Birth defects among offspring of Norwegian farmers, 1967-1991

We investigated birth defects (N = 4,565) reported to the Medical Birth Registry of Norway among 192,417 births between 1967 and 1991 to parents identified as farmers in five agricultural and horticultural censuses between 1969 and 1989. The prevalences at birth of all and specific birth defects deviated little from those among 61,351 births to non-farmers in agricultural municipalities. We classified exposure indicators on the basis of information provided at the agricultural censuses. The main hypotheses were that parental exposure to pesticides was associated with defects of the central nervous system, orofacial clefts, some male genital defects, and limb reduction defects. We found moderate increases in risk for spina bifida and hydrocephaly, the associations being strongest for exposure to pesticides in orchards or greenhouses [spina bifida: 5 exposed cases, odds ratio (OR) = 2.76, 95% confidence interval (CI) = 1.07-7.13; hydrocephaly: 5 exposed cases, OR = 3.49, 95% CI = 1.34-9.09]. Exposure to pesticides, in particular in grain farming, was also associated with limb reduction defects (OR = 2.50; 95% CI = 1.06-5.90). We also saw an association with pesticides for cryptorchism and hypospadias. We found less striking associations for other specific defects and pesticide indicators, animal farming, and fertilizer regimens.

Gestational age, birth weight, and perinatal death among births to Norwegian farmers, 1967-1991

Perinatal health was investigated by linkage with the Medical Birth Registry of Norway for 192,417 births that took place between 1967 and 1991 among parents identified as farm holders in Norwegian agricultural censuses in 1969-1989. In a comparison with 61,351 births to nonfarmers in agricultural municipalities, farmers' births had an advantageous distribution of gestational ages and birth weights. Perinatal mortality was similar in the two groups, but the proportion of late-term abortions (gestational weeks 16-27) was higher among farmers' birth (odds ratio (OR) = 1.9, 95% confidence interval (CI) 1.6-2.3). Exposure indicators were classified on the basis of information given in the agricultural censuses and climate data for the grain harvest seasons of 1966-1991. The main hypotheses were that perinatal death is associated with parental exposure to pesticides. Toxoplasma contracted from infected sheep or pigs, or mycotoxins found in grain farming. There was no convincing evidence that perinatal death is associated with use of pesticides, sheep farming, or pig farming. The increase in late-term abortion among the farmers could to some extent be attributed to an excess of midpregnancy (weeks 21-24) deliveries among grain farmers; grain farmers had 132 deliveries at this time in pregnancy (2.8 per 1,000 pregnancies), while the nongrain farmers had 236 deliveries in midpregnancy (1.8 per 1,000). The authors found odds ratios (95% CI) that indicated that grain farming risk was higher after the harvest (1.8, 1.1-2.8), in seasons with a poor quality harvest (2.4, 1.5-3.8), and in pregnancies with multiple births (3.8, 1.7-8.2). These results support the hypothesis that occupational exposure to mycotoxins in grain induces labor at an early stage of pregnancy.

Provocative appeals in anti-smoking mass media campaigns targeting adolescents--the accumulated effect of multiple exposures

This paper reports findings from a longitudinal study that evaluated the accumulated effect of three consecutive mass media campaigns using provocative and dissonance arousing appeals to prevent cigarette smoking by adolescents. In the spring of 1992, all eligible adolescents aged 14 and 15 in one intervention county (N = 4898) and one control county (N = 5439) in Norway were included in the study, and were followed until they were 17 and 18 years of age in 1995. Only students who completed questionnaires both in 1992 and 1995 were included in the analyses. Among the non-smokers at baseline, a significantly lower proportion of adolescents of both genders had started to smoke in the intervention county compared to the proportion in the control county. Among those who were smokers at baseline, significantly more girls in the intervention county had stopped smoking than in the control county, while no significant difference between the counties was detected among boys. Our findings suggest that provocative and dissonance arousing appeals that create affective reactions and lead to interpersonal communication should be given more attention in campaigns designed to influence adolescent smoking. However, such appeals may easily produce negative reactions and the normative context should be thoroughly considered when using such appeals in future interventions.

Cancer mortality among man-made vitreous fiber production workers

We have updated the follow-up of cancer mortality for a cohort study of man-made vitreous fiber production workers from Denmark, Finland, Norway, Sweden, United Kingdom, Germany, and Italy, from 1982 to 1990. In the mortality analysis, 22,002 production workers contributed 489,551 person-years, during which there were 4,521 deaths. Workers with less than 1 year of employment had an increased mortality [standardized mortality ratio (SMR) = 1.45; 95% confidence interval (CI) = 1.37-1.53]. Workers with 1 year or more of employment, contributing 65% of person-years, had an SMR of 1.05 (95% CI = 1.02-1.09). The SMR for lung cancer was 1.34 (95% CI = 1.08-1.63, 97 deaths) among rock/slag wool workers and 1.27 (95% CI = 1.07-1.50, 140 deaths) among glass wool workers. In the latter group, no increase was present when local mortality rates were used. Among rock/slag wool workers, the risk of lung cancer increased with time-since-first-employment and duration of employment. The trend in lung cancer mortality according to technologic phase at first employment was less marked than in the previous follow-up. We obtained similar results from a Poisson regression analysis limited to rock/slag wool workers. Five deaths from pleural mesothelioma were reported, which may not represent an excess. There was no apparent excess for other categories of neoplasm. Tobacco smoking and other factors linked to social class, as well as exposures in other industries, appear unlikely to explain the whole increase in lung cancer mortality among rock/slag wool workers. Limited data on other agents do not indicate an important role of asbestos, slag, or bitumen. These results are not sufficient to conclude that the increased lung cancer risk is the result of exposure to rock/slag wool; however, insofar as respirable fibers were an important component of the ambient pollution of the working environment, they may have contributed to the increased risk.

Risk of cancer and exposure to gasoline vapors

Until the introduction of self-service around 1970, service station workers in the Nordic countries were exposed to gasoline vapors. Based on measurements reported in the literature, the 8-hour time-weighted average benzene exposure was estimated to be in the range of 0.5-1 mg/m3. We studied the cancer incidence in a cohort of 19,000 service station workers from Denmark, Norway, Sweden, and Finland. They were identified from the 1970 censuses and followed through 20 years, where 1,300 incident cancers were observed. National incidence rates were used for comparison. The incidence was not increased for leukemia (observed = 28, standardized incidence ratio (SIR) = 0.9, 95% confidence interval (CI) 0.6-1.3) not for acute myeloid leukemia (observed = 13, SIR = 1.3, 95% CI 0.7-2.1). The incidence was slightly elevated for kidney cancer observed = 57, SIR = 1.3, 95% CI 1.0-1.7) and for pharyngeal, laryngeal, and lung cancer. A 3.5-fold risk of nasal cancer was found (observed = 12, SIR = 3.5, 95% CI 1.8-6.1). This cohort exposed to gasoline vapors with benzene levels estimated to be 0.5-1 mg/m3 showed no excess risk of leukemia or acute myeloid leukemia, a 30% elevated risk of kidney cancer, and a previously unnoticed risk of nasal cancer.

[Use of occupational disease benefits]

Persons with pleuramesothelioma were studied to find out the share receiving occupational injury benefit from the National Insurance Scheme. This disease, caused by inhaling asbestos, was chosen because it has been estimated that between 70 and 80 per cent of persons with pleuramesothelioma fulfil the criteria for compensation. During the period 1970-93, 662 men and 104 women were recorded as having this disease. Up to June 1996, the National Insurance Administration had considered the cases of only 163 men, and no women. A further 25-30 patients may have filed claims with the local national insurance office. This implies that, overall, maximum one third of those entitled to occupational injury benefit have received it. The fraction would probably be even lower in the case of diseases where the association with occupation is less certain. It is recommended that national disease registries, such as the Cancer Registry, should report possible cases of occupational disease to the National Insurance Administration.

Alterations in methotrexate pharmacokinetics by naproxen in the rat as measured by microdialysis

Reports of a potentially life-threatening interaction between the antifolate methotrexate (MTX) and drugs belonging to the NSAID class instigated a study of MTX pharmacokinetics by a microdialysis technique in the presence and absence of the NSAID naproxen in anesthetized rats. After pretreatment with naproxen, the animals received either 750 or 1,000 mg/kg MTX as a 6 h continuous intravenous infusion. During infusions, microdialysis effluents were obtained from probes situated intravenously, intrahepatically and intrarenally. In all three compartments, time-concentration AUCs for both MTX and its major extracellular metabolite, 7-hydroxymethotrexate (7-OH-MTX), increased about two-fold in the presence of naproxen. The mechanisms responsible for the MTX-NSAID interaction are briefly discussed. The study demonstrate that the microdialysis technique offers a means to investigate pharmacokinetic drug-drug interactions.

Continuous intratumoral microdialysis during high-dose methotrexate therapy in a patient with malignant fibrous histiocytoma of the femur: a case report

We used a microdialysis technique to assay intratumoral methotrexate (MTX) levels during high-dose (12 g/m2 given as a 4-h infusion) therapy in a 43-year-old man with a malignant fibrous histiocytoma in the medial femoral condyle. Additional microdialysis probes were implanted in muscle tissue contralateral to the tumor and in an antecubital vein. Microdialysis was attempted during the initial two high-dose courses, but the two latter probes were removed at the start of the second treatment cycle due to leakage. No attempt to correct for microdialysis recovery was made. The intratumorally localized probe gave reproducible data on tumor MTX exposure of 9.3-14% of unbound systemic MTX. There was a close correlation between tumor and systemic levels for both MTX and its major extracellular metabolite 7-hydroxymethotrexate. Although limited to the study of MTX pharmacokinetics in a single subject, the experiment demonstrates that intratumoral microdialysis may provide data on tumor drug exposure, although of an indirect nature and dependent on the probe characteristics, the flow rate, and, possibly, the time after probe implantation. We propose that the application of microdialysis may prove useful for elucidation of the relationship between local drug exposure and the therapeutic response in normally inaccessible compartments during cancer pharmacotherapy.

Truly late onset of eating disorders: a study of 11 cases averaging 60 years of age at presentation

OBJECTIVE

To study late-onset cases of eating disorders in order to (1) document the occurrence of these cases as truly new onset, even if postmenopausal; (2) to alert clinicians to the category of late-onset eating disorders, especially clinical features and treatment response; (3) to challenge some prevailing assumptions of etiology.

METHODS

Selection of cases of eating disorders with first onset after age 40 that met DSM-IV criteria, by review of eating disorders admissions to three university hospital programs.

RESULTS

Eleven patients, approximately 1% of all cases of eating disorders, had first onset of an eating disorder after age 40 and as late as 77, with an average onset of 56 and clinical presentation at 60 years. They met DSM-IV criteria for all subtypes of eating disorders. In general, concurrent medical and comorbid psychiatric symptoms made recognition and treatment more complex.

DISCUSSION

Truly late-onset cases do occur, challenging etiological theories requiring adolescent age of onset, premenopausal endocrine functioning, or adolescent psychodynamic conflicts. Late-occurring cases, after accurate diagnosis, require an appreciation of psychological themes pertinent to this age group, such as bereavement or unresolved body image issues. Age by itself is no barrier to onset of eating disorders, which may occur whenever self-starvation and/or binge-purge behaviors become entrenched as sustaining behaviors for amelioration of psychodynamic conflicts, mood disorders, or interpersonal distress.

Exposure to nickel compounds and smoking in relation to incidence of lung and nasal cancer among nickel refinery workers

OBJECTIVES

To investigate the relation between occupational hazards among nickel refinery workers and their exposure to different forms of nickel over time and the interaction between smoking and total exposure to nickel.

METHODS

The cohort consisted of 379 workers with first employment 1916-40 and at least three years of employment and 4385 workers with at least one year of employment 1946-83. Data on smoking (ever or never) were available for almost 95% of the cohort. Two analyses were used, indirect standardisation from observed and expected numbers and Poisson regression.

RESULTS

During the follow up 1953-93, 203 new cases of lung cancer were observed v 68 expected (standardised incidence ratio (SIR) 3.0, 95% confidence interval (95% CI) 2.6-3.4) and 32 cases of nasal cancer were observed v 1.8 expected (SIR 18.0, 95% CI 12-25). The Poisson regression analysis showed an excess risk of lung cancer in association with exposure to soluble forms of nickel, with a threefold increase in relative risk (RR) (P < 0.001) and a multiplicative effect of smoking and exposure to nickel. The RRs were 1.1 (95% CI 0.2-5.1) for exposed workers who had never smoked and 5.1 (95% CI 1.3-20.5) for exposed workers who smoked.

CONCLUSION

It is not possible to state with certainty which specific nickel compounds are carcinogenic, but a significant excess risk was found for workers exposed to soluble nickel alone or in combination with other forms of nickel. The present study suggests a multiplicative effect of smoking and nickel exposure.

Exposure to styrene and mortality from nervous system diseases and mental disorders

Chronic low-dose exposure to solvents has been associated in epidemiologic studies with chronic neurotoxicity, but the evidence is not consistent. Styrene causes acute disturbances in the central and peripheral nervous systems. To determine if exposure to styrene may contribute to chronic diseases of the central nervous system, the authors examined mortality from nervous system diseases, mental disorders, and suicide in relation to styrene exposure in an international historical cohort study. The cohort involved 35,443 workers employed during 1945-1991 in the reinforced plastics industry, where high exposures to styrene occur. Indicators of exposure were reconstructed through job histories and environmental and biologic monitoring data. Poisson regression was used for internal comparisons. Mortality from diseases of the central nervous system (27 deaths) increased with time since first exposure, duration of exposure, average level of exposure, and cumulative exposure to styrene. A quadratic model described best the dose-response shape for cumulative exposure and duration of exposure with the highest risks at around 300 ppm-years and 5 years, respectively, and a subsequent decrease in risk in the highest exposure categories. Mortality from epilepsy increased monotonically with all styrene exposure indicators, while associations for degenerative diseases of the central nervous system were generally weaker. Mortality from mental disorders and suicide decreased with increasing duration of exposure and cumulative exposure, while there was no trend with time since first exposure and average exposure to styrene. These findings suggest that, in addition to the known acute effects, exposure to styrene may contribute to chronic diseases of the central nervous system.

Smoking habits and risk of cancers other than lung cancer: 28 years' follow-up of 26,000 Norwegian men and women

The impact of tobacco smoking on lung cancer risk has been investigated thoroughly since the 1950s, but other types of cancer also have been associated with smoking. In the present study, the aim was to explore the variation in risk connected with cigarette, cigar, and pipe smoking of suspected smoking-associated cancers other than lung cancer. Data were obtained from a survey of a random sample of the Norwegian population. A self-administered mailed questionnaire, which included questions about smoking habits, was completed by 26,000 men and women in 1965 (response rate: 76 percent). The cohort was followed from 1966 through 1993, including registration of all incident cancer cases. A dose-response relationship of cigarette smoking to the risk of urinary bladder cancer and cancers of the upper digestive and respiratory tract was observed. For the latter forms of cancer, a dose-response relationship of pipe smoking also was observed. In cancer of the pancreas, a stronger association between cigarette smoking and cancer risk was observed when the analysis was confined to histologically confirmed cases only. Current cigarette smokers at baseline had a significantly higher risk of cervical cancer than those who never smoked cigarettes. In cancers of the stomach, colon, rectum, breast, corpus uteri, ovary, and prostate, and in leukemia, no association between smoking and cancer risk was observed.

Exposure to styrene and mortality from nonmalignant respiratory diseases

A cohort of 34,560 men and 6128 women employed in 660 European factories manufacturing reinforced plastic products, followed up originally to assess the risk of cancer, was used to assess the risk of non-malignant respiratory diseases associated with exposure to styrene. Mortality from pneumonia was associated with intensity of exposure to styrene, but this may have been due to chance. Mortality from bronchitis, emphysema, and asthma was not associated with styrene exposure.

Exposure to styrene and mortality from nonmalignant diseases of the genitourinary system

OBJECTIVES

A historical cohort study was carried out to investigate mortality from nonmalignant diseases of the genitourinary system among workers in the reinforced plastics industry, where high workroom concentrations of styrene are encountered.

METHODS

The external comparisons in this report were based on an average of 12.6 years of retrospective follow-up of 35 443 workers who were first employed in the reinforced plastics industry during 1945-1991 and were known to have been exposed to styrene in their work. For the internal comparisons, 2641 subjects with incomplete occupational histories were excluded, leaving 32 802 subjects. Previous individual exposure histories to styrene were reconstructed through job histories and environmental and biological monitoring data.

RESULTS

Mortality from nonmalignant diseases of the genitourinary system (N = 20) was associated with average exposure to styrene (P for trend 0.05). Weaker increasing trends in risk were seen for time since first exposure and cumulative exposure, while no increase was identified for duration of exposure. There was a significant increasing trend in mortality from nephritis and nephrosis (N = 5), associated with an increasing average level of exposure to styrene (P for trend 0.03). No clear trend was observed for time since first exposure, duration of exposure, or cumulative exposure.

CONCLUSIONS

In this large cohort study of workers exposed to styrene, mortality from nonmalignant diseases of the genitourinary system increased as the average intensity of exposure increased. This finding indicates that other data should be scrutinized.

The impact of smoking habits on lung cancer risk: 28 years' observation of 26,000 Norwegian men and women

While factory-made cigarettes dominate the market in most countries, the use of handrolled cigarettes accounts for a substantial proportion of the tobacco consumption in Norway. In the present study, we examined the impact of tobacco smoking on lung cancer in general, and the effect of handrolled cigarettes in particular. The data used was from a self-administered mailed questionnaire which included questions about smoking habits and which was completed by about 26,000 men and women in 1964-65. During the follow-up from 1966 to 1993, 333 lung cancers in men and 102 in women were registered. The analysis was performed by use of the Cox proportional hazards regression models. A clear dose-response relationship was found both for cigarette smoking, and for pipe smoking (in men). The dose-response relationship of cigarette smoking was seen in all the three histologic groups considered-squamous cell carcinoma, adenocarcinoma, and small cell carcinoma. The highest relative risks were noted in squamous cell and small cell carcinoma. A higher risk of lung cancer was found for cigarette-smoking women who started cigarette smoking before the age of 30 compared with similar groups of men. In a combined analysis of men and women, an elevated relative risk of 1.9 (95 percent confidence interval = 1.2-3.3) was found for those smoking only handrolled cigarettes compared with those smoking factory-made filter cigarettes only.

Incidence of cancer among Norwegian boiler welders

OBJECTIVES

The cancer incidence among 2957 boiler welders was investigated. The subjects were registered electrical welders from 1942 to 1981. A subcohort of 606 stainless steel welders was studied separately.

METHODS

The investigation was a historical prospective cohort study based on a national registry. The loss of follow up was 4.9%.

RESULTS

There were 625 deaths (659 expected). There were 269 cancer cases (264 expected). An excess of lung cancer was found; 50 cases v 37.5 expected. There were three cases of pleural mesotheliomas v 1.1 expected. The subcohort of stainless steel welders had six cases of lung cancer v 5.8 expected, and one case of pleural mesothelioma v 0.2 expected.

CONCLUSIONS

The welders in the study were assumed to represent a qualified work force. These welders had a small excess risk of lung cancer. The excess risk did not seem to be associated with stainless steel welding. Smoking and asbestos exposure were potential confounders.

Reversibility of brain tissue loss in anorexia nervosa assessed with a computerized Talairach 3-D proportional grid

We describe the results of our follow-up magnetic resonance imaging (MRI) study of underweight patients with anorexia nervosa, using rigorous methodology to control for head position across time. All subjects first underwent an initial scan and rescan to verify that our computerized three-dimensional co-planar grid method for volume measurement was reliable and accurate, regardless of head positioning. After a period of several months, subjects had a follow-up scan to assess for changes that may have occurred following significant weight gain. Ventricular and total brain volume measurements from the initial scans were compared with the scans from an age- and sex-matched normal control group to determine whether we could replicate previous findings of ventricular enlargement compared with controls and whether brain volume is reduced compared with controls. Anorexic subjects had significantly larger ventricles when compared with normal controls but did not differ significantly in total brain volume. Using a repeated measures analysis of variance, a priori contrasts compared the initial/rescan pair volumes with each other and the initial/rescan pair volumes with the follow-up volume. These analyses showed that ventricular and total brain volumes derived from the initial/rescan pair were nearly identical, but that at follow-up ventricular volume decreased significantly and total brain volume increased significantly after weight gain.

Incidence of breast cancer in Norwegian female radio and telegraph operators

Exposure to electromagnetic fields may cause breast cancer in women if it increases susceptibility to sex-hormone-related cancer by diminishing the pineal gland's production of melatonin. We have studied breast cancer incidence in female radio and telegraph operators with potential exposure to light at night, radio frequency (405 kHz-25 MHz), and, to some extent, extremely low frequency fields (50 Hz). We linked the Norwegian Telecom cohort of female radio and telegraph operators working at sea to the Cancer Registry of Norway to study incident cases of breast cancer. The cohort consisted of 2,619 women who were certified to work as radio and telegraph operators between 1920 and 1980. Cancer incidence was analyzed on the basis of the standardized incidence ratio (SIR), with the Norwegian female population as the comparison group. The incidence of all cancers was close to unity (SIR = 1.2). An excess risk was seen for breast cancer (SIR = 1.5). Analysis of a nested case-control study within the cohort showed an association between breast cancer in women aged 50+ years and shift work. In a model with adjustment for age, calendar year, and year of first birth, the rate ratio for breast cancer associated with being a radio and telegraph operator--in comparison with all Norwegian women born 1935 or later--analyzed with Poisson regression, was 1.5 after adjustment for fertility factors. These results support a possible association between work as a radio and telegraph operator and breast cancer. Future epidemiologic studies on breast cancer in women aged 50 and over, should address possible disturbances of chronobiological parameters by environmental factors.

Determination of extracellular methotrexate tissue levels by microdialysis in a rat model

We used a microdialysis technique to determine tissue methotrexate (MTX) levels during steady state in a rodent model. Two different approaches were employed to measure the actual extracellular MTX concentrations in muscle, liver, and kidney tissues of anesthetized Wistar rats. With the reduced-perfusion-rate technique, the flow in the microdialysis perfusate was gradually decreased toward zero to permit calculation of zero-flow intercepts. Using the net change technique, microdialysis probes were perfused with different MTX concentrations to allow an assessment of equilibrium drug levels. For these two methods to be used, drug concentrations in the matrix to be analyzed must remain unchanged during the experimental procedure. In the animal model, steady state was attained after 1.5 h and maintained throughout the rest of the experiments by the administration of MTX as continuous infusions through a venous catheter. In vitro and in vivo, both the reduced-perfusion-rate and net change techniques gave reproducible data that permitted the estimation of extracellular drug concentrations in the dialyzed tissue compartments.The data suggest that the level of unbound MTX in the circulation is fairly similar to the extracellular concentrations in the muscle and liver. In the kidney, MTX levels were measured to be 3-8 times higher than those of unbound, circulating MTX, and a considerable discrepancy between the two methods used for estimations was apparent. These results demonstrate that both the net change and reduced-flow microdialysis techniques can produce reproducible and precise data. The results may constitute a basis for determining recoveries and, thus, true extracellular drug levels during in vivo microdialysis of MTX. This may be of importance in delineation of the relationship between tissue MTX levels and outcome in a variety of normally inaccessible compartments during cancer pharmacotherapy.

Incidence and risk factors of cancer among men and women in Norwegian agriculture

OBJECTIVES

The objective of the study was to examine cancer incidence and identify risk factors among subjects born in 1925-1971 and engaged in agricultural activities in Norway.

METHODS

A cohort was established through linkage between agricultural censuses in 1969-1989 and the Central Population Register, which identifies farm holders and their spouses. Available census information on the activity of the farm provided the exposure indicators. Incident cancer in 1969-1991 was identified in the Cancer Register. In an analysis for standardized incidence ratios (SIR), the cohort was compared with the total rural population of Norway. Associations with exposure indicators were investigated in a Poisson regression analysis.

RESULTS

In the follow-up of 136,463 men for 1.5 million person-years and 109,641 women for 0.6 million person-years, 3333 and 2145 cancer cases were identified, respectively. The subset defined as farmers had an SIR of 77 [95% confidence interval (95% CI) 73-81] for the men and 92 (95% CI 85-99) for the women, with particularly low SIR values for lung cancer and other sites linked to life-style. The several positive associations found confirmed the a priori hypothesis of an association between dairy farming and acute leukemia among men [rate ratio 1.76, 95% CI 1.02-3.05]. Multiple myeloma was associated with pesticide indicators for both genders, mainly for subjects cultivating potatoes.

CONCLUSIONS

The results support the hypothesis of a relationship between acute leukemia and animal contact and between multiple myeloma and pesticides in potato cultivation. Other exposure associations, especially for cancer among women, warrant further investigation.

Selected novel flavones inhibit the DNA binding or the DNA religation step of eukaryotic topoisomerase I

Topoisomerases are involved in many aspects of DNA metabolism such as replication and transcription reactions. Camptothecins, which stabilize the covalent intermediate of topoisomerase I and DNA are effective, though toxic, drugs for cancer therapy. In this study, a new class of topoisomerase I inhibitors was identified, and their mode of action was characterized using recombinant human topoisomerase I preparations and human HL-60 leukemic cells. Quercetin and the related natural flavones, acacetin, apigenin, kaempferol, and morin, inhibit topoisomerase I-catalyzed DNA religation. In contrast to camptothecin, these compounds do not act directly on the catalytic intermediate and also do not interfere with DNA cleavage. However, formation of a ternary complex with topoisomerase I and DNA during the cleavage reaction inhibits the following DNA religation step. 3,3',4',7-Tetrahydroxy-substituted flavones stabilize the covalent topoisomerase I-DNA intermediate most efficiently. Enhanced formation of covalent topoisomerase I-DNA complexes was also demonstrated in human HL-60 cells. In contrast, synthetic 3,5'-dibromo- 4'-hydroxy-3-methylflavones bind selectively to topoisomerase I in its non-DNA-bound form and block the following DNA binding step. As a consequence, these synthetic flavonoids are capable of counteracting topoisomerase I-directed effects of camptothecin. Inhibition of DNA binding is obtained by voluminous hydrophobic substituents in 6-position of the flavone structure. Our data show that selective inhibitors of both half-reactions of topoisomerase I can be derived from the flavone structure.

Cancer in offspring of parents engaged in agricultural activities in Norway: incidence and risk factors in the farm environment

In this study of cancer in offspring we demonstrate that factors linked to horticulture and use of pesticides are associated with cancer at an early age, whereas factors in animal husbandry, in particular poultry farming, are associated with cancers in later childhood and young adulthood. Incident cancer was investigated in offspring born in 1952-1991 to parents identified as farm holders in agricultural censuses in Norway in 1969-1989. In the follow-up of 323,292 offspring for 5.7 million person-years, 1,275 incident cancers were identified in the Cancer Registry for 1965-1991. The standardized incidence for all cancers was equal to the total rural population of Norway, but cohort subjects had an excess incidence of nervous-system tumours and testicular cancers in certain regions and strata of time that could imply that specific risk factors were of importance. Classification of exposure indicators was based on information given at the agricultural censuses. Risk factors were found for brain tumours, in particular non-astrocytic neuroepithelial tumours: for all ages, pig farming tripled the risk [rate ratio (RR), 3.11; 95% confidence interval (CI), 1.89-5.13]; indicators of pesticide use had an independent effect of the same magnitude in a dose-response fashion, strongest in children aged 0 to 14 years (RR, 3.37; 95% CI, 1.63-6.94). Horticulture and pesticide indicators were associated with all cancers at ages 0 to 4 years, Wilms' tumour, non-Hodgkin's lymphoma, eye cancer and neuroblastoma. Chicken farming was associated with some common cancers of adolescence, and was strongest for osteosarcoma and mixed cellular type of Hodgkin's disease. The main problem in this large cohort study is the crude exposure indicators available; the resulting misclassification is likely to bias any true association towards unity.