3. Results and Discussion
3.1. Analysis of GABA from Rice Extracts by HPLC Method.PGBR ex with enhanced GABA level were tested comparable with BR ex and WR ex. The content of GABA in the PGBR ex, BR ex and WR ex were compared with standard GABA. The concentration of GABA in PGBR ex (9.90 mg±0.02/100g of flour) was 3 times and 8 times higher than the GABA content in BR ex (3.30±0.01 mg/100g of flour) and in WR ex (1.24±0.02 mg/100g offlour) respectively, as shown in Table.1 (the data average are base on three measurement of each sample).
Table 1. The content of GABA from rice extracts
aResults are given as Mean Values ± SD (n=3)
3.2. The Cytotoxicity of Rice Extracts and Aβ1-42 on SK-N- SH CellsFirst, we attempted to establish the cytotoxicity of rice ex by using the doses dependent on human neuronal SK-N-SH cells. PGBR ex, BR ex and WR ex was applied by increasing concentrations 0-4000 ⎧g/ml for 24 h. We found that the number of cells viability had no significantly different to decrease. The cells survival were up to 96.4 ± 0.052% (p>0.48), PGBR ex 98.9 ± 0.032% (p>0.30), BR ex 96.3 ± 0.039% (p>0.39), and WR ex 95.3 ± 0.037% (p>0.25) respectively. These data showed no toxicity of rice extracts affect on human neuronal SK-N-SH cells (Figure 1).
Figure 1. The Effects of rice ex on SK-N-SH cells viability using MTT assay. Pre-incubated cells with increasing concentrations of rice ex at 0- 4000 ⎧g/ml. Results are expressed as percentages of the control value (CON) and data shown are means ± S.D of three replicate experiments.
Figure 2. The Effects of Aβ1-42 on SK-N-SH cells viability using MTT assay. Cells viability was significantly decreased on time and concentration dependent manner. Results are expressed as percentages of the control value. * = P<0.05 compared to the untreated control.
Similar as Chan-Ho Oh and Suk-Heung Oh [16], they tested the effects of the BR ex on the viability of Hela cells,
by treated cells with the BR ex 2000 ⎧g/ml in cultured and the viability of the cells was assayed. They showed that BR ex had no effects on the retardation of HeLa cell survival and proliferation. To evaluated the cytotoxicity of Aβ1-42 by using time and concentrations dependent manner. Cells were treated with 0-20 ⎧M of Aβ1-42 for 24 h and 48 h The results showed that Aβ1-42 caused cells death 57.3±0.03 % (p<0.05) compared with control. These data indicated that Aβ1-42 was toxicity to SK-N-SH cells depending on time and concentration as shown in Figure 2.
3.3. Protective Effect of Rice Extracts Inhibit Neuronal Cell Death Induced by Aβ1-42
The protective effects of the rice ex on the viability of SK-N-SH cells were evaluated. The effects of PGBR ex with enhance levels of GABA against 10 μM Aβ1-42– induced cytotoxicity by compared with BR ex, and WR ex. Cells were pre-treated with the PGBR ex, BR ex and WR ex at 2000⎧g/well for 3 h and then added with Aβ1-42 for 24 h. These results showed that PGBR and BR extracts can protect cells by significantly increase cell survival up to 30.74±0.02 % and 21.53±0.04 % (p<0.05), but not WR ex comparable with Aβ1-42 alone which caused cells death 57.3±0.03% (p<0.05), when compared with control as shown in Figure 3. Recently, it has been reported that the long-term administration of ferulic acid acts to protect against A1-42-induced neurotoxicity and memory disturbance.
Figure 3. The Protective effects of rice ex on SK-N-SH cells viability induced by Aβ1-42 by MTT assay. Pre-treated with rice ex significantly increase cells viability. Results are expressed as percentages of the control value. The data shown are means ± SD (n=3). * = P <0.05 compared to the untreated control; # = P <0.05 compared to the Aβ1-42-treated group, respectively.
3.4. Effect of Rice Extracts on Apoptosis and DNA Fragmentation of SK-N-SH Cells
To verify the possible involvement of apoptosis in the Aβ1-42 induced death of neuronal SK-N-SH cells, DNA fragmentation was tested on these cells. We investigated its inhibitory effect on the apoptosis induced by Aβ1-42 by observing DNA fragmentation levels in SK-N-SH cells. As a control, we used DNA isolated from untreated cells. Only the degraded DNA was extracted, not the intact chromosomal DNA, from apoptotic and non-apoptotic cells.
Treatment with Aβ1-42to cells resulted in the characteristic apoptotic DNA ladder (Figure 4). These DNA fragmentation patterns are entirely consistent with the molecular weight patterns expected to result from internucleosomal DNA cleavage (20). DNA fragments smeared the whole lane in the condition of Aβ1-42 treated alone and smear band was decrease in the condition of pre- treatment with PGBR ex and followed added by Aβ1-42. According to administration of PGBR ex alone and non- treated cells (control) did not cause cell death. Similar as the previous studies have shown that intracellular ROS have been implicated with DNA fragmentation and apoptosis [21].
Figure 4. PGBR ex protect SK-N-SH cells against Aβ1-42-induced apoptosis examined by DNA fragmentation. Pre-treatment with PGBR ex were reduced DNA fragmentation. Genomic DNA was then extracted and subjected to gel electrophoresis. The image was captured with GelDocTm EQ (Bio-Rad Laboratories, Ltd. Hercules, CA). Marker; M., control (nontreated-cells);lane 1, PGBR ex; lane 2, 10 μM Aβ1-42;lane 3. PGBR ex and 10 μM Aβ1-42; lane 4.
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