The influence of genotype (selection), location, and year on antioxidant activity (AOA), total phenolics (TP), total carotenoids (TC), phenolic and carotenoid composition was studied using specialty (colored) potatoes (Solanum tuberosum L.) from the Texas Potato Variety Development Program, grown at two Texas locations (McCook and Dalhart), and in two years (2003 and 2004). Chlorogenic acid, gallic acid, catechin, caffeic acid, and malvidin-3-(p-coumaryl rutinoside)–5-galactoside were the major phenolics, and lutein and violaxanthin were the major carotenoids identified. The AOA, TP, and TC and phenolic composition differed significantly with genotype, location and year. However, genotypic effects were larger than location and year effects. Selection CO112F2-2 was high in all the measured parameters and also stable across locations and years, suggesting that this selection could be used as a parent in breeding varieties with improved health benefits. The AOA, TP and chlorogenic acid content were highly significantly correlated with one another. The effects of whole specialty potato extracts, fractions and individual compounds on LNCaP (androgen-dependent) and PC-3 (androgen-independent) prostate cancer cells were also investigated. Ethanol extract of the selection CO112F2-2 (5 µg chlorogenic acid eq/ml), the anthocyanin fraction (AF; 5 µg chlorogenic acid eq/ml), gallic acid and chaconine showed potent anti-proliferative properties and increased the cyclin-dependent kinase inhibitor p27 levels in LNCaP and PC-3 cells. Induction of apoptosis was cell context dependent and associated with JNK (c-Jun NH2-terminal Kinase) and Erk (extracellular signal regulated kinase) activation. Cell death pathways, induced by potato extract and the AF, were associated with Erk and JNK activation, and these kinases activated caspase-independent apoptosis through nuclear translocation of endonuclease G (endo G) and apoptosis-inducing factor (AIF) in both cell lines. Induction of caspase-dependent apoptosis was also kinase-dependent but was observed only in LNCaP cells. Kinase inhibitors reversed this nuclear translocation of endo G and AIF. This is the first report showing that the cytotoxic activities of potato extract/AF in cancer cells were due to activation of caspase-independent apoptosis.

μ -Calpain is localized to the mitochondrial intermembrane space. Apoptosisinducing factor (AIF), which executes caspase-independent cell death, is also localized to the mitochondrial intermembrane space. Following processing at the N-terminus, AIF becomes truncated (tAIF) and is released from mitochondria. The protease responsible for AIF processing has not been established. The same submitochondrial localization of mitochondrial μ-calpain and AIF gives support to the hypothesis that mitochondrial μ-calpain may be responsible for processing AIF. Atractyloside-induced tAIF release in rat liver mitochondria was inhibited by cysteine protease inhibitor MDL28170, but not by calpain inhibitors PD150606 or calpastatin. Moreover, μ-calpain immunoreactivity was difficult to detect in rat liver mitochondria. In a mitochondrial fraction from SH-SY5Y cells, incubation with 5 mM Ca2+ resulted in the activation of mitochondrial μ-calpain but not in AIF truncation. Finally, in hippocampal neurons calpain activation did not induce AIF processing or nuclear translocation and AIF translocation to nucleus was calpain independent. The localization of μ-calpain to the mitochondrial intermembrane space is suggestive of its possible involvement in AIF processing, but direct experimental evidence supporting such a role has been elusive. We observed that mitochondrial μ-calpain required high Ca2+ for activation. We examined the hypothesis that the endogenous calpain inhibitor, calpastatin, may be present in the neuronal mitochondria. Calpastatin was detected in the mitochondriaenriched fraction obtained from rat cerebral cortex and SH-SY5Y cells. The mitochondrial calpastatin was resistant to proteinase K digestion, indicating localization internal to the outer mitochondrial membrane. Submitochondrial fractionation revealed that the calpastatin was localized to the mitochondrial intermembrane space and mitoplasts (inner mitochondrial membrane and matrix) but not to the mitochondrial outer membrane fraction. Mitochondrial calpastatin was not detected when mitoplasts were incubated with proteinase K, suggesting that calpastatin is not present in the matrix. The N-terminus of XL domain of calpastatin, when fused to GFP and transfected to SH-SY5Y cells showed mitochondrial localization and thus confirmed the presence of a mitochondrial targeting sequence in calpastatin. Together, these results demonstrate the presence of calpastatin in the neuronal mitochondrial intermembrane space, the same submitochondrial compartment as mitochondrial μ-calpain. This finding explains the high Ca2+ requirements for mitochondrial μ-calpain activation.

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