Teaching an Old Drug New Tricks: Agonism, Antagonism, and Biased Signaling of Pilocarpine through M3 Muscarinic Acetylcholine Receptor

Laboratory features and pharmacological management of early and late-onset primary Sjögren's syndrome

BACKGROUND

Primary Sjögren's Syndrome (pSS) is a systemic chronic autoimmune disorder that contributes to dry mouth (xerostomia) and eyes (xerophthalmia). It mainly affects females between 40 and 60 years old. So far, there is no treatment to cure SS; however, there is a list of medications that can ameliorate the symptoms. In addition, there has been no single test until now to detect pSS, but clinical and immunological investigations are applied as diagnostic tools. Therefore, this study aimed to explore the characteristics of pSS in Saudi patients based on the onset of the disease through laboratory findings and pharmaceutical management.

METHODOLOGY

This retrospective study examined diagnosed patients with pSS between 2018 and 2023 from the National Guard Hospital, Saudi Arabia. Data of pSS patients was categorized into two groups: early (under 40 years old) and late-onset (40 years old and above). Data on demographic information, mortality rate, and blood tests such as complete blood count (CBC), creatinine, erythrocyte sedimentation rate (ESR), and vitamin levels, in addition to prescribed medications, were collected from the patient's medical record. Chi-square and t-tests were mainly used, and statistical significance was determined at a P-value less than 0.05.

RESULTS

A total of 453 patients were included in the study, where the early-onset group comprised 136 and the late-onset group comprised 317 patients. The mean age of the early and late onset was 34.2 and 60.4, respectively. ESR was significantly higher in the early (46.3 mm/hr) and late-onset (49.8 mm/hr). The most common medication used by all pSS patients was hydroxychloroquine. However, artificial tears were mainly observed in the late-onset group. Other medications, such as pilocarpine, methotrexate, and azathioprine, were prescribed to pSS patients to a lesser extent.

CONCLUSION

This study suggests that the onset of pSS could occur even before the age of 40 among Saudi citizens. Notably, elevated ESR levels appeared to be a feature of pSS, which was consistent with other previous findings. The variability of some medications between early-onset and late-onset pSS may indicate disease progression. However, further investigations are required to confirm this observation.

Muscarinic acetylcholine receptor-mediated phosphorylation of extracellular signal-regulated kinase in HSY salivary ductal cells involves distinct signaling pathways

OBJECTIVES

Typical agonists of G protein-coupled receptors (GPCRs), including muscarinic acetylcholine receptors (mAChRs), activate both G-protein and β-arrestin signaling systems, and are termed balanced agonists. In contrast, biased agonists selectively activate a single pathway, thereby offering therapeutic potential for the specific activation of that pathway. The mAChR agonists carbachol and pilocarpine are known to induce phosphorylation of extracellular signal-regulated kinase-1/2 (ERK1/2) via G-protein-dependent and -independent pathways, respectively. We investigated the involvement of β-arrestin and its downstream mechanisms in the ERK1/2 phosphorylation induced by carbachol and pilocarpine in the human salivary ductal cell line, HSY cells.

METHODS

HSY cells were stimulated with pilocarpine or carbachol, with or without various inhibitors. The cell lysates were analyzed by western blotting using the antibodies p44/p42MAPK and phosphor-p44/p42MAPK.

RESULTS

Western blot analysis revealed that carbachol elicited greater stimulation of ERK1/2 phosphorylation compared to pilocarpine. ERK1/2 phosphorylation was inhibited by atropine and gefitinib, suggesting that mAChR activation induces transactivation of epidermal growth factor receptors (EGFR). Moreover, inhibition of carbachol-mediated ERK1/2 phosphorylation was achieved by GF-109203X (a PKC inhibitor), a βARK1/GRK2 inhibitor, barbadin (a β-arrestin inhibitor), pitstop 2 (a clathrin inhibitor), and dynole 34-2 (a dynamin inhibitor). In contrast, pilocarpine-mediated ERK1/2 phosphorylation was only inhibited by barbadin (a β-arrestin inhibitor) and PP2 (a Src inhibitor).

CONCLUSION

Carbachol activates both G-protein and β-arrestin pathways, whereas pilocarpine exclusively activates the β-arrestin pathway. Additionally, downstream of β-arrestin, carbachol activates clathrin-dependent internalization, while pilocarpine activates Src.

Ryzumvi: pioneering advances in countering drug-induced mydriasis

This article discusses the prevalence and impact of pharmacologically-induced mydriasis, a condition where the pupil becomes excessively dilated due to certain drugs. It highlights the challenges faced by medical professionals in dealing with this condition and the limitations of current treatments, like pilocarpine and dapiprazole, which come with systemic side effects and specific contraindications, limiting their regular use. The article introduces Ryzumvi, a novel ophthalmic solution approved by the US FDA, which effectively reverses mydriasis caused by adrenergic agonists and antimuscarinic drugs. The article provides insights into its mechanism of action, clinical efficacy, pharmacokinetics, safety, and tolerance based on extensive clinical trials. It emphasizes its rapid onset of action and effectiveness in restoring pupils to their initial size. It also underlines the potential for expanded applications, including in pediatric patients, solidifying its importance in the field of ophthalmology. Furthermore, Ryzumvi represents a promising advancement in managing pharmacologically-induced mydriasis, offering swift and effective relief while highlighting the importance of adhering to safety precautions and the continuous research and development efforts in ophthalmology to comprehensively address vision-related disorders and enhance patient outcomes.

Differential effects of intra-RMTg infusions of pilocarpine or 4-DAMP on regulating depression- and anxiety-like behaviors

Depression and anxiety are associated with dysfunction of the mesolimbic dopamine system. The rostromedial tegmental nucleus (RMTg) is predominantly composed of GABAergic neurons that exhibit dense projections and strongly inhibit mesolimbic dopaminergic neurons, proposed as a major "brake" for the system. Consequently, the RMTg may be a crucial brain region for regulating these emotions. The central cholinergic system, particularly the muscarinic receptors, plays an important regulatory role in depression and anxiety. M3 muscarinic receptors are distributed on GABAergic neurons in the RMTg, but their involvement in the regulation of depression and anxiety remains uncertain. This study aimed to examine the effects of RMTg M3 muscarinic receptors on regulating depression- and anxiety-like behaviors in adult male Wistar rats, as assessed through the forced swim, tail suspension, and elevated plus maze tests. The results showed that intra-RMTg injections of the M1/M3 muscarinic receptors agonist, pilocarpine (3, 10, and 30 μg/side), or the M3 muscarinic receptors antagonist, 4-DAMP (0.5, 1, and 2 μg/side), did not alter the immobility time in the forced swim and tail suspension tests. Additionally, pilocarpine (30 μg/side) decreased time spent in open arms and increased time in closed arms in the elevated plus maze; while 4-DAMP (1 and 2 μg/side) played the opposite role by increasing time spent in open arms and decreasing time in closed arms. These findings suggest that RMTg M3 muscarinic receptors have differential effects on regulating depression- and anxiety-like behaviors. Enhancing or inhibiting these receptors can produce anxiogenic or anxiolytic effects, but have no impact on depression-like behavior. Therefore, RMTg M3 muscarinic receptors are involved in regulating anxiety and may be a potential therapeutic target for anxiolytic drugs.

Regulation of Src family kinases by muscarinic acetylcholine receptors in heterologous cells and neurons

Five muscarinic acetylcholine (mACh) receptor subtypes are divided into two classes: the M1 class (M1, M3, and M5) and the M2 class (M2 and M4). The former is coupled to Gq proteins, while the latter is coupled to Gi/o proteins. Accumulating evidence indicates that mACh receptors play a significant role in the regulation of the Src family kinase (SFK), a subfamily of non-receptor tyrosine kinases. mACh receptors exert their roles in a subtype-dependent fashion and preferentially target Src and Fyn, two members of SFKs that are expressed in the brain and enriched at synaptic sites. While the M1 receptor positively modulates SFK activity, the M4 receptor inhibits it. By modulating SFKs, mACh receptors are actively involved in the regulation of expression and function of a variety of receptors, structural proteins, and signaling molecules. In particular, the M4 receptor and the dopamine D1 receptor are coexpressed in striatonigral projection neurons of the striatum. Gi/o-coupled M4 and Gq-coupled D1 receptors antagonistically regulate SFK activity, thereby forming a dynamic balance controlling glutamate receptor activity, excitability of neurons, and synaptic plasticity. In summary, mACh receptors play a crucial role in regulating SFK activity in heterologous cells and neurons.

The applications of the pilocarpine animal model of status epilepticus: 40 years of progress (1983-2023)

Status epilepticus is a neurological disorder that can result in various neuropathological conditions and presentations. Various studies involving animal models have been accomplished to understand and replicating its prominent manifestations including characteristics of related clinical cases. Up to these days, there are variety of methods and techniques to be utilized in inducing this disorder that can be chemically or electrically applied which depending on the experimental designs and targets of the studies. In particular, the chemically induced pilocarpine animal model of status epilepticus is a reliable choice which has evolved for 40 years from its initial discovery back in 1983. Although the development of the model can be considered as a remarkable breakthrough in understanding status epilepticus, several aspects of the model have been improved, throughout the years. Among the major issues in developing this model are the morbidity and mortality rates during induction process. Several modifications have been introduced in the process by different studies to tackle the related problems including application of dose fractionation, adaptation of pilocarpine to lithium-pilocarpine model and utilization of various drugs. Despite all challenges and drawbacks, this model has proven its pertinent and relevance with improvements that have been adapted since it was introduced 40 years ago. In this review, we emphasize on the evolution of this animal model from the beginning until now (1983 - 2023) and the related issues that have made this model still a popular choice in status epilepticus studies.

Hybridization into a Bitopic Ligand Increased Muscarinic Receptor Activation for Isopilocarpine but Not for Pilocarpine Derivatives

Pilocarpine (1), a secondary metabolite of several Pilocarpus species, is a therapeutically used partial agonist of muscarinic acetylcholine receptors (mAChRs). The available pharmacological data and structure-activity relationships do not provide comparable data for all five receptor subtypes. In this study, pilocarpine (1), its epimer isopilocarpine (2), racemic analogues pilosinine (3) and desmethyl pilosinine (4), and the respective hybrid ligands with a naphmethonium fragment (5-C6 to 8-C6) were synthesized and analyzed in mini-G nano-BRET assays at the five mAChRs. In line with earlier studies, pilocarpine was the most active compound among the orthosteric ligands 1-4. Computational docking of pilocarpine and isopilocarpine to the active M2 receptor suggests that the trans-configuration of isopilocarpine leads to a loss of the hydrogen bond from the lactone carbonyl to N6.52, explaining the lower activity of isopilocarpine. Hybrid formation of pilocarpine (1) and isopilocarpine (2) led to an inverted activity rank, with the trans-configured isopilocarpine hybrid (6-C6) being more active. The hydrogen bond of interest is formed by the isopilocarpine hybrid (6-C6) but not by the pilocarpine hybrid (5-C6). Hybridization thus leads to a modified binding mode of the orthosteric moiety, as the binding mode of the hybrid is dominated by the high-affinity allosteric moiety.

Structural Insights into M1 Muscarinic Acetylcholine Receptor Signaling Bias between Gαq and β-Arrestin through BRET Assays and Molecular Docking

The selectivity of drugs for G protein-coupled receptor (GPCR) signaling pathways is crucial for their therapeutic efficacy. Different agonists can cause receptors to recruit effector proteins at varying levels, thus inducing different signaling responses, called signaling bias. Although several GPCR-biased drugs are currently being developed, only a limited number of biased ligands have been identified regarding their signaling bias for the M1 muscarinic acetylcholine receptor (M1mAChR), and the mechanism is not yet well understood. In this study, we utilized bioluminescence resonance energy transfer (BRET) assays to compare the efficacy of six agonists in inducing Gαq and β-arrestin2 binding to M1mAChR. Our findings reveal notable variations in agonist efficacy in the recruitment of Gαq and β-arrestin2. Pilocarpine preferentially promoted the recruitment of β-arrestin2 (∆∆RAi = -0.5), while McN-A-343 (∆∆RAi = 1.5), Xanomeline (∆∆RAi = 0.6), and Iperoxo (∆∆RAi = 0.3) exhibited a preference for the recruitment of Gαq. We also used commercial methods to verify the agonists and obtained consistent results. Molecular docking revealed that certain residues (e.g., Y404, located in TM7 of M1mAChR) could play crucial roles in Gαq signaling bias by interacting with McN-A-343, Xanomeline, and Iperoxo, whereas other residues (e.g., W378 and Y381, located in TM6) contributed to β-arrestin recruitment by interacting with Pilocarpine. The preference of activated M1mAChR for different effectors may be due to significant conformational changes induced by biased agonists. By characterizing bias towards Gαq and β-arrestin2 recruitment, our study provides insights into M1mAChR signaling bias.

Potential antiproliferative and apoptotic effects of pilocarpine combined with TNF alpha in chronic myeloid leukemia cells

Pilocarpine is a selective M₁/M₃ agonist of muscarinic acetylcholine receptor subtypes. Muscarinic acetylcholine receptors are G protein-coupled receptors. These receptors are different drug targets. The aim of the present work was to investigate the effect of pilocarpine on the expression of M₃ muscarinic acetylcholine receptor, the AChE activity, IL-8 release response, and proliferation in K562 cells, via muscarinic receptor activation. Human chronic myeloid leukemic cell cultures were incubated with drugs. Proliferation assays were performed by BrdU assay. Expression of M₃ muscarinic acetylcholine receptor and apoptosis proteins such as bcl, bax, cyt C, and caspases was assessed with the semiquantitative Western blotting method. Pilocarpine inhibits chronic myeloid cell proliferation and M₃ muscarinic acetylcholine receptor protein expression. Pilocarpine increases caspase-8 and -9 expression levels, upregulating the proapoptotic protein Bax and downregulating the expression levels of the antiapoptotic protein Bcl-2. The apoptotic activity of pilocarpine is associated with an increase in AChE activity. M₃ muscarinic acetylcholine receptors can activate multiple signal transduction systems and mediate inhibitory effects on chronic myeloid K562 cell proliferation depending on the presence of 1% FBS conditions. This apoptotic effect of pilocarpine may be due to the concentration of pilocarpine and the increase in AChE level. Our results suggest that inhibition of cell proliferation by inducing apoptosis of pilocarpine in K562 cells may be one of the targets. M₃ selective agonist may have therapeutic potential in chronic myeloid leukemia.

Comparison of the 1 and 2% pilocarpine mouthwash in a xerostomic population: a randomized clinical trial

AIMS & BACKGROUND

Pilocarpine is an accepted treatment for xerostomia, but limited research has been conducted on the oral, topical form. The present study aimed to compare the effects of 1 and 2% pilocarpine mouthwash on xerostomic participants.

METHODS

In this double-blind clinical trial study, 48 subjects with xerostomia were randomly divided into three groups to measure the effects of 1 and 2% pilocarpine and placebo mouthwashes on saliva levels. The amount of saliva in the 1st and 14th days was measured at 0, 45, 60, and 75 mins, while participants used their mouthwash three times a day for 14 days. On the 1st and 14th days, they filled out the information forms on xerostomia and the medicine's side effects before and after the intervention.

RESULTS

On the 1st day, the mean salivary flow at 45, 60, and 75 mins in the 2 and 1% pilocarpine mouthwash were significantly higher than in the placebo mouthwash group (p < 0.05). On the 14th day, the mean salivary flow time at 45 mins in the 2% pilocarpine mouthwash group was significantly higher than in the placebo mouthwash group (p = 0.007). Furthermore, the mean salivary flow at 60 and 75 mins in the 2% (p < 0.001) and 1% pilocarpine mouthwash (p = 0.028) was significantly higher than in the placebo group. Moreover, the salivary flow in the 2% pilocarpine mouthwash group was significantly higher than the 1% pilocarpine mouthwash (p < 0.05) during these two times. No side effects were observed in any of the subjects.

CONCLUSIONS

The study showed that 5 ml of 2 and 1% pilocarpine mouthwash for 2 weeks increased salivary flow in xerostomic participants compared to placebo without any side effects.

Prenatal stress induces changes in PAR2- and M3-dependent regulation of colon primitive cells

Prenatal stress is associated with a high risk of developing adult intestinal pathologies, such as irritable bowel syndrome, chronic inflammation, and cancer. Although epithelial stem cells and progenitors have been implicated in intestinal pathophysiology, how prenatal stress could impact their functions is still unknown. We have investigated the proliferative and differentiation capacities of primitive cells using epithelial crypts isolated from colons of adult male and female mice whose mothers have been stressed during late gestation. Our results show that stem cell/progenitor proliferation and differentiation in vitro are negatively impacted by prenatal stress in male progeny. This is promoted by a reinforcement of the negative proliferative/differentiation control by the protease-activated receptor 2 (PAR2) and the muscarinic receptor 3 (M3), two G protein-coupled receptors present in the crypt. Conversely, prenatal stress does not change in vitro proliferation of colon primitive cells in female progeny. Importantly, this maintenance is associated with a functional switch in the M3 negative control of colonoid growth, becoming proliferative after prenatal stress. In addition, the proliferative role of PAR2 specific to females is maintained under prenatal stress, even though PAR2-targeted stress signals Dusp6 and activated GSK3β are increased, reaching the levels of males. An epithelial serine protease could play a critical role in the activation of the survival kinase GSK3β in colonoids from prenatally stressed female progeny. Altogether, our results show that following prenatal stress, colon primitive cells cope with stress through sexually dimorphic mechanisms that could pave the way to dysregulated crypt regeneration and intestinal pathologies.NEW & NOTEWORTHY Primitive cells isolated from mouse colon following prenatal stress and exposed to additional stress conditions such as in vitro culture, present sexually dimorphic mechanisms based on PAR2- and M3-dependent regulation of proliferation and differentiation. Whereas prenatal stress reinforces the physiological negative control exerted by PAR2 and M3 in crypts from males, in females, it induces a switch in M3- and PAR2-dependent regulation leading to a resistant and proliferative phenotype of progenitor.

PD 102807 Induces M3 mAChR-Dependent GRK-/Arrestin-Biased Signaling in Airway Smooth Muscle Cells

G protein-coupled receptors (GPCRs) not only are turned on or off to control canonical G protein signaling but also may be fine-tuned to promote qualitative/biased signaling. Qualitative signaling by M3 muscarinic acetylcholine receptors (mAChRs) has been proposed, but its impact on physiologic systems remains unclear, and currently no biased M3 mAChR ligands have been described. Herein, we identify PD 102807 as a biased M3 ligand and delineate its signaling and function in human airway smooth muscle (ASM) cells. PD 102807 induced M3-mediated β-arrestin recruitment but not calcium mobilization. PD 102807 inhibited methacholine (MCh)-induced calcium mobilization in (M3-expressing) ASM cells. PD 102807 induced phosphorylation of AMP-activated protein kinase (AMPK) and the downstream effector acetyl-coenzyme A carboxylase (ACC). PD 102807- induced phosphorylated (p)-AMPK levels were greatly reduced in ASM cells with minimal M3 expression and were not inhibited by the Gq inhibitor YM-254890. Induction of p-AMPK and p-ACC was inhibited by β-arrestin 1 or GRK2/3 knockdown. Similarly, MCh induced phosphorylation of AMPK/ACC, but these effects were Gq dependent and unaffected by GRK2/3 knockdown. Consistent with the known ability of AMPK to inhibit transforming growth factor β (TGF-β)-mediated functions, PD 102807 inhibited TGF-β-induced SMAD-Luc activity, sm-α-actin expression, actin stress fiber formation, and ASM cell hypercontractility. These findings reveal that PD 102807 is a biased M3 ligand that inhibits M3-transduced Gq signaling but promotes Gq protein-independent, GRK-/arrestin-dependent, M3-mediated AMPK signaling, which in turn regulates ASM phenotype and contractile function. Consequently, biased M3 ligands hold significant promise as therapeutic agents capable of exploiting the pleiotropic nature of M3 signaling.

Endogenous DOPA inhibits melanoma through suppression of CHRM1 signaling

Melanoma risk is 30 times higher in people with lightly pigmented skin versus darkly pigmented skin. Using primary human melanocytes representing the full human skin pigment continuum and preclinical melanoma models, we show that cell-intrinsic differences between dark and light melanocytes regulate melanocyte proliferative capacity and susceptibility to malignant transformation, independent of melanin and ultraviolet exposure. These differences result from dihydroxyphenylalanine (DOPA), a melanin precursor synthesized at higher levels in melanocytes from darkly pigmented skin. We used both high-throughput pharmacologic and genetic in vivo CRISPR screens to determine that DOPA limits melanocyte and melanoma cell proliferation by inhibiting the muscarinic acetylcholine receptor M1 (CHRM1) signaling. Pharmacologic CHRM1 antagonism in melanoma leads to depletion of c-Myc and FOXM1, both of which are proliferation drivers associated with aggressive melanoma. In preclinical mouse melanoma models, pharmacologic inhibition of CHRM1 or FOXM1 inhibited tumor growth. CHRM1 and FOXM1 may be new therapeutic targets for melanoma.

A Review on the Role of Pilocarpine on the Management of Xerostomia and the Importance of the Topical Administration Systems Development

Xerostomia is linked to an increased risk of dental caries, oral fungal infections, and speaking/swallowing difficulties, factors that may significantly degrade patients’ life, socially- or emotionally-wise. Consequently, there is an increasing interest in developing management approaches for confronting this oral condition, at which pilocarpine, a parasympathomimetic agent, plays a vital role. Although the therapeutic effects of orally administrated pilocarpine on the salivary gland flow and the symptoms of xerostomia have been proved by numerous studies, the systemic administration of this drug is affiliated with various adverse effects. Some of the typical adverse effects include sweating, nausea, vomiting, diarrhea, rhinitis, dizziness and increased urinary frequency. In this vein, new strategies to develop novel and effective dosage forms for topical (i.e., in the oral cavity) pilocarpine administration, in order for the salivary flow to be enhanced with minimal systemic manifestations, have emerged. Therefore, the purpose of the current review is to survey the literature concerning the performance of topical pilocarpine delivery systems. According to the findings, the topical delivery of pilocarpine can be regarded as the equivalent to systemic delivery of the drug, efficacy-wise, but with improved patient tolerance and less adverse effects.

Synthesis and characterization of alkaloid derived hydrazones and their metal (II) complexes

Alkaloids have been known overtime to have medicinal uses. Exploring alkaloid derived hydrazones and their complexes as potential therapeutic agents with a view to improving the medicinal uses of alkaloids are imperative. 1,8-dichloroacridone hydrazone hydrochloride, 1-chloro pilocarpine nitrate-3-chlorophenyl hydrazone and 1-phenethyl-4-piperidone formyl hydrazone ligands were synthesized via Wolff–Kishner condensation reaction. Five metal (II) complexes of cobalt, nickel and manganese were prepared by stirring the ligands with the respective metal salts. The ligands and complexes were characterized using elemental analyses, molar conductivity, FTIR, 1H and 13C nmr, UV–Vis spectra, melting point and solubility. Antimicrobial activities of the ligands and their complexes were tested against four bacteria (Staphylococcus aureus, Streptococcus faecalis Escherichia coli, Salmonella paratyphimurium) and a fungus (Candida albican). The molar conductance values indicate that they are 1:1 and 1:2 type electrolytes while the elemental analyses of the complexes reveals a 1:1 metal to ligand stoichiometry. The relevant IR bands suggest coordination is through the C=N, C=O, N=C–O and C–N groups. Both 1H and 13C nmr corroborated the elemental analysis while the UV–Vis reveals intra-ligand charge transfer while the complexes exhibited the expected metal transitions bands. A proposed octahedral geometry is supported by spectral data. Only 1, 8-dichloroacridonehydrazone hydrochloride ligand was found to be active against all the organisms. Cobalt and nickel complexes of 1,8-dichloroacridonehydrazone hydrochloride were active against S. paratyphimurium and S. aureus, respectively, while cobalt complex of 1-chloropilocarpinenitrate-3-chlorophenylhydrazone was active against S. faecalis and S. paratyphimurium. The minimum inhibitory concentrations (MIC) were also recorded.

Inhibition of TRPC3 channels by a novel pyrazole compound confers antiseizure effects

OBJECTIVE

As a key member of the transient receptor potential (TRP) superfamily, TRP canonical 3 (TRPC3) regulates calcium homeostasis and contributes to neuronal excitability. Ablation of TRPC3 lessens pilocarpine-induced seizures in mice, suggesting that TRPC3 inhibition might represent a novel antiseizure strategy. Among current TRPC3 inhibitors, pyrazole 3 (Pyr3) is most selective and potent. However, Pyr3 only provides limited benefits in pilocarpine-treated mice, likely due to its low metabolic stability and potential toxicity. We recently reported a modified pyrazole compound 20 (or JW-65) that has improved stability and safety. The objective of this study was to explore the effects of TRPC3 inhibition by our current lead compound JW-65 on seizure susceptibility.

METHODS

We first examined the pharmacokinetic properties including plasma half-life and brain to plasma ratio of JW-65 after systemic administration in mice. We then investigated the effects of TRPC3 inhibition by JW-65 on behavioral and electrographic seizures in mice treated with pilocarpine. To ensure our findings are not model specific, we assessed the susceptibility of JW-65-treated mice to pentylenetetrazole (PTZ)-induced seizures with phenytoin as a comparator.

RESULTS

JW-65 showed adequate half-life and brain penetration in mice, justifying its use for central nervous system conditions. Systemic treatment with JW-65 before pilocarpine injection in mice markedly impaired the initiation of behavioral seizures. This antiseizure action was recapitulated when JW-65 was administered after pilocarpine-induced behavioral seizures were well established and was confirmed by time-locked electroencephalographic monitoring and synchronized video. Moreover, JW-65-treated mice showed substantially decreased susceptibility to PTZ-induced seizures in a dose-dependent manner.

SIGNIFICANCE

These results suggest that pharmacological inhibition of the TRPC3 channels by our novel compound JW-65 might represent a new antiseizure strategy engaging a previously undrugged mechanism of action. Hence, this proof-of-concept study establishes TRPC3 as a novel feasible therapeutic target for the treatment of some forms of epilepsy.

Disentangling bias between Gq, GRK2, and arrestin3 recruitment to the M3 muscarinic acetylcholine receptor

G protein-coupled receptors (GPCRs) transmit extracellular signals to the inside by activation of intracellular effector proteins. Different agonists can promote differential receptor-induced signaling responses – termed bias – potentially by eliciting different levels of recruitment of effector proteins. As activation and recruitment of effector proteins might influence each other, thorough analysis of bias is difficult. Here, we compared the efficacy of seven agonists to induce G protein, G protein-coupled receptor kinase 2 (GRK2), as well as arrestin3 binding to the muscarinic acetylcholine receptor M₃ by utilizing FRET-based assays. In order to avoid interference between these interactions, we studied GRK2 binding in the presence of inhibitors of G_i and G_q proteins and analyzed arrestin3 binding to prestimulated M₃ receptors to avoid differences in receptor phosphorylation influencing arrestin recruitment. We measured substantial differences in the agonist efficacies to induce M₃R-arrestin3 versus M₃R-GRK2 interaction. However, the rank order of the agonists for G protein- and GRK2-M₃R interaction was the same, suggesting that G protein and GRK2 binding to M₃R requires similar receptor conformations, whereas requirements for arrestin3 binding to M₃R are distinct.

Pilocarpine-Induced Effects on Salivary Secretion as a Pharmacological Biomarker for Cholinergic Parasympathetic Activation

Pilocarpine-induced salivary secretion could serve as a nontherapeutic target engagement biomarker in a clinical setting to test the activity of an M3 positive allosteric modulator (PAM). The potentiating effect on the reactivity of the M3 receptor to the agonistic effect of pilocarpine would support the mechanism of action of an M3 PAM in a variety of therapeutic areas. The aim of this study was to determine the optimal pilocarpine dose needed for evaluation of this potentiating effect. Therefore, the effects of pilocarpine on salivary secretion rate and its pharmacokinetics were explored at single doses of 2.5, 5, and 10 mg of pilocarpine or placebo. The study also explored the test-retest variability of the pilocarpine-induced effects on salivary secretion. Pilocarpine caused a reproducible, dose-related increase in overall and maximum salivary secretion rate, in line with pilocarpine exposure. Oral doses of pilocarpine from 2.5 to 10 mg were safe and well tolerated, consistent with the published safety profile. These results support the use of pilocarpine in single-dose pharmacological challenge studies. The recommended dose for evaluating M3 PAM activity would be between 2.5 and 5 mg, showing a small increase in salivary secretion rate with room for further increase due to PAM activation.

Efficacy and safety of two artificial saliva-based polymers containing 0.1% pilocarpine for treatment of xerostomia: A randomized clinical pilot trial

Background

Topical agents are the mainstay in the treatment of xerostomia, a common complaint most frequently associated with salivary dysfunction. This study aimed to compared the efficacy and safety for xerostomia treatment of 2 artificial saliva preparations containing 0.1% pilocarpine, and, either sodium carboxymethylcellulose (SCMC), or, sodium polyacrylate (SPA).

Material and Methods

Thirty-one xerostomia patients were randomly allocated into either a SCMC-treated group (15 patients), or, a SPA-treated group (16 patients). The formulations were taken 0.5 ml, 4 times daily for 6 weeks and double-blinded assessed before and after treatments using Xerostomia Inventory (XI) and Clinical Oral Dryness Score (CODs). Unstimulated and stimulated whole salivary flow rates were measured.

Results

After treatment, the SCMC-treated group had significantly lower CODs and higher unstimulated and stimulated whole salivary flow rates (p<0.001, p=0.035, and p=0.013, respectively), while the SPA-treated group showed significantly lower CODs only (p=0.004). In contrast, SCMC-treated and SPA-treated groups at the 6th week after treatments showed non-significant differences in all assessments (p>0.05, all). Some adverse events (AEs) were reported, e.g., burning tongue, dizziness and watery eyes, but no severe AEs.

Conclusions

This randomized controlled pilot trial demonstrated superior efficacy of SCMC-formula over a SPA-formula after 6 weeks of xerostomia treatment. These formulations with topical pilocarpine proved safe in clinical use with minimal reported AE.

Key words:Xerostomia, artificial saliva, sodium carboxymethylcellulose, sodium polyacrylate, pilocarpine.

New Structural Perspectives in G Protein-Coupled Receptor-Mediated Src Family Kinase Activation

Src family kinases (SFKs) are key regulators of cell proliferation, differentiation, and survival. The expression of these non-receptor tyrosine kinases is strongly correlated with cancer development and tumor progression. Thus, this family of proteins serves as an attractive drug target. The activation of SFKs can occur via multiple signaling pathways, yet many of them are poorly understood. Here, we summarize the current knowledge on G protein-coupled receptor (GPCR)-mediated regulation of SFKs, which is of considerable interest because GPCRs are among the most widely used pharmaceutical targets. This type of activation can occur through a direct interaction between the two proteins or be allosterically regulated by arrestins and G proteins. We postulate that a rearrangement of binding motifs within the active conformation of arrestin-3 mediates Src regulation by comparison of available crystal structures. Therefore, we hypothesize a potentially different activation mechanism compared to arrestin-2. Furthermore, we discuss the probable direct regulation of SFK by GPCRs and investigate the intracellular domains of exemplary GPCRs with conserved polyproline binding motifs that might serve as scaffolding domains to allow such a direct interaction. Large intracellular domains in GPCRs are often understudied and, in general, not much is known of their contribution to different signaling pathways. The suggested direct interaction between a GPCR and a SFK could allow for a potential immediate allosteric regulation of SFKs by GPCRs and thereby unravel a novel mechanism of SFK signaling. This overview will help to identify new GPCR-SFK interactions, which could serve to explain biological functions or be used to modulate downstream effectors.

Functionally selective and biased agonists of muscarinic receptors

Disruption of cholinergic signalling via muscarinic receptors is associated with various pathologies, like Alzheimer's disease or schizophrenia. Selective muscarinic agonists possess therapeutic potential in the treatment of diabetes, pain or Sjögren's syndrome. The orthosteric binding site of all subtypes of the muscarinic receptor is structurally identical, making the development of affinity-based selective agonists virtually impossible. Some agonists, however, are functionally selective; they activate only a subset of receptors or signalling pathways. Others may stabilise specific conformations of the receptor leading to non-uniform modulation of individual signalling pathways (biased agonists). Functionally selective and biased agonists represent a promising approach for selective activation of individual subtypes of muscarinic receptors. In this work we review chemical structures, receptor binding and agonist-specific conformations of currently known functionally selective and biased muscarinic agonists in the context of their intricate intracellular signalling. Further, we take a perspective on the possible use of biased agonists for tissue and organ-specific activation of muscarinic receptors.

Mixture interactions at mammalian olfactory receptors are dependent on the cellular environment

Functional characterization of mammalian olfactory receptors (ORs) remains a major challenge to ultimately understanding the olfactory code. Here, we compare the responses of the mouse Olfr73 ectopically expressed in olfactory sensory neurons using AAV gene delivery in vivo and expressed in vitro in cell culture. The response dynamics and concentration-dependence of agonists for the ectopically expressed Olfr73 were similar to those reported for the endogenous Olfr73, however the antagonism previously reported between its cognate agonist and several antagonists was not replicated in vivo. Expressing the OR in vitro reproduced the antagonism reported for short odor pulses, but not for prolonged odor exposure. Our findings suggest that both the cellular environment and the stimulus dynamics shape the functionality of Olfr73 and argue that characterizing ORs in 'native' conditions, rather than in vitro, provides a more relevant understanding of ligand-OR interactions.

Ectopically expressed olfactory receptors OR51E1 and OR51E2 suppress proliferation and promote cell death in a prostate cancer cell line

Olfactory receptors (ORs), the largest family of G protein–coupled receptors, are expressed in the nasal epithelium where they mediate the sense of smell. However, ORs are also found in other non-nasal tissues, but the role of these ectopic ORs in cell signaling, proliferation, and survival is not well understood. Here, using an inducible expression system in the lymph node carcinoma of the prostate (LNCaP) cell line, we investigated two ectopic ORs, OR51E1 and OR51E2, which have been shown to be upregulated in prostate cancer. We found that, consistent with previous studies, OR51E1 stimulated adenylyl cyclase in response to treatment by short-chain to medium-chain organic acids (C3–C9) but not by acetate. OR51E2 responded to acetate and propionate but not to the longer chain organic acids. Stimulation of LNCaP cells with butyrate inhibited their growth, and the knockdown of the endogenous OR51E1 negated this cytostatic effect. Most significantly, overexpression of OR51E1 or OR51E2 suppressed LNCaP cell proliferation. Overexpression of another ectopic OR OR2AT4, β2-adrenergic receptor, or treatment of cells with forskolin did not suppress cell proliferation, indicating that a rise in cAMP is not sufficient to induce cytostasis. Overexpression of OR51E1 caused an upregulation of cytostatic and cell death markers including p27, p21, and p53, strongly increased annexin V staining, and stimulated extracellular signal–regulated protein kinases 1 and 2. Overexpression and/or activation of OR51E1 did not affect human embryonic kidney 293 cell proliferation, indicating that cytotoxicity of OR51E1/OR51E2 is specific for LNCaP cells. Together, our results further our understanding of prostate cancer etiology and suggest that ectopic ORs may be useful therapeutic targets.

G protein-coupled receptors: structure- and function-based drug discovery

As one of the most successful therapeutic target families, G protein-coupled receptors (GPCRs) have experienced a transformation from random ligand screening to knowledge-driven drug design. We are eye-witnessing tremendous progresses made recently in the understanding of their structure-function relationships that facilitated drug development at an unprecedented pace. This article intends to provide a comprehensive overview of this important field to a broader readership that shares some common interests in drug discovery.

Cumulative effects of ciprofloxacin and pilocarpine on cytotoxicity and G0 phase arrest in hepatoma-derived Hep G2 cell line

OBJECTIVES

Uncontrolled cell proliferation was caused by multiple deficient pathways that inhibition of one pathway may result to activate an alternative pathway. Therefore, combination of drugs which targeted multiple pathways could be beneficial to overcome drug resistance. Ciprofloxacin (CPF) cytotoxicity was widely investigated on cancer cell lines, and results revealed hepatoma-derived Hep G2 cells are relatively resistant. So, this study aimed to increase CPF cytotoxicity by rational design of a supplement which targeted Ca²⁺ homoeostasis as major hub in unchecked proliferation.

METHODS

Cells were treated by CPF and/or pilocarpine (PILO), and cell cycle distribution, caspases activity and regulatory proteins were evaluated.

KEY FINDINGS

MTT and flow cytometry analysis confirmed administration of CPF + PILO causes more cytotoxicity. CPF-exposed cells accumulated in S phase due to DNA damages while PILO + CPF imposed G0 stage arrest through cyclin D1 and P-Akt downregulation. Caspase 8 was activated in cells treated by CPF but accompaniment of PILO with CPF led to activation of caspase 9, 8 and 3 and ROS overproduction.

CONCLUSIONS

Ciprofloxacin imposed mitochondrial-independent apoptosis while PILO + CPF caused mitochondrial-dependent and independent apoptosis simultaneously. Consequently, coadministration of PILO and CPF causes intense cytotoxic effects through targeting the mitochondria, DNA gyrase enzyme and other unknown mechanisms.

Carbachol dimers with primary carbamate groups as homobivalent modulators of muscarinic receptors

Although agonists and antagonists of muscarinic receptors have been known for long time, there is renewed interest in compounds (such as allosteric or bitopic ligands, or biased agonists) able to differently and selectively modulate these receptors. As a continuation of our previous research, we designed a new series of dimers of the well-known cholinergic agonist carbachol. The new compounds were tested on the five cloned human muscarinic receptors (hM_1-5) expressed in CHO cells by means of equilibrium binding experiments, showing a dependence of the binding affinity on the length and position of the linker connecting the two monomers. Kinetic binding studies revealed that some of the tested compounds were able to slow the rate of NMS dissociation, suggesting allosteric behavior, also supported by docking simulations. Assessment of ERK1/2 phosphorylation on hM₁, hM₂ and hM₃ activation showed that the new compounds are endowed with muscarinic antagonist properties. At hM₂ receptors, some compounds were able to stimulate GTPγS binding but not cAMP accumulation, suggesting a biased behavior. Classification, Molecular and cellular pharmacology.

Cholinergic modulation inhibits cortical spreading depression in mouse neocortex through activation of muscarinic receptors and decreased excitatory/inhibitory drive

Cortical spreading depression (CSD) is a wave of transient network hyperexcitability leading to long lasting depolarization and block of firing, which initiates focally and slowly propagates in the cerebral cortex. It causes migraine aura and it has been implicated in the generation of migraine headache. Cortical excitability can be modulated by cholinergic actions, leading in neocortical slices to the generation of rhythmic synchronous activities (UP/DOWN states). We investigated the effect of cholinergic activation with the cholinomimetic agonist carbachol on CSD triggered with 130 mM KCl pulse injections in acute mouse neocortical brain slices, hypothesizing that the cholinergic-induced increase of cortical network excitability during UP states could facilitate CSD. We observed instead an inhibitory effect of cholinergic activation on both initiation and propagation of CSD, through the action of muscarinic receptors. In fact, carbachol-induced CSD inhibition was blocked by atropine or by the preferential M1 muscarinic antagonist telenzepine; the preferential M1 muscarinic agonist McN-A-343 inhibited CSD similarly to carbachol, and its effect was blocked by telenzepine. Recordings of spontaneous excitatory and inhibitory post-synaptic currents in pyramidal neurons showed that McN-A-343 induced overall a decrease of the excitatory/inhibitory ratio. This inhibitory action may be targeted for novel pharmacological approaches in the treatment of migraine with muscarinic agonists.

G Protein-Coupled Receptors (GPCRs)-Mediated Calcium Signaling in Ovarian Cancer: Focus on GPCRs activated by Neurotransmitters and Inflammation-Associated Molecules

G-coupled protein receptors (GCPR) involve several signaling pathways, some of them being coupled with intracellular calcium (Ca²⁺) mobilization. GPCRs were involved in migration, invasion and metastasis of different types of cancers, including ovarian cancer. Many studies have discussed the essential contribution of GPCRs activated by steroid hormones in ovarian cancer. However, ovarian cancer is also associated with altered signals coming from the nervous system, the immune system or the inflammatory environment, in which GPCRs are ‘sensing’ these molecular signals. Many studies have been oriented so far on ovarian cell lines (most of them being of human cell lines), and only few studies based on animal models or clinical studies have been devoted to the expression changes or functional role of GPCRs in ovarian cancer. In this paper, we review the alterations of GPCRs activated by neurotransmitters (muscarinic receptors, serotonin receptors, dopamine receptors, adrenoceptors) or inflammation-associated molecules (bradykinin receptors, histamine receptors, chemokine receptors) in ovarian cancer and we discuss their potential as histological biomarkers.

G-Protein-Coupled Receptors in Heart Disease

GPCRs (G-protein [guanine nucleotide-binding protein]-coupled receptors) play a central physiological role in the regulation of cardiac function in both health and disease and thus represent one of the largest class of surface receptors targeted by drugs. Several antagonists of GPCRs, such as βARs (β-adrenergic receptors) and Ang II (angiotensin II) receptors, are now considered standard of therapy for a wide range of cardiovascular disease, such as hypertension, coronary artery disease, and heart failure. Although the mechanism of action for GPCRs was thought to be largely worked out in the 80s and 90s, recent discoveries have brought to the fore new and previously unappreciated mechanisms for GPCR activation and subsequent downstream signaling. In this review, we focus on GPCRs most relevant to the cardiovascular system and discuss traditional components of GPCR signaling and highlight evolving concepts in the field, such as ligand bias, β-arrestin-mediated signaling, and conformational heterogeneity.

Role of Muscarinic Acetylcholine Signaling in Gastrointestinal Cancers

In the tumor microenvironment, various stromal and immune cells accumulate and interact with cancer cells to contribute to tumor progression. Among stromal players, nerves have recently been recognized as key regulators of tumor growth. More neurotransmitters, such as catecholamines and acetylcholine (ACh), are present in tumors, as the cells that secrete neurotransmitters accumulate by the release of neurotrophic factors from cancer cells. In this short review, we focus on the role of nerve signaling in gastrointestinal (GI) cancers. Given that muscarinic acetylcholine receptor signaling seems to be a dominant regulator of GI stem cells and cancers, we review the function and mechanism of the muscarinic ACh pathway as a regulator of GI cancer progression. Accumulating evidence suggests that ACh, which is secreted from nerves and tuft cells, stimulates GI epithelial stem cells and contributes to cancer progression via muscarinic receptors.

Biased signaling of G protein coupled receptors (GPCRs): Molecular determinants of GPCR/transducer selectivity and therapeutic potential

G protein coupled receptors (GPCRs) convey signals across membranes via interaction with G proteins. Originally, an individual GPCR was thought to signal through one G protein family, comprising cognate G proteins that mediate canonical receptor signaling. However, several deviations from canonical signaling pathways for GPCRs have been described. It is now clear that GPCRs can engage with multiple G proteins and the line between cognate and non-cognate signaling is increasingly blurred. Furthermore, GPCRs couple to non-G protein transducers, including β-arrestins or other scaffold proteins, to initiate additional signaling cascades. Receptor/transducer selectivity is dictated by agonist-induced receptor conformations as well as by collateral factors. In particular, ligands stabilize distinct receptor conformations to preferentially activate certain pathways, designated 'biased signaling'. In this regard, receptor sequence alignment and mutagenesis have helped to identify key receptor domains for receptor/transducer specificity. Furthermore, molecular structures of GPCRs bound to different ligands or transducers have provided detailed insights into mechanisms of coupling selectivity. However, receptor dimerization, compartmentalization, and trafficking, receptor-transducer-effector stoichiometry, and ligand residence and exposure times can each affect GPCR coupling. Extrinsic factors including cell type or assay conditions can also influence receptor signaling. Understanding these factors may lead to the development of improved biased ligands with the potential to enhance therapeutic benefit, while minimizing adverse effects. In this review, evidence for ligand-specific GPCR signaling toward different transducers or pathways is elaborated. Furthermore, molecular determinants of biased signaling toward these pathways and relevant examples of the potential clinical benefits and pitfalls of biased ligands are discussed.