“Subclinical” gentamicin nephrotoxicity: a potential risk factor for exaggerated endotoxin-driven TNF-α production

Podocin, mTOR, and CHOP dysregulation contributes to nephrotoxicity induced of lipopolysaccharide/diclofenac combination in rats: Curcumin and silymarin could afford protective effect

AIM

Sepsis is a common cause of acute kidney injury (AKI). Lipopolysaccharides (LPS) are the main gram-negative bacterial cell wall component with a well-documented inflammatory impact. Diclofenac (DIC) is a non-steroidal anti-inflammatory drug with a potential nephrotoxic effect. Curcumin (CUR) and silymarin (SY) are natural products with a wide range of pharmacological activities, including antioxidant and anti-inflammatory ones. The objective of this study was to examine the protective impact of CUR and SY against kidney damage induced by LPS/DIC co-exposure.

MATERIALS AND METHODS

Four groups of rats were used; control; LPS/DIC, LPS/DIC + CUR, and LPS/DIC + SY group. LPS/DIC combination induced renal injury at an LPS dose much lower than a nephrotoxic one.

KEY FINDING

Nephrotoxicity was confirmed by histopathological examination and significant elevation of renal function markers. LPS/DIC induced oxidative stress in renal tissues, evidenced by decreasing reduced glutathione and superoxide dismutase, and increasing lipid peroxidation. Inflammatory response of LPS/DIC was associated with a significant increase of renal IL-1β and TNF-α. Treatment with either CUR or SY shifted measured parameters to the opposite side. Moreover, LPS/DIC exposure was associated with upregulation of mTOR and endoplasmic reticulum stress protein (CHOP) and downregulation of podocin These effects were accompanied by reduced gene expression of cystatin C and KIM-1. CUR and SY ameliorated LPS/DIC effect on the aforementioned genes and protein significantly.

SIGNIFICANCE

This study confirms the potential nephrotoxicity; mechanisms include upregulation of mTOR, CHOP, cystatin C, and KIM-1 and downregulation of podocin. Moreover, both CUR and SY are promising nephroprotective products against LPS/DIC co-exposure.

Arjunolic acid: a new multifunctional therapeutic promise of alternative medicine

IMPORTANCE OF THE FIELD

In recent years, a number of studies describing the effective therapeutic strategies of medicinal plants and their active constituents in traditional medicine have been reported. Indeed, tremendous demand for the development and implementation of these plant derived biomolecules in complementary and alternative medicine is increasing and appear to be promising candidates for pharmaceutical industrial research. These new molecules, especially those from natural resources, are considered as potential therapeutic targets, because they are derived from commonly consumed foodstuff and are considered to be safe for humans.

AREAS COVERED IN THIS REVIEW

This review highlights the beneficial role of arjunolic acid, a naturally occurring chiral triterpenoid saponin, in various organ pathophysiology and the underlying mechanism of its protective action. Studies on the biochemistry and pharmacology suggest the potential use of arjunolic acid as a novel promising therapeutic strategy.

WHAT THE READERS WILL GAIN

The multifunctional therapeutic application of arjunolic acid has already been documented by its various biological functions including antioxidant, anti-fungal, anti-bacterial, anticholinesterase, antitumor, antiasthmatic, wound healing and insect growth inhibitor activities. The scientific basis behind its therapeutic application as a cardioprotective agent in traditional medicine is justified by its ability to prevent myocardial necrosis and apoptosis, platelet aggregation, coagulation and lowering of blood pressure, heart rate, as well as cholesterol levels. Its antioxidant property coupled with metal chelating property (by its two hydroxyl groups) protects different organs from metal and drug-induced organ pathophysiology. Arjunolic acid also plays a beneficial role in the pathogenesis of diabetes and its associated complications. The mechanism of cytoprotection of arjunolic acid, at least in part, results from the detoxification of reactive oxygen species (ROS) produced in the respective pathophysiology. In addition to its other biological functions, it also possesses vibrant insecticidal properties and it has the potential to be used as a structural molecular framework for the design of molecular receptors in the general area of supramolecular chemistry and nanochemistry. Esters of arjunolic acid function as organogelators which has wide application in designing thermochromic switches and sensor devices. Arjunolic acid derived crown ether is an attractive candidate for the design of molecular receptors, biomimetics and supramolecular systems capable of performing some biological functions.

HOME MESSAGE

This review would provide useful information about the recent progress of natural product research in the domain of clinical science. This review also aims to untie the multifunctional therapeutic application of arjunolic acid, a nanometer-long naturally occurring chiral triterpenoid biomolecule.

Mammalian target of rapamycin complex 2 regulates inflammatory response to stress

OBJECTIVE AND DESIGN

To explore the role of mammalian target of rapamycin 2 (mTORC2) in the activation of inflammatory and oxidative responses in rodent models of acute injury and metabolic stress.

MATERIAL

The impact of nephrilin, an inhibitor of mTORC2 complex, was assessed in three CD-1 mouse models of acute xenobiotic stress and in a hypertensive Dahl rat model of metabolic stress.

METHODS

Animals received daily subcutaneous bolus injections of saline or 4 mg/kg nephrilin. Tissues were assayed by ELISA, gene arrays and immunohistochemical staining.

RESULTS

Nephrilin significantly inhibited elevations in plasma tumor necrosis factor-alpha, kidney substance P, and CX3CR1, and urinary lipocalin-2 [urinary neutrophil gelatinase-associated lipocalin (uNGAL)] in models of acute xenobiotic stress. UCHL1 gene expression levels dropped and plasma HMGB1 levels rose in the rhabdomyolysis model. Both effects were reversed by nephrilin. The inhibitor also blocked diet-induced elevations of uNGAL and albumin-creatinine ratio (UACR) as well as kidney tissue phosphorylation of PKC-beta-2-T641 and p66shc-S36, and reduced dark ring-like staining of nuclei by anti-phos-p66shc-S36 antibody in frozen sections of diseased kidneys from hypertensive Dahl rats fed an 8 % NaCl diet for 4 weeks.

CONCLUSIONS

Taken together, our results suggest a role for mTORC2 in the inflammatory-oxidative responses to stress.

Acetaminophen induced renal injury via oxidative stress and TNF-alpha production: therapeutic potential of arjunolic acid

Acetaminophen (APAP) causes acute and chronic renal failure. The mechanisms leading to hepatic injury have been extensively studied, but the molecular mechanisms regarding APAP-induced nephro-toxicity are poorly defined. In earlier studies, we have demonstrated that arjunolic acid (AA) possesses protective roles against chemically induced organ pathophysiology. The purpose of the present study was to explore whether AA plays any protective role against APAP induced acute renal toxicity; and if so, what pathways it utilizes for the mechanism of its protective action. Exposure of rats with a nephro-toxic dose of APAP altered a number of biomarkers (like blood urea nitrogen and serum creatinine levels, etc.) related to renal oxidative stress, decreased antioxidant activity, elevated renal tumor necrosis factor-alpha and nitric oxide levels. AA treatment both pre- and post to APAP exposure protected the alteration of these biomarkers, compensated deficits in the antioxidant defense mechanisms, and suppressed lipid peroxidation in renal tissue. Investigating the inherent molecular signaling of this pathophysiology and its protection, we found that the mitochondrial pathway was not activated during APAP-induced cell death as no dissipation of mitochondrial membrane potential or release of cytochrome C was detected in the respective experiments. Our experimental evidence suggests that APAP-induced nephro-toxicity is a caspase-dependent process that involves activation of caspase-9 and caspase-3 in the absence of cytosolic cytochrome C release. These results provide evidence that inhibition of NO overproduction and maintenance of intracellular antioxidant status may play a pivotal role in the protective effects of AA against APAP-induced renal damage. AA represents a potential therapeutic option to protect renal tissue from the detrimental effects of acute acetaminophen overdose.

Therapeutic potential of hemin in acetaminophen nephrotoxicity in rats

The therapeutic potential of hemin, the heme oxygenase-1 inducer, was investigated against renal damage induced by acute acetaminophen overdose in rats. Nephrotoxicity was induced by a single oral dose of acetaminophen (2.5g/kg). Hemin was given as a single s.c. injection (40μmol/kg), 1h following acetaminophen administration. Hemin treatment restored blood urea nitrogen and serum creatinine levels that were elevated by acetaminophen. Hemin also compensated deficits in the antioxidant defense mechanisms (reduced glutathione, and catalase and superoxide dismutase activities), and suppressed lipid peroxidation in renal tissue resulted from acetaminophen administration. Hemin attenuated the acetaminophen-induced elevations in renal tumor necrosis factor-α and nitric oxide levels, and caspase-3 activity. Additionally, hemin ameliorated acetaminophen-induced renal damage observed by light microscopic examination. The therapeutic effect afforded by hemin was abolished by prior administration of zinc protoporphyrin-IX, the heme oxygenase-1 inhibitor. It was concluded that hemin represents a potential therapeutic option to protect renal tissue from the detrimental effects of acute acetaminophen overdose.

Endotoxin mediates recruitment of RNA polymerase II to target genes in acute renal failure

Acute renal failure (ARF) sensitizes the kidney to endotoxin (LPS)-driven production of cytokines and chemokines. This study assessed whether this LPS hyperresponsiveness exists at the genomic level. Three heterogeneous mouse models of ARF were studied: Maleate nephrotoxicity, unilateral ureteral obstruction, and LPS preconditioning. In all cases, LPS was injected approximately 18 h after injury was induced, and over the next 0 to 90 min, RNA polymerase II recruitment to the genome at three LPS-responsive genes (TNF-alpha, monocyte chemoattractant-1 [MCP-1], and heme oxygenase-1 [HO-1]) was assessed by chromatin immunoprecipitation. LPS hyperresponsiveness was noted in each model, measured by exaggerated increases in TNF-alpha and MCP-1 mRNA (approximately two to 10 times higher than LPS-injected controls). Corresponding increases in the recruitment of RNA polymerase II to the TNF-alpha and MCP-1 genes were observed, and increased trimethylation of histone 3 lysine 4 (H3K4m3) at these sites may have played a role in this recruitment. Conversely, recruitment of RNA polymerase II to the HO-1 gene was suppressed ("tolerance"), and no increase in H3K4m3 was observed at HO-1 exons. The ARF-induced changes in mRNA did not correlate with mRNA stability, suggesting the mechanistic importance of RNA polymerase II-mediated transcriptional events. In conclusion, LPS hyperresponsiveness after ARF is likely mediated at the genomic level, possibly by H3K4m3.

Gentamicin suppresses endotoxin-driven TNF-alpha production in human and mouse proximal tubule cells

Gentamicin is a mainstay in treating gram-negative sepsis. However, it also may potentiate endotoxin (LPS)-driven plasma TNF-alpha increases. Because gentamicin accumulates in renal tubules, this study addressed whether gentamicin directly alters LPS-driven tubular cell TNF-alpha production. HK-2 proximal tubular cells were incubated for 18 h with gentamicin (10-2,000 microg/ml). Subsequent LPS-mediated TNF-alpha increases (at 3 or 24 h; protein/mRNA) were determined. Gentamicin effects on overall protein synthesis ([(35)S]methionine incorporation), monocyte chemoattractant protein-1 (MCP-1) levels, and LPS-stimulated TNF-alpha generation by isolated mouse proximal tubules also were assessed. Finally, because gentamicin undergoes partial biliary excretion, its potential influence on gut TNF-alpha/MCP-1 mRNAs was probed. Gentamicin caused striking, dose-dependent inhibition of LPS-driven TNF-alpha production (up to 80% in HK-2 cells/isolated tubules). Surprisingly, this occurred despite increased TNF-alpha mRNA accumulation. Comparable changes in MCP-1 were observed. These changes were observed at clinically relevant gentamicin concentrations and despite essentially normal overall protein synthetic rates. Streptomycin also suppressed LPS-driven TNF-alpha increases, suggesting an aminoglycoside drug class effect. Gentamicin doubled basal TNF-alpha mRNA in cecum and in small intestine after LPS. Gentamicin can suppress LPS-driven TNF-alpha production in proximal tubule cells, likely by inhibiting its translation. Overall preservation of protein synthesis and comparable MCP-1 suppression suggest a semiselective blockade within the LPS inflammatory mediator cascade. These results, coupled with increases in gut TNF-alpha/MCP-1 mRNAs, imply that gentamicin may exert protean, countervailing actions on systemic cytokine/chemokine production during gram-negative sepsis.