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Biomedical subjects

J S Leeder

Publications and source records attributed to J S Leeder.

At least 19 recordsLinked to original sources
PubMed1998

Chiral phase analysis of warfarin enantiomers in patient plasma in relation to CYP2C9 genotype.

A direct chiral-phase high-performance liquid chromatographic method for measuring the ratio of S-warfarin/R-warfarin in patient plasma is described. Plasma samples are first extracted using solid-phase C18 extraction columns, and the concentrated extracts analyzed using an (R,R) Whelk-O 1 column with a mobile phase of 0.5% glacial acetic acid in acetonitrile. The resulting chromatography provides baseline resolution of the warfarin enantiomers and internal standard (racemic ethylwarfarin), and is free from interference from other plasma components. Calibration curves were linear (mean r2 of 0.999 for both enantiomers) over the concentration range 0.25-1.5 microg/ml. The intra-day and inter-day coefficients of variation for analysis of plasma spiked with 0.33 microg/ml S-warfarin and 0.67 microg/ml R-warfarin (S/R=0.5:1) was less than 7% for each enantiomer, with an accuracy of more than 93%. Plasma extracts from thirty-one patients homozygous for wild-type CYP2C9*1 provided an S/R ratio of 0.51+/-0.15. Two warfarin patients homozygous for the mutant CYP2C9*2 and CYP2C9*3 alleles exhibited elevated S/R ratios relative to the mean for individuals homozygous for the wild-type CYP2C9*1 allele. This method is suitable for population studies aimed at establishing the effect of polymorphic expression of CYP2C9 alleles on S-warfarin elimination in humans.

Alleles↗
PubMed1998

Quantitation of three-month intraindividual variability and influence of sex and menstrual cycle phase on CYP1A2, N-acetyltransferase-2, and xanthine oxidase activity determined with caffeine phenotyping.

OBJECTIVE: To evaluate intraindividual variability and the effects of sex and menstrual cycle phase on the activity of cytochrome P450 1A2 (CYP1A2), N-acetyltransferase 2 (NAT2), and xanthine oxidase. METHODS: Ten white men were given 2 mg/kg caffeine orally every 14 days for 3 months. The same dosage of caffeine was given to 10 premenopausal white women during the midfollicular and midluteal phases of three complete menstrual cycles. Phenotype was determined with urinary caffeine metabolite ratios. RESULTS: For CYP1A2, mean metabolic ratio (+/- SD) was 5.97 +/- 2.78 during the midfollicular phase and 5.32 +/- 1.99 during the midluteal phase (p = 0.2). For extensive and poor metabolizer of NAT2. Mean midfollicular phase metabolite ratios were 0.71 +/- 0.060 and 0.37 +/- 0.030, and mean midluteal phase metabolite ratios were 0.69 +/- 0.076 and 0.39 +/- 0.053 (p = 0.9). For xanthine oxidase, mean midfollicular phase metabolite ratio was 0.63 +/- 0.06 and mean midluteal phase metabolite ratio was 0.63 +/- 0.05 (p = 0.3). Among the men, mean CYP1A2, NAT2 rapid and slow acetylator, and xanthine oxidase indices were 9.42 +/- 10.18, 0.66 +/- 0.021, 0.31 +/- 0.056, and 0.64 +/- 0.03. There were no differences in metabolite ratios between men and women for CYP1A2, NAT2 extensive metabolizers, or xanthine oxidase. A statistically significant sex difference was found for poor metabolizers of NAT2 (p < 0.05). Median coefficients of variation for CYP1A2, NAT2 extensive and poor metabolizers, and xanthine oxidase ratios were 16.8% (range, 4.5% to 49.3%), 2.9% (range, 2.2% to 4.7%), 13.4% (range, 7.5% to 27.2%), and 4.5% (range, 2.3% to 13.0%). CONCLUSION: Stratification by menstrual cycle phase or sex need not be performed for pharmacokinetic or clinical investigations of substrates for CYP1A2, NAT2, or xanthine oxidase in which the subject are adults.

Adult↗
PubMed1998

Effect of fluvoxamine therapy on the activities of CYP1A2, CYP2D6, and CYP3A as determined by phenotyping.

OBJECTIVE: To determine the effect of 150 mg/day fluvoxamine on the activities of CYP1A2, CYP2D6, CYP3A, N-acetyltransferase-2 (NAT2), and xanthine oxidase (XO) by phenotyping with caffeine, dextromethorphan, and midazolam. METHODS: Oral caffeine (2 mg/kg), oral dextromethorphan (30 mg), and intravenous midazolam (0.025 mg/kg) were administered to 10 white male volunteers every 14 days for 4 months and to 10 white premenopausal female volunteers during the midfollicular and midluteal phases of the menstrual cycle for 4 complete cycles (8 total phenotyping measures). The first 6 phenotyping measures were used to establish baseline activity. Subjects were given 150 mg/day fluvoxamine for the fourth month or cycle of the study. Enzyme activity for CYP1A2, CYP2D6, NAT2, and XO was expressed as urinary metabolite ratios. Midazolam plasma clearance was used to express CYP3A activity. RESULTS: No difference between baseline and weeks 2 and 4 of fluvoxamine therapy was observed for NAT2 or XO metabolite ratios. For CYP1A2, CYP2D6, and CYP3A phenotypes, significant differences existed between baseline and fluvoxamine therapy. For CYP1A2, the mean urinary metabolite ratio (+/-SD) was 7.53 +/- 7.44 at baseline and 4.30 +/- 2.82 with fluvoxamine ( P = .012). Mean CYP2D6 molar urinary dextromethorphan ratios before and after fluvoxamine therapy were 0.00780 +/- 0.00694 and 0.0153 +/- 0.0127, respectively (P = .011). Midazolam clearance decreased from 0.0081 +/ 0.0024 L/min/kg at baseline to 0.0054 +/- 0.0021 L/min/kg with therapy (P = .0091). For CYP1A2, CYP2D6, and CYP3A, fluvoxamine therapy changed the phenotyping measures by a median of -44.4%, 123.5%, and -34.4%, respectively. CONCLUSIONS: We concluded that fluvoxamine may cause significant inhibition of CYP1A2, CYP2D6, and CYP3A activity. This metabolic inhibition may have serious implications for a variety medications.

Acetyltransferases↗
PubMed1998

Non-monooxygenase cytochromes P450 as potential human autoantigens in anticonvulsant hypersensitivity reactions.

Antibodies recognizing rat cytochrome P450 (CYP) 3A1 but not the closely related human CYPs 3A4/5 have been identified in the sera of patients with hypersensitivity reactions to phenytoin and carbamazepine. Comparison of the mapped epitope to the comparable region in CYP3A4 revealed that Leu361 was essential for antibody recognition because of L361V mutation (mimicking human EYLDMVVNETLRL) abolished immunoreactivity. To identify alternative human autoantigens, a site-directed mutagenesis strategy was employed to identify amino acids critical for antibody recognition. A protein database search with the consensus sequence, DxVLxETLxx, from immunoblot analysis produced CYP8 (prostacyclin synthase), CYP5A1 (thromboxane synthase), CYP27 and CYP7A1 (cholesterol 7 alpha-hydroxylase) as possible candidates; considerable homology was also observed with the fungal CYP52A subfamily. Immunoblotting with patient sera and fragments of each candidate autoantigen expressed as Escherichia coli gene 10 fusion proteins confirmed CYP8 and CYP5A1 as possible antigens, and revealed the presence of IgG1 and IgG3 antibodies against a construct mimicking fungal CYP52A10. All patient sera contained IgG4 antibodies against CYP8, CYP5A1 and the fungal mimic suggestive of continual antigenic challenge. In genetically susceptible individuals, prior infectious challenge may be a determinant of risk for the development of anticonvulsant hypersensitivity reactions and has been incorporated into a model investigating the pathogenesis of these events.

Amino Acid Sequence↗
PubMed1998

NAD(P)H:quinone oxidoreductase: polymorphisms and allele frequencies in Caucasian, Chinese and Canadian Native Indian and Inuit populations.

NAD(P)H:quinone oxidoreductase (NQO1) catalyses the two-electron reduction of quinone compounds. NQO1 is involved in the reductive bioactivation of cytotoxic antitumour quinones such as mitomycin C, but also plays a protective role against the carcinogenicity and mutagenicity of quinones, their precursors and metabolites. Three alleles have been identified in the human population: the functional Arg139/Pro187 allele (which we have termed NQO1*1); the nonfunctional allele Arg139/Ser187 (NQO1*2) and the Trp139/Pro187 allele (NQO1*3), which is associated with a diminished activity. We applied polymerase chain reaction-based genotyping assays to characterize interethnic variability in the frequency of NQO1 alleles in Caucasian (n = 575), Canadian Native Indian (n = 110), Canadian Inuit (n = 83) and Chinese (n = 86) populations. The NQO1*2 allele was found at significantly higher frequencies in Chinese (0.49) and Native North American populations (Inuit 0.46; Canadian Native Indians 0.40) compared with Caucasians (0.16). The NQO1*3 allele was not observed in Inuit individuals, and occurred at a lower frequency than the NQO*2 allele in Caucasians (0.05), Chinese (0.04) and Canadian Native Indians (0.01). Our results predict that a greater proportion of Orientals and related ethnic groups lack, or have reduced, NQO activity relative to Caucasians. Affected individuals may not only exhibit resistance to quinone-based cancer therapy because of a decreased production of cytotoxic drug metabolites, but may also be more susceptible to toxicities associated with toxicants.

Alleles↗
PubMed1998

Quantification of intraindividual variability and the influence of menstrual cycle phase on CYP2D6 activity as measured by dextromethorphan phenotyping.

Intraindividual variability and the effects of menstrual cycle phase on CYP2D6 activity were evaluated by dextromethorphan phenotyping in 20 Caucasian normal volunteers. Dextromethorphan 30 mg was administered to 10 men every 14 days for 3 months, and to 10 premenopausal women during the mid-follicular and mid-luteal phases of each menstrual cycle for three complete cycles. Urinary dextromethorphan/dextrorphan molar ratios were obtained after an overnight urine collection. Ten women and nine men were extensive metabolizer phenotypes, and one man was a poor metabolizer phenotype (confirmed by genotyping). There was no difference in dextromethorphan metabolic ratios between the mid-follicular (mean +/- SD: 0.00728+/-0.00717) and mid-luteal (0.00745+/-0.00815) phases of the menstrual cycle (P = 0.88). Also, no significant difference was found in the intraindividual variability of the metabolic ratios between the two phases (P = 0.80). No statistically significant sex difference in CYP2D6 activity was found between men (0.00537+/-0.00431) and women (0.00737+/-0.00983) extensive metabolizers (P = 0.84). For all individuals, intraindividual variability in dextromethorphan ratios ranged from 12.1-136.6% with a median of 36.7%. Because hormonal fluctuations within the mid-follicular and mid-luteal phases of the menstrual cycle do not appear to affect CYP2D6 activity, pharmacokinetic or clinical investigations of CYP2D6 substrate activity may not require menstrual cycle phase stratification. Because baseline metabolic ratios may fluctuate an average of 37%, repeat baseline and treatment phenotyping assessments should be obtained for accurate determination of a given drug's effect on CYP2D6 activity when measured by dextromethorphan.

Adult↗
PubMed1998

Mechanisms of idiosyncratic hypersensitivity reactions to antiepileptic drugs.

Hypersensitivity reactions to the aromatic antiepileptic drugs (AEDs) phenytoin (PHT) and carbamazepine (CBZ) appear to have an immune etiology. Current models of drug hypersensitivity center around the concept of drug bioactivation to reactive metabolites that irreversibly modify cellular proteins. These modified proteins are believed to initiate (or serve as targets of) an autoimmune-like attack on specific drug-modified proteins in target organs (e.g., liver, skin) of susceptible individuals. Consistent with this model, antibodies to drug-modified and native proteins have been identified in the sera of patients experiencing several drug hypersensitivity reactions. New models must incorporate an understanding of the mechanisms by which drug-modified proteins are processed and presented to the immune system in the appropriate context to culminate in the clinical manifestations of "hypersensitivity." Idiosyncratic toxicities associated with new AEDs, such as lamotrigine and felbamate, appear mechanistically distinct from PHT and CBZ hypersensitivity but may involve similar processes: bioactivation, detoxification, covalent adduct formation, processing and presentation of antigen to the immune system, and consequent formation of antibody and T-cell immune effectors. The goal of research is to develop a "susceptibility profile" for identifying individuals at risk for these forms of drug toxicity.

Anticonvulsants↗
PubMed1998

A comparison of the covalent binding of clozapine and olanzapine to human neutrophils in vitro and in vivo.

Covalent binding of a reactive metabolite of clozapine to neutrophils or their precursors is thought to play a role in the development of clozapine-induced agranulocytosis. Immunoblotting studies with an anti-clozapine antiserum detected covalent binding of clozapine to human neutrophils in vitro when HOCl was used to generate clozapine reactive metabolite (major clozapine adducts of 31, 49, 58, 78, 86, 126, 160, and 204 kDa). In addition, incubating neutrophils with clozapine and H2O2 (major clozapine adducts of 49 and 58 kDa) or clozapine, H2O2, and human myeloperoxidase (major clozapine adducts of 31, 49, 58, and 126 kDa) also resulted in covalent binding of clozapine to the neutrophils. The covalent binding of clozapine to neutrophils was inhibited by extracellular glutathione when HOCl, but not H2O2 was used to generate reactive metabolite. We found that the antiserum against clozapine also recognized olanzapine, an antipsychotic drug that forms a similar reactive metabolite to clozapine but has not been associated with induction of agranulocytosis. Repeating the in vitro experiments with olanzapine revealed that the major olanzapine-modified polypeptides had molecular masses of 96, 130-170, and 218 kDa. Only relatively low levels of 31, 49, and 58 kDa adducts were observed. Clozapine-modified polypeptides also were detected in neutrophils from patients being treated with clozapine. A major 58-kDa clozapine-modified polypeptide was detected in all patients tested. In contrast, no drug-modified polypeptides were detected in neutrophils from patients taking olanzapine. The differences in covalent binding exhibited by the two compounds and, in particular, the lack of olanzapine binding to human neutrophils in vivo may help to explain the difference in toxicity of these two drugs.

Animals↗
PubMed1997

Pharmacogenetics in pediatrics. Implications for practice.

Cumulative experience with pharmacotherapy in children indicates that it is difficult to prescribe medications rationally solely on the basis of patient age. Furthermore, the apparent drug biotransformation phenotype may be influenced by disease (e.g., infection), environmental factors (e.g., diet and environmental contaminants), and concurrent medications. Therefore, characterization of drug biotransformation pathways during development and, at a given developmental stage, the effects of known modulators of drug biotransformation are essential for optimum treatment. This is particularly true when one considers that altered drug biotransformation may contribute significantly to therapeutic failure (e.g., graft rejection with inadequate serum and tissue concentrations of cyclosporin and myelotoxicity consequent to a relative inability to metabolize normal doses of certain antineoplastic agents). Accordingly, the goals of coordinated clinical and basic investigations should be to characterize important drug biotransformation pathways for compounds under development and intended for use in pediatrics and to identify the population extremes or "outliers" to aid in selection of an appropriate dosage range for efficacy studies. Acquired knowledge should then be incorporated into the drug-design process to further maximize the efficacy-toxicity ratio. The development of acceptable, preferably noninvasive, phenotyping procedures for all age ranges including neonates, infants, and older children is a major challenge for investigators but, if met, will be rewarded with improved pediatric pharmacotherapy.

Adolescent↗
PubMed1997

Tissue-specific expression and alternative splicing of human microsomal epoxide hydrolase.

Human microsomal epoxide hydrolase (HYL1) plays an important role in the detoxification of environmental compounds and drugs, such as the aromatic anticonvulsants phenytoin, carbamazepine, and phenobarbital, by converting their P450-generated epoxide metabolites into nontoxic diols. Recently, we have shown that a genetic defect altering the structure and function of the HYL1 protein is unlikely to be responsible for predisposing individuals to idiosyncratic hypersensitivity reactions from anticonvulsants. To evaluate the possible involvement of regulatory mechanisms, we used 5' rapid amplification of cDNA ends (RACE) and reverse transcription polymerase chain reaction (RT-PCR) to identify and characterize HYL1 5' cDNA ends. In addition to exon 1 (E1) previously isolated from a liver cDNA library, we isolated four new exons (E1-a, E1-c, E1-d, and E1-e) from various tissues. E1 was always directly connected to exon 2 (E2) where the translation start codon is located. E1-a, E1-c E1-d, and E1-e are alternatively spliced to E2, having either E1-a or E1-a' (a truncated form of E1-a) at the 5' end of their respective transcript. Genomic data indicate that exons E1-a and E1-c are located at least 7 kb upstream from E1. Furthermore, we demonstrated a tissue-specific expression pattern for E1-containing mRNA species, whereas E1-a-containing transcripts appear to be expressed ubiquitously. Our results provide evidence that microsomal epoxide hydrolase is regulated by multiple untranslated exons flanked by tissue-specific promoters.

Alternative Splicing↗
PubMed1997

Patients with delayed-onset sulfonamide hypersensitivity reactions have antibodies recognizing endoplasmic reticulum luminal proteins.

Sulfonamide antimicrobials cause a delayed-onset, hypersensitivity-type syndrome characterized by fever, skin rash and multiorgan toxicity occurring 7 to 14 days after initiation of therapy. The pathogenesis is believed to be immune-mediated. We investigated whether patients with delayed-onset sulfonamide hypersensitivity reactions had antibodies recognizing hapten-microsomal protein conjugates and/or native microsomal proteins. By immunoblotting using rat liver as a source of microsomal protein, 17 of 21 patients had antibodies recognizing one or more of three native endoplasmic reticulum proteins of 55 kDa (14 of 21 patients), 80 kDa (4 of 21 patients) or 96 kDa (3 of 21 patients) in size on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. No control subjects (n = 11) and only 1 of 18 patients with adverse events not consistent with sulfonamide hypersensitivity reactions had antibodies against these microsomal proteins under the conditions used. Only 1 patient had antibodies that recognized the sulfonamide hapten, sulfamethoxazole. The 55-kDa protein was identified as protein disulfide isomerase. The 80-kDa protein was identified as grp78. The 96-kDa protein was not identified. Delayed-onset sulfonamide hypersensitivity reactions are therefore primarily associated with antibodies recognizing specific protein epitopes and not anti-drug antibodies.

Animals↗
PubMed1996

Inhibition of acute lymphoblastic leukaemia by a Jak-2 inhibitor.

Acute lymphoblastic leukaemia (ALL) is the most common cancer of childhood. Despite the progress achieved in its treatment, 20% of cases relapse and no longer respond to chemotherapy. The most common phenotype of ALL cells share surface antigens with very early precursors of B cells and are therefore believed to originate from this lineage. Characterization of the growth requirement of ALL cells indicated that they were dependent on various cytokines, suggesting paracrine and/or autocrine growth regulation. Because many cytokines induce tyrosine phosphorylation in lymphoid progenitor cells, and constitutive tyrosine phosphorylation is commonly observed in B-lineage leukaemias, attempts have been made to develop protein tyrosine kinase (PTK) blockers of leukaemia cell growth. Here we show that leukaemic cells from patients in relapse have constitutively activated Jak-2 PTK. Inhibition of Jak-2 activity by a specific tyrosine kinase blocker, AG-490, selectively blocks leukaemic cell growth in vitro and in vivo by inducing programmed cell death, with no deleterious effect on normal haematopoiesis.

Animals↗
PubMed1996

Epitope mapping studies with human anti-cytochrome P450 3A antibodies.

A subset of patients with hypersensitivity reactions to the aromatic anticonvulsants phenytoin, carbamazepine, and phenobarbital have circulating antibodies that recognize members of the rat cytochrome P450 (CYP) 3A subfamily. These antibodies do not recognize related human CYP3A proteins despite the high degree of structural similarity. To investigate the relationship between P450-mediated drug metabolism and the development of anti-P450 antibodies, we initiated epitope mapping studies by screening a library of fusion proteins constructed from rat CYP3A1 with an anti-CYP3A1-positive patient serum sample. Positive signals from colony lifts were confirmed by sodium dodecyl sulfate/polyacrylamide gel electrophoresis and immunoblotting, and a 26-amino acid sequence corresponding to amino acids 342-367 of the CYP3A1 protein (NKAPPTY-DTVMEMEYLDMVLNETLRL) was identified as containing the epitope recognized by IgG3 antibodies in this serum sample. By subjecting inserts from two clones into a second round of library construction and screening by immunoblot analysis, we further defined the epitope to EYLDMVLNETLRL. Single amino acid deletions identified DMVLNETLRL as the minimum amino acid sequence required for antibody binding. The corresponding sequence in the four human CYP3A proteins differs by only one amino acid (DMVVNETLRL) This amino acid is critical to antibody recognition as immunoreactivity of the L361V mutant is markedly reduced. Anti-CYP3A antibodies in nine of nine additional sera also recognized the 13-amino acid epitope; for five of these sera, the minimum antibody binding sequence was DMVLNETLRL. The proximity of this epitope to a region determining substrate specificity may provide the link among reactive metabolite production, hapten formation, and the production of anti-P450 antibodies in anticonvulsant-induced idiosyncratic reactions.

Amino Acid Sequence↗
PubMed1995

Expression and inducibility of antigens in severe combined immunodeficient mice recognized by human anti-P450 antibodies.

Engrafting components of human immune systems in severe combined immunodeficient (SCID) mice has been utilized to investigate the pathogenesis of several human autoimmune diseases and may provide a model for studying idiosyncratic drug toxicity. The purpose of this investigation was to examine in SCID mice the tissue distribution and inducibility of antigens recognized by anti-cytochrome P450 (CYP) antibodies in sera from patients with hypersensitivity reactions to the aromatic anticonvulsants phenytoin, phenobarbital, and carbamazepine. Microsomal proteins were prepared from liver, skin, kidney, intestine, and lung of SCID mice pretreated with vehicle (50% propylene glycol/DMSO), phenytoin, carbamazepine, phenobarbital, or dexamethasone. Proteins immunoreactive with anti-CYP2C and anti-CYP3A antisera were detected in all organs examined. Antibodies in patient sera recognized a 53-kDa hepatic microsomal protein that was expressed to a limited extent in vehicle-pretreated microsomes, but which was induced by dexamethasone, phenytoin, and phenobarbital, but not carbamazepine. This antigen was very similar to a 52.5-kDa protein immunoreactive with anti-CYP3A polyclonal antibody. The expression and inducibility of the 53-kDa antigen correlated significantly with testosterone 6 beta-, 2 beta-, and 15 beta-hydroxylation and erythromycin N-demethylase activity, all markers of CYP3A activity, and is tentatively identified as CYP3A11. No immunoreactivity was observed in murine extrahepatic organs including skin, kidney, intestine, and lung. Therefore, further development of the SCID mouse model may require xenotransplantation of human target organs like skin together with transfer of patient immune systems to reproduce the serological and pathological features of human anticonvulsant hypersensitivity reactions.

Animals↗
PubMed1995

Safety of lidocaine-prilocaine cream in the treatment of preterm neonates.

The safety of lidocaine-prilocaine cream (EMLA) was evaluated in an open trial in 30 preterm neonates (mean gestational age, 32.8 weeks; birth weight, 1911 gm); 0.5 gm was applied to the heel for 1 hour. Mean baseline and follow-up (4, 8, or 12 hours after EMLA application) methemoglobin levels were not different, ranging from 1.15% to 1.45%, and from 1.13% to 1.49%, respectively.

Analgesics↗
PubMed1995

In vitro analysis of metabolic predisposition to drug hypersensitivity reactions.

Idiosyncratic hypersensitivity reactions may account for up to 25% of all adverse reactions, and pose a constant problem to physicians because of their unpredictable nature, potentially fatal outcome and resemblance to other disease processes. Current understanding of how drug allergy arises is based largely on the hapten hypothesis: since most drugs are not chemically reactive per se, they must be activated metabolically to reactive species which may become immunogenic through interactions with cellular macromolecules. The role of drug metabolism is thus pivotal to the hapten hypothesis both in activation of the parent compound and detoxification of the reactive species. Although conjugation reactions may occasionally produce potential immunogens (for example, the generation of acylglucuronides from non-steroidal anti-inflammatory drugs such as diclofenac), bioactivation is catalysed most frequently by cytochrome P450 (P450) enzymes. The multifactorial nature of hypersensitivity reactions, particularly the role of often unidentified, reactive drug metabolites in antigen generation, has hampered the routine diagnosis of these disorders by classical immunological methods designed to detect circulating antibodies or sensitized T cells. Similarly, species differences in drug metabolism and immune system regulation have largely precluded the establishment of appropriate animal models with which to examine the immunopathological mechanisms of these toxicities. However, the combined use of in vitro toxicity assays incorporating human tissues and in vivo phenotyping (or, ultimately, in vitro genotyping) methods for drug detoxification pathways may provide the metabolic basis for hypersensitivity reactions to several drugs. This brief review highlights recent efforts to unravel the bases for hypersensitivity reactions to these therapeutic agents (which include anticonvulsants and sulphonamides) using drug metabolism and immunochemical approaches. In particular, examples are provided which illustrate breakthroughs in the identification of the chemical nature of the reactive metabolites which become bound to cellular macromolecules, the enzyme systems responsible for their generation and (possibly) detoxification, and the target proteins implicated in the subsequent immune response.

Arylamine N-Acetyltransferase↗
PubMed1993

Reversion of the SCID phenotype by human T cell grafts. Development of cross-species immunocompetence.

Due to defective recombinase function, mice with severe combined immunodeficiency (SCID) lack functional lymphocytes and can accept human lymphoid xenografts. Xenografted animals (SCIDhum) are thought to provide a neutral environment for in vivo studies of normal, malignant or HIV-infected human cells. SCIDhum often develop endogenous, EBV+ lymphomas in the graft and in the our study two-thirds of 142 SCIDhum mice did so. Surprisingly, one-third of animals developed reversion of the SCID phenotype rapidly after human T cell engraftment. 90% of tumors occurred in nonrevertant and only 10% in revertant mice. These revertant animals showed immunologic tolerance for normal human B lymphocytes, maintained stable levels of mouse and human IgM and IgG. In addition, they generated competent mouse T cells able to kill transformed (EBV+) but not fresh B cells from the same donor nor unrelated human B cell lines. The tolerance for human lymphoid cells and the cross-species antitumor competence of host T lymphocytes imply unexpected recognition and selection events. Rather than a neutral "bioreactor," these observations mark the SCID host as potentially active participant in a composite immune system generated by xenografting.

Animals↗