Distinct regional expression of SNARE proteins in the feline oesophagus

Mechanical dilation, botulinum toxin A injection, and surgical myotomy with fundoplication for treatment of lower esophageal sphincter achalasia-like syndrome in dogs

Background

Megaesophagus (ME) carries a poor long‐term prognosis in dogs. In people, lower esophageal sphincter (LES) achalasia is a rare cause of ME that may respond to targeted intervention. Dogs with lower esophageal sphincter achalasia‐like syndrome (LES‐AS) have been described recently, warranting investigation of analogous targeted treatment.

Hypothesis/Objectives

Evaluate response of dogs with LES‐AS to LES mechanical dilation and botulinum toxin A (BTA) injections, with or without surgical myotomy and fundoplication. We hypothesized that clinical and videofluoroscopic swallow study (VFSS) features of LES‐AS would improve after treatment targeting functional LES obstruction.

Animals

Fourteen client‐owned dogs with LES‐AS diagnosed by VFSS.

Methods

Retrospective study. Dogs diagnosed with LES‐AS underwent treatment between April 2015 and December 2017. Outcome measures included client perception of clinical severity, body weight (BW), body condition score (BCS), regurgitation frequency, and VFSS parameters (ME, esophageal motility, gastric filling). Dogs with positive responses were considered candidates for LES myotomy with fundoplication.

Results

By a median IQR of 21 (IQR, 14‐25) days after mechanical dilation and BTA, clients reported clinical improvement in 100% of dogs, BW increased 20.4% (IQR, 12.7%‐25%), pre‐ and post‐treatment BCS was 3 (IQR, 3‐4) and 5 (IQR, 4‐5), respectively, and frequency of regurgitation decreased by 80% (IQR, 50%‐85%). Duration of effect was 40 (IQR, 17‐53) days. Despite clinical improvement, ME and abnormal esophageal motility persisted in 14 dogs. Six dogs subsequently underwent myotomy and fundoplication and maintained improvement observed after mechanical dilation and BTA.

Conclusions and Clinical Importance

Dogs with LES‐AS experienced significant, temporary, clinical improvement after mechanical dilation and BTA. Preliminary results suggest myotomy with fundoplication provide lasting clinical benefit despite persistence of ME.

The Inhibitory Effect of Botulinum Toxin Type A on Rat Pyloric Smooth Muscle Contractile Response to Substance P In Vitro

A decrease in pyloric myoelectrical activity and pyloric substance P (SP) content following intrasphincteric injection of botulinum toxin type A (BTX-A) in free move rats have been demonstrated in our previous studies. The aim of the present study was to investigate the inhibitory effect of BTX-A on rat pyloric muscle contractile response to SP in vitro and the distributions of SP and neurokinin 1 receptor (NK1R) immunoreactive (IR) cells and fibers within pylorus. After treatment with atropine, BTX-A (10 U/mL), similar to [D-Arg¹, D-Phe⁵, D-Trp^7,9, Leu¹¹]-SP (APTL-SP, 1 μmol/L) which is an NK1R antagonist, decreased electric field stimulation (EFS)-induced contractile tension and frequency, whereas, subsequent administration of APTL-SP did not act on contractility. Incubation with BTX-A at 4 and 10 U/mL for 4 h respectively decreased SP (1 μmol/L)-induced contractions by 26.64% ± 5.12% and 74.92% ± 3.62%. SP-IR fibers and NK1R-IR cells both located within pylorus including mucosa and circular muscle layer. However, fewer SP-fibers were observed in pylorus treated with BTX-A (10 U/mL). In conclusion, BTX-A inhibits SP release from enteric terminals in pylorus and EFS-induced contractile responses when muscarinic cholinergic receptors are blocked by atropine. In addition, BTX-A concentration- and time-dependently directly inhibits SP-induced pyloric smooth muscle contractility.

Role of SNARE proteins in tumourigenesis and their potential as targets for novel anti-cancer therapeutics

The function of soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) in cellular trafficking, membrane fusion and vesicle release in synaptic nerve terminals is well characterised. Recent studies suggest that SNAREs are also important in the control of tumourigenesis through the regulation of multiple signalling and transportation pathways. The majority of published studies investigated the effects of knockdown/knockout or overexpression of particular SNAREs on the normal function of cells as well as their dysfunction in tumourigenesis promotion. SNAREs are involved in the regulation of cancer cell invasion, chemo-resistance, the transportation of autocrine and paracrine factors, autophagy, apoptosis and the phosphorylation of kinases essential for cancer cell biogenesis. This evidence highlights SNAREs as potential targets for novel cancer therapy. This is the first review to summarise the expression and role of SNAREs in cancer biology at the cellular level, their interaction with non-SNARE proteins and modulation of cellular signalling cascades. Finally, a strategy is proposed for developing novel anti-cancer therapeutics using targeted delivery of a SNARE-inactivating protease into malignant cells.

A direct inhibitory effect of botulinum toxin type A on antral circular muscle contractility of guinea pig

PURPOSE

Recent studies suggest new mechanisms of Botulinum toxin (BoNT) other than inhibiting acetylcholine (ACh) release from nerve terminals. The aim of this study was to determine whether other mechanisms for BoNT exist, so that it directly inhibits smooth muscle contraction.

MATERIALS AND METHODS

Guinea pig antral muscle strips were studied in vitro after 2 hours of exposure to Botulinum toxin type A (BoNT/A). Contractile responses to electric field stimulation (EFS), high K(+) (60 mM) and ACh (100 μM) were evaluated 24 and 48 hours after antral intramuscular injection of BoNT/A or vehicle.

RESULTS

BoNT/A inhibited muscular contraction caused by high K(+) and ACh. Contractile responses to low (1 and 4 Hz) and high (8 and 20 Hz) frequency EFS of antral muscle strips 24 and 48 hours after antral intramuscular injection of BoNT/A were significantly inhibited.

CONCLUSION

The ability of BoNT/A to directly inhibit antral muscular contractility suggests a new mechanism for the pharmacologic actions of BoNT-direct inhibition of muscular contraction.

Regional differences in nitrergic innervation of the smooth muscle of murine lower oesophageal sphincter

BACKGROUND AND PURPOSE

Anatomical and pharmacological studies have demonstrated that the lower oesophageal sphincter (LES) is not a simple homogenous circular muscle with uniform innervation. Regional differences have been demonstrated in several species including humans. We investigated, for the first time in mice LES, regionally distinct physiological and pharmacological characteristics of the neuromusculature.

EXPERIMENTAL APPROACH

Conventional intracellular recordings and pharmacological techniques were employed to evaluate electrical properties and functional innervation of smooth muscle cells. Results from CD1 (control), nNOS((-/-)) and eNOS((-/-)) genetic knockout mice were compared.

KEY RESULTS

Smooth muscle of sling and clasp LES displayed unitary membrane potentials of 1- 4 mV. Transmural nerve stimulation produced a monophasic inhibitory junction potential (IJP) in the sling, whereas in the clasp a biphasic IJP, consisting of a brief IJP followed by a long-lasting slow IJP (lsIJP), was induced. Pharmacological interventions and genetically modified mice were used to demonstrate a monophasic apamin-sensitive (purinergic) component in both LES regions. However, the nitrergic IJP was monophasic in the sling and biphasic in the clasp. Unitary membrane potentials and IJPs were not different in CD1 and eNOS((-/-)) mice, suggesting no involvement of myogenic NOS.

CONCLUSION AND IMPLICATIONS

These data in mouse LES indicate that there are previously unreported regional differences in the IJP and that both the apamin-resistant monophasic and biphasic IJPs are mediated primarily by nitrergic innervation.

Distinct modulation of Kv1.2 channel gating by wild type, but not open form, of syntaxin-1A

SNARE proteins, syntaxin-1A (Syn-1A) and SNAP-25, inhibit delayed rectifier K(+) channels, K(v)1.1 and K(v)2.1, in secretory cells. We showed previously that the mutant open conformation of Syn-1A (Syn-1A L165A/E166A) inhibits K(v)2.1 channels more optimally than wild-type Syn-1A. In this report we examined whether Syn-1A in its wild-type and open conformations would exhibit similar differential actions on the gating of K(v)1.2, a major delayed rectifier K(+) channel in nonsecretory smooth muscle cells and some neuronal tissues. In coexpression and acute dialysis studies, wild-type Syn-1A inhibited K(v)1.2 current magnitude. Of interest, wild-type Syn-1A caused a right shift in the activation curves of K(v)1.2 without affecting its steady-state availability, an inhibition profile opposite to its effects on K(v)2.1 (steady-state availability reduction without changes in voltage dependence of activation). Also, although both wild-type and open-form Syn-1A bound equally well to K(v)1.2 in an expression system, open-form Syn-1A failed to reduce K(v)1.2 current magnitude or affect its gating. This is in contrast to the reported more potent effect of open-form Syn-1A on K(v)2.1 channels in secretory cells. This finding together with the absence of Munc18 and/or 13-1 in smooth muscles suggested that a change to an open conformation Syn-1A, normally facilitated by Munc18/13-1, is not required in nonsecretory smooth muscle cells. Taken together with previous reports, our results demonstrate the multiplicity of gating inhibition of different K(v) channels by Syn-1A and is compatible with versatility of Syn-1A modulation of repolarization in various secretory and nonsecretory (smooth muscle) cell types.

Vesicle-associated protein-A is differentially expressed during intestinal smooth muscle cell differentiation

Gastrointestinal (GI) smooth muscle diseases represent a major health concern affecting in excess of 2 million people each year. Little is currently known regarding the molecular mechanisms controlling either normal or pathogenic GI smooth muscle development. In an effort to identify the specific gene products responsible for modulating GI smooth muscle cell (SMC) differentiation, we performed differential display on distinct intestinal SMC (ISMC) phenotypes. This analysis identified over 40 unique transcripts that appeared to be differentially expressed in distinct SMC phenotypes. One such transcript that appeared to be preferentially expressed in immature smooth muscle myocytes was identified as vesicle-associated membrane protein, associated protein A (VAP-A). Northern blot analysis confirmed that VAP-A was expressed threefold higher in immature smooth muscle myocytes when compared with both smooth muscle myoblasts and mature smooth muscle myocytes. VAP-A mRNA was differentially expressed during normal rat development and showed peak levels of expression in the intestine during late embryogenesis and early neonatal development. These observations provide the first evidence that VAP-A-mediated membrane trafficking may play an important role in modulating ISMC differentiation.

Inhibitory effects of botulinum toxin on pyloric and antral smooth muscle

Botulinum toxin injection into the pylorus is reported to improve gastric emptying in gastroparesis. Classically, botulinum toxin inhibits ACh release from cholinergic nerves in skeletal muscle. The aim of this study was to determine the effects of botulinum toxin on pyloric smooth muscle. Guinea pig pyloric muscle strips were studied in vitro. Botulinum toxin type A was added; electric field stimulation (EFS) was performed every 30 min for 6 h. ACh (100 microM)-induced contractile responses were determined before and after 6 h. Botulinum toxin caused a concentration-dependent decrease of pyloric contractions to EFS. At a low concentration (2 U/ml), botulinum toxin decreased pyloric contractions to EFS by 43 +/- 9% without affecting ACh-induced contractions. At higher concentrations (10 U/ml), botulinum toxin decreased pyloric contraction to EFS by 75 +/- 7% and decreased ACh-induced contraction by 79 +/- 9%. In conclusion, botulinum toxin inhibits pyloric smooth muscle contractility. At a low concentration, botulinum toxin decreases EFS-induced contractile responses without affecting ACh-induced contractions suggesting inhibition of ACh release from cholinergic nerves. At higher concentrations, botulinum toxin directly inhibits smooth muscle contractility as evidenced by the decreased contractile response to ACh.

SNAP-25 inhibits L-type Ca2+ channels in feline esophagus smooth muscle cells

We recently reported that non-secretory gastrointestinal smooth muscle cells also possessed SNARE proteins, of which SNAP-25 regulated Ca(2+)-activated (K(Ca)) and delayed rectifier K(+) channels (K(V)). Voltage-gated, long lasting (L-type) calcium channels (L(Ca)) play an important role in excitation-contraction coupling of smooth muscle. Here, we show that SNAP-25 could also directly inhibit the L-type Ca(2+) channels in feline esophageal smooth muscle cells at the SNARE complex binding synprint site. SNARE proteins could therefore regulate additional cell actions other than membrane fusion and secretion, in particular, coordinated muscle membrane excitability and contraction, through their actions on membrane Ca(2+) and K(+) channels.