Michael A. Shetzline

Endoscopic therapy of acute diverticular hemorrhage

OBJECTIVE:Diverticular hemorrhage is a common cause of lower GI bleeding and can be diagnosed acutely during colonoscopy. However, whether early diagnosis leads to effective intervention remains controversial. The aim of this study was to evaluate whether urgent colonoscopic therapy is effective as acute and long term treatment for diverticular bleeding with stigmata of hemorrhage.METHODS:We reviewed the medical records of all patients who underwent endoscopic therapy for diverticular bleeding from January, 1994 to June, 2000 at Duke University Medical Center. Patients or their families were contacted to obtain complete follow-up including data on subsequent bleeding.RESULTS:We identified 13 patients who underwent colonoscopic hemostatic management for the treatment of acute diverticular bleeding. Therapy consisted of epinephrine injection and/or multipolar electrocoagulation. Five patients (38%) experienced early rebleeding, within 30 days of the index bleed, four of whom required surgery, and three patients (23%) had late rebleeding. There were no complications of endoscopic therapy.CONCLUSIONS:Endoscopic therapy can provide early hemostasis in some cases of acute diverticular hemorrhage. However, its value in preventing subsequent diverticular bleeding is unclear.

PROPERTIES OF SECRETIN RECEPTOR INTERNALIZATION DIFFER FROM THOSE OF THE BETA 2-ADRENERGIC RECEPTOR

The endocytic pathway of the secretin receptor, a class II GPCR, is unknown. Some class I G protein-coupled receptors (GPCRs), such as the β2-adrenergic receptor (β2-AR), internalize in clathrin-coated vesicles and this process is mediated by G protein-coupled receptor kinases (GRKs), β-arrestin, and dynamin. However, other class I GPCRs, for example, the angiotensin II type 1A receptor (AT1AR), exhibit different internalization properties than the β2-AR. The secretin receptor, a class II GPCR, is a GRK substrate, suggesting that like the β2-AR, it may internalize via a β-arrestin and dynamin directed process. In this paper we characterize the internalization of a wild-type and carboxyl-terminal (COOH-terminal) truncated secretin receptor using flow cytometry and fluorescence imaging, and compare the properties of secretin receptor internalization to that of the β2-AR. In HEK 293 cells, sequestration of both the wild-type and COOH-terminal truncated secretin receptors was unaffected by GRK phosphorylation, whereas inhibition of cAMP-dependent protein kinase mediated phosphorylation markedly decreased sequestration. Addition of secretin to cells resulted in a rapid translocation of β-arrestin to plasma membrane localized receptors; however, secretin receptor internalization was not reduced by expression of dominant negative β-arrestin. Thus, like the AT1AR, secretin receptor internalization is not inhibited by reagents that interfere with clathrin-coated vesicle-mediated internalization and in accordance with these results, we show that secretin and AT1A receptors colocalize in endocytic vesicles. This study demonstrates that the ability of secretin receptor to undergo GRK phosphorylation and β-arrestin binding is not sufficient to facilitate or mediate its internalization. These results suggest that other receptors may undergo endocytosis by mechanisms used by the secretin and AT1Areceptors and that kinases other than GRKs may play a greater role in GPCR endocytosis than previously appreciated.

G protein-coupled receptor desensitization as a measure of signaling: modeling of arrestin recruitment to activated CCK-B receptors.

Gastrin is one of the principle hormonal mediators of gastric acid secretion, and its cognate receptor (CCK-B) is a member of the superfamily of GPCRs. Patients with hypergastrinemia may present with a variety of symptoms, including gastric ulcers or malignant tumors. Thus, the molecular mechanisms that terminate CCK-B receptor signaling, as well as an ability to measure gastrin bioactivity in a timely manner, have important clinical implications. In order to assess CCK-B receptor regulation, we have constructed a single cell biosensor containing the CCK-B receptor and an arrestin/GFP chimera. The gastrin biosensor responded to both immunologically detectable gastrin-17 and undetectable pentagastrin, and was able to determine the gastrin bioactivity of serum from a patient with clinical hypergastrinemia. We determined that the CCK-B receptor binds arrestin with a pharmacology mirroring CCK-B receptor signaling through inositol phosphate, and that the rate of arrestin dissociation from internalized receptor mirrors receptor recycling to the plasma membrane. Moreover, the CCK-B recycling rate is intermediate between that of Class A GPCRs such as the beta2-adrenergic receptor and Class B GPCRs such as the vasopressin type 2 receptor. Mathematical modeling of these results indicates that a common receptor conformation may underlie both CCK-B signaling and desensitization. In addition to its use in drug screening, this methodology should generalize to other receptors for use in diagnosis and monitoring of bioactive ligands involved in GPCR-based disease.

Re: Percutaneous endoscopic gastrostomy

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G Proteins and G Protein-Coupled Receptors

Cells live in a constantly changing milieu. The structure and biochemical nature of this environment is dynamic and in order for normal cellular function to proceed in a manner appropriate for the benefit of the organism, cells must be able to access this changing information. The biochemical mediators of this information exchange are cell surface receptors. Receptors transduce information from the extracellular space to the intracellular compartment. This process involves the following steps: receptor activation, G protein coupling, and second messenger generation. Equally important in cell signaling is the termination of this signal including desensitization, internalization and resensitization. All these steps represent potential regulatory checkpoints and possible targets for therapeutic intervention. Cell surface receptors include G protein-coupled receptors (GPCRs), as well as, ion channels and enzyme-linked receptors. GPCRs are responsible for physiological responses as diverse as visual perception, neurotransmission, cell growth and cell differentiation.

The yield of push enteroscopy in a large tertiary care center

Aim: Compare public awareness of HCV to the more publicized HIV epidemic. Methods: A two-part Survey Questionnaire was administered. Part 1 requested demographic information and asked general questions on attitudes and beliefs. Part 2 asked 10 HCV-related and 10 HIV-related questions based on NY State Health Department public information pamphlets. Chi-square analysis, ANOVA and Student t-tests were used for statistical comparison. Information pamphlets and counseling were provided to all participants after testing. Results: 606 individuals participated, 290 were hospital staff (92 physicians). Mean age was 38.7 6 14 yrs, 238 were male, 550 had 12 1 years of education.