EPR examination of free radical properties of DOPA–melanin complexes with ciprofloxacin, lomefloxacin, norfloxacin and sparfloxacin

The Research Status, Potential Hazards and Toxicological Mechanisms of Fluoroquinolone Antibiotics in the Environment

Fluoroquinolone antibiotics are widely used in human and veterinary medicine and are ubiquitous in the environment worldwide. This paper recapitulates the occurrence, fate, and ecotoxicity of fluoroquinolone antibiotics in various environmental media. The toxicity effect is reviewed based on in vitro and in vivo experiments referring to many organisms, such as microorganisms, cells, higher plants, and land and aquatic animals. Furthermore, a comparison of the various toxicology mechanisms of fluoroquinolone antibiotic residues on environmental organisms is made. This study identifies gaps in the investigation of the toxic effects of fluoroquinolone antibiotics and mixtures of multiple fluoroquinolone antibiotics on target and nontarget organisms. The study of the process of natural transformation toward drug-resistant bacteria is also recognized as a knowledge gap. This review also details the combined toxicity effect of fluoroquinolone antibiotics and other chemicals on organisms and the adsorption capacity in various environmental matrices, and the scarcity of data on the ecological toxicology evaluation system of fluoroquinolone antibiotics is identified. The present study entails a critical review of the literature providing guidelines for the government to control the discharge of pollutants into the environment and formulate policy coordination. Future study work should focus on developing a standardized research methodology for fluoroquinolone antibiotics to guide enterprises in the design and production of drugs with high environmental biocompatibility.

Changes in the Oxidation-Reduction State of Human Dermal Fibroblasts as an Effect of Lomefloxacin Phototoxic Action

Phototoxicity induced by antibiotics is a real problem in health care. The discontinuation of antibiotic therapy due to a phototoxic reaction can lead to the development of resistant strains. Fluoroquinolones are widely used antibiotics that exhibit phototoxic activity under UVA radiation. The purpose of the study was to examine the redox status of human dermal fibroblasts exposed to UVA radiation and treated with lomefloxacin, the most phototoxic fluoroquinolone. Lomefloxacin alone was found to have an antiproliferative activity on fibroblasts by affecting the cell cycle. In addition, the drug caused a redox imbalance associated with the decreased expression of catalase and glutathione peroxidase. UVA radiation increased the drug cytotoxicity and oxidative stress induced by lomefloxacin. The decrease in cell viability was accompanied by a high level of reactive oxygen species and extensive changes in the antioxidant levels. The revealed data indicate that the phototoxic action of lomefloxacin results from both increased reactive oxygen species production and an impaired antioxidant defense system. Considering all of the findings, it can be concluded that lomefloxacin-induced phototoxic reactions are caused by an oxidoreductive imbalance in skin cells.

Fluoroquinolones as Tyrosinase Inhibitors; Enzyme Kinetics and Molecular Docking Studies to Explore Their Mechanism of Action

The binding of fluoroquinolones, the most commonly prescribed antibiotics, with melanin is well explored. However, their binding patterns and exact mechanism of interaction with tyrosinase, a key enzyme in melanogenesis, are not explored yet. Thus, in the present study, seven fluoroquinolone drugs were selected to characterize their interactions with the tyrosinase enzyme: ciprofloxacin, enoxacin sesquihydrate, ofloxacin, levofloxacin, sparfloxacin, moxifloxacin and gemifloxacin. The results confirmed that all the drugs execute excellent enzyme activity, with an inhibition range from IC50 = 28 ± 4 to 50 ± 1.9 μM, outperforming the standard hydroquinone (IC50 = 170 μM). Later, kinetic studies revealed that all the drugs showed irreversible, but mixed-type, tyrosinase inhibition, with a preferentially competitive mode of action. Further, 2D and 3D docked complexes and binding analyses confirmed their significant interactions in the active region of the target enzyme, sufficient for the downstream signaling responsible for the observed tyrosinase inhibition. Thus, this is the first report demonstrating their mechanism of tyrosinase inhibition, critical for melanin-dependent responses, including toxicity.

Toxicity induced by ciprofloxacin and enrofloxacin: oxidative stress and metabolism

Ciprofloxacin (CIP) (human use) and enrofloxacin (ENR) (veterinary use) are synthetic anti-infectious medications that belong to the second generation of fluoroquinolones. They have a wide antimicrobial spectrum and strong bactericidal effects at very low concentrations via enzymatic inhibition of DNA gyrase and topoisomerase IV, which are required for DNA replication. They also have high bioavailability, rapid absorption with favorable pharmacokinetics and excellent tissue penetration, including cerebral spinal fluid. These features have made them the most applied antibiotics in both human and veterinary medicine. ENR is marketed exclusively for animal medicine and has been widely used as a therapeutic veterinary antibiotic, resulting in its residue in edible tissues and aquatic environments, as well as the development of resistance and toxicity. Estimation of the risks to humans due to antimicrobial resistance produced by CIP and ENR is important and of great interest. Moreover, in rare cases due to their overdose and/or prolonged administration, the development of CIP and ENR toxicity may occur. The toxicity of these fluoroquinolones antimicrobials is mainly related to reactive oxygen species (ROS) and oxidative stress (OS) generation, besides metabolism-related toxicity. Therefore, CIP is restricted in pregnant and lactating women, pediatrics and elderly similarly ENR do in the veterinary field. This review manuscript aims to identify the toxicity induced by ROS and OS as a common sequel of CIP and ENR. Furthermore, their metabolism and the role of metabolizing enzymes were reported.

The Biochemical and Molecular Analysis of Changes in Melanogenesis Induced by UVA-Activated Fluoroquinolones-In Vitro Study on Human Normal Melanocytes

Fluoroquinolones cause phototoxic reactions, manifested as different types of skin lesions, including hyperpigmentation. The disturbances of melanogenesis indicate that fluoroquinolones may affect cellular processes in melanocytes. It has been reported that these antibiotics may bind with melanin and accumulate in pigmented cells. The study aimed to examine the changes in melanogenesis in human normal melanocytes exposed to UVA radiation and treated with lomefloxacin and moxifloxacin, the most and the least fluoroquinolone, respectively. The obtained results demonstrated that both tested fluoroquinolones inhibited melanogenesis through a decrease in tyrosinase activity and down-regulation of tyrosinase and microphthalmia-associated transcription factor production. Only lomefloxacin potentiated UVA-induced melanogenesis. Under UVA irradiation lomefloxacin significantly enhanced melanin content and tyrosinase activity in melanocytes, although the drug did not cause an increased expression of tyrosinase or microphthalmia-associated transcription factor. The current studies revealed that phototoxic activity of fluoroquinolones is associated with alterations in the melanogenesis process. The difference in phototoxic potential of fluoroquinolones derivatives may be connected with various effects on UVA-induced events at a cellular level.

Kanamycin induces free radicals formation in melanocytes: An important factor for aminoglycosides ototoxicity

Ototoxicity is well-documented but not fully understood undesirable side effect of aminoglycoside antibiotic, kanamycin. Kanamycin is capable of binding to melanin biopolymers-natural pigments of the skin, hair, and eyes. Melanin-producing cells, melanocytes, are also present in the inner ear and are known to be necessary for normal hearing. It was considered that melanin content in the inner ear may influence aminoglycoside-induced ototoxic effect. The impact of kanamycin on melanocytes homeostasis may thus play role in the antibiotic-induced ototoxic effect. Previously, we demonstrated that kanamycin disturbs homeostasis in light-pigmented melanocytes. To investigate if/how melanization contributes to this phenomenon, the study using in vitro model of dark-pigmented melanocytes is required. Spectrophotometric measurements and electron paramagnetic resonance (EPR) spectroscopy analysis were performed. Kanamycin induced a concentration-dependent loss in HEMn-DP melanocytes viability. The value of IC ₅₀ was estimated to be 5.0 mM. Modulation of the activity of analyzed antioxidant enzymes and increased production of free radicals as well as the decrease of the melanin content were observed. Our results confirmed that kanamycin generates oxidative stress in melanocytes. The increased level of free radicals caused by kanamycin may be responsible for the imbalance of antioxidant defense and the reduction of melanin content in melanocytes. The role of melanin in the mechanism of kanamycin-induced hearing impairment was discussed and the obtained results were compared with the previously demonstrated data concerning light-pigmented melanocytes.

Effect of fluoroquinolones on melanogenesis in normal human melanocytes HEMn-DP: a comparative in vitro study

PURPOSE

Fluoroquinolones are one of the most commonly prescribed classes of antibiotics. However, their use is often connected with high risk of phototoxic reactions that lead to various skin or eye disorders. The aim of this study was to examine the effect of ciprofloxacin, lomefloxacin, moxifloxacin and fluoroquinolone derivatives with different phototoxic potential, on the viability and melanogenesis in melanocytes.

MATERIALS AND METHODS

Normal human epidermal melanocytes, dark pigmented (HEMn-DP) were used as an in vitro model system. The effect of the tested antibiotics on cell viability and melanization in pigmented cells was investigated using a spectrophotometric method. The WST-1 assay was used to detect the cytotoxic effect of antibiotics.

RESULTS

Ciprofloxacin, lomefloxacin and moxifloxacin induced the concentration-dependent loss in melanocytes viability. The values of EC₅₀ for the tested fluoroquinolone derivatives were found to be 2.0 mM for ciprofloxacin, 0.51 mM for lomefloxacin and 0.27 mM for moxifloxacin. The exposure of cells to different concentrations of the analyzed drugs resulted in decrease in melanin content and tyrosinase activity. The highest decrease was observed for lomefloxacin which may explain its high phototoxic potential in vivo. The role of melanin in the mechanism of the toxicity of fluoroquinolones was discussed and the obtained results were compared with the previously obtained data concerning light-pigmented melanocytes (HEMa-LP).

CONCLUSIONS

The results obtained in vitro suggest that the phototoxic potential of fluoroquinolones in vivo depends on specific drug-melanin interaction, the ability of drugs to affect melanogenesis as well as on the degree of melanocytes pigmentation.

EPR spectroscopy of chlorpromazine-induced free radical formation in normal human melanocytes

The purpose of this study was to estimate the effect of chlorpromazine on free radical concentration in HEMn-DP melanocytes using electron paramagnetic resonance (EPR) spectroscopy. It was found that chlorpromazine at concentrations of 1 × 10(-7) and 1 × 10(-6) M contributed to the formation of free radicals (g values ~2) in a dose-dependent manner. The increase in free radical formation was accompanied by an increase in cytotoxicity, as shown by a tetrazolium assay. Homogeneous broadening of EPR lines, slow spin-lattice relaxation processes, and strong dipolar interactions characterized all the tested cellular samples. The performed examination of free radical formation in cells exposed to different chlorpromazine concentrations confirmed the usefulness of electron paramagnetic resonance spectroscopy to determine the effect of a drug on free radical production in a cellular model system in vitro.

EPR Studies of DOPA-Melanin Complexes with Netilmicin and Cu(II) at Temperatures in the Range of 105-300 K

The application of electron paramagnetic resonance (EPR) spectroscopy in pharmacy of melanin complexes with netilmicin and Cu(II) was presented. The continuous microwave saturation of EPR spectra of DOPA-melanin and the complexes was performed. EPR spectra were measured on an X-band (9.3 GHz) spectrometer at temperatures in the range of 105-300 K. Paramagnetic copper ions decrease the intensity of the EPR lines of melanin's free radicals. It was found that fast spin-lattice relaxation characterizes DOPA-melanin-Cu(II) complexes. Slow spin-lattice relaxation processes exist in melanin's paramagnetic centers of DOPA-melanin and DOPA-melanin-netilmicin, [DOPA-melanin-netilmicin]-Cu(II), [DOPA-melanin-Cu(II)]-netilmicin complexes. Spin-lattice relaxation processes are faster at higher temperatures. The homogeneous broadening of EPR lines for melanin complexes was observed. The practical consequences of differences between paramagnetic properties of melanin complexes with netilmicin and the complexes with Cu(II) were discussed.

Small molecule modulators of aggregation in synthetic melanin polymerizations

There are numerous potential applications for melanin-binding compounds, and new methods are of interest to identify melanin-binding agents. A portion of the polymerization to eumelanin, the black to brown pigment in humans, is thought to be supramolecular aggregation of nanoparticles derived from dihydroxyindoles. Starting with chloroquine, a known eumelanin-binding compound, the ability of small molecules to influence aggregation in synthetic eumelanin polymerizations was investigated. Twenty-eight compounds were tested, including pharmaceuticals, dyes, aromatics, and amines. Compounds that either accelerate or delay the appearance of macroscopic particles in synthetic eumelanin polymerizations were uncovered.

Interaction between ciprofloxacin and melanin: the effect on proliferation and melanization in melanocytes

There have been described serious adverse events caused by ciprofloxacin in pigmented tissues. It is known that some fluoroquinolones bind well to melanin rich tissues, but the relation between their affinity to melanin and the skin or eye toxicity is not well documented. The aim of this study was to examine whether ciprofloxacin binds to melanin, and how this interaction affects the proliferation and melanization in melanocytes. We have demonstrated that complexes which ciprofloxacin forms with melanin possess at least two classes of independent binding sites. Their association constants are K(1)~10(5) M(-1) and K(2)~10(2) M(-1), respectively. Ciprofloxacin has induced evident concentration-dependent loss in melanocytes viability. The value of ED(50) was found to be ~0.5 mM. It has also been shown that ciprofloxacin reduces melanin content, and decreases tyrosinase activity in human skin melanocytes. The ability of ciprofloxacin to interact with melanin and its inhibitory effect on melanization in melanocytes in vitro may explain a potential role of melanin in the mechanisms of ciprofloxacin toxic effects in vivo.