A G-protein subunit translocation embedded network motif underlies GPCR regulation of calcium oscillations

G-protein βγ subunits translocate reversibly from the plasma membrane to internal membranes on receptor activation. Translocation rates differ depending on the γ subunit type. There is limited understanding of the role of the differential rates of Gβγ translocation in modulating signaling dynamics in a cell. Bifurcation analysis of the calcium oscillatory network structure predicts that the translocation rate of a signaling protein can regulate the damping of system oscillation. Here, we examined whether the Gβγ translocation rate regulates calcium oscillations induced by G-protein-coupled receptor activation. Oscillations in HeLa cells expressing γ subunit types with different translocation rates were imaged and quantitated. The results show that differential Gβγ translocation rates can underlie the diversity in damping characteristics of calcium oscillations among cells. Mathematical modeling shows that a translocation embedded motif regulates damping of G-protein-mediated calcium oscillations consistent with experimental data. The current study indicates that such a motif may act as a tuning mechanism to design oscillations with varying damping patterns by using intracellular translocation of a signaling component.

Optimizing optogenetic constructs for control over signaling and cell behaviours

Optogenetic tools have recently been developed that enable dynamic control over the activities of select signaling proteins. They provide the unique ability to rapidly turn signaling events on or off with subcellular control in living cells and organisms. This capability is leading to new insights into how the spatial and temporal coordination of signaling events governs dynamic cell behaviours such as migration and neurite outgrowth. These tools can also be used to dissect a protein's signaling functions at different organelles. Here we review the properties of photoreceptors from diverse organisms that have been leveraged to control signaling in mammalian cells. We emphasize recent engineering approaches that have been used to create optogenetic constructs with optimized spectral, kinetic, and signaling properties for controlling cell behaviours.

Chemical, Bioactive, and Antioxidant Potential of Twenty Wild Culinary Mushroom Species

The chemical, bioactive, and antioxidant potential of twenty wild culinary mushroom species being consumed by the people of northern Himalayan regions has been evaluated for the first time in the present study. Nutrients analyzed include protein, crude fat, fibres, carbohydrates, and monosaccharides. Besides, preliminary study on the detection of toxic compounds was done on these species. Bioactive compounds evaluated are fatty acids, amino acids, tocopherol content, carotenoids (β-carotene, lycopene), flavonoids, ascorbic acid, and anthocyanidins. Fruitbodies extract of all the species was tested for different types of antioxidant assays. Although differences were observed in the net values of individual species all the species were found to be rich in protein, and carbohydrates and low in fat. Glucose was found to be the major monosaccharide. Predominance of UFA (65-70%) over SFA (30-35%) was observed in all the species with considerable amounts of other bioactive compounds. All the species showed higher effectiveness for antioxidant capacities.

Comparative study of glycated hemoglobin by ion exchange chromatography and affinity binding nycocard reader in type 2 diabetes mellitus

The aim of this study was to compare the level of glycated hemoglobin (HbA1c) in type 2 Diabetes Mellitus (DM) patients by two different methods namely Ion Exchange Chromatography and Affinity Binding Nycocard Reader. This is a cross-sectional study conducted on confirmed type 2 diabetes mellitus patients (n = 100) who visited Out Patients Department of the Universal College of Medical Sciences Teaching hospital, Bhairahawa, Nepal from November 2012 to March 2013. The diagnosis of diabetes mellitus was done on the basis of their fasting (164.46 ± 45.33 mg/dl) and random (187.93 ± 78.02 mg/dl) serum glucose level along with clinical history highly suggestive of type 2 DM. The HbA1c values of (7.8 ± 1.9%) and (8.0 ± 2.2%) were found in DM patients as estimated by those two different methods respectively. The highest frequency was observed in HbA1c > 8.0% indicating maximum cases were under very poor glycemic control. However, there were no significant differences observed in HbA1c value showing both methods are comparable in nature and can be used in lab for ease of estimation. The significant raised in HbA1c indicates complications associated with DM and monitoring of therapy become hard for those patients. Despite having standard reference method for HbA1c determination, the availability of report at the time of the patient visit can be made easy by using Nycocard Reader and Ion Exchange Chromatography techniques without any delay in communicating glycemic control, clinical decision-making and changes in treatment regimen.

The structure of dynamic GPCR signaling networks

G-protein-coupled receptors (GPCRs) stimulate signaling networks that control a variety of critical physiological processes. Static information on the map of interacting signaling molecules at the basis of many cellular processes exists, but little is known about the dynamic operation of these networks. Here we focus on two questions. First, Is the network architecture underlying GPCR-activated cellular processes unique in comparison with others such as transcriptional networks? We discuss how spatially localized GPCR signaling requires uniquely organized networks to execute polarized cell responses. Second, What approaches overcome challenges in deciphering spatiotemporally dynamic networks that govern cell behavior? We focus on recently developed microfluidic and optical approaches that allow GPCR signaling pathways to be triggered and perturbed with spatially and temporally variant input while simultaneously visualizing molecular and cellular responses. When integrated with mathematical modeling, these approaches can help identify design principles that govern cell responses to extracellular signals. We outline why optical approaches that allow the behavior of a selected cell to be orchestrated continually are particularly well suited for probing network organization in single cells.

Subcellular optogenetic inhibition of G proteins generates signaling gradients and cell migration

Cells sense gradients of extracellular cues and generate polarized responses such as cell migration and neurite initiation. There is static information on the intracellular signaling molecules involved in these responses, but how they dynamically orchestrate polarized cell behaviors is not well understood. A limitation has been the lack of methods to exert spatial and temporal control over specific signaling molecules inside a living cell. Here we introduce optogenetic tools that act downstream of native G protein-coupled receptor (GPCRs) and provide direct control over the activity of endogenous heterotrimeric G protein subunits. Light-triggered recruitment of a truncated regulator of G protein signaling (RGS) protein or a Gβγ-sequestering domain to a selected region on the plasma membrane results in localized inhibition of G protein signaling. In immune cells exposed to spatially uniform chemoattractants, these optogenetic tools allow us to create reversible gradients of signaling activity. Migratory responses generated by this approach show that a gradient of active G protein αi and βγ subunits is sufficient to generate directed cell migration. They also provide the most direct evidence so for a global inhibition pathway triggered by Gi signaling in directional sensing and adaptation. These optogenetic tools can be applied to interrogate the mechanistic basis of other GPCR-modulated cellular functions.

Liquid chromatography tandem mass spectrometry method for determination of antidiabetic chalcones derivative S001-469 in rat plasma, urine and feces: application to pharmacokinetic study

A sensitive and selective liquid chromatography tandem mass spectrometry assay was developed for quantitation of a novel antidiabetic chalcones derivative S001-469 in rat matrices. Plasma and urine samples were prepared by double liquid-liquid extraction with diethyl ether and feces by protein precipitation using acetonitrile. Chromatographic elution was carried on cyano guard column (30 mm × 4.6 mm i.d., 5 µm) in isocratic mode at a flow rate of 0.75 mL/min using mobile phase comprising of methanol: ammonium acetate buffer (pH 4.6, 10 mM) (90:10, v/v). Run time was 6 min. Detection was achieved by employing positive ionization mode on a triple-quadrupole LC-MS/MS system with an electrospray ionization (ESI) source. The calibration curves were linear over the range of 0.78-400 ng/mL for all 3 matrices. The method was validated and proved reliable through high and consistent intra- and inter- day accuracy and precision (<15%) values. Recoveries was >85% from spiked plasma, urine and feces samples. S001-469 was stable in plasma at room temperature till 8 h and at -60 °C for 30 d and 3 freeze-thaw cycles.

Serum total adenosine deaminase activity in Nepalese patients with Rheumatoid Arthritis

Objective: Several studies indicate that serum adenosine deaminase (ADA) activity could be a potential marker for the diagnosis of patients with rheumatoid arthritis (RA). However, there has been no such study that could independently verify this finding in Nepali population. The present study therefore aims to measure the total ADA activity in the sera of Nepalese RA patients and verify its diagnostic potential. Materials and Methods: A total of 69 RA patients who visited Universal College of Medical Sciences Teaching Hospital (UCMSTH), Bhairahawa, Nepal for their medical treatment were enrolled for this study. An equal number of age and sex-matched healthy controls were also included in the study. Blood samples were collected from each study subjects and analyzed for serum total ADA, Creactive protein (CRP) and rheumatoid factor (RF). Results: Serum total ADA activity was found to be significantly (p<0.0001) higher (30.0 }10.1 U/L) in all RA patients compared to healthy controls (13.5 } 3.6 U/L). However, no significant difference (p>0.05) in the ADA activity was found between the smokers and non-smoker RA patients. Out of total 69 RA patients, only 16 (23.1%) were positive for CRP and 11 (15.9%) were positive for RF. Conclusion: Measurement of serum total ADA activity could be a reliable marker for the diagnosis of RA in Nepali population with relevant clinical scenarios when there is absence of CRP and RF in the serum.  DOI: http://dx.doi.org/10.3126/ajms.v4i2.6208 Asian Journal of Medical Sciences 4(2013) 30-35

Effect of carbamazepine on the pharmacokinetic parameters of CDRI-97/78 following coadministration to rats

Coadministration of 2 or more drugs may result in unexpected toxicity. This study aimed to evaluate the effect of carbamazepine coadministration on the pharmacokinetics of CDRI-97/78, an 1,2,4-trioxane antimalarial agent. Firstly, 97/78 was administered alone and then 97/78 and carbamazepine were coadministered to male and female rats. An revalidated LC-MS/MS method was used for quantitation of 97/63 since 97/78 is instantly and completely converted to 97/63 (an in-vivo active metabolite). The Tmax and Cmax values of 97/63 were 1.75±0.77 h and 862±306 ng/mL in male rats whereas in female rats they were 5.45±0.76 h and 662.75±95.09 ng/mL after a single dose of 97/78 alone. However, following coadministration of 97/78 and carbamazepine, the values for Tmax and Cmax were 1.06±0.16 h and 533±153 ng/mL in male rats and 2.23±1.93 h and 636.5±112.4 ng/mL in female rats. The half life of 97/63 following a single oral dose of 97/78 or coadministration with carbamazepine to male rats was 6.98±0.63 h and 6.64±0.54 h, respectively; the values in female rats were 7.5±0.5 h and 5.48±0.37 h. A statistically insignificant difference (P>0.05) was observed with the student t-test for the pharmacokinetic parameters of 97/63 following oral administration of 97/78 alone or coadministration of 97/78 and carbamazepine except for MRT in female rats. Intersex statistical comparison also showed an insignificant difference for 97/63 following oral administration of 97/78 alone or in combination with carbamazepine except for MRT, which supports coadministration of 97/78 and carbamazepine.

Frequency of Type 2 Diabetes mellitus and Impaired Glycemia in a Teaching Hospital of South-Western Nepal

Objective: The aim of this study was to determine the frequency of type 2 diabetes, impaired fasting glucose (IFG) and impaired glucose tolerance (IGT) among patients visiting a tertiary level teaching hospital in south-western Nepal. Material & Methods: This is a retrospective study conducted among subjects (n=17082) who visited outpatient department of the Universal College of Medical Sciences Teaching Hospital (UCMSTH), Bhairahawa, Nepal for their medical checkup.  Data related to age, sex, hospital number and blood glucose concentration of the study subjects were collected from hospital records and analyzed for the frequency study. Results: The average frequency of type 2 diabetes was found to be 6.1% over a period of five years and it was significantly (p=0.0232) higher in males (3.4%) than in females (2.8%). Frequency of IFG and IGT were found to be 2.31% and 2.70% respectively. The frequency of type 2 diabetes, IFG and IGT was significantly higher in males and age group of 51-60 years. Conclusion: The frequency of type 2 diabetes and impaired glycemia is increasing every year in south-western part of Nepal. We recommend that efforts be made by all the stakeholders to curb this emerging medical problem before it becomes epidemic in the general population. DOI: http://dx.doi.org/10.3126/ajms.v2i3.5485 Asian Journal of Medical Sciences 2 (2011) 202-206  

All G protein βγ complexes are capable of translocation on receptor activation

Heterotrimeric G proteins transduce signals sensed by transmembrane G protein coupled receptors (GPCRs). A subfamily of G protein βγ subunit types has been shown to selectively translocate from the plasma membrane to internal membranes on receptor activation. Using 4D imaging we show here that Gβγ translocation is not restricted to some subunit types but rather all 12 members of the family of mammalian γ subunits are capable of supporting βγ translocation. Translocation kinetics varies widely depending on the specific γ subunit type, with t(1/2) ranging from 10s to many minutes. Using fluorescence complementation, we show that the β and γ subunits translocate as βγ dimers with kinetics determined by the γ subunit type. The expression patterns of endogenous γ subunit types in HeLa cells, hippocampal neurons and cardiomyocytes are distinctly different. Consistent with these differences, the βγ translocation rates vary widely. βγ translocation rates exhibit the same γ subunit dependent trends regardless of the specific receptor type or cell type showing that the translocation rates are intrinsic to the γ subunit types. βγ complexes with widely different rates of translocation had differential effects on muscarinic stimulation of GIRK channel activity. These results show that G protein βγ translocation is a general response to activation of GPCRs and may play a role in regulating signaling activity.

Intersex effect of lamotrigine on the pharmacokinetic parameters of CDRI-97/78, a novel trioxane antimalarial compound, in rats

Reports regarding drug toxicity and adverse events resulting from coadministration of multiple drugs are increasing at an alarming rate. CDRI-97/78 is an 1,2,4-trioxane antimalarial agent under development which gets metabolized to the in vivo active metabolite 97/63. In order to assess its drug interaction potential, CDRI-97/78 was administered alone and in combination with lamotrigine to male and female rats via the oral route. Quantification of the active metabolite 97/63 in rat plasma was achieved with an LC-MS/MS assay. After oral administration of 97/78, the Tmax and Cmax values of 97/63 in male rats were 1.75±0.77 h and 862±306 ng/mL while female rats showed values for Cmax of 622.75±95.09 ng/mL and for Tmax of 7.5±0.5 h. Coadministration of 97/78 and lamotrigine resulted in decreased Tmax and Cmax values in both male and female rats (Tmax and Cmax of 0.77±0.16 h and 58.58±6.43 ng/mL in male rats; 1.13±0.22 h and 62.95±12.00 ng/mL in female rats, respectively). A statistically significant difference (P<0.05) was observed for the pharmacokinetic parameters of 97/63 after oral administration of 97/78 alone and upon its coadministration with lamotrigine except for the Cmax and Tmax values in male and for the T1/2 value in female rats. Statistically, no significant difference for the pharmacokinetic parameters of 97/63 between male and female rats after oral administration of 97/78 alone or in combination with lamotrigine was determined except for Tmax. The study indicates that coadministration of 97/78, an antimalarial agent, and the antiepileptic lamotrigine may require dose adjustments. Additional clinical drug interaction trials may be required to confirm these findings.

Upper gastro-intestinal bleeding: aetiology and demographic profile based on endoscopic examination at Dhulikhel Hospital, Kathmandu University Hospital

BACKGROUND

The upper gastrointestinal bleeding (UGIB) is defined as bleeding within the intraluminal gastrointestinal tract from any location between the upper oesophagus to the duodenum at the ligament of Treitz. It is one of the important medical emergencies worldwide.

OBJECTIVE

The objective of this study is to study the aetiology of upper gastrointestinal bleeding based on endoscopic examination findings in patients of various demographic characteristics.

MATERIALS AND METHODS

This is a retrospective observational study. The endoscopic record book from 2007 January to 2009 October was reviewed for all the cases who underwent oesophago-gastro-duodenoscopic examination for upper GI bleeding. The clinico-epidemiological data of all the patients was reviewed and analyzed in concert with the aetiology of bleeding.

RESULTS

A total of 90 patients (58 males, 32 females; mean age 45.32+ 18.47 years) of upper gastrointestinal bleeding was studied and analyzed in terms of aetiology of bleeding and demographic profile. Among the ethnic groups, Aryan 46 (51%) was the most common ethnic group to have upper GI bleeding followed by Newars 24 (27%), Mongolians 16 (18%), Dalits 3 (3%) and others 1 (1%). Out of 90 patients, 47( 52.2%) cases was less than 45 years of age, 30(33.3%) of 46 to 65 age ; and 13(14.4 %) more than 65 years of age. Gastric ulcer 23(25.6%) was the most common endoscopic finding, followed by oesophageal varices 14 (15.6%), acute erosive/haemorrhagic gastropathy 11 (12.2%), duodenal ulcer 9(10%), growth 7(7.8%), vascular lesions 3(3.3%), Mallory-Weiss tear 1(1.1%), fundal varices 1(1.1%) and, no cause was identified in 21(23.3%) cases. The peptic ulcer bleeding was the most common finding in Aryan 22(47.9%), whereas oesophageal varices and growth were more common in Newar 7(29.2%) and 3 (12.5%) respectively.

CONCLUSION

Peptic ulcer disease is the most common cause of upper GI bleeding which was most commonly found in Aryan population; followed by oesophageal varices and growth as second and third most common causes and were more prevalent in Newar and Mongolian people.

Alteration of Golgi structure in senescent cells and its regulation by a G protein γ subunit

Cellular senescence is a process wherein proliferating cells undergo permanent cell cycle arrest while remaining viable. Senescence results in enhanced secretion of proteins that promote cancer and inflammation. We report here that the structure of the Golgi complex which regulates secretion is altered in senescent cells. In cells where senescence is achieved by replicative exhaustion or in cells wherein senescence has been induced with BrdU treatment dependent stress, the Golgi complex is dispersed. The expression of a G protein γ subunit, γ11, capable of translocation from the plasma membrane to the Golgi complex on receptor activation increases with senescence. Knockdown of γ11 or overexpression of a dominant negative γ3 subunit inhibits Golgi dispersal induced by senescence. Overall these results suggest that in cellular senescence an upregulated G protein gamma subunit mediates alterations in the structure of the Golgi.

Liquid chromatographic-tandem mass spectrometry assay for quantitation of a novel antidiabetic S002-853 in rat plasma and its application to pharmacokinetic study

A sensitive and selective LC-MS/MS method has been developed and validated for the estimation of novel antidiabetic synthetic flavonoid S002-853 in rat plasma using centchroman as an internal standard. The method involves a simple two-step liquid-liquid extraction with diethyl ether. The analyte was chromatographed on a Pierce Spheri-5, guard cyano column (30 x 4.6 mm i.d., 5 microm) with isocratic mobile phase consisting of methanol-ammonium acetate buffer (pH 4.6, 10 mm; 90 : 10, v/v) at a flow rate of 0.75 mL/min. The API 4000 triple-quadrupole LC-MS/MS system was operated under multiple reaction-monitoring mode. The ionization was performed by electrospray ionization technique in positive ion mode. The chromatographic run time was 6 min and the weighted (1/x(2)) calibration curves were linear over the range 0.78-400 ng/mL. The limit of detection and lower limit of quantification were 0.195 and 0.78 ng/mL, respectively. The intra- and inter-batch accuracy (%bias) and precision (%RSD) were found to be less than 8.47 and 11.6% respectively. The average absolute recoveries of S002-853 and internal standard from spiked plasma samples were >90%. S002-853 was stable for 8 h at ambient temperature, 4 weeks at -60 degrees C and after three freeze-thaw cycles. The assay was successfully applied to determine the pharmacokinetic parameters in male Sprague-Dawley rats after an oral dose administration at 25 mg/kg.

Transient left ventricular apical ballooning post-pneumoperitoneum: Takotsubo cardiomyopathy. A case report

The aim of this study was to describe the clinical features and management of Takotsubo cardiomyopathy manifesting during the intraoperative period in a patient undergoing laparoscopic cholecystectomy.

CLINICAL FEATURES

a 29-year-old ASA I female patient was posted for laparoscopic cholecystectomy. A standard general anesthetic technique was followed. Two minutes after the initiation of pneumoperitoneum, the patient developed clinical features of acute myocardial infarction with pulmonary edema. The surgery was postponed and the patient was shifted to the ICU. Echocardiography revealed hypokinesis of the left ventricle apex and anterolateral segment. Coronary angiography revealed normal arteries without any stenosis or obstruction. The patient required vasopressor and inotropic support for 4 days and was discharged on the 8th postoperative day. Repeat echocardiography 4 days later demonstrated complete resolution of regional systolic dysfunction. Transient left ventricular dysfunction is a possible occurrence during non-cardiac surgery. Awareness of this condition is essential as early diagnosis and prompt management can save the patient's life. To our knowledge this represents the first case of pneumoperitoneum-induced Takotsubo cardiomyopathy.

With a pinch of salt

This report highlights a case of severe hyponatraemia secondary to excessive sweating and salt [corrected] poor fluid consumption and low salt diet in hot conditions. The case was complicated by the presence of marked hypokalaemia caused by secondary hyperaldosteronism confirmed, for the first time, by the presence of grossly elevated serum renin and aldosterone concentrations. With the rise in global temperature affecting even temperate climates doctors, especially in acute and general medicine, may be faced with this condition more often.