Cardiovascular disease is a major cause of mortality and morbidity in patients on chronic haemodialysis (HD). One main contributing factor is renal dyslipidaemia, characterized by an impaired catabolism of triglyceride (TG)-rich lipoproteins with accumulation of atherogenic remnant particles. The enzyme lipoprotein lipase (LPL) is a key molecule in the lipolysis of TG-rich lipoproteins into free fatty acids. The activity of LPL is reduced in HD-patients. This study was performed to elucidate various conditions and factors that may have an impact on LPL-related lipid metabolism. I. The functional pool of LPL is located at the vascular surface. The enzyme is released by heparin and low molecular weight heparins (LMWH) into the circulating blood and extracted and degraded by the liver. Heparin and LMWH are used for anticoagulation during HD to avoid clotting in the extracorporeal devices. This raises a concern that the LPL system may become exhausted by repeated administration of LMWH in patients on HD. In a randomized cross over designed study twenty patients on chronic HD were switched from a primed infusion of heparin to a single bolus of LMWH (tinzaparin).  The LPL activity in blood was higher on HD with LMWH at 40 minutes but lower at 180 minutes compared to HD with heparin. These values did not change during the 6-month study period. With heparin a significant TG reduction was found at 40 minutes and a significantly higher TG value at 180 and 210 minutes than at start. TG was higher during the HD-session with tinzaparin than with heparin. Our data demonstrate that repeated HD with heparin or with LMWH does not exhaust the LPL-system in the long term but does disturb the LPL system and TG metabolism during every HD session. II. In this study HD patients were compared with patients on peritoneal dialysis (PD) in a case control fashion. PD patients showed the same reaction of the LPL system to LMWH as HD patients. This confirmed that both HD and PD patients had the same, reduced, heparin-releasable LPL pool. The main difference was that in PD patients the TG continued to be cleared effectively even at 180 minutes after the bolus of LMWH injection. This may be due to a slower removal of the released LPL by the liver in PD patients.  III. In recent years, citrate (Citrasate) in the dialysate has been used in Sweden as a local anticoagulant for chronic HD. We performed a randomized cross over study that included 23 patients (16 men and 7 women) to investigate if citrate in the dialysate is safe and efficient enough as anticoagulant. The study showed that citrate anticoagulation eliminated the need of heparin or LMWH as anticoagulation for HD in half of the patients. However, individual optimization of doses of anticoagulants used together with citrate have to be made. IV. Recently angiopoietin-like proteins, ANGPTL3 and 4 have emerged as important modulators of lipid metabolism as potent inhibitors of LPL. Twenty-three patients on chronic HD and 23 healthy persons were included as case and controls to investigate the levels of these proteins in plasma of HD-patients and to evaluate if HD may alter these levels. The data showed that plasma levels of ANGPTL3 and 4 were increased in patients with kidney disease compared to controls. This may lead to inactivation of LPL. High flux-HD, but not low flux-HD, reduced the levels of ANGPTL4, while the levels of ANGPTL3 were not significantly influenced.  On HD with local citrate as anticoagulant, no LPL activity was released into plasma during dialysis in contrast to the massive release of LPL with heparin (LMWH). Citrate HD was not associated with a significant drop in plasma TG at 40 minutes, while both HD with citrate and heparin resulted in significantly increased TG levels at 180 minutes compared to the start values. Conclusions:  Citrate as a local anticoagulant during haemodialysis eliminates the need of heparin or LMWH in about half of the HD patients. Citrate does not induce release of LPL from its endothelial binding sites. We have shown that although HD with heparin causes release of the endothelial pool of LPL during each dialysis session, the basal pool is similarly low in PD patients that do not receive heparin. This indicates that the LPL pool is lowered as a consequence of the uraemia, per se. One explanation could be the increased levels of ANGPTL3 and 4. HD with high flux filters can temporarily lower the levels of ANGPTL4. Further studies are, however, needed to understand why LPL activity is low in patients with kidney disease.

Indiana University-Purdue University Indianapolis (IUPUI) / The incidence of Metabolic Syndrome (MetS) is increasing worldwide and accompanied by elevated risks for cardiovascular disease (CVD) and other subsequent comorbidities. MetS is associated with increased circulating triglycerides. A key enzyme involved in triglyceride (TG) clearance is lipoprotein lipase (LPL) whose activity is modulated by a variety of factors. Recent literature has identified the importance of angiopoietin-like proteins (ANGPTL) as regulators of LPL activity and has hypothesized a model in which three of these proteins interact with LPL to regulate the partitioning of TG metabolism from adipose to skeletal muscle. The work detailed in this dissertation adds to the model of ANGPTL regulation of LPL by establishing how ANGPTL8 modulates the ability of ANGPTL3 and ANGPTL4 to inhibit LPL activity in the bloodstream and localized environments, respectively. In the updated model, elevated insulin concentrations result in increased hepatic ANGPTL3/8 secretion and increased ANGPTL4/8 in adipose tissue. ANGPTL3/8 works as an endocrine molecule to inhibit skeletal muscle LPL from hydrolyzing circulating TG. Simultaneously, ANGPTL4/8 works in a paracrine mechanism to bind LPL on the endothelial vasculature adjacent to adipose tissue to alleviate ANGPTL4-mediated LPL inhibition and also prevent ANGPTL3/8 inhibition of localized LPL. Thus, in the postprandial state free fatty acids (FFA) from the hydrolysis of TG are directed into adipocytes for storage. Under fasting conditions, ANGPTL8 production is decreased in adipocytes and hepatocytes. This decreased production results in diminished ANGPTL4/8 and ANGPTL3/8 secretion from their respective tissues. As a result, ANGPTL4 inhibits adipocyte localized LPL activity while ANGPTL3 at physiological concentrations has minimal effect on LPL activity. Furthermore, any ANGPTL3/8 which is produced has its LPL-inhibitory ability diminished by the circulating apolipoprotein ApoA5. LPL is more active in skeletal muscle compared to adipose tissue where energy is shunted towards utilization in the muscle and away from storage in adipose tissue. A complete understanding of LPL regulation by ANGPTL proteins can potentially provide therapeutics targets for MetS.