TABLE 1.

Obstructive sleep apnoea (OSA) and metabolomics (rodent and human studies)

First author [ref.]	Analytical techniques	Sample	Participants	Complications	Main results
Conotte [ 12 ]	NMR	Urine	Male C57BL6J mice		The energy metabolism pathway of mice under IH predominately switched to anaerobic metabolism The level of oxidation products increased in mice under IH
Yoon [ 14 ]	LC/MS	Hippocampi	Male Wistar rats		Metabolites related to neurotransmitters, such as glutamate and aspartate in the hippocampus decreased significantly in chronic SF groups Precursors (methionine and choline) of acetylcholine were shown to be below normal levels in the SF model
Ząbek [ 15 ]	NMR	Urine and serum	18 COPD and 28 OSA	Over half of the participants have cardiovascular disease	Urine metabolites presented the highest probability for identifying patients with COPD A combination of different biofluids detection did not improve the diagnosis power
Xu [ 17 ]	UPLC-Q-TOF-MS/GC-TOF-MS	Urine	60 OSA, 30 SS and 30 controls (AHI >10)	Without medical history of systemic disease	Metabolites from fatty acid and phospholipid metabolism expressed differentially in SS and OSA Dyslipidaemia caused by IH may be involved in the development of OSA
Cho [ 24 ]	MS	Urine	34 male OSA and 14 controls (AHI >8)	Without medical history of DM, hyperlipidaemia, and chronic hypoxia-related diseases	Three metabolites, long-chain acylcarnitine (C14:1), biogenic amines of SDMA and sphingomyelin (C18:1) were significantly elevated in OSA male patients
Xu [ 25 ]	UPLC-Q-TOF-MS/GC-TOF-MS	Urine	30 paediatric OSA and 30 controls (average AHI 4.1)	Without medical history of systemic disease	52 metabolites from nine pathway classes (amino acid, carbohydrate, microbial, vitamin, nucleic acid, fatty acid, butanoate, bilirubin metabolism and ornithine cycle) were identified in paediatric OSA
Ferrarini [ 28 ]	LC-QTOF-MS	Plasma	15 nonsevere OSA (AHI <30) and 18 severe OSA (AHI >30)	Without screening of complications	14 significant metabolites related to inflammation and hypoxia in plasma samples were identified to differentiate mild OSA patients from severe patients
Lebkuchen [ 29 ]	GC–MS/MS	Plasma	37 OSA and 16 controls (AHI ≥15)	Without medical history of diabetes	Glutamic acid, deoxy sugar, arachidonic acid, glycerophosphoethanolamines, sphingomyelin and lyso-phosphocholines were related to OSA

NMR: nuclear magnetic resonance; LC: liquid chromatography; MS: mass spectrometry; UPLC-Q-TOF-MS: ultra-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry; GC-TOF-MS: gas chromatography coupled with time-of-flight mass spectrometry; SS: simple snorers; IH: intermittent hypoxia; SF: sleep fragmentation; AHI: apnoea–hypopnoea index; DM: diabetes mellitus; SDMA: symmetric dimethylarginine; LC-QTOF-MS: liquid chromatography coupled with quadrupole time-of-flight mass spectrometry; GC–MS: gas chromatography–mass spectrometry.