Ultrastructure of the secretory epithelium, nerve fibers, and capillaries in the mouse sweat gland

Botulinum toxin A dissolving microneedles for hyperhidrosis treatment: design, formulation and in vivo evaluation

Multiple periodic injections of botulinum toxin A (BTX-A) are the standard treatment of hyperhidrosis which causes excessive sweating. However, BTX-A injections can create problems, including incorrect and painful injections, the risk of drug entry into the bloodstream, the need for medical expertise, and waste disposal problems. New drug delivery systems can substantially reduce these problems. Transdermal delivery is an effective alternative to conventional BTX-A injections. However, BTX-A's large molecular size and susceptibility to degradation complicate transdermal delivery. Dissolving microneedle patches (DMNPs) encapsulated with BTX-A (BTX-A/DMNPs) are a promising solution that can penetrate the dermis painlessly and provide localized translocation of BTX-A. In this study, using high-precision 3D laser lithography and subsequent molding, DMNPs were prepared based on a combination of biocompatible polyvinylpyrrolidone and hyaluronic acid polymers to deliver BTX-A with ultra-sharp needle tips of 1.5 ± 0.5 µm. Mechanical, morphological and histological assessments of the prepared DMNPs were performed to optimize their physicochemical properties. Furthermore, the BTX-A release and diffusion kinetics across the skin layers were investigated. A COMSOL simulation was conducted to study the diffusion process. The primary stability analysis reported significant stability for three months. Finally, the functionality of the BTX-A/DMNPs for the suppression of sweat glands was confirmed on the hyperhidrosis mouse footpad, which drastically reduced sweat gland activity. The results demonstrate that these engineered DMNPs can be an effective, painless, inexpensive alternative to hypodermic injections when treating hyperhidrosis.

Key factors to establish the ovalbumin-induced atopic dermatitis minipig model: age and body weight

Background

Given its similar structure and immune response to the human skin, porcine is a good model for dermal studies. Here, we sensitized ovalbumin (Ova) on minipig back skin for 2–4 weeks to induce chronic atopic dermatitis (AD).

Results

Gross observation, serum cytokine level, epidermal thickness, and epidermal integrity did not change after 4 weeks of Ova induction compared with the control, indicating AD modeling failure. Only the neutrophils in the blood and macrophages in bronchoalveolar lavage fluid changed slightly until 3 or 2 weeks after Ova sensitization, respectively. The successful and failed Ova-induced AD minipig models only differ in age and body weight of the minipigs. The minipigs, 12 months old with a 30-kg median weight, had a two-fold thicker dermis than minipigs 8–10 months old, with an 18.97-kg median weight, resulting in impaired Ova permeability and immune response.

Conclusion

Age and body weight are key factors that should be considered when developing an Ova-induced AD minipig model.

Supplementary Information

The online version contains supplementary material available at 10.1186/s42826-022-00141-4.

The evolution of eccrine sweat gland research towards developing a model for human sweat gland function

For several decades now, researchers, professional bodies, governments, and journals such as the journal of Experimental Dermatology have worked to reduce the number of animals used in experimentation. This review centres on investigations into how human sweat glands produce sweat and how that research has evolved over the years. It is hoped that this review will show that as methodologies advanced, sweat gland research has come to rely less and less on a variety of animal models as investigative tools and information is being primarily obtained through human and mouse material, with a view to further reductions in using animal models.

Ultrastructural and Immunohistochemical Study on the Lamina Propria Cells Beneath Paneth Cells in the Rat Ileum

Paneth cells secrete bactericidal substances in response to bacterial proliferation on the mucosal surface without directly contacting bacteria. However, the induction mechanism of this transient secretion has not been clarified, although nervous system and/or immunocompetent cells in the lamina propria (LP) might be involved. In this study, we ultrastructurally and immunohistochemically investigated which LP cells are localized beneath Paneth cells and examined the relationship between the Paneth cell-derived cellular processes which extended into the LP and the LP cells. The results showed that various cells-including blood capillary, subepithelial stromal cell, and nerve fiber-were present in the LP beneath Paneth cells. Endothelial cells of blood capillary were the cells most frequently found in this location; they were situated within 1 μm of the Paneth cells and possessed fenestration on the surfaces adjacent to Paneth cells. The Paneth cells rarely extended the cellular processes toward the LP across the basal lamina. Most of the cellular processes of Paneth cells contacted the subepithelial stromal cells. Immunohistochemistry revealed that the CD34⁺ CD31^- αSMA^- stromal cells preferentially localized in the LP beneath the intestinal crypt base, while PDGFRα^hi αSMA⁺ stromal cells mainly localized around the lateral portions of the intestinal crypt and PDGFRα^hi αSMA^- stromal cells localized in the intestinal villus. From these findings, the existence of blood capillaries beneath Paneth cells might reflect the active exocrine function of Paneth cells. Furthermore, subepithelial stromal cells, probably with a CD34⁺ CD31^- αSMA^- PDGFRα^-/lo phenotype, beneath the crypt base might affect Paneth cell activity by interacting with their cellular processes. Anat Rec, 301:1074-1085, 2018. © 2018 Wiley Periodicals, Inc.

Identification of the critical therapeutic entity in secreted Hsp90α that promotes wound healing in newly re-standardized healthy and diabetic pig models

Chronic and non-healing skin wounds represent a significant clinical, economic and social problem worldwide. Currently, there are few effective treatments. Lack of well-defined animal models to investigate wound healing mechanisms and furthermore to identify new and more effective therapeutic agents still remains a major challenge. Pig skin wound healing is close to humans. However, standardized pig wound healing models with demonstrated validity for testing new wound healing candidates are unavailable. Here we report a systematic evaluation and establishment of both acute and diabetic wound healing models in pigs, including wound-creating pattern for drug treatment versus control, measurements of diabetic parameters and the time for detecting delayed wound healing. We find that treatment and control wounds should be on the opposite and corresponding sides of a pig. We demonstrate a strong correlation between duration of diabetic conditions and the length of delay in wound closure. Using these new models, we narrow down the minimum therapeutic entity of secreted Hsp90α to a 27-amino acid peptide, called fragment-8 (F-8). In addition, results of histochemistry and immunohistochemistry analyses reveal more organized epidermis and dermis in Hsp90α-healed wounds than the control. Finally, Hsp90α uses a similar signaling mechanism to promote migration of isolated pig and human keratinocytes and dermal fibroblasts. This is the first report that shows standardized pig models for acute and diabetic wound healing studies and proves its usefulness with both an approved drug and a new therapeutic agent.

Development, structure, and keratin expression in C57BL/6J mouse eccrine glands

Eccrine sweat glands in the mouse are found only on the footpads and, when mature, resemble human eccrine glands. Eccrine gland anlagen were first apparent at 16.5 days postconception (DPC) in mouse embryos as small accumulations of cells in the mesenchymal tissue beneath the developing epidermis resembling hair follicle placodes. These cells extended into the dermis where significant cell organization, duct development, and evidence of the acrosyringium were observed in 6- to 7-postpartum day (PPD) mice. Mouse-specific keratin 1 (K1) and 10 (K10) expression was confined to the strata spinosum and granulosum. In 16.5 and 18.5 DPC embryos, K14 and K17 were both expressed in the stratum basale and diffusely in the gland anlagen. K5 expression closely mimicked K17 throughout gland development. K6 expression was not observed in the developing glands of the embryo but was apparent in the luminal cell layer of the duct by 6 to 7 PPD. By 21 PPD, the gland apertures appeared as depressions in the surface surrounded by cornified squames, and the footpad surface lacked the organized ridge and crease system seen in human fingers. These data serve as a valuable reference for investigators who use genetically engineered mice for skin research.

Sweat gland epithelial and myoepithelial cells are vitamin D targets

Nuclear receptor binding of 1,25(OH)(2)-vitamin D(3) (vitamin D) in skin keratinocytes of epidermis, hair sheaths and sebaceous glands was discovered through receptor microscopic autoradiography. Extended experiments with (3)H-1,25(OH)(2)-vitamin D(3) and its analog (3)H-oxacalcitriol (OCT) now demonstrate nuclear receptor binding in sweat gland epithelium of secretory coils and ducts as well as in myoepithelial cells, as studied in paws of nude mice after i.v. injection. The results suggest genomic regulation of cell proliferation and differentiation, as well as of secretory and excretory functions, indicating potential therapies for impaired secretion as in hypohidrosis of aged and diseased skin.

Cellular and tissue distribution of intravenously administered agalsidase alfa

alpha-Galactosidase A is the lysosomal hydrolase that is deficient in patients with Fabry disease. Intravenous infusion of agalsidase alfa, a preparation of alpha-Galactosidase A, is used for enzyme replacement therapy (ERT) in patients with Fabry disease. Although ERT appears to show some beneficial effects, most patients show only a modest response. We investigated using immunohistochemistry the relative tissue and cellular distribution of agalsidase alfa after a single intravenous injection in a mouse knockout model of Fabry disease. Specific immunostaining for agalsidase alfa was found only in liver, kidney, heart, testes, adrenal gland, spleen and bone marrow. There was no difference in distribution of the infused enzyme distribution among tissues sampled 4, 24, and 48h post-injection. The intracellular localization of immunopositivity varied considerably between organs with vascular endothelium being the most commonly positive site. alpha-Galactosidase A specific activity in tissue homogenates matched the relative extent of agalsidase alfa immunostaining distribution in the same organs. We conclude that intravenously injected agalsidase alfa has a very heterogeneous systemic distribution using an immunostaining technique.

Ultrastructural Analysis of the Integument of a Desert-Adapted Mammal, the One-Humped Camel (Camelus dromedarius)

In this study, we conducted a light microscopic and ultrastructural analysis of the integument of the one-humped camel (Camelus dromedarius). In general, the epidermal strata of the camel integument appeared typical of those found in non-desert mammals. Two cell populations were noted in the stratum basale: one with a flat, non-serrated base and the other with a highly serrated base. Typical fine structure was observed in keratinocytes of the stratum spinosum and stratum granulosum. The stratum corneum was six to 10 cells thick. Within the different strata, overall cell morphologies and the general distribution and relative abundance of cellular organelles appeared typical. Dermal features included the presence of myoepithelial cells surrounding apocrine tubular glands. Inter- or intracellular canaliculi within the secretory cells of the apocrine glands, reported to be present in certain other non-desert mammals, were not evident in the camel. Together, these data indicate that while the camel is clearly adapted for a desert lifestyle, these adaptations do not include significant specializations at the cellular or subcellular level in the integument.

Quantification of the response of equine apocrine sweat glands to beta2-adrenergic stimulation

The aim of the present study was to characterise the quantitative sweating response of the horse to beta2-adrenergic stimulation. The sweating responses of 6 horses to the randomised infusion of 8 different adrenaline concentrations (0.025, 0.05, 0.075, 0.1, 0.2, 0.4, 1.0 or 2.0 microg/kg bwt/min), was investigated. Sweating rate (SR) and skin temperature (TSK) on the neck (N) and gluteal region (G), and plasma adrenaline and noradrenaline concentrations were measured. Peak SR was approximately 15 (N) and approximately 9 g/m2/min (G) during infusion of both 1.0 and 2.0 microg/kg bwt/min adrenaline. Sweat produced per nmol/l plasma adrenaline peaked during the infusion of 0.075 microg/kg bwt/min adrenaline. Higher adrenaline infusion concentrations resulted in a progressive decrease in the amount of sweat produced per nmol/l plasma adrenaline and a plateau of 6 g/m2/(nmol/l) plasma adrenaline was reached for infusions between 1.0 and 2.0 microg/kg bwt/min. Peak SR were far lower than we have previously reported during exercise. There was no evidence of sweat gland fatigue or vasoconstriction during infusion, suggesting saturation of sweat gland beta2 receptors. We conclude that sweating in the horse is under dual control from a combination of hormonal and neural mechanisms.

Catecholamines are required for the acquisition of secretory responsiveness by sweat glands

The sympathetic innervation of sweat glands undergoes a developmental change in transmitter phenotype from catecholaminergic to cholinergic. Acetylcholine elicits sweating and is necessary for development and maintenance of secretory responsiveness, the ability of glands to produce sweat after nerve stimulation or agonist administration. To determine whether catecholamines play a role in the development or function of this system, we examined the onset of secretory responsiveness in two transgenic mouse lines, one albino and the other pigmented, that lack tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine synthesis. Although both lines lack TH, their catecholamine levels differ because tyrosinase in pigmented mice serves as an alternative source for catecholamine synthesis (Rios et al., 1999). At postnatal day 21 (P21), 28 glands on average are active in interdigital hind footpads of albino TH wild-type mice. In contrast, fewer than one gland is active in albino TH null mice, which lack catecholamines in gland innervation. Treatment of albino TH null mice with DOPA, a catecholamine precursor, from P11 to P21 increases the number of active glands to 14. Pigmented TH null mice, which have faint catecholamine fluorescence in the developing gland innervation, possess 12 active glands at P21, indicating that catecholamines made via tyrosinase, albeit reduced from wild-type levels, support development of responsiveness. Gland formation and the appearance of cholinergic markers occur normally in albino TH null mice, suggesting that catecholamines act directly on gland cells to trigger their final differentiation and to induce responsiveness. Thus, catecholamines, like acetylcholine, are essential for the development of secretory responsiveness.

Development of muscarinic receptors and regulation of secretory responsiveness in rodent sweat glands

Sweat glands are innervated by sympathetic neurons which undergo a change in transmitter phenotype from noradrenergic to cholinergic during development. As soon as the glands begin to differentiate, M3 muscarinic receptor mRNA and binding sites are detectable. Receptor expression appears in the absence of innervation and is maintained after denervation. While receptor expression is not regulated by innervation, secretory responsiveness is. Muscarinic blockade during development or in adult animals results in the loss of responsiveness and its reappearance requires several days. Cholinergic muscarinic activation is most likely to regulate one or more steps in the signalling cascade that are downstream of calcium mobilization. The anterograde regulation of sweat gland responsiveness is one facet of the reciprocal interactions are required to establish a functional synapse in this system.

Time evolution of the number of functional murine eccrine sweat glands after irradiation: a quantitative analysis of experimental data using a model of proliferative and functional organization

The function of eccrine sweat glands in the beta-pad of the mouse foot after irradiation was followed over time. Graded doses of X-rays were given to the foot, either as single doses or in two equal fractions separated by a 24-h interval. A quantitative, non-invasive, functional assay was used allowing repeated evaluation of the animals. Sweat gland function was assessed once a week for the first 6 weeks, and at 8, 10, 14, 18, 28, 38 and 45 weeks after irradiation. The beta-pad of the unirradiated foot was used as a control. The function dropped to a nadir within 8-10 weeks after irradiation, whereafter it gradually recovered, reaching a stable level 20-25 weeks after irradiation. These data were analyzed using a mathematical model of proliferative and functional organization of the sweat pore. The model provides a description of the time evolution of pore function, and its basic features were as follows. The functional subunit is a single sweat pore, which will be assayed as functional provided that it contains a number of functional cells above a critical threshold. The functional cells are capable of self renewal (a so-called 'flexible' tissue), and the proportion of proliferating cells is subject to homeostatic control. Irradiation is assumed to transfer a certain fraction of the cells into a state with a limited probability of successful division. This fraction is assumed to have a linear-quadratic dependence on dose. The values of all free model parameters were optimized by a maximum-likelihood fit to the experimental data. With optimized parameter values, the initial decrease, nadir, and long-term level of tissue function estimated from the model were in close agreement with the experimental observations for all the 28 dose groups. Some of the estimated model parameters are: growth fraction 4.2 +/- 0.2%; cell cycle time, 0.95 +/- 0.04 days; number of functional cells in a single pore in the unirradiated animal, 9.9 +/- 0.5; and alpha/beta ratio, 4.3 Gy (95% confidence interval 3.1-5.0 Gy). It is concluded that the present model, despite its relative mathematical simplicity, provides a close description of the postirradiation kinetics of functional cells in the mouse sweat gland.

Innervation of footpads of normal and mutant mice lacking sweat glands

Footpads of normal adult mice are innervated by sympathetic and sensory fibers. The sympathetic fibers associated with sweat glands contain acetylcholinesterase and immunoreactivity for vasoactive intestinal peptide. Although catecholamine histofluorescence is absent, the gland innervation exhibits immunoreactivity for tyrosine hydroxylase. A distinct population of sympathetic fibers, which possess catecholamines and neuropeptide Y as well as tyrosinehydroxylase immunoreactivity, innervates blood vessels. Sensory fibers containing immunoreactivity for substance P and calcitonin gene-related peptide course beneath the epidermis and some form endings in it. Treatment of neonatal mice with the adrenergic neurotoxin, 6-hydroxydopamine, results in loss of sympathetic innervation of sweat glands and blood vessels, permits growth of sensory axons into sweat glands, but does not alter the peptidergic sensory innervation of the dermis and epidermis. Three mouse mutations, Tabby (Ta), crinkled (cr), and downless (dl), disrupt the interactions between the mesenchyme and epidermis that are required for normal development of specific epidermal derivatives, including sweat glands. The sympathetic innervation of blood vessels and sensory innervation of footpad skin of the three mutant mice that lack sweat glands is indistinguishable from normal. The sympathetic fibers that normally innervate sweat glands, however, are not present. These results indicate that in the absence of their normal target, the sympathetic fibers that innervate sweat glands are lacking. Furthermore, they suggest that, although sensory fibers may sprout into sympathetic targets in the footpad, the domains occupied by sensory fibers are not normally accessible to sympathetic axons.

Harderian gland ultrastructure of the black sea bottlenose dolphin (Tursiops truncatus ponticus)

Examination of the Harderian gland structure of the Black Sea bottlenose dolphin, Tursiops truncatus ponticus, at macroscopic, microscopic, and electron microscopic levels shows significant sexual dimorphism. The epithelial cells of male and female glands are different cell types, capable of producing chemically different products. Secretory cells in both sexes contain secretion granules that produce a secretion consisting mainly of proteins and carbohydrates, but thought to be sex-specific in composition. The female glands also contain lipid secretion granules. It is suggested that in the bottlenose dolphin the Harderian gland functions to produce sexually distinct pheromones and may have other physiological activities, e.g., participating in local immunological or endocrine-related reactions.

Nerve remodelling during intestinal inflammation

The intestinal mucosa contains a dense nerve network and many inflammatory cells, and these may interact through the exchange of regulatory molecules. Evidence suggests that intestinal mucosal mast cells are innervated, and it is known that the density of this cell type changes significantly in nematode-infected rats. Recent data indicates that rat jejunal mucosal nerves remodel after Nippostrongylus brasiliensis infection, with degenerative and regenerative phases during the acute and recovery stages of inflammation. Seven weeks postinfection there is a net increase in the density and number per villus of mucosal nerves. These changes suggest that mucosal nerves exhibit structural plasticity in inflamed tissues, which must impact on interactions between the enteric nervous system and other mucosal elements in disease.

Characterization of a target-derived neuronal cholinergic differentiation factor

The sympathetic innervation of rat sweat glands undergoes a target-induced switch from a noradrenergic to a cholinergic and peptidergic phenotype during development. Treatment of cultured sympathetic neurons with sweat gland extracts mimics many of the changes seen in vivo. Extracts induce choline acetyltransferase activity and vasoactive intestinal peptide expression in the neurons in a dose-dependent fashion while reducing catecholaminergic properties and neuropeptide Y. The cholinergic differentiation activity appears in developing glands of postnatal day 5 rats and is maintained in adult glands. It is a heat-labile, trypsin-sensitive, acidic protein that does not bind to heparin-agarose. Immunoprecipitation experiments with an antiserum directed against an N-terminal peptide of a cholinergic differentiation factor (CDF/LIF) from heart cells suggest that the sweat gland differentiation factor is not CDF/LIF. The sweat gland activity is a likely candidate for mediating the target-directed change in sympathetic neurotransmitter function observed in vivo.

Destruction by anti-NGF of autonomic, sudomotor neurones and subsequent hyperinnervation of the foot pad by sensory fibres

Treatment of newborn rats with antiserum to nerve growth factor (NGF) for the first 6 postnatal days produced a loss of the sympathetic neurones that normally project to the sweat glands of the hind paws of the rat, indicating that cholinergic sympathetic neurones require NGF postnatally for their survival. Following this immunosympathectomy, there was an increase in the proportion of glands containing sensory fibres having substance-P-like immunoreactivity (SP-LI). This sensory sprouting was not as extensive as that after sympathectomy using 6-hydroxydopamine (6-OHDA). During normal development, fibres showing SP-LI are associated with the glands, particularly during the first and second postnatal weeks. Prolongation of the antibody treatment until the third postnatal week reduced the sensory fibre ingrowth from the region of the glands, suggesting that the basis of this growth is the increased availability of NGF following sympathetic denervation. Retrograde cell labelling using the fluorescent dye, fast blue, indicated that the anti-NGF treatment did not significantly decrease the number of sensory neurones projecting to an individual foot pad. These results support the hypothesis that sympathetic and sensory neurones compete for NGF produced by target tissues.