Low-density lipoprotein removal methods by membranes and future perspectives

Lipidfiltration--safe and effective methodology to perform lipid-apheresis

Familial hypercholesterolemia (FH) not adequately responding to diet and drug therapy represents an indication for extracorporeal lipid-apheresis, which has become an highly effective and approved therapy for those patients in several countries. Based on different methodology, five treatment options of lipid-apheresis exist and are in widespread practical use covered by regular reimbursement in Germany. All methods are safe and demonstrate equivalent efficacy of reducing LDL cholesterol with respect to the single apheresis session as well as during long-term treatment. Therefore German reimbursement guidelines leave the choice of the method to the discretion of the apheresis center. Related to properties of the used technology all methods exhibit characteristic patterns of additional plasma protein elimination, which do not impair, but in part may increase the therapeutic benefit of lipid-apheresis. Fibrinogen reduction has to be mentioned as an example. The Lipidfiltration system is based on plasmafiltration previously referred to as membrane differential filtration (MDF), synonymous with double filtration plasmapheresis (DFPP). The new term Lipidfiltration was the result of technological progress in the manufacturing process of the plasmafilter resulting in enhanced sieving characteristics and capacity. The Lipidfiltration system is completed by a specifically designed therapy machine with optimised performance characteristics.

Plasmapheresis for severe lipemia: comparison of serum-lipid clearance rates for the plasma-exchange and double-filtration variants

Patients with extremely high triglyceride levels and associated lipemia are at high risk for acute pancreatitis. To evaluate plasmapheresis efficacy for severe hypertriglyceridemia, 18 patients who had not responded to previous therapies were selected for either the plasma-exchange (PE) or double-filtration (DF) treatment variants. After treatment, the mean serum concentrations for triglyceride and cholesterol fell significantly from 1,977.1 and 436.7 mg/dl to 692.6 and 222 mg/dl, respectively. The cholesterol-removal rate was significantly higher for the PE group (P = 0.0082), which also had a lower incidence of hemolysis during the plasmapheresis treatment (P = 0.0430). Improved clearance of serum triglyceride was strongly associated with a lower level of maximal transmembrane pressure (TMP; P = 0.0030), reduced plasmapheresis duration (P = 0.0035), and higher rates of plasma (P = 0.0255) and blood flow (P = 0.0480) during plasmapheresis. In comparison to reports in the literature, the removal rates for serum lipids were lower in our study, possibly as a consequence of early saturation of the plasma separator resulting from blockage caused by the extremely high level of triglyceride-containing lipoproteins. Therefore, PE may be more suitable for the initial treatment of severe hypertriglyceridemia as saturation is prevented. Increasing blood and plasma flow rates, reduction of the TMP level, and reducing effective plasmapheresis duration will improve the clearance of serum lipids during treatment.

Low-density lipoprotein apheresis in the treatment of peripheral arterial disease

Low-density lipoprotein (LDL) apheresis is performed in patients with homozygous familial hyper-cholesterolemia who lack LDL receptors and with heterozygous familial hypercholesterolemia who are LDL receptor deficient with documented, symptomatic coronary artery disease who are resistant to diet changes and maximum drug therapy. LDL apheresis can reduce or abolish anginal symptoms and improve coronary lesions. Several reports reveal the improvement of insufficient peripheral blood flow. By extensively removing blood LDL and changing coagulation factors and various vasoactive substances, LDL apheresis improves blood rheology and thereby peripheral circulation. It seems worth trying on all patients with arteriosclerotic lesions, even if they are normocholesterolemic.

From membrane differential filtration to lipidfiltration: technological progress in low-density lipoprotein apheresis

Extracorporeal low-density lipoprotein (LDL) apheresis is an established and highly effective therapy for patients with familial hypercholesterolemia (FH) not adequately responding to diet and drug therapy alone. Based on different methodology, five treatment options of LDL apheresis are available and in widespread practical use in Germany. All methods are safe and demonstrate equivalent efficacy of reducing LDL cholesterol with respect to the single apheresis session as well as during long-term treatment. Owing to methodological properties all methods also exhibit characteristics of additional plasma protein elimination, which do not impair, but in part, increase the beneficial therapeutic effect of LDL apheresis. Fibrinogen reduction has to be mentioned as an example. The lipidfiltration system is based on plasmafiltration previously named membrane differential filtration (MDF), synonymous with double filtration plasmapheresis (DFPP). The new term lipidfiltration was the result of technological progress leading to a significant improvement of the efficiency. The system consists of a novel lipid filter with enhanced sieving characteristics and capacity, and is completed by an enhanced therapy machine with an optimized heating unit.

Combination of therapeutic apheresis and therapeutic ventricular assistance for end-stage heart failure patients

Dilated cardiomyopathy is a cardiac disease of unknown origin which is characterized by the gradual development of cardiac failure associated with four-chamber dilatation of the heart. Heart transplantation has been considered as the last resort for this disease. However, some patients who received support with a ventricular assist device (VAD) as a bridge-to-transplantation and then recovered without transplantation have been reported. This new concept of treating heart failure is termed bridge-to-recovery. A VAD can inhibit the heart failure compensatory mechanisms by extreme ventricular unloading. Also, heart failure is a complex neurohormonal/autocrine-paracrine syndrome, and these mechanisms consecutively lead to inflammatory response by proinflammatory cytokines; interleukin-1 alpha (IL-1 alpha), interleukin-1 beta (IL-1 beta), interleukin-2 (IL-2), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-alpha). Furthermore, the existence of anti-beta1-adrenoceptor autoantibodies (A-beta1-AABs) in a patient with dilated cardiomyopathy has been reported. These proinflammatory cytokines and this antibody accelerate a ventricular remodeling and a contractile dysfunction over the long term. Apheresis can also inhibit the vicious cycle in heart failure by removing the factors that are produced by activated neurohormonal/autocrine-paracrine compensatory mechanisms. Therefore, we propose that the combined therapies, therapeutic VAD and therapeutic apheresis, will provide a prominent outcome for a patient who is suffering from end-stage heart failure.

Comparison of two filter combinations for low-density lipoprotein apheresis by membrane differential filtration: a prospective crossover controlled clinical study

Membrane differential filtration is an accepted procedure for the extracorporeal removal of low-density lipoprotein (LDL). Reduction rates largely depend on the nature of the membranes and are ideally evaluated in a crossover study design. Four patients who had been treated by LDL apheresis for at least 6 months were included. Six consecutive weekly sessions (40 ml plasma/kg body weight) were scheduled per system (Plasmacure PS06/Evaflux Eval 5A [Kuraray] versus Plasmaflo OP05W/Cascadeflo AC1770 [Asahi]). Laboratory measurements indicated reductions of plasma concentrations for fibrinogen (37% [Kuraray] versus 44% [Asahi]), IgG (15% versus 20%), IgA (24% versus 28%), IgM (63% versus 53%), and total protein (11% versus 16%). Total cholesterol was eliminated by 52% versus 49%, LDL by 67% versus 66%, triglycerides by 56% versus 41%, and high-density lipoprotein by 10% versus 20%. Three therapies employing the Asahi filter combination were terminated prematurely due to saturation of the plasma fractionator. In conclusion, despite similar physical properties, the membranes differ significantly concerning selectivity and sensitivity to saturation.

Membrane plasmapheresis in the United States: a review over the last 20 years

Plasmapheresis is a general term involving extracorporeal plasma separation by centrifugation or primary membrane plasma separator (MPS). Further plasma processing can be accomplished by the use of secondary membrane plasma fractionation (PF), as in double filtration plasmapheresis, also called cascade filtration, low-density lipoprotein pheresis, thermofiltration, and cryofiltration apheresis. Otherwise, the separated plasma is replaced by colloid solution as in plasma exchange (PE). PE is used, unselectively, to treat patients with immunological, neurological, hematological, renal, and metabolic disorders. Secondary PF may be a more selective alternative. In general, the primary MPS and secondary PF are safe, effective, and biocompatible. The advantages of the primary MPS include its simplicity to use with blood pumps and no observed white blood cell or platelet loss, compared with centrifugation. The disadvantages are lack of versatility, the need to monitor transmembrane pressure to prevent hemolysis, and possible biocompatibility issues such as use of polyvinyl alcohol membranes. The advantages of secondary PF, compared with PE, include selective removal of macromolecules according to molecular weight and filter pore size. No deficiency syndromes or sepsis are observed, nor is replacement solution required. More than 1 plasma volume may be processed, and it is less expensive than PE. Cryofiltration apheresis, using the cryoglobulin filter, selectively removes cryoproteins and is a specific treatment for cryoprecipitate-induced diseases. The disadvantages of PF include biocompatibility, especially with concomitant ACE inhibitor use, and membrane plugging. An important disadvantage is that most PFs are investigational in the United States. This article reviews the availability, safety, efficacy, and biocompatibility of primary MPSs and secondary PF in the United States.

Incorporation of low-density lipoprotein apheresis into the treatment program of patients with severe hypercholesterolemia

Treatment to low-density lipoprotein (LDL) cholesterol targets has become a focus in the management of patients with coronary heart disease (CHD). Many patients with familial hypercholesterolemia (FH) are unable to reach targets because of drug intolerance or extremely high baseline LDL cholesterol levels. Consequently, LDL apheresis has become a useful modality for the treatment of patients with severe hypercholesterolemia. Commonly used LDL apheresis systems utilize immunoadsorption columns, dextran sulfate cellulose columns, or heparin precipitation. A new and simpler treatment modality is emerging which uses whole blood compatible columns. All systems require systemic anticoagulation, extracorporeal processing of blood, and venous vascular access. Acute LDL lowering is 70% to 80% and time-averaged LDL lowering is 40% to 50%. Lipoprotein(a) is also substantially lowered. Clinical efficacy has been shown in several studies. Mechanisms for clinical improvement in addition to regression of atherosclerotic plaque have been suggested by recent research.

Development of a totally implantable biventricular bypass centrifugal blood pump system

BACKGROUND

During the past 2 years, the development of a totally implantable biventricular bypass rotary blood pump system has been made.

METHODS

An extracorporeal gyro centrifugal pump, the CIE3, was miniaturized and developed into the PI601, a totally implantable plastic pump. Two-day anatomic and hemodynamic feasibility studies demonstrated that these two pump systems were easily implantable inside a calf's abdominal wall, directly under the diaphragm. The priming volume of the pump was 20 mL, with sufficient cardiac outputs at approximately 2,000 rpm and requiring less than 10 W of power. Two-week antithrombogenic screening tests also revealed these pump systems to be quite antithrombogenic. In addition, 1-month system reliability studies demonstrated fail-safe reliable performances.

RESULTS AND CONCLUSIONS

Encouraged by these preliminary studies, the PI601 model was converted to the permanently implantable titanium gyro pump PI702 model. The long-term implantations were initiated approximately 3 months ago, and two such long-term LVAD studies are currently underway with no sign of difficulty (October 10, 1997). They were followed 283 days and 72 days, respectively. Both terminated due to functional inflow obstruction. There were no blood clots or emboli at autopsy.

Double filtration plasmapheresis maintains normal adhesion molecule levels

Levels of plasma soluble vascular cell adhesion molecule-1 (sVCAM-1), soluble intercellular adhesion molecule-1 (sICAM-1), and von Willebrand factor (vWF) increase in patients with peripheral vascular or ischemic heart disease. These factors are related to the progression of atherosclerosis. Furthermore, these substances and thrombomodulin (TM) are indicators for assessing the degree of damage to the endothelium. To evaluate the effect of double filtration plasmapheresis (DFPP) on these molecules, the plasma levels of vWF, sICAM-1, sVCAM-1, and TM were measured in 4 familial hypercholesterolemia (FH) patients who underwent treatment with DFPP at 2 week intervals for more than 3 years. The levels of sVCAM-1 and sICAM-1 in hypercholesterolemia patients with ischemic heart disease as a control was 773 +/- 109 and 334 +/- 82 ng/ml. These values were higher than the normal value. In the FH patients who underwent DFPP treatment, the average sICAM-1 levels were 221 +/- 47 and 197 +/- 36 ng/ml before and after, respectively. The average sVCAM-1 levels were 601 +/- 87 and 486 +/- 60 ng/ml. There were no significant differences between the pre- and post-DFPP values. The activities of plasma vWF before and after DFPP treatment were 158 +/- 23 and 45 +/- 9%. The levels of plasma TM before and after treatment were 3.0 +/- 0.3 and 3.4 +/- 0.5 FU/ml. From these results, it is suggested that DFPP treatment does not damage the endothelium and may prevent the progression of atherosclerosis by removing the substances that induce the production of sICAM-1 and sVCAM-1 due to long-term treatment.

Design and development strategy for the rotary blood pump

Development of an antitraumatic antithrombogenic and durable blood pump is a very difficult task. Based upon this author's experience of over 35 years in the development of various types of cardiac prostheses, development strategies for a rotary blood pump are described. A step-by-step development strategy is thus proposed. Initially, the development of a 2 day antitraumatic pump (Phase 1) would be made. Then, conversion of this pump to a 2 week antithrombogenic pump (Phase 2) should be attempted. After the successful development of the Phase 2 pump, the conversion of this device to a durable, implantable, and long-term blood pump (Phase 3) should be established. Based upon this development strategy, 2 rotary blood pumps, namely, the axial flow blood pump and the centrifugal blood pump, have been developed in less than 6 years with modest development costs.