Selective inhibition of phospholipases by atiprimod, a macrophage targeting antiarthritic compound

Azaspiranes are cationic amphiphilic compounds that are active in a number of models of autoimmune disease and transplantation. Repeated administration of cationic amphiphiles induces phospholipid accumulation in a variety of species. The present study was conducted to explore the mechanism of phospholipid accumulation in rats caused by treatment with the novel azaspirane, SK&F 106615 (atiprimod). Atiprimod inhibited the activities of partially purified phospholipases A(2) and C, but not D, in a noncompetitive manner in vitro. Treatment of rats for 28 days with 10 mg/kg/day of atiprimod increased the contents of arachidonate-containing molecular species within plasmalogen subclasses of hepatic phosphatidylcholine and phosphatidylethanolamine. In contrast, diacyl-linked species were not affected, indicating a selective effect upon an hepatic plasmalogen-selective phospholipase A(2). Taken together, the data suggest that the beneficial effects of atiprimod in autoimmune diseases may involve inhibition of phospholipase A(2) and C activities. Further, the data suggest that atiprimod is a selective inhibitor of plasmalogen-selective phospholipase A(2) in vivo.

p38 mitogen-activated protein kinase inhibitors--mechanisms and therapeutic potentials

The pyridinylimidazole compounds, exemplified by SB 203580, originally were prepared as inflammatory cytokine synthesis inhibitors. Subsequently, the compounds were found to be selective inhibitors for p38 mitogen-activated protein kinase (MAPK), a member of the MAPK family. SB 203580 inhibits the catalytic activity of p38 MAPK by competitive binding in the ATP pocket. Four homologues of p38 MAPK have been identified to date, and interestingly, their biochemical properties and their respective sensitivities to the inhibitors are distinct. X-ray crystallographic analysis of p38-inhibitor complexes reinforces the observations made from site-directed mutagenesis studies, thereby providing a molecular basis for understanding the kinase selectivity of these inhibitors. The p38 MAPK inhibitors are efficacious in several disease models, including inflammation, arthritis and other joint diseases, septic shock, and myocardial injury.

Distinct membrane and cytosolic forms of inositol polyphosphate 5-phosphatase II. Efficient membrane localization requires two discrete domains

The 75-kDa inositol polyphosphate 5-phosphatase (5-phosphatase II) hydrolyzes various signaling molecules including the following: inositol 1,4,5-trisphosphate, inositol 1,3,4,5-tetrakisphosphate, phosphatidylinositol 4,5-bisphosphate, and phosphatidylinositol 3,4, 5-trisphosphate. Although studied extensively, a demonstrably full-length cDNA encoding 5-phosphatase II has yet to be isolated. In this study we used a human partial 2.3-kilobase pair (kb) cDNA to screen mouse brain and kidney cDNA libraries, resulting in the isolation of a 3.7-kb cDNA (M5), which by multiple criteria represents a full-length cDNA encoding a 115-kDa 5-phosphatase II. We also isolated a smaller cDNA (M22) with a unique N terminus that encodes a 104-kDa polypeptide. Analysis of these cDNAs suggests a further 87-kDa isoform may arise from differential splicing resulting in translation at methionine 234 in M5. RNA analysis of tissues demonstrates expression of two mRNA species of approximately 4.0 or 3.0 kb, respectively. Probes unique to the 5' end of M5 or M22 hybridized to the 4.0- or 3.0-kb transcripts, respectively. RNA analysis using probes derived from sequence 3' to the potential splice site in M5 and M22 hybridized to both transcripts. Expression of the recombinant 115-kDa protein, or a smaller recombinant protein lacking the N terminus transiently in COS-7 cells, showed localization of enzyme activity to the membrane. Removal of the C-terminal CAAX motif resulted in a significant translocation of the protein lacking the N terminus but not the 115-kDa 5-phosphatase to the cytosol. Western blot analysis of membrane and cytosolic fractions of multiple mouse tissues confirmed the 115-kDa 5-phosphatase II was located in the membrane, whereas the 104- and 87-kDa isoforms were prominent in the cytosol. Collectively these studies demonstrate the widespread expression of at least three isoforms of 5-phosphatase II derived from RNA splicing events. This allows differential distribution of the 5-phosphatase II activity between the membrane and cytosol of the cell and thereby may regulate enzyme access to phosphoinositide-derived signaling molecules.

Peptide aldehyde inhibitors of cathepsin K inhibit bone resorption both in vitro and in vivo

We have shown previously that cathepsin K, a recently identified member of the papain superfamily of cysteine proteases, is expressed selectively in osteoclasts and is the predominant cysteine protease in these cells. Based upon its abundant cell type-selective expression, potent endoprotease activity at low pH and cellular localization at the bone interface, cathepsin K has been proposed to play a specialized role in osteoclast-mediated bone resorption. In this study, we evaluated a series of peptide aldehydes and demonstrated that they are potent cathepsin K inhibitors. These compounds inhibited osteoclast-mediated bone resorption in fetal rat long bone (FRLB) organ cultures in vitro in a concentration-dependent manner. Selected compounds were also shown to inhibit bone resorption in a human osteoclast-mediated assay in vitro. Chz-Leu-Leu-Leu-H (in vitro enzyme inhibition Ki,app = 1.4 nM) inhibited parathyroid hormone (PTH)-stimulated resorption in the FRLB assay with an IC-50 of 20 nM and inhibited resorption by isolated human osteoclasts cultured on bovine cortical bone slices with an IC-50 of 100 nM. In the adjuvant-arthritic (AA) rat model, in situ hybridization studies demonstrated high levels of cathepsin K expression in osteoclasts at sites of extensive bone loss in the distal tibia. Cbz-Leu-Leu-Leu-H (30 mg/kg, intraperitoneally) significantly reduced this bone loss, as well as the associated hind paw edema. In the thyroparathyriodectomized rat model, Cbz-Leu-Leu-Leu-H inhibited the increase in blood ionized calcium induced by a 6 h infusion of PTH. These data indicate that inhibitors of cathepsin K are effective at reducing osteoclast-mediated bone resorption and may have therapeutic potential in diseases of excessive bone resorption such as rheumatoid arthritis or osteoporosis.

Single-organism model of host defense against infection: a novel immunotoxicologic approach to evaluate immunomodulatory drugs

The immunotoxicologic effects of drugs on host defense have been studied widely using various animal models of infection. Here we describe a new approach to testing host defense by using a single organism (Candida albicans) in CBA/J mice. The model is configured to test 3 effector systems via different routes of inoculation to stimulate different effector arms of the immune response. Nonspecific immunity was evaluated by C. albicans colony-forming unit (CFU) count from the spleen at 2 hr (uptake) and > or = 22 hr (clearance) following intravenous inoculation. Cell-mediated immunity was assessed by CFU count from an intramuscular injection site 6 days postinoculation. Humoral immunity was assessed by anti-Candida antibody titer, following multiple subcutaneous immunizations with C. albicans. Finally, overall immunity was evaluated following intravenous injection using survival as the endpoint. Histopathological, immunohistochemical, and electron microscopic evaluation of selected tissues revealed the involvement of the expected cell types in the different effector systems. Several immunomodulatory drugs--dexamethasone, cyclosporine, liposomal muramyltripeptide phosphatidylethanolamine, and SK&F 105685--were evaluated in the C. albicans model. Dexamethasone impaired host defense against C. albicans by suppressing all endpoints measured. Similarly, cyclosporine showed broad immunosuppressive activity, with the exception of yeast uptake from the spleen. In contrast, muramyl tripeptide-phosphatidylethanolamine enhanced all but cell-mediated immunity to C. albicans. SK&F 105685 displayed both stimulatory and inhibitory effects on immune responses to the infection. Our studies demonstrate that a single organism-based approach can be a useful method for evaluating the immunological hazards of drugs on host resistance to infection.

Cyclosporin analogs modified in the 3,7,8-positions: substituent effects on peptidylprolyl isomerase inhibition and immunosuppressive activity are nonadditive

Four analogs of cyclosporin A (CsA) were synthesized to determine if the biological activities of CsA analogs generated by multiple amino acid replacements are predictable from the effects on biological activity of analogs with single residue changes. CsA analogs [Phe7]CsA (8a), [D-MeAla3,Phe7]CsA (8b), [D-Ser8,Phe7]CsA (8c), and [D-MeAla3,Phe7,D-Ser8]CsA (8d) were designed by modification of positions 3, 7, and 8, which are adjacent to one effector region of the cyclophilin-bound CsA complex. The syntheses of CsA analogs 8a-d were carried out by suitable modifications of the reported strategy. Each analog was characterized by NMR in deuterated chloroform and DMSO solutions, and their biological activities as inhibitors of cis-trans-peptidyl prolyl isomerase (PPIase), inhibitors of proliferation in BDF1 mouse spleen cells stimulated with concanavalin A (Con A), and inhibitors of IL-2 release stimulated with PMA/ionomycin by Jurkat cells were determined. Incorporation of the phenylalanine residue in position 7 diminished activities 5-8-fold. Substitution at position 3 decreased activity nearly 2-fold, and substitution at position 8 did not lower activities. However, when all three modifications (D-MeAla3,Phe7, and D-Ser8) were incorporated into one molecule, the resulting analog, 8d, was found to bind more tightly to cyclophilin than CsA (Ki = 3 +/- 1.5 vs 6 +/- 2 nM) and to produce the full immunosuppressive effect in the other assay systems. Our structure-activity results show that combinations of substitutions that individually lower PPIase or immunosuppressive activity produce fully active analogs when combined in a single compound. These results suggest that other, multimodified CsA derivatives may be discovered that possess excellent or improved immunosuppressive activities even though they contain a substitution that otherwise reduces immunosuppressive activity.

SB 203347, an inhibitor of 14 kDa phospholipase A2, alters human neutrophil arachidonic acid release and metabolism and prolongs survival in murine endotoxin shock

Phospholipase A2 (PLA2) catalyzes the hydrolysis of the sn-2 fatty acyl group [predominantly arachidonic acid (AA)] of membrane phospholipids, the products of which are further metabolized, forming a variety of eicosanoids and/or platelet-activating factor. PLA2 activity is significantly enhanced during inflammation and therefore offers an intriguing target in designing anti-inflammatory drugs. SB 203347 (2-[2-[3,5-bis (trifluoromethyl) sulfonamido]-4- trifluoromethylphenoxy] benzoic acid) potently inhibits rh type II 14 kDa PLA2 (IC50 = 0.5 microM) but exhibits a 40-fold weaker inhibition of 85 kDa PLA2 (IC50 = 20 microM) using [3H]-AA E. coli as substrate. A specific interaction with rh type II 14 kDa PLA2 was confirmed both by observing the pH dependence of its IC50 and by demonstrating linear inhibition in a "scooting" kinetic model using radiolabeled phospholipid reporter substrate in a 1,2-dimyristoyl phosphatidylmethanol vesicle. Before evaluating the effect of SB 203347 on AA metabolism in intact human neutrophil, we showed that it fully inhibits PLA2 activity in acid extracted-intact human neutrophil homogenate (IC50 = 4.7 microM). SB 203347 inhibited A23187-induced intact human neutrophil AA mass release in a concentration-dependent manner (IC50 = 1 microM), which coincided with reductions in the biosynthesis of platelet-activating factor (IC50 = 1.5 microM) and leukotriene B4 (IC50 = 2.3 microM). Finally, SB 203347 prolonged survival in a mouse model of endotoxin shock delivered i.p. Taken together, the data support a role of cellular 14 kDa PLA2 in the formation of AA-derived proinflammatory lipid mediator.(ABSTRACT TRUNCATED AT 250 WORDS)