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Biomedical subjects

D M Lambert

Publications and source records attributed to D M Lambert.

At least 73 records · Page 4Linked to original sources
PubMed1995

[Simple glycine derivatives from lipid transporter systems of glycine. Carrier test of a small-size neutral acid amine to the central nervous system].

Glycine, an important amino acid, does not cross the blood-brain barrier. Some simple derivatives have been designed to improve the unfavourable physico-chemical parameters: N-benzyloxycarbonylglycine and its methyl ester exhibit anticonvulsant activities superior to the parent amino acid. The incorporation of N-benzyloxycarbonylglycine in a pseudo-triglyceride pattern led to more active substances.

Anticonvulsants↗
PubMed1994

An orally bioavailable HIV-1 protease inhibitor containing an imidazole-derived peptide bond replacement: crystallographic and pharmacokinetic analysis.

(2R,4S,5S,1'S)-2-Phenylmethyl-4-hydroxy-5-(tert-butoxycarbonyl) amino-6-phenylhexanoyl-N-(1'-imidazo-2-yl)-2'-methylpropanamide (compound 2) is a tripeptide analogue inhibitor of HIV-1 protease in which a C-terminal imidazole substituent constitutes an isoelectronic, structural mimic of a carboxamide group. Compound 2 is a potent inhibitor of the protease (K(i) = 18 nM) and inhibits HIV-1 acute infectivity of CD4+ T-lymphocytes (IC50 = 570 nM). Crystallographic analysis of an HIV-1 protease-compound 2 complex demonstrates that the nitrogen atoms of the imidazole ring assume the same hydrogen-bonding interactions with the protease as amide linkages in other peptide analogue inhibitors. The sole substitution of the C-terminal carboxamide of a hydroxyethylene-containing tripeptide analogue with an imidazole group imparts greatly improved pharmacokinetic and oral bioavailability properties on the compound compared to its carboxamide-containing homologue (compound 1). While the oral bioavailability of compound 1 in rats was negligible, compound 2 displayed oral bioavailabilities of 30% and 14%, respectively, in rats and monkeys.

Administration, Oral↗
PubMed1994

Single- and multilocus DNA fingerprinting of communally breeding pukeko: do copulations or dominance ensure reproductive success?

In behavioral and ecological studies the "function" of dominance hierarchies is thought to be related to reproductive success. In particular, dominant males are regarded as likely to gain a reproductive advantage due to enhanced "access" to females. We compare the dominance status of adults with the frequency of copulations and the patterns of parentage in communally breeding pukeko or purple swamphen (Porphyrio porphyrio melanotus). This avian species has an unusual social system, often breeding in polygynandrous groups in which there is a strong dominance hierarchy. Typically, during the breeding season, there is considerable sexual activity, with heterosexual and homosexual copulations between adults being commonplace. Hae III-digested DNA from individuals belonging to breeding groups was hybridized to the minisatellite DNA probe YNH24, revealing putative single-locus profiles, while hybridization of the same DNA to the minisatellite probes pV47-2, 3'HVR, and per revealed typical multilocus profiles. The numbers of unattributable restriction fragments allowed the maternity and paternity of all individuals to be conclusively determined, despite high levels of band sharing among individuals within breeding groups. These close genetic similarities are a likely consequence of strong philopatry and inbreeding. We report instances of males which are high on the dominance hierarchy but have only a limited reproductive output in comparison with others and males which are subordinate but achieve a significant proportion of fertilizations. Generally these data reveal no consistent relationship between dominance, the frequency of copulations, and parentage among males. We conclude that pukeko highlight some difficulties with conventional explanations for the "function" of dominance.

Animals↗
PubMed1994

Anticonvulsant activities of N-benzyloxycarbonylglycine after parenteral administration.

Although glycine does not cross easily the blood-brain barrier, it exhibits at very high doses (10-40 mmol kg-1) a modest anticonvulsant activity. In this study, carbamate derivatives--N-benzyloxycarbonylglycine (Z-glycine) and N,tert-butoxycarbonylglycine (Boc-glycine)--have been compared with glycine. Z-glycine (1 mmol kg-1), but not Boc-glycine, reduces the number of tonic convulsions in the 3-mercaptopropionic and in the bicuculline tests, increases the latency of seizures in the strychnine test and is as active 3 h after administration as sodium valproate 30 min after administration in the maximal electroshock seizure test. Overall, milacemide, a precursor of glycine, and Z-glycine have rather similar anticonvulsant profiles in mice. The lack of Z-glycine affinity for the strychnine sensitive glycine receptor and the strychnine insensitive glycine receptor associated with the NMDA receptor may indicate that Z-glycine acts either via a prodrug mechanism or per se via an alternative mechanism.

Animals↗
PubMed1994

Molecular evolution at subzero temperatures: mitochondrial and nuclear phylogenies of fishes from Antarctica (suborder Notothenioidei), and the evolution of antifreeze glycopeptides.

Most fishes of the perciform suborder Notothenioidei are endemic to the subzero marine waters of Antarctica. A number of remarkable physiological attributes allow them to inhabit this extreme environment; for example, the blood of almost all notothenioid species contains antifreeze glycopeptides. To establish a molecular phylogenetic hypothesis for these fishes, DNA sequences from two mitochondrial genes, portions of the 12S and 16S ribosomal genes (928 base pairs [bp]), were determined for 18 species. These belong to 15 genera in five families of the suborder. The DNA data suggest that two of these families are unnatural groups and consequently that the classification and phylogeny of this suborder is in need of revision. In terms of DNA variation, the Bovichtidae are a distantly related sister group to the other families of the suborder that includes the icefishes, the only vertebrates without hemoglobin. The fishes of the suborder (except the Bovichtidae) seem to have speciated rapidly, forming an adaptive radiation in the Antarctic waters. A phylogenetic analysis of published hemoglobin amino acid sequences for other notothenioid fishes supports these results from mtDNA. On the basis of molecular phylogeny, the evolution of antifreeze glycopeptides was studied. The age of the radiation of notothenioid fishes had been estimated to be at least 38 Mya. However, the level of mtDNA variation detected in notothenioid fishes appears to be too low to agree with this date of origin and might instead suggest a younger age (10-15 Mya). Alternatively, the low level of detected mtDNA variation would agree with the traditional old-age estimate if an extremely slow rate of mtDNA evolution is postulated for this group. This slow-rate hypothesis, if true, could be explained by decreased metabolic rates slowing down the tempo of molecular evolution.

Animals↗
PubMed1993

Analgesic potency of S-acetylthiorphan after intravenous administration to mice.

As hydrolysis in serum of acetorphan to acetylthiorphan (N-[(R,S)-3-acetylmercapto-2-benzylpropanoyl]glycine) has been evidenced, both the neutral endopeptidase inhibition in vitro by acetylthiorphan and analgesic potency of acetylthiorphan after intravenous administration to mice in two analgesic models, the hot-plate and the tail-flick tests, were compared with those of thiorphan and acetorphan. Acetylthiorphan showed a decreased degree of neutral endopeptidase inhibition (IC50 = 316 +/- 38 nM) compared to thiorphan (IC50 = 1.8 +/- 0.2 nM). After intravenous administration followed by the hot-plate jump latency test, acetylthiorphan elicited a degree of analgesia equivalent to that with acetorphan but longer lasting. Like acetorphan and thiorphan, acetylthiorphan was devoid of analgesic activity in the tail-flick test. The results indicated that S-acetylation of the thiol function in acetylthiorphan ensures sufficient lipophilicity to permit crossing of the blood-brain barrier and that acetylthiorphan acts via a prodrug mechanism.

Analgesics↗
PubMed1993

Synergistic drug interactions of an HIV-1 protease inhibitor with AZT in different in vitro models of HIV-1 infection.

Synthetic peptide mimetic inhibitors of HIV-1 protease effectively block spread of infectious virus in acutely infected T-cells. These compounds also inhibit production of infectious virions from chronically infected T-cell lines. In order to determine the potential for drug interaction effects on antiviral activity, an HIV-1 protease inhibitor (SK&F 108922) and AZT were studied in three different in vitro models of HIV-1 infection of T-cell lines, specifically, (1) acutely infected cells infected at low multiplicity, (2) HIV-1 chronically-infected cells and (3) co-cultivations of chronically infected with non-infected cells. Upon co-treatment, these compounds demonstrated synergy in Molt4 or H9 cells acutely infected with HIV-1 strain IIIB. Either compound alone was a potent inhibitor of HIV-1 in co-cultivations of uninfected and chronically infected cells. In combination treatments of co-cultures, SK&F 108922 demonstrated strong synergy with AZT. Treatment of H9/IIIB chronically infected cells demonstrated no inhibitory effect by AZT treatment (EC50 = > 100 microM) whereas SK&F 108922 was inhibitory (EC50 = 3 microM). Upon co-treatment of H9/IIIB chronically infected cultures with both compounds, the antiviral activity was similar to that of the protease inhibitor alone suggesting no drug interaction. In the co-cultivation experiments, AZT's antiviral effect was most likely due to blocking spread of acute infection to uninfected cells in the culture. No antagonistic effects were observed with AZT and SK&F 108922 co-treatments. These results clearly demonstrate that an HIV-1 protease inhibitor can exert a potent antiviral effect on chronically infected T-cells in contrast to AZT and is capable of potent synergy with AZT in acute and co-culture in vitro infection models.

Acquired Immunodeficiency Syndrome↗
PubMed1993

1,3-Diacylaminopropan-2-ols and corresponding 2-acyl derivatives as drug carriers: unexpected pharmacological properties.

The design of lipid vectors (pseudotriglycerides, PTGs), achieved by the amide isosteric substitution of the ester moieties of 1,3-diacylglycerols, is based on the structural similarity with natural triglycerides facilitating the passage of pharmacological agents across biological membranes. 2-S-Acetylthiorphan (hemiacetorphan) pseudotriglycerides, Z-glycine pseudotriglycerides and 1,3-diacylaminopropan-2-ols vector molecules differing by the nature of the acid side-chain are examined in acute toxicity, radioligand binding and guinea-pig ileum experiments. These evaluations have led us to distinguish two types of compounds. Linear derivatives, palmitoyl and decanoyl, are devoid of toxicity and intrinsic activity. Cyclic derivatives, which contain in the acyl chain a phenyl, cyclohexyl, cyclopentyl or adamantoyl ring, present additional properties. Cyclic derivatives of hemiacetorphan are lethal after intravenous administration. The mortality is governed by the 2-hemiacetorphan moiety in the cyclic vector molecules. Hemiacetorphan alone is also lethal. Cyclic vector molecules and related compounds inhibit the contractile response of the guinea-pig ileum induced by electrical stimulation, histamine or acetylcholine (noncompetitive antagonism) whereas linear entities and parent compounds are not active. In particular, the 2-hemiacetorphan 1,3-diadamantoylamide PTG presents pD'2 values 7.87 +/- 0.29 (vs histamine) and 7.97 +/- 0.12 (vs acetylcholine).

Animals↗
PubMed1993

Antiretroviral activities of protease inhibitors against murine leukemia virus and simian immunodeficiency virus in tissue culture.

Rationally designed synthetic inhibitors of retroviral proteases inhibit the processing of viral polyproteins in cultures of human immunodeficiency virus type 1 (HIV-1)-infected T lymphocytes and, as a result, inhibit the infectivity of HIV-1 for such cultures. The ability of HIV-1 protease inhibitors to suppress replication of the C-type retrovirus Rauscher murine leukemia virus (R-MuLV) and the HIV-related lentivirus simian immunodeficiency virus (SIV) was examined in plaque reduction assays and syncytium reduction assays, respectively. Three of seven compounds examined blocked production of infectious R-MuLV, with 50% inhibitory concentrations of < or = 1 microM. Little or no cellular cytotoxicity was detectable at concentrations up to 100 microM. The same compounds which inhibited the infectivity of HIV-1 also produced activity against SIV and R-MuLV. Electron microscopic examination revealed the presence of many virions with atypical morphologies in cultures treated with the active compounds. Morphometric analysis demonstrated that the active compounds reduced the number of membrane-associated virus particles. These results demonstrate that synthetic peptide analog inhibitors of retroviral proteases significantly inhibit proteolytic processing of the gag polyproteins of R-MuLV and SIV and inhibit the replication of these retroviruses. These results are similar to those for inhibition of HIV-1 infectivity by these compounds, and thus, R-MuLV and SIV might be suitable models for the in vivo evaluation of the antiretroviral activities of these protease inhibitors.

Antiviral Agents↗
PubMed1992

Hydroxyethylene isostere inhibitors of human immunodeficiency virus-1 protease: structure-activity analysis using enzyme kinetics, X-ray crystallography, and infected T-cell assays.

Analogues of peptides ranging in size from three to six amino acids and containing the hydroxyethylene dipeptide isosteres Phe psi Gly, Phe psi Ala, Phe psi NorVal, Phe psi Leu, and Phe psi Phe, where psi denotes replacement of CONH by (S)-CH(OH)CH2, were synthesized and studied as HIV-1 protease inhibitors. Inhibition constants (Ki) with purified HIV-1 protease depend strongly on the isostere in the order Phe psi Gly greater than Phe psi Ala greater than Phe psi NorVal greater than Phe psi Leu greater than Phe psi Phe and decrease with increasing length of the peptide analogue, converging to a value of 0.4 nM. Ki values are progressively less dependent on inhibitor length as the size of the P1' side chain within the isostere increases. The structures of HIV-1 protease complexed with the inhibitors Ala-Ala-X-Val-Val-OMe, where X is Phe psi Gly, Phe psi Ala, Phe psi NorVal, and Phe psi Phe, have been determined by X-ray crystallography (resolution 2.3-3.2 A). The crystals exhibit symmetry consistent with space group P6(1) with strong noncrystallographic 2-fold symmetry, and the inhibitors all exhibit 2-fold disorder. The inhibitors bind in similar conformations, forming conserved hydrogen bonds with the enzyme. The Phe psi Gly inhibitor adopts an altered conformation that places its P3' valine side chain partially in the hydrophobic S1' pocket, thus suggesting an explanation for the greater dependence of the Ki value on inhibitor length in the Phe psi Gly series. From the kinetic and crystallographic data, a minimal inhibitor model for tight-binding inhibition is derived in which the enzyme subsites S2-S2' are optimally occupied. The Ki values for several compounds are compared with their potencies as inhibitors of proteolytic processing in T-cell cultures chronically infected with HIV-1 (MIC values) and as inhibitors of acute infectivity (IC50 values). There is a rank-order correspondence, but a 20-1000-fold difference, between the values of Ki and those of MIC or IC50. IC50 values can approach those of Ki but are highly dependent on the conditions of the acute infectivity assay and are influenced by physiochemical properties of the inhibitors such as solubility.

Amino Acid Sequence↗
PubMed1992

Human immunodeficiency virus type 1 protease inhibitors irreversibly block infectivity of purified virions from chronically infected cells.

Synthetic peptide analog inhibitors of human immunodeficiency virus type 1 (HIV-1) protease were used to study the effects of inhibition of polyprotein processing on the assembly, structure, and infectivity of virions released from a T-cell line chronically infected with HIV-1. Inhibition of proteolytic processing of both Pr55gag and Pr160gag-pol was observed in purified virions from infected T cells after treatment. Protease inhibition was evident by the accumulation of precursors and processing intermediates of Pr55gag and by corresponding decreases in mature protein products. Electron microscopy revealed that the majority of the virion particles released from inhibitor-treated cells after a 24-h treatment had an immature or aberrant capsid morphology. This morphological change correlated with the inhibition of polyprotein processing and a loss of infectivity. The infectivity of virion particles purified from these chronically infected cell cultures was assessed following treatment with the inhibitor for 1 to 3 days. Virions purified from cultures treated with inhibitor for 1 or 2 days demonstrated a 95- to 100-fold reduction in virus titers, and treatment for 3 days resulted in complete loss of detectable infectivity. The fact that virions from treated cultures were unable to establish infection over the 7- to 10-day incubation period in the titration experiments strongly suggests that particles produced by inhibitor-treated cells were unable to reactivate to an infectious form when they were purified away from exogenous protease inhibitor. Thus, a block of HIV-1 protease processing of viral polyproteins by specific inhibitors results in a potent antiviral effect characterized by the production of noninfectious virions with altered protein structures and immature morphologies.

Blotting, Western↗
PubMed1991

Binding of soluble CD4 proteins to human immunodeficiency virus type 1 and infected cells induces release of envelope glycoprotein gp120.

Human immunodeficiency virus (HIV) infects cells after binding of the viral envelope glycoprotein gp120 to the cell surface recognition marker CD4. gp120 is noncovalently associated with the HIV transmembrane envelope glycoprotein gp41, and this complex is believed responsible for the initial stages of HIV infection and cytopathic events in infected cells. Soluble constructs of CD4 that contain the gp120 binding site inhibit HIV infection in vitro. This is believed to occur by competitive inhibition of viral binding to cellular CD4. Here we suggest an alternative mechanism of viral inhibition by soluble CD4 proteins. We demonstrate biochemically and morphologically that following binding, the soluble CD4 proteins sT4, V1V2,DT, and V1[106] (amino acids 1-369, 1-183, and -2 to 106 of mature CD4) induced the release of gp120 from HIV-1 and HIV-1-infected cells. gp120 release was concentration-, time-, and temperature-dependent. The reaction was biphasic at 37 degrees C and did not take place at 4 degrees C, indicating that binding of soluble CD4 was not sufficient to release gp120. The appearance of free gp120 in the medium after incubation with sT4 correlated with a decrease in envelope glycoprotein spikes on virions and exposure of a previously cryptic epitope near the amino terminus of gp41 on virions and infected cells. The concentration of soluble CD4 proteins needed to induce the release of gp120 from virally infected cells also correlated with those required to inhibit HIV-mediated syncytium formation. These results suggest that soluble CD4 constructs may inactivate HIV by inducing the release of gp120. We propose that HIV envelope-mediated fusion is initiated following rearrangement and/or dissociation of gp120 from the gp120-gp41 complex upon binding to cellular CD4, thus exposing the fusion domain of gp41.

Blotting, Western↗
PubMed1991

Synthesis of 1,3-diacylaminopropan-2-ols and corresponding 2-acyl derivatives as amide isosteres of natural lipids.

N,N'-diacyl-1,3-diaminopropan-2-ols as amide isosteres of 1,3-diacylglycerols are obtained in 50-79% yields by treatment of 1,3-diaminopropan-2-ol with acid chlorides either in ether or THF in the presence of triethylamine and catalytic amounts of 4-dimethyl-aminopyridine. Subsequent acylation of the secondary alcohol function with a variety of carboxylic acids (e.g. fatty acids, N-protected amino acids, drug compounds) can be effected by various techniques (i.e. acid chlorides, symmetrical anhydrides, isopropenyl chloroformate) with yields ranging from 56% to 76%.

Acylation↗
PubMed1991

The chronically infected cell as a target for the treatment of HIV infection and AIDS.

Infection of the T lymphocyte with HIV results in a cytopathic effect and cell death that has been linked to a selective loss of the helper T-lymphocyte function of the immune system. In addition to acute infection, which leads to cell death, a chronic or persistent infection also occurs. The persistence of these viral reservoirs has been implicated in the progression of HIV infection and AIDS. Rational drug discovery targeted to late-stage events in HIV replication has the potential to yield antiviral agents capable of blocking virus spread by inhibiting the production of infectious virions from these chronic reservoirs. Steve Petteway and colleagues discuss antiviral strategies that target the chronically infected cell, with a focus on HIV protease inhibitors.

Acquired Immunodeficiency Syndrome↗
PubMed1990

Inhibition of HIV-1 protease in infected T-lymphocytes by synthetic peptide analogues.

The gag and pol genes of the human immunodeficiency virus type 1 (HIV-1) (ref. 1) are translated as two polyproteins, Pr55gag and Pr160gag-pol (refs 2-6), which are subsequently cleaved by the action of a virus-encoded protease into the four structural gag proteins of the virion core (p17, p24, p7 and p6) and the pol-encoded enzymes essential for retrovirus replication (protease, reverse transcriptase, ribonuclease H, and endonuclease). Mutational inactivation of the proteases of HIV-1 and other retroviruses results in immature, non-infectious virions, indicating that exogenous inhibition of the protease may represent an attractive approach to anti-AIDS therapy. Here we demonstrate that synthetic peptide analogues, which are potent inhibitors of purified HIV-1 protease, inhibit the processing of the viral polyproteins in cultures of HIV-1-infected T lymphocytes and attenuate viral infectivity.

Amino Acid Sequence↗
PubMed1989

Sexual differentiation and mate recognition. The dynamics of structure.

Sexual differentiation results in an array of distinct sexual morphotypes and two biological sexes are not sufficient to describe all the forms that are observed. It is also plainly impossible to discuss mate recognition without reference to sexual morphology, because the body and the brain are inseparably linked throughout the sexual differentiation process. It follows that we must rework conceptually inadequate notions about sexual morphology before general theories of sexual behaviour can be developed.

Animals↗