## 4 Discussion  
In this study, we established a mass production system for GP cells based on tissue culture and bioreactors and identified six metabolites in GP extracts. Three of the identified metabolites (uridine, adenosine, and guanosine) were nucleosides. A previous study suggested that guanosine and uridine have therapeutic roles in asthma and exert anti-inflammatory effects [34]. Furthermore, we identified three aromatic amino acids, tyrosine, phenylalanine, and tryptophan, in the extracts. Tryptophan and phenylalanine play important roles in the human diet. For example, tryptophan metabolism is associated with serotonin production, whereas phenylalanine is necessary for tyrosine production [35]. Notably, GP-C and GP-CR contained much higher amounts of the six metabolites than GP-P. This result suggested the enrichment of major metabolites in the extract from the cultured GP cells. The effects of radiofrequency on plant growth have not yet been well-studied. A recent study showed that a weak radiofrequency magnetic field changed the cryptochrome-dependent plant growth response and gene expression in _Arabidopsis_[36]. We tested the possible applications of radiofrequency in plant cell culture. Similarly, we assumed that treatment with weak radiofrequency might alter the metabolites of GP cells; hence, treatment with the extract from such radiofrequency-treated GP cells may alter gene expression in HaCaT cells. However, we did not observe any significant differences in the gene expression profiles between GP-C and GP-CR, although the expression of some genes was condition-specific. We supposed that the radiofrequency treatment in our study might not have been high enough to change the metabolites of GP cells. Based on the metabolites identified from GP extracts, it might be of interest to examine the possible effects of GP extracts on human skin cells. To this end, we compared the gene expression profiles of HaCaT cells after treatment with the three different GP extracts. The gene expression profiles in response to the treatments were similar. For example, genes highly upregulated in the GP-P condition were also upregulated in the other three conditions and vice versa. Therefore, the metabolites and their concentrations in the three GP extracts may be very similar, with minor differences. Based on these results, we concluded that the extracts from plant cell tissue culture and bioreactors could replace those derived from whole plants. Most DEGs identified in GP-all showed similar expressions to the other three groups. Interestingly, we found that not only genes coding for proteins but also several lncRNAs were identified as DEGs after GP extract treatment. LncRNAs are non-coding RNA transcripts longer than 200 nucleotides in size, and at least 15,000 lncRNAs have been reported in genomic regions that do not include protein-coding genes in humans [37]. They also contain promoter- or enhancer-related RNA close to the gene region [37], and therefore, participate in a wide range of biological processes, including gene expression. In this study, we identified two upregulated (_LINC00052_ and _LINC00539_) and one downregulated (_LINC02355_) lncRNAs. Several studies have demonstrated that _LINC00052_ is involved in tumorigenesis, progression, and metastasis in several types of human cancers [38]. A previous study using gene expression data showed that _LINC00539_ might be involved in the immune response against lung adenocarcinoma [39]. These results suggest that GP extract might be associated with the immune response to tumors by inducing the expression of _LINC00052_ and _LINC00539_. However, the functional role of _LINC02355_ has not been reported. Human tissue-specific transcriptome data showed that _LINC02355_ was highly expressed in testis and thyroid tissues [40]. The most significantly upregulated gene under the four conditions was _LTBP1_. _LTBP1_ is a member of the latent transforming growth factor \(\beta\) (TGF\(\beta\))-binding protein (LTBPs) family, which is composed of four proteins (LTBP1-LTBP4).