Measurement of oxidative stress in stroke-prone spontaneously hypertensive rat brain using in vivo electron spin resonance spectroscopy

Characterizing CD38 Expression and Enzymatic Activity in the Brain of Spontaneously Hypertensive Stroke-Prone Rats

Background: CD38 is a transmembrane glycoprotein that catabolizes nicotinamide adenine dinucleotide (NAD+) and is the main source for the age-dependent decrease in NAD+ levels. Increased CD38 enzymatic activity has been implicated in several neurological diseases. However, its role in the pathogenesis of cerebral small vessel disease (CSVD) remains unknown. We aimed to characterize CD38 expression and enzymatic activity in the brain of spontaneously hypertensive stroke-prone rats (SHRSP), a genetic model for hypertension and human CSVD, in comparison to age-matched normotensive Wistar Kyoto rats (WKY). Materials and Methods: Age-matched male 7- and 24-week-old WKY and SHRSP were studied. CD38 enzymatic activity was determined in the brain homogenate. Immunohistochemistry and Western Blotting (WB) were used to characterize CD38 expression and localize it in the different cell types within the brain. In addition, expression of nitric oxide synthase (NOS) isoforms and the levels of nitric oxide (NO), superoxide, nicotinamide dinucleotide (phosphate) NAD(P)H were measured the brain of in WKY and SHRSP. Results: CD38 expression and enzymatic activity were increased in SHRSP brains compared to age matched WKY starting at 7 weeks of age. CD38 expression was localized to the endothelial cells, astrocytes, and microglia. We also identified increased CD38 expression using WB with age in SHRSP and WKY. CD38 enzymatic activity was also increased in 24-week SHRSP compared to 7-week SHRSP. In association, we identified evidence of oxidative stress, reduced NO level, reduced NAD(P)H level and endothelial NOS expression in SHRSP compared to age matched WKY. NAD(P)H also decreased with age in WKY and SHRSP. Additionally, activation of astrocytes and microglia were present in SHRSP compared to WKY. Conclusions: CD38 is overexpressed, and its enzymatic activity is increased in SHRSP, a genetic model for marked hypertension and human CSVD. Our results suggest a potential role for CD38 enzymatic activation in the pathogenesis of CSVD and points to the need for future mechanistic and pharmacological studies.

Low-frequency ESR studies on permeable and impermeable deuterated nitroxyl radicals in corn oil solution

Low-frequency electron spin resonance studies were performed for 2 mM concentration of deuterated permeable and impermeable nitroxyl spin probes, 3-methoxycarbonyl-2,2,5,5-tetramethyl-pyrrolidine-1-oxyl and 3-carboxy-2,2,5,5,-tetramethyl-1-pyrrolidinyloxy in pure water and various concentrations of corn oil solution. The electron spin resonance parameters such as the line width, hyperfine coupling constant, g factor, rotational correlation time, permeability, and partition parameter were estimated. The broadening of line width was observed for nitroxyl radicals in corn oil mixture. The rotational correlation time increases with increasing concentration of corn oil, which indicates the less mobile nature of spin probe in corn oil mixture. The membrane permeability and partition parameter values were estimated as a function of corn oil concentration, which reveals that the nitroxyl radicals permeate equally into the aqueous phase and oil phase at the corn oil concentration of 50%. The electron spin resonance spectra demonstrate the permeable and impermeable nature of nitroxyl spin probes. From these results, the corn oil concentration was optimized as 50% for phantom studies. In this work, the corn oil and pure water mixture phantom models with various viscosities correspond to plasma membrane, and whole blood membrane with different hematocrit levels was studied for monitoring the biological characteristics and their interactions with permeable nitroxyl spin probe. These results will be useful for the development of electron spin resonance and Overhauser-enhanced magnetic resonance imaging modalities in biomedical applications.

Assessment of oxidative stress and antioxidant property using electron spin resonance (ESR) spectroscopy

The pathophysiology of hypertension or stroke is associated with an excess of ROS generation in the vascular system, and results in induction of various pathological cascades of cerebrovascular damage. We have demonstrated that electron spin resonance methods using a spin trap or spin probe will be useful for understanding redox status under conditions of oxidative stress in the spontaneously hypertensive rat or stroke-prone spontaneously hypertensive rat brain. We have used electron spin resonance imaging and noninvasive L-band electron spin resonance to characterize the higher degree of brain oxidative stress in the stroke-prone spontaneously hypertensive rat and spontaneously hypertensive rat than in the Wistar-Kyoto rat brain, and the lower extent of oxidative stress in the spontaneously hypertensive rat than in the stroke-prone spontaneously hypertensive rat brain. Indeed, we may be able to confirm propofol medium-chain triglyceride/long-chain triglyceride (MCT/LCT) as neuroprotective anesthesia and crocetin as antioxidant food factor against human stroke after screening for antioxidant properties in stroke models such as stroke-prone spontaneously hypertensive rat. Thus, our electron spin resonance biomedical application suggests that it could be used to assess antioxidant effects on oxidative stress in the brain using spontaneously hypertensive rat and stroke-prone spontaneously hypertensive rat. We hope that further advances in the instrumentation used for electron spin resonance imaging and the development of optimized nontoxic spin probes will make this technology even more promising for novel clinical prediction or noninvasive diagnosis of human stroke. After screening drugs or foods for antioxidant property using in vitro or in vivo electron spin resonance assessment, it will be possible to find and develop novel drugs or food factors with such properties for the prevention of stroke in the near future.

Gingival vascular functions are altered in type 2 diabetes mellitus model and/or periodontitis model

The association of vascular reactivity between diabetes and periodontal disease has not been clarified. Gingival blood flow was measured by laser Doppler flowmetry for 31 weeks in Wistar rats, Wistar rats orally challenged with Porphyromonas gingivalis (Wistar rats + Porphyromonas gingivalis), Goto-Kakizaki rats, and Goto-Kakizaki rats orally challenged with Porphyromonas gingivalis (Goto-Kakizaki rats + Porphyromonas gingivalis). Effects of alveolar bone resorption on periodontal tissue was enhanced in Wistar rats + Porphyromonas gingivalis, and Goto-Kakizaki rats, with this effect being significantly enhanced by Goto-Kakizaki rats + Porphyromonas gingivalis. Using the L-band electron spin resonance technique, we succeeded in measuring oxidative stress as decay rate constant (K(1) and K(2)) of 3-carbamoyl-2,2,5,5-tetramethylpyrrolidin-1-yloxy in the oral and maxillofacial region of the animal models. The decay rate constant (K(1)) of 3-carbamoyl-2,2,5,5-tetramethylpyrrolidin-1-yloxy was significantly greater in the oral and maxillofacial region of Goto-Kakizaki rats + Porphyromonas gingivalis compared to Wistar rats, Wistar rats + Porphyromonas gingivalis and Goto-Kakizaki rats groups. Gingival reactive hyperemia was attenuated by periodontal disease, and this effect was also remarkable in the diabetes mellitus model. Taken together, we found that vascular endothelial function was decreased in diabetes mellitus and/or periodontal disease animal models due to increasing oxidative stress in the gingival circulation.

Crocetin reduces the oxidative stress induced reactive oxygen species in the stroke-prone spontaneously hypertensive rats (SHRSPs) brain

Crocetin is a natural carotenoid compound of gardenia fruits and saffron, which has various effects in biological systems. In this study, we investigated the antioxidant effects of crocetin on reactive oxygen species such as hydroxyl radical using in vitro X-band electron spin resonance and spin trapping. Crocetin significantly inhibited hydroxyl radical generation compared with the control. Moreover, we performed electron spin resonance computed tomography ex vivo with the L-band electron spin resonance imaging system and determined the electron spin resonance signal decay rate in the isolated brain of stroke-prone spontaneously hypertensive rats, a high-oxidative stress model. Crocetin significantly reduced oxidative stress in the isolated brain by acting as a scavenger of reactive oxygen species, especially hydroxyl radical, as demonstrated by in vitro and ex vivo electron spin resonance analysis. The distribution of crocetin was also determined in the plasma and the brain of stroke-prone spontaneously hypertensive rats using high-performance liquid chromatography. After oral administration, crocetin was detected at high levels in the plasma and the brain. Our results suggest that crocetin may participate in the prevention of reactive oxygen species-induced disease due to a reduction of oxidative stress induced by reactive oxygen species in the brain.

Direct assessment by electron spin resonance spectroscopy of the antioxidant effects of French maritime pine bark extract in the maxillofacial region of hairless mice

Flavangenol, one of extract of French maritime pine bark, is a complex mixture of bioflavonoids with oligometric proanthocyanidins as the major constituents. These constituents, catechin and procyanidin B(1), are water-soluble derivatives of flavangenol. In this study, we investigated the antioxidant effects of flavangenol on reactive oxygen species such as hydroxyl radical, superoxide anion and singlet oxygen using electron spin resonance and spin trapping. The effect of flavangenol on oxidative stress in the skin from the maxillofacial region of hairless mice was investigated using an in vivo L-band electron spin resonance imaging system. Flavangenol attenuated oxidative stress in the maxillofacial skin by acting as a reactive oxygen species scavenger, as demonstrated by in vitro and in vivo electron spin resonance imaging analysis. The absorption and metabolism of flavangenol were also examined. After oral administration of flavangenol in human and rat, most of the catechin in plasma was in the conjugated form, while 45% to 78% of procyanidin B(1) was unconjugated, indicating that non-conjugated procyanidin B(1) would be active in the circulation. The ability of flavangenol to reduce reactive oxygen species levels in the circulation of the maxillofacial region suggests that this extract may be beneficial for skin protection from exposure to ultraviolet irradiation.

Direct assessment by electron spin resonance spectroscopy of the antioxidant effects of French maritime pine bark extract in the maxillofacial region of hairless mice

Flavangenol, one of extract of French maritime pine bark, is a complex mixture of bioflavonoids with oligometric proanthocyanidins as the major constituents. These constituents, catechin and procyanidin B₁, are water-soluble derivatives of flavangenol. In this study, we investigated the antioxidant effects of flavangenol on reactive oxygen species such as hydroxyl radical, superoxide anion and singlet oxygen using electron spin resonance and spin trapping. The effect of flavangenol on oxidative stress in the skin from the maxillofacial region of hairless mice was investigated using an in vivo L-band electron spin resonance imaging system. Flavangenol attenuated oxidative stress in the maxillofacial skin by acting as a reactive oxygen species scavenger, as demonstrated by in vitro and in vivo electron spin resonance imaging analysis. The absorption and metabolism of flavangenol were also examined. After oral administration of flavangenol in human and rat, most of the catechin in plasma was in the conjugated form, while 45% to 78% of procyanidin B₁ was unconjugated, indicating that non-conjugated procyanidin B₁ would be active in the circulation. The ability of flavangenol to reduce reactive oxygen species levels in the circulation of the maxillofacial region suggests that this extract may be beneficial for skin protection from exposure to ultraviolet irradiation.

THE AUTODIGESTION HYPOTHESIS AND RECEPTOR CLEAVAGE IN DIABETES AND HYPERTENSION

One of the key features of cardiovascular complications, such as hypertension or diabetes, is that they often appear at the same time in the same individual together with other forms of co-morbidities. While clinically a recognized phenomenon, no molecular mechanism for such co-morbidities has received universal acceptance. We propose a new hypothesis that provides a molecular basis for co-morbidities in hypertension due to unchecked proteolytic activity and receptor destruction. Testing of the hypothesis in the spontaneously hypertensive rat reveals an unchecked matrix metalloproteinase and serine protease activity in plasma and on several cardiovascular and parenchymal cells. The elevated proteolytic activity causes extracellular cleavage of multiple receptor types, such that cleavage of one receptor type leads to loss of the function carried out by this receptor. Proteolytic cleavage of the extracellular domain of the β(2) adrenergic receptor in arteries and arterioles causes vasoconstriction and elevation of the central blood pressure while cleavage of the extracellular domain of the insulin receptor leads to insulin resistance and lack of transmembrane glucose transport. A diverse set of cell dysfunctions in the spontaneously hypertensive rat are accompanied by cleavage of the membrane receptors that are involved in these functions. Chronic inhibition of the unchecked protease activity in the spontaneously hypertensive rat serves to restore the extracellular receptor density and alleviates the corresponding cell dysfunctions. The mild unchecked proteolytic activity in the spontaneously hypertensive rat points towards a chronic autodigestion process as a contributor to the end organ injury encountered in this rat strain. The presence of various soluble receptors, which consist of extracellular fragments of membrane receptors, in the plasma of hypertensive and diabetic patients suggest that the autodigestion process may also be present in man.

Reactive oxygen species (ROS) reduce the expression of BRAK/CXCL14 in human head and neck squamous cell carcinoma cells

The present study investigated the effects of oxidative stress induced by reactive oxygen species (ROS), such as hydrogen peroxide (H(2)O(2)) and hydroxyl radical (HO(*)), on the expression of both BRAK , which is also known as non-ELR motif angiostatic CXC chemokine ligand 14 (CXCL14), in head and neck squamous cell carcinoma (HNSCC) cells. When HNSCC cells were cultured in the presence of ROS, the expression of BRAK was significantly decreased whereas that of IL-8 was increased. Interestingly, the effects on the expression of both genes in HNSCC cells were much greater with HO(blacksquare, square, filled) than with H(2)O(2). The effects of ROS on both BRAK and IL-8 expression were attenuated by pre-treatment with N-acetyl-L-cysteine (NAC), epidermal growth factor receptor (EGFR), and mitogen-activated protein kinase (MAPK) inhibitors. These results indicate that oxidative stress induced by H(2)O(2) or HO(*) stimulates angiogenesis and tumuor progression by altering the gene expression of BRAK and IL-8 via the EGFR/MEK/ERK pathway in human HNSCC cells.

[Biomedical application of electron spin resonance (ESR) spectroscopy--assessment of antioxidant property for development of drugs]

Reactive oxygen species (ROS) are associated with oxidative stress-mediated alterations under pathophysiological conditions, and particularly brain ischemia, brain tumor, and neurodegenerative diseases. Electron spin resonance (ESR) is recognized as one of the most powerful techniques available for the detection of ROS in tissues and cells. We previously developed an in vitro ESR-based technique for the detection of free radical reactions in biological systems. In addition, significant advances in the field of in vivo ESR techniques over recent years have now made it possible to visualize the distribution and metabolism of oxidative stress, and the degree of tissue oxygenation in vivo. Nitroxyl radicals are very useful as exogenous spin probes for measuring free radical distribution, oxygen concentration, and redox metabolism by in vivo ESR in biological systems, using a combination of these ESR methods collectively focused on animal models of disease such as spontaneously hypertensive rat (SHR) or stroke-prone SHR (SHRSP) for the assessment of antioxidant property of drugs. Our results suggest that ESR could be applied to the assessment of antioxidant property on oxidative stress in target organs, especially brain, using animal disease models, SHR or SHRSP. After screening drugs for antioxidant property using such as in vitro or in vivo ESR assessment, we'll be able to develop and find novel antioxidant drugs for ROS-induced brain disease in the near future.

Application of in vivo ESR/spin-probe technique to monitor tumor in vivo in mouse footpad

The redox status of tumors inoculated into the footpads of mice was investigated by using an in vivo ESR/spin-probe technique. A single-cell suspension of a metastatic subclone of colon carcinoma NL-17 was inoculated into the footpads of Balb/c mice. At 12, 24, 48, and 96 h after the inoculation, a spin probe, either carbamoylor carboxy-PROXYL, was intravenously injected, and then the ESR spectra of each footpad were separately obtained under a one-dimensional magnetic-field gradient. The change in the ESR signal intensity of the spin probe was closely related to the tumor volume in the footpads, but no significant difference was observed between carbamoyl- and carboxy-PROXYL. The in vivo ESR signal decay of carbamoyl-PROXYL, which is related to the conversion of the nitroxyl radical to hydroxylamine, was enhanced in the inoculated footpads but not in the reference one. The ESR signal decay was not influenced by coadministration of radical scavengers, SOD, catalase, mannitol, or dimethylthiourea, suggesting that the redox status but not reactive oxygen species generation played a role in the enhanced signal decay.

Microvascular display of xanthine oxidase and NADPH oxidase in the spontaneously hypertensive rat

OBJECTIVE

Oxygen free radical production in hypertension may be associated with elevated arteriolar tone and organ injury. Previous results suggest an enhanced level of oxygen free radical formation in microvascular endothelium and in circulating neutrophils associated with xanthine oxidase activity in the spontaneously hypertensive rats (SHR) compared with their normotensive controls, the Wistar Kyoto rats (WKY). The aim of this study was to gain more detailed understanding of where oxidative enzymes are located in the microcirculation.

METHODS

An approach was developed to delineate the cellular distribution of two selected oxidative enzymes, xanthine oxidase and nicotinamide adenine dinucleotide phosphate (NADPH) dependent oxidase (protein 67-kDa fraction). Immunolabeling with peroxidase substrate was utilized, which permits full delineation of the primary antibody in all microvascular structures of the mesentery.

RESULTS

Xanthine oxidase is present in the endothelium of all segments of the microcirculation, in mast cells, and in parenchymal cells of the mesentery. NADPH oxidase can be detected in the endothelium, leukocytes, and mast cells and with lower levels in parenchymal cells. The mesentery of WKY and SHR has similar enzyme distributions with enhancements on the arteriolar and venular side of the microcirculation that coincide with the sites of enhanced free radical production recently reported. Immune label measurements under standardized conditions indicate that both enzymes are significantly enhanced in the SHR. Adrenalectomy, which serves to reduce the blood pressure and free radical production of the SHR to normotensive levels, leads to a reduction of NADPH and xanthine oxidase to normotensive levels, while supplementation of adrenalectomized SHR with dexamethasone significantly increases the oxidase expression in several parts of the microcirculation to levels above the WKY rats.

CONCLUSION

The results indicate that enhanced expression of NADPH and xanthine oxidase in the SHR depends on an adrenal pathway that is detectable in the arteriolar and venular network at high and low pressure regions of the circulation.

Biting reduces acute stress-induced oxidative stress in the rat hypothalamus

We investigated the inhibitory effect of para-masticatory activity, namely biting, on restraint stress-induced oxidative stress. A blood brain barrier-permeable nitroxyl spin probe, 3-methoxycarbonyl-2,2,5,5,-tetramethylpyrrolidine-1-oxyl (MC-PROXYL), was administered to rats and L-band electron spin resonance (ESR) and ESR-computerized tomography (ESR-CT) imaging were used to show that the decay rate constant of MC-PROXYL in the hypothalamus of isolated brain after 30 min of restraint stress was more rapid than in unrestrained control rats, suggesting that restraint was associated with oxidative stress. Interestingly, biting during restraint stress caused the decay rate constant of MC-PROXYL in isolated brain to approach that of the control group. These observations suggest that biting suppresses oxidative stress induced by restraint stress, and that the anti-stress effect of masticatory motor activity movements, such as biting, are important for reducing the adverse effects associated with exposure to psychological stressors.

Molecular effects of fermented papaya preparation on oxidative damage, MAP Kinase activation and modulation of the benzo[a]pyrene mediated genotoxicity

The involvement of oxidative and nitrosative stress mechanisms in several biological and pathological processes including aging, cancer, cardiovascular and neurodegenerative diseases has continued to fuel suggestions that processes can potentially be modulated by treatment with free-radical scavengers and antioxidant. The fermented papaya preparation (FPP) derived from Carica papaya Linn was investigated for its ability to modulate oxidative DNA damage due to H2O2 in rat pheochromocytoma (PC12) cells and protection of brain oxidative damage in hypertensive rats. Cells pre-treated with FPP (50 microg/ml) prior to incubation with H2O2 had significantly increased viability and sustenance of morphology and shape. The human hepatoma (HepG2) cells exposed to H2O2 (50 microM) showed an olive tail moment of 10.56 +/- 1.44 compared to 1.37 +/- 0.29 of the solvent control. A significant reduction (P < or = 0.05) of DNA damage was observed at concentrations > or = 10 microg/ml FPP, with 50 microg/ml FPP reducing the genotoxic effect of H2O2 by about 1.5-fold compared to only H2O2 exposed cells.

Measurement of oxidative stress in the rodent brain using computerized electron spin resonance tomography

The strategy of this study was to improve the electronic spin resonance (ESR) application used to detect free radical-induced oxidative stress in animal models. We have developed an in vivo ESR imaging system with high-quality ESR-computed tomography (CT) images by using a nitroxyl spin probe--BBB-permeable, 3-methoxycarbonyl-2,2,5,5-tetramethyl-pyrrolidine-1-yloxy (MC-PROXYL)--in living small animals. We first measured the distribution of MC-PROXYL in the head region of a living mouse by using ESR-CT imaging after treatment with MC-PROXYL. In the ESR-CT experiments, it was clearly observed that MC-PROXYL was well distributed in the brain of head region of a living mouse. The ESR-CT images taken after treatment with MC-PROXYL demonstrate that the decay of MC-PROXYL in the isolated brain of a spontaneously hypertensive rat (SHR) was more rapid than that in a Wister Kyoto rat. ESR-CT analysis revealed that the region of rapid decay might be located in the cerebral cortex of the isolated brain of an SHR. These results suggest that the present study of ESR-CT imaging would be a useful tool for monitoring and detecting the locations of oxidative stress in the brains of rodent animal models.

Protective effect of antioxidant ebselen (PZ51) on the cerebral cortex of stroke-prone spontaneously hypertensive rats

An increase in reactive oxygen species has been shown to play a role in perpetuating hypertension and cerebral injury in stroke-prone spontaneously hypertensive rats (SHRsp). Lipid peroxidation in the cerebral cortex is much more intense in SHRsp after establishment of severe hypertension as compared to that in normotensive Wistar-Kyoto rats (WKY). Cortical neurons from SHRsp are more vulnerable to hypoxia and hyponutritional conditions. We sought to investigate whether long-term administration of seleno-glutathione peroxidase mimic ebselen (PZ51) would have a protective effect on cortical neurons in SHRsp, and, if so, the possible mechanisms of this effect. Twenty-two 8-week-old SHRsp were randomized into a PZ51 group and control group. Age-matched WKY were used as normal controls. We examined the levels of malonaldehyde (MDA) and nitric oxide (NO) in the cerebral cortex (CC) homogenate, detected the three isoforms of nitric oxide synthase (NOS) by Western blotting, and examined cortical neurons by transmission electron microscopy. The results showed that PZ51 treatment significantly decreased both MDA and NO in the CC, inhibited inducible nitric oxide synthase (iNOS) protein expression, and alleviated the damage to cortical neurons compared to the findings for the control group. In conclusion, the present study showed that PZ51 administration suppressed lipid peroxidation and inhibited iNOS protein expression in CC homogenate, and it was suggested that these mechanisms may play a role in the protective effects of PZ51 on cortical neurons of SHRsp.

Control of oxidative stress in microcirculation of spontaneously hypertensive rats

One mechanism for organ damage in individuals with arterial hypertension may be due to oxygen free radical production. This study was designed to localize free radicals in a microvascular network of mature spontaneously hypertensive rats (SHRs) and normotensive Wistar-Kyoto (WKY) rats. Because glucocorticoids play a role in pressure elevation of SHRs, we investigated their role in microvascular free radical formation. Oxygen radical production in mesentery was detected by tetranitroblue tetrazolium reduction to formazan aided by digital light-absorption measurements. Formazan deposits were observed in the endothelial cells and lumens of all microvessels and in lymphatic endothelia but were fewer in tissue parenchyma. The formazan distribution in younger (14-16 wk old) WKY rats and SHRs was heterogeneous with low values in capillaries and small arterioles/venules (<30 microm) but enhanced deposits in larger venules. Adrenalectomy served to reduce the formazan density in SHRs to the level of WKY rats, whereas dexamethasone supplementation of the adrenalectomized rats caused elevation in the larger venules of SHRs. In older (40 wk old) SHRs, formazan levels were elevated in all hierarchies of microvessels. After pressure reduction was employed with chronic hydralazine treatment, the formazan deposits were reduced in all locations of the microcirculation in both WKY rats and SHRs. Elevated formazan deposits were also found in lymphatic endothelium. These results suggest that oxygen free radical production is elevated in both high- and low-pressure regions of SHR microcirculation via a process that is controlled by glucocorticoids. Older SHRs have higher formazan levels than younger SHRs in all microvessels. Chronic hydralazine treatment, which serves to reduce arterial blood pressure, attenuates tetranitroblue tetrazolium reduction in WKY rats and SHRs even in venules of the microcirculation, which has no micropressure elevation. Free radical production may be a more global condition in SHRs and may not be limited to arteries and arterioles.

Oxidative stress in atherogenesis and arterial thrombosis: the disconnect between cellular studies and clinical outcomes

Atherosclerosis is a multifactorial disease for which the molecular etiology of many of the risk factors is still unknown. As no single genetic marker or test accurately predicts cardiovascular death, phenotyping for markers of inflammation may identify the individuals at risk for vascular diseases. Reactive oxygen species (ROS) are key mediators of signaling pathways that underlie vascular inflammation in atherogenesis, starting from the initiation of fatty streak development through lesion progression to ultimate plaque rupture. Various animal models of atherosclerosis support the notion that ROS released from NAD(P)H oxidases, xanthine oxidase, lipoxygenases, and enhanced ROS production from dysfunctional mitochondrial respiratory chain indeed have a causatory role in atherosclerosis and other vascular diseases. Human investigations also support the oxidative stress hypothesis of atherogenesis. This is further supported by the observed impairment of vascular function and enhanced atherogenesis in animal models that have deficiencies in antioxidant enzymes. The importance of oxidative stress in atherosclerosis is further emphasized because of its role as a unifying mechanism across many vascular diseases. The main contraindicator for the role oxidative stress plays in atherosclerosis is the lack of effectiveness of antioxidants in reducing primary endpoints of cardiovascular death and morbidity. However, this lack of effectiveness by itself does not negate the existence or causatory role of oxidative stress in vascular disease. Lack of proven markers of oxidative stress, which could help to identify a subset of population that can benefit from antioxidant supplementation, and the complexity and subcellular localization of redox reactions, are among the factors responsible for the mixed outcomes in the use of antioxidants for the prevention of cardiovascular diseases. To better understand the role of oxidative stress in vascular diseases, future studies should be aimed at using advances in mouse and human genetics to define oxidative stress phenotypes and link phenotype with genotype.

Oxidative stress and vascular disease

Growing evidence indicates that chronic and acute overproduction of reactive oxygen species (ROS) under pathophysiologic conditions is integral in the development of cardiovascular diseases (CVD). These ROS can be released from nicotinamide adenine dinucleotide (phosphate) oxidase, xanthine oxidase, lipoxygenase, mitochondria, or the uncoupling of nitric oxide synthase in vascular cells. ROS mediate various signaling pathways that underlie vascular inflammation in atherogenesis: from the initiation of fatty streak development through lesion progress to ultimate plaque rupture. Various animal models of oxidative stress support the notion that ROS have a causal role in atherosclerosis and other cardiovascular diseases. Human investigations also support the oxidative stress hypothesis of atherosclerosis. Oxidative stress is the unifying mechanism for many CVD risk factors, which additionally supports its central role in CVD. Despite the demonstrated role of antioxidants in cellular and animal studies, the ineffectiveness of antioxidants in reducing cardiovascular death and morbidity in clinical trials has led many investigators to question the importance of oxidative stress in human atherosclerosis. Others have argued that the prime factor for the mixed outcomes from using antioxidants to prevent CVD may be the lack of specific and sensitive biomarkers by which to assess the oxidative stress phenotypes underlying CVD. A better understanding of the complexity of cellular redox reactions, development of a new class of antioxidants targeted to specific subcellular locales, and the phenotype-genotype linkage analysis for oxidative stress will likely be avenues for future research in this area as we move toward the broader use of pharmacological and regenerative therapies in the treatment and prevention of CVD.

Assessment of Oxidative Stress in the Spontaneously Hypertensive Rat Brain Using Electron Spin Resonance (ESR) Imaging and in Vivo L-Band ESR

This study examined the blood brain barrier (BBB)-permeable nitroxyl compound, 3-methoxycarbonyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl (MC-PROXYL), as a spin probe for the assessment of oxidative stress in the brain by electron spin resonance (ESR) imaging and in vivo L-band ESR. Preliminary comparisons were made by ESR imaging of MC-PROXYL in the isolated brains of normal Wistar-Kyoto rats (WKY), spontaneously hypertensive rats (SHR), and stroke prone SHR (SHRSP). The decay of the ESR images of MC-PROXYL in the isolated brains was faster in SHR than in normal WKY, but was only moderate in SHRSP. In addition, the decay rate of MC-PROXYL in the heads of live rats, as measured noninvasively by L-band ESR, was faster in SHR than in WKY, and was slower in SHR than in SHRSP. Taken together, our data suggest that the oxidative stress of SHR is not as high as that in high oxidative stress animal models such as SHRSP. This is the first study to present reconstructed 3D images of the distribution of MC-PROXYL in the isolated SHR brain. The ESR technique employed herein appears to be a powerful tool for evaluating oxidative stress and for detecting the region of oxidative stress in the brain of SHR.