[Hepatic echinococcosis that required 11 years for a definitive diagnosis: a case report].

A woman in her 80s underwent computed tomography that revealed a 22-mm-sized unilocular mass in segment 4 of her liver. The mass grew to 26mm at the 4-year follow-up and to 36mm at the 11-year follow-up, becoming a multilocular mass that invaded the bile duct. At this point, the patient was diagnosed with hepatic echinococcosis based on a serological examination and oral albendazole treatment was initiated. The patient developed cholangitis and underwent endoscopic biliary stenting 12 years after her initial diagnosis. We consider this case valuable as it allowed us to follow the natural course of hepatic echinococcosis.

[A case of systemic amyloidosis presenting with gastric emphysema].

The patient was an elderly woman in her 80s. Upper and lower gastrointestinal endoscopies were conducted as a thorough analysis for cardiac amyloidosis, revealing no abnormal findings. A mucosal biopsy, however, resulted in an amyloid AA-type amyloidosis diagnosis. About 2 months later, she visited our department with sudden vomiting and epigastric pain onset. Plain abdominal radiography and computed tomography demonstrated gastric emphysema, and thus, she was admitted to our department. The gastric emphysema was alleviated with conservative treatment. Herein, we report a valuable case in which gastric emphysema manifested as a gastrointestinal tract lesion of amyloidosis.

Dynamic conformal arc radiotherapy for locally advanced lung cancer: a comparison with static-beam conformal radiotherapy.

Background: This study investigated whether the dose distribution of lung cancer can be improved by dynamic arc conformal radiotherapy (dynamic CRT) compared with static multiple-beam radiotherapy (static CRT). Materials and methods: A dummy study of static CRT and dynamic CRT was performed, designed to meet the predetermined dose constraints. A dose of 60 Gy in 30 fractions was administered using two dose prescription methods: dose prescribed to the isocenter (IC prescription), and dose prescribed to > 50% of the planning target volume (D50 prescription). Dose-volume parameters were compared between the plans. Results: Among 20 patients with locally advanced lung cancer, dose conformity was significantly better with dynamic CRT than static CRT (median conformity index: 1.3 vs. 2.2; p < 0.01). As for the lung dose, compared with static CRT, dynamic CRT did not increase the percentage lung volume receiving ≥ 20 Gy (18.9% vs. 19.3%, p = 0.09). The maximum spinal cord dose was significantly reduced by dynamic CRT (static vs. dynamic CRT: 44.1 vs. 25.2 Gy, p < 0.001). With the change from IC to D50 prescription, the 95% isodose volume increased by 18.3 cc in static CRT and by 4.1 cc in dynamic CRT, while doses to the lung and spinal cord remained within the acceptable ranges. Conclusion: The dynamic CRT technique showed better target coverage and lower doses to the spinal cord in exchange for increased low-dose lung area, compared with static CRT. Dynamic CRT with D50 prescription instead of prescription to the isocenter has excellent dose distribution profiles without compromising doses to organs at risk for lung cancer at favorable locations.

Phase Imaging of Phosphatidylcholine Bilayer Membranes by Prodan Fluorescence.

Prodan (6-propiponyl-2-(N,N-dimethylamino)naphthalene) is well known as a polarity-sensitive fluorescent probe and has a high capability of detecting structural changes occurring within phospholipid bilayer membranes. In this study, we carried out the fluorescence spectroscopic observation of bilayer phase behavior for a series of symmetric saturated diacylphosphatidylcholines (CnPCs) with different acyl-chain length n (n = 12-15 and 19-22) using Prodan as a membrane probe to confirm the availability of Prodan along with the previous results for the CnPC bilayer membranes (n = 16-18). The results were discussed by constructing spectral three-dimensional (3D) imaging plots for visualizing the change in bilayer phase states with temperature or pressure to verify the functionality of this 3D imaging plot. It was found that the Prodan fluorescence technique is applicable to the detection of the changes in the bilayer phase states of all CnPCs with a few exceptions. One of the most crucial exceptions was that Prodan cannot be used for the detection of the bilayer-gel state of the C21PC bilayer membrane. It was also found that it is only to the CnPC bilayer membranes with n = 15-18 that the 3D imaging plot is adequately and accurately applicable as a useful graphical tool for visually detecting the bilayer phase states. This is a disadvantageous feature of this technique brought about by the high sensitivity of Prodan as a membrane probe. Further detailed studies on the molecular behavior of Prodan will enable us to find a more useful way of utilizing this membrane probe.

Challenges in left sleeve pneumonectomy in the left lateral decubitus position.

We report the case of a 20-year-old woman with carinal adenoid cystic carcinoma who underwent left sleeve pneumonectomy in the left lateral decubitus position, during which severe desaturation was encountered. After transecting the left main bronchus, the left lung was selectively intubated and ventilated. However, oxygenation was inadequate. Hence, venoarterial extracorporeal membrane oxygenation (ECMO) was introduced. Initially, Barclay's procedure was planned to preserve the left lung, but this plan was altered due to the extent of the tumor and unstable ventilation. After the lesion was removed, the trachea and right main bronchus were anastomosed end-to-end. During left pneumonectomy, the right lung was selectively ventilated, but oxygen saturation (SpO2) dropped to <70% despite ECMO. SpO2 improved on additionally ventilating the left lung using another breathing circuit. Temporary right chest closure was performed with ventilation of the left lung across the thoracotomy wound. The patient was turned to the semi-supine position, and tolerated selective right lung ventilation with ECMO. Subsequently, left thoracotomy and pneumonectomy were successfully performed. Careful management is required for desaturation in left sleeve pneumonectomy in the left lateral decubitus position.

Skeletal muscle and related protein expression as prognostic factors in thymic squamous cell carcinoma.

Background: Sarcopenia and its marker, the psoas muscle index (PMI), have attracted attention as prognostic factors for various types of cancers. The fragile X-related 1 (FXR1) gene is highly expressed in myocytes, and FXR1 overexpression is a candidate biomarker for poor survival in several types of cancers. Thymic squamous cell carcinoma (TSQCC) is rare, and no studies assessing its prognostic factors, particularly in terms of skeletal muscle mass and FXR1 expression, are available. Methods: We retrospectively investigated the prognostic significance of PMI in 34 patients who underwent TSQCC resection, considering the status of FXR1 and tumor programmed death-ligand 1 (PD-L1). PMI was calculated from the bilateral psoas muscle using preoperative computed tomography (CT). Patients were divided into two groups: low PMI (<58.2%, n=17) and normal PMI (≥58.2%, n=17). Immunohistochemical analysis was performed to determine the FXR1 and PD-L1 expression levels. Results: Low PMI was significantly associated with worse overall survival (OS) (5-year survival rate; 86% vs. 100%; P=0.026) and marginally associated with worse disease-free survival (DFS) (5-year survival rate; 39% vs. 66%; P=0.090) compared with normal PMI. The immunohistochemical analysis revealed that the FXR1 intensity score (0-1+: 6% vs. 0%; 2+-3+: 94% vs. 100%; P=0.31), median FXR1 distribution (95% vs. 90%; P=0.63), and PD-L1 status (high: 47% vs. 59%; P=0.49) were not significantly different between the two groups. Conclusions: Our findings suggest that PMI might be considered as a potential prognostic factor in TSQCC and that FXR1 is widely expressed regardless of the PMI status. Skeletal muscle mass may play a role in the prognosis of TSQCC.

A survey of physical and occupational therapists' views on lumbar loading movements.

[Purpose] To identify the lumbar loading movements necessary in clinical practice. [Participants and Methods] A questionnaire survey was conducted among physical and occupational therapists in Japan. There were no exclusion criteria regarding the number of years of experience, age, or field of employment. The participants were randomly selected and administered the questionnaire. They were asked to list and rank the lumbar loadings they considered necessary. [Results] A total of 739 respondents participated in the survey. The results of this nationwide survey indicated that the lifting movement of heavy objects in the trunk flexion position was the most common movement (for 354 participants). [Conclusion] The main loading movements of the lumbar spine were reported to be heavy lifting movements (in the trunk flexion position) and trunk rotation movements. As perspectives, we aim to conduct an analytical study of some of lumbar spine loading movements outlined in this study, using a musculoskeletal simulator and electromyography.

Postoperative empyema complicated with descending necrotizing fasciitis: a case report.

BACKGROUND: Empyema is a serious complication of lung surgery. CASE PRESENTATION: We report a case of Streptococcus anginosus empyema complicated by descending necrotizing fasciitis after surgery. Ten days after the initial surgery, the patient presented with arrhythmia and hypotension with septic shock. Pleural fluid analysis led to the diagnosis of empyema, and surgical debridement (second surgery) was performed. One week after the emergency surgery, a palpable pink erythematous skin change was observed on the ipsilateral iliac crest. Hence, the second emergency surgery (third surgery) was performed to debride the subcutaneous and intramuscular abscesses. CONCLUSIONS: The possibility of descending abscess and necrotizing fasciitis should be considered when Streptococcus anginosus is detected.

Short tandem repeat polymorphism analysis for primary peritoneal choriocarcinoma: A case report and literature review.

The peritoneum is an extremely rare site for primary choriocarcinoma development. Primary peritoneal choriocarcinoma could be either gestational or nongestational, whereas it is straightforward to ascribe uterine or tubal choriocarcinoma to the gestational origin. Herein, we report a case of primary peritoneal choriocarcinoma that is genetically diagnosed as a gestational subtype originating from an occult complete hydatidiform mole. A 46-year-old female patient with two-time induced abortion histories underwent emergency laparotomy under clinical suspicion of ruptured tubal pregnancy. Laparotomy revealed a hemorrhagic tumor in the left mesosalpinx with apparently intact left ovary and fallopian tube. The excised tumor was pathologically diagnosed as choriocarcinoma. Multiplex short tandem repeat polymorphism analysis revealed an androgenetic/homozygous genotype tumor, identifying its origin as a complete hydatidiform mole. Our literature review of nine primary peritoneal choriocarcinoma cases, including ours, highlighted the importance of tumor genotyping in differentiating between gestational and non-gestational subtypes and identifying the causative pregnancy.

Relationship of smoking cessation period with the incidence of complications in lung cancer surgery.

OBJECTIVES: The incidence of postoperative complications is relatively high in smokers. Although 4-week smoking cessation before surgery is generally recommended, it has not been sufficiently studied in lung cancer surgery. This study investigated whether smoking cessation for a short period of time significantly reduced complications after lung cancer surgery. METHODS: This was a retrospective, observational study that investigated the relationship between the smoking cessation period and the incidence of complications in lung cancer surgery. Patients who underwent curative-intent surgery for lung cancer at our institution between January 2014 and December 2017 were included. The smokers were classified into the following 4 categories of smoking cessation period before surgery: current (<4 weeks), recent (4 weeks to 12 months), distant (12 months to 5 years) and ex-smokers (>5 years). RESULTS: A total of 911 patients were included in this study. The incidence of pulmonary complications was 5 times higher in the smoker group than in the never smoker group (12.9% vs 2.5%, P < 0.001). On multivariable analysis in both models, the odds ratio for complications was significantly higher in distant smokers than in recent smokers and never smokers. Across all models, low lung function significantly predicted the development of postoperative complications. CONCLUSIONS: The evidence-based smoking cessation duration that reduces the incidence of complications after thoracic surgery remains unclear. The incidence of postoperative complications was more strongly affected by low pulmonary function than by the duration of preoperative smoking cessation. For patients with marginal indications for surgery, postponing surgery to accommodate a smoking cessation period seemed unnecessary.

Risk Assessment for Loss-of-Exercise Capacity After Lung Cancer Surgery: Current Advances in Surgery and Systemic Treatment.

BACKGROUND: Considering advances in current post-recurrence treatment, we examined the prognostic significance of the number of risk factors for loss-of-exercise capacity (LEC) after lung cancer surgery, which were identified by our previous prospective observational study. METHODS: Risk factors for LEC were defined as a short baseline 6-min walk distance (<400 m), older age (≥75 years), and low predicted postoperative diffusing capacity for carbon monoxide (<60%). Patients were classified as Risk 0/I/II/III according to the number of risk factors. The survival data were retrospectively analyzed. RESULTS: Between 2014 and 2017, 564 patients (n = 307, 193, 57, 7; Risk 0/I/II/III) who underwent lung cancer surgery were included in the study. The number of risk factors was associated with smoking status, predicted postoperative forced expiratory volume in 1 s, histology, pathological stage, and adjuvant therapy. In a multivariate Cox regression analysis, compared to Risk 0, Risk I/II/III showed significant associations with overall survival (hazard ratios: 1.92, 3.35, 9.21; 95% confidence interval: 1.27-2.92, 2.01-5.58, 3.64-23.35; Risk I/II/III, respectively). In 141 patients with recurrence, molecular targeted therapies (MTTs) or immune checkpoint inhibitors (ICIs) were included in 58%, 47%, 32%, and 0% (Risk 0/I/II/III) during the course of treatment. In patients with MTT/ICI treatment, the estimated 1-year and 3-year post-recurrence survival rates were 88% and 58%, respectively. CONCLUSIONS: Risk classification for LEC was associated with survival after lung cancer surgery, as well as post-recurrence treatment. The concept of physical performance-preserving surgery may contribute to improving the outcomes of current lung cancer treatment.

Pleural Invasion Depth of Disseminated Nodules in Patients with Stage IVa or Recurrent Thymoma: Assessment, Curative Impact, and Surgical Outcomes.

BACKGROUND: Thymoma patients with pleural dissemination are difficult to manage, and their treatment strategy remains undefined. This study aimed to investigate the clinicopathologic features of these patients, focusing on the association between the depth of pleural invasion and prognosis. METHODS: Between 2003 and 2019, the study identified 120 disseminated lesions in 20 thymoma patients. Seven patients had de novo stage IVa thymoma and 13 were recurrent cases. Extrapleural pneumonectomy was performed for 8 patients and debulking surgery for 12 patients. Invasion depth of pleural tumors was classified into two groups: when the disseminated tumors invaded the pleura beneath the elastic layer, the tumor was diagnosed as Da, and when the disseminated tumors invaded the pleura beyond the elastic layer, the tumor was diagnosed as Db. RESULTS: Of 120 nodules, 31 (26%), found in eight patients with recurrent malignancies, were classified as Db. The pathologic status of the surgical margin (PSM) was positive in eight patients, seven of whom had Db nodules. The 5-year overall survival (OS) rate was 100% in the Da group and 75% in the Db group (P = 0.02). The 5-year progression-free survival (PFS) rate was 66.7% in the Da group and 25% in the Db group (P = 0.02). Cox univariate analysis showed that PFS was significantly influenced by the depth of invasion (P = 0.04) and PSM (P = 0.03). CONCLUSION: Depth of pleural invasion may influence survival outcomes for thymoma patients with pleural dissemination. The patients in this study with Da-disseminated nodules had an increased probability of a longer OS and PFS and tended to achieve negative PSM compared with the patients with Db.

Prognostic Value of Uncertain Resection for Overall Survival in Non-small Cell Lung Cancer.

BACKGROUND: In this study we evaluated the R(un) category proposed by the International Association for the Study of Lung Cancer (IASLC) for non-small cell lung cancer (NSCLC). METHODS: We retrospectively reviewed the medical records of patients with NSCLC who underwent segmentectomy or lobectomy between 2014 and 2015 at our institution. Residual tumor (R) status was reclassified from the Union for International Cancer Control designation to the IASLC-proposed R classification of R0 and R(un). The underlying reasons for the R(un) reclassification were analyzed according to pathologic stage, lymph node status, and resected lobe. A Cox proportional hazard model was used to evaluate the impacts of R(un) categorization on overall survival. RESULTS: Of 355 patients, 44.5% were reclassified as R(un). The most common reason for the reclassification was insufficient number of harvested lymph nodes or no station 7 lymph nodes. When stratified by tumor location, the absence of station 7 lymph nodes was especially prominent in both the right and left upper lung resections. In the multivariate Cox regression model, the IASLC R classification was associated with poor overall survival in node-positive patients (hazard ratio, 2.657; P = .016). CONCLUSIONS: Various factors resulted in reclassification to R(un) because the R(un) group was highly heterogeneous. Careful consideration is required to determine whether the R(un) classification can be used as an indicator of lymph node dissection quality. For advanced cases, the R(un) definition may be useful in predicting poor prognosis.

Lower systolic blood pressure levels in early pregnancy are associated with a decreased risk of early-onset superimposed preeclampsia in women with chronic hypertension: a multicenter retrospective study.

To clarify the impact of blood pressure (BP) management ranges on pregnancy outcomes, we conducted a multicenter retrospective analysis of 215 women with singleton pregnancies diagnosed with essential hypertension either before or within 14 weeks of gestation. Patients were classified according to systolic BP (sBP; <130, 130-139, 140-159, and ≥160 mmHg) or diastolic BP (dBP; <80, 80-89, 90-109, and ≥110 mmHg) at 8-11, 12-15, and 16-19 weeks of gestation. The risk of early-onset superimposed preeclampsia and small-for-gestational-age neonates was assessed in each BP group. Moreover, a subgroup analysis was performed in 144 eligible patients whose BP was measured at both 12-13 and 14-15 weeks of gestation. At 16-19 weeks of gestation, higher sBP significantly increased the incidence of early-onset superimposed preeclampsia (13.3%, 24.6%, 32.2% and 75.0%, respectively) and small-for-gestational-age neonates (6.0%, 13.1%, 16.9% and 50.0%, respectively). Multivariate logistic regression analyses showed that women with sBP < 130 mmHg at 16-19 weeks of gestation had a significantly lower risk of early-onset superimposed preeclampsia than women with sBP of 140-159 mmHg. Subgroup analyses also showed that even at 14-15 weeks of gestation, sBP < 130 mmHg was associated with a significantly lower risk of early-onset superimposed preeclampsia than an sBP of 140-159 mmHg. In conclusion, sBP < 130 mmHg within 14 weeks of gestation reduced the risk of developing early-onset superimposed preeclampsia in women with chronic hypertension.

Removal of hematoma due to massive hemoptysis after transbronchial biopsy: a case report.

BACKGROUND: Massive hemoptysis is a life-threatening complication after transbronchial biopsy (TBB). Reports on massive hemoptysis occurring several days after TBB are scarce. CASE PRESENTATION: A 62-year-old man presented with massive hemoptysis and was admitted to hospital as an emergency on the eighth day after TBB. On the 12th day after TBB, computed tomography showed complete atelectasis of the right middle and lower lobes. The patient underwent emergent right upper lobectomy. The right upper lobe bronchus was separated with a scalpel, the hematoma was pulled out with forceps, and the bronchus subsequently sutured shut. The patient was discharged from the hospital uneventfully. CONCLUSIONS: We experienced a case of massive hemoptysis on the eighth day after TBB, which required emergency surgery due to persistent bleeding into the airway and airway obstruction during follow-up. Postoperative pneumonia and atelectasis could be prevented by manual removal of the residual hematoma.

Diagnostic utility of metabolic parameters on FDG PET/CT for lymph node metastasis in patients with cN2 non-small cell lung cancer.

BACKGROUND: The aim of this study was to assess the diagnostic utility of metabolic parameters on fluorine-18-fluoro-2-deoxy-D-glucose-positron emission tomography (FDG-PET)/computed tomography (CT) for predicting lymph node (LN) metastasis in patients with cN2 non-small cell lung cancer (NSCLC). METHODS: We retrospectively reviewed patients who underwent surgery for cN2 NSCLC between 2007 and 2020. Those who had clinically diagnosed positive hilar and mediastinal LNs by routine CT and PET/CT imaging were investigated. To measure the metabolic parameters of LNs, the data according to maximum standardized uptake value (SUVmax), metabolic tumor volume (MTV), total lesion glycolysis (TLG), and LN-to-primary tumor ratio of SUVmax (LPR) were examined. The diagnosis of each retrieved LN was confirmed based on histopathological examination of surgical tissue specimens. Receiver operating characteristics (ROC) curves with area under the curve (AUC) calculations and multivariate analysis by logistic regression were performed. RESULTS: Forty-five patients with 84 clinically diagnosed positive hilar or mediastinal LNs were enrolled in the present study. Of the 84 LNs, 63 LNs were pathologically proven as positive (75%). The SUVmax, MTV, TLG, and LPR of LN metastasis were significantly higher than those of benign nodes. In the ROC analysis, the AUC value of LPR [AUC, 0.776; 95% confidence interval (CI), 0.640-0.913] was higher than that of LN SUVmax (AUC, 0.753; 95% CI, 0.626-0.880) or LN TLG3.5 (AUC, 0.746; 95% CI, 0.607-0.885). Using the optimal LPR cutoff value of 0.47, the sensitivity, specificity, positive predictive value, negative predictive value, and accuracy were 84.1, 66.7, 88.3, 58.3, and 79.8%, respectively. Multivariate analysis by logistic regression showed that LPR was an independent predictor for LN metastasis (odds ratio, 6.45; 95% CI, 1.785-23.301; P = 0.004). In the subgroup analysis of adenocarcinoma patients (n = 18; 32 LNs), TLG3.5 was a better predictor (AUC, 0.816; 95% CI, 0.639-0.985) than LPR (AUC, 0.792; 95% CI, 0.599-0.986) or LN SUVmax (AUC, 0.792; 95% CI, 0.625-0.959). CONCLUSIONS: Our findings suggest that LPR on FDG-PET is a useful predictor for LN metastasis in patients with cN2 NSCLC. TLG can be a good predictor for LN metastasis in patients with adenocarcinoma.

Lessons learned from hybrid surgery with preoperative coil embolization for an aberrant artery in pulmonary sequestration.

BACKGROUND: The optimal management of an aberrant artery in pulmonary sequestration (PS) is controversial. Several studies have shown that hybrid surgery with preoperative coil embolization for an aberrant artery and surgical resection of the sequestrated lung is effective. However, there are no clear indications for the procedure. CASE PRESENTATION: A 68-year-old woman without any complaints was diagnosed with right intralobar PS, which was supplied by an aberrant artery from the thoracic aorta, via computed tomography performed during a medical examination. In addition, lung adenocarcinoma was detected over the border between the right upper and middle lobes. Preoperative coil embolization was performed by an interventional radiologist the day before surgery to decrease the risk of severe intraoperative hemorrhage. On the following day, bi-lobectomy of the right upper and middle lobes for lung adenocarcinoma with systemic lymph node dissection and segmentectomy of the sequestrated lung with thoracotomy was performed. Although no active hemorrhage was observed during surgery, the aberrant artery was challenging to dissect using an energy device due to the presence of an intravascular coil. Eventually, the coil stump was exposed, and it was cut with scissors. The postoperative course was uneventful. CONCLUSIONS: We reported the pitfall of the hybrid surgery for intralobar PS. Preoperative coil embolization can prevent fatal intraoperative hemorrhage. If embolization is performed using a coil for an aberrant artery supplied from the thoracic aorta, where and how to dissect the aberrant artery should be cautiously determined based on preoperative images, with consideration of the presence of an intravascular coil.

＜Editors' Choice＞ Learning curve of robotic lobectomy for lung malignancies by certified thoracic surgeons.

Video-assisted thoracic surgery (VATS) has become widespread in the last 20 years, followed by robot-assisted thoracic surgery (RATS). Few studies compared the learning curve between RATS lobectomy and conventional VATS. This study included 79 RATS lobectomy cases performed in our hospital from November 2015 to October 2019. To estimate the required number for learning, the cumulative sum method, which is to plot a value obtained by sequentially accumulating a difference from a mean value was applied. As a result, the median total operative time and the median console time for all cases were 167 minutes and 138 minutes, respectively. Firstly, for our team, 28 cases were estimated to be required for learning curve for RATS lobectomy. For individual, each surgeon might be learned in only 5 to 6 cases. By contrast, the number of cases for learning VATS lobectomy which was underwent by a 'single' surgeon from 2009 was estimated to be 35 cases. The time to dock from start operation (median 14 minutes) reached plateau in 18 cases, but the time after rollout was median of 18 minutes and there was no significant change from the beginning. In conclusion, RATS lobectomy might be a technique that could be learned in a small number of cases compared to VATS. The results of this study might be helpful for certified surgeons who tried to get started with RATS and for establishing a learning program.

Subgel-phase formation of membranes of ether-linked phosphatidylcholines.

The formation of subgel (so-called hydrated crystal) phase of membranes of ether-linked phospholipids, dialkylphosphatidylcholines containing linear saturated alkyl chain (Cn = 14, 16 and 18), was examined under atmospheric and high pressure. The results of differential scanning calorimetry in 50 wt% aqueous ethylene glycol solution and water showed that these PC membranes undergo the subtransition from the subgel phase to the gel phase at a low temperature with or without the thermal pretreatment of lipid samples called annealing. The subtransition in water was clearly observed by light-transmittance measurements under high pressure and the transition temperature increased by applying pressure. The temperature-pressure phase diagrams and the thermodynamic quantities of the subtransition were obtained from the phase-transition data and compared with those of membranes of ester-linked phospholipids, diacylphosphatidylcholines. The phase diagrams indicated that all gel phases of the ether-linked PC membranes exist as stable phases while parts of the gel phases of the ester-linked PC membranes are metastable. The subtransition temperatures of the ether-linked PC membranes were lower than those of the ester-linked PC membranes by more than 10 °C and the corresponding thermodynamic quantities were extremely small. Further, it was revealed by high-pressure fluorometry that the difference in subgel phase between ether- and ester-linked PC membranes results from their phase structures: the nonbilayer interdigitated structure is maintained after the conversion from the gel phase to the subgel phase in the ether-linked PC membranes whereas the ester-linked PC membranes form the bilayer subgel phase with staggered structure.

Membrane fusion of phospholipid bilayers under high pressure: Spherical and irreversible growth of giant vesicles.

Membrane fusion of giant vesicles (GVs) for binary bilayers of unsaturated phospholipids, dioleoylphosphatidyl-ethanolamine (DOPE) having an ability to promote membrane fusion, and its homolog dioleoylphosphatidylcholine (DOPC) having an ability to form GV, was investigated under atmospheric and high pressure. While DOPC formed GVs in the presence of inorganic salts with a multivalent metal ion under atmospheric pressure, an equimolar mixture of DOPE and DOPC formed GVs both in the absence and the presence of LaCl3. We examined the change in size and shape of the GVs of this binary mixture in the absence and presence of LaCl3 as a function of time under atmospheric and high pressure. The size and shape of the GVs in the absence of LaCl3 under atmospheric and high pressure and those in the presence of LaCl3 under atmospheric pressure hardly changed with time. By contrast, the GV in the presence of LaCl3 under high pressure gradually changed in the size and shape with time on a time scale of several hours. Namely, the GV became larger than the original GV due to accelerated membrane fusion and its shape became more spherical. This pressure-induced membrane fusion was completely irreversible, and the growth rate was correlated with the applied pressure. The reason for the GV growth by applying pressure was considered on the basis of thermodynamic phase diagrams. We concluded that the growth is attributable to a closer packing of lipid molecules in the bilayer resulting from their preference of smaller volumes under high pressure. Furthermore, the molecular mechanism of the pressure-induced membrane fusion was explored by observing the fusion of two GVs with almost the same size. From their morphological changes, we revealed that the fusion is caused by the actions of Laplace and osmotic pressure.