.1) (see). Absence of tyrosinase (usually an autosomal inherited defect in the ability to synthesize the enzyme) results in albinism most groups of mammals occasionally produce albino individuals, which completely lack any M. pigmentation of eyes, skin, hair, feathers, etc. Albinism may also result from 1. deficient melanin polymerization, 2. failure to synthesize the protein matrix of the melanin granule, 3. lack of tyrosine, and 4. presence of tyrosinase inhibitors. 

Safety is a primary consideration for tyrosinase inhibitors, especially when utilized in unregulated quantities on a regular basis. On the other hand, the use of the inhibitors is primary in the cosmetic industry due to their skin-whitening effects. Since a huge number of tyrosinase inhibitors have been developed, assessing the validation of these inhibitors in skin-whitening efficiency has become more important. Most inhibitors have rarely been incorporated in topically applied cosmetics, often due to a lack of parallel human clinical trials (Chang, 2009 Khan, 2007 Kim, 2005). 

A number of research groups around the world are engaged and are expending much effort in the discovery of tyrosinase inhibitors. Various limitations are associated with many of these inhibitors, such as high cytotoxicity, poor skin penetration and low stabiUty in formulations. Therefore, it is very important to discover novel and potent inhibitors with potent activity and lower side effect. 

Khan, M.T.H. (2007). Molecular design of tyrosinase inhibitors A critical review of promising novel inhibitors from synthetic origins. Pure AppLChem. Vol.29(12), pp.2277-2295. 

More recently (2006) we performed and reported quantitative structure-activity relationship (QSAR) modeling of the same compounds based on their atomic linear indices, for finding fimctions that discriminate between the tyrosinase inhibitor compounds and inactive ones [50]. Discriminant models have been applied and globally good classifications of 93.51 and 92.46% were observed for nonstochastic and stochastic hnear indices best models, respectively, in the training set. The external prediction sets had accuracies of 91.67 and 89.44% [50]. In addition to this, these fitted models have also been employed in the screening of new cycloartane compounds isolated from herbal plants. Good behavior was observed between the theoretical and experimental results. These results provide a tool that can be used in the identification of new tyrosinase inhibitor compounds [50]. 

Lee HS (2002) Tyrosinase inhibitors of Pulsatilla cernua root-derived materials. J Agric Food Chem 50(6) 1400-1403... 

J. Wang, V.B. Nascimento, S.A. Kane, K. Rogers, M.R. Smyth, and L. Angnes, Screen-printed tyrosinase-containing electrodes for the biosensing of enzyme inhibitors. Talanta 43, 1903—1907 (1996). 

Cabanes J, Chazarra S and Garcia-Carmona F. 1994. Kojic acid, a cosmetic skin whitening agent, is a slow-binding inhibitor of catecholase activity of tyrosinase. J Pharm Pharmacol 46(12) 982—985. 

Before kinetic constants can be evaluated, it is critical to find the correct concentration of enzyme to use for the assays. If too little enzyme is used, the overall absorbance change for a reaction time period will be so small that it is difficult to detect differences due to substrate concentration changes or inhibitor action. On the other hand, too much enzyme will allow the reaction to proceed too rapidly, and the leveling off of the time course curve as shown in Figure E5.7 will occur very early because of the rapid disappearance of substrate. A rate that is intermediate between these two extremes is best. For the dopachrome assay, it is desirable to use the level of tyrosinase that gives a linear absorbance change at 475 nm for 2 minutes. 

To set up the inhibition assay, prepare a table similar to Table E5. 1. Inhibitor should appear in the list of reagents before tyrosinase. Use the same level of tyrosinase and the same dopa stereoisomer as in part C. Vary the amount of dopa as in part C. A constant amount of inhibitor (cinnamic acid or thiourea) should be added to each cuvette. You will have to determine this level of inhibitor by trial and error. The desired inhibition rate with saturating substrate is about 50% of the uninhibited rate. Add all reagents except tyrosinase, mix well, and determine the blank rate, if any. Add tyrosinase, mix, and immediately record AA75 for 2 minutes. From recorder traces or graphs of A475 vs. time, calculate AA/min for each assay. 

The mechanism of iris pigmentation due to latanoprost is unknown. In an in vitro experiment using uveal melanocytes, the addition of latanoprost increased melanin content, melanin production, and tyrosinase activity (18). Alpha-methyl-para-tyrosine, an inhibitor of tyrosinase (the enzyme that transforms tyrosine to levodopa), completely prevented the latanoprost-induced stimulation of melanogenesis. 

Further analysis of the UV spectrum revealed that this compound is a gallic acid derivative. A search of the Dictionary of Natural Products for molecular ion and plant genus name leads to the identification of a known compound - Pterocaryanin B. The compounds with poly-hydroxyl groups in their structures are very well known as tyrosinase inhibitors and are responsible for the inhibition of melanin synthesis. Therefore, no further isolation was necessary. 

Tyrosinase inhibitors prevent browning in foodbecause they inhibit the oxidation caused by the enzyme tyrosinase. Cuminaldehyde is identified as a potent mushroom tyrosinase monophenol monooxygenase inhibitor from cumin seeds, ft inhibits the oxidation of L-3,4-dihydroxyphenylalanine (l-DOPA) by mushroom tyrosinase with an ID50 of 7.7g/ml (0.05 mM). Its oxidized analogue, cumic acid (p-isopropylbenzoic acid), also inhibits this oxidation with an 1D50 of 43g/ml (0.26mM). These two inhibitors affect mushroom tyrosinase activity in different ways (Kubo and Kinst-Hori, 1998). 

Kubo, I. and Kinst-Hori, I. (1 998) Tyrosinase inhibitors from cumin, journal of Agricultural and Food Chemistry 46(12), 5338-5341. 

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