Is it possible that freshly secreted (pre beta) HDL particles aren't (oxidatively) modified whereas larger (alpha 4, alpha 3,..) HDL particles are? In other words; is there a certain time needed after the secretion of lipid free ApoA-I for it to become oxidized / ...?
Hi Winde: You can separate prebeta- HDL by agarose gel electrophoresis. Then you must take off the prebeta HDL band and run a measurement of TG by an enzymatic method. Larger HDL particles are rich in TG in comparison with normal HDL.
In general I would expect that freshly secreted HDL particles are not modified, within the ER and the Golgi system no oxidation should occur. As soon as the particle enters the blood (or the cell culture medium if you are working with isolated cells) its open for modifications and the time scale depend on several parameters (O2 saturation of the blood, antioxidant conc., free radicals, enzymatic activities in the blood and on the HDL particle itself ...).
We have found that lipid-poor apoA-I (prebeta-HDL) species are more prone to proteolytic degradation than the alpha-migrating mature HDL particles. It appears that lipid binding protects apoA-I from proteolysis. It can also occur with oxidation with the exception that the lipids themselves can be oxidized. Some epitopes that are more susceptible to oxidation (e.g. by MPO) are also more susceptible to proteolysis. So I agree with Dr. Hoffmann on the oxidability potential of prebeta-HDL.