Impaired Placental Pentose Phosphate Pathway Of IUGR Fetal Pig And Its Nutritional Regulation

Intrauterine growth restriction (IUGR) remains a major problem for both human health and animal production due to its association with high rates of neonatal morbidity and mortality, low efficiency of food utilization, permanent adverse effects on postnatal growth and development. However, the underlying mechanisms for IUGR are largely unknown. Our previous study showed that disturbed proteins expression associated with oxidative stress and glucose metabolism were found in IUGR fetal placenta. While the key regulatory pathway connecting glucose metabolism and redox balance is pentose cycle (pentose phosphate pathway). Therefore, five independent experiments were conducted to investigate the underlying mechanism of impairment of pig placenta and its nutritional intervention.(1) First, porcine trophectoderm cells (pTr) that become chorion cells of the mature placenta were used to determine whether the pentose cycle is active in pig placenta. pTr cells were cultured at37℃for2h in the same customized medium containing with5mmol/L either [1-14C]glucose or [6-14C]glucose. The activity of the pentose cycle was estimated by the difference in14CO2production between [1-14C]glucose and [6-14C]glucose. Our results indicated that the pentose cycle was highly active in pTr cells and about20%of glucose taken up by cells was metabolized via the pentose cycle.(2) To evaluate the activity of pentose phosphate pathway and redox state of IUGR fetal placenta, we measured activity of G6PDH (a rate-limiting enzyme of pentose phosphate pathway) and the levels of NADPH and GSH between IUGR and NBW fetal placenta during mid-to late-gestation. The concentrations of NADPH and GSH in IUGR fetal placenta on d60of gestation decreased significantly when compared to NBW group. While NADPH and GSH levels compensatory increased in IUGR fetal placenta on d110of gestation, which suggested a disorder of pentose phosphate pathway and redox imbalance in IUGR fetal placenta.(3) Study3was design to find out the nutrient transport from mother to the fetus influenced by impaired placental function. One IUGR fetus and one NBW fetus were obtained from each gilt at each of three gestational ages (d60,90and110). Metabolome of umbilical vein plasma and amniotic fluid in IUGR and NBW fetuses were determined by mass spectrometry, while hormones, amino acids and related metabolites in maternal and fetal plasma were measured using assay kits and chromatographic methods. Metabolites (including glucose, urea, ammonia, amino acids, and lipids) in umbilical venous plasma and amniotic fluid exhibited a cluster of differences between IUGR and NBW fetuses on d60,90and110of gestation. These changes in the IUGR group are associated with disorders of nutrient and energy metabolism as well as endocrine imbalances, which may contribute to the retardation of fetal growth and development. The findings help provide information regarding potential mechanisms responsible for IUGR in swine and also have important implications for the design of effective strategies to prevent, diagnose, and treat IUGR in other mammalian species, including humans.(4) The objective of this study was to determine whether functional amino acids (arginine and glutamine) could regulate the pentose phosphate pathway. pTr cells were cultured at37℃for2h in our customized medium containing different concentrations of L-arginine (0,0.2and0.5mM) and L-glutamine (0,0.5and1mM) within physiological ranges. Arginine had no effect on pentose cycle activity, and no utilization of extracellular L-arginine by pTr cells was detected within a2-h period of incubation. However, L-Glutamine (0.5and1mM) increased the production of14CO2from [1-14C]glucose, but had no effect on production of14CO2from [6-14C]glucose. Thus,0.5and1mM L-glutamine stimulated pentose cycle activity by12%and31%, respectively, as compared to the0mM L-glutamine treatment. Rates of utilization of glutamine, as well as production of glutamate, increased with increasing extracellular concentrations of glutamine from0to1mM.(5) This study was to design to determine whether fructose could regulate the pentose cycle and its difference from glucose. pTr cells were cultured at37℃for2h in our customized medium containing different concentrations of D-fructose (0,1.0and5.0mM) within physiological ranges.[U-14C]Fructose was used to detect whether pTr cells could utilize fructose to produce CO2. Fructose increased the production of14CO2from [1-14C]glucose, and then enhanced pentose cycle activity of pTr cells. Fructose can be metabolized to lactate but not CO2by pTr cells. When combined with glutamine, fructose can stimulate the pentose cycle to a larger extent. In summary, IUGR continuously impaired pentose phosphate pathway and disturbed redox balance of placenta. Impaired placenta function resulted in insufficient nutrients supply from mother to the fetus. Glutamine and fructose that are different in umbilical venous plasma and amniotic fluid between IUGR and NBW fetuses can individually and synergistically enhance the pentose cycle activity, improve redox balance of placenta, thus maintain embryo survival and conceptus growth.