Retinal Mitochondrial Flavoprotein Fluorescence in Sickle Cell Disease

Abstract

Purpose : Oxidative stress is integral to the pathophysiology of sickle cell disease (SCD). Chronic hemolysis and platelet activation are correlated with decreased platelet mitochondrial complex V activity, resulting in low nitric oxide bioavailability and increased oxidant production. In SCD, the precise role of mitochondrial dysfunction in facilitating retinal oxidative stress is unknown. Prior studies have shown that retinal mitochondrial flavoproteins emit a green fluorescence (520-540 nm) when exposed to blue light (450-470 nm). The emission signal, termed flavoprotein fluorescence (FPF), is a quantifiable marker of in vivo mitochondrial dysfunction. Here, we hypothesize that FPF is a noninvasive indicator of oxidative stress in SCD.

Methods : 25 eyes from 25 SCD (18 hemoglobin-SS, 7 hemoglobin-SC in steady state) subjects and 21 eyes from 21 healthy age-matched controls (hemoglobin-AA) were included in the present cross-sectional study. The macula was imaged with the OcuMet Beacon, a fundus camera equipped with 467 nm excitation and 535 nm emission filters (OcuSciences, Ann Arbor, MI). The device quantifies FPF from all retinal layers in a rectangular 17° x 21° region of interest centered at the fovea. Statistical tests were performed to determine differences in FPF between subjects. Spearman rank correlation coefficients were used to determine the association between FPF and laboratory markers of hemolysis obtained within one month of imaging.

Results : Median [IQR] age for SCD subjects and controls were 32 [11] and 31 [8]. Mean (±SD) FPF for SCD subjects and controls were 39.1±12.6 and 29.3±5.5, respectively. Mean (±SD) FPF for HbSS and HbSC genotypes were 40.3±13.9 and 35.8±8.4, respectively. SCD subjects displayed significantly elevated FPF compared to controls (Mann-Whitney U Test, p=0.018). SCD subjects with HbSS disease displayed significantly elevated FPF compared to controls (Kruskal Wallis Test, p=0.032). FPF was not significantly elevated in HbSC disease (Kruskal Wallis Test, p=0.448). FPF was moderately correlated with urine microalbuminuria (ρ=0.437, p=0.033) and pro-brain natriuretic peptide (ρ=0.524, p=0.009).

Conclusions : These findings indicate that SCD patients with HbSS disease display significantly elevated FPF levels compared to controls and patients with HbSC disease. This suggests that FPF can serve as an indicator of systemic disease severity and can be correlated with laboratory markers of hemolysis.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.