Elevation of the level of thiobarbituric acid-reactive products in hindleg skeletal muscle of dystrophic mice, but non-elevation in tongue muscle

In vivo CH3(CH2)11SAu SAM electrodes in the beating heart: in situ analytical studies relevant to pacemakers and interstitial biosensors

To study in vivo modification of the SAM equivalent circuit when a highly ordered SAM is used as a bioelectrode, dodecanethiolate SAM-Au intramuscular electrodes were studied in living rat heart in a challenging in situ perfused rat model by impedance spectroscopy, cyclic voltammetry, and neutron activation analysis (NAA). The SAM layer experienced disintegration in vivo biological system, as NAA detected the presence of Au atoms that had leached into the surrounding living tissue. Therefore, the underlying Au surface became exposed during biological implant. Study by impedance spectroscopy, however, revealed perfect capacitive behavior for the SAM, similar to in vitro behavior. Electrodes showed a pure capacitive Nyquist plot with 86.1-89.4 degrees near-vertical line segments as the equivalent circuit locus, as for a parallel plate capacitor. Impedance magnitude varied linearly with 1/omega excluding diffusionally limited ionic charge transport. There was no diffusional conductive element Z(W infinity ) or spatially confined Warburg impedance Z(D). The effect of in vivo exposure of a highly ordered SAM is a 'sealing over' effect of new defects by the binding of proteinaceous or lipid species in the biological milieu, a fact of significance for SAM electrodes used either as pacemaker electrodes or as a platform for in vivo biosensors.

Relationship between NADP-specific isocitrate dehydrogenase and glutathione peroxidase in aging rat skeletal muscle

The glutathione peroxidase (GPX) system detoxifies hydroperoxides in cells and uses NADPH to regenerate reduced glutathione. Enzymatic sources of NADPH in skeletal muscle include NADP-specific isocitrate dehydrogenase (ICDP), glucose-6-phosphate dehydrogenase (G6PD), and malic enzyme (ME). Our purpose was to explore the relationship in skeletal muscle between GPX and ICDP along with other NADPH-generating enzymes as a function of progressive age and muscle fiber-type. Soleus (SOL), red gastrocnemius (RG), and white gastrocnemius (WG) muscles were extracted from Fischer-344 rats of three different ages: 4 months old (Y); 18 months old (M); and 24 months old (O). Assays were conducted to determine activities of GPX, ICDP, G6PD, and ME along with levels of lipid hydroperoxides. GPX activities were significantly greater in RG and WG of old rats than in younger. ICDP activities were higher in the WG of old and middle aged rats when compared to young adults. GPX and ICDP activities exhibited similar differences among the muscles tested (SOL>RG>WG). In contrast, G6PD and ME activities were not significantly different across muscles. G6PD activities increased in RG with age, but were well over an order of magnitude lower than ICDP in all muscles. ME activities were universally lower than ICDP in all muscles, and decreased with old age in the WG and RG. Lipid hydroperoxides were significantly higher with aging in RG. Significant correlations were found between GPX and ICDP in all muscles. Stepwise regression resulted in a model (R(2)=0.82) that included ICDP and ME in predicting GPX. In summary, these data are consistent with the hypotheses that ICDP is higher in more oxidative fibers, inducible with aging, and most closely associated with the glutathione peroxidase system in skeletal muscle.

A G.U base pair in the eukaryotic selenocysteine tRNA is important for interaction with SePF, the putative selenocysteine-specific elongation factor

In Escherichia coli, selenocysteine biosynthesis and incorporation into selenoproteins requires the action of four gene products, including the specialized selenocysteine tRNA(Sec) and elongation factor SELB, different from the universal EF-Tu. In this regard, the situation is less clear in eukaryotes, but we previously reported the existence of SePF, a putative SELB homologue. The secondary structure of the tRNA(Sec) differs slightly in eukaryotes, due to a change in the lengths of several stems. Two non-Watson-Crick base pairs, G5a x U67b and U6 x U67, reside in the acceptor stem and are conserved in the course of evolution. Since it has already been reported that changing them to Watson-Crick base pairs did not affect the serylation or selenylation levels of tRNA(Sec), we asked whether these non-Watson-Crick base pairs are required for the interaction with SePF. To this end, tRNA(Sec) variants carrying Watson-Crick changes at these positions were tested for their ability to maintain the interaction with SePF. In these assays, the tRNA(Sec)-SePF interaction was determined by the protective action it confers against hydrolysis of the amino acid ester bond, under basic conditions. All the changes introduced at U6 x U67 did not significantly affect the interaction. Interestingly, however, the G5a x U67b to G5a-C67b substitution was sufficient, by itself, to lead to unprotection of the ester bond. Therefore, our finding strongly suggests that SePF is unable to interact with a tRNA(Sec) mutant version carrying a Watson-Crick G5a-C67b instead of the wild-type G5a x U67b base pair, establishing that G5a x U67b constitutes a structural determinant for SePF interaction.

Expression of the glutathione peroxidase gene lacking its 3' untranslated region

In order to investigate the expression of human cellular glutathione peroxidase (GPx), we mutated the gene encoding GPx by deleting either the 5' or 3' untranslated region (utr), subcloned the deleted fragments into plasmid pSVL followed by transfection into COS-7 cells and measured the amount of GPx expressed. When the 5' utr of the gene was deleted, GPx was not expressed. However, the deletion of the 3' utr resulted in some expression of GPx. Deletion of the poly A region of the GPx gene resulted in the expression of GPx but the level was lower than that of the full-length cGPx. The complete deletion of the 3' utr resulted in a half of the expression of the poly A deletion mutant. Thus, the expression of GPx increased according to the length of the 3' utr. These results suggest that the GPx gene carrying one SECIS on 5' utr (FEBS Lett. 312(1992)10-14) is essential for GPx expression. SECIS on 3' utr might not play a key role of GPx expression. Expression of GPx by COS-7 cells was not observed when a plasmid harboring an antisense gene was transfected.

Oxidative stress as a potential pathogenic mechanism in an animal model of Duchenne muscular dystrophy

Dystrophin-deficiency results in degeneration of most, but not all, skeletal muscles. The mechanisms responsible for degeneration of limb muscle and sparing of extraocular muscle are not known. To address the notion that muscle pathology may be free radical-mediated, we evaluated antioxidant enzyme activities and lipid peroxidation products (TBARS) content in mdx and control mice. TBARS content and the activities of total superoxide dismutase, selenium dependent glutathione peroxidase, glucose-6-phosphate dehydrogenase and catalase were consistently higher in both affected and spared muscles of mdx mice. These data suggest that oxidative stress may be constitutively present in mdx muscle, but may not be the principal pathogenic mechanism. To further test the hypothesis of oxidative stress involvement in dystrophinopathies, control strain and mdx mice were subjected to chronic hyperoxia. The pattern of antioxidant enzyme activities and TBARS content from hyperoxic control strain mice was similar to that of normoxic mdx mice, suggesting that a similar level of oxidative stress was induced. In conclusion, this study has provided indirect evidence for oxidative stress in dystrophin-deficient muscle.