| Abstract: | Serum from two patients with abetalipoproteinemia, a rare disorder of lipid metabolism characterized by the absence of chylomicrons and very low density and low density lipoproteins, did not stimulate the proliferation and growth of human smooth muscle cells or dermal fibroblasts in vitro as effectively as normal serum. The growth-promoting activity of this serum was comparable to that observed for lipoprotein-deficient plasma from normolipidemic subjects. Although the mitogenic effect of abetalipoproteinemic serum was improved with supplementation of low density lipoproteins, it was still about half the activity achieved with normal serum. However, the growth-promoting activity of this serum was completely restored to normal levels after addition of a lysate of normal platelets. In contrast, the mitogenic activity of lipoprotein-deficient plasma remained unchanged after addition of a lysate from abetalipoproteinemic platelets, whereas a similar supplementation of normal platelets completely restored its growth-promoting activity to normal. Thus, the inability of abetalipoproteinemic serum to promote growth appears to be due both to a deficiency of a platelet-releasable growth factor(s) and to the absence of serum lipoproteins. |
