Internal Herniation of the Transverse Colon and Stricture of the Gastric Body: A Case Report.

Internal herniation is a protrusion of the bowel limited to the abdominal cavity. This pathology is rare and difficult to diagnose due to a wide array of symptoms that may manifest. Internal hernias have the potential to affect surrounding organs such as the stomach and adjacent bowel due to the compressive force of the protruding bowel. The effects of internal herniation commonly present in one of two ways: acute obstruction which requires emergent intervention and subacute, vague symptoms that are difficult to diagnose. This case presents the findings of a post-mortem dissection of a 92-year-old willed body donor. Dissection of the abdominal cavity revealed a large internal hernia of the transverse colon that communicated superiorly posterior to the stomach. As a result of the hernia, the stomach in this patient had a stricture of the gastric body. We assert that this stricture was formed over an extended period of time due to the lack of diagnosis and treatment of the internal hernia.

The SON RNA splicing factor is required for intracellular trafficking structures that promote centriole assembly and ciliogenesis.

Control of centrosome assembly is critical for cell division, intracellular trafficking, and cilia. Regulation of centrosome number occurs through the precise duplication of centrioles that reside in centrosomes. Here we explored transcriptional control of centriole assembly and find that the RNA splicing factor SON is specifically required for completing procentriole assembly. Whole genome mRNA sequencing identified genes whose splicing and expression are affected by the reduction of SON, with an enrichment in genes involved in the microtubule (MT) cytoskeleton, centrosome, and centriolar satellites. SON is required for the proper splicing and expression of CEP131, which encodes a major centriolar satellite protein and is required to organize the trafficking and MT network around the centrosomes. This study highlights the importance of the distinct MT trafficking network that is intimately associated with nascent centrioles and is responsible for procentriole development and efficient ciliogenesis.

Allosteric conformational change of a cyclic nucleotide-gated ion channel revealed by DEER spectroscopy.

Cyclic nucleotide-gated (CNG) ion channels are essential components of mammalian visual and olfactory signal transduction. CNG channels open upon direct binding of cyclic nucleotides (cAMP and/or cGMP), but the allosteric mechanism by which this occurs is incompletely understood. Here, we employed double electron-electron resonance (DEER) spectroscopy to measure intersubunit distance distributions in SthK, a bacterial CNG channel from Spirochaeta thermophila Spin labels were introduced into the SthK C-linker, a domain that is essential for coupling cyclic nucleotide binding to channel opening. DEER revealed an agonist-dependent conformational change in which residues of the B'-helix displayed outward movement with respect to the symmetry axis of the channel in the presence of the full agonist cAMP, but not with the partial agonist cGMP. This conformational rearrangement was observed both in detergent-solubilized SthK and in channels reconstituted into lipid nanodiscs. In addition to outward movement of the B'-helix, DEER-constrained Rosetta structural models suggest that channel activation involves upward translation of the cytoplasmic domain and formation of state-dependent interactions between the C-linker and the transmembrane domain. Our results demonstrate a previously unrecognized structural transition in a CNG channel and suggest key interactions that may be responsible for allosteric gating in these channels.

Functional characterization and optimization of a bacterial cyclic nucleotide-gated channel.

Cyclic nucleotide-gated (CNG) channels produce the initial electrical signal in mammalian vision and olfaction. They open in response to direct binding of cyclic nucleotide (cAMP or cGMP) to a cytoplasmic region of the channel. However, the conformational rearrangements occurring upon binding to produce pore opening (i.e. gating) are not well understood. SthK is a bacterial CNG channel that has the potential to serve as an ideal model for structure-function studies of gating but is currently limited by its toxicity, native cysteines, and low open probability (Po). Here, we expressed SthK in giant Escherichia coli spheroplasts and performed patch-clamp recordings to characterize SthK gating in a bacterial membrane. We demonstrated that the Po in cAMP is higher than has been previously published and that cGMP acts as a weak partial SthK agonist. Additionally, we determined that SthK expression is toxic to E. coli because of gating by cytoplasmic cAMP. We overcame this toxicity by developing an adenylate cyclase-knockout E. coli cell line. Finally, we generated a cysteine-free SthK construct and introduced mutations that further increase the Po in cAMP. We propose that this SthK model will help elucidate the gating mechanism of CNG channels.

Bilateral internal mammary artery laceration after cardiac pulmonary resuscitation.

Cardiopulmonary resuscitation (CPR) is essential for the survival of cardiac arrest patients. High-quality chest compressions are critical for survival, but energetic resuscitation efforts can lead to chest injuries. Internal mammary artery (IMA) injury is a rare complication of CPR, but can lead to life-threatening intrathoracic hemorrhage. Early detection of IMA injury should be considered in all post cardiac arrest syndrome (PCAS) with anemia refractory to transfusion. To the best of our knowledge, no cases of CPR-associated bilateral IMA laceration have ever been reported. We report a unique CPR complication resulting in anterior mediastinal hemorrhage that was detected by ECHO, verified by computed tomography angiography, and treated with endovascular intervention.

Targeted Cancer Therapies With Pericardial Effusions Requiring Pericardiocentesis Focusing on Immune Checkpoint Inhibitors.

Case reports have reported immune checkpoint inhibitors (ICI), especially nivolumab, are associated with recurrent pericardial effusions. Our objective was to determine how often patients being treated with ICI develop hemodynamically significant pericardial effusion requiring pericardiocentesis compared with other cancer therapeutics and whether the survival of patients who underwent pericardiocentesis differs according to ICI use versus standard cancer therapeutics. Our institutional review board approved catheterization laboratory data collection for all pericardiocenteses performed and all patients receiving ICI from January 1, 2015 to December 31, 2017. Retrospective review of the electronic medical record was performed to identify cancer therapeutics given preceding pericardiocentesis. Log-rank analysis was performed to compare survival in patients requiring pericardiocentesis between those on ICI and those not on ICI. Overall, 3,966 patients received ICI of which only 15 pericardiocenteses were required, including 1 repeat pericardiocentesis in a patient on nivolumab. The prevalence of pericardiocentesis among patients on ICI was 0.38% (15/3,966). Eleven pericardiocenteses were performed after nivolumab infusion, 3 after pembrolizumab, and 1 after atezolizumab, with pericardiocentesis prevalences for each agent of 0.61% (11/1,798), 0.19% (3/1,560), and 0.32% (1/309), respectively. One hundred and twenty pericardiocentesis were performed on patients receiving other cancer therapeutics although no therapeutic agent was associated with more pericardiocenteses than nivolumab. In conclusion, the prevalence of hemodynamically significant pericardial effusions and ICI administration is uncommon, and survival durations after pericardiocentesis for patients receiving ICI and those not receiving ICI are similar, suggesting that frequent echocardiographic monitoring for pericardial effusions is not necessary.

Third-degree burns associated with transcutaneous pacing.

A 69-year-old severely obese diabetic woman developed nausea, vomiting and diarrhoea which caused multiple metabolic alterations leading to hypotension and bradycardia due to slow atrioventricular junctional rhythm. Transcutaneous pacing (TCP) was initiated and maintained until the underlying heart rate and blood pressure normalised. TCP gel pads were kept in place prophylactically after pacing was terminated. Gel pads remained attached to the anterior thorax and back for a total of 36 hours. During this time the patient developed third-degree burns at the side of gel pad attachment. With appropriate wound care and after a long hospitalisation, the patient was discharged in stable condition. This case demonstrates that prolonged use of TCP gel pads without frequent replacement may lead to third-degree burns. It also suggest that prophylactic use of TCP gel pads should be avoided.

Structure of a Type-1 Secretion System ABC Transporter.

Type-1 secretion systems (T1SSs) represent a widespread mode of protein secretion across the cell envelope in Gram-negative bacteria. The T1SS is composed of an inner-membrane ABC transporter, a periplasmic membrane-fusion protein, and an outer-membrane porin. These three components assemble into a complex spanning both membranes and providing a conduit for the translocation of unfolded polypeptides. We show that ATP hydrolysis and assembly of the entire T1SS complex is necessary for protein secretion. Furthermore, we present a 3.15-Å crystal structure of AaPrtD, the ABC transporter found in the Aquifex aeolicus T1SS. The structure suggests a substrate entry window just above the transporter's nucleotide binding domains. In addition, highly kinked transmembrane helices, which frame a narrow channel not observed in canonical peptide transporters, are likely involved in substrate translocation. Overall, the AaPrtD structure supports a polypeptide transport mechanism distinct from alternating access.

Lymphovascular invasion is associated with oncologic outcomes following radical cystectomy for squamous cell carcinoma of the urinary bladder.

OBJECTIVE: To evaluate the association of lymphovascular invasion (LVI) with oncologic outcomes of squamous cell carcinoma (SCC) of the urinary bladder following radical cystectomy (RC). PATIENTS AND METHODS: We performed a retrospective analysis of 1,280 patients who underwent RC for invasive bladder cancer between 1997 and 2003 in Mansoura, Egypt. Only patients with pure urothelial carcinoma of the bladder (UCB) or SCC pathology were included. Using multivariate Cox regression analyses and Kaplan-Meier analyses, prognostic significance of LVI in disease-free survival and cancer-specific survival was evaluated for patients with UCB and SCC. RESULTS: Our cohort included 519 (59%) patients with UCB and 360 (41%) with SCC. Median patient age and follow-up were 55 years (20-87) and 64 months (0-128), respectively. Median number of lymph nodes (LN) retrieved was 19 (4-70). LVI was present in 288 (32.8%) patients (241 [46.4%] UCB vs. 47 [13.1%] SCC; P<0.001). LVI was an independent predictor of oncologic outcomes in both UCB and SCC groups; however, LVI had more prognostic significance in SCC. LN negative, LVI positive (LVI+/LN-) patients with SCC had higher risk of recurrence and cancer-specific mortality compared to LN positive, LVI negative (LVI-/LN+) patients with SCC (hazard ratio = 2.8 vs. 1.9 and hazard ratio = 3.6 vs. 2.2, respectively). CONCLUSION: The presence of LVI is an independent predictor of poor oncologic outcomes after RC and had greater prognostic significance in patients with SCC compared to UCB.

Observing cellulose biosynthesis and membrane translocation in crystallo.

Many biopolymers, including polysaccharides, must be translocated across at least one membrane to reach their site of biological function. Cellulose is a linear glucose polymer synthesized and secreted by a membrane-integrated cellulose synthase. Here, in crystallo enzymology with the catalytically active bacterial cellulose synthase BcsA-BcsB complex reveals structural snapshots of a complete cellulose biosynthesis cycle, from substrate binding to polymer translocation. Substrate- and product-bound structures of BcsA provide the basis for substrate recognition and demonstrate the stepwise elongation of cellulose. Furthermore, the structural snapshots show that BcsA translocates cellulose via a ratcheting mechanism involving a 'finger helix' that contacts the polymer's terminal glucose. Cooperating with BcsA's gating loop, the finger helix moves 'up' and 'down' in response to substrate binding and polymer elongation, respectively, thereby pushing the elongated polymer into BcsA's transmembrane channel. This mechanism is validated experimentally by tethering BcsA's finger helix, which inhibits polymer translocation but not elongation.

Prevalence of Hyperoxaluria in Urinary Stone Formers: Chronological and Geographical Trends and a Literature Review.

PURPOSE: To report chronological trends and geographical distributions related to the prevalence of hyperoxaluria in stone-forming patients. MATERIALS AND METHODS: We systematically reviewed the existing literature between 1982 and 2013 seeking studies that assessed for hyperoxaluria (>45 mg/day [499.5 µmol/24 hour]) in recurrent stone formers. Studies that performed 24-hour urine analysis for urine oxalate in patients with recurrent urinary stones were included. Studies were divided chronologically and by geographical region, and prevalence rates of hyperoxaluria were compared between groups. RESULTS: Our literature search provided 22 peer-reviewed articles involving 3636 patients in total. Ten studies were performed between 1982 and 2000, and 12 studies were performed between 2001 and 2013. The prevalence of hyperoxaluria in stone-forming patient cohorts was 24.8% and 45.1% (p = 0.019) in studies performed between 1982 and 2000 and 2001 and 2013, respectively. Hyperoxaluria rates were significantly higher in non-American cohorts compared with American cohorts (40.7% vs 23.0%; p = 0.018). Reported hyperoxaluria rates were higher in Asian countries compared with Western countries (56.8% and 23.8%; p < 0.001). CONCLUSIONS: The prevalence of hyperoxaluria in stone-forming patients has increased over the past two decades and may be a contributing factor to the rising global prevalence of urolithiasis. A geographical disparity in hyperoxaluria may exist between Asian and Western countries. Future studies are needed to explain these trends and their consequences.

A molecular description of cellulose biosynthesis.

Cellulose is the most abundant biopolymer on Earth, and certain organisms from bacteria to plants and animals synthesize cellulose as an extracellular polymer for various biological functions. Humans have used cellulose for millennia as a material and an energy source, and the advent of a lignocellulosic fuel industry will elevate it to the primary carbon source for the burgeoning renewable energy sector. Despite the biological and societal importance of cellulose, the molecular mechanism by which it is synthesized is now only beginning to emerge. On the basis of recent advances in structural and molecular biology on bacterial cellulose synthases, we review emerging concepts of how the enzymes polymerize glucose molecules, how the nascent polymer is transported across the plasma membrane, and how bacterial cellulose biosynthesis is regulated during biofilm formation. Additionally, we review evolutionary commonalities and differences between cellulose synthases that modulate the nature of the cellulose product formed.

Bicelles coming of age: an empirical approach to bicelle crystallization.

Biological membranes represent a unique environment in which integral membrane proteins (MPs) fold to perform diverse biological functions. In many cases, lipids support the native conformation or mediate important interactions between MPs. It is therefore imperative to develop methods that maintain this support for the structural and functional analyses of an exceedingly important class of biological macromolecules. Bicelles are detergent-stabilized phospholipid bilayer discs into which MPs can be reconstituted for biophysical studies. Here, we review recent advances and emerging concepts in employing bicelles for the crystallization and structure determination of MPs. We discuss variations of established procedures as well as alternative approaches, and we present a summary and analysis of the conditions used for bicelle-mediated MP crystallization.

Mechanism of activation of bacterial cellulose synthase by cyclic di-GMP.

The bacterial signaling molecule cyclic di-GMP (c-di-GMP) stimulates the synthesis of bacterial cellulose, which is frequently found in biofilms. Bacterial cellulose is synthesized and translocated across the inner membrane by a complex of cellulose synthase BcsA and BcsB subunits. Here we present crystal structures of the c-di-GMP-activated BcsA-BcsB complex. The structures reveal that c-di-GMP releases an autoinhibited state of the enzyme by breaking a salt bridge that otherwise tethers a conserved gating loop that controls access to and substrate coordination at the active site. Disrupting the salt bridge by mutagenesis generates a constitutively active cellulose synthase. Additionally, the c-di-GMP-activated BcsA-BcsB complex contains a nascent cellulose polymer whose terminal glucose unit rests at a new location above BcsA's active site and is positioned for catalysis. Our mechanistic insights indicate how c-di-GMP allosterically modulates enzymatic functions.

Crystallographic snapshot of cellulose synthesis and membrane translocation.

Cellulose, the most abundant biological macromolecule, is an extracellular, linear polymer of glucose molecules. It represents an essential component of plant cell walls but is also found in algae and bacteria. In bacteria, cellulose production frequently correlates with the formation of biofilms, a sessile, multicellular growth form. Cellulose synthesis and transport across the inner bacterial membrane is mediated by a complex of the membrane-integrated catalytic BcsA subunit and the membrane-anchored, periplasmic BcsB protein. Here we present the crystal structure of a complex of BcsA and BcsB from Rhodobacter sphaeroides containing a translocating polysaccharide. The structure of the BcsA-BcsB translocation intermediate reveals the architecture of the cellulose synthase, demonstrates how BcsA forms a cellulose-conducting channel, and suggests a model for the coupling of cellulose synthesis and translocation in which the nascent polysaccharide is extended by one glucose molecule at a time.