Biomedical subjects

W L J Hinrichs

Publications and source records attributed to W L J Hinrichs.

9 recordsLinked to original sources

PubMed2006

The choice of a suitable oligosaccharide to prevent aggregation of PEGylated nanoparticles during freeze thawing and freeze drying.

In a previous study we have shown that the oligosaccharide inulin can prevent aggregation of poly(ethylene glycol) (PEG) coated plasmid DNA/cationic liposome complexes ("PEGylated lipoplexes") during freeze thawing and freeze drying [Hinrichs et al., 2005. J. Control. Release 103, 465]. By contrast, dextran clearly failed as stabilizer. These results were ascribed to the fact that inulin and PEG are compatible while dextran and PEG are not. In this study the stabilizing capacities of inulin and dextran (of various molecular weights) during freeze thawing and freeze drying of four different types of nanoparticles, each type with different amounts of PEG at their surface, were investigated. Freeze drying and freeze thawing of 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP)/dioleoyl-phosphatidyl-ethanolamine (DOPE) liposomes and egg phosphatidyl choline (EPC)/cholesterol (CHOL) liposomes showed that inulins are excellent stabilizers even for highly PEGylated liposomes while (especially higher molecular weight) dextrans dramatically lost their stabilizing capacity when increasing the degree of PEGylation of the liposomes. The same results were obtained for plasmid DNA/DOTAP/DOPE complexes. Finally, both inulin and dextran could prevent full aggregation of plasmid DNA/polyethylenimine (PEI) complexes independent whether PEI was PEGylated or not. It is concluded that inulins are preferred as stabilizers over dextrans for various types of PEGylated nanoparticles due to their compatibility with PEG.

Cholesterol↗

PubMed2006

Characterization of the molecular distribution of drugs in glassy solid dispersions at the nano-meter scale, using differential scanning calorimetry and gravimetric water vapour sorption techniques.

The molecular distribution in fully amorphous solid dispersions consisting of poly(vinylpyrrolidone) (PVP)-diazepam and inulin-diazepam was studied. One glass transition temperature (T(g)), as determined by temperature modulated differential scanning calorimetry (TMDSC), was observed in PVP-diazepam solid dispersions prepared by fusion for all drug loads tested (10-80 wt.%). The T(g) of these solid dispersions gradually changed with composition and decreased from 177 degrees C for pure PVP to 46 degrees C for diazepam. These observations indicate that diazepam was dispersed in PVP on a molecular level. However, in PVP-diazepam solid dispersions prepared by freeze drying, two T(g)'s were observed for drug loads above 35 wt.% indicating phase separation. One T(g) indicated the presence of amorphous diazepam clusters, the other T(g) was attributed to a PVP-rich phase in which diazepam was dispersed on a molecular level. With both the value of the latter T(g) and the DeltaC(p) of the diazepam glass transition the concentrations of molecular dispersed diazepam could be calculated (27-35 wt.%). Both methods gave similar results. Water vapour sorption (DVS) experiments revealed that the PVP-matrix was hydrophobised by the incorporated diazepam. TMDSC and DVS results were used to estimate the size of diazepam clusters in freeze dried PVP-diazepam solid dispersions, which appeared to be in the nano-meter range. The inulin-diazepam solid dispersions prepared by spray freeze drying showed one T(g) for drug loads up to 35 wt.% indicating homogeneous distribution on a molecular level. However, this T(g) was independent of the drug load, which is unexpected because diazepam has a lower T(g) than inulin (46 and 155 degrees C, respectively). For higher drug loads, a T(g) of diazepam as well as a T(g) of the inulin-rich phase was observed, indicating the formation of amorphous diazepam clusters. From the DeltaC(p) of the diazepam glass transition the amount of molecularly dispersed diazepam was calculated (12-27 wt.%). In contrast to the PVP-diazepam solid dispersions, DVS-experiments revealed that inulin was not hydrophobised by diazepam. Consequently, the size of diazepam clusters could not be estimated. It was concluded that TMDSC enables characterization and quantification of the molecular distribution in amorphous solid dispersions. When the hygroscopicity of the carrier is reduced by the drug, DVS in combination with TMDSC can be used to estimate the size of amorphous drug clusters.

Adsorption↗

PubMed2005

Inulin is a promising cryo- and lyoprotectant for PEGylated lipoplexes.

The aim of this study was to investigate whether the oligosaccharides dextran and inulin are able to prevent aggregation of lipoplexes based on 1,2-dioleoyl-3-trimethylammonium-propane and dioleoylphosphatidyl-ethanolamine with and without distearoylphosphatidylethanolamine-polyethyleneglycol (PEGylated and nonPEGylated lipoplexes, respectively) during storage. The lipoplexes, dispersed in the oligosaccharide solution were frozen and subsequently stored at subzero temperature or freeze dried and subsequently stored at 37 degrees C. When lipoplexes in frozen dispersions were stored below the glass transition temperature of the maximally freeze concentrated fraction (Tg') of the oligosaccharide solutions severe aggregation of the nonPEGylated lipoplexes was prevented for 3 months by both inulin and dextran. However, while dextran failed to stabilize the frozen PEGylated lipoplexes (as in most cases full aggregation occurred in short time) inulin successfully protected them against aggregation. Compared to dextran, inulin was also a superior lyoprotectant of PEGylated lipoplexes: during freeze drying and subsequent storage at 37 degrees C of the dried powders for 3 months the PEGylated lipoplexes maintained their original size when dispersed in inulin matrices while in dextran matrices they fully aggregated in most cases. It is hypothesized that the aggregation of the PEGylated lipoplexes in dextran solutions is caused by the well known incompatibility between dextrans and PEG. This is further supported by the observation that inulins and PEG are compatible. It is concluded that oligosaccharides can prevent severe aggregation of nonPEGylated lipoplexes. The same holds for PEGylated lipoplexes provided that the oligosaccharide is compatible with PEG. Finally, this work also shows that the higher Tg' of oligosaccharides makes them more versatile cryoprotectants than disaccharides like sucrose or trehalose as the frozen dispersions can be stored at higher temperatures for prolonged periods of time. Furthermore, it is proposed that oligosaccharides are also more versatile lyoprotectants than the disaccharides because they can be exposed to higher relative humidities without passing the glass transition temperature.

Drug Stability↗

PubMed2004

Anomalous dissolution behaviour of tablets prepared from sugar glass-based solid dispersions.

In this study, anomalous dissolution behaviour of tablets consisting of sugar glass dispersions was investigated. The poorly aqueous soluble diazepam was used as a lipophilic model drug. The release of diazepam and sugar carrier was determined to study the mechanisms governing dissolution behaviour. The effect of carrier dissolution rate and drug load was tested with four different sugars, in the order of decreasing dissolution rates: sucrose, trehalose and two oligo-fructoses; inulinDP11 and inulinDP23 having a number average degree of polymerization (DP) of 11 and 23, respectively. Diazepam was incorporated in these sugar glasses in the amorphous state by means of freeze drying using water and tertiary butyl alcohol (TBA) as solvents. None of the tablets disintegrated during dissolution. Dissolution of 80% of the lipophilic drug within 20 min was found when diazepam and sugar dissolution profiles coincided. The sugar carrier and diazepam dissolved at the same rate, which was constant in time and fast. This condition was met for relatively slow dissolving carriers like the inulins or for low drug loads. For relatively fast dissolving carriers like sucrose or trehalose with high drug loads, release profiles of diazepam and sugar did not coincide: diazepam dissolved much more slowly than the sugars. In case of non-coinciding release profiles, diazepam release was split into three phases. During the first phase non-steady-state dissolution was observed: diazepam release accelerated and a drug rich layer consisting of crystalline diazepam was gradually formed. This first phase determined the further release of diazepam. During the second phase a steady-state release rate was reached: zero-order release was observed for both drug and carrier. During this phase, the remaining (non-crystallised) solid dispersion is dissolved without the further occurrence of crystallisation. The third phase, starting when all carrier is dissolved, involved the very slow dissolution of crystallised diazepam, which was present either as the skeleton of a tablet resulting in a zero-order release profile or as separate particles dispersed in the dissolution medium resulting in a first-order release. To understand the anomalous dissolution behaviour, a model is proposed. It describes the phenomena during dissolution of amorphous solid dispersion tablets and explains that fast dissolution is observed for low drug loads or slow dissolving carriers like inulin.

Diazepam↗

PubMed2004

Incorporation of lipophilic drugs in sugar glasses by lyophilization using a mixture of water and tertiary butyl alcohol as solvent.

In this study, a new and robust method was evaluated to prepare physically stable solid dispersions. Trehalose, sucrose, and two inulins having different chain lengths were used as carrier. Diazepam, nifedipine, Delta(9)-tetrahydrocannabinol, and cyclosporine A were used as model drugs. The sugar was dissolved in water and the drug in tertiary butyl alcohol (TBA). The two solutions were mixed in a 4/6 TBA/water volume ratio and subsequently freeze dried. Diazepam could be incorporated at drug loads up to 63% w/w. DSC measurements showed that, except in some sucrose dispersions, 97-100% of the diazepam was amorphous. In sucrose dispersions with high drug loads, about 10% of the diazepam had crystallised. After 60 days of exposure at 20 degrees C and 45% relative humidity (RH), diazepam remained fully amorphous in inulin dispersions, whereas in trehalose and sucrose crystallization of diazepam occurred. The excellent physical stability of inulin containing solid dispersions can be attributed to the high glass transition temperature (T(g)) of inulin. For the other drugs similar results were obtained. The residual amount of the low toxic TBA was only 0.1-0.5% w/w after freeze drying and exposure to 45% RH and 20 degrees C. Therefore, residual TBA will not cause any toxicity problems. This study provides a versatile technique, to produce solid dispersions. Inulin glasses are preferred because they provide an excellent physical stability of the incorporated amorphous lipophilic drugs.

Butanols↗

PubMed2004

Solid dispersions based on inulin for the stabilisation and formulation of delta 9-tetrahydrocannabinol.

The aim of this study was to develop a dry powder formulation that stabilises the chemically labile lipophilic Delta(9)-tetrahydrocannabinol (THC), that rapidly dissolves in water in order to increase the bioavailability and that opens new routes of administration. It was investigated whether these aims can be achieved with solid dispersions consisting of a matrix of inulin, an oligo-fructose, in which THC is incorporated. These solid dispersions were prepared by lyophilisation of a solution of THC and inulin in a mixture of water and tertiary butyl alcohol (TBA). Both 4 and 8 wt.% of THC could be incorporated in a glassy matrix of inulin. In the solid dispersions only 0.4-0.5 wt.% of residual TBA was present after storage at 20 degrees C/45% relative humidity (RH) for 7 days. Unprotected THC was completely degraded after 40 days of exposure to 20 degrees C and 45% RH. However, solid dispersions exposed to the same conditions still contained about 80% non-degraded THC after 300 days. Dissolution experiments with tablets compressed from inulin glass dispersion material showed that THC and inulin dissolved at the same rate. Tablets weighing 125 mg and containing 2mg THC were prepared from a mixture of THC containing solid dispersion, polyvinylpolypyrrolidone (PVPP) and mannitol. Dissolution tests revealed that from these tablets 80% of the THC was dissolved within 3 min, which makes them promising for sublingual administration. It was concluded that THC can be strongly stabilized by incorporating it in a matrix of inulin. The aqueous dissolution rate was high which may improve bioavailability.

Calorimetry, Differential Scanning↗

PubMed2003

Investigations into the stabilisation of drugs by sugar glasses: II. Delivery of an inulin-stabilised alkaline phosphatase in the intestinal lumen via the oral route.

In this study the possibility to deliver the acid-sensitive enzyme alkaline phosphatase (AP) from calf intestine (CIAP) to the intestinal system by oral administration was investigated. Tablets were prepared and in vitro evaluated. Final proof of concept studies were performed in rats. This acid labile enzyme is potentially useful in the treatment of sepsis, a serious condition during which endotoxins can migrate into the blood stream. The CIAP was freeze-dried with inulin and subsequently compacted into round biconvex tablets with a diameter of 4mm and a weight of 25-30 mg per tablet. The tablets were coated with an enteric coating in order to ensure their survival in the stomach. In vitro evaluation of tablets containing alkaline phosphatase from bovine intestine (BIAP) was the first step in the development. It was found that tablets without enteric coating dissolved rapidly in 0.10 M HCl with total loss of enzymatic activity of the alkaline phosphatase. Tablets that were coated were stable for at least 2 h in 0.10 M HCl, but dissolved rapidly when the pH was increased to 6.8. Furthermore, it was shown that the enzymatic activity of the released BIAP was fully preserved. The in vivo test clearly showed that the oral administration of enteric coated tablets resulted in the release of enzymatically active CIAP in the intestinal lumen of rats. The location of the enhanced enzymatic activity of AP in the intestines varied with the time that had passed between the administration of the tablets and the sacrificing of the rats. Also, the level of enzymatic activity increased with an increasing number of tablets that were administered.

Administration, Oral↗

PubMed2003

Potential of capillary electrophoresis for the monitoring of the stability of placental alkaline phosphatase.

Alkaline phosphatase (AP) is a potential therapeutic agent in the treatment of sepsis. In this paper the potential of capillary zone electrophoresis (CZE) for the monitoring of the degradation of placental alkaline phosphatase (PLAP) was investigated. To induce degradation PLAP samples were exposed to high temperatures, low and high pH and freeze-drying. The samples were then analyzed by CZE and enzymatic activity assay. Upon exposure to temperatures above 65 degrees C, PLAP lost its activity exponentially over time, while CZE revealed both a linear decrease of the area of the main peak and a rise of degradation products. At acidic pH the enzyme appeared to lose its activity. CZE revealed a decrease of the area of the main peak, but no degradation products could be detected. At pH 12 the enzymatic activity and the area of the main peak both decreased linearly over time and, in addition, formation of degradation products could be detected by CZE. Activity and CZE profile of PLAP remained unchanged upon freeze-drying in the presence of inulin. Prolonged storage of freeze-dried samples at room temperature caused a slight decrease of enzymatic activity, while the potential formation of oligomers was revealed by CZE analysis. The examples in this study show that, in combination with activity assays, CZE can provide useful complementary information, especially on the status of the protein and the presence of degradation products.

Alkaline Phosphatase↗

PubMed2002

Investigations into the stabilisation of drugs by sugar glasses: I. Tablets prepared from stabilised alkaline phosphatase.

The aim of this study was to investigate the formulation of sugar glass stabilised alkaline phosphatase from bovine intestine (BIAP) into tablets. Two major subjects of tablet formulation were investigated. First, the compaction behaviour of the inulin sugar glass was investigated. Secondly, the effect of the compaction process on the physical stability of sugar glass stabilised BIAP was investigated, comparing inulin and trehalose glass. The tabletting properties of freeze-dried inulin without BIAP were studied first. Freeze-dried inulin conditioned at either 20 degrees C/0% relative humidity (RH) or 20 degrees C/45% RH was compacted at various pressures. As expected, the yield pressure of the material conditioned at 0% RH was higher (68 MPa) than after conditioning at 45% RH (39 MPa). Tablets made of the material stored at 0% RH showed severe capping tendency, especially at high compaction pressures. In contrast, material conditioned at 45% RH gave tablets without any capping tendency and a friability of less than 1%. Sugar glasses of BIAP and either inulin or trehalose were prepared by freeze-drying (BIAP/sugar 1/19 (w/w)). The material was subsequently compacted. Tablets and powders were stored at 60 degrees C/0% RH. The activity of the incorporated BIAP was measured at various time intervals. It was found that inulin was by far superior to trehalose as stabiliser of BIAP in tablets. The poor stabilising capacities of trehalose after compaction are explained by crystallisation of trehalose induced by the compaction process and moisture in the material. The results clearly show that inulin is an excellent stabiliser for BIAP. The tabletting properties are adequate, showing sufficient tablet strengths and low friability. Furthermore, the good (physical) stability of inulin glass with respect to exposure to high relative humidities makes it practical to work with.

Alkaline Phosphatase↗