Biomedical subjects

D R Lu

Publications and source records attributed to D R Lu.

At least 19 recordsLinked to original sources

PubMed2000

Targeted drug delivery for brain cancer treatment.

The blood brain barrier (BBB) and the systemic toxicity of conventional chemotherapy present obstacles to the success of future blood-borne drug therapies of brain tumors. The work with polymer-encapsulated cancer drugs suggests an alternative and more focused treatment approach. Our experimental strategy integrates direct intracerebral drug delivery, sustained drug release from liposomes or polymer implants, and increased targeting of the drug either by chemically modifying the drug or by using tumor-specific carriers. This review will present some of the recent work on targeted drug delivery for brain cancer treatment.

Animals↗

PubMed1998

Effect of gastrointestinal protein adsorption on the in vitro release of AZT from ethylcellulose microspheres.

The purpose of this study was to assess the effect of gastrointestinal proteins on the in vitro release of zidovudine (AZT) from ethylcellulose microspheres, and to investigate protein adsorption as a possible mechanism that mediates this effect. AZT release from ethylcellulose microspheres was tested in the presence of different gastrointestinal proteins, both dietary (casein and albumin) and endogenous (pepsin, pancreatin, and mucin) in simulated gastric fluid and/or simulated intestinal fluid. The resulting release profiles were compared with those produced in the corresponding release media without the presence of proteins. Protein adsorption on AZT-loaded ethylcellulose microspheres was studied for the five proteins under investigation. The amounts of adsorbed proteins were determined by fluorescent spectrometry after the protein solution was reacted with fluoraldehyde reagent. All of the investigated proteins were found to slow the release of AZT from ethylcellulose microspheres. At gastric pH, ovalbumin and casein had the maximum effect on AZT release. Mucin exerted a more pronounced effect at gastric pH compared with that at intestinal pH. The negative effect of pancreatin on AZT release increased when its concentration was increased. The five proteins were found to adsorb on AZT-loaded ethylcellulose microspheres with varying quantities. The observed protein adsorption is believed to cause blockage of the small pores and channels in the microsphere structure, and consequently slow the release of AZT.

Adsorption↗

PubMed1998

[Splicing and stability of intron in the expression retroviral vector with human clotting factor IX].

To study the role of intron in the expression of hFIX, retroviral vectors with intron containing hFIX were constructed. It is fundamental for the intron study whether the intron constructed in retroviral vector can be steadily transferred into target cell. First, we constructed two forward-orientation retroviral vectors: G1NaC-i-IX contains the exogenous intron from IL-2, and G1NaC-i'-IX contains the truncated intron I from hFIX gene, covering the splicing donor and acceptor sequences. RT-PCR result indicated that intron in the forward-orientation retroviral vector was spliced after packaging in PA317. Then, reverse-orientation retroviral vectors G1NaC-i'-IXR and G1NaPAIXi' BAM were constructed, in which the reverse and complimentary sequences of hFIX gene with intron appeared in retroviral RNA. RT-PCR assay combined with ELISA test indicated that intron was retained after packaging and hFIX gene with intron constructed in the reverse-orientation retroviral vector can be transduced intact and expressed hFIX at a high level in vitro.

Factor IX↗

PubMed1997

In vivo evaluation of zidovudine (AZT)-loaded ethylcellulose microspheres after oral administration in beagle dogs.

The purpose of this study was to evaluate the in vivo performance of sustained-release zidovudine (AZT) microspheres after oral administration in Beagle dogs, and to establish an in vitro-in vivo correlation. Two AZT microsphere formulations as well as AZT powder were administered to four Beagle dogs. Plasma samples were analyzed by HPLC. The plasma concentration-time data was analyzed by both compartmental and noncompartmental pharmacokinetic analyses. Based on the calculated pharmacokinetic parameters, in vivo release profiles were simulated and compared with in vitro release profiles in three different release media. Significantly longer mean residence time (MRT) was observed after administration of the sustained-release microspheres compared with AZT powder. Significantly lower maximum (Cmax) concentration values and longer times to Cmax (tmax) values were also observed. Formulation I showed the longest MRT (4.4 h). AZT plasma concentration was maintained above the minimum effective concentration for approximately 10 h after administration of Formulation I. The relative bioavailability of the microsphere formulations with respect to AZT powder was not significantly different from 1. The in vitro release of the three formulations was slower in simulated gastric fluid compared with simulated intestinal fluid. The addition of enzymes and mucin to the release media significantly lowered the in vitro release rate of AZT from the microspheres formulations, but not from AZT powder. A good level of in vitro-in vivo correlation (Level A correlation) was achieved with a release medium that was composed of simulated gastric fluid with pepsin and mucin for 2 h followed by simulated intestinal fluid with pancreatin and mucin for 8 h. This in vitro model may be used to predict the in vivo release of AZT, in the further development of controlled-release AZT formulations.

Administration, Oral↗

PubMed1997

Biodegradable cisplatin microspheres for direct brain injection: preparation and characterization.

The objectives of the present study were to prepare cisplatin loaded-PLGA microspheres that are suitable for direct brain injection and to characterize them in terms of their physicochemical properties, in vitro drug release, and self-removal mechanism. The microspheres were prepared by emulsification/solvent evaporation method using PLGA (50:50) as the biodegradable matrix forming polymer. The physicochemical characterization encompassed the following: surface morphology, particle size, entrapment efficiency, surface area, and density. The in vitro release and in vitro degradation studies were performed in phosphate buffer and in 10% rat brain preparation. SEM micrographs revealed that the microspheres have a rough porous surface and a smooth interior. Particle size typically ranged from 180 to 250 microns with an average of 230 T microns. Entrapment efficiency was approximately 70% and was found to be dependent on the particle size. Surface area and density ranged from 0.038 to 0.025 m2/g and from 1.44 to 1.39 g/cm3, respectively. Both were also dependent on particle size. In the in vitro release study in phosphate buffer, approximately 80% of cisplatin was released over 30 days, after which the release rate plateaued. The release profile in 10% rat brain preparation was comparable in shape to that obtained in phosphate buffer. However, the release rate was lower and the total amount released by the end of the study was only 55% of the total cisplatin content. The degradation of PLGA microspheres in phosphate buffer and in rat brain homogenate correlated well with the respective release profiles. Based on the evidence of self-removal and the sustained release of cisplatin for over a month, cisplatin-loaded PLGA microspheres may be useful for local delivery to brain tumors.

Animals↗

PubMed1996

Preparation and evaluation of sustained release AZT-loaded microspheres: optimization of the release characteristics using response surface methodology.

The purpose of the study was to prepare and optimize a sustained release formulation of zidovudine (AZT). Ethylcellulose microspheres containing AZT were prepared using an emulsification/solvent evaporation technique. The critical formulation variables were emulsifier concentration, drug to polymer ratio, and ethyl acetate concentration in the internal phase of the emulsion. The time to release 85% of the contents of the microspheres (t85) was used as a measure for the release time. A second-year polynomial equation was fitted to the release data to systemically investigate the effect of the formulation variables on the release rate. This equation was then used to predict t85 in the optimum region. The t85 was found to be dependent on the three formulation variables, with strong interactions observed between these variables. The microspheres were characterized in terms of their particle size and surface morphology. The study indicated no overall correlation between the mean diameter of the microspheres and the t85.

Drug Delivery Systems↗

PubMed1996

Preparation and evaluation of zidovudine-loaded sustained-release microspheres. 2. Optimization of multiple response variables.

The formulation of zidovudine-loaded (AZT-loaded) sustained-release microspheres was prepared and optimized using response surface methodology. The objective was to use this statistical procedure to obtain a formulation with optimized overall properties. The effect of formulation variables (emulsifier concentration, drug to polymer ratio, and composition of the internal phase of the emulsion) on a number of response variables was systemically investigated. The response variables were t85, entrapment efficiency, yield, and percentage of loose surface crystals. A desirability function that combines these four response variables was constructed. A second-order polynomial equation was fitted to the data, and the resulting equation was used to predict the responses in the optimal region. All the investigated response variable were found to be highly dependent on the formulation variables, with strong interactions observed between the formulation variables. It was found that optimum overall desirability of AZT microspheres can be obtained at low levels of SDS and ethyl acetate concentrations and at intermediate levels of drug to polymer ratio. An optimized formulation was prepared under these experimental conditions and evaluated for individual responses and overall desirability. The experimental values of the response variables highly agreed with the predicted values.

Chemistry, Pharmaceutical↗

PubMed1996

Targeted drug delivery for boron neutron capture therapy.

PURPOSE: Boron neutron capture therapy (BNCT) is a form of radiochemotherapy that is becoming increasingly important for the treatment of malignant gliomas, malignant melanomas and other forms of cancer. Targeted delivery of boron to tumors is a critical prerequisite for successful BNCT. METHODS: Strategies that involve synthetic chemical approaches and biochemical and biophysical approaches are employed to meet this requirement. Compounds developed for targeting to tumors include borocaptate sodium (BSH) and p-boronophenylalanine (BPA) which are currently in clinical use. RESULTS: Boronated porphyrins, nucleosides, nucleotides and other boronated compounds show potentials as targeting molecules. Conjugation of boron compounds to macromolecules such as monoclonal antibodies, epidermal growth factor and dextran is also employed for active or passive tumor targeting. CONCLUSIONS: Boron delivery via microparticulate carriers such as liposomes, high density lipoproteins and microcapsules is also attractive for its potential application in BNCT.

Animals↗

PubMed1996

Optima: a windows-based program for computer-aided optimization of controlled-release dosage forms.

The purpose of this work was to develop a computer program that assists optimization of controlled-release devices, both visually and mathematically, using response surface methodology (RSM). A Windows-based computer program, Optima, which interactively implemented a number of subroutines for the optimization procedure, was developed. Optima is an integrated, user-friendly, and graphically oriented program for pharmaceutical dosage form optimization. Central composite design is implemented in the program. First- and second-order models containing up to five variables can be fitted to the data. The user can also choose between linear and exponential individual desirability functions, and use them to construct an overall desirability function that combines all the response variables in a single response. The program can predict the optimum levels of experimental variables, with respect to individual responses and/or the overall desirability. Optima has been successfully used in the development of sustained-release AZT-loaded microspheres. During the optimization process, three experimental variables were investigated and four responses were measured. The experimental design was a central composite design that was generated by the program. The response values were used by the program to calculate the individual desirability functions, which were then combined into an overall desirability function. The individual responses as well as the overall desirability function were optimized by fitting to a second-order polynomial equation. The response surfaces were generated and optimum levels of the experimental variables were predicted. The observed responses of the optimized formulation were very close to those predicted by Optima. The program proved to be a very useful, integrated tool for optimization of the controlled-release microspheres.

Computer Graphics↗

PubMed1995

High-performance liquid chromatographic assay for sodium mercaptoundecahydrododecaborate in rat tissues.

Mercaptoundecahydrododecaborate (BSH) is an important agent for the boron neutron-capture therapy (BNCT). A sensitive high-performance liquid chromatographic (HPLC) method was developed for measuring BSH concentrations in rat tissues. Various tissue samples containing the drug were homogenized in a 1:1 (g/ml) mixture with phosphate buffered saline. The samples were then deproteinised with 4 volumes of acetonitrile and centrifuged. An aliquot of the supernatant was dried and reconstituted in 200 microliter of Tris-HC1 buffer. The samples were subjected to precolumn derivatization using the thiol reactive monobromobimane (mBB). The drug-mBB adduct was resolved by isocratic elution from a C18 reversed-phase column. The optimized mobile phase was methanol-0.02 M phosphate buffer (43:57, v/v) containing 0.01 M tetrabutylammonium dihydrogen phosphate as the ion-pairing agent with the final pH adjusted to 7.0. The flow-rate was set at 2.0 ml/min. The adduct was monitored by UV absorption at 373 nm. The analysis was completed in less than 15 min. The detection limit was 0.5 microgram/ml (0.25 microgram of boron). The assay method was linear over a concentration range of 0.5 to 50 micrograms/ml. This assay method could be used to evaluate the BSH concentrations in different tissues in studies on the targeted delivery of BSH.

Animals↗

PubMed1995

Interspecies pharmacokinetic scaling of BSH in mice, rats, rabbits, and humans.

Sodium mercaptoundecahydrododecaborate or BSH is an important compound for boron neutron capture therapy (BNCT). The total clearance and steady state volume of distribution of BSH in humans and in laboratory animals were analyzed as a function of species body weight using the allometric equation for interspecies scaling. Significant linear relationships were obtained between log CLt (Lh-1) and log W (kg) (r = 0.972; p = 0.028) as well as log VSS (L) and log W (kg) (r = 0.999; p = 0.0005). The corresponding allometric equations were CLt = 0.127 W0.68 and VSS = 1.557 W0.87, respectively. BSH clearance in various species was shown to be a constant fraction (0.26) of creatinine clearance, the relationship being independent of body weight. Thus BSH clearance in various species occurred at similar pace when measured by a physiological parameter (creatinine clearance) rather than chronological time. Interspecies scale-up of plasma concentration-time data for the four species using a complex Dedrick plot resulted in similar profiles. Our results indicate that the BSH data obtained in laboratory animals could be utilized to generate preliminary estimates of the pharmacokinetic parameters in humans. These parameters can serve as guidelines for better planning of clinical studies.

Animals↗

PubMed1995

Pharmacokinetics of sodium mercaptoundecahydrododecaborate after intravenous injection in rats.

Boron neutron capture therapy (BNCT) is a binary therapy aimed at treating various forms of cancer. Sodium mercaptoundecahydrododecaborate (Na2B12H11SH) or BSH is the compound most widely used for BNCT. The pharmacokinetics of BSH were studied in rats after intravenous bolus injection at two doses of BSH (50 mg/kg and 100 mg/kg). BSH was analyzed by a high performance liquid chromatography (HPLC) method specific to BSH. The elimination of BSH from plasma was slow; the average elimination half life was approximately 15 hr for both doses. Estimates of the steady state volume of distribution and total clearance were 2.11 +/- 0.49 liters/kg and 0.28 +/- 0.03 liters/hr/kg, respectively, for the 50 mg/kg dose and 2.06 +/- 0.38 liters/kg and 0.32 +/- 0.06 liters/hr/kg, respectively, for the 100 mg/kg dose. The differences in the mean values of the parameters for the two doses were not statistically significant; this indicates that BSH exhibits linear pharmacokinetics over the dose range studied. BSH was moderately bound to plasma proteins and the binding was linear over the concentration range studied. Approximately 60% of the drug was recovered unchanged in urine after 24 hr. When we compared our results with the limited data available in the literature on BSH disposition in rats with use of nonspecific analysis methods, it seems that the BSH disposition determined by our HPLC method is not likely to be different from the total boron disposition measured by other methods.

Animals↗

PubMed1994

Liquid chromatographic determination of sodium mercaptoundecahydrododecaborate in rat urine and plasma after precolumn derivatization.

A high-performance liquid chromatographic (HPLC) method was developed for the determination of disodium mercaptoundecahydrododecaborate (BSH) in biological fluids. Monobromobimane was used as a precolumn derivatizing agent. A stable derivative was obtained. The derivative was separated on a C18 column using reversed-phase ion-pairing chromatography and detected by a spectrophotometric detector at 373 nm. The detection limit was 200 ng/ml (0.1 ppm boron). Calibration curves were prepared for rat urine and plasma samples. The calibration curves were linear in the range of 1 microgram/ml to 100 micrograms/ml for urine samples and 0.2 micrograms/ml to 50 micrograms/ml for plasma samples.

Absorption↗

PubMed1994

Brain mitochondrial citrate synthase and glutamate dehydrogenase: differential inhibition by fatty acyl coenzyme A derivatives.

Organic acidemia is found in several metabolic encephalopathies (e.g., hepatic and valproate encephalopathies, Reye's syndrome, and hereditary organic acidemias). Although fatty acids are known to be neurotoxic, the underlying mechanisms have not been fully elucidated. It has been hypothesized that one mechanism underlying fatty acid neurotoxicity is the selective inhibition of rate-limiting and/or regulated tricarboxylic acid (TCA) cycle and related enzymes by fatty acyl-coenzyme A (CoA) derivatives. To test the hypothesis, this study has examined the effects of several fatty acyl-CoAs on citrate synthase (CS) and glutamate dehydrogenase (GDH) in brain mitochondria. At levels higher than 100 microM, butyryl-CoA (BCoA; a short-chain acyl-CoA; IC50 approximately 640 microM), octanoyl-CoA (OCoA; a medium-chain acyl-CoA; IC50 approximately 380 microM), n-decanoyl-CoA (DCoA; a medium-chain acyl-CoA; IC50 approximately 436 microM), and palmitoyl-CoA (PCoA; a long-chain acyl-CoA; IC50 approximately 340 microM) inhibited brain mitochondrial CS activity in a concentration-related manner. However, these fatty acyl-CoAs were less effective inhibitors (IC50 values for OCoA, DCoA, and PCoA being approximately 1260, 420, and 720 microM, respectively) of brain mitochondrial GDH activity. Compared to the other three acyl-CoAs investigated, BCoA was a very poor inhibitor of GDH. These results demonstrate that fatty acyl-CoAs are inhibitors of brain mitochondrial CS and GDH activities only at pathological/toxicological levels. Thus, the fatty acyl-CoA inhibition of brain mitochondrial CS and GDH is unlikely to assume major pathophysiological and/or pathogenetic importance.(ABSTRACT TRUNCATED AT 250 WORDS)

Acyl Coenzyme A↗

PubMed1994

FT-IR measurement of mercaptoundecahydrododecaborate in human plasma.

A simple and rapid method for the quantitative measurement of mercaptoundecahydrododecarborate (BSH), (which presently is one of the most useful agents for Boron Neutron Capture Therapy) in human plasma was developed by using Fourier transform infrared spectroscopy. Different spacer thicknesses of the liquid sampling cell were examined and the optimal results were obtained by the 0.05 mm spacer. The subtraction of water absorbance from sample spectra resolved a B-H band at 2493 cm-1. The quantitative measurement of BSH was carried out by integration of the B-H band in the wavenumber range of 2534-2440 cm-1. However, at the lower BSH concentration range, a visual inspection of the spectrum to determine the wavenumber range was necessary so as to avoid any negative areas to be integrated. The lower limit of detection of BSH in aqueous solution and human plasma was 5 micrograms ml-1 (about 2.5 ppm of boron).

Borohydrides↗

PubMed1993

An interactive program for pharmacokinetic modeling.

A computer program, PharmK, was developed for pharmacokinetic modeling of experimental data. The program was written in C computer language based on the high-level user-interface Macintosh operating system. The intention was to provide a user-friendly tool for users of Macintosh computers. An interactive algorithm based on the exponential stripping method is used for the initial parameter estimation. Nonlinear pharmacokinetic model fitting is based on the maximum likelihood estimation method and is performed by the Levenberg-Marquardt method based on chi 2 criterion. Several methods are available to aid the evaluation of the fitting results. Pharmacokinetic data sets have been examined with the PharmK program, and the results are comparable with those obtained with other programs that are currently available for IBM PC-compatible and other types of computers.

Administration, Oral↗

PubMed1993

Glucagon adsorption on polymer surfaces with alpha-helical and extended beta-strand conformations: a computational approach.

The adsorption of glucagon with alpha-helical and extended beta-strand conformations on polymer surfaces was investigated using a computer simulation approach. An X-ray crystallographic structure of glucagon was employed in the study of the alpha-helical glucagon adsorption. The X-ray structure was then modified to simulate an extended beta-strand structure in the study of the beta-strand glucagon adsorption. Totally, 1632 different adsorption orientations of glucagon with each conformation were examined on polystyrene, polypropylene, polyethylene, poly(hydroxyethyl methacrylate) and poly(vinyl alcohol) surfaces. The calculation of the average adsorption energies among different orientations did not reveal any marked difference between the two conformations. However, when the lowest-energy orientations were compared, the adsorption energy of the extended beta-strand glucagon was always much lower than that of the alpha-helical glucagon, indicating that the adsorption of extended beta-strand glucagon was more energy favorable. The lower adsorption energy for the extended beta-strand glucagon than for the alpha-helical glucagon appeared to be contributed by the lower interaction potential energy of the former conformation. A greater number of the surface atoms in the extended beta-strand glucagon than in the alpha-helical glucagon was also observed. Fourier transform infrared spectroscopic (FTIR) studies in the literature showed conformational changes in adsorption of various larger proteins. Our study appears to provide a theoretical insight for the results from the FTIR studies.

Adsorption↗

PubMed1993

Differential effects of fatty acyl coenzyme A derivatives on citrate synthase and glutamate dehydrogenase.

We investigated the hypothesis that one mechanism underlying fatty acid toxicity is the selective inhibition of rate-limiting and/or regulated tricarboxylic acid cycle and related enzymes by fatty acyl coenzyme A (CoA) derivatives by examining the effects of several fatty acyl CoAs on purified citrate synthase (CS) and glutamate dehydrogenase (GDH). The results indicate that, at pathophysiological levels, palmitoyl CoA, a long-chain acyl CoA, is a potent inhibitor of CS and GDH with IC50 values of 3-15 microM. At much higher levels (in the pathological and toxicological range), octanoyl and decanoyl CoA (medium-chain acyl CoAs) inhibited both enzymes with IC50 values of 0.4-1.6 mM. Butyryl CoA, a short-chain acyl CoA, inhibited CS (IC50 = 0.9 mM) at toxicological levels but inhibited GDH poorly. These results suggest that the long-chain fatty acyl CoA inhibition of CS and GDH may assume some pathophysiological importance in fatty acid toxicity and in metabolic encephalopathies in which organic acidemia is persistent. The findings also provide additional support for the original hypothesis.

Acyl Coenzyme A↗