**1. Introduction**

The pathogenesis of cardiovascular disease, such as atherosclerosis and aortic valve sclerosis, involves inflammatory reactions in response to a variety of stimuli including high

**Citation:** Chiang, Y.-F.; Tsai, C.-H.; Chen, H.-Y.; Wang, K.-L.; Chang, H.-Y.; Huang, Y.-J.; Hong, Y.-H.; Ali, M.; Shieh, T.-M.; Huang, T.-C.; et al. Protective Effects of Fucoxanthin on Hydrogen Peroxide-Induced Calcification of Heart Valve Interstitial Cells. *Mar. Drugs* **2021**, *19*, 307. https://doi.org/10.3390/ md19060307

Academic Editors: Masashi Hosokawa and Hayato Maeda

Received: 23 April 2021 Accepted: 22 May 2021 Published: 26 May 2021

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levels of low-density lipoprotein (LDL) and reactive oxygen species (ROS). The latter are triggered by increased oxidative stress, infections, and chemical damage. In cardiovascular diseases, increased load on myocardial cells or insufficient energy supply would cause an imbalance in energy supply and demand, resulting in an increase in energy metabolism and mitochondrial redox. This eventually leads to an increase in reactive oxygen species (ROS) and damage to heart cells [1].

Heart valves, such as the aortic valve, mainly comprise two types of cells: valve endothelial cells (VEC) on the surface and valve interstitial cells (VIC) in the matrix. VECs regulate message transmission and permeability and also prevent thrombosis [2]. VICs maintain the tissue structure of the valves. Normally, healthy valve cells are mainly of the fibroblast type, but cell apoptosis can be induced in cases of increased reactive oxygen species and this leads to valve damage [3]. Apoptosis is a regulatory pathway of programmed cell death in response to signals generated by environmental stimuli. In the process of apoptosis, a DNA repair protein called poly (ADP-ribose) polymerase-1 (PARP-1) is truncated, causing cell apoptosis [4].

Another role of elevated ROS is in affecting extracellular matrix (ECM) remodeling [5]. In heart valves, ECM remodeling occurs in layers enriched with VIC fibroblast cells with subsequent valve fibrosis potential. A previous study showed that valvular osteoblast induction could activate the ECM accumulation and calcification process [6,7]. Moreover, ROS-induced chronic inflammation resulted in an influx of macrophages and increased pro-osteogenic and angiogenic activities [5], which in return increased the production of proteolytic enzymes and triggered ECM remodeling and valve fibrosis [8].

Small-breed dogs weighing less than 20 kg can suffer from heart valve diseases [9]. In Taiwan, Maltese present the highest incidence [10]. The progression of valve disease is correlated with increased age, heart volume enlargement, and the regurgitation of blood flow [10].

Fucoxanthin (Fx) is a carotenoid with high anti-oxidative activity that is abundant in brown seaweeds [11]. Fx has shown a potential ability to lower lipid peroxidation [12] and exert anti-inflammatory [13], anti-tumor [14], and anti-hyperuricemia [15] effects. Additionally, in cardiovascular disease Fx has shown recovery effects related to DNA damage and cardioprotective effects [16]. However, studies of the protective role of Fx in heart valve interstitial cells are lacking. In this study, we investigated the potential mechanism of Fx in protecting the heart valves from fibrosis.
