RESUMEN
Ascorbate is an important cofactor in many cellular metabolic reactions and is intimately linked to iron homeostasis. Continuously cultured cells are ascorbate deficient due to the lability of the vitamin in solution and to the fact that daily supplementation of media with ascorbate is unusual. We found that ascorbate repletion alone did not alter ferritin synthesis. However, ascorbate-replete human hepatoma cells, Hep3B and HepG2, as well as K562 human leukemia cells achieved a substantially higher cellular ferritin content in response to a challenge with iron than did their ascorbate-deficient counterparts grown under standard culture conditions. Most of the elevation in ferritin content was due to an increase in de novo ferritin synthesis of greater than 50-fold, as shown by in vivo labeling with [35S]methionine and immunoprecipitation. RNA-blot analysis showed only minor changes in steady state levels of ferritin mRNA, suggesting that ascorbate enhances iron-induced ferritin synthesis primarily by post-transcriptional events. Transient gene expression experiments using chloramphenicol acetyltransferase reporter gene constructs showed that the ascorbate effect on ferritin translation is not mediated through the stem-loop near the translational start site that transduces ferritin synthesis in response to cytokines. The data suggest that ascorbate possibly modifies the action of the iron-responsive element on ferritin translation, although more precise structure-function studies are needed to clarify this issue. These data demonstrate a novel role of ascorbate as a signaling molecule in post-transcriptional gene regulation. The mechanism by which ascorbate modulates cellular iron metabolism is complex and requires additional detailed investigation.
Asunto(s)
Ácido Ascórbico/farmacología , Ferritinas/genética , Hierro/fisiología , Biosíntesis de Proteínas , Carcinoma Hepatocelular , Humanos , Leucemia , ARN Mensajero/genética , Células Tumorales CultivadasRESUMEN
The effect of written guidelines and pharmacist-conducted education on the prescribing of postoperative narcotics was studied. The postoperative narcotic regimens prescribed on a general surgery ward and patients' assessment of pain control were recorded during three eight-week study phases. After the first (baseline) phase, written guidelines for the use of postoperative narcotics were mailed to all physicians. Four weeks after the baseline phase ended, data were collected again for eight weeks. A pharmacist then began reinforcing the guidelines by presenting inservice educational sessions and participating in ward rounds. The pharmacist did not attempt to change narcotic regimens for individual patients. Four weeks after the pharmacist's efforts began, the final eight-week data-collection period commenced. In general, the appropriateness of narcotic orders increased as the educational efforts intensified. There was no difference in narcotic expenses or pain control among the study phases. The appropriateness of postoperative analgesic regimens increased as education efforts became more intense, but the efforts had no effect on drug expenses or pain control.