Englitazone administration to late pregnant rats produces delayed body growth and insulin resistance in their fetuses and neonates

Abstract

The level of maternal circulating triacylglycerols during late pregnancy has been correlated with the mass of newborns. PPARgamma (peroxisome-proliferator-activated receptor gamma) ligands, such as TZDs (thiazolidinediones), have been shown to reduce triacylglycerolaemia and have also been implicated in the inhibition of tissue growth and the promotion of cell differentiation. Therefore TZDs might control cell proliferation during late fetal development and, by extension, body mass of pups. To investigate the response to EZ (englitazone), a TZD, on perinatal development, 0 or 50 mg of englitazone/kg of body mass was given as an oral dose to pregnant rats daily from day 16 of gestation until either day 20 for the study of their fetuses, or until day 21 of gestation for the study of neonates. EZ decreased maternal triacylglycerol levels at day 20 of gestation and neonatal mass, but not fetal mass. Fetuses and neonates from EZ-treated mothers exhibited high levels of insulin and were found to be hyperglycaemic. The apparent insulin-resistant state in neonates from EZ-treated pregnant rats was corroborated, since they showed higher plasma NEFA [non-esterified ('free') fatty acid] levels, ketonaemia and liver LPL (lipoprotein lipase) activity and lower plasma IGF-I (type 1 insulin-like growth factor) levels, in comparison with those from control mothers. Moreover, at the molecular level, an increase in Akt phosphorylation was found in the liver of neonates from EZ-treated mothers, which confirms that the insulin pathway was negatively affected. Thus the response of fetuses and neonates to maternal antidiabetic drug treatment is the opposite of what would be expected, and can be justified by the scarce amount of adipose tissue impeding a normal response to PPARgamma ligands and by hyperinsulinaemia as being responsible for a major insulin-resistant condition.

Figure 1. Effect of maternal treatment with EZ on plasma glucose and insulin of fetuses and neonates

Plasma glucose (A) and insulin (B) levels in fetuses and neonates from mothers receiving medium (control) or EZ for 4 (fetuses) or 5 days (neonates). Values are means±S.E.M.; n=4–8. Statistically significant differences between groups receiving different treatments are indicated (***, P<0.001). Statistical significant differences between fetuses and neonates within each group of treatment are also indicated (#, P<0.05; ###, P<0.001).

Figure 2. Effect of maternal treatment with EZ on Akt phosphorylation of liver of neonates

Basal Akt phosphorylation in liver of neonates from mothers receiving medium (control) or EZ. The autoradiographs shown identify the hepatic Akt protein (lower part) and the corresponding (Ser⁴⁷³)-phosphorylated Akt (upper part). Autoradiographs were quantified by scanning densitometry, and so the Figure represents the signal due to the phosphorylation corrected by the Akt protein determined by Western immunoblotting, as described in the Materials and methods section. Results are means±S.E.M for four animals per group. Statistically significant differences between groups receiving different treatments are indicated (*, P<0.05).