The effects of glutamine-enriched total parenteral nutrition on tumor growth and host tissues

Effect of L-Glutamine on Chylomicron Formation and Fat-Induced Activation of Intestinal Mucosal Mast Cells in Sprague-Dawley Rats

Glutamine (Gln) is required for intestinal mucosal homeostasis, and it can promote triglyceride absorption. The intestinal mucosal mast cells (MMCs) are activated during fat absorption. This study investigated the potential role of Gln on fat absorption-induced activation of MMCs in rats. Lymph fistula rats (n = 24) were studied after an overnight recovery with the infusion of saline only, saline plus 85 mM L-glutamine (L-Gln) or 85 mM D-glutamine (D-Gln), respectively. On the test day, rats (n = 8/group) were given an intraduodenal bolus of 20% Intralipid contained either saline only (vehicle group), 85 mM L-Gln (L-Gln group), or 85 mM D-Gln (D-Gln group). Lymph was collected hourly for up to 6 h for analyses. The results showed that intestinal lymph from rats given L-Gln had increased levels of apolipoprotein B (ApoB) and A-I (ApoA-I), concomitant with an increased spectrum of smaller chylomicron particles. Unexpectedly, L-Gln also increased levels of rat mucosal mast cell protease II (RMCPII), as well as histamine and prostaglandin D2 (PGD2) in response to dietary lipid. However, these effects were not observed in rats treated with 85 mM of the stereoisomer D-Gln. Our results showed that L-glutamine could specifically activate MMCs to degranulate and release MMC mediators to the lymph during fat absorption. This observation is potentially important clinically since L-glutamine is often used to promote gut health and repair leaky gut.

Side Effects of Amino Acid Supplements

The aim of the article is to examine side effects of increased dietary intake of amino acids, which are commonly used as a dietary supplement. In addition to toxicity, mutagenicity and carcinogenicity, attention is focused on renal and gastrointestinal tract functions, ammonia production, and consequences of a competition with other amino acids for a carrier at the cell membranes and enzymes responsible for their degradation. In alphabetic order are examined arginine, β-alanine, branched-chain amino acids, carnosine, citrulline, creatine, glutamine, histidine, β-hydroxy-β-methylbutyrate, leucine, and tryptophan. In the article is shown that enhanced intake of most amino acid supplements may not be risk-free and can cause a number of detrimental side effects. Further research is necessary to elucidate effects of high doses and long-term consumption of amino acid supplements on immune system, brain function, muscle protein balance, synthesis of toxic metabolites, and tumor growth and examine their suitability under certain circumstances. These include elderly, childhood, pregnancy, nursing a baby, and medical condition, such as diabetes and liver disease. Studies are also needed to examine adaptive response to a long-term intake of any substance and consequences of discontinuation of supplementation.

Metabolic Intersection of Cancer and Cardiovascular Diseases: Opportunities for Cancer Therapy

According to data from the World Health Organization, cardiovascular diseases and cancer are the two leading causes of mortality in the world [1]. Despite the immense effort to study these diseases and the constant innovation in treatment modalities, the number of deaths associated with cardiovascular diseases and cancer is predicted to increase in the coming decades [1]. From 2008 to 2030, due to population growth and population aging in many parts of the world, the number of deaths caused by cancer globally is projected to increase by 45%, corresponding to an annual increase of around four million people [1]. For cardiovascular diseases, this number is six million people [1]. In the United States, treatments for these two diseases are among the most costly and result in a disproportionate impact on low- and middleincome people. As the fight against these fatal diseases continues, it is crucial that we continue our investigation and broaden our understanding of cancer and cardiovascular diseases to innovate our prognostic and treatment approaches. Even though cardiovascular diseases and cancer are usually studied independently [2-12], there are some striking overlaps between their metabolic behaviors and therapeutic targets, suggesting the potential application of cardiovascular disease treatments for cancer therapy. More specifically, both cancer and many cardiovascular diseases have an upregulated glutaminolysis pathway, resulting in low glutamine and high glutamate circulating levels. Similar treatment modalities, such as glutaminase (GLS) inhibition and glutamine supplementation, have been identified to target glutamine metabolism in both cancer and some cardiovascular diseases. Studies have also found similarities in lipid metabolism, specifically fatty acid oxidation (FAO) and synthesis. Pharmacological inhibition of FAO and fatty acid synthesis have proven effective against many cancer types as well as specific cardiovascular conditions. Many of these treatments have been tested in clinical trials, and some have been medically prescribed to patients to treat certain diseases, such as angina pectoris [13, 14]. Other metabolic pathways, such as tryptophan catabolism and pyruvate metabolism, were also dysregulated in both diseases, making them promising treatment targets. Understanding the overlapping traits exhibited by both cancer metabolism and cardiovascular disease metabolism can give us a more holistic view of how important metabolic dysregulation is in the progression of diseases. Using established links between these illnesses, researchers can take advantage of the discoveries from one field and potentially apply them to the other. In this chapter, we highlight some promising therapeutic discoveries that can support our fight against cancer, based on common metabolic traits displayed in both cancer and cardiovascular diseases.

Effect of glutamine enriched nutrition support on surgical patients with gastrointestinal tumor: a meta-analysis of randomized controlled trials

Background:

Associations between glutamine (Gln) enriched nutrition support and surgical patients with gastrointestinal (GI) tumor remain controversy. The purpose of this meta-analysis was to assess the effect of Gln enriched nutrition support on surgical patients with GI tumor in term of relevant biochemical indices, immune indices, and clinical outcomes.

Methods:

Six databases were systematically searched to find eligible randomized controlled trials (RCTs) from 1966 to May 2014. When estimated the analysis indexes, the relative risk (RR) was used as the effect size of the categorical variable, while the weighted mean difference (MD) was used as the effect size of a continuous variable. Meta-analysis was conducted with Rev Man 5.2.

Results:

Thirteen RCTs, involving 1034 patients, were included in the meta-analysis. The analysis showed that Gln enriched nutrition support was more effective in increasing serum albumin (MD: 0.10; 95% confidence interval [CI]: 0.02–0.18; P < 0.05), serum prealbumin (MD: 1.98; 95% CI: 1.40–2.55; P < 0.05) and serum transferring (MD: 0.35; 95% CI: 0.12–0.57; P < 0.05), concentration of IgG (MD: 1.26; 95% CI: 0.90–1.63; P < 0.05), IgM (MD: 0.18; 95% CI: 0.11–0.25; P < 0.05), IgA (MD: 0.22; 95% CI: 0.10–0.33; P < 0.05), CD3⁺ (MD: 3.71; 95% CI: 2.57–4.85; P < 0.05) and CD4/CD8 ratio (MD: 0.27; 95% CI: 0.12–0.42; P < 0.05). Meanwhile, it was more significant in decreasing the incidence of infectious complications (RR: 0.67; 95% CI: 0.50–0.90; P < 0.05) and shortening the length of hospital stay (MD: −1.72; 95% CI: −3.31–−0.13; P < 0.05).

Conclusions:

Glutamine enriched nutrition support was superior in improving immune function, reducing the incidence of infectious complications and shortening the length of hospital stay, playing an important role in the rehabilitation of surgical GI cancer patients.

Nutrition Modulation of Cardiotoxicity and Anticancer Efficacy Related to Doxorubicin Chemotherapy by Glutamine and ω-3 Polyunsaturated Fatty Acids

BACKGROUND

Doxorubicin (DOX) has been one of the most effective antitumor agents against a broad spectrum of malignancies. However, DOX-induced cardiotoxicity forms the major cumulative dose-limiting factor. Glutamine and ω-3 polyunsaturated fatty acids (PUFAs) are putatively cardioprotective during various stresses and/or have potential chemosensitizing effects during cancer chemotherapy.

METHODS

Antitumor activity and cardiotoxicity of DOX treatment were evaluated simultaneously in a MatBIII mammary adenocarcinoma tumor-bearing rat model treated with DOX (cumulative dose 12 mg/kg). Single or combined treatment of parenteral glutamine (0.35 g/kg) and ω-3 PUFAs (0.19 g/kg eicosapentaenoic acid and 0.18 g/kg docosahexaenoic acid) was administered every other day, starting 6 days before chemotherapy initiation until the end of study (day 50).

RESULTS

Glutamine alone significantly prevented DOX-related deterioration of cardiac function, reduced serum cardiac troponin I levels, and diminished cardiac lipid peroxidation while not affecting tumor inhibition kinetics. Single ω-3 PUFA treatment significantly enhanced antitumor activity of DOX associated with intensified tumoral oxidative stress and enhanced tumoral DOX concentration while not potentiating cardiac dysfunction or increasing cardiac oxidative stress. Intriguingly, providing glutamine and ω-3 PUFAs together did not consistently confer a greater benefit; conversely, individual benefits on cardiotoxicity and chemosensitization were mostly attenuated or completely lost when combined.

CONCLUSIONS

Our data demonstrate an interesting differentiality or even dichotomy in the response of tumor and host to single parenteral glutamine and ω-3 PUFA treatments. The intriguing glutamine × ω-3 PUFA interaction observed draws into question the common assumption that there are additive benefits of combinations of nutrients that are beneficial on an individual basis.

Effects of glutamine on wound healing

Studies reporting the need for replacing amino acids such as glutamine (Gln), hydroxymethyl butyrate (HMB) and arginine (Arg) to accelerate wound healing are available in the literature. The primary objective of this study was to present the effects of Gln on tissue hydroxyproline (OHP) levels in wound healing. This study was conducted on 30 female Sprague Dawley rats with a mean weight of 230 ± 20 g. Secondary wounds were formed by excising 2 × 1 cm skin subcutaneous tissue on the back of the rats. The rats were divided into three equal groups. Group C (Control): the group received 1 ml/day isotonic solution by gastric gavage after secondary wound was formed. Group A (Abound): the group received 0·3 g/kg/day/ml Gln, 0·052 g/kg/day/ml HMB and 0·3 g/kg/day/ml Arg by gastric gavage after secondary wound was formed. Group R (Resource): the group received 0·3 g/kg/day/ml Gln by gastric gavage after secondary wound was formed. The OHP levels of the tissues obtained from the upper half region on the 8th day and the lower half region on the 21st day from the same rats in the groups were examined. Statistical analysis was performed using the statistics program SPSS version 17.0. No statistically significant differences were reported with regard to the OHP measurements on the 8th and 21st days (8th day: F = 0·068, P = 0·935 > 0·05; 21st day: F = 0·018, P = 0·983 > 0·05). The increase in mean OHP levels on the 8th and 21st days within each group was found to be statistically significant (F = 1146·34, P = 0·000 < 0·001). We conclude that in adults who eat healthy food, who do not have any factor that can affect wound healing negatively and who do not have large tissue loss at critical level, Gln, Arg and HMB support would not be required to accelerate secondary wound healing.

Glutamine: A novel approach to chemotherapy-induced toxicity

Treatment of cancer is associated with short- and long-term side-effects. Cancer produces a state of glutamine deficiency, which is further aggravated by toxic effects of chemotherapeutic agents leading to increased tolerance of tumor to chemotherapy as well as reduced tolerance of normal tissues to the side-effects of chemotherapy. This article reviews the possible role of glutamine supplementation in reducing the serious adverse events in patients treated with anticancer drugs. The literature related to the possible role of glutamine in humans with cancer and the supportive evidence from animal studies was reviewed. Searches were made and the literature was retrieved using PUBMED, MEDLINE, COCHRANE LIBRARY, CENAHL and EMBASE, with a greater emphasis on the recent advances and clinical trials. Glutamine supplementation was found to protect against radiation-induced mucositis, anthracycline-induced cardiotoxicity and paclitaxel-related myalgias/arthralgias. Glutamine may prevent neurotoxicity of paclitaxel, cisplatin, oxaplatin bortezomib and lenolidamide, and is beneficial in the reduction of the dose-limiting gastrointestinal toxic effects of irinotecan and 5-FU-induced mucositis and stomatitis. Dietary glutamine reduces the severity of the immunosuppressive effect induced by methotrexate and improves the immune status of rats recovering from chemotherapy. In patients with acute myeloid leukemia requiring parenteral nutrition, glycyl-glutamine supplementation could hasten neutrophil recovery after intensive myelosuppressive chemotherapy. Current data supports the usefulness of glutamine supplementation in reducing complications of chemotherapy; however, paucity of clinical trials weakens the clear interpretation of these findings.

Total parenteral nutrition and cancer: from the beginning

The early development of total parenteral nutrition and its evolution as an adjunct to the nutritional, metabolic, and antineoplastic therapy of cancer patients is described. Examples related to the sine wave of responses to new data and discovery are placed in context to understand better past, present, and how and where to proceed in the future to achieve optimal results from multimodal comprehensive management of patients with malignancies. Practical and philosophic thoughts are proffered to justify continued, intensified, logical, controlled clinical studies directed toward establishing the most rational, safe, and effective use of total parenteral nutrition in treating patients with cancer.

Nutrition modulation of gastrointestinal toxicity related to cancer chemotherapy: from preclinical findings to clinical strategy

Chemotherapy-induced gut toxicity is a major dose-limiting toxicity for many anticancer drugs. Gastrointestinal (GI) complications compromise the efficacy of chemotherapy, promote overall malnutrition, aggravate cancer cachexia, and may contribute to worsened prognosis. The GI tract is an attractive target for nutrition modulation, owing to its direct exposure to the diet, participation in uptake and metabolism of nutrients, high rate of cell turnover, and plasticity to nutrition stimuli. Glutamine, ω-3 polyunsaturated fatty acids, and probiotics/prebiotics are therapeutic factors that potentially modulate GI toxicity related to cancer treatments. Preclinical and clinical evidence are reviewed to critically define plausible benefits of these factors and their potential development into adjuncts to cancer chemotherapy. Mechanisms underlying the action of these nutrients are being unraveled in the laboratory. Optimal strategies to translate these findings into clinical care still remain to be elucidated. Key questions that remain to be answered include the following: which nutrient or combination of nutrients is selected for which patient and chemotherapy regimen? What mechanisms are responsible for modulation, and how are nutrient(s) administered in a clinically optimal manner? Research exploring interactions between different nutrients in GI protection is ongoing and demands further understanding. How nutrition preparations given to chemotherapy-treated patients are formulated in terms of component selection and dose optimization should be carefully studied and justified.

Single and combined supplementation of glutamine and n-3 polyunsaturated fatty acids on host tolerance and tumour response to 7-ethyl-10-[4-(1-piperidino)-1-piperidino]carbonyloxy-camptothecin (CPT-11)/5-fluorouracil chemotherapy in rats bearing Ward colon tumour

Prior reports suggest that during irinotecan (7-ethyl-10-[4-(1-piperidino)-1-piperidino]carbonyloxy-camptothecin; CPT-11) chemotherapy in laboratory rats, the anti-tumour efficacy and diarrhoea toxicity could be modulated by n-3 PUFA and glutamine, respectively. We further examined how these two dietary elements, when provided individually and in combination, would affect the efficacy of a cyclical regimen of CPT-11/5-fluorouracil (5-FU), an accepted combination regimen for colorectal cancer. Prior to initiating chemotherapy, diets enriched either with glutamine (2 %, w/w total diet) or n-3 PUFA (0.88 %, w/w total diet) alone, inhibited Ward colon tumour growth (P < 0.05). These diets also completely or partially normalized the changes in peripheral leucocyte counts associated with the tumour-bearing state (e.g. neutrophil proportion/concentration and lymphocyte proportion). During chemotherapy, either glutamine- or n-3 PUFA-enriched diet enhanced tumour chemo-sensitivity, and reduced body weight loss, anorexia and muscle wasting (v. animals fed control diet, P < 0.05). Surprisingly, providing both glutamine and n-3 PUFA together did not confer a greater benefit on tumour inhibition either in the presence or absence of chemotherapy; individual benefits associated with single treatments, particularly in respect to host nutritional status (i.e. body weight, food intake and muscle weight) and immune (peripheral leucocyte counts) features were instead partially or completely lost when these two nutrients were combined. These results draw into question the common assumption that there are additive or synergistic benefits of combinations of nutrients, which are beneficial on an individual basis, and suggest that co-supplementation with glutamine and n-3 PUFA is not indicated during chemotherapy with CPT-11 and 5-FU.

Bolus oral glutamine protects rats against CPT-11-induced diarrhea and differentially activates cytoprotective mechanisms in host intestine but not tumor

Dietary glutamine has been suggested to preserve structural and functional integrity of the gut and high dose bolus glutamine has been hypothesized to protect against potentially fatal endotoxic shock, hyperthermic stress, and side effects of chemotherapy. In this study, we aimed to relate the ability of high dose oral bolus glutamine to mitigate the severe diarrhea induced by 7-ethyl-10-[4-(1-piperidino)-1-piperidino]carbonyloxy-camptothecin (CPT-11) chemotherapy to specific cytoprotective mechanisms [heat shock response, glutathione (GSH)] in gut and tumor tissues. Female rats bearing Ward colon tumor received CPT-11 (125 mg x kg(-1) x d(-1)x 3 d) with or without an oral glutamine bolus (0.75 g/kg) administered 30 min prior to each CPT-11 dose. Glutamine reduced incidence and severity of late-onset diarrhea following CPT-11 treatment (P < 0.05) and was associated with potentially beneficial and protective responses in the colon: 1) a 3.1- to 7.2-fold increase of heat shock protein (Hsp)25,-70, and -90alpha (P < 0.05); 2) increased reduced GSH (rGSH):oxidized GSH ratio (P < 0.05); 3) prevention of upregulated activity of a key bacterial enzyme (beta-glucuronidase) in the cecal content that mediates CPT-11 intestinal toxicity (P < 0.05); and 4) increased proportions of CD3+CD8+ lymphocytes and memory CD8+ subset in mesenteric lymph nodes following CPT-11 therapy. By contrast, glutamine treatment did not alter CPT-11's antitumor activity, the amino acid concentrations, Hsp expression, or the ratio of rGSH:oxidized GSH in the tumor. Our data demonstrate a striking dichotomy in the response of tumor and host to oral glutamine administration, concurring with the concept that this nutrient may favorably alter the balance between the host and tumor.

Stimulation of expression of the intestinal glutamine transporter ATB0 in tumor-bearing rats

BACKGROUND

Glutamine supplementation ameliorates host catabolic response in tumor bearing states. The purpose of this in vivo study was to investigate intestinal glutamine transport and expression of glutamine transporter ATB(0) in methyl-cholanthrene (MCA)-sarcoma bearing rats.

METHODS

Fisher-344 rats underwent subcutaneous flank implantation of MCA-sarcoma cells (saline as control) and were pair-fed an equal quantity of chow as controls, to account for tumor-induced anorexia, until tumors reached 10 or 20% body weight. Intestinal mucosal brush border membrane [3H]-Glutamine transport was measured. Glutamine transporter ATB(0) mRNA and protein levels were measured by real-time PCR and western blot techniques, respectively.

RESULTS

Glutamine transport activity across the intestinal brush border membrane (BBM) was 3.7-fold higher in tumor-bearing rats (TBR) than in controls (TBR 153 +/- 22.6 vs. Control 41.9 +/- 9.7 pmol/mg protein/10s, P < .01). Transporter ATB(0) mRNA levels were 1.4-fold higher in tumor-bearing rats (Relative value TBR .61 +/- .12 vs. Control .43 +/- .1, P < .05). A 1.4-fold increase in transporter ATB(0) protein levels was observed in the tumor-bearing rats (Relative value TBR .52 +/- .07 vs. Control .37 +/- .04, P < .05). Circulating aortic plasma glutamine levels were 1.3-fold higher in tumor bearing rats ([Glutamine] = .63 +/- .02 Control vs. [Glutamine] = .74 +/- .01 mmol/l TBR, P < .0001). Portal venous plasma glutamine levels were also higher in tumor bearing rats ([Glutamine] = .47 +/- .01 Control vs. [Glutamine] = .60 +/- .02 mmol/l TBR, P < .0001).

CONCLUSION

Intestinal brush border membrane glutamine transport activity, transporter ATB(0) mRNA and protein levels are up-regulate in tumor-bearing rats.

Short-term enteral glutamine does not enhance protein accretion in burned children: a stable isotope study

OBJECTIVE

Glutamine is a nonessential amino acid that, in recent years, has been found to play important roles in several metabolic and immunologic processes. It has been theorized that, in a stressed state, it may become "conditionally essential" because the patient's ability to manufacture glutamine may not be adequate to meet their needs under this condition. We chose to evaluate the ability of 48 hours of enteral glutamine to enhance immediate nitrogen accretion in stressed pediatric burn patients.

METHODS

Nine children with serious burns who were tolerating tube feedings were enrolled in a human studies committee-approved protocol in which they received 48 hours of enteral feedings with glutamine replacing 20% of essential and nonessential amino acids and 48 hours of isonitrogenous, isocaloric standard enteral feedings. This interval was chosen to help ensure that the study periods were comparable from a metabolic perspective. At the end of each period, protein kinetics were determined by a primed constant infusion of L-[1-(13)C] leucine tracer. The order of the studies was randomized. Seven children completed both phases of the study. Results were compared by paired t test and are presented as mean +/- standard error of the mean.

RESULTS

During the glutamine feeding period, the leucine flux and leucine oxidation rate were significantly lower than those in the conventional feeding period. This reflects a reduction in total leucine intake from 80 +/- 11 to 62 +/- 10 micromol/kg per hour. However, there was no significant difference in the net balance of leucine accretion into proteins between these 2 dietary periods, which indicated that enriched glutamine feeding for 48 hours did not result in an immediate whole body protein gain in this group of pediatric patients. In addition, plasma glutamine concentration showed a moderate increase after 48 hours of supplementation but did not reach significance.

CONCLUSION

Rapid protein accretion does not occur with short-term enteral glutamine supplementation. Several days of glutamine supplementation may be required to restore plasma glutamine levels and stimulate protein synthesis.

Glutamine supplementation in cancer patients

OBJECTIVES

Three series of studies investigated whether 1) glutamine deficiency occurs in tumor-bearing rats, 2) glutamine supplementation improves protein metabolism during chemotherapy in tumor-bearing rats, and 3) oral glutamine supplement improves systemic immune and gut-barrier function in patients with esophageal cancer receiving radiochemotherapy.

METHODS

In the animal studies, AH109A hepatoma cells or Yoshida sarcoma cells were inoculated into male Donryu rats to induce tumors. Glutamine production was measured by U-14C-glutamine infusion and the conversion of arginine to glutamine was measured by infusion of U-14C-arginine. The effect of glutamine on protein metabolism was investigated by 1-14C-leucine infusion. In the clinical study, 13 patients with esophageal cancer were randomized into two groups, control and glutamine supplemented (30 g/d), for 4 wk.

RESULTS

Glutamine levels in plasma and skeletal muscle were decreased in tumor-bearing rats, although glutamine production and the conversion of arginine to glutamine were increased. Glutamine-supplemented total parenteral nutrition reduced whole-body protein breakdown rate during chemotherapy in tumor-bearing rats. Oral supplementation of glutamine to the patients with esophageal cancer enhanced lymphocyte mitogenic function and reduced permeability of the gut during radiochemotherapy.

CONCLUSIONS

Glutamine depletion in host tissues occurs in tumor-bearing rats. Glutamine supplementation can attenuate loss of protein in the muscle in tumor-bearing animals and protect immune and gut-barrier function during radiochemotherapy in patients with advanced cancer.

Glutamine and cancer

Glutamine is the most abundant free amino acid in the human body; it is essential for the growth of normal and neoplastic cells and for the culture of many cell types. Cancer has been described as a nitrogen trap. The presence of a tumor produces great changes in host glutamine metabolism in such a way that host nitrogen metabolism is accommodated to the tumor-enhanced requirements of glutamine. To be used, glutamine must be transported into tumor mitochondria. Thus, an overview of the role of glutamine in cancer requires not only a discussion of host and tumor glutamine metabolism, but also its circulation and transport. Because glutamine depletion has adverse effects for the host, the effect of glutamine supplementation in the tumor-bearing state should also be studied. This communication reviews the state of knowledge of glutamine and cancer, including potential therapeutic implications.

Glutamine, as a precursor of glutathione, and oxidative stress

Oxidative stress is related to several pathologies and it is also associated with surgical operations. Reactive oxygen species generated during oxidative stress can induce severe damage to biomolecules. To prevent this damage, cells are endowed with both enzymatic and nonenzymatic defenses. One of the most important antioxidant molecules is glutathione. Since glutamine is a precursor of glutathione, its supplementation in the clinical diet can be used to maintain high levels of glutathione and to avoid oxidative stress damage. Here, recent literature concerning this recurrent topic is critically reviewed.

Effect of glutamine on methotrexate efficacy and toxicity

OBJECTIVE

To examine the effect of oral glutamine (GLN) on the efficacy and toxicity of methotrexate (MTX).

SUMMARY BACKGROUND DATA

The use of high-dose chemotherapy regimens is limited by the severity of their toxicities. Oral GLN has been shown to decrease the gut toxicity seen with MTX treatment while enhancing its tumoricidal effect.

METHODS AND RESULTS

Studies were done in laboratory rats and in breast cancer outpatients. Fischer 344 rats were randomized to 48 hours of prefeeding with GLN (1 g/kg/day) or an isonitrogenous amount of glycine. Rats were killed 24 hours after receiving a 20-mg/kg intraperitoneal dose of MTX. In the GLN group, there was a threefold increase in total MTX in the tumor as compared with the control group, and this increase was in both the diglutamated and pentaglutamated MTX. Inversely, there was a significant decrease in the total polyglutamated MTX in the gut in the GLN group. Given the results of this preclinical study, the authors performed a phase I trial. Nine patients diagnosed with inflammatory breast cancer received GLN (0.5 g/kg/day) during MTX neoadjuvant therapy, escalating from doses of 40 mg/m2 to 100 mg/m2 weekly for 3 weeks, followed by a doxorubicin-based regimen. No toxicity of oral GLN was detected. No patient showed any sign of chemotherapy-related toxicity. One patient had a grade I mucositis. Except for one, all patients responded to the chemotherapy regimen. Median survival was 35 months.

CONCLUSIONS

These studies suggest that GLN supplementation is safe in its administration to the tumor-bearing host receiving MTX. By preferentially increasing tumor retention of MTX over that of normal host tissue, GLN may serve to increase the therapeutic window of this chemotherapeutic age.

Adaptive alterations in cellular metabolism with malignant transformation

OBJECTIVE

The authors studied the differences between glutamine and glucose utilization in normal fibroblasts and in fibrosarcoma cells to gain insights into the metabolic changes that may occur during malignant transformation.

SUMMARY BACKGROUND DATA

The process of malignant transformation requires that cells acquire and use nutrients efficiently for energy, protein synthesis, and cell division. The two major sources of energy for cancer cells are glucose and glutamine. Glutamine is also essential for protein and DNA biosynthesis. We studied glucose and glutamine metabolism in normal and malignant fibroblasts.

METHODS

Studies were done in normal rat kidney fibroblasts and in rat fibrosarcoma cells. We measured glutamine transport across the cell membrane, breakdown of glutamine by the enzyme glutaminase (the first step in oxidation), glutamine and glucose oxidation rates to CO2, rates of protein synthesis from glutamine, and glutamine-dependent growth rates.

RESULTS

Glutamine transport rates were increased more than sixfold in fibrosarcomas compared to normal fibroblasts. In fibroblasts, glutamine transport was mediated by systems ASC and A. In malignant fibrosarcomas, only system ASC was identifiable, and its Vmax was 15 times higher than that observed in fibroblasts. Despite an increase in transport, glutaminase activity was diminished and glutamine oxidation to CO2 was reduced in fibrosarcomas versus normal fibroblasts. In fibroblasts, glutamine oxidation was 1.8 times higher than glucose oxidation. In contrast, glucose oxidation was 3.5 times greater than glutamine oxidation in fibrosarcomas. Protein synthesis from glutamine transported by fibrosarcomas was threefold greater than that observed in normal fibroblasts. Despite marked increases in glutamine utilization and glucose oxidation in fibrosarcoma cells, growth rates were higher in the normal fibroblasts.

CONCLUSIONS

The process of malignant transformation is associated with a marked increase in cellular glutamine transport, which is mediated by a single high-affinity, high-capacity plasma membrane carrier protein. In normal fibroblasts, the transported glutamine is used primarily for energy production via oxidation of glutamine carbons to CO2. In fibrosarcomas, glutamine oxidation falls and glutamine is shunted into protein synthesis; simultaneously, the malignant cell switches to a glucose oxidizer. The increased glutamine transport and glucose oxidation in fibrosarcomas appears to be related to the malignant phenotype and not merely to an increase in cell growth rates.

Metabolic alteration in patients with cancer: nutritional implications

During the past 20 years, efforts have been made to elucidate the metabolic changes observed in patients with cancer by using stable and radioactive isotopic tracers. These metabolic changes in patients with cancer may be similar to those in other stress conditions, in which glucose production and utilization, lipolysis and free fatty acid flux, and net protein catabolism are increased. Stress hormones, such as glucagon and catecholamines, and certain cytokines may be responsible for these metabolic changes. Although it has been shown that cachexia in patients with cancer signals a poor prognosis, efforts to improve the clinical outcomes with nutritional support have been disappointing. The failure of cancer patients to respond to nutritional support may be related to an alteration in the intermediate metabolism. Therefore, further research evaluating the metabolic abnormalities associated with cancer may lead to more effective nutritional therapies.

Effects of glutamine supplements and radiochemotherapy on systemic immune and gut barrier function in patients with advanced esophageal cancer

OBJECTIVE

The objective of this study was to determine whether oral glutamine supplements can protect lymphocyte and gut barrier function in patients with advanced esophageal cancer undergoing radiochemotherapy.

SUMMARY BACKGROUND DATA

Glutamine supplements improved protein metabolism in tumor bearing rats who underwent chemotherapy and reduced the toxicity of chemotherapy through an enhancement of glutathione production in rats.

METHODS

Thirteen patients with esophageal cancer were randomly placed in either a control or a glutamine group. Glutamine was administered orally (30 g/day) at the start of radiochemotherapy and for the subsequent 28 days. All patients underwent mediastinal irradiation and chemotherapy consisting of 5-fluorouracil and cisplatin. The lymphocyte count was determined, and blast formation was assessed after stimulation with phytohemagglutinin and concanavalin A. Gut barrier function was assessed by measuring the total amount of phenolsulfonphthalein excreted in the urine after the oral administration of phenolsulfonphthalein.

RESULTS

Glutamine supplements prevented a reduction in the lymphocyte count (control: 567 +/- 96/mm3 vs. glutamine: 1007 +/- 151, p < 0.05), and blast formation of lymphocyte (phytohemagglutinin, control: 19478 +/- 2121 dpm vs. glutamine: 33860 +/- 1433, p < 0.01, concanavalin A, control: 19177 +/- 1897 dpm vs. glutamine: 29473 +/- 2302, p < 0.01), and amount of phenolsulfonphthalein excretion in the urine was greater with control than with glutamine group (control: 15.4 +/- 2.4% vs. glutamine: 7.4 +/- 1.2, p < 0.05) 7 days after the initiation of radiochemotherapy.

CONCLUSIONS

Oral glutamine supplementation protects lymphocytes and attenuates gut permeability in patients with esophageal cancer during radiochemotherapy.

Glutamine supplementation in cancer patients receiving chemotherapy: a double-blind randomized study

The purpose of this study was to evaluate the efficacy of glutamine in preventing doxifluridine-induced diarrhea and the potential impact of glutamine on the tumor growth. We investigated 65 patients with advanced breast cancer receiving doxifluridine in a double-blind randomized fashion: 33 patients took glutamine (30 g/d, divided in 3 doses of 10 g each) for 8 consecutive days (5-12h) during each interval between chemotherapy, which was administered from day 1 to 4. Thirty-two patients took an equal dose of placebo (maltodextrine). The incidence of diarrhea was registered after each cycle of chemotherapy and severity was scored by the National Cancer Institute (NCI), Bethesda, Maryland, classification. The tumor response was evaluated by the World Health Organization (WHO) criteria. A total of 278 and 259 cycles (median 10 cycles), respectively, were delivered in glutamine and placebo groups. There were 34 and 32 episodes of diarrhea in glutamine and placebo groups, with no statistical difference overall, in the severity and duration of tumor growth, there was no difference in the response rate (21% and 28% of complete or partial response, respectively), in median time to response (2 mo), or in median duration of response. In conclusion, glutamine did not prevent the occurrence of the doxifluridine-induced diarrhea and did not have any impact on tumor response to chemotherapy.

The role of total parenteral nutrition for patients with irreversible bowel obstruction secondary to gynecological malignancy

Two patients received total parenteral nutrition (TPN) to manage irreversible bowel obstruction secondary to gynecological malignancy. The use of TPN prolonged their lives considerably, but also led to complications, both from the TPN and from the natural progression of the cancers. Although TPN is increasingly considered as a possible treatment for selected patients with malignant bowel obstruction who are not suitable for surgery, the literature regarding this practice is conflicting. It should be considered only in those patients with good performance status, and then after careful attention to not only the likely medical and symptomatic outcomes, but also the ethical implications of such a management strategy.

Dietary L-glutamine supplementation reduces the growth of the Morris Hepatoma 7777 in exercise-trained and sedentary rats

Dietary glutamine supplementation and exercise have been reported independently to enhance immune function and reduce tumor growth. We study the effect of both of these interventions on the growth of the Morris Hepatoma 7777, implanted in 59 female Sprague-Dawley Buffalo rats. Rats were fed a nutritionally complete, purified diet with or without L-glutamine 20 g/kg diet and randomized to swim 3 h/d or to remain sedentary. After 14 d, the mean tumor weight of glutamine-supplemented rats was lower (P < 0.0001) than that of unsupplemented rats (5.8 +/- 0.4 vs. 8.7 +/- 0.5 g, respectively). Exercise did not alter tumor growth. Glutamine supplementation increased [3H] thymidine incorporation by splenocytes incubated with Concanavalin A and the proportion of natural killer cells in spleen, but not cytotoxic activity against YAC-1 cells. Glutamine supplementation did not alter glutamine concentrations in plasma (691 +/- 12 mumol/L) or soleus muscle (5328 +/- 102 pmol/mg) but resulted in higher (P < 0.004) plasma concentrations of leucine, isoleucine and valine, precursors of glutamine. Splenocytes from exercised rats had a higher (P < 0.001) mitogen response than those from sedentary rats. Isolated tumor cells demonstrated high rates of non-oxidative glucose and glutamine metabolism and consumption of glutamine, tryptophan and methionine. However, neither diet nor exercise significantly affected glucose or glutamine metabolism by tumor cells. The precise mechanism of tumor growth suppression by oral glutamine supplementation is not clear but may be related to changes in substrate availability, improved tumor-directed natural killer cytotoxic activity or a faster response to an immune challenge.

Effect of glutamine supplementation on protein metabolism and glutathione in tumor-bearing rats

The effect of glutamine (GLN)-supplemented total parenteral nutrition (TPN) on tumor growth and protein metabolism was investigated in tumor-bearing rats. Six days after implantation of AH109A hepatoma, rats received isonitrogenous TPN without or with alanyl-glutamine (25% of total N) for a period of 6 days. Protein turnover was assessed by continuous infusion of l4C-leucine and levels of GLN and glutathione were determined in muscle, jejunum and liver. Diet had no effect on tumor parameters: weight (mean = 4.4 g), GLN and glutathione concentrations, protein synthesis rate and bromodeoxyuridine-labeling index. Body weight loss was less pronounced in the GLN group (-5.5 +/- 1.2 vs. -9.4 +/- 1.4 g/5d). Decrease in plasma and muscle GLN concentrations (-30% and -17% vs. healthy controls, respectively) was limited in tumor-bearing rats receiving GLN-enriched TPN (-15% and +3%). GLN-supplemented TPN increased muscle and jejunum fractional synthesis rates (36% and 25% vs. standard TPN, respectively) and reduced body protein breakdown in tumor-bearing animals (303 +/- 33 vs. 421 +/- 66 mumol Leu/Kg/h). Decrease in jejunum glutathione levels was partially abolished in the GLN group: -50% vs. -64% in the standard TPN group; no effect was noticed in other tissues. The authors conclude that GLN-supplemented TPN improves protein metabolism at both the whole body and the tissue level, and prevents GLN and glutathione deficiencies associated with tumor implantation.

Glutamine as a regulator of DNA and protein biosynthesis in human solid tumor cell lines

OBJECTIVE

The transport of glutamine by six different human solid tumor-derived cell lines (e.g., breast, colon, liver) was characterized and the impact of glutamine deprivation on rates of tumor cell proliferation and DNA and protein synthesis was assayed.

SUMMARY BACKGROUND DATA

Glutamine is added routinely to cell culture media and its importance for cellular growth has been established. However, carrier-mediated glutamine transport by solid tumors has not been studied extensively, and the mechanisms by which glutamine contributes to cell growth regulation require further investigation.

METHODS

In a panel of different human solid tumor-derived cells, sodium-dependent glutamine transport was characterized in vitro and rates of cell proliferation, protein and DNA synthesis, as well as thymidine transport, were correlated with glutamine concentrations in the culture media.

RESULTS

In all cells, regardless of tissue origin, sodium-dependent glutamine transport was mediated almost exclusively by a single carrier. There was a range of Michaelis constants (Km) and maximal transport velocities (Vmax) for the glutamine transporter in each cell type, but the amino acid inhibition profiles were nearly identical, consistent with uptake by the System ASC family of transporters. Rates of cell growth, DNA and protein synthesis, and thymidine transport correlated with the glutamine concentration in the culture media, indicating the central role of this amino acid in regulating cellular proliferation.

CONCLUSIONS

These data indicate that glutamine transport by all solid tumors is mediated by the System ASC family of transporters. The variation in Km values suggests that some cancers may be better suited to survive in a low glutamine environment than others. The mechanism by which glutamine supports cell proliferation and regulates cell cycle kinetics involves its modulation of DNA and protein biosynthetic rates.

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.

Effect of glutamine supplementation on protein metabolism and glutathione in tumor-bearing rats

BACKGROUND

Since tumor-bearing rats are deficient in glutamine, we investigated whether (1) glutamine and glutathione deficiency occur in tumor-bearing rats, (2) glutamine supplementation caused an increase of glutathione levels in host tissues and tumor, (3) glutamine enhances protein synthesis in host tissues, and (4) glutamine stimulated the tumor to synthesize protein and DNA.

METHODS

Male Donryu rats were randomized into four groups: (1) non-tumor-bearing rat (NTB) + standard total parenteral nutrition (STPN); (2) NTB + glutamine-supplemented TPN (GTPN); (3) tumor-bearing rat (TB) + STPN; (4) TB + GTPN. On day 0 AH109A rat hepatoma cells were subcutaneously injected into the backs of rats to induce tumor. The animals were maintained on TPN for 6 days from day 10 through day 15. On day 15, 1-14C-leucine was given by a 5-hour continuous infusion (2.0 microCi/h per rat) to determine the fractional synthesis rate and endogenous leucine production. The levels of glutamine and glutathione were measured by HPLC. the tumor DNA synthesis was estimated by bromodeoxyuridine labeling index.

RESULTS

Tumor development led to a significant weight loss, but this weight loss was significantly lessened by glutamine supplementation because of an increase in muscle protein synthesis. Glutamine did not enhance tumor weight, protein, and DNA synthesis in the tumor. Tumor development caused a significant reduction of glutathione in the muscle, jejunum, and liver, but supplemented glutamine increased the levels of glutathione in the jejunum.

CONCLUSION

Glutamine supplementation is beneficial in preventing deficiencies of glutamine and glutathione and in improving protein metabolism in tumor-bearing rats.

Normalization of tumor-induced increases in hepatic amino acid transport after surgical resection

BACKGROUND

The liver of the host with cancer requires increased amounts of amino acids to support the synthesis of glucose and key defense proteins. To study the effect of the growing tumor on hepatic amino acid uptake, the authors measured hepatic transport activity in tumor-bearing rats and in rats at various times after tumor resection.

METHODS

Fischer-344 rats were implanted subcutaneously with methylcholanthrene-induced fibrosarcoma cells (MCA sarcoma). When the tumors reached 10% of body weight, hepatic amino acid transport activity was assayed or the animals underwent surgical removal of the tumor. In animals that underwent tumor excision, livers were removed at 1, 3, or 5 days post-resection, and hepatic plasma membrane vesicles (HPMVs) were prepared. Nontumor-bearing pair-fed rats undergoing sham implantation or sham resection served as controls. System N (glutamine), System A (MeAIB), and System y+ (arginine) transport activity were assayed, which allowed the authors to compare differences in tumor-induced rates of transport and the influence of resection on transport activity.

RESULTS

System A transport activity was unaltered by tumor growth. In contrast, the presence of the growing tumor increased arginine and glutamine uptake by the liver. Hepatic glutamine transport remained elevated for 5 days after tumor resection, although by postoperative day 5 there was a trend toward normalization. In contrast, arginine transport remained increased by twofold onpost-resection day 1 and had normalized by postoperative day 3. The enhanced arginine transport was a result of an increase in maximal transport velocity (Vmax) rather than a change in carrier affinity.

CONCLUSIONS

Increases in hepatic amino acid transport normalize within several days of tumor resection, indicating a key role for the tumor in the induction of this response. The observation that hepatic glutamine transport activity remains augmented after tumor resection longer than any other transporter studied suggests a key role for this amino acid in overall hepatic nitrogen metabolism and may partially explain the persistent glutamine depletion that is characteristic of the tumor-bearing host.

Dietary regulation of the hepatic system n glutamine transporter in tumor-bearing rats

BACKGROUND

Hepatocytes possess a novel, plasma-membrane, sodium ion (Na+)-independent, glutamine transporter (system n), which functions to transport glutamine out of the cell into the blood. In the tumor-bearing rat, the activity of system n increases but its regulation is unknown. We hypothesized that the increase in system n that occurs in rats with cancer was related to a fall in the circulating glutamine concentration.

METHODS

Ten male rats underwent flank implantation with a cube of methylcholanthrene-induced fibrosarcoma cells and 10 rats underwent a sham operation. After 9 days of standard diet, all rats were randomized to receive either a glutamine-enriched oral diet or an isonitrogenous diet without supplemental glutamine, for 1 week. Tumors and livers were harvested 16 days postimplantation. Arterial blood samples were obtained from all animals. Hepatic plasma membrane vesicles were prepared and the carrier-mediated, Na(+)-independent transport of glutamine was assayed.

RESULTS

When compared to nontumor-bearing animals, tumor-bearing rats that were fed a control diet exhibited hypoglutaminemia and a 2.3-fold increase in the activity of system n. Glutamine dietary supplementation produced blood glutamine levels that were similar in both tumor-bearing and nontumor-bearing rats, apparently abrogating the increase in system n activity that was observed in tumor-bearing rats that were not fed supplemental glutamine. Tumor-bearing animals receiving supplemental glutamine had a decreased number of system n carriers (Vmax) in the hepatic plasma membrane compared to that of tumor-bearing animals receiving a control diet; this apparently abrogated the glutamine efflux rate. Glutamine feeding did not alter system n activity in nontumor-bearing controls.

CONCLUSIONS

In the tumor-bearing animal model, system n is modulated by the circulating glutamine concentration. This is the first study that demonstrates the ability of specialized nutrition to "downregulate" transport activity in vivo. Provision of glutamine-enriched diets to the host with cancer may maintain hepatic glutamine levels and prevent host glutamine depletion.

Effect of glutamine on tumor and host growth

BACKGROUND

Oral glutamine supplementation has been found to support gastrointestinal mucosal growth and increase intestinal and systemic toxicity after chemotherapy and radiation therapy. Glutamine is also an important nutrient for rapidly proliferating tumor cells. However, it is not clear whether long-term glutamine supplementation in the tumor-bearing host has a selective benefit for host growth or tumor cell proliferation.

METHODS

To study the effect of glutamine in tumor-bearing animals, 30 Lewis/Wistar rats with subcutaneous mammary tumor implants (MAC-33) were randomized to receive a 3% glutamine- or 3% glycerine-enriched (control) diet for 25 days.

RESULTS

No significant difference was found in carcass weight, primary tumor weight, or spontaneous pulmonary metastasis with glutamine supplementation. Tumor cell cycle kinetics (aneuploidy, %S and %S [synthetic] + G2/M [growth fraction]) were similar between glutamine-supplemented and control animals. A trophic effect of glutamine on distal ileal mucosa was seen with increased DNA content (344 +/- 68 vs. 184 +/- 38 micrograms/100 mg tissue) (p < 0.05) and RNA content (435 +/- 44 vs. 335 +/- 30 micrograms/100 mg tissue) (p = 0.06) compared with control animals. No detectable differences were observed in liver or muscle, or in tumor DNA, RNA, or protein content.

CONCLUSIONS

These findings confirm the trophic effect of glutamine on small intestinal mucosa and suggest that glutamine can be administered to the tumor-bearing host over a long period of time without significantly stimulating tumor growth kinetics or metastasis.

Arginine-enriched solution induces a marked increase in muscle glutamine concentration and enhances muscle protein synthesis in tumor-bearing rats

Using a transplantable Yoshida sarcoma in a rat model of total parenteral nutrition (TPN), we measured the effectiveness of an arginine-enriched amino acid solution (AI-82) on muscle glutamine concentration and muscle protein synthesis compared with that of a conventional amino acid solution (Proteamin12). After tumor-bearing rats had been given one of two isocaloric TPN regimens for 6 days, [15N]glycine (99 atom %) containing TPN solution was infused into animals at a constant rate of 8 mg of [15N]glycine per hour for 18 hours, after which the liver, skeletal muscle (gastrocnemius muscle), and tumor protein synthesis rates were measured. A significantly increased whole muscle protein synthesis rate was observed in the AI-82 group; there was no difference in the whole liver and tumor protein synthesis rates between the two groups. When each TPN solution was administered for 1 week, muscle concentrations of arginine, ornithine, glutamine, and glutamate were considerably higher in the AI-82 group than in the Proteamin12 group, and these differences were also accompanied by a decrease in the plasma branched-chain amino acid (BCAA) (leucine, isoleucine, and valine) levels in the AI-82 group. The high levels of muscle glutamine concentration in the AI-82 group were investigated in connection with the high use of exogenous branched-chain amino acids.

Use of total parenteral nutrition in children with cancer: a review and some recommendations

Total parenteral nutrition (TPN) is now a standard component of supportive treatment in many pediatric oncology units for patients undergoing intensive therapy. TPN incurs many risks and significant costs, however, that may not always be balanced by major benefits. Infection rates are reported to be high in patients receiving TPN, and TPN use is associated with a range of metabolic problems. With standard TPN regimens, the catabolic state of many intensively treated patients may not be adequately reversed. Because TPN may enhance tumor cell growth, there is justifiable concern about giving TPN when a cancer patient is not also receiving cytotoxic therapy. Recommendations for TPN use in pediatric oncology patients include using TPN formulas containing glutamine to stimulate anabolism and timing TPN cycles to be given just before cytotoxic chemotherapy, when stimulation of tumor growth might actually improve the effectiveness of antimitotic chemotherapy.

Glutamine metabolism and utilization: relevance to major problems in health care

Glutamine plays an important role in normal and pathophysiological states. In this review we describe the biochemical synthesis and degradation pathways of glutamine, as well as its utilization by the immune system and in rapidly dividing cells. Also discussed are glutamine behaviour in catabolic states and the therapeutic implications of this amino acid in total parenteral nutrition, digestive diseases and cancer.

Accelerated hepatic arginine transport in the tumor-bearing rat

BACKGROUND

Arginine plays a pivotal role in regulating ureagenesis, polyamine biosynthesis, and nitric oxide production, metabolic pathways that may be stimulated in the liver of the tumor-bearing host. Normally, plasma arginine is excluded from the hepatocyte intracellular space by the low basal activity of its membrane transporter. We hypothesized that progressive malignant disease is associated with an increase in carrier-mediated arginine transport across the hepatocyte plasma membrane.

METHODS

Twenty-four adult Fischer 344 rats were implanted subcutaneously with fibrosarcomas (TBR) and were studied when the tumors were small [10 +/- 1% of body weight (BW)], medium-sized (15 +/- 1% of BW), and large (25 +/- 1% of BW). Groups of control rats (n = 24) were pair-fed to match carcass weights of the three TBR groups. Livers were excised, and hepatocyte plasma membrane vesicles (HPMVs) were prepared by Percoll density gradient centrifugation. Arginine transport by HPMVs was assayed by a rapid mixing/filtration technique. Vesicle purity and functionality were assessed by membrane enzyme marker enrichments and transportability into an osmotically active space.

RESULTS

Arginine uptake by HPMVs was mediated by both saturable carrier-mediated (System y+) and nonsaturable (diffusion) components. The time course of arginine uptake in HPMVs in the three groups showed similar equilibrium transport rates, indicating similar vesicle sizes. The presence of the growing tumor resulted in a 40-120% increase in System y(+)-mediated arginine transport in HPMVs. This response was dependent on tumor size and was due to a stimulation of carrier Vmax, suggesting an increase in the number of functional System y+ carriers in the hepatocyte plasma membrane. The Na(+)-dependent transport of the System A analog MeAIB was also increased, but only in rats with large tumors.

CONCLUSIONS

Tumor growth results in a progressive increase in hepatic arginine transport, a response mediated primarily by an increase in the activity of System y+. This accelerated transport may amplify the availability of arginine to support key arginine-dependent metabolic pathways in the hepatocyte.

Glutamine protects Chinese hamster ovary cells from radiation killing

Chinese Hamster Ovary (CHO) cells were propagated in vitro and exposed to varying doses of ionizing radiation. The surviving fraction of cells was determined, being found to be a function of the radiation dose. The cell survival curves obtained as a function of radiation dose were modified by the inclusion of varying doses of glutamine in the medium with glutamine demonstrating a radioprotective effect. The radioprotectant effect of glutamine for CHO cells was more pronounced at higher radiation doses. Glutamine has been categorized as a non-essential amino acid in that it can be synthesized in some tissues; however, a number of cell lines require glutamine to survive and grow in vitro and supplementation of glutamine has been found to ameliorate the stress of surgery or irradiation to the gastrointestinal tract. It may be appropriate to consider glutamine as a conditionally essential amino acid.

Glutamine and cancer

OBJECTIVE

This overview on glutamine and cancer discusses the importance of glutamine for tumor growth, summarizes the alterations in interorgan glutamine metabolism that develop in the tumor-bearing host, and reviews the potential benefits of glutamine nutrition in the patient with cancer.

SUMMARY BACKGROUND DATA

Glutamine is the most abundant amino acid in the blood and tissues. It is essential for tumor growth and marked changes in organ glutamine metabolism are characteristic of the host with cancer. Because host glutamine depletion has adverse effects, it is important to study the regulation of glutamine metabolism in cancer and to evaluate the impact of glutamine nutrition in the tumor-bearing state.

METHODS

Data from a variety of investigations on glutamine metabolism and nutrition related to the host with cancer were compiled and summarized.

RESULTS

Numerous studies on glutamine metabolism in cancer indicate that many tumors are avid glutamine consumers in vivo and in vitro. As a consequence of progressive tumor growth, host glutamine depletion develops and becomes a hallmark. This glutamine depletion occurs in part because the tumor behaves as a "glutamine trap" but also because of cytokine-mediated alterations in glutamine metabolism in host tissues. Animal and human studies that have investigated the use of glutamine-supplemented nutrition in the host with cancer suggest that pharmacologic doses of dietary glutamine may be beneficial.

CONCLUSIONS

Understanding the control of glutamine metabolism in the tumor-bearing host not only improves the knowledge of metabolic regulation in the patient with cancer but also will lead to improved nutritional support regimens targeted to benefit the host.

Influence of progressive tumor growth on glutamine metabolism in skeletal muscle and kidney

OBJECTIVE

The effects of progressive malignant growth on glutamine metabolism in skeletal muscle and in kidney were investigated.

SUMMARY BACKGROUND DATA

Fast-growing tumors consume considerable quantities of glutamine and lead to a decrease in circulating glutamine concentrations.

METHODS

Experiments were performed at various stages of tumor growth in rats implanted subcutaneously with the non-metastasizing methylcholanthrene-induced (MCA) fibrosarcoma and in pair-fed non tumor-bearing controls.

RESULTS

Tumor growth stimulated a twofold increase in hindquarter (muscle) glutamine release, which was not due to an increase in blood flow, but rather to a doubling in the fractional release rate. Consequently, a progressive decrease in skeletal muscle glutamine concentrations was observed over time. Simultaneously, the activity of glutamine synthetase (GS), the principal enzyme of de novo glutamine biosynthesis, increased more than twofold. This increase in muscle GS activity was accompanied by an increase in GS mRNA but the augmentation in GS expression apparently could not match the increased rate of efflux since muscle depletion developed. In rats with large tumors and severe glutamine depletion, GS activity was not elevated. Glutamine feeding increased muscle glutamine concentrations and glutamine synthetase specific activity. Although tumor growth led to the development of mild systemic acidemia, the classic renal adaptations normally observed, i.e., elevated glutaminase activity and accelerated renal glutamine utilization, were not present in acidotic tumor-bearing rats. Instead, renal GS activity was increased in tumor-bearing animals and ammoniagenesis was enhanced, in spite of a reduction in net renal glutamine uptake.

CONCLUSIONS

These data suggest that marked alterations in muscle and renal glutamine handling occur in the host with cancer; the enhanced muscle glutamine release in conjunction with no increase in renal consumption is consistent with increased glutamine uptake in other organs, most likely the tumor itself and the liver.

Protein and amino acid metabolism in cancer cachexia: investigative techniques and therapeutic interventions

Cancer cachexia is a complex syndrome characterized primarily by diminished nutrient intake and progressive tissue depletion that is manifest clinically as anorexia and host weight loss. The gradual loss of host protein stores is central to this process. This review outlines the techniques that have been used to evaluate human amino acid metabolism, their application in patients with cancer cachexia, and possible therapeutic interventions designed to overcome alterations in host protein and amino acid metabolism associated with malignant cachexia. The techniques of nitrogen balance and 3-methylhistidine excretion provide indirect estimates of overall nitrogen metabolism and skeletal muscle myofibrillar protein breakdown. Measurement of circulating amino acid concentrations, particularly when combined with assessment of arterial-venous differences and regional amino acid balance allows for investigation of interorgan amino acid metabolism. One of the most significant advances in in vivo amino acid metabolic research has been the development of labeled amino acid tracer studies to evaluate whole body and regional amino acid kinetics. The use of stable and unstable amino acid isotopes in these techniques is reviewed in detail. Virtually all of these techniques have now been employed in the evaluation of human cancer cachexia. The results of studies evaluating amino acid concentrations, regional amino acid balance, and 3-methylhistidine excretion are summarized. The use of regional and whole body kinetic studies in cancer cachexia are reviewed extensively. Most investigators have observed increased rates of whole body protein turnover, synthesis, and catabolism in both weight-stable and weight-losing cancer patients. Some studies have suggested a relationship between the extent of disease and the degree of aberration in amino acid kinetic parameters. Investigators have attempted to reverse some of these alterations by provision of substrate (nutritional support) or administration of specific pharmacologic or anabolic agents such as hydrazine sulfate, insulin, growth hormone, and beta-2 agonists. The role of total parenteral nutrition (TPN) in cancer and its effects on protein and amino acid kinetics and tumor growth are addressed. The possible benefits of specific amino acid nutritional formulations with increased branched chain amino acids, arginine, and glutamine are reviewed. Although many of these approaches appear promising, significant impact on clinically definable parameters remains to be demonstrated. A better understanding of the underlying protein catabolic mechanisms of cancer cachexia will likely lead to more effective therapies to reverse the protein calorie malnutrition associated with cancer cachexia.

Na(+)-dependent glutamine transport in the liver of tumour-bearing rats

In rats with advanced malignant disease, the liver extracted circulating glutamine at a ratio three times faster than the liver of control non-tumour-bearing animals. This augmented uptake occurred in spite of a fall in circulating glutamine levels, implying an increase in hepatocyte plasma membrane transport. Na(+)-dependent glutamine transport activity (System N) was increased nearly two-fold in hepatocyte plasma membrane vesicles from tumour-bearing rats; this increase in System N activity was proportional to tumour size and was due to an increase in carrier Vmax with no change in carrier affinity. Measurement of System N activity in isolated hepatocytes incubated with serum from tumour-bearing rats demonstrated a significant increase in glutamine transport compared with cells incubated with serum from control rats. These data indicate that the liver of rats with advanced malignant disease displays accelerated glutamine consumption. This increased uptake is due, in part, to enhanced carrier-mediated transport activity, and is mediated by a circulating factor(s) that is not present (or inactive) in non-tumour-bearing controls.