Exposures in early life: associations with DNA promoter methylation in breast tumors.

There is evidence that epigenetic changes occur early in breast carcinogenesis. We hypothesized that early-life exposures associated with breast cancer would be associated with epigenetic alterations in breast tumors. In particular, we examined DNA methylation patterns in breast tumors in association with several early-life exposures in a population-based case-control study. Promoter methylation of E-cadherin, p16 and RAR-ß2 genes was assessed in archived tumor blocks from 803 cases with real-time methylation-specific PCR. Unconditional logistic regression was used for case-case comparisons of those with and without promoter methylation. We found no differences in the prevalence of DNA methylation of the individual genes by age at menarche, age at first live birth and weight at age 20. In case-case comparisons of premenopausal breast cancer, lower birth weight was associated with increased likelihood of E-cadherin promoter methylation (OR = 2.79, 95% CI, 1.15-6.82, for ⩽2.5 v. 2.6-2.9 kg); higher adult height with RAR-ß2 methylation (OR = 3.34, 95% CI, 1.19-9.39, for ⩾1.65 v. <1.60 m); and not having been breastfed with p16 methylation (OR = 2.75, 95% CI, 1.14-6.62). Among postmenopausal breast cancers, birth order was associated with increased likelihood of p16 promoter methylation. Being other than first in the birth order was inversely associated with likelihood of ⩾1 of the three genes being methylated for premenopausal breast cancers, but positively associated with methylation in postmenopausal women. These results suggest that there may be alterations in methylation associated with early-life exposures that persist into adulthood and affect breast cancer risk.

Familial and racial determinants of tumour suppressor genes promoter hypermethylation in breast tissues from healthy women.

To determine the hypermethylation status of the promoter regions of tumour suppressor genes in breast tissues from healthy women and identify the determinants of these epigenetic changes. Questionnaires and breast tissues were collected from healthy women without a history of cancer and undergoing reduction mammoplasty (N= 141). Methylation for p16(INK4), BRCA1, ERalpha and RAR-beta promoter regions from breast tissues were determined by methylation specific PCR. Associations were examined with chi-square and Fisher's exact test as well as logistic regression. All statistical tests were two-sided. p16(INK4), BRCA1, ERalpha and RAR-beta hypermethylation were identified in 31%, 17%, 9% and 0% of the women, respectively. Women with BRCA1 hypermethylation had an eight-fold increase in the risk of ERalpha hypermethylation (P= 0.007). p16(INK4) hypermethylation was present in 28% of African-Americans, but 65% in European-Americans (P= 0.02). There was an increased likelihood of p16(INK4) or BRCA1 hypermethylation for women with family history of cancer (OR 2.3; 95%CI: 1.05-4.85 and OR 5.0; 95%CI: 1.55-15.81, respectively). ERalpha hypermethylation was associated with family history of breast cancer (OR 6.6; 95%CI: 1.58-27.71). After stratification by race, p16(INK4) in European-Americans and BRCA1 hypermethylation in African-Americans were associated with family history of cancer (OR 3.8; 95%CI: 1.21-12.03 and OR 6.5; 95%CI: 1.33-31.32, respectively). Gene promoter hypermethylation was commonly found in healthy breast tissues from women without cancer, indicating that these events are frequent and early lesions. Race and family history of cancer increase the likelihood of these early events.

Smoking increases carcinogenic polycyclic aromatic hydrocarbons in human lung tissue.

Tobacco smoke is a major source of human exposure to polycyclic aromatic hydrocarbons (PAHs). The concentration of PAHs in lung tissue would reflect an individual's dose, and its variation could perhaps reflect cancer risk. Eleven PAHs were measured in 70 lung tissue samples from cancer-free autopsy donors by gas chromatography-mass spectrometry. There were 37 smokers and 33 nonsmokers as estimated by serum cotinine concentration. The sum of PAH concentrations was higher in smokers (P = 0.01), and there was a dose-response relationship for greater smoking (P < 0.01). Smoking increased the concentration of five PAHs including benzo(a)pyrene, which increased approximately 2-fold. The risk for increasing carcinogenic PAHs (odds ratio, 8.20; 95% confidence interval, 2.39-28.09) was 3-fold compared with noncarcinogenic PAHs (odds ratio, 2.61; 95% confidence interval, 0.75-9.12). A higher concentration of PAHs was detected in the lung tissue of males, although the estimated smoking was similar in males and females. Race was not associated with PAH concentrations overall, but PAH concentrations appeared to be higher in African-American males than in any other group. Age was weakly correlated with an increase in fluoranthene and pyrene. The measurement of PAHs in human lung tissue can be used to estimate the actual dose to the target organ.

Would decreased aluminum ingestion reduce the incidence of Alzheimer's disease?

Although the cause of Alzheimer's disease (AD) remains unknown there is mounting evidence that implicates aluminum as a toxic environmental factor of considerable importance. Four independent lines of evidence--laboratory studies of the effects of intracerebral aluminum on the cognitive and memory performance of animals, biochemical studies, epidemiologic studies and the slowing of the progress of the disease with the use of an agent that removes aluminum from the body--now support the concept that aluminum is one of the pathogenic factors in AD. The evidence warrants serious consideration of reducing human exposure to aluminum. We hypothesize that a public health effort to restrict human ingestion of aluminum would reduce the incidence of this common chronic illness in the elderly.

Studies of cadmium uptake in bone and its environmental distribution.

Rat experiments indicate that oral ingestion of cadmium through drinking water leads to an accumulation of cadmium in bone, in addition to liver and kidney. After five weeks of cadmium intake in drinking water (50 to 100 mg/L), the bone cadmium levels increased in proportion to the intake concentration. Bone and kidney histology showed no signs of bone or kidney damage up to 5 wk of cadmium ingestion. Cadmium accumulation in bone was a primary phenomenon and not secondary to renal failure. In addition, cadmium levels have been estimated in a variety of sources, e.g., foodstuff, fertilizer, and sewage sludge, using neutron and proton activation analyses and atomic absorption spectrophotometry. Cadmium levels of Canadian foods are in the range of 0.002-0.07 mg/kg, and soils are in the range of 0.55 to 1.72 mg/kg. Fertilizers contain cadmium from 0.3 to 1.25 mg/kg, whereas sewage sludge contains up to 122 mg/kg.

Aluminum toxicity to the brain.

The association between elevated brain aluminum levels and Alzheimer's disease (AD) is examined and critically reviewed. We found elevated aluminum levels in the brains of patients with AD (greater than 4 micrograms/g dry wt.) compared with normal subjects (approximately 1.5 micrograms/g dry wt.). Nine laboratories from different geographical regions have confirmed this finding. Two laboratories did not find any differences between AD and control brains. This discrepancy is traced to differences in sample sizes used for the aluminum assay and the sample selection criteria. It is found that it is essential to use small sizes (approximately 10 mg dry wt.) and to ensure that control brains do not contain neurofibrillary tangles (NFT) and that AD brains do. The exact pathogenic role of aluminum in AD is, as yet, unclear. It is the only element (other than calcium, which non-specifically accumulates at all degenerating tissue sites) that is found in elevated concentrations in NFTs. It is found elevated at four loci in the brain, i.e. the DNA-containing structures of the nucleus, the protein moities of NFTs, the amyloid cores of senile plaques and cerebral ferritin. The evidence thus far indicates that aluminum is toxic to the brain and it is probable that it has a pathogenic role in Alzheimer's disease.

Origin and resolution of the aluminum controversy concerning Alzheimer's neurofibrillary degeneration.

Elevated concentrations of aluminum are found in regions of neurofibrillary change in brains with senile or presenile dementia of Alzheimer's type. The concentrations of aluminum found in the human disease are comparable to those found in experimental animals with aluminum-induced neurofibrillary degeneration (NFD). Although there are a number of reports confirming these observations, two laboratories have been unable to detect elevated levels in Alzheimer's disease. We conducted an interlaboratory study to resolve this discrepancy and traced the discrepancy to difficulties in analytical procedures. We concluded that failure to detect elevated aluminum levels associated with NFD is the result of (a) lack of strict adherence to the criteria for sample selection; (b) selection of too large a sample for analysis; and (c) use of analytical methodology that has potential matrix interference for the measured signal.

Intranuclear aluminum content in Alzheimer's disease, dialysis encephalopathy, and experimental aluminum encephalopathy.

Nuclear and chromatin fractions were prepared from cerebral cortex of 34 human and 37 animal brains. Chromatin was separated into a heavy heterochromatin fraction and two euchromatin fractions: intermediate euchromatin and light euchromatin. Compared to age-matched controls, aluminum content expressed per gram of DNA was significantly increased in nuclear and heterochromatin fractions in pre-senile Alzheimer's disease. In contrast nuclear preparations from brains of patients who had died with dialysis encephalopathy contained less aluminum than controls, although whole tissue concentrations were elevated ten to fifteen times above the control concentrations. Direct injection of aluminum into the cerebrospinal fluid of cats resulted in a progressive encephalopathy with neurofibrillary degeneration and increased intranuclear aluminum content. It is speculated that in Alzheimer's disease the normal blood-brain and cytoplasmic barriers for this neurotoxic metal are defective permitting aluminum to gain access to DNA-containing constitutents of the nuclei.

Brain aluminum distribution in Alzheimer's disease and experimental neurofibrillary degeneration.

Neurofibrillary degeneration is an important pathological finding in senile and presenile dementia of the Alzheimer type. Experimentally, aluminum induces neurofibrillary degeneration in neurons of higher mammals. Aluminum concentrations approaching those used experimentally have been found in some regions of the brains of patients with Alzheimer's disease.