7 research outputs found
Aspects of the regulation of liver lipase
It is evident that factors that influence the activity of
liver lipase could be important because of the role of liver
lipase in HDL-cholesterol metabolism. At the start of this
study not much was known about the regulation of liver lipase.
The activity had been found to be decreased after fasting
(10,34), during hypercortisolism {12), hypothyreoidism {35).
insulin deficiency in diabetes {35,12) and by estrogen treatment
{36) suggesting a role for respectively insulin~ corticosteroids, thyroxine and estrogens in the regulation of the activity of the enzyme, respectively.
This thesis describes the effects of several hormones
(corticosteroids, catecholamines, insulin, thyroxin) on the
liver lipase activity in vivo and in vitro. In chapter II and
appendix paper I the model used to study the regulation of
liver lipase in vitro is shown in addition to several factors
influencing the liver lipase activity in vitro. Aspects of the
regulation of liver lipase in vivo are described in chapter
III including the turnover of liver lipase and the influence
of essential fatty acid (EFA) deficiency. In chapter IV factors
influencing the enzyme activity are discussed by an
integration of literature data with our own experiment
Identification of a heparin-releasable hepatic lipase binding protein from rat liver
Hepatic lipase (HL) plays a key role in the metabolism of several
lipoproteins. Metabolically active HL is bound in liver parenchymal cells
to specific binding sites. We studied the nature of the HL binding in rat
liver. Rat livers were perfused with heparin, which lead to a loss of 80%
of the HL binding capacity of the liver. The heparin-containing perfusates
possessed HL binding capacity, determined by slot-blot assay. The
perfusates were loaded on to a heparin-Sepharose column and eluted with a
linear salt gradient (0.2-1 M). HL binding activity, assessed by a
slot-blot binding assay, eluted both at 0.3 M and at 0.8 M NaCl. A 0.5 M
NaCl eluate was used to further characterize the HL binding activity. In
this fraction the major protein had a molecular mass of 70 kDa. The
fraction showed saturable HL binding in a solid-phase binding assay
Rat liver contains a limited number of binding sites for hepatic lipase
The binding of hepatic lipase to rat liver was studied in an ex vivo
perfusion model. The livers were perfused with media containing partially
purified rat hepatic lipase or bovine milk lipoprotein lipase. The
activity of the enzymes was determined in the perfusion media before and
after passage through the liver. During perfusion with a
hepatic-lipase-containing medium the lipase activity in the medium did not
change, indicating that there was no net binding of lipase by the liver.
In contrast, more than 80% of the lipoprotein lipase was removed from the
med
Hepatic lipase is localized at the parenchymal cell microvilli in rat liver
Hepatic lipase (HL) is thought to be located at the vascular endothelium
in the liver. However, it has also been implicated in the binding and
internalization of chylomicron remnants in the parenchymal cells. In view
of this apparent discrepancy between localization and function, we
re-investigated the localization of HL in rat liver using biochemical and
immunohistochemical techniques. The binding of HL to endothelial cells was
studied in primary cultures of rat liver endothelial cells. Endothelial
cells bound HL in a saturable manner with high affinity. However, the
binding capacity accounted for at most 1% of the total HL activity present
in the whole liver. These results contrasted with earlier studies, in
which non-parenchymal cell (NPC) preparations had been found to bind HL
with a high capacity. To study HL binding to the different components of
the NPC preparations, we separated endothelial cells, Kupffer cells and
blebs by counterflow elutriation. Kupffer cells and endothelial cells
showed a relatively low HL-binding capacity. In contrast, the blebs,
representing parenchymal-cell-derived material, had a high HL-binding
capacity (33 m-units/mg of protein) and accounted for more than 80% of the
total HL binding in the NPC preparation. In contrast with endothelial and
Kupffer cells, the HL-binding capacity of parenchymal cells could account
for almost all the HL activity found in the whole liver. These data
strongly suggest that HL binding occurs at parenchymal liver cells. To
confirm this conclusion in situ, we studied HL localization by
immunocytochemical techniques. Using immunofluorescence, we confirmed the
sinusoidal localization of HL. Immunoelectron microscopy demonstrated that
virtually all HL was located at the microvilli of parenchymal liver cells,
with a minor amount at the endothelium. We conclude that, in rat liver, HL
is localized at the microvilli of parenchymal cells
Functional molecular mass of rat hepatic lipase in liver, adrenal gland and ovary is different
Lipoprotein lipase (LPL) is functionally active only as a dimer. It is
also generally assumed that the highly homologous hepatic lipase functions
as a dimer, but no clear evidence has been presented. A hepatic
lipase-like activity, also indicated as L-type lipase, is present in
adrenal and ovary tissues. This enzyme is thought to originate from the
liver and to be identical to hepatic lipase. We determined the functional
molecular mass of hepatic lipase in rat liver, adrenal gland and ovary by
radiation inactivation, a method for determining the functional size of a
protein without the need of prior purification. Samples were exposed to
ionizing radiation at -135 degrees C. Hepatic lipase activity in liver
homogenate showed a single exponential decay. The functional molecular
mass was calculated to be 63 +/- 10 kDa. Hepatic lipase activity in
adrenal homogenate was found to have a functional molecular mass of 117
+/- 16 kDa. The functional molecular masses of the lipases partially
purified from rat liver perfusate, adrenal homogenate or ovarian
homogenate showed the same pattern, a target mass for the liver enzyme of
56 +/- 6 kDa and a target mass of 117 +/- 14 kDa for the enzyme from
adrenal gland or ovary. In Western blot analysis the mass of the
structural units of hepatic lipase in liver was 57 kDa and in adrenal and
ovary tissue 51 kDa. We conclude that the functional unit of hepatic
lipase in the liver is a monomer. The enzyme in adrenal gland and ovary is
different from the liver and the functional unit may be a dimer
Fibroblast growth factor 21 as a biomarker for long-term complications in organic acidemias
Background: There is increasing evidence that long-term complications in organic acidemias are caused by impaired mitochondrial metabolism. Currently, there is no specific biomarker to monitor mitochondrial dysfunction in organic acidemias. Serum fibroblast growth factor 21 (FGF-21) is a biomarker for mitochondrial disease and could be a candidate to monitor mitochondrial function in the deleterious course of disease. Methods: Data of 17 patients with classical organic acidemias (11 propionic acidemia (PA), four methylmalonic acidemia (MMA) and two isovaleric acidemia (IVA) patients) were included. The clinical course was evaluated; metabolic decompensations and long-term complications were correlated with plasma FGF-21 levels. Cardiomyopathy, prolonged QT interval, renal failure, and optic neuropathy were defined as long-term complications. Results: Patients ages ranged from 16 months up to 32 years. Serious long-term complications occurred in eight patients (five PA and three MMA patients). In MMA and PA patients plasma FGF-21 levels during stable metabolic periods were significantly higher in patients with long-term complications (Mdn = 2556.0 pg/ml) compared to patients without (Mdn = 287.0 pg/ml). A median plasma FGF-21 level above 1500 pg/ml during a stable metabolic period, measured before the occurrence of long-term complications, had a positive predictive value of 0.83 and a negative predictive value of 1.00 on long-term complications in MMA and PA patients. Conclusion: This study demonstrates the potential role of FGF-21 as a biomarker for long-term complications in classical organic acidemias, attributed to mitochondrial dysfunction
Non-invasive versus ex vivo measurement of mitochondrial function in an endotoxemia model in rat: Toward monitoring of mitochondrial therapy
Mitochondrial function has been predominantly measured ex vivo. Due to isolation and preservation procedures ex vivo measurements might misrepresent in vivo mitochondrial conditions. Direct measurement of in vivo mitochondrial oxygen tension (mitoPO2) and oxygen disappearance rate (ODR) with the protoporphyrin IX‐triplet state lifetime technique (PpIX-TSLT) might increase our understanding of mitochondrial dysfunction in the pathophysiology of acute disease. LPS administration decreased mitochondrial respiration (ODR) in vivo but did not alter mitochondrial function as assessed with ex vivo techniques (high resolution respirometry and specific complex determinations). PpIX-TSLT measures in vivo mitoPO2 and ODR and can be applied non-invasively at the skin