COVID-19 and renin-angiotensin system inhibition: role of angiotensin converting enzyme 2 (ACE2) - Is there any scientific evidence for controversy?

Renin-angiotensin system (RAS) blockers are extensively used worldwide to treat many cardiovascular disorders, where they are effective in reducing both mortality and morbidity. These drugs are known to induce an increased expression of angiotensin-converting enzyme 2 (ACE2). ACE2 acts as receptor for the novel SARS coronavirus-2 (SARS-CoV-2) which raising the important issue of possible detrimental effects that RAS blockers could exert on the natural history and pathogenesis of the coronavirus disease-19 (COVID-19) and associated excessive inflammation, myocarditis and cardiac arrhythmias. We review the current knowledge on the interaction between SARS-CoV-2 infection and RAS blockers and suggest a scientific rationale for continuing RAS blockers therapy in patients with COVID-19 infection.

Atomic force microscopy analysis of extracellular vesicles.

Extracellular vesicles (EVs) are small vesicles ensuring transport of molecules between cells and throughout the body. EVs contain cell type-specific signatures and have been proposed as biomarkers in a variety of diseases. Their small size (<1 µm) and biological and physical functions make them obvious candidates for therapeutic agents in immune therapy, vaccination, regenerative medicine and drug delivery. However, due to the complexity and heterogeneity of their origin and composition, the actual mechanism through which these vesicles exert their functions is still unknown and represents a great biomedical challenge. Moreover, because of their small dimensions, the quantification, size distribution and biophysical characterization of these particles are challenging and still subject to controversy. Here, we address the advantage of atomic force microscopy (AFM), for the characterization of isolated EVs. We review AFM imaging of EVs immobilized on different substrates (mica, glass) to identify the influence of isolation and deposition methods on the size distribution, morphology and mechanical properties of EVs.

Alteration of Notch signaling and functionality of adipose tissue derived mesenchymal stem cells in heart failure.

AIM: Circulating mesenchymal cells increase in heart failure (HF) patients and could be used therapeutically. Our aim was to investigate whether HF affects adipose tissue derived mesenchymal cell (adMSC) isolation, functional characteristics and Notch pathway. METHODS AND RESULTS: We compared 25 patients with different degrees of HF (11 NYHA classes I and II and 14 NYHA III and IV) with 10 age and gender matched controls. 100% adMSC cultures were obtained from controls, while only 72.7% and 35.7% from patients with mild or severe HF (p<0.0001). adMSC from HF patients showed higher markers of senescence (p16 positive cells: 14±2.3% in controls and 35.6±5.6% (p<0.05) and 69±14.7% (p<0.01) in mild or severe HF; γ-H2AX positive cells: 3.7±1.2%, 19.4±4.1% (p<0.05) and 23.7±3.4% (p<0.05) respectively), lower proliferation index (Ki67 positive cells: 21.5±4.9%, 13.2±2.8% and 13.7±3.2%, respectively), reduced pluripotency-associated genes (Oct4 positive cells: 86.7±4.9%, 55±12% (p<0.05) and 43.3±8.7% (p<0.05), respectively; NANOG positive cells: 89.8±3.7%, 39.6±14.4% (p<0.01) and 47±8.1%, respectively), and decreased differentiation markers (α-sarcomeric actin positive cells: 79.8±4.6%, 49±18.1% and 47±12.1% (p<0.05) and CD31-positive endothelial cells: 24.5±2.9%, 0.5±0.5% (p<0.001) and 2.3±2.3% (p<0.001), respectively). AdMSC from HF patients also showed reduced Notch transcriptional activity (lowered expression of Hey 1 and Hey 2 mRNAs). Stimulation with TNF-α of adMSC isolated from controls affected the transcription of several components of the Notch pathway (reduction of Notch 4 and Hes 1 mRNAs and increase of Notch 2 and Hey 1 mRNAs). CONCLUSIONS: In HF yield and functionality of adMSC are impaired and their Notch signaling is downregulated.

Stem cell senescence and regenerative paradigms.

The term "cellular senescence" denotes a cellular response to several stressors that results in irreversible growth arrest, alterations of the gene expression profile, epigenetic modifications, and an altered secretome, all of which eventually impair the reparative properties of primitive cells, adding a layer of complexity to the field of regenerative medicine. The purpose of this review is to illustrate how cellular senescence could affect tissue repair and to propose interventions that aim at interfering with it.

[Stem cells and regeneration of human myocardium].

A concept of impossibility of appearance of novel cardiomyocytes in the heart of adult men in exchange for those lost due to cardiovascular diseases had dominated medicine and biology for many long decades. However ability of human myocardium to regenerate was demonstrated during recent years in multiple studies. This dictated necessity to reconsider previously generally accepted concept. At present researchers and practicing physicians actively discuss possibility of the use of transplantation of bone marrow stem cells, proper cardiac stem cells, skeletal muscle myoblasts or precursors of endothelial cells in patients with myocardial infarction and heart failure in order to restore normal cardiac structure and function. Another potential method of restoration of the myocardium in patients with cardiovascular diseases is the use of cytokines which stimulate migration of stem cells into myocardium and their differentiation into cardiomyocytes.

Breath-by-breath alveolar oxygen transfer at the onset of step exercise in humans: methodological implications.

The effects of using different algorithms to estimate the time constant of changes in oxygen uptake at the onset of square-wave 120 W cycloergometric exercise were evaluated in seven subjects. The volume of oxygen taken up at the alveoli (VO(2Ai)) was determined breath-by-breath (BB) from the volume of O(2) transferred at the mouth (VO(2mi)) minus the corresponding volume changes in O(2) stores in the alveoli: VO(2Ai)= VO(2mi)-[V(Ai-1)(FO(2Ai)- FO(2Ai-1))+ FO(2Ai) x Delta V(Ai)], where V(Ai-1) is the alveolar volume at the end of the previous breath, FO(2Ai) and FO(2Ai-1) are estimated from the fractions of end-tidal O(2) in the current and previous breaths, respectively, and Delta V(Ai) is the change in volume during breath i. These quantities can be measured BB, with the exception of V(Ai-1) which must be assumed. The respiratory cycle has been defined as the time elapsing between identical fractions of expiratory gas in two successive breaths. Using this approach, since FO(2Ai)= FO(2Ai-1), any assumption regarding V(Ai-1) becomes unnecessary. In the present study, VO(2Ai) was calculated firstly, by using this approach, and secondly by setting different V(Ai-1) values (from 0 to FRC+0.5 l, where FRC is the functional residual capacity). Values for alveolar O(2) flow (VO(2Ai)), as calculated from the quotient of VO(2Ai) divided by breath duration, were then fitted bi-exponentially. The time constant of the phase II kinetics of VO(2Ai) (tau(2)) was linearly related to V(Ai-1), increasing from 36.6 s (V(Ai-1)=0) to 46.8 s (V(Ai-1)=FRC+0.5 l) while tau(2) estimated using the first approach amounted to 34.3 s. We concluded that, firstly, the first approach allowed us to calculate O(2A) during transitions in step exercise; and secondly, when using methods wherein V(Ai-1) must be assumed, tau(2) depended on V(Ai-1).

Oxidative stress-mediated cardiac cell death is a major determinant of ventricular dysfunction and failure in dog dilated cardiomyopathy.

Cell death has been questioned as a mechanism of ventricular failure. In this report, we tested the hypothesis that apoptotic death of myocytes, endothelial cells, and fibroblasts is implicated in the development of the dilated myopathy induced by ventricular pacing. Accumulation of reactive oxygen products such as nitrotyrosine, potentiation of the oxidative stress response by p66(shc) expression, formation of p53 fragments, release of cytochrome c, and caspase activation were examined to establish whether these events were coupled with apoptotic cell death in the paced dog heart. Myocyte, endothelial cell, and fibroblast apoptosis was detected before indices of severe impairment of cardiac function became apparent. Cell death increased with the duration of pacing, and myocyte death exceeded endothelial cell and fibroblast death throughout. Nitrotyrosine formation and p66(shc) levels progressively increased with pacing and were associated with cell apoptosis. Similarly, p50 (DeltaN) fragments augmented paralleling the degree of cell death in the failing heart. Moreover, cytochrome c release and activation of caspase-9 and -3 increased from 1 to 4 weeks of pacing. In conclusion, cardiac cell death precedes ventricular decompensation and correlates with the time-dependent deterioration of function in this model. Oxidative stress may be critical for activation of apoptosis in the overloaded heart.

Evidence that human cardiac myocytes divide after myocardial infarction.

BACKGROUND: The scarring of the heart that results from myocardial infarction has been interpreted as evidence that the heart is composed of myocytes that are unable to divide. However, recent observations have provided evidence of proliferation of myocytes in the adult heart. Therefore, we studied the extent of mitosis among myocytes after myocardial infarction in humans. METHODS: Samples from the border of the infarct and from areas of the myocardium distant from the infarct were obtained from 13 patients who had died 4 to 12 days after infarction. Ten normal hearts were used as controls. Myocytes that had entered the cell cycle in preparation for cell division were measured by labeling of the nuclear antigen Ki-67, which is associated with cell division. The fraction of myocyte nuclei that were undergoing mitosis was determined, and the mitotic index (the ratio of the number of nuclei undergoing mitosis to the number not undergoing mitosis) was calculated. The presence of mitotic spindles, contractile rings, karyokinesis, and cytokinesis was also recorded. RESULTS: In the infarcted hearts, Ki-67 expression was detected in 4 percent of myocyte nuclei in the regions adjacent to the infarcts and in 1 percent of those in regions distant from the infarcts. The reentry of myocytes into the cell cycle resulted in mitotic indexes of 0.08 percent and 0.03 percent, respectively, in the zones adjacent to and distant from the infarcts. Events characteristic of cell division--the formation of the mitotic spindles, the formation of contractile rings, karyokinesis, and cytokinesis--were identified; these features demonstrated that there was myocyte proliferation after myocardial infarction. CONCLUSIONS: Our results challenge the dogma that the adult heart is a postmitotic organ and indicate that the regeneration of myocytes may be a critical component of the increase in muscle mass of the myocardium.