Cysteine sulfinate decarboxylase and cysteine dioxygenase activities do not correlate with strain-specific changes in hepatic and cerebellar taurine content in aged rats

Age-related decline in the taurine content of the skin in rodents

Taurine, a sulfur-containing amino acid, occurs at high concentrations in the skin, and plays a role in maintaining the homeostasis of the skin. We investigated the effects of aging on the content and localization of taurine in the skin of mice and rats. Taurine was extracted from the skin samples of hairless mice and Sprague Dawley rats, and the taurine content of the skin was determined by high-performance liquid chromatography (HPLC). The results of the investigation revealed that the taurine content in both the dermis and epidermis of hairless mice declined significantly with age. Similar age-related decline in the skin taurine content was also observed in rats. In contrast, the taurine content in the sole remained unchanged with age. An immunohistochemical analysis also revealed a decreased skin taurine content in aged animals compared with younger animals, although no significant differences in the localization of taurine were observed between the two age groups. Supplementation of the drinking water of aged mice with 3% (w/v) taurine for 4 weeks increased the taurine content of the epidermis, but not the dermis. The present study showed for the first time that the taurine content of the skin decreased with age in mice and rats, which may be related to the impairment of the skin homeostasis observed with aging. The decreased taurine content of the epidermis in aged animals was able to be rescued by taurine supplementation.

Weaning Mice and Adult Mice Exhibit Differential Carbon Tetrachloride-Induced Acute Hepatotoxicity

Age is a risk factor for drug-induced liver injury (DILI). However, there is a limited understanding of pediatric DILI. Here, 2-week-old weaning and 8-week-old adult male ICR mice were intraperitoneally injected with CCl₄ (0.1 mmol/kg equal to 15.4 mg/kg) to comparatively evaluate the time-dependent liver damage and cellular events. CCl₄ significantly enhanced the serum alanine aminotransferase/aspartate aminotransferase levels and hepatic centrilobular necrosis in the weaning mice, whereas it induced mild liver injury in the adult mice. CCl₄-treated weaning mice exhibited higher hepatic levels of pro-apoptotic proteins (Bax, cleaved caspase-3, -7, and -9), activated MAPKs (p-JNK and p-Erk), and endoplasmic reticulum stress indicators (ATF6 and CHOP) and lower hepatic anti-apoptotic Bcl-2 levels than the adult mice. The weaning mice exhibited enhanced basal hepatic glutathione (GSH) levels due to high glutamate cysteine ligase (GCL) and low anti-cysteine dioxygenase (CDO) enzyme levels. However, CCl₄ markedly reduced the hepatic GSH levels only in the weaning mice. Furthermore, higher hepatic levels of oxidative stress-induced malondialdehyde, 4-hydroxynonenal, nitrotyrosine-protein adducts, and oxidized proteins were observed in CCl₄-treated weaning mice than in CCl₄-treated adult mice. The enhanced levels of hepatic cytochrome P450 (CYP) 2E1 and CYP3A, and decreased hepatic GSH S-transferase (GST)-π and GSH reductase (GR) levels in the weaning mice may contribute to their enhanced susceptibility to liver damage.

Identification of Reliable Components in Multivariate Curve Resolution-Alternating Least Squares (MCR-ALS): a Data-Driven Approach across Metabolic Processes

There is an increasing need to use multivariate statistical methods for understanding biological functions, identifying the mechanisms of diseases, and exploring biomarkers. In addition to classical analyses such as hierarchical cluster analysis, principal component analysis, and partial least squares discriminant analysis, various multivariate strategies, including independent component analysis, non-negative matrix factorization, and multivariate curve resolution, have recently been proposed. However, determining the number of components is problematic. Despite the proposal of several different methods, no satisfactory approach has yet been reported. To resolve this problem, we implemented a new idea: classifying a component as “reliable” or “unreliable” based on the reproducibility of its appearance, regardless of the number of components in the calculation. Using the clustering method for classification, we applied this idea to multivariate curve resolution-alternating least squares (MCR-ALS). Comparisons between conventional and modified methods applied to proton nuclear magnetic resonance (¹H-NMR) spectral datasets derived from known standard mixtures and biological mixtures (urine and feces of mice) revealed that more plausible results are obtained by the modified method. In particular, clusters containing little information were detected with reliability. This strategy, named “cluster-aided MCR-ALS,” will facilitate the attainment of more reliable results in the metabolomics datasets.

Branched-chain amino acids inhibit the TGF-beta-induced down-regulation of taurine biosynthetic enzyme cysteine dioxygenase in HepG2 cells

Taurine deficiency has been suggested to contribute to the pathogenesis and complications of advanced hepatic diseases. The molecular basis for a low level of taurine associated with hepatic failure is largely unknown. Using carbon tetrachloride (CCl₄)-induced cirrhotic rat model, we found that the activity and expression of cysteine dioxygenase (CDO), a rate-limiting enzyme in taurine synthesis, were significantly decreased in the liver of these rats. To investigate the underlying mechanisms for the suppression, we examined the effects of pathological cytokines on CDO expression in human hepatoma HepG2 cells. Among the several cytokines, transforming growth factor-β (TGF-β), one of the key mediators of fibrogenesis, suppressed Cdo1 gene transcription through the MEK/ERK pathway. Finally, we further examined potential effects of branched-chain amino acids (BCAA) on CDO expression, as it has been reported that oral BCAA supplementation increased plasma taurine level in the patients with liver cirrhosis. BCAA, especially leucine, promoted Cdo1 gene transcription, and attenuated TGF-β-mediated suppression of Cdo1 gene expression. These results indicate that the low plasma level of taurine in advanced hepatic disease is due to decreased hepatic CDO expression, which can be partly attributed to suppressive effect of TGF-β on Cdo1 gene transcription. Furthermore, our observation that BCAA promotes Cdo1 expression suggests that BCAA may be therapeutically useful to improve hepatic taurine metabolism and further suppress dysfunctions associated with low level of taurine in hepatic diseases.

Age-related retinal degeneration in animal models of aging: possible involvement of taurine deficiency and oxidative stress

There is strong evidence that the retina degenerates with age. Electroretinogram deficits and photoreceptor cell death and structural abnormalities have been observed in both animal and human studies of aging. The mechanism behind this phenomenon is a very interesting area for scientific and medical study. Current data support the link between retinal degeneration and increased oxidative stress. Taurine is a free amino acid found in high millimolar concentrations in the retina, and age-related deficiency in retinal levels of taurine may contribute to the retinal degeneration associated with age. Taurine acts as an antioxidant and taurine replenishment is known to alleviate oxidative stress in the retina. Thus taurine supplementation may be useful in the treatment of age-related retinal dysfunction.

Methods to examine molecular changes and behavioral effects of drug administration

Our laboratory has developed an integrative approach to study the molecular changes and behavioral effects of drug administration consisting of a combination of quantitative real-time reverse transcription polymerase chain reaction, RNA isolation and differential display, in situ hybridization, place preference conditioning and high-performance liquid chromatography. Although the techniques are not novel, this multi-systems approach allows for the examination of gene expression changes following the administration of drugs of abuse such as cocaine, and allows for an analysis of behavior and neurochemistry of gene knockout mice. As a result of this combination of techniques, we have been able to determine the expression, location and function of the CD81 protein. Specifically, CD81 was induced exclusively in the nucleus accumbens by cocaine treatment. Subsequent behavioral testing of CD81 knockout mice revealed these mice displayed altered sensitivity to cocaine.

Taurine as a micronutrient in development and regeneration of the central nervous system

Taurine is an amino acid known to possess trophic properties in the central nervous system. The relevance of its presence in maternal milk is related to its role as an essential nutrient. Taurine deficiency around birth produces anatomical and functional modifications in the brain and in the retina. In addition, taurine favors neuron proliferation and survival, as well as neurite extension. The mechanisms by which taurine exerts its trophic role in the regenerating retina are related to increases in calcium fluxes, to modifications of protein phosphorylation, and to influence of the target organ. Moreover, taurine-zinc interaction might be crucial in the development of structures such as the hippocampal formation. Thus, taurine can be considered as one of the determinant nutritional molecules during development and regeneration of the central nervous system.

Dietary taurine manipulations in aged male Fischer 344 rat tissue: taurine concentration, taurine biosynthesis, and oxidative markers11Abbreviations: CA, cysteic acid; CSA, cysteine sulfinic acid; CSD, cysteine sulfinic acid decarboxylase; CDO, cysteine dioxygenase; DNPH, 2,4-dinitrophenylhydrazin; DPPH, α,α-diphenyl-β-picrylhydrazyl; F344, Fischer 344; HPLC-ECD, high performance liquid chromatography with electrochemical detection; MDCK, Madin Darby canine kidney; PCA, perchloric acid; TAU, taurine; TBARS, thiobarbituric acid; and TCA, trichloroacetic acid

Taurine (TAU) is a ubiquitous sulfur-containing amino acid that has been proposed to be an antioxidant. The concentration of TAU decreases during aging, which may increase susceptibility to oxidative stress. Our study attempted to elucidate the mechanism for the age-dependent decrease in TAU content by examining TAU biosynthesis in aged rats. We also examined the effects of dietary TAU manipulations on TAU content and oxidative markers in aged male Fischer 344 (F344) rats. Adult (9 months) and aged (26 months) rats fed control diets, aged rats fed control diet and TAU-supplemented (1.5%) water, and aged rats fed a TAU-deficient diet were used. We observed a significant age-related decrease in TAU content in liver, kidney, and cerebellum. Dietary TAU supplementation increased tissue TAU content, whereas dietary TAU restriction had no effect. Enzyme-dependent TAU synthesis showed an age-dependent reduction in liver that was decreased further by TAU supplementation. Protein carbonyl content was elevated in the cerebral cortex and kidney of aged rats and was attenuated by TAU supplementation. A trend for a decrease in protein and acid-soluble thiol contents in hepatic tissue of aged rats was observed, and this was attenuated with dietary TAU supplementation. Our data show that a decrease in hepatic TAU biosynthesis may cause, in part, the observed decline in tissue TAU content in aged F344 rats, and TAU supplementation can restore TAU levels. Our study indicates that a decline in TAU content may exacerbate oxidative stress in aged rats, which can be reversed by dietary TAU supplementation.

Oxidative-stress-dependent up-regulation of Bcl-2 expression in the central nervous system of aged Fisher-344 rats

Oxidative stress has been shown to play a role in aging and in neurodegenerative disorders. Some of the consequences of oxidative stress are DNA base modifications, lipid peroxidation, and protein modifications such as formation of carbonyls and nitrotyrosine. These events may play a role in apoptosis, another factor in aging and neurodegeneration, in response to uncompensated oxidative stress. Bcl-2 is a mitochondrial protein that protects neurons from apoptotic stimuli including oxidative stress. Using immunohistochemistry and western blot analysis, here we show that Bcl-2 is up-regulated in the hippocampus and cerebellum of aged (24 months) Fisher 344 rats. Treatment with the free radical spin trap N-tert-butyl-alpha-phenylnitrone (PBN) effectively reverses this age-dependent Bcl-2 up-regulation indicating that this response is redox sensitive. This conclusion was further supported by inducing the same regional Bcl-2 up-regulation in young (3 months) Fisher 344 rats exposed to 100% normobaric O(2) for 48 h. Our results indicate that Bcl-2 expression is increased in the aged brain, possibly as a consequence of oxidative stress challenges. These results also illustrate the effectiveness of antioxidants in reversing age-related changes in the CNS and support further research to investigate their use in aging and in age-related neurodegenerative disorders.