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1.
Liu JJ  Nilsson A  Duan RD 《Lipids》2002,37(5):469-474
Dietary sphingomyelin (SM) may have regulatory effects on cell proliferation and tumorigenesis in the colon. Alkaline sphingomyelinase (SMase) is the major enzyme responsible for hydrolysis of SM in the gut. Previously we purified the enzyme and showed that the presence of glycerophospholipids inhibited SM hydrolysis induced by alkaline SMase in vitro. In the present work, we studied the effects of TG, DG, FA, ceramide, and cholesterol on SM hydrolysis catalyzed by purified alkaline SMase. The results showed that both TG (triolein and tristearin) and DG (1,2-dioleoyl-sn-glycerol and 1,2-distearoyl-rac-glycerol) inhibited the activity of alkaline SMase. 1-Mono-oleoyl-rac-glycerol, 1-monostearoyl-rac-glycerol, stearic acid, oleic acid, linoleic acid, linolenic acid, and arachidonic acid stimulated the activity of alkaline SMase at 0.4–0.8 mM concentrations but inhibited the enzyme at higher concentrations. There was no difference between the effects induced by saturated and unsaturated FA. A short-chain FA such as lauric acid had a stronger stimulatory effect at low concentrations and weaker inhibitory effect at high concentrations than long-chain FA. Choosing linoleic acid as an example, we found that FA had similar effects on both alkaline SMase and neutral SMase. Cholesterol and ceramide when mixed with FA to increase its solubility in bile salt micelles inhibited SMase activity. In conclusion, glycerides, FA, ceramide, and cholesterol influence SM hydrolysis catalyzed by intestinal alkaline SMase. The presence of lipids in the diet may thus influence the course of SM digestion in the gut and thereby the exposure of colon to SM metabolites.  相似文献   

2.
Purpose: Alkaline sphingomyelinase (alk‐SMase) is an enzyme that hydrolyses sphingomyelin in a bile salt‐dependent manner in the gastrointestinal tract, and has been proposed as an inhibitor of colon carcinogenesis. Ursolic acid (UA) is a plant‐derived pentacyclic triterpenoid that has been shown to have anti‐proliferative and apoptotic effects on HT29 human colon adenocarcinoma cells, with activation of alk‐SMase as an early event. The aim of this study was to study the in vitro effects of UA and its analogues on the activity of purified rat intestinal alk‐SMase. Methods: Rat intestinal alk‐SMase activity was determined after incubation with UA in the presence and absence of taurocholate (TC). The effect was compared with boswellic acids, another group of pentacyclic triterpenoids. Results: UA enhanced the activity of rat intestinal alk‐SMase in a dose‐dependent manner, without a similar effect on bacterial neutral SMase. Four types of boswellic acid also increased the enzyme activity, with the effect of acetyl‐keto‐β‐boswellic acid being most potent. Activation of alk‐SMase by TC at a low concentration (0.4 mM), but not at a high concentration, was enhanced by UA. Conclusions: Ursolic acid and four types of boswellic acid, all pentacyclic triterpenoids, have a stimulatory effect on the activity of intestinal alk‐SMase.  相似文献   

3.
Ezetimibe inhibits cholesterol absorption in the intestine. Sphingomyelin has strong interactions with cholesterol. We investigated the effects of ezetimibe on Sphingomyelinase (SMase) expression in intestine and liver. After feeding rats with ezetimibe (5 mg/kg per day) for 14 days, acid SMase activities in the liver and in the proximal part of small intestine were reduced by 34 and 25%, respectively. Alkaline SMase (alk-SMase) was increased in the proximal part of the small intestine. Administration of lower doses of ezetimibe reduced acid SMase only in the liver by 14% (P < 0.05). In cell culture studies, ezetimibe decreased acid SMase activity in Hep G2 and Caco-2 cells dose-dependently. The reductions were more rapid for Hep G2 cells than for Caco-2 cells. Western blot showed that acid SMase protein was decreased in both Hep G2 and Caco-2 cells by 100 μM ezetimibe. The SM content was increased in Hep G2 cells but not Caco-2 cells, and total cholesterol content was increased in both cell lines 24 h after stimulation with 100 μM ezetimibe. Mevastatin, the inhibitor of cholesterol synthesis, induced a mild increase in acid SMase activity in Hep G2 cells but not Caco-2 cells. Following the reduction of acid SMase, ezetimibe at high dose slightly increased alk-SMase activity. In conclusion, the study demonstrates an inhibitory effect of ezetimibe on acid SMase activity and expression in both liver and intestine.  相似文献   

4.
Liza M  Chico Y  Fresnedo O  Ochoa B 《Lipids》2003,38(1):53-63
To address the role of cell membrane neutral sphingomyelinase (EC 3.1.4.12; SMase) in the regulation of cholesterol metabolism in the liver parenchymal cell, we examined the effect of exogenous neutral SMase on the metabolism of cholesteryl esters and the secretion of VLDL and biliary lipids in isolated rat hepatocytes. We show that treatment of hepatocytes with SMase (20 mU/mL) resulted in the intracellular buildup of cholesteryl esters, increased ACAT (EC 2.3.1.26) activity without affecting the ACAT2 mRNA level, and increased cytosolic and microsomal cholesteryl ester hydrolase (EC 3.1.1.13) activity. This was accompanied by increases in the secretion of biliary. bile acid, phospholipid, and cholesterol and in increased cholesterol 7α-hydroxylase (EC 1.14.13.17) activity and levels of mRNA, as well as decreased levels of apoB mRNA and a decreased secretion of VLDL apoB (apoB-48, ∼45%; apoB-100, ∼32%) and lipids (∼55%). Moreover, the VLDL particles secreted had an abnormal size and lipid composition; they were larger than controls, were relatively enriched in cholesteryl ester, and depleted in TG and cholesterol. Cell-permeable ceramides did not replicate any of the reported effects. These findings demonstrate that the increased cholesteryl ester turnover, oversecretion of biliary cholesterol and bile acids, and undersecretion of VLDL cholesterol and particles are concerted responses of the primary hepatocytes to exogenous neutral SMase brought about by regulation at several levels. We suggest that plasma membrane neutral SMase may have a specific, ceramide-independent effect in the regulation of cholesterol out-put pathways in hepatocytes.  相似文献   

5.
The regulation of neutral cholesterol ester hydrolase activity by changes in its phosphorylation state was studied in rat liver microsomes. Treatment with cAMP-dependent protein kinase resulted in increased enzyme activity, which was further enhanced by the addition of cAMP and MgATP. Consistent activations were also achieved with MgCl2 and MgATP, the magnesium effect being abolished by ethylenediaminetetraacetic acid and adenosine triphosphate. Cholesterol ester hydrolase was activated twofold by free calcium and Ca2+/calmodulin; this latter effect was blocked by the chelator ethyleneglycol-bis(β-aminoethyl ether)N,N,N′,N′-tetraacetic acid and the calmodulin antagonist trifluoperazine. The phosphatase inhibitors pyrophosphate and glycerophosphate led to marked and dose-dependent increases in esterase activity, whereas okadaic acid elicited no effect. Furthermore, pyrophosphate and okadaic acid did not change the increases in enzyme activity promoted by Ca2+, Ca2+/calmodulin, Mg2+ and MgATP. Cholesterol ester hydrolase was inactivated in a concentration-dependent manner by nonspecific alkaline phosphatases. In cAMP-dependent protein kinase/cAMP- or Ca2+/calmodulin-activated microsomes, a time-dependent loss of activation in cholesteryl oleate hydrolysis was caused by alkaline phosphatase. These findings suggest that microsomal cholesterol ester hydrolase is activated through cAMP and Ca2+/calmodulin phosphorylation, whereas enzyme deactivation is dependent on phosphatase action.  相似文献   

6.
The ontogeny of the rat lingual serous and mucous glands was explored by light and electron immune microscopy using the peroxidase-antiperoxidase and streptavidin-gold techniques. Tissues from fetal and neonatal rats from day 18 of gestation through 4 wk after birth were fixed and embedded in paraffin or Epon for light and transmission electron microscopy, respectively. Electron microscopy revealed that the only cells containing lingual lipase were the developing serous cells; secretory granules containing lingual lipase of varying degrees of maturity were seen. Mucous cells did not show immunospecific staining in rats of any age. The neonatal “mixed” lingual glands secrete lingual lipase from serous components immediately after birth to aid in fat digestion.  相似文献   

7.
Kathleen M. Botham 《Lipids》1991,26(11):901-906
An acid cholesteryl ester hydrolase activity associated with a fraction containing mitochondria and lysosomes from rat lactating mammary glands was found to have a pH optimum of 5.0. Its sedimentation pattern was closely related to that of the lysosomal enzyme markers acid phosphatase and β-glucuronidase, suggesting that the activity is associated with the lysosomes. The enzyme was strongly inhibited by Cu2+, but was inhibited little by other divalent metal ions. Acid cholesteryl ester hydrolase activity was almost completely abolished byp-hydroxymercuribenzoate, but this effect was reversed in the presence of an equimolar concentration of reduced glutathione (GSH), indicating that the enzyme requires free sulfhydryl groups for activity. These properties are similar to those of acid, lysosomal cholesteryl ester hydrolases found in other tissues. Acid cholesteryl ester hydrolase activity was 8–14 fold higher in mammary tissue from lactating as compared to virgin rats. Neutral cholesteryl ester hydrolase activities associated with the microsomal and cytosolic subcellular fractions were also increased in lactating glands, but to a lesser extent. In addition, a 2-fold increase in the activities of both the acid and microsomal neutral enzymes was seen during the first few days of lactation, while the cytosolic neutral activity remained constant. These results suggest that mammary gland cholesteryl ester hydrolases have a role in the regulation of cholesterol metabolism in mammary cells, and in the provision of cholesterol for secretion into milk.  相似文献   

8.
Ceramide 2-aminoethylphosphonate (CAEP), a sphingophosphonolipid containing a carbon–phosphorus bond, is frequently found in marine organisms and has a unique triene type of sphingoid base in its structure. CAEP has not been evaluated as a food ingredient, although it is generally contained in Mollusca organisms such as squids and shellfish, which are consumed worldwide. In this study, we aimed to elucidate the effects of CAEP as a food component by evaluating the digestion of CAEP extracted from the skin of the jumbo flying squid Dosidicus gigas. Our results revealed that dietary CAEP was digested to free sphingoid bases via ceramides by the mouse small intestinal mucosa. At pH 7.2, CAEP was hydrolyzed more rapidly than the major mammalian sphingolipid sphingomyelin; however, the hydrolysis of CAEP was similar to that of sphingomyelin at pH 9.0. Thus, the digestion of CAEP may be catalyzed by alkaline spingomyelinase and other enzymes. Our findings provide important insights into the digestion of the dietary sphingophosphonolipid CAEP in marine foods.  相似文献   

9.
J. H. Shand  D. W. West 《Lipids》1991,26(2):150-154
Cholesterol esterification by acyl-CoA:cholesterol acyltransferase (ACAT; EC 2.3.1.26) has been studied in microsomes isolated from the mammary glands of rats in late pregnancy, in early and mid-lactation, and following premature weaning. The mammary glands were freeze-clamped and the microsomes prepared in the presence of phosphatase inhibitors to preserve the phosphorylation status of the enzyme. Optimal conditions were established for the assay of enzyme activity in the presence of endogenous cholesterol. Supplementation of the microsomes with exogenous cholesterol as a dispersion in Triton WR-1339 was shown to lead to an increase in enzyme activity. Incubation of microsomes with MgATP led to an increase in ACAT activity which could be reversed by treatment of the microsomes with a phosphoprotein phosphatase preparation from rat liver. The results suggested that ACAT activity in the mammary gland was activated by phosphorylation in a similar way to that observed for the hepatic enzyme. The mammary glands from pregnant animals contained a higher level of ACAT activity than did the glands of the lactating animals and this correlated with the higher cholesteryl ester content of the pregnant glands. The highest level of ACAT activity was found in the weaned animals but the cholesteryl ester content of the microsomes was lower than expected. The influence of progesterone levels and changes in feeding patterns during gestation were considered as factors in these variations in ACAT activity.  相似文献   

10.
Morifuji  Masashi  Higashi  Seiichiro  Oba  Chisato  Ichikawa  Satomi  Kawahata  Keiko  Yamaji  Taketo  Itoh  Hiroyuki  Manabe  Yuki  Sugawara  Tatsuya 《Lipids》2015,50(10):987-996
Supplementation with sphingomyelin has been reported to have beneficial effects on disease prevention and health maintenance. However, compared with glycerolipids, intact sphingomyelin and ceramides are poorly absorbed. Therefore, if the bioavailability of dietary sphingomyelin is increased, then the dose administered can be reduced. This study was designed to identify molecular species of ceramide in rat lymph after the ingestion of milk sphingomyelin, and to compare the effect of purified sphingomyelin with milk phospholipids concentrate (MPL, 185 mg sphingomyelin/g) on lymphatic absorption of milk sphingomyelin. Lymph was collected hourly for 6 h from lymph‐cannulated rats (n = 8/group) after the administration of a control emulsion (triolein, bovine serum albumin, and sodium taurocholate), a sphingomyelin emulsion (control + purified sphingomyelin), or a MPL emulsion (control + MPL). Molecular species of ceramide in lymph were analyzed using high‐performance liquid chromatography‐tandem mass spectrometry (HPLC–MS/MS). Molecular species of ceramide, containing not only d18:1, but also d17:1 and d16:1 sphingosine with 16:0, 22:0, 23:0, and 24:0 fatty acids (specific to milk sphingomyelin), were increased in rat lymph after the administration of milk sphingomyelin. Their molecular species were similar to those of dietary milk sphingomyelin. Recovery of ceramide moieties from dietary sphingomyelin was 1.28‐ to 1.80‐fold significantly higher in the MPL group than in the sphingomyelin group. Our results demonstrated that dietary sphingomyelin from milk was transported to lymph as molecular species of ceramide hydrolyzed from milk sphingomyelin and co‐ingestion of sphingomyelin with glycerophospholipids enhanced the bioavailability of dietary sphingomyelin.  相似文献   

11.
Limited data are available on the serum levels of different sphingomyelin (CerPCho) and ceramide (CER) species in sickle‐cell disease (SCD). This study was aimed at identifying the levels of C16–C24 CerPCho and C16–C24 CER in serum obtained from SCD patients and controls. Circulating levels of neutral sphingomyelinase (N‐SMase) activity, ceramide‐1‐phosphate (C1P), and sphingosine‐1‐phosphate (S1P) were also determined. Blood was collected from 35 hemoglobin (Hb)A volunteers and 45 homozygous HbSS patients. Serum levels of C16–C24 CerPCho and C16–C24 CER were determined by an optimized multiple reaction monitoring (MRM) method using ultrafast liquid chromatography (UFLC) coupled with tandem mass spectrometry (MS/MS). Serum activity of N‐SMase was assayed by standard kit methods, and C1P and S1P levels were determined by enzyme‐linked immunosorbent assay. A significant decrease was observed in the serum levels of C18–C24 CerPCho in patients with SCD compared to controls. No significant difference was found in C16 CerPCho levels between the two groups. Very‐long‐chain C22–C24 CER were significantly decreased in SCD, while long‐chain C16–C20 CER levels showed no significant difference between SCD patients and controls. Significant positive correlation was found between the serum total cholesterol levels and C18–C24 CerPCho and C22–C24 CER in SCD patients. Patients with SCD had significantly elevated serum activity of N‐SMase as well as increased circulating levels of C1P and S1P compared to controls. The decrease in serum levels of C18–C24 CerPCho in patients with SCD was accompanied by decreased levels of C22–C24 CER. Future studies are needed to understand the role of decreased CerPCho and CER in the pathophysiology of SCD.  相似文献   

12.
Duan RD  Cheng Y  Yang L  Ohlsson L  Nilsson A 《Lipids》2001,36(8):807-812
A neutral ceramidase activity stimulated by bile salt was previously identified in the intestinal content. Recently, bile salt stimulated lipase (BSSL) was found to have ceramidase activity. It is unknown whether the ceramidase activity previously found is attributable to BSSL. To address this question, we compared the behaviors of high quaternary aminoethyl (HQ) anion exchange chromatography, the distributions, the stability, and the responses to lipase inhibitor between ceramidase and pancreatic BSSL. The proteins from whole small intestinal contents of humans and rats were precipitated by acetone and dissolved in 20 mM Tris buffer pH 8.2. These proteins had neutral ceramidase activity but not BSSL activity against p-nitrophenyl acetate. When the proteins were subject to HQ chromatography, two peaks of ceramidase activity were identified, which had acid and neutral pH optima, respectively. Neither of them had BSSL activity against p-nitrophenyl acetate. Western blot using BSSL antiserum failed to identify BSSL protein in the fractions, with high neutral ceramidase activity. In rat intestinal tract, pancreatic BSSL activity was high in the duodenum and declined rapidly in the small intestine, whereas neutral ceramidase activity was low in the duodenum and maintained a high level until the distal part of the small intestine. In addition, orlistat, the inhibitor of lipase, abolished human BSSL activity against p-nitrophenyl acetate and slightly reduced its activity against ceramide but had no inhibitory effect on ceramidase activity isolated by HQ chromatography. In conclusion, we provide the evidence for a specific ceramidase other than pancreatic BSSL present in the intestinal content. The enzyme may play important roles in digestion of dietary sphingolipids.  相似文献   

13.
A. J. Sinclair 《Lipids》1974,9(10):809-818
The fatty acid composition of triglycerides and phospholipids from rat liver was determined throughout the period of growth in the rat. Major changes in the triglyceride fatty acid composition were observed during the period studied. The triglycerides from fetal and newborn rats contained only a small percentage of polyunsaturated acids compared with suckling and weanling rats. During the suckling phase the liver triglycerides were rich in long chain polyunsaturated acids such as 20∶4, 20∶5, 22∶5, and 22∶6; once the pups were weaned, the percentage of these acids in the liver triglycerides fell. In these experiments, 18∶2 and 18∶3 were the only polyunsaturated acids in the maternal diet. However, the stomach contents of the suckling pups contained 18∶2 and 18∶3, as well as the long chain polyunsaturated acids. Radioactive 18∶3 and 22∶6 were fed to suckling pups, and the results suggested that the LCP in the rat liver triglycerides during the suckling period were derived from the long chain polyunsaturated acids in the dam's milk, rather than by synthesis from either 18∶2 or 18∶3 within the pups.  相似文献   

14.
Recent evidence pinpoints extracellular vesicles (EVs) as key players in intercellular communication. Given the importance of cholesterol and sphingomyelin in EV biology, and the relevance of mitochondria-associated endoplasmic reticulum membranes (MAMs) in cholesterol/sphingomyelin homeostasis, we evaluated if MAMs and sphingomyelinases (SMases) could participate in ethanol-induced EV release. EVs were isolated from the extracellular medium of BV2 microglia treated or not with ethanol (50 and 100 mM). Radioactive metabolic tracers combined with thin layer chromatography were used as quantitative methods to assay phospholipid transfer, SMase activity and cholesterol uptake/esterification. Inhibitors of SMase (desipramine and GW4869) and MAM (cyclosporin A) activities were also utilized. Our data show that ethanol increases the secretion and inflammatory molecule concentration of EVs. Ethanol also upregulates MAM activity and alters lipid metabolism by increasing cholesterol uptake, cholesterol esterification and SMase activity in microglia. Notably, the inhibition of either SMase or MAM activity prevented the ethanol-induced increase in EV secretion. Collectively, these results strongly support a lipid-driven mechanism, specifically via SMases and MAM, to explain the effect of ethanol on EV secretion in glial cells.  相似文献   

15.
C. G. Rogers 《Lipids》1974,9(8):541-547
Fatty acids and phospholipids of adult and newborn rat hearts and of cultured, neonatal rat heart cells were determined by gas liquid and thin layer chromatographies. In adult heart, the proportion of linoleic acid was higher and that of palmitic acid lower than in newborn hearts or in cultured cells. The relative amounts of linoleic and arachidonic acids in adult heart were affected by the source and amount of dietary fat. In heart cells, after 3 days in culture, the proportion of arachidonic acid resembled that in the newborn and adult rat hearts but showed a gradual and significant decline with age. The gradual shift in fatty acid composition as the cells aged in culture was attributed to outgrowth of mesenchymal cells (fibroblasts and endothelioid cells) characterized by a low relative proportion of arachidonic acid. The amounts of phospholipids in heart cells after 3 days in culture differed from those in the newborn or adult rat hearts. Phosphatidylethanolamine was highest in adult heart (34% of lipid phosphorus) and lowest in cells (26%); lecithin was higher in newborn heart (43%) than in adult heart (37%) or in cells (39%), while sphingomyelin was higher in cells (8%) than in newborn (5%) or adult heart (3%). Phospholipid levels in cultured heart cells were unrelated to those of serum in the growth medium. The absence of a significant change in phospholipid composition after continued incubation of the heart cell cultures for periods up to 3 weeks reflected the major structural role of these lipid components in cell membranes.  相似文献   

16.
Compared with triacylglycerol (TAG), dietary 1,3‐diacylglycerol (1,3‐DAG) is associated with reduced serum lipid and glucose levels. We investigated the metabolism of 1,3‐DAG by assaying its intermediate metabolites during digestion and absorption in the rat small intestine. After gavage with TAG emulsion, TAG was digested mainly to 2‐monoacylglycerol (2‐MAG) and unesterified fatty acid (FFA) in the rat small intestinal lumen. 2‐MAG was directly absorbed into the small intestinal epithelial cells and esterified to 1,2(2,3)‐DAG, and further esterified to TAG. After gavage with 1,3‐DAG emulsion, 1,3‐DAG was digested mainly to 1(3)‐MAG and FFA in the rat small intestinal lumen with subsequent significant increase of 1‐MAG and 1,3‐DAG concentrations in small intestinal mucosal epithelial cells, and the 2‐MAG, 1,2(2,3)‐DAG, and TAG concentrations in mucosal epithelial cells were not significantly different after 1,3‐DAG than after TAG gavage, suggesting that the metabolic pathway of 1,3‐DAG is different from that of TAG. In intestinal mucosal epithelial cells, we further assayed enzyme levels and gene expression of proteins in the phosphatidic acid (PtdOH) pathway. The glycerol kinase, phosphatidate phosphatase, and diacylglycerol acyltransferase‐2 expression and the relative expression of mRNA of enzymes were significantly increased in the 1,3‐DAG group compared with the TAG group, suggesting that TAG synthesis from dietary 1,3‐DAG was mainly via PtdOH pathways, which may partially account for the effect of dietary DAG on postprandial serum TAG.  相似文献   

17.
The biochemical composition of the renal medulla and the blood pressures of pregnant rats and nonpregnant controls were compared on days 15, 18, 20, and 22 of pregnancy. Deoxyribonucleic acid and protein content of the renal medulla changed together with the tissue weight (wet weight) during gestation except on day 20 when a slight increase in protein was observed. However, the glycerophospholipids (phosphatidyl ethanolamine, phosphatidyl choline, and phosphatidyl serine) and sphingomyelin showed significant increases throughout the latter stages of pregnancy with the maxima in most cases occurring on day 20 of the gestation period. Medullary hypertrophy and increased lipid content per cell coexist with the decrease in blood pressure and may indicate peak activity in production of antihypertensive renal lipids. Authorized for publication on 3/17/76 as paper No. 5040 in journal series of Pa. Ag. Exp. Station. Submitted to the Graduate School of The Pennsylvania State University in partial fulfillment of the requirements for the Ph.D.  相似文献   

18.
The influence of long duration rapeseed oil feeding with high or low levels of erucic acid has been investigated on rat heart phospholipids. The rats treated for 20 wk with rapeseed oil containing 46.2% erucic acid showed a twofold increase in the sphingomyelin content of the heart. Treatment with primor rapeseed oil (3.7% erucic acid) for 20 wk did not modify phospholipid composition of rat heart. The fatty acid patterns of phosphatidylethanolamine and phosphatidylcholine were slightly influenced by the high erucic rapeseed oil; eicosenoic acid was incorporated preferentially into position one, but erucic acid showed a random distribution in both. After high erucic rapeseed oil feeding, 22∶1 was incorporated into cardiolipin (5.6%) and sphingomyelin (10.5%). The incorporation of 22∶1 into sphingomyelin was associated with an increase of the percentage of 24∶1 (14.6%) and a decrease of saturated long chain fatty acid (22∶0, 24∶0) percentages. Primor rapeseed oil caused a slight increase of 24∶1 and a decrease of 22∶0 and 24∶0 in rat heart sphingomyelin. As cardiolipin is localized in the inner membrane of mitochondria and sphingomyelin in plasma and microsomal membranes, the acyl-moiety alterations of both phospholipids might be correlated to the pathological lesions of rat heart after a long duration of rapeseed oil feeding.  相似文献   

19.
Sphingomyelin (SM) has emerged as an important source of lipid messengers affecting cell proliferation, differentiation and apoptosis. SM is present in mammalian cell membranes as a lipid constituent and also found as a component of dietary products such as milk, egg and meat. Digestion of SM has been found to have important implications in colon cancer development, gut maturation, and cholesterol absorption. SM in the intestine is sequentially digested by alkaline sphingomyelinase and neutral ceramidase before absorption. In the last decade, rapid progress has been made in many aspects of these two enzymes. The review intends to provide a short summary of the current knowledge on the properties, functions and the pathological changes of the enzymes in the intestinal tract.  相似文献   

20.
The association between increased serum alkaline phosphatase activity and increased hepatic microsomal-enzyme activity in the beagle has been investigated. Low doses of a combination of ethanol (633 μl/kg/day), propylene glycol (672 μl/kg/day) and chloroform (30 μl/kg/day) raised alkaline phosphatase activities in both serum and liver without concurrently increasing three microsomal enzymes (amidopyrine N-demethylase, p-nitroanisole O-demethylase and benzo[a]pyrene hydroxylase). Studies with enzyme inhibitors suggested that the increases in hepatic and serum alkaline-phosphatase levels were predominantly due to enzyme of the hepatic type.  相似文献   

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