Purpose: To study the effects of dexamethasone sodium phosphate (Dex) on human trabecular meshwork (HTM) cells in vitro.
Methods: HTM cells were treated with Dex 2 mg/ml, 1 mg/ml, 0.5 mg/ml, 0.25 mg/ml, 0.1 mg/ml, or 0.05 mg/ml for 24 h. Cell viability was measured by a trypan blue exclusion test. Caspase-3/7, -8, -9 and -12 activities were measured by fluorochrome assays as mean signal intensity (msi) to assess apoptosis. Mitochondrial dehydrogenase activity was determined by a WST assay to quantify mitochondrial damage.
Results: Mean cell viabilities of HTM cells exposed to Dex at the higher doses of 2 mg/ml, 1 mg/ml, and 0.5 mg/ml were reduced: 11.9 % ± 3.5 (P < 0.001), 31.2 % ± 3.2 (P < 0.001), and 76.6 % ± 4.4 (P < 0.01). At the lower doses of 0.25 mg/ml, 0.1 mg/ml or 0.05 mg/ml, no significant cell viability reductions were seen: 96.3 % ± 0.7 (P > 0.05), 95.3 % ± 2.5 (P > 0.05) and 93.8 % ± 2.3 (P > 0.05), respectively compared to untreated HTM cells (97.0 % ± 1.9). Caspase-3/7 activity (msi) of HTM cells exposed to Dex 2, 1 or 0.5 mg/ml was 21068 ± 2498 (P < 0.001), 26994 ± 3104 (P < 0.001) and 20416 ± 1150 (P < 0.001) compared to untreated HTM cells 1148 ± 803. Caspase-9 activity (msi) of HTM cells after exposure to Dex 2, 1 or 0.5 mg/ml was 14188 ± 1203 (P < 0.001), 13256 ± 1564 (P < 0.001) and 15041 ± 1584 (P < 0.001) compared to untreated HTM cells 1748 ± 524. The lower doses of Dex did not significantly increase caspase-3/7 or -9 activities. There were no increases for caspase-8 or -12 activities at any of the tested Dex doses. The WST assay showed mitochondrial dehydrogenase activities of 14.3 ± 0.7 (P < 0.001), 9.6 ± 0.3 (P < 0.001) and 56.0 ± 7.6 (P < 0.001) at 2 mg/ml, 1 mg/ml and 0.5 mg/ml Dex compared to untreated HTM cells (186.1 ± 15.0).
Conclusions: Dex at 0.25, 0.1 and 0.05 mg/ml clinical dose did not cause significant reduction in cell viability, increased apoptosis, or mitochondrial dysfunction of HTM cells in vitro. At high doses (2, 1 or 0.5 mg/ml) Dex caused apoptosis via mitochondrial pathways.