Application Of Neomycin Research Articles

Prevalence and Determinants of Sensitisation to Neomycin in North-Eastern Italy, 1997-2021.

Allergic contact dermatitis (ACD) induced by topical application of neomycin is frequently reported. This multi-center study investigated prevalence and determinants of neomycin sensitisations in 30 629 outpatients from North-eastern Italy during 1997-2021. European baseline and extended Triveneto series were applied on the upper back of patients patch testing for suspected ACD and removed after 48 h. Prevalence of neomycin sensitisation was 2.29% (=701/30 629), significantly decreasing over time, especially after 2003. Neomycin sensitisation increased with age, especially in female patients older than 60 with leg dermatitis. The majority of patients sensitised to neomycin (74.5%) tested positive also against other haptens, particularly ingredients included in creams and emollients, as lanolin or benzocaine or preservatives as thimerosal or parabens. The decreasing prevalence of neomycin sensitisation over time likely reflected reduced accessibility and circulation of neomycin in Italy, due to containment of prescriptions and over-the-counter accessibility. Older individuals are typically more likely to be treated by topical medications and antibiotics as neomycin for various conditions, including stasis dermatitis. Since ACD caused by topical medications is relatively easy to miss, comprehensive drug history and patch testing are essential for any patient with suspected sensitisation caused by neomycin.

6'-sialyllactose ameliorates the ototoxic effects of the aminoglycoside antibiotic neomycin in susceptible mice.

Sialic acids are terminal sugars of the cellular glycocalyx and are highly abundant in the nervous tissue. Sialylation is sensed by the innate immune system and acts as an inhibitory immune checkpoint. Aminoglycoside antibiotics such as neomycin have been shown to activate tissue macrophages and induce ototoxicity. In this study, we investigated the systemic subcutaneous application of the human milk oligosaccharide 6'-sialyllactose (6SL) as a potential therapy for neomycin-induced ototoxicity in postnatal mice. Repeated systemic treatment of mice with 6SL ameliorated neomycin-induced hearing loss and attenuated neomycin-triggered macrophage activation in the cochlear spiral ganglion. In addition, 6SL reversed the neomycin-mediated increase in gene transcription of the pro-inflammatory cytokine interleukin-1β (Il-1b) and the apoptotic/inflammatory kinase Pik3cd in the inner ear. Interestingly, neomycin application also increased the transcription of desialylating enzyme neuraminidase 3 (Neu3) in the inner ear. In vitro, we confirmed that treatment with 6SL had anti-inflammatory, anti-phagocytic, and neuroprotective effects on cultured lipopolysaccharide-challenged human THP1-macrophages. Thus, our data demonstrated that treatment with 6SL has anti-inflammatory and protective effects against neomycin-mediated macrophage activation and ototoxicity.

The Involvement of Leptospira Spp. in Swine Abortion and Susceptibility of the Pathogen to Antibiotics

The involvement of Leptospira spp. in thirty-five (35) out of fifty (50) cases of swine abortion was investigated which further required evaluation of pathogen susceptibility to a panel of antibiotics. Samples of urine from aborting sows were collected to recover the pathogen, amplify its 16S rRNA gene to confirm its identity and monitor cell density in McFarland Units (MFU) as a measure of susceptibility to antibiotics. The study permitted the isolation and evaluation of Leptospira spp. morphology, demonstration of 3 amplicon products of the 16S rRNA genes with molecular sizes of 1050 to 1080 bp and identification of 2 Leptospira spp. and L. hyos after gene sequencing. The susceptibility of the identified L. hyos to Cephalexin, Neomycin, Clindamycin, Ciprofloxacin and Sulfamethoxazole prepared at different concentrations (25 µg, 35 µg and 50 µg) and evaluated after 6 and 12 hour-exposure time was marked by lower cell densities of recovered L. hyos relative to the application of higher (35 µg and 50 µg) antibiotic concentrations. Significant reduction in cell densities at 12-hr compared to data obtained on the 6-hour were demonstrated and underscored the susceptibility of L. hyos as effects of antibiotic concentration and duration of exposure time. The bactericidal action of 25 µg Ciprofloxacin; and 25 and 35 µg Sulfamethoxazole against L. hyos were established at 6-hour exposure time and that this bactericidal action was maintained until the 12-hr with the application of Neomycin and Ciprofloxacin at 35 and 50 µg and Sulfamethoxazole at 50 µg. These data highlight usefulness of the antibiotics in the treatment of abortion-associated Leptospira infections when administered at the concentrations described.

Component Optimization of Neomycin Biosynthesis via the Reconstitution of a Combinatorial Mini-Gene-Cluster in Streptomyces fradiae.

Neomycin, a multicomponent aminoglycoside antibiotic, is mainly utilized in livestock husbandry and feed additives in animals. The antimicrobial potency of the main product neomycin B is higher than that of its stereoisomer neomycin C. However, the content of neomycin C as an impurity in the high-producing strain is relatively high, and its isolation or removal from neomycin B is quite difficult, which influences the widespread application of neomycin. In this work, the essential genes responsible for neomycin biosynthesis were evaluated and overexpressed to reduce the content of neomycin C. Among them, neoG and neoH are two novel regulatory genes for neomycin biosynthesis, aphA is a resistance gene, neoN encoding a radical SAM-dependent epimerase is responsible for the conversion of neomycin C to B using SAM as the cofactor, and metK is a SAM synthetase coding gene. We demonstrated that the reconstitution and overexpression of a mini-gene-cluster (PkasO*-neoN-metK-PkasO*-neoGH-aphA) could effectively reduce the accumulation of neomycin C from 19.1 to 12.7% and simultaneously increase neomycin B by ∼13.1% in the engineered strain Sf/pKCZ04 compared with the wild-type strain (Sf). Real-time quantitative polymerase chain reaction analysis revealed the remarkable up-regulation of the neoE, neoH, neoN, and metK genes situated in the mini-gene-cluster. The findings will pave a new path for component optimization and the large-scale industrial production of significant commercial antibiotics.

Cutting Edge: The Use of Topical Aminoglycosides as an Effective Pull in "Prime and Pull" Vaccine Strategy.

The presence of tissue-resident memory T cells at barrier tissues is critical for long-lasting protective immune responses. Previous work has shown that tissue-resident memory T cells can be established by "pulling" virus-specific effector T cells from circulation to the genital mucosa via topical vaginal application of chemokines in mice. Once established, these cells protect hosts against genital herpes infection. We recently showed that vaginal application of aminoglycoside antibiotics induces robust activation of the IFN signaling pathway, including upregulation of chemokine expression within the tissue in mice. In this study, we show that a single topical application of neomycin, an inexpensive and vaginally nontoxic antibiotic, is sufficient to pull CD8 T cells to the vaginal mucosa and provide protection against genital herpes infection in mice.

The NADPH oxidase inhibitor diphenyleneiodonium activates the human TRPA1 nociceptor.

Transient receptor potential ankyrin 1 (TRPA1) is a Ca(2+)-permeable nonselective cation channel expressed in neuronal and nonneuronal cells and plays an important role in acute and inflammatory pain. Here, we show that an NADPH oxidase (NOX) inhibitor, diphenyleneiodonium (DPI), functions as a TRPA1 activator in human embryonic kidney cells expressing human TRPA1 (HEK-TRPA1) and in human fibroblast-like synoviocytes. Application of DPI at 0.03-10 μM induced a Ca(2+) response in HEK-TRPA1 cells in a concentration-dependent manner. The Ca(2+) response was effectively blocked by a selective TRPA1 antagonist, HC-030031 (HC). In contrast, DPI had no effect on HEK cells expressing TRPV1-V4 or TRPM8. Four other NOX inhibitors, apocynin (APO), VAS2870 (VAS), plumbagin, and 2-acetylphenothiazine, also induced a Ca(2+) response in HEK-TRPA1 cells, which was inhibited by pretreatment with HC. In the presence of 5 mM glutathione, the Ca(2+) response to DPI was effectively reduced. Moreover, mutation of cysteine 621 in TRPA1 substantially inhibited the DPI-induced Ca(2+) response, while it did not inhibit the APO- and VAS-induced responses. The channel activity was induced by DPI in excised membrane patches with both outside-out and inside-out configurations. Internal application of neomycin significantly inhibited the DPI-induced inward currents. In inflammatory synoviocytes with TRPA1, DPI evoked a Ca(2+) response that was sensitive to HC. In mice, intraplantar injection of DPI caused a pain-related response which was inhibited by preadministration with HC. Taken together, our findings demonstrate that DPI and other NOX inhibitors activate human TRPA1 without mediating NOX.

Middle Ear Application of a Sodium Hyaluronate Gel Loaded with Neomycin in a Guinea Pig Model

Establishing methods for topical administration of drugs to the inner ear have great clinical relevance and potential even in a relatively short perspective. To evaluate the efficacy of sodium hyaluronate (HYA) as a vehicle for drugs that could be used for treatment of inner ear disorders. The cochlear hair cell loss and round window membrane (RWM) morphology were investigated after topical application of neomycin and HYA into the middle ear. Sixty-five albino guinea pigs were used and divided into groups depending on the type of the treatment. Neomycin was chosen as tracer for drug release and pharmacodynamic effect. HYA loaded with 3 different concentrations of neomycin was injected to the middle ear cavity of guinea pigs. Phalloidin stained surface preparations of the organ of Corti were used to estimate hair cell loss induced by neomycin. The thickness of the midportion of the RWM was measured and compared with that of controls using light and electron microscopy. All animal procedures were pe rformed in accordance with the ethical standards of Karolinska Institutet. Neomycin induced a considerable hair cell loss in guinea pigs receiving a middle ear injection of HYA loaded with the drug, demonstrating that neomycin was released from the gel and delivered to the inner ear. The resulting hair cell loss showed a clear dose-dependence. Only small differences in hair cell loss were noted between animals receiving neomycin solution and animals exposed to neomycin in HYA suggesting that the vehicle neither facilitated nor hindered drug transport between the middle ear cavity and the inner ear. One week after topical application, the thickness of the RWM had increased and was dependent upon the concentration of neomycin administered to the middle ear. At 4 weeks the thickness of the RWM had returned to normal. HYA is a safe vehicle for drugs aimed to pass into the inner ear through the RWM. Neomycin was released from HYA and transported into the inner ear as evidenced by hair cell loss.

Aminoglycoside-Induced Phosphatidylserine Externalization in Sensory Hair Cells Is Regionally Restricted, Rapid, and Reversible

The aminophospholipid phosphatidylserine (PS) is normally restricted to the inner leaflet of the plasma membrane. During certain cellular processes, including apoptosis, PS translocates to the outer leaflet and can be labeled with externally applied annexin V, a calcium-dependent PS-binding protein. In mouse cochlear cultures, annexin V labeling reveals that the aminoglycoside antibiotic neomycin induces rapid PS externalization, specifically on the apical surface of hair cells. PS externalization is observed within approximately 75 s of neomycin perfusion, first on the hair bundle and then on membrane blebs forming around the apical surface. Whole-cell capacitance also increases significantly within minutes of neomycin application, indicating that blebbing is accompanied by membrane addition to the hair cell surface. PS externalization and membrane blebbing can, nonetheless, occur independently. Pretreating hair cells with calcium chelators, a procedure that blocks mechanotransduction, or overexpressing a phosphatidylinositol 4,5-biphosphate (PIP2)-binding pleckstrin homology domain, can reduce neomycin-induced PS externalization, suggesting that neomycin enters hair cells via transduction channels, clusters PIP2, and thereby activates lipid scrambling. The effects of short-term neomycin treatment are reversible. After neomycin washout, PS is no longer detected on the apical surface, apical membrane blebs disappear, and surface-bound annexin V is internalized, distributing throughout the supranuclear cytoplasm of the hair cell. Hair cells can therefore repair, and recover from, neomycin-induced surface damage. Hair cells lacking myosin VI, a minus-end directed actin-based motor implicated in endocytosis, can also recover from brief neomycin treatment. Internalized annexin V, however, remains below the apical surface, thereby pinpointing a critical role for myosin VI in the transport of endocytosed material away from the periphery of the hair cell.

Optical stimulation of auditory neurons: Effects of acute and chronic deafening

In developing neural prostheses, particular success has been realized with cochlear implants. These devices bypass damaged hair cells in the auditory system and electrically stimulate the auditory nerve directly. In contemporary cochlear implants, however, the injected electric current spreads widely along the scala tympani and across turns. Consequently, stimulation of spatially discrete spiral ganglion cell populations is difficult. In contrast to electrical stimulation, it has been shown that extremely spatially selective stimulation is possible using infrared radiation (e.g. [Izzo, A.D., Su, H.S., Pathria, J., Walsh Jr., J.T., Whitlon, D.S., Richter, C.-P., 2007a. Selectivity of neural stimulation in the auditory system: a comparison of optic and electric stimuli. J. Biomed. Opt. 12, 1–7]). Here, we explore the correlation between surviving spiral ganglion cells, following acute and chronic deafness induced by neomycin application into the middle ear, and neural stimulation using optical radiation and electrical current. In vivo experiments were conducted in gerbils. Before the animals were deafened, acoustic thresholds were obtained and neurons were stimulated with optical radiation at various pulse durations, radiation exposures, and pulse repetition rates. In one group of animals, measurements were made immediately after deafening, while the other group was tested at least four weeks after deafening. Deafness was confirmed by measuring acoustically evoked compound action potentials. Optically and electrically evoked compound action potentials and auditory brainstem responses were determined for different radiation exposures and for different electrical current amplitudes, respectively. After completion of the experiments, the animals were euthanized and the cochleae were harvested for histology. Acoustically evoked compound action potential thresholds were elevated by more than 40 dB after neomycin application in acutely deaf and more than 60 dB in chronically deaf animals. Compound action potential thresholds, which were determined with optical radiation pulses, were not significantly elevated in acutely deaf animals. However, in chronically deaf animals optically evoked CAP thresholds were elevated. Changes correlated with the number of surviving spiral ganglion cells and the optical parameters that were used for stimulation.

1141635071 Suppressor of Cytokine Signalling 3 (SOCS3) controls trophoblast invasion and proliferation

Introduction: Signal Transducer and Activator of Transcription 3 (STAT3) is an intracellular mediator of trophoblast invasion. In other cells, Suppressor Of Cytokine Signalling 3 (SOCS3) is known to be a major antagonist of STAT3 activation. For auto‐regulation and to avoid excessive signals, SOCS3 gene expression is partly induced by STAT3.Methods: The human choriocarcinoma cell line JEG‐3 was used for all experiments. STAT3 expression and STAT3 tyrosine (705) phosphorylation were analyzed by polyacrylamid gele electrophoresis followed by Western blotting. Interleukin‐6 (IL‐6) or Leukemia Inhibitory Factor (LIF) were used for stimulation. SOCS3 expression was silenced by RNA interference. For this approach in a first step, small interfering RNA (siRNA) was used. Subsequently, Jeg‐3 cells were transfected with genes for the respective, self‐designed small hairpin RNA (shRNA), neomycin resistance and green fluorescent protein. Application of neomycin and cell sorting by green fluorescence were used for elimination of non‐transfected cells. Non‐genomic siRNA and shRNA were respectively used for controls. Colorimetric proliferation assays were performed.Results: In IL‐6 stimulated cells, SOCS3 knockdown leads to increased STAT3 tyrosine phosphorylation. After LIF stimulation, proliferation in SOCS3 knockdown cells is significantly higher than in controls. STAT3 expression is not affected by SOCS3 knockdown.Conclusion: SOCS3 plays a major role in intracellular regulation of trophoblast proliferation and invasiveness. The balance of STAT3 and SOCS3 may tune the behavior of invading trophoblast cells.

Disruption and restoration of cell–cell junctions in mouse vestibular epithelia following aminoglycoside treatment

The intracellular junction complexes, which consist of tight junctions (TJ), adherens junctions (AJ), and desmosomes, mediate cell–cell adhesion in epithelial cells. E-cadherin, which is a major component of AJ, plays a role not only in the maintenance of cell–cell junctions, but also in repressing cell proliferation. In this study, we examined changes of E-cadherin expression in mouse vestibular epithelia following local application of neomycin using immunohistochemistry and western blotting, and morphology of cell–cell junctions by transmission electron microscopy (TEM). Immunohistochemistry and western blotting revealed down-expression of E-cadherin and its consecutive recovery. TEM demonstrated temporal disruption of cell–cell junctions. Morphology of cell–cell junctions was more rapidly restored than recovery of E-cadherin expression. Transient disruption of cell–cell junctions and down-expression of E-cadherin is a rational response for the deletion of dying hair cells, and may be associated with a limited capacity for cell proliferations in mammalian vestibular epithelia following their rapid restoration.

Regulation of Cardiac IKs Potassium Current by Membrane Phosphatidylinositol 4,5-Bisphosphate

Regulation of the slowly activating component of delayed rectifier K+ current (IKs) by membrane phospholipid phosphatidylinositol 4,5-bisphosphate (PtdIns-(4,5)P2) was examined in guinea pig atrial myocytes using the whole-cell patch clamp method. IKs was elicited by depolarizing voltage steps given from a holding potential of -50 mV, and the effect of various test reagents on IKs was assessed by measuring the amplitude of tail current elicited upon return to the holding potential following a 2-s depolarization to +30 mV. Intracellular application of 50 microM wortmannin through a recording pipette evoked a progressive increase in IKs over a 10-15-min period to 208.5 +/- 14.6% (n = 9) of initial magnitude obtained shortly after rupture of the patch membrane. Intracellular application of anti-PtdIns(4,5)P2 monoclonal antibody also increased the amplitude of IKs to 198.4 +/- 19.9% (n = 5). In contrast, intracellular loading with exogenous PtdIns(4,5)P2 at 10 and 100 mum produced a marked decrease in the amplitude of IKs to 54.3 +/- 3.8% (n = 5) and 44.8 +/- 8.2% (n = 5), respectively. Intracellular application of neomycin (50 microM) or aluminum (50 microM) evoked an increase in the amplitude of IKs to 161.0 +/- 13.5% (n = 4) and 150.0 +/- 8.2% (n = 4), respectively. These results strongly suggest that IKs channel is inhibited by endogenous membrane PtdIns(4,5)P2 through the electrostatic interaction with the negatively charged head group on PtdIns(4,5)P2. Potentiation of IKs by P2Y receptor stimulation with 50 microM ATP was almost totally abolished when PtdIns(4,5)P2 was included in the pipette solution, suggesting that depletion of membrane PtdIns(4,5)P2 is involved in the potentiation of IKs by P2Y receptor stimulation. Thus, membrane PtdIns(4,5)P2 may act as an important physiological regulator of IKs in guinea pig atrial myocytes.

Signaling pathway for apoptosis of vestibular hair cells of Mice due to aminoglycosides

Previous studies on regeneration of mammalian vestibular hair cells have indicated the potential for self-repair of damaged hair cells. The rescue of damaged hair cells from cell death may therefore increase regenerated hair cells in affected vestibular epithelia. The role of apoptosis in the degradation of vestibular hair cells following aminoglycoside treatment has been elucidated. To seek a method of protecting vestibular hair cells from aminoglycoside toxicity, we examined the apoptosis signaling pathway of vestibular hair cells due to aminoglycoside toxicity. Induction of apoptosis in hair cells of mouse ampullar cristae damaged by local application of neomycin was evaluated by the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) method and transmission electron microscopy (TEM). Immunohistochemistry for apoptosis-related proteins was employed to determine the signaling pathway of apoptosis of hair cells. The occurrence of apoptosis in hair cells was demonstrated by TUNEL staining and TEM. In apoptotic hair cells, activation of caspase-3 and -9, and redistribution of cytochrome c was identified, while there was no expression of activated caspase-8 or apoptosis-inducing factor. In conclusion, these findings indicate that the mitochondria-mediated pathway of apoptosis may play a role in inducing the apoptosis of vestibular hair cells due to aminoglycoside toxicity. Stabilization of the mitochondrial membrane may therefore rescue vestibular hair cells from apoptosis, leading to an increase in self-repaired hair cells in affected vestibular epithelia.

A novel technique for inducing local inner ear damage

With significant development of mouse genomics and the availability of transgenic and knockout mice, the mouse will be the preferred animal model for inner ear research. However, few studies have used mice as experimental animals for examination of hair cell degeneration, because of their relative resistance to ototoxic agents and difficulties in surgical treatment. This study presents a model for induction of apoptotic cell death in sensory epithelia of the mouse inner ear using injection of neomycin into the posterior semicircular canal. Terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) assay revealed that local application of neomycin produced sufficient induction of apoptotic cell death in both auditory and vestibular epithelia over a definite time course. Supplementation of the general caspase-inhibitor significantly reduced induction of TUNEL-positive cells, indicating caspase-dependency of apoptotic cell death observed in the present model. In addition, the approach to the posterior semicircular canal was an easy technique, and sham-operation induced no significant induction of TUNEL-positive cells. This model, hence, enables the use of various genetic tools in studies for mechanisms of hair cell apoptosis.

GEA3162 stimulates Ca 2+ entry in neutrophils

We showed that 5-amino-3-(3,4-dichlorophenyl)1,2,3,4-oxatriazolium (GEA3162), a lipophilic nitric oxide (NO)-releasing agent, induced Ca 2+ entry into rat neutrophils in a concentration-dependent manner, whereas the guanylyl cyclase inhibitors, 6-anilino-5,8-quinolinequinone (LY83583) and 1 H-[1,2,4]oxadiazolo[4,3- a]quinoxalin-1-one (ODQ), had no effect on GEA3162-induced response. The GEA3162-induced Ca 2+ entry was not observed in a Ca 2+-free medium. GEA3162 did not potentiate but reduced the store-emptying activated Ca 2+ entry caused by cyclopiazonic acid. Stimulation of cells with GEA3162 in the absence of extracellular Ca 2+ followed by addition of cations showed that only Ca 2+ but not Ba 2+ and Sr 2+ entry occurs. Store-operated Ca 2+ entry was sensitive to La 3+ and Ni 2+ inhibition, whereas the GEA3162-induced Ca 2+ entry was sensitive to La 3+ but resistant to Ni 2+. cis- N-(2-Phenylcyclopentyl)azacyclotridec-1-en-2-amine (MDL-12,330A) and calyculin A diminished the Ca 2+ entry activated by cyclopiazonic acid as well as by GEA3162. In contrast, 2-aminoethyldiphenyl borate (2-APB) diminished cyclopiazonic acid–but enhanced GEA3162-induced [Ca 2+] i change. Genistein effectively attenuated the cyclopiazonic acid–but slightly inhibited GEA3162-induced [Ca 2+] i change. Application of neomycin and high extracellular Ca 2+ concentration did not induce [Ca 2+] i rise. These data suggest that GEA3162 induced Ca 2+ entry and regulated Ca 2+ signal, through direct protein thiol oxidation. The action of GEA3162 demonstrates characteristics that distinguish it from the store-operated mechanism in neutrophils and therefore is likely to represent an entirely distinct pathway. Extracellular Ca 2+-sensing receptor is not existing in neutrophils.

Effects of neomycin on high-threshold Ca 2+ currents and tetrodotoxin-resistant Na + currents in rat dorsal root ganglion neuron

High-threshold Ca 2+ channels and tetrodotoxin-resistant Na + channels are highly expressed in small dorsal root ganglion neurons. In acutely isolated rat dorsal root ganglion neurons, the effects of neomycin, one of the aminoglycoside antibiotics, on high-threshold Ca 2+ currents and tetrodotoxin-resistant Na + currents were examined using whole-cell patch recording. We showed for the first time that neomycin dose-dependently inhibited peak high-threshold Ca 2+ currents and peak tetrodotoxin-resistant Na + currents with half-maximal inhibitory concentrations at 3.69 μM ( n=20) and 1213.44 μM ( n=25), respectively. Inactivation properties of high-threshold Ca 2+ currents and activation properties of tetrodotoxin-resistant Na + currents were also affected by neomycin with reduction of excitability of small dorsal root ganglion neurons. Half-maximal inactivation voltage of high-threshold Ca 2+ currents was −45.56 mV before and −50.46 mV after application of neomycin ( n=10). Half-maximal activation voltage of tetrodotoxin-resistant Na + currents was −19.93 mV before and −11.19 mV after administration of neomycin ( n=15). These results suggest that neomycin can inhibit high-threshold Ca 2+ currents and tetrodotoxin-resistant Na + currents in small dorsal root ganglion neurons, which may contribute to neomycin-induced peripheral and central analgesia.

Topical Perioperative Antibiotic Prophylaxis for Minor Clean Inguinal Surgery

In minor clean procedures, such as inguinal hernia repair and varicocelectomy, the efficacy of systemic perioperative antibiotic prophylaxis is not well established. To determine the efficacy of topical antibiotic prophylaxis alone in preventing postoperative wound infection in a minor urologic clean procedure, we retrospectively reviewed the medical records of 1,654 patients who had undergone microsurgical varicocelectomy. From September 1985 until December 2000, 1,654 men underwent 2,554 microsurgical varicocelectomies (900 bilateral) by a single surgeon (MG). The skin was shaved and then prepped with standard Betadine gel (Purdue Frederick) that was wiped away with 70% ethanol. No systemic antibiotics were used. The wound was irrigated with 1% neomycin at the moment the incision was made, and then every few minutes until the completion of the procedure, which averaged 45 minutes per side. No postoperative antibiotics were used. No wound infections occurred. No patient developed an adverse reaction to topical application of neomycin. One can conclude that the infection rate in this study is no higher than 0.2% with 95% confidence. Our review of a large series of consecutive clean urologic procedures indicates that by combining a skin preparation of Betadine gel and 70% ethanol with perioperative topical neomycin irrigation at the moment of skin incision, the risk of postoperative wound infection when performing microsurgical varicocelectomy can be effectively reduced to less than 0.2%.

A new aspect of aminoglycoside ototoxicity: impairment of cochlear dopamine release.

Aminoglycoside ototoxicity is a well-documented process via several pathophysiological pathways. The protective role of cochlear dopamine, released from the lateral olivocochlear efferents, was implicated previously in case of ischemia or acoustic trauma, as it postsynaptically inhibits the effect of excessively released glutamate from the hair cells. In our in vitro superfusion experiments we showed that neomycin dose- dependently inhibits the dopamine release from isolated guinea pig cochlea, while gentamicin and kanamycin was ineffective on it. After chronic application of neomycin the dopamine outflow did not change significantly, suggesting an adaptive process. In our experiments we have found a possibly new action site of one of the aminoglycoside antibiotics, neomycin.

Actions of neomycin on electrical light responses, Ca 2+ release, and intracellular Ca 2+ changes in photoreceptors of the honeybee drone

Neomycin, known to inhibit phospholipase C-mediated IP3 formation, was applied in the bath or injected into cells and its effects on electrical light responses were analyzed. Neomycin effects on inositol 1,4,5-trisphosphate- and Ca2+-induced Ca2+ release from the endoplasmic reticulum and/or the light-induced Ca2+ elevation were also studied. Neomycin (0.5 mmol x l(-1)) blocked inositol 1,4,5-trisphosphate-, caffeine-, and Ca2+-induced Ca2+ release. Bath application of neomycin decreased the sensitivity to 20-ms light flashes by a factor of up to 100 and slowed the kinetics of dim flash responses. Intracellularly injected neomycin desensitized the photoreceptors more than 1 log unit, increased the latency, and slowed the rate of rise of the light response. Neomycin (0.5 mmol x l(-1)) in the bath delayed and reduced the transient component of responses to 1-s steps of light at intermediate intensities. It also decreased and slowed the light-induced, and it blocked the caffeine-induced intracellular Ca2+ elevation. The combined pharmacological effects of neomycin are suggested to decrease the Ca2+-mediated amplification of the phototransduction cascade and the Ca2+-mediated acceleration of processes determining the kinetics of light responses.

Light-dependent repetitive Ca2+ spikes induced by extracellular application of neomycin in honeybee drone photoreceptors.

Photoreceptor cells of the honeybee drone fire, in the presence of the polycationic aminoglycoside neomycin, repetitive slow spike-like potentials superimposed on the receptor potential plateau phase. We have used conventional intracellular recordings and microfluorometric intracellular Ca2+ measurements to characterize these spike potentials. We have shown that the spike frequency increases in a light-intensity-dependent manner. The spikes are fired only when light stimuli depolarize the cell from a resting potential of -50 to -60 mV to at least -40 to -45 mV; they are tetrodotoxin insensitive and blocked by the Ca2+ channel blockers Ni2+, Cd2+, omega-agatoxin TK, verapamil and methoxyverapamil. Depolarization of the photoreceptors with high extracellular K+ in the presence of neomycin in darkness does not generate spikes. Small intracellular Ca2+ oscillations superimposed on the plateau phase of the light-induced increase in intracellular free Ca2+ concentration have a similar temporal pattern as the spike-like potentials. We conclude that the spike-like potentials require stimulation by light and are generated by voltage-dependent Ca2+ channels localized on the soma of the photoreceptors, distal to the basal lamina.