## 4 Discussion
Currently, research is also being conducted on animals using preparations such as ointments containing procyanidins to accelerate wound healing. The results of these studies are promising [28]. Studies confirm also the lack of cytotoxicity in a wide range of catechin and epicatechin concentrations towards gingival fibroblasts. [PERSON] et al. [29] indicated different cytotoxicity of flavan-3-ols towards normal human gingival fibroblast (HGF-2) cells. The simple flavan-3-ols, such as (+)-epicatechin, (\(-\))-catechin, and (\(-\))-epigallocatechin showed the lowest cytotoxicity with midpoint cytotoxicity--NR50 values above 500 \(\upmu\)M. Conversely, the flavan-3-ols with a galloyl moiety: (\(-\))-catechin gallate, (\(-\))-epicatechin gallate, and (\(-\))-epigallocatechin gallate showed cytotoxicity at lower concentrations ((NR50) = 131 \(\upmu\)M, 100 \(\upmu\)M, and 256 \(\upmu\)M, respectively). In our decoctions, among the galloyl monomers, only epicatechin gallate was present in relatively high concentrations, with no significant differences between the decoctions. The observed differences in the activity of the decoctions could also be due to different concentrations of stilbenes, including resveratrol and piceid. Both piceid and resveratrol are present in the PH decoction in significantly higher concentrations (Table 2). While piceid revealed a stimulating effect on gingival fibroblast viability at all tested concentrations (5-100 \(\upmu\)g/mL), resveratrol showed this effect only at a dose of 10 \(\upmu\)g/mL (\(-\)44 \(\upmu\)M) and was cytotoxic to the cells at the highest tested concentration-100 \(\upmu\)g/mL (\(-\)439 \(\upmu\)M), (Figure 3). Similar results were obtained in the study by [PERSON] et al. [30], where resveratrol increased the viability of human gingival fibroblasts after 24 h incubation at a concentration of 10 \(\upmu\)M but showed cytotoxicity at higher concentrations of 100 and 200 \(\upmu\)M. Our results are also consistent with other studies that have shown that the viability and proliferation rate of gingival fibroblasts is dependent on the resveratrol concentration [31; 32] and it is cytotoxic at higher doses. The compounds found in greater amounts in the PH decoction are also intraquinones (Tables 1 and 2), mainly emodin and its derivatives. Considering the reports of cytotoxicity of emodin, even at low concentrations (10 \(\upmu\)M), towards fibroblasts [33; 34], it seems that this compound could also have contributed to the weaker activity of the PH decoction. The PH decoction also contains a significantly higher amount of emodin hexosides (compound 41, 43, 45, 47, and 51) and torchrysone hexoside (compound 46). Several studies have shown the toxicity of emodin hexosides and torchrysone hexoside toward hepatocytes [23]. Moreover, these compounds showed severe toxicity against zebrafish embryos and appear to be responsible for _Polygonum multiform_-induced idiosyncratic liver injury (IDILI) [35]. According to traditional Chinese medicine, plant materials should be properly processed before used, which affects the chemical composition, activity, as well as the toxicity of the final preparation. Specific recommendations are included in the Chinese Pharmacopoeia [36]. Regarding _Polygonum multiform_ (PM), the Chinese Pharmacopoeia (2015 edition) recommends steaming the root of PM with black soybean decoction [23]. According to [PERSON] et al. [23], such processing significantly reduced the cytotoxicityof the PM final preparation and was associated with a reduction in the amounts of these two potentially toxic compounds (emodin-8-O-glucose and torachrysone-O-hexose) in it. Another important aspect is that, the main form of application in traditional Chinese pharmacotherapy is the decoction [36; 37]. Our studies conducted on gingival fibroblasts are in line with these recommendations, showing that the decoction is a preparation with activity higher or equal to ethanol and acetone extracts, but it has significantly lower cytotoxicity [9; 10].