title: The lowering of hepatic fatty acid uptake improves liver function and insulin sensitivity without affecting hepatic fat content in humans.
abstract: Lipolysis may regulate liver free fatty acid (FFA) uptake and triglyceride accumulation; both are potential causes of insulin resistance and liver damage. We evaluated whether 1) systemic FFA release is the major determinant of liver FFA uptake in fasting humans in vivo and 2) the beneficial metabolic effects of FFA lowering can be explained by a reduction in liver triglyceride content. Sixteen healthy subjects were subdivided in two groups of similar characteristics to undergo positron emission tomography with [(11)C]acetate and [(11)C]palmitate to quantify liver FFA metabolism (n = 8), or magnetic resonance spectroscopy (MRS) to measure hepatic fat content (n = 8), before and after the acute lowering of circulating FFAs by using the antilipolytic agent acipimox. MRS was again repeated after a 1-wk treatment period. Acipimox suppressed FFA levels while stimulating hepatic fractional extraction of FFAs (P < 0.05). As a result, fasting liver FFA uptake was decreased by 79% (P = 0.0002) in tight association with lipolysis (r = 0.996, P < 0.0001). The 1-wk treatment induced a significant improvement in systemic (+30%) and liver (+70%) insulin sensitivity (P < 0.05) and decreased circulating triglycerides (-20%, P = 0.06) and liver enzymes (ALT -20%, P = 0.03). No change in liver fat content was observed after either acute or sustained FFA suppression. We conclude that acute and sustained inhibitions of lipolysis and liver FFA uptake fail to deplete liver fat in healthy human subjects. Liver FFA uptake was decreased in proportion to FFA delivery. As a consequence, liver and systemic insulin sensitivity were improved, together with liver function, independently of changes in hepatic triglyceride accumulation.
authors.affiliation: Turku Positron Emission Tomography Centre, University of Turku, Turku, Finland.
authors.forename: Sara
authors.initials: S
authors.lastname: Rigazio
authors.forename: Hanna-Riikka
authors.initials: HR
authors.lastname: Lehto
authors.forename: Helena
authors.initials: H
authors.lastname: Tuunanen
authors.forename: Kjell
authors.initials: K
authors.lastname: Någren
authors.forename: Mikko
authors.initials: M
authors.lastname: Kankaanpaa
authors.forename: Claudia
authors.initials: C
authors.lastname: Simi
authors.forename: Ronald
authors.initials: R
authors.lastname: Borra
authors.forename: Alexandru G
authors.initials: AG
authors.lastname: Naum
authors.forename: Riitta
authors.initials: R
authors.lastname: Parkkola
authors.forename: Juhani
authors.initials: J
authors.lastname: Knuuti
authors.forename: Pirjo
authors.initials: P
authors.lastname: Nuutila
authors.forename: Patricia
authors.initials: P
authors.lastname: Iozzo
mesh_terms: D000410:Alanine Transaminase / Q000097:blood; D005230:Fatty Acids, Nonesterified / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D007328:Insulin / Q000097:blood / Q000378:metabolism; D007333:Insulin Resistance / Q000502:physiology*; D008066:Lipolysis / Q000187:drug effects / Q000502:physiology; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D008875:Middle Aged; D049268:Positron-Emission Tomography; D011719:Pyrazines / Q000494:pharmacology*; D014280:Triglycerides / Q000097:blood / Q000378:metabolism
chemical_list: D005230:Fatty Acids, Nonesterified; D007004:Hypoglycemic Agents; D007328:Insulin; D011719:Pyrazines; D014280:Triglycerides; D000410:Alanine Transaminase; D005947:Glucose; C027696:acipimox