Effect of some simple manoeuvres on the course of acute renal failure after gentamycin treatment in rats

Fenofibrate exerts protective effects against gentamicin-induced toxicity in cochlear hair cells by activating antioxidant enzymes

Fenofibrate, an activator of peroxisome proliferator-activated receptors (PPARs), has been shown to protect the kidneys and brain cells from oxidative stress; however, its role in preventing hearing loss has not been reported to date, at least to the best of our knowledge. In this study, we demonstrated the protective effects of fenofibrate against gentamicin (GM)-induced ototoxicity. We found that the auditory brainstem response threshold which was increased by GM was significantly reduced by pre-treatment with fenofibrate in rats. In cochlear explants, the disruption of hair cell layers by GM was also markedly attenuated by pre-treatment with fenofibrate. In addition, fenofibrate almost completely abolished GM-induced reactive oxygen species generation, which seemed to be mediated at least in part by the restoration of the expression of PPAR-α-dependent antioxidant enzymes, including catalase and superoxide dismutase (SOD)-1. Of note, fenofibrate markedly increased the expression of heme oxygenase-1 (HO-1) which was also induced to a certain degree by GM alone. The induced expression of HO-1 by fenofibrate appeared to be essential for mediating the protective effects of fenofibrate, as the inhibition of HO-1 activity significantly diminished the protective effects of fenofibrate against the GM-mediated death of sensory hair cells in cochlea explant culture, as well as in zebrafish neuromasts. These results suggest that fenofibrate protects sensory hair cells from GM-induced toxicity by upregulating PPAR-α-dependent antioxidant enzymes, including HO-1. Our results provide insight into the preventive therapy for hearing loss caused by aminoglycoside antibiotics.

Amphiphilic Aminoglycoside Antimicrobials in Antibacterial Discovery

Amphiphilic aminoglycoside antimicrobials (AAAs) are an emerging class of polycationic antibacterial agents with broad-spectrum antibacterial activity. In contrast to aminoglycosides, which interfere with protein synthesis by interacting with the 30S ribosomal subunit, AAAs appear to target the bacterial cell wall by interactions with extracellular lipids or proteins or by enhancing the permeability of the bacterial cell wall. The physicochemical similarities between amphiphilic aminoglycosides and antimicrobial peptides, another class of polycationic amphiphiles with broad-spectrum antibacterial activity, suggest similar mode(s) of action. However, in contrast to antimicrobial peptides, AAAs are not composed of peptide bonds and as such promise to display superior metabolic stability. As a result, AAAs may be considered to be a novel class of antimicrobial peptidomimetics. Many AAAs possess impressive potent antibacterial activity against Gram-positive and Gram-negative bacteria, especially against bacterial strains that are resistant to clinically used antibiotics. In summary, AAAs promise to provide a new and rich source of antibacterial lead structures to combat antibiotic-resistant and multidrug-resistant pathogens.

New developments in aminoglycoside therapy and ototoxicity

After almost seven decades in clinical use, aminoglycoside antibiotics still remain indispensible drugs for acute infections and specific indications such as tuberculosis or the containment of pseudomonas bacteria in patients with cystic fibrosis. The review will describe the pathology and pathophysiology of aminoglycoside-induced auditory and vestibular toxicity in humans and experimental animals and explore contemporary views of the mechanisms of cell death. It will also outline the current state of protective therapy and recent advances in the development of aminoglycoside derivatives with low toxicity profiles for antimicrobial treatment and for stop-codon suppression in the attenuation of genetic disorders.

Reactive oxygen species and the pathogenesis of radiocontrast-induced nephropathy

Experimental findings in vitro and in vivo illustrate enhanced hypoxia and the formation of reactive oxygen species (ROS) within the kidney following the administration of iodinated contrast media, which may play a role in the development of contrast media-induced nephropathy. Clinical studies indeed support this possibility, suggesting a protective effect of ROS scavenging or reduced ROS formation with the administration of N-acetyl cysteine and bicarbonate infusion, respectively. Furthermore, most risk factors, predisposing to contrast-induced nephropathy are prone to enhanced renal parenchymal hypoxia and ROS formation. In this review, the association of renal hypoxia and ROS-mediated injury is outlined. Generated during contrast-induced renal parenchymal hypoxia, ROS may exert direct tubular and vascular endothelial injury and might further intensify renal parenchymal hypoxia by virtue of endothelial dysfunction and dysregulation of tubular transport. Preventive strategies conceivably should include inhibition of ROS generation or ROS scavenging.

Possible mechanism for the anemia induced by candesartan cilexetil (TCV-116), an angiotensin II receptor antagonist, in rats

Candesartan cilexetil (TCV-116), an angiotensin II receptor antagonist, was administered orally to male F344/Jcl and Crj:CD (SD) rats at 1000 mg kg(-1) day(-1) for 1-28 days, and the possible mechanism for the anemia induced by TCV-116 was investigated. In the TCV-116 group, the erythrocyte count, hematocrit value and hemoglobin concentration were decreased by 7-8% as compared with the values in the control group after dosing for 28 days. The plasma and renal erythropoietin levels, the reticulocyte count in the peripheral blood and the erythroid cell count upon bone marrow examination were decreased on day 7, but there were no accompanying histopathological renal lesions. Renal blood flow was increased, and mean blood pressure was decreased after TCV-116. These results suggest that the primary cause of the anemia induced by TCV-116 treatment is the increase in renal blood flow followed by a decrease in erythropoietin production.

Effect of recombinant human erythropoietin on new anaemic model rats induced by gentamicin

The effects of recombinant human erythropoietin (r-HuEPO) on haematological parameters were studied in rats in which uraemia and anaemia had been induced by gentamicin, an aminoglycoside antibiotic and a nephrotoxic agent. After the occurrence of slight polycythaemia, the red blood cell count, haematocrit and haemoglobin concentration decreased by 20-30% compared with those of the control (saline-injected) rats. At the end of gentamicin treatment, the endogenous serum EPO level had decreased to about 40% compared with that of control rats. Gentamicin-treated rats showed marked elevation of blood urea nitrogen, extensive tubular necrosis in the kidney and haemosiderin deposition in the spleen. In the osmotic fragility test, the fragility of erythrocytes significantly increased compared with that of control rats. These findings indicate that the anaemia induced by gentamicin is due not only to a deficiency of EPO but also to an enhancement of fragility of erythrocytes in an azotaemic environment. The administration of r-HuEPO during anaemia markedly increased red blood cell count, haematocrit and haemoglobin concentration. It is suggested that a gentamicin-treated rat is a useful and convenient anaemic model and r-HuEPO is useful for treatment of anaemia in acute renal failure.

Effects of dietary electrolyte supplementation on gentamicin nephrotoxicity

The effects of electrolyte supplementation via drinking solutions on gentamicin-induced nephrotoxicity were studied in rats. Four groups of animals were injected with gentamicin, 120 mg/kg daily for 5 days and were studied 2-4 days after the last injection. Electrolyte supplements were begun before the gentamicin injections and were continued throughout the study. The drinking solutions were tap water, NaCl, NaCl + KCl, or NaHCO3 + KHCO3 + diamox. At the end of the study, blood urea nitrogen (BUN) and serum creatinine were markedly increased only in the group receiving tap water. Nevertheless, 24 hour creatinine clearance in awake rats and inulin clearance in anesthetized rats were found to be severely reduced in all gentamicin-treated animals. However, the rats receiving NaHCO3 + KHCO3 + diamox had significantly higher creatinine clearance than all other experimental groups. Proximal intratubular free-flow pressure, measured by micropuncture, and internal proximal diameters were significantly increased above normal controls in all groups, but were least abnormal in the rats receiving HCO3- and diamox. Semiquantitative histologic evaluation revealed significantly less tubular necrosis and cast formation in this group than in all the other experimental groups. The observations suggest that dietary sodium, potassium, and chloride supplements, even accompanied by large fluid intake, provide relatively little protection against gentamicin nephrotoxicity. In contrast, HCO3- and diamox supplements resulted in significant, albeit incomplete, protection of GFR and renal histology.