PPARγ: the dominant regulator among PPARs in dry eye lacrimal gland and diabetic lacrimal gland

Comparison of tear cytokines and neuropeptides, ocular surface parameters, and corneal nerve structure in patients with early-stage diabetes mellitus and control subjects

PURPOSE

This study aimed to assess the impact of diabetes mellitus (DM) on the corneal nerve, ocular surface, and tear cytokine and substance P (SP) levels and to compare the findings with those in control subjects.

METHODS

This cross-sectional study included 23 patients diagnosed with DM within the last 5 years and who had no systemic involvement, including diabetic retinopathy, and 22 control subjects. The ocular surface and tear film were assessed using the Ocular Surface Disease Index (OSDI) questionnaire, ocular surface staining, Schirmer, and corneal sensitivity. In vivo confocal microscopy was used to assess the architecture of the corneal nerves. The tear levels of cytokines were examined by Luminex and SP levels were measured by ELISA.

RESULTS

Both groups had similar OSDI scores, ocular surface staining, Schirmer, and corneal sensitivity measurements. The patient group had higher corneal nerve tortuosity (p = 0.015) but showed no significant difference in short or long nerve fibre density compared with the control group. Tear IL-6 and IL-8 levels were higher in the DM group (p = 0.002 and p = 0.01, respectively), whereas tear SP levels were lower in the DM group (p = 0.05). The tear SP level exhibited a strong positive correlation with total and long nerve fibre parameters (both p = 0.00).

CONCLUSIONS

The study results indicated that DM affected corneal nerve structure, tear SP, and inflammatory cytokine levels. The corneal nerves were affected and the tear SP level decreased even in patients without peripheral neuropathy, which is one of the most common complications of DM. In addition, ocular surface inflammation was observed in patients with DM, despite no ocular surface symptoms.

An update on ocular effects of antidiabetic medications

The global increase in the prevalence of type 2 diabetes has led to the development and implementation of new classes of antidiabetic medications, introducing advanced therapeutic options for the management of the disease. These new medications, though primarily designed to regulate blood glucose levels, also have applications in weight management, potentially transforming the current approaches to diabetes treatment. Newer medications, however, have ophthalmic side effects with controversies in trials and real-life data. We comprehensively assessed the ocular benefits and adverse effects of traditional and newer-generation anti-diabetic drugs. Our primary focus is on how these newer medications affect the stage of diabetic retinopathy. Additionally, we explore the associations between these medications and other ocular conditions, including age-related macular degeneration, glaucoma, orbital conditions, and diseases impacting the ocular surface. Furthermore, we provide contextual background by discussing the ocular effects of traditional anti-diabetic drugs.

Potential therapeutic effects of peroxisome proliferator-activated receptors on corneal diseases

The cornea is an avascular tissue in the eye that has multiple functions in the eye to maintain clear vision which can significantly impair one's vision when subjected to damage. Peroxisome proliferator-activated receptors (PPARs), a family of nuclear receptor proteins comprising three different peroxisome proliferator-activated receptor (PPAR) isoforms, namely, PPAR alpha (α), PPAR gamma (γ), and PPAR delta (δ), have emerged as potential therapeutic targets for treating corneal diseases. In this review, we summarised the current literature on the therapeutic effects of PPAR agents on corneal diseases. We discussed the role of PPARs in the modulation of corneal wound healing, suppression of corneal inflammation, neovascularisation, fibrosis, stimulation of corneal nerve regeneration, and amelioration of dry eye by inhibiting oxidative stress within the cornea. We also discussed the underlying mechanisms of these therapeutic effects. Future clinical trials are warranted to further attest to the clinical therapeutic efficacy.

Effect of PPARγ on oxidative stress in diabetes-related dry eye

Oxidative stress is closely associated with diabetes and can cause free radical accumulation and eventually lead to ocular surface tissue damage. The purpose of this study was to investigate peroxisome proliferator-activated receptor-γ (PPARγ) expression in the lacrimal gland (LG), meibomian gland, and cornea of diabetes-related dry eye mice and whether the PPARγ agonist rosiglitazone can alleviate the oxidative stress of the ocular surface, thereby improving the condition of diabetes-related dry eye. Quantitative RT-PCR (Q-PCR) showed that the PPARγ, catalase, glutathione peroxidase 3, and heme oxygenase-1 (HO-1) mRNA expression levels in the LG of diabetes-related dry eye mice decreased at 8 and 12 weeks. In addition, the increased levels of oxidative stress were confirmed by western blot. Although the mRNA expression levels of antioxidant enzymes in the cornea and meibomian gland decreased at 8 weeks, some of them recovered by 12 weeks. Rosiglitazone alleviated ocular surface damage and increased corneal sensitivity and tear production in diabetes-related dry eye mice. Moreover, the reactive oxygen species accumulation was reduced and the PPARγ, HO-1, and glutathione peroxidase 3 mRNA expression levels were increased in the LG. The PPARγ, HO-1, translocase of the outer membrane 20, and mitochondrial transcription factor A protein levels were also significantly increased. These results demonstrated that rosiglitazone reduced oxidative stress in the LG of diabetes-related dry eye mice, at least in part, by activating PPARγ to up-regulate antioxidant enzyme expression.

Changes in the meibomian glands in postmenopausal women with primary acquired nasolacrimal duct obstruction: a prospective study

BACKGROUND

Primary acquired nasolacrimal duct obstruction (PANDO) is frequently encountered in perimenopausal women, causing tear flow stagnation and resulting in a variety of ocular discomfort symptoms. However, little is known about the alterations in the meibomian gland in postmenopausal women with PANDO. Hence, this study investigated the changes in the meibomian gland and ocular surface in postmenopausal women with PANDO.

METHODS

This prospective study included 60 eyes of 60 postmenopausal women with PANDO (PANDO group) and 30 eyes of 30 postmenopausal women without PANDO (control group). The PANDO group was further subdivided into incomplete and complete PANDO groups, based on the degree of nasolacrimal duct obstruction. The patients' symptoms were evaluated using the ocular surface disease index questionnaire. The meibomian gland and ocular surface were assessed using the Keratograph 5 M. Other ophthalmologic examinations included the tear break-up time, corneal fluorescein staining, meibomian gland expression, and Schirmer I test. The correlations between the degree of nasolacrimal duct obstruction and other metrics were analyzed.

RESULTS

The loss ratio of the upper eyelid was greater in the incomplete PANDO group than in the control group (p = 0.023). Meibomian gland distortion of the upper eyelid was more severe in the control group than in the complete PANDO group (p = 0.022). The non-invasive tear meniscus height was greater, whereas the intensity of corneal fluorescein staining was lower in the PANDO group than in the control group (all p < 0.05). The degree of nasolacrimal duct obstruction was positively associated with the non-invasive tear meniscus height and ocular surface disease index scores (p < 0.001 and p < 0.001, respectively). Corneal fluorescein staining and meibomian gland distortion of the upper eyelid were negatively correlated with the degree of nasolacrimal duct obstruction (p = 0.01 and p = 0.007, respectively).

CONCLUSION

Postmenopausal women with PANDO exhibit significant morphological changes in the meibomian gland. More attention should be paid to meibomian gland loss in postmenopausal women with incomplete PANDO, as it is crucial for identifying meibomian gland impairments in patients with PANDO.

The role of sphingolipids in meibomian gland dysfunction and ocular surface inflammation

Inflammation occurs in response to tissue injury and invasion of microorganisms and is carried out by the innate and adaptive immune systems, which are regulated by numerous chemokines, cytokines, and lipid mediators. There are four major families of bioactive lipid mediators that play an integral role in inflammation - eicosanoids, sphingolipids (SPL), specialized pro-resolving mediators (SPM), and endocannabinoids. SPL have been historically recognized as important structural components of cellular membranes; their roles as bioactive lipids and inflammatory mediators are recent additions. Major SPL metabolites, including sphingomyelin, ceramide, ceramide 1-phosphate (C1P), sphingosine, sphingosine 1-phosphate (S1P), and their respective enzymes have been studied extensively, primarily in cell-culture and animal models, for their roles in cellular signaling and regulating inflammation and apoptosis. Less focus has been given to the involvement of SPL in eye diseases. As such, the aim of this review was to examine relationships between the SPL family and ocular surface diseases, focusing on their role in disease pathophysiology and discussing the potential of therapeutics that disrupt SPL pathways.

Potential Mechanisms of White Peony against Primary Sjögren's Syndrome Based on Network Pharmacology and Molecular Docking

BACKGROUND

Multiple system and organ damage occurs with the continuous progression of primary Sjögren's syndrome (pSS), and the lack of specific drugs against this disease is a huge challenge. White peony (WP), a widely used traditional Chinese herb, has been confirmed to have a therapeutic value in pSS. However, the specific mechanisms of WP in the treatment of pSS are unknown.

METHODS

The active ingredients and their targets in WP were searched on the Traditional Chinese Medicine Systems Pharmacology Database and Analysis Platform (TCMSP), and disease-related targets were collected from GeneCards, Online Mendelian Inheritance in Man (OMIM), and the Therapeutic Target Database (TTD). The overlapping targets were acquired by taking the intersection. A protein-protein interaction (PPI) network was structured using the STRING database. A disease-drug-ingredient-target (D-D-I-T) network was built using Cytoscape software. By filtering twice, core targets were acquired. Gene Ontology (GO) and Kyoto Encyclopedia Gene and Genome (KEGG) pathway enrichment analysis were accompanied by R packages. Finally, molecular docking was used to verify the abovementioned results.

RESULTS

In total, we screened 88 WP-related targets, 1480 pSS-related targets, and 32 overlapping targets. D-D-I-T Network analysis displayed six main active ingredients of WP, which played a significant therapeutic role in pSS. Further topological analysis selected seven core target genes, including IL-6, TNF, PPARγ, AKT1, CASP3, NOS3, and JUN. GO and KEGG analysis were used to elucidate pharmacological mechanisms, mainly acting in the AGE-RAGE signaling pathway. Molecular docking proved that paeoniflorin bound well with core targets.

CONCLUSION

Our study revealed that IL-6, TNF, AKT1, CASP3, NOS3, and JUN may be pathogenic target genes, and PPARγ may be a protective target gene. The main active ingredients of WP mainly played a therapeutic role via the AGE-RAGE signaling pathway. These findings provide a fundamental and theoretical basis for the clinical application of WP.

Targeting of gallbladder megalin receptors with DHA-conjugated limonene albumin nanoparticles

Gallbladder stones are a major pathogenic factor leading to cholecystitis, and it is increasingly important to explore innovative drug delivery methods for gallstones. In the present study, docosahexaenoic acid-coupled limonene bovine serum albumin nanoparticles (LIM-DHA-BSA-NPs) were constructed. The LIM-DHA-BSA-NPs are spherical structures, and the distribution was relatively uniform, and, more importantly, it has low cytotoxicity and good safety. The LIM-DHA-BSA-NPs solution shows higher uptake rates by RAW264.7 cells when compared with free limonene (LIM). The fluorescence intensity of FITC-modified BSA NPs was significantly higher than that of free FITC, which further indicated that the uptake of DHA-conjugated BSA NPs by RAW264.7 cells was stronger than that of the free drugs. Moreover, the in vivo distribution experiment showed that the enrichment of DiD-loaded BSA NPs in the gallbladder was significantly enhanced when compared with that of free DiD. The semi-quantitative fluorescence intensity results showed that the uptake of DiD-DHA-BSA-NPs was 4.5 times higher when compared with the free DiD. It is preliminarily shown that the DHA-conjugated BSA NPs that were constructed, have an ability to target the gallbladder. Furthermore, the Pearson colocalization coefficient Rcoloc from in vivo colocalization results indicates that the DHA-BSA-NPs had a good colocalization effect on the gallbladder epithelial cells (GBECs). In addition, the LIM-DHA-BSA-NPs solution not only significantly reduced the concentration of nitric oxide (NO) secreted by inflammatory model cells and the number of peripheral blood leukocytes in guinea pigs with cholecystitis, but also significantly decreased the activities of the aspartate transaminase (AST), alkaline phosphatase (ALP), alanine aminotransferase (ALT), glutamyl endopeptidase (GGT), total bile acid (TBA), and total bilirubin (TBIL) enzymes. Collectively, the LIM-DHA-BSA-NPs could be used as an effective anti-inflammatory agent at the cellular and animal levels. This experiment, for the first time, showed that DHA-conjugated BSA NPs could be absorbed into GBECs by megalin receptor-mediated endocytosis and then they exert an anti-cholecystitis effect because of the LIM. The active uptake of DHA-conjugated BSA NPs by the megalin receptors of the GBECs is expected to become an effective therapeutic strategy for cholecystolithiasis.

CannabinEYEds: The Endocannabinoid System as a Regulator of the Ocular Surface Nociception, Inflammatory Response, Neovascularization and Wound Healing

The endocannabinoid system (ECS) is a complex regulatory system, highly conserved among vertebrates. It has been widely described in nearly all human tissues. In the conjunctiva and cornea, the ECS is believed to play a pivotal role in the modulation of the local inflammatory state as well as in the regulation of tissue repair and fibrosis, neo-angiogenesis and pain perception. This review aims to summarize all the available data on ECS expression and its function in ocular surface structures to provide a specific insight concerning its modulation in dry eye disease, and to propose directions for future research.