GNMT Expression Increases Hepatic Folate Contents and Folate-Dependent Methionine Synthase-Mediated Homocysteine Remethylation

Table 2 Intracellular folate concentrations and folate dependent homocysteine remethylation fluxes in HepG2 cells with and without GNMT expression.^a

	Leu +3	Ser +1	Met +1	Met +1 from
	enrichment^b	enrichment^b	enrichment^b	¹³C-serine^b
Adequate folate^c
GNMT−	0.161 ± 0.002	0.131 ± 0.004	0.007 ± 0.001	0.055 ± 0.001
GNMT+	0.153 ± 0.01	0.181 ± 0.014	0.028 ± 0.001	0.156 ± 0.016
P value	0.231	0.004	<0.001	<0.001
% Difference	−4.9 ± 5.9	+38.6 ± 10.5	+288.9 ± 13.6	+10.1 ± 1.7
Low folate^c
GNMT−	0.149 ± 0.022	0.138 ± 0.008	0.008 ± 0.001	0.056 ± 0.008
GNMT+	0.154 ± 0.002	0.173 ± 0.003	0.021 ± 0.001	0.118 ± 0.01
P value	0.725	0.002	<0.001	0.001
% Difference	3.2 ± 1.6	+25.2 ± 2.4	+163.2 ± 18.7	+6.2 ± 1.04

^aAll data are presented as means ± SD (n = 3). The P value, calculated by t test, compared two cell lines under each condition. The % difference was calculated by comparing the mean with negative control cells under the same culture condition. Cell lines. GNMT-: WT HepG2 cells transfected with vector only were used as negative control. GNMT+: HepG2 cells transfected with GNMT.
^bFolate dependent homocysteine remethylation fluxes were calculated as the relative enrichments in methionine +1 from ¹³C-serine. Cells were cultured in α-MEM medium supplemented with l-(¹³C)-serine (237.8 µnmol/L, 100% of total serine) combined with L-(5),5,5-²H₃)-leucine (200 µnmol/L, 50% of total leucine) for 72 h.
^cCulture conditions. Cells were cultured in a modified α-MEM medium under folate abundance (100 nmol/L folinate) or mild folate restriction (10 nmol/L folinate) for 144 h.

ISSN: 1528-3658