Evidence for renal ischaemia as a cause of mercuric chloride nephrotoxicity

Changes in the renal function after acute mercuric chloride exposure in the rat are associated with renal vascular endothelial dysfunction and proximal tubule NHE3 inhibition

Mercury is an environmental pollutant and a threat to human health. Mercuric chloride (HgCl₂)-induced acute renal failure has been described by several reports, but the mechanisms of renal dysfunction remain elusive. This study tested the hypothesis that HgCl₂ directly impairs renal vascular reactivity. Additionally, due to the mercury toxicity on the proximal tubule, we investigated whether the HgCl₂-induced natriuresis is accompanied by inhibition of Na⁺/H⁺ exchanger isoform-3 (NHE3). We found that 90-min HgCl₂ infusion (6.5 μg/kg i.v.) remarkably increased urinary output, reduced GFR and renal blood flow, and increased vascular resistance in rats. "In vitro" experiments of HgCl₂ infusion in isolated renal vascular bed demonstrated an elevation of perfusion pressure in a concentration- and time-dependent manner, associated with changes on the endothelium-dependent vasodilatation and the flow-pressure relationship. Moreover, by employing "in vivo" stationary microperfusion of the proximal tubule, we found that HgCl₂ inhibits NHE3 activity and increases the phosphorylation of NHE3 at serine 552 in the renal cortex, in line with the HgCl₂-induced diuresis. Changes in renal proximal tubular function induced by HgCl₂ were parallel to increased urinary markers of proximal tubular injury. Besides, atomic spectrometry showed that mercury accumulated in the renal cortex. We conclude that acute HgCl₂ exposure causes renal vasoconstriction that is associated with reduced endothelial vasodilator agonist- and flow-mediated responses and inhibition of NHE3-mediated sodium reabsorption. Thus, our data suggest that HgCl₂-induced acute renal failure may be attributable at least in part by its direct effects on renal hemodynamics and NHE3 activity.

Alterations in biochemical markers due to mercury (Hg) exposure and its influence on infant's neurodevelopment

This study examined the role of oxidative stress due to mercury (Hg) exposure on infant's neurodevelopmental performance. A total of 944 healthy Saudi mothers and their respective infants (aged 3-12 months) were recruited from 57 Primary Health Care Centers in Riyadh City. Total mercury (Hg) was measured in mothers and infants urine and hair samples, as well as mother's blood and breast milk. Methylmercury (MeHg) was determined in the mothers and infants' hair and mother's blood. Urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG), malondialdehyde (MDA), and porphyrins were used to assess oxidative stress. The infant's neurodevelopment was evaluated using Denver Developmental Screening Test II (DDST-II) and Parents' Evaluation of Developmental Status. The median total Hg levels in mother's urine, infant's urine, mother's hair, infant's hair, and mother's blood and breast milk were 0.995μg/l, 0.716μg/l, 0.118μg/g dw, 0.101μg/g dw, 0.635μg/l, and 0.884μg/l respectively. The median MeHg levels in mother's hair, infant's hair, and mother's blood were 0.132μg/g dw, 0.091μg/g dw, and 2.341μg/l respectively. A significant interrelationship between mothers and infants Hg measures in various matrices was noted. This suggests that mother's exposure to different forms of Hg (total and/or MeHg) from various sources contributed significantly to the metal body burden of their respective infants. Even though Hg exposure was low, it induced high oxidative stress in mothers and infants. The influence of multiplicative interaction terms between Hg measures and oxidative stress biomarkers was tested using multiple regression analysis. Significant interactions between the urinary Hg levels in mothers and infants and oxidative stress biomarkers (8-OHdG and MDA) were noted. The MeHg levels in mother-infant hair revealed similar interaction patterns. The p-values for both were below 0.001. These observations suggest that the exposure of our infants to Hg via mothers either during pregnancy and/or neonatal life, promoted oxidative stress that might have played a role in infant neurodevelopmental delays that we reported previously. The results confirmed that the interaction between infant's MeHg in hair and 8-OHdG and MDA levels was significantly associated with a delay in DDST-II performance (ß=-0.188, p=0.028). This finding provides an insight into the potential consequences of Hg-induced oxidative stress to infant's cognitive neurodevelopment for the first time. This observation still needs future studies to be validated. Given the low MeHg levels in our population, these findings are of particular importance.

Effect of mercury vapour exposure on urinary excretion of calcium, zinc and copper: relationship to alterations in functional and structural integrity of the kidney

Background: The kidney has a remarkable capacity to concentrate mercury (Hg) and as such is a primary target organ when exposure to Hg occurs, and it is also an organ for Hg excretion. Objective: The present work aims to investigate the effect of occupational Hg vapour exposure on the urinary excretion of calcium (Ca), zinc (Zn) and copper (Cu), and the possible association of this excretion to work duration as well as renal alterations. Methods: 83 non-smoker participants (36 referents, age: 35.69/9.5 years; 27 Hg vapour-exposed workers with 5/10 years work duration, age: 33.09/5.1 years; and 20 Hg vapour-exposed workers with]/11 years work duration, age: 39.509/8.50 years) were included in the present study. Urinary levels of microalbumin (U-Malb) and retinol-binding protein (U-RBP) as well as cytosolic glutathione S-transferase activity (U-GST) were measured to assess the glomerular and proximal tubular reabsorption functions as well as structural integrity of proximal tubules; respectively. In addition, blood Hg (B-Hg), serum levels of Hg (S-Hg) and Ca (S-Ca), and urinary levels of Hg (U-Hg), Ca (U-Ca), Zn (U-Zn), Cu (U-Cu) and creatinine (U-cr) were estimated. Results: In comparison to referents, all investigated parameters showed significant increase (except S-Ca and U-Zn/U-Cu ratio that significantly decreased among the workers as one group, S-Ca and U-Zn/U-Cu ratio that significantly and nonsignificantly decreased; respectively among workers with 5/10 years work duration, S-Ca and U-Zn/U-Cu ratio that significantly decreased among workers with]/11 years work duration). In addition, B-Hg was nonsignificantly increased and S-Ca was significantly decreased; also, both U-Hg and U-Zn/U-Cu were nonsignificantly decreased among workers with]/11 years work duration in comparison to those with 5/10 years work duration. Also, each of U-Hg, U-Ca, U-Zn and U-Cu was related to one another, while each of U-Ca, U-Zn and U-Cu was related to each of U-Malb, U-RBP and U-GST (except U-Zn was not related to U-GST). Conclusion: Hg vapour exposure leads to renal alterations which may parallel the change in proteinuria and enzymuria as well as the increased loss in urine of each of Ca, Zn and Cu. The urinary assessment of these metals may be used as a good indicator for renal dysfunction.

Interleukin-20 induced cell death in renal epithelial cells and was associated with acute renal failure

Acute renal failure is an abrupt decrease in renal function. Interleukin (IL)-10 inhibits ischemic and cisplatin-induced acute renal failure. We aimed to determine whether IL-20 affects renal tubular epithelial cells and is associated with acute renal failure. We analyzed the expression of IL-20 and its receptor (R) in the kidneys of rats with HgCl(2)-induced acute renal failure. Reverse transcription-PCR showed upregulated IL-20, and its receptors and immunohistochemical staining showed strongly expressed IL-20 protein in proximal tubular epithelial cells. We analyzed human proximal tubular epithelial (HK-2) cells, which expressed both IL-20 and its receptors. IL-20 specifically induced mitochondria-dependent apoptosis by activating caspase 9 in HK-2 cells. IL-20 also activated c-Jun N-terminal kinase and extracellular signal-regulated kinase 1/2, the downstream signals implicated in the apoptosis of HK-2 cells. Furthermore, IL-20 upregulated the transcripts of transforming growth factor (TGF)-beta1, a critical mediator of renal injury. In hypoxic HK-2 cells, IL-20 and IL-22R1 transcripts increased, and IL-20 upregulated IL-1 beta transcripts. In vivo study further demonstrated that anti-IL-20 antibody reduced the expression of TGF-beta1 and IL-1 beta and the number of damaged tubular cells in the kidneys of rats with acute renal failure. We concluded that IL-20 may be involved in the injury of renal epithelial cells in acute renal failure.

Effectiveness of ZnCl2 in protecting against nephrotoxicity induced by HgCl2 in newborn rats

This work investigated the preventive effects of ZnCl(2) on renal and hepatic alterations induced by HgCl(2) in young rats. Wistar rats of 3 days old were treated (s.c.) on consecutive days with saline or ZnCl(2) 27 mg/kg/day from the 3rd to the 7th and with saline or HgCl(2) 5.0mg/kg/day from the 8th to the 12th day of life. Pups were sacrificed 24h after the last dose and samples were collected. The creatinine and urea dosages, used as renal parameters, presented increases of 35% and 500%, respectively. The alanine aminotransferase and lactic dehydrogenase activities, used as hepatic parameters, presented a decrease (40%) and no alteration, respectively, by mercury exposure. The glycemia was diminished and the hepatic glycogen was not modified by mercury. All the mercury effects were prevented by zinc. These results suggest that mercury intoxication of young rats alters the renal function but does not modify the hepatic parameters, and previous exposure to zinc is able to avoid the renal damage.

Molecular response to cytotoxic injury: role of inflammation, MAP kinases, and endoplasmic reticulum stress response

Nephrotoxicants have varied direct and indirect effects on the vasculature, tubules, and interstitium of the kidney. In most cases the molecular components of the toxic insult are poorly understood. In this review some common themes of injury, repair, and adaptive protective responses that represent characteristic responses of the cells and kidney tissue that transcend the specifics of a particular toxin are presented. Particular attention is paid to the vascular and inflammatory aspects of nephrotoxicity as well as the activation of the MAP kinase families and the endoplasmic reticulum stress response by the tubular epithelial cell.

alpha-Melanocyte-simulating hormone and interleukin-10 do not protect the kidney against mercuric chloride-induced injury

The anti-inflammatory cytokines alpha-melanocyte-stimulating hormone (MSH) and interleukin (IL)-10 inhibit acute renal failure (ARF) after ischemia or cisplatin administration; however, these agents have not been tested in a pure nephrotoxic model of ARF. Therefore, we examined the effects of alpha-MSH and IL-10 in HgCl(2)-induced ARF. Mice were injected subcutaneously with HgCl(2) and then given vehicle, alpha-MSH, or IL-10 by intravenous injection. Animals were killed to study serum creatinine, histology, and myeloperoxidase activity. Treatment with either alpha-MSH or IL-10 did not alter the increase in serum creatinine, tubular damage, or leukocyte accumulation at 48 h after HgCl(2) injection. Because alpha-MSH and IL-10 are active in other injury models that involve leukocytes, we studied the time course of tubular damage and leukocyte accumulation to investigate whether leukocytes caused the tubular damage or accumulated in response to the tubular damage. Tubular damage was present in the outer stripe 12 h after HgCl(2) injection. In contrast, the number of leukocytes and renal myleoperoxidase activity were normal at 12 h but were significantly increased at 24 and 48 h after injection. We conclude that neither alpha-MSH nor IL-10 altered the course of HgCl(2)-induced renal injury. Because the tubular damage preceded leukocyte infiltration, the delayed leukocyte accumulation may play a role in the removal of necrotic tissue and/or tissue repair in HgCl(2)-induced ARF.

Verapamil protection against mercuric chloride-induced renal glomerular injury in rats

We have examined the effects of the calcium channel blocker verapamil on the renal glomerular structural damage produced by mercuric chloride in rats. Verapamil (75 micrograms/kg body wt iv) was administered 30 min prior to mercuric chloride injection (HgCl2, 5 mg/kg body wt sc). Verapamil prevented the glomerular proteinuria observed in HgCl2-treated rats. Isolated glomeruli from mercury-treated rats 1 h after injection presented a diminished cross-sectional area as compared with control glomeruli (control [micron2], 26,310 +/- 2545; HgCl2 [micron2], 18,474 +/- 1828) and increased glomerular calcium content (control, 23 +/- 6 nmol/mg protein; HgCl2, 43 +/- 7 nmol/mg protein). Verapamil pretreatment prevented glomerular cross-sectional area (GCSA) diminution and glomerular calcium content rise (GCSA [micron2] Vp + Hg, 28,281 +/- 4654, Ca2+ [nmol/mg protein] Vp + Hg, 18 +/- 5). Renal sections prepared for immunohistochemical detection and histochemical analysis showed increased deposits of fibronectin and lipids and enhanced cellularity in glomerular structures from HgCl2-treated rats. Renal sections from animals pretreated with verapamil showed fibronectin and lipid contents not different from control sections and their histological studies did not show any changes when compared with control. Verapamil pretreatment also protected glomeruli from enhanced leukocyte content (myeloperoxidase activity/mg protein): control, 59 +/- 7; HgCl2, 134 +/- 10; Vp + Hg, 79 +/- 11). HgCl2 also contracts GCSA in vitro; Vp prevented this GCSA diminution. The results described in this study indicate that mercuric chloride nephrotoxicity may be associated not only with changes in renal glomerular haemodynamics, but also with a direct effect on glomerular cells.