Perfusion culture promotes differentiation of oral keratinocytes in vitro

In order to reconstruct the mucosal lining of the oral cavity tissue engineered autologous mucosa grafts could be of great benefit. In conventional stagnant cultures cells often tend to dedifferentiate. Perfusion culture has been demonstrated to reestablish differentiation in various epithelial cell types. Thus, in secondary cultures of human oral keratinocytes from ten patients conventional stagnant culture versus perfusion culture technique was compared. Proliferation and state of differentiation as expressed morphologically and immunohistochemically were assessed. After 14 days oral keratinocytes in a perfusion culture system tend to be further differentiated. They build up a thicker epithelium (3.4+/-1.0 vs. 2.4+/-0.4 layers), form microridges, express cytokeratins 1, 2, 10, 11, 19 but not 13 in all cells and cytokeratins 5, 6 particularly in cells attached to the carrier membrane. In contrast, oral keratinocytes in stagnant culture do not form microridges and rather express cytokeratins 13, 14, and 19 in mattering amounts.

Spin transfer from protein to DNA in X-irradiated 'dry' and hydrated chromatin: an electron spin resonance investigation of spectral components between 77 K and room temperature

PURPOSE

To investigate the potential total and relative free-radical transfer from histones to DNA in X-irradiated chromatin, by analysing the relative contributions of individual radicals from protein and from DNA.

MATERIALS AND METHODS

Chromatin was isolated from calf thymus, freeze-dried and either used as such or after equilibration at 76% relative humidity. A mixture of histones was purchased. X-irradiation was performed at 77 K (liquid nitrogen). Data acquisition was on a Bruker ESP 380 ESR-spectrometer (X-band, 9.5 GHz) and at high magnetic fields (285 GHz, Y-band, GHMFL Grenoble). Data analysis involved computer treatment of spectra.

RESULTS

Three components were isolated from an annealing series of histones and assigned to specific radicals (X-band). Chromatin revealed the existence of radicals from both DNA, as well as from the histone compartment. The presence of the oxidized guanine base, as well as the reduced cytosine and thymine bases from DNA at 77 K was confirmed by high-field ESR. Relative radical yields were determined by superposition of individual components from DNA and histones in order to give complete reconstructions of the experimental spectra of the annealing series.

CONCLUSIONS

The relative yields of individual radicals in chromatin differ from those in histones or DNA, respectively. Their behaviour upon annealing is, on the other hand, not significantly changed. Since the total radical yield of DNA radicals is about two times higher in the chromatin complex than in pure DNA, the hypothesis of spin transfer from protein to DNA prior to radical stabilization at 77 K is substantiated.

Free radicals from lyophilized 'dry' DNA bombarded with heavy-ions as studied by electron spin resonance spectroscopy

PURPOSE

To investigate the number and species of free radicals from dry DNA after bombardment with heavy-ions at low temperature in comparison with X-irradiation at 77 K by electron spin resonance (ESR) spectroscopy.

MATERIALS AND METHODS

Solid DNA samples were either X-irradiated at 77 K as cylinder samples or heavy-ion-bombarded (LET range 1500-12400keV/microm) at the Gesellschaft für Schwerionenforschung (GSI Darmstadt) as very thin tablets. Data acquisition was on a Bruker ESP 380 ESR-spectrometer (X-band, 9.5 GHz). Data analysis involved computer treatment of spectra.

RESULTS

Spectra from heavy-ion-bombarded samples were found to reveal the same free radical species with about the same relative contributions for most components as those from X-irradiated samples at comparable doses. Only two components, a thymine allyl radical and a Cl' deoxyribose located species, were enhanced after heavy-ion bombardment. Dose effects in both cases involved a higher relative amount of deoxyribose-derived free radicals. The analysis of G (total free radicals, taken from dose-response curves) were typically smaller than those for X-rays but showed no clear dependence on LET.

CONCLUSIONS

The differing biological response to high-LET particle bombardment compared with low-LET irradiation is not strongly reflected by the chemical structure and total number of initial free radicals. It might rather derive from an inhomogeneous distribution of energy deposition (resulting in 'clustered damages') or from effects at higher chemical and biological levels (e.g. product formation and repair) which is not strongly apparent in the free radical characteristics obtained by ESR-spectroscopy.

Free radicals from X-irradiated 'dry' and hydrated lyophilized DNA as studied by electron spin resonance spectroscopy: analysis of spectral components between 77K and room temperature

PURPOSE

To investigate the number, spectroscopic signatures and chemical structures of free radicals from X-irradiated lyophilized DNA (dry and equilibrated at 76% relative humidity) between 77 K and room temperature by electron spin resonance (ESR) spectroscopy.

MATERIALS AND METHODS

Samples were prepared by freeze drying DNA (sodium salt, salmon testes) in H2O or D2O and used as such ('dry' DNA) or after equilibration at 76% relative humidity. K3[Fe(CN)6] was co-lyophilized in some samples as an electron scavenger. X-irradiation was performed at 77 K (liquid nitrogen). Data acquisition was on a Bruker ESP 380 ESR-spectrometer (X-band, 9.5 GHz) and at high magnetic fields (245 GHz, Y-band; GHMFI, Grenoble, France). Data analysis involved computer treatment of spectra.

RESULTS

There were 12 different radical components isolated from DNA in four different conditions (dry and after equilibration at 76% relative humidity in either H2O or D2O) with the additional help of high magnetic field ESR and the use of K3[Fe(CN)6] as an electron scavenger. Several components were detected at 77 K and were found to be common for both hydration conditions, although their spectral shape varied considerably. These involved reduced thymine and cytosine bases, the oxidized guanine base, probably a C1'-located sugar radical, a thymine allyl radical and a secondary thymine H-addition radical. For the reduced cytosine base the amino-protonated form was observed in H2O samples, which was only partially exchanged in the D2O samples. At high water content another species, perhaps due to a sugar radical, contributes in addition even at low temperatures. All radical components anneal out with temperature, with only small secondary reactions taking place. A peroxy radical and a sharp singlet, probably due to the deprotonated radical cation from guanine, come into the balance together with the secondary thymine radical. At high doses, a further sugar radical (perhaps at the C3'-position) was detected in dry DNA. The relative yields of the isolated patterns were determined by precise reconstruction of the experimental spectra.

CONCLUSIONS

The comprehensive component delineation performed at 77 K and upon annealing to room temperature for lyophilized DNA showed a larger diversity and a higher variance of radicals at 77 K than discussed so far. Thermal annealing brings about only a few reactions to produce secondary species. Most components decay without paramagnetic successors.

Formation of C1' located sugar radicals from X-irradiated cytosine nucleosides and -tides in BeF2 glasses and frozen aqueous solutions

Free radical formation in nucleosides and nucleotides containing cytosine as base was studied after X-irradiation at 77 K of samples prepared in frozen aqueous BeF2 glasses and in frozen aqueous solutions by means of electron spin resonance (ESR) spectroscopy. By comparison with radical patterns from the cytosine base and from 1-CH3-cytosine, by using specifically base-deuterated nucleosides and by comparison between the 2'-deoxy- and the ribonucleotide it could be demonstrated that a radical at the C1'-position of the sugar was formed in nucleosides and nucleotides in both matrices. Quantitative analysis showed that in the BeF2 glass an initial population of about 10% of substrate located species due to this radical was present at 77 K and developed to about 25% after decay of the .OH (.OD) radicals at about 140 K. This was taken as proof that at least part of these radicals were formed from .OH radicals. In frozen aqueous solutions about 20% of C1' located sugar radicals were found to be present at 77 K, the population remaining roughly constant with increasing temperature to 140 K. The mechanistic findings of these unexpected results are discussed in terms of mobile .OH radicals and/or hole transfer in the glass and in the glassy regions of the frozen aqueous solutions.

Influence of electron scavengers on the radical formation in thymidine-5'-monophosphate and DNA in frozen aqueous solution and glasses

Structural and quantitative effects of different electron scavenger concentrations on the free radical formation in the nucleotide thymidine-5'-monophosphate (TMP) and in deoxyribonucleic acid (DNA) after X-irradiation in frozen aqueous solution and glasses (BeF2/H2O for TMP and LiCl/H2O for DNA) at 77K are investigated. At the highest concentration used (100 mmol dm-3) about 80% (TMP) and 70% (DNA) of the radicals are scavenged compared with the control in both matrices. In TMP, allyl radicals form the major population of radicals left unscavenged at 77 K. These are shown to transform into a quintet pattern upon annealing (> or = 220 K). Analysis of various substances for quintet formation shows that a sugar-group and a C4-carbonyl group are necessary structural prerequisites. For DNA three components can be extracted from spectra obtained with different scavenger concentration in frozen solutions. There are two components in LiCl glasses, which are comparable with two of the three in frozen aqueous solution. Their potential origin is discussed in comparison with nucleotide spectra.