Physiology and effects of nucleosides in mice lacking all four adenosine receptors

Adenosine is a constituent of many molecules of life; increased free extracellular adenosine indicates cell damage or metabolic stress. The importance of adenosine signaling in basal physiology, as opposed to adaptive responses to danger/damage situations, is unclear. We generated mice lacking all four adenosine receptors (ARs), Adora1^−/−;Adora2a^−/−;Adora2b^−/−;Adora3^−/− (quad knockout [QKO]), to enable investigation of the AR dependence of physiologic processes, focusing on body temperature. The QKO mice demonstrate that ARs are not required for growth, metabolism, breeding, and body temperature regulation (diurnal variation, response to stress, and torpor). However, the mice showed decreased survival starting at about 15 weeks of age. While adenosine agonists cause profound hypothermia via each AR, adenosine did not cause hypothermia (or bradycardia or hypotension) in QKO mice, indicating that AR-independent signals do not contribute to adenosine-induced hypothermia. The hypothermia elicited by adenosine kinase inhibition (with A134974), inosine, or uridine also required ARs, as each was abolished in the QKO mice. The proposed mechanism for uridine-induced hypothermia is inhibition of adenosine transport by uridine, increasing local extracellular adenosine levels. In contrast, adenosine 5′-monophosphate (AMP)–induced hypothermia was attenuated in QKO mice, demonstrating roles for both AR-dependent and AR-independent mechanisms in this process. The physiology of the QKO mice appears to be the sum of the individual knockout mice, without clear evidence for synergy, indicating that the actions of the four ARs are generally complementary. The phenotype of the QKO mice suggests that, while extracellular adenosine is a signal of stress, damage, and/or danger, it is less important for baseline regulation of body temperature.

A study of mice lacking all four adenosine receptors shows that while they mediate effects of uridine, inosine and adenosine, these receptors are dispensable for growth, metabolism, breeding, and body temperature regulation. This suggests that extracellular adenosine is a damage or danger signal, rather than a major regulator of baseline physiology.

Elevated extracellular adenosine generally indicates metabolic stress or cell damage and regulates many aspects of physiology. We studied “QKO” mice lacking all four adenosine receptors. Young QKO mice do not appear obviously ill, but do show decreased survival later in life. QKO mice demonstrate that adenosine receptors are not required for growth, metabolism, breeding, and body temperature regulation. QKO mice are missing the pharmacologic effects of adenosine on body temperature, heart rate, and blood pressure. Therefore, all of these effects are mediated by the four adenosine receptors. We also determined that the hypothermic effects of a pharmacologic adenosine kinase inhibitor (A134974), uridine, or inosine each requires adenosine receptors. The uridine-induced hypothermia is likely due to its inhibition of adenosine uptake into cells. QKO mouse physiology appears to be the sum of the individual knockout mice, without evidence for synergy, indicating that the actions of the four adenosine receptors are generally complementary.

A practical toxicity bioassay for vicine and convicine levels in faba bean (Vicia faba)

BACKGROUND

Faba bean (Vicia faba) vicine and convicine (V-C) aglycones (divicine and isouramil respectively) provoke an acute hemolytic anemia called favism in individuals with a glucose-6-phosphate dehydrogenase (G6PD) enzyme defect in their red blood cells. Geneticists/plant breeders are working with faba bean to decrease V-C levels to improve public acceptance of this high-protein pulse crop. Here, we present a fast and simple ex vivo in vitro bioassay for V-C toxicity testing of faba bean or faba bean food products.

RESULTS

We have shown that 1,3-bis (2-chloroethyl)-1-nitrosourea (BCNU)-treated (i.e., sensitized) normal red blood cells, like G6PD-defective blood, displayed (i) continuous glutathione (GSH) depletion with no regeneration as incubation time and the dose of aglycones increased, (ii) progressive accumulation of denatured hemoglobin products into high molecular weight (HMW) proteins with increased aglycone dose, (iii) both band 3 membrane proteins and hemichromes, in HMW protein aggregates. We have also demonstrated that sensitized red blood cells can effectively differentiate various levels of toxicity among faba bean varieties through the two hemolysis biomarkers: GSH depletion and HMW clumping.

CONCLUSION

BCNU-sensitized red blood cells provide an ideal model for favism blood, to assess and compare the toxicity of faba bean varieties and their food products. © 2018 Society of Chemical Industry.

The role of contamination history and gender on the genotoxic responses of the crayfish Procambarus clarkii to a penoxsulam-based herbicide

The responses of non-target organisms to pesticide exposure are still poorly explored in what concerns the development of adjustments favouring population success. Owing to the vital role of DNA integrity, it is important to identify genome-maintenance skills and their determinant factors. Thus, the major aims of the present study were: (i) to assess the genotoxicity of the penoxsulam-based herbicide (Viper^®) to the crayfish Procambarus clarkii; (ii) to understand the influence of gender and contamination history in the genotoxic responses following exposure to this herbicide; (iii) to investigate the damage mechanisms involved in putative adjustments shown by P. clarkii. Two populations were tested, one from a reference site and the other from a historically contaminated site. Specimens from both populations were exposed to Viper^®, considering environmentally relevant penoxsulam concentrations (20 and 40 µg L^-1) and to a model genotoxicant (EMS). Comet assay was adopted to assess the genetic damage in gills. The results disclosed the genotoxicity of the herbicide to crayfish (a non-target organism). Additionally, organisms exposed to the highest concentration of penoxsulam signalized the influence of factor "population" towards the genotoxic pressure (measured as effective DNA breaks): P2 males from the historically impacted population displayed a significantly higher susceptibly (by up to 53.98%) when compared to control, while the homologous group from the reference population presented levels similar to its respective control. When DNA lesion-repair enzymes were considered, DNA oxidation patterns suggested an increased ability of this gender (39.75% lower than negative control) to deal with this particular type of damage, namely considering pyrimidines oxidation. It is worth remarking that the influence of the exposure history on the protection/vulnerability to the penoxsulam-based herbicide was only evident in males, despite depending on the type of DNA damage: when the non-specific damage was considered, organisms from the impacted population seemed to be more vulnerable while regarding to the oxidative damage, males from the impacted population appeared to be more protected than organisms that have never been exposed to penoxsulam. Overall, the influence of factors "gender" and "contamination history" was demonstrated as well as its dependence on DNA damage type was evident. EMS groups did not present the differences between populations, reinforcing the agent-specific adjustment hypothesis.These findings highlighted the importance of considering differential physiological backgrounds in ecogenotoxicological analysis, hence favouring the elaboration of more plausible and holistic approaches integrating the environmental risk assessment of pesticides.

Influences of Chlorella vulgaris dietary supplementation on growth performance, hematology, immune response and disease resistance in Oreochromis niloticus exposed to sub-lethal concentrations of penoxsulam herbicide

Little is known regarding the impact of penoxsulam, a fluorinated benzenesulfonamid rice herbicide, on Oreochromis niloticus (O. niloticus). Therefore, the current study was undertaken to highlight the effects of penoxsulam exposure on O. niloticus and to evaluate the advantages of Chlorella vulgaris (CV) dietary supplementation against the induced effects. The 96-h lethal concentration 50 (LC₅₀) penoxsulam value for O. niloticus was estimated at 8.948 mg/L by probit analysis in a static bioassay experiment. Next, 360 healthy fish were randomly allocated into 6 treatment groups. The T1 group served as the negative control and was fed a basal diet. The T2 group served as the positive control and was fed a basal diet supplemented with 10% CV. The fish in the T3 and T4 groups were exposed to 1/10 the 96-h LC₅₀ of penoxsulam (0.8948 mg/L) and were fed the basal diet alone or the basal diet supplemented with 10% CV, respectively. The fish in the T5 and T6 groups were exposed to 1/5 the 96-h LC₅₀ of penoxsulam (1.7896 mg/L) and fed the basal diet alone or the basal diet supplemented with 10% CV, respectively. Sub-acute penoxsulam exposure significantly altered hematological indices, as well as compromised the fish's immune defense mechanisms, including the phagocytic percentage, phagocytic index, nitric oxide production, immunoglobulin M levels and lysozyme, anti-trypsin and bactericidal activities subsequently decreasing O. niloticus's resistance to the Aeromonus sobria challenge and increasing disease symptoms and the mortality rate. Furthermore, sub-chronic penoxsulam exposure markedly altered growth performance, oxidant/antioxidant status and liver status and down-regulated the expression of interleukin-1β (IL-1β) and tumor necrosis-α (TNF-α). Interestingly, incorporating 10% CV into the diet protects fish against sub-acute penoxsulam-induced immunotoxicity via improvement of immune responses that increases the resistance against bacterial infection. Further, it improved the growth performance, oxidant/antioxidant status, liver status and markedly up-regulated immune-related gene expression, IL-1β and TNF-α, in the spleens of fish sub-chronically exposed to penoxsulam. These outcomes showed that dietary CV supplementation can protect the commercially valuable freshwater fish O. niloticus against penoxsulam toxicity and may be a potential feed supplement for Nile tilapia in aquaculture.

Sub-lethal effects of herbicides penoxsulam, imazamox, fluridone and glyphosate on Delta Smelt (Hypomesus transpacificus)

Concerns regarding non-target toxicity of new herbicides used to control invasive aquatic weeds in the San Francisco Estuary led us to compare sub-lethal toxicity of four herbicides (penoxsulam, imazamox, fluridone, and glyphosate) on an endangered fish species Delta Smelt (Hypomesus transpacificus). We measured 17β-estradiol (E2) and glutathione (GSH) concentrations in liver, and acetylcholinesterase (AChE) activity in brain of female and male fish after 6 h of exposure to each of the four herbicides. Our results indicate that fluridone and glyphosate disrupted the E2 concentration and decreased glutathione concentration in liver, whereas penoxsulam, imazamox, and fluridone inhibited brain AChE activity. E2 concentrations were significantly increased in female and male fish exposed to 0.21 μM of fluridone and in male fish exposed to 0.46, 4.2, and 5300 μM of glyphosate. GSH concentrations decreased in males exposed to fluridone at 2.8 μM and higher, and glyphosate at 4.2 μM. AChE activity was significantly inhibited in both sexes exposed to penoxsulam, imazamox, and fluridone, and more pronounced inhibition was observed in females. The present study demonstrates the potential detrimental effects of these commonly used herbicides on Delta Smelt.

Degradation of vicine, convicine and their aglycones during fermentation of faba bean flour

In spite of its positive repercussions on nutrition and environment, faba bean still remains an underutilized crop due to the presence of some undesired compounds. The pyrimidine glycosides vicine and convicine are precursors of the aglycones divicine and isouramil, the main factors of favism, a genetic condition which may lead to severe hemolysis after faba bean ingestion. The reduction of vicine and convicine has been targeted in several studies but little is known about their degradation. In this study, the hydrolysis kinetics of vicine and convicine and their derivatives during fermentation with L. plantarum DPPMAB24W was investigated. In particular, a specific HPLC method coupled to ESI-MS and MS/MS analysis, including the evaluation procedure of the results, was set up as the analytical approach to monitor the compounds. The degradation of the pyrimidine glycosides in the fermented flour was complete after 48 h of incubation and the aglycone derivatives could not be detected in any of the samples. The toxicity of the fermented faba bean was established through ex-vivo assays on human blood, confirming the experimental findings. Results indicate that mild and cost effective bioprocessing techniques can be applied to detoxify faba bean also for industrial applications.

Toxic effects of penoxsulam herbicide in two fish species reared in southern Brazil

Toxic effects of penoxsulam herbicide on acetylcholinesterase, thiobarbituric acid-reactive substances and protein carbonyl were studied in silver catfish (Rhamdia sp.) and carp (Cyprinus carpio). Acetylcholinesterase activity was inhibited in both brain and muscle tissue, with the inhibition being greater in carp than in silver catfish. The levels of malondialdehyde (MDA), an indicator of lipid peroxidation, decreased in silver catfish brain tissue, but increased in the carp brain. MDA also increased significantly in muscle tissue of silver catfish. The levels of protein carbonyl, another measure of oxidative damage, increased in the brain of both fish species, and in the muscle of carp. However, silver catfish exhibited a decrease in muscle protein carbonyl. It appears that silver catfish may possess better mechanisms of defense against penoxsulam toxicity than carp.

Biomarkers in marine mussels, Mytilus galloprovincialis, exposed to environmentally relevant levels of the pesticides, chlorpyrifos and penoxsulam

The present study examines the influence of environmentally relevant concentrations of two pesticides, chlorpyrifos and penoxsulam on mussel physiological status. For this reason, lysosomal membrane stability (LMS), reactive oxygen species (ROS), DNA damage, protein carbonylation (PCC) and antioxidant capacity (TAC) in hemaolymph and hemocytes of the mussels was measured. Mussels were exposed to a range of concentrations of the pesticides chlorpyrifos and penoxsulam and the response of animals to the destabilization of lysosomal membrane in hemocytes (LMS) was studied. Subsequently, the half maximal effective concentration (EC50) for both pesticides was calculated. The animals were subsequently exposed for 0, 1, 3, 5, 7, 15 and 30 days to 10 times less concentration than EC50 of each pesticide (0.05 μg/l) and changes in LMS, ROS, DNA damage, protein carbonylation and antioxidant capacity of mussels was evaluated. Our results showed a significant change in the response of mussels for all parameters tested after 30 days exposure, in relation to the controls. The pesticides at the environmental concentrations used induced changes to the animal physiology through causing oxidative stress and lysosomal abnormalities and their usage in the agriculture demands great care. In addition, the results show that ROS, DNA damage, protein carbonylation and antioxidant capacity could constitute, after further investigation, reliable biomarkers for the evaluation of pollution or other environmental stressors.

Protective effect of uridine on cornea in a rabbit dry eye model

PURPOSE

To investigate the effect of uridine on cultured human corneal epithelial cells and keratocytes in vitro and to evaluate whether the application of uridine-containing eye drops could improve ocular surface health in an in vivo dry eye model.

METHODS

Uridine was added to cultured epithelial cells (3 x 10(4) cells/well) and keratocytes (1 x 10(4) cells/well) at various concentrations (0.5-50 microM). Cytotoxicity was tested with the use of MTT assay, and the cells were assessed for apoptosis with the use of flow cytometry. Expressions of hyaluronic acid (HA), glycosaminoglycan (GAG), nitric oxide (NO), and matrix metalloproteinase (MMP)-9 were measured. In vivo, the degree of reepithelialization was assessed after topical application of uridine (100 microM) in a rabbit corneal wound model. Changes in tear production and conjunctival goblet cell counts were investigated after instillation of various concentrations of uridine-containing eye drops in a rabbit dry eye model.

RESULTS

In vitro, uridine showed no cellular toxicity. It increased the biosynthesis of HA and GAG and reduced MMP-9 levels in cultured corneal epithelial cells and keratocytes. In vivo, uridine enhanced corneal wound healing and significantly increased the number of conjunctival goblet cells in rabbits.

CONCLUSIONS

Uridine can restore the health of the ocular surface in a rabbit corneal wound and dry eye model.

Enantioselective syntheses and cytotoxicity of N,O-nucleosides

Enantiomers of 4'-aza-2',3'-dideoxynucleosides have been prepared by two different synthetic approaches, on the basis of 1,3-dipolar cycloaddition of a chiral nitrone. Cytotoxicity and apoptotic activity have been investigated. (5'S)-5-Fluoro-1-isoxazolidin-5-yl-1H-pyrimidine-2,4-dione [(-)-AdFU], while showing low level of cytotoxicity, is a good inductor of apoptosis on lymphoid and monocytoid cells, acting as a strong potentiator of Fas-induced cell death.

Studies on novel bacterial translocase I inhibitors, A-500359s. II. Biological activities of A-500359 A, C, D and G

A-500359 A, C, D, G and capuramycin inhibited bacterial phospho-N-acetylmuramyl-pentapeptide-translocase (translocase I: EC 2.7.8.13) with IC50 values of 0.017, 0.12, 0.53, 0.14 and 0.018 microM, respectively. Consistently, A-500359 A, C and capuramycin inhibited in vitro peptidoglycan biosynthesis. A-500359 A exhibited reversible inhibition, which was mixed type and noncompetitive with respect to UDP-MurNAc-(N(epsilon)-Dns)pentapeptide (Ki=0.0079 microM) and undecaprenyl-phosphate, respectively. A-500359 A, C, D and G showed antimicrobial activity against Mycobacterium smegmatis. As a single intravenous injection of A-500359 A at a dose of 500 mg/kg showed no toxicity in mice, it was suggested that the capuramycin derivatives might become candidates as novel therapeutic agents for various diseases caused by Mycobacteria including tuberculosis.

Vicine and convicine in common vetch (Vicia sativa) seeds enhance beta-cyanoalanine toxicity in male broiler chicks

Two studies were conducted to investigate the effects of feeding raw and water-soaked vetch seeds to male broiler chicks on performance, organ weights, and blood parameters. Intact and ground vetch seeds were soaked in water (1:5) at room temperature for 24 hours (study 1), and (1:10) at 40 degrees C for 24, 48, and 72 hours, with water change every 12 hours (study 2). In study 1, untreated vetch contained, on dry matter basis, 0.530%, 0.731%, and 0.081% total beta-cyanoalanine (BCA), vicine, and convicine, respectively. Toxins were not appreciably reduced in soaked intact and ground vetch. Diets containing untreated, soaked intact, and soaked ground vetch, each at 0%, 20%, 40%, and 60%, were fed to 7-day-old male broilers until onset of neurotoxicity symptoms. Survival time was not only decreased by BCA level but also by those of vicine and convicine (p <.05). In study 2, 60% of untreated or treated vetch seeds were incorporated in chick diets. Although untreated vetch used in this study contained 32% less BCA but 8% and 81% more vicine and convicine, respectively, yet, the chicks on 60% untreated vetch showed toxicity symptoms earlier than those of study 1. Soaking ground vetch for 48 hours or more reduced BCA and totally removed vicine and convicine. Consequently, birds on 60% ground vetch soaked for 48 and 72 hours survived through the starter period and had mean corpuscular hemoglobin concentration and organ weights comparable to those of control at 4 days post trial. The results indicated that "high levels" of vicine or convicine or both might have shortened the birds' survival time by enhancing the neurotoxicity induced by "lower levels" of BCA.

5-Formyluracil and its nucleoside derivatives confer toxicity and mutagenicity to mammalian cells by interfering with normal RNA and DNA metabolism

Oxidation of the methyl group of thymine yields 5-(hydroxymethyl)uracil (5-hmU) and 5-formyluracil (5-foU) as major products. Whereas 5-hmU appears to have normal base pairing properties, the biological effects of 5-foU are rather poorly characterised. Here, we show that the colony forming ability of Chinese hamster fibroblast (CHF) cells is greatly reduced by addition of 5-foU, 5-formyluridine (5-foUrd) and 5-formyl-2'-deoxyuridine (5-fodUrd) to the growth medium. There are no toxic effects of 5-fodUrd on cells defective in thymidine kinase or thymidylate synthetase, suggesting that the toxicity may be caused by 5-fodUrd phosphorylation and subsequent inhibition of thymidylate synthetase. Whereas 5-fodUrd was the most effective 5-foU derivative causing cell growth inhibition, the corresponding ribonucleoside 5-foUrd was more effective in inhibiting [3H]uridine incorporation in non-dividing rat nerve cells in culture, suggesting that 5-foUrd exerts its toxicity through interference with RNA rather than DNA synthesis. Addition of 5-foU and 5-fodUrd was also found to promote mutagenicity at the hypoxanthine-guanine phosphoribosyltransferase (HPRT) locus of CHF cells; 5-fodUrd being three orders of magnitude more potent than 5-foU. In contrast, neither 5-hmU nor 5-(hydroxymethyl)-2'-deoxyuridine induced HPRT mutations. The mutation induction indicates that 5-foU will be incorporated into DNA and has base pairing properties different from that of thymine. These results suggest that 5-foU residues, originating from incorporation of oxidised bases, nucleosides or nucleotides or by oxidation of DNA, may contribute significantly to the damaging effects of oxygen radical species in mammalian cells.

Cytotoxic mechanisms of new antitumor nucleoside analogues, 3'-ethynylcytidine (ECyd) and 3'-ethynyluridine (EUrd)

The cytotoxic mechanisms of 1-(3-C-ethynyl-beta-D-ribo-pentofuranosyl)cytosine (ECyd) and 1-(3-C-ethynyl-beta-D-ribo-pentofuranosyl)uracil (EUrd) were studied with mouse mammary tumor FM3A cells and human fibrosarcoma HT1080 cells. ECyd and EUrd are converted to ECyd 5'-triphosphate (ECTP) in the cells. ECTP has also outstanding stability in the cells; the half life of ECTP in FM3A cells was more than 3 days. The metabolisms and mechanisms of these analogues may play a key role in a potent antitumor activities against slow-growing solid tumors.

Pharmacokinetics and retinal toxicity of intravitreal liposome-encapsulated 5-fluorouridine

BACKGROUND

Fluoropyrimidines may be effective in preventing proliferative vitreoretinopathy after repair of complicated retinal detachments. Liposome encapsulation of these antiproliferative drugs may extend the intravitreal half-life and increase their efficacy.

METHODS

The current study evaluated the pharmacokinetic behavior of intravitreally injected 5-fluorouridine (5-FUR), free and encapsulated in liposomes, either conventionally or coated with collagen into 25 New Zealand rabbits. Additionally, we investigated the retinal toxicity of intravitreal injections of 100, 250 and 500 microg as well as 1 mg 5-FUR as free drug or encapsulated in liposomes in the rabbit eye.

RESULTS

The half-life of free 5-FUR after liposome injection into the vitreous cavity was 18.17+/-2.43 h, considerably longer than the half-life of free 5-FUR (0.82 h). Electrophysiologic tests did not show any changes in latency and a-wave amplitude and minimal changes in the b-wave amplitude. Histopathologic studies revealed integrity of the inner limiting membrane, and mild vacuolization in the outer retina.

CONCLUSION

Encapsulation of 5-FUR within liposomes markedly increases its intravitreal half-life. Our study suggests that liposome-encapsulated 5-FUR is not toxic to the retina even at doses of 1 mg.

Synthesis and cytotoxic activity of 6-vinyl- and 6-ethynyluridine and 8-vinyl-and 8-ethynyladenosine

It is well-known that the introduction of vinyl and ethynyl moieties into nucleosides is of crucial importance for cytostatic, antiviral, or other biological activities. In this study 6- and 8-vinyl-and -ethynyluridine and -adenosine were prepared by a general procedure involving the palladium-catalyzed cross-coupling of trimethylsilylacetylene or vinyltributyltin. The introduction of a vinyl group at C-6 of uridine or an ethynyl group at C-8 of adenosine resulted in nucleoside derivatives showing cytostatic activity against several murine and/or human tumor cell lines. Interestingly, 8-vinyladenosine had pronounced selective inhibitory effects on human (Molt/4F and MT-4) versus murine (L1210 and FM3A) tumor cell lines.

Evaluation of toxicity and efficacy of a combination of antineoplastic agents in the prevention of PVR

The retinal toxicity of a combination of antineoplastic drugs in free and liposome-encapsulated form was determined in the rabbit eye. Bleomycin sulfate and 5-fluorouridine were evaluated by clinical observation, electroretinogram, and histological study. Forty-five eyes were injected with combinations of various doses of bleomycin and 5-FUR in free and encapsulated form; 10 eyes served as controls. The nontoxic free dose was found to be 3.5 micrograms bleomycin and 150 micrograms 5-FUR. Liposome encapsulation increased the nontoxic dose to 4.7 micrograms bleomycin and 200 micrograms 5-FUR. Four groups of rabbits in which proliferative vitreoretinopathy had been induced were used for the efficacy study; the control group received an injection of PBS; the second group was injected with a combination of 3.5 micrograms bleomycin and 150 micrograms 5-FUR in free form; the third group was injected with the identical doses in liposome-encapsulated form; and the fourth group received encapsulated bleomycin (4.7 micrograms) and 5-FUR (200 micrograms). The dose used in Group 4 was significantly more effective (P < 0.01) in preventing tractional retinal detachment and marginally more effective (P = 0.054) in preventing neovascularization.

Effect of neomycin on the hydrolysis and toxicity of vicine and convicine in rats

This study in the rat established the effects that a broad-spectrum and poorly absorbed antibiotic, neomycin sulfate, had on the in vitro and in vivo hydrolysis of vicine and convicine by the intestinal microflora, and on vicine- and convicine-induced depletion of blood glutathione and the resulting toxicity. The in vitro studies demonstrated that digesta from the caecum and large intestine were highly effective in hydrolysing vicine and convicine, whereas digesta from the same sections of the gastro-intestinal tract of neomycin-treated rats were much less effective (P < 0.0001). The in vivo studies showed that the total amount of vicine and convicine excreted in the urine and faeces was much greater in neomycin-treated rats compared with controls (P < 0.05), indicating the ability of neomycin to increase the amount of glycosides, particularly that of vicine, excreted in the faeces. The ability of glycosides to decrease the concentration of glutathione in blood (P < 0.05) and to increase rat mortality was greatly reduced in rats that were treated with neomycin, particularly in those treated ip with the toxin. Thus, the results demonstrated that neomycin reduced the rate at which vicine and convicine were hydrolysed in the lower section of the gastro-intestinal tract, and that neomycin treatment was associated with a reduced toxicity of the glycosides.

Mouse strain differences in induction of micronuclei by base analogues and nucleosides

The frequency of induced micronucleated polychromatic erythrocytes (MNPCEs) was compared in BALB/c, C57BL/6, and DBA/2 mice after intraperitoneal (i.p.) injection of 5-bromodeoxyuridine (BUdR), 5-fluorodeoxyuridine (FUdR), cytosine arabinoside (Ara-C), 6-mercaptopurine (6-MP), 5-bromouracil (5-BU), thymidine (TdR), uridine (UdR), adenosine (AdR) and guanosine (GdR). The experimental procedure was a single i.p. injection followed by harvest at 30 h. The frequency of MNPCEs was significantly increased in all strains by treatment with BUdR, FUdR, Ara-C and 6-MP compared to vehicle control. TdR and UdR induced MNPCEs slightly in BALB/c mice but showed no effect on C57BL/6 and DBA/2 mice. 5-BU, AdR, and GdR did not increase the frequency of MNPCEs in any mouse strain used. These results suggest that BALB/c mice are more susceptible to induction of MNPCEs by clastogenic base analogues and nucleosides than are C57BL/6 or DBA/2 mice.

Effects of fluorouracil and fluorouridine on protein synthesis in rabbit retina

5-Fluorouracil (5-FU) and its active metabolite 5-fluorouridine (FUR) are currently being evaluated for the treatment of proliferative vitreoretinopathy and the control of scarring after glaucoma filtering procedures. To test for retinal toxicity, the authors examined the effect of intravitreal injections of 5-FU and FUR on protein synthesis in rabbit retinal photoreceptors and ganglion cells. In addition, the toxic effect of subconjunctival 5-FU injections, after a trephine filtering procedure, on ganglion cell protein synthesis was examined. Albino rabbit eyes were given either unilateral intravitreal injections of 1 mg of 5-FU, 2.5 mg of 5-FU, or 0.1 mg of FUR, or subconjunctival injections of 3 mg of 5-FU twice daily after a trephine procedure. Quantitative autoradiography was used to study ganglion cells and photoreceptor outer segment renewal, and scintillation counting was used to quantify newly synthesized protein transported axonally from ganglion cell bodies to the superior colliculus (SC). Marked reduction of labeled protein reaching the SC was noted after either intravitreal 0.1 mg of FUR (41% inhibition after a single injection and 53% after two injections) or 2.5 mg of 5-FU (41% after one injection and 26% after two injections). This reduction was still present after 8 days in eyes receiving 0.1 mg of FUR (32%) and 2.5 mg of 5-FU (22%). Quantitative autoradiography of retinal photoreceptors and ganglion cells corroborated these data, demonstrating inhibition of outer segment renewal after one or two injections of either 0.1 mg of FUR or 2.5 mg of 5-FU. This inhibitory effect was statistically significant using the paired t-test for both drugs. No mean inhibition was observed after intravitreal 1 mg of 5-FU injections or after subconjunctival injections of 5-FU.

Antimalarial activity of a combination of 5-fluoroorotate and uridine in mice

Malarial parasites, in contrast to mammalian cells, utilize orotic acid more efficiently than uracil or uridine. Recently, chloroquine-susceptible and chloroquine-resistant clones of Plasmodium falciparum were shown to be inhibited by 5-fluoroorotate, with a 50% inhibitory concentration of 6 nM in vitro. Mammalian cells were far less sensitive to 5-fluoroorotate, particularly in the presence of uridine. In this report, the antimalarial activity of 5-fluoroorotate was tested in vivo. Initially, levels of 5-fluoroorotate in plasma were determined in Swiss mice injected intraperitoneally with radioactive 5-fluoroorotate. On the basis of the pharmacokinetics profile, mice infected with Plasmodium yoelii were treated with 5-fluoroorotate at a dose of 0.2 or 5 mg/kg (body weight) every 4 h for 3 days. At the nontoxic dose of 0.2 mg/kg, the reduction in parasitemia was followed by a temporary resurgence of parasitemia. This second wave of parasitemia cleared without additional 5-fluoroorotate treatment. To radically eliminate P. yoelii from mice and avoid the second wave of parasitemia, a higher dose of 5 mg of 5-fluoroorotate per kg had to be used. In the absence of uridine, repeated doses of 5 mg/kg were toxic to mice, as judged by weight loss, diarrhea, decreased numbers of leukocytes, and increased mortality. However, in the presence of uridine, repeated doses of 5 mg/kg could be used for antimalarial chemotherapy without obvious toxicity. Mice cured with 5-fluoroorotate and uridine were immune to subsequent challenge with a potentially lethal inoculum of P. yoelii.

Calcium leucovorin and 5-fluorouridine cytotoxicity

The action of fluoropyrimidine (FP) drugs at thymidylate synthase (TS) is associated with enhanced chemotherapeutic response. Calcium leucovorin (CF) increases the cytotoxicity of the FP drugs, 5-fluorouracil and 5-fluorodeoxyuridine, in human laryngeal carcinoma HEp-2 cells by directing the action of these drugs at TS. Thus, the effect of CF on the cytotoxicity and site of action of the FP, 5-fluorouridine (FUrd), was investigated in HEp-2 cells. The cytotoxicity of FUrd was unaffected by CF. Moreover, CF was unable to alter the growth-limiting target of FUrd to TS. HEp-2 cells convert FUrd to FdUMP, the FP metabolite that is the direct inhibitor of TS; thus, the inability of CF to modulate FUrd action is not due to lack of inhibitor formation. In addition, greater than 90 percent of TS activity is inhibited at concentrations of FUrd that inhibit HEp-2 cell growth by 50 percent. Thus, while TS is significantly inhibited by FUrd, it is not the growth-limiting target of this drug. It is likely that the RNA-directed effects of FUrd are so extensive that CF, which maximizes TS-directed action, is ineffective at reducing the cytotoxicity further. An approach to overcoming the RNA-directed effects of FUrd is suggested.

Glaucoma filtration surgery in monkeys using 5-fluorouridine in polyanhydride disks

We performed filtration surgery in glaucomatous monkeys to determine if bioerodible polyanhydride disks that contained 5-fluorouridine (5-FUR) prolonged the success of the operation. First, in vitro studies demonstrated that 5-fluorouridine was released from the disks for at least 16 days in a bioactive form that inhibited fibroblast proliferation. Next, a preliminary series of six eyes suggested that using disks that contained 5-fluorouridine extended the intraocular pressure-lowering effect of filtration surgery. This finding was confirmed in eight additional eyes of four animals in which one eye received a disk with 5-fluorouridine and the other received a disk without the drug. The duration of success of the operation was significantly longer in the eyes that received polyanhydride with 5-fluorouridine (mean +/- SD, 26.0 +/- 9.2 days) than in the controls (8.5 +/- 4.0 days). The histologic findings of the experimental eyes correlated with their prolonged clinical success.

Modulation of 5-fluorouracil and 5-fluorouridine toxicity by membrane transport inhibitors in normal tissues of rats with liver adenocarcinoma

The cytotoxicity of 5-FU and 5-FUrd, given via the hepatic artery, was measured by its incorpotation into the acid soluble fraction, RNA and DNA in normal tissues and an adenocarcinoma transplanted into the liver in rats. Drugs inhibiting the membrane transport of, especially, nucleosides were simultaneously administered by a femoral vein to modulate the cytotoxicity. None of them (dipyridamole, lidoflazine nor dilazep) had any statistically significant influence on the tumour. Dipyridamole and lidoflazine decreased the incorporation of 5-FU into the acid soluble fraction, RNA and DNA of the intestine. Dipyridamole probably decreased the incorporation of 5-FUrd into the acid soluble fraction and RNA of the intestine. Lidoflazine has not been tested with 5-FUrd. Dipyridamole increased the incorporation of 5-FU into the acid soluble fraction of liver, bone marrow and kidney, and of 5-FUrd into the acid soluble fraction of liver and bone marrow and liver RNA. Lidoflazine had fewer adverse effects. Both dipyridamole and lidoflazine increased the combined peak of UTP and FUTP in the liver, and dipyridamole also in the intestine of 5-FU treated rats. Dipyridamole which undergoes an enterohepatic circulation increased the combined peak of UDP-glucuronic acid and FUDP-glucuronic acid in 5-FU and 5-FUrd treated rats, as well as UDP-glucuronic acid in rats given neither 5-FU nor 5-FUrd in the liver. Membrane transport inhibitors seem to offer the opportunity to protect normal tissues from the cytotoxicity of 5-fluoropyrimidines, but the tissues can also be more exposed.

Uridine-induced hypothermia in mice and rats in relation to plasma and tissue levels of uridine and its metabolites

Administration of high-dose uridine or cytidine (3500 mg/kg) resulted in severe hypothermia of 6-10 degrees C in mice. This effect of uridine was observed in three different mouse strains, C57B1/6, Balb/c, and Swiss. A high-dose of uridine also caused hypothermia in Wistar rats. Co-infusion of uridine with benzylacyclouridine, an inhibitor of uridine phosphorylase, partially prevented uridine-mediated hypothermia in mice. A low dose of uridine (100 mg/kg) resulted in a slight increase in temperature. Plasma pharmacokinetics of uridine (at 3500 mg/kg) were studied in two mouse strains, C57B1/6 and Balb/c, and those of cytidine only in C57B1/6 mice. Peak plasma concentrations of uridine in both strains after uridine administration were about 20 mM (at 30-60 min). The peak plasma concentration of cytidine in C57B1/6 mice after cytidine administration was about 12 mM and that of uridine, 1.3 mM. The mean residence time for uridine was about 105 min. The area under the plasma concentration-time curve for uridine was about 50 mmol h/l, and that for cytidine, about 25 mmol h/l. In various tissues of C57B1/6 mice the levels of uridine, uracil and total uracil and cytosine nucleotide pools were determined before and 2 h after uridine administration. Uridine levels increased about 53-fold in liver, about 70-fold in a colon tumor, and only about 7-fold in brain, while the corresponding uracil levels increased about 9-fold, 4-fold and 11-fold, respectively. Total uracil nucleotide pools increased about 8-fold, 3.2-fold and 1.6-fold, respectively. Cytosine nucleotide pools did not increase in the brain. In conclusion, high-dose uridine administration caused severe hypothermia. Plasma levels of uridine and uracil were enhanced to a considerably higher extent than the levels in the tissues. The hypothermia might be related to breakdown products of uridine, since inhibition of uridine breakdown partially prevented hypothermia and since in brain uracil nucleotide levels were only slightly increased after uridine administration, while those of uracil were more markedly increased than in other tissues.

Selection of therapeutic agents for intraocular proliferative disease. II. Differing antiproliferative activity of the fluoropyrimidines

We confirm the potent antiproliferative effects of the fluoropyrimidines on cellular proliferation in vitro in three different nonmalignant cell types. All fluoropyrimidines tested, except for fluorocytosine, decrease proliferation of human dermal fibroblasts, bovine aortic vascular endothelial cells, and human retinal pigment epithelial cells in vitro. Fluorouridine, an intracellular metabolite of fluorouracil, is nearly 100-fold more potent than fluorouracil and its deoxymetabolite. Human dermal fibroblasts are more sensitive to the inhibitory effects of deoxymetabolites than the cells of either human retinal pigment epithelium or bovine aortic vascular endothelium. Fluorouridine and other fluoropyrimidines may prove to be valuable second-generation drugs in the treatment of intraocular proliferative disorders.

Modulation of fluoropyrimidine metabolism by chlorpromazine

Chlorpromazine is a potent inhibitor of calmodulin and can alter the accumulation, metabolism, and incorporation into RNA of several fluoropyrimidine drugs. Using S-180 murine sarcoma cells, the accumulation of the base Fluorouracil and its metabolism to ribonucleotides is enhanced by chlorpromazine treatment, as measured by HPLC. In contrast, the accumulation and metabolism of the nucleoside Fluorouridine was suppressed by chlorpromazine. Cytotoxicity studies revealed that non-toxic concentrations of chlorpromazine were synergistic with Fluorouracil, but were antagonistic with Fluorouridine. These findings suggest that modulation by chlorpromazine of specific nucleoside kinase involved in Fluorouracil metabolism can result in increased therapeutic utility.

An analysis of multiple mechanisms of adenosine toxicity in baby hamster kidney cells

Analysis of the response of baby hamster kidney cells to adenosine in the presence of the adenosine deaminase inhibitor erythro-9-(2-hydroxy-3-nonyl) adenine has revealed two distinct mechanisms of toxicity. The first is apparent at low concentrations of adenosine (less than 5 microM) and is dependent upon the presence of a functional adenosine kinase. The initial toxicity is abolished by uridine, is unrelated to the inhibition of ribonucleotide reductase, and is accompanied by a decrease in the size of the pyrimidine nucleotide pool. Toxicity at higher concentrations of adenosine is adenosine kinase independent and is potentiated by homocysteine thiolactone. An elevation in the intracellular level of S-adenosylhomocysteine, which was observed following treatment with higher concentrations of adenosine (greater than 10 microM), is believed to mediate toxicity at these levels. Interestingly, BHK cells were resistant to intermediate levels of adenosine. The mechanism of resistance is currently unknown, but appears unrelated to a lack of inhibition of adenosine deaminase. It is proposed that substrate inhibition of adenosine kinase may be a determinant of this property.

Pharmacology and toxicology of a seven-day infusion of 1-beta-D-arabinofuranosylcytosine plus uridine in dogs

In vitro studies of certain lymphoid tumor cells show potentiation of 1-beta-D-arabinofuranosylcytosine (ara-C) effects by uridine because it elevates intracellular uridine triphosphate, resulting in increased ara-C triphosphate levels. Seven-day continuous i.v. infusions of uridine at 123 mg/kg/h (2.5 g/sq m/h) were studied in 5 male beagles. Steady state levels of uridine were reached within 4 to 6 h and ranged from 2 to 5 X 10(-4) M over the course of the infusion. Steady state uracil levels ranged from 4 to 10 X 10(-4) M. After the end of infusion, uridine and uracil levels fell with a half-life of approximately 15 and 18 min, respectively. Toxicity in 2 dogs treated at this dose was limited to minimal diarrhea and a transient rise of alkaline phosphatase to 2 to 3 times normal. No drug toxicity was evident at sacrifice on Days 7 or 72. Three dogs received a 7-day infusion of ara-C plus uridine followed approximately 4 weeks later by an infusion of ara-C alone (or the same drugs in the reverse sequence). Coinfusion of 2.5 or 5.0 mg/kg/day (50 or 100 mg/sq m/day) of ara-C had no significant effects on uridine plasma levels or postinfusion half-lives. Similarly, no consistent effect was seen of uridine on ara-C plasma levels. Uridine coinfusion with ara-C resulted in a definite potentiation of myelosuppression; at 5.0 mg/kg/day X 7 of ara-C white blood cell and platelet nadirs (X 10(3)/microliters) were 0.8 and 15 as compared to 3.6 and 66, respectively, with ara-C alone. One-third of the dogs developed reversibly elevated transaminases with the combination treatment. The results show that a minimally toxic dose of uridine enhances bone marrow and probably hepatic toxicity of coadministered ara-C.

Use of uridine rescue to enhance the antitumor selectivity of 5-fluorouracil

We examined the ability of uridine to increase the therapeutic index of 5-fluorouracil (FUra) against C57BL/6 X DBA/2 F1 mice bearing a Day 1 B16 melanoma or L1210 leukemia. FUra (400, 600, or 800 mg/kg, i.p.) followed in 24 hr by a 5-day s.c. infusion with uridine (5 g/kg/day, s.c.) was compared with the maximum tolerated dose of FUra (200 mg/kg, i.p.) plus a 5-day infusion with 0.9% NaCl solution. High-dose FUra plus delayed infusion with uridine was more effective than FUra (200 mg/kg) in inhibiting the growth of the B16 melanoma. High-dose FUra plus uridine rescue was, however, no more effective than FUra (200 mg/kg) in increasing the survival times of mice bearing the L1210 leukemia. To see if uridine rescue from FUra toxicity correlated with effects against a sensitive normal tissue, bone marrow nucleated cellularity of normal, non-tumor-bearing mice was monitored after drug treatment. In mice treated with FUra (200 mg/kg) followed in 24 hr by a 5-day infusion with either uridine (5 g/kg/day) or 0.9% NaCl solution, there was not as great a decrease in cellularity at the nadir with uridine, and, in addition, uridine accelerated recovery as compared to 0.9% NaCl solution. Furthermore, uridine (5 g/kg/day), but not thymidine (dThd) (5 g/kg/day) or 2'-deoxyuridine (dUrd) (5 g/kg/day), had a sparing effect on the depression in bone marrow nucleated cellularity seen at the nadir on Day 4 after Fura (200 mg/kg). The specificity of uridine to rescue mice from the lethal toxicity of the related fluorinated pyrimidines, 5-fluorouridine and 5-fluoro-2'-deoxyuridine, was also examined. Mice were treated with 5-fluorouridine (250 mg/kg, i.p.) followed in 24 hr by a 5-day infusion with uridine (1, 5, or 10 g/kg/day), dThd (1, 5, or 10 g/kg/day), or dUrd (1 or 5 g/kg/day). Uridine (1, 5, or 10 g/kg/day) rescued mice from the lethal toxicity of 5-fluorouridine, whereas dThd or dUrd was ineffective. Similarly, a 5-day infusion with uridine, but not dThd or dUrd, rescued mice from the lethal toxicity of 5-fluoro-2'-deoxyuridine (1800 mg/kg, i.p.).

Decreased immunosuppression associated with antitumor activity of 5-deoxy-5-fluorouridine compared to 5-fluorouracil and 5-fluorouridine

5-Fluorouracil (5-FUra), 5-deoxy-5-fluorouridine (5'dFUrd), and 5-fluorouridine were compared for their relative antitumor activity, their capacity to inhibit leukocyte exudation and macrophage (macrophage) killing of tumor cells in vivo and in vitro, and their ability to induce leukopenia and monocytopenia. 5'dFUrd was less toxic than 5-FUra and exhibited anti-Ehrlich ascites activity over a wider range of drug doses. Inflammatory exudates induced by thioglycollate or pyran were inhibited up to 91% by prior 5-FUra injection but were inhibited not more than 62% by 5'dFUrd. Pyran-induced macrophage inhibition of Ehrlich ascites proliferation in vivo was diminished up to 5-fold by 5-FUra but was never diminished more than 2-fold by 5'dFUrd, while neither agent suppressed in vitro macrophage cytotoxicity of in vivo pyran-activated macrophage. At high doses, 5-FUra reduced white blood cell counts 73%, in contrast to the 8% reduction caused by 5'dFUrd, while at their optimal anti-Ehrlich ascites doses, 5-FUra and 5'dFUrd both lowered white blood cell counts by only 20%. However, 5-FUra caused a severe monocytopenia not seen in animals given injections of comparable doses of 5'dFUrd. Therefore, 5-FUra appeared to inhibit the inflammatory response and antitumor activity by inhibiting the influx of immature macrophage into the peritoneal cavity, not by inhibiting the function of mature effector cells.

[Toxicological study of the new antiviral agent, 5-bromuridine]

Toxicity of the new antiviral drug 5-bromuridine was studied in experiments on laboratory animals at systemic and local administration. The drug proved to be little toxic. Studies of acute toxicity of the drug administered systemically (intraperitoneally, intravenously and per os) showed it to be well tolerable by animals at concentrations 10-20 fold and 150-300 fold (with reference to an average weight of human body) exceeding the doses recommended for humans at local administration. As compared to controls no changes in the animals' state, peripheral blood and in its principal functional and biochemical parameters, in the activity of serum enzymes as well as in the microstructure of internal organ tissue were revealed during prolonged local administration of the drug to the animals under conditions similar to clinical ones but at higher concentrations and longer exposure.

[Pharmacology of uridine and cytidine]

It was established that with intraperitoneal introduction of uridine and cytidine their DL50 for mice equals 5100 and 2700 mg/kg, respectively. In doses of 1/27 and 1/50 of DL50 cytidine reduces by 50 per cent the edema of the rat's paw in a dextran-and formaldehyde-induced inflammation, brings down the body temperature by 1.0--1.2 degrees and cuts down the death-rate among the animals in hyperthermia produced by 2,4-dinitrophenol. Uridine does not affect significantly the course of aseptic inflammation. In adrenalectomized rats the antiexudative action of cytidine does not manifest itself. Both nuclesides fail to exercise any significant influence on the cardiac activity and respiration in cats.