Substituting ornithine for arginine in total parenteral nutrition eliminates enhanced tumor growth

Tumour cell growth in culture: dependence on arginine

The amino acid arginine has been shown to affect the growth of several tumours, although the mechanisms of its action are not clear. In the present study, using a human breast tumour cell line (MCF-7), we investigated the arginine requirements of tumour cells for optimal protein synthesis and growth, and the metabolic pathway responsible for the arginine-dependent growth. The results showed that MCF-7 cells are highly dependent on arginine for growth and that the requirement for arginine is much higher than for an indispensable amino acid, leucine, indicating that arginine is needed for pathways other than protein synthesis. In arginine-free cultures, growth could be completely restored by the urea cycle intermediate citrulline. However, arginine could not be replaced by the urea cycle intermediate and the direct precursor for polyamine synthesis, ornithine, or by the polyamine putrescine, suggesting that the high dependence on arginine is not due to a requirement for polyamine synthesis. Moreover, inhibition of NOS [NO (nitric oxide) synthase] did not affect cell protein synthesis and growth, and the arginine analogue and substrate for NOS, homoarginine, could not replace arginine, implying that the conversion of arginine into NO is not involved in the growth-promoting effects of arginine. The major determinant for the high dependence of MCF-7 cells for arginine was found to be the irreversible conversion of this amino acid into ornithine by the intracellular enzyme arginase. The conversion into ornithine caused a progressive depletion of arginine from the culture medium, which ultimately inhibited cell protein synthesis and halted growth. Intracellular arginase activity may be the major factor determining the requirement for arginine of all cells in culture.

Antiapoptotic and proapoptotic action of various amino acids and analogs in starving MOLT-4 cells

This study is based on our previous findings showing that certain amino acids may protect hybridoma cells against starvation-induced apoptosis. In the present work we have screened 44 amino acids and analogs for their capacity of modulating apoptosis in human T-lymphoblastic leukemia cell line MOLT-4 exposed to starvation in a nutrient-poor medium. The panel of tested substances was found to contain not only compounds with antiapoptotic activity (e.g., l-glutamine, l-histidine, glycine, l-proline, and l-2-aminopentanoic acid), but also compounds with proapoptotic activity (e.g., l-phenylalanine, l-tryptophan, l-arginine, and l-2-aminohexanoic acid). The apoptosis-modulating effects were dependent on fine details of the structure of the compounds. A switch from antiapoptotic activity to proapoptotic activity was found between 6-aminohexanoic acid and 7-aminoheptanoic acid, as well as between l-2-aminopentanoic acid and l-2-aminohexanoic acid. D-amino acids tested were without effect.

Effect of ornithine in parenteral nutrition regimens on difluoromethylornithine-induced platelet suppression and changes in tumor polyamine content

We have demonstrated that DFMO-induced thrombocytopenia can be ameliorated with concomitant ornithine (Orn) in chow-fed rats; a reversal in DFMO-associated tumor polyamine reduction and antitumor activity, however, was also evident. To determine the effect of Orn in total parenteral nutrition (TPN) regimens on DFMO-induced thrombocytopenia and changes in tumor polyamine concentrations, Ward-colon-tumor-bearing (WCT) rats were given TPN with arginine (ENA) or with ornithine substituted for arginine (ENO) alone or with DFMO (1.5 g/day) added directly to the infusate. After 4 days, the peripheral blood platelet counts for ENA (917 +/- 151 x 10(3)/mm3) or ENO (908 +/- 67 x 10(3)/mm3) were equivalent to those of chow fed rats (901 +/- 42 x 10(3)/mm3). ENA/DFMO rats had significant thrombocytopenia (607 +/- 185 x 10(3)/mm3), which was completely ameliorated for ENO/DFMO rats (939 +/- 111 x 10(3)/mm3). Peripheral white blood count, hematocrit, and other hematological parameters were not affected. Tumor putrescine content for ENA rats (46.9 +/- 8.7 nmol/g) was equal to that for chow-fed rats (44.8 +/- 6.2 nmol/g) and ENO rats (53.6 +/- 8.3 nmol/g). The reduction in tumor putrescine content for ENO/DFMO rats (19.6 +/- 6.9 nmol/g) was equivalent to that of ENA/DFMO rats (14.7 +/- 3.0 nmol/g). Tumor spermidine was reduced only for the ENA/DFMO rats while spermine was slightly elevated. Tumor spermine content for ENO/DFMO rats (57.2 +/- 12.0 nmol/g) was equal to that for ENO rats (65.6 +/- 8.7 nmol/g) but was significantly (p = 0.004) reduced when compared with rats receiving ENA/DFMO (89.4 +/- 20.4 nmol/g). The results of this study show that TPN with Orn substituted for arginine can be used with a chemotherapeutic dose of DFMO to ameliorate the thrombocytopenia. The DFMO-induced reduction in tumor putrescine content, however, was not affected when Orn was substituted for arginine in a parenteral nutrition regimen. These results suggest that the antitumor activity of DFMO would not be adversely affected by coadministering DFMO with a TPN regimen with Orn substituted for arginine.

Influence of the Ward colon tumor on the host response to endotoxin

Cachexia and a decreased immune function are negative prognostic factors for cancer patients. While the decreased immunity results in a greater susceptibility to bacterial infection, the response of the host to the resulting infection is not clear. The experiments reported here were designed to evaluate the toxicity of endotoxin to rats with a transplantable Ward colon tumor (WCT) and to evaluate the mechanism of the observed increase in lethal toxicity. The lethal toxicity of endotoxin (lipopolysaccharide, LPS) at 5 mg/kg, i.p. was evaluated in the first of two experiments. Rats received LPS and were observed for morbidity and weight loss for a period of 11 days. A second experiment was done to evaluate the effect of LPS on the plasma nitrate/nitrite concentrations and plasma indicators of host tissue dysfunction. LPS was administered as previously described but blood and tissues were collected 5 h after LPS administration. LPS resulted in the death of 1 of 12 nontumor-bearing (NTB) rats and a transient weight loss in the survivors. This same dose of LPS, however, resulted in death for 10 of 12 WCT rats with tumor burdens less than 4% of body weight. The response of WCT rats 5 h after LPS was then compared with that of age-matched NTB rats. Plasma albumin concentrations were not affected by LPS in NTB rats but were significantly decreased in WCT rats. Peripheral blood gases were not consistently affected by LPS in either group. Peripheral blood white cell counts, except monocytes, were significantly decreased by LPS in both groups. Monocyte counts in peripheral blood were further reduced in WCT rats compared with NTB rats receiving LPS. The presence of the WCT significantly enhanced the LPS-associated increase in spleen weight. Liver weights were lower in LPS rats but there was no effect of the presence of WCT. The LPS-associated increase in plasma nitrate/nitrite concentration was enhanced by the WCT. The plasma arginine and citrulline concentrations were altered in a manner consistent with an increase in nitric oxide synthesis. An increase in plasma ornithine concentration suggests an increase in arginine metabolism by arginase. The plasma concentration of alanine aminotransferase was significantly elevated when WCT rats received LPS, suggesting enhanced hepatic dysfunction. The plasma blood urea nitrogen concentration was elevated by LPS to a greater extent in the WCT rats than in the NTB controls, indicating increased renal dysfunction. These results demonstrate that the Ward colon tumor increases the host lethal response to the endotoxin, a toxic product of bacterial infections. The mechanisms of lethality may include an increased nitric oxide synthesis in WCT rats and enhanced liver and renal toxicity.

A parenteral nutrition regimen with ornithine substituted for arginine alters the amino acid, but not polyamine, content of the ward colon tumor

Substituting ornithine for arginine in total parenteral nutrition (TPN) regimens eliminates the TPN-enhanced growth of the Ward colon tumor. Plasma arginine was increased when tumor growth was increased, suggesting a role for this amino acid. The erythrocyte polyamine content, however, was elevated in rats receiving both TPN regimens, indicating an increased synthesis and availability for tumors receiving arginine- and ornithine-containing regimens. The objective of this study, therefore, was to evaluate the effect of substituting ornithine for arginine in a TPN regimen on the amino acid and polyamine content of the Ward colon tumor compared with that of rats fed chow ad libitum. Male Fischer 344 rats with a transplantable Ward colon tumor implanted subcutaneously were randomized to three groups and fed for four days. One group received a TPN regimen with arginine (1,300 mg/100 ml, ENA), whereas a second group received a regimen with an isonitrogenous substitution of ornithine (ENO). A control group received chow ad libitum. Serum and tumors were evaluated for arginine, ornithine, lysine, and polyamine content. The arginine concentration in the serum and tumor increased when rats received ENA. In contrast, the serum and tumor arginine content for rats receiving ENO was significantly lower than that for rats receiving chow or ENA. Tumor and serum ornithine content was increased severalfold when ornithine was included in the regimen. Tumor polyamine content was not affected by TPN. The results show that serum and tumor arginine content are significantly altered by substituting ornithine for arginine in a TPN regimen. These and previous results suggest that TPN-enhanced growth of the Ward colon tumor when arginine is included in the formulation occurs by a mechanism other than increased polyamine synthesis.

Nutritional issues in cancer management

The objective of this article was to investigate the relationship between nutrition and cancer, as it relates to the initiation, promotion, and treatment of tumor growth. English-language studies published in the last 25 years were retrieved using MEDLINE, bibliographies, and consultation with experts. MEDLINE search terms included "cancer", "malnutrition," and "nutritional support." In vitro and in vivo controlled studies addressing the impact of nutritional factors on cancer prevention and treatment were selected. Approximately 30% of cancers in the Western countries are diet-related. The presence of malignancy affects patients' nutritional status negatively, leading to increased morbidity and mortality. Standard nutritional support (both enteral and parenteral) is not always effective in significantly improving outcome in malnourished cancer patients, due to characteristic changes in host metabolism. Preliminary studies suggest that newer nutritional-pharmacologic agents may be beneficial in counteracting the derangement of host metabolism, and consequently in ameliorating cancer patients' nutritional status and outcome of malnourishment. This review suggests that dietary manipulations and nutritional-pharmacologic therapy might be highly effective adjuncts in controlling the symptoms of patients with neoplastic disease.

From laboratory to bedside: new strategies in the treatment of malnutrition in cancer patients

The objective of this review is to present and discuss the current and the possible future perspectives of artificial nutrition in preventing and treating cancer cachexia. English-language studies published in the last 25 years were retrieved using MEDLINE, bibliographies and consultation with experts. MEDLINE search terms included "cancer," "malnutrition," and "nutritional support." In vivo and in vitro controlled studies were selected, and data from each study were independently abstracted by the authors. Data obtained indicate that cancer cachexia is a common manifestation of advanced malignant disease, characterized by marasmus due to impaired nutrient metabolism, weight loss, and anemia. In patients, the presence of cachexia increases morbidity and mortality, delays or impedes the delivery of the adequate treatment, reduces the efficacy of anti-neoplastic therapy, and impairs patient's quality of life. Indirect evidence indicates that cancer cachexia is mediated by circulating cytokines, produced by the host in response to the presence of the malignancy. In the past two decades, nutritional support was used to counteract the detrimental effect of cancer cachexia on the host, but with limited success. More recently, the better understanding of the mechanisms of cancer cachexia and the identification of pharmacologic effects provided by specific nutrients, has formed the rationale for a "new" mode of nutrition therapy/nutritional support, adding pharmacotherapy to adjunctive initial care.

Growth inhibition of subcutaneously transplanted hepatomas by alterations of the dietary arginine-methionine balance

We hypothesized that alteration of the dietary arginine-methionine balance might inhibit tumor growth and suggest nutritional strategies for cancer therapy. The Morris hepatoma 3924A was subcutaneously transplanted in ACI rats. Control diets containing normal levels of arginine, methionine, and other amino acids in replacement of protein (24%), carbohydrates (59%), fat (10%), and fiber, vitamins, and minerals (7%) were fed for 28 days. Six experimental diets were adjusted to maintain amino acids at 23-25% and carbohydrates at 58-60%; these diets were 1%-2% deficient in arginine or supplemented with 1-2% arginine (expressed as percent amino acid content of diet) in combination with normal, deficient, and supplementary levels of methionine. Daily food intake was unaffected by the experimental diets. The control groups gained 26.4 +/- 2.8 g body weight, and small body weight decrements ranged from 3.5% to 8.4% in the groups fed the experimental diets. Tumor weight of controls was 8.5 +/- 1.5% of body weight. The experimental diets that produced significant tumor growth inhibition (TGI) were 1) the arginine-methionine-deficient diet, 2) the arginine-excess-methionine-deficient diet, 3) the arginine-deficient diet, and 4) the excess-arginine diet. Diets containing excess methionine failed to produce TGI. TGI resulted in tumor weights 41-46% of control values. TGI was associated with significantly lower blood urea nitrogen, plasma protein, and tumor spermidine-to-spermine ratio than in tumor-bearing controls. It is concluded that dietary alteration of a single amino acid, arginine, might be a potentially useful nutritional strategy for controlling tumor growth.

Citrulline and arginine increase the growth of the Ward colon tumor in parenterally fed rats

Arginine is considered a necessary component of parenteral regimens because of the high nitrogen intake. The effect of arginine on tumor growth, however, is controversial. Our results suggest that substituting ornithine for arginine in parenteral regimens will ameliorate an arginine-related increase in growth of a Ward colon tumor. Although a metabolite of arginine and ornithine in the urea cycle, citrulline has differential effects on growth in vivo and in vitro. To evaluate the effect of citrulline on tumor growth, Ward colon tumor-bearing rats were given parenteral nutrition regimens with ornithine (ENO) or citrulline (ENC) substituted for arginine (ENA). The plasma amino acid profiles and tumor growth were compared. Tumor growth was evaluated by changes in the calculated tumor weight over an eight-day feeding period. The initial tumor weight for all groups was equivalent. The final tumor weights of rats receiving ENA (14.1 +/- 3.3 g) and ENC (12.7 +/- 1.4 g) were significantly (p < 0.05) greater than those of rats receiving ENO (8.8 +/- 2.0 g) or the chow-fed controls (8.9 +/- 2.1 g). Plasma concentrations of arginine, ornithine, and citrulline were significantly increased when the respective amino acids were components of the regimen. The plasma arginine concentration of rats receiving ENO (60.4 +/- 3.8 microM) was significantly lower than the control (149.9 +/- 24.1 microM). The plasma arginine concentration was significantly increased for rats receiving ENA (280.3 +/- 68.1 microM) and was even further increased for rats receiving ENC (481.8 +/- 94.1 microM). The plasma glutamine concentration for ENO rats (536.4 +/- 37.5 microM) was significantly higher than that for controls (483.5 +/- 53.5 microM). The plasma glutamine concentration for rats receiving ENA (402.3 +/- 50.3 microM) and ENC (379.9 +/- 37.6 microM) was significantly lower than that of the control fed chow. These results further implicate arginine as a major factor for the total parenteral nutrition-enhanced growth of the Ward colon tumor.

Blood polyamines in the rat

The physiological concentrations of polyamines in plasma, serum and red blood cells were determined in male Wistar rats, using HPLC with fluorometric detection. The analysis of the metabolic ratio between polyamines and the frontal cortex/plasma relationship for putrescine, spermidine and spermine, suggest the existence of common mechanisms in the regulation of spermidine in blood and brain.

Influence of diet with or without amino acids on polyamine excretion in multiple trauma victims

Elevated levels of urinary polyamines (PA) in severely injured trauma patients are further enhanced by total parenteral nutrition (TPN) that contains both glucose and amino acids (AAs). Since TPN solutions contain arginine, the AA precursor of PA, it is not certain whether the increased urinary PA are due to this substrate. Nutritional factors can evidently modify PA metabolism. We measured the daily excretion of the PA, putrescine (PU) and spermidine (SD) in 18 multiply injured (injury severity score [ISS], 32 +/- 2), hypermetabolic (resting energy expenditure [REE]/basal energy expenditure [BEE], 1.41 +/- 0.06), and highly catabolic (daily N loss, 17.2 +/- 1.8 g N/d) acute trauma patients for 5 days in the early flow phase of injury. The patients were fed only maintenance fluids without calories or nitrogen for the first day 60 to 72 hours after injury, and then were randomized to receive glucose alone ([GLUC] 4.1 mg/kg/min, 80% measured REE, n = 8) or the same amount of glucose with AAs (TPN, 275 mg N/kg/d, n = 10) for the following 4 days. There was no significant difference in the enhanced daily PA excretion either in the free or acetylated form between the two dietary regimens. The addition of AAs in the TPN mixture did not seem to further stimulate PA metabolism in the trauma patients. The source of the nutrient content of the diet appears to be important for enhancing total PA excretion in critically ill patients.

Protein metabolism in the cancer patient

The 'flooding' method has been widely used for measuring protein synthesis in animal tissues in vivo and in vitro, employing radioactively labelled amino acids, because it minimises errors in determining the specific radioactivity of the direct precursor of protein synthesis. This approach has now been modified for measuring protein synthesis rates in tumours and healthy tissues of humans by injection of the stable isotopic labels, [1(-13)C]leucine or [2H5]phenylalanine, followed by tissue sampling during surgery. Based on the observation that rates of protein synthesis correlate with changes in the expression of cell proliferation markers, we have suggested that changes in protein synthesis in tumours can be used as indices of changes in tumour growth. Measurements in colorectal cancer patients have shown that protein synthesis is stimulated 80% by feeding, suggesting that the tumour is not a pure parasite, but responds to exogenous nutrients. Moreover, when the composition of the amino acids given to the patient was changed from a balanced mixture to one supplemented with branched chain amino acids, the response of the tumour to feeding was significantly diminished, suggesting that tumour growth might be modulated by diet composition. Dietary supplements of arginine have been shown previously to inhibit tumour growth in animals, probably by activating the immune system. However, in breast cancer patients arginine stimulated tumour protein synthesis, suggesting that arginine might have separate stimulatory effects on the tumour and the immune system, the outcome depending on which effect predominates.