Human incubation, effects

The investigation of incubation effects, i.e., that the optical, chemical, and mechanical properties of a (transparent) material can be changed during repetitive illumination of the same spot without ablation, is rather difficult because of the complicated surface structure of a biological composite material. It can be stated that one femtosecond laser pulse at F0=2.0 J cm-2 (roughly three times Fth) applied to healthy human enamel led to minor ablation (Fig. 32a). Five pulses of the same fluence resulted in a crater with a depth of 2-3 pm (Fig. 32b). The shape of the excision is well defined, and no cracks could be observed. 

A 2-h incubation with another PGE2 analogue, nocloprost (9P-chloro-DMPG) protects normal human fibroblasts but has no effect on the survival of colon adenocarcinoma cells exposed to 10 Gy (1000 rad) (218). Nocloprost protects against radiation-induced DSBs in normal cells but not in tumor cells. Moreover, incubation using nocloprost for 2 h after irradiation enhances the rate of DSB rejoining in fibroblasts but not in adenocarcinoma cells. These data possibly reflect a different distribution of PG receptors on the plasma membrane of the two cell types. 

BLswas, S. D. (1982). Effect of urea on pH, ammonia, amino acids and lactic acid in the human salivary sediment system incubated with varying levels of glucose. Arch. Oral Biot. 27, 68.3-691. 

In order to assess the effect of the corn cob xylan on the cell viability and proliferation rate, xylan solutions at concentrations of 0.1, 0.25, 0.50, 0.75, and 1 mg/ml were placed in contact with human cervical adenocarcinoma cells (HeLa cells) for 24 and 72 h. Finally, the cell viability was determined by the MTT assay. It was observed that regardless of the xylan concentration, the samples tested did not affect the viability of HeLa cells after incubation for 24 h (Figure 13) (Unpublished data). 

The test system was considerably less sensitive to endosulfan when mouse ER, rather than human ER, was used to mediate (3-gal activity (Ramamoorthy et al. 1997). In similar assays, endosulfan at 10 jM had no effect on (3-gal activity in yeast Saccharomyces) transfected with either the human or rainbow trout ER (Andersen et al. 1999). In addition, no effect was observed on transcriptional activation of HeLa cells transfected with plasmids containing an estrogen receptor as a responsive element (Shelby et al. 1996). Endosulfan also did not induce transient reporter gene expression in MCF-7 human breast cancer cells at an incubation concentration of 2.5 pM (Andersen et al. 1999). Maximum endosulfan-induced ER-mediated luciferase reporter gene expression occurred in vitro in a T47D human breast adenocarcinoma cell line at approximately 10 pM, while 50% expression of luciferase occurred at about 5.9 pM the maximum expression was approximately 59% of the effect from exposure to 0.03 nM estradiol (0.00003 pM) (Legler et al. 1999). Luciferase expression from combined treatment with endosulfan and dieldrin was additive over concentrations ranging from 3 to 8 pM. 

Kaneko et al. (1993) have described a group of lipophilic ascorbic-acid analogues that have been studied in cultured human umbilical vein endothelial cells that were first incubated with test drug and then exposed to lipid hydroperoxides. Although ascorbate itself did not protect the endothelial cells, derivatives like CV3611 protected. Pretreatment was necessary. CV3611 was synergistic with vitamin E. The authors concluded that these lipophilic antioxidants incorporate into endothelial cell membranes where they are effective inhibitors of lipid peroxidation. In contrast, lipophobic antioxidants were not effective in their hands (Kaneko et al., 1993). 

On the other hand, microsomes may also directly oxidize or reduce various substrates. As already mentioned, microsomal oxidation of carbon tetrachloride results in the formation of trichloromethyl free radical and the initiation of lipid peroxidation. The effect of carbon tetrachloride on microsomes has been widely studied in connection with its cytotoxic activity in humans and animals. It has been shown that CCI4 is reduced by cytochrome P-450. For example, by the use of spin-trapping technique, Albani et al. [38] demonstrated the formation of the CCI3 radical in rat liver microsomal fractions and in vivo in rats. McCay et al. [39] found that carbon tetrachloride metabolism to CC13 by rat liver accompanied by the formation of lipid dienyl and lipid peroxydienyl radicals. The incubation of carbon tetrachloride with liver cells resulted in the formation of the C02 free radical (identified as the PBN-CO2 radical spin adduct) in addition to trichoromethyl radical [40]. It was found that glutathione rather than dioxygen is needed for the formation of this additional free radical. The formation of trichloromethyl radical caused the inactivation of hepatic microsomal calcium pump [41]. 

Mehorta and coworkers (1989) observed that isolated fractions of brain and heart cells from rats orally administered 0.5-10 mg endrin/kg showed significant inhibition of Ca+2 pump activity and decreased levels of calmodulin, indicating disruption of membrane Ca+2 transport mechanisms exogenous addition of calmodulin restored Ca+2-ATPase activity. In vitro exposure of rat brain synaptosomes and heart sarcoplasmic reticuli decreased total and calmodulin-stimulated calcium ATPase activity with greater inhibition in brain preparations (Mehorta et al. 1989). However, endrin showed no inhibitory effects on the calmodulin-sensitive calcium ATPase activity when incubated with human erythrocyte membranes (Janik and Wolf 1992). In vitro exposure of rat brain synaptosomes to endrin had no effect on the activities of adenylate cyclase or 3, 5 -cyclic phosphodiesterase, two enzymes associated with synaptic cyclic AMP metabolism (Kodavanti et al. 1988). 

Figure 7.1. Effect of GM-CSF on neutrophil protein biosynthesis. Human neutrophils were incubated in RPMI1640 medium supplemented with 2.5% foetal calf serum and 60 jtCi/ml [35S]-methionine, in the presence and absence of 50 U/ml GM-CSF. After 4 h incubation at 37 °C, the cells were pelleted by low-speed centrifugation. The proteins in the cell pellets were precipitated by 10% trichloracetic acid and then analysed by two-dimensional polyacrylamide gel electrophoresis, using iso-electrofocussing in the first dimension. Electrophoresis in the second dimension was performed in the presence of SDS and used a 12% acrylamide gel. Source Experiment of Becky Stringer.

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