Solubilization of retinoids by bile salt/phospholipid aggregates

Microencapsulation of amorphous solid dispersions of fenretinide enhances drug solubility and release from PLGA in vitro and in vivo

The purpose of this study was to develop solid dispersions of fenretinide(4HPR), incorporate them into poly(lactic-co-glycolic)(PLGA) millicylindrical implants, and evaluate the resulting implants in vitro and in vivo for future applications in oral cancer chemoprevention. Due to the extreme hydrophobicity of 4HPR, 4HPR-polyvinylpyrrolidone (PVP) amorphous solid dispersions(ASDs) were prepared for solubility enhancement. The optimal PVP-4HPR ratio of 9/1(w/w) provided a 50-fold solubility enhancement in aqueous media, which was sustained over 1 week. PVP-4HPR ASD particles were loaded into PLGA millicylinders and drug release was evaluated in vitro in PBST and in vivo by recovery from subcutaneous injection in rats. While initial formulations of PLGA PVP-4HPR millicylinders only released 10% 4HPR in vitro after 28 days, addition of the plasticizer triethyl-o-acetyl-citrate(TEAC) into PVP-4HPR ASDs resulted in a 5.6-fold total increase in drug release. Remarkably, the TEAC-PVP-4HPR PLGA implants demonstrated slow, continuous, and nearly complete release over 1 month in vivo compared to a 25% release for our previously reported formulation incorporating solubilizers and pore-forming agents. Hence, a combination of PLGA plasticizer and ASD formation provides an avenue for long-term controlled release in vivo for the exceptionally difficult drug to formulate, 4HPR, and a suitable formulation for future evaluation in rodent models of oral cancer.

Recent insights on the role and regulation of retinoic acid signaling during epicardial development

The vitamin A metabolite, retinoic acid, carries out essential and conserved roles in vertebrate heart development. Retinoic acid signals via retinoic acid receptors (RAR)/retinoid X receptors (RXRs) heterodimers to induce the expression of genes that control cell fate specification, proliferation, and differentiation. Alterations in retinoic acid levels are often associated with congenital heart defects. Therefore, embryonic levels of retinoic acid need to be carefully regulated through the activity of enzymes, binding proteins and transporters involved in vitamin A metabolism. Here, we review evidence of the complex mechanisms that control the fetal uptake and synthesis of retinoic acid from vitamin A precursors. Next, we highlight recent evidence of the role of retinoic acid in orchestrating myocardial compact zone growth and coronary vascular development.

In vivo controlled release of fenretinide from long-acting release depots for chemoprevention of oral squamous cell carcinoma recurrence

Local, long-acting release fenretinide (4HPR) millicylindrical implants were prepared and evaluated for their release kinetics in vivo and their ability to suppress oral cancer tumor explant growth. Poly(lactic-co-glycolic acid)(PLGA) implants were prepared as a function of drug loading and the presence of various excipients (pore-formers, solubilizers, crystallization inhibitors) to enhance release of the insoluble 4HPR. Release kinetics and bioerosion of PLGA were monitored both in vitro in a PBS/Tween 80 buffer and in vivo by recovery of the drug remaining at the injection site. 4HPR was released from PLGA implants much slower in vivo than in the drug solubilizing media in vitro, with a 3-week lag phase and continuous release of >2 months, but showed some release enhancement by addition of solubilizers. Water-soluble PVA/sucrose implants for release of 4HPR served to determine if drug dissolution provided suitable controlled release without the PLGA, and this formulation showed continuous drug release over 6 weeks in vivo. Placement of PLGA-4HPR implants adjacent to oral cancer tumor murine xenografts showed inhibition of tumor growth relative to sham implants, indicating the potential for the local 4HPR delivery approach to be useful for oral cancer chemoprevention.

CTG-loaded liposomes as an approach for improving the intestinal absorption of asiaticoside in Centella Total Glucosides

Centella Total Glucosides (CTG),obtained from Centella asiatica (L.), have been shown to possess a multitude of pharmacological activities, however, oral administeration of CTG failed to fulfill their therapeutic potentials due to the low bioavailability. In this study, the author prepared the liposomes encapsulated CTG using the ethanol injection method in order to enhance their intestinal absorption. The average particle size and the polydispersityindex(PDI) of CTG-loaded liposome in a batch are 137.0nm and 0.283, and the CTG-loaded amounts in CTG-loaded liposomes were 0.177mgmL(-1) and the zeta potential of CTG-loaded lipsomes is -21.2mV. The TEM images of CTG-loaded lipsomes showed that CTG-loaded liposomes are round and maintain high structural integrity, and their DSC thermograms indicated that CTG might be incorporated into the aqueous phase of DPPC to become more stable. The everted rat gut sac model was used to study the absorption characteristic of CTG-loaded solution in rat intestines. The cumulative absorption amount (Q) and the cumulative absorption percentage (P%) of asiaticoside in the CTG-loaded liposome was significantly higher than that in CTG (P<0.05), both the steady-state infiltration rate (Jss, μgcm(-2)s(-1)) and the permeability coefficient (Papp, cms(-1)) of asiaticoside in CTG-loaded liposomes were significantly higher than those in CTG (P<0.05), which revealed that the liposomes encapsulated CTG can promote the absorption of asiaticoside in the ileum of the rats by enhancing its transmembrane permeability. The above study will provide the experimental evidence and a reference for the development of the oral dosage forms of Centella total glucosides.

Preparation and in vitro evaluation of hydrophilic fenretinide nanoparticles

Fenretinide is an effective anti-cancer drug with high in vitro cytotoxicity and low in vivo systemic toxicity. In clinical trials, fenretinide has shown poor therapeutic efficacy following oral administration - attributed to its low bioavailability and solubility. The long term goal of this project is to develop a formulation for the oral delivery of fenretinide. The purpose of this part of the study was to prepare and characterize hydrophilic nanoparticle formulations of fenretinide. Three different ratios of polyvinyl pyrrolidone (PVP) to fenretinide were used, namely, 3:1, 4:1, and 5:1. Both drug and polymer were dissolved in a mixture of methanol and dichloromethane (2:23 v/v). Rotary evaporation was used to remove the solvents, and, following reconstitution with water, a high pressure homogenizer was used to form nanoparticles. The particle size and polydispersity index were measured before and after lyophilization. The formulations were studied by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and X-ray powder diffraction (XRPD). The effectiveness of the formulations was assessed by release studies and Caco-2 cell permeability assays. As the PVP content increased, the recovered particle size following lyophilization became more consistent with the pre-lyophilization particle size, especially for those formulations with less lactose. The DSC scans of the formulations did not show any fenretinide melting endotherms, indicating that the drug was either present in an amorphous form in the formulation or that a solid solution of the drug in PVP had formed. For the release studies, the highest drug release among the formulations was 249.2±35.5ng/mL for the formulation with 4:1 polymer-to-drug. When the permeability of the formulations was evaluated in a Caco-2 cell model, the mean normalized flux for each treatment group was significantly higher (p<0.05) from the fenretinide control. The formulation containing 4:1 polymer-to-drug ratio and 6:5 lactose-to-formulation ratio emerged as the optimal choice for further evaluation as a potential oral delivery formulation for fenretinide.

Development and in vitro-in vivo evaluation of fenretinide-loaded oral mucoadhesive patches for site-specific chemoprevention of oral cancer

PURPOSE

To develop fenretinide oral mucoadhesive patch formulations and evaluate their in vitro and in vivo release performance for future site-specific chemoprevention of oral cancer.

METHODS

Solubilization of fenretinide in simulated saliva (SS) was studied by incorporating nonionic surfactants (Tween® 20 and 80, and Brij® 35 and 98), bile salts (sodium salt of cholic, taurocholic, glycocholic, and deoxycholic acids), phospholipid (lecithin), and novel polymeric solubilizer (Souplus®). Adhesive (polycarbophil: hydroxypropyl methylcellulose 4KM) and drug release (Fenretinide/Eudragit® RL PO with or without solubilizers) layers were prepared by solvent casting. Oral mucoadhesive patches were formed by attaching drug and adhesive layers onto backing layer (Tegaderm™ film). Physical state of drug in Eudragit® films was examined by X-ray diffraction (XRD). Evaluation of in vitro and in vivo fenretinide release from the patch was conducted in SS containing 5%w/v sodium deoxycholate and rabbits, respectively. Fenretinide was quantified by HPLC.

RESULTS

Tween® 20 and 80, Brij® 98, and sodium deoxycholate exhibited the highest fenretinide solubilization potential among the solubilizers. Drug loading efficiency in Eudragit® films was 90%-97%. XRD suggested fenretinide was amorphous in solubilizer-free and solubilizer-loaded films. Solubilizer-free patch exhibited poor in vitro and in vivo controlled drug release behavior. Increases in drug loading (5-10 wt%) or changes in polymeric matrix permeability did not provide continuous drug release. Co-incorporation of either single or mixed solubilizers in fenretinide/Eudragit® patches, (20 wt% Tween® 20, Tween® 80 and sodium deoxycholate or 20 wt% Tween® 80 + 40 wt% sodium deoxycholate solubilizers) led to significantly improved continuous in vitro/in vivo fenretinide release.

CONCLUSION

Fenretinide/Eudragit® RL PO patches with 20 wt% Tween® 80 + 40 wt% sodium deoxycholate solubilizers exhibit excellent release behavior for further preclinical and/or clinical evaluation in oral cancer chemoprevention.

Enhancing intestinal drug solubilisation using lipid-based delivery systems

Lipid-based delivery systems are finding increasing application in the oral delivery of poorly water-soluble, lipophilic drugs. Whilst lipidic dose forms may improve oral bioavailability via several mechanisms, enhancement of gastrointestinal solubilisation remains argueably the most important method of absorption enhancement. This review firstly describes the mechanistic rationale which underpins the use of lipid-based delivery systems to enhance drug solubilisation and briefly reviews the available literature describing increases in oral bioavailability after the administration of lipid solution, suspension and self-emulsifying formulations. The use of in vitro methods including dispersion tests and more complex models of in vitro lipolysis as indicators of potential in vivo performance are subsequently described, with particular focus on recent data which suggests that the digestion of surfactants present in lipid-based formulations may impact on formulation performance. Finally, a series of seven guiding principles for formulation design of lipid-based delivery systems are suggested based on an analysis of recent data generated in our laboratories and elsewhere.

Physicochemical and biopharmaceutical characterization of endo-2-(8-methyl-8-azabicyclo[3.2.1]oct-3-yl)-2,3-dihydro-1H-benz[e]isoindol-1-one (CR3124) a novel potent 5-HT3 receptor antagonist

The physicochemical and biopharmaceutical properties, such as pK(a), crystal habit, water solubility, logD, molecular structure and dynamics, and membrane permeability of CR3124 (endo-2-(8-methyl-8-azabicyclo[3.2.1]oct-3-yl)-2,3-dihydro-1H-benz[e]isoindol-1-one, a novel potent 5-HT(3) receptor antagonist) have been studied in order to obtain preformulation information. The study showed that CR3124 is a very rigid molecule in which conformational freedom due to the presence of a rotatable bond is restricted by the interaction between an activated hydrogen and the amide oxygen and the conformation of the tropane piperidine ring is regulated by the environment in such a manner as to optimize the intermolecular interactions with the solvent. This chameleon behavior appears to be capable of explaining the biopharmaceutical properties showed by CR3124, such as low wettability, relatively good solubility, and very high membrane permeability.

Development and assessment of an innovative soil-washing process based on the use of cholic acid-derivatives as pollutant-mobilizing agents

Surfactant-aided soil washing is often proposed for the restoration of aged organic pollutant-contaminated soils. As many of commercial surfactants have been found to be toxic and recalcitrant, the opportunity to use in this process cheap, non-toxic, and biodegradable pollutant-mobilizing agents, such as deoxycholic acid (DA), bovine bile (BB), and the residue resulting from DA extraction from BB (BBR), was studied in this work. A soil historically contaminated by chlorinated anilines and benzenes, thiophenes, and several polycyclic aromatic hydrocarbons was suspended at 15% w/v and washed in water or water amended at 1.0% (w/v) with DA, BB, BBR, or Triton X-100 (TX). The resulting effluents were supplemented with nutrients and subjected to aerobic bioremediation. The biogenic agents enhanced the water pollutant elution potential by 230/440%. TX enhanced the same parameter by about 540%; however, it mediated a lower depletion of the initial soil ecotoxicity and a more extensive mobilization of soil constituents with respect to the biogenic agents. Furthermore, TX adversely affected the biotreatability of resulting effluents, by adversely affecting the growth of cultivable bacterial biomass and the structure of eubacterial community of the effluent. On the contrary, the biogenic agents, and in particular DA and BB, enhanced the effluents bioremediation, by sustaining the growth and increasing the complexity of the effluent eubacterial communities. Thus, DA and BB are very promising additives for an effective and environmental friendly soil washing treatment of aged (chloro)organics contaminated soils.

Retinosomes: new insights into intracellular managing of hydrophobic substances in lipid bodies

Lipid bodies form autonomous intracellular structures in many model cells and in some cells of specific tissue origin. They contain hydrophobic substances, a set of structural proteins such as perilipin or adipose differentiation-related protein, enzymes implicated in lipid metabolism, and proteins that participate in signaling and membrane trafficking. Retinosomes, particles reminiscent of lipid bodies, have been identified in retinal pigment epithelium as distinct structures compartmentalizing a metabolic intermediate involved in regeneration of the visual chromophore. These observations suggest that lipid bodies, including retinosomes, carry out specific functions that go beyond those of mere lipid storage organelles.

Noninvasive two-photon imaging reveals retinyl ester storage structures in the eye

Visual sensation in vertebrates is triggered when light strikes retinal photoreceptor cells causing photoisomerization of the rhodopsin chromophore 11-cis-retinal to all-trans-retinal. The regeneration of preillumination conditions of the photoreceptor cells requires formation of 11-cis-retinal in the adjacent retinal pigment epithelium (RPE). Using the intrinsic fluorescence of all-trans-retinyl esters, noninvasive two-photon microscopy revealed previously uncharacterized structures (6.9 +/- 1.1 microm in length and 0.8 +/- 0.2 microm in diameter) distinct from other cellular organelles, termed the retinyl ester storage particles (RESTs), or retinosomes. These structures form autonomous all-trans-retinyl ester-rich intracellular compartments distinct from other organelles and colocalize with adipose differentiation-related protein. As demonstrated by in vivo experiments using wild-type mice, the RESTs participate in 11-cis-retinal formation. RESTs accumulate in Rpe65-/- mice incapable of carrying out the enzymatic isomerization, and correspondingly, are absent in the eyes of Lrat-/- mice deficient in retinyl ester synthesis. These results indicate that RESTs located close to the RPE plasma membrane are essential components in 11-cis-retinal production.

Retinoid cycle in the vertebrate retina: experimental approaches and mechanisms of isomerization

Retinoid cycle describes a set of chemical transformations that occur in the photoreceptor and retinal pigment epithelial cells. The hydrophobic and labile nature of the retinoid substrates and the two-cell chromophore utilization-regeneration system imposes significant constraints on the experimental biochemical approaches employed to understand this process. A brief description of the recent developments in the investigation of the retinoid cycle is the current topic, which includes a review of novel results and techniques pertaining to the retinoid cycle. The chemistry of the all-trans-retinol to 11-cis-retinol isomerization is also discussed.

Solubilization of drugs by physiological mixtures of bile salts

PURPOSE

The solubilization of a number of steroids was determined in bile salt simple micelles and a bile salt/phospholipid micellar system to provide a better basis to predict the extent of drug solubilization in vivo.

METHODS

Excess solid drug was dispersed in taurodeoxycholate or mixed micelle solutions prepared with fixed mole ratios of taurocholate, taurodeoxycholate, taurochenodeoxycholate, glycodeoxycholate, glycocholate, and glycochenodeoxycholate with egg phosphatidylcholine. Drug concentrations were determined from the absorbance following centrifugation. Using NMR spectroscopy, the diffusivities of the simple and mixed micelles were 2 x 10(-6) and 8 x 10(-7) cm2/s, respectively.

RESULTS

From the change in the concentration of drug in solution with a change in the lipid concentration, the solubilization ratio (SR) was calculated. The SR and aqueous solubility were used to calculate the micelle/aqueous partition coefficients (Km/w). Km/w was correlated with octanol/water partition (Po/w) for the TDC and mixed micelle data sets with correlation lines of logKm/w = 0.74logPo/w + 1.55 (r2 = 0.91) and logKm/w = 0.61 logPo/w + 2.44 (r2 = 0.95), respectively.

CONCLUSIONS

With such data, a refined, predictive relationship between the in vitro and the in vivo solubilization with additional information concerning the bile salt/lipid concentration in the human intestine appears possible.

Examination of the solubilization of drugs by bile salt micelles

The purpose of this review is to provide a critical examination of the reported solubilization of drugs by bile salt micelles. The underlying premise is that with better information regarding the inherent biological complexity, efforts to predict the oral bioavailability of drug will be enhanced. The common means of comparing the reported values was chosen to be the solubilization ratio. This is equal to the moles of drug solubilized per mole of bile salt. The values were segregated according to bile salt type, temperature, ionic strength, and the presence and absence of added lipids. Only segregation by bile salt type was pairwise statistically significant. From the solubilization ratios and the reported values of the aqueous solubility, the logarithms of the mole fraction micelle partition coefficients, log K(m/a), were calculated. The log K(m/w) was found to be correlated with the reported logarithm of the octanol/water partition coefficient. The rank order of slopes of the log K(m/a) as a function of log K(o/w) was cholate approximately taurodeoxycholate > glycocholate approximately taurocholate approximately glycodeoxycholate, with deoxycholate not being statistically different from the other data sets. The slope and intercept for the bile salt mixed micelle systems were 0.600 and 2.44, respectively, which were statistically indistinguishable from glycocholate, taurocholate, and glycodeoxycholate bile salt data. The existence of statistically significant correlations suggests that predicting the solubilization in the intestine may be possible with in vitro measurements if additional information is gathered in the appropriate micellar solutions.

Distribution and diffusion of sodium taurocholate and egg phosphatidylcholine aggregates in rat intestinal mucin

PURPOSE

The permeability of rat intestinal mucin (RIM) to sodium taurocholate/egg phosphatidylcholine (TC/PC)-mixed micelles has been investigated.

METHODS

The time dependence for the equilibration of TC/PC-mixed lipid micelles with isolated RIM was determined. Thereafter the distribution of TC/PC-mixed lipid micelles was assessed at low and high PC and intermicellar concentrations (IMC) and with different RIM concentrations. The equilibrium distribution of PC and TC was determined by analysis for phosphorus and by high-performance liquid chromatography, respectively, as well as by nuclear magnetic resonance spectroscopy. In addition, the diffusion coefficients of water, PC, and TC were measured by pulsed field gradient nuclear magnetic resonance spectroscopy. Two model solutes, phenylmethyltrimethylsilane (PTMS) and tetramethylsilyl-tetradeutero-proprionic acid (TSP), were added to the high PC, low IMC samples, and the diffusion coefficients were determined.

RESULTS

The time to reach equilibrium was 2 days for a system with a high intermicellar concentration of sodium taurocholate. At low PC concentrations, RIM had slightly higher PC concentrations relative to the control. In contrast, at high PC concentrations, RIM samples had lower PC concentrations. The concentration of TC was largely independent of mucin concentration. The water diffusivity was reduced proportionately to the concentration of RIM, and analysis indicated that about 150 g of water moved as a kinetic unit with each gram of mucin. The diffusion coefficients of PC were also reduced with increasing RIM concentration. The magnetization decay of TC did not always follow a monoexponential decay, reflecting the simultaneous diffusion and exchange among sites imparting different relaxation behavior on the TC. Magnetization decay curves were simulated and the diffusivity of TC in mucin was estimated. The diffusion coefficient of TSP was 10 times larger than that of PTMS in the presence of micelles and mucin.

CONCLUSIONS

RIM is highly hydrated, and dilute solutions have a minor exclusive effect on the high concentration of PC/TC micelles. At low concentrations of PC, there appears to be preferential association of the PC with the RIM. The permeability of mucin to solutes in the presence of bile salt mixed micelles critically depends on the degree of association of the solute with the micelle.

Surface active drugs: self-association and interaction with membranes and surfactants. Physicochemical and biological aspects

Many pharmacologically active compounds are of amphiphilic (or hydrophobic) nature. As a result, they tend to self-associate and to interact with biological membranes. This review focuses on the self-aggregation properties of drugs, as well as on their interaction with membranes. It is seen that drug-membrane interactions are analogous to the interactions between membranes and classical detergents. Phenomena such as shape changes, vesiculation, membrane disruption, and solubilization have been observed. At the molecular level, these events seem to be modulated by lipid flip-flop and formation of non-bilayer phases. The modulation of physicochemical properties of drugs by self-association and membrane binding is discussed. Pathological consequences of drug-membrane interaction are described. The mechanisms of drug solubilization by surfactants are reviewed from the physicochemical point of view and in relation to drug carrying and absorption by the organism.

Ionization and solubilization of 4 alkyl benzoic acids and 4 alkyl anilines in sodium taurodeoxycholate solutions

PURPOSE

The aqueous solubility and the extent of solubilization and ionization constant in sodium taurodeoxycholate (NaTDC) solutions of a series of benzoic acid and aniline derivatives were measured as a basis to characterize and thereby help predict the nature of the interaction of drugs with bile aggregates.

METHODS

The aqueous solubility and the solubilization of two series of compounds, 4-alkyl benzoic acids and 4-alkyl anilines, was measured as a function of NaTDC in 0 and 150 mM NaCl. The ionization constants were determined in water and in 50 mM NaTDC at sodium chloride concentration of 0, 75 and 150 mM by spectrophotometric titration. The diffusion coefficients of NaTDC and the solutes were measured by pulsed-field gradient spin echo NMR spectroscopy.

RESULTS

The aqueous solubilities decreased with increasing alkyl chain length in both series, and the aniline derivatives had larger solubilities than the benzoic acid derivatives. The number of moles of solute solubilized per mole of bile salt ranged from 0.17 to 0.31 for the benzoic acid derivatives and from 1.3 to 3.0 for the aniline derivatives. The pKa values of the benzoic acid derivatives in the presence of NaTDC were higher relative to the controls, and the difference in the pKa (delta pKa,obs) increased with increasing chain length. With the aniline derivatives, the pKa values were also shifted to higher values in NaTDC relative to the control but only in the absence of salt. The presence of the solute caused a decrease in the diffusion coefficient of NaTDC, and the diffusion coefficients of the solutes decreased with increasing alkyl chain length. With the hexyl derivative, the diffusion coefficient of the solute was smaller than the diffusion coefficient of the bile salt. The chemical shift of the protons attached to carbon 18 and 19 of the salt were decreased to a greater extent in the presence of the solutes than the protons attached to carbon 26.

CONCLUSION

Both the solubilization and ionization behavior of solutes were affected by the presence of bile salt aggregates. The surface potential and effective polarity of NaTDC aggregates were found to be dependent on the alkyl chain length for these two homologous series of solutes. The solubilization ratio was largely independent of alkyl chain length, but the unitary partition coefficient was dependent on both alkyl chain length as well as ionization state. The derivatives reduced the diffusivity of the micelles suggesting the formation of larger size aggregates and the solutes (hexyl derivatives) appear to favor association with the larger sized aggregates. The phenyl ring of the solutes appears to be oriented parallel to the plane of the steroid frame with preferential positioning near the hydrophobic rings.