Effects of GLP-1 on Gastric Emptying, Antropyloric Motility, and Transpyloric Flow in Response to a Nonnutrient Liquid

Glucagon-like polypeptide 1 (GLP-1) may be amajor enterogastrone, slowing gastric emptying whenreleased by intestinal nutrients. In six conscious dogs,we studied the effects of GLP-1, on antropyloric motility, gastric emptying, and transpyloricflow after instillation of 500 ml of saline into thestomach. The meal was given and recordings were started15 min after intravenous bolus and infusion of either saline or three different doses of GLP-1.Intravenous GLP-1 produced a dose-related retardation ofgastric emptying associated with a decrease in thenumber and volume of flow pulses in comparison tosaline. This change in transpyloric flow was associatedwith an inhibition of antropyloric pressure waves, astimulation of isolated pyloric pressure waves, and anincrease in basal pyloric tone induced by intravenous GLP-1 infusion. Our findings show that GLP-1has a potent dose-dependent inhibitory effect ontranspyloric flow and gastric emptying. This effect istemporally associated with inhibition of antralpumping and stimulation of pyloricbraking mechanisms.     

Protective hinge in insulin opens to enable its receptor engagement

Insulin provides a classical model of a globular protein, yet how the hormone changes conformation to engage its receptor has long been enigmatic. Interest has focused on the C-terminal B-chain segment, critical for protective self-assembly in β cells and receptor binding at target tissues. Insight may be obtained from truncated “microreceptors” that reconstitute the primary hormone-binding site (α-subunit domains L1 and αCT). We demonstrate that, on microreceptor binding, this segment undergoes concerted hinge-like rotation at its B20-B23 β-turn, coupling reorientation of Phe^B24 to a 60° rotation of the B25-B28 β-strand away from the hormone core to lie antiparallel to the receptor''s L1–β₂ sheet. Opening of this hinge enables conserved nonpolar side chains (Ile^A2, Val^A3, Val^B12, Phe^B24, and Phe^B25) to engage the receptor. Restraining the hinge by nonstandard mutagenesis preserves native folding but blocks receptor binding, whereas its engineered opening maintains activity at the price of protein instability and nonnative aggregation. Our findings rationalize properties of clinical mutations in the insulin family and provide a previously unidentified foundation for designing therapeutic analogs. We envisage that a switch between free and receptor-bound conformations of insulin evolved as a solution to conflicting structural determinants of biosynthesis and function.How insulin engages the insulin receptor has inspired speculation ever since the structure of the free hormone was determined by Hodgkin and colleagues in 1969 (1, 2). Over the ensuing decades, anomalies encountered in studies of analogs have suggested that the hormone undergoes a conformational change on receptor binding: in particular, that the C-terminal β-strand of the B chain (residues B24–B30) releases from the helical core to expose otherwise-buried nonpolar surfaces (the detachment model) (3–6). Interest in the B-chain β-strand was further motivated by the discovery of clinical mutations within it associated with diabetes mellitus (DM) (7). Analysis of residue-specific photo–cross-linking provided evidence that both the detached strand and underlying nonpolar surfaces engage the receptor (8).The relevant structural biology is as follows. The insulin receptor is a disulfide-linked (αβ)₂ receptor tyrosine kinase (Fig. 1A), the extracellular α-subunits together binding a single insulin molecule with high affinity (9). Involvement of the two α-subunits is asymmetric: the primary insulin-binding site (site 1^*) comprises the central β-sheet (L1–β₂) of the first leucine-rich repeat domain (L1) of one α-subunit and the partially helical C-terminal segment (αCT) of the other α-subunit (Fig. 1A) (10). Such binding initiates conformational changes leading to transphosphorylation of the β-subunits’ intracellular tyrosine kinase (TK) domains. Structures of wild-type (WT) insulin (or analogs) bound to extracellular receptor fragments were recently described at maximum resolution of 3.9 Å (11), revealing that hormone binding is primarily mediated by αCT (receptor residues 704–719); direct interactions between insulin and L1 were sparse and restricted to certain B-chain residues. On insulin binding, αCT was repositioned on the L1–β₂ surface, and its helix was C-terminally extended to include residues 711–714. None of these structures defined the positions of C-terminal B-chain residues beyond B21. Support for the detachment model was nonetheless provided by entry of αCT into a volume that would otherwise be occupied by B-chain residues B25–B30 (i.e., in classical insulin structures; Fig. 1B) (11).Open in a separate windowFig. 1.Insulin B-chain C-terminal β-strand in the μIR complex. (A) Structure of apo-receptor ectodomain. One monomer is in tube representation (labeled), the second is in surface representation. L1, first leucine-rich repeat domain; CR, cysteine-rich domain; L2, second leucine-rich repeat domain; FnIII-1, -2 and -3; first, second and third fibronectin type III domains, respectively; αCT, α-subunit C-terminal segment; coral disk, plasma membrane. (B) Insulin bound to μIR; the view direction with respect to L1 in the apo-ectodomain is indicated by the arrow in A. Only B-chain residues indicated in black were originally resolved (11). The brown tube indicates classical location of residues B20-B30 in free insulin, occluded in the complex by αCT. (C) Orthogonal views of unmodeled 2F_obs-F_calc difference electron density (SI Appendix), indicating association of map segments with the αCT C-terminal extension (transparent magenta), insulin B-chain C-terminal segment (transparent gray), and Asn^A21 (transparent yellow). Difference density is sharpened (B_sharp = −160 Ų). (D–F) Refined models of respective segments insulin B20–B27, αCT 714–719, and insulin A17-A21 within postrefinement 2F_obs-F_calc difference electron density (B_sharp = −160 Ų). D is in stereo.We describe here the structure and interactions of the detached B-chain C-terminal segment of insulin on its binding to a “microreceptor” (μIR), an L1–CR domain-minimized version of the α-subunit (designated IR310.T) plus exogenous αCT peptide 704–719 (11). Our analysis defines a hinge in the B chain whose opening is coupled to repositioning of αCT between nonpolar surfaces of L1 and the insulin A chain. To understand the role of this hinge in holoreceptor binding and signaling, we designed three insulin analogs containing structural constraints (d-Ala^B20, d-Ala^B23]-insulin, ∆Phe^B25-insulin, and ∆Phe^B24-insulin, where ∆Phe is (α,β)-dehydrophenylalanine (Fig. 2) (12). The latter represents, to our knowledge, the first use of ∆Phe—a rigid “β-breaker” with extended electronic conjugation between its side chain and main chain (SI Appendix, Fig. S1)—as a probe of induced fit in macromolecular recognition. In addition, a fourth analog, active but with anomalous flexibility in the B chain (5, 6) (

Individualizing glycemic targets in type 2 diabetes mellitus: implications of recent clinical trials

One of the first steps in the management of patients with type 2 diabetes mellitus is setting glycemic goals. Professional organizations advise setting specific hemoglobin A(1c) (HbA(1c)) targets for patients, and individualization of these goals has more recently been emphasized. However, the operational meaning of glycemic goals, and specific methods for individualizing them, have not been well-described. Choosing a specific HbA(1c) target range for a given patient requires taking several factors into consideration, including an assessment of the patient's risk for hyperglycemia-related complications versus the risks of therapy, all in the context of the overall clinical setting. Comorbid conditions, psychological status, capacity for self-care, economic considerations, and family and social support systems also play a key role in the intensity of therapy. The individualization of HbA(1c) targets has gained more traction after recent clinical trials in older patients with established type 2 diabetes mellitus failed to show a benefit from intensive glucose-lowering therapy on cardiovascular disease (CVD) outcomes. The limited available evidence suggests that near-normal glycemic targets should be the standard for younger patients with relatively recent onset of type 2 diabetes mellitus and little or no micro- or macrovascular complications, with the aim of preventing complications over the many years of life. However, somewhat higher targets should be considered for older patients with long-standing type 2 diabetes mellitus and evidence of CVD (or multiple CVD risk factors). This review explores these issues further and proposes a framework for considering an appropriate and safe HbA(1c) target range for each patient.     

Safety and patient selection of totally implantable hearing aid surgery: Envoy system,Esteem

Patient’s low compliance of conventional hearing aids has lead to innovation of totally implantable hearing devices such as Esteem, Envoy system. This study was designed to evaluate safety of device implantation, patient’s hearing gain, importance of anatomic landmarks, and to describe suitable criteria for patient selection. Via a non-randomized controlled clinical trial, ten patients with moderate-to-severe sensorineural hearing loss were implanted from 2007 to 2009. Mean follow-up period was 29.4 months. Correlation of pre-operative temporal bone CT scan anatomy with postoperative outcome was evaluated. Except one, all other implanted devices are active and patients’ overall average hearing gain are similar to conventional hearing aids (10–22 dB), but patients reported relatively better subjective sound quality compared with their pre-operative conventional hearing aids. One implanted device was explanted in a patient due to facial weakness and low-hearing gain. Revision surgery was done successfully in another patient secondary to excessive bone growth. Totally implantable hearing device surgery seems to be relatively safe and correct patient selection could lead to good outcomes. Lateral location of facial nerve, sclerotic mastoid air cells and narrow facial recess space seems to be related to postoperative complications.     

Preoperative symptom evaluation and esophageal acid infusion predict response to laparoscopic Nissen fundoplication in gastroesophageal reflux patients who present with cough

BACKGROUND: Most patients with cough and gastroesophageal reflux disease (GERD) improve on medical treatment with proton pump inhibitors (PPI). Nonresponders may be considered for antireflux surgery, but the selection of patients is difficult. METHODS: We have performed laparoscopic Nissen fundoplications (LNF) in 677 patients. Of these patients, 81% have undergone 6-month follow-up assessment with 24-h pH testing, esophageal manometry, symptom scores, and quality-of-life scores. RESULTS: LNF controlled heartburn in 93% and improved cough in 81%. Stepwise multiple regression showed that the preoperative cough score (r = 0.620, p <0.0001) and change in cough on and off PPI (r = 0.296, p = 0.0002) predicted improvement after surgery. A positive result on a randomized acid infusion test was associated with a greater improvement in cough after surgery (p = 0.0243). CONCLUSION: An acid infusion test and assessment of cough on and off PPI may be useful preoperative tools for the selection of patients with cough for LNF.     

Effects of cryogen spray cooling and high radiant exposures on selective vascular injury during laser irradiation of human skin

BACKGROUND: Increasing radiant exposure offers a means to increase treatment efficacy during laser-mediated treatment of vascular lesions, such as port-wine stains; however, excessive radiant exposure decreases selective vascular injury due to increased heat generation within the epidermis and collateral damage to perivascular collagen. OBJECTIVE: To determine if cryogen spray cooling could be used to maintain selective vascular injury (ie, prevent epidermal and perivascular collagen damage) when using high radiant exposures (16-30 J/cm2). DESIGN: Observational study. SETTING: Academic hospital and research laboratory. PATIENTS: Twenty women with normal abdominal skin (skin phototypes I-VI). INTERVENTIONS: Skin was irradiated with a pulsed dye laser (wavelength = 585 nm; pulse duration = 1.5 milliseconds; 5-mm-diameter spot) using various radiant exposures (8-30 J/cm2) without and with cryogen spray cooling (50- to 300-millisecond cryogen spurts). MAIN OUTCOME MEASURE: Hematoxylin-eosin-stained histologic sections from each irradiated site were examined for the degree of epidermal damage, maximum depth of red blood cell coagulation, and percentage of vessels containing perivascular collagen coagulation. RESULTS: Long cryogen spurt durations (>200 milliseconds) protected the epidermis in light-skinned individuals (skin phototypes I-IV) at the highest radiant exposure (30 J/cm2); however, epidermal protection could not be achieved in dark-skinned individuals (skin phototypes V-VI) even at the lowest radiant exposure (8 J/cm2). The red blood cell coagulation depth increased with increasing radiant exposure (to >2.5 mm for skin phototypes I-IV and to approximately 1.2 mm for skin phototypes V-VI). In addition, long cryogen spurt durations (>200 milliseconds) prevented perivascular collagen coagulation in all skin types. CONCLUSIONS: Cryogen spurt durations much longer than those currently used in therapy (>200 milliseconds) may be clinically useful for protecting the epidermis and perivascular tissues when using high radiant exposures during cutaneous laser therapies. Additional studies are necessary to prove clinical safety of these protocols.