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    • However one should keep in mind that these results

    2023-11-17

    However, one should keep in mind that these results may not reflect exactly in vivo antioxidant activity. Many other issues such as absorption, metabolism and physicochemical properties of different antioxidants must also be considered (Prior et al., 2007, Wu et al., 2004). Some research groups are recently interested in this topic and compare the in vitro and in vivo methods to reveal the exact antioxidant capacity of diet. Pastoriza, Roncero-Ramos, Rufián-Henares, and Delgado-Andrade (2014) investigated the antioxidant capacity of diet using GAR method and estimated the uptake of antioxidant compounds in model rats using QUENCHER approach. They also determined the oxidative stress biomarkers protecting tissues from oxidative damages such as catalase activity, superoxide dismutase activity and glutathione peroxidase activity. Although there were no statistically significant differences between in vitro measured antioxidant capacity of subjected different types of diets or in estimated antioxidant compounds uptake, bread crust added diet showed positive effects on in vivo antioxidant activity while other fractions impaired the antioxidant defense system. Same group also showed that model maillard reaction products in diet increased the intake and uptake of antioxidant capacity and improved the antioxidant level in rat blood while they showed no significant effects on oxidative stress biomarkers (Pastoriza, Rufián-Henares, & Delgado-Andrade, 2015). The most striking observation to emerge from these results is that considering the metabolism and activity of antioxidants in human body is critical to design the in vitro models representing their in vivo antioxidant activity.
    Physiological effects of antioxidants Identification of compounds having antioxidant activity in biological fluids like blood and urine indicated that antioxidant compounds might have important role in gpr44 inhibitor of organism (Kadin and Osadca, 1959, Jacob, 1996, Tappel and Zalkin, 1959). Earlier studies focused on the inhibition of tissue peroxidation in vivo by vitamin E. It was reported that antioxidants like vitamin E and selenium inhibited early critical oxidation and reduction reactions necessary for tumor formation (Shamberger & Rudolph, 1966). The studies also showed that synthetic phenolic antioxidants (BHA, BHT) inhibited the carcinogenesis in rats (Benson et al., 1978, Ito et al., 1986, Slaga and Bracken, 1977, Ulland et al., 1973). After that, several epidemiological and clinical studies with other antioxidant compounds such as vitamin C, carotenoids and polyphenols were conducted to show their antioxidant activity against cancer, cardiovascular diseases and their preventive roles in biological systems (Khan et al., 1992, Knekt et al., 1991, Meerson et al., 1982, Vanpoppel, 1993). Ames, Shigenaga, and Hagen (1993) reviewed the effects of dietary antioxidants on the degenerative diseases and reported that low dietary intake of fruits and vegetables increased the risk of most types of cancer, heart diseases and cataracts. Southon (2000) remarked that the normal diet with vegetables and fruits achieved the natural balance of carotenoids, decreased the susceptibility of LDL to oxidation and lowered the oxidative DNA damage, although carotenoid supplementation did not cause any additional protective effects. It has obviously proved that dietary antioxidants have critical roles in oxidation-reduction balance in the body leading to prevent oxidative stress related disorders. In another study, Hertog et al. (1993) revealed that flavonoids in regularly consumed foods and beverages (tea, onion, apples) might reduce the risk of death from coronary heart disease in elderly men. Several studies showed the preventive effects of antioxidants against oxidative related diseases although there were not enough evidences to prove the therapeutic effects of antioxidants in sick people. In addition, it was known that epidemiological and in vivo intervention studies in sick people might show contradictory results. For example, 15 randomized trials with large cohorts of patients for 12years showed that tocopherols and β-carotene did not provide benefit in mortality since patients already diagnosed with a disease could respond less. However, the daily administration of β-carotene and tocopherol to people with a sub-optimal intake over a period of several years resulted in a 20% risk reduction for cancer of the stomach, and the total mortality was decreased by about 10% at the same time (Berger, Lunkenbein, Ströhle, & Hahn, 2012). Similarly, the Nurses' Health Study conducted a cohort study involved more than 87,000 woman between 34 and 59years old with no history of cardiovascular diseases (CVD) to investigate the association between dietary vitamin E intake and CVD risk. After an 8-year follow-up, women consumed vitamin E in diet had a 34% lower risk of CVD (Wang, Chun, & Song, 2013). Another prospective cohort study with over 8000 individuals revealed that the daily consumption of green tea delayed the cancer onset and a follow-up study of breast cancer patients found that stages I and II breast cancer patients experienced a lower recurrence rate and longer disease free period (Singh, Shankar, & Srivastava, 2011).