Evidence for a new model of tumor progression from carcinogenesis and tumor promotion studies with 7-bromomethylbenz[a]anthracene.

7-Bromoethylbenz[a]anthracene (BrMeBA) has been shown previously to be a modest initiator of tumors in mouse skin and a powerful promoter. Evidence has also been presented that carcinomas and papillomas arising in mouse skin from a two-stage induction regimen (initiation and promotion) originate in two separate populations, rather than representing progressive stages on a single pathway. In this report, we show that 10 nmol of BrMeBA applied biweekly to female SENCAR mice initiated with 7,12-dimethylbenz[a]anthracene (DMBA) is an effective promoting dose. The question of whether BrMeBA or its solvolysis product, 7-hydroxymethylbenz[a]anthracene, is the effective promoter was tested in Charles River CD-1 mice, in which 90 nmol of BrMeBA applied weekly following a single dose of 200 nmol of DMBA induced papillomas in 17 weeks (median induction time) and carcinomas in 43 weeks after beginning of promotion. Without DMBA initiation, papillomas appeared 11 weeks later in much lower yield, while carcinomas appeared 14 weeks later. Animals treated with 7-hydroxymethylbenz[a]anthracene for 82 weeks had developed only 16 tumors in eight animals (initiated) or six tumors in five animals (uninitiated), with survivals of 18 of 30 and 19 of 30, respectively. In SENCAR mice treated with 90, 30, or 10 nmol of BrMeBA biweekly, the ratio of total carcinomas to total papillomas in initiated mice was about half that in uninitiated mice, due primarily to a large reduction in papilloma incidence in uninitiated mice. When adjusted for the number of papillomas, the risk of developing the first carcinomas at any time was dependent only on the dose of BrMeBA and not on whether DMBA was given first. An attempt to inhibit BrMeBA promotion with the antiinflammatory steroid fluocinolone acetonide resulted in inhibition of DMBA-initiated papillomas but had no effect on the carcinoma latent period of incidence. The results are explained in terms of new models of tumor progression which suggest either that promotors with the capabilities of 12-O-tetradecanoylphorbol-13-acetate can divert cells at a minimum level of initiation from progression to cancer or that initiation can create at least two populations of altered cells, one (or more) of which is less likely to progress to cancer than normal cells.

First trimester serum zinc concentrations in human pregnancy.

Serum zinc concentrations in the 1st trimester of human pregnancy were evaluated in 106 women whose dates of conception were precisely determined by basal body temperature monitoring and human chorionic gonadotropin levels. Data are reported by intervals of postovulatory days. Sera were analyzed for zinc by atomic absorption spectrophotometry after acid digestion. Mean 1st trimester serum zinc concentrations, determined by 20-day increments from ovulation, were 0.97 +/- 0.22, 0.68 +/- 0.14, 0.77 +/- 0.18, and 0.70 +/- 0.15 micrograms/ml; differences between means were significant at p less than 0.005, less than 0.005, and less than 0.01, respectively. These differences could not be related to diet, supplement use, or hematocritic changes. No differences were apparent between diabetic and nondiabetic subjects. Of the 25 samples from women who aborted spontaneously, zinc concentration of seven were lower than interval means.

Advantages of using aquatic animals for biomedical research on reproductive toxicology.

Major advantages of the use of aquatic animals, such as trout, English sole, or sea urchins, for studying the mechanisms of reproductive toxicology are discussed. The remarkable synchrony of differentiation of gametes in large quantities for detailed morphologic and biochemical measurements enables research not readily done on mammalian nonseasonal breeders. Structural differences such as the absence of a fibrous sheath in the more simple structure of fish and sea urchin sperm flagella facilitates comparative study of the mechanism of action of microtubules in flagella movement and the coupling of mitochondrial energy production to microtubules movement.

Health risks from increases in methylmercury exposure.

Our present knowledge of the human health effects of methylmercury exposure is derived from study of major outbreaks of human poisonings in Japan and Iraq and experimental studies on primates. Methylmercury readily passes through such physiological barriers as the blood-brain barrier, blood-testes barrier, and the placenta. Its major pathological effects are on the nervous and reproductive systems and the developing embryo/fetus. The neurotoxicity of methylmercury is well established in both humans and non-human primates. Lesions in the cerebral and cerebellar gray matter consist of necrosis and lysis of neurons, phagocytosis and gliosis. The changes are most prominent in the deep sulci and may have a vascular component. A late effect is cerebral atrophy. At high dose levels the liver, kidneys, and other organs may also have degenerative changes. Although not yet described in humans, a major effect of exposure of female primates is an adverse effect on pregnancy. Maternal female M. fascicularis blood mercury levels above 1 ppm are associated with a decreased pregnancy rate and increased abortion rate. To date our experimental data lack sufficient numbers to detect infrequent pregnancy effects below 1 ppm. Preliminary studies also reveal that methylmercury may also decrease the number and function (swim speed) of sperm. Both human and primate studies demonstrate deleterious effects of methylmercury on the developing embryo/fetus. Autopsies on human and primate infants reveal retarded brain development and the occurrence of a cerebral palsy-like behavior in the newborns, whereas the mother may be free of signs and symptoms of methylmercury toxicity. The fetal blood level of mercury is higher than the maternal level.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of variable environmental arsenic contamination on urinary concentrations of arsenic species.

Urinary arsenic species have been determined for approximately 3000 urine samples obtained from residents of a community surrounding an arsenic-emitting copper smelter. Levels of inorganic, monomethylated and dimethylated arsenic species ranged from less than 1 microgram/L (the instrumental detection limit) to 180 micrograms/L seen for dimethyl arsenic. Comparison of a subsample of this population that had the least environmental contamination with the subsample having highest environmental arsenic concentrations showed small but statistically significant differences in urinary arsenic levels for all species except dimethylated arsenic. However, for children under 7 years of age living in areas with increased environmental arsenic contamination, there was a larger and equally significant (p less than 0.001) increase in all urinary species. This effect was more pronounced in males (5-fold increase in median sum of species concentration over control group) than in females (2-fold increase in median sum of species concentration over control group) and was observed as a weaker effect in the next higher age group (7-13 years of age). Reported consumption of seafood also was significantly related to increased urinary dimethyl arsenic, but changes in distribution among the urinary arsenic species detected was not a sensitive indicator of recent seafood consumption.

Malignant mesothelioma with minimal asbestos exposure.

The association of malignant mesothelioma and asbestos fibers is well established. The minimal exposure that may produce the tumor is not known. The present report documents the minimal exposure by thorough examination of occupational history and personal hobbies, and counting of the number of asbestos fibers in the lungs. The evidence for the elemental composition of asbestos fibers by electron probe (EDAX) is also presented.

Aluminum induced pulmonary granulomatosis.

The association of aluminum dusts and pulmonary fibrosis with emphysema in workers in the aluminum processing and manufacturing industries is well established. The early and minimal reactions of the lungs to the aluminum dusts are not known. This report presents the first case of pulmonary granulomatosis associated with aluminum inhalation. The occupational history of this patient was thoroughly examined, and the aluminum was identified by electron probe microanalysis of the lung biopsy specimen. The granulomatous response in this patient was similar to that observed in rabbits following aluminum dust inhalation. Hypersensitivity or individual idiosyncrasy may play a role in the development of the pulmonary granulomas following exposure to aluminum.

Pathogenic mechanisms of heterotopic neural tissue associated with anencephaly.

Central nervous tissue was found in both the lung and the abdominal surface of the diaphragm in an anencephalic baby with gastroschisis. These findings support the hypothesis that the heterotopic neural tissue in anencephalic babies is due to transamniotic implantation. It thus appears that the pathogenic mechanism of the heterotopic neural tissue in the lung is aspiration.

Laser light-scattering study of the toxic effects of methylmercury on sperm motility.

An in vitro study was designed using the laser light-scattering technique to obtain further information on the dose-effect relationship of methylmercury on sperm motility. The technique provided a quantitative evaluation of sperm swimming speed. Semen samples were collected from normal male Macaca fascicularis monkeys by anal electroejaculation. Methylmercury was added to aliquots of sperm suspensions in BWW medium in doses of 10, 5, 2, and 1 ppm. After 3 hours, the relative speed was 35%, 59%, 69%, and 92% of the corresponding controls at doses of 10, 5, 2, and 1 ppm, respectively. The percentage of motile spermatozoa decreased significantly at 10 ppm. By microscopic observation abnormal motility was detected at 5 and 10 ppm, especially after 20 to 40 minutes. Head movement increased from side to side, and many spermatozoa developed coiled tails. The technique proved useful for defining the dose-effect relationship of methylmercury and sperm swimming speed.

Changes in the number of astrocytes and microglia in the thalamus of the monkey Macaca fascicularis following long-term subclinical methylmercury exposure.

The effects of long-term subclinical exposure to methylmercury on the number of neurons, oligodendrocytes, astrocytes, microglia, endothelial cells and pericytes within the thalamus from the left side of the brain of the monkey Macaca fascicularis has been determined by use of the Optical Volume Fractionator stereological method. The accumulated burden of inorganic mercury (IHg) within these same cell types has been determined by autometallographic methods. Four groups of monkeys were exposed to methylmercury (MeHg; 50 micrograms Hg/kg body weight/day) by mouth for 6 months, 12 months, 18 months, or 12 months followed by 6 months without exposure (clearance group). Neurons, oligodendrocytes, endothelia, and pericytes did not show a significant change in cell number for any exposure group. Astrocyte cell number exhibited a significant decline for both the 6 month and clearance exposure groups. The microglia, in contrast, showed a significant increase in the 18 month and clearance exposure groups. Results from mercury speciation and quantification analysis of contralateral matched samples from the thalamus of the right side of the brain from these same monkeys indicated that MeHg concentrations plateaued at around 12 months exposure, whereas the inorganic levels, presumably derived from demethylation of MeHg, continued to increase throughout all exposure durations. Autometallographic determination of the distribution of IHg by cell type indicates that both the astrocytes and microglia contain substantially elevated IHg deposits relative to all other cell types. The data suggest that the inorganic mercury present in the brains, accumulating after long-term subclinical methyl mercury exposure, may be a proximate toxic form of mercury responsible for the changes within the astrocyte and microglial populations.

Effect of methylmercury body burden on kidney following unilateral nephrectomy.

The model of renal enlargement after unilateral nephrectomy is chosen to study the effect of methylmercury (MeHg) burden on organ growth. The results show that MeHg burden only impedes DNA synthesis, but not other macromolecular synthesis (RNA and protein). Despite the gradual increase of kidney weight and increase of total RNA and protein content in the remaining kidney, DNA remained unchanged. There is no difference between the control and the MeHg-treated group. 3H-thymidine incorporation study shows that unilateral nephrectomy elicited minimal DNA synthesis in the remaining kidney. Again there is no statistically significant difference of 3H-thymidine incorporation between the control and the MeHg-treated group. On a separate experiment, the folic-acid-induced renal DNA synthesis is also suppressed by MeHg burden. From these data it is concluded that chronic exposure to MeHg does not affect one of the cellular repair mechanisms: hypertrophy.

Methylmercury effects on the social behavior of Macaca fascicularis infants.

Observations of the social behavior of Macaca fascicularis exposed in utero to methylmercury (MeHg) and nonexposed control infants were performed as part of a study of the toxic, reproductive and developmental effects of maternal MeHg intake. Infants were tested twice weekly from 2 weeks to 8 months of age. Data were summarized into 6 categories of social behavior and 7 categories of nonsocial behavior. Analysis of the most prevalent behavior indicated that MeHg-exposed offspring exhibited a decrease in social play behavior and a concomitant increase in nonsocial passive behavior. The MeHg effect on social play behavior tended to decrease with age, while the group differences in nonsocial passive behavior tended to increase. The results indicate that maternal intake of MeHg during pregnancy can affect the social development of infant primates by suppressing social interactions and increasing nonsocial behavior.

Visual recognition memory deficits in methylmercury-exposed Macaca fascicularis infants.

Infant Macaca fascicularis exposed prenatally to maternal subclinical levels of methylmercury (MeHg) and their nonexposed controls were administered a test of visual recognition memory beginning at 210 days postconception (mean postnatal age = 51.88 days, SD = 5.30). The test consisted of a series of problems in which two identical 35 mm slides of a monkey's face were presented for a study period, followed by a test trial in which the previously exposed stimulus was paired with a novel one, and the looking time to each was recorded. The nonexposed group showed differential visual attention to the novel stimuli, indicating visual recognition abilities. The exposed group's visual attention to the novel stimuli was random. These results, in conjunction with earlier findings, suggest that prenatal MeHg exposure is associated with impaired visual recognition memory performance.

Fatty metamorphosis of the liver associated with jejunoileal bypass. Report of five cases.

Detailed postmortem examination was carried out on five patients who died three months to four years after jejunoileal bypass for obesity. A spectrum of histological changes was observed in the liver, with pericentral fat deposition being a common feature. Evidence of previous and/or ongoing liver cell dropout with accompanying polymorphonuclear and mononuclear infiltration was seen in all cases, but Mallory hyalin was not detected. Liver function abnormalities included decreased plasma protein levels, decreased prothrombin activity, increased serum alkaline phosphatase levels, and variable elevations of the serum transaminases, bilirubin, and ammonia concentrations. The pattern of the hepatic disease does not resemble protein deficiency. An uncharacterized hepatotoxin or toxic effect of hepatic fat accumulation may play a significant role in the changes observed in these patients.

Accumulation of methylmercury and inorganic mercury in the brain.

Differences in metabolism between different mercury species are well recognized. Conclusions that only a minor demethylation of methylmercury takes place in the brain are based primarily on results from short term studies. Results from a number of studies on humans exposed for many years to methylmercury have shown high concentrations of inorganic mercury in the brain in relation to total mercury. Similar evidence is available from studies on monkeys exposed for several years to methylmercury. The results indicate that a significant accumulation of inorganic mercury takes place with time despite the fact that the demethylation rate is slow. Differences in biological halftimes between different mercury species will explain the results. Some data do still need confirmation using different analytical methods. There is reason to believe that the one-compartment model for methyl mercury cannot be used without reservations. Inorganic mercury has a complicated metabolism. After exposure to metallic mercury vapor, inorganic mercury, probably bound to selenium, accumulates in the brain. A fraction of the mercury is excreted, with a long biological halftime. Studies on rats and monkeys indicate that inorganic mercury penetrates the blood-brain barrier only to a very limited extent.

Chronic methylmercury exposure in the monkey (Macaca mulatta). Behavioral test of peripheral vision, signs of neurotoxicity, and blood concentration in relation to dose and time.

Small daily doses of methylmercury hydroxide were administered to rhesus monkeys for periods of up to 17 months. Behavioral tests of peripheral vision and of the accuracy and rapidity of hand movements did not disclose any early subtle deficits preceding the onset of obvious signs of neurotoxicity. These signs appeared suddenly and involved reduced food intake (anorexia), clumsiness of jumping, loss of fine control of the digits, and uncoordinated mastication. With a constant daily dose of 0.1 mg/kg or less, blood concentration of mercury reached a peak after about 2 months, and then decreased to about half the peak value. Subsequently, increasing the daily dose level above 0.1 mg/kg (range of 0.12-0.21 mg/kg) produced an increase of blood concentration which tended to stabilize in the range of 2.0-2.5 ppm. After several months at these elevated concentrations all animals exhibited signs of neurotoxicity.