Table 3.

Main characteristics of metabolomics studies on diabetic retinopathy and diabetic peripheral neuropathy

Reference	Group	Type	Platform	Altered metabolites	Conclusion
Munipally et al. (2011)	35 control subjects, 22 NPDR patients and 24 PDR patients	Serum	HPLC	Greater expression of kynurenine, kynurenic acid and 3‐hydroxykynurenine in NPDR and PDR↑	Results indicate a probable association of IDO and tryptophan metabolites with DR
Barba et al. (2010)	22 patients with T1DM with PDR and 22 non‐diabetic patients with a macular hole	Vitreous	1H NMR	Lactate and glucose↑; galactitol and ascorbic acid↓	Apart from the greater abundance of lactate and glucose, significant deficits of galactitol and ascorbic acid are the main metabolic fingerprints of vitreous fluid from PDR patients
Li et al. (2011)	2 perspectives studies	Serum	GC‐MS	Fatty acids, amino acids and glucose	Results showed the usefulness and validity of combining both Western and Chinese medicine to study the subtypes of DR and the mechanisms involved
Freeman et al. (2011)	STZ‐diabetic and healthy control rats	SN, DRG, TG	GC‐MS, UHPLC‐MS	Increase in glucose and polyol pathway intermediates in diabetes; upregulation of mitochondrial oxidative phosphorylation and perturbation of lipid metabolism were found in the distal SN that were not present in the corresponding cell bodies of the DRG or the cranial TG↑	Spatial metabolic dysfunction suggests a failure of energy homeostasis and/or oxidative stress, specifically in the distal axon/Schwann cell‐rich SN

DR, diabetic retinopathy; DRG, lumbar 4/5 dorsal root ganglia; GC‐MS, gas chromatography‐mass spectrometry; HPLC, high‐performance liquid chromatography; IDO, indoleamine 2, 3‐dioxygenase; NPDR, non‐proliferative diabetic retinopathy; PDR, proliferative diabetic retinopathy; STZ, streptozotocin; SN, sciatic nerve; T1DM, type 1 diabetes mellitus; TG, the trigeminal ganglia; UHPLC‐MS, ultra‐high‐performance liquid chromatography‐mass spectrometry.