1 1358 142 DEVELOPMENT OF RATIOMETRIC ELECTROCHEMICAL MOLECULAR SWITCHES TO ASSAY ENDOGENOUS FORMALDEHYDE IN LIVE CELLS, WHOLE BLOOD AND CREATININE IN SALIVA. FORMALDEHYDE IS A REACTIVE CARBONYL SPECIES (RCS) THAT IS PRODUCED NATURALLY IN THE HUMAN BODY VIA METABOLIC AND EPIGENETIC BIOCHEMICAL PROCESSES, YET IN HIGH CONCENTRATIONS IS HIGHLY TOXIC TO THE ENVIRONMENT AS WELL AS TO LIVING ORGANISMS. THEREFORE, WE DESIGNED TWO RATIOMETRIC ELECTROCHEMICAL MOLECULAR REDOX PROBES, FORMALDEHYDE OXIDATIVE LATENT PROBE (FOLP) AND DIHYDROXY-FORMALDEHYDE OXIDATIVE LATENT PROBE (HFOLP), FOR THE SELECTIVE PROFILING OF ENDOGENOUS FORMALDEHYDE. FOLP AND HFOLP EACH UNDERWENT THE AZA-COPE REACTION WITH FORMALDEHYDE FOLLOWED BY HYDROLYSIS TO ELIMINATE UNMASK REDOX REPORTER N-ALKYLATED AMINOFERROCENE (AAF) TO MONITOR THEIR RESPONSE CURRENT. THE FOLP AND HFOLP SENSORS SHOWED BROAD DYNAMIC RANGES OF 0.12-1000 MUM AND 0.09-3 MM FOR FORMALDEHYDE WITH DETECTION LIMITS OF 48.2 NM AND 31.6 MUM, RESPECTIVELY. ALSO, SINCE FORMALDEHYDE IS THE BYPRODUCT OF BIOCHEMICAL REACTIONS FOR DETECTING CREATININE AND CREATININE IS AN IMPORTANT BIOMARKER FOR CHRONIC KIDNEY DISEASE (CKD), WE TESTED THE FOLP PROBE FOR ITS ABILITY TO MONITOR CREATININE. IT SUCCESSFULLY DID SO, AND THIS ABILITY WAS USED TO DEVELOP AN ELECTROCHEMICAL PLATFORM FOR THE QUANTIFICATION OF CREATININE; IT SHOWED A DYNAMIC RANGE OF 3.25-200 MUM AND A LIMIT OF DETECTION (1.3 MUM). IN ADDITION, THE FOLP-BASED ASSAY PLATFORM DELIVERED A RELIABLE ANALYTICAL PERFORMANCE FOR THE QUANTIFICATION OF FORMALDEHYDE IN HUMAN WHOLE BLOOD AND OF CREATININE IN SALIVA, AND ALSO FOR THE REAL-TIME MONITORING OF ENDOGENOUS FORMALDEHYDE SECRETION IN HELA CELLS. MOREOVER, THE CONCENTRATIONS DETERMINED USING OUR METHOD WERE FOUND TO BE CONSISTENT WITH THOSE DETERMINED USING FORMALDEHYDE AND CREATININE FLUOROMETRIC ASSAY KITS. 2021 2 2838 33 FORMALDEHYDE CARCINOGENICITY RESEARCH: 30 YEARS AND COUNTING FOR MODE OF ACTION, EPIDEMIOLOGY, AND CANCER RISK ASSESSMENT. FORMALDEHYDE IS A WIDELY USED HIGH PRODUCTION CHEMICAL THAT IS ALSO RELEASED AS A BYPRODUCT OF COMBUSTION, OFF-GASSING OF VARIOUS BUILDING PRODUCTS, AND AS A FIXATIVE FOR PATHOLOGISTS AND EMBALMERS. WHAT IS NOT OFTEN REALIZED IS THAT FORMALDEHYDE IS ALSO PRODUCED AS A NORMAL PHYSIOLOGIC CHEMICAL IN ALL LIVING CELLS. IN 1980, CHRONIC INHALATION OF HIGH CONCENTRATIONS OF FORMALDEHYDE WAS SHOWN TO BE CARCINOGENIC, INDUCING A HIGH INCIDENCE OF NASAL SQUAMOUS CELL CARCINOMAS IN RATS. SOME EPIDEMIOLOGIC STUDIES HAVE ALSO FOUND INCREASED NUMBERS OF NASOPHARYNGEAL CARCINOMA AND LEUKEMIA IN HUMANS EXPOSED TO FORMALDEHYDE THAT RESULTED IN FORMALDEHYDE BEING CONSIDERED A KNOWN HUMAN CARCINOGEN. THIS ARTICLE REVIEWS THE DATA FOR RODENT AND HUMAN CARCINOGENICITY, EARLY MODE OF ACTION STUDIES, MORE RECENT MOLECULAR STUDIES OF BOTH ENDOGENOUS AND EXOGENOUS DNA ADDUCTS, AND EPIGENETIC STUDIES. IT GOES ON TO DEMONSTRATE THE POWER OF THESE RESEARCH STUDIES TO PROVIDE CRITICAL DATA TO IMPROVE OUR ABILITY TO DEVELOP SCIENCE-BASED CANCER RISK ASSESSMENTS, INSTEAD OF DEFAULT APPROACHES. THE COMPLEXITY OF CONSTANT PHYSIOLOGIC EXPOSURE TO A KNOWN CARCINOGEN REQUIRES THAT NEW WAYS OF THINKING BE INCORPORATED INTO DETERMINATIONS OF CANCER RISK ASSESSMENT FOR FORMALDEHYDE, OTHER ENDOGENOUS CARCINOGENS, AND THE ROLE OF BACKGROUND ENDOGENOUS DNA DAMAGE AND MUTAGENESIS. 2013 3 2961 31 GENETIC AND EPIGENETIC MECHANISMS IN METAL CARCINOGENESIS AND COCARCINOGENESIS: NICKEL, ARSENIC, AND CHROMIUM. CHRONIC EXPOSURE TO NICKEL(II), CHROMIUM(VI), OR INORGANIC ARSENIC (IAS) HAS LONG BEEN KNOWN TO INCREASE CANCER INCIDENCE AMONG AFFECTED INDIVIDUALS. RECENT EPIDEMIOLOGICAL STUDIES HAVE FOUND THAT CARCINOGENIC RISKS ASSOCIATED WITH CHROMATE AND IAS EXPOSURES WERE SUBSTANTIALLY HIGHER THAN PREVIOUSLY THOUGHT, WHICH LED TO MAJOR REVISIONS OF THE FEDERAL STANDARDS REGULATING AMBIENT AND DRINKING WATER LEVELS. GENOTOXIC EFFECTS OF CR(VI) AND IAS ARE STRONGLY INFLUENCED BY THEIR INTRACELLULAR METABOLISM, WHICH CREATES SEVERAL REACTIVE INTERMEDIATES AND BYPRODUCTS. TOXIC METALS ARE CAPABLE OF POTENT AND SURPRISINGLY SELECTIVE ACTIVATION OF STRESS-SIGNALING PATHWAYS, WHICH ARE KNOWN TO CONTRIBUTE TO THE DEVELOPMENT OF HUMAN CANCERS. DEPENDING ON THE METAL, ASCORBATE (VITAMIN C) HAS BEEN FOUND TO ACT EITHER AS A STRONG ENHANCER OR SUPPRESSOR OF TOXIC RESPONSES IN HUMAN CELLS. IN ADDITION TO GENETIC DAMAGE VIA BOTH OXIDATIVE AND NONOXIDATIVE (DNA ADDUCTS) MECHANISMS, METALS CAN ALSO CAUSE SIGNIFICANT CHANGES IN DNA METHYLATION AND HISTONE MODIFICATIONS, LEADING TO EPIGENETIC SILENCING OR REACTIVATION OF GENE EXPRESSION. IN VITRO GENOTOXICITY EXPERIMENTS AND RECENT ANIMAL CARCINOGENICITY STUDIES PROVIDED STRONG SUPPORT FOR THE IDEA THAT METALS CAN ACT AS COCARCINOGENS IN COMBINATION WITH NONMETAL CARCINOGENS. COCARCINOGENIC AND COMUTAGENIC EFFECTS OF METALS ARE LIKELY TO STEM FROM THEIR ABILITY TO INTERFERE WITH DNA REPAIR PROCESSES. OVERALL, METAL CARCINOGENESIS APPEARS TO REQUIRE THE FORMATION OF SPECIFIC METAL COMPLEXES, CHROMOSOMAL DAMAGE, AND ACTIVATION OF SIGNAL TRANSDUCTION PATHWAYS PROMOTING SURVIVAL AND EXPANSION OF GENETICALLY/EPIGENETICALLY ALTERED CELLS. 2008 4 865 34 CHRONIC ACRYLAMIDE EXPOSURE IN MALE MICE RESULTS IN ELEVATED DNA DAMAGE IN THE GERMLINE AND HERITABLE INDUCTION OF CYP2E1 IN THE TESTES. ACUTE ACRYLAMIDE EXPOSURE IN MALE RODENTS RESULTS IN REDUCED REPRODUCTIVE PERFORMANCE AND DOMINANT LETHALITY. HOWEVER, THE REPRODUCTIVE EFFECTS OF LOW DOSE CHRONIC EXPOSURE, WHICH BETTER REFLECTS THE NATURE OF HUMAN EXPOSURE, REMAIN FAR LESS CERTAIN. HUMAN DIETARY CONSUMPTION OF ACRYLAMIDE HAS BEEN ESTIMATED AT AN AVERAGE OF 1-4 MICROG/KG BW/DAY. IN ORDER TO SIMULATE THIS EXPOSURE, MALE MICE WERE PROVIDED WITH ACRYLAMIDE (1 MICROG/ML) VIA THEIR DRINKING WATER CONTINUOUSLY FOR SIX MONTHS, WHICH WAS EQUIVALENT TO A HUMAN DOSE OF 10.5 MICROG/ KG BW/DAY. THIS EXPOSURE REGIME INCREASED DNA DAMAGE IN THE SPERMATOZOA, WITHOUT AFFECTING A CONCOMITANT REDUCTION IN OVERALL FERTILITY. THE OFFSPRING OF ACRYLAMIDE TREATED MICE DID NOT HAVE AN INCREASED INCIDENCE OF SKIN PAPILLOMA FORMATION FOLLOWING THE TWO-STAGE TUMOR INDUCTION PROTOCOL. HOWEVER, THE MALE OFFSPRING OF ACRYLAMIDE TREATED FATHERS HAD SIGNIFICANTLY INCREASED LEVELS OF DNA DAMAGE IN THEIR SPERMATOZOA, DESPITE HAVING HAD NO DIRECT TOXICANT EXPOSURE. IT WAS ALSO FOUND THAT THE F0, AND MOST CRUCIALLY, F1 MICE HAD INCREASED LEVELS OF CYP2E1 PROTEIN IN THEIR GERM CELLS. THIS IS SIGNIFICANT AS CYP2E1 IS THE SOLE ENZYME RESPONSIBLE FOR CONVERSION OF ACRYLAMIDE TO ITS HARMFUL METABOLITE GLYCIDAMIDE. THIS ALTERED EXPRESSION MAY BE DUE TO EPIGENETIC ALTERATIONS. ADDITIONALLY, THE F0 AND F1 MICE HAD INCREASED OXIDATIVE ADDUCTS IN THE DNA OF THEIR GERM CELLS, WHICH WAS HYPOTHESIZED TO ARISE AS A BYPRODUCT OF INCREASED CYP2E1 ACTIVITY. THEREFORE, CHRONIC PATERNAL ACRYLAMIDE EXPOSURE IN MICE HAS CONSEQUENCES FOR THEIR OFFSPRING, AND RAISES CONCERNS FOR THE EFFECTS OF ACRYLAMIDE EXPOSURE IN THE HUMAN POPULATION AND THE ACCUMULATED EFFECTS WITH MULTIPLE GENERATIONS OF EXPOSURE. 2016 5 696 24 BROMATE-INDUCED CHANGES IN P21 DNA METHYLATION AND HISTONE ACETYLATION IN RENAL CELLS. BROMATE (BRO3-) IS A WATER DISINFECTION BYPRODUCT (DBP) PREVIOUSLY SHOWN TO INDUCE NEPHROTOXICITY IN VITRO AND IN VIVO. WE RECENTLY SHOWED THAT INHIBITORS OF DNA METHYLTRANSFERASE 5-AZA-2'-DEOXYCYTIDINE (5-AZA) AND HISTONE DEACETYLASE TRICHOSTATIN A (TSA) INCREASED BRO3- NEPHROTOXICITY WHEREAS ALTERING THE EXPRESSION OF THE CYCLIN-DEPENDENT KINASE INHIBITOR P21. HUMAN EMBRYONIC KIDNEY CELLS (HEK293) AND NORMAL RAT KIDNEY (NRK) CELLS WERE SUB-CHRONICALLY EXPOSED TO BRO3- OR EPIGENETIC INHIBITORS FOR 18 DAYS, FOLLOWED BY 9 DAYS OF WITHDRAWAL. DNA METHYLATION WAS STUDIED USING A MODIFICATION OF BISULFITE AMPLICON SEQUENCING CALLED TARGETED GENE BISULFITE SEQUENCING. BASAL PROMOTER METHYLATION IN THE HUMAN P21 PROMOTER REGION WAS SUBSTANTIALLY LOWER THAN THAT OF THE RAT DNA. FURTHERMORE, 5-AZA DECREASED DNA METHYLATION IN HEK293 CELLS AT THE SIS-INDUCIBLE ELEMENT AT 3 DISTINCT CPG SITES LOCATED AT 691, 855, AND 895 BP UPSTREAM OF TRANSCRIPTION START SITE (TSS). 5-AZA ALSO DECREASED METHYLATION AT THE RAT P21 PROMOTER ABOUT 250 BP UPSTREAM OF THE P21 TSS. IN CONTRAST, SUB-CHRONIC BRO3- EXPOSURE FAILED TO ALTER METHYLATION IN HUMAN OR RAT RENAL CELLS. BRO3- EXPOSURE ALTERED HISTONE ACETYLATION IN NRK CELLS AT THE P21 TSS, BUT NOT IN HEK293 CELLS. INTERESTINGLY, CHANGES IN DNA METHYLATION INDUCED BY 5-AZA PERSISTED AFTER ITS REMOVAL; HOWEVER, TSA- AND BRO3--INDUCED HISTONE HYPERACETYLATION RETURNED TO BASAL LEVELS AFTER 3 DAYS OF WITHDRAWAL. THESE DATA DEMONSTRATE NOVEL SITES WITHIN THE P21 GENE THAT ARE EPIGENETICALLY REGULATED AND FURTHER SHOW THAT SIGNIFICANT DIFFERENCES EXIST IN THE EPIGENETIC LANDSCAPE BETWEEN RAT AND HUMAN P21, ESPECIALLY WITH REGARDS TO TOXICANT-INDUCED CHANGES IN HISTONE ACETYLATION. 2019 6 3739 32 INS AND OUTS OF CADMIUM-INDUCED CARCINOGENESIS: MECHANISM AND PREVENTION. CADMIUM (CD) IS A HEAVY METAL AND A HIGHLY TOXIC POLLUTANT THAT IS RELEASED INTO THE ENVIRONMENT AS A BYPRODUCT OF MOST MODERN FACTORIES AND INDUSTRIES. CD ENTERS OUR BODY IN SIGNIFICANT QUANTITIES FROM CONTAMINATED WATER, CIGARETTE SMOKE, OR FOOD PRODUCT TO MANY DETRIMENTAL HEALTH HAZARDS. BASED ON CAUSAL ASSOCIATION ALL THE CD-RELATED OR DERIVED COMPOUNDS HAVE BEEN CLASSIFIED AS CARCINOGENS. IN THIS STUDY, WE PRESENT AN OVERVIEW OF THE PUBLISHED LITERATURE TO UNDERSTAND THE MOLECULAR MECHANISMS FOR CD-INDUCED CARCINOGENESIS AND ITS PREVENTION. IN ACUTE CD POISONING PRODUCTION OF REACTIVE OXYGEN SPECIES IS A KEY FACTOR. HOWEVER, CHRONIC CD EXPOSURE CAN TRANSFORM CELLS TO BECOME MORE RESISTANT TO OXIDATIVE STRESS. ALSO, AS AN EPIGENETIC MECHANISM CD ACTS INDIRECTLY ON DNA REPAIR MECHANISMS VIA ALTERATION OF REACTIONS UPSTREAM. THOSE TRANSFORMED CELLS ACQUIRE RESISTANCE TO APOPTOSIS AND DEREGULATION OF CALCIUM HOMEOSTASIS. LEADING TO UNCONTROLLED CARCINOGENIC CELL PROLIFERATION AND INHERENT DNA LESIONS. FLAVONOIDS COMMONLY FOUND IN PLANT FOODS HAVE BEEN SHOWN TO HAVE A PROTECTIVE EFFECT AGAINST CD-INDUCED CARCINOGENICITY. A WIDE VARIETY OF TUMORIGENIC MECHANISMS INVOLVED IN CHRONIC CD EXPOSURE AND THE BENEFICIAL EFFECTS OF FLAVONOIDS AGAINST CD-INDUCED CARCINOGENICITY NECESSITATE FURTHER INVESTIGATIONS. 2021 7 2466 31 EPIGENETIC THERAPY: NOVEL TRANSLATIONAL IMPLICATIONS FOR ARREST OF ENVIRONMENTAL DIOXIN-INDUCED DISEASE IN FEMALES. INCREASED TOXICANT EXPOSURE AND RESULTANT ENVIRONMENTALLY INDUCED DISEASES ARE A TRADEOFF OF INDUSTRIAL PRODUCTIVITY. DIOXIN [2,3,7,8 TETRACHLORODIBENZO-P-DIOXIN (TCDD)], A UBIQUITOUS BYPRODUCT, IS ASSOCIATED WITH A SPECTRUM OF DISEASES INCLUDING ENDOMETRIOSIS, A COMMON, CHRONIC DISEASE IN WOMEN. TCDD ACTIVATES CYTOCHROME (CYP) P450 METABOLIC ENZYMES THAT ALTER ORGAN FUNCTION TO CAUSE DISEASE. IN CONTRAST, THE TRANSCRIPTION FACTOR, KRUPPEL-LIKE FACTOR (KLF) 11, REPRESSES THESE ENZYMES VIA EPIGENETIC MECHANISMS. IN THIS STUDY, WE CHARACTERIZED THESE OPPOSING MECHANISMS IN VITRO AND IN VIVO AS WELL AS DETERMINING POTENTIAL TRANSLATIONAL IMPLICATIONS OF EPIGENETIC INHIBITOR THERAPY. KLF11 ANTAGONIZED TCDD-MEDIATED ACTIVATION OF CYP3A4 GENE EXPRESSION AND FUNCTION IN ENDOMETRIAL CELLS. THE REPRESSION WAS PHARMACOLOGICALLY REPLICATED BY SELECTIVE USE OF AN EPIGENETIC HISTONE ACETYLTRANSFERASE INHIBITOR (HATI). WE FURTHER SHOWED PHENOTYPIC RELEVANCE OF THIS MECHANISM USING AN ANIMAL MODEL FOR ENDOMETRIOSIS. FIBROTIC EXTENT IN TCDD-EXPOSED WILD-TYPE ANIMALS WAS SIMILAR TO THAT PREVIOUSLY OBSERVED IN KLF11-/- ANIMALS. WHEN TCDD-EXPOSED ANIMALS WERE TREATED WITH A HATI, CYP3 MESSENGER RNA LEVELS AND PROTEIN EXPRESSION DECREASED ALONG WITH DISEASE PROGRESSION. FIBROTIC PROGRESSION IS UBIQUITOUS IN ENVIRONMENTALLY INDUCED CHRONIC, UNTREATABLE DISEASES; THIS REPORT SHOWS THAT RELENTLESS DISEASE PROGRESSION CAN BE ARRESTED THROUGH TARGETED EPIGENETIC MODULATION OF PROTECTIVE MECHANISMS. 2018 8 6663 32 UPREGULATION OF HISTONE-LYSINE METHYLTRANSFERASES PLAYS A CAUSAL ROLE IN HEXAVALENT CHROMIUM-INDUCED CANCER STEM CELL-LIKE PROPERTY AND CELL TRANSFORMATION. WHILE HEXAVALENT CHROMIUM [CR(VI)] IS GENERALLY CONSIDERED AS A GENOTOXIC ENVIRONMENTAL CARCINOGEN, STUDIES SHOWED THAT CR(VI) EXPOSURE ALSO CAUSES EPIGENETIC CHANGES. HOWEVER, WHETHER CR(VI)-CAUSED EPIGENETIC DYSREGULATIONS PLAYS AN IMPORTANT ROLE IN CR(VI) CARCINOGENICITY REMAIN LARGELY UNKNOWN. THE AIM OF THIS STUDY WAS TO DETERMINE IF CHRONIC LOW DOSE CR(VI) EXPOSURE CAUSES EPIGENETIC CHANGES, THE UNDERLYING MECHANISM AND WHETHER CHRONIC LOW DOSE CR(VI) EXPOSURE-CAUSED EPIGENETIC DYSREGULATION CONTRIBUTES CAUSALLY TO CR(VI)-INDUCED CANCER STEM CELL (CSC)-LIKE PROPERTY AND CELL TRANSFORMATION. TWO IMMORTALIZED HUMAN BRONCHIAL EPITHELIAL CELL LINES (BEAS-2B AND 16HBE) WERE EXPOSED TO 0.25 MUM OF K(2)CR(2)O(7) FOR 20 AND 40 WEEKS TO INDUCE CELL TRANSFORMATION, RESPECTIVELY. CR(VI)-INDUCED EPIGENETIC CHANGES WERE EXAMINED IN CR(VI)-TRANSFORMED CELLS AND CR(VI) EXPOSURE-CAUSED HUMAN LUNG CANCER TISSUES. PHARMACOLOGICAL INHIBITORS AND GENE KNOCKDOWN EXPERIMENTS WERE USED TO DETERMINE THE ROLE OF EPIGENETIC DYSREGULATION IN CR(VI) CARCINOGENICITY. WE FOUND THAT CHRONIC CR(VI) EXPOSURE CAUSES EPIGENETIC DYSREGULATION AS EVIDENCED BY THE INCREASED LEVELS OF HISTONE H3 REPRESSIVE METHYLATION MARKS (H3K9ME2 AND H3K27ME3) AND THE RELATED HISTONE-LYSING METHYLTRANSFERASES (HMTASES). PHARMACOLOGICAL INHIBITION OR KNOCKDOWN OF HMTASES REDUCES H3 REPRESSIVE METHYLATION MARKS AND MALIGNANT PHENOTYPES OF CR(VI)-TRANSFORMED CELLS. MOREOVER, KNOCKDOWN OF HMTASES IN PARENTAL CELLS SIGNIFICANTLY REDUCES CHRONIC CR(VI) EXPOSURE-INDUCED CSC-LIKE PROPERTY AND CELL TRANSFORMATION. FURTHER MECHANISTIC STUDY REVEALED THAT KNOCKDOWN OF HMTASES DECREASES CR(VI) EXPOSURE-CAUSED DNA DAMAGE. OUR FINDINGS INDICATE THAT CHRONIC CR(VI) EXPOSURE INCREASES H3 REPRESSIVE METHYLATION MARKS BY INCREASING THE RELATED HMTASES EXPRESSION; AND THAT INCREASED EXPRESSION OF HMTASES PLAYS A CAUSAL ROLE IN CR(VI)-INDUCED CSC-LIKE PROPERTY AND CELL TRANSFORMATION. 2018 9 192 31 ACETYLATED H4K16 BY MYST1 PROTECTS UROTSA CELLS FROM ARSENIC TOXICITY AND IS DECREASED FOLLOWING CHRONIC ARSENIC EXPOSURE. ARSENIC, A HUMAN CARCINOGEN THAT IS ASSOCIATED WITH AN INCREASED RISK OF BLADDER CANCER, IS COMMONLY FOUND IN DRINKING WATER. AN IMPORTANT MECHANISM BY WHICH ARSENIC IS THOUGHT TO BE CARCINOGENIC IS THROUGH THE INDUCTION OF EPIGENETIC CHANGES THAT LEAD TO ABERRANT GENE EXPRESSION. PREVIOUSLY, WE REPORTED THAT THE SAS2 GENE IS REQUIRED FOR OPTIMAL GROWTH OF YEAST IN THE PRESENCE OF ARSENITE (AS(III)). YEAST SAS2P IS ORTHOLOGOUS TO HUMAN MYST1, A HISTONE 4 LYSINE 16 (H4K16) ACETYLTRANSFERASE. HERE, WE SHOW THAT H4K16 ACETYLATION IS NECESSARY FOR THE RESISTANCE OF YEAST TO AS(III) THROUGH THE MODULATION OF CHROMATIN STATE. WE FURTHER EXPLORED THE ROLE OF MYST1 AND H4K16 ACETYLATION IN ARSENIC TOXICITY AND CARCINOGENESIS IN HUMAN BLADDER EPITHELIAL CELLS. THE EXPRESSION OF MYST1 WAS KNOCKED DOWN IN UROTSA CELLS, A MODEL OF BLADDER EPITHELIUM THAT HAS BEEN USED TO STUDY ARSENIC-INDUCED CARCINOGENESIS. SILENCING OF MYST1 REDUCED ACETYLATION OF H4K16 AND INDUCED SENSITIVITY TO AS(III) AND TO ITS MORE TOXIC METABOLITE MONOMETHYLARSONOUS ACID (MMA(III)) AT DOSES RELEVANT TO HIGH ENVIRONMENTAL HUMAN EXPOSURES. IN ADDITION, BOTH AS(III) AND MMA(III) TREATMENTS DECREASED GLOBAL H4K16 ACETYLATION LEVELS IN A DOSE- AND TIME-DEPENDENT MANNER. THIS INDICATES THAT ACETYLATED H4K16 IS REQUIRED FOR RESISTANCE TO ARSENIC AND THAT A REDUCTION IN ITS LEVELS AS A CONSEQUENCE OF ARSENIC EXPOSURE MAY CONTRIBUTE TO TOXICITY IN UROTSA CELLS. BASED ON THESE FINDINGS, WE PROPOSE A NOVEL ROLE FOR THE MYST1 GENE IN HUMAN SENSITIVITY TO ARSENIC. 2009 10 1819 20 EFFECTS OF CHRONIC OCHRATOXIN A EXPOSURE ON P53 HETEROZYGOUS AND P53 HOMOZYGOUS MICE. EXPOSURE TO THE MYCOTOXIN OCHRATOXIN A (OTA) CAUSES NEPHROPATHY IN DOMESTIC ANIMALS AND RODENTS AND RENAL TUMORS IN RODENTS AND POULTRY. HUMANS ARE EXPOSED TO OTA BY CONSUMING FOODS MADE WITH CONTAMINATED CEREAL GRAINS AND OTHER COMMODITIES. MANAGEMENT OF HUMAN HEALTH RISKS DUE TO OTA EXPOSURE DEPENDS, IN PART, ON ESTABLISHING A MODE OF ACTION (MOA) FOR OTA CARCINOGENESIS. TO FURTHER INVESTIGATE OTA'S MOA, P53 HETEROZYGOUS (P53+/-) AND P53 HOMOZYGOUS (P53+/+) MICE WERE EXPOSED TO OTA IN DIET FOR 26 WEEKS. THE FORMER ARE SUSCEPTIBLE TO TUMORIGENESIS UPON CHRONIC EXPOSURE TO GENOTOXIC CARCINOGENS. OTA-INDUCED RENAL DAMAGE BUT NO TUMORS WERE OBSERVED IN EITHER STRAIN, INDICATING THAT P53 HETEROZYGOSITY CONFERRED LITTLE ADDITIONAL SENSITIVITY TO OTA. RENAL CHANGES INCLUDED DOSE-DEPENDENT INCREASES IN CELLULAR PROLIFERATION, APOPTOSIS, KARYOMEGALY, AND TUBULAR DEGENERATION IN PROXIMAL TUBULES, WHICH WERE CONSISTENT WITH OCHRATOXICOSIS. THE LOWEST OBSERVED EFFECT LEVEL FOR RENAL CHANGES IN P53+/- AND P53+/+ MICE WAS 200 MUG OTA/KG BW/DAY. BASED ON THE LACK OF TUMORS AND THE SEVERITY OF RENAL AND BODY WEIGHT CHANGES AT A MAXIMUM TOLERATED DOSE, THE RESULTS WERE INTERPRETED AS SUGGESTIVE OF A PRIMARILY NONGENOTOXIC (EPIGENETIC) MOA FOR OTA CARCINOGENESIS IN THIS MOUSE MODEL. 2015 11 1993 27 EPIGENETIC AND EPITRANSCRIPTOMIC MECHANISMS OF CHROMIUM CARCINOGENESIS. HEXAVALENT CHROMIUM [CR(VI)], A GROUP I CARCINOGEN CLASSIFIED BY THE INTERNATIONAL AGENCY FOR RESEARCH ON CANCER (IARC), REPRESENTS ONE OF THE MOST COMMON OCCUPATIONAL AND ENVIRONMENTAL POLLUTANTS. THE FINDINGS FROM HUMAN EPIDEMIOLOGICAL AND LABORATORY ANIMAL STUDIES SHOW THAT LONG-TERM EXPOSURE TO CR(VI) CAUSES LUNG CANCER AND OTHER CANCER. ALTHOUGH CR(VI) IS A WELL-RECOGNIZED CARCINOGEN, THE MECHANISM OF CR(VI) CARCINOGENESIS HAS NOT BEEN WELL UNDERSTOOD. DUE TO THE FACT THAT CR(VI) UNDERGOES A SERIES OF METABOLIC REDUCTIONS ONCE ENTERING CELLS TO GENERATE REACTIVE CR METABOLITES AND REACTIVE OXYGEN SPECIES (ROS) CAUSING GENOTOXICITY, CR(VI) IS GENERALLY CONSIDERED AS A GENOTOXIC CARCINOGEN. HOWEVER, MORE AND MORE STUDIES HAVE DEMONSTRATED THAT ACUTE OR CHRONIC CR(VI) EXPOSURE ALSO CAUSES EPIGENETIC DYSREGULATIONS INCLUDING CHANGING DNA METHYLATION, HISTONE POSTTRANSLATIONAL MODIFICATIONS AND REGULATORY NON-CODING RNA (MICRORNA AND LONG NON-CODING RNA) EXPRESSIONS. MOREOVER, EMERGING EVIDENCE SHOWS THAT CR(VI) EXPOSURE IS ALSO CAPABLE OF ALTERING CELLULAR EPITRANSCRIPTOME. GIVEN THE INCREASINGLY RECOGNIZED IMPORTANCE OF EPIGENETIC AND EPITRANSCRIPTOMIC DYSREGULATIONS IN CANCER INITIATION AND PROGRESSION, IT IS BELIEVED THAT CR(VI) EXPOSURE-CAUSED EPIGENETIC AND EPITRANSCRIPTOMIC CHANGES COULD PLAY IMPORTANT ROLES IN CR(VI) CARCINOGENESIS. THE GOAL OF THIS CHAPTER IS TO REVIEW THE EPIGENETIC AND EPITRANSCRIPTOMIC EFFECTS OF CR(VI) EXPOSURE AND DISCUSS THEIR ROLES IN CR(VI) CARCINOGENESIS. BETTER UNDERSTANDING THE MECHANISM OF CR(VI) CARCINOGENESIS MAY IDENTIFY NEW MOLECULAR TARGETS FOR MORE EFFICIENT PREVENTION AND TREATMENT OF CANCER RESULTING FROM CR(VI) EXPOSURE. 2023 12 6587 25 TUMOR DORMANCY AND RELAPSE: FROM A NATURAL BYPRODUCT OF EVOLUTION TO A DISEASE STATE. SPECIES EVOLVE BY MUTATIONS AND EPIGENETIC CHANGES ACTING ON INDIVIDUALS IN A POPULATION; TUMORS EVOLVE BY SIMILAR MECHANISMS AT A CELLULAR LEVEL IN A TISSUE. THIS ARTICLE REVIEWS GROWING EVIDENCE ABOUT TUMOR DORMANCY AND SUGGESTS THAT (I) CELLULAR MALIGNANCY IS A NATURAL BYPRODUCT OF EVOLUTIONARY MECHANISMS, SUCH AS GENE MUTATIONS AND EPIGENETIC MODIFICATIONS, WHICH IS MANIFESTED IN THE FORM OF TUMOR DORMANCY IN HEALTHY INDIVIDUALS AS WELL AS IN CANCER SURVIVORS; (II) CANCER METASTASIS COULD BE AN EARLY DISSEMINATION EVENT THAT COULD OCCUR DURING MALIGNANT DORMANCY EVEN BEFORE PRIMARY CANCER IS CLINICALLY DETECTABLE; AND (III) CHRONIC INFLAMMATION IS A KEY FACTOR IN AWAKENING DORMANT MALIGNANT CELLS AT THE PRIMARY SITE, LEADING TO PRIMARY CANCER DEVELOPMENT, AND AT DISTANT SITES, LEADING TO ADVANCED STAGE DISEASES. ON THE BASIS OF THIS EVIDENCE, IT IS REASONABLE TO PROPOSE THAT WE ARE ALL CANCER SURVIVORS RATHER THAN CANCER-FREE INDIVIDUALS BECAUSE OF HARBORING DORMANT MALIGNANT CELLS IN OUR ORGANS. A BETTER UNDERSTANDING OF LOCAL AND METASTATIC TUMOR DORMANCY COULD LEAD TO NOVEL CANCER THERAPEUTICS FOR THE PREVENTION OF CANCER. CANCER RES; 77(10); 2564-9. (C)2017 AACR. 2017 13 4822 26 OCHRATOXIN A: 50 YEARS OF RESEARCH. SINCE OCHRATOXIN A (OTA) WAS DISCOVERED, IT HAS BEEN UBIQUITOUS AS A NATURAL CONTAMINANT OF MOLDY FOOD AND FEED. THE MULTIPLE TOXIC EFFECTS OF OTA ARE A REAL THREAT FOR HUMAN BEINGS AND ANIMAL HEALTH. FOR EXAMPLE, OTA CAN CAUSE PORCINE NEPHROPATHY BUT CAN ALSO DAMAGE POULTRIES. HUMANS EXPOSED TO OTA CAN DEVELOP (NOTABLY BY INHALATION IN THE DEVELOPMENT OF ACUTE RENAL FAILURE WITHIN 24 H) A RANGE OF CHRONIC DISORDERS SUCH AS UPPER UROTHELIAL CARCINOMA. OTA PLAYS THE MAIN ROLE IN THE PATHOGENESIS OF SOME RENAL DISEASES INCLUDING BALKAN ENDEMIC NEPHROPATHY, KIDNEY TUMORS OCCURRING IN CERTAIN ENDEMIC REGIONS OF THE BALKAN PENINSULA, AND CHRONIC INTERSTITIAL NEPHROPATHY OCCURRING IN NORTHERN AFRICAN COUNTRIES AND LIKELY IN OTHER PARTS OF THE WORLD. OTA LEADS TO DNA ADDUCT FORMATION, WHICH IS KNOWN FOR ITS GENOTOXICITY AND CARCINOGENICITY. THE PRESENT ARTICLE DISCUSSES HOW RENAL CARCINOGENICITY AND NEPHROTOXICITY CAUSE BOTH OXIDATIVE STRESS AND DIRECT GENOTOXICITY. CAREFUL ANALYSES OF THE DATA SHOW THAT OTA CARCINOGENIC EFFECTS ARE DUE TO COMBINED DIRECT AND INDIRECT MECHANISMS (E.G., GENOTOXICITY, OXIDATIVE STRESS, EPIGENETIC FACTORS). ALTOGETHER THIS PROVIDES STRONG EVIDENCE THAT OTA CARCINOGENICITY CAN ALSO OCCUR IN HUMANS. 2016 14 482 26 ARSENITE BINDS TO THE ZINC FINGER MOTIF OF TIP60 HISTONE ACETYLTRANSFERASE AND INDUCES ITS DEGRADATION VIA THE 26S PROTEASOME. ARSENIC IS A UBIQUITOUS ENVIRONMENTAL CONTAMINANT WITH WIDESPREAD PUBLIC HEALTH CONCERN. EPIDEMIOLOGICAL STUDIES HAVE REVEALED THAT CHRONIC HUMAN EXPOSURE TO ARSENIC IN DRINKING WATER IS ASSOCIATED WITH THE PREVALENCE OF SKIN, LUNG, AND BLADDER CANCERS. ABERRANT HISTONE MODIFICATIONS (E.G., METHYLATION, ACETYLATION, AND UBIQUITINATION) WERE PREVIOUSLY FOUND TO BE ACCOMPANIED BY ARSENIC EXPOSURE; THUS, PERTURBATION OF EPIGENETIC PATHWAYS IS THOUGHT TO CONTRIBUTE TO ARSENIC CARCINOGENESIS. ARSENITE IS KNOWN TO INTERACT WITH ZINC FINGER MOTIFS OF PROTEINS, AND ZINC FINGER MOTIF IS PRESENT IN AND INDISPENSABLE FOR THE ENZYMATIC ACTIVITIES OF CRUCIAL HISTONE-MODIFYING ENZYMES ESPECIALLY THE MYST FAMILY OF HISTONE ACETYLTRANSFERASES (E.G., TIP60). HENCE, WE REASONED THAT TRIVALENT ARSENIC MAY TARGET THE ZINC FINGER MOTIF OF THESE ENZYMES, DISTURB THEIR ENZYMATIC ACTIVITIES, AND ALTER HISTONE ACETYLATION. HEREIN, WE FOUND THAT AS(3+) COULD BIND DIRECTLY TO THE ZINC-FINGER MOTIF OF TIP60 IN VITRO AND IN CELLS. IN ADDITION, EXPOSURE TO AS(3+) COULD LEAD TO A DOSE-DEPENDENT DECREASE IN TIP60 PROTEIN LEVEL VIA THE UBIQUITIN-PROTEASOME PATHWAY. THUS, THE RESULTS FROM THE PRESENT STUDY REVEALED, FOR THE FIRST TIME, THAT ARSENITE MAY TARGET CYSTEINE RESIDUES IN THE ZINC-FINGER MOTIF OF THE TIP60 HISTONE ACETYLTRANSFERASE, THEREBY ALTERING THE H4K16AC HISTONE EPIGENETIC MARK. OUR RESULTS ALSO SHED SOME NEW LIGHT ON THE MECHANISMS UNDERLYING THE ARSENIC-INDUCED EPIGENOTOXICITY AND CARCINOGENESIS IN HUMANS. 2017 15 3842 23 IRON- AND 2-OXOGLUTARATE-DEPENDENT DIOXYGENASES: AN EMERGING GROUP OF MOLECULAR TARGETS FOR NICKEL TOXICITY AND CARCINOGENICITY. NICKEL COMPOUNDS ARE IMPORTANT OCCUPATIONAL AND ENVIRONMENTAL POLLUTANTS. CHRONIC EXPOSURE TO THESE POLLUTANTS HAS BEEN CONNECTED WITH INCREASED RISKS OF RESPIRATORY CANCERS AND CARDIOVASCULAR DISEASES. HOWEVER, IT IS STILL NOT CLEAR WHAT ARE THE SPECIFIC MOLECULAR TARGETS FOR NICKEL TOXICITY AND CARCINOGENICITY. HERE, WE PROPOSE THAT THE IRON- AND 2-OXOGLUTARATE-DEPENDENT DIOXYGENASE FAMILY ENZYMES ARE IMPORTANT INTRACELLULAR TARGETS THAT MEDIATE THE TOXICITY AND CARCINOGENICITY OF NICKEL. IN SUPPORT OF THIS HYPOTHESIS, OUR DATA SHOW THAT THREE DIFFERENT CLASSES OF ENZYMES IN THIS IRON- AND 2-OXOGLUTARATE-DEPENDENT DIOXYGENASE FAMILY, INCLUDING HIF-PROLYL HYDROXYLASE PHD2, HISTONE DEMETHYLASE JHDM2A/JMJD1A, AND DNA REPAIR ENZYME ABH3, ARE ALL HIGHLY SENSITIVE TO NICKEL INHIBITION. INACTIVATION OF THESE ENZYMES ACCOUNTS FOR A NUMBER OF DELETERIOUS EFFECTS CAUSED BY NICKEL IN CELLS, NAMELY HYPOXIA-MIMIC STRESS AND ABERRANT EPIGENETIC CHANGES. FUTURE STUDIES ON NICKEL'S EFFECTS ON THESE IRON- AND 2-OXOGLUTARATE-DEPENDENT DIOXYGENASES WOULD DEEPEN OUR UNDERSTANDING ON NICKEL TOXICITY AND CARCINOGENICITY. 2009 16 4208 19 METAL CARCINOGEN EXPOSURE INDUCES CANCER STEM CELL-LIKE PROPERTY THROUGH EPIGENETIC REPROGRAMING: A NOVEL MECHANISM OF METAL CARCINOGENESIS. ARSENIC, CADMIUM, NICKEL AND HEXAVALENT CHROMIUM ARE AMONG THE MOST COMMON ENVIRONMENTAL POLLUTANTS AND POTENT CARCINOGENS. CHRONIC EXPOSURE TO THESE METALS CAUSES VARIOUS TYPES OF CANCER IN HUMANS, REPRESENTING A SIGNIFICANT ENVIRONMENTAL HEALTH ISSUE. ALTHOUGH UNDER ACTIVE INVESTIGATION, THE MECHANISMS OF METAL CARCINOGENESIS HAVE NOT BEEN CLEARLY DEFINED. ONE COMMON FEATURE OF THESE METAL CARCINOGENS IS THAT THEY ARE ALL ABLE TO CAUSE VARIOUS EPIGENETIC DYSREGULATIONS, WHICH ARE BELIEVED TO PLAY IMPORTANT ROLES IN THEIR CARCINOGENICITY. HOWEVER, HOW METAL CARCINOGEN-CAUSED EPIGENETIC DYSREGULATION CONTRIBUTES TO METAL CARCINOGENESIS REMAINS LARGELY UNKNOWN. THE EVOLUTION OF CANCER STEM CELL (CSC) THEORY HAS OPENED EXCITING NEW AVENUES FOR STUDYING THE MECHANISM OF METAL CARCINOGENESIS. INCREASING EVIDENCE INDICATES THAT CHRONIC METAL CARCINOGEN EXPOSURE PRODUCES CSC-LIKE CELLS THROUGH DYSREGULATED EPIGENETIC MECHANISMS. THIS REVIEW WILL FIRST PROVIDE SOME BRIEF INTRODUCTIONS ABOUT CSC, EPIGENETICS AND EPIGENETIC REGULATION OF CSCS; THEN SUMMARIZE PROGRESSES IN RECENT STUDIES ON METAL CARCINOGEN-INDUCED CSC-LIKE PROPERTY THROUGH EPIGENETIC REPROGRAMING AS A NOVEL MECHANISM OF METAL CARCINOGENESIS. SOME PERSPECTIVES FOR FUTURE STUDIES IN THIS FIELD ARE ALSO PRESENTED. 2019 17 6086 26 THE EFFECTS OF ACETALDEHYDE EXPOSURE ON HISTONE MODIFICATIONS AND CHROMATIN STRUCTURE IN HUMAN LUNG BRONCHIAL EPITHELIAL CELLS. AS THE PRIMARY METABOLITE OF ALCOHOL AND THE MOST ABUNDANT CARCINOGEN IN TOBACCO SMOKE, ACETALDEHYDE IS LINKED TO A NUMBER OF HUMAN DISEASES ASSOCIATED WITH CHRONIC ALCOHOL CONSUMPTION AND SMOKING INCLUDING CANCERS. IN ADDITION TO DIRECT DNA DAMAGE AS A RESULT OF THE FORMATION OF ACETALDEHYDE-DNA ADDUCTS, ACETALDEHYDE MAY ALSO INDIRECTLY IMPACT PROPER GENOME FUNCTION THROUGH THE FORMATION OF PROTEIN ADDUCTS. HISTONE PROTEINS ARE THE MAJOR COMPONENT OF THE CHROMATIN. POST-TRANSLATIONAL HISTONE MODIFICATIONS (PTMS) ARE CRITICALLY IMPORTANT FOR THE MAINTENANCE OF GENETIC AND EPIGENETIC STABILITY. HOWEVER, LITTLE IS KNOWN ABOUT HOW ACETALDEHYDE-HISTONE ADDUCTS AFFECT HISTONE MODIFICATIONS AND CHROMATIN STRUCTURE. THE RESULTS OF PROTEIN CARBONYL ASSAYS SUGGEST THAT ACETALDEHYDE FORMS ADDUCTS WITH HISTONE PROTEINS IN HUMAN BRONCHIAL EPITHELIAL BEAS-2B CELLS. THE LEVEL OF ACETYLATION FOR N-TERMINAL TAILS OF CYTOSOLIC HISTONES H3 AND H4, AN IMPORTANT MODIFICATION FOR HISTONE NUCLEAR IMPORT AND CHROMATIN ASSEMBLY, IS SIGNIFICANTLY DOWNREGULATED FOLLOWING ACETALDEHYDE EXPOSURE IN BEAS-2B CELLS, POSSIBLY DUE TO THE FORMATION OF HISTONE ADDUCTS AND/OR THE DECREASE IN THE EXPRESSION OF HISTONE ACETYLTRANSFERASES. NOTABLY, THE LEVEL OF NUCLEOSOMAL HISTONES IN THE CHROMATIN FRACTION AND AT MOST OF THE GENOMIC LOCI WE TESTED ARE LOW IN ACETALDEHYDE-TREATED CELLS AS COMPARED WITH THE CONTROL CELLS, WHICH IS SUGGESTIVE OF INHIBITION OF CHROMATIN ASSEMBLY. MOREOVER, ACETALDEHYDE EXPOSURE PERTURBS CHROMATIN STRUCTURE AS EVIDENCED BY THE INCREASE IN GENERAL CHROMATIN ACCESSIBILITY AND THE DECREASE IN NUCLEOSOME OCCUPANCY AT GENOMIC LOCI FOLLOWING ACETALDEHYDE TREATMENT. OUR RESULTS INDICATE THAT REGULATION OF HISTONE MODIFICATIONS AND CHROMATIN ACCESSIBILITY MAY PLAY IMPORTANT ROLES IN ACETALDEHYDE-INDUCED PATHOGENESIS. ENVIRON. MOL. MUTAGEN. 59:375-385, 2018. (C) 2018 WILEY PERIODICALS, INC. 2018 18 474 25 ARSENIC BIOTRANSFORMATION AS A CANCER PROMOTING FACTOR BY INDUCING DNA DAMAGE AND DISRUPTION OF REPAIR MECHANISMS. CHRONIC EXPOSURE TO ARSENIC IN DRINKING WATER POSES A MAJOR GLOBAL HEALTH CONCERN. POPULATIONS EXPOSED TO HIGH CONCENTRATIONS OF ARSENIC-CONTAMINATED DRINKING WATER SUFFER SERIOUS HEALTH CONSEQUENCES, INCLUDING ALARMING CANCER INCIDENCE AND DEATH RATES. ARSENIC IS BIOTRANSFORMED THROUGH SEQUENTIAL ADDITION OF METHYL GROUPS, ACQUIRED FROM S-ADENOSYLMETHIONINE (SAM). METABOLISM OF ARSENIC GENERATES A VARIETY OF GENOTOXIC AND CYTOTOXIC SPECIES, DAMAGING DNA DIRECTLY AND INDIRECTLY, THROUGH THE GENERATION OF REACTIVE OXIDATIVE SPECIES AND INDUCTION OF DNA ADDUCTS, STRAND BREAKS AND CROSS LINKS, AND INHIBITION OF THE DNA REPAIR PROCESS ITSELF. SINCE SAM IS THE METHYL GROUP DONOR USED BY DNA METHYLTRANSFERASES TO MAINTAIN NORMAL EPIGENETIC PATTERNS IN ALL HUMAN CELLS, ARSENIC IS ALSO POSTULATED TO AFFECT MAINTENANCE OF NORMAL DNA METHYLATION PATTERNS, CHROMATIN STRUCTURE, AND GENOMIC STABILITY. THE BIOLOGICAL PROCESSES UNDERLYING THE CANCER PROMOTING FACTORS OF ARSENIC METABOLISM, RELATED TO DNA DAMAGE AND REPAIR, WILL BE DISCUSSED HERE. 2011 19 5057 16 PHENOBARBITAL MECHANISTIC DATA AND RISK ASSESSMENT: ENZYME INDUCTION, ENHANCED CELL PROLIFERATION, AND TUMOR PROMOTION. CHRONIC EXPOSURE TO HIGH DOSES OF PHENOBARBITAL (PB) CAUSES HEPATOCELLULAR ADENOMAS IN BOTH MICE AND RATS AND HEPATOCELLULAR CARCINOMAS IN SOME STRAINS OF MICE. LONG-TERM PB THERAPY HAS NOT BEEN FOUND TO CAUSE HUMAN TUMORS. PB IS NOT DNA REACTIVE, AND MOST GENOTOXICITY TESTS HAVE YIELDED NEGATIVE RESULTS. PB HAS BEEN EXTENSIVELY STUDIED AS AN EPIGENETIC, RODENT LIVER TUMOR PROMOTER. AT EXPOSURES CAUSING RODENT LIVER TUMORS, PB HAS MEASURABLE EFFECTS ON HEPATOCYTES: PB INHIBITS CELL-TO-CELL COMMUNICATION; PB INDUCES ENZYMES, INCLUDING P450 CYTOCHROMES; PB STIMULATES PROLIFERATION AND INHIBITS APOPTOSIS OF HEPATOCYTES IN NEOPLASTIC FOCI. THRESHOLD EXPOSURES FOR SOME OF THESE ENDPOINTS COINCIDE WITH THE THRESHOLD EXPOSURE FOR TUMORIGENESIS. 1996 20 4819 21 OCCURRENCE OF TOXICITY AND CELL PROLIFERATION AFTER A SINGLE GAVAGE ADMINISTRATION OF CHLOROFORM TO MALE F344 RATS. CHLOROFORM, AN INDUSTRIAL SOLVENT AND ONE OF THE MOST COMMON ENVIRONMENTAL CONTAMINANTS WHICH PRODUCES CARCINOGENIC EFFECTS IN THE LIVER AND KIDNEY OF RODENTS, IS NOT GENOTOXIC IN MOST TRADITIONAL BACTERIAL AND MAMMALIAN TEST SYSTEMS. ITS CARCINOGENIC POTENTIAL APPEARS ATTRIBUTABLE TO THE SUSTAINED CELL TURNOVER (REGENERATIVE HYPERPLASIA) WHICH RESULTS FROM CHRONIC CHLOROFORM TOXICITY. IN THIS PRESENT STUDY, CELL PROLIFERATION (REPLICATIVE DNA SYNTHESIS, RDS) AND HISTOPATHOLOGICAL CHANGES IN HEPATOCYTES AND RENAL TUBULAR EPITHELIAL CELLS WERE ASSESSED IN MALE F344 RATS FOLLOWING A SINGLE GAVAGE CHLOROFORM EXPOSURE (50, 150 OR 500 MG/KG). IN ADDITION, BIOCHEMICAL PARAMETERS (BUN, GOT, LDH AND NAG) WERE EXAMINED USING PLASMA AND URINE SAMPLES. CELL PROLIFERATION AND HISTOPATHOLOGICAL CHANGES (E.G. HYPERTROPHY, NECROSIS, VACUOLATION) WERE ONLY SEEN AT THE DOSE OF 500 MG/KG IN THE LIVER AND KIDNEY. AT THE SAME DOSE, ALL BIOCHEMICAL MARKERS WERE INCREASED AT THE 24 TO 48 HR TIME POINTS. THESE RESULTS OBTAINED ARE THUS IN LINE WITH EARLIER FINDINGS POINTING TO EPIGENETIC CARCINOGENICITY. 1998