Quantitative freeze-fracture study of plasmalemma and nuclear envelope of Zea mays root cells during early germination

Clinical and cardiac magnetic resonance findings in post-COVID patients referred for suspected myocarditis

Objectives

We assessed possible myocardial involvement in previously cardiac healthy post-COVID patients referred for persisting symptoms with suspected myocarditis.

Background

Prior studies suggested myocardial inflammation in patients with coronavirus-induced disease 2019 (COVID-19). However, the prevalence of cardiac involvement among COVID patients varied between 1.4 and 78%.

Methods

A total of 56 post-COVID patients without previous heart diseases were included consecutively into this study. All patients had positive antibody titers against SARS-CoV-2. Patients were referred for persistent symptoms such as chest pain/discomfort, shortness of breath, or intolerance to activity. All patients underwent standardized cardiac assessment including electrocardiogram (ECG), cardiac biomarkers, echocardiography, and cardiac magnetic resonance (CMR).

Results

56 Patients (46 ± 12 years, 54% females) presented 71 ± 66 days after their COVID-19 disease. In most patients, the course of COVID-19 was mild, with hospital treatment being necessary in five (9%). At presentation, patients most often reported persistent fatigue (75%), chest pain (71%), and shortness of breath (66%). Acute myocarditis was confirmed by T1/T2-weighed CMR and elevated NTpro-BNP levels in a single patient (2%). Left ventricular ejection fraction was 56% in this patient. Additional eight patients (14%) showed suspicious CMR findings, including myocardial edema without fibrosis (n = 3), or non-ischemic myocardial injury suggesting previous inflammation (n = 5). However, myocarditis could ultimately not be confirmed according to 2018 Lake Louise criteria; ECG, echo and lab findings were inconspicuous in all eight patients.

Conclusions

Among 56 post-COVID patients with persistent thoracic complaints final diagnosis of myocarditis could be confirmed in a single patient using CMR.

Graphic abstract

SARS-CoV-2, myocardial injury and inflammation: insights from a large clinical and autopsy study

Objective

Despite growing evidence about myocardial injury in hospitalized COronaVIrus Disease 2019 (COVID-19) patients, the mechanism behind this injury is only poorly understood and little is known about its association with SARS-CoV-2-mediated myocarditis. Furthermore, definite evidence of the presence and role of SARS-CoV-2 in cardiomyocytes in the clinical scenario is still lacking.

Methods

We histologically characterized myocardial tissue of 40 patients deceased with severe SARS-CoV-2 infection during the first wave of the pandemic. Clinical data were also recorded and analyzed. In case of findings supportive of myocardial inflammation, histological analysis was complemented by RT-PCR and immunohistochemistry for SARS-CoV-2 viral antigens and in situ RNA hybridization for the detection of viral genomes.

Results

Both chronic and acute myocardial damage was invariably present, correlating with the age and comorbidities of our population. Myocarditis of overt entity was found in one case (2.5%). SARS-CoV-2 genome was not found in the cardiomyocytes of the patient with myocarditis, while it was focally and negligibly present in cardiomyocytes of patients with known viral persistence in the lungs and no signs of myocardial inflammation. The presence of myocardial injury was not associated with myocardial inflammatory infiltrates.

Conclusions

In this autopsy cohort of COVID-19 patients, myocarditis is rarely found and not associated with SARS-CoV-2 presence in cardiomyocytes. Chronic and acute forms of myocardial damage are constantly found and correlate with the severity of COVID-19 disease and pre-existing comorbidities.

Graphic abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s00392-021-01910-2.

COVID-19, hydroxychloroquine and sudden cardiac death: implications for clinical practice in patients with rheumatic diseases

Sudden cardiac death is commonly seen due to arrhythmias, which is a common cardiac manifestation seen in COVID-19 patients, especially those with underlying cardiovascular disease (CVD). Administration of hydroxychloroquine (HCQ) as a potential treatment option during SARS-CoV-2, initially gained popularity, but later, its safe usage became questionable due to its cardiovascular safety, largely stemming from instances of cardiac arrhythmias in COVID-19. Moreover, in the setting of rheumatic diseases, in which patients are usually on HCQ for their primary disease, there is a need to scale the merits and demerits of HCQ usage for the treatment of COVID-19. In this narrative review, we aim to address the association between usage of HCQ and sudden cardiac death in COVID-19 patients. MEDLINE, EMBASE, ClinicalTrials.gov and SCOPUS databases were used to review articles in English ranging from case reports, case series, letter to editors, systematic reviews, narrative reviews, observational studies and randomized control trials. HCQ is a potential cause of sudden cardiac death in COVID-19 patients. As opposed to the reduction in CVD with HCQ in treatment of systemic lupus erythematous, rheumatoid arthritis, and other rheumatic diseases, safe usage of HCQ in COVID-19 patients is unclear; whereby, it is observed to result in QTc prolongation and Torsades de pointes even in patients with no underlying cardiovascular comorbidity. This is occasionally associated with sudden cardiac death or cardiac arrest; hence, its clinical efficacy needs further investigation by large-scale clinical trials.

Membrane-bounded nucleoid in the eubacterium Gemmata obscuriglobus

The freshwater budding eubacterium Gemmata obscuriglobus possesses a DNA-containing nuclear region that is bounded by two nuclear membranes. The membrane-bounded nature of the nucleoid in this bacterium was shown by thin sectioning of chemically fixed cells, thin sectioning of freeze-substituted cells, and freeze-fracture/freeze-etch. The fibrillar nucleoid was surrounded by electron-dense granules that were in turn enveloped by two nuclear membranes separated by an electron-transparent space. Immunogold labeling of thin sections of conventionally fixed cells with anti-double-stranded DNA antibody demonstrated double-stranded DNA associated with fibrillar material within the membrane boundary. The occurrence of a membrane-bounded nucleoid in a eubacterial prokaryote is a significant exception to the evidence supporting the prokaryote/eukaryote dichotomous classification of cell structure.

A multidisciplinary approach to the study of the plasma membrane of Zea mays pollen during controlled dehydration

A multidisciplinary approach (freeze-fracture, nuclear magnetic resonance, differential scanning calorimetry, isoelectric focusing and fluorochromatic reaction test) has been used to follow the behaviour of Zea mays pollen during dehydration - and to estimate its quality. At anthesis, the water content of maize pollen is 57-58% and the vegetative plasma membrane is continous and well structured with a very low density of intramembraneous particles on the extraplasmic fracture face. Maize pollen grains can withstand the drying process until a water content of 28% is reached, at which point 60-80% of the individuals show a negative reaction in the fluorochromatic test. At this water content, there is no more crystallizable water and thus metabolism decreases, leading to oxidative damage and the formation of gelphase microdomains in the plasma membrane. Consequently, the plasma-membrane permeability is modified. At 15-13% water content, all pollen grains show a negative fluorochromatic reaction, and gel-phase microdomains are more numerous but membranes still have a bilayer structure. Relaxation-time experiments indicate the occurrence of water replacement at the membrane level. Thus, sugar may stabilize the membrane structure at water contents as low as 3%. During the dehydration process, pollen walls act as elastic structures and remain closely applied to the protoplast. The combination of wall deformation and water replacement would permit pollen survival until oxidative damage occurs in the dehydrated grain.

Freeze-fracture replica study of capillary endothelium after embolization in the dog

The underlying mechanisms that lead to brain edema following ischemic insult have been subject to much debate. In this study, experimental cerebral infarction was produced in 25 dogs by injecting 1 or 2 silicone rubber cylinders through the cervical internal carotid artery. The animals were sacrificed 24 hours after embolization. Freeze-fracture studies were conducted on the plasma membrane of the capillary endothelium from 15 control and 25 ischemic dogs. No definite findings of tight junction opening were made in the ischemic preparations. Pinocytotic vesicles were seen as concave areas on the protoplasmic face (PF) of the plasma membrane and as protrusions on the extracellular face (EF). The average pinocytotic vesicle count per square micron was increased in ischemic animals. On the luminal side, it reached 22.0 +/- 1.2/sq mu in the 50 PF samples and 29.5 +/- 1.3/sq mu in the 50 EF samples in the experimental preparations, as compared to 7.2 +/- 0.5 sq mu in the 50 PF samples and 9.0 +/- 0.6 sq mu in the 50 EF samples in normal cortex. The average area of the vesicles was also enlarged in experimental animals: 4990.7 +/- 798 sq nm in the 50 PF samples and 4762.8 +/- 878 sq nm in the 50 EF samples, as compared to 3567.7 +/- 570 sq nm in the 50 PF samples and 3404.5 +/- 573 sq nm in the 50 EF samples in normal cortex (p greater than 0.01). These results indicate that transcellular transportation by pinocytotic vesicles plays an important role in the increase of capillary permeability observed in an ischemic model.

Plasma-membrane rosettes in root hairs of Equisetum hyemale

Particle arrangement in the plasma membrane during cell wall formation was investigated by means of the double-replica technique in root hairs of Equisetum hyemale. Particle density in the protoplasmic fracture face of the plasma membrane was higher than in the extraplasmic fracture face. Apart from randomly distributed particles, particle rosettes were visible in the PF face of the plasma membrane. The rosettes consisted of six particles arranged in a circle and had an outer diameter of approx. 26 nm. No gradient in the number of rosettes was found, which agrees with micrifibril deposition taking place over the whole hair. The particle rosettes were found individually, which might indicate that they spin out thin microfibrils as found in higher-plant cell walls. Indeed microfibril width in these walls, measured in shadowed preparations, is 8.5±1.5 nm. It is suggested that the rosettes are involved in microfibril synthesis. Non-turgid cells lacked microfibril imprints in the plasma membrane and no particle rosettes were present on their PF face. Fixation with glutaraldehyde caused, probably as a result of plasmolysis, the microfibril imprints to disappear together with the particle rosettes. The PF face of the plasma membrane of non-turgid hairs sometimes showed domains in which the intramembrane particles were aggregated in a hexagonal pattern. Microfibril orientation during deposition will be discussed.