Clinical pharmacology and therapeutic use of antioxidant vitamins

Abstract

The clinical use of antioxidants has gained considerable interest during the last decade. It was suggested from epidemiological studies that diets high in fruits and vegetables might help decrease the risk of cardiovascular disease. Therefore, supplements of vitamins C and E were applied through protocols aimed to prevent diseases such as atherosclerosis, preeclampsia or hypertension, thought to be mediated by oxidative stress. Despite the biological properties of these vitamins could account for an effective protection, as shown by several clinical and experimental studies, their efficacy remains controversial in the light of some recent clinical trials and meta-analyses. However, the methodology of these studies, criteria for selection of patients, the uncertain extent of progression of the disease when initiating supplementation, the lack of mechanistic studies containing basic scientific aspects, such as the bioavailability, pharmacokinetic properties, and the nature of the antioxidant sources of vitamins, could account for the inconsistency of the various clinical trials and meta-analyses assessing the efficacy of these vitamins to prevent human diseases. This review presents a survey of the clinical use of antioxidant vitamins E and C, proposing study models based on the biological effects of these compounds likely to counteract the pathophysiological mechanisms able to explain the structural and functional organ damage.

Influence of Ascorbic Acid Supplementation on Type 2 Diabetes Mellitus in Observational and Randomized Controlled Trials; A Systematic Review with Meta-Analysis

“…It is expected that co-administration of two or more vitamins and antioxidants is more effective than single supplementation ( 90), and selecting the kind of antioxidants to combine together has a crucial importance. The benefits of mixture consumption of a hydrophilic (AA) with a hydrophobic (VE) antioxidant have been reported ( 91) as this benefit was shown in our included studies (34,41,42,47,52). However, as we mentioned previously, observed benefitial effects in our RCTs and most of observational studies were related to sole intake of AA.…”

Oxidative stress in psychiatric disorders: evidence base and therapeutic implications

“…Vitamin E, for example, has a principal antioxidant action of scavenging peroxyl radicals in biological lipid phases (Traber and Atkinson, 2007), in addition to multiple nonantioxidant properties that include modulation of signal transduction, transcriptional and translational processes (Zingg and Azzi, 2004), yet its antioxidant efficacy in pathological redox states has not been established (Azzi, 2007). Vitamin C, on the other hand, is a scavenger of free radicals in water phases (Rodrigo et al, 2007), while Ginkgo biloba has antioxidant properties that probably include the prevention of lipid peroxidation (Drieu et al, 2000). The specific antioxidant actions of these agents, when applied to neuropsychiatric conditions where the precise oxidative defects are not yet clear, may account for some inefficacious trial findings (Boothby and Doering, 2005).…”

Relationship between Oxidative Stress and Essential Hypertension

“…In addition, the administration of candesartan and valsartan has been shown to cause a decrease in oxidative stress in essential hypertensives (2,48). Along these lines, antioxidant vitamins have been shown to exert antihypertensive effects in spontaneously hypertensive rats, although the extensibility of these results to human beings remain controversial (49), and awaits the completion of large scale clinical trials that are currently underway.…”