综述与专论: 高压氧疗法治疗脑缺血的相关机制

脑缺血是指大脑各部分血液供应不足导致脑组织缺血缺氧，进而导致密集缺血区脑组织出现不可逆的损伤坏死，其高致残率、高死亡率会对患者及其家庭造成严重的伤害。在脑缺血发生后，及时采取一定的治疗措施控制梗死灶的大小，并挽救半暗带中的细胞是脑缺血预后的关键。高压氧疗法是针对脑缺血的一种潜在治疗方法，在近年来得到了越来越广泛的关注和研究，本文旨在综述近年来国内外关于高压氧疗法治疗脑缺血的相关机制及研究进展，为脑缺血患者的治疗和预后提供新思路。     

Acute and chronic effects of hyperbaric oxygen therapy on blood circulation of human muscle and tendon in vivo

ABSTRACT: Kubo, K and Ikebukuro, T. Acute and chronic effects of hyperbaric oxygen therapy on blood circulation of human muscle and tendon in vivo. J Strength Cond Res 26(10): 2765-2770, 2012-This study aimed to investigate the acute and chronic effects of hyperbaric oxygen therapy on blood circulation of human muscle and tendon in vivo. Using near-infrared spectroscopy and red laser lights, we determined acute changes in blood volume (THb) and oxygen saturation (StO2) of the medial gastrocnemius muscle and Achilles tendon during 60 minutes of hyperbaric oxygen therapy (1.3 atm absolute and 50% O2, experiment 1). In addition, we determined the chronic effects of hyperbaric oxygen therapy (60 minutes, 2 times per week, 6 weeks) on THb and StO2 of muscle and tendon (experiment 2). In experiment 1, THb of the muscle increased gradually from resting level, but StO2 did not change. On the other hand, THb and StO2 of the tendon increased during hyperbaric oxygen therapy. In experiment 2, the pattern of changes in the measured variables during 60 minutes of therapy was similar for both the muscle and tendon between the first and last therapies. During resting, THb and StO2 of the tendon were significantly lower after 6 weeks of therapy, although those of the muscle were not. In conclusion, oxygen saturation of the tendon increased during hyperbaric oxygen therapy, whereas that of the muscle did not. This result would be related to the difference in the treated effects between muscle and tendon. However, oxygen saturation of the tendon, but not the muscle, during resting decreased after 6 weeks of therapy.     

Modification of contractile proteins by oxygen free radicals in rat heart

This study was undertaken to investigate the effects of oxygen free radicals on myofibrillar creatine kinase activity. Isolated rat heart myofibrils were incubated with xanthine+xanthine oxidase (a superoxide anion radical-generating system) or hydrogen peroxide and assayed for creatine kinase activity. To clarify the involvement of changes in sulfhydryl groups in causing alterations in myofibrillar creatine kinase activity, 1) effects of N-ethylmaleimide (sulfhydryl groups reagent) on myofibrillar creatine kinase activity, 2) effect of oxygen free radicals on myofibrillar sulfhydryl groups content, and 3) protective effects of dithiothreitol (sulfhydryl groups-reducing agent) on the changes in myofibrillar creatine kinase activity due to oxygen free radicals were also studied. Xanthine+xanthine oxidase inhibited creatine kinase activity both in a time-and a concentration-dependent manner. Superoxide dismutase (SOD) showed a protective effect on the depression in creatine kinase activity caused by xanthine+xanthine oxidase. Hydrogen peroxide inhibited creatine kinase activity in a concentration-dependent manner; this inhibition was prevented by the addition of catalase. N-ethylmaleimide reduced creatine kinase activity in a dose-dependent manner. The content of myofibrillar sulfhydryl groups was decreased by xanthine+xanthine oxidase; this reduction was protected by SOD. Furthermore, the depression in myofibrillar creatine kinase activity by xanthine+xanthine oxidase was protected by the addition of dithiothreitol. Oxygen free radicals may inhibit myofibrillar creatine kinase activity by modifying sulfhydryl groups in the enzyme protein. The reduction of myofibrillar creatine kinase activity may lead to a disturbance of energy utilization in the heart and may contribute to cardiac dysfunction due to oxygen free radicals.     

最大等速离心运动诱发肌肉损伤程度与肌酸激酶水平的关系

为探讨人体进行最大等速离心运动(ECC)诱发血液肌酸激酶(CK)水平变化、血清肌酸激酶水平与肌肉损伤(EIMD)的关系,本研究筛选出150名"缺乏运动"的健康大学生为受试者,进行血样采集,进行前测包括血清肌酸激酶(CK)、最大等长肌力(MVC)、肘关节活动角度(ROM)、上臂围(CIR)、肌肉感受(VAS)。受试者进行5组×12次最大等速离心运动,运动后恢复期,将全部受试者血清肌酸激酶值进行排序:血清肌酸激酶值最高和最低20%样本,高肌酸激酶水平组(HCK组)和低肌酸激酶水平组(low LCK组),利用SPSS18.0统计学软件,以方差分析和多元回归分析进行统计分析。本研究发现全部受试者、高肌酸激酶水平组、低肌酸激酶水平组在最大等速离心运动后各评估指标均显著高于比前测结果,p<0.05。全部受试者、高肌酸激酶水平组受试者在最大等速离心运动后各指标变化皆明显大于低肌酸激酶水平组受试者,p<0.05。受试者血清肌酸激酶峰值与最大等长肌力、肘关节活动角度、上臂围、肌肉感受最大变化值有相关,p<0.05。本研究认为肌肉损伤程度与肌酸激酶水平具有显著相关,尤其高血清肌酸激酶水平者肌酸激酶水平较大程度反映肌肉损伤程度趋势。本研究表明,肘关节活动角度、上臂围具有预测肌酸激酶峰值的效果。     

Immunomodulatory effect of oxygen and pressure

The immunomodulatory effect of hyperbaric oxygen, involving altered cytokine release by macrophages, is well described. Importantly, however, it is not known what the relative contribution is of the hyperbaric environment of the cells vs. increased oxygen tension on these hyperbaric oxygen-dependent effects. We compared, therefore, cytokine release by murine macrophages under hyperbaric oxygen, hyperpressure of normal air and normobaric conditions. We observed that hyperbaric oxygen enhanced cytokine release of both unstimulated as well as lipopolysaccharide (LPS)-challenged macrophages. Hyperpressure of normal air, however, enhanced LPS-induced cytokine production but did not elicit cytokine release in unstimulated macrophages. To further investigate the molecular details underlying the effects of hyperbaric oxygen, we investigated the effect of the p42/p44 mitogen-activated protein (MAP) kinase inhibitor PD98059 and the p38 MAP kinase inhibitor SB203580. Neither inhibitor, however, had a significant effect on the modulatory effects of hyperbaric oxygen on cytokine release. We concluded that the immunomodulatory effect of hyperbaric oxygen contains a component for which hyperpressure is sufficient and a component that apart from hyperpressure also requires hyperoxygenation.     

高压氧治疗糖尿病视网膜病变的研究进展

糖尿病视网膜病变是糖尿病最常见、最主要的微血管并发症之一,具有高发病率,高致盲率的特点,严重影响了人类的生存质量。控制高血糖和改善组织缺氧无疑是防治糖尿病微血管病变的有效方法。如果对糖尿病视网膜病变及时进行治疗,能延缓其发展并能提高病人的生活质量。近年来,随着对糖尿病发病机制的深入研究,很多方法用于防治糖尿病视网膜病人都取得了一定的疗效。而高压氧治疗是许多急慢性疾病的首选治疗方法。已有基础和临床研究证实,高压氧治疗对糖尿病视网膜病变安全有效。因此,作为一种新疗法,高压氧疗法可能会为糖尿病视网膜病变的治疗带来更广泛的应用前景。     

高压氧的应用进展

高压氧逐渐被广泛的应用于多个医疗实践领域。作为一种特殊的治疗手段,临床医生会为他们的病人提供这种治疗选择,但对其机制却不十分了解。通过对高压氧作用机制详细阐述,为临床医生在医疗实践中提供科学依据。通过全面阐述高压氧的临床应用、并发症及禁忌症,更全面、系统的了解高压氧这种治疗手段,全面评估高压氧的治疗安全性。因高压氧具有增加氧输送、免疫功能和改变血液流变学的复合效应,而且安全性较高,用于治疗创伤、栓塞、感染等多种疾病。突发性耳聋是耳鼻咽喉科常见的急症,患者主要表现为突然发生的不同程度的感音神经聋,影响患者的生活。因目前突发性耳聋的病因尚不明确,治疗方案多种多样,如激素、抗凝药物、抗病毒药物等,但疗效均为得到肯定,无有效的统一治疗方案。通过分析评价多个随机对照试验,发现高压氧治疗可明显改善突发性耳聋(Sudden hearing loss,SHL)的听力下降,希望能为临床医生的治疗提供科学依据。可能存在其他的尚未发掘的治疗领域,期待临床上有更多的相关研究。     

Hyperbaric oxygen toxicity and ribosome destruction in Escherichia coli K12

The viability of resting suspensions of Escherichia coli K12 Ymel exposed to air plus 300 psi (1 psi = 6.895 kPa) oxygen (hyperbaric oxygen) decreased as an apparent first-order process after an initial period of constant viability. Control suspensions exposed to air plus 300 psi nitrogen (hyperbaric nitrogen) did not lose viability over the 96 h of the experiment. It was observed that a decrease in the refractive index of the cells preceded the loss of viability in hyperbaric oxygen. This finding together with electron micrographs, which showed extensive loss of ribosomal particles in bacteria incubated in hyperbaric oxygen, led us to suspect that ribosome injury or disassociation might be important in hyperbaric oxygen toxicity. In support of this we found that cellular RNA, labeled with [5-3H]uridine, was much more rapidly and more completely degraded in hyperbaric oxygen than in hyperbaric nitrogen. Furthermore, a far greater proportion of RNA was degraded than was DNA or protein. A direct assay for ribosome particles by sucrose gradient centrifugation showed that only 34% of the 70S ribosome particles was lost during the first 24 h in hyperbaric nitrogen whereas in hyperbaric oxygen 99.6% of the 70S particles was degraded during the same period. In hyperbaric oxygen the rate of viability loss between 24 and 72 h was equal to the rate of 70S ribosome degradation during the first 24 h. If 70S ribosome disassociation in hyperbaric oxygen continues at the same rate after first 24 h, then cumulative 70S ribosome disassociation or injury may lead to and provide an explanation for irreversible bacterial cell injury and the loss of viability.     

Velocity of the creatine kinase reaction in the neonatal rabbit heart: role of mitochondrial creatine kinase

To examine the role of changes in the distribution of the creatine kinase (CK) isoenzymes [BB, MB, MM, and mitochondrial CK (mito-CK)] on the creatine kinase reaction velocity in the intact heart, we measured the creatine kinase reaction velocity and substrate concentrations in hearts from neonatal rabbits at different stages of development. Between 3 and 18 days postpartum, total creatine kinase activity did not change, but the isoenzyme distribution and total creatine content changed. Hearts containing 0, 4, or 9% mito-CK activity were studied at three levels of cardiac performance: KCl arrest and Langendorff and isovolumic beating. The creatine kinase reaction velocity in the direction of MgATP production was measured with 31P magnetization transfer under steady-state conditions. Substrate concentrations were measured with 31P NMR (ATP and creatine phosphate) and conventional biochemical analysis (creatine) or estimated (ADP) by assuming creatine kinase equilibrium. The rate of ATP synthesis by oxidative phosphorylation was estimated with oxygen consumption measurements. These results define three relationships. First, the creatine kinase reaction velocity increased as mito-CK activity increased, suggesting that isoenzyme localization can alter reaction velocity. Second, the reaction velocity increased as the rate of ATP synthesis increased. Third, as predicted by the rate equation, reaction velocity increased with the 3-fold increase in creatine and creatine phosphate contents that occurred during development.     

高压氧的应用进展

高压氧逐渐被广泛的应用于多个医疗实践领域。作为一种特殊的治疗手段,临床医生会为他们的病人提供这种治疗选择,但对其机制却不十分了解。通过对高压氧作用机制详细阐述,为临床医生在医疗实践中提供科学依据。通过全面阐述高压氧的临床应用、并发症及禁忌症,更全面、系统的了解高压氧这种治疗手段,全面评估高压氧的治疗安全性。因高压氧具有增加氧输送、免疫功能和改变血液流变学的复合效应,而且安全性较高,用于治疗创伤、栓塞、感染等多种疾病。突发性耳聋是耳鼻咽喉科常见的急症,患者主要表现为突然发生的不同程度的感音神经聋,影响患者的生活。因目前突发性耳聋的病因尚不明确,治疗方案多种多样,如激素、抗凝药物、抗病毒药物等,但疗效均为得到肯定,无有效的统一治疗方案。通过分析评价多个随机对照试验,发现高压氧治疗可明显改善突发性耳聋（Sudden hearing loss,SHL）的听力下降,希望能为临床医生的治疗提供科学依据。可能存在其他的尚未发掘的治疗领域,期待临床上有更多的相关研究。     

The levels of creatine kinase and adenylate kinase in the plasma of dystrophic chickens reflect the rates of loss of these enzymes from the circulation

The rates of loss of adenylate kinase and creatine kinase from the circulation after intravenous injection of homogenous chicken skeletal muscle enzymes were examined to determine the role of plasma clearance rates in determining the plasma levels of these enzymes in normal and dystrophic chickens. The rapid clearance of adenylate kinase activity (average half-life of 5 min) and the slower biphasic clearance of creatine kinase activity (average half-lives of 0.95 and 11 hr) are consistent with the elevation of creatine kinase but not adenylate kinase in the blood plasma of dystrophic chickens compared to normal chickens. The rates of clearance of these enzymes were similar in normal chickens compared to dystrophic chickens. Radioiodinated enzymes were cleared at similar, but slightly more rapid rates than the loss of enzyme activity. The loss of adenylate kinase activity from the circulation may be due in part to inactivation since adenylate kinase activity is rapidly inactivated in serum in vitro, and because no increase in adenylate kinase activity is observed in the most specific sites of clearance of the radioiodinated enzyme, the liver and spleen. The comparison of enzyme activities in press juices to the activities in high-ionic-strength homogenates of muscle tissue from normal and dystrophic muscle, indicates that adenylate kinase activity is not associated with intracellular structures to the extent that would prohibit release from dystrophic muscle tissue. These results, and those presented previously with regard to plasma levels and clearance rates of AMP aminohydrolase and pyruvate kinase in normal and dystrophic chickens (11) support our hypothesis that the rates of loss of muscle enzyme activities from the circulation are important in determining the circulating levels of muscle enzymes in dystrophic chickens. Furthermore, from the measurement of plasma levels and clearance rates of creatine kinase, it was estimated that the efflux rate of creatine kinase from dystrophic muscle tissue is 2.0% of the total breast muscle creatine kinase per day.     

Compartmentation of multiple forms of creatine kinase in the distal nephron of the rat kidney

Creatine kinase enzymes are present in tissues such as muscle and brain to interconvert creatine phosphate and ADP, thus providing a system to interconnect energy production and utilization (Bessman, S. P., and Carpenter, C. L. (1985) Annu. Rev. Biochem. 54, 831-862). Creatine kinase isoenzymes in kidney have received little attention since kidney contains relatively low creatine kinase activity compared with muscle and brain and because there is disagreement regarding the identity of the specific isoforms expressed in kidney. Using a combination of chromatographic and immunological techniques, we have identified two isoforms of creatine kinase in rat kidney supernatants, B creatine kinase, and the non-sarcomeric form of the mitochondrial creatine kinase, which represent 82 and 15%, respectively, of the total creatine kinase activity in this tissue. The identity of the non-muscle form of the mitochondrial creatine kinase was confirmed by N-terminal sequence analysis and compared with recently published cDNA sequences (Haas, R. C., and Strauss, A. W. (1990) J. Biol. Chem. 265, 6921-6927). We prepared multiple antisera specific for each isoform using synthetic peptide immunogens based upon nonhomologous regions from the primary sequence of each creatine kinase isoform. Immunocytochemical results demonstrate that both creatine kinase isoforms are colocalized in the inner stripe of the outer medulla in tubules of the distal nephron. A similar distribution of creatine kinase isoforms was obtained when different layers of the renal cortex and medulla were examined for creatine kinase activity and isozyme content using nondenaturing electrophoresis. In general, the distribution of creatine kinase enzymes in kidney corresponds to the regions of greatest ATP utilization, oxygen consumption, and sodium transport. These results suggest a role for creatine kinase enzymes in the coupling of ion transport and oxidative phosphorylation in the distal nephron of the mammalian kidney.     

Free ADP levels in transgenic mouse liver expressing creatine kinase. Effects of enzyme activity, phosphagen type, and substrate concentration

ADP is an important regulator of hepatic metabolism. Despite its importance the level of free ADP in the liver remains controversial. Recently, we engineered transgenic mice which express high levels of creatine kinase in liver. The reaction catalyzed by creatine kinase was assumed to be at equilibrium and used to calculate a free ADP level of 0.059 mumol/g wet weight. In this report we test the equilibrium assumption by studying the free ADP level as a function of enzyme activity or substrate content. Over a 5-fold range of creatine kinase activity, from 150-800 mumol/min/g wet weight, there was no change in the free ADP level. The average value of ADP for these mice was 0.061 +/- 0.016 mumol/g wet weight. Similarly, altering hepatic creatine content from 1.6 to 30 mumol/g wet weight had no effect on the calculated total free ADP level. The average value of ADP for the creatine levels was 0.048 +/- 0.015 mumol/g wet weight. Finally, the free ADP level was calculated using the equilibrium with cyclocreatine rather than creatine as substrate. The equilibrium of the reaction with cyclocreatine lies 30 times more toward phosphorylation than does the equilibrium with creatine. A free ADP level of 0.063 +/- 0.031 mumol/g wet weight was calculated using cyclocreatine. This value is not different from that found with creatine. These results show that the equilibrium assumption used to calculate free ADP levels in transgenic mouse liver is valid, and the presence of creatine kinase does not affect ADP levels.     

Decrease in heart mitochondrial creatine kinase activity due to oxygen free radicals.

This study was undertaken to examine the effects of oxygen free radicals on mitochondrial creatine kinase activity in rat heart. Xanthine plus xanthine oxidase (superoxide anion radical generating system) reduced mitochondrial creatine kinase activity both in a dose- and a time-dependent manner. Superoxide dismutase showed a protective effect on depression in creatine kinase activity due to xanthine plus xanthine oxidase. Hydrogen peroxide inhibited creatine kinase activity in a dose-dependent manner, this inhibition was protected by the addition of catalase. In order to understand the detailed mechanisms by which oxygen free radicals inhibit mitochondrial creatine kinase activity, the effects of oxygen free radicals on mitochondrial sulfhydryl groups were examined. Mitochondrial sulfhydryl groups contents were decreased by xanthine plus xanthine oxidase or hydrogen peroxide; this depression in sulfhydryl groups contents was prevented by the addition of superoxide dismutase or catalase. N-Ethylmaleimide (sulfhydryl group reagent) expressed inhibitory effects on the creatine kinase activity both in a dose- and a time-dependent manner; dithiothreitol or cysteine (sulfhydryl group reductant) showed protective effects on the creatine kinase activity depression induced by N-ethylmaleimide. Dithiothreitol or cysteine also blocked the depression of mitochondrial creatine kinase activity caused by xanthine plus xanthine oxidase or hydrogen peroxide. These results lead us to conclude that oxygen free radicals may inhibit mitochondrial creatine kinase activity by modifying sulfhydryl groups in the enzyme protein.     

Effect of hypothermia on radiosensitization

Hypothermia reduces metabolism and oxygen utilization by tissues. If the blood supply to a solid tumour can be maintained at a sufficient level, the hypoxic fraction of tumour cells may be reduced and radiosensitivity increased. This may be achieved if hyperbaric oxygen is used in combination with the hypothermia. The blood supply and oxygen tension have been measured in C3H mouse mammary tumours under hypothermia and hyperbaric oxygen, and the enhancement of radiosensitivity by hyperbaric oxygen has been estimated in mice irradiated at different temperatures with and without anaesthesia. Measurement of xenon-133 clearance showed that the blood supply of a tumour tended to increase when anaesthetized mice became hypothermic. Oxygen cathode data showed that the oxygen tension tended to be relatively higher in tumours and lower in subcutaneous tissue when mice exposed to hyperbaric oxygen became hypothermic under anaesthesia. Hyperbaric oxygen enhanced the radiation response of the tumour in terms of an increase in regrowth delay by a factor of 1.7 when the mice had been anaesthetized, whether or not they became hypothermic. A lower factor of 1.4 was obtained without anaesthesia although induced hypothermia increased the response to a small extent. We conclude that anaesthesia and hypothermia affect oxygen metabolism in tumours by different mechanisms.     

Alterations in the creatine kinase system in the myocardium of cardiomyopathic hamsters

Immunochemical and biochemical methods were used to assess quantitatively the changes in the heart creatine kinase system in the myopathic Syrian hamsters, line CHF I46. Cardiomyopathy in I75-200 day old animals was characterized by decreased content of mitochondria and lower total creatine kinase activity. In isolated mitochondria only the creatine kinase activity was decreased while cytochromes aa3 content and respiration rate were unchanged. The share of mitochondrial creatine kinase in the total tissue enzyme activity was decreased from 33% to I8% and that of BB form was elevated from 5% in control to 20%, at unchanged relative level of MM. Immunoassay showed decreased amount of the mitochondrial creatine kinase in the tissue and its decreased ratio to cytochromes aa3. The results show altered expression of creatine kinase isoenzymes in cardiomyopathy.     

Hyperbaric Oxygen Therapy Ameliorates Local Brain Metabolism,Brain Edema and Inflammatory Response in a Blast-Induced Traumatic Brain Injury Model in Rabbits

Many studies suggest that hyperbaric oxygen therapy (HBOT) can provide some clinically curative effects on blast-induced traumatic brain injury (bTBI). The specific mechanism by which this occurs still remains unknown, and no standardized time or course of hyperbaric oxygen treatment is currently used. In this study, bTBI was produced by paper detonators equivalent to 600 mg of TNT exploding at 6.5 cm vertical to the rabbit’s head. HBO (100 % O₂ at 2.0 absolute atmospheres) was used once, 12 h after injury. Magnetic resonance spectroscopy was performed to investigate the impact of HBOT on the metabolism of local injured nerves in brain tissue. We also examined blood–brain barrier (BBB) integrity, brain water content, apoptotic factors, and some inflammatory mediators. Our results demonstrate that hyperbaric oxygen could confer neuroprotection and improve prognosis after explosive injury by promoting the metabolism of local neurons, inhibiting brain edema, protecting BBB integrity, decreasing cell apoptosis, and inhibiting the inflammatory response. Furthermore, timely intervention within 1 week after injury might be more conducive to improving the prognosis of patients with bTBI.     

The effect of hyperbaric oxygenation on the antioxidant status of Xenopus laevis after its preliminary adaptation to oxygen]

We studied the level of lipid peroxidation and the activity of antioxidant enzymes (superoxide dismutase and catalase) in various tissues of adult Xenopus laevis after an initial exposure to hyperbaric oxygenation at the developmental stage 38. We have found that irrespective to the mode of treatment, the level of lipid peroxidation and activity of antioxidant enzymes in the brain, lungs, and blood of these animals were higher as compared to control animals. We demonstrate that, after the exposure of adult animals to hyperoxia, if they were earlier subjected to hyperbaric oxygenation (0.2 MPa) at stage 38, there was no intensification of lipid peroxidation or changes in the activity of superoxide dismutase and catalase. In adult animals initially subjected to hyperbaric oxygenation at the same stage of development but at the pressure--0.7 MPa, the second exposure to hyperoxia led to a drastic intensification of lipid peroxidation in the brain; in some animals, an increased level of lipid peroxidation products in the lungs was observed.     

Humidity does not affect central nervous system oxygen toxicity.

Central nervous system (CNS) oxygen toxicity can occur as convulsions and loss of consciousness when hyperbaric oxygen is breathed in diving and hyperbaric medical therapy. Lin and Jamieson (J Appl Physiol 75: 1980-1983, 1993) reported that humidity in the inspired gas enhances CNS oxygen toxicity. Because alveolar gas is fully saturated with water vapor, we could not see a cause and effect and surmised that other factors, such as metabolic rate, might be involved. Rats were exposed to 507- and 608-kPa O(2) in dry (31 or 14%) or humid (99%) atmosphere until the appearance of the first electrical discharge preceding the clinical convulsions. Each rat served as its own control. A thermoneutral temperature (28 +/- 0.4 degrees C) yielded resting CO(2) production of 0.81 +/- 0.06 ml x g(-1) x h(-1). Latency to the first electrical discharge was not affected by humidity. At 507-kPa O(2), latency was 23 +/- 0.4 and 22 +/- 0.7 min in dry and humid conditions, respectively, and, at 608-kPa O(2), latency was 15 +/- 4 and 14 +/- 3 min in dry and humid conditions, respectively. When no effects of CO(2) and metabolic rate are present, humidity does not affect CNS oxygen toxicity. Relevance of the findings to diving and hyperbaric therapy is discussed.     

Dependence of Escherichia coli hyperbaric oxygen toxicity on the lipid acyl chain composition.

This study examines certain membrane-related aspects of oxygen poisoning in Escherichia coli K1060 (fabB fadE lacI) and its parent strain, K-12 Ymel. Cells were grown to exponential or stationary phase in a minimal medium and exposed to air plus 300 lb/in2 of O2 as a suspension in minimal salts. After an initial lag, both strains lost viability with apparent first-order kinetics. Hypebaric oxygen was more toxic to cells harvested during the exponential phase of growth than to cells harvested from the stationary phase of growth for both strains K-12 Ymel and K1060. Control suspensions exposed to air plus 300 lb/in2 of N2 did not lose viability during a 96-h exposure. The sensitivity of the unsaturated fatty acid auxotroph, strain K1060, to hyperbaric oxygen increased as the degree of unsaturation of the fatty acid supplement increased. Cells grown with a cyclopropane fatty acid (9,10=methylenoctadecanoate) were the most resistant; cells grown with a monounsaturated fatty acid (oleate) were intermediate; and those grown with polyunsaturated fatty acids (linoleate and linolenate) were most sensitive to hyperbaric oxygen. The parent strain, K-12 Ymel, lost viability in hyperbaric oxygen most similarly to strain K1060 supplemented with oleate. To determine the relative effect of hyperbaric oxygen on the survival of E. coli with saturated membranes, substrains of K1060 were selected for growth on 12-methyltetrade-canoate or on 9 or 10-monobromostearate. Substrains grown with a saturated fatty acid supplement were equally or more sensitive to hyperbaric oxygen than when the same substrains were grown with a cyclopropane fatty acid supplement. The lipid acyl chain composition was determined in E. coli K1060 before and after exposure to hyperbaric oxygen or hyperbaric nitrogen. The proportion of nonsaturated acyl chain lipid of either the oleate- or the 9,10-methyleneoctade-canoate-supplemented K1060 remained unchanged after hyperbaric gas exposure. In strain K1060 supplemented with linoleate and grown to stationary phase, however, the relative unsaturated acyl chain content after hyperbaric exposure decreased in both gases. This finding prompted an investigation of the role of lipid oxidation in hyperbaric oxygen toxicity. Assays of potential lipid oxidation products were performed with linoleate-grown cells. The lipid hydroperoxide and peroxide content of the lipid extract increased by 6.9 times after 48 h of air plus 300 lb/in2 of O2; malondialdehyde and fluorescent complex lipid oxidation products showed much smaller or no changes. Lipid extracts from hyperbaric oxygen-exposed cells were not toxic to viable E. coli K1060, nor did they increase the rate of loss of viability in cells simultaneously exposed to hyperbaric oxygen. Linoleic acid hydroperoxide at 1.0 mM had no effect on the viability of E. coli K-12 Ymel and only marginally decreased the viability of E. coli K1060 supplemented with linoleate. We conclude that the kinetics of oxygen toxicity in E...