Inactivation of pancreatic and gastric lipases by THL and C12:0-TNB: a kinetic study with emulsified tributyrin

Coupling in vitro food digestion with in vitro epithelial absorption; recommendations for biocompatibility

As food transits the gastrointestinal tract, food structures are disrupted and nutrients are absorbed across the gut barrier. In the past decade, great efforts have focused on the creation of a consensus gastrointestinal digestion protocol (i.e., INFOGEST method) to mimic digestion in the upper gut. However, to better determine the fate of food components, it is also critical to mimic food absorption in vitro. This is usually performed by treating polarized epithelial cells (i.e., differentiated Caco-2 monolayers) with food digesta. This food digesta contains digestive enzymes and bile salts, and if following the INFOGEST protocol, at concentrations that although physiologically relevant are harmful to cells. The lack of a harmonized protocol on how to prepare the food digesta samples for downstream Caco-2 studies creates challenges in comparing inter laboratory results. This article aims to critically review the current detoxification practices, highlight potential routes and their limitations, and recommend common approaches to ensure food digesta is biocompatible with Caco-2 monolayers. Our ultimate aim is to agree a harmonized consensus protocol or framework for in vitro studies focused on the absorption of food components across the intestinal barrier.

Pancreatic lipase digestion: The forgotten barrier in oral administration of lipid-based delivery systems?

This review highlights the importance of controlling the digestion process of orally administered lipid-based delivery systems (LBDS) and their performance. Oral LBDS are prone to digestion via pancreatic lipase in the small intestine. Rapid or uncontrolled digestion may cause the loss of delivery system integrity, its structural changes, reduced solubilization capacity and physical stability issues. All these events can lead to uncontrolled drug release from the digested LBDS into the gastrointestinal environment, exposing the incorporated drug to precipitation or degradation by luminal proteases. To prevent this, the digestion rate of orally administered LBDS can be estimated by appropriate choice of the formulation type, excipient combinations and their ratios. In addition, in vitro digestion models like pH-stat are useful tools to evaluate the formulation digestion rate. Controlling digestion can be achieved by conventional lipase inhibitors like orlistat, sterically hindering of lipase adsorption on the delivery system surface with polyethylene glycol (PEG) chains, lipase desorption or saturation of the interface with surfactants as well as formulating LBDS with ester-free excipients. Recent in vivo studies demonstrated that digestion inhibition lead to altered pharmacokinetic profiles, where Cmax and Tmax were reduced in spite of same AUC compared to control or even improved oral bioavailability.

Signaling pathways in obesity: mechanisms and therapeutic interventions

Obesity is a complex, chronic disease and global public health challenge. Characterized by excessive fat accumulation in the body, obesity sharply increases the risk of several diseases, such as type 2 diabetes, cardiovascular disease, and nonalcoholic fatty liver disease, and is linked to lower life expectancy. Although lifestyle intervention (diet and exercise) has remarkable effects on weight management, achieving long-term success at weight loss is extremely challenging, and the prevalence of obesity continues to rise worldwide. Over the past decades, the pathophysiology of obesity has been extensively investigated, and an increasing number of signal transduction pathways have been implicated in obesity, making it possible to fight obesity in a more effective and precise way. In this review, we summarize recent advances in the pathogenesis of obesity from both experimental and clinical studies, focusing on signaling pathways and their roles in the regulation of food intake, glucose homeostasis, adipogenesis, thermogenesis, and chronic inflammation. We also discuss the current anti-obesity drugs, as well as weight loss compounds in clinical trials, that target these signals. The evolving knowledge of signaling transduction may shed light on the future direction of obesity research, as we move into a new era of precision medicine.

The Influence of Fed State Lipolysis Inhibition on the Intraluminal Behaviour and Absorption of Fenofibrate from a Lipid-Based Formulation

The bioavailability of lipophilic drugs may or may not be increased when administered with food due to increased solubilisation in fed state gastrointestinal (GI) fluids. The in vivo interplay between drug solubilisation, lipid phase digestion and drug absorption is complex and remains poorly understood. This study aimed to investigate the role of fed state GI lipolysis on the intraluminal behaviour and absorption of fenofibrate, formulated as the lipid-based formulation Fenogal. Therefore, a crossover study was performed in healthy volunteers using orlistat as lipase inhibitor. Fenofibrate concentrations were determined in the proximal jejunum and linked to simultaneously assessed systemic fenofibric acid concentrations. Inhibition of lipolysis by orlistat resulted in a faster onset of absorption in 4 out of 6 volunteers, reflected by a decrease in systemic T_max between 20 and 140 min. In addition, the increase of undigested lipids present in the small intestine upon orlistat co-administration sustained drug solubilisation for a longer period, resulting in higher fenofibrate concentrations in the jejunum and improved absorption in 5 out of 6 volunteers (median AUC_0–8h 8377 vs. 5832 μM.min). Sustaining drug solubilisation in the lipid phase may thus contribute to the absorption of lipophilic drugs. More research into the different mechanisms underlying lipophilic drug absorption from fed state media at different levels of digestion is warranted.

Modulating the release of pharmaceuticals from lipid cubic phases using a lipase inhibitor

Lipid cubic phase formulations have gained recognition as potential controlled delivery systems for a range of active pharmaceutical and biological agents on account of their desirable physiochemical properties and ability to encapsulate both hydrophobic and hydrophilic molecules. The most widely studied lipid cubic systems are those of the monoacylglycerol lipid family. These formulations are susceptible to lipolysis by a variety of enzymes, including lipases and esterases, which attack the ester bond present on the lipid chain bridging the oleic acid component to the glycerol backbone. The release of poorly soluble molecules residing in the lipid membrane portions of the phase is limited by the breakdown of the matrix; thus, presenting a potential means for further controlling and sustaining the release of therapeutic agents by targeting the matrix stability and its rate of degradation. The aims of the present study were twofold: to evaluate an approach to regulate the rate of degradation of lipid cubic phase drug delivery systems by targeting the enzyme interactions responsible for their demise; and to study the subsequent drug release profiles from bulk lipid cubic gels using model drugs of contrasting hydrophobicity. Here, hybrid materials consisting of cubic phases with monoacylglycerol lipids of different chain lengths formulated with a potent lipase inhibitor tetrahydrolipstatin were designed. Modulation of the release of a hydrophobic model pharmaceutical, a clofazimine salt, was obtained by exploiting the matrices' enzyme-driven digestion. A stable cubic phase is described, displaying controlled degradation with at least a 4-fold improvement compared to the blank systems shown in inhibitor-containing cubic systems. Sustained release of the model hydrophobic pharmaceutical was studied over 30 days to highlight the advantage of incorporating an inhibitor into the cubic network to achieve tunable lipid release systems. This is done without negatively affecting the structure of the matrix itself, as shown by comprehensive small-angle x-ray scattering experiments.

Dissecting the Interaction Deficiency of a Cartilaginous Fish Digestive Lipase with Pancreatic Colipase: Biochemical and Structural Insights

A full-length cDNA encoding digestive lipase (SmDL) was cloned from the pancreas of the smooth-hound (Mustelus mustelus). The obtained cDNA was 1350 bp long encoding 451 amino acids. The deduced amino acid sequence has high similarity with known pancreatic lipases. Catalytic triad and disulphide bond positions are also conserved. According to the established phylogeny, the SmDL was grouped with those of tuna and Sparidae lipases into one fish digestive lipase cluster. The recently purified enzyme shows no dependence for bile salts and colipase. For this, the residue-level interactions between lipase-colipase are yet to be clearly understood. The structural model of the SmDL was built, and several dissimilarities were noticed when analyzing the SmDL amino acids corresponding to those involved in HPL binding to colipase. Interestingly, the C-terminal domain of SmDL which holds the colipase shows a significant role for colipase interaction. This is apt to prevent the interaction between fish lipase and the pancreatic colipase which and can provide more explanation on the fact that the classical colipase is unable to activate the SmDL.

Inhibition of CpLIP2 Lipase Hydrolytic Activity by Four Flavonols (Galangin, Kaempferol, Quercetin, Myricetin) Compared to Orlistat and Their Binding Mechanisms Studied by Quenching of Fluorescence

The inhibition of recombinant CpLIP2 lipase/acyltransferase from Candida parapsiolosis was considered a key model for novel antifungal drug discovery and a potential therapeutic target for candidiasis. Lipases have identified recently as potent virulence factors in C. parapsilosis and some other yeasts. The inhibition effects of orlistat and four flavonols (galangin, kaempferol, quercetin and myricetin) characterized by an increasing degree of hydroxylation in B-ring, were investigated using ethyl oleate hydrolysis as the model reaction. Orlistat and kaempferol (14 µM) strongly inhibited CpLIP2 catalytic activity within 1 min of pre-incubation, by 90% and 80%, respectively. The relative potency of flavonols as inhibitors was: kaempferol > quercetin > myricetin > galangin. The results suggested that orlistat bound to the catalytic site while kaempferol interacted with W294 on the protein lid. A static mechanism of interactions between flavonols and CpLIP2 lipase was confirmed by fluorescence quenching analyses, indicating that the interactions were mainly driven by hydrophobic bonds and electrostatic forces. From the Lehrer equation, fractions of tryptophan accessibility to the quencher were evaluated, and a relationship with the calculated number of binding sites was suggested.

Nutritional properties, identification of phenolic compounds, and enzyme inhibitory activities of Feijoa sellowiana leaves

The nutritional values, the identification of individual phenolic compounds as well as the functional properties (in vitro acetylcholinesterase (AChE) and pancreatic lipase inhibition) of Tunisian Feijoa sellowiana (O.Berg) leaves were determined by high-performance liquid chromatography coupled with diode array and mass spectrometry detector. Feijoa Sellowiana  leaves Extract (FSLE) were evaluated in the present work. Macronutrient components (proteins, carbohydrates, dietary fiber, lipids, and ashes) of FSLE as well as their fatty acids and mineral content were determined. The individual phenolic composition was characterized by the presence of flavonols (mostly quercetin glycosides), flavan-3-ols (procyanidins and catechins), and phenolic acid derivatives. To understand the possible inhibition mechanism exerted by the extract components, enzyme kinetic studies using derived Lineweaver-Burk (LB) plots and Michaelis-Menten were performed. The obtained results evidenced that FSLE exhibited important AChE inhibitory effect, behaving as a noncompetitive inhibitor. Furthermore, the leaves' extract inhibited irreversibly the pancreatic lipase, with maximum inhibition (70%) achieved at 1 mg/ml. PRACTICAL APPLICATIONS: In many countries of the world, Feijoa Sellowiana leaves are used as an alternative to tea drinks and as a folkloric medicine. Moreover, it is well known that the phytochemical compounds are a practical alternative for the prevention of many chronic diseases such as Alzheimer's and obesity. For this reason, the present study aimed to evaluate the nutritional, individual phenolic compounds, and functional properties of Feijoa Sellowiana leaves to valorize them as a food and pharmaceutical bioactive human source.

Rhaponticum acaule (L) DC essential oil: chemical composition, in vitro antioxidant and enzyme inhibition properties

BACKGROUND

α-glucosidase is a therapeutic target for diabetes mellitus (DM) and α-glucosidase inhibitors play a vital role in the treatments for the disease. Furthermore, xanthine oxidase (XO) is a key enzyme that catalyzes hypoxanthine and xanthine to uric acid which at high levels can lead to hyperuricemia which is an important cause of gout. Pancreatic lipase (PL) secreted into the duodenum plays a key role in the digestion and absorption of fats. For its importance in lipid digestion, PL represents an attractive target for obesity prevention.

METHODS

The flowers essential oil of Rhaponticum acaule (L) DC (R. acaule) was characterized using gas chromatography-mass spectrometry (GC-MS). The antioxidant activities of R. acaule essential oil (RaEO) were also determined using 2,2'-azinobis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS), reducing power, phosphomolybdenum, and DNA nicking assays. The inhibitory power of RaEO against α-glucosidase, xanthine oxidase and pancreatic lipase was evaluated. Enzyme kinetic studies using Michaelis-Menten and the derived Lineweaver-Burk (LB) plots were performed to understand the possible mechanism of inhibition exercised by the components of this essential oil.

RESULTS

The result revealed the presence of 26 compounds (97.4%). The main constituents include germacrene D (49.2%), methyl eugenol (8.3%), (E)-β-ionone (6.2%), β-caryophyllene (5.7%), (E,E)-α-farnesene (4.2%), bicyclogermacrene (4.1%) and (Z)-α-bisabolene (3.7%). The kinetic inhibition study showed that the essential oil demonstrated a strong α-glucosidase inhibiton and it was a mixed inhibitor. On the other hand, our results evidenced that this oil exhibited important xanthine oxidase inhibitory effect, behaving as a non-competitive inhibitor. The essential oil inhibited the turkey pancreatic lipase, with maximum inhibition of 80% achieved at 2 mg/mL. Furthermore, the inhibition of turkey pancreatic lipase by RaEO was an irreversible one.

CONCLUSION

The results revealed that the RaEO is a new promising potential source of antioxidant compounds, endowed with good practical applications for human health.

Inhibition of pancreatic lipase and amylase by extracts of different spices and plants

The aim of this study is to search new anti-obesity and anti-diabetic agents from plant and spices crude extracts as alternative to synthetic drugs. The inhibitory effect of 72 extracts was evaluated, in vitro, on lipase and amylase activities. Aqueous extracts of cinnamon and black tea exhibited an appreciable inhibitory effect on pancreatic amylase with IC₅₀ values of 18 and 87 μg, respectively. Aqueous extracts of cinnamon and mint showed strong inhibitory effects against pancreatic lipase with IC₅₀ of 45 and 62 μg, respectively. The presence of bile salts and colipase or an excess of interface failed to restore the lipase activity. Therefore, the inhibition of pancreatic lipase, by extracts of spices and plants, belongs to an irreversible inhibition. Crude extract of cinnamon showed the strongest anti-lipase and anti-amylase activities which offer a prospective therapeutic approach for the management of diabetes and obesity.

Chemoenzymatic Kinetic resolution of (R)-malathion in aqueous media

BACKGROUND

Malathion (R,S)-diethyl-2-[(dimethoxyphosphorothioyl)sulfanyl]butanedioate is a chiral organophosphorus compound used widely as pesticide for suppression of harmful insects such as mosquitoes. It is well known that in biological systems (R)-malathion is the active enantiomer, therefore a sustainable approach could be the use of only the biologically active enantiomer. The resolution of the commercial racemic mixture to obtain the pure active enantiomer combined with a recycling of the undesired enantiomer through a racemization process could be an attractive alternative to reduce the environmental impact of this pesticide. Thus, this work evaluates the use of four commercially available lipases for enantioselective hydrolysis and separation of malathion enantiomers from the commercial racemic mixture.

RESULTS

Several lipases were methodologically assessed, considering parameters such as enzyme concentration, temperature and reaction rates. Among them, Candida rugosa lipase exhibited the best performance, in terms of enantioselectivity, E = 185 (selective to the (S)-enantiomer). In this way, the desired unreacted (R)-enantiomer was recovered in a 49.42 % yield with an enantiomeric excess of 87 %. The monohydrolized (S)-enantiomer was recovered and racemized in basic media, followed by esterification to obtain the racemic malathion, which was recycled. In this way, an enantioenriched mixture of (R)-malathion was obtained with a conversion of 65.80 % considering the recycled (S)-enantiomer.

CONCLUSION

This work demonstrated the feasibility of exploiting Candida rugosa lipase to kinetically resolve racemic malathion through an environmentally friendly recycling of the undesired (S)-enantiomer. Graphical AbstractLipase catalyzed enantioselective resolution of (R)-malathion in aqueous solvent.

A broad pH range indicator-based spectrophotometric assay for true lipases using tributyrin and tricaprylin

A continuous assay is proposed for the screening of acidic, neutral, or alkaline lipases using microtiter plates, emulsified short- and medium-chain TGs, and a pH indicator. The lipase activity measurement is based on the decrease of the pH indicator optical density due to protonation which is caused by the release of FFAs during the hydrolysis of TGs and thus acidification. Purified lipases with distinct pH optima and an esterase were used to validate the method. The rate of lipolysis was found to be linear with time and proportional to the amount of enzyme added in each case. Specific activities measured with this microplate assay method were lower than those obtained by the pH-stat technique. Nevertheless, the pH-dependent profiles of enzymatic activity were similar with both assays. In addition, the substrate preference of each enzyme tested was not modified and this allowed discriminating lipase and esterase activities using tributyrin (low water solubility) and tricaprylin (not water soluble) as substrates. This continuous lipase assay is compatible with a high sample throughput and can be applied for the screening of lipases and lipase inhibitors from biological samples.

Toward the establishment of standardized in vitro tests for lipid-based formulations. 5. Lipolysis of representative formulations by gastric lipase

PURPOSE

Lipid-based formulations (LBF) are substrates for digestive lipases and digestion can significantly alter their properties and potential to support drug absorption. LBFs have been widely examined for their behaviour in the presence of pancreatic enzymes. Here, the impact of gastric lipase on the digestion of representative formulations from the Lipid Formulation Classification System has been investigated.

METHODS

The pHstat technique was used to measure the lipolysis by recombinant dog gastric lipase (rDGL) of eight LBFs containing either medium (MC) or long (LC) chain triglycerides and a range of surfactants, at various pH values [1.5 to 7] representative of gastric and small intestine contents under both fasting and fed conditions.

RESULTS

All LBFs were hydrolyzed by rDGL. The highest specific activities were measured at pH 4 with the type II and IIIA MC formulations that contained Tween®85 or Cremophor EL respectively. The maximum activity on LC formulations was recorded at pH 5 for the type IIIA-LC formulation. Direct measurement of LBF lipolysis using the pHstat, however, was limited by poor LC fatty acid ionization at low pH.

CONCLUSIONS

Since gastric lipase initiates lipid digestion in the stomach, remains active in the intestine and acts on all representative LBFs, its implementation in future standardized in vitro assays may be beneficial. At this stage, however, routine use remains technically challenging.

Triterpene acids from apple peel inhibit lepidopteran larval midgut lipases and larval growth

Fruit extracts from apple, kiwifruit, feijoa, boysenberry, and blueberry were screened for the presence of lipase inhibitory compounds against lepidopteran larval midgut crude extracts. From 120 extracts, six showed significant inhibition with an extract from the peel of Malus × domestica cv. "Big Red" showing highest levels of inhibition. Because this sample was the only apple peel sample in the initial screen, a survey of peels from seven apple cultivars was undertaken and showed that, despite considerable variation, all had inhibitory activity. Successive solvent fractionation and LC-MS of cv. "Big Red" apple peel extract identified triterpene acids as the most important inhibitory compounds, of which ursolic acid and oleanolic acid were the major components and oxo- and hydroxyl-triterpene acids were minor components. When ursolic acid was incorporated into artificial diet and fed to Epiphyas postvittana Walker (Tortricidae: Lepidoptera) larvae at 0.16% w/v, a significant decrease in larval weight was observed after 21 days. This concentration of ursolic acid is less than half the concentration reported in the skin of some apple cultivars.

Apple peels, from seven cultivars, have lipase-inhibitory activity and contain numerous ursenoic acids as identified by LC-ESI-QTOF-HRMS

Apple peel contains numerous phytochemicals, many of which show bioactivity. This study investigated the identity of triterpenoid compounds contained in ethanolic extracts of peel from seven apple cultivars. Using HPLC-ESI-QTOF-HRMS, accurate mass information was obtained for 43 compounds, and chemical identity was inferred from the calculated elemental composition, fragment masses, ms/ms, and a limited set of authentic standards. Compounds were identified as triterpene acids and tentatively identified as ursenoic (or oleanoic) acid derivatives containing hydroxyl, oxo, and coumaroyloxy groups. These apple skin extracts exhibited lipase-inhibitory activity, which may be linked to the ursenoic acid content. Furthermore, both triterpene content and lipase-inhibitory activity varied by cultivar.

Direct Measurement of Lipase Inhibition by Orlistat Using a Dissolution Linked In Vitro Assay

PURPOSE

To develop a bio-assay that would be able to directly test gastrointestinal and/or dissolution samples to determine lipase activity and inhibition by Orlistat.

METHODS

Enzyme assays were performed with porcine pancreatic lipase and para-Nitrophenyl Palmitate (pNPP) in pH 8.0 reaction buffer at 37°C. Substrate hydrolysis was monitored by absorbance changes at 410 nm. The dissolution of two Orlistat formulations was tested with a USP II apparatus. Samples were HPLC analyzed to determine release profile in addition to being diluted and directly assayed for inhibitory effect.

RESULTS

The lipase-pNPP system demonstrates linearity and Michalis-Menten kinetics with a K_m=2.7 ± 0.2 μM and K_cat = 0.019 s^-1. Orlistat showed highly potent and time dependent inhibition with 5 ng/ml effecting 50% activity after 5 minutes in the Lipase-pNPP system. Dissolution studies showed a correlation of the drug release profile to the inhibitory effect of dissolution samples in the assay.

CONCLUSIONS

The lipase-pNPP method can be used as an in vitro assay to monitor orlistat inhibition from drug release or dissolution samples.

Lipases or esterases: does it really matter? Toward a new bio-physico-chemical classification

Carboxylester hydrolases, commonly named esterases, consist of a large spectrum of enzymes defined by their ability to catalyze the hydrolysis of carboxylic ester bonds and are widely distributed among animals, plants, and microorganisms. Lipases are lipolytic enzymes which constitute a special class of carboxylic esterases capable of releasing long-chain fatty acids from natural water-insoluble carboxylic esters. However, up to now, several unsuccessful attempts aimed at differentiating "lipases" from "esterases" by using various criteria. These criteria were based on the first substrate used chronologically, primary sequence comparisons, some kinetic parameters, or some structural features.Lipids are biological compounds which, by definition, are insoluble in water. Taking into account this basic physico-chemical criterion, we primarily distinguish lipolytic esterases (L, acting on lipids) from nonlipolytic esterases (NL, not acting on lipids). In view of the biochemical data accumulated up to now, we proposed a new classification of esterases based on various criteria of physico-chemical, chemical, anatomical, or cellular nature. We believe that the present attempt matters scientifically for several reasons: (1) to help newcomers in the field, performing a few key experiments to figure out if a newly isolated esterase is lipolytic or not; (2) to clarify a debate between scientists in the field; and (3) to formulate questions which are relevant to the still unsolved problem of the structure-function relationships of esterases.

The effects of the broad-specificity lipase inhibitor, tetrahydrolipstatin, on the growth, development and survival of the larvae of Epiphyas postvittana (Walker) (Tortricidae, Lepidoptera)

The effects of the lipase inhibitor, tetrahydrolipstatin (THL), on neonate Epiphyas postvittana (Walker) (Lepidoptera, Tortricidae) larvae were investigated by feeding on control artificial diets (with and without 2% ethanol) and diets containing 2% ethanol and one of three concentrations of THL (0.011%, 0.037% and 0.11%). Small but significant reductions in growth rate, percent pupation and time to pupation were observed for larvae feeding on 2% ethanol control diet compared with standard control diet, but larger reductions in all parameters occurred with increasing THL concentration. Third instar larvae fed 0.011% THL in the diet had 40% of the midgut lipase activity in the relevant control larvae and showed up-regulation of gene expression of the gastric lipase-like family but not the pancreatic lipase-like family of midgut lipases.

Purification and biochemical characterization of digestive lipase in whiteleg shrimp

Penaeus vannamei lipase was purified from midgut gland of whiteleg shrimp. Pure lipase (E.C. 3.1.1.3) was obtained after Superdex 200 gel filtration and Resource Q anionic exchange. The pure lipase, which is a glycosylated molecule, is a monomer having a molecular mass of about 44.8 kDa, as determined by SDS-PAGE analysis. The lipase hydrolyses short and long-chain triacylglycerols and naphthol derivates at comparable rates. A specific activity of 1787 U mg(-1) and 475 U mg(-1) was measured with triolein and tributyrin as substrates, respectively, at pH 8.0 and 30°C in the absence of colipase. The lipase showed a K (m, app) of 3.22 mM and k (cat, app)/K (m, app) of 0.303 × 10(3) mM(-1) s(-1) using triolein as substrate. Natural detergents, such as sodium deoxycholate, act as potent inhibitors of the lipase. This inhibition can be reversed by adding fresh oil emulsion. Result with tetrahydrolipstatin, an irreversible inhibitor, suggests that the lipase is a serine enzyme. Peptide sequences of the lipase were determined and compared with the full-length sequence of lipase which was obtained by the rapid amplification of cDNA ends method. The full cDNA of the pvl was 1,186 bp, with a deduced protein of 362 amino acids that includes a consensus sequence (GXSXG) of the lipase superfamily of α/β-hydrolase. The gene exhibits features of conserved catalytic residues and high homology with various mammalian and insect lipase genes. A potential lid sequence is suggested for pvl.

Crab digestive lipase acting at high temperature: Purification and biochemical characterization

In recent years, recovery and characterization of enzymes from fish and aquatic invertebrates have taken place and this had led to the emergence of some interesting new applications of these enzymes. However, much less is known about lipases from crustaceans. A lipolytic activity was located in the crab digestive glands (hepatopancreas), from which a crab digestive lipase (CDL) was purified. Pure CDL has a molecular mass of 65kDa as determined by SDS/PAGE analysis. Unlike known digestive lipases, CDL displayed its maximal activity on long and short-chain triacylglycerols at a temperature of 60 degrees C. A specific activity of 500U/mg or 130U/mg was obtained with TC(4) or olive oil as substrate, respectively. Only 10% of the maximal activity was detected at 37 degrees C. The enzyme retained 80% of its maximal activity when incubated during 10 min at 60 degrees C, and was completely inactivated at a temperature higher than 65 degrees C. Interestingly, neither colipase, nor bile salts were detected in the crab hepatopancreas. Which suggests that colipase evolved in invertebrates simultaneously with the appearance of an exocrine pancreas and a true liver which produce bile salts. No similarity between the 13 N-terminal amino acid residues of CDL was found with those of known other digestive lipases.

Assaying lipase activity from oil palm fruit (Elaeis guineensis Jacq.) mesocarp

The mesocarp of mature oil palm fruit undergoes intensive triglycerides hydrolysis upon abscission and bruising. This generates such a high amount of free fatty acids that the oil might become unfit for human consumption without appropriate refining. The lipase (EC 3.1.1.3) involved in the breakdown of the oil is not stable after homogenization of the tissue in aqueous buffers. In this study, we have devised a solvent-based procedure that allowed us to obtain fractions with stable lipase activity. Using these fractions, we have determined the optimal conditions for assaying mesocarp lipase activity. The activity was highest at a temperature of 35 degrees C and a pH of 9. The lipase was found to be strictly calcium dependent. The specific activity of the lipase measured in optimal conditions was found to be 33 mumol fatty acids released min(-1) mg(-1) protein using olive oil as substrate. The mesocarp contains about 190 U of lipase g(-1) fresh weight. This activity was found to be inhibited by the lipase inhibitor tetrahydrolipstatin (THL), suggesting that the lipase is a serine hydrolase.

Exploring the specific features of interfacial enzymology based on lipase studies

Many enzymes are active at interfaces in the living world (such as in the signaling processes at the surface of cell membranes, digestion of dietary lipids, starch and cellulose degradation, etc.), but fundamental enzymology remains largely focused on the interactions between enzymes and soluble substrates. The biochemical and kinetic characterization of lipolytic enzymes has opened up new paths of research in the field of interfacial enzymology. Lipases are water-soluble enzymes hydrolyzing insoluble triglyceride substrates, and studies on these enzymes have led to the development of specific interfacial kinetic models. Structure-function studies on lipases have thrown light on the interfacial recognition sites present in the molecular structure of these enzymes, the conformational changes occurring in the presence of lipids and amphiphiles, and the stability of the enzymes present at interfaces. The pH-dependent activity, substrate specificity and inhibition of these enzymes can all result from both "classical" interactions between a substrate or inhibitor and the active site, as well as from the adsorption of the enzymes at the surface of aggregated substrate particles such as oil drops, lipid bilayers or monomolecular lipid films. The adsorption step can provide an alternative target for improving substrate specificity and developing specific enzyme inhibitors. Several data obtained with gastric lipase, classical pancreatic lipase, pancreatic lipase-related protein 2 and phosphatidylserine-specific phospholipase A1 were chosen here to illustrate these specific features of interfacial enzymology.

Biochemical and molecular characterization of Staphylococcus xylosus lipase

The Staphylococcus xylosus strain secretes a non-induced lipase in culture medium: S. xylosus lipase (SXL). Pure SXL is a monomeric protein (43 kDa). The 23 N-terminal amino acid residues were sequenced. This sequence is identical to that of Staphylococcus simulans lipase (SSL); in addition, it exhibits a high degree of homology with Staphylococcus aureus lipase (SAL NCTC 8530) sequences. The cloning and sequencing of gene part encoding the mature lipase shows one nucleotide difference with SSL, which corresponds to the change of one residue at a position 311. The lipase activity is maximal at pH 8.2 and 45 degrees C. SXL is able to hydrolyse triacylglycerols without chain length specificity. The specific activity of about 1900 U/mg was measured using tributyrin or triolein as substrate at pH 8.2 and at 45 degrees C in the presence of 2 mM CaCl2. In contrast to some previously characterized staphylococcal lipases, Ca2+ is not required to trigger the activity of SXL. SXL was found to be stable between pH 5 and pH 8.5. The enzyme maintains 50% of its activity after a 15-min incubation at 60 degrees C. Using tripropionin or vinyl esters as substrates, SXL does not present the interfacial activation phenomenon. Unlike many lipases, SXL is able to hydrolyse its substrate in the presence of bile salts or amphiphilic proteins. SXL is a serine enzyme, which is inhibited by THL.

Importance of lipolysis in oral cavity for orosensory detection of fat

Lingual lipase is usually secreted from von Ebner's glands, although there is great variation between species. Lingual lipase is thought to be an auxiliary enzyme for fat digestion and absorption in mammals; however, the reason for lipolysis in the oral cavity is not known. We focused on the gustatory sense and investigated the significance of lingual lipase in the perception of a fat taste by using orlistat, a potent lipase inhibitor. Five-minute two-bottle preference tests demonstrated that the addition of orlistat diminished the preference for triacylglycerides but not for free fatty acids. Radioactive triolein applied on rats' circumvallate papilla revealed that lingual lipase was released continuously to generate significant amounts of fatty acids and other lipolytic products within 1-5 s, which was enough time to taste fat. These findings suggest that lingual lipase is released to perceive the taste of triacylglycerides and to find nutritive lipids in food.

In vitro lipolysis by human pancreatic lipase is specifically abolished by its inactive forms

In human adults, the enzymatic hydrolysis of dietary fat along the digestive tract is sequentially catalyzed by two main enzymes, human gastric lipase (HGL) and human pancreatic lipase (HPL). Both a chemically inhibited form of HPL as well as an inactive HPL mutant with a glycine residue substituted for its catalytic serine were found to be strong inactivators of HPL activity. In the presence of bile salts, this inhibition was clearly due to competition for colipase. We established that the chemically inhibited HPL, probably in its open conformation, had a much greater affinity for colipase than the closed native form of HPL. These inhibitory effects are quite substantial, because a 0.2-M excess of the chemically inhibited HPL form relative to HPL reduced the catalytic lipolytic activity by 50% in the presence of an equimolar amount of colipase.

Transfer of orlistat through oil-water interfaces

The transfer of radiolabelled orlistat ([14C]orlistat), a potent gastrointestinal lipase inhibitor, through an oil-water interface from a single oil droplet to an aqueous phase was investigated, using an oil drop tensiometer. The absolute transfer fluxes were found to be very low, even in the presence of micellar concentrations of bile salts, which increased their values from 0.2 to 2.5 and 6.5 pmol cm(-2) min(-1) in the presence of 0, 4 and 15 mM NaTDC, respectively. Adding either a lipid emulsion or pure human pancreatic lipase (HPL) or human serum albumin or beta-lactoglobulin had no effect on the flux of transfer of orlistat. The presence of colipase or a mixture of colipase and HPL was found, however, to reduce the flux of orlistat transfer, probably because it partly covered the single oil drop surface, even in the presence of bile salts. Using a finely emulsified system, we investigated the partitioning of orlistat between the aqueous and oil phases, in the absence or presence of bile salts above their CMC (4 mM NaTDC, final concentration). Under these emulsified conditions, orlistat was found to be mostly associated with the oil phase, since more than 98.8% of the total radioactivity was recovered after decantation with the oil phase. The low transfer rates of orlistat, as well as its partitioning coefficient between the oil and the aqueous phases, should help us to better understand the inhibitory effects of orlistat on lipid digestion in humans.

Continuous enantioselective esterification of trans-2-phenyl-1-cyclohexanol using a new Candida rugosa lipase in a packed bed bioreactor

Enantioselective resolution of trans-2-phenyl-1-cyclohexanol (TPCH) by a Candida rugosa lipase, obtained by fermentation in the laboratory, and immobilised on EP100 polypropylene powder has been carried out using isooctane as solvent and propionic acid as esterifying agent. The study have included the utilisation of this biocatalyst in a batch process and the optimisation of the esterification conditions by means of a Box-Hunter-based experimental design. The main variables controlling the process, concentration of acid and alcohol, have been numerically optimised using initial esterification rate as objective function. The optimal concentrations for the batch process were 50 mM for the alcohol and 71 mM for the acid. This esterification reaction kinetics corresponded to a reversible Michaelis-Menten kinetic law for the optimal conditions, which has permitted to select a plug-flow packed bed bioreactor as the most appropriate configuration to minimise the residence time and to avoid shear stress effect on the biocatalyst. The behaviour of the continuous packed bed bioreactor at two different residence times (302 and 582 min) was in accordance with predictions from batch experiments, with slightly deviations (less than 10%). Continuous experiments maintained high values of enantioselectivity (enantiomeric factor was practically 1) and conversion near equilibrium value (35%) when long-time operation was carried out. Besides, long-time stability of biocatalyst has permitted to scale-up the production of enantioenriched (1R,2S)-TPCH propionate to yield gram quantities.

Inhibition of gastrointestinal lipolysis by Orlistat during digestion of test meals in healthy volunteers

The inhibition of digestive lipases by the antiobesity drug Orlistat along with lipolysis levels and fecal fat excretion were measured in healthy humans. Orlistat was found to be a powerful gastric lipase inhibitor, achieving 46.6--91.4% enzyme inhibition and thus greatly reducing gastric lipolysis of solid and liquid meals (11--33% of respective controls). Gastric lipase inhibition by Orlistat was extremely fast (half-inhibition time < 1 min). Duodenal lipolysis was reduced significantly by Orlistat given with the solid meal (32.6--37.6% of controls) but was only slightly reduced by Orlistat given with the liquid meal (74.5--100% of controls). Human pancreatic lipase (HPL) inhibition was found to be high (51.2--82.6%), however, regardless of the meal. These paradoxical results were explained when in vitro lipolysis experiments were performed. The rates of HPL inhibition by Orlistat were found to be similar with both types of meals (half-inhibition time 5--6 min), but the preemulsified triglycerides of the liquid meal were rapidly hydrolyzed by HPL before the enzyme was significantly inhibited by Orlistat. With the solid meal, the rate of hydrolysis of the meal triglycerides by HPL was slower than the rate of HPL inhibition by Orlistat. As predicted from the previous results, the effects of Orlistat on fat excretion levels were found to be much greater with the solid (40.5--57.4% of ingested fat) than with the liquid (4.2--18.8%) test meal.

Surface behaviour of bile salts and tetrahydrolipstatin at air/water and oil/water interfaces

The surface behaviour of two bile salts, sodium deoxycholate (NaDC) and sodium taurodeoxycholate (NaTDC), as well as that of tetrahydrolipstatin (THL), a potent gastrointestinal lipase inhibitor, was studied at air/water and oil/water interfaces, using interfacial tensiometry methods. The surface behaviour of NaDC and NaTDC was comparable at both oil/water and air/water interfaces. A fairly compact interfacial monolayer of bile salts is formed well below the critical micellar concentration (CMC) and can help to explain the well-known effects of bile salts on the kinetic behaviour of pancreatic lipases. Using the Wilhelmy plate technique, the surface pressure-molecular area curves recorded with THL at the air/water interface showed a collapse point at a surface pressure of 24.5 mN.m(-1), corresponding to a molecular area of 70 A(2). Surprisingly, using the oil drop method, a limiting molecular area of 160 A(2) was found to exist at the oil/water interface. On the basis of the above data, space-filling models were proposed for bile salts and THL at air/water and oil/water interfaces.

Highly enantioselective esterification of racemic ibuprofen in a packed bed reactor using immobilised Rhizomucor miehei lipase

A systematic study of the enantioselective resolution of ibuprofen by commercial Rhizomucor miehei lipase (Lipozyme(R) IM20) has been carried out using isooctane as solvent and butanol as esterificating agent. The main variables controlling the process (temperature, ibuprofen concentration, ratio butanol:ibuprofen) have been studied using an orthogonal full factorial experimental design, in which the selected objective function was enantioselectivity. This strategy has resulted in a polynomial function that describes the process. By optimizing this function, optimal conditions for carrying out the esterification of racemic ibuprofen have been determined. Under these conditions, enantiomeric excess and total conversion values were 93.8% and 49.9%, respectively, and the enantioselectivity was 113 after 112 h of reaction. These conditions have been considered in the design of a continuous reactor to scale up the process. The esterification of ibuprofen was properly described by pseudo first-order kinetics. Thus, a packed bed reactor operating as a plug-flow reactor (PFR) is the most appropriate in terms of minimizing the residence time compared with a continuous stirred tank reactor (CSTR) to achieve the same final conversion. This reactor shows a similar behavior in terms of enantioselectivity, enantiomeric excess, and conversion when compared with batch reactors. A residence-time distribution (RTD) shows that the flow model is essentially a plug flow with a slight nonsymmetrical axial dispersion (Peclet number = 43), which was also corroborated by the model of CSTR in series. The stability of the system (up to 100 h) and the possibility of reutilization of the enzyme (up to four times) lead to consider this reactor as a suitable configuration for scale up of the process.

Interactions of fluorescent triacylglycerol analogs covalently bound to the active site of a lipase from Rhizopus oryzae

Fluorescent triacylglycerol analogs were synthesized as covalent inhibitors of lipase activity. The respective 1(3), 2-O-dialkylglycero-3(1)-alkyl-phosphonic acid p-nitrophenyl esters contain a fluorescent pyrenealkyl chain and a long-chain alkyl residue bound to the sn-2 and sn-1(3) positions of glycerol, respectively. The phosphonic acid p-nitrophenyl ester bond is susceptible to nucleophilic substitution by the active serine residue in the catalytic triad of a lipase, leading to inactivation of the enzyme. The fluorescent dialkylglycerophosphonates contain two chiral centers, the sn-2 carbon of glycerol and the phosphorus atom. The (1-O-hexadecyl-2-O-pyrenedecyl-sn-glycero)-O-(p-nitrophenyl)-n-hex yl- phosphonate, first peak during HPLC separation and the (3-O-hexadecyl-2-O-pyrenedecyl-sn-glycero)-O-(p-nitrophenyl)-n-hex yl- phosphonate, second peak during HPLC separation were found to be potent lipase inhibitors. After incubation of an equimolar amount of these isomers with lipase from Rhizopus oryzae complete inactivation was observed. Stable conjugates containing a 1 : 1 molar ratio of lipid to protein were formed. The spatial proximity of the fluorescently labeled sn-2 alkyl chain of the inhibitor and tryptophan residues of the lipase was assessed by fluorescence resonance energy transfer. The extent of tryptophan fluorescence quenching and the concomitant increase in pyrene fluorescence upon excitation of lipase tryptophans was found to be similar for the above-mentioned isomers. Thus, the (labeled) sn-2 alkyl chains of a triacylglycerol analog are likely to interact with the same binding site of the R. oryzae lipase, irrespective of their steric configuration. However, it was shown that the extent of resonance energy transfer is strongly influenced by the reaction medium, indicating conformational changes of the lipase in different environments.