Photomodulation of enzymes

Studies on the in vitro inversion of flurbiprofen

This paper reports in vitro studies on the metabolic inversion of flurbiprofen (FL), an arylpropionic acid antiinflammatory agent (2-APA). The inversion was studied with both rac-FL and R-FL, by incubation with rat hepatic microsomes, in the presence of either CoASH and ATP or NADPH. The two isomers of the drug were separated as their (+)-(R)-1-phenylethylamides by direct phase high-performance liquid chromatography on a silica gel column with an achiral mobile phase. The inversion was more pronounced in the presence of CoASH and ATP for both the racemate and the R-isomer, which supports the key role of CoA thioesters in the metabolic inversion of profens. The inversion observed in the presence of NADPH suggests that, when the incubation is run with hepatic microsomes, a CYP450-mediated pathway is also active. In order to get more insight into the CYP450-mediated inversion pathway, we studied the effect of irradiating microsomes with a low dose of He-Ne laser radiation (0.2 J). Such irradiation caused a significant increase in inversion at all times studied and normalized the anomalous value of inversion observed at 15 min in this pathway.

Determination of glutamate decarboxylase by high-performance liquid chromatography

An improved method for the determination of glutamate decarboxylase (GAD) activity is described. The enzyme was evaluated by incubation with glutamic acid (L-Glu) in the presence of pyridoxal 5'-phosphate (PLP): the gamma-aminobutyric acid (GABA) formed was derivatized to PTC-GABA; the latter was subsequently separated and assayed by isocratic HPLC (LiChrospher RP-18 column; isocratic elution with pH 5.8 acetate buffer in acetonitrile-water) with UV absorbance detection at 254 nm. The method described is a sensitive, reproducible and specific assay useful for following variations of GAD activity in vitro; this assay was subsequently used for the evaluation of GAD activity variations after irradiation with low doses of He-Ne laser radiation.

Protection against ultraviolet B radiation-induced effects in the skin of SKH-1 hairless mice by a polyphenolic fraction isolated from green tea

In prior studies we and others have shown that oral feeding of a polyphenolic fraction isolated from green tea (GTP) or water extract of green tea affords protection against ultraviolet B (UVB) radiation-induced carcinogenesis in SKH-1 hairless mice (Wang et al., Carcinogenesis 12, 1527-1530, 1991). It is known that exposure of murine skin to UVB radiation results in cutaneous edema, depletion of the antioxidant-defense system and induction of ornithine decarboxylase (ODC) and cyclooxygenase activities. In this study we assessed the protective effect of GTP on these UVB radiation-caused changes in murine skin. Oral feeding of 0.2% GTP (wt/vol) as the sole source of drinking water for 30 days to SKH-1 hairless mice followed by irradiation with UVB (900 mJ/cm2) resulted in significant protection against UVB radiation-caused cutaneous edema (P < 0.0005) and depletion of the antioxidant-defense system in epidermis (P < 0.01-0.02). The oral feeding of GTP also resulted in significant protection against UVB radiation-caused induction of epidermal ODC (P < 0.005-0.01) and cyclooxygenase activities (P < 0.0001) in a time-dependent manner. Our data indicate that the inhibition of UVB radiation-caused changes in these markers of tumor promotion in murine skin by GTP may be one of the possible mechanisms of chemopreventive effects associated with green tea against UVB-induced tumorigenesis. The results of this study suggest that green tea, specifically polyphenols present therein, may be useful against inflammatory responses associated with the exposure of skin to solar radiation.

Photomodulation of glutamate dehydrogenase properties by red light

To gain some insight into the mechanism by which red light-biosystem interaction occurs, an investigation was made of certain features of purified glutamate dehydrogenase from beef liver (E.C. 1.4.1.3.) irradiated with either an He-Ne laser (632.8 nm) or a red light-emitting diode (650 +/- 20 nm). In both cases the energy dose was 0.24 J cm-2. Significant changes in the glutamate dehydrogenase extinction coefficient measured at 275 nm, the capability of the enzyme to bind the reduced form of nicotinamide adenine dinucleotide (NADH), certain kinetic parameters, the pH and temperature dependence and the sensitivity to guanosine 5 triphosphate (GTP) and adenosine diphosphate (ADP) were found, probably due to the interaction of light with a protein domain containing a metal ion or ions. He-Ne laser and diode irradiation were found to differ with regard to their interaction with glutamate dehydrogenase. Interestingly, different effects were also found when an He-Ne laser and a non-coherent Xe-Hg lamp were used to irradiate glutamate dehydrogenase under the same experimental conditions. This confirms that non-coherent light at various power levels affects the isolated glutamate dehydrogenase.

An immunofluorescence study of the effects of ultraviolet radiation on the organization of microfilaments, keratin intermediate filaments, and microtubules in human keratinocytes

Indirect immunofluorescence microscopy has been used to investigate the ultraviolet (UV) radiation induced disruption of the organization of microfilaments, keratin intermediate filaments, and microtubules in cultured human epidermal keratinocytes. Following irradiation, concurrent changes in the organization of the three major cytoskeletal components were observed in cells incubated under low Ca2+ (0.15 mM) conditions. UV irradiation induced a dose-dependent condensation of keratin filaments into the perinuclear region. This collapse of the keratin network was accompanied by the reorganization of microfilaments into rings and a restricted distribution of microtubules, responses normally elicited by exposure to high Ca2+ (1.05 mM) medium. The UV induced alteration of the keratin network appears to disrupt the interactions between keratin and actin, permitting the reorganization of actin filaments in the absence of Ca2+ stimulation. In addition to the perinuclear condensation of keratin filaments, UV irradiation inhibits the Ca2+ induced formation of keratin alignments at the membrane of apposed cells if UV treatment precedes exposure to high Ca2+ medium. Incubation of keratinocytes in high Ca2+ medium for 24 hours prior to irradiation results in the stabilization of membrane associated keratin alignments and a reduced susceptibility of cytoplasmic keratin filaments to UV induced disruption. Unlike results from investigations with isogenic skin fibroblasts, no UV induced disassembly of microtubules was discernible in irradiated human keratinocytes.