Concentration of plasma albumin in its accessible space in postmortem human dermis

High stability resistive switching mechanism of a screen-printed electrode based on BOBZBT2 organic pentamer for creatinine detection

The resistive switching (RS) mechanism is resulted from the formation and dissolution of a conductive filament due to the electrochemical redox-reactions and can be identified with a pinched hysteresis loop on the I-V characteristic curve. In this work, the RS behaviour was demonstrated using a screen-printed electrode (SPE) and was utilized for creatinine sensing application. The working electrode (WE) of the SPE has been modified with a novel small organic molecule, 1,4-bis[2-(5-thiophene-2-yl)-1-benzothiopene]-2,5-dioctyloxybenzene (BOBzBT2). Its stability at room temperature and the presence of thiophene monomers were exploited to facilitate the cation transport and thus, affecting the high resistive state (HRS) and low resistive state (LRS) of the electrochemical cell. The sensor works based on the interference imposed by the interaction between the creatinine molecule and the radical cation of BOBzBT2 to the conductive filament during the Cyclic Voltammetry (CV) measurement. Different concentrations of BOBzBT2 dilution were evaluated using various concentrations of non-clinical creatinine samples to identify the optimised setup of the sensor. Enhanced sensitivity of the sensor was observed at a high concentration of BOBzBT2 over creatinine concentration between 0.4 and 1.6 mg dL-1-corresponding to the normal range of a healthy individual.

Application of the Tissue Composition-Based Model to Minipig for Predicting the Volume of Distribution at Steady State and Dermis-to-Plasma Partition Coefficients of Drugs Used in the Physiologically Based Pharmacokinetics Model in Dermatology

The minipig continues to build a reputation as a viable alternative large animal model to predict humans in dermatology and toxicology studies. Therefore, it is essential to describe and predict the pharmacokinetics in that species to speed up the clinical candidate selection. Essential input parameters in whole-body physiologically based pharmacokinetic models are the tissue-to-plasma partition coefficients and the resulting volume of distribution at steady-state (V_ss). Mechanistic in vitro- and in silico-based models used for predicting these parameters of tissue distribution of drugs refer to the tissue composition-based model (TCM). Robust TCMs were initially developed for some preclinical species (e.g., rat and dog) and human; however, there is currently no model available for the minipig. Therefore, the objective of this present study was to develop a TCM for the minipig and to estimate the corresponding tissue composition data. Drug partitioning into the tissues was predominantly governed by lipid and protein binding effects in addition to drug solubilization and pH gradient effects in the aqueous phase on both sides of the biological membranes; however, some more complex tissue distribution processes such as drug binding to the collagen-laminin material in dermis and a restricted drug partitioning into membranes of tissues for compounds that are amphiphilic and contain sulfur atom(s) were also challenged. The model was validated by predicting V_ss and the dermis-to-plasma partition coefficients (K_p-dermis) of 68 drugs. The prediction of K_p-dermis was extended to humans for comparison with the minipig. The results indicate that the extended TCM provided generally good agreements with observations in the minipig showing that it is also applicable to this preclinical species. In general, up to 86% and 100% of the predicted V_ss values are respectively within 2-fold and 3-fold errors compared to the experimentally determined values, whereas these numbers are 78% and 94% for K_p-dermis when the anticipated outlier compounds are not included. Binding data to dermis are comparable between minipigs and humans. Overall, this study is a first step toward developing a mechanistic TCM for the minipig, with the aim of increasing the use of physiologically based pharmacokinetic models of drugs for that species in addition to rats, dogs, and humans because such models are used in preclinical and clinical transdermal studies.

Dissolving Microneedle Arrays for Transdermal Delivery of Amphiphilic Vaccines

Amphiphilic vaccine based on lipid-polymer conjugates is a new type of vaccine capable of self-delivering to the immune system. When injected subcutaneously, amphiphilic vaccines efficiently target antigen presenting cells in the lymph nodes (LNs) via a unique albumin-mediated transport and uptake mechanism and induce potent humoral and cellular immune responses. However, whether this new type of vaccine can be administrated via a safe, convenient microneedle-based transdermal approach remains unstudied. For such skin barrier-disruption systems, a simple application of microneedle arrays (MNs) is desired to disrupt the stratum corneum, and for rapid and pain-free self-administration of vaccines into the skin, the anatomic place permeates with an intricate mesh of lymphatic vessels draining to LNs. Here the microneedle transdermal approach is combined with amphiphilic vaccines to create a simple delivery approach which efficiently traffic molecular vaccines into lymphatics and draining LNs. The rapid release of amphiphilic vaccines into epidermis upon application of dissolving MNs to the skin of mice generates potent cellular and humoral responses, comparable or superior to those elicited by traditional needle-based immunizations. The results suggest that the amphiphilic vaccines delivered by dissolving MNs can provide a simple and safer vaccination method with enhanced vaccine efficacy.

Effects of hydration on steric and electric charge-induced interstitial volume exclusion--a model

The presence of collagen and charged macromolecules like glycosaminoglycans (GAGs) in the interstitial space limits the space available for plasma proteins and other macromolecules. This phenomenon, known as interstitial exclusion, is of importance for interstitial fluid volume regulation. Physical/mathematical models are presented for calculating the exclusion of electrically charged and neutral macromolecules that equilibrate in the interstitium under various degrees of hydration. Here, a central hypothesis is that the swelling of highly electrically charged GAGs with increased hydration shields parts of the neutral collagen of the interstitial matrix from interacting with electrically charged macromolecules, such that exclusion of charged macromolecules exhibits change due to steric and charge effects. GAGs are also thought to allow relatively small neutral, but also charged macromolecules neutralized by a very high ionic strength, diffuse into the interior of GAGs, whereas larger macromolecules may not. Thus, in the model, relatively small electrically charged macromolecules, such as human serum albumin, and larger neutral macromolecules such as IgG, will have quite similar total volume exclusion properties in the interstitium. Our results are in agreement with ex vivo and in vivo experiments, and suggest that the charge of GAGs or macromolecular drugs may be targeted to increase the tissue uptake of macromolecular therapeutic agents.

Design and performance of a spreadsheet-based model for estimating bioavailability of chemicals from dermal exposure

A comprehensive transient model of chemical penetration through the stratum corneum, viable epidermis and dermis formulated in terms of an Excel™ spreadsheet and associated add-in is presented. The model is a one-dimensional homogenization of underlying microscopic transport models for stratum corneum and dermis; viable epidermis is treated as unperfused dermis. The model's salient features are a detailed structural description of the skin layers, a combination of first-principles based transport equations and empirical partition and diffusion coefficients, and the capability of simulating a variety of exposure scenarios. Model predictions are compared with representative in vitro skin permeation data obtained from the literature using as summary parameters total absorption (Q(abs)), maximum flux (J(max)) and skin permeability coefficient (k(p)). The results of this evaluation demonstrate the current state-of-the-art in prediction of transient skin absorption and highlight areas in which further elaborations are needed to obtain satisfactory predictions.

[Anatomical heterogeneity in the proteome of human subcutaneous adipose tissue]

BACKGROUND

Human subcutaneous (SQ) white adipose tissue (WAT) can vary according to its anatomical location, with subsequent differences in its proteomic profile.

PATIENTS AND METHODS

SQ-WAT aspirates were obtained from six overweight (BMI>25kg/m(2)) women who underwent extensive liposuction. SQ-WAT was removed from six different locations (upper abdominal, lower abdominal, thigh, back, flank, and hip), and the protein profiles were determined by two-dimensional gel electrophoresis. In addition, the proteomic profiles of upper abdominal and hip SQ-WAT were subjected to further analysis, comparing samples obtained from two layers of WAT (deep and superficial).

RESULTS

Twenty one protein spots showed differential intensities among the six defined anatomical locations, and 14 between the superficial and the deep layer. Among the proteins identified were, vimentin (structural protein), heat-shock proteins (HSPs), superoxide-dismutase (stress-resistance/chaperones), fatty-acid-binding protein (FABP) 4, and alpha-enolase (lipid and carbohydrate metabolism), and ATP-synthase (energy production). Among the WAT samples analyzed, the back sub-depot showed significant differences in the levels of selected proteins when compared to the other locations, with lower level of expression of several proteins involved in energy production and metabolism (ATP-synthase, alpha-enolase, HSPs and FABP-4).

CONCLUSIONS

The levels of several proteins in human SQ-WAT are not homogeneous between different WAT depots. These changes suggest the existence of inherent functional differences in subcutaneous fat depending upon its anatomical location. Thus, caution must be used when extrapolating data from one subcutaneous WAT region to other depots.

Interstitial Fluid and Lymph Formation and Transport: Physiological Regulation and Roles in Inflammation and Cancer

The interstitium describes the fluid, proteins, solutes, and the extracellular matrix (ECM) that comprise the cellular microenvironment in tissues. Its alterations are fundamental to changes in cell function in inflammation, pathogenesis, and cancer. Interstitial fluid (IF) is created by transcapillary filtration and cleared by lymphatic vessels. Herein we discuss the biophysical, biomechanical, and functional implications of IF in normal and pathological tissue states from both fluid balance and cell function perspectives. We also discuss analysis methods to access IF, which enables quantification of the cellular microenvironment; such methods have demonstrated, for example, that there can be dramatic gradients from tissue to plasma during inflammation and that tumor IF is hypoxic and acidic compared with subcutaneous IF and plasma. Accumulated recent data show that IF and its convection through the interstitium and delivery to the lymph nodes have many and diverse biological effects, including in ECM reorganization, cell migration, and capillary morphogenesis as well as in immunity and peripheral tolerance. This review integrates the biophysical, biomechanical, and biological aspects of interstitial and lymph fluid and its transport in tissue physiology, pathophysiology, and immune regulation.

Convective transport of highly plasma protein bound drugs facilitates direct penetration into deep tissues after topical application

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

Many products are applied to human skin for local effects in deeper tissues. Animal studies suggest that deep dermal and/or subcutaneous delivery may be facilitated by both dermal diffusion and transport via the cutaneous vasculature. However, the relationship between the extent and pathways of penetration, drug physicochemical properties and deeper tissue physiology is not well understood.

WHAT THIS STUDY ADDS

We have used a physiologically based pharmacokinetic model to analyze published human cutaneous microdialysis data, complemented by our own in vitro skin penetration studies. We found that convective blood, lymphatic and interstitial flow led to significant deep tissue concentrations for drugs that are highly plasma protein bound. In such cases, deeper tissue concentrations will occur earlier and may be several orders of magnitude greater than predicted by passive dermal diffusion alone.

AIMS

To relate the varying dermal, subcutaneous and muscle microdialysate concentrations found in man after topical application to the nature of the drug applied and to the underlying physiology.

METHODS

We developed a physiologically based pharmacokinetic model in which transport to deeper tissues was determined by tissue diffusion, blood, lymphatic and intersitial flow transport and drug properties. The model was applied to interpret published human microdialysis data, estimated in vitro dermal diffusion and protein binding affinity of drugs that have been previously applied topically in vivo and measured in deep cutaneous tissues over time.

RESULTS

Deeper tissue microdialysis concentrations for various drugs in vivo vary widely. Here, we show that carriage by the blood to the deeper tissues below topical application sites facilitates the transport of highly plasma protein bound drugs that penetrate the skin, leading to rapid and significant concentrations in those tissues. Hence, the fractional concentration for the highly plasma protein bound diclofenac in deeper tissues is 0.79 times that in a probe 4.5 mm below a superficial probe whereas the corresponding fractional concentration for the poorly protein bound nicotine is 0.02. Their corresponding estimated in vivo lag times for appearance of the drugs in the deeper probes were 1.1 min for diclofenac and 30 min for nicotine.

CONCLUSIONS

Poorly plasma protein bound drugs are mainly transported to deeper tissues after topical application by tissue diffusion whereas the transport of highly plasma protein bound drugs is additionally facilitated by convective blood, lymphatic and interstitial transport to deep tissues.

Evaluation of percutaneous permeation of flurbiprofen and ketoprofen after application of transdermal patches using a lateral sectioning approach in hairless rats

OBJECTIVES

The dispositions and pharmacokinetic parameters of non-steroidal anti-inflammatory drugs (NSAIDs) after patch applications have typically been evaluated on a whole-skin basis, and the detailed permeation profiles remain unclear. The aim of this study was to establish a new method for clearly analyzing the flow of drugs in the skin layers and evaluating the drug levels in the target area of the skin tissue.

METHODS

The skin tissue areas where flurbiprofen and ketoprofen patches were applied were cut into 20 μm-thick lateral slices from the surface to the deepest layer and the drug concentrations in the slices were measured.

RESULTS

The results revealed the presence of depth-dependent concentration gradients from the surface to the deep layer and that the drug concentration in the deepest layer was less than one tenth of the surface concentration for both flurbiprofen and ketoprofen. In addition, flurbiprofen yielded higher and more rapid concentrations in the deepest skin layer adjacent to the intramuscular tissue.

CONCLUSIONS

The present data suggest that our technique involving lateral slicing of skin tissues and measurement of drug concentrations allows visual understanding of drug dispositions in the skin layers and makes it possible to evaluate the drug levels in the target area of the skin tissue.

Effect of hydration on interstitial distribution of charged albumin in rat dermis in vitro

At physiological pH, negatively charged glycosaminoglycans in the extracellular matrix may influence distribution volume of macromolecular probes, a phenomenon of importance for hydration of the interstitium and therefore for body fluid balance. We hypothesized that such charge effect was dependent on hydration. Human serum albumin (HSA) (the pH value for the isoelectric point (pI) = 4.9) was made neutral by cationization (cHSA) (pI = 7.6). Rat dermis was studied in vitro in a specially designed equilibration cell allowing control of hydration. Using a buffer containing labelled native HSA and cHSA, the distribution volumes were calculated relative to that of 51Cr-EDTA, an extracellular tracer. During changes in hydration (H), defined as (wet weight - dry weight) (dry weight)(-1)), the slope of the equation describing the relationship between extracellular fluid volume (V(x)) (in g H2O (g dry weight)(-1)) and H (V(x) = 0.925 H + 0.105) differed significantly from that for available volumes of cHSA (V(a,cHSA) = 0.624 H - 0.538) and HSA (V(a,HSA) = 0.518 H - 0.518). A gradual reduction in H led to a reduction in difference between available volumes for the two albumin species. Screening the fixed charges by 1 m NaCl resulted in similar available and excluded volumes of native HSA and neutral cHSA. We conclude that during gradual dehydration, there is a reduced effect of fixed negative charges on interstitial exclusion of charged macromolecules. This effect may be explained by a reduced hydration domain surrounding tissue and probe macromolecules in conditions of increased electrostatic interactions. Furthermore, screening of negative charges suggested that hyaluronan associated with collagen may influence intrafibrillar volume of collagen and thereby available and excluded volume fraction.

In vivo determination of steric and electrostatic exclusion of albumin in rat skin and skeletal muscle

In order to estimate the magnitude of electrostatic exclusion provided by the fixed negative charges of the skin and muscle interstitia of rat in vivo we measured the distribution volumes of two differently charged albumin probes within these tissues. An implanted osmotic pump was used to reach and maintain a steady-state extracellular concentration of a mixture containing two iodine-labelled probes: a charged-modified human serum albumin, cHSA (i.e. a positive probe, isoelectirc point (pI) = 7.6) and a native human serum albumin, HSA (i.e. a normally charged, negative probe, pI = 5.0). Steady-state tissue concentrations were achieved after intravenous infusion of probes for 5-7 days. At the end of this period the animals were nephrectomized and a bolus of 51Cr-EDTA was administered for estimating the extracellular volume. Plasma volumes were measured as 5-min distribution volume of 125I-HSA in separate experiments. The steady-state interstitial fluid concentrations of all probes were determined using nylon wicks implanted postmortem. Calculations of labelled probes were made for interstitial fluid volumes (Vi), extravascular albumin distribution volumes (Vav,a) and relative interstitial excluded volume fractions (Vex,a/Vi). We found that the positive probe is excluded from a significantly smaller fraction of the interstitium. Specifically, the average relative albumin exclusion fractions obtained were: 16% and 26% in skeletal muscle and 30% and 40% in skin, for cHSA and HSA, respectively. On average, the fixed negative charges of the interstitium are responsible for about 40% of the total albumin exclusion in skeletal muscle and 25% in the whole skin tissue and thus, contribute significantly to volume exclusion in these tissues.

Effect of charge on interstitial distribution of albumin in rat dermis in vitro

At physiological pH, negatively charged glycosaminoglycans in the extracellular matrix may influence distribution volume of a probe. We hypothesized that by varying the probe charge we would be able to observe a graded response of available volume fraction. Human serum albumin (HSA) (isoelectric point (pI) 5.0) was made more positive by cationization. Using reaction times of 10, 45 and 60 min, cationized HSA (cHSA) with respective pIs of 6.5, 7.3 and 8.0 were made. After eight days of equilibration in a buffer containing labelled native HSA and cHSA, the distribution volumes were calculated relative to that of 51Cr-EDTA, an extracellular tracer. The available volume in fully swollen dermis for native albumin relative to that of the extracellular tracer averaged 0.485+/-0.008 (n=49), with corresponding volumes for cHSA-10 min, cHSA-45 min and cHSA-60 min of 0.554+/-0.012 (n=17), 0.647+/-0.026 (n=17) and 0.718+/-0.021 (n=12), respectively. Increasing the ionic strength of the bathing solution to 1 M NaCl, thereby screening the fixed charges of tissue elements and probes alike, resulted in similar available and thereby excluded volumes of native HSA and neutral cHSA-45 min. These experiments suggest that fixed negative charges, most likely glycosaminoglycans, contribute significantly to interstitial exclusion of charged macromolecules, a phenomenon of importance for hydration of the interstitial fluid phase and therefore for body fluid balance. Moreover, the data indicate that previous findings of similar excluded volumes for the two differently sized major plasma proteins albumin (molecular mass 66 kDa) and IgG (molecular mass 160 kDa) may be explained by a more pronounced electrostatic repulsion of the former by the extracellular matrix.

Isolation of interstitial fluid from rat mammary tumors by a centrifugation method

Access to interstitial fluid is of fundamental importance to understand tumor transcapillary fluid balance, including the distribution of probes and therapeutic agents. Tumors were induced by gavage of 9,10-dimethyl-1,2-benzanthracene to rats, and fluid was isolated after anesthesia by exposing tissue to consecutive centrifugations from 27 to 6,800 g. The observed (51)Cr-EDTA (extracellular tracer) tissue fluid-to-plasma ratio obtained from whole tumor or from superficial tumor tissue by centrifugation at 27-424 g was not significantly different from 1.0 (0.92-0.99), suggesting an extracellular origin only. However, fluid collected from excised central tumor parts had a significantly lower ratio (0.66-0.77) for all imposed G forces, suggesting dilution by fluid deriving from a space unavailable for (51)Cr-EDTA. The colloid osmotic pressure in tumor fluid was generally higher than in fluid isolated from the subcutis, attributable to less selective capillaries and impaired lymphatic drainage in tumors. HPLC analysis of tumor fluid showed that low-molecular-weight macromolecules not present in arterial plasma were present in tumor fluid obtained by centrifugation and in venous blood draining the tumor, most likely representing proteins derived from tumor cells. We conclude that low-speed centrifugation may be a simple and reliable method to isolate interstitial fluid from tumors.

The quantitative 19F-imaging of albumin at 1.5 T: a potential in-vivo tool

19F-MR-imaging has been used to quantitate albumin concentration in a phantom at 1.5 T. The experimentally derived relationship between albumin concentration and the T1 relaxation time of a fluorinated marker, tetrafluorosuccinic acid (TFSA) was used to calculate the albumin concentration from a quantitative 19F T1 map acquired using a gradient echo sequence. There was close correlation between calculated and actual BSA concentrations (r = 0.99, SE = 0.15). The potentially interfering effect of paramagnetic species on T1 relaxation times was also investigated. Relaxivity data show that albumin concentration measurements should be performed prior to any contrast agent administration.

Macromolecule uptake in human melanoma xenografts. relationships to blood supply, vascular density, microvessel permeability and extracellular volume fraction

The uptake of albumin-Evans blue in human melanoma xenografts was studied and related to blood supply, vascular density, microvessel permeability and extracellular volume fraction in an attempt to identify transport barriers limiting the delivery of macromolecular therapeutic agents to tumours. Three melanoma lines (A-07, R-18, U-25) were included in the study. Tissue concentrations of albumin-Evans blue were determined by spectrophotometry. The [86Rb] uptake method was used to measure tumour blood supply. Vascular density was determined by stereological analysis of histological sections. Microvessel permeability was measured by using the indicator diffusion method. Contrast-enhanced magnetic resonance imaging was used to measure tumour extracellular volume fraction. The fractional volume of the extracellular space governed the uptake of albumin-Evans blue in the tumours. The uptake of albumin-Evans blue in the extracellular space was primarily limited by transport in the vasculature and not by transport across the microvascular wall or the transport through the interstitium. Our study thus suggests that novel strategies for improving the delivery of macromolecular therapeutic agents to tumours should focus on enhancing the tumour blood supply, increasing the half-life of the therapeutic agent in the blood plasma and/or enhancing the volume of the extracellular space available to macromolecules rather than on increasing the permeability of the microvascular wall or improving diffusion conditions in the tumour interstitium.

Interstitial fluid pressure, composition of interstitium, and interstitial exclusion of albumin in hypothyroid rats

Lack of thyroid hormones may affect the composition and structure of the interstitium. Hypothyrosis was induced in rats by thyroidectomy 4-12 wk before the experiments. In hypothyroid rats (n = 16), interstitial fluid pressure measured with micropipettes in hindlimb skin and muscle averaged +0.1 +/- 0.2 and +0.5 +/- 0.2 mmHg, respectively, with corresponding pressures in control rats (n = 16) of -1.5 +/- 0.1 (P < 0.001) and -0.8 +/- 0.1 mmHg (P < 0.001). Interstitial fluid volume, measured as the difference between the distribution volumes of (51)Cr-EDTA and (125)I-labeled BSA, was similar or lower in skin and higher in hypothyroid muscle. Total protein and albumin concentration in plasma and interstitial fluid (isolated from implanted wicks) was lower in hypothyroid compared with control rats. Hyaluronan content (n = 9) in rat hindlimb skin was 2.05 +/- 0.15 and 1.92 +/- 0.09 mg/g dry wt (P > 0.05) in hypothyroid and control rats, respectively, with corresponding content in hindlimb skeletal muscle of 0.35 +/- 0.07 and 0.23 +/- 0. 01 mg/g dry wt (P < 0.01). Interstitial exclusion of albumin in skin and muscle was measured after (125)I-labeled rat serum albumin infusion for 120-168 h with an implanted osmotic pump. Relative excluded volume for albumin (V(e)/V(i)) was calculated as 1 - V(a)/V(i), and averaged 28 and 28% in hindlimb muscle (P > 0.05), 44 and 45% in hindlimb skin (P > 0.05), and 19 and 32% in back skin (P < 0.05) in hypothyroid and control rats, respectively. Albumin mass was higher in back skin in spite of a lower interstitial fluid albumin concentration, a finding explained by a reduced V(e)/V(i) in back skin in hypothyroid rats. These experiments suggest that lack of thyroid hormones in rats changes the interstitial matrix again leading to reduced interstitial compliance and changes in the transcapillary fluid balance.