One of the possibilities of HO targeting is

One of the possibilities of HO-1 targeting is gene therapy. So far, the majority of preclinical studies have focused on recombinant adeno-associated viral (rAAV) vectors as DNA carriers. They not only provide stable, long-term transgene expression in non-dividing bromfenac australia but also have very limited immunogenicity after in vivo administration [135]. In case of MI, it was demonstrated that HO-1 delivery can exert strong cardioprotective effects and therefore be particularly beneficial as a pre-emptive therapy. Administration of rAAV vectors encoding HO-1 several weeks before induction of heart I/R injury resulted in substantial reduction of infarct size, as well as upregulation of anti-apoptotic signalling [136]. In addition, similar conclusions can be drawn also from chronic, recurrent myocardial ischemic injury model, where apart from decreased apoptosis, AAV-mediated HO-1 delivery diminished cardiac fibrosis and inflammatory response [137]. Interestingly, advantageous effects of HO-1 overexpression can be still observed even a year after MI. Long-term studies revealed a significant reduction of mortality together with markedly improved LV function basing on echocardiographic measurements [138]. Moreover, AAV vectors enable very stable and relatively persistent expression of the chosen transgene in heart. Cardioprotective properties of HO-1 could be still noticed, even when MI procedure was performed a year after gene delivery [139]. The promising outcome of preclinical studies in small animals encouraged similar experiments in the porcine model of MI. In this case, administration of rAAV-HO-1 vectors resulted in a considerable decrease of monocyte and neutrophil infiltration with concomitant improvement of LV function [111]. Despite positive results of implemented gene therapy in animal models, there are still many challenges to be overcome prior to starting such treatment of patients. Although many of the experimental procedures involved intramyocardial administration of vectors, such intervention may be very risky in humans. While the systemic administration will be preferable in this case, it also may cause additional adverse effects due to transduction of off-target tissues. This, however, can be at least partially prevented by using regulated expression systems, for example, tissue-specific promoters (MLC2v for heart ventricles), hypoxia-inducible promoters or miRNA-dependent expression constructs [[140], [141], [142]]. Moreover, selection of appropriate AAV serotype of the vector may allow efficient targeting of gene delivery into the heart tissue [143]. Nonetheless, obtaining sufficient level of transgene expression in humans is still one of the most crucial obstacles to successful gene therapy. Since HO-1 gene delivery methods are not yet available for clinical applications, pharmacological induction of HO-1 expression seems to be a promising alternative. In case of heart I/R injury models, it was demonstrated that pre-treatment of animals with hemin considerably reduced infarct area [144,145]. Of note, this effect was completely reversed after administration of tin protoporphyrin IX (SnPP) – an HO-1 inhibitor [145]. Comparable results were obtained for MI in diabetic mice, where HO-1 expression was induced with cobalt protoporphyrin IX (CoPP). In this study, apart from improved cardiac function, also activation of anti-apoptotic pathways and phosphorylation of glycogen synthase kinase-3 beta (GSK3-β) were observed, thus indicating cardioprotective properties of HO-1 upregulation [146]. Even though these results may be encouraging, possible adverse effects of the application of such HO-1 inducers in patients are still an obstacle. So far, numerous experiments pointed out a very limited specificity of protoporphyrins, together with possible toxicity [147,148]. Another group of compounds that can influence HO-1 level are statins, the inhibitors of hydroxymethyl glutaryl coenzyme A reductase [149]. Due to their anti-inflammatory and pro-angiogenic properties, they were widely studied in terms of cardiovascular diseases. It appears that their beneficial effects can be exerted through HO-1 upregulation mediated by stabilisation of its mRNA via PI3K/Akt pathway [150]. Interestingly, the therapeutic potential of HO-1 induction, to a large extent is comparable to the direct utilisation of heme catabolism end products. Administration of CO (in form of CO-releasing molecule, CORM) resulted in improved post-ischemic heart function recovery, with significantly reduced infarct size and anti-arrhythmic protection [133,151,152]. In case of post-MI treatment, an alternative approach may involve targeting of cardiac macrophages rather than the whole heart. It was recently shown, that lipid-encapsulated hemin can be efficiently delivered to the macrophages what may change their polarization and therefore influence restoration of heart function [153].