Metabolic pathways are altered in mitochondrial haplogroups that affect severity of diabetic retinopathy

Abstract

Purpose: To identify metabolic pathways that are altered in patients from mitochondrial haplogroups H and Uk, which have previously been demonstrated to be risk and protective factors, respectively, for proliferative diabetic retinopathy (PDR) among patients with diabetic retinopathy (DR).

Methods: Caucasian DR patients (44 with non-proliferative diabetic retinopathy [NPDR] and 57 with PDR) were genotyped using a Sequenom pool of 22 mitochondrial SNPs, and haplogroups were determined with HaploGrep. Untargeted metabolomic analysis using C18 liquid chromatography-Fourier-transform mass spectrometry (LC-FTMS) was performed on frozen plasma samples from the 101 patients. Data were collected from mass/charge ratio (m/z) 85-2000 on a Thermo LTQ-Velos Orbitrap mass spectrometer, and metabolic features were extracted using an adaptive processing software package with xMSanalyzer. Haplogroup H patients were compared to non-H patients, and haplogroup Uk patients to non-Uk patients. For each comparison, the top 500 metabolite features (p value cutoff of approximately 0.001) were used as input for pathway analysis in mummichog, a software program designed for high-resolution metabolomics data. The influence of haplogroups H and Uk on metabolite levels were examined using linear regression models that included age, gender, HgbA1c, and interaction between haplogroup and HgbA1c as covariates.

Results: For the haplogroup H vs. non-H comparison, the TCA cycle (p=0.0079), and the Vitamin B3 (p=0.015) and Vitamin A (p=0.016) pathways significantly differed between the groups. Comparing haplogroup Uk vs. non-Uk, twelve pathways significantly differed, including the sphingolipid pathway (p=0.0023), the TCA cycle (p=0.0092), the carnitine shuttle (p=0.023), and the Vitamin E (p=0.026) and Vitamin A (p=0.029) pathways.

Conclusions: Multiple pathways plausibly related to mitochondrial function based on mitochondrial site of action or relationship to mitochondrially-produced reactive oxygen species have altered funtion in H and Uk haplogroups in patients with DR. These results suggest that metabolic changes related to specific mitochondrial haplogroups may influence diabetic retinopathy severity.