Mitochondrial oxygen metabolism in primary human lens epithelial cells: Association with age, diabetes and glaucoma

PURPOSE

The hypoxic environment around the lens is important for maintaining lens transparency. Lens epithelial cells (LECs) play a key role in lens metabolism. We measured oxygen consumption to assess the role of human LECs in maintaining hypoxia around the lens, as well as the impact of systemic and ocular diagnosis on these cells.

METHODS

Baseline cellular respiration was measured in rabbit LECs (NN1003A), canine kidney epithelial cells (MDCK), trabecular meshwork cells (TM-5), and bovine corneal endothelial cells (CCEE) using a XF96 Extracellular Flux Analyzer (Seahorse Bioscience, North Billerica, MA), which measures oxygen consumption rate (OCR) and extracellular acidification rate (ECAR) in vitro. Following informed written consent, lens capsule epithelial cells were obtained from patients during cataract surgery and were divided into small explants in 96-well plates. Capsules were removed when LECs became confluent. OCR was normalized to the number of cells per well using rabbit LECs as a standard. The effect of patient age, sex, race, and presence of diabetes or glaucoma on oxygen consumption was assessed by using the Mann-Whitney U test and multivariate regression analysis.

RESULTS

Primary LECs were obtained from 69 patients. The OCR from donors aged 70 and over was lower than that of those under 70 years (2.21±1.037 vs. 2.86±1.383 fmol/min/cell; p<0.05). Diabetic patients had lower OCR than non-diabetic patients (2.02±0.911 vs. 2.79±1.332fmol/min/cell; p<0.05), and glaucoma patients had lower OCR than non-glaucoma patients (2.27±1.19 vs. 2.83±1.286 fmol/min/cell; p<0.05). Multivariate regression analysis confirmed that donors aged 70 and over (p<0.05), diabetic patients (p<0.01), and glaucoma patients (p<0.05) had significantly lower OCR, independent of other variables. Gender and race had no significant effect on OCR.

CONCLUSIONS

The lower oxygen consumption rate of human LECs in older donors and patients with diabetes or glaucoma could contribute to cataract development. Diabetes and glaucoma are particularly important factors associated with decreased OCR, independent of age. Ongoing studies are examining pO2 at the anterior surface of the lens in vivo and oxygen consumption in the patient's LECs.

Melanin can deplete immunosuppressive substances from the aqueous humor

Heavily pigmented eyes tend to experience greater inflammation than lightly pigmented eyes following trauma and surgery. The purpose of these studies was to test the possibilities that: (i) melanin augments T cell-responses by depleting or neutralizing anti-inflammatory substances that are normally present in the aqueous humor, and (ii) melanin augments extraocular T cell-mediated inflammatory responses. Two types of experiments were performed. First, the capacity of melanin-adsorbed and non-adsorbed rabbit aqueous humor to inhibit the proliferative response of the T cell line D10.G4.1 to IL-1 was tested. Non-adsorbed aqueous humor inhibited T cell proliferation to the background level in unstimulated cultures, whereas melanin-adsorbed aqueous humor enhanced the proliferation of stimulated, but not resting T cells. Next, mice were sensitized to the antigen conalbumin, and challenged in the ear pinna with conalbumin alone, conalbumin + melanin, or melanin alone and delayed-type hypersensitivity (DTH) was measured. Challenge with melanin alone caused some ear swelling, and melanin increased the DTH response to conalbumin. Our findings are consistent with the notion that melanin can augment intraocular inflammation by depleting or neutralizing the inhibitory components of normal aqueous humor, possibly exposing stimulatory components that are normally masked.