Cytotoxic triterpenoid saponins from the fruits of Aesculus pavia L

Continued chemical investigation on the fruits of North American Aesculus pavia L. resulted in the isolation and identification of 13 polyhydroxyoleanene pentacyclic triterpenoid saponins, named aesculiosides IIe-IIk (1-7), and IIIa-IIIf (8-13), together with 18 known compounds: aesculiosides Ia-Ie (14-18), IIa-IId (19-22), IVa-IVc (23-25), 3-O-[beta-D-galactopyranosyl(1-->2)]-alpha-L-arabinofuranosyl(1-->3)-beta-D-glucuronopyranosyl-21,22-O-diangeloyl-3beta,15 alpha,16 alpha,21 beta,22 alpha,28-hexahydroxyolean-12-ene (26), 3-O-[beta-D-glucopyranosyl(1-->2)]-alpha-L-arabinofuranosyl(1-->3)-beta-D-glucuronopyranosyl-21,22-O-diangeloyl-3beta,16 alpha,21 beta,22 alpha,24 beta,28-hexahydroxyolean-12-ene (27), 3-O-[beta-D-galactopyranosyl(1-->2)]-alpha-L-arabinofuranosyl(1-->3)-beta-D-glucuronopyranosyl-21,22-O-diangeloyl-3beta,16 alpha,21 beta,22 alpha,28-pentahydroxyolean-12-ene (28), R(1)-barrigenol (29), scopolin (30), and 5-methoxyscopolin (31). The structures of these compounds were elucidated by spectroscopic and chemical analyses. Compounds 14-22 and 26-28 were tested in vitro for their activity against 59 cell lines from nine different human cancers including leukemia, non-small cell lung, colon, CNS, melanoma, ovarian, renal, prostate, and breast. It was found that compounds with two-acyl groups at C-21 and C-22 had cytotoxic activity for all cell lines tested with GI(50) 0.175-8.71 microM, while compounds without acyl groups at C-21 and C-22 had weak or no cytotoxic activity. These results suggest that the acyl groups at C-21 and C-22 are essential for their activity.     

Steroidal saponins and cytoxicity of the wild edible vegetable-Smilacina atropurpurea

Four new steroidal saponins, smilacinoside A (1), B (2), C (3), and D (4), together with three known saponins, funkioside D (5), aspidistrin (6) and 26-O-beta-d-glucopyranosyl-22-methoxyl-(25R)-furost-5-en-3beta,26-diol 3-O-beta-d-glucopyranosyl-(1-->2)-beta-d-glucopyranosyl-(1-->4)-beta-d-galactopyranoside (7) were isolated from the dried tender aerial parts of Smilacina atropurpurea (Franch.) Wang et Tang. The structures of new compounds were elucidated as diosgenin 3-O-alpha-l-rhamnopyranosyl-(1-->2)-O-beta-d-galactopyranoside (1), diosgenin 3-O-alpha-l-rhamnopyranosyl-(1-->3)-[6-O-palmitoxyl]-O-beta-d-galactopyranoside (2), 26-O-beta-d-glucopyranosyl-(25R)-furost-5-en-3beta,22xi,26-triol 3-O-alpha-l-rhamnopyranosyl-(1-->2)}-beta-d-galactopyranoside (3) and 26-O-beta-d-glucopyranosyl-22-methoxyl-(25R)-furost-5-en-3beta,26-diol 3-O-alpha-l-rhamnopyranosyl-(1-->2)-beta-d-galactopyranoside (4) on the basis of chemical methods and detailed spectroscopic analysis, including 1D and 2D NMR techniques and single-crystal X-ray diffraction, respectively. Six of these compounds and MeOH extract were tested for their in vitro cytotoxicity toward K562 human tumor cells by an improved MTT method. Smilacinoside A, funkioside D and aspidistrin exhibited significant in vitro cytotoxicity against K562 with IC(50) values of 1.09, 2.93 and 0.47microg/mL, respectively.     

Synthesis, in vitro anti-inflammatory and cytotoxic evaluation, and mechanism of action studies of 1-benzoyl-β-carboline and 1-benzoyl-3-carboxy-β-carboline derivatives

In the present study, various 1-substituted and 1,3-disubstituted β-carboline derivatives were synthesized by a modified single-step Pictet-Spengler reaction. The compounds were examined for cytotoxicity and anti-inflammatory activity, as measured by the inhibition of prostaglandin E(2) (PGE(2)) production and nitric oxide (NO) production. While only two compounds (28 and 31) showed marginal cytotoxicity against four human cancer cell lines, most of the tested compounds exhibited potent inhibitory activity of both NO and PGE(2) production. Moreover, compounds 6 and 16 significantly reduced the expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase 2 (COX2), suggesting that β-carboline analogs can inhibit NO and PGE(2) production at the translational level. In addition, several of the β-carboline derivatives (1, 2, 4-8, 11, 13, 22, 25, 27, 31, and 41-43) displayed significant inhibitory activity of superoxide anion (O(2)(·-)) generation or elastase release compared to the reference compound, with 6 being the most potent. N-Formyl-L-methionyl-phenylalanine (FMLP)-induced phosphorylation of c-JunN-terminal kinase (JNK) and protein kinase B (AKT) were also inhibited by 6, suggesting that it suppresses human neutrophil functions by inhibiting the activation of JNK and AKT signaling pathways. Therefore, the synthetic 1-benzoyl-3-carboxy β-carboline analogs may have great potential to be developed as anti-inflammatory agents.     

Synthesis and biological activity of (22E,25R)- and (22,25S)-22-dehydro- 1 alpha,25-dihydroxy-26-methylvitamin D3

Both 25-epimers of (22E)-22-dehydro-1 alpha,25-dihydroxy-26-methylvitamin D3 [22-dehydro-26-methyl-1,25-(OH)2D3] were synthesized. The biological activity of these compounds was tested in binding affinity to chick intestinal receptor protein of 1 alpha,25-dihydroxy-vitamin D3 [1,25-(OH)2D3] and in stimulating for intestinal calcium transport and bone calcium mobilization with vitamin D-deficient rats. The relative potency of (25R)- and (25S)-22-dehydro-26-homo-1,25-(OH)2D3 and 1,25-(OH)2D3 in competing for the intestinal cytosolic binding was 1.7:1.5:1. A similar order of activity was observed on intestinal calcium transport and bone calcium mobilization. In the ability for stimulation of intestinal calcium transport, (25R)- and (25S)-22-dehydro-26-methyl-1,25-(OH)2D3 were about 3.6 and 2.1 times as active as 1,25-(OH)2D3, respectively. In bone calcium mobilization tests, (25R)- and (25S)-22-dehydro-26-methyl-1,25-(OH)2D3 were estimated to be 2.2 and 1.6 times as potent as 1,25-(OH)2D3, respectively.     

旋花茄新鲜果实中的三个甾体皂苷

从茄科食用植物旋花茄(Solanum spirde)的新鲜果实中分离得到3个化合物,其中一个为新成分,经现代波谱学方法鉴定为26-0-β-D-葡萄吡喃糖基-(25R)-呋甾-3β,22ξ,26-三醇-5-烯-3-0-α-L-鼠李吡喃糖基-(1-2)-[3-0-(3-O-乙酰基)-α-L-鼠李吡喃糖基-(1-4)]-β-D-葡萄吡喃糖苷(1).2个已知化合物分别为26-O-β-D-葡萄吡喃糖基-(25R)-呋甾-22ξ-甲氧基-3β,26-二醇-5-烯-3-O-α-L-鼠李吡哺糖基-(1-2)-β-D-葡萄吡喃糖苷(2)和26-O-β-D-葡萄吡喃糖基-(25R)-呋甾-3β,22ξ,26-三醇-5-烯-3-O-α-L-鼠李吡喃糖基-(1-2)-[α-L-鼠李吡喃糖基-(1-4)]-β-D-葡萄吡喃糖苷(protodioscin)(3),均为首次从该植物中分离得到.     

Three new polyhydroxysteroids from the tropical starfish Asteropsis carinifera

Thirteen steroidal compounds including three new polyhydroxysteroids, (24R,25S)-24-methyl-5α-cholestane-3β,6α,8,15β,16β,26-hexaol, (22E,24R,25S)-24-methyl-5α-cholest-22-ene-3β,6α,8,15β,16β,26-hexaol and (22E,24R,25S)-24-methyl-5α-cholest-22-ene-3β,4β,6α,8,15β,16β,26-heptaol, have been isolated along with the previously known ten polyhydroxysteroids from the tropical starfish Asteropsis carinifera collected near the coast of Vietnam. The structures of new compounds were elucidated by spectroscopic methods (mainly 2D NMR and ESI-mass-spectrometry).     

Steroidal glycosides from the bulbs of Lilium dauricum.

The bulbs of Lilium dauricum yielded 11 compounds, including six new steroidal glycosides. The structures have been determined by spectral analysis and hydrolysis to be (25R,26R)-26-methoxyspirost-5-en-3 beta-ol 3-O-alpha-L-rhamnopyranosyl-(1----2)-O-[alpha-L-arabinopyranosyl-( 1----3)]- beta-D-glucopyranoside, (25R,26R)-26-methoxyspirost-5-en-3 beta-ol 3-O-alpha-L-rhamnopyranosyl-(1----2)-O-[beta-D-glucopyranosyl-(1----4)]- beta-D-glucopyranoside, (25R)-spirost-5-en-3 beta-ol (diosgenin) 3-O-alpha-L-rhamnopyranosyl-(1----2)-O-[alpha-L-arabinopyranosyl- (1----3)]-beta-D-glucopyranoside, (25R)-3 beta,17 alpha-dihydroxy-5 alpha-spirostan-6-one 3-O-alpha-L-rhamnopyranosyl-(1----2)-beta-D-glucopyranoside, (25R)-3 beta, 17 alpha-dihydroxy-5 alpha-spirostan-6-one 3-O-alpha-L-rhamnopyranosyl-(1----2)-O-[alpha-L- arabinopyranosyl-(1----3)]-beta-D-glucopyranoside and (20R,22R)-3 beta,20,22-trihydroxy-5 alpha-cholestan-6-one (tenuifoliol) 3-O-alpha-L-rhamnopyranosyl-(1----2)-beta-D-glucopyranoside. The absolute configurations of C-20 and C-22 of tenuifoliol were further confirmed by detailed analysis of the NOE difference spectrum of the corresponding isopropylidene derivative. Several known compounds were also isolated and identified.     

Synthesis and anticancer evaluation of thiazolyl-chalcones

Thirty-seven (E)-1-(4-methyl-2-arylaminothiazol-5-yl)-3-arylprop-2-en-1-ones were synthesized via Claisen-Schmidt condensation of 1-(4-methyl-2-(arylamino)thiazol-5-yl)ethanone with the corresponding arylaldehydes. All these thiazolyl-chalcones were characterized and evaluated by MTT assay on human cancer cell lines BGC-823, PC-3, NCI-H460, BEL-7402 in vitro. Compounds 5, 8, 26, 37 and 41 are effective against cancer cell lines with IC(50)s below 10 μM. The antitumor activity in ICR mice bearing sarcoma 180 tumors indicates compounds 10 and 41 have moderate in vivo activity with 22-25% tumor-weight inhibition.     

Cytotoxic heterocyclic triterpenoids derived from betulin and betulinic acid

The aim of this work was to synthesize a set of heterocyclic derivatives of lupane, lup-20(29)-ene, and 18α-oleanane, and to investigate their cytotoxic activities. Some of those heterocycles were previously known in the oleanane (allobetulin) group; however, to our knowledge the syntheses and biological activities of lupane heterocycles have not been reported before. Starting from betulin (1) and betulinic acid (2), we prepared 3-oxo compounds and 2-bromo-3-oxo compounds 3-10, 2-hydroxymethylene-3-oxo compounds 11-13 and β-oxo esters 14-16. Condensation of these intermediates with hydrazine, phenylhydrazine, hydroxylamine, or thiourea yielded the pyrazole and phenylpyrazole derivatives 17-22, pyrazolones 23-25, isoxazoles 26 and 27, and thiazoles 28-31. Fifteen compounds (14-16, 18-25, and 29-32) have not been reported before. The cytotoxicity was measured using panel of seven cancer cell lines with/without MDR phenotype and non tumor MRC-5 and BJ fibroblasts. The preferential cytotoxicity to cancer cell lines, particularly to hematological tumors was observed, the bromo acids 5, 6 showed highest activity and selectivity against tumor cells.     

Synthesis and antitumor activity of icogenin and its analogue

Natural saponin icogenin, namely 25(S)-22-O-methyl-furost-5-en-3beta,26-dio-3-O-alpha-L-rhamnopyranosyl-(1-->2)-[beta-D-glucopyranosyl-(1-->3)]-beta-D-glucopyranoside, and one of its analogues, 25(S)-22-O-methyl-furost-5-en-3beta,26-dio-3-O-alpha-L-rhamnopyranosyl-(1-->2)-[beta-D-glucopyranosyl-(1-->3)]-alpha-D-glucopyranoside, were first synthesized via line strategy and convergent approach, respectively. It was observed that icogenin and its analogue show potent antitumor activity in vitro.     

Polysaccharides from Astragalus membranaceus promote phagocytosis and superoxide anion (O2-) production by coelomocytes from sea cucumber Apostichopus japonicus in vitro

The potential immunostimulatory effects of Astralagus membranaceus polysaccharides (APS) on sea cucumber, Apostichopus japonicus (Selenka), were investigated in vitro. Phagocytosis and superoxide anion (O(2)(-)) production by phagocytic amoebocytes (PA) from A. japonicus coelomic fluid were measured during incubation at 18 degrees C, 22 degrees C, or 25 degrees C with APS at 0, 10, 20, or 40 microg mL(-1) (n=3). Phagocytic activity against yeast cells was quantified by direct visualization, and O(2)(-) production by nitroblue tetrazolium (NBT) reduction assay. Compared with controls, including APS at 20 microg mL(-1) significantly increased (P<0.05) the percentage of phagocytic capacity (PC) and phagocytic index (PI) at 18 degrees C and 22 degrees C, but no significant enhancement was observed at 25 degrees C. In contrast, the coelmocytes of A. japonicus can have an obvious generation of O(2)(-) after the stimulation. The concentration of 20 microg mL(-1) APS resulted in a significant increase in nitroblue tetrazolium (NBT) positive cells (P<0.05) at different temperature and even 10 microg mL(-1) APS could increase O(2)(-) generation significantly at 18 degrees C and 22 degrees C. Both phagocytosing and O(2)(-) production increased with the increase of APS concentration from 0 to 20 microg mL(-1) at different temperature, and when APS at 40 microg mL(-1), they were decreased. It suggested that immunocytes activity in A. japonicus decreased with the temperature increasing from 18 degrees C to 25 degrees C, and APS could be an effective immunostimulant to enhance phagocytic activity and O(2)(-) production.     

An efficient, convenient synthesis of novel medium-sized 13H-dibenzo[d,h][1,3,7]oxadiazecine-8,14-dione macrolides as anticipated antineoplastic agents

A series of novel medium-sized 13H-dibenzo[d,h][1,3,7]oxadiazecine-8,14-dione macrolides (18-27, 30, 32) were synthesized in an ongoing effort to develop new antineoplastic agents. The synthon 2-(2-aminobenzoylamino)-benzoic acid (7), for preparation of the target compounds, was prepared via the reaction of isatoic anhydride 5 and anthranilic acid 6. Nine compounds (18-20, 24-27, 30, 32) were subjected to National Cancer Institute (NCI) in vitro disease-oriented human cells screening panel assay. Among the compounds tested, 6-benzyl-13H-dibenzo[d,h][1,3,7]oxadiazecine-8,14-dione (26, NSC 721327), bearing the benzyl group at position 6, showed cytotoxic activity and subpanel selectivity against leukemia (CCRF-CEM), colon (HCC-2998), CNS (SNB-75) and melanoma (UACC-257) panels at log(10) GI(50) (M), compound concentration that inhibits 50% of cell growth, ranging from -4.08 to -4.59.     

Potential inhibitors of angiogenesis. Part I: 3-(imidazol-4(5)-ylmethylene)indolin-2-ones

The synthesis and pharmacological evaluation of new 3-(imidazol-4(5)-ylmethylene)indolin-2-ones, analogues of SU-5416, are reported. The final compounds 20-51 were obtained by Knoevenagel coupling between the substituted indolin-2-ones 1-15 and either the formylimidazole derivatives 16-18 or 2-formyl-3,5-dimethylpyrrole 19. Methylation at the nitrogen atom of the indolin-2-one and/or imidazole moities was carried out in the presence of the couple NaH/DMF. A Mannich reaction afforded the 1-dimethylaminomethyl derivatives 43 and 48. The antiangiogenic activity of these compounds was evaluated in a three dimensional in vitro rat aortic ring assay. In this test, compound 20 induced a decrease of angiogenesis comparable to that observed with SU-5416; the vascular density indexes at 1 microM were 30 +/- 18 and 22 +/- 4% of control, respectively. The compounds were also evaluated, in an independent manner, as inhibitors of the human EGF-receptor tyrosine kinase activity. As expected, only minor activities were observed with four compounds, out of thirty-one, exerting inhibitory effects in the range of 40-55% at 10 microM concentration.     

Synthesis, structural elucidation, DNA-PK inhibition, homology modelling and anti-platelet activity of morpholino-substituted-1,3-naphth-oxazines

A number of new angular 2-morpholino-(substituted)-naphth-1,3-oxazines (compound 10b), linear 2-morpholino-(substituted)-naphth-1,3-oxazines (compounds 13b-c), linear 6, 7 and 9-O-substituted-2-morpholino-(substituted)-naphth-1,3-oxazines (compounds 17-22, 24, and 25) and angular compounds 14-16 and 23 were synthesised. The O-substituent was pyridin-2yl-methyl (15, 18, and 21) pyridin-3yl-methyl (16, 19, and 22) and 4-methylpipreazin-1-yl-ethoxy (23-25). Twelve compounds were tested for their inhibitory effect on collagen induced platelet aggregation and it was found that the most active compounds were compounds 19 and 22 with IC(50)=55±4 and 85±4 μM, respectively. Furthermore, the compounds were also assayed for their ability to inhibit DNA-dependent protein kinase (DNA-PK) activity. The most active compounds were 18 IC(50)=0.091 μM, 24 IC(50)=0.191 μM, and 22 IC(50)=0.331 μM. Homology modelling was used to build a 3D model of DNA-PK based on the X-ray structure of phosphatidylinositol 3-kinases (PI3Ks). Docking of synthesised compounds within the binding pocket and structure-activity relationships (SAR) analyses of the poses were performed and results agreed well with observed activity.     

Endocardial endothelium in the avascular frog heart: role for diffusion of NO in control of cardiac O2 consumption

We investigated the role of nitric oxide (NO) in the control of myocardial O(2) consumption in the hearts of female Xenopus frogs, which lack a coronary vascular endothelium and in which the endocardial endothelium is the only source of NO to regulate cardiac myocyte function. Hence, frogs are an ideal model in which to explore the role of diffusion of NO from the endocardial endothelium (EE) without vascular endothelial or cardiac cell NO production. In Xenopus hearts we examined the regulation of cardiac O(2) consumption in vitro at 25 degrees C and 37 degrees C. The NO-mediated control of O(2) consumption by bradykinin or carbachol was significantly (P < 0.05) lower at 25 degrees C (79 +/- 13 or 73 +/- 11 nmol/min) than at 37 degrees C (159 +/- 26 or 201 +/- 13 nmol/min). The response to the NO donor S-nitroso-N-acetyl penicillamine was also markedly lower at 25 degrees C (90 +/- 8 nmol/min) compared with 37 degrees C (218 +/- 15 nmol/min). When Triton X-100 was perfused into hearts, the inhibition of myocardial O(2) consumption by bradykinin (18 +/- 2 nmol/min) or carbachol (29 +/- 4 nmol/min) was abolished. Hematoxylin and eosin slides of Triton X-100-perfused heart tissue confirmed the absence of the EE. Although endothelial NO synthase protein levels were decreased to a variable degree in the Triton X-100-perfused heart, NO(2) production (indicating eNOS activity) decreased by >80%. It appears that the EE of the frog heart is the sole source of NO to regulate myocyte O(2) consumption. When these cells are removed, the ability of NO to regulate O(2) consumption is severely limited. Thus our results suggest that the EE produces enough NO, which diffuses from the EE to cardiac myocytes, to regulate myocardial O(2) consumption. Because of the close proximity of the EE to underlying myocytes, NO can diffuse over a distance and act as a messenger between the EE and the rest of the heart to control mitochondrial function and O(2) consumption.     

Novel vitamin D3 derivatives, 26-homo-delta 22-dehydro-1 alpha,25(S)-dihydroxyvitamin D3 and 26-homo-delta 22-dehydro-1 alpha,25(R)-dihydroxyvitamin D3: preferential activity in c-myc mRNA production and in induction of phenotypic differentiation of HL-60 cells

Novel vitamin D3 derivatives, 26-homo-delta 22-1 alpha,25(S)-dihydroxyvitamin D3 and 26-homo-delta 22-1 alpha,25(R)-dihydroxyvitamin D3 were compared with the native hormone, 1,25-dihydroxyvitamin D3, and with other vitamin D3 derivatives, in inhibition of cell growth, induction of phenotypic differentiation, and c-myc mRNA reduction of HL-60 cells. The degree of inhibition in cell growth caused by 26-homo-delta 22-1 alpha,25(S)-(OH)2D3 was the greatest followed by 26-homo-delta 22-1 alpha,25(R)-(OH)2D3. The ability to reduce NBT was parallel to that to inhibit cellular proliferation. 26-homo-delta 22-1 alpha,25(S)-(OH)2D3, 26-homo-delta 22-1 alpha,25(R)-(OH)2D3, 24-homo-24-F2-1 alpha,25-(OH)2D3, and 1 alpha,24(R)-(OH)2-26-Cl-D3 were more active than 1 alpha,25-(OH)2D3 in the induction of OK-M1+ and OK-Mo-2+ HL-60 cells. Using two color flow cytometric analysis, the percentages of OK-M5(+)- and OK-DR(+)-HL-60 cells were 33% in the treatment with 26-homo-delta 22-1 alpha,25(S)-(OH)2D3 plus interferon-gamma (IFN-gamma) but 14% in the treatment with 1 alpha,25-(OH)2D3 plus IFN-gamma. 26-Homo-delta 22-1 alpha,25(S)-(OH)2D3 has an inhibitory effect on c-myc reduction in treated HL-60 cells. These results suggest that the novel vitamin D3 derivatives, 26-homo-delta 22-1 alpha,25(S)-(OH)2D3 and 26-homo-delta 22-1 alpha,25(R)-(OH)2D3, have preferential activity in inducing phenotypic differentiation and in inducing cell proliferation related c-myc mRNA activity.     

The Reaction Rates of NO with Horseradish Peroxidase Compounds I and II

In this study the reactions between nitric oxide (NO) and horseradish peroxidase (HRP) compounds I and II were investigated. The reaction between compound I and NO has biphasic kinetics with a clearly dominant initial fast phase and an apparent second-order rate constant of (7.0 +/- 0.3) x 10(5) M(-1) s(-1) for the fast phase. The reaction of compound II and NO was found to have an apparent second-order rate constant of k(app) = (1.3 +/- 0.1) x 10(6) M(-1) s(-1) or (7.4 +/- 0.7) x 10(5) M(-1) s(-1) when measured at 409 nm (the isosbestic point between HRP and HRP-NO) and 419 nm (lambda(max) of compound II and HRP-NO), respectively. Interestingly, the reaction of compound II with NO is unusually high relative to that of compound I, which is usually the much faster reaction. Since horseradish peroxidase is prototypical of mammalian peroxidases with respect to the oxidation of small substrates, these results may have important implications regarding the lifetime and biochemistry of NO in vivo after inflammation where both NO and H(2)O(2) generation are increased several fold.     

L-DOPA produced nitric oxide in the vitreous and caused greater vasodilation in the choroid and the ciliary body of melanotic rats than in those of amelanotic rats

The nitrogen cycle initiates direct reduction of N2 to NH3 by enzymatic reactions. We hypothesize that L-dihydroxyphenylalanine (L-DOPA), a catecholamine, could be a source of nitric oxide (NO). In order to determine whether L-DOPA generates NO and induces any biological change in the eye, we measured the generation of NO in vitro and in vivo, and investigated the histopathological changes caused by injection of L-DOPA into the vitreous of rats. We also hypothesized that melanin granules may affect the generation of NO during the metabolism of L-DOPA, since L-DOPA is a precursor of melanin in the brain and the eye. Therefore, we compared the effects of L-DOPA on the generation of NO between amelanotic and melanotic rats. NO was measured as diffusion currents by NO electrodes. In vitro, various concentrations of L-DOPA (5, 29.9, 79.4, 152.7, and 249 microM) were added to the medium. The inhibition of NO generation by 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazole-1-oxyl 3-oxide (carboxy-PTIO) was tested. In vivo, NO generation in the vitreous of rats was measured and the eyes were enucleated under anesthesia after L-DOPA injection. The ocular tissues were subjected to histological examination. NO was produced from L-DOPA in a dose-dependent manner and was scavenged by carboxy-PTIO in vitro. NO in the vitreous of melanotic rats was generated from L-DOPA. Histological examination with hematoxylin-eosin staining revealed vasodilation in the ciliary vessels and the choroid after L-DOPA injection. Both effects were greater in melanotic rats than in amelanotic rats. The vasodilation may be attributable to NO as well as to superoxides, which can be regulated by the existence of melanin.