By U. Grok. Webster University Orlando.
Both generic 25 mg phenergan amex, glutathione reductase and glucose-6-phosphate de hydrogenase are involved in the glutathione recycling system  order 25 mg phenergan. Secondary Antioxidant Defenses Although efficient, the antioxidant enzymes and compounds do not prevent the oxidative damage completely. Many of these essential maintenance and repair systems become deficient in senescent cells, thus a high amount of biological garbage is accumulated (e. Age-related oxidative changes are most common in non-prolifer ating cells, like the neurons and cardiac myocites, as there is no dilution effect of damaged structures through cell division . There is an age-related decline in proteasome activity and proteasome content in different tissues (e. On the other hand, proteasome acti vation was shown to enhance the survival during oxidative stress, lifespan extension and maintenance of the juvenile morphology longer in specific cells, e. The total amount of oxidatively modified proteins of an 80-year-old man may be up to 50% . It is likely that changes in proteasome dynamics could generate a prooxidative conditions that could cause tissue injury during aging, in vivo . There appears to be no great reserve of antioxidant de fenses in mammals, but as previously mentioned, some oxygen-derived species perform useful metabolic roles . Exogenous Antioxidant Defenses: Compounds Derived from the Diet The intake of exogenous antioxidants from fruit and vegetables is important in preventing the oxidative stress and cellular damage. Natural antioxidants like vitamin C and E, carote noids and polyphenols are generally considered as beneficial components of fruits and vege tables. Their antioxidative properties are often claimed to be responsible for the protective effects of these food components against cardiovascular diseases, certain forms of cancers, photosensitivity diseases and aging . However, many of the reported health claims are based on epidemiological studies in which specific diets were associated with reduced risks for specific forms of cancer and cardiovascular diseases. The identification of the actual in gredient in a specific diet responsible for the beneficial health effect remains an important bottleneck for translating observational epidemiology to the development of functional food ingredients. When ingesting high amounts of synthetic antoxidants, toxic pro-oxidant ac tions may be important to consider . Adaptive responses and hormesis The adaptive response is a phenomenon in which exposure to minimal stress results in in creased resistance to higher levels of the same stressor or other stressors. Stressors can in duce cell repair mechanisms, temporary adaptation to the same or other stressor, induce autophagy or trigger cell death . The molecular mechanisms of adaptation to stress is the least investigated of the stress responses described above. Early stress responses result also in the post-translational activation of pre-existing defenses, as well as activation of signal transduction pathways that initiate late responses, namely the de novo synthesis of stress proteins and antioxidant defenses . Hormesis is characterized by dose-response relationships displaying low-dose stimulation and high-dose inhibition . Hormesis is observed also upon the exposure to low dose of a toxin, which may increase cell s tolerance for greater toxicity . They are beneficial in moderate amounts and harmful in the amounts that cause the oxidative stress. Many studies investigated the 342 Oxidative Stress and Chronic Degenerative Diseases - A Role for Antioxidants induction of adaptive response by oxidative stress [72, 73, 74, 75]. In order to survive, the cells induce the antioxidant defenses and other pro tective factors, such as stress proteins. Finkel and Holbrook  stated that the best strategy to enhance endogenous antioxidant levels may be the oxidative stress itself, based on the classical physiological concept of hormesis. The effects of these stresses are linked also to changes in intracellular redox potential, which are transmitted to changes in activity of numerous enzymes and pathways. The main physiological benefit of adaptive response is to protect the cells and organisms from moderate doses of a toxic agent [82, 69]. As such, the stress responses that result in en hanced defense and repair and even cross protection against multiple stressors could have clinical or public-health use. Sequestration of metal ions; Fenton-like reactions Many metal ions are necessary for normal metabolism, however they may represent a health risk when present in higher concentrations. The above mentioned transition metal ions are redox active: reduced forms of redox active metal ions participate in already discussed Fenton reaction where hydroxyl radical is generated from hydrogen peroxide . Therefore, the valence state and bioavailability of redox active metal ions contribute significantly to the generation of reactive oxygen species. The unifying factor in determining toxicity and carcinogenicity for all these metals is the abitliy to generate reactive oxygen and nitrogen species. Common mechanisms involving the Fenton reaction, generation of the superoxide radical and the hy droxyl radical are primarily associated with mitochondria, microsomes and peroxisomes. Enzymatic and non-enzymatic antioxidants protect against deleterious metal-mediated free radical attacks to some extent; e. Iron Chelators A chelator is a molecule that has the ability to bind to metal ions, e. In this case the free radicals are formed at the biding site of the metal ions to chelating agent.
The ability of the immune system to repress malignancy may be particularly important in certain kinds of cancers that are very immunogenic; for example 25 mg phenergan overnight delivery, those resulting from viral infections or which have tumor neo-antigens generic phenergan 25mg with visa. Since the immune system plays an active role in cancer repression throughout life, the waning of immunity with aging, and in particular cellular immunity as mediated by T cells, likely plays an important role in tumori- genesis. For example, an increase in the number of senescent cells in aging tissues is thought to cause a signicant increase in the local concentrations of pro-inammatory cytokines secreted by senescent cells. It should be noted that this model is somewhat contro- versial, with many authors suggesting senescence-related cytokines can also deter tumorigenesis, and therefore the effect of senescent cells with regard to cancer are likely tissue- and context-specic. While our understanding of the molecular basis of cancer and aging continues to grow, it is possible to design strategies to both decrease the incidence of cancer as well as slow the rate of aging. Indeed, it has been shown that quitting smok- ing has a myriad of health benets in both target tissues such as the lung (e. Evidence suggests that tobacco exposure widely promotes aging-like phenotypes in many tissues, and therefore has been argued to represent the prototypical human gerontogen [96, 97]; that is, an environmental exposure that promotes physiological aging. Therefore, nding ways to protect stem cell function in cancer patients may help to reduce the aging-promoting effects of cyto- toxic therapy in this special scenario. Another potential way to reduce cellular damage is through modulating energy metabolism. One possible explanation for this is that decreased cellular energy metabolism may reduce the generation of harmful 78 S. As humans age, the function of the immune system declines sharply, resulting in increased susceptibility of the elderly to external infection. This aging-associated decline in adaptive immune response may also contribute to impaired immune sur- veillance and clearance of damaged or senescent cells from the body, which can contribute to aging and cancer development. On the other hand, an aberrant immune response such as autoimmune diseases also increases with age. Therefore, nding ways to augment the normal immune system function without over-activation in old individuals may ameliorate certain aspects of aging while providing an important anti-cancer defense. Therefore, an important goal of aging research is to nd ways to maintain functional stem cells throughout life. Therefore, reducing the rate of stem cell prolifera- tion may provide a way to slow stem cell aging. Alternatively, providing an exoge- nous source of healthy somatic stem cells, for example through a regenerative medicine approach, could provide a means to reduce both aging and cancer. The choice between these two seemingly distinct outcomes depends on the effectiveness of The Impact of Aging on Cancer Progression and Treatment 79 cellular tumor suppression mechanisms against oncogenic mutation failed tumor suppression results in cancer, while successful tumor suppression causes functional attrition of self-renewing cells, contributing to physiological aging. The increased incidence of cancer with aging reects the time-dependent accumulation of muta- tions in somatic self-renewing cells, as well as waning immune surveillance and possibly pro-oncogenic changes to the tissue milieu with aging. While preventing aging or curing cancer is unlikely, minimizing cellular damage, enhancing immune system function, and maintaining a functional stem cell pool may slow the rate of aging while simultaneously reducing the risk of cancer. Variation in cancer risk among tissues can be explained by the number of stem cell divisions. Oncogene addiction: pathways of therapeutic response, resistance, and road maps toward a cure. Runi A, Tucci P, Celardo I, Melino G (2013) Senescence and aging: the critical roles of p53. Campisi J, d Adda di Fagagna F (2007) Cellular senescence: when bad things happen to good cells. Samassekou O, Gadji M, Drouin R, Yan J (2010) Sizing the ends: normal length of human telomeres. This opens a new era in cancer care that is chal- lenged with not only enhancing treatment efcacy but also improving the quality of the clinical outcome. There is an urgent need to address the highly complex and multifaceted problems that arise as a result of the therapy itself. Modern cancer therapy evolved from a cytotoxic approach, using chemothera- peutics and ionizing radiation that are limited in their ability to distinguish healthy and cancerous cells, to drugs with specic molecular targets, such as tyrosine kinase inhibitors or antibodies recognizing specic receptors. Despite the leap in sophisti- cation achieved through research and development, toxicity still remains the major limiting factor for many types of therapy, including the more targeted ones. This is especially relevant considering that many of the patients receiving these toxic thera- pies are older and are likely to have co-morbidities. More importantly, undesired side effects pose serious clinical challenges, including a negative impact on the quality of life and healthspan of cancer survivors. We are now faced with an unprecedented range of dysfunctions and diseases resulting from the very interventions that have signicantly improved the chance and length of survival after cancer diagnosis. The emerging interdisciplinary eld of geroscience may hold the key to under- standing the mechanisms involved in preventing and treating many of these side effects. This is especially important as the side effects involve damage to a wide- range of tissues, cells, organelles, and molecules that manifest over time and which can resemble phenotypes observed during aging.