title: Lipoprotein lipase activity and interactions studied in human plasma by isothermal titration calorimetry.
abstract: LPL hydrolyzes triglycerides in plasma lipoproteins. Due to the complex regulation mechanism, it has been difficult to mimic the physiological conditions under which LPL acts in vitro. We demonstrate that isothermal titration calorimetry (ITC), using human plasma as substrate, overcomes several limitations of previously used techniques. The high sensitivity of ITC allows continuous recording of the heat released during hydrolysis. Both initial rates and kinetics for complete hydrolysis of plasma lipids can be studied. The heat rate was shown to correspond to the release of fatty acids and was linearly related to the amount of added enzyme, either purified LPL or postheparin plasma. Addition of apoC-III reduced the initial rate of hydrolysis by LPL, but the inhibition became less prominent with time when the lipoproteins were triglyceride poor. Addition of angiopoietin-like protein (ANGPTL)3 or ANGPTL4 caused reduction of the activity of LPL via a two-step mechanism. We conclude that ITC can be used for quantitative measurements of LPL activity and interactions under in vivo-like conditions, for comparisons of the properties of plasma samples from patients and control subjects as substrates for LPL, as well as for testing of drug candidates developed with the aim to affect the LPL system.
authors.affiliation: Department of Chemistry, Tallinn University of Technology, Tallinn 12618, Estonia.
authors.forename: Mart
authors.initials: M
authors.lastname: Reimund
authors.affiliation: Department of Chemistry, Tallinn University of Technology, Tallinn 12618, Estonia.|Department of Medical Biosciences, Umeå University, SE-901 87 Umeå, Sweden.
authors.forename: Oleg
authors.initials: O
authors.lastname: Kovrov
authors.affiliation: Department of Medical Biosciences, Umeå University, SE-901 87 Umeå, Sweden.
authors.forename: Gunilla
authors.initials: G
authors.lastname: Olivecrona
authors.affiliation: Department of Chemistry, Tallinn University of Technology, Tallinn 12618, Estonia aivar.lookene@ttu.ee.
authors.forename: Aivar
authors.initials: A
authors.lastname: Lookene
mesh_terms: D000328:Adult; D000091303:Angiopoietin-Like Protein 3; D000075803:Angiopoietin-Like Protein 4; D000075802:Angiopoietin-like Proteins; D042682:Angiopoietins / Q000008:administration & dosage; D000818:Animals; D053305:Apolipoprotein C-III / Q000008:administration & dosage; D002151:Calorimetry; D002417:Cattle; D005227:Fatty Acids / Q000097:blood*; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D006868:Hydrolysis; D007700:Kinetics; D008066:Lipolysis / Q000187:drug effects*; D008071:Lipoprotein Lipase / Q000097:blood*; D008079:Lipoproteins, VLDL / Q000097:blood; D008297:Male; D014280:Triglycerides / Q000097:blood
chemical_list: C479896:ANGPTL3 protein, human; C474772:ANGPTL4 protein, human; D000091303:Angiopoietin-Like Protein 3; D000075803:Angiopoietin-Like Protein 4; D000075802:Angiopoietin-like Proteins; D042682:Angiopoietins; D053305:Apolipoprotein C-III; D005227:Fatty Acids; D008079:Lipoproteins, VLDL; D014280:Triglycerides; D008071:Lipoprotein Lipase
keywords: angiopoietin-like proteins; apolipoproteins; enzymology; lipolysis; triglycerides; very low density lipoprotein