In a metabolic study of [1-(14)C]geranylgeranial involving rat thymocytes, the radioactivity was mainly incorporated into two metabolites, Z1 and Z2, the latter moving slower than the former on a silica-gel thin-layer plate. The time course of Z1 and Z2 formation superficially suggested a precursor-product relationship between Z1 and Z2. The two metabolites were chemically converted to their methyl esters on treatment with trimethylsilyl diazomethane. Z1 was cochromatographed with E,E,E-geranylgeranoic acid (GGA). Z2 was prepared in a large quantity from geranylgeranial using thymocytes, and purified by TLC followed by ESI (negative ion mode) or EI mass-spectrometry. The observation of a negative ion at m/z 305 on ESI and a molecular ion at m/z 306 (C(20)H(34)O(2)) with fragments similar to GGA on EI implied that Z2 was dihydroGGA, which has been detected in the urine and serum of patients with Refsum disease. The EI mass spectrum of (R)-2,3-dihydroGGA was identical to that of Z2. The diastereomeric amide synthesized from metabolite Z2 with (R)-1-(1-naphtyl)ethylamine was cochromatographed with (R acid, R) amide, not with (S acid, R) amide, which were similarly synthesized from (R)- and (S)-2,3-dihydroGGAs, respectively. In another metabolic study on [1-(14)C]geranylgeraniol (GGOH), the radioactivity was similarly incorporated into a metabolite corresponding to (R)-2,3-dihydroGGA. (R)-2,3-DihydroGGA induced DNA ladder formation with a maximum at 15 mciroM in thymocytes. However, 2,3-dihydrofarnesoic acid did not induce it at all.

Geranylgeranoic acid (GGA) and 2,3-dihydrogeranylgeranoic acid (2,3-diGGA) are geranylgeraniol-derived metabolites (Kodaira et al. (2002) J Biochem 132: 327-334). In the present study, we examined the effects of these acids on HL-60 cells. The cells were differentiated into neutrophils by GGA stimulation like retinoic acid stimulation. In the case of cells stimulated with 2,3-diGGA, neutrophils were not detected, but the formation of lipid droplets was induced. On the other hand, when the cells were cultured in the presence of 0.1% FBS instead of 10% FBS, apoptotic cells were induced not only by GGA stimulation but also with 2,3-diGGA. In the latter case, when the cells were cultured in the co-presence of a caspase-3 inhibitor (Ac-DMQD-CHO), the lipid droplets formation was observed in the cells. These results suggest that GGA and 2,3-diGGA are extremely different from each other with respect to their effects on HL-60 cells.