Fat digestion by lingual lipase: mechanism of lipolysis in the stomach and upper small intestine

Ten to 30% of dietary fat is hydrolyzed in the stomach by lingual lipase, an enzyme secreted from lingual serous glands. We investigated the substrate specificity of this enzyme as well as the potential of lingual lipase to act in the upper small intestine i.e., in the presence of bile salts and lecithin. The data presented show that partially purified preparations of rat lingual lipase and the lipase in gastric aspirates of newborn infants have identical substrate specificity: medium-chain triglycerides were hydrolyzed at rates 5-8-fold higher than long-chain triglycerides; the rat and human enzymes do not hydrolyze the ester bond of lecithin or cholesteryl-ester. In contrast to pancreatic lipase, the hydrolysis of triglycerides by lingual lipase is not inhibited by lecithin. But, similar to pancreatic lipase the activity of lingual lipase is inhibited by bile salts, the extent of inhibition varying with its nature and concentration. This inactivation is not prevented by colipase but is partially averted by lipids and protein, suggesting that lingual lipase can remain active in the duodenum. The pH optimum of the enzyme (2.2-6.5 in the rat and 3.5-6.0 in human gastric aspirates) is compatible with continued activity in the upper small intestine, especially during the neonatal period, when the luminal pH is under 6.5. The marked variation in lipase activity levels in gastric aspirates of newborn infants is probably due to individual variations in enzyme amounts. The characteristics of the lipase are however identical in infants with low, intermediate or high activity levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Chronic donepezil treatment is associated with slowed cognitive decline in Alzheimer's disease

OBJECTIVE

To compare rates of cognitive decline between probable Alzheimer's disease (AD) patients treated with long-duration cholinesterase inhibitors (ChE-Is) and those who remained untreated.

BACKGROUND

ChE-Is, including donepezil and tracrine, have shown beneficial effects on cognition and global functioning in patients with AD. The duration of these benefits is unknown because the longest double-blind placebo-controlled studies reported were only approximately 6 months long. Ethical concerns regarding randomization of patients to placebo for long periods make it difficult to undertake trials of longer duration.

METHODS

We identified patients in 4 AD centers who were or were not consistently treated with ChE-Is and who had demographic, psychometric and follow-up data. We compared 205 ChE-I-treated and 218 untreated AD patients on baseline variables hypothesized to differ between these groups, on baseline Mini Mental Status Examination (MMSE) scores and on rates of MMSE change at 1 year. The analysis was performed initially with all ChE-I-treated patients as a single group versus untreated subjects, and then with donepezil versus untreated subjects and tacrine versus untreated subjects.

RESULTS

As expected, treated and untreated patients differed with respect to age, education, ethnicity, percentage of community dwelling and exact days of follow-up (ANOVA and chi2) in several comparisons, but did not differ on baseline MMSE score. These baseline variables were highly intercorrelated. MMSE scores declined significantly more slowly after 1 year of ChE-I treatment compared to untreated patients (p = 0.05) after controlling for baseline differences in age, education, ethnicity and percentage of community dwelling. Slowing of decline was significant in the donepezil-treated patients (p = 0.007) but not in the tacrine-treated group (p = 0.33).

CONCLUSIONS

This study, utilizing concurrent, nonrandomized controls, suggests that donepezil continues to have efficacy over at least the first year of therapy. Other studies are needed to determine whether the benefits are maintained beyond 1 year.

Vitamin D: a novel therapeutic approach for keloid, an in vitro analysis

BACKGROUND

Vitamin D and its metabolites play an important role in calcium homeostasis, bone remodelling, hormone secretion, cell proliferation and differentiation. Recent studies also suggest a beneficial role of vitamin D in slowing the progression of tissue fibrosis. However, their effects on dermal fibrosis and keloids are unknown. Objectives  To investigate the effect of 1,25-dihydroxyvitamin D3 (1,25D) in the pathogenesis of tissue fibrosis by keloid fibroblasts (KFs).

METHODS

KFs were cultured and exposed to different concentrations of 1,25D in the presence or absence of transforming growth factor (TGF)-β1. KF phenotypes and protein production were analysed by real-time reverse transcriptase-polymerase chain reaction, Western blot, immunofluorescence and multiplex enzyme-linked immunosorbent assay techniques. Collagen synthesis was evaluated by measuring (3) H-proline incorporation. The effect of 1,25D on cell proliferation and viability was evaluated by Formazan assay, proliferating cell nuclear antigen expression and the colorimetric conversion of 3-[4, 5-dimethylthiazol-2-yl]-2, 5-diphenyltetrazolium bromide.

RESULTS

We confirmed the presence of vitamin D receptors (VDRs) in cultured keloid fibroblasts. Fibroblasts transfected with a vitamin D response element reporter construct and exposed to the active vitamin D metabolite 1,25D showed increased promoter activity indicating VDR functionality in these cells. Incubation of KFs with 1,25D suppressed TGF-β1-induced collagen type I, fibronectin and α-smooth muscle actin expression. 1,25D also modulated plasminogen activator inhibitor-1 and matrix metalloproteinase-9 expression induced by TGF-β1. Interestingly, 1,25D induced hepatocyte growth factor mRNA expression and protein secretion in keloid fibroblasts.

CONCLUSIONS

This study highlights key mechanistic pathways through which vitamin D decreases fibrosis, and provides a rationale for studies to test vitamin D supplementation as a preventive and/or early treatment strategy for keloid and related fibrotic disorders.

Hydrolysis of triacylglycerol emulsions by lingual lipase. A microscopic study

The effect of lingual lipase on four different triacylglycerol emulsions was observed by light microscopy at pH 5-6. The extent of hydrolysis on the microscope slide was determined with the aid of radioactive emulsions or by analyzing the products by gas-liquid chromatography. Artificial emulsions that had been stabilized with amphiphilic lipids gradually coalesced during the unstirred lipase reactions. Gum arabic-stabilized emulsions and human milk fat droplets did not stick to each other or coalesce during lingual lipase hydrolysis. No visible liquid-crystalline product phases, as are seen with pancreatic lipase (Patton, J.S. and Carey, M.C. (1979) Science 204, 145-148), were observed with lingual lipase. The products of lingual lipase activity, protonated fatty acid and diacylglycerol, appear to remain dissolved in the oil phase of the triacylglycerol particle.

The lipolytic triad: human lingual, breast milk, and pancreatic lipases: physiological implications of their characteristics in digestion of dietary fats

The characteristics of human lingual, breast milk, and pancreatic lipases as related to the digestion of dietary fats in infants are discussed. The activity and specificity of these enzymes and structure of the dietary fats largely determine the rates of lipolysis, the types of digestion products formed, and the rates of absorption. Also possibly influenced are micelle formation, intestinal health, breast milk jaundice, and the absorption of other nutrients. In premature infants, the action of lingual and breast milk lipase are particularly important in the absorption of dietary fatty acids.

A novel regulatory function for miR-29a in keloid fibrogenesis

BACKGROUND

A growing body of evidence has shown that microRNA-29 (miR-29) plays a central role in the progression of fibrosis. However, the mechanisms underlying the role of miR-29 in keloid fibrogenesis remain unknown.

AIM

To investigate the roles of miR-29 in dermal fibroblasts in the pathogenesis of keloids.

METHODS

Primary fibroblasts from 9 patients with keloid and 6 healthy controls (HCs) were cultured and pretreated with transforming growth factor (TGF)-β1. Next, fibroblasts were transfected with precursor miRNA and anti-miR-29a miRNA. TGF-β1-associated miR-29 alterations were investigated by quantitative real-time PCR. Collagen I and collagen III protein levels were analysed by western blotting.

RESULTS

miR-29a, miR-29b and miR-29c levels were significantly lower in keloid compared with healthy fibroblasts (P < 0.05), and in particular, miR-29a was especially markedly reduced (P < 0.001). Type I and type III collagen mRNA and protein levels were decreased in keloid fibroblasts transfected with pre-miR-29a (P < 0.05), whereas knockdown with anti-miR-29a increased type I and type III collagen mRNA and protein expression (P < 0.05) in the fibroblasts. Interestingly, pretreatment of fibroblasts with TGF-β1 significantly decreased miR-29a (P < 0.05), whereas miR-29b and miR-29c were reduced to a lesser extent, which was not significant.

CONCLUSIONS

These findings show that miR-29a exerts as a novel regulator in the fibrogenesis of keloid, suggesting that miR-29a might be a novel marker for keloid.

Porcine spleen deoxyribonuclease II. Covalent structure, cDNA sequence, molecular cloning, and gene expression

Porcine spleen DNase II, a lysosomal acid hydrolase, is a noncovalently linked alpha.beta heterodimer (Liao, T.-H. (1985) J. Biol. Chem. 260, 10708-10713). The alpha subunit, after disulfide cleavage, yields two chains, alpha1 and alpha2. The complete amino acid sequences of the alpha1, beta, and alpha2 chains were elucidated by protein sequencing, and the pairings of one interchain disulfide between alpha1 and alpha2 and of three intrachain disulfides in alpha2 were assigned. Six carbohydrate attachment sites, two in beta and four in alpha2, were detected by sugar analyses. The cDNA of DNase II was amplified using primers synthesized on the basis of the amino acid sequences determined. The amplified fragments shown to be a cDNA sequence of 1,292 bases. This cDNA sequence has an open reading frame encoding a 364-amino acid polypeptide containing a putative transmembrane peptide at the NH2-end, two small connecting peptides in the middle, and a peptide at the COOH terminus. These are evidently removed to form mature DNase II. Thus, all three chains in the sequence alpha1, beta, and alpha2 are coded by the same cDNA. When Chinese hamster ovary cells were transfected with a cloned plasmid with an inserted cDNA fragment encoding the entire reading frame, the expressed protein was released into the growth medium as an active form of DNase II.

Effects of leptin deficiency and short-term repletion on hepatic gene expression in genetically obese mice

By supplying most organs of the body with metabolic substrates, the liver plays a central role in maintaining energy balance. Hepatic metabolism of glucose, fatty acids, and lipoproteins is disrupted in the leptin-deficient obese (Lep(ob)/Lep(ob)) mouse, leading to hyperglycemia, steatosis, and hypercholesterolemia. Microarray expression profiles were used to identify transcriptional perturbations that underlie the altered hepatic physiology of Lep(ob)/Lep(ob) mice. A wide variety of genes involved in fatty acid metabolism are altered in expression, which suggests that both fatty acid synthesis and oxidation programs are activated in obese mice. The expression of a small subset of genes is upregulated by leptin deficiency, not modulated by caloric restriction, and markedly suppressed by short-term leptin treatment. Among these leptin-regulated genes, apolipoprotein A-IV is a strong candidate for mediating the atherogenic-resistant phenotype of Lep(ob)/Lep(ob) mice.

Deoxyribonuclease II purified from the isolated lysosomes of porcine spleen and from porcine liver homogenates. Comparison with deoxyribonuclease II purified from porcine spleen homogenates

Porcine spleen DNase II (EC 3.1.22.1), one of the best-characterized DNases II, is subcellularly located in lysosomes because the enzyme is co-sedimented with two of the lysosomal marker enzymes, cathepsin D and acid phosphatase. The physicochemical properties, including the subunit structure, sensitivity to iodoacetate inactivation, native molecular weight and chromatographic behavior, of the DNase II purified from the isolated lysosomes of porcine spleen are indistinguishable from those of the same enzyme purified from the whole porcine spleen homogenate. DNase II can also be extracted from porcine liver with 0.05 M H2SO4 or 0.1 M NaCl and purified from either extract by a series of column chromatographies. The purified liver DNase II from either extract has the same subunit structure (alpha-chain, Mr 35,000 and beta-chain, Mr 10,000) as the purified DNase II of porcine spleen. The two liver extracts as well as the extracts of spleen and gastric mucosa contain DNase II with very similar properties on Sephadex G-100 gel filtration, on acid polyacrylamide gel electrophoresis under non-denaturing conditions, and on isoelectric focusing. The data strongly suggest that, for the same species of animal, the DNase II activities in various tissues are associated with protein molecules of identical structure.

T cell-tumor interaction directs the development of immunotherapies in head and neck cancer

The competent immune system controls disease effectively due to induction, function, and regulation of effector lymphocytes. Immunosurveillance is exerted mostly by cytotoxic T-lymphocytes (CTLs) while specific immune suppression is associated with tumor malignancy and progression. In squamous cell carcinoma of the head and neck, the presence, activity, but also suppression of tumor-specific CTL have been demonstrated. Functional CTL may exert a selection pressure on the tumor cells that consecutively escape by a combination of molecular and cellular evasion mechanisms. Certain of these mechanisms target antitumor effector cells directly or indirectly by affecting cells that regulate CTL function. This results in the dysfunction or apoptosis of lymphocytes and dysregulated lymphocyte homeostasis. Another important tumor-escape mechanism is to avoid recognition by dysregulation of antigen processing and presentation. Thus, both induction of functional CTL and susceptibility of the tumor and its microenvironment to become T cell targets should be considered in CTL-based immunotherapy.

Gastric lipolysis of milk lipids in suckling rats

Fatty acid composition of the major lipid classes in stomach contents of suckling rats at 1, 5, 10, 17 and 20 days of lactation was compared to that of milk lipids. In milk, 98% of fatty acids were in triacylglycerols at all lactation times. Medium-chain fatty acid concentrations increased from 8% in colostrum to 26% at day 5. Fatty acid composition of stomach acylglycerols at all lactation times was different from that of milk triacylglycerols, containing less medium-chain fatty acids, 8:0 and 10:0. This preferential hydrolysis was also shown by higher concentrations of medium-chain fatty acids in the free fatty acid fraction. The lipolysis of medium-chain fatty acids from triacylglycerols resulted in the appearance of di- and monoacylglycerols with 50-100% higher amounts of 14:0 and 16:0. The similar fatty acid composition of products suggests that considerable lipolysis occurred in stomachs of suckling rats even at 1 day of age. Although there was a 10-fold increase in milk consumption, the extent of lipolysis was similar throughout the suckling period because of a parallel rise in lingual lipase levels.

Gastric lipolysis in the developing rat. Ontogeny of the lipases active in the stomach

The first step in fat digestion occurs in the stomach, where 10-30% of dietary triacylglycerols are hydrolyzed to partial (di- and mono-) acylglycerols and free fatty acids. Preduodenal fat digestion is an important compensatory mechanism in the newborn because of immature pancreatic (lipase) and hepatic (bile acid synthesis) function. Since hydrolysis of fat in the stomach can be catalyzed by enzymes of lingual (Hamosh, M. (1979) Pediatr. Res. 13, 615-622) and possibly gastric origin, we have studied the developmental pattern and quantitative contribution of these two enzymes to intragastric fat digestion by measuring lipase activity in homogenates of lingual glands and gastric mucosa of rats from birth until 60 days of age. Total lipolytic activity in rat gastric mucosa was only 2-10% of that in the lingual glands throughout the entire period studied. Lingual lipase activity increased steadily from birth until day 50, whereas the activity in the gastric mucosa reached peak levels at 17-20 days and declined sharply after weaning. Throughout the period of study--suckling, weaning, and young adulthood--lingual and gastric lipase had very similar characteristics: pH optimum in the range of 5.0-6.0 and 2.5-5.0-fold higher activity on medium-chain (tri[14C]octanoin) than long-chain (tri[3H]olein) triacylglycerols. In the lingual glands, lipase activity was higher during fasting, probably because of accumulation of enzyme (without depletion during meals), whereas in the gastric mucosa lipase levels were higher after feeding, suggesting adsorption of lingual lipase (which reaches the stomach with the ingested food) onto the gastric mucosa. From birth to weaning, there was rapid and extensive hydrolysis of triacylglycerol in the stomach (decrease from 98 mol% in rat milk to 33.6-48.9 mol% in the stomach contents half an hour after feeding). The intragastric lipolysis remained almost constant from birth until day 20, in spite of a marked increase in food consumption, probably because of the continued rise of lingual lipase levels. The direct relationship between high intragastric lipolysis and high lingual lipase activity suggests that lingual lipase is the major digestive enzyme in the newborn.

Isolation and characterization of multiple forms of ovine pancreatic deoxyribonuclease. Chromatograhpic behavior of the enzyme on concanavalin A-agarose and carboxymethylcellulose columns

A new procedure has been devised for the purification of ovine DNase, including (NH/4)2SO4 fractionation, two steps of CM-cellulose chromatography, concanavalin A-agarose chromatography, and gel filtration on Sephadex G--100. The enzyme, like bovine DNase, exhibits multiplicity due to changes in the primary structure and the sugar structure of the carbohydrate moiety. Unlike bovine DNase, ovine DNase does not have sialic acid in any of its multiple forms. Concanavalin A-agarose is useful in the purification of not only ovine but also bovine DNase. For ovine DNase, it is a necessary and key step of purification; for bovine DNase, it can be used to purify commercial preparations of DNase free from proteases in a single step as judged by its stability in Ca2+-free media at pH 8.0. The purified enzyme has a specific activity equal to that of a highly purified DNase and presumably contains predominantly DNases A and C. Two of the four forms of ovine DNase have been purified to apparent homogeneity and subjected to chemical analysis. The present results show that bovine and ovine DNases have indistinguishable molecular weights and identical end groups, suggesting that they may have the same number of amino acid residues. The amino acid composition indicates that two enzymes may have six residues of amino acids subject to substitution which can be explained by single base changes in their genetic code words. Amino acid analyses also indicate that the most likely difference between two forms of ovine DNase is the substitution of Leu for Arg.

Role of caveolin-1 in the pathogenesis of tissue fibrosis by keloid-derived fibroblasts in vitro

BACKGROUND

Recent studies have suggested that caveolin-1 (cav-1) plays an important role in the regulation of transforming growth factor (TGF)-β1 signalling and participates in the pathogenesis of tissue fibrosis. However, its effects on dermal fibrosis keloids are unknown.

OBJECTIVES

To investigate the effect of cav-1 in the pathogenesis of tissue fibrosis by keloid fibroblasts.

METHODS

Keloid fibroblasts were cultured and exposed to different concentrations of cav-1 cell-permeable peptides (cav-1p) in the presence of TGF-β1. Keloid fibroblast phenotypes and protein production were analysed by real-time reverse transcriptase-polymerase chain reaction, Western blot, and multiplex enzyme-linked immunosorbent assay techniques. The effect of cav-1p on cell viability was evaluated by MTT assay.

RESULTS

Cav-1 was markedly decreased in the keloid-derived fibroblasts. Moreover, cav-1p significantly reduced TGF-β receptor type I levels and Smad2/3 phosphorylation in response to added TGF-β1. Additionally, TGF-β1 decreased cav-1 expression in human skin fibroblasts. Cav-1 was able to suppress TGF-β1-induced extracellular matrix production in cultured keloid fibroblasts through regulation of the mitogen-activated protein kinase pathway.

CONCLUSIONS

Cav-1 appears to participate in the pathogenesis of tissue fibrosis in keloid. Restoration of cav-1 function by treatment with a cell-permeable peptide corresponding to the cav-1 scaffolding domain may be a novel therapeutic approach in keloid.

Deoxyribonuclease of Syncephalastrum racemosum--enzymatic properties and molecular structure

Among the isolated fungal species of soil, one filamentous fungus, Syncephalastrum racemosum, produces a relatively large amount of DNase. This enzyme has been purified to apparent homogeneity by column chromatography on DEAE-cellulose, hydroxylapatite, phenyl-Sepharose CL-4B, and Sephadex G-100. The active enzyme requires divalent metal ions and has an optimum pH of 7.0 with Mg2+ and 7.2 with Mn2+. This enzyme is an acidic glycoprotein with a pI 5.0 and is relatively unstable at low concentrations. The M(r) of the enzyme is 56,000 during gel filtration under nondenaturing conditions but is 28,000 during polyacrylamide gel electrophoresis in sodium dodecyl sulfate. These results suggest a structure consisting of two subunits. The subunits of the holoenzyme can be cross-linked with glutaraldehyde. The yield of N-terminal phenylthiohydantoin-alanine from the holoenzyme is 140% and that of one peptide (D-Y-V-S-S-G-Y-D-R), obtained from the tryptic digest is 160%, indicating that the native enzyme is composed of two identical subunits and probably has two active domains. Fungal DNase can be inactivated by Cu(2+)-iodoacetate under conditions that inactivate bovine pancreatic DNase. The specific activity (units/mg of protein) of fungal DNase is 6.5 times that of bovine DNase. The amino acid content of fungal DNase, relative to bovine DNase, is higher in Gly and lower in Ser and Val. The fungal N-terminal 40-residue sequence shows a high degree of homology with a consensus sequence derived from DNase of three mammalian species.

Does APO epsilon4 correlate with MRI changes in Alzheimer's disease?

OBJECTIVE

To assess the relation between APO E genotype and MRI white matter changes in Alzheimer's disease. The APO epsilon4 allele is correlated with amyloid angiopathy and other neuropathologies in Alzheimer's disease and could be associated with white matter changes. If so, there should be a dose effect.

METHODS

104 patients with probable Alzheimer's disease (NINCDS-ADRDA criteria) in this Alzheimer's Disease Research Centre were studied. Patients received MRI and APO E genotyping by standardised protocols. Axial MRI was scored (modified Schelten's scale) for the presence and degree of white matter changes and atrophy in several regions by a neuroradiologist blinded to genotype. Total white matter and total atrophy scores were also generated. Data analysis included Pearson's correlation for regional and total imaging scores and analysis of variance (ANOVA) (or Kruskal-Wallis) and chi(2) for demographic and disease related variables.

RESULTS

30 patients had no epsilon4, 53 patients were heterozygous, and 21 patients were homozygous. The three groups did not differ in sex distribution, age of onset, age at MRI, MMSE, clinical dementia rating, or modified Hachinski ischaemia scores. There were no significant correlations between total or regional white matter scores and APO E genotype (Pearson correlation).

CONCLUSIONS

No correlation between total or regional white matter scores and APO E genotype was found. The pathogenesis of white matter changes in Alzheimer's disease may be independent of APO E genotype.