Skin Interstitial Fluid Research Articles

Hydrogel-Forming Microneedles Increase in Volume During Swelling in Skin, but Skin Barrier Function Recovery is Unaffected

We describe, for the first time, quantification of in-skin swelling and fluid uptake by hydrogel-forming microneedle (MN) arrays and skin barrier recovery in human volunteers. Such MN arrays, prepared from aqueous blends of hydrolyzed poly(methylvinylether/maleic anhydride) (15%, w/w) and the cross-linker poly(ethyleneglycol) 10,000 Da (7.5%, w/w), were inserted into the skin of human volunteers (n = 15) to depths of approximately 300 μm by gentle hand pressure. The MN arrays swelled in skin, taking up skin interstitial fluid, such that their mass had increased by approximately 30% after 6 h in skin. Importantly, however, skin barrier function recovered within 24 h after MN removal, regardless of how long the MN had been in skin or how much their volume had increased with swelling. Further research on closure of MN-induced micropores is required because transepidermal water loss measurements suggested micropore closure, whereas optical coherence tomography indicated that MN-induced micropores had not closed over, even 24 h after MN had been removed. There were no complaints of skin reactions, adverse events, or strong views against MN use by any of the volunteers. Only some minor erythema was noted after patch removal, although this always resolved within 48 h, and no adverse events were present on follow-up.

Microneedle-Mediated Minimally Invasive Patient Monitoring

The emerging field of microneedle-based minimally invasive patient monitoring and diagnosis is reviewed. Microneedle arrays consist of rows of micron-scale projections attached to a solid support. They have been widely investigated for transdermal drug and vaccine delivery applications since the late 1990s. However, researchers and clinicians have recently realized the great potential of microneedles for extraction of skin interstitial fluid and, less commonly, blood, for enhanced monitoring of patient health. We reviewed the journal and patent literature, and summarized the findings and provided technical insights and critical analysis. We describe the basic concepts in detail and extensively review the work performed to date. It is our view that microneedles will have an important role to play in clinical management of patients and will ultimately improve therapeutic outcomes for people worldwide.

Hydrogel-Forming Microneedle Arrays for Enhanced Transdermal Drug Delivery.

Unique microneedle arrays prepared from crosslinked polymers, which contain no drug themselves, are described. They rapidly take up skin interstitial fluid upon skin insertion to form continuous, unblockable, hydrogel conduits from attached patch-type drug reservoirs to the dermal microcirculation. Importantly, such microneedles, which can be fabricated in a wide range of patch sizes and microneedle geometries, can be easily sterilized, resist hole closure while in place, and are removed completely intact from the skin. Delivery of macromolecules is no longer limited to what can be loaded into the microneedles themselves and transdermal drug delivery is now controlled by the crosslink density of the hydrogel system rather than the stratum corneum, while electrically modulated delivery is also a unique feature. This technology has the potential to overcome the limitations of conventional microneedle designs and greatly increase the range of the type of drug that is deliverable transdermally, with ensuing benefits for industry, healthcare providers and, ultimately, patients.

Isolation of interstitial fluid in skin during volume expansion: evaluation of a method in pigs

The ability to isolate interstitial fluid (IF) from skin would make it possible to study the microcirculation and proteins in this environment both during normal and pathophysiological conditions. Traditional IF sampling using implanted wicks suffer from low volumes with risk of contamination by local inflammatory, intracellular, and vascular proteins. To sample larger volumes of true IF, a recently described tissue centrifugation method was compared with dry and wet wicks from porcine skin under normal conditions and following volume expansion. With all three methods, volume expansion caused a significant lowering of interstitial colloid osmotic pressure as expected, and the fluid was similar to plasma when compared using size-exclusion HPLC. The centrifugation method was superior with respect to isolating larger amounts of true IF for further studies. Mass spectrometry of IF sampled with centrifugation showed that most of the proteins reflected the major plasma proteins with some tissue-specific proteins like decorin, gelsolin, and orosomucoid-1. Lumican, pigment epithelium-derived factor, and fatty acid-binding protein 4 were only identified in IF after volume expansion, possibly reflecting a local response to increased fluid filtration. Tissue centrifugation to collect IF from skin should be applicable to both clinical and experimental studies on IF balance during different pathophysiological conditions and interventions.

Differential cytokine response in interstitial fluid in skin and serum during experimental inflammation in rats.

Tumour necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) are important mediators produced during inflammation. We hypothesized that the pro-inflammatory cytokine response in the interstitial fluid (IF) is different from that in serum, and we aimed at quantifying the amount of TNF-alpha and IL-1beta in the IF. By centrifugation of rat skin at < 424 g pure IF is extracted. Using ELISA such fluid was analysed for cytokines in back and/or paw skin of pentobarbital-anaesthetized rats, after either induction of endotoxaemia or ischaemia-reperfusion (I/R) injury. During endotoxaemia, TNF-alpha increased in the IF from 0 in control to 640 +/- 100 pg ml(-1) (mean +/-s.e.m.) after 90 min, with the serum concentration being 5-10 times higher at all time points. The response pattern of IL-1beta after lipopolysaccharide (LPS) challenge differed greatly from that of TNF-alpha with a large increase in IF from 390 +/- 90 to 28 000 +/- 1500 pg ml(-1) after 210 min, and a significantly smaller increase in serum (600 +/- 45 pg ml(-1)). During reperfusion of the hind paw after 2 h of ischaemia, there was a gradual increase of TNF-alpha in both IF of the paw skin and serum after 3 min of reperfusion. Both declined after 20 min. The pattern for IL-1beta differed, increasing significantly less in serum (25 +/- 15 pg ml(-1) after 20 min of reperfusion) than in the IF (1100 +/- 200 pg ml(-1)). Immunostaining of the inflamed tissues showed increased expression of the two cytokines in cells of both epidermis and dermis compared to controls. Subdermal injections of TNF-alpha and IL-1beta at the same concentrations found in IF after LPS infusion affected interstitial fluid pressure significantly. Local TNF-alpha production dominates after I/R injury, whereas in endotoxaemia systemic production predominates. For IL-1beta local production dominates in both conditions. Thus, there is a differential pattern of cytokine production and the current method allows the study of the role of cytokines in IF during different inflammatory reactions.

Familial high serum PICP: high even in skin interstitial fluid, suppressible by topical corticosteroid treatment

Circulating C-terminal propeptide of type I procollagen (PICP), mostly originating from bone, is mainly cleared by mannose receptors (MRs) in liver endothelial cells (LECs). We hypothesized that skin macrophage MRs could also play a role in local (in situ) clearance of PICP originating from skin type I procollagen synthesis. We tested this hypothesis in a male subject with a genetic systemic clearance defect, apparently due to an abnormality in MR function in LECs (or in PICP structure). Since skin macrophages may express the same MRs as LECs do, the genetic defect could affect them as well; hence, if elevated PICP concentrations even in skin interstitial fluid (IF) were found in our subject, it would suggest a role for local MR-mediated PICP clearance in skin. Since glucocorticoids (GCs) upregulate MRs in vitro, we measured the effect of topical GC on suction blister fluid (SBF)-PICP of the test person as compared with normal subjects. SBF-PICP was elevated in the case, which was consistent with the hypothesis. Furthermore, the GC-induced decrease was accentuated. The results suggest that skin macrophage MRs can have a role in skin PICP clearance in situ.

Extracellular fluid and its proteins: dehydration, shock, and recovery.

This review highlights characteristics of extracellular fluid (ECF) that are often overlooked. ECF has, in addition to plasma and interstitial fluid (ISF) surrounding cells, a third large compartment, the ISF of skin and connective tissue. This acts as a reservoir that gives up ECF to plasma volume (PV) in order to sustain circulation in the event of either shock or dehydration. While Starling forces drive filtration, ECF is returned to PV more by lymph and less by Starling forces than previously appreciated. Lymph return to PV is dependent on physical activity and muscle contraction to overcome gravity. Regional change in metabolic rate alters the need for oxygen and nutrients that is met by a regional increase in capillary blood flow. Blood flow is controlled by vasoactive compounds released in response to a drop in PO(2); these relax capillary smooth muscle to increase blood flow and delivery of oxygen and nutrients. Plasma proteins, including albumin, are filtered into the interstitium through larger pores than those filtering ECF. The rate of protein filtration is set by size and charge of these larger endothelial pores and by size and charge of proteins. Charge of these pores, hence albumin permeability, is regulated by many of the same vasoactive compounds that control capillary flow. As a consequence, in response to gravitational stress and other forms of shock that reduce effective circulation, albumin as well as ECF is rapidly shifted from plasma and sequestered in ISF. When this has occurred, as in burn shock, restoration is better effected by generous expansion of ECF with Ringer's solution alone, rather than with Ringer's solution supplemented with human serum albumin or other colloid. Restoring both PV and ISF volume restores lymph circulation and returns sequestered albumin to PV.

Fluorescein Kinetics in Interstitial Fluid Harvested from Diabetic Skin during Fluorescein Angiography: Implications for Glucose Monitoring

Glucose monitoring based on sampling skin interstitial fluid (ISF) is being developed as an alternative to fingerstick blood glucose monitoring. Time delays between rapidly changing levels of glucose in blood and interstitial fluid have been reported in the literature to be between 5 and 20 minutes. This study investigated the time delay between the injection of a small molecular weight fluorescent tracer into the circulation and interstitial fluid. Diabetic subjects undergoing fluorescein angiography were studied. Skin ISF was sampled using a proprietary microporation and harvesting process. ISF was drawn through micropores created in the stratum corneum. After intravenous injection of sodium fluorescein, samples of ISF were drawn from 2 sites for 30 seconds over a period of 20 minutes. Fluorescence levels in ISF were measured with a fluorometer and used to create ISF fluorescein concentration versus time profiles. The ISF fluorescein versus time profiles were characterized by a rapid rise followed by a slow decay. The time to peak of the ISF fluorescein concentration ranged from 2-4 minutes for the patients studied. Intravenous injection of a bolus of low molecular weight fluorescent tracer was used to estimate the time delay between changing glucose levels in blood and ISF. The results indicate that the ISF sampling technology utilized here is capable of tracking rapidly rising levels of blood glucose.

Proteolysis of Insulin-Like Growth Factor-Binding Protein-3 by Human Skin Keratinocytes in Culture in Comparison to that in Skin Interstitial Fluid: The Role and Regulation of Components of the Plasmin System

Proteolysis of Insulin-Like Growth Factor-Binding Protein-3 by Human Skin Keratinocytes in Culture in Comparison to that in Skin Interstitial Fluid: The Role and Regulation of Components of the Plasmin System

Insulin-like growth factors (IGFs) and IGF-binding proteins in human skin interstitial fluid

Insulin-like growth factors (IGFs) and IGF-binding proteins in human skin interstitial fluid

Insulin-like growth factors (IGFs) and IGF-binding proteins in human skin interstitial fluid.

Despite extensive investigation of the insulin-like growth factor (IGF)/IGF-binding protein (IGFBP) system in the circulation and body fluids, there is no information on this in interstitial fluid. We have compared the IGF/IGFBP system in the circulation with that in fluid obtained from blisters artificially raised by negative pressure in 10 healthy volunteers. IGFBP-1, -2, -3, and -4 were all found in blister fluid, but in concentrations much lower than those in matched serum. The IGF-I, IGF-II, and IGFBP-3 levels measured by RIA were 18%, 14%, and 16% of those in serum, respectively. Fast protein liquid chromoatography showed that both IGF-I and IGFBP-3 in 150- and 50-kilodalton complexes were approximately 13% and 37%, respectively, of the corresponding peaks found in matched serum. Compared to that in serum, the IGFBP-3 in the blister fluid was predominantly in a modified 29-kilodalton form, and there was increased activity of an IGFBP-3 protease. Therefore, although IGF concentrations are much lower in interstitial fluid than in the circulation, a greater proportion of this IGF is in forms more readily available for interaction with tissue receptors. The blister fluid appears to represent physiological interstitial fluid and may provide a model for studying the physiology and pathophysiology of growth factors in the interstitial environment.

Tissue IGFBP-3 proteolysis: Contrasting pathophysiology to that in the circulation

Endogenous IGFBP-3 has been examined in the circulation and in four different extravascular fluids in normal healthy adults and in patients with psoriasis or arthritis. In all of these cases there was no apparent increase of IGFBP-3 protease activity in the circulation. In contrast, endogenous IGFBP-3 from normal skin interstititial fluid and synovial fluid from healthy adults was found to be predominantly in the 29 kDa proteolytically modified form. This indicated that in these extravascular fluids in normal healthy adults a protease was active which was similar, if not identical, to that found in the circulation in pregnancy and other conditions. This was confirmed by the fragmentation of recombinant IGFBP-3 when incubated with these fluids. When the skin interstitial fluid or synovial fluid were taken from abnormal tissues (psoriasis in the former and osteoarthritis or rheumatoid arthritis in the latter) there was a considerable reduction in the amount of endogenous IGFBP-3 in the ‘clipped’ form and a reduction in the protease activity. In psoriatic lesions, this reduction in IGFBP-3 protease activity was shown to be due to the presence of an inhibitor in the interstitial fluid but not in the circulation. In both peritoneal and follicular fluid, the ratio of intact to fragmented IGFBP-3 appeared to relate to the oestrogen status. In peritoneal fluid there was a decrease in intact IGFBP-3 during the late proliferative/early secretory phase of the endometrial cycle. In the ovary there was an increase in the amount of fragmented IGFBP-3 in the follicular fluid from the dominant follicle in comparison with atretic follicles from the same ovary. There is normally little proteo-lysis of IGFBP-3 in the circulation but this increases in many conditions where there is increased metabolic activity. The same enzyme(s) appear to be active in many extravascular fluids but under very different regulation. The activity in these extravascular fluids is normally high but can be decreased with local tissue inflammation; this decrease appears to be mediated by the induction of a local inhibitor.

Prostaglandin D 2 and histamine during the immediate and the late-phase components of allergic cutaneous responses

With a skin blister technique in which the mediators generated by the trauma of forming the blister are allowed to subside, we have collected human interstitial skin fluid during the course of allergic reactions to ragweed, and measured levels of histamine and prostaglandin D 2 (PGD 2). Of 18 ragweed-allergic individuals tested, 11 developed both an immediate and a late-phase reaction (LPR) with fivefold-elevated levels of histamine (40 ng/ml) at 30 minutes and a peak level of PGD 2 (6.5 ng/ml) later at 2 1 2 hours after ragweed challenge. The other seven allergic individuals had immediate reactions without an LPR lesion and demonstrated somewhat smaller elevations of histamine (25 ng/ml) but much lower levels of PGD 2 (1.6 ng/ml; p < 0.05). The time course of appearance of these mediators was identical in both groups of patients. The fluids from unchallenged blisters of allergic and nonallergic patients and the fluids of nonallergic patients challenged with ragweed had similar levels of histamine, at the lower limit of detection, and undetectable PGD 2 levels. The peak levels of PGD 2 in allergic individuals correlated with the size of the LPR lesion ( p < 0.05). These data suggest that the LPR involves the secondary elaboration of mediators different from mediators responsible for the immediate manifestations of the allergic skin reaction.

Bile Acid Profiles of Human Serum and Skin Interstitial Fluid and Their Relationship to Pruritus Studied by Gas Chromatography–Mass Spectrometry

1. Pruritus was assessed in 19 patients by measurement of nocturnal limb movement. 2. Serum (nine pruritic, ten non-pruritic) and interstitial fluid (five pruritic, three non-pruritic) bile acids were fractionated according to their mode of conjugation by using DEAP-Sephadex LH-20 and measured by gas chromatography-mass spectrometry. 3. No correlation was found between serum or interstitial fluid total bile acid or individual bile acid concentrations and pruritus. Bile acid profiles in the two groups of patients were similar and there was no correlation between pruritus and the conjugation pattern. 4. Te bile acid profile of interstitial fluid reflected that of serum and a linear relationship was found between serum and interstitial fluid bile acid concentrations (r ;.95, P less than 0.001). 5. The proportion of bile acid sulphate in interstitial fluid was significantly smaller than that in serum (P less than 0.025), where sulphates accounted for up to 46% of the total bile acids. 6. In three patients, a decrease in serum bile acid concentrations achieved by percutaneous transhepatic biliary drainage had little or no effect on pruritus. 7. These findings suggest that bile acids do not have a causative role in the pruritus of cholestatic liver disease.

Iron kinetics in the skin.

Summary. The clearance of transferrin‐bound iron from the interstitial fluid of skin has been measured in normal and iron‐deficient subjects. It is possible to interpret the results by means of a two‐compartment model and to calculate the rate of entry and exit of iron in skin cells. There is a decrease in the amount of iron entering skin cells in patients with iron‐deficiency anaemia.The demonstration of an intracellular exchangeable iron pool in the skin suggests that there may also be large parenchymal pools in other organs, which are indirectly in equilibrium with the plasma pool.