Disruption of intermolecular disulfide bonds in PDGF-BB dimers by N-acetyl-L-cysteine does not prevent PDGF signaling in cultured hepatic stellate cells

N-acetyl-cysteine increases cellular dysfunction in progressive chronic kidney damage after acute kidney injury by dampening endogenous antioxidant responses

Oxidative stress and mitochondrial dysfunction exacerbate acute kidney injury (AKI), but their role in any associated progress to chronic kidney disease (CKD) remains unclear. Antioxidant therapies often benefit AKI, but their benefits in CKD are controversial since clinical and preclinical investigations often conflict. Here we examined the influence of the antioxidant N-acetyl-cysteine (NAC) on oxidative stress and mitochondrial function during AKI (20-min bilateral renal ischemia plus reperfusion/IR) and progression to chronic kidney pathologies in mice. NAC (5% in diet) was given to mice 7 days prior and up to 21 days post-IR (21d-IR). NAC treatment resulted in the following: prevented proximal tubular epithelial cell apoptosis at early IR (40-min postischemia), yet enhanced interstitial cell proliferation at 21d-IR; increased transforming growth factor-β1 expression independent of IR time; and significantly dampened nuclear factor-like 2-initiated cytoprotective signaling at early IR. In the long term, NAC enhanced cellular metabolic impairment demonstrated by increased peroxisome proliferator activator-γ serine-112 phosphorylation at 21d-IR. Intravital multiphoton microscopy revealed increased endogenous fluorescence of nicotinamide adenine dinucleotide (NADH) in cortical tubular epithelial cells during ischemia, and at 21d-IR that was not attenuated with NAC. Fluorescence lifetime imaging microscopy demonstrated persistent metabolic impairment by increased free/bound NADH in the cortex at 21d-IR that was enhanced by NAC. Increased mitochondrial dysfunction in remnant tubular cells was demonstrated at 21d-IR by tetramethylrhodamine methyl ester fluorimetry. In summary, NAC enhanced progression to CKD following AKI not only by dampening endogenous cellular antioxidant responses at time of injury but also by enhancing persistent kidney mitochondrial and metabolic dysfunction.

Measurement of Mitochondrial Mass by Flow Cytometry during Oxidative Stress

Properly assessing mitochondrial health is crucial to understand their role in disease. MitoTracker green (MTG) and nonylacridine orange (NAO) are fluorescent probes which have been commonly used to assess mitochondrial mass. This is based on the assumption that both MTG and NAO accumulate in mitochondria regardless of the mitochondrial transmembrane potential (ΔΨ_m). Here, we utilized flow cytometry to evaluate the performance of these probes for assessment of mitochondrial mass relative to forward (FSC) and side scatter (SSC) in human peripheral blood lymphocytes (PBL). In isolated mitochondria, two subpopulations were identified by FSC and SSC measurements which were matched to subpopulations stained by MTG and NAO. The performance of these dyes was examined under oxidative and nitrosative stress induced by rotenone and NOC-18 while N-acetylcysteine (NAC) was employed as an antioxidant. Production of reactive oxygen species (ROS) and ΔΨ_m were monitored in parallel. With respect to representation of mitochondrial mass, neither MTG nor NAO was affected by ΔΨ_m. However, MTG showed significant correlation with cytosolic and mitochondrial ROS production and nitrosative stress. Our data suggest that NAO may be more suitable than MTG for assessment of mitochondrial mass by flow cytometry during oxidative stress.

α-Lipoic acid inhibits liver fibrosis through the attenuation of ROS-triggered signaling in hepatic stellate cells activated by PDGF and TGF-β

Reactive oxygen species (ROS) have been implicated in hepatic stellate cell activation and liver fibrosis. We previously reported that α-lipoic acid (LA) and its reduced form dihydrolipoic acid (DHLA) inhibited toxicant-induced inflammation and ROS generation. In the present study, we further examined the effects of LA/DHLA on thioacetamide (TAA)-induced liver fibrosis in rats and the possible underlying mechanisms in hepatic stellate cells in vitro. We found that co-administration of LA to rats chronically treated with TAA inhibited the development of liver cirrhosis, as indicated by reductions in cirrhosis incidence, hepatic fibrosis, and AST/ALT activities. We also found that DHLA inhibited TGF-β/PDGF-stimulated HSC-T6 activation and ROS generation. These effects could be mediated by the MAPK and PI3K/Akt pathways. According to our current results, LA may have a beneficial role in the treatment of chronic liver diseases caused by ongoing hepatic damage.

[Liver fibrosis - pathogenesis and novel therapeutic approaches]

Chronic liver injury, such as viral hepatitis, alcohol, metabolic syndrome or other toxic damages, leads to an inflammatory response including the infiltration and activation of immune cells and to the proliferation and transdifferentiation of mesenchymal cells within the liver, especially of hepatic stellate cells. These cells produce an excess of extracellular matrix proteins that are deposited in the liver. Hepatic fibrosis may progress to liver cirrhosis and liver failure. This review aims at summarizing the current view on the pathogenic sequence during fibrogenesis highlighting the essential role of cytokines and chemokines. Understanding the complex cellular interactions in liver fibrosis may help to develop novel antifibrotic therapies in the near future.

N-acetylcysteine attenuates progression of liver pathology in a rat model of nonalcoholic steatohepatitis

A "2-hit" model for nonalcoholic steatohepatitis (NASH) has been proposed in which steatosis constitutes the "first hit" and sensitizes the liver to potential "second hits" resulting in NASH. Oxidative stress is considered a candidate for the second hit. N-acetylcysteine (NAC), an antioxidant, has been suggested as a dietary therapy for NASH. We examined the effects of NAC in a rat total enteral nutrition (TEN) model where NASH develops as the result of overfeeding dietary polyunsaturated fat. Male Sprague-Dawley rats consumed pelleted AIN-93G diets ad libitum or were overfed a 9200 kJ.kg(-0.75).d(-1) liquid diet containing 70% corn oil with or without 2 g.kg(-1).d(-1) NAC i.g. for 65 d. Hepatic steatosis was not influenced by dietary supplementation with NAC; however, the liver pathology score was lower (P Collapse

Key Words

• steatosis
• oxidative stress
• lipid peroxidation
• tnf-α
• fibrosis

Collapse

MESH Headings

• Acetylcysteine/pharmacology
• Animals
• Autoantibodies/blood
• Disease Models, Animal
• Energy Intake
• Fatty Liver/immunology
• Fatty Liver/pathology
• Fatty Liver/physiopathology
• Fatty Liver/prevention & control
• Glutathione/metabolism
• Inflammation
• Liver/drug effects
• Liver/metabolism
• Liver/pathology
• Liver Function Tests
• Male
• Oxidative Stress
• Rats
• Rats, Sprague-Dawley
• Reverse Transcriptase Polymerase Chain Reaction
• Triglycerides/blood

Collapse

Grants

• R01 AA012819 NIAAA NIH HHS
• R01 AA012819-05 NIAAA NIH HHS
• R01 AA018282 NIAAA NIH HHS
• R01 AA 12819 NIAAA NIH HHS

Collapse

Affiliation(s)

January N. Baumgardner Department of Pharmacology and Toxicology, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA Arkansas Children’s Nutrition Center, Little Rock, AR, 72202, USA
Kartik Shankar Department of Pharmacology and Toxicology, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA Arkansas Children’s Nutrition Center, Little Rock, AR, 72202, USA
Leah Hennings Department of Pathology, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA
Emanuele Albano Department of Medical Sciences, University "Amedeo Avogadro" of East Piedmont, Via Solaroli, Novara, Italy
Thomas M. Badger Department of Pharmacology and Toxicology, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA Department of Physiology and Biophysics, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA Department of Pediatrics, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA Arkansas Children’s Nutrition Center, Little Rock, AR, 72202, USA
Martin J. J. Ronis Department of Pharmacology and Toxicology, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA Department of Pediatrics, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA Arkansas Children’s Nutrition Center, Little Rock, AR, 72202, USA

Collapse

Extracts of Lindera obtusiloba induce antifibrotic effects in hepatic stellate cells via suppression of a TGF-beta-mediated profibrotic gene expression pattern

Liver fibrosis is characterized by high expression of the key profibrogenic cytokine transforming growth factor (TGF)-beta and the natural tissue inhibitor of metalloproteinases (TIMP)-1, leading to substantial accumulation of extracellular matrix. Liver fibrosis originates from various chronic liver diseases, such as chronic viral hepatitis that, to date, cannot be treated sufficiently. Thus, novel therapeutics, for example, those derived from Oriental medicine, have gained growing attention. In Korea, extracts prepared from Lindera obtusiloba are used for centuries for treatment of inflammation, improvement of blood circulation and prevention of liver damage, but experimental evidence of their efficacy is lacking. We studied direct antifibrotic effects in activated hepatic stellate cells (HSCs), the main target cell in the fibrotic liver. L. obtusiloba extract (135 mug/ml) reduced the de novo DNA synthesis of activated rat and human HSCs by about 90%, which was not accompanied by cytotoxicity of HSC, primary hepatocytes and HepG2 cells, pointing to induction of cellular quiescence. As determined by quantitative polymerase chain reaction, simultaneous treatment of HSCs with TGF-beta and L. obtusiloba extract resulted in reduction of TIMP-1 expression to baseline level, disruption of the autocrine loop of TGF-beta autoinduction and increased expression of fibrolytic matrix metalloproteinase (MMP)-3. In addition, L. obtusiloba reduced gelatinolytic activity of HSC by interfering with profibrogenic MMP-2 activity. Since L. obtusiloba extract prevented intracellular oxidative stress experimentally induced by tert-butylhydroperoxide, we concluded that the direct antifibrotic effect of L. obtusiloba extract might be mediated by antioxidant activity. Thus, L. obtusiloba, traditionally used in Oriental medicine, may complement treatment of chronic liver disease.

Participation of reactive oxygen species generated by NADPH oxidase in regulating signal transduction in hepatic stellate cells

Reactive oxygen species (ROS) are established molecules that are injurious to such biomolecules as DNA and protein, and that can induce lipid peroxidation. However, it is now held that Nox/Duox family of NADPH oxidases generate ROS in a carefully regulated manner, which can act as second messengers influencing signal transduction in various cells including hepatic stellate cells (HSCs). This paper focused on mechanism of ROS generated by NOX/Duox regulating signal transduction, and then reviewed signal transduction of ROS-mediated liver profibrogenic factors, e.g., transforming growth factor-β (TGF-β), platelet-derived growth factor (PDGF), Angiotensin II (Ang II) and leptin, et al in HSCs.