Stoichiometry and assembly of mTOR complexes revealed by single-molecule pulldown

The mammalian target of rapamycin (mTOR) kinase is a master regulator of cellular, developmental, and metabolic processes. Deregulation of mTOR signaling is implicated in numerous human diseases including cancer and diabetes. mTOR functions as part of either of the two multisubunit complexes, mTORC1 and mTORC2, but molecular details about the assembly and oligomerization of mTORCs are currently lacking. We use the single-molecule pulldown (SiMPull) assay that combines principles of conventional pulldown assays with single-molecule fluorescence microscopy to investigate the stoichiometry and assembly of mTORCs. After validating our approach with mTORC1, confirming a dimeric assembly as previously reported, we show that all major components of mTORC2 exist in two copies per complex, indicating that mTORC2 assembles as a homodimer. Interestingly, each mTORC component, when free from the complexes, is present as a monomer and no single subunit serves as the dimerizing component. Instead, our data suggest that dimerization of mTORCs is the result of multiple subunits forming a composite surface. SiMPull also allowed us to distinguish complex disassembly from stoichiometry changes. Physiological conditions that abrogate mTOR signaling such as nutrient deprivation or energy stress did not alter the stoichiometry of mTORCs. On the other hand, rapamycin treatment leads to transient appearance of monomeric mTORC1 before complete disruption of the mTOR-raptor interaction, whereas mTORC2 stoichiometry is unaffected. These insights into assembly of mTORCs may guide future mechanistic studies and exploration of therapeutic potential.

Comparison of the anaesthetic efficacy of different volumes of 4% articaine (1.8 and 3.6 mL) as supplemental buccal infiltration after failed inferior alveolar nerve block

AIM

To compare the anaesthetic efficacy of different volumes (1.8 mL vs. 3.6 mL) of 4% articaine with 1 : 100 000 epinephrine injected as buccal infiltrations after a failed inferior alveolar nerve block (IANB) in patients with symptomatic irreversible pulpitis.

METHODOLOGY

Two hundred and thirty-four adult patients, diagnosed with irreversible pulpitis in a mandibular tooth, participated in this multicentre, randomized double-blinded trial. Patients received IANB with 1.8 mL of 4% articaine with 1 : 100 000 epinephrine. Pain during treatment was recorded using the Heft-Parker visual analogue scale (HP VAS). The primary outcome measure, and the definition of 'success', was the ability to undertake pulp chamber access and canal instrumentation with no or mild pain (HP VAS score <55 mm). Patients who experienced 'moderate-to-severe' pain (HP VAS score ≥ 55 mm) were randomly allocated into two groups and received buccal infiltrations with either 1.8 mL or 3.6 mL of 4% articaine with 1 : 100 000 epinephrine. Root canal treatment was re-initiated after 10 min. Success was again defined as no pain or weak/mild pain during endodontic access preparation and instrumentation. Statistical analysis was performed using Mann-Whitney U and chi-square tests.

RESULTS

The initial IANB of 4% articaine gave an overall success rate of 37%. The success rate of supplementary buccal infiltration with 1.8 and 3.6 mL volumes was 62% and 64%, respectively. The difference between the success rates of the two volumes was not statistically significant.

CONCLUSIONS

Increasing the volume of 4% articaine with 1 : 100 000 epinephrine from 1.8 to 3.6 mL, given as supplementary buccal infiltrations after a failed primary IANB with 1.8 mL of 4% articaine with 1 : 100 000, did not improve the anaesthetic success rates in patients with symptomatic irreversible pulpitis.

Comparison of the anaesthetic efficacy of epinephrine concentrations (1 : 80 000 and 1 : 200 000) in 2% lidocaine for inferior alveolar nerve block in patients with symptomatic irreversible pulpitis: a randomized, double-blind clinical trial

AIM

The aim of this randomized controlled, double-blind trial was to comparatively evaluate the anaesthetic efficacy and injection pain of 1.8 mL of 2% lidocaine with different concentrations of epinephrine (1 : 80 000 and 1 : 200 000) in patients with symptomatic irreversible pulpitis.

METHODOLOGY

Sixty-two adult volunteers, actively experiencing pain, were randomly allocated into 2 groups and received 1.8 mL of 2% lidocaine with either 1 : 80 000 or 1 : 200 000 epinephrine concentration. Endodontic access preparation was initiated 15 min after the initial IANB. Pain during treatment was recorded using the Heft-Parker visual analogue scale (HP VAS). The primary outcome measure, and the definition of 'success', was the ability to undertake pulp access and canal instrumentation with no or mild pain (HP VAS score <55 mm). Secondary outcome measure was the pain experienced during LA solution deposition. Statistical analysis was performed using Mann-Whitney U-test and chi-square test.

RESULTS

The anaesthetic success rates of 2% lidocaine solutions containing 1 : 80 000 and 1 : 200 000 epinephrine concentrations were 20% and 28%, respectively. The difference was not statistically significant. There was also no significant difference in the pain experienced during deposition of the solutions.

CONCLUSIONS

Two percent lidocaine solution used for IANB achieved similar success rates when used with 1 : 80 000 or 1 : 200 000 epinephrine concentration.

Esophageal Foreign Body in a Neonate: An Unusual Age of Presentation

Ingestion of foreign bodies in neonates is very rare and can be life threatening. We describe a 20 days old neonate presented with vomiting, drooling of saliva and poor feeding tolerance. Chest radiograph showed a metallic foreign body in superior mediastinum. Foreign body was removed by rigid oesophagoscopy. The case describes the unusual age of presentation of foreign body and options available to remove these foreign bodies in neonates. Key words: Esophagus; Foreign body; Neonate DOI: http://dx.doi.org/10.3126/jnps.v32i1.5306   J. Nepal Paediatr. Soc. Vol.32(1) 2012 79-80

Ligand-modulated parallel mechanical unfolding pathways of maltose-binding proteins

Protein folding and unfolding are complex phenomena, and it is accepted that multidomain proteins generally follow multiple pathways. Maltose-binding protein (MBP) is a large (a two-domain, 370-amino acid residue) bacterial periplasmic protein involved in maltose uptake. Despite the large size, it has been shown to exhibit an apparent two-state equilibrium unfolding in bulk experiments. Single-molecule studies can uncover rare events that are masked by averaging in bulk studies. Here, we use single-molecule force spectroscopy to study the mechanical unfolding pathways of MBP and its precursor protein (preMBP) in the presence and absence of ligands. Our results show that MBP exhibits kinetic partitioning on mechanical stretching and unfolds via two parallel pathways: one of them involves a mechanically stable intermediate (path I) whereas the other is devoid of it (path II). The apoMBP unfolds via path I in 62% of the mechanical unfolding events, and the remaining 38% follow path II. In the case of maltose-bound MBP, the protein unfolds via the intermediate in 79% of the cases, the remaining 21% via path II. Similarly, on binding to maltotriose, a ligand whose binding strength with the polyprotein is similar to that of maltose, the occurrence of the intermediate is comparable (82% via path I) with that of maltose. The precursor protein preMBP also shows a similar behavior upon mechanical unfolding. The percentages of molecules unfolding via path I are 53% in the apo form and 68% and 72% upon binding to maltose and maltotriose, respectively, for preMBP. These observations demonstrate that ligand binding can modulate the mechanical unfolding pathways of proteins by a kinetic partitioning mechanism. This could be a general mechanism in the unfolding of other large two-domain ligand-binding proteins of the bacterial periplasmic space.

Complicated crown fractures - management and treatment options

AIM

Complicated crown fractures involve enamel, dentine and the pulp. The incidence of complicated crown fractures ranges from 2% to 13% of all dental injuries and the most commonly involved tooth is the maxillary central incisor. Various treatment modalities are available depending upon the clinical, physiological and radiographic status of the involved tooth. The aim of this article was to discuss techniques for the management of complicated crown fractures.

SUMMARY

Management of complicated crown fractures depends upon several factors with the result that various clinical modalities have been suggested. Seven case reports of complicated crown fractures are presented and risks/benefits of the treatment plans are discussed.

KEY LEARNING POINTS

Proper diagnosis, treatment planning and follow-up care are important factors in the prognosis of complicated crown fractures. Thorough understanding of the available treatment modalities and their specific indications is critical. The risks and benefits of each treatment option should be carefully evaluated during the treatment planning process.

Predictive tool for estimating the potential effect of water fluoridation on dental caries

OBJECTIVE

To provide a tool for public health planners to estimate the potential improvement in dental caries in children that might be expected in a region if its water supply were to be fluoridated.

BASIC RESEARCH DESIGN

Recent BASCD (British Association for the Study of Community Dentistry) dental epidemiological data for caries in 5- and 11-year-old children in English primary care trusts in fluoridated and non-fluoridated areas were analysed to estimate absolute and relative improvement in dmft/DMFT and caries-free measures observed in England. Where data were sufficient for testing significance this analysis included the effect of different levels of deprivation.

RESULTS

A table of observed improvements was produced, together with an example of how that table can be used as a tool for estimating the expected improvement in caries in any specific region of England. Observed absolute improvements and 95% confidence intervals were: for 5-year-olds reduction in mean dmft 0.56 (0.38, 0.74) for IMD 12, 0.73 (0.60, 0.85) for IMD 20, and 0.94 (0.76, 1.12) for IMD 30, with 12% (9%, 14%) more children free of caries; for 11-year-olds reduction in mean DMFT 0.12 (0.04, 0.20) for IMD 12, 0.19 (0.13, 0.26) for IMD 20, 0.29 (0.18, 0.40) and for IMD 30, with 8% (5%, 11%) more children free from caries.

CONCLUSIONS

The BASCD data taken together with a deprivation measure are capable of yielding an age-specific, 'intention to treat' model of water fluoridation that can be used to estimate the potential effect on caries levels of a notional new fluoridation scheme in an English region.

Tumoral calcinosis (Teutschlander disease) in a dialysis patient

Tumoral calcinosis is an uncommon and severe complication of hemodialysis therapy. It is generally associated with the presence of the high serum calcium-and-phosphorus product. We report here a case of a patient on hemodialysis who presented with progressively increasing, multiple, tumor-like, subcutaneous swellings. These are rare manifestations of extraosseous calcification in uremic patients that are termed as tumoral calcinosis. A 25 year-old male presented with multiple, nodular, painful, cutaneous swellings all over his body that had been progressively increasing over the last four years. He was a known case of chronic glumerulonephritis who was on regular hemodialysis. The patient was investigated and diagnosed as having tumoral calcinosis and was treated with a low calcium dialysate of pure reverse osmosis water.

Indirect hyperbilirubinemia with indinavir

Indinavir is a protease inhibitor used in the treatment of HIV infected individuals and as post-exposure prophylaxis. Indinavir is associated with various adverse effects including gastrointestinal, a lipodystrophy syndrome and nephrolithiasis. We describe indirect hyperbilirubinemia as an adverse effect of indinavir in a person on post-exposure prophylaxis (PEP).

Effect of intraesophageal acid instillation on airway reactivity in patients with asthma

OBJECTIVE

To study the change in airway reactivity due to presence of acid in lower esophagus and its reversibility by antacid.

METHOD

In this double blind study 12 subjects with asthma and gastroesophageal reflux received acid (N/10 hydrochloric acid) and antacid (mixture of magnesium trisilicate and aluminum hydroxide) perfusion in lower esophagus via a nasogastric tube. The four combinations were antacid-antacid (control), antacid-acid, acid-antacid and acid-acid. Airway reactivity (Histamine PD20) was recorded after each perfusion.

RESULTS

Histamine PD20 significantly decreased (airway reactivity increased) (p < 0.05) with all three combinations containing acid as compared to control. No significant difference in airway reactivity was observed if the antacid was given before or after the acid.

CONCLUSION

Presence of acid in lower esophagus can increase airway reactivity. This effect lasts longer than the presence of acid in esophagus itself.

Aetiology of chronic diarrhoea in tropical children

AIM

We studied the causes and presentations of chronic diarrhoea in post-weaned children.

METHODS

Forty seven children (6 months to 12 years) with diarrhoea of more than 2 weeks duration were recruited and subjected to detailed clinical examination and investigations.

RESULTS

Primarily on the basis of history, clinical examination and duodenal biopsy, children could be classified into 5 groups namely tropical enteropathy (46.8%), irritable bowel syndrome (10.6%), giardiasis (14.8%), celiac disease (6.8%) and non specific diarrhoea (21.8%). Children with tropical enteropathy improved with broad spectrum antimicrobial therapy, those with irritable bowel syndrome and non specific chronic diarrhoea with dietary interventions while children with celiac disease required definite withdrawal of gluten from diet.

Poisoning in children: Indian scenario

The retrospective data on childhood poisoning from eight regional hospitals in India has been reviewed. The demographic features and types of poisonings encountered have been compared. The analysis of the data indicated that pediatric poisonings constituted 0.23-3.3% of the total poisoning. The mortality ranged from 0.64-11.6% with highest being from Shimla. Accidental poisoning was common involving 50-90% of children below 5 years of age and males outnumbered the females. Suicidal poisoning was seen after 13 years of age and was due to drugs and household chemicals. One of the hospitals in Delhi recorded a very high incidence (66.6%) of drug poisoning in children. The drugs consumed belonged to phenothiazines, antiepileptics and antipyretics. Iron poisoning was seen in younger children. Kerosene was one of the causes of accidental poisoning at all hospitals except Shimla and rural Maharashtra were probably wood charcoal is widely used. Pesticide poisoning was more prevalent in Punjab and West Bengal whereas plant poisoning was very common in Shimla. Significant number of snake envenomation has been recorded from rural Maharashtra. Other less common accidental poisonings in children included alcohol, corrosives, heavy metals, rodenticides, detergents and disinfectants. Thus various regions in the country showed some variation in types and frequency of childhood poisoning which could be attributed to different geographical and socio-economic background.

Telephone mouthpiece as a possible source of hospital infection

A bacterial culture from telephone mouthpiece showed that 47 percent of the instruments carried pathogenic bacteria. Wiping with a disinfectant swab reduced the number of contaminated telephones. But for complete elimination of bacterial contamination changes in design of mouthpiece holes or type of instrument or using a polythene plastic cover over mouthpiece is recommended.

Prevalence of transfusion associated infections in multitransfused children in relation to mandatory screening of HIV in donated blood

Any change in risk behavior related to acquisition of human immunodeficiency virus (HIV) infection is likely to reduce simultaneously the risk for other agents transmitted through identical routes. A study carried out in the city of Delhi, India on the load of transfusion associated infections among multitransfused (MT) children in relation to mandatory screening of HIV infection in donated blood indicated unchanged prevalence of hepatitis B virus (HBV), hepatitis C virus (HCV) and hepatitis D virus (HDV) infections among the group of MT children transfused after the implementation of mandatory screening of HIV infections in blood banks, i.e. post-implementation period (prevalence of HBV, HCV and HDV being 32.8%, 31.3% and 1.6% respectively) compared to a group of MT children transfused over a similar duration before the implementation of mandatory screening i.e. pre-implementation period (prevalence of HBV, HCV and HDV being 28.1%, 26.6% and 1.6% respectively). However, reduction could be recorded in the prevalence of IgM and IgG classes of antibodies to both CMV and HSV-2 infections among MT children receiving transfusion during the post-implementation period (prevalence of 3.1% and 37.1% for CMV IgM and CMV IgG respectively; prevalence of 3.1% and 25% for HSV-2 IgM and HSV-2 IgG, respectively) compared to the group of MT children transfused in the pre-implementation period (prevalence of 15.6% and 56.3% for CMV IgM and CMV IgG respectively; prevalence of 18.8% and 45.2% for HSV-2 IgM and HSV-2 IgG, respectively). These reductions were statistically significant (p values < 0.02 and < 0.05 for CMV IgM and CMV IgG; p values < 0.01 and < 0.02 for HSV-2 IgM and HSV-2 IgG respectively). These observations were in accordance with the recorded reduction in the prevalence of CMV and HSV-2 infections and unaltered prevalence of HBV, HCV and HDV infections in the group of donors donating blood during the post-implementation period compared to those donating in the pre-implementation period. Study of epidemiological risk factors among blood donors showed a change in behavior towards safer sex practice with only 13.0% of donors in the post-implementation period having history of sex with one or more female commercial sex workers during their donation periods compared to 41.5% of donors in the pre-implementation period having similar history (p < 0.001). However no change could be recorded in the proportion of donors donating at frequency higher than the permissible guidelines among the two groups. The present study points out nosocomial transmission as well as limitations in the existing guidelines for screening of infectious agents in blood banks as possible incriminating factors towards acquisition of hepatitis virus infections in blood donors as well as in MT children.

Clinical spectrum of chronic liver disease in north Indian children

Recent advances in serodiagnosis of hepatotropic viruses have revolutionized the approach to diagnosis and understanding of chronic liver disease (CLD). There are few studies on CLD in children from India. The present study was planned to define the clinical spectrum of CLD in children, its histopathology and seroepidemiology. Forty children with clinical features satisfying the criteria for diagnosing chronic liver disease were studied. All underwent routine laboratory investigations, liver function tests and ultrasound scan of the abdomen. Liver biopsy, upper GI endoscopy and other special investigations were done wherever indicated. The most common presenting features were jaundice (70%), fever (67%), and abdominal distention (60%). On examination hepatomegaly and icterus (80% each) and splenomegaly (67%) were the commonest findings. Serum transaminases were raised in 62.5% of children while prothrombin time was prolonged in 75% patients. Oesophageal and/or gastric varices were seen in 13 out of 29 patients subjected to upper GI endoscopy. Hepatitis B surface antigen (HbsAg) was positive in 5 children (12.5%) while 3 (7.5%) tested positive for anti HCV antibody. The commonest histopathological diagnosis was infantile cholangiopathy (20%) followed by cryptogenic cirrhosis and idiopathic chronic active hepatitis (17.5% each). The study suggests that the incidence of chronic hepatitis B and C is rather low in childhood. However larger and longer studies are required to delineate the exact incidence of these conditions in childhood and their progression in adolescence and early adulthood.