Encapsulation of curcumin within oil-in-water emulsions prepared by premix membrane emulsification: Impact of droplet size and carrier oil on the chemical stability of curcumin.

Oil-in-water emulsions containing curcumin with different droplet sizes were produced by premix membrane emulsification with different carrier oils: tributyrin (short chain triglycerides, SCT), medium chain triglycerides (MCT) and corn oil (long chain triglycerides, LCT). The influence of carrier oil type and droplet size on the physical stability, chemical stability of curcumin and lipid oxidation stability of emulsions were investigated. Turbiscan results indicated that the physical stability of emulsions was related to both carrier oils and emulsion droplet sizes. The oil type and droplet size of emulsions stored at 25 °C showed limited effect on the stability of curcumin, but significantly affected the stability of curcumin at 55 °C. Chemical stability of curcumin decreased with the decrease of emulsion droplet sizes. For each droplet size emulsions, the stability of curcumin decreased in the order SCT > MCT > LCT. Moreover, the lipid oxidation in LCT-based emulsions resulted in lower zeta potential of droplets, which was independent of emulsion droplet sizes. The presence of curcumin improved the oxidative stability of emulsions.

Classical and Recent Developments of Membrane Processes for Desalination and Natural Water Treatment.

Water supply and water treatment are of major concern all around the world. In this respect, membrane processes are increasingly used and reported for a large range of applications. Desalination processes by membranes are well-established technologies with many desalination plants implemented in coastal areas. Natural water treatment is also well implemented to provide purified water for growing population. This review covers various aspects of desalination: membranes and modules, plants, fouling (scaling, biofouling, algal blooms), cleaning, pretreatment (conventional and membrane treatments), energy and environmental issues, renewable energies, boron removal and brine disposal. Treatment of natural water focuses on removal of natural organic matter, arsenic, iron, nitrate, fluoride, pesticides and herbicides, pharmaceutical and personal care products. This review underlines that desalination and natural water treatment require identical knowledge of membrane fouling, construction of large plants, cleaning procedures, energy and environmental issues, and that these two different fields can learn from each other.

Bicelles as a carrier for bioactive compounds in beverages: application to nerolidol, an active sesquiterpene alcohol.

ABSTRACT: Nerolidol is a natural sesquiterpene alcohol with promising but limited application in food and pharmaceutical fields due to several factors including low photostability and low aqueous solubility. Recently, several carriers loading nerolidol were prepared and tested in fresh orange juice. Lipid vesicles loading nerolidol did not exhibit satisfactory organoleptic properties in this beverage. Hence, DMPC/DHPC bicelles were prepared as a new phospholipid-based carrier for nerolidol at different molar ratios. The bicelle suspensions were characterized in terms of homogeneity, particles size, and morphology. The optimal formulation (phospholipid:nerolidol molar ratio 100:1) was selected based on transparent appearance, homogeneity, and particle size (~ 45 nm). Besides, it showed a high encapsulation efficiency of nerolidol and a high incorporation rate of phospholipids. Transmission electron microscopy analysis demonstrated the formation of bicelles. The bicelles membrane fluidity was assessed by 1,6-diphenyl-1,3,5-hexatriene fluorescence anisotropy and differential scanning calorimetry analysis. The membrane fluidity of bicelles appeared to increase in the presence of nerolidol in a concentration dependent manner. To our knowledge this is the first study dealing with the encapsulation of an essential oil component in bicelles.

Effect of cysteamine hydrochloride-loaded liposomes on skin depigmenting and penetration.

Skin hyperpigmentation is caused by an excessive production of melanin. Cysteamine, an aminothiol compound physiologically synthetized in human body cells, is known as depigmenting agent. The aim of this study was to evaluate the depigmenting activity and skin penetration of liposome formulations encapsulating cysteamine hydrochloride. First, cysteamine hydrochloride-loaded liposomes were prepared and characterized for their size, polydispersity index, zeta potential and the encapsulation efficiency of the active molecule. The stability of cysteamine hydrochloride in the prepared liposome formulations in suspension and freeze-dried forms was then assessed. The in vitro cytotoxicity of cysteamine and cysteamine-loaded liposome suspensions (either original or freeze-dried) was evaluated in B16 murine melanoma cells. The measurement of melanin and tyrosinase activities was assessed after cells treatment with free and encapsulated cysteamine. The antioxidant activity of the free and encapsulated cysteamine was evaluated by the measurement of ROS formation in treated cells. The ex vivo human skin penetration study was also performed using Franz diffusion cell. The stability of cysteamine hydrochloride was improved after encapsulation in liposomal suspension. In addition, for the liposome re-suspended after freeze-drying, a significant increase of vesicle stability was observed. The free and the encapsulated cysteamine in suspension (either original or freeze-dried) did not show any cytotoxic effect, inhibited the melanin synthesis as well as the tyrosinase activity. An antioxidant activity was observed for the free and the encapsulated cysteamine hydrochloride. The encapsulation enhanced the skin penetration of cysteamine hydrochloride. The penetration of this molecule was better for the re-suspended freeze-dried form than the original liposomal suspension where the drug was found retained in the epidermis layer of the skin.

Encapsulation of curcumin within oil-in-water emulsions prepared by premix membrane emulsification: Impact of droplet size and carrier oil type on physicochemical stability and in vitro bioaccessibility.

Oil-in-water emulsions containing curcumin with different droplet size (small ≈ 0.5 µm, medium ≈ 0.8 µm, large ≈ 3.7 µm and premix ≈ 60 µm) were prepared through premix membrane emulsification using different carrier oils: tributyrin (short chain triglycerides, SCT), medium chain triglycerides (MCT) and corn oil (long chain triglycerides, LCT). An in vitro gastrointestinal model was used to evaluate the impact of oil and droplet size on lipid digestion and curcumin bioaccessibility. Lipid digestion and bioaccessibility decreased with the increase of droplet size for LCT-based emulsions, whereas there was no significant difference for small, medium and large emulsions in SCT and MCT-based emulsions. In addition, encapsulation efficiency played an important role in determining bioaccessibility. Bioaccessibility in MCT premix was significantly lower than that in other size MCT-based emulsions because of its low encapsulation efficiency. The bioaccessibility decreased in the order MCT > SCT > LCT in each size of emulsions..

Pentacyclic triterpenes modulate liposome membrane fluidity and permeability depending on membrane cholesterol content.

Since the membrane-related processes represent an integral part of the biological activities of drugs, their effect on the membrane dynamics is actually considered. In this study, we investigated the effect of pentacyclic triterpenes (TTPs), oleanolic acid (OA) and erythrodiol (ER), on the fluidity and permeability of liposomes membranes differing by their cholesterol content. All liposomes were prepared by reverse phase evaporation technique (REV). Spin-labeled liposomes exposed or not to TTPs were used for fluidity studies by using 5- and 16-doxyl stearic acids (DSA). TTPs-loaded liposomes (phospholipid:cholesterol of 1:1), and preformed vesicles exposed to TTPs were used for permeability studies by monitoring the release of sulforhodamine B (SRB) at 37 °C. The apparent release constants of SRB were determined by Higuchi model based on a biphasic curve shape (0-10 h; 10-48 h). TTPs-loaded liposomes were characterized for their size and homogeneity. Results showed that ER increased the membrane fluidity at the upper region of the membrane while the both TTPs produced a condensing effect at the deeper region of the membrane. The membrane composition was a critical parameter modulating the effect of TTPs on the membrane permeability. Also, this study consolidated the fact that a fluidizing membrane agent is not necessarily a permeabilizing-membrane compound.

Preparation of perfluorocarbon emulsions by premix membrane emulsification for Acoustic Droplet Vaporization (ADV) in biomedical applications.

Perfluorocarbon (PFC) droplets are used in acoustic droplet vaporization (ADV), a phenomenon where droplets vaporize into gas microbubbles under exposure to ultrasound. The size and the size distribution of a phase change contrast agent is an important factor in determining the ADV threshold and the biodistribution. Thus, high throughout manufacturing of uniform-sized droplets, required to maintain spatial control of the vaporization process, remains challenging. This work describes a parametric evaluation of a novel process using premix membrane emulsification (PME) to produce homogeneous PFC emulsions at high rate with moderate pressure using Shirasu Porous Glass (SPG) membranes. In this study, we investigated the effect of several process parameters on the resulting pressure and droplet size: membrane pore size, flow rate, and dispersed phase type. The functionality of the manufactured emulsions for ADV was also demonstrated. Vaporization of the PFC emulsions was obtained using an imaging ultrasound transducer at 7.813 MHz, and the ADV thresholds were determined. Here, the pressure threshold for ADV was determined to be 1.49 MPa for uniform-sized perfluorohexane (PFHex) droplets with a mean size of 1.51 µm and a sharp distribution (CV and span respectively of 20% and 0.6). Thus, a uniform-sized droplet showed a more homogeneous vaporization with a uniform response in the focal region of the transducer. Indeed, polydispersed droplets had a more diffuse response outside the focal region due to the presence of large droplets that vaporize at lower energies. The ADV threshold of uniform-sized PFC droplets was found to decrease with the droplet diameter and the bulk fluid temperature, and to increase with the boiling temperature of PFC and the presence of an oil layer surrounding the PFC core.

Development of cysteamine loaded liposomes in liquid and dried forms for improvement of cysteamine stability.

Despite the high aqueous solubility of cysteamine, its unpleasant organoleptic properties, hygroscopicity, instability in solutions, and poor pharmacokinetic profile are the main drawbacks that limit its use for medical and cosmetic purposes. In this study, cysteamine-loaded liposomes were prepared using the ethanol injection method. Liposomes were characterized for their size, homogeneity, surface charge, and morphology. The incorporation ratios of cholesterol and phospholipids, the encapsulation efficiency and the loading ratio of cysteamine in liposomes were determined. Moreover, the stability of free and encapsulated cysteamine was assessed at different temperatures (4, 25, and 37 °C) in the presence and absence of light. Cysteamine-loaded liposomes were freeze-dried and reconstituted liposomes were characterized. Finally, the storage stability of the freeze-dried cysteamine-loaded liposomes was studied. Liposomes were nanometric, oligolamellar, and spherical. The encapsulation efficiency and the loading ratio of cysteamine varied between 12 and 40% in the different formulations. The encapsulation improved the stability of cysteamine in the various storage conditions. The dried form of cysteamine-loaded liposomes conserved the size of the vesicles and retained 33% of cysteamine present in the liposomal suspension before lyophilization. The freeze-dried liposomes formulations were stable after four months of storage at 4 °C.

Recent advances in encapsulation of curcumin in nanoemulsions: A review of encapsulation technologies, bioaccessibility and applications.

Curcumin is widely acknowledged for its beneficial activities. However, its application has remained challenging due to its low aqueous solubility, biochemical/structural degradation and poor bioavailability. For these reasons, many researches are aimed at overcoming these limitations using lipid-based nanosystems to encapsulate curcumin, especially nanoemulsions. This review highlights the theoretical aspects and recent advances of preparation technologies (phase inversion temperature, phase inversion composition, ultrasonication, high pressure homogenization and microfluidization) for encapsulation of curcumin in nanoemulsions. Additionally, the specific factors in designing nanoemulsions systems that affect the chemical stability and in vitro bioaccessibility of the encapsulated curcumin are discussed. Also, the importance of nanoemulsions in improving antioxidant, anti-inflammatory and anticancer activities of curcumin is underlined. Curcumin-loaded nanoemulsions preparation technologies have been proposed to provide efficient, systematic, and practical protocols for improved applications of curcumin. Additionally, key factors that influence curcumin delivery include the nature of emulsifier, the type and the amount of carrier oil and emulsifier-curcumin interactions. The pharmacological activities of curcumin including antioxidant, anti-inflammatory and anticancer activities can be improved by nanoemulsions.

Challenges for cysteamine stabilization, quantification, and biological effects improvement.

The aminothiol cysteamine, derived from coenzyme A degradation in mammalian cells, presents several biological applications. However, the bitter taste and sickening odor, chemical instability, hygroscopicity, and poor pharmacokinetic profile of cysteamine limit its efficacy. The use of encapsulation systems is a good methodology to overcome these undesirable properties and improve the pharmacokinetic behavior of cysteamine. Besides, the conjugation of cysteamine to the surface of nanoparticles is generally proposed to improve the intra-oral delivery of cyclodextrin-drug inclusion complexes, as well as to enhance the colorimetric detection of compounds by a gold nanoparticle aggregation method. On the other hand, the detection and quantification of cysteamine is a challenging mission due to the lack of a chromophore in its structure and its susceptibility to oxidation before or during the analysis. Derivatization agents are therefore applied for the quantification of this molecule. To our knowledge, the derivatization techniques and the encapsulation systems used for cysteamine delivery were not reviewed previously. Thus, this review aims to compile all the data on these methods as well as to provide an overview of the various biological applications of cysteamine focusing on its skin application.

Challenges for cysteamine stabilization, quantification, and biological effects improvement / 药物分析学报

The aminothiol cysteamine, derived from coenzyme A degradation in mammalian cells, presents several biological applications. However, the bitter taste and sickening odor, chemical instability, hygroscopicity, and poor pharmacokinetic profile of cysteamine limit its efficacy. The use of encapsulation systems is a good methodology to overcome these undesirable properties and improve the pharmacokinetic behavior of cysteamine. Besides, the conjugation of cysteamine to the surface of nanoparticles is generally pro-posed to improve the intra-oral delivery of cyclodextrin-drug inclusion complexes, as well as to enhance the colorimetric detection of compounds by a gold nanoparticle aggregation method. On the other hand, the detection and quantification of cysteamine is a challenging mission due to the lack of a chromophore in its structure and its susceptibility to oxidation before or during the analysis. Derivatization agents are therefore applied for the quantification of this molecule. To our knowledge, the derivatization techniques and the encapsulation systems used for cysteamine delivery were not reviewed previously. Thus, this review aims to compile all the data on these methods as well as to provide an overview of the various biological applications of cysteamine focusing on its skin application. Cysteamine Detection Encapsulation Skin Stability The aminothiol cysteamine, derived from coenzyme A degradation in mammalian cells, presents several biological applications. However, the bitter taste and sickening odor, chemical instability, hygroscopicity, and poor pharmacokinetic profile of cysteamine limit its efficacy. The use of encapsulation systems is a good methodology to overcome these undesirable properties and improve the pharmacokinetic behavior of cysteamine. Besides, the conjugation of cysteamine to the surface of nanoparticles is generally pro-posed to improve the intra-oral delivery of cyclodextrin-drug inclusion complexes, as well as to enhance the colorimetric detection of compounds by a gold nanoparticle aggregation method. On the other hand, the detection and quantification of cysteamine is a challenging mission due to the lack of a chromophore in its structure and its susceptibility to oxidation before or during the analysis. Derivatization agents are therefore applied for the quantification of this molecule. To our knowledge, the derivatization techniques and the encapsulation systems used for cysteamine delivery were not reviewed previously. Thus, this review aims to compile all the data on these methods as well as to provide an overview of the various biological applications of cysteamine focusing on its skin application.

Use of free and encapsulated nerolidol to inhibit the survival of Lactobacillus fermentum in fresh orange juice.

Lactobacillus fermentum is commonly responsible for fruit juice fermentation and spoilage. The aim of this study was to investigate the potential use of nerolidol to control the spoilage of fresh orange juice by L. fermentum. Nerolidol was incorporated into hydroxypropyl-ß-cyclodextrin inclusion complex, conventional liposome, and drug-in-cyclodextrin-in liposome systems. The systems were lyophilized and characterized with respect to their nerolidol content, size, and morphology. The effects of the acidity and cold storage of orange juice on the survival of L. fermentum were evaluated. Subsequently, the antibacterial activity of nerolidol in refrigerated orange juice was assessed at pH 3.3. Nerolidol showed a faster antibacterial activity at 4 000 µM (5 days) compared to 2 000 µM (8 days). Under the same conditions, the inclusion complex completely killed bacteria within 6 days of incubation at 4 000 µM, suggesting its potential application in fruit juices. Nerolidol-loaded liposomes did not exhibit an antibacterial activity and altered the appearance of juice.

Comparison of Three Processes for Parenteral Nanoemulsion Production: Ultrasounds, Microfluidizer, and Premix Membrane Emulsification.

Nanoemulsions are of great interest for pharmaceutical applications, including parenteral dosage forms. However, their production is still limited and requires more efficient and adaptive technologies. The more common systems are high-shear homogenization such as microfludizers at industrial scale and ultrasounds at research scale, both based on high energy, limiting their application for sensitive drugs. Recently a process based on premix membrane emulsification (PME) was developed to produce nanoemulsions. These 3 processes have been compared for the production of a model parenteral nanoemulsion containing all-trans retinoic acid, a thermolabile molecule that is used in the treatment of acute promyelocytic leukemia in a parenteral form. Droplet size and active integrity were studied because of their major interest for efficacy and safety assessment. Regarding droplet size, PME produced monodispersed droplets of 335 nm compared with the other processes that produced nanoemulsions of around 150 nm but with the presence of micron-size droplets detected by laser diffraction and optical microscopy. No real difference between the 3 processes was observed on active degradation during emulsifcation. However regarding stability, especially at 40°C, nanoemulsions obtained with the microfluidizer showed a greater molecule degradation and unstable nanoemulsion with a 4-times droplet size increase under stress conditions.

Hydroxypropyl-ß-cyclodextrin as a membrane protectant during freeze-drying of hydrogenated and non-hydrogenated liposomes and molecule-in-cyclodextrin-in- liposomes: Application to trans-anethole.

The effect of hydrogenation of phospholipids on the characteristics of freeze-dried liposomes was investigated using hydroxypropyl-ß-cyclodextrin (HP-ß-CD) as membrane protectant. The ethanol-injection method was applied to prepare liposomes using hydrogenated (Phospholopion-90H and 80H) and non-hydrogenated phospholipids (Lipoid-S100) in combination with cholesterol. Various liposomal formulations were tested: conventional liposomes (CL) and HP-ß-CD-loaded liposomes (CDL). Liposome suspensions were concentrated by ultracentrifugation; the pellets were reconstituted in water or CD solution and the dispersions were characterized for their size, polydispersity index and zeta potential. Results demonstrated that HP-ß-CD protected only the hydrogenated batches (CL and CDL) during freeze-drying. Moreover, the presence of HP-ß-CD in the aqueous phase of CDL protected them during freeze-drying. Freeze-dried CL and CDL made of phospholipon-90H loading anethole were demonstrated to be physically stable upon reconstitution in HP-ß-CD solutions, and are able to retain anethole after 6 months of storage at 4 °C thereby making them valuable for food applications.

Corticoids modulate liposome membrane fluidity and permeability depending on membrane composition and experimental protocol design.

Given that literature data may give inconsistent results on the effect of a drug on lipid membrane properties, this work aims to investigate the impact of the liposome composition and experimental protocol design on glucocorticoids (GRs: cortisol, cortisone, fludrocortisone acetate, methylprednisolone, prednisolone and prednisone)-modulating membrane fluidity and permeability. GRs-loaded liposomes consisting of dipalmitoylphosphatidylcholine (DPPC) and cholesterol (CHOL) were prepared by reverse phase evaporation technique (REV) at DPPC:CHOL:GR molar ratios of 100:100:2.5, and 100:100:10. The formulations were characterized for their size and homogeneity, encapsulation efficiency and loading rates of GRs, incorporation rates and loading rates of DPPC and CHOL. Changes in DPPC membrane fluidity (CHOL% 0, 10, 20, 30 and 100) after exposure to methylprednisolone were monitored by using 5- and 16-doxyl stearic acids (DSA) as spin probes. For permeability studies, the above-mentioned GRs-loaded liposomes and the preformed liposomes exposed to GRs (2.5 mol%) were compared for the leakage of an encapsulated fluorescent dye, sulforhodamine B (SRB), at 37 °C in buffer (pH 7.5) containing NaCl. The SRB release kinetics were analyzed by the Higuchi model for two release phases (from 0 to 10 h, and from 10 to 48 h). All formulations exhibited a monodispersed size distribution of liposomes with a mean particle value close to 0.4 µm, also the DPPC and CHOL were highly incorporated (>95%). High loading rate values of DPPC and CHOL were also obtained. Except for fludrocortisone acetate (51%) and prednisolone (77%), high loading rate values of GRs were obtained (>81%). Fluidity and permeability studies showed that the GR concentration, CHOL content, experimental protocol design including the period of incubation represent critical parameters to be considered in analyzing the effect of drugs on the membrane properties.

Biophysical methods: Complementary tools to study the influence of human steroid hormones on the liposome membrane properties.

Human steroid hormones are involved in many aspects of physiology and have long been known to exert rapid and delayed effects. They are lipophilic molecules which can be incorporated into the lipid membranes. Through non-covalent interactions they can alter the properties of the membrane, including fluidity, lipid raft formation and others. In this review, different biophysical techniques were described to study the interaction of human steroid hormones with biological and biomimetic membranes such as differential scanning calorimetry, electron paramagnetic resonance, fluorescence spectroscopy and Fourier transform infrared spectroscopy. The aim of this review is to overview the results of these complementary biophysical techniques summarizing the effects of these hormones on thermotropic and dynamic membrane properties. Meanwhile, the disorder induced by human steroid hormones is discussed in terms of hydrophobicity and chemical structure.

Cholesterol modulates the liposome membrane fluidity and permeability for a hydrophilic molecule.

The effect of cholesterol (CHOL) content on the permeability and fluidity of dipalmitoylphosphatidylcholine (DPPC) liposome membrane was investigated. Liposomes encapsulating sulforhodamine B (SRB), a fluorescent dye, were prepared by reverse phase evaporation technique (REV) at various DPPC:CHOL molar ratios (from 100:0 to 100:100). The release kinetics of SRB was studied during 48 h in buffer (pH 7.4) containing NaCl at 37 °C. The DPPC:CHOL formulations were also characterized for their size, polydispersity index and morphology. Increasing CHOL concentration induced an increase in the mean liposomes size accompanying with a shape transition from irregular to nanosized, regular and spherical vesicles. The release kinetics of SRB showed a biphasic pattern; the release data was then analyzed using different mathematical models. On the overall, the SRB release was governed by a non-Fickian diffusion during the first period (0-10 h) while it followed a Fickian diffusion between 10 and 48 h. Changes in DPPC liposome membrane fluidity of various batches (CHOL% 0, 10, 20, 30 and 100) were monitored by using 5- and 16 doxyl stearic acids (DSA) as spin labels. CHOL induced a decrease in the bilayer fluidity. Concisely, CHOL represents a critical component in modulating the release of hydrophilic molecules from lipid vesicles.

Interaction of triterpenoids with human serum albumin: A review.

Triterpenoids are a large group of natural and synthetic products. This review deals with the current state of knowledge on their interaction with serum albumin. The binding of drugs to albumin may control their distribution in tissues. In literature, different techniques were used to investigate the albumin-triterpenoid interaction and include fluorescence spectroscopy, Fourier transform infrared spectroscopy, circular dichroism, calorimetric techniques and molecular modeling. Changes in fluorescence intensity of albumin were observed upon triterpenoid-albumin complex formation. Thermodynamic analyses proved that hydrophobic interactions and hydrogen bonds were the mainly binding forces in triterpenoid-albumin systems. Molecular docking and site marker competitive experimental results revealed that triterpenoids bound to Sudlow's site I of albumin. Furthermore, Fourier transform infrared spectroscopy and circular dichroism spectra analysis indicated that the native conformation of the protein is affected upon binding to triterpenoids.

Interaction of Selected Phenylpropenes with Dipalmitoylphosphatidylcholine Membrane and Their Relevance to Antibacterial Activity.

The effect of structurally closely related phenylpropenes (PPs), estragole, anethole, eugenol, and isoeugenol, on the fluidity of dipalmitoyl phosphatidyl choline (DPPC) liposome membrane was investigated by DSC, Raman, and fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene (DPH). Liposomes were prepared by thin-film hydration method at various DPPC:PP molar ratios. The DPH anisotropy measurements of blank and PP-loaded liposomes were performed at 28, 41, and 50 °C, which correspond, respectively, to gel phase, main transition temperature of DPPC, and liquid phase. The Raman images showed the formation of nano- and micrometric spherical multi-lamellar vesicles. All studied PPs exhibited a membrane fluidizing effect which was reinforced by the presence of phenolic hydroxyl group in eugenol and isoeugenol. The PPs interacted with the choline head group and the alkyl chains of DPPC membrane, wherein isoeugenol and anethole possessing the same C7-C8 position of the double bond in the propenyl side chain, incorporated deeply in the bilayer. Additionally, the PPs were analyzed for antibacterial activity against E. coli by macrobroth dilution method. Anethole and estragole were more efficient in inhibiting the bacterial growth than eugenol and isoeugenol. We conclude that the fluidizing effect of PPs on the membrane is a common mechanism that is not related to the hydrophobicity of the PP molecule. Besides, other target sites may be involved in PP antibacterial activity against Gram-negative bacteria. The greater hydrophobicity of these PPs may contribute to their penetrability through the outer bacterial membrane.

Interaction of glucocorticoids and progesterone derivatives with human serum albumin.

Glucocorticoids (GCs) and progesterone derivatives (PGDs) are steroid hormones with well-known biological activities. Their interaction with human serum albumin (HSA) may control their distribution. Their binding to albumin is poorly studied in literature. This paper deals with the interaction of a series of GCs (cortisol, cortisone, prednisolone, prednisone, 6-methylprednisolone and 9-fluorocortisol acetate) and PGDs (progesterone, hydroxylated PGDs, methylated PGDs and dydrogesterone) with HSA solution (pH 7.4) at molar ratios steroid to HSA varying from 0 to 10. Similar titrations were conducted using Trp aqueous solution. Fluorescence titration method and Fourier transform infrared spectroscopy (FTIR) are used. PGDs (except dydrogesterone), cortisone and 9-fluorocortisol acetate affected weakly the fluorescence of Trp in buffer solution while they decreased in a dose-dependent manner that of HSA. Their binding constants to HSA were then calculated. Moreover, displacement experiment was performed using bilirubin as a site marker. The binding constant of bilirubin to albumin was determined in the absence and presence of a steroid at a molar ratio steroid to HSA of 1. The results indicate that the steroids bind to HSA at site I in a pocket different from that of bilirubin. Furthermore, the peak positions of amide I and amide II bands of HSA were shifted in the presence of progesterone, dydrogesterone and GCs. Also a variation was observed in amide I region indicating the formation of hydrogen bonding between albumin and steroids.