Over expression of Glo can suppress inflammatory

Over-expression of Glo-1 can suppress inflammatory responses. Methylglyoxal mediates vascular inflammation in human endothelial Phosphatase Inhibitor Cocktail 3 (100X in DMSO) [33], indicating that Glo-1 may attenuate inflammation via eliminating methylglyoxal. Glo-1 knockdown mediated methylglyoxal accumulation provokes collagen expression and endothelial inflammation in human aortic endothelial cells resulting in vascular damage [34]. Importantly, a review paper collects original researches indicating that hesperidin and its aglycone hesperetin have wide anti-inflammatory efficacy [17]. Moreover, a recent report demonstrates that hesperetin shows strong protective effects against fulminant hepatitis in vivo and in vitro [35]. In our study, inflammatory cytokines IL-1β and TNF-α were markedly declined in renal cortex of diabetic rats after treatment with hesperetin, further confirming the inhibitory effects of hesperetin on inflammatory responses. Together with the above reports, we deduce that the anti-inflammatory efficacy of hesperetin should be likely related to the up-regulation of Glo-1. Additionally, there are studies indicating interactions between inflammation and AGEs/RAGE axis in many pathological conditions [[36], [37], [38]], including diabetes [39,40]. These further reflect that Glo-1 induction is highly pleiotropic. Up-regulation of Glo-1 is associated with the activation of Nrf2/ARE pathway. Transcription factor Nrf2 regulates gene expression of many antioxidant enzymes and phase II detoxification enzymes. The research team of Thornalley PJ firstly reports that Glo-1 is regulated and controlled by Nrf2/ARE signaling [24], and our research group further proved that down-regulation of Glo-1 was associated with the inactivation of Nrf2/ARE pathway in rat primary hippocampal and cerebral cortical neurons exposed to chronic high glucose [8]. Furthermore, in our previous report, Glo-1 was found markedly down-regulated in DN, and a natural product mangiferin ameliorated the pathological features at the early stage of DN in rats through the enhancement of renal Glo-1 functions [5]. The present study demonstrated that hesperetin significantly attenuated the functional and morphological injuries in the kidney of diabetic rats, accompanied by the enhancement of Nrf2/ARE pathway, as evidenced by the increased p-Nrf2 levels in both cytoplasma and nucleus as well as the elevated mRNA level, protein expression, and enzymatic activity (reflected by GSH levels) of γ-GCS, a well-known target gene of Nrf2/ARE signaling. Moreover, reports show that hesperidin inhibits H2O2-induced oxidative stress in hepatocytes via heme oxygenase 1 (HO-1) induction mediated by activation of MAPK/Nrf2 pathway [25], and hesperetin suppresses inflammatory responses in lipopolysaccharide-induced RAW 264.7 cells via the inhibition of NF-κB and activation of Nrf2/HO-1 pathways [26]. Together, these results confirm that hesperetin activates Nrf2/ARE pathway in DN, subsequently inducing Glo-1 up-regulation. Additionally, Zhang et al. report that hesperidin attenuates DN in type 2 diabetic mice via suppression of the TGFβ1 - ILK - Akt signaling pathway [21].
Contributors
Conflict of interest
Acknowledgments The work was supported through funding from the National Natural Science Foundation of China (81371210), and the Priority Academic Program Development of Jiangsu Higher Education Institutions, China.
Introduction Advanced glycation endproducts, sugar derived protein modifications, including imidazolone, pentosidine, N(epsilon)-(carboxymethyl)lysine (CML), accumulate in human pyramidal neurons in an age-dependent manner [3], [6]. Since AGEs are predominantly produced by the reaction of proteins with reactive carbonyl and dicarbonyl compounds, it might be of particular interest to investigate the age-dependent activity of their detoxification systems. The formation of methylglyoxal is an intrinsic feature of glycolysis via degradation of triose phosphate intermediates. Under normal physiological conditions, 0.1–0.4% of the glucose flux are diverted into methylglyoxal [18]. The electrophilic character of these dicarbonyl compounds enables these reactive oxoaldehydes to damage DNA by reacting with nucleophilic groups on DNA, and to modify proteins by reaction with arginine and lysine residues [12]. In addition to their damaging properties to macromolecules, oxoaldehydes also exert direct cellular effects. For example, methylglyoxal has also been shown to be cytotoxic by an apoptotic mechanism [2], [9]. In addition, it has been suggested to disturb physiological signaling by activation of different kinases including p38 MAPK and c-Jun N-terminal kinase (JNK) [5], [8]. Efficient cellular systems minimize the concentration of these toxic compounds. One of these dicarbonyl detoxification system, the glyoxalase system, consisting of glyoxalase I, glyoxalase II and using a catalytic amount of reduced glutathione, converts dicarbonyl compounds (α-oxoaldehydes) to their corresponding hydroxy acids such as methylylglyoxal to d-lactate [17]. Since the reaction of the dicarbonyl compounds (or their thiol esters) with glyoxalase I is the rate-limiting step, glyoxalase I activity indirectly determines the rate of AGE formation, and therefore might be of particular interest in aging and age-related diseases. Therefore, we investigated the age-dependent expression of glyoxalase I by PCR and determined its protein level by immunohistochemistry, Western blot, and its activity by enzyme activity assay in samples of healthy human brains of 19–82 years of age.