Hepatic triacylglycerol lipase in circulating blood of normal and tumor-bearing mice and its hydrolysis of very-low-density lipoprotein and synthetic acylglycerols

1986 ◽  
Vol 879 (3) ◽  
pp. 339-344 ◽  
Author(s):  
Masuno Hiroshi ◽  
Okuda Hiromichi
Keyword(s):  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Very Low Density Lipoprotein ◽  
Low Density ◽  
Triacylglycerol Lipase ◽  
Tumor Bearing ◽  
Hepatic Triacylglycerol ◽  
Hydrolysis Of

scholarly journals The lipolysis/esterification cycle of hepatic triacylglycerol. Its role in the secretion of very-low-density lipoprotein and its response to hormones and sulphonylureas

1992 ◽  
Vol 284 (2) ◽  
pp. 457-462 ◽  
Author(s):  
D Wiggins ◽  
G F Gibbons
Keyword(s):  
Fatty Acids ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Very Low Density Lipoprotein ◽  
Low Density ◽  
Intracellular Pool ◽  
Hepatocyte Cultures ◽  
Vldl Secretion ◽  
Vldl Assembly ◽  
Hepatic Triacylglycerol

In hepatocyte cultures maintained in the absence of extracellular fatty acids, at least 70% of the secreted very-low-density lipoprotein (VLDL) triacylglycerol was derived via lipolysis of intracellular triacylglycerol. This proportion was unchanged when the cells were exposed for 24 h to insulin or glucagon, hormones which decreased the overall secretion of intracellular triacylglycerol, or to chloroquine or tolbutamide, agents which inhibit lysosomal lipolysis. The rate of intracellular lipolysis was 2-3-fold greater than that required to maintain the observed rate of triacylglycerol secretion. Most of the fatty acids released were returned to the intracellular pool. Neither insulin nor glucagon had any significant effect on the overall lipolysis and re-esterification of intracellular triacylglycerol. In these cases a greater proportion of the released fatty acids re-entered the cellular pool, rather than being recruited for VLDL assembly. Tolbutamide inhibited intracellular lipolysis, but suppressed VLDL secretion to a greater extent. 3,5-Dimethylpyrazole did not affect lipolysis or VLDL secretion. The increased secretion of VLDL triacylglycerol observed after exposure of cells to insulin for 3 days was not accompanied by an increased rate of intracellular lipolysis. However, a larger proportion of the triacylglycerol secreted under these conditions may not have undergone prior lipolysis.

scholarly journals Hepatic very-low-density lipoprotein and apolipoprotein B production are increased following in vivo induction of betaine–homocysteine S-methyltransferase

2006 ◽  
Vol 395 (2) ◽  
pp. 363-371 ◽  
Author(s):  
Janet D. Sparks ◽  
Heidi L. Collins ◽  
Doru V. Chirieac ◽  
Joanne Cianci ◽  
Jenny Jokinen ◽  
...  
Keyword(s):  
Apolipoprotein B ◽  
Serum Insulin ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Very Low Density Lipoprotein ◽  
Low Density ◽  
Mrna Levels ◽  
Apob Mrna ◽  
Hepatic Triacylglycerol

We have previously reported a positive correlation between the expression of BHMT (betaine–homocysteine S-methyltransferase) and ApoB (apolipoprotein B) in rat hepatoma McA (McArdle RH-7777) cells [Sowden, Collins, Smith, Garrow, Sparks and Sparks (1999) Biochem. J. 341, 639–645]. To examine whether a similar relationship occurs in vivo, hepatic BHMT expression was induced by feeding rats a Met (L-methionine)-restricted betaine-containing diet, and parameters of ApoB metabolism were evaluated. There were no generalized metabolic abnormalities associated with Met restriction for 7 days, as evidenced by control levels of serum glucose, ketones, alanine aminotransferase and L-homocysteine levels. Betaine plus the Met restriction resulted in lower serum insulin and non-esterified fatty acid levels. Betaine plus Met restriction induced hepatic BHMT 4-fold and ApoB mRNA 3-fold compared with Met restriction alone. No changes in percentage of edited ApoB mRNA were observed on the test diets. An increase in liver ApoB mRNA correlated with an 82% and 46% increase in ApoB and triacylglycerol production respectively using in vivo Triton WR 1339. Increased secretion of VLDL (very-low-density lipoprotein) with Met restriction plus betaine was associated with a 45% reduction in liver triacylglycerol compared with control. Nuclear run-off assays established that transcription of both bhmt and apob genes was also increased in Met-restricted plus betaine diets. No change in ApoB mRNA stability was detected in BHMT-transfected McA cells. Hepatic ApoB and BHMT mRNA levels were also increased by 1.8- and 3-fold respectively by betaine supplementation of Met-replete diets. Since dietary betaine increased ApoB mRNA, VLDL ApoB and triacylglycerol production and decreased hepatic triacylglycerol, results suggest that induction of apob transcription may provide a potential mechanism for mobilizing hepatic triacylglycerol by increasing ApoB available for VLDL assembly and secretion.

Sources of blood glycerol during fasting

2001 ◽  
Vol 281 (5) ◽  
pp. E998-E1004 ◽  
Author(s):  
Michael D. Jensen ◽  
Visvanathan Chandramouli ◽  
William C. Schumann ◽  
Karin Ekberg ◽  
Stephen F. Previs ◽  
...  
Keyword(s):  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Very Low Density Lipoprotein ◽  
Low Density ◽  
Free Glycerol ◽  
Isotopic Equilibrium ◽  
Significant Percentage ◽  
Adipose Tissue Triglyceride ◽  
Vldl Triglyceride ◽  
Hydrolysis Of

To determine the source(s) of blood and very low density lipoprotein (VLDL)-triglyceride glycerol during fasting, four men ingested 2H2O from 14 to 20 h into a 60-h fast to achieve ∼0.5% body water enrichment. At 60 h of fasting, glycerol flux was measured using [2-14C]glycerol. Blood was taken for measurement of2H enrichment at carbon 6 of glucose and at carbon 3 of free glycerol and VLDL-triglyceride glycerol. 2H enrichment of the 2 hydrogens bound to carbon 3 of VLDL-triglyceride glycerol was 105 ± 2% of the 2H enrichment of the 2 hydrogens bound to carbon 6 of glucose, indicating isotopic equilibrium between hepatic glyceraldehyde 3- P and glycerol 3- P. The2H enrichment of the 2 hydrogens bound to carbon 3 of free glycerol was 17 ± 3% of VLDL-triglyceride glycerol, indicating that a significant percentage of free glycerol in blood originated from the hydrolysis of circulating VLDL-triglyceride or a pool of glycerol with similar 2H enrichment. Glycerol flux was 6.3 ± 1.1 μmol · kg−1 · min−1. Glycerol appearing from nonadipose tissue sources was then ∼1.1 μmol · kg−1 · min−1. Seven other subjects were fasted for 12, 42, and 60 h. A small percentage of glycerol in the circulation after 12 h of fasting was enriched with 2H. The enrichment of the 2 hydrogens bound to carbon 3 of free glycerol in the longer periods of fasting was ∼16% of the enrichment of the 2 hydrogens bound to carbon 6 of glucose. Therefore, as much as 15–20% of systemic glycerol turnover during fasting is not from lipolysis of adipose tissue triglyceride.

scholarly journals Characterization of two triacylglycerol lipase activities in pig post-heparin plasma

1977 ◽  
Vol 163 (2) ◽  
pp. 347-355 ◽  
Author(s):  
C Ehnholm ◽  
A Bensadoun ◽  
W V Brown
Keyword(s):  
Lipase Activity ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Partial Purification ◽  
Very Low Density Lipoprotein ◽  
Low Density ◽  
Triacylglycerol Lipase ◽  
Heparin Plasma ◽  
Covalently Linked

Two triacylglycerol lipase activities were characterized after partial purification from pig post-heparin plasma. These two lipase activities were eluted sequentially with a NaCl gradient from columns containing Sepharose with covalently linked heparin. The first lipase activity, which was eluted at 0.75M-NaCl, was not inhibited at 28 degrees C in the presence of 1M-NaCl and was not further activated by plasma apolipoproteins. The absence of this lipase activity from post-heparin plasma from hepatectomized pigs indicates that the liver plays a role in the synthesis of this enzyme. A second lipase activity, which was eluted at 1.2M-NaCl, was inhibited when assayed in the presence of 1.0M-NaCl and was activated 14-fold by an apolipoprotein isolated from human very-low-density lipoprotein. The characteristics are identical with those of lipoprotein lipase purified from pig adipose tissue.

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