Radiochemical Kinetic Uptake of Three Lipids on Silicone Hydrogel and Conventional Hydrogel Contact Lens Materials

Abstract

Purpose: : To analyze the in vitro kinetic uptake of radiolabelled cholesterol, triolein and phosphatidyl choline on silicone hydrogel (SH) and polyHEMA-based conventional hydrogel (CH) contact lens materials.

Methods: : Four SH (PureVision®, balafilcon A [PV]; Air OPTIX®, lotrafilcon B [AOp] ; Biofinity®, comfilcon A [Bio]; Acuvue OASYS®, senofilcon A [AvO]) and two CH (Acuvue 2®, etafilcon A [AV2] and ProClear®, omafilcon A [PC]) contact lens materials were incubated in a complex artificial tear solution (ATS) containing six common tear film lipids, proteins, mucin, salts and a trace amount of one of the radioactive lipids; ¹⁴C-cholesterol, ¹⁴C-triolein, or ¹⁴C-phosphatidylcholine. Lenses (n=4) were incubated for different durations: 1 day, 3 days, 7 days, 14 days and 28 to mimic wear patterns. Following incubation, each lens was extracted twice in 2mL of 2 chloroform: 1 methanol for three hours, evaporated under nitrogen, re-suspended in chloroform then scintillation cocktail. Extracts were counted in a LS6500 Beckman Coulter beta counter and raw data was translated into absolute amounts (µg/lens) via extrapolation from standard curves run for each of the test lipids.

Results: : All three radioactive lipids showed continuous and accumulating lipid uptake throughout the 28 days of incubation. SH deposited statistically more lipid than CH lens materials and each of the three radioactive lipids had statistically significant repeated measures ANOVAs with p<0.001. For ¹⁴C-cholesterol, the deposition order was: PV>AvO>Bio>AOp>PC>AV2 with PV depositing 3.14 ± 0.15 µg/lens and AV2 depositing 0.05 ± 0.003 µg/lens after 28 days. For ¹⁴C-triolein, the deposition order was: PV>AvO> AOp >Bio>AV2 >PC with PV depositing 4.29 ± 0.67 µg/lens and PC depositing 0.53 ± 0.03 µg/lens after 28 days. For ¹⁴C-phosphatidylcholine, the deposition order was: AOp>PV>Bio >AvO>AV2=PC with AOp depositing 1.09± 0.08 µg/lens and AV2 and PC depositing 0.12 ± 0.004 µg/lens after 28 days.

Conclusions: : This study demonstrated that cholesterol, triolein and phosphatidylcholine deposition was cumulative up to 28 days of incubation without a plateau. SH lens materials deposited significantly more than CH. In general, PV lenses accumulated the most lipid, with triolein.

Keywords: lipids • contact lens