Effect of cell-photosensitizer binding and cell density on microbial photoinactivation

Photodynamic therapy involves the use of nontoxic dyes called photosensitizers and visible light to produce reactive oxygen species and cell killing. It is being studied as an alternative method of killing pathogens in localized infections due to the increasing problem of multiantibiotic resistance. Although much has been learned about the mechanisms of microbial killing, there is still uncertainty about whether dyes must bind to and penetrate various classes of microbe in order to produce effective killing after illumination. In this report, we compare the interactions of three antimicrobial photosensitizers: rose bengal (RB), toluidine blue O (TBO), and a poly-L-lysine chlorin(e6) conjugate (pL-ce6) with representative members of three classes of pathogens; Escherichia coli (gram-negative bacteria), Staphylococcus aureus (gram-positive bacteria), Candida albicans (yeast). We compared fluence-dependent cell survival after illumination with the appropriate wavelengths of light before and after extracellular dye had been washed out and used three 10-fold dilutions of cell concentration. pL-ce6 was overall the most powerful photosensitizer, was equally effective with and without washing, and showed a strong dependence on cell concentration. TBO was less effective in all cases after washing, and the dependence on cell concentration was less pronounced. RB was ineffective after washing (except for S. aureus) but still showed a dependence on cell concentration. The overall order of susceptibility was S. aureus>E. coli>C. albicans, but C. albicans cells were 10 to 50 times bigger than the bacteria. We conclude that the number and mass of the cells compete both for available dye binding and for extracellularly generated reactive oxygen species.

Photosensitizers neutral red (type I) and rose bengal (type II) cause light-dependent toxicity in Chlamydomonas reinhardtii and induce the Gpxh gene via increased singlet oxygen formation

The connection between the mode of toxic action and the genetic response caused by the type I photosensitizer and photosynthesis inhibitor neutral red (NR) and the type II photosensitizer rose bengal (RB) was investigated in the green alga Chlamydomonas reinhardtii. For both photosensitizers, a light intensity-dependent increase in toxicity and expression of the glutathione peroxidase homologous gene (Gpxh) was found. The toxicity of RB was reduced by the singlet oxygen (1O2) quenchers 1,4-diazabicyclo[2.2.2]octane and L-histidine, and the RB-induced Gpxh expression was stimulated in deuterium oxide-supplemented growth medium. These observations clearly indicate the involvement of 1O2 in both toxicity and the genetic response caused by RB. NR up-regulated the expression of typical oxidative and general stress response genes, probably by a type I mechanism, and also strongly induced the Gpxh expression. The stimulating effect of deuterium oxide in the growth medium suggested the involvement of 1O2 also in the NR-induced response. Indeed, an increased 1O2 formation was detected with EPR-spin trapping in NR-treated spinach thylakoids. However, none of the 102 quenchers could reduce the light-dependent toxicity of NR in C. reinhardtii, indicating that NR has a different mode of toxic action than RB.

Rebamipide increases the amount of mucin-like substances on the conjunctiva and cornea in the N-acetylcysteine-treated in vivo model

PURPOSE

Rebamipide increases the amount of mucin-like substances in the stomach. We aimed to determine the effects of rebamipide on the amount of mucin-like substances in the conjunctiva and cornea of N-acetylcysteine-treated eyes. Furthermore, we attempted to evaluate the effects of rebamipide on the wound healing of N-acetylcysteine-treated eyes.

METHODS

The model was created by instilling 10% N-acetylcysteine solutions into rabbit eyes. Rebamipide was then applied on the day following the completion of N-acetylcysteine treatment. The amount of mucin-like substances on the conjunctiva and cornea was measured using the Alcian-blue binding method. The degree of damage was evaluated using scores based on the areas and densities of the cornea and conjunctival after staining using a rose Bengal solution under blind conditions.

RESULTS

Rebamipide increased the level of mucin-like substances on the conjunctiva of N-acetylcysteine-treated eyes when instilled at concentrations of 0.3% or higher, and 1% rebamipide increased the amount of mucin-like substances covering the cornea. Moreover, 1% rebamipide improved the rose Bengal scores of the cornea and conjunctiva in N-acetylcysteine-treated eyes.

CONCLUSIONS

Rebamipide increased mucin-like substances on the cornea and conjunctiva of N-acetylcysteine-treated eyes. In accordance with the mucin-increasing effects, rebamipide improved the rose Bengal scores for the cornea and conjunctiva of N-acetylcysteine-treated eyes. However, the relevance of these findings to dry eyes is unclear because it is not known whether the change in mucus expression in the N-acetylcysteine model is similar to what occurs in aqueous tear deficiency. Consequently, it may be worth trying on an animal model of keratoconjunctivitis sicca.

Antibody response and antigen-specific gamma-interferon profiles of vaccinated and unvaccinated pregnant sheep experimentally infected with Brucella melitensis

It is well known that the immune response in sheep against Brucella melitensis is subject to individual variation, depending on diverse factors. It bears asking whether these factors (e.g. clinical disease, active infection, state of previous immunity), when affecting a group, can cause variation in the performance of different diagnostic tests. To clarify some of the circumstances in which this immune response can vary, we examine the immune-response profile of sheep protected against the clinical disease by prior vaccination with strain Rev. 1 in comparison with the profile of unprotected females showing the classical brucellosis symptoms. An experimental infection was provoked at midpregnancy under controlled conditions of both non-vaccinated (n=7) and previously Rev.1-vaccinated ewes (n=5). Their immune response was monitored from 7 to 9 weeks before abortion or normal birth to 30 weeks afterwards. Antibody response was assessed by classical tests (Rose Bengal test, complement fixation test (CFT)) in comparison with other diagnostic tests (indirect ELISA (iELISA), competitive ELISA (cELISA), fluorescence polarization assay (FPA), immunocapture test (ICT)). In addition, the cell-mediated immune response was indirectly evaluated by the in vitro antigen-specific release of gamma-interferon. The antibody levels and antigen-specific gamma-IFN profile of the non-vaccinated ewes having the disease and excreting the pathogen was notably high and differed significantly (P<0.05 or P<0.01) from those of vaccinated ewes that neither contracted brucellosis nor excreted the pathogen. In general, all the tests detect the infection in the non-vaccinated ewes with substantial effectiveness. It can be concluded that the high levels of circulating antibodies and of antigen-specific gamma-IFN are related to active Brucella infection. Similarly, the state of protection against the disease, but not necessarily against infection, due to a previous immunization with the Rev. 1 vaccination, appears to be responsible for a low level of detectable immune response. Nevertheless, the design of the study limits conclusions to pregnant ewes and cannot be extrapolated to non-pregnant ewes or rams. Likewise, the study provides no information on animals which are carriers of B. melitensis.

Trehalose Versus Hyaluronan or Cellulose in Eyedrops for the Treatment of Dry Eye

PURPOSE

Trehalose eyedrops were found by a previous study to be safe and effective compared with saline in the treatment of moderate-to-severe dry eye syndrome. The present study was designed to compare the efficacy of trehalose eyedrops with that of the commercially available eyedrops containing hyaluronan or cellulose now used in the treatment of moderate-to-severe dry eye syndrome.

METHODS

In a randomized, double-masked, 4-week crossover, controlled clinical trial, 36 patients with moderate-to-severe dry eye syndrome were divided into two groups: the hyaluronan (Hyalein)-comparison group (18 patients) and the hydroxyethylcellulose (Mytear)-comparison group (18 patients). Each group used either trehalose or one of the commercially available medications contained in a masked eyedrop container for the first 4 weeks, and then for the second 4 weeks, switched to either trehalose or the commercial eyedrop not used for the first 4 weeks. Symptoms and signs in both eyes were recorded at the baseline, at 4 weeks, and at 8 weeks.

RESULTS

At 4 weeks after the treatment, fluorescein and rose bengal staining scores of the ocular surface as well as the tear film breakup time had improved significantly with trehalose eyedrops compared with the commercially available eyedrops containing either hyaluronan or hydroxyethylcellulose (P < 0.001, Wilcoxon signed ranks test). In addition, all the objective signs were significantly better in patients who finished with trehalose at the end of the 8-week trial compared with those who finished with either of the two commercially available drugs. A larger number of patients evaluated trehalose as a better treatment than the commercially available eyedrops.

CONCLUSIONS

Trehalose solution was a better treatment for moderate-to-severe dry eye syndrome in comparison with two commercially available eyedrops containing hyaluronan or hydroxyethylcellulose.

Photo-oxidation of cells generates long-lived intracellular protein peroxides

Singlet oxygen is generated by several cellular, enzymatic, and chemical reactions as well as by exposure to UV or visible light in the presence of a sensitizer. Consequently, this oxidant has been proposed to be a damaging agent many pathologies. Proteins are major targets for singlet oxygen as a result of their abundance and high rate constants for reaction. In this study, we show that illumination of viable rose bengal-loaded THP-1 (human monocyte-like) cells with visible light gives rise to intracellular protein-derived peroxides. The peroxide yield increases with illumination time, requires the presence of rose bengal, is enhanced in D(2)O, and is decreased by azide, consistent with the mediation of singlet oxygen. The concentration of peroxides detected, which is not affected by glucose or ascorbate loading of the cells, corresponds to about 1.5 nmoles peroxide per 10(6) cells, or 10 nmoles/mg cell protein, and account for up to approximately 15% of the O(2) consumed by the cells. Similar peroxides have been detected on isolated cellular proteins exposed to light in the presence of rose bengal and oxygen. After cessation of illumination, cellular protein peroxide levels decrease with t(1/2) about 4 h at 37 degrees C. Decomposition of protein peroxides formed within cells, or on isolated cellular proteins, by metal ions gives rise to radicals as detected by EPR spin trapping. These studies demonstrate that exposure of intact cells to visible light in the presence of a sensitizer leads to novel long-lived, but reactive, intracellular protein peroxides via singlet oxygen-mediated reactions.

Targeted tissue oxidation in the cerebral cortex induces local prolonged depolarization and cortical spreading depression in the rat brain

Spreading depression (SD) has been linked to several neurological disorders as epilepsy, migraine aura, trauma, and cerebral ischemia, which were also influenced by disorderliness of the brain redox homeostasis. To investigate whether local tissue oxidation directly induces SD, we oxidized a restricted local area of the rat cerebral cortex using photo-dynamic tissue oxidation (PDTO) technique and examined the cerebral blood flow (CBF) and direct current (DC) potential in and around the oxidized area. Intensive PDTO induced prolonged depolarization only in the photo-oxidized area, which led to global changes of CBF and DC potential: synchronous negative shifts of DC potential (with an amplitude of approximately 20 mV) and hyperperfusion of CBF occurred. The changes in DC potential and CBF spread at a rate of around 3mm/min beyond the oxidized area to the whole hemisphere of the cerebral cortex, indicating that intensive local oxidation induces SD in the rat brain.

Serological diagnosis of brucellosis caused by Brucella canis

Blood serum samples from 2,328 dogs were tested to detect antibodies against Brucella canis with the agar gel immunodiffusion (AGID) and 2-mercaptoethanol slide agglutination test (ME-SAT) using Brucella ovis as the antigen. All blood serum samples were also evaluated for antibodies against Brucella abortus and Brucella melitensis using the Rose Bengal test. Twentyfive (1.07%) of the sera evaluated were considered positive with AGID test. Only 4 (16%) of these blood serum samples were positive when evaluated with ME-SAT. The 25 AGID positive samples and 25 AGID negative serum samples were also examined by: the complement fixation test (CFT) using B. ovis hot saline extract (HSE) as the antigen, indirect enzyme linked immunosorbent assay (ELISA) and immunoblotting (IB) using B. canis and B. ovis HSE antigens. Two positive canine sera from culture positive dogs and the serum of an experimentally RM6/66 B. canis-infected rabbit were employed as positive controls and one serum from a known uninfected dog as a negative control. ELISA with B. canis antigen gave 9 (18%) positive results (6 AGID-positive and 3 AGID-negative sera). ELISA performed with B. ovis antigen detected 15 (30%) positive samples (10 AGID-positive, 5 AGID-negative and 8 B. canis ELISA positive sera). IB analysis of known positive controls sera employing B. canis antigen detected bands with molecular weights of 94-80, 64-50, 35, 32-30, 28, 23, 20-18, 15-12 kDa. The same sera tested with B. ovis antigen revealed bands of 35, 32-30, 25, 23, 20-18, 15-12 kDa. No bands were observed with the negative control serum and the 50 canine tested sera.

Effects of singlet oxygen on the extracellular matrix protein collagen: oxidation of the collagen crosslink histidinohydroxylysinonorleucine and histidine

The reaction of singlet oxygen, a putative agent of skin photodamage, with the dermal collagen crosslink histidinohydroxylysinonorleucine (HHL) and its precursor histidine is reported. Reaction studies were performed with both purified HHL and bovine dermal tissue. We demonstrate that singlet oxygen can selectively oxidize HHL and histidine amino acid residues in dermal tissue and that intermediate oxidation products of histidine lead to new crosslink products. A novel mechanism for crosslink formation was proposed to involve nucleophilic addition to a transient imidazolone intermediate formed from singlet oxygen oxidation of the histidine imidazole moiety. The implication for such adduct formation and histidine oxidation in collagen proteins is the expression of aberrant collagen crosslinks, perturbation of the dermal collagen function, and hence an altered dermal state.

Use of prawn blood agar hemolysis to screen for bacteria pathogenic to cultured tiger prawns Penaeus monodon

A newly developed prawn blood agar consisting of 1 ml of tiger prawn hemolymph in medium containing 200 ppm Rose Bengal was used to determine the hemolytic activity of 35 isolates of bacteria obtained from cultured tiger prawns Penaeus monodon and their rearing water. For comparison, the hemolytic activity of these isolates was also determined in sheep blood agar. Nine isolates (25.7% of total) showed different hemolytic reactions on prawn blood agar and sheep blood agar. From the 35 isolates, 8 with various hemolytic characteristics were selected and the relationship between the type of hemolytic activity and pathogenicity was determined and compared. Four isolates that showed hemolytic activity in prawn blood agar caused high mortality to cultured tiger prawns. By contrast, a significantly lower mortality rate was observed for tiger prawns injected with 4 isolates that did not exhibit hemolytic activity on prawn blood agar. Results further showed that mortality did not correlate with hemolytic activity determined using sheep blood agar. Prawn blood agar containing P. monodon hemocytes was faster and more accurate for determining prawn hemolytic activity of bacterial isolates.

Singlet oxygen, but not oxidizing radicals, induces apoptosis in HL-60 cells

Oxidizing species (OS), produced by photosensitization or derived from cytotoxic agents, activate apoptotic pathways. We investigated whether two different OS, formed at the same subcellular sites, have equivalent ability to initiate apoptosis in HL-60 cells. Our previous work showed that absorption of visible light by rose bengal (RB) produces singlet oxygen exclusively, whereas absorption of ultraviolet A produces RB-derived radicals in addition to singlet oxygen. Singlet oxygen, but not the RB-derived radicals, induced nuclear condensation and DNA fragmentation into nucleosome-size fragments in a dose dependent manner. In contrast, the RB-derived radicals caused greater lipid oxidation than singlet oxygen. These results indicate that different OS, produced at the same subcellular sites, do not have the same ability to induce apoptosis and that the ability of an OS to initiate lipid oxidation does not necessarily correlate with its ability to induce apoptosis.

Evidence that histidine-163 is critical for catalytic activity, but not for substrate binding to Escherichia coli agmatinase

Agmatinase (agmatine ureohydrolase, EC 3.5.3.11) from Escherichia coli was inactivated by diethyl pyrocarbonate (DEPC) and illumination in the presence of Rose bengal. Protection against photoinactivation was afforded by the product putrescine, and the dissociation constant of the enzyme-protector complex (12 mM) was essentially equal to the K(i) value for this compound acting as a competitive inhibitor of agmatine hydrolysis. Upon mutation of His163 by phenylalanine, the agmatinase activity was reduced to 3-5% of wild-type activity, without any change in K(m) for agmatine or K(i) for putrescine inhibition. The mutant was insensitive to DEPC and dye-sensitized inactivations. We conclude that His163 plays an important role in the catalytic function of agmatinase, but it is not directly involved in substrate binding.

Morphology and barrier function of the corneal epithelium after penetrating keratoplasty: association with original diseases, tear function, and suture removal

PURPOSE

To study changes in structure and barrier function of the corneal epithelium after penetrating keratoplasty.

METHODS

Sixty-nine eyes of 56 patients undergoing penetrating keratoplasty were studied. Fifty-six age-matched normal eyes served as controls. Corneal epithelial structure was studied by using specular microscopy. Barrier function of the corneal epithelium was examined by slit-lamp fluorophotometry. Vital staining, tear function, and corneal sensitivity also were examined.

RESULTS

Fluorescein and rose bengal staining scores, incidence of elongated cells, the mean epithelial area, and mean fluorescein uptake were significantly increased in postkeratoplasty eyes compared with controls. Original disease influenced the results of barrier function, where keratoconus revealed better function than bullous keratopathy or corneal scar. However, no such differences were noted in epithelial structure. Six eyes with absence of palisades of Vogt had revealed significantly increased epithelial area and fluorescein uptake. Removal of the running suture caused a decrease in elongated cells and epithelial cell area without significant changes in barrier function.

CONCLUSION

Corneal epithelial structure was significantly impaired in postkeratoplasty eyes. Epithelial barrier function of postkeratoplasty eyes was influenced by original diseases. Removal of sutures improves epithelial structure but not barrier function.

Effect of lipo-pro-prostaglandin E1, AS-013 on rat inner ear microcirculatory thrombosis

We investigated effects of lipo-pro-prostaglandin E1 (lipo-[11alpha, 13E, 15S]-11,15-dihydroxy-9-[1-oxobutoxy]-prosta-8, 13-dien-1-oic acid butyl ester), AS-013 in two models of hearing disturbance and equilibrium dysfunction induced by rat inner ear microcirculatory thrombosis. Inner ear microcirculatory thrombosis was induced by photochemical reaction between systemic injection of Rose Bengal and irradiation of green light to the cochlea and vestibule. Photochemical reaction causes endothelial injury followed by platelet adhesion, aggregation and formation of a platelet- and fibrin-rich thrombus. In the hearing disturbance model, a compound cochlear nerve action potential was recorded by electrocochleography every minute. Photochemical reaction induced inner ear microcirculatory thrombosis, followed by disappearance of the action potential. AS-013 significantly (P<0.05) prolonged time to disappearance of the action potential compared with control group. In the equilibrium dysfunction model, the irradiation to the vestibule was applied for 10 min after Rose Bengal injection. The behavior of rats in the swimming test and nystagmus were observed 24 h after the completion of irradiation. In the swimming test, two of 12 animals treated with AS-013 showed no rotating about their longitudinal axes, which indicates equilibrium dysfunction and the duration of well-balanced swimming prolonged. AS-013 suppressed the appearance of nystagmus. These results suggest that lipo-pro-prostaglandin E1, AS-013 may prevent hearing disturbance and equilibrium dysfunction due to inner ear microcirculatory disorders.

High sensitivity of Deinococcus radiodurans to photodynamically-produced singlet oxygen

PURPOSE

To study the sensitivity of two bacterial cell systems to photodynamic treatment and X-ray irradiation as part of a project to establish efficient procedures for waste water disinfection.

MATERIALS AND METHODS

Stationary-phase cells of Deinococcus radiodurans (Gram-positive) and Escherichia coli (Gram-negative) were exposed to visible light in a buffer solution containing up to 5 microg/ml sensitizer rose bengal (RB) and to X-rays at dose rates of 32.8 Gy/min or 14.6 Gy/min, respectively.

RESULTS

Survival of both cell types decreased with increasing exposure time to visible light and increasing concentration of RB, and therefore with an increase in singlet oxygen production. Surprisingly, D. radiodurans, the most resistant cell system to ionizing radiation, was more sensitive to photodynamic treatment than E. coli by about a factor of 100.

CONCLUSIONS

The main target of singlet oxygen reaction is the cell membrane. The repair of such damage in D. radiodurans is less effective than in E. coli.

Meibomian gland dysfunction in patients with Sjögren syndrome

OBJECTIVE

Changes in the ocular surface of patients with Sjögren syndrome (SS) often are more severe than those in patients with dry eye without SS. This study was conducted to investigate the possible involvement of meibomian gland dysfunction in SS-related ocular surface abnormalities.

DESIGN

A nonrandomized, prospective, clinical study.

PARTICIPANTS

Twenty-seven eyes of 27 consecutive patients with SS (SS group) were studied. Twenty-nine eyes of age- and gender-matched non-SS patients with aqueous tear deficiency (non-SS group) were examined as control subjects.

INTERVENTION

Changes in the ocular surface, tear function, and meibomian gland were examined.

MAIN OUTCOME MEASURES

Tear evaporation rate, meibomian gland expression, and meibography were measured.

RESULTS

Fluorescein and rose bengal staining scores were significantly higher in the SS group than in the non-SS group (P = 0.0001). Evaporation of tears was increased significantly in the SS group compared with the non-SS group. There were no significant differences in the rate of tear production between the SS and non-SS groups. Meibography showed that 11 (57.9%) of 19 eyes in the SS group had gland dropout (i.e., histologic destruction of meibomian glands) in more than half of the tarsus. The incidence was significantly higher than that in the non-SS group (5 [18.5%] of 27 eyes; P = 0.005).

CONCLUSIONS

The results of this study indicate that destruction of meibomian glands and an increase in tear evaporation often are associated with changes in the ocular surface in patients with SS. Severe ocular surface changes in patients with SS may be attributed, in part, to the meibomian gland dysfunction.

The antibiotic ceftazidime is a singlet oxygen quencher as demonstrated by ultra-weak chemiluminescence and by inhibition of AAP consumption

We demonstrated that the cephalosporin antibiotic ceftazidime (CAZ) deactivated singlet oxygen (1O2). We then studied the mechanisms of the CAZ effects on the ultra weak chemiluminescence (uwCL) associated with the energy decay of 1O2 generated by the Mallet reaction (H2O2 + HOCl --> HCl + H2O + 1O2), and on the anthracene-9,10-dipropionic acid (AAP) consumption by 1O2 generated by irradiation of Rose Bengal (RB). The uwCL generated by the Mallet reaction was amplified (6.2 times) by CAZ. The use of red and blue filters, which absorb radiation below 610 nm and between 470 and 700 nm respectively, demonstrated that CAZ increased the uwCL by a radiation emission at wavelengths shorter than the 633 and 704 nm wavelength emissions of 1O2. CAZ was excited by scavenging the energy excess of 1O2, which so returned to its fundamental state, while CAZ deactivated with light emission between 430-480 nm. CAZ also inhibited in a dose-dependent manner the consumption of AAP by 1O2 generated by the irradiation of RB. The protection of AAP by 5 x 10(-3) M CAZ was equivalent to that of 10(-3) M histidine and 3 X 10(-6) M sodium azide. This process of 1O2 deactivation will be useful in diseases characterized by an excessive PMN activation with a release of activated oxygen species.

Microspectrophotometric analysis of accumulation of the fluorones K-fluorescein, rose Bengal and phloxine red in living plant cells

Spectrophotometric investigations of dye solutions in different media and of living stained cells from the upper epidermis of the scaleleaf of Allium cepa were carried out with the dyes K-fluorescein, rose Bengal and phloxine red to elucidate the mechanism of the accumulation of these dyes in the cytoplasm, the nucleus and the cell sap. Thin layer chromatography and paper electrophoresis indicate that the K-fluorescein used here contains no detectable contaminants. Besides the main component, rose Bengal contains two components in small quantities with Rf values of 0.64 and 0.57, plus three more components in traces. Besides the two main components (Rf values of 0.83 and 0.73), phloxine red also contains five more components in traces. Electrophoretic investigations reveal that in aqueous solution the fluorones rose Bengal and phloxine red from pH 2.0-11 show a migration toward the anode. K-fluorescein from pH 2.9-10.4 shows a migration toward the anode, but at pH 1.9 a migration toward the cathode. By shaking aqueous solutions of K-fluorescein, rose Bengal and phloxine red at different pH values with different organic solvents, the above used stainings show different spectral absorption curves according to the polarity of the solvent. The position of the absorption maxima and the shape of the absorption curves of these three anionic dyes lead to the conclusion that the staining of the living cytoplasm and nucleus is due to ion accumulation by means of the "ion trap mechanism" within the aqueous phase of the cytoplasm (cytosol) and the nucleus. Adsorption of dye particles in the protein phase of the cytoplasm cannot be excluded. There seems to be a fundamental difference in the vital staining of the protoplasm by anionic and cationic dyes, the latter apparently accumulating as neutral dye molecules in the lipid phase of the protoplasm. The concentration of the dyes used in the living cytoplasm (cytosol) is approximately 0.2-0.05%. During natural and artificial displacement of K-fluorescein from the cytoplasm to the vacuole, it appears that accumulation of the dye within the vacuole is performed through an ion trap mechanism in the form of bivalent ions. Along with natural displacement, it is possible that ion accumulation also occurs in metabolic products.

Enzyme-assisted cell photosensitization: a proposal for an efficient approach to tumor therapy and diagnosis. The rose bengal fluorogenic substrate

Rose bengal, a xanthene derivative among the most efficient producer of singlet oxygen, was submitted to a chemical modification consisting in the introduction of an acetate group into the aromatic ring fluorophore structure. The acetate group acts as a quencher, thus inactivating both fluorescence and photosensitization properties of the molecule. In the modified structure, rose bengal acts as a fluorogenic substrate giving rise to the cellular reaction termed fluorochromasia. The acetate group is recognized by a carboxylic esterase activity that splits it. Removal of the quencher group results in restoring the native structure of photosensitizer inside the cells. The intracellular turnover of rose bengal acetate was studied in rat glioma-derived cultures cells, in terms of the balance of the processes of influx and enzyme hydrolysis of the fluorogenic substrate, and of the efflux of the fluorescent product. A large intracellular accumulation of photosensitizer is obtained when treatments are performed with the fluorogenic substrate, even at the drug concentration at which rose bengal does not enter the cells. The intracellular localization allows rose bengal to exert a more effective photosensitization effect. Provided that the quencher group is selected according to the metabolic properties of the tumor cells, the use of fluorogenic substrates as photosensitizer precursors could improve fluorescence diagnosis and the photodynamic therapy of tumors, exploiting the biological properties that distinguish pathological from normal conditions.

Kinetic characterization of binding and internalization of fractionated [3H]heparin in rat liver parenchymal cells in primary culture

The binding and internalization of fractionated [3H]heparin (FH) was kinetically analyzed in rat liver parenchymal cells to clarify its cellular uptake mechanism. The binding of FH to the cell surface was saturable with the dissociation constant (Kd) of 53.5 nM and a maximum binding capacity (Bmax) of 19.9 pmol/mg protein. The binding of FH to the cell surface was competitively inhibited not only by heparan sulfate, a polyanion analogous to heparin, but also by rose bengal, an organic anion, suggesting the binding is based on an electric interaction requiring an anionic charge for substrates and consistent with the earlier suggestion of the involvement of the scavenger-like receptor. According to kinetic model analysis, the rate constants of association (K(on)), dissociation (k(off)), and internalization (k(int).app) were estimated to be 0.0005 nM-1 min-1, 0.0112 min-1, and 0.0056 min-1, respectively. Although both Kd and Bmax were larger than those reported in Kupffer cells, suggesting lower affinity and higher capacity in liver parenchymal cells, the apparent internalization rate constant was similar to that in Kupffer cells. We thus provided additional evidence suggesting that a scavenger-like receptor exists in rat liver parenchymal cells, and then kinetically characterized the surface binding and internalization of fractionated heparin by this receptor.

Inhibition by singlet molecular oxygen of the vascular reactivity in rabbit mesenteric artery

1. The effects of reactive oxygen intermediates derived from photoactivated rose bengal on the vascular reactivity have been evaluated in rabbit mesenteric artery ring preparations. The artery rings were exposed to xanthene dye rose bengal (50 nM) illuminated (6,000 lux) at 560 nm for 30 min. Spin trapping studies with 2,2,6,6-tetramethylpiperidine (TEMP) and 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) with electron spin resonance spectrometry were also conducted in solution (and not within tissues) to determine quantitatively the reactive oxygen species generated from photoactivated rose bengal. 2. Contraction of the ring preparations induced by noradrenaline (10(-8) to 10(-4) M) was attenuated by previous exposure to photolysed rose bengal; the observation that the pD2 decreased without a significant reduction in maximum tension generation is consistent with the view that receptor dysfunction may be involved in the effect of photolysed rose bengal. 3. Prior exposure to photolysed rose bengal of the ring preparations inhibited the endothelium-dependent relaxation evoked by acetylcholine (10(-6) M) and calcium ionophore A23187 (10(-7) M), but not the endothelium-independent relaxation evoked by nitroglycerin (10(-6) M). 4. A variety of scavengers, superoxide dismutase (33 units ml-1), catalase (32 units ml-1) and 1,3-dimethyl-2-thiourea (DMTU, 10 mM), which should eliminate the superoxide anion radical, H2O2 and the hydroxyl radical, had no effect on the attenuated responses to noradrenaline and acetylcholine induced by photolysed rose bengal. In contrast, the inhibition of the observed effect of photolysed rose bengal was obtained with addition of histidine (25 mM), a singlet molecular oxygen quencher. 5. It was found that photolysis of rose bengal from a 1:2:2:1 quartet, characteristic of the hydroxyl radical-DMPO spin adduct, which was effectively blunted by DMTU, superoxide dismutase and catalase whereas histidine was ineffective. The results of the electron spin resonance study also showed that a singlet molecular oxygen was produced by photoactivation of rose bengal; this was detected as singlet oxygen-TEMP product (TEMPO; 2,2,6,6-tetramethylpiperidine-N-oxyl). The formation of the TEMPO signal was strongly inhibited by histidine, but not by DMTU, superoxide dismutase and catalase. 6. It is suggested that the superoxide anion radical, H2O2 and hydroxyl radical are formed in addition to singlet molecular oxygen, and the data obtained from the present study indicate that singlet molecular oxygen is one of the most destructive oxygen species. Endothelium-dependent relaxation is quite vulnerable to singlet molecular oxygen. Singlet oxygen also depresses noradrenaline-induced contraction possibly via alpha-adrenoceptor dysfunction. This, in turn, may lead to vascular incompetence.

Possible mechanism for the inhibition of lectin-erythrocyte interaction in presence of endogenous lectin receptor

The presence of hydrophobic sites in the lectin-I molecule was indicated by hydrophobic probes like 1-anilinonapthalene-8-sulfonic acid (ANS), 2-p-toluidinyl napthalene-6-sulfonic acid (TNS). N-phenyl-1-napthylamine (NA) and rose bengal (RB). This was further confirmed by amino acid modifications in the hydrophobic region of the lectin-I molecule. The binding of ANS, TNS, NA and RB to lectin-I was affected in the presence of NaCl. The involvement of hydrophobic interactions in rice-bean lectin-I-endogenous lectin receptor (ELR) complex were indicated by alterations in the circular dichroism and fluorescence emission spectra. The percentage of beta-conformation (55-63%) of lectin-I was decreased by addition of ELR. ELR on reacting with lectin-I reduced the fluorescence emissions of the hydrophobic probes while fluorescence emission of ANS, TNS, NA and RB were greatly enhanced in presence of lectin-I alone. N-aceyl-galactosamine did not change the fluorescence emissions of any of the hydrophobic probes in presence or in absence of lectin-I. This demonstrates that carbohydrate and hydrophobic sites may be different and non-interacting. It is proposed that the ELR in reacting with lectin-I, induced conformational changes in the lectin-I molecule and thereby affected its erythroagglutinating activity with human blood group "A" erythrocytes.

Skeletal sarcoplasmic reticulum dysfunction induced by reactive oxygen intermediates derived from photoactivated rose bengal

We investigated the role of reactive oxygen intermediates generated from photoactivation of xanthene dye rose bengal on skeletal sarcoplasmic reticulum (SR) function, which plays a major role in the regulation of intracellular Ca++ and thereby in the generation of force. We used SR microsomes of canine masseter muscle as a model system in which to explore the effect of oxidation by determining oxalate-supported Ca++ uptake, Ca++, Mg++-adenosine triphosphatase (Ca++-ATPase) activity and Ca++ permeability of the SR vesicles. Skeletal SR vesicles exposed to rose bengal (50 nM) illuminated at 560 nm resulted in significant inhibition of Ca++ uptake velocity and Ca++-ATPase activity and in stimulation of Ca++ permeability. The observed effect afforded by illuminated rose bengal was dependent on intensity of light. Most reactive oxygen species scavengers tested had no protective effect; histidine (a powerful quenching agent for singlet oxygen), however, significantly protected the effect of illuminated rose bengal on Ca++ uptake velocity and Ca++-ATPase activity. The illumination of rose bengal also caused histidine-inhibitable loss of total sulfhydryl groups of SR. The increased Ca++ permeability elicited by illuminated rose bengal was blunted by a cocktail of histidine-catalase, but not by histidine alone. Generation of reactive oxygen species (singlet oxygen, superoxide and hydroxyl radical) from photoactivation of rose bengal was studied by electron spin resonance spectroscopy by use of the spin trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) and 2,2,6,6-tetramethylpiperidine (TEMP). We found that illumination of rose bengal formed a 1:2:2:1 quartet, characteristic of the hydroxyl radical-DMPO spin adduct, which was effectively blunted by hydroxyl radical scavenger, dimethyl sulfoxide, and by superoxide scavenger, superoxide dismutase. The results of electron spin resonance study also showed that singlet oxygen was produced by photoactivation of rose bengal was detected as singlet oxygen-TEMP product (TEMPO); 2,2,6,6-tetramethylpiperidine-N-oxyl). The formation of TEMPO signal was strongly inhibited by histidine. Similarly, we could detect hydrogen peroxide production from illuminated rose bengal. It is suggested that photoactivation of rose bengal generated singlet oxygen, superoxide, hydrogen peroxide and hydroxyl radical, and the data obtained from the present study indicate that singlet oxygen, rather than superoxide, hydrogen peroxide and hydroxyl radical, to be the active agent in the Ca++ transport system of SR; the observed effect of singlet oxygen may be due to sulfhydryl group oxidation. Our results are also consistent with the view that singlet oxygen does not appear to be an exclusive species that increases Ca++ permeability of SR vesicles, but the increased Ca++ permeability may be caused in part by hydrogen peroxide as well as singlet oxygen.

Hepatic transport of rose bengal by perfused rabbit liver: the effect of albumin binding on the unidirectional rate constants

The effect of albumin on the unidirectional rate constants for the hepatic transport of rose bengal was studied using perfused rabbit livers. Rabbit livers were perfused in a recirculating system with albumin concentrations between 10 and 600 microM and the disappearance of I-125 rose bengal following a bolus injection was recorded. A distributed model of hepatic transport was used to estimate the rate constants for influx into cells, efflux from cells to plasma and biliary excretion. When the rate constants were corrected for albumin binding, the influx, but not the efflux or excretion constant, was a steeply rising function of the perfusate albumin concentration. The result that the influx but not efflux constant is albumin dependent suggests that the phenomenon is not due to slow diffusion across an unstirred fluid layer or to nonequilibrium binding within such a layer. The possibility that the albumin-dependent influx is due to a direct exchange of rose bengal between albumin and a membrane carrier protein is also considered. The independence of the efflux constant and the albumin concentration makes this hypothesis less tenable. However, these data are consistent with the facilitation of albumin-ligand dissociation by liver cells. This analysis represents the first reduction to practice of distributed modeling of disappearance curves. The fact that the excretion constant is independent of the perfusate albumin concentration serves to validate the model that has previously only been considered on theoretical grounds.

Interaction between rose bengal and different protein components

Bindings of rose bengal to several proteins were determined by Sephadex G-75 chromatography. Their respective blocking effect against dye uptake was demonstrated in an assay using a rabbit corneal epithelial cell layer. The total binding capacity of nonmucin proteins was measured using fluorometry and Scatchard analysis. The results showed that albumin, lactoferrin, transferrin, and lysozyme could--but serum prealbumin, IgA, carboxymethyl cellulose (CMC), and Sepharose 4B-purified porcine stomach mucin (PSM) could not--bind rose bengal. Lysozyme formed precipitates with rose bengal. Sufficient concentrations of albumin, lactoferrin, transferrin, or lysozyme premixed with rose bengal could block dye uptake by cells, but IgA and serum prealbumin could not. Premixed PSM was not as effective as precoated PSM in blocking dye uptake. The dissociation constant (Kd) was 1.2 x 10(-7) M, 3.6 x 10(-7) M, 3.9 x 10(-7) M, and 1.6 x 10(-6) M for albumin, transferrin, lactoferrin, and lysozyme, respectively. Based on these values, the total maximal binding capacity of nonmucin proteins in normal 7-microliters tears was extrapolated to be 0.249 micrograms rose bengal, which is too small to explain the negative staining of rose bengal on the normal ocular surface. Rose bengal, but not fluorescein, could interact with carbohydrate-containing Sephadex, CMC, and PSM to slow down its elution via Sephadex column chromatography. Therefore, the normal negative staining to rose bengal might be caused by the blocking effect of preocular mucus tear layer, which serves as a diffusion barrier. Rose bengal remains a unique dye for detecting the protective function of the preocular mucus tear.