Metallothionein induction in rat liver by dietary restriction or exercise and reduction of exercise-induced hepatic lipid peroxidation

Electric Pulse Stimulation of Myotubes as an In Vitro Exercise Model: Cell-Mediated and Non-Cell-Mediated Effects

Regular exercise has emerged as one of the best therapeutic strategies to prevent and treat type-2-diabetes. Exercise-induced changes in the muscle secretome, consisting of myokines and metabolites, may underlie the inter-organ communication between muscle and other organs. To investigate this crosstalk, we developed an in vitro system in which mouse C2C12 myotubes underwent electric pulse stimulation (EPS) to induce contraction. Subsequently the effects of EPS-conditioned media (EPS-CM) on hepatocytes were investigated. Here, we demonstrate that EPS-CM induces Metallothionein 1/2 and Slc30a2 gene expression and reduces Cyp2a3 gene expression in rat hepatocytes. When testing EPS-CM that was generated in the absence of C2C12 myotubes (non-cell EPS-CM) no decrease in Cyp2a3 expression was detected. However, similar inductions in hepatic Mt1/2 and Slc30a2 expression were observed. Non-cell EPS-CM were also applied to C2C12 myotubes and compared to C2C12 myotubes that underwent EPS: here changes in AMPK phosphorylation and myokine secretion largely depended on EPS-induced contraction. Taken together, these findings indicate that EPS can alter C2C12 myotube function and thereby affect gene expression in cells subjected to EPS-CM (Cyp2a3). However, EPS can also generate non-cell-mediated changes in cell culture media, which can affect gene expression in cells subjected to EPS-CM too. While EPS clearly represents a valuable tool in exercise research, care should be taken in experimental design to control for non-cell-mediated effects.

The transcriptional response of Caenorhabditis elegans to Ivermectin exposure identifies novel genes involved in the response to reduced food intake

We have examined the transcriptional response of Caenorhabditis elegans following exposure to the anthelmintic drug ivermectin (IVM) using whole genome microarrays and real-time QPCR. Our original aim was to identify candidate molecules involved in IVM metabolism and/or excretion. For this reason the IVM tolerant strain, DA1316, was used to minimise transcriptomic changes related to the phenotype of drug exposure. However, unlike equivalent work with benzimidazole drugs, very few of the induced genes were members of xenobiotic metabolising enzyme families. Instead, the transcriptional response was dominated by genes associated with fat mobilization and fatty acid metabolism including catalase, esterase, and fatty acid CoA synthetase genes. This is consistent with the reduction in pharyngeal pumping, and consequential reduction in food intake, upon exposure of DA1316 worms to IVM. Genes with the highest fold change in response to IVM exposure, cyp-37B1, mtl-1 and scl-2, were comparably up-regulated in response to short–term food withdrawal (4 hr) independent of IVM exposure, and GFP reporter constructs confirm their expression in tissues associated with fat storage (intestine and hypodermis). These experiments have serendipitously identified novel genes involved in an early response of C. elegans to reduced food intake and may provide insight into similar processes in higher organisms.

Exercise-induced metallothionein expression in human skeletal muscle fibres

Exercise induces free oxygen radicals that cause oxidative stress, and metallothioneins (MTs) are increased in states of oxidative stress and possess anti-apoptotic effects. We therefore studied expression of the antioxidant factors metallothionein I and II (MT-I + II) in muscle biopsies obtained in response to 3 h of bicycle exercise performed by healthy men and in resting controls. Both MT-I + II proteins and MT-II mRNA expression increased significantly in both type I and II muscle fibres after exercise. Moreover, 24 h after exercise the levels of MT-II mRNA and MT-I + II proteins were still highly increased and the MT-II mRNA expression reached a 15-fold increase. As expected, immunohistochemical detection of malondialdehyde (MDA) and nitrotyrosine (NITT) showed that formation of free radicals and oxidative stress were clearly increased in exercising muscle peaking shortly after the end of exercise in both type I and II muscle fibres. This is the first report demonstrating that MT-I + II are significantly induced in human skeletal muscle fibres following exercise. As MT-I + II are antioxidant factors that protect various tissues during pathological conditions, the MT-I + II increases post exercise may represent a mechanism whereby contracting muscle fibres are protected against cellular stress and injury.

Effects of steroid hormones on the Zn, Cu and MTI/II levels in the mouse brain

The effects of some steroid hormones (corticosterone, hydrocortisone, testosterone and estrone) on the Zn, Cu metabolism and metallothioneins levels in the mouse brain were studied. To administrate the hormones, aqueous suspensions and olive oil solutions injected subcutaneously were used alternatively. The quantification of metals and metallothioneins concentrations in brain homogenates revealed significant alterations of both metal ions and protein expression levels, yet the subcutaneous oil injection increased per se the tissue metallothionein expression and metal content. We have also defined by immunohistochemistry the area-specific distribution of metallothioneins isoforms-I/II and of glial fibrillar acid protein. Upon treatment, corpus callosum, mesencephalon, pons, hippocampus and cerebellum were found to be the areas that increase the protein expression levels, whereas all other brain areas were marginally affected or were unaffected in terms of immunopositive metallothionein reaction. The metallothionein-I/II expression was compared with the immunopositivity of glial fibrillar acid protein and the results are discussed within the framework of the physiological role of corticosteroids and the potential therapeutical importance of sexual hormones.

The role of metallothionein II in neuronal differentiation and survival

Metallothionein I and II (MT-I+II) are antioxidant and tissue protective factors. We have previously shown that MT-I+II prevent oxidative stress and apoptotic cell death and are of therapeutic value in brain inflammation. However, MT-I+II are expressed in glia and it remains to be elucidated if MT-I+II can affect neurons directly. It is likely that MT isoforms could be beneficial also during neurodegenerative disorders. In this study, we have examined if MT-II affects survival and neurite extension of dopaminergic and hippocampal neurons. We show for the first time that MT-II treatment can significantly stimulate neurite extension from both dopaminergic and hippocampal neurons. Moreover, MT-II treatment significantly increases survival of dopaminergic neurons exposed to 6-hydroxydopamine (6-OHDA) and protects significantly hippocampal neurons from amyloid beta-peptide-induced neurotoxicity. Accordingly, treatment with MT-II may be of therapeutic value in neurodegenerative disorders.

Treatment with metallothionein prevents demyelination and axonal damage and increases oligodendrocyte precursors and tissue repair during experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is an animal model for the human demyelinating disease multiple sclerosis (MS). EAE and MS are characterized by significant inflammation, demyelination, neuroglial damage, and cell death. Metallothionein-I and -II (MT-I + II) are antiinflammatory and neuroprotective proteins that are expressed during EAE and MS. We have shown recently that exogenous administration of Zn-MT-II to Lewis rats with EAE significantly reduced clinical symptoms and the inflammatory response, oxidative stress, and apoptosis of the infiltrated central nervous system areas. We show for the first time that Zn-MT-II treatment during EAE significantly prevents demyelination and axonal damage and transection, and stimulates oligodendroglial regeneration from precursor cells, as well as the expression of the growth factors basic fibroblast growth factor (bFGF), transforming growth factor (TGF)beta, neurotrophin-3 (NT-3), NT-4/5, and nerve growth factor (NGF). These beneficial effects of Zn-MT-II treatment could not be attributable to its zinc content per se. The present results support further the use of Zn-MT-II as a safe and successful therapy for multiple sclerosis.

Influence of dietary methionine level on the liver metallothionein mRNA level in rats

The effects of some methyl-containing compounds added to a choline-deficient diet on the metallothionein mRNA level in the rat liver were studied. The addition of choline or carnitine to the choline-deficient diet did not induce a gain in body weight, while the addition of either betaine or methionine to the choline-deficient diet, or of methionine to the choline-deficient diet with choline significantly increased the body weight. The metallothionein mRNA level in the liver of rats fed on the choline-deficient diet was similar to that of rats fed on the choline-deficient diet with choline, betaine or carnitine. However, the addition of methionine to the choline-deficient diet with or without choline caused a marked suppression in the metallothionein mRNA level in the liver. It is thus surmised that the metallothionein mRNA level in the liver might be regulated by the dietary content of methionine.

Expression of metallothionein in the liver and kidney of rats is influenced by excess dietary histidine

It is well known that excess dietary histidine induces the metabolic changes in copper and zinc. Therefore, this study was carried out to clarify whether excess dietary histidine alters the gene expressions of metallothionein-1 and metallothionein-2 in the liver and kidney. Male rats were fed the control (ad libitum and pair-fed) or histidine-excess (50 g of L-histidine per kg of diet) diet for 0, 1 and 3 days. The levels of liver metallothionein-1 and metallothionein-2 mRNA were markedly lower in the rats fed the histidine-excess diet as compared to those of the control (ad libitum and pair-fed) diet, when fed for 1 or 3 days. The levels of renal metallothionein-1 and metallothionein-2 mRNA in the rats fed the histidine-excess diet were higher or tended to be higher as compared with the rats fed the control (ad libitum and pair-fed) diet when fed for 1 or 3 days, respectively. At the same time, hepatic copper content was decreased and renal zinc content was increased by dietary histidine. It thus appears, that such a response on the level of liver metallothionein mRNA might be related to the contents of liver copper, but of kidney metallothionein mRNA might be due to the content of zinc.

Induction, regulation, degradation, and biological significance of mammalian metallothioneins

MTs are small cysteine-rich metal-binding proteins found in many species and, although there are differences between them, it is of note that they have a great deal of sequence and structural homology. Mammalian MTs are 61 or 62 amino acid polypeptides containing 20 conserved cysteine residues that underpin the binding of metals. The existence of MT across species is indicative of its biological demand, while the conservation of cysteines indicates that these are undoubtedly central to the function of this protein. Four MT isoforms have been found so far, MT-1, MT-2, MT-3, and MT-4, but these also have subtypes with 17 MT genes identified in man, of which 10 are known to be functional. Different cells express different MT isoforms with varying levels of expression perhaps as a result of the different function of each isoform. Even different metals induce and bind to MTs to different extents. Over 40 years of research into MT have yielded much information on this protein, but have failed to assign to it a definitive biological role. The fact that multiple MT isoforms exist, and the great variety of substances and agents that act as inducers, further complicates the search for the biological role of MTs. This article reviews the current knowledge on the biochemistry, induction, regulation, and degradation of this protein in mammals, with a particular emphasis on human MTs. It also considers the possible biological roles of this protein, which include participation in cell proliferation and apoptosis, homeostasis of essential metals, cellular free radical scavenging, and metal detoxification.