Motor networks: shifting coalitions

Are central motor networks composed of task-specific dedicated neurons or are the neurons multifunctional, entering shifting coalitions for particular tasks to form different functional networks? Recent experiments elegantly indicate the latter.     

beta-Alkylthio indolyl carbinols: potent nonsteroidal antiandrogens with oral efficacy in a prostate cancer model

Through an in vivo screening model, we developed the in vivo SAR of beta-alkylthio indolyl carbinols. Through these efforts we identified a compound with potent oral in vivo efficacy in both immature and mature rat prostate weight reduction models and in a murine xenograft prostate cancer model.     

Is glycine a surrogate for a d‐amino acid in the collagen triple helix?

Collagen is the most abundant protein in animals. Every third residue in a collagen strand is a glycine with phi, psi = -70 degrees, 175 degrees. A recent computational study suggested that replacing these glycine residues with D-alanine or D-serine would stabilize the collagen triple helix. This hypothesis is of substantial importance, as the glycine residues in collagen constitute nearly 10% of the amino acid residues in humans. To test this hypothesis, we synthesized a series of collagen mimic peptides that contain one or more D-alanine or D-serine residues replacing the canonical glycine residues. Circular dichroism spectroscopy and thermal denaturation experiments indicated clearly that the substitution of glycine with D-alanine or D-serine greatly disfavors the formation of a triple helix. Host-guest studies also revealed that replacing a single glycine residue with D-alanine is more destabilizing than is its replacement with L-alanine, a substitution that results from a common mutation in patients with collagen-related diseases. These data indicate that the glycine residues in collagen are not a surrogate for a D-amino acid and support the notion that the main-chain torsion angles of a glycine residue in the native structure (especially, phi > 0 degrees ) are critical determinants for its beneficial substitution with a D-amino acid in a protein.     

The antiviral drug ribavirin is a selective inhibitor of S-adenosyl-L-homocysteine hydrolase from Trypanosoma cruzi

Ribavirin (1,2,4-triazole-3-carboxamide riboside) is a well-known antiviral drug. Ribavirin has also been reported to inhibit human S-adenosyl-L-homocysteine hydrolase (Hs-SAHH), which catalyzes the conversion of S-adenosyl-L-homocysteine to adenosine and homocysteine. We now report that ribavirin, which is structurally similar to adenosine, produces time-dependent inactivation of Hs-SAHH and Trypanosoma cruzi SAHH (Tc-SAHH). Ribavirin binds to the adenosine-binding site of the two SAHHs and reduces the NAD(+) cofactor to NADH. The reversible binding step of ribavirin to Hs-SAHH and Tc-SAHH has similar K(I) values (266 and 194 microM), but the slow inactivation step is 5-fold faster with Tc-SAHH. Ribavirin may provide a structural lead for design of more selective inhibitors of Tc-SAHH as potential anti-parasitic drugs.     

Enterohepatic circulation of organochlorine compounds: a site for nutritional intervention

Organochlorine compounds enter the body primarily as components of the diet. Their removal from the body is via excretion into the feces. There is evidence that many people are in a positive balance, with the rate of intake of organochlorines exceeding that of their excretion. A desirable nutritional approach to this problem would both reduce dietary intake and increase fecal excretion. Nonabsorbable dietary lipids reduce the absorption of dietary organochlorines and also increase the rate of their fecal excretion. Organochlorine compounds that are stored in the body enter the intestine both in bile and through a poorly understood nonbiliary mechanism. Part of the amount that enters the intestine is excreted, and part is reabsorbed in an enterohepatic circulation. There is evidence that an increase in excretion can be achieved by interference with the enterohepatic circulation of organochlorine compounds and their metabolites. Data from animals and humans show that the presence of nonabsorbed lipid in the intestine can increase the rate of excretion in a clinically significant manner.     

The new clinical trials with thiazolidinediones--DREAM, ADOPT, and CHICAGO: promises fulfilled?

PURPOSE OF REVIEW: Despite extensive documentation of their insulin-sensitizing and antihyperglycemic effects, the importance and place of the thiazolidinediones in diabetes management remain unclear. Three new controlled clinical trials of thiazolidinediones offer new information on the clinical utility of these agents. RECENT FINDINGS: During the past year, three new trials of thiazolidinediones were reported. In Diabetes Reduction Assessment with Ramipril and Rosiglitazone Medication, rosiglitazone reduced progression to diabetes in prediabetic patients by 60%. A Diabetes Outcome Progression Trial found rosiglitazone to have greater antihyperglycemic durability than metformin and glyburide in patients with recently diagnosed type 2 diabetes. Finally, in the Carotid Intima-media Thickness in Atherosclerosis using Pioglitazone, treatment with pioglitazone in patients with type 2 diabetes slowed progression of carotid wall thickness compared with the sulfonylurea glimepiride. SUMMARY: These trials support the contention that thiazolidinediones have superior efficacy in improving and stabilizing glycemic control than older antihyperglycemic agents, especially early in the course of type 2 diabetes. Findings from the Carotid Intima-media Thickness in Atherosclerosis using Pioglitazone add to the evidence that these agents have clinically meaningful vasculoprotective effects. Although generally well tolerated, they promote weight gain, limiting their acceptability to some extent, and occasionally lead to a diagnosis of heart failure, mostly in susceptible individuals.     

Polymorphism in the intermediates and products of amyloid assembly

Amyloid formation reactions exhibit two classes of polymorphisms: the metastable intermediates commonly observed during amyloid formation and the range of conformationally distinct mature fibrils often seen at the reaction endpoint. Although recent data suggest that spherical oligomers and protofibrils in most cases are not obligate intermediates of amyloid assembly, oligomeric states might sometimes serve as on-pathway intermediates. Mature amyloid polymorphs self-propagate as a result of the normally very high fidelity of amyloid elongation, giving rise to strain behavior and species barriers in prion phenomena. Oligomers, protofibrils and various polymorphic forms of mature amyloid fibrils seem to be distinguished by differences in atomic structure that give rise to differences in observed morphologies.     

Screening of Vitamin D activity (VDA) of Solanum glaucophyllum leaves measured by radioimmunoassay (RIA)

The ingestion of Solanum glaucophyllum (SG) causes a calcinosis of cattle named Enteque Seco (ES). The toxic principle is the 1,25-(OH)₂D₃, mainly conjugated as glycoside. This study aims to validate a simple novel method of evaluation of the VDA of SG leaves. Aqueous extracts of SG were purified using C₁₈ minicolumns and assayed by RIA with an antibody raised in rabbits by injection of the acid—C22, 1-(OH)Vitamin D₃. Data were expresed as glycoside equivalent to 1,25-(OH)₂D₃ in ng/g of dry leaves. We compared this data with 1,25-(OH)₂D₃ levels measured, in the same samples, by liquid chromatography (HPLC) after enzyme cleavage. This procedure involved the incubation of SG leaves with rumen fluid, followed by C₁₈-OH solid phase extraction. The 1,25-(OH)₂D₃ fraction was run by HPLC and detection was achieved using a photodiode array detector. Data were expressed as micrograms of 1,25-(OH)₂D₃/g dry leaves. A significant regression of 1,25-(OH)₂D₃ levels (Y) as a function of glycoside RIA 1,25-(OH)₂D₃ equivalents (X) was found: Y = 12.02 + 0.35X [R = 0.81; P = 0,0002; N = 15], allowing us to conclude that this novel assay could be used to estimate the amount of this active principle contained in SG leaves.     

Spermatinamine, the first natural product inhibitor of isoprenylcysteine carboxyl methyltransferase, a new cancer target

Isoprenylcysteine methyltransferase (Icmt) catalyzes the carboxyl methylation of oncogenic proteins in the final step of a series of post-translational modifications. The inhibition of Icmt provides an attractive and novel anticancer target. A natural product high-throughput screening campaign was conducted to discover inhibitors of Icmt. The Australian marine sponge, Pseudoceratina sp., yielded spermatinamine, a novel alkaloid with a bromotyrosyl-spermine-bromotyrosyl sequence, as the bioactive constituent. Its structure was determined by 1D and 2D NMR spectroscopy. Spermatinamine is the first natural product inhibitor of Icmt.     

Conformationally restricted homotryptamines 3. Indole tetrahydropyridines and cyclohexenylamines as selective serotonin reuptake inhibitors

A series of indole tetrahydropyridine and indole cyclohexenylamines was prepared, and their binding affinities at the human serotonin transporter (SERT) were determined. In particular, a nitrile substituent at the C5 position of the indole ring gave potent SERT activity. The stereochemistry of the N,N-dimethylamine substituent was determined for the most potent indole cyclohexenylamine, 6a. The enantiomers of 6a were energy minimized and compared to other conformationally restricted SSRIs. Compound 6a was found to give a dose-response similar to the SSRI fluoxetine in microdialysis studies in rats.