Biomedical subjects

L Hovgaard

Publications and source records attributed to L Hovgaard.

12 recordsLinked to original sources

PubMed2006

Characterisation of salmon calcitonin in spray-dried powder for inhalation. Effect of chitosan.

Salmon calcitonin (sCT) powders suitable for inhalation, containing chitosan and mannitol as absorption enhancer and protection agent, respectively, were prepared using a spray-drying process. The effect of chitosan on physicochemical stability of sCT in the dry powder was investigated by different analytical techniques. High-performance liquid chromatography (HPLC) analysis indicated that sCT was chemically stable upon spray-drying. With the proportion of chitosan in spray-drying formulation being increased, dissolution of sCT from the dry powders was decreased both in phosphate buffer and acetate buffer. The thioflavine T fluorescence assay showed that no fibrils were present in the spray-dried powder. However, sCT partly fibrillated in the phosphate buffer, but not in acetate buffer. Fourier transform infrared (FTIR) spectra showed that the secondary structure of sCT was slightly changed in the dry powder, yet no aggregate signal was observed. Circular dichroism analysis indicated that the structure of sCT in an aqueous formulation was slightly altered by addition of chitosan. Nevertheless, recovery of sCT was not influenced by chitosan in the aqueous formulation as indicated by HPLC analysis. This study suggested that sCT, in absence of any additives, was stable during the spray-drying process under certain conditions. Addition of chitosan affects recovery of sCT from spray-dried powders, which may be due to formation of a partially irreversible complex between the protein and chitosan during the spray-drying process.

Administration, Inhalation↗

PubMed2001

Direct estimation of the in vivo dissolution of spironolactone, in two particle size ranges, using the single-pass perfusion technique (Loc-I-Gut) in humans.

AIM: The objective of this in vivo dissolution study was to investigate the usefulness of the Loc-I-Gut technique for differentiating between the in vivo dissolution rate of two particle sizes of spironolactone, and to compare these in vivo results with corresponding in vitro data. METHODS: The study included six volunteers, and consisted of three sequential parts (I, II, III). In parts I and III the in vivo dissolution was measured directly by perfusing a semi-open segment in the proximal jejunum. In part II, a solution of spironolactone was administered orally, and the plasma concentration time profile was followed for 48 h. The in vitro dissolution was measured using flow-through cells and different dissolution media simulating human gastrointestinal fluids. RESULTS: A difference in in vivo dissolution rate of the two different particle sizes was observed, based on perfusion data. This difference was not pronounced in the relative bioavailability of spironolactone administered in two different particle sizes. The relative bioavailability was dependent on the bile acid concentration in vivo. In vitro, dissolution rate of the smaller particles was improved at fasted state bile acid concentrations, while the larger particles were only significantly affected at fed state bile acid concentrations. CONCLUSION: In vivo dissolution studies discriminated between the dissolution rate of the two different particle sizes of spironolactone, based on the perfusate samples. The lack of difference in relative bioavailability, might be explained by the insufficient wash-out of particles after ending the perfusion, reabsorption of surface active ingredients along the GI tract, relatively small difference in particle size and the large inter- and intra-individual differences in pharmacokinetic variables.

Adsorption↗

PubMed2001

A dynamic in vitro lipolysis model. I. Controlling the rate of lipolysis by continuous addition of calcium.

Lipolysis by pancreatic lipase was investigated with the aim to establish an in vitro lipolysis model, which can be used to investigate the dissolution of poorly soluble lipophilic drug substances at controlled hydrolysis rates. The effects of three experimental parameters -- the concentrations of bile salts and Ca(2+) and the lipase activity -- were investigated. The effect on the rate of hydrolysis of emulsified soybean oil was investigated in experiments in a pH-stat at pH 6.5 and 37 degrees C. The free fatty acids produced by the hydrolysis were titrated at pH 6.5. It was shown that all three investigated parameters influence the initial rate of hydrolysis, whereas only the lipase activity and the concentration of Ca(2+) affect the subsequent stages. It was also shown that the rate of lipolysis can be controlled by the rate of adding Ca(2+). Thus, it is possible to design an in vitro model using readily available and inexpensive materials in which the hydrolysis rate can be controlled by the continuous addition of Ca(2+).

Animals↗

PubMed2001

A dynamic in vitro lipolysis model. II: Evaluation of the model.

A lipolysis model was characterised and evaluated by investigating the composition of the aqueous phase and the concentration of probucol and danazol in the aqueous phase. Effects of bile salt levels at 5, 10, 20, and 30 mM were investigated. Samples were taken at 0%, 50%, 75% and 95% hydrolysis of the triglycerides, and the aqueous phases were isolated by ultra-centrifugation, whereby the concentrations of bile salts, fatty acids, mono-, di-, triglycerides, and drug substances were measured. At high Ca(2+)-concentrations, bile salts were believed to precipitate with Ca(2+). The concentration of lipolytic products (fatty acids + monoglycerides) was dependent on the bile salt concentration. The ratio between lipolytic product and bile salts was 1.55+/-0.09 (S.D.). This ratio is equivalent to mixed bile salt micelles and vesicles in equilibrium. The aqueous solubility of probucol and danazol was increased in the presence of bile salts. The concentration of danazol in the aqueous phase was dependent on the solubilisation capacity of the aqueous phase. In the case of probucol, the concentration in the aqueous phase was dependent on the partition of probucol between the aqueous phase and the remaining triglyceride phase. This difference between danazol and probucol was attributed to the effect of different lipophilicity.

Bile Acids and Salts↗

PubMed2000

Structure-property model for membrane partitioning of oligopeptides.

The aim of this study was to develop a structure-property model for membrane partitioning of oligopeptides using statistical design methods and multivariate data analysis. A set of 20 tetrapeptides with optional N-methylations at residues 2 and 4 was designed by a D-optimal design procedure. After synthesis and purification, the membrane partitioning abilities of the peptides were tested in two chromatographic systems with phospholipids as the stationary phase: immobilized artificial membrane chromatography (IAM) and immobilized liposome chromatography (ILC). The relationship between these measures and three different sets of calculated descriptors was analyzed by partial least-squares projection to latent structures (PLS). The descriptors used were the molecular surface area, Molsurf parameters, and Volsurf parameters. All three models were of good statistical quality and supported that a large hydrogen-bonding potential and the presence of a negative charge impair membrane partitioning, whereas hydrophobic parameters promote partitioning. The findings are in accordance with what has been found for absorption of known drugs and have implications for the design of peptide-like drugs with good oral bioavailability.

Chromatography, High Pressure Liquid↗

PubMed2000

Rational selection of antisense oligonucleotide sequences.

The purpose of this review is to identify rational selection procedures for the identification of optimal antisense oligonucleotide sequences. The review is firstly focused on how to find optimal hybridization sites, and secondly on how to select sequences that bind to structured RNA. The methods reviewed range from the more empirical testing of large numbers of mRNA complementary sequences to the more systematic techniques, i.e. RNase H mapping, use of combinatorial arrays and prediction of secondary structure of mRNA by computational methods. Structures that bind to structured RNA, i.e. aptastrucs and tethered oligonucleotide probes, and foldback triplex-forming oligonucleotides are also discussed. Relating to selection of antisense sequences by aid of computational analysis, valuable www addresses are given along with examples of folded structures of mRNA.

Base Sequence↗

PubMed1999

A comparison between direct determination of in vivo dissolution and the deconvolution technique in humans.

AIM: The primary objective of this study was to investigate the in vivo dissolution of carbamazepine in humans and to compare it with the dissolution estimated by deconvolution of plasma concentrations as well as the in vitro dissolution. METHODS: The in vivo study included six healthy volunteers, and consisted of two sequential parts. In part 1 the dissolution was measured by perfusing a semi-open segment in the proximal jejunum in humans. In part 2 the volunteers were given a solution of carbamazepine orally. In both parts of the study, plasma samples were collected up to 48 h after administration of the dose. The in vitro dissolution was measured in a flow-through cell using dissolution medium with and without the addition of bile acids (3 mM). RESULTS: The direct measured in vivo dissolution profile of carbamazepine and the deconvoluted profile were found to be similar. The two dissolution profiles of carbamazepine obtained in vitro were statistically lower than the two in vivo dissolution profiles. The higher in vivo dissolution rate is probably due to efficient sink conditions as a consequence of the high permeability of carbamazepine and more pronounced intestinal motility. CONCLUSION: The jejunal perfusion system was successfully used for in vivo dissolution measurements of carbamazepine and agreed with the deconvoluted plasma profile regarding rate and extent of dissolution. Single-pass perfusion is therefore a meaningful tool for further studies of in vivo dissolution.

Algorithms↗

PubMed1998

Crosslinked dextran--a new capsule material for colon targeting of drugs.

In the work presented here we have studied the application of glutaraldehyde crosslinked dextran as a capsule material for colon-specific drug delivery. A reaction mixture containing dextran, MgCl2, glutaraldehyde and polyethyleneglycol 400 in water was applied onto molding pins of nylon producing capsule caps and bodies. The capsule materials were characterized by measuring of the mechanical strength in compression and equilibrium degree of swelling. Based on these results an optimal composition for the capsule material was selected. The dextran capsules were loaded with hydrocortisone and subsequently, drug release was studied. The release was found to be about 10% during the initial 3 h in a buffer solution. Over a period of 24 h the release was about 35%. However, when the dextran capsules were challenged with a dextranase solution, simulating the arrival of the drug delivery system to the colon, the capsules quickly broke and the drug was released as a dose dump. The study shows that the dextran capsules are promising candidates for providing a colon-specific drug delivery.

Capsules↗

PubMed1998

Predicting drug absorption from molecular surface properties based on molecular dynamics simulations.

PURPOSE: To develop an efficient method for generating representative conformations for calculation of the conformationally dependent molecular surface area, and to investigate the relation between this parameter and the permeability in Caco-2 cells. METHODS: High temperature molecular dynamics (MD) simulations were used to obtain 1000 conformations of six beta-blocking agents and their prodrugs. The Boltzmann averaged (B.a.) polar surface area of the 1000 conformations was correlated to the apparent permeability coefficients (Papp) for transport across filter-grown Caco-2 cells. RESULTS: Sampling of 1000 conformations during the MD simulations was sufficient for obtaining a representative set of conformations. The B.a. polar water accessible surface area (PWASA) yielded an excellent linear correlation with Papp for both series of compounds under study (R2 = 0.98). Thus, the improved permeability of the prodrugs could be explained by a reduced PWASA. The improvement of permeability after derivatization correlated positively with the size of the non-polar water accessible surface area-suggesting a synergistic effect of the cyclopropyl and the non-polar parts of the molecule to shield the polar parts from contact with water. CONCLUSIONS: An efficient method for generating the representative conformations for calculation of the B.a. polar surface area has been established. An excellent linear correlation explaining the improved permeability of the prodrugs was obtained.

Adrenergic beta-Antagonists↗

PubMed1996

Current applications of polysaccharides in colon targeting.

Polysaccharides have over the years been used widely in pharmaceutical, chemical, and biochemical drug delivery. This family of natural polymers has an appeal to the area of drug delivery as it is comprised of polymers with a large number of derivatizable groups, a wide range of molecular weights, varying chemical compositions, and for the most part, a low toxicity and biodegradability, yet a high stability. The main scope of this review is to relate the polysaccharides available now to the rapidly growing field of colonic drug delivery. Polysaccharides have been applied to the area as controlled release coatings, matrices, macromolecular carriers, and biodegradable carriers. Bacterial sources of polysaccharidases as well as a detailed treatise of the enzymatic flora of the colonic region are discussed, followed by a presentation of the polysaccharides available for the purpose of colon-specific drug delivery. A final overview of the various approaches to obtain colon-specific delivery by using polysaccharides and a summary of available in vitro and in vivo testing methods will lead to the conclusion that polysaccharides at this point appear to be very promising compounds for use in obtaining colon-specific drug delivery systems.

Animals↗

PubMed1995

Drug delivery studies in Caco-2 monolayers. Synthesis, hydrolysis, and transport of O-cyclopropane carboxylic acid ester prodrugs of various beta-blocking agents.

A series of O-cyclopropane carboxylic acid ester prodrugs of various beta-blocking agents was synthesized. All prodrugs were hydrolyzed to give their parent compounds in aqueous phosphate buffer of pH 7.4 and in 80% human plasma. The half-lives in buffer solutions varied from 4 hours for the timolol prodrug to about 1 day for the prodrug of alprenolol. In human plasma the half-lives were shorter, ranging from 1 to 7 hours. The formation of the O-cyclopropane carboxylic acid ester derivatives significantly increased the lipophilicities of the beta-blockers as measured by the distribution coefficient between n-octanol and aqueous phosphate buffer of pH 7.4. To characterize the biomembrane permeability characteristics of the beta-blockers, transport properties across Caco-2 cell monolayers were investigated. An increase in lipophilicity resulted in a higher permeability of the prodrugs as compared to the parent compounds. Hence, acebutolol experienced an increment of a factor 17 on the apparent permeability coefficient, Papp, whereas Papp for the more lipophilic drug propranolol was increased by a factor of only 1.26. Some conversion of the prodrugs to their parent compounds was observed during the transport and appeared to be due to enzymatic intracellular metabolism.

Acebutolol↗

PubMed1995

Drug delivery studies in Caco-2 monolayers. IV. Absorption enhancer effects of cyclodextrins.

PURPOSE: The purpose of the present study was to use the human colorectal carcinoma cell line. Caco-2, as a human intestinal epithelial model for studying the effects of cyclodextrins as absorption enhancers. METHODS: Cyclodextrins of varying sizes and physicochemical characters were investigated. The effects of the cyclodextrins were evaluated by means of staining of the cytoplasma and determination of the mitochondrial dehydrogenase activity as well as by transport enhancement of the macromolecular pore marker polyethylene glycol 4000 (PEG-4000) across the Caco-2 monolayers. RESULTS: The transport enhancing properties of the cyclodextrins were found to follow the lipophilicity of the core in their cyclic structure. Dimethyl-beta-cyclodextrin was the most powerful in all aspects and caused an increase in the permeability of the cytoplasma membrane in a concentration dependent manner. It was possible to increase the overall transport of PEG-4000 10-fold by the use of dimethyl-beta-cyclodextrin in low concentrations where the toxic effects on the monolayers were insignificant. It was further observed that the basolateral membrane was significantly more sensitive to cyclodextrins than the apical membrane. CONCLUSIONS: Since dimethyl-beta-cyclodextrin was able to produce an absorption enhancing effect on PEG-4000 in concentrations where the toxic effects on Caco-2 monolayers were low it is worth to pursue the compound as an absorption enhancer.

Biological Transport, Active↗