Neurodegenerative diseases and oxidative stress

Oxidative stress has been implicated in the progression of Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis. Oxygen is vital for life but is also potentially dangerous, and a complex system of checks and balances exists for utilizing this essential element. Oxidative stress is the result of an imbalance in pro-oxidant/antioxidant homeostasis that leads to the generation of toxic reactive oxygen species. The systems in place to cope with the biochemistry of oxygen are complex, and many questions about the mechanisms of oxygen regulation remain unanswered. However, this same complexity provides a number of therapeutic targets, and different strategies, including novel metal-protein attenuating compounds, aimed at a variety of targets have shown promise in clinical studies.

Pioglitazone, vitamin E, or placebo for nonalcoholic steatohepatitis

BACKGROUND

Nonalcoholic steatohepatitis is a common liver disease that can progress to cirrhosis. Currently, there is no established treatment for this disease.

METHODS

We randomly assigned 247 adults with nonalcoholic steatohepatitis and without diabetes to receive pioglitazone at a dose of 30 mg daily (80 subjects), vitamin E at a dose of 800 IU daily (84 subjects), or placebo (83 subjects), for 96 weeks. The primary outcome was an improvement in histologic features of nonalcoholic steatohepatitis, as assessed with the use of a composite of standardized scores for steatosis, lobular inflammation, hepatocellular ballooning, and fibrosis. Given the two planned primary comparisons, P values of less than 0.025 were considered to indicate statistical significance.

RESULTS

Vitamin E therapy, as compared with placebo, was associated with a significantly higher rate of improvement in nonalcoholic steatohepatitis (43% vs. 19%, P=0.001), but the difference in the rate of improvement with pioglitazone as compared with placebo was not significant (34% and 19%, respectively; P=0.04). Serum alanine and aspartate aminotransferase levels were reduced with vitamin E and with pioglitazone, as compared with placebo (P<0.001 for both comparisons), and both agents were associated with reductions in hepatic steatosis (P=0.005 for vitamin E and P<0.001 for pioglitazone) and lobular inflammation (P=0.02 for vitamin E and P=0.004 for pioglitazone) but not with improvement in fibrosis scores (P=0.24 for vitamin E and P=0.12 for pioglitazone). Subjects who received pioglitazone gained more weight than did those who received vitamin E or placebo; the rates of other side effects were similar among the three groups.

CONCLUSIONS

Vitamin E was superior to placebo for the treatment of nonalcoholic steatohepatitis in adults without diabetes. There was no benefit of pioglitazone over placebo for the primary outcome; however, significant benefits of pioglitazone were observed for some of the secondary outcomes. (ClinicalTrials.gov number, NCT00063622.)

Effects of a combination of beta carotene and vitamin A on lung cancer and cardiovascular disease

BACKGROUND

Lung cancer and cardiovascular disease are major causes of death in the United States. It has been proposed that carotenoids and retinoids are agents that may prevent these disorders.

METHODS

We conducted a multicenter, randomized, double-blind, placebo-controlled primary prevention trial -- the Beta Carotene and Retinol Efficacy Trial -- involving a total of 18,314 smokers, former smokers, and workers exposed to asbestos. The effects of a combination of 30 mg of beta carotene per day and 25,000 IU of retinol (vitamin A) in the form of retinyl palmitate per day on the primary end point, the incidence of lung cancer, were compared with those of placebo.

RESULTS

A total of 388 new cases of lung cancer were diagnosed during the 73,135 person-years of follow-up (mean length of follow-up, 4.0 years). The active-treatment group had a relative risk of lung cancer of 1.28 (95 percent confidence interval, 1.04 to 1.57; P=0.02), as compared with the placebo group. There were no statistically significant differences in the risks of other types of cancer. In the active-treatment group, the relative risk of death from any cause was 1.17 (95 percent confidence interval, 1.03 to 1.33); of death from lung cancer, 1.46 (95 percent confidence interval, 1.07 to 2.00); and of death from cardiovascular disease, 1.26 (95 percent confidence interval, 0.99 to 1.61). On the basis of these findings, the randomized trial was stopped 21 months earlier than planned; follow-up will continue for another 5 years.

CONCLUSIONS

After an average of four years of supplementation, the combination of beta carotene and vitamin A had no benefit and may have had an adverse effect on the incidence of lung cancer and on the risk of death from lung cancer, cardiovascular disease, and any cause in smokers and workers exposed to asbestos.

Plant phenolics: extraction, analysis and their antioxidant and anticancer properties

Phenolics are broadly distributed in the plant kingdom and are the most abundant secondary metabolites of plants. Plant polyphenols have drawn increasing attention due to their potent antioxidant properties and their marked effects in the prevention of various oxidative stress associated diseases such as cancer. In the last few years, the identification and development of phenolic compounds or extracts from different plants has become a major area of health- and medical-related research. This review provides an updated and comprehensive overview on phenolic extraction, purification, analysis and quantification as well as their antioxidant properties. Furthermore, the anticancer effects of phenolics in-vitro and in-vivo animal models are viewed, including recent human intervention studies. Finally, possible mechanisms of action involving antioxidant and pro-oxidant activity as well as interference with cellular functions are discussed.

Oxidative stress and neurodegeneration: where are we now?

The brain and nervous system are prone to oxidative stress, and are inadequately equipped with antioxidant defense systems to prevent 'ongoing' oxidative damage, let alone the extra oxidative damage imposed by the neurodegenerative diseases. Indeed, increased oxidative damage, mitochondrial dysfunction, accumulation of oxidized aggregated proteins, inflammation, and defects in protein clearance constitute complex intertwined pathologies that conspire to kill neurons. After a long lag period, therapeutic and other interventions based on a knowledge of redox biology are on the horizon for at least some of the neurodegenerative diseases.

Hydrogen acts as a therapeutic antioxidant by selectively reducing cytotoxic oxygen radicals

Acute oxidative stress induced by ischemia-reperfusion or inflammation causes serious damage to tissues, and persistent oxidative stress is accepted as one of the causes of many common diseases including cancer. We show here that hydrogen (H(2)) has potential as an antioxidant in preventive and therapeutic applications. We induced acute oxidative stress in cultured cells by three independent methods. H(2) selectively reduced the hydroxyl radical, the most cytotoxic of reactive oxygen species (ROS), and effectively protected cells; however, H(2) did not react with other ROS, which possess physiological roles. We used an acute rat model in which oxidative stress damage was induced in the brain by focal ischemia and reperfusion. The inhalation of H(2) gas markedly suppressed brain injury by buffering the effects of oxidative stress. Thus H(2) can be used as an effective antioxidant therapy; owing to its ability to rapidly diffuse across membranes, it can reach and react with cytotoxic ROS and thus protect against oxidative damage.

Flavonoids: a review of probable mechanisms of action and potential applications

The aim of this review, a summary of the putative biological actions of flavonoids, was to obtain a further understanding of the reported beneficial health effects of these substances. Flavonoids occur naturally in fruit, vegetables, and beverages such as tea and wine. Research in the field of flavonoids has increased since the discovery of the French paradox,ie, the low cardiovascular mortality rate observed in Mediterranean populations in association with red wine consumption and a high saturated fat intake. Several other potential beneficial properties of flavonoids have since been ascertained. We review the different groups of known flavonoids, the probable mechanisms by which they act, and the potential clinical applications of these fascinating natural substances.

Effect of selenium and vitamin E on risk of prostate cancer and other cancers: the Selenium and Vitamin E Cancer Prevention Trial (SELECT)

CONTEXT

Secondary analyses of 2 randomized controlled trials and supportive epidemiologic and preclinical data indicated the potential of selenium and vitamin E for preventing prostate cancer.

OBJECTIVE

To determine whether selenium, vitamin E, or both could prevent prostate cancer and other diseases with little or no toxicity in relatively healthy men.

DESIGN, SETTING, AND PARTICIPANTS

A randomized, placebo-controlled trial (Selenium and Vitamin E Cancer Prevention Trial [SELECT]) of 35,533 men from 427 participating sites in the United States, Canada, and Puerto Rico randomly assigned to 4 groups (selenium, vitamin E, selenium + vitamin E, and placebo) in a double-blind fashion between August 22, 2001, and June 24, 2004. Baseline eligibility included age 50 years or older (African American men) or 55 years or older (all other men), a serum prostate-specific antigen level of 4 ng/mL or less, and a digital rectal examination not suspicious for prostate cancer.

INTERVENTIONS

Oral selenium (200 microg/d from L-selenomethionine) and matched vitamin E placebo, vitamin E (400 IU/d of all rac-alpha-tocopheryl acetate) and matched selenium placebo, selenium + vitamin E, or placebo + placebo for a planned follow-up of minimum of 7 years and a maximum of 12 years.

MAIN OUTCOME MEASURES

Prostate cancer and prespecified secondary outcomes, including lung, colorectal, and overall primary cancer.

RESULTS

As of October 23, 2008, median overall follow-up was 5.46 years (range, 4.17-7.33 years). Hazard ratios (99% confidence intervals [CIs]) for prostate cancer were 1.13 (99% CI, 0.95-1.35; n = 473) for vitamin E, 1.04 (99% CI, 0.87-1.24; n = 432) for selenium, and 1.05 (99% CI, 0.88-1.25; n = 437) for selenium + vitamin E vs 1.00 (n = 416) for placebo. There were no significant differences (all P>.15) in any other prespecified cancer end points. There were statistically nonsignificant increased risks of prostate cancer in the vitamin E group (P = .06) and type 2 diabetes mellitus in the selenium group (relative risk, 1.07; 99% CI, 0.94-1.22; P = .16) but not in the selenium + vitamin E group.

CONCLUSION

Selenium or vitamin E, alone or in combination at the doses and formulations used, did not prevent prostate cancer in this population of relatively healthy men.

TRIAL REGISTRATION

clinicaltrials.gov identifier: NCT00006392.

Lack of effect of long-term supplementation with beta carotene on the incidence of malignant neoplasms and cardiovascular disease

BACKGROUND

Observational studies suggest that people who consume more fruits and vegetables containing beta carotene have somewhat lower risks of cancer and cardiovascular disease, and earlier basic research suggested plausible mechanisms. Because large randomized trials of long duration were necessary to test this hypothesis directly, we conducted a trial of beta carotene supplementation.

METHODS

In a randomized, double-blind, placebo-controlled trial of beta carotene (50 mg on alternate days), we enrolled 22,071 male physicians, 40 to 84 years of age, in the United States; 11 percent were current smokers and 39 percent were former smokers at the beginning of the study in 1982. By December 31, 1995, the scheduled end of the study, fewer than 1 percent had been lost to follow-up, and compliance was 78 percent in the group that received beta carotene.

RESULTS

Among 11,036 physicians randomly assigned to receive beta carotene and 11,035 assigned to receive placebo, there were virtually no early or late differences in the overall incidence of malignant neoplasms or cardiovascular disease, or in overall mortality. In the beta carotene group, 1273 men had any malignant neoplasm (except nonmelanoma skin cancer), as compared with 1293 in the placebo group (relative risk, 0.98; 95 percent confidence interval, 0.91 to 1.06). There were also no significant differences in the number of cases of lung cancer (82 in the beta carotene group vs. 88 in the placebo group); the number of deaths from cancer (386 vs. 380), deaths from any cause (979 vs. 968), or deaths from cardiovascular disease (338 vs. 313); the number of men with myocardial infarction (468 vs. 489); the number with stroke (367 vs. 382); or the number with any one of the previous three end points (967 vs. 972). Among current and former smokers, there were also no significant early or late differences in any of these end points.

CONCLUSIONS

In this trial among healthy men, 12 years of supplementation with beta carotene produced neither benefit nor harm in terms of the incidence of malignant neoplasms, cardiovascular disease, or death from all causes.

Simvastatin and niacin, antioxidant vitamins, or the combination for the prevention of coronary disease

BACKGROUND

Both lipid-modifying therapy and antioxidant vitamins are thought to have benefit in patients with coronary disease. We studied simvastatin-niacin and antioxidant-vitamin therapy, alone and together, for cardiovascular protection in patients with coronary disease and low plasma levels of HDL.

METHODS

In a three-year, double-blind trial, 160 patients with coronary disease, low HDL cholesterol levels and normal LDL cholesterol levels were randomly assigned to receive one of four regimens: simvastatin plus niacin, vitamins, simvastatin-niacin plus antioxidants; or placebos. The end points were arteriographic evidence of a change in coronary stenosis and the occurrence of a first cardiovascular event (death, myocardial infarction, stroke, or revascularization).

RESULTS

The mean levels of LDL and HDL cholesterol were unaltered in the antioxidant group and the placebo group; these levels changed substantially (by -42 percent and +26 percent, respectively) in the simvastatin-niacin group. The protective increase in HDL2 with simvastatin plus niacin was attenuated by concurrent therapy with antioxidants. The average stenosis progressed by 3.9 percent with placebos, 1.8 percent with antioxidants (P=0.16 for the comparison with the placebo group), and 0.7 percent with simvastatin-niacin plus antioxidants (P=0.004) and regressed by 0.4 percent with simvastatin-niacin alone (P<0.001). The frequency of the clinical end point was 24 percent with placebos; 3 percent with simvastatin-niacin alone; 21 percent in the antioxidant-therapy group; and 14 percent in the simvastatin-niacin-plus-antioxidants group.

CONCLUSIONS

Simvastatin plus niacin provides marked clinical and angiographically measurable benefits in patients with coronary disease and low HDL levels. The use of antioxidant vitamins in this setting must be questioned.

The role of oxidative stress in the pathogenesis of age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of blind registration in the developed world, and yet its pathogenesis remains poorly understood. Oxidative stress, which refers to cellular damage caused by reactive oxygen intermediates (ROI), has been implicated in many disease processes, especially age-related disorders. ROIs include free radicals, hydrogen peroxide, and singlet oxygen, and they are often the byproducts of oxygen metabolism. The retina is particularly susceptible to oxidative stress because of its high consumption of oxygen, its high proportion of polyunsaturated fatty acids, and its exposure to visible light. In vitro studies have consistently shown that photochemical retinal injury is attributable to oxidative stress and that the antioxidant vitamins A, C, and E protect against this type of injury. Furthermore, there is strong evidence suggesting that lipofuscin is derived, at least in part, from oxidatively damaged photoreceptor outer segments and that it is itself a photoreactive substance. However, the relationships between dietary and serum levels of the antioxidant vitamins and age-related macular disease are less clear, although a protective effect of high plasma concentrations of alpha-tocopherol has been convincingly demonstrated. Macular pigment is also believed to limit retinal oxidative damage by absorbing incoming blue light and/or quenching ROIs. Many putative risk-factors for AMD have been linked to a lack of macular pigment, including female gender, lens density, tobacco use, light iris color, and reduced visual sensitivity. Moreover, the Eye Disease Case-Control Study found that high plasma levels of lutein and zeaxanthin were associated with reduced risk of neovascular AMD. The concept that AMD can be attributed to cumulative oxidative stress is enticing, but remains unproven. With a view to reducing oxidative damage, the effect of nutritional antioxidant supplements on the onset and natural course of age-related macular disease is currently being evaluated.

Curcumin: from ancient medicine to current clinical trials

Curcumin is the active ingredient in the traditional herbal remedy and dietary spice turmeric (Curcuma longa). Curcumin has a surprisingly wide range of beneficial properties, including anti-inflammatory, antioxidant, chemopreventive and chemotherapeutic activity. The pleiotropic activities of curcumin derive from its complex chemistry as well as its ability to influence multiple signaling pathways, including survival pathways such as those regulated by NF-kappaB, Akt, and growth factors; cytoprotective pathways dependent on Nrf2; and metastatic and angiogenic pathways. Curcumin is a free radical scavenger and hydrogen donor, and exhibits both pro- and antioxidant activity. It also binds metals, particularly iron and copper, and can function as an iron chelator. Curcumin is remarkably non-toxic and exhibits limited bioavailability. Curcumin exhibits great promise as a therapeutic agent, and is currently in human clinical trials for a variety of conditions, including multiple myeloma, pancreatic cancer, myelodysplastic syndromes, colon cancer, psoriasis and Alzheimer's disease.

Health benefits of fruit and vegetables are from additive and synergistic combinations of phytochemicals

Cardiovascular disease and cancer are ranked as the first and second leading causes of death in the United States and in most industrialized countries. Regular consumption of fruit and vegetables is associated with reduced risks of cancer, cardiovascular disease, stroke, Alzheimer disease, cataracts, and some of the functional declines associated with aging. Prevention is a more effective strategy than is treatment of chronic diseases. Functional foods that contain significant amounts of bioactive components may provide desirable health benefits beyond basic nutrition and play important roles in the prevention of chronic diseases. The key question is whether a purified phytochemical has the same health benefit as does the whole food or mixture of foods in which the phytochemical is present. Our group found, for example, that the vitamin C in apples with skin accounts for only 0.4% of the total antioxidant activity, suggesting that most of the antioxidant activity of fruit and vegetables may come from phenolics and flavonoids in apples. We propose that the additive and synergistic effects of phytochemicals in fruit and vegetables are responsible for their potent antioxidant and anticancer activities, and that the benefit of a diet rich in fruit and vegetables is attributed to the complex mixture of phytochemicals present in whole foods.

Polyphenols and disease risk in epidemiologic studies

Plant polyphenols, a large group of natural antioxidants, are serious candidates in explanations of the protective effects of vegetables and fruits against cancer and cardiovascular diseases. Epidemiologic studies are useful for evaluation of the human health effects of long-term exposure to physiologic concentrations of polyphenols, but reliable data on polyphenol contents of foods are still scarce. The aim of this review is to summarize available epidemiologic data on the health effects of polyphenols, focusing on the flavonoid subclasses of flavonols, flavones, and catechins and on lignans. Data obtained to date suggest beneficial effects of both flavonoids and lignans on cardiovascular diseases but not on cancer, with the possible exception of lung cancer. There is a need for more research on stroke and lung diseases such as asthma and chronic obstructive pulmonary disease. Most studies to date have included only flavonols and flavones. With data becoming available for other polyphenols, these compounds should be included in future studies. Careful design of prospective studies is important to offset some of the major drawbacks of epidemiologic studies, including residual confounding (by smoking and other dietary factors) and exposure assessment.

The Role of Oxidative Stress and Antioxidants in Liver Diseases

A complex antioxidant system has been developed in mammals to relieve oxidative stress. However, excessive reactive species derived from oxygen and nitrogen may still lead to oxidative damage to tissue and organs. Oxidative stress has been considered as a conjoint pathological mechanism, and it contributes to initiation and progression of liver injury. A lot of risk factors, including alcohol, drugs, environmental pollutants and irradiation, may induce oxidative stress in liver, which in turn results in severe liver diseases, such as alcoholic liver disease and non-alcoholic steatohepatitis. Application of antioxidants signifies a rational curative strategy to prevent and cure liver diseases involving oxidative stress. Although conclusions drawn from clinical studies remain uncertain, animal studies have revealed the promising in vivo therapeutic effect of antioxidants on liver diseases. Natural antioxidants contained in edible or medicinal plants often possess strong antioxidant and free radical scavenging abilities as well as anti-inflammatory action, which are also supposed to be the basis of other bioactivities and health benefits. In this review, PubMed was extensively searched for literature research. The keywords for searching oxidative stress were free radicals, reactive oxygen, nitrogen species, anti-oxidative therapy, Chinese medicines, natural products, antioxidants and liver diseases. The literature, including ours, with studies on oxidative stress and anti-oxidative therapy in liver diseases were the focus. Various factors that cause oxidative stress in liver and effects of antioxidants in the prevention and treatment of liver diseases were summarized, questioned, and discussed.

Role of free radicals in the neurodegenerative diseases: therapeutic implications for antioxidant treatment

Free radicals and other so-called 'reactive species' are constantly produced in the brain in vivo. Some arise by 'accidents of chemistry', an example of which may be the leakage of electrons from the mitochondrial electron transport chain to generate superoxide radical (O2*-). Others are generated for useful purposes, such as the role of nitric oxide in neurotransmission and the production of O2*- by activated microglia. Because of its high ATP demand, the brain consumes O2 rapidly, and is thus susceptible to interference with mitochondrial function, which can in turn lead to increased O2*- formation. The brain contains multiple antioxidant defences, of which the mitochondrial manganese-containing superoxide dismutase and reduced glutathione seem especially important. Iron is a powerful promoter of free radical damage, able to catalyse generation of highly reactive hydroxyl, alkoxyl and peroxyl radicals from hydrogen peroxide and lipid peroxides, respectively. Although most iron in the brain is stored in ferritin, 'catalytic' iron is readily mobilised from injured brain tissue. Increased levels of oxidative damage to DNA, lipids and proteins have been detected by a range of assays in post-mortem tissues from patients with Parkinson's disease, Alzheimer's disease and amyotrophic lateral sclerosis, and at least some of these changes may occur early in disease progression. The accumulation and precipitation of proteins that occur in these diseases may be aggravated by oxidative damage, and may in turn cause more oxidative damage by interfering with the function of the proteasome. Indeed, it has been shown that proteasomal inhibition increases levels of oxidative damage not only to proteins but also to other biomolecules. Hence, there are many attempts to develop antioxidants that can cross the blood-brain barrier and decrease oxidative damage. Natural antioxidants such as vitamin E (tocopherol), carotenoids and flavonoids do not readily enter the brain in the adult, and the lazaroid antioxidant tirilazad (U-74006F) appears to localise in the blood-brain barrier. Other antioxidants under development include modified spin traps and low molecular mass scavengers of O2*-. One possible source of lead compounds is the use of traditional remedies claimed to improve brain function. Little is known about the impact of dietary antioxidants upon the development and progression of neurodegenerative diseases, especially Alzheimer's disease. Several agents already in therapeutic use might exert some of their effects by antioxidant action, including selegiline (deprenyl), apomorphine and nitecapone.

Reactive oxygen species in living systems: source, biochemistry, and role in human disease

Reactive oxygen species are constantly formed in the human body and removed by antioxidant defenses. An antioxidant is a substance that, when present at low concentrations compared to that of an oxidizable substrate, significantly delays or prevents oxidation of that substrate. Antioxidants can act by scavenging biologically important reactive oxygen species (O2-., H2O2.OH, HOCl, ferryl, peroxyl, and alkyl), by preventing their formation, or by repairing the damage that they do. One problem with scavenging-type antioxidants is that secondary radicals derived from them can often themselves do biologic damage. These various principles will be illustrated by considering several thiol compounds.

Advanced glycation endproducts--role in pathology of diabetic complications

Diabetes mellitus is a common endocrine disorder characterised by hyperglycaemia and predisposes to chronic complications affecting the eyes, blood vessels, nerves and kidneys. Hyperglycaemia has an important role in the pathogenesis of diabetic complications by increasing protein glycation and the gradual build-up of advanced glycation endproducts (AGEs) in body tissues. These AGE form on intra- and extracellular proteins, lipids, nucleic acids and possess complex structures that generate protein fluorescence and cross-linking. Protein glycation and AGE are accompanied by increased free radical activity that contributes towards the biomolecular damage in diabetes. There is considerable interest in receptors for AGEs (RAGE) found on many cell types, particularly those affected in diabetes. Recent studies suggest that interaction of AGEs with RAGE alter intracellular signalling, gene expression, release of pro-inflammatory molecules and free radicals that contribute towards the pathology of diabetic complications. This review introduces the chemistry of glycation and AGEs and examines the mechanisms by which they mediate their toxicity. The role of AGEs in the pathogenesis of retinopathy, cataract, atherosclerosis, neuropathy, nephropathy, diabetic embryopathy and impaired wound healing are considered. There is considerable interest in anti-glycation compounds because of their therapeutic potential. The mechanisms and sites of action of selected inhibitors, together with their potential in preventing diabetic complications are discussed.

The role of oxidized lipoproteins in atherogenesis

This article reviews our current understanding of the mechanisms of low-density lipoprotein (LDL) oxidation and the potential role of oxidized lipoproteins in atherosclerosis. Studies in hypercholesterolemic animal models indicate that oxidation of LDL is likely to play an important role in atherogenesis. Epidemiological investigations further suggest that the dietary intake of antioxidants is inversely associated with the risk of vascular disease, suggesting that oxidized LDL may be important in human atherosclerosis. By activating inflammatory events, oxidized lipoproteins may contribute to all stages of the atherosclerotic process. Lipoprotein oxidation is promoted by several different systems in vitro, including free and protein-bound metal ions, thiols, reactive oxygen intermediates, lipoxygenase, peroxynitrite, and myeloperoxidase. Intracellular proteins that bind iron or regulate iron metabolism might also play an important role. The physiologically relevant pathways have yet to be identified, however. We assess recent findings on the effects of antioxidants in vivo and suggest potential strategies for inhibiting oxidation in the vessel wall.

The effects of oxidative stress on female reproduction: a review

Oxidative stress (OS), a state characterized by an imbalance between pro-oxidant molecules including reactive oxygen and nitrogen species, and antioxidant defenses, has been identified to play a key role in the pathogenesis of subfertility in both males and females. The adverse effects of OS on sperm quality and functions have been well documented. In females, on the other hand, the impact of OS on oocytes and reproductive functions remains unclear. This imbalance between pro-oxidants and antioxidants can lead to a number of reproductive diseases such as endometriosis, polycystic ovary syndrome (PCOS), and unexplained infertility. Pregnancy complications such as spontaneous abortion, recurrent pregnancy loss, and preeclampsia, can also develop in response to OS. Studies have shown that extremes of body weight and lifestyle factors such as cigarette smoking, alcohol use, and recreational drug use can promote excess free radical production, which could affect fertility. Exposures to environmental pollutants are of increasing concern, as they too have been found to trigger oxidative states, possibly contributing to female infertility. This article will review the currently available literature on the roles of reactive species and OS in both normal and abnormal reproductive physiological processes. Antioxidant supplementation may be effective in controlling the production of ROS and continues to be explored as a potential strategy to overcome reproductive disorders associated with infertility. However, investigations conducted to date have been through animal or in vitro studies, which have produced largely conflicting results. The impact of OS on assisted reproductive techniques (ART) will be addressed, in addition to the possible benefits of antioxidant supplementation of ART culture media to increase the likelihood for ART success. Future randomized controlled clinical trials on humans are necessary to elucidate the precise mechanisms through which OS affects female reproductive abilities, and will facilitate further explorations of the possible benefits of antioxidants to treat infertility.

Antioxidants and atherosclerotic heart disease

Epidemiologic studies have provided evidence of an inverse relation between coronary artery disease and antioxidant intake, and vitamin E supplementation in particular. The oxidative-modification hypothesis implies that reduced atherosclerosis is a result of the production of LDL that is resistant to oxidation, but linking the reduced oxidation of LDL to a reduction in atherosclerosis has been problematic. Several important additional mechanisms may underlie the role of antioxidants in preventing the clinical manifestations of coronary artery disease (Fig. 2). Specifically, there is evidence that plaque stability, vasomotor function, and the tendency to thrombosis are subject to modification by specific antioxidants. For example, cellular antioxidants inhibit monocyte adhesion, protect against the cytotoxic effects of oxidized LDL, and inhibit platelet activation. Furthermore, cellular antioxidants protect against the endothelial dysfunction associated with atherosclerosis by preserving endothelium-derived nitric oxide activity. We speculate that these mechanisms have an important role in the benefits of antioxidants.

MRC/BHF Heart Protection Study of antioxidant vitamin supplementation in 20,536 high-risk individuals: a randomised placebo-controlled trial

BACKGROUND

It has been suggested that increased intake of various antioxidant vitamins reduces the incidence rates of vascular disease, cancer, and other adverse outcomes.

METHODS

20,536 UK adults (aged 40-80) with coronary disease, other occlusive arterial disease, or diabetes were randomly allocated to receive antioxidant vitamin supplementation (600 mg vitamin E, 250 mg vitamin C, and 20 mg beta-carotene daily) or matching placebo. Intention-to-treat comparisons of outcome were conducted between all vitamin-allocated and all placebo-allocated participants. An average of 83% of participants in each treatment group remained compliant during the scheduled 5-year treatment period. Allocation to this vitamin regimen approximately doubled the plasma concentration of alpha-tocopherol, increased that of vitamin C by one-third, and quadrupled that of beta-carotene. Primary outcomes were major coronary events (for overall analyses) and fatal or non-fatal vascular events (for subcategory analyses), with subsidiary assessments of cancer and of other major morbidity.

FINDINGS

There were no significant differences in all-cause mortality (1446 [14.1%] vitamin-allocated vs 1389 [13.5%] placebo-allocated), or in deaths due to vascular (878 [8.6%] vs 840 [8.2%]) or non-vascular (568 [5.5%] vs 549 [5.3%]) causes. Nor were there any significant differences in the numbers of participants having non-fatal myocardial infarction or coronary death (1063 [10.4%] vs 1047 [10.2%]), non-fatal or fatal stroke (511 [5.0%] vs 518 [5.0%]), or coronary or non-coronary revascularisation (1058 [10.3%] vs 1086 [10.6%]). For the first occurrence of any of these "major vascular events", there were no material differences either overall (2306 [22.5%] vs 2312 [22.5%]; event rate ratio 1.00 [95% CI 0.94-1.06]) or in any of the various subcategories considered. There were no significant effects on cancer incidence or on hospitalisation for any other non-vascular cause.

INTERPRETATION

Among the high-risk individuals that were studied, these antioxidant vitamins appeared to be safe. But, although this regimen increased blood vitamin concentrations substantially, it did not produce any significant reductions in the 5-year mortality from, or incidence of, any type of vascular disease, cancer, or other major outcome.

Prevention of radiographic-contrast-agent-induced reductions in renal function by acetylcysteine

BACKGROUND

Radiographic contrast agents can cause a reduction in renal function that may be due to reactive oxygen species. Whether the reduction can be prevented by the administration of antioxidants is unknown.

METHODS

We prospectively studied 83 patients with chronic renal insufficiency (mean [+/-SD] serum creatinine concentration, 2.4+/-1.3 mg per deciliter [216+/-116 micromol per liter]) who were undergoing computed tomography with a nonionic, low-osmolality contrast agent. Patients were randomly assigned either to receive the antioxidant acetylcysteine (600 mg orally twice daily) and 0.45 percent saline intravenously, before and after administration of the contrast agent, or to receive placebo and saline.

RESULTS

Ten of the 83 patients (12 percent) had an increase of at least 0.5 mg per deciliter (44 micromol per liter) in the serum creatinine concentration 48 hours after administration of the contrast agent: 1 of the 41 patients in the acetylcysteine group (2 percent) and 9 of the 42 patients in the control group (21 percent; P=0.01; relative risk, 0.1; 95 percent confidence interval, 0.02 to 0.9). In the acetylcysteine group, the mean serum creatinine concentration decreased significantly (P<0.001), from 2.5+/-1.3 to 2.1+/-1.3 mg per deciliter (220+/-118 to 186+/-112 micromol per liter) 48 hours after the administration of the contrast medium, whereas in the control group, the mean serum creatinine concentration increased nonsignificantly (P=0.18), from 2.4+/-1.3 to 2.6+/-1.5 mg per deciliter (212+/-114 to 226+/-133 micromol per liter) (P<0.001 for the comparison between groups).

CONCLUSIONS

Prophylactic oral administration of the antioxidant acetylcysteine, along with hydration, prevents the reduction in renal function induced by contrast agents in patients with chronic renal insufficiency.