Optimization and application of glutamate cysteine ligase measurement in wildlife species

Serine Supplementation Alleviates Doxorubicin-Induced Oxidative Damage in Skeletal Muscle of Mice

Muscle weakness affects physical activity and quality of life of patients. Serine, a nutritionally non-essential amino acid has been reported to enhance protein synthesis and implicate in biosynthesis of multiple bioactive molecules. It remains unknown whether it can protect mice against oxidative stress-induced muscles weakness. This study was conducted to test the hypothesis that serine administration alleviates doxorubicin-induced oxidative damage in skeletal muscle of mice. Mice pre-treated with or without serine were intraperitoneally injected with either doxorubicin or equal volume of saline. Reactive oxygen species (ROS) accumulation, activity of antioxidant enzymes, oxidation product of protein, DNA, and lipid, activity of mitochondrial complex, and protein level of nuclear-factor-erythroid-2-related factor 2 (NRF2)/constitutive-androstane-receptor (CAR) signaling in skeletal muscle of mice were determined. Compared with the control, doxorubicin exposure led to oxidative damage as shown by increased ROS accumulation, decreased activity of antioxidant enzymes, and enhanced oxidative product of protein, DNA, and lipid in the skeletal muscle of mice. These effects of doxorubicin were associated with increased activity of complex I and reduced glutathione. Interestingly, doxorubicin-induced oxidative damage was alleviated by serine administration. Further study showed that the beneficial effect of serine was associated with enhanced NRF2/CAR signaling. Our result showed that serine attenuated doxorubicin-induced muscle weakness in mice. Serine supplementation might be a nutritional strategy to improve the function of skeletal muscle in patients exposed to doxorubicin.

Serine is required for the maintenance of redox balance and proliferation in the intestine under oxidative stress

Serine has critical roles in maintaining cell growth and redox balance in cancer cells. However, the role of exogenous serine played in oxidative response and proliferation in normal mammalian intestine need to be further elucidated. We used a mouse model and intestinal porcine epithelial cells (IPEC-J2) to reveal that exogenous serine deficiency did not lead to redox imbalance and inhibition of proliferation in the intestine. However, serine deficiency exacerbated oxidative stress, mitochondrial dysfunction, apoptosis, and inhibition of proliferation in IPEC-J2 cells challenged by hydrogen peroxide, while serine supplementation rescued redox imbalance and those proliferation defects. Importantly, serine supplementation restored the glutathione content and decreased the accumulation of reactive oxygen species, while no such effects were observed when glutathione synthesis was inhibited. Additionally, serine supplementation increased nuclear nrf2 expression in IPEC-J2 cells. These results suggested that serine alleviates oxidative stress through supporting glutathione synthesis and activating nrf2 signaling. We further found that serine supplementation activated the mTOR pathway, while inhibition of mTOR diminished the effects of serine on promoting proliferation, suggesting critical roles of the mTOR pathway in this context. Taken together, our study underlines the importance of serine in the maintenance of redox status and proliferation in the intestine and reveals a novel potential mechanism that mediates these effects.

Hydrogen Sulfide Donor NaHS Improves Metabolism and Reduces Muscle Atrophy in Type 2 Diabetes: Implication for Understanding Sarcopenic Pathophysiology

Sarcopenia, a loss of muscle mass and functionality, constitutes a major contributor to disability in diabetes. Hydrogen sulfide (H₂S) dynamics and muscle mass regulatory signaling were studied in GK rats, a model for type 2 diabetes (T2D). GK rats exhibited a number of features that are consistent with sarcopenia and T2D including loss of muscle mass and strength, in addition to glucose intolerance, insulin resistance, and impaired β-cell responsiveness to glucose. Mechanistically, activation levels of Akt, a key modulator of protein balance, were decreased in T2D. Consequently, we confirmed reduced activity of mTOR signaling components and higher expression of atrophy-related markers typified by FoxO1/atrogin-1/MuRF1 and myostatin-Smad2/3 signaling during the course of diabetes. We observed in GK rat reduced antioxidant capacity (↓GSH/GSSG) and increased expression and activity of NADPH oxidase in connection with augmented rate of oxidation of lipids, proteins, and DNA. H₂S bioavailability and the expression of key enzymes involved in its synthesis were suppressed as a function of diabetes. Interestingly, GK rats receiving NaHS displayed increased muscle Akt/mTOR signaling and decreased expression of myostatin and the FoxO1/MuRF1/atrogin-dependent pathway. Moreover, diabetes-induced heightened state of oxidative stress was also ameliorated in response to NaHS therapy. Overall, the current data support the notion that a relationship exists between sarcopenia, heightened state of oxidative stress, and H₂S deficiency at least in the context of diabetes. Moreover, treatment with a potent H₂S donor at an early stage of diabetes is likely to mitigate the development of sarcopenia/frailty and predictably reduces its devastating sequelae of amputation.

Serine prevented high-fat diet-induced oxidative stress by activating AMPK and epigenetically modulating the expression of glutathione synthesis-related genes

Serine deficiency has been observed in patients with nonalcoholic fatty liver disease (NAFLD). Whether serine supplementation has any beneficial effects on the prevention of NAFLD remains unknown. The present study was conducted to investigate the effects of serine supplementation on hepatic oxidative stress and steatosis and its related mechanisms. Forty male C57BL/6J mice (9week-old) were randomly assigned into four groups (n=10) and fed: i) a low-fat diet; ii) a low-fat diet supplemented with 1% (wt:vol) serine; iii) a high-fat (HF) diet; and iv) a HF diet supplemented with 1% serine, respectively. Palmitic acid (PA)-treated primary hepatocytes separated from adult mice were also used to study the effects of serine on oxidative stress. The results showed that serine supplementation increased glucose tolerance and insulin sensitivity, and protected mice from hepatic lipid accumulation, but did not significantly decreased HF diet-induced weight gain. In addition, serine supplementation protected glutathione (GSH) antioxidant system and prevented hypermethylation in the promoters of glutathione synthesis-related genes, while decreasing reactive oxygen species (ROS) in mice fed a HF diet. Moreover, we found that serine supplementation increased phosphorylation and S-glutathionylation of AMP-activated protein kinase α subunit (AMPKα), and decreased ROS, malondialdehyde and triglyceride contents in PA-treated primary hepatocytes. However, while AMPK activity or GSH synthesis was inhibited, the abovementioned effects of serine on PA-treated primary hepatocytes were not observed. Our results suggest that serine supplementation could prevent HF diet-induced oxidative stress and steatosis by epigenetically modulating the expression of glutathione synthesis-related genes and through AMPK activation.

Arsenic responsive microRNAs in vivo and their potential involvement in arsenic-induced oxidative stress

Arsenic exposure is postulated to modify microRNA (miRNA) expression, leading to changes of gene expression and toxicities, but studies relating the responses of miRNAs to arsenic exposure are lacking, especially with respect to in vivo studies. We utilized high-throughput sequencing technology and generated miRNA expression profiles of liver tissues from Sprague Dawley (SD) rats exposed to various concentrations of sodium arsenite (0, 0.1, 1, 10 and 100mg/L) for 60days. Unsupervised hierarchical clustering analysis of the miRNA expression profiles clustered the SD rats into different groups based on the arsenic exposure status, indicating a highly significant association between arsenic exposure and cluster membership (p-value of 0.0012). Multiple miRNA expressions were altered by arsenic in an exposure concentration-dependent manner. Among the identified arsenic-responsive miRNAs, several are predicted to target Nfe2l2-regulated antioxidant genes, including glutamate-cysteine ligase (GCL) catalytic subunit (GCLC) and modifier subunit (GCLM) which are involved in glutathione (GSH) synthesis. Exposure to low concentrations of arsenic increased mRNA expression for Gclc and Gclm, while high concentrations significantly reduced their expression, which were correlated to changes in hepatic GCL activity and GSH level. Moreover, our data suggested that other mechanisms, e.g., miRNAs, rather than Nfe2l2-signaling pathway, could be involved in the regulation of mRNA expression of Gclc and Gclm post-arsenic exposure in vivo. Together, our findings show that arsenic exposure disrupts the genome-wide expression of miRNAs in vivo, which could lead to the biological consequence, such as an altered balance of antioxidant defense and oxidative stress.

Fibroblast growth factor 9 upregulates heme oxygenase-1 and gamma-glutamylcysteine synthetase expression to protect neurons from 1-methyl-4-phenylpyridinium toxicity

Oxidative stress and lower levels of trophic factors involved in nigrostriatal dopaminergic neurodegeneration are a hallmark of Parkinson disease. Our previous studies found that fibroblast growth factor 9 (FGF9) prevented 1-methyl-4-phenylpyridinium (MPP(+))-induced nigral dopaminergic neuron death and was involved in the neuroprotection of the antioxidant melatonin. However, the protective mechanisms mediated by FGF9 remain unclear. Herein, we explored whether FGF9 regulated the cellular antioxidant defense protecting dopaminergic neurons against MPP(+) intoxication. We found that FGF9 treatment alone induced a decrease in hydrogen peroxide (H(2)O(2)) level, an increase in glutathione content, and an upregulation of gamma-glutamylcysteine synthetase (gamma-GCS) and heme oxygenase 1 (HO-1) expression in primary cortical neurons but not in astrocytes. Simultaneous treatment with FGF9 and MPP(+) prevented MPP(+)-induced neuron death and H(2)O(2) overproduction but did not affect the FGF9-increased gamma-GCS and HO-1 protein expression. Inhibition of gamma-GCS or HO-1 prevented the inhibitory effect of FGF9 on MPP(+)-induced H(2)O(2) production and death in mesencephalic dopaminergic and cortical neurons. However, in the absence of MPP(+), the FGF9-induced H(2)O(2) reduction was blocked by HO-1 inhibitors, but not by gamma-GCS inhibitors. These results indicate that FGF9 upregulates gamma-GCS and HO-1 expression to protect cortical and dopaminergic neurons from MPP(+)-induced oxidative insult.

Aging impairs the expression of the catalytic subunit of glutamate cysteine ligase in soleus muscle under stress

This study investigated the mechanisms responsible for the disrupted homeostasis of reduced glutathione (GSH) in aging muscles with stress (14 days of hind-limb unloading [HU]). Adult and old rats were randomized into four groups: weight bearing and 3, 7, and 14 days of HU. Soleus muscles were harvested to investigate the activity or content of enzymes involved in GSH metabolism (utilization and synthesis). The activities of glutathione S transferase, glutathione reductase, gamma-glutamyl transpeptidase, and glutamate cysteine ligase (GCL) were determined. The protein content of the two subunits of GCL, catalytic subunit (GCLC) and modifier subunit (GCLM), were evaluated. The major results, failure to maintain the accelerated GCLC production and GCL activity, are associated with the GSH depletion in aging muscles with 14 days of HU. The results suggest that the regulation of GCL, especially the catalytic subunit, with stress may be compromised in aging muscles.

Responses of glutamate cysteine ligase and glutathione to oxidants in deer mice (Peromyscus maniculatus)

Sensitivities of a wildlife species, deer mice, to oxidants were evaluated. A single dose (1589 mg/kg body weight by intraperitoneal injection) of carbon tetrachloride, a typical hepatotoxicant, caused changes in GCL activity and GSH content in multiple organs of deer mice. Hepatic GCL activity and GSH content were depleted substantially (P<0.01), renal GCL activity increased (P<0.05). Blood, brain and heart GCL activities increased (P<0.05), whereas GSH contents decreased significantly. Deer mice were exposed to Pb, or Pb together with Cu and Zn via drinking water for 4 weeks. GCL activities were not significantly affected by treatments. GSH contents were increased significantly by Pb alone, Pb with medium and high concentrations of Cu and Zn. Effects of multi-metal-contaminated soil were investigated via lactational, juvenile and lifelong exposure to feed supplemented with soils. Metal-contaminated soils did not lead to significant effects in pups via lactation, 50-day exposure altered GSH content marginally, while 100-day exposure resulted in marked GCL activity depletion. After 100-day exposure, GCL activities of the medium soil-, high soil- and Pb-treated deer mice were only 53%, 40% and 46% of the control, respectively (P<0.0001).