Adding more pieces to the puzzle
Adding more pieces to the puzzle, using a human-to-animal crossover study, blood taken from healthy volunteers that underwent exercise was used as a dialysate to perfuse a rabbit heart in a Langendorff model of MI . Unprecedentedly, dialysate of plasma from exercised humans reduced infarct size to the same extent as plasma from humans exposed to RIPC. Moreover, this transferrable humoral protection against IR injury was demonstrated to be dependent on the activation the opioid receptor . Not coincidentally, stimulation of opioid receptors with morphine (1 μM for 10 min) significantly increases NO production in isolated cardiomyocytes triggering a RIPC response .
In summary, here we show that acute RE triggers a RIPC effect by limiting cardiac eNOS uncoupling. In clinical terms, exercise RIPC may emerge as a feasible, inexpensive, and contemporary reliable therapy that deserves greater attention, while ascertainment of individual optimal “dose” remains to be established. However, although the majority of proof-of-concept studies show beneficial effects of RIPC, more robust clinical studies are certainly needed to validate the translation of cardioprotection by conditioning therapies in humans, as recently emphasized [47,48].
Funding This study was supported by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), Fundação de Amparo à Pesquisa de Minas Gerais (FAPEMIG), and Fundação de Apoio à Equipe e à Inovação Tecnológica do Estado de Sergipe (FAPITEC/SE). SLS and SG are CNPq research fellows. DSS, JMNP, ICGJ, and JASN are recipients of a CAPES scholarship.
Introduction Tetrahydrobiopterin (BH4), originally identified as an indispensable cofactor for the activity of nitric oxide synthases (NOSs) [1,2] with dimeric formation, was reported to be concerned with NO synthesis , which has multiple actions in the Dyngo-4a of such as maintenance of blood pressure, regulation the force and rate of heart contraction, widening blood vessels and increasing blood flow [4,5]. When BH4 bioavailability is low because of oxidation or insufficient bio-synthesis in vivo, the ferric heme-NO complex can\'t be reduced to the ferrous heme-NO species in NOS, resulting in NOS dissociation and superoxide (·O2−) release, a process termed “NOS uncoupling” . This ability for NOS to generate reactive oxygen species (ROS), such as ·O2−, instead of NO is considered to be related with vascular dysfunction. Furthermore, it\'s important to sustain sufficient BH4 levels in vivo for full NOS functionality. Endothelial NOS (eNOS) is the major source of NO production in endocardial endothelial cells and cardiomyocytes . Ischemia/reperfusion (I/R) in hearts is associated with reduced NO and increased ROS generation [8,9] that is concerned with cellular defects involved with both endothelial and myocyte dysfunction . More importantly, with oxidative stress during I/R injury in hearts, intracellular BH4 can fall below critical level leading to eNOS uncoupling with shift from NO to ROS generation [11,12]. Studies supplementing BH4, by either genetic or pharmacological means, have shown improvements in cardiovascular function [, , , , ]. BH4 is not only highly redox-sensitive and easy to be oxidized [5,18], but also an effective scavenger of ROS [, , ]. Until now a lot of efforts have been made to enhance BH4 bioavailability by combining with other pharmacological agent such as liposome , folic acid, vitamin C or statins , however the clinical effects of these combinations are either poor, not related to BH4 or associated with unavailable technique clinically. Therefore, there is a great need to develop an appropriate BH4 formulation for clinical therapy. Gum Arabic (GA) is a complex polysaccharide consisting mainly of potassium, calcium and magnesium salts of polyarabic acid, with residues of rhamnose, galactose, arabinose and glucuronic acid. It is degraded slowly in the colon by bacterial enzymes to achieve effective drug delivery . It is a kind of effective stabilizer, which can form a protective matrix around dispersed compounds, entraps them inside the matrix and prevents them contact with air and oxidation ; and GA-coated formulations are informed to improve the stability and efficiency of poorly available drugs . Importantly, its characteristics of solubility, emulsification qualities, low viscosity and excellent retention of volatile compounds make GA primarily used in the food and pharmaceutical industries . Therefore, instead of cosupplementation of BH4 with another pharmacological agent, we developed a novel BH4 formulation within GA and demonstrated that this novel GA-coated BH4 oral administration can rapidly increase BH4 content and reverse the loss of myocardial eNOS activity during in vivo I/R and protect heart against acute and chronic I/R injury.