Optical monitoring of retinal respiration in real time: 670 nm light increases the redox state of mitochondria

Abstract

Mitochondria play a key role in ageing and disease. Their membrane potentials and ATP production decline with age and this is associated with progressive inflammation, cell loss and death. Here we use broadband Near-Infrared Spectroscopy (NIRS) to non-invasively measure in-vivo changes in aged retinal mitochondrial respiration following exposure to 670 nm, which improves mitochondrial performance and reduces inflammation. Low power NIR light was shone into the eye via a fibre optic and the reflection monitored to measure signature changes in the oxidation of cytochrome c oxidase (COX) in complex IV of the electron transport chain. Changes in retinal haemodynamics and oxygenation were also recorded simultaneously with COX by measuring changes in oxygenated and deoxygenated haemoglobin (Δ[HbO2] and Δ[HHb]). Retinae of aged rats exposed to 670 nm for 5 mins showed consistent progressive increases in oxidation of COX 5 mins post exposure. This remained significantly greater than baseline for up to 2 h. This was not seen when retinae were exposed to 420 nm light of the same power or when no light was applied. 670 nm exposure significantly increased total haemoglobin concentration (Δ[HbT] = Δ[HbO2] +Δ[HHb]) but not haemoglobin difference (Δ[HbDiff] = Δ[HbO2] -Δ[HHb]). There were no changes in blood metrics in association with 420 nm light or when no light exposure was given. Hence, brief 670 nm exposure that is associated with reduced inflammation has a significant positive impact on the redox state of COX in aged retinae. The relative redox state of retinal COX may provide a valuable biomarker in ageing and macular degeneration where declining mitochondrial function is implicated.

Photobiomodulation Mediates Neuroprotection against Blue Light Induced Retinal Photoreceptor Degeneration

“…Most studies regarding PBM postulate that the mechanism of 670 nm RL irradiation rests on photon absorption by mitochondrial complex IV, leading to enhanced ATP production and mitochondrial function in general [21,24,25,28]. Our results confirm that 670 nm RL, but also the less analyzed 810 nm NIRL photo-stimulates mitochondrial activity.…”

“…In comparison to former studies on RL/NIRL, our results demonstrate the participation of additional complexes I and II besides the proposed photoacceptor CCO [12,21,24,25,28,44]. Our results indicate that CCO may not be the main target of PBM action, leading to reduced oxidative stress.…”

“…Most of these retina-related studies concentrate especially on the beneficial effects of 670 nm red light on retinal function, while other wavelengths are only rarely studied [4,27]. Results support the hypothesis of CCO as the primary target of the mitochondrial respiratory chain leading to enhanced retinal ATP production in AMD models [21,24,25,28] and increased mitochondrial membrane potential, shown in murine RPE [26].…”

“…Several studies showed that stress markers and inflammatory markers in diseased retinas can be reduced by 670 nm red light exposure in the outer retina. RL is selectively absorbed by CCO of mitochondria; however, the exact mechanism or impact on transcription factors and gene expression is largely unknown [21,24,25,28]. While authors postulate CCO to be the main target of RL action leading to improved mitochondrial function and thus reduced cell death, there is still limited information about the impact of RL/NIRL on other respiratory complexes or mitochondria-induced apoptosis in retinal diseases.…”

Improving mitochondrial function significantly reduces metabolic, visual, motor and cognitive decline in aged Drosophila melanogaster

“…Age related decline in mitochondrial function can be partly corrected in rodents by exposure to specific longer wavelengths of light that are absorbed by cytochrome c oxidase (COX) in the mitochondrial respiratory chain (Gibson and Greenwood, 1965;Karu, 1999Karu, , 2014Mason et al, 2014). Changes in the redox state of COX can be monitored in real time optically in the rodent retina in vivo where it increases rapidly 5 mins after exposure to 670nm light (Kaynezhad et al, 2016). Subsequently, mitochondrial membrane potentials improve (Kokkinopoulos et al, 2013), there is an increase in ATP (Calaza et al, 2015;Gkotsi et al, 2014), and a reduction in both ROS and inflammation (Begum et al, 2013;Kokkinopoulos et al, 2013).…”