Fatty liver induction: inverse relationship between hepatic neutral lipid accumulation and dietary polyunsaturated fatty acids in orotic acid-fed rats

An investigation of orotic acid levels in the breastmilk of smoking and non-smoking mothers

AIM

In this study; orotic acid levels in the milk of smoking and non-smoking mothers were investigated by high-performance liquid chromatography (HPLC).

RESULTS

It was found that the amount of orotic acid in the milk of smoking mothers (3.92+/-0.20 micro g/ml) was higher than that of non-smoking mothers (1.66+/-0.15 micro g/ml). Orotic acids levels in the milk of smoking mothers in comparison with non-smokers were found to be statistically significant (P<0.005).

CONCLUSION

Smoking may have increased the orotic acid levels by affecting pyrimidine biosynthesis pathway.

Association between hepatic triacylglycerol accumulation induced by administering orotic acid and enhanced phosphatidate phosphohydrolase activity in rats

Orotic acid is known to cause fatty liver, but it is unclear whether this is caused partly by stimulation of the enzymes for triacylglycerol (TG) synthesis. To understand the change of hepatic TG metabolism in fatty liver induced by orotic acid, we determined the liver tissue TG level and phosphatidate phosphohydrolase (PAP) activity over time in rats fed on a diet containing orotic acid (OA). A dietary lipid content of 10% was achieved by using n-6 fatty acid-rich corn oil in experiment 1, and n-6 fatty acid-rich safflower oil (SO) and n-3 fatty acid-rich fish oil (FO) with the same polyunsaturated fatty acid/monounsaturated fatty acid/saturated fatty acid (P/M/S) ratio in experiment 2. In experiment 1, an increase in the hepatic TG level due to OA intake was observed from day 5 onwards, the level rising approximately 6-fold by day 10. The activity of hepatic microsomal PAP, the rate-limiting enzyme in TG synthesis, increased markedly from day 5 onwards, concurrent with the liver diacylglycerol concentration. A strong correlation (r = 0.974) was observed between the hepatic TG level and microsome-bound PAP activity. In experiment 2, we investigated the effects of dietary fatty acid on OA-induced fatty liver. Compared with the n-6 fatty acid-rich vegetable oil diet, the relative increase in hepatic TG was smaller with the n-3 fatty acid-rich FO diet, and hepatic PAP activity fell markedly to the level for an OA-free diet. In addition, the hepatic TG accumulation and serum TG concentration were lower in the FO group than in the SO group. Nevertheless, because the hepatic TG level was low, it seems that the inhibition of liver PAP activity by FO possibly had a strong influence on the accumulation of TG in the liver. In conclusion, enhanced TG synthesis mediated by changes in liver PAP activity was involved in the hepatic TG accumulation induced by OA administration, this change being markedly suppressed by dietary n-3 fatty acids.

Failure of orotic acid to suppress activity of plasma lecithin:cholesterol acyltransferase

There are theoretical reasons for postulating a relationship between turnover of triglyceride-rich lipoproteins and plasma cholesterol esterifying activity, and some experimental evidence exists to support such a hypothesis. Orotic acid has been given to rats to determine whether blocking the hepatic release of very-low-density lipoproteins would also reduce hepatic secretion of lecithin:cholesterol acyltransferase (LCAT). No evidence of such an effect was found. In a single human experiment orotic acid exerted only minimal effects on serum concentrations of lipoproteins, and LCAT activity was apparently unaffected.