Elevated hepatic and depressed renal cytochrome P450 activity in the Tg2576 transgenic mouse model of Alzheimer's disease.

Recent studies indicate that the Tg2576 transgenic mouse model of Alzheimer's disease [tg(hAPP)] demonstrates disturbances in plasma glucose and neuroendocrine function reminiscent of Alzheimer's disease (AD). Alterations in any one of these systems can have a profound effect on hepatic cytochrome P450 (CYP) expression. Additionally, the recent discovery that amyloid beta 1-42 can induce the expression of CYP reductase in neuronal cultures further suggests that hepatic CYP-related metabolism may be affected by the expression of mutant human amyloid precursor protein in these tg(hAPP) mice. Therefore, the current study was conducted to investigate the activity and protein content of several CYP isoforms in the livers and kidneys of aged (20-month-old) tg(hAPP) mice. tg(hAPP) mice exhibit significant elevations in hepatic CYP2B, CYP2E1-, CYP3A- and CYP4A-associated activities and CYP4A immunoreactive protein compared with wild-type. In contrast to the liver, a significant depression in renal CYP2E1- and CYP4A-associated activities were demonstrated in tg(hAPP) mice. The presence of the mutant hAPP protein was detected in the brain, kidney and livers of tg(hAPP) mice.

Cytochrome P450 and antioxidant activity in interleukin-6 knockout mice after induction of the acute-phase response.

Hepatic cytochrome P450 (CYP) expression and antioxidant activity have been shown to decrease following endotoxin (lipopolysaccharide [LPS]) or proinflammatory cytokine administration. Using mice deficient in interleukin-6 (IL-6), the role of IL-6 in the regulation of hepatic CYP activity, glutathione (GSH) metabolism, and catalase (CAT) activity was analyzed after LPS administration. Administration of LPS produced comparable decreases in hepatic CYP3A activity in WT B6x129 (WT) mice and IL-6 knockout mice. No decrease was observed for CYP2D9 activity after LPS administration in either WT or IL-6 knockout mice. LPS administration significantly increased hepatic and renal CYP2E1 and CYP4A activity in WT mice, with no effect in IL-6 knockout mice. CYP2A12 activity increased in IL-6 knockout, mice with no change in WT mice after LPS administration. LPS administration had no significant effect on hepatic GSH reductase, GST peroxidase, GSH-S-transferase (GST), or total GSH in either WT or IL-6 knockout. However, hepatic CAT activity was significantly reduced in WT mice after LPS administration, with no effect in IL-6 knockout mice. These results support IL-6 as a critical mediator of the effects of LPS on specific hepatic and renal CYP activities and hepatic CAT activity.

Localization of epidermal growth factor receptors in first- and third-trimester human placentas.

Studies to date have demonstrated epidermal growth factor (EGF) receptors primarily on the outer plasma membrane of the human placental syncytiotrophoblasts facing maternal blood and to a lesser extent on the cytotrophoblast stem cells. In the present studies, first- and third-trimester human placental tissues were immunostained with monoclonal antibodies (MAb) to the EGF binding domain of the human EGF receptor or to the activated (tyrosine-phosphorylated) human EGF receptor. Cytotrophoblasts, syncytiotrophoblasts, and fetal connective tissue cells in first-trimester tissues immunostained with both MAb, with the notable exception of the absence of staining of activated EGF receptor over cytotrophoblast plasma membranes. In contrast, staining of third-trimester placentas with either MAb yielded little to no staining of either trophoblast cell layer but intense staining of fetal connective tissue cells. Staining for EGF receptors over cytotrophoblasts in the first trimester is consistent with the hypothesis that maternal EGF or TGF-alpha derived from the endometrium or placenta may be the mitogen responsible for cytotrophoblast cell division and that the receptors localized to the syncytiotrophoblast are involved in EGF regulation of differentiated function. The absence of heavy staining of activated EGF receptor on trophoblast plasma membranes in third-trimester placentas is consistent with down-regulation of EGF receptor activity.

In situ demonstration and characterization of progonadotropin-releasing hormone messenger ribonucleic acid in first trimester human placentas.

GnRH has been shown to play a role in the regulation of secretion of hCG by human placenta. Immunocytochemical studies have demonstrated the presence of the peptide, but do not address whether the GnRH is maternal, fetal, or placental in origin. In situ hybridization studies using a biotinylated pro-GnRH cDNA were, therefore, undertaken to determine the distribution of pro-GnRH mRNA in first trimester placental samples. Using an avidin-biotin-Cy.5 detection system in conjunction with laser scanning confocal microscopy, pro-GnRH mRNA was shown to be present in both the cytotrophoblast and syncytiotrophoblast cells of placental villi, although not in the cells of the fetal connective tissue. Prior hybridization with a 200-fold excess of unlabeled probe blocked hybridization of the labeled pro-GnRH probe. Southern and sequence analysis demonstrated that the probe hybridized to a transcript identical to hypothalamic GnRH. Immunocytochemical staining using an antiserum to amino acids 6-16 of pro-GnRH demonstrated the presence of translated pro-GnRH in both the cytotrophoblast and syncytiotrophoblast epithelia. We conclude that the synthesis of pro-GnRH by both the cytotrophoblast and the syncytiotrophoblast of human placenta is consistent with either an autocrine or a paracrine mode of GnRH regulation of hCG secretion.