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Biomedical subjects

A M Clark

Publications and source records attributed to A M Clark.

At least 73 records · Page 4Linked to original sources
PubMed1997

Accumulation of clusterin/sulfated glycoprotein-2 in degenerating pachytene spermatocytes of adult rats treated with methoxyacetic acid.

Clusterin is a ubiquitous glycoprotein that is produced constitutively by Sertoli cells at relatively high amounts. Its association with apoptosis, damage, disease, and repair in nongonadal tissues led us to investigate whether clusterin could be part of a damage-induced response in Sertoli cells brought on by apoptosis of an adjacent cell type. Therefore, the objective of this study was to treat adult rats with methoxyacetic acid (MAA) to selectively destroy pachytene spermatocytes, examine the localization and expression of testicular clusterin, and relate this to the timing of DNA fragmentation, a hallmark of apoptosis. Clusterin protein was localized to the cytoplasm of pachytene spermatocytes at 6 h post-MAA, whereas clusterin mRNA was localized to Sertoli cells. Morphological degeneration of dying cells and DNA fragmentation were not seen until 12 h. Thus, Sertoli cell-derived clusterin had accumulated in the cytoplasm of degenerating spermatocytes early in the apoptotic process. On the basis of these results and the known binding of clusterin to hydrophobic macromolecules, we hypothesize that clusterin is produced by Sertoli cells as a mechanism to "clear" potentially harmful cellular components during the degeneration of germ cells and remodeling of their membranes that occur normally during spermatogenesis.

Acetates↗
PubMed1996

Transcriptional regulation of the lutropin/human choriogonadotropin receptor and three enzymes of steroidogenesis by growth factors in cultured pig Leydig cells.

Recent data have shown that Leydig-cell-specific functions, and therefore steroidogenic capacity, can be regulated by lutropin/human choriogonadotropin collectively termed gonadotropin and by several growth factors that are produced by and act within the testis. However, the molecular mechanisms by which these factors regulate Leydig cells are not understood. In the present study, we have investigated the effects of basic fibroblast growth factor (bFGF), epidermal growth factor (EGF), insulin-like growth factor I (IGF-I) and transforming growth factor beta (TGF-beta) on mRNA for the gonadotropin receptor and three steroidogenic enzymes: cytochrome P-450scc, cytochrome P-450 17 alpha-hydroxylase/C17-20 lyase (17 alpha-hydroxylase), and 3 beta-hydroxysteroid dehydrogenase. IGF-1, which can enhance testosterone production, increased gonadotropin-receptor density after an increase in receptor mRNA levels, and it increased the level of mRNA for cytochrome P-450scc and 17 alpha-hydrolyase. Micromolar concentrations of insulin had similar effects to those of IGF-I. Moreover, the three factors that decreased testosterone production (EGF, bFGF and TGF beta 1) decreased gonadotropin receptor density, receptor mRNA levels and the mRNA levels for 17 alpha-hydroxylase. The potential effects of these growth factors on the transcription on the gonadotropin genes for the receptor and these three steroidogenic enzymes were measured by means of nuclear run-on assays. We demonstrated that the long-term inhibitory (EGF, bFGF, TGF beta 1) or stimulatory (IGF-I) effects of these growth factors are primarily due to a variation in the transcription rates of genes for the gonadotropin receptor, cytochrome P-450scc and 17 alpha-hydroxylase. Moreover, since previous studies have shown than some of these growth factors are expressed within the testis, they may play a physiological role in the regulation of differentiated testicular functions.

3-Hydroxysteroid Dehydrogenases↗
PubMed1996

The Dictyostelium MAP kinase ERK2 regulates multiple, independent developmental pathways.

We showed previously that the MAP kinase ERK2 is essential for aggregation. erk2 null cells lack cAMP stimulation of adenylyl cyclase and thus cannot relay the cAMP chemotactic signal, although the cells chemotax to cAMP (Segall et al. 1995). In this paper we have examined the role of ERK2 in controlling developmental gene expression and morphogenesis during the multicellular stages, making use of a temperature-sensitive ERK2 mutation. Using suspension assays, we show that ERK2 is not essential for aggregation-stage, cAMP pulse-induced gene expression, or for the expression of postaggregative genes, which are induced at the onset of mound formation in response to cAMP in wild-type cells. In contrast, the prespore-specific gene SP60 is not induced and the prestalk-specific gene ecmA is induced but at a significantly reduced level. Chimeric organisms, comprised of wild-type and erk2 null cells expressing the prestalk-specific ecmA/lacZ reporter, show an abnormal spatial patterning, in which Erk2ts/erk2 cells are excluded from the very anterior prestalk A region. To further examine the function of ERK2 during the multicellular stages, we bypassed the requirement of ERK2 for aggregation by creating an ERK2 temperature-sensitive mutant. erk2 null cells expressing the ERK2ts mutant develop normally at 20 degrees C and express cell-type-specific genes but do not aggregate at temperatures above 25 degrees C. Using temperature shift experiments, we showed that ERK2 is essential for proper morphogenesis and for the induction and maintenance of prespore but not prestalk gene expression. Our results indicate that ERK2 functions at independent stages during Dictyostelium development to control distinct developmental programs: during aggregation, ERK2 is required for the activation of adenylyl cyclase and during multicellular development, ERK2 is essential for morphogenesis and cell-type-specific gene expression. Analysis of these results and other supports the conclusion that the requirement of ERK2 for cell-type differentiation is independent of its role in the activation of adenylyl cyclase.

Amino Acid Sequence↗
PubMed1996

Natural products as a resource for new drugs.

Natural products have served as a major source of drugs for centuries, and about half of the pharmaceuticals in use today are derived from natural products. The aim of this review is to provide an overview of the continuing central role of natural products in the discovery and development of new pharmaceuticals. In this context, selected examples of important natural product-derived drugs are cited, focusing on some of the most recent introductions to the clinical setting, and a brief overview of some of the important recent developments and remaining challenges in the process of discovering and developing bioactive natural products is provided. Interest in natural products research is strong and can be attributed to several factors, including unmet therapeutic needs, the remarkable diversity of both chemical structures and biological activities of naturally occurring secondary metabolites, the utility of bioactive natural products as biochemical and molecular probes, the development of novel and sensitive techniques to detect biologically active natural products, improved techniques to isolate, purify, and structurally characterize these active constituents, and advances in solving the demand for supply of complex natural products. Opportunities for multidisciplinary research that joins the forces of natural products chemistry, molecular and cellular biology, synthetic and analytical chemistry, biochemistry, and pharmacology to exploit the vast diversity of chemical structures and biological activities of natural products are discussed.

Adjuvants, Immunologic↗
PubMed1996

Regulation by gonadotropins of the messenger ribonucleic acid for P450 side-chain cleavage, P450(17) alpha-hydroxylase/C17,20-lyase, and 3 beta-hydroxysteroid dehydrogenase in cultured pig Leydig cells.

The Leydig cell from the immature pig provides a good model for studying testicular steroidogenesis. Regulation of the enzymes involved, which has been well studied in rodents, has not been characterized in the pig. The objectives of this study were to examine the regulation of three steroidogenic enzymes in pig Leydig cells by LH/hCG and testosterone. The mRNA for P450 side-chain cleavage and P450(17) alpha-hydroxylase/C17-20-lyase, although constitutively expressed, decreased over time in culture, while that for 3 beta-hydroxysteroid dehydrogenase (3 beta HSD) remained relatively constant. The mRNA for all three enzymes was increased in a dose- and time-dependent manner by treatment with hCG. Run-on experiments demonstrated that the main effect of the hormone was at the level of transcription. Treatment with hydroxyflutamide, either alone or in combination with hCG, had no effect on the mRNA for these enzymes. Treatment with hCG plus aminoglutethimide, an inhibitor of steroidogenesis, had no effect on the mRNA for the two P450 enzymes, but resulted in an increase in mRNA for 3 beta HSD when compared to treatment with hCG alone. However, exogenous testosterone could not block the effect of aminoglutethimide. Therefore, the steroidal regulation of 3 beta HSD in pig Leydig cells may act through a mechanism separate from the androgen receptor. While aspects of the regulation of these enzymes are similar to those seen in rodents, some significant differences exist. Our results support the concept that regulation of steroidogenic enzymes in Leydig cells is species-specific.

3-Hydroxysteroid Dehydrogenases↗
PubMed1995

Synthesis and antimicrobial activity of 6,7-annulated pyrido[2,3-d]pyrimidines.

Four new 6H-indeno[2',1':5,6]pyrido[2,3-d]pryimidines (10-13) were synthesized via cyclocondensation reactions involving chlorovinyl aldehyde 1 or ketoaldehyde 3 and appropriately substituted 6-aminopyrimidines. The regiochemistry of the compounds was established by 1H NMR and 13C NMR spectral data as well as X-ray crystal data. Compounds 10 and 11 and previously reported homologues 14 and 15 were screened for antimicrobial activity. Moderate antimicrobial activity was observed for some of these compounds. Compound 14 was especially active against Staphylococcus aureus. Crystal data for 13 (C14H7N3Cl2) follows: monoclinic space group, P21/n; Unit cell dimensions, a = 7.284(1) A, b = 12.800(1) A, c = 13.108(1) A, beta = 93.98(1) degree, V = 1219.2(2) A3, Z = 4.

Anti-Bacterial Agents↗
PubMed1995

Antifungal evaluation of pseudolaric acid B, a major constituent of Pseudolarix kaempferi.

Pseudolaric acid B [1] was isolated and identified as the main antifungal constituent of Pseudolarix kaempferi using bioassay-directed fractionation. Pseudolaric acid B was active against Trichophyton mentagrophytes, Torulopsis petrophilum, Microsporum gypseum, and Candida spp., while its methylated or hydrolyzed derivatives were not active against these same organisms. The minimum inhibitory concentrations and minimum fungicidal concentrations of pseudolaric acid B [1] against Candida and Torulopsis species were comparable with those of amphotericin B. The in vivo activity of pseudolaric acid B was evaluated in a murine model of disseminated candidiasis. Pseudolaric acid B [1] reduced the number of recovered colony-forming units significantly at different dosages. Infected mice treated intravenously with pseudolaric acid B [1] also had a longer survival time than those treated with vehicle alone.

Animals↗
PubMed1995

Microbial metabolites of ophiobolin A and antimicrobial evaluation of ophiobolins.

Ophiobolin A [1], 3-anhydroophiobolin A [2], ophiobolin B [3], and ophiobolin L [4] were isolated from fermentation broths of Cochliobolus heterostrophus. Preliminary screening showed that a number of organisms were capable of metabolizing the sesterterpene ophiobolin A [1]. Large-scale transformations of ophiobolin A [1] with Polyangium cellulosum produced 6 and 7 while Pseudomonas aeruginosa produced 8. Resting-cell preparations of Penicillium patulum afforded 9 and 10. The structures of these metabolites were established by spectroscopic methods and by comparison of the spectral data with those of the starting material. The antimicrobial activity of the ophiobolins was also evaluated.

Anti-Bacterial Agents↗
PubMed1995

Weight loss results in significant improvement in pregnancy and ovulation rates in anovulatory obese women.

Obesity can affect ovulation and the chances of pregnancy. In this prospective study, a weight loss programme was assessed to determine whether it could help infertile overweight anovulatory women to establish ovulation and assist in achieving pregnancy, ideally without further medical intervention. The subjects acted as their own historical controls. They underwent a weekly programme of behavioural change in relation to exercise and diet over 6 months; those who did not complete the 6 months were treated as the comparison group. Women in the study group lost an average of 6.3 kg, with 12 of the 13 subjects resuming ovulation and 11 becoming pregnant, five of these spontaneously. Fitness, diet and psychometric measurements all improved. Fasting insulin and testosterone concentrations dropped significantly, while sex hormone binding globulin concentrations rose. None of these changes occurred in the comparison group. Thus, weight loss with a resultant improvement in ovulation, pregnancy outcome, self-esteem and endocrine parameters is the first therapeutic option for women who are infertile and overweight.

Adult↗