Effect of melatonin on cell growth, metabolic activity, and cell cycle distribution.

We have recently demonstrated that the pineal secretory product melatonin inhibits the key transcriptional regulator nuclear factor-kappa B (NF-kappa B). As the activation of NF-kappa B is known to regulate the expression of cellular genes associated with cell cycle progression, cell growth, and differentiation, we investigated the effect of melatonin treatment on several cellular processes. These include cell viability, metabolic activity, and cell cycle phase distribution. Human embryonic kidney (293S) cells were treated with melatonin at concentrations of 0.02, 0.2, or 2 mM. When cell viability was measured 24, 48, and 72 hr after continuous exposure to melatonin using the trypan blue dye exclusion method, no significant cell death was observed. Even after exposure to 2 mM melatonin for 72 hr, cell viability remained at 98%. In contrast, another antioxidant compound, pyrrolidine dithiocarbomate (PDTC), at a 2 mM concentration reduced cell viability to 80.7+/-2.1% as early as 24 hr compared with untreated controls (P<0.05). When the metabolic activity was determined at 24, 48, and 72 hr using the colorimetric MTT assay, no significant changes in metabolic activity were observed. Even if the cells were treated with 10 mM melatonin for 72 hr, the metabolic activity was similar to that of the control cells. When cell cycle analysis was performed by flow cytometry, no marked difference in cell cycle distribution was observed. Melatonin at a concentration of 2 mM, however, did slightly alter the cell cycle (percentage of S phase cells) at 48 hr. This study revealed that when 293S cells are treated with concentrations of melatonin up to 2 mM, no significant alterations in three important cellular functions occurred. Exogenously added melatonin appeared to have a limited influence on the normal functioning of the cells even when the exposure continued for 72 hr.

Interaction of hyperthermia with Taxol in human MCF-7 breast adenocarcinoma cells.

Hyperthermia treatments (43 degrees C, 1 h) were performed on exponentially growing MCF-7 breast adenocarcinoma cells at the beginning, middle, or end of 24 h incubations of the cells in vitro with Taxol (paclitaxel). When the cells were heated at the beginning or middle of the Taxol incubation, the hyperthermia treatment protected against the toxic effect of each of the Taxol concentrations examined (5, 10 and 100 nM). Consistent with earlier studies, Taxol treatment at 37 degrees C resulted in an accumulation of greater than 94% of the cells in G2/M at 24 h. Heating the cells at the middle or end of the Taxol treatment resulted in a similar accumulation. However, heat treatment during the first hour of Taxol exposure resulted in a significantly smaller percentage of cells (approximately 50%) in G2/M. HPLC analysis showed that at 37 degrees C, Taxol uptake into MCF-7 cells approached maximum within 0.25 h and increased only slightly more over the next 11.75 h. The parental Taxol level was markedly lower by 24 h. In contrast, 1 h hyperthermia treatments at the beginning or middle of the Taxol incubation resulted in higher Taxol concentrations at 12 and 24h, and higher intracellular concentrations overall than at 37 degrees C. These results indicate that hyperthermia inhibits Taxol related cell cycle effects and cytotoxicity, in spite of causing higher concentrations of Taxol to be present in heated cells.

Hyperbaric oxygen as a prophylaxis for radiation-induced delayed enteropathy.

This trial was accomplished in C3H mice to determine whether hyperbaric oxygen (HBO) could be administered to prevent delayed radiation enteropathy. Fifty mice randomized into two equal groups received 30 Gy abdominopelvic irradiation in 10 fractions. The study group received a course of 30 HBO treatments beginning 7 weeks after the radiation exposure. The control group received only housing and nutritional support after irradiation. A third group of three animals had no radiation or HBO. All animals were sacrificed 7 months after radiation. Animals were inspected grossly for signs of enteropathy. In addition, a special stretch apparatus was used to quantify narrowing and rigidity of ileum just proximal to the ileocecal junction. Those animals who received HBO had fewer gross signs of enteropathy and had less narrowing and less rigidity in their harvested bowel segments. These differences were highly statistically significant. Treatment with HBO drastically reduces signs of radiation enteropathy. Further study including clinical trials are recommended.

Hyperthermic effects on viability and growth kinetics of human lymphoblastoid cells.

During clinical hyperthermia, various blood elements may be exposed to elevated temperatures. The effect of heat on human lymphocyte viability and human lymphoblastoid cell viability and growth was therefore measured. In the viability studies, cells were heated for different times and temperatures and stained with fluorescein diacetate either immediately of at various times after treatment; dye uptake was then analysed using fluorescence microscopy. There was no significant decrease in lymphocyte viability when assayed at 0 and 24 h after heating at 42-43 degrees C for varying times. Similarly, when proliferating lymphoblastoid cells were heated at 42-43 degrees C, there was no decrease measured in viability immediately after heating. However, in contrast to the lymphocyte results, a progressive decrease of lymphoblastoid cell viability was observed with increasing time after treatment. A nadir in viability was observed 48-72 h after heating, followed by a subsequent apparent recovery. This recovery showed a correlation with cell growth, as well as lysis of non-viable cells. The cell population doubling time was also lengthened, with longer doubling times observed for more severe heat treatments.