Quantitating polyunsaturated fatty acids in neonates with hypoxic-ischemic brain injury
Jessica Lee Wisnowski1,2, Aaron J Reitman3,4, Tai-Wei Lee Wu3, Eugenia Ho5, Claire McLean6, Douglas Lee Vanderbilt6, Marvin D Nelson1, Ashok Panigrahy7, Philippe Lee Friedlich3,8, and Stefan Lee Bluml1

1Radiology, Children's Hospital Los Angeles, Los Angeles, CA, United States, 2Rudi Schulte Research Institute, Santa Barbara, CA, United States, 3Center for Fetal and Neonatal Medicine, Children's Hospital Los Angeles, Los Angeles, CA, United States, 4Division of Neonatal Medicine, LAC + USC Medical Center, Los Angeles, CA, United States, 5Division of Child Neurology, Children's Hospital Los Angeles, Los Angeles, CA, United States, 6Children's Hospital Los Angeles, Los Angeles, CA, United States, 7Radiology, Children's Hospital of Pittsburgh of UPMC, Pittsburgh, PA, United States, 8Division of Neonatal Medicine, University of Southern California, Los Angeles, CA, United States

Synopsis

Polyunsaturated fatty acids (PUFA) are endogenous components of cellular membranes and a potential biomarker for apoptosis following hypoxic-ischemic (HI) brain injury. Prior studies have applied 1H-MRS techniques for quantifying PUFA in human carcinomas. Here, using a retrospective dataset of 1,046 neonatal 1H-MRS spectra, we demonstrate that PUFA can be routinely characterized in newborns using a modified LCModel (Provencher, Inc) pipeline.

Introduction

Polyunsaturated fatty acids (PUFA) are endogenous components of cellular membranes and a potential biomarker for apoptosis following hypoxic-ischemic (HI) brain injury [Figure 1]. Prior studies have applied 1H-MRS techniques for quantifying PUFA in human carcinomas (1,2). We assessed the validity of 1H-MRS measurements of PUFA in neonates with HI brain injury.

Methods

We retrospectively analyzed 1,046 1H-MRS spectra from 285 neonates (age: 0 – 30 days), who were scanned for various clinical indications, including 40 neonates who were scanned during and after hypothermia for hypoxic-ischemic encephalopathy (HIE). 1H-MRS spectra were acquired on a 3T MR system (Philips Medical, Best, The Netherlands) using a SV-PRESS sequence (TE = 35ms, TR = 2000ms; ~ 2.0 cm3). Data were processed using modified LCModel (Ver. 6.3-1c, Provencher Inc) pipeline (3), which included simulated peaks at 5.3 and 2.8 ppm corresponding to the olefinic (-CH ═ CH-) and bisallylic methylene (=CH-CH2-HC=) protons, respectively, of the unsaturated acyl chain. (Note: although both signals should be present in spectra containing PUFA, the latter, i.e., bisallylic protons, are specific to PUFA). Validity was determined both by examining Cramer Rao values and the cross-correlations between the lipid signals and other neuronal markers.

Results

Clinically-relevant concentrations (CRLB < 50%) of olefinic protons (5.3 ppm) and bisallylic methylene protons (i.e., PUFA at 2.8 ppm) were present in 176 and 82 out of 1046 spectra, respectively. There were only two spectra where bisallylic methylene protons were detected at such concentrations but olefinic protons were not. The correlation between the bisallyic protons and olefinic protons was highly significant (ρ = 0.573, p < 0.001), while correlations among the bisallylic protons and the allylic protons =HC-CH2- [at 2.0 ppm], -(CH2)n- protons [at 1.3 ppm], and –CH3 protons [at 0.9 ppm] were slightly lower, as expected, but still highly significant (ρ = 0.311, ρ = 0.273, ρ = 0.303, respectively, all p’s < 0.001). PUFA was nominally positively correlated with lactate (ρ = 0.164, p < 0.001). In contrast, PUFA was negatively correlated with n-acetyl-aspartate (ρ = -0.229, p < 0.001) and phosphocreatine (ρ = -0.251, p < 0.001), neuronal/energy markers.

Discussion

PUFA concentrations can be quantitated from standard, short-echo 1H-MRS data, providing a potential means of monitoring membrane breakdown. Considering that a number of drugs currently in development and in early stage clinical trials aim to reduce apoptosis (4,5), 1H-MRS PUFA measurements may provide an early endpoint for monitoring therapeutic responses in large-scale clinical trials. Furthermore, 1H-MRS measurements of lipids may not only help visualize the stage of acute brain injury, thereby providing a means of directing targeted therapies, but even shed light on the apparent timing of injury.

Acknowledgements

No acknowledgement found.

References

1. Hakumaki JM, Poptani H, Sandmair AM, Yla-Herttuala S, Kauppinen RA. 1H MRS detects polyunsaturated fatty acid accumulation during gene therapy of glioma: implications for the in vivo detection of apoptosis. Nat Med 1999;5(11):1323-1327.

2. Schmitz JE, Kettunen MI, Hu DE, Brindle KM. 1H MRS-visible lipids accumulate during apoptosis of lymphoma cells in vitro and in vivo. Magn Reson Med 2005;54(1):43-50.

3. Provencher SW. Automatic quantitation of localized in vivo 1H spectra with LCModel. NMR Biomed 2001;14(4):260-264.

4. Fan X, van Bel F. Pharmacological neuroprotection after perinatal asphyxia. J Matern Fetal Neonatal Med 2010;23 Suppl 3:17-19.

5. Traudt CM, McPherson RJ, Bauer LA, Richards TL, Burbacher TM, McAdams RM, Juul SE. Concurrent erythropoietin and hypothermia treatment improve outcomes in a term nonhuman primate model of perinatal asphyxia. Dev Neurosci 2013;35(6):491-503.

Figures

1H-MRS Spectra demonstrating the temporal evolution of PUFA and related lipid signals in a newborn with HIE. Note that during hypothermia (2 days of age) no PUFA was detected. After hypothermia, low concentrations were detected (~ 1.5 mmol/kg), which increased further over time, coincident with injury progression and membrane breakdown. For reference, corresponding ADC (top, middle) and T2- weighed images (bottom) are shown.



Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)
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