Grantee Research Project Results
2001 Progress Report: Bioavailability of Haloacetates in Human Subjects
EPA Grant Number: R828044Title: Bioavailability of Haloacetates in Human Subjects
Investigators: Schultz, Irvin R. , Shangraw, Robert
Institution: Pacific Northwest National Laboratory
Current Institution: Pacific Northwest National Laboratory , Oregon Health & Sciences University
EPA Project Officer: Hahn, Intaek
Project Period: September 30, 2000 through September 29, 2003 (Extended to April 1, 2005)
Project Period Covered by this Report: September 30, 2000 through September 29, 2001
Project Amount: $524,928
RFA: Drinking Water (1999) RFA Text | Recipients Lists
Research Category: Drinking Water , Water
Objective:
The objective of this research project is to characterize the absorption, disposition, and oral bioavailability of chlorinated and brominated haloacetates in human volunteers after consumption of drinking water containing a naturally occurring mixture of these compounds. We hypothesize that accurate assessment of the oral bioavailability of haloacetates can be achieved by the simultaneous administration of an oral dose of 12C-labeled haloacetate with an intravenous dose of 13C-labeled haloacetate. Controlled dosing experiments, were used to directly test the hypothesis that prolonged exposure to low concentrations of dihaloacetates reduces their metabolism and increases their systemic bioavailability in humans. Dichloroacetate (DCA) will be used as a model dihaloacetate in human volunteer studies. A similar experiment will be performed using mixtures of chlorinated and brominated haloacetates in rhesus monkeys. These experimental results will be used to validate a physiologically based pharmacokinetic (PBPK) model for haloacetates in humans.
Progress Summary:
Work during the reporting year proceeded in three separate areas: (1) synthesizing the 13C-labeled haloacetates with the Isotech chemical company; (2) confirming both the isotopic and chemical purity of the synthesized 13C-labeled haloacetates, and performing a pilot study of the experimental design in male rats; and (3) finalizing all experimental protocols to be used in both the human volunteer and rhesus monkey studies, and to satisfy the continuing requirements of both the human subject review board and animal welfare review boards.
Progress was made in all areas of the research project. The successful synthesis of 13C-labeled (C1 position) dichloroacetate, bromochloroacetate, dibromoacetate, trichloroacetate, bromo-dichloroacetate, dibromo-chloroacetate, and tribromoacetate was achieved at an acceptable chemical purity level (97-99 percent); isotopic purity was exceptionally high (>99.9 percent). Several pilot studies were performed in male rats using the experimental protocols to be used in the volunteer and rhesus monkey experiments. All continuing human subject review boards matters and animal welfare concerns were addressed during the reporting period.
Preliminary Data Results. Prior to initiating animal studies, preliminary experiments were conducted using blood plasma standards fortified with the 13C-haloacetates mixed with various quantities of their 12C- equivalents. These tests were analyzed using gas chromatography-mass spectrometry (GC-MS), and indicated that analytical sensitivities to 1 ng/ml haloacetate could be achieved using a 12C/13C ratio ranging between 3:1 and 5:1. Based on this information, animal dosing studies were performed in male rats using an oral dose of 4 mg/kg 12C-haloacetate followed by an intravenous injection of a 1 mg/kg 13C-haloacetate dose 3 minutes later. In this experimental design, the intravenous dose serves as a reference for 100 percent bioavailability and can be used in conjunction with the simultaneous measurement of the 12C-labeled oral dose for calculation of the oral bioavailability. An example of these studies is presented in Figure 1.
Figure 1.
In this example, the oral bioavailability of DCA was calculated to be 73 percent. Based on the results of these pilot studies, we are ready to begin volunteer studies with DCA using an administered dose having a 12C/13C ratio of 3:1 and 5:1.
Difficulties Encountered/Remedial Actions. An extended delay occurred in receiving all of the synthesized haloacetates from Isotec. The final delivery of the haloacetates was received in September 2001, and the custom synthesized haloacetates have been verified by Battelle for their chemical and isotopic purity and meet acceptable criteria.
We encountered a difficulty with the planned rhesus monkey experiments. Currently, all reagents (haloacetates) and protocols needed for this study are ready and we are waiting on the availability of research animals. We have been informed by the Oregon Regional Primate Center (ORPC) that current demand for rhesus monkeys exceeds their ability to supply them. The earliest date that monkeys will be available for this project is between March-May 2002. This should not present a serious problem in the completion of this portion of the study, as the rhesus monkey experiments can be performed concurrently with the human volunteer studies.
Future Activities:
Volunteers for participation in this study will be recruited during the winter and spring. The rhesus monkey experiments will begin immediately after animals become available, probably after May 2002.
Journal Articles:
No journal articles submitted with this report: View all 13 publications for this projectSupplemental Keywords:
stable isotope, simultaneous bioavailability, renal elimination., RFA, Scientific Discipline, Health, PHYSICAL ASPECTS, Toxics, Water, Waste, Ecosystem Protection/Environmental Exposure & Risk, Bioavailability, National Recommended Water Quality, Toxicology, Health Risk Assessment, Fate & Transport, Risk Assessments, Monitoring/Modeling, Environmental Monitoring, Disease & Cumulative Effects, Physical Processes, Drinking Water, Biology, monitoring, health effects, risk assessment, haloacetates, exposure and effects, DBPs , stable isotope, physiologically based pharmacokinetic model, renal eliminatio, disinfection byproducts (DPBs), dose response, dose-response, exposure, pharmacokinetics, cellular physiology, chlorinated DBPs, treatment, brominated DPBs, PBPK modeling, human exposure, metabolism, PBPK, absorption, elimination, microbial exposure, water quality, dose estimates, DBPs, drinking water contaminants, DBP exposure, exposure assessment, human health risk, dosimetryProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.