Amphotericin B severely affects expression and activity of the endothelial constitutive nitric oxide synthase involving altered mRNA stability

Regulation of renal nitric oxide and eNOS/iNOS expression by tadalafil participates in the mitigation of amphotericin B-induced renal injury: Down-regulation of NF-κB/iNOS/caspase-3 signaling

Amphotericin B (AmB)-induced acute kidney injury (AKI) is a common health problem having an undesirable impact on its urgent therapeutic utility for fatal systemic fungal infections. Tadalafil (TAD), a phosphodiesterase-5 (PDE-5) inhibitor, has been observed to have a wide range of pharmacological actions, including nephroprotection. The study's objective was to examine the possible underlying protective mechanism of TAD against AmB-induced nephrotoxicity. Experimentally, animals were divided randomly into four groups: control, TAD (5 mg/kg/day; p.o.), AmB (18.5 mg/kg/day; i.p.), and TAD+AmB groups. Sera and tissue samples were processed for biochemical, molecular, and histological analyses. The biochemical investigations showed that TAD significantly ameliorated the increase of kidney function biomarkers (creatinine, urea, CysC, KIM-1) in serum, renal nitric oxide (NO), lipid peroxidation (MDA), and inflammatory cytokines (TNF-α, IL-6) in AmB-treated rats. Meanwhile, TAD significantly retarded AmB-induced decrease in serum magnesium, sodium, potassium, and renal glutathione content. Molecular analysis revealed that TAD reduced AmB-induced imbalance in the protein expression of eNOS/iNOS, which explains its regulatory effect on renal NO content. These results were also supported by the down-regulation of nuclear NF-κB p65 and cleaved caspase-3 protein expressions, as well as the improvement of histological features by TAD in AmB-treated rats. Therefore, it can be suggested that TAD could be a promising candidate for renoprotection against AmB-induced AKI. That could be partly attributed to its regulatory effect on renal eNOS/iNOS balance and NO, the inhibition of NF-κB p65 nuclear translocation, its downstream inflammatory cytokines and iNOS, and ultimately the inhibition of caspase-3-induced renal apoptosis.

Antifungal agents and the kidney: pharmacokinetics, clinical nephrotoxicity, and interactions

INTRODUCTION

Invasive fungal infections continue to be important causes of morbidity and mortality in severely ill and immunocompromised patient populations. The past three decades have seen a considerable expansion in antifungal drug research, resulting in the clinical development of different classes of antifungal agents with different pharmacologic properties. Among drug-specific characteristics of antifungal agents, renal disposition and nephrotoxicity are important clinical considerations as many patients requiring antifungal therapy have compromised organ functions or are receiving other potentially nephrotoxic medications.

AREAS COVERED

The present article reviews incidence, severity and mechanisms of nephrotoxicity associated with antifungal agents used for prevention and treatment of invasive fungal diseases by discussing distribution, metabolism, elimination and drug-related adverse events in the context of safety data from phase II and III clinical studies.

EXPERT OPINION

Based on the available data amphotericin B deoxycholate has the highest relative potential for nephrotoxicity, followed by the lipid formulations of amphotericin B, and, to a much lesser extent and by indirect mechanisms, the antifungal triazoles.

Assessment of the mutagenic, recombinogenic, and carcinogenic potential of amphotericin B in somatic cells of Drosophila melanogaster

Amphotericin B (AmB) is an antifungal antibiotic extracted from Streptomyces nodosus. Its fungicidal activity depends primarily on its binding to the sterol group that is present in fungal membranes. In view of the toxicity of this drug, the purpose of this study was to evaluate its mutagenic, carcinogenic, and recombinogenic activity, based on the wing somatic mutation and recombination test (SMART) and the epithelial tumor detection test (wts) applied to Drosophila melanogaster. Larvae were chronically treated with different concentrations of AmB (0.01, 0.02, and 0.04 mg/mL). The results revealed that AmB is a promutagen exhibiting increase in the number of spots on individuals from high bioactivation (HB) cross with a high level of cytochrome P450. The results also indicate that the main genotoxic event induced by AmB is recombinogenicity. Homologous recombination can act as a determinant at different stages of carcinogenesis. For verification of carcinogenic potential of this compound, larvae from the wts/mwh and wts/ORR, flr³ were treated with the same three AmB concentrations used in the SMART assay. The results did not provide evidence that AmB has carcinogenic potential in wts/mwh individuals. However, individuals from wts/ORR, flr³ developed tumors at the highest concentration tested.

It only takes one to do many jobs: Amphotericin B as antifungal and immunomodulatory drug

“Amphotericin B acts through pore formation at the cell membrane after binding to ergosterol” is an accepted dogma about the action mechanism of this antifungal, and this sentence is widely found in the literature. But after 60 years of investigation, the action mechanism of Amphotericin B is not fully elucidated. Amphotericin B is a polyene substance that is one of the most effective drugs for the treatment of fungal and parasite infections. As stated above, the first mechanism of action described was pore formation after binding to the ergosterol present in the membrane. But it has also been demonstrated that AmB induces oxidative damage in the cells. Moreover, amphotericin B modulates the immune system, and this activity has been related to the protective effect of the molecule, but also to its toxicity in the host. This review tries to provide a general overview of the main aspects of this molecule, and highlight the multiple effects that this molecule has on both the fungal and host cells.

Amphotericin B membrane action: role for two types of ion channels in eliciting cell survival and lethal effects

The formation of aqueous pores by the polyene antibiotic amphotericin B (AmB) is at the basis of its fungicidal and leishmanicidal action. However, other types of nonlethal and dose-dependent biphasic effects that have been associated with the AmB action in different cells, including a variety of survival responses, are difficult to reconcile with the formation of a unique type of ion channel by the antibiotic. In this respect, there is increasing evidence indicating that AmB forms nonaqueous (cation-selective) channels at concentrations below the threshold at which aqueous pores are formed. The main foci of this review will be (1) to provide a summary of the evidence supporting the formation of cation-selective ion channels and aqueous pores by AmB in lipid membrane models and in the membranes of eukaryotic cells; (2) to discuss the influence of membrane parameters such as thickness fluctuations, the type of sterol present and the existence of sterol-rich specialized lipid raft microdomains in the formation process of such channels; and (3) to develop a cell model that serves as a framework for understanding how the intracellular K(+) and Na(+) concentration changes induced by the cation-selective AmB channels enhance multiple survival response pathways before they are overcome by the more sustained ion fluxes, Ca(2+)-dependent apoptotic events and cell lysis effects that are associated with the formation of AmB aqueous pores.

Acute amphotericin B overdose

OBJECTIVE

To report the clinical course of a woman with cryptococcal meningitis and no previous cardiac disease who developed a fatal cardiac arrhythmia after an acute overdose of amphotericin B and to review its toxicity.

CASE SUMMARY

A 41-year-old woman with a history of proliferative glomerulonephritis from systemic lupus erythematosus was admitted with a diagnosis of cryptococcal meningitis. Liposomal amphotericin B was prescribed at the standard dose of 5 mg/kg/day; however, amphotericin B deoxycholate 5 mg/kg was inadvertently administered (usual dose of the deoxycholate formulation is 0.5-0.8 mg/kg/day). The patient developed cardiac arrhythmias, acute renal failure, and anemia. The medication error was noticed after she had received 2 doses of amphotericin B deoxycholate, and it was then discontinued. Despite treatment in the intensive care unit, the woman died on the sixth day after admission.

DISCUSSION

Amphotericin B deoxycholate has been reported to produce significant cardiac toxicity, with ventricular arrhythmias and bradycardia reported in overdoses in children and in adults with preexisting cardiac disease, even when administered in conventional dosages and infusion rates. Use of the Naranjo probability scale indicated a highly probable relationship between the observed cardiac toxicity and amphotericin B deoxycholate therapy in this patient.

CONCLUSIONS

Given the fulminant course of amphotericin B deoxycholate overdosage and lack of effective therapy, stringent safeguards against its improper administration should be in place.

Recent advances in the understanding of the role of nitric oxide in cardiovascular homeostasis

Nitric oxide synthases (NOS) are the enzymes responsible for nitric oxide (NO) generation. To date, 3 distinct NOS isoforms have been identified: neuronal NOS (NOS1), inducible NOS (NOS2), and endothelial NOS (NOS3). Biochemically, NOS consists of a flavin-containing reductase domain, a heme-containing oxygenase domain, and regulatory sites. NOS catalyse an overall 5-electron oxidation of one Nomega-atom of the guanidino group of L-arginine to form NO and L-citrulline. NO exerts a plethora of biological effects in the cardiovascular system. The basal formation of NO in mitochondria by a mitochondrial NOS seems to be one of the main regulators of cellular respiration, mitochondrial transmembrane potential, and transmembrane proton gradient. This review focuses on recent advances in the understanding of the role of enzyme and enzyme-independent NO formation, regulation of NO bioactivity, new aspects of NO on cardiac function and morphology, and the clinical impact and perspectives of these recent advances in our knowledge on NO-related pathways.

The antifungal drug amphotericin B promotes inflammatory cytokine release by a Toll-like receptor- and CD14-dependent mechanism

Amphotericin B is the most effective drug for treating many life-threatening fungal infections. Amphotericin B administration is limited by infusion-related toxicity, including fever and chills, an effect postulated to result from proinflammatory cytokine production by innate immune cells. Because amphotericin B is a microbial product, we hypothesized that it stimulates immune cells via Toll-like receptors (TLRs) and CD14. We show here that amphotericin B induces signal transduction and inflammatory cytokine release from cells expressing TLR2 and CD14. Primary murine macrophages and human cell lines expressing TLR2, CD14, and the adapter protein MyD88 responded to amphotericin B with NF-kappaB-dependent reporter activity and cytokine release, whereas cells deficient in any of these failed to respond. Cells mutated in TLR4 were less responsive to amphotericin B stimulation than cells expressing normal TLR4. These data demonstrate that TLR2 and CD14 are required for amphotericin B-dependent inflammatory stimulation of innate immune cells and that TLR4 may also provide stimulation of these cells. Our results provide a putative molecular basis for inflammatory responses elicited by amphotericin B and suggest strategies to eliminate the acute toxicity of this drug.

Antileishmanial drugs cause up-regulation of interferon-gamma receptor 1, not only in the monocytes of visceral leishmaniasis cases but also in cultured THP1 cells

Apparently for the first time, the peripheral blood monocytes of individuals with active visceral leishmaniasis (VL) have been found to show reduced expression of interferon gamma receptor-1 (IFNGR1). Since interferon gamma is the main cytokine responsible for defence against leishmanial parasites, it was thought possible that effective antileishmanial drugs may up-regulate IFNGR1. Confocal microscopy confirmed that monocytes from VL patients who had been treated, with sodium antimony gluconate (SAG), did display IFNGR1 up-regulation. To see if this effect could be mimicked in vitro, IFNGR1 expression was investigated using a human macrophage cell line (THP1), northern blotting and confocal microscopy. When the THP1 cells were treated with SAG or pentamidine, their expression of the receptor was increased. This drug-induced up-regulation was more intense if the macrophages were infected with Leishmania donovani than if they were left uninfected. The possibility that at least some antileishmanial drugs act by up-regulating IFNGR1 expression needs to be explored further. A good model for investigating the mechanisms of action of antileishmanial drugs might be based on the THP1 cell line.

Acute renal failure: is nitric oxide the bad guy?

Nephrotoxicity is a major side effect in clinical practice, frequently leading to acute renal failure (ARF). Many physiological mechanisms have been implicated in drug-induced renal injury. Currently, nitric oxide (NO) is considered to be an important regulator of renal vascular tone and a modulator of glomerular function under both basal and physiopathological conditions. Historically, NO has been implicated in ARF and, after its discovery, several publications have suggested that changes in NO production could play an important role in the hemodynamic alterations observed in ARF. In this review, we evaluate the participation of NO in ARF and summarize many of the findings in this research area in an attempt to elucidate the role of NO in ARF.

Revisiting an old antimicrobial drug: amphotericin B induces interleukin-1-converting enzyme as the main factor for inducible nitric-oxide synthase expression in activated endothelia

We have investigated the impact of the widely used antifungal agent Amphotericin B (AmB) on cytokine activated aortic endothelial cells (AEC) and their inflammatory response as monitored by cytokine and inducible nitric-oxide synthase (iNOS) expression as well as high-output nitric oxide synthesis. Because both blood-borne infections and systemically administered drugs will first encounter vessel lining endothelial cells, this cell type represents an important participant in innate immune reactions against xenobiotics. Culturing cytokine-activated AEC in the presence of 1.25 microg/ml AmB, a concentration equivalent to serum levels during patient treatment, we find increases in iNOS promoter activity up to 120%, in iNOS mRNA or protein expressions by factors of up to 3.5 +/- 1.1, and in iNOS activity of up to 180% compared with cells with cytokines only. In parallel, a strong increase in endothelial interleukin (IL)-1beta-converting enzyme (ICE) and IL-1beta expression and activity was observed. Specific inhibition of ICE activity or IL-1beta functionality significantly reduces expression and activity of the iNOS to control values. Because ICE activity is essential for the endogenous synthesis of active IL-1beta, ICE overexpression represents the key signal in the AmB-induced and IL-1beta-mediated effects on iNOS activity. In summary, in endothelial cells, AmB strongly augments cytokine-induced iNOS expression and activity by increasing the expression and activity of the ICE. This adjuvant activity for augmented endogenous cytokine processing adds to the efficacy of the antimycotic activity of AmB. Furthermore, our data underline the relevance of the endothelial iNOS as a potent effector of the innate immune system.

Physiological mechanisms regulating the expression of endothelial-type NO synthase

Although endothelial nitric oxide synthase (eNOS) is a constitutively expressed enzyme, its expression is regulated by a number of biophysical, biochemical, and hormonal stimuli, both under physiological conditions and in pathology. This review summarizes the recent findings in this field. Shear stress, growth factors (such as transforming growth factor-beta, fibroblast growth factor, vascular endothelial growth factor, and platelet-derived growth factor), hormones (such as estrogens, insulin, angiotensin II, and endothelin 1), and other compounds (such as lysophosphatidylcholine) upregulate eNOS expression. On the other hand, the cytokine tumor necrosis factor-alpha and bacterial lipopolysaccharide downregulate the expression of this enzyme. The growth status of cells, the actin cytoskeleton, and NO itself are also important regulators of eNOS expression. Both transcriptional and posttranscriptional mechanisms are involved in the expressional regulation of eNOS. Different signaling pathways are involved in the regulation of eNOS promoter activity and eNOS mRNA stability. Changes in eNOS expression and activity under pathophysiological conditions and the pharmacological modulation of eNOS expression are subject of a subsequent brief review (part 2) to be published in the next issue of this journal.