Effect of endurance training and branched-chain amino acids on the signaling for muscle protein synthesis in CKD model rats fed a low-protein diet.

A low-protein diet (LPD) protects against the progression of renal injury in patients with chronic kidney disease (CKD). However, LPD may accelerate muscle wasting in these patients. Both exercise and branched-chain amino acids (BCAA) are known to increase muscle protein synthesis by activating the mammalian target of rapamycin (mTOR) pathway. The aim of this study was to investigate whether endurance exercise and BCAA play a role for increasing muscle protein synthesis in LPD-fed CKD (5/6 nephrectomized) rats. Both CKD and sham rats were pair-fed on LPD or LPD fortified with a BCAA diet (BD), and approximately one-half of the animals in each group was subjected to treadmill exercise (15 m/min, 1 h/day, 5 days/wk). After 7 wk, renal function was measured, and soleus muscles were collected to evaluate muscle protein synthesis. Renal function did not differ between LPD- and BD-fed CKD rats, and the treadmill exercise did not accelerate renal damage in either group. The treadmill exercise slightly increased the phosphorylation of p70s6 kinase, a marker of mTOR activity, in the soleus muscle of LPD-fed CKD rats compared with the sham group. Furthermore, BCAA supplementation of the LPD-fed, exercise-trained CKD rats restored the phosphorylation of p70s6 kinase to the same level observed in the sham group; however, the corresponding induced increase in muscle protein synthesis and muscle mass was marginal. These results indicate that the combination of treadmill exercise and BCAA stimulates cell signaling to promote muscle protein synthesis; however, the implications of this effect for muscle growth remain to be clarified.

Suppressive effects of phosphorylated ascorbate on ultraviolet B radiation-induced DNA damage and differential expression of the wild-type and mutated p53 tumor-suppressor gene in keratinocytes.

Ultraviolet B radiation (UVB)-induced DNA damage such as cyclobutane pyrimidine dimers (CPDs) and (6-4) photoproducts (6-4PP) in mouse epidermal keratinocytes (Pam212) was suppressed by pre-irradiation administration of two autooxidation-resistant vitamin C derivatives, ascorbic acid (Asc)-2-O-phosphate (Asc2P) and dehydro-Asc, but not by Asc or Asc-2-O-α-glucoside (Asc2G). According to Western blot analysis of the UVB-irradiated keratinocytes, expression of the tumor suppressor gene p53 was immediately enhanced from low pre-irradiation levels to the nearly maximum level at 2 h post-irradiation. In contrast, the p53-antagonizing oncogene mdm2 was scarcely expressed at 0-1 h post-irradiation, but was drastically enhanced at 2-3 h post-irradiation, eventually paralleling p53 expression. This suggests that the period for the actual effective function of p53 proteins may be restricted to the initial 0-3 h after UVB irradiation. p53 expression reached the maximum at 3 h post-irradiation and remained unchanged until at least 6 h, reaching its maximum at UVB doses of 20-100 mJ/cm2 - nearly equal to the minimum erythema dose (MED) or to the doubled score for human skin. However, at 200-500 mJ/cm2, p53 expression was markedly suppressed. This suggests a risk for potential photocarcinogenesis at doses greater than double the MED. UVB-induced p53 expression was notably suppressed by Asc2P or dehydro-Asc, but not by Asc. Nuclear expression of the wild-type p53 gene (wt-p53) was markedly promoted at 6 h post-irradiation, and significantly suppressed by Asc, Asc2G or dehydro-Asc, as well as by Asc2P. In contrast, mutation-type p53 (mt-p53), which is known to interfere with wt-p53 function, was not markedly expressed in the nuclei and was explicitly suppressed by Asc2P but not by Asc, dehydro-Asc or Asc2G, which was not cytoprotective against UVB. Thus, compared to non-cytoprotective Asc or the other derivatives, Asc2P suppressed UVB-induced CPD and 6-4PP formation, resulting in both cytoprotective effects and the preferential suppression of mt-p53 over wt-p53.

Telomere length of the skin in association with chronological aging and photoaging.

BACKGROUND: Telomere shortening has been implicated in cellular senescence, which may cause certain aging phenotypes. OBJECTIVE: To reveal whether telomere shortening is associated with chronological aging and/or photoaging of the skin, we measured telomere length in the epidermis and in the dermis from sun-protected and from sun-exposed sites of the skin. METHODS: Seventy-six specimens of epidermis from sun-protected sites and 24 specimens of epidermis from sun-exposed sites were analyzed. Sixty specimens of the dermis were also analyzed. In six cases, epidermal specimens from sun-protected and from sun-exposed sites of the same individual were analyzed. RESULTS: Comparison of telomere lengths revealed that the epidermis has shorter telomeres than the dermis. Telomere length in the epidermis and in the dermis was reduced with age, and average telomere shortening rates in the epidermis and in the dermis were 9 and 11 bp/yr, respectively. Unexpectedly, telomere length was not significantly different between epidermis from sun-exposed sites and from sun-protected sites. CONCLUSION: We could not show the evidence that telomere shortening is associated with photoaging of the skin.

Preventive effects of phosphorylated ascorbate on ultraviolet-B induced apoptotic cell death and DNA strand cleavage through enrichment of intracellular vitamin C in skin epidermal keratinocytes.

Mortality of mouse keratinocytes Pam212 that were irradiated with ultraviolet-B (UVB) was shown to be repressed by pre-irradiated administration with L-ascorbic acid (Asc) or more markedly with Asc-2-O-phosphate (Asc2P), but not with dehydroascorbic acid (DehAsc) or Asc-2-O-alpha-glucoside (Asc2G), although not repressed by post-irradiated administration. The cytoprotection by Asc2P was restricted against UVB below 5-20 mJ/cm2, and exhibited markedly by administration for a period over 2 h, which may be caused by intracellular Asc that was accumulated via dephosphorylation of Asc2P and was increased, 6-24 h after, to levels above twice as abundant as those of Asc-administration. Pre-irradiated Asc2P-administration slightly repressed a DNA ladder-like electrophoretic pattern for UVB-irradiated keratinocytes, containing the histone-bound DNA fragments as shown by ELISA assay, and appreciably repressed the DNA-3'OH cleavage terminals as shown by terminal deoxyribonucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) stain. Thus, prevention of UVB-induced cell death by Asc2P was shown to occur concurrently with inhibition of DNA cleavages and enrichment of intracellular Asc.