Short-Term Fellow-Eye Aqueous Humor Cytokine and Metabolomic Changes After First-Eye Surgery in Age-Related, Diabetic, and High Myopia– Associated Cataracts

Technical Summary: Short-Term Fellow-Eye Aqueous Humor Cytokine and Metabolomic Changes After First-Eye Surgery in Age-Related, Diabetic, and High Myopia–Associated Cataracts

Problem Statement
Sequential bilateral cataract surgery is common, yet the optimal inter-surgical interval remains debated. While previous studies suggest that first-eye surgery may induce molecular changes in the contralateral (second) eye, results regarding aqueous humor cytokine alterations have been inconsistent. These discrepancies may stem from heterogeneous study populations and a lack of stratification by cataract etiology. Furthermore, while some evidence suggests subclinical contralateral responses in uncomplicated age-related cataracts (ARC), it is unclear whether patients with systemic or structural ocular comorbidities—specifically diabetes and high myopia—exhibit amplified or distinct inflammatory and metabolic responses in the fellow eye following unilateral surgery.

Methodology
This prospective, paired-eye observational study enrolled 107 patients (214 eyes) undergoing sequential bilateral cataract surgery at the Second Affiliated Hospital of Zunyi Medical University. Patients were stratified into three etiology groups: Age-Related Cataract (ARC), Diabetic Cataract (DM-C), and High Myopia–Associated Cataract (HM-C). Within each group, patients were further categorized by the inter-surgical interval: 1, 2, or 3 weeks.

The study employed a multi-layered analytical approach:

1. Sample Collection: Approximately 100–200 µL of aqueous humor was aspirated from the anterior chamber of both the first and second eyes prior to phacoemulsification.
2. Cytokine Profiling: Thirteen cytokines (including IL-1β, IL-2, IL-6, IL-8, IL-10, IL-12, IL-18, MCP-1, TNF-α, TGF-β, IFN-γ, Substance P, and CSF3) were quantified using double-antibody sandwich ELISA.
3. Metabolomic Profiling: Untargeted metabolomics were performed using Ultra-Performance Liquid Chromatography–Quadrupole Time-of-Flight Mass Spectrometry (UPLC-QTOF-MS).
4. Statistical Analysis: Cytokine data were analyzed using paired t-tests. Metabolomic data underwent Principal Component Analysis (PCA) and Orthogonal Partial Least Squares–Discriminant Analysis (OPLS-DA). Differential metabolites were identified based on Variable Importance in Projection (VIP) > 1.0 and adjusted P < 0.05. Pathway enrichment was conducted using the KEGG database.

Key Results
The study revealed that molecular responses in the second eye are etiology-dependent and transient, primarily occurring within the first postoperative week.

• Cytokine Alterations:

  • ARC Group: No significant cytokine alterations were detected between the first and second eyes at any time point (1, 2, or 3 weeks).
  • HM-C Group (1 Week): Significant decreases in Substance P (SP) and increases in Transforming Growth Factor–β (TGF-β) were observed in the second eye compared to the first. These differences resolved by weeks 2 and 3.
  • DM-C Group (1 Week): Significant elevation of Interleukin-18 (IL-18) was detected in the second eye, which also normalized by weeks 2 and 3.
  • Baseline Differences: Preoperative analysis confirmed that baseline cytokine profiles differed significantly among the three groups (e.g., HM-C had lower IL-2, IL-1β, and TNF-α compared to ARC; DM-C had higher IL-8 and TGF-β).

• Metabolomic Alterations:

  • HM-C (1 Week): Differential metabolites were enriched in pathways related to pyruvate metabolism, glutathione metabolism, ascorbate and aldarate metabolism, and the pentose phosphate pathway. Key metabolites included pyruvaldehyde, ascorbic acid, and Lys–Val.
  • DM-C (1 Week): Differential metabolites were primarily enriched in carbon metabolism and the pentose phosphate pathway (PPP), with Glucono-1,5-lactone identified as a key differential metabolite.
  • ARC: While some metabolite differences were noted, the study emphasizes that the significant cytokine fluctuations were absent in this group.

Key Contributions

1. Etiologic Stratification: The study demonstrates that the "contralateral eye response" to unilateral cataract surgery is not uniform but varies significantly based on the underlying cataract etiology (ARC vs. DM-C vs. HM-C).
2. Temporal Dynamics: It establishes that molecular perturbations in the fellow eye are transient, peaking at 1 week post-first-eye surgery and resolving by weeks 2 and 3.
3. Mechanistic Insights:
   • In High Myopia, the reduction in Substance P and elevation of TGF-β suggest a neurohumoral regulatory mechanism, potentially mediated by the trigeminal ganglion, aimed at limiting neurogenic inflammation. The metabolic profile suggests a transient state of oxidative stress and redox imbalance.
   • In Diabetes, the elevation of IL-18 and enrichment of the pentose phosphate pathway suggest a priming of the NLRP3 inflammasome via oxidative stress (ROS) and NADPH oxidase activity, driven by the diabetic metabolic environment.
4. Clarification of Inconsistencies: The findings provide a framework for understanding why previous studies yielded conflicting results, attributing discrepancies to the inclusion of heterogeneous patient populations without stratification by systemic or ocular comorbidities.

Significance and Claims
The authors claim that these findings offer experimental and theoretical insights into the short-term intraocular changes following cataract surgery. Specifically, the paper posits that:

• Patients with diabetic cataracts or high myopia–associated cataracts are more susceptible to early postoperative inflammatory and metabolic perturbations in the fellow eye compared to those with uncomplicated age-related cataracts.
• The observed molecular changes (reduced SP, increased TGF-β, elevated IL-18) may represent adaptive or compensatory regulatory responses rather than uncontrolled inflammation, potentially explaining why the second eye sometimes exhibits milder postoperative inflammation despite higher intraoperative sensitivity.
• These etiology-dependent molecular profiles may inform the individualized timing of second-eye surgery and perioperative management strategies, suggesting that patients with DM or HM might require closer monitoring or different management during the first postoperative week.

The study acknowledges limitations, including the need for targeted metabolomic validation and the inability to assess longitudinal changes within the same individual for weeks 2–3 due to the cross-sectional nature of the sampling at those intervals. However, it concludes that the evidence supports a model where systemic and structural factors modulate the contralateral eye's response to surgical stress.