Lipoproteins containing apolipoprotein B-100 are secreted by the heart.

It generally is assumed that lipoproteins containing apolipoprotein B (apo B) are secreted only by the intestine and the liver. However, we recently demonstrated that the human apo-B gene also is expressed in the hearts of human apo-B transgenic mice and in human heart tissue. Using metabolic labeling techniques, we showed that heart tissue from human apo-B transgenic mice and nontransgenic mice, as well as human heart tissue, synthesize and secrete apo-B-containing lipoproteins. The reason why the heart makes lipoproteins is unknown, but we hypothesized that the heart may use lipoprotein synthesis to unload surplus cellular lipids, particularly triglycerides, which are not immediately required for mitochondrial beta-oxidation.