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Biomedical subjects

A M Diehl

Publications and source records attributed to A M Diehl.

At least 19 recordsLinked to original sources
PubMed2004

Metformin in the treatment of non-alcoholic steatohepatitis: a pilot open label trial.

BACKGROUND: Insulin sensitizing agents may be useful in treatment of non-alcoholic fatty liver disease. AIM: A pilot study to evaluate the efficacy and safety of metformin in non-alcoholic fatty liver disease. METHODS: In an open labelled study, patients with histologically confirmed non-alcoholic fatty liver disease were given metformin (20 mg/kg) for 1 year. Insulin resistance (by log homeostasis assessment model analysis for insulin resistance and Quantitative Insulin Sensitivity Check Index) and post-treatment hepatic histology were compared with pre-treatment histology. RESULTS: Fifteen patients completed 1 year of treatment. During the initial 3 months, there was improvement in alanine aminotransferase and aspartate aminotransferase (P-value 0.01 and 0.02, respectively) along with improvement in insulin sensitivity. However, after 3 months, there was no further improvement in insulin sensitivity and there was gradual rise in aspartate aminotransferase and alanine aminotransferase back to pre-treatment levels. Among the 10 patients with post-treatment biopsy, three (33%), showed improvement in steatosis, two (20%) showed improvement in inflammation score and one (10%) showed improvement in fibrosis. CONCLUSION: Metformin treatment was associated with only a transient improvement in liver chemistries. A progressive, sustainable reduction in insulin sensitivity was not noted during treatment.

Alanine Transaminase↗
PubMed2004

Hepatic fibrogenesis requires sympathetic neurotransmitters.

BACKGROUND AND AIMS: Hepatic stellate cells (HSC) are activated by liver injury to become proliferative fibrogenic myofibroblasts. This process may be regulated by the sympathetic nervous system (SNS) but the mechanisms involved are unclear. METHODS: We studied cultured HSC and intact mice with liver injury to test the hypothesis that HSC respond to and produce SNS neurotransmitters to promote fibrogenesis. RESULTS: HSC expressed adrenoceptors, catecholamine biosynthetic enzymes, released norepinephrine (NE), and were growth inhibited by alpha- and beta-adrenoceptor antagonists. HSC from dopamine beta-hydroxylase deficient (Dbh(-/-)) mice, which cannot make NE, grew poorly in culture and were rescued by NE. Inhibitor studies demonstrated that this effect was mediated via G protein coupled adrenoceptors, mitogen activated kinases, and phosphatidylinositol 3-kinase. Injury related fibrogenic responses were inhibited in Dbh(-/-) mice, as evidenced by reduced hepatic accumulation of alpha-smooth muscle actin(+ve) HSC and decreased induction of transforming growth factor beta1 (TGF-beta1) and collagen. Treatment with isoprenaline rescued HSC activation. HSC were also reduced in leptin deficient ob/ob mice which have reduced NE levels and are resistant to hepatic fibrosis. Treating ob/ob mice with NE induced HSC proliferation, upregulated hepatic TGF-beta1 and collagen, and increased liver fibrosis. CONCLUSIONS: HSC are hepatic neuroglia that produce and respond to SNS neurotransmitters to promote hepatic fibrosis.

Animals↗
PubMed2001

Hepatic hyperplasia in noncirrhotic fatty livers: is obesity-related hepatic steatosis a premalignant condition?

It is not known whether obesity increases the risk for hepatocellular carcinoma (HCC) simply because it promotes cirrhosis, a general risk factor for HCC, or via some other mechanism that operates independently of cirrhosis. If the latter occurs, then hepatocyte hyperplasia, an early event during the neoplastic process, might begin before liver cirrhosis develops. Genetically obese, leptin-deficient ob/ob mice are models for nonalcoholic fatty liver disease (NAFLD), a type of liver disease that is strongly associated with obesity and type 2 diabetes. Similar to obese, diabetic patients, ob/ob mice have an increased incidence of HCC. However, unlike humans with NAFLD, they rarely, if ever, develop cirrhosis spontaneously. To determine whether the noncirrhotic livers of ob/ob mice with NAFLD exhibit hepatocyte hyperplasia, parameters of proliferation and apoptosis were compared in adult ob/ob mice and their healthy litter mates. Adult ob/ob mice have an increase in liver mass relative to body mass. This hepatomegaly cannot be explained solely by lipid accumulation and is accompanied by significant increases in hepatocyte proliferative activity (as evidenced by increased Erk activation, cell-cycle related gene expression, bromodeoxyuridine incorporation, and hepatic DNA content) with concomitant inhibition of hepatocyte apoptosis (as evidenced by decreased numbers of apoptotic hepatocytes, induction of several antiapoptotic mechanisms, and decreased activation of procaspase 3). Thus, liver hyperplasia is evident at the earliest stage of NAFLD in ob/ob mice, which supports the concept that obesity-related metabolic abnormalities, rather than cirrhosis, initiate the hepatic neoplastic process during obesity.

Animals↗
PubMed2001

Disrupted signaling and inhibited regeneration in obese mice with fatty livers: implications for nonalcoholic fatty liver disease pathophysiology.

The impaired regenerative capacity of fatty livers might promote the progression of nonalcoholic fatty liver disease (NAFLD). To identify mechanisms involved, regenerative responses were compared in normal mice and ob/ob mice (a model for NAFLD) after partial hepatectomy (PH). We hypothesized that the usual PH activation of oxidant-sensitive, growth-regulatory kinase cascades would be abnormal in fatty hepatocytes, which have adapted to chronic oxidant stress, and expected that this might interfere with the induction of proliferative- and stress-related genes. The normal coordinated induction of Jun N-terminal kinases (Jnks) and extracellular regulated kinases (Erks) does not occur after PH in ob/ob mice, which cannot activate Jnks but can superinduce Erks. Jnk inhibition is associated with enhanced activation of Akt, which inhibits phosphoenolpyruvate carboxykinase (PEPCK) induction, causing severe hypoglycemia and increased lethality in the ob/ob group. Activation of nuclear factor kappaB (NF-kappaB) is also inhibited, but liver damage is increased only modestly, perhaps because Akt-regulated survival factors are protective. Despite enhanced Erk activity, induction of cyclin D-1, an NF-kappaB target gene, is abolished and this, together with hyperphosphorylated signal transducer and activator of transcription-3 (Stat-3) and reduced adenosine triphosphate (ATP) levels, arrests fatty hepatocytes in G(1). Thus, in mice with NAFLD that have adapted hepatocyte signaling mechanisms to survive chronic oxidative stress, the cellular response to an acute regenerative stimulus is altered. This contributes to NAFLD pathophysiology by inhibiting proliferation, increasing injury, and limiting function in fatty livers.

Adenosine Triphosphate↗
PubMed2001

Animal models of steatosis.

The lipid content of hepatocytes is regulated by the integrated activities of cellular enzymes that catalyze lipid uptake, synthesis, oxidation, and export. When "input" of fats into these systems (either because of increased fatty acid delivery, hepatic fatty acid uptake, or fatty acid synthesis) exceeds the capacity for fatty acid oxidation or export (i.e., "output"), then hepatic steatosis occurs. Genetic causes of increased fatty acid input promote excessive hepatic lipogenesis. These include mutations that cause leptin deficiency or leptin receptor inhibition and mutations that induce insulin, insulin-like growth factors, or insulin-responsive transcription factors. Genetic causes of impaired hepatic fatty acid oxidation inhibit the elimination (i.e., output) of fat from the liver. These include mutations that inhibit various components of the peroxisomal and/or mitochondrial pathways for fatty acid beta-oxidation. Environmental factors, such as diets and toxins, can also unbalance hepatic fatty acid synthesis and oxidation. Hepatic lipogenesis is increased by dietary sucrose, fructose, or fats and certain toxins, such as ethanol. Hepatic fatty acid oxidation is inhibited by choline- or methionine-deficient diets and other toxins, such as etomoxir. Animals with genetic or environmental induction of hepatic lipogenesis appear to be useful models for human nonalcoholic fatty liver disease in which hyperinsulinemia and defective leptin signaling are conspicuous at early stages of the disease process.

Animals↗
PubMed2001

Obesity and female gender increase breath ethanol concentration: potential implications for the pathogenesis of nonalcoholic steatohepatitis.

OBJECTIVES: Similarities between histological features of alcoholic hepatitis and obesity-related liver disease suggest a common pathogenic mechanism. Because intestinal bacteria can produce ethanol, it is conceivable that intestinally derived alcohol may contribute to fatty liver disease. An indirect way of measuring endogenous ethanol is to measure the breath ethanol concentration. In a previous study in ob/ob mice, breath ethanol decreased with a course of non-absorbable antibiotics, suggesting that the ethanol is derived from intestinal bacterial flora. The aims of this study were 1) to determine whether alcohol can be detected in the breath of human subjects, and 2) to assess whether there is any correlation between ethanol and obesity in patients with nonalcoholic steatohepatits (NASH) and control subjects without known liver disease. METHODS: Breath ethanol concentration was determined in 21 patients with biopsy-proven NASH and in 10 control subjects by gas chromatography. An abnormal breath ethanol level was defined as two standard deviations above the mean value of the breath ethanol of lean controls. RESULTS: Minute quantities of ethanol were detected in the breath of human subjects who had not consumed alcohol in the recent past. Patients who were obese were more likely to have higher breath ethanol concentrations. Women also had higher breath alcohol than men. However, there was no difference between patients with NASH and controls. Severity of liver disease, as evidenced by cirrhosis, did not influence the breath ethanol concentration. CONCLUSIONS: Higher breath ethanol concentrations are observed in obese subjects than in leaner ones. It is possible that intestinally derived ethanol may contribute to the pathogenesis of NASH.

Adult↗
PubMed2001

Fatty liver vulnerability to endotoxin-induced damage despite NF-kappaB induction and inhibited caspase 3 activation.

Fatty livers are sensitive to lipopolysaccharide (LPS) damage. This study tests the hypothesis that this vulnerability occurs because protective, antiapoptotic mechanisms are not upregulated appropriately. Genetically obese, leptin-deficient ob/ob mice, a model for nonalcoholic fatty liver disease, and their lean litter mates were treated with a small dose of LPS. General measures of liver injury, early (i.e., cytochrome c release) and late (i.e., activation of caspase 3) events that occur during hepatocyte apoptosis, and various aspects of the signal transduction pathways that induce nuclear factor-kappaB (NF-kappaB) and several of its antiapoptotic transcriptional targets (e.g., inducible nitric oxide synthase, bfl-1, and bcl-xL) were compared. Within 0.5-6 h after LPS exposure, cytochrome c begins to accumulate in the cytosol of normal livers, and procaspase 3 cleavage increases. Coincident with these events, kinases (e.g., AKT and Erk-1 and -2) that result in the degradation of inhibitor kappa-B are activated; NF-kappaB activity is induced, and NF-kappaB-regulated gene products accumulate. Throughout this period, there is negligible histological evidence of liver damage, and serum alanine aminotransferase values barely increase over baseline values. Although ob/ob livers have significant histological liver injury and 11-fold greater serum alanine aminotransferase values than those of lean mice by 6 h post-LPS, they exhibit greater activation of AKT and Erk, more profound reductions in inhibitor kappa-B, enhanced activation of NF-kappaB, and greater induction of NF-kappaB-regulated genes. Consistent with this heightened antiapoptotic response, increases in cytochrome c and procaspase 3 cleavage products are inhibited. Together with evidence that ob/ob hepatocytes have a reduced ATP content and undergo increased lysis after in vitro exposure to tumor necrosis factor-alpha, these findings suggest that fatty livers are sensitive to LPS damage because of vulnerability to necrosis, rather than because of apoptosis.

Adenosine Triphosphate↗
PubMed2000

Mitochondrial adaptations to obesity-related oxidant stress.

It is not known why viable hepatocytes in fatty livers are vulnerable to necrosis, but associated mitochondrial alterations suggest that reactive oxygen species (ROS) production may be increased. Although the mechanisms for ROS-mediated lethality are not well understood, increased mitochondrial ROS generation often precedes cell death, and hence, might promote hepatocyte necrosis. The aim of this study is to determine if liver mitochondria from obese mice with fatty hepatocytes actually produce increased ROS. Secondary objectives are to identify potential mechanisms for ROS increases and to evaluate whether ROS increase uncoupling protein (UCP)-2, a mitochondrial protein that promotes ATP depletion and necrosis. Compared to mitochondria from normal livers, fatty liver mitochondria have a 50% reduction in cytochrome c content and produce superoxide anion at a greater rate. They also contain 25% more GSH and demonstrate 70% greater manganese superoxide dismutase activity and a 35% reduction in glutathione peroxidase activity. Mitochondrial generation of H(2)O(2) is increased by 200% and the activities of enzymes that detoxify H(2)O(2) in other cellular compartments are abnormal. Cytosolic glutathione peroxidase and catalase activities are 42 and 153% of control values, respectively. These changes in the production and detoxification of mitochondrial ROS are associated with a 300% increase in the mitochondrial content of UCP-2, although the content of beta-1 ATP synthase, a constitutive mitochondrial membrane protein, is unaffected. Supporting the possibility that mitochondrial ROS induce UCP-2 in fatty hepatocytes, a mitochondrial redox cycling agent that increases mitochondrial ROS production upregulates UCP-2 mRNAs in primary cultures of normal rat hepatocytes by 300%. Thus, ROS production is increased in fatty liver mitochondria. This may result from chronic apoptotic stress and provoke adaptations, including increases in UCP-2, that potentiate necrosis.

Animals↗
PubMed2000

Altered hepatic lymphocyte subpopulations in obesity-related murine fatty livers: potential mechanism for sensitization to liver damage.

Although obesity-related fatty livers are vulnerable to damage from endotoxin, the mechanisms involved remain obscure. The purpose of this study was to determine if immunologic priming might be involved by determining if fatty livers resemble normal livers that have been sensitized to endotoxin damage by Propionibacterium acnes infection. The latter induces interleukin (IL)-12 and -18, causing a selective reduction of CD4+NK T cells, diminished IL-4 production, deficient production of T-helper type 2 (Th-2) cytokines (e.g., IL-10), and excessive production of Th-1 cytokines (e.g., interferon gamma [IFN-gamma]). Liver and spleen lymphocyte populations and hepatic cytokine production were compared in genetically obese, ob/ob mice (a model for obesity-related fatty liver) and lean mice. Obese mice have a selective reduction of hepatic CD4+NK T cells. Serum IL-18 is also increased basally, and the hepatic mRNA levels of IL-18 and -12 are greater after endotoxin challenge. Thus, up-regulation of IL-18 and IL-12 in fatty livers may reduce hepatic CD4+NK T cells. In addition, mononuclear cells from fatty livers have decreased expression of the adhesion molecule, leukocyte factor antigen-1 (LFA-1), which is necessary for the hepatic accumulation of CD4+NK T cells. Consistent with reduced numbers of hepatic CD4+NK T cells, mononuclear cells from fatty livers produce less IL-4. Furthermore, after endotoxin treatment, hepatic induction of IL-10 is inhibited, while that of IFN-gamma is enhanced. Thus, fatty livers have inherent immunologic alterations that may predispose them to damage from endotoxin and other insults that induce a proinflammatory cytokine response.

Animals↗
PubMed2000

Cytokine regulation of liver injury and repair.

By comparing the hepatic responses to tumor necrosis factor (TNF)-alpha that occur during situations that promote liver injury (such as obesity or chronic exposure to ethanol) with those that occur after stimuli (such as partial hepatectomy) that lead to liver regeneration, it is apparent that hepatocytes are usually able to constrain noxious responses to TNF-alpha, such as the release of reactive oxygen from mitochondria. It appears that by promptly upregulating survival genes that regulate mitochondrial membrane permeability, hepatocytes are usually able to constrain noxious responses, including the release of mitochondrial-generated reactive oxygen species, that follow exposure to potentially toxic cytokines, such as TNF-alpha. Indeed, transient TNF-alpha-mediated increases in ROS may even be exploited by hepatocytes to evoke a subsequent proliferative response. Thus, the healthy liver has well-developed defense mechanisms that permit hepatocytes to adapt to cytokine-initiated stress, protecting them from cytokine-mediated lethality. Nevertheless, these same cytokines may cause liver injury when hepatocytes have been pre-exposed to toxins (e.g. ethanol) that interfere with their usual protective responses. Furthermore, while transient adaptations to cytokine-initiated stress permit hepatocytes to survive and proliferate, persistence of these anti-apoptotic, adaptative responses (as occurs, for example, in fatty livers) may inadvertently enhance hepatocyte vulnerability to necrosis when the liver is confronted by secondary insults that promote mitochondrial membrane depolarization.

Adaptation, Physiological↗
PubMed2000

Kupffer cell depletion by CI2MDP-liposomes alters hepatic cytokine expression and delays liver regeneration after partial hepatectomy.

BACKGROUND: Although Kupffer cells (KCs) are capable of producing important growth-stimulating cytokines, their role in liver regeneration following partial hepatectomy (PH) remains poorly understood. METHODS: In the present study liver regeneration was studied after KC-depletion by intravenous administration of liposome-encapsulated dichloromethylene-diphosphonate (C12MDP), a method known to physically eliminate KCs. Furthermore, splenectomy was performed one week prior to PH to exclude the effect of C12MDP-liposomes on macrophage populations in the spleen. RESULTS: KC-depletion was confirmed in cryostat liver sections stained with the monoclonal antibody ED2, a marker for resident tissue macrophages. Forty-eight hours after PH, the cumulative hepatocyte DNA synthesis, as determined in liver sections by the hepatocyte bromodeoxyuridine labeling index, was significantly decreased in KC-depleted rats when compared to control-rats. The weight of the remnant liver, expressed as a percentage of the initial liver weight, was significantly less at 96 h after PH in KC-depleted rats. KC-depletion abolished the hepatic interleukin-6 (IL-6) and interleukin-10 (IL-10) mRNA synthesis and decreased hepatic expression of tumor necrosis factor-alpha (TNF-alpha), hepatocyte growth factor (HGF) and transforming growth factor-beta1(TGF-beta1) mRNA after PH, as was assessed by reverse-transcriptase polymerase chain reaction (RT-PCR). Moreover, at 4 h after PH the systemic release of IL-6 was significantly decreased in KC-depleted rats. CONCLUSION: We conclude that KCs are important for hepatocyte regeneration after PH. Delayed liver regeneration in KC-depleted rats can be explained, at least in part, by an imbalanced hepatic cytokine expression, thereby suppressing important growth-stimulating cytokines.

Animals↗