Fig. 7.

NAD⁺ depletion and p38 activation occur before caspase cleavage. Neuronal cultures were exposed to 100 μm DTDP for 10 min in the presence of niacinamide (Nia; 3 mm), BAF (10 μm), or SB 239063 (20 μm) as above and harvested 7 hr later. Data were analyzed and expressed as in Figure 6and represent the mean ± SEM of four to six independent experiments performed in duplicate. There was a statistically significant decrease in caspase cleavage by blocking either NAD⁺-catabolization or p38 on caspase cleavage, suggesting that activation of these pathways occurs before caspase involvement in DTDP toxicity. Values represent the mean ± SEM;asterisks denote a significant difference versus matched DTDP treatment (*p < 0.05; paired ttest). All DTDP treatment groups were pooled for presentation purposes.