Formation of radicals by mechanical processes

Behavior of the electron spin resonance signals in X-ray irradiated human fingernails for the establishment of a dose reconstruction procedure

The retrospective dosimetry that follows accidental X-ray exposure is becoming more significant for improving radiation diagnosis and treatment. We investigated the dosimetric properties of electron spin resonance (ESR) signals in X-ray irradiated fingernails under conditions that resemble realistic situations. We collected fingernails from 12 Japanese donors between the ages of 30 to 70. The sampled fingernails were utilized for X-ray irradiation, mechanical stimulation and background measurements. We also collected 10 toenails from one of the donors to evaluate their differences from fingernails. Additionally, we prepared 15 samples from two donors to compare the signals generated by γ-rays to those by X-rays. After observing the linear dose-response for both X- and γ-ray irradiated samples, we found that the sensitivity of the air-absorbed dose of γ-ray irradiated samples was identical to that of X-ray irradiated samples. The effect from secondary electrons seemed to be small in fingernails. The inter-individual variation in the sensitivity was no greater than the intra-individual variation. The signal intensities in each measurement fluctuated about the linear response curve, and the size of the fluctuation was dependent on the sample. The average fluctuation corresponded to 1.7 Gy, and the standard deviation was 1.3 Gy. The signal induced by X-rays could be erased by soaking the samples in water and subsequently drying them for four days, which allowed us to estimate the signal intensity prior to the exposure. These characteristics of the ESR signal induced by X-rays facilitate the development of a feasible protocol for fingernail dose reconstruction.

Pathogenesis of degenerative temporomandibular joint arthritides

Over the past decade, remarkable progress has been made in the study of molecular mechanisms involved in degenerative temporomandibular joint arthritides. Based on recent findings, models of degenerative temporomandibular joint disease predict that mechanical loads trigger a cascade of molecular events leading to disease in susceptible individuals. These events involve the production or release of free radicals, cytokines, fatty acid catabolites, neuropeptides, and matrix-degrading enzymes. Under normal circumstances, these molecules may be involved in the remodeling of articular tissues in response to changing functional demands. However, if functional demands exceed the adaptive capacity of the temporomandibular joint or if the affected individual is susceptible to maladaptive responses, then a disease state will ensue. An individual's susceptibility to degenerative temporomandibular joint disease may be determined by several factors, including genetic backdrop, sex, age, and nutritional status. It is hoped that, by furthering our understanding of the molecular events that underlie degenerative temporomandibular joint diseases, improved diagnostics and effective therapies for these debilitating conditions will be developed.

Commentary: possible mechanisms for strand-breaks in DNA induced by stirring

When aqueous solutions of DNA are stirred at room temperature, strand breaks occur extensively. Using various spin-traps, coupled with epr spectroscopy, we have shown that this does not proceed via homolysis. It is suggested that breaks occur by hydrolysis at strongly bent regions, momentarily induced by the stirring.

Oxidative stress and degenerative temporomandibular joint disease: a proposed hypothesis

The molecular events that underlie degenerative temporomandibular joint diseases are poorly understood. Recent studies have provided evidence that a variety of molecular species, including cytokines, matrix degrading enzymes, neuropeptides, and arachidonic acid catabolites may be involved. This paper advances the theory that mechanical stresses lead to the accumulation of damaging free radicals in affected articular tissues of susceptible individuals. This condition is called oxidative stress. The authors postulate mechanisms that may be involved in the production of free radicals in the temporomandibular joint and in the subsequent induction of molecular events that may amplify damage of articular tissues initiated by free radicals. If the proposed model is correct, then future therapeutic strategies directed at the control of oxidative stress could be effective in the management of degenerative temporomandibular joint diseases.

Free radicals, exercise and antioxidant supplementation

Although conflicting data exist, the preponderance of available information suggests that physical exercise promotes an increase in free-radical generation. However, few studies have actually measured exercise-induced free radicals directly, primarily because of a lack of sophisticated methodologies to measure this phenomenon. Instead, researchers have relied heavily on the measurement of lipid peroxidation as the principal indicator of exercise-induced free radicals. It should be noted that free radicals can also alter and inactivate enzyme complexes, damage DNA and RNA, and promote mutations and cancer, among other activities. However, there have been few reported studies dealing with exercise and oxidant stress which have measured these outcomes. It should also be noted that free-radical species are continuously produced in the human body, and that some have beneficial effects (Arouma, 1994), notably as a part of the body's natural immune system. It is not presently known if long-term ingestion of antioxidant compounds will affect these positive aspects of free-radical generation. The preponderance of available evidence suggests that antioxidant supplementation, particularly with the vitamins C and E, has favourable effects on markers of lipid peroxidation following exercise. Although the physiological implications of these effects remain to be elucidated, the prudent use of an antioxidant supplement can provide insurance against a suboptimal diet and/or the elevated demands of physical activity. Future research may uncover additional nutritional antioxidants that can benefit the physically-active individual. Numerous additional questions regarding the antioxidant needs for physical activity remain to be answered. Little is known about the needs of physically-active women, particularly those who habitually consume an energy-restricted diet, or the effects of monthly menstrual blood loss (coupled with exercise) on antioxidant requirements. The needs of the 'weekend warrior' (an individual who participates in strenuous activity sporadically) v. those of the habitual exerciser have not been addressed adequately. The needs of the ageing athlete are largely unknown; a study by Meydani et al. (1993) suggested that elderly, physically-active people can benefit from antioxidant supplementation more than their younger counterparts, but follow-up studies have not been reported to-date. Dietary issues also need to be addressed. How much supplementation is too much, and can chronically-elevated antioxidant intakes have an adverse impact on the positive effects of free radicals in living systems? Does a high-carbohydrate diet raise antioxidant needs, particularly of the fat-soluble vitamin E? Does a high polyunsaturated fat intake, or increased Fe intake affect needs? Obviously, there are a number of issues regarding the antioxidant needs of the physically-active individual that need to be elucidated. Future research utilizing newer, more sophisticated methodologies should provide answers to many of these questions.

Radicals generated by bone cutting and fracture

When bone fractures, a remarkably high yield of radicals is generated. By working at 77K, these are stable enough for detection and study. Major species have been identified by ESR (EPR) spectroscopy as alkyl peroxyl radicals and RCH2. radicals. Also, a species thought to be O.- radicals, formed in the mineral phase, was detected in relatively low yield. It is suggested that as a break is generated, the mineral crystallites separate at grain boundaries with no major chemical damage, but that the tightly bound collagen strands running through the mineral phase are forced to break homolytically. Some probably react together, others react with oxygen, while the remainder are trapped in their primary form. The characteristic hyperfine triplet is assigned in part to RCH2. radicals from glycine units, which constitute about one-third of the total amino acid components in collagen, and in part to RNHCO radicals. The possible significance of the formation of active radicals during bone fracture is discussed.

Exercise, oxidative stress, and antioxidants: a review

Elemental and gaseous oxygen presents a conundrum in that it is simultaneously essential for and potentially destructive to human life. Traditionally the ability to consume large volumes of oxygen has been assumed to be totally beneficial to the organism. In the past 10 years it has become clear that oxygen radicals are generated even during normal resting metabolism. Nevertheless, such radicals are usually of no appreciable threat since a wide array of protective biochemical systems exist. However, under certain circumstances aerobic exercise may increase free radical production to a level that overwhelms those defenses. A broad array of nutrients such as vitamin C, vitamin E, beta-carotene, and so forth are known to suppress such radical events. This paper reviews the status of our knowledge relative to the potential benefits of nutritional modification in augmenting the organism's normal defense against harmful radical chemistry.

Glutathione-related enzyme activities and lipoperoxide levels in human internal mammary artery and ascending aorta. Relations with serum lipids

The relation among glutathione-related enzyme activities, thiobarbituric acid-reactive substances of the human aorta and internal mammary artery, and serum lipids was studied in 40 male patients undergoing coronary revascularization. Glutathione peroxidase and glutathione reductase activities were significantly higher in the internal mammary artery, whereas glutathione transferase activity was elevated in the aortic wall. Moreover, non-selenium-dependent glutathione peroxidase activity was detectable only in the aorta. The levels of thiobarbituric acid-reactive substances were significantly higher in the aorta. A positive correlation was found among the activity of glutathione peroxidase, glutathione reductase, and thiobarbituric acid-reactive substances in the internal mammary artery and total cholesterol, low density lipoprotein cholesterol, and triglycerides. In the aortic wall, a positive correlation among the activity of glutathione peroxidase, glutathione transferase, thiobarbituric acid-reactive substances, and the previously mentioned serum lipids was evident. In contrast, high density lipoprotein cholesterol was inversely related to enzymatic activities and thiobarbituric acid-reactive substances in both the internal mammary artery and aorta. In conclusion, significant differences in the levels of glutathione-related enzyme activities and thiobarbituric acid-reactive substances in the internal mammary artery and aorta were found, suggesting a different ability of the two tissues to counteract oxidative stress: the glutathione-related antioxidant properties and the level of lipid peroxidation in the arterial tissue seem to be specifically influenced by serum lipids.

Regional distribution of glutathione-related antioxidant defences in the normal rabbit aorta

In 6 normal rabbits, the aortic arch, the descending thoracic and the abdominal aorta were tested for non proteic thiol compounds, selenium-dependent and selenium-independent glutatione peroxidase, glutatione reductase, glutatione transferase and thiobarbituric acid reactive substances. The aortic arch showed the greatest content of non proteic thiol compounds and thiobarbituric acid reactive substances, associated to the highest activities of glutathione-related enzymes. However, not significant differences were detectable between aortic arch and descending thoracic aorta, except for the glutathione transferase activity (0.395 +/- 0.031 vs 0.330 +/- 0.053 U/mg protein, p less than 0.05). Furthermore, both aortic arch and descending thoracic aorta showed significantly higher values of non proteic thiol compounds (46.05 +/- 10.15% and 33 +/- 13.5%, p less than 0.05), selenium-dependent glutathione peroxidase activity (70.35 +/- 26% and 54.3 +/- 9.5%, p less than 0.05), glutathione reductase activity (25.4 +/- 7% and 18.4 +/- 4.5%, p less than 0.05) and thiobarbituric acid reactive substances (65.8 +/- 18% and 47.2 +/- 17%, p less than 0.05) with respect to the abdominal aorta. The selenium-independent glutathione peroxidase activity was not detectable. In conclusion, a biochemical gradient in glutathione-related antioxidant defences and thiobarbituric acid reactive substances proceeding from the proximal to the distal segments seems to exist in the normal rabbit aorta. These results could contribute to explain the non homogeneous distribution of experimental atherosclerosis in the rabbit aorta.

A new approach to the direct detection of free radicals in the intact myocardium

A new method for the direct ESR detection of free radicals in rat myocardial tissue is described. Isolated rat atria are continuously monitored for heart rate and contractile force; at the end of the experimental period the beating organs are inserted into quartz ESR tubes and immediately frozen in liquid nitrogen. Spectra obtained from these preparations show the presence of very weak radical signals. When ESR spectra are recorded on samples obtained from pools of rat atria pulverized under liquid nitrogen, the radical lines are markedly stronger than those observed for intact organs; contaminating metals are also frequently detected. These findings indicate that crushing or grinding procedures carried out under liquid nitrogen produce artifactual ESR active species. The new method described in the present paper does not involve mechanical interventions and therefore should yield reliable artifact-free results.