Brain tryptophan, plasma free tryptophan and distribution of plasma neutral amino acids.

Although rat brain tryptophan is strikingly elevated following portacaval shunt, plasma total tryptophan is unchanged and plasma free tryptophan is not elevated to the same degree as brain tryptophan. Investigation of the concentrations of the neutral amino acids (phenylalanine, tyrosine, methionine, threonine, leucine, isoleucine, and valine) revealed that their distribution and the sum of their concentrations were altered following portacaval shunt, and that this pattern was similar to that seen in humans with cirrhosis of the liver. It is suggested that both the elevation in plasma free tryptophan and the decrease in the competing neutral amino acids, act together to increase the transport of tryptophan into brain when portal blood is diverted around the liver. The implications of these findings in therapy of hepatic coma is discussed.     

Effect of polyunsaturated isocaloric fat diets on plasma lipids, apolipoproteins and fatty acids

The effect of an increased polyunsaturated fatty acid concentration in the diet on the plasma lipoproteins from a normal group of healthy persons and from a group of hypercholesterolemic patients, consuming an isoenergetic and an isocholesterolemic diet, was examined and the changes in the plasma phospholipids were measured. Nine normal and 10 hypercholesterolemic patients were treated with a polyunsaturated diet for 1 month. Controls and hypercholesterolemic patients were screened on their lipid and lipoprotein profiles and their P/S ratio in the diet was calculated and increased with a factor 4. In the control group the P/S ratio was increased from 0.35 to 1.38 and in the hypercholesterolemic group from 0.46 to 1.59. They received the diet for at least 4 weeks before a second analysis of lipids and lipoproteins. The most important results are a decrease of plasma cholesterol, followed by a significant increase of HDL cholesterol. The cholesterol-lowering effect results largely from the plasma LDL decrease, especially in the patient group. Apo A-I is decreased accompanied by a significant increase of the ratio HDL-C/apo A-I. The observed changes are most pronounced in the hypercholesterolemic group. There is no change in apo B but a significant change in the linoleic acid concentration especially in the HDL cholesterol esters. The major phospholipids in plasma are identical in both groups and there is an identical change under the PUFA diet, sphingomyelin is increased and phosphatidylcholine is decreased, which may be related to an increase of the HDL2/HDL3 ratio.     

Behavior of plasma amino acids in alcohol-induced chronic liver diseases

In chronic liver diseases of alcoholic and non-alcoholic origin there are strikine differences of aspartate, glutamate and prolin. Where as plasma levels of aspartate and prolin are in most cases higher than in non-alcoholics, glutamate shows a contrary behaviour except in hepatic coma. The plasma ratio of alpha-amino-butyric acid to leucin allows no distinction of alcoholic from non-alcoholic liver lesion.     

Effects of amino acids on bile acid-dependent and independent bile flow in the isolated perfused rat liver.

BACKGROUND/AIMS: Conflicting data on the effects of amino acids on biliary function led us to investigate their interaction with taurocholate in the perfused rat liver model. METHODS: To investigate the influence of amino acids on the bile acid-independent component of bile flow, 12 livers were perfused with (n = 6) and without (n = 6) amino acid addition from t30 min. For the study of bile acid-dependent bile flow, 24 livers were perfused under 8 experimental conditions according to the perfusate taurocholate concentration (12.5, 25, 37.5 or 50 microM) and whether amino acids were or were not added from t30 min. RESULTS: In the absence of taurocholate, amino acids induced a 40% (p<0.01) decrease in bile flow together with an increase in hepatic water content (17.8%, p< 0.05). Thus, amino acids exert an inhibitory effect on bile acid-independent bile flow despite the postulated cell swelling-dependent increase in bile flow. When livers were perfused at various taurocholate concentrations, amino acids induced, in addition to their inhibitory effect on bile acid-independent bile flow, a significant increase in taurocholate apparent choleretic activity (13.2 microl/micromol vs. 10.6 microl/micromol; p = 0.05), while taurocholate intrinsic clearance was significantly decreased (4.5+/-1.2 ml x min(-1) x g(-1) vs. 6.1+/-1.3 ml x min(-1) x g(-1); p<0.01). CONCLUSIONS: These data suggest that at physiological bile acid concentrations amino acids exert an inhibitory effect on both bile acid-dependent and- independent bile flow, whereas at higher taurocholate concentrations this inhibitory effect disappears, probably because of cell swelling-dependent mechanisms.     

Oral administration of branched-chain amino acids activates the mTOR signal in cirrhotic rat liver.

BCAA granules (a mixture of branched-chain amino acids) have been used to reverse the hypoalbuminemia of decompensated liver cirrhotic patients in Japan. Our previous studies showed that BCAA promoted albumin secretion through the mTOR signal transduction pathway in rat primary hepatocyte culture [Ijichi C, Matsumura T, Tsuji T, Eto Y. Branched-chain amino acids promote albumin synthesis in rat primary hepatocytes through the mTOR signal transduction system. Biochem Biophys Res Commun 2003;303:59-64]. However, the mTOR-activating effect of BCAA in the experimental cirrhotic animals presenting with hypoalbuminemia has not yet been examined. The purpose of this study is to assess whether oral administration of BCAA induces mTOR activity in the livers of normal rats and CCl(4)-induced cirrhotic rats (CCl(4) rats). Biochemical analysis of liver extracts isolated from several rats showed that oral administration of BCAA (0.75g/kg body weight (BW)) induced phosphorylation of 4E-BP1 and stimulated the enzymatic activity of p70 S6K. Both of these molecules act downstream of mTOR. From the results, we conclude that orally administrated BCAA augments albumin synthesis in the liver, not only by supplementation of material substrates for protein synthesis, but also by induction of an mTOR signal that is critical for translational initiation. Furthermore, we conclude that induction of mTOR signaling is one of the major pharmacological mechanisms by which BCAA granules reverse the hypoalbuminemia of cirrhotic patients.     

Effect of amino acids on the plasma concentration and urinary excretion of uric acid and uridine.

To determine the effect of amino acids on the plasma level and urinary excretion of uric acid and uridine, 200 mL 12% amino acid solution, and 2 weeks later, 100 mL physiological saline solution containing glucagon (1.2 microg/kg weight), was infused into five healthy men. Both increased the urinary excretion of uric acid and the concentration of glucagon, insulin, and glucose in plasma and pyruvic acid in blood, whereas they decreased the concentration of uridine and inorganic phosphate in plasma. However, neither the amino acid infusion nor glucagon infusion affected the concentration of purine bases (hypoxanthine, xanthine, and uric acid), cyclic adenosine monophosphate (cAMP) in plasma, or lactic acid in blood or the urinary excretion of oxypurines (hypoxanthine and xanthine), uridine, or sodium. These results suggest that glucagon may have an important role in the amino acid-induced increase in urinary excretion of uric acid and decrease in plasma uridine.     

Free amino acids in plasma and skeletal muscle of patients with liver cirrhosis

Free amino acids were measured under postabsorptive conditions in plasma and intracellular water of skeletal muscle obtained by needle biopsy in nine healthy controls and 14 subjects suffering from clinically stable liver cirrhosis. The aromatic amino acids phenylalanine and tyrosine in cirrhotics were elevated to the same extent in plasma and in muscle water. Branched-chain amino acids were uniformly reduced in plasma, but in muscle water only valine was significantly lower (222 +/- 92 mumoles per kg intracellular water vs. 368 +/- 82, p less than 0.001), while isoleucine (142 +/- 63 vs. 103 +/- 30), leucine (223 +/- 88 vs. 226 +/- 36) and branched-chain amino acids as a whole (589 +/- 186 vs. 681 +/- 88) were normal or elevated with an increased muscle:plasma ratio (3.12 +/- 2.03 vs. 1.41 +/- 0.37, p less than 0.05 for isoleucine; 3.00 +/- 1.28 vs. 1.85 +/- 0.27, p less than 0.025 for leucine; 2.24 +/- 0.64 vs. 1.69 +/- 0.13, p less than 0.05 for total branched-chain amino acids. Our data show that, in cirrhosis, plasma concentrations of branched-chain amino acids do not reflect their levels in muscle cellular water; only the intracellular pool of valine is severely depleted. This suggests that higher amounts of valine supplementation may be useful in nutritional treatment of liver cirrhosis. The elevated muscle:plasma gradients for branched-chain amino acids may result from abnormalities in their transport through muscle-plasma membrane.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of somatostatin on the plasma amino acid response to ingested protein in man.

To evaluate the effect of somatostatin on the plasma amino acid response to ingested protein and amino acids, normal subjects received a 6-hr intravenous infusion of somatostatin or saline initiated 2 hr before consuming a lean beef meal (3 g/kg) or oral leucine (5 g). The effect of somatostatin on intravenous leucine disposal was also examined. In the saline control study, the branched-chain amino acids exhibited the largest elevations in plasma concentration after protein ingestion. Somatostatin markedly reduced the protein-induced increments in plasma branched-chain amino acids by 50%–75% (p < 0.001) throughout the study period. This effect was not attributable to augmented systemic disposal of these amino acids since somatostatin exaggerated by 70%–75% the rise in plasma leucine produced by intravenous leucine (p < 0.05). Somato-statin also blunted by 40%–80% the elevations in most other amino acids after protein feeding. When leucine alone was ingested, somatostatin delayed the peak rise in plasma leucine by 1 hr, but did not alter the total area under the plasma leucine response curve. We conclude that somatostatin causes a sustained reduction in the systemic availability of amino acids contained in ingested protein, while availability of free leucine is only transiently delayed. These findings raise the possibility that somatostatin reduces systemic availability of protein-derived amino acids primarily by interfering with the digestive process.     

Effects of carbohydrate and protein meals on plasma large neutral amino acids, glucose, and insulin plasma levels of anorectic patients

The response of large neutral amino acids (LNAA), glucose, and insulin plasma levels to a protein-rich and a carbohydrate-rich test meal was studied in anorectic patients (upon admission to hospital and after weight gain) and in a control group of young women. Patients showed reduced glucose tolerance, as well as increased and prolonged insulin secretion. After the protein meal, the ratio of tyrosine to other LNAA (a predictor of tyrosine flow into brain) was increased in patients and the ratio of tryptophan to other LNAA (a predictor of tryptophan flow into brain) depressed. The carbohydrate meal resulted in a smaller increase in the ratio of tryptophan to other LNAA in patients. Not all alterations showed a trend to normalization with weight gain. Implications of findings for monoamine metabolism and regulation of food choice are discussed.     

Nucleic acids,total and glial protein changes in rat brain with aging

The wet weights and the amounts of total protein, RNA, DNA, S100 protein and carbonic anhydrase were measured in cerebrum, cerebellum and brain stem of adult and old rats. We found a general increase of wet weight, DNA and total protein and an important increase of the amounts of S100 protein and carbonic anhydrase relatively to the soluble proteins in brain of old rats (30 months) compared to that of young adults (3 months). These findings show that in older rat brain, the total number of cells is increased whereas the average quantity of protein and wet weight per unit of DNA remained constant. A decrease of RNA to DNA ratio is found in old rat brain. This fact together with the increase of the relative amount of glial specific proteins suggest an increase of the glial cell population referred to neurons with aging. However, modifications of the neuronal and/or glial cell metabolism cannot be excluded.     

Ammonia and related amino acids in the pathogenesis of brain edema in acute ischemic liver failure in rats.

The pathogenesis of brain edema in acute liver failure is poorly understood. We have previously shown that rats with ischemic acute liver failure (portacaval anastomosis followed by hepatic artery ligation) exhibit brain edema and intracranial hypertension, with swelling of cortical astrocytes as the most prominent neuropathological abnormality. Because ammonia has been shown to induce swelling of astrocytes in vivo and in vitro, we examined the relationship between brain ammonia, amino acids generated from ammonia metabolism and brain water content in this model. Four groups of animals were studied: rats subjected to two sham operations, rats subjected to portacaval anastomosis and a sham operation, rats subjected to a sham operation and hepatic artery ligation and rats subjected to portacaval anastomosis and hepatic artery ligation. The last group of animals was studied at three progressive stages of encephalopathy. Cortical gray matter water increased from 80.26% +/- 0.22% (sham + sham) to 82.46% +/- 0.06% (last stage of devascularization). In cerebral cortex, brain ammonia increased to a maximum of 5.4 mmol/L. Glutamine, generated in glial cells from ammonia and glutamate, increased sixfold to 24 mmol/L and remained at this level throughout all stages of encephalopathy. Alanine, which may be generated from the transamination of glutamine, increased in parallel to the increase in water (r = 0.80, n = 15). In this model of fulminant liver failure and associated brain edema, brain ammonia increases to levels associated with in vitro swelling of brain slices and glial cells. The accumulation of osmogenic aminoacids such as glutamine and alanine may contribute to the selective astrocyte swelling seen in this condition.(ABSTRACT TRUNCATED AT 250 WORDS)     

Protective effects of regulatory amino acids on ischaemia-reperfusion injury in the isolated perfused rat liver

Objective. Some amino acids (AAs) display potent regulatory activities on cell metabolism, including via anti-oxidative defences. The aim of this study was to evaluate the protective effect of these AAs on warm ischaemia-reperfusion (I/R) injury in the isolated perfused rat liver.

Material and methods. Livers from fasted male Sprague-Dawley rats were isolated and perfused without (control group) or with (AP group) a mixture of regulatory AAs (glutamine, histidine, leucine, methionine, proline, phenylalanine, tryptophan and alanine). After 45 min of perfusion, warm ischaemia was induced for 45 min by clamping the portal vein catheter; thereafter, reperfusion was performed for 30 min.

Results. TNF-α production was significantly lower in the AP group during reperfusion (Control: 39±7 versus AP: 16±2 pg min^?1 g^?1, p<0.05), and lactate dehydrogenase (LDH) release decreased significantly during the last 15 min of reperfusion (Control: 0.13±0.03 versus AP: 0.04±0.02 IU min^?1 g^?1, p<0.05), despite similar levels of oxidative stress. The addition of regulatory AAs was not associated with variations in portal flow, bile flow, hepatic glucose or urea metabolism. However, significant changes in intrahepatic glutamine (Control: 1.4±0.2 versus AP: 2.6±0.5 µmol g^?1, p<0.05) together with higher glutamate release in the AP group (Control: 10.2±5.4 versus AP: 42.6±10.9 nmol min^?1 g^?1, p<0.05) indicated modifications in nitrogen metabolism.

Conclusions. Taken together, the lower TNF-α production, suggesting decreased inflammatory response, the decrease in LDH release in the AP group, demonstrating a better preservation of liver viability, and the increase in hepatic glutamine indicate that AAs play an important role in the liver's response to I/R.     

Protective effects of regulatory amino acids on ischemia-reperfusion injury in the isolated perfused rat liver

OBJECTIVE: Some amino acids (AAs) display potent regulatory activities on cell metabolism, including via anti-oxidative defences. The aim of this study was to evaluate the protective effect of these AAs on warm ischaemia-reperfusion (I/R) injury in the isolated perfused rat liver. MATERIAL AND METHODS: Livers from fasted male Sprague-Dawley rats were isolated and perfused without (control group) or with (AP group) a mixture of regulatory AAs (glutamine, histidine, leucine, methionine, proline, phenylalanine, tryptophan and alanine). After 45 min of perfusion, warm ischaemia was induced for 45 min by clamping the portal vein catheter; thereafter, reperfusion was performed for 30 min. RESULTS: TNF-alpha production was significantly lower in the AP group during reperfusion (Control: 39+/-7 versus AP: 16+/-2 pg min-1 g-1, p<0.05), and lactate dehydrogenase (LDH) release decreased significantly during the last 15 min of reperfusion (Control: 0.13+/-0.03 versus AP: 0.04+/-0.02 IU min-1 g-1, p<0.05), despite similar levels of oxidative stress. The addition of regulatory AAs was not associated with variations in portal flow, bile flow, hepatic glucose or urea metabolism. However, significant changes in intrahepatic glutamine (Control: 1.4+/-0.2 versus AP: 2.6+/-0.5 micromol g-1, p < 0.05) together with higher glutamate release in the AP group (Control: 10.2+/-5.4 versus AP: 42.6+/-10.9 nmol min-1 g-1, p < 0.05) indicated modifications in nitrogen metabolism. CONCLUSIONS: Taken together, the lower TNF-alpha production, suggesting decreased inflammatory response, the decrease in LDH release in the AP group, demonstrating a better preservation of liver viability, and the increase in hepatic glutamine indicate that AAs play an important role in the liver's response to I/R.