Adrian Türkcan

Apoptosis, necrosis, or autophagy—it is the mode of cell demise that defines the response of surrounding cells and organs. In case of one of the most toxic substances known to date, cadmium (Cd), and despite a large number of studies, the mode of cell death induced is still unclear. As there exists conflicting data as to which cell death mode is induced by Cd both across various cell types and within a single one, we chose to analyse Cd-induced cell death in primary human endothelial cells by investigating all possibilities that a cell faces in undergoing cell death. Our results indicate that Cd-induced death signalling starts with the causation of DNA damage and a cytosolic calcium flux. These two events lead to an apoptosis signalling-related mitochondrial membrane depolarisation and a classical DNA damage response. Simultaneously, autophagy signalling such as ER stress and phagosome formation is initiated. Importantly, we also observed lysosomal membrane permeabilization. It is the integration of all signals that results in DNA degradation and a disruption of the plasma membrane. Our data thus suggest that Cd causes the activation of multiple death signals in parallel. The genotype (for example, p53 positive or negative) as well as other factors may determine the initiation and rate of individual death signals. Differences in the signal mix and speed may explain the differing results recorded as to the Cd-induced mode of cell death thus far. In human endothelial cells it is the sum of most if not all of these signals that determine the mode of Cd-induced cell death: programmed necrosis.

The deleterious effects of increased Cd serum levels on the cardiovascular system are proven by epidemiological and basic science studies. Cd exposure of animals and humans is known to impair myocardial function, possibly leading to heart failure. The present study aims at investigating the effect of Cd treatment on the cardiac system with emphasis on the combined effect of Cd and high serum cholesterol levels as an important cardiovascular risk factor. Detailed analyses of Cd induced effects on the heart of ApoE-/- mice fed a high fat diet, ApoE-/- mice fed a normal diet, and C57BL/6J mice fed a normal diet revealed pro-inflammatory and fibrotic changes in the presence of cellular hypertrophy but in the absence of organ hypertrophy. Hypercholesterolemia in ApoE-/- mice alone and in combination with Cd treatment resulted in significant cardiomyocyte cell death. Based on further analyses of heart sections we conclude that severe hypercholesterolemia in combination with ApoE-/- genotype as well as Cd treatment results in necrotic cardiomyocyte death. These data were supported by in vitro experiments showing a Cd induced depolarisation of the mitochondrial membrane and the permeabilization of the plasma membrane arguing for the occurrence of Cd induced necrotic cell death. In summary, we were able to show for the first time that the combination of high cholesterol and Cd levels increase the risk for heart failure through cardiac fibrosis. This observation could in part be explained by the dramatically increased deposition of Cd in the hearts of ApoE-/- mice fed a high fat diet.

Insufficient angiogenesis and arteriogenesis in cardiac tissue after myocardial infarction (MI) is a significant factor hampering the functional recovery of the heart. To overcome this problem we screened for compounds capable of stimulating angiogenesis, and herein investigate the most active molecule, 5-Methoxyleoligin (5ML), in detail. 5ML potently stimulated endothelial tube formation, angiogenic sprouting, and angiogenesis in a chicken chorioallantoic membrane assay. Further, microarray- and knock down- based analyses revealed that 5ML induces angiogenesis by upregulation of CYP26B1. In an in vivo rat MI model 5ML potently increased the number of arterioles in the peri-infarction and infarction area, reduced myocardial muscle loss, and led to a significant increase in LV function (plus 21% 28 days after MI). The present study shows that 5ML induces CYP26B1-dependent angiogenesis in vitro, and arteriogenesis in vivo. Whether or not CYP26B1 is relevant for in vivo arteriogenesis is not clear at the moment. Importantly, 5ML-induced arteriogenesis in vivo makes the compound even more interesting for a post MI therapy. 5ML may constitute the first low molecular weight compound leading to an improvement of myocardial function after MI.