RNA polymerase activity and protein synthesis in mouse tumor-host liver compared to benign para-neoplastic reactions

The effect of recombinant human IGF-I on protein metabolism in post-operative patients without nutrition compared to effects in experimental animals

This study has evaluated the effects of recombinant human insulin-like growth factor I (rhIGF-I) to moderately stressed post-operative patients provided with dextrose as the only exogeneous substrate. Thirty patients who underwent elective colorectal surgery were randomized to receive either rhIGF-I (80 micrograms kg-1 bw) subcutaneously twice daily or placebo injections in a double-blind parallel group design. Nitrogen balance, urinary 3-methyl-histidine excretion plasma growth hormone (GH), serum cortisol, IGF-I binding proteins (IGFBP-1,3), glomerular filtration rate, plasma amino acid concentrations and whole-body energy expenditures were measured as effector variables during days 1-5 post-operatively. Animal and isolated tissue experiments were performed as additional control experiments to confirm cellular effectiveness of the recombinant material. rhIGF-I increased significantly the glomerular filtration rate and prevented the adaptive decrease in whole-body energy expenditure in response to partial starvation in the postoperative period. Serum and plasma concentrations of IGFBP-1,3 cortisol, blood glucose and amino acids were not significantly influenced by rhIGF-I administration, while plasma GH levels decreased significantly as expected. rhIGF-I had no effect on either nitrogen balance or protein breakdown (3-methylhistidine excretion) in post-operative patients on dextrose supplementation only, although plasma concentrations of IGF-I increased from 130-140 ng mL-1 to a range of 300-450 ng mL-1. In contrast, IGF-I stimulated the synthesis of both globular and myofibrillar proteins (+50%, P < 0.01), when given as a single dose (100 micrograms kg-1) 2 h before measurements of protein synthesis in skeletal muscles of overnight fasted adult mice. This stimulatory effect by IGF-I (1 microgram mL-1) was also confirmed by measurements of skeletal muscle protein synthesis in vitro (+40%, P < 0.05). Orally re-fed mice had a normal transcription of IGF-I mRNA in skeletal muscle cells, while overnight fasted mice showed a trend to down-regulated transcription. Our results demonstrate that rhIGF-I has several significant physiological effects, without major side-effects, when supplied to partially starved patients in the post-operative phase. The lack of a whole-body nitrogen sparing effect by rhIGF-I alone to post-operative patients is not clear, but was most likely explained by subnormal plasma concentrations of amino acids.

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

BACKGROUND

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

Isolation of radiopure plasma and hepatic albumin in acute phase conditions

It is essential to obtain biochemically and radioactively pure albumin in studies on albumin metabolism and kinetics in stress and nutrition related conditions. However, published work on albumin metabolism, in both animals and man with acute phase reactions has usually been based on inadequate chemical methods for isolation of homogeneous albumin free from acute phase proteins and other contaminants. Applications of conventional antibody precipitating techniques was usually either not sufficient to give radiopure albumin, or did not allow determination of the true specific radioactivity during in vivo experiments. Thus, the lack of applicable methods to achieve radiopure albumin from small plasma and tissue samples for subsequent analyses and determination of the true specific radioactivity in albumin initiated the present method development. The combination of HPLC ionchromatography (DEAE-sepharose), affinity chromatography (Blue sepharose CL-6B, Con A sepharose) and HPLC based size exclusion chromatography (Protein PAK 300 SW, Waters) was applied. By this procedure we obtained radiopure albumin from both plasma and hepatic samples from individual mice with acute phase response as confirmed by two-dimensional electrophoresis and immune precipitation.

Altered phosphorylation status, phospholipid metabolism and gluconeogenesis in the host liver of rats with prostate cancer: a 31P magnetic resonance spectroscopy study

31P magnetic resonance spectroscopy (MRS) in vivo and in vitro was used to study modulation of host liver (HL) metabolism in rats bearing the MAT-LyLu variant of the Dunning prostate tumour. Animals were inoculated either with 10(6) or 10(7) MAT-LyLu cells, or with saline to serve as controls. Carcass weight in tumour-bearing (TB) animals decreased despite similar food and water intake in both groups. Absence of metastatic tumour cells from HL of all TB animals was confirmed by histological examination. Twenty-one days after inoculation, 31P MRS showed a 2.5-fold increase in [Pi]/[ATP] ratios in HL in vivo (P < 0.001) which was confirmed by 31P MRS of liver extracts in vitro (P < 0.005). Phosphodiester to ATP ratios were significantly increased (P < 0.05) in HL in vivo, but absolute PDE levels were similar in both groups. Phosphomonoester to ATP ratios did not change, although absolute phosphomonoester levels in HL were reduced by -41% (not significant). In HL extracts in vitro, sharp reductions in the levels of glucose-6-phosphate (P < 0.05), fructose-6-phosphate (P = 0.05), phosphocholine (P < 0.001), glycerophosphocholine (P < 0.001), and glycerophosphoethanolamine (P < 0.001) were observed. Electron microscopy revealed increased amounts and altered distribution of rough endoplasmic reticulum in HL. These findings show that experimental prostate cancer significantly affects hepatic phosphorylation status, phospholipid metabolism, and gluconeogenesis in the host animal, and demonstrate the value of combined MRS in vivo and in vitro in monitoring HL metabolism in cancer.

Pretranslational regulation of albumin synthesis in tumor-bearing mice. The role of anorexia and undernutrition

Hepatic albumin synthesis, serum albumin turnover, and hepatic albumin messenger RNA (mRNA) content were evaluated in mice bearing a transplantable low differentiated tumor (MCG 101). Results obtained on tumor-bearing mice were compared with results obtained from non-tumor-bearing animals that were either freely fed, food restricted so that their body composition was similar to tumor-bearing animals (pair-weighed), fed a protein-free diet for 5 days, or fasted for 48 hours. Tumor-bearing animals became hypoalbuminemic (33 +/- 5 vs. 44 +/- 3 g/L in freely fed mice), which could be explained by both depressed albumin synthesis (1.95% +/- 0.20% vs. 2.67% +/- 0.27%/h in freely fed mice) and increased albumin degradation. Pair-weighed and protein-calorie malnourished controls had reductions in albumin synthesis (1.81% +/- 0.18% and 1.67% +/- 0.17%/h, respectively) similar to tumor-bearing animals, and the starved controls had the lowest synthetic rates (1.07% +/- 0.10%/h). Albumin degradation was increased only in tumor-bearing animals. Hepatic albumin mRNA in undernourished animals was less (tumor bearing, 32% +/- 5%; pair weighed, 47% +/- 4%; 48 hours fasted, 18% +/- 2%; and protein-calorie malnourished, 26% +/- 3%) than 50% of the mRNA content in the livers of freely fed control mice. Messenger RNA-directed synthesis of albumin in vitro was also depressed to a variable degree in tumor-bearing and malnourished non-tumor-bearing controls. The hypoalbuminemia in tumor-bearing animals could not be prevented by daily injections of a prostaglandin synthesis inhibitor (indomethacin, 1 microgram/g body wt), but the hepatic acute phase protein serum amyloid P decreased from 157 +/- 12 to 103 +/- 9 micrograms/mL in indomethacin-treated tumor-bearing mice (P less than 0.01). It is concluded that increased albumin degradation seen in tumor-bearing animals cannot be explained by associated malnutrition, whereas tumor-associated malnutrition can explain to a large extent the depressed albumin synthesis. Decreased albumin synthesis in tumor-bearing animals correlated in part with a decreased quantity of liver albumin mRNA. The results of the current study are consistent with either a reduced transcription of the albumin gene or a change in albumin mRNA processing and stability communicated by anorexia and malnutrition.

Nucleic acid labeling with [3H]orotic acid and nucleotide profile in rats in protein deprivation, enteral and parenteral essential amino acid administration, and 5-fluorouracil treatment

Rats were fed a 0% casein diet for 1 week, with or without enteral or parenteral administration of essential amino acids, or a 25% casein diet, in one group supplemented with 5-fluorouracil treatment. Ninety minutes before sacrifice the rats were given a tracer of [3H]orotic acid. Incorporation into the acid soluble fraction, RNA, and DNA was determined in liver, small intestine, bone marrow, and kidney. Nucleotide profile was examined in liver and intestine. Protein deficiency caused inter alia a decrease in body weight; a decrease in RNA/DNA ratio and an increase in the specific RNA labeling in liver and kidney; an altered nucleotide profile in the liver; an increase in the nucleotide/DNA and RNA/DNA ratios and a decrease in the specific labeling of the acid soluble fraction, RNA, and DNA in the bone marrow. These changes were prevented to the same extent by giving essential amino acids, either orally or intravenously. The minor changes in intestinal nucleotide profile in protein deprivation were prevented to a slightly larger extent by amino acids orally than parenterally. 5-Fluorouracil treatment gave a decrease in the RNA/DNA ratio in the liver and kidney but an increase in the nucleotide/DNA and RNA/DNA ratios in the bone marrow. Nucleotide profiles were unaltered. The amount of DNA per gram of tissue decreased in bone marrow and increased in kidney. Parenteral administration per se resulted in almost no changes.