Rat dental pulp stem cells (DPSCs) can be used to elucidate mesenchymal stem cell (MSC) applications in regenerative medicine. However, information on rat DPSCs during long-term passage, which could lead to replicative senescence, is limited. In this study, we investigated the phenotypic changes in DPSCs after 3–26 passages (3P–26P). The results show that cell morphology and nuclear size increase proportionally with passage number. The phosphorylated histone H2A.X (γ-H2A.X) positive cells (indicating DNA damage) increased significantly earlier than the 4-Hydroxynonenal (4-HNE) stained cells (indicating an abundance of intracellular reactive oxygen species). Compared to the cells subjected to 3P and 5P, the cells subjected to 15P showed reduced proliferation despite being positive for Ki67. Furthermore, cell growth was completely arrested after 26P. The senescence markers, senescence-associated β-galactosidase (SA-β-gal) and p16, exhibited similar expression patterns that were not correlated with those of p21 and urokinase-type plasminogen activator receptor (uPAR). Nearly all cells expressed SA-β-gal and p16 after 26P, whereas only half expressed p21 and uPAR. These results will contribute to understanding the characteristics of DPSCs toward replicative senescence, which are applicable to elucidate mechanisms related to regenerative medicine and stem cell aging.

Epigallocatechin gallate (EGCG)—the most abundant catechin in green tea—is a promising component of advanced composite biomaterials. The pharmacological activity of EGCG is typically attenuated upon thermal processing, although the exact effects of heating free and modified EGCG in air and vacuum are unknown. To bridge this gap, we herein examined the effects of heating free and modified (in gelatin containing beta-tricalcium phosphate granules) EGCG in vacuum and air (100–220 °C, 1–16 h) on its physicochemical and antioxidant properties using water and ethanol solubility measurements, discoloration and antioxidant activity (2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid) assays, ultraviolet–visible spectroscopy, mass spectrometry, nuclear magnetic resonance spectroscopy, and attenuated total reflectance Fourier transform infrared spectroscopy. The antioxidant activity of EGCG-modified gelatin sponges was assessed in vitro using the DPPH assay and in vivo using a calvarial bone defect model in eight-week-old male Sprague–Dawley rats. Free and modified EGCG showed antioxidant activities, which were largely retained after heating in vacuum at 150 °C. These findings show that appropriate heating procedures preserve the antioxidant activity of EGCG and provide insights for the development of EGCG-based biomaterials.