It is well known that angiogenic factors such as VEGF play an important role in patients suffering atherosclerosis and diabetes  and might even be used as therapeutic targets . Endostatin is suggested to be a modulator of angiogenesis with angiostatic effects and therefore a target in therapies for cancer and cardiovascular disease. The aim of the present study was to investigate baseline levels and the influence of physical exercise on serum endostatin levels in patients suffering from T2DM compared to controls. We could show for the first time that endostatin baseline levels, measured in serum, are decreased in patients suffering from T2DM compared to age- and sex-matched healthy controls. With regard to the findings by Boodhwani et al.,  who showed that T2DM results in a profound impairment in the myocardial angiogenic response to chronic ischemia, these observations are of distinct interest. Additionally, we stated a significant exercise-induced increase in endostatin levels in T2DM patients as well as in healthy controls.
Our first study aim was to investigate the influence of acute exercise in T2DM-patients and controls. Bruserud et al. observed higher serum baseline levels of endostatin in 68–88 year old female and male people than in 18 year old male athletes and an increase in endostatin levels after physical exercise . An exercise-induced increase in endostatin levels was also observed by Suhr and co-workers, who measured endostatin levels in twelve male cyclists ages 27.8 ± 5.4 years  and in short- and long-track elite runners . Similar results were delivered by Gu et al. who measured plasma endostatin levels in seven healthy male subjects aged 18–49 years. Gu et al.  could show in a rat model (Sprague–Dawley rats), that continuous exercise leads to an decrease in endostatin levels (measured in tissue of skeletal muscle). Brixius et al. stated a decrease of endostatin plasma levels in 50–60 year old male overweight and untrained men after 6 months of moderate exercise 3 times/week . However, Makey et al.  did not find an exercise-induced increase of endostatin in overweight/obese women, but in this study the participants “only” walked on a treadmill at moderate intensity. Nevertheless, considering the results of the mentioned studies both unique and regular physical exercise seems to have an impact on endostatin levels in healthy individuals, where endostatin seems to increase during exercise and to decrease after regular sportive activity. Our results support the theory of exercise-induced endostatin increase which was observable in controls as well as in patients suffering from T2DM. Although exercise-induced stress led to a significant rise in endostatin in both groups it should be mentioned that male controls showed the highest surge by 15% whereas female controls and T2DM-patients only increased by about 10–12%. Furthermore, the increase in endostatin did not seem to be connected to the extent of physical workload: Our subjects were asked to proceed with the bicycle stress test till exhaustion. Although T2DM-patients showed significantly lower performance compared to controls, there was no correlation observable between the extent of endostatin-increase, stress levels of endostatin and performance (Pearson Correlation).
Our second aim was to investigate baseline endostatin levels of T2DM-patients compared to controls with regard to sex-specific differences. Boodhwani et al.  measured 3,6-fold higher endostatin levels (myocardium) in Yucatan miniswine compared to controls. Sodha et al.  was able to show that endostatin levels are elevated 2,02-fold in diabetic patients with CAD in myocardial tissue and that their levels showed a positive correlation to blood glucose levels. Interestingly, we found significantly lower levels in both female and male patients suffering T2DM compare to controls. Additionally, female controls showed significantly higher levels compared to male controls suggesting a hormonal influence on endostatin levels. These two findings are of distinct interest.
On the one hand atherosclerotic vessels often present intra-plaque angiogenesis , supporting plaque expansion and leading to plaque rupture by enhancing its vulnerability [31, 32]. Due to its angiostatic potential, endostatin might enable plaque stabilization by inhibiting sprouting and ingrowth of new vessels into the plaque reducing plaque neovascularisation [33, 34] and therefore could reduce CVD progression. Furthermore, Wenzel et al. recently were able to show, in vitro, that endostatin reduces the vascular tonus by increasing the production of NO by endothelial cells . Following this chain of thought, individuals with high levels of endostatin would be protected more effectively from CVD progression and would have more NO available.
On the other hand, Gu et al.  showed in rats that high endostatin levels correlate with low capillary density. Similar results were obtained from Sodha et al.  who found elevated endostatin levels in the myocardial tissue of diabetic patients together with a strong negative correlation to coronary collateralization. As an organ with a high metabolic demand meaning a high oxidative capacity, the myocardium is dependent on a pronounced capillary network. In this case, high endostatin levels would be prejudicial because impaired collateralization is one of the most important problems in T2DM, in particular in T2DM-patients with coronary artery disease.
With regard to our results and those of the mentioned studies, it is now quite safe to assume that acute exercise leads to an increase in endostatin in healthy individuals and also T2DM-patients nearly to the same extent. Although some studies found increased amounts in animals and patients suffering from T2DM, out data do not support this thesis. To our knowledge, the present study is the first one showing an exercise-induced surge in serum endostatin also in T2DM-patients and a sex-specific difference in baseline endostatin levels with female T2DM-patients and controls showing higher levels than male individuals.
Endostatin levels seem to be dependent on a great number of factors such as sex, age, race, underlying diseases, level of physical fitness and many more. Additionally, the medium in which endostatin is analysed (serum, plasma, muscle tissue, myocardial tissue, arterial, venous…) seems to be of importance in determining its scope of action. Further studies with higher numbers of participants are needed to 1) investigate the influence of regular physical exercise on endostatin release and 2) study the role of endostatin in diabetes. At the present time it seems that endostatin is involved in various mechanisms dealing with angiogenesis and therefore it would be advisable to regard it as modifier of angiogenesis with possible influence in both physiological and pathological angiogenesis.