The ocular surface toxicity of paraquat

Experimental glaucoma triggers a pro-oxidative and pro-inflammatory state in the rat cornea

BACKGROUND

Increasing evidence suggests that glaucoma affects the ocular surface. We aimed to investigate the cellular mechanisms underlying the glaucoma-associated corneal alterations in an animal model.

METHODS

Wistar rats underwent the cauterization of two episcleral veins of the left eye to elevate the intraocular pressure (ipsilateral, G-IL). Control animals received a sham procedure (C-IL). Contralateral eyes did not receive any procedure (G-CL or C-CL). Enzymes related to the redox status, oxidative damage to macromolecules, and inflammatory markers were assessed in corneal lysates.

RESULTS

Compared to C-IL, NOX4, NOX2, and iNOS expression was increased in G-IL (68%, p < 0.01; 247%, p < 0.01; and 200%, p < 0.001, respectively). We found an increase in SOD activity in G-IL (60%, p < 0.05). The GSH/GSSG ratio decreased in G-IL (80%, p < 0.05), with a decrease in GR activity (40%, p < 0.05). G-IL displayed oxidative (90%, p < 0.01) and nitrosative (40%, p < 0.05) protein damage, and enhanced lipid peroxidation (100%, p < 0.01). G-IL group showed an increased in CD45, CD68 and F4/80 expression (50%, p < 0.05; 190%, p < 0.001 and 110%, p < 0.05, respectively). G-CL displayed a higher expression of Nrf2 (60%, p < 0.001) and increased activity of SOD, CAT, and GPx (60%, p < 0.05; 90%, p < 0.01; and 50%, p < 0.05, respectively).

CONCLUSIONS

Glaucoma induces a redox imbalance in the ipsilateral cornea with an adaptive response of the contralateral one.

GENERAL SIGNIFICANCE

Our study provides a possible mechanism involving oxidative stress and inflammation that explains the corneal alterations observed in glaucoma. We demonstrate that these changes extend not only to the ipsilateral but also to the contralateral cornea.

Toxic External Exposure Leading to Ocular Surface Injury

The surface of the eye is directly exposed to the external environment, protected only by a thin tear film, and may therefore be damaged by contact with ambient particulate matter, liquids, aerosols, or vapors. In the workplace or home, the eye is subject to accidental or incidental exposure to cleaning products and pesticides. Organic matter may enter the eye and cause infection. Ocular surface damage can trigger a range of symptoms such as itch, discharge, hyperemia, photophobia, blurred vision, and foreign body sensation. Toxin exposure can be assessed clinically in multiple ways, including via measurement of tear production, slit-lamp examination, corneal staining, and conjunctival staining. At the cellular level, environmental toxins can cause oxidative damage, apoptosis of corneal and conjunctival cells, cell senescence, and impaired motility. Outcomes range from transient and reversible with complete healing to severe and sight-compromising structural changes. Classically, evaluation of tolerance and safety was carried out using live animal testing; however, new in vitro and computer-based, in silico modes are superseding the gold standard Draize test. This review examines how environmental features such as pollutants, temperature, and seasonality affect the ocular surface. Chemical burns to the eye are considered, and approaches to protect the ocular surface are detailed.

Novel computational models offer alternatives to animal testing for assessing eye irritation and corrosion potential of chemicals

Eye irritation and corrosion are fundamental considerations in developing chemicals to be used in or near the eye, from cleaning products to ophthalmic solutions. Unfortunately, animal testing is currently the standard method to identify compounds that cause eye irritation or corrosion. Yet, there is growing pressure on the part of regulatory agencies both in the USA and abroad to develop New Approach Methodologies (NAMs) that help reduce the need for animal testing and address unmet need to modernize safety evaluation of chemical hazards. In furthering the development and applications of computational NAMs in chemical safety assessment, in this study we have collected the largest expertly curated dataset of compounds tested for eye irritation and corrosion, and employed this data to build and validate binary and multi-classification Quantitative Structure-Activity Relationships (QSAR) models that can reliably assess eye irritation/corrosion potential of novel untested compounds. QSAR models were generated with Random Forest (RF) and Multi-Descriptor Read Across (MuDRA) machine learning (ML) methods, and validated using a 5-fold external cross-validation protocol. These models demonstrated high balanced accuracy (CCR of 0.68–0.88), sensitivity (SE of 0.61–0.84), positive predictive value (PPV of 0.65–0.90), specificity (SP of 0.56–0.91), and negative predictive value (NPV of 0.68–0.85). Overall, MuDRA models outperformed RF models and were applied to predict compounds’ irritation/corrosion potential from the Inactive Ingredient Database, which contains components present in FDA-approved drug products, and from the Cosmetic Ingredient Database, the European Commission source of information on cosmetic substances. All models built and validated in this study are publicly available at the STopTox web portal (https://stoptox.mml.unc.edu/). These models can be employed as reliable tools for identifying potential eye irritant/corrosive compounds

Occupational Paraquat and Glyphosate Exposure May Decline Renal Functions among Rural Farming Communities in Sri Lanka

Extensive use of herbicides is common among rural agricultural workers in Sri Lanka. Recent studies have postulated their role in the development of chronic kidney disease of unknown etiology (CKDu). Paraquat and glyphosate are leading herbicides used by sugarcane farmers (SF), hence occupational exposure is inevitable. This study examined the expression of urinary paraquat, glyphosate and biomarkers among residential SF in CKDu emerging regions, Warunagama (WA) and Rahathangama (RH), in the Uva Province with non-endemic Matara (MA) in the Southern Province of Sri Lanka. Urinary glyphosate, Paraquat, kidney injury molecule -1 (KIM-1), neutrophil gelatinase-associated lipocalin (NGAL) and β2-microglobulin (B2M) were determined using enzyme-linked immunosorbent assays (ELISA). Urinary creatinine, microalbumin, serum creatinine (SCr), serum cystatin C, estimated glomerular filtration rate (eGFR), and albumin creatinine ratio (ACR) were also assessed. Generally, herbicide residues and kidney injury biomarkers were higher in SF compared to the non-endemic MA. Creatinine-adjusted urinary glyphosate and paraquat levels were significantly higher in WA compared to MA. ACR in RH (median 14.9; IQR 5.4-393.1 mg/g) and WA (23.7; 11.5-64.6) was significantly higher than MA (4.3; 2.2-6.7). This study reports 39 individuals with impaired kidney function among SF in Sri Lanka for the first time. Urinary NGAL levels were significantly higher in both WA (median 2.14; IQR 1.28-6.15 ng/mg Cr) and RH (3.09; 1.15-9.09) compared to MA (1.28; 0.56-2.81). However, urinary KIM-1 levels in RH (3.2; 1.29-106.1 ng/g Cr) and WA (3.6; 1.94-115.1) were not significantly higher in MA (1.74; 0.76-116.9). Urinary NGAL (r = 0.493), eGFR (r = -0.147) and ACR (r = 0.171) significantly correlated with urinary glyphosate, but not with urinary paraquat levels. Urinary KIM-1 levels did not correlate with either urinary glyphosate or paraquat, while urinary B2M and serum cystatin C levels showed significant correlation with urinary glyphosate levels. The current study reports higher urinary herbicide levels among sugarcane farmers in WA and RH, and that is potentially linked to the subsequent decline in kidney function, as indicated by ACR, eGFR, and NGAL. We posit that these indicators may serve as markers to detect renal injury among herbicide-exposed SF in Rural Sri Lanka.

Systemic Paraquat Intoxication Presenting with Peripheral Ulcerative Keratitis: A Case Report and Literature Review

PURPOSE

To describe a rare case of systemic paraquat poisoning presenting with peripheral ulcerative keratitis.

METHODS

Case report and literature review.

RESULTS

Two days after a mouthful of paraquat ingestion, a 48-year-old man presented with painful oral ulcers, abnormal liver functions, and acute kidney injury, followed by the development of crescent-shaped corneal erosions along the limbus and progressive visual impairment in both eyes. Paraquat-induced peripheral ulcerative keratitis was suspected and the patient was treated with intensive topical steroid along with systemic steroid. He recovered completely with good visual outcomes after treatment.

CONCLUSIONS

Peripheral ulcerative keratitis is usually an immune-mediated ocular condition, and may be a complication associated with systemic paraquat poisoning. Proper diagnosis and adequate treatment are important for visual recovery.

The role of endocrine disruptors in ocular surface diseases

Endocrine disruptors are a group of compounds that occur in increasing amounts in the environment. These compounds change the hormone homeostasis of the target organs regulated by those hormones, mostly by binding to their receptors and affecting their signaling pathways. Among the hormones altered by endocrine disruptors are sex hormones, thyroid hormones, and insulin. Studies have documented abnormalities in the reproductive and metabolic systems of various animal species exposed to endocrine disruptors. Endocrine disruptors can play a significant role in ocular diseases once hormone deficiency or excess are involved in the mechanism of that disease. Cataracts, dry eye disease and retinal diseases, such as macular hole and diabetic retinopathy, are some of the frequent problems where hormones have been implicated. We found that some compounds function as endocrine disruptors in the metabolism of body organs and systems. The increasing frequency of dry eye and other ocular diseases indicates the need to better investigate the potential relationships beyond the isolated associations mentioned by patients and documented as rare case reports. The evidence from case-control studies and experimental assays can provide the information necessary to confirm the endocrine effects of these chemicals in the pathophysiology of dry eye disease. We hypothesize that endocrine disruptors may contribute to the increase of ocular diseases, such as dry eye disease, in recent years.

Effectiveness of heparin eye drops in paraquat-induced ocular injury

PURPOSE

To evaluate the efficacy of heparin eye drops in the treatment of paraquat-induced ocular surface injury.

DESIGN AND METHODS

In this retrospective study, we included 25 patients (31 eyes) with paraquat-induced ocular surface injury, who attended the Affiliated Hospital of Weifang Medical University between October 2008 and October 2013. The patients were split into two groups according to whether or not received heparin eye drops. The clinical data were compared between the two groups, i.e. clinical histories, results of examinations, treatments and outcomes.

RESULTS

Eleven patients (group A, 15 eyes) received prompt irrigation with 0.9% saline every two hours, 0.1% pranoprofen eye drops four times a day, 20% autologous serum every two hours, recombinant bovine basic fibroblast growth factor eye-gel two times a day, oral vitamin C 2.0 g and prednisone 30 mg daily. Fourteen patients (group B, 16 eyes) received additional treatment with heparin eye drops. Ten eyes in group A and seven eyes in group B developed a pseudomembrane on the ocular surface at significantly different rate (mean ± SD) of 1.20 ± 1.01 and 0.43 ± 0.51, respectively (t = 2.66, p = 0.01). Seven eyes among 10 had a pseudomembrane reoccurred in group A while none had a pseudomembrane reoccurred in group B (Fisher's exact test, p = 0.01). No significant differences were seen in the duration of epithelial recovery between the two groups: 15.13 ± 5.13 days in group A and 16.81 ± 5.56 days in group B (t = 0.87, p = 0.39). After the treatment, mild corneal opacity and pannus were observed in five patients of group A and four patients of group B, without any significant difference between the two groups (p = 0.70).

CONCLUSIONS

The paraquat-induced ocular surface injury observed in this case series was characterized by the formation of conjunctival pseudomembrane with good prognosis and mild complications. Heparin eye drops reduce the occurrence, especially the reoccurrence of pseudomembrane. Further studies are warranted.

Total ocular surface amniotic membrane transplantation for paraquat-induced ocular surface injury

OBJECTIVE

To evaluate the therapeutic efficacy of modified amniotic membrane transplantation (MAMT) for paraquat-induced ocular surface injury.

DESIGN

Retrospective case series.

PARTICIPANTS

Thirty patients (30 eyes) with paraquat-induced ocular surface injury.

METHODS

Among the patients, 8 underwent MAMT, 14 received conventional amniotic membrane transplantation (AMT), and 8 were treated with simple drug therapy (DT). Features related to the damage, corneal epithelial defect closure time, visual acuity, stromal haze, and complications were recorded.

RESULTS

In the MAMT and AMT groups, visual acuity in all eyes recovered to the preinjury level; in the DT group, visual acuity in 3 eyes (37.5%) recovered to the preinjury level. The mean corneal epithelial defect closure time was 7.6 ± 2.7 days in the MAMT group, 9.8 ± 3.6 days in the AMT group, and 18.2 ± 5.2 days in the DT group (p < 0.05). There was a significant difference in the symblepharon rate after treatment among the 3 groups (MAMT: 0%, AMT: 35.7%, DT: 87.5%; p < 0.05). Although the tear secretion was reduced in all groups, it was significantly lower in the DT group compared with the MAMT and AMT groups (p < 0.05).

CONCLUSIONS

Paraquat-induced ocular injuries can lead to whole ocular surface damage. MAMT treatment in a timely manner can effectively promote the repair of the ocular surface and reduce the complications from symblepharon.

Ocular toxicity from pesticide exposure: A recent review

Toxic effects on eyes result from exposure to pesticides via inhalation, ingestion, dermal contact and ocular exposure. Exposure of unprotected eyes to pesticides results in the absorption in ocular tissue and potential ocular toxicity. Recent literature on the risks of ocular toxicity from pesticide exposure is limited.Ocular toxicity from pesticide exposure, including the dose-response relationship, has been studied in different animal species. Cholinesterase enzymes have been detected in animal ocular tissue, with evidence of organophosphate-induced inhibition. Pathological effects of pesticides have been observed in conjunctiva, cornea, lens, retina and the optic nerve. Pesticide exposure has been associated with retinopathy in agricultural workers and wives of farmers who used pesticides. Saku disease, an optico-autonomic peripheral neuropathy, has been described in Japan in people living in an area where organophosphates were used. Pesticide exposure is also associated with abnormal ocular movements.Progressive toxic ocular effects leading to defective vision are a serious health concern. Agricultural workers are at high risk of exposure to pesticides and associated ocular toxicity. Primary prevention is the appropriate method of protecting eyes from pesticide-related damage. This includes improved eye safety and care in workplaces, and effective pesticide regulation for maintenance of public eye health.

Suicide victim of paraquat poisoning make suitable corneal donor

This report addresses the possibility of expanding transplant corneal donor pool by inclusion of more patients who have suffered poisoning with paraquat pre-mortem. A 27-year-old depressed man committed suicide by ingesting 50 mL of 24% paraquat (Gramoxone, Syngenta, Taiwan). He was treated aggressively with gastric lavage, with large amounts of normal saline, followed by infusion of activated charcoal and magnesium citrate. Blood paraquat level was 1.90 μg/mL. Charcoal hemoperfusion was performed for 8 hours using a charcoal-containing dialysis machine. Furthermore, pulse therapies of cyclophosphamide (15 mg/kg/day for 2 days) and methylprednisolone (1 g/day for 3 days) were administered, followed by dexamethasone (20 mg/day for 14 days). Methylprednisolone pulse therapy was repeated since PaO(2) on the 15th day of poisoning was <60 mm Hg. Chest radiography demonstrated diffuse ground glass opacities of both lungs, with thickening of the intralobular interstitium, compatible with interstitial pneumonitis. Arterial blood gas found persistent hypoxemia and large alveolar-arterial oxygen tension differences. Respiratory failure developed on the 21st day and he was intubated for mechanical ventilatory support. As the patient expressed his wish for organ donation, the corneas were harvested after expiration on the 22nd day. His corneas were transplanted in two recipients and visual acuities of the recipients were doing well at 6 months after transplantation.

Oxidative stress in diseases of the human cornea

Intense exposure to light, robust metabolic activity, and high oxygen tension render the human eye particularly vulnerable to oxidative damage and the list of ophthalmological disorders implicating reactive oxygen and nitrogen species is rapidly expanding. Here, we review the roles of oxidative stress in the etiopathogeneses and pathophysiology of diseases of the human cornea including pterygium, keratoconus, trauma and chemical injury, and a host of inflammatory, metabolic, degenerative, and iatrogenic conditions. Data from animal and tissue culture experimentation germane to these conditions are also adduced.

Paraquat poisonings: mechanisms of lung toxicity, clinical features, and treatment

Paraquat dichloride (methyl viologen; PQ) is an effective and widely used herbicide that has a proven safety record when appropriately applied to eliminate weeds. However, over the last decades, there have been numerous fatalities, mainly caused by accidental or voluntary ingestion. PQ poisoning is an extremely frustrating condition to manage clinically, due to the elevated morbidity and mortality observed so far and due to the lack of effective treatments to be used in humans. PQ mainly accumulates in the lung (pulmonary concentrations can be 6 to 10 times higher than those in the plasma), where it is retained even when blood levels start to decrease. The pulmonary effects can be explained by the participation of the polyamine transport system abundantly expressed in the membrane of alveolar cells type I, II, and Clara cells. Further downstream at the toxicodynamic level, the main molecular mechanism of PQ toxicity is based on redox cycling and intracellular oxidative stress generation. With this review we aimed to collect and describe the most pertinent and significant findings published in established scientific publications since the discovery of PQ, focusing on the most recent developments related to PQ lung toxicity and their relevance to the treatment of human poisonings. Considerable space is also dedicated to techniques for prognosis prediction, since these could allow development of rigorous clinical protocols that may produce comparable data for the evaluation of proposed therapies.