Gluconeogenesis from serine in rabbit hepatocytes

Area of Science:

• Biochemistry
• Cellular Metabolism
• Hepatology

Background:

• L-Serine gluconeogenesis differs between rabbit and rat hepatocytes.
• Understanding species-specific metabolic pathways is crucial for comparative physiology.
• Isolated rabbit hepatocytes were used to investigate L-serine's role in glucose synthesis.

Purpose of the Study:

• To elucidate the mechanism of L-serine gluconeogenesis in rabbit hepatocytes.
• To explain the observed species difference in L-serine's gluconeogenic capacity compared to rats.
• To investigate the role of L-lactate and pyruvate in facilitating L-serine metabolism.

Main Methods:

• Isolation and incubation of rabbit hepatocytes from 48-h-starved animals.
• Measurement of gluconeogenesis rates using various substrates: L-serine, L-lactate, pyruvate, hydroxypyruvate, and their combinations.
• Assessment of hepatocyte viability via ATP levels and gluconeogenesis from L-lactate.

Main Results:

• L-Serine alone did not significantly produce glucose or pyruvate; hydroxypyruvate was detected.
• L-Serine combined with L-lactate increased glucose production by 35% compared to L-lactate alone.
• L-Lactate and hydroxypyruvate yielded near-maximal gluconeogenesis rates, suggesting synergistic effects and potential roles in redox balance and substrate supply.

Conclusions:

• The primary pathway for L-serine gluconeogenesis in rabbit hepatocytes is likely initiated by L-serine:pyruvate aminotransferase.
• L-Lactate significantly contributes by generating cytoplasmic reducing equivalents (NADH), supplying pyruvate, and potentially preventing hydroxypyruvate reduction.
• These findings highlight a distinct mechanism of L-serine utilization in rabbits compared to rats, emphasizing the importance of co-substrates like L-lactate.