Systemic Hypoxia Increases Circulating Concentration of Apelin in Humans

Changes in serum levels of apelin and nitric oxide in hospitalized patients with COVID-19: association with hypertension, diabetes, obesity, and severity of disease

Background

COVID-19 is an infectious disease currently spreading worldwide. The COVID-19 virus requires angiotensin-converting enzyme 2, an enzyme that plays a vital role in regulating the apelinergic system for entry into target cells. The underlying diseases of hypertension, diabetes mellitus, and obesity are risk factors for the severity of COVID-19 infection. This study aimed to compare the serum levels of apelin and nitric oxide in hospitalized COVID-19 patients and non-COVID-19 subjects with and without the mentioned risk factors.

Methods

Serum samples were taken from 69 COVID-19 patients and 71-matched non-COVID-19 participants enrolled in the Kerman coronary artery disease risk factors cohort study. Study participants were divided into eight groups of control (healthy), hypertension, diabetes mellitus, obesity, COVID-19, COVID-19 + hypertension, COVID-19 + diabetes mellitus, and COVID-19 + obesity (n = 15–20 in each group). Serum apelin and nitrite were measured by the enzyme-linked immunosorbent assay and colorimetric methods, respectively.

Results

Hypertensive and obese patients had lower serum apelin compared to the control group. In addition, apelin content was lower in the COVID-19 and COVID-19 + diabetes mellitus groups compared to the non-COVID-19 counterpart groups. Serum apelin levels were positively associated with arterial O₂sat. and negatively with the severity of lung involvement. Nitric oxide metabolites were significantly lower in the COVID-19, COVID-19 + diabetes mellitus, and COVID-19 + obesity groups.

Conclusions

The lower apelin and nitric oxide levels in patients with hypertension and obesity or their reduction due to infection with COVID-19 or concomitant COVID-19 + diabetes mellitus may make them vulnerable to experiencing severe diseases.

The Role of Adipokines in Cardiovascular Pathology

The recent decades saw a steady growth of obesity incidence worldwide. Obesity is an independent risk factor for cardiovascular diseases (CVDs) and type 2 diabetes mellitus and is also associated with a shorter life expectancy. Not only hemodynamic but also hormone metabolic processes, arising from excessive accumulation of adipose tissue in human body, underlie the development of CVDs. Adipose tissue has now been proved to be a hormone-active substrate. Studies of the influence of adipokines will bring us closer to understanding cardiovascular pathogenesis and help personalize prophylactic strategies.

Apelin/APJ system: an emerging therapeutic target for respiratory diseases

Apelin is an endogenous ligand of G protein-coupled receptor APJ. It is extensively expressed in many tissues such as heart, liver, and kidney, especially in lung tissue. A growing body of evidence suggests that apelin/APJ system is closely related to the development of respiratory diseases. Therefore, in this review, we focus on the role of apelin/APJ system in respiratory diseases, including pulmonary arterial hypertension (PAH), pulmonary embolism (PE), acute lung injury (ALI)/acute respiratory distress syndrome (ARDS), obstructive sleep apnoea syndrome (OSAS), non-small cell lung cancer (NSCLC), pulmonary edema, asthma, and chronic obstructive pulmonary diseases. In detail, apelin/APJ system attenuates PAH by activating AMPK-KLF2-eNOS-NO signaling and miR424/503-FGF axis. Also, apelin protects against ALI/ARDS by reducing mitochondrial ROS-triggered oxidative damage, mitochondria apoptosis, and inflammatory responses induced by the activation of NF-κB and NLRP3 inflammasome. Apelin/APJ system also prevents the occurrence of pulmonary edema via activating AKT-NOS3-NO pathway. Moreover, apelin/APJ system accelerates NSCLC cells' proliferation and migration via triggering ERK1/2-cyclin D1 and PAK1-cofilin signaling, respectively. Additionally, apelin/APJ system may act as a predictor in the development of OSAS and PE. Considering the pleiotropic actions of apelin/APJ system, targeting apelin/APJ system may be a potent therapeutic avenue for respiratory diseases.

Elabela and Apelin actions in healthy and pathological pregnancies

Pregnancy is a dynamic and precisely organized process during which one or more baby develops. Embryonic development relies on the formation of the placenta, allowing nutrient and oxygen exchange between the mother and the fetus. Dysfunction of placental formation lead to pregnancy disorders such as preeclampsia (PE) with serious deleterious consequences for fetal and maternal health. Identifying factors involved in fetoplacental homeostasis could inform better diagnostic and therapeutic strategies for these pathological pregnancies. Here, we summarize actions of elabela, apelin and their common receptor APJ in the fetoplacental unit. Studies indicate that elabela is crucial for embryo cardiovascular system formation and early placental development, while apelin acts in mid/late gestation to modulate fetal angiogenesis and energy homeostasis. Most of these findings, drawn from animal models, indicate a key role of elabela/apelin-APJ system in the fetoplacental unit. This review also provides an overview of clinical studies investigating elabela/apelin-APJ system in pathological complicated pregnancies such as PE and gestational diabetes mellitus (GDM). While elabela-deficient mice display all the features of PE, current clinical studies show no difference in circulating elabela levels between PE and control patients which does not support a role in PE development. Conversely, apelin levels are increased during PE, but the use of apelin as an early PE marker remains to be fully investigated.

Daily Intermittent Normobaric Hypoxia Over 2 Weeks Reduces BDNF Plasma Levels in Young Adults - A Randomized Controlled Feasibility Study

Background: The results from animal and human research indicate that acute intermittent hypoxia can enhance brain-derived neurotrophic factor (BDNF) plasma levels and gene expression. As BDNF is known to promote the differentiation of new neurons and the formation of synapses, it has been proposed to mediate adult neuroplasticity. Thus, the present study aimed to analyze the long-term effects of daily intermittent exposure to normobaric hypoxia (simulating high altitude exposure at approximately 4000–5000 m) over 2 weeks on BDNF levels in young adults.

Methods: Twenty-eight young adults (age: 19–33 years) were randomized into a hypoxic intervention group (N = 14) or the control group (N = 14). Participants in the intervention group breathed intermittent normobaric hypoxic air at resting conditions (5 min intervals, 80–85% SpO₂ measured via a finger pulse oximeter, 12 sessions for 60 min/day for 2 weeks) via a hypoxic generator. BDNF plasma and serum levels were determined at baseline and at 2 weeks after intervention using sandwich ELISAs.

Results: After 2 weeks of daily intermittent hypoxic treatment (IHT), we found a significant group x time interaction effect for BDNF plasma levels based on a significant decrease in BDNF levels in the hypoxia group.

Conclusion: Our results demonstrate that daily intermittent administration of hypoxic air has a significant effect on BDNF regulation in healthy young adults. Contrary to other results reporting an increase in BDNF levels under hypoxic conditions, the present data suggest that hypoxic treatment using intensive IHT can reduce BDNF plasma levels for at least 2 weeks. This finding indicates that the daily application of hypoxic air is too frequent for the aimed physiological response, namely, an increase in BDNF levels.