Increased nitric oxide synthase activity is essential for electromagnetic-pulse-induced blood-retinal barrier breakdown in vivo

Panax notoginseng saponins alleviate diabetic retinopathy by inhibiting retinal inflammation: Association with the NF-κB signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Diabetic retinopathy (DR) is a neurovascular disease that causes blindness in adults and is the most serious and common complication of diabetes mellitus. Retinal inflammation is an early stage of DR, and it is believed to play a crucial role in the development of DR. Panax notoginseng saponins (PNS) are the major active constituent in the main root of P. notoginseng, and they exhibit various biological activities, including anti-inflammatory, antioxidant, neuroprotective, and immunomodulatory functions. However, the protective effects and underlying mechanisms of PNS against DR remain unclear.

AIM OF THE STUDY

This study aimed to investigate the alleviation effects of PNS on DR and the mechanisms involved. Furthermore, it intended to explore the major components that exert efficacy in vivo.

MATERIALS AND METHODS

Streptozotocin (STZ) was administered intraperitoneally to Sprague Dawley rats, and PNS was administered orally for 1 month after 2 months of STZ injection. The morphological structure of the retina and retinal acellular capillaries were assessed via hematoxylin and eosin (H&E) staining assay. The disruption of the blood-retinal barrier (BRB) was detected through Evans blue dye leakage assay, and retinal leukocyte adhesion was achieved via fluorescein isothiocyanate-coupled concanavalin A lectin labeling assay. Immunofluorescence staining and Western blot assays were conducted to detect the expression of tight junction proteins, adhesion molecules, and the ionized calcium-binding adapter molecule-1 (Iba-1) in the retina. Enzyme-linked immunosorbent assay was performed to detect the levels of tumor necrosis factor (TNF)-α, interleukin (IL)-6, and IL-1β in serum. In addition, the protein expression levels of nuclear factor (NF)-κB p65, phosphorylated IκB kinase (p-IKK), phosphorylated NF-κB inhibitor (p-IκB), and phosphorylated NF-κB p65 (p-p65) were measured using Western blot assay. The ocular tissue distribution of PNS in normal and diabetic rats was determined through ultra-performance liquid chromatography-tandem mass spectrometry. The in vitro anti-inflammatory effects of PNS, notoginsenoside (NGR1), ginsenoside Rg1, Re, Rb1, and Rd (GRg1, GRe, GRb1, and GRd) were evaluated on human Müller (MIO-M1) cells.

RESULTS

PNS increased the reduction in retinal inner nuclear layer thickness, reduced the increase in retinal acellular capillaries, and attenuated elevated BRB disruption by upregulating the decrease in protein expression of claudin-1 and occludin. Furthermore, PNS significantly abrogated microglial cell activation and reversed the increase in leukocyte adhesion by downregulating the increase in the protein expression of intercellular adhesion molecule-1 and vascular cell adhesion molecule-1. Moreover, PNS reduced the elevated levels of TNF-α, IL-6, and IL-1β in serum and inhibited the increased protein expression of p-IKK, p-IκB, and p-p65, and the nuclear translocation of p65. The tissue distribution results revealed that NGR1, GRg1, GRe, GRb1, and GRd were detected in the ocular tissue, while GRg1 and GRb1 were found at the highest levels compared with the other components. The cellular results showed that PNS, NGR1, GRg1, GRe, GRb1, and GRd suppressed the development of cellular inflammatory responses by inhibiting the activation of the NF-κB signaling pathway in MIO-M1 cells and that their anti-inflammatory effects were comparable.

CONCLUSION

PNS suppressed retinal inflammation by inhibiting the activation of the NF-κB signaling pathway, alleviating DR. GRg1 and GRb1 may be the primary components that exert anti-inflammatory effects in vivo.

Breaking barriers: Neurodegenerative repercussions of radiotherapy induced damage on the blood-brain and blood-tumor barrier

Exposure to radiation during the treatment of CNS tumors leads to detrimental damage of the blood brain barrier (BBB) in normal tissue. Effects are characterized by leakage of the vasculature which exposes the brain to a host of neurotoxic agents potentially leading to white matter necrosis, parenchymal calcification, and an increased chance of stroke. Vasculature of the blood tumor barrier (BTB) is irregular leading to poorly perfused and hypoxic tissue throughout the tumor that becomes resistant to radiation. While current clinical applications of cranial radiotherapy use dose fractionation to reduce normal tissue damage, these treatments still cause significant alterations to the cells that make up the neurovascular unit of the BBB and BTB. Damage to the vasculature manifests as reduction in tight junction proteins, alterations to membrane transporters, impaired cell signaling, apoptosis, and cellular senescence. While radiotherapy treatments are detrimental to normal tissue, adapting combined strategies with radiation targeted to damage the BTB could aid in drug delivery. Understanding differences between the BBB and the BTB may provide valuable insight allowing clinicians to improve treatment outcomes. Leveraging this information should allow advances in the development of therapeutic modalities that will protect the normal tissue while simultaneously improving CNS tumor treatments.

Dendrobium chrysotoxum Lindl. alleviates diabetic retinopathy by preventing retinal inflammation and tight junction protein decrease

Diabetic retinopathy (DR) is a serious complication of diabetes mellitus. This study aimed to observe the alleviation of the ethanol extract of Dendrobium chrysotoxum Lindl. (DC), a traditional Chinese herbal medicine, on DR and its engaged mechanism. After DC (30 or 300 mg/kg) was orally administrated, the breakdown of blood retinal barrier (BRB) in streptozotocin- (STZ-) induced diabetic rats was attenuated by DC. Decreased retinal mRNA expression of tight junction proteins (including occludin and claudin-1) in diabetic rats was also reversed by DC. Western blot analysis and retinal immunofluorescence staining results further confirmed that DC reversed the decreased expression of occludin and claudin-1 proteins in diabetic rats. DC reduced the increased retinal mRNA expressions of intercellular adhesion molecule-1 (ICAM-1), tumor necrosis factor α (TNFα), interleukin- (IL-) 6, and IL-1β in diabetic rats. In addition, DC alleviated the increased 1 and phosphorylated p65, IκB, and IκB kinase (IKK) in diabetic rats. DC also reduced the increased serum levels of TNFα, interferon-γ (IFN-γ), IL-6, IL-1β, IL-8, IL-12, IL-2, IL-3, and IL-10 in diabetic rats. Therefore, DC can alleviate DR by inhibiting retinal inflammation and preventing the decrease of tight junction proteins, such as occludin and claudin-1.

Protection of blood retinal barrier and systemic vasculature by insulin-like growth factor binding protein-3

Previously, we showed that insulin growth factor (IGF)-1 binding protein-3 (IGFBP-3), independent of IGF-1, reduces pathological angiogenesis in a mouse model of the oxygen-induced retinopathy (OIR). The current study evaluates novel endothelium-dependent functions of IGFBP-3 including blood retinal barrier (BRB) integrity and vasorelaxation. To evaluate vascular barrier function, either plasmid expressing IGFBP-3 under the regulation of an endothelial-specific promoter or a control plasmid was injected into the vitreous humor of mouse pups (P1) and compared to the non-injected eyes of the same pups undergoing standard OIR protocol. Prior to sacrifice, the mice were given an injection of horseradish peroxidase (HRP). IGFBP-3 plasmid-injected eyes displayed near-normal vessel morphology and enhanced vascular barrier function. Further, in vitro IGFBP-3 protects retinal endothelial cells from VEGF-induced loss of junctional integrity by antagonizing the dissociation of the junctional complexes. To assess the vasodilatory effects of IGFBP-3, rat posterior cerebral arteries were examined in vitro. Intraluminal IGFBP-3 decreased both pressure- and serotonin-induced constrictions by stimulating nitric oxide (NO) release that were blocked by L-NAME or scavenger receptor-B1 neutralizing antibody (SRB1-Ab). Both wild-type and IGF-1-nonbinding mutant IGFBP-3 (IGFBP-3NB) stimulated eNOS activity/NO release to a similar extent in human microvascular endothelial cells (HMVECs). NO release was neither associated with an increase in intracellular calcium nor decreased by Ca²⁺/calmodulin-dependent protein kinase II (CamKII) blockade; however, dephosphorylation of eNOS-Thr⁴⁹⁵ was observed. Phosphatidylinositol 3-kinase (PI3K) activity and Akt-Ser⁴⁷³ phosphorylation were both increased by IGFBP-3 and selectively blocked by the SRB1-Ab or PI3K blocker LY294002. In conclusion, IGFBP-3 mediates protective effects on BRB integrity and mediates robust NO release to stimulate vasorelaxation via activation of SRB1. This response is IGF-1- and calcium-independent, but requires PI3K/Akt activation, suggesting that IGFBP-3 has novel protective effects on retinal and systemic vasculature and may be a therapeutic candidate for ocular complications such as diabetic retinopathy.

Effect of Electromagnetic Pulses (EMP) on associative learning in mice and a preliminary study of mechanism

PURPOSE

To investigate the effects of electromagnetic pulses (EMP) on associative learning in mice and test a preliminary mechanism for these effects.

MATERIALS AND METHODS

A tapered parallel plate gigahertz transverse electromagnetic (GTEM) cell with a flared rectangular coaxial transmission line was used to expose male BALB/c mice to EMP (peak-intensity 400 kV/m, rise-time 10 ns, pulse-width 350 ns, 0.5 Hz and total 200 pulses). Concurrent sham-exposed mice were used as a control. Associative learning, oxidative stress in the brain, serum chemistry and the protective action of tocopherol monoglucoside (TMG) in mice were measured, respectively.

RESULTS

(1) Twelve hour and 1 day post EMP exposure associative learning was reduced significantly compared with sham control (p<0.05) but recovered at 2 d post EMP exposure. (2) Compared with the sham control, lipid peroxidation of brain tissue and chemiluminescence (CL) intensity increased significantly (p<0.05), while the activity of the antioxidant enzymes Superoxide Dismutase [SOD], Glutathione [GSH], Glutathione Peroxidase [GSH-Px], Catalase [CAT]) decreased significantly (p<0.05) at 3 h, 6 h, 12 h and 1 d post EMP exposure. All these parameters recovered at 2 d post EMP exposure. (3) No significant differences between the sham control group and EMP exposed group were observed in serum cholesterol and triglycerides. (4) Pretreatment of mice with TMG showed protective effects to EMP exposure.

CONCLUSIONS

EMP exposure significantly decreased associative learning in mice and TMG acted as an effective protective agent from EMP exposure. This mechanism could involve an increase of oxidative stress in brain by EMP exposure.