Estrogenic diazenes: heterocyclic non-steroidal estrogens of unusual structure with selectivity for estrogen receptor subtypes.

Estrogens regulate many biological functions, often acting in a tissue-selective manner. Their tissue-selective action is believed to involve differential estrogen action through the two estrogen receptor (ER) subtypes, ERalpha and ERbeta, as well as differential interaction of the ligand-receptor complexes with promoters and coregulator proteins. In the latter case, selectivity is based on the induction of specific conformations of the ligand-ER complex, conformations that are influenced by the structure of the ligand. Estrogen pharmaceuticals having an ideal balance of tissue-selective activity are being sought for menopausal hormone replacement, breast cancer prevention and therapy, and other actions. To expand on the structural diversity of ER ligands that might show such tissue selectivity, we have prepared a series of diazenes (pyrazines, pyrimidines, and pyridazines) substituted with two to four aryl groups and various short-chain aliphatic substituents. All of the pyrazine and pyrimidines bind to ER, some with high affinity and with a considerable degree of preferential binding to either ERalpha or ERbeta. One pyrimidine and one pyrazine have ERalpha affinity preferences as high as 23 and 9, respectively, and one pyrimidine has an ERbeta affinity preference of 8. The pyridazines, by contrast, are quite polar and have only very low binding affinity for the ER. In cell-based transcription assays, several of the pyrimidines and a pyrazine were found to be considerably more agonistic on ERalpha than on ERbeta. Because these triaryl diazenes have the largest volumes among the ER ligands so far investigated, their high affinity demonstrates the flexibility of the ligand binding pocket of the ERs and its tolerance for large substituents. Thus, these novel heterocyclic ligands expand the repertoire of chemical structures that bind to the estrogen receptor, and they could prove to be useful in elucidating the biological behavior of the two ER subtypes and in forming the basis for new estrogen pharmaceuticals having desirable tissue selectivity.

Selective growth of mucolytic bacteria including Clostridium perfringens in a neonatal piglet model of total parenteral nutrition.

BACKGROUND: Compromised barrier function and intestinal inflammation are common complications of total parenteral nutrition (TPN). OBJECTIVE: We tested the hypothesis that the lack of enteral nutrients in TPN might select commensal or pathogenic bacteria that use mucus as a substrate, thereby weakening the protection provided by the intestinal mucus layer. DESIGN: Ileal microbiota profiles of piglets fed by total enteral nutrition (TEN; n = 6) or TPN (n = 5) were compared with the use of 16S ribosomal DNA polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis and with a PCR-based method developed to specifically measure Clostridium perfringens concentrations. Ileal bacteria from TEN and TPN piglets were also examined for their ability to grow on mucin or sulfated monosaccharides. RESULTS: Bacterial community structure was equally complex in the ileum of TEN and TPN piglets, but profiles clustered according to mode of nutrition. Sixty-two percent of total mucus-associated bacteria (100 colonies tested) in TPN compared with 33% of mucus-associated bacteria (100 colonies tested) in TEN ileal samples grew on mucin. Bacteria capable of using sulfated monosaccharides were also enriched in TPN samples. C. perfringens, an opportunistic pathogen, was specifically enriched in the TPN ileum (P < 0.05). These results were corroborated by cultivation-based studies that showed rapid growth of C. perfringens on mucin-based substrates. CONCLUSIONS: Mucolytic potential is widespread among intestinal bacteria. Mucolytic bacteria in general and C. perfringens in particular were selected when enteral nutrients were withheld in this TPN piglet model. Similar enrichment processes may occur in humans nourished by TPN and may thereby contribute to intestinal dysfunction.