## 4 Discussion
Based on the results of ALP activity and mineralized nodule formation, APG was verified to promote marker genes that are involved in the bone mineralization, OCN, COL1 and ALP. It was found that other phenolic compounds favored bone preservation and repair by increasing the expression of genes related to osteoblasts, including RUNX-2, OSX, COL1, OSC and ALP [39]. In the present study, the expression of examined genes, mainly ALP and COL1, resulted in up-regulation after treatment with 5 \(\upmu\)M APG. Considering that other phenolic compounds were found to stimulate bone tissue regeneration by acting on the bone morphogenetic protein (BMP) signaling pathway and that BMPs, in turn, act on the expression of bone-related genes, such as ALP [40; 41; 42], this pathway might be a possible molecular mechanism underlying the activity of apigenin in bone. Recently, the correlation between nutrients and bone health focused the attention of researchers to highlight the flavonoids from diet as important factors able to affect bone physiology [26; 43]. Taken together, the data in the present study suggest that apigenin, a flavonoid compound, may have a beneficial effect on oral bone physiology, favoring osteoblast activities. These findings suggest that apigenin might provide insights into the development of tools useful for bone formation during clinical procedures, such as maxillary sinus floor elevation. In dentistry fields, apigenin might be taken into account for different aspects considering that the ideal periodontal biomaterials should fight against pathogenic bacteria and promote bone regeneration in bone reconstruction lesions or in bone defects. The antibacterial activities of apigenin against various Gram-negative and -positive bacterial species were reported [44]. Studies strongly recommend apigenin because of its antibacterial activities for the treatment of oral bacteria. These studies also showed the better effectiveness of antibiotics in combination with apigenin against these bacteria as compared to antibiotic treatment alone, indicating a synergic effect between apigenin and antibiotics [44; 45]. Antiviral activities of apigenin were reported against different viruses [46; 47]. Apigenin, due to its multiple properties, might be taken into account also for tissue engineering scaffolds in maintaining space, in supporting cell attachment and proliferation after being grafted to a bone defect. Indeed, tissue engineering scaffolds are developed in combination with growth factors or stem cells, as well as antibacterial components to improve osteoinduction, osteogenesis and antibacterial activity of bone grafting [48]. The beneficial effects of apigenin, on oral osteoblasts, here demonstrated, in addition to the already known other biological properties of apigenin [1; 7], might potentially make apigenin a multifunctional bioactive agent, helping different situations in the dentistry field, considering that apigenin is a natural molecule, safe, with a very low risk of toxicity. Current treatment options for bone-related diseases, consisting of antiresorptive agents (such as bisphosphonates, hormone-replacement therapy, selective estrogen-receptor modulators and anti-RANKL antibodies) and/or anabolic agents (such as intermittent low doses of teriparatide and antisclerostin antibodies), are not free from adverse effects that limit their use [49]. Thus, the beneficial properties of apigenin on oral osteoblasts include that it is a natural molecule, safe, representing its strength for future use in the dentistry field, in which bone regeneration and new bone formation represent a challenge. The limit of APG clinical application is its poor solubility. At present, to overcome this limit, some approaches to nanoparticle drug carriers have been formulated to improve the solubility, dissolution and the oral bioavailability of APG [50].