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Results from recent prevention and intervention trials imply that consumption of antioxidant-rich foods early in disease states provides a protective advantage, while late intervention with dietary carotenoids/retinoids may exacerbates cancer. We are conducting a series of mechanism-based hypothesis driven studies designed to explain the paradoxical results observed in human intervention trials. We hypothesize that increased antioxidant cellular environment (provided by high levels of dietary supplementation with the chemical antioxidant N-acetyl-L-cysteine (NAC), or carotenoids/retinoids, will alter the cellular redox state and promote cancer in carcinogen initiated mice.
The following specific aims are being carried out:<ol>
<li>Determination of the association between high levels of dietary supplementation with the antioxidant N-acetyl-L-cysteine (NAC) and the alteration of tumor progression of benzo[a]pyrene by quantitatively assessing cancer latency and incidence using genetically-altered mouse models of cancer.
<li>Determination of the mechanism an/or mode of action of the antioxidant N-acetyl-L-cysteine (NAC) altered cellular redox state on tumor progression via dysregulation of cell proliferation and apoptosis by investigation of altered patterns of gene expression in critical signal transduction pathways in situ.* Determination of the mechanism an/or mode of action of the antioxidant N-acetyl-L-cysteine (NAC) altered cellular redox state in vitro in splenocytes via dysregulation of cell proliferation and apoptosis by investigation of altered patterns of proliferation, apoptosis, and gene expression in critical signal transduction pathways. </ol>
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Thus far, we have observed that dietary NAC increases survival and reduces multiplicity of skin malignancies but increases the fraction of malignancies induced by topically administered B[a]P. The majority of the malignancies (keratoacanthomas, squamous carcinomas, and spindle cell tumors) induced in FVB/N-p53 deficient Tg.AC mice demonstrated mutant transgene ras expression and were nucleus positive for p53 (variable intensity from 0to+4 areas) and treatment independent. Malignancies, both negative and positive for transgene expression were also negative for mutations in codon 12 and codon 61 of endogenous c-Ha-ras protooncogene. NAC alone is mitogenic to splenocytes. Currently, we are conducting an in life study (gamma irradiated FVB/N-heterozygous p53+/- mice at 0, 2, 4, or 6 Gy) with and without NAC supplementation in the diet. We have observed a decreased latency for thymic lymphoma and an increased incidence of thymic lymphoma after 24 wks (0/15 vs 10/15) in the controls versus 4 Gy plus NAC.
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These results may be explained, at least in part, by in vitro studies that show that lipopolysaccharide (LPS, a B-lymphocyte mitogen) induced splenic cell proliferation (3:1 T- to B-cell ratio) is significantly increased by NAC, but apoptosis was significantly suppressed. Suppression of apoptosis was confirmed by independent assays (TUNEL and Annexin V). B-lymphocyte specificity was confirmed by flow cytometry using B- and T-lymphocyte specific monoclonal antibodies. When current post- and in-life studies are completed for histopathology, we will focus on investigation of the molecular mechanisms involved in antioxidant exacerbation of lymphomagenesis. These studies will include changes in gene expression at the mRNA and protein level as well as molecular genetic changes in signaling pathways critical to proliferation and apoptosis.
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In addition, in vitro studies will be focused on mechanisms of NAC associated suppression of apoptosis using microarray based gene expression, followed by confirmation using protein 2D gel electrophoresis and western analysis (where required for confirming dysregulated pathways).