Genome-Wide Identification and Analysis of the Metallothionein Genes in Oryza Genus

Metallothionein (MT) proteins are low molecular mass, cysteine-rich, and metal-binding proteins that play an important role in maintaining metal homeostasis and stress response. However, the evolutionary relationships and functional differentiation of MT in the Oryza genus remain unclear. Here we identified 53 MT genes from six Oryza genera, including O. sativa ssp. japonica, O. rufipogon, O. sativa ssp. indica, O. nivara, O. glumaepatula, and O. barthii. The MT genes were clustered into four groups based on phylogenetic analysis. MT genes are unevenly distributed on chromosomes; almost half of the MT genes were clustered on chromosome 12, which may result from a fragment duplication containing the MT genes on chromosome 12. Five pairs of segmental duplication events and ten pairs of tandem duplication events were found in the rice MT family. The Ka/Ks values of the fifteen duplicated MT genes indicated that the duplicated MT genes were under a strong negative selection during evolution. Next, combining the promoter activity assay with gene expression analysis revealed different expression patterns of MT genes. In addition, the expression of OsMT genes was induced under different stresses, including NaCl, CdCl₂, ABA, and MeJ treatments. Additionally, we found that OsMT genes were mainly located in chloroplasts. These results imply that OsMT genes play different roles in response to these stresses. All results provide important insights into the evolution of the MT gene family in the Oryza genus, and will be helpful to further study the function of MT genes.

Protective effects of 1,25 dihydroxyvitamin D3 and its analogs on ultraviolet radiation-induced oxidative stress: a review

The active vitamin D compound, 1,25-dihydroxyvitamin D3 (1,25D) is produced in skin cells following exposure to ultraviolet radiation (UV) from the sun. However, there are many harmful effects of UV which include DNA damage caused by direct absorption of UV, as well as that caused indirectly via UV-induced reactive oxygen species (ROS). Interestingly, 1,25D and analogs have been shown to reduce both direct and indirect UV-induced DNA damage in skin cells. This was accompanied by reductions in ROS and in nitric oxide products with 1,25D following UV. Moreover, following acute UV exposure, 1,25D has been demonstrated to increase p53 levels in skin, which would presumably allow for repair of cells with damaged DNA, or apoptosis of cells with irreparably damaged DNA. Previous studies have also shown that p53 reduces intracellular ROS. Furthermore, 1,25D has been shown to induce metallothioneins, which are potent free radical scavengers. In addition to these protective effects, 1,25D has been demonstrated to inhibit stress-activated c-Jun N-terminal kinases following UV exposure, and to increase levels of the stress-induced protein heme oxygenase-1 in a model of oxidative stress. Herein, we discuss the protective effects of 1,25D and analogs in the context of UV, oxidative stress and skin cancer.

The Enigmatic Metallothioneins: A Case of Upward-Looking Research

In the mid-1950s, Bert Lester Vallee and his colleague Marvin Margoshes discovered a molecule referred to today as metallothionein (MT). Meanwhile, MTs have been shown to be common in many biological organisms. Despite their prevalence, however, it remains unclear to date what exactly MTs do and how they contribute to the biological function of an organism or organ. We investigate why biochemical research has not yet been able to pinpoint the function(s) of MTs. We shall systematically examine both the discovery of and recent research on Dr. Vallee's beloved family of MT proteins utilizing tools from philosophy of science. Our analysis highlights that Vallee's initial work exhibited features prototypical of a developing research tradition: it was upward-looking, exploratory, and utilized mere interactions. Since the 1960s, MT research has increasingly become intervention- and hypothesis-based while it remained largely upward-looking in character. Whilst there is no reason to think that upward-looking research cannot successfully yield structure-function mappings, it has not yet been successful in the case of MTs. Thus, we suggest it might be time to change track and consider other research strategies looking into the evolution of MTs. Recent studies in mollusks render research in this direction worthy of pursuit.

Zinc deficiency and cellular oxidative stress: prognostic implications in cardiovascular diseases

Zinc is an essential nutrient for human health and has anti-oxidative stress and anti-inflammatory functions. The association between zinc deficiency and the development of cardiovascular diseases (CVDs) has been supported by numerous studies. Supplementing zinc can reduce the risk of atherosclerosis and protect against myocardial infarction and ischemia/reperfusion injury. In this review we summarize the evidence in the literature, to consolidate the current knowledge on the dysregulation of zinc homeostasis in CVDs, and to explore the significant roles of the zinc homeostasis-regulatory proteins in cardiac physiology and pathophysiology. Moreover, this review also deliberates on the potential diagnostic and prognostic implications of zinc/zinc homeostasis-associated molecules (ZIP, ZnT, and MTs) in CVDs.

METALLOTHIONEIN genes encoding ROS scavenging enzymes are down-regulated in the root cortex during inducible aerenchyma formation in rice

Under waterlogged conditions, roots of gramineous plants form lysigenous aerenchyma (internal gas spaces) by inducing the death of cortical cells. Rice (Oryza sativa) roots induce aerenchyma formation through ethylene- and reactive oxygen species (ROS)-mediated signaling. Metallothionein (MT) is a small, cysteine-rich protein that acts as a ROS scavenger. In rice roots, the expression of MT1a, MT1b, MT1c and MT1Ld were higher than those of the other MT genes. In the root cortex, where aerenchyma forms exclusively, the expression of MT1a, MT1b and MT1Ld was reduced prior to aerenchyma formation. These findings suggest that ROS accumulation in the cortex, which is aided by downregulation of MT1 genes, is needed for aerenchyma formation in rice roots.

Depuration of Cadmium from Blue Mussel (Mytilus edulis) by Protein Hydrolysate-Fe2+ Complex: The Role of Metallothionein

Metallothionein (MT) plays a major role in the detoxification of toxic metal ions in mussel. This study served to investigate the effects of prepared protein hydrolysate-Fe²⁺ (PH-Fe²⁺ ) on depuration of cadmium salt (Cd²⁺ ) from blue mussel (Mytilus edulis). The results indicated that Cd²⁺ concentrations in control ranged from 46.1 to 47.1 μg/g during 15 d of depuration. While, 40 mg/L PH-Fe²⁺ feed mussels exhibited obvious changes in Cd²⁺ concentration variables, which decreased by 22.8 μg/g after 15 d of depuration, making them significantly lower than the values of the control. Our assumption was that Cd²⁺ could be dissociated effectively from the complex of MT-Cd²⁺ in mussels affected by the incorporation of PH-Fe²⁺ during the feeding period. Further results of homology modeling and molecular dynamics (MD) confirmed that the combined power between MT and Cd²⁺ weakened significantly by PH-Fe²⁺ . This condition affected the charge density and/or the loop flexibility of MT and decreased the interaction energy within MT-Cd²⁺ complex and resulted in the release of Cd²⁺ from the complex, thereby exhibiting excretion detoxification. Finally, by comparing the experimental results to MD results, significant positive correlations were observed between PH-Fe²⁺ and the depuration of Cd²⁺ from MT-Cd²⁺ complex. Overall, the findings of this study may help better understand the depuration mechanisms of Cd²⁺ combined with MT, and the PH-Fe²⁺ can be recommended as a depuration agent to decrease Cd²⁺ concentrations in mussels.

PRACTICAL APPLICATION

Metallothionein (MT) is a low-molecular-weight protein with high metal-ion affinity. If the intracellular concentrations of metals are too high or if toxic metals are present within the cell, then the synthesis of MTs is induced and generated. In our previous work, it was found that the prepared hydrolysate-metal element complex showed obvious depuration activity of heavy metals (Cd²⁺ ) from blue mussel (Mytilus edulis). This study provided further the depuration mechanisms of Cd²⁺ from mussel (M. edulis), in particular to the role of MT and its chelate during the depuration process.

Toxicological profile of small airway epithelial cells exposed to gold nanoparticles

Gold nanoparticles (AuNPs) have diverse applications in the biomedical industry such as in diagnosis, labeling, delivering and sensing. Despite their prevalent medical use, nanotoxicity induced by AuNPs is still largely unknown. We have previously shown that AuNPs could exert cytotoxic effects on lung fibroblasts. In this study, we investigated the in vitro toxicological effects of AuNPs in small airway epithelial cells (SAECs) which are the first cells of contact for inhaled NPs and compared expression of metallothionein (MT), a reactive oxygen species scavenger, in SAECs and lung fibroblasts in vitro. Transmission electron microscopy (TEM) and energy-dispersive X-ray (EDX) spectroscopy study revealed cellular uptake of aggregates of AuNPs into the cytoplasm at the ultrastructural level. A significant increase in lipid peroxide as well as substantial DNA damage and cytotoxicity was observed in AuNP-treated cells. For MT expression, AuNPs induced down-regulation of the MT-1X isoform in SAECs, but up-regulation of the MT-1X and MT-2 A isoforms in MRC5 lung fibroblasts. The present study suggests that AuNPs could induce oxidative stress-related cytotoxicity and genotoxicity in SAECs.

Effect of Chlorella intake on Cadmium metabolism in rats

This study was performed to investigate the effect of chlorella on cadmium (Cd) toxicity in Cd- administered rats. Sixty male Sprague-Dawley rats (14 week-old) were blocked into 6 groups. Cadmium chloride was given at levels of 0 or 325 mg (Cd: 0, 160 ppm), and chlorella powder at levels of 0, 3 and 5%. Cadmium was accumulated in blood and tissues (liver, kidney and small intestine) in the Cd-exposed groups, while the accumulation of Cd was decreased in the Cd-exposed chlorella groups. Fecal and urinary Cd excretions were remarkably increased in Cd-exposed chlorella groups. Thus, cadmium retention ratio and absorption rate were decreased in the Cd exposed chlorella groups. Urinary and serum creatinine, and creatinine clearance were not changed in experimental animals. In addition, metallothionein (MT) synthesis in tissues was increased by Cd administration. The Cd-exposed chlorella groups indicated lower MT concentration compared to the Cd-exposed groups. Moreover, glomerular filtration rate (GFR) was not changed by dietary chlorella and Cd administration. According to the results above, this study could suggest that Cd toxicity can be alleviated by increasing Cd excretion through feces. Therefore, when exposed to Cd, chlorella is an appropriate source which counteracts heavy metal poisoning, to decrease the damage of tissues by decreasing cadmium absorption.

Low-Dose Cadmium Exposure Reduces Human Prostate Cell Transformation in Culture and Up-Regulates Metallothionein and MT-1G mRNA

Chronic low-level exposure to environmental toxins, including cadmium (Cd), is a growing problem in the industrialized world. One promising strategy for protection from these toxins is the use of low-dose exposure of environmental chemicals to induce cell tolerance and recovery, a phenomenon known as "protective hormesis". Hormetic [low-dose stimulatory] effects occur in a variety of systems and with a number of chemicals. Cd is a potent carcinogen in rodents and has also been linked to human lung and prostate cancers. In the present study, we have evaluated the protective effects of low and ultra-low dose, long-term Cd exposure in the normal human prostate cells, RWPE-1. Cells were exposed to low and ultra-low doses (0, 0 (S(-36)), 10(-6), 10(-7), 10(-18), 10(-21), 10(-32), or 10(-36)M) of Cd for 20 weeks followed by treatment with 10(-5)M Cd for another 8 weeks. Continuous exposure of RWPE-1 cells to 10(-5)M Cd results in malignant transformation. However, cells pretreated with low and ultra-low doses of Cd had delayed transformation compared with controls. In addition, the number of transformed cell mounds was lower in pretreated cells indicating that low and ultra-low dose exposure had protective effects against high-dose Cd induced carcinogenesis. The expression of metallothionein (MT), the primary Cd detoxification protein, was induced by low-dose exposure to Cd and maintained during the 20 weeks. In addition, MT-1G mRNA was up-regulated 2- to 3-fold by low-dose and ultralow-dose Cd exposures and may be the mechanism of protective hormesis in this model. MT-1G mRNA might also serve as a biological indicator of very low-dose environmental Cd exposure.