Effects of vitamin C supplementation on antioxidants and lipid peroxidation markers in elderly subjects with type 2 diabetes

Integrated approach to reducing polypharmacy in older people: exploring the role of oxidative stress and antioxidant potential therapy

Increased life expectancy, attributed to improved access to healthcare and drug development, has led to an increase in multimorbidity, a key contributor to polypharmacy. Polypharmacy is characterised by its association with a variety of adverse events in the older persons. The mechanisms involved in the development of age-related chronic diseases are largely unknown; however, altered redox homeostasis due to ageing is one of the main theories. In this context, the present review explores the development and interaction between different age-related diseases, mainly linked by oxidative stress. In addition, drug interactions in the treatment of various diseases are described, emphasising that the holistic management of older people and their pathologies should prevail over the individual treatment of each condition.

Vitamin C supplementation improves blood pressure and oxidative stress after acute exercise in patients with poorly controlled type 2 diabetes mellitus: A randomized, placebo-controlled, cross-over study

This study aimed to assess the effect of Vitamin C on blood pressure (BP), and subsequently on oxidative stress and nitric oxide (NO) release, following the low-intensity exercise in the patients. This study included 24 patients with type 2 diabetes mellitus (T2D) (age, 53 ± 7 years; hemoglobin A1c, 10.1% ± 0.9%) randomized into two 6-week daily arms based on the consumption of either placebo or 1000 mg Vitamin C. The crossover trial occurred after a 6-week washout. Before and after both supplementation arms, all patients performed cycling exercise at 33% of peak oxygen consumption for 20 min. BP was measured before, immediately, and 60 min after the exercise. Blood samples were drawn immediately before and after the exercise to determine plasma ascorbate, malondialdehyde (MDA), F₂-isoprostanes (F₂-IsoPs), and NO concentrations. Data showed significant lower BP in the Vitamin C arm when compared with the placebo arm (systolic BP [SBP] P < 0.001 at every time point, diastolic BP [DBP] P < 0.001 except at immediately after exercise, P < 0.05). Plasma ascorbate concentration (P < 0.05 at every time point) and plasma NO (at resting P < 0.001, immediately after exercise P < 0.05) were significantly increased in the Vitamin C arm than in the placebo arm. Plasma MDA (P < 0.05 at every time point) and F₂-IsoPs (P < 0.05 at every time point) concentrations were significantly lower in the Vitamin C arm than in the placebo arm. In addition, data showed significantly lower SBP (P < 0.001 at every time point), DBP (P < 0.001 except at immediately after exercise P < 0.05), plasma MDA (P < 0.001 at every time point), and F₂-IsoPs (P < 0.05 at every time point) at post-supplementation than at pre-supplementation. Besides, there were significantly higher plasma ascorbate (P < 0.05 at every time point) and NO (at rest P < 0.01, immediately after exercise P < 0.05) concentrations at post-supplementation than at pre-supplementation. This is in contrast to the placebo treatment arm which demonstrated no statistical difference in all outcomes throughout the experiment. This study suggests that 6-week Vitamin C supplementation decreased preexercise and postexercise BPs, possibly due to improved oxidative stress and NO release. However, exercise had no effect on any outcome measures.

Effects of Vitamin C Supplementation on Glycemic Control and Cardiovascular Risk Factors in People With Type 2 Diabetes: A GRADE-Assessed Systematic Review and Meta-analysis of Randomized Controlled Trials

BACKGROUND

Evidence suggests that vitamin C supplementation could be a potential therapy in type 2 diabetes. However, its effectiveness and evidence quality require further evaluation.

PURPOSE

To investigate the efficacy of oral vitamin C supplementation in improving glycemic control, cardiovascular risk factors, and oxidative stress in people with type 2 diabetes.

DATA SOURCES

Databases (PubMed, Embase, Scopus, Cochrane Library) and clinical trial registries were searched for randomized controlled trials up to 8 September 2020.

STUDY SELECTION

Trials in adults with type 2 diabetes were included. Trials were excluded if supplements were not exclusive to vitamin C and if <2 weeks in duration.

DATA EXTRACTION

Primary outcomes were HbA_1c, glucose, cholesterol, triglycerides, and blood pressure (BP). Data were extracted for changes in outcomes between vitamin C and control groups. Evidence certainty was assessed using Grading of Recommendations, Assessment, Development, and Evaluation methods.

DATA SYNTHESIS

Twenty-eight studies (N = 1,574 participants) were included in the review. Outcomes that changed to a statistically and clinically significant extent with vitamin C were systolic BP (mean difference -6.27 [95% CI -9.60, -2.96] mmHg; P = 0.0002), with moderate evidence certainty, and HbA_1c (-0.54% [-0.90, -0.17]; P = 0.004) and diastolic BP (-3.77 [-6.13, -1.42] mmHg; P = 0.002) with very low evidence certainty.

LIMITATIONS

Studies were predominantly short term (<6 months) with a small number of participants (n < 100).

CONCLUSIONS

While evidence from short-term studies suggests that vitamin C supplementation may improve glycemic control and BP in people with type 2 diabetes, vitamin C supplementation cannot currently be recommended as a therapy until larger, long-term, and high-quality trials confirm these findings.

Antioxidant properties of drugs used in Type 2 diabetes management: could they contribute to, confound or conceal effects of antioxidant therapy?

OBJECTIVES

This is a narrative review, investigating the antioxidant properties of drugs used in the management of diabetes, and discusses whether these antioxidant effects contribute to, confound, or conceal the effects of antioxidant therapy.

METHODS

A systematic search for articles reporting trials, or observational studies on the antioxidant effect of drugs used in the treatment of diabetes in humans or animals was performed using Web of Science, PubMed, and Ovid. Data were extracted, including data on a number of subjects, type of treatment (and duration) received, and primary and secondary outcomes. The primary outcomes were reporting on changes in biomarkers of antioxidants concentrations and secondary outcomes were reporting on changes in biomarkers of oxidative stress.

RESULTS

Diabetes Mellitus is a disease characterized by increased oxidative stress. It is often accompanied by a spectrum of other metabolic disturbances, including elevated plasma lipids, elevated uric acid, hypertension, endothelial dysfunction, and central obesity. This review shows evidence that some of the drugs in diabetes management have both in vivo and in vitro antioxidant properties through mechanisms such as scavenging free radicals and upregulating antioxidant gene expression.

CONCLUSION

Pharmaceutical agents used in the treatment of type 2 diabetes has been shown to exert an antioxidant effect..

Antioxidant effects of vitamins in type 2 diabetes: a meta-analysis of randomized controlled trials

BACKGROUND

Vitamins are essential micronutrients with antioxidant potential that may provide a complementary treatment for patients with chronic diseases. Our aim was to assess the effect of vitamin supplementation on the antioxidant status and glycemic index of type 2 diabetes mellitus patients.

METHODS

We performed a systematic review with meta-analyses. Electronic searches were conducted in PubMed, Scopus, and Web of Science (December 2017). Randomized controlled trials evaluating the effect of any vitamin or vitamin complex supplementation on antioxidant status as primary outcome were included. The outcomes considered were: reduction of malondialdehyde (MDA); augmentation of glutathione peroxidase (GPx); changes in total antioxidant capacity (TAC), enhance in superoxide dismutase enzyme-SOD, and thiobarbituric acid reactive substances (TBARS). Outcomes of glycemic control were also evaluated. Pairwise meta-analyses were performed using software Review Manager 5.3.

RESULTS

Thirty trials fulfilled the inclusion criteria, but only 12 could be included in the meta-analyses of antioxidant outcomes. The most commonly studied vitamins were B, C, D and E. Vitamin E was related to significant reduction of blood glucose as well as glycated hemoglobin compared to placebo, while both vitamins C and E were mainly associated with reducing MDA and TBARS and elevating GPx, SOD and TAC, compared to placebo. However, outcome reports in this field are still inconsistent (e.g. because of a lack of standard measures).

CONCLUSIONS

Supplementation of vitamin E may be a valuable strategy for controlling diabetes complications and enhancing antioxidant capacity. The effects of other micronutrients should be further investigated in larger and well-designed trials to properly place these complementary therapies in clinical practice.

Paraoxonase-1 (PON1) inhibition by tienilic acid produces hepatic injury: Antioxidant protection by fennel extract and whey protein concentrate

This study evaluated the effect of whey protein concentrate (WPC) or fennel seed extract (FSE) on paraoxonase-1 activity (PON1) and oxidative stress in liver of tienilic acid (TA) treated rats. Six groups of rats were treated for six weeks as follows: control; WPC (0.5g/kg/day); FSE (200mg/ kg/day); TA (1g/kg/twice a week); TA (1g/kg/twice a week) plus WPC (0.5g/kg/day); TA (1g/kg/twice a week) plus FSE (200mg/kg/day). TA administration significantly increased ALT and AST besides to total- and direct bilirubin levels. Also, serum tumor necrosis factor-α and nitric oxide levels were significantly increased. Furthermore, serum PON1, and hepatic reduced glutathione, glutathione-S-transferase and Na(+)/K(+)-ATPase values were diminished matched with a significant rise in the level of hepatic lipid peroxidation. Also, triglycerides, total- and LDL-cholesterol levels were significantly elevated while HDL-cholesterol was unchanged. The administration of either WPC or FSE to TA-treated animals significantly protected the liver against the injurious effects of tienilic acid. This appeared from the improvement of hepatic functions, atherogenic markers, Na(+)/K(+) ATPase activity, endogenous antioxidants and hepatic lipid peroxidation level; where WPC showed the strongest protection effect. In conclusion, the present study indicated that WPC and FSE improve PON1 activity and attenuate liver dysfunction induced by TA. This may be attributed to the high content of antioxidant compounds in WPC and fennel extract.

Response of thymus lymphocytes to streptozotocin-induced diabetes and exogenous vitamin C administration in rats

Diabetes causes oxidative stress, which in turn generates excessive free radicals resulting in cellular damage. Vitamin C is an antioxidant that protects tissues and organs from oxidative stress. The thymus is one of the most important lymphoid organs, which regulates T-lymphocyte proliferation and maturation. The aim of this study is to investigate the protective effects of vitamin C on the thymus of streptozotocin (STZ)-induced diabetic rats. The mitotic activity and cell integrity of thymic lymphocytes were explored. Wistar Albino rats were divided into three groups: control (Group 1), STZ-diabetes (Group 2) and vitamin C-treated STZ-diabetics (Group 3). Rats received a single intraperitoneal injection of 45 mg/kg STZ to induce diabetes. Vitamin C (20 mg/kg) was administered intragastrically. Semithin and ultrathin sections were examined under a light or an electron microscope, respectively. Considerable numbers of mitotic lymphocytes were observed in the thymus of control rats. In the diabetic rats, however, numbers of mitotic lymphocytes decreased to ∼57% of controls, and cell division abnormalities were observed. Additionally, diabetic rats showed degeneration in the structure of the thymus including trabecular thickening, accumulation of lipid vacuoles, heterochromatic nuclei and loss of mitochondrial cristae. Degradation of medullar and cortical integrity was also detected. In the vitamin C-treated STZ-diabetic group, the structure of the thymus and mitotic activity of the lymphocytes were similar to the control group. These results suggest that vitamin C protects the thymus against injury caused by diabetes and restores thymocyte mitotic activity.

Possible potentiation by certain antioxidants of the anti-inflammatory effects of diclofenac in rats

In the present study, we investigated the potential beneficial impact of the addition of antioxidant supplements to diclofenac regimen in a model of carrageenan-induced paw. Rats were treated daily with antioxidants, that is, a-lipoic acid (50 mg/kg), selenium (2.5 mg/kg), vitamin C (1 g/kg), vitamin E (300 mg/kg), or zinc (25 mg/kg) on seven successive days and then received a single treatment with diclofenac or saline before carrageenan was injected to induce paw inflammation. The results indicated that these combinations did not significantly affect the percentage inhibition of paw edema caused by diclofenac alone; however, some combination treatments ameliorated signs of concomitant oxidative stress (such as alterations in plasma malondialdehyde (MDA) levels, hemolysate reduced glutathione levels, and erythrocytic superoxide dismutase enzyme activities) imparted by diclofenac alone. In some cases, few tested antioxidants in combination with diclofenac resulted in increased plasma levels of interleukin- (IL-) 6 and C-reactive protein (CRP). In conclusion, the results of these studies suggested to us that the added presence of natural antioxidants could be beneficial as standard anti-inflammatory therapeutics for a patient under diclofenac treatment, albeit that these effects do not appear to significantly build upon those that could be obtained from this common anti-inflammatory agent per se.

Combating oxidative stress in diabetic complications with Nrf2 activators: how much is too much?

Diabetes is increasing at an alarming rate and, despite anti-hypertensive and insulin therapies, diabetic patients are still at risk of developing complications such as chronic kidney disease, cardiovascular disease, and retinopathy. There is therefore an urgent need for more effective therapies to prevent the development and progression of diabetic complications. Oxidative stress is a major player in the aetiology of diabetic complications. However, results from clinical trials thus far using general antioxidants have been disappointing. Mechanism-based antioxidants have gained considerable attention due to their more targeted approach at reducing oxidative stress and associated complications in diabetes. The transcription factor, NFE2-related factor 2 (Nrf2), is a master regulator of redox homeostasis and the cellular detoxification response. Instead of relying on a single antioxidant, activation of Nrf2 results in the concerted upregulation of several antioxidant enzymes and cytoprotective genes, making it an attractive therapeutic target for diabetic complications. Several Nrf2 activators have been discovered and have proven effective at activating Nrf2 signalling through different mechanisms in both in vitro and in vivo models of diabetes. This review will address some of the most promising and well-known Nrf2 activators and their roles in preventing the development and progression of diabetic complications. Challenges facing the advancement of this drug class into the clinic will be discussed, as will be the future of Nrf2 activation as a therapeutic strategy in preventing the development of diabetic complications.

Extra virgin olive oil (EVOO) consumption and antioxidant status in healthy institutionalized elderly humans

Recent studies show that the elderly have increased oxidative stress and impaired antioxidant defense systems. Our study aims to evaluate the effects of daily consumption of EVOO in the healthy institutionalized elderly. We studied anthropometric, biochemical and antioxidant parameters in 62 subjects aged 65-96 years after a 6-week daily intake of polyphenol-rich EVOO with high oleuropein derivative contents. Subjects were divided into a control group (CG) who maintained their dietary habits (n=39) and an olive group (OG) who consumed EVOO as the only added fat, plus a daily dose of 50ml (n=23). We found a significant reduction of total cholesterol (TC), HDL, LDL and TGs in OG subjects and a significant increase of HDL levels. There was no significant variation in the CG parameters. In OG the total antioxidant capacity (TAC) in plasma increased with significant differences over CG. Plasma hydroxytyrosol (OH-Tyr) concentration showed a significant increase after EVOO intervention. Daily consumption of EVOO was found to have positive effects on lipid profiles, OH-Tyr levels and TAC. The results also show a significant increase of catalase (CAT) in erythrocytes and a decrease (p<0.05) in superoxide dismutase (SOD) and glutathione peroxidase (GH-PX) activity after EVOO intake. To our knowledge, no other study has examined the effects of EVOO consumption on biochemical parameters, antioxidant capacity and antioxidant enzyme activity in healthy elderly subjects. In conclusion, our results show that nutritional intervention with EVOO improves antioxidant status in healthy elderly people.

Combined effects of treatment with vitamin C, vitamin E and selenium on the skin of diabetic rats

The aim of this study was to investigate the effects of vitamin C, vitamin E and selenium (Se) on the skin tissue of streptozotocin-induced diabetic rats. Swiss albino rats were divided into four groups: control, control + antioxidants, diabetic, diabetic + antioxidants groups. Diabetes was induced by intraperitoneal injection of 65 mg/kg streptozotocin. Vitamin C (250 mg/kg), vitamin E (250 mg/kg) and Se (0.2 mg/kg) were given by gavage technique to rats of one diabetic and one control group for 30 days. In the diabetic group, the levels of serum urea and creatinine, skin lipid peroxidation and nonenzymatic glycosylation levels increased, but skin glutathione levels decreased. Treatment with vitamin C, vitamin E and Se reversed these effects. The present study showed that vitamin C, vitamin E and Se exerted antioxidant effects and consequently may prevent skin damage caused by streptozotocin-induced diabetes.

Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases

BACKGROUND

Our systematic review has demonstrated that antioxidant supplements may increase mortality. We have now updated this review.

OBJECTIVES

To assess the beneficial and harmful effects of antioxidant supplements for prevention of mortality in adults.

SEARCH METHODS

We searched The Cochrane Library, MEDLINE, EMBASE, LILACS, the Science Citation Index Expanded, and Conference Proceedings Citation Index-Science to February 2011. We scanned bibliographies of relevant publications and asked pharmaceutical companies for additional trials.

SELECTION CRITERIA

We included all primary and secondary prevention randomised clinical trials on antioxidant supplements (beta-carotene, vitamin A, vitamin C, vitamin E, and selenium) versus placebo or no intervention.

DATA COLLECTION AND ANALYSIS

Three authors extracted data. Random-effects and fixed-effect model meta-analyses were conducted. Risk of bias was considered in order to minimise the risk of systematic errors. Trial sequential analyses were conducted to minimise the risk of random errors. Random-effects model meta-regression analyses were performed to assess sources of intertrial heterogeneity.

MAIN RESULTS

Seventy-eight randomised trials with 296,707 participants were included. Fifty-six trials including 244,056 participants had low risk of bias. Twenty-six trials included 215,900 healthy participants. Fifty-two trials included 80,807 participants with various diseases in a stable phase. The mean age was 63 years (range 18 to 103 years). The mean proportion of women was 46%. Of the 78 trials, 46 used the parallel-group design, 30 the factorial design, and 2 the cross-over design. All antioxidants were administered orally, either alone or in combination with vitamins, minerals, or other interventions. The duration of supplementation varied from 28 days to 12 years (mean duration 3 years; median duration 2 years). Overall, the antioxidant supplements had no significant effect on mortality in a random-effects model meta-analysis (21,484 dead/183,749 (11.7%) versus 11,479 dead/112,958 (10.2%); 78 trials, relative risk (RR) 1.02, 95% confidence interval (CI) 0.98 to 1.05) but significantly increased mortality in a fixed-effect model (RR 1.03, 95% CI 1.01 to 1.05). Heterogeneity was low with an I(2)- of 12%. In meta-regression analysis, the risk of bias and type of antioxidant supplement were the only significant predictors of intertrial heterogeneity. Meta-regression analysis did not find a significant difference in the estimated intervention effect in the primary prevention and the secondary prevention trials. In the 56 trials with a low risk of bias, the antioxidant supplements significantly increased mortality (18,833 dead/146,320 (12.9%) versus 10,320 dead/97,736 (10.6%); RR 1.04, 95% CI 1.01 to 1.07). This effect was confirmed by trial sequential analysis. Excluding factorial trials with potential confounding showed that 38 trials with low risk of bias demonstrated a significant increase in mortality (2822 dead/26,903 (10.5%) versus 2473 dead/26,052 (9.5%); RR 1.10, 95% CI 1.05 to 1.15). In trials with low risk of bias, beta-carotene (13,202 dead/96,003 (13.8%) versus 8556 dead/77,003 (11.1%); 26 trials, RR 1.05, 95% CI 1.01 to 1.09) and vitamin E (11,689 dead/97,523 (12.0%) versus 7561 dead/73,721 (10.3%); 46 trials, RR 1.03, 95% CI 1.00 to 1.05) significantly increased mortality, whereas vitamin A (3444 dead/24,596 (14.0%) versus 2249 dead/16,548 (13.6%); 12 trials, RR 1.07, 95% CI 0.97 to 1.18), vitamin C (3637 dead/36,659 (9.9%) versus 2717 dead/29,283 (9.3%); 29 trials, RR 1.02, 95% CI 0.98 to 1.07), and selenium (2670 dead/39,779 (6.7%) versus 1468 dead/22,961 (6.4%); 17 trials, RR 0.97, 95% CI 0.91 to 1.03) did not significantly affect mortality. In univariate meta-regression analysis, the dose of vitamin A was significantly associated with increased mortality (RR 1.0006, 95% CI 1.0002 to 1.001, P = 0.002).

AUTHORS' CONCLUSIONS

We found no evidence to support antioxidant supplements for primary or secondary prevention. Beta-carotene and vitamin E seem to increase mortality, and so may higher doses of vitamin A. Antioxidant supplements need to be considered as medicinal products and should undergo sufficient evaluation before marketing.

Effect of vitamin C supplementation on postprandial oxidative stress and lipid profile in type 2 diabetic patients

Diabetes mellitus is one of the most wide spread endocrine disorders and an important developing health problem in the world. Cardiovascular disease is a common complication of type 2 diabetes. Several risk factors for coronary heart disease cosegregate in type 2 diabetes, including hyperglycemia, hyperlipaemia, increases production of free radical and decrease in antioxidant defense system. In this study we evaluated the effect of vitamin C supplementation on fasting and postprandial oxidative stress and lipid profile in type 2 diabetic patients. 30 patients with type 2 diabetes from Nader Kazemi Clinic, Shiraz, Iran were randomly divided into 2 groups; vitamin C treatment group (1000 mg d(-1)) and placebo group from May to September 2010. Fasting and postprandial lipid profile and Malondialdehyde (MDA) level were measured at the beginning of the study and after six weeks of supplementation. Data analysis was carried out using Mann-Whitney U test with p < 0.05 being significant by SPSS software version 16.The result of the study showed a significantly decrease in fasting (p = 0.006) and postprandial MDA (p < 0.001) in vitamin C group compare to placebo group but not in lipid profile. This study suggests that vitamin C supplementation can decrease fasting and postprandial oxidative stress and may prevent diabetes complication.

Absorption, transport, and bioavailability of vitamin e and its role in pregnant women

Vitamin E is an important lipophilic antioxidant. The term refers to eight essential naturally occurring fat-soluble nutrients called tocopherols or tocotrienols. Among these isomers, alpha-tocopherol has the highest biologically active form and is found in all lipoprotein fractions. Vitamin E deficiency during pregnancy may cause miscarriage, preterm birth, preeclampsia, and intrauterine growth restriction. This review highlights recent findings that have led to a better understanding of vitamin E absorption, transport, bioavailability, and its role in pregnancy, and that underline the need for re-evaluation of the potential benefits of vitamin E supplementation in pregnant women.

The response of gamma vitamin E to varying dosages of alpha vitamin E plus vitamin C

Vitamin E has been studied extensively in the prevention of atherosclerosis. Cross-sectional population studies as well as randomized controlled intervention trials have demonstrated conflicting results. A recent meta-analysis of these trials has emphasized the ineffectiveness of vitamin E in atherosclerosis prevention, with a possibility of harm at higher dosages. However, vitamin E has several isomers, with the alpha form being available via dietary supplements and the gamma form being available via dietary foodstuffs. The gamma form of vitamin E demonstrates several superior properties (such as trapping reactive nitrogen species and detoxifying nitrogen dioxide) compared with alpha vitamin E. All clinical trials have used the alpha isomer, with little concern that this isomer of vitamin E may actually suppress the gamma isomer of vitamin E. We undertook a dose-response study in volunteers with type 2 diabetes mellitus to include all the dosages of alpha vitamin E that have been used in cardiovascular prevention trials to determine the effect of alpha vitamin E on gamma vitamin E. We also assessed the effect of alpha vitamin E on several traditional markers of atherosclerotic risk. We added vitamin C to the vitamin E because several clinical trials included this vitamin to enhance the antioxidant effects of alpha vitamin E. Volunteers received, in randomized order for a 2-week period, one of the following vitamin dosage arms: (1) no vitamins, (2) low-dose supplemental vitamins E plus C, (3) medium-dose supplemental vitamins E plus C, and (4) high-dose supplemental vitamins E plus C. Blood levels of both alpha and gamma vitamin E were measured as well as surrogate markers of oxidative stress, hypercoagulation, and inflammation during a high-fat atherogenic meal (to increase the ambient oxidative stress level during the study). The results demonstrate that alpha vitamin E levels increased in proportion to the dose administered. However, at every dose of alpha vitamin E, gamma vitamin E concentration was significantly suppressed. No beneficial changes in surrogate markers of atherosclerosis were observed, consistent with the negative results of prospective clinical trials using alpha vitamin E. Our results suggest that all prospective cardiovascular clinical trials that used vitamin E supplementation actually suppressed the beneficial antioxidant gamma isomer of vitamin E. No beneficial effects on several potential cardiovascular risk factors were observed, even when the vitamin E was supplemented with vitamin C. If a standardized preparation of gamma vitamin E (without the alpha isomer) becomes available, the effects of gamma vitamin E on atherosclerotic risk will warrant additional studies.