Exercise training prevents increased intraocular pressure and sympathetic vascular modulation in an experimental model of metabolic syndrome

Link Between Metabolic Syndrome, Inflammation, and Eye Diseases

Metabolic syndrome (MetS)-a cluster of conditions including obesity, hypertension, dyslipidemia, and insulin resistance-is increasingly recognized as a key risk factor for the development of various eye diseases. The metabolic dysfunctions associated with this syndrome contribute to vascular and neurodegenerative damage within the eye, influencing disease onset and progression. Understanding these links highlights the importance of early diagnosis and management of metabolic syndrome to prevent vision loss and improve ocular health outcomes. This review explores the intricate interplay between metabolic syndrome, chronic low-grade inflammation, and eye diseases such as diabetic retinopathy, age-related macular degeneration, glaucoma, and dry eye syndrome. It highlights how inflammatory mediators, oxidative damage, and metabolic dysregulation converge to compromise ocular structures, including the retina, optic nerve, and ocular surface. We discuss the molecular and cellular mechanisms underpinning these associations and examine evidence from clinical and experimental studies. Given the rising global prevalence of metabolic syndrome, addressing this connection is crucial for improving overall patient outcomes and quality of life. Future research should focus on delineating the precise mechanisms linking these diseases as well as exploring targeted interventions that address both metabolic and ocular health.

Insulin resistance in the retina: possible implications for certain ocular diseases

Insulin resistance (IR) is becoming a worldwide medical and public health challenge as an increasing prevalence of obesity and metabolic disorders. Accumulated evidence has demonstrated a strong relationship between IR and a higher incidence of several dramatically vision-threatening retinal diseases, including diabetic retinopathy, age-related macular degeneration, and glaucoma. In this review, we provide a schematic overview of the associations between IR and certain ocular diseases and further explore the possible mechanisms. Although the exact causes explaining these associations have not been fully elucidated, underlying mechanisms of oxidative stress, chronic low-grade inflammation, endothelial dysfunction and vasoconstriction, and neurodegenerative impairments may be involved. Given that IR is a modifiable risk factor, it may be important to identify patients at a high IR level with prompt treatment, which may decrease the risk of developing certain ocular diseases. Additionally, improving IR through the activation of insulin signaling pathways could become a potential therapeutic target.

Long-term high fructose intake promotes lacrimal gland dysfunction by inducing gut dysbiosis in mice

The lacrimal gland is essential for maintaining ocular surface health through the secretion of the aqueous layer of the tear film. It is therefore important to explore the intrinsic and extrinsic factors that affect the structure and function of the lacrimal gland and the mechanisms underlying them. With the prevalence of Westernized diets characterized by high sugar and fat content, the susceptibility to many diseases, including ocular diseases, is increased by inducing dysbiosis of the gut microbiome. Here, we found that the composition, abundance, and diversity of the gut microbiome was significantly altered in mice by drinking 15% high fructose water for one month, as determined by 16S rRNA sequencing. This was accompanied by a significant increase in lipid deposition and inflammatory cell infiltration in the extraorbital lacrimal glands (ELGs) of mice. Transcriptome analysis based on bulk RNA-sequencing revealed abnormal activation of some of several metabolic and immune-related pathways. In addition, the secretory response to stimulation with the cholinergic receptor agonist pilocarpine was significantly reduced. However, when the composition and diversity of the gut microbiome of high fructose intake (HFI)-treated mice were improved by transplanting feces from normal young healthy mice, the pathological alterations in ELG structure, inflammatory cell infiltration, secretory function and transcriptome analysis described above were significantly reversed compared to age-matched control mice. In conclusion, our data suggest that prolonged HFI may cause pathological damage to the structure and function of the ELG through the induction of gut dysbiosis. Restoration of intestinal dysbiosis in HFI-treated mice by fecal transplantation has a potential role in ameliorating these pathological impairments.

Sympathetic activation leads to Schlemm's canal expansion via increasing vasoactive intestinal polypeptide secretion from trabecular meshwork

We previously demonstrated vasoactive intestinal polypeptide (VIP) eyedrops reduce intraocular pressure (IOP) and stabilize cytoskeleton of the Schlemm's canal (SC) endothelium in a chronic ocular hypertension rat model. Here we determine if the trabecular meshwork (TM) releases endogenous VIP and affect SC in paracrine manner, and whether this cellular interaction via VIP is strengthened under stimulated sympathetic activity. A rat model of moderate-intensity exercise was established to stimulate sympathetic activation. IOP post exercise was measured by a rebound tonometer. Sympathetic nerve activity at the TM was immunofluorescence-stained with DβH and PGP9.5. Morphological changes of TM and SC were quantitatively measured by hematoxylin-eosin (HE) staining. Further, epinephrine was applied to mimic sympathetic excitation on primary rat TM cells, and ELISA to measure VIP levels in the medium. The cytoskeleton protective effect of VIP in the epinephrine-stimulated conditioned medium (Epi-CM) was evaluated in oxidative stressed human umbilical vein endothelial cells (HUVECs). Elevated sympathetic nerve activity was found at TM post exercise. Changes accompanying the sympathetic excitation included thinned TM, expanded SC and decreased IOP, which were consistent with epinephrine treatment. Epinephrine decreased TM cell size, enhanced VIP expression and release in the medium in vitro. Epi-CM restored linear F-actin and cell junction integrity in H₂O₂ treated HUVECs. Blockage of VIP receptor by PG99-465 attenuated the protective capability of Epi-CM. VIP expression was upregulated at TM and the inner wall of SC post exercise in vivo. PG99-465 significantly attenuated exercise-induced SC expansion and IOP reduction. Thus, the sympathetic activation promoted VIP release from TM cells and subsequently expanded SC via stabilizing cytoskeleton, which resulted in IOP reduction.

Do Age and Sex Play a Role in the Intraocular Pressure Changes after Acrobatic Gymnastics?

To evaluate the effects of an acrobatic gymnastics (AG) training session on intraocular pressure (IOP), a familiarization session was employed to confirm the participant's suitability for the study. Forty-nine gymnasts (63.27% females, 18-40 years old) voluntarily agreed to participate. As age, sex, baseline IOP, and central corneal thickness (CCT) were considered as potential predictors of the IOP variations, in the second session measurements of the above parameters were taken before and after 90 min of AG. A mixed-factorial analysis of variance evaluated differences. Linear regression was conducted to potentially predict the IOP variation with the exercise. After the scheduled exercise, highly significant (p < 0.001, effect size: 0.73) reductions in IOP, but no significant changes in CCT (p = 0.229), were observed. IOP was significantly modified in males, older than 25 years, and subjects with baseline IOP > 14 mmHg (p ≤ 0.001, effect sizes: 0.57-1.02). In contrast, the IOP of females, younger participants, and subjects with baseline IOP ≤ 14 mmHg was not significantly modified (p = 0.114). With the regression analyses, we concluded that both sex and baseline IOP levels were significant predictors of the IOP fluctuation with AG. These findings could be of interest for gymnasts, coaches, ophthalmologists, and/or optometrists in the prevention and control of risk factors associated with glaucoma.

Choroidal Thickness and Volume Modifications Induced by Aerobic Exercise in Healthy Young Adults

INTRODUCTION

Our aim was to evaluate the changes in choroidal thickness (CT) and volume (CV) following aerobic physical exercise in healthy young adults.

METHODS

This study included 72 eyes from healthy volunteers between 22 and 37 years old. Using the International Physical Activity Questionnaire, total physical activity was computed. Measurements using an autorefractometer, ocular biometry, and spectral-domain optical coherence tomography using the Enhanced Depth Imaging protocol were taken. OCT was performed as a baseline measurement and after performing 10 min of dynamic physical exercise (3 and 10 min post-exercise). The choroidal layer was manually segmented, and the CT and CV in different areas from the Early Treatment Diabetic Retinopathy Study grid were obtained.

RESULTS

In healthy adults, at 3 min post-exercise, CT was higher in the subfoveal, the 3-mm nasal, and the 6-mm superior areas. Between 3 and 10 min post-exercise, the CT was reduced in all areas, and in some areas, the values were even smaller than the baseline measurements. The CV values showed changes after exercise similar to those of thickness. The total CV recovery after exercise was related to sex and physical activity level.

CONCLUSION

Individuals with higher physical activity habits had greater CV at rest than those with lower physical activity levels. During exercise, healthy young people adjust CT and CV. At 3 min post-exercise, CT and CV increase. Women and individuals with greater physical activity levels reduce their total CV more than others during recovery.

Lactate: More Than Merely a Metabolic Waste Product in the Inner Retina

The retina is an extension of the central nervous system and has been considered to be a simplified, more tractable and accessible version of the brain for a variety of neuroscience investigations. The optic nerve displays changes in response to underlying neurodegenerative diseases, such as stroke, multiple sclerosis, and Alzheimer's disease, as well as inner retinal neurodegenerative disease, e.g., glaucoma. Neurodegeneration has increasingly been linked to dysfunctional energy metabolism or conditions in which the energy supply does not meet the demand. Likewise, increasing lactate levels have been correlated with conditions consisting of unbalanced energy supply and demand, such as ischemia-associated diseases or excessive exercise. Lactate has thus been acknowledged as a metabolic waste product in organs with high energy metabolism. However, in the past decade, numerous beneficial roles of lactate have been revealed in the central nervous system. In this context, lactate has been identified as a valuable energy substrate, protecting against glutamate excitotoxicity and ischemia, as well as having signaling properties which regulate cellular functions. The present review aims to summarize and discuss protective roles of lactate in various model systems (in vitro, ex vivo, and in vivo) reflecting the inner retina focusing on lactate metabolism and signaling in inner retinal homeostasis and disease.

Excessive consumption of fructose causes cardiometabolic dysfunctions through oxidative stress and inflammation

A rapid rise in obesity, as well as physical inactivity, in industrialized countries is associated with fructose-consumption-mediated metabolic syndrome having a strong association with cardiovascular disease. Although insulin resistance is thought to be at the core, visceral obesity, hypertension, and hypertriglyceridemia are also considered important components of this metabolic disorder. In addition, various other abnormalities such as inflammation, oxidative stress, and elevated levels of uric acid are also part of this syndrome. Lifestyle changes through improved physical activity, as well as nutrition, are important approaches to minimize metabolic syndrome and its deleterious effects.