Low-density lipoprotein removal methods by membranes and future perspectives

Since the application by Thompson et al. in 1975 of plasma exchange for the treatment of 2 patients with familial hyperlipidemia, plasma purification techniques for selective low-density lipoprotein (LDL) removal (i.e., LDL apheresis) have been developed and adopted for the management of this disease. Thermofiltration is one of the LDL apheresis systems that utilizes membrane techniques developed by Nose and Malchesky's group in 1985. This article reviews its rationale, in vitro studies, animal studies, and clinical investigation. Thermofiltration effectively and selectively removes LDL cholesterol while retaining in the plasma physiologically important macromolecules such as albumin and high-density lipoprotein (HDL) cholesterol. Based on the global view of the treatment of atherosclerosis by LDL apheresis, membrane techniques are as effective, safe, and simpler to apply than other methods. Additionally, these methods are effective for the removal of lipoprotein (a) and fibrinogen; thus, they can address the needs in these application areas.

Selective removal of cholesterol by plasmapheresis and the progression of atherosclerosis

There is a strong correlation of plasma cholesterol levels with the risk of coronary heart diseases as shown by epidemiologic studies. This study was undertaken to evaluate the effect of plasma cholesterol lowering on the progression of atherosclerosis in the homozygous Watanabe heritable hyperlipidemic (WHHL) rabbit. The effect of cholesterol lowering, which was accomplished by thermofiltration (on-line plasma separation with plasma filtration at 39 degrees C) was evaluated by comparison between treated and untreated control groups. Thermofiltration reduced significantly the mean plasma level of total cholesterol (284 vs. 655 mg/dl, P = 0.0005) and the percent aortic area occupied by atherosclerotic plaque (15.0 vs. 44.2%, P = 0.0003). The total lipid and cholesterol contents in the aortas in the treated group were also significantly lower than those in the control group. Microscopically, thickness measurements of the lesions showed that the mean thickness of the fibrous cap and the ratio of the thickness of the intima to that of the media were smaller for the treated group than the control group. This study demonstrated the slowing or stopping of the progression of atherosclerosis by lowering the plasma total cholesterol level in WHHL rabbits.

Extracorporeal methods in lipid reduction pursuant to improvement in risk factors associated with atherosclerosis

Atherosclerosis is the leading cause of death in the United States. Elevated plasma levels of low-density lipoprotein and lipoprotein(a) [Lp(a)] and subnormal levels of high density lipoprotein are risk factors in atherosclerotic coronary heart disease. Extracorporeal methods of affecting these risk factors are reviewed. The limited information on the effects of apheresis procedures on Lp(a) is discussed and extended from a kinetic modeling approach. An estimate, made of the number of patients who could be expected to benefit from extracorporeal lipid lowering, is presented.