Abstract
Purpose :
Diclofenac instillation is useful for preventing intraoperative miosis and suppressing postoperative inflammation and macular edema in cataract surgery; however, optimum efficacy is not attained when the instilled diclofenac strongly binds to albumin in patients’ aqueous humor. Therefore, a method that inhibits diclofenac binding and increases the concentration of its free fraction is required. We conducted a study regarding the effects of inhibitors on the binding of diclofenac to albumin and endogenous substances in the aqueous humor.
Methods :
At the time of cataract surgery, aqueous humor samples from 15 patients with cataract who had received diclofenac instillations were collected and mixed to prepare pooled aqueous humor, from which diclofenac was extracted. The free-fraction and concentrations of diclofenac were measured using ultra-high performance liquid chromatography in various experiments with pooled and mimic aqueous humor samples. The endogenous substances in the aqueous humor were quantified using a BiOLiS 24i premium, gas chromatography-mass spectrometry, and liquid chromatography-mass spectrometry.
Results :
The binding of diclofenac, a site-II drug, to albumin in pooled aqueous humor was significantly inhibited by phenylbutazone (PB), a site-I inhibitor; however, no significant inhibition by ibuprofen, a site-II inhibitor, was observed. To unravel this unexpected result, endogenous substances associated with albumin binding in pooled aqueous humor were investigated. The inhibition of diclofenac binding by PB in mimic aqueous humor containing these endogenous substances revealed significant binding inhibition in the presence of palmitic acid (PA) and L- tryptophan (L-Trp) (PA > L-Trp).
Conclusions :
The presence of PA and L-Trp in the aqueous humor inhibited diclofenac from binding to site II, the high-affinity binding site on albumin, and induced a conformational change in albumin. This change caused site I, the low-affinity binding site, to become high-affinity; thus, diclofenac was strongly bound to site I. Therefore, PB, a site-I inhibitor, significantly inhibited the albumin binding of diclofenac. Instilling site-I inhibitors prior to diclofenac may increase the free fraction of diclofenac and enhance its effect.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.