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

Streptomycin generates oxidative stress in melanin-producing cells: In vitro study with EPR spectroscopy evidence

Streptomycin (STR) is an aminoglycoside antibiotic with a broad-spectrum of activity and ototoxic potential. The mechanism of STR-induced inner ear damage has not been fully elucidated. It was previously found that STR binds to melanin, which may result in the accumulation of the drug in melanin-containing tissues. Melanin pigment is present in various parts of the inner ear, including the cochlea and vestibular organ. The present study aimed to assess if streptomycin generates oxidative stress and affects melanogenesis in normal human melanocytes. Moreover the variation of free radical concentration in STR-treated melanocytes was examined by electron paramagnetic resonance spectroscopy (EPR). We found that STR decreases cell metabolic activity and reduces melanin content. The observed changes in the activity of antioxidant enzymes activity in HEMn-DPs treated with streptomycin may suggest that the drug affects redox homeostasis in melanocytes. In this work EPR study expanded knowledge about free radicals in interactions of STR and melanin in melanocytes. The results may help elucidate the mechanisms of STR toxicity on pigment cells, including melanin-producing cells in the inner ear. This is important because understanding the mechanism of STR-induced ototoxicity would be helpful in developing new therapeutic strategies to protect patients' hearing.

The phenomenon of phototoxicity and long-term risks of commonly prescribed and structurally diverse drugs

Photosensitivity to structurally diverse drugs is a common but under-reported adverse cutaneous reaction and can be classified as phototoxic or photoallergic. Phototoxic reactions occur when the skin is exposed to sunlight after administering topical or systemic medications that exhibit photosensitizing activity. These reactions depend on the dose of medication, degree of exposure to ultraviolet light, type of ultraviolet light, and sufficient skin distribution volume. Accurate prediction of the incidence and phototoxic response severity is challenging due to a paucity of literature, suggesting that phototoxicity may be more frequent than reported. This paper reports an extensive literature review on phototoxic drugs; the review employed pre-determined search criteria that included meta-analyses, systematic reviews, literature reviews, and case reports freely available in full text. Additional reports were identified from reference sections that contributed to the understanding of phototoxicity. The following drugs and/or drug classes are discussed: amiodarone, voriconazole, chlorpromazine, doxycycline, fluoroquinolones, hydrochlorothiazide, nonsteroidal anti-inflammatory drugs, and vemurafenib. In reviewing phototoxic skin reactions, this review highlights drug molecular structures, their reactive pathways, and, as there is a growing association between photosensitizing drugs and the increasing incidence of skin cancer, the consequential long-term implications of photocarcinogenesis.

A review on oxidant and antioxidant effects of antibacterial agents: impacts on bacterial cell death and division and therapeutic effects or adverse reactions in humans

Reactive oxygen species (ROS) are produced in the mitochondrial respiratory pathway and cellular metabolism. They are responsible for creating oxidative stress and lipid peroxidation. In living organisms, there is a balance between oxidative stress and the antioxidant system, but some factors such as medicines disturb the balance and cause many problems. These effects can impact bacterial death and division and also in humans can induce therapeutic or adverse reactions. Web of Science and Pubmed databases were used for searching. This review focuses on the oxidant and antioxidant effects of different classes of antibacterial agents and the mechanisms of oxidative stress. Some of these agents have beneficial effects on killing bacteria due to their antioxidant or oxidant effects. However, some of their side effects may be due to their oxidative effects. Based on the results of this review, minocycline is an antioxidant, but aminoglycosides, chloramphenicol, glycopeptides, antituberculosis drugs, fluoroquinolones, and sulfamethoxazole agents have oxidant effects. Furthermore, cephalosporins, penicillins, metronidazole, and macrolides have both oxidant and antioxidant effects in different studies. It is concluded that some antibacterial agents have oxidant and other antioxidant effects. These activities may affect their therapeutic effects or side effects. Some antioxidants can prevent the adverse effects of antibacterial agents. Clarifying the exact oxidant and antioxidant effects of some antimicrobial agents needs more research projects.

Dual-mode photoelectrochemical/electrochemical sensor based on Z-scheme AgBr/AgI-Ag-CNTs and aptamer structure switch for the determination of kanamycin

A "signal-on" dual-mode aptasensor based on photoelectrochemical (PEC) and electrochemical (EC) signals was established for kanamycin (Kana) assay by using a novel Z-scheme AgBr/AgI-Ag-CNTs composite as sensing platform, an aptamer structure switch, and K₃[Fe(CN)₆] as photoelectron acceptor and electrochemical signal indicator. The aptamer structure switch was designed to obtain a "signal-off" state, which included an extended Kana aptamer (APT), one immobilized probe (P1), and one blocking probe (P2) covalently linked with graphdiyne oxide (GDYO) nanosheets. P1, P2, and aptamer formed the double helix structure, which resulted in the inhibited photocurrent intensity because of the weak conductivity of double helix layer and serious electrostatic repulsion of GDYO towards K₃[Fe(CN)₆]. In the presence of Kana, APT specifically bound to the target and dissociated from P1 and P2, and thus, a "signal-on" state was initiated by releasing P2-GDYO from the platform. Based on the sensing platform and the aptamer structure switch, the dual-mode aptasensor realized the linear determination ranges of 1.0 pM-2.0 μM with a detection limit (LOD) of 0.4 pM (for PEC method) and 10 pM-5.0 μM with a LOD of 5 pM (for EC method). The aptasensor displayed good application potential for Kana test in real samples.

Recognition of Melanocytes in Immuno-Neuroendocrinology and Circadian Rhythms: Beyond the Conventional Melanin Synthesis

Melanocytes produce melanin to protect the skin from UV-B radiation. Notwithstanding, the spectrum of their functions extends far beyond their well-known role as melanin production factories. Melanocytes have been considered as sensory and computational cells. The neurotransmitters, neuropeptides, and other hormones produced by melanocytes make them part of the skin’s well-orchestrated and complex neuroendocrine network, counteracting environmental stressors. Melanocytes can also actively mediate the epidermal immune response. Melanocytes are equipped with ectopic sensory systems similar to the eye and nose and can sense light and odor. The ubiquitous inner circadian rhythm controls the body’s basic physiological processes. Light not only affects skin photoaging, but also regulates inner circadian rhythms and communicates with the local neuroendocrine system. Do melanocytes “see” light and play a unique role in photoentrainment of the local circadian clock system? Why, then, are melanocytes responsible for so many mysterious functions? Do these complex functional devices work to maintain homeostasis locally and throughout the body? In addition, melanocytes have also been shown to be localized in internal sites such as the inner ear, brain, and heart, locations not stimulated by sunlight. Thus, what can the observation of extracutaneous melanocytes tell us about the “secret identity” of melanocytes? While the answers to some of these intriguing questions remain to be discovered, here we summarize and weave a thread around available data to explore the established and potential roles of melanocytes in the biological communication of skin and systemic homeostasis, and elaborate on important open issues and propose ways forward.

Association of vitiligo with high-frequency sensorineural hearing loss: a systematic review and meta-analysis

The association between vitiligo and hearing loss has been noted but the specific frequencies and degrees of hearing impairment remain unclear. The objective of this systematic review was to investigate the relationship between vitiligo and hearing thresholds at various specific frequencies. We followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. We searched MEDLINE and Embase for relevant studies from inception to 10th April 2021. Case-control studies, cross-sectional, or cohort studies that compared the frequency-specific hearing thresholds between vitiligo patients and age-matched non-vitiligo controls were included. There were neither language nor geographic limitations. We used the Newcastle-Ottawa Scale to assess the risk of bias of included studies. The DerSimonian and Laird random-effects model was utilized in meta-analyses due to expected clinical heterogeneity. We included 9 case-control studies with 371 vitiligo patients and 349 controls, which were rated with low or unclear risk. We found neither relevant cross-sectional nor cohort studies. The meta-analysis showed that when compared with controls, vitiligo patients had significantly higher pure-tone hearing thresholds at 2000, 4000, and 8000 Hz. In conclusions, vitiligo patients are prone to high-frequency sensorineural hearing loss.

SOD2 Alleviates Hearing Loss Induced by Noise and Kanamycin in Mitochondrial DNA4834-deficient Rats by Regulating PI3K/MAPK Signaling

Superoxide dismutase 2 (SOD2)-mediated gene therapy has significant protective effects against kanamycin-induced hearing loss and hair cell loss in the inner ear, but the underlying mechanisms are still unclear. Herein, an in vivo aging model of mitochondrial DNA (mtDNA)4834 deletion mutation was established using D-galactose, and the effects of noise or kanamycin on inner ear injury was investigated. Rats subjected to mtDNA4834 mutation via D-galactose administration showed hearing loss characterized by the disruption of inner ear structure (abnormal cell morphology, hair cell lysis, and the absence of the organ of Corti), increased SOD2 promoter methylation, and an increase in the degree of apoptosis. Exposure to noise or kanamycin further contributed to the effects of D-galactose. SOD2 overexpression induced by viral injection accordingly counteracted the effects of noise and kanamycin and ameliorated the symptoms of hearing loss, suggesting the critical involvement of SOD2 in preventing deafness and hearing-related conditions. The PI3K and MAPK signaling pathways were also regulated by noise/kanamycin exposure and/or SOD2 overexpression, indicating that they may be involved in the therapeutic effect of SOD2 against age-related hearing loss.

Antioxidant Property and Bactericidal Activity of Linum usitatissimum Seed Essential Oil Nanoemulsion (LSEO-NE) on Staphylococcus aureus

Background: Linum usitatissimum Seed Essential Oil (LSEO) as an efficient antimicrobial compound contains various types of phytochemicals, such as lignans and phenols. Objectives: In the current study, we produced LSEO nanoemulsion (LSEO-NE) to study its antioxidant capacity and bactericidal activity against Staphylococcus aureus. Methods: The LSEO-NE was produced using the ultrasonication method and characterized by Atomic Force Microscopy (AFM), Dynamic Light Scattering (DLS), and Scanning Electron Microscopy (SEM). Then, we measured its antioxidant activity utilizing both ABTS and DPPH tests at four different LSEO-NE concentrations (200, 600, 800, and 1000 µg/mL) compared to glutathione. Finally, we evaluated its bactericidal activity on S. aureus by studying Antibiotic Susceptibility Testing (AST) using LSEO-NE-smeared discs compared to non-smeared and kanamycin discs. Results: The 67.3 nm droplets of LSEO-NE with PDI of 0.452 exhibited strong antioxidant activity, similar to glutathione, in both ABTS (IC50 = 350 µg/mL) and DPPH (IC50 = 235 µg/mL) tests. Moreover, the AST results revealed the significant sensitivity of S. aureus to LSEO-NE-smeared discs when compared to non-smeared and kanamycin discs. Conclusions: According to the results, LSEO-NE can be applied as a safe, natural, and effective antibiotic for bacterial infections caused by S. aureus in most organs, such as the respiratory system and skin. However, further in vivo studies are required to evaluate the LSEO-NE antibacterial efficiency against other pathogenic S. aureus strains.

Cobalamin Deficiency: Effect on Homeostasis of Cultured Human Astrocytes

Cobalamin deficiency is an important health problem. The major non-hematological symptoms of hypocobalaminemia are nervous system disorders, but the molecular and cellular mechanisms underlying this phenomenon have not yet been fully explained. Increasing scientific evidence is stressing the pivotal role of astrocyte dysfunction in the pathogenesis of a wide range of neurological disorders. In light of the above, the aim of this study was to develop an in vitro model of cobalamin deficiency by optimizing the conditions of astrocyte culture in the presence of vitamin B₁₂ antagonist, and then the model was used for multidirectional analysis of astrocyte homeostasis using image cytometry, immunoenzymatic and colorimetric assays, and fluorescence spectroscopy. Our results indicated that long-term incubation of normal human astrocytes with hydroxycobalamin(c-lactam) causes an increase of extracellular homocysteine level, a reduction of cell proliferation, and an accumulation of cells in the G₂/M cell cycle phase. Moreover, we observed dramatic activation of caspases and an increase of catalase activity. Interestingly, we excluded extensive apoptosis and oxidative stress. The study provided significant evidence for astrocyte homeostasis disturbance under hypocobalaminemia, thus indicating an important element of the molecular mechanism of nervous system diseases related to vitamin B₁₂ deficiency.

Nephrotoxicity and ototoxic symptoms of injectable second-line anti-tubercular drugs among patients treated for MDR-TB in Ethiopia: a retrospective cohort study

Background

Nephrotoxicity and ototoxicity are clinically significant dose-related adverse effects associated with second-line anti-tubercular injectables drugs (aminoglycosides and capreomycin) used during intensive phase of treatment of multi-drug resistant tuberculosis (MDR-TB) patients. Data are scarce on injectable-induced nephrotoxicity and ototoxicity in Ethiopian MDR-TB patients. The aim of this study was to assess the prevalence, management of nephrotoxicity and ototoxic symptoms and treatment outcomes of patients treated for MDR-TB with injectable-based regimens.

Method

This was retrospective cohort study based on review of medical records of about 900 patients on MDR-TB treatment from January 2010 to December 2015 at two large TB referral hospitals in Addis Ababa, Ethiopia. Nephrotoxicity in study participants was screened using baseline and monthly measurement of serum creatinine and clinical diagnosis and patient reports.

Results

Overall, 473 (54.2%) of participants were male. Children accounted for 47 (5.5%) of cases and the mean age of participants was 32 ± 12.6 years with range of 2–75 years. The majority (n = 788, 84.6%) of participants had past history of TB. The most commonly used injectable anti-TB drug was capreomycin (n = 789, 84.7%), while kanamycin and amikacin were also used. There was a statistically significant increment (p<0.05) in the mean serum creatinine values from baseline throughout intensive phase of treatment with a 10–18% prevalence of nephrotoxicity. Based on clinical criteria, nephrotoxicity was detected in 62 (6.7%) and ototoxic symptoms were detected in 42 (4.8%) participants. Nephrotoxicity and ototoxic symptoms were clinically managed by modification of treatment regimens including dose and frequency of drug administration.

Conclusion

Nephrotoxicity and ototoxic symptoms were significant problems among patients on follow-up for MDR-TB treatment. Based on laboratory criteria (serum creatinine), nephrotoxicity remained significant adverse events throughout intensive phase of treatment, indicating close monitoring of patients for successful outcome is mandatory until countries adopt the recent injectable-free WHO guideline and under specific conditions.