The protection of 4,4′-diphenylmethane-bis(methyl) carbamate from Cortex Mori on advanced glycation end product-induced endothelial dysfunction: Via inhibiting AGE formation or blocking AGEs–RAGE axis?

Pharmacological management of vascular endothelial dysfunction in diabetes: TCM and western medicine compared based on biomarkers and biochemical parameters

Diabetes, a worldwide health concern while burdening significant populace of countries with time due to a hefty increase in both incidence and prevalence rates. Hyperglycemia has been buttressed both in clinical and experimental studies to modulate widespread molecular actions that effect macro and microvascular dysfunctions. Endothelial dysfunction, activation, inflammation, and endothelial barrier leakage are key factors contributing to vascular complications in diabetes, plus the development of diabetes-induced cardiovascular diseases. The recent increase in molecular, transcriptional, and clinical studies has brought a new scope to the understanding of molecular mechanisms and the therapeutic targets for endothelial dysfunction in diabetes. In this review, an attempt made to discuss up to date critical and emerging molecular signaling pathways involved in the pathophysiology of endothelial dysfunction and viable pharmacological management targets. Importantly, we exploit some Traditional Chinese Medicines (TCM)/TCM isolated bioactive compounds modulating effects on endothelial dysfunction in diabetes. Finally, clinical studies data on biomarkers and biochemical parameters involved in the assessment of the efficacy of treatment in vascular endothelial dysfunction in diabetes was compared between clinically used western hypoglycemic drugs and TCM formulas.

The Effect and Mechanism of TRPC1, 3, and 6 on the Proliferation, Migration, and Lumen Formation of Retinal Vascular Endothelial Cells Induced by High Glucose

OBJECTIVE

Transient receptor potential canonical (TRPC) channels are involved in neovascularization repairing after vascular injury in many tissues. However, whether TRPCs play a regulatory role in the development of diabetic retinopathy (DR) has rarely been reported. In the present study, we selected TRPC1, 3, and 6 to determine their roles and mechanism in human retina vascular endothelial cells (HREC) under high glucose (HG) conditions.

METHODS

HRECs were cultured in vitro under HG, hyper osmosis, and normal conditions. The expression of TRPC1, 3, and 6 in the cells at 24 and 48 h were detected by RT-polymerase chain reaction (PCR), Western blot and cell immunohistochemistry (IHC); In various concentrations, SKF96365 acted on HG cultured HRECs, the expression of vascular endothelial growth factor (VEGF) were detected by the same methods above; and the CCK-8, Transwell, cell scratch assay, and Matrigel assay were used to assess cell proliferation, migration, and lumen formation.

RESULTS

The RT-PCR, Western blot, and IHC results showed that TRPC1 expression was increased, and TRPC6 mRNA expression was increased under high-glucose conditions. SKF96365 acted on HG cultured HRECs that VEGF expression was significantly decreased. The CCK-8 assay, Transwell assay, cell scratch assay, and Matrigel assay showed that cell proliferation, migration, and lumen formation were downregulated by SKF96365.

CONCLUSION

HG can induce increased expression of TRPC1 and 6 in HRECs. Inhibition of the TRPC pathway not only can decrease VEGF expression but also can prevent proliferation, migration, and lumen formation of HRECs induced by HG. Inhibition of TRPC channels is expected to become a drug target for DR.

Methylglyoxal in Metabolic Disorders: Facts, Myths, and Promises

Glucose and fructose metabolism originates the highly reactive byproduct methylglyoxal (MG), which is a strong precursor of advanced glycation end products (AGE). The MG has been implicated in classical diabetic complications such as retinopathy, nephropathy, and neuropathy, but has also been recently associated with cardiovascular diseases and central nervous system disorders such as cerebrovascular diseases and dementia. Recent studies even suggested its involvement in insulin resistance and beta-cell dysfunction, contributing to the early development of type 2 diabetes and creating a vicious circle between glycation and hyperglycemia. Despite several drugs and natural compounds have been identified in the last years in order to scavenge MG and inhibit AGE formation, we are still far from having an effective strategy to prevent MG-induced mechanisms. This review summarizes the endogenous and exogenous sources of MG, also addressing the current controversy about the importance of exogenous MG sources. The mechanisms by which MG changes cell behavior and its involvement in type 2 diabetes development and complications and the pathophysiological implication are also summarized. Particular emphasis will be given to pathophysiological relevance of studies using higher MG doses, which may have produced biased results. Finally, we also overview the current knowledge about detoxification strategies, including modulation of endogenous enzymatic systems and exogenous compounds able to inhibit MG effects on biological systems.

Identification and characterization of naturally occurring inhibitors against human carboxylesterase 2 in White Mulberry Root-bark

White Mulberry Root-bark (WMR) is an edible Chinese herbal used for the treatment of inflammation, nephritis and asthma. This study aimed to investigate the inhibitory effects of ethanol extract from WMR against human carboxylesterase 2 (hCE2), as well as to identity and character natural hCE2 inhibitors in this herbal. Our results demonstrated that the ethanol extract of WMR displayed potent inhibitory effects against hCE2, while three major bioactive constitutes in WMR were identified on the basis of LC fingerprinting combined with activity-based screening of LC fractions. Three bioactive compounds including SD, KG and SC were efficiently identified by comparison of LC retention times, UV and MS spectral data, with the help of authentic standards. The inhibition potentials and inhibition types of these natural compounds against hCE2 were further investigated in human liver microsomes. The results demonstrated that these bioactive compounds are potent non-competitive inhibitors against hCE2, with the K_i values ranging from 0.76μM to 1.09μM. All these findings suggested that three abundant natural compounds in WMR displayed potent inhibitory effects against hCE2, which could be used as lead compounds to develop more potent hCE2 inhibitors for the alleviation of hCE2-mediated severe delayed-onset diarrhea.

The C-terminal tails of 4,4'-diphenylmethane-bis(methyl) carbamate are essential for binding to receptor for advanced glycation end products to attenuate advanced glycation end products-induced inflammation and apoptosis responses in human umbilical vein endothelial cells

OBJECTIVES

A novel compound 4,4'-diphenylmethane-bis(methyl) carbamate (CM1) was shown to possess preventive activity on AGEs-induced human umbilical vein endothelial cells (HUVECs) damage via binding to RAGE. However, the underlying structural basis of CM1 on binding to RAGE was not fully understood.

METHODS

In the present study, CM1 analogues were designed and synthesized to compare the activity differences on inhibiting AGEs-induced inflammatory response including TGF-β1, RAGE protein expression in HUVECs, and macrophages migration and adhesion to HUVECs. In addition, the cell viability and anti-apoptosis activities of CM1 analogues were also examined.

KEY FINDINGS

These results indicated that CM1 had higher activities on preventing AGEs-induced HUVECs damage (inflammation, cell viability and apoptosis) than other analogues. The bioaffinity assay was conducted by CMC and demonstrated that the IC50 and dissociation equilibrium constants (Kd) of CM1 were lower whereas the Bmax was higher than other analogues. The incubation of RAGE protein with CM1 analogues by equilibrium dialysis method showed CM1 had a stronger binding rate than other CM1 analogues.

CONCLUSION

Our findings suggested that the C-terminal tails (methoxycarbonyl groups) of CM1 were the active groups for binding to RAGE and then led to the attenuation on RAGE-mediated endothelial dysfunction.

Curcumin inhibits advanced glycation end product-induced oxidative stress and inflammatory responses in endothelial cell damage via trapping methylglyoxal

Methylglyoxal (MGO)-induced carbonyl stress and pro-inflammatory responses have been suggested to contribute to endothelial dysfunction. Curcumin (Cur), a polyphenolic compound from Curcuma longa L., may protect endothelial cells against carbonyl stress-induced damage by trapping dicarbonyl compounds such as MGO. However, Cur-MGO adducts have not been studied in depth to date and it remains to be known whether Cur-MGO adducts are able to attenuate endothelial damage by trapping MGO. In the present study, 1,2-diaminobenzene was reacted with MGO to ensure the reliability of the reaction system. Cur was demonstrated to trap MGO at a 1:1 ratio to form adducts 1, 2 and 3 within 720 min. The structures of these adducts were identified by high-performance liquid chromatography/electrospray ionization tandem mass spectrometry. The kinetic curves of Cur (10(-7), 10(-6) and 10(-5) M) were measured from 0-168 h by fluorescent intensity. Cur significantly inhibited the formation of advanced glycation end products (AGEs). The differences in oxidative damage and the levels of pro-inflammatory cytokines following MGO + HSA or Cur-MGO treatment were investigated in human umbilical vein endothelial cells (HUVECs). Exposure of HUVECs to the Cur-MGO reaction adducts significantly reduced the intracellular ROS levels and improved cell viability compared with MGO alone. Furthermore, there was a significant reduction in the expression levels of transforming growth factor-β1 and intercellular adhesion molecule(-1) following treatment with Cur-MGO adducts compared with MGO alone. These results provide further evidence that the trapping of MGO by Cur inhibits the formation of AGEs. The current study indicates that the protective effect of Cur on carbonyl stress and pro-inflammatory responses in endothelial damage occurs via the trapping of MGO.

HMGB1 in health and disease

Complex genetic and physiological variations as well as environmental factors that drive emergence of chromosomal instability, development of unscheduled cell death, skewed differentiation, and altered metabolism are central to the pathogenesis of human diseases and disorders. Understanding the molecular bases for these processes is important for the development of new diagnostic biomarkers, and for identifying new therapeutic targets. In 1973, a group of non-histone nuclear proteins with high electrophoretic mobility was discovered and termed high-mobility group (HMG) proteins. The HMG proteins include three superfamilies termed HMGB, HMGN, and HMGA. High-mobility group box 1 (HMGB1), the most abundant and well-studied HMG protein, senses and coordinates the cellular stress response and plays a critical role not only inside of the cell as a DNA chaperone, chromosome guardian, autophagy sustainer, and protector from apoptotic cell death, but also outside the cell as the prototypic damage associated molecular pattern molecule (DAMP). This DAMP, in conjunction with other factors, thus has cytokine, chemokine, and growth factor activity, orchestrating the inflammatory and immune response. All of these characteristics make HMGB1 a critical molecular target in multiple human diseases including infectious diseases, ischemia, immune disorders, neurodegenerative diseases, metabolic disorders, and cancer. Indeed, a number of emergent strategies have been used to inhibit HMGB1 expression, release, and activity in vitro and in vivo. These include antibodies, peptide inhibitors, RNAi, anti-coagulants, endogenous hormones, various chemical compounds, HMGB1-receptor and signaling pathway inhibition, artificial DNAs, physical strategies including vagus nerve stimulation and other surgical approaches. Future work further investigating the details of HMGB1 localization, structure, post-translational modification, and identification of additional partners will undoubtedly uncover additional secrets regarding HMGB1's multiple functions.