Ultrastructure and organization of the cutaneous microvasculature in normal and pathologic states

Cutaneous vasculitis: insights into pathogenesis and histopathological features

The mechanisms underlying the onset and progression of vasculitis remain poorly understood. This condition is characterized by damage to the vascular wall, recruitment of inflammatory cells, and subsequent structural remodeling, which are hallmarks of vasculitis. The histopathological classification of vasculitis relies on the size of the affected vessel and the predominant type of inflammatory cell involved - neutrophils in acute cases, lymphocytes in chronic conditions, and histiocytes in granulomatous forms. Pathological changes progress in every context, and a single vasculitic pattern can be associated with various systemic conditions. Conversely, a single causative agent may lead to multiple distinct clinical and pathological manifestations of vasculitis. Moreover, many cases of vasculitis have no identifiable cause. A foundational understanding of the normal structure of the cutaneous vascular network is crucial. Similarly, identifying the cellular and molecular participants and their roles in forming the "dermal microvascular unit" is propedeutical.

This review aims to elucidate the complex mechanisms involved in the initiation and progression of vasculitis, offering a comprehensive overview of its histopathological classification, underlying causes, and the significant role of the cutaneous vascular network and cellular dynamics. By integrating the latest insights from studies on NETosis and the implications of lymphocytic infiltration in autoimmune diseases, we seek to bridge gaps in current knowledge and highlight areas for future research. Our discussion extends to the clinical implications of vasculitis, emphasizing the importance of identifying etiological agents and understanding the diverse histopathological manifestations to improve diagnostic accuracy and treatment outcomes.

Gradual Not Sudden Change: Multiple Sites of Functional Transition Across the Microvascular Bed

In understanding the role of the neurovascular unit as both a biomarker and target for disease interventions, it is vital to appreciate how the function of different components of this unit change along the vascular tree. The cells of the neurovascular unit together perform an array of vital functions, protecting the brain from circulating toxins and infection, while providing nutrients and clearing away waste products. To do so, the brain's microvasculature dilates to direct energy substrates to active neurons, regulates access to circulating immune cells, and promotes angiogenesis in response to decreased blood supply, as well as pulsating to help clear waste products and maintain the oxygen supply. Different parts of the cerebrovascular tree contribute differently to various aspects of these functions, and previously, it has been assumed that there are discrete types of vessel along the vascular network that mediate different functions. Another option, however, is that the multiple transitions in function that occur across the vascular network do so at many locations, such that vascular function changes gradually, rather than in sharp steps between clearly distinct vessel types. Here, by reference to new data as well as by reviewing historical and recent literature, we argue that this latter scenario is likely the case and that vascular function gradually changes across the network without clear transition points between arteriole, precapillary arteriole and capillary. This is because classically localized functions are in fact performed by wide swathes of the vasculature, and different functional markers start and stop being expressed at different points along the vascular tree. Furthermore, vascular branch points show alterations in their mural cell morphology that suggest functional specializations irrespective of their position within the network. Together this work emphasizes the need for studies to consider where transitions of different functions occur, and the importance of defining these locations, in order to better understand the vascular network and how to target it to treat disease.

Lymphatic vessels interact dynamically with the hair follicle stem cell niche during skin regeneration in vivo

Lymphatic vessels are essential for skin fluid homeostasis and immune cell trafficking. Whether the lymphatic vasculature is associated with hair follicle regeneration is, however, unknown. Here, using steady and live imaging approaches in mouse skin, we show that lymphatic vessels distribute to the anterior permanent region of individual hair follicles, starting from development through all cycle stages and interconnecting neighboring follicles at the bulge level, in a stem cell-dependent manner. Lymphatic vessels further connect hair follicles in triads and dynamically flow across the skin. At the onset of the physiological stem cell activation, or upon pharmacological or genetic induction of hair follicle growth, lymphatic vessels transiently expand their caliber suggesting an increased tissue drainage capacity. Interestingly, the physiological caliber increase is associated with a distinct gene expression correlated with lymphatic vessel reorganization. Using mouse genetics, we show that lymphatic vessel depletion blocks hair follicle growth. Our findings point toward the lymphatic vasculature being important for hair follicle development, cycling, and organization, and define lymphatic vessels as stem cell niche components, coordinating connections at tissue-level, thus provide insight into their functional contribution to skin regeneration.

Simultaneous Blood Flow Measurement and Dermoscopy of Skin Lesions Using Dual-Mode Dermascope

Dermascopes are commonly utilized for the qualitative visual inspection of skin lesions. While automated image processing techniques and varied illumination strategies have been used to aid in structural analysis of lesions, robust quantification of functional information is largely unknown. To address this knowledge gap, we have developed a compact, handheld dermascope that enables real-time blood flow measurements of skin during conventional visual inspection. In-vitro characterization demonstrated that the dermascope is capable of quantifying changes in flow across a physiologically relevant range even when used in a handheld manner with clinic lighting and dermascope LEDs on. In a small pilot clinical study, we demonstrated the dermascope’s ability to detect flow differences between two distinct lesion types.

Plasmodium falciparum gametocyte transit through the cutaneous microvasculature: A new target for malaria transmission blocking vaccines?

Malaria remains one of the most significant infectious diseases worldwide. Concordant with scaled intervention efforts and the emphasis of elimination and eradication on the agenda of many malaria control programs, the development of a malaria vaccine that reduces transmission of the parasite from human host to mosquito vector has been incorporated as an important new strategic goal. Transmission of malaria from man to mosquito relies on gametocytes, highly specialized sexual-stage parasites, that once mature, circulate in the peripheral vasculature of the human host. The complex interplay between mature gametocytes, their uptake in the mosquito bloodmeal and forward maturation/fertilization events provide unique opportunities for intervention. Although recent advances have yielded greater understanding into the mechanisms that mediate sequestration of immature gametocytes in the human host, the spatial dynamics of circulating mature gametocytes in the cutaneous microvaculature remains far less defined, which is the focus of this review.

Toward reliable retrieval of functional information of papillary dermis using spatially resolved diffuse reflectance spectroscopy

Spatially resolved diffuse reflectance spectroscopy (SRDRS) has been employed to quantify tissue optical properties and its interrogation volume is majorly controlled by the source-to-detector separations (SDSs). To noninvasively quantify properties of dermis, a SRDRS setup that includes SDS shorter than 1 mm is required. It will be demonstrated in this study that Monte Carlo simulations employing the Henyey-Greenstein phase function cannot always precisely predict experimentally measured diffuse reflectance at such short SDSs, and we speculated this could be caused by the non-negligible backward light scattering at short SDSs that cannot be properly modeled by the Henyey-Greenstein phase function. To accurately recover the optical properties and functional information of dermis using SRDRS, we proposed the use of the modified two-layer (MTL) geometry. Monte Carlo simulations and phantom experiment results revealed that the MTL probing geometry was capable of faithfully recovering the optical properties of upper dermis. The capability of the MTL geometry in probing the upper dermis properties was further verified through a swine study, and it was found that the measurement results were reasonably linked to histological findings. Finally, the MTL probe was utilized to study psoriatic lesions. Our results showed that the MTL probe was sensitive to the physiological condition of tissue volumes within the papillary dermis and could be used in studying the physiology of psoriasis.

Angiogenesis and lymphangiogenesis in inflammatory skin disorders

Angiogenesis, the growth of new blood vessels from pre-existing vessels, occurs physiologically in wound healing, during inflammatory diseases, and in tumor growth. Lymphangiogenesis can be activated in inflammation and tumor metastasis. The family of vascular endothelial growth factors (VEGFs) and angiopoietins are essential for angiogenesis and lymphangiogenesis. The angiogenic process is tightly regulated by VEGFs, angiopoietins, and endogenous inhibitors. VEGFs and angiopoietins exert their effects by activating specific receptors present on blood and lymphatic endothelial cells. There is now compelling evidence that cells of innate and adaptive immunity (macrophages, mast cells, neutrophils, eosinophils, lymphocytes) are a major source of angiogenic and lymphangiogenic factors. Chronic inflammatory skin diseases such as psoriasis and atopic dermatitis are characterized by altered angiogenesis, lymphangiogenesis, or both. Also such acute inflammatory skin disorders as urticaria, ultraviolet B-induced damage, and angioedema are associated with changes in angiogenic factors. In systemic sclerosis there is a switch from proangiogenic to antiangiogenic factors that play a role in the defective vascular process of this disorder. As yet, there are no clinical trials showing that canonical VEGF/VEGF receptor-targeted strategies can modulate inflammatory skin diseases. Novel strategies targeting other angiogenic/lymphangiogenic pathways should also be investigated.

Quantitative comparison of angiogenesis and lymphangiogenesis in cutaneous lichen planus and psoriasis: immunohistochemical assessment

Recent experimental studies revealed that angiogenesis and lymphangiogenesis are closely related to chronic inflammation. The present study aims to evaluate quantitative changes of blood and lymphatic microcirculatory beds in cutaneous lichen planus (CLP) and psoriatic lesions using immunohistochemical analysis with antibodies to CD34, D2-40 and VEGF. Morphometric software was used to determine the area of blood and lymphatic vessels (BVA and LVA) and also the VEGF positive area. Statistical analysis of these parameters confirmed a significant enlargement of both the blood and lymphatic microcirculatory beds in psoriatic and CLP lesions. BVA in CLP lesions was increased by 56% however this augmentation was not as great as in psoriatic lesions where BVA was increased by 123%. Interestingly, LVA in psoriatic and CLP lesions was increased equally by 85%. The strongest VEGF expression was detected in psoriatic lesions, with lower, but still significant, overexpression in CLP lesions. VEGF-C was significantly increased in both psoriatic and CLP lesions in comparable level. Noticeably higher VEGF and VEGF-C expression was observed in the epidermis than in the dermis. Finally, our results indicate that the level of angiogenesis is considerably greater in psoriatic lesions than in CLP lesions, but the level of lymphangiogenesis is equal in both psoriatic and CLP lesions.

Inflammation and the blood microvascular system

Acute and chronic inflammation is associated with changes in microvascular form and function. At rest, endothelial cells maintain a nonthrombogenic, nonreactive surface at the interface between blood and tissue. However, on activation by proinflammatory mediators, the endothelium becomes a major participant in the generation of the inflammatory response. These functions of endothelium are modified by the other cell populations of the microvessel wall, namely pericytes, and smooth muscle cells. This article reviews recent advances in understanding the roles played by microvessels in inflammation.

Skin blood flow dynamics and its role in pressure ulcers

Pressure ulcers are a significant healthcare problem affecting the quality of life in wheelchair bounded or bed-ridden people and are a major cost to the healthcare system. Various assessment tools such as the Braden scale have been developed to quantify the risk level of pressure ulcers. These tools have provided an initial guideline on preventing pressure ulcers while additional assessments are needed to improve the outcomes of pressure ulcer prevention. Skin blood flow function that determines the ability of the skin in response to ischemic stress has been proposed to be a good indicator for identifying people at risk of pressure ulcers. Wavelet spectral and nonlinear complexity analyses have been performed to investigate the influences of the metabolic, neurogenic and myogenic activities on microvascular regulation in people with various pathological conditions. These findings have contributed to the understanding of the role of ischemia and viability on the development of pressure ulcers. The purpose of the present review is to provide an introduction of the basic concepts and approaches for the analysis of skin blood flow oscillations, and present an overview of the research results obtained so far. We hope this information may contribute to the development of better clinical guidelines for the prevention of pressure ulcers.

Segmental cherry angiomas associated with extragenital lichen sclerosus: a report of two cases

Cherry angiomas (Campbell de Morgan spots) are common acquired red skin papules composed of dilated capillary loops, usually of unknown aetiology. Extragenital lichen sclerosus (LS) presents as porcelain-white scaly atrophic lesions with or without genital involvement. We report two cases of segmental multiple cherry angiomas in association with extragenital LS. Two unrelated women, aged 46 and 66 years, presented with extragenital LS affecting their axillae and lower abdomen. During the examination, both patients were noted to have several hundred red skin papules in a segmental distribution, affecting the left thigh and flank of one woman, and the right abdomen and back of the other. Clinically and histologically, the papules were consistent with cherry angiomas. The striking segmental distribution of multiple cherry angiomas may be due to genetic mosaicism; however, segmental Fabry disease was excluded by sequence analysis of the α-galactosidase A gene. Any causal link between cherry angiomas and LS remains uncertain.

An important role of blood and lymphatic vessels in inflammation and allergy

Angiogenesis and lymphangiogenesis, the growth of new vessels from preexisting ones, have received increasing interest due to their role in tumor growth and metastatic spread. However, vascular remodeling, associated with vascular hyperpermeability, is also a key feature of many chronic inflammatory diseases including asthma, atopic dermatitis, psoriasis, and rheumatoid arthritis. The major drivers of angiogenesis and lymphangiogenesis are vascular endothelial growth factor- (VEGF-)A and VEGF-C, activating specific VEGF receptors on the lymphatic and blood vascular endothelium. Recent experimental studies found potent anti-inflammatory responses after targeted inhibition of activated blood vessels in models of chronic inflammatory diseases. Importantly, our recent results indicate that specific activation of lymphatic vessels reduces both acute and chronic skin inflammation. Thus, antiangiogenic and prolymphangiogenic therapies might represent a new approach to treat chronic inflammatory disorders, including those due to chronic allergic inflammation.

Claudin-5 controls intercellular barriers of human dermal microvascular but not human umbilical vein endothelial cells

OBJECTIVE

To assess the role claudin-5, an endothelial cell (EC) tight junction protein, plays in establishing basal permeability levels in humans by comparing claudin-5 expression levels in situ and analyzing junctional organization and function in 2 widely used models of cultured ECs, namely human dermal microvascular (HDM)ECs and human umbilical vein (HUV)ECs.

METHODS AND RESULTS

By immunofluorescence microscopy, ECs more highly express claudin-5 (but equivalently express vascular endothelial-cadherin) in human dermal capillaries versus postcapillary venules and in umbilical and coronary arteries versus veins, correlating with known segmental differences in tight junction frequencies and permeability barriers. Postconfluent cultured HDMECs express more claudin-5 (but equivalent vascular endothelial-cadherin) and show higher transendothelial electric resistance and lower macromolecular flux than similarly cultured HUVECs. HDMEC junctions are more complex by transmission electron microscopy and show more continuous claudin-5 immunofluorescence than HUVEC junctions. Calcium chelation or dominant negative vascular endothelial-cadherin overexpression decreases transendothelial electric resistance and disrupts junctions in HUVECs, but not in HDMECs. Claudin-5 overexpression in HUVECs fails to increase transendothelial electric resistance or claudin-5 continuity, whereas claudin-5 knockdown in HDMECs, but not in HUVECs, reduces transendothelial electric resistance and increases antibody accessibility to junctional proteins.

CONCLUSIONS

Claudin-5 expression and junctional organization control HDMEC and arteriolar-capillary paracellular barriers, whereas HUVEC and venular junctions use vascular endothelial-cadherin.

A special construction of subepidermal capillary loops in the hippopotamus (Hippopotamus amphibius)

Based on LM, TEM, and histochemical methods, the study describes the specific structure of subepidemal capillary loops in the integument of the hippopotamus (Hippopotamus amphibius). At 25- 60 µm, the diameter of the capillaries was more than twenty times larger than those found in other mammals, as was the diameter of the epidermal contact area of the hairpin turn, which had enlarged up to 200-400 µm(2). At about 13,400, the number of loops per cm(2) was three times higher than in the few other mammalian species measured to date. The remarkable sheath (thickness 2- 20 µm) of the capillary loops consists of a multitude of fine collagen IV fibres, which were in direct contact with the epidermal stratum (str.) basale, emphasizing an origin from the lamina fibroreticularis of the basement membrane. Additionally, the sheath contained many regions filled with free fatty acids. All observations confirmed the view that the walls of the subepidermal capillaries in the hippopotamus are adapted to withstand high blood pressure, permitting a high rate of blood vesselbased heat transfer from the periphery of the body. Until now this function is only known as an important thermoregulatory response in highly active mammals, e.g. dolphins. However, under hot climatic conditions but without strong exercise for cooling, such ability could be an effective and energy-saving procedure in semi-aquatic mammals.

The cutaneous vascular system in chronic skin inflammation

The blood and lymphatic vasculature have an important role in skin homeostasis. Angiogenesis and lymphangiogenesis-the growth of new vessels from existing ones-have received tremendous interest because of their role in promoting cancer spread. However, there is increasing evidence that both vessel types also have a major role in acute and chronic inflammatory disorders. Vessels change their phenotype during inflammation (vascular remodeling). In inflamed skin, vascular remodeling consists of a hyperpermeable, enlarged network of vessels with increased blood flow, and influx of inflammatory cells. During chronic inflammation, the activated endothelium expresses adhesion molecules, cytokines, and other molecules that lead to leukocyte rolling, attachment, and migration into the skin. Recent studies reveal that inhibition of blood vessel activation exerts potent anti-inflammatory properties. Thus, anti-angiogenic drugs might be used to treat inflammatory conditions. In particular, topical application of anti-angiogenic drugs might be ideally suited to circumvent the adverse effects of systemic therapy with angiogenesis inhibitors. Our recent results indicate that stimulation of lymphatic vessel growth and function unexpectedly represents a new approach for treating chronic inflammatory disorders.

Enhanced absorption of millimeter wave energy in murine subcutaneous blood vessels

The aim of the present study was to determine millimeter wave (MMW) absorption by blood vessels traversing the subcutaneous fat layer of murine skin. Most calculations were performed using the finite-difference time-domain (FDTD) technique. We used two types of models: (1) a rectangular block of multilayer tissue with blood vessels traversing the fat layer and (2) cylindrical models with circular and elliptical cross-sections simulating the real geometry of murine limbs. We found that the specific absorption rate (SAR) in blood vessels normally traversing the fat layer achieved its maximal value at the parallel orientation of the E-field to the vessel axis. At 42 GHz exposure, the maximal SAR in small blood vessels could be more than 30 times greater than that in the skin. The SAR increased with decreasing the blood vessel diameter and increasing the fat thickness. The SAR decreased with increasing the exposure frequency. When the cylindrical or elliptical models of murine limbs were exposed to plane MMW, the greatest absorption of MMW energy occurred in blood vessels located on the lateral areas of the limb model. At these areas the maximal SAR values were comparable with or were greater than the maximal SAR on the front surface of the skin. Enhanced absorption of MMW energy by blood vessels traversing the fat layer may play a primary role in initiating MMW effects on blood cells and vasodilatation of cutaneous blood vessels.

Hereditary haemorrhagic telangiectasia: pathophysiology, diagnosis and treatment

Hereditary haemorrhagic telangiectasia, inherited as an autosomal dominant trait, affects approximately 1 in 5000 people. The abnormal vascular structures in HHT result from mutations in genes (most commonly endoglin or ACVRL1) whose protein products influence TGF-ß superfamily signalling in vascular endothelial cells. The cellular mechanisms underlying the generation of HHT telangiectasia and arteriovenous malformations are being unravelled, with recent data focussing on a defective response to angiogenic stimuli in particular settings. For affected individuals, there is often substantial morbidity due to sustained and repeated haemorrhages from telangiectasia in the nose and gut. Particular haematological clinical challenges include the management of severe iron deficiency anaemia; handling the intricate balance of antiplatelet or anticoagulants for HHT patients in whom there are often compelling clinical reasons to use such agents; and evaluation of apparently attractive experimental therapies promoted in high profile publications when guidelines and reviews are quickly superseded. There is also a need for sound screening programmes for silent arteriovenous malformations. These occur commonly in the pulmonary, cerebral, and hepatic circulations, may haemorrhage, but predominantly result in more complex pathophysiology due to consequences of defective endothelium, or shunts that bypass specific capillary beds. This review will focus on the new evidence and concepts in this complex and fascinating condition, placing these in context for both clinicians and scientists, with a particular emphasis on haematological settings.

Chromophore concentrations, absorption and scattering properties of human skin in-vivo

Absorption and reduced scattering coefficients of in-vivo human skin provide critical information on non-invasive skin diagnoses for aesthetic and clinical purposes. To date, very few in-vivo skin optical properties have been reported. Previously, we reported absorption and scattering properties of in-vivo skin in the wavelength range from 650 to 1000 nm using the diffusing probe in the "modified two-layer geometry". In this study, we determine the spectra of skin optical properties continuously in the range from 500 to 1000 nm. It was found that the concentration of chromophores, such as oxy-hemoglobin, deoxy-hemoglobin, and melanin, calculated based on the absorption spectra of eighteen subjects at wavelengths above and below 600 nm were distinct because of the inherent difference in the interrogation region. The scattering power, which is related to the average scatterer's size, demonstrates a clear contrast between skin phototypes, skin sites, and wavelengths. We also applied venous occlusion on forearms and found that the concentrations of oxy- and deoxy-hemoglobin as assessed at wavelengths above and below 600 nm were different. Our results suggest that diffuse reflectance techniques with the visible and near infrared light sources can be employed to investigate the hemodynamics and optical properties of upper dermis and lower dermis.

Plasmodium sporozoite passage across the sinusoidal cell layer

Malaria sporozoites must cross at least two cell barriers to reach their initial site of replication in the mammalian host. After transmission into the skin by an infected mosquito, they migrate towards small dermal capillaries, traverse the vascular endothelial layer, and rapidly home to the liver. To infect hepatocytes, the parasites must cross the sinusoidal cell layer, composed of specialized highly fenestrated sinusoidal endothelia and Kupffer cells, the resident macrophages of the liver (Fig. 1). The exact route Plasmodium sporozoites take to hepatocytes has been subject of controversial discussions for many years. Recent cell biological, microscopic, and genetic approaches have considerably enhanced our understanding of the initial events leading to the establishment of a malaria infection in the liver.

Decoding rule from vasoconstrictor skin sympathetic nerve activity to nonglabrous skin blood flow in humans at normothermic rest

Although an importance of vasoconstrictor skin sympathetic nerve activity (SNA) in control of cutaneous circulation is widely recognized, the decoding rule that translate dynamic fluctuations of vasoconstrictor skin SNA into skin blood flow is not fully understood. In 10 male subjects who rested in supine position under normothermic condition, we measured skin blood flow index (by laser-Doppler flowmetry) at the dorsum pedis, and vasoconstrictor skin SNA (by microneurography) that was confirmed to innervate the same region as the flow index. We determined the transfer and coherence functions from the neural activity input to the flow and quantified the contribution and predictability from the input to output by system engineering technique. The results showed that in frequency-domain analysis, the transfer function from vasoconstrictor skin SNA to skin blood flow had low-pass filter characteristics with 3.6+/-0.1s of pure time delay. The coherence function was approximately 0.5 between 0.01 and 0.1Hz and less above 0.1Hz. In time-domain analysis, the predictability from the SNA to the skin blood flow was approximately 50%. These findings indicate that at normothermic rest, the decoding rule from vasoconstrictor skin SNA to skin blood flow of skin is characterized by low-pass filter with 3-4s of pure time delay, and that the vasoconstrictor skin SNA contributes to a half of fluctuation of skin blood flow in the condition. The incomplete dependence of skin blood flow on vasoconstrictor skin SNA may confirm nonneural mechanisms to control cutaneous circulation even at normothermic rest.

Color homogeneity and visual perception of age, health, and attractiveness of female facial skin

BACKGROUND

Evolutionary psychology suggests that skin signals aspects of mate value, yet only limited empirical evidence exists for this assertion.

OBJECTIVES

We sought to study the relationship between perception of skin condition and homogeneity of color/chromophore distribution.

METHODS

Cropped skin cheek images from 170 girls and women (11-76 years) were blind-rated for attractiveness, healthiness, youthfulness, and biological age by 353 participants. These skin images and corresponding melanin/hemoglobin concentration maps were analyzed objectively for homogeneity.

RESULTS

Homogeneity of unprocessed images correlated positively with perceived attractiveness, healthiness, and youthfulness (all r > 0.40; P < .001), but negatively with estimated age (r = -0.45; P < .001). Homogeneity of hemoglobin and melanin maps was positively correlated with that of unprocessed images (r = 0.92, 0.68; P < .001) and negatively correlated with estimated age (r = -0.32, -0.38; P < .001).

LIMITATIONS

Female skin only was studied.

CONCLUSIONS

Skin color homogeneity, driven by melanin and hemoglobin distribution, influences perception of age, attractiveness, health, and youth.

Perivascular cells in a skin graft are rapidly repopulated by host cells

Survival of grafted tissues is dependent upon revascularisation. This study investigated revascularisation in a murine skin graft model, using two methods. The first involved 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine (DiI) labelling of the wound bed, prior to replacing the skin graft, to allow tracking of host cells into the grafts. At time points between day 3 and day 14 post-surgery, DiI-labelled cells which had tracked into the grafts, were found to co-localise with CD31 positive endothelial cells and patent perfused vessels (fluorescein isothiocyanate (FITC)-dextran perfusion), to show possible association with the vasculature. To further differentiate between graft and host-derived cells, C57BL/6 wild-type grafts were placed on enhanced-green fluorescent protein (e-GFP) transgenic mouse hosts, and at set times post-grafting examined using confocal microscopy. Patent vessels were found at all depths of the graft by day 3. Host (DiI- or GFP-positive) cells were predominantly co-localised with graft vessels in grafts from day 3 onwards, with a similar morphology to control skin. Significantly more GFP labelled host cells were visualised in the superficial dermis at day 5 compared to day 3. Initial restoration of circulation appears to be due to linkage between existing graft and bed vessels, followed by an influx of host cells with a definite perivascular distribution. These findings have implications for skin autografts and tissue engineered skin substitutes.

Observations on the actual structural conditions in the stratum superficiale dermidis of porcine ear skin, with special reference to its use as model for human skin

The results obtained from the outer ear skin of female pigs (German Landrace) by light microscopy (LM), transmission electron microscopy (TEM), and cryo scanning electron microscopy (cryo SEM) methods, in particular relying on careful and artefact-free tissue processing, exhibited that the stratum superficiale dermidis of the auricle had a very homogeneous and compact construction, especially in one area (central dorsum auriculae). Based upon the important measurements made [average thickness of stratum superficiale dermidis: 94 (+/-16) microm, region A: 81 (+/-10); average thickness of collagen fibre bundles: 12 (+/-2) microm, region A: 13 (+/-0.5); average density of subepidermal capillaries: 3134 (+/-459) loops/cm2, region A: 3497 (+/-247)], this impression was confirmed by low standard deviations for all parameters, in comparison to marginal locations studied. The capillary system present was analysed by LM and TEM for specific structural features, whereby it generally compared to the microvasculature in human skin. Moreover, a regular pattern of diffusion-relevant punctiform contacts of the capillary loop apex with the epidermal basement membrane became obvious. Cryo SEM, particularly offering the advantages of dispensation of chemical fixation, dehydration and solvents during processing, highlighted delicate structures without shrinkage and without loss of soluble sample components. Thus rather real spatial conditions in the region of the epidermo-dermal junction and the upper dermis were visualized, whereby very regular arrangements of the structures present became obvious. This pertained also to a correct demonstration of all components of the epidermal basement membrane, in particular the lamina lucida. In addition, the water-based stable character of the entire stratum superficiale dermidis could be emphasized as a basic feature for controlled diffusion processes.

The role of anti-endothelial cell antibody-mediated microvascular injury in the evolution of pulmonary fibrosis in the setting of collagen vascular disease

We encountered 16 patients with connective tissue disease in whom pulmonary fibrosis developed. Routine light microscopic, ultrastructural, and direct immunofluorescent analyses were conducted, and circulating antibodies, including those of endothelial cell derivation, were assessed using indirect immuno-fluorescence and Western blot assays. Underlying diseases were dermatomyositis, scleroderma, mixed connective tissue disease, sclerodermatomyositis, Sjögren syndrome, rheumatoid arthritis, and anti-Ro-associated systemic lupus erythematosus. Antibodies to one or more Ro, RNP, Jo 1, OJ, and/or nucleolar antigens were seen in all cases and antiphospholipid antibodies in half. All biopsies revealed microvascular injury in concert with intraparenchymal fibrosis; in some cases, there were corroborative ultrastructural findings of microvascular injury. Patterns of fibroplasia represented nonspecific interstitial pneumonitis and usual interstitial pneumonitis. We noted IgG, IgA, and/or complement in the septal microvasculature. In 6 cases with available serum samples, indirect immunofluorescent endothelial cell antibody studies were positive and Western Blot studies showed reactivity of serum samples to numerous endothelial cell lysate-derived proteins. Pulmonary fibrosis, a recognized complication of systemic connective tissue disease, develops in connective tissue disease syndromes with pathogenetically established immune-based microvascular injury at other sites. A similar mechanism of antibody-mediated endothelial cell injury may be the basis of the tissue injury and fibrosing reparative response.

Cutaneous blood flow and sweat rate responses to exogenous administration of acetylcholine and methacholine

The aim of this study was to evaluate cutaneous vasodilation and sweating responses to exogenous administration of acetylcholine (ACh) and methacholine (MCh), which have different sensitivities to endogenous cholinesterase. Four intradermal microdialysis probes were placed in dorsal forearm skin: two sites were perfused with ACh (1 x 10(-7)-1 M) and the other two with the same molar concentrations of MCh. Sweat rate (SR) and cutaneous blood flow were simultaneously assessed directly over each microdialysis membrane. Dose-response curves were constructed, and the effective concentration of the drug resulting in 50% of the maximal response (EC(50)) was identified. For SR and cutaneous vascular conductance (CVC), there were no significant differences in EC(50) between sites receiving the same drug: -1.52 +/- 0.18 and -1.19 +/- 0.09 log-molar concentration of ACh at distal and proximal sites, respectively, and -2.35 +/- 0.24 and -2.42 +/- 0.23 log-molar concentration of MCh at distal and proximal sites, respectively, for SR (P > 0.05) and -3.87 +/- 0.32 and -3.97 +/- 0.27 log-molar concentration of ACh at distal and proximal sites, respectively, and -4.78 +/- 0.17 and -4.46 +/- 0.16 log-molar concentration of MCh at distal and proximal sites, respectively, for CVC (P > 0.05). However, the EC(50) for CVC and SR was significantly lower at the MCh than at the ACh sites. A second procedure was performed to confirm that differences in responses between ACh and MCh could be attributed to different cholinesterase sensitivities. Similarly, four microdialysis membranes were placed in dorsal forearm skin: two sites were perfused with ACh and other two with MCh. However, one of each of the ACh and MCh sites was also perfused with 10 microM neostigmine (an acetylcholinesterase inhibitor). Neostigmine at the ACh site induced a leftward shift (i.e., lower EC(50)) of the SR and CVC dose-response curves compared with the site treated with ACh alone, resulting in no difference in the EC(50) for SR and CVC between the ACh + neostigmine and the MCh site. These results suggest that elevations in SR and CVC occur earlier with MCh than with ACh treatment because of differences in cholinesterase susceptibility between these drugs.

Sternal erythema: A distinctive postsurgical eruption

BACKGROUND/OBJECTIVE

Wound complications constitute a diverse array of surgical and dermatologic entities. We sought to describe the clinical and pathologic attributes of a series of patients in whom a distinctive thoracic surgical wound eruption developed after coronary bypass grafting.

METHODS

We performed a detailed chart review, including history, surgical procedure notes, and biopsy findings, obtained from 3 patients; we examined the data and reconciled them with conventional etiologies in an attempt to discern a shared diagnosis and pathogenesis.

RESULTS

The patients were white men (59, 68, and 73 years of age) in whom roughly symmetrical asymptomatic erythema developed within the borders of their sternal thoracotomy wounds between 1 and 2 years after open heart surgery. The cutaneous findings consisted of macular erythema and poikiloderma that blanched with external pressure. Biopsy findings yielded epithelial atrophy with capillary telangiectases.

CONCLUSION

Although cellulitis, dermal hypersensitivity to surgically implanted hardware including sternal wire, and an anatomic variant of costal fringe remain as possible diagnoses, an additional consideration includes a form of postsurgical reflex sympathetic dystrophy.

The human choriocapillaris: evidence for an intrinsic regulation of the endothelium?

The aim of the present study was to describe the ultrastructure of particular cells observed in the microvascular bed of the healthy human choroid, in close relation to the wall of the microvessels and resembling the periadventitial cells of other vascular areas of the human body. Serial sections of 12 fresh human eyes were studied by transmission electron microscopy. In all the eyes, the sections were obtained by cutting from the same zones (inner and outer choroid at the posterior pole of the eye). Standard techniques were used for transmission electron microscopy. Round cell bodies were found in the inner choroid at the posterior pole of the eye, mainly located in the intercapillary connective tissue. The cells were composed of an electron-transparent cytoplasm containing a few small mitochondria, and a dilated smooth surface of endoplasmic reticulum, at some points continuous with the nuclear membrane. These cells showed processes forming contact with the capillary wall. Some of these processes extended to the elastic layer of Bruch's membrane, but none had contact with the retinal pigment epithelium. A thin basement membrane surrounded both the cell bodies and processes. We believe that these cells are special cells resembling some type of periendothelial cells also localized in other microvascular districts of the human body. The close topographic correlation with the endothelial cells seems to indicate that these special cells play a role in the intrinsic control of proper endothelial functions.

Treating vascular lesions

The treatment of acquired vascular lesions is one of the most commonly requested and performed cutaneous laser procedures. Furthermore, every year, 40,000 children are born in the United States each with congenital vascular lesions and malformations. Laser treatment of vascular lesion is based on the principle of selective photothermolysis, conceived in the 1980s. A variety of different lasers and light sources have since been used in the treatment of vascular lesions: lasers with wavelengths between green and yellow, near infrared lasers, and broadband light sources. Despite limitations, this remains the treatment of choice today. This publication addresses acquired and congenital vascular lesions as different entities and proposes a separation of vascular lesions into those that can easily be treated from those where clearance is difficult. Different treatment modalities and the various endpoints of individual vascular lesions will be discussed.

[Cutaneous oxygen supply. With special consideration of skin uptake of oxygen from the atmosphere]

Oxygen reaches the skin from the blood as well as from the atmosphere. The diffusion gradient is a key factor in oxygen delivery. Measurements with puncture electrodes show a maximum oxygen partial pressure on the skin surface and a minimum in the deeper dermis. Non-invasive measures show that oxygen uptake depends on location. Assuming the oxygen consumption is 0.276+/-0.029 ml O(2).100 g(-1).min(-1) (37 degrees) and no oxygen is removed by capillaries, then the skin can be supplied by atmospheric oxygen to a depth of 0.25 to 0.40 mm, well into the dermis. Only the deeper dermis receives oxygen from the blood. The stratum corneum is a significant barrier to diffusion from the atmosphere. When this barrier is damaged, the oxygen diffusion increases Keratinocytes in culture proliferate in response to increased oxygen pressure; the same mechanism may explain epidermal hyperplasia following stratum corneum damage in vivo.

Effects of nitric oxide synthase inhibitor on cochlear blood flow

We observed in rats the changes in cochlear blood flow (CoBF) and cutaneous blood flow of the abdominal wall (AbBF) after the administration of the NO synthase inhibitor, N-nitro-L-arginine-methyl ester (L-NAME). Ten minutes after i.v. infusion of L-NAME (0.2, 1, 5, 10 mg/kg), L-arginine, which is a substrate of NO, was infused (100 mg/kg) i.v. Employing a laser Doppler flowmeter, the changes in blood flow were recorded from the basal turn of the right cochlea or the abdominal wall and blood pressure (BP) was recorded from the left femoral artery simultaneously. Vascular conductance (VC) was calculated from CoBF/mean BP (cochlear VC) or AbBF/mean BP (abdominal VC). The findings in rats generally agreed with those in guinea pigs [Brechtelsbauer et al., Hear. Res. 77 (1994) 38-42]. Intravenous infusion of L-NAME produced a dose-dependent depression of cochlear VC at 0.2 mg/kg (-18.9), 1 mg/kg (-37.9%), 5 mg/kg (-45.8%) and 10 mg/kg (-48.3%). AbBF also decreased after infusion of L-NAME (5 mg/kg) but to a lesser degree (-41.1% in VC) with no significance compared to CoBF (5 mg/kg). Infusion of L-arginine partially reversed the CoBF decrease caused by L-NAME. The group of 0.2 mg/kg infusion of L-NAME showed the largest degree of recovery with L-arginine, while the 10 mg/kg group showed the smallest. The decrease in AbBF did not recover substantially with L-arginine, the degree being less than that of each group in the CoBF experiment. It was suggested that the NO/soluble guanylate cyclase/cGMP system is more active in the cochlear microcirculation. With the round window (RW) application of 1% L-NAME (2 microl), cochlear VC was decreased by 21.6%, which was closest to that of the 0.2 mg/kg group of L-NAME i.v. infusion. The cochlear VC depression after local application of L-NAME did not show any recovery (-0.3%) by RW application of 5% L-arginine (2 microl) 25 min after L-NAME application; a slight gradual increase was observed when a higher concentration (20%) of L-arginine was applied to the RW. We propose that i.v. infusions of L-NAME and L-arginine primarily affect the precapillary arteriole of the spiral modiolar artery which effectively regulates microcirculation as a resistance vessel, and that RW application affects the vessels of the lateral wall, not the spiral modiolar artery because of the difficulty of substance diffusion.

The cutaneous uptake of atmospheric oxygen contributes significantly to the oxygen supply of human dermis and epidermis

It has been known since 1851 that atmospheric oxygen is taken up by the human epidermis. The contribution to total respiration is negligible. Until now the significance for the local oxygen supply of the skin has remained unknown. With a newly developed sensor, the oxygen fluxoptode, it has become possible to make local measurements of the transcutaneous oxygen flux (tcJ(O2)). In this study the sensor was calibrated so that absolute values of tcJ(O2) could be reported. At rest, tcJ(O2) was determined on normal, humidified skin on the volar forearm of 20 volunteers of different age groups. In order to evaluate the contribution of the blood flow to the oxygen supply of the skin, tcJ(O2) was recorded at the end of a 5 min suprasystolic occlusion of the forearm. At normal skin surface partial oxygen pressure (163 +/- 9 Torr), tcJ(O2) was 0.53 +/- 0.27 ml O2 min(-1) x m(-2). A 5 min interruption of blood flow resulted in an increase of 9.5 +/- 6.3 % in tcJ(O2). The value of tcJ(O2) was unaffected by the age of the subject. Published data on the oxygen diffusion properties of skin and simulations of intracutaneous profiles of oxygen partial pressure indicated that under these conditions, the upper skin layers to a depth of of 0.25-0.40 mm are almost exclusively supplied by external oxygen, whereas the oxygen transport of the blood has a minor influence. As a consequence, a malfunction in capillary oxygen transport cannot be the initiator of the development of superficial skin defects such as those observed in chronic venous incompetence and peripheral arterial occlusive disease.

Structure, function, and molecular control of the skin lymphatic system

The mechanisms of angiogenesis have been studied extensively over the past years. The focus, however, has been almost exclusively on blood vessels, whereas little effort has been directed toward understanding lymphangiogenesis and the role of lymphatic vessels in physiology and pathology. The lymphatic system, acting in concert with the blood vascular system, is of fundamental importance in maintaining tissue homeostasis, and disorders of the lymphatic system are common, often resulting in chronic, disabling conditions. This overview summarizes the most important aspects of the structure and function of the lymphatic system with emphasis on the skin lymphatic vasculature and the differences between blood and lymphatic vessels. Special attention has been given to the methods employed in research of the lymphatic system. Finally, we describe molecular mechanisms involved in the regulation of lymphangiogenesis. Vascular endothelial growth factor and vascular endothelial growth factor-C, expressed by distinct skin cell populations, play an important role in the molecular control of skin angiogenesis and lymphangiogenesis.

The cutaneous microcirculation

The cutaneous microcirculation is organized as two horizontal plexuses. One is situated 1-1.5 mm below the skin surface and the other is at the dermal-subcutaneous junction. Ascending arterioles and descending venules are paired as they connect the two plexuses. From the upper layer, arterial capillaries rise to form the dermal papillary loops that represent the nutritive component of the skin circulation. There are sphincter-like smooth muscle cells at the point where the ascending arterioles divide to form the arteriolar component of the upper horizontal plexus. At the dermal-subcutaneous junction, there are collecting veins with two cusped valves that are oriented to prevent the retrograde flow of blood. Laser Doppler flowmetry has demonstrated vasomotion of red cell flux localized to the sites of ascending arterioles. The simultaneous recording by laser Doppler flowmetry of red cell flux and the concentration of moving red blood cells from individual sites allows one to construct topographic maps of these two values. These two maps, based on initial studies using correlative skin biopsies, can define 1 mm3 volumes of skin that are predominantly arteriolar in composition, venular in composition, or essentially devoid of all microvascular elements. The electron and light microscopic features that define the microvascular segments, when coupled with that ability of laser Doppler flowmetry to define the predominant microvascular segments under the probe, allow one to study both the mechanisms of normal physiologic states and the pathogenetic mechanisms underlying pathologic skin disorders in which the microvasculature plays a predominant role.

Time-sequence histologic imaging of laser-treated cherry angiomas with in vivo confocal microscopy

OBJECTIVE

To chronicle the pathophysiologic changes that occur subsequent to laser treatment of vascular lesions, we used a confocal scanning laser microscope that yields high-resolution microscopic images of skin in vivo.

METHODS

Cherry angiomas were treated with the 585-nm flashlamp-pumped pulsed-dye laser (PDL) and the 568-nm continuous-wave krypton laser. Repeated confocal reflectance imaging was performed before and immediately after treatment, as well as after several hours, 1 day, 2 days, 1 week, 2 weeks, 3 weeks, and 4 weeks.

RESULTS

Before treatment, confocal images revealed dilated blood vessels ranging from 10 to 50 microm in caliber, closely spaced at 5 to 50 microm apart. After PDL treatment, amorphous cords of refractile material conformed to the shape of the original vessels, followed by dark nonrefractile spaces where the vessels once were. Inflammation and necrosis ensued, with eventual replacement after 3 weeks by normal-appearing skin. After krypton laser treatment, dark nonrefractile spaces appeared immediately, with subsequent inflammation, necrosis, and eventual healing by 4 weeks.

CONCLUSION

Confocal laser microscopic imaging elucidates the dynamic pathophysiologic events that occur after laser treatment of vascular lesions and has added insight into the different mechanisms of vessel damage induced by the PDL and krypton laser.

Hypoxia potentiates ultraviolet A-induced riboflavin cytotoxicity

Flavins are thought to be important chromophores for chronic photo-induced skin injury, but the mechanism is not well known. We have reported that the primary cytotoxicity remaining in ultraviolet A-irradiated riboflavin solution is attributable to hydrogen peroxide. Because the dermis is more hypoxic than the atmosphere, we investigated the cytotoxicity of riboflavin solution during and after ultraviolet A irradiation under hypoxia. Riboflavin solution showed stronger cytotoxicity during irradiation under hypoxia than under air. Riboflavin solution that had been irradiated under hypoxia at lower ultraviolet A doses showed stronger cytotoxicity and contained more hydrogen peroxide than solution irradiated under air at the same doses. At higher ultraviolet A doses, however, the cytotoxicity and hydrogen peroxide quantity were similar in riboflavin solutions irradiated under different oxygen conditions. The effect of a singlet oxygen quencher, sodium azide, on the induction of cytotoxicity and production of hydrogen peroxide by ultraviolet A irradiation of riboflavin solution was examined. The presence of sodium azide in the solution during ultraviolet A irradiation suppressed the cytotoxicity and hydrogen peroxide production to similar levels at various ultraviolet A doses regardless of oxygen conditions. At the maximum suppression by sodium azide, hydrogen peroxide production decreased to 10% of the unsuppressed production. About 40% of the oxygen molecules of hydrogen peroxide produced was thought to be derived from oxygen dissolved in the riboflavin solution.

Tumor growth inhibition and regression induced by photothermal vascular targeting and angiogenesis inhibitor retinoic acid

The effect of photothermal vascular targeting, alone and in combination with antiangiogenic therapy, was evaluated using tumors produced in mice by transplantation of KB cells. Tumor growth inhibition and regression followed vascular damage produced by pulsed dye laser (PDL) radiation. Administration of the antiangiogenic agent all-trans-retinoic acid (RA) was associated with smaller average tumor volumes in the presence and absence of PDL irradiation, but this effect was not statistically significant. The ability of PDL photothermal vascular targeting to cause regression of tumors without harming normal tissue may be a consequence of preferential damage to supplying vessels at the tumor periphery.

Sensitivity of cross-reacting antihuman antibodies in formalin-fixed porcine skin: including antibodies to proliferation antigens and cytokeratins with specificity in the skin

Although no animal is a perfect skin model for the study of toxicological and therapeutic agents, structurally the pig may be superior to even non-human primates. Because our work involves effects of toxicological and therapeutic agents on the skin, we wanted to identify stains which may prove useful as well as determine cross-reactivity of some newer antihuman antibodies. We performed a battery of formalin-fixed skin from weanling pigs and minipigs. The battery of antibodies included LCA, CD3, OPD-4, CD34, UCHL-1, L-26, KP-1, MAC-387, Factor XIIIa, Leu-7, S-100 protein, HMB-45, GFAP, synaptophysin, neurofilament protein, ubiquitin, vimentin, type IV collagen, laminin, fibronectin, Factor VIII related antigen, Desmin-M, smooth muscle actin, cytokeratin 7, cytokeratin 20, AEI/AE3, CAM 5.2, EMA, GCDFP, Ki-67, and PCNA. Immunohistochemical stains for CD3, Leu-7, S-100 protein, type IV collagen, laminin, Factor VIII related antigen, GFAP, synaptophysin, neurofilament protein, ubiquitin, smooth muscle actin, vimentin, Desmin-M, cytokeratin 7, cytokeratin 20, AE1/AE3, CAM 5.2, Ki-67 and PCNA showed consistent cross-reactivity. In formalin-fixed tissue, only antibodies to lymphoreticular cells showed poor cross-reactivity. A high percentage of the remaining antibodies did show good cross-reactivity but with some interesting similarities and differences in specificity.

Physiological and pathological factors of human breast disease that can influence optical diagnosis

The 'normal' human female breast is a very complex organ that changes considerably during development, pregnancy and menopause. In addition, it is an excretory organ that, during lactation, discharges various metabolites and certain drugs that can be optically active. Optical diagnosis of breast cancers requires detection of differential concentrations of 1) various absorbers and scatterers or 2) native or exogenous fluorophores to distinguish cancers from surrounding 'normal' and benign breast tissues. The differential concentrations are due to the biology of the cancer cells and the host responses to the cancer growth. For most patients, the cancer will be intermixed with a complex 3-dimensional array of 'normal' breast tissue and benign breast lesions. This complexity will challenge the optical biopsy investigator but, with the recent advances in our understanding of light transport, optical diagnostic techniques and devices can be developed to complement and supplement current breast cancer screening techniques.

The structure and function of the cutaneous vasculature

The cutaneous vasculature is a dynamic network that responds to its environment depending upon specific demands in time and space. Changes in its functional role can be observed as changes in gross structure, or by alterations in specific gene expression or function. The improved understanding in mechanisms by which EC participate in inflammatory, neoplastic, and reparative processes will likely reap great benefits in our understanding and treatment of cutaneous disease.