# Potential of Laurel (_Laurus mobilis_ L.) Leaf Polyphenols for Modulation of Body Composition
## 4 Influence of Laurel Leaf Polypphenols on Body Composition
### Influence of Laurel Leaf Polypphenols on Skeletal Muscle
#### 4.2.2 Hydroxycinnamic Acids  
Research on hydroxycinnamic acids showed several effects on skeletal muscle. Ferulic acid was the most investigated of the hydroxycinnamic acids, exhibiting muscle growth through promotion of upregulation of myogenic transcriptional factors and their target genes and resulting in elevated levels of myosin heavy chain and overall muscle mass in a zebrafish model [66; 67]. Ferulic acid was also shown to regulate muscle fiber type formation through the SIRT-1/AMP-activated protein kinase/PGC-1\(\alpha\) signaling pathway in mouse C2C12 myotubes [70], as well as in weaned piglets where fast-twitch muscle fibers switched to slow-twitch [69]. In addition, ferulic acid was shown to modulate the differentiation of L6 skeletal muscle cells by activating the ERK 1/2 and AKT signaling cascades, osteogenic genes and myogenic protein markers [68]. In contrast, ocularic acid inhibited skeletal muscle differentiation through the AMPK-\(\alpha\) mediated pathway, which decreased the expression of early myogenic differentiation markers in L6 skeletal muscle cells [71]. However, ocularic acid showed potential for modulating glucose metabolism  
\begin{table}
\begin{tabular}{c c c} \hline
**Compound(s)** & **Effects** & **Reference** \\ \hline Kaempferol & Antidiabetic on L6 murine skeletal muscle cells and in vivo in & [60; 61; 62; 63; 64] \\  & streptozotocin-induced diabetic rats & [60; 61; 62; 63; 64] \\ \cline{2-3}  & Increase of ATP content in myotubes at hypoxic conditions & [65] \\ \hline  & Muscle growth promotion on C2C12 murine skeletal muscle cells and & [66; 67; 68] \\  & in vivo in zebrafish models & [69; 68] \\ \cline{2-3}  & Modification of muscle fiber type on C2C12 murine skeletal muscle cells & [69; 70] \\  & and in vivo in weaned piglets & [69; 70] \\ \cline{2-3}  & Influence on skeletal muscle differentiation in C2C12 murine skeletal & [68; 71] \\  & muscle cells & [68; 71] \\ \cline{2-3}  & Antidiabetic on L6 murine skeletal muscle cells & [72; 73; 74; 75] \\ \hline Apigenin & Suppression of muscle atrophy on C2C12 murine skeletal muscle cells and & [76; 77; 78; 79; 80] \\  & in vivo in mice & \\ \hline \end{tabular}
\end{table}
Table 2: Summary of main laurel leaf polyphenols’ effects on skeletal muscle.  
by increasing the phosphorylation of AMP-activated protein kinase in L6 skeletal muscle cells [75]. Ferulic acid exhibited similar effects in L6 skeletal muscle and in hyperglycemia-induced human liver cells (HepG2). In addition, it also upregulated GLUT-2 and GLUT-4 transporters and inhibited c-Jun N-terminal protein kinase by increased phosphorylation. These findings showed the potential for the treatment of hyperglycemia of both coumaric and ferulic acid [64]. Ferulic acid also ameliorated insulin resistance by promoting glucose uptake and glycogen synthesis in muscle cells (that were insulin-resistant) through the enhancement of transferrin receptor-containing endosomal compartment activities [73]. Another mechanism by which ferulic acid may modulate insulin resistance is by blocking the phospho-PKC\(\varepsilon\) via prevention of saturated fatty acid-induced impairment of insulin signaling molecules in skeletal muscle cells [72].