Increased levels of superoxide were observed in SOD deleted wild type worms or in ISP-1 and NOU-6 mutants. The effect of deletion of SOD on C. elegans lifespan is shown in Table 2. The impact of SOD deletion on the lifespan appears to be contradictory, depending upon the C. elegans model used. For example, SOD2 deletion markedly increased the lifespan of mutant clk-1 worms, but it decreased the lifespan of mutant isp-1worms. In addition, deletion of individual SOD genes from wild type C. elegans did not decrease the lifespan of these worms. This is in sharp contrast to other model, such as yeast, flies, and mice in which deletion of cytoplasmic or mitochondrial SOD caused decreased in the lifespan. In another study, it was demonstrated that the levels of superoxide were elevated in nou-6 mutant and isp-1 mutant and they lived longer than the wild type, however, the oxidative stress was low and overall levels of ROS did not change. From these results, it was concluded that elevation of superoxide is sufficient to increase the lifespan of these mutant worms. Based on these results, the role of oxidative stress in aging was questioned. It should be pointed out that if superoxide is precursor of ROS, the levels of ROS and oxidative stress should have been increased. This was not observed in the above study, suggesting that reduced oxidative stress possibly due to adaptive response by other antioxidant enzymes, such as catalase and glutathione peroxidase and improved repair mechanisms was responsible for the extension of lifespan of these mutant worms. In the same article, it was observed that addition of N-acetylcysteine and vitamin C individually abolished the effect of superoxide on life extension and other associated changes in nou-6 and isp-1 mutants. Vitamin C in water is rapidly oxidized and can act as a pro-oxidant.
The antioxidant effect of NAC is mediated via glutathione, which in the presence of the high superoxide environment of mutant worms can be oxidized and then act as a pro-oxidant. Therefore,raspberry container growing observed abolition of the effect of superoxide on life extension could be related to pro-oxidant effects of NAC and vitamin C. In order to assess the role of SOD on life extension further, a model of C. elegans was developed in which all five SODs were deleted. The results showed that SOD 12345 worms were viable and exhibited a normal lifespan similar to that of wild-type despite increased sensitivity to multiple stressors. However, these SOD lacking worms showed reduced fertility, slow development, slower defecation cycle and decreased movement . From these results, it was concluded that SOD is dispensable for normal lifespan of C. elegans. This is in sharp contrast to mammals in which SOD is considered indispensable for survival. Thus, the results obtained on some genetic models of C. elegans cannot readily be extrapolated to the genetic models of mammals. If SOD is dispensable for the survival and lifespan of C. elegans as reported recently, over expression of SOD should have no impact on the lifespan of these worms. On the contrary, it was reported that over expression of the major cytosolic Cu/Zn-SOD increased lifespan of wild type worms which was not related to reduced lipid oxidation or glycation. As a matter of fact, the levels of protein oxidation were increased in these worms. The life extension effect of over expression of SOD-1 was due to activation of longevity-promoting transcriptional factors, such as DAF-16/FoxO, heat shock factor-1 protein. Similarly, over expression of mitochondrial Mn-SOD also increased lifespan of the worms, which was dependent on daf-16. It was suggested that over expression of SOD-1 may trigger a daf-16 and HSF-1-dependent stress response that extends lifespan and not by removing superoxide.
It is interesting to note that over expression of SOD causes increased oxidation of protein and no change in lipid peroxidation. This would imply that proteins are more susceptible to oxidative damage than membrane lipids. It is possible that over expression of SOD causes translocation of this antioxidant enzyme from the cytoplasm to the membrane where it protects lipid against oxidative damage in C. elegans. It has been difficult to deliver single antioxidants orally in C. elegans. Using a newly devised technique for an oral administration, it was demonstrated that supplementation with lipid soluble antioxidants tocotrienol, astaxanthin or gamma-tocopherol prolonged the lifespan of C. elegans. In contrast, the same study revealed that adding these antioxidants to the growth medium or the plate did not enhance the lifespan. These results suggest that adding antioxidant directly to the media may no yield consistent results in extending the lifespan. Treatment of worms during pre-reproductive and young adult stages with astaxanthin, a carotenoid present in marine animals and sea weeds, significantly extended the lifespan; this treatment was not effective in worms lacking daf-16. The results also showed that astaxanthin treatment of wild-type worms increased expression of SOD and catalase in two weeks after hatching and daf-16 protein was translocated to the nucleus. It was proposed that the effect of astaxanthin on extension of lifespan was in part mediated via an Ins/Gf-1 signaling pathway. Treatment of C. elegans with cypermethrin increased ROS and H2O2. Elevation of peptide carbonylation suggested free radical damage to proteins, and decreased lifespan. Treatment with alphatocopherol prevented CYP-induced increase in oxidative stress and decline in lifespan. Supplementation of C. elegans media with a mixture of polyphenols derived from blueberries increased lifespan and age-related declines in C. elegans. This treatment also increased survival during acute heat stress.
The blueberry extract used contained 3 major fractions all of which exhibited antioxidant activity, but only the fraction containing proanthocyanidins enhanced lifespan and thermotolerance. Treatment with crude Ginkgo biloba extract increased the lifespan of C. elegans. However, purified ingredients of G. biloba especially flavonoids and tamarixetin were most effective in extending lifespan. G. biloba extract also increased resistance to oxidative stress and thermal stress in wild-type and premature aging C. elegans mutant. Supplementation of C. elegans incubation media with a strain of lactic acid bacteria Lactobacillus rhamnosus CNCMI-3690, which exhibits antioxidant activity, increased lifespan and protected against oxidative stress. This strain of lactic acid producing bacteria also reduced inflammation. These studies suggest that increased levels of antioxidants extend the lifespan by reducing oxidative stress and possibly by other mechanisms, such as preventing deregulation of protective transcriptional factors. In another study, it was reported that superoxide generators paraquat and plumbagin reduced the length of lifespan. This is consistent with oxidative theory of aging. It was further reported that treatment that treatment with synthetic SOD mimetics EUK-8 or EUK-134, increased the activities of SOD, but not the levels of SOD proteins. Treatment with EUK-8 or EUK-134 in combination with a superoxide generator increased the lifespan of wild type worms; however, in the absence of a superoxide generator, it failed to increase the lifespan. It is possible that superoxide generator induces adaptive responses led by catalase and glutathione peroxidase and other longevity factors such as transcriptional regulators of antistress proteins, and repair mechanisms. These adaptive responses help SOD mimetic in extending the lifespan. However,blueberry plant pot in the absence of these adaptive responses produced by treatment with a superoxide generator, SOD mimetic is ineffective in extending the lifespan. The role of chronic inflammation on the lifespan has not been adequately investigated in C. elegans. In order to assess the role of chronic inflammation on the lifespan, antiinflammatory agents have been used. Treatment with aspirin and salicylate treatment increased lifespan and delayed age related declines, such as learning behavior , motor activity, thermal tolerance, osmotic resistance, brood size and intracellular protein aggregation in C. elegans by reducing ROS and increasing expressions of antioxidants genes encoding for SOD , catalase and glutathione peroxidase. Aspirin and salicylate treatment also reduced intracellular protein aggregation that is associated with increased aging. Aspirin treatment did not extend lifespan but improved resistance to stressors in worms lacking daf-16. Supplementation with a potent specific inhibitor of cyclooxygenase-2 celecoxib increased lifespan and age-related decline in C. elegans. This effect of celecoxib was not related to its inhibitory effect on COX-2 activity because an analog of celecoxib, which lacks the COX-2 inhibitory effect, also enhanced lifespan of C. elegans. The life-extending effect of celecoxib appears to be mediated via insulin/IGF-1 signaling pathways. Thus the effect of celecoxib on C. elegans life span resembles the consequence of SOD-3 over expression in the daf-2 mutant. Lifespan can be extended by multiple pathways that include reduced oxidative stress and activation of longevity promoting transcriptional factors, such as Daf-16 and heat shock factor-1 protein. Oxidative stress can be reduced by multiple pathways which include reduced activity of mitochondria by inhibiting activities of complexes, increased transcriptional factor Nrf2 which regulate antioxidant enzymes and elevated antioxidant levels which directly scavenge free radicals as well as enhance antioxidant enzymes levels.
It is now established that low levels of superoxide is required to activate and translocate Nrf2 from the cytoplasm to the nucleus which reduces oxidative stress by upregulating antioxidant enzymes. In C. elegans, the presence of increased levels of superoxide by deleting SOD-2 decreases the oxidative stress and extends the lifespan. It is possible that increased levels of superoxide triggers activation of Nrf2 that decreases oxidative stress by up-regulating other antioxidant enzymes. The role of Nfr2 in regulating antioxidant enzymes has not been evaluated. Although deletion of all 5 SODs had no impact on the lifespan of C. elegans, the worms lacking all SODs showed reduced fertility, slow development, slower defecation cycle and decreased movement. These data suggest that adaptive responses by other antioxidant enzymes and transcriptional factors may have prevented reduction in lifespan. These data also suggest that all SODs are needed for normal growth and healthy life of worms.Refrigeration can lead to post harvest loss and waste , although it is the most effective strategy to maintain the quality and prolong the shelf-life of horticultural products. The rates of metabolic reactions increase 2–3-fold for every 10°C rise in temperature, and low-storage temperature delays deterioration by slowing down respiration and ethylene production, and by reducing pathogen growth and water loss. Commodities such as apples, blackberries, blueberries, cherries, and grapes benefit from refrigeration, however, in produce originating from tropical and subtropical regions, such as tomato, banana, pineapple, potato, and basil, refrigeration may lead to injury. Post harvest chilling injury is initiated when the tissues of cold-sensitive species are stored between 0 and 15°C, but becomes apparent after transfer to warmer conditions. Because the affected species are taxonomically diverse and the organs affected vary, for example, fruit, tuber, root, leaf, and stem, PCI symptoms can be variable . However, some common phenotypes include tissue browning or blackening, pitted surfaces, shriveling, negative changes in texture, carbohydrates and aroma volatiles, and fungal infection. PCI severity is determined by many factors with temperature and storage time being the most important. If low temperatures are mild and exposure istransient, many metabolic functions will resume after rewarming, and visible symptoms may not develop. Under sustained low-temperature stress, tissue acclimation fails, leading to exhaustion and the onset of severe PCI . Preharvest factors, including genotype, environmental variables, and agronomic practices, all interact to influence PCI severity . PCI is more severe in tissues harvested before reaching horticultural maturity , as the developmental pathways are incomplete and will be largely disrupted by chilling and rewarming. Although PCI is a significant problem, determining the PLW that can be ascribed to PCI is challenging because of the difficulty in identifying when it occurs. Most damage appears in retail outlets or in consumers’ homes, which is hard to monitor. Further, symptoms are internal in many species, for example, pineapple, nectarines, and so on, and some abnormalities in texture and flavor are only detected when the fruit or vegetable is eaten . PCI symptoms are also misdiagnosed. For example, PCI increases susceptibility to pathogens, which is often mistaken as the primary cause of loss, and poor-quality produce due to PCI may be attributed to early harvest or poor varietal selection. Given the above factors, quantifying economic losses due to PCI is also difficult. The global trade of fresh fruits and vegetables was worth 115 billion USD in 2018. More than half of the 50 highest-traded global commodities are PCI-susceptible, and PLW globally is estimated at ∼33%.