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Biomedical subjects

R G Kilbourn

Publications and source records attributed to R G Kilbourn.

At least 37 records · Page 2Linked to original sources
PubMed1995

Phase I study of tumor necrosis factor plus actinomycin D in patients with androgen-independent prostate cancer.

Based on preclinical studies which reveal enhanced antitumor activity of tumor necrosis factor (TNF) when combined with actinomycin D in human prostate cancer cell lines, we performed a phase I clinical study combining TNF and actinomycin D. All patients had metastatic prostatic carcinoma exhibiting androgen-independent growth. Patients were treated with a combination of a short infusion of actinomycin D followed by a TNF infusion daily for five consecutive days. Soluble TNF receptor p60 was not modulated by treatment but p80 receptor increased significantly following treatment with a combination of TNF and actinomycin D (baseline median 3.4 ng/ml) range 2.5-6.6 ng/ml follow up (9.3 ng/ml) range 6-24 ng/ml. We concluded that the maximum tolerated dose of continuous infusion TNF and short infusion actinomycin D is 400 micrograms/m2 of actinomycin D and 400 micrograms/m2 of TNF. The increased soluble receptor isoform (p80) may account for the lack of clinical activity seen in this trial. Should these results be confirmed, a strategy focused on overcoming the upregulation of the TNF soluble receptor will be required before further study of TNF should be considered.

Aged↗
PubMed1995

NG-methyl-L-arginine, an inhibitor of nitric oxide synthase, reverses interleukin-2-induced hypotension.

OBJECTIVE: To evaluate the role of NG-methyl-L-arginine as a modulator of the hyperdynamic shock induced by the administration of interleukin-2 (IL-2). DESIGN: A prospective, pilot clinical study. SETTING: Intensive care unit of a tertiary care center. PATIENTS: Three sequential patients with metastatic renal cell carcinoma who developed hypotension during their first course of treatment with high-dose IL-2 (18 x 10(6) IU/m2/day by continuous infusion for 5 days). INTERVENTIONS: Upon developing hypotension during their subsequent therapy with IL-2, patients were administered 12 mg/kg of NG-methyl-L-arginine. Thereafter, a dose of 4 mg/kg was given every 4 hrs, as needed, to maintain the systolic blood pressure above 100 mm Hg. MEASUREMENTS AND MAIN RESULTS: Invasive hemodynamic monitoring was instituted before the initiation of treatment with IL-2. Differences noted before, and 15 mins after, the administration of NG-methyl-L-arginine were analyzed using the paired t-test. NG-methyl-L-arginine (12 mg/kg) induced a significant antihypotensive effect (mean blood pressure increased from 87 +/- 4 to 121 +/- 7 mm Hg), accompanied by an increase of the systemic vascular resistance (549 +/- 51 to 860 +/- 167 dyne.sec/cm5) and pulmonary vascular resistance (81 +/- 16 to 117 +/- 29 dyne.sec/cm5). A decrease in the cardiac index was also documented (4.5 +/- 0.5 to 3.6 +/- 0.3 L/min/m2). No significant changes in pulmonary artery occlusion and central venous pressures were observed. Maintenance doses of 4 mg/kg of NG-methyl-L-arginine induced similar hemodynamic results, although the duration of the antihypotensive effect of NG-methyl-L-arginine decreased with sequential doses. CONCLUSIONS: The hemodynamic effects induced by IL-2 administration are reversed by NG-methyl-L-arginine, a nitric oxide synthesis inhibitor. These results provide evidence for the biological activity of NG-methyl-L-arginine when administered alone to hypotensive patients. While no adverse effects were observed in this preliminary study, issues of toxicity and effectiveness need to be defined further in formal clinical trials. NG-methyl-L-arginine may play a therapeutic role in the modulation of the extreme vasodilation induced by cytokine administration or in septic shock.

Adult↗
PubMed1995

Characterization of the effects of two new arginine/citrulline analogues on constitutive and inducible nitric oxide synthases in rat aorta.

1. New potent inhibitors of nitric oxide synthase (NOS) may be useful in the treatment of septic shock, a disorder characterized by a vascular hyporeactivity to catecholamines caused by an overproduction of nitric oxide (NO-). We examined the effects of L-thiocitrulline (L-TC) and S-methyl-L-thiocitrulline (L-SMTC), novel NOS inhibitors, on the constitutive and inducible NOS in rat aorta and compared those effects with inhibition due to NG-methyl-L-arginine (L-NMA). 2. Phenylephrine evoked similar concentration-contraction curves in the control rings and in the rings treated with these different NOS inhibitors (10 microM), whereas 100 microM of L-NMA, L-TC or L-SMTC increased significantly, and to a similar extent, contractions evoked by phenylephrine in aortic rings with endothelium without significantly affecting the maximal responses. 3. Relaxations evoked by acetylcholine, adenosine triphosphate, or calcium ionophore were significantly inhibited in a dose-dependent manner by L-NMA, L-SMTC, or L-TC (10-100 microM). The potencies of these inhibitors in reducing the relaxations of these vasodilators were not significantly different. 4. In endotoxin-treated preparations with endothelium, the three L-arginine analogues (10 microM) significantly potentiated contractile responses to phenylephrine (pEC50: 6.73 +/- 0.12 and 7.3 +/- 0.12, 7.34 +/- 0.13, or 7.22 +/- 0.14; in the absence and the presence of L-NMA, L-TC, or L-SMTC respectively) and increased maximal contractions from 1.53 +/- 0.15 g to 1.95 +/- 0.13 g, 2.08 +/- 0.12 g, and 2.03 +/- 0.13 g with L-NMA, L-TC, and L-SMTC respectively. A higher concentration of these NOS inhibitors (100 microM)further increased contractions evoked by this alpha1-agonist without further enhancing the maximal contractions; however, contractions evoked by 10 nM phenylephrine were significantly greater in the presence of L-SMTC or L-TC than in the presence of L-NMA (100 microM) (L-NMA: 0.4 +/- 0.11 g; L-TC:0.78 +/- 0.14 g and L-SMTC: 0.82+/-0.17 g). The effects of these inhibitors on NO- synthesis induced by endotoxin were significantly reversed by addition of L-arginine (1 mM) but not by L-citrulline (1 mM). InLPS-treated rings with endothelium, all three NOS inhibitors (100 microM) shifted the concentration contraction curves evoked by phenylephrine significantly to the left (pEC5o: 7.19 +/- 0.03 and 7.79 +/- 0.08,8.01 +/- 0.07, or 8.02 +_ 0.07, in the absence and the presence of L-NMA, L-TC, or L-SMTC, respectively)and increased significantly maximal contractions from 2.05 +/- 0.05 g to 2.38 +/- 0.14 g, 2.5 +/- 0.12 g, and 2.4 +_ 0.21 g with L-NMA, L-TC, and L-SMTC, respectively. L-TC and L-SMTC were significantly more potent than L-NMA in potentiating contractions evoked by 10 nM and 30 nM phenylephrine.5. L-TC and L-SMTC produced dose-dependent increases in tone in LPS-treated aortic rings with and without endothelium. In LPS-treated rings with endothelium, L-NMA induced contractions but in preparations without endothelium low concentrations of L-NMA induced small contractions while high concentrations of this inhibitor evoked relaxations. In both preparations L-TC and L-SMTC were significantly more potent than L-NMA in increasing vascular tone.6. These results suggest that L-SMTC, L-TC and L-NMA were equipotent on basal and agonist stimulated NO- synthesis produced by the constitutive isoform of NOS, whereas the two new L-arginine analogues were more potent than L-NMA in inhibiting the production of NO- induced by endotoxin in rat aorta.

Acetylcholine↗
PubMed1995

Escalated MVAC with or without recombinant human granulocyte-macrophage colony-stimulating factor for the initial treatment of advanced malignant urothelial tumors: results of a randomized trial.

PURPOSE: Hematopoietic growth factors have been shown to ameliorate the side effects of chemotherapy. Here we assess the ability of recombinant human granulocyte-macrophage colony-stimulating factor (rhGM-CSF) to increase the dose-intensity and reduce the side effects of escalated methotrexate, vinblastine, doxorubicin, and cisplatin (MVAC) chemotherapy. PATIENTS AND METHODS: A prospective randomized trial to compare escalated MVAC versus escalated MVAC with rhGM-CSF was conducted. All patients were treated at The University of Texas M.D. Anderson Cancer Center (UTMDACC) and had a metastatic or unresectable urothelial tumor. Forty-eight patients were randomized (25 to MVAC with rhGM-CSF and 23 to escalated MVAC alone). The clinical characteristics of the study populations were similar (ie, degree of tumor dissemination and performance status). RESULTS: The dose-intensity in the two arms of the study did not differ significantly. No difference in the frequency of bacteriologically documented infections occurred between the two study arms. CONCLUSION: The use of the hematopoietic growth factor rhGM-CSF did not result in an increased dose-intensity of escalated MVAC. The inability to increase the dose-intensity of MVAC further was a result of nonhematologic side effects of the chemotherapy. Escalation of treatment delivered at its median-tolerated dose is unlikely to result in additional therapeutic benefit for patients with common solid tumors. Future development of therapy may require the development of new agents or concepts, rather than modification of existing therapies.

Adult↗
PubMed1994

Effects of NG-methyl-L-arginine, NG-nitro-L-arginine, and aminoguanidine on constitutive and inducible nitric oxide synthase in rat aorta.

A new selective inhibitor of the inducible nitric oxide synthase in the treatment of pathogenesis characterized by overproduction of nitric oxide may be useful. Therefore, we have examined the effects of two L-arginine analogues, NG-methyl-L-arginine (L-NMA) and NG-nitro-L-arginine (L-NNA), and aminoguanidine (AG) on the constitutive and inducible nitric oxide synthase in rat aorta. L-NNA induced greater contractions to phenylephrine than L-NMA whereas AG had no effect on dose-response curves to this alpha 1-agonist in rat aorta with endothelium. Relaxations to acetylcholine, adenosine triphosphate, and A 23187 were fully abolished by L-NNA, while L-NMA partially inhibited and AG did not affect the relaxations to these three vasodilators. L-NNA, L-NMA, and AG were equipotent in inhibiting the vascular hyporeactivity to phenylephrine induced by endotoxin in rat aortic rings with endothelium; however, the rate of onset of the maximum inhibitory effects of AG was slower than that obtained with L-NNA and L-NMA. L-arginine completely abolished the effects of AG, but only partially reversed the effects of L-NNA and L-NMA in LPS-treated rings. These results suggest that AG selectively inhibits inducible nitric oxide synthase, whereas L-NNA and L-NMA exert their effects on both the constitutive and inducible nitric oxide synthase.

Amino Acid Oxidoreductases↗
PubMed1994

Cell-free hemoglobin reverses the endotoxin-mediated hyporesponsivity of rat aortic rings to alpha-adrenergic agents.

Hemoglobin (Hbg) and lysates of red blood cells act as vasoconstrictors in isolated vessels by a mechanism that may involve nitric oxide (NO.) scavenging. To determine if such a mechanism indeed occurs, we investigated the effects of cell-free Hgb, modified Hgp (met Hgb and cyan met Hgb), and red blood cells on the formation of NO. induced by endotoxin in rat aorta. Incubation of rat aortic rings with endotoxin induced a delayed and prolonged release of NO. that resulted in a decrease in the contractile response to phenylephrine. Hgb significantly potentiated contractions to phenylephrine in control rings and also reversed the hyporeactivity to this alpha 1-agonist in endotoxin-treated rings with and without endothelium. Lysed red blood cells but not whole red blood cells shifted the concentration-contraction response curves to phenylephrine significantly to the right in endotoxin-treated preparations. Neither picket-fence porphyrin-albumin (PFP-albumin) or metheme-albumin affected the contractile response to phenylephrine. Oxidation of Hgb to met Hgb did not alter the contractions to an alpha 1-agonist in endotoxin-treated rings. In contrast, the formation of cyan met Hgb abolished the action of Hgb on the vascular reactivity of endotoxin-treated preparations. Together, these results demonstrate that free Hgb can scavenge NO. produced in endotoxin-treated vascular tissue and that the ability to bind NO. requires a cell-free form of Hgb with an intact heme center capable of undergoing redox reactions.

Adrenergic alpha-Antagonists↗
PubMed1994

Phase II trial of low dose gamma-interferon in metastatic renal cell carcinoma.

We conducted a phase II trial to confirm the activity of fixed, low dose gamma-interferon in metastatic renal cell carcinoma. A total of 35 patients with metastatic renal cell carcinoma, who had not received prior immunotherapy and who had a Zubrod performance status of 2 or less, was enrolled in this study. Primary tumors were controlled by nephrectomy or embolization before treatment began. gamma-Interferon was administered weekly as a subcutaneous injection at a fixed dose of 100 micrograms. Toxic effects were limited to low grade fever, chills and myalgias within 24 hours of injection. There were no incidences of grade 3 or 4 toxicity. Responses could be evaluated in 34 patients. There were 1 complete and 4 partial responses, for an objective response rate of 15% (95% confidence interval 5 to 32%). Durations of response to date are 21+, 17+, 13+, 9 and 2 months. We conclude that gamma-interferon is an active agent for metastatic renal cell carcinoma when administered according to this dose and schedule. The response rate compares favorably with those of alpha-interferon and interleukin-2, and toxicity is minimal. gamma-Interferon has excellent potential for use in combination with other biological or chemotherapeutic agents and in the adjuvant setting.

Adult↗
PubMed1994

Phase I study of interleukin-2 combined with interferon-alpha and 5-fluorouracil in patients with metastatic renal cell cancer.

Interferon-alpha (IFN-alpha) and interleukin-2 (IL-2) each has produced a 15%-20% response in metastatic renal cell cancer. Combining IFN-alpha with either IL-2 or 5-fluorouracil (5-FU) enhanced IFN-alpha activity. We have therefore conducted a Phase I Study combining IL-2, IFN-alpha, and 5-FU. The patients were continuously infused with IL-2 (1-3 x 10(6) u/m2) and 5-FU (600-750 mg/m2) for a 5-day period every 28 days, and IFN-alpha (4-5 x 10(6) u/m2) was injected subcutaneously daily. Lymphokine-activated killer (LAK) and natural killer (NK) cell activity was measured on days 0 and 8. Twenty-one patients received 76 courses. All primary tumors were controlled by surgery (81%) or angioinfarction. Hematologic toxicity was mild; median nadir of platelets was 117 K/microL and of granulocytes was 1.2 K/microL. Dose-limiting toxicity included mucositis, liver damage, and hypotension. No treatment-related death occurred, and only one patient required intensive-care-unit support. Two patients had an objective response, one of which was a complete response. Increased LAK cell and NK cell activity occurred at all IL-2 dose levels. Simultaneous delivery of IL-2, IFN-alpha, and 5-FU is safe and shows antitumor and biologic activity. 5-FU did not appear to suppress IL-2-induced LAK and NK cell activation. Maximum tolerated dose of the three-drug combination is IL-2, 2 x 10(6) u/m2, 5-FU 600 mg/m2, and IFN-alpha, 4 x 10(6) u/m2.

Adult↗
PubMed1994

NG-methyl-L-arginine, an inhibitor of nitric oxide formation, reverses IL-2-mediated hypotension in dogs.

The effects of NG-methyl-L-arginine (L-NMA), an inhibitor of nitric oxide formation, were studied in dogs treated with interleukin-2 (IL-2). The administration of IL-2 to dogs resulted in hypotension within 3 days of treatment. The development of hypotension correlated with accumulation in the serum of nitrate, which is a stable breakdown product of nitric oxide. Administration of L-NMA decreased serum nitrate levels and increased the mean arterial pressure. The antihypotensive effect was dose dependent with a maximum effect observed at a dose of 20 mg/kg. Administration of a continuous infusion of L-NMA (5 mg.kg-1.h-1) maintained the mean arterial pressure for 48 h with concurrent administration of IL-2. Evaluation of IL-2-induced lymphokine-activated killer cell proliferation and tumoricidal activity toward a canine glioblastoma target cell line was unaffected by L-NMA. These studies imply that L-NMA may effectively ameliorate the dose-limiting hypotension associated with administration of IL-2 without adversely affecting the antitumor effects.

Animals↗
PubMed1994

Cardiovascular effects of NG-methyl-L-arginine in chronically instrumented conscious dogs.

The cardiovascular effects of nitric oxide blockade were examined in five conscious chronically instrumented dogs. The hypothesis tested was that nitric oxide release plays a role in vascular tone and regional organ blood flow under physiological conditions. Aortic pressures; the first derivative of the left ventricular pressure; cardiac output (CO); heart rate; and carotid, coronary, renal, hepatic, and portal blood flows were recorded before and after bolus injection of 5, 10, and 20 mg/kg of NG-methyl-L-arginine (L-NMA). In response to L-NMA, mean arterial pressure increased by 7, 20, and 35%, respectively, in a dose-dependent manner, whereas CO decreased. CO reduction was sustained at the highest dose, whereas peripheral blood flows were not altered. These data suggest that blocking basal nitric oxide synthesis by administering L-NMA leads to a modest dose-dependent pressor response despite a marked and sustained reduction in CO recorded at the highest dose of L-NMA. Moreover, within our dose range, although the nitric oxide synthase inhibition provides a significant pressor response, it does not alter the resting carotid, coronary, renal, hepatic, and portal blood flows.

Amino Acid Oxidoreductases↗
PubMed1994

NG-methyl-L-arginine, an inhibitor of nitric oxide formation, acts synergistically with dobutamine to improve cardiovascular performance in endotoxemic dogs.

OBJECTIVE: To evaluate the hemodynamic effects of the nitric oxide inhibitor, NG-methyl-L-arginine, and dobutamine during experimental endotoxemia. DESIGN: Prospective, randomized, controlled animal study. SETTING: University research laboratory. SUBJECTS: Adult, male mongrel dogs. INTERVENTIONS: After catheterization with a flow-directed, thermal-dilution pulmonary artery flotation catheter and arterial catheter, awake dogs received either NG-methyl-L-arginine or dobutamine alone or in combination (controls; n = 5). Other animals were administered endotoxin (50 micrograms/kg), then received either NG-methyl-L-arginine alone or in combination with dobutamine after the onset of hypotension (endotoxin-treated; n = 5). MEASUREMENTS AND MAIN RESULTS: Both dobutamine and NG-methyl-L-arginine alone had a small, but significant vasopressor effect on control animals. In contrast, administration of the combination of NG-methyl-L-arginine and dobutamine resulted in a 48.6% increase in mean arterial pressure, an effect which was dose-dependent with respect to NG-methyl-L-arginine. In dogs treated with 50 micrograms/kg of endotoxin, hypotension could be only partially reversed by NG-methyl-L-arginine, mainly due to a decline in cardiac output. Co-infusion of dobutamine reversed this depression of cardiac output and resulted in a complete restoration of blood pressure. CONCLUSIONS: Later stages of septic shock are characterized by hypotension and decreased myocardial performance. A major mediator of hypotension is nitric oxide, a vasodilatory agent derived from L-arginine. Administration of the arginine derivative, NG-methyl-L-arginine, improved systemic vascular resistance but not myocardial performance. The addition of an inotropic agent to NG-methyl-L-arginine, a nitric oxide synthase inhibitor, resulted in an enhancement of the antihypotensive action of NG-methyl-L-arginine through the restoration of cardiac output. The synergistic action between dobutamine and NG-methyl-L-arginine may be of therapeutic value in the treatment of septic shock.

Animals↗
PubMed1992

Inhibition of interleukin-1-alpha-induced nitric oxide synthase in vascular smooth muscle and full reversal of interleukin-1-alpha-induced hypotension by N omega-amino-L-arginine.

BACKGROUND: Interleukin-1-alpha (IL-1) is a cytokine with potentially therapeutic immunoproliferative and tumoricidal activities. Preliminary clinical studies suggest that use of IL-1 may be restricted by dose-limiting hypotension. PURPOSE: The purpose of this study was to investigate the role of nitric oxide (NO.) as a possible mediator of this hypotension. METHODS: Cytokine-treated rat aortic smooth muscle cells were assayed for nitrite production, a stable breakdown product of nitric oxide. Nitric oxide synthase from smooth muscle cells was partially characterized in cytosol preparations using a novel Fe(2+)-myoglobin method to test for nitric oxide production. To determine the role of NO. on the immunorestorative and antineoplastic activity of IL-1, N omega-amino-L-arginine (NAA) or N omega-monomethyl-L-arginine (NMA), inhibitors of nitric oxide synthase, were added to either cultures of IL-1-dependent T cells or A375 melanoma cells exposed to IL-1. To investigate the effects of NAA in vivo, pentobarbital anesthetized dogs, which were made hypotensive by administration of IL-1, received a single intravenous bolus dose of NAA. The effects of NAA were then reversed by the administration of L-arginine. RESULTS: Our results show that cultured IL-1-activated rat aortic smooth muscle cells synthesize nitric oxide, a potent vasodilator. Induction of nitric oxide synthase is augmented by interferon-gamma and blocked by IL-1 receptor antagonist and by inhibitors of RNA or protein synthesis. Nitric oxide synthesis by IL-1-activated smooth muscle cells is inhibited by NAA, NMA, and N omega-nitro-L-arginine (NNA) with ED50 (i.e., effective dose for 50% inhibition) values of 20, 60, and 1000 microM, respectively; this rank order of inhibition is characteristic of an agonist-unregulated, inducible isoform of nitric oxide synthase. In smooth muscle cells, inhibition of NO. synthesis by NAA is reversed by excess L-arginine. Consistent with the induction of unregulated NO. synthesis in vascular smooth muscle in vivo, administration of IL-1 (50 micrograms/kg) to dogs caused a 33.5% decrease in systemic vascular resistance and a 28% decrease in blood pressure within 3 hours. Subsequent administration of NAA (20 mg/kg) rapidly and completely reversed the hypotension and increased systemic vascular resistance; these effects of NAA were reversed by L-arginine. Neither the immunoproliferative nor the tumoricidal activity of IL-1 was diminished by NAA. CONCLUSIONS: Our results indicate that (a) vascular smooth muscle is a likely source as well as a target of IL-1-induced NO. synthesis, causing vasodilatation and hypotension, (b) nitric oxide synthase inhibitors can fully reverse this hypotension, and (c) the therapeutically useful properties of IL-1 are not diminished by nitric oxide synthase inhibitors. IMPLICATIONS: Administration of inhibitors of nitric oxide synthase can reverse the pathological cardiovascular effects of IL-1 at concentrations that do not interfere with the potentially useful immunoproliferative or tumoricidal effects of this cytokine. In the context of the current clinical trials of IL-1, this finding would represent a very significant advantage.

Amino Acid Oxidoreductases↗
PubMed1991

Cytokine-activated endothelial cells express an isotype of nitric oxide synthase which is tetrahydrobiopterin-dependent, calmodulin-independent and inhibited by arginine analogs with a rank-order of potency characteristic of activated macrophages.

We have previously reported that cultured murine brain endothelial cells (MBE) produce large quantities of nitric oxide (NO) after activation with interferon-gamma in combination with any of several immunoactivators including: bacterial endotoxin, tumor necrosis factor and interleukin-1. Since endothelial cells are the first example of a cell-type which may possess both a constitutive and an inducible type of NO synthase, it was of interest to compare the requirements of these two enzyme activities. Induction of NO synthesis in MBE by cytokines was abolished by the protein synthesis inhibitor, cycloheximide, and by 2,4-diamino-6-hydroxypyridine (DAHP), a selective inhibitor of GTP cyclohydrolase I, the rate-limiting enzyme for de novo synthesis of tetrahydrobiopterin (THB). In the presence of DAHP, NO synthesis was restored by sepiapterin (SEP), a substrate for the alternative pathway of THB synthesis occurring via pterin salvage. Moreover, SEP increased NO synthesis to greater than 150% of control values, suggesting that THB availability is rate-limiting for NO synthesis by cytokine-induced MBE. Methotrexate, an inhibitor of the pterin salvage pathway of THB synthesis, completely reversed the stimulation of NO synthesis by sepiapterin. Thus, cytokine-induced MBE NO synthase appears to have an absolute requirement for THB as cofactor. In additional studies we found that NO synthesis by cytokine-activated MBE was inhibited by NG-monosubstituted arginine analogs with a rank-order of potency NH2 greater than CH3 greater than NO2, in contrast with the rank-order of NO2 greater than NH2 greater than CH3 previously described for inhibition of the constitutive endothelial cell enzyme. Using a kinetic assay for NO synthase activity, based on oxidation of myoglobin heme-iron, we have found that these rank orders of potency also apply to cytosol preparations of cytokine-induced and untreated endothelial cells, respectively. Further differences between constitutive and cytokine-induced NO synthase were observed with regard to calmodulin requirements. Whereas constitutive NO synthase was potently inhibited by the calmodulin antagonists mellitin and trifluoperazine, cytokine-induced NO synthase was unaffected. In summary, NO synthesis by cytokine-activated MBE is THB-dependent, calmodulin-independent and inhibited by NG-substituted arginine analogs with a rank-order profile distinct from that for untreated endothelial cells but identical to that for cytokine-activated macrophages.

Amino Acid Oxidoreductases↗
PubMed1991

Role of nitric oxide in lysis of tumor cells by cytokine-activated endothelial cells.

The purpose of these studies was to determine whether nitric oxide produced by cytokine-activated murine lung vascular endothelial cells plays a role in their lytic destruction of M-5076 reticulum cell sarcoma. Vascular endothelial cells harvested from perfused lungs of mice were adapted to grow in culture. Cloned lines ascertained to be of endothelial origin were incubated in vitro with interferon gamma and tumor necrosis factor. Lysis of radiolabeled tumor cells and accumulation of nitrite in the culture medium were determined at several time points. The concentration of nitrite in the culture medium directly correlated with endothelial cell-mediated tumor cell lysis. Endothelial cells cultured in L-arginine-free medium did not produce significant tumor cell lysis nor accumulation of nitrite in the medium. Both tumor cell lysis and nitrite accumulation were observed when the deficient medium was reconstituted with L-arginine, suggesting that endothelial cell-mediated tumor lysis was dependent on L-arginine, a precursor of nitric oxide. Moreover, specific inhibition of nitric oxide synthesis by NG-methyl-L-arginine resulted in complete inhibition of endothelial cell-mediated lysis of the M-5076 reticulum cell sarcoma. Similarly, treatment of cytokine-activated endothelial cells with dexamethasone inhibited both target cell lysis and production of nitrite. Collectively, these results suggest that nitric oxide plays a major role in the lysis of tumor cells mediated by cytokine-activated endothelial cells.

Animals↗