Skin epidermal thickness and vascular density in type 1 diabetes

Engineering transferrable microvascular meshes for subcutaneous islet transplantation

The success of engineered cell or tissue implants is dependent on vascular regeneration to meet adequate metabolic requirements. However, development of a broadly applicable strategy for stable and functional vascularization has remained challenging. We report here highly organized and resilient microvascular meshes fabricated through a controllable anchored self-assembly method. The microvascular meshes are scalable to centimeters, almost free of defects and transferrable to diverse substrates, ready for transplantation. They promote formation of functional blood vessels, with a density as high as ~220 vessels mm-2, in the poorly vascularized subcutaneous space of SCID-Beige mice. We further demonstrate the feasibility of fabricating microvascular meshes from human induced pluripotent stem cell-derived endothelial cells, opening a way to engineer patient-specific microvasculature. As a proof-of-concept for type 1 diabetes treatment, we combine microvascular meshes and subcutaneously transplanted rat islets and achieve correction of chemically induced diabetes in SCID-Beige mice for 3 months.

Reference values for skin microanatomy: A systematic review and meta-analysis of ex vivo studies

BACKGROUND

Few studies have characterized reference values of normal human skin microanatomy parameters.

OBJECTIVE

To quantify histologic measurements of epidermal thickness, melanocyte density, hair follicle density, and eccrine gland density as a function of age and anatomic site.

METHOD

We searched the PubMed, Embase, Web of Science, and Cochrane databases for articles published through May 25, 2017. Two reviewers independently screened 2016 articles; 327 relevant articles and 151 additional articles found via forward or reference citations underwent full-text review by 1 of 4 reviewers for relevance, data extraction, and critical appraisal. Weighted averages, meta-analysis, and meta-regression were used in statistical analysis.

RESULTS

A total of 56 articles were included; when all anatomic locations were used, the overall estimates for epidermal thickness, melanocyte density, hair follicle density, and eccrine gland density were 99.75 μm (95% confidence interval [CI], 83.25-116.25), 955.05 cells/mm² (95% CI. 880.89-1029.21), 1.40 hairs/mm² (95% CI. 0.91-1.89), and 1.28 glands/mm² (95% CI. 0.91-1.64), respectively.

LIMITATIONS

There was significant data heterogeneity across studies, possibly because of differences in histological techniques and absence of standardized microanatomy definitions.

CONCLUSIONS

We established summary estimates for normal human skin microanatomy parameters.

Poorer glycaemic control is associated with increased skin thickness at injection sites in children with type 1 diabetes

We aimed to assess the association between skin thickness and glycaemic control in children with type 1 diabetes. Forty-five children (51% males) aged 10.5 ± 2.1 years were studied. Thickness of skin layers were determined by ultrasonography, with participants having ultrasound scans of three anatomical regions (abdomen, thigh, and buttocks). Poorer glycaemic control (increasing HbA1c values) was associated with greater thickness of the dermis (p = 0.015), with an estimated thickening of 87 μm with every 1% increase in HbA1c. Our data suggest that dermal changes associated with poorer glycaemic control in adults are also observed in childhood.

Microvascular dysfunction in the context of diabetic neuropathy

Microvascular dysfunction in diabetes plays a crucial role in the development of diabetic complications. The skin, as one of the most accessible organs, serves as a model for the investigation of microvascular dysfunction. Several non-invasive, mostly laser-Doppler-based methods have been developed lately to assess microvascular function in the skin. Microvascular functional changes occur even in the prediabetic state and become more complex with overt diabetes, being exacerbated by the presence of peripheral and/or autonomic diabetic neuropathy. The present article aims at shedding light on the implication of endothelial and neurovascular dysfunction in microvascular changes in diabetes, highlighting the contribution of different forms of diabetic neuropathy.

Neurovascular factors in wound healing in the foot skin of type 2 diabetic subjects

OBJECTIVE

Delayed wound healing in diabetic patients without large-vessel disease has been attributed to microvascular dysfunction, neuropathy, and abnormal cellular and inflammatory responses. The role of these abnormalities has mainly been examined in animal models. Few studies have been undertaken in diabetic patients, and those that have are limited due to analysis in wounds from chronic ulcers. In this study, we quantified the rate of wound healing in relation to skin neurovascular function and structure following a dorsal foot skin biopsy in type 2 diabetes.

RESEARCH DESIGN AND METHODS

Twelve healthy control subjects and 12 type 2 diabetic subjects with neuropathy but without macrovascular disease were studied. We quantified rate of wound healing and related it to skin microvascular function (laser Doppler imager [LDI](max)), blood vessel density, small nerve fiber function (LDI(flare)) and nerve fiber density, vascular endothelial growth factor (VEGF) and its receptor (FLK1), and hypoxia-inducible factor (HIF)-1alpha expression.

RESULTS

The rate of wound closure was identical between control subjects and diabetic patients despite a significant reduction in maximum hyperemia (LDI(max)), epidermal and dermal VEGF-A, and epidermal and dermal blood vessel VEGFR-2 expression as well as the neurogenic flare response (LDI(flare)) and dermal nerve fiber density. There was no significant difference in HIF-1alpha and dermal blood vessel density between control subjects and diabetic patients.

CONCLUSIONS

In conclusion, the results of this study suggest that wound closure in subjects with type 2 diabetes is not delayed despite significant alterations in neurovascular function and structure.

Noise contribution to the correlation between temperature-induced localized reflectance of diabetic skin and blood glucose

We used the effect of temperature on the localized reflectance of human skin to assess the role of noise sources on the correlation between temperature-induced fractional change in optical density of human skin (DeltaOD(T)) and blood glucose concentration [BG]. Two temperature-controlled optical probes at 30 degrees C contacted the skin, one was then cooled by -10 degrees C; the other was heated by +10 degrees C. DeltaOD(T) upon cooling or heating was correlated with capillary [BG] of diabetic volunteers over a period of three days. Calibration models in the first two days were used to predict [BG] in the third day. We examined the conditions where the correlation coefficient (R2) for predicting [BG] in a third day ranked higher than R2 values resulting from fitting permutations of randomized [BG] to the same DeltaOD(T) values. It was possible to establish a four-term linear regression correlation between DeltaOD(T) upon cooling and [BG] with a correlation coefficient higher than that of an established noise threshold in diabetic patients that were mostly females with less than 20 years of diabetes duration. The ability to predict [BG] values with a correlation coefficient above biological and body-interface noise varied between the cases of cooling and heating.

Diabetic neuropathy and microcirculation

The microcirculation in diabetic and neuropathic feet is subject to the same changes found in other end organs of diabetic patients, such as the retina or the kidney. Complications such as foot ulceration lead to further morbidity and hospitalizations. Research into the causes of microcirculatory dysfunction has revealed an interplay of numerous factors. The most prominent findings are impaired endothelium-dependent and -independent vasodilation and reduced or absent nerve-axon reflex-related vasodilation. This renders the diabetic foot unable to mount a vasodilatory response under conditions of stress, such as injury, and makes it functionally ischemic even in the presence of satisfactory blood flow under normal conditions.

Dermatome setting for autografts to cover INTEGRA

Using the INTEGRA Dermal Regeneration Template requires the outer silastic layer to be replaced with an autograft. We followed the manufacturer's directions for epidermal autografting and frequently obtained shredded, useless grafts, therefore, it seemed important to determine the proper dermatome setting. We evaluated dermatome settings from 0.002 to 0.012 inches. First, with feeler gauges, we verified the dermatome settings. Second, we harvested skin at various dermatome settings and measured the thickness histologically. We found that 1) the dermatome settings are reasonably accurate; 2) harvesting useful sheets at 0.002 and 0.004 inches is virtually impossible; 3) the variability of histologic graft thickness is enormous; and 4) a dermatome setting of 0.006 inches yields useful grafts. We no longer use the term epidermal autografting but rather ultrathin split-thickness grafting. To harvest these grafts, we now merely set the dermatome to 0.006 inches and make whatever midcourse corrections are necessary to obtain translucent grafts.

Blood extraction from lancet wounds using vacuum combined with skin stretching

Key factors and practical limits of blood extraction from lancet wounds on body sites other than the finger were determined by testing a large number of conditions. During these tests, the pain associated with lancing alternate body sites was rated as less painful than a fingerstick 98% of the time. Vacuum combined with skin stretching was effective in extracting an adequate volume of blood from the forearm for glucose testing, up to an average of 16 microl in 30 s. The amount of blood extracted increases with the application of heat or vacuum before lancing, the level of vacuum, the depth of lancing, the time of collection, and the amount of skin stretching. Vacuum and skin stretching led to significant increases, up to fivefold in the perfusion of blood in the skin as measured by laser Doppler. Our observations suggest that vacuum combined with skin stretching increases blood extraction at alternate sites by increasing the lancet wound opening, increasing the blood available for extraction by vasodilatation, and reducing the venous return of blood through capillaries.

Vacuum-assisted lancing of the forearm: an effective and less painful approach to blood glucose monitoring

A vacuum-lancet device was applied to the forearm for the purpose of obtaining capillary blood samples for glucose monitoring with minimal pain. In four clinical trials, a total of 215 individuals aged 12-77 years were tested four times using standard conditions and four times with either a different depth of lancing, different brand of lancet or a larger-sized device. The volume of blood collected using one-half atmosphere of vacuum in 40 sec was measured. The sensation and visual appearance of each lancet puncture on the forearm was recorded. Glucose was measured in forearm and in conventional fingerstick blood samples. The distribution of volumes was skewed to higher values with median values for each trial in the range of 3-10 microL. Ninety-five percent of the lancet sticks were judged as less painful than a fingerstick. Redness and bruising around the lanced sites were noted in some patients but disappeared within a few days. Overall correlation of the forearm versus fingerstick glucose values was 0.96. The vacuum-lancet device was very successful in obtaining capillary blood samples for glucose testing in a relatively painless manner. Incorporation of a glucose measuring system into the device might improve testing compliance among those who fear pain or the sight of blood.

Alpha-particle dosimetry for the basal layer of the skin and the radon progeny 218-Po and 214-Po

The population average dose to the basal layer of the skin is evaluated, in terms of dose per alpha-particle decay per unit area, for radon progeny 218-Po and 214-Po attached to the skin surface. Account is taken of the variation in basal layer depth between different individuals, and results are presented for several anatomical regions. On the face, for example, the population average dose to the basal layer from 218-Po is of the order of 0.5 microSv/decay/cm2 while that from 214-Po is of the order of 1 microSv/decay/cm2. Radiation induced stochastic effects in the skin are generally assumed to originate from target cells located in the basal layer. Provided this assumption is correct, these results suggest that both 218-Po and 214-Po could be regarded as potential carcinogenic agents for the induction of skin cancer.

Association between "diabetic thick skin syndrome" and neurological disorders in diabetes mellitus

Skin thickness on the extremities of patients with diabetes mellitus has been described controversially. Using high resolution ultrasonography, we were able to show a significant increase in skin thickness at the forearm (P < 0.05), thigh (P < 0.001) and lower limb (P < 0.05) of diabetic patients, most prominent at the thigh. No difference in skin thickness was found at the dorsum of the foot. In addition, skin thickness was not related to the duration of diabetes, age or HbA1. A close association was found between diabetic neuropathy and increasing skin thickness. Diabetic patients with neurological disorders had a significant increase in skin thickness versus diabetic patients without neuropathy. The present findings suggest that diabetic neuropathy and abnormalities of connective tissue have a common etiological link in their development or that both are time-dependent processes. Whether changes in capillary blood flow, increase of nonenzymatic glycosylation, polyol accumulation or other metabolic disorders are responsible for these findings remains still to be established.