Expression of protein kinase C inhibitor blocks cerebellar long-term depression without affecting Purkinje cell excitability in alert mice

A longstanding but still controversial hypothesis is that long-term depression (LTD) of parallel fiber-Purkinje cell synapses in the cerebellum embodies part of the neuronal information storage required for associative motor learning. Transgenic mice in which LTD is blocked by Purkinje cell-specific inhibition of protein kinase C (PKC) (L7-PKCI mutants) do indeed show impaired adaptation of their vestibulo-ocular reflex, whereas the dynamics of their eye movement performance are unaffected. However, because L7-PKCI mutants have a persistent multiple climbing fiber innervation at least until 35 d of age and because the baseline discharge of the Purkinje cells in the L7-PKCI mutants is unknown, factors other than a blockage of LTD induction itself may underlie their impaired motor learning. We therefore investigated the spontaneous discharge of Purkinje cells in alert adult L7-PKCI mice as well as their multiple climbing fiber innervation beyond the age of 3 months. We found that the simple spike and complex spike-firing properties (such as mean firing rate, interspike interval, and spike count variability), oscillations, and climbing fiber pause in the L7-PKCI mutants were indistinguishable from those in their wild-type littermates. In addition, we found that multiple climbing fiber innervation does not occur in cerebellar slices obtained from 3- to 6-month-old mutants. These data indicate (1) that neither PKC inhibition nor the subsequent blockage of LTD induction disturbs the spontaneous discharge of Purkinje cells in alert mice, (2) that Purkinje cell-specific inhibition of PKC detains rather than prevents the developmental conversion from multiple to mono-innervation of Purkinje cells by climbing fibers, and (3) that as a consequence the impaired motor learning as observed in older adult L7-PKCI mutants cannot be attributable either to a disturbance in the baseline simple spike and complex spike activities of their Purkinje cells or to a persistent multiple climbing fiber innervation. We conclude that cerebellar LTD is probably one of the major mechanisms underlying motor learning, but that deficits in LTD induction and motor learning as observed in the L7-PKCI mutants may only be reflected in differences of the Purkinje cell signals during and/or directly after training.

Identification of R146225 as a novel, orally active inhibitor of interleukin-5 biosynthesis

Interleukin (IL)-5 regulates the growth, differentiation, and activation of eosinophils. When activated, eosinophils release an array of proinflammatory and cytotoxic products and act as prominent effector cells in the process of allergic inflammation. Depriving eosinophils of IL-5 may therefore represent a viable approach to treat allergic disorders. This study describes the identification of R146225, a novel six-substituted azauracil derivative, as a potent, orally active inhibitor of IL-5 biosynthesis, capable of reducing pulmonary eosinophilia in mice. In vitro, R146225 inhibited IL-5 protein formation by activated human whole blood (IC(50) = 34 nM), human peripheral blood mononuclear cells (IC(50) = 24 nM), and murine spleen cells (IC(50) = 6 nM). In contrast, the compound enhanced generation of interferon-gamma and had little or no inhibitory effect on the production of IL-2 and IL-4. Reverse transcription-polymerase chain reaction analysis of stimulated whole blood cells indicated R146225's ability to down-regulate IL-5 mRNA expression. In vivo p.o. administration of R146225 (2.5 mg/kg) to mice before an i.v. anti-CD3 antibody challenge reduced IL-5 but enhanced interferon-gamma serum levels, without affecting IL-2 and IL-4 production. Analogous to the in vitro results, R146225 suppressed splenic IL-5 mRNA expression, while message levels of the other cytokines remained unchanged. Moreover, p.o. dosing of R146225 (0.6-2.5 mg/kg) dose dependently reduced the pulmonary accumulation of eosinophils induced in mice by an intranasal instillation of Cryptococcus neoformans. Based on these data, R146225 may be useful in the therapy of eosinophil-driven allergic conditions.

R115866 inhibits all-trans-retinoic acid metabolism and exerts retinoidal effects in rodents

All-trans-retinoic acid (RA) regulates epithelial differentiation and growth through activation of specific nuclear RA receptors (RARs). Because high-rate metabolism largely impairs the biological efficacy of RA, we have sought for compounds capable of inhibiting the metabolic breakdown of the retinoid. This study identifies R115866 as a novel inhibitor of the cytochrome P450 (CYP)-mediated metabolism of RA. In vitro, nanomolar concentrations of R115866 inhibited the conversion of RA by CYP26, a RA-inducible RA metabolizing enzyme. In vivo, oral administration of R115866 (2.5 mg/kg) to rats induced marked and transient increases of endogenous RA levels in plasma, skin, fat, kidney, and testis. Consistent with its ability to enhance endogenous RA content in tissues, R115866 was found to exert retinoidal activities. Like RA, the title compound: 1) inhibited vaginal keratinization in estrogen-stimulated rats; 2) induced epidermal hyperplasia in mouse ear skin; 3) transformed mouse tail epidermis from a para- to an orthokeratotic skin type; and 4) up-regulated the CYP26 mRNA expression in rat liver. Furthermore, we found that the keratinization-suppressive and CYP26-inducing activities of R115866 could be reversed by concomitant administration of the RAR antagonist, AGN193109. Our data characterize R115866 as a potent, orally active inhibitor of RA metabolism, capable of enhancing RA levels and displaying retinoidal actions. These activities are reversed by RAR antagonism, supporting the idea that the actions of R115866 result from increased availability of endogenous RA and improved RAR triggering.

Inversely-correlated inhibition of human 5-lipoxygenase activity by BAY X1005 and other quinoline derivatives in intact cells and a cell-free system--implications for the function of 5-lipoxygenase activating protein

A series of quinoline derivatives were analysed for the influence on leukotriene synthesis as a parameter for 5-LOX (EC 1.13.11.34) activity in a cell-free system of the 10,000 g supernatant of human PMNL (polymorphonuclear leukocytes). The ratios of the IC50 values for leukotriene synthesis inhibition in this cell-free system and in A23187-stimulated intact PMNL ranged from 1-1100. Consequently, plotting of the two values resulted in a random distribution (r = -0.281, N = 18) suggesting that no relationship between the inhibition of leukotriene synthesis in the cell-free system and in intact cells exists. At first sight this finding was not surprising since we have shown earlier that in intact cells this class of quinoline derivatives shares the same mode of action as MK-886, i.e. an indirect inhibition of 5-LOX activity by binding to FLAP. However, we found that the potency of these compounds in intact cells is strongly influenced by the K value (partition coefficient) which is a parameter for the ability of a substance to accumulate in a lipid (membrane) phase compared to the water phase. Therefore, the IC50 values for leukotriene synthesis inhibition in intact PMNL were corrected for the corresponding K value of the compounds and the resulting values again plotted against the IC50 values for inhibition of leukotriene synthesis in the cell-free system. As a result, a significant correlation (r = -0.878, N = 18) was obtained. In order to simplify this relationship the influence of the partition coefficient was eliminated by comparing compounds with about the same K value (K = 7243 +/- 1646, N = 7). As a result, the IC50 values for inhibition of leukotriene synthesis in the 10,000 g supernatant fraction (indicative for the affinity of the compounds to 5-LOX) and in intact cells (indicative for the affinity of the compounds to FLAP) were highly, but inversely correlated (r = -0.992). That means that a compound with a high affinity to 5-LOX will have a low affinity to FLAP and vice versa. We hypothesized that this pharmacologically obtained relationship could be indicative of a physiologically occurring equivalent. We therefore propose a model in which FLAP binds arachidonic acid as its physiological substrate with low affinity and allows 5-LOX to get access to its substrate (assuming a higher affinity of 5-LOX to arachidonic acid) after 5-LOX translocation from the cytosol to the membrane.(ABSTRACT TRUNCATED AT 400 WORDS)

Liarozole fumarate inhibits the metabolism of 4-keto-all-trans-retinoic acid

The metabolism of 4-keto-all-trans-retinoic-acid (4-keto-RA), a biologically active oxygenated metabolite of all-trans-retinoic (RA), has been examined. In vitro, incubation of [14C]4-keto-RA with hamster liver microsomes in the presence of NADPH produced two major radioactive metabolites which were more polar than the parent compound. Following isolation, appropriate derivatization and analysis by GC-MS, these compounds were tentatively identified as 2-hydroxy- and 3-hydroxy-4-ketoretinoic acid. Formation of both hydroxy-keto derivatives was suppressed by the imidazole-containing P450 inhibitor liarozole fumarate (IC50, 1.3 microM). In vitro, an i.v. injection of 4-keto-RA (20 micrograms) into rats was followed by rapid disappearance of the retinoid from plasma with a half-life of 7 min. Pretreatment with liarozole fumarate (40 mg/kg, -60 min) reduced the elimination rate of 4-keto-RA: it prolonged the plasma half-life of the retinoid to 12 min, without affecting its distribution volume. These results indicate the important role of the P450 enzyme system in the metabolism of 4-keto-RA both in vitro and in vivo. The inhibitory effect of liarozole fumarate on this metabolic process may contribute to the reported retinoid-mimetic activity of this drug.

Liarozole, an inhibitor of retinoic acid metabolism, exerts retinoid-mimetic effects in vivo

Liarozole is an imidazole-containing compound that inhibits the cytochrome P-450-dependent metabolism of all-trans-retinoic acid (RA). In vitro, liarozole (IC50, 2.2 microM) suppressed the P-450-mediated conversion of RA to more polar metabolites by hamster liver microsomes. In vivo, it enhanced the plasma level of RA from mostly undetectable values (less than 0.5 ng/ml) in control rats to 1.4 +/- 0.1 and 2.9 +/- 0.1 ng/ml in animals treated p.o. with 5 and 20 mg/kg of liarozole, respectively. Moreover, liarozole possessed antikeratinizing activity: when dosed subchronically (5-20 mg/kg, once daily for 3 days) to ovariectomized rats, the compound reversed the vaginal keratinization induced in these animals by estrogenic stimulation. Dose response experiments indicated that the antikeratinizating effect of liarozole was as potent as that of RA. One-dimensional electrophoresis and immunoblotting of extracted vaginal epithelia showed that liarozole shared with RA the ability to inhibit the synthesis of high molecular weight (57-60 kDa) keratin proteins, and to enhance the expression of the 45 to 47 kDa keratin polypeptides. Furthermore, we found that antikeratinizing doses of liarozole doubled the RA concentration in the vagina of ovariectomized rats: the mean amount of RA extracted from 200 mg of vaginal tissue was increased from 1.1 +/- 0.1 ng in vehicle-treated animals to 2.2 +/- 0.2 and 2.6 +/- 0.2 ng after treatment with 5 and 20 mg/kg of liarozole, respectively. These findings indicate that liarozole, an inhibitor of RA metabolism and RA produce similar morphologic and biochemical effects on the differentiation process of rat vaginal epithelium.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of cytochrome P-450 inhibitors on the in vivo metabolism of all-trans-retinoic acid in rats

This study examines the effects of ketoconazole, R 75 251 and some other cytochrome P-450 inhibitors on the in vivo metabolism of all-trans-retinoic acid (RA) in normal rats. Oral treatment with ketoconazole or R 75 251 (40 mg/kg, -1 hr) reduced the elimination rate of i.v. injected RA from plasma: the half-life of RA increased from 27 min in control-treated animals to 43 min and 76 min after dosing with ketoconazole and R 75 251, respectively. However, neither drug had an effect on the distribution volume of the retinoid. Two hours after i.v. injection of RA, residual plasma levels of the retinoid were 11.2 ng/ml in ketoconazole and 22.7 ng/ml in R 75 251-treated rats. The other P-450 inhibitors, aminoglutethimide, cimetidine, itraconazole, metyrapone and saperconazole, showed no sparing effect on RA elimination: plasma levels of the acid were below 1 ng/ml, as in control-treated animals. Administration of ketoconazole or R 75 251 (40 mg/kg, -2 hr) to rats also enhanced endogenous plasma concentrations of RA. Levels of the retinoid were raised from mostly undetectable values (less than 0.5 ng/ml) to 1.3 +/- 0.1 and 2.5 0.1 ng/ml after treatment with ketoconazole and R 75 251, respectively. These data are indicative of the important contribution of the cytochrome P-450 enzyme system to the in vivo metabolic process of RA. In vivo inhibition of the P-450 pathway not only increased the biological half-life of exogenously administered RA, but also enhanced the endogenous plasma level of this vitamin A derivative.

Ketoconazole inhibits the in vitro and in vivo metabolism of all-trans-retinoic acid

Ketoconazole, an antifungal agent and inhibitor of certain mammalian cytochrome P-450-dependent enzymes, was studied for its effects on the in vitro and in vivo metabolism of all-trans-retinoic acid (RA). In vitro, ketoconazole (Ki = 0.75 microM) inhibited, in an apparently competitive manner, the cytochrome P-450-mediated metabolism to 4-hydroxy- and 4-keto-retinoic acids by hamster liver microsomes. In vivo, ketoconazole suppressed the formation of polar RA metabolites by normal rats dosed intrajugularly with 200 ng of [3H]RA. After p.o. treatment with ketoconazole (2.5-40 mg/kg) given 1 hr before the [3H]RA injection, the radioactivity extracted from the liver consisted of 25 to 50% polar metabolites (control 66 +/- 1%) and 50 to 75% undegraded RA (control 34 +/- 1%) as evidenced by reverse-phase high-performance liquid chromatography. Time course experiments showed that ketoconazole's inhibitory effects lasted for 3 hr. Our data indicate the quantitative importance of the cytochrome P-450 enzymatic pathway in the biotransformation of RA. They also suggest that ketoconazole is capable of prolonging the biological half-life of RA and of improving the tissue levels of this compound.

Influence of praziquantel and Ca2+ on the bilayer-isotropic-hexagonal transition of model membranes

Praziquantel induces a bilayer to isotropic transition in the absence of Ca2+ in a mixed phospholipid membrane consisting of phosphatidylethanolamine (PE) and phosphatidylserine (PS) at a molar ratio of 2:1 at 25 degrees C or 35 degrees C, irrespective of the lipid/drug molar ratio (10:1; 2:1). Addition of Ca2+ at different PS/Ca2+ molar ratios (4:1, 2:1 or 1:1) leads to a transition to a hexagonal (HII) state. With a phospholipid membrane of different composition (PE/PS molar ratio 4:1) praziquantel exerts quite different effects in the presence of Ca2+ (PS/Ca2+ molar ratio 1:1). An isotropic-signal appears together with a bilayer one at 25 degrees C, while a HII-signal can be detected at 35 degrees C. Thus, two separate phases coexist at this PE/PS molar ratio, while at a PE/PS molar ratio of 2:1, praziquantel and Ca2+ induce only a HII-signal. The results with these model membranes show that praziquantel and Ca2+ exert drastic influences on bilayer-isotropic-hexagonal transitions. The possibility that this drug might act in the schistosomal tegumental membranes in the same way is discussed.

Cytoprotective effects of disodium cromoglycate on rat stomach mucosa

The cytoprotective effects of the anti-asthmatic drug, disodium cromoglycate (DSCG), on gastric mucosal necrosis induced by ethanol in rats were studied. Subcutaneous, but not oral, DSCG prevented the formation of gastric lesions and this effect was dose-dependent between 1.25 and 40 mg kg-1, with an ED50 value of 6.8 mg kg-1. Maximal cytoprotection occurred 15-30 min after DSCG treatment. Histological examination revealed that DSCG effectively protected the gastric mucosa against ethanol-induced vascular congestion, haemorrhage, epithelial desquamation and mucosal oedema. Enhanced production of endogenous prostaglandins, which are known cytoprotective compounds, could not explain the mucosal protection. At a dose of 40 mg kg-1, DSCG did not change prostaglandin E2 or 6-keto-prostaglandin F1 alpha concentrations in gastric mucosal tissue, although its cytoprotective activity was partially inhibited by prior treatment of the animals with indomethacin.

Inhibition of lymphocyte proliferation by monoclonal antibody directed against the T3 antigen on human T cells

Peripheral blood mononuclear cells from 40% of normal donors are mitogenically unresponsive to UCHT1, a monoclonal antibody reactive to the T3 surface molecule on human T lymphocytes. Cell preparations from non-UCHT1 responders were used to examine whether and how interaction of UCHT1 with the T3 molecule affects T-cell functionality. It was found that UCHT1 profoundly (greater than 85%) suppressed lymphocyte proliferation induced by plant mitogens (phytohemagglutinin (PHA) and concanavalin A (Con A], recall antigen (candidin), and allogeneic non-T cells. The antibody abrogated both the production of interleukin 2 (IL-2) by and the expression of IL-2-specific receptors on T lymphocytes stimulated by PHA or allogeneic non-T cells. UCHT1 was maximally suppressive when added to cells within 2 hr (PHA stimulation) or 1 day (allogeneic non-T cell activation) after the initiation of the culture period. The inhibiting activity of UCHT1 could be related to its ability to modulate T3 molecules from the T-cell surface: both actions displayed the same antibody concentration dependence and had a comparable time dependence. Moreover, after modulation, unresponsive lymphocytes regained responsiveness to PHA in parallel with reexpression of surface T3 molecules. These findings are consistent with the idea that the human T3 molecule functions as an essential signal transducer during the early phases of T-cell activation.

Effects of antioxidants on cyclooxygenase and lipoxygenase activities in intact human platelets: comparison with indomethacin and ETYA

Five antioxidative agents (BW755C, 1-naphtol, NDGA, propylgallate and quercetin) were compared with indomethacin and ETYA for their effects on (14C) arachidonic acid metabolism by cyclooxygenase (CO) and lipoxygenase (LPO) enzymes in intact human platelets. All tested compounds inhibited CO activity in a concentration-dependent manner. LPO activity was suppressed by NDGA, propylgallate, quercetin and ETYA but strongly enhanced by BW755C, 1-naphtol and indomethacin. Whereas NDGA and ETYA showed almost equi-potent inhibitory effects towards both fatty acid oxygenases, propylgallate and quercetin were found to be respectively 6.5 and 4 times better inhibitors of LPO than of CO activities. These data indicate that antioxidants affect arachidonic acid metabolism in intact human platelets in different ways: BW755C and 1-naphtol exerted the same activity as indomethacin, a selective CO blocker, whereas NDGA, propylgallate and quercetin behaved as ETYA, a dual CO-LPO inhibitor. Considering their inhibition selectivity, propylgallate and quercetin may serve as prototypes for more specific blockers of LPO activity.

Suppression of human T-cell mitogenesis and E-rosette formation by the monoclonal antibody OKT11A

OKT11A, a monoclonal anti-human T-cell antibody was studied for its in vitro effects on lymphocyte functions. At a concentration as low as 10 ng/ml, OKT11A significantly suppressed T-cell proliferation induced by OKT3, purified protein derivative (PPD), tetanus toxoid and allogeneic non-T cells. Total inhibition of proliferation was noticed at concentrations of 1-10 microgram OKT11A/ml. The antibody was only fully effective when added to stimulated cell cultures within the first 2 hr of the culturing period. OKT11A also blocked total and active sheep erythrocyte (E)-rosette formation by T lymphocytes: this activity closely paralleled the suppression of proliferative response. Quantitative studies on the binding of 125I-labelled IKT11A indicated that an average of 2 x 10(4) antibody molecules were bound per T cell. Taken together, these findings show that OKT11A recognizes a sparsely represented T-cell surface determinant that is associated with the inhibition of mitogenic responsiveness and E-rosette formation. Furthermore, our data imply that the E-rosette receptor of T cells is involved in the regulation of immune functions.

Mitogenic actions of Orthoclone OKT3 on human peripheral blood lymphocytes: effects of monocytes and serum components

The Orthoclone monoclonal antihuman T lymphocyte antibody, OKT3, induced maximal DNA, RNA and protein synthesis in peripheral mononuclear blood cells (PMBC) at concentrations as low as 10 ng ml-1. This pronounced mitogenic activity was highly dependent on the presence of monocytes: removal of these cells from PMBC suspensions by complement (C)-dependent lysis with the antimonocyte antibody OKM1, completely abrogated the proliferative responsiveness of the remaining lymphocytes. The addition of adherent cells to OKM1-treated PMBC demonstrated the strict monocyte requirement for the mitogenic activity of OKT3. Mitogenic responses to OKT3 were most marked when PMBC were cultured in media containing heat-inactivated fetal calf serum (FCS) but they were considerably weaker in cultures supplemented with heat-inactivated human serum (HS). Moreover, aggregated human IgG and its Fc fragments (but not monomeric IgG and its Fab fragments) inhibited the mitogenicity of OKT3: their inhibition could be explained by stimulation of monocytes, resulting in increased prostaglandin E release, since (a) prostaglandin E2 itself strongly suppressed OKT3 activity and (b) indomethacin blocked the inhibitory effects of aggregated HuIgG. The present data demonstrate that OKT3 shows a particular pattern of mitogenicity: the strict monocyte requirement, the inhibitory effects of HS, aggregated human IgG and prostaglandin E2 were not observed for the phytomitogen PHA.

Monoclonal anti-human T-lymphocyte antibodies: enumeration and characterization of T-cell subsets

The complement-mediated lysis of human lymphocytes by three monoclonal anti-human T-cell antibodies OKT3.PAN, OKT4.INd and OKT8.SUP was studied. The percentages of Ficoll-Hypaque-isolated mononuclear cells lysed by these antibodies were respectively: 65% for OKT3.PAN, 39% for OKT4.IND and 20% for OKT8.SUP. Optimal lymphocytotoxic reactions were noticed when unabsorbed rabbit serum was used as the source of complement (C). Addition of heat-inactivated human, mouse and newborn calf sera but not of foetal calf serum inhibited the lytic activity of the antibodies. Treatment of peripheral mononuclear blood cells with OKT3.PAN and C abrogated their mitotic response to PHA and Con-A. Sheep erythrocyte rosetting lymphocytes (E+ cells) treated with OKT4.IND or OKT8.SUP and C exhibited no marked changes in responsiveness to PHA, Con-A or allogeneic non-T cells. However, only E+ cells enriched with OKT4.IND-reactive cells responded to purified protein derivative, proliferated in the autologous mixed lymphocyte reaction and were highly sensitive to hydrocortisone suppression when stimulated by PHA. Our data indicate that these monoclonal antibodies can be regarded as invaluable tools for enumeration, characterization and functional assessment of human T cells and their subclasses.

Lack of platelet factor-3 activation after incubation of platelet-rich plasma with kaolin in the rat

Stypven times, measured in rat platelet-rich plasma (P.R.P.) after incubation with kaolin, did not shorten as incubation proceeded, thus reflecting the lack of development of platelet factor-3 (PF3) availability in this test system. Repeated freezing and thawing of P.R.P. or aggregation with collegan did result in PF-3 availability. Aggregation and PF-3 availability were inhibited by the compound VK774. These findings add another aspect to the list of species differences in platelet function.