Localisation and quantification of benzalkonium chloride in eye tissue by TOF-SIMS imaging and liquid chromatography mass spectrometry

Differential Effects of Benzalkonium Chloride on Human Trabecular Meshwork Cells Not Treated or Treated with Transforming Growth Factor-β2 or Dexamethasone

Purpose: The objective of the present study was to evaluate the effects of low concentrations of benzalkonium chloride (BAC) (10-7%, 10-6%, or 10-5%) on healthy and glaucomatous human trabecular meshwork (HTM) cells. For this purpose, we used in vitro models replicating a healthy HTM and HTM with primary open-angle glaucoma (POAG) or steroid-induced glaucoma (SG) using two-dimensional (2D) cultures of HTM cells not treated or treated with a 5 ng/mL solution of transforming growth factor-β2 or 250 nM dexamethasone (DEX). Methods: Analyses were carried out for (1) the intercellular affinity function of 2D HTM monolayers, as determined by transepithelial electrical resistance (TEER) measurements; (2) cell viability; (3) cellular metabolism by using a Seahorse bioanalyzer; and (4) expression of extracellular matrix (ECM) molecules, an ECM modulator, and cell junction-related molecules. Results: In the absence and presence of BAC (10-7% or 10-5%), intercellular affinity function determined by TEER and cellular metabolic activities were significantly and dose dependently affected in both healthy and glaucomatous HTM cells despite the fact that there was no significant decrease in cell viabilities. However, the effects based on TEER values were significantly greater in the healthy HTM. The mRNA expression of several molecules that were tested was not substantially modulated by these concentrations of BAC. Conclusions: The findings reported herein suggest that low concentrations of BAC may have unfavorable adverse effects on cellular metabolic capacity by inducing increases in the intercellular affinity properties of the HTM, but those effects of BAC were different in healthy and glaucomatous HTM cells.

MALDI-TOF imaging analysis of benzalkonium chloride penetration in ex vivo human skin

Benzalkonium chloride (BZK), alkyldimethylbenzlamonium chloride, is a cationic surfactant that is used as an antiseptic. BZK is classified as a quaternary ammonium compound composed of molecules of several alkyl chains of differing lengths, that dictate its effectiveness towards different microbes. As a result, BZK has become one of the most used preservatives in antibacterial solutions. Despite its widespread use, it is not clear whether BZK penetrates human skin. To answer this question, BZK treated skin was analyzed using matrix assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry imaging. Solutions containing BZK and differing excipients, including citric acid, caprylyl glycol, and vitamin E, were applied ex vivo to excised human skin using Franz diffusion cells. Treated skin was embedded in gelatin and sectioned prior to MALDI-TOF imaging. BZK penetrates through the epidermis and into the dermis, and the penetration depth was significantly altered by pH and additives in tested solutions.

The use of benzalkonium chloride in topical glaucoma treatment: An investigation of the efficacy and safety of benzalkonium chloride-preserved intraocular pressure-lowering eye drops and their effect on conjunctival goblet cells

ENGLISH SUMMARY

Glaucoma is a leading cause of the global prevalence of irreversible blindness. The pathogenesis of glaucoma is not entirely known, but the major risk factors include advancing age, genetic predisposition, and increased intraocular pressure (IOP). The only evidence-based treatment is a lowering of IOP through the use of eye drops, laser procedures, or surgical interventions. Although laser treatment is gaining recognition as a first-choice treatment option, the most common approach for managing glaucoma is IOP-lowering eye drops. A major challenge in the treatment is the occurrence of adverse events and poor adherence. In this context, the ocular surface is an area of great concern, as most glaucoma patients have dry eye disease (DED), which is largely caused by eye drops. Preservation with benzalkonium chloride (BAK) is a controversial topic due to its potential role as a significant cause of DED. A systematic review and meta-analyses investigate potential differences in efficacy and safety between BAK-preserved and BAK-free anti-glaucomatous eye drops (I). Many of the included studies report on ocular surface damage caused by the application of BAK-preserved eye drops. However, the meta-analyses addressing hyperemia, number of ocular adverse events, and tear break-up time did not identify any significant differences. The latter is likely due to varying measurement methods, different endpoints, and study durations. It is, therefore, possible that the large variations between the studies conceal differences in the safety profiles. The efficacy meta-analysis finds that there are no differences in the IOP-lowering effect between BAK-preserved and BAK-free eye drops, indicating that BAK is not necessary for the effectiveness of eye drops. To promote more homogeneous choices of endpoints and methods when evaluating BAK-preserved and BAK-free glaucoma treatments, a Delphi consensus statement was performed. In this study, glaucoma experts and ocular surface disease experts reached consensus on the key factors to consider when designing such studies (II). The hope is to have more studies with comparable endpoints that can systematically show the potentially adverse effects of BAK. The preclinical studies in the current Ph.D. research focus on conjunctival goblet cells (GCs). GCs are important for the ocular surface because they release the mucin MUC5AC, which is an essential component of the inner layer of the tear film. BAK preservation may damage the GCs and result in a low GC density, leading to an unstable tear film and DED. The most commonly used IOP-lowering drugs are prostaglandin analogs (PGAs). Thus, the conducted studies investigate the effect of PGAs preserved in different ways on GCs. BAK-preserved latanoprost is cytotoxic to primary cultured human conjunctival GCs and results in a scattered expression of MUC5AC, in contrast to negative controls, where MUC5AC is localized around the cell nucleus (III). Preservative-free (PF) latanoprost is not cytotoxic and does not affect the MUC5AC expression pattern. Furthermore, BAK-preserved travoprost is found to be cytotoxic in a time-dependent manner, while Polyquad®-preserved travoprost does not affect GC survival at any measured time point (IV). Both Polyquad and BAK induce scattered expression of MUC5AC. The cytotoxicity of BAK-preserved PGA eye drops is higher compared to the safer profile of PF and Polyquad-preserved PGA eye drops (V). Additionally, PF latanoprost does not increase the release of the inflammatory markers interleukin (IL)-6 and IL-8, unlike BAK-preserved latanoprost. A review highlights the active and inactive components of IOP-lowering eye drops (VI). Several preclinical and clinical studies have identified adverse effects of BAK. Although other components, such as the active drug and phosphates, can also cause adverse events, the review clearly states that BAK alone is a major source of decreased tolerability. The conclusion of this thesis is that BAK preservation is unnecessary and harmful to the ocular surface. The preclinical studies demonstrate that GCs die when exposed to BAK. Furthermore, they find that BAK induces a pro-inflammatory response. The review included in the thesis concludes that BAK should be phased out of eye drops for chronic use. Overall, the inclusion of BAK poses a risk of developing DED and poor adherence, which can ultimately lead to disease progression and blindness.

The molecular aspect of anti-glaucomatous eye drops - are we harming our patients?

Glaucoma is one of the leading causes of irreversible blindness. Progression is halted with a reduction in intraocular pressure (IOP), which is most often achieved with eye drops. A major challenge in the topical treatment of glaucoma patients is the many side effects and the resulting reduced adherence. Side effects may of course be due to the molecular properties of the active pharmaceutical ingredients (APIs). There are currently six different APIs available: prostaglandin analogues, β-adrenergic inhibitors, α-adrenergic agonists, carbonic anhydrase inhibitors, rho-kinase inhibitors and muscarinic 3 agonists. But the additives used in eye drops are also known to cause damage to the ocular surface and to some extent also to the deeper tissues. Said additives are considered inactive molecular components and are added to secure for instance viscosity and pH value, and to prevent contamination. There has been an increasing focus on the harmful effects of preservatives, with the most commonly used preservative benzalkonium chloride (BAK) being particularly controversial. BAK has long been recognized as a toxin that increases the risk of ocular discomfort. This can affect the adherence and ultimately result in lack of disease control. Other issues include the addition of certain buffers, such as phosphates, and varying pH values. This review will address the different molecular components of the IOP-lowering eye drops and what to be aware of when prescribing topical glaucoma treatment.

Cytotoxicity, Mitochondrial Functionality, and Redox Status of Human Conjunctival Cells after Short and Chronic Exposure to Preservative-Free Bimatoprost 0.03% and 0.01%: An In Vitro Comparative Study

Prostaglandin analogues (PGAs), including bimatoprost (BIM), are generally the first-line therapy for glaucoma due to their greater efficacy, safety, and convenience of use. Commercial solutions of preservative-free BIM (BIM 0.03% and 0.01%) are already available, although their topical application may result in ocular discomfort. This study aimed to evaluate the in vitro effects of preservative-free BIM 0.03% vs. 0.01% in the human conjunctival epithelial (HCE) cell line. Our results showed that long-term exposure to BIM 0.03% ensues a significant decrease in cell proliferation and viability. Furthermore, these events were associated with cell cycle arrest, apoptosis, and alterations of ΔΨ_m. BIM 0.01% does not exhibit cytotoxicity, and no negative influence on conjunctival cell growth and viability or mitochondrial activity has been observed. Short-time exposure also demonstrates the ability of BIM 0.03% to trigger reactive oxygen species (ROS) production and mitochondrial hyperpolarisation. An in silico drug network interaction was also performed to explore known and predicted interactions of BIM with proteins potentially involved in mitochondrial membrane potential dissipation. Our findings overall strongly reveal better cellular tolerability of BIM 0.01% vs. BIM 0.03% in HCE cells.

Ocular Tolerability of Bimatoprost 0.1 mg/mL Preservative-Free versus Bimatoprost 0.1 mg/mL with Benzalkonium Chloride or Bimatoprost 0.3 mg/mL Preservative-Free in Patients with Primary Open-Angle Glaucoma

This study aimed to evaluate whether the therapeutic switch from a formulation of Bimatoprost 0.1 mg/mL with benzalkonium chloride (BAK) or Bimatoprost 0.3 mg/mL preservative-free to a formulation of Bimatoprost 0.1 mg/mL preservative-free could improve eye surface conditions in patients with glaucoma; intraocular pressure (IOP) was also evaluated. All patients meeting the inclusion criteria were eligible for the therapeutic switch to Bimatoprost 0.1 mg/mL preservative-free. At each check visit, enrolled patients underwent a break-up time (BUT) test, an ocular surface disease index (OSDI) test, and a three-point tonometric curve. A total of 40 patients were enrolled (23 were in therapy with Bimatoprost 0.1 mg/mL with BAK and 17 with Bimatoprost 0.3 mg/mL preservative-free). Significant differences of OSDI and BUT between Bimatoprost 0.1 mg/mL with BAK at baseline vs. Bimatoprost 0.1 mg/mL preservative-free at 14 and 28 days (p < 0.0001 and p = 0.0003, respectively) were recorded. Similarly, significant differences of OSDI and BUT between Bimatoprost 0.3 mg/mL preservative-free at baseline vs. Bimatoprost 0.1 mg/mL preservative-free at 14 and 28 days (p < 0.0001 for both) were found. Bimatoprost 0.1 mg/mL preservative-free has a better tolerability profile associated with non-therapeutical inferiority in the control of IOP compared to the other Bimatoprost formulations.

Advanced applications of mass spectrometry imaging technology in quality control and safety assessments of traditional Chinese medicines

ETHNOPHARMACOLOGICAL RELEVANCE

Traditional Chinese medicines (TCMs) have made great contributions to the prevention and treatment of human diseases in China, and especially in cases of COVID-19. However, due to quality problems, the lack of standards, and the diversity of dosage forms, adverse reactions to TCMs often occur. Moreover, the composition of TCMs makes them extremely challenging to extract and isolate, complicating studies of toxicity mechanisms.

AIM OF THE REVIEW

The aim of this paper is therefore to summarize the advanced applications of mass spectrometry imaging (MSI) technology in the quality control, safety evaluations, and determination of toxicity mechanisms of TCMs.

MATERIALS AND METHODS

Relevant studies from the literature have been collected from scientific databases, such as "PubMed", "Scifinder", "Elsevier", "Google Scholar" using the keywords "MSI", "traditional Chinese medicines", "quality control", "metabolomics", and "mechanism".

RESULTS

MSI is a new analytical imaging technology that can detect and image the metabolic changes of multiple components of TCMs in plants and animals in a high throughput manner. Compared to other chemical analysis methods, such as liquid chromatography-mass spectrometry (LC-MS), this method does not require the complex extraction and separation of TCMs, and is fast, has high sensitivity, is label-free, and can be performed in high-throughput. Combined with chemometrics methods, MSI can be quickly and easily used for quality screening of TCMs. In addition, this technology can be used to further focus on potential biomarkers and explore the therapeutic/toxic mechanisms of TCMs.

CONCLUSIONS

As a new type of analysis method, MSI has unique advantages to metabolic analysis, quality control, and mechanisms of action explorations of TCMs, and contributes to the establishment of quality standards to explore the safety and toxicology of TCMs.

Cell and Tissue Imaging by TOF-SIMS and MALDI-TOF: An Overview for Biological and Pharmaceutical Analysis

The potential of mass spectrometry imaging (MSI) has been demonstrated in cell and tissue research since 1970. MSI can reveal the spatial distribution of a wide range of atomic and molecular ions detected from biological sample surfaces, it is a powerful and valuable technique used to monitor and detect diverse chemical and biological compounds, such as drugs, lipids, proteins, and DNA. MSI techniques, notably matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) and time of flight secondary ion mass spectrometry (TOF-SIMS), witnessed a dramatic upsurge in studying and investigating biological samples especially, cells and tissue sections. This advancement is attributed to the submicron lateral resolution, the high sensitivity, the good precision, and the accurate chemical specificity, which make these techniques suitable for decoding and understanding complex mechanisms of certain diseases, as well as monitoring the spatial distribution of specific elements, and compounds. While the application of both techniques for the analysis of cells and tissues is thoroughly discussed, a briefing of MALDI-TOF and TOF-SIMS basis and the adequate sampling before analysis are briefly covered. The importance of MALDI-TOF and TOF-SIMS as diagnostic tools and robust analytical techniques in the medicinal, pharmaceutical, and toxicology fields is highlighted through representative published studies.

Innovation in drug toxicology: Application of mass spectrometry imaging technology

Mass spectrometry imaging (MSI) is a powerful molecular imaging technology that can obtain qualitative, quantitative, and location information by simultaneously detecting and mapping endogenous or exogenous molecules in biological tissue slices without specific chemical labeling or complex sample pretreatment. This article reviews the progress made in MSI and its application in drug toxicology research, including the tissue distribution of toxic drugs and their metabolites, the target organs (liver, kidney, lung, eye, and central nervous system) of toxic drugs, the discovery of toxicity-associated biomarkers, and explanations of the mechanisms of drug toxicity when MSI is combined with the cutting-edge omics methodologies. The unique advantages and broad prospects of this technology have been fully demonstrated to further promote its wider use in the field of pharmaceutical toxicology.

Efficacy and safety of newly developed preservative-free latanoprost 0.005% eye drops versus preserved latanoprost 0.005% in open angle glaucoma and ocular hypertension: 12-week results of a randomized, multicenter, controlled phase III trial

AIM

To evaluate the therapeutic efficacy, safety and tolerability of newly developed preservative-free (PF) latanoprost generic [TJO-002] and compare it with benzalkonium chloride (BAK)-preserved latanoprost [Xalatan^®] in patients with primary open angle glaucoma (POAG) and ocular hypertension (OHT).

METHODS

Included patients were aged ≥19y with POAG/OHT. After a washout period, patients with IOP 21-35 mm Hg at 9 a.m. were enrolled. After a full ophthalmic and glaucoma examination, 144 patients with POAG and OHT participated in this study. Subjects were randomly assigned either PF latanoprost (74 eyes) or BAK-preserved latanoprost (70 eyes). All subjects were examined at 4, 8, and 12wk after first administration. At each follow-up visit, IOP was measured at 9 a.m. and 5 p.m. and compliance was assessed. Throughout the study, all adverse events were recorded and monitored by the masked investigators who measured IOP.

RESULTS

Both groups showed a statistically significant decrease of average diurnal IOP at 12wk compared to baseline (-7.21±3.10 mm Hg in the PF latanoprost group and -7.02±3.17 mm Hg in the BAK latanoprost group, both P<0.0001). There was no statistically significant diurnal IOP variation between the groups. In terms of tolerability, pruritus, burning/stinging, and sticky eye sensation, severity was significantly lower in the PF latanoprost group than in the BAK latanoprost group (P<0.05).

CONCLUSION

PF latanoprost has at least similar efficacy in terms of IOP reduction and better tolerability compared with BAK latanoprost.

The trabecular meshwork in glaucoma: An inflammatory trabeculopathy?

Glaucoma is an optic neuropathy in which the primary risk factor is increased intraocular pressure (IOP), attributed to increased resistance to trabecular outflow of aqueous humor (AH). This resistance is believed to result from trabecular degeneration secondary to chronic oxidative stress and cellular senescence but may also involve inflammatory mechanisms whose roles are little known. In fact, inflammatory processes play a major role in the pathophysiology of glaucoma to varying degrees, affecting all structures of the eye, including the ocular surface, the anterior and posterior segments, and even the visual pathways of the brain. These processes are thought to result from dysfunction of a regulatory, protective para-inflammation, becoming chronic and harmful in glaucoma. While the mechanisms of the retinal inflammation which accelerates the degeneration of retinal ganglion cells (RGCs) as well as the inflammation of the ocular surface aggravated by long-term use of preserved glaucoma eye drops have been described for several years, very little is known about the pathophysiology of trabecular inflammation in glaucoma. The objective of this literature review is to provide a synthesis of knowledge on the roles and mechanisms of inflammation in both the healthy and glaucomatous trabecular meshwork, as well as its role in the pathophysiology of glaucoma. Therefore, after a review of the mechanisms of cellular senescence and oxidative stress - sources of trabecular inflammation, we will approach the study of the expression and roles of the main inflammatory mediators within the trabecular meshwork. Finally, we will discuss current knowledge on the toxicity of glaucoma eye drops and their preservatives on the ocular surface and trabecular meshwork as well as their role in trabecular inflammation.

Therapeutic Potential of a Self-Assembling Peptide Hydrogel to Treat Colonic Injuries Associated with Inflammatory Bowel Disease

BACKGROUND AND AIMS

The Self-assembling Peptide Hydrogel [SAPH, PuraMatrix], a fully synthetic peptide solution designed to replace collagen, has recently been used to promote mucosal regeneration in iatrogenic ulcers following endoscopic submucosal dissection. Herein, we evaluated its utility in ulcer repair using a rat model of topical trinitrobenzene sulphonic acid [TNBS]-induced colonic injuries.

METHODS

Colonic injuries were generated in 7-week-old rats by injecting an ethanol solution [35%, 0.2 mL] containing 0.15 M TNBS into the colonic lumen. At 2 and 4 days post-injury, the rats were subjected to endoscopy, and SAPH [or vehicle] was topically applied to the ulcerative lesion. Time-of-flight secondary ion mass spectrometry [TOF-SIMS] was used to detect SAPH. Colonic expression of cytokines and wound healing-related factors were assessed using real-time polymerase chain reaction or immunohistochemistry.

RESULTS

SAPH treatment significantly reduced ulcer length [p = 0.0014] and area [p = 0.045], while decreasing colonic weight [p = 0.0375] and histological score [p = 0.0005] 7 days after injury. SAPH treatment also decreased colonic expression of interleukin [IL]-1α [p = 0.0233] and IL-6[p = 0.0343] and increased that of claudin-1 [p = 0.0486] and villin [p = 0.0183], and β-catenin staining [p = 0.0237]. TOF-SIMS revealed lesional retention of SAPH on day 7 post-injury. Furthermore, SAPH significantly promoted healing in in vivo mechanical intestinal wound models.

CONCLUSIONS

SAPH application effectively suppressed colonic injury, downregulated inflammatory cytokine expression, and upregulated wound healing-related factor expression in the rat model; thus, it may represent a promising therapeutic strategy for IBD-related colonic ulcers.

Comparison of the Intraocular Pressure-Lowering Effect and Safety of Preservative-Free And Preservative-Containing Brimonidine/Timolol Fixed-Combination Ophthalmic Solutions in Patients with Open-Angle Glaucoma

Purpose: To compare the therapeutic efficacy and safety of newly developed preservative-free (PF) brimonidine/timolol fixed-combination (BTFC) ophthalmic solutions and a preservative-containing (PC) BTFC ophthalmic solution in patients with open-angle glaucoma.Methods: This study was conducted as a multicenter, randomized, open-label, parallel-group clinical trial to evaluate the efficacy and safety of PF BTFC as compared with PC BTFC in adult patients (aged ≥ 19 years) with open-angle glaucoma (OAG) and ocular hypertension (OHT). A total of the 106 patients were enrolled, with 53 patients each randomized to the two treatment groups and included in the analysis of the safety set (SS).After a washout period, patients with an IOP below 35 mmHg at 9 a.m. were enrolled. After a full ophthalmic and glaucoma examination, a total of 106 OAG and OHT patients were randomized to the PF group or PC group.All subjects were examined 4 and 12 weeks after first administration. At each follow-up visit, IOP was measured at 9 a.m. and 11 a.m. and the efficacy, safety, and compliance were evaluated. Throughout the study, all adverse events were recorded and monitored by the investigators.Results The mean IOP changes from baseline to 12 weeks at 11:00 a.m. were -3.45 ± 2.53 mmHg in the PF group and -3.65 ± 2.76 mmHg in the PC group (p < .0001 for both). The difference in mean IOP change between the two groups was 0.20 ± 2.65 mmHg, which was not significantly different. The proportion of patients with IOP reductions of ≥ 15% and ≥ 20% and IOP at all-time points in the PF group were not significantly different when compared with in the PC group. There were no specific differences between the two groups regarding the incidence of adverse events.Conclusions PF BTFC ophthalmic solution shows a similar efficacy and safety profile to that of PC BTFC.

Chemical Imaging of Retinal Pigment Epithelium in Frozen Sections of Zebrafish Larvae Using ToF-SIMS

Variants of the SLC24A5 gene, which encodes a putative potassium-dependent sodium-calcium exchanger (NCKX5) that most likely resides in the melanosome or its precursor, affect pigmentation in both humans and zebrafish (Danio rerio). This finding suggests that genetic variations influencing human skin pigmentation alter melanosome biogenesis via ionic changes. Gaining an understanding of how changes in the ionic environment of organelles impact melanosome morphogenesis and pigmentation will require a spatially resolved way to characterize the chemical environment of melanosomes in pigmented tissue such as retinal pigment epithelium (RPE). The imaging mass spectrometry technique most suited for this type of cell and tissue analysis is time-of-flight secondary ion mass spectrometry (ToF-SIMS) because it is able to detect many biochemical species with high sensitivity and with submicron spatial resolution. Here, we describe chemical imaging of the RPE in frozen-hydrated sections of larval zebrafish using cryo-ToF-SIMS. To facilitate the data interpretation, positive and negative polarity ToF-SIMS image data were transformed into a single hyperspectral data set and analyzed using principal component analysis. The combination of a novel protocol and the use of multivariate data analysis allowed us to discover new marker ions that are attributable to leucodopachrome, a metabolite specific to the biosynthesis of eumelanin. The described methodology may be adapted for the investigation of other classes of molecules in frozen tissues from zebrafish and other organisms.

Inflammation in Glaucoma: From the back to the front of the eye, and beyond

The pathophysiology of glaucoma is complex, multifactorial and not completely understood. Elevated intraocular pressure (IOP) and/or impaired retinal blood flow may cause initial optic nerve damage. In addition, age-related oxidative stress in the retina concurrently with chronic mechanical and vascular stress is crucial for the initiation of retinal neurodegeneration. Oxidative stress is closely related to cell senescence, mitochondrial dysfunction, excitotoxicity, and neuroinflammation, which are involved in glaucoma progression. Accumulating evidence from animal glaucoma models and from human ocular samples suggests a dysfunction of the para-inflammation in the retinal ganglion cell layer and the optic nerve head. Moreover, quite similar mechanisms in the anterior chamber could explain the trabecular meshwork dysfunction and the elevated IOP in primary open-angle glaucoma. On the other hand, ocular surface disease due to topical interventions is the most prominent and visible consequence of inflammation in glaucoma, with a negative impact on filtering surgery failure, topical treatment efficacy, and possibly on inflammation in the anterior segment. Consequently, glaucoma appears as an outstanding eye disease where inflammatory changes may be present to various extents and consequences along the eye structure, from the ocular surface to the posterior segment, and the visual pathway. Here we reviewed the inflammatory processes in all ocular structures in glaucoma from the back to the front of the eye and beyond. Our approach was to explain how para-inflammation is necessary to maintain homoeostasis, and to describe abnormal inflammatory findings observed in glaucomatous patients or in animal glaucoma models, supporting the hypothesis of a dysregulation of the inflammatory balance toward a pro-inflammatory phenotype. Possible anti-inflammatory therapeutic approaches in glaucoma are also discussed.

Plant-derived angiogenin fusion protein's cytoprotective effect on trabecular meshwork damage induced by Benzalkonium chloride in mice

Background

Benzalkonium chloride (BAK), commonly used in glaucoma treatment, is an eye drop preservative with dose-dependent toxicity. Previous studies have observed the multi-functional benefits of angiogenin (ANG) against glaucoma. In our study, we evaluated ANG’s cytoprotective effect on the trabecular meshwork (TM) damage induced by BAK. Additionally, we developed a plant-derived ANG fusion protein and evaluated its effect on TM structure and function.

Methods

We synthesized plant-derived ANG (ANG-FcK) by fuzing immunoglobulin G’s Fc region and KDEL to conventional recombinant human ANG (Rh-ANG) purified from transgenic tobacco plants. We established a mouse model using BAK to look for degenerative changes in the TM, and to evaluate the protective effects of ANG-FcK and Rh-ANG. Intraocular pressure (IOP) was measured for 4 weeks and ultrastructural changes, deposition of fluorescent microbeads, type I and IV collagen, fibronectin, laminin and α-SMA expression were analyzed after the mice were euthanized.

Results

TM structural and functional degeneration were induced by 0.1% BAK instillation in mice. ANG co-treatment preserved TM outflow function, which we measured using IOP and a microbead tracer. ANG prevented phenotypic and ultrastructure changes, and that protective effect might be related to the anti-fibrosis mechanism. We observed a similar cytoprotective effect in the BAK-induced degenerative TM mouse model, suggesting that plant-derived ANG-FcK could be a promising glaucoma treatment.

In vitro effects of benzalkonium chloride and prostaglandins on human meibomian gland epithelial cells

PURPOSE

Benzalkonium chloride is the most widely used preservative in ophthalmic topical solutions. The aim of this study was to investigate the influence of BAC as a single substance or as a component of several commercially available ophthalmic solutions on meibomian gland epithelial cells in vitro.

MATERIALS AND METHODS

An immortalized human meibomian gland epithelial cell line (HMGEC) was used and cells were cultured in the absence or presence of fetal bovine serum to assess cell morphology, cell proliferation, cell viability (MTS assay) and impedance sensing (ECIS) after stimulation with BAC. Further, the viability of HMGECs stimulated with BAC-containing and BAC-free bimatoprost, travoprost and latanoprost was evaluated using the MTS assay. Real-time PCR analysis for hyperkeratinization associated genes (cornulin, involucrin) was performed.

RESULTS

In the absence of serum, the proliferation rate of HMGECs decreased starting with 0.1μg/ml BAC. At concentrations of 50μg/ml BAC and higher, cell viability was reduced after 10min exposure with a corresponding change in cell morphology. Toxicity of BAC-containing ophthalmic solutions was greater than that of BAC alone, whereas BAC-free alternative products did not significantly influence cell viability. Confluence, cell-cell contacts and serum-containing medium appeared to facilitate HMGECs survival. Expression rate of involucrin and cornulin declined after exposure to preserved bimatoprost and BAC.

CONCLUSIONS

BAC showed cytotoxic effects on HMGECs starting with a concentration of 0.1μg/ml. The combination of BAC and prostaglandin-analogs might have a synergistic effect which results in higher toxicity than BAC alone. Unpreserved eye drops and eye drops preserved with Polyquaternium-1 are less damaging to HMGECs.

Mass spectrometry imaging for clinical research - latest developments, applications, and current limitations

Mass spectrometry is being used in many clinical research areas ranging from toxicology to personalized medicine. Of all the mass spectrometry techniques, mass spectrometry imaging (MSI), in particular, has continuously grown towards clinical acceptance. Significant technological and methodological improvements have contributed to enhance the performance of MSI recently, pushing the limits of throughput, spatial resolution, and sensitivity. This has stimulated the spread of MSI usage across various biomedical research areas such as oncology, neurological disorders, cardiology, and rheumatology, just to name a few. After highlighting the latest major developments and applications touching all aspects of translational research (i.e. from early pre-clinical to clinical research), we will discuss the present challenges in translational research performed with MSI: data management and analysis, molecular coverage and identification capabilities, and finally, reproducibility across multiple research centers, which is the largest remaining obstacle in moving MSI towards clinical routine.

Effects of Several Cosmetic Preservatives on ROS-Dependent Apoptosis of Rat Neural Progenitor Cells

Benzalkonium chloride, diazolidinyl urea, and imidazolidinyl urea are commonly used preservatives in cosmetics. Recent reports suggested that these compounds may have cellular and systemic toxicity in high concentration. In addition, diazolidinyl urea and imidazolidinyl urea are known formaldehyde (FA) releasers, raising concerns for these cosmetic preservatives. In this study, we investigated the effects of benzalkonium chloride, diazolidinyl urea, and imidazolidinyl urea on ROS-dependent apoptosis of rat neural progenitor cells (NPCs) in vitro. Cells were isolated and cultured from embryonic day 14 rat cortices. Cultured cells were treated with 1–1,000 nM benzalkonium chloride, and 1–50 μM diazolidinyl urea or imidazolidinyl urea at various time points to measure the reactive oxygen species (ROS). PI staining, MTT assay, and live-cell imaging were used for cell viability measurements. Western blot was carried out for cleaved caspase-3 and cleaved caspase-8 as apoptotic protein markers. In rat NPCs, ROS production and cleaved caspase-8 expression were increased while the cell viability was decreased in high concentrations of these substances. These results suggest that several cosmetic preservatives at high concentrations can induce neural toxicity in rat brains through ROS induction and apoptosis.

Preservatives in glaucoma medication

Preservatives continue to be in widespread use in ophthalmic medications due to the convenience they provide, regulatory requirements and the higher cost of alternatives. Benzalkonium chloride (BAK) remains the most commonly used preservative but there is a trend towards the use of preservative-free (PF) drops for glaucoma, although at a higher price. An extensive body of literature explores BAK toxicity on ocular structures in animal and laboratory studies (in vitro and in vivo). Non-randomised controlled studies have provided some supporting evidence of its toxicity in patients, especially in those with pre-existing ocular surface disease (OSD) or on multiple medications. However, there have been very few randomised controlled trials that compare the same medication with and without BAK preservative. Several of these trials have never been published in any peer reviewed journals. Notwithstanding, those that have been published, have not demonstrated any clear benefits of the BAK-free formulations. Short duration and exclusion of those with OSD are limitations of these studies. There is a lack of evidence of clinically significant harm from a small number of BAK preserved drops in patients without OSD. This means that generally more expensive PF glaucoma medications should only be recommended for those on poly pharmacy or those with OSD but are not necessarily required for all patients.

Transition metals and trace elements in the retinal pigment epithelium and choroid: correlative ultrastructural and chemical analysis by analytical electron microscopy and nano-secondary ion mass spectrometry

Understanding the localisation and abundance of structural elements, trace elements and especially transition metals like Cu and Zn in ocular tissue sections is important for physiology, and also for the characterisation of diseases related to oxidative stress like age-related macular degeneration. Transition metal abundances were investigated in an aged donor eye by nano-secondary ion mass spectrometry (nano-SIMS) elemental mapping using Cs⁺ and O^- primary ions, respectively, and correlated to their respective mole fractions investigated by analytical electron microscopy (AEM). The ultrastructure of the tissue and the elemental composition of melanosomes of the choroid and RPE, and RPE lipofuscin and melanolipofuscin granules can adequately be investigated by nano-SIMS using the secondary ion maps. Melanosomes, 0.5-1 μm in size, yield sulphur maps and maps of stored metals like calcium, sodium and copper. Lipofuscin shows especially high phosphorus signals. Elements with mole fractions of about 0.1 at%, e.g. for P and Cu, as investigated by AEM before, can be validated using simultaneous SIMS maps with an estimated lateral resolution of 66 nm with typical acquisition times of 30 minutes for each area of interest. However, Zn (0.19 at%) was not detected by SIMS. Nano-SIMS imaging of CN^-, PO₂^-, S^-, Cu^-, Ca⁺, Fe⁺ and Na⁺ ions provides excellent detection limits demonstrating the possibilities for chemical mapping with high-sensitivity trace element detection and reduced acquisition times. Quantification of nano-SIMS data was achieved by correlating mole fractions obtained by AEM to secondary ions per pixel obtained by nano-SIMS. Both methods yield the melanin type in melanosomes and trace metal storage.

Evaluating solid phase (micro-) extraction tools to analyze freely ionizable and permanently charged cationic surfactants

Working with and analysis of cationic surfactants can be problematic since aqueous concentrations are difficult to control, both when taking environmental aqueous samples as well as performing laboratory work with spiked concentrations. For a selection of 32 amine based cationic surfactants (including C8- to C18-alkylamines, C14-dialkyldimethylammonium, C8-tetraalkylammonium, benzalkonium and pyridinium compounds), the extraction from aqueous samples was studied in detail. Aqueous concentrations were determined using solid phase extraction (SPE; 3 mL/60 mg Oasis WCX-SPE cartridges) with recoveries of ≥80% for 30 compounds, and ≥90% for 16 compounds. Sorption to glassware was evaluated in 120 mL flasks, 40 mL vials and 1.5 mL autosampler vials, using 15 mM NaCl, where the glass binding of simple primary amines and quaternary ammonium compounds increased with alkyl chain length. Sorption to the outside of pipette tips (≤20% of total amount in solution) when sampling aqueous solutions may interfere with accurate measurements. Polyacrylate solid phase microextraction (PA-SPME) fibers with two coating thicknesses (7 and 35 μm) were tested as potential extraction devices. The uptake kinetics, pH-dependence and influence of ionic strength on sorption to PA fibers were studied. Changing medium from 100 mM Na⁺ to 10 mM Ca²⁺ decreases K_fw with one order of magnitude. Results indicate that for PA-SPME neutral amines are absorbed rather than adsorbed, although the exact sorption mechanism remains to be elucidated. Further research remains necessary to establish a definitive applicability domain for PA-SPME. However, results indicate that alkyl chain lengths ≥14 carbon atoms and multiple alkyl chains become problematic. A calibration curve should always be measured together with the samples. In conclusion, it seems that for amine based surfactants PA-SPME does not provide the reliability and reproducibility necessary for precise sorption experiments, specifically for alkyl chain lengths beyond 12 carbon atoms.

Preservative-free fixed combination of tafluprost 0.0015% and timolol 0.5% in patients with open-angle glaucoma and ocular hypertension: results of an open-label observational study

Background

Efficacy, tolerability and safety of the novel preservative-free fixed combination of tafluprost 0.0015%/timolol 0.5% (Taptiqom^®) were investigated in an observational study in Germany.

Objective

To assess efficacy, tolerability and safety of the preservative-free fixed combination of tafluprost 0.0015%/timolol 0.5% in a real-life setting.

Methods

Intraocular pressure (IOP) was recorded for each eye at baseline (any previous therapy or untreated) and 4–16 weeks after changing medical treatment to or initiating treatment with the preservative-free fixed combination of tafluprost 0.0015%/timolol 0.5%. Change in IOP was evaluated over the study period for all patients and for specific pretreatment subgroups. Clinical signs such as conjunctival hyperemia and lid-parallel conjunctival folds (LIPCOF) were recorded using standardized comparative photographs. Corneal staining, subjective symptoms and local comfort were measured using a four-step scale. All adverse events were recorded.

Results

Among 1,157 patients enrolled, 1,075 patients were treated with the preservative-free fixed combination as the only medication at the final visit. Medical treatment was initiated in 741 patients because of an insufficient IOP-lowering effect of the prior medication. In 343 patients, medication was changed because of tolerability issues. The preservative-free fixed combination lowered IOP significantly in the subgroup of naïve patients, all subgroups with prior monotherapy and patients with prior fixed combinations: naïve patients: −8.9 mmHg, alpha- 2-agonists: −6.4 mmHg, beta-blockers: −5.7 mmHg, carbonic anhydrase inhibitors: −5.2 mmHg, prostaglandins: −4.7 mmHg, fixed-combination prostaglandins/timolol: −2.4 mmHg. At the final visit, clinical signs and subjective symptoms were improved in patients with prior medical therapy. Local comfort was rated as “very good” or “good” by 89.1% of patients at the final visit. Only few adverse events occurred during the treatment period.

Conclusion

The preservative-free fixed combination of tafluprost 0.0015%/timolol 0.5% was effective, well tolerated and showed a good safety profile.

The Eye Drop Preservative Benzalkonium Chloride Potently Induces Mitochondrial Dysfunction and Preferentially Affects LHON Mutant Cells

Purpose

Benzalkonium chloride (BAK) is the most commonly used eye drop preservative. Benzalkonium chloride has been associated with toxic effects such as "dry eye" and trabecular meshwork degeneration, but the underlying biochemical mechanism of ocular toxicity by BAK is unclear. In this study, we propose a mechanistic basis for BAK's adverse effects.

Method

Mitochondrial O2 consumption rates of human corneal epithelial primary cells (HCEP), osteosarcoma cybrid cells carrying healthy (control) or Leber hereditary optic neuropathy (LHON) mutant mtDNA [11778(G>A)], were measured before and after acute treatment with BAK. Mitochondrial adenosine triphosphate (ATP) synthesis and cell viability were also measured in the BAK-treated control: LHON mutant and human-derived trabecular meshwork cells (HTM3).

Results

Benzalkonium chloride inhibited mitochondrial ATP (IC50, 5.3 μM) and O2 consumption (IC50, 10.9 μM) in a concentration-dependent manner, by directly targeting mitochondrial complex I. At its pharmaceutical concentrations (107-667 μM), BAK inhibited mitochondrial function >90%. In addition, BAK elicited concentration-dependent cytotoxicity to cybrid cells (IC50, 22.8 μM) and induced apoptosis in HTM3 cells at similar concentrations. Furthermore, we show that BAK directly inhibits mitochondrial O2 consumption in HCEP cells (IC50, 3.8 μM) at 50-fold lower concentrations than used in eye drops, and that cells bearing mitochondrial blindness (LHON) mutations are further sensitized to BAK's mitotoxic effect.

Conclusions

Benzalkonium chloride inhibits mitochondria of human corneal epithelial cells and cells bearing LHON mutations at pharmacologically relevant concentrations, and we suggest this is the basis of BAK's ocular toxicity. Prescribing BAK-containing eye drops should be avoided in patients with mitochondrial deficiency, including LHON patients, LHON carriers, and possibly primary open-angle glaucoma patients.

External eye symptoms in indoor environments

Eye irritation, for example dry or irritated eyes, is generally among top three reported symptoms in office-like environments, in particular among workplaces with cognitive demanding visual display unit (VDU) work. The symptoms are especially among middle and advanced ages and particularly among women more than men. The symptoms are also among the most commonly reported complaints in the eye clinic. To be in a position to interpret the high prevalence of eye symptoms, a multidisciplinary and integrated approach is necessary that involves the external eye physiology (separate from internal eye effects), eye diseases (evaporative dry eye (DE), aqueous-deficient DE, and gland dysfunctions), and risk factors that aggravate the stability of precorneal tear film (PTF) resulting in hyperosmolarity and initiation of inflammatory reactions. Indoor environmental, occupational and personal risk factors may aggravate the PTF stability; factors such as age, contact lenses, cosmetics, diet, draft, gender, low humidity and high temperature, medication, outdoor and combustion pollutants, and VDU work. Psychological stressors may further influence the reporting behavior of eye symptoms. The impact of the risk factors may occur in a combined and exacerbating manner.

Ocular surface toxicity from glaucoma topical medications and associated preservatives such as benzalkonium chloride (BAK)

INTRODUCTION

This review discusses the evidence concerning the effect of topical medications and their preservatives on the ocular surface in glaucoma patients. The role of topical anti-glaucoma medication remains critical in the management of chronic glaucoma worldwide but the beneficial effects of treatment are counterbalanced by the adverse effects of corneal and conjunctival toxicity. Areas covered: This article covers the effect of topical ocular drops and preservatives, particularly benzalkonium chloride, on the cornea and conjunctiva. Both basic science and clinical evidence will be presented. The first part reviews the relationship between ocular surface disease and benzalkonium chloride and the evidence from non-benzalkonium chloride preserved drops. The second part discusses the effects of benzalkonium chloride on the histopathology of the conjunctiva and its impact on clinical care as well as quality of life. Expert opinion: Topical anti-glaucoma medication will continue to be used in the management of this blinding disease for the foreseeable future. Treatment outcomes will benefit from minimized exposure to benzalkonium chloride. The development of alternative preservatives, preservative-free topical options, and non-drop therapeutics such as drug-eluting systems for the delivery of ocular medications, will be very helpful in the care of glaucoma patients.

Effect of preservative removal from fixed-combination bimatoprost/timolol on intraocular pressure lowering: a potential timolol dose-response phenomenon

PURPOSE

Many patients with glaucoma require combination therapies to achieve target intraocular pressure (IOP) and preserve visual function. Ocular hypotensives often contain a preservative (eg, benzalkonium chloride [BAK]), but preservative-free (PF) formulations have been developed for patients with sensitivity. A Phase III study found the efficacy of bimatoprost 0.03%/timolol 0.5% (bim/tim, Ganfort(®)) PF to be equivalent to that of preserved bim/tim, although a trend favoring bim/tim PF was observed. As BAK is a corneal penetration enhancer, this literature review aims to explain these findings by exploring the relationship between timolol concentration and its IOP-lowering effect.

METHODS

Systematic searches were performed in Scopus and PubMed for clinical trials published in English between 1960 and July 2014 using the keywords "timolol", "intraocular pressure", and the concentrations "1%, 0.5%, OR 0.25%". Articles that directly compared IOP-lowering effects of ≥2 concentrations of timolol were identified by manual screening, and cross-checked for duplication.

RESULTS

Seventeen studies that included 10-371 patients were evaluated; the majority were randomized (16/17), double-masked (14/17), and enrolled patients with open-angle glaucoma or ocular hypertension (12/17). All studies investigated timolol in preserved formulations. Timolol concentrations tested ranged from 0.008% to 1.5%. Of 13 studies comparing timolol 0.25% versus 0.5%, two found the 0.25% dose to have greater IOP-lowering effects, and three reported the opposite; eight reported similar IOP lowering. Results also indicate that timolol 0.5% may be more effective than higher concentrations.

CONCLUSION

The evidence suggests that timolol may have an inverted U-shaped dose-response curve, and that its optimal IOP-lowering concentration is between 0.25% and 0.5%. Compared with bim/tim, removal of the permeability enhancer BAK in bim/tim PF could have resulted in a lower timolol concentration at the target site, bringing the effective concentration within the 0.25%-0.5% range and enhancing the efficacy of bim/tim PF.

Imaging mass spectrometry of the visual system: Advancing the molecular understanding of retina degenerations

Visual sensation is fundamental for quality of life, and loss of vision to retinal degeneration is a debilitating condition. The eye is the only part of the central nervous system that can be noninvasively observed with optical imaging. In the clinics, various spectroscopic methods provide high spatial resolution images of the fundus and the developing degenerative lesions. However, the currently utilized tools are not specific enough to establish the molecular underpinnings of retinal diseases. In contrast, mass spectrometric imaging (MSI) is a powerful tool to identify molecularly specific disease indicators and classification markers. This technique is particularly well suited to the eye, where molecular information can be correlated with clinical data collected via noninvasive diagnostic imaging modalities. Recent studies during the last few recent years have uncovered a plethora of new spatially defined molecular information on several vision-threatening diseases, including age-related macular degeneration, Stargardt disease, glaucoma, cataract, as well as lipid disorders. Even though MS inside the eye cannot be performed noninvasively, by linking diagnostic and molecular information, these studies are the first step toward the development of smart ophthalmic diagnostic and surgical tools. Here, we provide an overview of current approaches applying MSI technology to ocular pathology.

Effect of topical anti-glaucoma medications on late pupillary light reflex, as evaluated by pupillometry

Purpose

The late post-illumination pupillary response (PIPR_10–30s) to blue light is reduced in glaucoma, suggesting that pupillometry can be used in clinical glaucoma evaluation. Since animal studies have indicated that common anti-glaucomatous agents affect the iris muscle, we investigated the short-term effect of the anti-glaucoma drugs on the pupillary light reflex and in particular on the PIPR_10–30s.

Methods

In this randomized, double-masked, crossover trial, pupillometry was performed before and after topical administration of latanoprost, dorzolamide, and timolol in 20 healthy subjects. Stimulus was blue (463 nm) and red light (633 nm) of 2 log (lux). Main outcome was the PIPR_10–30s to blue light. Additionally, pupil size, maximal contraction, and the early post-illumination pupillary response (PIPR_0–10s) to blue and red light were investigated. Pupil response variations between 8 a.m. and 2 p.m. were also assessed. Intraocular pressure (IOP) was measured before and 3.5 h after drug instillation.

Results

We found no drug effect on the blue light PIPR_10–30s or any other blue light pupil parameters. During the control day, the only significant variation over time was observed for the red light PIPR_0–10s (p = 0.02). Pupillary size decreased slightly with timolol (0.1 mm, p = 0.03) and dorzolamide (0.2 mm, p < 0.001), but not with latanoprost. Timolol also reduced the maximal contraction amplitude significantly during red light (p = 0.02). Intraocular pressure was significantly reduced by all three drugs after 3.5 h (p < 0.01), while it remained unchanged during the control day (p = 0.3).

Conclusion

Anti-glaucoma medications did not interfere with the blue light elicited PIPR. Dorzolamide reduced pupil size, while timolol reduced both pupil size and maximal contraction to red light, but the effect was minute and not of clinical importance.

[Original preparations versus generics--latanoprost: how similar is different?]

BACKGROUND

To test the interchangeability of the commercially available (in Germany) latanoprost drugs and their generics respectively, the concentration of the active substance was tested. Guidelines of the European Medicines Agency postulate a sufficient bioequivalence, if the range of the agent is within 80-125% of the original drug.

METHODS

All compounds of latanoprost were procured registered. The concentration of latanoprost and benzalkoniumchloride was measured by high-performance liquid chromatography (HPLC) in a validated reference labroratory for 23 generics. In addition, the mean volume of drops and the pH of the formulation were measured. The packaging label and the readability of the enclosed information leaflet were checked.

RESULTS

All products contained less than 50 μg/ml latanoprost. The deviating reduction of the active substance (mean: - 7.39%, ± 2.8%) was accompanied by fluctions of the eyedrops' mass (mean: 0.03 g, ± 0.002 g). The concentration of benzalkonium chloride was mostly increased (median: 5.45%, min: - 2.5%, max: 11.5%). The pH of the original drug and the generics (median 6.78, min: 6.62, max: 6.81) was similar to the original drug, but was significantly different from an unpreserved formulation (pH 7.18). Due to type size, the packaging leaflet was illegible for humans with impaired vision.

CONCLUSIONS

Before prescribing generics in ophthalmology, different factors have to be considered, which might influence the amount of IOP lowering in effect. In the absence of healthcare research it is still unclear, how different bottle forms of eyedrops--such as appearance (e.g. Cyrillic characters) or pressure point (administration)--reduce the adherence of glaucoma patients.

Mechanisms of benzalkonium chloride toxicity in a human trabecular meshwork cell line and the protective role of preservative-free tafluprost

BACKGROUND

Benzalkonium chloride (BAK) is a controversial ophthalmic preservative because of its prominent side-effect profile. In this study, we examined the mechanism of BAK toxicity in human trabecular meshwork cells (HTMC) and compared the effects of BAK with tafluprost free acid, which is an active form of tafluprost commercially available in a preservative-free formulation.

METHODS

Primary HTMC were treated with different BAK concentrations over various exposure times. Cell viability was quantified using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenol tetrazolium bromide assay, and apoptosis was measured by enzyme-linked immunosorbent assay. The cell viability of primary HTMC exposed to various concentrations and times of tafluprost free acid was also determined. Cells were treated with BAK and tafluprost free acid for 30 min at 37°C, and cell viability was again assessed. The effect of BAK on the gap junction protein Connexin-43 (Cx43) expression was subsequently examined.

RESULTS

BAK treatment resulted in a dose- and time-dependent decline in cell viability. Apoptosis increased following BAK treatment. Tafluprost-free acid treatment did not significantly affect cell viability. Tafluprost co-treatment with BAK resulted in an increase in cell viability as compared with BAK treatment alone. BAK treatment upregulated Cx43 expression in HTMC.

CONCLUSIONS

These results demonstrate that BAK is harmful to the health of cultured HTMC. Tafluprost is both safe and cytoprotective against BAK for these HTMC. The effect of tafluprost on the gap junctions of the HTM should be further investigated.

Cluster secondary ion mass spectrometry microscope mode mass spectrometry imaging

RATIONALE

Microscope mode imaging for secondary ion mass spectrometry is a technique with the promise of simultaneous high spatial resolution and high-speed imaging of biomolecules from complex surfaces. Technological developments such as new position-sensitive detectors, in combination with polyatomic primary ion sources, are required to exploit the full potential of microscope mode mass spectrometry imaging, i.e. to efficiently push the limits of ultra-high spatial resolution, sample throughput and sensitivity.

METHODS

In this work, a C60 primary source was combined with a commercial mass microscope for microscope mode secondary ion mass spectrometry imaging. The detector setup is a pixelated detector from the Medipix/Timepix family with high-voltage post-acceleration capabilities. The system's mass spectral and imaging performance is tested with various benchmark samples and thin tissue sections.

RESULTS

The high secondary ion yield (with respect to 'traditional' monatomic primary ion sources) of the C60 primary ion source and the increased sensitivity of the high voltage detector setup improve microscope mode secondary ion mass spectrometry imaging. The analysis time and the signal-to-noise ratio are improved compared with other microscope mode imaging systems, all at high spatial resolution.

CONCLUSIONS

We have demonstrated the unique capabilities of a C60 ion microscope with a Timepix detector for high spatial resolution microscope mode secondary ion mass spectrometry imaging.

Benzalkonium chloride and glaucoma

Glaucoma patients routinely take multiple medications, with multiple daily doses, for years or even decades. Benzalkonium chloride (BAK) is the most common preservative in glaucoma medications. BAK has been detected in the trabecular meshwork (TM), corneal endothelium, lens, and retina after topical drop installation and may accumulate in those tissues. There is evidence that BAK causes corneal and conjunctival toxicity, including cell loss, disruption of tight junctions, apoptosis and preapoptosis, cytoskeleton changes, and immunoinflammatory reactions. These same effects have been reported in cultured human TM cells exposed to concentrations of BAK found in common glaucoma drugs and in the TM of primary open-angle glaucoma donor eyes. It is possible that a relationship exists between chronic exposure to BAK and glaucoma. The hypothesis that BAK causes/worsens glaucoma is being tested experimentally in an animal model that closely reflects human physiology.