Jean-François Cavalier

MmPPOX Inhibits Mycobacterium tuberculosis Lipolytic Enzymes Belonging to the Hormone-Sensitive Lipase Family and Alters Mycobacterial Growth

Lipid metabolism plays an important role during the lifetime of Mycobacterium tuberculosis, the causative agent of tuberculosis. Although M. tuberculosis possesses numerous lipolytic enzymes, very few have been characterized yet at a biochemical/pharmacological level. This study was devoted to the M. tuberculosis lipolytic enzymes belonging to the Hormone-Sensitive Lipase (HSL) family, which encompasses twelve serine hydrolases closely related to the human HSL. Among them, nine were expressed, purified and biochemically characterized using a broad range of substrates. In vitro enzymatic inhibition studies using the recombinant HSL proteins, combined with mass spectrometry analyses, revealed the potent inhibitory activity of an oxadiazolone compound, named MmPPOX. In addition, we provide evidence that MmPPOX alters mycobacterial growth. Overall, these findings suggest that the M. tuberculosis HSL family displays important metabolic functions, thus opening the way to further investigations linking the involvement of these enzymes in mycobacterial growth.

Analysis of the discriminative inhibition of mammalian digestive lipases by 3-phenyl substituted 1,3,4-oxadiazol-2(3H)-ones.

We report here the reactivity and selectivity of three 5-Methoxy-N-3-Phenyl substituted-1,3,4-Oxadiazol-2(3H)-ones (MPOX, as well as meta and para-PhenoxyPhenyl derivatives, i.e.MmPPOX and MpPPOX) with respect to the inhibition of mammalian digestive lipases: dog gastric lipase (DGL), human (HPL) and porcine (PPL) pancreatic lipases, human (HPLRP2) and guinea pig (GPLRP2) pancreatic lipase-related proteins 2, human pancreatic carboxyl ester hydrolase (hCEH), and porcine pancreatic extracts (PPE). All three oxadiazolones displayed similar inhibitory activities on DGL, PLRP2s and hCEH than the FDA-approved anti-obesity drug Orlistat towards the same enzymes. These compounds appeared however to be discriminative of HPL (poorly inhibited) and PPL (fully inhibited). The inhibitory activities obtained experimentally in vitro were further rationalized using in silico molecular docking. In the case of DGL, we demonstrated that the phenoxy group plays a key role in specific molecular interactions within the lipases active site. The absence of this group in the case of MPOX, as well as its connectivity to the neighbouring aromatic ring in the case of MmPPOX and MpPPOX, strongly impacts the inhibitory efficiency of these oxadiazolones and leads to a significant gain in selectivity towards the lipases tested. The powerful inhibition of PPL, DGL, PLRP2s, hCEH and to a lesser extend HPL, suggests that oxadiazolone derivatives could also provide useful leads for the development of novel and more discriminative inhibitors of digestive lipases. These inhibitors could be used for a better understanding of individual lipase function as well as for drug development aiming at the regulation of the whole gastrointestinal lipolysis process.

Interfacial and/or molecular recognition by lipases of mixed monomolecular films of 1,2-dicaprin and chiral organophosphorus glyceride analogues?

Abstract Enantiomerically pure sn-1,2- and sn-2,3-O-didecanoylphosphonoglycerides, were synthesised and investigated as inhibitors of human pancreatic lipase (HPL) and human gastric lipase (HGL). The inhibition studies were performed using the monomolecular film technique coupled with ELISA tests. All the four stereoisomers investigated reduced the hydrolysis of 1,2-dicaprin by both lipases. With HPL, they exhibited a rather weak inhibitory power and no significant differences were observed among them. With HGL, the inhibition depended much more strongly on the chirality at the sn-2 carbon of the glycerol backbone, while the chirality at the phosphorus had no influence. Moreover, a clear correlation was observed between the HGL surface concentration and the inhibitor surface molar fraction (α50) leading to half inhibition. The greatest enzymatic inhibition was observed with films containing the enantiomeric inhibitor to which the HGL was best adsorbed, assuming thus that the interfacial lipase binding was controlled by a supramolecular chiral recognition process.

New insights into the pH-dependent interfacial adsorption of dog gastric lipase using the monolayer technique.

The access to kinetic parameters of lipolytic enzyme adsorption onto lipids is essential for a better understanding of interfacial enzymology and lipase-lipid interactions. The interfacial adsorption of dog gastric lipase (DGL) was monitored as a function of pH and surface pressure (Π), independently from the catalytic activity, using non-hydrolysable 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC) monomolecular films. The acid-stable DGL, which initiates fat digestion in the stomach, was then selected because its adsorption kinetics onto hydrophobic solid surfaces were already studied. This gastric lipase was therefore used as a model enzyme to validate both experimental and theoretical approaches. Results show that the adsorption process of DGL at the lipid/water interface depends on a pH-dependent adsorption equilibrium coefficient which is optimum at pH 5.0 (K(Ads) = 1.7 ± 0.05 × 10(8)M(-1)). KAds values further allowed an indirect estimation of the molar fraction (ΦE*(%), mol%) as well as the molecular area (AE*) of DGL adsorbed onto DLPC monolayer. Based on these data, a model for DGL adsorption onto DLPC monolayer at pH 5.0 is proposed for a surface pressure range of 15-25 mNm(-1).

Application to the Synthesis of Enantiopure Phosphonates Analogous to Triglycerides: A New Class of Inhibitors of Lipases

Phosphonate compounds mimic the first transition state occurring during enzymatic carboxyester hydrolysis of natural substrates by forming a covalent bond with the catalytic serine. However, until now the organophosphorus compounds used in the inhibition studies more or less resembled a natural triglyceride substrate. In order to elucidate the interfacial activation and the mechanism of action of lipases, specific inhibitors need to be prepared. To achieve this goal, enantiomerically pure sn-1,2- and sn-2,3-O-didecanoylglycerol compounds were prepared – starting from a C-4 chiral synthon, 3-buten-1,2-diol – and treated with n-pentylphosphonic dichloride and p-nitrophenol to afford the corresponding diastereomeric phosphonates, which were acylglycerol analogs. Subsequent separation of each of the phosphonate diastereomers A/B or ent-A/ent-B, performed by HPLC, led to four enantiopure stereoisomers that will be investigated as inhibitors of Human Pancreatic Lipase (HPL) and Human Gastric Lipase (HGL) using the monomolecular film technique.

Validation of lipolysis product extraction from aqueous/biological samples, separation and quantification by thin-layer chromatography with flame ionization detection analysis using O-cholesteryl ethylene glycol as a new internal standard

A general and easily accessible method for the extraction followed by the simultaneous separation and quantitative determination of triacylglycerols, diacylglycerols, monoacylglycerols and free fatty acids has been improved and optimized based on existing protocols using liquid-phase extraction and thin-layer chromatography coupled to flame ionization detection (TLC/FID Iatroscan). After lipid extraction in the presence of a suitable new synthetic internal standard, namely CholE1, a single elution step using n-heptane/diethyl ether/formic acid (55:45:1, v/v/v) was applied. This method was validated in line with international bioanalytical method validation guidelines using two different matrix systems: purified water and human gastro-intestinal fluid. Overall, the assay was found to have high levels of precision with coefficients of variation ranging from 1.48% to 11.0% and accuracy ranging from -13.3% to +5.79% RE. The confidence limits of the lipid mean recovery rates varied between 89.9% and 104%. This method is therefore highly suitable for quantifying the lipolysis products generated in vitro during the hydrolysis of various fats and oils by digestive lipases, as well as those collected from the gastro-intestinal tract in the course of human clinical studies on lipid digestion.

Adsorption of gastric lipase onto multicomponent model lipid monolayers with phase separation

The enzymatic lipolysis of complex natural lipoproteic assemblies such as milk fat globules is central in neonatal digestion. This process first requires the rapid adsorption of a lipolytic enzyme, gastric lipase, onto the membrane enveloping the triglyceride substrate before the onset of catalytic activity. The interactions governing lipase adsorption onto this complex lipid/water interface are not fully elucidated. This study was designed to unravel the interactions of recombinant dog gastric lipase (rDGL) with model monolayers presenting liquid-liquid phase coexistence and mimicking the outer leaflet of the milk fat globule membrane. Combining biophysical tools (ellipsometry, tensiometry and atomic force microscopy), it was evidenced that rDGL partitions toward liquid expanded phase and at phase boundaries. rDGL gets adsorbed at several levels of insertion suggesting molecular cooperation that may favor insertion and strongly impacts on the lipid phase lateral organization. The addition of phosphatidylserine, negatively charged, reinforced adsorption; hence besides hydrophobic interactions and as further investigated through surface potential modeling, rDGL adsorption is favored by electrostatic interactions.

Enantioselective Inhibition of Microbial Lipolytic Enzymes by Nonracemic Monocyclic Enolphosphonate Analogues of Cyclophostin

Four nonracemic enolphosphonate analogues of Cyclophostin were obtained by asymmetric synthesis, and their absolute configurations at both phosphorus and C-5 carbon chiral centers were unambiguously assigned. The influence of chirality was studied by testing the inhibitory effects of these four stereoisomers toward the lipolytic activity of three microbial lipases: Fusarium solani cutinase, Rv0183, and LipY from Mycobacterium tuberculosis . Cutinase was highly diastereoselective for the (Sp) configuration using (Sc) inhibitors, whereas no obvious stereopreference at phosphorus was observed with (Rc) compounds. Conversely, Rv0183 exhibited strong enantioselective discrimination for (Sp) configuration regardless of the chirality at the asymmetric carbon atom. Lastly, LipY discriminated only the unusual diastereoisomeric configuration (Rc, Rp) leading to the most potent inhibitor. This work, which provides a fundamental premise for the understanding of the stereoselective relationships between nonracemic enolphosphonates and their inhibitory activity, also opens new prospects on the design and synthesis of highly specific enantioselective antimicrobial agents.

Using the reversible inhibition of gastric lipase by Orlistat for investigating simultaneously lipase adsorption and substrate hydrolysis at the lipid-water interface.

The lipolysis reaction carried out by lipases at the water-lipid interface is a complex process including enzyme conformational changes, adsorption/desorption equilibrium and substrate hydrolysis. Mixed monomolecular films of the lipase inhibitor Orlistat and 1,2-dicaprin were used here to investigate the adsorption of dog gastric lipase (DGL) followed by the hydrolysis of 1,2-dicaprin. The combined study of these two essential catalysis steps was made possible thanks to the highest affinity of DGL for Orlistat than 1,2-dicaprin and the fact that the inhibition of DGL by Orlistat is reversible. Upon DGL binding to mixed 1,2-dicaprin/Orlistat monolayers, an increase in surface pressure reflecting lipase adsorption was first recorded. Limited amounts of Orlistat allowed to maintain DGL inactive on 1,2-dicaprin during a period of time that was sufficient to determine DGL adsorption and desorption rate constants. A decrease in surface pressure reflecting 1,2-dicaprin hydrolysis and product desorption was observed after the slow hydrolysis of the covalent DGL-Orlistat complex was complete. The rate of 1,2-dicaprin hydrolysis was recorded using the surface barostat technique. Based on a kinetic model describing the inhibition by Orlistat and the activity of DGL on a mixed 1,2-dicaprin/Orlistat monolayer spread at the air-water interface combined with surface pressure measurements, it was possible to monitor DGL adsorption at the lipid-water interface and substrate hydrolysis in the course of a single experiment. This allowed to assess the kcat/KM* ratio for DGL acting on 1,2-dicaprin monolayer, after showing that mixed monolayers containing a low fraction of Orlistat were similar to pure 1,2-dicaprin monolayers.

An interfacial and comparative in vitro study of gastrointestinal lipases and Yarrowia lipolytica LIP2 lipase, a candidate for enzyme replacement therapy.

Lipolytic activities of Yarrowia lipolytica LIP2 lipase (YLLIP2), human pancreatic (HPL) and dog gastric (DGL) lipases were first compared using lecithin-stabilized triacylglycerol (TAG) emulsions (Intralipid) at various pH and bile salt concentrations. Like DGL, YLLIP2 was able to hydrolyze TAG droplets covered by a lecithin monolayer, while HPL was not directly active on that substrate. These results were in good agreement with the respective kinetics of adsorption on phosphatidylcholine (PC) monomolecular films of the same three lipases, YLLIP2 being the most tensioactive lipase. YLLIP2 adsorption onto a PC monolayer spread at the air/water interface was influenced by pH-dependent changes in the enzyme/lipid interfacial association constant (KAds) which was optimum at pH 6.0 on long-chain egg PC monolayer, and at pH 5.0 on medium chain dilauroylphosphatidylcholine film. Using substrate monolayers (1,2-dicaprin, trioctanoin), YLLIP2 displayed the highest lipolytic activities on both substrates in the 25-35 mN m(-1) surface pressure range. YLLIP2 was active in a large pH range and displayed a pH-dependent activity profile combining DGL and HPL features at pH values found in the stomach (pH 3-5) and in the intestine (pH 6-7), respectively. The apparent maximum activity of YLLIP2 was observed at acidic pH 4-6 and was therefore well correlated with an efficient interfacial binding at these pH levels, whatever the type of interfaces (Intralipid emulsions, substrate or PC monolayers). All these findings support the use of YLLIP2 in enzyme replacement therapy for the treatment of pancreatic exocrine insufficiency, a pathological situation in which an acidification of intestinal contents occurs.