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PubMed2000

Membrane fusion mechanisms: the influenza hemagglutinin paradigm and its implications for intracellular fusion.

The mechanism of membrane fusion induced by the influenza virus hemagglutinin (HA) has been extensively characterized. Fusion is triggered by low pH, which induces conformational changes in the protein, leading to insertion of a hydrophobic 'fusion peptide' into the viral membrane and the target membrane for fusion. Insertion perturbs the target membrane, and hour glass-shaped lipidic fusion intermediates, called stalks, fusing the outer monolayers of the two membranes, are formed. Stalk formation is followed by complete fusion of the two membranes. Structures similar to those formed by HA at the pH of fusion are found not only in many other viral fusion proteins, but are also formed by SNAREs, proteins involved in intracellular fusion. Substances that inhibit or promote HA-induced fusion because they affect stalk formation, also inhibit or promote intracellular fusion, cell-cell fusion and even intracellular fission similarly. Therefore, the mechanism of influenza HA-induced fusion may be a paradigm for many intracellular fusion events.

Animals↗

PubMed2005

Radiological changes in the bone fusion site after posterior lumbar interbody fusion using carbon cages impacted with laminar bone chips: follow-up study over more than 4 years.

STUDY DESIGN: A retrospective clinical study with a follow-up of more than 4 years was conducted. OBJECTIVES: To know the radiologic changes in the interbody bone fusion site in patients who had received posterior lumbar interbody fusion (PLIF) using carbon fiber cages. SUMMARY OF BACKGROUND DATA: PLIF using cages is a popular surgical method for treating degenerative lumbar spinal diseases. However, there are few reports on the radiologic changes in the bone fusion site after this procedure. METHOD: Forty-one patients were observed (male-to-female ratio 12:29; mean age 51 years; 1-level-to-2-level PLIF 37:4) for 56 months (range 48-78). Anteroposterior and lateral radiograph films were taken from all patients immediately after bone fusion, at 6 and 12 months after surgery, and at follow-up. The extent of the bone fusion was classified as: only inside the cage; around the cage; extending to the vertebral cortical margin; and overgrowth beyond the vertebral cortical margin. The extent of bone fusion was observed anterior and posterior to the cages. RESULTS: Of the 45 fusion levels examined in these 41 patients, successful bone fusion was observed in 40 levels of 36 patients (88%). All the successful fusions occurred inside and posterior to the cages. Of the 40 successful fusion levels at 6 and 12 months after surgery, 10% and 35% of the levels showed the fusion mass to be both inside and around the cages, while the remaining 90% and 65% of the levels showed the fusion mass only inside the cages, respectively. More than 4 years after surgery, 82% of the levels showed the fusion mass extending to the posterior cortical margin, and 2 levels (5%) with shallowly inserted cages showed bony overgrowth into the spinal canal. CONCLUSION: All the intervertebral bone fusion after PLIF occurred inside the cages and in the posterior intervertebral space. We suggest the complete removal of discmaterial and deep insertion of the cages to create sufficient posterior intervertebral space for bone growth. PLIF using cages impacted with laminar bone chips is a useful method when considering the time required for surgery and the morbidity of the autograft donor sites.

Adult↗

PubMed2002

Relationship between SU subdomains that regulate the receptor-mediated transition from the native (fusion-inhibited) to the fusion-active conformation of the murine leukemia virus glycoprotein.

Envelope glycoproteins (Env) of retroviruses are trimers of SU (surface) and TM (transmembrane) heterodimers and are expressed on virions in fusion-competent forms that are likely to be metastable. Activation of the viral receptor-binding domain (RBD) via its interaction with a cell surface receptor is thought to initiate a cascade of events that lead to refolding of the Env glycoprotein into its stable fusion-active conformation. While the fusion-active conformation of the TM subunit has been described in detail for several retroviruses, little is known about the fusion-competent structure of the retroviral glycoproteins or the molecular events that mediate the transition between the two conformations. By characterizing Env chimeras between the ecotropic and amphotropic murine leukemia virus (MLV) SUs as well as a set of point mutants, we show that alterations of the conformation of the SU glycoprotein strongly elevate Env fusogenicity by disrupting the stability of the Env complex. Compensatory mutations that restored both Env stability and fusion control were also identified, allowing definition of interactions within the Env complex that maintain the stability of the native Env complex. We show that, in the receptor-unbound form, structural interactions between the N terminus of the viral RBD (NTR domain), the proline-rich region (PRR), and the distal part of the C-terminal domain of the SU subunit maintain a conformation of the glycoprotein that is fusion inhibitory. Additionally, we identified mutations that disrupt this fusion-inhibitory conformation and allow fusion activation in the absence of viral receptors, provided that receptor-activated RBD fragments are added in trans during infection. Other mutations were identified that allow fusion activation in the absence of receptors for both the viral glycoprotein and the trans-acting RBD. Finally, we found mutations of the SU that bypass in cis the requirement for the NTR domain in fusion activation. All these different mutations call for a critical role of the PRR in mediating conformational changes of the Env glycoprotein during fusion activation. Our results suggest a model of MLV Env fusion activation in which unlocking of the fusion-inhibitory conformation is initiated by receptor binding of the viral RBD, which, upon disruption of the PRR, allows the NTR domain to promote further events in Env fusion activation. This involves a second type of interaction, in cis or in trans, between the receptor-activated RBD and a median segment of the freed C-terminal domain.

Binding Sites↗

PubMed2000

Fusion protein of the paramyxovirus SV5: destabilizing and stabilizing mutants of fusion activation.

The fusion (F) protein of the paramyxovirus SV5 strain W3A causes syncytium formation without coexpression of the SV5 hemagglutinin-neuraminidase (HN) glycoprotein, whereas the F protein of the SV5 strain WR requires coexpression of HN for fusion activity. SV5 strains W3A and WR differ by three amino acid residues at positions 22, 443, and 516. The W3A F protein residues P22, S443, and V516 were changed to amino acids found in the WR F protein (L22, P443, and A516, respectively). Three single-mutants, three double-mutants, and the triple-mutant were constructed, expressed, and assayed for fusion using three different assays. Mutant P22L did not cause fusion under physiological conditions, but fusion was activated at elevated temperatures. Compared with the W3A F protein, mutant S443P enhanced the fusion kinetics with a faster rate and greater extent, and had a lower activation temperature. Mutant V516A had little effect on F protein-mediated fusion. The double-mutant P22L,S443P was capable of causing fusion, suggesting that the two mutations have opposing effects on fusion activation. The WR F protein requires coexpression of HN to cause fusion at 37 degrees C, and does not cause fusion at 37 degrees C when coexpressed with influenza virus hemagglutinin (HA); however, at elevated temperatures coexpression of WR F protein with HA resulted in fusion activation. In the crystal structure of the core trimer of the SV5 F protein (Baker, K. A., Dutch, R. E., Lamb, R.A., and Jardetzky, T. S. (1999). Mol. Cell 3, 309-319), S443 is the last residue (with interpretable electron density) in an extended chain region and the temperature factor for S443 is high, suggesting conformational flexibility at this point. Thus, the presence of prolines at residues 22 and 443 may destabilize the F protein and thereby decrease the energy required to trigger the presumptive conformational change to the fusion-active state.

Amino Acid Substitution↗

PubMed2006

Paramyxovirus fusion: real-time measurement of parainfluenza virus 5 virus-cell fusion.

Although cell-cell fusion assays are useful surrogate methods for studying virus fusion, differences between cell-cell and virus-cell fusion exist. To examine paramyxovirus fusion in real time, we labeled viruses with fluorescent lipid probes and monitored virus-cell fusion by fluorimetry. Two parainfluenza virus 5 (PIV5) isolates (W3A and SER) and PIV5 containing mutations within the fusion protein (F) were studied. Fusion was specific and temperature-dependent. Compared to many low pH-dependent viruses, the kinetics of PIV5 fusion was slow, approaching completion within several minutes. As predicted from cell-cell fusion assays, virus containing an F protein with an extended cytoplasmic tail (rSV5 F551) had reduced fusion compared to wild-type virus (W3A). In contrast, virus-cell fusion for SER occurred at near wild-type levels, despite the fact that this isolate exhibits a severely reduced cell-cell fusion phenotype. These results support the notion that virus-cell and cell-cell fusion have significant differences.

Animals↗

PubMed2005

Viral membrane fusion: is glycoprotein G of rhabdoviruses a representative of a new class of viral fusion proteins?

Enveloped viruses always gain entry into the cytoplasm by fusion of their lipid envelope with a cell membrane. Some enveloped viruses fuse directly with the host cell plasma membrane after virus binding to the cell receptor. Other enveloped viruses enter the cells by the endocytic pathway, and fusion depends on the acidification of the endosomal compartment. In both cases, virus-induced membrane fusion is triggered by conformational changes in viral envelope glycoproteins. Two different classes of viral fusion proteins have been described on the basis of their molecular architecture. Several structural data permitted the elucidation of the mechanisms of membrane fusion mediated by class I and class II fusion proteins. In this article, we review a number of results obtained by our laboratory and by others that suggest that the mechanisms involved in rhabdovirus fusion are different from those used by the two well-studied classes of viral glycoproteins. We focus our discussion on the electrostatic nature of virus binding and interaction with membranes, especially through phosphatidylserine, and on the reversibility of the conformational changes of the rhabdovirus glycoprotein involved in fusion. Taken together, these data suggest the existence of a third class of fusion proteins and support the idea that new insights should emerge from studies of membrane fusion mediated by the G protein of rhabdoviruses. In particular, the elucidation of the three-dimensional structure of the G protein or even of the fusion peptide at different pH's might provide valuable information for understanding the fusion mechanism of this new class of fusion proteins.

Animals↗

PubMedDate not supplied

What studies of fusion peptides tell us about viral envelope glycoprotein-mediated membrane fusion (review).

This review describes the numerous and innovative methods used to study the structure and function of viral fusion peptides. The systems studied include both intact fusion proteins and synthetic peptides interacting with model membranes. The strategies and methods include dissecting the fusion process into intermediate stages, comparing the effects of sequence mutations, electrophysiological patch clamp methods, hydrophobic photolabelling, video microscopy of the redistribution of both aqueous and lipophilic fluorescent probes between cells, standard optical spectroscopy of peptides in solution (circular dichroism and fluorescence) and attenuated total reflection-Fourier transform infrared spectroscopy of peptides bound to planar bilayers. Although the goal of a detailed picture of the fusion pore has not been achieved for any of the intermediate stages, important properties useful for constraining the development of models are emerging. For example, the presence of alpha-helical structure in at least part of the fusion peptide is strongly correlated with activity; whereas, beta-structure tends to be less prevalent, associated with non-native experimental conditions, and more related to vesicle aggregation than fusion. The specific angle of insertion of the peptides into the membrane plane is also found to be an important characteristic for the fusion process. A shallow penetration, extending only to the central aliphatic core region, is likely responsible for the destabilization of the lipids required for coalescence of the apposing membranes and fusion. The functional role of the fusion peptides (which tend to be either nonpolar or aliphatic) is then to bind to and dehydrate the outer bilayers at a localized site; and thus reduce the energy barrier for the formation of highly curved, lipidic 'stalk' intermediates. In addition, the importance of the formation of specific, 'higher-order' fusion peptide complexes has also been shown. Recent crystallographic structures of core domains of two more fusion proteins (in addition to influenza haemagglutinin) has greatly facilitated the development of prototypic models of the fusion site. This latter effort will undoubtedly benefit from the insights and constraints gained from the studies of fusion peptides.

Amino Acid Sequence↗

PubMed2000

Deployment of membrane fusion protein domains during fusion.

It is clear that both viral and intracellular membrane fusion proteins contain a minimal set of domains which must be deployed at the appropriate time during the fusion process. An account of these domains and their functions is given here for the four best-described fusion systems: influenza HA, sendai virus F1, HIV gp120/41 and the neuronal SNARE core composed of synaptobrevin (syn), syntaxin (stx) and the N- and C-termini of SNAP25 (sn25), together with the Ca(2+)binding protein synaptotagmin (syt). Membrane fusion begins with the binding of the virion or vesicle to the target membrane via receptors. The committed step in influenza HA- mediated fusion begins with an aggregate of HAs (at least eight) with some of their HA2 N-termini, a.k.a. fusion peptides, embedded into the viral bilayer (Bentz, 2000 a). The hypothesis presented in Bentz (2000 b) is that the conformational change of HA to the extended coiled coil extracts the fusion peptides from the viral bilayer. When this extraction occurs from the center of the site of restricted lipid flow, it exposes acyl chains and parts of the HA transmembrane domains to the aqueous media, i.e. a hydrophobic defect is formed. This is the 'transition state' of the committed step of fusion. It is stabilized by a 'dam' of HAs, which are inhibited from diffusing away by the rest of the HAs in the aggregate and because that would initially expose more acyl chains to water. Recruitment of lipids from the apposed target membrane can heal this hydrophobic defect, initiating lipid mixing and fusion. The HA transmembrane domains are required to be part of the hydrophobic defect, because the HA aggregate must be closely packed enough to restrict lipid flow. This hypothesis provides a simple and direct coupling between the energy released by the formation of the coiled coil to the energy needed to create and stabilize the high energy intermediates of fusion. Several of these essential domains have been described for the viral fusion proteins SV5 F1 and HIV gp120/41, and for the intracellular SNARE fusion system. By comparing these domains, we have constructed a minimal set which appears to be adequate to explain how the conformational changes can produce a successful fusion event, i.e. communication of aqueous compartments.

Animals↗

PubMed2001

An alpha-helical domain within the carboxyl terminus of herpes simplex virus type 1 (HSV-1) glycoprotein B (gB) is associated with cell fusion and resistance to heparin inhibition of cell fusion.

Previous studies from our laboratory indicated that a 28-amino-acid carboxyl-terminal truncation of gB caused extensive virus-induced cell fusion (Baghian et al., 1993, J Virol 67, 2396-2401). We tested the ability of additional truncations and mutations within gB to cause cell fusion in the recently established virus-free cell fusion assay (Turner et al., 1998, J. Virol. 72, 873-875). Deletion of the carboxyl-terminal 28 amino acids of gB (gBDelta28), which removed part of the predicted alpha-helical structure H17b, caused extensive cell fusion. A gB truncation specified by gBDelta36, which removed the entire H17b domain, caused as much cell fusion as the gBDelta28 truncation. Similarly, gB(A874P) containing a substitution of an Ala with Pro within H17b caused cell fusion. Heparin, a gB-specific inhibitor of virus-induced cell fusion, inhibited both wild-type gB and gB(syn3)-mediated cell fusion. In contrast, fusion of cells transfected with gB(Delta28), gB(Delta36), or gB(A874P) was resistant to heparin inhibition of cell fusion. We concluded the following: (1) The predicted alpha-helical structure of H17b within the carboxyl terminus of gB is involved in both virus-induced and virus-free cell fusion. (2) Heparin is a specific inhibitor of gB-mediated fusion in both systems. (3) Resistance to heparin inhibition of gB-mediated cell fusion is associated with the predicted alpha-helical structure H17b within the carboxyl terminus of gB.

Amino Acid Sequence↗

PubMedDate not supplied

A preliminary comparative study of radiographic results using mineralized collagen and bone marrow aspirate versus autologous bone in the same patients undergoing posterior lumbar interbody fusion with instrumented posterolateral lumbar fusion.

BACKGROUND CONTEXT: Multiple bone graft substitutes for spinal fusion have been studied with varying results. PURPOSE: The purpose of this study was to assess the effectiveness of a mineralized collagen matrix combined with bone marrow, versus autologous bone, in the same patients undergoing a posterior lumbar interbody fusion and an instrumented posterolateral lumbar fusion. STUDY DESIGN/SETTING: A prospective, comparative study. PATIENT SAMPLE: Patients indicated for one-level posterior lumbar interbody fusion and instrumented posterolateral lumbar fusion, serving as self-controls. OUTCOME MEASURES: Thin-cut computed tomographic scans with sagittal reconstruction and plain radiographs, including lateral flexion/extension views were performed and assessed at 12 and 24 months after surgery. Oswestry Disability Index and Visual Analog Scale questionnaires were completed by all patients preoperatively and at 12 and 24 months after surgery. METHODS: After informed consent and failure of nonoperative treatment, 25 consecutive patients requiring one-level instrumented posterolateral fusion combined with posterior interbody fusion were enrolled in the study. Mineralized collagen bone graft substitute combined with bone marrow aspirate was used on one side of the posterolateral fusion, with iliac crest autograft on the contralateral side. RESULTS: A fusion rate of 84% (21/25) was achieved for the autologous bone grafts and 80% (20/25) for the bone graft substitute. The interbody fusion rate was 92% (23/25). Mean Oswestry Disability Index (ODI) scores decreased 57.2% at 12 months and 55.6% at 24 months, compared with baseline. CONCLUSIONS: Mineralized collagen bone graft substitute exhibited similar radiographic results compared with autograft in this model. Further trials incorporating bilateral fusion, as well as posterolateral fusion alone without interbody fusion are warranted to confirm the results of this study.

Adult↗

PubMed2000

Increased fusion rates with cervical plating for two-level anterior cervical discectomy and fusion.

STUDY DESIGN: A retrospective review of all patients surgically treated with a two-level anterior cervical discectomy and fusion with and without anterior plate fixation by a single surgeon. OBJECTIVES: To compare the clinical and radiographic success of two-level discectomy and the effect of anterior cervical plate fixation. SUMMARY OF BACKGROUND DATA: Prior studies of multisegment fusions have shown decreased fusion rates correlating with the number of increased levels. The use of anterior plates for single-level cervical fusions is controversial. However, their use in multilevel fusions may be warranted because of the increased pseudarthrosis rates. METHODS: Over a 6-year period, 60 patients were treated surgically with a two-level anterior cervical discectomy and fusion by the senior author. Thirty-two patients had cervical plates, and 28 underwent fusions without plates. These patients were followed for an average of 2.7 years. Clinical and radiographic follow-up evaluations were performed. RESULTS: Of the 60 patients, 7 had a pseudarthrosis. The pseudarthrosis rates were 0% for patients with plating and 25% for those with no plating. This difference was statistically significant (P = 0.003). No correlation of pseudarthrosis with gender, age, level of surgery, history of tobacco use, or the presence of prior anterior surgery was found. There was significantly less graft collapse (P = 0.0001) in the patients without plates in whom pseudarthrosis developed (1.4 mm) than in those who had fusions with plates (0.3 mm). The amount of kyphotic deformity of the fused segment was 0.4 degree in patients with plating compared with 4.9 degrees in those without plating who developed a pseudarthrosis (P = 0.0001). CONCLUSIONS: The addition of plate fixation for two-level anterior cervical discectomy and fusion is a safe procedure with no significant increase in complication rates. The pseudarthrosis rates are significantly higher in patients treated without plate fixation. No nonunions occurred in the patients treated with plate fixation. There was significantly less disc space collapse and kyphotic deformity with the plated fusions than with the nonplated fusions, in which a pseudarthrosis developed. The complication rates for plated fusions are extremely low and do not differ from those for nonplated fusions.

Adult↗

PubMed2001

Increased fusion rates with cervical plating for three-level anterior cervical discectomy and fusion.

STUDY DESIGN: A retrospective review of all patients surgically treated by a single surgeon with a three-level anterior cervical discectomy and fusion with and without anterior plate fixation. OBJECTIVES: To compare the clinical and radiographic success of anterior three-level discectomy and fusion performed with and without anterior cervical plate fixation. SUMMARY OF BACKGROUND DATA: Previous studies of multilevel cervical discectomies and fusions have shown fusion rates to decrease as the number of surgical levels increases. Anterior cervical plate stabilization can provide more stability and may increase fusion rates for multilevel fusions. METHODS: Over a 7-year period, 59 patients were treated surgically with a three-level anterior cervical discectomy and fusion by the senior author. Forty patients had cervical plates, whereas 19 had fusions with no plates. These patients were observed for an average of 3.2 years. Clinical and radiographic follow-up data were obtained. RESULTS: Of the 59 patients, 14 had a pseudarthrosis (7 in each group). The pseudarthrosis rates were 18% (7 of 40) for patients with plating and 37% (7 of 19) for patients with no plating. Although the nonunion rate for unplated fusions was double that of plated fusions, this difference was not statistically significant. There was no statistically significant correlation between pseudarthrosis and gender, age, level of surgery, history of tobacco use, or previous anterior surgery. The fusion rates were improved with the use of a cervical plate. Inferior clinical results were demonstrated in patients with a pseudarthrosis, regardless of the use of a cervical plate. CONCLUSIONS: The addition of plate fixation for three-level anterior cervical discectomy and fusion is a safe procedure and does not result in higher complication rates. In this study, the pseudarthrosis rate was lower for patients with a cervical plate. However, this difference was not statistically significant. Patients treated with cervical plating had overall better results when compared with those of patients treated without cervical plates. Although the use of cervical plates decreased the pseudarthrosis rate, a three-level procedure is still associated with a high nonunion rate, and other strategies to increase fusion rates should be explored.

Bone Plates↗

PubMed2005

Initial fusion rates with recombinant human bone morphogenetic protein-2/compression resistant matrix and a hydroxyapatite and tricalcium phosphate/collagen carrier in posterolateral spinal fusion.

STUDY DESIGN: Prospective, randomized, unblinded study of iliac crest bone graft (ICBG) versus recombinant human bone morphogenetic protein-2/compression resistant matrix (rhBMP-2/CRM)in a posterolateral instrumented fusion procedure. OBJECTIVES: Document initial radiographic characteristics, based on computed tomography, with rhBMP-2/CRM for posterolateral fusion at 6 and 12-month intervals. SUMMARY OF BACKGROUND DATA: As the acceptance of INFUSE bone graft as an ICBG replacement becomes more widespread, surgeons have begun to study applications for rhBMP-2 in posterior spinal fusion. Preclinical studies have examined variables including carrier composition, rhBMP-2 concentration, and rhBMP-2 dose. Pilot studies have been performed with encouraging initial results. METHODS: Patients with single level lumbar degenerative disease were enrolled in a randomized study of ICBG versus rhBMP-2/CRM in a posterolateral instrumented fusion procedure. Computed tomography scans at 6 and 12 months were graded as demonstrating no fusion (grade 1), partial or limited unilateral fusion (grade 2), partial or limited bilateral fusion (grade 3), solid unilateral fusion (grade 4), or solid bilateral fusion (grade 5). RESULTS: At our institution, 74 patients (38 rhBMP-2/CRM, 36 ICBG) reached minimum 1-year follow-up and were included in this analysis. Mean fusion grade (scale1-5) at 6 months after surgery was 4.35 in the rhBMP-2/CRM group versus 3.09 in the ICBG group (P < 0.0001). At 1 year after surgery mean fusion grade was 4.62 in the rhBMP-2/CRM group versus 3.77 in the ICBG group (P < 0.0023). CONCLUSIONS: These early results are encouraging and suggest a more rapid incorporation and development of the fusion mass with rhBMP-2/CRM than iliac crest autograft in a single level posterior instrumented fusion.

Adult↗

PubMed2006

Circumferential fusion improves outcome in comparison with instrumented posterolateral fusion: long-term results of a randomized clinical trial.

STUDY DESIGN: Prospective randomized clinical study with a 5- to 9-year follow-up period. OBJECTIVE: The aim of the present study was to analyze the long-term outcome with respect to functional disability, pain, and general health of patients treated by means of circumferential lumbar fusion in comparison with those treated by means of instrumented posterolateral lumbar fusion. SUMMARY OF BACKGROUND DATA: Circumferential fusion has become a common procedure in lumbar spinal fusion both as a primary and salvage procedure. However, the claimed advantages of circumferential fusion over conventional posterolateral fusion lack scientific documentation. (The primary report with a 2-year follow-up has been published in Spine in 2002.) METHODS: From April 1996 to November 1999, a total of 148 patients (mean age, 45 years) with severe chronic low back pain were randomly selected for either posterolateral lumbar fusion (titanium Cotrel-Dubousset) or circumferential lumbar fusion (instrumented posterolateral fusion with anterior intervertebral support by a Brantigan cage). The primary outcome measure was the Dallas Pain Questionnaire (DPQ). The secondary outcome measures were the Oswestry Disability Index, the SF-36 instrument, and the Low Back Pain Rating Scale. All measures assessed the endpoint outcomes at 5 to 9 years after surgery. RESULTS: The available response rate was 93%. The circumferential group showed a significantly better improvement (P < 0.05) in comparison with the posterolateral group with respect to all four DPQ categories: daily activities, work/leisure, anxiety/depression, and social interest. The Oswestry Disability Index supported these results (P < 0.01). General health, as assessed by means of the SF-36, also showed significantly better physical health (P < 0.01) in the circumferential group, whereas no significant difference was found with respect to mental health compared with the posterolateral group. The circumferential group experienced significantly less back pain (P < 0.05) in comparison with the posterolateral group. In regard to leg pain, no significant difference was found. CONCLUSION: Circumferential lumbar fusion demands more extensive operative resources compared with posterolateral lumbar fusion. However, 5 to 9 years after surgery, the circumferentially fused patients had a significantly improved outcome compared with those treated by means of posterolateral fusion. These new results not only emphasize the superiority of circumferential fusion in the complex pathology of the lumbar spine but are also strongly supported in all of the validated questionnaires used in the study.

Adult↗

PubMed2003

In vitro biomechanical effects of reconstruction on adjacent motion segment: comparison of aligned/kyphotic posterolateral fusion with aligned posterior lumbar interbody fusion/posterolateral fusion.

OBJECT: Posterior lumbar interbody fusion (PLIF) was developed to overcome the limitations of posterolateral fusion in correcting spinal deformity and maintaining lumbar lordosis. In this study the authors compare the biomechanical effects of three different posterior reconstructions on the adjacent motion segment. METHODS: Ten calf spinal (L2-S1) specimens underwent nondestructive flexion-extension testing (+/- 6 Nm). The specimens were destabilized at the L5-S1 levels after intact testing. This was followed by pedicle screw fixation with and without interbody cages as follows: 1) with straight rods ("aligned" posterolateral fusion); 2) with kyphotically prebent rods ("kyphotic" posterolateral fusion); and 3) with interbody cages combined with straight rods ("aligned" PLIF/posterolateral fusion). The range of motion (ROM) of the operative segments, the intradiscal pressure (IDP), and longitudinal lamina strain in the superior adjacent segment (L4-5) were analyzed. The ROM associated with aligned PLIF/posterolateral fusion-treated specimens was significantly less than both the aligned and kyphotic posterolateral fusion-treated procedures in both flexion and extension loading (p < 0.05). The aligned PLIF/posterolateral fusion was associated with greater IDP and the lamina strain compared with the aligned and kyphotic posterolateral fusion groups in flexion loading. Under extension loading, greater IDP and lamina strain were present in the kyphotic posterolateral fusion group than in the aligned posterolateral fusion group. The highest IDP and lamina strain were shown in the aligned PLIF/posterolateral fusion group. CONCLUSIONS: Compared with kyphotic posterolateral fusion, PLIF may lead to even higher load at the superior adjacent level because of the increased stiffness of the fixed segments even if local kyphosis is corrected by PLIF.

Animals↗

PubMed2006

[The dependence of the range of fusion on some selected functions of the visual system. Part I: Study on convergent and divergent fusion].

After examined 132 patients, the authors selected 90 patients with correct visual acuity of both eyes, correct range of eyeballs' mobility, parallel setting of the eyeballs, no difference in refraction between both eyes and with muscular balance. These 90 patients were divided into 3 groups: children between 8 and 10 years old, teenagers between 11 and 20 years old and adult people between 21 and 40. All the groups were subject to the main examination of the study carried out by means of prism bar and synoptophore for each of the eye separately. The results were compared in order to define the difference in the range of fusion between both eyes. The study involved an examination of horizontal range of convergent and divergent synoptophoric fusion as well as that of free space for near and for far. A statistically significant difference between both eyes was observed in range of synoptophoric, for near and for far convergent fusion. The difference was confirmed in an average of 35.6% of patients for convergent fusion for near, in 34.4% of patients for convergent fusion for far, and in 65.6% of patients for synoptophoric convergent fusion. The mean difference between the eyes in the range of fusion was: 4.6 degrees for convergent fusion for near, 3.9 degrees for convergent fusion for far and 6.4 degrees for synoptophoric convergent fusion. No significant differences between both eyeballs were detected in the range of divergent fusion. The authors suggested calling the phenomenon connected with the difference between both eyeballs in convergent fusion the following term: "visual unevenness of the range of convergent fusion".

Adolescent↗

PubMed1999

Peptides and membrane fusion: towards an understanding of the molecular mechanism of protein-induced fusion.

Processes such as endo- or exocytosis, membrane recycling, fertilization and enveloped viruses infection require one or more critical membrane fusion reactions. A key feature in viral and cellular fusion phenomena is the involvement of specific fusion proteins. Among the few well-characterized fusion proteins are viral spike glycoproteins responsible for penetration of enveloped viruses into their host cells, and sperm proteins involved in sperm-egg fusion. In their sequences, these proteins possess a "fusion peptide, " a short segment (up to 20 amino acids) of relatively hydrophobic residues, commonly found in a membrane-anchored polypeptide chain. To simulate protein-mediated fusion, many studies on peptide-induced membrane fusion have been conducted on model membranes such as liposomes and have employed synthetic peptides corresponding to the putative fusion sequences of viral proteins, or de novo synthesized peptides. Here, the application of peptides as a model system to understand the molecular details of membrane fusion will be discussed in detail. Data obtained from these studies will be correlated to biological studies, in particular those that involve viral and sperm-egg systems. Structure-function relationships will be revealed, particularly in the context of protein-induced membrane perturbations and bilayer-to-nonbilayer transition underlying the mechanism of fusion. We will also focus on the involvement of lipid composition of membranes as a potential regulating factor of the topological fusion site in biological systems.

Animals↗

PubMed1983

Fusion of Sendai virus with liposomes: dependence on the viral fusion protein (F) and the lipid composition of liposomes.

The characteristics of fusion of the membrane of Sendai virus with that of liposomes has been investigated using two different methods to monitor the fusion reaction. The first method, which permits quantitation of lipid fused with virus, depends on separation by centrifugation of unfused liposomes from those fused with virus. The second involves the digestion after fusion of internal viral proteins by trypsin contained in liposomes; this assay is completely independent of exchange of lipid between liposomal and viral membranes in the absence of fusion. A fusion-inactive mutant virus, pa-cl, with an uncleaved F protein served as the appropriate control in these experiments. It was found that fusion of the virus with liposomes that contained no protein required cleavage of the F protein; such cleavage was previously shown to be required for fusion of the virus with cell membranes. This indicates the relevance of this model system for studies of fusion. Kinetic studies indicated that at neutral pH fusion was 88% complete in 10 min at 37 degrees. Investigation of the effects of liposomal lipid composition indicated that the presence of cholesterol in the liposomal membrane was required for fusion; a 0.3-0.4-mole fraction of cholesterol was optimal. The presence of neuraminic acid in the membrane was not essential for fusion. The results obtained are compatible with previous evidence suggesting a hydrophobic interaction between the cleaved F protein and the target membrane during fusion.

Chemical Phenomena↗