Protein Synthesis In Liver Research Articles

Dietary protein effects on growth and fractional protein synthesis and degradation rates in liver and white muscle of rainbow trout ( Oncorhynchus mykiss)

We have studied the effects of a decrease in dietary protein on the growth and proteinturnover parameters [fractional protein synthesis ( K S), degradation ( K D) and accumulation ( K G) rates, synthesis capacity ( C S), synthesis efficiency ( K RNA and K DNA), and protein retention efficiency (PRE)]. The administration of a low-protein diet caused a significant decrease in the availability of protein precursors due to a decline in feed efficiency and thus a concomitant decrease in whole-body, white-muscle and liver growth capacity throughout the experimental period. The reduction in dietary protein caused a significant decrease in the K G value in the liver as a consequence of a decrease in protein retention efficiency (PRE). In white muscle, however, a considerable reduction in the K G value was due to a decrease in K S, C S, K DNA and K RNA rather than a decrease in PRE.

Influence of dietary lysine availability on the fractional rates of protein synthesis and degradation in liver and white muscle of rainbow trout ( Oncorhynchus mykiss)

Influence of dietary lysine availability on the fractional rates of protein synthesis and degradation in liver and white muscle of rainbow trout ( Oncorhynchus mykiss)

Effect of growth hormone on tumor and host in an animal model

The relative effects of growth hormone on tumor versus host growth and protein metabolism are not known. This study examines the influence of recombinant rat growth hormone (r-rGH) on host and tumor growth, host body composition, and protein synthesis of tumor and host in tumor-bearing rats. After left flank implantation of methylcholanthrene-induced sarcoma, 28 Fischer rats with palpable tumor were treated with s.c. saline or 1 mg/kg/day r-rGH for 11 days. At death, fractional protein synthetic rates (FSRs) of tumor, liver, and gastrocnemius muscle were determined. In a separate experiment, 27 tumor-bearing rats received saline or 1 mg/kg/day r-rGH for 2 weeks. Tumor and host growth and host body composition were analyzed. Animals treated with r-rGH had significantly higher liver FSR than did controls (233 +/- 27%/day vs. 110 +/- 4%/day, respectively). No significant differences were associated with growth hormone administration with respect to tumor growth, host composition, or FSR of tumor or muscle. Growth hormone stimulates liver protein synthesis, without changing tumor growth, protein synthesis, or host composition in this rat sarcoma model. Further investigation of growth hormone as an anticachectic agent is warranted.

Nitrogen Balance, Plasma Free Amino Acid Concentrations and Urinary Orotic Acid Excretion during Long-Term Fasting in Cats1–4

The purpose of this study was to ascertain the changes in nitrogen balance, plasma free amino acid concentrations, urinary orotic acid excretion and body weight during long-term fasting in adult obese cats. Results from eight cats that fasted rather than eat an unpalatable diet are reported. After 5 to 6 wk of weight loss, six of the eight cats developed signs of hepatic lipidosis, and the livers of all cats were severely infiltrated with lipids. Cats lost (mean +/- SE) 33.2 +/- 1.4% of their pre-fasting body weight. Mean nitrogen balance (+/- SE) was -547 +/- 54 mg.d-1.kg-2/3 for the first week, and then the net nitrogen losses decreased to a plateau (-303 +/- 52 mg.d-1.kg-2/3) after 4 wk. Fasting was associated with a decrease in plasma concentration of essential amino acids. When plasma amino acid concentrations were considered individually, concentrations of alanine, methionine, taurine, citrulline, arginine and tryptophan decreased the most (> or = 50%), whereas concentrations of glutamine, glutamate and ornithine significantly increased. Orotic acid was not detected in the urine during the fast. After 1 wk of fasting, obese cats had reduced nitrogen excretion, but not to the same extent as has been shown in obese humans or obese rats. It is suggested that the availability of several amino acids may become limiting for liver protein synthesis during fasting and that these deficiencies may contribute to the development of hepatic lipidosis. Orotic acid was not linked to hepatic lipidosis caused by fasting in cats.

Age Affects Brain Protein Synthesis in Rats

The purpose of the present study was to determine whether age affected the rate of brain protein synthesis in rats. Experiments were conducted on three groups of rats, ages 4, 7 or 24 wk. The fractional rates of protein synthesis in brain, liver and kidney decreased and the RNA concentration (mg RNA/g protein) declined with age. In brain, liver and kidney, the RNA concentrations were significantly correlated with the fractional rates of protein synthesis. The RNA activity [g protein synthesized/(g RNA.d)] was not related to the fractional rate of protein synthesis in any organs except cerebral cortex. The results suggest that the rate of protein synthesis in brain declines with age after weaning, and that RNA concentration is at least partly related to the fractional rate of brain protein synthesis.

Plasma protein synthesis and serum amino acids in dry and lactating dairy cows.

Blood serum concentrations of protein, albumin, prealbumin, transferrin, amino acids and urea were measured in 31 healthy cows 0 to 6 weeks before and 3 to 8 weeks after parturition. In comparison to the precalving values the concentrations of albumin, prealbumin and transferrin were all lower after parturition. Alanine, glutamine, leucine, methionine, serine, and urea concentrations were also lower after calving. Multiple correlation analysis between plasma protein and amino acid concentrations reveals that the synthesis of export proteins in liver may be reduced due to limitation in amino acid availability.

Immunoglobulin Levels in Workers Exposed to Inorganic Mercury

The serum immunoglobulin (IgG, IgM and IgA) concentrations of 44 mercury-exposed workers were examined and compared with those of non-exposed, age- and sex-matched individuals. At the time of testing, the exposed population had a mean (+/- S.D.) mercury urinary concentration of 24.7 +/- 19.1 and in 40 of them urinary mercury levels were below the currently accepted limit of 50 micrograms/g creatinine. Increased IgG, IgA and IgM levels were found in the mercury-exposed individuals and in 16, a second evaluation was performed six months later. During the intervening six months, the level of hygiene was improved throughout the plant, and urinary mercury concentrations were determined monthly in each worker. Despite a significant reduction in mercury urinary concentrations, serum immunoglobulin levels did not return to the normal range. There was no correlation between the length or level of exposure and the immunoglobulin levels. Liver protein synthesis, as studied by factor V, prothrombin time, prealbumin and transaminase activity, was normal and liver injury, as evaluated by serum aspartate and alanine aminotransferase activities (AST and ALT, respectively), was not observed. No haematological abnormalities were noted. These results indicate that "safe" levels of mercury exposure may lead to humoral immunological stimulation.

Effects of albumin-bilirubin complexes with syngeneic or allogeneic albumin on DNA and protein synthesis in liver and spleen of partially hepatectomized rats

The effects of non-covalently bound complexes of allogeneic or syngeneic albumin with bilirubin and of albumin alone on DNA and protein synthesis in rat liver and spleen cells after partial hepatectomy were studied. The assay procedure was based on different intravenous doses of these compounds in rats after partial hepatectomy. The allogeneic albumin-bilirubin complex (at protein doses of 0.9 and 90 micrograms/100 g body weight) stimulated DNA and protein synthesis in liver cells irrespective of the dose. At a dose of 0.9 micrograms the syngeneic albumin-bilirubin complex enhanced DNA synthesis insignificantly and produced no effect on protein synthesis, while at a dose of 90 micrograms, both DNA and protein synthesis were considerably increased. Allogeneic or syngeneic albumin at the above doses stimulated only protein, not DNA, synthesis in the liver, while the highest stimulation was at 90 micrograms allogeneic albumin. It was found also that partial hepatectomy decreased DNA and protein synthesis in spleen cells. Albumin-bilirubin complex with allogeneic or syngeneic albumin and albumin alone either significantly enhanced DNA and protein synthesis in the spleen, compared to controls, or only restored synthesis to control levels. Thus DNA and protein synthesis in the regenerating liver and spleen was significantly enhanced after the injection of small doses of the albumin-bilirubin complex, indicating the existence of small amounts of a similar endogenous complex in the blood stream.

Protein synthesis in regenerating rat liver during malnutrition

To examine the effect of malnutrition on liver protein metabolism and synthesis during liver regeneration, 104 rats were allocated to semi-starvation or ordinary food intake for 1 week. Half of each group was sham operated and the other half was partially hepatectomized. Specimens were taken from the liver at the time of liver resection and from animals killed 24, 48 and 72 h after the primary operation. Liver samples were analysed for DNA and protein, and in the 48-h groups RNA and protein synthesis were also analysed. Protein synthesis was measured by the flooding method using L[4-3H] phenylalanine. The liver weight during regeneration increased very rapidly in the well-nourished animals, but when expressed as percent of body weight or as proportional increases, the difference between well-nourished and malnourished animals disappeared. The fractional rate of protein synthesis was not changed in sham-operated malnourished or well-nourished animals. During regeneration, protein synthesis in well-nourished animals was elevated compared to sham-operated controls, but a lesser stimulation was seen in malnourished rats. It was concluded that the mechanism of liver regeneration depends on nutritional state, involving an increase in protein synthesis in well-nourished animals, but relying more on a decrease in protein degradation or cessation of secretory protein synthesis in malnourished animals.

Relationship between lipoprotein(a) levels in serum and some indices of protein synthesis in liver cirrhosis

Recent research has demonstrated that the major site of apolipoprotein(a) synthesis, the characteristic protein of lipoprotein(a) (Lp(a)), is the liver and that patients affected by liver cirrhosis have low serum concentrations of Lp(a). Nevertheless, it is still not clear whether Lp(a) behaviour in these patients is related to reduced hepatic protein synthesis, or to decreased serum lipid levels or to both these conditions. In order to investigate further the behaviour of Lp(a) and, in particular, its relationship with some indices of blood lipids and coagulation, 30 patients affected by liver cirrhosis have been studied. Significantly low serum values of Lp(a) were observed in patients with more severe hepatic injury included in classes B and C according to the Child-Pugh score. Lipoprotein(a) was directly correlated with prothrombin plasma activity and with apolipoprotein B-100 and albumin concentrations in serum. This study confirms low serum levels of Lp(a) in cirrhotic patients and suggests that its decrease could be partly due to impaired liver protein synthesis.

Stress protein synthesis induced by cadmium-cysteine in rat kidney

Biomarkers are important tools which enable toxicologists to reliably predict and detect exposures to xenobiotics and resultant cell injury, ultimately improving risk assessments. Since the de novo synthesis of stress proteins can be detected early after exposure to some agents, analysis of toxicant-induced changes in gene expression, i.e. alterations in patterns of protein synthesis, may be useful to develop as biomarkers of exposure and toxicity. We are utilizing various xenobiotics as tools to study stress protein synthesis in target organs in order to evaluate the target tissue-specificity of this response. Previous data from this laboratory have demonstrated that induction of stress proteins in rat liver, but not kidney, after acute exposure to CdCl 2 precedes hepatotoxicity. Since kidney is a target tissue after chronic Cd exposure, it was of interest to examine stress protein synthesis in this tissue. However, dose-limiting hepatotoxicity precluded this evaluation. Cd complexed with molecules such as cysteine (cys) or metallothionein has been used in acute dosing regimens as a tool in order to study the nephrotoxicity of Cd. Therefore, this study was undertaken in order to evaluate Cd-induced stress protein synthesis in an important tissue known to be injured after chronic exposure, i.e. kidney. Specific objectives included comparing stress protein synthesis in rat kidney and liver after acute exposure to Cd-cys and CdCl 2, determining the Cd threshold concentration for renal stress protein synthesis and assessing the relationship between stress protein synthesis and nephropathy. Male rats were exposed to equivalent doses of Cd as CdCl 2 or Cd-cysteine (molar ratio Cd:cys=1:15). Kidney Cd concentrations increased 5-fold after a.v. injection of Cd-cys compared to CdCl 2, mimicking Cd distribution following chronic exposure. After exposure to Cd, tissue slices were incubated with 35S-methionine. Slices were subsequently homogenized and centrifuged, and the 16 000 g supernatants were subjected to SDS-polyacrylamide gel electrophoresis. Proteins which had incorporated 35S-methionine were detected by autoradiography. De novo synthesis of 70, 90 and 110 kDa proteins was enhanced in liver, but not in kidney, 4 h after injection of 2 mg Cd/kg as CdCl 2. In contrast, dose-related increases in synthesis of these proteins were observed in kidney 4 h after injection of 1 and 2 mg Cd/kg as Cd-cys, but not at lower dosages. In addition, synthesis of a 68 kDa kidney protein was inhibited at 2 mg Cd/kg as Cd-cys, The threshold for Cd-induced stress protein synthesis was shown to be between 4 and 8 μg Cd/g tissue. These alterations in protein synthesis in kidney occured at tissue Cd concentrations lower than those which resulted in renal injury, as assessed by histopathology and PAH uptake into renal slices. Thus, altered patterns of protein synthesis may serve as markers of cell injury or indicators of cellular stress in target organs.

Amino Acids Suppress Intracellular Protein Degradation in Rat Liver during Parenteral Nutrition

The effects of variations in the amino acid supply on the rates of synthesis and degradation of liver proteins and on the rate of synthesis and secretion of plasma proteins were investigated. Rats were nourished by infusion of total parenteral nutrition solutions containing four different levels (0, 1.65, 3.3 and 6.6%) of amino acids for 7 d. The fractional rate of total protein synthesis in the liver was determined by injecting a flooding dose of [3H]phenylalanine. The proportion of newly synthesized proteins retained and exported by the liver was estimated by injecting a tracer dose of [14C]leucine and then measuring the protein radioactivity remaining in the liver and present in the plasma after secretion was completed. The rate of plasma albumin synthesis was significantly lower in the 0 and 1.65% amino acid groups than in the other groups. The fractional synthesis rates of liver domestic proteins, however, were essentially the same in rats administered all levels of amino acids except for the 0% amino acid group, which showed a slightly higher value than the other groups. The fractional degradation rates of liver domestic proteins, calculated as the difference between the fractional synthesis rate of liver domestic proteins and the net gain of liver proteins, were found to be inversely related (r = -0.999, P < 0.05) to the level of amino acids in infusion solutions up to 3.3% amino acids. It was concluded that protein degradation plays the predominant role in the regulation of liver protein mass.

Pentoxifylline decreases body weight loss and muscle protein wasting characteristics of sepsis.

Sepsis induces metabolic disorders that include loss of body weight, muscle wasting, and acute-phase protein synthesis in liver. Cytokines are generally recognized as active mediators of these disorders, and the implication of tumor necrosis factor (TNF) has been frequently discussed in the recent past. However, the identity of the active agent in alterations of protein metabolism is still controversial. To improve our understanding of the role of cytokines in mediating muscle wasting observed in sepsis, we investigated muscle and liver protein metabolism in the following three groups of rats: infected control rats (INF-C); infected rats pretreated with pentoxifylline (PTX-INF), which is a potent inhibitor of TNF secretion; and pair-fed rats for the PTX-INF group pretreated with pentoxifylline. Pentoxifylline nearly completely suppressed TNF secretion but did not influence the transient fall in rectal temperature, the decreased hematocrit, and the increased liver protein mass and synthesis observed in INF-C rats. Pentoxifylline decreased the anorexia, the loss of body weight and muscle protein observed in INF-C animals, and partially prevented the decrease in muscle protein synthesis induced by infection. The overall data indicate that pentoxifylline is an effective agent in mitigating the characteristic muscle protein wasting induced by sepsis and confirm the limited role of TNF in the mediation of the acute-phase protein synthesis. Our results suggest a probable implication of TNF in the regulation of protein balance in muscle but do not allow discarding possible implication of other mediators that would be inhibited by pentoxifylline.

Responses of tissue protein synthesis to nutrient intake in rats exposed to interleukin-1 beta or turpentine.

1. The influence of an acute-phase reaction on the ability of protein synthesis rates in liver and three different muscles (gastrocnemius, soleus and heart) to respond to a short intravenous infusion of nutrients (glucose plus amino acids) was investigated during experimental inflammation induced by injection of human recombinant interleukin-1 beta or turpentine in young male rats. 2. Interleukin-1 beta induced a consistent increase of 3 degrees C in body temperature between 3 and 5 h after injection, whereas turpentine induced a delayed fever, peaking by 13 h. 3. Interleukin-1 beta and turpentine stimulated fractional rates of protein synthesis in liver. The synthesis rate was inhibited by interleukin-1 beta in gastrocnemius and soleus muscle, but an elevation was seen in heart muscle. In this study there was no significant response of muscle to turpentine injection. 4. Two hours of parenteral nutrition increased fractional synthesis rates in all tissues when compared with Ringer's lactate. Somewhat larger responses to feeding were observed as a result of either interleukin-1 beta or turpentine injection in all tissues, but these improvements were not significant. 5. We conclude that the response of protein synthesis rates in liver and skeletal muscle to parenteral nutrition is not inhibited, and may be somewhat enhanced, during acute inflammatory conditions in the growing rat.

Stress Protein Synthesis Induced in Rat Liver by Cadmium Precedes Hepatotoxicity

A diverse array of chemical and physical stressors increases the synthesis of a class of proteins referred to as heat shock proteins (hsp) or stress proteins. We are investigating the potential of using altered protein synthesis patterns, including the enhanced synthesis of stress proteins, as biomarkers of exposure and cellular injury. The purpose of the present study was to evaluate the effect of a model hepatotoxicant, cadmium (Cd(II)), on stress protein synthesis in male rat liver. To assess target tissue specificity, stress protein synthesis was also studied in kidney. Liver and kidney slices from exposed rats were incubated with [35S]methionine for 1.5 hr, subjected to one-dimensional SDS-PAGE, and 35S-labeled proteins were analyzed by autoradiography. Enhanced de novo synthesis of 70-, 90-, and 110-kilodalton (kDa) relative molecular mass (Mr) proteins was detected 2 hr after exposure to 2 mg Cd/kg, with maximum activity occurring at 2-4 hr. By 8-16 hr postinjection, synthesis of these proteins had decreased. Synthesis of a 68-kDa protein present in control liver was inhibited 2 hr after exposure with synthesis restored at 16-24 hr. Dose-related increases in synthesis of the three stress proteins were observed 4 hr after iv injection of 1.0 and 2.0 mg Cd/kg, with concomitant inhibition of synthesis of the 68-kDa protein. Mild single cell necrosis of hepatocytes was observed 8 hr after injection of 2 mg Cd/kg which progressed to mild multifocal necrotic foci at 16 hr. No lesions were evident at lower dosages. Increases in plasma sorbitol dehydrogenase activity, a clinical indicator of hepatic injury, was not apparent until 8 hr after exposure. A functional deficit, decreased hepatic microsomal N-demethylase activity, was not observed until 16 hr after iv injection of 2 mg/kg. No changes in kidney de novo stress protein synthesis were observed. No evidence of renal injury was apparent, as evaluated by histopathology, uptake of [para-3H]aminohippurate into renal slices, and blood urea nitrogen values. The 70-kDa stress protein induced early after Cd treatment was identified with a monclonal antibody as the 72-kDa-inducible hsp. The 90-kDa protein induced by Cd reacted negatively with three monoclonal antibodies to hsp90 and was subsequently identified as a glucose regulated protein (grp94). The data demonstrate that Cd induces alterations in the expression of hepatic gene products in vivo as evidenced by enhanced stress protein synthesis and inhibition of synthesis of constitutive proteins. These changes in liver protein synthesis occurred prior to overt hepatic injury based on histopathologic evidence and two biochemical assays used to assess hepatic injury. Altered patterns of stress protein synthesis in response to Cd appeared to be target organ specific, as no changes in protein synthesis or evidence of renal injury were demonstrated. The data suggest that chemical-induced changes in protein synthesis, including enhanced synthesis of stress proteins, may serve as biomarkers of hepatic injury or represent an adaptation response to toxic insult.

Dietary medium chain triglyceride increase liver protein synthesis in chicks

Dietary medium chain triglyceride increase liver protein synthesis in chicks

Protein synthesis in the liver and breast muscle of chicks fed on a high protein diet

Abstract 1. The influence of feeding a high protein diet containing 400 g crude protein (CP)/kg on liver and breast muscle protein synthesis in chicks was investigated using a large dose injection of l‐[4 ‐3H]phenylalanine. 2. Liver weight of chicks fed on the high protein diet was significantly heavier than that of chicks fed on a control diet with 200 g CP/kg, and breast muscle weight was not affected by the treatment. 3. Fractional and absolute protein synthesis rates, RNA and protein contents, and RNA:protein ratio of breast muscle were not influenced by feeding the high protein diet. 4. Feeding the high protein diet decreased fractional synthesis rate of liver protein, an observation explained by reduced RNA:protein ratio. Liver protein content was elevated by feeding the high protein diet and this resulted in no change in the absolute synthesis rate of liver protein.

Genetic variation in mouse apolipoprotein A-IV expression is determined pre- and post-transcriptionally

Among inbred mouse strains there is a striking genetic variation in the levels of apolipoprotein A-IV (apoA-IV) mRNA in the liver, although intestinal mRNA levels vary only twofold in these strains. In the present study we have characterized the apoA-IV expression phenotypes in strains C57BL/6J and 129/J, and investigated the molecular basis for the genetic variation. We report that the two strains differ eight- to tenfold both in the levels of apoA-IV mRNA and in the rate of apoA-IV protein synthesis in liver. Presumably due to the increased synthetic rate, strain 129 exhibits a threefold higher concentration of apoA-IV protein in the circulation. mRNA synthesis and turnover studies indicate that both transcriptional and post-transcriptional events contribute to the genetic variation in steady state apoA-IV mRNA levels. An analysis of the levels of apoA-IV mRNA derived from 129 and C57BL/6 alleles in F1 mice indicates that the genetic control of apoA-IV mRNA levels involves both cis-acting elements linked to the apoA-IV gene, and genetically distinct trans-acting factors.

Age-related changes in protein synthesis measured in vivo in rat liver and gastrocnemius muscle

This study analyses in detail the effects of ageing on gastrocnemius muscle and liver protein synthesis measured in vivo at three ages, 1.5 months (young), 12 months (adult) and 24 months (old) in Sprague-Dawley rats. Comparing adult and old rats, muscle protein synthesis was decreased in old rats when expressed per unit of RNA and per day (translational efficiency), was unchanged when expressed in absolute terms and increased when expressed in fractional terms as a result of protein loss due to muscle atrophy. In the liver, only translational efficiency tended to decrease in old rats compared to adult rats. It is concluded that the decline in protein turnover described in vitro is consistent with a decrease in translational efficiency, but that absolute synthesis rates are maintained during ageing. Muscle atrophy is unlikely to result from alterations in protein synthesis pathways.

Effect of amino acids alone or with insulin on muscle and liver protein synthesis in adult and old rats

This study was carried out to analyze age-related changes on amino acid and insulin effects on muscle and liver protein synthesis. Conscious male rats, aged 12 (adult) and 24 (old) mo, were infused for 90 min with either saline, amino acids, or amino acids with insulin and glucose. Protein synthesis was measured during the last 15 min of infusion (flooding dose of valine with L-[2,3,4-3H]valine). Gastrocnemius protein mass was 29% lower in old rats than in adults. However, basal muscle absolute synthesis rates were unchanged with age, and fractional synthesis rates (FSR) were increased. Amino acids significantly stimulated muscle FSR to a similar extent (18-20%) in adult (P < 0.01) and old rats (P = 0.03 when variability introduced by muscle atrophy was taken into account by a variance-covariance analysis). Insulin did not elicit any additional effect. Liver protein synthesis did not change with age or in response to infusions. We conclude that, despite an age-related loss of muscle proteins, capacity of muscle protein synthesis to be stimulated is preserved with age.