Renal accumulation and intrarenal distribution of inorganic mercury in the rabbit: effect of unilateral nephrectomy and dose of mercuric chloride

Ubiquitous toxicity of Mercuric Chloride in target tissues and organs: Impact of Ubidecarenone and liposomal-Ubidecarenone STAT 5A/ PTEN /PI3K/AKT signaling pathways

BACKGROUND

Mercuric chloride (HgCl3) is categorized as class II B hazardous metal that is present in many occupational and environmental conditions. In the meantime, Hg exists in the environment in such an abundant manner, it is virtually impossible for humans to avoid exposure to different forms of Hg. In addition to environmental exposure, individuals may be exposed to Hg from dental amalgams, medicinal treatments and dietary sources. Nevertheless, Liposomal drug delivery system is a promising era in the field of Nano-medicine and have the advantageous of increasing drug bioavailability and retention phenomena in addition to targeting organ for all mentioned the present study was designed to investigate the hypothesis that messenger RNA gene expression of Signal transducer and activator of transcription- 5 A (STAT-5A), Phosphatase and tensin homolog (PTEN), phosphoinositol kinase (PI3K) and alpha serine/threonine-protein kinase (AKT) can trigger HgCl3 induced nephrotoxicity post Ubidecarenone and liposomal Ubidecarenone therapy.

METHODS

HgCl3 toxicity was induced in rats via a dose of 5 mg/kg BW for one week followed by Ubidecarenone and liposomal Ubidecarenone therapy in a dose of 10 & 3 mg/kg BW for one month, respectively. Then kidney function tests, Glutathione and gene expression for PI3K, AKT, PTEN and STAT-5A was investigated.

RESULTS

HgCl3 intoxication significantly up regulated PI3K, AKT, PTEN and STAT-5A signaling pathways meanwhile, Ubidecarenone and liposomal- Ubidecarenone treatment significantly reduced PI3K, AKT, PTEN and STAT-5A gene expression post HgCl3 intoxication with the liposomal regimen revealing the most significant impact. Furthermore, renal toxicity was confirmed via monitoring urea and creatinine which were modulated post Ubidecarenone and liposomal-Ubidecarenone treatment. Wide evidence declared that mercuric S-conjugates of small endogenous thiols (such as Hcy, NAC and Cys) are probably the main transportable forms of Hg²⁺ to the kidneys thus reduced glutathione was investigated which reflected a significant down regulation post Hgcl3 toxicity.

CONCLUSION

liposomal drug delivery system including liposomal-Ubidecarenone can be considered as a prospective candidate for treating HgCl3 renal toxicity via modulating STAT-5A, PTEN, PI3K and AKT signaling pathways and via increasing retention time, bioavailability, shielding from macrophage recognition and targeting organs.

Toxicometabolomics approach to urinary biomarkers for mercuric chloride (HgCl₂)-induced nephrotoxicity using proton nuclear magnetic resonance (¹H NMR) in rats

The primary objective of this study was to determine and characterize surrogate biomarkers that can predict nephrotoxicity induced by mercuric chloride (HgCl₂) using urinary proton nuclear magnetic resonance (¹H NMR) spectral data. A procedure for (1)H NMR urinalysis using pattern recognition was proposed to evaluate nephrotoxicity induced by HgCl₂ in Sprague-Dawley rats. HgCl₂ at 0.1 or 0.75 mg/kg was administered intraperitoneally (i.p.), and urine was collected every 24 h for 6 days. Animals (n=6 per group) were sacrificed 3 or 6 days post-dosing in order to perform clinical blood chemistry tests and histopathologic examinations. Urinary ¹H NMR spectroscopy revealed apparent differential clustering between the control and HgCl₂ treatment groups as evidenced by principal component analysis (PCA) and partial least square (PLS)-discriminant analysis (DA). Time- and dose-dependent separation of HgCl₂-treated animals from controls was observed by PCA of ¹H NMR spectral data. In HgCl₂-treated rats, the concentrations of endogenous urinary metabolites of glucose, acetate, alanine, lactate, succinate, and ethanol were significantly increased, whereas the concentrations of 2-oxoglutarate, allantoin, citrate, formate, taurine, and hippurate were significantly decreased. These endogenous metabolites were selected as putative biomarkers for HgCl₂-induced nephrotoxicity. A dose response was observed in concentrations of lactate, acetate, succinate, and ethanol, where severe disruption of the concentrations of 2-oxoglutarate, citrate, formate, glucose, and taurine was observed at the higher dose (0.75 mg/kg) of HgCl₂. Correlation of urinary (1)H NMR PLS-DA data with renal histopathologic changes suggests that ¹H NMR urinalysis can be used to predict or screen for HgCl₂-induced nephrotoxicity.

Transport of inorganic mercury and methylmercury in target tissues and organs

Owing to the prevalence of mercury in the environment, the risk of human exposure to this toxic metal continues to increase. Following exposure to mercury, this metal accumulates in numerous organs, including brain, intestine, kidneys, liver, and placenta. Although a number of mechanisms for the transport of mercuric ions into target organs were proposed in recent years, these mechanisms have not been characterized completely. This review summarizes the current literature related to the transport of inorganic and organic forms of mercury in various tissues and organs. This review identifies known mechanisms of mercury transport and provides information on additional mechanisms that may potentially play a role in the transport of mercuric ions into target cells.

Seventy-five percent nephrectomy and the disposition of inorganic mercury in 2,3-dimercaptopropanesulfonic acid-treated rats lacking functional multidrug-resistance protein 2

In the present study, we evaluated the disposition of inorganic mercury (Hg(2+)) in sham-operated and 75% nephrectomized (NPX) Wistar and transport-deficient (TR(-)) rats treated with saline or the chelating agent meso-2,3-dimercaptosuccinic acid (DMSA). Based on previous studies, DMSA and TR(-) rats were used as tools to examine the potential role of multidrug-resistance protein 2 (MRP2) in the disposition of Hg(2+) during renal insufficiency. All animals were treated with a low dose (0.5 mumol/kg i.v.) of mercuric chloride (HgCl(2)). At 24 and 28 h after exposure to HgCl(2), matched groups of Wistar and TR(-) rats received normal saline or DMSA (intraperitoneally). Forty-eight hours after exposure to HgCl(2), the disposition of Hg(2+) was examined. A particularly notable effect of 75% nephrectomy in both strains of rats was enhanced renal accumulation of Hg(2+), specifically in the outer stripe of the outer medulla. In addition, hepatic accumulation, fecal excretion, and blood levels of Hg(2+) were enhanced in rats after 75% nephrectomy, especially in the TR(-) rats. Treatment with DMSA increased both the renal tubular elimination and urinary excretion of Hg(2+) in all rats. DMSA did not, however, affect hepatic content of Hg(2+), even in the 75% NPX TR(-) rats. We also show with real-time polymerase chain reaction that after 75% nephrectomy and compensatory renal growth, expression of MRP2 (only in Wistar rats) and organic anion transporter 1 is enhanced in the remaining functional proximal tubules. We conclude that MRP2 plays a significant role in the renal and corporal disposition of Hg(2+) after a 75% reduction of renal mass.

Mercury induces the externalization of phosphatidyl-serine in human renal proximal tubule (HK-2) cells

The underlying mechanism for the biological activity of inorganic mercury is believed to be the high affinity binding of divalent mercuric cations to thiols of sulfhydryl groups of proteins. A comprehensive analysis of published data indicates that inorganic mercury is one of the most environmentally abundant toxic metals, is a potent and selective nephrotoxicant that preferentially accumulates in the kidneys, and is known to produce cellular injury in the kidneys. Binding sites are present in the proximal tubules, and it is in the epithelial cells of these tubules that toxicants such as inorganic mercury are reabsorbed. This can affect the enzymatic activity and the structure of various proteins. Mercury may alter protein and membrane structure and function in the epithelial cells and this alteration may result in long term residual effects. This research was therefore designed to evaluate the dose-response relationship in human renal proximal tubule (HK-2) cells following exposure to inorganic mercury. Cytotoxicity was evaluated using the MTT assay for cell viability. The Annexin-V assay was performed by flow cytometry to determine the extent of phosphatidylserine externalization. Cells were exposed to mercury for 24 hours at doses of 0, 1, 2, 3, 4, 5, and 6 microg/mL. Cytotoxicity experiments yielded a LD50 value of 4.65 +/- 0.6 microg/mL indicating that mercury is highly toxic. The percentages of cells undergoing early apoptosis were 0.70 +/- 0.03%, 10.0 +/- 0.02%, 11.70 +/- 0.03%, 15.20 +/- 0.02%, 16.70 +/- 0.03%, 24.20 +/-0.02%, and 25.60 +/- 0.04% at treatments of 0, 1, 2, 3, 4, 5, and 6 microg/mL of mercury respectively. This indicates a dose-response relationship with regard to mercury-induced cytotoxicity and the externalization of phosphatidylserine in HK-2 cells.

A novel method for the evaluation of proximal tubule epithelial cellular necrosis in the intact rat kidney using ethidium homodimer

BACKGROUND

Ethidium homodimer is a cell-membrane impermeant nuclear fluorochrome that has been widely used to identify necrotic cells in culture. Here, we describe a novel technique for evaluating necrosis of epithelial cells in the proximal tubule that involves perfusing ethidium homodimer through the intact rat kidney. As a positive control for inducing necrosis, rats were treated with 3.5, 1.75, 0.87 and 0.43 mg/kg mercuric chloride (Hg2+, intraperitoneal), treatments which have previously been shown to rapidly cause dose-dependent necrosis of the proximal tubule. Twenty-four h after the administration of Hg2+, ethidium homodimer (5 microM) was perfused through the intact left kidney while the animal was anesthetized. The kidney was then removed, placed in embedding medium, frozen and cryosectioned at a thickness of 5 microm. Sections were permeabilized with -20 degrees C methanol and then stained with 4',6-diamidino-2-phenylindole (DAPI) to label total nuclei. Total cell number was determined from the DAPI staining in random microscopic fields and the number of necrotic cells in the same field was determined by ethidium homodimer labeling.

RESULTS

The Hg2+-treated animals showed a dose-dependent increase in the number of ethidium labeled cells in the proximal tubule, but not in other segments of the nephron. Other results showed that a nephrotoxic dose of gentamicin also caused a significant increase in the number of ethidium labeled cells in the proximal tubule.

CONCLUSION

These results indicate that this simple and sensitive perfusion technique can be used to evaluate cellular necrosis in the proximal tubule with the three-dimensional cyto-architecture intact.

Molecular and ionic mimicry and the transport of toxic metals

Despite many scientific advances, human exposure to, and intoxication by, toxic metal species continues to occur. Surprisingly, little is understood about the mechanisms by which certain metals and metal-containing species gain entry into target cells. Since there do not appear to be transporters designed specifically for the entry of most toxic metal species into mammalian cells, it has been postulated that some of these metals gain entry into target cells, through the mechanisms of ionic and/or molecular mimicry, at the site of transporters of essential elements and/or molecules. The primary purpose of this review is to discuss the transport of selective toxic metals in target organs and provide evidence supporting a role of ionic and/or molecular mimicry. In the context of this review, molecular mimicry refers to the ability of a metal ion to bond to an endogenous organic molecule to form an organic metal species that acts as a functional or structural mimic of essential molecules at the sites of transporters of those molecules. Ionic mimicry refers to the ability of a cationic form of a toxic metal to mimic an essential element or cationic species of an element at the site of a transporter of that element. Molecular and ionic mimics can also be sub-classified as structural or functional mimics. This review will present the established and putative roles of molecular and ionic mimicry in the transport of mercury, cadmium, lead, arsenic, selenium, and selected oxyanions in target organs and tissues.

Effect of mercury vapor exposure on metallothionein and glutathione s-transferase gene expression in the kidney of nonpregnant, pregnant, and neonatal rats

Elemental mercury (Hg(0)) is a ubiquitous toxic pollutant. Exposure to Hg(0) vapor typically is by inhalation, and the kidney is the primary target organ. Glutathione (GSH) and metallothionein (MT) appear to mitigate mercury toxicity. However, little is known about GSH or MT regulation after Hg(0) vapor exposure, particularly during pregnancy, a time of high sensitivity to most metals. Thus, this study sought to determine renal mercury accumulation and MT- and GSH-related gene expression following Hg(0) vapor exposure in nonpregnant, pregnant, and neonatal rats exposed in utero. Groups (n = 5) of pregnant rats (Long-Evans) were exposed to Hg(0) vapor (4 mg/m(3)) or air (control) for 2 h/d from gestational day (GD) 6 to 15, and kidneys from dams and pups were removed at various times during and after the onset of exposure. For comparative purposes, nonpregnant female rats were exposed to Hg(0) for 10 d under the same conditions. Renal mercury, MT protein, and GST activity were assayed by standard analytical techniques. Western blot analysis was also performed using antibodies against MT and GST-pi. GSH-related gene expression was studied by cDNA microarray. Hg(0) vapor exposure produced renal accumulation of mercury in nonpregnant, pregnant, and neonatal rats. However, the transplacentally exposed neonates accumulated approximately 1000-fold less mercury than adults. Hg(0) vapor exposure produced a time-dependent increase in renal MT protein in nonpregnant and pregnant rats, but not in neonatal rats. Maximum MT increases were observed on d 10 (fivefold) in nonpregnant and GD 15 (threefold) in pregnant rats. Activation of the MT gene by Hg(0) was confirmed at the translational level by Western blot analysis and at the transcriptional level by Northern blot analysis. Microarray analysis revealed a significant upregulation in the renal expression of the GST-pi, GST-Ya, and microsomal GST and GST5-5 genes in nonpregnant and pregnant rats. Western blot and enzyme assay confirmed the upregulation of GST genes after Hg(0) exposure. Thus, in response to Hg(0) vapor exposure, the expression of the MT gene and various GST genes is activated in nonpregnant and pregnant rats. Activation of these genes could be part of a defensive response directed at decreasing renal mercury toxicity, and may help divert the metal away from the fetus.

Influence of different degrees of reduced renal mass on the renal and hepatic disposition of administered cadmium

The present study was designed to evaluate, in rats, the effect of varying degrees of reduced renal mass on the disposition of administered cadmium. As part of this evaluation, the intrarenal, hepatic, and hematological disposition of cadmium and the urinary and fecal excretion of cadmium were studied and characterized in control, uninephrectomized (NPX), and 75% nephrectomized (75% NPX) rats 1 d, 2 d, and 7 d after the intravenous injection of a nonnephrotoxic 8.9 mumol/kg dose of cadmium chloride. Renal accumulation of cadmium, especially in the cortex and outer stripe of the outer medulla, was reduced significantly in the 75% NPX rats, but not in the NPX rats, between d 2 and 7 after the injection of cadmium. The diminution in the renal accumulation of cadmium in the 75% NPX rats was most likely due to diminished glomerular filtration rate and renal clearance of cadmium induced by 75% nephrectomy. Despite reduced glomerular filtration rate, the cumulative urinary excretion of cadmium in the 75% NPX rats was significantly greater than that in either the NPX rats or the control rats. It should be mentioned, however, that very little of the administered dose of cadmium was excreted in the urine by any of the three groups of rats. Interestingly, the content of cadmium in the liver was significantly greater in 75% NPX rats than in NPX or control rats between d 1 and 7 after the injection of cadmium. Moreover, the 75% NPX rats excreted significantly less cadmium in the feces over the 7 d of study than did the other 2 groups of rats, indicating that 75% nephrectomy causes a significant alteration in one or more of the mechanisms involved in the fecal excretion of cadmium. In summary, the findings from the present study indicate that the renal and hepatic handling of administered cadmium in rats changes significantly when renal mass is reduced by 75%. Further studies are needed to better characterize the effects of reductions of renal mass, which impair renal function significantly, on both the disposition and toxicity of cadmium in renal and hepatic tissues.

Reductions in renal mass and the nephropathy induced by mercury

The severity of renal injury induced by several graded doses of mercuric chloride and the disposition of mercury were evaluated and compared in control, uninephrectomized (50% NPX), and 75% nephrectomized (75% NPX) rats in an attempt to determine the effect of increased reductions of renal mass on the nephropathy induced by inorganic mercury. Consistent with previously published findings, proximal tubular necrosis (as assessed histopathologically and by the urinary excretion of lactate dehydrogenase (LDH) and total protein) was significantly more severe in 50% NPX rats than in control rats 24 hr after the administration of any of three lowest (1.0, 1.5, or 1.75 micromol/kg) doses of mercuric chloride used in the study. Interestingly, the severity of proximal tubular necrosis in the 75% NPX rats was not greater than that in control rats at these same doses. The reason for this appeared to be due to decreased renal accumulation of mercury, particularly in the renal cortex and outer stripe of the outer medulla. At the highest (8.0 micromol/kg) dose of mercuric chloride used, renal tubular injury was very extensive in all three groups of rats, with the level of injury being greatest in the 50% NPX rats. The injury was so severe in all three groups that acute renal failure was induced within the first 24 hr after the injection of mercury. An important finding that was made at this dose was that the level of blood urea nitrogen (BUN) was significantly greater in the 75% NPX rats than in either the 50% NPX or control rats, which indicates that 75% NPX rats may have entered into acute renal failure sooner than the 50% NPX or control rats. Overall, the findings from the present study indicate that as renal mass is reduced to a level at which renal function is not significantly impaired (50% NPX), the severity of the nephropathy induced by mercury is increased. By contrast, when the reduction of renal mass progresses to a level at which renal function begins to become impaired, the level of proximal tubular injury is not greatly different from that of animals with two kidneys, especially at low nephrotoxic doses of inorganic mercury. In addition, low nephrotoxic doses of inorganic mercury do not appear to affect significantly the reduced glomerular filtration rate in 75% NPX rats. However, it does appear that 75% NPX rats may be at greater risk of entering into acute renal failure at higher toxic doses of inorganic mercury than 50% NPX or control rats.