Hepatic encephalopathy: experimental studies on the pathogenesis

Aims of this thesis: 1. To study, in rabbits, the suitability of experimental acute liver failure and acute hyperammonemia simulating acute liver failure for the study of hepatic encephalopathy and ammonia toxicity. 2. To study glutamate neurotransmission in rabbits with acute liver failure and acute hyperammonentia. 3. To determine the role of the changes in glutamate neurotransntission found in 2 in the development of hepatic encephalopathy. 18The pathogenesis of hepatic encephalopathy is largely unknown. Ammonia was the flrst toxin seriously considered to be of importance in the pathogenesis, has been subsequently rejected, but now appears to return to the forefront of "hepatic neurochemistry" (58). In theory, hyperammonemia can disturb normal brain ftmction through interference with basic cell metabolism (e.g. pH-regulation and water and energy balance)(59-61), electrophysiologic membrane ftmction (depending on ion pumps)(62) and biochemical communication between neurons, i.e. neurotransmission (depending on neurotransmitters). With regard to neurotransmission, one of the current opinions on the pathogenesis of hepatic encephalopathy is a dysbalance between neuro-inhibitory and neuro-excitatory neurotransmitters (63). Several groups have proposed that neuroinhibition via GABA or endogenous benzodiazepines is enhanced; we are investigating whether excitatory neurotransmission -especially glutamate neurotransmission- is altered during hepatic

45CaCl2 autoradiography in brain from rabbits with encephalopathy from acute liver failure or acute hyperammonemia

In experimental hepatic encephalopathy and hyperammonemia, extracellular levels of glutamate are increased in hippocampus and cerebral cortex. It has been suggested that overstimulation of glutamate receptors causes a pathological entry of calcium into neurons via receptor-operated (NMDA- and AMPA-type) or voltage-dependent calcium channels leading to calcium overload and cell death. Neurodegeneration as a result of exposure to excitotoxins, including glutamate, can be localized and quantified using45CaCl2 autoradiography. This approach was used to study cerebral calcium accumulation in rabbits with acute liver failure and acute hyperammonemia. Acute liver failure was induced in 6 rabbits, acute hyperammonemia in 4 rabbits; 4 control rabbits received sodium-potassium-acetate. At the start of the experiment 500 µCi45CaCl2 was given intravenously. After development of severe encephalopathy, the animals were killed by decapitation. All rabbits with acute liver failure or acute hyperammonemia developed severe encephalopathy, after 13.2±1.7 and 19.3±0.5 hours respectively (mean±SEM). Plasma ammonia levels were 425±46 and 883±21 µmol/l, respectively (p<0.05). Control rabbits maintained normal plasma ammonia levels (13±5 µmol/l), demonstrated normal behaviour throughout the study and were sacrificed after 16 hours.45Ca2+-autoradiograms of 40 µm brain sections were analyzed semiquantitatively using relative optical density and computerized image analysis. As compared to background levels45Ca was not increased in hippocampus or any other brain area of rabbits with severe encephalopathy from acute liver failure or acute hyperammonemia. This suggests that, despite increased extracellular brain glutamate levels in these conditions, glutamate neurotoxicity was not important for the development of encephalopathy in these rabbits

Sex-specific normal values and determinants of infrarenal abdominal aortic diameter among non-aneurysmal elderly population

To establish age- and sex-specific distribution of the infrarenal abdominal aortic diameters (IAD) among non-aneurysmal elderly population and to investigate the associations between traditional cardiovascular risk factors and IAD in men and women. We included 4032 participants (mean age 67.2 years; 60.4% women) from the population-based Rotterdam Study, free of cardiovascular disease, who underwent IAD ultrasound assessment between 2009–2014. Linear regression analysis was used to identify determinants of IAD. The medians (inter-quartile range) of absolute IAD and body surface area (BSA)-adjusted IAD were 17.0 (15.0–18.0) mm and 9.3 (8.5–10.2) mm for women and 19.0 (18.0–21.0) mm and 9.4 (8.6–10.3) mm for men, respectively. There was a non-linear relationship between age and IAD. IAD increased steeply with advancing age and up to 70 years. After around 75 years of age, the diameter values reached a plateau. Waist circumference and diastolic blood pressure were associated with larger diameters in both sexes. Body mass index [Effect estimate (95% CI): 0.04 (0.00 to 0.08)], systolic blood pressure [− 0.01(− 0.02 to 0.00)], current smoking [0.35 (0.06 to 0.65)], total cholesterol levels [− 0.21 (− 0.31 to − 0.11)], and lipid-lowering medication [− 0.43 (− 0.67 to − 0.19)] were significantly associated with IAD in women. Sex differences in IAD values diminished after taking BSA into account. The increase in diameters was attenuated after 70 years. Differences were observed in the associations of several cardiovascular risk factors with IAD among men and women.</p

Sex-specific normal values and determinants of infrarenal abdominal aortic diameter among non-aneurysmal elderly population

To establish age- and sex-specific distribution of the infrarenal abdominal aortic diameters (IAD) among non-aneurysmal elderly population and to investigate the associations between traditional cardiovascular risk factors and IAD in men and women. We included 4032 participants (mean age 67.2 years; 60.4% women) from the population-based Rotterdam Study, free of cardiovascular disease, who underwent IAD ultrasound assessment between 2009–2014. Linear regression analysis was used to identify determinants of IAD. The medians (inter-quartile range) of absolute IAD and body surface area (BSA)-adjusted IAD were 17.0 (15.0–18.0) mm and 9.3 (8.5–10.2) mm for women and 19.0 (18.0–21.0) mm and 9.4 (8.6–10.3) mm for men, respectively. There was a non-linear relationship between age and IAD. IAD increased steeply with advancing age and up to 70 years. After around 75 years of age, the diameter values reached a plateau. Waist circumference and diastolic blood pressure were associated with larger diameters in both sexes. Body mass index [Effect estimate (95% CI): 0.04 (0.00 to 0.08)], systolic blood pressure [− 0.01(− 0.02 to 0.00)], current smoking [0.35 (0.06 to 0.65)], total cholesterol levels [− 0.21 (− 0.31 to − 0.11)], and lipid-lowering medication [− 0.43 (− 0.67 to − 0.19)] were significantly associated with IAD in women. Sex differences in IAD values diminished after taking BSA into account. The increase in diameters was attenuated after 70 years. Differences were observed in the associations of several cardiovascular risk factors with IAD among men and women.</p

Baseline anti-NS4a antibodies in combination with on-treatment quantitative HCV-RNA reliably identifies nonresponders to pegylated interferon-ribavirin combination therapy after 4 weeks of treatment

Background Early detection of nonresponders to hepatitis C therapy limits unnecessary exposure to treatment and its side-effects. A recent algorithm combining baseline anti-NS4a antibodies and on-treatment quantitative PCR identified nonresponders to a combination of interferon and ribavirin after 1 week of treatment. Aim To validate a stopping rule based on baseline anti-NS4a antibody levels and early on-treatment virological response in treatment-naive genotype 1 chronic hepatitis C patients treated with the current standard pegylated interferon and ribavirin combination therapy. Methods Eighty-nine genotype 1 patients from the Dynamically Individualized Treatment of hepatitis C Infection and Correlates of Viral/Host dynamics Study treated for 48 weeks with standard 180 mu g pegylated interferon (PEG-IFN)-alpha-2a (weekly) and ribavirin 1000-1200mg (daily) were analysed. Baseline anti-NS4a antibody enzyme-linked immunosorbent assay (NS4a AA 1687-1718) was performed on pretreatment serum. Hepatitis C virus-RNA was assessed at days 0, 1, 4, 7, 8, 15, 22, 29, weeks 6, 7, 8, 10, 12 and 6 weekly thereafter until end of treatment. Multiple regression logistic analysis was performed. Results Overall 54 of 89 (61%) patients achieved sustained virological response. A baseline anti-NS4a antibody titre less than 1/1250 correlated with absence of favourable initial viral decline according to variable response types (P=0.015). The optimal algorithm was developed using the combination of the absence of anti-NS4a Ab (= 100.000 IU/ml at week 4. This algorithm has a specificity of 43% and negative predictive value of 100% to detect nonresponse to standard PEG-IFN-alpha-2a and ribavirin therapy at fourth week of therapy (intention-to-treat analysis). Conclusion The decision to stop the therapy in genotype 1 chronic hepatitis C patients treated with PEG-IFN-alpha-2a and ribavirin can be confidently made after 4 weeks of treatment based on the absence of baseline anti-NS4a Ab and a week-4 hepatitis C virus-RNA above 100.000 IU/ml. Eur J Gastroenterol Hepatol 22:1443-1448 (C) 2010 Wolters Kluwer Health vertical bar Lippincott Williams & Wilkins

The Steatosis-associated fibrosis estimator (SAFE) score:validation in the general US population

Background: Noninvasive tests are important in the initial risk stratification of people at risk of fibrosis. The recently developed steatosis-associated fibrosis estimator (SAFE) score may have such potential but awaits external validation. Methods: We analyzed 6973 participants aged 18-80 in the National Health and Nutrition Examination Survey 2017-2020 cycle with data on liver stiffness and SAFE score without prevalent heart failure. Fibrosis was defined as liver stiffness ≥ 8.0 kPa. Accuracy was evaluated by AUC and assessment of test characteristics at the prespecified cutoffs for ruling out/ruling in fibrosis. Results: The SAFE score categorized 14.7% of the population as high risk, 30.4% as intermediate risk, and 54.9% as low risk for fibrosis. The actual fibrosis prevalence in these groups was 28.0%, 10.9%, and 4.0%, respectively, translating into a positive predictive value of 0.28 at the high-risk cutoff and a negative predictive value of 0.96 at the low-risk cutoff. The AUC of the SAFE score (0.748) was significantly higher than the fibrosis-4 index (0.619) or NAFLD fibrosis score (0.718). However, test performance strongly depended on age categories: 90% of participants aged 18-40 years were considered at low risk for fibrosis, including 89/134 (66%) of clinically significant fibrosis cases. In the oldest group (60-80 y), fibrosis could only be safely ruled out among 17%, corresponding to a high referral rate of up to 83%. The best SAFE score performance was found in the middle-aged group (40-60 y). The results were consistent in target populations with metabolic dysfunction or steatosis. Conclusions: The SAFE score has overall good diagnostic accuracy in detecting fibrosis but was highly dependent on age. The SAFE score lacked sensitivity in younger populations and the ability to rule out fibrosis in older populations.</p