Association of POC-based Measurement of Skin AGEs with Serum AGEs as well as AGE Biomarkers in Individuals with and without Glucose Intolerance

Aim: Accumulation of advanced glycation end products (AGEs) occurs with aging and in various disease states. There are no reliable screening techniques to measure AGEs in clinical settings. In this study, a point-of-care (POC) device was used to validate skin AGE measurements with serum AGE levels and to assess its usefulness to identify individuals with abnormal glucose tolerance (AGT). Materials and methods: The study group comprised individuals with normal glucose tolerance (NGT: n = 47) and with AGT, that is, either diabetes or prediabetes (n = 68). Intrinsic AGE fluorescence was measured spectrofluorimetrically using multimode plate reader in the serum by exciting the samples at 370 nm and emission readouts at 440 nm. Skin AGEs were acquired using a CE-marked Scout DS commercial device. Serum levels of biomarkers carboxymethyl lysine (CML), carboxyethyl lysine (CEL), and pentosidine were analyzed by enzyme-linked immunosorbent assay (ELISA). Results: In subjects with AGT, the skin AGEs [61.3 vs 53.7 arbitrary units (AU), p<0.0001] and serum AGEs (3.5 vs 2.8 AU, p<0.0001) were significantly higher than in individuals with NGT. The levels of CML, CEL, and pentosidine were also significantly higher in the subjects with AGT when compared with NGT (138 vs 89 pg/mL; 2.4 vs 1.4 nmol/mL, and 64 vs 48 pmol/mL, p<0.0001), respectively. Pearson correlation analysis showed a significant positive association of skin AGEs with serum AGEs (r = 0.344) (p<0.001), CML (r = 0.323) (p<0.001), CEL (r = 0.308) (p<0.001), and pentosidine (r = 0.251) (p<0.001). In addition, it also showed a positive correlation with fasting plasma glucose (FPG) (p<0.001), 2-hour post-glucose (p<0.001), glycated hemoglobin (HbA1c) (p<0.001), and body mass index (BMI) (p<0.05). Multiple logistic regression analysis using AGT as a dependent variable showed that skin AGE scores were significantly (p<0.001) associated with AGT (odds ratio: 1.133, confidence intervals: 1.067–1.203). Conclusion: This study shows that the measurement of skin AGEs using a POC device may be suitable for mass screening of AGT even in low-resource settings.

Accelerated fat cell aging links oxidative stress and insulin resistance in adipocytes.

Telomere shortening is emerging as a biological indicator of accelerated aging and aging-related diseases including type 2 diabetes. While telomere length measurements were largely done in white blood cells, there is lack of studies on telomere length in relation to oxidative stress in target tissues affected in diabetes. Therefore, the aim of this study is to induct oxidative stress in adipocytes and to test whether these adipocytes exhibit shortened telomeres, senescence and functional impairment. 3T3-L1 adipocytes were subjected to oxidative stress and senescence induction by a variety of means for 2 weeks (exogenous application of H2O2, glucose oxidase, asymmetric dimethylarginine (ADMA) and glucose oscillations). Cells were probed for reactive oxygen species generation (ROS), DNA damage, mRNA and protein expression of senescent and pro-inflammatory markers, telomere length and glucose uptake. Compared to untreated cells, both ROS generation and DNA damage were significantly higher in cells subjected to oxidative stress and senescence. Adipocytes subjected to oxidative stress also showed shortened telomeres and increased mRNA and protein expression of p53, p21, TNFα and IL-6. Senescent cells were also characterized by decreased levels of adiponectin and impaired glucose uptake. Briefly, adipocytes under oxidative stress exhibited increased ROS generation, DNA damage, shortened telomeres and switched to senescent/pro-inflammatory phenotype with impaired glucose uptake.

Benefits of early glycemic control by insulin on sensory neuropathy and cataract in diabetic rats.

While there is an emphasis on the early glycemic control for its long-term benefits in preventing microvascular complications of diabetes, the biochemical mechanisms responsible for the long-lasting effects are not clearly understood. Therefore the impact of early insulin (EI) versus late insulin (LI) treatment on diabetic sensory neuropathy and cataract in streptozotocin-induced diabetic Wistar male rats were evaluated. EI group received insulin (2.5 IU/animal, once daily) treatment from day 1 to 90 while LI group received insulin from day 60 to 90. Early insulin treatment significantly reduced the biochemical markers like glucose, triglyceride, glycated hemoglobin, thiobarbituric acid reactive substances, advanced glycation end products and ratio of reduced glutathione and oxidized glutathione in diabetic rats. The late insulin treatment failed to resist the biochemical changes in diabetic rats. Diabetic rats developed sensory neuropathy as evidenced by mechanical and thermal hyperalgesia and showed a higher incidence and severity of cataract as revealed by slit lamp examination. Early insulin treatment protected the rats from the development of neuropathy and cataract, but late insulin administration failed to do so. The results demonstrate the benefits of early glycemic control in preventing neuropathy and cataract development in diabetic rats.