Pentose phosphate pathway in cellular trophoblasts from full-term human placentas

Glucose metabolism was investigated in cellular trophoblasts isolated from full-term human placentas. The specific yields of ¹⁴CO₂ from D-[1-¹⁴C]glucose and D-[6-¹⁴C]glucose were used to determine glucose metabolism via the pentose cycle for cells freshly isolated or cells grown in culture for 1 and 3 days. Cells were mononucleated on day 1 but fused to form multinucleated syncytiotrophoblasts by day 3. The principal product of glucose metabolism under all conditions was lactate, accounting for approximately three-fourths of recovered ¹⁴C in products. Pentose cycle activity contributed 0.57 ± 0.01, 0.39 ± 0.06, and 0.21 ± 0.05% of the glucose metabolized by cells freshly isolated, cultured for 1 day, and cultured for 3 days, respectively. In the presence of the electron acceptor methylene blue, pentose cycle activity increased to 16.5 ± 2.1, 13.8 ± 1.5, and 18.2 ± 1.7% for cells freshly isolated, cultured for 1 day, and cultured for 3 days, respectively. Trace amounts of ¹⁴C were recovered in other products including amino acids and glycogen. These data suggest that pentose cycle activity in cellular trophoblasts from full-term placenta, like those in full-term villous tissue, is a minor component of glucose metabolism. However, these cultured cells maintain a capacity to oxidize glucose via the pentose cycle at relatively high rates.