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A E Cribb

Publications and source records attributed to A E Cribb.

10 recordsLinked to original sources
PubMed1992

Sulfamethoxazole is metabolized to the hydroxylamine in humans.

The oxidation of sulfamethoxazole to its hydroxylamine metabolite was investigated in vitro with human liver microsomes and in vivo by detection in the urine. Sulfamethoxazole was oxidized to the hydroxylamine in an NADPH-dependent process by liver microsomes prepared from two human livers. Three healthy volunteers ingested 1000 mg sulfamethoxazole, and urine was collected for 24 hours. Sulfamethoxazole hydroxylamine constituted 3.1% +/- 0.7% of the drug excreted in the urine in 24 hours. Fifty-four percent of the ingested dose was excreted during this same time period. We conclude that sulfamethoxazole hydroxylamine is an authentic in vivo metabolite in humans, probably formed predominantly by cytochrome P450 in the liver. It could be responsible for mediation of sulfonamide adverse reactions, particularly hypersensitivity reactions.

Adult↗
PubMed1992

Drug-induced hypothyroidism: the thyroid as a target organ in hypersensitivity reactions to anticonvulsants and sulfonamides.

Inherited defects in detoxification of reactive metabolites of drugs predispose patients to "hypersensitivity" reactions. Covalent interaction of metabolites with cell macromolecules leads to cytotoxic and immunologic outcomes, manifested clinically by multisystem syndromes with variable organ involvement. Hypothyroidism developed in 5 of 202 patients (age range, 1 to 81 years) we investigated for hypersensitivity reactions to anticonvulsants or sulfonamides shortly after their reaction. None had previous personal or family histories of autoimmune disease. All had low thyroxine levels, elevated levels of thyroid stimulating hormone, and autoantibodies including antimicrosomal antibodies. Patients were 2 to 18 years of age at presentation, and two were male. All returned to a euthyroid state within a year of presentation, and all remain well. The demographics, clinical presentation, and course of the patients is atypical of idiopathic lymphocytic thyroiditis. We investigated the pathogenesis of thyroid toxicity using the hydroxylamine metabolite of sulfamethoxazole as a model. The hydroxyalmine was toxic to thyroid cells in vitro, which did or did not express thyroid peroxidase activity, whereas the parent sulfonamide was toxic only to cells with active thyroid peroxidase. The purified enzyme converted sulfamethoxazole to the hydroxylamine. Formation of reactive drug metabolites by thyroid peroxidase in a host who is genetically unable to detoxify the metabolites may lead directly to cytotoxicity. Covalent binding to macromolecules, including thyroid peroxidase, also may lead to expression of neoantigens and formation of autoantibodies. Patients who have sustained hypersensitivity reactions to drugs should be investigated for possible involvement of the thyroid.

Adolescent↗
PubMed1991

Glutathione transferase mu deficiency is not a marker for predisposition to sulphonamide toxicity.

Glutathione transferase mu activity, a marker for susceptibility to lung cancer and chemically induced cytogenetic damage, is not a predictive index for the predisposition to sulphonamide hypersensitivity reactions. However, considering the functional diversity and broad, overlapping substrate specificity of GSH-dependent enzymes, it is conceivable that an as yet unidentified deficiency in another GST isozyme or GSH-related enzyme may be a marker for sulphonamide toxicity. In addition, heterogeneity in cellular repair mechanisms and the diversity of the human immune response [22] may also contribute to the manifestation of the toxic effects of sulphonamides. Experiments are currently in progress to determine which of this myriad of variables is predominantly responsible for inter-individual susceptibility to the idiosyncratic reactions produced by these antibacterial agents.

Adolescent↗
PubMed1991

Expression of monomorphic arylamine N-acetyltransferase (NAT1) in human leukocytes.

The expression of arylamine N-acetyltransferase (NAT) in leukocytes was investigated using p-aminobenzoic acid (PABA) and sulfamethazine (SMZ), substrates which are preferentially acetylated by the monomorphic NAT1 and polymorphic NAT2 enzymes, respectively. Activity towards both substrates was detected in mononuclear leukocytes (MNL; preparation containing approximately 80% lymphocytes), monocytes and neutrophils. PABA and SMZ acetylation rates were highly correlated in each of the isolated cell types. The NAT in leukocytes displayed a much higher affinity and turnover rate for the acetylation of PABA than for SMZ. These kinetic characteristics suggest that the acetylating activity in human leukocytes is predominantly attributable to the monomorphic enzyme NAT1. Neutrophils showed evidence of biphasic kinetics for SMZ which would indicate the coexpression of NAT1 and low levels of the polymorphic enzyme, NAT2. NAT activity in MNL was not influenced by the acetylator phenotype of the individual. There was, however, a significant correlation between NAT activity in MNL and the in vivo acetylation (urinary metabolite ratio) of p-aminosalicylic acid, which is monomorphically acetylated in humans. The expression of NAT1 in leukocytes and the virtuall absence of NAT2 may have important toxicological implications. The in vitro/in vivo correlation suggests that leukocytes may be a useful marker of systemic NAT1 activity.

4-Aminobenzoic Acid↗
PubMed1990

An in vitro investigation of predisposition to sulphonamide idiosyncratic toxicity in dogs.

Sulphonamide idiosyncratic toxicosis has been reported in 28 dogs. Non-septic polyarthritis and fever occurring after 8 to 21 days therapy was the most common manifestation. Of 22 dogs with this syndrome, 7 were Doberman Pinschers. In humans, inherited decreased ability to detoxify sulphonamide hydroxylamine metabolites (as reflected in an in vitro mononuclear leukocyte (MNL) toxicity assay) has been associated with susceptibility to sulphonamide idiosyncratic toxicity. We have demonstrated that microsomes obtained from the liver of a dog were capable of metabolizing sulphamethoxazole to sulphamethoxazole hydroxylamine (SMX-HA). Production of SMX-HA was an NADPH dependent process and the yield was increased by the presence of 1 mmol/L ascorbic acid. SMX-HA was toxic to isolated MNL from mixed breed dogs (MBD) and Doberman Pinschers. The toxicity of SMX-HA to MNL from Dobermans was significantly different from that to MNL from MDB. MNL from 7 out of 15 Dobermans (including a dog with a history of an idiosyncratic reaction to a sulphonamide) had an LD-50 (concentration of SMX-HA required to produce 50% cytotoxicity in MNL) less than 100 mumols/L, while MNL from 0 out of 10 MBD had an LD-50 less than 100 mumols/L. These results suggest that the basis for the observed predisposition of Dobermans to sulphonamide idiosyncratic toxicity may be a limited capacity to detoxify the hydroxylamine metabolites of sulphonamides.

Animals↗
PubMed1990

Peroxidase-dependent oxidation of sulfonamides by monocytes and neutrophils from humans and dogs.

The hydroxylamine and nitroso metabolites formed by N4-oxidation of sulfonamides are thought to be involved in the pathogenesis of idiosyncratic reactions to this class of drugs. Idiosyncratic reactions to sulfonamides are characterized by multisystemic toxicity, including hepatitis, nephritis, dermatitis, and blood dyscrasias (aplastic anemia, agranulocytosis). We have previously shown that cytochrome P-450 in the liver metabolizes sulfamethoxazole to its hydroxylamine metabolite. In this paper we report the N4-oxidation of sulfamethoxazole by activated monocytes and neutrophils (human and canine) to form sulfamethoxazole hydroxylamine and nitrosulfamethoxazole. The presumed nitroso intermediate was not detected. Purified myeloperoxidase and prostaglandin H synthase were also capable of mediating the oxidation of sulfamethoxazole. The present studies suggest that myeloperoxidase is responsible for the observed oxidation by phagocytic cells. Oxidation by neutrophils may play a role in agranulocytosis, and oxidation by monocytes may facilitate antigen presentation. Extrahepatic bioactivation of sulfonamides by peroxidases in phagocytic cells and other tissues may be important in determining the range of adverse reactions to sulfonamides that occur.

Animals↗
PubMedDate not supplied

Reactions of the nitroso and hydroxylamine metabolites of sulfamethoxazole with reduced glutathione. Implications for idiosyncratic toxicity.

N4-oxidation of sulfonamides has been implicated in the pathogenesis of idiosyncratic reactions to these antimicrobials. In vitro toxicity assays employing mononuclear leukocytes as target cells have shown that the toxicity of sulfamethoxazole hydroxylamine (SMX-HA) is inhibited by exogenous glutathione, suggesting that conjugation with glutathione is an important detoxification pathway. However, in these experiments, significant depletion of cellular glutathione only occurred at concentrations of SMX-HA greater than or equal to 300 microM. At concentrations of SMX-HA which produce 50% toxicity in mononuclear leukocytes (approximately 100 microM), there was not a significant loss of glutathione. SMX-HA also caused a small but significant increase in oxidized glutathione concentrations. In cell-free experiments, reduced glutathione (GSH) prevented the autooxidation of SMX-HA to nitrososulfamethoxazole (nitroso-SMX). During this process, oxidized glutathione was formed. GSH rapidly reacted with nitroso-SMX to form a labile semimercaptal conjugate. Physiologically relevant concentrations of GSH (i.e. 1 mM) favored thiolytic cleavage of the semimercaptal to form SMX-HA. Isomerization of the semimercaptal to the more stable sulfinamide occurred at low GSH concentrations. Purified glutathione transferases had no effect on the reaction of SMX-HA with GSH. Therefore, glutathione is important in protecting cells from the toxicity of SMX-HA largely by preventing its further oxidation to nitroso-SMX. Stable glutathione conjugates are likely to be formed only in small quantities under physiological conditions. Conjugation with glutathione would not be expected to be a major pathway for clearance of the hydroxylamine and nitroso metabolites of sulfonamides.

Cell-Free System↗
PubMedDate not supplied

Hepatic microsomal metabolism of sulfamethoxazole to the hydroxylamine.

Sulfonamides are oxidized to protein reactive cytotoxic metabolites by murine hepatic microsomes. Mononuclear leukocytes from patients with idiosyncratic reactions to sulfonamides were more susceptible to toxicity from these metabolites than were leukocytes from a control population, suggesting that these metabolites play a role in the pathogenesis of such reactions. Here we have shown that murine hepatic microsomes oxidize sulfamethoxazole at the N4-position to form the hydroxylamine. Formation of the hydroxylamine was dependent on the presence of microsomes, NADPH, and oxygen. The addition of SKF 525-A, cimetidine, or gassing with carbon monoxide inhibited formation. The enzymic activity was stable at 37 degrees C in the absence of NADPH. Ascorbic acid, N-acetylcysteine, and reduced glutathione significantly increased the yield of hydroxylamine, presumably by decreasing further oxidation and covalent binding. Microsomes prepared from mice treated with phenobarbital or beta-naphthoflavone catalyzed the formation of the hydroxylamine more readily than did microsomes from untreated mice. These results demonstrate that cytochrome P-450-mediated oxidation of sulfamethoxazole results in the formation of hydroxylamines, which can be further oxidized to more reactive intermediates. These metabolites are likely involved in the pathogenesis of idiosyncratic reactions.

Animals↗