Durability of pulmonary vein isolation following cryoballoon ablation: lessons from a large series of repeat ablation procedures

Funding Acknowledgements

Type of funding sources: None.

Background

The cryoballoon technology has been widely proven to be effective in achieving acute pulmonary vein (PV) isolation and favorable clinical outcome. To date, little information is still available about occurrence of late PV reconnection after cryoballoon ablation.

Purpose

To assess the rate of durable PV isolation following cryoballoon ablation of atrial fibrillation in the setting of repeat procedures.

Methods and Results

A total of 154 consecutive patients (90 male, 58.4%; mean age 60.6±12.6 years) underwent a repeat procedure, after a mean 21.5±12.4 months (median 14 months), after index ablation using the 28-mm second-generation cryoballoon. All repeat ablations were performed using a 3-dimensional electro-anatomical mapping system. Among all 590 PVs, including 26 left common ostiums (LCOs), 99 (16.8%) showed a PV reconnection in 86 patients (1.15 per patient). Persistent PV isolation could be documented in 491 of 590 PVs (83.2%). In 68 of 154 patients (44%), all PVs were electrically isolated. In the multivariable analysis, balloon nadir temperature (p<0.01) and time to PV isolation (P=0.02) independently predicted late PV reconnection.

Conclusions

The rate of late PV reconnection after second-generation cryoballoon ablation was low (1.15 PVs/patient). Globally, the rate of durable PV isolation assessed during repeat procedures was 83.2%. The balloon nadir temperature and faster time to isolation were independently associated with durable PV isolation.

Comparison between oral procainamide and mexiletine for the treatment of recurrent and refractory ventricular tachyarrhythmias

Funding Acknowledgements

Type of funding sources: None.

Background

The antiarrhythmic therapy of recurrent ventricular arrhythmias in patients having undergone catheter ablation and in whom amiodarone and/or beta blockers were ineffective or contraindicated, is a controversial issue.

Purpose

The present study sought to compare the efficacy and tolerability of oral procainamide and mexiletine in patients with recurrent ventricular arrhythmias, when the standard therapy strategy failed.

Methods

All patients with an implantable cardioverter defibrillator (ICD) treated with oral procainamide or mexiletine for recurrent ventricular tachycardia (VT) or ventricular fibrillation (VF) in 2 Cardiology Divisions between January 2010 and January 2020 were enrolled. The patients were divided in group A (oral procainamide) and group B (mexiletine) and the 2 groups were compared to each other. The primary endpoint was the efficacy of therapy; the secondary endpoint was the discontinuation of therapy. All the events occurring during procainamide or mexiletine treatment were compared with a matched duration period before the initiation of the therapy. Antiarrhythmic therapy was considered effective when an ≥80% reduction of the sustained ventricular arrhythmias (SVA) burden recorded by the ICD was achieved.

Results

A total of 68 consecutive patients (61 males, 89.7%; mean age 74 ± 10 years) were included in this retrospective analysis. In 27 (39.7%) patients catheter ablation of VT was attempted before therapy initiation. A concomitant therapy with amiodarone was present in 25 (36.8%) patients. The mean dose of procainamide was 1207±487 mg/die. The mean dose of mexiletine was 576±66 mg/die. After a median follow-up of 19 months, 38 (56%) patients had a significant reduction in the SVA burden. After multivariable adjustment (Table 1), therapy with procainamide was independently associated with an almost 3-fold higher efficacy on VA suppression compared to mexiletine (HR 2.54, 95% CI 1.06-6.14, p=0.03). Similar results (HR 2.89, 95% CI 1.26-6.62, p=0.01) were found after adjustment using inverse probability weighting by a propensity score including age, gender, left ventricular ejection fraction, ischemic heart disease and concomitant amiodarone therapy. Only 3 patients (9%) treated with procainamide presented severe side effects (dyspnea or hypotension) requiring discontinuation of therapy against 6 patients (18%) treated with mexiletine who interrupted therapy because of severe side effects (p=0.47).

Conclusions

Compared to mexiletine, oral procainamide has a higher efficacy for the treatment of recurrent and refractory VAs and shows a good profile of tolerability

Table 1. Multivariable Cox Proportional Hazards Analysis of Baseline Covariates in Relation to effective VAs suppression.

P1027Left atrial hypertension invasively measured during pulmonary vein isolation as a predictor of atrial fibrillation recurrence

Background

The clinical role of left atrial hypertension (LAH) in patients with atrial fibrillation (AF) and its role as predictor in those undergoing pulmonary vein (PV) isolation is still unknown.

Purpose

The aim of the present study was to analyse the prevalence of LAH in patients with nonvalvular AF and preserved left ventricular ejection fraction having undergone PV isolation and its implication for AF catheter ablation.

Methods

Consecutive patients with drug resistant AF who underwent PV isolation at San Maurizio Regional Hospital of Bolzano (Italy) as index procedure were retrospectively included in this analysis. Left atrial hypertension was defined as the LA mean pressure >15 mm Hg.

Results

A total of 98 consecutive patients (71 males, 72%; mean age 60.3 ± 8.4 years) with drug resistant, non valvular AF and preserved LV ejection fraction having undergone index PV isolation procedure were included in the analysis. Eleven patients (11%) underwent radiofrequency ablation and 87 (89%) cryoballoon ablation. The mean LA pressure was 10.7 ± 4.5 mmHg; LAH occurred in 24 (24%) patients. At a mean follow up of 14.6 ± 7.1 months (median 14 months), the success rate without antiarrhythmic therapy was 71.4% (70/98; considering the blanking period). On multivariate analysis, LAH remained the only independent predictor of definitive AF recurrence (HR 3.02, 1.36-6.72, p = 0.007).

Conclusion

Left atrial hypertension was found in 24% of patients undergoing PV isolation and was found to be significantly related to both early and late AF recurrences.

Univariate and multivariate Cox regressi Univariate analysis Multivariate analysis Early Recurrence (during BP) HR 95%CI P value HR 95%CI P value Age (years) 1.06 1.02-1.10 0.005 1.05 1.00-1.09 0.03 LA volume (ml/m2) 1.02 1.00-1.05 0.04 1.02 1.00-1.05 0.05 LA hypertension 2.46 1.32-4.57 0.004 1.97 1.03-3.79 0.04 Recurrence after the BP HR 95%CI P value HR 95%CI P value Age (years) 1.05 1.00-1.11 0.04 1.04 0.98-1.09 0.15 LA hypertension 3.51 1.62-7.60 0.001 3.02 1.36-6.72 0.007 BP recurrence 1.83 0.84-3.99 0.13 AF atrial fibrillation. BMI: body mass index. LA: left atrium. CAD: coronary artery disease. BP: blanking period. HR: hazard ratio. CI: confidence intervals.

P2882Sustainable organization of a management model for CIED remote control: data from a single tertiary center

Introduction

The remote control (RC) of CIED has become necessary, though the human resources and technical facilities needed are limited. In most of Centers, the ratio of RC CIED /CIED with in-office follow up, is continuously increasing and is expected to reach the 100% of CIED remotely controlled.

We sought assess an organizational model based on available facilities and a long-term projection of RC data burden. Pacemakers, ICD and implantable loop recorders were considered.

Methods

The total population served by the Hospital area has been obtained (271.260 citizens), timed at December 31st 2014. By checking our Hospital data files, the total number of followed up CIED patients timed at January 1st 2011 (3995; 1.47% of all population), was compared with the same data timed at January 1st 2015 (3902; 1.43% of all population), in order to the check for the “stability” of that data over time.

At the analyzed time 1582/3902 (40,5%) of CIED were followed by RC.

We have then considered an yearly average of 465 CIEDs implanted/replaced (yearly implants 2012 to 2015) and excluded a roughly 10% of them because not provided of RC facilities (unwilling patients or CIED not RC “ready”); all the other patients were provided with RC. On these basis, we can assume a ratio of RC CIEDs /non-RC CIED, deemed to increase by 10 to 11% per year, to reach the break-even of 100% of RC CIEDs, in 2021 (projection).

The number of RC transmissions (Tx) have been gathered in 5 types of events (Fig. left upper).

The timing of RC patient managing from opening the CIED web site to complete patient file assessment (RC file analysis) performed by expert nurses, was arbitrarily calculated over a sample of 10 Tx per day in 3 different days.

Results

Of 3902 CIED patient, 1582 (40.5%) were RC followed up (3261 pacemakers, 594 ICDs and 47 implantable loop recorder); the CIED brands were represented as follows: Medtronic 685 (43.3%); St. Jude 180 (11.4%), Boston Sc. 330 (20.8%), Biotronik 318 (20.1%) and Livanova (previously SorinGroup) 69 (4.4%).

During the year 2015 we received a total number of 10396 Tx: 128 (1.2%) red alert; 1944 (18.6%) yellow alert, 141 (1.3%) atrial fibrillation; 403 (3.9%) lost Tx (disconnected transmitters or un-compliant patients for remote interrogation) and 7780 (75%) Tx “OK” with NO events. (Fig. right upper).

The projection model at 2021 with 100% RC patients (break-even) shows a total 25990 Tx: 320 red alert; 1944 yellow alert, 352 atrial fibrillation; 1007 lost Tx and 19459 Tx “OK”. The 2021 monthly Tx would be 2320 (26 red alert; 405 yellow alert, 29 atrial fibrillation; 91 lost Tx and 1769 (75%) Tx “OK”) (Fig. both lower panels)

The RC file analysis was roughly calculated around 3 minutes (116 hours/month); 5.8 hours/business day (Monday–Friday).

Conclusion

The rate of RC followed up CIEDs will inexorably increase by time. The projection management model presented could help to build a sustainable organization.

P1915Time to freeze - An updated meta-analysis on the efficacy and safety of cryoballoon versus radiofrequency ablation for atrial fibrillation

Background and aim

Pulmonary vein isolation (PVI) is the cornerstone of atrial fibrillation (AF) ablation. Its efficacy to prevent recurrent arrhythmias in patients nonresponsive to antiarrhythmic drugs is proven. This procedure has a higher efficacy rate in patients with paroxysmal AF (PAF) compared with persistent AF (sustained AF - SAF). Radiofrequency (RF) ablation represents a standard of care for PVI, while, cryoballoon (CB) ablation has emerged as a valid alternative therapy. The aim of the present meta-analysis was to explore the comparative efficacy, and safety of CB compared with RF ablation for AF.

Methods

We searched PubMed and EMBASE for studies that investigated the comparative efficacy and safety of CB versus RF ablation for AF. The efficacy outcome was AF recurrence after the procedure. The safety outcomes were: incidence of pericardial effusion or cardiac tamponade, permanent phrenic nerve palsy, transient phrenic nerve palsy, vascular complications and major bleedings. The performance outcomes were: procedural time and fluoroscopy time. Random-effects Risk Ratios (RRs) were estimated using a DerSimonian-Laird model. Two subgroup sensitivity analyses were performed to stratify the result on the efficacy outcome according to type of AF (PAF versus SAF) and study design (randomized clinical trial (RCT) versus observational study (OS)).

Results

12 RCT and 34 OS were included in the analysis (n=13103). Mean follow-up was 14±6 months. 37 studies included only patients with PAF, while, 2 studies included only patients with SAF and the remaining 7 studies included both patients with SAF or PAF. Overall, CB ablation reduced the incidence of AF recurrence compared with RF ablation (RR 0.85; 95% CI 0.77–0.95; P=0.002 - Figure). However, this reduction was not consistent in the RCT subgroup (RR 0.90; 95% CI 0.72–1.13) and it was marginally non-significant in the SAF subgroup (RR 0.76; 95% CI 0.57–1.01). Regarding the safety outcomes, although CB had a significantly higher rate of transient nerve palsy compared with RF procedure (RR 7.46; 95% CI 4.67–11.90) this difference became non-significant when considering permanent phrenic nerve palsy (RR 1.24; 95% CI 0.66–2.34). Moreover, CB was related to a lower incidence of pericardial effusion or cardiac tamponade compared with RF (RR 0.51; 95% CI 0.37–0.69) and there was no significant difference in vascular complications or major bleedings between the two strategies. Focusing on performance outcomes, CB ablation had a shorter procedural time compared with RF (mean difference −20 minutes; 95% CI −30 to −10; P<0.001); whereas, there was no significant difference in fluoroscopy time between the two.

CB vs. RF in preventing AF recurrence

Conclusions

This large study level meta-analysis demonstrates that CB is at least as effective as RF ablation in preventing arrhythmic recurrence both in patients with PAF and SAF. Moreover, our study suggests that CB has a safer profile and shorter procedural time compared with RF ablation.

Interaction of tumor cells with vascular endothelia: role of platelet-activating factor

We investigated whether tumor cell/endothelia interaction can be influenced by platelet-activating factor (PAF, 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine), a lipid mediator that promotes adhesiveness and extravasation of leukocytes in the inflammatory reaction. We found that the PAF receptor antagonist WEB 2086 prevents adhesion of melanoma Hs294T and colon carcinoma LS180 lines to IL-1-stimulated endothelial cells. Moreover, PAF stimulated the adhesiveness of Hs294T and LS180 cells to VCAM-1 and E- selectin, respectively, in an artificial model consisting of recombinant adhesive proteins bound to protein A-coated substrata. Thus, tumoral and not endothelial cell surface seems to be involved in the PAF-mediated enhancement of tumor cell adhesiveness to IL-1-activated endothelia. This observation is supported by the finding that Hs294T and LS180 cells express high affinity and functionally active receptors for PAF. By using specific inhibitors, we found that PAF-induced enhancement of cell adhesiveness was mediated by G-protein activation and protein tyrosine phosphorylation. In addition, protein tyrosine phosphorylation was observed in Hs294T and LS180 cells stimulated by PAF. In conclusion, we demonstrated that PAF-mediated activation of tumor cells enhances their adhesiveness to IL-1-stimulated vascular endothelia.

Biological properties associated with the enhanced lung-colonizing potential in a B16 murine melanoma line grown in a medium conditioned by syngeneic Corynebacterium parvum-elicited macrophages

A previous study by our laboratory showed that the peritoneal murine Corynebacterium parnum-elicited macrophages released into their growth medium an activity which enhanced the ability of B16-F10 melanoma cells to form experimental metastases in the lung of syngeneic mice. In the present study, we used a clone of B16-F10 line (F10-M3 cells) to investigate whether the increase in lung-colonizing potential due to the pro-clonogenic activity released by C. parvum-elicited macrophages was associated with biological properties characteristic of a metastatic phenotype. We have found that the pulmonary retention, growth rate in lung parenchyma, invasiveness through Matrigel, adhesiveness to IL-1-activated endothelium and MHC class I expression were increased in F10-M3 cells stimulated by the macrophage pro-clonogenic activity. By using an in vitro experimental protocol, the enhancement of lung-colonizing potential in the stimulated melanoma cells turned out to be a transient phenomenon as was the increase of invasiveness through Matrigel and the higher expression of MHC class I antigens. In conclusion, the melanoma cells stimulated by the pro-clonogenic activity released by C. parvum-elicited macrophages showed changes in biological parameters which are relevant to metastatic diffusion. These changes appeared as a temporary phenomenon which sustains the view that the metastatic phenotype represents a transient biological character influenced by host factors.

The change in leukotrienes and lipoxins in activated mouse peritoneal macrophages

The aim of this study was to investigate to what extent the generation of leukotrienes (LTs) and lipoxins (LXs) was affected by the expression of definite levels of macrophage activation. We used a system of murine peritoneal macrophages at different states of activation consisting in resident macrophages and FCS-, thioglycollate- or Corynebacterium parvum-elicited macrophages. The profile of lipoxygenase metabolites in resident macrophages was characterized by the presence of high levels of 12-HETE, followed by 15-HETE, 5-HETE, LTB(4) and 6-trans-LTB(4), 6-trans-12-epi-LTB(4). A comparable pattern was also found in FCS-elicited macrophages which appeared not to be responsive to the challenge with interferon gamma plus LPS, as measured by the generation of NO and tumor necrosis factor alpha. Resident as well as FCS-elicited macrophages also generated appreciable quantities of LXs (A(4) and B(4)). Thioglycollate-elicited macrophages, which expressed a state of 'responsive' macrophages, showed a block of the LT and LX synthesis. This block was also present in C. parvum-elicited macrophages which expressed a fully 'activated' phenotype, reflected by their capacity of releasing NO and tumor necrosis factor alpha even though they were not challenged. These results provide the first evidence that the level of 'responsive' as well as 'activated' macrophages was associated with of a simultaneous block of LTB(4) and LXs.

Lipid characteristics in metastatic cells

Interest in lipid characteristics of metastatic cells was aroused by the consideration that the various lipid components of cell membranes influence a broad spectrum of cell surface biological functions which are involved in different steps of the metastatic cascade. Correlation between invasive properties and characteristics of cell surface components has been appropriately studied in a limited number of metastatic cell systems isolated by in vivo and in vitro procedures. The major findings of this study have been reported in this review. Among membrane lipid components, glycolipids and phospholipids appeared particularly affected in tumor cells which acquired a metastatic phenotype. In fact, the reduction of complex gangliosides typical of transformed cell lines was even more evident in a highly metastatic variant selected from RSV-transformed murine fibroblasts. The reduction of complex gangliosides, mainly GD1a, particularly affected the adhesion sites of this variant. In a fibrosarcoma line, T3 cells, the metastatic properties appeared to be correlated with the content and cell surface expression of Gb3ose, a glycolipid characteristic of this line. Moreover, a particularly high level of ether-linked lipids was found in high metastatic variants isolated from murine melanoma and fibrosarcoma lines, as well as in human mammary carcinomas. The findings considered in this review are discussed for their possible relevance to the invasive properties of metastatic cells.

Diminution of the development of experimental metastases produced by murine metastatic lines in essential fatty acid-deficient host mice

In a previous study we found that the capacity for spontaneous metastases of tumors developed after subcutaneous transplantation of RSV-transformed Balb/c 3T3 cells was reduced in essential fatty acids (EFA)-deficient host animals. In the present study, we have extended our investigation by considering the requirement of EFA for the formation of lung colonies obtained by i.v. injection of two metastatic murine cell lines of different origin: (1) T3 cells, a highly metastatic cell line isolated from a fibrosarcoma, and (2) the F10 variant of B16 melanoma (B16-F10 cells). We found that EFA deficiency reduces the lung colonization of both T3 cells and B16-F10 cells without affecting the retention of tumor cells in the lung. NK cells did not seem to be involved in the diminution of lung colonization in EFA-deficient animals. Furthermore, by examining histologically the lung parenchyma at successive intervals after tumor cell injection, we found that, in comparison with control mice, EFA-deficient animals had fewer lung colonies and a prevalence of smaller microcolonies during the entire period of observation. This led us to conclude that the diminution in development of tumor colonies in the lungs of EFA-deficient host animals was related to a reduced growth rate of tumor cells at this site.

Inverse relationship between invasiveness and differentiative capacity in different human neuroblastoma cell lines

In order to clarify the relationship between invasiveness and loss of cellular differentiation in tumor cells, we studied the invasive properties on Matrigel of (a) a series of clones we isolated from human neuroblastoma LaN1 and Platt cell lines inducible to differentiation by adhesion on fibronectin, and (b) SY5Y human neuroblastoma cells inducible to differentiation by retinoic acid. We found that, regardless of the parental line, the more differentiated clones were scarcely invasive, while the less differentiated clones showed a higher degree of invasiveness. Differences in invasiveness between differentiated and non-differentiated neuroblastoma clones did not reflect differences in adhesiveness to laminin, the major component of Matrigel. The retinoic acid-sensitive SY5Y human neuroblastoma cells also reduced their invasiveness on Matrigel after differentiation induced by growth in media supplemented with retinoic acid. These results point to an inverse relationship between differentiative properties and invasiveness in human neuroblastoma cell lines.

Enhancement of lung-colonizing potential of murine tumor cell lines co-cultivated with activated macrophages

In order to explore the influence of activated macrophages on tumor cells, we cultured a series of weakly metastatic clones isolated from the murine T3 fibrosarcoma line (T3 clones) and the B16-F10 melanoma cells on feeder layers of C. parvum- or thioglycollate-elicited macrophages, or 'resident' (unstimulated) macrophages. Co-cultivation with C. parvum-elicited macrophages, but not with resident macrophages, induced an increase of the lung-colonizing potential of T3 clones and B16-F10 cells. An enhancement of lung-colonizing potential was also found in tumor cells grown in media conditioned by C. parvum-elicited macrophages. Thioglycollate-elicited macrophages also generated a pro-clonogenic activity which was however effective only on T3 clones but not on B16-F10 cells. The increase in the lung-colonizing potential of tumor cells stimulated by activated macrophages was retained to some degree after subcultivation in tissue culture medium or transplantation into syngeneic animals. In conclusion, our data support the notion that macrophages at different states of activation may enhance lung colonization of tumor cells by inducing a partially stable change of phenotype.

An inward rectifier K+ current modulates in neuroblastoma cells the tyrosine phosphorylation of the pp125FAK and associated proteins: role in neuritogenesis

The relationships between the integrin-mediated activation of inward rectifyier K+ channels (KIR), the phosphorylation of pp125FAK and the rescue of neuritogenesis were studied in 41A3 mouse neuroblastoma cells. Neuritogenesis, elicited by adhesion to FN-enriched substrata, was reversibly impaired by pretreating these cells with the tyrosine kinase inhibitor Herbimycin A. This impairment mimicked that operated by Cs+ ions, which selectively inhibited the integrin-mediated activation of KIR channels. Various phosphotyrosine containing cellular proteins underwent a marked increase upon cell adhesion to FN-coated dishes. This increase was significantly reduced by Cs+ addition. Immunoprecipitation of pp125FAK revealed that the phosphorylation of this kinase and several associated proteins was significantly and reversibly inhibited by Cs+, indicating that integrin-mediated activation of KIR channels is a limiting step upstream to the phosphorylation of pp125FAK in the commitment to neuritogenesis.

Integrin-mediated neurite outgrowth in neuroblastoma cells depends on the activation of potassium channels

Electrical signals elicited by integrin interaction with ECM components and their role in neurite outgrowth were studied in two clones (N1 and N7) isolated from 41A3 murine neuroblastoma cell line. Although the two clones similarly adhered to fibronectin (FN) and vitronectin (VN), this adhesion induced neurite outgrowth in N1 but not in N7 cells. Patch clamp recordings in whole cell configuration showed that, upon adhesion to FN or VN but not to platelet factor 4 (PF4), N1 cells undergo a marked (approximately equal to 20 mV) hyperpolarization of the resting potential (Vrest) that occurred within the first 20 min after cell contact with ECM, and persisted for approximately 1 h before reverting to the time zero values. This hyperpolarization was totally absent in N7 cells. A detailed analysis of the molecular mechanisms involved in N1 and N7 cell adhesion to ECM substrata was performed by using antibodies raised against the FN receptor and synthetic peptides variously competing with the FN or VN binding to integrin receptor (GRGDSP and GRGESP). Antibodies, as well as GRGDSP, abolished adhesion of N1 and N7 clones to FN and VN, revealing a similar implication of integrins in the adhesion of these clones to the ECM proteins. However, these anti-adhesive treatments, while ineffective on Vrest of N7 cells, abolished in N1 cells the FN- or VN-induced hyperpolarization and neurite outgrowth, that appeared therefore strictly associated and integrin-mediated phenomena. The nature of this association was deepened through a comparative analysis of the integrin profiles and the ion channels of N1 and N7 cells. The integrin immunoprecipitation profile resulted very similarly in the two clones, with only minor differences concerning the alpha V containing complexes. Both clones possessed Ca2+ and K+ delayed rectifier (KDR) channels, while only N1 cells were endowed with inward rectifier K+ (KIR) channels. The latter governed the Vrest, and, unlike KDR channels, were blocked by Ba2+ and Cs+. By moving patched cells in contact with FN-coated beads, it was shown that KIR channel activation was responsible for the FN-mediated hyperpolarization of Vrest. Treatment with Pertuxis toxin (PTX) abolished this hyperpolarization and neurite outgrowth, indicating that a G protein is interposed between integrins and KIR channels and that the activation of these channels is required for neuritogenesis. In fact, the block of KIR channels by Cs+ abolished both hyperpolarization and neurite outgrowth, provided that the cation was supplied during the first two hours after N1 cell contact with FN.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of phosphatidylcholine structure on the adenylate cyclase activity of a murine fibroblast cell line

To determine which structural characteristics of membrane phospholipids influence adenylate cyclase activity, we measured basal and sodium fluoride-or forskolin-stimulated activity in a murine fibroblast cell line, i.e., Balb/c3T3 cells grown in media supplemented with fetal calf serum (FCS), lipid-depleted FCS (LD-FCS) or LD-FCS complexed with different phosphatidylcholine (PC) molecular species. Cells grown in the presence of LD-FCS showed a substantial decrease in their basal and NaF-stimulated adenylate cyclase activities; however, their forskolin-stimulated activity was not altered, suggesting that the enzyme's catalytic site is not affected by changes in membrane lipids. Media supplemented with different LD-FCS/PC complexes were shown to prevent the LD-FCS-mediated reduction of basal and NaF-stimulated adenylate cyclase activity to different extents. Addition of cis-9-16:1, cis-9-18:1/cis-9-18:1 or cis-9-18:1/cis-9,12-18:2 sn-glycerophosphocholine (GPC) completely restored adenylate cyclase activity, while cis-11-18:1/cis-11-18:1 GPC was not effective and only a partial recovery was observed with 16:0/16:0, 16:0/cis-9-18:1 and trans-9-18:1 GPC. Considering the structural features of these seven PC molecular species, the findings suggest that an optimal lipid environment is conferred to the enzyme by the presence of two cis double bonds, each located in delta 9 position of the PC acyl chains. The limited effect of cis-9-16:1/cis-9-18:1 GPC and cis-9-18:1/cis-9-16:1 GPC suggests that an equal length of the terminal hydrocarbon chains extending beyond the delta 9 double bonds is also important.(ABSTRACT TRUNCATED AT 250 WORDS)

Complex gangliosides modulate the integrin-mediated adhesion in a rat hepatoma cell line

In this study, we investigated whether complex gangliosides influence cell adhesion by modulating the activity of integrin receptors. Our experimental model was represented by CMH5123 cells, a line of neoplastic hepatocytes derived from the minimal deviation Morris hepatoma 5123c of the rat, which adhered to substrata coated with fetal calf serum (FCS) by an integrin-mediated mechanism, being vitronectin the specific serum protein which sustained cell adhesion. We found that ganglioside depletion, obtained by inhibiting complex ganglioside biosynthesis, was accompanied by a reduction of cell adhesiveness to FCS-coated substrata. Integrins appeared to mediate the effect of ganglioside depletion on cell adhesiveness. In fact, sensitivity to the integrin inhibitor GRGDSPC peptide was ten times higher in ganglioside-depleted cells compared to control cells. Moreover, growth of ganglioside-depleted CMH5123 cells in media supplemented with complex gangliosides restored the cell sensitivity to the integrin inhibitor to the same level as that found in control cells. Furthermore, ganglioside depletion of CMH5123 cells decreased the affinity of vitronectin receptors for vitronectin without modifying their number, affinity of vitronectin receptors was re-established in ganglioside-depleted cells by supplementing their growth media with complex gangliosides. In conclusion, these results support the participation of gangliosides to cell adhesion as modulators of integrin receptors.

Use of N-acetylpsychosine as internal standard for quantitative high-performance liquid chromatographic analysis of glycosphingolipids

The use of N-acetylpsychosine as an internal standard for the quantitative high-performance liquid chromatography (HPLC) of p-nitrobenzoyl derivatives of glycosphingolipids is described. It is suitable because the chromogen reacts on equimolar basis with both N-acetylpsychosine and sample glycosphingolipids. The use of N-acetylpsychosine as an internal standard was validated by determining the glycosphingolipid content of a system of metastatic variants selected from a murine fibrosarcoma line (T3 cells). Reproducible results were obtained throughout several quantitative analyses of cellular glycosphingolipids and it was possible to determine the glycosphingolipid content of as few as 5 x 10(6) cells.

Lectin reactivity of murine fibrosarcoma lines with a different metastatic potential

Lectins are suitable tools for investigating the glycoconjugate characteristics of metastatic cells. In the present study, we investigated whether there were differences between high metastatic T3 cells and a low metastatic isolate in their reactivities to several lectins specific for galactosyl and sialyl groups. Analysis of reactivity of the two cell lines to wheat germ agglutinin revealed a complex pattern. In fact, T3 cells had high-affinity, neuraminidase-resistant as well as low-affinity, neuraminidase-sensitive receptors. Instead, the low metastatic isolate showed only high-affinity receptors, both neuraminidase-resistant and neuraminidase-sensitive The two cell lines reacted similarly to galactose-specific lectins. These findings indicate that sialyl groups, rather than galactosyl groups, affect the metastatic behavior of our cell system.

Role of glycolipids in the metastatic process: characteristics of neutral glycolipids in clones with different metastatic potentials isolated from a murine fibrosarcoma cell line

We investigated whether metastatic phenotype is associated with a characteristic glycolipid pattern. For this study, we developed a system of variants with different metastatic potentials that we isolated from the highly metastatic T3 murine fibrosarcoma line by culture in 0.3% agar or on plastic. The glycolipid profiles of T3 cells and of their highly metastatic isolates were characterized by a high level of globotriaosylceramide (Gb3ose). On the other hand, Gb3ose was reduced in a weakly metastatic clone isolated from T3 cells. A reduced level of Gb3ose was also found in a weakly metastatic subclone isolated from a highly metastatic T3 clone. Propagation of this subclone led to the emergence of a series of variants which expressed a high metastatic potential together with a high Gb3ose level. We also observed that Gb3ose was 10 times more prevalent on the cell surface in T3 cells than in a weakly metastatic clone. On the whole, these findings indicate that, in our system of metastatic cells, a high Gb3ose level correlates with metastatic phenotype. It is possible that the highly exposed Gb3ose in metastatic cells is relevant to the metastatic process in view of the role played by the unique molecular structure of this glycolipid in other models of cell-to-cell interaction.

Lipid characteristics of RSV-transformed Balb/c 3T3 cell lines with different spontaneous metastatic potentials

To determine whether a metastatic phenotype may be correlated with a characteristic lipid pattern, we compared the lipid composition of low metastasizing Balb/c 3T3 cells transformed by the B77 strain of Rous sarcoma virus (B77-3T3 cells) with that of a subclone isolated by growth in 0.6% agar, the B77-AA6 cells, which exhibit a high capacity for spontaneous metastasis. B77-3T3 cells revealed characteristics in their lipid composition common to other systems of transformed cells, i.e., an accumulation of ether-linked lipids, a reduction of the more complex gangliosides, an increase of oleic acid (18:1) and a decrease of arachidonic (20:4) and C22 polyunsaturated fatty acids in phospholipids. High metastatic B77-AA6 cells showed: a) an even more marked decrease of complex gangliosides; b) a more pronounced increase of 18:1 and decrease of 20:4 and 22 polyunsaturated fatty acids in certain phospholipid classes; and c) a higher percentage of alkyl-acyl subfractions in both phosphatidylcholine and phosphatidylethanolamine than B77-3T3 cells. Comparing the data for other systems of metastatic cells with those of lipid studies of spontaneously metastasizing B77-AA6 cell system leads us to conclude that the metastatic phenotype is characterized by a change in ether-linked lipids, rather than in fatty acids.

Morphological characteristics and ganglioside composition of substratum adhesion sites in a hepatoma cell line (CMH5123 cells) during different phases of growth

This study compares the ganglioside composition of tissue culture substrate-attached material (SAM) with that of cell bodies in a line of transformed hepatocytes derived from the minimal deviation Morris hepatoma 5123 c (CMH5123 cells). We examined both confluent cultures (late-phase cultures) and cells which were allowed to attach for only 3 h (early-phase cultures). We also determined to what extent ganglioside compositions of SAM and cell bodies from early- and late-phase cultures of CMH5123 cells are affected by the block of complex ganglioside biosynthesis induced by treatment with chelating agents (EGTA + EDTA). The morphological characteristics of SAM were monitored by scanning electron microscopy during the different steps of this study. In early-phase cultures, SAM was composed of fragments of filopodia and small vesicles probably representing newly formed substratum adhesion sites. In contrast, SAM of late-phase cultures was made up of large pools of membranous material resulting from the breakage of thick retraction fibers connecting the cell body with broad, mature adhesion sites. SAM of early-phase cultures yielded ganglioside profiles with a higher content of GM1 and GD1 a than those of cell bodies, while in late-phase cultures there was no difference between SAM and cell body gangliosides. When cells were grown in the presence of chelating agents, SAM of early-phase cultures was composed of vesicles and filopodial fragments similar to those found in early-phase cultures grown in regular media; these morphological features also appeared in SAM of confluent cultures (in contrast to the membranous material characteristic of late-phase cultures grown in regular media). In early-phase cultures grown in the presence of chelating agents, gangliosides of SAM were enriched in complex homologs relative to their content in cell bodies. These ganglioside characteristics were also found in SAM of confluent cultures grown in the presence of chelating agents, reflecting the presence of newly formed adhesion sites. On the basis of these results, we may conclude that the molecular assembly of newly formed adhesion sites implies the preferential distribution of several surface components involved in cell adhesion, including complex gangliosides.

Heparan sulfate proteoglycans of Ras-transformed 3T3 or neuroblastoma cells. Differing functions in adhesion on fibronectin

Initial studies described the significance of heparan sulfate proteoglycans of Balb/c 3T3 cells in their adhesion on fibronectin matrices, including their binding to multiple domains in FN, the importance of this binding in microfilament and close contact formation, and the cooperativity of both HS-PG and 140k glycoprotein integrin's binding to FN to achieve tight-focal contacts under cells. These analyses utilized model HS-binding proteins, such as platelet factor 4, and proteolytic fragments of FN with differing binding activities in both cell biological analyses of adhesion responses and in biochemical analyses of the HS-PG in the adhesion sites. In contrast, dermatan sulfate proteoglycans (DS-PG) inhibit 3T3 adhesion on FN but not on collagen; of special note is the discovery that certain integrin-binding fragments of FN also contain a third HS/DS-binding domain that is cryptic and that provides a more effective mechanism for inhibiting integrin: FN binding. Kirsten Ras oncogene-transformed 3T3 cells and their nude-mouse-derived primary or lung metastatic tumors are also being analyzed by similar approaches. HS-PGs in the adhesion sites of these tumor populations undergo extensive catabolism, resulting in alteration of their binding to FN affinity columns (and by implication alteration in adhesion responses of these tumor cells on FN matrices). Functions for HS-PG on the surface of neuronal cell derivatives, e.g., neuroblastoma cells derived from the neural crest of the embryo and potentially related in some ways to peripheral neurons, are also being explored. HS-binding fragments of FN or PF4 facilitate attachment and spreading of neuroblastoma cells but not neurite outgrowth, contrasting with the ability of dorsal root ganglion neurons to extend neurites on HS-binding substrata. The catabolism of HS-PG in neuroblastoma adhesion sites is minimal, indicating that this cannot be the explanation for incompetence in neurite extension. Neurite extension by neuroblastoma cells on FN results from three different and overlapping binding activities of non-PG receptors on the cell surface--RGDS-dependent binding to integrin, an RGDS-independent mechanism (perhaps a cell type-specific domain), and a ganglioside-dependent process. However, these neurite-extending reactions can be modulated either by exogenous addition of proteoglycans acting in a "trans" manner with the cell surface or by endogenous HG-PG acting in a "cis" manner with one or more of these receptors.(ABSTRACT TRUNCATED AT 400 WORDS)

Multiple and alternative adhesive responses on defined substrata of an immortalized dorsal root neuron hybrid cell line

Attachment and neurite extension processes have been evaluated for an immortalized derivative cell of a rat dorsal root neuron after fusion with a mouse neuroblastoma cell (the clonal F11 hybrid cell line) and these processes compared with previous studies of neuroblastoma cells, since both cell types may be derived from the neural crest of the developing embryo. Biochemically defined substrata were provided by human plasma fibronectin (pFN), the heparan sulfate-binding protein platelet factor-4 (PF4), and the ganglioside GM1-binding protein cholera toxin B subunit (CTB). While some attachment of unsupplemented cells was noted on CTB substrata, GM1 supplementation permitted F11 cells to attach as well on CTB as on pFN or PF4. On PF4, very few neurite processes were observed while on pFN two morphologically distinct types of neurites could be identified: short, linear processes in a low percentage of cells resembling those of neuroblastoma cells and long, irregular and narrow processes in a higher percentage of cells resembling those of dorsal root neurons. On CTB, neurites of the latter class were even more prominent; however, cell bodies on CTB failed to spread by cytoplasmic extension as commonly observed in F11 cells on pFN and, to some extent, on PF4. The formation of both neurite classes on either pFN or CTB was completely inhibited by low concentrations of an RGDS (Arg-Gly-Asp-Ser) peptide in the medium of cultures, indicating the significance of pFN's binding to cell surface integrin or ganglioside GM1's possible interaction with integrin for mediating the differentiative process. In contrast, neurite formation of neuroblastoma cells is refractile to the soluble peptide as reported previously. Neurite extensions of F11 cells on either pFN or CTB were comparably sensitive to low concentrations of cytochalasin D, revealing the mediation of microfilament reorganization in these processes. Treatment of F11 cells with cycloheximide failed to inhibit neurite extension on pFN but did partially inhibit extension on CTB; this contrasts with the very high sensitivity of neurite formation by neuroblastoma cells on CTB substrata reported previously.(ABSTRACT TRUNCATED AT 400 WORDS)

Ganglioside-dependent adhesion events of human neuroblastoma cells regulated by the RGDS-dependent fibronectin receptor and proteoglycans

Human neuroblastoma cells (Platt and La-N1) adhere and extend neurites on a ganglioside GM1-binding substratum provided by cholera toxin B (CTB). These adhesive responses, similar to those on plasma fibronectin (pFN), require the mediation of one or more cell-surface proteins [G. Mugnai and L. A. Culp (1987) Exp. Cell Res. 169, 328]. The involvement of two pFN receptor molecules in ganglioside GM1-mediated responses on CTB have now been tested. In order to test the role of cellular FN binding to its glycoprotein receptor integrin, a soluble peptide containing the Arg-Gly-Asp-Ser (RGDS) sequence was added to the medium. It did not inhibit attachment on CTB but completely inhibited formation of neurites; in contrast, the RGDS peptide minimally inhibited attachment or neurite formation on pFN. Once formed, neurites on CTB became resistant to the peptide. In order to test the role of cell-surface heparan sulfate proteoglycan (HS-PG), two approaches were used. First, the HS-binding protein platelet factor-4 (PF4) was used to dilute CTB or pFN on the substratum or, alternatively, added to the medium. Diluting the substratum ligand with PF4 had no effects on attachment on either CTB or pFN. However, neurite formation on CTB was readily inhibited and on pFN partially inhibited; the effects of PF4 were far greater than a similar dilution with nonbinding albumin. When PF4 was added to the medium of cells, attachment on either substratum was unaffected as was neurite outgrowth on pFN, revealing differences in PF4's inhibition as the substratum-bound or medium-borne component. In contrast, PF4 in the medium at low concentrations (1 microgram/ml) was highly inhibitory for neurite formation on CTB. The second approach utilized the addition of bovine cartilage dermatan sulfate proteoglycan (DS-PG), shown to bind to pFN as well as to substratum-bound CTB by ELISA, or cartilage chondroitin sulfate/keratan sulfate proteoglycan (CS/KS-PG) to the substratum or to the medium. At low concentrations, DS-PG but not CS/KS-PG actually stimulated neurite formation on CTB while at higher concentrations DS-PG completely inhibited attachment and neurite formation. While DS-PG partially inhibited attachment on pFN, it had no effect on neurite formation of the attached cells. Neuroblastoma cells adhered to some extent to substrata coated only with DS-PG, indicating "receptors" for PGs that permit stable interaction.(ABSTRACT TRUNCATED AT 400 WORDS)

Modulation of matrix adhesive responses of human neuroblastoma cells by neighboring sequences in the fibronectins

Attachment and neurite extension have been measured when Platt or La-N1 human neuroblastoma cells respond to tissue culture substrata coated with a panel of complementary fragments from the individual chains of human plasma (pFN) or cellular fibronectins (cFN) purified from thermolysin digests. A 110-kD fragment (f110), which contains the Arg-Gly-Asp-Ser sequence (RGDS)-dependent cell-binding domain but no heparin-binding domains and whose sequences are shared in common by both the alpha- and beta-subunits of pFN, facilitated attachment of cells that approached the level observed with either intact pFN or the heparan sulfate-binding platelet factor-4 (PF4). This attachment on f110 was resistant to RGDS-containing peptide in the medium. Neurite outgrowth was also maximal on f110, and half of these neurites were also resistant to soluble RGDS peptide. Treatment of cells with glycosaminoglycan lyases failed to alter these responses on f110. Therefore, there is a second "cell-binding" domain in the sequences represented by f110 that is not RGDS- or heparan sulfate-dependent and that facilitates stable attachment and some neurite outgrowth; this domain appears to be conformation-dependent. Comparisons were also made between two larger fragments generated from the two subunits of pFN-f145 from the alpha-subunit and f155 from the beta-subunit--both of which contain the RGDS-dependent cell-binding domain and the COOH-terminal heparin-binding domain but which differ in the former's containing some IIICS sequence at its COOH terminus and the latter's having an additional type III homology unit. Heparin-binding fragments (with no RGDS activity) of f29 and f38, derived from f145 or f155 of pFN, respectively, and having the same differences in sequence, were also compared with f44 + 47 having the "extra domain" characteristic of cFN. Attachment on f145 was slightly sensitive to soluble RGDS peptide; attachment on f155 was much more sensitive. There were also differences in the percentage of cells with neurites on f145 vs. f155 but neurites on either fragment were completely sensitive to RGDS peptide. Mixing of f29, f38, or PF4 with f110 could not reconstitute the activities demonstrated in f145 or f155, demonstrating that covalently linked sequences are critical in modulating these responses. However, mixing of f44 + 47 from cFN with f110 from pFN increased the sensitivity to RGDS peptide.(ABSTRACT TRUNCATED AT 400 WORDS)

Lipid composition of cultured B16 melanoma cell variants with different lung-colonizing potential

Lipid components influence several cell surface properties that are critical in different stages of the metastatic process. In this study, we examined whether the different lung-colonizing potential of B16-F1 and B16-F10 melanoma cells could be related to a characteristic lipid profile. The lipid analyses, carried out on the same cell cultures used for the assay of lung-colonizing potential, revealed characteristics in the lipid composition of both B16-F1 and B16-F10 melanoma cells that are common to other systems of malignant cells: a high level of 18:1 associated with low proportions of polyunsaturated fatty acids in phospholipids, accumulation of ether-linked lipids and absence of complex gangliosides. The two B16 melanoma variants differed significantly only with respect to ether-linked lipids, due to a higher level of alkyl-PC in B16-F10 than in B16-F1.

Cooperativity of ganglioside-dependent with protein-dependent substratum adhesion and neurite extension of human neuroblastoma cells

The potential involvement of gangliosides in the adherence and neurite extension of human neuroblastoma cells (Platt and La-N1) was investigated on tissue culture substrata coated with the ganglioside GM1-binding protein, cholera toxin B (CTB) subunit, for comparison with similar processes on plasma fibronectin (pFN)-coated substrata. Cells attached with reduced efficiency on CTB substrata as compared with pFN substrata and required a much longer time to form neurite processes for a small percentage of cells on CTB. The specificity of these processes for GM1 binding was tested in a variety of ways. Supplementation of the cells with exogenous GM1, but not GD1a, identified a larger population of cells adherent on CTB (comparable to pFN-adherent cells) and dramatically increased the proportion of cells capable of forming neurites without reducing the time requirement. In ultrastructural studies using the scanning electron microscope (SEM) and immunofluorescence (IF) analyses to discriminate microtubule distributions, neurites of GM1-supplemented cells on CTB were virtually identical with pFN-adherent neurites, whereas unsupplemented cells on CTB generated processes with fine-structural differences. Treatment of cells during the GM1 supplementation period with cycloheximide completely abolished the ability of cells to generate neurites on CTB and decreased the adhesive capacity of cells as well; a similar treatment of cells had no adverse effect on adherence or neurite extension on pFN. The importance of one or more proteins in GM1-dependent processes was further confirmed by demonstrating the trypsin sensitivity of a cell surface component(s) required to achieve maximal attachment on CTB; in contrast, adherence and neurite extension on pFN were much more resistant to this treatment process. Therefore, these experiments demonstrate that certain cell surface gangliosides are capable of mediating adherence and neurite outgrowth of human neuroblastoma cells on a suitable ganglioside-binding substratum; this ganglioside dependence is cooperative with one or more cell surface proteins which can now be analysed. These results are discussed in light of the identification in ref. [16] (Exp cell res 169 (1987) 311) of a second 'cell-binding' domain on the pFN molecule competent for adherence and neurite extension of these neuroblastoma cells, as well as the potential role of pFN binding to a complex ganglioside on the surface of these neural tumor cells in these processes.

A second cell-binding domain on fibronectin (RGDS-independent) for neurite extension of human neuroblastoma cells

Human neuroblastoma cells (Platt and La-N1) have previously been shown to adhere and extend neurites on tissue-culture substrata coated with a 120K chymotryptic cell-binding fragment (CBF) of plasma fibronectin (pFN), a fragment which lacks heparan sulfate- and collagen-binding activities, and to adhere to--but not extend neurites on--substrata coated with the heparan sulfate (HS)-binding protein, platelet factor-4 (PF4) (Tobey et al., Exp Cell Res 158 (1985) 395 [3]). The mechanisms of these processes on CBF, on the intact pFN molecule, or on heparin-binding fragments of pFN have been tested using a heptapeptide (peptide A) containing the Arg-Gly-Asp-Ser (RGDS) sequence which recognizes a specific 'receptor' on the surface of a variety of cells or a control peptide with a single amino acid substitution. Adherence and neurite extension were completely inhibited on the 120K CBF by peptide A but not by control peptide; these results indicate that the RGDS-dependent 'receptor' is solely responsible for adhesive responses to the 120K CBF-containing region of the pFN molecule. When peptide A was added to cells on CBF which had already formed neurites to test reversibility, retraction of all neurite processes was induced by 1 h and cells eventually detached. In contrast, on intact pFN, peptide A had very limited effects on either initial adherence or neurite extension, revealing a second 'cell-binding' domain on the fibronectin molecule outside of the 120K region competent for neurite differentiation; addition of peptide A at later times to pFN-adherent, neurite-containing cells could induce only a small subset of neurites to retract, thus supporting evidence for the presence of this second domain. A second 'cell-binding' domain was further confirmed by quantitation of neurite outgrowth on these substrata and by analyses of cells on substrata coated with mixtures of CBF/PF4. When substrata coated with chymotrypsin-liberated HBF were tested in a similar fashion, adherence was rapid but neurite outgrowth required much longer times and was completely sensitive to RGDS peptides; supplementation of cells with the complex ganglioside GT1b could not induce RGDS-resistant neurites on heparin-binding fragments (HBF). These latter results indicate that neurite extension on HBF is a consequence of a low concentration of RGDS-dependent activity in HBF (but not to HS-binding activity as characterized by Tobey et al. [3]) and that the second 'cell-binding' domain is sensitive to chymotrypsin digestion of pFN during the liberation of HBF.(ABSTRACT TRUNCATED AT 400 WORDS)

Glycosphingolipids in detergent-insoluble substrate attachment matrix (DISAM) prepared from substrate attachment material (SAM). Their possible role in regulating cell adhesion

The glycosphingolipids isolated from the detergent-insoluble material (DIM) of whole cells as well as from a similar detergent-insoluble substrate attachment matrix (DISAM) have been investigated in comparison with the glycosphingolipids of whole cells. The proportion of glycolipids in the total lipid extract was enriched in the DISAM as well as DIM fractions as compared to whole cells. The ratio of ganglioside (GM3) to neutral glycolipids was also higher in the DISAM fractions than in whole cells. The radioactivity incorporated into DISAM glycolipids of BHK cells, metabolically labeled with radioactive glucosamine, was greater in confluent cells than in sparsely growing cells; however, label incorporation into glycolipids of the DISAM fraction of BHKpy cells was 2-3-fold higher than that of confluent BHK cells, although the chemical quantity of GM3 in whole cells was much lower in BHKpy cells than in BHK cells. In order to confirm the enhanced label in DISAM glycolipids of BHKpy cells by other procedures, the labeled cells were detached by EGTA, washed, and reattached on plates. The amount of label in DISAM glycolipids of the reattached matrix of BHKpy cells was much higher than that of BHK cells. Cell spreading and cell attachment on plastic plate were inhibited by inclusion of GM3 in the medium. These data suggest that: (i) glycolipids, particularly GM3, at the cell attachment site have different metabolic activity from those of whole cells; the label in glycolipids goes preferentially into cell attachment sites, and may have some functional role in regulating cell attachment of BHK cells; (ii) metabolic activity and turnover of GM3 in cell attachment sites of confluent cells are higher than actively growing cells, yet those of transformed cells are much higher than any state of non-transformed cells.

Ganglioside composition of substrate-adhesion sites of normal and virally-transformed Balb/c 3T3 cells

The ganglioside composition of the so-called substrate-attached material (SAM), which remains tightly bound to the tissue culture dish after cells are detached by chelating agents, was compared with the ganglioside composition of released cell bodies in the cultures of normal and various virally-transformed Balb/c 3T3 cells. Regardless of whether the cells were untransformed or transformed, the SAM of their cultures shows a ganglioside structure characterized by a prevalence of the higher homologs, mainly GD1a, over the simpler gangliosides, even when the level of higher homologs was reduced in the cell bodies of transformed cells. This result cannot be ascribed to the presence of plasmamembranes in the SAM as shown by ganglioside analysis of the plasmamembranes of some of the cells under study. Only in a highly metastatic transformed cell line did the SAM contain the same low GD1a level as found in the cell bodies.

Roles of gangliosides in the surface properties of normal and malignant cells

Gangliosides are ubiquitous plasma membrane components whose structural characteristics make it possible to establish multiple interactions with the pericellular microenvironment. Several receptorial activities of gangliosides have already been recognized and the possible involvement of gangliosides in growth control, adhesion, differentiation, and immunologic recognition is at present under study. The study of the role of gangliosides in cell growth control has been approached in our laboratory by investigating whether the ganglioside changes found in SV40-transformed Balb/c3T3 cells (SV3T3 cells) revert to a normal pattern in a variant of SV3T3 cells with growth properties similar to those of normal parental cells, the concanavalin A-selected SV3T3 revertant cells. These latter cells showed the same reduction of the more complex gangliosides as found in SV3T3 cells, while their amount of II3NeuAC-LacCer (GM3) was greatly increased compared to that found in either normal or transformed 3T3 cells. In order to study the role of gangliosides in the adhesion process, we analyzed the ganglioside structure of the so-called substrate-attached material, a cell surface structure involved in the adhesion of cells to substrate, from cultures of Balb/c3T3, SV3T3, and concanavalin A-selected SV3T3 revertant cells and from cultures of a system of transformed cells with different metastatic potential: the nonmetastatic B77-3T3 and the highly metastatic AA6 cells. Compared to normal cells, all the transformed cells contained smaller quantities of gangliosides in their substrate-attached material.(ABSTRACT TRUNCATED AT 250 WORDS)

Ether-linked lipids of Balb/c3T3, SV3T3 and concanavalin A-selected SV3T3 revertant cells

Ether-linked lipids were analyzed in Balb/c3T3, SV3T3 and Concanavalin A-selected SV3T3 revertant cells. The three cell lines were found to contain significant quantities of alk-1-enyl- and alkyl-linked phosphatidylethanolamine (PE) and phosphatidylcholine (PC) and small amounts of alkyldiacylglycerols. Compared to 3T3 cells, SV3T3 cells contain a higher amount of alk-1-enyl-linked PC, while in SV3T3 revertant cells the concentrations of the various ether lipids are similar to those of 3T3 cells. The major difference in the composition of ether groups of SV3T3 cells, compared to 3T3 cells, is an increase of 18:0 accompanied by a decrease of 18:1 in the alk-1-enyl-linked PE and PC. Alk-1-enyl-linked PC of SV3T3 revertant cells also shows an increase of 18:0, while the decrease of 18:1 was not statistically significant.

Lipid composition of Balb/c3T3, SV3T3, and Concanavalin A-selected revertant cells grown in media containing lipid-depleted serum

The effects of growth in media supplemented with lipid-depleted fetal calf serum (LDS-media) on morphology, saturation density, and lipid composition were studied in Balb/c3T3, SV3T3, and Concanavalin A selected SV3T3 revertant cells (SV3T3 Rev cells). Cells grown in media containing complete fetal calf serum (FCS-medium) or reconstituted FCS (RS-medium) were used as controls. Growth in LDS-media reduced saturation densities of both SV3T3 and SV3T3 Rev cells while it affected only slightly the saturation density of normal parental cells. Similar inhibitory effects on growth were also induced by exposure of RS-medium. Growth in LDS-medium did not change the typical morphology of the three cell lines. 3T3, SV3T3, and SV3T3 Rev cells grown in LDS-medium showed an accumulation of triacylglycerols and free fatty acids together with a reduction of free cholesterol. All these changes were also present, however, in cells grown in these changes were also present, however, in cells grown in RS-Medium. Growth in LDS-medium induced an increase of 16:1 and 18:1, a decrease of 20:4, and an accumulation of 20:3 (n-9) in phosphatidylethanolamine, phosphatidylcholine, and phosphatidylinositol + phosphatidylserine of 3T3 cells. By contrast, only a slight accumulation of 20:3 (n-9) accompanied by a moderate increase of monoenoic acids was found in the phospholipids of SV3T3 cells grown in LDS-medium. SV3T3 Rev cells grown in LDS-medium showed changes in phospholipid fatty acids composition similar to those found in SV3T3 cells grown under the same conditions.

Neutral glycolipids and gangliosides of concanavalin A-selected SV3T3 revertant cells and of normal and SV40-transformed Balb/c 3T3 cells

The structural analysis of neutral glycolipids and gangliosides of the SV40 transformed Balb/c3T3 cells (SV3T3 cells) and concanavalin A-selected SV3T3 revertant cells, both compared with untransformed Balb/c3T3 cells, has shown: (i) a content of neutral glycolipids in revertant cells near to that found in the untransformed parental cells; (ii) a similar decrease of the higher gangliosides in transformed and revertant cells; (iii) a content of ganglioside GM3 in revertant cells much higher than that found in both SV3T3 and untransformed Balb/3T3 cells. The possible role of ganglioside GM3 in growth control is discussed.

Stearoyl-CoA desaturase in mitochondrial membrane fractions

Several arguments suggested the possibility that the stearoyl-CoA desaturase might be located in the outer mitochondrial membrane in addition to its well presence in the microsomes. In the present investigation, preparations of rat liver microsomes and submitochondrial fractions (outer and inner membranes) were comparatively studied with respect to their stearoyl-CoA desaturase activities. Each fraction has been characterized by determinations of enzymic and chemical markers. This study revealed that while the activity of the stearoyl-CoA desaturase in microsomes was comparable to that found in other laboratories, a very low level of activity was detected in the mitochondrial outer membrane. The possible implications of the lack of stearoyl-CoA desaturase in mitochondria are discussed with respect to the lipid metabolism of these organelles.