The sodium-vitamin C co-transporter SVCT2 is primarily responsible for the accumulation of the important antioxidant ascorbate into brain cells. In vitro studies have demonstrated strong expression of this transporter in cultured astrocytes, whereas in situ hybridization analysis has so far detected SVCT2 only in neurons. In the present study, we examined the response of SVCT2 mRNA expression in the brain to focal ischemia induced for 2 h by unilateral middle cerebral artery occlusion. The mRNA expression patterns of SVCT2 and the glutamate-activated immediate early gene Arc were investigated at 2 and 22 h after ischemia. SVCT2 and Arc mRNA expression was lost in the ischemic core at both time points. In areas outside the core, Arc was strongly up-regulated, primarily at 2 h, whereas SVCT2 showed an increase at 2 and 22 h. SVCT2 expression was increased in neurons as well as in astrocytes, providing the first evidence for SVCT2 expression in astrocytes in situ. These findings underscore the importance of ascorbate as a neuroprotective agent and may have implications for therapeutic strategies. In addition, the increase of SVCT2 in astrocytes after ischemia suggests that cultured astrocytes are exposed to chronic oxidative stress.
Forty Fischer-344 male rats were given a high-risk diet (HRD) that was high in fat, low in fiber and low in calcium. After 4 weeks, the rats were given two weekly s.c. injections of azoxymethane (AOM, 15 mg/kg body wt), and remained on the same diet till death. Eight rats were killed at 12 weeks and again at 20 weeks in order to microdissect aberrant crypt foci (ACF) containing four or more crypts/focus from their colons. The remaining 24 rats were killed at 30 weeks to harvest colonic tumors. The polymerase chain reaction (PCR) was used to amplify specific DNA segments in the K-ras gene from ACF and colonic tumors. The PCR-amplified DNAs were sequenced to identify the point mutations in codons 12 and 13. All the mutations detected in the ACF and colonic tumors were G to A transitions in the second position of codon 12. These mutations were present in the ACF of 2/8 (25%) and 3/8 (37%) rats at 12 and 20 weeks respectively. The mutations were present in colonic tumors of 7/24 (29%) rats. These results provide important evidence for the significance of K-ras mutations in ACF (> 4 crypts/focus) as early markers of malignant potential in the colons of F344 rats exposed to AOM while receiving a high-risk western style diet.
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