Biomedical subjects

L H Sanders

Publications and source records attributed to L H Sanders.

5 recordsLinked to original sources

PubMed2003

Phenotype of the zebrafish masterblind (mbl) mutant is dependent on genetic background.

The zebrafish masterblind (mbl) mutant is characterized by the lack of olfactory placodes and optic vesicles, reduced telencephalon, an expanded epiphysis (Heisenberg et al. [1996] Development 123:191-203), and enlarged jaw. To understand the cellular events giving rise to the olfactory placode defect of this mutant, we examined the expression pattern of the distal-less-3 (dlx3) gene in mbl. In the mutant, dlx3, which is normally expressed in the developing nose and ear, showed reduced expression in the olfactory placode field, but normal expression in the developing ear. To determine whether the loss of dlx3 expression was due to cell loss, we assayed cell death by using TUNEL labeling. Although cell death in the mutant was not concentrated in the region of dlx3 expression, there was increased cell death in the forebrain, epiphysis, and jaw region, as compared with that in wild-type controls. This cell death phenotype was cyclical in nature, showing an increase and decrease in cell death on a roughly 24-hr cycle. Further analysis showed that this cyclical phenotype was specific to the genetic background. The severity of the mbl phenotype, including cell death, expanded epiphysis, and enlarged jaw, decreased when the mutation was moved from the original "TL" background to the "AB" background. Thus, the severity of developmental defects in the mbl mutant is strongly dependent on genetic background. We examined the contribution of cell death to the morphologic defects of mbl by blocking cell death by using zVADfmk, a known caspase inhibitor. We found that this treatment partially rescued the expanded jaw defect and that this rescue was dependent on the genetic background. Therefore, the mbl mutant phenotypes result, in part, from genetic background effects that alter the pattern of programmed cell death early in development.

Animals↗

PubMed1998

Flavonoid derivatives as adenosine receptor antagonists: a comparison of the hypothetical receptor binding site based on a comparative molecular field analysis model.

Flavonoid derivatives have been optimized as relatively rigid antagonists of adenosine receptors with particular selectivity for the A3 receptor subtype. A quantitative study of the structure-activity relationships for binding of flavonoids to adenosine A1, A2A, and A3 receptors has been conducted using comparative molecular field analysis (CoMFA). Correlation coefficients (cross-validated r2) of 0.605, 0.595, and 0.583 were obtained for the three subtypes, respectively. All three CoMFA models have the same steric and electrostatic contributions, implying similar requirements inside the binding cavity. Similarities were seen in the topology of steric and electrostatic regions with the A1 and A3 receptors, but not the A2A. Substitutions on the phenyl ring at the C-2 position of the chromone moiety may be considered important for binding affinity at all adenosine receptors. In the A3 model a region of favorable bulk interaction is located around the 2'-position of the phenyl ring. The presence of a C-6 substituent in the chromone moiety is well tolerated and increases the A1/A3 selectivity. The CoMFA coefficient contour plots provide a self-consistent picture of the main chemical features responsible for the pKi variations and also result in predictions which agree with experimental values.

Binding Sites↗

PubMed1995

Comparative molecular field analysis of selective A3 adenosine receptor agonists.

A series of 48 N6-benzyladenosine 5'-uronamide derivatives has been described recently as moderately selective A3 adenosine receptor agonists of nanomolar potency (Gallo-Rodriguez, C. et al. J. Med. Chem. 1994, 37, 636). Quantitative structure activity relationships in this series, including some novel derivatives, have been investigated using a Comparative Molecular Field Analysis (CoMFA), with emphasis on the N6-substituent. The resulting three dimensional pharmacophore model defines the steric and electronic factors which modulate in vitro affinities in binding to rat brain A3 adenosine receptors. The model indicates a positive correlation of affinity with the steric characteristics of the compounds (major factor), particularly toward the 3-position of the benzyl ring of N6-benzyl NECA, and a weak correlation with the electrostatic effects of the N6-substituent. A comparison of active and inactive compounds using volume maps showed that bulk at the 3-position of the benzyl ring of the molecule is conducive to high affinity at A3 receptors, while steric bulk at other positions of the benzyl ring leads to poor binding. t-Boc-amino acid conjugates of a 3-aminobenzyl derivative were synthesized to probe the steric and hydrophobic limitations at that position. We have discovered a subregion of the N6-benzyl binding pocket occupied by a 3-(L-prolylamino) group that is sterically disallowed at A3 receptors and allowed in A1 and A2a receptors. 6-N-Phenylhydrazino and 6-O-phenylhydroxylamino derivatives, incorporating major changes in electrostatic character of the ligand proximal to the purine, were predicted by the CoMFA model to have high A3 affinity. Such analogs were synthesized and found to be well tolerated at the A3 receptor binding site.

Adenosine↗

PubMed1994

Structure-activity relationships of N6-benzyladenosine-5'-uronamides as A3-selective adenosine agonists.

Adenosine analogues modified at the 5'-position as uronamides and/or as N6-benzyl derivatives were synthesized. These derivatives were examined for affinity in radioligand binding assays at the newly discovered rat brain A3 adenosine receptor and at rat brain A1 and A2a receptors. 5'-Uronamide substituents favored A3 selectivity in the order N-methyl > N-ethyl approximately unsubstituted carboxamide > N-cyclopropyl. 5'-(N-Methylcarboxamido)-N6-benzyladenosine was 37-56-fold more selective for A3 receptors. Potency at A3 receptors was enhanced upon substitution of the benzyl substituent with nitro and other groups. 5'-N-Methyluronamides and N6-(3-substituted-benzyl)adenosines are optimal for potency and selectivity at A3 receptors. A series of 3-(halobenzyl)-5'-N-ethyluronamide derivatives showed the order of potency at A1 and A2a receptors of I approximately Br > Cl > F. At A3 receptors the 3-F derivative was weaker than the other halo derivatives. 5'-N-Methyl-N6-(3-iodobenzyl)adenosine displayed a Ki value of 1.1 nM at A3 receptors and selectivity versus A1 and A2a receptors of 50-fold. A series of methoxybenzyl derivatives showed that a 4-methoxy group best favored A3 selectivity. A 4-sulfobenzyl derivative was a specific ligand at A3 receptors of moderate potency. An aryl amino derivative was prepared as a probe for radioiodination and receptor cross-linking.

Adenosine↗

PubMed1978

Evaluation of compounding accuracy and aseptic techniques for intravenous admixtures.

Intravenous admixtures containing potassium collected from three hospital pharmacies were analyzed for compounding accuracy, sterility and pyrogenicity. The study was performed in two stages. During stage I, pharmacists and technicians were not informed of the study, but during stage II they were informed. In each stage 10 samples were collected from each person in the two personnel groups, analyzed and the results compared between the two personnel groups and the two stages. Results of the study showed that without monitoring (stage I) pharmacists had a higher mean percent error and contamination level than technicians. With monitoring, however, pharmacists showed a lower mean percent error and contamination level than technicians. Both personnel groups showed a decline in their mean percent error in the second stage, but there were still 83 (39.5%) errors in compounding accuracy greater than +/- 6%. No positive results with the Limulus test for pyrogens were obtained. It is recommended that a planned program of quality control be instituted for the preparation of i.v. admixtures by both pharmacists and technicians.

Antisepsis↗