Natural,semisynthetic and synthetic tyrosinase inhibitors

Tyrosinase plays a pivotal role in the synthesis of melanin pigment synthesis on skin utilizing tyrosine as a substrate. Melanin is responsible for the protection against harmful ultraviolet irradiation, which can cause significant pathological conditions, such as skin cancers. However, it can also create esthetic problems when accumulated as hyperpigmented spots. Various skin-whitening ingredients which inhibit tyrosinase activity have been identified. Some of them, especially ones with natural product origins, possess phenolic moiety and have been employed in cosmetic products. Semi-synthetic and synthetic inhibitors have also been developed under inspiration of the natural inhibitors yet some of which have no phenolic groups. In this review, tyrosinase inhibitors with natural, semi-synthetic and synthetic origins are listed up with their structures, activities and characteristics. Further, a recent report on the adverse effect of a natural melanin synthesis inhibitor which was included in skin-whitening cosmetics is also briefly discussed.     

An Inhibitor of the UDP-N-Acetylgalactosamine:GM3, N-Acetylgalactosaminyltransferase: Purification and Properties, and Preparation of an Antibody to This Inhibitor

An inhibitor of the UDP-N-acetylgalactosamine:GM3, N-acetylgalactosaminyltransferase (EC 2.4.1.92) has been purified close to 100-fold from chicken blood serum. The method of purification includes heating, dialysis, passage through a column of DEAE-Sephadex, filtration through Amicon XM 100, and passage through Sepharose 6B. The molecular weight determined by Sepharose 6B was 200,000, but on sodium dodecyl sulfate-polyacrylamide gel electrophoresis it appears as if the compound dissociated into components of 68,000. The inhibitor was not active on other glycosyl transferases and lost its inhibitory activity following treatment with pronase and trypsin. alpha-Chymotrypsin did not affect the inhibitor. An antibody to this inhibitor was prepared which decreased its inhibitory capability and precipitated with it in a radial double immunodiffusion experiment.     

Revision of the theory of phototropism in plants: a new interpretation of a classical experiment

Went's classical experiment on the diffusion of auxin activity from unilaterally illuminated oat coleoptile tips (Went 1928), was repeated as precisely as possible. In agreement with Went's data with theAvena curvature assay, the agar blocks from the illuminated side of oat (Avena sativa L. cv. Victory) coleoptile tips had, on an average, 38% of the auxin activity of those from the shaded side. However, determination of the absolute amounts of indole-3-acetic acid (IAA) in the agar blocks, using a physicochemical assay following purification, showed that the IAA was evenly distributed in the blocks from the illuminated and shaded sides. In the blocks from the shaded and dark-control halves the amounts of IAA were 2.5 times higher than the auxin activity measured by theAvena curvature test, and in those from the illuminated half even 7 times higher. Chromatography of the diffusates prior to theAvena curvature test demonstrated that the amounts of two growth inhibitors, especially of the more polar one, were significantly higher in the agar blocks from the illuminated side than in those from the shaded side and the dark control. These results show that the basic experiment from which the Cholodny-Went theory was derived, does not justify this theory. The data rather indicate that phototropism is caused by the light-induced, local accumulation of growth inhibitors against a background of even auxin distribution, the diffusion of auxin being unaffected.Abbreviation IAA indole-3-acetic acid     

Essential role of phosphatidylinositol 3-kinase in insulin-induced activation and phosphorylation of the cGMP-inhibited cAMP phosphodiesterase in rat adipocytes studies using the selective inhibitor wortmannin

Incubation of rat adipocytes with wortmannin, a potent and selective phosphatidylinositol 3-kinase (PI 3-kinase) inhibitor, completely blocked the antilipolytic action of insulin (IC₅₀≈ 100 nM), the insulin-induced activation and phosphorylation of cGMP-inhibited cAMP phosphodiesterase (cGI-PDE) as well as the activation of the insulin-stimulated cGI-PDE kinase (IC₅₀≈ 10–30 nM). No direct effects of the inhibitor on the insulin-stimulated cGI-PDE kinase, the cGI-PDE and the hormone-sensitive lipase were observed. These data suggest that activation of PI 3-kinase upstream of the insulin-stimulated cGI-PDE kinase in the antilipolytic insulin signalchain has an essential role for insulin-induced cGI-PDE activation/ phosphorylation and anti-lipolysis.     

Saponin-like substances inhibit α-galactosidase production in the endosperm of fenugreek seeds

When fenugreek (Trigonella foenum-graecum L.) endosperms plus testa (endosperms), which had been isolated from 5-h-imbibed seeds, were incubated for at least 2 h under germination conditions, they leaked substances which, like exogenous abscisic acid (ABA), inhibited the production of fenugreek endosperm -galactosidase. However, unlike ABA, 8 h treatment with these inhibitors had no effect on fenugreek endosperms which had been isolated from 15-h-imbibed seeds and leached for 2 h. This indicated that either their inhibitory action was on processes which were related to the production of -galactosidase and had been completed by this time, or that there might be factors present which inactivate these inhibitors. It was also concluded that the action of the endosperm leachate could not be attributed to the presence of ABA. The activity of the leachate decreased when it originated from endosperms imbibed for periods longer than 25 h and thin-layer chromatography (TLC) of extracts from these endosperms showed decreased contents of the leachable inhibitors as imbibition proceeded. From the seed leachate, which had a TLC pattern and inhibitory action similar to that of the endosperm, were isolated three substances which, when applied to endosperms, inhibited the production of -galactosidase activity. According to their chromatographic behaviour and their reaction with specific reagents, there are strong indications that these substances are saponins. These diffusible saponin-like substances were located in both endosperm and perisperm and their physiological role is discussed.Abbreviations ABA abscisic acid - PEG polyethylenglycol - TLC thin-layer chromatography We wish to thank the Alexander S. Onasis Public Benefit Foundation for a grant to K.Z. and Dr. J.S.G. Reid (University of Stirling, Scotland) for a kind gift of fenugreek seeds.     

In vivo anti inflammatory effects of the M20 IL-1 Inhibitor: I. Effects on acute inflammatory parameters

Previous studies have described an IL-1 Inhibitor produced by a myelomonocytic line developed in our laboratory (Eur J Immunol 1986; 16: 1449). This IL-1 Inhibitor was secreted by the M20 line constitutively in addition to IL-1, from which it could be separated. We have recently shown that the M20 IL-1 Inhibitor is distinct from the IL-1ra.In vitro this factor inhibited IL-1 induced proliferative responses as well as PGE₂ secretion by IL-1 induced fibroblasts. We also showed for the first time (Lymphokine Research 1988; 7(3): 268) that an IL-1 inhibitor can reduce IL-1 induced inflammatory effects. This study describes the specific effect of the M20 IL-1 Inhibitor on IL-1 induced parameters of inflammation: fever, leukocytosis and local foot pad swelling or lymph node enlargement. Purified preparations of the IL-1 Inhibitor, when injected together with IL-1, or before the IL-1, reduced fever, leukocytosis, foot pad swelling and lymph node enlargement caused by IL-1. Similar responses were obtained by injection of IL-6 or TNF, but were unaffected by the IL-1 Inhibitor, when injected together.These results indicate that the M20 IL-1 Inhibitor acts specifically on IL-1 induced responsesin vivo. The potential importance of this factor as an anti-inflammatory and immune regulatory factor, is supported by the findings of this study.Abbreviations IL-1 Interleukin 1 - IL-6 Interleukin 6 - IL-1ra Interleukin 1 receptor antagonist - TNF tumor necrosis factor     

Inhibition of Taq DNA polymerase by seaweed extracts from British Columbia, Canada and Korea

Fifty-nine species of marine macrophytes from the coasts of British Columbia, Canada and Korea have been screened for the presence of PCR inhibitors, namely inhibitors of Taq DNA polymerase. Eleven of the species displayed some inhibitor activity. At the concentration of 5 μg of methanol extract in 25μL reaction mixture of PCR containing 1.5 unit of Taq DNA polymerase, one (Ulva sp.) of 8 Chlorophyta, eight (Colpomenia bullosa, Ecklonia cava, Endarachne binghamiae, Fucus distichus, Hizikia fusiformis, Sargassum confusum, Sargassum sagamianum, and Sargassum thunbergii) of 28 Phaeophyta, and one (Symphyocladia latiuscula) of 34 Rhodophyta showed inhibition in PCR amplification. In the case of the water extract, two (Cladophora columbiana, Ulva sp.) Chlorophyta, seven (Endarachne binghamiae, Fucus distichus, Hizikia fusiformis, Sargassum confusum, Sargassum sagamianum, Sargassum horneri, Scytosiphon dotyi) Phaeophyta, no Rhodophyta and one (Phyllospadix scouleri) seagrass showed inhibition in PCR amplification. the methanol fraction of Sargassum confusum and the water fraction of Fucus gardneri (mid–intertidal) have been found to inhibit PCR at level as low as 0.5 μg in 25μL of PCR reaction mixture. This revised version was published online in August 2006 with corrections to the Cover Date.     

(Z)-9-tetradecenal: a potent inhibitor of pheromone-mediated communication in the oriental tobacco budworm moth,Helicoverpa assulta

The behavioural significance of (Z)-9-tetradecenal to male H. assulta was tested by comparing the number of moths attracted to lures containing a standard synthetic female sex pheromone with lures in which (Z)-9-tetradecenal was also added. The standard pheromone mixture used contained 1000 g (Z)-9-hexadecenal, 50 g (Z)-11-hexadecenal, 300 g (Z)-9-hexadecenyl acetate and 15 g (Z)-11-hexadecenyl acetate impregnated on rubber septa. Addition of (Z)-9-tetradecenal to the standard pheromone was shown to significantly reduce the caught of male H. assulta when added in amounts greater than 10 g or 1% of the major pheromone component in both field and net-house experiments. The reduction in catch was found to be dependent on the quantity of (Z)-9-tetradecenal added to the standard pheromone. The implications of these results on conspecific and inter-specific pheromone-mediated communication in H. assulta and related sympatric heliothine species is discussed.Abbreviations Z9-16:AL (Z)-9-hexadecenal - Z11-16:AL (Z)-11-hexadecenal - Z9-16:AC (Z)-9-hexadecenyl acetate - Z11-16:AC (Z)-11-hexadecenyl acetate - Z9-14:AL (Z)-9-tetradecenal - Z9-16:OH (Z)-9-hexadecen-1-ol - Z11-16:OH (Z)-11-hexadecen-1-ol - RH relative humidity     

Inhibiting nitrification and increasing yield of barley by band placement of thiourea with fall-applied urea

Incubation and field experiments were conducted on the influence of thiourea in inhibiting nitrification of urea N, and subsequently on reducing over-winter losses of fallapplied N. Under incubation, most of the added urea placed in bands was nitritified within five or six weeks. However, thiourea when pelleted with urea (21 urea to thiourea by weight) reduced the amount of nitrification to less than one-half during the same period.In two uncropped field experiments in an early dry fall, the application of pelleted urea+thiourea (21) in bands resulted in almost complete inhibition of nitrification of urea for four weeks. In two other uncropped field experiments begun in June with the same fertilizer in bands, half or less of applied N appeared as nitrate after eight weeks. In 10 cropped field experiments with 56 kg N ha^–1, urea+thiourea placed in bands depressed nitrification of fall-applied urea over the winter. By early May, the urea mixed into the soil in the previous fall was nearly all nitrified, while only one-half of the banded urea+thiourea was nitrified. The loss of mineral N by early May was 38% with urea mixed into the soil, but only 18% with bands of urea+thiourea.The 10 sites were cropped to spring barley. The increase in yield of grain or the increase in %N uptake from fertilier N was approximately only one-half as much with fall-applied urea mixed into the soil as compared to spring-applied urea added in the same way. Specifically, fall-applied mixed urea produced 930 kg ha^–1 less grain yield and 32% less N uptake from fertilizer N than did mixed urea in spring. On fall-application there was some benefit from banding of urea or with mixing urea+thiourea pellets into the soil, but the banding of urea+thiourea pellets gave more benefit. Among the fall applications, banded urea+thiourea pellets produced 670 kg ha^–1 more grain yield and 26% more N uptake in grain from fertilizer N than did urea mixed into the soil.     

Distribution of growth regulators in relation to the light-induced geotropic responsiveness in Zea roots

Growth regulators were measured in extracts from the upper and lower halves of 7-mm apical segments of horizontally oriented, red-light-irradiated and non-irradiated roots of Zea mays L. cv. Golden Cross Bantam 70 which exhibit a georesponse only after an exposure to light. Abscisic acid (ABA) was measured by gas-liquid chromatography, auxin (indole-3-acetic acid, IAA) by the Avena straight-growth assay, and an unidentified growth inhibitor by a Zea root-growth assay. The ratio of ABA in the upper and lower halves was 1.6 in the irradiated roots and 1.0 in the non-irradiated ones. The total amount of ABA after irradiation was increased by a factor of ca. 1.8. The ratio of IAA in the upper and lower halves of irradiated and non-irradiated roots was 1:3.4 and 1:2.9, respectively. The content (or activity) of an unidentified growth inhibitor was highest in the lower halves of horizontally oriented roots which had been irradiated with red light. The unidentified growth inhibitor, rather than IAA or ABA, may be the major factor in the light-induced geotropic responsiveness in Zea roots.