Free Radical-mediated Damage Research Articles

Oxidation of serum low-density lipoprotein (LDL) and antioxidant status in young and elderly humans

The incidence of atherosclerosis increases with age, as do various indices of free-radical mediated damage, e.g., lipid peroxidation. Because lipid peroxidation plays a prominent role in lipoprotein oxidation, likely a prelude to atherosclerosis, we compared the susceptibility of lipoproteins to oxidation in young (19–30 years) and elderly (59–86 years) groups. Although we found no significant differences in serum malondialdehyde (MDA) or oxidized LDL antibodies (OLAB) between young and elderly lipoproteins, MDA was directly related to OLAB regardless of age ( r = 0.322, p = 0.005) and there was a trend for lower OLAB levels (30.5%, p = 0.079) in the elderly compared to the young population. Overall, serum antioxidant status was either similar or greater in the elderly group compared to the young group, likely reflecting antioxidant supplementation by the elderly group. OLAB was inversely related to Vitamin C ( r = −0.310, p = 0.008) and Vitamin E intake ( r = −0.277, p = 0.018) from foods and supplements. Serum levels of Vitamin C and Vitamin E were significantly higher (18.5%, p = 0.021 and 58.1 %, p < 0.001, respectively) in the elderly group compared to the young group and the ratio of Vitamin E to Vitamin C was significantly higher (30.4%, p = 0.042) in the serum of the elderly group. Oxidation of serum LDL and antioxidant status were not affected by age; however, the ratio of serum Vitamin E to Vitamin C was higher in the elderly group which may affect Vitamin E recycling.

Ischemia-reperfusion-induced calpain activation and SERCA2a degradation are attenuated by exercise training and calpain inhibition

The Ca2+-activated protease calpain has been shown to play a deleterious role in the heart during ischemia-reperfusion (I/R). We tested the hypothesis that exercise training would minimize I/R-induced calpain activation and provide cardioprotection against I/R-induced injury. Hearts from adult male rats were isolated in a working heart preparation, and myocardial injury was induced with 25 min of global ischemia followed by 45 min of reperfusion. In sedentary control rats, I/R significantly increased calpain activity and impaired cardiac performance (cardiac work during reperfusion = 24% of baseline). Compared with sedentary animals, exercise training prevented the I/R-induced rise in calpain activity and improved cardiac work (recovery = 80% of baseline). Similar to exercise, pharmacological inhibition of calpain activity resulted in comparable cardioprotection against I/R injury (recovery = 86% of baseline). The exercise-induced protection against I/R-induced calpain activation was not due to altered myocardial protein levels of calpain or calpastatin. However, exercise training was associated with increased myocardial antioxidant enzyme activity (Mn-SOD, catalase) and a reduction in oxidative stress. Importantly, exercise training also prevented the I/R-induced degradation of sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA)2a. These findings suggest that increases in endogenous antioxidants may diminish the free radical-mediated damage and/or degradation of Ca2+ handling proteins (such as SERCA2a) typically observed after I/R. In conclusion, these results support the concept that calpain activation is an important component of I/R-induced injury and that exercise training provides cardioprotection against I/R injury, at least in part, by attenuating I/R-induced calpain activation.

Free Radical Mechanisms of Aging Processes Under Physiological Conditions

Free radical theory of aging predicts crucial role for free radicals produced by external factors (environmental contamination, irradiation, etc.) or pathological disorders (hereditary diseases or infections) in the initiation of aging. Does it mean that under hypothetical completely physiological conditions aging processes could be fully suppressed? To answer this question, we will consider the possible mechanisms of free radical formation in such hypothetical state. There are two major mechanisms, which are responsible for free radical-mediated damage in a living organism: superoxide overproduction by mitochondria and nonenzymatic lipid peroxidation. Superoxide overproduction causes the inhibition of nitric oxide formation and bioavailability, one of principal characteristics of aging, while nonenzymatic lipid peroxidation, which is already demonstrated at physiological conditions, produces toxic isoprostanes. We suggest that major initiators of free radical-mediated damaging processes leading to aging at physiological state are oxidizable components of diet. The possibility of inhibition of aging processes by supplementation of nontoxic antioxidants and calorie restriction is discussed. Scheme demonstrating the potential mechanisms of starting the free radical-mediated aging processes is presented, which are discussed on the grounds of known literature data.

Protective effect of red grape seeds proanthocyanidins against induction of diabetes by alloxan in rats

It has been documented that impaired homeostasis in diabetes mellitus is associated with increased production of reactive oxygen species and depletion of the antioxidant defense systems. Natural grape seed proanthocyanidins (GSP) are potent free radical scavengers and hence provide significant protection against oxidative stress. Accordingly, the present study focused on investigating the possible protective role of GSP against free radical-mediated damage in pancreatic tissues of alloxan-induced diabetes in rats. The results revealed that oral administration of 50 and 100 mg kg −1 (body weight) of GSP for 72 h significantly increased pancreatic glutathione (GSH) levels and inhibited the increase in lipid peroxidation caused by alloxan ( p < 0.001). On the other hand, a significant reduction in pancreatic total nitrate/nitrite content ( p < 0.001) was observed. Furthermore, GSP caused significant decline in the hyperglycemia induced by alloxan ( p < 0.001). Such antihyperglycemic effect of GSP was accompanied by a significant increase in serum insulin levels in diabetic rats following 72 h of administration ( p < 0.001). In conclusion, the study suggests that GSP are effective in ameliorating the damage to pancreatic tissue in experimental diabetes mellitus. Such effect may be related to their potent antioxidant properties as evidenced by the increase in pancreatic GSH and reduction of lipid peroxidation as well as total nitrate/nitrite levels.

Oxidative stress in organ preservation: a multifaceted approach to cardioplegia

Every transplant is a reperfused organ and, therefore, undergoes some degree of oxidative damage. Postischemic reperfusion injury results in non-specific free radical-mediated acute endothelial damage, cell death and organ failure. The endothelium is a key site of injury from reactive oxygen species (ROS), and the endothelial cell dysfunction is central to the pathogenesis of arteriosclerosis. Accelerated arteriosclerosis, secondary to chronic allograft rejection, is a major long-term complication of heart transplantation. Therefore, preservation methods that would decrease injury during reperfusion are very important. We have developed a unique preservation solution, with a multifaceted approach, which best preserves the organ from ROS for an extended period of time before transplantation. The advantages of extending this period of preservation include an expansion of the donor pool, by permitting more distant procurement, the ability to perform detailed tissue typing, therefore, improves histocompatibility match and a reduction in emergency surgery as a result of graft rejection.

Copper(II)–Quercetin complexes in aqueous solutions: spectroscopic and kinetic properties

Quercetin (Querc), one of the most common dietary flavonols, was investigated in the presence of Cu(II) ions under basic conditions by different techniques in order to obtain some elucidation on the mechanism of its beneficial action against free radical-mediated damage. The spectroscopic studies (UV/Vis, Raman and IR) were useful to assess the relevant interaction of Querc with Cu(II) ions, the chelation sites and the dependence of the complex structure from the metal/ligand ratio. In the presence of a slight excess of the ligand (0.5 M/ L) Querc acts as a bidentate ligand trough the catechol moiety on B ring. At M/ L>1 the metal interaction also involves the C O group and a close hydroxyl group. Thermogravimetric analysis confirmed the stoichiometry of the proposed complexes. Information on the reactivity of the Cu(II) chelates towards oxidizing radicals ( OH, N 3 ⋅ and Br 2 − ⋅ ) were obtained by the pulse radiolysis data. The chelates appear to fast react with these oxidizing radicals, giving rise to intermediates transients, namely resonance-stabilised phenoxyl radicals.

Malondialdehyde and carbonyl contents in the erythrocytes of streptozotocin-induced diabetic rats

Oxidative stress is involved in degenerative disease, including atherosclerosis and diabetes mellitus. Impaired antioxidantdefense mechanism may be an important factor in the pathogenesis of diabetes. Oxidative stress can be measured bymonitoring the changes in blood malondialdehyde and carbonyl content. Determination of carbonyl level is used as anindex of the extent of the oxidative damage of protein. Moreover, malondialdehyde level is a marker of lipid oxidation. Weinvestigated the status of lipid peroxidation and protein oxidative damage in erythrocytes of streptozotocin (STZ) induceddiabetic rats by measuring erythrocyte malondialdehyde and carbonyl levels using a spectrophotometer. We found thatcarbonyl and malondialdehyde levels were significantly increased in the erythrocytes of STZ-induced diabetic rats. Thisobservation indirectly suggests an increase in free radical-mediated damage of the cell membrane.

Superoxide dismutase failed to attenuate allergen-induced nasal congestion in ragweed-sensitized dogs

We hypothesized that augmentation of antioxidant defenses with exogenous superoxide dismutase (SOD), an enzyme that provides an initial defense against oxidative injury, would attenuate allergen-induced nasal congestion in the canine model of allergic rhinitis. Nasal congestion was evaluated by the measurements of nasal resistance and the volume of the nasal passage. In five nonsensitized dogs, 30,000 U of SOD from bovine erythrocytes delivered by aerosol to the nasal passages before histamine challenge reduced the histamine-induced nasal congestion. At 30 min postchallenge, nasal resistance was 1.14 +/- 0.2 cmH2O.l(-1).min(-1) in the saline pretreatment study vs. 0.36 +/- 0.02 cmH2O.l(-1).min(-1) in the SOD pretreatment study (P < 0.05), and volume of nasal passage was 10.9 +/- 0.5 cm3 vs. 17.4 +/- 1.3 cm3 (P < 0.05), respectively. In five sensitized dogs, however, neither an analogous pretreatment with SOD nor intranasal aerosolized pretreatment with 30,000 U of SOD conjugated to polyethylene glycol attenuated ragweed-induced nasal congestion. Also, systemic application of SOD did not attenuate responses to challenges with histamine and ragweed in nonsensitized and sensitized dogs, respectively. The antioxidant-induced attenuation of nasal congestion in nonsensitized dogs confirms validity of the model and indicates the involvement of free radical-mediated damage in the genesis of the histamine-induced congestion. In sensitized dogs, the data do not support the hypothesis that oxidative stress is a clinically significant component of acute ragweed-induced nasal congestion. The data do not support the use of SOD for acute protection against allergic rhinitis.

Proteomic analysis of specific brain proteins in aged SAMP8 mice treated with alpha-lipoic acid: implications for aging and age-related neurodegenerative disorders

Free radical-mediated damage to neuronal membrane components has been implicated in the etiology of Alzheimer's disease (AD) and aging. The senescence accelerated prone mouse strain 8 (SAMP8) exhibits age-related deterioration in memory and learning along with increased oxidative markers. Therefore, SAMP8 is a suitable model to study brain aging and, since aging is the major risk factor for AD and SAMP8 exhibits many of the biochemical findings of AD, perhaps as a model for and the early phase of AD. Our previous studies reported higher oxidative stress markers in brains of 12-month-old SAMP8 mice when compared to that of 4-month-old SAMP8 mice. Further, we have previously shown that injecting the mice with α-lipoic acid (LA) reversed brain lipid peroxidation, protein oxidation, as well as the learning and memory impairments in SAMP8 mice. Recently, we reported the use of proteomics to identify proteins that are expressed differently and/or modified oxidatively in aged SAMP8 brains. In order to understand how LA reverses the learning and memory deficits of aged SAMP8 mice, in the current study, we used proteomics to compare the expression levels and specific carbonyl levels of proteins in brains from 12-month-old SAMP8 mice treated or not treated with LA. We found that the expressions of the three brain proteins (neurofilament triplet L protein, α-enolase, and ubiquitous mitochondrial creatine kinase) were increased significantly and that the specific carbonyl levels of the three brain proteins (lactate dehydrogenase B, dihydropyrimidinase-like protein 2, and α-enolase) were significantly decreased in the aged SAMP8 mice treated with LA. These findings suggest that the improved learning and memory observed in LA-injected SAMP8 mice may be related to the restoration of the normal condition of specific proteins in aged SAMP8 mouse brain. Moreover, our current study implicates neurofilament triplet L protein, α-enolase, ubiquitous mitochondrial creatine kinase, lactate dehydrogenase B, and dihydropyrimidinase-like protein 2 in process associated with learning and memory of SAMP8 mice.

The role of oxidants and antioxidants in generalized vitiligo at tissue level.

The role of oxidative stress has not been fully understood in the aetiopathogenesis of vitiligo in different studies. We aimed to investigate the role of the oxidative stress in the pathogenesis of vitiligo. In this study, we examined levels of superoxide dismutase, glutathione peroxidase, malondialdehyde and nitric oxide in tissue of 25 patients with generalized vitiligo and 25 healthy controls. Our results revealed that levels of superoxide dismutase, glutathione peroxidase and malondialdehyde in tissue were significantly increased in patients with generalized vitiligo (P < 0.05). However, there was no statistically significantly difference between two groups at tissue level of nitric oxide (P > 0.05). Our results demonstrate the presence of an imbalance in the oxidant-antioxidant system in vitiligo at tissue level and provide further support for a free radical-mediated damage as an initial pathogenic event in melanocyte degeneration in vitiligo.

Antisense directed at the Aβ region of APP decreases brain oxidative markers in aged senescence accelerated mice

Amyloid β-peptide (Aβ) is known to induce free radical-mediated oxidative stress in the brain. Free radical-mediated damage to the neuronal membrane components has been implicated in the etiology of Alzheimer's disease (AD). Aβ is produced by proteolytic processing of the amyloid precursor protein (APP). The senescence accelerated mouse prone 8 (SAMP8) strain was developed by phenotypic selection from a common genetic pool. The SAMP8 strain exhibits age-related deterioration in memory and learning as well as Aβ accumulation, and it is considered an effective model for studying brain aging in accelerated senescence. Previous research has shown that a phosphorothiolated antisense oligonucleotide directed against the Aβ region of APP decreases the expression of APP and reverses deficits in learning and memory in aged SAMP8 mice. Consistent with other reports, our previous study showed that 12-month-old SAMP8 mice have increased levels of oxidative stress markers in the brain compared with that in brains from 4-month-old SAMP8 mice. In the current study, 12-month-old SAMP8 mice were treated with antisense oligonucleotide directed against the Aβ region of APP, and the oxidative markers in brain were decreased significantly. Therefore, we conclude that Aβ may contribute to the oxidative stress found in aged SAMP8 mice that have learning and memory impairments. These results are discussed in reference to AD.

M.451 Fibrinogen in patients with hyperlipidemia in treatment

Oxidative stress is associated with many chronic diseases. In this review, we look at the role that oxidative stress may play in diabetes and related cardiovascular disease (CVD) and how oxidative damage may be measured in the plasma. Increased production of reactive oxygen species (ROS) has been implicated in the initiation and progression of both of these conditions and it may be that oxidative stress accounts for the unexplained increase in cardiovascular risk observed in diabetes. Plasma measurements are difficult because of the highly reactive nature of these molecules. Several studies have focused on measuring the total antioxidant buffering capacity of plasma or alternatively specific measures of free radical-mediated damage such as F2-isoprostane or oxidised-LDL (Ox-LDL). Perhaps, in the future, the discovery of an ‘easy to measure marker’ of oxidative stress might be incorporated into risk prediction in diabetes and cardiovascular disease.

The role of antioxidants in protection from ototoxic drugs

A number of studies have shown that cisplatin and gentamicin ototoxic effects may result from free radical-mediated damage due to the reduction of antioxidant substances and an increased lipid peroxidation. The authors summarize the results obtained evaluating the auditory and vestibular functions and the inner ear hair cell morphology and survival after administration of antioxidant agents against cisplatin and gentamicin. In the first experiment, albino guinea pigs were treated with gentamicin (100 mg/kg per day, i.m.) alone or gentamicin (100 mg/kg per day, i.m.) plus α-tocopherol (100 mg/kg per day, i.m.) for 2 weeks. In a second experiment, albino guinea pigs were injected with cisplatin (2.5 mg/kg per day) or cisplatin (2.5 mg/kg per day) plus tiopronin (300 mg/kg) for 6 days. Electrocochleographic recordings were made from an implanted round window electrode. In all experiments compound action potentials (CAPs) were measured at 2–16 kHz. Changes in cochlear function were characterized as CAP threshold shifts. To evaluate vestibular function, the animals underwent sinusoidal oscillations in the dark about their vertical and longitudinal axes to evoke horizontal and vertical vestibulo-ocular reflexes (VOR). Frequency stimulation parameters ranged from 0.02 to 0.4 Hz and peak-to-peak amplitude was 20°. Morphological changes were analysed by light microscopy and scanning electron microscopy. Both hearing loss and vestibular dysfunction induced by gentamicin were significantly attenuated by α-tocopherol. However, tiopronin co-therapy slowed the progression of hearing loss in cisplatin-treated animals and significantly attenuated the final threshold shifts. Cisplatin had little effect on the hair cells of cristae ampullares and maculae. Vestibular function was completely preserved in tiopronin co-treated animals. In conclusion, antioxidants such as α-tocopherol or tiopronin interfere with gentamicin and cisplatin damage and this suggests that they may be useful in preventing oto-vestibulotoxicity. Therefore, it is important to develop protective strategies that permit the avoidance of the toxic side effects of these drugs without interfering with their therapeutic effects.

Bcl-x L blocks mitochondrial multiple conductance channel activation and inhibits 6-OHDA-induced death in SH-SY5Y cells.

Apoptosis is an active process that is regulated by different signalling pathways. One of the more important organelles involved in apoptosis regulation is the mitochondrion. Electron chain transport disruption increases free radical production leading to multiple conductance channel opening, release of cytochrome c and caspase activation. This death pathway can be blocked by anti-apoptotic members of the Bcl-2 protein family that might shift redox potential to a more reduced state, preventing free radical-mediated damage. 6-Hydroxydopamine (6-OHDA) has been widely used to generate Parkinson's disease-like models. It is able to generate free radicals and to induce catecholaminergic cell death. In this paper we have used the human neuroblastoma cell line SH-SY5Y overexpressing Bcl-x(L) as a model to gain insights into the mechanisms through which Bcl-x(L) blocks 6-OHDA-induced cell death and to identify the molecular targets for this action. Herein, we present evidence supporting that the Bcl-x(L)-anti-apoptotic signal pathway seems to prevent mitochondrial multiple conductance channel opening, cytochrome c release and caspase-3 like activity following 6-OHDA treatment in the human neuroblastoma cell line SH-SY5Y.

Inhibitory Effects of Flavonoids on Free Radical-Induced Hemolysis and Their Oxidative Effects on Hemoglobin

To investigate the effects of flavonoids on free radical-mediated biological membrane damage and the interaction of flavonoids with heme proteins, we studied the effects of quercetin, its glycosides (rutin and quercetin-3-O-glucoside), morin and (-)epicatechin on the hemolysis of the bovine erythrocytes induced by the hydrophilic free radical initiator, 2,2'-azobis(2-amidinopropane)dihydrochloride (AAPH), and their interaction with hemoglobin. These flavonoids retarded the onset of the hemolysis dose-dependently. The effects of quercetin and other flavonoids were much greater than those of dihydric-phenols studied previously. The inhibitory effects of quercetin and its glycosides were stronger than those of morin and (-)epicatechin. In the absence of AAPH, the relatively hydrophobic flavonoids quercetin and morin induced the oxidation of oxyhemoglobin to methemoglobin. Oxidation by quercetin was especially marked. However, this oxidation did not induce hemolysis. These findings indicate that relatively hydrophobic flavonoids penetrate the cytoplasm of erythrocytes, interact with hemoglobin, and oxidize the heme iron.

Green vegetable drink consumption protects peripheral lymphocytes DNA damage in Korean smokers

Smoking increases indices of free radical-mediated damage of DNA which are potential underlying processes in the pathogenesis of many diseases. In this study, we evaluated whether 8 weeks of green vegetable drink (Angelica keiskei based juice) supplementation to smokers can be protective against lymphocytic DNA damage. Twenty smokers were given 240 ml of commercially available green vegetable drink every day for 8 weeks. The DNA damage was determined using single cell gel electrophoresis (COMET assay) and the damage was quantified by measuring tail length (TL), tail moment (TM), and percent DNA in tail. Eight weeks of green vegetable drink consumption resulted in a significant in lymphocytes DNA damage in all three measurements; TL, TM and % DNA in tail. These results support the hypothesis that green vegetable drink exerts a cancer-protective effect via a decrease in oxidative damage to DNA in humans.

Protective Effect of Superoxide Dismutase Against Hair Graying in a Mouse Model¶

Oxygen free radicals play a role in the aging process, and the protective effect of various antioxidants has been intensively studied, in particular for cutaneous aging. Besides hereditary factors, free radical-mediated damage to melanocytes of the hair follicle has been considered as a mechanism for aging of the hair. It was the aim of this study to evaluate the role of photosensitization reactions for hair graying and to demonstrate potential protective effects of superoxide dismutase (SOD). Mice with black hair were depilated with the fingertips on a surface of 6 x 2.5 cm on both sides of the dorsum. The right side received five applications of a SOD-containing gel before exposure to psoralen (concentration 0.5 mg/mL) plus UV-A (365 nm, 4 J/cm2). The left side was pretreated in the same way with a gel free of SOD. When the hair started growing again, the SOD-protected side was covered with black hair, whereas the hair on the vehicle-treated side was gray or white in 27 of the 30 animals studied. The 0.01% SOD concentration was as protective as the 0.1% concentration. Heat-inactivated SOD, applied in another five animals, was not protective. Using fluorescent labeling of the SOD with fluorescein isothiocyanate, epifluorescence microscopy and digital imaging processing, we show that SOD applied to the skin surface penetrates through the follicular appendages, as well as through the unbroken stratum corneum. Our findings suggest that superoxide radicals, generated by interaction of UV-A light with the sensitizer, initiated the formation of secondary products with well-known DNA-damaging effects, such as lipid peroxidation products and tumor necrosis factor alpha. SOD prevented the damage to melanocyte DNA by dismutating superoxide. Photosensitization may be another mechanism for hair graying, which can be influenced by antioxidants. Given the large number of exogenous and endogenous sensitizers, this mechanism deserves further study for human hair graying.

Amrita Bindu—an antioxidant inducer therapy in asthma children

Studies all over the world on the therapeutic use of antioxidants as supplements has revealed their capacity to control inflammatory processes. Amrita Bindu an Ayurvedic health food supplement has already shown to be an antioxidant inducer and to combat free radical-mediated tissue damage studied in rats. Amrita Bindu is a salt–spice herbal mixture designed for positive health. It was tested as a supplement to therapy for a period of 12 months in 36 children suffering from asthma. Asthma is a chronic inflammatory disease with excessive free radical generation in lungs and blood cells. The patients were followed up by monitoring their clinical conditions, therapeutic doses of anti-asthmatic drugs, free radical generation, lipid peroxidation (LPO) and antioxidants in blood. At the end of 3 months of Amrita Bindu supplementation, the patients had stopped all anti-asthmatic medications and were free from attacks of asthma.

Oestrogenic compounds and oxidative stress (in human sperm and lymphocytes in the Comet assay).

Reactive oxygen species (ROS) are produced by a wide variety of chemicals and physiological processes in which enzymes catalyse the transfer of electrons from a substrate to molecular oxygen. The immediate products of such reactions, superoxide anion radicals and hydrogen peroxide can be metabolised by enzymes such as superoxide dismutase (SOD) and catalase (CAT), respectively, and depending on its concentration by Vitamin C (Vit C). Under certain circumstances the ROS form highly reactive hydroxyl radicals. We examined human sperm and lymphocytes after treatment with six oestrogenic compounds in the Comet assay, which measures DNA damage, and observed that all caused damage in both cell types. The damage was diminished in nearly all cases by catalase, and in some instances by SOD and Vit C. This response pattern was also seen with hydrogen peroxide. This similarity suggests that the oestrogen-mediated effects could be acting via the production of hydrogen peroxide since catalase always markedly reduced the response. The variable responses with SOD indicate a lesser involvement of superoxide anion radicals due to SOD-mediated conversion of superoxide to hydrogen peroxide generally causing a lower level of DNA damage than other ROS. The variable Vit C responses are explained by a reduction of hydrogen peroxide at low Vit C concentrations and a pro-oxidant activity at higher concentrations. Together these data provide evidence that inappropriate exposure to oestrogenic compounds could lead to free-radical mediated damage. It is believed that the observed activities were not generated by cell free cell culture conditions because increased responses were observed over and above control values when the compounds were added, and also increasing dose-response relationships have been found after treatment with such oestrogenic compounds in previously reported studies.

Pathophysiological significance of peroxidative stress, neuronal damage, and membrane permeability in acute mountain sickness.

Free radical-mediated changes in vascular permeability and subsequent inflammatory response may be a contributory pathogenetic cofactor responsible for the development of neurological sequelae associated with acute mountain sickness (AMS). To investigate this, 49 subjects were examined at sea level and serially after rapid ascent to 4,559 m. Although the venous concentration of total creatine phosphokinase activity was measured in all subjects, a complementary examination of lipid peroxidation (F(2)-isoprostanes), inflammatory (TNF-alpha, IL-1beta, IL-2, IL-6, IL-8, C-reactive protein), and cerebrovascular tissue damage (neuron-specific enolase) biomarkers was confined to a subcohort of 24 subjects. A selective increase (P < 0.05) in total creatine phosphokinase was observed in subjects diagnosed with AMS at high altitude (n = 25) compared with apparently healthy controls (n = 24). However, despite a marked increase in IL-6 and C-reactive protein attributable primarily to subjects developing high-altitude pulmonary edema, subcohort analyses demonstrated no selective differences in F(2)-isoprostanes, neuron-specific enolase, or remaining proinflammatory cytokines due to AMS (n = 14). The present findings are the first to demonstrate that free radical-mediated neuronal damage of sufficient degree to be detected in the peripheral circulation does not occur and is, therefore, unlikely to be an important, initiating event that is critical for the development of AMS. The pathophysiological significance of increased sarcolemmal membrane permeability and inflammatory response, either as a cause or epiphenomenon of AMS and/or high-altitude pulmonary edema, remains to be elucidated.