State-specific morphological deformations of the lipid bilayer explain mechanosensitive gating of MscS ion channels

The force-from-lipids hypothesis of cellular mechanosensation posits that membrane channels open and close in response to changes in the physical state of the lipid bilayer, induced for example by lateral tension. Here, we investigate the molecular basis for this transduction mechanism by studying the mechanosensitive ion channel MscS from Escherichia coli and its eukaryotic homolog MSL1 from Arabidopsis thaliana. First, we use single-particle cryo-electron microscopy to determine the structure of a novel open conformation of wild-type MscS, stabilized in a thinned lipid nanodisc. Compared with the closed state, the structure shows a reconfiguration of helices TM1, TM2, and TM3a, and widening of the central pore. Based on these structures, we examined how the morphology of the membrane is altered upon gating, using molecular dynamics simulations. The simulations reveal that closed-state MscS causes drastic protrusions in the inner leaflet of the lipid bilayer, both in the absence and presence of lateral tension, and for different lipid compositions. These deformations arise to provide adequate solvation to hydrophobic crevices under the TM1-TM2 hairpin, and clearly reflect a high-energy conformation for the membrane, particularly under tension. Strikingly, these protrusions are largely eradicated upon channel opening. An analogous computational study of open and closed MSL1 recapitulates these findings. The gating equilibrium of MscS channels thus appears to be dictated by opposing conformational preferences, namely those of the lipid membrane and of the protein structure. We propose a membrane deformation model of mechanosensation, which posits that tension shifts the gating equilibrium towards the conductive state not because it alters the mode in which channel and lipids interact, but because it increases the energetic cost of the morphological perturbations in the membrane required by the closed state.

58 The Unfolding Situation of Caecal Volvulus: A Review of 36 Cases

Aim

Caecal Volvulus is a rare cause of bowel obstruction. However, there has been a steady rise in the number of cases over the decades. The demographic profile of patients developing Caecal Volvulus has changed to a much older population. We conducted a retrospective review to find the incidence, demographic profile, management, and outcomes of Caecal Volvulus patients in our institution during the last nine years.

Method

A total of 38 patients were diagnosed with Caecal Volvulus at Worcestershire Acute Hospitals NHS Trust between 01.01.2011 to 31.03.2020.

Results

Most of our patients were females (78%) with a median age was 76 years. The majority (86%) had at least one medical comorbidity, and 36% had a previous abdominal operation. Abdominal pain was the main complaint in 94% of patients. All patients had a CT scan to confirm their diagnosis. Most of our patients (84%) underwent surgery. Open right hemicolectomy was the most commonly performed operation (87%). Out of the six patients who did not undergo surgery, three responded to bowel rest and nasogastric tube decompression; one patient underwent successful colonoscopic decompression. In contrast, two patients, unfortunately, passed away. The median length of hospital stay was 9 days, with a 30-day mortality of 3%.

Conclusion

Caecal Volvulus remains a rare cause of bowel obstruction. Most of our patients were old, frail and had medical comorbidities. More than a third of them had undergone previous abdominal surgery. Early CT scan followed by surgery was associated with low mortality.

Mechanism of C-type inactivation in the hERG potassium channel

The fast C-type inactivation displayed by the voltage-activated potassium channel hERG plays a critical role in the repolarization of cardiac cells, and malfunction caused by nonspecific binding of drugs or naturally occurring missense mutations affecting inactivation can lead to pathologies. Because of its impact on human health, understanding the molecular mechanism of C-type inactivation in hERG represents an advance of paramount importance. Here, long-time scale molecular dynamics simulations, free energy landscape calculations, and electrophysiological experiments are combined to address the structural and functional impacts of several disease-associated mutations. Results suggest that C-type inactivation in hERG is associated with an asymmetrical constricted-like conformation of the selectivity filter, identifying F627 side-chain rotation and the hydrogen bond between Y616 and N629 as key determinants. Comparison of hERG with other K⁺ channels suggests that C-type inactivation depends on the degree of opening of the intracellular gate via the filter-gate allosteric coupling.

Molecular basis of force-from-lipids gating in the mechanosensitive channel MscS

Prokaryotic mechanosensitive (MS) channels open by sensing the physical state of the membrane. As such, lipid-protein interactions represent the defining molecular process underlying mechanotransduction. Here, we describe cryo-electron microscopy (cryo-EM) structures of the E. coli small-conductance mechanosensitive channel (MscS) in nanodiscs (ND). They reveal a novel membrane-anchoring fold that plays a significant role in channel activation and establish a new location for the lipid bilayer, shifted ~14 Å from previous consensus placements. Two types of lipid densities are explicitly observed. A phospholipid that ‘hooks’ the top of each TM2-TM3 hairpin and likely plays a role in force sensing, and a bundle of acyl chains occluding the permeation path above the L105 cuff. These observations reshape our understanding of force-from-lipids gating in MscS and highlight the key role of allosteric interactions between TM segments and phospholipids bound to key dynamic components of the channel.

Clinical studies on progressive retinal atrophy in 31 dogs

During a 2-year period, 31 cases of a hereditary retinal degeneration in dogs bred in India were found mainly suspected for progressive retinal atrophy (PRA) with typical history of initial nyctalopia followed by hemeralopia. Out of 31 PRA suspected dogs, 8 dogs (26%) were from the age group of 1-5 years, 15 (48%) 6-10 years and the rest (26%) 11-15 years. The most predominant breed was Spitz (18 dogs, 58%). Detailed ophthalmologic examinations included Schirmer's tear test, fluorescein stain, applanation tonometry, slit lamp biomicroscopy and ocular ultrasound in appropriate cases. Ophthalmoscopic and fundoscopic changes included hyperreflectivity and discoloration of the tapetal area, marked attenuation of retinal vessels, depigmentation in non-tapetal area and optic disc atrophy with scalloped borders. Electroretinograms (ERG) recorded in 13 PRA-affected cases revealed non-recordable extinguished (flatline) ERG responses. A reduction mainly of a- and b-wave amplitudes in the ERG indicated a generalized photoreceptor disease.

Reduction in medication expenditure: Review of strategies at a children's psychiatric facility

Prescription drug costs rise about 15% annually. Solnit Center has been exploring ways to reduce overall expenditure on medications while promoting best practice of care. Lack of facility-based pharmacy has posed specific challenges in ordering medications, optimal usage and minimizing wastage of drugs. Each of these areas were examined and reviewed at Pharmacy and Therapeutics Committee of the facility. This information was shared with the ordering physicians and standard prescribing practices were established. This project was aimed at tracking medication costs over a 11-year period while monitoring supplies and destruction of unused medications.

Aims

1. Reduce overall medication expenditure while maintaining standard of care. 2. Develop a program to return unused medications for refund.

Methods

1. Monthly review of pharmacy cost by facility, patient and medication. 2. Development and legislative approval of a program to return drugs. 3. Collaborate with contracted pharmacy to explore ways to cut costs. 4. Train nurses and physicians to understand optimal ordering practice. 5. Demonstrate medications wasted with associated financial impact to the facility.

Results

The expenditure to the facility over 11 years has gradually decreased despite increase in medication costs. In 2004, the facility spent $ 712,904 and in 2014, the expenditure was $ 584,022.

Conclusions

Awareness about costs and optimal ordering practices led to significant savings to the facility.

Disclosure of interest

The authors have not supplied their declaration of competing interest.

Blast phase transformation of chronic myelogenous leukemia presenting with central nervous system manifestation

Chronic myelogenous leukemia (CML) is the most common of all leukemia constituting 15–20% of all leukemia. The clinical course of the diseases runs in two to three phases, initial chronic phase followed by accelerated phase or blast phase. Blast phase most commonly presents clinically as fever, splenomegaly, and bone pain. Here, we present a case of CML in blast phase presenting with central nervous system manifestation in a 55-year-old patient with a brief review of the literature.

A microfluidic biochip for complete blood cell counts at the point-of-care

Complete blood cell counts (CBCs) are one of the most commonly ordered and informative blood tests in hospitals. The results from a CBC, which typically include white blood cell (WBC) counts with differentials, red blood cell (RBC) counts, platelet counts and hemoglobin measurements, can have implications for the diagnosis and screening of hundreds of diseases and treatments. Bulky and expensive hematology analyzers are currently used as a gold standard for acquiring CBCs. For nearly all CBCs performed today, the patient must travel to either a hospital with a large laboratory or to a centralized lab testing facility. There is a tremendous need for an automated, portable point-of-care blood cell counter that could yield results in a matter of minutes from a drop of blood without any trained professionals to operate the instrument. We have developed microfluidic biochips capable of a partial CBC using only a drop of whole blood. Total leukocyte and their 3-part differential count are obtained from 10 μL of blood after on-chip lysing of the RBCs and counting of the leukocytes electrically using microfabricated platinum electrodes. For RBCs and platelets, 1 μL of whole blood is diluted with PBS on-chip and the cells are counted electrically. The total time for measurement is under 20 minutes. We demonstrate a high correlation of blood cell counts compared to results acquired with a commercial hematology analyzer. This technology could potentially have tremendous applications in hospitals at the bedside, private clinics, retail clinics and the developing world.

Floral double mesiodentes: A rare case report

Mesiodens is the most commonly erupting supernumerary in the midline between two maxillary central incisors. Mesiodentes is a rare condition when mesiodens erupt in multiples, which may present as either labial or palatal to permanent central incisors. We report a rare case of double mesiodentes (non-syndromic mesiodentes) with floret like appearance. The presence of mesiodens has functional and esthetic implications. Careful radiographic evaluation should be done to prevent complications during their extraction.

Endovascular management of proximal lower limb deep venous thrombosis - A prospective study with six-month follow-up

BACKGROUND

Catheter-directed thrombolysis with assisted mechanical thrombolysis is the standard of medical care for proximal deep vein thrombosis. We studied the immediate and intermediate (six months) safety and effectiveness of catheter-directed thrombolysis in patients with proximal lower limb deep vein thrombosis.

METHODOLOGY

Thirty consecutive patients aged between 20 and 70 years with proximal lower limb deep vein thrombosis formed the study group. Catheter-directed thrombolysis was done with streptokinase infuse through a catheter kept in the ipsilateral popliteal vein. Unfractionated heparin was given along with streptokinase. Mechanical thromboaspiration using guiding catheter was performed in addition to thrombolytic therapy. After six months, post-thrombotic syndrome and deep venous patency were assessed by using Villalta scale and duplex ultrasound, respectively.

RESULTS

Thirty patients with proximal lower limb deep vein thrombosis were treated with catheter-directed thrombolysis. Mean age of the study patients was 41.7 ± 15 years. Mean duration of illness was 13.3 ± 12 days. The mean duration of thrombolysis was 4.5 ± 1.3 days. Grade III (complete) lysis was achieved in 10 (33%) and Grade II (50-90%) lysis in 20 (67%) of patients. Patients with significant residual lesion in Grade II lysis following catheter-directed thrombolysis underwent percutaneous transluminal angioplasty alone (12/20) or venous stenting (8/20). All patients improved clinically following catheter-directed thrombolysis or assisted catheter-directed thrombolysis. Four patients (13%) developed pulmonary embolism during course of hospital stay and among them two (6.5%) patients died. Eleven patients (37%) had minor bleeding or hematoma at local site, and seven (23%) developed anemia requiring blood transfusion and four (13%) patients had thrombocytopenia. After six months, iliofemoral patency was found in 20 (72%) and post-thrombotic syndrome was seen in six (21%) patients. Two (6.5%) patients died during follow-up due to nephrotic syndrome and carcinoma breast.

CONCLUSION

Catheter-directed thrombolysis and conventional manual aspiration thrombectomy are an effective treatment for proximal lower extremity deep vein thrombosis with good short and intermediate outcome.

Metagenomic analysis of buffalo rumen microbiome: Effect of roughage diet on Dormancy and Sporulation genes

Buffalo rumen microbiome experiences a variety of diet stress and represents reservoir of Dormancy and Sporulation genes. However, the information on genomic responses to such conditions is very limited. The Ion Torrent PGM next generation sequencing technology was used to characterize general microbial diversity and the repertoire of microbial genes present, including genes associated with Dormancy and Sporulation in Mehsani buffalo rumen metagenome. The research findings revealed the abundance of bacteria at the domain level and presence of Dormancy and Sporulation genes which were predominantly associated with the Clostridia and Bacilli taxa belonging to the phyla Firmicutes. Genes associated with Sporulation cluster and Sporulation orphans were increased from 50% to 100% roughage treatment, thereby promoting sporulation all along the treatments. The spore germination is observed to be the highest in the 75% roughage treatment both in the liquid and solid rumen fraction samples with respect to the decrease in the values of the genes associated with spore core dehydration, thereby facilitating spore core hydration which is necessary for spore germination.

Acute pulmonary embolism being the first presentation of undetected HIV infection: report of two cases

Though HIV infection is considered as a hypercoagulable state, but occurrence of acute pulmonary embolism (PE) is rare and usually seen in the advanced stage of the disease. PE as a presentation in a case where there is no previous history of having HIV infection is very rare; a Medline search revealed only one case reported previously. We describe two cases who presented with acute PE and were treated; they were subsequently diagnosed as having HIV infection.

Molecular markers as intermediate end-points in chemoprevention of colon-cancer - modulation of ras activation by sulindac and phenylhexylisothiocyanate during colon carcinogenesis

Recent evidence suggests that activation of ras proto-oncogenes and inactivation of suppressor genes induce malignant phenotype in colonic cells. Thus the identification of clonal population of cells expressing activated ras may lead to a valuable intermediate biomarker to detect premalignant lesions amenable to chemoprevention. Previously, we demonstrated that sulindac inhibited the carcinogen-induced colon tumor development whereas phenylhexylisothiocyanate (PHITC) promoted the tumor outcome. The present study was conducted to investigate the effect of sulindac and PHITC on azoxymethane (AOM)induced activation of ras proto-oncogenes in order to explore the plausibility of using ras as an intermediate biomarker in chemoprevention of colon cancer. Male F344 rats were fed the AIN-76A diet containing 0, 320 ppm sulindac or 640 ppm PHITC and administered s.c. AOM dissolved in normal saline at a dose rate of 15 mg/kg body wt/week for 2 weeks. Vehicle control groups received s.c. equal volume of normal saline. Animals were sacrificed 52 weeks after AOM or saline treatment and their colonic mucosa and tumors were analyzed for mutations in codon 12 and 13 of K-ras and the expression of ras p21. As an alternative non-invasive approach, we developed a simple and sensitive one-step mutant-enriched PCR method to detect these genetic lesions in stools collected at 16, and again at 24 weeks after AOM treatment. AOM-induced G to A transitions were observed at the second nucleotide of 12th codon of K-ras substituting amino acid asp with wild-type gly. Sulindac not only suppressed the selective amplification of initiated cells possessing AOM-induced mutated K-ras codon 12, but significantly inhibited the AOM-induced expression of total and mutant ras-p21. PHITC did not exert any inhibitory effect on AOM-induced ras activation. Results indicated a strong correlation between ras activation and tumor outcome. Data suggest that ras activation may be a useful intermediate molecular marker in chemoprevention of colon cancer.