Dietary antioxidants and glucose metabolism

The association of dietary total antioxidant capacity and gestational diabetes: a prospective cohort study from the Mothers and their children's health (MATCH)

BACKGROUND/OBJECTIVES

There is evidence to support the hypothesis that a diet rich in antioxidants can help safeguard against the development of gestational diabetes mellitus (GDM). This study aimed to investigate the association between dietary total antioxidant capacity (DTAC) during early pregnancy and the risk of GDM.

SUBJECTS/METHODS

We included 1856 pregnant women in their first trimester from the Mothers and their Children's Health (MATCH) prospective cohort study. Prepregnancy dietary intake was assessed using a validated food frequency questionnaire (FFQ) and was used to calculate the DTAC score. Incident GDM was diagnosed based on the American Diabetes Association criteria. We estimated the association between DTAC and GDM using propensity score-based inverse probability weighting (IPW).

RESULTS

Overall, 369 (14.6%) of the pregnant women were identified with GDM. The mean DTAC score and the corresponding standard deviation (SD) was 2.82± (2.56) mmol/100 g, with a range of 0.01 to 18.55. The adjusted risk of GDM decreased by 34% (95% CI = 10%, 52%, p = 0.023) for each DTAC score increase. The results showed that women in the highest quartile of DTAC had a lower risk of developing GDM compared to those in the lowest quartile (adjusted RR: 0.29, 95% CI: 0.12, 0.68, p = 0.005).

CONCLUSION

DTAC in early pregnancy is significantly associated with a lower risk of GDM. Additional larger cohort studies are needed to validate these findings.

Lifestyle, Insulin Resistance and Semen Quality as Co-Dependent Factors of Male Infertility

Infertility is a problem that affects millions of couples around the world. It is known as a disease of couples, not individuals, which makes diagnosis difficult and treatment unclear. Male infertility can have many causes, from mechanical ones to abnormal spermatogenesis or spermiogenesis. Semen quality is determined by a number of factors, including those dependent on men themselves, with the number of infertile men growing every year. These include, e.g., diet, physical activity, sleep quality, stress, among many others. As these factors co-exist with insulin resistance, which is a disease closely related to lifestyle, it has been singled out in the study due to its role in affecting semen quality. In order to examine connections between lifestyle, insulin resistance, and semen quality, a review of literature published from 1989 to 2020 in the following databases PubMed/Medline, EMBASE (Elsevier), Scopus, Web of Science, and Google Scholar was performed. Hence, semen quality, environment, and insulin resistance are interrelated, thus it is difficult to indicate which aspect is the cause and which is the effect in a particular relationship and the nature of possible correlations. Since the influence of lifestyle on semen quality has been extensively studied, it is recommended that more thorough research be done on the relationship between insulin resistance and semen quality, comparing the semen quality of men with and without insulin resistance.

Dietary total antioxidant capacity is inversely associated with the odds of non-alcoholic fatty liver disease in people with type-2 diabetes

BACKGROUND

This study was conducted to evaluate possible associations between Dietary Total Antioxidant Capacity (DTAC) and odds of non-alcoholic fatty liver disease (NAFLD) in people with type-2 diabetes mellitus (T2DM).

MATERIALS AND METHODS

We recruited two hundred people with T2DM, and evaluated their liver steatosis using Fibroscan. Dietary intakes of participants were assessed using a validated food frequency questionnaire. DTAC was computed via ferric reducing antioxidant power (FRAP).

RESULTS

In the crude model, no statistically significant association was found between DTAC and the odds of NAFLD in people with diabetes. However, after adjustment for potential confounders including age, gender, diabetes duration, smoking status, physical activity, BMI, waist circumference, and energy, the most reduced adjusted OR was indicated for the third tertile vs. the first one (OR: 0.28, 95% CI: 0.09-0.81, P = 0.02), meaning that diabetic patients in the third tertile of DTAC had 72% decreased risk of NAFLD in comparison to those in the first one. The relationship was remained significant after additional adjustment for HOMA-IR, HbA1c, serum Triglyceride (TG), and low-density lipoprotein-cholesterol (LDL) levels (OR: 0.29, 95% CI: 0.09-0.93, P = 0.03). Importantly, a dose-response pattern was demonstrated for DTAC and risk of NAFLD (P = 0.04).

CONCLUSION

Higher DTAC was related with a decreased risk of NAFLD in individuals with diabetes.

Interaction between dietary total antioxidant capacity and BDNF Val66Met polymorphism on lipid profiles and atherogenic indices among diabetic patients

Brain-derived neurotrophic factor (BDNF) belongs to the "neurotrophin" family of growth factors, and it has recently been associated to cardiovascular disease (CVD). We anticipated that BDNF Val66Met polymorphisms may alter CVD risk markers such as serum lipid profile differences, and interaction with total antioxidant capacity of diet (DTAC) could alter these clinical parameters. This cross-sectional study consisted of 667 diabetic patients (39.7% male and 60.3% female). DTAC was calculated by international databases. Biochemical markers including total cholesterol (TC), low-density lipoprotein (LDL), high-density lipoprotein (HDL), triglyceride (TG), superoxide dismutase (SOD), C-reactive protein (CRP), total antioxidant capacity (TAC), pentraxin-3 (PTX3), isoprostaneF2α (PGF2α). interleukin 18 (IL18), leptin and ghrelin were measured by standard protocol. Atherogenic indices (AIP, AC, CR-I, CR-II) were calculated. Genotyping of the BDNF Val66Met polymorphisms was conducted by the real-time PCR-RFLP method. The gene-diet interactions were evaluated using a generalized linear mode (GLMs). Carriers of the Val/Met genotype who were in the higher median intake of FRAP had lower HDL (P:0.04) and higher TG (P:0.005), AIP (P:0.02) and AC (P:0.02) index compared to Val/Val genotypes with lower median intake. Moreover, diabetic patients with Val/Met genotype who consumed higher ORAC intake had increased odds for anthropometric indices (BMI (P:0.01) and WC (P:0.03)), lipid profiles (TG) (P:0.01), and atherogenic index (AIP) (P:0.02), also decreased odds for HDL (P:0.03) concentration compared to reference group whit lower ORAC intake. Individuals with Val/Met genotype who consumed higher TRAP intake had increased odds for WC (P:0.04), TC (P:0.001), TG (P < 0.001), AIP (P < 0.001) and AC (P < 0.001). Finally, Val/Met patients with a higher median intake of TEAC had higher TG (P:0.02), AIP (P:0.009) and AC (P:0.03) compared to the reference group whit lower TEAC intake. Our study showed that Val/Met genotype had also the highest lipid profile and atherogenic indices even in the highest adherence to DTAC. While it seems that the presence of the Val/Val wild-type and BDNF Met/Met homozygotes in diabetic patients with a high DTAC is a protective factor.

The effect of dietary total antioxidant capacity (DTAC) and Caveolin-1 gene variant interaction on cardiovascular risk factors among overweight and obese women: A cross-sectional investigation

BACKGROUND

Previous studies have shown that the Caveolin-1 (CAV-1) gene variant may be associated with Cardiovascular disease (CVD) risk. Moreover, dietary total antioxidant capacity (DTAC) has been shown to potentially elicit favorable effects on CVD risk. Therefore, this study sought to investigate the effect of DTAC and CAV-1 interaction on CVD risk factors.

METHODS

This cross-sectional study consisted of 352 women, with overweight and/or obesity, aged 18-48years from Iran. A food frequency questionnaire (FFQ), with 147 items, was used to assess dietary intake. The CAV-1 rs 3807992 and anthropometric data were measured by the PCR-RFLP method and bioelectrical impedance analysis (BIA), respectively. Serum profiles were measured by standard protocols. Participants were also divided into two groups based on DTAC score and rs3807992 genotype.

RESULTS

The mean age of the participants was 37.34 ± 9.11 and 36.01 ± 9.12 years for homozygous (GG) and minor allele carriers (AG + AA) respectively.The mean ± SD of insulin, total cholesterol (TC),high-density lipoprotein (HDL), low-density lipoprotein (LDL) and TG of participants were 1.21 ± 0.23, 185.3 ± 35.77, 46.58 ± 10.86, 95.3 ± 24.12 and 118.1 ± 58.88, respectively. There was a significant difference between genotypes for physical activity (P = 0.05), HDL (P < 0.001), insulin (P = 0.04), CRI-I (TC/HDL-C) (P = 0.01), and CRI-II (LDL-C/HDL-C) (P = 0.04). Our findings also showed, after controlling for confounding factors, significant interactions between DTAC score and the A allele carrier group on TC (Pinteraction = 0.001), LDL (Pinteraction = 0.001), insulin (Pinteraction = 0.08), HOMA-IR (Pinteraction = 0.03), AC ((TC - HDL - C)/HDL - C) (Pinteraction = 0.001), and CHOLINDEX (LDL-C-HDL-C) (Pinteraction = 0.02).

CONCLUSION

The results of the present study indicate that high DTAC intake may modify the odds of risk factors for CVD in AA and AG genotypes of rs 3807992. These results highlight that diet, gene variants, and their interaction, should be considered in CVD risk assessment.

Dietary Total Antioxidant Capacity and Gestational Diabetes Mellitus: A Case-Control Study

Background

Elevated oxidative stress status has been reported among pregnant women with gestational diabetes mellitus (GDM). In diabetic condition, glucose and lipid peroxidation, and alteration in antioxidant defense lead to increased free radicals. The objective of this study was to investigate the association between dietary total antioxidant capacity (DTAC) and GDM.

Methods

This hospital-based case-control study was conducted in 463 pregnant women (healthy, n = 263; GDM, n = 200). Anthropometric indices, blood pressure, and biochemical analyses were measured. Dietary intake was assessed by the average of three 24-hour dietary intake records. DTAC was calculated by three indices: ferric reducing ability of plasma (FRAP), total radical-trapping antioxidant parameter (TRAP), and Trolox equivalent antioxidant capacity (TEAC). Multivariable logistic regression was performed to examine the relationship between DTAC and GDM risk in crude and adjusted models.

Results

The mean age and BMI were 28.33 ± 6.23 years and 29.67 ± 4.73 kg/m², respectively. Total energy, protein, and selenium intakes were significantly higher in cases than controls (P < 0.05). Moreover, intakes of carbohydrate, vitamins C, B6, and A, manganese, fruits, fruit juices, vegetables, legumes, and FRAP were significantly lower in cases than controls (P < 0.05). The risk of gestational diabetes mellitus was 85% lower among those in the highest tertile of FRAP (OR: 0.15; 95% CI: 0.08-0.29). There was no significant association between the risk of GDM and TRAP (OR: 1.62; 95% CI: 0.94-2.79) as well as TEAC (OR: 1.56; 95% CI: 0.89-2.72).

Conclusion

Pregnant women who were in the highest tertile of FRAP were at lower risk of GDM. However, larger prospective studies are needed to confirm our findings.

Serum Uric Acid, Alzheimer-Related Brain Changes, and Cognitive Impairment

Background

Despite known associations of lower serum uric acid (UA) with Alzheimer’s disease (AD) dementia or AD-related cognitive impairment, little is known regarding the underlying patho-mechanisms. We aimed to examine the relationships of serum UA with in vivo AD pathologies including cerebral beta-amyloid (Aβ) and tau deposition, AD-signature region cerebral glucose metabolism (AD-CM), and white matter hyperintensities (WMH). We also investigated the association between serum UA and cognitive performance, and then assessed whether such an association is mediated by the brain pathologies.

Methods

A total of 430 non-demented older adults underwent comprehensive clinical assessments, measurement of serum UA level, and multimodal brain imaging, including Pittsburgh compound B-positron emission tomography (PET), AV-1451 PET, fluorodeoxyglucose (FDG)-PET, and magnetic resonance imaging scans. Mini-Mental State Examination (MMSE) and word list recall (WLR) test scores were used to measure cognitive performance.

Results

Serum UA level was significantly associated with AD-CM, but not with Aβ deposition, tau deposition, or WMH volume. Serum UA levels also had significant association with WLR and marginal association with MMSE; such associations disappeared when AD-CM was controlled as a covariate, indicating that AD-CM has a mediating effect.

Conclusion

The findings of the present study indicate that there is an association of low serum UA with AD-related cerebral hypometabolism, and whether this represents a causal relationship remains to be determined.

Sulforaphane: Its "Coming of Age" as a Clinically Relevant Nutraceutical in the Prevention and Treatment of Chronic Disease

A growing awareness of the mechanisms by which phytochemicals can influence upstream endogenous cellular defence processes has led to intensified research into their potential relevance in the prevention and treatment of disease. Pharmaceutical medicine has historically looked to plants as sources of the starting materials for drug development; however, the focus of nutraceutical medicine is to retain the plant bioactive in as close to its native state as possible. As a consequence, the potency of a nutraceutical concentrate or an extract may be lower than required for significant gene expression. The molecular structure of bioactive phytochemicals to a large extent determines the molecule's bioavailability. Polyphenols are abundant in dietary phytochemicals, and extensive in vitro research has established many of the signalling mechanisms involved in favourably modulating human biochemical pathways. Such pathways are associated with core processes such as redox modulation and immune modulation for infection control and for downregulating the synthesis of inflammatory cytokines. Although the relationship between oxidative stress and chronic disease continues to be affirmed, direct-acting antioxidants such as vitamins A, C, and E, beta-carotene, and others have not yielded the expected preventive or therapeutic responses, even though several large meta-analyses have sought to evaluate the potential benefit of such supplements. Because polyphenols exhibit poor bioavailability, few of their impressive in vitro findings have been replicated in vivo. SFN, an aliphatic isothiocyanate, emerges as a phytochemical with comparatively high bioavailability. A number of clinical trials have demonstrated its ability to produce favourable outcomes in conditions for which there are few satisfactory pharmaceutical solutions, foreshadowing the potential for SFN as a clinically relevant nutraceutical. Although myrosinase-inert broccoli sprout extracts are widely available, there now exist myrosinase-active broccoli sprout supplements that yield sufficient SFN to match the doses used in clinical trials.

Interplay of Glycemic Index, Glycemic Load, and Dietary Antioxidant Capacity with Insulin Resistance in Subjects with a Cardiometabolic Risk Profile

Background: Dietary total antioxidant capacity (TAC), glycemic index (GI), and glycemic load (GL) are accepted indicators of diet quality, which have an effect on diet–disease relationships. The aim of this study was to evaluate potential associations of dietary TAC, GI, and GL with variables related to nutritive status and insulin resistance (IR) risk in cardiometabolic subjects. Methods: A total of 112 overweight or obese adults (age: 50.8 ± 9 years old) were included in the trial. Dietary intake was assessed by a validated 137-item food frequency questionnaire (FFQ), which was also used to calculate the dietary TAC, GI, and GL. Anthropometrics, blood pressure, body composition by dual-energy X-ray absorptiometry (DXA), glycemic and lipid profiles, C-reactive protein (CRP), as well as fatty liver quantification by magnetic resonance imaging (MRI) were assessed. Results: Subjects with higher values of TAC had significantly lower circulating insulin concentration and homeostatic model assessment of insulin resistance (HOMA-IR). Participants with higher values of HOMA-IR showed significantly higher GI and GL. Correlation analyses showed relevant inverse associations of GI and GL with TAC. A regression model evidenced a relationship of HOMA-IR with TAC, GI, and GL. Conclusion: This data reinforces the concept that dietary TAC, GI, and GL are potential markers of diet quality, which have an impact on the susceptible population with a cardiometabolic risk profile.

Dietary Total Antioxidant Capacity and Cardiovascular Disease Risk Factors: A Systematic Review of Observational Studies

OBJECTIVE

Measurement of dietary total antioxidant capacity (DTAC) is considered a new holistic dietary approach and assesses total antioxidants present in the overall diet. Our aim was to perform a comprehensive review of the literature on the association between DTAC and cardiovascular disease (CVD) risk factors.

METHODS

PubMed, Web of Science, and Scopus were used to conduct a comprehensive search for articles published on this topic through September 2017. There was no limit on earliest year of publication. The search was based on the following keywords: dietary total antioxidant capacity, nonenzymatic antioxidant capacity, total radical-trapping antioxidant parameter, ferric reducing ability of plasma, oxygen radical absorbance capacity, Trolox equivalent antioxidant capacity, high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), triglycerides (TG), total cholesterol (TC), waist circumference (WC), insulin resistance, homeostatic model assessment of insulin resistance (HOMA-IR), insulin, obesity, glucose, C-reactive protein (CRP), blood pressure (BP), and body mass index. In total, 16 papers were identified for inclusion in the present systematic review.

RESULTS

Most well-designed studies that evaluated associations between DTAC and CVD risk factors showed inverse associations for fasting blood glucose, CRP, BP, and WC and positive associations for HDL-C. However, there was no association between DTAC and LDL-C or TC in any of the studies. Results regarding the association of DTAC with insulin, HOMA-IR, high-sensitivity CRP, and TG in the published literature were inconsistent.

CONCLUSIONS

Findings indicated a substantial association between high DTAC and most CVD-related risk factors.

Oral supplementation of diabetic mice with propolis restores the proliferation capacity and chemotaxis of B and T lymphocytes towards CCL21 and CXCL12 by modulating the lipid profile, the pro-inflammatory cytokine levels and oxidative stress

BACKGROUND

Type 1 diabetes mellitus (T1D) is a chronic autoimmune disease caused by the selective destruction of pancreatic β cells, followed by hyperglycemia, oxidative stress and the subsequent extensive impairment of immune cell functions, a phenomenon responsible for the development of chronic diabetic complications. Propolis, a natural bee product that is extensively used in foods and beverages, significantly benefits human health. Specifically, propolis exerts antioxidant, anti-inflammatory and analgesic effects that may improve diabetic complications. To further elucidate the potential benefits of propolis, the present study investigated the effect of dietary supplementation with propolis on the plasma cytokine profiles, free radical levels, lipid profile and lymphocyte proliferation and chemotaxis in a streptozotocin (STZ)-induced type I diabetic mouse model.

METHODS

Thirty male mice were equally distributed into 3 experimental groups: group 1, non-diabetic control mice; group 2, diabetic mice; and group 3, diabetic mice supplemented daily with an ethanol-soluble derivative of propolis (100 mg/kg body weight) for 1 month.

RESULTS

First, the induction of diabetes in mice was associated with hyperglycemia and significant decreases in the insulin level and the lymphocyte count. In this context, diabetic mice exhibited severe diabetic complications, as demonstrated by a significant decrease in the levels of IL-2, IL-4 and IL-7, prolonged elevation of the levels of pro-inflammatory cytokines (IL-1β, IL-6 and TNF-α) and reactive oxygen species (ROS) and altered lipid profiles compared with control non-diabetic mice. Moreover, antigen stimulation of B and T lymphocytes markedly reduced the proliferative capacity and chemotaxis of these cells towards CCL21 and CXCL12 in diabetic mice compared with control mice. Interestingly, compared with diabetes induction alone, treatment of diabetic mice with propolis significantly restored the plasma cytokine and ROS levels and the lipid profile to nearly normal levels. Most importantly, compared with untreated diabetic mice, diabetic mice treated with propolis exhibited significantly enhanced lymphocyte proliferation and chemotaxis towards CCL21 and CXCL12.

CONCLUSION

Our findings reveal the potential immuno-modulatory effects of propolis, which acts as a natural antioxidant to enhance the function of immune cells during diabetes.

Oxidative stress and metabolic syndrome: Effects of a natural antioxidants enriched diet on insulin resistance

BACKGROUND & AIMS

Oxidative stress (OS) could play a role in metabolic syndrome-related manifestations contributing to insulin resistance (IR). The aim of the present study was to gain insight the relationships between OS, IR and other hormones involved in caloric balance, explaining the effects of a natural antioxidant-enriched diet in patients affected by metabolic syndrome.

METHODS

We investigated the effects of dietary antioxidants on IR, studying 53 obese (20 males and 33 females, 18-66 years old, BMI 36.3 ± 5.5 kg/m²), with IR evaluated by Homeostasis Model Assessment (HOMA)-index, comparing 4 treatments: hypocaloric diet alone (group A) or plus metformin 1000 mg/daily (group B), natural antioxidants-enriched hypocaloric diet alone (group C) or plus metformin (group D). A personalized program, with calculated antioxidant intake of 800-1000 mg/daily, from fruit and vegetables, was administered to group C and D. The glycemic and insulinemic response to oral glucose load, and concentrations of total-, LDL- and HDL-cholesterol, triglycerides, uric acid, C reactive protein, fT3, fT4, TSH, insulin-like growth factor 1 were evaluated before and after 3-months. Plasma Total antioxidant capacity was determined by H₂O₂-metmyoglobin system, which interacting with the chromogen ABTS generates a radical with latency time (LAG) proportional to antioxidant content.

RESULTS

Despite a similar BMI decrease, we found a significant decrease of HOMA and insulin peak only in group B and D. Insulin response (AUC) showed the greatest decrease in group D (25.60  ±  8.96%) and was significantly lower in group D vs B. No differences were observed in glucose response, lipid metabolism and TAC (expressed as LAG values). TSH values were significantly suppressed in group D vs B.

CONCLUSIONS

These data suggest that dietary antioxidants ameliorate insulin-sensitivity in obese subjects with IR by enhancing the effect of insulin-sensitizing drugs albeit with molecular mechanisms which remain yet to be elucidated.

Antihyperglycaemic mechanisms of an aceteoside polymer from rose flowers and a polysaccharide-protein complex from abalone mushroom

Oral administration of an aceteoside polymer from rose Rosa rugosa (P1-b) and a polysaccharide-peptide complex from abalone mushroom Pleurotus abalonus (LB-1b), both with antioxidant activity, produced antihyperglycaemic effects in alloxan-induced diabetic mice. The expression of insulin, superoxide dismutase and pancreas duodenum homeobox factor-1 essential for pancreatic islet function as estimated by real-time PCR was augmented. The reactive oxygen species-scavenging ability of the rose constituent was notably stronger than the mushroom constituent. Thus, the two biomolecules protected the pancreas from oxidative stress, elevated pancreatic insulin expression and lowered circulating glucose level.

Sestrin2 inhibits uncoupling protein 1 expression through suppressing reactive oxygen species

Uncoupling protein 1 (Ucp1), which is localized in the mitochondrial inner membrane of mammalian brown adipose tissue (BAT), generates heat by uncoupling oxidative phosphorylation. Upon cold exposure or nutritional abundance, sympathetic neurons stimulate BAT to express Ucp1 to induce energy dissipation and thermogenesis. Accordingly, increased Ucp1 expression reduces obesity in mice and is correlated with leanness in humans. Despite this significance, there is currently a limited understanding of how Ucp1 expression is physiologically regulated at the molecular level. Here, we describe the involvement of Sestrin2 and reactive oxygen species (ROS) in regulation of Ucp1 expression. Transgenic overexpression of Sestrin2 in adipose tissues inhibited both basal and cold-induced Ucp1 expression in interscapular BAT, culminating in decreased thermogenesis and increased fat accumulation. Endogenous Sestrin2 is also important for suppressing Ucp1 expression because BAT from Sestrin2(-/-) mice exhibited a highly elevated level of Ucp1 expression. The redox-inactive mutant of Sestrin2 was incapable of regulating Ucp1 expression, suggesting that Sestrin2 inhibits Ucp1 expression primarily through reducing ROS accumulation. Consistently, ROS-suppressing antioxidant chemicals, such as butylated hydroxyanisole and N-acetylcysteine, inhibited cold- or cAMP-induced Ucp1 expression as well. p38 MAPK, a signaling mediator required for cAMP-induced Ucp1 expression, was inhibited by either Sestrin2 overexpression or antioxidant treatments. Taken together, these results suggest that Sestrin2 and antioxidants inhibit Ucp1 expression through suppressing ROS-mediated p38 MAPK activation, implying a critical role of ROS in proper BAT metabolism.

Dietary total antioxidant capacity is related to glucose tolerance in older people: the Hertfordshire Cohort Study

BACKGROUND AND AIMS

Dietary antioxidants may play a protective role in the aetiology of type 2 diabetes. However, observational studies that examine the relationship between the antioxidant capacity of the diet and glucose metabolism are limited, particularly in older people. We aimed to examine the relationships between dietary total antioxidant capacity (TAC) and markers of glucose metabolism among 1441 men and 1253 women aged 59-73 years who participated in the Hertfordshire Cohort Study, UK.

METHODS AND RESULTS

Diet was assessed by food frequency questionnaire. Dietary TAC was estimated using published databases of TAC measured by four different assays: oxygen radical absorbance capacity (ORAC), ferric-reducing ability of plasma (FRAP), total radical-trapping antioxidant parameter (TRAP) and trolox equivalent antioxidant capacity (TEAC). Fasting and 120-min plasma glucose and insulin concentrations were measured during a standard 75-g oral glucose tolerance test. In men, dietary TAC estimated by all four assays was inversely associated with fasting insulin concentration and homoeostasis model assessment of insulin resistance (HOMA-IR); with the exception of ORAC, dietary TAC was also inversely related to 120-min glucose concentration. There were no associations with fasting glucose or 120-min insulin concentrations. In women, with the exception of the association between ORAC and 120-min insulin concentration, dietary TAC estimated by all assays showed consistent inverse associations with fasting and 120-min glucose and insulin concentrations and HOMA-IR. These associations were more marked among women with BMI ≥ 30 kg/m(2).

CONCLUSION

These findings suggest dietary TAC may have important protective effects on glucose tolerance, especially in older obese women.

Lifestyle impact on meal-induced insulin sensitization in health and prediabetes: A focus on diet, antioxidants, and exercise interventions

The augmented whole-body glucose uptake response to insulin during the postprandial state is described as meal-induced insulin sensitization (MIS). MIS occurs when the presence of food in the upper gastrointestinal tract activates 2 feeding signals (activation of hepatic parasympathetic nerves and elevation of hepatic glutathione level), and causes insulin to release hepatic insulin sensitizing substance (HISS), which stimulates glucose uptake in skeletal muscle, heart, and kidneys. HISS action results in nutrient storage, primarily as glycogen. Impairment of HISS release results in the absence of meal-induced insulin sensitization (AMIS), which causes postprandial hyperglycemia and hyperinsulinemia, and chronically leads to the progression to a cluster of metabolic, vascular, and cardiac dysfunctions, which we refer to as components of the AMIS syndrome. Manipulation of the MIS process in health and in disease, by pharmacological and nonpharmacological interventions, is outlined in this review. High fat or sugar supplemented diet reduces MIS; exercise elevates MIS; and antioxidants protect MIS against reductions associated with diet and age.

Dietary antioxidant capacity is inversely associated with diabetes biomarkers: the ATTICA study

BACKGROUND AND AIMS

Elevated dietary antioxidant activity has been regarded as providing potential benefits to health. The present work aimed at evaluating the association of glycemic indices with total dietary antioxidant capacity in healthy adults.

METHODS AND RESULTS

The ATTICA study consisted of men and women, randomly selected from all areas of Attica region in Greece. In this work, a random sub-sample from the ATTICA study's database was studied, consisting of 551 men (41 ± 11 years) and 467 women (38 ± 11 years), with complete nutritional and biochemical information. Dietary habits were evaluated using a validated food-frequency questionnaire. The dietary antioxidant capacity was based on published values for Italian foods measured by three different assays: ferric-reducing antioxidant power (FRAP), total radical-trapping antioxidant parameter (TRAP) and Trolox equivalent antioxidant capacity (TEAC). Inverse, age-energy adjusted correlations were observed between FRAP and log-glucose (r = -0.149, p = 0.001), log-insulin (r = -0.221, p = 0.001) and log-HOMA-IR (r = -0.186, p = 0.001) concentration, as well as with TRAP and TEAC. After controlling for age, gender, body mass index, physical activity status, smoking habits and energy intake, multi-adjusted analysis confirmed the previous relationships only among participants who were not on the Mediterranean dietary pattern.

CONCLUSIONS

Although more prospective studies are required, the data presented support the view that dietary modification towards higher consumption of antioxidants should be implemented in public health strategies, in order to better control glycemic markers in individuals, and prevent the development of diabetes at the population level.

Effect of antioxidant supplementation on insulin sensitivity in response to endurance exercise training

While production of reactive oxygen and nitrogen species (RONS) is associated with some of the beneficial adaptations to regular physical exercise, it is not established whether RONS play a role in the improved insulin-stimulated glucose uptake in skeletal muscle obtained by endurance training. To assess the effect of antioxidant supplementation during endurance training on insulin-stimulated glucose uptake, 21 young healthy (age 29 ± 1 y, BMI 25 ± 3 kg/m(2)) men were randomly assigned to either an antioxidant [AO; 500 mg vitamin C and 400 IU vitamin E (α-tocopherol) daily] or a placebo (PL) group that both underwent a supervised intense endurance-training program 5 times/wk for 12 wk. A 3-h euglycemic-hyperinsulinemic clamp, a maximal oxygen consumption (Vo(2max)) and maximal power output (P(max)) test, and body composition measurements (fat mass, fat-free mass) were performed before and after the training. Muscle biopsies were obtained for determination of the concentration and activity of proteins regulating glucose metabolism. Although plasma levels of vitamin C (P < 0.05) and α-tocopherol (P < 0.05) increased markedly in the AO group, insulin-stimulated glucose uptake increased similarly in both the AO (17.2%, P < 0.05) and the PL (18.9%, P < 0.05) group in response to training. Vo(2max) and P(max) also increased similarly in both groups (time effect, P < 0.0001 for both) as well as protein content of GLUT4, hexokinase II, and total Akt (time effect, P ≤ 0.05 for all). Our results indicate that administration of antioxidants during strenuous endurance training has no effect on the training-induced increase in insulin sensitivity in healthy individuals.

Biological activities of chinese propolis and brazilian propolis on streptozotocin-induced type 1 diabetes mellitus in rats

Propolis is a bee-collected natural product and has been proven to have various bioactivities. This study tested the effects of Chinese propolis and Brazilian propolis on streptozotocin-induced type 1 diabetes mellitus in Sprague-Dawley rats. The results showed that Chinese propolis and Brazilian propolis significantly inhibited body weight loss and blood glucose increase in diabetic rats. In addition, Chinese propolis-treated rats showed an 8.4% reduction of glycated hemoglobin levels compared with untreated diabetic rats. Measurement of blood lipid metabolism showed dyslipidemia in diabetic rats and Chinese propolis helped to reduce total cholesterol level by 16.6%. Moreover, oxidative stress in blood, liver and kidney was improved to various degrees by both Chinese propolis and Brazilian propolis. An apparent reduction in levels of alanine transaminase, aspartate transaminase, blood urea nitrogen and urine microalbuminuria-excretion rate demonstrated the beneficial effects of propolis in hepatorenal function. All these results suggested that Chinese propolis and Brazilian propolis can alleviate symptoms of diabetes mellitus in rats and these effects may partially be due to their antioxidant ability.

A Regenerative Antioxidant Protocol of Vitamin E and α-Lipoic Acid Ameliorates Cardiovascular and Metabolic Changes in Fructose-Fed Rats

Type 2 diabetes is a major cause of cardiovascular disease. We have determined whether the metabolic and cardiovascular changes induced by a diet high in fructose in young adult male Wistar rats could be prevented or reversed by chronic intervention with natural antioxidants. We administered a regenerative antioxidant protocol using two natural compounds: α-lipoic acid together with vitamin E (α-tocopherol alone or a tocotrienol-rich fraction), given as either a prevention or reversal protocol in the food. These rats developed glucose intolerance, hypertension, and increased collagen deposition in the heart together with an increased ventricular stiffness. Treatment with a fixed combination of vitamin E (either α-tocopherol or tocotrienol-rich fraction, 0.84 g/kg food) and α-lipoic acid (1.6 g/kg food) normalized glucose tolerance, blood pressure, cardiac collagen deposition, and ventricular stiffness in both prevention and reversal protocols in these fructose-fed rats. These results suggest that adequate antioxidant therapy can both prevent and reverse the metabolic and cardiovascular damage in type 2 diabetes.

Antidiabetic effect of propolis: reduction of expression of glucose-6-phosphatase through inhibition of Y279 and Y216 autophosphorylation of GSK-3α/β in HepG2 cells

Propolis is a sticky, resinous material that honey bees collect from various plants, and mix with wax and other secretions. The aim of this study was to evaluate the antidiabetic effect of propolis through an analysis of the expression and enzyme activity of glucose-6-phosphatase (G6Pase) and to elucidate the mechanism by which propolis inhibits G6Pase gene expression. When HepG2 cells were incubated in high glucose media (25 mm), G6Pase expression was induced. Propolis significantly reduced the expression and enzyme activity of G6Pase; however, the hypoglycemic effect was not abolished by the phosphoinositide 3-kinase inhibitor, LY294002, and by the mitogen-activated protein kinase (MAPK) inhibitor, U0126. Propolis inhibited the activity of GSK3α and β via the inhibition of serine and tyrosine phosphorylation, specifically, Y279 for GSK3α and Y216 for GSK3β. The phosphorylations of Y279 and Y216 occur through autophosphorylation by GSK3α/β and are involved in their own activity. Although propolis showed antioxidant activity, antidiabetic effect of propolis was not influenced by hydrogen peroxide and N-acetylcysteine. These results suggest that propolis inhibits the expression of G6Pase by inhibiting the autophosphorylation of Y279 and Y216 of GSK3α and β, respectively, which are involved in the activation of GSK3. These findings suggest that propolis may be a potential antidiabetic agent for the treatment of insulin-insensitive diabetes.

Fermented wheat germ extract (avemar) in the treatment of cardiac remodeling and metabolic symptoms in rats

Avemar, a product of industrial fermentation of wheat germ with a standardized content of benzoquinone and plant flavonoids, has been tested as an anti-cancer and immunomodulatory dietary supplement. Proposed mechanisms include anti-oxidant and anti-inflammatory actions. This study has determined whether these actions of Avemar may also be useful in the treatment of cardiovascular diseases. Two experimental rat models of cardiovascular remodeling were used in this project: the deoxycorticosterone acetate (DOCA)-salt-induced model of chronic hypertension (study I) and a high-carbohydrate/high-fat diet-induced model producing chronic symptoms of the metabolic syndrome and its associated cardiovascular complications (study II). Our results in these rat models of hypertension and diet-induced obesity show that treatment with Avemar improved cardiac function, decreased macrophage infiltration resulting in decreased collagen deposition in the ventricular myocardium, reversed an increased stiffness of the left ventricle in the diseased hearts and attenuated increased plasma malondialdehyde concentrations. In addition to the changes in the heart, Avemar reversed glucose intolerance, normalized systolic blood pressure and decreased visceral fat deposition in rats fed a high-fat/high-carbohydrate diet. In conclusion, the fermented wheat germ extract Avemar has a potential role in attenuating chronic hypertension, diabetes or metabolic syndrome-induced cardiovascular symptoms along with metabolic abnormalities such as glucose tolerance and obesity.

Reconvene and reconnect the antioxidant hypothesis in human health and disease

The antioxidants are essential molecules in human system but are not miracle molecules. They are neither performance enhancers nor can prevent or cure diseases when taken in excess. Their supplemental value is debateable. In fact, many high quality clinical trials on antioxidant supplement have shown no effect or adverse outcomes ranging from morbidity to all cause mortality. Several Chochrane Meta-analysis and Markov Model techniques, which are presently best available statistical models to derive conclusive answers for comparing large number of trials, support these claims. Nevertheless none of these statistical techniques are flawless. Hence, more efforts are needed to develop perfect statistical model to analyze the pooled data and further double blind, placebo controlled interventional clinical trials, which are gold standard, should be implicitly conducted to get explicit answers. Superoxide dismutase (SOD), glutathione peroxidase and catalase are termed as primary antioxidants as these scavenge superoxide anion and hydrogen peroxide. All these three enzymes are inducible enzymes, thereby inherently meaning that body increases or decreases their activity as per requirement. Hence there is no need to attempt to manipulate their activity nor have such efforts been clinically useful. SOD administration has been tried in some conditions especially in cancer and myocardial infarction but has largely failed, probably because SOD is a large molecule and can not cross cell membrane. The dietary antioxidants, including nutrient antioxidants are chain breaking antioxidants and in tandem with enzyme antioxidants temper the reactive oxygen species (ROS) and reactive nitrogen species (RNS) within physiological limits. Since body is able to regulate its own requirements of enzyme antioxidants, the diet must provide adequate quantity of non-enzymic antioxidants to meet the normal requirements and provide protection in exigent condition. So far, there is no evidence that human tissues ever experience the torrent of reactive species and that in chronic conditions with mildly enhanced generation of reactive species, the body can meet them squarely if antioxidants defense system in tissues is biochemically optimized. We are not yet certain about optimal levels of antioxidants in tissues. Two ways have been used to assess them: first by dietary intake and second by measuring plasma levels. Lately determination of plasma/serum level of antioxidants is considered better index for diagnostic and prognostic purposes. The recommended levels for vitamin A, E and C and beta carotene are 2.2-2.8 μmol/l; 27.5-30 μmol/l; 40-50 μmol/l and 0.4-0.5 μmol/l, respectively. The requirement and recommended blood levels of other dietary antioxidants are not established. The resolved issues are (1) essential to scavenge excess of radical species (2) participants in redox homeostasis (3) selective antioxidants activity against radical species (4) there is no universal antioxidant and 5) therapeutic value in case of deficiency. The overarching issues are (1) therapeutic value as adjuvant therapy in management of diseases (2) supplemental value in developing population (3) selective interactivity of antioxidant in different tissues and on different substrates (4) quantitative contribution in redox balance (5) mechanisms of adverse action on excess supplementation (6) advantages and disadvantages of prooxidant behavior of antioxidants (7) behavior in cohorts with polymorphic differences (8) interaction and intervention in radiotherapy, diabetes and diabetic complications and cardiovascular diseases (9) preventive behavior in neurological disorders (10) benefits of non-nutrient dietary antioxidants (11) markers to assess optimized antioxidants status (12) assessment of benefits of supplementation in alcoholics and heavy smokers. The unresolved and intriguing issues are (1) many compounds such as vitamin A and many others possessing both antioxidant and non-antioxidant properties contribute to both the activities in vivo or exclusively only to non-antioxidant activity and (2) since human tissues do not experience the surge of FR, whether there is any need to develop stronger synthetic antioxidants. Theoretically such antioxidants may do more harm than good.

Reactive oxygen species, reactive nitrogen species and antioxidants in etiopathogenesis of diabetes mellitus type-2

Diabetes mellitus type-2 (DMT-2) is a hyperglycemic syndrome with several characteristic features. It continues to rise unabatedly in all pockets of the world, parallels with affluence and can be controlled but not cured. It has a definite involvement of genetic component but environmental factors play overwhelmingly dominant role in etiopathogenesis. Insulin resistance (IR) and obesity are singular instigators of DMT-2. The various events cause critical defects in insulin signaling cascade followed by beta-cell dysfunction. Over a period of time, numerous other metabolic aberrations develop, resulting in diabetic complications which could be both vascular (cardiovascular complications, nephropathy, neuropathy, retinopathy and embryopathy) or a-vascular (cataract and glaucoma etc). It has been proposed that all these abnormal events are initiated or activated by a common mechanism of superoxide anion, which is accompanied with generation of a variety of reactive oxygen species (ROS), reactive nitrogen specie (RNS) and resultant heightened oxidative stress (OS). Provoked OS causes IR and altered gene expressions. Hyperglycemia induces OS through multiple routes: a)stimulated polyol pathway where in ≤ 30% glucose can be diverted to sorbitol and fructose, b)increased transcription of genes for proinflammatory cytokines and plasminogen activator inhibitor-1 (PAI-1) c) activation of protein kinase-C (PKC) leading to several molecular changes d)increased synthesis of Advanced Glycation End Products (AGEs) e)changes in a receptor far AGEs and f) autooxidation of glucose with formation of ketoimines and AGEs. All these processes are accompanied with alteration in redox status, ROS, RNS and OS which trigger DMT-2 and its complications. Initial hurriedly planned and executed experimental and clinical studies showed promising results of antioxidant therapies, but recent studies indicate that excess intake/supplement may have adverse outcomes including increased mortality. It is advocated that antioxidants should be given only if preexisting deficiency is present. Selection of antioxidant is another important aspect. Lastly but most importantly the impact of OS is not obligatory but facultative. As such only those diabetic patients will be benefited by antioxidant therapies that have impelling punch of prooxidants.

Hyperglycemia-induced alterations in synaptosomal membrane fluidity and activity of membrane bound enzymes: beneficial effect of N-acetylcysteine supplementation

Diabetic encephalopathy is characterized by impaired cognitive functions that appear to underlie neuronal damage triggered by glucose driven oxidative stress. Hyperglycemia-induced oxidative stress in diabetic brain may initiate structural and functional changes in synaptosomal membranes. The objective of the present study was to examine the neuroprotective role of N-acetylcysteine (NAC) in hyperglycemia-induced alterations in lipid composition and activity of membrane bound enzymes (Na(+),K(+)-ATPase and Ca(2+)-ATPase) in the rodent model of type 1 diabetes. Male Wistar rats weighing between 180 and 200 g were rendered diabetic by a single injection of streptozotocin (50 mg/kg body weight, i.p.). The diabetic animals were administered NAC (1.4-1.5 g/kg body weight) for eight weeks and lipid composition along with membrane fluidity were determined. A significant increase in lipid peroxidation was observed in cerebral cortex of diabetic rats. NAC administration on the other hand lowered the hyperglycemia-induced lipid peroxidation to near control levels. The increased lipid peroxidation following chronic hyperglycemia was accompanied by a significant increase in the total lipids which can be attributed to increase in the levels of cholesterol, triglycerides and glycolipids. On the contrary phospholipid and ganglioside levels were decreased. Hyperglycemia-induced increase in cholesterol to phospholipid ratio reflected decrease in membrane fluidity. Fluorescence polarization (p) with DPH also confirmed decrease in synaptosomal membrane fluidity that influenced the activity of membrane bound enzymes. An inverse correlation was found between fluorescence polarization with the activities of Na(+),K(+)-ATPase (r(2)=0.416, P<0.05) and Ca(2+) ATPase (r(2)=0.604, P<0.05). NAC was found to significantly improve lipid composition, restore membrane fluidity and activity of membrane bound enzymes. Our results clearly suggest perturbations in lipid composition and membrane fluidity as a major factor in the development of diabetic encephalopathy. Furthermore, NAC administration ameliorated the effect of hyperglycemia on oxidative stress and alterations in lipid composition thereby restoring membrane fluidity and activity of membrane bound enzymes.