Rose Bengal

Ki: 19 and 64 nM for VGlut andVMAT, respectively

Rose Bengal is a potent VGlut and vesicular monoamine transporter (VMAT) inhibitor.

The common biochemical l-glutamate (Glu) is widely recognized as the major excitatory neurotransmitter in the vertebrate CNS. Proper Glu transmission plays a critical role in physiological brain functions, such as learning and memory formation as well as basic neural communication.

In vitro: Rose Bengal was a quite potent membrane-permeant inhibitor of glutamate uptake into isolated synaptic vesicles. Such vesicular Glu uptake inhibition was achieved without affecting H1-pump ATPase. It was found that various degrees of reduction elicited by Rose Bengal in [3H]Glu in synaptic vesicles inside the synaptosome [1].

In vivo: The distribution of i.v. administered rose bengal was found to depend on its dose. At a low dose, rose bengal could be found almost solely in the liver and plasma. However, at higher doses, the amount of rose bengal found in extra-hepatic tissues gradually increased. The hepatic transfer maximum of rose bengal amounted to 146 micrograms/kg/min. By increasing the dose from 10 to 200 mg/kg, the hepatic concentration of rose bengal also approached a maximum. The storage capacity of the liver, however, did not limit the transfer maximum of rose bengal [1].

Clinical trial: N/A

References:
[1] Ogita K,Hirata K,Bole DG,Yoshida S,Tamura Y,Leckenby AM,Ueda T.  Inhibition of vesicular glutamate storage and exocytotic release by Rose Bengal. J Neurochem.2001 Apr;77(1):34-42.
[2] Fischer E,Varga F.  Hepatic storage and biliary excretion of rose bengal in the rat. Acta Physiol Acad Sci Hung.1979;54(1):89-94.

Cationic Phosphorus Dendrimer Enhances Photodynamic Activity of Rose Bengal against Basal Cell Carcinoma Cell Lines.[Pubmed:28350966]

Mol Pharm. 2017 May 1;14(5):1821-1830.

In the last couple of decades, photodynamic therapy emerged as a useful tool in the treatment of basal cell carcinoma. However, it still meets limitations due to unfavorable properties of photosensitizers such as poor solubility or lack of selectivity. Dendrimers, polymers widely studied in biomedical field, may play a role as photosensitizer carriers and improve the efficacy of photodynamic treatment. Here, we describe the evaluation of an electrostatic complex of cationic phosphorus dendrimer and Rose Bengal in such aspects as singlet oxygen production, cellular uptake, and phototoxicity against three basal cell carcinoma cell lines. Rose Bengal-cationic dendrimer complex in molar ratio 5:1 was compared to free Rose Bengal. Obtained results showed that the singlet oxygen production in aqueous medium was significantly higher for the complex than for free Rose Bengal. The cellular uptake of the complex was 2-7-fold higher compared to a free photosensitizer. Importantly, Rose Bengal, Rose Bengal-dendrimer complex, and dendrimer itself showed no dark toxicity against all three cell lines. Moreover, we observed that phototoxicity of the complex was remarkably enhanced presumably due to high cellular uptake. On the basis of the obtained results, we conclude that Rose Bengal-cationic dendrimer complex has a potential in photodynamic treatment of basal cell carcinoma.

Biomechanical Changes After In Vivo Collagen Cross-Linking With Rose Bengal-Green Light and Riboflavin-UVA.[Pubmed:28297026]

Invest Ophthalmol Vis Sci. 2017 Mar 1;58(3):1612-1620.

Purpose: To compare corneal biomechanical properties after in vivo and ex vivo cross-linking (CXL) using Rose Bengal-green light (RGX) or riboflavin-UVA (UVX). Methods: Corneas of 30 rabbits were treated in vivo by the two CXL modalities monolaterally (Group 1) or bilaterally (Group 2). Rabbits in Group 1 were euthanized 1 month after treatments and in Group 2 two months after treatment. Ex vivo CXL was also performed. Eyes were measured by Scheimpflug air puff corneal deformation imaging (Corvis ST) under constant IOP. Corneal deformation parameters were assessed. Inherent corneal biomechanical properties were estimated using inverse finite element modeling. Results: Peak to peak distance decreased 16% 2 months after RGX, and 4% and 20% 1 and 2 months after UVX, respectively. The equivalent Young's modulus (Eeq) increased relative to the control during the post treatment period for both RGX and UVX. The Eeq increased by factors of 3.4 (RGX) and 1.7 (UVX) 1 month and by factors of 10.7 (RGX) and 7.3 (UVX) 2 months after treatment. However, the Eeq values for ex vivo CXL were much greater than produced in vivo. The ex vivo Eeq was greater than the 1-month in vivo values by factors of 8.1 (RGX) and 9.1 (UVX) and compared with 2 month by factors of 2.5 (RGX) and 2.1 (UVX). Conclusions: These results indicate that corneal stiffness increases after CXL, and further increases as a function of time after both RGX and UVX. Also, while biomechanical properties determined after ex vivo CXL are indicative of corneal stiffening, they may not provide entirely accurate information about the responses to CXL in vivo.

Influence of iron oxide nanoparticles (Fe3O4) on erythrocyte photohemolysis via photofrin and Rose Bengal sensitization.[Pubmed:28232076]

Photodiagnosis Photodyn Ther. 2017 Jun;18:111-118.

BACKGROUND: Iron oxide (Fe3O4) nanoparticles (IO-NP) were recently employed in medical applications as a diagnostic tool and drug carrier. Photofrin (PF) is a photosensitizer that clinically is used in Photodynamic therapy (PDT). STUDY DESIGN: The photosensitivity of PF and Rose Bengal (RB) mixed with (IO-NP) on red blood cells (RBCs) lysis was investigated. Second, Photohemolysis for post-irradiation (delayed) and during irradiation (continuous) with PF, RB and IO-NP combinations at different concentrations was investigated. Third, the photohemolysis rate, relative lysis steepness and power-concentration dependant parameter were evaluated by modeling and fitting the data using Gompertz function and power law. METHODS: RBCs were isolated from healthy male human volunteer. Washed cells (7.86x10(6) cells/mm(3)) were incubated with PF only or with IO-NP for 45min at 37 degrees C then irradiated to a range of temperatures (4-41 degrees C). CPH results were recorded and evaluated using Gompertz function. RESULTS: The relative steepness of the photohemolysis curves was approximately independent on light dose for delayed irradiation. The presence of IO-NP increases the rupturing time for 50% of the RBCs. Photohemolysis rate for delayed irradiation using the power law, led to 1.7 and 2.3 power dependence, respectively, for PF only and PF mixed with IO-NP. The power dependence of continuous irradiation measurements showed inverse proportionality for different concentrations of IO-NP combined with 2mug/ml PF concentration and 1.5mug/ml for RB concentration. CONCLUSION: Photosensitization of RBC with PF or RB mixed with IO-NP inhibited rupturing erythrocyte membrane and therefore a consideration should be taken against their combination in clinical applications.

Rose bengal in poly(2-hydroxyethyl methacrylate) thin films: self-quenching by photoactive energy traps.[Pubmed:28276341]

Methods Appl Fluoresc. 2017 Mar 9;5(1):014010.

The effect of dye concentration on the fluorescence,PhiF, and singlet molecular oxygen,PhiDelta, quantum yields of Rose Bengal loaded poly(2-hydroxyethyl methacrylate) thin films ( approximately 200 nm thick) was investigated, with the aim of understanding the effect of molecular interactions on the photophysical properties of dyes in crowded constrained environments. Films were characterized by absorption and fluorescence spectroscopy, singlet molecular oxygen ((1)O2) production was quantified using a chemical monitor, and the triplet decay was determined by laser flash-photolysis. For the monomeric dilute dye, PhiF = 0.05 +/- 0.01 and PhiDelta = 0.76 +/- 0.14. The effect of humidity and the photostability of the dye were also investigated. Spectral changes in absorption and fluorescence in excess of 0.05 M and concentration self-quenching after 0.01 M are interpreted in the context of a quenching radius model. Calculations of energy migration and trapping rates were performed assuming random distribution of the dye. Best fits of fluorescence quantum yields with concentration are obtained in the whole concentration range with a quenching radius r Q = 1.5 nm, in the order of molecular dimensions. Agreement is obtained only if dimeric traps are considered photoactive, with an observed fluorescence quantum yield ratio PhiF,trap/PhiF,monomer approximately 0.35. Fluorescent traps are capable of yielding triplet states and (1)O2. Results show that the excited state generation efficiency, calculated as the product between the absorption factor and the fluorescence quantum yield, is maximized at around 0.15 M, a very high concentration for random dye distributions. Relevant information for the design of photoactive dyed coatings is provided.

Modulation of hippocampal synaptic transmission by the kynurenine pathway member xanthurenic acid and other VGLUT inhibitors.[Pubmed:23303071]

Neuropsychopharmacology. 2013 May;38(6):1060-7.

Xanthurenic acid (XA), an endogenous kynurenine, is a known vesicular glutamate transport (VGLUT) inhibitor and has also been proposed as an mGlu2/3 receptor agonist. Changes in these systems have been implicated in the pathophysiology of schizophrenia and other psychiatric disorders; however, little is known of how XA affects synaptic transmission. We therefore investigated the effects of XA on synaptic transmission at two hippocampal glutamatergic pathways and evaluated the ability of XA to bind to mGlu2/3 receptors. Field excitatory postsynaptic potentials (fEPSPs) were recorded from either the dentate gyrus (DG) or CA1 region of mouse hippocampal slices in vitro. Addition of XA to the bathing medium (1-10 mM) resulted in a dose-related reduction of fEPSP amplitudes (up to 52% reduction) in both hippocampal regions. In the DG, the VGLUT inhibitors Congo Red and Rose Bengal, and the mGlu2/3 agonist LY354740, also reduced fEPSPs (up to 80% reduction). The mGlu2/3 antagonist LY341495 reversed the LY354740 effect, but not the XA effect. LY354740, but not XA, also reduced DG paired-pulse depression. XA had no effect on specific binding of 1 nM [(3)H]LY341495 to membranes with human mGlu2 receptors. We conclude that XA can modulate synaptic transmission via a mechanism that may involve VGLUT inhibition rather than activation of mGlu2/3 receptors. This could be important in the pathophysiology of nervous system disorders including schizophrenia and might represent a target for developing novel pharmacological therapies.

Rose Bengal analogs and vesicular glutamate transporters (VGLUTs).[Pubmed:20708942]

Bioorg Med Chem. 2010 Sep 15;18(18):6922-33.

Vesicular glutamate transporters (VGLUTs) allow the loading of presynaptic glutamate vesicles and thus play a critical role in glutamatergic synaptic transmission. Rose Bengal (RB) is the most potent known VGLUT inhibitor (Ki 25 nM); therefore we designed, synthesized and tested in brain preparations, a series of analogs based on this scaffold. We showed that among the two tautomers of RB, the carboxylic and not the lactonic form is active against VGLUTs and generated a pharmacophore model to determine the minimal structure requirements. We also tested RB specificity in other neurotransmitter uptake systems. RB proved to potently inhibit VMAT (Ki 64 nM) but weakly VACHT (Ki>9.7 microM) and may be a useful tool in glutamate/acetylcholine co-transmission studies.

Inhibition of vesicular glutamate storage and exocytotic release by Rose Bengal.[Pubmed:11279259]

J Neurochem. 2001 Apr;77(1):34-42.

It had been thought that quantal size in synaptic transmission is invariable. Evidence has been emerging, however, that quantal size can be varied under certain conditions. We present evidence that alteration in vesicular [(3)H]L-glutamate (Glu) content within the synaptosome (a pinched-off nerve ending preparation) leads to a change in the amount of exocytotically released [(3)H]Glu. We found that Rose Bengal, a polyhalogenated fluorescein derivative, is a quite potent membrane-permeant inhibitor (K(i) = 19 nM) of glutamate uptake into isolated synaptic vesicles. This vesicular Glu uptake inhibition was achieved largely without affecting H(+)-pump ATPase. We show that various degrees of reduction elicited by Rose Bengal in [(3)H]Glu in synaptic vesicles inside the synaptosome result in a corresponding decrease in the amount of [(3)H]Glu released in a depolarization- (induced by 4-aminopyridine) and Ca(2+)-dependent manner. In contrast, fluorescein, the halogen-free analog of Rose Bengal, which is devoid of inhibitory activity on vesicular [(3)H]Glu uptake, failed to change the amount of exocytotically released [(3)H]Glu. These observations suggest that glutamate synaptic transmission could be altered by pharmacological intervention of glutamate uptake into synaptic vesicles in the nerve terminal, a new mode of synaptic manipulation for glutamate transmission.

What is actually stained by rose bengal?[Pubmed:1637285]

Arch Ophthalmol. 1992 Jul;110(7):984-93.

It has been believed that 1% Rose Bengal does not stain normal, healthy cells but rather stains degenerated or dead cells and mucous strands. In contrast to this conventional knowledge, we discovered that both commercial additive-containing and additive-free Rose Bengal solutions stained four different types of healthy cultured cells, including rabbit corneal epithelial cells. Rose Bengal staining was rapid, dose dependent, predominantly nuclear, and detectable with the naked eye at concentrations as low as 0.05% and 0.025% for the commercial additive-containing or additive-free solutions, respectively, and with the fluorescence microscope at a concentration of 0.001%. It is surprising to discover that Rose Bengal is not a vital dye; after staining, cells actually lost vitality, as evidenced by instant morphologic changes, subsequent loss of cellular motility, cell detachment, and cell death. Such an intrinsic toxic effect was augmented by light exposure. The Rose Bengal staining of live as well as detergent-treated (Triton X-100) cells could be blocked by such tear components as mucin and albumin, suggesting that normally negative Rose Bengal staining is due to the protective function of the preocular tear film, ie, staining is not dictated by lack of cell vitality. These data indicate that Rose Bengal staining ensues whenever there is poor protection of surface epithelium by the preocular tear film; this represents a new interpretation for Rose Bengal stains seen in various ocular surface disorders.