Cardiac Function

 

Cardiovascular Research Section

In the cardiovascular research section of the Cox laboratory we focus on myocardial protection to ischemia / reperfusion injuries and the associated pathophysiology. The laboratory is equipped for myocardial performance and hemodynamic measurements in both small and large animals (e.g. Langendorff-perfusion-system, transonic Flow probes, Millar Aria Induction Catheter System). Furthermore, the laboratory has a complete setup for cardiac surgery related research including a cardiopulmonary bypass pump, a heat exchanger, and a blood gas analyzer.

Current projects:

Myocardial gene transfer for improved apoptosis prevention

Apoptosis plays an important role in the cardiovascular system in the process of homeostasis and development but also plays a role in the pathogenesis of certain diseases. Apoptosis is implicated in the death of myocytes in animal models of myocardial ischemia, in humans with acute myocardial infarction, and in congestive heart failure. Even though it is clear that the extensive death of cardiac myocytes after I/R contributes to the decline of ventricular function and mortality, the pathways that initiate apoptosis during ischemia/reperfusion (I/R) in the heart are poorly understood. Studies have suggested that many factors, including Bcl-2 homologous proteins, ATP depletion, acidosis, calcium fluxes, and reactive oxygen species, cause cytochrome c release and apoptosis during I/R in cardiac myocytes.
In recent studies we could demonstrate that apoptosis induction already occurs during global cardioplegic arrest in the majority of both cardiomyocytes and coronary endothelium and that apoptosis induction at least in part depends on reactive oxygen species generation during ischemia. In a series of experiments in rats we could identify different time courses of the apoptosis signal-pathway depending on global ischemia with and without cardioplegia with calcium concentration as crucial factor. Furthermore, in a clinically relevant animal model of cardioplegic arrest on cardiopulmonary bypass we found significantly improved left ventricular (LV) function following ischemia with apoptosis inhibition. Another experimental study in rats showed a markedly better preserved LV function following 4 and even 18 hours of cold cardioplegic arrest with inhibition of apoptosis (unpublished data). Together with results from other groups regarding apoptosis inhibition during regional myocardial ischemia, we provide evidence for apoptosis inhibition as promising and effective strategy to improve myocardial protection during both regional and global ischemia.
However, the efficacy of a pharmaceutical approach to myocardial apoptosis inhibition depends on several variables such as time point, dosage and route of application. Furthermore, the systemical side effects have not been investigated yet.
An alternative approach for an anti-apoptotic strategy in myocardial protection during ischemia and reperfusion would be to enhance the physiological defense system against apoptosis.
The apoptosis repressor with CARD (ARC) protein expressed in heart and skeletal muscle represents such a physiological anti-apoptotic system. ARC was initially reported to interact with caspase-2 and –8 and to inhibit apoptosis induced by caspase-8 and receptor-induced apoptosis by Fas and TNF-R1, leading to the proposal that ARC protects interfering with the function of initiator caspases. However, other studies have reported that ARC-mediated protection may not necessarily operate through the inhibition of caspases. For instance, ARC suppressed hypoxia-induced apoptosis by inhibiting cytochrome c release from the mitochondria in a caspase-independent manner. In addition, ARC overexpression inhibited oxidant stress-induced cell death in H9c2 cells by preserving mitochondrial function independently of caspase inhibition, suggesting that ARC might act at the level of the mitochondria.
In summary, ARC is a master regulator of cardiac death signaling because it is the only known factor that specifically inhibits both the intrinsic and extrinsic apoptotic death pathway. In addition, ARC is also effective against oxidant stress-induced cell death and is specifically expressed in striated muscle. Hence, ARC is an ideal system for targeted manipulation in order to improve myocardial protection during I/R.

Study purpose/Study aims

The study aim is the prophylactic long-term conditioning of the heart using gene transfer to improve cellular defense mechanisms for myocardial protection during/following ischemia and reperfusion. Primary strategy is myocardial apoptosis inhibition using ARC gene transfer.

Specific aims:

  1. ARC overexpression in myocardium via targeted gene transfer
  2. Improved apoptosis inhibition during/following mycardial ischemia/reperfusion
  3. Improved myocardial protection during/following both regional and global myocardial ischemia
  4. Improved cardiac allograft protection and ischemic tolerance during between expantation and implantation

Study purpose is the prophylactic use of gene transfer to enhance anti-apoptotic defence mechanisms for improved myocardial protection. To assess for the prophylactic effect we will compare gene transfer two weeks before and immediately following ischemia. An additional, group of animals will receive pharmacological inhibition of apoptosis. We will investigate for both regional (myocardial infarction) and global ischemia (cardiac surgery, heart transplantation). The study design includes two levels of experiments. The first experiments will be carried out in a small animal model (rats). We will then proceed to large animal studies (pigs). With the large animal studies we also plan to build the basis for transplantation studies in order to assess for gene transfer technique as potential method for cardiac allograft protection and survival.

Improving stem cell homing to injured myocardium

Peripheral and bone marrow-derived stem cells (BMDCs) represent a promising therapeutical strategy for the treatment of ischemic myocardial diseases. Although the differentiation capacity of BMDCs directly injected into the heart after myocardial infarction (MI) is controversial they result in improved ventricular function, which may be due to production of cytokines that potentially restore heart function and vascularisation. Early experience with autologous unfractionated bone marrow (BM) via the endocardial and intracoronary routes has been promising with respect to improvement in ischemic parameters. The invasive nature of BM harvest and subsequent cardiac delivery, however, has limited the clinical utility of cell therapies. Despite beneficial effects of direct BMDC injection into the myocardium there is evidence that a considerable amount of directly injected cells die shortly after application. Thus, a physiological way to attract or deliver stem cells to the injured myocardium to assure survival of the majority of progenitor cells is preferable.
Another crucial factor for stem cell survival and regeneration of injured myocardium is environmental conditions of the homing site and the timing of stem cell therapy. The adverse hypoxic and inflammatory environment, with its high oxidative stress, might be deleterious if cells are administered too early after reperfusion without sufficient defence capacities.

The proposed studies address the following key aspects of stem cell therapy for myocardial repair in a clinically relevant animal model:

  1. Improving cell homing and cell migration to injured sites (gene transfer to myocardium)
  2. Improving stem cell capacity to withstand the adverse environment (gene transfer to stem cells) and improved migration to site of injury.