Biomedical subjects

C F Bearer

Publications and source records attributed to C F Bearer.

At least 19 recordsLinked to original sources

PubMed2005

Biomarkers in paediatric research and practice.

Children's health is, to a large extent, a function of their environment. Infectious agents remain the leading cause of death and disability in the world. In contrast, many of the new morbidities--asthma, intellectual impairments, behavioural problems, and cancer--are linked with industrial pollutants or other environmental influences. Our understanding of the risk factors for many diseases is incomplete, but it is widely recognised that disability and death result largely from interactions of environmental factors, broadly defined, and host susceptibility.

Biomarkers↗

PubMed2001

A developmental approach to pediatric environmental health.

Children cannot be considered "little adults" in the field of environmental medicine. There are differences in exposures, pathways of absorption, tissue distribution, ability to biotransform or eliminate chemicals from the body, and responses to chemical and radiation. The differences vary with the developmental stages of the child. Children all respond differently to environmental toxicants. Knowledge, although rapidly increasing, is still incomplete regarding the impact of the environment on children. As health care providers, prevention is an ally but must be approached differently at each stage of a child's life.

Adolescent↗

PubMed2001

Developmental neurotoxicity. Illustration of principles.

The magnitude of the problem of neurodevelopmental disorders is enormous. Frequently, the mechanism of injury is unknown. In this article, several common developmental neurotoxins are discussed, and the function of one cell adhesion molecule, L1, will be reviewed to illustrate the principles of developmental neurotoxicology. L1 is critical for proper central nervous system development. Similarities between patients with fetal alcohol syndrome and with L1 mutations suggest that the mechanism of developmental neurotoxicity of ethanol is partly due to effects on L1 cell adhesion molecule.

Cell Adhesion Molecules↗

PubMed2001

L1 cell adhesion molecule signal cascades: targets for ethanol developmental neurotoxicity.

A major mechanism guiding neural development is through cell-cell and cell-matrix adhesions and signaling mediated by cell adhesion molecules (CAMs). The majority of CAMs have been grouped into three families: the cadherins, the integrins and the members of the immunoglobulin superfamily including L1. While the elucidation of new receptors and matrix components has become a frequent occurrence, the elucidation of the mechanisms by which they operate, and the function of those mechanisms in complex developmental events remains rudimentary. Members of all three families participate in differential adhesion, signal transduction and physical/mechanical effects. Each of these modes of action is a potential target for developmental neurotoxicants. In this brief review, the role of L1 in normal and abnormal neurodevelopment will be summarized. L1 is a cell surface transmembrane glycoprotein with a single copy gene on the X chromosome. There are two alternatively spliced exons, with the RSLE containing form found only on axons and growth cones of post-mitotic neurons. L1 mediates the following functions: adhesion, neurite extension, neuronal migration, and axon fasciculation. L1 is critical for normal neural development; humans with genetic defects in L1, termed corpus callosum hypoplasia, mental retardation, adducted thumbs, spasticity and hydrocephalus (CRASH) syndrome, and mice lacking expression of L1 have extensive neuropathologic and aberrant behaviors. The observation that patients with fetal alcohol syndrome share similar features to patients with CRASH has lead to the investigation of the effects of ethanol on L1. Physiologic concentrations of ethanol have been shown to inhibit L1 mediated neurite outgrowth in cerebellar granule neurons. Such inhibition may result from decreased expression, altered cell surface distribution, impaired signal transduction, or impaired interaction with the cytoskeleton. These data indicate that L1 and its associated signaling pathways are potentially targets for developmental neurotoxicants.

Animals↗

PubMed2001

Mechanisms of brain injury: L1 cell adhesion molecule as a target for ethanol-induced prenatal brain injury.

The magnitude of the problem of neurodevelopmental disorders is enormous. Frequently, the mechanism of injury is unknown. In this article, the function of one cell adhesion molecule, L1, will be reviewed. L1 is critical for proper central nervous system development. Similarities between patients with fetal alcohol syndrome and with L1 mutations suggest that the mechanism of developmental neurotoxicity of ethanol is partly due to effects on L1 cell adhesion molecule.

Adult↗

PubMed2001

Markers to detect drinking during pregnancy.

Detecting alcohol use among pregnant women is an important step toward preventing alcohol-related birth defects. A biomarker that could detect alcohol use during pregnancy would aid in earlier identification and intervention for affected infants. The existing potential biomarkers for identifying alcohol use during pregnancy can detect varying degrees of alcohol exposure, or use. However, further research is needed to evaluate these biomarkers.

Alcohol Drinking↗

PubMed2000

Lead exposure from blood transfusion to premature infants.

OBJECTIVE: The objective of this study was to determine the exposure of premature infants to lead from blood transfusions. STUDY DESIGN: Blood lead concentrations were determined for 19 very premature infants at the time of admission, at 4 weeks of life, and before and after transfusions and in the donor packed red blood cells of 79 transfusions. RESULTS: The number of transfusions per patient was 4. 2 +/- 2.8 (mean +/- SD) with 15.7 +/- 1.9 mL/kg packed red blood cells for a lead dose of 1.56 +/- 1.77 microg/dL. The total dose of lead from these transfusions over the 4-week period was 4.0 +/- 2.8 microg/kg (range, 0.9-10.6 microg/kg). Increases in post-transfusion blood lead concentration were linear with doses higher than 1.5 microg/dL. Packed red blood cells with a blood lead concentration of > or = 5 microg/dL resulted in an elevated post-transfusion blood lead concentration in some infants. CONCLUSIONS: The lead exposure to these infants through blood transfusion exceeds the acceptable daily intake values for lead and may result in unacceptably high post-transfusion blood lead concentrations. Use of packed red blood cells with lead concentrations <3.3 microg/dL is one cost-effective means to reduce exposure.

Blood Transfusion↗

PubMed2000

The special and unique vulnerability of children to environmental hazards.

There are several factors that alter an individual's risk for an environmentally related illness. A major determinant is the developmental stage of the individual. The environment can be divided into three spheres: physical, biological and social. The components of each sphere are dependent on developmental stage. This presentation will discuss the components of each of these spheres and their variability with age. The discussion will be illustrated with known examples of environmentally related disease.

Adolescent↗

PubMed1999

Ethanol inhibits L1-mediated neurite outgrowth in postnatal rat cerebellar granule cells.

The neuropathology of the effects of ethanol on the developing central nervous system are similar to those of patients with mutations in L1, a neural cell adhesion molecule. This observation suggests that inhibition of L1 plays a role in the pathogenesis of alcohol-related neurodevelopmental disorders. Here we examine the effects of ethanol on L1 homophilic binding and on L1-mediated neurite outgrowth. Ethanol had no effect on cell adhesion or aggregation in a myeloma cell line expressing full-length human L1. In contrast, the rate of L1-mediated neurite outgrowth of rat postnatal day 6 cerebellar granule cells grown on a substratum of NgCAM, the chick homologue of L1, was inhibited by 48.6% in the presence of ethanol with a half-maximal concentration of 4.7 mM. The same effect was found with soluble L1-Fc, thus showing that the inhibitory effect is not dependent on cell adhesion. In contrast, neither laminin nor N-cadherin-mediated neurite outgrowth was inhibited by physiologic concentrations of ethanol. We conclude that one mechanism of ethanol's toxicity to the developing central nervous system may be the inhibition of L1-mediated neurite outgrowth.

Animals↗

PubMed1999

Assessment of the U.S. Environmental Protection Agency methods for identification of hazards to developing organisms, Part I: The reproduction and fertility testing guidelines.

BACKGROUND: Successful reproduction depends on the coordination of many processes, particularly the normal development and subsequent maturation of the sexual organs. The Food Quality Protection Act of 1996 mandates that the U.S. Environmental Protection Agency must protect infants and children from the effects of toxins, including those that affect the reproductive system. Therefore, the Agency finds itself at a critical juncture to make sure that the methods it requires for toxicity testing, the Health Effects Test Guidelines or Series 870 Guidelines, are adequate to determine possible toxicity to children. METHODS AND RESULTS: We found that two testing protocols included in the core guidelines assess toxicological effects on developing animals. This article aims to provide a detailed analysis of the protocols included in the Reproduction and Fertility Effects Test Guideline. An accompanying article assesses the Developmental Toxicity Testing Guideline. We conducted this analysis on the basis of whether the test would yield the information needed to adequately determine risk to infants and children. CONCLUSIONS: Our analysis concludes that given the limitations inherent in testing for reproduction and fertility effects during development, it is necessary to include a safety factor during risk assessment of chemicals. This action will fulfill the mandate expressed in the FQPA to protect infants and children from environmental hazards.

Animals↗

PubMed1999

Assessment of the U.S. Environmental Protection Agency methods for identification of hazards to developing organisms, Part II: The developmental toxicity testing guideline.

BACKGROUND: The effects of toxins on developing animals depend not only on the nature of the chemical but also on the timing of exposure and assessment of outcomes. This complicates the task of regulatory agencies such as the U.S. Environmental Protection Agency (EPA), which must comply with the 1996 Food Quality Protection Act to ensure that their standards and policies protect infants and children from environmental toxins. For this task, the Agency relies heavily on scientific data obtained by manufacturers of industrial chemicals and pesticides following protocols collected under EPA's Health Effects Test Guidelines. METHODS AND RESULTS: This article reviews the protocols included in the EPA guidelines to assess developmental toxicity, which are required for food-use pesticides under the core testing battery. We reviewed these protocols on the basis of their adequacy for identifying hazards to infants and children. Our analysis found limitations in the protocols that hinder their potential for identifying developmental hazards. CONCLUSIONS: Methods that the EPA currently depends upon to identify developmental toxicity of chemicals have limitations that impede obtaining complete and reliable data on which to base regulatory decisions that protect children. Other methodological approaches need to be explored as alternatives or supplements to the current protocols. Until more accurate testing protocols become available, it may well be necessary under existing laws to employ safety factors that are more protective of the health of children at all stages of development.

Animals↗

PubMed1999

Ethyl linoleate in meconium: a biomarker for prenatal ethanol exposure.

BACKGROUND: Fetal alcohol syndrome, fetal alcohol effects, alcohol-related neurodevelopmental disorder, and alcohol-related birth defects, all terms referring to the spectrum of consequences of in utero exposure to ethanol, are a major public health burden. There is currently no laboratory test to identify newborns exposed to ethanol in utero. Meconium was analyzed for ethyl linoleate, a metabolite of ethanol, as a biological marker for fetal ethanol exposure. METHODS: Samples of meconium were obtained from 248 infants and analyzed for fatty acid ethyl esters. Detailed maternal alcohol, tobacco, and drug use histories were obtained within 1 month of giving birth. RESULTS: The detection of ethyl linoleate in meconium was called a positive test. The mean number of drinks reported per week in the month before pregnancy, the first trimester, and overall were significantly higher in the positive group (unadjusted: 9.2 +/- 1.9 vs. 4.3 +/- 1.4, p = 0.004; 7.3 +/- 1.7 vs. 3.8 +/- 1.2, p = 0.03; and 6.1 +/- 1.3 vs. 3.0 +/- 1.0, p = 0.006). A positive test was not associated with marijuana, cocaine, or tobacco use. Sensitivity and specificity of the test were 72% and 51% to distinguish women who reported 1 or more drinks/week in the third trimester from women who denied use, and 68% and 48% to distinguish women who used > or =1 drink/week from women who used <1 drink/week in the month before pregnancy. CONCLUSIONS: The presence of ethyl linoleate in meconium is the first reported biological marker for maternal ethanol use during pregnancy. Because of the inherent inaccuracy associated with the use of self-reporting, the establishment of true values of sensitivity and specificity will require validation where the presence, quantity, and timing of exposure to alcohol is known. Further validation of this marker will permit identification and intervention of at-risk infants.

Adult↗

PubMed1998

Children's health and the environment: a new agenda for prevention research.

Patterns of illness in American children have changed dramatically in this century. The ancient infectious diseases have largely been controlled. The major diseases confronting children now are chronic and disabling conditions termed the "new pediatric morbidity"--asthma mortality has doubled; leukemia and brain cancer have increased in incidence; neurodevelopmental dysfunction is widespread; hypospadias incidence has doubled. Chemical toxicants in the environment as well as poverty, racism, and inequitable access to medical care are factors known and suspected to contribute to causation of these pediatric diseases. Children are at risk of exposure to over 15,000 high-production-volume synthetic chemicals, nearly all of them developed in the past 50 years. These chemicals are used widely in consumer products and are dispersed in the environment. More than half are untested for toxicity. Children appear uniquely vulnerable to chemical toxicants because of their disproportionately heavy exposures and their inherent biological susceptibility. To prevent disease of environmental origin in America's children, the Children's Environmental Health Network (CEHN) calls for a comprehensive, national, child-centered agenda. This agenda must recognize children's vulnerabilities to environmental toxicants. It must encompass a) a new prevention-oriented research focus; b) a new child-centered paradigm for health risk assessment and policy formulation; and c) a campaign to educate the public, health professionals, and policy makers that environmental disease is caused by preventable exposures and is therefore avoidable. To anchor the agenda, CEHN calls for long-term, stable investment and for creation of a national network of pediatric environmental health research and prevention centers.

Child↗

PubMed1998

Biomarkers in pediatric environmental health: a cross-cutting issue.

It is not yet known the extent to which the environment adversely affects the health of the developing individual. Difficulties in this determination are the problems of a) the assessment of exposure, b) the long latency of many diseases induced by the environment, c) the number of confounding exposures, and d) the extrapolation of animal models to critical stages of human development. Biomarkers have the potential to be quantitative dosimeters of exposure and biologic effective dose, as well as early warning signals of biologic effect. Biomarkers may document interindividual susceptibilities, as well as defining critical windows of exposure. To be useful, biomarkers need to be validated in terms of their specificity and sensitivity. Biomarkers are useful across all disciplines including asthma and respiratory problems, developmental neurotoxicity, childhood cancer, and endocrine disruptors. Biomarkers have not been developed nor used widely in pediatric environmental health. Research by our group and others has documented the validity of biomarkers in pediatric environmental health. Advances in the field of biomarkers may have important implications for the detection, prevention, and treatment of environmentally induced diseases in children. Ongoing validation of promising biomarkers should be a research priority.

Age Factors↗

PubMed1997

Placental transfer of N-acetylcysteine following human maternal acetaminophen toxicity.

OBJECTIVE: To determine whether the antidote for acetaminophen poisoning, N-acetylcysteine, administered to pregnant women with acetaminophen toxicity, crosses the placenta and can be measured in the newborn circulation following delivery. DESIGN: Over a 15-month period, four pregnant women with acetaminophen toxicity, who delivered their infants while receiving the antidote N-acetylcysteine, were studied. Maternal and cord blood from three viable infants, and cardiac blood sampled during an autopsy on the fourth, were analyzed for the presence of N-acetylcysteine using high-performance liquid chromatography. Maternal and cord blood aminotransferase activities, and autopsy findings on the nonviable infant were used to assess hepatic injury. RESULTS: N-Acetylcysteine was detected in the cord blood of three viable infants and in cardiac blood of a fourth, sampled at the time of autopsy. The mean N-acetylcysteine concentration in cord blood was 9.4 micrograms/mL (+/-1.3). This is well within the range associated with therapeutic doses of N-acetylcysteine typically administered to adults with acetaminophen poisoning. No adverse sequelae developed in the three viable infants. The fourth infant, delivered at 22 weeks gestational age died 3 h after birth. All mothers recovered and none of the four infants had evidence of acetaminophen-related toxicity. CONCLUSIONS: This is the first study documenting placental transfer of N-acetylcysteine in humans and provides impetus for research establishing a direct antidotal effect of N-acetylcysteine in the fetus.

Acetaminophen↗

PubMed1996

Mercury exposure in high school chemistry teachers.

To assess whether high school chemistry teachers had higher urinary mercury concentrations than other high school teachers, 24 high school teachers from nine schools in northeastern Ohio were studied. First morning voided urine samples and air samples from the teachers' classrooms were analyzed for total mercury content by cold vapor atomic absorption. The median adjusted urinary mercury concentration in the 12 chemistry teachers was 4.6 microg/g creatinine (range 2.2-8.2 microg/g creatinine) and it was 6.3 microg/g creatinine in the 12 non-chemistry teachers. All classroom air samples contained mercury levels below detection limits. No evidence was provided that high school chemistry teachers are at increased risk of chronic mercury exposure from their teaching activities compared to other high school teachers.

Adult↗

PubMed1995

How are children different from adults?

Several factors alter an individual's risk for an environmentally related illness. A major determinant is the age of the individual. The toxicodynamic processes that determine exposure, absorption, metabolism, excretion, and tissue vulnerability are all age related. This paper discusses each of these processes and their variability with age, and illustrates these points with examples of environmentally related disease cases.

Adult↗

PubMed1993

Pediatric environmental health training. Impact on pediatric residents.

OBJECTIVE: To determine whether incorporation of a course in pediatric environmental health into a pediatric residency program would alter residents' behavior in history taking. DESIGN: Retrospective chart review. SETTING: Large pediatric training hospital in northern California. PARTICIPANTS: Twenty-three children admitted with asthma by 12 pediatric residents in June 1991 and a control group of 28 children admitted with asthma by 17 pediatric residents in June 1990. INTERVENTIONS: None. MEASUREMENTS/MAIN RESULTS: The initial history and physical assessments were examined for all patients with status asthmaticus admitted to Children's Hospital Oakland (Calif) in June 1990 and 1991. Chi-square analysis revealed a significant difference in the number of environmental questions asked in the group trained in pediatric environmental health compared with the group that received no instruction. CONCLUSIONS: The incorporation of a course in pediatric environmental health markedly affected pediatric residents' behavior in assessing environmental causes for common illnesses. We recommend that the course, "Kids and the Environment," be incorporated into other pediatric residency programs, and that the efficacy of the course be determined by chart review.

Asthma↗