The role of gadolinium chelates in the mechanism of nephrogenic systemic fibrosis: A critical update

Nephrogenic systemic fibrosis (NSF) is an iatrogenic scleroderma-like fibrosing systemic disorder occurring in patients with severe or end-stage renal disease. It was established as a new clinical entity in the year 2000. A causal role for gadolinium chelates (GC), widely used as contrast agents for magnetic resonance imaging, was suggested six years later. It rapidly appeared that the occurrence of NSF was associated with prior administration of GCs with lower thermodynamic stability, leading to warnings being published by health authorities and learned societies worldwide. Although a role for the chelated form of the less stable GCs has been proposed, the most commonly accepted hypothesis involves the gradual release of dissociated gadolinium in the body, leading to systemic fibrosis. However, the entire chain of events is still not fully understood in a causal way and many uncertainties remain.     

Osteotomies through a fusion mass in the lumbar spine

Introduction

Flat-back syndrome is one of the main causes of surgical failure after lumbar fusion and can lead to a revision surgery to correct it. Three-column pedicle subtraction osteotomy is an efficient technique to restore lumbar lordosis (LL) for fixed sagittal malalignment. The fusion mass stemming from the past surgeries makes the procedure demanding as most anatomical landmarks are missing.

Material and methods

This review article will focus on the correction of this lack of LL through the fusion mass. We will successively review the preoperative management, the surgical specificities, and various types of clinical cases that can be encountered in flat-back syndromes.

Conclusion

PSO in the fixed fusion mass is technically demanding. Preoperative CT-scan and preoperative navigation allow us to push the limits when anatomical landmarks disappear. Bleeding and neurologic are the two major complications feared by the surgeon. The best way to avoid these revision surgeries is to restore a proper lumbar lordosis at the time of initial surgery by considering lumbo-pelvic indexes.

     

Chlorotoxin: A Helpful Natural Scorpion Peptide to Diagnose Glioma and Fight Tumor Invasion

Chlorotoxin is a small 36 amino-acid peptide identified from the venom of the scorpion Leiurus quinquestriatus. Initially, chlorotoxin was used as a pharmacological tool to characterize chloride channels. While studying glioma-specific chloride currents, it was soon discovered that chlorotoxin possesses targeting properties towards cancer cells including glioma, melanoma, small cell lung carcinoma, neuroblastoma and medulloblastoma. The investigation of the mechanism of action of chlorotoxin has been challenging because its cell surface receptor target remains under questioning since two other receptors have been claimed besides chloride channels. Efforts on chlorotoxin-based applications focused on producing analogues helpful for glioma diagnosis, imaging and treatment. These efforts are welcome since gliomas are very aggressive brain cancers, close to impossible to cure with the current therapeutic arsenal. Among all the chlorotoxin-based strategies, the most promising one to enhance patient mean survival time appears to be the use of chlorotoxin as a targeting agent for the delivery of anti-tumor agents. Finally, the discovery of chlorotoxin has led to the screening of other scorpion venoms to identify chlorotoxin-like peptides. So far several new candidates have been identified. Only detailed research and clinical investigations will tell us if they share the same anti-tumor potential as chlorotoxin.     

Direct inhibition by nitric oxide of the transcriptional ferric uptake regulation protein via nitrosylation of the iron

Ferric uptake regulation protein (Fur) is a bacterial global regulator that uses iron as a cofactor to bind to specific DNA sequences. The function of Fur is not limited to iron homeostasis. A wide variety of genes involved in various mechanisms such as oxidative and acid stresses are under Fur control. Flavohemoglobin (Hmp) is an NO-detoxifying enzyme induced by NO and nitrosothiol compounds. Fur recently was found to regulate hmp in Salmonella typhimurium, and in Escherichia coli, the iron-chelating agent 2,2'-dipyridyl induces hmp expression. We now establish direct inhibition of E. coli Fur activity by NO. By using chromosomal Fur-regulated lacZ reporter fusion in E. coli, Fur activity is switched off by NO at micromolar concentration. In vitro Fur DNA-binding activity, as measured by protection of restriction site in aerobactin promoter, is directly sensitive to NO. NO reacts with Fe(II) in purified FeFur protein to form a S = 12 low-spin FeFur-NO complex with a g = 2.03 EPR signal. Appearance of the same EPR signal in NO-treated cells links nitrosylation of the iron with Fur inhibition. The nitrosylated Fur protein is still a dimer and is stable in anaerobiosis but slowly decays in air. This inhibition probably arises from a conformational switch, leading to an inactive dimeric protein. These data establish a link between control of iron metabolism and the response to NO effects.     

Activation of the pseudokinase MLKL unleashes the four-helix bundle domain to induce membrane localization and necroptotic cell death

Necroptosis is considered to be complementary to the classical caspase-dependent programmed cell death pathway, apoptosis. The pseudokinase Mixed Lineage Kinase Domain-Like (MLKL) is an essential effector protein in the necroptotic cell death pathway downstream of the protein kinase Receptor Interacting Protein Kinase-3 (RIPK3). How MLKL causes cell death is unclear, however RIPK3–mediated phosphorylation of the activation loop in MLKL trips a molecular switch to induce necroptotic cell death. Here, we show that the MLKL pseudokinase domain acts as a latch to restrain the N-terminal four-helix bundle (4HB) domain and that unleashing this domain results in formation of a high-molecular-weight, membrane-localized complex and cell death. Using alanine-scanning mutagenesis, we identified two clusters of residues on opposing faces of the 4HB domain that were required for the 4HB domain to kill cells. The integrity of one cluster was essential for membrane localization, whereas MLKL mutations in the other cluster did not prevent membrane translocation but prevented killing; this demonstrates that membrane localization is necessary, but insufficient, to induce cell death. Finally, we identified a small molecule that binds the nucleotide binding site within the MLKL pseudokinase domain and retards MLKL translocation to membranes, thereby preventing necroptosis. This inhibitor provides a novel tool to investigate necroptosis and demonstrates the feasibility of using small molecules to target the nucleotide binding site of pseudokinases to modulate signal transduction.Programmed necrosis or “necroptosis” has emerged in the past 5 years as a cell death mechanism that complements the conventional cell death pathway, apoptosis, in multicellular organisms. In contrast to apoptosis, necroptosis does not appear to serve an important role in multicellular organism development (1–3) but participates in the defense against pathogens and is a likely culprit in destructive inflammatory conditions (4–7). Receptor Interacting Protein Kinase-3 (RIPK3) was identified as a key effector of necroptosis in 2009 (4, 5) and its substrate, the pseudokinase Mixed Lineage Kinase Domain-Like (MLKL), in 2012 (8, 9), but the molecular events following RIPK3-mediated phosphorylation of MLKL required to induce cell death are unclear. The RIPK1/RIPK3/MLKL necrosome has been proposed to activate PGAM5 (phosphoglycerate mutase 5) and Drp1 (Dynamin-related protein 1) to cause mitochondrial fragmentation and cell death (10), but the requirement for PGAM5, Drp1, and mitochondria for necroptosis has been questioned (1, 11–13).We described the structure of mouse MLKL revealing that MLKL contains a C-terminal pseudokinase domain and an N-terminal four-helix bundle (4HB) domain connected by a two-helix linker (the “brace” helices) (1). Based on our mutational and biochemical analyses, we proposed that the catalytically inactive pseudokinase domain functions as a molecular switch and that RIPK3-mediated phosphorylation triggers this switch by inducing a conformational change in MLKL (1, 14).Recently it has been proposed that the 4HB domain is the death effector domain within MLKL and that the killing function of MLKL relies on its oligomerization and plasma membrane association (15–18). The stoichiometry of the oligomer is, however, contentious and has been reported to contain three (15), four (16), and possibly six (17) MLKL protomers. Furthermore, several mechanisms for how this oligomer causes cell death have been proposed: Cai et al. proposed it activates the calcium channel protein Tprm7 and promotes calcium influx (15), Chen et al. showed it increased sodium influx (16), and Wang et al. proposed that the oligomerized form of MLKL has the ability to bind negatively charged lipids, including phosphoinositides and cardiolipin, which facilitates its disruption of membrane integrity (17), a model supported by a subsequent paper (18).Here, we show that the MLKL 4HB domain is sufficient to induce necroptosis and identify several charged residues clustered on two faces that are required for this function. Surprisingly the polarity of several of these charged residues is not conserved between mouse and human MLKL, and alanine substitution of negatively charged residues on the α4 helix of the 4HB domain disrupted function. This finding challenges the importance of phospholipid binding to the killing activity of the 4HB domain and illustrates that membrane association cannot solely be attributed to the interaction of poorly conserved basic residues within the MLKL 4HB domain. Intriguingly, mutation of a second cluster of residues on the 4HB domain did not preclude membrane localization or oligomerization but did prevent cell death, illustrating that additional function(s) beyond membrane translocation are required for the 4HB domain to induce cell death. MLKL oligomerization and membrane translocation were also inhibited by a small molecule, compound 1, which we identified on the basis of its affinity for the nucleotide binding site of the MLKL pseudokinase domain. These data support a model for MLKL function whereby the pseudokinase domain of MLKL holds the 4HB domain in check until phosphorylated by RIPK3, which causes a conformational change in the pseudokinase domain to unleash the 4HB domain to oligomerize and associate with membranes. Activation of MLKL can be thwarted by a small MLKL binding molecule, indicating the feasibility of targeting the nucleotide binding or “pseudoactive” sites of pseudokinases, a hitherto unexplored class of therapeutic targets.     

Endoscopic Internal Drainage with Enteral Nutrition (EDEN) for Treatment of Leaks Following Sleeve Gastrectomy

Background

Endoscopic treatment of gastric leaks (GL) following sleeve gastrectomy (SG) involves different techniques; however, standard management is not yet established. We report our experience about endoscopic internal drainage of leaks using pigtail stents coupled with enteral nutrition (EDEN) for 4 to 6 weeks until healing is achieved.

Methods

In 21 pts (18 F, 41 years), one or two plastic pigtail stents were delivered across the leak 25.6 days (4–98) post-surgery. In all patients, nasojejunal tube was inserted. Check endoscopy was done at 4 to 6 weeks with either restenting if persistent leak, or removal if no extravasation of contrast in peritoneal cavity, or closure with an Over-the-Scope Clip® (OTSC®) if contrast opacifying the crossing stent without concomitant peritoneal extravasation.

Results

Twenty-one out of 21 (100 %) patients underwent check endoscopy at average of 30.15 days (26–45) from stenting. In 7/21 (33.3 %) patients leak sealed, 2/7 needed OTSC®. Second check endoscopy, 26.7 days (25–42) later, showed sealed leak in 10 out 14; 6/10 had OTSC®. Four required restenting. One patient, 28 days later, needed OTSC®. One healed at 135 days and another 180 days after four and seven changes, respectively. One patient is currently under treatment. In 20/21 (95.2 %), GL have healed with EID treatment of 55.5 days (26–?180); all are asymptomatic on a normal diet at average follow-up of 150.3 days (20–276).

Conclusions

EDEN is a promising therapeutic approach for treating leaks following SG. Multiple endoscopic sessions may be required.