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Biomedical subjects

J W Nyce

Publications and source records attributed to J W Nyce.

25 records · Page 2Linked to original sources
PubMed1993

Quantitation of 5-methylcytosine by one-dimensional high-performance thin-layer chromatography.

A method for the quantitative analysis of DNA 5-methylcytosine by one-dimensional high-performance thin-layer chromatography using alkylamino modified silica (HPTLC-NH2) plates is described. The preparative method is simple, involving enzymatic digestion of DNA with micrococcal nuclease and phosphodiesterase II to 3'-monophosphate nucleosides, conversion by T4 polynucleotide kinase to 32P-labeled 3',5'-bisphosphate nucleosides, and chromatographic separation of nuclease P1-cleaved 5'-monophosphate nucleosides. The weak, basic anion exchanger property of the HPTLC-NH2 plate enables separation of multiple samples in one dimension, whereas traditional polyethyleneimine cellulose plates require development of individual samples in two dimensions for analysis of 5'-methylcytosine.

5-Methylcytosine↗
PubMed1992

Mechanisms of cell growth inhibition and cell cycle arrest in human colonic adenocarcinoma cells by dehydroepiandrosterone: role of isoprenoid biosynthesis.

We have previously demonstrated that the chemopreventive agent dehydroepiandrosterone (DHEA) inhibits the isoprenylation of cellular proteins by depletion of endogenous mevalonate. We now report that treatment of HT-29 SF human colonic adenocarcinoma cells with DHEA at concentrations ranging from 12.5 to 200 microM for up to 72 h inhibited growth and arrested cells in the G1 phase of the cell cycle in a time- and dose-dependent manner. Exposure to 25 or 50 microM DHEA also transiently delayed cells in G2M phase after 48 h. Addition of mevalonic acid partially overcame both the growth and cell cycle effects of 25 microM DHEA in the initial 48 h. During prolonged exposure (72 h), the addition of mevalonic acid as well as cholesterol was required to reconstitute cell cycle progression. This suggests that the depletion of endogenous mevalonate and other isoprenoids is involved in DHEA-mediated growth inhibition and cell cycle arrest.

Adenocarcinoma↗
PubMed1991

Inhibition of protein isoprenylation and p21ras membrane association by dehydroepiandrosterone in human colonic adenocarcinoma cells in vitro.

Treatment of mice and rats with the adrenal steroid, dehydroepiandrosterone (DHEA), protects against spontaneous and chemically induced tumors. The mechanism of the chemopreventive action of DHEA, however, remains uncertain. DHEA has been reported to inhibit cholesterol biosynthesis. Mevalonic acid constitutes the basic precursor not only for cholesterol but also for a variety of nonsterol isoprenoids involved in cell growth. Certain of these nonsterol isoprenoids are utilized for posttranslational modification of proteins including p21ras. We therefore investigated the effects of DHEA upon protein isoprenylation. Twenty-four-h exposure of HT-29 SF human colonic adenocarcinoma cells to 50 microM DHEA was associated with significant incorporation of products of [3H]mevalonate metabolism into several size classes of cellular proteins. The pattern of incorporation was similar to that obtained after treatment with 25 microM lovastatin, a specific 3-hydroxy-3-methyl-glutaryl-CoA reductase inhibitor. Very little incorporation of label from [3H]mevalonate was observed in untreated cells. This suggests that [3H]mevalonate gains entrance to isoprenylation sites after treatment with DHEA or lovastatin because of depletion of endogenous mevalonate and subsequent inhibition of protein isoprenylation. Isoprenylation plays a critical role in promoting the association of p21ras with the cell membrane. Posttranslational processing and membrane association of p21ras were both found to be inhibited by DHEA. Thus, it is possible that the inhibition of isoprenylation of p21ras and other cellular proteins by DHEA may contribute to its anti-cancer effects.

Adenocarcinoma↗
PubMed1991

Differential feeding responses evoked in the rat by NPY and NPY1-27 injected intracerebroventricularly.

Neuropeptide Y (NPY) given by the intracerebroventricular (ICV) route in the rat evokes hyperphagic-like feeding. To examine the molecular nature of action of NPY, comparisons were made between the central effects of this peptide and a newly synthesized amino-terminus fragment, NPY1-27. A single guide tube was implanted stereotaxically to rest just above a lateral cerebral ventricle so that ICV injections in a volume of 10 microliters of either CSF control vehicle or peptide could be given in the unrestrained rat. Native NPY or NPY1-27 was given in doses of 5.0 or 10.0 micrograms, whereas nondeprotected NPY was infused in a dose of 10.0 micrograms. The intakes of either regular commercial rat diet or specially prepared chocolate-flavored biscuits as well as water were recorded intermittently for 4.0 h following each ICV infusion. Although a clear-cut dose response with a latency of similar magnitude emerged for both molecules, NPY was found to be nearly twice as potent as NPY1-27 in inducing spontaneous feeding. A corresponding infusion in the same volume of either nondeprotected NPY or CSF control vehicle was without effect. When chocolate-flavored biscuits were provided to the rat, an ICV infusion of a 10.0 micrograms dose of NPY enhanced significantly both rate of eating and total cumulative intake of flavored food in comparison to that after a similar infusion of NPY1-27 or either control solution. These results suggest that native NPY acting centrally affects gustatory and/or olfactory systems to a much greater degree than does NPY1-27.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Inhibition of 1,2-dimethylhydrazine-induced colon tumorigenesis in Balb/c mice by dehydroepiandrosterone.

Long-term administration of dehydroepiandrosterone (DHEA) to Balb/c mice significantly inhibits the rate of appearance of 1,2-dimethylhydrazine (DMH)-induced macroscopic colon and anal tumors and microscopic precursor and malignant lesions. The steroid, which has previously been shown to inhibit spontaneous breast cancer and chemically induced lung tumors in mice, may find application as a chemopreventive in individuals at high risk for developing colon cancer.

Animals↗
PubMedDate not supplied

Chemotherapy of murine colorectal carcinoma with cisplatin and cisplatin plus 3'-deoxy-3'-azidothymidine.

In light of the discouraging results obtained with conventional chemotherapy of human colon cancer using 5-fluorouracil, we examined the effects of cis-diamminedichloroplatinum (cisplatin) alone and combined with 3'-deoxy-3'-azidothymidine (AZT) on chemotherapy of colorectal adenocarcinomas induced by dimethyldrazine in CD-1 mice. Thirteen weeks after a 20 week tumor induction period (15 mg/kg dimethylhydrazine weekly) groups of 19 mice were given either no therapy, or weekly cisplatin (6 mg/kg for 4 wks), AZT (400 mg/kg, wks 3 and 4), or cisplatin and AZT. Animals were autospied at death or after euthanasia on day 99 post initiation of therapy, their colons excised, fixed in buffered formalin and the number and volume of tumors measured. Cisplatin alone or with AZT decreased tumor size by 47-52%, and enhanced survival, leaving 55% of the mice alive at day 99 compared to 18% in controls. These therapeutic effects were amplified when animals were given chemotherapy during recovery from the effects of short-term dietary provision of the anti-carcinogenic steroid, dehydroepiandrosterone (DHEA). Our results suggest cisplatin is an effective chemotherapeutic agent against colon cancer in this murine model, and warrant further studies of its interaction with AZT and DHEA in enhancing this effect.

Animals↗