Submucosal Tunnel Endoscopic Resection of Gastric Lesion Before Obesity Surgery: a Case Series.

BACKGROUND: Submucosal tumors (SMTs) of the gastrointestinal tract are a rare pathological entity comprising a wide variety of neoplastic and non-neoplastic lesions. Even if most SMTs are benign tumors (e.g., leiomyomas), a smaller portion may have a malignant potential (e.g., gastrointestinal stromal tumor (GIST)). Preoperative diagnosis of SMT in bariatric patients may arise challenging clinical dilemmas. Long-term surveillance may be difficult after bariatric surgery. Moreover, according to SMT location, its presence may interfere with planned surgery. Submucosal tunneling endoscopic resection (STER) has emerged as an effective approach for minimally invasive en bloc excision of SMTs. This is the first case series of STER for SMTs before bariatric surgery. METHODS: Seven female patients underwent STER for removal of SMTs before bariatric surgery. All lesions were incidentally diagnosed at preoperative endoscopy. STER procedural steps comprised mucosal incision, submucosal tunneling, lesion enucleation, and closure of mucosal defect. RESULTS: En bloc removal of SMT was achieved in all cases. Mean procedural time was of 45 min (SD 18.6). No adverse event occurred. Mean size of the lesions was 20.6 mm (SD 5.8). Histological diagnoses were 5 leyomiomas, 1 lipoma, and 1 low grade GIST. Bariatric procedure was performed after a mean period of 4.1 months (SD 1.6) from endoscopic resection. CONCLUSION: STER is a safe and effective treatment for the management of SMT even in bariatric patients awaiting surgery. Preoperative endoscopic resection of SMTs has the advantages of reducing the need for surveillance and removing lesions that could interfere with planned surgery. STER did not altered accomplishment of bariatric procedures.

Annexin-A6 presents two modes of association with phospholipid membranes. A combined QCM-D, AFM and cryo-TEM study.

Annexins are soluble proteins that bind to biological membranes in a Ca(2+)-dependent manner. Annexin-A6 (AnxA6) is unique in the annexin family as it consists of the repeat of two annexin core modules, while all other annexins consist of a single module. AnxA6 has been proposed to participate in various membrane-related processes, including endocytosis and exocytosis, yet the molecular mechanism of association of AnxA6 with biological membranes, especially its ability to aggregate membranes, is still unclear. To address this question, we studied the association of AnxA6 with model phospholipid membranes by combining the techniques of quartz crystal microbalance with dissipation monitoring (QCM-D), (cryo-) transmission electron microscopy (TEM) and atomic force microscopy (AFM). The properties of membrane binding and membrane aggregation of AnxA6 were compared to two reference systems, annexin A5 (AnxA5), which is the annexin prototype, and a chimerical AnxA5-dimer molecule, which is able to aggregate two membranes in a symmetrical manner. We show that AnxA6 presents two modes of association with lipid membranes depending on Ca(2+)-concentration. At low Ca(2+)-concentration ( approximately 60-150microM), AnxA6 binds to membranes via its two coplanar annexin modules and is not able to associate two separate membranes. At high Ca(2+)-concentration ( approximately 2mM), AnxA6 molecules are able to bind two adjacent phospholipid membranes and present a conformation similar to the AnxA6 3D crystallographic structure. Possible biological implications of these novel membrane-binding properties of AnxA6 are discussed.

Crystal structure and biochemical properties of the human mitochondrial ferritin and its mutant Ser144Ala.

Mitochondrial ferritin is a recently identified protein precursor encoded by an intronless gene. It is specifically taken up by the mitochondria and processed to a mature protein that assembles into functional ferritin shells. The full mature recombinant protein and its S144A mutant were produced to study structural and functional properties. They yielded high quality crystals from Mg(II) solutions which diffracted up to 1.38 Angstrom resolution. The 3D structures of the two proteins resulted very similar to that of human H-ferritin, to which they have high level of sequence identity (approximately 80%). Metal-binding sites were identified in the native crystals and in those soaked in Mn(II) and Zn(II) solutions. The ferroxidase center binds binuclear iron at the sites A and B, and the structures showed that the A site was always fully occupied by Mg(II), Mn(II) or Zn(II), while the occupancy of the B site was variable. In addition, distinct Mg(II) and Zn(II)-binding sites were found in the 3-fold axes to block the hydrophilic channels. Other metal-binding sites, never observed before in H-ferritin, were found on the cavity surface near the ferroxidase center and near the 4-fold axes. Mitochondrial ferritin showed biochemical properties remarkably similar to those of human H-ferritin, except for the difficulty in renaturing to yield ferritin shells and for a reduced ( approximately 41%) rate in ferroxidase activity. This was partially rescued by the substitution of the bulkier Ser144 with Ala, which occurs in H-ferritin. The residue is exposed on a channel that connects the ferroxidase center with the cavity. The finding that the mutation increased both catalytic activity and the occupancy of the B site demonstrated that the channel is functionally important. In conclusion, the present data define the structure of human mitochondrial ferritin and provide new data on the iron pathways within the H-type ferritin shell.

Structural description of the active sites of mouse L-chain ferritin at 1.2 A resolution.

The first ferritin structure refined at the atomic level has been achieved on recombinant mouse L-chain apoferritin (rMoLF) crystals. These latter diffract to 1.2 A resolution under cryogenic conditions. When cryo-cooling the sample, the thermal disorder usually observed at room temperature is reduced and the low-temperature structure reveals several details concerning the protein putative active sites and their properties. Within the pores built up by the molecular three-fold symmetry axes, the iron entry route to the ferritin cavity, residues H118, D131 and E134, exhibit alternate conformations associated with the binding of partially hydrated cadmium ions, a metal used as a crystallization agent. At the mineral ferrihydrite nucleation center, the electron density maps evidence the orientation of E57, E60, E61 and E64 glutamate side chains (whereas they were observed highly disordered in previous ferritin structures determined at room temperature) and allow a description of the site taking into account the binding geometry of four Cd(2+) ions. Moreover, the side chain of residue K140, lying in the vicinity of the ferrihydrite nucleation center, is shown to interact with residue E61. As previously highlighted, this observation confirms the importance of K140 in the rMoLF sequence, as being responsible for the low level of iron incorporation by mousel L-chain ferritin compared to human L-chain ferritin. Finally, the diffusion of small molecules within the ferritin cavity is illustrated here by the presence of ordered molecules of glycerol used as a cryo-protectant, which bind the inner cavity surface of the protein.