Treatment of head and neck and esophageal xenografts employing Alimta and concurrent ionizing radiation.

We examined the interaction between Alimta and ionizing radiation (IR) as a potential strategy to enhance the therapeutic ratio of combined-modality cancer treatment. Mice bearing human esophageal adenocarcinoma xenografts (Seg-1) or squamous cell carcinoma xenografts (SQ-20B) were treated with Alimta and IR employing a fractionated treatment schedule. Treatment with Alimta alone slowed the growth of Seg-1 but not SQ-20B tumors compared with control tumors. In Seg-1 xenografts combined treatment with Alimta and IR produced significant tumor growth inhibition compared with Alimta alone or IR alone. In SQ-20B xenografts, treatment with Alimta did not enhance IR-mediated tumor growth inhibition suggesting that sensitivity to Alimta is necessary for an interactive cytotoxic effect with IR. The present data suggest the potential clinical efficacy of combining Alimta administration with radiotherapy for Alimta-sensitive cells and indicate that further testing needs to be conducted to optimize the dosing schedule to enhance the interaction between the therapeutic agents.

Antitumor interaction of short-course endostatin and ionizing radiation.

PURPOSE: The purpose of this study was to evaluate whether endostatin, an antiangiogenic cleavage fragment of collagen XVIII, enhances the antitumor effects of ionizing radiation (IR). Endostatin was injected to coincide with fractionated radiotherapy. METHODS: Xenografts of radioresistant SQ-20B tumor cells were established in athymic nude mice. Lewis lung carcinoma cells were injected into C57BI/6 mice. Mice bearing SQ-20B xenografts were injected intraperitoneally with 2.5 mg/kg/day of murine recombinant endostatin 5 times per week for 2 weeks 3 hours before IR treatment (50 Gy total dose). Mice bearing Lewis lung carcinoma tumors were injected intraperitoneally with endostatin (2.5 mg/kg/day) four times; the first injection was given 24 hours before the first IR dose (15 Gy) and then 3 hours before IR (15 Gy/day) for 3 consecutive days. Microvascular density was assessed on tumor tissue sections by use of CD31 immunohistochemistry and light microscopy. Endothelial cell survival analyses were employed to evaluate endostatin effects on human aortic endothelial cells and human umbilical vein endothelial cells. Endothelial cell apoptosis was examined by use of FACS analysis and DAPI microscopy. RESULTS: In SQ-20B xenografts, combined treatment with endostatin and IR produced tumor growth inhibition that was most pronounced at the nadir of regression (day 21). By day 35, tumors receiving combined treatment with endostatin and IR were 47% smaller than tumors treated with endostatin alone. Interactive cytotoxic treatment effects between endostatin and IR were also demonstrated in mice bearing Lewis lung carcinoma tumors. Significant tumor growth inhibition was observed in the endostatin/IR group at days 11 and 13 compared with IR alone. Histologic analyses demonstrated a reduction in microvascular density after combined treatment with endostatin and IR compared with endostatin treatment alone. Survival analyses confirmed interactive cytotoxicity between endostatin and IR in both human aortic endothelial cells and human umbilical vein endothelial cells but not in SQ-20B tumor cells. Combined treatment with endostatin and IR produced an increase in cow pulmonary artery endothelial apoptosis compared with either treatment alone. DISCUSSION: The tumor regression observed after combined treatment with endostatin and IR suggests additive antitumor effects in both human and murine tumors. Importantly, the concentrations of endostatin employed produced little tumor regression when endostatin was employed as a single agent. The results from the clonogenic and apoptosis assays support the hypothesis that the endothelial compartment is the target for the endostatin/IR interaction.

NM-3, an isocoumarin, increases the antitumor effects of radiotherapy without toxicity.

We examined the effects of a new antiangiogenic isocoumarin, NM-3, as a radiation modifier in vitro and in vivo. The present studies demonstrate that NM-3 is cytotoxic to human umbilical vein endothelial cells (HUVECs) but not to Lewis lung carcinoma (LLC) cells nor Seg-1, esophageal adenocarcinoma cells, in clonogenic survival assays. When HUVEC cultures are treated with NM-3 combined with ionizing radiation (IR), additive cytotoxicity is observed. In addition, the combination of NM-3 and IR inhibits HUVEC migration to a greater extent than either treatment alone. The effects of treatment with NM-3 and IR were also evaluated in tumor model systems. C57BL/6 female mice bearing LLC tumors were given injections for 4 consecutive days with NM-3 (25 mg/kg/day) and treated with IR (20 Gy) for 2 consecutive days. Combined treatment with NM-3 and IR significantly reduced mean tumor volume compared with either treatment alone. An increase in local tumor control was also observed in LLC tumors in mice receiving NM-3/IR therapy. When athymic nude mice bearing Seg-1 tumor xenografts were treated with NM-3 (100 mg/kg/day for 4 days) and 20 Gy (four 5 Gy fractions), significant tumor regression was observed after combined treatment (NM-3 and IR) compared with IR alone. Importantly, no increase in systemic or local tissue toxicity was observed after combined treatment (NM-3 and IR) when compared with IR alone. The bioavailability and nontoxic profile of NM-3 suggests that the efficacy of this agent should be tested in clinical radiotherapy.

Blockage of the vascular endothelial growth factor stress response increases the antitumor effects of ionizing radiation.

The family of vascular endothelial growth factor (VEGF) proteins include potent and specific mitogens for vascular endothelial cells that function in the lation of angiogenesis Inhibition of VEGF-induced angiogenesis either by neutralizing antibodies or dominant-negative soluble receptor, blocks the growth of primary and metastatic experimental tumors Here we report that VEGF expression is induced in Lewis lung carcinomas (LLCs) both in vitro and vivo after exposure to ionizing radiation (IR) and in human tumor cell lines (Seg-1 esophageal adenocarcinoma, SQ20B squamous cell carcinoma, T98 and U87 glioblastomas, and U1 melanoma) in vitro. The biological significance of IR-induced VEGF production is supported by our finding that treatment of tumor-bearing mice (LLC, Seg-1, SQ20B, and U87) with a neutralizing antibody to VEGF-165 before irradiation is associated with a greater than additive antitumor effect. In vitro, the addition of VEGF decreases IR-induced killing of human umbilical vein endothelial cells, and the anti-VEGF treatment potentiates IR-induced lethality of human umbilical vein endothelial cells. Neither recombinant VEGF protein nor neutralizing antibody to VEGF affects the radiosensitivity of tumor cells These findings support a model in which induction of VEGF by IR contributes to the protection of tumor blood vessels from radiation-mediated cytotoxicity and thereby to tumor radioresistance.

Potentiation of the antitumor effect of ionizing radiation by brief concomitant exposures to angiostatin.

Angiostatin, a proteolytic fragment of plasminogen, inhibits the growth of primary and metastatic tumors by suppressing angiogenesis. When used in combination with ionizing radiation (IR), angiostatin demonstrates potent antitumor synergism, largely caused by inhibition of the tumor microvasculature. We report here the temporal interaction of angiostatin and IR in Lewis lung carcinoma (LLC) tumors growing in the hind limbs of syngeneic mice. Tumors with an initial mean volume of 510 +/- 151 mm3 were treated with IR alone (20 Gy x 2 doses on days 0 and 1), angiostatin alone (25 mg/kg/day divided twice daily) on days 0 through 13, or a combination of the two as follows: (a) IR plus angiostatin (days 0 through 13); (b) IR plus angiostatin (days 0 and 1); and (c) IR followed by angiostatin beginning on the day after IR completion and given daily thereafter (days 2 through 13). By day 14, tumors in untreated control mice had grown to 6110 +/- 582 mm3, whereas in mice treated with: (a) IR alone, tumors had grown to 2854 +/- 338 mm3 (P < 0.05 compared with untreated controls); and (b) angiostatin alone, tumors had grown to 3666 +/- 453 mm3 (P < 0.05 compared with untreated controls). In combined-treatment groups, in mice treated with: (a) IR plus longer-course angiostatin, tumors reached 2022 +/- 282 mm3 (P = 0.036 compared with IR alone); (b) IR followed by angiostatin, tumors reached 2677 +/- 469 mm3 (P > 0.05 compared with IR alone); and (c) IR plus short-course angiostatin, tumors reached 1032 +/- 78 mm3 (P < 0.001 compared with IR alone). These findings demonstrate that the efficacy of experimental radiation therapy is potentiated by brief concomitant exposure of the tumor vasculature to angiostatin.

Regulation of small intestinal glutamine transport by epidermal growth factor.

BACKGROUND: Epidermal growth factor (EGF) stimulates cell replication and increases DNA content of the small intestine, but its effects on mucosal amino acid transport are unknown. METHODS: To investigate these effects, we treated adult rats with vehicle or EGF (10 micrograms/100 gm body weight subcutaneously every 8 hours for three doses). Jejunal brush border membrane vesicles (BBMVs) from each group were prepared by Mg++ aggregation/differential centrifugation. BBMVs were enriched fifteen-fold in alkaline phosphatase, indicating BBMV purity. Transport of 3H-glutamine and 3H-alanine was studied by a rapid mixing filtration technique. Uptakes were primarily Na+ dependent, occurred in an osmotically active space, exhibited classic overshoots, and had similar 2-hour equilibrium values. RESULTS: Glutamine transport by BBMVs more than doubled in rats treated with EGF (16.4 +/- 0.1 pmol glutamine/mg protein/10 sec in EGF vs 7.1 +/- 0.5 pmol glutamine/mg protein/10 sec in controls; p < 0.001). Kinetic studies of the glutamine transporter showed that the increase in transport was the result of a 70% increase in maximal transport velocity (total maximum glutamine uptake = 193 +/- 8 pmol glutamine/mg protein/10 sec in EGF vs 114 +/- 7 pmol glutamine/mg protein/10 sec in controls; p < 0.0001 with no change in transporter affinity (transporter affinity = 224 +/- 6 mumol/L in EGF vs 242 +/- 37 mumol/L in controls; difference, not significant). Alanine uptake by BBMVs was also increased with EGF administration (10.2 +/- 2.0 pmol alanine/mg protein/10 sec in EGF vs 4.5 +/- 0.5 pmol alanine/mg protein/10 sec in controls; p < 0.005). Simultaneously, glucose transport was decreased by 50% in EGF-treated rats, indicating that the Na(+)-dependent glucose cotransporter is regulated independently from and opposite to amino acid transporters. CONCLUSIONS: We conclude that EGF up-regulates amino acid transport activity in jejunal BBMVs, an event that is most likely caused by an increase in de novo biosynthesis of transporter protein. The increase in amino acid uptake not only may support de novo protein synthesis but, in the case of glutamine, also may be required for energy production and nucleotide biosynthesis.

Characteristics of L-glutamine transport in equine jejunal brush border membrane vesicles.

The sodium-dependent transporter system responsible for L-glutamine uptake by brush border membrane vesicles prepared from equine jejunum was characterized. Vesicle purity was ascertained by a 14- to 17-fold increase in activity of the brush border enzyme markers. Glutamine uptake was found to occur into an osmotically active space with negligible membrane binding. The sodium-dependent velocity represented approximately 80% of total uptake and demonstrated overshoots. Kinetic studies of sodium-dependent glutamine transport at concentrations between 5 microM and 5 mM revealed a single saturable high-affinity carrier with a Michaelis constant of 519 +/- 90 microM and a maximal transport velocity of 3.08 +/- 0.97 nmol/mg of protein/10 s. Glutamine uptake was not affected by changes in environmental pH. Lithium could not substitute for sodium as a contransporter ion. 2-Methylaminoisobutyric acid inhibited the sodium-dependent carrier only minimally, but marked inhibition (> 90%) was observed in the presence of histidine, alanine, cysteine, and nonradioactive glutamine. Kinetic analysis of the sodium-independent transporter revealed it to have a Michaelis constant = 260 +/- 47 microM and a maximal transport velocity of 0.32 +/- 0.06 nmol/mg of protein/10 s. We conclude that glutamine transport in equine jejunal brush border membrane vesicles occurs primarily via the system B transporter and, to a lesser extent, by a sodium-independent carrier.

The early response of the jejunal brush border glutamine transporter to endotoxemia.

The early effects of endotoxin (4 hr after a single dose of Escherichia coli LPS, 7.5 mg/kg) on L-glutamine (GLN) transport across the jejunal brush border of rats were studied. Jejunal brush border membrane vesicles (BBMVs) were prepared by a Mg2+ aggregation/differential centrifugation technique. Vesicle purity and integrity were confirmed by a 15-fold enrichment of brush border marker enzymes, osmotic activity, transport overshoots in the presence of sodium, and similar 1- and 2-hr equilibrium values. L-[3H]GLN transport in jejunal BBMVs was measured by a millipore filtration technique. Na(+)-dependent glutamine transport, which accounted for greater than 80% of total transport, was increased twofold in BBMVs from endotoxin-treated rats (67 +/- 5 pmole/mg protein/15 sec vs 38 +/- 3, P less than 0.01). Endotoxin treatment did not alter the activity of the Na(+)-independent carrier. Simultaneously, intestinal extraction of glutamine from the bloodstream fell by 56% (15.1 +/- 2.3% in controls vs 6.6 +/- 1.3% in endotoxin-treated rats, P less than 0.01). This reduction in the uptake of circulating glutamine could not be accounted for by a fall in the arterial concentration. Thus, soon after endotoxemia brush border glutamine uptake is increased while consumption of glutamine across the basolateral membrane is decreased. This increased uptake may support protein synthesis and may provide a biochemical rationale for the use of early enteral nutrition after the onset of critical illness.

Cytokine modulation of glutamine transport by pulmonary artery endothelial cells.

The effects of tumor necrosis factor and interleukin-1 on sodium-dependent glutamine transport by cultured pulmonary artery endothelial cells (PAECs) were studied. Incubation of PAECs with cytokines (10 to 1000 units/ml) resulted in a significant increase in System ASC-mediated glutamine transport that was dose-dependent, first observable after 8 hours, and maximal after 12 hours of exposure. Kinetic studies indicated that the increase in carrier-mediated activity was not due to a change in Km (transporter affinity) but instead to a 45% to 75% increase in maximal transport rate (Vmax). The cytokine-stimulated increase in glutamine uptake by PAECs was completely blocked by actinomycin D and cycloheximide, indicating that the accelerated glutamine transport was dependent on de novo RNA and protein synthesis, perhaps of the transporter itself. The data indicate that these cytokines accelerate glutamine uptake by PAECs, either directly or indirectly, a response which may be required to support endothelial metabolism, structure, and function during infection and inflammation. The results of this study represent, to our knowledge, the first reports of cytokine-mediated modulation of System ASC activity, a carrier that has historically been unresponsive to hormonal regulation in other tissues.

Glutamine metabolism by the endotoxin-injured lung.

The alterations in lung glutamine (GLN) metabolism that occurs in the endotoxin-injured lung were studied in rats and subsequently correlated with flux changes that occur in patients with the adult respiratory distress syndrome (ARDS). Measurements in animals were made at various time-points following the administration of endotoxin, while studies in surgical patients were done in a group of healthy controls, in patients with "early" sepsis who had normal chest x-ray films, and in patients with radiographic and physiologic evidence of ARDS. In healthy control rats, net amounts of GLN are released by the lungs into the systemic circulation. This release rate doubled 30 minutes after intravenous endotoxin (1,580 +/- 320 nmol GLN/100 g BW/min vs. 736 +/- 179 in controls, p less than 0.01) but glutamine synthetase activity was unchanged, suggesting an outpouring of cellular glutamine stores. Two hours after endotoxin treatment, this accelerated fractional release of glutamine by the lungs was no longer detected. By the 12-hour time-point, the lungs reversed to an organ of net glutamine balance (234 +/- 248 nmol/100 g BW/min, p less than 0.05 vs. controls and ENDO30 min) despite a more than two-fold increase in glutamine synthetase activity (p less than 0.01). Simultaneously, lung weights were increased by 21% (p less than 0.01) and histologic examination showed an interstitial infiltrate and pulmonary edema. Similar observations were made in humans; patients with "early" sepsis exhibited a marked increase in lung glutamine release, while patients with ARDS demonstrated glutamine balance across the lungs (4,030 +/- 910 nmol GLN/kg BW/min vs. 637 +/- 496 in ARDS, p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptive regulation of brush-border amino acid transport in a chronic excluded jejunal limb.

We examined the alterations in brush-border glutamine transport that occurred in a surgically defunctionalized jejunal limb excluded from mucosal food contact. Dogs were surgically prepared with Roux-en-Y gastrojejunostomies to permit same-intestine comparisons of glutamine transport and glutaminase activity in jejunal segments that were in incontinuity or excluded for a 6-mo period. Transport of glutamine, alanine, and glucose was measured in brush-border membrane vesicles prepared from each intestinal section; membrane marker enzymes were enriched to the same degree in incontinuity and excluded portions. The Na(+)-dependent glutamine cotransport apparent Km was the same in the excluded (779 +/- 63 microM) and incontinuity (873 +/- 105 microM) limbs. However, the Jmax for Na(+)-independent glutamine transport in the incontinuity jejunum (158.7 +/- 15.7 pmol.mg protein-1.s-1) was double that in the excluded limb (71.2 +/- 4.6 pmol.mg protein-1.s-1). Na(+)-dependent carrier-mediated glutamine transport rates were lower than the Na(+)-dependent system, but Na(+)-independent kinetic parameters were not significantly different in incontinuity vs. excluded limbs (Jmax 7.9 +/- 0.6 pmol.mg protein-1.s-1; Km 140 +/- 20 microM). Similarly, the passive diffusion permeability coefficient was the same for both excluded and incontinuity jejunal limbs (22.7 +/- 0.9 nl.mg protein-1.s-1). Mucosal glutaminase enzyme activity was increased by 28% in the incontinuity limb (4.32 +/- 0.21 vs. 3.36 +/- 0.35 mumol.mg protein-1.h-1; P less than 0.02). Transport rates of alanine and glucose were also diminished in the excluded limb (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Brush border transport of glutamine and other substrates during sepsis and endotoxemia.

The effects of severe infection on luminal transport of amino acids and glucose by the small intestine were investigated. Studies were done in endotoxin-treated rats and in septic patients who underwent resection of otherwise normal small bowel. In rats the kinetics of the brush border glutamine transporter and the glutaminase enzyme were examined. In patients the effects of severe infection on the transport of glutamine, alanine, leucine, and glucose were studied. Transport was measured using small intestinal brush border membrane vesicles that were prepared by Mg++ aggregation/differential centrifugation. Uptake of radiolabeled substrate was measured using a rapid mixing/filtration technique. Vesicles demonstrated 15-fold enrichments of enzyme markers, classic overshoots, transport into an osmotically active space, and similar 2-hour equilibrium values. The sodium-dependent pathway accounted for nearly 90% of total carrier-mediated transport. Kinetic studies on rat jejunal glutaminase indicated a decrease in activity as early as 2 hours after endotoxin secondary to a decrease in enzyme affinity for glutamine (Km = 2.23 +/- 0.20 mmol/L [millimolar] in controls versus 4.55 +/- 0.67 in endotoxin, p less than 0.03), rather than a change in Vmax. By 12 hours the decrease in glutaminase activity was due to a decrease in Vmax (222 +/- 36 nmol/mg protein/min in controls versus 96 +/- 16 in endotoxin, p less than 0.03) rather than a significant change in Km. Transport data indicated a decrease in sodium-dependent jejunal glutamine uptake 12 hours after endotoxin secondary to a 35% reduction in maximal transport velocity (Vmax = 325 +/- 12 pmol/mg protein/10 sec in controls versus 214 +/- 8 in endotoxin, p less than 0.0001) with no change in Km (carrier affinity). Sodium-dependent glutamine transport was also decreased in septic patients, both in the jejunum (Vmax for control jejunum = 786 +/- 96 pmol/mg protein/10 sec versus 417 +/- 43 for septic jejunum, p less than 0.01) and in the ileum (Vmax of control ileum = 1126 +/- 66 pmol/mg protein/10 sec versus 415 +/- 24 in septic ileum, p less than 0.001) The rate of jejunal transport of alanine, leucine, and glucose was also decreased in septic patients by 30% to 50% (p less than 0.01). These data suggest that there is a generalized down-regulation of sodium-dependent carrier-mediated substrate transport across the brush border during severe infection, which probably occurs secondary to a decrease in transporter synthesis or an increase in the rate of carrier degradation.(ABSTRACT TRUNCATED AT 400 WORDS)

Selective stimulation of brush border glutamine transport in the tumor-bearing rat.

Intestinal extraction of circulating glutamine across the basolateral membrane is diminished in the tumor-bearing rat (TBR). This study was designed to investigate the effects of progressive malignant growth on brush border glutamine transport in order to gain further insight into the adaptive/regulatory changes in intestinal glutamine metabolism that occur in the tumor-bearing rat. Fischer 344 rats (225 +/- 5 g) were implanted with fibrosarcoma cells and were studied at various time points after implantation when the tumors comprised 7%, 20%, and 29% of total body weight. Control and tumor-bearing rats were pair-fed throughout the study. Jejunal brush border membrane vesicles (BBMVs) were prepared by magnesium aggregation/differential centrifugation and transport of radioactively labeled L-glutamine, L-leucine, L-alanine, and D-glucose by BBMVs was measured using a Millipore filtration technique. BBMVs were enriched 15-fold in alkaline phosphatase, indicating brush border vesicle purity. Uptake of all substrates occurred into an osmotically active space, exhibited overshoots, and had similar 1-hr equilibrium values. The rate of glutamine uptake by BBMVs from all tumor-bearing rats was significantly greater than controls, regardless of tumor size. The increase in transport activity was not due to a change in carrier affinity but rather to an increase in maximal transport velocity. In rats with small tumors (7% of body weight), the Vmax was 431 +/- 40 pmole/mg protein/10 sec compared to 259 +/- 30 in control animals (P less than 0.01). In marked contrast, the mean transport of alanine was diminished in BBMVs from TBR (31 +/- 3 pmole/mg protein/10 sec in TBR vs 23 +/- 2 in controls, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Tumor regulation of hepatic glutamine metabolism.

Fast-growing tumors are major glutamine consumers and may alter host glutamine metabolism to benefit the tumor. Previous studies from our laboratory have demonstrated that the liver switches from an organ of glutamine balance to one of glutamine release with progressive malignant growth. However, the regulation of this change is unclear. This study examined tumor modulation of hepatic glutamine metabolism by determining the activities of glutaminase, the principle enzyme of glutamine degradation, and glutamine synthetase, the principal enzyme of glutamine synthesis. Hepatic glutamine content was also determined. Rats with a fast-growing subcutaneous fibrosarcoma (TBR) and pair-fed controls were studied at 2 and 3 weeks after tumor or sham implantation, when the tumors comprised approximately 5% and 20% of total body weight. Arterial glutamine fell with progressive tumor growth (608 +/- 26 mumol/L in controls vs 494 +/- 15 in TBR, p less than 0.005) and was not attributable to a diminished food intake. Hepatic glutamine content was increased 45% (p less than 0.01) in tumor rats at 2 weeks due in part to a 35% fall in liver glutaminase activity. At 3 weeks, glutamine synthetase activity increased by 43% (0.58 +/- 0.07 mumol/mg of protein/hr in controls vs 0.83 +/- 0.04 in TBR, p less than 0.01) whereas glutaminase remained depressed (2.68 +/- 0.12 mumol/mg of protein/hr in controls vs 2.22 +/- 0.15 in TBR, p less than 0.05) and glutamine content fell compared to 2 week tumor-bearing rats, consistent with accelerated hepatic glutamine release. Tumors may alter liver glutamine metabolism by modulating hepatic enzyme activity in order to provide circulating glutamine for the growing malignancy.

Role of the lungs in maintaining amino acid homeostasis.

The relative contributions of skeletal muscle and the pulmonary bed in maintaining amino acid homeostasis were studied. Inasmuch as more than 60% of whole blood amino acid nitrogen is transported as glutamine and alanine, the flux of these two amino acids across the lungs (n = 20) and hindquarter (n = 20) was determined in the postabsorptive adult rat. Both skeletal muscle and the lungs released net amounts of glutamine and alanine in the postabsorptive state. Blood flow to the hindquarter was approximately 16% of cardiac output (3.8 +/- 0.3 cc/100 g BW/min), while pulmonary blood flow (cardiac output) was 23.7 +/- 1.7 cc/100 g BW/min. Thus, despite a lower glutamine concentration difference across the lungs (-32 +/- 6 mumol/liter) compared with the hindquarter (-59 +/- 10 mumol/liter (p less than 0.01), the lungs released significantly more glutamine (741 +/- 142 nmol/100 g BW/min) than the hindquarter (208 +/- 39 nmol/100 g BW/min) (p less than 0.01) because of the significantly higher pulmonary blood flow. Similarly, the concentration difference for alanine across the lungs was less than that of the hindquarter (-24 +/- 8 mumol/liter vs -60 +/- 12 mumol/liter, p less than 0.01) but the lungs released significantly more alanine than the hindquarter (553 +/- 159 nmol/100 g BW/min vs 221 +/- 41 nmol/100 g BW, p less than 0.01. Compositional studies demonstrated that the hindquarter comprises 40% of total body muscle mass in the rat; thus both total skeletal muscle mass and the lungs contribute approximately equally to the maintenance of blood glutamine and alanine levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Glutamine nutrition: theoretical considerations and therapeutic impact.

In critically ill surgical patients, nutritional therapy is an important component of overall care. As our knowledge increases, "tailor-made" diets designed to meet specific nutritional requirements in specific patients may play an important role. Although the data reviewed here suggest that glutamine-supplemented diets may have a significant impact in some clinical settings, it should be emphasized that additional carefully designed studies are necessary before the use of glutamine-enriched nutrition in critically ill patients should be advocated. It is clear, however, that the concept that the intestine is an organ of inactivity during critical illness merits reconsideration.

Effects of glucocorticoids on lung glutamine and alanine metabolism.

The role of the glucocorticoid hormones as possible mediators of the accelerated lung glutamine and alanine release that occurs during critical illness was investigated. Studies were done in adult rats receiving dexamethasone (0.6 mg intramuscularly/100 gm body weight/day for 2 consecutive days; n = 24) or saline solution (controls; n = 20). Measurements were made in the postabsorptive state and amino acid flux was calculated by multiplying pulmonary blood flow by the right ventricular-arterial concentration difference for glutamine and alanine. Lung glutamine release was 703 +/- 184 nmol/100 gm body weight/min in control rats. This release rate doubled in the dexamethasone-treated rats (1476 +/- 256; p less than 0.05). The activity of the glutamine synthetase enzyme increased by 33% in the dexamethasone-treated animals and there was a 50% decrease in lung glutamine content (p less than 0.01). Likewise, dexamethasone accelerated the release of alanine by the lungs twofold (559 +/- 173 nmol/100 gm body weight/min in controls vs 1113 +/- 184 nmol/100 gm body weight/min in dexamethasone-treated rats; p less than 0.05). The increased release of both amino acids was caused by a significant increase in the concentration difference across the lungs and not a change in pulmonary blood flow. Glucocorticoids appear to be key mediators of the accelerated lung amino acid release that characterizes catabolic diseases.

Oral glutamine accelerates healing of the small intestine and improves outcome after whole abdominal radiation.

The healing effects of glutamine given orally for 8 days as a single amino acid nutrient after treatment with whole abdominal radiation (10 Gy) were studied. Rats received isonitrogenous and isovolumic diets containing 3% glutamine or 3% glycine. Control rats were not irradiated but were given identical diets. In irradiated animals, survival was 100% in animals receiving glutamine compared with 45% in animals receiving glycine. Glutamine ingestion diminished bloody diarrhea and the incidence of bowel perforation. Arterial glutamine level was higher in animals receiving glutamine in the diet, as were gut glutamine extraction (35% +/- 8% vs 12% +/- 7%) and intestinal glutaminase activity. These metabolic improvements were associated with a marked increase in villous height, villous number, and the number of mitoses per crypt in rats receiving glutamine. Glutamine was not beneficial in control nonirradiated animals. The data demonstrated that provision of oral glutamine after abdominal radiation supported gut glutamine metabolism, improved mucosal morphometrics, and decreased the morbidity and mortality associated with this abdominal radiation model.

Gut glutamine metabolism.

The gut plays a key role in interorgan glutamine metabolism in normal and catabolic states. During critical illness, the gut responds to prevailing metabolic pressures that may result in a temporary "reset" in interorgan glutamine flow. As the body recovers from the disease process, the alterations in gut glutamine metabolism revert to normal, which helps restore glutamine homeostasis. Overwhelming stresses, such as severe systemic infection, may lead to permanent organ dysfunction and further adaptive changes in glutamine metabolism.

Prophylactic glutamine protects the intestinal mucosa from radiation injury.

Glutamine may be an essential dietary component, especially for the support of intestinal mucosal growth and function. This study evaluated the effects of a glutamine-enriched elemental diet, administered before whole-abdominal radiation on gut glutamine metabolism, mucosal morphometrics, and bacterial translocation. Rats were randomized to receive a nutritionally complete elemental diet that was glutamine-enriched or glutamine-free for 4 days. The animals were then subjected to a single dose of 1000 cGy x-radiation to the abdomen. After irradiation, all animals received the glutamine-free diet. Four days later the animals underwent laparotomy for sampling of arterial and portal venous blood, culture of mesenteric lymph nodes, and removal of the small intestine for microscopic examination. There was no difference in arterial glutamine or gut glutamine extraction between the two groups, but body weight loss was significantly diminished in the glutamine-fed rats. Rats receiving the glutamine-enriched elemental diet before radiation had a significant increase in jejunal villous number, villous height, and number of metaphase mitoses per crypt. Scanning electron microscopy confirmed the presence of an intact gut epithelium in eight of eight rats receiving prophylactic glutamine compared to one of eight animals in the glutamine-free group. Three of eight rats fed glutamine had culture positive mesenteric lymph nodes compared with five of seven rats receiving the glutamine-free diet. Glutamine exerts a protective effect on the small bowel mucosa by supporting crypt cell proliferation effect on accelerate healing of the acutely radiated bowel.