Implication of CO inactivation on myoglobin function

Elevated plasma myoglobin level is closely associated with type 2 diabetic kidney disease

BACKGROUND

Diabetic kidney disease (DKD) is the most frequent complication in patients with type 2 diabetes mellitus (T2DM). It causes a chronic and progressive decline in kidney function, and ultimately patients require renal replacement therapy. To date, an increasing number of clinical studies have been conducted to explore the potential and novel biomarkers, which can advance the diagnosis, estimate the prognosis, and optimize the therapeutic strategies at the early stage of DKD. In the current study, we sought to investigate the association of plasma myoglobin with DKD.

METHODS

A total of 355 T2DM patients with DKD and 710 T2DM patients without DKD were enrolled in this study. Laboratory parameters including blood cell count, hemoglobin A1c, biochemical parameters, and plasma myoglobin were recorded. Patients were classified on admission according to the tertile of myoglobin and clinical parameters were compared between the groups. Pearson correlation analysis, linear regression, logistic regression, receiver operating characteristics (ROC) analysis, and spline regression were performed.

RESULTS

Plasma myoglobin significantly increased in patients with DKD and was associated with renal function and inflammatory parameters. Plasma myoglobin was an independent risk factor for the development of DKD. The area under ROC curve of myoglobin was 0.831. Spline regression showed that there was a significant linear association between DKD incidence and a high level of plasma myoglobin when it exceeded 36.4 mg/mL.

CONCLUSIONS

This study shows that elevated plasma myoglobin level is closely associated with the development of kidney injury in patients with T2DM.

Carbon Monoxide Signaling: Examining Its Engagement with Various Molecular Targets in the Context of Binding Affinity, Concentration, and Biologic Response

Carbon monoxide (CO) has been firmly established as an endogenous signaling molecule with a variety of pathophysiological and pharmacological functions, including immunomodulation, organ protection, and circadian clock regulation, among many others. In terms of its molecular mechanism(s) of action, CO is known to bind to a large number of hemoproteins with at least 25 identified targets, including hemoglobin, myoglobin, neuroglobin, cytochrome c oxidase, cytochrome P450, soluble guanylyl cyclase, myeloperoxidase, and some ion channels with dissociation constant values spanning the range of sub-nM to high μM. Although CO's binding affinity with a large number of targets has been extensively studied and firmly established, there is a pressing need to incorporate such binding information into the analysis of CO's biologic response in the context of affinity and dosage. Especially important is to understand the reservoir role of hemoglobin in CO storage, transport, distribution, and transfer. We critically review the literature and inject a sense of quantitative assessment into our analyses of the various relationships among binding affinity, CO concentration, target occupancy level, and anticipated pharmacological actions. We hope that this review presents a picture of the overall landscape of CO's engagement with various targets, stimulates additional research, and helps to move the CO field in the direction of examining individual targets in the context of all of the targets and the concentration of available CO. We believe that such work will help the further understanding of the relationship of CO concentration and its pathophysiological functions and the eventual development of CO-based therapeutics. SIGNIFICANCE STATEMENT: The further development of carbon monoxide (CO) as a therapeutic agent will significantly rely on the understanding of CO's engagement with therapeutically relevant targets of varying affinity. This review critically examines the literature by quantitatively analyzing the intricate relationships among targets, target affinity for CO, CO level, and the affinity state of carboxyhemoglobin and provide a holistic approach to examining the molecular mechanism(s) of action for CO.

Attenuation of Glucose-Induced Myoglobin Glycation and the Formation of Advanced Glycation End Products (AGEs) by (R)-α-Lipoic Acid In Vitro

High-carbohydrate containing diets have become a precursor to glucose-mediated protein glycation which has been linked to an increase in diabetic and cardiovascular complications. The aim of the present study was to evaluate the protective effect of (R)-α-lipoic acid (ALA) against glucose-induced myoglobin glycation and the formation of advanced glycation end products (AGEs) in vitro. Methods: The effect of ALA on myoglobin glycation was determined via the formation of AGEs fluorescence intensity, iron released from the heme moiety of myoglobin and the level of fructosamine. The extent of glycation-induced myoglobin oxidation was measured via the levels of protein carbonyl and thiol. Results: The results showed that the co-incubation of ALA (1, 2 and 4 mM) with myoglobin (1 mg/mL) and glucose (1 M) significantly decreased the levels of fructosamine, which is directly associated with the decrease in the formation of AGEs. Furthermore, ALA significantly reduced the release of free iron from myoglobin which is attributed to the protection of myoglobin from glucose-induced glycation. The results also demonstrated a significant protective effect of ALA on myoglobin from oxidative damage, as seen from the decreased protein carbonyls and increased protein thiols. Conclusion: The anti-glycation properties of ALA suggest that ALA supplementation may be beneficial in the prevention of AGEs-mediated diabetic and cardiovascular complications.

(R)-α-Lipoic acid inhibits fructose-induced myoglobin fructation and the formation of advanced glycation end products (AGEs) in vitro

Background

Fructose-mediated protein glycation (fructation) has been linked to an increase in diabetic and cardiovascular complications due to over consumption of high-fructose containing diets in recent times. The objective of the present study is to evaluate the protective effect of (R)-α-lipoic acid (ALA) against fructose-induced myoglobin fructation and the formation of advanced glycation end products (AGEs) in vitro.

Methods

The anti-glycation activity of ALA was determined using the formation of AGEs fluorescence intensity, iron released from the heme moiety of myoglobin and the level of fructosamine. The fructation-induced myoglobin oxidation was examined using the level of protein carbonyl content and thiol group estimation.

Results

The results showed that co-incubation of myoglobin (1 mg/mL), fructose (1 M) and ALA (1, 2 and 4 mM) significantly inhibited the formation of AGEs during the 30 day study period. ALA markedly decreased the levels of fructosamine, which is directly associated with the reduction of AGEs formation. Furthermore, ALA significantly reduced free iron release from myoglobin which is attributed to the protection of myoglobin from fructose-induced glycation. The results also demonstrated a significant protective effect of ALA on myoglobin oxidative damages, as seen from decreased protein carbonyl content and increased protein thiols.

Conclusion

These findings provide new insights into the anti-glycation properties of ALA and emphasize that ALA supplementation is beneficial in the prevention of AGEs-mediated diabetic and cardiovascular complications.

Differential Interaction of Myoglobin with Select Fatty Acids of Carbon Chain Lengths C8 to C16

Previous studies have shown that palmitic acid (PAM) and oleic acid (OLE) can bind myoglobin (Mb). How fatty acids (FA) with different carbon chain lengths and sulfate substitution interact with Mb remains uncertain. Indeed, C8:0 and C10:0 fatty acids do not perturb the intensities of the ¹H-NMR MbCN signal intensity at FA:Mb ratios below 2:1. Starting with C12:0, C12:0-C16:0, FA induce a noticeable spectral change. C12:0 and C14:0 FA affect both the 5- and 8-heme methyl signals, whereas the C16:0 FA perturbs only the 8-heme methyl signal. All C12:0-C16:0 saturated FA induce upfield shifts in the -CH₂ peak of different FA in the presence of Mb. Increasing the apparent solubility with a sulfate group substitution enhances the FA interaction of lauric sulfate (LAU 1-SO₄) but not palmitate sulfate acid (PAM 1-SO₄). The detergent (DET) property of FA has no significant contribution. Common positive, neutral, and negative DET at DET:Mb ratio of 1:1 induce no perturbation of the MbCN spectra. The experiment observations establish a basis to investigate the molecular mechanism underlying the FA interaction with Mb.

Effect of fatty acid interaction on myoglobin oxygen affinity and triglyceride metabolism

Recent studies have suggested myoglobin (Mb) may have other cellular functions in addition to storing and transporting O₂. Indeed, NMR experiments have shown that the saturated fatty acid (FA) palmitate (PA) can interact with myoglobin (Mb) in its ligated state (MbCO and MbCN) but does not interact with Mb in its deoxygenated state. The observation has led to the hypothesis that Mb can also serve as a fatty acid transporter. The present study further investigates fatty acid interaction with the physiological states of Mb using the more soluble but unsaturated fatty acid, oleic acid (OA). OA binds to MbCO but does not bind to deoxy Mb. OA binding to Mb, however, does not alter its O₂ affinity. Without any Mb, muscle has a significantly lower level of triglyceride (TG). In Mb knock-out (MbKO) mice, both heart and skeletal muscles have lower level of TG relative to the control mice. Training further decreases the relative TG in the MbKO skeletal muscle. Nevertheless, the absence of Mb and lower TG level in muscle does not impair the MbKO mouse performance as evidenced by voluntary wheel running measurements. The results support the hypothesis of a complex physiological role for Mb, especially with respect to fatty acid metabolism.

COHb Level and High-Sensitivity Cardiac Troponin T in 2012 in Bursa, Turkey: A Retrospective Single-Center Study

Background

Intoxication due to carbon monoxide (CO) is one of the most common types of poisoning. Cardiac effects of carboxyhemoglobin (COHb) range from simple arrhythmias to myocardial infarction.

Objectives

The current study aimed to investigate the relationship between blood carboxyhemoglobin and high-sensitivity cardiac troponin T (hs-cTnT) level with a highly sensitive assay in patients with acute carbon monoxide poisoning.

Patients and Methods

This retrospective study was conducted on 141 (54 males and 87 females) patients, with acute CO intoxication, admitted to the Sevket Yilmaz research and education hospital emergency unit during a one-year period (January 2012 - January 2013). The patients were divided into three groups based on COHb levels: Group I, mild COHb level < 15%; Group II, COHb between 15% and 25%; Group III, severe acute CO intoxication COHb levels > 25%. COHb, hs-cTnT (Stat), creatine kinase (CK) and creatine kinase-myocardial band (CK-MB) levels were measured on admission.

Results

The mean age of the patients was 38 ± 16 years. COHb levels ranged from 8 to 35. hs-cTnT levels on inclusion in this study were slightly different between the groups (P = 0.05). COHb levels with hs-cTnT values were weakly correlated (r = 0.173, P = 0.041); on the other hand, CK-MB levels were not correlated with COHb (r = 0.013, P = 0.883).

Conclusions

In patients without clear signs of myocardial infarction, even mild CO poisoning was associated with quantifiable circulating levels of hs-cTnT when TnT was measured using a highly sensitive assay in the current study patients. Plasma levels of the hs-TnT and CK-MB assays were not correlated with the COHb levels in the current study patients.

Interaction of myoglobin with oleic acid

Previous studies have shown that palmitate (PA) can interact with myoglobin (Mb). The present study has investigated the interaction of the more soluble unsaturated fatty acid, oleic acid (OA). Indeed, (1)H NMR measurements of the Mb signal during OA titration also show signal changes consistent with specific and non-specific binding. At OA:Mb ratio<4:1, OA perturbs selectively the 8-heme methyl signal, consistent with a local and specific fatty acid-protein interaction. As OA:Mb ratio increases from 4:1 to 40:1, all hyperfine shifted MbCN signals decrease, consistent with a non-selective, global perturbation of the protein. The pH titration analysis indicates that the observed OA methylene signal in the presence of Mb reflects a non-specific interaction and does not originate from a shift in the lamella-micelle equilibrium. Given the OA interaction with Mb, a fatty acid flux model suggests that Mb can play a fatty acid transport role under certain physiological conditions.

Palmitate interaction with physiological states of myoglobin

BACKGROUND

Previous studies have shown that palmitate (PA) can bind specifically and non-specifically to Fe(III)MbCN. The present study has observed PA interaction with physiological states of Fe(II)Mb, and the observations support the hypothesis that Mb may have a potential role in facilitating intracellular fatty acid transport.

METHODS

1H NMR spectra measurements of the Mb signal during PA titration show signal changes consistent with specific and non-specific binding.

RESULTS

Palmitate (PA) interacts differently with physiological states of Mb. Deoxy Mb does not interact specifically or non-specifically with PA, while the carbonmonoxy myoglobin (MbCO) interaction with PA decreases the intensity of selective signals and produces a 0.15ppmupfield shift of the PAmethylene peak. The selective signal change upon PA titration provides a basis to determine an apparent PA binding constant,which serves to create a model comparing the competitive PA binding and facilitated fatty acid transport of Mb and fatty acid binding protein(FABP).

CONCLUSIONS

Given contrasting PA interaction of ligated vs. unligated Mb, the cellular fatty acid binding protein(FABP) and Mb concentration in the cell, the reported cellular diffusion coefficients, the PA dissociation constants from ligated Mb and FABP, a fatty acid flux model suggests that Mb can compete with FABP transporting cellular fatty acid.

GENERAL SIGNIFICANCE

Under oxygenated conditions and continuous energy demand, Mb dependent fatty acid transport could influence the cell's preference for carbohydrate or fatty acid as a fuel source and regulate fatty acid metabolism.

Expression patterns and adaptive functional diversity of vertebrate myoglobins

Recent years have witnessed a new round of research on one of the most studied proteins - myoglobin (Mb), the oxygen (O2) carrier of skeletal and heart muscle. Two major discoveries have stimulated research in this field: 1) that Mb has additional protecting functions, such as the regulation of in vivo levels of the signaling molecule nitric oxide (NO) by scavenging and generating NO during normoxia and hypoxia, respectively; and 2) that Mb in vertebrates (particularly fish) is expressed as tissue-specific isoforms in other tissues than heart and skeletal muscle, such as vessel endothelium, liver and brain, as found in cyprinid fish. Furthermore, Mb has also been found to protect against oxidative stress after hypoxia and reoxygenation and to undergo allosteric, O2-linked S-nitrosation, as in rainbow trout. Overall, the emerging evidence, particularly from fish species, indicates that Mb fulfills a broader array of physiological functions in a wider range of different tissues than hitherto appreciated. This new knowledge helps to better understand how variations in Mb structure and function may correlate with differences in animals' lifestyles and hypoxia-tolerance. This review integrates old and new results on Mb expression patterns and functional properties amongst vertebrates and discusses how these may relate to adaptive variations in different species. This article is part of a special issue entitled: Oxygen Binding and Sensing Proteins.

Carbon monoxide re-breathing during low-flow anaesthesia in infants and children

BACKGROUND

Carbon monoxide (CO) has been detected within anaesthesia breathing systems. One potential source in this setting is exhaled endogenous CO. We hypothesized that CO is re-breathed during low-flow anaesthesia (LFA) in infants and children.

METHODS

Twenty children (age 2 months-7 yr) undergoing general anaesthesia were evaluated in a prospective observation study. LFA was established for 60 min followed by high-flow anaesthesia (HFA) for the next 60 min. Exhaled and inspired CO were measured every 5 min within the breathing circuit. Carboxyhaemoglobin (COHb%) was measured at baseline, at 60 min, after LFA, and at 120 min, after HFA.

RESULTS

CO concentrations increased during LFA. Inspired CO peaked at 14 ppm. During HFA, exhaled CO levels remained constant whereas inspired CO decreased markedly. Exhaled and inspired CO during HFA differed significantly from LFA. The trajectory of change in exhaled and inspired CO was most closely associated with the fresh-gas flow (FGF):minute ventilation ratio. COHb% significantly increased in children <2 yr of age at 60 min after LFA and remained increased.

CONCLUSIONS

LFA increased exhaled and inspired CO and increased COHb% in children <2 yr of age. Thus, LFA resulted in re-breathing of exhaled CO and exposure, especially in the youngest children. Re-breathing exhaled gas during LFA could pose a risk for an acute CO exposure in patients who have elevated COHb and high baseline levels of exhaled CO. If practitioners match or exceed minute ventilation with FGF to avoid LFA, CO re-breathing can be limited.

‘It's hollow’: the function of pores within myoglobin

Despite a century of research, the cellular function of myoglobin (Mb), the mechanism regulating oxygen (O2) transport in the cell and the structure–function relationship of Mb remain incompletely understood. In particular, the presence and function of pores within Mb have attracted much recent attention. These pores can bind to Xe as well as to other ligands. Indeed, recent cryogenic X-ray crystallographic studies using novel techniques have captured snapshots of carbon monoxide (CO) migrating through these pores. The observed movement of the CO molecule from the heme iron site to the internal cavities and the associated structural changes of the amino acid residues around the cavities confirm the integral role of the pores in forming a ligand migration pathway from the protein surface to the heme. These observations resolve a long-standing controversy – but how these pores affect the physiological function of Mb poses a striking question at the frontier of biology.

Direct measurement of myocardial oxygen tension and high energy phosphate content under varying ventilatory conditions in rabbits

Effective myocardial oxygen supply should not be compromised during cardiac surgery as it is essential to avoid circulatory and cardiac dysfunction. Local measurement of myocardial oxygen partial pressure (pO2) was therefore introduced into the operative monitoring of myocardial ischemia. The aim of the present study was to assess whether myocardial oxygen partial pressure correlates with the content of high energy phosphates (HEPs). Seven male rabbits were examined in parallel with measurement of myocardial pO2 by an implanted Clark electrode and 31phosphorus-NMR spectroscopy. The ventilatory management established hyperoxygenation followed by systemic hypoxia with hypercapnia for 20 min. Additionally, analysis of end-expiratory gas composition in combination with blood gas analysis was performed simultaneously, and hemodynamic parameter was recorded. Under hypoxic conditions the cardiovascular system was severely compromised, whereas the myocardial pO2 was only moderately impaired (pO2M 45.0+/-16.0 mm Hg). Immediately before cardiac arrest, low values of arterial and venous pO2 were found (17.6+/-6.0 and 12.9+/-6.1 mm Hg). In contrast to near normal myocardial pO2, HEP content in the myocardium was considerably reduced and inorganic phosphorus was increased. Artificial ventilation leading to systemic hypoxia and eventually circulatory arrest resulted in almost normal myocardial pO2 but severely compromised HEP content. This somewhat unexpected finding requires further clarification, but is in accordance with findings reported previously where regulatory mechanisms have been shown to play a role in the pathophysiology of severe hypoxic conditions such as those for cellular oxygen delivery and demand, P/O coupling and finally control of HEP production facilitating the interaction between respiratory chain and myoglobin oxygen transport.

Angiotensin II, mitochondria, cytoskeletal, and extracellular matrix connections: an integrating viewpoint

Malfunctioning mitochondria strongly participate in the pathogenesis of cardiovascular damage associated with hypertension and other disease conditions. Eukaryotic cells move, assume their shape, resist mechanical stress, accommodate their internal constituents, and transmit signals by relying on the constant remodeling of cytoskeleton filaments. Mitochondrial ATP is needed to support cytoskeletal dynamics. Conversely, mitochondria need to interact with cytoskeletal elements to achieve normal motility, morphology, localization, and function. Extracellular matrix (ECM) quantity and quality influence cellular growth, differentiation, morphology, survival, and mobility. Mitochondria can sense ECM composition changes, and changes in mitochondrial functioning modify the ECM. Maladaptive ECM and cytoskeletal alterations occur in a number of cardiac conditions and in most types of glomerulosclerosis, leading to cardiovascular and renal fibrosis, respectively. Angiotensin II (ANG II), a vasoactive peptide and growth factor, stimulates cytosolic and mitochondrial oxidant production, eventually leading to mitochondrial dysfunction. Also, by inducing integrin/focal adhesion changes, ANG II regulates ECM and cytoskeletal composition and organization and, accordingly, contributes to the pathogenesis of cardiovascular remodeling. ANG II-initiated integrin signaling results in the release of transforming growth factor-β1 (TGF-β1), a cytokine that modifies ECM composition and structure, induces reorganization of the cytoskeleton, and modifies mitochondrial function. Therefore, it is possible to hypothesize that the depression of mitochondrial energy metabolism brought about by ANG II is preceded by ANG II-induced integrin signaling and the consequent derangement of the cytoskeletal filament network and/or ECM organization. ANG II-dependent TGF-β1 release is a potential link between ANG II, ECM, and cytoskeleton derangements and mitochondrial dysfunction. It is necessary to emphasize that the present hypothesis is among many other plausible explanations for ANG II-mediated mitochondrial dysfunction. A potential limitation of this proposal is that the results compiled here were obtained in different cells, tissues, and/or experimental models.

Chronic NF-{kappa}B blockade reduces cytosolic and mitochondrial oxidative stress and attenuates renal injury and hypertension in SHR

Nuclear factor-kappaB (NF-kappaB) plays an important role in hypertensive renal injury; however, its roles in perpetuating mitochondrial oxidative stress and renal dysfunction remain unclear. In this study, we assessed the effects of chronic NF-kappaB blockade with pyrrolidine dithiocarbamate (PDTC) on renal dysfunction and mitochondrial redox status in spontaneously hypertensive rats (SHR). PDTC (150 mg.kg body wt(-1).day(-1)) or vehicle was administered orally to 8-wk-old SHR and their respective controls for 15 wk. Systolic blood pressure (SBP) was measured by tail-cuff plethysmography at the start of and at every third week throughout the study. After 15 wk of treatment, anesthetized rats underwent acute renal experiments to determine renal blood flow and glomerular filtration rate using PAH and inulin clearance techniques, respectively. Following renal experiments, kidneys were excised from killed rats, and cortical mitochondria were isolated for reactive oxygen species (ROS) measurements using electron paramagnetic resonance. Tissue mRNA and protein levels of NF-kappaB and oxidative stress genes were determined using real-time PCR and immunofluorescence or Western blotting, respectively. PDTC treatment partially attenuated the increase in SBP (196.4 +/- 9.76 vs. 151.4 +/- 2.12; P < 0.05) and normalized renal hemodynamic and excretory parameters and ATP production rates in SHR. PDTC treatment also attenuated the higher levels of cytosolic and mitochondrial ROS generation and tissue mRNA and protein expression levels of NF-kappaB and oxidative stress genes in SHR without any comparable responses in control rats. These findings suggest that NF-kappaB activation by ROS induces the cytosolic and mitochondrial oxidative stress and tissue injury that contribute to renal dysfunction observed in SHR.

Interaction of fatty acid with myoglobin

Upon titration with palmitate, the (1)H NMR spectra of metmyoglobin cyanide (MbCN) reveal a selective perturbation of the 8 heme methyl, consistent with a specific interaction of myoglobin (Mb) with fatty acid. Other detectable hyperfine shifted resonances of the heme group remain unchanged. Mb also enhances fatty acid solubility, as reflected in a more intense methylene peak of palmitate in Mb solution than in Tris buffer. Ligand binding analysis indicates an apparent palmitate dissociation constant (K(d)) of 43microM. These results suggest that Mb can bind fatty acid and may have a role in facilitating fatty acid transport in the cell.

Renal mitochondrial impairment is attenuated by AT1 blockade in experimental Type I diabetes

To investigate whether ANG II type 1 (AT(1)) receptor blockade could protect kidney mitochondria in streptozotocin-induced Type 1 diabetes, we treated 8-wk-old male Sprague-Dawley rats with a single streptozotocin injection (65 mg/kg ip; STZ group), streptozotocin and drinking water containing either losartan (30 mg.kg(-1).day(-1); STZ+Los group) or amlodipine (3 mg.kg(-1).day(-1); STZ+Amlo group), or saline (intraperitoneally) and pure water (control group). Four-month-long losartan or amlodipine treatments started 30 days before streptozotocin injection to improve the antioxidant defenses. The number of renal lesions, plasma glucose and lipid levels, and proteinuria were higher and creatinine clearance was lower in STZ and STZ+Amlo compared with STZ+Los and control groups. Glycemia was higher in STZ+Los compared with control. Blood pressure, basal mitochondrial membrane potential and mitochondrial pyruvate content, and renal oxidized glutathione levels were higher and NADH/cytochrome c oxidoreductase activity was lower in STZ compared with the other groups. In STZ and STZ+Amlo groups, mitochondrial H(2)O(2) production rate was higher and uncoupling protein-2 content, cytochrome c oxidase activity, and renal glutathione level were lower than in STZ+Los and control groups. Mitochondrial nitric oxide synthase activity was higher in STZ+Amlo compared with the other groups. Mitochondrial pyruvate content and H(2)O(2) production rate negatively contributed to electron transfer capacity and positively contributed to renal lesions. Uncoupling protein-2 content negatively contributed to mitochondrial H(2)O(2) production rate and renal lesions. Renal glutathione reduction potential positively contributed to mitochondria electron transfer capacity. In conclusion, AT(1) blockade protects kidney mitochondria and kidney structure in streptozotocin-induced diabetes independently of blood pressure and glycemia.

From mitochondria to disease: role of the renin-angiotensin system

Mitochondria are energy-producing organelles that conduct other key cellular tasks. Thus, mitochondrial damage may impair various aspects of tissue functioning. Mitochondria generate oxygen- and nitrogen-derived oxidants, being themselves major oxidation targets. Dysfunctional mitochondria seem to contribute to the pathophysiology of hypertension, cardiac failure, the metabolic syndrome, obesity, diabetes mellitus, renal disease, atherosclerosis, and aging. Mitochondrial proteins and metabolic intermediates participate in various cellular processes, apart from their well-known roles in energy metabolism. This emphasizes the participation of dysfunctional mitochondria in disease, notwithstanding that most evidences supporting this concept come from animal and cultured-cell studies. Mitochondrial oxidant production is altered by several factors related to vascular pathophysiology. Among these, angiotensin-II stimulates mitochondrial oxidant release leading to energy metabolism depression. By lowering mitochondrial oxidant production, angiotensin-II inhibition enhances energy production and protects mitochondrial structure. This seems to be one of the mechanisms underlying the benefits of angiotensin-II inhibition in hypertension, diabetes, and aging rodent models. If some of these findings can be reproduced in humans, they would provide a new perspective on the implications that RAS-blockade can offer as a therapeutic strategy. This review intends to present available information pointing to mitochondria as targets for therapeutic Ang-II blockade in human renal and CV disease.

Measuring oxygenation in vivo with MRS/MRI--from gas exchange to the cell

Oxygen plays a major role as a substrate in metabolic processes in numerous signaling pathways, in redox metabolism, and in free radical metabolism. To study the role of oxygen in normal and pathophysiological states, methods that can be used noninvasively are required. This review examines the potential of nuclear magnetic resonance techniques to study tissue oxygenation. It is written from a systems perspective, looking at detection methods with respect to the path that oxygen takes in the mammalian system-from the lungs, through the vascular system, into the interstitial space, and finally into the cell. Methods discussed range from those that are quantifiable, such as the assessment of spin lattice relaxation time in fluorocarbon solutions, to those that are more correlative, such as assessment of lactate and high energy phosphates. Since the methods vary in their site of application, sensitivity, and specificity to the quantification of oxygen, this review provides examples of how each method has been applied. This may facilitate the reader's understanding of how to optimally apply different methods to study specific biomedical problems.

Role of oxygen in postischemic myocardial injury

Myocardial function is dependent on a constant supply of oxygen from the coronary circulation. A reduction of oxygen supply due to coronary obstruction results in myocardial ischemia, which leads to cardiac dysfunction. Reperfusion of the ischemic myocardium is required for tissue survival. Thrombolytic therapy, coronary artery bypass surgery and coronary angioplasty are some of the treatments available for the restoration of blood flow to the ischemic myocardium. However, the restoration of blood flow may also lead to reperfusion injury, resulting in myocyte death. Thus, any imbalance between oxygen supply and metabolic demand leads to functional, metabolic, morphologic, and electrophysiologic alterations, causing cell death. Myocardial ischemia reperfusion (IR) injury is a multifactorial process that is mediated by oxygen free radicals, neutrophil activation and infiltration, calcium overload, and apoptosis. Controlled reperfusion of the ischemic myocardium has been advocated to prevent the IR injury. Studies have shown that reperfusion injury and postischemic cardiac function are related to the quantity and delivery of oxygen during reperfusion. Substantial evidence suggests that controlled reoxygenation may ameliorate postischemic organ dysfunction. In this review, we discuss the role of oxygenation during reperfusion and subsequent biochemical and pathologic alterations in reperfused myocardium and recovery of heart function.

Anisotropy and temperature dependence of myoglobin translational diffusion in myocardium: implication for oxygen transport and cellular architecture

Pulsed field gradient NMR methods have determined the temperature-dependent diffusion of myoglobin (Mb) in perfused rat myocardium. Mb diffuses with an averaged translational diffusion coefficient (DMb) of 4.24-8.37x10(-7)cm2/s from 22 degrees C to 40 degrees C and shows no orientation preference over a root mean-square displacement of 2.5-3.5 microm. The DMb agrees with the value predicted by rotational diffusion measurements. Based on the DMb, the equipoise diffusion PO2, the PO2 in which Mb-facilitated and free O2 diffusion contribute equally to the O2 flux, varies from 2.72 to 0.15 in myocardium and from 7.27 to 4.24 mmHg in skeletal muscle. Given the basal PO2 of approximately 10 mmHg, the Mb contribution to O2 transport appears insignificant in myocardium. In skeletal muscle, Mb-facilitated diffusion begins to contribute significantly only when the PO2 approaches the P50. In marine mammals, the high Mb concentration confers a predominant role for Mb in intracellular O2 transport under all physiological conditions. The Q10 of the DMb ranges from 1.3 to 1.6. The Mb diffusion data indicate that the postulated gel network in the cell must have a minimum percolation cutoff size exceeding 17.5 A and does not impose tortuosity within the diffusion root mean-square displacement. Moreover, the similar Q10 for the DMb of solution versus cell Mb suggests that any temperature-dependent alteration of the postulated cell matrix does not significantly affect protein mobility.

Mitochondrial function and nitric oxide metabolism are modified by enalapril treatment in rat kidney

The renal and cardiac benefits of renin-angiotensin system (RAS) inhibition in hypertension exceed those attributable to blood pressure reduction, and seem to involve mitochondrial function changes. To investigate whether mitochondrial changes associated with RAS inhibition are related to changes in nitric oxide (NO) metabolism, four groups of male Wistar rats were treated during 2 wk with a RAS inhibitor, enalapril (10 mg x kg(-1) x day(-1); Enal), or a NO synthase (NOS) inhibitor, N(omega)-nitro-L-arginine methyl ester (L-NAME) (1 mg x kg(-1) x day(-1)), or both (Enal+L-NAME), or were untreated (control). Blood pressure and body weight were lower in Enal than in control. Electron transfer through complexes I to III and cytochrome oxidase activity were significantly lower, and uncoupling protein-2 content was significantly higher in kidney mitochondria isolated from Enal than in those from control. All of these changes were prevented by L-NAME cotreatment and were accompanied by a higher production/bioavailability of kidney NO. L-NAME abolished mitochondrial NOS activity but failed to inhibit extra-mitochondrial kidney NOS, underscoring the relevance of mitochondrial NO in those effects of enalapril that were suppressed by L-NAME cotreatment. In Enal, kidney mitochondria H(2)O(2) production rate and MnSOD activity were significantly lower than in control, and these effects were not prevented by L-NAME cotreatment. These findings may clarify the role of NO in the interactions between RAS and mitochondrial metabolism and can help to unravel the mechanisms involved in renal protection by RAS inhibitors.

Myoglobin translational diffusion in rat myocardium and its implication on intracellular oxygen transport

Current theory of respiratory control invokes a role of myoglobin (Mb)-facilitated O2 diffusion in regulating the intracellular O2 flux, provided Mb diffusion can compete effectively with free O2 diffusion. Pulsed-field gradient NMR methods have now followed gradient-dependent changes in the distinct 1H NMR gamma CH3 Val E11 signal of MbO2 in perfused rat myocardium to obtain the endogenous Mb translational diffusion coefficient (D(Mb)) of 4.24 x 10(-7) cm2 s(-1) at 22 degrees C. The D(Mb) matches precisely the value predicted by in vivo NMR rotational diffusion measurements of Mb and shows no orientation preference. Given values in the literature for the Krogh's free O2 diffusion coefficient (K0), myocardial Mb concentration and a partial pressure of O2 that half saturates Mb (P50), the analysis yields an equipoise diffusion P(O2) of 1.77 mmHg, where Mb and free O2 contribute equally to the O2 flux. In the myocardium, Mb-facilitated O2 diffusion contributes increasingly more than free O2 diffusion when the P(O2) falls below 1.77 mmHg. In skeletal muscle, the P(O2) must fall below 5.72 mmHg. Altering the Mb P50 induces modest change. Mb-facilitated diffusion has a higher poise in skeletal muscle than in myocardium. Because the basal P(O2) hovers around 10 mmHg, Mb does not have a predominant role in facilitating O2 transport in myocardium but contributes significantly only when cellular oxygen falls below the equipoise diffusion P(O2).