Antioxidant enzymes and human diseases
Objectives: To describe the importance of the antioxidant enzymes superoxide dismutase, glutathione peroxidase, and catalase working together in human cells against toxic reactive oxygen species, their relationship with several pathophysiologic processes and their possible therapeutic implications.
Conclusions: Reactive oxygen species (ROS) are involved in the cell growth, differentiation, progression, and death. Low concentrations of ROS may be beneficial or even indispensable in processes such as intracellular signaling and defense against micro-organisms. Nevertheless, higher amounts of ROS play a role in the aging process as well as in a number of human disease states, including cancer, ischemia, and failures in immunity and endocrine functions. As a safeguard against the accumulation of ROS, several non-enzymatic and enzymatic antioxidant activities exist. Therefore, when oxidative stress arises as a consequence of a pathologic event, a defense system promotes the regulation and expression of these enzymes. 
Regulation of antioxidant enzymes
Free radicals generated by a partial reduction of O2 pose a serious hazard to tissues and vital organs, especially membrane lipids, connective tissues, and the nucleic acids of cells. For protection, enzymes have evolved that specifically attack O2–, hydrogen, and organic peroxides, and repair any damage incurred to DNA. With few exceptions, antioxidant enzymes are found in all aerobic and aerotolerant anaerobic organisms. Logic assumes that a basal level of antioxidant enzyme activity is maintained at all times. This may be true. Yet cells must have ways to amplify antioxidant enzyme activity to counter sudden increases in oxygen metabolites. The full details of that regulation arc slowly coming to light. Bacteria possess a series of elaborate and interacting genes that can sense specific increases in intracellular H2O2 and O2–. In higher organisms, hormones and metal ion cofactors impose pre- and posttranslational control over the genetic expression of antioxidant enzymes. Furthermore, aging, cellular differentiation, and organ specificity must also be factored into the final equation in higher organisms. 
Antioxidant enzymes and cancer
Although oxidation is the most common biological and energy producing reaction, oxidative stress is harmful to cell, because the products of oxidation such as free radicals and peroxides damage the cellular components, causing several diseases. Damage in DNA is responsible for cancer formation and progression. However, several enzymes such as superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, glutathione S-transferase etc. act as antioxidants to influence oxidative stress. Polymorphisms in these enzymes are supposed to be associated with DNA damage and subsequently the individual’s risk of cancer susceptibility. This review article aims to further elucidate the relationship between antioxidant enzymes and cancers by summarizing the findings of some of the important study concerning expression levels and genetic polymorphisms of antioxidant enzymes in cancer patients. 
Antioxidant Enzymes Activity and Hormonal Changes Following Administration of Ethanolic Leaves Extracts of Nauclea latifolia and Gongronema latifolium in Streptozotocin Induced-Diabetic Rats
Aim of the Study: To evaluate the effects of ethanolic leaf extracts of Gongronema latifolium (G.L) and Nauclea latifolia (N.L) on antioxidant enzymes activity (GPx, SOD and CAT) and hormonal status (T3, T4, Insulin, c-peptide) in streptozotocin-induced diabetic Wistar rats.
Material and Methods: Thirty six (36) albino Wistar rats of both sexes weighing 150-250g were divided into 6 groups of 6 rats each. Groups 1, 2 and 3 received 400mg/kg body weight (b.w) of G.L, N.L and 200mg/kg b.w each of G.L and N.L respectively while group 4 received 5 iu/kg b.w of insulin subcutaneously daily for 21 days, Groups 5 and 6 served as controls (diabetic and Normal) and received placebo. Fasting blood glucose was determined at the start of the experiment and thereafter at 72 hours interval and at the end of experimental period. The animals were sacrificed and sera preparations were used for antioxidant enzymes and hormonal assays.
Results: Blood glucose in diabetic animals decreased significantly (P=.05) by 66.34%, 18.12%, 67.73% and 86.62% of initial values upon treatment with G.l, N.l, G.I plus N.I and insulin respectively. There was only a 24.44% decrease in the diabetic control. A significant decrease (P=.05) in insulin and T3 levels was observed in the diabetes-induced rats (65 and 85% respectively) compared to NC. The levels of the hormones where however significantly increased (P=.05) on treatment of the diabetic animals with G.l, N.l, G.I plus N.I and insulin. Whereas a significant decrease (P=.05) was observed in T4 level of DC rats compared to the NC, treatment with the leaf extracts and insulin did not result in any elevation of the hormone relative to DC. The C-peptide levels for all groups were much lower than the corresponding insulin levels, suggesting a type 1 diabetes in the diabetes-induced rats. A significant decrease (P=.05) in activity was observed for GPx and SOD in the DC group relative to NC. A combination of G.l and N.l gave a much higher reversal in activity (P<.01) when compared to treatments with individual leaf extracts. There was a significant increase (P=.05) in CAT activity in the DC animals relative to NC. This was potentiated in all treatment groups with the combination group showing a synergy in its potentiating effect.
Conclusion: There was a reversal in the level of the hormones and the activity of the antioxidant enzymes towards normal control, and comparable to the reversals by treatment with insulin, on treatment of the diabetic animals with the leaves extracts especially in combination. The results taken together indicate a synergy that makes the combination of the two plants extracts a potent antidiabetic remedy.
Determination of SOD, POD, PPO and CAT Enzyme Activities in Rumex obtusifolius L.
Aims: The purpose of this study was to measure antioxidant enzyme (polyphenol oxidase, peroxidase, catalase and superoxide dismutase) activities of crude extract of Rumex obtusifolius L. in order to gain insight about this plant’s antioxidant potential.
Study Design: The study was composed of the collection of plant material, extractions of the antioxidant enzymes, activity measurements of the enzymes and finally evaluation of the experimental results.
Place and Duration of Study: Department of Chemistry (biochemistry laboratories), Faculty of Science and Arts of Sakarya University, between June 2015 and July 2015.
Methodology: Enzymatic antioxidant activity of this plant was investigated by carrying out catalase, superoxide dismutase, peroxidase and polyphenol oxidase enzyme activity assays. Enzyme activities of the crude extract were measured by using spectrophotometric method. Optimum pH and temperature values of each enzyme were also determined for measurement of enzyme activities in ideal conditions.
Results: Finally, our results showed that Rumex obtusifolius L. crude extract had good activity for all the enzymatic procedures tested. The activity levels of enzymatic antioxidants polyphenol oxidase, peroxidase, catalase and superoxide dismutase of the plant were found to be 12.8; 195.2; 38.7; 11.6 EU/mL, respectively. Optimum pH and temperature values of all the enzymes (except PPO: optimum temperature 30°C) tested were also found to be 7.0 and 25°C, respectively.
Conclusion: Our results demonstrate that this edible plant, Rumex obtusifolius L., might be a potential source of natural antioxidants with good antioxidant enzyme capacity.
 Matés, J.M., Pérez-Gómez, C. and De Castro, I.N., 1999. Antioxidant enzymes and human diseases. Clinical biochemistry, 32(8), pp.595-603.
 Harris, E.D., 1992. Regulation of antioxidant enzymes 1. The FASEB Journal, 6(9), pp.2675-2683.
 Khan, M.A., Tania, M., Zhang, D.Z. and Chen, H.C., 2010. Antioxidant enzymes and cancer. Chinese Journal of Cancer Research, 22(2), pp.87-92.
 Effiong, G.S., Mgbeje, B.I., Igile, G.O., Atangwho, J.I., Eyong, E.U. and Ebong, P.E., 2013. Antioxidant enzymes activity and hormonal changes following administration of ethanolic leaves extracts of Nauclea latifolia and Gongronema latifolium in streptozotocin induced-diabetic rats. European Journal of Medicinal Plants, pp.297-309.
 Alici, E.H. and Arabaci, G., 2016. Determination of SOD, POD, PPO and cat enzyme activities in Rumex obtusifolius L. Annual Research & Review in Biology, pp.1-7.