Dose-response analysis of epigenetic, metabolic, and apical endpoints after short-term exposure to experimental hepatotoxicants

Abstract

Identification of sensitive and novel biomarkers or endpoints associated with toxicity and carcinogenesis is of a high priority. There is increasing interest in the incorporation of epigenetic and metabolic biomarkers to complement apical data; however, a number of questions, including the tissue specificity, dose-response patterns, early detection of those endpoints, and the added value need to be addressed. In this study, we investigated the dose-response relationship between apical, epigenetic, and metabolomics endpoints following short-term exposure to experimental hepatotoxicants, clofibrate (CF) and phenobarbital (PB). Male F344 rats were exposed to PB (0, 5, 25, and 100 mg/kg/day) or CF (0, 10, 50, and 250 mg/kg/day) for seven days. Exposure to PB or CF resulted in dose-dependent increases in relative liver weights, hepatocellular hypertrophy and proliferation, and increases in Cyp2b1 and Cyp4a1 transcripts. These changes were associated with altered histone modifications within the regulatory units of cytochrome genes, LINE-1 DNA hypomethylation, and altered microRNA profiles. Metabolomics data indicated alterations in the metabolism of bile acids. This study provides the first comprehensive analysis of the apical, epigenetic and metabolic alterations, and suggests that the latter two occur within or near the dose response curve of apical endpoint alterations following exposure to experimental hepatotoxicants.

Pilot studies evaluating the nongenotoxic rodent carcinogens phenobarbital and clofibrate in the rat Pig‐a assay

“…In the present study, PB and CF treatment resulted in an increase in relative liver weight of 61% and 116%, respectively, which exceeds the criteria established for a maximum tolerated dose (MTD) as defined by numerous regulatory agencies for an adverse response in a repeat‐dose study (WHO, ). These observations are consistent with previous publications, which suggested similar increases in relative liver weights, hepatomegaly, and hepatocellular hypertrophy following PB and CF exposures (Corton et al, ; Elcombe et al, ; Miousse et al, ). Following oral administration, both PB and CF are rapidly absorbed and transported via the blood, consistent with their pharmaceutical applications (Cayen et al, ; Geter et al, ).…”

“…Following seven‐day acclimatization, rats were randomly assigned to treatment groups based on body weight (i.e., approximately equal mean body weights and variances across groups), and administered respective solvent vehicle or PB or CF by oral gavage at dose levels of 100 mg/kg/day (PB) or 300 mg/kg/day (CF) for 28 days (n = 5 rats/dose) (based on weekly body weights). The selected doses were identified to be the lowest carcinogenic doses in prior studies (Miousse et al, ). All animal studies were conducted at The Dow Chemical Company, Toxicology and Environmental Research & Consulting (TERC), Midland, MI, which is accredited by the American Association for Accreditation of Laboratory Animal Care.…”

Loci specific epigenetic drug sensitivity

“…Locus-specific sensitivity measurements will support the development of new treatment strategies that use existing drugs and the development of new, more precise drugs. Identification of correct dosage of epi-drugs is challenging [80][81][82] . Comparison of the dose-response curve of the overall change in gene expression to the dose-response changes in gene expression that are due to locus-specific modification will help identifying drug concentrations that maximally impact target genes while limiting non-specific effects.…”

Modern approaches for the screening of epigenetically active xenobiotics

“…Это позволило разработать ряд методик тестирования соединений на эпигенетическую активность. Актуальность выявления эпигенетически активных ксенобиотиков обусловлена тем, что экспозиция организма к различным новым соединениям, синтезированным в медицинских целях или для выполнения специальных народно-хозяйственных задач, может существенно изменить регулируемый эпи-генетически профиль экспрессии генов, способствуя или препятствуя развитию патологических процессов и заболеваний [8]. В данном обзоре приводятся результаты анализа опубликованных данных по особенностям функционирования системы эпигенетической регуляции на уровне метилирования ДНК и модификации гистонов, используемые при этом модельные системы, а также представлены методы анализа влияния различных факторов окружающей среды, в том числе различных ксенобиотиков, на механизмы эпигенетической регуляции транскрипции.…”