Propionate modulation of ruminal ketogenesis

Area of Science:

• Ruminant nutrition and metabolism
• Cellular biochemistry
• Volatile fatty acid (VFA) pathways

Background:

• The ruminal epithelium is a key site for volatile fatty acid (VFA) metabolism in ruminants.
• Butyrate metabolism by ruminal epithelial cells produces circulating ketone bodies, essential energy sources.
• Understanding how other VFAs influence butyrate metabolism is crucial for optimizing ruminant energy utilization.

Purpose of the Study:

• To investigate the impact of key volatile fatty acids (VFAs) on butyrate metabolism in isolated sheep ruminal epithelial cells.
• To determine how propionate, acetate, and succinate affect beta-hydroxybutyrate (beta-HBA) and acetoacetate (AcAc) production from butyrate.
• To elucidate the mechanisms underlying VFA interactions in ruminal epithelial cell energy production.

Main Methods:

• Isolated sheep ruminal epithelial cells were incubated with varying concentrations of butyrate, propionate, acetate, and succinate.
• Measured outcomes included beta-hydroxybutyrate (beta-HBA) and acetoacetate (AcAc) production from butyrate.
• [14C]butyrate oxidation to 14CO2, and lactate/pyruvate formation from propionate/succinate were quantified.

Main Results:

• Butyrate oxidation to CO2, beta-HBA, and total ketones showed linear increases over a 2-h incubation period.
• Acetate inhibited beta-HBA formation from butyrate at concentrations above 5 mM.
• Propionate stimulated beta-HBA production but decreased AcAc, with no net change in total ketone bodies, and increased lactate/pyruvate.

Conclusions:

• Butyrate metabolism in ruminal epithelial cells is significantly influenced by the presence of other VFAs.
• Propionate's stimulatory effect on beta-HBA production appears linked to mitochondrial redox state changes rather than succinate mediation.
• These findings highlight the complex interplay of VFAs in ruminal energy metabolism and ketone body production.