The application and mechanisms of polyethylene glycol 8000 on stabilizing lactate dehydrogenase during lyophilization

The purpose of this paper is to explore the application and mechanisms of polyethylene glycol 8000 (PEG 8000) on stabilizing lactate dehydrogenase (LDH) during lyophilization. In earlier freeze-thawing experiments, different molecular weights and concentrations of PEGs were formulated with LDH, and ultraviolet (UV) enzymatic activity and circular dichroism (CD) wavelength scanning studies were conducted. In lyophilization studies, different molecular weights of saccharides, e.g., glucose, sucrose, dextran 37,000 (D 37K), and dextran 160,000 (D 160K), with or without PEG 8000, were formulated with LDH at various molar ratios. UV assays, size exclusion chromatography -high performance liquid chromatography (SEC-HPLC), CD, fourier transform infrared spectroscopy (FTIR) were conducted for LDH. Upon lyophilization, enzymatic activity and tetrameric structure recoveries of LDH-saccharide formulations reached over 90% with PEG 8000 vs. 60-80% without PEG 8000. LDH-PEG 8000-saccharide formulations shifted the melting temperature (Tm) to higher temperatures than did LDH-saccharide formulations. Most LDH-PEG 8000-saccharide formulations at 1:100:1000 molar ratio showed better preservation of LDH secondary structures than did LDH-saccharide formulations at 1:1000 molar ratio. Since PEG 8000 was confirmed an effective cryoprotectant, saccharides were assumed to be protecting LDH from destabilization during drying. However, LDH-PEG 8000-dextran formulations preserved more LDH secondary structure than did LDH-dextran formulations, but preserved less LDH secondary structures than did LDH-PEG 8000 formulations. This indicated that dextrans not only did not stabilize LDH during drying, but they disrupted the stabilization effect of PEG 8000 on LDH during freezing. After reconstitution, CD wavelength scanning showed that some of the unfolded or denatured structures of LDH were refolded. Based on the steric hindrance of the bulky dextrans and the "water replacement mechanism", sucrose with PEG 8000 had synergistic protective effects, and dextrans with PEG 8000 had antagonistic effects, on stabilization of LDH during lyophilization.     

Effects of polyethylene glycol molecular weight and concentration on lactate dehydrogenase activity in solution and after freeze-thawing

Lactate dehydrogenase (LDH) is a tetrameric enzyme that has been used as a model for labile protein drugs. Polyethylene glycols (PEGs) have been proposed as excipients to stabilize labile proteins in solution and during the freezing portion of the lyophilization cycle. The aim of this study was to determine the effects of PEG molecular weight and concentration on the activity of LDH. In general, PEG protection increases with PEG molecular weight and concentration. PEGs slow the loss of activity in LDH solutions stored at 4 degrees C, but are not sufficiently effective to allow for a solution product. PEGs 8000, 10,000, and 20,000 show full freezing protection at less than 0.01%, while lower molecular weight PEGs need higher concentrations to produce protection upon freezing. Circular dichroism (CD) studies of LDH solutions before and after freezing with PEG 400 and PEG 8000 confirm the activity studies. The CD spectrum of LDH before freezing shows the classic alpha helix pattern. After unprotected LDH solution is frozen and thawed, the CD spectrum erodes. Low concentrations of PEG 8000 (1% or less) preserve the alpha helix profile after freezing of the samples. PEG 400 preserves the alpha helix CD profile in a stepwise fashion with increasing concentrations. The CD and activity data suggest that PEGs can protect alpha helix structures and activity of LDH through the freezing process.     

Appearance of 14C-polyethylene glycol 4000 in intestinal venous blood: Influence of osmolarity and laxatives,effect on net water flux determination

Summary In anaesthetized rats the appearance rate of ¹⁴C-polyethylene glycol 4000 (¹⁴C-PEG 4000) was measured in the intestinal venous blood after intraluminal administration into a jejunal, ileal, and colonic segment. The absorption rate was small, especially in the colon (0.5–4.2 % within 60 min in an intestinal segment of about 300 mg wet tissue weight depending on the batch of ¹⁴C-PEG 4000). The absorbed PEG in the plasma consisted mainly of molecules with lower molecular weight than 4000 which were included in the commercial batches of ¹⁴C-PEG 4000. The appearance rate of ¹⁴C-PEG decreased with time after single dose but remained constant, when a ¹⁴C-PEG solution was perfused continuously through the intestinal lumen. A hypotonic solution increased and a hypertonic one decreased slightly the absorption of PEG in the jejunum and ileum but not in the colon. The influence of bisacodyl (100 mg l^–1) and ricinoleate (10 mmol l^–1) on the absorption of PEG was small or absent, while deoxycholate (5 mmol l^–1) raised the absorption rate considerably, predominantly of the high molecular weight fraction. If in intestinal absorption studies a batch of commercial ¹⁴C-PEG 4000 with a small low molecular weight fraction is used, the error in the determination of net water flux caused by the absorption of PEG can be neglected. The influence of osmolarity and laxatives is insignificant. Bile acids increase the intestinal permeability of PEG 4000, so that the net water flux determination can be biased considerably.     

A comparison between the protection of LDH during freeze-thawing by PEG 6000 and Brij 35 at low concentrations

The protection of lactate dehydrogenase (LDH) by low concentrations of the non-surface-active polyethylene glycol (PEG 6000) or the non-ionic surfactant PEG dodecyl ether (Brij 35) was investigated during freeze-thawing. The freeze-thawing process was performed with a controlled temperature history, and the protective mechanisms were elaborated. The systems were examined by differential scanning calorimetry (DSC), fluorescence spectroscopy and surface tension measurements. LDH activity assays were performed spectrophotometrically. Very low concentrations of PEG 6000 (8 x 10(-5) mM) or Brij 35 (4 x 10(-3) mM) protected LDH during freeze-thawing with a low cooling rate. With an increased freezing rate, higher concentrations of the additives were needed for full protection. No interaction was detected between LDH and Brij molecules. The strong interaction between LDH and PEG molecules disappeared with a small change in the protein structure, using a hybrid of LDH. The protein was nevertheless completely protected. The amount of Brij required for complete protection at high cooling rates correlated with the created ice surface area. The protection by PEG indicated a certain correlation with the ice crystal size and with the formation of a PEG hydrate. Brij or PEG hydrate molecules might compete with the protein for adsorption at the ice surface and thereby protect the protein during freeze-thawing.     

Synthesis of poly(ethylene glycol)-metaxalone conjugates and study of its controlled release in vitro

Metaxalone (Met), a drug for treatment of pain and stiffness due to muscular injuries, was covalently linked to poly(ethylene glycols) (PEG) via a chloroacetyl chloride spacer. The average weight molecular weights used for PEG are 4000, 6000 and 10,000, respectively, and the procedure of chemical modification for PEGs was conducted by a two-step protocol: (1) synthesis of N-chloroacetyl-metaxalone; (2) synthesis of PEG(4000)-Met, PEG(6000)-Met and PEG(10000)-Met. The controlled drug release studies were performed in buffer solutions with pH values equal to 1.1, 7.4 and 10.0. The results demonstrate that, in the same condition, the rate of hydrolysis for PEG(10000)-Met is the slowest among three prodrugs, and more amount of metaxalone can be detected releasing from prodrug matrices at the presence of alpha-chymotrypsin in a buffer solution with pH 8.0. It was also found that these novel prodrugs can effectively improve the metaxalone's pharmacokinetics, and furthermore can markedly increase its half-life period.     

Formulation and Evaluation of Tramadol hydrochloride Rectal Suppositories

Rectal suppositories of tramadol hydrochloride were prepared using different bases and polymers like PEG, cocoa butter, agar and the effect of different additives on in vitro release of tramadol hydrochloride was studied. The agar-based suppositories were non-disintegrating/non-dissolving, whereas PEGs were disintegrating/dissolving and cocoa butter were melting suppositories. All the prepared suppositories were evaluated for various physical parameters like weight variation, drug content and hardness. The PEG and cocoa butter suppositories were evaluated for macromelting range, disintegration and liquefaction time. In vitro release study was performed by USP type I apparatus. The prepared suppositories were within the permissible range of all physical parameters. In vitro drug release was in the order of PEG>Agar>cocoa butter. Addition of PVP, HPMC in agar suppositories retards the release. The mechanism of drug release was diffusion controlled and follows first order kinetics. The results suggested that blends of PEG of low molecular weight (1000) with high molecular weight (4000 and 6000) in different percentage and agar in 10% w/w as base used to formulate rapid release suppositories. The sustained release suppositories can be prepared by addition of PVP, HPMC in agar-based suppositories and by use of cocoa butter as base.     

Factors affecting the formation of eutectic solid dispersions and their dissolution behavior

The objective of this work was to obtain a fundamental understanding of the factors, specifically the properties of poorly water-soluble drugs and water-soluble carriers, which influence predominantly, the formation of eutectic or monotectic crystalline solid dispersion and their dissolution behavior. A theoretical model was applied on five poorly water-soluble drugs (fenofibrate, flurbiprofen, griseofulvin, naproxen, and ibuprofen) having diverse physicochemical properties and water-soluble carrier (polyethylene glycol (PEG) 8000) for the evaluation of these factors. Of these, two drugs, fenofibrate and flurbiprofen, and PEG of different molecular weights (3350, 8000, and 20000), were chosen as model drugs and carriers for further investigation. Experimental phase diagrams were constructed and dissolution testing was performed to assess the performance of the systems. The theoretical model predicted the formation of eutectic or monotectic solid dispersions of fenofibrate, griseofulvin, ibuprofen, and naproxen with PEG, holding the contribution of specific intermolecular interactions between compound and carrier to zero. In the case of the flurbiprofen-PEG eutectic system, intermolecular interactions between drug and polymer needed to be taken into consideration to predict the experimental phase diagram. The results of the current work suggest that the thermodynamic function of melting point and heat of fusion (as a measure of crystal energy of drug) plays a significant role in the formation of a eutectic system. Lipophilicity of the compound (as represented by cLog P) was also demonstrated to have an effect. Specific interactions between drug and carrier play a significant role in influencing the eutectic composition. Molar volume of the drug did not seem to have an impact on eutectic formation. The polymer molecular weight appeared to have an impact on the eutectic composition for flurbiprofen, which exhibits specific interactions with PEG, whereas no such impact of polymer molecular weight on eutectic composition was observed for fenofibrate, which does not exhibit specific interactions with PEG. The impact of polymer molecular weight on dissolution of systems where specific drug-polymer interactions are exhibited was also observed. The current work provides valuable insight into factors affecting formation and dissolution of eutectic systems, which can facilitate the rational selection of suitable water-soluble carriers.     

Solidification Studies of Polyethylene Glycols,Gelucire 44/14 or their Dispersions with Triamterene or Temazepam

The solidification of polyethylene glycols (PEG 1500, PEG 2000, PEG 4000, PEG 6000), gelucire 44/14 or their dispersions containing triamterene or temazepam were studied to assess the feasibility of using these dispersions to liquid-fill hard gelatin capsules. Solidification from melts, investigated by differential scanning calorimetry using cooling cycles, showed a tendency of the drugs, carriers or their dispersions to supercool. The degree of supercooling depended on the rate of cooling, the drug content and, for the PEGs, on the molecular weight. PEG 1500 and PEG 2000 gave one morphological form, irrespective of cooling rate; PEG 4000 and PEG 6000 solidified into at least two forms, depending on the cooling rate. Incorporation of drugs affected the morphology of the PEGs during solidification. The rate of crystal growth was, furthermore, influenced by the fusion temperature, molecular weight and the degree of supercooling. The degree of crystallinity, as measured by the enthalpies of solidification, decreased with increasing cooling rate. The results show that reducing the rate of solidification could lead to incomplete solidification, giving products that are liable to change on storage.     

Modulation of intestinal P-glycoprotein function by polyethylene glycols and their derivatives by in vitro transport and in situ absorption studies

We examined the effect of polyethylene glycols (PEGs) with different molecular weights and their derivatives on the intestinal absorption of rhodamine123, a P-glycoprotein (P-gp) substrate, across the isolated rat intestinal membranes by an in vitro diffusion chamber system. The serosal to mucosal (secretory) transport of rhodamine123 was greater than its mucosal to serosal (absorptive) transport, indicating that the net movement of rhodamine123 across the intestinal membranes was preferentially secretory direction. The secretory transport of rhodamine123 was inhibited by the addition of PEGs with average molecular weights of 400, 2000 and 20,000, irrespective of its molecular weight. The inhibitory effects of these PEGs for the intestinal P-gp function were concentration dependent over the range 0.1-20% (v/v or w/v). Similar inhibitory effect for the intestinal P-gp function was observed when PEG derivatives including PEG monolaurate, PEG monooleate and PEG monostearate were added to the mucosal site of the chambers. Furthermore, we also examined effect of PEG20,000 on the intestinal absorption of rhodamine123 by an in situ closed loop method. The intestinal absorption of rhodamine123 was enhanced in the presence of PEG20,000. These findings suggest that PEGs and their derivatives are useful excipients to inhibit the function of intestinal P-gp, thereby improving the intestinal absorption of P-gp substrates, which are secreted by a P-gp-mediated efflux system.     

A multiparticulate drug-delivery system based on pellets incorporated into congealable polyethylene glycol carrier materials

As a novel alternative to the incorporation into hard gelatin capsules or tablets, extended-release (Aquacoat- or Eudragit RS-coated) or enteric (Eudragit L-coated) pellets were embedded into congealed tablet-shaped PEG-plugs of different molecular weights, which rapidly released the pellets upon contact with aqueous fluids. The lower-molecular-weight PEGs (600 and 1000) were not suitable carrier materials: they dissolved the coatings or significantly increased their permeability. The release characteristics of the original pellets were maintained after embedding the pellets into the higher-molecular-weight PEGs 4000 or 10000. The shelf-life stability was a function of storage temperature and coating material. Stored at 40 degrees C, Aquacoat-coated pellets embedded in PEG 4000 exhibited a decreased drug release because of curing effects, while storage at 20 degrees C or below resulted in stable release profiles over a 3 month period. Eudragit RS-coated pellets, stored at room temperature or above, showed an increased release, and the carrier material possibly migrated into the film, thus increasing its permeability. At 4 degrees C, the release was stable over a 6 month period.     

Effect of polyethylene glycols on the trans-ungual delivery of terbinafine

Topical nail drug delivery could be improved by identifying potent chemical penetration enhancers. The purpose of this study was to assess the effect of polyethylene glycols (PEGs) on the trans-ungual delivery of terbinafine. In vitro permeation studies were carried out by passive and iontophoresis (0.5 mA/cm2) processes for a period of 1 h using gel formulations containing different molecular weight PEGs (30%w/w). The release of drug from the loaded nail plates and the possible mechanisms for the enhanced delivery was studied. Passive delivery using formulation with low molecular weight PEGs (200 and 400 MW) indicated moderate enhancement in the permeation and drug load in the nail plate, compared to the control formulation. However, the effect of low molecular weight PEGs was predominant during iontophoresis process with greater amount of terbinafine being permeated (≈35 μg/cm2) and loaded into the nail plate (≈2.7 μg/mg). However, little or no effect on drug delivery was observed with high molecular weight PEGs (1000- 3350 MW) in passive and iontophoresis processes. Release of drug from the nail plates loaded by iontophoresis using low molecular weight PEG (400 MW) exhibited sustain effect which continued over a period of 72 days. The enhancement in drug permeation by low molecular weight PEGs is likely due to their ability to lead to greater water uptake and swelling of nail. This study concluded that the low molecular weight PEGs are indeed a promising trans-ungual permeation enhancer.     

Physical Stability of Solid Dispersions Containing Triamterene or Temazepam in Polyethylene Glycols

The effect of storage on the physical stability of solid dispersions of triamterene or temazepam in polyethylene glycols was studied using differential scanning calorimetry (DSC), particle-size analysis and dissolution methods. The enthalpies of fusion of the carriers, without included drug and previously fused and crystallized, increased on storage. Analysis of similarly treated solid dispersions, containing either 10% temazepam or 10% triamterene, showed that each drug influenced the morphology of the polyethylene glycol (PEG). The enthalpies and melting points of the solidus components of the dispersions' carriers were initially reduced after preparation, but on storage these increased. The particle sizes of the drugs dispersed in the PEGs increased on storage. The changes in dissolution after storage of triamterene or temazepam dispersions were smaller for dispersions in PEG 1500 than for dispersions in PEGs of higher molecular weight (PEG 2000, PEG 4000 or PEG 6000) in which the reduction in dissolution was particularly marked during the first month of storage. The rank order of changes in dissolution were PEG 1500 ? PEG 2000 < PEG 4000 ～ PEG 6000.     

Effect of PEGylation on protein hydrodynamics

We studied the effect of PEGylation on protein hydrodynamic behavior using hen egg-white lysozyme (HEWL) as a model protein. HEWL was PEGylated with a linear, 20 kDa PEG using reductive amination to produce PEG1-, PEG2-, and PEG3-HEWL. Near- and far-UV-CD spectroscopy revealed no significant effect of PEGylation on HEWL higher order structure. SDS-PAGE, mass spectrometry, online static light scattering (SLS) and sedimentation velocity analytical ultracentrifugation (SV-AUC) were employed to characterize the heterogeneity and molecular weights of the purified PEG-HEWL molecules, the results of which underscored the importance of using first-principle based methods for such analyses along with the underlying complexities of characterizing PEG-protein conjugates. Hydrodynamic characterization of various linear and branched PEGs (5-40 kDa) and PEG-HEWL molecules was performed using dynamic light scattering (DLS) and SV-AUC. The PEG polymer exhibited a random-coil conformation in solution with the M(w) ∝ R(h)(n) scaling relationship yielding a scaling exponent (n) = 2.07. Singly branched PEGs were also observed to exhibit random-coil behavior with Stokes radii identical to those of their linear counterparts. SV-AUC studies of PEG-HEWL showed PEG has a "parachute" like effect on HEWL, and dramatically increases the frictional drag; PEG-HEWL also exhibited random-coil-like characteristics in solution (n = 1.8). The sedimentation coefficient (s) of PEG-HEWL remained invariant with increasing degree of PEGylation, indicating that the increase in molecular mass from PEG was compensated by an almost equivalent increase in frictional drag. Our studies draw caution to using SV-AUC for the characterization of size heterogeneity of PEG-protein mixtures.     

The apparent plasticizing effect of polyethylene glycol (PEG) on the crystallinity of spray dried lactose/PEG composites.

Aqueous solutions of lactose and polyethylene glycol (PEG) were spray dried in a Büchi Model 191 spray dryer with the aim to investigate the effect of PEG on the crystallinity of the composite. A PEG concentration of 10.7% by weight of solids was studied for PEG 200, 600, 1500, 4000 and 8000. For PEG 200 and 4000 additional concentrations from 1.5-19.3% to 1.5-32.4%, respectively, were investigated. The spray dried composites were analysed with X-ray powder diffraction and modulating differential scanning calorimetry. The crystallinity of lactose in the composites varied from 0% to 60%, dependent on the molecular weight and concentration of PEG. Apparently, lactose crystallinity is promoted by low molecular weight and high concentration of the PEG. PEG did not affect the lactose glass transition temperature. It is suggested that lactose and PEG are solidified separately during spray drying and that partial crystallization of lactose is associated with effects of PEG on the rate of drying.     

Poloxamer-based in situ hydrogels for controlled delivery of hydrophilic macromolecules after intramuscular injection in rats

Abstract

This study is aimed to investigate the applicability of poloxamer 407 (P407) and 188 (P188)-based temperature-sensitive in situ hydrogel (TSHG) in sustained delivery of hydrophilic macromolecules following intramuscular administration. Polyethylene glycols (PEGs) with molecular weight of 5-, 20-, and 40-kDa were used as model drugs, which can represent the common size range of hydrophilic macromolecular drugs using TSHG. The correlation between the level of poloxamers and thermogelling transition temperatures (T_sol–gel) was established and two formulations “20% P407/10% P188” and “24% P407/10% P188” were chosen for further study. The results showed that the release kinetics of PEGs was close to zero order. Sustained in vivo behaviors were achieved by both of the two formulations for all the PEGs though variations were seen. Lower molecular weight PEG showed more remarkable pharmacokinetic improvements. No significant differences in pharmacokinetics were observed between the two formulations for the same PEG. This suggested that 20–24% P407/10% P188 formulations, with accordingly T_sol–gel in the range of 24.6?°C–31.7?°C, might be freely chosen to achieve comparable pharmacokinetics for hydrophilic macromolecular drugs after intramuscular injection.     

The compaction properties of polyethylene glycols

The mechanical properties of polyethylene glycol (PEG) powders of different average molecular weights have been characterized in terms of their yield pressure, determined from the densification of compacts by the method of Heckel. The yield pressure was found to be proportional to the molecular weight of the PEG. The densification which occurred during compaction was greater the lower the molecular weight. In terms of compact tensile strength, PEG 10 000 produced the greatest strength for a given pressure. This arises from its ability to deform plastically to form a compact and be of sufficient intrinsic strength to resist fracture during the diametral compression test. Higher molecular weights PEGs do not allow sufficient plastic flow during consolidation for their inherent higher strength to be used.     

生物粘附性达那唑缓释栓剂的处方筛选与体外释放度考察

目的 :生物粘附性达那唑栓剂的处方筛选 ,并考察其体外释放规律。方法 :以羟丙甲基纤维素 (HPMC)为缓释材料 ,将等量聚乙二醇6000(PEG6000)和聚乙二醇600(PEG600)以熔融法制备含不同HPMC量的缓释栓剂 ,考察释放度与HPMC用量之间的关系。结果 :随着HPMC用量增加 ,栓剂释药减慢 ,当HPMC与PEG的比例为1∶6 5时 ,栓剂中药物在体外12h内缓慢释放 ,符合一级释放规律。结论 :生物粘附性骨架材料HPMC能延缓达那唑从栓剂中释放 ,当HPMC与PEG的比例为1∶6 5时栓剂能达到设计要求。     

An investigation into the critical surfactant concentration for solid solubility of hydrophobic drug in different polyethylene glycols

Solid dispersions of 10% w/w griseofulvin in different polyethylene glycols (PEGs) with or without incorporation of alkali dodecyl sulphates (MDS) were prepared by the melting method. The investigations concerned the solid state (X-ray powder diffraction), the transition from solid to liquid state (Oscillating DSC) and the liquid state (low frequency dielectric spectroscopy). The critical concentrations of SDS for the formation of solid solutions in varying PEGs were evaluated. In PEG 3000 this formation occurs at 1.4% w/w SDS, whereas PEG 6000 and PEG 20 000 require solely 1.0% w/w SDS to transfer a dispersion into a solid solution. PEG 3000 was also investigated with the addition of MDS. The critical surfactant concentrations for the formation of solid solutions with the counterions Li ⁺, Na ⁺ and K ⁺ were 1.0%, 1.4% and 2.1% w/w, respectively. The investigated systems had varying degrees of crystallinity. With the addition of SDS to PEGs with a range of molecular weights, the highest crystallinity was seen in the PEG 3000 sample. The different polymers contained different amounts of folded and extended chains which influences the amount of amorphous material within the polymer structure. When surfactants with different counterions were added to PEG 3000, the lithium sample showed the highest crystallinity. In the melt the Li ⁺ sample showed the lowest dielectric mobility. The results show that concentration and structure of surfactant together with the presence of folded and extended chains form the conditions for the formation of solid solutions.     

Magnesium ascorbyl phosphate vesicular carriers for topical delivery; preparation,in-vitro and ex-vivo evaluation,factorial optimization and clinical assessment in melasma patients

Ascorbic acid (vitamin C) is an antioxidant that is widely used in cosmetics in skincare products. Due to the excessive low stability of ascorbic acid in cosmetic formulations, the stabilized ascorbic acid derivative, magnesium ascorbyl phosphate (MAP) was formulated as vesicular carriers; ethosomes and niosomes. The aim was to deliver MAP at the intended site of action, the skin, for sufficient time with enhanced permeation to get an effective response. Ethosomes were formulated using a full 3² factorial design to study ethanol and phospholipid concentration effect on ethosomes properties. Niosomes were formulated using 2³ factorial designs to study the effect of surfactant type, surfactant concentration and cholesterol concentration on niosomes properties. The prepared formulations were evaluated for their Entrapment efficiency, particle size, polydispersity index, zeta potential and % drug permeated. The optimized ethosomal and niosomal formulations were incorporated into carbopol gel and evaluated for their permeation, skin retention and stability. A comparative split-face clinical study was done between the ethosomal and niosomal formulations for melasma treatment using Antera 3 D^® camera. The optimized ethosomal and niosomal gels showed comparable controlled permeation and higher skin retention over their ethosomes and niosomes formulations respectively. Magnesium ascorbyl phosphate ethosomal gel showed clinically and statistically significant melanin level decrease after one month while MAP niosomal gel showed clinically and statistically significant melanin level decrease after six months. A combination of MAP ethosomes and niosomes could be promising skincare formulations for melasma and hyperpigmentation short and long-term treatment.     

Production of insulin-loaded poly(ethylene glycol)/poly(l-lactide) (PEG/PLA) nanoparticles by gas antisolvent techniques.

Insulin and insulin/poly(ethylene glycol) (PEG)-loaded poly(l-lactide) (PLA) nanoparticles were produced by gas antisolvent (GAS) CO(2) precipitation starting from homogeneous polymer/protein organic solvent solutions. Different amounts of PEG 6000 (0, 10, 30, 50, 100, and 200% PEG/PLA w/w) or concentration of 30% PEG/PLA with PEGs with different molecular weight (MW; 350, 750, 1900, 6000, 10,000, and 20,000) were used in the preparations. The process resulted in high product yield, extensive organic solvent elimination, and maintenance of > 80% of the insulin hypoglycemic activity. Nanospheres with smooth surface and compact internal structure were observed by scanning electron microscopy. The nanospheres presented a mean particle diameter in the range 400-600 nm and narrow distribution profiles. More than 90% of drug and PEG were trapped in the PLA nanoparticles when low MW PEGs were used in the formulation, whereas the addition of high MW PEGs significantly reduced the loading yield. In all cases, in vitro release studies showed that only a little amount of drug was released from the preparations. However, formulations containing low MW PEGs allowed for a slow but constant drug release throughout 1500 h, whereas a burst was obtained by increasing the PEG MW. In conclusion, the GAS process offers a mean to produce protein-loaded nanoparticles possessing the prerequisites for pharmaceutical applications. The PEG added to the formulation was found to play a key role in the simultaneous solute precipitation phenomena and in determining the release behavior and the chemical-physical properties of the formulation.