The pool of free proline in acute and chronic liver injury and its effect on the synthesis of collagen and globular proteins

Development, validation, and application of a liquid chromatography-tandem mass spectrometry method for quantitative determination of trans-4-hydroxy-l-proline concentration in the serum of dogs with chronic hepatitis

OBJECTIVE

To develop and analytically validate a liquid chromatography-tandem mass spectrometry method for measurement of endogenous trans-4-hydroxy-l-proline concentrations in canine serum and to assess serum trans-4-hydroxy-l-proline concentrations in dogs with chronic hepatitis.

SAMPLE

Serum samples obtained from 20 dogs with histopathologically confirmed chronic hepatitis and 20 healthy control dogs.

PROCEDURES

A liquid chromatography-tandem mass spectrometry method for quantification of trans-4-hydroxy-l-proline concentration was developed and assessed for analytic sensitivity, linearity, accuracy, precision, and reproducibility. Serum concentration of trans-4-hydroxy-l-proline in dogs with chronic hepatitis and healthy control dogs was measured.

RESULTS

Observed-to-expected ratios for dilutional parallelism ranged from 72.7% to 111.5% (mean ± SD, 91.3 ± 19.6%). Intra-assay and interassay coefficients of variation ranged from 2.1% to 3.0% and 3.2% to 5.3%, respectively. Relative error ranged from -2.3% to 7.8%. Trans-4-hydroxy-l-proline concentrations were significantly lower in serum obtained from dogs with chronic hepatitis (median, 0.24 ng/mL; range, 0.06 to 1.84 ng/mL) than in serum obtained from healthy control dogs (median, 0.78 ng/mL; range, 0.14 to 4.90 ng/mL).

CONCLUSIONS AND CLINICAL RELEVANCE

The method described here for the quantification of trans-4-hydroxy-l-proline concentration in canine serum was found to be sensitive, specific, precise, accurate, and reproducible. Dogs with chronic hepatitis had significantly lower serum trans-4-hydroxy-l-proline concentrations than did healthy control dogs, possibly as a result of altered hepatic metabolism of amino acids.

Hepatoprotective activity of Trichilia roka on carbon tetrachloride-induced liver damage in rats

Trichilia roka Chiov. (Meliaceae) is a tree widely distributed in tropical Africa. It has been used in Mali folk medicine for the treatment of various illnesses. A decoction of the roots is taken as a remedy for colds and pneumonia, and it is used as a diuretic and in hepatic disorders. We have evaluated the hepatoprotective effects of a decoction of Trichilia roka root on CCl4-induced acute liver damage in rats. Treatment with the decoction showed a significant protective action made evident by its effect on the levels of glutamate oxalacetate transaminase and glutamate pyruvate transaminase in the serum, on the protein content and lipid peroxidation levels in the liver homogenate. Histopathological changes produced by CCl4, such as necrosis, fatty change, ballooning degeneration and inflammatory infiltration of lymphocytes around the central veins, were clearly recovered by the treatment with Trichilia root decoction. On fractionating this extract into diethyl ether-soluble and water-soluble fractions, the activity was retained in the diethyl ether-soluble fraction. Moreover, the administration of decoction prevented a preferential deposition of collagen around the sinusoidal cell layer, which is responsible for the perisinusoidal fibrosis in the early stage of CCl4 damage. This study showed that treatment with Trichilia roka extracts or silymarin (as reference) appeared to enhance the recovery from CCl4-induced hepatotoxicity. The hepatoprotective properties of Trichilia roka may be correlated to polyphenol content of the decoction and its diethyl ether-soluble fraction.

Mechanism of ethanol induced hepatic injury

Ethanol is hepatotoxic through redox changes produced by the NADH generated in its oxidation via the alcohol dehydrogenase pathway, which in turn affects the metabolism of lipids, carbohydrates, proteins and purines. Ethanol is also oxidized in liver microsomes by an ethanol-inducible cytochrome P-450 (P-450IIE1) which contributes to ethanol metabolism and tolerance, and activates xenobiotics to toxic radicals thereby explaining increased vulnerability of the heavy drinker to industrial solvents, anesthetic agents, commonly prescribed drugs, over-the-counter analgesics, chemical carcinogens and even nutritional factors such as vitamin A. Induction also results in energy wastage and increased production of acetaldehyde. Acetaldehyde, in turn, causes injury through the formation of protein adducts, resulting in antibody production, enzyme inactivation, decreased DNA repair, and alterations in microtubules, plasma membranes and mitochondria with a striking impairment of oxygen utilization. Acetaldehyde also causes glutathione depletion and lipid peroxidation, and stimulates hepatic collagen synthesis, thereby promoting fibrosis.

Metabolism and metabolic effects of alcohol

The author provides an excellent overview of the three major pathways for the metabolism of ethanol. Many of the toxic effects of ethanol can be attributed to two specific products, hydrogen and acetaldehyde, and these effects are explored in detail.

Influence of extracellular proline on collagen synthesis in rat liver slices

The synthesis of collagen was measured in incubated rat liver slices. The concentration of proline in the medium was varied, but the specific radioactivity of proline was kept constant. The synthesis of total protein was found to be about 500-fold that of collagen. The incorporation into hydroxyproline--that is, the synthesis of collagen--and the total incorporation of proline into protein were dependent on the concentration of proline in the medium, by Michaelis-Menten kinetics, with an apparent Km of 0.40 mM for the synthesis of collagen and 0.43 mM for the synthesis of total protein.

Plasma concentrations and tissue uptake of free amino acids in dogs in sepsis and starvation: effects of glucose infusion--some effects of low alimentation

The plasma concentrations of substrates, together with transhepatic and transgut balances, have been studied in six control and eight septic awake fasted dogs. Four severely ill septic dogs (typically fluid in chest and/or abdomen, extensive peritonitis, respiratory difficulties) had high concentrations of threonine, glycine, tyrosine, lysine, histidine, tryptophan, and triglycerides (p less than or equal to 0.05). The other septic dogs (less severely ill) showed fewer and less pronounced alterations in the plasma substrates (aspartate and tryptophan were elevated, p less than or equal to 0.05). The infusion of glucose increased the concentration of glucose, lactate, and pyruvate and depressed the concentrations of most amino acids in both normal and septic dogs. Threonine, asparagine, glutamine, leucine, isoleucine, alpha-aminobutyrate, and tyrosine were significantly depressed in the severely ill septic dogs (p less than or equal to 0.05). In the normal dogs most amino acids were removed by the liver, with alanine accounting for approximately 40% of the total. Glutamine removal was negligible. In the septic dogs hepatic removal of amino acids was variable; livers of two severely ill septic dogs did not remove amino acids. In the control dogs glucose infusion (0.015--0.017 g/kg/min) tended to lower hepatic removal of amino acids. Hepatic dye removal in the septic dogs was always very poor. In the gut glutamine was removed and alanine, glutamate, glycine, and ammonia produced, but the overall sum of amino acid uptake was negligible in both the control and septic dogs. The ratio of tryptophan to the sum of valine, isoleucine, leucine, tyrosine, and phenylalanine concentrations was greatly elevated in all septic dogs in which it was measured. The free concentrations of amino acids in the liver, heart, and muscle tissues were grossly elevated in the low intravenous alimented septic state relative to the fasted normal state, whereas the tissue concentrative ability as measured by nonmetabolizable amino acids, alpha-aminoisobutyrate and cycloleucine, was not similarly increased. Sepsis clearly alters plasma and tissue concentrations, and in some instances hepatic uptake of amino acids.

Fascioliasis: role of proline in bile duct hyperplasia

In animals fascioliasis, extensive hyperplasia of the main bile duct occurs that often results in enlargement of the duct to more than 20 times the normal. We report that proline infused into the abdominal cavity of rats caused hyperplasia of the bile duct resembling that produced in the early stages of the disease. We suggest that Fasciola hepatica, which synthesizes and releases large amounts of proline, induces enlargement of the bile duct by a similar mechanism.

Factors stimulating collagen synthesis from the livers of hypercholesterolemic rats

Hypercholesterolemia was induced in rats by feeding them a high cholesterol olive oil diet. The livers were homogenized in modified Krebs-Ringer medium and centrifuged at 35,000 x g. The supernatants from livers of both hypercholesterolemic and normal rats were found to stimulate collagen synthesis in freshly isolated embryonic chick-tendon fibroblasts. However, this was significantly greater in the supernatants from fatty livers. The stimulating principle proceed to be dialyzable, non-lipid and heat-stable. There were at least two factors involved, the more effective of which was trypsin-sensitive, with a molecular weight below 2,000. The results suggest that a mediator is formed in the livers of hypercholesterolemic rats which might be responsible for the enhanced collagen synthesis of fibrotic processes vivo, e.g., in atherosclerosis and liver cirrhosis.