METHODS: The mammalian expression plasmid pCMV-p16INK4a was used to induce p16INK4a overexpression in THP-1 macrophages. Next, wild-type and p16INK4a-overexpressed macrophages were incubated with oxidized LDL to induce foam cells formation. Lipids accumulation was evaluated using Oil-red-O staining and cholesterol efflux assay, as well as expression of scavenger receptors CD36 and LOX-1. Cellular senescence in macrophage foam cells were determined through analysis of senescence-associated β-galactosidase activity and other SASP factors expression. Meanwhile, autophagy induction was assessed through detection of autophagosome formation and LC3B/p62 markers expression.
RESULTS: The findings showed that p16INK4a enhanced foam cells formation with increased scavenger receptors CD36 and LOX-1 expression and reduced cholesterol efflux in THP-1 macrophages. Besides, β-galactosidase activity was enhanced, and SASP factors such as IL-1α, TNF-α, and MMP9 were up-regulated. In addition, p16INK4a is also shown to induce autophagy, as well as increasing autophagy markers LC3B and p62 expression.
CONCLUSIONS: This study provides insights on p16INK4a in mediating macrophages foam cells formation, cellular senescence, and foam cells formation.
METHODS: NIH 3T3 mouse fibroblasts were cultured in Dulbecco's Modified Eagle's Medium and incubated for 3 days. The cells (3×104) were seeded on the pulpal side of dentine discs and the occlusal side of the discs were treated with different cavity disinfectants: Group 1: de-ionized water (control); Group 2: 2% chlorhexidine (CHX); Group 3: 2% QAS; Group 4: 5% QAS, and Group 5: 10% QAS. Cell morphology of NIH 3T3 cells was examined using scanning electron microscopy (SEM) and cell viability was assessed using Trypan blue assay. The eluates were collected and applied on cells seeded in 24-well plates. The total protein production, alkaline phosphatase activity and deposition of mineralized nodules were evaluated after 7 and 14 days. Immunofluorescence staining was performed on the samples with primary antibodies of CD68+, CD80+, and CD163+ assessing the macrophage M1/M2 phenotypes. The macrophages were imaged using a confocal scanning light microscope with an excitation wavelength of 488nm.
RESULTS: No significant difference in cell viability (p<0.0001), total protein production (p<0.01) and mineralized nodule production (p<0.05) was found between 2% QAS and the control, which was significantly higher than 2% CHX, 5% and 10% QAS after 14 days. Alkaline phosphatase production of 2% QAS was significantly lower than the control (p<0.001), but higher than 2% CHX at 14 days. The M1/M2 macrophage ratio was also significantly lower in the 2% and 10% QAS groups (p<0.05) compared to the control and 2% CHX groups.
SIGNIFICANCE: The 2% QAS cavity disinfectant does not have cytotoxic effects on 3T3 NIH mouse fibroblast cells and the predominance of the anti-inflammatory phenotype after its application may stimulate healing and tissue repair.