Melanins are natural pigments of skin, hair and eyes and can be classified into two main types: brown to black eumelanin and yellow to reddish-brown pheomelanin. Biosynthesis of melanins takes place in melanosomes, which are specialized cytoplasmic organelles of melanocytes - dendritic cells located in the basal layer of the epidermis, uveal tract of the eye, hair follicles, as well as in the inner ear, central nervous system and heart. Melanogenesis is a multistep process and begins with the conversion of amino acid L-tyrosine to DOPAquinone. The addition of cysteine or glutathione to DOPAquinone leads to the intermediates formation, followed by subsequent transformations and polymerization to the final product, pheomelanin. In the absence of thiol compounds DOPAquinone undergoes an intramolecular cyclization and oxidation to form DOPAchrome, which is then converted to 5,6-dihydroksyindole (DHI) or 5,6-dihydroxyindole-2-carboxylic acid (DHICA). Eumelanin is formed by polymerization of DHI and DHICA and their quinones. Regulation of melanogenesis is achieved by physical and biochemical factors. The article presents the intracellular signaling pathways: cAMP/PKA/CREB/MITF cascade, MAP kinases cascade, PLC/DAG/PKCβ cascade and NO/cGMP/PKG cascade, which are involved in the regulation of expression and activity of the melanogenesis-related proteins by ultraviolet radiation and endogenous agents (cytokines, hormones). Activity of the key melanogenic enzyme, tyrosinase, is also affected by pH and temperature. Many pharmacologically active substances are able to inhibit or stimulate melanin biosynthesis, as evidenced by in vitro studies on cultured pigment cells.

Fluoroquinolone antibiotics induce cytotoxicity in various cancer cell lines and may therefore represent a potentially important source of novel anticancer agents. The aim of the present study was to examine the effect of ciprofloxacin on the viability, redox balance, apoptosis, expression of p53, Bax and Bcl-2, cell cycle distribution and DNA fragmentation of triple-negative MDA-MB-231 breast cancer cells. The results of the present study demonstrated that ciprofloxacin decreases cell viability in a dose- and time-dependent manner. The half maximal inhibitory concentration values of ciprofloxacin in MDA-MB-231 cells following treatment for 24, 48 and 72 h were 0.83, 0.14 and 0.03 µmol/ml, respectively. Furthermore, it was demonstrated that ciprofloxacin altered the redox signaling pathway, as determined by intracellular glutathione depletion. The results of Annexin V/propidium iodide staining revealed that ciprofloxacin triggered the apoptosis of MDA-MB-231 cells. Furthermore, cipfloxacin treatment stimulated the loss of the mitochondrial transmembrane potential via the Bax/Bcl-2-dependent pathway, thus inducing apoptosis. Ciprofloxacin induced cell cycle arrest at the S-phase; therefore it was hypothesized that ciprofloxacin inhibits topoisomerase II. Oligonucleosomal DNA fragmentation and the elevation of p53 expression were observed in the present study, indicating that this late-apoptotic event may be mediated by the p53-dependent pathway. Therefore, the results of the current study provide important molecular data concerning the cellular cascade, which may explain the cytotoxicity induced by ciprofloxacin in human triple-negative breast cancer cells, thus providing a novel insight into the therapeutic properties of this drug.

Background A large body of research has focused on fluoroquinolones. It was shown that this class of synthetic antibiotics could possess antiviral activity as a broad range of anti-infective activities. Based on these findings, we have undertaken in silico molecular docking study to demonstrate, for the first time, the principle for the potential evidence pointing ciprofloxacin and moxifloxacin ability to interact with COVID-19 Main Protease. Methods In silico molecular docking and molecular dynamics techniques were applied to assess the potential for ciprofloxacin and moxifloxacin interaction with COVID-19 Main Protease (Mpro). Chloroquine and nelfinavir were used as positive controls. Results We revealed that the tested antibiotics exert strong capacity for binding to COVID-19 Main Protease (Mpro). According to the results obtained from the GOLD docking program, ciprofloxacin and moxifloxacin bind to the protein active site more strongly than the native ligand. When comparing with positive controls, a detailed analysis of the ligand–protein interactions shows that the tested fluoroquinolones exert a greater number of protein interactions than chloroquine and nelfinavir. Moreover, lower binding energy values obtained from KDEEP program were stated when compared to nelfinavir. Conclusions Here, we have demonstrated for the first time that ciprofloxacin and moxifloxacin may interact with COVID-19 Main Protease (Mpro).

The obtained results for COLO829 melanoma cells were compared with data for normal dark pigmented melanocytes and the use of ciprofloxacin as a potential anticancer drug for the treatment of melanoma in vivo was considered.

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Vitamin B12 deficiency causes significant changes in cellular metabolism leading to various clinical symptoms, such as hematological, psychiatric, and neurological disorders. We hypothesize that skin pigmentation disorders may be a diagnostically important manifestation of vitamin B12 deficiency, however the cellular and molecular mechanisms underlying these effects remain unknown. The aim of this study was to examine the effect of vitamin B12 deficiency on melanocytes homeostasis. Hypocobalaminemia in vitro model was developed by treating epidermal melanocytes with synthesized vitamin B12 antagonist—hydroxycobalamin(c-lactam). The cells were examined using immunoenzymatic, spectrophotometric, and fluorimetric assays as well as image cytometry. Significant melanogenesis stimulation—the increase of relative melanin content and tyrosinase activity up to 131% and 135%, respectively—has been indicated. Cobalamin-deficient cells displayed the elevation (by 120%) in reactive oxygen species level. Moreover, the redox status imbalance was stated. The study provided a scientific evidence for melanocytes homeostasis disturbance under hypocobalaminemia, thus indicating a significant element of the hyperpigmentation mechanism due to vitamin B12 deficiency. Furthermore, the implication between pigmentary and hematological and/or neuropsychiatric symptoms in cobalamin-deficient patients may be an important issue.

Abstract:Backround: Lomefloxacin is a potent bactericidal antibiotic. The use of this drug in treatment of various infections is accompanied by serious adverse effects on pigmented tissues. The exact mechanisms of lomefloxacin side effects have not been well established yet. The aim of this study was to characterize the interaction between lomefloxacin and melanin, and to examine how this interaction affects the cell viability and melanization in melanocytes. Methods: Normal human epidermal melanocytes and the model DOPA-melanin were used. The binding parameters of lomefloxacin-melanin complexes as well as the antibiotic effect on cell viability and melanization in pigmented cells were investigated using a spectrophotometric method. Results: Our results indicate that lomefloxacin forms stable complexes with melanin. The analysis of drug binding to melanin has shown that at least two classes of independent binding sites are involved in formation of these complexes. The WST-1 assay was used to detect the antibiotic cytotoxic effect. The value of ED 50 for lomefloxacin was about 0.75 mmol/l. It has been shown that lomefloxacin causes inhibition of tyrosinase activity, and reduces melanin content in human skin melanocytes in a dose-dependent manner. Conclusion:The ability of the analyzed fluoroquinolone to form complexes with melanin, and the demonstrated inhibitory effect on a melanization process in melanocytes in vitro may explain a potential role of melanin biopolymer in the mechanisms of undesirable side effects of lomefloxacin in vivo resulting from its accumulation in pigmented tissues.

Phototoxicity of fluoroquinolones is connected with oxidative stress induction. Lomefloxacin (8-halogenated derivative) is considered the most phototoxic fluoroquinolone and moxifloxacin (8-methoxy derivative) the least. Melanin pigment may protect cells from oxidative damage. On the other hand, fluoroquinolone–melanin binding may lead to accumulation of drugs and increase their toxicity to skin. The study aimed to examine the antioxidant defense system status in normal melanocytes treated with lomefloxacin and moxifloxacin and exposed to UV-A radiation. The obtained results demonstrated that UV-A radiation enhanced only the lomefloxacin-induced cytotoxic effect in tested cells. It was found that fluoroquinolones alone and with UV-A radiation decreased superoxide dismutase (SOD) activity and SOD1 expression. UV-A radiation enhanced the impact of moxifloxacin on hydrogen peroxide-scavenging enzymes. In turn, lomefloxacin alone increased the activity and the expression of catalase (CAT) and glutathione peroxidase (GPx), whereas UV-A radiation significantly modified the effects of drugs on these enzymes. Taken together, both analyzed fluoroquinolones induced oxidative stress in melanocytes, however, the molecular and biochemical studies indicated the miscellaneous mechanisms for the tested drugs. The variability in phototoxic potential between lomefloxacin and moxifloxacin may result from different effects on the antioxidant enzymes.