Caffeine and catechin towards prevention of drug induced oxidation of hemoglobin: A spectroscopic study.

Administration of low doses of nitrates over prolonged periods in patients suffering from coronary heart disease may lead to chronic methemoglobinemia, a disease caused by oxidation of hemoglobin. Previous reports have shown that natural products like curcumin, vitamin E, vitamin C, resveratrol, etc., are capable of inhibition of nitrite induced oxidation of hemoglobin. Hence in this study we aimed to investigate the preventive role of antioxidants present in our diet, like caffeine and catechin hydrate which are commonly found in coffee and tea towards methemoglobin (met-Hb) formation. Our study revealed that when the hemolysate was pre-incubated with equimolar concentration of caffeine and its metabolite with respect to nitrite, the rate of the nitrite induced oxidation of HbA decreased from (7.33 ± 0.54) × 10-5 min-1 to (7.09 ± 1.05) × 10-5 min-1 and (2.98 ± 0.06) × 10-5 min-1 respectively. Hence it was evident that the metabolite of caffeine, 1-methyluric acid, exhibited better efficiency at physiological concentration than its precursor. On the contrary, only 4 mM catechin hydrate could enhance the rate of methemoglobin formation even in absence of nitrite and the rate of the reaction was (6.088 ± 0.31) × 10-5 min-1 which is comparable with that of 400 µM nitrite.

Boletus edulis Nitrite Reductase Reduces Nitrite Content of Pickles and Mitigates Intoxication in Nitrite-intoxicated Mice.

Pickles are popular in China and exhibits health-promoting effects. However, nitrite produced during fermentation adversely affects health due to formation of methemoglobin and conversion to carcinogenic nitrosamine. Fruiting bodies of the mushroom Boletus edulis were capable of inhibiting nitrite production during pickle fermentation. A 90-kDa nitrite reductase (NiR), demonstrating peptide sequence homology to fungal nitrite reductase, was isolated from B. edulis fruiting bodies. The optimum temperature and pH of the enzyme was 45 °C and 6.8, respectively. B. edulis NiR was capable of prolonging the lifespan of nitrite-intoxicated mice, indicating that it had the action of an antidote. The enzyme could also eliminate nitrite from blood after intragastric administration of sodium nitrite, and after packaging into capsule, this nitrite-eliminating activity could persist for at least 120 minutes thus avoiding immediate gastric degradation. B. edulis NiR represents the first nitrite reductase purified from mushrooms and may facilitate subsequent applications.

CO binding improves the structural, functional, physical and anti-oxidation properties of the PEGylated hemoglobin.

CONTEXT: PEGylated hemoglobin (Hb) is a promising oxygen therapeutic agent for clinical application. However, it suffered from structural perturbation, functional instability and methemoglobin (metHb) formation. OBJECTIVE: To improve the structural, functional, physical and anti-oxidation properties of the PEGylated Hb. MATERIALS AND METHODS: PEGylation of Hb with CO binding (HbCO) was conducted using maleimide and acylation chemistry, respectively. Physical and chemical parameters were measured for Hb samples. The circular dichroism spectra, dynamic light scattering and analytical ultracentrifugation were used to investigate the structure and conformation of PEGylated HbCO. RESULTS: CO binding can inhibit the autoxidation of the PEGylated Hb, structurally stabilize its tetramer and improve its thermal and pH stability. Importantly, the circular dichroism spectra showed that CO binding can decrease the structural perturbation of Hb induced by PEGylation. The PEGylated HbCO with CO release showed slightly higher oxygen-delivery capacity than the PEGylated Hb. The PEGylated HbCO did not show metHb formation after 30-day storage at 4°C. DISCUSSION AND CONCLUSION: CO binding structurally stabilized the PEGylated Hb, abolished its metHb formation, and significantly increased its physical stability. In particular, it also avoided the perturbation of PEG chains on the heme microenvironment. The functional property of the PEGylated HbCO can be maintained during its long-term storage, which is of great significance for field transfusion.

High-fat diet-induced met-hemoglobin formation in rats prone (WOKW) or resistant (DA) to the metabolic syndrome: effect of CoQ10 supplementation.

The aim of this study was to evaluate the effects of a high-fat diet (HFD) on oxidative indexes in WistarOttawaKarlsburg W (WOKW) rats used as a model of metabolic syndrome in comparison with Dark Agouti (DA) rats used as a control strain. This syndrome is defined by the occurrence of two or more risk factors including obesity, hypertension, dyslipidemia, and insulin resistance. Forty rats were used in the study and the effect of HFD was evaluated in terms of body weight and both hemoglobin and CoQ oxidative status. Moreover, 16 rats (8 of each strain) were supplemented with 3 mg/100 g b.w. of CoQ10 for 1 month in view of its beneficial properties in cardiovascular disease due to its antioxidant activity in the lipid environment. HFD promoted an increase in body weight, in particular in WOKW males, and in the methemoglobin (met-Hb) index in both strains. Moreover, HFD promoted endogenous CoQ10 oxidation. CoQ10 supplementation was able to efficiently counteract the HFD pro-oxidant effects, preventing met-Hb formation and CoQ oxidation.

Inhibition of methemoglobin formation in aqueous solutions under aerobic conditions by the addition of amino acids.

Hemoglobin (Hb) as an important iron-containing oxygen-transport protein is easily oxidized to the ferric met-form, methemoglobin (metHb), and loses the capacity of binding oxygen during storage. In this study, the experimental data indicate that the presence of Tyr and Glu significantly suppress the metHb formation in the Hb solutions in aqueous environment under aerobic conditions at the temperature of 25 and 37 °C, respectively. At pO2 of 144Torr the metHb percentage in the Hb solutions was the lowest with less than 10% at day 7 after incubation with Tyr at the ratio of 24 at pH 9.5 at 25 °C. At 37 °C, the metHb percentage did not reach 5% after 12h of incubation with Glu at the ratio of 24 at pH 9. Molecular simulation analysis suggest that the presence of Tyr or Glu may contribute to the formation of the breakwater network, the stabilization of distal histidine, the changes in the size of heme pocket, and eventually result in the inhibition of metHb formation. This study provides insight into a new design for Hb-oxygen based carriers with strongly inhibition of metHb formation in aqueous environment under aerobic conditions, even at physiological temperature in vitro.

[Effect of selenium on resistance of hemoglobin to photooxidative processes].

On an example of a guinea pig it is shown that exogenous selenium (0.5 mg Na2SeO3 per 1 kg of the animal weight) during 2-hour exposition in the animal organism increases the resistance to the photo-induced oxidation of haemoglobin in erythrocyte lysates without additional stimulation of glutathione peroxidase mechanism of haemoglobin protection by exogenous selenium. It is shown that the saturation of haemoglobin fractions by selenium hampers the oxidative modification of haemoglobin. Using pregnancy of women as a natural model of selenium-deficiency condition, it has been shown that physiological debilitation of saturation erythrocytes with selenium, including haemoglobin fractions of lysates erythrocytes caused debilitation of resistance of haemoglobin to photooxidative destruction. Under these conditions not only activity of enzyme glutathione peroxidise in erythrocyte lysates, but also the peroxidase activity of haemoglobin (in the presence of glutathione) were decreased. It is more characteristic of erythrocyte lysates with a less content of selenium, i.e. for the erythrocytes of women on late terms of pregnancy that testifies to the presence of certain relation between haemoglobin saturation with selenium and its peroxidase activity (in the presence of glutathione).

In vitro suppression of drug-induced methaemoglobin formation by Intralipid(®) in whole human blood: observations relevant to the 'lipid sink theory'.

To provide further evidence for the lipid sink theory, we have developed an in vitro model to assess the effect of Intralipid® 20% on methaemoglobin formation by drugs of varying lipid solubility. Progressively increasing Intralipid concentrations from 4 to 24 mg.ml⁻¹ suppressed methaemoglobin formation by the lipid soluble drug glyceryl trinitrate in a dose-dependent manner (p < 0.001). Both dose and timing of administration of Intralipid to blood previously incubated with glyceryl trinitrate for 10 and 40 min resulted in significant suppression of methaemoglobin formation (p < 0.0001 and p < 0.05, respectively). Mathematical modelling demonstrated that the entire process of methaemoglobin formation by glyceryl trinitrate was slowed down in the presence of Intralipid. Intralipid did not significantly suppress methaemoglobin formation induced by 2-amino-5-hydroxytoluene (partially lipid soluble) or sodium nitrite (lipid insoluble; both p > 0.5). This work may assist determination of the suitability of drugs taken in overdose for which Intralipid might be deployed.

Methemoglobinemia following unintentional ingestion of sodium nitrite--New York, 2002.

Methemoglobinemia is an unusual and potentially fatal condition in which hemoglobin is oxidized to methemoglobin and loses its ability to bind and transport oxygen. The most common cause of methemoglobinemia is the ingestion or inhalation of oxidizing agents such as nitrates or nitrites (e.g., sodium nitrite, which is used commonly as a preservative in curing meats and fish). This report summarizes the investigation of an incident of methemoglobinemia in five members of a household in New York who became ill after eating a meal seasoned with a white crystalline substance from a plastic bag labeled "Refined Iodized Table Salt" (Figure). The findings underscore the need for proper storage of hazardous materials to avoid unintentional ingestion and the importance of collaboration by multiple agencies to address a potential public health emergency.

Direct and metabolism-dependent toxicity of sulphasalazine and its principal metabolites towards human erythrocytes and leucocytes.

1. The role of metabolites in sulphasalazine-mediated toxicity has been investigated in vitro by the use of human red blood cells and mononuclear leucocytes as target cells, with methaemoglobin formation and cytotoxicity respectively, being the defined toxic end-points. 2. Of the metabolites of sulphasalazine investigated, only sulphapyridine was bioactivated by human liver microsomes in the presence of NADPH to a metabolite which caused marked methaemoglobinaemia and a small, but statistically significant degree of mononuclear leucocyte cell death. 3. Methaemoglobinaemia was inhibited by ketoconazole but not by ascorbic acid (100 microM), glutathione (500 microM) and N-acetylcysteine (50 microM). In contrast, ascorbic acid and the thiols afforded complete protection for mononuclear leucocytes. 4. Sulphapyridine (100 microM) was converted in vitro to a metabolite (metabolite conversion 6.8 +/- 0.3%), the retention time of which on h.p.l.c. corresponded to synthetic sulphapyridine hydroxylamine. The half-life of sulphapyridine hydroxylamine in phosphate buffer (pH 7.4) was found to be 8.1 min. 5. In the absence of microsomes and NADPH, sulphapyridine hydroxylamine caused a concentration-dependent (10-500 microM) increase in methaemoglobinaemia (2.9%-24.4%) and cytotoxicity (5.4%-51.4%), whereas sulphasalazine, sulphapyridine, 5-hydroxy sulphapyridine and 5-aminosalicylic acid had no effect.

[Effect of thyroxine on methemoglobin content and the activity of antioxidant enzymes of human erythrocytes in vitro]. / Deistvie tiroksina na soderzhanie metgemoglobina i aktivnost' antiokislitel'nykh fermentov éritrotsitov cheloveka in vitro.

A study was made of the effect of thyroxine in vitro on the activity of antioxidant enzymes: superoxide dismutase (SOD) and catalase, and on the methemoglobin content in the erythrocytes of 23 healthy persons aged 17-25. Erythrocyte incubation was performed in different media: in their own plasma, a weak solution of NaOH, tris-HCl buffer solution (pH 7.4) with thyroxine in the physiological concentration and without it. The enzyme activity was compared in the native and incubated erythrocytes. After the incubation of erythrocytes with thyroxine in their own plasma the SOD and catalase activity showed a statistically significant rise, and the methemoglobin content decreased. This effect was undetectable in the incubation of erythrocytes with thyroxine in tris-buffer solution. Direct incubation of SOD with thyroxine isolated from the erythrocytes did not cause any changes in enzyme activity. Probably the interaction of thyroxine with erythrocyte membrane components is important for the implementation of the hormonal effect. Some unidentified factors contained in the blood plasma may play a role in the SOD activation. The authors discuss thyroxine ab to cause rapid regulation of the activity antioxidant enzymes.