Ultrasensitive determination of nitrite based on electrochemical platform of AuNPs deposited on PDDA-modified MXene nanosheets.

An ultrasensitive and high-performance electrochemical nitrite sensing platform based on gold nanoparticles deposited on poly (dimethyl diallyl ammonium chloride)-decorated MXene (Ti3C2Tx) (AuNPs/Ti3C2Tx-PDDA) was constructed. AuNPs/Ti3C2Tx-PDDA on the surface of electrode displayed synergetic catalytic effect for oxidizing NO2‾ originating from especially catalytic activity of AuNPs, large area and excellent conductivity of Ti3C2Tx, as well as electrostatic interaction of PDDA. The amperometry technique was employed for quantitative determination of nitrite, in which the AuNPs/Ti3C2Tx-PDDA/GCE sensing platform showed outstanding linear relationship in 0.1-2490 µM and 2490-13490 µM for nitrite, meanwhile the detection limit of 0.059 µM. Besides, the prepared sensor possessed high sensitivity of 250 µA mM-1 cm-2 yet excellent selectivity, stability and reproducibility. Furthermore, this platform also exhibited satisfactory feasibility of nitrite sensing in running water and ham sausage sample. This work would broaden a facile approach to construct high sensitivity electrochemical sensing platform via two-dimension materials and its nanocomposites.

Novel peptide VIP-TAT with higher affinity for PAC1 inhibited scopolamine induced amnesia.

A novel peptide VIP-TAT with a cell penetrating peptide TAT at the C-terminus of VIP was constructed and prepared using intein mediated purification with an affinity chitin-binding tag (IMPACT) system to enhance the brain uptake efficiency for the medical application in central nervous system. It was found by labeling VIP-TAT and VIP with fluorescein isothiocyanate (FITC) that the extension with TAT increased the brain uptake efficiency of VIP-TAT significantly. Then short-term and long-term treatment with scopolamine (Scop) was used to evaluate the effect of VIP-TAT or VIP on Scop induced amnesia. Both short-term and long-term administration of VIP-TAT inhibited the latent time reduction in step-through test induced by Scop significantly, but long-term administration of VIP aggravated the Scop induced amnesia. Long-term i.p. injection of VIP-TAT was shown to have positive effect by inhibiting the oxidative damage, apoptosis and the cholinergic system activity reduction that induced by Scop, while VIP exerted negative effect in brain opposite to that in periphery system. The in vitro data showed that VIP-TAT had not only protective but also proliferative effect on Neuro2a cells which was inhibited by PAC1 antagonist PACAP(6-38). Competition binding assay and cAMP assay confirmed that VIP-TAT had higher affinity and activation for PAC1 than VIP. So it was concluded that the significantly stronger protective effect of VIP-TAT against Scop induced amnesia than VIP was due to (1) the enhanced brain uptake efficiency of VIP-TAT and (2) the increased affinity and activation of VIP-TAT for receptor PAC1.

Transduced protein transduction domain linked HSP27 protected LECs against UVB radiation-induced damage.

PTD-fusion protein technology was used to transduce heat shock protein 27 (HSP27), an anti-apoptotic protein, into human lens epithelial cells (HLECs) (SRA01/04). The protein transduction domain (PTD) of the 11-amino acid YGRKKRRQRRR was tagged at the N-terminus of HSP27. The fusion protein was purified from bacteria transformed with a pKYB-PTD-HSP27 construct. The HLECs were incubated with PTD-HSP27-FITC and the fluorescence inside HLECs was found by fluorescence microscopic examination. To test the ability of PTD-HSP27 to pass through the corneas, PTD-HSP27-FITC was dropped onto the conjunctival sacs of rabbits; fluorescent labeled PTD-HSP27 was then observed in the rabbit aqueous humor. After being incubated with the PTD-HSP27 protein and irradiated with ultraviolet-B (UVB) light, HLECs was analyzed by flow cytometry, Hoechst 33258 staining and measurement of the potential of the mitochondrial transmembrane. HLECs incubated with PTD-HSP27 had a lower apoptotic rate and a higher mitochondrial membrane potential than the control cells. PTD-HSP27 appears to be sufficient to protect HLECs against UVB-induced apoptosis.

The TAT peptide endows PACAP with an enhanced ability to traverse bio-barriers.

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a potential therapeutic neuropeptide. The 11-amino acid human immunodeficiency virus TAT protein transduction domain is able to deliver protein cargoes across the cell membrane and the blood-brain barrier. A novel fusion protein PACAP-TAT, containing TAT at the C-terminus of PACAP was therefore produced and studied for the ability to cross blood barriers. The gene encoding PACAP-TAT was cloned into the expression vector pKYB, and the target peptide PACAP-TAT was purified using the Intein Mediated Purification with an Affinity Chitin-binding Tag (IMPACT) system. The results of cell assays showed that PACAP-TAT stimulated the cell viability of PAC1-CHO cells with the same potency as PACAP, which indicated that the fusion of TAT did not affect the ability of PACAP-TAT to activate the PACAP-specific receptor PAC1. The transfer efficiencies of PACAP-TAT and PACAP across the blood-brain barrier (BBB), blood-air barrier (BAB) and blood-testis barrier (BTB) were assayed using peptides labeled with fluorescein isothiocyanate (FITC). The results showed that PACAP-TAT traversed blood barriers with an efficiency approximately 2.5-fold greater than PACAP. Fluorescence microscopic examination showed that PACAP-TAT traversed the BBB significantly more efficiently than PACAP. Furthermore, intraperitoneal (i.p.) injection of PACAP-TAT induced a stronger inhibitory effect on food intake than PACAP (p<0.01, PACAP-TAT vs. PACAP), which indicated that TAT helped to increase the localization of PACAP-TAT in the brain. Preparation of PACAP-TAT with the enhanced ability to cross biological barriers will improve its route of administration and expand its scope of application.

The expression of PAC1 increases in the degenerative thymus and low dose PACAP protects female mice from cyclophosphamide induced thymus atrophy.

Pituitary adenylate cyclase activating polypeptide (PACAP) is a neuropeptide with cytoprotective ability mediated by its specific receptor PAC1. In this research, firstly the thymus index and the expression of PAC1 in the normal and degenerative thymus with different gender were assayed; secondly PACAP in different dose was used to treat the female mice with cyclophosphamide (CPS) and the changes in thymus index, the expression of PAC1, histopathology, apoptosis, oxidative status and the caspase 3 activity in thymus were determined and compared. It was found that in the mice of age from 1 to 9 weeks in the stage of sex development, the thymus index was significantly higher in female mice than in male mice. And it was found for the first time that the PAC1 expression level in thymus of female mice was significantly higher than that of male mice and the expression of the PAC1 and PACAP increased significantly in the degenerative thymus induced by CPS. After PACAP was co-injected with CPS to the female mice, it was shown that only low dose (1 nmol/kg) of PACAP promoted the thymus index, inhibited the cell apoptosis, ameliorated the oxidative status and decreased the caspase activity significantly, while high dose (10 nmol/kg) of PACAP had no significant protective effects against CPS-induced thymus atrophy. It was concluded that the expression of PAC1 in the thymus changes in reverse ratio with thymus index and in direct ratio with cell apoptosis and only low dose of PACAP had positive effects against the CPS-induced thymus atrophy.

The novel peptide PACAP-TAT with enhanced traversing ability attenuates the severe lung injury induced by repeated smoke inhalation.

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a potential therapeutic peptide with anti-inflammatory and anti-oxidative effects. In order to increase the efficiency of traversing biological barriers, a novel fusion peptide PACAP-TAT was produced by tagging PACAP at its C-terminus with 11-amino acid TAT protein transduction domain. The results of characteristic assays showed that PACAP-TAT activated PACAP specific receptor PAC1 with the same potency as PACAP and PACAP-TAT crossed blood-brain barrier (BBB), blood-air barrier (BAB) and blood-testis barrier (BTB) with the efficiency about 2.5-fold higher than that of PACAP. Both PACAP-TAT and PACAP were used treat the mice with lung injury induced by repeated smoke inhalation. It was shown that both PACAP-TAT and PACAP decreased the mortality, increased the body weight and inhibited the edema and vascular permeability in the lungs of the mice received repeated smoke inhalation, while PACAP-TAT displayed more marked effects than PACAP. PACAP-TAT decreased myeloperoxidase (MPO) activity, increased catalase (CAT) activity and down-regulated interleukin 6 (IL-6) and malondialdehyde (MDA) levels in the lungs with a significantly higher efficiency than PACAP. The histopathological analysis also showed that PACAP-TAT attenuated the cell filtration and bronchi epithelial hyperplasia more significantly than PACAP. Moreover the leukocyte count in blood and the serum superoxide dismutase (SOD) activity in the mice treated with PACAP-TAT were significantly different from that in mice treated with PACAP (p<0.05). All these data indicated that PACAP-TAT with increased traversing ability was more effective than PACAP in protecting the mice from the lung injury induced by repeated smoke inhalation.

The N-terminal HSDCIF motif is required for cell surface trafficking and dimerization of family B G protein coupled receptor PAC1.

PAC1 is PACAP (pituitary adenylate cyclase-activating polypeptide) preferring receptor belonging to class B G protein coupled receptor (GPCR) mediating the most effects of PACAP. The important role of G protein coupled receptor homo/heteromerization in receptor folding, maturation, trafficking, and cell surface expression has become increasingly evident. The bimolecular fluorescence complementation (BiFC) and bioluminescence resonance energy transfer (BRET) assay were used in this research to confirm the dimerization of PAC1 for the first time. The structure-activity relationship focused on the N-terminal HSDCIF motif, which locates behind the signal sequence and has high homology with PACAP (1-6), was assayed using a receptor mutant with the deletion of the HSDCIF motif. The fluorescence confocal microscope observation showed that the deletion of the HSDCIF motif impaired the cell delivery of PAC1. The results of BiFC, BRET and westernblot indicated that the deletion of HSDCIF motif and the replacement of the Cys residue with Ala in HSDCIF motif resulted in the disruption of receptor dimerization. And the exogenous chemically synthesized oligopeptide HSDCIF (100 nmol/L) not only down-regulated the dimerization of PAC1, induced the internalization of PAC1, but also inhibited the proliferation of CHO cells expressing PAC1 stably and decreased the activity of PACAP on the cell viability. All these data suggested that the N-terminal HSDCIF motif played key role in the trafficking and the dimerization of PAC1, and the exogenous oligopeptide HSDCIF had effects on the cell signaling, trafficking and the dimerization of PAC1.