Urinary exosomes as a novel biomarker for evaluation of α-lipoic acid's protective effect in early diabetic nephropathy

Abstract

Background: Long-term administration of α-lipoic acid (α-LA) is proved to ameliorate renal impairment. Herein we assessed serum, urinary biomarkers and vascular endothelium function to evaluate its short-period therapeutic effect and identify novel biomarkers for diabetic nephropathy (DN).

Methods: Sixty-two microalbuminuria-stage DN patients were randomly divided into two groups and received the following treatment for 8 weeks: (1) routine treatment(DM group); (2) routine treatment with 600 mg/d α-lipoic acid intravenously (α-LA group). Another total of 21 patients were recruited for the second-stage study and randomly divided into two groups: normoalbuminuria (UAER <30 mg/24 h) and microalbuminuria (UAER from 30-300 mg/24 h).

Results: With α-LA treatment, urinary albumin excretion rates (UAER), serum creatinine (SCr) and malonaldehyde (MDA) declined significantly, whereas plasma superoxide dismutase (SOD)activity increased and endothelium-dependent flow mediated vasodilation (FMD) flexibility improved dramatically. Furthermore, the improvement of FMD showed positive correlation with the variation in MDA and SOD as well (r values are .516 and .435, P<.01 and P<.05, respectively). In contrast, these markers have no significant difference in the DM group with routine treatment. Notably, the CD63 expressing of exosomes in urine was found higher in the normoalbuminuria patients compared with those in microalbuminuria, parallelly only declined markedly after α-LA administration in normoalbuminuria patients.

Conclusion: In summary, we emphasize short-term α-LA could protect the kidney in the early DN against general oxidative stress, particularly the urinary CD63-positive exosome could be a potential sensitive and therapeutic indicator.

Keywords: diabetic nephropathy; exosomes; α-lipoic acid.

Figure 1

Correlation between the improvement of FMD and variation in MDA and SOD. The improvement of FMD was evaluatedby FMD after α‐LA treatment deducting FMD before treatment, ΔFMD=FMD _after‐ FMD _before. The variations in MDA and SOD were calculated in the same way (ΔMDA=MDA _after‐MDA _before, ΔSOD=SOD _after‐SOD _before). The correlation analysis between mentioned ΔFMD vs ΔMDA and ΔSOD were carried out with the SPSS 18.0 software, respectively. (A) Correlation of ΔFMD and ΔMDA with α‐LA treatment; (B) Correlation of ΔFMD and ΔSOD with α‐LA treatment

Figure 2

α‐lipoic acid affected the urinary exosomes (A) Quality assessment of isolated urinary exosomes by electronic microscopy images (A~D). Samples with size in the range 50‐150 nm were examined by a FEI Tecnai G2 Spirit transmission electron microscope at 120 kV. (B) Histogram of CD63‐PE expression on urinary exosomes by FACS in normoalbuminuria group before (red) and after (blue) administration of α‐lipoic acid, as well as PE isotype staining (yellow), are shown. (C and D) Mean fluorescence intensity of CD63 in urinary exosomes in normoalbuminuria group and microalbuminuria group (before and after administration of α‐lipoic acid) are shown. Data are representative of independent samples and is shown as means±SEM (normoalbuminuria group n=13, microalbuminuria group n=8, *P<.05). Normoalbuminuria: normoalbuminuria group; Microalbuminuria: microalbuminuria group; before: before administration of α‐lipoic acid; after: after administration of α‐lipoic acid