Quantification of the severity of hypoxic-ischemic brain injury in a neonatal preclinical model using measurements of cytochrome-c-oxidase from a miniature broadband-near-infrared spectroscopy system

Abstract

We describe the development of a miniaturized broadband near-infrared spectroscopy system (bNIRS), which measures changes in cerebral tissue oxyhemoglobin (½HbO 2) and deoxyhemoglobin ([HHb]) plus tissue metabolism via changes in the oxidation state of cytochrome-c-oxidase ([oxCCO]). The system is based on a small light source and a customized mini-spectrometer. We assessed the instrument in a preclinical study in 27 newborn piglets undergoing transient cerebral hypoxia-ischemia (HI). We aimed to quantify the recovery of the HI insult and estimate the severity of the injury. The recovery in brain oxygenation (Δ½HbDiff ¼ Δ½HbO 2 − Δ½HHb), blood volume (Δ½HbT ¼ Δ½HbO 2 þ Δ½HHb), and metabolism (Δ½oxCCO) for up to 30 min after the end of HI were quantified in percentages using the recovery fraction (RF) algorithm, which quantifies the recovery of a signal with respect to baseline. The receiver operating characteristic analysis was performed on bNIRS-RF measurements compared to proton (1 H) magnetic resonance spectroscopic (MRS)-derived thalamic lactate/N-acetylaspartate (Lac/NAA) measured at 24-h post HI insult; Lac/NAA peak area ratio is an accurate surrogate marker of neurodevelopmental outcome in babies with neonatal HI encephalopathy. The Δ½oxCCO-RF cutoff threshold of 79% within 30 min of HI predicted injury severity based on Lac/NAA with high sensitivity (100%) and specificity (93%). A significant difference in thalamic Lac/NAA was noticed (p < 0.0001) between the two groups based on this cutoff threshold of 79% Δ½oxCCO-RF. The severe injury group (n ¼ 13) had ∼30% smaller recovery in Δ½HbDiff-RF (p ¼ 0.0001) and no significant difference was observed in Δ½HbT-RF between groups. At 48 h post HI, significantly higher 31 P-MRS-measured inorganic phosphate/exchangeable phosphate pool (epp) (p ¼ 0.01) and reduced phosphocreatine/epp (p ¼ 0.003) were observed in the severe injury group indicating persistent cerebral energy depletion. Based on these results, the bNIRS measurement of the oxCCO recovery fraction offers a noninvasive real-time biomarker of brain injury severity within 30 min following HI insult.

Metabolic brain measurements in the newborn: Advances in optical technologies

“…In a study combining bNIRS and 31 P MRS in 22 piglets we showed that following HI the recovery of oxCCO was correlated with the recovery of nucleotide‐triphosphate (NTP)/total exchangeable phosphate pool (epp) and outcome (Bainbridge et al., 2013). Our results suggested that if NTP/epp and oxCCO recovery is not above a threshold following HI, unfavorable outcome is likely (Kaynezhad et al., 2019). In addition, we observed that the measurements of the changes in brain tissue hemoglobin difference (HbD = HbO 2 − HHb) which is indicative of brain oxygenation show a poor correlation with NTP/epp and outcome.…”

“…Regarding bNIRS, the relative changes of oxCCO needs to be assessed with respect to other systemic or cerebral changes; hence allowing a better interpretation of the physiology as recently demonstrated by our group (Mitra et al., 2019; Bale et al., 2018). However, in preclinical studies when the initial hypoxic‐ischemic insult is recorded this measurement has demonstrated a great potential to predict the MRS metabolic markers and assess injury severity (Bainbridge et al., 2013; Kaynezhad et al., 2019). DCS can provide an absolute measurement of blood flow and therefore CMRO 2 , it also suffers from limitations that are intrinsic to all optical monitoring such as motion artifacts and tissue inhomogeneities.…”

Watching synchronous mitochondrial respiration in the retina and its instability in a mouse model of macular degeneration

“…Mitochondrial activity in the retinae of mice were measured in real time using a miniature broadband near-infrared spectroscopy (bNIRS) system called miniCYRIL (Cytochrome Research Instrument and application) described previously 16 , 46 . miniCYRIL consists of a miniature halogen-based white light source (HL2000-HP) and a miniature spectrometer (QE65 pro) by Ocean Optics, USA.…”

“…The oxCCO measurement has been used in our previous animals and human studies as a reliable marker for cellular oxidative metabolism 31 , 46 , 49 – 52 . Changes in total hemoglobin (Δ[HbT] = Δ[HHb] + Δ[HbO 2 ]) as a measure for retinal blood volume as well as hemoglobin difference (Δ[HbDiff] = Δ[HbO 2 ] − Δ[HHb]), which is indicative of retinal oxygenation, were also derived.…”

Attention and Capacity Limits in Perception: A Cellular Metabolism Account

“…Conventional functional near-infrared spectroscopy systems, in contrast, have just 2-3 wavelengths of light and thus can only be used to measure concentration changes in oxygenated hemoglobin (HbO 2 ) and deoxygenated hemoglobin (HHb) in the blood vessels surrounding the brain areas of interest. The intracellular BNIRS measure of oxCCO has been validated both in animal and human studies, for example, demonstrating its correlation with phosphorous magnetic resonance spectroscopy ( 31 P MRS) measures of nucleotide triphosphate levels (which is mainly ATP) (Peeters-Scholte et al, 2004;Bainbridge et al, 2014;Kaynezhad et al, 2019) and measures of the lactate/pyruvate ratio, a marker of aerobic metabolism (i.e., mitochondrial ATP synthesis), as obtained with microdialysis (Tisdall et al, 2008; for review, see Bale et al, 2016).…”