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At least 91 records · Page 5Linked to original sources
PubMed2003

Multivariate calibration standardization across instruments for the determination of glucose by Fourier transform near-infrared spectrometry.

The transfer of multivariate calibration models is investigated between a primary (A) and two secondary Fourier transform near-infrared (near-IR) spectrometers (B, C). The application studied in this work is the use of bands in the near-IR combination region of 5000-4000 cm(-)(1) to determine physiological levels of glucose in a buffered aqueous matrix containing varying levels of alanine, ascorbate, lactate, triacetin, and urea. The three spectrometers are used to measure 80 samples produced through a randomized experimental design that minimizes correlations between the component concentrations and between the concentrations of glucose and water. Direct standardization (DS), piecewise direct standardization (PDS), and guided model reoptimization (GMR) are evaluated for use in transferring partial least-squares calibration models developed with the spectra of 64 samples from the primary instrument to the prediction of glucose concentrations in 16 prediction samples measured with each secondary spectrometer. The three algorithms are evaluated as a function of the number of standardization samples used in transferring the calibration models. Performance criteria for judging the success of the calibration transfer are established as the standard error of prediction (SEP) for internal calibration models built with the spectra of the 64 calibration samples collected with each secondary spectrometer. These SEP values are 1.51 and 1.14 mM for spectrometers B and C, respectively. When calibration standardization is applied, the GMR algorithm is observed to outperform DS and PDS. With spectrometer C, the calibration transfer is highly successful, producing an SEP value of 1.07 mM. However, an SEP of 2.96 mM indicates unsuccessful calibration standardization with spectrometer B. This failure is attributed to differences in the variance structure of the spectra collected with spectrometers A and B. Diagnostic procedures are presented for use with the GMR algorithm that forecasts the successful calibration transfer with spectrometer C and the unsatisfactory results with spectrometer B.

Algorithms↗
PubMed1993

Lipoamidase activity in normal and mutagenized pancreatic cholesterol esterase (bile salt-stimulated lipase).

Purified human milk lipoamidase was digested with endoproteinase Lys-C and the digested peptides were subjected to gasphase microsequence analysis. The sequencing of three isolated peptides of human milk lipoamidase revealed the identity of this protein with human milk bile salt-stimulated lipase (pancreatic cholesterol esterase). The identity of the cholesterol esterase with lipoamidase was confirmed by expressing a recombinant form of rat pancreatic cholesterol esterase and testing for lipoamidase activity of the recombinant protein. The results showed that the recombinant cholesterol esterase displayed both lipolytic and lipoamidase activities and was capable of hydrolysing triacetin and lipoyl-4-aminobenzoate (LPAB). The mechanisms of the esterase and amidase activities of the enzyme were further tested by determining enzyme activity in a mutagenized cholesterol esterase with a His435-->Gln435 substitution. This mutation has been shown previously to abolish enzyme activity against esterase substrates [DiPersio, Fontaine and Hui (1991) J. Biol. Chem. 266, 4033-4036]. We showed that the mutagenized protein was effective in hydrolysing the amidase substrate LPAB and displayed similar enzyme kinetics to those of the native enzyme. These data indicate that the mechanism for the cholesterol esterase hydrolysis of lipoamides is different from that of the hydrolysis of substrates with an ester linkage. The presence of an enzyme in the gastrointestinal tract capable of both ester and amide hydrolysis suggests an important role for this protein in the digestion and absorption processes.

4-Aminobenzoic Acid↗
PubMedDate not supplied

Controlled delivery of drugs from a novel injectable in situ formed biodegradable PLGA microsphere system.

A novel method for in situ preparation of injectable biodegradable microspheres from the copolymer, poly(lactide-co-glycolide) (PLGA), without incorporating unacceptable organic solvents is described. The delivery system is a dispersion of PLGA microglobules ('premicrospheres' or 'embryonic microspheres') in an acceptable vehicle mixture (continuous phase) and whose integrity is maintained by the use of appropriate stabilizers. A solution of PLGA, triacetin, a model protein (cytochrome c), PEG 400, and Tween 80 (oil phase 1) is added dropwise with continuous homogenization to Miglyol 812-Span 80 solution (oil phase 2), thereby inducing phase separation (coacervation) of PLGA and forming PLGA microglobules (containing cytochrome c) dispersed in the continuous phase. This novel drug delivery system (NDDS) is a dispersion and has a viscous consistency, but is sufficiently syringeable. When injected, it comes in contact with water from an aqueous buffer or physiological fluid and, as a result, the microglobules harden to form solid matrix type microparticles entrapping cytochrome c (in situ formed microspheres). Cytochrome c is then released from these microspheres in a controlled fashion. The composition, rationale, and optimization of the NDDS are described here. Various formulation variables such as the PLGA concentration and type and the substitution of the continuous phase by a fresh oil phase 2 influenced the characteristics of this system. A preliminary investigation of the reproducibility and stability of the NDDS, as well as the physical stability of the encapsulated cytochrome c, revealed that these characteristics were not adversely affected.

Antifungal Agents↗
PubMed1991

Experimental short-bowel syndrome: effect of an elemental diet supplemented with short-chain triglycerides.

To determine whether short-chain triglycerides (SCTs, 1:1 triacetin:tributyrin, wt:wt) enhance intestinal adaptation in short-bowel syndrome (SBS), male Sprague-Dawley rats underwent 60% distal small-bowel resection with cecectomy and received either a chemically defined diet (CD) or a CD containing 40% of nonprotein energy as either medium-chain triglycerides (MCTs) or SCTs. After 12 d the SCT group had significantly increased jejunal mucosal weight compared with the MCT and CD groups and had significantly increased segment weight and mucosal protein compared with the CD group. In the colon the SCT group had significantly increased segment and mucosal weights and mucosal protein and DNA compared with both the MCT and CD groups. Body-weight change and measurements of serum ketones, albumin, glucose, and triglycerides revealed no significant differences among groups. SCTs improved jejunal and colonic adaptive growth and maintained comparable nutritional status in SBS when compared with CD alone or CD with MCTs.

3-Hydroxybutyric Acid↗
PubMed2002

Dynamics and fragmentation of thick-shelled microbubbles.

Localized delivery could decrease the systemic side effects of toxic chemotherapy drugs. The unique delivery agents we examine consist of microbubbles with an outer lipid coating, an oil layer, and a perfluorobutane gas core. These structures are 0.5-12 microm in radius at rest. Oil layers of these acoustically active lipospheres (AALs) range from 0.3-1.5 microm in thickness and thus the agents can carry a large payload compared to nano-scale drug delivery systems. We show that triacetin-based drug-delivery vehicles can be fragmented using ultrasound. Compared with a lipid-shelled contrast agent, the expansion of the drug-delivery vehicle within the first cycle is similar, and a subharmonic component is demonstrated at an equivalent radius, frequency, and driving pressure. For the experimental conditions explored here, the pulse length required for destruction of the drug-delivery vehicle is significantly greater, with at least five cycles required, compared with one cycle for the contrast agent. For the drug-delivery vehicle, the observed destruction mechanism varies with the initial radius, with microbubbles smaller than resonance size undergoing a symmetric collapse and producing a set of small, equal-sized fragments. Between resonance size and twice resonance size, surface waves become visible, and the oscillations become asymmetrical. For agents larger than twice the resonance radius, the destruction mechanism changes to a pinch-off, with one fragment containing a large fraction of the original volume.

Contrast Media↗
PubMed2006

Cell surface expression of bacterial esterase A by Saccharomyces cerevisiae and its enhancement by constitutive activation of the cellular unfolded protein response.

Yeast cell surface display is a powerful tool for expression and immobilization of biocatalytically active proteins on a unicellular eukaryote. Here bacterial carboxylesterase EstA from Burkholderia gladioli was covalently anchored into the cell wall of Saccharomyces cerevisiae by in-frame fusion to the endogenous yeast proteins Kre1p, Cwp2p, and Flo1p. When p-nitrophenyl acetate was used as a substrate, the esterase specific activities of yeast expressing the protein fusions were 103 mU mg(-1) protein for Kre1/EstA/Cwp2p and 72 mU mg(-1) protein for Kre1/EstA/Flo1p. In vivo cell wall targeting was confirmed by esterase solubilization after laminarinase treatment and immunofluorescence microscopy. EstA expression resulted in cell wall-associated esterase activities of 2.72 U mg(-1) protein for Kre1/EstA/Cwp2p and 1.27 U mg(-1) protein for Kre1/EstA/Flo1p. Furthermore, esterase display on the yeast cell surface enabled the cells to effectively grow on the esterase-dependent carbon source glycerol triacetate (Triacetin). In the case of Kre1/EstA/Flo1p, in vivo maturation within the yeast secretory pathway and final incorporation into the wall were further enhanced when there was constitutive activation of the unfolded protein response pathway. Our results demonstrate that esterase cell surface display in yeast, which, as shown here, is remarkably more effective than EstA surface display in Escherichia coli, can be further optimized by activating the protein folding machinery in the eukaryotic secretion pathway.

Bacterial Proteins↗
PubMed1974

Cell-bound lipase and esterase of Brevibacterium linens.

The activities of glycerol ester hydrolase, lipase (EC 3.1.1.3) and carboxylesterase, and esterase (EC 3.1.1.1) were determined for whole cell preparations of Brevibacterium linens by using the pH-stat assay. The culture growth liquors were inactive against the three substrates, tributyrin emulsion, triacetin, and methyl butyrate. Cells washed in water had less activity than cells washed in 5% NaCl; the ratio of activities was close to 1:2 for all strains using tributyrin emulsion as the substrate. For the esterase substrates, this relationship varied widely and was strain dependent. The ability to hydrolyze the two esterase substrates varied independently of the level of lipase activity.

Brevibacterium↗
PubMed1966

Hydrolysis of synthetic esters by the antibacterial agent in serum.

Yotis, William W. (Loyola University, Chicago, Ill.). Hydrolysis of synthetic esters by the antibacterial agent in serum. J. Bacteriol. 91:488-493. 1966.-An antistaphylococcal serum agent was assayed colorimetrically, manometrically, and titrimetrically for esterase activity. p-Nitrophenol acetate, triacetin, l-lysine methyl and ethyl ester, and norleucine methyl ester were hydrolyzed by the antistaphylococcal agent. Acetylcholine and benzoylcholine esters, triolein, tristearin, and p-tosylarginine methyl ester were not attacked by this agent. With p-nitrophenol acetate as substrate, optimal activity occurred at pH 7.4. Incubation at 60 C for 30 min reduced drastically the esterase activity of the antistaphylococcal agent, and incubation at 75 C for 30 min abolished the esterase activity of this agent. Almost complete inhibition of esterase activity was observed with 0.001 m HgCl(2), ZnSO(4), and ethylenediaminetetraacetic acid (EDTA). EDTA inhibition could be reversed by the addition of CaCl(2), but not MgCl(2). Cysteine reversed the inhibition of HgCl(2). NaF, atoxyl, diisopropyl fluorophosphate, quinine, and physostigmine did not influence the esterase activity of the antibacterial agent. The demonstration of esterase activity of both the antistaphylococcal agent and coagulase may shed further light on the reported ability of coagulase to neutralize the antistaphylococcal activity of this agent, or the prevention of absorption of the agent on the staphylococcal cell surface. In addition, the colorimetric procedure described in this report may be a convenient tool in assaying the potency of the antistaphylococcal agent.

Acetates↗
PubMed1983

Acetate-glucose relationship in growing pigs.

Twelve crossbred barrows from four litters (average initial body weight of 21 kg) were used to examine the relationship between acetate and glucose metabolism in pigs. The treatments were the addition of acetate in the form of triacetin to the basal diet at 0, 5 and 10% of the metabolizable energy intake. In the immediate postprandial period, the administered acetate decreased the venous plasma glucose concentration linearly (P less than .05) and increased linearly the venous plasma concentrations of lactate (P less than .01) and ketone bodies (P less than .001). There was a linear increase in the glycogen content of the liver (P less than .001), heart (P less than .001) and femoral muscle (P less than .01), as the level of acetate intake was increased. In the remote postprandial period (12 h after the last meal), glucose, which was considered to have been derived from hepatic glycogen storage, became the dominant blood metabolite in place of the acetate administered with the diet. This led to the reduction in hepatic production of endogenous acetate, arterial acetate concentration and in acetate utilization in the hind limb. Hepatic urea production was also decreased. Thus, there was a reciprocal change in acetate and glucose metabolism.

Acetates↗
PubMedDate not supplied

Application of encapsulated enzyme as a continuous packed-bed reactor.

In the previous report, microencapsulation of lipase employing a (w/o)/w multiple phase emulsion technique, with 2:1 polystyrene (PS)-SBR mixture being used as a wall material, was proposed. Catalysis of the encapsulated enzyme was investigated, and the hydrolysis of triacetin (triglyceride of acetic acid) was successfully simulated by the reaction model based upon the Michaelis-Menten mechanism. Other factors affecting the mechanism such as the mass-transfer resistance of the substrate molecules through the wall and the decrease in pH due to the formation of acetic acid were also taken into consideration. In this report, the particular microcapsules were applied to the continuous tubular reactor system, essentially a packed column reactor, and longevity and mechanical strength of the microcapsules were fully demonstrated. The reaction model derived for a well-stirred batch reactor was also applicable to simulate the behaviour in the packed-column reactor as it was proved that there is no mass transfer resistance between the reactant stream and the surface of microcapsules. The observed data agreed quite well with the calculated values. Similarity of the behaviours of catalysis observed between two reactor systems was thoroughly confirmed. No leakage of the enzyme was detected after repeated usage over the duration of a few months, the temperature being maintained in the range between 293 and 323 K, and pH reset after each operation. Commercial feasibility of the microcapsules for the enzyme catalysis with substrates, small enough to permeate through the wall, was established by these fundamental investigations.

Capsules↗
PubMedDate not supplied

Immobilization of enzyme by microencapsulation and application of the encapsulated enzyme in the catalysis.

Microencapsulation of lipase (Pseudomonas fluorescens) was carried out using (W/O)/W two-phase emulsion technique. Polystyrene (PS) and Styrene-Butadiene Rubber (SBR) were utilized as wall materials either separately or in mixture. A particular composition of 2:1 PS-SBR yielded homogeneous and tough wall structure, resilient to the impact and tight confinement of enzyme macromolecules. Performance of the encapsulated enzyme was evaluated employing the hydrolysis of triacetin (triglyceride of acetic acid) as a model substrate of the enzyme catalysis. A mathematical model was developed to simulate the behaviour of hydrolysis, which was derived under the assumption that the diffusion of small molecules (substrate and products) through the wall of microcapsules plays a dominant role to the reaction rate. Inhibition of the reaction by the decreasing pH due to the release of acetic acid was also taken into account. The calculated values agreed quite well with the observed data.

Drug Compounding↗
PubMed1969

Intestinal absorption and lymphatic transport of cholesterol in the rat: influence of the fatty acid chain length of the carrier triglyceride.

This paper deals with the effect of the fatty acid chain length of dietary triglyceride on the intestinal uptake and lymphatic transport of exogenous and endogenous cholesterol in the rat. This question seemed of interest as the chain length of the monoglyceride and fatty acids formed in the intestinal lumen from the triglyceride fed could be expected to affect the concentration of cholesterol in the micellar or isotropic phase of intestinal content. Feeding rats medium- or short-chain triglycerides (C(12) to C(2)) did not affect the lymphatic transport of endogenous cholesterol from the intestine compared to the fasting state. The extent of lymphatic transport of cholesterol added to these fats increased proportionally with chain length (C(6)-C(18)) of the component fatty acids. The uptake of exogenous cholesterol into the intestinal wall was similarly related to the chain length of the carrier triglyceride, with the exception of triacetin, which gave a much higher intestinal uptake than lymphatic transport. When cholesterol was fed in octadecane, negligible amounts only were transported to the thoracic duct lymph. This again indicates the importance of the polar split products of dietary fat for cholesterol absorption.

Alkanes↗
PubMed1977

TLG medium for pigment detection of staphylococci.

The semidefined medium (TLG) for carotenoid pigment production of staphylococci consists of 0.3% triacetin, 0.1% sodium lactate and 0.1% glucose in nutrient agar. The TLG is used for harvesting of cells for pigment extraction or, with calcium carbonate added, for colour determination of colonies.

Carotenoids↗
PubMed1992

An environmental survey in chrysotile asbestos milling processes in India.

Environmental monitoring to determine airborne asbestos fiber levels has been carried out in four different mills processing chrysotile asbestos in the Cuddapah District (Andhra Pradesh) of India. The "membrane filter method" comprising standard asbestos sampling techniques, acetone-triacetin method for sample preparation, fiber counting, and sizing using the phase contrast optical microscope were adopted in the study. Fiber concentrations both with respect to personal exposures and processing areas were found in most of the cases to be much higher than the prescribed Threshold Limit Value (TLVs) of the developed and developing countries for chrysotile asbestos. By optical microscopy, fiber length distribution showed 70% of fibers in the milling processes were in size range > 5-10 microns, whereas in > 10-20 and > 20 microns, 20% and 8%, respectively. Fiber identification for major elemental content, also done by using scanning electron microscope equipped with an energy dispersive X-ray analyzer, indicated the presence of tremolite along with chrysotile. The study stresses the urgent need to adopt suitable engineering controls at the dust generating sources to reduce the fiber level in the mill environment below the threshold limit.

Air Pollutants, Occupational↗
PubMed2002

Starch acetate--a novel film-forming polymer for pharmaceutical coatings.

Starch acetates (SA) have been investigated as novel, multifunctional excipients for the direct compression tableting process. In this study, the film-forming ability of SA (DS 2.8) and the effect of commonly used plasticizers on the physical properties of SA films were evaluated. The results were compared with the properties of ethylcellulose (EC). Free films were prepared by a solvent-cast method. Mechanical studies, water vapor and drug permeability tests, and thermal analysis (DSC) were used to characterize the film-forming ability of SA and efficiency of tested plasticizers. SA films were tougher and stronger than EC films at the same plasticizer concentration. Also, in most cases, the water vapor permeability of SA films was lower than that of EC films. DSC thermograms supported the findings of the tensile test: plasticizers with several small ester groups (e.g., triacetin and triethyl citrate) were the most compatible with SA. Due to the good mechanical properties, low water vapor, and drug permeabilities of the films, SA seems to be a promising film-former for pharmaceutical coatings. The toughness of SA films may result from their dense film structure, which is due to strong interaction forces between adjacent SA molecular chains.

Permeability↗
PubMed1988

A colony procedure for transformation of Saccharomyces cerevisiae.

A rapid and simple yeast transformation procedure has been developed using colonies on agar plates. Saccharomyces cerevisiae SHY3 cells were picked up from colonies on YPD plates grown freshly or stored at 4 degrees C and incubated with M13RK9-T DNA at 30 degrees C for 1-2 h in a solution of Li+, Ca2+, Mg2+, triacetin and polyethylene glycol. About 3,500 transformants were obtained per microgram of double stranded M13RK9-T DNA. Unlike the existing spheroplast techniques, single stranded M13RK9-T DNA transformed intact cells below one-hundredth frequency of the duplex form.

Genetic Engineering↗
PubMed1983

Experience with an industrially manufactured gel PGE2 for cervical priming.

An industrially manufactured ready-to-use PGE2 gel for cervical ripening was clinically evaluated. The study included 42 primiparous and eight multiparous women with an unfavourable cervix (Bishop score less than or equal to 5) admitted to hospital for induction of labour on medical grounds. PGE2, 0.5 mg, in 2 ml triacetin gel was instilled into the cervical canal. In nine patients (18%) the gel induced labour and subsequent delivery. In the remaining women the mean Bishop score increased from 3.0 to 7.7 during a 24-h period and labour was induced by either i.v. oxytocin or PGF2 alpha. None of the 50 patients experienced gastrointestinal side effects during pretreatment with PGE2. In 50% of the patients slight uterine contractility was noticed. All patients went into labour. The incidence of Cesarean section was 10%. Except for two patients treated because of intrauterine fetal death there was no perinatal mortality. The 5-min Apgar score was 8 or more in all newborn but 1. The main advantage of the new gel is that it is ready to use without any mixing procedure. Moreover, the stability of PGE2 is sufficient to allow routine clinical use.

Adolescent↗
PubMed2002

Distinction between esterases and lipases: a kinetic study with vinyl esters and TAG.

The better to characterize enzymes hydrolyzing carboxyl ester bonds (carboxyl ester hydrolases), we have compared the kinetic behavior of various lipases and esterases against solutions and emulsions of vinyl esters and TAG. Short-chain vinyl esters are hydrolyzed at comparable rates by esterases and lipases and have higher limits of solubility in water than corresponding TAG. Therefore, they are suited to study the influence of the physical state of the substrate on carboxyl ester hydrolase activity within a large concentration range. Enzymes used in this study are TAG lipases from microorganisms, lipases from human and guinea pig pancreas, pig liver esterase, and acetylcholinesterase. This study also includes cutinase, a fungal enzyme that displays functional properties between esterases and lipases. Esterases display maximal activity against solutions of short-chain vinyl esters (vinyl acetate, vinyl propionate, and vinyl butyrate) and TAG (triacetin, tripropionin, and tributyrin). Half-maximal activity is reached at ester concentrations far below the solubility limit. The transition from solution to emulsion at substrate concentrations exceeding the solubility limit has no effect on esterase activity. Lipases are active on solutions of short-chain vinyl esters and TAG but, in contrast to esterases, they all display maximal activity against emulsified substrates and half-maximal activity is reached at substrate concentrations near the solubility limit of the esters. The kinetics of hydrolysis of soluble substrates by lipases are either hyperbolic or deviate from the Michaelis-Menten model and show no or weak interfacial activation. The presence of molecular aggregates in solutions of short-chain substrates, as evidenced by a spectral dye method, likely accounts for the activity of lipases against soluble esters. Unlike esterases, lipases hydrolyze emulsions of water-insoluble medium- and long-chain vinyl esters and TAG such as vinyl laurate, trioctanoin, and olive oil. In conclusion, comparisons of the kinetic behavior of carboxyl ester hydrolases against solutions and emulsions of vinyl esters and TAG allows the distinction between lipases and esterases. In this respect, it clearly appears that guinea pig pancreatic lipase and cutinase are unambiguously classified as lipases.

Acetylcholinesterase↗