Testing the dogma that total phospholipid fatty acid composition of blood plays a role in kidney stone pathogenesis, using a high–low risk human model: results from a pilot study
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Previous studies have suggested that ω-3 and ω-6 polyunsaturated fatty acid (PUFA) composition in plasma and red blood cell (RBC) total phospholipids plays a role in urolithiasis. Our aim was to test the robustness of this dogma by retrospectively comparing baseline profiles of these parameters in subjects from high- and low-stone-risk groups. The documented difference in stone occurrence in white (relatively common) (W) and black (rare) (B) subjects prompted us to select these groups as the high–low risk model for the study. Blood and urine samples were obtained from ten subjects in each group and were analysed for PUFAs and stone risk factors, respectively. Concentrations of linoleic acid (LA), eicosadienoic acid (EDA) and arachidonic acid (AA) in plasma and or/RBC total phospholipids were significantly higher in B. Differences in other PUFA profiles were also observed. There was no inter-group difference in AA/LA ratios. Urinary oxalate was significantly higher while urinary phosphate was significantly lower in B. We speculate that elevated AA in B might arise because of a possibly enhanced elongation of LA to EDA, as well as an enhanced ∆-8-desaturation of EDA to dihomo-gamma-linolenic acid (DGLA), which is the immediate precursor of AA. Alternatively, we speculate that the ∆-5-desaturation step of DGLA to AA might be more highly activated in this group. Irrespective of the mechanism, our observed inter-group differences in phospholipid PUFA composition are in conflict with previously published dogma which relates PUFA characteristics to high- and low-stone risk.
KeywordsArachidonic acid Inter-race comparisons Kidney stone risk factors Phospholipid fatty acid composition Polyunsaturated fatty acids Urolithiasis
Gamma (γ) linolenic acid
Monounsaturated fatty acid
Polyunsaturated fatty acid
Saturated fatty acid
Tiselius Risk Index
The financial support of the South African Medical Research Council, the South African National Research Foundation and the University of Cape Town is gratefully acknowledged. The authors would like to extend their appreciation to Johanna van Wyk of the NCDRU of the SAMRC for her invaluable laboratory assistance analyzing plasma and RBC total phospholipid fatty acids.
Compliance with ethical standards
Conflict of interest
The authors declare that they do not have any conflicts of interest. The authors also wish to declare that the data in Table 1 were collected as part of a 30-day study in which intra-group effects of the ingestion of a fatty acid supplement on total phospholipid FA composition were investigated. These data have been published in a paper in which intra-group comparisons were made of the effects from day 0 to day 30 . No inter-group baseline comparisons, as those described in the present paper, were made in the published paper.
Research involving human participants and/or animals
The study was approved by the Human Research Ethics Committee of the University of Cape Town (HRE REF: 366/2011). All procedures were performed in accordance with the ethical standards of the University of Cape Town and with the 1964 Declaration of Helsinki and its later amendments.
A signed informed consent declaration was obtained from all individual participants in the study.
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