The potential and benefits of nanoparticles in nanobiotechnology have been enthusiastically discussed in recent literature; however, little is known about the potential risks of contamination by accidental contact during production or use. Although theories of transdermal drug delivery suggest that skin structure and composition do not allow the penetration of materials larger than 600 Da, some articles on particle penetration into the skin have been recently published. Consequently, we wanted to evaluate whether metallic nanoparticles smaller than 10 nm could penetrate and eventually permeate the skin. Two different stabilized nanoparticle dispersions were applied to excised human skin samples using vertical diffusion cells. At established time points, solutions in receiving chambers were quantified for nanoparticle concentration, and skin was processed for light transmission and electron microscope examination. The results of this study showed that nanoparticles were able to penetrate the hair follicle and stratum corneum (SC), occasionally reaching the viable epidermis. Yet, nanoparticles were unable to permeate the skin. These results represent a breakthrough in skin penetration because it is early evidence where rigid nanoparticles have been shown to passively reach the viable epidermis through the SC lipidic matrix.

The nature of chemical defenses in poison frogs has been explored in a variety of species, and most studies focus on the types of chemical defenses and their sources. The defensive compounds of frogs are stored in dermal granular glands that have been described for several species that are chemically protected from predators and/or microorganisms. Gland ultrastructure is known for some species of dendrobatoid frogs, but the relationship between body size and chemical defense has heretofore not been explored. It might be expected that the capacity for defensive protection increases as a function of body size, especially given the fact that juvenile poison frogs are known to have smaller quantities of alkaloids than adults. We examined poison glands histologically in a sample of the poison frog Oophaga pumilio to determine if the physical basis of the defensive system changes as a function of body size. We measured average gland size, estimated the number of glands, and calculated the density and percentage of skin area occupied by glands in a patch of dorsal skin for 25 individuals. For males and females, the size, number and percentage of skin area occupied by poison glands increased allometrically as a function of body size, whereas poison gland density decreased with body size. Adults have a larger capacity to store alkaloids and more of their dorsal skin is associated with poison glands as compared with juveniles, which may translate into greater protection from predators in adults and could explain why adults are more apparent (active above the leaf litter) than juveniles at our study site in north-eastern Costa Rica. Furthermore, juveniles and subadults may benefit from automimicry because they resemble adults in appearance.

The results indicate that diabetes affects submandibular gland structure even when glandular function appears unaltered and suggest that morphological changes reflect functional changes chiefly regarding the secretory activity.

The preferential sites of melatonin reactivity were the granules and vesicles of serous cells. Our results suggested that the acinar cells are able to store melatonin and that the hormone can be released into saliva through granule and vesicle exocytosis. The quantitative evaluation of labelling showed that the parotid gland is the most involved in the release of melatonin in saliva.

The hormone melatonin influences oral health through a variety of actions, such as anti-inflammatory, antioxidant, immunomodulatory and antitumour. Many of these melatonin functions are mediated by a family of membrane receptors expressed in the oral epithelium and salivary glands. Using immunoblotting and immunohistochemistry, recent studies have shown that the melatonin membrane receptors, MT1 and MT2, are present in rat and human salivary glands. To date, no investigation has dealt with the ultrastructural distribution of the melatonin receptors. This was the aim of the present study, using the immunogold method applied to the human parotid gland. Reactivity to MT1 and, with less intensity, to MT2 appeared in the secretory granules of acinar cells and in the cytoplasmic vesicles of both acinar and ductal cells. Plasma membranes were also stained, albeit slightly. The peculiar intracytoplasmic distribution of these receptors may indicate that there is an uptake/transport system for melatonin from the circulation into the saliva.

Salivary secretion is principally regulated by autonomic nerves. However, recent evidence from in vivo animal experiments suggests that gastrointestinal peptide hormones can also influence saliva production. The aim of the present study was to define the secretagogue activity of the gastrin-analogue pentagastrin in human salivary glands. For this purpose, parotid tissues were exposed to pentagastrin in vitro. Morphological techniques were used to evaluate modifications to serous acinar cells associated with secretion. Using a variant of the osmium maceration method, high resolution scanning electron microscopy allowed assessment of the morphology of the cytoplasmic aspect of the plasmalemma to demonstrate secretory activity. To quantify responses to pentagastrin, we recorded morphometric data on microvilli, microbuds, and protrusions. Dose-dependent morphological changes were observed, whereas protein concentration increased in the incubate. The use of selective receptor antagonists showed pentagastrin to act principally via cholecystokinin-A receptors. The morphological responses observed following exposure to pentagastrin differed from those elicited following exposure to the pan-muscarinic agonist carbachol. This study provides the first demonstration of a direct secretory action of gastrointestinal peptides on salivary glands in humans.

Oral Diseases (2011) 17, 217–220 Background and Objectives:  Statherin is a salivary protein involved in the formation of enamel pellicle and in regulation of calcium homeostasis. Diabetes and other pathologies affect both salivary flow and protein secretion by salivary glands, causing increased susceptibility to mucosal infections, tooth demineralization, and caries. The purpose of this study was to compare the statherin expression in submandibular glands of healthy and diabetic subjects. Materials and Methods:  Fragments of submandibular glands obtained from diabetic and non diabetic patients were fixed, dehydrated, embedded in Epon Resin and processed for the immunogold histochemistry. The results were statistically evaluated. Results:  Specific statherin labeling was demonstrated in secretory granules of acinar cells in both diabetic and normal samples. The staining was much more intense in the latter compared to those of diabetics. The labeling density was quantified by evaluating the number and spatial distribution of gold particles within the granules. The number of gold particles was significantly lower in glands from diabetics than in control glands. Conclusions:  The results obtained suggest that a reduced statherin secretion by salivary glands might be partly responsible for a less effective protection of the oral tissues, resulting in an higher incidence of caries and oral infections associated with diabetes.

Recently we reported on the detailed localization of melatonin (and its receptors) in human salivary glands, revealing that serous cells are able to store and secrete melatonin into saliva. Since we found that type 2 diabetic patients display reduced melatonin content in saliva, our next step was to examine the presence of melatonin in salivary glands removed from type 2 diabetic subjects. The resulting data were compared with those previously obtained by identical procedures in non-diabetics, to establish if the diabetic status may affect melatonin distribution. Bioptic samples of diabetic parotid and submandibular glands were fixed, dehydrated, embedded in Epon Resin and processed to demonstrate melatonin reactivity by the immunogold staining method. The labeling density (expressed as the number of gold particles per μm /granule) and the percentage of melatonin-positive granules were assessed in diabetic samples. These values were compared with those in non-diabetic samples and differences were evaluated. In parotid and submandibular diabetic glands the reactivity for melatonin was specifically associated with secretory granules and small vesicles in serous cells. Melatonin reactivity was higher in parotid than in submandibular glands. Our data were in line with those obtained in our previous study on non-diabetic glands. Diabetic salivary glands showed a higher labeling density and a lower number of melatonin-positive granules compared to non-diabetic glands. Taken together, these data might explain the decreased salivary melatonin content and the associated oral problems observed in diabetics. Anat Rec, 301:711-716, 2018. © 2017 Wiley Periodicals, Inc.