The role of tetrahydrobiopterin and dihydrobiopterin in ischemia/reperfusion injury when given at reperfusion

Cardiomyocyte-derived small extracellular vesicles can signal eNOS activation in cardiac microvascular endothelial cells to protect against Ischemia/Reperfusion injury

Rationale: The crosstalk between cardiac microvascular endothelial cells (CMECs) and cardiomyocytes (CMs) has emerged as a key component in the development of, and protection against, cardiac diseases. For example, activation of endothelial nitric oxide synthase (eNOS) in CMECs, by therapeutic strategies such as ischemic preconditioning, plays a critical role in the protection against myocardial ischemia/reperfusion (I/R) injury. However, much less is known about the signals produced by CMs that are able to regulate CMEC biology. Here we uncovered one such mechanism using Tongxinluo (TXL), a traditional Chinese medicine, that alleviates myocardial ischemia/reperfusion (I/R) injury by activating CMEC eNOS. The aim of our study is to identify the signals produced by CMs that can regulate CMEC biology during I/R. Methods: Ex vivo, in vivo, and in vitro settings of ischemia-reperfusion were used in our study, with the protective signaling pathways activated in CMECs identified using genetic inhibition (p70s6k1 siRNA, miR-145-5p mimics, etc.), chemical inhibitors (the eNOS inhibitor, L-NNA, and the small extracellular vesicles (sEVs) inhibitor, GW4869) and Western blot analyses. TritonX-100 at a dose of 0.125% was utilized to inactivate the eNOS activity in endothelium to investigate the role of CMEC-derived eNOS in TXL-induced cardioprotection. Results: We found that while CMEC-derived eNOS activity was required for the cardioprotection of TXL, activation of eNOS in CMECs by TXL did not occur directly. Instead, eNOS activation in CMECs required a crosstalk between CMs and CMECs through the uptake of CM-derived sEVs. We further demonstrate that TXL induced CM-sEVs contain increased levels of Long Intergenic Non-Protein Coding RNA, Regulator Of Reprogramming (Linc-ROR). Upon uptake into CMECs, linc-ROR downregulates its target miR-145-5p leading to activation of the eNOS pathway by facilitating the expression of p70s6k1 in these cells. The activation of CMEC-derived eNOS works to increase survival in both the CMECs and the CMs themselves. Conclusions: These data uncover a mechanism by which the crosstalk between CMs and CMECs leads to the increased survival of the heart after I/R injury and point to a new therapeutic target for the blunting of myocardial I/R injury.

Controlled exposure to particulate matter from urban street air is associated with decreased vasodilation and heart rate variability in overweight and older adults

Background

Exposure to particulate matter (PM) is generally associated with elevated risk of cardiovascular morbidity and mortality. Elderly and obese subjects may be particularly susceptible, although short-term effects are poorly described.

Methods

Sixty healthy subjects (25 males, 35 females, age 55 to 83 years, body mass index > 25 kg/m²) were included in a cross-over study with 5 hours of exposure to particle- or sham-filtered air from a busy street using an exposure-chamber. The sham- versus particle-filtered air had average particle number concentrations of ~23.000 versus ~1800/cm³ and PM_2.5 levels of 24 versus 3μg/m³, respectively. The PM contained similar fractions of elemental and black carbon (~20-25%) in both exposure scenarios. Reactive hyperemia and nitroglycerin-induced vasodilation in finger arteries and heart rate variability (HRV) measured within 1 h after exposure were primary outcomes. Potential explanatory mechanistic variables included markers of oxidative stress (ascorbate/dehydroascorbate, nitric oxide-production cofactor tetrahydrobiopterin and its oxidation product dihydrobiopterin) and inflammation markers (C-reactive protein and leukocyte differential counts).

Results

Nitroglycerin-induced vasodilation was reduced by 12% [95% confidence interval: −22%; −1.0%] following PM exposure, whereas hyperemia-induced vasodilation was reduced by 5% [95% confidence interval: −11.6%; 1.6%]. Moreover, HRV measurements showed that the high and low frequency domains were significantly decreased and increased, respectively. Redox and inflammatory status did not change significantly based on the above measures.

Conclusions

This study indicates that exposure to real-life levels of PM from urban street air impairs the vasomotor function and HRV in overweight middle-aged and elderly adults, although this could not be explained by changes in inflammation, oxidative stress or nitric oxide-cofactors.

Electronic supplementary material

The online version of this article (doi:10.1186/s12989-015-0081-9) contains supplementary material, which is available to authorized users.

The role of uridine adenosine tetraphosphate in the vascular system

The endothelium plays a pivotal role in vascular homeostasis, and endothelial dysfunction is a major feature of cardiovascular diseases, such as arterial hypertension, atherosclerosis, and diabetes. Recently, uridine adenosine tetraphosphate (Up(4)A) has been identified as a novel and potent endothelium-derived contracting factor (EDCF). Up(4)A structurally contains both purine and pyrimidine moieties, which activate purinergic receptors. There is an accumulating body of evidence to show that Up(4)A modulates vascular function by actions on endothelial and smooth muscle cells. In this paper, we discuss the effects of Up(4)A on vascular function and a potential role for Up(4)A in cardiovascular diseases.

Targeting endothelial and myocardial dysfunction with tetrahydrobiopterin

Tetrahydrobiopterin (BH(4)) is an essential cofactor for aromatic amino acid hydroxylases and for all three nitric oxide synthase (NOS) isoforms. It also has a protective role in the cell as an antioxidant and scavenger of reactive nitrogen and oxygen species. Experimental studies in humans and animals demonstrate that decreased BH(4)-bioavailability, with subsequent uncoupling of endothelial NOS (eNOS) plays an important role in the pathogenesis of endothelial dysfunction, hypertension, ischemia-reperfusion injury, and pathologic cardiac remodeling. Synthetic BH(4) is clinically approved for the treatment of phenylketonuria, and experimental studies support its capacity for ameliorating cardiovascular pathophysiologies. To date, however, the translation of these studies to human patients remains limited, and early results have been mixed. In this review, we discuss the pathophysiologic role of decreased BH(4) bioavailability, molecular mechanisms regulating its metabolism, and its potential therapeutic use as well as pitfalls as an NOS-modulating drug. This article is part of a special issue entitled ''Key Signaling Molecules in Hypertrophy and Heart Failure.''