Role of carbon monoxide and nitric oxide in adult rat hepatocytes proliferating in vitro: Effects of CAS 1609

The implication of cigarette smoking and cessation on macrophage cholesterol efflux in coronary artery disease patients

We investigated ATP-binding cassette transporters A1/G1 expression and function in mediating cholesterol efflux by examining the macrophages of cigarette-smoking patients with coronary artery disease (CAD) before and after smoking abstinence. Peripheral blood monocyte cells were collected from nonsmokers (n = 17), non-CAD (NCAD) smokers (n = 35), and CAD smokers (n = 32) before and after 3 months of smoking cessation. We found that the ABCA1 expression level was lower in macrophages from NCAD and CAD smokers than from nonsmokers at baseline. The ABCA1 function of mediating cholesterol efflux was reduced in NCAD and CAD smokers as compared with nonsmokers. After 3 months of smoking cessation, ABCA1 expression and function were improved in CAD smokers. However, ABCG1 expression and function did not change after smoking cessation. Furthermore, ABCA1 expression was inhibited by tar in human acute monocytic leukemia cell line THP-1-derived macrophages through the inhibition of liver X receptors. Nicotine and carbon monoxide did not inhibit ABCA1 expression. Our results indicate that chronic cigarette smoking impaired ABCA1-mediated cholesterol efflux in macrophages and that tobacco abstinence reversed the function and expression of ABCA1, especially in CAD patients. It was tobacco tar, rather than nicotine or carbon monoxide, that played a major role in the tobacco-induced disturbance of cellular cholesterol homeostasis.

Human blood platelets lack nitric oxide synthase activity

Reports on expression and functionality of nitric oxide synthase (NOS) activity in human blood platelets and erythrocytes are contradictory. We used a specific gas chromatography-mass spectrometry (GC-MS) method to detect NOS activity in human platelets. The method measures simultaneously [(15)N]nitrite and [(15)N]nitrate formed from oxidized (15)N-labeled nitric oxide ((15)NO) upon its NOS-catalyzed formation from the substrate l-[guanidino-(15)N2]-arginine. Using this GC-MS assay, we did not detect functional NOS in non-stimulated platelets and in intact platelets activated by various agonists (adenosine diphosphate, collagen, thrombin, or von Willebrand factor) or lysed platelets. l-[guanidino-nitro]-Arginine-inhibitable NOS activity was measured after addition of recombinant human endothelial NOS to lysed platelets. Previous and recent studies from our group challenge expression and functionality of NOS in human platelets and erythrocytes.

Effects of paracetamol on NOS, COX, and CYP activity and on oxidative stress in healthy male subjects, rat hepatocytes, and recombinant NOS

Paracetamol (acetaminophen) is a widely used analgesic drug. It interacts with various enzyme families including cytochrome P450 (CYP), cyclooxygenase (COX), and nitric oxide synthase (NOS), and this interplay may produce reactive oxygen species (ROS). We investigated the effects of paracetamol on prostacyclin, thromboxane, nitric oxide (NO), and oxidative stress in four male subjects who received a single 3 g oral dose of paracetamol. Thromboxane and prostacyclin synthesis was assessed by measuring their major urinary metabolites 2,3-dinor-thromboxane B₂ and 2,3-dinor-6-ketoprostaglandin F_1α, respectively. Endothelial NO synthesis was assessed by measuring nitrite in plasma. Urinary 15(S)-8-iso-prostaglanding F_2α was measured to assess oxidative stress. Plasma oleic acid oxide (cis-EpOA) was measured as a marker of cytochrome P450 activity. Upon paracetamol administration, prostacyclin synthesis was strongly inhibited, while NO synthesis increased and thromboxane synthesis remained almost unchanged. Paracetamol may shift the COX-dependent vasodilatation/vasoconstriction balance at the cost of vasodilatation. This effect may be antagonized by increasing endothelial NO synthesis. High-dosed paracetamol did not increase oxidative stress. At pharmacologically relevant concentrations, paracetamol did not affect NO synthesis/bioavailability by recombinant human endothelial NOS or inducible NOS in rat hepatocytes. We conclude that paracetamol does not increase oxidative stress in humans.

Cultured hepatocytes adopt progenitor characteristics and display bipotent capacity to repopulate the liver

Clinical studies have proved the therapeutic potential of hepatocyte transplantation as a promising alternative to whole organ liver transplantation in the treatment of hereditary or end-stage liver disease. However, donor shortage seriously restricts cell availability, and the lack of appropriate cell culture protocols for the storage and maintenance of donor cells constitutes a significant obstacle. The aim of this study was to stimulate mature hepatocytes in culture to multiply in vitro and track their fate on transplantation. Rat hepatocytes isolated nonenzymatically were cultured serum free for up to 10 days. They were stimulated into proliferation in the presence of growth factors and conditioned media from nonparenchymal and hepatocyte culture supernatants, as well as 10 mM lithium chloride (LiCl). Cell proliferation was assessed by determining DNA content. Additionally, the extent of cell differentiation was estimated using immunofluorescence staining of hepatic, biliary, progenitor, and mesenchymal markers and gene expression analyses. Transplantation studies were performed on the Fischer CD26-mutant rat following pretreatment with retrorsine and partial hepatectomy. Proliferating hepatocytes increasingly adopted precursor characteristics, expressing progenitor (OV6, CD133), hepatic lineage (CK18), biliary (CD49f, CK7, CK19), and mesenchymal (vimentin) markers. The supplement of LiCl further enhanced the proliferative capacity by 30%. Transplantation studies revealed extensive repopulation by large donor hepatocyte clusters. Furthermore, bile duct-like structures deriving from donor cells proved to be immunoreactive to ductular markers and formed in close proximity to endogenous bile ducts. Mature hepatocytes reveal their potential to "switch" between phenotypes, adopting progenitor characteristics during proliferation in vitro. Following transplantation, these "retrodifferentiated" cells further expanded in vivo, thereby generating bipotentially differentiated progenies (hepatocytes and bile duct-like structures). This apparent plasticity of mature hepatocytes may open new approaches for cell-based strategies to treat liver disease.

High-performance liquid chromatography ultraviolet assay for human erythrocytic catalase activity by measuring glutathione as o-phthalaldehyde derivative

The most frequently used catalase (CAT) activity assay is based on the spectrophotometric measurement of hydrogen peroxide (H(2)O(2)) absorbance decrease at 240 nm. Here we report an alternative high-performance liquid chromatography (HPLC) assay for human erythrocytic CAT (heCAT) activity measurement based on glutathione (GSH) analysis as a highly stable, H(2)O(2)-insensitive o-phthalaldehyde (OPA) derivative. The method was developed and validated using an isolated heCAT in phosphate-buffered saline at pH 7.4 and was applied to measure CAT activity in lysed human erythrocytes. heCAT activity was measured at initial concentrations of 5 nM for heCAT, 5mM for H(2)O(2), and 10mM for GSH, and the incubation time was 10 min. Nitrite (NO(2)(-)) was found to be an uncompetitive inhibitor of heCAT activity (IC(50)=9 μM) and of CAT activity in hemolysate (IC(50)∼750 μM). Nitrate (NO(3)(-)) at concentrations up to 100 μM did not inhibit heCAT activity. Azide (N(3)(-)) was found to be a very strong inhibitor of the heCAT (IC(50)=0.2 nM) but a relatively weak CAT inhibitor (IC(50)∼10 μM) in human hemolysates. The novel CAT activity assay works under redox conditions that more closely resemble those prevailing in cells and allows high-throughput analysis despite the required HPLC step.