Abnormal prothrombin in the plasma of rats carrying hepatic tumors

Vitamin K is required for the posttranslational formation of gamma- carboxyglutamyl residues in a number of plasma clotting factors. Interference with vitamin K action results in the appearance of abnormal (des-gamma-carboxy) forms of prothrombin in human plasma. Vitamin K-sufficient patients with primary hepatocellular carcinoma also secrete significant quantities of abnormal prothrombin; this response has now been studied in a rat model. Normal Buffalo strain rats had 9 micrograms/mL of circulating plasma abnormal prothrombin, whereas Buffalo strain rats carrying the transplantable Morris hepatoma tumor no. 7777 had 33 micrograms/mL at 3 weeks after transplant. Vitamin K-dependent carboxylase activity was normal in the liver of these rats, but very low in the tumor tissue. Rats carrying Morris hepatoma tumors no. 9618A and 5123D did not secrete significant amounts of abnormal prothrombin. Carboxylase activity in these tumors was 15 times that of the 7777 tumor. The data suggest that the secretion of abnormal prothrombin by hepatocellular tumors is the result of normal expression of the prothrombin gene by those tumors and a failure of the tumor to express the carboxylase gene.     

Differential regulation of IRP1 and IRP2 by nitric oxide in rat hepatoma cells

Iron-regulatory proteins (IRP1 and IRP2) are RNA-binding proteins that bind to stem-loop structures known as iron-responsive elements (IREs). IREs are located in the 5'- or 3'-untranslated regions (UTRs) of specific mRNAs that encode proteins involved in iron homeostasis. The binding of IRPs to 5' IREs represses translation of the mRNA, whereas the binding of IRPs to 3' IREs stabilizes the mRNA. IRP1 and IRP2 binding activities are regulated by intracellular iron levels. In addition, nitric oxide (NO.) increases the affinity of IRP1 for IREs. The role of NO. in the regulation of IRP1 and IRP2 in rat hepatoma cells was investigated by using the NO.-generating compound S-nitroso-N- acetylpenicillamine (SNAP), or by stimulating cells with multiple cytokines and lipopolysaccharide (LPS) to induce NO. production. Mitochondrial and IRP1 aconitase activities were decreased in cells producing NO(.). NO. increased IRE binding activity of IRP1, but had no effect on IRE binding activity of IRP2. The increase in IRE binding activity of IRP1 was coincident with the translational repression of ferritin synthesis. Transferrin receptor (TfR) mRNA levels were increased in cells treated with NO.-generating compounds, but not in cytokine- and LPS-treated cells. Our data indicate that IRP1 and IRP2 are differentially regulated by NO. in rat hepatoma cells, suggesting a role for IRP1 in the regulation of iron homeostasis in vivo during hepatic inflammation.     

Interleukin-1, tumor necrosis factor, and the production of colony- stimulating factors by cultured mesenchymal cells

Although the genes for four hematopoietic colony-stimulating factors (CSFs) have been cloned, neither the mechanism of the regulation of their production nor their cellular origins have been established with certainty. Monocytes are known to produce colony-stimulating and burst- promoting activities, as well as several monokines such as interleukin- 1 (IL-1) and tumor necrosis factor (TNF). These monokines indirectly stimulate other mesenchymal cells to produce certain colony-stimulating factors such as granulocyte-macrophage CSF (GM-CSF). To determine whether monocytes produce other CSFs and if so, to compare the mechanism of regulation of production with that of endothelial cells and fibroblasts, we investigated the synthesis of CSFs by monocytes, human umbilical vein endothelial cells, and fibroblasts. We used total cellular RNA blot analysis to determine interleukin-3 (IL-3), GM-CSF, granulocyte CSF (G-CSF), and monocyte CSF (M-CSF) messenger RNA (mRNA) content and immunoprecipitation or bioassay to confirm the presence of the specific secreted proteins. The results indicate that M-CSF mRNA and protein are produced constitutively by all three cell types and their level of expression does not increase after induction. In contrast, GM-CSF and G-CSF mRNAs are barely detectable in uninduced monocytes and show an increase in expression after lipopolysaccharide treatment. Retrovirus-immortalized endothelial cells, unlike primary endothelial cells or both primary and immortalized fibroblasts, produce IL-1 constitutively; this correlates with their constitutive production of GM-CSF and G-CSF. IL-3 mRNA was not detectable in any of these cells either before or after induction. The results indicate that these mesenchymal cells can produce three CSFs: GM-CSF, G-CSF, and M-CSF; furthermore, the data suggest that the mechanism of regulation of M-CSF production is different from that of GM-CSF and G-CSF, and that the latter two inducible CSFs are regulated by different factors in monocytes compared with the other mesenchymal cells.     

Experimental acute tubular necrosis: US appearance

Dichromate-induced acute tubular necrosis (ATN) was created in 16 experimental animals and compared with four controls. An increase in cortical echogenicity, greatest on days 4 and 7 after injection, was noted using both histogram analysis and blinded observer readings. These findings closely correlated with proportional outer cortical blood flow. Good interobserver correlation was noted. Based on this experiment, clinical observations, and the literature, we propose that three different entities with different sonographic appearances are included under the term ATN. Drug-induced nephrotoxicity is associated with increased cortical echogenicity; ischemic ATN leads to no change in cortical echogenicity with normal medullary echogenicity; and precipitation of Tamm-Horsfall protein in the pyramids leads to echogenic pyramids with normal cortical echogenicity.     

Steady‐state amprenavir and tenofovir pharmacokinetics after coadministration of unboosted or ritonavir‐boosted fosamprenavir with tenofovir disoproxil fumarate in healthy volunteers

Objective

An open‐label, three‐period pharmacokinetic study was conducted to investigate the drug interaction potential between fosamprenavir (FPV) and tenofovir disoproxil fumarate (TDF).

Methods

Thirty‐six healthy subjects received TDF 300 mg once daily (qd) for 7 days (period 1), and then were randomized to 14 days of either FPV 1400 mg twice daily (bid) or FPV/ritonavir (RTV) 700/100 mg bid alone or with TDF (period 2). Subjects continued their randomized dose of FPV for 14 more days, adding or removing TDF based upon its receipt in period 2 (period 3). Twenty‐four‐hour pharmacokinetic sampling was carried out on day 7 of period 1 and on day 14 of periods 2 and 3. Steady‐state plasma amprenavir (APV) and tenofovir (TFV) pharmacokinetics were assessed by noncompartmental analysis and parameter values observed with each regimen were compared using geometric mean ratios with 90% confidence intervals.

Results

After TDF coadministration, APV geometric mean minimum concentration (C_min), maximum concentration (C_max), and area under the plasma concentration–time curve (AUC) increased by 31, 3 and 7% above values observed with unboosted FPV alone; they also increased by 31, 4 and 16% above values observed with FPV/RTV alone. TFV C_min, C_max and AUC decreased by 12, 25 and 15% after FPV coadministration and by 9, 18 and 7% after FPV/RTV coadministration. No significant changes in RTV pharmacokinetics were observed. No differences were noted in adverse events among dosing periods.

Conclusions

In this evaluation of the interaction between FPV and TDF, increases in APV exposures and modest decreases in TFV exposures were observed. These were unlikely to be clinically significant.