## 4 Discussion
In its inactive form, Beclin-1 presents in a homodimer configuration, with Bcl-2/Bcl-XL proteins attached to the specific binding site (Bcl-2 homology-3) on each Beclin-1 molecule [35]. Tocotrienols inhibit the PI3K/Akt/mTOR-signaling pathway [14], resulting in increased ULK1 activity due to reduced MTORC1 activity, which is required to inactivate ULK1 [35]. LC3 also plays an essential role in the formation of the autophagosome. LC3 II is an autophagosome marker produced by LC3I conversion, via a series of ATG reactions that mediate the incorporation of LC3 II into the membrane of the autophagosome [36]. Then, the autophagosome fuses with a lysosome, forming an autolysosome that degrades the accumulated products [35]. Another mechanism that contributes to locotrienol-induced cardioprotective effects is the regulation of a variety of signaling molecules via caveolin. Caveolin is an integral protein that is associated with caveolae, the lipid rafts in the plasma membrane that forms an invagination in the presence of multiple oligomerized caveolins [37]. Both caveolin-1 and -3 are critical regulators in myocardial I/R injury. [PERSON] et al. [10] reported that \(\gamma\)-tocotrienol promotes caveolin-1 interaction with p38\(\alpha\), while reducing the interaction of caveolin-3 with p38\(\beta\), resulting in the inhibition of the mitogen-activated protein kinase (MAPK) pathway [10]. The former p38 isoform is associated with the pro-apoptotic pathway, while the latter promotes anti-apoptotic pathway [38]. Moreover, locotrienols attenuate mitochondrial injury, reducing cytochrome c translocation from mitochondria into the cytoplasm, and the activation of caspase-3 that promotes apoptosis [10]. Other than that, locotrienols also increase the interaction of another pro-apoptotic marker (Src kinase) and caveolin-1 but weaken the binding to anti-apoptotic markers of eNOS and HO-1 [10]. In addition, locotrienols promote cardioprotection via the regulation of angiogenesis [15]. [PERSON] et al. [15] reported that the microRNA-20b level was significantly elevated in the \(\gamma\)-tocotrienol-treated group. In contrast, both hypoxia-induced factor-1\(\alpha\) (HIF-1\(\alpha\)) and vascular endothelial growth factor (VEGF) were significantly reduced. In the event of acute myocardial ischemia, HIF-1\(\alpha\) expression is elevated, promoting the transcription of various molecules, including VEGF [39]. The exact reason why the locotrienol modulation of angiogenesis leads to cardioprotective effects is unclear. However, it may be partly related to the attenuation of vascular permeability, reducing the inflammatory reaction. Interestingly, the dose ranges for both cardioprotective and neuroprotective effects are distinct and broad. The studies involving the myocardial I/R injury model utilized long-term individual locotriends (\(\alpha\), \(\gamma\), \(\delta\)) with a dose of between 0.02 and 5 mg/kg/day [10; 11; 14; 15]. This dose range is substantially lower than in the studies of the cerebral I/R injury model that used either combined locotriends and \(\alpha\)-tocopherol (200 mg/kg) [17; 21], mixed locotriends (400 mg/day) [20], or \(\alpha\)-tocotrienol (50 mg/kg/day) [19]. The human equivalent dose (HED) calculated (based on a 60-kg human) [40] for cardioprotective effects ranged from 0.2 to 48 mg/day [9; 10; 22; 30], while the dose range for neuroprotective effects was 240-960 mg/day [17; 19; 21]. The question of the tolerability of the dose might arise, as the upper limit of the dose required is remarkably high. In an open-label, randomized study, [PERSON] et al. [41] reported that 750-1000 mg of locotrienols given orally were tolerated well and showed a similar pharmacokinetic profile compared to lower doses. Furthermore, no adverse effects were reported [41]. This study indicates that the HED derived from the studies is safe to be consumed. The reason for the higher dose requirement for neuroprotection is obscure but is probably due to the different pharmacokinetic properties of locotriends.