ARCH Projects

Research Project
Meharry PI: D. B. Hood / Vanderbilt Collaborator: M. Aschner
"Mechanisms of B(a)P Induced Neurotoxicity"
The long-term objective of the proposed studies is to determine whether gestational B(a)P exposure interferes with normal behavior and neural function in C57BL mice as demonstrated by significant deficits in hippocampal synaptic plasticity and behavior. The central hypothesis to be tested is that gestational exposure to B(a)P aerosol (PM2.5|a) at levels seen in humans in certain environments results in lifelong learning and memory deficits and that these deficits are mediated, at least in part, through modulation of developmental NMDA/AMPA glutamate receptor subunit expression and function at a time when excitatory synapses are being formed in the hippocampus of C57BL mice. Aim 1 will determine the disposition of B(a)P in F1 fetal brain (in C57BL mice) on gestational day (GD) 14, 16, 18, and postnatal day (PND) 0 in the hippocampus after GD14-17 inhalation exposure at doses of 0, 50, 100 and 200 ^g/m3A. Simultaneous determination of the effect on glutamate receptor subunit expression in utero will be conducted, using ex vivo primary neuronal cultures. Aim 2 will test whether gestational exposure to the same inhalational doses of B(a)P results in deficits in learning, using behaviors previously shown to depend on hippocampal function. Aim 3 will correlate gestational exposure to B(a)P with measures of hippocampal long-term potentiation (LTP), evaluated at PND 60 and 120 in F1 generation mice. The involvement of NMDA and/or, AMPA receptors in this LTP, and changes due to B(a)P exposure, will be assessed by application of NMDA- or AMPA-selective receptor antagonists prior to LTP analysis of control and B(a)P exposed F1 generation mice. Aim 4 will test whether gestational exposure to the doses of B(a)P which lead to behavioral learning and physiological deficits also modulate the expression of various NMDA and AMPA receptor subnits, profiled for expression levels on GD18 and PND 0, 5, 10, 20, and 60 using real time PCR (for mRNA assessment) and Western blot analyses (for subunit protein assessment) in control and B(a)P-exposed F1 generation C57BL mice. These studies will serve as the first step in querying the causality of altered glutamate receptor subunit expression subsequent to gestational exposure to B(a)P in attenuation of learning behaviors in adult animals, which will be extended in future studies by exploiting mice genetically altered to modify the expression of relevant AMPA or NMDA receptor subunits or their downstream effector molecules. These studies are directly relevant to human consequences of B(a)P exposure, and these studies are expected to lead to the rigorous characterization of an important animal model both to understand the etiology of environmental toxin-induced neurological dysfunction and to test hypotheses regarding effective therapeutic or other interventions.

Pilot Project #1
Meharry PI: T. A. Ansah / Vanderbilt Collaborator: A. Deutch
"Effect of B(a)P Exposure on Dopaminergic Mechanisms"
Benzo(a)pyrene [B(a)P] is a member of the polycyclic aromatic hydrocarbon (PAH) compounds. Potential sources of B(a)P include combustion of coal, wood heating, cigarette smoking, and consumption of contaminated food and water. Whereas the carcinogenicity of PAHs including B(a)P has been extensively studied, much less is known about the neurotoxic effects of B(a)P. Maternal exposure to airborne PAHs during pregnancy was associated with a reduction in head circumference in children that may correlate with lower IQ and poorer cognitive functioning. In rats, gestational exposure to B(a)P induced decrements in birth index, N-methyl-D-aspartate receptor mRNA expression, long-term potentiation, and fixed-ratio performance learning behavior. Alterations in motor behavior (a measure of sensory, motor, and associative function) have been widely used as an early indicator of nervous system dysfunction. In that regard, studies show that acute exposure to B(a)P and fluroranthene produces a variety of behavioral deficits that are specific to the nervous system, including decreased motor activity and decreased responsiveness to sensory stimuli. The neurochemical pathways mediating acute neurotoxic effects of B(a)P have not been elucidated, but there are indications that the dopaminergic system may be involved. Studies using radiolabeled B(a)P revealed that B(a)P is capable of crossing the blood-brain barrier with the highest levels of radioactivity found in the olfactory lobes, striatum, and cerebellum. Intracranial injections of PAHs induced marked inhibition of tyrosine hydroxylase in the striatum and hippocampus. Furthermore, a single dose of B(a)P produced decreases in striatal concentrations of dopamine and noradrenaline. Given that oxidative stress plays a prominent role in B(a)P carcinogenicity, the hypothesis is that B(a)P exposure will induce oxidative stress and lead to deficits in dopaminergic function. The proposed Specific Aims are 1) to determine if subacute inhalation exposure to B(a)P will decrease locomotor activity in mice; 2) to determine if the presence of reactive metabolites of B(a)P and markers of oxidative stress are localized to dopaminergic brain regions that are implicated in motor function; and 3) to assess the susceptibility of transgenic mice overexpressing the antioxidant enzymes Cu.ZnSOD or catalase to B(a)P-induced deficits in dopaminergic markers. Studies will provide information on the mechanism of the neurotoxic effects of B(a)P and strategies for intervention.

Pilot Project #2
Meharry PI: O. B. Ogunkua / Vanderbilt Collaborator: R. Matusik
"B(a)P Induced Activation of Prostatic Specific Genes"
Benzo(a)pyrene [B(a)P] is a lipophilic aromatic hydrocarbon that belongs to the polycyclic aromatic hydrocarbon family and has been implicated in toxicity and in increased incidence of cancer in various organs. The incidence of advanced prostate cancer and mortality has been disproportionately high in some population groups, which have also been exposed to higher concentrations of aromatic hydrocarbons (AHCs), the prototype of which is B(a)P. To test whether B(a)P alters the rate or extent of cancer development, this project proposes to study a genetically engineered mouse model that permits the study of prostate carcinogenesis in an experimentally amenable time frame. This unique LPB-Tag transgenic mouse model of prostate cancer develops a spatial pathological pattern of preneoplastic lesions and small foci of locally invasive carcinoma. The central hypothesis to be tested is that exposure to B(a)P aerosol at levels experienced by human beings in certain environments results in alteration of prostatic function leading to induction or acceleration of prostate cancer formation. This hypothesis can be narrowed down to two questions: 1) Does B(a)P alter specific steroidal hormone and androgen events in a temporal manner to alter prostatic function? and 2) Does B(a)P accelerate prostatic intraepithelial neoplasm that progresses to prostate adenocarcinoma? Investigators intend to address these questions and test the hypothesis that B(a)P accelerates prostate cancer progression using two Specific Aims. Specific Aim 1 will exploit a range-finding study to determine the disposition of B(a)P in the prostate of the mouse model in order to establish the dose of aerosolized B(a)P to use in subsequent studies. Specific Aim 2 will determine the effect of B(a)P on the progression of prostatic intraepithelial neoplasia to adenocarcinoma, monitoring both histopathological changes and specific gene expression. In addition, researchers will also assess the relative proliferation rate of prostate tissues in control and B(a)P-exposed mice. These studies will advance knowledge of the role of environmental toxicants on the initiation and progression of prostate cancer and provide preliminary data to seek extramural funding to delinate the mechanism by which environmental pollutants, like the ubiquitous AHCs, alter initiation and progression of cancer as a first step in the prevention, diagnosis, prognosis, and better management of prostate cancer. This will also help in redressing health disparity among different population groups.

Pilot Project #3
Meharry PI: A. Ramesh / Vanderbilt Collaborator: J. D. Morrow
"Dietary Fat Potentiation of B(a)P Induced Colon Cancer"
Benzo(a)pyrene [B(a)P] is a lipophilic, widely distributed environmental toxicant that belongs to the polycyclic aromatic hydrocarbon (PAH) family of compounds. This chemical is known to cause toxicity and cancer in various organ systems. Preliminary studies have shown that exposure of rats to B(a)P and other PAHs causes induction of the cytochrome P450 (CYP) family of enzymes, resulting in the formation and distribution of reactive metabolites in plasma and target tissues. Studies have also shown that dietary exposure of rats to PAHs via saturated fat results in increased concentration of reactive metabolites, which stayed in target tissues for a longer period of time, causing DMA damage, compared to those that received these chemicals through unsaturated fat. The hypothesis of this project is that dietary fat contributes to B(a)P-induced colon  carcinogenesis through CYP-mediated epoxide and quinone pathways. The rationale behind this study is that every year 56,000 deaths are attributed to colorectal cancer in United States, and in a great majority of the cases surveyed, consumption of well-done, red meat and other saturated fats rich in PAHs were implicated as a possible causative factor. This implies that formation and progression of colon tumors depends on altered B(a)P biotransformation by the type of dietary lipids ingested. Investigators intend to test this hypothesis by studying the effects of oral exposure of adult Ape Min mice to B(a)P in saturated fat, using the following Specific Aims: 1) Investigate the potentiating effect of dietary fat on B(a)P-induced adenomas in small intestine and colon of adult Ape Min mice; 2) determine the dietary fat-induced alteration of B(a)P biotransformation enzyme activities and pharmacokinetics in Ape Min mice; 3) assess the contribution of dietary fat to B(a)P-DNA adduct formation and persistence in Ape Min mice; and 4) evaluate the role of dietary fat in B(a)P-induced oxidative damage and isoprostane production in Ape Min mice. This pilot project is expected to provide new information to conduct mechanism-based chemoprevention studies for colorectal carcinogenesis. Information gained from these studies will help to understand the contribution of fatty foods contaminated with toxic chemicals towards the development of colorectal cancers in humans. Furthermore, the knowledge gained from these studies will help to synthesize drugs that could be used to prevent the development of tumors in colon.