## 4 Discussion
Taken together, the experimental results indicate that the liver lyophilized powder of porcine origin is not cytotoxic on either of the two cell types. LLP instead determines a positive metabolic (evaluated by MTT assay) and replicative (measured by DNA synthesis) stimulus to HepG2 and At-MSCs, while a statistically significant increase in cell number was observed only in At-MSC cultures. Although our data do not provide information regarding the components of the LLP responsible for these effects, recent contributions from the literature, in addition to vitamins, minerals, and other bioactive molecules, emphasize the presence in liver tissue of more complex multi-molecular particles, such as exosomes and microvesicles capable of controlling and stimulating the metabolic activity of the organ both in physiological and pathological conditions [45; 46]. Interestingly, it has been observed that exosomes derived from liver cells modulate various biological activities (such as control of cell proliferation and apoptosis, regulation of gene transcription) on cultured hepatocytes [47] and other cell types [43]. Furthermore, the maintenance of hepatocyte-specific functions of primary cultures expanded in the presence of liver extracellular matrix [11; 42] has been observed, suggesting that that liver tissue extracts can support in vitro hepatocyte culture and could be considered a candidate for the development of treatment for liver diseases [42]. Our results indicate that a porcine liver lyophilized powder derived from the whole organ without any chemical treatment is safe and maintains an in vitro stimulatory effect on HepG2 and At-MSC, although a different response was observed for the two cell types. Interestingly, the LLP stimulates proliferation in At-MSCs, in agreement with other results indicating a reciprocal cross-talk between liver cells and MSCs [21; 38]. The work has some weak points that need to be addressed in the future. We are aware that our results do not evaluate the effect of the LLP on biological features typical of hepatocytes (glycogen, urea, and albumin synthesis) or MSCs (differentiation ability, immunomododulation, secretome production). Furthermore, the effects of LLP on other cell types, such as, for example immune cells, should be evaluated to explore a possible role of the preparation in the complex biological pathways involved in tissue maintenance and regeneration. In conclusion, we think that the liver lyophilized powder prepared from whole porcine organs deserves a more extensive study to elucidate on one side its specific composition in terms of bioactive molecules, and on the other, to define their roles in the complex metabolic activity of hepatic tissue. Conceptualization, S.G., P.B., O.F. ; methodology, S.G., V.C., P.B., O.F., R.R. ; software, G.B. ; validation, S.G., R.R., G.B. ; formal analysis, G.B., S.G.; data curation, S.G., P.B. ; writing--original draft preparation, P.B., S.G.; writing--review and editing, P.B., S.G., R.R., G.B. ; visualization, P.B., S.G. All authors have read and agreed to the published version of the manuscript. This research was partially funded by the company GUNA spa (Italy). The study did not involve humans or animals. The study did not involve humans. O.F. is the sole shareholder of Neorland(r), which provided the lyophilized liver powder. The procedure for the liver powder preparation is protected by secrecy. O.F. contributed to the conceptualization of the study. GUNA spa partially funded the study. GUNA had no role in the design of the study; in the collection, analysis, or interpretation of the data, as well as in writing the manuscript, or in the decision to publish the results.