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Biomedical subjects

L Long

Publications and source records attributed to L Long.

At least 19 recordsLinked to original sources
PubMed2003

Tinea capitis in Cleveland: survey of elementary school students.

BACKGROUND: Tinea capitis, a fungal infection of the scalp, is of increasing public health importance, and Trichophyton tonsurans has become the primary causative agent in North America. OBJECTIVES: To determine the prevalence of dermatophyte-positive scalp cultures among elementary schoolchildren in Cleveland, Ohio, describe predisposing factors, and measure the antifungal susceptibility of isolates collected. OBSERVATIONS: A total of 937 children from 8 Cleveland elementary schools were cultured for the presence of dermatophytes; 122 children (13%), all of whom were African American, had dermatophyte-positive cultures of the scalp. Sixty percent of cases were asymptomatic, indicating a carrier state. Race, scaling, and the use of anti-dandruff shampoo were associated with increased likelihood of infection. T tonsurans was the only organism isolated (except 1 Microsporum canis isolate). All isolates were susceptible to fluconazole, griseofulvin, itraconazole, and terbinafine. CONCLUSIONS: T tonsurans was the predominant dermatophyte isolated. Further multicenter studies are needed to confirm the predominance of dermatophyte-positive scalp cultures among African American children and to determine modifiable and preventable risk factors.

Child↗
PubMed2002

Leaf stomatal and epidermal cell development: identification of putative quantitative trait loci in relation to elevated carbon dioxide concentration in poplar.

Genetic variation in stomatal initiation and density, and epidermal cell size and number were examined in a hybrid pedigree of Populus trichocarpa T. & G. and P. deltoides Marsh in both ambient ([aCO2]) and elevated ([eCO2]) concentrations of CO2. We aimed to link anatomical traits with the underlying genetic map of F2 Family 331, composed of 350 markers across 19 linkage groups. Leaf stomatal and epidermal cell traits showed pronounced differences between the original parents. We considered the following traits in the F2 population: stomatal density (SD), stomatal index (SI), epidermal cell area (ECA) and the number of epidermal cells per leaf (ECN). In [eCO2], adaxial SD and SI were reduced in the F2 population, whereas ECA increased and ECN remained unchanged. In [aCO2], four putative quantitative trait loci (QTL) with logarithm of the odds ratio (LOD) scores greater than 2.9 were found for stomatal traits on linkage group B: adaxial SI (LOD scores of 5.4 and 5.2); abaxial SI (LOD score of 3.3); and SD (LOD score of 3.2). These results imply that QTL for SI and SD share linkage group B and are under genetic control. More moderate LOD scores (LOD scores >/= 2.5) suggest QTL for SI on linkage groups A and B and for SD on linkage groups B, D and X with a probable co-locating quantitative trait locus for SI and SD on linkage group D (position 46.3 cM). The QTL in both [aCO2] and [eCO2] for adaxial SD were co-located on linkage group X (LOD scores of 3.5 and 2.6, respectively) indicating a similar response across both treatments. Putative QTL were located on linkage group A (position 89.2 cM) for both leaf size and ECN in [aCO2] and for ECA at almost the same position. The data provide preliminary evidence that leaf stomatal and cell traits are amenable to QTL analysis.

Carbon Dioxide↗
PubMed2002

Effects of fluconazole singly and in combination with 5-fluorocytosine or amphotericin B in the treatment of cryptococcal meningoencephalitis in an intracranial murine model.

In this study we developed a highly reproducible intracranial murine model of cryptococcosis. Mice (Balb/c, 5-7 weeks old) were challenged intracranially and treated with intermediate (30 mg/kg) or high (90 mg/kg) dose fluconazole, and amphotericin B (0.75 mg/kg), administered singly or in combination with flucytosine (100 mg/kg). Survival and brain CFU analyses were performed. Effect of fluconazole prophylaxis was also determined. Our data show that the developed model mimics clinical signs of cryptococcal meningitis. In single treatment, fluconazole (30 mg/kg) was more efficacious than amphotericin B or flucytosine (P < 0.0001). Combination treatment led to significantly increased anticryptococcal activity, which was highest for high dose fluconazole + flucytosine (P < 0.0001). However, no significant difference was observed between high dose fluconazole treatment with and without flucytosine (P >0.05). Fluconazole prophylaxis led to a significant decrease in brain CFU. In conclusion, high dose fluconazole administered post-infection, or as prophylaxis, may be highly efficacious in the treatment and prevention of meningoencephalitis.

Amphotericin B↗
PubMed2001

A new mouse model for evaluating the immunotherapy of human colorectal cancer.

A new murine model of human colorectal cancer was generated by crossing human carcinoembryonic antigen (CEA) transgenic mice (H-2K(b)) with adenomatous polyposis coli (Apc1638N) knockout mice (H-2K(b)). The resulting hybrid mice developed gastrointestinal polyps in 6-8 months that progressed to invasive carcinomas with a similar pattern of dysplasia and CEA expression as observed in human colorectal cancer. These animals exhibited incomplete or partial tolerance to CEA as evidenced by delayed growth of CEA-expressing tumors and the inability to inhibit CEA-specific CTL responses. These results have important implications for understanding the role of CEA-specific immunity in human colon cancer patients and suggest that vaccine strategies targeting CEA may be feasible. This model provides a powerful system for evaluating antigen-specific tumor immunity against spontaneous tumors arising in an orthotopic location and permits evaluation of therapeutic vaccine strategies for human colorectal cancer.

Adenocarcinoma↗
PubMed2001

Management of horses showing stereotypic behaviour, owner perception and the implications for welfare.

A telephone survey was conducted of 100 racing stables, 100 riding schools and 100 competition establishments (8,427 horses in total) to determine what management practices were being applied to horses showing stereotypic behaviour, and to determine the underlying reasons for them by assessing the perceptions and opinions of the people working with the horses. The results indicated that horse owners are concerned about stereotypic behaviour, first, because it reduces the performance of the animal (31, 30 and 27 per cent of the owners of racing stables, riding schools and competition establishments respectively), secondly, because it has adverse clinical effects on the horse (52, 55 and 56 per cent), and thirdly, because it reduces the monetary value of the animal (45, 59 and 31 per cent). The belief that these behaviours are learnt or copied also affects the management of affected horses: they are not allowed on to the premises by 4, 32 and 17 per cent of owners of racing stables, riding schools and competition establishments, respectively; attempts are made to remove the causal factors of the stereotypy by 35, 43 and 36 per cent; the behaviours are physically prevented by 77, 67 and 79 per cent, and the affected horses are kept separate from other horses by 39, 30 and 48 per cent.

Animal Husbandry↗
PubMed2001

Mutagenicity at the Hprt locus in T cells of female mice following inhalation exposures to low levels of 1,3-butadiene.

A study was conducted to test the hypothesis that repeated low level exposures to 1,3-butadiene (BD), approaching the OSHA occupational threshold for this chemical, produce a significant mutagenic response in mice. Female B6C3F1 mice (4-5 weeks of age) were exposed by inhalation for 2 weeks (6 h/day, 5 days/week) to 0 or 3 ppm BD, and then necropsied at 4 weeks after the cessation of exposures to measure the frequency of mutations (MF) at the Hprt locus using the T-lymphocyte clonal assay. At necropsy, T cells were isolated from spleen and cultured in the presence of mitogen, growth factors, and a selection agent. Cells were scored for growth on days 8-9 after plating to determine cloning efficiencies (CEs) and Hprt MFs. There was a marginal but significant reduction in the growth of splenic T cells from mice exposed to 3 ppm (n=27) compared with control mice (n=24) (P=0.004), suggesting the occurrence of BD-induced cytotoxicity at this low exposure concentration. In addition, the average Hprt MF in mice exposed to 3 ppm BD [1.54+/-0.82 (S.D.)x10(-6)] was significantly increased by 1.6-fold over the average control value of 0.96+/-0.51 (S.D.)x10(-6) (P=0.004). Comparisons of these data to earlier Hprt mutagenicity studies of mice exposed to high concentrations of BD (where significant mutagenic but not cytotoxic effects were observed) indicate that the ability to detect the cytotoxic and mutagenic responses of T cells to low levels of BD was enhanced by using a much larger sample size than usual for both the control and treatment groups. Additional analyses of the quantitative relationships between CE and MF demonstrated that CE had no significant effect upon MF values in sham-exposed control mice or mice exposed to low-level BD. Furthermore, the approaches for assessing the impact of CE and clonality on Hprt MFs in these control and BD-exposed mice were applied with the same rigor as in in vivo Hprt mutagenicity studies in human children. The overall study results support the conclusion that short-term low-level BD exposure is mutagenic in the mouse.

Administration, Inhalation↗
PubMed2001

Immucillin H, a powerful transition-state analog inhibitor of purine nucleoside phosphorylase, selectively inhibits human T lymphocytes.

Transition-state theory has led to the design of Immucillin-H (Imm-H), a picomolar inhibitor of purine nucleoside phosphorylase (PNP). In humans, PNP is the only route for degradation of deoxyguanosine, and genetic deficiency of this enzyme leads to profound T cell-mediated immunosuppression. This study reports the biological effects and mechanism of action of Imm-H on malignant T cell lines and on normal activated human peripheral T cells. Imm-H inhibits the growth of malignant T cell leukemia lines with the induction of apoptosis. Imm-H also inhibits activated normal human T cells after antigenic stimulation in vitro. However, Imm-H did not inhibit malignant B cells, colon cancer cell lines, or normal human nonstimulated T cells, demonstrating the selective activity of Imm-H. The effects on leukemia cells were mediated by the cellular phosphorylation of deoxyguanosine and the accumulation of dGTP, an inhibitor of ribonucleotide diphosphate reductase. Cells were protected from the toxic effects of Imm-H when deoxyguanosine was absent or when deoxycytidine was present. Guanosine incorporation into nucleic acids was selectively blocked by Imm-H with no effect on guanine, adenine, adenosine, or deoxycytidine incorporation. Imm-H may have clinical potential for treatment of human T cell leukemia and lymphoma and for other diseases characterized by abnormal activation of T lymphocytes. The design of Imm-H from an enzymatic transition-state analysis exemplifies a powerful approach for developing high-affinity enzyme inhibitors with pharmacologic activity.

Apoptosis↗
PubMed2001

Debenzylation of O(6)-benzyl-8-oxoguanine in human liver: implications for O(6)-benzylguanine metabolism.

O(6)-Benzylguanine (BG) effectively inactivates the DNA repair protein O(6)-alkylguanine-DNA alkyltransferase, and enhances the effectiveness of 1,3-bis(2-chloroethyl)-1-nitrosourea in cells in culture and tumor-bearing animals. BG is presently in phase II clinical trials. In humans, BG is converted to O(6)-benzyl-8-oxoguanine (8-oxoBG), a longer-lived, yet equally potent inactivator. We have isolated and identified the debenzylated product, 8-oxoguanine, in plasma and urine of patients following administration of BG. The purpose of this work was to determine the human liver enzymes responsible for the debenzylation of 8-oxoBG. Therefore, 8-oxoBG was incubated with human liver microsomes and cytosol, and the concentration of 8-oxoguanine was determined. No appreciable product was formed in the cytosol; however, increasing amounts of 8-oxoguanine were formed with increasing concentrations of pooled human liver microsomes. The amount of 8-oxoguanine formed increased with time and substrate concentration. Co-incubation of human liver microsomes with 8-oxoBG and various cytochrome P450 isoform-selective inhibitors suggested the possible involvement of CYP1A2, 2E1, and/or 2A6 in this reaction. Incubation of 8-oxoBG with baculovirus cDNA-overexpressed CYP1A2, 2E1, 2A6, and 3A4 demonstrated that formation of 8-oxoguanine was due mainly to CYP1A2. Debenzylation of 8-oxoBG complied with Michaelis-Menten kinetics with K(m) and V(max) values of 35.9 microM and 0.59 pmol/min/pmol of CYP1A2, respectively. CYP1A2 appears to be mainly responsible for the debenzylation of 8-oxoBG in human liver.

Cytochrome P-450 CYP1A2↗
PubMed2001

Right ventricular hypertrophy secondary to pulmonary hypertension is linked to rat chromosome 17: evaluation of cardiac ryanodine Ryr2 receptor as a candidate.

BACKGROUND: Fischer 344 (F344) rats are relatively resistant to hypoxia-induced right ventricular (RV) hypertrophy compared with the Wistar-Kyoto (WKY) strain. These 2 strains were used to examine the genetic basis for the differential response. METHODS AND RESULTS: Male F(2) offspring from an F344xWKY intercross were exposed to hypoxia (10% O(2)) for 3 weeks, and pulmonary artery pressure and cardiac chamber weights were measured. Genomic DNA was screened by use of polymorphic microsatellite markers across the whole genome (excluding the sex chromosomes). A quantitative trait locus (QTL) for RV weight was identified on rat chromosome 17 (lod score 6.5) that accounted for 22% of the total variance of RV weight in the F(2) population and was independent of pulmonary artery pressure. The peak was centered over marker D17Rat41, close to Chrm3, with a 1-lod support interval of 5 cM. Comparison of homologous regions in mice and humans suggested that Ryr2, the cardiac isoform of the ryanodine receptor, colocalizes with our QTL. A panel of somatic cell hybrids and fluorescence in situ hybridization mapped Ryr2 close to the gene Chrm3 within our QTL. [(3)H]Ryanodine binding to cardiac membranes from the parental strains showed a 21% reduction in B(max) in the WKY compared with the F344 strain, with no difference in K:(d). CONCLUSIONS: These data provide the first demonstration of a QTL linked to the RV response to hypoxia-induced pulmonary hypertension. The Ryr2 receptor gene lies within this QTL and merits further investigation as a candidate for this differential RV response.

Animals↗
PubMed2001

Fractionation of Corynebacterium pekinense AS 1.299 phage subtypes by anion-exchange chromatography.

A novel method to fractionate phage into its subtypes while fully retaining biological function is reported. Corynebacterium pekinense AS 1.299 phage samples, purified by either conventional ultracentrifugation or gel chromatography on a Superose(R) 6 Prep column (0.78 x 30 cm), were fractionated further into four fractions by anion-exchange chromatography on a Toyopearl SuperQ 650C column (0.5 x 20 cm) with a linear gradient of NaCl concentration from 0.2 to 1.0 M in 0.02 M carbonate-biocarbonate buffer, pH 10.0. Two peaks were identified to be C. pekinense AS 1.299 phages by their ability to infect the host bacteria when inoculated into the culture media, and when examined by electron microscopy. These two types of the phage were found to be morphologically the same except for the difference in the length of their non-contractile tails. Both possessed an isometric head with a diameter of 50 +/- 3 nm, while their tails were 170 +/- 10 and 210 +/- 10 nm, respectively. This simple technique provides a convenient method for phage isolation not only to its species homogeneity, but also to determine its subtype or variant homogeneity.

Bacteriophages↗
PubMed2001

Serum concentration of adhesion molecules in postoperative biliary atresia patients: relationship to disease activity and cirrhosis.

BACKGROUND/PURPOSE: Biliary atresia (BA) is associated with progressive liver fibrosis, which may be mediated by immunologic abnormalities involving adhesion molecules. This study investigates the relationship between serum intercellular adhesion molecule-1 (sICAM-1), serum vascular cell adhesion molecule-1 (sVCAM-1), and the clinical and histologic severity of BA. METHODS: Serum ICAM-1 and VCAM-1 levels were measured by enzyme-linked immunosorbent assay in 35 patients with BA and 20 healthy controls. Standard liver function tests (LFTs), and frozen section liver biopsy specimens were used to determine liver status. On the basis of LFT results, the BA patients were classified into group I (n = 10; normal LFTs), group II (n = 15; elevated LFTs, anicteric), and group III (n = 10; elevated LFTs, icteric). Eight subjects in group II, and all subjects in group III had portal hypertension (PH). RESULTS: sICAM-1 levels were significantly elevated in group III (1760.0 +/- 717.5 ng/mL) compared with group II (555.1 +/- 199.4 ng/mL), group I (272.1 +/- 59.9 ng/mL) and controls (256.3 +/- 71.6 ng/mL). Although sVCAM-1 levels were significantly elevated in group III (1932.9 +/- 282.6 ng/mL) compared with group II (1054.3 +/- 297.0 ng/mL), group I (605.4 +/- 112.4 ng/mL), and controls (616.0 +/- 112.0 ng/mL; P <.001), there was no statistically significant difference between groups I, II, or controls. sVCAM-1 levels were elevated significantly in BA subjects in group II with PH (1253.0 +/- 245.1 ng/mL) compared with those who did not have PH (827.3 +/- 151.7 ng/mL; P <.01). PH did not affect sICAM-1 levels. There was strong expression of ICAM-1 and VCAM-1 in proliferating bile ductules, endothelial cells, and liver cells in group III compared with group II and controls. CONCLUSIONS: In BA, sICAM-1 and sVCAM-1 levels could be useful as markers of end-stage liver disease, with sVCAM-1 being more specific for PH. Induction of ICAM-1 and VCAM-1 may be an important factor in the development of cirrhosis.

Adolescent↗
PubMed2001

Which complementary and alternative therapies benefit which conditions? A survey of the opinions of 223 professional organizations.

UNLABELLED: With the increasing demand and usage of complementary/alternative medicine (CAM) by the general public, it is vital that healthcare professionals can make informed decisions when advising or referring their patients who wish to use CAM. Therefore they might benefit from advice by CAM-providers as to which treatment can be recommended for which condition. AIM: The primary aim of this survey was to determine which complementary therapies are believed by their respective representing professional organizations to be suited for which medical conditions. METHOD: 223 questionnaires were sent out to CAM organizations representing a single CAM therapy. The respondents were asked to list the 15 conditions they felt benefited most from their CAM therapy, the 15 most important contra-indications, the typical costs of initial and any subsequent treatments and the average length of training required to become a fully qualified practitioner. The conditions and contra-indications quoted by responding CAM organizations were recorded and the top five of each were determined. Treatment costs and hours of training were expressed as ranges. RESULTS: Of the 223 questionnaires sent out, 66 were completed and returned. Taking undelivered questionnaires into account, the response rate was 34%. Two or more responses were received from CAM organizations representing twelve therapies: aromatherapy, Bach flower remedies, Bowen technique, chiropractic, homoeopathy, hypnotherapy, magnet therapy, massage, nutrition, reflexology, Reiki and yoga. The top seven common conditions deemed to benefit by all twelve therapies, in order of frequency, were: stress/anxiety, headaches/migraine, back pain, respiratory problems (including asthma), insomnia, cardiovascular problems and musculoskeletal problems. Aromatherapy, Bach flower remedies, hypnotherapy, massage, nutrition, reflexology, Reiki and yoga were all recommended as suitable treatments for stress/anxiety. Aromatherapy, Bowen technique, chiropractic, hypnotherapy, massage, nutrition, reflexology, Reiki and yoga were all recommended for headache/migraine. Bowen technique, chiropractic, magnet therapy, massage, reflexology and yoga were recommended for back pain. None of the therapies cost more than ł60 for an initial consultation and treatment. No obvious correlation between length of training and treatment cost was apparent. CONCLUSION: The recommendations by CAM organizations responding to this survey may provide guidance to health care professionals wishing to advise or refer patients interested in using CAM.

Complementary Therapies↗
PubMed2001

Homeopathic remedies for the treatment of osteoarthritis: a systematic review.

Osteoarthritis is a common rheumatic disease. Limitations of conventional medical management of this condition indicate a real need for safe and effective treatment of osteoarthritic patients. The authors review the clinical evidence for and against the effectiveness of homeopathic medicines in the treatment of patients with osteoarthritis. A systematic review of all randomised controlled clinical trials of homeopathic treatment of patients with this condition is presented. A comprehensive search yielded four trials which are discussed in detail. The authors conclude that the small number of randomised clinical trials conducted to date, although favouring homeopathic treatment, do not allow a firm conclusion as to the effectiveness of homeopathic remedies in the treatment of patients with osteoarthritis. The clinical evidence appears promising, however, and more research into this area seems warranted.

Homeopathy↗
PubMed2001

Herbal medicines for the treatment of osteoarthritis: a systematic review.

OBJECTIVE: Limitations in the conventional medical management of osteoarthritis indicate a real need for safe and effective treatment of osteoarthritis patients. Herbal medicines may provide a solution to this problem. The aim of this article was to review systematically all randomized controlled trials on the effectiveness of herbal medicines in the treatment of osteoarthritis. METHODS: Computerized literature searches were carried out on five electronic databases. Trial data were extracted in a standardized, predefined manner and assessed independently. RESULTS: Twelve trials and two systematic reviews fulfilled the inclusion criteria. The authors found promising evidence for the effective use of some herbal preparations in the treatment of osteoarthritis. In addition, evidence suggesting that some herbal preparations reduce consumption of non-steroidal anti-inflammatory drugs was found. The reviewed herbal medicines appear relatively safe. CONCLUSIONS: Some herbal medicines may offer a much-needed alternative for patients with osteoarthritis.

Databases, Factual↗
PubMed2001

Molecular confirmation of Ewing sarcoma.

OBJECTIVE: To analyze retrospectively results of reverse transcription polymerase chain reaction (RT-PCR) testing and demographic information in patients with known or suspected Ewing sarcoma/primitive neuroectodermal tumor family of tumors referred to the National Cancer Institute and to describe factors influencing the determination of molecular marker status. PATIENTS AND METHODS: Tumor samples from 76 patients from February 1997 to December 1999 were analyzed. In all cases, the diagnosis of this family of tumors was confirmed by histopathologic review. RESULTS: In 58 patients, the presence of a translocation associated with this family of tumors was confirmed using RT-PCR. Specifically, there were 45 Ewing sarcoma (EWS)-FLI type 1 translocations, four EWS-FLI type 2 translocations, five EWS-ERG translocations, and four less common EWS-FLI variants. Of patients with a confirmed translocation, four were confirmed only after nested RT-PCR techniques were used. In five patients who initially underwent needle biopsy, the diagnosis was confirmed only after open biopsy or repeat needle biopsy was undertaken. Samples from 18 patients were translocation-negative. Of these, seven samples were deemed inadequate for RT-PCR testing as a result of inappropriate tissue handling or the presence of necrotic material. Five patients were found to have a different diagnosis after complete histopathologic and molecular characterization. Six samples remained, in which adequate tissue was obtained with no evidence of a characteristic translocation. CONCLUSIONS: In apparently translocation-negative samples, close attention should be given to the possibility of an alternative diagnosis, the potential need for nested RT-PCR, and the possibility of an inadequate sample. Strong consideration should be given to the use of open biopsy as opposed to needle biopsy to avoid the need for repeat biopsies and the potential for inaccurate assessment of molecular marker status.

12E7 Antigen↗
PubMed2001

Characterization of adenylyl cyclase isoforms in rat peripheral pulmonary arteries.

Activation of adenylyl cyclase (AC), of which there are 10 diversely regulated isoforms, is important in regulating pulmonary vascular tone and remodeling. Immunohistochemistry in rat lungs demonstrated that AC2, AC3, and AC5/6 predominated in vascular and bronchial smooth muscle. Isoforms 1, 4, 7, and 8 localized to the bronchial epithelium. Exposure of animals to hypoxia did not change the pattern of isoform expression. RT-PCR confirmed mRNA expression of AC2, AC3, AC5, and AC6 and demonstrated AC7 and AC8 transcripts in smooth muscle. Western blotting confirmed the presence of AC2, AC3, and AC5/6 proteins. Functional studies provided evidence of cAMP regulation by Ca(2+) and protein kinase C-activated but not G(i)-inhibited pathways, supporting a role for AC2 and a Ca(2+)-stimulated isoform, AC8. However, NKH-477, an AC5-selective activator, was more potent than forskolin in elevating cAMP and inhibiting serum-stimulated [(3)H]thymidine incorporation, supporting the presence of AC5. These studies demonstrate differential expression of AC isoforms in rat lungs and provide evidence that AC2, AC5, and AC8 are functionally important in cAMP regulation and growth pathways in pulmonary artery myocytes.

Adenylyl Cyclases↗
PubMed2001

Role of cytochrome P450 isoenzymes in metabolism of O(6)-benzylguanine: implications for dacarbazine activation.

O(6)-Benzylguanine (BG) effectively inactivates the DNA repair protein O(6)-alkylguanine-DNA alkyltransferase and enhances the effectiveness of alkylating agents, such as 1,3-bis(2-chloroethyl)-1-nitrosourea and temozolomide, in vitro and in vivo. BG is presently in clinical trials with 1,3-bis(2-chloroethyl)-1-nitrosourea and temozolomide. Preclinical data demonstrate that BG enhances the sensitivity of cells to 5-[3-methyl-triazen-1-yl]-imidazole-4-carboxamide, the active intermediate of dacarbazine (DTIC), making the combination BG plus DTIC attractive for additional clinical development. DTIC requires metabolism by cytochrome P450 (CYP450) isoforms, 1A1, 1A2, and 2E1 to form two reactive N-demethylated metabolites, 5-[3-hydroxy-methyl-3-methyl-triazen-1-yl]-imidazole-4-carboxamide and 5-[3-methyl-triazen-1-yl]-imidazole-4-carboxamide, ultimately forming a methylating species responsible for its cytotoxicity. The objective of this study was to examine the role of CYP450 1A1 and 1A2 in the metabolism of BG and identify possible drug-drug interactions with DTIC. Our data show that CYP450 isoforms 1A1 and 1A2 are primarily responsible for both BG oxidation to O(6)-benzyl-8-oxoguanine (8-oxoBG) and additional debenzylation to 8-oxoguanine. The catalytic efficiency of BG oxidation is 16 times lower for CYP1A1 than CYP1A2; however, the catalytic efficiency of 8-oxoBG debenzylation is 11 times greater for CYP1A1 than CYP1A2. Furthermore, BG inhibits CYP1A1 and 1A2 catalyzed conversion of DTIC to active methylating species. 8-OxoBG also inhibited conversion of DTIC to active methylating species but to a much lesser extent. The concentrations of BG required to inhibit 50% of DTIC N-demethylation were 2.8, 0.13, and 3.8 microM in human liver microsomes, baculovirus overexpressed CYP1A1, and CYP1A2, respectively. Our results suggest that treating patients with BG as a means to enhance the effectiveness of DTIC is unlikely to result in a therapeutic benefit as a result of inhibition of the enzymes responsible for conversion of DTIC to its active methylating species.

Antineoplastic Agents↗