June 2011

Food for thought: commentaries on the kinetics of fatty acid transport

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Commentaries are a special, semiregular feature of the Journal of Lipid Research, where experts in various fields of lipid research highlight the findings of a new article being published in the journal and provide their own unique perspective. In the June 2011 issue of JLR, we have not one but two commentaries that together provide an opposing viewpoint to the data presented in “Plasma apolipoprotein C-III metabolism in patients with chronic kidney disease,” a patient-oriented research paper by Esther M. M. Ooi and collaborators published in April. 

The first commentary, “Complexities of plasma apoliprotein C-III metabolism,” by Frank M. Sacks, Chunyu Zheng and Jeffrey S. Cohn, calls into question a key conclusion made in the April JLR paper. Specifically, Sacks et al. cast doubt on the one-pool model of plasma apolipoprotein C-III that Ooi and colleagues propose to account for the similarity of enrichment-time curves for apoCIII in very low density lipoprotein as well as in high density lipoprotein (sometimes referred to as “good cholesterol”). The model suggests apoCIII “‘jumps off’ lipoproteins,” according to Sacks et al., before they are delivered to cells. 

In addition, Ooi et al. reported that apoCIII in VLDL in patients with chronic kidney failure was broken down at a lower rate in comparison to healthy counterparts, but the authors drew this conclusion by utilizing the rate of apolipoprotein B (apoB) in VLDL as a reference. Sacks, Zheng and Cohn, suggesting that the model offered by Ooi et al. may be too simplistic, point out that there are three physically different forms of apoCIII, each with its particular rate of breakdown, and that apoCIII is present in different percentages across naturally occurring lipoproteins in the body, so that relative determination of apoB content may not be an appropriate indicator of apoCIII content. The commentary also points out that free apoCIII is not, in fact, found in plasma. 

Associate Editor Henry N. Ginsberg and Columbia University colleague Rajasekhar Ramakrishnan have similar concerns in their commentary, “Investigations of apoCIII metabolism using stable isotopes: what information can you acquire and how can you interpret your results.” They emphasize that until there is methodology to clarify specific fractional catabolic rates and breakdown pathways for lipoproteins, relative measurements may not be reliable. 

Since the topic of apoCIII currently is very much in the spotlight, the paper and two commentaries provide very timely, and very worthy, food for thought. The controversy particularly highlights the complexities of performing kinetic analyses concerning the constituents of lipoproteins as they are transported through the body. 

Mary L. Chang (mchang@asbmb.org) is managing editor of the Journal of Lipid Research.

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