Characterisation of chlorinated fatty acid metabolites in human cells after uptake of dichlorostearic acid, as determined by a halogen-specific detector (XSD).

Licentiate's dissertation.
Gunilla Åkesson-Nilsson

10.00 am 24 november 2000
Undervisningshuset, Sal L, SLU, Uppsala



Chlorinated fatty acids (ClFAs) have been found to account for a considerable portion of the extractable organically bound chlorine in aquatic animals. Methods particularly suitable for the determination of ClFAs have relatively newly been developed, which may explain why these compounds did not come to attention as a potentially hazardous environmental pollutant until during the recent decade. The presence of ClFAs in human tissues has not yet been reported, and it is not known if human cells can incorporate and metabolise these compounds.

Recently a new halogen specific detector (XSD) has been introduced. It is described to be a sensitive, selective, and robust detector in the determination of halogenated pesticides. It has been declared to be more stable and easier to maintain than other halogen selective detectors. The XSD operates in an oxidative pyrolysis mode and the sample compounds are converted into their oxidation products. When halogen-containing compounds enter the hot detector, the detector current will increase. ClFAs have not earlier been studied by an XSD.

The aim of this work was to study i) the XSD, connected to a gas chromatograph, in the determination of ClFA methyl esters (ClFAMEs), and ii) the incorporation and metabolism of ClFAs in human cell lines, as determined by XSD detection.
It was shown that the XSD provides a detection limit (0.2 ng of dichlorostearic acid methyl ester) and a selectivity ((response ClFAMEs)/(response unchlorinated fatty acid methyl esters)) >> 10E4, similar to that of the electrolytic conductivity detector (ELCD), commonly used in determination of ClFAMEs. Furthermore, the XSD was found to be very easy and stable to maintain in the analysis of ClFAMEs.

In the determination of ClFAs obtained from human cell lines, it was established that human cells can incorporate dichlorostearic acid and degrade it to dichloropalmitic acid and dichloromyristic acid, probably through b-oxidation. ClFAs were found both in the neutral lipid and in the phospholipid fraction of the cultured cells. Dichloromyristic acid was the shortest ClFAs detected and was found to be released to the culture medium to a higher extent than the other ClFAs.
The XSD was found to be a good alternative to the ELCD in the determination of ClFAs and the XSD is suitable for use in continued studies of the turnover of ClFAs in human cells.

Keywords: halogenated fatty acids, halogen-selective detection, phospholipids, neutral lipids, dichloropalmitic acid, dichloromyristic acid, b-oxidation

Swedish University of Agricultural Sciences Uppsala 2000
Department of Environmental Assessment ISSN 1403-977X
Box 7050, SE-750 07 Uppsala, Sweden Rapport 2000:9