The effects of curcumin, mangiferin, resveratrol and other natural plant products on aminopeptidase B activity

Aminopeptidase B (Ap-B) is a Zn²⁺-aminopeptidase of the M1 family which is implicated, in conjunction with the nardilysin endoprotease, in the generation of miniglucagon, a peptide involved in the maintenance of glucose homeostasis. Other in vivo physiological roles have been established for this vertebrate enzyme, such as the processing of Arg-extended forms of human insulin and cholecystokinin 9 and the degradation of viral epitopes in the cytoplasm. Among M1 family members, Ap-B is phylogenetically close to leukotriene A₄ hydrolase (LTA₄H), a bi-functional aminopeptidase also able to transform LTA₄ in LTB₄ (a lipid mediator of inflammation). As the activities of LTA₄H are reported to be inhibited by resveratrol, a polyphenolic molecule from red wine, the effect of this molecule was investigated on the Ap-B activity. Several other active phenolic compounds produced in plants were also tested. Among them, curcumin and mangiferin are the most effective inhibitors. Dixon analysis indicates that curcumin is a non-competitive inhibitor with a Ki value of 46 μmol.L^-1. Dixon and Lineweaver-Burk representations with mangiferin show a mixed non-competitive inhibition with Ki' and Ki values of 194 μmol.L^-1 and 105 μmol.L^-1, respectively. At 200 μmol.L^-1, no significant effect was observed with caffeic, chlorogenic, ferulic, salicylic and sinapic acids as well as with resveratrol. Analyses on the 3D-structure of LTA₄H with resveratrol (pdb: 3FTS) and the Ap-B 3D-model allow hypothesis to explain theses results.

The M1 family of vertebrate aminopeptidases: role of evolutionarily conserved tyrosines in the enzymatic mechanism of aminopeptidase B

Aminopeptidase B (Ap-B), a member of the M1 family of Zn(2+)-aminopeptidases, removes basic residues at the NH2-terminus of peptides and is involved in the in vivo proteolytic processing of miniglucagon and cholecystokinin-8. M1 enzymes hydrolyze numerous different peptides and are implicated in many physiological functions. As these enzymes have similar catalytic mechanisms, their respective substrate specificity and/or catalytic efficiency must be based on subtle structural differences at or near the catalytic site. This leads to the hypothesis that each primary structure contains a consensus structural template, strictly necessary for aminopeptidase activity, and a specific amino acid environment localized in or outside the catalytic pocket that finely tunes the substrate specificity and catalytic efficiency of each enzyme. A multiple sequence alignment of M1 peptidases from vertebrates allowed to identify conserved tyrosine amino acids, which are members of this catalytic backbone. In the present work, site-directed mutagenesis and 3D molecular modeling of Ap-B were used to specify the role of four fully (Y281, Y229, Y414, and Y441) and one partially (Y409) conserved residues. Tyrosine to phenylalanine mutations allowed confirming the influence of the hydroxyl groups on the enzyme activity. These groups are implicated in the reaction mechanism (Y414), in substrate specificity and/or catalytic efficiency (Y409), in stabilization of essential amino acids of the active site (Y229, Y409) and potentially in the maintenance of its structural integrity (Y281, Y441). The importance of hydrogen bonds is verified by the Y229H substitution, which preserves the enzyme activity. These data provide new insights into the catalytic mechanism of Ap-B in the M1 family of aminopeptidases.

The efficiency of human cytomegalovirus pp65(495-503) CD8+ T cell epitope generation is determined by the balanced activities of cytosolic and endoplasmic reticulum-resident peptidases

Control of human CMV (HCMV) infection depends on the cytotoxic activity of CD8(+) CTLs. The HCMV phosphoprotein (pp)65 is a major CTL target Ag and pp65(495-503) is an immunodominant CTL epitope in infected HLA-A*0201 individuals. As immunodominance is strongly determined by the surface abundance of the specific epitope, we asked for the components of the cellular Ag processing machinery determining the efficacy of pp65(495-503) generation, in particular, for the proteasome, cytosolic peptidases, and endoplasmic reticulum (ER)-resident peptidases. In vitro Ag processing experiments revealed that standard proteasomes and immunoproteasomes generate the minimal 9-mer peptide epitope as well as N-terminal elongated epitope precursors of different lengths. These peptides are largely degraded by the cytosolic peptidases leucine aminopeptidase and tripeptidyl peptidase II, as evidenced by increased pp65(495-503) epitope presentation after leucine aminopeptidase and tripeptidyl peptidase II knockdown. Additionally, with prolyl oligopeptidase and aminopeptidase B we identified two new Ag processing machinery components, which by destroying the pp65(495-503) epitope limit the availability of the specific peptide pool. In contrast to cytosolic peptidases, silencing of ER aminopeptidases 1 and 2 strongly impaired pp65(495-503)-specific T cell activation, indicating the importance of ER aminopeptidases in pp65(495-503) generation. Thus, cytosolic peptidases primarily interfere with the generation of the pp65(495-503) epitope, whereas ER-resident aminopeptidases enhance such generation. As a consequence, our experiments reveal that the combination of cytosolic and ER-resident peptidase activities strongly shape the pool of specific antigenic peptides and thus modulate MHC class I epitope presentation efficiency.

Cathepsin L plays a major role in cholecystokinin production in mouse brain cortex and in pituitary AtT-20 cells: protease gene knockout and inhibitor studies

Cholecystokinin (CCK) is a peptide neurotransmitter whose production requires proteolytic processing of the proCCK precursor to generate active CCK8 neuropeptide in brain. This study demonstrates the significant role of the cysteine protease cathepsin L for CCK8 production. In cathepsin L knockout (KO) mice, CCK8 levels were substantially reduced in brain cortex by an average of 75%. To evaluate the role of cathepsin L in producing CCK in the regulated secretory pathway of neuroendocrine cells, pituitary AtT-20 cells that stably produce CCK were treated with the specific cathepsin L inhibitor, CLIK-148. CLIK-148 inhibitor treatment resulted in decreased amounts of CCK secreted from the regulated secretory pathway of AtT-20 cells. CLIK-148 also reduced cellular levels of CCK9 (Arg-CCK8), consistent with CCK9 as an intermediate product of cathepsin L, shown by the decreased ratio of CCK9/CCK8. The decreased CCK9/CCK8 ratio also suggests a shift in the production to CCK8 over CCK9 during inhibition of cathepsin L. During reduction of the PC1/3 processing enzyme by siRNA, the ratio of CCK9/CCK8 was increased, suggesting a shift to the cathepsin L pathway for the production of CCK9. The changes in ratios of CCK9 compared to CCK8 are consistent with dual roles of the cathepsin L protease pathway that includes aminopeptidase B to remove NH2-terminal Arg or Lys, and the PC1/3 protease pathway. These results suggest that cathepsin L functions as a major protease responsible for CCK8 production in mouse brain cortex, and participates with PC1/3 for CCK8 production in pituitary cells.

Miniglucagon (MG)-generating endopeptidase, which processes glucagon into MG, is composed of N-arginine dibasic convertase and aminopeptidase B

Miniglucagon (MG), the C-terminal glucagon fragment, processed from glucagon by the MG-generating endopeptidase (MGE) at the Arg17-Arg18 dibasic site, displays biological effects opposite to that of the mother-hormone. This secondary processing occurs in the glucagon- and MG-producing alpha-cells of the islets of Langerhans and from circulating glucagon. We first characterized the enzymatic activities of MGE in culture media from glucagon and MG-secreting alphaTC1.6 cells as made of a metalloendoprotease and an aminopeptidase. We observed that glucagon is a substrate for N-arginine dibasic convertase (NRDc), a metalloendoprotease, and that aminopeptidase B cleaves in vitro the intermediate cleavage products sequentially, releasing mature MG. Furthermore, immunodepletion of either enzyme resulted in the disappearance of the majority of MGE activity from the culture medium. We found RNAs and proteins corresponding to both enzymes in different cell lines containing a MGE activity (mouse alphaTC1.6 cells, rat hepatic FaO, and rat pituitary GH4C1). Using confocal microscopy, we observed a granular immunostaining of both enzymes in the alphaTC1.6 and native rat alpha-cells from islets of Langerhans. By immunogold electron microscopy, both enzymes were found in the mature secretory granules of alpha-cells, close to their substrate (glucagon) and their product (MG). Finally, we found NRDc only in the fractions from perfused pancreas that contain glucagon and MG after stimulation by hypoglycemia. We conclude that MGE is composed of NRDc and aminopeptidase B acting sequentially, providing a molecular basis for this uncommon regulatory process, which should be now addressed in both physiological and pathophysiological situations.

Expression of aminopeptidase B in the developing and adult rat retina

Aminopeptidase B (Ap-B), a ubiquitous enzyme, catalyses the amino-terminal cleavage of basic residues of peptide or protein substrates, indicating a role in precursor processing. The physiological function of Ap-B still remains an open question, even though its activity suggests that it could be involved in inflammatory processes and proliferation of tumor cells. This study was conducted to determine the expression of Ap-B in the developing and adult retina as a path to envisage physiological roles of Ap-B. RT-PCR and in situ hybridization were used to detect expression of Ap-B mRNA and activity tests, Western blotting and immunofluorescence microscopy were performed to identify and localize the enzyme in the rat retina. These biochemical and morphological methods show that Ap-B is expressed in the retina from embryo to adult. Expression level is restricted to specific layers (pigmented epithelium, outer and inner plexiform layers and ganglion cell layer) and is developmentally regulated. Moreover, a preliminary analysis indicates that Ap-B, the glucose transporter GLUT3 and choline acetyltransferase (ChAT) share a similar expression pattern in retina. Altogether, Ap-B appears predominantly expressed in neuronal cells lying in retinal layers containing neuritic extensions and synaptic junctions. Such expression is up-regulated during ontogenesis allowing to hypothesized that Ap-B participates in processes accompanying retinal neuronal cell differentiation.

Expression and purification of rat recombinant aminopeptidase B secreted from baculovirus-infected insect cells

Aminopeptidase B (Ap-B) is a ubiquitous enzyme and its physiological function still remains an open question. This Zn2+ -exopeptidase catalyzes the amino-terminal cleavage of basic residues of peptide or protein substrates, indicating a role in precursor processing. In addition, the enzyme exhibits a residual capacity to hydrolyze leukotriene A4 (LTA4) into the pro-inflammatory lipid mediator leukotriene B4 (LTB4) in vitro. This potential bi-functional nature of Ap-B is supported by a close structural relationship with LTA4 hydrolase, which hydrolyzes LTA4 into LTB4, in vivo, and exhibits an aminopeptidase activity, in vitro. Structural studies are necessary for the detailed understanding of the bi-functional enzymatic mechanism of Ap-B. In this study, we report cDNA cloning, baculovirus expression, and purification of the rat Ap-B (rAp-B). The Ap-B cDNA was constructed from extracted rat testes total RNA and introduced into the pBAC1 baculovirus transfer vector to generate recombinant baculoviruses. rAp-B expression, with or without COOH-hexahistidine tag, was tested in two different insect cell hosts (Sf9 and H5). The enzyme is secreted into the insect cell culture medium, which allowed a rapid purification of the protein. The His-tagged rAp-B was purified using metal affinity resin while the native recombinant rAp-B was partially purified using a single step DEAE Trisacryl ion exchange column. Although the recombinant rAp-B exhibits biochemical properties equivalent to those of the rat testes purified protein, the presence of the histidine-tag seems to partially inhibit the exopeptidase activity. However, this report shows that baculovirus-infected cells are a useful system to produce rat Ap-B for use in studying enzymatic mechanisms in vitro and 3D structure.

Human aminopeptidase B (rnpep) on chromosome 1q32.2: complementary DNA, genomic structure and expression

Aminopeptidase B (APB) is a Zn(2+)-metalloexopeptidase, which selectively removes Arg and/or Lys residues from the N-terminus of several peptide substrates. Several data strongly support the hypothesis that this enzyme could participate in the final stages of precursor processing mechanisms and/or in particular inflammatory processes and tumor developments. Therefore, we have cloned the complementary DNA encoding the human APB, a 658-residues protein, containing the canonical "HEXXH(X(18))E", a signature allowing its classification in the M1 family of metallopeptidases. The genomic structure of the human APB gene (rnpep; 1q32.1-q32.2) was also determined. rnpep is bracketed by pre-protein translocase of the inner mitochondrial membrane gene and ETS family transcription factor ELF3 gene. It spans more than 24 kbp and contains 11 exons ranging from 109 to 574 bp. Finally, expression of the human APB messenger RNA (mRNA) was investigated using a pre-made dot-blot. This mRNA seems to be ubiquitous although its expression level varies depending of the cells or tissues considered.

Production, purification, and characterization of recombinant prohormone convertase 5 from baculovirus-infected insect cells

The discovery of the prohormone convertase (PC) family of enzymes has provided several good candidates (PC1, PC2, and PC5) for the enzymes responsible for the endoproteolytic cleavage of procholecystokinin (pro-CCK). Determination of the role of individual pro-hormone convertases in the processing of pro-CCK is complicated because several of these enzymes are found in endocrine tumor cells expressing CCK mRNA and in identified neurons in the brain. Production of active recombinant PC5 permits the determination of its ability to cleave substrates related to pro-CCK. Active PC5, secreted from baculovirus-infected Sf9 cells, was partially purified by ion-exchange chromatography. Western blot analysis confirmed the presence of the active form of the enzyme in infected cell media and its absence from uninfected cell media. The enzyme is most active at acidic pH 6.5 and is maximally activated by 5 mM calcium. PC5 was able to cleave both monobasic and dibasic substrates without a requirement for a basic residue at P-4 and it displayed a K(m) in the micromolar range. The enzyme was inhibited by EDTA, 1,10-phenanthroline, and p-CMS, as well as by two specific PC inhibitors. This is the first reported preparation of active recombinant PC5. Like the other members of its family, it has the correct catalytic characteristics in vitro to play a role in the processing of neuropeptide precursor proteins into their final bioactive forms.

Aminopeptidase B (EC 3.4.11.6)

Aminopeptidase B (EC 3.4.11.6) is a Zn(2+)-dependent exopeptidase which selectively removes arginine and/or lysine residues from the NH2-terminus of several peptide substrates including Arg0-Leu-enkephalin, Arg0-Met-enkephalin and Arg-1-Lys0-somatostatin-14. Analysis of its primary structure showed that aminopeptidase-B is structurally related to leukotriene A4 hydrolase, an important enzyme of the arachidonic acid pathway. This structural relationship is further supported by the capacity of aminopeptidase-B to hydrolyse leukotriene A4. Aminopeptidase-B is widely distributed in a number of tissues, including endocrine and non-endocrine cells. Moreover, in rat PC12 pheochromocytoma cells, the enzyme is secreted and associated with the external face of the plasma membrane. Together these data strongly argue in favour of a role of this bi-functional enzyme in the final stages of precursor processing mechanisms occurring either in the secretory pathway, at the plasma membrane, or at both locations.

Glucose transporter Glut3 is targeted to secretory vesicles in neurons and PC12 cells

In rat brain and cultured neuroendocrine PC12 cells, Glut3 is localized at the cell surface and, also, in a distinct population of homogenous synaptic-like vesicles. Glut3-containing vesicles co-purify with "classical" synaptic vesicles, but can be separated from the latter by sucrose gradient centrifugation. Unlike classical synaptic vesicles, Glut3-containing vesicles possess a high level of aminopeptidase activity, which has been identified as aminopeptidase B. This enzyme has recently been shown to be a marker of the secretory pathway in PC12 cells (Balogh, A., Cadel, S., Foulon, T., Picart, R., Der Garabedian, A., Rousselet, A., Tougard, C., and Cohen, P. (1998) J. Cell Sci. 111, 161-169). We, therefore, conclude that Glut3 is targeted to secretory vesicles in both neurons and PC12 cells.

PC18, a specific aminopeptidase N inhibitor, induces vasopressin release by increasing the half-life of brain angiotensin III

Angiotensin III (AngIII), which is metabolized in vivo by aminopeptidase N (APN), was previously shown to be one of the main effector peptides of the brain renin-angiotensin system (RAS) in the control of vasopressin release. Recently, a potent APN inhibitor, PC18 (2-amino-4-methylsulfonyl butane thiol, methionine thiol), has been developed. In this study, we first checked the in vitro selectivity of PC18 towards APN, aminopeptidase A (APA) and aminopeptidase B (APB), three zinc metalloproteases with significant identity between their amino acid sequences. The Ki values of this compound on APN were found to be in the nanomolar range (Ki = 8.0 +/- 1.7 nM) but it was 2,150 and 125 times less active on APA and APB, respectively. Secondly, we evaluated in vivo the effect of brain APN inhibition with PC18 on the inactivation of brain AngIII and on vasopressin secretion in mice. For this purpose, mice received [3H]AngII intracerebroventricularly in the presence or absence of the APN inhibitor PC18 (30 microg). At different times after the injection, [3H]AngIII levels were evaluated from hypothalamus homogenates after separation by cation-exchange chromatography. PC18 induced an accumulation of [3H]AngIII, increasing its half-life 3.9 times as compared with control values. In addition, the effect of PC18 on vasopressin release was studied in mice. PC18 (10-100 microgram) was injected intracerebroventricularly, and plasma vasopressin levels were estimated by radioimmunoassay. PC18 increased vasopressin levels in a dose-dependent manner. The maximal increase in vasopressin release (+220%) is observed for a dose of PC18 of 100 microgram and was inhibited 75% by the coadministration of the AngII receptor antagonist (Sar1-Ala8)-AngII (0.5 microgram). These results indicate that in vivo, in the mouse brain, APN inhibition by PC18 increases the half-life of endogenous AngIII, resulting in an enhanced vasopressin release.

Evidence for a leukotriene A4 hydrolase in Xenopus laevis skin exudate

Leukotriene A4 hydrolase is a cytosolic metalloenzyme of the arachidonic acid biosynthetic pathway responsible for leukotriene A4 conversion into leukotriene B4. In addition to its epoxide hydrolase properties, this enzyme exhibits an aminopeptidase activity which was used as an assay to monitor the purification of a novel form of leukotriene A4 hydrolase from Xenopus laevis skin exudate. This 70 kDa, secreted, form of leukotriene A4 hydrolase was identified by immunochemical cross-reactivity with anti-human leukotriene A4 hydrolase antibodies and by its capacity to convert leukotriene A4 into leukotriene B4. Moreover this enzyme produced a second metabolite which could be the leukotriene B4 isomer 5S,12R-dihydroxy-6,10-trans-8,14-4-cis-eicosatetraenoic acid, previously shown by Strömberg et al. (Eur.J. Biochem. 238 (1996) 599-605) to be formed by incubation of the leukotriene A4 with amphibian tissue extracts. Partial amino acid sequencing of peptides generated by endolysin C fragmentation of the purified enzyme confirmed the presence, in X. laevis skin secretions, of a related but distinct form of leukotriene A4 hydrolase which is likely to be responsible for the production of these eicosanoid metabolites of leukotriene A4.

NRD convertase and aminopeptidase B: two processing metallopeptidases with a selectivity for basic residues

An endoprotease and an aminopeptidase B were isolated from rat testis and characterized. The first one is a metalloendopeptidase of 1161 residues which contains a canonical HXXEHX76E Zn(2+)-binding site and an acidic stretch of 71 amino acids containing 79% of Glu and Asp. It exhibits an in vitro selectivity for peptide bonds at the N-terminus of Arg (R) moieties in dibasic sites and was thus called NRD convertase (Nardilysin: EC 3.4.24.61). It belongs to the pitrilysin family and shows 24 and 34% identity with E. coli protease III (EC 3.4.24.54) and insulysin (EC 3.4.24.55) respectively. The aminopeptidase B component is a 72 kDa metalloexopeptidase which is able to remove Lys and Arg residues from naphtylamide derivatives and from the N-terminus of various peptide substrates. A combination of biochemical and immunochemical studies revealed its ubiquitous character. In the testis, both enzymes are highly expressed at late stages of spermatogenesis and NRD convertase expression is exclusively restricted to the germ cells. The subcellular localization of both enzymes supports the involvement of aminopeptidase B in processing events associated with the secretory pathway but led to new hypothesis on the possible physiological role(s) of NRD convertase.

Aminopeptidase B: a processing enzyme secreted and associated with the plasma membrane of rat pheochromocytoma (PC12) cells

Aminopeptidase B (Ap-B) is a Zn2+-dependent exopeptidase which selectively removes Arg and/or Lys residues from the N terminus of several peptide substrates. Isolated and characterized from rat testes, this ubiquitous enzyme may participate in the final stages of precursor processing mechanisms. To test this hypothesis, we have investigated the secretion and subcellular localization of this enzyme in a rat cell line of pheochromocytoma (PC12 cells). By using a combination of biochemical and immunocytochemical methods, the following observations were made: (i) the level of aminopeptidase B detectable in the cell culture medium increased with time; (ii) 8-bromo-adenosine 3′-5′-cyclic monophosphate and the Ca2+ ionophore A23187 both stimulated enzyme liberation in the culture medium; (iii) brefeldin A, an inhibitor of vesicular transport from the endoplasmic reticulum to the Golgi apparatus, decreased enzyme secretion in a time-dependent manner; (iv) whereas nocodazole, a microtubule depolymerizing agent, inhibited enzyme secretion, cytochalasin D, a microfilament disruption agent, had no effect on released aminopeptidase B level; (v) immunofluorescence demonstrated the presence of aminopeptidase B in the Golgi apparatus; (vi) immunofluorescence, electron microscopy and tests of enzyme activity on intact cells showed an association of the peptidase with the external face of the plasma membrane. Together these data strongly argued in favour of the enzyme secretion by PC12 cells. It is concluded that aminopeptidase B may participate in processing events occurring either during its intracellular transport along the secretory pathway or at the plasma membrane level, or both.

Aminopeptidase B from the rat testis is a bifunctional enzyme structurally related to leukotriene-A4 hydrolase

An aminopeptidase B (Ap-B) was previously purified to homogeneity from rat testis extracts and characterized. In the present work, by using oligonucleotides selected on the basis of partial amino acid microsequences of pure Ap-B and PCR techniques, the nucleotide sequence of a 2.2-kb cDNA was obtained. The deduced amino acid sequence corresponds to a 648-residue protein (72.3 kDa) containing the canonical "HEXXHX18E" signature, which allowed its classification as a member of the M1 family of metallopeptidases. It exhibits 33% identity and 48% similarity with leukotriene-A4 hydrolase, a relation further supported by the capacity of Ap-B to hydrolyze leukotriene A4. Both enzymes also were closely related to a partially sequenced protein from Dictyostelium discoideum, which might constitute the putative common ancestor of either aminopeptidase or epoxide hydrolase, or both. Ap-B and its mRNA were detected in the germ line and in the Sertoli and peritubular cells of the seminiferous tubules. Because the enzyme was found in the medium conditioned by spermatocytes and spermatids and in the acrosome during spermatozoa formation, together these observations suggested an involvement of this exometallopeptidase in the secretory pathway. It is concluded that this ubiquitous enzyme may be involved in multiple processing mechanisms.

Expression and retinoid modulation of N-arginine dibasic convertase and an aminopeptidase-B in human neuroblastoma cell lines

Under retinoic acid exposure, the three SK-N-BE(2)-derived human neuroblastoma cell lines, BE(2)-NA, BE(2)-SA and BE(2)-M17 undergo mainly differentiation, apoptosis or continue to proliferate, respectively. We have used this model system to study the modulation of the transcriptional expression of putative processing enzymes, two novel metallopeptidases; i.e. N-arginine dibasic convertase (NRD convertase; EC 3.4,24,61) and an aminopeptidase-B after exposure of the cells either to retinoic acid or to synthetic retinoid analogs. The data indicate that the two respective enzymes are differently modulated in the various cell lines. Whereas aminopeptidase-B expression is enhanced in most cases, NRD convertase appears to undergo opposite regulation in proliferating versus differentiating neuroblastoma cells. It is concluded that both genes might contain retinoic acid regulatory elements (RARE) in their promoters.

Ipriflavone does not alter bone apatite crystal structure in adult male rats

We have previously found that a short-term treatment with high doses of ipriflavone increased bone density and improved the biomechanical properties of adult male rat bones, without altering their mineral composition. To determine whether this effect can be associated with alterations of bone crystal structure, we have performed X-ray diffraction analysis of bones obtained from rats treated with ipriflavone at doses that were effective in inducing favorable changes on bone density and biomechanics. Eighteen-week-old male Sprague Dawley rats were treated by oral route with either ipriflavone (200 or 400 mg/kg/day), or its vehicle for 12 weeks. The treatment was well tolerated and body weight increased to the same extent in all animals. As a measure of bone crystallinity, we examined the (310) and (002) reflections of the X-ray diffraction patterns, corresponding to the directions perpendicular and parallel to the c-axis of the crystals, respectively. No major differences were observed between ipriflavone-treated and control animals for the broadening parameter beta(1/2) for (310) and (002) peaks, as well as for lattice parameters. Therefore, a 12-week treatment with ipriflavone at high doses does not induce significant modifications of bone "crystallinity." Thus, the positive effect of ipriflavone on bone mineral density appears to be associated with an increased apatite crystal formation rather than an increase of crystal size. These results provide further evidence for the safety and usefulness of ipriflavone in the treatment of osteoporotic syndromes.

Investigation of potential oncogenetic effects of beta-cyclodextrin in the rat and mouse

The results of oncogenicity studies of beta-cyclodextrin in inbred Fischer 344 rats and CD-1 outbred mice are presented. Chronic feeding of beta-cyclodextrin to Fischer 344 rats and CD-1 mice did not cause any treatment related carcinogenic effects. The only toxic effect was seen in mice as macroscopic distension of the large intestine with soft or fluid contents, histologically associated with the mucosa covered by mucous secretion containing exfoliated cells, and mucosal flattening and intestinal gland atrophy. Despite these observations, no differences between control and treated groups were observed concerning mortality, clinical observations or body weight and food consumption.

Aminopeptidase-B in the rat testes: isolation, functional properties and cellular localization in the seminiferous tubules

An aminopeptidase of the B-type, with an apparent M(r) 72,000 and pI = 4.9, was isolated from rat testes and characterized. The enzyme was able to remove only Arg and/or Lys residues from L-amino acid beta-naphthylamide derivatives and from the N-terminus of several peptides. No cleavage occurred in the case of Arg-Pro bonds as found in bradykinin and substance P. The enzyme was sensitive to cysteinyl reagents and to aminopeptidase inhibitors, such as bestatin, amastatin and arphamenines A and B. The aminopeptidase activity, tested with L-Arg beta-naphthylamide and with Arg0-Met-enkephalin as substrates, was inhibited by o-phenanthroline, and restored by Zn2+ suggesting its metallopeptidase character. The partial characterization of an aminopeptidase-B activity in rat brain cortex identified a protein which is biochemically and immunologically related to the testis enzyme. By immunohistochemistry, the aminopeptidase-B was found to be particularly abundant in the seminiferous tubules at late stages of spermatogenesis and was clearly detected in a restricted area of elongated spermatids. Remarkably, the enzyme was observed to concentrate massively in the residual bodies. Since this aminopeptidase-B was able in vitro to trim out N-terminal Arg and/or Lys residues from peptides mimicking processing intermediates, it is proposed that this enzyme may be involved in propeptide and proprotein processing mechanisms in the course of spermatid differentiation.

Effect of long-term treatment with L-deprenyl on the age-dependent microanatomical changes in the rat hippocampus

Chronic treatment with L-deprenyl increases both mean and maximum life span and improves cognitive functions in the aged rat. The present study was designed to evaluate whether long-term treatment with L-deprenyl at a dosage not inhibiting the monoamine oxidase-B (MAO-B) (1.25 mg/kg/day) or inhibiting the enzyme activity (5 mg/kg/day) had any effect on the age-dependent microanatomical changes in the rat hippocampus. The hippocampus was chosen in view of its key role in learning and memory functions. Treatment with L-deprenyl started at 19 months and lasted until the 24th month of age. Age-matched untreated rats were used as a control, whereas 11-month-old rats were used as an adult reference group. The number of nerve cell and glial fibrillary acidic protein-immunoreactive astrocyte profiles in the CA1 and CA3 fields of the hippocampus and in the dentate gyrus was decreased and increased, respectively in aged compared with adult rats. Treatment with 5 mg/kg/day, but not with 1.25 mg/kg/day L-deprenyl increased the number of neuronal profiles and decreased the number of astrocytes in the hippocampus of aged rats. The density of zinc stores in the associative intrahippocampal pathway of mossy fibres, which was decreased in aged animals, was increased after treatment with the two doses of L-deprenyl. Lipofuscin accumulation within the cytoplasm of pyramidal neurons of the hippocampus was reduced dose dependently by L-deprenyl treatment. These results suggest that long-term treatment with L-deprenyl is able to counter the expression of age-dependent microanatomical changes in the rat hippocampus. These effects seem only partially correlated with the MAO-B inhibitory activity of L-deprenyl.

Influence of treatment with L-deprenyl on the structure of the cerebellar cortex of aged rats

Treatment with L-deprenyl increases mean and maximum life span in the rat and reverses memory and learning deficits associated with old age. Since only sparse information is available concerning the influence of L-deprenyl administration on the aging brain microanatomy, we have investigated the effect of long-term treatment with L-deprenyl on the structure of the cerebellar cortex in the aged rat. The cerebellar cortex was used since it represents a useful model for assessing age-related changes in nervous system anatomy and function. Male Sprague-Dawley rats were treated from the 19th to the 24th month of age with a daily oral dose of 1.25 mg/kg or 5 mg/kg L-deprenyl. Age-matched rats were left untreated and used as a control group. Eleven-month-old untreated rats were used as an adult reference group. The density of Purkinje and granule neuron profiles as well as the intensity of Nissl's staining within the cytoplasm of Purkinje neurons were reduced in 24-month in comparison with 11-month rats. Moreover, an increased accumulation of lipofuscin was noticeable in the cytoplasm of Purkinje neurons of old rats as well as an increase in MAO-B activity in the molecular layer of the cerebellar cortex. The two doses of L-deprenyl increased the density of both Purkinje and granule neuron profiles and the intensity of Nissl's staining in the cytoplasm of Purkinje neurons and reduced lipofuscin deposition within Purkinje neurons. The lower dose of L-deprenyl caused only a slight decrease in MAO-B activity, whereas the 5-mg/kg/day dose remarkably reduced it. These results suggest that long-term treatment with L-deprenyl counters the expression of some age-related microanatomical changes in the rat cerebellar cortex. The possible independence of the effects of the compound on age-related microanatomical changes of the cerebellar cortex and on MAO-B inhibitory activity is discussed.

Neuroanatomy of aging brain. Influence of treatment with L-deprenyl

The present study was designed to assess the influence of long term L-deprenyl treatment on some microanatomical parameters of aging rat frontal cortex and hippocampus. Male Sprague-Dawley rats of 19 months of age were divided into three groups. Rats of the first group received an oral daily dose of 1.25 mg/kg L-deprenyl; animals of the second group were treated with an oral daily dose of 5 mg/kg L-deprenyl, whereas rats of the third group were left untreated and used as control. Treatment lasted for 5 months, and rats were sacrificed at 24 months. At this age they were considered to be old. Another group of 11-month-old rats was used as an adult reference group. The density of nerve cell profiles and of glial fibrillary acidic protein (GFAP) immunoreactive astrocytes was decreased and increased respectively in the frontal cortex and in the different portions of the hippocampus in old in comparison with adult rats. A decrease in the intensity of sulfide silver staining in the mossy fibers of the hippocampus was also observed in old rats. Moreover, a cytoplasmatic accumulation of lipofuscin was noticeable in old rats as well as a significant increase of the monoamine-oxidase (MAO) B reactivity both in the frontal cortex and in the hippocampus. A higher density of nerve cell profiles, of sulfide silver staining, and fewer astrocyte profiles were noticeable in the frontal cortex and in the hippocampus of old rats treated with 5 mg/kg/day of L-deprenyl. This dose of the compound also significantly reduced lipofuscin accumulation and MAO-B reactivity in old rats. However, the lower dose of the compound did not cause any statistically significant effect on the microanatomical parameters investigated with the exception of sulfide silver staining and lipofuscin accumulation, which were increased and decreased respectively after 1.25 mg/kg per day of L-deprenyl. The above results suggest that long-term treatment with L-deprenyl is able to counter some microanatomical changes typical of the aging frontal cortex and hippocampus in the rat. These changes seem to be in part related to the MAO-B inhibitory activity of L-deprenyl.

Influence of long-term treatment with L-deprenyl on the age-dependent changes in rat brain microanatomy

The present study was designed to assess whether treatment with the monoamine oxidase-B (MAO-B) inhibitor L-deprenyl, which has been documented to increase both mean and maximum survival in aged rats as well as sexual performance and cognitive function, has any effect on the age-related microanatomical changes occurring in the rat brain. Male Sprague-Dawley rats received a subcutaneous injection of 0.25 mg/kg L-deprenyl every other day from the 19th to the 24th month of age. Age-matched control rats were injected with saline, whereas 11-month-old untreated rats were used as an adult reference group. Both body and brain weight were increased as a function of age, and they were unaffected by treatment with L-deprenyl. The density of nerve cell profiles in the frontal cortex, in the CA-1 and CA-3 subfields of the hippocampus, in the dentate gyrus and in the cerebellar cortex were decreased in aged rats in comparison with adult rats. The density of nerve cell profiles in the above brain areas of L-deprenyl-treated rats was not significantly higher in comparison with age-matched control animals with the exception of Purkinje neuron profiles. The intensity of Nissl's staining, which may be related to the protein synthetic capabilities of nerve cells, is reduced within pyramidal neurons of the hippocampus and Purkinje neurons of the cerebellar cortex of aged rats. The intensity of Nissl's staining in L-deprenyl-treated rats was not different from adult rats. Lipofuscin deposition was significantly increased within the cytoplasm of pyramidal neurons of the frontal cortex, of the CA-3 subfield of the hippocampus and of Purkinje neurons of the cerebellar cortex. L-Deprenyl administration decreased lipofuscin accumulation within the cytoplasm of the above mentioned nerve cell types. The density of sulphide-silver staining in the intrahippocampal pathway of mossy fibres, which participate in the elaboration of passive avoidance responses, is decreased in aged rats. Treatment with L-deprenyl counters this age-related reduction. The above results suggest that long-term treatment with L-deprenyl is able to counter the expression of some microanatomical changes typical of aging brain.

Microanatomical changes in the frontal cortex of aged rats: effect of L-deprenyl treatment

The present study was designed to assess whether treatment with L-deprenyl has any effect on the age-related microanatomical changes in the rat frontal cortex. Male Sprague-Dawley rats of 19 months of age were treated until the 24th month with an oral daily dose of 1.25 mg/kg or of 5 mg/kg of L-deprenyl. Eleven-month-old untreated rats were used as an adult reference group. The density of nerve cell profiles and of glial fibrillary acidic protein-(GFAP) immunoreactive astroglial profiles, lipofuscin accumulation within the cytoplasm of pyramidal neurons, and MAO-B reactivity were assessed. A decreased density of nerve cell profiles and an increased density of astroglial profiles as well as augmented lipofuscin deposition and MAO-B reactivity were observed in the frontal cortex of rats of 24 months in comparison with 12-month-old animals. In the frontal cortex of rats treated with 5 mg/kg/day L-deprenyl, which is a dose inhibiting MAO-B activity, the density of nerve cell and GFAP-immunoreactive astrocyte profiles is increased and decreased respectively in comparison with age-matched untreated subjects. Lipofuscin deposition is reduced. The lower dose of L-deprenyl (1.25 mg/kg/day) which did not affect MAO-B activity, decreased lipofuscin deposition but was without effect on the density of nerve cell or GFAP-immunoreactive astrocyte profiles. The above findings suggest that treatment with L-deprenyl is able to counter some microanatomical changes occurring in the frontal cortex of aged rats. Some of these effects are probably not related to the inhibitory MAO-B activity of the compound.

Improvement of cognitive function by MAO-B inhibitor L-deprenyl in aged rats

This study evaluated the ability of the selective MAO-B inhibitor, L-deprenyl, to reverse cognitive impairments appearing in aged rats, using the reference memory, Morris Water Maze paradigm. L-Deprenyl significantly improved learning and memory deficits associated with old age in doses of 1.25 and 5 mg/kg PO (escape latency measure) and doses of 1.25, 2.5 and 5 mg/kg PO (path length measure). L-Deprenyl also improved reversal learning impairments in doses of 1.25, 2.5 and 5 mg/kg PO, as expressed by the escape latency measure. The data suggest that L-deprenyl possesses potential cognitive enhancement abilities probably due to an increase in dopaminergic activity.

[Chemistry and pharmacology of pyrane derivatives. XVII. Synthesis of substituted 2-(dialkylamino)-3-formylchromones and their tricyclic derivatives]

Substituted 2-(dialkylamino)-3-formylchromones (II) were obtained from the reaction of substituted 2-(dialkylamino)chromones (I) either with the N,N-dimethylformamide-POCl3 reagent [compounds (IIa-e)] or with dichloromethylmethylether in the presence of TiCl4 [compounds (IIf-i)]. By treating (IIa,f) with hydroxylamine the oximes (IIIa,f) were prepared, which in turn were converted into the nitriles (IVa,f) by treatment with acetic anhydride. Compound (IIa), selected for the smallest steric hindrance of the 2-dialkylamino substituent, by reaction with hydrazines afforded [1]benzopyrano [2,3-c]pyrazole derivatives (VI), whereas reaction of (IIa) with guanidine, benzamidine or S-methylisothiourea gave rise to the formation of 5H-[1]benzopyrano[2,3-d]pyrimidine derivatives (IX). Among the compounds tested for their antiallergic properties, (IIf) showed an appreciable activity, but also high toxicity.

[Derivatives of pyrimidine 1,2-condensate. IV. Synthesis and pharmacological properties of the N,N-disubstituted 4-amino-2H-pyrido(1,2-a)pyrimidin- 2-ones and 2-amino-4H-pyrido(1,2-a)pyrmidin-4-ones]

The N,N-disubstituted 4-amino-2H-pyrido[1,2-a]pyrimidin-2-ones (III) and isomer 2-amino-4H-pyrido[1,2-a]pyrimidin-4-ones (IV) were obtained from the reaction of 2-aminopyridine with the N,N-disubstituted ethyl malonamate/phosphorus oxychloride reagent (II), in refluxing 1,2-dichloroethane. 2-[(N-Benzyl, N-ethyl)amino]derivative (IV b) was also prepared in excellent yield by treating 2-chloro-4H-pyrido[1,2-a]pyrimidin-4-one (V) with N-ethylbenzylamine. Finally, hydrogenation (Raney Nickel) of 4-[(N-ethyl,N-phenyl)amino]-2H-pyrido[1,2-a]pyrimidin-2-one (III e) afforded 6,7,8,9-tetrahydroderivative (VI) which in turn was treated with potassium borohydride to give 1,6,7,8,9,9a-hexahydroderivative (VII). Several compounds described in the present paper, along with some other compounds (III) and (IV) previously synthesized by us (1,2), were tested for various pharmacological activities. The antiallergic activity (PCA in the rat), even though found in several compounds examined, turned out to be submaximal in any case, in spite of the high dose administered (500 mg/kg p.o. as a rule). The most active compound (the activity being estimated at 0.42 times that of thiaramide hydrochloride) was the 4-aminoderivative (III e). The 2-aminoderivatives (IV) series, was found to have marked antiinflammatory properties (carrageenin oedema in the rat); nevertheless, this activity was related to toxic symptoms with the exception of compound (IV b), almost asymptomatic at the administered dose (200 mg/kg p.o.). Moreover the 2-aminoderivatives (IV) generally showed weak adrenolitic activity in vitro (rat seminal vesicles), which was estimated to be from 100 to 1000 times less than that of phenoxybenzamine.

[Chemistry and pharmacology of pyran derivatives. XVII. Synthesis of 2-(dialkylamino)-5-hydroxychromones and their transformation to derivatives of 2H-pyran[4,3,2-de]-1-benzopyran]

Through the reaction of resorcin with N,N-dialkylethoxy-carbonylacetamides in suitable conditions 2-(dialkylamino)-5-hydroxychromones (II) were available. Transformation of these compounds into [5-acetoxy-2-(dialkylamino)-4H-chromen-4-ylidene] malononitriles (VII) by reaction with malononitrile in acetic anhydride and treatment of (VII) with hydrochloric acid gave rise to the formation of 5-(dialkylamino)-2-imino-2H-pyrano [4,3,2-de]-1-benzo-pyrans (VIII). Furthermore 5-hydroxychromones (II) when treated with methyl iodide gave the corresponding 5-methoxychromones (III) which in turn yielded 4H-chromen-4-ylidene derivatives (X) by reaction with malononitrile in acetic anhydride. The hydrolysis of the latter compounds with hydrochloric acid resulted in the formation of 2-(dialkylamino)-4-methyl-5-methoxychromenilium salts (XI). Among the compounds which were submitted to pharmacological screening for their antiallergic properties 5-methoxychromone (III a) and 2H-pyrano [4,3,2-de]-1-benzopyran (VIII b) showed a notable activity but also high toxicity.

[Chemistry and pharmacology of pyran derivatives. 16. Derivatives of 2-(dialkylamino)-7-methoxychromone with antiallergic activity]

Since 2-(diethylamino)-7-methoxychromone (III a) showed remarkable activity in the rat PCA test, some modifications to its structure were made. For instance new substituents such as chlorine or nitro group were introduced into the molecule and the diethylamino group modified. Thus, 2-(ethylamino)-7-methoxychromone (IX) was prepared by treating 3-methoxyphenol with N-ethylethoxycarbonylacetamide in the presence of phosphorus oxychloride. In this case a small amount of 4-chloro-7-methoxycoumarin was also isolated from the reaction mixture. Moreover compounds (XIV), (XV), (XVII) structurally related to sodium cromoglycate were prepared. The pharmacological screening of some compounds showed a useful antiallergic activity.

Gastroprotective effects of morniflumate, an esterified anti-inflammatory drug

An experimental study on morniflumate, the beta-morpholinoethyl ester of niflumic acid, was undertaken in the rat to test its gastroprotective and "cytoprotective" properties and to assess its effects on gastric secretion and on the prostaglandin contents in the stomach wall. Morniflumate induced intense and usually dose-dependent inhibition of the gastric hemorrhagic lesions caused by acetylsalicylic acid, indomethacin, diclofenac, ketoprofen, naproxen and phenylbutazone and of the gastric necrotic lesions caused by absolute ethanol, HCl 0.6 mol l-1, NaOH 0.2 mol l-1 and NaCl 25%. Morniflumate also exerted marked inhibition of gastric acid secretion both in normal and in pylorus-ligated rats. The compound raised the concentration of "cytoprotective" prostaglandins in the glandular portion of the stomach but did not reverse the synthesis-block effect of the ulcerogenic nonsteroidal anti-inflammatory drugs whose gastric effects it inhibited.

A gastroprotective anti-inflammatory agent: the beta-morpholinoethyl ester of niflumic acid (morniflumate)

In several animal models orally administered morniflumate, the beta-morpholinoethyl ester of niflumic acid, proved almost equal to the parent compound in anti-inflammatory, analgesic and antipyretic activity with the advantage of complete freedom from the ulcerogenic effects of the acidic parent compound. Further, it was 5 times less active in intestinal perforation experiments and 10 times less toxic in acute toxicity experiments than niflumic acid. Bioavailability and pharmacokinetics tests after oral and intravenous administration suggest that morniflumate is absorbed as such from the gastrointestinal tract and then undergoes rapid hydrolysis in the plasma, releasing the free acidic form, the molecule responsible for the pharmacological effects. In addition to being free from ulcerogenic effects, the ester actually displayed a gastroprotective effect against the ulcerogenic effects of niflumic acid; this finding is discussed in the light of the concept of 'cytoprotection' recently reported for a series of mild gastric irritants.

Investigation of the activity of bronchodilators using a simple but accurate inhalation procedure: forced insufflation

A simple but accurate inhalation procedure for investigating the activity of antiasthmatic drugs is proposed. The procedure consists of the forced insufflation of the powdered drug, blended with micronised lactose, direct into the tracheobronchial tree. Beta-adrenoceptor agonists (isoproterenol and fenoterol) and antimuscarinics (atropine and ipratropium bromide) were tested using the method of Konzett and Rössler in the guinea-pig; their bronchodilator effects were tested both after forced insufflation and after intravenous administration. The proposed inhalation method supplied close-response curves qualitatively comparable to those obtained by the intravenous route, with the added advantage of more detailed information on the time-course effect. Forced insufflation may be the best procedure for investigating antiasthmatic drugs intended for use as inhalants.

Piroxicam pharmacologic activity and gastrointestinal damage by oral and rectal route. Comparison with oral indometacin and phenylbutazone

An experimental comparative study was conducted on 4-hydroxy-2-methyl-N-(2-pyridyl)-2H-1,2-benzothiazine-3-carboxamide-1,1-dioxide (piroxicam), indometacin and phenylbutazone for antiinflammatory and analgesic effects and for gastric and intestinal damage. In some of the experimental models used a comparison was made between oral and rectal piroxicam. The upshot was that: the antiinflammatory activity of piroxicam on carrageenin edema in the rat is equivalent by oral and by rectal route, about twice that of indometacin and 20 times that of phenylbutazone. The inhibition of leucocyte migration in the rat was equal to that of indometacin and 20 times that of phenylbutazone. The analgesic activity of piroxicam (phenylquinone writhings in the mouse) was about 1/4 that of indometacin and 70 times that of phenylbutazone. The ulcerogenic effect of piroxicam on the stomach of the rat was about 1/3 that of indometacin and 5 times greater than that of phenylbutazone. Rectal administration halves the ulcerogenic effect of oral piroxicam. The intestinal perforating effect of piroxicam in the rat is about 1/6 that of indometacin and about 15 times that of phenylbutazone. The therapeutic index, i.e., the ratio of antiinflammatory potency to gastrointestinal damage, proved to be appreciably higher for piroxicam than for the two reference standards. Rectal administration carries an even higher therapeutic index and so appears to be a potentially valuable alternative route in clinical practice.

[Pharmacological and toxicological investigation of 2,2-diethyl-2,3,5,10-tetrahydro-1H-pyrazolo(1,2-b)phthalazine-1,3-dione, a new compound with anti-inflammatory activity]

As part of research on 1H-pyrazole[1,2-b]phthalazine compounds with anti-inflammatory activity, the results of preliminary pharmacological and toxicological investigation of 2,2-diethyl-2,2,5,10-tetrahydro-1H-pyrazolo[1,2-b]phthalazine-1,3-dione are reported.

[1H-pyrazolo/1,2-b/phthalazines with anti-inflammatory activity]

The synthesis of forty-one 2,2,6,7-substituted 2,3,5,10-tetrahydro-1H-pyrazolo[1,2-b]phthalazine-1,3-diones A) by reaction of 4,4-di-substituted pyrazolidine-3,5-diones with substituted or unsubstituted alpha,alpha'-dibromoxylene and B) by tetrahydrophthalazine and 2-substituted malonic acid chlorides is described. The antinflammatory activity was tested on carrageenan oedema in comparison with phenylbutazone.

[Toxicological and pharmacological studies of glycerol]

The toxicological effects of 10% glycerol were investigated in the mouse and rat. This product displayed very low acute toxicity on i.v. and intraperitoneal administration while no toxic effects were noted in the rat as a result of repeated administration over 3 months. Teratogenic effects were not observed after daily i.v. administration in the rabbit. Changes in arterial pressure and globular osmotic resistance did not appear during or after continuous infusion. The relevant literature is also examined. Glycerol has been found active in experimental various models of cerebral oedema. It also has a useful effect on cerebral metabolism.