Diss. (sammanfattning) Umeå : Univ., 2005. / Härtill 4 uppsatser.

No description available.

Thesis (doctoral)--University of Helsinki, 1986. / Includes bibliographical references (p. 31-38).

Stuttgart, Univ., Diss., 2002.

The present study cloned successfully two lipid-metabolism genes, lipoprotein lipase (LPL) and fatty acid binding protein (FABPs) from cobia and studied the mRNA expressions of the two genes and their upstream gene PPARs when the cobia were fed diets containing 15% lipid. Among the lipids, 6% was fish oil and the remaining 9% were supplemented by fish oil (FO, rich in n-3 HUFA), perilla oil (PE, rich in 18:2 n-6), safflower oil (SA, rich in 18:2 n-6), olive oil (OL, rich in 18:1 n-9) or palm oil (PA, rich in 16:0). The whole sequences of LPL, liver-FABP (L-FABP) and muscle-FABP (M-FABP) encode 520, 126 and 133 amino acids, respectively. RT-PCR and real time PCR analyses based on these gene sequences show that the mRNA expressions of L-FABP and M-FABP in the tissue of the cobia were diet-specific. The mRNA expression of LPL, on the other hand, did not respond to the treatments, except in visceral fat depot. Linear regression analysis shows that the mRNA expression of LPL in the liver and muscle was positively (P<0.05) related to dietary fatty acids and ther concentration, but that in the visceral fat depot was negatively related. The mRNA expression of FABPs was also positively correlated with dietary fatty acid levels. Among all fatty acids, the levels of C14:0, C20:1 n-9, EPA and DHA were positively correlated with the mRNA expression of PPAR£^and also with FABPs mRNA expression in the visceral fat depot and LPL mRNA expression in the muscle. Thus, LPL, L-FABP and M-FABP mRNA expression of the cobia were highly influenced by the kind and amount of dietary fatty acids. The role of PPARs was not clearly demonstrated.

Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (leaves 82-89).

Stuttgart, Univ., Diss., 2007.

University, Diss., 2002--Stuttgart. / Gedr. Ausg. im Inst. für Technische Biochemie der Univ. Stuttgart.

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.

Lipoprotein lipase (LPL) is a central enzyme in lipid metabolism. It is a non-covalent, homodimeric and N-glycosylated protein, which is regulated in a tissue-specific manner and is dependent on an activator protein, apolipoprotein CII. Dissociation of active LPL dimers to monomers leads to loss of activity. This was previously found to be an important event in the rapid regulation of LPL in tissues. The mechanisms involved in the processing of LPL to active dimers, as well as in LPL inactivation through monomerization, were unknown. We have investigated the folding properties of the LPL protein, in particular the requirements for LPL to attain its active quaternary structure and to remain in the native conformation. On expression of LPL in insect cells we found that most of the LPL protein was synthesized in an inactive monomeric form. By co-expression of LPL with human molecular haperones, especially with calreticulin (CRT), the activity of LPL increased greatly, both in the cells and in the media. The effect of CRT on LPL activity was not due to increased levels of the LPL protein, but was due to an increased proportion of active dimeric LPL. Co-immunoprecipitation experiments showed direct interaction between LPL and CRT supporting the idea that this ER-based molecular chaperone supports the formation of active LPL dimers. We showed that, bis-ANS, the aromatic hydrophobic probe 1,1.-bis(aniline)-4,4.- bis(naphthalene)-8,8.disulfonate, can be used to obtain specific information about the interaction of LPL with lipid substrates and with apoCII. Bis-Ans was found to be a potent inhibitor of LPL activity, but apoCII prevented the inhibition. Our results suggest that bis-Ans binds to three exposed hydrophobic sites, of which one is at or close to the binding site(s) for apoCII. In studies of the mechanisms responsible for the spontaneous inactivation of LPL, we showed that active LPL is a dynamic dimer in which the subunits rapidly exchange partners. The rapid equilibrium between dimers and monomers exists even under conditions where LPL is relatively stable. This supports the idea that the dimer is in equilibrium with dimerization-competent, possibly active monomers. This dimerization-competent intermediate was also implicated in studies of the inactivation kinetics. The inactive LPL monomer was found to have a stable, defined conformation irrespective of how it was formed. The main differences in conformation between the inactive monomer and the active dimer were located in the middle part of the LPL subunit. Experiments with bis-Ans demonstrated that more hydrophobic regions were exposed in the inactive monomer, indicating a molten globule conformation. We concluded that the middle part of the LPL subunit is most likely engaged in the formation of the active LPL dimer. The dimerization-competent LPL monomer is a hypothetical conformational state, because it has not been possible to isolate it. To study complete refolding of LPL we used fully denatured LPL and were able to demonstrate that the recovery of LPL activity was about 40% when the denaturant was diluted by a buffer containing 20% human serum and 2M NaCl. Further studies identified calcium as the component in serum that was crucial for the reactivation of LPL. The refolding of LPL was shown to involve at least two steps, of which the first one was rapid and resulted in folded, but inactive monomers. The second step, from inactive monomers to active dimers, was slow and calcium-dependent. Also inactive monomers isolated from human tissue were able to recover activity under the influence of calcium. We proposed that calcium-dependent control of LPL dimerization might be involved in the normal post-translational regulation of LPL activity. In conclusion, LPL is a relatively unstable enzyme under physiological conditions due to its noncovalent dimeric structure. The energy barrier for folding to the active dimer is high and requires the presence of calcium ions and molecular chaperones to be overcome. The dimeric arrangement is probably essential to accomplish rapid down-regulation of LPL activity according to metabolic demand, e.g. in adipose tissue on fasting.