Thiazol-4(5H)-one analogs as potent tyrosinase inhibitors: Synthesis, tyrosinase inhibition, antimelanogenic effect, antioxidant activity, and in silico docking simulation.

As the ß-phenyl-α,ß-unsaturated carbonyl (PUSC) structure was previously identified to play a key role in tyrosinase inhibition, 14 analogs with a PUSC structure built on a thiazol-4(5H)-one scaffold were synthesized using Knoevenagel condensation to serve as potential tyrosinase inhibitors. Through mushroom tyrosinase inhibition experiments, two analogs 9 and 11 were identified as potent tyrosinase inhibitors, with 11 exhibiting an IC50 value of 0.4 ± 0.01 µM, which indicates its 26-fold greater potency than kojic acid. Kinetic studies using Lineweaver-Burk plots revealed that 9 and 11 are competitive and mixed-type inhibitors, respectively; these kinetic results were supported by docking simulations. According to the B16F10 cell-based experiments, 9 and 11 inhibited melanogenesis more effectively than kojic acid due to their potent cellular tyrosinase inhibitory activity. In addition, analogs 9 and 11 exhibited moderate-to-strong antioxidant capacity, scavenging ABTS+, DPPH, and ROS radicals. In particular, analog 12 with a catechol moiety exhibited very strong ROS-scavenging activity, similar to Trolox. These results suggest that analogs 9 and 11, which exhibit potent tyrosinase inhibitory activity in mushroom and mammalian cells and anti-melanogenic effects in B16F10 cells, are promising antibrowning agents for crops and skin lightening agents for hyperpigmentation-related diseases.

Identification and molecular mechanism of novel 5-alkenyl-2-benzylaminothiazol-4(5H)-one analogs as anti-melanogenic and antioxidant agents.

Mushroom tyrosinase is a tetramer, whereas mammalian tyrosinase is a monomeric glycoprotein. In addition, the amino acid sequence of mushroom tyrosinases differs from that of mammalian tyrosinases. MHY2081 exhibits potent inhibitory activity against both mushroom and mammalian tyrosinases. Accordingly, based on the MHY2081 structure, 5-alkenyl-2-benzylaminothiazol-4(5H)-one analogs were designed as a novel anti-tyrosinase agent and synthesized using 2-((3,4-dimethoxybenzyl)amino)thiazol-4(5H)-one (16), a key intermediate obtained via the rearrangement of a benzylamino group. Compounds 6 and 9 (IC50 = 1.5-4.6 µM) exhibited higher mushroom tyrosinase inhibitory activity than kojic acid (IC50 = 20-21 µM) in the presence of l-tyrosine and/or l-dopa. Based on kinetic analysis using Lineweaver-Burk plots, 6 was a mixed inhibitor, whereas 9 was a competitive inhibitor, and docking simulation results supported that these compounds could bind to the active site of mushroom tyrosinase. Using B16F10 mammalian cells, we demonstrated that these compounds inhibited melanogenesis more potently than kojic acid, and their anti-melanogenic effects could be attributed to tyrosinase inhibition. All synthesized compounds could scavenge reactive oxygen species (ROS), with five compounds exhibiting mild-to-strong ABTS+ and DPPH radical-scavenging abilities. Compounds 6 and 9 were potent tyrosinase inhibitors with strong antioxidant activities against ROS, ABTS+, and DPPH radicals. Moreover, the compounds significantly suppressed tyrosinase expression in a dose-dependent manner. Collectively, these results suggest that the novel 5-alkenyl-2-benzylaminothiazol-4(5H)-one analogs, especially 6 and 9, are potential anti-melanogenic agents with antioxidant activity.

Anti-tyrosinase flavone derivatives and their anti-melanogenic activities: Importance of the ß-phenyl-α,ß-unsaturated carbonyl scaffold.

Flavone derivatives were designed and synthesized based on the hypothesis that flavones containing the ß-phenyl-α,ß-unsaturated carbonyl (PUSC) scaffold have potential anti-tyrosinase activity. Flavones 1a and 1e inhibited mushroom tyrosinase more potently than kojic acid, and 1e inhibited monophenolase and diphenolase 61- and 28-fold more than kojic acid, respectively. Kinetic studies on mushroom tyrosinase indicated that 1a and 1e competitively inhibit monophenolase and diphenolase, and docking results supported these results. In an in vitro assay using B16F10 murine cells, 1a and 1e inhibited melanin production more potently than kojic acid, and this was attributed to the inhibition of tyrosinase. Furthermore, 1a and 1e strongly scavenged DPPH and ABTS radicals and ROS, which suggested that their antioxidant properties were at least partly responsible for their anti-melanogenic effects. Moreover, flavone 1a also inhibited the gene expressions of the melanogenesis-related genes tyrosinase, tyrosinase-related protein (TRP)-1, and TRP-2. Our findings that flavone derivatives (i) directly inhibit tyrosinase, (ii) act as antioxidants, and (iii) inhibit the expressions of melanogenesis-related genes suggest their potential use as natural melanogenesis inhibitors. Furthermore, the study confirms that the PUSC scaffold confers anti-tyrosinase activity.

Diminished Tubule Epithelial Farnesoid X Receptor Expression Exacerbates Inflammation and Fibrosis Response in Aged Rat Kidney.

The age-associated functional decline of the kidney is accompanied by structural changes including glomerular sclerosis and interstitial fibrosis. Aging kidneys also exhibit increased vulnerability in stressful environmental conditions. In this study, we assessed the differences in responses between young and aged animals to folic acid (FA)-induced renal fibrosis. To monitor the effects of aging on FA-induced kidney fibrosis, we administered FA (250 mg/kg) to young (6-month old) and aged (20-month old) rats. The development of severe fibrosis was only detected in aged rat kidneys, which was accompanied by increased kidney injury and inflammation. Furthermore, we found that FA-treated aged rats had significantly lower farnesoid X receptor (FXR) expression in the tubular epithelial cells than the rats not treated with FA. Interestingly, the extent of inflammation was severe in the kidneys of aged rat, where the FXR expression was low. To explore the role of FXR in kidney inflammation, in vitro studies were performed using NRK52E kidney tubule epithelial cells. NF-κB activation by lipopolysaccharide treatment induces chemokine production in NRK52E cells. The activation of FXR by obeticholic acid significantly reduced the transcriptional activity of NF-κB and chemokine production. In contrast, FXR knockdown increased LPS-induced chemokine production in NRK52E cells. Finally, FXR-knockout mice that were administered FA showed increased inflammation and severe fibrosis. In summary, we demonstrated that diminished FXR expression in the epithelial cells of the renal tubules exacerbated the fibrotic response in aged rat kidneys by upregulating pro-inflammatory NF-κB activation.

Identification of (Z)-2-benzylidene-dihydroimidazothiazolone derivatives as tyrosinase inhibitors: Anti-melanogenic effects and in silico studies.

As part of our continuous search for novel tyrosinase inhibitors, we designed 5,6-dihydroimindazo[2,1-b]thiazol-3(2H)-one (DHIT) derivatives based on the structure of MHY773; a potent tyrosinase inhibitor with a 2-iminothiazolidin-4-one template. Of the 11 DHIT derivatives synthesized using a Knoevenagel condensation, three DHIT derivatives 1a (IC50 = 36.14 ± 3.90 µM), 1b (IC50 = 0.88 ± 0.91 µM), and 1f (IC50 = 17.10 ± 1.01 µM) inhibited mushroom tyrosinase more than kojic acid (IC50 = 84.41 ± 2.87 µM). Notably, compound 1b inhibited mushroom tyrosinase around 100- and 3.3-fold more potently than kojic acid and MHY773, respectively. Lineweaver-Burk plots demonstrated that compounds 1b and 1f competitively inhibited mushroom tyrosinase, and in silico docking results supported our kinetic results and indicated that these two compounds bind more strongly to the active site of tyrosinase than kojic acid. Docking simulation results using a human tyrosinase homology model confirmed the abilities of 1b and 1f to strongly inhibit human tyrosinase. B16F10 murine melanoma cells were used to investigate whether these two compounds display tyrosinase inhibitory activities and anti-melanogenesis effects in cells. Both compounds were found to significantly and dose-dependently inhibit cellular tyrosinase activity and intracellular and extracellular melanin production more potently than kojic acid. The similarities observed between the cellular tyrosinase and melanogenesis inhibitory effects of 1b and 1f suggest their observed anti-melanogenic effects were due to tyrosinase inhibition. These results indicate that compounds 1b and 1f, which possess the DHIT template, are promising candidates as anti-browning agents and therapeutic agents for hyperpigmentation disorders.

Prolactin and Its Altered Action in Alzheimer's Disease and Parkinson's Disease.

BACKGROUND: Prolactin (PRL) is one of the most diverse pituitary hormones and is known to modulate normal neuronal function and neurodegenerative conditions. Many studies have described the influence that PRL has on the central nervous system and addressed its contribution to neurodegeneration, but little is known about the mechanisms responsible for the effects of PRL on neurodegenerative disorders, especially on Alzheimer's disease (AD) and Parkinson's disease (PD). SUMMARY: We review and summarize the existing literature and current understanding of the roles of PRL on various PRL aspects of AD and PD. KEY MESSAGES: In general, PRL is viewed as a promising molecule for the treatment of AD and PD. Modulation of PRL functions and targeting of immune mechanisms are needed to devise preventive or therapeutic strategies.

Associations between Prolactin, Diabetes, and Cognitive Impairment: A Literature Review.

BACKGROUND: Converging evidence indicates prolactin (PRL) and diabetes play an important role in the pathophysiology of cognitive impairment. However, little is known about the mechanisms responsible for the effects of PRL and diabetes on cognitive impairment. SUMMARY: We summarize and review the available literature and current knowledge of the association between PRL and diabetes on aspects of cognitive impairment. KEY MESSAGES: The phosphatidylinositol 3-kinase/protein kinase B pathway is central to the molecular mechanisms underlying how PRL and diabetes interact in cognitive impairment. Further work is needed to identify the interaction between PRL and diabetes, especially in the molecular aspects of cognitive impairment, which can suggest novel strategies for cognitive dysfunction treatment.

In silico and in vitro insights into tyrosinase inhibitors with a 2-thioxooxazoline-4-one template.

The ß-phenyl-α,ß-unsaturated carbonyl (PUSC) scaffold confers tyrosinase inhibitory activity, and in the present study, 16 (Z)-5-(substituted benzylidene)-3-phenyl-2-thioxooxazolidin-4-one analogues containing this scaffold were synthesized. Mushroom tyrosinase inhibitory activities were examined. Compound 1c (IC50 = 4.70 ± 0.40 µM) and compound 1j (IC50 = 11.18 ± 0.54 µM) inhibited tyrosinase by 4.9 and 2.1-fold, respectively, and did so more potently than kojic acid (IC50 = 23.18 ± 0.11 µM). Kinetic analysis of tyrosinase inhibition revealed that 1c and 1j inhibited tyrosinase competitively. Results of docking simulation with mushroom tyrosinase using four docking programs suggested that 1c and 1j bind more strongly than kojic acid to the active site of tyrosinase and supported kinetic findings that both compounds are competitive inhibitors. The docking results of human tyrosinase homology model indicated that 1c and 1j can also strongly inhibit human tyrosinase. EZ-cytox assays revealed 1c and 1j were not cytotoxic to B16F10 melanoma cells. The effects of 1c and 1j on cellular tyrosinase activity and melanin production were also investigated in α-MSH- and IBMX-co-stimulated these cells. Both compounds significantly and dose-dependently reduced tyrosinase activity, and at 10 µM were more potent than kojic acid at 20 µM. Compounds 1c and 1j also inhibited melanogenesis, which suggested that the inhibitory effects of these compounds on melanin production were mainly attributable to their inhibitions of tyrosinase. These results indicate that compounds 1c and 1j with the PUSC scaffold have potential use as whitening agents for the treatment of hyperpigmentation-associated diseases.

Oxidative stress induces inactivation of protein phosphatase 2A, promoting proinflammatory NF-κB in aged rat kidney.

The molecular inflammation hypothesis of aging proposes that redox dysregulation causes an age-related activation of NF-κB and its signaling to upregulate various proinflammatory genes. In the present study, we focused on the inactive form of the protein phosphastase 2A (PP2A). More specifically, we aimed to define the correlation between PP2A inactivation and NF-κB activation by age-related oxidative stress. Experimentations were designed to determine the effect of oxidative stress-induced PP2A inactivation on NF-κB activity, utilizing prooxidants t-BHP and AAPH, the PTP inhibitor Na3VO4, and the PP2A inhibitor Calyculin A and PP2A siRNA, in HEK293T cells. We also assessed the phosphorylation of PP2A catalytic subunit (PP2Ac) and the activities of PP2A and NF-κB in aged rat kidney, utilizing aging-retarding 40% calorie restriction (CR) -60% of food intake and inflammation-triggering LPS paradigms. Results revealed that an oxidative stress-induced PTK/PTP imbalance led to phosphorylation of PP2Ac, following exposures to t-BHP, AAPH, and Na3VO4 in HEK293T cells. Subsequently, we found that Calyculin A and PP2A siRNA activates NIK/IKK and MAPKs, leading to upregulation of NF-κB and its dependent oxidative stress. Also, the contrasting relation between PP2A inactivation and NF-κB activation was confirmed by AAPH-induced oxidative status in mice, and non-induced normal status or LPS-induced inflammatory status in aged rats while the antioxidative, anti-inflammatory, anti-aging effects of CR significantly blunted these actions. Thus, we present evidence that PP2A inactivation via PTK/PTP imbalance provoked by oxidative stress causes NF-κB activation, which contributes to the accumulation of oxidative stress in aged rat kidney.

Computational approach to identify enzymes that are potential therapeutic candidates for psoriasis.

Psoriasis is well known as a chronic inflammatory dermatosis. The disease affects persons of all ages and is a burden worldwide. Psoriasis is associated with various diseases such as arthritis. The disease is characterized by well-demarcated lesions on the skin of the elbows and knees. Various genetic and environmental factors are related to the pathogenesis of psoriasis. In order to identify enzymes that are potential therapeutic targets for psoriasis, we utilized a computational approach, combining microarray analysis and protein interaction prediction. We found 6,437 genes (3,264 upregulated and 3,173 downregulated) that have significant differences in expression between regions with and without lesions in psoriasis patients. We identified potential candidates through protein-protein interaction predictions made using various protein interaction resources. By analyzing the hub protein of the networks with metrics such as degree and centrality, we detected 32 potential therapeutic candidates. After filtering these candidates through the ENZYME nomenclature database, we selected 5 enzymes: DNA helicase (RUVBL2), proteasome endopeptidase complex (PSMA2), nonspecific protein-tyrosine kinase (ZAP70), I-kappa-B kinase (IKBKE), and receptor protein-tyrosine kinase (EGFR). We adopted a computational approach to detect potential therapeutic targets; this approach may become an effective strategy for the discovery of new drug targets for psoriasis.