Biomedical subjects

P Eyer

Publications and source records attributed to P Eyer.

At least 73 records · Page 4Linked to original sources

PubMed1987

Formation of cyanide after i.v. administration of the oxime HI 6 to dogs.

HI 6(pyridinium, 1-[[[4-(aminocarbonyl)pyridinio]methoxy]-2- [(hydroxyimino)methyl]-dichloride belongs to a series of bisquaternary pyridinium oximes that are effective against poisoning with extremely toxic organophosphates. Since HI 6 has been shown to be unstable at pH 7.4 and to release significant amounts of cyanide, a study was undertaken to determine the degree of cyanide formation from HI 6 in vivo. When HI 6 (100 mumol/kg) was administered i.v. to dogs, the animals showed no signs of cyanide toxicity but exhibited some cholinomimetic symptoms, including retching, hypersalivation and enhanced intestinal motility. Cyanide content in whole blood was monitored after production of methemoglobinemia (30%) by 4-dimethylaminophenol in order to sequester cyanide within red cells. Maximal cyanide contents of 20 mumol/l were found in blood after 90 min. Calculation of the area under the concentration versus time curve for blood cyanide indicates that about 4% of HI 6 produced cyanide. Determination of the pharmacokinetic parameters of HI 6 (VD = 0.31 l/kg; kel = 0.76 h-1) and of cyanide (VD = 0.086 l/kg; kel = 0.52 h-1) together with the apparent first order rate constant of cyanide formation from HI 6 in vitro (0.17 h-1, pH 7.4, 37 degrees) allowed the simulation of a cyanide concentration curve that fitted with the experimental data points, indicating that cyanide formation in vivo was not bio-catalyzed. It is concluded that cyanide formation from HI 6 may not be regarded as a potential hazard, since cyanide elimination exceeded markedly its formation. Whether this conclusion also holds true for man has to be established.

Aminophenols↗

PubMed1987

Reactions of para-substituted nitrosobenzenes with human hemoglobin.

Bio-monitoring the covalent binding of nitrosoarenes to the SH groups of human hemoglobin has been proposed as a reliable approach to get an integral parameter for exposure control and possibly risk assessment of persons exposed to aromatic amines and nitro compounds. Availability of nitrosoarenes to bind to the cysteine residues is greatly influenced by the competition of hemoglobin iron with nitrosoarenes. In contrast to earlier reports, we found that nitrosobenzene has a 14 fold higher affinity for "stripped" human hemoglobin than oxygen. The binding mode is similar to gaseous ligands and exhibits the same free energy of cooperation and sensitivity to heterotropic effectors like inositol hexaphosphate. To elucidate the electronic influence of para substituents, 4-chloronitrosobenzene, 4-nitrosotoluene and 4-nitrosophenetole were tested. A linear free energy relationship was found for all equilibrium parameters with a reaction constant rho = 3, when using Hammett sigma p constants. Similarly, the apparent second order rate constants for binding of para-substituted nitrosobenzenes to the cysteine residues (Cys beta 93) in hemoglobin followed the Hammett relationship with lg k-lg k0 = 1.7 X sigma p (r2 = 0.99). In case of 4-chloronitrosobenzene covalent binding proceeded biphasically and a "semimercaptal"-like intermediate was observed. The affinities for hemoglobin iron and for the SH groups were highest with 4-chloronitrosobenzene and lowest with 4-nitrosophenetole. All nitrosobenzenes were capable to produce ferrihemoglobin. In the absence of oxygen, 4-chloronitrosobenzene hemoglobin decayed with formation of ferrihemoglobin. Presumably the nitroxide radical anion is formed as an intermediate which comproportionates into the azoxy derivative. It is assumed that the efficiency of the microscopic compartmentation of nitrosoarenes by binding to hemoglobin iron has important impacts on the toxicokinetics of these compounds.

Cysteine↗

PubMed1987

Formation of 4-ethoxy-4'-nitrosodiphenylamine in the reaction of the phenacetin metabolite 4-nitrosophenetol with glutathione.

Phenacetin, a constituent of several analgesic and antipyretic formulations has been made responsible for a variety of toxic and carcinogenic actions. 4-Nitrosophenetol, the N-oxydation product of intermediate 4-phenetidine, forms methemoglobin and binds covalently to sulfhydryl groups of proteins and glutathione. In the reaction of 4-nitrosophenetol with glutathione and other thiols an intermediate so-called "semimercaptal" is formed from which N-(thiol-S-yl)-4-phenetidine S-oxide, N-(thiol-S-yl)-4-phenetidine and 4-phenetidine derive. Besides thiol adducts, a yellow compound is formed which was isolated as a pure crystalline product (elemental analysis) and identified by FAB-MS, EI-MS, 13C-, 1H-NMR, and UV-VIS spectroscopy as 4-ethoxy-4'-nitrosodiphenylamine. This nitrosoarene is formed by an unknown mechanism from 4-nitrosophenetol and 4-phenetidine under liberation of ethanol. In human erythrocytes this compound is easily reduced to 4-amino-4'-ethoxydiphenylamine (FAB-MS, EI-MS, 13C-NMR). During the reaction of 4-nitrosophenetol with red cells only traces of 4-ethoxy-4'-nitrosodiphenylamine were formed, whereas up to 10% appeared as the reduction product 4-amino-4'-ethoxydiphenylamine. This latter compound is unstable in red cells and is metabolized further to unidentified products.

Chemical Phenomena↗

PubMed1986

Evaluation of the micromethod for determination of glutathione using enzymatic cycling and Ellman's reagent.

Evaluation of the kinetic parameters of the various reactions involved in the determination of glutathione provided the rationale for a modification of the frequently used assay (F. Tietze, 1969, Anal. Biochem. 27, 502-522) whereby the enzymatic reaction is no longer rate limiting. At pH 6.0, the nonenzymatic thiol interchange reaction of reduced glutathione (GSH) with Ellman's reagent becomes rate limiting, and inhibition of glutathione reductase up to 50% has no influence on the accuracy of the determination. The lower level of sensitivity is 10(-10) mol glutathione with a linear response up to 5 X 10(-9) mol. For determination of glutathione disulfide, GSH is alkylated by N-ethylmaleimide (NEM), and excess NEM is removed by extraction with ethyl acetate. Since the glutathione adduct is not stable, extracted samples are kept deep-frozen prior to analysis. Using this precaution, less than 0.05% of GSSG was determined in GSH-containing samples which had been previously freed from GSSG.

Dithionitrobenzoic Acid↗

PubMed1986

Formation and transport of xenobiotic glutathione-S-conjugates in red cells.

In vitro studies with freshly drawn human erythrocytes showed 4-dimethylaminophenol, a cyanide antidote, to be rapidly metabolized with the formation of a transient S,S-(2-dimethylamino-5-hydroxy-1,3-phenylene)bis-glutathione conjugate and a stable S,S,S-(2-dimethylamino-5-hydroxy-1,3,4-phenylene)tris-glutathione conjugate. The stable tri-glutathionyl derivative was actively transported across the red cell membrane with an apparent Vmax = 1 nmol/min/ml red cell suspension (15 g hemoglobin/100 ml) and Km = 0.5 mM. The transport system was strictly unidirectional, inhibited completely by sodium fluoride and reduced to one-fifth by lowering the temperature from 37 to 22 degrees. Similarly S-(2,4-dinitrophenyl)-glutathione, the glutathione-S-transferase mediated glutathione-S-conjugate with 1-chloro-2,4-dinitrobenzene, was unidirectionally transported, a process which was inhibited by sodium fluoride. Kinetic analysis revealed two different transport processes: Vmax = 0.9 nmol/min/ml, Km = 1.4 microM and Vmax = 4.5 nmol/min/ml, Km = 700 microM. Mutual inhibition of the low affinity transport system was found for both glutathione-S-conjugates. The apparent energies of activation for all these transport processes and for GSSG were identical (70 kJ/mol) suggesting at least one common carrier for the excretion of the three glutathione-S-conjugates.

Aminophenols↗

PubMed1986

Studies on the decomposition of the oxime HI 6 in aqueous solution.

HI 6 has been shown to be efficacious in soman intoxication of laboratory animals by reactivation of acetylcholinesterase. To assess possible risks involved in the administration of HI 6 its degradation products were analyzed at pH 2.0, 4.0, 7.4, and 9.0. At pH 2.0, where HI 6 in aqueous solution has its maximal stability, attack on the aminal-acetal bond of the "ether bridge" predominates, with formation of formaldehyde, isonicotinamide, and pyridine-2-aldoxime. Besides, HI 6 decomposes at the oxime group yielding 2-cyanopyridine. Liberation of hydrocyanic acid at pH 2.0 is below 5%. At pH 7.4, primary attack is on the oxime group, resulting in formation of the corresponding pyridone via an intermediate nitrile. The pyridone has been isolated and identified as 2-pyridinone, 1-[(4-carbamoylpyridinio)methoxy)methyl)formate. This major metabolite deaminates further to the 2-pyridinone, 1-[(4-carboxypyridinio)methoxy)methyl) derivative, which ultimately decomposes into formaldehyde, isonicotinic acid, and 2-pyridone. Hydrolysis of the acid amide group probably also occurs with HI 6 itself. Significant amounts of free hydrocyanic acid were only detected in the presence of an alkali trap; otherwise hydrocyanic acid reacts with formaldehyde to yield hydroxyacetonitrile from which hydrocyanic acid can be liberated again. Up to 0.6 equivalents of hydrocyanic acid were evolved at pH 7.4. After repetitive administration and impaired renal elimination of HI 6, e.g. during renal shock, there might be some risk of cyanide intoxication.

Acetonitriles↗

PubMed1986

Pharmacokinetics and pharmacodynamics of the oxime HI6 in dogs.

The pharmacokinetics and pharmacodynamics of the oxime HI6 were investigated in conscious and anesthetized beagle dogs following intramuscular injection. The absorption of HI6 (100 mumol/kg) was slower in conscious dogs as compared to the anesthetized dogs, and the maximum concentrations in plasma were lower (200 instead of 300 mumol/l). In comparison, the elimination of HI6 (100 mumol/kg) was twice as rapid in the conscious dogs (ke = 0.013 instead of 0.006 min-1) as in the anesthetized animals and was equal to the elimination after injection of 50 mumol/kg (likewise in anesthesia). The more rapid elimination was accompanied by a greater renal excretion of unchanged HI6 (60% instead of 40% in 3 h). HI6 penetrated the blood-brain barrier. The concentration of the oxime in CSF increased rapidly during the absorption phase (by 30 min after injection). The maximum concentrations (1-3 mumol/l) were reached between 60 and 120 min. The peak concentrations in plasma and CSF did not correlate with each other. In the anesthetized dogs the higher dose of HI6 (100 mumol/kg) caused a steady decrease in mean blood pressure (20 mm Hg) and blood flow (50%) in the femoral artery and a fall in left ventricular pressure (20 mm Hg), lasting for at least 60 min; the lower dose (50 mumol/kg) did not cause circulatory effects. EKG, respiration, hematocrit, arterial blood gases, and pH were not influenced.

Anesthesia↗

PubMed1985

Formation and disposition of nitrosochloramphenicol in rat liver.

It has been suggested that in the chloramphenicol-induced aplastic anemia nitrosochloramphenicol may be involved as a toxic intermediate. We found that aminochloramphenicol, which reportedly is formed from chloramphenicol by intestinal bacteria, is N-oxygenated by liver microsomes of untreated rats with apparent Km = 0.4 mM and Vmax = 0.28 nmole/min/mg protein. These values are in close agreement with those reported for aniline N-oxygenation. Reductive reactions, however, eliminate the N-oxygenation products at markedly higher rates. As judged from hemoglobin-free single-pass liver perfusion experiments, N-hydroxy-chloramphenicol is reduced at rates faster than 300 nmole/min/g liver wet, and nitrosochloramphenicol is eliminated at rates faster than 1.5 mumole/min/g liver. At least two NADPH- and two NADH-dependent cytosolic enzymes are responsible for nitrosochloramphenicol reduction. Determination of the kinetic parameters of these enzymes by stop-flow analysis revealed the contribution of enzymes, one of it being alcohol dehydrogenase, with Michaelis constants in the micromolar range. Despite this high reducing capacity, about 10% of nitrosochloramphenicol reacted with GSH under formation of glutathionesulfinamidochloramphenicol and GSSG released from the liver into bile and venous effluent. At high nitrosochloramphenicol load these reactions led to glutathione depletion of the liver, caused membrane damage, and impaired bile production. At low nitrosochloramphenicol load, i.e. below 0.5 mumole/min/g, no relevant nitrosochloramphenicol passed the liver. These data together with the previously reported reactions of nitrosochloramphenicol within human blood suggest that nitrosochloramphenicol, if formed at all in the intestine or liver, is rather unlikely to be transferred to the critical target.

Administration, Oral↗

PubMed1985

Pharmacokinetics and toxicity of the oxime HGG 12 in dogs.

The pharmacokinetics, pharmacodynamics, and toxicity of the oxime HGG 12 were studied in conscious and anesthetized dogs. IV administration. The mean value of the half-time for terminal elimination of HGG 12 was 47 min; plasma clearance amounted to 4.6 ml kg-1 min-1 and Vapp to 0.315 1 kg-1. At doses above 1 mumol/kg heart rate, left ventricular pressure and mean arterial pressure decreased, while central venous pressure and femoral blood flow increased. The dose-response curves were very flat. Repetitive administration of various doses of HGG 12 in 30 min intervals did not enhance the negative chronotropic effect when the preceding total dose amounted to about 1 mumol/kg. IM administration. The half-times for the absorption of HGG 12 dichloride and HGG 12 dinitrate were about 3.5 min; the corresponding value for HGG 12 dibromide was 9.4 min. In the elimination phase the half-time was comparable with that of the IV experiments. About 60% of the oxime was excreted unchanged in the urine within 24 h. The circulatory changes showed the same tendency as after IV injection. Conscious dogs tolerated well daily doses of 10 mumol/kg for 6 weeks. At 30 mumol/kg all dogs survived, displaying symptoms reminiscent of a cholinergic syndrome. Five out of eight dogs survived at 90 mumol/kg. Macroscopic and microscopic examinations and blood chemistry data showed no abnormality.

Anesthesia↗

PubMed1985

On the mechanism of reactions of nitrosoarenes with thiols. Formation of a common intermediate "semimercaptal".

To get more insight into the reactions of nitrosoarenes with thiols which may be responsible for cytotoxic effects, the reaction mechanism was studied with nitrosobenzene and 1-thioglycerol as model compounds. A transient intermediate was isolated by high performance liquid chromatography and identified as 2,3-dihydroxypropanesulfenic N-hydroxyphenylamide ("semimercaptal") by UV, 13C-NMR, and FAB mass spectroscopy. In aqueous solution this labile compound reassembles into 2,3-dihydroxypropanesulfinic phenylamide in a first order reaction. In the presence of excess thiol or ascorbic acid the "semimercaptal" is reduced to 2,3-dihydroxypropanesulfenic phenylamide without transient formation of a complete "mercaptal". Hydrolysis rather than thiolysis liberates aniline from the sulfenic phenylamide. Both the sulfinic and sulfenic phenylamides were obtained in crystalline form and identified by NMR and FAB mass spectroscopy. A scheme is presented of the known reactions of nitrosoarenes with thiols.

Glycerol↗

PubMed1984

Reactions of nitrosochloramphenicol in blood.

It has been suggested that nitrosochloramphenicol (NOCAP), a possible metabolite of chloramphenicol (CAP), may be involved in CAP-induced aplastic anemia. We found that NOCAP was rapidly eliminated from human blood in vitro (more than 90% in less than 15 sec). Analysis of the different reactions showed that 5% of NOCAP was covalently bound to plasma proteins, mainly to albumin, the remainder being metabolized in red cells. The most important reaction in red cells was the very rapid adduct formation with GSH (k = 5,500 M-1S-1), yielding presumably a semimercaptal which either isomerized to a sulfinamide (GSONHCAP, k = 0.05 s-1) or was thiolytically cleaved by another GSH molecule with formation of the hydroxylamine (NHOHCAP) and GSSG (k = 7.1 M-1S-1). Another important elimination reaction was the covalent binding of NOCAP to the SH groups of hemoglobin (k = 5M-1S-1), also yielding a sulfinamide. Besides these reactions with thiols, NOCAP was enzymatically reduced to NHOHCAP in the presence of NADPH (Km NADPH = 10(-5) M; Km NOCAP = 10(-4) M; Vmax = 2 mumole/min per ml). This reaction was only effective at NOCAP concentrations below 10(-4)M, probably because of limited NADPH-regeneration. Further reduction of NHOHCAP to NH2CAP was a slow process which did not exceed 0.5 nmole/min per ml. NH2CAP was mainly formed from GSONHCAP, a reaction which depended on NADPH and the presence of hemolysate, indicating an enzymatic reaction. In contrast to smaller nitrosoarenes, NOCAP was a poor ligand for ferrohemoglobin (probably due to steric hindrance by its bulky molecule) and was therefore much more exposed to biotransformation. NOCAP and NHOHCAP formed ferrihemoglobin at a rate 5000 times slower than did phenylhydroxylamine. In contrast to NOCAP, NHOHCAP penetrated slowly the red cell membrane (4 about 5 min), and its disposition in blood was quite ineffective. From these data, it seems likely that most of the NOCAP formed by microorganisms in the intestine or produced in the liver, will be degraded in blood before it can reach the bone marrow.

Biological Transport↗

PubMed1984

Radical formation during autoxidation of 4-dimethylaminophenol and some properties of the reaction products.

4-Dimethylaminophenol (DMAP), after intravenous injection, rapidly forms ferrihaemoglobin and has been successfully used in the treatment of cyanide poisoning. Since DMAP produces many equivalents of ferrihaemoglobin, it was of interest to obtain further insight into this catalytic process. DMAP autoxidizes readily at pH regions above neutrality, a process which is markedly accelerated by oxyhaemoglobin. The resulting red-coloured product was identified as the 4-(N,N-dimethylamino) phenoxyl radical by EPR spectroscopy. The same radical was also produced by pulse radiolysis and oxidation with ferricyanide. The 4-(N,N-dimethylamino)phenoxyl radical is quite unstable and decays in a pseudo-first order reaction (k = 0.4 sec-1 at pH 8.5, 22 degrees) with the formation of p-benzoquinone and dimethylamine. This observed decay rate is identical with the rate of hydrolysis of N,N-dimethylquinonimine. When a solution containing the phenoxyl radical was extracted with ether, half the stoichiometric amount of DMAP was recovered. Hence it is apparent that the phenoxyl radical decays by disproportionation yielding DMAP and N,N-dimethylquinonimine. The latter product then quickly hydrolyses. The equilibrium of this disproportionation reaction is far towards the radical side, and the pseudo-first order hydrolysis controls the radical decay rate. p-Benzoquinone rapidly reacts with DMAP (k2 = 2 X 10(4) M-1 sec-1) with the formation of the 4-(N,N-dimethylamino)phenoxyl and the semiquinone radicals. This reaction explains the autocatalytic phenoxyl radical formation during autoxidation of DMAP. DMAP is not oxidized by H2O2 or O-.2 but the 4-(N,N-dimethylamino)phenoxyl radical is very rapidly reduced by O-.2 (k2 = 2 X 10(8) M-1 sec-1). In addition, the phenoxyl radical is quickly reduced by NAD(P)H or GSH with the formation of NAD(P)+ or GSSG. Since DMAP is also able to reduce two equivalents of ferrihaemoglobin (provided that the ferrohaemoglobin produced is trapped by carbon monoxide), electrophilic addition reactions of the phenoxyl radical seem unimportant in contrast to N,N-dimethylquinonimine. Hence, during the catalytic ferrihaemoglobin formation, DMAP is oxidized by oxygen which is activated by haemoglobin, and the phenoxyl radical oxidizes ferrohaemoglobin. This catalytic process is terminated by covalent binding of N,N-dimethylquinonimine to SH groups of haemoglobin (and GSH in red cells).

Aminophenols↗

PubMed1983

Differences in the reactions of isomeric ortho- and para-aminophenols with hemoglobin.

The metabolites of phenacetin, 2-hydroxyphenetidine and 4-nitrosophenetol, rapidly produced ferrihemoglobin both in vivo (dogs) and in vitro. At low concns, 2-hydroxyphenetidine was superior to 4-nitrosophenetol in ferrihemoglobin formation. The kinetics of ferrihemoglobin formation by 2-hydroxyphenetidine in solutions of purified human hemoglobin was biphasic and exhibited an unusual dose response. Similar to p-aminophenols, 2-hydroxyphenetidine was oxidized by oxyhemoglobin, and the oxidation product(s) were reduced by ferrohemoglobin with the formation of ferrihemoglobin. In addition, these oxidation products condensed to 2-amino-7-ethoxy-3H-phenoxazine-3-one (u.v., i.r., 1H-NMR and mass spectroscopy). This metabolite produced ferrihemoglobin by itself and was responsible for the slow phase of ferrihemoglobin formation observed with 2-hydroxyphenetidine. This condensation reaction, which was also observed with 2-aminophenol, prevented thioether formation of the transient o-quinonimines with the cysteine residues of hemoglobin and reduced glutathione as observed with 4-aminophenol and 4-dimethylaminophenol. Phenoxazone formation, which depends on the square of the o-quinonimine concn, was negligible at micromolar concns. At similar concns addition reactions to thiols prevailed also with 2-hydroxyphenetidine and 2-aminophenol. Other electrophilic reactions, e.g. with primary amino groups of amino acids, were insignificant. These dose-dependent differences in the reactions of isomeric aminophenols may explain the low nephrotoxicity of those o-aminophenols capable of forming phenoxazones when given in a single dose. This self-detoxication of some o-quinonimines, however, should not function during long-term exposure to repetitive low doses of such o-aminophenols.

Aminophenols↗

PubMed1983

Reactions of the nitroso analogue of chloramphenicol with reduced glutathione.

Nitroso-chloramphenicol (NOCAP) was synthetized by reduction of chloramphenicol (CAP) with zinc dust in a modification of the procedure published by Corbett and Chipko. The radioactive derivative was similarly prepared from [dichloroacetamido-1-14C]CAP. NOCAP rapidly reacted with GSH with the formation of hydroxylamino-chloramphenicol (NHOHCAP), D-(-)-threo-1-(p-hydroxylaminophenyl)-2-dichloroacetamido-1,3-propanediol and glutathione disulfide (GSSG). In addition, a hydrophilic sulfinamide was formed (GSONHCAP), D-(-)-threo-1-(p-glutathionesulfinamidophenyl)-2-dichloroacetamido-1, 3-propanediol. Free amino-chloramphenicol (NH2CAP), D-(-)-threo-1-(p-aminophenyl)-2-dichloracetamido-1,3-propanediol, was not detected. The proportion of NHOHCAP formed increased with increasing GSH concn, at the expense of GSONHCAP. Analysis by stopped-flow spectroscopy revealed formation of a labile adduct in the reaction of NOCAP with GSH (k = 5500 M-1 sec-1 at 37 degrees, pH 7.4). This reaction was reversible because nearly all NOCAP could be extracted with ether from the labile intermediate. The equilibrium adduct/NOCAP was dependent on GSH concn (K = 4500 M-1 at 37 degrees, pH 7.4). The labile intermediate either isomerized to the sulfinamide, GSONHCAP (favoured by decreasing pH at constant GSH), or it was thiolytically cleaved by another GSH molecule to NHOHCAP and GSSG (favoured by increasing GSH at constant pH). At acid pH, GSONHCAP readily hydrolyzed to NH2CAP and glutathionesulfinic acid. Thus, NOCAP reacts with thiols similar to nitrosobenzene. A scheme is presented for the proposed reaction mechanism. It is concluded that most of the NOCAP, if formed in the intestine or liver, will be rapidly disposed by reactions with GSH. Hence, toxic concns at the sensitive target, i.e. the bone marrow, may usually be prevented.

Chemical Phenomena↗

PubMed1983

The red cell as a sensitive target for activated toxic arylamines.

During biotransformation of arylamines, activated phase I metabolites, like aminophenols and hydroxylamines, occasionally escape the liver and exert allergic, toxic or carcinogenic effects in sensitive target organs. The first organ in contact with these proximate toxic compounds is the blood where oxyhemoglobin activates proximate to ultimate toxic derivatives. Thereby hydroxylamines and oxyhemoglobin are co-oxidized to nitrosoarenes and ferrihemoglobin. Because of an enzymic cycle, severe methemoglobinemia can occur even with small, catalytic amounts of hydroxylamines. Reactive oxygen intermediates, if not eliminated enzymically, may be responsible for hemolysis, Heinz body formation, and green pigments. In addition, nitrosoarenes bind covalently to hemoglobin and membranes and deplete glutathione by formation of glutathione-sulfinamides. Aminophenols, on the other hand, have to be activated first by oxyhemoglobin to phenoxyl radicals and quinonimines, which are reduced back with simultaneous ferrihemoglobin formation. Hence, aminophenols catalytically transfer electrons from iron to oxygen. This catalytic cycle is terminated by side reactions: p-quinonimines form adducts with glutathione and hemoglobin. Thereby the physiological functions of hemoglobin can be greatly altered as shown for 4-dimethylaminophenol. o-Quinonimines either condense to the respective phenoxazones, or if condensation is hindered, they form adducts, mainly with thiols. The different pathways for o-aminophenols are concentration-dependent, with adduct formation being favoured at low concentrations. Thus, methemoglobin formation poorly correlates with the implications of reactive electrophilic intermediates.

Amines↗

PubMed1983

Effects and biotransformation of 4-dimethylaminophenol in man and dog.

The cyanide antidote 4-dimethylaminophenol . HCl (DMAP) was administered orally, i.v., or i.m. to man and dog. Ferrihemoglobin formation and changes of several parameters in human blood were investigated to obtain information on damage to liver, kidney, muscle, and red blood cells; in addition, the metabolism of DMAP was studied. In dogs, the initial rate of ferrihemoglobin production (DMAP, 3.25 mg/kg i.v. or i.m., 15 mg/kg orally) amounted to 28%, 3.5%, and 2% of the total hemoglobin per min; the corresponding values for man were 9%, 2%, and 2% per min. The dogs behaved normally while CPK increased after i.m. injection. In man, only i.m. injection of DMAP (3.25 mg/kg) was followed by increases in LDH, GOT, and CPK of 110, 260, and 490%, resp.; while total bilirubin, conjugated bilirubin, and iron concentration rose by 270, 120, and 50%, respectively. Bilirubin and iron concentration increased also after DMAP i.v. (3.25 mg/kg) or when it was taken orally (600 or 900 mg). The lactate concentration was not influenced while the pyruvate concentration increased by 50%. DMAP produced hemolysis in vitro. Generally, the values determined in vivo approached the starting level within 1 week. Intramuscular injection of DMAP induced reversible subjective and objective symptoms, e.g., local pain, swollen buttock, fever reaction. The urine showed no pathological changes. About 54% of DMAP taken orally was excreted as metabolites in the urine, 41% as glucuronide, 7% as sulfate, and 6% as thioethers. After i.v. administration the total of metabolites was somewhat higher, and the thioether proportion was 15%. The results indicate that DMAP is readily absorbed after oral administration but undergoes significant first pass effect in the liver. Therefore, the 4-fold i.v. dose must be administered orally to achieve the same ferrihemoglobin formation.

Administration, Oral↗

PubMed1983

The metabolism of 3-benzoylpyridine.

3-Benzoylpyridine (3-BP), a decomposition product of the soman antidote, HGG-12 (3-benzoylpyridino(1)-methyl 2'-hydroxyiminomethylpyridino(1')methyl ether dichloride) was rapidly metabolized in the isolated perfused rat liver, giving 3-(alpha-hydroxybenzyl)pyridine and its corresponding glucuronide, 3-benzoylpyridine-N-oxide, and 3-(alpha-hydroxybenzyl)pyridine-N-oxide. The latter is formed both from 3-(alpha-hydroxybenzyl)pyridine and 3-benzoylpyridine-N-oxide. Metabolism of 3-BP studied in rats and dogs in vivo revealed significant species differences. In rat, 80% of 14C-3-BP was excreted as N-oxides and alpha-hydroxybenzyl derivatives in the urine. In dogs, 95% dose was excreted in urine mostly as the glucuronide of 3-(alpha-hydroxybenzyl)pyridine and as the quaternary pyridinium compounds, 3-benzoyl-1-methylpyridinium and 3-(alpha-hydroxybenzyl)-1-methylpyridinium. These latter were hardly detected in rat urine. In contrast to rats, the N-oxides were present only in small amounts in dog urine.

Animals↗

PubMed1983

Site and mechanism of covalent binding of 4-dimethylaminophenol to human hemoglobin, and its implications to the functional properties.

4-Dimethylaminophenol, after i.v. injection, rapidly forms ferrihemoglobin and has been successfully used in the treatment of cyanide poisoning. The catalytic ferrihemoglobin formation is terminated by thioether formation of oxidized 4-dimethylaminophenol with reduced glutathione or cysteine 93 beta of hemoglobin. Hereby the physiological functions of human hemoglobin are markedly altered. After binding of two molecules of 4-dimethylaminophenol to tetrameric hemoglobin, the rate of autoxidation is increased about 6-fold. The oxygen affinity is 10 times higher than normal, the Hill coefficient is diminished nearly to unity, and the Bohr effect is reduced by about 50%. The physiologically important allosteric regulation of the oxygen affinity by 2,3-diphosphoglycerate is abolished, and the binding of 2,3-diphosphoglycerate to deoxyhemoglobin no longer functions. By molecular sieving, two alkylated hemoglobins were separated: a hemoglobin fraction with an unchanged low tetramer dimer dissociation, normal electronic spectra, and normal digestibility by carboxypeptidase A; and a second fraction with a high degree of dissociation, altered electronic spectra, and impaired digestibility. A tryptic peptide was isolated containing cysteine 93 beta and histidine 146 beta cross-linked by an arylic compound missing the dimethylamine label. The following reaction mechanism is concluded: Oxy-hemoglobin catalyzes the oxidation of 4-dimethylaminophenol, and the oxidation product, presumably N,N-dimethylquinonimine, is bound covalently to cysteine 93 beta by a thioether linkage. This adduct is unstable and autoxidizes further with the liberation of dimethylamine. The resulting quinoid thioether electrophilically attacks the COOH-terminal histidine of the beta-chain, thereby forming an intramolecular cross-link. By this latter reaction, hemoglobin lacks allosteric transition upon ligation and is obviously frozen in its quaternary R-state.

Aminophenols↗