Inhibition of diphenolase activity of tyrosinase by vitamin b(6) compounds

Biological activities and cytotoxicity of diterpenes from Copaifera spp. Oleoresins

Copaifera spp. are Amazonian species widely studied and whose oleoresins are used by local people for various medicinal purposes. However, a detailed study of the activity of the main phytochemical components of these oleoresins remains to be done. Here, we studied the cytotoxicity and in vitro anti-inflammatory effects of six diterpene acids: copalic, 3-hydroxy-copalic, 3-acetoxy-copalic, hardwickiic, kolavic-15-metyl ester, and kaurenoic, isolated from the oleoresins of Copaifera spp. The diterpenes did not show cytotoxicity in normal cell lines, nor did they show significant changes in viability of tumoral line cells. The 3-hydroxy-copalic was able to inhibit the enzyme tyrosinase (64% ± 1.5%) at 250 µM. The kolavic-15-metyl ester at 200 µM showed high inhibitory effect on lipoxygenase (89.5% ± 1.2%). Among the diterpenes tested, only kaurenoic and copalic acids showed significant hemolytic activities with 61.7% and 38.4% at 100 µM, respectively. In addition, it was observed that only the copalic acid (98.5% ± 1.3%) and hardwickiic acid (92.7% ± 4.9%) at 100 mM inhibited nitric oxide production in macrophages activated by lipopolysaccharide. In this assay, the diterpenes did not inhibit tumor necrosis factor-α production. The acids inhibited the production of IL-6, 3-acetoxy-copalic (23.8% ± 8.2%), kaurenoic (11.2% ± 5.7%), kolavic-15-methyl ester (17.3% ± 4.2%), and copalic (4.2% ± 1.8%), respectively, at 25 µM. The kaurenoic, 3-acetoxy-copalic and copalic acids increased IL-10 production. This study may provide a basis for future studies on the therapeutic role of diterpenic acids in treating acute injuries such as inflammation or skin disorders.

Enzymatic hybridization of α-lipoic acid with bioactive compounds in ionic solvents

The lipase-catalyzed molecular hybridization of α-lipoic acid (LA) with bioactive compounds pyridoxine, tyrosol and tyramine was performed in ionic solvents and deep eutectic solvents. The biocatalytic reactions were catalyzed by Candida antarctica lipase B immobilized onto various functionalized multi-walled carbon nanotubes (f-CNTs-CaLB), as well as by commercial Novozym 435. The use of f-CNTs-CaLB leads, in most cases, to higher conversion yields as compared to Novozym 435. The nature and ion composition of ionic solvents affect the performance of the biocatalytic process. The highest conversion yield was observed in (mtoa)NTf2. The high enzyme stability and the relatively low solubility of substrates in specific media account for the improved biocatalytic synthesis of molecular hybrids of LA. Principal component analysis was used to screen for potential lipoxygenase inhibitors. In vitro studies showed that the synthesized compounds exhibit up to 10-fold increased inhibitory activity on lipoxygenase mediated lipid peroxidation as compared to parent molecules.

Vitamin B6s inhibit oxidative stress caused by Alzheimer's disease-related Cu(II)-β-amyloid complexes-cooperative action of phospho-moiety

Cu(II) complexes of Alzheimer's disease-related β-amyloid (Aβ) peptides exhibit metal-centered oxidation chemistry. The metallo-Aβ complexes are the hallmark of the disease and have been attributed to the generation of reactive oxygen species (ROS), causing oxidative stress. In this communication, the inhibitions of the oxidative activity of Cu(II)-Aβ by vitamin B6 compounds pyridoxamine (PM), pyridoxine (PN), pyridoxal (PL), and pyridoxal-5'-phosphate (PLP) are presented. These B6's are competitive inhibitors toward dopamine oxidation by Cu(II)-Aβ(1-20), with K(i) values of 1.4, 8.3, 1.2, and 0.2mM, respectively. The phospho-moiety in PLP seems to exhibit cooperative inhibition, affording a clue for future design of inhibitors.

Bond-based 2D quadratic fingerprints in QSAR studies: virtual and in vitro tyrosinase inhibitory activity elucidation

In this report, we show the results of quantitative structure-activity relationship (QSAR) studies of tyrosinase inhibitory activity, by using the bond-based quadratic indices as molecular descriptors (MDs) and linear discriminant analysis (LDA), to generate discriminant functions to predict the anti-tyrosinase activity. The best two models [Eqs (6) and (12)] out of the total 12 QSAR models developed here show accuracies of 93.51% and 91.21%, as well as high Matthews correlation coefficients (C) of 0.86 and 0.82, respectively, in the training set. The validation external series depicts values of 90.00% and 89.44% for these best two equations (6) and (12), respectively. Afterwards, a second external prediction data are used to perform a virtual screening of compounds reported in the literature as active (tyrosinase inhibitors). In a final step, a series of lignans is analysed using the in silico-developed models, and in vitro corroboration of the activity is carried out. An issue of great importance to remark here is that all compounds present greater inhibition values than Kojic acid (standard tyrosinase inhibitor: IC₅₀ = 16.67 μm). The current obtained results could be used as a framework to increase the speed, in the biosilico discovery of leads for the treatment of skin disorders.

Synthesis and biological evaluation of novel 4-hydroxybenzaldehyde derivatives as tyrosinase inhibitors

A series of novel 4-hydroxybenzaldehyde derivatives were synthesized and their inhibitory effects on the diphenolase activity of mushroom tyrosinase were investigated. Most of target compounds had more potent inhibitory activities than the parent compound 4-hydroxybenzaldehyde (IC(50)=1.22 mM). Interestingly, compound 3c bearing a dimethoxyl phosphate was found to be the most potent inhibitor with IC(50) value of 0.059 mM. The inhibition kinetics analyzed by Lineweaver-Burk plots revealed that compound 3c was a non-competitive inhibitor (K(I)=0.0368 mM). In particular, compound 3c showed no side effects at dose of 1600 mg/kg in mice. These results suggested that such compounds might be served as lead compounds for further designing new potential tyrosinase inhibitors.

Prediction of tyrosinase inhibition activity using atom-based bilinear indices

A set of novel atom-based molecular fingerprints is proposed based on a bilinear map similar to that defined in linear algebra. These molecular descriptors (MDs) are proposed as a new means of molecular parametrization easily calculated from 2D molecular information. The nonstochastic and stochastic molecular indices match molecular structure provided by molecular topology by using the kth nonstochastic and stochastic graph-theoretical electronic-density matrices, M(k) and S(k), respectively. Thus, the kth nonstochastic and stochastic bilinear indices are calculated using M(k) and S(k) as matrix operators of bilinear transformations. Chemical information is coded by using different pair combinations of atomic weightings (mass, polarizability, vdW volume, and electronegativity). The results of QSAR studies of tyrosinase inhibitors using the new MDs and linear discriminant analysis (LDA) demonstrate the ability of the bilinear indices in testing biological properties. A database of 246 structurally diverse tyrosinase inhibitors was assembled. An inactive set of 412 drugs with other clinical uses was used; both active and inactive sets were processed by hierarchical and partitional cluster analyses to design training and predicting sets. Twelve LDA-based QSAR models were obtained, the first six using the nonstochastic total and local bilinear indices and the last six with the stochastic MDs. The discriminant models were applied; globally good classifications of 99.58 and 89.96 % were observed for the best nonstochastic and stochastic bilinear indices models in the training set along with high Matthews correlation coefficients (C) of 0.99 and 0.79, respectively, in the learning set. External prediction sets used to validate the models obtained were correctly classified, with accuracies of 100 and 87.78 %, respectively, yielding C values of 1.00 and 0.73. This subset contains 180 active and inactive compounds not considered to fit the models. A simulated virtual screen demonstrated this approach in searching tyrosinase inhibitors from compounds never considered in either training or predicting series. These fitted models permitted the selection of new cycloartane compounds isolated from herbal plants as new tyrosinase inhibitors. A good correspondence between theoretical and experimental inhibitory effects on tyrosinase was observed; compound CA6 (IC(50)=1.32 microM) showed higher activity than the reference compounds kojic acid (IC(50)=16.67 microM) and L-mimosine (IC(50)=3.68 microM).

New constituent from Podocarpus macrophyllus var. macrophyllus shows anti-tyrosinase effect and regulates tyrosinase-related proteins and mRNA in human epidermal melanocytes

A new biflavonoid, 2,3-dihydro-4',4'''-di-O-methylamentoflavone (5), and five known compounds, (-)-catechin (1), quercetin (2), 2,3-dihydrosciadopitysin (3), sciadopitysin (4), and isoginkgetin (6), were isolated from Podocarpus macrophyllus var. macrophyllus (Podocarpaceae). These compounds were evaluated their ability to inhibit cellular tyrosinase activity and for their melanin inhibitory activity in human epidermal melanocytes (HEMn). In the melanin synthesis assay, 2,3-dihydro-4',4'''-di-O-methylamentoflavone (5) showed a potent anti-tyrosinase effect with IC(50)=0.098 mM in HEMn. It also significantly decreased both protein and mRNA levels of the tyrosinase-related protein-2 (TRP-2) by Western blot and quantitative real-time PCR (qRT-PCR) analysis. These findings suggest that the new compound, 2,3-dihydro-4',4'''-di-O-methylamentoflavone (5), is the most active component of P. macrophyllus var. macrophyllus in inhibiting pigmentation and that this inhibition is exerted through inhibition of transcription of the genes encoding TRP2.

Modulating effects of a novel skin-lightening agent, α-lipoic acid derivative, on melanin production by the formation of DOPA conjugate products

Sodium zinc dihydrolipoylhistidinate (DHLHZn) is a compound of Zn(2+)/dihydrolipoic acid derivate complex, which was developed for cosmetic/medical use. To characterize DHLHZn as a novel skin-lightening agent, inhibitory actions of DHLHZn on tyrosinase (including its reaction pathway) have been elucidated in this study. In a B16 melanoma cell system, DHLHZn was active in suppressing the synthesis of melanins as well as alpha-arbutin, well known as a depigmenting drug. Furthermore, in a tyrosinase assay, DHLHZn showed stronger inhibitory effect on DOPAchrome formation than other tyrosinase inhibitors such as kojic acid. Our previous report demonstrated that the sulfhydryl groups of lipoyl motif react with DOPAquinone to form lipoyl DOPA conjugates. We therefore postulated that conjugated products between DHLHZn and DOPAquinone might be formed. Upon reaction of DHLHZn with L-DOPA following tyrosinase-catalyzed oxidation, the formation of DHLH DOPA conjugated products was confirmed by HPLC-tandem mass spectrometry using reserpine as the internal standard. In addition, the inhibitory kinetics analyzed by a Lineweaver-Burk plot exhibited the reversibility of DHLHZn as a competitive inhibitor with a KI value of 0.35 microM. These results indicate that this covalent reaction might contribute to alternating DOPAquinone, which is a tyrosinase reaction product, and result in the competitive inhibitory effect of DHLHZn on DOPAchrome formation. DHLHZn may thus serve as a potentially effective skin-lightening agent, an effectiveness that is based on the compound's covalent scavenging of DOPAquinone resulting in depigmentation.

Hemolysis of human red blood cells by riboflavin-Cu(II) system: enhancement by azide

Photoactivated riboflavin in the presence of Cu(II) generates reactive oxygen species (ROS) which can hemolyze human red blood cells (RBC). In the present work we examined the effect of sodium azide (NaN3) on RBC in the presence of riboflavin and Cu(II). The addition of NaN3 to the riboflavin-Cu(II) system enhanced K+ loss and hemolysis. The extent of K+ loss and hemolysis were time and concentration dependent. Bathocuproine, a Cu(I)-sequestering agent, inhibited the hemolysis completely. Among various free radical scavengers used to identify the major ROS involved in the reaction, thiourea was found to be the most effective scavenger. Thiourea caused almost 85% inhibition of hemolysis suggesting that *OH is the major ROS involved in the reaction. Using spectral studies and other observations, we propose that when NaN3 is added to the riboflavin-Cu(II) system, it inhibits the photodegradation of riboflavin resulting in increased *OH generation. Also, the possibility of azide radical formation and its involvement in the reaction could not be ruled out.

Tyrosinase inhibitors isolated from the edible brown alga Ecklonia stolonifera

Extracts from seventeen seaweeds were determined for tyrosinase inhibitory activity using mushroom tyrosinase with L-tyrosine as a substrate. Only one of them, Ecklonia stolonifera OKAMURA (Laminariaceae) belonging to brown algae, showed high tyrosinase inhibitory activity. Bioassay-guided fractionation of the active ethyl acetate (EtOAc) soluble fraction from the methanolic extract of E. stolonifera, led us to the isolation of phloroglucinol derivatives [phloroglucinol (1), eckstolonol (2), eckol (3), phlorofucofuroeckol A (4), and dieckol (5)]. Compounds 1 approximately 5 were found to inhibit the oxidation of L-tyrosine catalyzed by mushroom tyrosinase with IC50 values of 92.8, 126, 33.2, 177, and 2.16 microg/mL, respectively. It was compared with those of kojic acid and arbutin, well-known tyrosinase inhibitors, with IC50 values of 6.32 and 112 microg/ mL, respectively. The inhibitory kinetics analyzed from Lineweaver-Burk plots, showed compounds 1 and 2 to be competitive inhibitors with Ki of 2.3x10(-4) and 3.1x10(-4) M, and compounds 3 approximately 5 to be noncompetitive inhibitors with Ki of 1.9x10(-5), 1.4x10(-3) and 1.5x10(-5) M, respectively. This work showed that phloroglucinol derivatives, natural compounds found in brown algae, could be involved in the control of pigmentation in plants and other organisms through inhibition of tyrosinase activity using L-tyrosine as a substrate.

Amplification of Inhibitory Activity of Catechin against Disease-Related Enzymes by Conjugation on Poly(ε-lysine)

A new inhibitor against disease-related enzymes, collagenase, hyaluronidase, and xanthine oxidase, has been developed by the laccase-catalyzed conjugation of catechin on poly(epsilon-lysine). The resulting poly(epsilon-lysine)-catechin conjugate showed greatly improved inhibition effects on activity of these enzymes, whereas the catechin monomer showed very low inhibition activity. The kinetic analysis on the inhibition of collagenase exhibited that the conjugate was a mixed-type inhibitor. The amplified activities might offer high potential as a therapeutic agent for prevention of various enzyme-related diseases.