Monitoring of endothelial dysfunction in critically ill patients: the role of endothelial progenitor cells

Endothelial progenitor cells in the host defense response

Extensive injury of endothelial cells in blood vasculature, especially in the microcirculatory system, frequently occurs in hosts suffering from sepsis and the accompanied systemic inflammation. Pathological factors, including toxic components derived from invading microbes, oxidative stress associated with tissue ischemia/reperfusion, and vessel active mediators generated during the inflammatory response, are known to play important roles in mediating endothelial injury. Collapse of microcirculation and tissue edema developed from the failure of endothelial barrier function in vital organ systems, including the lung, brain, and kidney, are detrimental, which often predict fatal outcomes. The host body possesses a substantial capacity for maintaining vascular homeostasis and repairing endothelial damage. Bone marrow and vascular wall niches house endothelial progenitor cells (EPCs). In response to septic challenges, EPCs in their niche environment are rapidly activated for proliferation and angiogenic differentiation. In the meantime, release of EPCs from their niches into the blood stream and homing of these vascular precursors to tissue sites of injury are markedly increased. The recruited EPCs actively participate in host defense against endothelial injury and repair of damage in blood vasculature via direct differentiation into endothelial cells for re-endothelialization as well as production of vessel active mediators to exert paracrine and autocrine effects on angiogenesis/vasculogenesis. In recent years, investigations on significance of EPCs in host defense and molecular signaling mechanisms underlying regulation of the EPC response have achieved substantial progress, which promotes exploration of vascular precursor cell-based approaches for effective prevention and treatment of sepsis-induced vascular injury as well as vital organ system failure.

A Novel Hypothesis and Characterization to Isolate Microvascular Endothelial Cells Simultaneously with Adipose-Derived Stem Cells from the Human Adipose-Derived Stromal Vascular Fraction

BACKGROUND

Angiogenesis and vasculogenesis are essential processes for successful tissue regeneration in tissue engineering and regenerative medicine. The adipose-derived stromal vascular fraction (SVF) is not only a source of adipose stem cells (ASC) but also a suitable source of microvascular endothelial cells because it is a rich capillary network. So, we propose a new hypothesis for isolating adipose-derived human microvascular endothelial cells (HMVEC-A) from the SVF and developed a dual isolation system that isolates two cell types from one tissue.

METHOD

To isolate HMVEC-A, we analyzed the supernatant discarded when ASC is isolated from the adipose-derived SVF. Based on this analysis, we assumed that the SVF adherent to the bottom of the culture plate was divided into two fractions: the stromal fraction as the ASC-rich fraction, and the vascular fraction (VF) as the endothelial cells-rich fraction floating in the culture supernatant. VF isolation was optimized and the efficiency was compared, and the endothelial cells characteristics of HMVEC-A were confirmed by flow cytometric analysis, immunocytochemistry (ICC), a DiI-acetylated low-density lipoprotein (DiI-Ac-LDL) uptake, and in vitro tube formation assay.

RESULTS

Consistent with the hypothesis, we found a large population of HMVEC-A in the VF and isolated these HMVEC-A by our isolation method. Additionally, this method had higher yields and shorter doubling times than other endothelial cells isolation methods and showed typical morphological and phenotypic characteristics of endothelial cells.

CONCLUSION

Cells obtained by the method according to our hypothesis can be applied as a useful source for studies such as tissue-to-tissue networks, angiogenesis and tissue regeneration, patient-specific cell therapy, and organoid chips.

Pulmonary Endothelial Dysfunction and Thrombotic Complications in Patients with COVID-19

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a new strain of a Coronaviridae virus that presents 79% genetic similarity to the severe acute respiratory syndrome coronavirus, has been recently recognized as the cause of a global pandemic by the World Health Organization, implying a major threat to world public health. SARS-CoV-2 infects host human cells by binding through the viral spike proteins to the ACE-2 (angiotensin-converting enzyme 2) receptor, fuses with the cell membrane, enters, and starts its replication process to multiply its viral load. Coronavirus disease (COVID-19) was initially considered a respiratory infection that could cause pneumonia. However, in severe cases, it extends beyond the respiratory system and becomes a multiorgan disease. This transition from localized respiratory infection to multiorgan disease is due to two main complications of COVID-19. On the one hand, it is due to the so-called cytokine storm: an uncontrolled inflammatory reaction of the immune system in which defensive molecules become aggressive for the body itself. On the other hand, it is due to the formation of a large number of thrombi that can cause myocardial infarction, stroke, and pulmonary embolism. The pulmonary endothelium actively participates in these two processes, becoming the last barrier before the virus spreads throughout the body. In this review, we examine the role of the pulmonary endothelium in response to COVID-19, the existence of potential biomarkers, and the development of novel therapies to restore vascular homeostasis and to protect and/or treat coagulation, thrombosis patients. In addition, we review the thrombotic complications recently observed in patients with COVID-19 and its potential threatening sequelae.

Vascular precursor cells in tissue injury repair

Vascular precursor cells include stem cells and progenitor cells giving rise to all mature cell types in the wall of blood vessels. When tissue injury occurs, local hypoxia and inflammation result in the generation of vasculogenic mediators which orchestrate migration of vascular precursor cells from their niche environment to the site of tissue injury. The intricate crosstalk among signaling pathways coordinates vascular precursor cell proliferation and differentiation during neovascularization. Establishment of normal blood perfusion plays an essential role in the effective repair of the injured tissue. In recent years, studies on molecular mechanisms underlying the regulation of vascular precursor cell function have achieved substantial progress, which promotes exploration of vascular precursor cell-based approaches to treat chronic wounds and ischemic diseases in vital organ systems. Verification of safety and establishment of specific guidelines for the clinical application of vascular precursor cell-based therapy remain major challenges in the field.

Are closed-loop systems for intensive insulin therapy ready for prime time in the ICU?

PURPOSE OF REVIEW

Recent findings suggest that the effects of tight glycemic control (TGC) performing intensive insulin therapy (IIT) in medical and surgical ICU have had conflicting results. The purpose of this review is to summarize the current evidence in humans how closed-loop systems for IIT are ready for prime time in the ICU.

RECENT FINDINGS

Current evidence suggests that maintaining normoglycemia postoperatively can improve the outcome and reduce the mortality and morbidity of critically ill patients by TGC performing IIT according to the large randomized trials. However, trials examining the effects of TGC have had conflicting results. Systematic reviews and meta-analyses have also led to differing conclusions. The main reason these clinical trials and meta-analyses were negative results for TGC was because of the high incidence of hypoglycemia. This could not be prevented as there is no reliable technique currently able to avoid this condition during IIT. The development of accurate, continuous blood glucose monitoring devices, and closed-loop systems for computer-assisted blood glucose control in the ICU, will probably help avoid hypoglycemia in these situations.

SUMMARY

The challenge in the hospital setting demonstrated that a closed-loop glycemic control system is expected to the achievement of TGC with no occurrence of hypoglycemia induced by IIT after surgery. Closed-loop glycemic control systems for IIT are now ready for prime time in the ICU.

Stem cell-derived endothelial cells for cardiovascular disease: a therapeutic perspective

Stem cell therapy and organ regeneration are therapeutic approaches that will, we suggest, become mainstream for the treatment of human disease. Endothelial cells, which line the luminal surface of every vessel in the body, are essential components in any organ regeneration programme. There are a number of potentially therapeutic endothelial cell types, including embryonic, adult progenitor and induced pluripotent stem cell-derived endothelial cells, as well as host vascular cells. The features (benefits as well as disadvantages) of each cell type that make them potentially useful in therapy are important to consider. The field of stem cell biology is well developed in terms of protocols for generating endothelium. However, where there is a distinct and urgent unmet need for knowledge concerning how the endothelial cells from these different sources function as endothelium and how susceptible they may be to inflammation and atherosclerosis. Furthermore, where stem cells have been used in clinical trials there is little commonality in protocols for deriving the cells (and thereby the specific phenotype of cells used), administering the cells, dosing the cells and/or in assessing efficacy attributed to the cells themselves. This review discusses these and other issues relating to stem cell-derived endothelial cells in cell therapy for cardiovascular disease.

CXCL12/CXCR4 signaling and other recruitment and homing pathways in fracture repair

Cell recruitment, migration and homing to the fracture site are essential for the inflammatory process, neovascularization, chondrogenesis, osteogenesis and ultimately bone remodeling. Mesenchymal stem cells (MSCs) are required to navigate from local sources such as the periosteum and local bone marrow, and may also be recruited from the circulation and distant bone marrow. While the local recruitment process may involve matrix binding and degradation, systemic recruitment may utilize extravasation, a process used by leukocytes to exit the vasculature. CXCL12 (stromal cell-derived factor-1 (SDF-1)), a member of the CXC family of chemokines, is thought to have an important role in cell migration at the fracture site. However, there are many molecules upregulated in the hematoma and callus that have chemotactic potential not only for inflammatory cells but also for endothelial cells and MSCs. Surprisingly, there is little direct data to support their role in cell homing during bone healing. Current therapeutics for bone regeneration utilize local or systemic stem cell transplantation. More recently, a novel strategy that involves mobilization of large numbers of endogenous stem and progenitor cells from bone marrow into the circulation has been shown to have positive effects on bone healing. A more complete understanding of the molecular mechanisms underlying cell recruitment and homing subsequent to fracture will facilitate the fine-tuning of such strategies for bone.

Hydrogel-embedded endothelial progenitor cells evade LPS and mitigate endotoxemia

Sepsis and its complications are associated with poor clinical outcomes. The circulatory system is a well-known target of lipopolysaccharide (LPS). Recently, several clinical studies documented mobilization of endothelial progenitor cells (EPCs) during endotoxemia, with the probability of patients' survival correlating with the rise in circulating EPCs. This fact combined with endotoxemia-induced vascular injury led us to hypothesize that the developing functional EPC incompetence could impede vascular repair and that adoptive transfer of EPCs could improve hemodynamics in endotoxemia. We used LPS injection to model endotoxemia. EPCs isolated from endotoxemic mice exhibited impaired clonogenic potential and LPS exerted Toll-like receptor 4-mediated cytotoxic effects toward EPCs, which was mitigated by embedding them in hyaluronic acid (HA) hydrogels. Therefore, intact EPCs were either delivered intravenously or embedded within pronectin-coated HA hydrogels. Adoptive transfer of EPCs in LPS-injected mice improved control of blood pressure and reduced hepatocellular and renal dysfunction. Specifically, EPC treatment was associated with the restoration of renal microcirculation and improved renal function. EPC therapy was most efficient when cells were delivered embedded in HA hydrogel. These findings establish major therapeutic benefits of adoptive transfer of EPCs, especially when embedded in HA hydrogels, in mice with LPS-induced endotoxemia, and they argue that hemodynamic and renal abnormalities of endotoxemia are in significant part due to developing incompetence of endogenous EPCs.

Endothelial progenitors in sepsis: vox clamantis in deserto?

In this issue of Critical Care, Patschan and colleagues present a study of endothelial progenitor cells (EPCs) in patients with sepsis. The importance of this study is in focusing attention on several frequently ignored aspects of sepsis. Among those are the phenomenon of microvascular dysfunction, which is potentially responsible for profound metabolic perturbations at the tissue level, and the role of endothelial progenitors in repair processes. Other important aspects of the study are the regenerative capacity of mobilized EPCs and the dissociation between the numerical value and clonogenic competence. Attempting to restore the competence to EPCs should be a priority in the future.

Circulating endothelial and endothelial progenitor cells in patients with severe sepsis

Elevated circulating endothelial cell (CEC) and circulating endothelial progenitor cell (CEPC) counts may indicate vascular damage and disease status, but data on these cell populations in patients with severe sepsis are limited. This study compared CEC and CEPC counts in patients with and without severe sepsis following intensive care unit (ICU) admission. Venous blood samples were collected within 24 h, 48-72 h, and 120-144 h. Baseline demographics, 28-day mortality, ICU and hospital days, and Sequential Organ Failure Assessment (SOFA) scores were recorded. Patients with (n=18) and without (n=28) severe sepsis were balanced for mean age (63.7 and 61.3 years, respectively) and gender. There were no differences in 28-day mortality, ICU days, or hospital days. Baseline SOFA scores were higher in the sepsis group. At 48-72 h, patients with severe sepsis had significantly higher median CEC counts (51.5 vs. 28.0 cells/4 ml of blood, P=0.02). CEC values for all ICU patients were significantly (P<0.05) higher than in healthy volunteers. CEPC counts in both cohorts ranged from 0 to >21 colonies/4 ml blood (mean=1.13±2.25; median=0) without significant differences at any time point. This study demonstrates the ability to quantify CECs and CEPCs using consensus methodology. Understanding the relationship between CEC/CEPC counts and outcomes may provide insight into the mechanisms of endothelial cell changes in severe sepsis.

Consensus statement: minimal criteria for reporting the systemic inflammatory response to cardiopulmonary bypass

The lack of established cause and effect between putative mediators of inflammation and adverse clinical outcomes has been responsible for many failed anti-inflammatory interventions in cardiopulmonary bypass (CPB). Candidate interventions that impress in preclinical trials by suppressing a given inflammation marker might fail at the clinical trial stage because the marker of interest is not linked causally to an adverse outcome. Alternatively, there exist examples in which pharmaceutical agents or other interventions improve clinical outcomes but for which we are uncertain of any antiinflammatory mechanism. The Outcomes consensus panel made 3 recommendations in 2009 for the conduct of clinical trials focused on the systemic inflammatory response. This panel was tasked with updating, as well as simplifying, a previous consensus statement. The present recommendations for investigators are the following: (1) Measure at least 1 inflammation marker, defined in broad terms; (2) measure at least 1clinical end point, drawn from a list of practical yet clinically meaningful end points suggested by the consensus panel; and(3) report a core set of CPB and perfusion criteria that maybe linked to outcomes. Our collective belief is that adhering to these simple consensus recommendations will help define the influence of CPB practice on the systemic inflammatory response, advance our understanding of causal inflammatory mechanisms, and standardize the reporting of research findings in the peer-reviewed literature.

Pathophysiology and treatment of septic shock in neonates

Neonatal septic shock is a devastating condition associated with high morbidity and mortality. Definitions for the sepsis continuum and treatment algorithms specific for premature neonates are needed to improve studies of septic shock and assess benefit from clinical interventions. Unique features of the immature immune system and pathophysiologic responses to sepsis, particularly those of extremely preterm infants, necessitate that clinical trials consider them as a separate group. Keen clinical suspicion and knowledge of risk factors will help to identify those neonates at greatest risk for development of septic shock. Genomic and proteomic approaches, particularly those that use very small sample volumes, will increase our understanding of the pathophysiology and direct the development of novel agents for prevention and treatment of severe sepsis and shock in the neonate. Although at present antimicrobial therapy and supportive care remain the foundation of treatment, in the future immunomodulatory agents are likely to improve outcomes for this vulnerable population.

Dysfunctional endothelial progenitor cells in chronic kidney disease

Putative endothelial progenitor cells play a role in organ regeneration, and their incompetence may be important in the development of chronic kidney disease. The mechanisms of this incompetence are broad and range from poor mobilization, viability, and engraftment to impaired differentiation into mature endothelial cells. By contrasting the role of endothelial progenitor cells in tissue regeneration with their developing incompetence in chronic kidney disease, we emphasize the importance of designing rational pharmacologic strategies to tackle such incompetence in the broader search for therapies to attenuate chronic disease.