Inhibition of lymphocyte function by 9-deazaadenosine

9-Deazaadenosine (c9Ado), a novel C-nucleoside, has been found to inhibit lymphocyte-mediated cytolysis (LMC) in a time-dependent manner. c9Ado inhibited LMC by 50% at concentrations of 10 and 0.07 microM after drug-pretreatment periods of 3 and 22 hr, respectively, although a 1-hr pretreatment of cytolytic lymphocytes with 100 microM c9Ado had no effect upon this lymphocyte function. c9Ado was metabolized rapidly and extensively to 9-deazaadenosine 5'-triphosphate (c9ATP) both by mouse cytolytic lymphocytes and by human erythrocytes. Adenosine kinase purified from rabbit liver phosphorylated c9Ado with a Km of 200 microM and a Vmax of 8% that for adenosine. The metabolic buildup of c9ATP in lymphocytes was accompanied by a large, time-dependent decrease in cellular ATP and by smaller percentage decreases in CTP, UTP and GTP. Among other biochemical effects examined, c9Ado was found to cause a decrease in lymphocyte cAMP content and appeared to be neither an inhibitor nor a substrate for S-adenosylhomocysteine hydrolase. Consistent with this latter result, L-homocysteine thiolactone had no effect on the inhibition of LMC by c9Ado. Neither the inhibition of LMC by c9Ado nor the metabolic formation of c9ATP in lymphocytes was affected by erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA), indicating that c9Ado is not a substrate for adenosine deaminase. 5-Iodotubercidin, a non-competitive inhibitor (Kis = 9 nM, Ku = 20 nM) of adenosine kinase, prevented the above effects of c9Ado on lymphocyte function, c9ATP formation, and ATP levels. Either complete preservation (with coformycin) or partial replenishment (with adenosine plus EHNA) of ATP levels in c9Ado-treated lymphocytes resulted in partial restoration of cytolytic function to cells containing large amounts of c9ATP. These results suggest that c9Ado is inhibitory to LMC both because it causes a decrease in the absolute concentration of ATP within the cytolytic lymphocytes and because it permits the establishment within these cells of an unfavorable c9ATP:ATP ratio which impedes the utilization of ATP in a reaction essential to the execution of this lymphocyte function.

Inhibition of lymphocyte-mediated cytolysis and cyclic AMP phosphodiesterase by erythro-9-(2-hydroxy-3-nonyl)adenine

The adenosine deaminase (ADA) inhibitor erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA), at low concentrations (less than 10 microM), enhances the inhibitory activity of adenosine against lymphocyte-mediated cytolysis (LMC) without itself being inhibitory. At higher concentrations, EHNA alone is inhibitory to LMC with an IC50 of 160 microM. This inhibition is reversible upon washout, appears to affect an early stage of the lytic process, and does not appear to involve changes in basal levels of cyclic AMP (cAMP), ribonucleoside 5'-triphosphate pool sizes, S-adenosylhomocysteine levels, or protein carboxymethylation. EHNA does enhance the cAMP response of cytolytic lymphocytes (CL) to activators of adenylate cyclase such as prostaglandin E1. EHNA inhibits lymphocyte high-affinity cAMP phosphodiesterase at immunosuppressive levels, exhibiting hyperbolic mixed-type inhibition (Ki = 83 microM, alpha = 0.47, beta = 0.18). Whereas inhibition of intralymphocytic ADA is complete at low concentrations (less than 25 microM) of EHNA, inhibition of LMC and intralymphocytic cAMP phosphodiesterase increases linearly with EHNA concentration to at least 200 microM. The presence of 200 microM EHNA during the centrifugation of mixtures of CL and EL4 leukemia target cells leads to increased CL cAMP levels. 2'-Deoxycoformycin, a more potent ADA inhibitor than EHNA, is not inhibitory to LMC and shows none of these cAMP-related effects. These results suggest that CL-target cell contact stimulates adenylate cyclase in the CL and that EHNA inhibits LMC due to its enhancement of this target cell-stimulated elevation of cAMP.

Modulation of cyclic AMP metabolism by S-adenosylhomocysteine and S-3-deazaadenosylhomocysteine in mouse lymphocytes

Mouse lymphocytes incubated with micromolar concentrations of adenosine or 3-deazaadenosine, in medium supplemented with L-homocysteine, rapidly accumulated supramillimolar concentrations of S-adenosylhomocysteine (AdoHcy) or S-3-deazaadenosylhomocysteine (c3AdoHcy), respectively. Lymphocytes thus preloaded with high levels of AdoHcy or c3AdoHcy exhibited markedly enhanced (5- to 40-fold) cyclic AMP responses to prostaglandin E1, adenosine, 2-chloroadenosine, isoproterenol, and cholera toxin. This enhancement of cyclic AMP response by intracellular AdoHcy or c3AdoHcy was attributable both to amplification of the activity of adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] and to inhibition of cyclic AMP phosphodiesterase (3',5'-cyclic-nucleotide 5'-nucleotidohydrolase, EC 3.1.4.17). Basal and prostaglandin E1- and isoproterenol-stimulated activities of adenylate cyclase, assayed in lymphocyte homogenates, were increased 1.3- to 2.0-fold after treatment of the cells with homocysteine plus either adenosine or 3-deazaadenosine. AdoHcy and c3AdoHcy were found to be competitive inhibitors (with Ki values of 1.7 and 4.8 mM, respectively) of the high-affinity cyclic AMP phosphodiesterase present in lymphocyte homogenates. It is evident, therefore, that increased cellular levels of AdoHcy or c3AdoHcy can affect cellular physiology via perturbation of cyclic AMP metabolism as well as via inhibition of S-adenosylmethionine-dependent methylation reactions.

Adenosine analogues as substrates and inhibitors of S-adenosylhomocysteine hydrolase in intact lymphocytes

A number of adenosine analogues have been examined for their ability to interact with S-adenosyl-L-homocysteine (SAH) hydrolase in intact mouse lymphocytes. In the presence of erythro-9-(2-hydroxy-3-nonyl)adenine, 3-deazaadenosine, 8-azaadenosine, formycin A, 2-aminoadenosine, 2-fluoroadenosine, N6-methyladenosine, N6-hydroxyadenosine, purine ribonucleoside and inosine were each metabilized to radioactive analogues of SAH when cells were labeled with either L-[2-3H]methionine or L-[35S]homocysteine. Tubercidin was shown to undergo metabolism both to S-[3H]tubercidinyl-L-methionine and to S-[3H]tubercidinyl-L-homocysteine in cells labeled with [2-3H]methionine. 9-beta-D-Arabinofuranosyladenine and 2'-deoxyadenosine caused marked elevations of [3H]SAH in cells preloaded with [2-3H]methionine but were not themselves metabolized detectably to SAH analogues. Adenine and 5'-deoxyadenosine also caused substantial elevations of [3H]SAH under these same conditions. Some of the adenosine analogues shown to be metabolized to SAH analogues also caused an elevation of SAH in the lymphocytes. These results indicate the potential of adenosine analogues to interfere with cellular methylation reactions due either to their inhibition of SAH hydrolase or to their metabolism, via this enzyme, to SAH analogues.

Therapeutic nerve blocks for chronic pain

Nerve blocks are an effective treatment in patients with many types of acute pain. However, they are much less effective in patients with chronic pain. Candidates for therapeutic nerve blocks should be carefully screened by: assessment of organic disease; evaluation of psychologic and behavioral disorders, and differential nerve blocks. The best candidates for therapeutic nerve blocks have known or inferred organic disease, minimal psychologic or behavioral disorders, and evidence of sympathetic or somatic pain mechanisms.

Inhibition of lymphocyte-mediated cytolysis by 3-deazaadenosine: evidence for a methylation reaction essential to cytolysis

3-Deazaadenosine (deazaAdo) inhibits lymphocyte-mediated cytolysis in vitro at micromolar concentrations and is potentiated markedly in this activity by L-homocysteine thiolactone. DeazaAdo alone causes a rapid, dose-dependent buildup of S-[(3)H]adenosylhomocysteine (AdoHcy) and S-[(3)H]adenosylmethionine in cytolytic lymphocytes labeled with L-[2-(3)H]methionine; smaller amounts of S-3-[(3)H]deazaadenosylhomocysteine (deazaAdoHcy) are also formed in these cells. The simultaneous addition of deazaAdo and L-homocysteine thiolactone to the lymphocytes results in a massive intracellular accumulation of deazaAdoHcy. Both the inhibition of lymphocyte-mediated cytolysis and the cellular accumulation of [(3)H]AdoHcy caused by deazaAdo alone are reversed rapidly by removal of drug from the medium. However, the inhibition of cytolysis and the large cellular buildup of deazaAdoHcy resulting from treatment of the lymphocytes with deazaAdo plus L-homocysteine thiolactone are dissipated more slowly under these same conditions. Unlike adenosine, deazaAdo is not potentiated in its inhibition of lymphocyte-mediated cytolysis by Ro 20-1724 [4-(3-butoxy-4-methoxybenzyl)-2-imidazolidinone], an inhibitor of cyclic AMP phosphodiesterase, and has little or no effect upon the level of lymphocytic cyclic AMP. DeazaAdo is not metabolized detectably to 5'-nucleotides in the lymphocytes and does not cause a decrease in the pool sizes of CTP, UTP, ATP, or GTP. Both AdoHcy and deazaAdoHcy have been reported to be powerful inhibitors of a variety of S-adenosylmethionine-utilizing methyltransferases. The present results, therefore, indicate that the effect of deazaAdo upon lymphocyte-mediated cytolysis is due ultimately to the inhibition of an unidentified but crucial methyltransferase within the cytolytic lymphocytes and provide an insight into the biochemical processes involved in lymphocyte-mediated cytolysis.

Antibody to Corynebacterium parvum in normal human and animal sera

Using a microtiter bacterial agglutination test, we have estimated antibodies to Corynebacterium parvum in "normal" human and "normal" and immune animal sera. Widely differing levels of C. parvum antibodies were found in the normal human sera. The median titer for all 310 human sera was 1:128, whereas that for the 1- to 17-year and 18- to 50-year subgroups was 1:64 and 1:512, respectively. Antibody titers in the various animal species were generally much lower.

2-Fluoroadenosine 3':5'-monophosphate. A metabolite of 2-fluoroadenosine in mouse cytotoxic lymphocytes

2-Fluoroadenosine (F-Ado) is a potent inhibitor of lymphocyte-mediated cytolysis studied in vitro. The inhibition of cytolysis by F-Ado was potentiated markedly by an inhibiotr (Ro 20-1724) of adenosine 3':5'-monophosphate (cAMP) phosphodiesterase and, unlike the inhibition caused by adenosine, was irreversible when the cytotoxic lymphocytes were incubated with F-Ado and were then washed free of exogenous nucleoside. Incubation of cytotoxic lymphocytes with F-Ado resulted in the rapid, dose-dependent formation of 2-fluoroadenosine 5'-triphosphate (F-ATP); the build-up of F-ATP within these cells was accompanied by a reciprocal depletion of ATP. Once formed intracellularly, the F-ATP was not diminished during a subsequent 30-min incubation of the cells in F-Ado-free medium. 2-Fluoroadenosine 3':5'-monophosphate (F-cAMP), a novel compound, was synthesized chemically. This cAMP analogue was found to be highly cross-reactive in a radioimmunoassay specific for cAMP and to be equipotent to cAMP in its ability to activate a crude preparation of protein kinase derived from rat brain. A column chromatographic procedure was devised whereby F-cAMP and cAMP could be purified simultaneously from tissue extracts. Treatment of cytotoxic lymphocytes with F-Ado resulted in the formation of presumptive F-cAMP in amounts greater than that of cAMP, as determined by the concentration of F-Ado added to the medium and was not observed when the lymphocytes were incubated with either adenosine or 2-chloroadenosine, two agents which caused large increases in cAMP. The simultaneous presence of Ro 20-1724 enhances greatly the formation of F-cAMP from F-Ado without affecting the pool size of F-ATP. Removal of exogenous F-Ado from cells previously incubated with this drug and subsequent incubation of these cells in drug-free medium did not result in a substantial reduction in intracellular F-Ado (via prior incubation with F-Ado); 2'-deoxyadenosine was also effective in this capacity, while 9-beta-D-arabinofulanosyladenine was without effect. The level of cAMP was elevated transiently, in a dose-dependent manner, by F-Ado, and returned to control value after removal of exogenous F-Ado from the cells. Ro 20-1724 enhanced greatly this transient elevation of cAMP caused by F-Ado.