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PubMed2001

Radial and longitudinal diffusion of myoglobin in single living heart and skeletal muscle cells.

We have used a fluorescence recovery after photobleaching (FRAP) technique to measure radial diffusion of myoglobin and other proteins in single skeletal and cardiac muscle cells. We compare the radial diffusivities, D(r) (i.e., diffusion perpendicular to the long fiber axis), with longitudinal ones, D(l) (i.e., parallel to the long fiber axis), both measured by the same technique, for myoglobin (17 kDa), lactalbumin (14 kDa), and ovalbumin (45 kDa). At 22 degrees C, D(l) for myoglobin is 1.2 x 10(-7) cm(2)/s in soleus fibers and 1.1 x 10(-7) cm(2)/s in cardiomyocytes. D(l) for lactalbumin is similar in both cell types. D(r) for myoglobin is 1.2 x 10(-7) cm(2)/s in soleus fibers and 1.1 x 10(-7) cm(2)/s in cardiomyocytes and, again, similar for lactalbumin. D(l) and D(r) for ovalbumin are 0.5 x 10(-7) cm(2)/s. In the case of myoglobin, both D(l) and D(r) at 37 degrees C are about 80% higher than at 22 degrees C. We conclude that intracellular diffusivity of myoglobin and other proteins (i) is very low in striated muscle cells, approximately 1/10 of the value in dilute protein solution, (ii) is not markedly different in longitudinal and radial direction, and (iii) is identical in heart and skeletal muscle. A Krogh cylinder model calculation holding for steady-state tissue oxygenation predicts that, based on these myoglobin diffusivities, myoglobin-facilitated oxygen diffusion contributes 4% to the overall intracellular oxygen transport of maximally exercising skeletal muscle and less than 2% to that of heart under conditions of high work load.

Animals↗
PubMed1993

Gradients of transgene expression directed by the human myoglobin promoter in the developing mouse heart.

Prior studies using transient transfection assays in cultured avian and murine skeletal myotubes indicate that the proximal 2-kb segment of the 5' flanking region of the human myoglobin gene contains transcriptional control elements sufficient to direct muscle-specific and developmentally regulated expression of reporter genes. To examine the function of the human myoglobin gene promoter during development of skeletal and cardiac myocytes in the intact animal, a 2.0-kb myoglobin gene upstream fragment was fused to an Escherichia coli lacZ reporter gene and injected into fertilized mouse oocytes. beta-Galactosidase (beta-gal) activity was detected selectively in cardiac and skeletal myocytes of fetal and adult transgenic mice. A distinctive spatial pattern of myoglobin promoter activity was observed in fetal hearts: beta-gal staining was more pronounced within the left ventricular subendocardium than within the subepicardium and was essentially undetectable in the ventricular trabeculae or atria. Expression of endogenous myoglobin mRNA and protein, assessed by in situ hybridization and immunohistochemistry, demonstrated a similar spatial pattern. In contrast, hearts from adult transgenic mice demonstrated essentially homogeneous expression of beta-gal and of endogenous myoglobin mRNA and protein throughout the myocardium, including the trabeculae and atria. These data indicate that the 2.0-kb upstream region of the human myoglobin gene includes cis-acting regulatory elements sufficient to direct transgene expression during murine cardiac development that is myocyte-specific and responsive to positional cues in a similar manner to the endogenous myoglobin gene.

Age Factors↗
PubMed1985

Biochemical changes following suxamethonium. Serum myoglobin, potassium and creatinine kinase changes before commencement of surgery.

Forty patients were investigated for serum myoglobin changes following induction of anaesthesia but before the commencement of surgery. Blood was drawn for potassium, creatinine kinase and serum myoglobin immediately prior to and 5, 10 and 20 minutes after administration of thiopentone 4 mg/kg and suxamethonium 1.2 mg/kg. Twenty patients were given either 2 mg alcuronium or 20 mg gallamine as pretreatment 2 to 3 minutes before the suxamethonium to reduce the fasciculations. Anaesthesia was maintained with artificial ventilation and alcuronium, or spontaneous ventilation with halothane. Serum myoglobin was assayed by radioimmunoassay. All pre-induction myoglobin levels were within the normal range. Of the 20 patients who were not pretreated, six showed a marked rise of serum myoglobin within 5 minutes, increasing to 150-200 micrograms/litre at 20 minutes. The remaining 14 patients had no such rise. No patients in the pretreatment group had any significant rise in serum myoglobin, suggesting that although the fasciculations were not completely abolished, there was protection against one of the effects of suxamethonium on the muscle. Although there was no clear relationship between intensity of fasciculations and increase in serum myoglobin, there was no marked rise in serum myoglobin values in any patient who did not have muscle fasciculations. There were no consistent changes in potassium or creatinine kinase in any group during the period of study.

Adolescent↗
PubMed2003

Hypoxia-induced left ventricular dysfunction in myoglobin-deficient mice.

Myoglobin-deficient mice are viable and have preserved cardiac function due to their ability to mount a complex compensatory response involving increased vascularization and the induction of the hypoxia gene program (hypoxia-inducible factor-1alpha, endothelial PAS, heat shock protein27, etc.). To further define and explore functional roles for myoglobin, we challenged age- and gender-matched wild-type and myoglobin-null mice to chronic hypoxia (10% oxygen for 1 day to 3 wk). We observed a 30% reduction in cardiac systolic function in the myoglobin mutant mice exposed to chronic hypoxia with no changes observed in the wild-type control hearts. The cardiac dysfunction observed in the hypoxic myoglobin-null mice was reversible with reexposure to normoxic conditions and could be prevented with treatment of an inhibitor of nitric oxide (NO) synthases. These results support the conclusion that hypoxia-induced cardiac dysfunction in myoglobin-null mice occurs via a NO-mediated mechanism. Utilizing enzymatic assays for NO synthases and immunohistochemical analyses, we observed a marked induction of inducible NO synthase in the hypoxic myoglobin mutant ventricle compared with the wild-type hypoxic control ventricle. These new data establish that myoglobin is an important cytoplasmic cardiac hemoprotein that functions in regulating NO homeostasis within cardiomyocytes.

Animals↗
PubMed2004

Vascular endothelial growth factor overexpression in ischemic skeletal muscle enhances myoglobin expression in vivo.

Therapeutic angiogenesis using vascular endothelial growth factor (VEGF) is considered a promising new therapy for patients with arterial obstructive disease. Clinical improvements observed consist of improved muscle function and regression of rest pain or angina. However, direct evidence for improved vascularization, as evaluated by angiography, is weak. In this study, we report an angiogenesis-independent effect of VEGF on ischemic skeletal muscle, ie, upregulation of myoglobin after VEGF treatment. Mice received intramuscular injection with adenoviral VEGF-A or either adenoviral LacZ or PBS as control, followed by surgical induction of acute hindlimb ischemia at day 3. At day 6, capillary density was increased in calf muscle of Ad.VEGF-treated versus control mice (P<0.01). However, angiographic score of collateral arteries was unchanged between Ad.VEGF-treated and control mice. More interestingly, an increase in myoglobin was observed in Ad.VEGF-treated mice. Active myoglobin was 1.5-fold increased in calf muscle of Ad.VEGF-treated mice (P< or =0.01). In addition, the number of myoglobin-stained myofibers was 2.6-fold increased in Ad.VEGF-treated mice (P=0.001). Furthermore, in ischemic muscle of 15 limb amputation patients, VEGF and myoglobin were coexpressed. Finally, in cultured C2C12 myotubes treated with rhVEGF, myoglobin mRNA was 2.8-fold raised as compared with PBS-treated cells (P=0.02). This effect could be blocked with the VEGF receptor tyrosine kinase inhibitor SU5416. In conclusion, we show that VEGF upregulates myoglobin in ischemic muscle both in vitro and in vivo. Increased myoglobin expression in VEGF-treated muscle implies an improved muscle oxygenation, which may, at least partly, explain observed clinical improvements in VEGF-treated patients, in the absence of improved vascularization.

Adenoviridae↗
PubMed2002

Chemical regulation of nitric oxide: a role for intracellular myoglobin?

The detailed chemistry of nitric oxide (*NO) and regulation of this potent signal molecule through interactions with cellular components are complex and not clearly understood. In the vasculature, *NO plays a crucial role in vessel dilation by activating soluble guanylyl cyclase (sGC) in vascular smooth muscle cells (VSMC). *NO is responsible for maintaining coronary blood flow and normal cardiac function. However, *NO is a highly reactive molecule and this reactivity toward a range of alternate substrates may interfere with the activation of its preferred molecular target within VSMC. Interestingly, marked changes to *NO homeostasis are linked to disease progression. Thus, the physiological concentration of *NO is carefully regulated. Myoglobin is a haem-containing protein that is present in relatively high concentration in cardiac and skeletal muscle. Recently, the presence of myoglobin has been confirmed in human smooth muscle. The role of intracellular myoglobin is generally accepted as that of a passive di-oxygen storage protein. However, oxygenated myoglobin readily reacts with *NO to yield higher order N-oxides such as nitrate, while both the ferrous and ferric forms of the protein form a stable complex with *NO. Together, these two reactions effectively eliminate *NO on the physiological time-scale and strongly support the idea that myoglobin plays a role in maintaining *NO homeostasis in tissues that contain the protein. Interestingly, human myoglobin contains a sulfhydryl group and forms an S-nitroso-adduct similar to haemoglobin. In this article we discuss the potential for human myoglobin to actively participate in the regulation of *NO by three distinct mechanisms, namely oxidation, ligand binding, and through formation of biologically active S-nitroso-myoglobin.

Enzyme Activation↗
PubMed1983

The presence of myoglobin in human thyroid tissue.

In the present study we sought to determine the presence of myoglobin in human thyroid tissue. When reacted with antihuman myoglobin antibody on the Ouchterlony plate, homogenates of human thyroid tissue formed a precipitation line. When the human thyroid extract was included in human myoglobin RIA, the dilution curve of thyroid extract was parallel to the standard curve of myoglobin. When the myoglobin immunoreactivity in thyroid extract was fractionated with Sephadex G 75 column, the immunoreactivity was eluted in a peak identical with authentic myoglobin. The position of the peak was different from that of thyroglobulin. Myoglobin concentration in thyroid tissue was estimated to be 0.7-110 mg/g wet wt, being about 1/6000 to 1/40 of that in skeletal muscle. Histochemical studies demonstrated the presence of myoglobin immunoreactivity in thyroid tissue, especially in the apical border of thyroid epithelial cells, implying a functional role in iodinating process or exocytotic-endocytotic process.

Adolescent↗
PubMed2004

Reevaluation of myoglobin for acute chest pain evaluation: would false-positive results on "first-draw" specimens lead to increased hospital admissions?

Myoglobin is an early marker of cardiac injury, although positive results occur in the absence of cardiac myonecrosis. We studied data for 537 patients admitted to the emergency department with symptoms suggestive of myocardial injury who underwent testing for troponin I (TnI), creatine kinase isoenzyme (CK-MB), and myoglobin at the point of care. Physicians were blinded to the myoglobin results. Myoglobin had a sensitivity of 69.7% and a negative predictive value of 97.4% for the diagnosis of acute coronary syndrome (ACS) on "first-draw" specimens. Receiver operating characteristic curve analysis suggested that myoglobin demonstrated optimal sensitivity for ACS, while TnI had optimal specificity. CK-MB was neither the most specific nor the most sensitive marker. More than 80% of the patients with false-positive myoglobin results were admitted to the hospital. These data invalidate concerns regarding the putative overtreatment effect of false-positive cases owing to myoglobin results. Furthermore, our data suggest that myoglobin is superior to CK-MB as an adjunct to TnI.

Biomarkers↗
PubMed1994

Fatty acid binding of myoglobin depends on its oxygenation.

In the present work we show with different binding assays chicken gizzard myoglobin is able to bind fatty acids and bromosulphophthalein (BSP) in vitro. The fatty acid binding depends on the oxygenation of the myoglobin. Freshly prepared chicken gizzard, chicken or bovine heart myoglobin have a high fatty acid binding capability. However, when oxy-myoglobin in converted to met-myoglobin by dialysis against acidic buffer at high ionic strength (or when commercially available myoglobins are used) a 60-70% lower fatty acid binding capacity is found. Like bovine serum albumin (BSA), gizzard myoglobin has the highest affinity for unsaturated fatty acids and a lower affinity for saturated fatty acids or dyes. Chicken gizzard smooth muscle myoglobin may function as an additional fatty acid binding protein in vivo.

Animals↗
PubMed1997

Estimation of myocardial infarct size from plasma myoglobin or fatty acid-binding protein. Influence of renal function.

Myoglobin (M(r) 18,000) and fatty acid-binding protein (M(r) 15,000), are low molecular mass cytoplasmic proteins that are considered useful biochemical markers for early detection or exclusion of acute myocardial infarction, and also for early estimation of infarct size. As each of these proteins shows renal clearance, we studied the influence of renal function on the estimation of infarct size from their plasma concentration curves. For this, infarct size estimated from plasma myoglobin or fatty acid-binding protein release curves was compared with that estimated with the established infarct size markers hydroxybutyrate dehydrogenase and creatine kinase, which are not influenced by changes in renal function. The discordance between infarct size estimates was related to renal function. Creatine kinase (EC 2.7.3.2), hydroxybutyrate dehydrogenase (EC 1.1.1.27), myoglobin, fatty acid-binding protein and creatinine were assayed serially in plasma samples obtained frequently and for at least 72 hours after the start of thrombolytic therapy in 20 patients with acute myocardial infarction. Cumulative release of the different cardiac markers was calculated by using a two-compartment model for circulating proteins. Mean tissue contents of 156 U/g for hydroxybutyrate dehydrogenase, 2163 U/g for creatine kinase, 2.79 mg/g for myoglobin and 0.57 mg/g wet weight for fatty acid-binding protein, were used to express infarct size in gram-equivalents of healthy myocardium per litre of plasma (g-eq/l). Mean plasma creatinine was obtained by averaging the creatinine concentrations measured in all plasma samples taken during the first 24 hours after acute myocardial infarction. A relation was found between the mean plasma creatinine concentration during the first 24 hours after acute myocardial infarction and the discordance between infarct size estimated from cumulative hydroxybutyrate dehydrogenase release, compared to infarct size estimated from cumulative myoglobin or fatty acid-binding protein release. For patients with mean plasma creatinine concentrations within the reference interval for creatinine (group 1, n = 15) a good agreement was found between infarct size estimated from myoglobin or fatty acid-binding protein plasma curves and that estimated with either hydroxybutyrate dehydrogenase or creatine kinase. However, for patients with a mean creatinine concentration above the upper reference limit (group 2, n = 5), infarct size calculated from plasma myoglobin or fatty acid-binding protein release curves was markedly overestimated, especially for larger infarcts. Estimation of infarct size from serial plasma myoglobin or fatty acid-binding protein concentrations is possible in the first 24 hours after the onset of symptoms, but only in patients with normal renal function, as estimated from plasma creatinine concentrations.

Adult↗
PubMed2000

Human heart-type cytoplasmic fatty acid-binding protein (H-FABP) for the diagnosis of acute myocardial infarction. Clinical evaluation of H-FABP in comparison with myoglobin and creatine kinase isoenzyme MB.

Heart-type fatty acid-binding protein (H-FABP) is a low molecular weight cytoplasmic protein and present abundantly in the myocardium. When the myocardium is injured, as in the case of myocardial infarction, low molecular weight cytoplasmic proteins including H-FABP are released into the circulation and H-FABP is detectable in a blood sample. We have already developed a direct sandwich-ELISA for quantification of human H-FABP using two distinct types of monoclonal antibodies specific for human H-FABP. In this study we investigated the clinical validity of H-FABP as a biochemical diagnostic marker in the early phase of acute myocardial infarction (AMI). To evaluate the diagnostic usefulness of H-FABP in the early phase of AMI, blood samples were obtained from the following patients within 12 hours after the appearance of symptoms, and serum levels of H-FABP were compared with those of conventional diagnostic markers, such as myoglobin and creatine kinase isoenzyme MB (CK-MB). Blood samples were collected from patients with confirmed AMI (n=140), patients with chest pain who were afterwards not classified as AMI by normal CK-MB levels (non-AMI) (n=49) and normal healthy volunteers (n=75). The serum concentration of H-FABP was quantified with our direct sandwich-ELISA. The concentration of myoglobin mass was measured with a commercial RIA kit. The serum CK-MB activity was determined with an immuno-inhibition assay kit. The overall sensitivity of H-FABP, within 12 hours after the appearance of symptoms, was 92.9%, while it was 88.6% with myoglobin and 18.6% with CK-MB. The overall specificity of H-FABP was 67.3%, while it was 57.1% with myoglobin and 98.0% with CK-MB. The diagnostic efficacy rates with these markers were 86.2% (H-FABP), 80.4% (myoglobin) and 39.2% (CK-MB), respectively. The diagnostic validity of H-FABP was further assessed by receiver operating characteristic (ROC) curve analysis. The area under the curve (AUC) of H-FABP was 0.921, which was significantly greater than with myoglobin (AUC: 0.843) and CK-MB (AUC: 0.654). These parameters, such as sensitivity, specificity, diagnostic efficacy and diagnostic accuracy, obtained for patients with chest pain within 3 hours and/or 6 hours after the onset of symptoms were almost the same as those for patients within 12 hours after symptoms. H-FABP is more sensitive than both myoglobin and CK-MB, more specific than myoglobin for detecting AMI within 12 hours after the onset of symptoms, and shows the highest values for both diagnostic efficacy and ROC curve analysis. Thus, H-FABP has great potential as an excellent biochemical cardiac marker for the diagnosis of AMI in the early phase.

Aged↗
PubMed1992

A prospective study of urine and serum myoglobin levels in patients with acute rhabdomyolysis.

Serum and urine myoglobin levels, measured by radioimmunoassay, were determined prospectively in eight patients with acute rhabdomyolysis, within 24 hours of admission. Five patients had urine myoglobin concentrations greater than 1,000 ng/ml (normal < 5 ng/ml); four of these patients subsequently developed acute renal failure. In three patients whose urinary myoglobin levels ranged from 19 to 275 ng/ml, acute renal failure did not occur. This difference in the occurrence of acute renal failure between the two patient groups was statistically significant (p < 0.05). Mean peak serum creatinine was significantly higher in the patients with high urine myoglobin (6.4 +/- 1.3 mg/dl) compared to those with low urine myoglobin (2.2 +/- 0.3 mg/dl), p < 0.02. There was no statistical correlation between level of serum creatine phosphokinase and serum or urine myoglobin, although the serum and urine myoglobin levels correlated well with each other. These findings suggests that among other factors, urine myoglobin may need to reach a critical level in order for myoglobinuric renal failure to ensue.

Acute Disease↗
PubMed1990

Quantitative nephelometric assay for determining myoglobin evaluated.

A recently introduced automated nephelometric immunoassay involving shell/core particles for determination of myoglobin (Behringwerke) was evaluated with the BNA Nephelometer. Method precision was good: the intra-assay CV varied between 1.5% and 6.1%; with daily calibration, the interassay CV ranged between 1.5% and 7.5%. For usual sample dilutions, the assay response varied linearly with myoglobin concentrations up to 23.1 nmol/L. After automatic dilution by the instrument, concentrations up to 2310 nmol/L could be measured without high-dose "hook" effect. Further manual dilution allowed measurement of myoglobin concentrations up to 26,000 nmol/L. Calibration was stable for at least seven days. We detected no significant interferences from hemoglobin, haptoglobin, bilirubin, iodine-containing contrast media, and rheumatoid factors. Treating lipemic samples with Lipoclean (Behringwerke) decreased test results. Simultaneously drawn serum and plasma samples from the same subject showed no consistent differences in myoglobin concentrations. The mean reference myoglobin concentration was 1.380 (SD 0.82) nmol/L for men and 0.878 (SD 0.45) nmol/L for women. In patients with renal insufficiency, serum creatinine values were moderately related to serum myoglobin values (r = 0.465). Although a commercial radioimmunoassay (Byk-Sangtec) and the nephelometric assay intercorrelated well (r = 0.929), values obtained by nephelometry were significantly lower (P less than 0.05). By both assays, results for heart and skeletal muscle tissue extracts showed no correlation, a finding that suggests the existence of multiple forms of myoglobin in human tissues. We conclude that immunonephelometry is a rapid, practical, and reliable method for measuring myoglobin in serum.

Adult↗
PubMed1990

Analysis of the kinetic barriers for ligand binding to sperm whale myoglobin using site-directed mutagenesis and laser photolysis techniques.

Time courses for NO, O2, CO, methyl and ethyl isocyanide rebinding to native and mutant sperm whale myoglobins were measured at 20 degrees C following 17-ns and 35-ps laser excitation pulses. His64 (E7) was replaced with Gly, Val, Leu, Phe, and Gln, and Val68 (E11) was replaced with Ala, Ile, and Phe. For both NO and O2, the effective picosecond quantum yield of unliganded geminate intermediates was roughly 0.2 and independent of the amino acids at positions 64 and 68. Geminate recombination of NO was very rapid; 90% rebinding occurred within 0.5-1.0 ns for all of the myoglobins examined; and except for the Gly64 and Ile68 mutants, the fitted recombination rate parameters were little influenced by the size and polarity of the amino acid at position 64 and the size of the residue at position 68. The rates of NO recombination and ligand movement away from the iron atom in the Gly64 mutant increased 3-4-fold relative to native myoglobin. For Ile68 myoglobin, the first geminate rate constant for NO rebinding decreased approximately 6-fold, from 2.3 x 10(10) s-1 for native myoglobin to 3.8 x 10(9) s-1 for the mutant. No picosecond rebinding processes were observed for O2, CO, and isocyanide rebinding to native and mutant myoglobins; all of the observed geminate rate constants were less than or equal to 3 x 10(8) s-1. The rebinding time courses for these ligands were analyzed in terms of a two-step consecutive reaction scheme, with an outer kinetic barrier representing ligand movement into and out of the protein and an inner barrier representing binding to the heme iron atom by ligand occupying the distal portion of the heme pocket. Substitution of apolar amino acids for His64 decreased the absolute free energies of the outer and inner kinetic barriers and the well for non-covalently bound O2 and CO by 1 to 1.5 kcal/mol, regardless of size. In contrast, the His64 to Gln mutation caused little change in the barrier heights for all ligands, showing that the polar nature of His64 inhibits both the bimolecular rate of ligand entry into myoglobin and the unimolecular rate of binding to the iron atom from within the protein. Increasing the size of the position 68(E11) residue in the series Ala to Val (native) to Ile caused little change in the rate of O2 migration into myoglobin or the equilibrium constant for noncovalent binding but did decrease the unimolecular rate for iron-O2 bond formation.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

[Effect of induction methods of pediatric anesthesia on serum myoglobin].

Two hundred and twenty nine children from infancy to middle teens divided into six groups were studied to determine the effect of induction methods of pediatric general anesthesia on serum myoglobin. After the slow induction with nitrous oxide-oxygen-halothane (GOF), the serum myoglobin increased significantly to 1774.7 +/- 4285.8 ng.ml-1 (mean +/- SD) by iv administration of succinylcholine 1 mg.kg-1. This significant increase of serum myoglobin was reduced by pretreatment with d-tubocurarine (dTc) 0.05 mg.kg-1 before administration of succinylcholine. However, it was not reduced by pretreatment with thiopental 3 mg.kg-1. After the rapid induction with thiopental 5 mg.kg-1 and succinylcholine 1 mg.kg-1, the serum myoglobin increased slightly to 387.6 +/- 596.5 ng.ml-1. But this increase in serum myoglobin was stopped by pretreatment with dTc 0.05 mg.kg-1 before the rapid induction. Serum myoglobin was not changed without succinylcholine after the slow induction with GOF. In each group, there was no relation with serum myoglobin and ages or fasciculation. Serum myoglobin was more influenced by the induction methods of pediatric general anesthesia than by ages.

Adolescent↗
PubMed1989

[The content of the chief amount of myoglobin in the blood serum as an immune complex].

Pooled serum of health blood donors was tested for myoglobin and naturally occurring antibodies to myoglobin containing by competitive enzyme immunoassay. Data obtained show that myoglobin and autoantibodies of myoglobin are present in serum in the form of circulating immunocomplexes. Based on these results the suggestion about elimination of the main quantities of myoglobin by reticuloendothelial system is arisen. Estimated level of myoglobin concentration in the sera of health individuals established by different methods (80 ng/ml) is concerned apparently to free-circulated myoglobin and is not adequate to absolute myoglobin quantities.

Antigen-Antibody Complex↗
PubMed1988

Modulation of myoglobin-H2O2-mediated peroxidation reactions by sulfhydryl compounds.

The ability of specific low molecular weight sulfhydryl compounds to inhibit the myoglobin-H2O2 peroxidation of uric acid and arachidonic acid was investigated. alpha-Mercaptopropionyl glycine, N-acetylcysteine, and reduced glutathione inhibited both the oxymyoglobin and metmyoglobin H2O2-mediated peroxidation of uric acid in a dose-dependent manner. The IC50 for each drug ranged between 20 to 100 microM and was dependent on the presence of a reduced sulfhydryl group since neither oxidized glutathione nor methionine effectively blocked uric acid peroxidation. Similar inhibition of oxymyoglobin and metmyoglobin H2O2-mediated peroxidation of arachidonic acid was also observed with alpha-mercaptopropionyl glycine, reduced glutathione, and cysteine. Under conditions of this assay, the ferrous form of myoglobin and H2O2 produced approximately three times the amount of formaldehyde from dimethylsulfoxide than ferric myoglobin (metmyoglobin) and H2O2. However, metmyoglobin and H2O2 were more effective than either oxymyoglobin and deoxymyoglobin in mediating arachidonic acid peroxidation. Further, neither mannitol nor benzoic acid (known scavengers of .OH) effectively blocked myoglobin H2O2-induced peroxidation of either uric acid or arachidonic acid. Visible absorption spectra of oxymyoglobin and metmyoglobin after incubation with H2O2 indicates the formation of a relatively stable ferriperoxide derivative of myoglobin. The formation of the ferriperoxide myoglobin derivative was partially inhibited by the addition of reduced sulfhydryl compounds. These data are consistent with the hypothesis that during reperfusion injury of the ischemic myocardium, the phagocytic cell or intracellular-derived H2O2 may react with myoglobin and initiate peroxidation reactions independent of .OH formation leading to cell injury. The cardioprotective effects of alpha-mercaptopropionyl glycine and other sulfhydryl-containing compounds during reperfusion injury may be attributed, at least in part, to their ability to inhibit myoglobin-H2O2-mediated peroxidation reactions.

Arachidonic Acids↗
PubMedDate not supplied

Serum myoglobin does not predict cardiac allograft rejection.

Noninvasive studies are useful, but limited, in detecting rejection among cardiac allograft recipients. Because an elevated serum myoglobin level is a sensitive indicator of necrosis in acute myocardial infarction, we postulated that myoglobin levels might correlate with the presence, absence, or degree of rejection. Therefore we prospectively measured serum myoglobin levels at the time of endomyocardial biopsy in 45 heart transplant recipients and correlated these levels with biopsy scores (grade 0 through grade 4). There was no significant difference in mean myoglobin levels among patients with grade 0 biopsy scores and those with grade 1 through grade 4 scores. Serial myoglobin levels and endomyocardial biopsy specimens were obtained in five patients during a 4- to 9-week period; no significant directional change in myoglobin levels appeared to correlate with changes in endomyocardial biopsy score. In addition, a normal myoglobin level did not exclude, nor did an elevated level confirm, any grade of rejection. We conclude that neither the absolute level nor a directional change in serum myoglobin is useful in identifying rejection among heart transplant recipients.

Biomarkers↗