# Xanthone Derivatives and Their Potential Usage in the Treatment of Telangiectasia and Rosacea
## 1 Introduction  
Vascular disorders are abnormalities in the structure and function of blood vessels. Vascular disorders of the skin are visible as dilated, sometimes cracked capillaries, veins, and arterioles but also as spots or nodules with an erythematosus basis. They arise as a result of pathogenic processes, such as blood disorders in the vessels or abnormal vascular development [1]. Normally, blood vessels are formed by two mechanisms: vasculogenesis and angiogenesis. Vasculogenesis is the formation of blood vessels from the cells of the insular endothelium, leading to the blood vessel plexus. Then, the vessels are formed from the vascular endothelium in a process called angiogenesis. Under pathological conditions, various factors interfere with angiogenesis and result in excessive growth of capillaries in a tumor, a process called neangiogenesis. Vascular endothelial growth factor (VEGF) plays a key role in the processes mentioned above [2; 3; 4]. In addition, with aging, blood vessels are degraded by the enzyme hyaluronidase, which depolymerizes hyaluronic acid and leads to a weakening of the endothelium, resulting in increased vascular permeability [5]. Chemical agents that can minimize skin lesions related to vascular abnormalities are mostly highly effective antioxidants and inhibitors of hyaluronidase. The most-used active substances are compounds from the group of flavonoids and vitamins (e.g., C, K, and B3). The vascular structure, comprising arteries, veins, and capillaries, plays a pivotal role in maintaining physiological homeostasis within the human body. Arteries transportoxygenated blood away from the heart to various tissues and organs, while veins return deoxygenated blood back to the heart. Capillaries, the smallest blood vessels, facilitate nutrient and gas exchange between the bloodstream and surrounding tissues. Structurally, arteries possess thicker walls rich in smooth muscle and elastic fibers, enabling them to withstand high pressure and maintain blood flow. Veins exhibit thinner walls with less muscle and more valves to prevent backflow, aiding in the return of blood to the heart. Capillaries, in contrast, consist of a single layer of endothelial cells, facilitating the efficient exchange of gases, nutrients, and waste products, such as carbon dioxide or urea. This intricate network of vessels is regulated by complex physiological mechanisms involving neural, hormonal, and local factors to ensure proper distribution of blood throughout the body. Dysfunction in vascular structure and function underlies numerous pathological conditions, including hypertension, atherosclerosis, and peripheral vascular disease, highlighting the critical importance of understanding vascular biology for the advancement of medical interventions and treatments [6]. This structure is intimately associated with the glycocalyx, a gel-like layer composed of glycoproteins and proteoglycans that coats the luminal surface of the endothelial cells lining the blood vessels. The glycocalyx serves as a dynamic interface between the bloodstream and the vessel wall, contributing significantly to vascular function and health. Within arteries and veins, the glycocalyx acts as a protective barrier, preventing the direct contact of circulating blood components with the endothelial cells and underlying tissues. This barrier function is crucial for maintaining vascular integrity and preventing inflammation and thrombosis. Moreover, the glycocalyx participates in the regulation of vascular permeability and endothelial cell signaling. It modulates the passage of nutrients, hormones, and immune cells across the vessel wall, thereby influencing tissue perfusion and immune response. Additionally, the glycocalyx plays a vital role in mechanotransduction, sensing and transducing the mechanical forces exerted by blood flow into biochemical signals that regulate vascular tone and remodeling.