Solution studies, synthesis and antibacterial activity of Ga(III) complexes with bis-kojate derivatives

Given the recognized major problem of microbial drug resistance for human health, new metal-based drugs have been currently explored for their antimicrobial properties, including gallium-based compounds as potential metallophores that could perturb Fe's interactions with proteins. Herein we have designed and synthesized two bis-kojate ligands (named L4 and L6) and studied their Ga(III) complexes for their physico-chemical and biological properties. In particular a detailed study of their complexation properties in aqueous solution, showed equilibrium models with formation of quite stable dinuclear 2:3 metal:ligand complexes, though with different stability. Solid state complexes were also prepared and characterized and complementary DFT studies indicated that [Ga2(L4)3] complex, with higher stability, seems to adopt a three-ligand bridging conformation, while that for L6 adopt a one ligand bridging conformation. Preliminary investigation of the antibacterial activity of these gallium complexes showed antipseudomonal activity, which appeared higher for the complex with L4, a feature of potential interest for the scientific community.

Chemical and Biological Characterization of the Ethyl Acetate Fraction from the Red Sea Marine Sponge Hymedesmia sp

Hymedesmiidae is one of the largest families of marine sponges and stands out as an exceptional source of variable metabolites with diverse biological activities. In this study, the ethyl acetate fraction (HE) of a Hymedesmia sp. marine sponge from the Red Sea, Egypt, was analyzed for the first time using Ultra-performance liquid chromatography electrospray ionization tandem mass spectrometry (UPLC-ESI-MS/MS) analysis. The analysis tentatively identified 29 compounds in this fraction, including the isolation and identification of six compounds (two pyrimidine nucleosides, one purine, and two pyrimidine bases in addition to one cerebroside) for the first time. The structures of the isolated compounds were established by 1D and 2D NMR (nuclear magnetic resonance), MS (mass spectrometry), and IR (infrared) spectroscopy. Furthermore, the cytotoxic, antioxidant, and antimicrobial activities of the ethyl acetate fraction were evaluated in vitro. The fraction exhibited strong DPPH scavenging activity with an IC50 of 78.7 µg/mL, compared to ascorbic acid as a positive control with an IC50 of 10.6 µg/mL. It also demonstrated significant cytotoxic activity with IC50 values of 13.5 µg/mL and 25.3 µg/mL against HCT-116 and HEP-2 cell lines, respectively, compared to vinblastine as a positive control with IC50 values of 2.34 µg/mL and 6.61 µg/mL against HCT-116 and HEP-2, respectively. Additionally, the ethyl acetate fraction displayed promising antibacterial activity against S. aureus with a MIC value of 62.5 µg/mL, compared to ciprofloxacin as a positive control with MIC values of 1.56 µg/mL for Gram-positive bacteria and 3.125 µg/mL for Gram-negative bacteria. It also exhibited activity against E. coli and P. aeruginosa with MIC values of 250 µg/mL and 500 µg/mL, respectively. Briefly, this is the first report on the biological activities and secondary metabolite content of the ethyl acetate fraction of Hymedesmia sp. marine sponge, emphasizing the potential for further research against resistant bacterial and fungal strains, as well as different cancer cell lines. The ethyl acetate fraction of Hymedesmia sp. is a promising source of safe and unique natural drugs with potential therapeutic and pharmaceutical benefits.

Strategies for the Enhancement of Secondary Metabolite Production via Biosynthesis Gene Cluster Regulation in Aspergillus oryzae

The filamentous fungus Aspergillus oryzae (A. oryzae) has been extensively used for the biosynthesis of numerous secondary metabolites with significant applications in agriculture and food and medical industries, among others. However, the identification and functional prediction of metabolites through genome mining in A. oryzae are hindered by the complex regulatory mechanisms of secondary metabolite biosynthesis and the inactivity of most of the biosynthetic gene clusters involved. The global regulatory factors, pathway-specific regulatory factors, epigenetics, and environmental signals significantly impact the production of secondary metabolites, indicating that appropriate gene-level modulations are expected to promote the biosynthesis of secondary metabolites in A. oryzae. This review mainly focuses on illuminating the molecular regulatory mechanisms for the activation of potentially unexpressed pathways, possibly revealing the effects of transcriptional, epigenetic, and environmental signal regulation. By gaining a comprehensive understanding of the regulatory mechanisms of secondary metabolite biosynthesis, strategies can be developed to enhance the production and utilization of these metabolites, and potential functions can be fully exploited.

The Identification of a Target Gene of the Transcription Factor KojR and Elucidation of Its Role in Carbon Metabolism for Kojic Acid Biosynthesis in Aspergillus oryzae

DNA-binding transcription factors are broadly characterized as proteins that bind to specific sequences within genomic DNA and modulate the expression of downstream genes. This study focused on KojR, a transcription factor involved in the metabolism of kojic acid, which is an organic acid synthesized in Aspergillus oryzae and is known for its tyrosinase-inhibitory properties. However, the regulatory mechanism underlying KojR-mediated kojic acid synthesis remains unclear. Hence, we aimed to obtain a comprehensive identification of KojR-associated genes using genomic systematic evolution of ligands by exponential enrichment with high-throughput DNA sequencing (gSELEX-Seq) and RNA-Seq. During the genome-wide exploration of KojR-binding sites via gSELEX-Seq and identification of KojR-dependent differentially expressed genes (DEGs) using RNA-Seq, we confirmed that KojR preferentially binds to 5'-CGGCTAATGCGG-3', and KojR directly regulates kojT, as was previously reported. We also observed that kojA expression, which may be controlled by KojR, was significantly reduced in a ΔkojR strain. Notably, no binding of KojR to the kojA promoter region was detected. Furthermore, certain KojR-dependent DEGs identified in the present study were associated with enzymes implicated in the carbon metabolic pathway of A. oryzae. This strongly indicates that KojR plays a central role in carbon metabolism in A. oryzae.

Natural Compounds with Antifungal Properties against Candida albicans and Identification of Hinokitiol as a Promising Antifungal Drug

Candida albicans is an opportunistic yeast that causes most fungal infections. C. albicans has become increasingly resistant to antifungal drugs over the past decade. Our study focused on the identification of pure natural compounds for the development of antifungal medicines. A total of 15 natural compounds from different chemical families (cinnamic derivatives, aromatic phenols, mono- and sesquiterpenols, and unclassified compounds) were screened in this study. Among these groups, hinokitiol (Hi), a natural monoterpenoid extracted from the wood of the cypress family, showed excellent anti-C. albicans activity, with a MIC value of 8.21 µg/mL. Hi was selected from this panel for further investigation to assess its antifungal and anti-inflammatory properties. Hi exhibited significant antifungal activity against clinically isolated fluconazole- or caspofungin-resistant C. albicans strains. It also reduced biofilm formation and hyphal growth. Treatment with Hi protected Caenorhabditis elegans against infection with C. albicans and enhanced the expression of antimicrobial genes in worms infected with C. albicans. Aside from its antifungal activities against C. albicans, Hi challenge attenuated the LPS-induced expression of pro-inflammatory cytokines (IL-6, IL-1β, and CCL-2) in macrophages. Overall, Hi is a natural compound with antifungal and anti-inflammatory properties, making Hi a promising platform with which to fight against fungal infections.

Recent advances in triazoles as tyrosinase inhibitors

The tyrosinase enzyme, which is widely found in microorganisms, animals and plants, has a significant position in melanogenesis, plays an important role in undesirable browning of fruits and vegetables, antibiotic resistance, skin pigment formation, sclerotization of cuticle, neurodegeneration, etc. Therefore, with the wide potential application fields of tyrosinase in food, agriculture, cosmetics and pharmaceutical industries, which has become the target enzyme for the development of therapeutic agents such as antibrowning, anticancer, antibacterial, skin whitening, insecticides, etc., a large number of synthetic tyrosinase inhibitors have been widely reported in recent years. The triazole ring, which has a broad spectrum of biological action, is of increasing interest in the synthesis of new tyrosinase inhibitors. In this review, tyrosinase inhibition effects, structure-activity relationships, enzyme inhibition kinetics and mechanisms of action of 1,2,3- or 1,2,4-triazole derivatives were investigated. The data gathered is anticipated to supply rational guidance and an influential strategy for the development of novel, potent and safe tyrosinase inhibitors for better practical application in the future.

Anhydrous Alum Inhibits α-MSH-Induced Melanogenesis by Down-Regulating MITF via Dual Modulation of CREB and ERK

Melanogenesis, the intricate process of melanin synthesis, is central to skin pigmentation and photoprotection and is regulated by various signaling pathways and transcription factors. To develop potential skin-whitening agents, we used B16F1 melanoma cells to investigate the inhibitory effects of anhydrous alum on melanogenesis and its underlying molecular mechanisms. Anhydrous alum (KAl(SO4)2) with high purity (>99%), which is generated through the heat-treatment of hydrated alum (KAl(SO4)2·12H2O) at 400 °C, potentiates a significant reduction in melanin content without cytotoxicity. Anhydrous alum downregulates the master regulator of melanogenesis, microphthalmia-associated transcription factor (MITF), which targets key genes involved in melanogenesis, thereby inhibiting α-melanocyte-stimulating hormone (α-MSH)-induced melanogenesis. Phosphorylation of the cAMP response element-binding protein, which acts as a co-activator of MITF gene expression, is attenuated by anhydrous alum, resulting in compromised MITF transcription. Notably, anhydrous alum promoted extracellular signal-regulated kinase phosphorylation, leading to the impaired nuclear localization of MITF. Overall, these results demonstrated the generation and mode of action of anhydrous alum in B16F1 cells, which constitutes a promising option for cosmetic or therapeutic use.

Screening of Tyrosinase, Xanthine Oxidase, and α-Glucosidase Inhibitors from Polygoni Cuspidati Rhizoma et Radix by Ultrafiltration and HPLC Analysis

Polygoni Cuspidati Rhizoma et Radix (PCR), the rhizome and root of Polygonum cuspidatum Sieb. et Zucc., has been used as an herbal medicine for a long time. In this study, the ultrafiltration combined with high performance liquid chromatography (UF-HPLC) method was developed to screen tyrosinase (TYR), α-glucosidase (α-GLU), and xanthine oxidase (XOD) inhibitors from PCR. Firstly, the inhibitory activity of 50% methanol PCR extract on TYR, α-GLU, XOD, and acetylcholinesterase (ACHE) was tested. The extract showed a good inhibition on the enzymes, except for ACHE. Therefore, UF-HPLC experiments were carried out to screen TYR, α-GLU, and XOD inhibitors from PCR extract. Seven potential bioactive components were discovered, including methylgallate (1), 1,6-di-O-galloyl-D-glucose (2), polydatin-4'-O-D-glucoside (3), resveratrol-4'-O-D-glucoside (4), polydatin (5), malonyl glucoside resveratrol (6), and resveratrol-5-O-D-glucoside (7). Most of them were found as enzyme inhibitors from PCR for the first time, except polydatin (5), which had been reported as an α-GLUI in PCR in the literature. Finally, molecular docking analysis was applied to validate the interactions of these seven potential active components with the enzymes. Compounds 1-7 were proven as TYR inhibitors, compounds 2, 4-7 were identified as XOD inhibitors, and compounds 4-6 were confirmed as α-GLU inhibitors. In short, the current study provides a good reference for the screening of enzyme inhibitors through UF-HPLC, and provides scientific data for future studies of PCR.

Hirsutanone Isolated from the Bark of Alnus japonica Attenuates Melanogenesis via Dual Inhibition of Tyrosinase Activity and Expression of Melanogenic Proteins

Hirsutanone (Hir) and oregonin (Ore) are diarylheptanoids isolated from the bark of Alnus japonica. In this study, we investigated the anti-melanogenic activity of Hir and Ore in B16-F1 murine melanoma and normal human epidermal melanocytes (HEMn-DP) and elucidated the mechanisms of action. In B16-F1 cells, Hir and Ore suppressed melanin synthesis induced by α-melanocyte-stimulating hormone (α-MSH) without cytotoxicity. The inhibitory effect of Hir on melanin synthesis was much stronger than that of Ore. In addition, Hir reduced melanin content in HEMn-DP cells. As tyrosinase is a key enzyme in melanin synthesis, the effect of Hir on tyrosinase activity was assessed. The results demonstrated that Hir partially decreased tyrosinase activity and intracellular tyrosinase activity. Moreover, Hir suppressed the protein expression of melanogenic enzymes, including tyrosinase, tyrosinase-related protein (TRP)-1, and TRP-2, leading to reduced melanin biosynthesis. Hir also led to the suppression of cAMP response element-binding protein (CREB) phosphorylation and microphthalmia-associated transcription factor (MITF) expression, which control the expression of melanogenic enzymes. These results suggest that Hir suppressed melanin synthesis by dual inhibition of tyrosinase activity and the CREB/MITF pathway leading to the expression of melanogenic enzymes and may be a potent cosmetic and therapeutic agent for hyperpigmentation disorders.