Activation of transient receptor potential vanilloid subtype 1 increases secretion of the hypofunctional, transplanted submandibular gland

Salivary Gland Transplantation as a Promising Approach for Tear Film Restoration in Severe Dry Eye Disease

With increased awareness of dry eye disease (DED), a multitude of therapeutic options have become available. Nevertheless, the treatment of severe DED remains difficult. In a patient whose DED is related to the loss of lacrimal function without severe destruction of the salivary glands, autologous transplantation of the latter as functioning exocrine tissue to rebuild a stable tear film is an attractive idea. All three major and minor salivary glands have been used for such transplantation. Due to the complications associated with and unfavorable prognosis of parotid duct and sublingual gland transplantation, surgeons now prefer to use the submandibular gland (SMG) for such procedures. The transplantation of the SMG not only has a high survival rate, but also improves dry eye symptoms and signs for more than 20 years post-surgery. The regulation of the secretion of the transplanted SMG is critical because the denervated SMG changes its mechanism of secretion. Innovative procedures have been developed to stimulate secretion in order to prevent the obstruction of the Wharton's duct and to decrease secretion when postoperative "epiphora" occurs. Among the minor salivary glands, the transplantation of the labial salivary glands is the most successful in the long-term. The measurement of the flow rates of minor salivary glands and donor-site selection are critical steps before surgery.

The role and mechanism of tight junctions in the regulation of salivary gland secretion

Tight junctions (TJs) are cell-cell interactions that localize at the most apical portion of epithelial/endothelial cells. One of the predominant functions of TJs is to regulate material transport through paracellular pathway, which serves as a selective barrier. In recent years, the expression and function of TJs in salivary glands has attracted great interest. The characteristics of multiple salivary gland TJ proteins have been identified. During salivation, the activation of muscarinic acetylcholine receptor and transient receptor potential vanilloid subtype 1, as well as other stimuli, promote the opening of acinar TJs by inducing internalization of TJs, thereby contributing to increased paracellular permeability. Besides, endothelial TJs are also redistributed with leakage of blood vessels in cholinergic-stimulated submandibular glands. Furthermore, under pathological conditions, such as Sjögren's syndrome, diabetes mellitus, immunoglobulin G4-related sialadenitis, and autotransplantation, the integrity and barrier function of TJ complex are impaired and may contribute to hyposalivation. Moreover, in submandibular glands of Sjögren's syndrome mouse model and patients, the endothelial barrier is disrupted and involved in hyposecretion and lymphocytic infiltration. These findings enrich our understanding of the secretory mechanisms that link the importance of epithelial and endothelial TJ functions to salivation under both physiological and pathophysiological conditions.

The Utility of Capsicum annuum L. in Internal Medicine and In Dentistry: A Comprehensive Review

Capsaicin is a chili peppers extract, genus Capsicum, commonly used as a food spice. Since ancient times, Capsaicin has been used as a "homeopathic remedy" for treating a wild range of pathological conditions but without any scientific knowledge about its action. Several studies have demonstrated its potentiality in cardiovascular, nephrological, nutritional, and other medical fields. Capsaicin exerts its actions thanks to the bond with transient receptor potential vanilloid subtype 1 (TRPV1). TRPV1 is a nociceptive receptor, and its activation starts with a neurosensitive impulse, responsible for a burning pain sensation. However, constant local application of Capsaicin desensitized neuronal cells and leads to relief from neuropathic pain. In this review, we analyze the potential adjuvant role of Capsaicin in the treatment of different pathological conditions either in internal medicine or dentistry. Moreover, we present our experience in five patients affected by oro-facial pain consequent to post-traumatic trigeminal neuropathy, not responsive to any remedy, and successfully treated with topical application of Capsaicin. The topical application of Capsaicin is safe, effective, and quite tolerated by patients. For these reasons, in addition to the already-proven beneficial actions in the internal field, it represents a promising method for the treatment of neuropathic oral diseases.

Pivotal role of Transient Receptor Potential Channels in oral physiology

BACKGROUND

Transient Receptor Potential (TRP) Channels constitute a large family of non-selective permeable ion channels involved in the perception of environmental stimuli with a central and continuously expanding role in oral tissue homeostasis. Recent studies indicate the regulatory role of TRPs in pulp physiology, oral mucosa sensation, dental pain nociception and salivary gland secretion. This review provides an update on the diverse functions of TRP channels in the physiology of oral cavity, with emphasis on their cellular location, the underlying molecular mechanisms and clinical significance.

METHODS

A structured search of bibliographic databases (PubMed and MEDLINE) was performed for peer reviewed studies on TRP channels function on oral cavity physiology the last ten years. A qualitative content analysis was performed in screened papers and a critical discussion of main findings is provided.

RESULTS

TRPs expression has been detected in major cell types of the oral cavity, including odontoblasts, periodontal ligament, oral epithelial, salivary gland cells, and chondrocytes of temporomandibular joints, where they mediate signal perception and transduction of mechanical, thermal, and osmotic stimuli. They contribute to pulp physiology through dentin formation, mineralization, and periodontal ligament formation along with alveolar bone remodeling in dental pulp and periodontal ligament cells. TRPs are also involved in oral mucosa sensation, dental pain nociception, saliva secretion, swallowing reflex and temporomandibular joints' development.

CONCLUSION

Various TRP channels regulate oral cavity homeostasis, playing an important role in the transduction of external stimuli to intracellular signals in a cell type-specific manner and presenting promising drug targets for the development of pharmacological strategies to manage oral diseases.

Phytocompounds modulating Aquaporins: Clinical benefits are anticipated

A series of plant-derived bioactive compounds belonging to the class of polyphenols, terpenes and capsaicinoids, interact with important pathophysiological pathways at a molecular, cellular and systemic level. Mechanisms of action include altering cell growth and differentiation, apoptosis, autophagy, inflammation, redox balance and metabolic and energy homeostasis. These effects might also involve the expression and function of Aquaporins (AQPs), a family of membrane channel proteins, involved in several body functions. The ultimate translational beneficial effect of such phytocompounds on AQPs in health and disease is a matter of intensive research. Results might provide novel therapeutic approaches to a number of human diseases. Here, we give an updated overview of this fast growing and promising field, discussing a number of phytocompounds and their action on AQPs and related potential clinical achievements.

Aquaporins as Targets of Dietary Bioactive Phytocompounds

Plant-derived bioactive compounds have protective role for plants but may also modulate several physiological processes of plant consumers. In the last years, a wide spectrum of phytochemicals have been found to be beneficial to health interacting with molecular signaling pathways underlying critical functions such as cell growth and differentiation, apoptosis, autophagy, inflammation, redox balance, cell volume regulation, metabolic homeostasis, and energy balance. Hence, a large number of biologically active phytocompounds of foods have been isolated, characterized, and eventually modified representing a natural source of novel molecules to prevent, delay or cure several human diseases. Aquaporins (AQPs), a family of membrane channel proteins involved in many body functions, are emerging among the targets of bioactive phytochemicals in imparting their beneficial actions. Here, we provide a comprehensive review of this fast growing topic focusing especially on what it is known on the modulatory effects played by several edible plant and herbal compounds on AQPs, both in health and disease. Phytochemical modulation of AQP expression may provide new medical treatment options to improve the prognosis of several diseases.

Aquaporin Membrane Channels in Oxidative Stress, Cell Signaling, and Aging: Recent Advances and Research Trends

Reactive oxygen species (ROS) are produced as a result of aerobic metabolism and as by-products through numerous physiological and biochemical processes. While ROS-dependent modifications are fundamental in transducing intracellular signals controlling pleiotropic functions, imbalanced ROS can cause oxidative damage, eventually leading to many chronic diseases. Moreover, increased ROS and reduced nitric oxide (NO) bioavailability are main key factors in dysfunctions underlying aging, frailty, hypertension, and atherosclerosis. Extensive investigation aims to elucidate the beneficial effects of ROS and NO, providing novel insights into the current medical treatment of oxidative stress-related diseases of high epidemiological impact. This review focuses on emerging topics encompassing the functional involvement of aquaporin channel proteins (AQPs) and membrane transport systems, also allowing permeation of NO and hydrogen peroxide, a major ROS, in oxidative stress physiology and pathophysiology. The most recent advances regarding the modulation exerted by food phytocompounds with antioxidant action on AQPs are also reviewed.

Muscarinic acetylcholine receptor-mediated tight junction opening is involved in epiphora in late phase of submandibular gland transplantation

Submandibular gland (SMG) autotransplantation is an effective therapy for treating severe dry eye syndrome. However, epiphora occurs in more than 40% of patients 6 months after operation. We previously found that muscarinic acetylcholine receptor (mAChR) plays a crucial role in regulating SMG secretion partially through the modulation on tight junction (TJ)-based paracellular pathway. Therefore, the present study aimed to investigate the possible involvement of mAChR and TJ in a rabbit long-term model of SMG transplantation. We found that SMG secretion was significantly increased on postoperative days 90 and 180, which imitated epiphora observed in the patients with SMG transplantation. Although the mRNA expression and fluorescence intensity of M1 and M3 mAChR subtypes were reversed to control levels on postoperative days 30, 90, and 180, the content of β-arrestin2, but not β-arrestin1, was gradually decreased after transplantation, which suggests that mAChR may be hypersensitive in late phase of SMG transplantation. The width of acinar TJs was enlarged and fluorescence intensity of F-actin in peri-apicolateral membranes were remarkably increased on postoperative days 90 and 180. Topical treatment with atropine gel significantly reduced SMG secretion, TJ width, as well as F-actin intensity in peri-apicolateral membranes on postoperative days 180. Moreover, in a perfused rabbit SMG, carbachol increased salivary secretion, enlarged TJ width, and induced F-actin rearrangement, whereas these responses were inhibited by atropine pretreatment. Taken together, our findings suggest that the hypersensitive mAChR may contribute to epiphora in late phase of SMG transplantation through modulating TJ-based paracellular permeability.

An Experimental Study on Botulinum Toxin Type A for the Treatment of Excessive Secretion after Submandibular Gland Transplantation in Rabbits

Objectives. To investigate whether botulinum toxin type A (BTXA) could control excessive secretion after submandibular gland (SMG) transplantation in rabbits and its possible mechanisms. Methods. A new SMG transplantation model was established in rabbit. 30 successfully constructed models were randomly assigned to five groups including control group and four experimental groups. Secretion outputs were used to analyze the effect of BTXA injection on excessive secretion. Hematoxylin and eosin (HE) staining, transmission electron microscopy (TEM), Western blot, and immunofluorescence were performed to analyze its possible mechanisms. Results. After BTXA injection, a significant decrease of excessive secretion after SMG transplantation was found in 2 and 4 weeks groups, but no significant effect on 12 and 24 weeks groups. HE and TEM results showed that BTXA led to morphological and ultrastructural changes of acinar cells of transplanted SMG. Western blot results suggested that BTXA decreased the aquaporin-5 (AQP5) protein expression after BTXA injection for 2 and 4 weeks. Immunofluorescence results showed that AQP5 protein was mainly expressed in the cytoplasm after BTXA injection for 2 and 4 weeks, which might indicate that BTXA promoted AQP5 expression from the cell membrane to cytoplasm. Conclusion. BTXA could effectively control excessive secretion after SMG transplantation in rabbits.

The Effect of Capsaicin on Salivary Gland Dysfunction

Capsaicin (trans-8-methyl-N-vanilyl-6-nonenamide) is a unique alkaloid isolated from hot chili peppers of the capsicum family. Capsaicin is an agonist of transient receptor potential vanilloid subtype 1 (TRPV1), which is expressed in nociceptive sensory neurons and a range of secretory epithelia, including salivary glands. Capsaicin has analgesic and anti-inflammatory properties in sensory neurons. Recently, increasing evidence has indicated that capsaicin also affects saliva secretion and inflammation in salivary glands. Applying capsaicin increases salivary secretion in human and animal models. Capsaicin appears to increase salivation mainly by modulating the paracellular pathway in salivary glands. Capsaicin activates TRPV1, which modulates the permeability of tight junctions (TJ) by regulating the expression and function of putative intercellular adhesion molecules in an ERK (extracelluar signal-regulated kinase) -dependent manner. Capsaicin also improved dysfunction in transplanted salivary glands. Aside from the secretory effects of capsaicin, it has anti-inflammatory effects in salivary glands. The anti-inflammatory effect of capsaicin is, however, not mediated by TRPV1, but by inhibition of the NF-κB pathway. In conclusion, capsaicin might be a potential drug for alleviating dry mouth symptoms and inflammation of salivary glands.

Effects of Capsaicin and Carbachol on Secretion From Transplanted Submandibular Glands and Prevention of Duct Obstruction

PURPOSE

To investigate whether capsaicin and carbachol promote secretion from and prevent duct obstruction in transplanted submandibular glands (SMGs).

METHODS

This retrospective cohort study included consecutive patients with severe keratoconjunctivitis sicca and successful SMG transplantation. Patients were divided into 2 groups: an exposed group receiving both capsaicin and carbachol after surgery and an unexposed group receiving neither. Secretion changes in response to capsaicin and carbachol administration were recorded in the exposed group. The main outcome measures were the secretory flow rate and duct obstruction rate in the transplanted SMGs.

RESULTS

Forty-four patients (44 eyes) in the unexposed group and 115 patients (128 eyes) in the exposed group were followed up for more than 3 months postoperatively. The baseline characteristics were similar between the groups. The secretory flow rate before and 5, 25, 55 minutes after administration was 1 mm (0-2 mm) (median with interquartile range), 3 mm (1-5 mm), 4 mm (2-5 mm), 1 mm (0-2.5 mm), respectively, for capsaicin and 1 mm (0-3 mm), 1050 mm (450-1500 mm), 375 mm (150-600 mm), 0 mm (0-150 mm), respectively, for carbachol (P < 0.001 for both). In the exposed group, 6.2% of eyes had duct obstruction, whereas 18.2% of eyes in the unexposed group had duct obstruction (P = 0.031) (odds ratio = 0.3, 95% confidence interval, 0.105-0.856).

CONCLUSIONS

This study provides evidence that capsaicin and carbachol effectively promote secretion from and prevent duct obstruction in transplanted SMGs during at least 3 months after transplantation.

Microvascular autologous submandibular gland transplantation in severe cases of keratoconjunctivitis sicca

Dry eye syndrome is a relatively common disease of the tears and ocular surfaces that results in discomfort, visual disturbance, and tear film instability with possible damage to the ocular surfaces. Microvascular submandibular gland (SMG) transfer offers a surgical alternative for a permanent autologous substitution of tears using the basal secretion of a transplanted SMG. Long-term follow-up reveals that this technique is a lasting and effective solution for patients with severe dry eye syndrome. The uncomfortable symptoms were relieved, and the frequency of use of pharmaceutical tear substitutes was reduced. Objective examination showed significant improvement in tear film and some features of ocular surface such as breakup time of tear film and corneal staining. Patients may suffer from obstruction of Wharton's duct or epiphora after surgery. Activation of secretion-related receptors could improve the early hypofunction of the denervated SMG and prevent the duct obstruction. Reduction surgery, partial SMG transplantation, uses of atropine gel or Botulinum toxin A could be the choices of treatment for epiphora.

A simple test for salivary gland function measuring resting and stimulated submandibular and sublingual secretions

OBJECTIVE

This study examined the application of a simple screening test for salivary gland function by measuring resting and stimulated submandibular and sublingual secretions.

STUDY DESIGN

An assay system was designed to use filter paper incorporating the chromophore of melanoidin or stimuli such as capsaicin and citric acid. We investigated the relationship between resting and stimulated secretions and melanoidin migration at 2 minutes for healthy and dry mouth groups.

RESULTS

The healthy group showed a significant increase in the migration of melanoidin in the paper after citric acid or capsaicin stimulation. In contrast, patients with Sjögren syndrome showed no significant migration in spite of the stimulation. However, some participants with Sjögren syndrome or dry mouth showed a significant increase in the migration of melanoidin after stimulation.

CONCLUSIONS

These results show that the newly developed method should be useful for evaluation of residual salivary gland function and screening for hyposalivation with dry mouth.

Effects of protease-activated receptors (PARs) on intracellular calcium dynamics of acinar cells in rat lacrimal glands

Protease-activated receptors (PARs) represent a novel class of seven transmembrane domain G-protein coupled receptors, which are activated by proteolytic cleavage. PARs are present in a variety of cells and have been prominently implicated in the regulation of a number of vital functions. Here, lacrimal gland acinar cell responses to PAR activation were examined, with special reference to intracellular Ca(2+) concentration ([Ca(2+)]i) dynamics. In the present study, detection of acinar cell mRNA specific to known PAR subtypes was determined by reverse transcriptase polymerase chain reaction. Only PAR2 mRNA was detected in acinar cells of lacrimal glands. Both trypsin and a PAR2-activating peptide (PAR2-AP), SLIGRL-NH2, induced an increase in [Ca(2+)]i in acinar cells. The removal of extracellular Ca(2+) and the use of Ca(2+) channel blockers did not inhibit PAR2-AP-induced [Ca(2+)]i increases. Furthermore, U73122 and xestospongin C failed to inhibit PAR2-induced increases in [Ca(2+)]i. The origin of the calcium influx observed after activated PAR2-induced Ca(2+) release from intracellular Ca(2+) stores was also evaluated. The NO donor, GEA 3162, mimicked the effects of PAR2 in activating non-capacitative calcium entry (NCCE). However, both calyculin A (100 nM) and a low concentration of Gd(3+) (5 μM) did not completely block the PAR2-AP-induced increase in [Ca(2+)]i. These findings indicated that PAR2 activation resulted primarily in Ca(2+) mobilization from intracellular Ca(2+) stores and that PAR2-mediated [Ca(2+)]i changes were mainly independent of IP3. RT-PCR indicated that TRPC 1, 3 and 6, which play a role in CCE and NCCE, are expressed in acinar cells. We suggest that PAR2-AP differentially regulates both NCCE and CCE, predominantly NCCE. Finally, our results suggested that PAR2 may function as a key receptor in calcium-related cell homeostasis under pathophysiological conditions such as tissue injury or inflammation.

TRPV4 activation in mouse submandibular gland modulates Ca2+ influx and salivation

Transient receptor potential vanilloid subtype 4 (TRPV4) is a ligand-gated nonselective cation channel that participates in the transduction of mechanical and osmotic stimuli in different tissues. TRPV4 is activated by endogenous arachidonic acid metabolites, 4α-phorbol-12,13 didecanoate, GSK1016790A, moderate heat, and mechanical stress. TRPV4 is expressed in the salivary glands, but its expression pattern and function are poorly understood. The aim of this study was to evaluate the functional role of TRPV4 channels in the mouse submandibular gland. Using RT-PCR and Western blot analysis, we detected expression of TRPV4 message and protein, respectively, in the submandibular gland. Immunolocalization studies showed that TRPV4 targeted to the basolateral membrane of mouse submandibular gland acinar cells. Pharmacological TRPV4 activation using the selective agonist GSK1016790A caused Ca(2+) influx in isolated acinar cells in a basal-to-apical wave. Consistent with these observations, GSK1016790A elicited salivation in the perfused submandibular gland that was dependent on extracellular Ca(2+). In summary, we report that activation of TRPV4 channels induced Ca(2+) influx and salivation and, thus, may contribute a novel nonadrenergic, noncholinergic secretion pathway in the mouse submandibular gland.

Activation of transient receptor potential vanilloid subtype 1 increases expression and permeability of tight junction in normal and hyposecretory submandibular gland

Tight junction (TJ) is an important structure that regulates material transport through the paracellular pathway across the epithelium, but its significance in salivary physiology and pathogenesis of salivary dysfunctional diseases is not fully understood. We previously demonstrated that a functional transient receptor potential vanilloid subtype 1 (TRPV1) expresses in submandibular gland (SMG). However, association of TRPV1-induced saliva secretion with TJ remains unknown. Here we explored the effect of TRPV1 activation on expression and function of TJ of rabbit SMG in vitro and in vivo. RT-PCR and western blot analysis revealed that capsaicin upregulated expression of zonula occludin-1 (ZO-1), claudin (Cldn)-3, and -11, but not Cldn-1, -2, -4, -5, and -7 in cultured SMG cells. Capsaicin also increased the entering of 4 kDa FITC-dextran into the acinar lumen, induced redistribution of cytoskeleton F-actin under confocal microscope, and these effects were abolished by preincubation of capsazepine, a TRPV1 antagonist, indicating that activation of TRPV1 increases expression and permeability of TJ in SMG. Additionally, in a hyposecretory model induced by rabbit SMG transplantation, the expression of ZO-1, Cldn-3, and -11 was decreased, whereas other TJs remained unaltered. The structure of TJ was impaired and the width of apical TJs was reduced under transmission electron microscope, concomitant with diminished immunofluorescence of F-actin in peri-apicolateral region, indicating impaired TJ expression and decreased paracellular permeability in the transplanted SMG. Moreover, topical capsaicin cream increased secretion, decreased TJ structural injury, reversed TJ expression levels, and protected F-actin morphology from disarrangement in transplanted SMGs. These data provide the first evidence to demonstrate that TJ components, particularly ZO-1, Cldn-3, and -11 have important roles in secretion of SMG under both physiological and pathophysiological conditions. The injury in TJ integrity was involved in the hypofunctional SMGs, and TRPV1 might be a potential target to improve saliva secretion through modulating expression and function of TJs.

Expression of TRPV1 in rabbits and consuming hot pepper affects its body weight

The capsaicin receptor, known as transient receptor potential vanilloid subfamily member 1 (TRPV1), is an important membrane receptor that has been implicated in obesity, diabetes, metabolic syndrome and cardiovascular diseases. The rabbit model is considered excellent for studying cardiovascular and metabolic diseases, however, the tissue expression of TRPV1 and physiological functions of its ligand capsaicin on diet-induced obesity have not been fully defined in this model. In the current study, we investigated the tissue expression of TRPV1 in normal rabbits using real-time RT-PCR and Western blot analysis. Rabbit TRPV1 mRNA was highly expressed in a variety of organs, including the kidneys, adrenal gland, spleen and brain. A phylogenetic analysis showed that the amino acid sequence of rabbit TRPV1 was closer to human TRPV1 than rodent TRPV1. To examine the effect of capsaicin (a pungent compound in hot pepper) on body weight, rabbits were fed with either a high fat diet (as control) or high fat diet containing 1% hot pepper. We found that the body weight of the hot pepper-fed rabbits was significantly lower than the control group. We conclude that the intake of capsaicin can prevent diet-induced obesity and rabbit model is useful for the study of TRPV1 function in cardiovascular and metabolic diseases.

Transient receptor potential (TRP) channels as drug targets for diseases of the digestive system

Approximately 20 of the 30 mammalian transient receptor potential (TRP) channel subunits are expressed by specific neurons and cells within the alimentary canal. They subserve important roles in taste, chemesthesis, mechanosensation, pain and hyperalgesia and contribute to the regulation of gastrointestinal motility, absorptive and secretory processes, blood flow, and mucosal homeostasis. In a cellular perspective, TRP channels operate either as primary detectors of chemical and physical stimuli, as secondary transducers of ionotropic or metabotropic receptors, or as ion transport channels. The polymodal sensory function of TRPA1, TRPM5, TRPM8, TRPP2, TRPV1, TRPV3 and TRPV4 enables the digestive system to survey its physical and chemical environment, which is relevant to all processes of digestion. TRPV5 and TRPV6 as well as TRPM6 and TRPM7 contribute to the absorption of Ca²⁺ and Mg²⁺, respectively. TRPM7 participates in intestinal pacemaker activity, and TRPC4 transduces muscarinic acetylcholine receptor activation to smooth muscle contraction. Changes in TRP channel expression or function are associated with a variety of diseases/disorders of the digestive system, notably gastro-esophageal reflux disease, inflammatory bowel disease, pain and hyperalgesia in heartburn, functional dyspepsia and irritable bowel syndrome, cholera, hypomagnesemia with secondary hypocalcemia, infantile hypertrophic pyloric stenosis, esophageal, gastrointestinal and pancreatic cancer, and polycystic liver disease. These implications identify TRP channels as promising drug targets for the management of a number of gastrointestinal pathologies. As a result, major efforts are put into the development of selective TRP channel agonists and antagonists and the assessment of their therapeutic potential.