Julio M. Mayol

Levamisole inhibits intestinal Cl- secretion via basolateral K+ channel blockade.

BACKGROUND & AIMS Phenylimidazothiazoles have recently been shown to activate wild-type and mutant cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channels in transfected cells and were proposed as therapy for cystic fibrosis. The aim of this study was to investigate the effects of phenylimidazothiazoles on regulated transepithelial Cl- transport in intact epithelia. METHODS T84 intestinal epithelial cells grown on permeable supports and stripped human colonic mucosal sheets were studied by conventional current-voltage clamping. Selective permeabilization of apical or basolateral membranes with the monovalent ionophore nystatin was used to isolate basolateral K+ and apical Cl- channel activity, respectively. 86Rb+ uptake was assessed for Na/K/2Cl cotransporter and Na+,K(+)-adenosine triphosphatase activity. RESULTS In T84 monolayers and human colon, levamisole and its brominated derivative bromotetramisole failed to activate transepithelial secretion. In fact, these compounds dose-dependently inhibited secretory responses to the cyclic adenosine monophosphate agonist forskolin and the Ca2+ agonist carbachol. In permeabilized T84 monolayers, phenylimidazothiazoles weakly activated apical Cl- currents (consistent with their reported action on CFTR) and did not affect bumetanide-sensitive or bumetanide-insensitive 86+Rb+ uptake. Instead, they profoundly inhibited the basolateral Ba(2+)-sensitive and Ba(2+)-insensitive K+ currents. CONCLUSIONS Phenylimidazothiazoles block K+ channels required for Cl(-)-secretory responses elicited by diverse pathways in model epithelia and native colon, an effect that outweighs their ability to activate apical Cl- channels.

Ammonia blockade of intestinal epithelial K+ conductance

Ammonia profoundly inhibits cAMP-dependent Cl- secretion in model T84 human intestinal crypt epithelia. Because colonic lumen concentrations of ammonia are high (10-70 mM), ammonia may be a novel regulator of secretory diarrheal responsiveness. We defined the target of ammonia action by structure-function analysis with a series of primary amines (ammonia, methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, heptylamine, and octylamine) that vary principally in size and lipid solubilities. The amine concentrations required for 50% inhibition of Cl- secretion in intact monolayers and 50% inhibition of outward K+ current ( I K) in apically permeabilized monolayers vs. the logs of the respective amine partition coefficients give two plots that are strikingly similar in character. Half-maximal inhibition of short-circuit current ( I sc) by ammonia was seen at 6 mM and for I K at 4 mM; half-maximal inhibition for octylamine was 0.24 mM and 0.19 mM for I sc and I K, respectively. The preferentially water-soluble hydrophilic amines (ammonia, methylamine, ethylamine) increase in blocking ability with decreasing size and lipophilicity. Conversely, the preferentially lipid-soluble hydrophobic (propylamine, butylamine, pentylamine, hexylamine, heptylamine, octylamine) amines increase in blocking ability with increasing size and lipophilicity. Ammonia does not affect isolated apical Cl- conductance; amine-induced changes in cytosolic and endosomal pH do not correlate with secretory inhibition. We propose that ammonia in its protonated ammonium form ([Formula: see text]) inhibits cAMP-dependent Cl- secretion in T84 monolayers by blocking basolateral K+ channels.Ammonia profoundly inhibits cAMP-dependent Cl- secretion in model T84 human intestinal crypt epithelia. Because colonic lumen concentrations of ammonia are high (10-70 mM), ammonia may be a novel regulator of secretory diarrheal responsiveness. We defined the target of ammonia action by structure-function analysis with a series of primary amines (ammonia, methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, heptylamine, and octylamine) that vary principally in size and lipid solubilities. The amine concentrations required for 50% inhibition of Cl- secretion in intact monolayers and 50% inhibition of outward K+ current (IK) in apically permeabilized monolayers vs. the logs of the respective amine partition coefficients give two plots that are strikingly similar in character. Half-maximal inhibition of short-circuit current (Isc) by ammonia was seen at 6 mM and for IK at 4 mM; half-maximal inhibition for octylamine was 0.24 mM and 0.19 mM for Isc and IK, respectively. The preferentially water-soluble hydrophilic amines (ammonia, methylamine, ethylamine) increase in blocking ability with decreasing size and lipophilicity. Conversely, the preferentially lipid-soluble hydrophobic (propylamine, butylamine, pentylamine, hexylamine, heptylamine, octylamine) amines increase in blocking ability with increasing size and lipophilicity. Ammonia does not affect isolated apical Cl- conductance; amine-induced changes in cytosolic and endosomal pH do not correlate with secretory inhibition. We propose that ammonia in its protonated ammonium form (NH4+) inhibits cAMP-dependent Cl- secretion in T84 monolayers by blocking basolateral K+ channels.

Total mesorectal excision for rectal cancer: The truth lies underneath

The surgical technique itself has emerged as a crucial factor for local recurrence since the popularization of total mesorectal excision for the treatment of rectal cancer. This procedure is associated with lower local recurrence rates after “curative” surgery compared to traditional dissection of the rectum. The aim is to remove an intact mesorectal envelope from the promontorium down to the pelvic floor by sharp dissection with tumorfree margins and without causing injury to the pelvic nerves. However, the description of total mesorectal excision has been confusing. Moreover, the implication that total excision of all the perirectal fat contained within the perirectal fascia en bloc in all patients with rectal cancer can minimize local recurrence remains contentious. Therefore a critical appraisal of the procedure is required. Nonrandomized clinical studies have shown that total mesorectal excision reduces the local recurrence rate and increases disease-free survival in patients with adenocarcinoma of the middle and distal third of the rectum. Circumferential resection margins of 2 mm or more are associated with a lower local recurrence rate. Additional benefits in local control can be obtained with neoadjuvant treatment. Thus the modern treatment of rectal cancer combining total mesorectal excision with neoadjuvant chemoradiation results in excellent local tumor control. However, it is achieved at the cost of significant functional sequelae and impaired quality of life. The development of therapeutic alternatives that can achieve similar rates of local and distant tumor control without the mortality, morbidity, and functional consequences of radical surgery is a major challenge for colorectal surgeons.RésuméDepuis la popularisation de l’excision mésorectale totale (TME) pour le traitement du cancer rectal, la qualité de la technique chirurgicale tend à émerger comme facteur crucial dans la prévalence de récidive. Ce procédé est associé à un taux de récidive locale plus bas après chirurgie à visée “curative” comparé au taux de récidive après dissection traditionnelle du rectum. Le but de la TME est d’enlever par une dissection précise, instrumentale, l’enveloppe mésorectale intacte entre le niveau du promontoire jusqu’au plancher pelvien, en obtenant des marges de sécurité sans tissu tumoral, et sans provoquer de lésions nerveuses au niveau du pelvis. Cependant, la description de la TME n’est pas claire. De plus, l’implication que l’excision en bloc, de toute la graisse périrectale contenue dans le fascia périrectal, améliore le taux de récidive locale chez tous les patients reste discutée. Ainsi une évaluation critique du procédé est nécessaire. Les études cliniques non randomisées ont montré que la TME réduit le taux de récidive locale et augmente la survie sans maladie chez les patients atteints d’adénocarcinome du rectum moyen et distal. Des marges circonférentielles de 2 mm ou plus sont associées à un taux de récidive locale plus bas. On peut encore augmenter ces bénéfices dans le contrôle local du cancer du rectum par un traitement néoadjuvant Ainsi le traitement moderne du cancer rectal associe la TME à une chimioradiothérapie adjuvante et donne un excellent contrôle local de la tumeur. Cependant, ce contrôle est obtenu grâce à d’importantes séquelles fonctionnelles et des conséquences néfastes pour la qualité de vie. Le développement d’alternatives thérapeutiques capables d’obtenir des résultats similaires en ce qui concerne la récidive locale et à distance mais sans la mortalité, la morbidité et les conséquences fonctionnelles de la chirurgie radicale, reste le principal challenge futur pour les chirurgiens colorectaux.ResumenLa técnica quirúrgica ha surgido como un factor de importancia crucial en cuanto a recurrencia local desde la popularizatión de la resectión mesorrectal total en el tratamiento del cáncer rectal. El procedimiento se asocia con menores tasas de recurrencia tras de cirugía “curativa” en comparaciôn con la disección tradicional del recto. El propósito de la operatión es resecar la envoltura mesorrectal desde el peritoneo hasta el piso pélvico, mediante disección no roma, con márgenes libres de tumor y evitando lesión de los nervios pélvicos. Sin embargo, la descriptión de la resección mesorrectal total ha sido confusa. Además, la implicación de que la resección total en bloque de la grasa perirrectal contenida por la fascia perirrectal en todos los pacientes con cáncer rectal minimiza la tasa de recurrencia sigue siendo motivo de controversia, por lo cual se hace necesaria una evaluación crítica del procedimiento. Estudios clínicos no aleatorizados han demostrado que la resección mesorrectal total reduce la tasa de recurrencia local y aumenta la supervivencia libre de enfermedad en pacientes con adenocarcinomas de los tercios medio y distal del recto. La resección circunferencial con márgenes de 2 mm o más se asocia con menores tasas de recurrencia. Beneficios adicionales pertinentes al control local se pueden obtener con terapia neoadyuvante. Por consiguiente, el tratamiento moderno del cáncer rectal que combina la resección mesorrectal total con quimio-radiación neoadyuvante resulta en excelente control local del tumor. Sin embargo, esto se logra a costa de secuelas funcionales significativas y desmejoramiento de la calidad de vida. El desarrollo de modalidades terapéuticas alternativas que logren tasas similares de control local y distal del tumor sin la mortalidad, morbilidad y consecuencias funcionales de la cirugía radical, constituye el gran desafío que se plantea a los cirujanos colorrectales.