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Biomedical subjects

D Ross

Publications and source records attributed to D Ross.

At least 109 records · Page 6Linked to original sources
PubMed1998

Stepwise health surveillance for bronchial irritability syndrome in workers at risk of occupational respiratory disease.

OBJECTIVES: Questionnaires, lung function tests, and peak flow measurements are widely used in occupational health care to screen for subjects with respiratory disease. However, the diagnostic performance of these tests is often poor. Application of these tests in a stepwise manner would presumably result in a better characterisation of subjects with respiratory disease. METHODS: Cross sectional data from workers exposed to acid anhydrides, to laboratory animals, and to flour dusts were used. Sensitivity and specificity were calculated from cross tables of different (combinations of) tests for bronchial hyperresponsiveness and bronchial irritability in the past four weeks (BIS). From sensitivity and specificity likelihood ratios were computed and change in probability of BIS was calculated. RESULTS: The prevalence of BIS was 7%, 7%, and 5%, respectively. In all groups questionnaire data provided excellent sensitivity but poor specificity, which was inherent on the broad definition of symptoms. Adding the forced expiratory volume in one second/forced vital capacity (FEV1/FVC) ratio yields almost perfect specificity, and peak expiratory flow (PEF) variability is intermediate in populations in which smoking induced or non-allergic respiratory diseases predominates. In occupational groups in which asthma is a problem, adding PEF measurements will optimise sensitivity and specificity in detection of BIS. The probability of BIS for subjects with a negative combined test outcome was lower than the probability before testing. Subjects with a positive combined test outcome had a probability of BIS after the tests at least three times the probability before. CONCLUSIONS: Combined testing yields better sensitivity and specificity. An advantage of combined testing is an economy in the effort to screen for subjects with BIS. Combined testing resulted in more detailed estimation of the probability of BIS.

Anhydrides↗
PubMed1998

Placebo run-in period in studies of depressive disorders. Clinical, heuristic and research implications.

BACKGROUND: In spite of the virtually ubiquitous nature of the initial 10-day placebo run-in period (IPR) in drug trials, there is little empirical data establishing its relevance. METHOD: Data from 593 subjects were examined retrospectively to determine whether or not the prognosis of subjects minimally improved during the IPR was different to those who were unimproved. The IPR period was single-blind and was followed by a six-week double-blind phase in all studies. RESULTS: Twenty-six per cent of the subjects were minimally improved and 74% were unimproved. Approximately 10% of the subjects who were much improved were not followed systematically. Across a range of diagnosis, severity and chronicity subjects minimally improved (versus unimproved) after IPR had a more favourable prognosis whether assigned to drug or placebo. CONCLUSIONS: Change during IPR appears to be a meaningful predictor. Stratification should be considered in future antidepressant studies.

Adolescent↗
PubMed1998

Single lead VDD pacing in children with complete heart block.

OBJECTIVE: To evaluate clinically transvenous single lead VDD pacing in children with complete heart block. DESIGN: Case series. SETTING: Tertiary care unit of a pediatric teaching hospital. PATIENTS: Consecutive sample of children with complete heart block requiring pacing and meeting the criteria for VDD pacing. INTERVENTIONS: VDD single lead pacing systems (Thera VDD 8948 generator, Capsure VDD 5032 single pass lead) were implanted in nine children (mean age 10.7 years, 95% CI 8.9 to 12.3). All patients were reviewed six weeks and six months post-implantation with clinical review, detailed pacemaker interrogation, optimal device programming, treadmill exercise testing, 24 h Holter monitoring and echocardiography. RESULTS: Mean procedure time was 62.5 mins (CI 52 to 73), mean fluoroscopy time 3.8 mins (CI 2.4 to 5.1) and mean P wave sensing amplitude 2.75 mV (CI 2.5 to 3), without significant decrease during Valsalva manoeuvre (mean 2.4 mV, CI 2.2 to 2.8). Low pacing thresholds of mean amplitude 0.39 V (CI 0.38 to 0.4) were established at pulse width 0.5 ms. Two patients required early revision--one lead dislodged and one patient had a loose set screw. Follow-up showed satisfactory pacemaker function, and mean percentage atrioventricular (AV) synchronous pacing 96.8% (CI 93 to 99) at six weeks and 97% (CI 95 to 99) at six months. P wave sensing failures were less than 1%. AV synchronous pacing was maintained for more than 99% of the period of treadmill exercise testing. There was a significant mean increase in cardiac output of 24% (CI 8 to 40, P < 0.05) at rest in VDD mode compared with VVIR mode. CONCLUSIONS: Single lead VDD pacing is an effective and reliable method of 'physiological' rate responsive AV synchronous pacing in children with complete heart block and should be considered a viable alternative to dual lead pacing systems.

Adolescent↗
PubMed1998

Immunohistochemical detection of NAD(P)H:quinone oxidoreductase in human lung and lung tumors.

NAD(P)H:quinone oxidoreductase (NQO1) is a flavoenzyme that catalyzes the two-electron reduction of quinones and related compounds. With the use of biochemical assays, NQO1 has been shown to be overexpressed in many types of cancer, including non-small cell lung cancer (NSCLC). NQO1 can bioactivate antitumor quinones such as mitomycin C, and new quinone-based drugs are currently being developed to target this enzyme in tumors such as NSCLC. Because there is no information on the cell-specific expression of NQO1 in lung, the purpose of this study was to examine the expression of NQO1 in human NSCLC, small cell lung cancer, carcinoid lung tumors, and normal lung using immunohistochemistry. A high level of NQO1 protein expression was detected by immunohistochemistry in NSCLC (adenocarcinoma, squamous cell carcinoma, and bronchoalveolar carcinoma), but no NQO1 protein could be detected in small cell lung cancer or carcinoid lung tumors. In addition, NQO1 protein expression was examined by immunohistochemistry in normal lung tissue. A high level of NQO1 protein expression was detected by immunohistochemistry in normal lung respiratory epithelium, with the highest levels of expression observed in ciliated columnar epithelial cells. Significant amounts of NQO1 protein were also detected in the vascular endothelium and adipocytes. These data demonstrate that NQO1 is overexpressed in NSCLC. Cells in normal lung also contain marked NQO1 protein and may be damaged by drugs activated by NQO1. These data validate NSCLC as a target for NQO1-directed agents and suggest that the potential for lung toxicity be considered in the preclinical development of quinone-based antitumor drugs.

Humans↗
PubMed1998

A new screening system for NAD(P)H:quinone oxidoreductase (NQO1)-directed antitumor quinones: identification of a new aziridinylbenzoquinone, RH1, as a NQO1-directed antitumor agent.

NAD(P)H:quinone oxidoreductase (NQO1; DT-diaphorase) is elevated in certain tumors, such as non-small cell lung cancer (NSCLC). Compounds such as mitomycin C and streptonigrin are efficiently bioactivated by NQO1 and have been used in an enzyme-directed approach to chemotherapy. Previously, 2,5-diaziridinyl-3,6-dimethyl-1,4-benzoquinone (MeDZQ) was identified as a potential antitumor agent based on its high rate of bioactivation by human NQO1 and its selective cytotoxicity to cells containing elevated NQO1. RH1, a water-soluble analogue of MeDZQ synthesized in this work, was a better substrate for recombinant human NQO1 than the parent compound. RH1 was, correspondingly, more cytotoxic to human tumor cells expressing elevated NQO1 activity (H460 NSCLC and HT29 human colon carcinoma), as measured by 3-(4,5-dimethylthiazol-2,5-diphenyl)tetrazolium assay, than it was to cells deficient in NQO1 activity (H596 NSCLC and BE human colon carcinoma). RH1 exhibited a greater selective toxicity (ratio of IC50s in H596:H460 and BE:HT29) to cells with elevated NQO1 activity relative to MeDZQ. Additionally, we report the establishment of a stable line of BE human colon carcinoma cells transfected with wild-type human NQO1 (BE-NQ7). BE cells are devoid of NQO1 activity due to a homozygous point mutation in the NQO1 gene. In comparison to the parental cell line, RH1, MeDZQ, and mitomycin C were significantly more cytotoxic to BE-NQ7 cells (17-, 7-, and 3-fold, respectively), confirming that the presence of NQO1 is sufficient to increase cytotoxicity of these antitumor quinones. These data suggest that RH1 may be an effective NQO1-directed antitumor agent for the therapy of tumors with elevated NQO1 activity, such as NSCLC.

Antineoplastic Agents↗
PubMed1997

Radiotherapy in stage IIA and IIB testicular seminoma with reduced portals: a prospective multicenter study.

PURPOSE: A prospective multicenter study was carried out to estimate the treatment outcome of radiotherapy in Stage II seminoma after the application of modern staging and radiotherapy techniques. The lower margin of the iliac field was positioned on the upper rim of the acetabulum to reduce the amount of scattered irradiation to the remaining testicle. METHODS AND MATERIALS: The study was carried out in 25 centers in Germany. Patients with pure seminoma, negative AFP-values, and retroperitoneal lymph node metastases of less than 5 cm in diameter were entered into the study. All patients received a ventrodorsal opposed field irradiation of the para-aortic and the ipsilateral iliac lymph nodes. The fields extended from the top of the 11th thoracic vertebra to the top of the acetabulum. Patients in Stage IIA (lymph nodes <2 cm ) received 30 Gy, and patients with Stage IIB (lymph nodes between 2 and 5 cm) 36 Gy total dose. RESULTS: 39 patients in Stage IIA and 19 patients in Stage IIB were evaluated. After a median observation time of 37 months all patients are alive and disease free. Recurrence free survival in stage IIA was 100%. Two patients in Stage IIB experienced a recurrence 10 and 17 months after the end of radiotherapy. The actuarial recurrence free survival estimate in Stage IIB was 94.1% for 1 year and 87.4% for 2 years. One recurrence in Stage IIB occurred in the mediastinum, one in the mediastinum, and one the lung. Both patients could be salvaged by chemotherapy. There were no pelvic recurrences. The treatment was well tolerated, with nausea being the most common side effect (56.9% Grade 1, 15.5% Grade 2, and 8.6% Grade 3). Diarrhea occurred in 15.5% (Grade 1), 15.5% (Grade 2), and 5.2% (Grade 3) of the patients. CONCLUSIONS: The outcome of para-aortic and ipsilateral iliac irradiation in Stage IIA/B testicular seminoma is excellent with the currently available staging methods and treatment facilities. The treatment is well tolerated. The lower margin of the iliacal field can be placed at the acetabulum.

Adult↗
PubMed1997

Burden and outcomes of hospitalisation for congestive heart failure.

OBJECTIVE: To describe the hospital burden and health outcomes associated with admission for congestive heart failure (CHF). DESIGN AND SETTING: Descriptive follow-up study in a tertiary-level metropolitan teaching hospital. PATIENTS: Acute adult inpatients with a clinical diagnosis of CHF for more than 24 hours admitted to Westmead Hospital, Sydney, during the four months from September 1993 to January 1994. At baseline, 122 patients were assessed; 88 patients were assessed at four-month follow-up. INTERVENTIONS: Usual clinical care. MAIN OUTCOME MEASURES: Length of stay; hospital bed-days; readmissions; mortality; health related quality of life (SF-36); patient knowledge. RESULTS: The average age of subjects was 73.4 years. Many were using informal domiciliary care before admission. Mean length of stay for the baseline admission was 13.8 days, accounting for 7.6% of hospital separations and 1683 hospital bed-days, or 4.2% of bed-days for all inpatients aged 65 years and over. Fifteen patients were readmitted for CHF during the following four months, with a total of 26 CHF-related admissions. Twenty-one patients (17.2%) died during the course of the study. Quality of life at baseline was poor compared with population normative data, with a slight improvement among survivors at four-month follow-up. Patient knowledge of CHF was poor in a subsample survey (n = 24). CONCLUSIONS: CHF represents a significant burden to patients (through morbidity and mortality), their carers (through provision of daily care), and hospitals (through multiple admissions for acute decompensation). It is difficult to monitor the hospital burden of CHF using routine data sources.

Adult↗
PubMed1997

Benzene poisoning, a risk factor for hematological malignancy, is associated with the NQO1 609C-->T mutation and rapid fractional excretion of chlorzoxazone.

Benzene is a ubiquitous occupational hematotoxin and leukemogen, but people vary in their response to this toxic agent. To evaluate the impact of interindividual variation in enzymes that activate (i.e., CYP2E1) and detoxify (i.e., NQO1) benzene and its metabolites, we carried out a case-control study in Shanghai, China, of occupational benzene poisoning (BP; i.e., hematotoxicity), which we show is itself strongly associated with subsequent development of acute nonlymphocytic leukemia and the related myelodysplastic syndromes (relative risk, 70.6; 95% confidence interval, 11.4-439.3). CYP2E1 and NQO1 genotypes were determined by PCR-RFLP, and CYP2E1 enzymatic activity was estimated by the fractional excretion of chlorzoxazone (fe(6-OH)) for 50 cases of BP and 50 controls. Subjects with both a rapid fe(6-OH). and two copies of the NQO1 609C-->T mutation had a 7.6-fold (95% confidence interval, 1.8-31.2) increased risk of BP compared to subjects with a slow fe(6-OH) who carried one or two wild-type NQO1 alleles. In contrast, the CYP2E1 PstI/RsaI polymorphism did not influence BP risk. This is the first report that provides evidence of human susceptibility to benzene-related disease. Further evaluation of susceptibility for hematotoxicity and hematological malignancy among workers with a history of occupational exposure to benzene is warranted.

Benzene↗
PubMed1997

Bioreductive alkylating agent porfiromycin in combination with radiation therapy for the management of squamous cell carcinoma of the head and neck.

Porfiromycin (methyl mitomycin C) has been shown in laboratory studies to have increased preferential cytotoxicity to hypoxic cells and therefore may provide enhanced therapeutic efficacy over mitomycin C when used in combination with radiation therapy (RT). The purpose of the two clinical studies reported here is to evaluate the concomitant use of porfiromycin with RT in the management of squamous cell carcinoma of the head and neck. Between October 1989 and July 1992, 21 patients presenting with locally advanced stage III/IV squamous cell carcinoma of the head and neck were entered into a phase I toxicity trial evaluating porfiromycin as an adjunct to RT. Patients were eligible if they had biopsy documented squamous cell carcinoma of the head and neck with a low probability of cure by conventional means. Patients were treated with standard fractionated daily RT to a total median dose of 63 Gy, with porfiromycin administered on days 5 and 47 of the course of RT. Upon completion of this phase I trial, a phase III trial was initiated in November 1992 randomizing patients with squamous cell carcinoma of the head and neck to RT with mitomycin C vs. RT with porfiromycin. There is no radiation only arm in this current trial. To date, 75 patients have been entered on this trial and acute toxicity data are available on 67 patients (34 porfiromycin, 31 mitomycin C) who have completed their entire course of treatment. Median follow-up of the 21 patients enrolled in the phase I porfiromycin trial is 58.5 months. Of the 21 patients, 5 were treated at a dose of 50 mg/M2, 4 at 45 mg/M2, and the final 12 at 40 mg/M2, which appeared to result in acceptable acute hematological and nonhematological toxicities. As of December 1995, 14 of the 21 patients have died with disease and 7 remain alive and free of disease, resulting in a 5-year actuarial survival of 32%. Of the patients enrolled to date in the phase III randomized trial of mitomycin C vs. porfiromycin, there have been no statistically significant differences between the two arms with respect to white blood cell count (WBC), platelet, or hemoglobin nadirs. Acute nonhematological toxicities including mucositis, epidermitis, odynophagia, and nausea have also been comparable. Two patients in this current randomized trial died during treatment, apparently of nondrug-related causes. We conclude that the bioreductive alkylating agent porfiromycin has demonstrated an acceptable toxicity profile to date. Final analysis of the phase I trial, which revealed a 5-year no evidence of disease survival rate of 32% in patients with locally advanced disease and a low probability of cure, appears encouraging. We anticipate completion of the current ongoing trial comparing mitomycin C to porfiromycin in the next 2 years. Further investigations, including large-scale multiinstitutional trials employing bioreductive alkylating agents or other hypoxic cell cytotoxins as adjuncts to RT, are warranted.

Antibiotics, Antineoplastic↗
PubMed1997

Randomized, double-blind, dose-ranging study of the endometrial effects of a vaginal progesterone gel in estrogen-treated postmenopausal women.

OBJECTIVE: Our purpose was to assess the endometrial effects of two doses of natural progesterone administered by a bioadhesive vaginal gel in estrogen-treated postmenopausal women. STUDY DESIGN: This was a double-blind, randomized, dose-ranging study of 31 postmenopausal women attending a specialist menopause clinic. Endometrial histologic features, sex steroid hormone concentrations, and vaginal bleeding patterns were assessed during three 28-day cycles of continuous oral conjugated estrogens (0.625 mg/day) and two doses of sequential vaginally administered natural progesterone (45 or 90 mg every 48 hours). Histologic results are presented descriptively. Between-group comparisons of other parameters were made with the use of the Mann-Whitney U and Student t tests. RESULTS: Secretory endometrium was found in 35 of 41 histologic samples that yielded adequate tissue for diagnosis. There was one case of proliferative endometrium in the 45 mg progesterone group and none in the 90 mg group and no cases of hyperplasia. Mean plasma progesterone concentrations of 4.6 ng/ml and 6.8 ng/ml were achieved in the 45 and 90 mg groups, respectively. CONCLUSIONS: Very low doses of natural progesterone, when administered vaginally in a bioadhesive gel, cause secretory endometrial transformation in estrogen-treated postmenopausal women.

Adult↗
PubMed1997

Ictal patterns in temporal lobe epilepsy recorded by epidural screw electrodes.

In a consecutive series of 11 patients with a history of medically refractory temporal lobe epilepsy, we studied the appearance of ictal patterns detected by epidural screw electrodes (ESE) placed in an effort to obviate depth electrode recording. All had prior scalp-sphenoidal monitoring with significant obscuration of ictal EEG by movement and muscle artifact. Six to 10 ESE were placed at bilateral temporal locations of the 10% system. Ictal findings in 4-15 partial seizures from 8 patients with mesiobasal (MBTLE) and 3 patients with neocortical (NCTLE) epilepsy were correlated with imaging and histology. Five of 8 patients with MBTLE had discrete high frequency discharges at onset, evolving within 10 s to focal theta at ESE, before appearing at scalp electrodes. All had Class IA outcome with mesial temporal sclerosis (MTS). Three of 8 patients with MBTLE and MTS had less discrete onsets, with Class 1A, 1B and 3A outcomes. Two patients with NCTLE had lesions; a grade II oligoastrocytoma with rhythmic delta at ESE and Class 4 outcome, and an anterior temporal cavernous angioma with variable onsets, some of which were high frequency, with a Class 1A outcome. The third NCTLE patient demonstrated focal theta as an ictal pattern, had no lesion and a Class 1A outcome. Ictal onsets may be well localized in selected patients by ESE. A majority of patients with MTS display well defined high frequency ictal discharges.

Adolescent↗
PubMed1997

Radiotherapy for treatment of localized gastrointestinal non-Hodgkin's lymphoma.

BACKGROUND: The study analyses a standardized, risk-adapted radiotherapy for stage IE-IIE primary extranodal lymphoma of the stomach and bowel. METHODS: Sixty eight patients (31 females, 37 males, median age 56 years) were treated from 1987-1992 in 15 centers. Fifty six patients had gastric and 12 patients had bowel lymphomas. Gastric lymphomas (low or intermediate grade stage I-II: 38 patients/high grade stage I: 18 patients) were treated by whole abdominal irradiation (25/30 Gy), booster dose to involved field (30/40 Gy) and additional boost to macroscopic residual lymphoma (40/50 Gy). Surgery consisted of gastrectomy (19 patients), partial gastric resection (30) or biopsy (7). In 8/18 stage II patients, supradiaphragmal irradiation was added. In 10/12 patients with bowel lymphoma, segment resection was performed, two received biopsy only. Radiation doses equalled those used for gastric lymphoma: RESULTS: In 51/56 patients (91%) with gastric lymphoma, the recommended dose for whole abdominal irradiation was given. A total of 40/56 patients (71%) received the required dose to the upper abdominal region, in 22/56 patients (39%) a booster dose for residual disease was applied. Five-year overall survival was 87%, 5-year disease-free survival 84%. Of nine relapses, two were in the gastric stump of low grade patients after reinfection with Helicobacter pylori. Three infield, intraabdominal relapses were observed in intermediate and high grade lymphoma, all other relapses were outfield. Eleven patients experienced late toxicity (bowel obstruction after laparatomy and irradiation, four patients; chronic gastritis, three patients; asymptomatic left kidney atrophy, two patients; asymptomatic hepathopathia, two patients). In bowel lymphoma, 5-year disease-free survival was 65%. CONCLUSION: This study demonstrates the high efficacy of risk-adapted radiotherapy in gastric lymphoma. In low grade gastric lymphoma, whole abdominal irradiation may be reduced in dose or omitted. Total gastrectomy does not improve results and should therefore be avoided if possible.

Adult↗
PubMed1997

Endometrial effects of three doses of trimegestone, a new orally active progestogen, on the postmenopausal endometrium.

OBJECTIVE: To study the effects of oral trimegestone on endometrial histology and vaginal bleeding when given in combination with oral 17-beta-oestradiol. METHODS: This was a prospective, randomised, double-blind, parallel groups, pilot comparative study. Thirty-eight healthy postmenopausal women with normal endometrial histology were given oral 17-beta-oestradiol, 2 mg/day for three continuous cycles of 28 days, plus oral trimegestone, 0.10, 0.25 or 0.50 mg/day from day 15 to day 28 of each cycle. A Vabra biopsy was performed late in the oestradiol/trimegestone phase of cycle 3 and examined for histological evidence of secretory transformation of the endometrium. Characteristics of vaginal bleeding were recorded on a daily basis. RESULTS: Thirty-seven women completed the study, of whom 31 yielded adequate tissue for histological assessment. All showed secretory transformation of the endometrium. Bleeding was of earlier onset and longer duration with the lowest dose of trimegestone. CONCLUSIONS: Trimegestone is a highly effective oral progestogen for endometrial protection, all doses inducing secretory endometrial transformation. Although bleeding patterns suggest a weaker effect of the lowest dose used, the minimum effective dose for endometrial protection has still to be determined and may be lower than those used in this study.

Administration, Oral↗
PubMed1997

Stereochemical aspects of 1,3-butadiene metabolism and toxicity in rat and mouse liver microsomes and freshly isolated rat hepatocytes.

1,3-Butadiene (BD) is a gas used heavily in the rubber and plastics industry. BD and its epoxide metabolites have been shown to be carcinogenic and mutagenic in rodents, and BD has been classified by IARC as a group 2A carcinogen. We have examined the role of stereochemistry in species-dependent metabolism and toxicity of BD. Diastereo- and enantioselective synthetic routes to butadiene monoxide (BMO), butadiene bisoxide (BBO), and 3,4-epoxybutane-1,2-diol isomers have been developed. These routes have allowed the development of chiral gas chromatographic and GC/MS analytical procedures for quantitation of these metabolites in biological experiments. We have utilized hepatic microsomes from male B6C3F1 mice and hepatic microsomes and intact hepatocytes from male Sprague-Dawley rats as experimental systems. At 30 min, BMO production from BD was two times higher in mouse hepatic microsomes than in rats, and stereoselective analysis was used to determine the relative formation of (R)- and (S)-BMO. Formation of BBO from both (R)- and (S)-BMO was characterized in rat and mouse microsomal systems. As expected, more BBO was formed in mouse hepatic microsomes (3-4-fold) than in rat hepatic microsomes. No difference in total BBO formed from either isomer was observed in rat microsomes, but in mouse microsomes significantly more BBO was produced from (S)-BMO than from (R)-BMO. The cytotoxicity of each BMO and BBO enantiomer was examined in freshly isolated rat hepatocytes. (R)-BMO showed greater cytotoxicity than (S)-BMO. Stereospecific cytotoxicity was also observed using BBO enantiomers and (meso)-BBO was more cytotoxic than either the (R:R) or the (S:S)-BBO. The results show that stereochemistry plays an important role in BD metabolism and cytotoxicity and for the purposes of risk assessment needs to be compared across species.

Animals↗
PubMed1997

Characterization of a polymorphism in NAD(P)H: quinone oxidoreductase (DT-diaphorase).

NAD(P)H:quinone oxidoreductase (NQO1, EC 1.6.99.2) is an obligate two-electron reductase that can either bioactivate or detoxify quinones and has been proposed to play an important role in chemoprevention. We have previously characterized a homozygous point mutation in the BE human colon carcinoma cell line that leads to a loss of NQO1 activity. Sequence analysis showed that this mutation was at position 609 of the NQO1 cDNA, conferring a proline to serine substitution at position 187 of the NQO1 enzyme. Using polymerase chain reaction (PCR) analysis, we have found that the H596 human non-small-cell lung cancer (NSCLC) cell line has elevated NQO1 mRNA, but no detectable enzyme activity. Sequencing of the coding region of NQO1 from the H596 cells showed the presence of the identical homozygous point mutation present in the BE cell line. Expression and purification of recombinant wild-type and mutant protein from E. coli showed that mutant protein could be detected using immunoblot analysis and had 2% of the enzymatic activity of the wild-type protein. PCR and Northern blot analysis showed moderate to low levels of expression of the correctly sized transcript in the mutant cells. Immunoblot analysis also revealed that recombinant mutant protein was immunoreactive; however, the mutant protein was not detected in the cytosol of either BE or H596 cells, suggesting that the mutant proteins were either not translated or were rapidly degraded. The absence of any detectable, active protein, therefore, appears to be responsible for the lack of NQO1 activity in cells homozygous for the mutation. A polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis for the mutation at position 609 conducted on 90 human lung tissue samples (45 matched sets of tumour and uninvolved tissue) revealed a 7% incidence of individuals homozygous for the mutation, and 42% heterozygous for the mutation. These data suggest that the mutation at position 609 represents a polymorphism in an important xenobiotic metabolizing enzyme, which has implications for cancer therapy, chemoprevention and chemoprotection.

Adult↗