Assessment of antioxidants in foods and biological samples: a short critique

Evaluation of free radical scavenging capacity of methoxy containing-hybrids of thiosemicarbazone-triazole and their influence on glucose transport

Background

Diabetes mellitus is a metabolic disease in which the body is unable to produce insulin or respond to insulin production, consequently leading to abnormal metabolism of carbohydrates, lipids and proteins causing elevation of glucose in the blood. Oxidative stress, an imbalance between the production of free radicals and body antioxidant system has been implicated in the pathogenesis of diabetes. Free radicals attack important macromolecules leading to cell damage. Antioxidants are intimately involved in the prevention of damage caused by free radicals.

Methods

The anti-diabetic effects of hybrid compounds (2a-h) of thiosemicarbazone and triazole containing methoxy groups at C (4) positions were tested against genes involved in glucose metabolism (Glut-4, Mef2a and Nrf-1) using quantitative real time PCR (qPCR). Free radical scavenging capacity (FRAP, TEAC, DPPH and ORAC) of the hybrids was also carried out by using established antioxidant capacity assays.

Results

From the results, hybrid compounds 2b and 2h showed more pronounced effects in up-regulating diabetes associated genes which are important in the up-regulation of glucose uptake. All the hybrid compounds also showed free radical scavenging abilities.

Conclusion

In conclusion, hybrid compounds (2b and 2h) can be useful as potential drugs for the management of diabetes mellitus.

Total Antioxidant Capacity in beta-thalassemia: A systematic review and meta-analysis of case-control studies

Total Antioxidant Capacity (TAC), a biomarker measuring the antioxidant potential of body fluids, including redox synergistic interactions, is influenced by the presence of products of catabolism such as bilirubin (BR) and uric acid (UA). Hyperuricaemia and increased BR levels were observed in thalassemia. In order to evaluate the differences in TAC values between thalassemic patients and healthy subjects, we performed a systematic review and meta-analysis of case-control studies. After the exclusion of data deemed unsuitable for meta-analysis inclusion and a study imputed of bias by Trim-and-fill analysis, mean difference (MD) and confidence intervals 95% (CI 95%) were calculated by the random effect model for beta-thalassemia major (BTM) (1351 subjects: 770 thalassemic and 581 controls, from 15 studies) and Trait (BTT) or Hemoglobin E (BTE) (475 subjects: 165 thalassemic and 310 controls, from 5 studies). Despite the differences in clinical symptoms and severity, similar decreased levels of TAC were found in BTM [MD -0.22 (-0.35 -0.09) p<0.001] and BTT or BTE [MD -0.22 (-0.44 -0.01) p<0.05]. In conclusion, UA and BR interference on TAC suggests that corrected TAC and in particular the UA-independent TAC, considering the prominent influence of UA, might be the better approach to evaluate body antioxidant status.

Salivary and Urinary Total Antioxidant Capacity as Biomarkers of Oxidative Stress in Humans

Total Antioxidant Capacity (TAC) is a biomarker often used in order to investigate oxidative stress in many pathological conditions. Saliva and urine can be collected noninvasively and represent attractive diagnostic fluids for detecting biomarkers of various pathological conditions. The reviewed case-control and intervention studies that measured salivary or urinary TAC revealed that diseases, antioxidant foods, or supplements and age, gender, and lifestyle factors influenced salivary or urinary TAC. Salivary and urinary TAC were particularly affected by oral or renal status, respectively, as well as by infection; therefore these factors must be taken into account in both case-control and intervention studies. Furthermore, some considerations on sample collection and normalization strategies could be made. In particular, unstimulated saliva could be the better approach to measure salivary TAC, whereas 24 h or spontaneous urine collection should be chosen on the basis of the study outcome and of the creatinine clearance. Finally, the uric acid-independent TAC could be the better approach to evaluate red-ox status of body, in particular after nutritional interventions and in diseases associated with hyperuricaemia.

Insights on antioxidant assays for biological samples based on the reduction of copper complexes-the importance of analytical conditions

Total antioxidant capacity assays are recognized as instrumental to establish antioxidant status of biological samples, however the varying experimental conditions result in conclusions that may not be transposable to other settings. After selection of the complexing agent, reagent addition order, buffer type and concentration, copper reducing assays were adapted to a high-throughput scheme and validated using model biological antioxidant compounds of ascorbic acid, Trolox (a soluble analogue of vitamin E), uric acid and glutathione. A critical comparison was made based on real samples including NIST-909c human serum certified sample, and five study samples. The validated method provided linear range up to 100 µM Trolox, (limit of detection 2.3 µM; limit of quantification 7.7 µM) with recovery results above 85% and precision <5%. The validated developed method with an increased sensitivity is a sound choice for assessment of TAC in serum samples.