Detection of P-glycoprotein activity in endotoxemic rats by 99mTc-sestamibi imaging.

UNLABELLED: (99m)Tc-sestamibi is a widely used radiopharmaceutical agent for myocardial and oncologic imaging. Because of its unique role as a P-glycoprotein (Pgp)-specific substrate, this compound can be used to examine Pgp functional activity in vitro and in vivo under pathologic conditions. Our objective was to use (99m)Tc-sestamibi as a tool to investigate whether systemic inflammation induced by Escherichia coli lipopolysaccharide (LPS) would affect in vivo Pgp function in the brain, heart, liver, and kidneys of rats. Moreover, we also wanted to examine LPS-mediated effects in the placenta of pregnant rats because of the limited amount of in vivo data on this tissue. METHODS: Rats were injected intraperitoneally with LPS or an equal volume of saline as controls. After certain time periods (6 or 24 h), animals were administered 20 MBq of (99m)Tc-sestamibi intravenously, and then images were taken at 0.5, 1, 2, and 3 h. Tissues of rats were excised for (99m)Tc-sestamibi biodistribution analysis by gamma-counting and messenger RNA (mRNA) analysis by reverse transcription-polymerase chain reaction. Western blot analysis with antibody C-219 was used to detect Pgp levels. RESULTS: LPS treatment for 6 h caused a significant downregulation of mdr1a mRNA levels in the brain, heart, and liver, whereas 24 h of LPS treatment significantly reduced mdr1a mRNA levels only in the liver. A significant downregulation of mdr1a mRNA was seen in the brain, heart, and liver within 6 h after LPS administration. Imaging and biodistribution studies demonstrated a higher accumulation of (99m)Tc-sestamibi in the brain, heart, and liver of LPS-treated rats. In the brain, LPS-imposed downregulation of mdr1a mRNA levels was transient, with significant suppression at 4, 6, and 12 h, and the levels recovered to nearly normal by 24 h. This time-dependent downregulation of mRNA correlated with protein levels determined by Western blot analysis. Biodistribution studies of pregnant rats demonstrated a 3.5-fold-higher accumulation of (99m)Tc-sestamibi in the fetal tissues of LPS-treated pregnant rats than in saline-treated control rats. Furthermore, placental mdr1a and mdr1b mRNA levels were also significantly downregulated by LPS treatment. CONCLUSION: Our results indicate that LPS-induced systemic inflammation caused an increased retention of (99m)Tc-sestamibi in the brain, heart, liver, and fetal tissues. These results correlated with a reduction in mdr1a mRNA levels in each organ.

Infection-related perinatal brain injury: the pathogenic role of impaired fetal cardiovascular control.

There is a growing body of evidence from clinical and epidemiologic studies that in utero exposure to infection plays an important role in the genesis of fetal or neonatal injury leading to cerebral palsy and chronic lung disease. Thus, after chorioamnionitis the incidence of immature neonates with periventricular white matter damage and periventricular or intraventricular hemorrhage is significantly elevated. Recent clinical and experimental data support the hypothesis that a fetal inflammatory response links antenatal infection with brain white matter damage and subsequent motor handicap. A variety of studies support the view that cytokines released during intrauterine infection directly cause injury to the immature brain. In this review, we provide evidence that in utero exposure to bacterial infection can severely alter fetal cardiovascular function, resulting in dysregulation of cerebral blood flow and subsequent hypoxic-ischemic brain injury.

Desensitization of soluble guanylate cyclase in renal cortex during endotoxemia in mice.

Acute endotoxemic renal failure involves renal vasoconstriction, which presumably occurs despite increased nitric oxide (NO) generation by inducible NO synthase in the kidney. The present study examined the hypothesis that the renal vasoconstriction during endotoxemia occurs in part because of desensitization of soluble guanylate cyclase (sGC). Endotoxic shock was induced in male B6/129F2/J mice by an intraperitoneal injection of Escherichia coli lipopolysaccharide. The endotoxemia resulted in shock and renal failure as evidenced by a decrease in mean arterial pressure and an increase in serum creatinine and urea nitrogen. Serum NO increased in a time-dependent manner, reaching the highest levels at 24 h, in parallel with induction of inducible NO synthase protein in the renal cortex. In renal cortical slices obtained from endotoxemic mice, cyclic guanosine monophosphate (cGMP) increased significantly at 6 h and 15 h as compared with control but normalized at 24 h after injection of lipopolysaccharide. Incubation of renal cortical slices in the presence of a phosphodiesterase inhibitor isobutylmethylxantine did not alter the pattern of changes in cGMP. Incubation of renal cortical slices with 2 mM sodium nitroprusside resulted in a similar accumulation of cGMP in slices taken from control and endotoxemic mice at 6 h and 15 h. However, in slices from 24-h endotoxemic mice, accumulation of cGMP in response to sodium nitroprusside was significantly lower. This lower stimulability of sGC was not paralleled by a decrease in its abundance in renal cortex on immunoblot. Taken together, these results demonstrate a desensitization of sGC in renal cortex during endotoxemia, which may contribute to the associated renal vasoconstriction.