In vitro effect of FGIN-1-27, a ligand to 18 kDa mitochondrial translocator protein, in human osteoblast-like cells.

Ligands of 18 kDa mitochondrial translocator protein (TSPO) differ in their cellular effects. We hypothesize that different TSPO ligands might exert different cellular responses. Therefore, following previous studies that showed different cellular responses to two specific TSPO ligands, PK 11195 and protoporphyrin IX, in human osteoblast-like cells in vitro, we now report the cellular response to another specific TSPO ligand, FGIN-1-27 (10(-5) M) (MW 436 kDa), in order to characterize the effects of each TSPO ligand. We found in primary culture of the human osteoblast-like cells that cell numbers were decreased by an average of 30% (p < 0.001) following exposure to 10(-5) M of FGIN-1-27 in comparison to vehicle controls. Cellular [(18)F]-FDG incorporation and ATP content were suppressed, by an average of 43% (p < 0.001) and 83% (p < 0.001), respectively. Mitochondrial mass and ΔΨm increased by an average of 26% (p < 0.01) and 425% (p < 0.0001) respectively. Lactate dehydrogenase activity was enhanced in culture media by 60% (p < 0.05), indicating overall cell death, while no increase in apoptotic levels was observed. Cellular proliferation, as determined by BrdU assay, was not affected. Synthesis of mRNA of TSPO, VDAC 1, and hexokinase 2 decreased in 0.3, 0.3 and 0.5 fold respectively, with accompanying decreases in protein expression of TSPO and Voltage Dependent Anion Channel 1 by 23% (p < 0.001) and 98% (p < 0.001), respectively, but without changes in hexokinase 2 protein expression. Thus it appears that 10(-5) M FGIN-1-27 reduces cell viability, cell metabolism, and mitochondrial function. Previously we found similar effects of PK 11195 on mitochondrial function and cell metabolism and of protoporphyrin IX on cell death in primary osteoblast-like cells.