An inactive receptor-G protein complex maintains the dynamic range of agonist-induced signaling

Agonist binding promotes activation of G protein-coupled receptors (GPCRs) and association of active receptors with G protein heterotrimers. The resulting active-state ternary complex is the basis for conventional stimulus-response coupling. Although GPCRs can also associate with G proteins before agonist binding, the impact of such preassociated complexes on agonist-induced signaling is poorly understood. Here we show that preassociation of 5-HT₇ serotonin receptors with G_s heterotrimers is necessary for agonist-induced signaling. 5-HT₇ receptors in their inactive state associate with G_s, as these complexes are stabilized by inverse agonists and receptor mutations that favor the inactive state. Inactive-state 5-HT₇–G_s complexes dissociate in response to agonists, allowing the formation of conventional agonist–5-HT₇–G_s ternary complexes and subsequent G_s activation. Inactive-state 5-HT₇–G_s complexes are required for the full dynamic range of agonist-induced signaling, as 5-HT₇ receptors spontaneously activate G_s variants that cannot form inactive-state complexes. Therefore, agonist-induced signaling in this system involves two distinct receptor-G protein complexes, a conventional ternary complex that activates G proteins and an inverse-coupled binary complex that maintains the inactive state when agonist is not present.

G protein-coupled receptors (GPCRs) transduce a wide variety of physiological signals and are targeted by a substantial fraction of all therapeutic drugs (1). GPCRs are conformationally dynamic and transition between inactive and active states, the latter being capable of interacting with and activating heterotrimeric G proteins (2). Although some level of constitutive activity is common, the conformational equilibrium “setpoint” usually favors the inactive state of the receptor, thus keeping the system turned off and ready to respond to agonists. Agonist binding stabilizes active conformations and promotes the formation of transient active-state ternary agonist-receptor-G protein complexes (3). This positive allosteric interaction between agonist and G protein binding is the hallmark of conventional GPCR coupling. Receptor-G protein complexes that form before agonist binding have also been described (4–8) and are generally thought of as a means to promote rapid or specific signaling after agonist binding. However, the properties and functional significance of such “preassociated” complexes are largely unknown, and inactive receptor conformations are generally considered unable to interact with G proteins. Here we show that unliganded 5-HT₇ serotonin receptors form complexes with G_s heterotrimers, and that these complexes help maintain the receptor in an inactive state. Agonist binding leads to dissociation of inactive-state 5-HT₇–G_s complexes, which in turn allows increased formation of active-state 5-HT₇–G_s complexes and G protein activation. Thus, a negative allosteric interaction between agonist and G protein binding is required for the full sensitivity of these receptors to serotonin.     

Pharmacological profile of survivors of acute myocardial infarction at Turkish academic hospitals

AIM: The purpose of this study was to document treatment profiles in 850 patients surviving acute myocardial infarction at 17 academic hospitals in Turkey. METHODS AND RESULTS: Pharmacological management data of acute myocardial infarction survivors were collected and divided into three categories: drugs which patients received before hospitalization, during the hospitalization, and at hospital discharge. Data regarding medical history, complications during hospitalization, MI extent (Q wave or non-Q wave), infarct location and diagnostic and revascularization procedures were also recorded. This study is based on the 850 patients who met the diagnostic criteria for initial acute MI in the period examined. Among 850 patients with myocardial infarction enrolled 408 (48%) received thrombolytic therapy. The median time interval from symptom onset to initiation of thrombolytic therapy was 196 min. The most commonly used thrombolytic agent was streptokinase (93%). Thrombolytic recipients were younger, and presented sooner after onset of symptoms. Among patients receiving thrombolytic therapy, concomitant pharmacotherapy included aspirin (95%), intravenous heparin (93%), intravenous nitroglycerin (91%), oral beta-blockers (44%), calcium channel antagonists (13%), and angiotensin converting enzyme inhibitors (41%). The lipid lowering therapy was only used in 4% of all patients, and was given to 18% of patients with hyperlipidemia. CONCLUSION: Current usage rates of thrombolytic therapy in Turkey are lower than expected, but when compared with previous reports it increased. Although adjunctive treatment with intravenous heparin and intravenous nitroglycerin is usually used, beta-blockers appear to be underused and calcium channel blockers appear to be overused. The lipid reducing therapies were infrequently prescribed.     

Hesperidin attenuates oxidative and neuronal damage caused by global cerebral ischemia/reperfusion in a C57BL/J6 mouse model

The aim of this study was to determine the effects of hesperidin (HP) on neuronal damage in brain tissue caused by global cerebral ischemia/reperfusion (I/R) in C57BL/J6 mice. For this purpose, a total of 40 mice were divided equally into four groups: (1) sham-operated (SH), (2) global cerebral I/R, (3) HP, and (4) HP+I/R. The SH group was used as a control. In the I/R group, the bilateral carotid arteries were clipped for 15 min, and the mice were treated with vehicle for 10 days. In the HP group, mice were administered HP (100 mg/kg) for 10 days without carotid occlusion. In the HP+I/R group, the I/R model was applied to the mice exactly as in the I/R group, and they were then treated with 100 mg/kg HP for 10 days. Cerebral I/R significantly induced oxidative stress via an increase in lipid peroxidation and a decrease in the components of the antioxidant defense system. Furthermore, cerebral I/R increased the incidence of histopathological damage and apoptosis in brain tissue. HP treatment significantly reversed the oxidative effects of I/R and inhibited the development of neurodegenerative histopathology. Therefore, the current study demonstrates that HP treatment effectively prevents oxidative and histological damage in the brain caused by global I/R. In this context, the beneficial effects of HP are likely a result of its strong antioxidant and free radical-scavenging properties. HP may be an useful treatment to attenuate the negative effects of global cerebral I/R.     

Molecular analysis in X-linked adrenoleukodystrophy patients: identification of a novel mutation

X linked adrenoleukodystrophy (X-ALD) is a neurodegenerative disease characterized by progressive demyelination of the central nervous system, adrenocortical insufficiency and elevated levels of very long chain fatty acids (VLCFAs). It is caused by mutations in ABCD1 gene located at Xq28. More than 1,300 mutations have been identified to date which is unique to each patient. In this study we report the mutational analysis of 2 X-ALD patients (1 male and 1 female) showing variable clinical spectrum. The mutation analysis of the female patient revealed IVS5-6delC (c.1489-6delC) and p. P543L variations in compound heterozygous state. The male patient was found to be hemizygous for a novel mutation, p. R104P. In conclusion, while defining a novel mutation, the cases presented herein may contribute to the mutation and clinical spectrum of X-ALD.     

Management of fistula of ileal conduit in open abdomen by intra-condoit negative pressure system

INTRODUCTION

We aimed to present the management of a patient with fistula of ileal conduit in open abdomen by intra-condoid negative pressure in conjunction with VAC Therapy and dynamic wound closure system (ABRA).

PRESENTATION OF CASE

65-Year old man with bladder cancer underwent radical cystectomy and ileal conduit operation. Fistula from uretero-ileostomy anastomosis and ileus occurred. The APACHE II score was 23, Mannheim peritoneal index score was 38 and Björck score was 3. The patient was referred to our clinic with ileus, open abdomen and fistula of ileal conduit. Patient was treated with intra-conduid negative pressure, abdominal VAC therapy and ABRA.

DISCUSSION

Management of urine fistula like EAF in the OA may be extremely challenging. Especially three different treatment modalities of EAF are established in recent literature. They are isolation of the enteric effluent from OA, sealing of EAF with fibrin glue or skin flep and resection of intestine including EAF and re-anastomosis. None of these systems were convenient to our case, since urinary fistula was deeply situated in this patient with generalized peritonitis and ileus.

CONCLUSION

Application of intra-conduid negative pressure in conjunction with VAC therapy and ABRA is life saving strategies to manage open abdomen with fistula of ileal conduit.     

Intrarectal negative pressure system in the management of open abdomen with colorectal fistula: A case report

INTRODUCTION

To present the management of open abdomen with colorectal fistula by application of intrarectal negative pressure system (NPS) in addition to abdominal NPS.

PRESENTATION OF CASE

Twenty-year old man had a history of injuries by a close-range gunshot to the abdomen eight days ago and he had been treated by bowel repairs, resections, jejunal anastomosis and Hartman''s procedure. He was referred to our center after deterioration, evisceration with open abdomen and enteric fistula in septic shock. There were edematous, fibrinous bowels and large multiple fistulas from the edematous rectal stump. APACHE II, Mannheim Peritoneal Index and Björck scores were 18, 33 and 3, respectively (expected mortality 100%). After intensive care for 5 days, he was treated by abdominal and intrarectal NPS. NPS repeated for 5 times and the fistula was recovered on day 18 completely. Fascial closure was facilitated with a dynamic abdominal closure system (ABRA) and he was discharged on day 33 uneventfully. There was no herniation and any other problem after 12 months follow-up.

DISCUSSION

Management of fistula in OA can be extremely challenging. Floating stoma, fistula VAC, nipple VAC, ring and silo VAC, fistula intubation systems are used for isolation of the enteric effluent from OA. Several biologic dressings such as acellular dermal matrix, pedicled flaps have been used to seal the fistula opening with various success. Resection of the involved enteric loop and a new anastomosis of the intestine is very hard and rarely possible. In all of these reports, usually patients are left to heal with a giant hernia. In contrast to this, there is no hernia in our case during one year follow up period.

CONCLUSION

Combination of intra and extra luminal negative pressure systems and ABRA is a safe and successful method to manage open abdomen with colorectal fistula.     

Amyloid goiter related with Crohn's disease: A rare association: Amyloid goiter secondary to Crohn's disease

INTRODUCTION

Amyloid goiter (AG) is characterized by enlargement of the thyroid gland as a result of extensive amyloid deposition in a bilateral and diffuse manner.

PRESENTATION OF CASE

A 58-year-old male patient was diagnosed of Crohn''s Disease (CD). He was admitted to our clinic with complaint of respiratory distress and rapid growth swelling in the neck. Ultrasound examination revealed huge multinodular goiter on both sides of thyroid gland. We performed bilateral total thyroidectomy. Pathological evaluation revealed AG.

DISCUSSION

Amyloid leads to degeneration in tissues, thereby disrupts the function of the relevant organs. It is important to distinguish AG from other reasons of goiter, particularly thyroid medullary cancer that can cause amyloid deposition in thyroid gland. Secondary amyloidosis frequently involves thyroid gland at microscopic level, but rarely causes goiter. An analysis of current literature revealed that only few cases of AG occurred secondary to CD. Herein we presented a case of AG who has rapidly growing goiter that associated with CD.

CONCLUSION

AG must be kept in mind in case of rapidly growing goiter, especially in patients with chronic inflammatory bowel diseases.     

Hemodynamic,Autonomic, and Vascular Effects of Exposure to Coarse Particulate Matter Air Pollution from a Rural Location

Background: Fine particulate matter (PM) air pollution is associated with numerous adverse health effects, including increased blood pressure (BP) and vascular dysfunction. Coarse PM substantially contributes to global air pollution, yet differs in characteristics from fine particles and is currently not regulated. However, the cardiovascular (CV) impacts of coarse PM exposure remain largely unknown.Objectives: Our goal was to elucidate whether coarse PM, like fine PM, is itself capable of eliciting adverse CV responses.Methods: We performed a randomized double-blind crossover study in which 32 healthy adults (25.9 ± 6.6 years of age) were exposed to concentrated ambient coarse particles (CAP; 76.2 ± 51.5 μg/m³) in a rural location and filtered air (FA) for 2 hr. We measured CV outcomes during, immediately after, and 2 hr postexposures.Results: Both systolic (mean difference = 0.32 mmHg; 95% CI: 0.05, 0.58; p = 0.021) and diastolic BP (0.27 mmHg; 95% CI: 0.003, 0.53; p = 0.05) linearly increased per 10 min of exposure during the inhalation of coarse CAP when compared with changes during FA exposure. Heart rate was on average higher (4.1 bpm; 95% CI: 3.06, 5.12; p < 0.0001) and the ratio of low-to-high frequency heart rate variability increased (0.24; 95% CI: 0.07, 0.41; p = 0.007) during coarse particle versus FA exposure. Other outcomes (brachial flow-mediated dilatation, microvascular reactive hyperemia index, aortic hemodynamics, pulse wave velocity) were not differentially altered by the exposures.Conclusions: Inhalation of coarse PM from a rural location is associated with a rapid elevation in BP and heart rate during exposure, likely due to the triggering of autonomic imbalance. These findings add mechanistic evidence supporting the biological plausibility that coarse particles could contribute to the triggering of acute CV events.Citation: Brook RD, Bard RL, Morishita M, Dvonch JT, Wang L, Yang HY, Spino C, Mukherjee B, Kaplan MJ, Yalavarthi S, Oral EA, Ajluni N, Sun Q, Brook JR, Harkema J, Rajagopalan S. 2014. Hemodynamic, autonomic, and vascular effects of exposure to coarse particulate matter air pollution from a rural location. Environ Health Perspect 122:624–630; http://dx.doi.org/10.1289/ehp.1306595     

Intracranial hemorrhage in infants as a serious,and preventable consequence of late form of vitamin K deficiency: a selfie picture of Turkey,strategies for tomorrow

Purpose

Vitamin K deficiency bleeding is one of the most common causes of acquired hemostatic disorder in early infancy. Although vitamin K is practiced routinely after every birth in Turkey, children with type of vitamin K deficiency bleedings (L-VKDB) can be encountered. We aimed to evaluate the clinical features of the children with L-VKDB reported from Turkey.

Methods

Between 1995 and 2013, 48 studies reporting 534 children with L-VKDB were evaluated in this study.

Results

Of the 534 reported children (178 girls, 356 boys), 486 (91 %) were extremely breastfed. The most common bleeding sites were intracranial hemorrhage, gastrointestinal, and umbilical in 414 (77.4 %), 33 (6.2 %), and 33 (6.2 %) children, respectively, and 35 (6.6 %) children had been diagnosed incidentally without any bleeding. The etiology of 399 (74.7 %) children were classified as idiopathic, whereas 135 (25.3 %) were secondary. Intramuscular vitamin K was administered in 248 (46.4 %), not administered in 228 (42.7 %), and the administration of vitamin K were not determined in 58 (10.9 %) children. The outcomes of Turkish cohort showed that 111 (20.8) children died, 257 (48.1 %) cases developed neurologic deficit (mainly epilepsy and psychomotor retardation), and only 166 (31.1 %) patients recovered without squeal.

Conclusions

The compliance of prophylactic measures in Turkey does not seem to be satisfactory. As a further measure of tomorrow, we vigorously emphasize that a national surveillance program may be initiated. An additional intramuscular dose or oral supplementation of vitamin K especially for exclusively breast-fed infants may reduce this catastrophic problem in our country.