Oxyphytosterol formation in humans: identification of high vs. low oxidizers

Animal studies suggest that oxyphytosterols are atherogenic. However, we have previously shown that plasma oxyphytosterol concentrations did not increase after consuming a diet enriched in plant sterol esters (3g/day), while minor reductions were seen after consuming a plant stanol ester-enriched diet. Large variations in oxyphytosterol concentrations between individuals however existed. The aim of this study was to identify factors that may explain inter-individual differences in plasma oxyphytosterol concentrations. For this, 43 subjects consumed for 4 weeks in random order a plant sterol, stanol and control margarine. Plasma oxyphytosterol concentrations were determined in butylated hydroxytoluene (BHT)-enriched EDTA plasma via GC-MS and serum oxidized low-density lipoprotein (oxLDL) concentrations were analyzed via ELISA. Trolox equivalent antioxidant capacity (TEAC) values, α-tocopherol concentrations and iron/copper status were determined to assess plasma oxidative and anti-oxidative capacity. Serum (non-oxidized) sitosterol and campesterol concentrations did not correlate with plasma oxysitosterol and oxycampesterol concentrations during any of the three dietary interventions. Moreover, plasma oxyphytosterol concentrations remained relatively stable over time. Six subjects could be arbitrarily classified as having consistent low or high plasma oxyphytosterol concentrations, which was also reflected in oxLDL concentrations. However, oxidative and anti-oxidative capacity markers, such as iron/copper status, α-tocopherol concentrations and TEAC values, could not explain these differences. In conclusion, subjects seem to have consistent plasma oxyphytosterol concentrations, which resulted in the identification of 'low and high oxidizers'. Differences, however, could not be attributed to the oxidative and anti-oxidative capacity markers analyzed.