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Biomedical subjects

R Pellicciari

Publications and source records attributed to R Pellicciari.

At least 73 records · Page 4Linked to original sources
PubMed1992

Effect of intraduodenal administration of 23-methyl-UDCA diastereoisomers on bile flow in hamsters.

3 alpha,7 beta-Dihydroxy-23-methyl-5 beta-cholan-24-oic acid (MUDCA) and its two diastereoisomers, alpha- and beta-MUDCA, were infused intraduodenally in biliary fistula hamsters in order to evaluate the effect on bile flow and their hepatic biotransformation processes compared with the natural analog ursodeoxycholic acid (UDCA). In addition, the corresponding glycine conjugates were compared. The bile acids were administered at different doses (0.7-6 mumol/min/kg) over periods of 90 min. The results indicate that the racemic mixture exhibits a potent choleretic effect at both low and high doses, while the two individual diastereoisomers show this effect only at high doses. The presence of a C-23 methyl group in the side chain prevents hepatic amidation and alternative conjugations occur, such as glucuronidation, in order to facilitate their biliary secretion. Biotransformation of the methyl derivatives of UDCA occurred mainly by conversion to more polar glucuronide conjugates. There was little alteration to the molecule and, unlike UDCA, very little amidation occurred. These data indicate that the presence of a C-23 methyl group prevents the usual side-chain amidation common to the most naturally occurring bile acids and that glucuronidation is a requisite for efficient biliary excretion.

Acute Disease↗
PubMed1992

Nicotinylalanine increases the formation of kynurenic acid in the brain and antagonizes convulsions.

Kynurenic acid (KYNA) was quantified in the extracellular spaces of the rat hippocampus using microdialysis and HPLC (fluorimetric detection) to study the possible role of this tryptophan metabolite in the modulation of the function of the N-methyl-D-aspartate (NMDA) receptor. Addition of probenecid (1 mM), which is an inhibitor of the organic acid transport system, to the Ringer's solution perfusing the dialysis probe increased the KYNA concentration in the dialysate from 10.4 +/- 0.9 to 48 +/- 6 nM. Addition of 2 mM aminooxyacetic acid, a nonspecific inhibitor of KYNA synthesis, reduced this concentration by 50%. These data suggest that KYNA is continuously synthesized in the rat hippocampus. Nicotinylalanine (NAL), 200-400 mg/kg i.p., an analogue of kynurenine that is able to direct the flow of tryptophan metabolites toward the synthesis of KYNA, significantly increased the KYNA concentration in the hippocampal dialysate and significantly potentiated the effect of tryptophan on the accumulation of KYNA in the brain and other organs. This increase resulted in pharmacological actions compatible with an antagonism of the NMDA receptors. In fact, NAL antagonized sound-induced seizures and prevented death in DBA/2 mice. Pretreatment of the mice with D-serine (100 micrograms intracerebroventricularly), a glycine agonist and a competitive antagonist of KYNA, completely prevented the anticonvulsive action of NAL. These data suggest that changes in the extracellular concentration of KYNA in the brain are associated with a modulation of NMDA receptor function.

Alanine↗
PubMed1991

Thiokynurenates: a new group of antagonists of the glycine modulatory site of the NMDA receptor.

Several substituted derivatives of kynurenic acid were tested on the N-methyl-D-aspartate (NMDA) receptor/ion channel complex present in the guinea pig myenteric plexus, on the binding of [3H]glycine and of [3H]N-[1-(2-thienyl)cyclohexyl]piperidine [( 3H]TCP) to rat cortical membranes and on the depolarization of mice cortical wedges induced by NMDA or quisqualic acid (QA). Kynurenic acid derivatives, having a chlorine (CI) or a fluorine atom in position 5 or 7 but not in position 6 or 8 had significantly lower IC50s than the parent compound when tested on the antagonism of glutamate-induced ileal contraction and in the glycine binding assay. A further significant increase in potency was obtained by substituting a thio group for the hydroxy group in position 4 of kynurenic acid: the IC50 was 160 +/- 20 microM of kynurenic acid and 70 +/- 15 microM of thiokynurenic acid in the myenteric plexus whereas these IC50s for glycine binding were 25 +/- 3 and 9 +/- 2 microM respectively. Several thiokynurenic acid derivatives were synthetized and showed an increased affinity for the glycine recognition site over the corresponding kynurenic acid derivatives. Glycine competitively antagonized the actions of the thiokynurenates in the ileum, in cortical wedges and on [3H]TCP binding. In this preparation, 7-Cl-thiokynurenic acid had an IC50 of 8 microM for antagonizing 10 microM NMDA-induced depolarization while 50% of the 10 microM QA depolarization was antagonized at 300 microM. Thus thiokynurenic acid derivatives seem to be a new group of potent and selective antagonists of strychnine-insensitive glycine receptors.

Animals↗
PubMed1991

Synthesis and biological evaluation of cyclopropyl analogues of 2-amino-5-phosphonopentanoic acid.

A series of cyclopropyl analogues related to 2-amino-5-phosphonopentanoic acid (AP5) were synthesized and their biological activity was assessed as competitive antagonists for the N-methyl-D-aspartate (NMDA) receptor. In vitro receptor binding using [3H]-L-glutamate as the radioligand provided affinity data, while modulation of [3H]MK-801 binding was used as a functional assay. The analogues were also evaluated in [3H]kainate binding to assess selectivity over non-NMDA glutamate receptors. Of the compounds tested, 4,5-methano-AP5 analogue 26 was the most potent selective NMDA antagonist; however, potency was lower than that for [[(+/-)-2-carboxypiperidin-4-yl]methyl]phosphonic acid (CGS 19755, 5).

2-Amino-5-phosphonovalerate↗
PubMed1991

Modulation of quinolinic and kynurenic acid content in the rat brain: effects of endotoxins and nicotinylalanine.

Quinolinic acid, an endogenous excitotoxin, and kynurenic acid, an antagonist of excitatory amino acid receptors, are believed to be synthesized from tryptophan after the opening of the indole ring. They were measured in the rat brain and other organs using gas chromatography-mass spectrometry or HPLC. The enzyme indoleamine 2,3-dioxygenase, capable of cleaving the indole ring of tryptophan, was induced by administering bacterial endotoxins to rats, which significantly increased the brain content of both quinolinic and kynurenic acids. Nicotinylalanine, an analogue of kynurenine, inhibited this endotoxin-induced accumulation of quinolinic acid while potentiating the accumulation of kynurenic acid. The possibility of significantly increasing brain concentrations of kynurenic acid without a concomitant increase in quinolinic acid may provide a useful approach for studying the role of these electrophysiologically active tryptophan metabolites in brain function and preventing the possible toxic actions of abnormal synthesis of quinolinic acid.

Alanine↗
PubMed1991

Synthesis, absolute configuration and activity at N-methyl-D-aspartic acid (NMDA) receptor of the four D-2-amino-4,5-methano-adipate diastereoisomers.

The four D-2-amino-4,5-methano-adipates 26, 27, 32, 33 were synthesized and their biological activity at the N-methyl-D-aspartate (NMDA) receptor was assessed. The synthesis involved as a key step a rhodium acetate dimer catalyzed addition of ethyl diazoacetate to the protected D-allylglycine (17). In vitro receptor binding using L-[3H]glutamate as the radioligand provided affinity data, while modulation of [3H]TCP binding was used as a functional assay. The analogues were also evaluated in [3H]kainate and [3H]AMPA binding to assess selectivity over non-NMDA glutamate receptors. Three of the four diastereoisomer, D-CAA B (27), C (32) and D (33) were shown to have agonist properties at the NMDA-site, while the fourth, (2R,4R,5R) D-CAA A (26) was characterized as an NMDA-site atypic antagonist.

2-Aminoadipic Acid↗
PubMed1990

Characterization of D-3,4-cyclopropylglutamates as N-methyl-D-aspartate receptor agonists.

The 4 configurational isomers of D-3,4-cyclopropylglutamate (D-CGA) have been synthesized and analyzed for their interactions as excitatory amino acid recognition sites. Additionally, functional assessment of the action of these compounds at the N-methyl-D-aspartate (NMDA) receptor was performed. All 4 analogs function as agonists at the NMDA receptor as evidenced by their ability to stimulate [3H]MK-801 binding to the coupled PCP recognition site. Furthermore, the rank order of potency of these compounds in stimulating [3H]MK-801 binding corresponds with their Ki values for the displacement of NMDA-selective L-[3H]glutamate and [3H]CGS-19755 binding (D-CGA-C greater than D-CGA-B greater than D-CGA-D greater than D-CGA-A). The D-CGA-C isomer has affinity and potency at the NMDA receptor similar to the endogenous agonist, L-glutamate. This high potency coupled with greater specificity than L-glutamate, makes D-CGA-C a potentially useful pharmacological tool for the study of this receptor.

Amino Acids, Dicarboxylic↗
PubMed1990

Physicochemical and biological properties of natural and synthetic C-22 and C-23 hydroxylated bile acids.

In order to define the effect of a side chain hydroxy group on bile acid (BA) physicochemical and biological properties, 23-hydroxylated bile acids were synthesized following a new efficient route involving the alpha-oxygenation of silylalkenes. 22-Hydroxylated bile acids were also studied. The synthesized bile acids included R and S epimers of 3 alpha,7 alpha,23-trihydroxy-5 beta-cholan-24-oic acid (23R epimer: phocaecholic acid), 3 alpha,12 alpha,23-trihydroxy-5 beta-cholan-24-oic (23R epimer: bitocholic acid), and 3 alpha,7 beta,23-trihydroxy-5 beta-cholan-24-oic acid. A 3 alpha,7 alpha,22-trihydroxy-5 beta-cholan-24-oic acid (haemulcholic acid) was also studied. The presence of a hydroxy group on the side chain slightly modified the physicochemical behavior in aqueous solution with respect to common BA: the critical micellar concentration (CMC) and the hydrophilicity were similar to naturally occurring trihydroxy BA such as cholic acid. The pKa value was lowered by 1.5 units with respect to common BA, being 3.8 for all the C-23 hydroxy BA. C-22 had a higher pKa (4.2) as a result of the increased distance of the hydroxy group from the carboxy group. When the C-23 hydroxylated BA were intravenously administered to bile fistula rats, they were efficiently recovered in bile (more than 80% unmodified) while the corresponding analogs, lacking the 23- hydroxy group, were almost completely glycine- or taurine-conjugated. On the other hand, the C-22 hydroxylated BA were extensively conjugated with taurine and less than 40% of the administered dose was secreted without being conjugated. In the presence of intestinal bacteria, they were mostly metabolized to the corresponding 7-dehydroxylated compound similar to common BA with the exception of bitocholic acid which was relatively stable. The presence of a hydroxy group at the C-23 position increased the acidity of the BA and this accounted for poor absorption within the biliary tree and efficient biliary secretion without the need for conjugation. 3 alpha,7 beta-23 R/S trihydroxy-5 beta-cholan-24-oic acids could improve the efficiency of ursodeoxycholic acid (UDCA) for gallstone dissolution or cholestatic syndrome therapy, as it is relatively hydrophilic and efficiently secreted into bile without altering the glycine and taurine hepatic pool.

Animals↗
PubMed1989

Structure-activity relationship studies on natural and synthetic bile acid analogs.

The objective of our research was to develop ursodiol analogs that are structurally modified to modulate hepatic side-chain amidation and prevent 7-dehydroxylation by intestinal bacteria while at the same time maintaining the critical micellar concentration (CMC) and hydrophilicity of ursodiol. More than 20 naturally occurring bile acids were screened for physicochemical properties. Then, two generations of analogs were studied, and those with physicochemical properties similar to ursodiol's were analyzed for physiologic properties. The first generation of analogs included molecules with steric and/or electronic hindrance on the side chain; the second group consisted of the same molecules conjugated with glycine or taurine and also "pseudoconjugated" analogs (23-hydroxylated, esterified, and amidated with other amino acids). Of the first-generation analogs, only cyclopropane D derivative and trans-olefin were useful to our purposes, being conjugated by the liver and almost completely recovered in bile. These two analogs were deconjugated and 7-dehydroxylated but with slower kinetics. The hydrophilicity of the molecules could be augmented by increasing the polarity of the steroid ring. Among the pseudoconjugated analogs, the CMC values were similar to those of the natural analogs, although hydrophobicity differed among the group. The analogs that were not deconjugated were not 7-dehydroxylated either. All of the pseudoconjugated bile acids were efficiently taken up by the liver, and their recovery in bile was similar to that of glycine and taurine ursodiol. From these studies we now know that side chain configuration and conformation are important in the conjugation and deconjugation processes. Mild modification of the side chain can prevent 7-dehydroxylation and thus yield a bile acid more resistant to intestinal bacteria and more bioavailable. Prevention of hepatic conjugation improves biliary secretion and recovery of many analogs.

Animals↗
PubMed1988

Quantitative relationship between bile acid structure and biliary lipid secretion in rats.

A series of unconjugated and taurine conjugated bile acids (BAs) differing in water solubility (SWo), critical micellar concentration (CMC), and hydrophilicity (K') were infused iv to rats at a tracer dose and a dose of 6 mumol/min/kg over a 1-h period. Bile was collected for 3 h to evaluate the role of BA structure on cholesterol, phospholipids secretions, and bile flow. The BAs studied differ in the number (2-3), position (-3, -6, -7, -12), and orientation of the hydroxyls (alpha/beta); the side chain structure was modified by shortening (C-23, nor-BA) and by lengthening (C-25, homo-BA), while maintaining the same structure of nuclear hydroxyls (3 alpha 7 beta). At a "tracer" dose, all C-24 natural BAs are efficiently recovered in bile when administered in both unconjugated and taurine conjugated forms. At a "high dose", all taurine conjugated BAs are efficiently recovered in bile (80-100%). However, a variable recovery was observed among unconjugated BAs: trihydroxy BAs are efficiently recovered (85-100%), while dihydroxy BAs are only partially recovered (25-40%). The side chain-modified BAs [i.e., C-23 nor and C-25 homo analogs of ursodeoxycholic acid (UDCA)] are partially recovered at a tracer dose (20-30%), but less at a high dose (10-20%) when administered in the unconjugated form. In contrast, the corresponding taurine conjugates are more efficiently recovered in bile (60-80%). Conjugation with taurine increases total recovery of unconjugated BAs in bile by not more than 30-40%. Highly hydrophilic and water-soluble BAs, such as ursocholic acid (SWo = 1.67 mM) and cholic acid (SWo = 0.27 mM), can also be secreted as unconjugates, and this accounts for their complete recovery. The conjugation step is rate limiting for poorly soluble BAs such as ursodeoxycholic acid (SWo = 0.009 mM) when administered at a high dose, and critical for nor and homo analogs which are poorly soluble and whose side chain modification partially suppresses their conjugation with taurine or glycine and thereby induces alternative pathways such as glucuronidation or sulfation. The induced bile flow is directly related to the hydrophilicity of the natural C-24 bile acid.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1988

Bile acids with a cyclopropyl-containing side chain. 3. Separation, identification, and properties of all four stereoisomers of 3 alpha,7 beta-dihydroxy-22,23-methylene-5 beta-cholan-24-oic acid.

3 alpha,7 beta-Dihydroxy-22,23-methylene-5 beta-cholan-24-oic acid (CUDCA) (2a), a side-chain cyclopropylog of ursodeoxycholic acid (UDCA) was shown to be a mixture of four stereoisomers (CUDCA A-D). The 22S,23R, and 22R,23S diastereoisomers have been separated, their respective configurations assigned by 13C NMR spectroscopy, and original synthetic schemes for their preparation elaborated. Moreover, theoretical models of the structure of UDCA and CUDCA A-D were built by using molecular computer graphic techniques. It was shown that the four diastereoisomers greatly differ in hydrophilicity, in critical micellar concentration (CMC) in water, and exhibit a different interaction with intestinal bacterial enzymes. It was also shown that CUDCA A-C are not conjugated with glycine or taurine in the liver, while CUDCA D is secreted into bile predominantly as taurine and glycine conjugate.

Animals↗
PubMed1987

Bile acids with a cyclopropyl-containing side chain. IV. Physicochemical and biological properties of the four diastereoisomers of 3 alpha,7 beta-dihydroxy-22,23-methylene-5 beta-cholan-24-oic acid.

To define the influence of the side chain modification on physicochemical and biological properties of bile acids, 3 alpha,7 beta-dihydroxy-22,23-methylene-5 beta-cholan-24-oic acid, a cyclopropyl analog of ursodeoxycholic acid (UDCA) was synthesized in both unconjugated and taurine-conjugated form. The presence of a cyclopropyl ring at C-22, C-23 position introduces chirality generating four diasteroisomers (A, B, C, and D) which greatly differ for the hydrophilicity and critical micellar concentration: A and B are more hydrophilic (K' = 0.21, 0.80 and CMC = 25,20 mM, respectively) than UDCA (K' = 0.95; CMC = 19 mM) while C and D are more hydrophobic and with lower CMC (K' = 1.30, 2.05; CMC = 14, 10 mM, respectively) than UDCA. Differences in these properties are related to the orientation of the C-25 carboxyl which in isomers A and B is oriented toward the back of the steroid body, reducing the continuity of the hydrophobic area. Using the isolated perfused rat liver we found that the isomers inhibited [3H]UDCA uptake differently. Isomer D (noncompetitive) was the most potent (51%) while isomer A (competitive) was the least potent (15%). When infused intravenously to rats, only D isomer and UDCA were quantitatively recovered in bile. They were secreted predominantly as taurine and glycine conjugates. Isomers A, B, C are not conjugated and only partially recovered in bile as unconjugates (less than 15% of the administered dose). The increase in bile flow per unit increase in bile acid secretion induced by isomers A, B, and C, was much greater than that induced by isomer D which is similar to that of UDCA (0.32 +/- 0.04 and 0.22 +/- 0.01, respectively) while it is reduced during infusion of the other isomers. When infused as taurine conjugates they behaved similarly to tauroursodeoxycholic acid. When incubated in anaerobic conditions with human stools only isomer D is partially 7-dehydroxylated (t/2 = 18 hr) even though slower than UDCA (t/2 = 5 hr). The substrate specificity of the taurine conjugated toward cholyglycine hydrolase is very poor, only isomers C and D are partially deconjugated with a kinetics much slower than that of UDCA (10 hr vs. 0.2 hr). By using molecular models it is possible to explain these differences due to the conformation of the side chain that, in the case of isomer D, is quite similar to UDCA. These data are useful to explain the metabolism of dihydroxy bile acids and to design new analogs with enhanced cholelitholytic activity.

Animals↗
PubMed1985

Bile acids with cyclopropane-containing side chain. 2. Synthesis and properties of 3 alpha,7 beta-dihydroxy-22,23-methylene-5 beta-cholan-24-oic acid (2-sulfoethyl)amide.

The preparation of 3 alpha,7 beta-dihydroxy-22,23-methylene-5 beta-cholan-24-oic acid (2-sulfoethyl)amide (5) by the one-step EEDQ-induced conjugation between ursodeoxycholic acid "cyclopropylog" (4) and taurine is described. The presence of a cyclopropyl ring adjacent to the amide bond is shown to make it resistant to degradation by intestinal bacteria. This new cyclopropylog is neither deconjugated at the C-24 amide bond nor 7-dehydroxylated when incubated with human stools in anaerobic conditions.

Anaerobiosis↗
PubMed1984

Bile acids with a cyclopropyl-containing side chain. 1. Preparation and properties of 3 alpha, 7 beta-dihydroxy-22,23-methylene-5 beta-cholan-24-oic acid.

3 alpha, 7 beta-Dihydroxy-22, 23-methylene-5 beta-cholan-24-oic acid (5), a side-chain cyclopropyl analogue of ursodeoxycholic acid (1b), has been prepared by the cyclopropanation of 3 alpha, 7 beta-diacetoxy-24-nor-5 beta-chol-22-ene (2) with ethyl diazoacetate , followed by saponification of the resulting cyclopropyl ester (3). The new bile acid presents similar properties to 1b in water. The sodium salt self-aggregates to form micelles at a concentration of 15.5 mM. The cyclopropane ring does not modify the pKa with respect to compound 1b. Cyclopropyl acid 5 is taken up efficiently by rat liver and promptly secreted into bile. It is partially (70%) conjugated with taurine. The bile flow and bile acids and phospholipids secretion are stimulated by 5, while the cholesterol secretion is stimulated by 5 to a lesser extent.

Animals↗
PubMed1980

Adamantane derivatives of biological interest. Synthesis and antiviral activity of 2-(1-adamantyl)imidazole derivatives.

The methods of synthesis and antiviral evaluation of 2-(1-adamantyl)imidazole (2a), N-methyl-2-(1-adamantyl)imidazole (2b) and 2-(1-adamantyl)benzimidazole (3a) are reported. These compounds are prepared by the selective homolytic substitution reaction by the adamantyl radical (Ad.) on the C-2 carbon atom of the heterocycles. Ad. radicals were generated by oxidative decarboxylation of 1-adamantyl carboxylic acid. Antiviral activities compounds 2a, 2b and 3a were tested in chick embryos against A-2 Victoria virus. Compounds 2a and 2b showed significant antiviral activity, whereas compound 3a was found inactive.

Adamantane↗