Ophthalmic nutrition and prevention of eye disorder and blindness

Mitochondrial-Targeted Antioxidants Attenuate TGF-β2 Signaling in Human Trabecular Meshwork Cells

Purpose

POAG is a progressive optic neuropathy that is currently the leading cause of irreversible blindness worldwide. While the underlying cause of POAG remains unclear, TGF-β2-dependent remodeling of the extracellular matrix (ECM) within the trabecular meshwork (TM) microenvironment is considered an early pathologic consequence associated with impaired aqueous humor (AH) outflow and elevated IOP. Early studies have also demonstrated markedly elevated levels of oxidative stress markers in AH from POAG patients along with altered expression of antioxidant defenses. Here, using cultured primary or transformed human TM cells, we investigated the role oxidative stress plays at regulating TGF-β2-mediated remodeling of the ECM.

Methods

Primary or transformed (GTM3) human TM cells conditioned in serum-free media were incubated in the absence or presence of TGF-β2 and relative changes in intracellular reactive oxygen species (ROS) were measured using oxidation-sensitive fluorogenic dyes CellROX green or 6-carboxy-2',7'-dichlorodihydrofluorescein diacetate (carboxy-H2DCFDA). TGF-β2-mediated changes in the content of connective tissue growth factor (CTGF) and collagen types 1α1 (COL1A1) and 4α1 (COL4A1) mRNA or collagens I and IV isoform proteins were determined in the absence or presence of mitochondrial-targeted antioxidants (XJB-5-131 or MitoQ) and quantified by quantitative PCR or by immunoblot and immunocytochemistry. Smad-dependent canonic signaling was determined by immunoblot, whereas Smad-dependent transcriptional activity was quantified using a Smad2/3-responsive SBE-luciferase reporter assay.

Results

Primary or transformed human TM cells cultured in the presence of TGF-β2 (5 ng/mL; 2 hours) exhibited marked increases in CellROX or fluorescein fluorescence. Consistent with previous reports, challenging cultured human TM cells with TGF-β2 elicited measurable increases in regulated Smad2/3 signaling as well as increases in CTGF, COL1A1, and COL4A1 mRNA and collagen protein content. Pretreating human TM cells with mitochondrial-targeted antioxidants XJB-5-131 (10 μM) or MitoQ (10 nM) attenuated TGF-β2-mediated changes in Smad-dependent transcriptional activity.

Conclusions

The multifunctional profibrotic cytokine TGF-β2 elicits a marked increase in oxidative stress in human TM cells. Mitochondrial-targeted antioxidants attenuate TGF-β2-mediated changes in Smad-dependent transcriptional activity, including marked reductions in CTGF and collagen isoform gene and protein expression. These findings suggest that mitochondrial-targeted antioxidants, when delivered directly to the TM, exhibit potential as a novel strategy by which to slow the progression of TGF-β2-mediated remodeling of the ECM within the TM.

Post-measles corneal ulceration in children in northern Nigeria: the role of vitamin A, malnutrition and measles

This work was prompted by the observation that corneal ulceration was apparently more common in young children in the guinea savannah area of northern Nigeria than in children in the tropical rainforest areas of southern Nigeria, where the intake of vitamin A, as the provitamin in red palm oil, is higher. Since corneal ulceration was usually seen in association with measles, a study was carried out to clarify the relationship between nutritional status, measles infection and vitamin A status in young children. The concentration of total retinol was measured in the plasma of well-nourished and malnourished children under three years of age, with or without a clinical record of recent measles. One hundred and twenty children were studied of whom 17 had corneal lesions. Malnutrition and measles were both found to depress the plasma concentrations of retinol and albumin. Measles depressed retinol levels (-20 to -30%) more than did malnutrition (-4 to -12%) while malnutrition had a greater depressing effect on albumin concentration (-23 to -30%) than did measles (-11 to -23%). The results support the hypothesis that corneal ulceration found in association with measles in northern Nigeria, although clinically similar to xerophthalmia, is not simply mediated through an effect of measles on the concentrations of vitamin A in plasma.