pH-sensitive Receptors Research Articles

PH sensing in skin tumors: Methods to study the involvement of GPCRs, acid-sensing ion channels and transient receptor potential vanilloid channels.

Solid tumors exhibit an inversed pH gradient with increased intracellular pH (pHi ) and decreased extracellular pH (pHe ). This inside-out pH gradient is generated via sodium/hydrogen antiporter 1, vacuolar-type H+ATPases, monocarboxylate transporters, (bi)carbonate (co)transporters and carboanhydrases. Our knowledge on how pHe -signals are sensed and what the respective receptors induce inside cells is scarce. Some pH-sensitive receptors (GPR4, GPR65/TDAG8, GPR68/OGR1, GPR132/G2A, possibly GPR31 and GPR151) and ion channels (acid-sensing ion channels ASICs, transient receptor potential vanilloid receptors TRPVs) transduce signals inside cells. As little is known on the expression and function of these pH sensors, we used immunostainings to study tissue samples from common and rare skin cancers. Our current and future work is directed towards investigating the impact of all the pH-sensing receptors in different skin tumors using cell culture techniques with selective knockdown/knockout (siRNA/CRISPR-Cas9). To study cell migration and proliferation, novel impedance-based wound healing assays have been developed and are used. The field of pH sensing in tumors and wounds holds great promise for the development of pH-targeting therapies, either against pH regulators or sensors to inhibit cell proliferation and migration.

Efficacy and safety of plecanatide in treating constipation predominant irritable bowel syndrome

ABSTRACTIntroduction: Uroguanylin interacting with intestinal Guanylate Cyclase C (GC-C) receptors plays an important role in gastrointestinal fluid and electrolyte homeostasis. Plecanatide is the first uroguanylin analog that stimulates GC-C receptors on gastrointestinal mucosa with pH-sensitive receptor binding. Binding to the GC-C receptor activates intracellular conversion of GTP to cGMP resulting in the stimulation of intestinal fluid secretion.Areas covered: Herein, all published research regarding the development of and clinical experience with plecanatide is reviewed. Clinical study results in patients with Chronic Idiopathic Constipation (CIC) and Irritable Bowel Syndrome with Constipation (IBS-C) are also reviewed. Success in the treatment of CIC and IBS-C is supported by beneficial effects on stool viscosity, Complete Spontaneous Bowel Movements and visceral sensation. Finally, the discussion within focuses on the importance of plecanatide in understanding the physiology of uroguanylin, the pathophysiology of IBS-C and the potential for development of uroguanylin and guanylin analogs.Expert opinion: Given this broad spectrum of potential activity for GC-C agonists, it would not be surprising to see that the use of agents such as plecanatide in new areas grow to a level even greater than the use for the present CIC and IBS-C indications.

PH-Triggered and Enhanced Simultaneous Photodynamic and Photothermal Therapy Guided by Photoacoustic and Photothermal Imaging

Developing smart photosensitizers sensitively responding to tumor-specific signals for reduced side effects and enhanced anticancer efficacy is a major challenge for tumor phototherapy. Herein, a pH-sensitive photosensitizer has been synthesized through introducing a pH-sensitive receptor (dimethylaminophenyl unit) onto the aza-BODIPY core (abbreviated as NAB). Through enveloping hydrophobic NAB with amphiphilic DSPE-mPEG2000, NAB nanoparticles (NPs, diameter ∼ 30 nm) with strong near-infrared absorption (∼792 nm) are obtained. NAB NPs can be activated in weak acidic environment to give high rate of reactive oxygen species (ROS) generation and enhanced photothermal effect. NAB NPs can selectively accumulate in the lysosomes of tumor cells and subsequently activate under the acidic microenvironment of lysosome (pH 5.0) to produce ROS for photodynamic therapy, due to switch-off of the photoinduced electron transfer (PET) pathway. In vivo, pH-enhanced photoacoustic imaging (PAI) and photothermal imaging (PTI...

Determination of Alkali-Sensing Parts of the Insulin Receptor-Related Receptor Using the Bioinformatic Approach

IRR (insulin receptor-related receptor) is a receptor tyrosine kinase belonging to the insulin receptor family, which also includes insulin receptor and IGF-IR receptor. We have previously shown that IRR is activated by extracellular fluid with pH > 7.9 and regulates excess alkali excretion in the body. We performed a bioinformatic analysis of the pH-sensitive potential of all three members of the insulin receptor family of various animal species (from frog to man) and their chimeras with swapping of different domains in the extracellular region. An analysis using the AcalPred program showed that insulin receptor family proteins are divided into two classes: one class with the optimal working pH in the acidic medium (virtually all insulin receptor and insulin-like growth factor receptor orthologs, except for the IGF-IR ortholog from Xenopus laevis) and the second class with the optimal working pH in the alkaline medium (all IRR orthologs). The program had predicted that the most noticeable effect on the pH-sensitive property of IRR would be caused by the replacement of the L1 and C domains in its extracellular region, as well as the replacement of the second and third fibronectin repeats. It had also been assumed that replacement of the L2 domain would have the least significant effect on the alkaline sensitivity of IRR. To test the in silico predictions, we obtained three constructs with swapping of the L1C domains, the third L2 domain, and all three domains L1CL2 of IRR with similar domains of the insulin-like growth factor receptor. We found that replacement of the L1C and L1CL2 domains reduces the receptor's ability to be activated with alkaline pH, thus increasing the half-maximal effective concentration by about 100%. Replacement of the L2 domain increased the half-maximal effective concentration by 40%. Thus, our results indicate the high predictive potential of the AcalPred algorithm, not only for the pH-sensitive enzymes, but also for pH-sensitive receptors.

Neurobiology of panic and pH chemosensation in the brain

Panic disorder is a common and disabling illness for which treatments are too frequently ineffective. Greater knowledge of the underlying biology could aid the discovery of better therapies. Although panic attacks occur unpredictably, the ability to provoke them in the laboratory with challenge protocols provides an opportunity for crucial insight into the neurobiology of panic. Two of the most well-studied panic provocation challenges are CO(2) inhalation and lactate infusion. Although it remains unclear how these challenges provoke panic animal models of CO(2) and lactate action are beginning to emerge, and offer unprecedented opportunities to probe the molecules and circuits underlying panic attacks. Both CO(2) and lactate alter pH balance and may generate acidosis that can influence neuron function through a growing list of pH-sensitive receptors. These observations suggest that a key to better understanding of panic disorder may He in more knowledge of brain pH regulation and pH-sensitive receptors.

A Novel Lysophospholipid- and pH-Sensitive Receptor, GPR4, in Brain Endothelial Cells Regulates Monocyte Transmigration

Abundant evidence documents the highly proinflammatory actions of lysophosphatidylcholine (LPC). Further, LPC, found in high amounts in oxidized low-density lipoprotein (LDL), is implicated as an atherogenic factor. In endothelial cells, LPC impairs endothelial barrier function through GPR4, a novel receptor hypothesized to be sensitive to LPC and protons. The authors investigated the stimulation by LPC or low pH of GPR4 in human brain microvascular endothelial cells (HBMECs) and whether the activated GPR4 regulates in vitro monocyte transmigration. The results indicated that HBMECs stimulated by LPC (5 microM), but not low pH, showed a twofold increase in monocyte transmigration. Using retroviruses containing siRNA to GPR4, a > 60% reduction of GPR4 expression resulted in blockade of the LPC-stimulated transmigration. The inhibited response was restored by co-expression with an small interference RNA (siRNA)-resistant, but functional, GPR4 mutant construct. To investigate potential signaling mechanisms, the siRNA-mediated knockdown of GPR4 also prevented LPC-induced RhoA activation. C3 transferase, a Rho inhibitor, prevented approximately approximately 65% of the LPC-stimulated transmigration. LPC also increased MLC phosphorylation by 5 min, which was inhibited by the Rho kinase inhibitor, Y-27632 (10 microM) or ML-7 (myosin light chain kinase (MLCK) inhibitor). The findings indicate that the proinflammatory and atherogenic LPC stimulated endothelial GPR4, which promoted monocyte transmigration through a RhoA-dependent pathway.

The science behind metastatic bone pain

Abstract Metastatic bone pain is a significant cause of morbidity in patients with advanced cancer and greatly reduces quality of life. Standard palliative treatments such as opioids may not provide effective relief of metastatic bone pain, particularly acute breakthrough pain, without unacceptable side effects at the high doses required. A mouse model of metastatic bone pain has been developed in which tumor cells are injected directly into the marrow space of mice femora. As the tumor cells proliferate, mice display reproducible behaviors associated with pain, such as flinching or guarding the affected limb, that increase as bone destruction progresses. The model also enables measurement of other endpoints, including tumor growth and migration, and monitoring of relevant cell types such as osteoclasts, macrophages, and neurons. Mouse studies have provided important information on the mechanisms behind metastatic bone pain and the specific effects of potential therapies. These studies have demonstrated that metastatic bone disease is caused by multiple factors and that osteoclasts are particularly important in pain generation through destruction of bone and nerve fibers and acidotic stimulation of pH-sensitive receptors. Clinical studies with bisphosphonates demonstrate that these agents provide relief of metastatic bone pain, and preliminary experiments using the mouse model suggest that this may occur via multiple mechanisms. Further studies are under way.

The Treatment of Posterior Drooling by Botulinum Toxin in a Child with Cerebral Palsy

Drooling is the unintentional loss of saliva from the mouth, known as anterior drooling (1). However, anterior drooling has to be distinguished from posterior drooling which refers to saliva that is spilled over the tongue through the faucial isthmus. Under physiological conditions this initiates the pharyngeal phase of swallowing, during which the larynx closes to protect the airways followed by relaxation of the upper esophageal sphincter. Whenever the trigger to swallow is impaired or missing, pooled saliva may lead to posterior drooling mostly apparent from an alarming congested breathing, coughing, gagging, vomiting, and at times aspiration into the trachea. Unrecognized and silent pneumonia can occur (2). The risk of posterior drooling can be enhanced by the fact that many disabled children are taken care of in a supine position for a substantial part of the day. Many children with cerebral palsy (CP) suffer from gastroesophageal reflux (3). In healthy subjects, exposure of the distal esophagus to acid results in an immediate increase of saliva secretion. The possible function of this is that swallowed saliva plays a role in the defense of esophageal mucosa to acid–induced injuries. Reflux in children with CP causes stimulation of pH-sensitive receptors in the mucosa of the distal esophagus which activates the esophageal-salivary reflex leading to an increase of salivary flow rate (3,4). This may exacerbate anterior and posterior drooling. Botulinum neurotoxin (BoNT) injections in the salivary glands in the treatment of anterior drooling demonstrate promising efficacy (5–8). This case report summarizes the results of repeated bilateral single-dose BoNT injections into the submandibular glands in a patient with CP with severe drooling, aspiration, and recurrent pneumonia. The primary treatment intention was to decrease salivary flow in an effort to reduce anterior as well as posterior drooling.

Cloning of a Streptococcus sanguis adhesin which mediates binding to saliva-coated hydroxyapatite.

Chromosomal DNA from a salivary aggregating strain of Streptococcus sanguis 12 was partially digested with PstI and ligated into the plasmid vector pUC18 and transformed into Escherichia coli JM83. A total of 1,700 recombinant clones of E. coli were examined by a colony immunoassay with antisera raised against either S. sanguis 12 whole cells or S. sanguis 12 surface fibrils. Five clones which reacted with one or the other antiserum were shown to be unique by Western blotting (immunoblotting) and restriction endonuclease digestion. One recombinant plasmid pSA2 expressed two proteins with Mrs of 20,000 and 36,000. The 36,000-Mr protein has been designated SsaB. Both proteins were purified to homogeneity by Sephadex G-75 and ion-exchange chromatography. The proteins were present in mutanolysin digests of whole-cell lysates of S. sanguis 12 and in the non-saliva-aggregating variant 12na and the hydrophilic variant 12L. Polyclonal antiserum raised against the SsaB protein reacted strongly with the cell surfaces of S. sanguis 12 and 12na but not with that of 12L. SsaB inhibited the adhesion of S. sanguis 12na to saliva-coated hydroxyapatite, indicating that the adhesin mediates the binding to the pH-sensitive receptor.

Ventriculocisternal pH and cerebral blood flow.

ALTHOUGH many laboratories have confirmed Kety and Schmidt's1finding that a rise in the arterial blood carbon dioxide tension (Paco2) increases the cerebral blood flow (CBF) while a fall in Paco2decreases it, the mechanism mediating this response is unknown. Carbon dioxide diffuses rapidly across the blood-brain barrier and, theoretically, this blood gas could exert direct action on structures lying in any layer of the vessel wall or even on a pH sensitive receptor lying outside the vessel itself, in the adjacent brain extracellular space. An alternate proposal has been that carbon dioxide alters the pH of a brainstem regulatory center, which in turn produces reflex cerebral vasodilatation or constriction in a manner analogous to the control of pulmonary ventilation. Lassen2has summarized the evidence that brain extracellular pH is the main factor controlling CBF: in severe diabetic acidosis, CBF is increased above normal