Patients with neuroglycopenia after gastric bypass surgery have exaggerated incretin and insulin secretory responses to a mixed meal.

CONTEXT AND OBJECTIVE: Hyperinsulinemic hypoglycemia is newly recognized as a rare but important complication after Roux-en-Y gastric bypass (GB). The etiology of the syndrome and metabolic characteristics remain incompletely understood. Recent studies suggest that levels of incretin hormones are increased after GB and may promote excessive beta-cell function and/or growth. PATIENTS AND METHODS: We performed a cross-sectional analysis of metabolic variables, in both the fasting state and after a liquid mixed-meal challenge, in four subject groups: 1) with clinically significant hypoglycemia [neuroglycopenia (NG)] after GB surgery, 2) with no symptoms of hypoglycemia at similar duration after GB surgery, 3) without GB similar to preoperative body mass index of the surgical cohorts, and 4) without GB similar to current body mass index of the surgical cohorts. RESULTS: Insulin and C-peptide after the liquid mixed meal were both higher relative to the glucose level achieved in persons after GB with NG compared with asymptomatic individuals. Glucagon, glucagon-like peptide 1, and glucose-dependent insulinotropic peptide levels were higher in both post-GB surgical groups compared with both overweight and morbidly obese persons, and glucagon-like peptide 1 was markedly higher in the group with NG. Insulin resistance, assessed by homeostasis model assessment of insulin resistance, the composite insulin sensitivity index, or adiponectin, was similar in both post-GB groups. Dumping score was also higher in both GB groups but did not discriminate between asymptomatic and symptomatic patients. Notably, the frequency of asymptomatic hypoglycemia after a liquid mixed meal was high in post-GB patients. CONCLUSION: A robust insulin secretory response was associated with postprandial hypoglycemia in patients after GB presenting with NG. Increased incretin levels may contribute to the increased insulin secretory response.

Severe hypoglycaemia post-gastric bypass requiring partial pancreatectomy: evidence for inappropriate insulin secretion and pancreatic islet hyperplasia.

AIMS/HYPOTHESIS: Postprandial hypoglycaemia following gastric bypass for obesity is considered a late manifestation of the dumping syndrome and can usually be managed with dietary modification. We investigated three patients with severe postprandial hypoglycaemia and hyperinsulinaemia unresponsive to diet, octreotide and diazoxide with the aim of elucidating the pathological mechanisms involved. METHODS: Glucose, insulin, and C-peptide were measured in the fasting and postprandial state, and insulin secretion was assessed following selective intra-arterial calcium injection. Pancreas histopathology was assessed in all three patients. RESULTS: All three patients had evidence of severe postprandial hyperinsulinaemia and hypoglycaemia. In one patient, reversal of gastric bypass was ineffective in reversing hypoglycaemia. All three patients ultimately required partial pancreatectomy for control of neuroglycopenia; pancreas pathology of all patients revealed diffuse islet hyperplasia and expansion of beta cell mass. CONCLUSIONS/INTERPRETATION: These findings suggest that gastric bypass-induced weight loss may unmask an underlying beta cell defect or contribute to pathological islet hyperplasia, perhaps via glucagon-like peptide 1-mediated pathways.

Protein kinase epsilon dampens the secretory response of model intestinal epithelia during ischemia.

BACKGROUND: Luminal fluid sequestration and diarrhea are early manifestations of mesenteric ischemia. This can be modeled in vitro with the use of T84 intestinal epithelia, where ischemia induces Cl(-) secretion with adenosine-mediated autocrine feedback. Protein kinase C (PKC) regulates epithelial transport and, in some organ systems, is involved in the response to ischemic stress. The purpose of this study was to define the role of PKC on epithelial transport during ischemia. METHODS: By voltage-current clamp, short-circuit current (Isc) equals Cl(-) secretion. Ischemic conditions were simulated with the use of a well-established chemical hypoxia protocol. RESULTS: Chemical hypoxia briskly activated Isc. Gö6850, an antagonist of novel and conventional PKC isoforms, markedly enhanced the ischemia-induced Isc response, although Gö6976 (which inhibits only conventional isoforms) had no effect. Rottlerin, a specific inhibitor of PKC delta, did not attenuate ischemic Isc. Both phorbol 12-myristate, 13-acetate and bryostatin-1, which selectively activate PKC epsilon in T84 cells, markedly attenuated the Isc response to ischemia. Both agents also inhibited the Isc response to exogenous adenosine. CONCLUSIONS: PKC (likely the novel epsilon isoform) in intestinal epithelia modulates ischemia-induced alterations in ion transport. Inhibition of PKC epsilon exaggerates the secretory response that is induced by ischemia and by authentic adenosine; conversely, augmented activation of PKC epsilon inhibits secretion. Manipulation of PKC epsilon could limit luminal fluid sequestration during mesenteric ischemia.

Current status of medical and surgical therapy for obesity.

The incidence of obesity (especially childhood obesity) and its associated health-related problems have reached epidemic proportions in the United States. Recent investigations suggest that the causes of obesity involve a complex interplay of genetic, environmental, psychobehavioral, endocrine, metabolic, cultural, and socioeconomic factors. Several genes and their protein products, such as leptin, may be particularly important in appetite and metabolic control, although the genetics of human obesity appear to involve multiple genes and metabolic pathways that require further elucidation. Severe obesity is frequently associated with significant comorbid medical conditions, including coronary artery disease, hypertension, type II diabetes mellitus, gallstones, nonalcoholic steatohepatitis, pulmonary hypertension, and sleep apnea. Long-term reduction of significant excess weight in these patients may improve or resolve many of these obesity-related health problems, although convincing evidence of long-term benefit is lacking. Available treatments of obesity range from diet, exercise, behavioral modification, and pharmacotherapy to surgery, with varying risks and efficacy. Nonsurgical modalities, although less invasive, achieve only relatively short-term and limited weight loss in most patients. Currently, surgical therapy is the most effective modality in terms of extent and duration of weight reduction in selected patients with acceptable operative risks. The most widely performed surgical procedure, Roux-en-Y gastric bypass, achieves permanent (followed up for more than 14 years) and significant weight loss (more than 50% of excess body weight) in more than 90% of patients.

Protein kinase C activation downregulates the expression and function of the basolateral Na+/K+/2Cl(-) cotransporter.

The basolateral Na+/K+/2Cl(-) cotransporter (NKCC1) has been shown to be an independent regulatory site for electrogenic Cl(-) secretion. The proinflammatory phorbol ester, phorbol 12-myristate 13-acetate (PMA), which activates protein kinase C (PKC), inhibits basal and cyclic adenosine monophosphate (cAMP)-stimulated NKCC1 activity in T84 intestinal epithelial cells and decreases the steady state levels of NKCC1 mRNA in a time- and dose-dependent manner. The levels of NKCC1 protein also fall in accordance with the NKCC1 mRNA transcript and these levels are unaffected by 4alpha-phorbol, which does not activate PKC. Inhibition of maximal (cAMP-stimulated) NKCC1 functional activity by PMA was first detected by 1 h, whereas decreases in the steady state levels of NKCC1 mRNA were not detectable until 4 h. NKCC1 mRNA expression recovers toward control levels with extended treatment of cells with PMA suggesting that the PMA effects on NKCC1 expression are mediated through activation of PKC. Although NKCC1 mRNA and protein levels return to control values after extended PMA exposure, NKCC1 functional activity does not recover. Immunofluorescence imaging suggest that the absence of functional recovery is due to failure of newly synthesized NKKC1 protein to reach the cell surface. We conclude that NKCC1 has the capacity to be regulated at the level of de novo expression by PKC, although decreased NKCC1 expression alone cannot account for either early or late loss of NKCC1 function.

Effects of bryostatin 1, a novel anticancer agent, on intestinal transport and barrier function: role of protein kinase C.

BACKGROUND: Bryostatin 1 is a novel chemotherapeutic agent that activates specific members of the protein kinase C (PKC) family in a complex pattern overlapping with, but distinct from, that of tumor-promoting phorbol esters. Phorbol esters profoundly altered epithelial phenotype, abolishing both barrier function and Cl secretion (the latter due to loss of a key transport site, the Na-K-Cl cotransporter). The effects of bryostatin 1 on these parameters are unknown. METHODS: Cl secretion and barrier function of T84 human intestinal epithelia were assessed as cyclic adenosine monophosphate-stimulated short-circuit current and transepithelial resistance, respectively. Na-K-Cl cotransporter function and mRNA expression were assayed by 86Rb uptake and Northern analysis. RESULTS: Bryostatin 1 reduced Cl secretion, Na-K-Cl cotransport, and cotransporter mRNA expression. Unlike phorbol esters, these effects were largely transient. In contrast to phorbol esters, bryostatin 1 did not decrease barrier function. CONCLUSIONS: Bryostatin 1 transiently inhibits Na-K-Cl cotransport and Cl secretion, possibly through a PKC isoform also targeted by phorbol esters. Unlike phorbol esters, bryostatin 1 does not impair barrier function. The data imply that bryostatin 1 and phorbol esters differentially affect a PKC isoform involved in junctional regulation, and that epithelial transport and barrier function may be regulated by distinct PKC isoforms.

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.

Osmotic regulation of intestinal epithelial Na(+)-K(+)-Cl- cotransport: role of Cl- and F-actin.

Previous data indicate that adenosine 3',5'-cyclic monophosphate activates the epithelial basolateral Na(+)-K(+)-Cl- cotransporter in microfilament-dependent fashion in part by direct action but also in response to apical Cl- loss (due to cell shrinkage or decreased intracellular Cl-). To further address the actin dependence of Na(+)-K(+)-Cl- cotransport, human epithelial T84 monolayers were exposed to anisotonicity, and isotopic flux analysis was performed. Na(+)-K(+)-Cl- cotransport was activated by hypertonicity induced by added mannitol but not added NaCl. Cotransport was also markedly activated by hypotonic stress, a response that appeared to be due in part to reduction of extracellular Cl- concentration and also to activation of K+ and Cl- efflux pathways. Stabilization of actin with phalloidin blunted cotransporter activation by hypotonicity and abolished hypotonic activation of K+ and Cl- efflux. However, phalloidin did not prevent activation of cotransport by hypertonicity or isosmotic reduction of extracellular Cl-. Conversely, hypertonic but not hypotonic activation was attenuated by the microfilament disassembler cytochalasin D. The results emphasize the complex interrelationship among intracellular Cl- activity, cell volume, and the actin cytoskeleton in the regulation of epithelial Cl- transport.

Characterization and regulation of adenosine transport in T84 intestinal epithelial cells.

Adenosine release from mucosal sources during inflammation and ischemia activates intestinal epithelial Cl- secretion. Previous data suggest that A2b receptor-mediated Cl- secretory responses may be dampened by epithelial cell nucleoside scavenging. The present study utilizes isotopic flux analysis and nucleoside analog binding assays to directly characterize the nucleoside transport system of cultured T84 human intestinal epithelial cells and to explore whether adenosine transport is regulated by secretory agonists, metabolic inhibition, or phorbol ester. Uptake of adenosine across the apical membrane displayed characteristics of simple diffusion. Kinetic analysis of basolateral uptake revealed a Na(+)-independent, nitrobenzylthioinosine (NBTI)-sensitive facilitated-diffusion system with low affinity but high capacity for adenosine. NBTI binding studies indicated a single population of high-affinity binding sites basolaterally. Neither forskolin, 5'-(N-ethylcarboxamido)-adenosine, nor metabolic inhibition significantly altered adenosine transport. However, phorbol 12-myristate 13-acetate significantly reduced both adenosine transport and the number of specific NBTI binding sites, suggesting that transporter number may be decreased through activation of protein kinase C. This basolateral facilitated adenosine transporter may serve a conventional function in nucleoside salvage and a novel function as a regulator of adenosine-dependent Cl- secretory responses and hence diarrheal disorders.

Adenosine scavenging: a novel mechanism of chloride secretory control in intestinal epithelial cells.

BACKGROUND: Adenosine released by cells during ischemia typically serves as a feedback inhibitor of further organ work. However, in ischemic intestine, adenosine appears to act via stimulatory A2b receptors to increase work in the form of chloride ion (Cl-) secretion. This unusual response may contribute to luminal fluid sequestration in intestinal ischemia. In nonischemic cells feed-forward activation of Cl- secretion does not occur despite the fact that adenosine may be continuously generated during normal cell metabolism. Thus we postulated that intestinal epithelia normally control the disposition of adenosine to prevent inappropriate activation of secretion. METHODS: Model T84 intestinal epithelia were studied by means of electrophysiologic and isotopic techniques. RESULTS: Dipyridamole and nitrobenzylthioinosine (inhibitors of nucleoside transport) and iodotubercidin (an inhibitor of adenosine kinase) caused adenosine to accumulate extracellularly and induced a Cl- secretory response that was prevented by adenosine receptor blockade. Uptake of exogenous adenosine was restricted to the basolateral compartment and was blocked by nucleoside transport inhibitors. CONCLUSIONS: Adenosine released from nonischemic intestinal epithelial cells is scavenged by a basolaterally restricted adenosine transporter. This system maintains extracellular adenosine levels below the prosecretory threshold and thus limits adenosine-elicited activation of Cl- secretion (and hence diarrhea) under normal conditions).