Alterations in ether lipid metabolism and the consequences for the mouse lipidome

Alkylglycerol monooxygenase (AGMO) and plasmanylethanolamine desaturase (PEDS1) are enzymes involved in ether lipid metabolism. While AGMO degrades plasmanyl lipids by oxidative cleavage of the ether bond, PEDS1 exclusively synthesizes a specific subclass of ether lipids, the plasmalogens, by introducing a vinyl ether double bond into plasmanylethanolamine phospholipids. Ether lipids are characterized by an ether linkage at the sn-1 position of the glycerol backbone and they are found in membranes of different cell types. Decreased plasmalogen levels have been associated with neurological diseases like Alzheimer's disease. Agmo-deficient mice do not present an obvious phenotype under unchallenged conditions. In contrast, Peds1 knockout mice display a growth phenotype. To investigate the molecular consequences of Agmo and Peds1 deficiency on the mouse lipidome, five tissues from each mouse model were isolated and subjected to high resolution mass spectrometry allowing the characterization of up to 2013 lipid species from 42 lipid subclasses. Agmo knockout mice moderately accumulated plasmanyl and plasmenyl lipid species. Peds1-deficient mice manifested striking changes characterized by a strong reduction of plasmenyl lipids and a concomitant massive accumulation of plasmanyl lipids resulting in increased total ether lipid levels in the analyzed tissues except for the class of phosphatidylethanolamines where total levels remained remarkably constant also in Peds1 knockout mice. The rate-limiting enzyme in ether lipid metabolism, FAR1, was not upregulated in Peds1-deficient mice, indicating that the selective loss of plasmalogens is not sufficient to activate the feedback mechanism observed in total ether lipid deficiency.

The Platelet Lipidome Is Altered in Patients with COVID-19 and Correlates with Platelet Reactivity

BACKGROUND

 Activated platelets have been implicated in the proinflammatory and prothrombotic phenotype of coronavirus disease 2019 (COVID-19). While it is increasingly recognized that lipids have important structural and signaling roles in platelets, the lipidomic landscape of platelets during infection has remained unexplored.

OBJECTIVE

 To investigate the platelet lipidome of patients hospitalized for COVID-19.

METHODS

 We performed untargeted lipidomics in platelets of 25 patients hospitalized for COVID-19 and 23 noninfectious controls with similar age and sex characteristics, and with comparable comorbidities.

RESULTS

 Twenty-five percent of the 1,650 annotated lipids were significantly different between the groups. The significantly altered part of the platelet lipidome mostly comprised lipids that were less abundant in patients with COVID-19 (20.4% down, 4.6% up, 75% unchanged). Platelets from COVID-19 patients showed decreased levels of membrane plasmalogens, and a distinct decrease of long-chain, unsaturated triacylglycerols. Conversely, platelets from patients with COVID-19 displayed class-wide higher abundances of bis(monoacylglycero)phosphate and its biosynthetic precursor lysophosphatidylglycerol. Levels of these classes positively correlated with ex vivo platelet reactivity-as measured by P-selectin expression after PAR1 activation-irrespective of disease state.

CONCLUSION

 Taken together, this investigation provides the first exploration of the profound impact of infection on the human platelet lipidome, and reveals associations between the lipid composition of platelets and their reactivity. These results warrant further lipidomic research in other infections and disease states involving platelet pathophysiology.

An autosomal dominant neurological disorder caused by de novo variants in FAR1 resulting in uncontrolled synthesis of ether lipids

PURPOSE

In this study we investigate the disease etiology in 12 patients with de novo variants in FAR1 all resulting in an amino acid change at position 480 (p.Arg480Cys/His/Leu).

METHODS

Following next-generation sequencing and clinical phenotyping, functional characterization was performed in patients' fibroblasts using FAR1 enzyme analysis, FAR1 immunoblotting/immunofluorescence, and lipidomics.

RESULTS

All patients had spastic paraparesis and bilateral congenital/juvenile cataracts, in most combined with speech and gross motor developmental delay and truncal hypotonia. FAR1 deficiency caused by biallelic variants results in defective ether lipid synthesis and plasmalogen deficiency. In contrast, patients' fibroblasts with the de novo FAR1 variants showed elevated plasmalogen levels. Further functional studies in fibroblasts showed that these variants cause a disruption of the plasmalogen-dependent feedback regulation of FAR1 protein levels leading to uncontrolled ether lipid production.

CONCLUSION

Heterozygous de novo variants affecting the Arg480 residue of FAR1 lead to an autosomal dominant disorder with a different disease mechanism than that of recessive FAR1 deficiency and a diametrically opposed biochemical phenotype. Our findings show that for patients with spastic paraparesis and bilateral cataracts, FAR1 should be considered as a candidate gene and added to gene panels for hereditary spastic paraplegia, cerebral palsy, and juvenile cataracts.

Peroxisomal Multifunctional Protein 2 Deficiency Perturbs Lipid Homeostasis in the Retina and Causes Visual Dysfunction in Mice

Patients lacking multifunctional protein 2 (MFP2), the central enzyme of the peroxisomal β-oxidation pathway, develop retinopathy. This pathway is involved in the metabolism of very long chain (VLCFAs) and polyunsaturated (PUFAs) fatty acids, which are enriched in the photoreceptor outer segments (POS). The molecular mechanisms underlying the retinopathy remain, however, elusive. Here, we report that mice with MFP2 inactivation display decreased retinal function already at the age of 3 weeks, which is accompanied by a profound shortening of the photoreceptor outer and inner segments, but with preserved photoreceptor ultrastructure. Furthermore, MFP2 deficient retinas exhibit severe changes in gene expression with downregulation of genes involved in the phototransduction pathway and upregulation of inflammation related genes. Lipid profiling of the mutant retinas revealed a profound reduction of DHA-containing phospholipids. This was likely due to a hampered systemic supply and retinal traffic of this PUFA, although we cannot exclude that the local defect of peroxisomal β-oxidation contributes to this DHA decrease. Moreover, very long chain PUFAs were also reduced, with the exception of those containing ≥ 34 carbons that accumulated. The latter suggests that there is an uncontrollable elongation of retinal PUFAs. In conclusion, our data reveal that intact peroxisomal β-oxidation is indispensable for retinal integrity, most likely by maintaining PUFA homeostasis.

Clinical implementation of guidelines for cardioverter defibrillator implantation: lost in translation?

PURPOSE

Guidelines for implantation of cardioverter defibrillators (ICD) are increasingly including indications for primary prevention of sudden cardiac death in high-risk groups, where ICDs were traditionally implanted for secondary prevention. We performed a single-centre audit to evaluate adherence to the recent Dutch guidelines.

METHODS

All 1886 patients visiting a large regional Dutch teaching hospital (attending 1.8 to 2.0% of the Dutch population) in November 2005 were screened using the recently updated Dutch guidelines. Patients fulfilling these criteria were categorised as having an ICD indication for primary or secondary prevention.

RESULTS

135 patients had an indication for ICD, 19 of whom had one or received one. Of the remaining 116 patients, 14 were 'new' to the department of cardiology. The 102 'known' patients had 466 doctor-patient contacts in the previous year, which averages 4.57 cardiology contacts per patient per year. Patients were more likely to receive an ICD for the secondary prevention of SCD (10/11, 91%) than for primary prevention (9/124, 7%).

CONCLUSION

In a large regional teaching hospital in the Netherlands, only a small proportion of patients eligible for ICD implantation actually receive one. Cardiologists tend to implant ICDs for secondary prevention of SCD. The low ICD implantation rate for primary prevention of SCD may relate to logistics (e.g. permission to implant ICDs, the presence of an electrophysiology lab) or the perceived low cost-benefit ratio. Our results indicate that once the substantial backlog (13,500 ICDs) has been addressed, the annual implantation of new ICDs should rise from the current 125 to at least 510 per million inhabitants per year in the Netherlands. (Neth Heart J 2007;15:129-32.).

Torsade de pointes with short coupling interval

Torsade de pointes (TdP), a ventricular tachycardia (VT) with the peaks of QRS complexes twisting around the iso-electric baseline and progressive amplitude and polarity variations, is mostly associated with long (congenital or acquired) QT syndromes (LQTS) and long coupling intervals of the initiating complex. We describe a patient with variant, short-coupled TdP, a normal QTc interval and without demonstrable structural heart disease. Mechanisms remain unclear but there may be a relationship with autonomic nervous system imbalance. Since anti-arrhythmic drug efficacy is uncertain, ICD-implantation seems the first-line therapy. If ventricular arrhythmia recurs despite drug therapy, catheter-ablation of initiating premature ventricular beats may be warranted.

[Atrial fibrillation: a growing problem in clinical practice]

The first revision of the the practice guideline 'Atrial fibrillation' from the Dutch College of General Practitioners has provided an important document. Atrial fibrillation is a growing problem in clinical practice. Harmonization of general practice with cardiological guidelines will undoubtedly have favourable results, with as consequences improvement of the diagnostic outcome and state of the art treatment at an earlier moment. It can be expected, that the revised version of the Dutch College of General Practitioners' practice guideline will greatly contribute to the dialogue between cardiologist and general practitioner and may perhaps lead to joint research.

Voltage analysis after multi-electrode ablation with duty-cycled bipolar and unipolar radiofrequency energy: a case report

Pulmonary vein ablation with a single-tip catheter remains long and complex. We describe a typical case of a novel efficient technique with a decapolar ring catheter utilizing alternating unipolar/bipolar radiofrequency energy. Voltage analysis and electrical mapping demonstrate the potential for antrum ablation and pulmonary vein isolation.

Symptomatic arrhythmogenic right ventricular dysplasia/cardiomyopathy. A two-centre retrospective study of 15 symptomatic ARVD/C cases and focus on the diagnostic value of MRI in symptomatic ARVD/C patients

BACKGROUND

Arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C) is associated with sudden death in the young and heart failure in the elderly. The purpose is to review 15 symptomatic ARVD/C cases and also to describe the use of MRI as a diagnostic tool.

METHODS AND RESULTS

This retrospective analysis includes 15 patients who presented with symptomatic ARVD/C. Diagnosis was made upon the criteria proposed by the European Society of Cardiology. In all patients there was at least 1 or more abnormal MRI sign. The most frequent abnormalities were focal right ventricular dyskinesia (64%), MRI fatty infiltration (57%) and right ventricular aneurysm or right ventricular outflow tract microaneurysms (57%). Presenting symptoms were palpitations (60%), atypical chest pain (46%), syncope (40%), and aborted sudden death (26%). T-inversion in V2-V3 was seen in 60% of the patients. Thirteen patients (86%) received an ICD implantation. The mean follow-up per patient was 89 months, which resulted in a total follow-up of 111 patient years. Forty-six percent of the patients with an ICD had one or more appropriate shocks during follow-up. To this date no mortality was reported.

CONCLUSION

This retrospective study demonstrates that symptomatic ARVD/C patients typically present with symptoms of syncope, palpitations in association with ventricular tachycardia and in a quarter of the cases with aborted sudden cardiac death. The electrocardiogram mostly shows T inversion in the anterior leads. All patients were treated with medication and ICD-implantation or VT-ablation. The malignant nature of the disease in symptomatic ARVD/C patients is stressed by the fact that the presenting symptom is aborted sudden death in a quarter of the cases and the fact that nearly half of the patients with an ICD had at least one appropriate shock during follow-up. There was an abnormal MRI in 100% of the investigated patients. In 20% (3 patients), the MRI criterion (right ventricular dilatation/bulging/aneurysm) was necessary to meet the ESC criteria. Therefore it has become an important tool in our diagnostic work-up when ARVD/C is suspected. We also suggest a change in the diagnostic criteria of ARVD/C. Whereas fatty infiltration seen on RV biopsy is a major criterion, MRI fatty infiltration is not regarded as a diagnostic criterion by the task force to this day.

Implantable defibrillator early after primary percutaneous intervention for ST-elevation myocardial infarction: rationale and design of the Defibrillator After Primary Angioplasty (DAPA) trial

BACKGROUND

It has been shown that an implantable cardioverter defibrillator (ICD) may be beneficial when added to optimal drug treatment in patients with reduced left ventricular function who survive a myocardial infarction (MI). However, it is not known whether patients with increased risk of death after primary percutaneous coronary intervention (PCI) for ST-elevation MI also have benefit of prophylactic ICD therapy to reduce sudden cardiac death.

METHODS AND STUDY DESIGN

The DAPA trial is designed to evaluate the efficacy and safety of ICD in high-risk patients after primary PCI for ST-elevation MI. In this randomized multicenter controlled study, a total of 700 patients will be included. Enrolment started in October 2004. Inclusion criteria are thrombolysis in myocardial infarction flow less than 3 after primary PCI or left ventricular ejection fraction lower than 30% as measured short after admission for the index MI. Patients will be randomized between 30 and 60 days after their MI. The primary end point will be total death during the follow-up period of at least 3 years for each patient.

CONCLUSIONS

This multicenter trial of patients at high risk of death after primary angioplasty for ST-elevation MI will evaluate prophylactic ICD therapy in addition to the current standard of care.

Transesophageal two-dimensional echocardiographic evaluation of biventricular dimension and function during positive end-expiratory pressure ventilation after coronary artery bypass grafting

Transesophageal 2-dimensional echocardiography was performed in 21 patients soon after uncomplicated coronary artery bypass grafting to determine the mechanism of positive end-expiratory pressure (PEEP) ventilation-induced decreased cardiac output. End-diastolic and end-systolic short-axis area and percent area reduction of right and left ventricles were determined during 5-cm H2O stepwise increments of PEEP ventilation. Simultaneously, cardiac output and right- and left-sided hemodynamic values were determined. Cardiac output, mean arterial pressure and end-diastolic area of both ventricles gradually decreased, and right and left atrial and pulmonary arterial pressures (mainstem and capillary wedge) increased. Left ventricular end-systolic area did not change, whereas right ventricular area decreased. Percent area reduction of both ventricles decreased (p less than 0.01). Thus, decrease in cardiac output during PEEP ventilation is primarily caused by decrease of preload rather than compromised contractility.