Prolonged Ocular Inflammation in Endotoxin-Induced Uveitis in Lysosomal Phospholipase A2-Deficient Mice

Morroniside Ameliorates Endotoxin-Induced Uveitis by Regulating the M1/M2 Polarization Balance of Macrophages

Background

Inflammation is closely associated with the pathogenesis of various ocular diseases. Uveitis is a condition characterized by the inflammation of the uvea and ocular tissues that causes extreme pain, decreases visual acuity, and may eventually lead to blindness. The pharmacological functions of morroniside, isolated from Cornus officinalis, are multifarious. Morroniside exerts various therapeutic effects, e.g., it ameliorates inflammation. However, the specific anti-inflammatory effect of morroniside on lipopolysaccharide-induced uveitis has not been reported widely. In this study, we investigated the anti-inflammatory effect of morroniside on uveitis in mice.

Methods

An endotoxin-induced uveitis (EIU) mouse model was constructed and treated with morroniside. The inflammatory response was observed using slit lamp microscopy, and histopathological changes were observed by hematoxylin-eosin staining. The cell count in the aqueous humor was measured using a hemocytometer. The concentrations of TNF-α, IL-6, and IL-1β in the ciliary body and retina were measured using ELISA kits. The expression of iNOS and Arg-1 in the ciliary body and retina was measured by immunofluorescence costaining, and western blotting was performed to measure the protein expression of JAK2, p-JAK2, STAT3, and p-STAT3 in the ciliary body and retina.

Results

Morroniside effectively ameliorated the inflammatory response in EIU mice. Furthermore, morroniside significantly reduced the concentrations of IL-1β, IL-6, and TNF-α in the ciliary body and retina. Morroniside treatment significantly reduced the expression of iNOS in the ciliary body and retinal tissues. It also significantly inhibited p-JAK2 and p-STAT3 expression and promoted Arg-1 expression. In addition, morroniside boosted the effect of JAK inhibitors on the above indices.

Conclusions

Collectively, these findings suggest that morroniside may protect against LPS-induced inflammation in uveitis by promoting M2 polarization through the inhibition of the JAK/STAT pathway.

Inhibition of lysosomal phospholipase A2 predicts drug-induced phospholipidosis

Phospholipidosis, the excessive accumulation of phospholipids within lysosomes, is a pathological response observed following exposure to many drugs across multiple therapeutic groups. A clear mechanistic understanding of the causes and implications of this form of drug toxicity has remained elusive. We previously reported the discovery and characterization of a lysosome-specific phospholipase A2 (PLA2G15) and later reported that amiodarone, a known cause of drug-induced phospholipidosis, inhibits this enzyme. Here, we assayed a library of 163 drugs for inhibition of PLA2G15 to determine whether this phospholipase was the cellular target for therapeutics other than amiodarone that cause phospholipidosis. We observed that 144 compounds inhibited PLA2G15 activity. Thirty-six compounds not previously reported to cause phospholipidosis inhibited PLA2G15 with IC₅₀ values less than 1 mM and were confirmed to cause phospholipidosis in an in vitro assay. Within this group, fosinopril was the most potent inhibitor (IC₅₀ 0.18 μM). Additional characterization of the inhibition of PLA2G15 by fosinopril was consistent with interference of PLA2G15 binding to liposomes. PLA2G15 inhibition was more accurate in predicting phospholipidosis compared with in silico models based on pKa and ClogP, measures of protonation, and transport-independent distribution in the lysosome, respectively. In summary, PLA2G15 is a primary target for cationic amphiphilic drugs that cause phospholipidosis, and PLA2G15 inhibition by cationic amphiphilic compounds provides a potentially robust screening platform for potential toxicity during drug development.

Drops of Lactiplantibacillus plantarum CRL 759 culture supernatant attenuates eyes inflammation induced by lipopolysaccharide

Anti-inflammatory effect of soluble secreted compounds of probiotic bacteria was widely demonstrated as therapy for different inflammatory diseases, but was not investigated in inflammatory eye disorders. The aim of this study was to determine whether Lactiplantibacillus plantarum CRL759 cell-free supernatant reduced inflammatory parameters and clinical signs in ocular inflammations. First, we evaluated the effect of L. plantarum CRL759 supernatant in vitro on human retinal cell line, ARPE-19 cells, stimulated with lipopolysaccharide (LPS). Then, we investigated in vivo its capacity to decrease inflammation by local administration on the eyes of mice with endotoxin induced inflammation. In vitro assays demonstrated that L. plantarum CRL759 supernatant reduced the production of interleukin (IL)-6, IL-8, nitric oxide and thiobarbituric acid reactive substances in LPS-stimulated ARPE-19 cells. Our in vivo data proved that L. plantarum supernatant significantly reduced the clinical score of endotoxin treated mice and diminished levels of tumour necrosis factor alpha, interferon gamma and protein concentration in aqueous humour. Histological examination showed reduction of infiltrating inflammatory cells in the posterior segment of the eyes. As far as we know, this is the first report showing that Lactobacillus spp. supernatant administered as drops reduces some parameters of ocular inflammation. This promising strategy is safe and could alleviate symptoms and signs of ocular inflammation in people that are refractories to the conventional therapies.

Lysosomal phospholipase A2

Lysosomal phospholipase A2 (PLA2G15) is a ubiquitous enzyme uniquely characterized by a subcellular localization to the lysosome and late endosome. PLA2G15 has an acidic pH optimum, is calcium independent, and acts as a transacylase in the presence of N-acetyl-sphingosine as an acceptor. Recent studies aided by the delineation of the crystal structure of PLA2G15 have clarified further the catalytic mechanism, sn-1 versus sn-2 specificity, and the basis whereby cationic amphiphilic drugs inhibit its activity. PLA2G15 has recently been shown to hydrolyze short chain oxidized phospholipids which access the catalytic site directly based on their aqueous solubility. Studies on the PLA2G15 null mouse suggest a role for the enzyme in the catabolism of pulmonary surfactant. PLA2G15 may also have a role in host defense and in the processing of lipid antigens for presentation by CD1 proteins. This article is part of a Special Issue entitled Novel functions of phospholipase A2 Guest Editors: Makoto Murakami and Gerard Lambeau.