Thermally induced molecular disorder in human stratum corneum lipids compared with a model phospholipid system; FT-Raman spectroscopy

In Vitro-In Vivo Correlation of Buprenorphine Transdermal Systems Under Normal and Elevated Skin Temperature

PURPOSE

Application of external heat using a heating pad over buprenorphine transdermal system, Butrans® has been shown to increase systemic levels of buprenorphine in human volunteers. The purpose of this study was to perform in vitro permeation studies at normal as well as elevated temperature conditions to evaluate the correlation of in vitro data with the existing in vivo data.

METHODS

In vitro permeation tests (IVPT) were performed on human skin from four donors. The IVPT study design was harmonized to a previously published clinical study design and skin temperature was maintained at either 32 ± 1 °C or 42 ± 1 °C to mimic normal and elevated skin temperature conditions, respectively.

RESULTS

IVPT studies on human skin were able to demonstrate heat induced enhancement in flux and cumulative amount of drug permeated from Butrans® which was reasonably consistent with the corresponding enhancement observed in vivo. Level A in vitro-in vivo correlation (IVIVC) was established using unit impulse response (UIR) based deconvolution method for both baseline and heat arms of the study. The percent prediction error (%PE) calculated for AUC and C_max values was less than 20%.

CONCLUSIONS

The studies indicated that IVPT studies performed under the same conditions as those of interest in vivo may be useful for comparative evaluation of the effect of external heat on transdermal delivery system (TDS). Further research may be warranted to evaluate factors, beyond cutaneous bioavailability (BA) assessed using an IVPT study, that can influence plasma exposure in vivo for a given drug product.

Raman Microscopy Techniques to Study Lipid Droplet Composition in Cancer Cells

Raman spectroscopy using feature selection schemes has considerable advantages over gas chromatography for the analysis of fatty acids' composition changes. Here, we introduce an educational methodology to demonstrate the potential of micro-Raman spectroscopy to determine with high accuracy the unsaturation or saturation degrees and composition changes of the fatty acids found in the lipid droplets of the LNCaP prostate cancer cells that were treated with various fatty acids. The methodology uses highly discriminatory wavenumbers among fatty acids present in the sample selected by using the Support Vector Machine algorithm.

Lipid profiling using Raman and a modified support vector machine algorithm

Lipid droplets are dynamic organelles that play important cellular roles. They are composed of a phospholipid membrane and a core of triglycerides and sterol esters. Fatty acids have important roles in phospholipid membrane formation, signaling, and synthesis of triglycerides as energy storage. Better non-invasive tools for profiling and measuring cellular lipids are needed. Here we demonstrate the potential of Raman spectroscopy to determine with high accuracy the composition changes of the fatty acids and cholesterol found in the lipid droplets of prostate cancer cells treated with various fatty acids. The methodology uses a modified least squares fitting (LSF) routine that uses highly discriminatory wavenumbers between the fatty acids present in the sample using a support vector machine algorithm. Using this new LSF routine, Raman micro-spectroscopy can become a better non-invasive tool for profiling and measuring fatty acids and cholesterol for cancer biology.

Determination of milk fat authenticity in ultra-filtered white cheese by using Raman spectroscopy with multivariate data analysis

Cheese is one of the most widely consumed food products in the world. However, the increasing demand for nutritionally enhanced or functional products by the cheese industry has created new approaches that partially or fully replace milk fat. With this, new methods of adulteration have also been noted, potentially leading to these fully/partially-replaced products being offered as cheese. In this study, Raman spectroscopy was used to determine origins of fats in margarine, corn, and palm oils present in white and ultra-filtered cheese samples. Raman spectra were evaluated with partial least square-discriminant (PLS-DA) and PLS to identify fat/oil origins and adulteration ratios. The coefficients of determination and limits of detection for margarine, and corn and palm oil adulteration were found to be 0.990, 0.993, 0.991 and 3.38%, 3.36% and 3.59%, respectively.

Review of Modern Techniques for the Assessment of Skin Hydration

Skin hydration is a complex process that influences the physical and mechanical properties of skin. Various technologies have emerged over the years to assess this parameter, with the current standard being electrical probe-based instruments. Nevertheless, their inability to provide detailed information has prompted the use of sophisticated spectroscopic and imaging methodologies, which are capable of in-depth skin analysis that includes structural and composition details. Modern imaging and spectroscopic techniques have transformed skin research in the dermatological and cosmetics disciplines, and are now commonly employed in conjunction with traditional methods for comprehensive assessment of both healthy and pathological skin. This article reviews current techniques employed in measuring skin hydration, and gives an account on their principle of operation and applications in skin-related research.

Raman spectroscopy coupled with chemometric methods for the discrimination of foreign fats and oils in cream and yogurt

The adulteration of milk fat in dairy products with cheaper non-milk based fats or oils is frequently encountered in the dairy industry. In this study, Raman spectroscopy with chemometric was used for the discrimination of foreign fats and oils in milk cream and yogurt. Firstly, binary mixtures of cream and oils (corn and sunflower oil), and vegetable fat blends which are potentially or currently used by the dairy industry were prepared. All fat or oil samples and their binary mixtures were examined by using Raman spectroscopy. Then, fat content of skim milk was adjusted to 3% (w/w) by the milk fat, external oils or fats, and binary mixtures, and was used in yogurt production. The lipid fraction of yogurt was extracted and characterized by Raman spectroscopy. The spectral data were then pre-processed and principal component analysis (PCA) was performed. Raman spectral data showed successful discrimination for about the source of the fats or oils. Temperature effect was also studied at six different temperatures (25, 30, 40, 50, 60 and 70 °C) in order to obtain the best spectral information. Raman spectra collected at higher temperatures were more intense. Obtained results showed that the performance of Raman spectroscopy with PCA was very promising and can be expected to provide a simple and quick way for the discrimination of foreign fats and oils in both milk cream and yogurt. Fermentation and yogurt processing affected clustering of fat samples by PCA, probably depending on some lipolysis or production of new products that can affect the Raman scattering. However, those changes did not affect differentiation of samples by Raman spectroscopy.

ATR-IR study of skin components: Lipids, proteins and water. Part I: Temperature effect

In this work we report the studies of the effect of temperature on skin components, such as lipids, proteins and water. Modifications of lipids structure induced by increasing temperature (from 20 to 90°C) have been studied using ATR-IR (Attenuated Total Reflectance Infrared) spectroscopy, which is a powerful tool for characterization of the molecular structure and properties of tissues, such as skin. Due to the small depth of penetration (0.6-5.6μm), ATR-IR spectroscopy probes only the outermost layer of the skin, i.e. the stratum corneum (SC). The assignment of main spectral features of skin components allows for the determination of phase transitions from the temperature dependencies of band intensities [e.g. ν_as(CH₂) and ν_s(CH₂)]. The phase transitions were determined by using two methods: the first one was based on the first derivative of the Boltzmann function and the second one employed tangent lines of sigmoidal, aforementioned dependencies. The phase transitions in lipids were correlated with modifications of the structure of water and proteins.

Effect of Ultrasound on Transdermal Permeation of Diclofenac

During the last two decades the effects of ultrasound on the transdermal permeability to a wide variety of drugs have been extensively investigated. There is still some uncertainty regarding the mechanisms involved in ultrasonic permeation enhancement, thus we investigated the effect of ultrasonic treatment on the transdermal permeation of the NSAID, diclofenac. Experiments were conducted over two phases, consisting of different time periods, using a continuous flow-through diffusion system. It is clear from the present study that ultrasound enhanced the permeability of human skin to diclofenac released from a commercially available gel. These results were in contrast to those obtained for ibuprofen in an in vitro study across human skin, but in agreement with those obtained in two in vivo studies of the latter NSAID. Steady state flux values of diclofenac remained approximately 1.26 times higher than those of controls during the 24 h of the experiment. These observations concurred with those made in two previous in vivo studies. It was concluded that the enhancement of diclofenac permeation by sonication could not be adequately explained primarily on a thermal basis. Furthermore, the in vitro flow-through diffusion model was shown to have predictive value as an in vivo method for sonophoresis.

How Confocal Is Confocal Raman Microspectroscopy on the Skin? Impact of Microscope Configuration and Sample Preparation on Penetration Depth Profiles

BACKGROUND/AIMS

The aim of the study was to elucidate the effect of sample preparation and microscope configuration on the results of confocal Raman microspectroscopic evaluation of the penetration of a pharmaceutical active into the skin (depth profiling).

METHODS

Pig ear skin and a hydrophilic formulation containing procaine HCl were used as a model system. The formulation was either left on the skin during the measurement, or was wiped off or washed off prior to the analysis. The microscope configuration was varied with respect to objectives and pinholes used.

RESULTS

Sample preparation and microscope configuration had a tremendous effect on the results of depth profiling. Regarding sample preparation, the best results could be observed when the formulation was washed off the skin prior to the analysis. Concerning microscope configuration, the use of a 40 × 0.6 numerical aperture (NA) objective in combination with a 25-µm pinhole or a 100 × 1.25 NA objective in combination with a 50-µm pinhole was found to be advantageous.

CONCLUSION

Complete removal of the sample from the skin before the analysis was found to be crucial. A thorough analysis of the suitability of the chosen microscope configuration should be performed before acquiring concentration depth profiles.

Hydration effects on the barrier function of stratum corneum lipids: Raman analysis of ceramides 2, III and 5

The stratum corneum is the outermost layer of the skin; its barrier function is highly dependent on the composition and the structure as well as the organization of lipids in its extracellular matrix. Ceramides, free fatty acids and cholesterol represent the major lipid classes present in this matrix. They play an important role in maintaining the normal hydration levels required for the normal physiological function. Despite the advancement in the understanding of the structure, composition and the function of the stratum corneum (SC), the concern of "dry skin" remains important in dermatology and care research. Most studies focus on the quantification of water in the skin using different techniques including Raman spectroscopy, while the studies that investigate the effect of hydration on the quality of the barrier function of the skin are limited. Raman spectroscopy provides structural, conformational and organizational information that could help elucidate the effect of hydration on the barrier function of the skin. In order to assess the effect of relative humidity on the lipid barrier function; we used Raman spectroscopy to follow-up the evolution of the conformation and the organization of three synthetic ceramides (CER) differing from each other by the nature of their polar heads (sphingosine, phytosphingosine and α hydroxyl sphingosine), CER 2, III and 5 respectively. CER III and 5 showed a more compact and ordered organization with stronger polar interactions at intermediate relative humidity values, while CER 2 showed opposite tendencies to those observed with CER III and 5.

Turning theory into practice: the development of modern transdermal drug delivery systems and future trends

Despite its remarkable barrier function, the skin remains an attractive site for systemic drug delivery given its easy accessibility, large surface area and the possibility to bypass the gastrointestinal tract and the liver and so modify drug absorption kinetics. The pioneering work of Scheuplein, Higuchi and others in the 1960s helped to explain the processes involved in passive percutaneous absorption and led to the development of mathematical models to describe transdermal drug delivery. The intervening years have seen these theories turned to practice and a significant number of transdermal systems are now available including some that employ active drug delivery. This review briefly discusses the evolution of transdermal therapeutic systems over the years and the potential of newer transdermal technologies to deliver hydrophilic drugs and macromolecules through the skin.

Brian Barry: Innovative Contributions to Transdermal and Topical Drug Delivery

Brian Barry published over 300 research articles across topics ranging from colloid science, vasoconstriction and the importance of thermodynamics in dermal drug delivery to exploring the structure and organisation of the stratum corneum barrier lipids and numerous strategies for improving topical and transdermal drug delivery, including penetration enhancers, supersaturation, coacervation, eutectic formation and the use of varied liposomes. As research in the area blossomed in the early 1980s, Brian wrote <i>the</i> book that became essential reading for both new and established dermal delivery scientists, explaining the background mathematics and principles through to formulation design. Brian also worked with numerous scientists, as collaborators and students, who have themselves taken his rigorous approach to scientific investigation into their own research groups. This paper can only describe a small fraction of the many significant contributions that Brian made to the field during his 40-year academic career.

A label-free indicator for tumor cells based on the CH2-stretch ratio

In this paper, we assess the potential of a label-free infrared absorbance based measurement method for determination of the CH(2)-symmetric to CH(2)-antisymmetric stretch ratio, to aid in the detection of the presence of cancer cells and to differentiate between various cancer cells. For this study a normal epithelial kidney cell line, two carcinoma epithelial kidney cell lines, an adult primary human melanocyte cell line, and three human melanoma cell lines were investigated. For the measurements we used a self-designed IR sensor which has the potential to be further developed in a point-of-care instrument. To investigate the mechanism influencing the CH(2)-stretch ratio of mammalian cell membranes, a normal epithelial kidney cell line was exposed to the plasma membrane bound cholesterol reducing agent methyl-β-cyclodextrin. This methodology yielded statistically significant CH(2)-stretch ratio differences between the individual cell lines, normal and tumorous, of both epithelial kidney and melanocyte origin. Measurement results of normal epithelial kidney cells exposed to methyl-β-cyclodextrin indicate that an increase in the CH(2)-stretch ratio arises when there is a decrease in, or redistribution of, the membrane stabilizing agent cholesterol. This study proves that the proposed cell type discrimination method, based on the CH(2)-symmetric to CH(2)-antisymmetric stretch ratio, allows the discrimination between normal and tumor cells. In addition, the method shows high potential for improvement of staging of suspicious tissues.

Fast and minimally invasive determination of the unsaturation index of white fat depots by micro-Raman spectroscopy

In the last 20 years increasing interest has been devoted to the investigation of white adipose tissue (WAT) because hypo- or hyperfunction of WAT is involved in the pathogenesis of obesity and other pathologies. The investigation and discrimination of different characteristics in adipose tissues by means of spectroscopic techniques appears as a topic of current interest, also in view of possible medical-technological applications. The aim of this work was to establish micro-Raman spectroscopy as a tool for the characterization of mammals fat tissue. After preliminary tests aimed at defining a suitable sample preparation protocol, Raman spectra of WAT specimens excised from mice of different ages were recorded in the energy range 750-3,350 cm⁻¹. Quantitative values of the unsaturation index were obtained through the calibration with HR-NMR spectra of lipid extracts. Raman spectroscopy detected a sharp increase in the unsaturation index between 22 and 30 days of age in close correspondence with the weaning of mice (21 days). The present results show that Raman spectroscopy is an inexpensive, fast and robust technique to analyze the unsaturation index of mammals fat tissues that could be routinely used in bioptic samples.

Damage/recovery by additive on lipid membrane as a mimicry of human stratum corneum

The effects of sodium dodecyl sulfate (SDS) on the model lipid membrane of human stratum corneum, composed of three main lipids of ceramide III, palmitic acid, and cholesterol, have been examined as a function of exposure period. Cholesterol first got to elute, palmitic acid followed it late, and the remaining solid was mainly ceramide III. The removal of lipids influenced the configurational structure of remaining lipid and the intralayer structure of lamellae. Monitoring of structural reorganization in the damaged membrane was carried out on the recovering procedure of palmitic acid and cholesterol. Both lipids were penetrated in the damaged membrane and recovered mostly the configurational lipid structure and the lamellar structure. Especially, it can be noted that cholesterol is more effective than palmitic acid on recovery.

Identifying the spatial distribution of vitamin E, pulmonary surfactant and membrane lipids in cells and tissue by confocal Raman microscopy

Every organ compromises of several different cell types. When studying the effects of a chosen compound within this organ or tissue uptake, localisation, metabolism, and the effect itself can be expected to differ between cells. Using the example of Vitamin E in pulmonary tissue we introduce confocal Raman Microscopy as a superior method to localise lipid-soluble compounds within tissues and cells. We describe the analyses of vitamin E, its oxidation products, and metabolites as well as pulmonary surfactant phospholipids in fixed lung tissue sections. Examples of main structural membrane lipids (PC, cholesterol) and an example of a lipid-signalling molecule (ceramide) are also included. Confocal Raman microscopy is a non-destructive optical method of analysing chemical and physical composition of solids, liquids, gases, gels, and solutions. The method is rich in information allowing discrimination of chemically similar molecules (including geometric isomers) and sensitive monitoring of subtle physical interactions. Additionally, Raman spectroscopy is relatively insensitive to water allowing the analysis of aqueous solutions and suspensions typical in biochemistry. In contrast, Raman spectroscopy is sensitive to non-polar molecules making it ideal for lipidomics research.

On the interpretation of the 1100 cm(-1) Raman band in phospholipids and other alkyl-containing molecular entities

The long-standing issue on the interpretation of a Raman band at 1100 cm(-1) is discussed. By combining observations from studies on lipid bilayers, alkanes, and polyethylenes, one can now definitely assign this band to the presence of isolated gauche bonds. In addition, we discuss the use of an order parameter S(trans) in lipid bilayer structures.

Prediction of adipose tissue composition using raman spectroscopy: Average properties and individual fatty acids

Raman spectroscopy has been used for the first time to predict the FA composition of unextracted adipose tissue of pork, beef, lamb, and chicken. It was found that the bulk unsaturation parameters could be predicted successfully [R2 = 0.97, root mean square error of prediction (RMSEP) = 4.6% of 4 sigma], with cis unsaturation, which accounted for the majority of the unsaturation, giving similar correlations. The combined abundance of all measured PUFA (> or = 2 double bonds per chain) was also well predicted with R2 = 0.97 and RMSEP = 4.0% of 4 sigma. Trans unsaturation was not as well modeled (R2 = 0.52, RMSEP = 18% of 4 sigma); this reduced prediction ability can be attributed to the low levels of trans FA found in adipose tissue (0.035 times the cis unsaturation level). For the individual FA, the average partial least squares (PLS) regression coefficient of the 18 most abundant FA (relative abundances ranging from 0.1 to 38.6% of the total FA content) was R2 = 0.73; the average RMSEP = 11.9% of 4 sigma. Regression coefficients and prediction errors for the five most abundant FA were all better than the average value (in some cases as low as RMSEP = 4.7% of 4 sigma). Cross-correlation between the abundances of the minor FA and more abundant acids could be determined by principal component analysis methods, and the resulting groups of correlated compounds were also well-predicted using PLS. The accuracy of the prediction of individual FA was at least as good as other spectroscopic methods, and the extremely straightforward sampling method meant that very rapid analysis of samples at ambient temperature was easily achieved. This work shows that Raman profiling of hundreds of samples per day is easily achievable with an automated sampling system.

The phase transition behavior of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) model membrane influenced by 2,4-dichlorophenol—an FT-Raman Spectroscopy Study

The effect of 2,4-dichlorophenol (DCP) on the structures and phase transitions of fully hydrated 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) liposomes was studied using FT-Raman spectroscopy. Whereas the Raman frequency shifts of the most frequently investigated bands of C-C and C-H stretching regions only indicate the main phase transition (P(beta')-L(alpha)) of the pure DPPC/water system, the Raman shift of C-H scissoring vibration at 1440 cm(-1) was found to be able to reveal the pretransition (L(beta')-P(beta')) as well. Analyzing the spectral parameters of the trans band at 1128 cm(-1), which does not overlap with DCP vibrational modes, a continuous decrease of trans conformations was found with increasing DCP concentration at 26 degrees C accompanying the phase transitions L(beta')-P(beta') and P(beta')-L(alpha). The intensity ratio of the symmetrical and asymmetrical methylene stretching bands (at 2850 cm(-1) and 2880 cm(-1)), defined as the disorder parameter by Levin [Levin, I.W., 1985. Two types of hydrocarbon chain interdigitation in sphingomielin bilayers. Biochemistry 24, 6282-6286], indicated that in the interdigitated phase (L(I)) the order is markedly high and comparable with that of L(beta). Both the phase transition P(beta')-L(alpha) in the DCP/DPPC molar ratio range of 10/100-50/100 and the phase transition L(I)-L(alpha) led to a significant increase of disordered chains and the presence of DCP molecules induced a more disordered chain region than that observed in the L(alpha) phase of DPPC. Nevertheless, it was found that the L(alpha) phase with DCP contains approximately the same amount of trans conformers than that without DCP.

Mechanisms of action of novel skin penetration enhancers: Phospholipid versus skin lipid liposomes

Employing thermal analysis, we investigated the mechanism of action of novel enhancers and probed phospholipid (PL) versus stratum corneum lipid (SCL) liposomes as model membranes. The enhancers included octyl salicylate (OS), padimate O (PADO) and 2-(1-nonyl)-1,3-dioxolane (ND). The negative controls were the empty liposomes. Positive controls employed dimethylsulfoxide (DMSO) and Azone (AZ). For PL liposomes, DMSO sharpened the transitions. AZ abolished the pre-transition, broadened the main transition and linearly reduced its transition temperature (T(m)). OS or PADO reduced T(m) and size of pre-transition, broadened the main transition and decreased its T(m) (non-linearly). ND abolished the pre-transition but increased T(m) of the main endotherm, suggesting retardation rather than enhancement. The results of SCL correlated with PL liposomes except for ND. In SCL liposomes, ND reduced T(m) and broadened the peaks indicating lipid disruption, which indicated its enhancing effects. In conclusion, OS, PADO and ND can enhance drugs by disrupting intercellular lipid domain but they differ from AZ in terms of the relationship between efficacy and concentration. Although PL liposomes are simple model membranes with sharp transitions which give detailed information about the effects of enhancers, they can provide misleading results. Simultaneous use of other models like SCL liposomes is recommended.

Remote temperature monitoring in ocular tissue using confocal Raman spectroscopy

We demonstrated the feasibility of Raman spectroscopy for remote temperature monitoring within the aqueous humor of the rabbit eye in vivo. Using a confocal Raman spectroscopy system, Raman spectra from 2580 to 3800 cm(-1) were recorded in HPLC-grade water and in the aqueous humor of the rabbit eye under in vivo and ex vivo conditions within a temperature range of 14-34 degrees C. The ratio between the integrated Raman intensities of two temperature dependent OH-vibrational regions (OH2/OH1) in the spectra of water showed high linear dependence on temperature both in pure water [0.0049(+/-1.2%)T+0.4522(+/-0.5%), R2=0.99, n=50, p<0.05], as well as in the rabbit aqueous humor [0.0036(+/-2.8%)T+0.4966(+/-0.6%), R2=0.98, n=162, p<0.05] with a high degree of reproducibility and sensitivity ( approximately 0.2-0.7 degrees C). Raman spectroscopy can be used for high resolution and remote monitoring of temperature in the aqueous humor under in vivo conditions.

Raman spectroscopy detects biochemical changes due to proliferation in mammalian cell cultures

Raman spectra of cells and nuclei from cultures in the plateau (nonproliferating) and exponential (proliferating) phases of growth were measured and show that Raman spectroscopy can monitor changes due to cell proliferation. A simple fitting routine was developed using a basis set (lipid, protein, DNA, RNA) to estimate the relative amounts of biochemical components in cells and nuclei. Using relative amounts and ratios of biochemical components, reproducible differences can be detected and quantified that are not readily apparent by visual analysis of vibrational bands in the spectra. These differences, due to cell proliferation, can be assigned to specific biochemical changes. They include a decrease in the relative lipid and increases in the relative protein and RNA for both nontumorigenic exponential cells and nuclei, and an increase in the relative RNA for tumorigenic exponential cells. The lipid/RNA ratio decreases for nontumorigenic exponential cells and nuclei and tumorigenic exponential cells. The protein/lipid ratio increases for both tumorigenic and nontumorigenic exponential cells and nuclei. Finally, the lipid/DNA ratio decreases for tumorigenic exponential nuclei. This knowledge will be important for Raman detection of rapidly dividing populations of cancer cells in vivo.

A critical evaluation of Raman spectroscopy for the analysis of lipids: fatty acid methyl esters

The work presented here is aimed at determining the potential and limitations of Raman spectroscopy for fat analysis by carrying out a systematic investigation of C4-C24 FAME. These provide a simple, well-characterized set of compounds in which the effect of making incremental changes can be studied over a wide range of chain lengths and degrees of unsaturation. The effect of temperature on the spectra was investigated over much larger ranges than would normally be encountered in real analytical measurements. It was found that for liquid FAME the best internal standard band was the carbonyl stretching vibration v(C=O), whose position is affected by changes in sample chain length and physical state; in the samples studied here, it was found to lie between 1729 and 1748 cm(-1). Further, molar unsaturation could be correlated with the ratio of the nu(C=O) to either nu(C=C) or delta(H-C=) with R2 > 0.995. Chain length was correlated with the delta(CH2)tw/v(C=O) ratio, (where "tw" indicates twisting) but separate plots for odd- and even-numbered carbon chains were necessary to obtain R2 > 0.99 for liquid samples. Combining the odd- and even-numbered carbon chain data in a single plot reduced the correlation to R2 = 0.94-0.96, depending on the band ratios used. For molal unsaturation the band ratio that correlated linearly with unsaturation (R2 > 0.99) was nu(C=C)/delta(CH2)sc (where "sc" indicates scissoring). Other band ratios show much more complex behavior with changes in chemical and physical structure. This complex behavior results from the fact that the bands do not arise from simple vibrations of small, discrete regions of the molecules but are due to complex motions of large sections of the FAME so that making incremental changes in structure does not necessarily lead to simple incremental changes in spectra.

Drug interaction and location in liposomes: correlation with polar surface areas

An important step in liposome characterization is to determine the location of a drug within the liposome. This work thus investigated the interaction of dipalmitoylphosphatidylcholine liposomes with drugs of varied water solubility, polar surface area (PSA) and partition coefficient using high sensitivity differential scanning calorimetry. Lipophilic estradiol (ES) interacted strongest with the acyl chains of the lipid membrane, followed by the somewhat polar 5-fluorouracil (5-FU). Strongly hydrophilic mannitol (MAN) showed no evidence of interaction but water soluble polymers inulin (IN) and an antisense oligonucleotide (OLG), which have very high PSAs, interacted with the lipid head groups. Accordingly, the drugs could be classified as: hydrophilic ones situated in the aqueous core and which may interact with the head groups; those located at the water-bilayer interface with some degree of penetration into the lipid bilayer; those lipophilic drugs constrained within the bilayer.

Multivariate prediction of clarified butter composition using raman spectroscopy

Raman spectroscopy has been used to predict the abundance of the FA in clarified butterfat that was obtained from dairy cows fed a range of levels of rapeseed oil in their diet. Partial least squares regression of the Raman spectra against FA compositions obtained by GC showed good prediction for the five major (abundance >5%) FA with R2 = 0.74-0.92 and a root mean SE of prediction (RMSEP) that was 5-7% of the mean. In general, the prediction accuracy fell with decreasing abundance in the sample, but the RMSEP was <10% for all but one of the 10 FA present at levels >1.25%. The Raman method has the best prediction ability for unsaturated FA (R2 = 0.85-0.92), and in particular trans unsaturated FA (best-predicted FA was 18:1 t delta9). This enhancement was attributed to the isolation of the unsaturated modes from the saturated modes and the significantly higher spectral response of unsaturated bonds compared with saturated bonds. Raman spectra of the melted butter samples could also be used to predict bulk parameters calculated from standard analyzes, such as iodine value (R2 = 0.80) and solid fat content at low temperature (R2 = 0.87). For solid fat contents determined at higher temperatures, the prediction ability was significantly reduced (R2 = 0.42), and this decrease in performance was attributed to the smaller range of values in solid fat content at the higher temperatures. Finally, although the prediction errors for the abundances of each of the FA in a given sample are much larger with Raman than with full GC analysis, the accuracy is acceptably high for quality control applications. This, combined with the fact that Raman spectra can be obtained with no sample preparation and with 60-s data collection times, means that high-throughput, on-line Raman analysis of butter samples should be possible.

Interactions of surfactants (edge activators) and skin penetration enhancers with liposomes

Incorporating edge activators (surfactants) into liposomes was shown previously to improve estradiol vesicular skin delivery; this phenomenon was concentration dependent with low or high concentrations being less effective. Replacing surfactants with limonene produced similar behaviour, but oleic acid effects were linear with concentration up to 16% (w/w), beyond which it was incompatible with the phospholipid. This present study thus employed high sensitivity differential scanning calorimetry to probe interactions of additives with dipalmitoylphosphatidylcholine (DPPC) membranes to explain such results. Cholesterol was included as an example of a membrane stabiliser that removed the DPPC pre-transition and produced vesicles with a higher transition temperature (T(m)). Surfactants also removed the lipid pre-transition but reduced T(m) and co-operativity of the main peak. At higher concentrations, surfactants also formed new species, possibly mixed micelles with a lower T(m). The formation of mixed micelles may explain reduced skin delivery from liposomes containing high concentrations of surfactants. Limonene did not remove the pre-transition but reduced T(m) and co-operativity of the main peak, apparently forming new species at high concentrations, again correlating with vesicular delivery of estradiol. Oleic acid obliterated the pre-transition. The T(m) and the co-operativity of the main peak were reduced with oleic acid concentrations up to 33.2mol%, above which there was no further change. At higher concentrations, phase separation was evident, confirming previous skin transport findings.

Temperature Influences the Postelectroporation Permeability State of the Skin

The influence of temperature on the electrical conductance and transport of macromolecules across porcine epidermis during and after electroporation were studied. The passive diffusion of fluorescein isothiocyanate labeled dextran (molecular weight 10 kDa, FD10K), across the epidermis did not differ much at temperatures below 37 degrees C, but became significantly higher above 40 degrees C. The resistance drop during pulse application was less sensitive to temperature within the temperature range (10-50 degrees C) of this study. The kinetics of decrease in postpulse conductance of the electroporated epidermis was fit to a monoexponential function. The rate of decrease in postpulse conductance was significantly less and FD10K transport was markedly high at temperature over 40 degrees C relative to those observed at temperatures less than 37 degrees C. This jump in transport cannot be explained by electrophoresis induced by the pulse, or by the increased diffusion kinesis of the molecules. The enhanced transport is most likely due to the prolonged postpulse permeable state of the skin. Electroporation at mild hyperthermia temperatures resulted in delivering much higher quantities of macromolecules.

Effect of heat on the percutaneous absorption and skin retention of three model penetrants

The effect of heat on the transdermal delivery of model penetrants of differing lipophilicity through artificial membranes (non-rate limiting) and human epidermis was investigated in vitro. Saturated suspensions of the model penetrants; methyl paraben (MP), butyl paraben (BP) and caffeine (CF) in deionised water (vehicle) were used to attain maximal thermodynamic activity. Franz cell experiments were performed at temperatures ranging from 23 to 45 degrees C using the infinite dose method. Artificial membrane studies showed the penetrant diffusivity (diffusion coefficient) in the vehicle to be totally dependent on temperature and not changes in donor solubility. Epidermal flux and retention of all penetrants was found to be affected by temperature. The amount of penetrant retained in the epidermis was found to be in the order BP>CF>MP whilst the transdermal fluxes increased in the order MP>BP>CF with increasing receptor temperature. Estimated epidermal diffusivity of MP was found to be significantly affected by temperature (P< or =0.05) compared to BP and CF. Using Arrhenius plots, a lower activation energy was recorded for CF and may suggest a difference in permeation kinetics compared to the other penetrants.

pH-induced modifications to stratum corneum lipids investigated using thermal, spectroscopic, and chromatographic techniques

The effects of nonphysiological pH on stratum corneum lipid content and structure have been studied. Human stratum corneum samples were soaked in solutions at pH 1, 2, 6, 11, or 12 for up to 24 h. After removal of the stratum corneum, the buffer solutions were analyzed for lipid composition using thin-layer chromatography analysis and the stratum corneum sheets were examined using differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy. The results demonstrate that only buffers of pH 11 or higher affect the stratum corneum lipids. No large difference in the contents of ceramides and cholesterol extracted by buffers of varying pH was observed. In contrast, free fatty acid extraction was pH dependent; amounts removed by 24-h treatment with pH 11 or 12 buffers were comparable, and were similar to amounts extracted with a methanol-chloroform mixture for 15 min. No appreciable changes in DSC and FTIR spectra were detected between untreated stratum corneum and stratum corneum samples treated with buffers at pHs in the range 1-6. For tissue treated with pH 11 and 12, the position of the endothermal melting peak T2 shifted from 72 to 74 degrees C on the DSC thermograms. Small changes in the broadness of spectral peaks at 2855 cm(-1) [attributable to upsilon(CH(2)) stretching of stratum corneum lipids and 1655 cm(-1) upsilon(C=O) stretching amide I band] can be seen in the FTIR spectra from the treated stratum corneum samples, although no shifts in peak positions were observed. Intensity changes in peaks from extraneous lipids [upsilon(C=O) stretching mode at 1735 cm(-1)] were observed after buffer treatments. The changes provoked by the alkaline buffers are not dramatic and it may be concluded that the stratum corneum appears remarkably resilient to extended exposure in both highly acidic (pH 1) and highly alkaline (pH 12) environments.

Quantitative structure-permeability relationships (QSPRs) for percutaneous absorption

Quantitative structure-permeability relationships (QSPRs) have been derived by many researchers to model the passive, diffusion-controlled, percutaneous penetration of exogenous chemicals. Most of these relationships are based on experimental data from the published literature. They indicate that molecular size (as molecular weight) and hydrophobicity (as the logarithm of the octanol-water partition coefficient; log k(ow)) are the main determinants of transdermal penetration. This article reviews the current state of the art in QSPRs for absorption of chemicals through the skin, and where this technology can be exploited in future research. The main shortfalls in QSPR models result from inconsistency and error of the experimental values used to derive them. This is probably caused by the manner in which they employ data from a variety of sources and, in some cases, slightly different experimental protocols. Further, most current models are based on data generated from either aqueous or ethanolic solution, where each penetrant is present at its saturated solubility or a fraction of its saturated solubility. No models currently account for the influences of formulation upon percutaneous penetration. Current QSPR models provide a significant tool for assessing the percutaneous penetration of chemicals. They may be important in determining the bioavailability of a range of topically applied exogenous chemicals, and in issues of dermal toxicology and risk assessment. However, their current use may be limited by their lack of applicability across different formulation types. As a consequence, their true value may be to make predictions within specific formulation types, as opposed to a general model based on a range of formulation types. In addition, the endpoint of models may be inappropriate for specific applications other than the systemic delivery of topically applied chemicals.

Medical applications of Raman spectroscopy: from proof of principle to clinical implementation

Raman spectroscopy has recently been applied ex vivo and in vivo to address various biomedical issues such as the early detection of cancers, monitoring of the effect of various agents on the skin, determination of atherosclerotic plaque composition, and rapid identification of pathogenic microorganisms. This leap in the number of applications and the number of groups active in this field has been facilitated by several technological advancements in lasers, CCD detectors, and fiber-optic probes. However, most of the studies are still at the proof of concept stage. We present a discussion on the status of the field today, as well as the problems and issues that still need to be resolved to bring this technology to hospital settings (i.e., the medical laboratory, surgical suites, or clinics). Taken from the viewpoint of clinicians and medical analysts, the potential of Raman spectroscopic techniques as new tools for biomedical applications is discussed and a path is proposed for the clinical implementation of these techniques.

Direct observation of domains in model stratum corneum lipid mixtures by Raman microspectroscopy

Several studies on intact and model stratum corneum (SC), the top layer of the epidermis, have suggested the presence of crystalline domains. In the present work, we used micro-Raman mapping to detect lipid domains in model lipid mixtures formed by an equimolar mixture of ceramides, cholesterol, and palmitic acid, the three main lipid species of SC. We were able to determine the spatial distribution of the three compounds individually based on the systematic analysis of band areas. As a control, we studied freeze-dried lipid mixtures, and the Raman microspectroscopy reported faithfully the homogeneous distribution of the three compounds. Spectral mapping was then performed on hydrated equimolar mixtures carefully annealed. In this case, clear phase separations were observed. Domains enriched in cholesterol, ceramides, or palmitic acid with a size of a few tens of square microns were detected. These findings constitute the first direct evidence of the formation of heterogeneous domains in the SC lipid models in a bulk phase. Raman microspectroscopy is an innovative approach to characterize the conditions leading to the formation of domains and provides new insights into the understanding of the skin barrier.

Noninvasive characterization of human stratum corneum of undiseased skin of patients with atopic dermatitis and psoriasis as studied by Fourier transform Raman spectroscopy

Etiopathogenetic regulatory disorders of epidermal metabolism and the subsequent changes in the molecular pattern of the stratum corneum play an important role in the clinical differentiation of particular dermatoses (e.g., psoriasis, atopic dermatitis). In this study we present in vitro Fourier transform Raman spectra of the stratum corneum from healthy skin, as well as from clinically undiseased skin of the right heel of atopic and psoriatic volunteers. Differences in the averaged spectra were detected, particularly in the spectral ranges of 1112-1142 (lipid band), 1185-1220, and 1394-1429 cm(-1). By using the first derivative of the averaged spectra and/or a statistical evaluation of the spectroscopic data it was possible to distinguish the skin types examined.

Oestradiol skin delivery from ultradeformable liposomes: refinement of surfactant concentration

The aims of this study were to refine ultradeformable liposomes for oestradiol skin delivery and to evaluate Span 80 and Tween 80 as edge activators compared with sodium cholate. Vesicles containing phosphatidylcholine (PC) mixed with edge activators and oestradiol were prepared. Entrapment efficiency and vesicle size were determined. Interactions between activators and vesicles were investigated using differential scanning calorimetry. Transepidermal permeation of oestradiol from vesicles was studied compared to saturated aqueous control in vitro. The maximum flux (J(max)) and its time (T(max)) were calculated from the flux curves and skin deposition was assessed. The compositions of refined formulations were predicted, liposomes prepared, and tested against control. Entrapment efficiency depended on PC concentration with some contribution from sodium cholate and Tween 80. Vesicle sizes ranged from 124 to 135 nm. Edge activators interacted with lipid bilayers and disrupted packing. The refined edge activator concentrations in PC vesicles were 14.0, 13.3 and 15.5% w/w for sodium cholate, Span 80 and Tween 80, respectively; they increased J(max) by 18, 16 and 15-fold and skin deposition by 8, 7 and 8-fold compared with control. Ultradeformable vesicles thus improved skin delivery of oestradiol compared to control and Span 80 and Tween 80 were equivalent to sodium cholate as edge-activators.