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R Motterlini

Publications and source records attributed to R Motterlini.

At least 37 records · Page 2Linked to original sources
PubMed1999

Peroxynitrite induces haem oxygenase-1 in vascular endothelial cells: a link to apoptosis.

Peroxynitrite (ONOO-) is a potent oxidizing agent generated by the interaction of nitric oxide (NO) and the superoxide anion. In physiological solution, ONOO- rapidly decomposes to a hydroxyl radical, one of the most reactive free radicals, and nitrogen dioxide, another species able to cause oxidative damage. In the present study we investigated the effect of ONOO- on the expression of haem oxygenase-1 (HO-1), an inducible protein that is highly up-regulated by oxidative stress. Exposure of bovine aortic endothelial cells to ONOO- (250-1000 microM) produced a concentration-dependent increase in haem oxygenase activity and HO-1 protein expression. This effect was completely abolished by the ONOO- scavengers uric acid and N-acetylcysteine, and partly attenuated by 1,3-dimethyl-2-thiourea, a scavenger of hydroxyl radicals. ONOO- also produced a concentration-dependent increase in apoptosis and cytotoxicity, which were considerably decreased by uric acid and N-acetylcysteine. A 70% decrease in apoptosis was observed when cells were exposed to ONOO- in the presence of 10 microM tin protoporphyrin IX (SnPPIX), an inhibitor of haem oxygenase activity. When SnPPIX was added 5 min after ONOO-, apoptosis decreased by only 40%, which suggests that an interaction between ONOO- and the protoporphyrin occurs in our system. Increased haem oxygenase activity by pretreatment of cells with haemin resulted in elevated bilirubin production and was associated with a substantial decrease (35%) in ONOO--mediated apoptosis. These results indicate the ability of ONOO- to modulate the expression of the stress protein HO-1 and suggest that the haem oxygenase pathway contributes to protection against the cytotoxic action of ONOO-.

Acetylcysteine↗
PubMed1999

The heme oxygenase pathway and its interaction with nitric oxide in the control of cellular homeostasis.

Heme oxygenase is the rate limiting enzyme in heme degradation to carbon monoxide (CO), iron and bilirubin. The inducible isoform of the protein, heme oxygenase-1 (HO-1), is susceptible to up-regulation by a diverse variety of conditions and agents in mammalian tissue, leading to the common conception that HO-1 is a stress related enzyme. However, as attempts are made to unravel the mechanisms by which HO-1 is induced and as we discover that CO, iron and bilirubin may be important effector molecules, we are learning to appreciate that heme oxygenases may be central to the regulation of many physiological and pathophysiological processes besides their established function in heme catabolism. One such process may be closely linked to nitric oxide (NO). It has been demonstrated that NO and NO donors are capable of inducing HO-1 protein expression, in a mechanism depending on the de novo synthesis of RNA and protein. Thus, it is postulated that NO may serve as a signaling molecule in the modulation of the tissue stress response. This review will highlight the current ideas on the role of CO-heme oxygenase and NO-nitric oxide synthase in cell signaling and discuss how the two systems are interrelated.

Animals↗
PubMed1998

The comparative effects of the NOS inhibitor, Nomega-nitro-L-arginine, and the haemoxygenase inhibitor, zinc protoporphyrin IX, on tumour blood flow.

PURPOSE: To determine the relative effects of inhibiting nitric oxide synthase (NOS) and haemoxygenase (HO) on blood flow to the rat P22 carcinosarcoma. METHODS AND MATERIALS: HO is the enzyme responsible for in vivo production of carbon monoxide (CO). The vascular effects of zinc protoporphyrin IX (ZnPP), a competitive inhibitor of HO, were compared with those of copper protoporphyrin IX (CuPP), a poor inhibitor of HO, in isolated ex vivo perfusions of the P22 tumour and in intact tumour-bearing rats. In ex vivo perfusions, tumour vascular resistance was calculated from measurements of perfusion pressure at a known flow rate. In intact animals, blood flow to tumour and normal tissues was calculated using a radiotracer uptake method. The effects of ZnPP were compared with those of the NOS inhibitor, N(omega)-nitro-L-arginine (L-NNA), and the combination of the two drugs. RESULTS: HO activity in the P22 tumour was reduced by 50% following administration of either ZnPP or CuPP directly to ex vivo perfused tumours, suggesting an indirect effect on the enzyme. Enzyme inhibition was not associated with any significant vasoactive effect. Neither ZnPP nor CuPP, at a dose of 45 micromol x kg(-1) administered i.p., inhibited tumour HO in vivo. However, they did significantly decrease tumour blood flow to 60-70% of control, with similar effects in skin and brain. Skeletal muscle blood flow was increased to 150% of control. L-NNA decreased both tumour and skeletal muscle blood flow to around 40% of control. These differences suggest that the nonspecific effects of ZnPP and CuPP were not mediated by NOS inhibition. The combination of ZnPP and L-NNA improved the selective reduction in tumour blood flow achieved with either agent alone. CONCLUSION: This suggests that the HO/CO pathway does not play a major vasodilatory role in this tumour. However, ZnPP and CuPP could be useful for inducing a relatively selective decrease in tumour blood flow via mechanisms unrelated to HO inhibition, especially when combined with NOS inhibition.

Animals↗
PubMed1998

Heme oxygenase-1-derived carbon monoxide contributes to the suppression of acute hypertensive responses in vivo.

The enzyme heme oxygenase, which exists in inducible (HO-1) and constitutive (HO-2) isoforms, catalyzes the degradation of heme to biliverdin and CO in mammalian tissues. CO has been implicated in the control of vascular tone in a manner similar to that for NO. In the present study, we investigated the contribution of the heme oxygenase/CO pathway to the modulation of acute hypertensive responses in vivo induced by (1) alphaalphaHb, a chemically modified hemoglobin known to scavenge NO, and (2) NG-nitro-L-arginine methyl ester (L-NAME), a competitive NOS inhibitor. Experiments were carried out in conscious rats in which femoral arteries and veins were surgically catheterized 1 or 5 days before treatment with the vasoconstrictor agents. Intravenous infusion of alphaalphaHb (8% solution) or L-NAME (30 micromol/kg) [corrected] produced an acute and significant increase in mean arterial pressure (P<0.05) in rats at 5 days after catheter implantation. In contrast, no change in blood pressure was observed when alphaalphaHb or L-NAME was infused 1 day after the surgical intervention. The suppression of the hypertensive response observed at 1 day after surgery correlated with a significant (P<0.05) HO-1 expression in aorta, heart, and liver as well as increased aortic CO production and cGMP levels. At 1 day after surgery, pretreatment of animals with the heme oxygenase inhibitor zinc protoporphyrin IX (50 micromol/kg IP) markedly decreased aortic CO and cGMP levels and completely restored the vasoconstrictor effects of both alphaalphaHb and L-NAME. These results provide evidence for a crucial role of the heme oxygenase/CO pathway in the regulation of blood pressure under stress conditions in vivo.

Acute Disease↗
PubMed1998

Carbon monoxide is a major contributor to the regulation of vascular tone in aortas expressing high levels of haeme oxygenase-1.

The contribution of haeme oxygenase-derived carbon monoxide (CO) to the regulation of vascular tone in thoracic aorta was investigated following induction of the inducible isoform of haeme oxygenase (HO-1). Isometric smooth muscle contractions were recorded in isolated rat aortic ring preparations. Rings were incubated in the presence of the nitric oxide (NO) donor S-nitroso-N-acetyl penicillamine (SNAP, 500 microM) for 1 h, then repetitively washed and maintained for a further 4 h prior to producing a concentration-response curve to phenylephrine (PE, 1-3000 nM). Treatment with SNAP resulted in increased mRNA and protein expression of aortic HO-1 and was associated with a significant suppression of the contractile response to PE (P<0.05 vs control). Immunohistochemical staining procedures revealed marked HO-1 expression in the endothelial layer and, to a lesser extent, in smooth muscle cells. Induction of HO-1 in SNAP-treated rings was associated with a higher 14CO release compared to control, as measured by scintillation counting after incubation of aortas with [2-14C]-L-glycine, the precursor of haeme. Guanosine 3',5'-monophosphate (cyclic GMP) content was also greatly enhanced in aortas expressing high levels of HO-1. Incubation of aortic rings with the NO synthase inhibitor, NG-monomethyl-L-arginine (100 microM), significantly (P<0.05) increased the contractile response to PE in controls but failed to restore PE-mediated contractility in SNAP-treated rings. In contrast, the selective inhibitor of haeme oxygenase, tin protoporphyrin IX (SnPP-IX, 10 microM), restored the pressor response to PE in SNAP-treated rings whilst markedly reducing CO and cyclic GMP production. We conclude that up-regulation of the HO-1/CO pathway significantly contributes to the suppression of aortic contractility to PE. This effect appears to be mediated by the elevation of cyclic GMP levels and can be reversed by inhibition of the haeme oxygenase pathway.

Animals↗
PubMed1998

Heme oxygenase-1 induction in skeletal muscle cells: hemin and sodium nitroprusside are regulators in vitro.

The heat shock protein heme oxygenase-1 (HO-1) is regulated by a variety of physiological and pharmacological factors. In skeletal muscle tissue, HO-1 has been shown to be induced only by exercise and electrical stimulation in vivo. Both hemin and sodium nitroprusside (SNP) are potent inducers of HO-1 in other tissues. In this study, we examined the effects of these two agents on HO-1 induction in L6.G8 rat skeletal myoblast cells. Hemin and SNP increased cellular heme oxygenase activity in both a time- and concentration-dependent manner. Increases in the HO-1 mRNA level and protein expression accompanied changes in heme oxygenase activity. The ability of SNP to induce HO-1 in L6.G8 cells was reduced by coincubation with hydroxocobalamin, a known nitric oxide (NO) scavenger, suggesting that NO itself may be involved in HO-1 gene stimulation. These results indicate that HO-1 expression is sensitive to both hemin and SNP in skeletal myoblast cells and may indicate an important regulatory mechanism of heme catabolism in skeletal muscle tissue.

Animals↗
PubMed1998

Depression of endothelial and smooth muscle cell oxygen consumption by endotoxin.

An optical method based on the oxygen-dependent quenching of a phosphorescent probe (palladium-porphyrin) was used to investigate the effect of bacterial endotoxin [lipopolysaccharide (LPS)] on oxygen consumption (VO2) by vascular cells. Endothelial (EC) and smooth muscle (SMC) cells from pig aorta were suspended in culture medium in the presence of palladium-porphyrin and transferred to glass capillary tubes that were sealed to create a hypoxic environment. Measured PO2 changed as a function of time in a highly predictable fashion when cell suspensions were exposed to agents or treatment known to affect cellular metabolism. Both EC and SMC showed a significant decrease in VO2 as cell density increased, and SMC VO2 was significantly higher than EC (1.94 +/- 0.09 vs. 1.0 +/- 0.15 nmol . min-1 . 10(6) cells-1). Exposure to LPS (1 microg/ml) caused a decrease in VO2 of 46% and 15% for EC and SMC, respectively. Pretreatment of cells with N-acetyl-L-cysteine, a substrate for glutathione synthesis with antioxidant properties, restored VO2 to normal values after exposure to LPS. These data suggest that endotoxin impairs VO2 in cells derived from the vascular wall and indicate the importance of EC and SMC respiration in maintaining vascular homeostasis under conditions of sepsis.

Acetylcysteine↗
PubMed1997

Involvement of the heme oxygenase-carbon monoxide pathway in keratinocyte proliferation.

It has been suggested that nitric oxide (NO), a small gaseous molecule with a multiplicity of cellular functions, plays an important part in the regulation of cellular proliferation. We have examined the effect of the NO donor sodium nitroprusside (SNP) on heme oxygenase-1 (HO-1) expression in human epidermal keratinocytes and investigated the contribution of the heme oxygenase pathway in the control of keratinocyte proliferation. Incubation of keratinocytes with 0.5 mM SNP resulted in a 2.5-fold increase in heme oxygenase activity which was reflected by a significant increase in HO-1 protein expression, as measured by Western blot. This effect was associated with a 200% increase in keratinocyte proliferation. The proliferative effect of the NO donor was totally abolished by co-incubation of SNP with tin protoporphyrin IX, a potent inhibitor of heme oxygenase, or hydroxocobalamin, a NO scavenger. These results suggest that the heme oxygenase pathway is involved in keratinocyte proliferation mediated by NO.

Carbon Monoxide↗
PubMed1997

Cyclophilins are induced by hypoxia and heat stress in myogenic cells.

This is a novel study demonstrating that cyclophilins are heat and stress inducible proteins in eukaryotic myogenic cells. We investigated the expression of cyclophilins in embryonal rat heart derived H9c2 myocytes following heat stress and chronic hypoxia. We report here that cyclophilins, the proteins capable of catalysing the interconversion of cis and trans isomers (PPIses) in proteins and peptides, are heat and stress inducible, and are involved in the complex stress response, as their level is significantly elevated after heat stress and hypoxia. A time course analysis showed the gradual increase in expressed levels of cyclophilin after heat stress of cells, with maximal expression as measured by Western blot at 48 hours after the actual treatment. Rat myogenic cells exposed to chronic hypoxia followed by 5 hours reoxygenation resulted in approximately threefold expression of PPI-ases. The results showing that cyclophilins are heat and stress inducible suggest a multiple role for cyclophilins in ischemia: a potential functional association with the different heat shock proteins, with the established protective role in ischaemic injury, as well as the possible involvement of cyclophilins in the protein folding in cooperation with molecular chaperones.

Amino Acid Isomerases↗
PubMed1997

Thiol compounds interact with nitric oxide in regulating heme oxygenase-1 induction in endothelial cells. Involvement of superoxide and peroxynitrite anions.

Thiols are very important antioxidants that protect cells against oxidative insults. Recently, a different and new physiological role has been defined for these compounds because of their involvement in nitric oxide (NO) binding and transport in biological systems. In view of these characteristics, we examined the effect of thiols and NO on the expression of the inducible form of heme oxygenase (HO-1), a stress protein that degrades heme to carbon monoxide and biliverdin. Cultured bovine aortic endothelial cells exposed to the NO donors sodium nitroprusside (SNP) and S-nitroso-N-acetylpenicillamine (SNAP) resulted in increased heme oxygenase activity and HO-1 expression. Co-incubation with N-acetylcysteine, a precursor of glutathione synthesis, significantly attenuated heme oxygenase induction by SNP and SNAP, and a reduction in heme oxygenase activity was also observed when cells were preincubated with N-acetylcysteine for 16 h prior to exposure to NO donors. This effect appears to be associated with NO stabilization by thiols through the formation of S-nitrosothiols. Hydroxocobalamin, a specific NO scavenger, significantly decreased endothelial heme oxygenase activity, indicating a direct involvement of NO released by NO donors to regulate the expression of this stress protein. Moreover, superoxide anion (O-2) and its reaction product with NO, peroxynitrite (ONOO-), were found to partially contribute to the observed NO-mediated activation of endothelial heme oxygenase. Thus, we suggest the existence of a dynamic equilibrium among free NO, O-2, and endogenous glutathione, which might constitute an interactive signaling mechanism modulating stress and adaptive responses in tissues.

Acetylcysteine↗
PubMed1996

A precursor of the nitric oxide donor SIN-1 modulates the stress protein heme oxygenase-1 in rat liver.

In this study the effect of increased nitric oxide (NO) production on the expression of rat liver heme oxygenase-1, an inducible stress protein responsible for the catalysis of heme to biliverdin and carbon monoxide, was investigated. Rats were injected intraperitoneally with molsidomine (SIN-10), a long acting drug that is enzymatically converted in the liver to yield the active NO-releasing agent 3-morpholinosydnonimine (SIN-1). Administration of SIN-10 resulted in a significant time- and dose-dependent increase in plasma levels of nitrite/nitrate, an index of NO release. A time course of heme oxygenase-1 mRNA levels in liver showed a gradual increase in the expression of the gene encoding for this protein, which was maximal at 4 hours and returned to normal levels by 6 hours after SIN-10 treatment. Heme oxygenase activity also increased by 50% at 4 hours and was maximal 12 hours after SIN-10 administration (63% increase over baseline). These results indicate a possible role for locally generated NO in the modulation of hepatic stress response in vivo suggesting that NO mediates cell adaptation to stress by activation of endogenous defensive mechanisms.

Animals↗
PubMed1996

NO-mediated activation of heme oxygenase: endogenous cytoprotection against oxidative stress to endothelium.

We investigated the effect of nitric oxide (NO) on the induction of the stress protein heme oxygenase and its protective role in vascular endothelial cells exposed to hydrogen peroxide. Treatment of porcine aortic endothelial cells for 6 h with the NO-releasing compounds (0.1-1 mM) sodium nitroprusside (SNP), S-nitroso-N-acetylpenicillamine (SNAP), and 3-morpholinosydnonimine (SIN-1) resulted in a concentration-dependent increase in heme oxygenase activity. At 1 mM, the activity of heme oxygenase was augmented 8.5-fold with SNP, 5.8-fold with SNAP, and 5.7-fold with SIN-1 over the control value. In contrast, endothelial cells exposed to 100 microM S-bromoguanosine 3',5'-cyclic monophosphate, a tissue-permeable analogue that mimics the action of guanosine 3',5'-cyclic monophosphate, did not show any change in heme oxygenase activity. Activation of the inducible NO synthase by the synergistic action of bacterial lipopolysaccharide (250 ng/ml) and interferon-gamma (100 U/ml) also increased endothelial heme oxygenase activity by 3.2-fold (P < 0.05 vs control). Methylene blue (1 microM), an inhibitor of both NO synthase and guanylate cyclase activities, completely abolished this effect. Cells previously exposed to SNAP and SIN-1 exhibited a significant protection against the cytotoxicity mediated by hydrogen peroxide (250 microM) (P < 0.05). Conversely, SNP did not show any protective effects, possibly because of catalytic iron released during its chemical decomposition. In fact, the iron chelator deferoxamine (5 mM) completely suppressed the SNP-mediated cytotoxicity and partially attenuated the activity of heme oxygenase to a level equal to that mediated by SIN-1 and SNAP. These results indicate that NO is a determinant in the modulation of the activity of heme oxygenase leading to a major resistance of the endothelium to oxidative stress.

Animals↗
PubMed1995

Myocardial metabolism and function in acutely ischemic and hypoxemic isolated rat hearts.

We tested the hypothesis that residual oxygen supply during acute low-flow ischaemia or hypoxemia is a major regulator of myocardial performance, metabolism and recovery. Rat hearts were exposed for 20 min to either ischemia (coronary flow reduced to 10% of baseline), hypoxemia (oxygen content reduced to 10% baseline) or a "mixed" condition (combined ischaemia and hypoxemia). The oxygen supply (coronary flow x oxygen content) was matched in all groups (n = 16 per group). Hypoxemic hearts had the highest performance (systolic and developed pressures, +/- dP/dtmax and oxygen uptake) and content of IMP and AMP. Ischaemic hearts had the highest content of ATP, phosphocreatine, adenine nucleotides and purines. As flow and/or oxygenation were restored, post-ischemic hearts showed better functional and metabolic recovery than post-hypoxemic ones. "Mixed" hearts were more similar to hypoxemic ones during oxygen shortage but to ischemic ones during recovery. We conclude that as oxygenation is critically limiting, coronary flow is relatively more important than oxygen supply in determining myocardial function, metabolism and recovery, most likely secondary to changes in the metabolism of diffusible substances.

Adenine Nucleotides↗
PubMed1995

Oxidative-stress response in vascular endothelial cells exposed to acellular hemoglobin solutions.

We investigated the effect of different hemoglobins on the activation of endothelial heme oxygenase (HO), an inducible "stress" protein, which is responsible for heme catabolism, and we determined whether the propensity of hemoglobins to autoxidize correlates with endothelial heme uptake and cell injury. Porcine aortic endothelial cells were incubated for 6 h in the presence of 60 microM unmodified hemoglobin A0 (HbA0), hemoglobin cross-linked between the alpha-chains with bis-(3,5-dibromosalicyl)fumarate (alpha alpha Hb), or cyanomet-alpha alpha-hemoglobin (CNmet alpha alpha Hb). Endothelial HO activity augmented 4.1-fold in the presence of alpha alpha Hb, 2.7-fold with HbA0, and 1.8-fold with CNmet alpha alpha Hb over the control value. Deferoxamine, but not catalase or dimethylthiourea, partially attenuated the HO induction produced by alpha alpha Hb. The rates of methemoglobin formation exhibited a linear relationship over the time of incubation (r = 0.94), and the apparent rate constant was 1.8-fold higher for alpha alpha Hb (0.023 h-1) than for HbA0 (0.013 h-1). Endothelial heme content and lactate dehydrogenase (LDH) release, an index of cell injury, were also higher in alpha alpha Hb compared with HbA0 and CNmet alpha alpha Hb groups (P < 0.05). Deferoxamine but not catalase markedly reduced the release of LDH induced by alpha alpha Hb, whereas dimethylthiourea provided only a partial cytoprotection. These studies suggest that 1) the higher rate of oxidation of alpha alpha Hb contributes to the augmented endothelial HO activity, and 2) both heme release and iron-mediated oxygen radical formation are major contributors to endothelial oxidative stress and cytotoxicity generated by the cross-linked hemoglobin.

Animals↗
PubMed1995

The autoxidation of alpha alpha cross-linked hemoglobin: a possible role in the oxidative stress to endothelium.

The aim of the present study was to investigate the role of hemoglobin autoxidation in the induction of endothelial heme oxygenase (HO), an inducible "stress" protein which is responsible for heme catabolism. Porcine aortic endothelial cells were incubated for six hours in the presence of 60 microM unmodified hemoglobin (HbA0), hemoglobin cross-linked between the alpha chains with bis-(3,5-dibromosalicyl) fumarate (alpha alpha Hb) or cyanomet-alpha alpha-hemoglobin (CNmet alpha alpha Hb). Microsomal HO content increased 4.1-fold in the presence of alpha alpha Hb, 2.7-fold with HbA0 and 1.8-fold with CNmet alpha alpha Hb over the control value. The rates of methemoglobin formation exhibited a linear relationship over the time of incubation (r = 0.94) and the apparent rate constant was 1.8-fold higher for alpha alpha Hb (0.023 h-1) than HbA0 (0.013 h-1). In addition, a linear relationship was obtained by plotting the rates of autoxidation of hemoglobins versus the HO activity (r = 0.99). When cells were incubated with 100% methemoglobin, HO activity increased 5.0-fold and 4.7-fold for HbA0 and alpha alpha Hb, respectively. Intracellular heme concentration, measured after 24 hours of incubation, was also significantly greater in the presence of alpha alpha Hb (52.6% over baseline) compared to HbA0 (10.8%) and CNmet alpha alpha Hb (15.3%) groups (p < 0.05). However, lactate dehydrogenase (LDH) release, measured as an index of endothelial cell injury, increased in all the hemoglobins examined: alpha alpha Hb, 33.8 +/- 1.1 U/l; HbA0, 38.5 +/- 3.5 U/l; CNmet alpha alpha Hb, 41.9 +/- 4.0 U/l; (control group, 19.4 +/- 2.8 U/l). We conclude that: 1) the higher rate of oxidation of alpha alpha Hb renders the molecule more susceptible to induce endothelial oxidative stress (HO induction); 2) the accelerated methemoglobin formation is directly correlated to intracellular HO content and endothelial heme uptake; 3) persistent cell injury suggests that other factors besides heme release may contribute to the hemoglobin-mediated cytotoxicity.

Animals↗
PubMed1994

Oxidative injury in reoxygenated and reperfused hearts.

In this study, we separated the effects of low oxygen supply and low coronary flow in isolated perfused rat hearts to focus on the genesis of free radicals-induced reperfusion injury. Hearts were exposed to either hypoxemia/reoxygenation or ischemia/reperfusion in various sequences, with hypoxemia and ischemia matched for duration (20 min), temperature (37 degrees C), and oxygen supply (10% of baseline). Hypoxemia/reoxygenation (n = 7) resulted in lower (developed pressure) x (heart rate) (p < 0.001) and higher end-diastolic pressure (p < 0.001) than ischemia/reperfusion (n = 9). The presence of 40 IU/ml superoxide dismutase and 104 IU/ml catalase nearly blunted the rise of the end-diastolic pressure (p = 0.02 vs. baseline), but could only partially prevent the depression of myocardial contractility (p < 0.001 vs. baseline, n = 7). Similar patterns were observed when hearts were made ischemic after hypoxemia, eliminating the intermediate reoxygenation step. We conclude that the major determinant of the reperfusion injury is associated with low oxygen supply rather than low coronary flow. Part of the injury is mediated by oxygen-derived free radicals, but a substantial portion of it is associated with energetic processes.

Analysis of Variance↗
PubMed1994

Enhanced oxidation of bis(3,5-dibromosalicyl) fumarate alpha-alpha cross linked hemoglobin by free radicals generated by xanthine/xanthine oxidase.

The xanthine/xanthine oxidase reaction produces reproducible amounts of oxygen-derived free radicals that oxidize human oxyhemoglobin (Hb). We monitored the kinetics of the oxidation of stripped Hb (sHb), purified HbA0 and alpha-alpha cross-linked Hb (HbXL99 alpha) at [Hb] in the 5 to 150 microM (heme) range. For increasing [Hb], the oxidation halftime (t1/2) increased for all Hbs, but t1/2 was always less for HbXL99 alpha than for HbA0 and sHb. Such feature was attributed to the lower affinity for O2 of HbXL99 alpha and may represent a serious problem for use of this Hb as blood substitute.

Aspirin↗