Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.1.1.34 (lipoprotein lipase)
7,025 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Intestinal apolipoproteins play a major role in lipoprotein metabolism. Apolipoproteins (Apo) AI, AIV and B48 are synthesized with chylomicrons in the mucosa and secreted into intestinal lymph. Apo B48 and B100 are coded for by the same gene on chromosome 2 and are identical in their aminoterminus. While apo B100 mRNA can be translated to the 4536 amino acid protein, the apo B48 mRNA is edited to contain a stopcodon at amino acid 2152. Apo B48 seems to be important for the secretion of chylomicrons and stays with chylomicrons during their lipolysis in plasma. Hydrolysis only takes place after the particle has acquired apo CII, the obligate cofactor for the enzyme lipoprotein lipase. The ligand for final irreversible uptake into the liver, mediated by a putative chylomicron-remnant receptor, seems to be apo E which only associates during lipolysis in plasma. Although apo E is not synthesized to a significant extent in the gut it was reported to influence intestinal cholesterol absorption: carriers of the genetic apo E2 isoform seem to absorb cholesterol to a lesser extent than those with apo E4 as compared to apo E3. Despite the almost exclusive synthesis of apo AIV and the significant extent of apo AI synthesis in the human gut these two apoproteins do not seem to have a chylomicron specific function. They seem to be more involved in the "reversed cholesterol transport", believed to be antiatherogenic. After entering the plasma compartment apo AI and AIV leave the chylomicrons during lipolysis as "surface remnants" to become high density- (HDL)-and apo AIV containing lipoproteins.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:[Intestinal apolipoprotein metabolism]. 208 69

Hyperlipidemia is common in patients with glomerular proteinuria. It may contribute to atherosclerotic complications and accelerate glomerular damage. Early trials of the fibric acid derivative clofibrate led to a myositis syndrome causing many nephrologists to abandon attempts at treatment of nephrotic hyperlipidemia. Recent trials with lipid-lowering medications have been successful without major side effects. The bile acid sequestrants colestipol and cholestyramine bind bile acids in the gut and deplete the hepatic cholesterol pool, thus inducing LDL hepatocyte receptors. Recent studies showed a reduction of total cholesterol of 8-20% and LDL cholesterol of 19-31% without significant changes in HDL cholesterol. Probucol has reduced total cholesterol 23-30% and LDL cholesterol 23-25% in nephrotic patients. Although HDL cholesterol was reduced, the LDL/HDL ratio remains favorably changed. The fibric acid derivative gemfibrozil inhibits adipose lipolysis and enhances lipoprotein lipase activity thus decreasing LDL synthesis and increasing its removal. It caused a large decrease in triglycerides with a 13-15% decrease in total and LDL cholesterol in a recent trial. HDL cholesterol increased 18%. The HMG-CoA reductase inhibitors inhibit the rate-limiting step in cholesterol biosynthesis hence inducing an increase in LDL receptors on hepatocytes. Trials have shown decreases of 18-36% in total cholesterol and 18-47% in LDL cholesterol, while HDL cholesterol was either increased or unchanged. The use of lipid-lowering agents of several classes has been effective in ameliorating the progression of glomerular damage in a number of different models of glomerulosclerosis. Nevertheless, so far in humans lipid lowering drugs have not been established to have an effect on either the degree of proteinuria or the progression of glomerulosclerosis.
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PMID:Lipid-lowering agents in proteinuric diseases. 225 70

Long chain n-3 fatty acids present in fish oils have been shown to reduce fasting plasma triglyceride and very low density lipoprotein levels in normal and hyperlipidemic human subjects. The present studies were designed to examine whether dietary n-3 fatty acids influence chylomicron formation and metabolism in healthy volunteers. In the first study seven subjects were fed either saturated fat, vegetable oil, or fish oil-based diets for 4 weeks each, and test meals containing 50 g of the background fat were administered after the second week of each diet. The postprandial rise in triglyceride levels was significantly lower following the fish oil test meal as compared to the saturated fat or vegetable oil test meals. In the second study, six subjects eating their usual home diets were given two fat tolerance tests. The first contained saturated fat and the second, given 1 week later, contained fish oil. There was no difference in the postprandial triglyceride response between the fish oil and the saturated fat meals. A third study was then conducted with eight volunteers in which saturated fat and fish oil test meals were administered during saturated fat and fish oil background diets in a crossover design. The presence of fish oil in the background diet reduced postprandial lipemia regardless of the type of fat in the test meal. Although there was no effect of the fish oil diet on the lipoprotein lipase and hepatic lipase activity of postheparin plasma measured in vitro, stimulation of in vivo lipolysis was not ruled out. Our results suggest that chronic (but not acute) intake of fish oil may inhibit the synthesis or secretion of chylomicrons from the gut. However, accelerated clearance due to decreased VLDL competition cannot be excluded.
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PMID:Reduction of postprandial triglyceridemia in humans by dietary n-3 fatty acids. 324 Nov 21

On the basis of bibliographic references and new own data, major adaptations of lipid metabolism occurring at late gestation are reviewed. Maternal hypertriglyceridemia at late gestation results from the juxtaposition of several factors: enhanced adipose tissue lipolysis facilitating the availability to the liver of substrates for triglyceride synthesis and contributing to augmented flux of very low density lipoproteins (VLDL) into the circulation; maternal hyperphagia and unmodified gut lipid absorption increasing chylomicron formation from dietary lipid; reduced lipoprotein lipase (LPL) activity in extrahepatic tissues (especially adipose tissue) which does not allow a triglyceride removal proportional to their enhanced production. It is proposed that these changes are also responsible for the altered composition of VLDL in late pregnancy. In conditions of food deprivation the use of glycerol released from adipose tissue as preferential gluconeogenic substrate, and the enhanced maternal ketogenesis warrants the availability of fuels for the fetus. Just prior to parturition the increase in mammary gland LPL activity is responsible for the reduction in circulating triglycerides and prepares the mother for lactation.
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PMID:Lipid metabolism in pregnancy. 355 60

Mechanisms for hypercholesterolemia and hypertriglyceridemia and the effects of KCD-232, a new hypolipidemic agent, on them were studied in male Wistar rats with daunorubicin (DR)-induced nephrosis. Single intravenous injection of DR dose-dependently increased urinary protein loss and serum lipid levels (0,3,6 and 12 mg/kg). Twenty-four days after the injection of DR (6 mg/kg), serum cholesterol (Ch) and triglyceride (TG) levels markedly increased and free fatty acid level tended to decrease with no effects on liver lipid levels. Hepatic Ch synthesis from [14C]acetate in vitro increased by 2.1-fold, while exogenous Ch absorption slightly decreased. The clearance of intravenously injected [3H]Ch from the circulation was delayed. Hepatic fatty acid (FA) synthesis also increased by 2.7-fold, and hepatic TG lipase activity tended to decrease. KCD-232 improved the hypercholesterolemia and hypertriglyceridemia of DR-treated rats. The drug inhibited the elevated hepatic Ch synthesis and exogenous Ch absorption and thus improved the delayed Ch clearance from the circulation. KCD-232 markedly inhibited the elevated hepatic FA synthesis and stimulated both hepatic FA oxidation and lipoprotein lipase activity from the epididymal adipose tissue of the nephrotic rats. These results suggest that 1. DR-induced hypercholesterolemia is due to both an increased Ch synthesis in the liver and delayed clearance of Ch from the circulation; 2. DR-induced hypertriglyceridemia is caused by both an increased hepatic FA synthesis and depressed TG hydrolysis in the circulation; 3. KCD-232 improves the hypercholesterolemia by inhibiting the elevated Ch synthesis and Ch absorption from the gut; and 4. KCD-232 improves the hypertriglyceridemia by inhibiting the elevated hepatic FA synthesis and by stimulating both hepatic FA oxidation and TG hydrolysis activity in the circulation.
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PMID:[Experimental nephrotic hyperlipidemia induced in rats by daunorubicin and effects of KCD-232[4-(4'-chlorobenzyloxy)benzyl nicotinate] on lipid metabolism]. 402 7

The identity of the enzymes responsible for lipase and cholesterol esterase activities in the small intestinal mucosa is not known. Because hormone-sensitive lipase (HSL) catalyzes the hydrolysis of acylglycerols and cholesteryl esters, we sought to determine whether HSL could be involved. HSL mRNA and protein were detected in all segments of the small intestine by Northern and Western blot analyses, respectively. Immunocytochemistry experiments revealed that HSL was expressed in the differentiated enterocytes of the villi and was absent in the undifferentiated cells of the crypt. Diacylglycerol lipase and cholesterol esterase activities were found in the different segments. Analysis of gut from HSL-null mice showed that diacylglycerol lipase activity was unchanged in the duodenum and reduced in jejunum. Neutral cholesterol esterase activity was totally abolished in duodenum, jejunum, and ileum of HSL-null mice. Analysis of HSL mRNA structure showed two types of transcripts expressed in equal amounts with alternative 5'-ends transcribed from two exons. This work demonstrates that HSL is expressed in the mucosa of the small intestine. The results also reveal that the enzyme participates in acylglycerol hydrolysis in jejunal enterocytes and cholesteryl ester hydrolysis throughout the small intestine.
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PMID:Hormone-sensitive lipase is a cholesterol esterase of the intestinal mucosa. 1248 47

New therapeutic targets for noncognitive reductions in energy intake, absorption, or storage are crucial given the worldwide epidemic of obesity. The gut microbial community (microbiota) is essential for processing dietary polysaccharides. We found that conventionalization of adult germ-free (GF) C57BL/6 mice with a normal microbiota harvested from the distal intestine (cecum) of conventionally raised animals produces a 60% increase in body fat content and insulin resistance within 14 days despite reduced food intake. Studies of GF and conventionalized mice revealed that the microbiota promotes absorption of monosaccharides from the gut lumen, with resulting induction of de novo hepatic lipogenesis. Fasting-induced adipocyte factor (Fiaf), a member of the angiopoietin-like family of proteins, is selectively suppressed in the intestinal epithelium of normal mice by conventionalization. Analysis of GF and conventionalized, normal and Fiaf knockout mice established that Fiaf is a circulating lipoprotein lipase inhibitor and that its suppression is essential for the microbiota-induced deposition of triglycerides in adipocytes. Studies of Rag1-/- animals indicate that these host responses do not require mature lymphocytes. Our findings suggest that the gut microbiota is an important environmental factor that affects energy harvest from the diet and energy storage in the host. Data deposition: The sequences reported in this paper have been deposited in the GenBank database (accession nos. AY 667702--AY 668946).
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PMID:The gut microbiota as an environmental factor that regulates fat storage. 1550 15

Dietary sphingomyelin (SM) is hydrolyzed by intestinal alkaline sphingomyelinase and neutral ceramidase to sphingosine, which is absorbed and converted to palmitic acid and acylated into chylomicron triglycerides (TGs). SM digestion is slow and is affected by luminal factors such as bile salt, cholesterol, and other lipids. In the gut, SM and its metabolites may influence TG hydrolysis, cholesterol absorption, lipoprotein formation, and mucosal growth. SM accounts for approximately 20% of the phospholipids in human plasma lipoproteins, of which two-thirds are in LDL and VLDL. It is secreted in chylomicrons and VLDL and transferred into HDL via the ABCA1 transporter. Plasma SM increases after periods of large lipid loads, during suckling, and in type II hypercholesterolemia, cholesterol-fed animals, and apolipoprotein E-deficient mice. SM is thus an important amphiphilic component when plasma lipoprotein pools expand in response to large lipid loads or metabolic abnormalities. It inhibits lipoprotein lipase and LCAT as well as the interaction of lipoproteins with receptors and counteracts LDL oxidation. The turnover of plasma SM is greater than can be accounted for by the turnover of LDL and HDL particles. Some SM must be degraded via receptor-mediated catabolism of chylomicron and VLDL remnants and by scavenger receptor class B type I receptor-mediated transfer into cells.
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PMID:Absorption and lipoprotein transport of sphingomyelin. 1625 22

Studies of germ-free and conventional mice revealed that the intestinal bacterial population of the latter contributed to the provision of calories to the host by hydrolysis of indigestible plant polysaccharides to absorbable monosaccharides. The gut microbiota at the same time caused the suppression of a circulating inhibitor of lipoprotein lipase, resulting in increased lipoprotein lipase activity and thus fat deposition. Both of these effects bring about a significantly increased body fat deposition in conventional mice compared with germ-free mice. Therefore, the intestinal microbiota, living in mutual beneficial symbiosis with the host organism, is an important regulator of energy uptake and storage.
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PMID:Gut microbiota: a factor in energy regulation. 1649 70

The trillions of microbes that colonize our adult intestines function collectively as a metabolic organ that communicates with, and complements, our own human metabolic apparatus. Given the worldwide epidemic in obesity, there is interest in how interactions between human and microbial metabolomes may affect our energy balance. Here we report that, in contrast to mice with a gut microbiota, germ-free (GF) animals are protected against the obesity that develops after consuming a Western-style, high-fat, sugar-rich diet. Their persistently lean phenotype is associated with increased skeletal muscle and liver levels of phosphorylated AMP-activated protein kinase (AMPK) and its downstream targets involved in fatty acid oxidation (acetylCoA carboxylase; carnitine-palmitoyltransferase). Moreover, GF knockout mice lacking fasting-induced adipose factor (Fiaf), a circulating lipoprotein lipase inhibitor whose expression is normally selectively suppressed in the gut epithelium by the microbiota, are not protected from diet-induced obesity. Although GF Fiaf-/- animals exhibit similar levels of phosphorylated AMPK as their wild-type littermates in liver and gastrocnemius muscle, they have reduced expression of genes encoding the peroxisomal proliferator-activated receptor coactivator (Pgc-1alpha) and enzymes involved in fatty acid oxidation. Thus, GF animals are protected from diet-induced obesity by two complementary but independent mechanisms that result in increased fatty acid metabolism: (i) elevated levels of Fiaf, which induces Pgc-1alpha; and (ii) increased AMPK activity. Together, these findings support the notion that the gut microbiota can influence both sides of the energy balance equation, and underscore the importance of considering our metabolome in a supraorganismal context.
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PMID:Mechanisms underlying the resistance to diet-induced obesity in germ-free mice. 1721 Sep 19


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