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Teratogenesis, Mutagenesis, and Carcinogenesis

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Teratogenesis, Mutagenesis, and Carcinogenesis Food Toxicology Learning Objectives • Define teratogenesis, mutagenesis, and carcinogenesis. • Describe the relevance of replication, transcription, Teratogenesis, Mutagenesis, and and translation to teratogenesis, mutagenesis, and Carcinogenesis carcinogenesis. • Summarize the mechanism of action for Food Toxicology teratogenesis, mutagenesis, Instructor: Gregory Möller, Ph.D. and carcinogenesis. University of Idaho • Discuss examples of known teratogens, mutagens, and carcinogens. 2 Food Toxicology Food Toxicology Molecules of Life The Cell • Toxicants can react with or modify DNA or RNA. – Can lead to heritable change in offspring or changes in replication cellular growth and development. DNA • Replication → perpetuate genetic transcription nucleus information. RNA • Transcription and translation → express genetic information. translation ribosomes Proteins cytoplasm 3Hughes 4 Food Toxicology Food Toxicology Protein Functions Endpoints • Antibodies. • Teratogenesis. – Recognize molecules of invading organisms. – Origin or production of malformed fetuses or offspring. • Receptors. • Mutagenesis. – Part of the cell membrane; recognize other proteins, or – Production of a mutation or change in the genetic code of chemicals, and inform the cell. an organism. • Enzymes • Carcinogenesis. – Assemble or digest. – Cancer formation including • Neurotransmitters, hormones carcinoma and malignant neoplasms. – Trigger receptors. • Channels and pores. 5 Rothamsted 6 Hughes •1 Food Toxicology Food Toxicology DNA Replication Replication • Structure implies replication • Duplicates cell DNA. • Occurs via multiple enzyme action • Mitosis - one somatic cell with 2n chromosomes • Helix unravels, strands part, DNA replicates divides to create two cells with 2n chromosomes (humans, n = 23). • Mitosis, meiosis • Number, quality and quantity of chromosomes per • Not always perfect cell is conserved. – Repair enzymes – Triggers for mitosis (receptors + proteins). • External signals. • Hormones. • Internal factors. • Growth factors. 7 8Hughes Food Toxicology Food Toxicology Replication, 2 DNA Transcription • Meiosis - germ cells are cells that divide into gametes. • DNA is copied via expendable mRNA – 2 cell divisions. • mRNA codes for specific proteins – Four daughter cells. • Occurs in nucleus of cell • Each with a different set of chromosomes. • Each with 1 set that will be joined by another in fertilization. 9Hughes 10 Food Toxicology Food Toxicology DNA Translation Transcription and Translation • Occurs in the cytosol • DNA: double strand of nucleotides. • Interaction of mRNA, tRNA, – Nucleotide = nucleic acid, sugar and phosphate. amino acids and enzymes – Cytosine, Thymine, Uracil; Adenine, Guanine. • tRNA has three-base codons – Base pairing = A-T, G-C. which correspond to different aa – Gene: sequence of bases that code for a specific sequence of amino acids (protein). • AA are added one at a time to – Codon: sequence of 3 bases form chain - polypeptide that code for a single amino • Polypeptide corresponds to acid, i.e. protein with a specific aa •AGC → Serine. sequence • AAA → Lysine. 11 12Hughes •2 Food Toxicology Food Toxicology Transcription and Translation, 2 DNA Structure - Function • Transcription = copying. • Nucleotides form chains – DNA unzips and enzymes make RNA “copy”. • 3 nucleotides form a codon – Differences: • Multiple codons form genes •T → U (UA not TA). • Deoxyribose → ribose. • Multiple genes form chromosomes – mRNA formation; transport to cytoplasm. • Multiple chromosomes form DNA • Translation = protein formation. – mRNA (blueprint). – rRNA (support). – TRNA (a.a. transport). 13Hughes 14 Food Toxicology Food Toxicology DNA/RNA Complex DNA/RNA Complex, 2 15 16 Errors in DNA Replication, Food Toxicology Food Toxicology Transcription and Translation DNA/Chemical Interactions • Base pairing • Alkylation - covalent adduct • Repair enzymes and other enzymes between DNA and chemical • Regulatory genes, operons, • Intercalation - noncovalent termination sequences binding of chemical between two • Methylation patterns adjacent base pairs • Post transcriptional/translational • Cross-linkage - Inter or processing intrastrand covalent binding of chemical • Breakage - scission of one or both strands of DNA 17 18 •3 Food Toxicology Food Toxicology Afltoxin B1 – DNA Adduct Teratogenesis • Teratology: the study of the frequency, causation, and development of congenital malformations. • Complex mechanisms and timing of disruptive interaction during embryogenesis. • Some natural “bad path” spontaneous abortion. – Humans: critical 1st 8 wks gestation. • Embryonic stage. • Morphological defects in specialized tissues and organs. – Fetal stage exposure. • Developmental or neoplastic endpoints. • Known human teratogens. 19 20 Food Toxicology Food Toxicology Example: Teratogenesis Example: Teratogenesis, 2 Five Legged Frog Ovine Cyclopia Veratrum Californicum 21 22 W. False Helebore Food Toxicology Food Toxicology Example: Teratogenesis, 3 Case Study: Lupine Alkaloid Birth Defects Crooked Calf • In September 1980, a baby boy born in the Disease OH mountainous back-country of northwestern California (Trinity County) was brought to the UC Medical Center in Sacramento with severe bone deformities in his arms and hands, including a partial absence of forearm bones (radial aplasia) N Lupine and absent thumbs. • Extensive medical histories and genetic analyses Quinolizidine alkaloids of his parents indicated that the probable cause Anagyrine was environmental rather than hereditary. • His mother feared that somehow exposure to herbicide spraying was responsible. Association of forest spraying and a reportedly high incidence of birth defects in northwestern California and southern Oregon has been highly publicized in recent years and has become controversial. Indeed, it appears likely that this herbicide had been applied to a forested ridge several miles distant from the mother's home more than a year before the child's conception. 23 24 •4 Food Toxicology Food Toxicology Case Study: Lupine Alkaloid Birth Defects Mutagenesis • The mother provided the evidence that her goats also gave birth to kids stillborn or with deformed • Somatic cell mutations → metabolic dysfunction; legs during and after the period of her carcinogenesis. pregnancy, and that puppies born to a dog fed the goat's milk during pregnancy were likewise deformed. • Germ cell mutation → heritable change. • Local goat's milk has become a common food • Point mutation. item in the area, and the child's mother drank it regularly herself throughout pregnancy. – Base substitution (including analogues). • A thorough survey of nearby areas where the goats had regularly browsed at the time of the – Frame shift. mother's early pregnancy showed that a perennial lupine, identified as the widely • Chromosomal aberration. distributed Lupinus latifolius, often formed the principal low-growing forage as well as wild – Structural anomaly. tobacco (Nicotiana), poison hemlock (Conium), – Numerical anomaly. and skunk cabbage (Veratrum). • Circumstantial evidence. UC Davis Env Tox Newsletter Hughes 25 2:3 November 5, 1981 26 Food Toxicology Food Toxicology Karotypes Abberations • Aneuploidy/Polyploidy Patterns photographed • Loss or gain of complete chromosomes during metaphase help – Microscopically visible examine for chromosomal 1 2 3 4 5 – Down’s Syndrome - (47,21+) trisomy 1 2 3 4 5 defects. – Klinefelder’s Syndrome (47,XXY) trisomy – Turner’s Syndrome (45,XO) monosomy 6 7 8 9 10 11 12 6 7 8 9 10 11 12 13 14 15 16 17 18 13 14 15 16 17 18 19 20 21 22 X Y 19 20 21 22 X Y 27 28 Food Toxicology Food Toxicology Ames Test for Chemical Mutagenicity Carcinogenesis • Salmonella bacteria strain with histidine coding Procarcinogen (nonreactive) defect. Multi-step, • Mutagenic chemicals can change the defect to allow multi-factorial disease cell division and growth. Carcinogen • Add salmonella + test chemical + rat hepatocytes Carcinogen + DNA (for biotransformation). – Growth indicates Mutation/ mutagenic effect. Mutation Initiation Promoting agent Promotion 29 30 Cancer Cancer •5 Food Toxicology Food Toxicology Cancer Definitions Cancer Definitions, 2 • Cancer. NLM • Benign tumor. – A malignant tumor that has the ability to metastasize or – A tumor that does not invade into surrounding tissues. metastasize. • Tumor (Neoplasm). • Metastasis. – A general term for the uncontrolled growth of cells that – Ability to establish secondary becomes progressively tumor growth at a new location. worse with time. • Neoplasia. – The growth of new tissue with abnormal and unregulated cell proliferation. NLM 31 32 Copyright © 2006 Gary Carlson Food Toxicology Food Toxicology Cancer Definitions, 3 Multistage Carcinogenesis: Initiation • Carcinoma. NLM • Chemical-virus-spontaneous causes DNA lesion – Malignant tumor arising in the epithelium. • Cell division perpetuates DNA lesion – Most common form of cancer. • No outcome if not promoted – Usually spreads in the lymphatic system. – Some chemicals can initiate and promote • Sarcoma. – May remain indefinitely if not promoted – Malignant tumor in muscle • One hit or connective tissue. – No threshold; irreversible – Usually spread in the blood stream. – Frequently metastasizes to the lung. 33 34 Copyright © 2006 Gary Carlson Food Toxicology Food Toxicology Properties of Initiated Cells Multistage Carcinogenesis: Promotion • No phenotypic differences • Change in micro-environment of cells • Excess/deficiency of enzymes • Chemical, viral, spontaneous-induced clonal –e.g.
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