Methylxanthines Research Articles

Radical oxidation of xanthines: a reaction pathway to uric acid?

L'oxydation radicalaire de l'isocafeine (1,3,9-trimethylxanthine) a ete etudiee, d'une part par radiolyse pulsee afin de caracteriser la formation des radicaux intermediaires et la cinetique de leur transformation, d'autre part par analyse HPLC pour detecter les produits stables formes. L'isocafeine reagit avec le radical OH . en formant un adduit en C(8) qui conduit, apres oxydation, a la formation de l'acide urique correspondant (1,3,9-trimethyl-8-hydroxyxanthine). L'oxidation par le radical SO 4 -. conduit au meme acide urique par hydratation du radical cation primaire suivie de l'oxydation du radical resultant. Ce resultat est different de celui obtenu avec l'adenine et ses derives. En effet, dans ce dernier cas, on observe la formation de derives hydroxyles en C(8) apres oxydation par OH . mais non par SO 4 -. .

Clinical relevance of drug interactions with lithium.

Although lithium continues to be regarded as the treatment of choice for bipolar disorders, the clinical use of this mood stabiliser is associated with an extremely narrow therapeutic range. Relatively minor increases in serum concentrations may induce serious adverse sequelae, and concentrations within the therapeutic range may result in toxic reactions. The safety of combining lithium with other medications, therefore, is a major concern, and extensive clinical experience has served to identify several significant drug interactions. Lithium removal from the body is achieved almost exclusively via renal means. As a result, any medication that alters glomerular filtration rates or affects electrolyte exchange in the nephron may influence the pharmacokinetic disposition of lithium. Concomitant use of diuretics has long been associated with the development of lithium toxicity, but the risk of significant interactions varies with the site of pharmacological action of the diuretic in the renal tubule. Thiazide diuretics have demonstrated the greatest potential to increase lithium concentrations, with a 25 to 40% increase in concentrations often evident after initiation of therapy. Osmotic diuretics and methyl xanthines appear to have the opposite effect on lithium clearance and have been advocated historically as antidotes for lithium toxicity. Loop diuretics and potassium-sparing agents have minor variable effects. Nonsteroidal anti-inflammatory drugs (NSAIDs) have also been associated with lithium toxicity, although the relative interactive potential of specific NSAIDs is difficult to determine. Small prospective studies have demonstrated large interindividual differences in lithium clearance values associated with different NSAIDs. A growing body of evidence also suggests that ACE inhibitors may impair lithium elimination, but further investigations are needed to identify patients at risk. Anecdotal reports have linked numerous medications with the development of neurotoxicity without an apparent effect on the pharmacokinetic disposition of lithium. Antipsychotics, anticonvulsants and calcium antagonists have all be implicated in a sufficient number of case reports to warrant concern. As these medications have all been commonly coadministered with lithium, the relative risk of serious interactions appears to be quite low, but caution is advised.

Functional motion changes during sperm transit to the site of fertilization and in-vitro applications: a review.

Continued research to define the parameters of sperm function should aid the evaluation of various approaches in infertility as well as the efficacy of contraceptives for men which do not necessarily achieve azoospermia. Many treatment forms have been advocated for male factor infertility but have yielded little effect. These included, for example, gonadotrophins, clomiphene citrate, the weakly androgenic steroid, mesterolone. Often, improvements in oligoasthenozoospermia that are not related to genital infection, do not attain normozoospermic levels. Owing to lack of success with various treatment modalities, assisted reproductive technology encompassing artificial insemination by husband or donor following in vitro enhancement of sperm function have assumed an important role in male infertility. Agents that have been shown to induce and support sperm capacitation processes such as hyperactivation, could serve an important role. These include human follicular fluid (HFF), maternal serum, fetal cord serum and methyl xanthine derivatives.

Regulatory Effects of Pentoxifylline on T-Helper Cell-Derived Cytokine Production in Human Blood Cells

Pentoxifylline (PTX), a methyl xanthine derivative, was examined for its regulatory effect on Th1-and Th2-cell-derived cytokines in human whole blood and peripheral blood mononuclear cells stimulated with phytohemagglutinin (PHA) and phorbol myristate acetate (PMA). Cytokine production was analyzed by enzyme-linked immunosorbent assay and cytokine mRNA expression was examined by the polymerase chain reaction (PCR) after reverse transcription (RT). The results showed that PTX at 5 x 10(-4) M concentration selectively suppressed Th-1 cytokines [interleukin-2 (IL-2) and interferon-gamma (IFN-gamma)] but not IL-4, as observed by the measurement of protein secretion. Using sensitive RT-PCR assays, data show that at this same PTX concentration (5 x 10(-4) M), these cells also exhibited inhibition in the expression of IL-4 and IL-10 mRNA, together with inhibition of IL-2 and IFN-gamma mRNA expression. At 1 x 10(-4) M, no apparent change in IL-4 and IL-10 mRNA expression was observed, whereas IL-2 mRNA was still inhibited. It was noted that PTX at 1 x 10(-3) M induced a generalized inhibition of all cytokines. Our findings showed that PTX at the appropriate concentrations could induce selective suppression of IL-2 and IFN-gamma, whereas at high concentrations this drug could act as a suppressive agent of both Th1- and Th2-derived cytokines. Moreover, these data provide further evidence that the induction of IL-2 gene transcription is highly sensitive to an elevation of cAMP, whereas IL-4 gene transcription appeared to be less affected.

Interleukin-10 and pentoxifylline inhibit C-reactive protein-induced tissue factor gene expression in peripheral human blood monocytes

Fibrin deposition is an integral feature of the inflammatory response. In response to C-reactive protein (CRP), an acute-phase reactant, blood monocytes synthesize and express tissue factor (TF), the main initiator of blood coagulation. We report the inhibitory effect of interleukin 10 (IL-10) and that of pentoxifylline, a methyl xanthine derivative, on monocyte expression of TF activity, TF protein and TF mRNA in response to CRP. These agents may be of use in diseases where a TF-induced prothrombotic state is detrimental.

Different pial arteriolar responses to acetylcholine in the newborn and juvenile pig.

Using the closed cranial window technique, the present study was designed to test the hypothesis that the pial arteriolar response to acetylcholine is age dependent. In newborn pigs (1-5 days old) pretreated with the phosphodiesterase inhibitor isobutyl methyl xanthine (IBMX), acetylcholine (10(-5) M) produced pial arteriolar constriction with no change in CSF cyclic GMP (cGMP) that was blocked by indomethacin (5 mg/kg i.v.). In contrast, in indomethacin- and IBMX-treated juvenile pigs (3-4 weeks old), acetylcholine (10(-) M) increased the pial arteriolar diameter by 17 +/- 1% and increased CSF cGMP by 2.1 +/- 0.3-fold. Similar vascular and biochemical changes for acetylcholine were observed in juvenile pigs pretreated with only IBMX. In the absence of IBMX, acetylcholine produced modest pial constriction in juvenile pigs. In the IBMX-pretreated juvenile pigs, L-nitroarginine (LNA; 10(-6) M) decreased pial arteriolar diameter by 15 +/- 2% and blocked acetylcholine-induced dilation and associated changes in CSF cGMP. A23187, a calcium ionophore, and sodium nitroprusside (SNP) elicited similar dilation and changes in CSF cGMP in both age groups. LNA blocked A23187 dilation, but SNP dilation was unchanged. L-Arginine (10(-3) M) partially restored acetylcholine- and A23187-induced dilation to indomethacin- and LNA-pretreated juvenile pigs. These data show that acetylcholine produces dilation in the juvenile pig through the production of the putative endothelium-derived relaxing factor (EDRF) nitric oxide but does not do so in the new born period. We speculate that contributions of EDRF to the acetylcholine-induced changes in pial arteriolar diameter develop with age.

Electronic spectra and structures of some biologically important xanthines

Abstract Electronic absorption and fluorescence spectra of aqueous solutions of xanthine, caffeine, theophylline and theobromine have been studied at different pH. The observed spectra have been interpreted in terms of neutral and ionic forms of the molecules with the help of molecular orbital calculations. At neutral and acidic pH, the spectra can be assigned to the corresponding most stable neutral forms, with the exception that the fluorescence of xanthine at acidic pH appears to originate from the lowest singlet excited state of a cation of the molecule. At alkaline pH, xanthine and theophylline exist mainly as their monoanions. In xanthine and theophylline at alkaline pH, fluorescence originates from the lowest singlet excited state of the corresponding anion. However, in caffeine and theobromine, even at alkaline pH, fluorescence belongs to the neutral species. On the whole, the properties of xanthine are quite different from those of the methyl xanthines.

PTP-PEST: a protein tyrosine phosphatase regulated by serine phosphorylation.

The protein tyrosine phosphatase PTP-PEST is an 88 kDa cytosolic enzyme which is ubiquitously expressed in mammalian tissues. We have expressed PTP-PEST using recombinant baculovirus, and purified the protein essentially to homogeneity in order to investigate phosphorylation as a potential mechanism of regulation of the enzyme. PTP-PEST is phosphorylated in vitro by both cyclic AMP-dependent protein kinase (PKA) and protein kinase C (PKC) at two major sites, which we have identified as Ser39 and Ser435. PTP-PEST is also phosphorylated on both Ser39 and Ser435 following treatment of intact HeLa cells with TPA, forskolin or isobutyl methyl xanthine (IBMX). Phosphorylation of Ser39 in vitro decreases the activity of PTP-PEST by reducing its affinity for substrate. In addition, PTP-PEST immunoprecipitated from TPA-treated cells displayed significantly lower PTP activity than enzyme obtained from untreated cells. Our results suggest that both PKC and PKA are capable of phosphorylating, and therefore inhibiting, PTP-PEST in vivo, offering a mechanism whereby signal transduction pathways acting through either PKA or PKC may directly influence cellular processes involving reversible tyrosine phosphorylation.

Screening of non-steroidal anti-inflammatory drugs, barbiturates and methyl xanthines in equine urine by gas chromatography-mass spectrometry.

A gas chromatographic-mass spectrometric (GC-MS) screening procedure for 23 acidic drugs in equine urine is described. With the GC-MS method fifteen anti-inflammatory drugs, five barbiturates and three methyl xanthines can be detected with good sensitivity and selectivity. The method consists of alkaline hydrolysis, extraction with organic solvent using salting-out, clean-up extraction, methylation and screening with GC-MS in selected-ion monitoring mode. The limit of detection is 10 micrograms 1(-1) or lower, for most drugs.

Risk factors associated with fungal peritonitis in very low birth weight neonates with severe necrotizing enterocolitis

Fungal peritonitis is uncommon in infants with severe necrotizing enterocolitis with intestinal perforation. In our institution we noted a significant (P < 0.01) increase in fungal peritonitis from 7% (3 of 45 cases of peritonitis) from January, 1980, to June, 1989, to 35% (8 of 23 cases of peritonitis) from July, 1989, to December, 1991. The mean birth weight of 11 infants with fungal peritonitis (946 +/- 70 g) (mean +/- SE) was significantly less (P = 0.008) than that of 57 infants with bacterial peritonitis (1282 +/- 52 g). In a case-control study to identify risk factors associated with fungal peritonitis, 11 infants with bacterial peritonitis were matched to the 11 infants with fungal peritonitis by age at bowel perforation and birth weight. Infants with fungal compared with bacterial peritonitis had significantly longer (P < 0.05): median duration of umbilical vessel catheterization before bowel perforation, 10 vs. 3 days, respectively; median duration of antibiotic therapy before bowel perforation, 23 vs. 14 days, respectively; and median duration of intubation, 13 vs. 5 days, respectively. Other potential risk factors that were not significant in this study included duration of central venous catheterization, total parenteral nutrition, intravenous lipid administration, aminoglycoside use, dexamethasone use or methyl xanthine therapy. In summary fungal peritonitis in neonates with necrotizing enteritis was significantly related to extremely low birth weight, prolonged umbilical vessel catheterization, prolonged exposure to antibiotics and prolonged intubation.

Mechanism of Action of KRN2391, a Novel Vasodilator, in Canine Mesenteric Artery

The effect of vesnarinone (OPC-8212), an orally active positive inotropic agent was studied in tracheal muscle isolated from guinea pigs, and the mechanism of its action was analyzed. Vesnarinone (10(-6)-10(-4) M) caused a concentration-dependent relaxation of tracheal muscle pre-contracted by 10(-4) M histamine. The potency of the relaxing effect of vesnarinone was greater than that of theophylline; the pD2 values for vesnarinone and theophylline were 4.9 and 4.5, respectively. Vesnarinone reduced the high-K(+)-induced contracture of depolarized tracheal muscle non-competitively (pD'2 = 3.7). Vesnarinone at the low concentration of 3 x 10(-6) M shifted the concentration-response curve for isoproterenol in a parallel fashion to the left. Vesnarinone additively acted on the relaxing effect of isobutyl methyl xanthine. Propranolol (10(-5) M) and reserpine pre-treatment (5 mg/kg, i.p., 24 hr) had no effect on the relaxing effect of vesnarinone. These results suggested that vesnarinone elevated the intracellular cyclic AMP level via phosphodiesterase inhibition, resulting in the tracheal muscle relaxation.

Small-cell lung carcinoma: Inhibition of proliferation by vasoactive intestinal peptide and helodermin and enhancement of inhibition by anti-bombesin antibody

Small-cell lung cancer (SCLC) is a common and highly fatal malignancy for which there is no satisfactory treatment. The amphibian peptide bombesin and its mammalian counterpart, gastrin-releasing peptide, serve as autocrine growth factors for the SCLC cells, but little is known about endogenous substances that inhibit the growth and proliferation of these tumor cells. We report that the neuropeptide vasoactive intestinal peptide (VIP) markedly inhibits the growth and multiplication of SCLC cell lines NCI-H345 and NCI-H69, and that the closely related peptide helodermin inhibits the proliferation of NCI-H345 cells with even higher efficacy. In the latter cells, the inhibition by VIP and isobutyl methyl xanthine paralleled their ability to stimulate cyclic adenosine monophosphate production within the cells. The peptide-induced suppression of SCLC proliferation is enhanced in the presence of an anti-bombesin monoclonal antibody. The anti-mitogenic activities of VIP and helodermin, and their enhancement by anti-bombesin antibody, offer the potential for a new approach to the pharmacologic control of SCLC.

Effect of oral pentoxifylline in exercise-induced silent myocardial ischemia

Pentoxifylline, a methyl xanthine derivative with hemorheologic properties, has been used in the treatment of peripheral and cerebrovascular occlusive diseases. To assess its effect in myocardial ischemia, 20 patients with previous myocardial infarction and silent ischemia at exercise were randomized to receive pentoxifylline 1.2 gm/day or placebo during a 3-month double-blind trial. There were no differences in age, body mass index, or risk factors between groups. At the end of the study, patients in the placebo group showed no changes in physical work capacity or ST segment depression. In contrast, patients in the pentoxifylline group showed a slight but significant increase in physical work capacity (+0.24 ± 0.07 watts/kg; P < 0.01) and a decrease in both maximal exercise-induced ST segment depression (−0.80 ± 0.18 mm; P < 0.01) and at the ninth minute of recovery (−0.38 ± 0.13 mm; P < 0.05). The drug was generally well tolerated. We conclude that pentoxifylline diminishes exercise-induced electrocardiographic changes of myocardial ischemia and improves physical work capacity.

Comparison of Calmodulin Gene Expression in Human Neonatal Melanocytes and Metastatic Melanoma Cell Lines

The qualitative and quantitative expression of three calmodulin genes (CAM I, CAM II and CAM III) was characterized in human neonatal melanocytes and metastatic melanoma cell lines in the absence and presence of serum, other growth modulators, and/or 12-O-tetradecanoyl-phorbol-13-acetate (TPA). Results indicated that the qualitative expression in melanocytes was the same as that of melanomas, that is, CAM I gene expressed two transcripts, 4.4 kb and 2.1 kb, whereas CAM II and CAM III expressed one transcript each, 1.95 kb and 2.37 kb, respectively. Differential quantitative expression was seen particularly with CAM I. The average levels of both CAM I transcripts in melanomas were less than one-half those of melanocytes. Serum and other growth modulators (including Ca++, isobutyl methyl xanthine, bovine pituitary extract, and insulin) enhanced CAM I and CAM II gene expression in melanocytes; in contrast, the net effect of serum in melanomas was to decrease expression of CAM I and CAM III. This effect was most prominent in melanoma C81-46C. TPA markedly inhibited expression of all three CaM genes in melanocytes; however, in melanomas the net effect of TPA was to increase their expression. CAM I in melanoma C81-46C was the most sensitive to TPA stimulation.

Methyl xanthine, adenosine, and human taste responsivity.

The influences of three methyl xanthines (MX) on human taste responsivity, caffeine, theophylline, and theobromine, were examined using blind control procedures. Taste responsivity in the same subjects was determined using the matching procedure described by Schiffman (Study 1) and the whole-mouth procedure described by Sheperd (Study 2). In each study, the duration of MX pretreatment necessary to enhance taste responsivity was examined. No potentiation of overall- and taste-quality specific intensity ratings was observed for any tastant, independent of test procedure, type, and concentration of MX pretreatment, or length of MX pretreatment. Taste intensity ratings, especially for NaCl, were higher following pretreatment with water than methyl xanthine or adenosine combined with caffeine. Adenosine, added at several concentrations to caffeine pretreatments, influenced neither taste responsivity nor taste intensity ratings.

The function of (Na(+)-K+)ATPase in the beta cell: characterization of the enzyme in a glucose-responsive insulinoma.

(Na(+)-K+)ATPase is necessary for the maintenance of the membrane potential. The activity of this enzyme was studied in purified plasma membranes from a glucose-responsive rat insulinoma. Ouabain-sensitive (Na(+)-K+)ATPase activity showed expected ATP dependency with a Km of 0.4 mM. It was also dependent on Mg2+ (Km range 70-80 microM). In the presence of Mg and ATP, half-maximal activity was obtained at a Na concentration of 30 mM and the enzyme activity increased sigmoidally with a Hill coefficient of 1.5. No direct effect on enzyme activity was observed with the insulin secretagogues glucose, fructose, glyceraldehyde, and ketoisocaproate, or with dibuturyl-cAMP and the phosphodiesterase-inhibitor isobutyl methyl xanthine. It is concluded that (Na(+)-K+)ATPase is not directly influenced by known secretagogues associated with insulin release by the beta cell.

Antisense oligodeoxynucleotides to GS protein alpha-subunit sequence accelerate differentiation of fibroblasts to adipocytes.

Fully-differentiated mouse 3T3-L1 fibroblasts accumulate large amounts of lipid at 7-10 days after induction by insulin or by dexamethasone and a methyl xanthine. G proteins mediate transmembrane signalling from a diverse group of cell-surface receptors to effector units that include phospholipase C, adenylyl cyclase and ion channels. They are also targets of regulation themselves. 3T3-L1 fibroblasts display marked changes in levels of G protein when induced to differentiate to adipocytes. Here we show that cholera toxin, which ADP-ribosylates and activates the G protein subunit Gs alpha, blocks the induction of differentiation, whereas increasing intracellular cyclic AMP directly with the dibutyryl analogue or indirectly with pertussis toxin or forskolin does not affect differentiation. Oligodeoxynucleotides antisense to the sequence encoding Gs alpha accelerate differentiation markedly. The time course of adipogenesis declined from 7-10 days in controls to roughly 3 days in cultures treated with antisense-Gs alpha oligodeoxynucleotides, whereas oligodeoxynucleotides, antisense to Gi alpha 1, Gi alpha 3, and sense and missense to Gs alpha, had no such effect. Antisense-Gs alpha alone induced differentiation by day 7, indicating that Gs alpha activity modulates differentiation in 3T3-L1 cells, acting in a new role which is independent of increased intracellular cAMP.

Inhibitory actions of dopamine on Limulus visceral muscle involve a cyclic AMP-dependent mechanism.

1. The catecholamines dopamine, epinephrine and norepinephrine were detected in alumina extracts of Limulus midgut tissue using high performance liquid chromatography with electrochemical detection. Moderate levels of norepinephrine (28.2 +/- 2.1 ng/g) and dopamine (24.0 +/- 5.2 ng/g) were detected in the midgut, while epinephrine levels (7.4 +/- 0.9 ng/g) were less. Catecholamines were present in all regions along the longitudinal axis of the midgut, and norepinephrine and dopamine levels were highest in posterior regions. 2. Catecholamines decreased muscle tonus and inhibited spontaneous contractions of the Limulus midgut. Dopamine typically decreased spontaneous midgut activity at doses of 10(-8) M or greater, and produced inhibitory actions on all regions of the Limulus midgut. In some preparations epinephrine and norepinephrine elicited a secondary rhythmicity. The actions of dopamine opposed the excitatory effects produced by either proctolin or octopamine. 3. Catecholamines significantly elevated levels of cyclic AMP in Limulus midgut muscle rings. Dopamine (10(-5) M) increased cyclic AMP with a time course consistent with its physiological effects. Forskolin and several methyl xanthines increased Limulus midgut cyclic AMP levels and mimicked the inhibitory effects of dopamine on the isolated midgut preparation. Cyclic nucleotide analogues also produced dopamine-like effects on the isolated midgut preparation. Inhibition of cyclic nucleotide phosphodiesterase prior to addition of dopamine enhanced the effect of this amine to decrease baseline muscle tension. 4. The inhibitory effects of 10(-5) M dopamine on the midgut persisted in solutions of zero sodium and in the presence of tetrodotoxin. Zero calcium solutions gradually reduced spontaneous midgut activity and the effects of dopamine. Calcium channel blockers did not prohibit dopamine-induced relaxation.(ABSTRACT TRUNCATED AT 250 WORDS)

Suppressive effects of pentoxifylline on natural killer cell activity.

The methylxanthine derivative pentoxifylline, widely used as a hemorrheologic agent in the treatment of peripheral vascular disease, is now being evaluated for potential applications in patients with cancer. Recent studies have shown that pentoxifylline can modulate a number of neutrophil functions at in vitro concentrations of at least 50 micrograms/ml. Using a standard51chromium-release assay, we studied the suppressive effects of pentoxifylline on natural killer (NK) cell activity and found that pentoxifylline, at concentrations of 50 and 100 micrograms/ml, suppressed the in vitro NK cell activity of healthy volunteers by 25% and 75%, respectively. Postreaction supernatants from chromium-release studies were then assayed for prostaglandin E2 (PGE2) and tumor necrosis factor-alpha (TNF-alpha) by using enzyme-linked immunosorbent assay. Concentrations of both PGE2 and TNF-alpha were increased by more than five times in those assay wells containing pentoxifylline. Moreover, the addition of 1 microgram/ml indomethacin to the NK assay system containing pentoxifylline, completely inhibited PGE2 production and abrogated the pentoxifylline-induced NK suppression. The addition of PGE2 (1 x 10(-6) mol/L) to the assay system suppressed NK activity, whereas addition of 1 or 10 ng/ml TNF-alpha did not. Theophylline, another methylxanthine, failed to suppress NK activity like pentoxifylline at equimolar concentrations. Our studies provide the first evidence that concentrations of pentoxifylline of at least 50 micrograms/ml suppressed NK cell function by inducing PGE2 synthesis from effector peripheral-blood mononuclear cells.

A comparison of rat peritoneal mast cells purified using Percoll and Path-O-Cyte 4

Rat peritoneal mast cells (RPMC) purified through Percoll and a commercially available 35% bovine serum albumin (BSA) solution (Path-O-Cyte 4) are compared over a range of criteria with mixed peritoneal cell suspensions. Both the purity and spontaneous histamine release were slightly better in RPMC isolated through Percoll and histamine recovery was considerably greater using this method as opposed to Path-O-Cyte 4. The responsitivity of cells isolated by either method to compound 48/80 and ionomycin was comparable with that seen in non-purified RPMC. However, the histamine release induced by anti-rat IgE and concanavalin A was reduced in the purified cells especially in those isolated through BSA. Histamine release induced by IgE-directed ligands was potently inhibited by theophylline, isobutyl methyl xanthine, disodium cromoglycate and nedocromil sodium in both non-purified and Percoll-purified RPMC. In total, this study has shown that highly purified and viable RPMC can be obtained through Percoll purification. This method was seen to be generally superior to that of Path-O-Cyte 4.