Homocysteinethiolactone and paraoxonase: novel markers of diabetic retinopathy.
OBJECTIVE
Paraoxonase (PON) exhibits esterase activity (PON-AREase) and lactonase activity (PON-HCTLase), which prevent LDL oxidation and detoxify homocysteine thiolactone (HCTL). The role of HCTL and PON-HCTLase as a risk factor for the microvascular complication in diabetic retinopathy at the level of vitreous has not been investigated.


METHODS
Undiluted vitreous from patients with proliferative diabetic retinopathy (PDR) (n = 13) and macular hole (MH) (n = 8) was used to determine PON-HCTLase and PON-AREase activity spectrophotometrically. HCTL levels were detected by liquid chromatography-tandem mass spectrometry. In vitro studies were done in primary cultures of bovine retinal capillary endothelial cells (BRECs) to determine the dose- and time-dependent effect of HCTL and homocysteine (Hcys) on PON-HCTLase activity, as well as to determine mRNA expression of PON by RT-PCR.


RESULTS
A significant increase in HCTL and PON-HCTLase activity was observed in PDR compared with MH (P = 0.036, P = 0.001), with a significant positive correlation between them (r = 0.77, P = 0.03). The in vitro studies on BRECs showed a dose- and time-dependent increase in the PON-HCTLase activity and mRNA expression of PON2 when exposed to HCTL and Hcys.


CONCLUSIONS
This is the first study showing elevated levels of vitreous HCTL and PON-HCTLase activity in PDR. These elevations are probably a protective effect to eliminate HCTL, which mediates endothelial cell dysfunction. Thus, vitreous levels of HCTL and PON activity can be markers of diabetic retinopathy. The bioinformatics analysis reveals that the structure and function of PON that can be modulated by hyperhomocysteinemia in PDR can affect the dual-enzyme activity of PON.
Barathi
Subramaniam
S
Biochemistry and Cell Biology Department, Sankara Nethralaya Hospital, Chennai, Tamil Nadu, India.
Angayarkanni
Narayanasamy
N
Pasupathi
Aarthi
A
Natarajan
Sulochana Konerirajapuram
SK
Pukraj
Rishi
R
Dhupper
Maneesh
M
Velpandian
Thirumurthy
T
Muralidharan
Charanya
C
Sivashanmugham
Muthukumaran
M
D000368:Aged; D043303:Aryldialkylphosphatase / Q000378:metabolism*; D002478:Cells, Cultured; D002851:Chromatography, High Pressure Liquid; D003930:Diabetic Retinopathy / Q000175:diagnosis* / Q000201:enzymology / Q000378:metabolism*; D005260:Female; D006710:Homocysteine / Q000031:analogs & derivatives* / Q000378:metabolism; D006801:Humans; D008297:Male; D008875:Middle Aged; D012167:Retinal Perforations / Q000378:metabolism; D053719:Tandem Mass Spectrometry; D014822:Vitreous Body / Q000378:metabolism
D006710:Homocysteine; C007957:homocysteine thiolactone; D043303:Aryldialkylphosphatase