Liposomes as fatty acids carriers in isolated rat liver: effect on energy metabolism and on isolated mitochondria activity

Decrease in oxidative phosphorylation yield in presence of butyrate in perfused liver isolated from fed rats

Background

Butyrate is the main nutrient for the colonocytes but the effect of the fraction reaching the liver is not totally known. A decrease in tissue ATP content and increase in respiration was previously demonstrated when livers were perfused with short-chain fatty acids (SCFA) such as butyrate, or octanoate.

In fed rats the oxidative phosphorylation yield was determined on the whole isolated liver perfused with butyrate in comparison with acetate and octoanoate (3 mmol/L). The rate of ATP synthesis was determined in the steady state by monitoring the rate of ATP loss after inhibition of (i) cytochrome oxidase (oxidative phosphorylation) with KCN (2.5 mmol/L) and (ii) glyceraldehyde 3-phosphate dehydrogenase (glycolysis) with IAA (0.5 mmol/L). The ATP flux, estimated by ³¹P Nuclear Magnetic Resonance, and the measured liver respiration allowed the ATP/O ratio to be determined.

Results

ATP turnover was significantly lower in the presence of butyrate (0.40 ± 0.10 μmoles/min.g, p = 0.001, n = 7) and octanoate (0.56 ± 0.10 μmoles/min.g, p = 0.01, n = 5) than in control (1.09 ± 0.13 μmoles/min.g, n = 7), whereas perfusion with acetate induced no significant decrease (0.76 ± 0.10 μmoles/min.g, n = 7). Mitochondrial oxygen consumption was unchanged in the presence of acetate (1.92 ± 0.16 vs 1.86 ± 0.16 for control) and significantly increased in the presence of butyrate (p = 0.02) and octanoate (p = 0.0004) (2.54 ± 0.18 and 3.04 ± 0.15 μmoles/min.g, respectively). The oxidative phosphorylation yield (ATP/O ratio) calculated in the whole liver was significantly lower with butyrate (0.07 ± 0.02, p = 0.0006) and octanoate (0.09 ± 0.02, p = 0.005) than in control (0.30 ± 0.05), whereas there was no significant change with acetate (0.20 ± 0.02).

Conclusion

Butyrate or octanoate decrease rather than increase the rate of ATP synthesis, resulting in a decrease in the apparent ATP/O ratio. Butyrate as a nutrient has the same effect as longer chain FA. An effect on the hepatic metabolism should be taken into account when large quantities of SCFA are directly used or obtained during therapeutic or nutritional strategies.

Butyrate impairs energy metabolism in isolated perfused liver of fed rats

This study was designed to test the effects of short-chain fatty acids (SCFA) with an even number of carbon atoms on hepatic energy metabolism. The effect of the SCFA was evaluated by measuring liver ATP content and oxygen consumption. The ATP content was evaluated using (31)P nuclear magnetic resonance in isolated liver from fed rats. In addition, respiratory activity (VO(2)) was assessed using Clark electrodes. The livers were perfused with acetate, butyrate or a medium chain length fatty acid, octanoate, at a concentration of 0.05--5.0 mmol/L. The addition of each substrate enhanced the rate of the net ATP consumption (V(i)), establishing a new ATP steady state that required a perfusion time of > or = 20 min, dependent on the chain length and concentration of the fatty acid (FA). The initial V(i) was unchanged for acetate and the ATP level stabilized at 58% of the initial level. Both butyrate and octanoate induced a dose-dependent increase in V(i). This may reflect an ATP-consuming process for the intracellular pH regulation observed during the acidosis associated with the beta-oxidation pathway. At the new steady state, the ATP concentration was approximately 45% of the initial level for both FA. VO(2) was both rapidly and reversibly increased, and the change was a function of butyrate or octanoate concentration and of the chain length. K(m) values were similar for butyrate and octanoate. Because all of the effects were similar for butyrate and octanoate, in contrast to acetate, we suggest that the impairment of the energy metabolism by butyrate resulted from an increase in the FADH(2)/NADH ratio due to beta-oxidation. In conclusion, the difference in the hepatic oxidation pathways of two products of intestinal fermentation (acetate and butyrate) explains their different actions on energy metabolism.