Maintaining gut integrity during parenteral nutrition of tumor-bearing rats: effects of glucagon-like peptide 2.

Maintaining tumor-bearing rats on total parenteral nutrition (TPN) for eight days significantly reduced mass, protein, and DNA in small intestine and colon. Coinfusion of glucagon-like peptide 2 (GLP-2) significantly increased each of these variables in the duodenum, jejunum, and ileum, but not in the colon. Histological analysis of tissue revealed normal mucosa thickness and villus height in the small intestine of GLP-2-treated rats, whereas non-treated rats maintained on TPN exhibited villus shortening and thinning of the mucosa. Compared with TPN alone, no significant effects of GLP-2 were noted on tumor growth, liver weight, or heart weight. Coinfusion of GLP-2 with TPN had no significant effect on TPN-associated immunosuppression, as measured by mitogen-induced proliferation of cultured splenocytes. Although translocation of bacteria to the mesenteric lymph nodes appeared to be reduced in GLP-2-treated rats, the difference between groups was not statistically significant. These results suggest that hormonal alterations may be more important than an absence of luminal nutrition in TPN-associated mucosa changes in tumor-bearing rats. Additionally, maintenance of gut integrity during TPN does not appear to be a sufficient condition for the avoidance of the negative sequelae associated with this route of supplemental nutrition.

Prevention of parenteral nutrition-induced gut hypoplasia by coinfusion of glucagon-like peptide-2.

Maintaining rats on total parenteral nutrition (TPN) for 6 days significantly reduced mass (-34%), protein (-32%), and DNA (-35%) in small intestine and colon (29-37% decrease). Coinfusion of glucagon-like peptide-2 (GLP-2) normalized each of these variables in duodenum, jejunum, and ileum, but not in colon. Histological analysis of tissue revealed normal mucosa thickness and villus height in small intestine of GLP-2-treated rats, whereas nontreated rats maintained on TPN exhibited villus shortening (-30%) and thinning (-23%) of mucosa. These results suggest that hormonal alterations may be more important than an absence of luminal nutrition in TPN-associated mucosal changes. Additionally, GLP-2 normalization of gut mucosa permits accurate assessment of the influence of reversal of hypoplasia on gut barrier function.

Anticatabolic effect of the beta 2-agonist cimaterol in vivo in tumor-bearing animals.

Loss of lean body mass occurs in cancer and may adversely affect outcome. The beta 2-agonist cimaterol increases muscle mass and protein content in tumor-bearing animals, in part by decreasing protein degradation, but the effect of the drug on protein synthesis remains uncertain. To determine the influence of cimaterol on protein synthesis, a methylcholanthrene sarcoma was transplanted sc into the dorsum of male Fischer-344 rats. After 3 weeks of tumor growth, tumor-bearing and control animals received daily sc injections of the beta 2-agonist cimaterol (0.15 mg/kg) for 5 days. Rate of protein synthesis was measured using iv [3H]-phenylalanine (25 microCi/100 g body wt) and cold phenylalanine (150 mumole/100 g body wt) in a flooding dose. Extensor digitorum longus muscles were harvested 10 min later, homogenized, and assayed for [3H]-phenylalanine uptake (bound) (dpm/mg muscle) and tissue-specific (free) radioactivity to determine protein synthesis rate (Ks: %/24 hr). There was a significant increase in protein synthesis rate in control and tumor-bearing animals receiving cimaterol compared to that in freely feeding, food-deprived, or matched-carcass-weight nontumor-bearing controls, as well as compared to that in tumor-bearing controls. We conclude that the anabolic effects of cimaterol are due to both decreased protein degradation and increased muscle protein synthesis. Therefore, beta 2-agonists may prove useful in prevention and/or treatment of cancer cachexia.

Parenteral vs enteral nutrition in tumor-bearing rats.

The development of cachexia may complicate cancer therapy, yet controversy exists concerning its nutritional management. For example, use of total parenteral nutrition (TPN) may not be appropriate because of gut atrophy, possible stimulation of tumor growth, and lack of total host protein repletion. In the present experiment, host and tumor responses were compared after identical parenteral or enteral nutritional supplementation (EN). Eighteen days after subcutaneous inoculation of adult male Fischer-344 rats with fresh methylcholanthrene-induced sarcoma (tumor-bearing [TB] rats), catheters were placed into either the external jugular vein or the stomach. Four days later, rats were started on an 11-day course of either TPN or EN with a Freamine-III-based formula (amino acids = 6%, dextrose = 21.5%, lipid = 1.5%). When the rats were killed, there was no difference in tumor weight between the various TB groups. Carcass weight was increased significantly in both the TB-TPN and TB-EN groups, and there was an elevation in gastrocnemius protein content in both groups compared with the TB-rat food group. Small intestine protein was preserved in the TB-EN group to the level observed in the control-rat food animals. Total lipids in the liver were increased in both TB-TPN and TB-EN groups; however, the magnitude of the increase was less in the TB-EN animals. Neither treatment resulted in complete protein repletion of tumor-bearing rats. EN may be more appropriate than TPN in that gut mass is preserved. The maintenance of gut mucosa may prove to be beneficial in the treatment of the depleted, immunocompromised, and metabolically stressed host.

Effects of increased beta 2-agonist dose in tumor-bearing animals.

Cachexia and malnutrition are major contributing causes of significant morbidity and mortality in the cancer patient. Although supplemental nutrition alone does not reverse the cachectic process, the use of anabolic beta 2-adrenergic agonists in conjunction with supplemental nutrition does significantly reverse cachectic processes in tumor-bearing (TB) animals. To determine the most efficacious dose of the beta 2-agonist cimaterol (CIM), male Fischer-344 rats with dorsal subcutaneous methylcholanthrene sarcomas were maintained on supplemental enteral nutrition via surgically placed gastrostomy tubes. TB rats were given daily subcutaneous injections of either saline (Sal) or one of three doses of CIM for seven days. TB-Sal animals demonstrated significant cachexia with decreased extensor digitorum longus and gastrocnemius muscle dry weight and protein content. There was a significant increase in both extensor digitorum longus and gastrocnemius muscle dry weight and protein content in all treatment groups compared with TB controls. The greatest increase was in the 0.30 mg/kg CIM treatment group. Increased cardiac mass was associated with increasing dosage, with the greatest effect being observed in the 0.60 mg/kg CIM treatment group. This dosage, however, was associated with a decreased effect on muscle weight and protein content compared with the 0.30 mg/kg CIM dose. Thus the peak anabolic effect in TB animals was reached with the 0.30 mg/kg dose of CIM. Therefore, use of the beta 2-agonist CIM may prove useful in the treatment of cancer-induced cachexia.

Reversal of cancer cachexia in rats by cimaterol and supplemental nutrition.

The anabolic beta 2-agonist cimaterol was used in conjunction with supplemental nutrition to reverse cancer-induced cachexia and malnutrition in tumor-bearing rats. Cimaterol was administered to tumor-bearing rats receiving total parenteral nutrition or enteral nutrition for 10 days, beginning 2 weeks after subcutaneous transplantation of methylcholanthrene sarcoma. A significant increase occurred in both muscle weight and muscle protein in animals receiving cimaterol in conjunction with either enteral or parenteral feeding, compared to food fed tumor-bearing animals. Muscle protein content was increased significantly by 16% in cimaterol-treated rats maintained on parenteral nutrition and by 11% in cimaterol-treated enterally fed rats compared with the respective tumor-bearing controls. Urinary concentrations of 3-methylhistidine, an estimation of muscle turnover or catabolism, were significantly reduced in both tumor-bearing groups treated with cimaterol compared to 3-methylhistidine levels of the untreated tumor-bearing groups. The anabolic effects of cimaterol were expressed in the presence of a large tumor burden resulting in reversal of muscle depletion and muscle breakdown regardless of the route of supplemental nutrition. Thus, beta 2-agonists may be considered as a possible therapy for cancer cachexia.

Clenbuterol treatment increases muscle mass and protein content of tumor-bearing rats maintained on total parenteral nutrition.

Treatment of tumor-bearing (TB) and control rats with the anabolic beta-2 agonist drug clenbuterol (CLE) for 14 days reduced food intake for 4 days initially. Feeding was increased in anorectic TB rats, however, during the last 7 days of drug administration. Since minimal muscle savings were observed in chow-fed TB rats treated with CLE, the anabolic effects of this drug were investigated in a second experiment on TB rats maintained on total parenteral nutrition (TPN). Sixteen days after the subcutaneous transplantation of methylcholanthrene-induced sarcomas rats was begun on a 2-week schedule of TPN. One group of these rats was treated daily for 14 days with CLE, while the remaining rats received injections of saline. Additional groups of TB and nonTB rats were maintained on rat chow for this period and treated with saline. Although TB rats maintained on rat chow or TPN and treated with saline exhibited significantly decreased gastrocnemius muscle weight and protein content, treatment of TB-TPN rats with clenbuterol normalized muscle mass and increased muscle protein content significantly and increased plasma concentrations of branched-chain amino acids. These results indicate that although nutritional support of TB organisms does not result in protein repletion, the addition of an anabolic drug renders the nutritional support highly efficacious.

Hyperammonemia and anorexia in Morris hepatoma-bearing rats.

Inoculation of Buffalo rats with Morris hepatoma produced significant anorexia within four weeks and reduced body weight within two weeks. Blood ammonia concentration was increased by 113% when the rats were euthanized, five days after the development of anorexia. Infusing ammonium salts into normal Buffalo rats also induced anorexia at a blood ammonia concentration comparable to that observed in the tumor-bearing rats. Although ammonia-infused rats exhibited expected increases in brain tyrosine, tryptophan, and metabolites of dopamine and serotonin, these alterations were attenuated in the tumor-bearing rats. These results indicate that hyperammonemia may be a general consequence of experimental cancer and that the increase in ammonia concentration may be of primary importance in the development of experimental cancer-induced anorexia. The rather small alterations in neurotransmitter metabolism in anorectic tumor-bearing rats deemphasize the role aberrations in DA and 5-HT systems in the development of experimental cancer anorexia.

Pertussis toxin inhibits neuropeptide Y-induced feeding in rats.

Neuropeptide Y (NPY) is the most powerful peptide drug stimulating feeding in rats. Rats with paraventricular hypothalamic (PVH) cannulae were used to investigate the mechanisms involved in NPY-induced feeding. Consistent with previous reports, injection of 2 micrograms of NPY into the PVH significantly increased the cumulative food intake over 1-, 2- and 4-hr periods. Ad lib feeding decreased significantly two days after pertussis toxin (PT) administration, but recovered to nearly normal levels on the fourth day. PT had no immediate effect on NPY-induced feeding; however, four days after PT was injected NPY (2 micrograms) did not increase the food intake compared to control. In vitro investigations showed that isoproterenol-stimulated adenylate cyclase activity in the hypothalamus of control rats was inhibited by NPY. In PT-treated rats, however, no inhibition of cAMP production was observed. These results suggest that cAMP may mediate NPY-induced feeding and that a PT-sensitive G protein may be involved in this signal transduction.

Possible role of ammonia in experimental cancer anorexia.

Plasma concentrations of ammonia were elevated significantly in tumor-bearing rats prior to the onset of anorexia and continued to increase as the tumor grew and anorexia developed. Associated with this hyperammonemia were elevated levels of brain glutamine and large neutral amino acids (phenylalanine, tyrosine, tryptophan, methionine, histidine). Concentrations of the dopamine metabolites, DOPAC or HVA were elevated in the corpus striatum, nucleus accumbens, hypothalamus and amygdala of anorectic tumor-bearing rats only, while levels of the serotonin metabolite, 5-HIAA, were increased in these brain regions in both anorectic and non-anorectic tumor-bearing rats. Infusing ammonium salts into non-tumor-bearing rats elicited anorexia and alterations in brain amino acid profile and neurotransmitter metabolism that were similar to those observed in anorectic tumor-bearing rats. Therefore, we conclude that ammonia released by tumor tissue may have a direct role in the etiology of experimental cancer anorexia.

Hyperammonemia in anorectic tumor-bearing rats.

Plasma ammonia concentrations were significantly elevated by 150% in anorectic rats bearing methylcholanthrene sarcomas. Assessment of ammonia levels in blood draining these sarcomas indicated nearly a 20-fold increase as compared with venous blood in control rats, suggesting the tumor mass as the source of this increase in ammonia. Infusing increasing concentrations of ammonium salts produced anorexia and alterations in brain amino acids in normal rats that were similar to those observed in anorectic tumor-bearing rats. Therefore, these results suggest that ammonia released by tumor tissue may be an important factor in the etiology of cancer anorexia.

Reversal of neurochemical aberrations after tumor resection in rats.

Assessment of biochemical parameters in methylcholanthrene sarcoma-bearing rats 2 days after the onset of anorexia revealed several biochemical aberrations in blood and brain. Plasma levels of glucose were decreased and lactate concentrations were increased. The plasma and brain amino acid profiles were also greatly altered in these rats, characterized by increased brain concentrations of glutamine and large neutral amino acids. Analysis of regional neurotransmitter and metabolite levels by high-performance liquid chromatography suggested increases in the neuronal activity of dopamine and serotonin in each brain region examined. Surgical removal of the tumors in another group of anorectic tumor-bearing rats was followed by the return of normal feeding within 6 days. Associated with the normalization of food intake was the reversal of these biochemical aberrations in blood and brain. It is hypothesized that the utilization of glutamine and excretion of ammonia by tumor tissue is the precursor of these alterations in brain amino acids and neurotransmitters, which may be causing anorexia.

Acivicin reduces tumor growth during total parenteral nutrition (TPN).

Glutamine appears to be an important substrate for tumor growth. Since tumor growth rate may be stimulated by total parenteral nutrition (TPN), we investigated the effect of the glutamine antimetabolite, acivicin, on methylcholanthrene sarcoma growth in rats maintained on TPN or on rat chow. Acivicin treatment significantly reduced tumor growth by 67% in rats receiving TPN and by 71% in rats maintained on chow. Carcass weights were significantly increased by TPN in both acivicin-treated and saline solution-treated tumor-bearing rats. Tumor-carcass ratios were significantly decreased in both groups of acivicin-treated tumor-bearing rats. Acivicin treatment or a similar approach may therefore be useful for stabilizing tumor growth in patients receiving TPN.

Burn-induced alterations in feeding, energy expenditure, and brain amine neurotransmitters in rats.

A 30% body surface area, open-flame, full-thickness burn of adult rats induced a 4-day period of anorexia that was followed by hyperphagia beginning on postburn day 10. The hyperphagic burned rats also exhibited increased resting energy expenditure and no gain in body weight, suggesting hypermetabolism. Plasma levels of immunoreactive insulin and albumin were decreased in both groups of burned rats; immunoreactive pancreatic glucagon concentrations were elevated only in the anorectic burned rats. Plasma levels of epinephrine were elevated in the hyperphagic burned rats. In the brain, dopamine metabolism appeared to be increased in the corpus striatum, nucleus accumbens, and amygdala of anorectic burned rats; norepinephrine levels were elevated in the hypothalamus and nucleus accumbens of the hyperphagic-hypermetabolic rats. These data indicate that this animal model of major burn trauma exhibits anorexia, hyperphagia, catabolism, and hypermetabolism. Furthermore, elevated dopamine metabolism appears to be associated with the anorexia, while the hyperphagia-hypermetabolism may be mediated by norepinephrine.