International Journal of Pharmaceutics (v.294, #1-2)
TITLE PAGE (EDI BOARD) (iii).
An investigation into the thermal behaviour of a model drug mixture with amorphous trehalose by M. Horvat; E. Meštrović; A. Danilovski; D.Q.M. Craig (1-10).
The thermal and structural properties of amorphous trehalose mixed with a model drug, paracetamol, have been studied with a view to developing understanding of the thermal events undergone by such binary systems. A physical mixture of paracetamol and spray dried trehalose (1:9 weight ratio) was studied using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), hot stage microscopy (HSM), and variable temperature powder X-ray diffraction (VTPXRD). The presence of the drug resulted in a lower temperature recrystallisation exotherm for the trehalose compared to the disaccharide alone. Evidence is presented for the trehalose recrystallisation being triggered by the melting rather than simply the presence of the paracetamol particles. HSM studies indicated that the trehalose recrystallised around the drug on heating, with the recrystallisation temperature again corresponding to the melting of the drug. VTPXRD indicated that the presence of the drug again lowered the recrystallisation temperature of the trehalose, although the trehalose anhydrate diffraction peaks were discernible at a lower temperature for both the pure trehalose and the mixed systems than was observed for the DSC studies, suggesting that the association between recrystallisation and drug melting was not apparent when using this approach. It is suggested that while the trehalose recrystallisation process is not significantly influenced by the presence of the drug when studied over relatively long time periods such as those used for the VTPXRD studies, the process is triggered by the melting of the paracetamol when short experimental times and scanning conditions are used such as those relevant to DSC studies. These data have implications for the quality control of trehalose products using DSC, the characterisation of the physical structure of the binary systems and the prediction of the corresponding physical stability.
Keywords: Trehalose; Calorimetry; Amorphous; Spray dried; X-ray diffraction;
Absorption-enhancing effect of glycyrrhizin induced in the presence of capric acid by Teruko Imai; Michinori Sakai; Hiroshi Ohtake; Hidekazu Azuma; Masaki Otagiri (11-21).
The absorption-enhancing effect of the simultaneous administration of sodium caprate (Cap-Na) and dipotassium glycyrrhizinate (Grz-K) was investigated to clarify an effect of Grz-K. A combination of 0.1% (w/v) Cap-Na and 2% (w/v) Grz-K had a rapid and long-lasting absorption-enhancing activity in Caco-2 cell monolayers under conditions where Cap-Na and Grz-K showed a weak and no activity, respectively. The simultaneous treatment of a Caco-2 cell monolayer with Cap-Na and Grz-K showed no change in intracellular calcium ion level, although a major mechanism of absorption-enhancing effect for Cap-Na was elevation of intracellular calcium ion level. On the other hand, the simultaneous enhancing effect of Cap-Na and Grz-K was inhibited by H7, a PKC inhibitor. Possibly, Grz-K showed an absorption-enhancing effect via PKC cellular signaling pathway after penetration into cell according to increasing membrane permeability by Cap-Na. The absorption of sCT by the rat colon was enhanced by a combination of 0.1% (w/v) Cap-Na and 2% (w/v) Grz-K, and its effect continued even 9 h after the onset of the experiment. Furthermore, the simultaneous treatment of 0.1% (w/v) Cap-Na and 2% (w/v) Grz-K showed a negligible histological changes to the colon mucosal membrane and a negligible toxicity on Caco-2 cell monolayer. A combination of Cap-Na and Grz-K shows a synergistic absorption-enhancing effect with little mucosal injury, which is applicable to colon-specific delivery.
Keywords: Absorption enhancer; Sodium caprate; Glycyrrhizin; Caco-2 cell; Colon delivery;
Development of a single dose tetanus toxoid formulation based on polymeric microspheres: a comparative study of poly(d,l-lactic-co-glycolic acid) versus chitosan microspheres by K.S. Jaganathan; Y.U.B. Rao; Paramjit Singh; D. Prabakaran; Swati Gupta; Anubhav Jain; Suresh P. Vyas (23-32).
Stable polymeric microspheres capable of controlled release of tetanus toxoid (TT) for periods ranging from days to over months were developed. TT was stabilized, encapsulated in microspheres prepared from poly(d,l)-lactide-co-glycolide (PLGA) and chitosan by using protein stabilizer (trehalose) and its immune response was compared. The influence of co-encapsulated protein stabilizer on tetanus toxoid's stability and release from the microspheres was studied. The protein stabilizer (trehalose) prevented structural losses and aggregation of microencapsulated TT. To neutralize the acids liberated by the biodegradable lactic/glycolic acid-based polymer, we also co-incorporated into the polymer an antacid, (Mg(OH)2), which neutralized the acidity during degradation of the polymer and also prevented TT structural losses and aggregation. The in vitro release experiments with PLGA and chitosan microspheres were performed and the release of TT was increased up to 80–90%. The antigen integrity was investigated by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) followed by coomassie brilliant blue staining. The SDS-PAGE analysis confirmed that antigen integrity was not affected by the encapsulation procedure. In addition, the immunogenicity of PLGA and chitosan microspheres based single dose vaccine was evaluated in guinea pigs and compared with multiple doses of alum adsorbed TT. Results indicated that a single injection of PLGA and chitosan microspheres containing TT could maintain the antibody response at a level comparable to the booster injections of conventional alum adsorbed vaccines. The both PLGA and chitosan based stable vaccine formulations produced an equal immune response. Hence chitosan can be used to replace the expensive polymer PLGA. This approach should have potential application in the field of vaccine delivery.
Keywords: Chitosan microspheres; PLGA microspheres; Protein stability; Tetanus toxoid; Single shot vaccine;
Effect of hexacosanol on the characteristics of novel sustained-release allopurinol solid lipospheres (SLS): factorial design application and product evaluation by I. El-Gibaly; S.K. Abdel-Ghaffar (33-51).
This investigation involved the evaluation of the effect of hexacosanol (HC, ceryl alcohol), a new hydrophobic wax modifier (WM) in comparison with conventional modifiers, on the development of sustained-release allopurinol (AP) solid lipospheres (SLS) intended for use in a suspension formulation and other oral dosage forms. Various beeswax (BW)/WM blends (composition ratio 1:1) were thus used to prepare SLS by a modified oil-in-water emulsion meltable disperse-phase (MDP) encapsulation method without using organic solvents and the influence of these blends on the drug encapsulation efficiency (EE), size distribution and the time for 50% of the drug to be released (t 50%) was investigated. Results indicated that incorporation of HC in wall matrix of SLS provided the means to enhance the EE of AP and to modulate the rate of drug release into dissolution media (simulated gastric fluid (S.G.F.: pH 1.2) and simulated intestinal fluid (S.I.F.: pH 7.4). The effects of the process variables; HC concentration, dispersant (pluronic F-68: PF-68) concentration and drug:wax ratio were also studied on the properties of AP-loaded SLS by a 23 factorial design. The EE values were in the range of 80.8–92.67%. The only significant parameter affecting (P < 0.01) the size and size distribution of the SLS formulations was the amount of the PF-68, whereas the factor with the biggest influence (P < 0.05) on the drug EE was the initial loading of AP (in terms of the drug:wax ratio). The amount of HC blended with wax and the initial drug loading significantly (P < 0.01) affected the t 50% values of all of the formulations. The release of AP was more extended (t 50% values (S.I.F.; pH 7.4) = 9.91–25.36 h, depending on the drug:wax ratio) and surface morphology of SLS was improved with higher HC content (15%, w/w) formulations. The release patterns fitted the Baker–Lonsdale dissolution kinetics for spherical matrices. A significant decrease of plasma uric acid levels (P < 0.05) and hepatic impairment in male rats was observed after oral administration of a SLS (mean size: 120 μm) suspensions of the optimum formulation, compared to suspensions of pure AP.
Keywords: Allopurinol; Sustained-release solid lipospheres; Hexacosanol; Melt dispersion; Histopathology;
Skin targeted DNA vaccine delivery using electroporation in rabbits by Babu M. Medi; Scott Hoselton; Rao B. Marepalli; Jagdish Singh (53-63).
Genetic immunization through skin is highly desirable as skin has plenty of antigen presenting cells (APCs) and is easily accessible. The purpose of this study was to investigate the effects of electroporation pulse amplitude, pulse length and number of pulses on cutaneous plasmid DNA vaccine delivery and immune responses, following intradermal injection in vivo in rabbits. Expression of the delivered plasmid was studied using a reporter plasmid, coding for β-galactosidase. The efficiency of DNA vaccine delivery was investigated using a DNA vaccine against Hepatitis B, coding for Hepatitis B surface antigen (HBsAg). Serum samples and peripheral blood mononuclear cells (PBMC) were analyzed for humoral and cellular immunity, respectively, following immunization. The expression of transgene in the skin was transient and reached its peak in 2 days post-delivery with 200 and 300 V pulses. The expression levels with 200 and 300 V pulses were 48- and 129-fold higher, respectively, compared with the passive on day 2. In situ histochemical staining of skin with X-gal demonstrated the localized expression of β-galactosidase with electroporation pulses of 200 and 300 V. Electroporation mediated cutaneous DNA vaccine delivery significantly enhanced both humoral and cellular immune responses (p < 0.05) to Hepatitis B compared to passive delivery. The present study demonstrates the enhanced DNA vaccine delivery to skin and immune responses by topical electroporation. Hence, electroporation mediated cutaneous DNA vaccine delivery could be developed as a potential alternative for DNA vaccine delivery.
Keywords: DNA vaccine; Cutaneous DNA vaccine delivery; Electroporation; Skin; Gene delivery;
Effects of Isoflurane on gastrointestinal motility after brief exposure in rats by Marc C. Torjman; Jeffrey I. Joseph; Carey Munsick; M. Morishita; Zvika Grunwald (65-71).
In pre-clinical studies, investigation of oral formulations often necessitates the use of general anesthesia to facilitate deposition of material directly into the stomach. Since the effectiveness of intestinal drug absorption is dependent on gastric emptying (GE) and intestinal motility, drugs that influence either will also influence drug absorption. This study investigated gastrointestinal motility in rats after brief exposure to Isoflurane (ISO) general anesthesia for orogastric gavage. The use of metochlopramide was also evaluated.Twenty-five fasted rats were induced with brief ISO anesthesia (<6 min). Rats were gavaged a gelatin capsule (8 mm (L) × 2.0 mm (o.d.)) containing 9 mg of activated charcoal powder (gastrointestinal marker) and rapidly recovered. Gavage was performed using a 15 cm feeding device with a soft hollow tip to hold the capsule. Study included three groups (60 and 120 min recovery, metochlopramide pre-treatment with 60 min recovery) and control. Animals were sacrificed for exposure and examination of the gastrointestinal tract following the allocated recovery period.Gastrointestinal transit of charcoal was reduced approximately 50% 120 min after brief ISO anesthesia. Metochlopramide pre-treatment did not increase gastrointestinal propulsion despite increased GE. These data warrant consideration in intestinal drug absorption studies where ISO is the anesthetic of choice.
Keywords: Anesthesia; Gavage; Gastrointestinal; Isoflurane; Motility; Metochlopramide;
Aqueous two-phase systems as a formulation concept for spray-dried protein by Jessica Elversson; Anna Millqvist-Fureby (73-87).
This study investigates to what extent an aqueous two-phase system (ATPS) can encapsulate and protect the secondary structure of a protein during spray drying. The ATPSs contained polyvinyl alcohol (PVA) and dextran solutions, in different proportions. A model protein, bovine serum albumin (BSA) and, in some experiments, trehalose were added to the ATPS prior to spray drying. Electron spectroscopy for chemical analysis (ESCA), differential scanning calorimetry (DSC), UV spectrophotometry, size exclusion high-performance liquid chromatography (SEC-HPLC) and Fourier transform infrared spectroscopy (FTIR) were used for analysis of solid and reconstituted samples. The anticipated function of the ATPS was to improve the stability of the protein by preventing interactions with the air–liquid interface during drying and by improving the encapsulation of the protein in the dried powder. BSA was found to preferentially partition to the dextran phase and in the absence of PVA, BSA dominated the powder surface. In samples containing PVA, the polymer mainly covered the powder surface, even though the dextran-rich phase was continuous, thus preventing protein surface interactions and providing improved encapsulation. However, PVA was found to cause partial loss of the native structure of BSA although the protein was well encapsulated during spray drying.
Keywords: Aqueous two-phase system; Trehalose; Fourier transform infrared spectroscopy; Electron spectroscopy for surface analysis; Spray drying; Bovine serum albumin; Encapsulation; Protein formulation;
Optimization and characterization of controlled release multi-particulate beads coated with starch acetate by Mohammad T.H. Nutan; Mahmoud S. Soliman; Ehab I. Taha; Mansoor A. Khan (89-101).
The objectives of the present study were (1) to model the effects of process and formulation variables on in vitro release profile of a model drug dyphylline from multi-particulate beads coated with starch acetate (SA); (2) to validate the models using R 2 and lack of fit values; (3) to optimize the formulation by response surface methodology (RSM); (4) to characterize the optimized product by thermal, X-ray and infrared spectroscopic analyses. Dyphylline loaded inert beads were coated using organic solution of SA with high degree of substitution. A three-factor, three-level Box–Behnken design was used for the optimization procedure with coating weight gain (X 1), plasticizer concentration (X 2) and curing temperature (X 3) as the independent variables. The regression equation generated for Y 5 (cumulative percent drug released after 12 h) was Y 5 = 89.83 − 11.98X 1 + 2.82X 2 − 4.31 X 1 2 + 1.90X 1 X 2. Optimization was done by maximizing drug release in 12 h and placing constraints at dissolution time points of 0.5, 1, 4 and 8 h. The drug release data of the optimized product were close to that predicted by the model. The models could explain 99% of variability in responses. Thermal, X-ray and infrared analyses suggested absence of any significant interaction of the drug with the excipients used in the formulation. SEM photographs showed the integrity of the coating layer.
Keywords: Starch acetate; Multi-particulate coated beads; Box–Behnken optimization design; Controlled release; Excipient compatibility; Mathematical modeling;
Injectable biodegradable temperature-responsive PLGA–PEG–PLGA copolymers: Synthesis and effect of copolymer composition on the drug release from the copolymer-based hydrogels by Mingxi Qiao; Dawei Chen; Xichen Ma; Yanjun Liu (103-112).
Injectable biodegradable temperature-responsive poly(dl-lactide-co-glycolide-b–ethylene glycol-b-dl-lactide-co-glycolide) (PLGA–PEG–PLGA) triblock copolymers with dl-lactide/glycolide molar ratio ranging from 6/1 to 15/l were synthesized from monomers of dl-lactide, glycolide and polyethylene glycol and characterized by 1H NMR. The resulting copolymers are soluble in water to form free flowing fluid at room temperature but become hydrogels at body temperature. The hydrophobicity of the copolymer increased with the increasing of dl-lactide/glycolide molar ratio. In vitro dissolution studies with two different hydrophobic drugs (5-fluorouracil and indomethacin) were performed to study the effect of dl-lactide/glycolide molar ratio on drug release and to elucidate drug release mechanism. The release mechanism for hydrophilic 5-fluorouracil was diffusion-controlled, while hydrophobic indomethacin showed an biphasic profile comprising of an initial diffusion-controlled stage followed by the hydrogel erosion-dominated stage. The effect of dl-lactide/glycolide molar ratio on drug release seemed to be dependent on the drug release mechanism. It has less effect on the drug release during the diffusion-controlled stage, but significantly affected drug release during the hydrogel erosion-controlled stage. Compared with ReGel system, the synthesized copolymers showed a higher gelation temperature and longer period of drug release. The copolymers can solubilize the hydrophobic indomethacin and the solubility (13.7 mg/ml) was increased 3425-fold compared to that in water (4 μg/ml, 25 °C). Two methods of physical mixing method and solvent evaporation method were used for drug solubilization and the latter method showed higher solubilization efficiency.
Keywords: Temperature-responsive; Injection; Drug release; Hydrogel;
Characteristics of interpolyelectrolyte complexes of Eudragit E 100 with sodium alginate by R.I. Moustafine; V.A. Kemenova; G. Van den Mooter (113-120).
With a view to the application in oral drug delivery formulations, the possibility to form interpolyelectrolyte complexes (IPEC) of Eudragit E 100 (EE) with sodium alginate (AL) was investigated, employing turbidimetry, apparent viscosity measurements, FT-IR and elementary analysis. The interaction or binding ratio of a unit molecule of AL with EE was largely affected by the pH value of the media, showing a change from 1.5:1 to 1:1.25 (0.66 < Z < 1.25) with increase in pH value from 2.5 to 6.0. Based on the results of elementary analysis and FT-IR, the interaction ratio of each component in the solid complexes was very close to that observed in turbidity and apparent viscosity measurements thus proving that the synthesized products actually can be considered as IPEC.
Keywords: Interpolyelectrolyte complex; Eudragit E 100; Sodium alginate; Solution apparent viscosimetry; Infrared spectroscopy; Turbidimetry; Elementary analysis;
Characterisation of the water–isopropyl myristate system by Michael H. Abraham; William E. Acree (121-128).
Partition coefficients for compounds (solutes) from water to isopropyl myristate, IPM, have been obtained from the literature, either as directly determined partition coefficients or from solubilities in water and in IPM. The general solvation equation of Abraham has been applied to 141 such partition coefficients, as log Pipm, and it is shown that the main solute factors that influence partition are dipolarity/polarisability, hydrogen bond acidity and hydrogen bond basicity that reduce partition, and volume that increases partition. These factors are quantitatively very similar to those that influence partition in the water to olive oil system, and indicate that IPM has the expected behaviour of a long chain, hydrophobic ester. It is shown that the water to IPM system is a poor model for partition between water and human stratum corneum and for permeation from water through human skin.
Keywords: Isopropyl myristate; Partition; Solvation equation; Hydrogen bonding;
The use of inverse gas chromatography and gravimetric vapour sorption to study transitions in amorphous lactose by Ameet V. Ambarkhane; Kim Pincott; Graham Buckton (129-135).
The aim of this study was to measure the glass transition of amorphous lactose under well-controlled temperature and humidity, using inverse gas chromatography (IGC) and to relate these data to gravimetric vapour sorption experiments. Amorphous lactose (spray-dried) was exposed to a stepwise increment in the relative humidity (%RH) under isothermal conditions in an IGC. At the end of each conditioning step a decane injection was made, and the retention volumes were calculated using the maximum peak height (V max) method. The pressure drop across the column was recorded using the pressure transducers. These measurements were performed at various temperatures from 25 to 40 °C. The extent of water sorption at identical humidity (%RH) and temperature conditions was determined gravimetrically using dynamic vapour sorption (DVS). At each T, it was possible to determine: (1) a transition at low RH relating to the onset of mobility; (2) changes in retention volume relating to the point, where T g = T; (3) changes in pressure drop, which were related to the sample collapse. The rate and extent of water sorption was seen to alter at T g and also at a collapse point. Combinations of temperature and critical %RH (%cRH required to lower the dry glass transition temperature to the experimental temperature) obtained from IGC were comparable to those obtained from DVS. It was shown that at each T, the sample spontaneously crystallised, when T g was 32 °C below T. Inverse gas chromatograph can be used in this novel way to reveal the series of transitions that occur in amorphous materials.
Keywords: Amorphous; mobility; Glass transition; Collapse; Crystallisation; Inverse gas chromatography; Water sorption;
Alginate rafts and their characterisation by F.C. Hampson; A. Farndale; V. Strugala; J. Sykes; I.G. Jolliffe; P.W. Dettmar (137-147).
Alginate/antacid anti-reflux preparations are designed to provide symptom relief by forming a physical barrier on top of the stomach contents in the form of a neutral floating gel or raft. This study tested the in vitro effectiveness of a range of liquid products in forming rafts that were cohesive, buoyant, voluminous, resistant to reflux and durable under conditions of movement (resilient). The products tested had a wide range of acid neutralising capacities (ANCs). It was found that products with a high ANC and no calcium ion source formed rafts of low strength, weight and volume, which appeared more as floating precipitates than coherent gels. Products with a high ANC and a calcium ion source formed medium strength, weight and volume rafts. Products with a low ANC formed strong coherent rafts with medium to large weight and volume, and those with low ANC and a calcium ion source formed the strongest rafts. Products with stronger rafts were found to be more resilient and more resistant to reflux in an in vitro reflux model. Significant overall differences in raft buoyancy were found between products forming coherent rafts but these could not be related to the product formulation or amount of available carbon dioxide.
Keywords: Alginate; Gastro-oesophageal reflux; Raft; Formulation;
Interaction of phloretin and 6-ketocholestanol with DPPC-liposomes as phospholipid model membranes by Barbara G. Auner; Michael A.A. O’Neill; Claudia Valenta; Jonathan Hadgraft (149-155).
Phloretin and 6-ketocholestanol are penetration enhancers for percutaneous delivery of certain topically applied drugs. In the present study some physicochemical experiments have been performed to elucidate the mechanism of action of phloretin and 6-ketocholestanol. The penetration enhancing effect of phloretin and 6-ketocholestanol is believed to be due to their increase of the fluidity of the intercellular lipid bilayers of the stratum corneum. Phospholipid vesicles were chosen as a simple model to represent these bilayers. The effect of phloretin and 6-ketocholestanol on phase transition temperature and enthalpy was studied using differential scanning calorimetry. Beside of that the size of liposomes was monitored when the amount of penetration enhancer in the liposome preparation was changed. Addition of increasing amounts of phloretin and 6-ketocholestanol to the bilayer resulted in lowering of phase transition temperatures and increasing the enthalpy. Additionally the size of the liposomes was increased when penetration enhancer was added. The results suggest that phloretin as well as 6-ketocholestanol would interact with stratum corneum lipids in a similar manner, both reduce the diffusional resistance of the stratum corneum to drugs with balanced hydrophilic–lipophilic characteristics.
Keywords: Phloretin; 6-ketocholestanol; DPPC; Liposomes; DSC;
Plasticizer di(2-ethylhexyl)phthalate (DEHP) release in wet-primed extracorporeal membrane oxygenation (ECMO) circuits by Jihong Han; Allison Beeton; Paul Long; Ann Karimova; Alex Robertson; Nigel Cross; Liz Smith; Maura O’Callaghan; Allan Goldman; Kate Brown; Catherine Tuleu (157-159).
A wet-primed ready-to-use extracorporeal membrane oxygenation (ECMO) circuit is used in some centres for rapid deployment of ECMO during cardiopulmonary resuscitation. Yet, the potential release of plasticizer di(2-ethylhexyl)phthalate (DEHP) from the polyvinyl chloride tubing in the circuit during storage is a concern. In this study, a high performance liquid chromatography method was used to determine the concentration of DEHP in the priming solution (Plasmalyte®) from an ECMO circuit stored for up to 14 days at 8 °C. No accumulation of DEHP in the circulating fluid was detected. The results provide important information for centres where ECMO circuits are kept wet-primed prior to clinical use.
Keywords: Di(2-ethylhexyl)phthalate; DEHP; Plasticizer; ECMO; Release; HPLC;
Cubic liquid crystalline glyceryl monooleate matrices for oral delivery of enzyme by Manish H. Shah; Anant Paradkar (161-171).
In situ cubic phase transforming system of glyceryl monooleate (GMO) has been prepared which offers protection to the metaloenzyme, seratiopeptidase (STP), in gastric environment and provides delayed and controlled release with no initial burst after oral administration. Effect of magnesium trisilicate (MTS) on floating, proteolytic activity and drug release was studied. Gelucire® 43/01 was incorporated in the system to provide prolonged lag time. The drug-loaded matrices required 100 mg of MTS to overcome floatability of GMO matrix. Plain GMO matrices showed 85.3% loss of proteolytic activity in acidic medium, whereas matrices containing MTS showed retention of activity (111.6%). The hydrophobic nature of MTS induced formation of cubic phase at faster rate and the existence of cubic phase was confirmed by polarizing light microscopy. Furthermore, MTS provided alkaline microenvironment, which prevented acid-catalyzed hydrolysis and protein unfolding. The magnesium ions restored the activity of STP. The release of STP was decreased with increasing amount of MTS in the matrix. Gelucire did not affect proteolytic activity. The water uptake of matrices with gelucire was decelerated due to formation of hexagonal phase. However, the rate of STP release from these matrices was very slow due to incorporation of gelucire into lipid bilayers, which provided resistance to movement of STP. Thus, microenvironment-controlled in situ cubic phase transforming GMO matrices provided protection to STP and controlled release.
Keywords: In situ cubic phase transformation; Glyceryl monooleate; Proteolytic activity; Serratiopeptidase; Gelucire® 43/01;
A critical evaluation of the relevant parameters for drug redispersion from adhesive mixtures during inhalation by A.H. de Boer; B.H.J. Dickhoff; P. Hagedoorn; D. Gjaltema; J. Goede; D. Lambregts; H.W. Frijlink (173-184).
In this paper, the parameters that are relevant to the drug redispersion from adhesive mixtures during inhalation are discussed and evaluated. The results obtained with air classifier technology give strong evidence for a dominating influence of carrier surface properties on the fraction of drug detached during inhalation at a low carrier payload (≤1%, w/w), versus a dominating effect of carrier bulk properties at higher payloads. Furthermore, the results indicate that there is a fundamental difference between so-called active carrier sites and large surface discontinuities. The difference refers to the saturation concentrations, the rates of saturation and their effects on drug detachment during inhalation. The degree of saturation of the active sites appears to be proportional with the square root of the carrier surface payload (after 10 min mixing time in a Turbula mixer at 90 rpm). The storage volume of the discontinuities seems largely independent of the carrier diameter for particles derived from the same batch of crystalline lactose. Saturation of these discontinuities is completed at a much lower carrier surface payload than saturation of the active sites. Relatively large discontinuities are beneficial to de-agglomeration principles that make use of inertial separation forces during inhalation, as they provide shelter from inertial and frictional press-on forces during mixing which increase the strength of the interparticulate bonds in the powder mixture. For de-agglomeration principles generating frictional, drag or lift forces, carrier surface depressions and projections are disadvantageous however, as they also provide shelter from these removal forces.
Keywords: Adhesive mixtures; Press-on forces; Active sites; Large carrier surface discontinuities; Carrier payload; Carrier size;
Comparison of the octanol/water partition coefficients calculated by ClogP®, ACDlogP and KowWin® to experimentally determined values by Stephen G. Machatha; Samuel H. Yalkowsky (185-192).
The experimental octanol/water partition coefficient data, of 108 compounds from the data set [Rytting, E., Lentz, K.A., Chen, X., Qian, F., Venkatesh, S., 2004. A quantitative structure–property relationship for predicting drug solubility in PEG 400/water cosolvent systems. Pharm. Res. 21, 237–244] was compared to calculated values using the computer programs ClogP®, ACD/logPdb® and KowWin®. It was found that all the three programs have a user friendly interface but ClogP® appears to be the more accurate predictor of log K ow.
Keywords: Comparison; Calculated; Octanol/water partition coefficient;
Second derivative tryptophan fluorescence spectroscopy as a tool to characterize partially unfolded intermediates of proteins by Vineet Kumar; Vikas K. Sharma; Devendra S. Kalonia (193-199).
The application of second derivative tryptophan (Trp) fluorescence spectroscopy to characterize partially unfolded intermediates of proteins relevant to protein formulation was investigated. The second derivatives of the normalized emission scans of N-acetyl tryptophanamide (NATA), single-Trp containing proteins, somatostatin and human serum albumin (HSA), and two-Trp containing proteins previously shown to form partially unfolded intermediates, β-lactoglobulin (βLg) and interferon α-2a (IFNα2a), were studied in solution. The second derivative of NATA in water showed three bands at 340, 348 and 367 nm. The 340 nm band showed a blue shift, whereas the intensity of all three bands was affected by a decrease in solution polarity. Second derivative of single-Trp containing proteins, somatostatin and HSA, showed three negative bands, whereas, the second derivative of the two-Trp containing proteins, βLg and IFNα2a, showed four bands, two of which lie in the 320–340 nm range. These two bands were attributed to the presence of the Trps in different microenvironments. The characteristic changes in the intensities of these two bands on addition of guanidine hydrochloride (βLg) and with a decrease in solution pH (IFNα2a) were related to the presence of partially unfolded intermediates of these proteins. Thus, second derivative Trp fluorescence spectroscopy can be used as an important tool to identify partially unfolded states of proteins during formulation utilizing order of magnitude lower concentrations compared to such other technique as near UV CD.
Keywords: Second derivative; Fluorescence; Tryptophan; Proteins; Tertiary structure; Partially unfolded intermediates;
Current strategies used to enhance the paracellular transport of therapeutic polypeptides across the intestinal epithelium by Nazila Salamat-Miller; Thomas P. Johnston (201-216).
The intent of this paper is to update the reader on various strategies which have been utilized to increase the paracellular permeability of protein and polypeptide drugs across the intestinal epithelium. Structural features of protein and polypeptide drugs, together with the natural anatomical and physiological features of the gastrointestinal (GI) tract, have made oral delivery of this class of compounds extremely challenging. Interest in the paracellular route for the transport of therapeutic proteins and polypeptides following oral administration has recently intensified and continues to be explored. The assumption that molecules with a large molecular weight are not able to diffuse through the tight junctions of the intestinal membrane has been challenged by current research, along with an increased understanding of tight junction physiology.
Keywords: Paracellular permeability; Therapeutic polypeptides; Molecular geometry and size;
Preparation and characterization of triclosan nanoparticles for periodontal treatment by E. Piñón-Segundo; A. Ganem-Quintanar; V. Alonso-Pérez; D. Quintanar-Guerrero (217-232).
The aim of this work was to produce and characterize triclosan-loaded nanoparticles (NPs) by the emulsification–diffusion process, in an attempt to obtain a novel delivery system adequate for the treatment of periodontal disease. The NPs were prepared using poly(d,l-lactide-co-glycolide) (PLGA), poly(d,l-lactide) (PLA) and cellulose acetate phthalate (CAP). Poly(vinyl alcohol) (PVAL) was used as stabilizer. Batches were prepared with different amounts of triclosan (TCS) in order to evaluate the influence of drug on NP properties. Solid NPs of less than 500 nm in diameter were obtained. Entrapment efficiencies were higher than 63.8%. The characterization by scanning electron microscopy and light scattering indicated that high concentrations of TCS seemingly caused the increase of NP mean size. A decrease in the PLGA glass transition temperature was observed by differential scanning calorimetry. This could indicate that TCS in PLGA-NPs behaves as a non-conventional plasticizer.Subsequently, in vitro release studies were carried out under sink conditions using a device designed in our laboratory to allow a direct contact between the particles and the dissolution medium. A fast release of TCS from NPs was detected. A preliminary in vivo study in dogs with induced periodontal defects suggested that TCS-loaded NPs penetrate through the junctional epithelium.
Keywords: Nanoparticles; Emulsification–diffusion; Triclosan; Periodontal diseases; Gingivitis; Periodontitis;
Preparation of a PLA–PEG block copolymer using a PLA derivative with a formyl terminal group and its application to nanoparticulate formulation by Masanaho Sasatsu; Hiraku Onishi; Yoshiharu Machida (233-245).
A novel poly(dl-lactic acid) (PLA) derivative with a diethoxy propanol ester at the end, named PLA-acetal, was synthesized by ring opening polymerization using dl-lactide and 3,3-diethoxy propanol. PLA-acetal was hydrolyzed to a PLA derivative with a formyl group, named PLA-aldehyde, by acid treatment. Reductive amination between PLA-aldehyde and methoxypolyethylene glycol amine (MeO-PEG(N)) gave the block copolymer (PLA–(MeO-PEG(N))). Nanoparticles were prepared by emulsification-solvent evaporation or solvent diffusion using PLA–(MeO-PEG(N)) or a conventional methoxypolyethylene glycol–PLA block copolymer, PLA–(MeO-PEG(O)). PLA–(MeO-PEG(N)) nanoparticles had a particle size of 60–340 nm, dependent on the preparative procedure, while PLA–(MeO-PEG(O)) nanoparticles prepared by solvent diffusion showed a particle size of 60 nm. The PLA–(MeO-PEG) nanoparticles with a smaller PEG introduction degree exhibited a more negative zeta potential. 1,1′-Dioctadecyl-3,3,3′,3′-tetramethylindodicarbocyanine perchlorate (DiD) could be incorporated efficiently in PLA–(MeO-PEG(N)) nanoparticles. It is suggested that PLA-aldehyde should be useful as a functional intermediate for derivatization of PLA, and PLA–(MeO-PEG(N)) can be used for the preparation of PEG-coated PLA nanoparticles.
Keywords: PLA-aldehyde; PLA-acetal; Methoxypolyethylene glycol-PLA block copolymer; Nanoparticle; Reductive amination;
Investigation of lectin-modified insulin liposomes as carriers for oral administration by Na Zhang; Qi N. Ping; Gui H. Huang; Wen F. Xu (247-259).
The aim of this study was to design and characterize lectin-modified liposomes containing insulin and to evaluate the potential of these modified colloidal carriers for oral administration of peptide and protein drugs. Wheat germ agglutinin (WGA), tomato lectin (TL), or Ulex europaeus agglutinin 1 (UEA1) were conjugated by coupling their amino groups to carbodiimide-activated carboxylic groups of N-glutaryl-phosphatidylethanolamine (N-glut-PE). Insulin liposomes dispersions were prepared by the reverse-phase evaporation technique and modified with the lectin-N-glut-PE conjugates. Lectin-modified liposomes were characterized according to particles size, zeta potential and entrapment efficiency. The hypoglycemic effect indicated by pharmacological bioavailability of insulin liposomes modified with WGA, TL and UEA1 were 21.40, 16.71 and 8.38% in diabetic mice as comparison with abdominal cavity injection of insulin, respectively. After oral administration of the insulin liposomes modified with WGA, TL and UEA1 to rats, the relative pharmacological bioavailabilities were 8.47, 7.29 and 4.85%, the relative bioavailability were 9.12, 7.89 and 5.37% in comparison with subcutaneous injection of insulin, respectively. In the two cases, no remarkable hypoglycemic effects were observed with the conventional insulin liposomes. These results confirmed that lectin-modified liposomes promote the oral absorption of insulin due to the specific-site combination on GI cell membrane.
Keywords: Wheat germ agglutinin; Tomato lectin; Ulex europaeus agglutinin 1; Insulin; Liposomes; Oral administration;
Preparation and characterization of poly-ɛ-caprolactone nanoparticles containing griseofulvin by Zohra Zili; Souad Sfar; Hatem Fessi (261-267).
Griseofulvin is an antifungal agent with poor solubility and low bioavailability. The aim of this work was to prepare poly-ɛ-caprolactone nanospheres and nanocapsules of griseofulvin by nanoprecipitation and to characterize them. Nanoparticles of griseofulvin were obtained with high encapsulation efficiency. The particle size was about 250–326 nm for nanospheres and 390–400 nm for nanocapsules.The dissolution rate of griseofulvin nanoparticles was higher than that of micronized griseofulvin therefore recourse to nanoencapsulation of griseofulvin should enhance its bioavailability and possibly its efficiency for the treatment of dermatomycosis.
Keywords: Griseofulvin; Nanospheres; Nanocapsules; Preparation; Characterization; Dissolution rate;
Calculation of the brittle fracture tendency (BFP) of tablets by F. Podczeck; J.M. Newton (269-270).
Anomalous effect of compression pressure on the brittle fracture tendency of α-cellulose tablets by M.U. Uhumwangho; R.S. Okor (271-272).