Ryuhei Funabiki

Fractional catabolic rates of myosin and actin estimated by urinary excretion of N -methylhistidine: the effect of dietary protein level on catabolic rates under conditions of restricted food intake

1. Critical studies on the distribution of Ntau-methylhistidine (3-methylhistidine; Me-His) among organs and tissues in adult rats are reported. Adult rats contained 46-5+/-3-6 mg Me-His/kg body-weight. Almost 90% of the Me-His in the body was recovered from skeletal muscle. These results support the hypothesis that fractional catabolic rates of myosin and actin in skeletal muscle can be estimated by measuring urinary excretion of Me-His. 2. Dietary protein level did not affect the total amount of Me-His in the body. However, urinary excretion of Me-His increased as dietary protein intake was increased. 3. From these results it was concluded that fractional catabolic rates of myosin and actin increase as dietary protein intake increases.

Translational regulation of protein synthesis in the liver and skeletal muscle of mice in response to refeeding

To identify the mechanism that modulates the rate of protein synthesis in different tissues responding to food intake, several parameters of translational activities were measured together with the rate of protein synthesis in the liver and skeletal muscle. In 18-hour fasted mice, protein synthesis in muscle and the liver was stimulated by refeeding a complete diet after 1 hour. Refeeding a protein-free diet increased the protein synthesis in the liver but not in muscle. Injection of anti-insulin serum suppressed the response to refeeding in both tissues except to a complete diet in the liver. The response of liver protein synthesis to food intake is not necessarily mediated by insulin, provided an abrupt, large increase in plasma amino acid concentration occurs. In contrast to the liver, an elevation of insulin level is essential for the stimulation of protein synthesis in muscle along with a high concentration of plasma amino acids. The stimulation of elongation activity in addition to stimulation of the initiation activity contributed to the enhancement of protein synthesis induced by refeeding in both the liver and muscle. In another set of experiments, we also observed a delayed rise of elongation coupled with an immediate rise of initiation in the liver after refeeding.

Fractional flux rates of N-methylhistidine in skin and gastrointestine: the contribution of these tissues to urinary excretion of N-methylhistidine in the rat

1. Fractional flux rates of Ntau-methylhistidine (3-methylhistidine; Me-His) of skin and gastrointestine were measured by administering [methyl-3H]methionine to rats. 2. The results showed that the contribution of these tissues to urinary excretion of Me-His was at least 16-6%. This means that when fractional catabolic rates of myosin and actin were estimated from urinary excretion of Me-His, the part of Me-His derived from skin and gastrointestine should not be neglected.

Effects of dietary methionine and cystine on lipid metabolism in hepatoma-bearing rats with hyperlipidemia.

Abnormal lipid metabolism and its restoration by dietary methionine (Met) and cystine (Cys) were studied in Donryu rats subcutaneously implanted with an ascites hepatoma cell line of AH109A. The hepatoma-bearing rats exhibited byperlipidemia characterized by rises in serum triglyceride and cholesterol levels. Decreased lipoprotein lipase (LPL) activities in epididymal adipose tissue, cardiac muscle, and gastrocnemius as well as increased fatty acid mobilization from adipose tissue were considered to be responsible for the hepatoma-induced hypertriglyceridemia, while increased hepatic cholesterogenesis and decreased steroid excretion into feces were thought to be responsible for the hepatoma-induced hypercholesterolemia. Dietary-supplemented Met or Cys reduced the AH109A-induced hypertriglyceridemia with suppression of fatty acid synthesis in the host liver. Met restored the fall of LPL activities, while Cys did not. Dietary Met or Cys also reduced the hypercholesterolemia with restoration of decreased bile acid excretion into feces. These results suggest that dietary Met or Cys is hypolipidemic in the hepatoma-bearing rats with slight differences in their modes of action.

REDUCTION OF HYPERLIPIDEMIA IN HEPATOMA-BEARING RATS BY DIETARY FISH OIL

The effect of dietary fish oil on serum lipid levels was studied by comparing it with dietary corn oil in Donryu rats subcutaneously implanted with an ascites hepatoma cell line (AH109A). The hepatoma-bearing rats exhibited hyperlipidemia charactarized by a rise in both serum cholesterol and triglyceride levels. Increased cholesterogenesis in the host liver and decrease steroid excretion into feces are suggested to be responsible for the hepatoma-induced hypercholesterolemia, and increased fatty acid mobilization from peripheral adipose tissues and decreased triglyceride clearance from the blood circulation are considered causes for the hepatoma-induced hypertriglyceridemia. Dietary fish oil reduced the hyperfipidemia in these animals, suppressed the hepatoma-induced increase in hepatic cholesterogenesis and fatty acid mobilization from adipose tissue. Dietary fish oil also tended to increase fatty acid oxidation in the liver. Such diverse effects of fish oil may lead to the reduction of the hepatoma-induced hyperlipidemia. These results suggest that studies on dietary fish oil may be warranted in patients with cancer-related hyperlipidemia.

RNA degrading activity is tightly associated with the multicatalytic proteinase, ingensin

The multicatalytic proteinase, ingensin, was purified to homogeneity from chicken liver. rRNA‐degrading activity was co‐eluted with the purified multicatalytic proteinase from a TSK‐3000SW column. This RNA‐degrading activity was inactivated by heat treatment and the addition of a low concentration of SDS. Therefore, the RNA‐degrading activity co‐eluted with the multicatalytic proteinase was not due to contamination by low‐molecular‐mass RNases. These results strongly suggest that this RNA‐degrading activity was tightly associated with the multicatalytic proteinase, ingensin.

Correlation between the urinary excretion of acid-soluble peptides, fractional synthesis rate of whole body proteins, and plasma immunoreactive insulin-like growth factor-1/somatomedin C concentration in the rat

The relations between the urinary excretion of acid-soluble peptide (ASP)-form amino acids, the rate of whole body protein synthesis and plasma immunoreactive insulin-like growth factor-1/somatomedin C concentration were investigated in rats. The urinary ASP-form leucine plus valine excretion correlated well with the rate of whole body protein synthesis and with the plasma immunoreactive insulin-like growth factor-1 concentration. The results provide further evidence for the hypothesis that urinary excretion of ASP is an excellent index of the status of protein metabolism in animals.

In vivo effect of l-leucine administration on protein synthesis in mice

Abstract To clarify the in vivo effect of leucine on protein synthesis within a short period, the fractional formation rate of peptidyl puromycin (FFR) was measured in the liver and skeletal muscle of mice. FFR was calculated as the ratio of specific activity of peptide-bound puromycin at 10 minutes after injection of [3H]puromycin to the area under the specific activity-time curve of free puromycin. The value of FFR corresponds to the amount of tracer puromycin bound in unit time, expressed as a fraction of the total amount of puromycin potentially bound to the aminoacyl-site on the functional ribosome pool. In 12-hour fasted, streptozotocin-induced diabetic mice, l -leucine injection (360 μmol/100 g body weight) increased the FFR in the liver but not in muscle, while the injection of insulin (0.5 unit/100 g body weight) raised the rate in muscle but not in the liver. The leucine-induced rise of FFR in the liver was blocked by a cyclooxygenase inhibitor, indomethacin, although this inhibitor did not block the insulin-stimulated rise of FFR in muscle. No significant increase in FFR was detected in the liver or muscle of non-diabetic mice by leucine injection. l -leucine injection caused a slight decrease of ribosome aggregation in the liver but not in muscle, while insulin injection led to ribosome aggregation in muscle but not in the liver of diabetic mice. The enhancement of FFR in the liver of diabetic animals by leucine injection suggests that leucine may stimulate protein synthesis in part by increasing the rate of elongation.

Modification of tumor necrosis factor and interleukin-1 productivity in macrophages from hepatoma-bearing rats by dietary proteins

Abstract Changes in tumor necrosis factor (TNF) and interleukin-1 (IL-1) productivity in resident peritoneal macrophages and those in the serum lipid levels were traced for up to 14 days after subcutaneous implantation of hepatoma (AH109A) cells to rats kept on a 20% casein diet (20C). Elevated levels of serum triglyceride and cholesterol were found to be associated with growth of the solid hepatoma. The ability of macrophages to produce TNF and IL-1 rose twice at both the early (days 2–4) and late (day 14) stages. To examine the effects of dietary proteins, hepatoma-free (normal) and -bearing rats were maintained on the 20C or a 20% gluten diet (20G) for 14 days after sham or hepatoma implantation. No significant changes were noticed in the serum lipid levels between the 20C and 20G groups in either hepatoma-free or -bearing rats. TNF and IL-1 production by macrophages from hepatoma-bearing rats was significantly higher in the 20C group than in the 20G group. These results indicate that TNF and IL-1 productivity in macrophages is enhanced by hepatoma implantation and that their productivity may be modified by dietary proteins in the hepatoma-bearing state.

Comparison of the changes in lipid metabolism between hepatoma-bearing and lipopolysaccharide-treated rats.

To elucidate the mechanism for hyperlipidemia in the hepatoma-bearing state, changes in some parameters related to the lipid metabolism and serum tumor necrosis factor-α (TNF-α) level were examined in Donryu rats that had been subcutaneously implanted with an ascites hepatoma cell line of AH109A. These parameters were also examined in rats that had been given a single injection of lipopolysaccharide (LPS), a model for acute infection with TNF-α secretion into the blood circulation. The serum triglyceride and total cholesterol (Ch) levels were significantly higher in both the hepatoma-implanted and LPS-injected rats than in normal rats. The level of adipose tissue lipoprotein lipase was decreased by hepatoma implantation and LPS injection, while the hormone-sensitive lipase activity was increased by the same treatments. Fatty acid (FA) oxidation and Ch synthesis were also stimulated by both treatments. The serum TNF-α level was noticably elevated by hepatoma implantation and greatly by the LPS injection. This LPS injection increased hepatic FA synthesis. The serum high-density lipoprotein Ch level and hepatic Ch 7α-hydroxylase activity were not changed by the LPS injection. Hepatoma implantation led to hyperlipidemia and elevated the serum TNF-α level, as did the LPS injection.