Dissolution of hydrocortisone in human and simulated intestinal fluids.

PURPOSE: To compare solubility and dissolution rate of hydrocortisone in aspirated human intestinal fluids (HIFs) with simulated intestinal fluids (SIFs) and buffer. METHODS: Solubility and flux from a rotating disk of hydrocortisone were measured. The bile salt content, pH and osmotic pressure were determined in HIFs. RESULTS: In fasted state the solubility of hydrocortisone was higher in HIFs than in the buffer and SIFs. The flux of hydrocortisone in HIFs was similar to the flux in the buffer but lower than the flux in SIFs at fasted state. Addition of intestinal surfactants in SIFs increased solubility and flux at both fasted and fed state. The increase in solubility was caused by micelle formation in SIFs. The increase in flux may partly be explained by increased solubility. The bile salt content of the HIFs did not correlate with the solubility or the flux but pH in the HIFs seems to have some effect on the components of the HIFs resulting in increased solubility. CONCLUSIONS: It is possible to perform comparable dissolution tests in HIFs and SIFs. The lack of correlation between the results in HIFs and the bile salt content may be explained by the relatively low lipophilicity of the model drug.

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.

Fat emulsions based on structured lipids (1,3-specific triglycerides): an investigation of the in vivo fate.

PURPOSE: Structured lipids (1,3-specific triglycerides) are new chemical entities made by enzymatic transesterification of the fatty acids in the 1,3 positions of the triglyceride. The purpose of this study is to characterize structured lipids with either short chain fatty acids or medium chain fatty acids in the 1,3 positions with regard to their hydrophobicity, and investigate the in vivo fate in order to evaluate the potential of structured lipids as core material in fat emulsions used as parenteral drug delivery system. METHODS: The lipids were characterized by employing reversed phase high performance liquid chromatography. The biodistribution of radioactively labeled emulsions was studied in rats. RESULTS: By employing high performance liquid chromatography a rank order of the hydrophobicities of the lipids could be given, with the triglycerides containing long chain fatty acids being the most hydrophobic and the structured lipid with short chain fatty acids in the 1,3 positions the least. When formulated as fat emulsions, the emulsion based on structured lipids with short fatty acids in the 1,3 positions was removed slower from the general blood circulation compared to emulsions based on lipids with long chain fatty acids in the 1,3 positions. CONCLUSIONS: The type of core material influences the in vivo circulation time of fat emulsions.

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.

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.

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.

Hydrogels for site-specific drug delivery to the colon: in vitro and in vivo degradation.

Novel hydrogels based on N,N-dimethylacrylamide, N-t-butylacrylamide, and acrylic acid cross-linked with azoaromatic compounds of varying length and electron density of the azo bond were synthesized. The cross-links are degradable by microbial azoreductases present predominantly in the colon, and the gels appear to be suitable for colon-specific drug delivery. The degradability in vitro and in vivo was found to be related to the degree of swelling of the gels. The higher the degree of swelling, the higher the degradability. However, structural and electronic factors were also shown to influence reduction of azo bonds.

Hydrogels for site-specific oral drug delivery: synthesis and characterization.

Novel types of hydrogels based on hydrophilic N-substituted (meth)acrylamides, N-tert-butylacrylamide and acrylic acid cross-linked with 4,4'-di(methacryloylamino)azobenzene were synthesized. The gels were characterized by the equilibrium degree of swelling as a function of pH, modulus of elasticity in compression at pH 2 and 7.4 and permeability of insulin at pH 2 and 7.4. It was found that the structure of the polymer backbone influenced the pH-dependent swelling. In all cases, the degree of swelling was lower at pH 2 than at 7.4. As the degree of swelling decreased, the modulus of elasticity was found to increase and the permeability of insulin decreased. These gels are enzymatically degradable by microbial azoreductases present in the colon and have a potential use in site-specific drug delivery to the colon.

Regional glucose phosphorylation rate in rat brain during acute ethanol intoxication.

The effect of ethanol on regional cerebral metabolic rate for glucose (rCMRglc) was studied in rats using [6-14C]glucose. After intravenous injection, radioactivity was determined in 14 brain regions, corrected for loss of label, and divided by the integral of the arterial plasma glucose concentration measured during tracer circulation. When blood ethanol concentration was maintained at 6 g/l by intravenous infusion of ethanol for approximately 1 h, rCMRglc was found to be reduced significantly in 7 forebrain regions, compared to values of conscious control animals. In 7 further regions including brain stem regions, rCMRglc was not significantly reduced. We conclude that the effects of severe acute alcohol intoxication resemble those of global anesthesia.

Glucose phosphorylation rate in rat parietal cortex during normoglycemia, hypoglycemia, acute hyperglycemia, and in diabetes-prone rats.

Cerebral metabolic rate for glucose (CMRglc) was studied in rats using [6-14C]glucose. After intravenous injection, the radioactivity of the parietal cortex was corrected for loss of labeled CO2 and divided by the integral of the arterial plasma glucose concentration, determined during tracer circulation. Treatment with insulin, resulting in plasma glucose concentrations less than 2.6 mmol/l, reduced CMRglc to 64% of the values found in control animals. CMRglc did not change in animals with acute hyperglycemia produced by intraperitoneal injection of a glucose solution or in diabetes-prone rats with or without insulin treatment.

Measuring brain glucose phosphorylation with labeled glucose.

This study tested whether glucose labeled at the C-6 position generates metabolites that leave brain so rapidly that C-6-labeled glucose cannot be used to measure brain glucose phosphorylation (CMRGlc). In pentobarbital-anesthetized rats, the parietal cortex uptake of [14C]glucose labeled in the C-6 position was followed for times ranging from 10 s to 60 min. We subtracted the observed radioactivity from the radioactivity expected with no loss of labeled metabolites from brain by extrapolation of glucose uptake in an initial period when loss was negligible. The observed radioactivity was a monoexponentially declining function of the total radioactivity expected in the absence of metabolite loss. The constant of decline was 0.0077.min-1 for parietal cortex. Metabolites were lost from the beginning of the experiment. However, with correction for the loss of labeled metabolites, it was possible to determine an average CMRGlc between 4 and 60 min of circulation of 64 +/- 4 (SE; n = 49) mumol.hg-1.min-1.

Repetitive measurements of intracranial pressure in awake rabbits.

Previous measurements of the intracranial pressure in experimental animals suffer from acute and subacute effects of cannulation. In order to obtain reliable, repetitive or continuous values, we measured the intracranial pressures in awake rabbits with a new permanent adjustable ventricular cannula that included a separate entrance to the subarachnoid space. The mean intraventricular pressure ten days after the operation was 5.2 +/- 1.1 mmHg (SD) (70 animals). Manipulation of the cannula system and infusion of artificial cerebrospinal fluid did not damage the blood-brain barrier (indicated by extravasation of Evans Blue). The intracranial pressure was constant for as long as 6 months and as many as 22 separate measurements and infusions. The cerebrospinal fluid cells and protein content did not change in animals with permanent cannulae and in animals perfused with 2-4 ml artificial cerebrospinal fluid. In 30 animals the ventricular cannula functioned for 10-180 (median 65) days and the subarachnoid entrance for 11-23 (median 16) days.

Increased vesicular transfer of horseradish peroxidase across cerebral endothelium, evoked by acute hypertension.

Acute hypertension in rats was produced by intravenous infusion of metaraminol bitartrate (Aramine). The permeability to intravenously injected horseradish peroxidase (HRP) was increased across the cerebral arterioles, capillaries and venules. From the basement membranes of the vessel walls the protein tracer moved into the extracellular spaces of the adjacent neuropil. No endothelial cell damage was observed. The tight junctions between endothelial cells were intact and prevented intercellular movement of peroxidase. Many HRP-labeled vesicles within the endothelial cells or connected with the luminal or abluminal surface, occurred in segments of the microvasculature. Otherwise the endothelium was unchanged. Diffuse uptake of HRP into the cytoplasm of neurons and glial cells was not observed. The alphablocker phentolamine (Regitin) was given to a group of rats simultaneously to Aramine. The increase in blood pressure was thus prevented; furthermore, the permeability remained as under normal conditions. The Aramine, Regitin and HRP did not significantly influence the pH, PO2 and pCO2 of the arterial blood. It is concluded that acute hypertension increases the vesicular transport of HRP across the endothelium of cerebral arterioles, venules and capillaries that normally occurs to a small extent only after intravenous injection of the tracer.

Sodium-dependent transport of sugars and iodide from the cerebral venticles of the rabbit.

1. The objective was to discover whether the extraction of sugars and iodide from the perfused cerebral ventricles is Na(+)-dependent.2. In the ventriculo-aqueductal and ventriculo-cisternal perfusion systems in the rabbit the extraction of (14)C-labelled D-hexoses (glucose, 3-O-methyl-glucose, alpha-methyl-glucoside and galactose), (131)I(-) and (24)Na was inhibited when 82% of the Na(+) in the perfusion fluid was replaced by choline. The extraction returned to control levels when the Na(+) concentration in the perfusion fluid was returned to normal.3. Ouabain, 5 x 10(-5)M in the perfusion fluid inhibited the extraction of the above (14)C sugars and (131)I(-), but hardly affected that of [(3)H]2-deoxy-D-glucose. It enhanced the extraction of (24)Na. C.s.f. production was usually totally inhibited.4. The extraction of [(14)C]urea remained unchanged during perfusion with low Na(+) fluid or ouabain.5. Recovery from brain of [(14)C]3-O-methyl-glucose, [(3)H]2-deoxy-glucose and (131)I(-) was low while recovery of [(14)C]alpha-methyl-glucoside and (24)Na was high. On an equal weight basis recovery of [(14)C]3-O-methyl-glucose was about twelve times higher from the choroid plexus than from the brain.6. Part of the movement of (14)C sugars may be explained on basis of a Na(+)-gradient hypothesis with involvement of the Na(+) pump at the blood-c.s.f. or blood-brain barriers.7. The rate of c.s.f. production from the first three ventricles comprised about 40% of the rate from all four ventricles. The extraction of sugars, urea and cations was similar in both perfusion systems while the extraction of (131)I(-) was higher in the ventriculo-cisternal system than in the ventriculo-aqueductal system.