Potential of gene therapy for myocardial ischemia

Cell-based therapy for heart failure: skeletal myoblasts

Satellite cells are committed precursor cells residing in the skeletal muscle. These cells provide an almost unlimited regeneration potential to the muscle, contrary to the heart, which, although proved to contain cardiac stem cells, possesses a very limited ability for self-renewal. The idea that myoblasts (satellite cell progenies) may repopulate postinfarction scar occurred around the mid-1990s. Encouraging results of preclinical studies triggered extensive research, which led to the onset of clinical trials. These trials have shown that autologous skeletal myoblast transplantation to cure heart failure is feasible and relatively safe (observed incidences of arrhythmia). Because most of the initial studies on myoblast application into postischemic heart have been carried out as an adjunct to routine surgical procedures, the true clinical outcome of such therapy in regard to cell implantation is blurred and requires to be elucidated. The mechanism by which implantation of skeletal myoblast may improve heart function is not clear, especially in the light of inability of these cells to couple electromechanically with a host myocardium. Successful myoblast therapy depends on a number of factors, including: delivery to the target tissue, long-term survival, efficacious engraftment, differentiation into cardiomyocytes, and integration into the new, unique microenvironment. All these steps constitute a potential goal for cell manipulation aiming to improve the overall outcome of such therapy. Precise understanding of the mechanism by which cells improve cardiac function is essential in giving the sensible direction of further research.

Double oxygen-sensing vector system for robust hypoxia/ischemia-regulated gene induction in cardiac muscle in vitro and in vivo

High-fidelity genetically encoded bio-sensors that respond to changes in cellular environmental milieu in disease offer great potential in a range of patho-physiological settings. Here a unique hypoxia-regulated vector-based system with double oxygen-sensing transcriptional elements was developed for rapid and robust hypoxia-regulated gene expression in the heart. Hypoxia-responsive cis elements were used in tandem with a single proline-modified oxygen-dependent degradation (ODD) domain of hypoxia-inducible factor-1alpha to form a double oxygen-sensing vector system (DOSVS). In adult cardiac myocytes in vitro, the DOSVS demonstrated a low background expression not different from baseline control in normoxia, and with 100% efficiency, robust, 1,000-fold induction upon hypoxia. In the heart in vivo, hypoxic and ischemic challenges elicited rapid 700-fold induction in living animals, exceeding that obtained by a high-fidelity constitutive cytomegalovirus (CMV) viral promoter. DOSVS also showed high temporal resolution in the heart in response to cyclical bouts of hypoxia in vivo. We propose that DOSVS will be valuable for a range of applications, including bio-sensing and therapeutic gene expression in the heart and other organ systems that are confronted by chronic or episodic hypoxic/ischemic stresses in vivo.

Gene and cell therapy for chronic ischaemic heart disease

Viable treatment options are becoming available for the 'no-option' patient with chronic ischaemic heart disease. Instead of revascularising the highly diseased epicardial coronary arteries, scientists and clinicians have been looking at augmenting mother nature's way of providing biological bypass in an attempt to provide symptomatic relief in these patients. The novel use of gene and cell therapies for myocardial neovascularisation has exploded into a flurry of early clinical trials. This translational research has been motivated by an improved understanding of the biological mechanisms involved in tissue repair after ischaemic injury. While safety concerns will be top in priority in these trials, different types or combination of therapies, dose and route of delivery are being tested before further optimisation and establishment. With cautious optimism, a new era in the treatment of ischaemic heart disease is being entered. This article reviews the present state in gene and cell therapies for ischaemic heart disease, the modalities of their delivery, novel imaging techniques and future perspectives.