Contribution of formaldehyde to respiratory cancer

This article reviews the available data on the carcinogenicity of formaldehyde from experimental and epidemiologic studies and makes recommendations for further research. Two definitive chronic inhalation bioassays on rodents have demonstrated that formaldehyde produces nasal cancer in rats and mice at 14 ppm and in rats at 6 ppm, which is within the domain of present permissible human exposure (8-hr time-weighted average of 3 ppm, a 5 ppm ceiling, and a 10 ppm short-term exposure limit). Biochemical and physiologic studies in rats have shown that inhaled formaldehyde can depress respiration, inhibit mucociliary clearance, stimulate cell proliferation, and crosslink DNA and protein in the nasal mucosa. No deaths from nasal cancer have been reported in epidemiologic studies of cohorts exposed to formaldehyde, but three case-control studies suggest the possibility of increased risk. Although excesses of lung cancer deaths have been observed in some studies at industrial plants with formaldehyde exposure, uncertainties in interpretation limit the evaluation of these findings. Excess cancers of the brain and of lymphatic and hematopoietic tissues have been reported in certain studies of industrial groups and in most studies of formaldehyde-exposed professionals, but whether these excesses are related to formaldehyde exposure is not known. Several properties of formaldehyde pose unique problems for future research: the mechanisms responsible for its nonlinear response; its probable mechanism of carcinogenic action as a cross-linking agent; its formation in tissues as a normal metabolite; its possible action as a promoter and/or a cocarcinogen; and the importance of glutathione as a host defense at low exposure.

Heart disease in workers exposed to dinitrotoluene

To determine whether the carcinogenicity of dinitrotoluene (DNT) in rodent bioassays was predictive for humans, we examined the mortality experience of exposed workers at two ammunition plants. Cohorts of 156 and 301 men who had worked a month or more during the 1940s and 1950s at jobs with opportunity for substantial DNT exposure were followed through the end of 1980. Numbers of expected deaths and standardized mortality ratios (SMRs) were computed, using mortality rates of US white males as the standard. No evidence of a carcinogenic effect was found, but unsuspected excesses of mortality from ischemic heart disease were noted at both plants (SMRs) 131 and 143; 95% confidence limits 65 to 234 and 107 to 187, respectively). Deaths from ischemic heart disease remained high even when compared with expected numbers derived using mortality rates of the counties in which the plants were located. Additional analyses revealed evidence of a 15-year latent period and suggested a relationship with duration and intensity of exposure. Epidemiologic investigations of other heavily exposed populations are needed to confirm the etiologic significance of the association between DNT and heart disease described here.

Referral of patients with cancer for participation in randomized clinical trials: ethical considerations

Physicians with patients with cancer may be faced with two conflicting ethical obligations. One is to contribute to the advancement of scientific knowledge. Among the ways available to respond to this duty is to refer patients for participation in RCTs. The second obligation is to serve the health interests of the individual patient. When these two duties conflict, the latter obligation to the individual takes priority. In the words of the Declaration of Helsinki, "Concern for the interests of the subject (patient) must always prevail over the interests of science and society." Quite often there is no conflict. The patient can pursue his or her health interests most effectively by enrollment in an RCT. In such cases, the referring physician can contribute to the success of the patient's participation in the RCT by explaining what the patient can expect to experience as a patient-subject. It is usually important to explain that referral does not necessarily entail severing the original doctor-patient relationship.

Fertility of workers. A comparison of logistic regression and indirect standardization

Estimates of the effect of occupational exposure on the fertility of men employed at three chemical plants were obtained from data stored at the Chemical Industry Institute of Toxicology using logistic regression and indirect standardization. Logistic regression was explored as a possible alternative to indirect standardization because it 1) permits consideration of potential confounding variables, such as the relative spacing between consecutive births, that are not included in the characterization of the fertility of an external reference population, and 2) may enable the study of occupational cohorts for which fertility data from an appropriate external reference population are not available. In addition to the main effects of age, parity, and birth cohort, main effects of certain lag variables which characterize the timing of birth events during the five-year period preceding each person-year were found to be significant at all three plants. Interactions of some of these lag variables with age also emerged as significant. Despite this, both methods were consistent in accepting or rejecting the null hypothesis regarding the effect of exposure at two of the plants. At the third plant, however, the logistic regression yielded a significant interaction between exposure status and one of the lag variables. The net exposure effect was significantly increased fertility in exposed person-years for which no birth had occurred 2-3 years prior, and nonsignificantly decreased fertility in exposed person-years for which such a prior birth had occurred. While this may be a spurious finding, it suggests that both methods of analysis should continue to be explored until a larger body of similar comparative studies has accumulated.

Artificial heart and assist devices: directions, needs, costs, societal and ethical issues

A Working Group appointed by the Director of the National Heart, Lung, and Blood Institute (NHBLI) has reviewed the current status of mechanical circulatory support systems (MCSS), and has examined the potential need for such devices, their cost, and certain societal and ethical issues related to their use. The media have reported the limited clinical investigative use of pneumatically energized total artificial hearts (which actually replace the patient's heart) and left ventricular assist devices (which support or replace the function of the left ventricle by pumping blood from the left heart to the aorta with the patient's heart in place). However, electrically energized systems, which will allow full implantation, permit relatively normal everyday activity, and involve battery exchange or recharge two or three times a day, are currently approaching long-term validation in animals prior to clinical testing. Such long-term left ventricular assist devices have been the primary goal of the NHLBI targeted artificial heart program. Although the ventricular assist device is regarded as an important step in the sequence of MCSS development, the Working Group believes that a fully implantable, long-term, total artificial heart will be a clinical necessity and recommends that the mission of the targeted program include the development of such systems. Past estimates of the potential usage of artificial hearts have been reviewed in the context of advances in medical care and in the prevention of cardiovascular disease. In addition, a retrospective analysis of needs was carried out within a defined population. The resulting projection of 17,000-35,000 cases annually, in patients below age 70, falls within the general range of earlier estimates, but is highly sensitive to many variables. In the absence of an actual base of data and experience with MCSS, projection of costs and prognoses was carried out using explicit sets of assumptions. The total cost of a left ventricular assist device, its implantation and maintenance for a projected average of 4 1/2 years of survival might be approximately $150,000 (in 1983 dollars). The gross annual cost to society could fall in the range of $2.5-$5 billion. Ethical issues associated with use of the artificial heart are not unique. For individual patients these relate primarily to risk-benefit, informed consent, patient selection, and privacy. However, for society as a whole, the larger concern relates to the distribution of national resources.(ABSTRACT TRUNCATED AT 400 WORDS)

Identification and quantification of urinary metabolites of dinitrotoluenes in occupationally exposed humans

Rats exposed to technical grade dinitrotoluene (DNT) develop hepatocellular carcinomas. Humans may be exposed to DNT during its manufacture and use. To permit comparisons of human excretion patterns of DNT metabolites with those previously observed in rats, urine specimens were collected over a 72-hr period from workers at a DNT manufacturing plant. Samples were analyzed for 2,4- and 2,6-DNT and putative metabolites by gas chromatography-mass spectrometry. Urine from workers exposed to DNT contained 2,4- and 2,6-DNT, 2,4- and 2,6-dinitrobenzoic acid, 2,4- and 2,6-dinitrobenzyl glucuronide, 2-amino-4-nitrobenzoic acid, and 2-(N-acetyl)amino-4-nitrobenzoic acid. Excretion of these metabolites peaked near the end of the workshift, but declined to either very low or undetectable concentrations by the start of work the following day. The calculated half-times for elimination of total DNT-related material detected in urine ranged from 1.0 to 2.7 hr, and those of individual metabolites from 0.8 to 4.5 hr. The most abundant metabolites were 2,4-dinitrobenzoic acid and 2-amino-4-nitrobenzoic acid, collectively accounting for 74 to 86% of the DNT metabolites detected. The data indicate that urinary metabolites of DNT in humans are qualitatively similar to those found in rats, but quantitative differences exist in the relative amounts of each metabolite excreted.

Electron microscopic and optical diffraction analysis of the structure of scorpion muscle thick filaments

We rapidly and gently isolated thick filaments from scorpion tail muscle by a modification of the technique previously described for isolating Limulus thick filaments. Images of negatively stained filaments appeared to be highly periodic, with a well-preserved myosin cross-bridge array. Optical diffraction patterns of the electron micrograph images were detailed and similar to optical diffraction patterns from Limulus and tarantula thick filaments. Analysis of the optical diffraction patterns and computed Fourier transforms, together with the appearance of the filaments in the micrographs, suggested a model for the filaments in which the myosin cross-bridges were arranged on four helical strands with 12 cross-bridges per turn of each strand, thus giving the observed repeat every third cross-bridge level. Comparison of the scorpion thick filaments with those isolated from the closely related chelicerate arthropods, Limulus and tarantula, revealed that they were remarkably similar in appearance and helical symmetry but different in diameter.

Three-dimensional reconstruction of thick filaments from Limulus and scorpion muscle

We have produced three dimensional reconstructions, at a nominal resolution of 5 nm, of thick filaments from scorpion and Limulus skeletal muscle, both of which have a right-handed four-stranded helical arrangement of projecting subunits. In both reconstructions there was a distinct division of density within projecting subunits consistent with the presence of two myosin heads. Individual myosin heads appeared to be curved, with approximate dimensions of 16 X 5 X 5 nm and seemed more massive at one end. Our reconstructions were consistent with the two heads in a projecting subunit being arranged either antiparallel or parallel to each other and directed away from the bare zone. Although we cannot exclude the second of these interpretations, we favor the first as being more consistent with both filament models and also because it would enable easy phosphorylation of light chains. The antiparallel interpretation requires that the two heads within a subunit derive from different myosin molecules. In either interpretation, the two heads have different orientations relative to the thick filament shaft.

Structure of short thick filaments from Limulus muscle

Shortened Limulus thick filaments, isolated from stimulated muscle, are structurally similar to long filaments, isolated from unstimulated muscle, except for length. Both have 3-fold screw symmetry with a helical repeat at approximately 43 nm, axial spacing of 14.5 nm between successive crowns of crossbridges and 4-fold rotational symmetry as estimated from the Bessel argument, by analysis of optical transforms of electron micrograph negatives of negatively stained samples. Both short and long filaments also have similar radii for the location of their crossbridges, thus similar diameters. Equal numbers of subunits/helical strand are also apparent on images of metal-shadowed long and short filaments. Since these data argue against molecular reorganization during filament shortening, it is suggested that the change in length of Limulus thick filaments may occur by reversible disaggregation of constituent protein molecules.

The mortality of Ontario undertakers and a review of formaldehyde-related mortality studies

In a study of the mortality of Ontario undertakers, a cohort of 1,477 men first licensed during 1928 through 1957 was followed up until the end of 1977. Numbers of observed and expected deaths were determined for the period 1950 through 1977, using mortality rates of Ontario men as the standard. In all, 319 persons had died, compared with 322 expected. Ontario undertakers were not at increased risk of death from cancers at sites of contact with formaldehyde. Cirrhosis of the liver (standardized mortality ratio, 238) and chronic rheumatic heart disease (standardized mortality ratio, 199) were the only causes of death found to be significantly in excess. The data are discussed in the context of current epidemiologic information on the mortality experience of persons exposed to formaldehyde.