Episode 21 - Measuring Acetyl-CoA in a live rat, for the sake of metabolism
Show notes:
A Non-invasive Method to Assess Hepatic Acetyl-CoA In Vivo (Perry and Shulman et al. 2017)
Background
- Futile fat cycling “Regulation is easier if competing reactions are maintained in a cycling steady-state and then biased in one or another direction. This becomes, in the end, more efficient than starts and stops in response to different conditions”
- Acetyl-CoA contributes to GNG, glucose oxidation, protein acetylation and the synthesis of steroids as well as fatty acids
- Episode 1 Break Nutrition study reviewed ⇒ “reduction in hepatic acetyl-CoA content is a key mediator of insulin’s ability to acutely suppress hepatic gluconeogenesis in vivo”
- The hepatic acetyl-CoA content in the liver of rats subjected to the following 5 experimental conditions ranges from 40 to 250 nmol/g
- Chow-fed rats
- HFD-fed rats
- poorly controlled T1D rats
- poorly controlled T2D rats
- hyperinsulinemic-euglycemic clamped rats
- safflower-oil-based HFD (59% fat, 26% carbs, 15% protein) for 4 weeks
Methods
- In vivo
- Used ketone salt ?-OHB
- DIDN’T look at acetoacetate
- measures performed after a 16-hr overnight fast ⇒ almost totally depletes hepatic glycogen content ⇒ here, rates of hepatic glucose almost entirely reflect rates of hepatic gluconeogenesis
- other measures after a 6-hr fast (hepatic glycogen repleted) vs 48hr-fast (hepatic glycogen depleted) group
Results
“rates of ?-OHB turnover correlate very strongly with hepatic acetyl-CoA content in vivo (R2 = 0.86, p < 0.0001) across a 5-fold range of acetyl-CoA concentrations in five rat models with varying degrees of fasting hyperglycemia and insulin resistance”
- 4.5-fold difference in total endogenous glucose production (1 to 6 µmol/min)
- 3.5-fold difference in hepatic acetyl-CoA
- R2 = 0.95, p = 0.005 ⇒ ?-OHB turnover rates and hepatic acetyl-CoA concentrations in the five groups studied
- R2 = 0.79, p < 0.0001⇒ between rates of HGP and hepatic acetyl-CoA content
- Hans Krebs et al. “failed to observe a relationship between blood ketone concentrations and hepatic acetyl-CoA content” ⇒ another textbook claim falls…
- Glycerol at 60 µmol/(kg/min) ⇒ 3-fold increase plasma glycerol ⇒ increased HGP ⇒ compensatory rise in insulin
- “mirror the findings of Rawat and Menahan, who showed that intramuscular injection of gluconeogenic substrates (fructose, glyceraldehyde, and sorbitol) raised blood glucose concentrations and suppressed both hepatic acetyl-CoA content and blood ketone concentrations”
- “in the physiologically relevant comparison between starved and recently fed animals, rates of whole-body glucose production do not track with hepatic acetyl-CoA content”
- What tracks better in both starved/recently fed states is rates of ?-OHB turnover
- “whole-body glucose production cannot be used as a reliable surrogate for hepatic acetyl-CoA content”
- “rates of whole-body glucose turnover correlate with hepatic acetyl CoA content only when glucose turnover is mostly derived from pyruvate carboxylase flux”