Update on Gastroesophageal Adenocarcinoma Targeted Therapies

Gastroesophageal cancer (GEC) remains a major cause of cancer-related mortality worldwide. Although the incidence of distal gastric adenocarcinoma (GC) is declining in the United States, proximal esophagogastric junction adenocarcinoma (EGJ) incidence is rising. GC and EGJ, together, are treated uniformly in the metastatic setting as GEC. Overall survival in the metastatic setting remains poor, with few molecular targeted approaches having been successfully incorporated into routine care to date-only first-line anti-HER2 therapy for ERBB2 amplification and second-line anti-VEGFR2 therapy. This article reviews aberrations in epidermal growth factor receptor, MET, and ERBB2, their therapeutic implications, and future directions in targeting these pathways.

HER2 Testing and Clinical Decision Making in Gastroesophageal Adenocarcinoma: Guideline From the College of American Pathologists, American Society for Clinical Pathology, and the American Society of Clinical Oncology

Context ERBB2 (erb-b2 receptor tyrosine kinase 2 or HER2) is currently the only biomarker established for selection of a specific therapy for patients with advanced gastroesophageal adenocarcinoma (GEA). However, there are no comprehensive guidelines for the assessment of HER2 in patients with GEA. Objectives To establish an evidence-based guideline for HER2 testing in patients with GEA, formalize the algorithms for methods to improve the accuracy of HER2 testing while addressing which patients and tumor specimens are appropriate, and to provide guidance on clinical decision making. Design The College of American Pathologists (CAP), American Society for Clinical Pathology (ASCP), and the American Society of Clinical Oncology (ASCO) convened an Expert Panel to conduct a systematic review of the literature to develop an evidence-based guideline with recommendations for optimal HER2 testing in patients with GEA. Results The Panel is proposing 11 recommendations with strong agreement from the open comment participants. Recommendations The Panel recommends that tumor specimen(s) from all patients with advanced GEA, who are candidates for HER2-targeted therapy, should be assessed for HER2 status before the initiation of HER2-targeted therapy. Clinicians should offer combination chemotherapy and an HER2-targeted agent as initial therapy for all patients with HER2-positive advanced GEA. For pathologists, guidance is provided for morphologic selection of neoplastic tissue, testing algorithms, scoring methods, interpretation and reporting of results, and laboratory quality assurance. Conclusion This guideline provides specific recommendations for assessment of HER2 in patients with advanced GEA while addressing pertinent technical issues and clinical implications of the results.

HER2 testing in gastric cancer: An update

Human epidermal growth factor receptor 2 (HER2) overexpression is increasingly recognized as a frequent molecular abnormality in gastric and gastroesophageal cancer. With the recent introduction of HER2 molecular targeted therapy for patients with advanced gastric cancer, determination of HER2 status is crucial in order to select patients who may benefit from this treatment. This paper provides an update on our knowledge of HER2 in gastric and gastroesophageal cancer, including the prognostic relevance of HER2, the key differences between HER2 protein expression interpretation in breast and gastric cancer, the detection methods and the immunohistochemistry scoring system.

Anti-reflux anastomosis following esophagectomy for adenocarcinoma of the esophagogastric junction: impact of duodenogastroesophageal reflux and expression of cyclooxygenase-2 in the remnant esophagus

OBJECTIVE

Reflux is the principal complication for patients after esophagectomy with gastric reconstruction. The aim of this study was to investigate the effect of the modified Nissen fundoplication after resection of adenocarcinoma from the esophagogastric junction (AEG) on controlling the reflux and the role of duodenogastroesophageal reflux (DGER) and cyclooxygenase-2 (COX-2) expression level in the remnant esophagus.

PATIENTS AND METHODS

Sixty patients with AEG were randomly divided into two groups: (i) the conventional anastomosis group and (ii) the anti-reflux anastomosis group. Fifty esophagectomized patients were invited to participate in postoperative follow-up after 6 to 12 months. Among those we had 29 cases in the conventional anastomosis group and 21 in the anti-reflux anastomosis group. We used endoscopy, simultaneous 24 hours esophageal pH and bilirubin monitoring in this study. The COX-2 expression level in the remnant esophagus was detected using real-time PCR.

RESULTS

The reflux esophagitis prevalence in anti-reflux anastomosis group was comparable to that in the conventional group (p = 0.154). DeMeester score and fraction time of bilirubin abs >0.14 decreased more intensely in the anti-reflux anastomosis group (p < 0.05). The COX-2 expression level in of anti-reflux anastomosis group was evidently lower than that in the conventional anastomosis group (p = 0.022) while it was meaningfully higher compared to the normal control group (p = 0.046). COX-2 up-regulation as well as high prevalence of esophagitis were observed in simultaneous acid reflux and DGER (p < 0.05).

CONCLUSIONS

Although modified fundoplication following resection of AEG did not achieve an optimal effect on controlling reflux, it was very effective in decreasing the reflux. COX-2 expression monitoring can be considered as a possible new way to evaluate the impact of anti-reflux surgery. DGER occurring in acidic environment could develop severe reflux esophagitis and up-regulate the COX-2 expression.

Role of human epidermal growth factor receptor 2 in gastric cancer: biological and pharmacological aspects

Amplification of the human epidermal growth factor receptor 2 (HER2) gene and overexpression of the HER2 protein is found in 15%-20% of patients with gastric and gastroesophageal junction cancer. The degree of HER2 overexpression and amplification varies with the location of the carcinoma, with higher expression in the gastroesophageal and proximal parts compared to the distal parts of the stomach. Further, HER2 overexpression and amplification also seems to be related to the Lauren histological classification, with higher levels found in the intestinal phenotype compared to the diffuse and mixed types. The prognostic properties of HER2 overexpression and amplification are still under debate, but a large number of studies seem to indicate that HER2 is a negative prognostic factor. The usefulness of HER2 targeted therapy in gastric cancer was demonstrated in the ToGA trial, where HER2-positive patients with advanced gastric and gastroesophageal junction adenocarcinoma were randomized to receive 5-FU/capecitabine and cisplatin, either alone or in combination with trastuzumab. A statically significant gain in overall survival was seen in patients who received the combined treatment of trastuzumab and chemotherapy. Patients with a strong overexpression of the HER2 protein (IHC3+) specifically benefited from the treatment, with a median overall survival of 17.9 mo. As a consequence of the positive results of the ToGA trial, patients with advanced gastric or gastroesophageal junction adenocarcinoma are now routinely tested for HER2. The ToGA trial must be characterized as a landmark in the treatment of gastric cancer and it has paved the way for a number of new HER2 targeted compounds such as pertuzumab, ado-trastuzumab emtansine, lapatinib, afatinib, and dacomitinib, which are currently undergoing phase II and III clinical testing. Overall, this review will discuss the current status of HER2 in gastric and gastroesophageal junction cancer and the future direction in relation to HER2 target therapy.

Aldo-keto reductase family 1 member C3 (AKR1C3) is expressed in adenocarcinoma and squamous cell carcinoma but not small cell carcinoma

Human aldo-keto reductase family 1 member C3 (AKR1C3) was initially identified as a critical enzyme in reducing 5α-dihydrotestosterone (5α-DHT) to 5α-androstane-3α,17β-diol (3α-diol) and oxidizing 3α-diol to androsterone. Based on these enzymatic activities, AKR1C3 was originally named type 2 3α-hydroxysteroid dehydrogenase (HSD)/type 5 17β-HSD. Additionally, AKR1C3 was demonstrated to be capable of metabolizing other steroids including estrogen and progesterone. Subsequently, AKR1C3 was shown to possess 11-ketoprostaglandin reductase activity in metabolizing prostaglandins and dihydrodiol dehydrogenase x (DDx) activity in metabolizing xenobiotics. Tissue distribution of AKR1C3 has been detected in both sex hormone-dependent organs such as the testis, breast, endometrium, and prostate as well as sex hormone-independent organs including the kidney and urothelium. Although prominent expression of AKR1C isozymes has been reported in human non-small cell lung carcinoma (NSCLC), the expression of AKR1C3 in small cell carcinoma of the lung has not been described. Also, the expression of AKR1C3 in normal lung has not been described. In this study, we demonstrated strong AKR1C3 immunoreactivity in bronchial epithelium but not in bronchial glands or alveolar pneumocytes. Strong AKR1C3 immunoreactivity was also demonstrated in columnar epithelium but only weak immunoreactivity in squamous epithelium of the gastrointestinal junction. Although AKR1C3 immunoreactivity was absent in small cell carcinoma of the lung, positive AKR1C3 immunoreactivity was extensively present in both adenocarcinoma and squamous cell carcinoma arising from the lung and the gastroesophageal junction. AKR1C3 may serve as an adjunct marker for differentiating small cell carcinoma from NSCLC. However, roles of AKR1C3 in adenocarcinoma, squamous cell carcinoma, and small cell carcinoma pathogenesis require further studies.

[The indices of pro- and antioxidant state of the gastro-esophageal junction tissues in experimental gastroesophageal reflux disease]

Experimental investigation on studying of pro- and antioxidant state in esophageal tissues was performed. It was established, that accumulation of products of the proteins and lipids oxidation during inflammatory process course coincides with significant lowering of the antioxidant enzymes activity. The data obtained trusts the various diagnostic significance of diienic conjugates and malonic dialdehyde (MDA) levels. The increase of MDA concentration as well as of products of the oxidational modifications proteins, owing basic character, was revealed as a typical biochemical marker of acid-peptic injury of esophageal tissues.

Bile acids induce ectopic expression of intestinal guanylyl cyclase C Through nuclear factor-kappaB and Cdx2 in human esophageal cells

BACKGROUND & AIMS

Although progression to adenocarcinoma at the gastroesophageal junction reflects exposure to acid and bile acids associated with reflux, mechanisms mediating this transformation remain undefined. Guanylyl cyclase C (GC-C), an intestine-specific tumor suppressor, may represent a mechanism-based marker and target of transformation at the gastroesophageal junction. The present studies examine the expression of GC-C in normal tissues and tumors from esophagus and stomach and mechanisms regulating its expression by acid and bile acids.

METHODS

Gene expression was examined by reverse-transcription polymerase chain reaction, promoter analysis, immunohistochemistry, immunoblotting, and functional analysis. Promoter transactivation was quantified by using luciferase constructs and mutational analysis. DNA binding of transcription factors was examined by electromobility shift analysis.

RESULTS

GC-C mRNA and protein were ectopically expressed in approximately 80% of adenocarcinomas arising in, but not in normal, esophagus and stomach. Similarly, in OE19 human esophageal cancer cells, deoxycholate and acid induced expression of GC-C. This was associated with the induction of expression of Cdx2, a transcription factor required for GC-C expression. In turn, induction of Cdx2 expression by deoxycholate was mediated by binding sites in the proximal promoter for nuclear factor kappaB (NF-kappaB). Furthermore, deoxycholate increased NF-kappaB activity, associated with nuclear translocation and Cdx2 promoter binding of the NF-kappaB subunit p50. Moreover, a dominant negative construct for NF-kappaB prevented deoxycholate-induced p50 nuclear translocation and activation of the Cdx2 promoter.

CONCLUSIONS

Transformation associated with reflux at the gastroesophageal junction reflects activation by bile acid and acid of a transcriptional program involving NF-kappaB and Cdx2, which mediate intestinal metaplasia and ectopic expression of GC-C.

Hypermethylation and loss of expression of glutathione peroxidase-3 in Barrett's tumorigenesis

Chronic gastroesophageal reflux disease is a known risk factor for Barrett's esophagus (BE), which induces oxidative mucosal damage. Glutathione peroxidase-3 (GPx3) is a secretory protein with potent extracellular antioxidant activity. In this study, we have investigated the mRNA and protein expression of GPx3, and explored promoter hypermethylation as an epigenetic mechanism for GPx3 gene inactivation during Barrett's carcinogenesis. Quantitative real-time reverse transcription polymerase chain reaction on 42 Barrett's adenocarcinomas (BAs) revealed consistently reduced levels of GPx3 mRNA in 91% of tumor samples. GPx3 promoter hypermethylation was detected in 62% of Barrett's metaplasia, 82% of dysplasia, and 88% of BA samples. Hypermethylation of both alleles of GPx3 was most frequently seen in BAs (P = .001). Immunohistochemical staining of GPx3 in matching tissue sections (normal, BE, Barrett's dysplasia, and BA) revealed strong immunostaining for GPx3 in normal esophageal and gastric tissues. However, weak to absent GPx3 staining was observed in Barrett's dysplasia and adenocarcinoma samples where the promoter was hypermethylated. The degree of loss of immunohistochemistry correlated with the hypermethylation pattern (monoallelic versus biallelic). The observed high frequency of promoter hypermethylation and progressive loss of GPx3 expression in BA and its associated lesions, together with its known function as a potent antioxidant, suggest that epigenetic inactivation and regulation of glutathione pathway may be critical in the development and progression of BE.

Distinct kinases are involved in contraction of cat esophageal and lower esophageal sphincter smooth muscles

Contraction of smooth muscle depends on the balance of myosin light chain kinase (MLCK) and myosin light chain phosphatase (MLCP) activities. Because MLCK activation depends on the activation of calmodulin, which requires a high Ca2+concentration, phosphatase inhibition has been invoked to explain contraction at low cytosolic Ca2+levels. The link between activation of the Ca2+-independent protein kinase Cε (PKCε) and MLC phosphorylation observed in the esophagus (ESO) (Sohn UD, Cao W, Tang DC, Stull JT, Haeberle JR, Wang CLA, Harnett KM, Behar J, and Biancani P. Am J Physiol Gastrointest Liver Physiol 281: G467–G478, 2001), however, has not been elucidated. We used phosphatase and kinase inhibitors and antibodies to signaling enzymes in combination with intact and saponin-permeabilized isolated smooth muscle cells from ESO and lower esophageal sphincter (LES) to examine PKCε-dependent, Ca2+-independent signaling in ESO. The phosphatase inhibitors okadaic acid and microcystin-LR, as well as an antibody to the catalytic subunit of type 1 protein serine/threonine phosphatase, elicited similar contractions in ESO and LES. MLCK inhibitors (ML-7, ML-9, and SM-1) and antibodies to MLCK inhibited contraction induced by phosphatase inhibition in LES but not in ESO. The PKC inhibitor chelerythrine and antibodies to PKCε, but not antibodies to PKCβII, inhibited contraction of ESO but not of LES. In ESO, okadaic acid triggered translocation of PKCε from cytosolic to particulate fraction and increased activity of integrin-linked kinase (ILK). Antibodies to the mitogen-activated protein (MAP) kinases ERK1/ERK2 and to ILK, and the MAP kinase kinase (MEK) inhibitor PD-98059, inhibited okadaic acid-induced ILK activity and contraction of ESO. We conclude that phosphatase inhibition potentiates the effects of MLCK in LES but not in ESO. Contraction of ESO is mediated by activation of PKCε, MEK, ERK1/2, and ILK.

Effects of nitric oxide synthase inhibitor to esophagus in a feline esophagitis model

The present study explores the effects of nitric oxide synthase inhibitor on esophageal motility in a feline model with esophagitis. Perfusion of the esophagus with acid produced inflammatory changes of esophageal mucosa. The esophageal motility was measured before and after the perfusion. One group of cats was given nitric oxide inhibitor orally at the same time as the perfusion of acid. The control group was given water instead. Esophagitis impairs the motility of the esophagus. However, the esophageal motility of the cats that were given nitric oxide synthase inhibitor decreased less than that of the control group. The results suggested that during esophagitis there is an alteration of the nitric oxide synthase/nitric oxide pathway in the esophagus, which may be one of the important mechanisms of esophageal motility dysfunction.

Effects of phosphodiesterase inhibitors on oesophageal neuromuscular functions

The cyclic nucleotides adenosine 3',5'-cyclic monophosphate (cAMP) and guanosine 3',5'-cyclic monophosphate (cGMP) mediate the inhibitory effects of vasoactive intestinal polypeptide and nitric oxide on oesophageal smooth muscle. Phosphodiesterases (PDE) terminate their actions. We hypothesized that PDE inhibitors alter nerve-induced responses of oesophageal and lower oesophageal sphincter (LES) smooth muscle. An electrical field known to activate intrinsic oesophageal nerves was used to stimulate transverse muscle strips from the opossum oesophagus. This produced a contractile off-response from circular oesophageal muscle and a biphasic relaxation of the LES - an initial rapid relaxation (R1) and a slower sustained relaxation (R2). The effects on LES and oesophageal muscle of zaprinast (type V), zardaverine (type III/IV) and theophylline (non-specific) PDE inhibitors were explored. All three PDE inhibitors decreased LES tone and attenuated the off-response. Zaprinast and theophylline increased the latency of the off-response. Zaprinast prolonged R1, and slowed its recovery. It also increased the percentage relaxation of the second R2. Zardaverine increased the percentage relaxation of R2. Theophylline slowed the recovery of R2. PDEs play a role in maintaining LES tone and its recovery after LES relaxation. They may also modulate oesophageal motor activity.

MAPK mediates PKC-dependent contraction of cat esophageal and lower esophageal sphincter circular smooth muscle

Esophageal (ESO) circular muscle contraction and lower esophageal sphincter (LES) tone are PKC dependent. Because MAPKs may be involved in PKC-dependent contraction, we examined ERK1/ERK2 and p38 MAPKs in ESO and LES. In permeabilized LES muscle cells, ERK1/2 antibodies reduced 1,2-dioctanoylglycerol (DG)- and threshold ACh-induced contraction, which are PKC dependent, but not maximal ACh, which is calmodulin dependent. LES tone was reduced by the ERK1/2 kinase inhibitor PD-98059 and by the p38 MAPK inhibitor SB-203580. In permeable ESO cells, ACh contraction was reduced by ERK1/ERK2 and p38 MAPK antibodies and by PD-98059 and SB-203580. ACh increased MAPK activity and phosphorylation of MAPK and of p38 MAPK. The 27-kDa heat shock protein (HSP27) antibodies reduced ACh contraction. HSP27 and p38 MAPK antibodies together caused no greater inhibition than either one alone. p38 MAPK and HSP27 coprecipitated after ACh stimulation, suggesting that HSP27 is linked to p38 MAPK. These data suggest that PKC-dependent contraction in ESO and LES is mediated by the following two distinct MAPK pathways: ERK1/2 and HSP27-linked p38 MAPK.

Roles of guanylate cyclase in responses to myogenic and neural nitric oxide in canine lower esophageal sphincter

Whether cGMP and cytosolic guanylate cyclase (cGC) mediate responses of canine lower esophageal sphincter (LES) to nitric oxide (NO) released from nerves, produced in muscle, or added exogenously was evaluated in vitro. 1-H-(1,2,4)oxadiazole(4,3-alpha)quinoxalin-1-1 (ODQ), inhibitor of cGC, reduced relaxations to nerve stimulation and sodium nitroprusside but not to nitric-oxide synthase activity-dependent outward K(+)-currents in isolated muscle cells. ODQ also failed to increase tone after nerve blockade. Nonspecific K(+) channel blocker, TEA ion at 20 mM was previously shown to increase tone, occlude NO-mediated modulation of tone, and inhibit NO-dependent outward currents but not neural relaxation in LES cells. In this study, TEA abolished neural relaxation and nearly abolished relaxation to sodium nitroprusside when present with ODQ. We conclude that mechanisms coupling NO in canine LES to responses vary with the source of NO. ODQ-dependent mechanisms, presumably involving cGC, mediate actions of NO from nerves, but NO from muscle utilizes TEA-sensitive but not ODQ-dependent mechanisms to modulate tone and outward currents. Exogenous NO utilizes both TEA- and ODQ-dependent mechanisms.

Inducible and neuronal nitric oxide synthase involvement in lipopolysaccharide-induced sphincteric dysfunction

We examined the effect of endotoxin lipopolysaccharide (LPS) on the basal tone and on the effects of different stimuli and agonists and transcriptional and translational expression of nitric oxide (NO) synthase (NOS) isozymes in the lower esophageal sphincter (LES), pyloric sphincter (PS), and internal anal sphincter (IAS). NO release was also examined before and after LPS. LPS caused a dose-dependent fall in the basal tone and augmentation of the relaxation caused by nonadrenergic, noncholinergic (NANC) nerve stimulation in the LES and IAS. In the PS, LPS had no significant effect on the basal tone and caused an attenuation of the NANC relaxation and an augmentation of the contractile response of muscarinic agonist. Interestingly, the smooth muscle relaxation by atrial natriuretic factor was suppressed in the LES and IAS but not in the PS. These changes in the sphincteric function following LPS may be associated with increase in the inducible NOS (iNOS) expression since they were blocked by iNOS inhibitor L-canavanine. Augmentation of NANC relaxation in the LES and IAS smooth muscle by LPS may be due to the increased activity of neuronal NOS and NO production.

Innervation of the esophagus in mice that lack MASH1

The striated muscle of the esophagus differs from other striated muscle, because it develops by the transdifferentiation of smooth muscle, and the motor end plates receive a dual innervation from vagal (cholinergic) motor neurons and nitric oxide synthase (NOS)-containing enteric neurons. Mash1-/- mice have no enteric neurons in their esophagus and die within 48 hours of birth without milk in their stomachs (Guillemot et al. [1993] Cell 75:463-476). In this study, the innervation of the esophagus of newborn Mash1-/-, Mash1+/- and wild type mice was examined. There was no difference between Mash1-/-, Mash1+/-, and wild type mice in the transdifferentiation of the muscle and the development of nicotinic receptor clusters. However, there were significantly more cholinergic nerve terminals per motor end plate in Mash1-/- mice than Mash1+/- or wild type mice. Each of the Mash1-/- mice had fewer than 50 NOS neurons per esophagus, compared with approximately 3,000 in wild type mice. Newborn Mash1+/- mice also contained significantly fewer NOS neurons than wild type mice. In Mash1-/- mice, NOS nerve fibers were virtually absent from the external muscle but were present at the myenteric plexus. Unlike that of newborn wild type mice, the lower esophageal sphincter of Mash 1-/- mice lacked NOS nerve fibers; this may explain the absence of milk in the stomach. We conclude that 1) the transdifferentiation of the esophageal muscle and the development of the extrinsic innervation do not require enteric neurons or MASH1, 2) extrinsic NOS neurons only innervate the myenteric plexus.

Myogenic NOS in canine lower esophageal sphincter: enzyme activation, substrate recycling, and product actions

Depolarization elicited outward K+ currents from canine lower esophageal sphincter (LES) muscle cells, primarily through iberiotoxin (IbTX)- and tetraethylammonium-sensitive Ca(2+)-dependent K+ channels. Current magnitudes varied with pipette Ca2+ concentration (EC50 = 108.5 nM). NG-nitro-L-arginine (L-NNA, 10(-4)M), IbTX (10(-8)M), or buffering intracellular Ca2+ to 8 nM decreased outward currents > 80%. Sodium nitroprusside (NaNP, 10(-4)M) restored L-NNA-inhibited or low intracellular Ca2+ concentration (not IbTX)-inhibited currents. L-NNA or IbTX application depolarized LES cells from -43 to -35 mV. NaNP restored the membrane potential to -46 mV after L-NNA but not after IbTX application. Nifedipine (30 microM) reduced outward currents and abolished or reduced L-NNA or NaNP effects, respectively. Immunocytochemistry revealed the presence of both argininosuccinate synthetase and argininosuccinate lyase in LES muscle cells. L-Citrulline, like L-arginine, reversed L-NNA inhibition of outward currents; only L-arginine reversed inhibition of outward currents by an antibody to argininosuccinate synthetase. Therefore, endogenous nitric oxide production, activated by Ca2+ entrance involving L-type Ca2+ channels, may continuously enhance outward currents to modulate LES muscle cell membrane potential and excitability.

Myogenic nitric oxide synthase activity in canine lower oesophageal sphincter: morphological and functional evidence

1. Studies on canine lower oesophageal sphincter (LOS) evaluated the existence and function of a myogenic, nitric oxide synthase (NOS) by use of immunocytochemistry for NOS isozymes, NADPH-d histochemistry, [3H]-L-arginine to [3H]-L-citrulline transformation. In addition, functional studies in the muscle bath were performed. 2. Smooth muscle bundles or freshly isolated smooth muscle cells of LOS were NADPH-d reactive but did not recognize some antibodies against neural, endothelial or inducible NOS. NADPH-d reactivity and immunoreactivity to a neural NOS antibody were colocalized in LOS enteric nerves. Muscle plasma membrane-enriched fractions from fresh and cultured LOS cells converted [3H]-L-arginine to [3H]-L-citrulline; activity was mostly Ca2+/calmodulin-dependent. 3. N-Nitro-L-arginine (L-NOARG) persistently increased tone (blocked by L-arginine) in muscle strips despite blockade of nerve function. Nifedipine prevented or abolished L-NOARG-induced, but not carbachol-induced, contraction showing that tone increase by L-NOARG required functional L-Ca channels. 4. Membrane-bound, myogenic NOS in canine LOS may release NO continuously when Ca2+ entry through L-Ca channels occurs under physiological conditions and thereby modulate tone in LOS.

Nonadrenergic-noncholinergic relaxations of isolated circular muscle from South American opossum esophagogastric junction: is nitric oxide the inhibitory mediator?

Nonadrenergic-noncholinergic (NANC) inhibitory nerves are responsible for most of the nerve induced relaxations of gastrointestinal muscle. It has recently been proposed that NANC nerves may release nitric oxide (NO) or a related compound derived from L-arginine. We have recently shown that the South American (SA) opossum is another suitable model to elucidate the mechanism involved in these NANC relaxations. In the present study the effect of NO synthase inhibitors as well as NO inactivators on the NANC-nerve induced relaxations of the circular muscle of the esophagogastric junction (EGJ) of the SA opossum was investigated. It was observed that the NO synthase inhibitors, L-NOARG and L-NAME, caused a concentration-dependent reduction of NANC-nerve induced relaxations which was reversed by L- but not D-arginine. The NO-donors sodium nitroprusside and hydroxilamine as well as NO caused concentration-dependent relaxations of the EGJ circular muscle. In the myenteric plexus of this region, NADPH-diaphorase positive neurons and nerve fibers were observed while in the circular muscle layer only numerous positive fibers were found. The NO inactivators, hydroquinone, pyrogallol and carboxy-PTIO, reduced NO-induced relaxations but failed to affect NANC nerve- and sodium nitroprusside-induced relaxations. Taken together, these findings indicate that NANC nerve induced relaxation of the SA opossum EGJ circular muscle is dependent on neural NO synthase activity and suggest that the neurotransmitter being released is a superoxide resistant molecule, which is unlikely to be the NO radical, or that the activity of NO synthase is required for the release of the actual neurotransmitter rather than for synthesizing the neuromediator.

Morphological relations between haem oxygenases, NO-synthase and VIP in the canine and feline gastrointestinal tracts

Carbon monoxide (CO), produced by haem oxygenase (HO), has been suggested as a messenger molecule in the central and peripheral nervous systems. In the present study, we have investigated the occurrence of the two isoforms of HO, HO-2 and HO-1 in the canine and feline gastrointestinal tracts, including the small and large intestine and the gastrointestinal sphincters. An abundance of nerve cell bodies that contained immunoreactivity for HO-2 was found in the submucosal and myenteric plexuses. HO-2 immunoreactivity was frequently co-localized with nitric oxide synthase (NOS) or vasoactive intestinal peptide (VIP) immunoreactivities and was also observed in some nerve fibres, certain non-neuronal cells dispersed among smooth muscle bundles, and in vascular endothelium. The antiserum against HO-1 revealed immunoreactivity in nerve cell bodies in the enteric plexuses, in nerve fibres and in non neuronal cells in the smooth muscle layers. Some of the nerve structures were also NOS- or VIP-immunoreactive. These results demonstrate the presence of HO isoenzymes in nerves and other structures of the canine and feline gastrointestinal tracts and support the view that CO may have a role as a messenger molecule in the enteric nervous system.

Different protein kinase C isozymes mediate lower esophageal sphincter tone and phasic contraction of esophageal circular smooth muscle

Circular muscle of the esophagus (ESO) is normally relaxed and contracts phasically in response to neural stimuli. In contrast, lower esophageal sphincter (LES) circular muscle maintains spontaneous tone and relaxes in response to neural stimuli. We have previously shown that in vitro, spontaneous LES tone and contraction of ESO in response to acetylcholine (ACh) are antagonized by protein kinase C (PKC) inhibitors, suggesting that PKC activation is responsible for these functions. In the current study, Western blot analysis of LES and ESO revealed PKC-alpha, -betaII, and -gamma isozymes in LES circular muscle, but only PKC-betaII translocated from the cytosolic to the membrane fraction in response to ACh. In contrast, ESO contained PKC-betaII, -gamma, and -epsilon, and only PKC-epsilon translocated to the membrane fraction in response to ACh. In LES single cells isolated by enzymatic digestion and permeabilized by saponin, 1-2-dioctanoylglycerol-mediated contraction was inhibited by preincubation with PKC-betaII antiserum but not by other PKC antisera. In esophageal cells, contraction was inhibited by the PKC-epsilon antiserum but not by antisera against other PKC isozymes. N-Myristoylated peptides derived from the pseudosubstrate sequences of PKC isozymes were used to inhibit saponin, 1-2-dioctanoylglycerol-induced contraction of LES and ESO smooth muscle cells. Contraction of LES cells was reduced by the alpha beta gamma pseudosubstrate but not by the alpha, delta, or epsilon pseudosubstrate. Contraction of ESO cells was reduced by the epsilon pseudosubstrate but not by the alpha, delta, or alpha beta gamma pseudosubstrate. We conclude that different types of contractile activity in the ESO and LES are mediated by different PKC isozymes. LES contraction is mediated by the calcium-dependent PKC-betaII, whereas contraction of ESO is mediated by the calcium-independent PKC-epsilon.

Carbon monoxide-induced relaxation and distribution of haem oxygenase isoenzymes in the pig urethra and lower oesophagogastric junction

1. The distribution of the carbon monoxide (CO) producing enzymes haem oxygenase (HO)-1 and -2 was studied by immunohistochemistry in the pig's lower urinary tract, including bladder extramural arteries, and the oesophagogastric junction (OGJ). In isolated smooth muscle from the urethra and the OGJ, the mechanisms for CO-induced relaxations were characterized by measurement of cyclic nucleotide levels and by responses to the guanylate cyclase inhibitor methylene blue and some K+ channel inhibitors. 2. HO-2 immunoreactivity was observed in coarse nerve trunks within the smooth muscle of the urethra and OGJ, and in nerve cell bodies of the enteric plexuses of the OGJ. Furthermore, the vascular endothelium of the intramural vessels of the urethra, bladder and OGJ, and the extramural vessels of the bladder, displayed HO-2 immunoreactivity. Two different antisera against HO-1 were used, but only one displayed immunoreactivity in neuronal structures. HO-1 immunoreactivity, as displayed by this antiserum, was seen in nerve cells, coarse nerve trunks and varicose nerve fibres in the smooth muscle of the urethra and OGJ. Some HO-2 and/or HO-1 (as displayed by both HO-1 antisera) immunoreactive cells with a non-neuronal appearance were observed within the smooth muscle of the OGJ, bladder and urethra. 3. In the urethral preparations, exogenously applied CO (72 microM) evoked a relaxation amounting to 76 +/- 6%. The relaxation was associated with an increase in cyclic GMP, but not cyclic AMP, content. CO-evoked relaxations were not significantly reduced by treatment with methylene blue, or by inhibitors of voltage-dependent (4-aminopyridine), high (iberiotoxin, charybdotoxin) and low (apamin) conductance Ca(2+)-activated, and ATP-sensitive (glibenclamide) K+ channels. Bladder strips, and ring preparations from the extramural arteries of the bladder, did not respond to exogenously administered CO (12-72 microM). 4. In the OGJ, exogenously applied CO evoked a relaxation of 86 +/- 6%, which was associated with an increase in cyclic GMP, but not cyclic AMP, content. Treatment with 30 microM methylene blue raised the spontaneously developed muscle tone, and reduced the maximum relaxation evoked by CO to 33 +/- 9%. Addition of 4-aminopyridine, apamin, glibenclamide, iberiotoxin, charybdotoxin or glibenclamide had no effect on the relaxations. 4-aminopyridine (0.1-1 mM), iberiotoxin (0.1 microM) and charybdotoxin (0.1 microM) increased the spontaneously developed tone, and a combination of charybdotoxin and apamin reduced CO-induced (24 microM CO) relaxations. 5. The present findings demonstrate the presence of HO in both neuronal and non-neuronal cells in the pig OGJ and lower urinary tract. CO produces relaxation of the smooth muscle in the OGJ and urethra, associated with a small increase in cyclic GMP concentration in both regions. Relaxations evoked by CO in the urethra do not seem to involve voltage-dependent, low and high conductance, or ATP-dependent K+ channels. However, in the OGJ relaxations evoked by CO can be attenuated by methylene blue and a combination of charybdotoxin and apamin.

Localization and activity of haem oxygenase and functional effects of carbon monoxide in the feline lower oesophageal sphincter

1. In the feline lower oesophageal sphincter (LOS), the distribution of the carbon monoxide (CO) producing enzymes haem oxygenase (HO)-1 and -2 was studied by immunohistochemistry and confocal microscopy, the HO activity was measured and the possible role for CO as a mediator of relaxation was investigated. 2. HO-2 immunoreactivity was abundant in nerve cell bodies of the submucosal and myenteric plexus. Approximately 50% of the HO-2-containing myenteric cell bodies were also nitric oxide synthase- and vasoactive intestinal peptide (VIP)-immunoreactive. In addition, HO-2 immunoreactivity was seen in nerve fibres, in non-neuronal cells dispersed in the smooth muscle and in arterial endothelium. HO-1 immunoreactivity was confined to non-neuronal cells in the smooth muscle, similar to those positive for HO-2. 3. Activity of HO, measured as CO production, was observed in LOS homogenates at a rate of 1.00 +/- 0.05 nmol mg-1 protein h-1. This production was inhibited by the HO inhibitor, zinc protoporphyrin-IX (ZnPP). 4. In isolated circular smooth muscle strips of LOS, developing spontaneous tone, exogenously administered CO evoked a concentration-dependent relaxation reaching a maximum of 93 +/- 3%. This relaxation was accompanied by an increase in cyclic GMP, but not cyclic AMP levels. The relaxant response was attenuated by methylene blue, but unaffected by tetrodotoxin. Repeated exposure to CO resulted in a progressive reduction of the relaxant response. 5. ZnPP caused a rightward-shift of the concentration-response curves for the relaxant responses to VIP, peptide histidine isoleucine, and pituitary adenylate cyclase activating peptide 27. 6. ZnPP and tin protoporphyrin-IX (another inhibitor of HO) did not affect nonadrenergic, noncholinergic relaxations induced by electrical field stimulation. Nor did ZnPP affect relaxations induced by 3-morpholino-sydnonimine or forskolin. 7. The present findings, showing localization of HO immunoreactivity to both neuronal and nonneuronal cells of the feline LOS, ability of LOS to produce CO and a relaxant effect of CO in circular LOS muscle, suggest a role for CO as a peripheral messenger.

Carbon monoxide as a putative messenger molecule in the feline lower oesophageal sphincter of the cat

The distribution of the carbon monoxide (CO) producing enzymes haem oxygenase (HO) type 1 and 2 were studied in the feline lower oesophageal sphincter (LOS), as were HO activity and functional effects of CO. HO-2 immunoreactivity was observed in nerve cell bodies in the submucosal and myenteric plexus, nerve fibres, non-neuronal cells surrounding smooth muscle bundles, and in arterial endothelium, HO-1 immunoreactivity was confined to non-neuronal cells in the smooth muscle layer. CO production, indicating HO activity, was demonstrated in tissue homogenates. CO relaxed the LOS, and activated the cyclic GMP system. These results show that HO is present in the LOS, and suggest that CO can be generated by neuronal and non-neuronal structures and may have a role as a peripheral messenger.

Characterization of nitric oxide synthase in the opossum esophagus

BACKGROUND/AIMS

Nitric oxide mediates the nonadrenergic, noncholinergic neural control of esophageal motor function. The purpose of this study was to characterize the NO synthase found in the muscularis propria of the opossum esophagus and determine its distribution along the esophagus.

METHODS

Esophageal muscle was homogenized in HEPES buffer and ultracentrifuged. The supernatant was exposed to [3H]L-arginine. The [3H]L-citrulline produced by NO synthase was separated from [3H]L-arginine with a Dowex AG 50 W-X8 column (Biorad, Hercules, CA). Assays were performed in the presence and absence of Ca2+ or reduced nicotinamide adenine dinucleotide phosphate (NADPH). The distribution of NO synthase activity along the esophagus was determined.

RESULTS

The apparent Michaelis constant and maximum velocity of NO synthase were 7.5 +/- 1.4 mumol/L L-arginine and 76.0 +/- 17.3 pmol.mg protein-1.min-1, respectively. The enzyme required both Ca2+ and NADPH for activity. Smooth muscle tissue from the lower esophageal sphincter and the esophageal body 1-2 cm or 5-6 cm above the lower esophageal sphincter differed little in enzymatic activity, ranging from 0.97 to 1.27 pmol.mg wet wt-1.min-1. Striated muscle had less activity with 0.40 pmol.mg wet wt-1.min-1.

CONCLUSIONS

These data indicate the presence of a constitutive NO synthase in the esophagus of the opossum.

The role of the L-arginine/nitric oxide pathway for relaxation of the human lower oesophageal sphincter

Smooth muscle specimens were taken from the oesophagogastric junction (OGJ) in patients operated on for gastrointestinal malignancies not involving the OGJ. The smooth muscle bundles of the inner, circular layer of the OGJ were richly innervated by fine nerve fibres staining positively for NADPH diaphorase. The outer longitudinal layer had a markedly lower number of NADPH-diaphorase positive nerve fibres. When the preparations were suspended in organ baths for recording of isometric tension, they developed active tension. Transmural field stimulation (TMS) induced frequency-dependent relaxations, which were abolished by NG-nitro-L-arginine (L-NNA; 10(-4) M), and were often converted to atropine-sensitive contractions. The effect of L-NNA was concentration-dependent, and the concentration-response curve for L-NNA was shifted to the right by L-arginine pre-incubation. The enantiomer NG-nitro-D-arginine (10(-4) M) also showed inhibitory actions on the responses to TMS, but significantly less than L-NNA. Relaxant responses to vasoactive intestinal polypeptide (VIP), forskolin, and sodium nitroprusside were unaffected by L-NNA pre-incubation. Exposure to a 124 mM K+ solution resulted in a biphasic relaxation of the preparations. This relaxation was not seen in preparations treated with scorpion venom (20 micrograms ml-1) or L-NNA (10(-4) M). Instead, a contractile response to 124 mM K+ solution was found. The results suggest that NANC responses to electrical stimulation of nerves in the human OGJ are mediated by a product generated from L-arginine.(ABSTRACT TRUNCATED AT 250 WORDS)

Patients with achalasia lack nitric oxide synthase in the gastro-oesophageal junction

The abnormal function of the lower oesophageal sphincter in achalasia is likely to be due to impaired nonadrenergic, noncholinergic (NANC) inhibitory input. Since recent studies in animals suggest that nitric oxide (NO) is implicated physiologically in the inhibitory responses of the lower oesophageal sphincter, we have investigated whether the synthesis of NO is altered in the gastro-oesophageal junction of patients with achalasia. NO synthase activity was investigated in samples of tissue from the gastro-oesophageal junction obtained during surgery in eight patients with typical achalasia and six non-achalasic controls who underwent oesophagectomy for reasons other than sphincter dysfunction. The NO synthase activity was determined by the transformation of 14C-L-arginine into 14C-L-citrulline in tissue homogenates. In addition, immunohistochemical staining of the tissues was performed using a polyclonal antibody raised against a peptide sequence of rat brain NO synthase. Furthermore, the relaxant response to an exogenous NO donor (sodium nitroprusside, SNP) was measured in vitro in muscle strips obtained from two patients with achalasia and in two non-achalasic controls. NO synthase activity was detected in each of the samples obtained from six control patients (0.59 +/- 0.21 pmol mg-1 min-1; mean +/- SE). By contrast, none of the samples obtained from the eight patients with achalasia had any detectable NO synthase activity. Immunohistochemical studies confirmed the presence of NO synthase in the myenteric plexus of the gastro-oesophageal junction of control patients and its absence in achalasia. SNP relaxed muscle strips precontracted with bethanechol in both control samples and those from patients with achalasia.(ABSTRACT TRUNCATED AT 250 WORDS)

Activation of cyclic AMP-dependent protein kinase during canine lower esophageal sphincter relaxation

In isolated strips of opossum lower esophageal sphincter (LES) smooth muscle, elevation of cyclic AMP (cAMP) content is associated with relaxation. Because the activation state of cyclic nucleotide-dependent protein kinases may be a more sensitive measure of functionally important changes in cyclic nucleotide levels, we examined the ability of several pharmacological agents and electrical stimulation of the enteric neurons to activate cAMP dependent-protein kinase (cA-PK) and to relax isolated strips of LES smooth muscle. Addition of either isoproterenol or SK&F 94120, a selective inhibitor of the low Km cAMP phosphodiesterase to isolated strips of canine LES produced concentration-dependent increases in the activity ratio of cA-PK and concentration-dependent relaxations of canine LES. In contrast, although both zaprinast (M&B 22948), a selective inhibitor of the cyclic GMP selective phosphodiesterase, and sodium nitroprusside relaxed canine LES neither drug significantly increased the activity ratio of cA-PK. Furthermore, electrical stimulation of the enteric neurons produced a frequency-dependent relaxation but did not significantly activate cA-PK. To eliminate the possibility that the rapid metabolism of cAMP prevented us from observing a significant activation of cA-PK during electrical field stimulation, the ability of electrical field stimulation (1.0 Hz) to activate cA-PK was examined in the presence of 0.1 mM 3-isobutyl-1-methylxanthine. At at concentration of 0.1 mM, 3-isobutyl-1-methylxanthine, by itself, significantly increased the activity ratio of cA-PK; however, there was no additional activation produced by electrical field stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Differences in cytochrome c oxidase capacity in smooth muscle of opossum esophagus and lower esophageal sphincter

The tonic contraction that defines the lower esophageal sphincter is exclusively aerobic, whereas the rhythmic contractions that characterize the smooth muscle of the esophageal body can be partially sustained anaerobically. Also, relative mitochondrial mass is greater in the sphincter than it is in the body of the esophagus. Full-thickness strips of the muscularis propria of the opossum esophagus were examined as to cytochrome c oxidase capacity to test the hypothesis that differences in oxidative metabolism exist among different levels of the smooth-muscled esophagus. Homogenates were examined as to rate of cytochrome c oxidation, deoxyribonucleic acid content, and protein content. The rate of cytochrome c oxidation was greatest at the top of the smooth muscle segment and declined distally to reach the lowest value in the lower esophageal sphincter. Deoxyribonucleic acid content did not differ among levels examined. Protein/deoxyribonucleic acid ratios were lower in the sphincter than at other levels of the smooth-muscled esophagus. The results indicate that the sphincter muscle has a lower capacity for oxidative metabolism than does the body, that a gradient exists along the esophageal body in oxidative capacity, and that smooth muscle cells in the sphincter are likely to be smaller than are those of the esophageal body. The gradient in oxidative capacity along the esophageal body may be related to other gradients that have been described in this region.

Variation in the lactase dehydrogenase activity of the esophagus

Quantitative assay and electrophoretic study of lactate dehydrogenase (LDH) from various tissues of the opossum esophagus were performed. On the basis of expression of the LDH isozymes, we concluded that the smooth muscle of the body of the esophagus carry on more anaerobic glycolysis than the striated muscle. The smooth muscle of the gastroesophageal junction carry on both anaerobic as well aerobic glycolysis.