Zinc-induced metallothionein synthesis could protect from gentamicin nephrotoxicity in suspended proximal tubules of rats

Zinc is a strong stimulant of metallothionein synthesis in the ischaemic testis tissue

This study was performed to determine the effect of zinc supplementation effects on metallothionein levels in testis ischaemia-reperfusion of rats. The experimental groups were designed as Control, Sham, Ischaemia-Reperfusion (I/R) and I/R + Zinc supplemented. Zinc supplemented as 5 mg/kg day for 3 weeks. Testis tissues were analysed for metallothionein by immunohistochemical staining procedures. Group comparison showed that the zinc-supplemented ischaemia-reperfusion group had a significantly higher level of cells strongly stained with metallothionein than all other groups. A general evaluation of the results suggests that zinc supplementation is a strong stimulant of metallothionein synthesis in the ischaemic testis tissue.

Effect of diethyldithiocarbamate in cyclophosphamide-induced nephrotoxicity: Immunohistochemical study of superoxide dismutase 1 in rat

OBJECTIVES:

To investigate the role of diethyldithiocarbamate (DEDTC) in cyclophosphamide (CP)-induced nephrotoxicity in Sprague–Dawley rat. DEDTC is a known chelating agent for copper and zinc. It is also used as a thiol protecting agent, as nuclear factor kappa-light-chain-enhancer of activated B-cells inhibitor and nitric oxide synthase inhibitor. It is also reported to inhibit superoxide dismutase (SOD) both in vitro and in vivo conditions. Considering this wide range of actions, current study investigated the role of DEDTC in CP-induced nephrotoxicity in experimental rat model.

MATERIALS AND METHODS:

Thirty-two male rats were randomized into four groups. Group 1, control received only saline ip; Group 2 and 4, received CP at the dose of 150 mg/kg body weight ip on the 4^th day, while Group 3 and 4, received DEDTC at the dose of 250 mg/kg alternatively (fractionated dose of 1000 mg/kg). All the experimental animals were sacrificed on the 7^th day and organs of interest were collected for biochemical, histopathological, DNA damage, and immunohistochemical assessments.

RESULTS:

DEDTC administration was found to further exacerbate the condition of CP-induced kidney damage as assessed by several biochemical and histological parameters. Further, the damage was also significantly reflected in the bladder in DEDTC-treated animals as compared to controls. SOD1 (Cu/Zn- dependent enzyme) expression was found to be decreased and this might be due to the action of DEDTC on SOD and other antioxidants.

CONCLUSION:

The present study indicates that DEDTC administration further exacerbated the CP-induced kidney damage in rat.

The role of metallothionein in oxidative stress. Int J Mol Sci. 2013;14:6044-6066. [PMID: 23502468 PMCID: PMC3634463 DOI: 10.3390/ijms14036044]

Free radicals are chemical particles containing one or more unpaired electrons, which may be part of the molecule. They cause the molecule to become highly reactive. The free radicals are also known to play a dual role in biological systems, as they can be either beneficial or harmful for living systems. It is clear that there are numerous mechanisms participating on the protection of a cell against free radicals. In this review, our attention is paid to metallothioneins (MTs) as small, cysteine-rich and heavy metal-binding proteins, which participate in an array of protective stress responses. The mechanism of the reaction of metallothioneins with oxidants and electrophilic compounds is discussed. Numerous reports indicate that MT protects cells from exposure to oxidants and electrophiles, which react readily with sulfhydryl groups. Moreover, MT plays a key role in regulation of zinc levels and distribution in the intracellular space. The connections between zinc, MT and cancer are highlighted.

Antioxidant defense against anthracycline cardiotoxicity by metallothionein

Anthracycline cardiotoxicity is related to oxidative stress generated from the metabolism of anthracyclines in the heart. Studies using transgenic mice with high levels of antioxidants such as catalase or metallothionein (MT) specifically in the heart have demonstrated that elevation of cardiac antioxidant defense leads to intervention of anthracycline cardiotoxicity. MT protection against anthracycline-induced cardiac toxicity is related to its anti-apoptotic effect by inhibiting both p38-MAPK-mediated and mitochondrial cytochrome c-release-mediated apoptotic signaling. The anti-apoptotic effect of MT is closely related to its antioxidant action, which involves regulation of zinc homeostasis by the MT redox cycle. MT interferes with oxidant-mediated detrimental process through at least in part zinc release and zinc transfers directly from MT to acceptor proteins. In addition, MT posttranslationally modulates critical proteins involved in mitochondrial respiration and energy metabolism. All of these processes constitute the mechanisms by which MT protects from anthracycline cardiotoxicity.

Metallothionein redox cycle and function

The biologic function of metallothionein (MT) has been a perplexing topic ever since the discovery of this protein. Many studies have suggested that MT plays a role in the homeostasis of essential metals such as zinc and copper, detoxification of toxic metals such as cadmium, and protection against oxidative stress. However, mechanistic insights into the actions of MT have not been adequately achieved. MT contains high levels of sulfur. The mutual affinity of sulfur and transition metals makes the binding of these metals to MT thermodynamically stable. Under physiologic conditions, zinc-MT is the predominant form of the metal-binding protein. The recognition of the redox regulation of zinc release from or binding to MT provides an alternate perspective on biologic function of MT. Oxidation of the thiolate cluster by a number of mild cellular oxidants causes zinc release and formation of MT-disulfide (or thionin if all metals are released from MT, but this is unlikely to occur in vivo), which have been demonstrated in vivo. Therefore, the thermodynamic stability of zinc binding makes MT an ideal zinc reservoir in vivo, and the redox regulation of zinc mobilization enables MT function in zinc homeostasis. MT-disulfide can be reduced by glutathione in the presence of selenium catalyst, restoring the capacity of the protein to bind zinc. This MT redox cycle may play a crucial role in MT biologic function. It may link to the homeostasis of essential metals, detoxification of toxic metals and protection against oxidative stress.

Protective effect of trans-resveratrol on gentamicin-induced nephrotoxicity

Reactive oxygen species (ROS) have been involved in glomerular filtration rate (GFR) reduction observed after gentamicin treatment. trans-Resveratrol (TR), a natural hydroxystilbene, has been identified to be a potent inhibitor of ROS production. The aim of this work has been to study whether TR has a protective effect on gentamicin-induced nephrotoxicity in vivo and the effect of TR on lipid peroxidation and the oxidative stress induced by gentamicin. Animals that received a daily intraperitoneal injection of gentamicin (100 mg/kg body weight) showed lower GFR and renal blood flow (RBF) and higher urinary excretion of N-acetyl-beta-D-glucosaminidase (NAG) than control rats. Rats receiving TR together with gentamicin showed higher GFR and RBF and lower NAG urinary excretion than rats receiving gentamicin alone. Moreover, renal lipid peroxidation increased in rats receiving gentamicin alone, and this increase was prevented by the administration of TR. The concentration in plasma of antioxidants was higher in the group that received TR with gentamicin than in the gentamicin and control groups. The activities of lactate dehydrogenase and alkaline phosphatase were higher in rats treated with gentamicin than in control rats and were reduced by the treatment with TR. This study demonstrates an improvement in renal function in response to the administration of TR in gentamicin-induced nephrotoxicity. At least a part of this effect of TR could be based on its antioxidant activity.

Metallothionein and zinc as potential antioxidants in radical-induced lipid peroxidation in cultured hepatocytes

Rat hepatocytes were isolated by a two-step collagenase perfusion technique and introduced to the hydroxyl radical (OH)-generating xanthine-xanthine oxidase-iron (X/XO/Fe) system. The amount of thiobarbituric acid reactive substances (TBA) and thiobarbituric acid bound malondialdehyde (TBA-MDA) were assayed in homogenates after different phases of cultivation. The effects on lipid peroxidation of supplemented metallothionein (MT) ranging from 25 to 75 microM and zinc ranging from 14.5 to 77.8 microM, as well as the effect of a Zn-pretreatment for 18 h were investigated. The addition of X/XO/Fe resulted in a 3 to 4-fold increase in the levels of TBA and TBA-MDA. These results show that X/XO/Fe initiated the lipid peroxidation in the hepatocyte cell system. High doses of supplemented MT inhibited the production of TBA and TBA-MDA. Neither Zn nor the Zn-pretreatment, which resulted in an increase of intracellular MT, had any effect on TBA and TBA-MDA levels. This study suggests that MT can act as an antioxidant in high concentrations via the cysteinyl groups of the protein. The postulated protective effects of Zn via its release from the oxidized MT can be ruled out.

Renal cortical mitochondria are the source of oxygen free radicals enhanced by gentamicin

Rat renal cortical mitochondria were isolated from Wistar male rats weighing 80 to 120 g to investigate whether the source of oxygen free radicals was renal cortical mitochondria enhanced by gentamicin. In renal cortical mitochondria with or without the addition of gentamicin, DMSO, DFO, CAT, SOD, and MT1 were added separately, then incubated at 37 degrees C for 90 min. Superoxide anions and hydroxyl radicals were then determined. The results showed that superoxide anions and hydroxyl radicals generated in mitochondria were enhanced by the addition of in vitro gentamicin (12.4 mg/mL) when compared to those without the addition of gentamicin. Dimethylsulfoxide (DMSO), catalase (CAT), and deferoxamine (DFO) significantly inhibited hydroxyl radicals enhanced by gentamicin, but superoxide dismutase (SOD) and metallothionein-1 (MT1) did not. SOD significantly inhibited the production of superoxide anions. Our data indicated that renal cortical mitochondria are the source of oxygen free radicals and that production is enhanced by gentamicin. This provides more insight on the pathogenetic role of hydroxyl radicals and superoxide anions in gentamicin-induced nephrotoxicity in vitro.