Tissue engineering and peripheral nerve regeneration (III) -- Sciatic nerve regeneration with PDLLA nerve guide

The biodegradation rate and biocompatibility of poly(d, l -lactide) (PDLLA) in vivo were evaluated. The aim of this study was to establish a nerve guide constructed by the PDLLA with 3-D microenvironment and to repair a 10 mm of sciatic nerve gap in rats. The process of the nerve regeneration was investigated by histological assessment, electrophysiological examination, and determination of wet weight recovery rate of the gastrocnemius muscle. After 3 weeks, the nerve guide had changed from a transparent to an opaque status. The conduit was degraded and absorbed partly and had lost their strength with breakage at the 9th week of postoperation. At the conclusion of 12 weeks, proximal and distal end of nerves were anastomosed by nerve regeneration and the conduit vanished completely. The results suggest that PDLLA conduits may serve for peripheral nerve regeneration and PDLLA is a sort of hopeful candidate for tissue engineering.     

Materials for peripheral nerve regeneration

Recent efforts in scientific research in the field of peripheral nerve regeneration have been directed towards the development of artificial nerve guides. We have studied various materials with the aim of obtaining a biocompatible and biodegradable two layer guide for nerve repair. The candidate materials for use as an external layer for the nerve guides were poly(caprolactone) (PCL), a biosynthetic blend between PCL and chitosan (CS) and a synthesised poly(ester-urethane) (PU). Blending PCL, which is a biocompatible synthetic polymer, with a natural polymer enhanced the system biocompatibility and biomimetics, fastened the degradation rates and reduced the production costs. Various novel block poly(ester-urethane)s are being synthesised by our group with tailored properties for specific tissue engineering applications. One of these poly(ester-urethane)s, based on a low molecular weight poly(caprolactone) as the macrodiol, cycloesandimethanol as the chain extender and hexamethylene diisocyanate as the chain linker, was investigated for the production of melt extruded nerve guides. We studied natural polymers such as gelatin (G), poly(L-lysine) (PL) and blends between chitosan and gelatin (CS/G) as internal coatings for nerve guides. In vitro and in vivo tests were performed on PCL guides internally coated either with G or PL to determine the differences in the quality of nerve regeneration associated with the type of adhesion protein. CS/G natural blends combined the good cell adhesion properties of the protein phase with the ability to promote nerve regeneration of the polysaccharide phase. Natural blends were crosslinked both by physical and chemical crosslinking methods. In vitro neuroblast adhesion tests were performed on CS/G film samples, PCL/CS and PU guides internally coated with G to evaluate the ability of such materials towards nerve repair.     

Improvement of nerve conduction velocity in mutant diabetic mice by aldose reductase inhibitor without affecting nerve myo-inositol content

The sciatic motor nerve conduction velocity of mutant diabetic C57BL/Ks mice was significantly improved from 30.0 +/- 1.4 to 38.0 +/- 4.6 m/s by treatment with the aldose reductase inhibitor 1-[(beta-naphthyl)sulfonyl]hydantoin (30 mg/kg/d) for 2 weeks. The treatment, however, did not cause any significant change in myo-inositol concentration in the sciatic nerve. The results indicate that the ameliorating effect of the aldose reductase inhibitor on nerve conduction velocity in mutant diabetic mice is not due to alteration of myo-inositol content in the nerve.     

Rapid fluorophosphate nerve agent detection with lanthanides

We explore the detection of vapors of diisopropylfluorophosphate, a model compound for nerve agents such as Sarin, by means of photoluminescence quenching of filter paper impregnated with sensitized complexes of lanthanides, involving thenoyltrifluoroacetone and 1,10-phenanthroline as sensitizing ligands. We find that the presence of the fluorophosphate vapor is detectable in as little as 2 s, by simple visual observation under illumination with a hand-held low intensity ultraviolet lamp.     

Fluorescent sensors for organophosphorus nerve agent mimics

We present a small molecule sensor that provides an optical response to the presence of an organophosphorus (OP)-containing nerve agent mimic. The design contains three key features: a primary alcohol, a tertiary amine in close proximity to the alcohol, and a fluorescent group used as the optical readout. In the sensor's rest state, the lone pair of electrons of the basic amine quenches the fluorescence of the nearby fluorophore through photoinduced electron transfer (PET). Exposure to an OP nerve agent mimic triggers phosphorylation of the primary alcohol followed rapidly by an intramolecular substitution reaction as the amine displaces the created phosphate. The quaternized ammonium salt produced by this cyclization reaction no longer possesses a lone pair of electrons, and a fluorescence readout is observed as the nonradiative PET quenching pathway of the fluorophore is shut down.     

QSAR of chemical polarizability and nerve toxicity. 2

Polarizability is a property of molecules that has long been of interest to scientists from a variety of viewpoints. However, in the area of the QSAR of chemical-biological interactions, it has received little attention. Recently we have shown that one can use the simple summation of the valence electrons (H = 1, C = 4, O = 6, etc.) in a molecule as a measure of its polarizability. We have found this parameter to correlate nerve toxicity of a wide variety of chemicals acting on nerves of frogs, rabbits, cockroaches, and humans.     

Detection of nerve agent markers by liquid chromatography-mass spectrometry

An approach to the detection of metabolites of organophosphorous agents (OPA), such as O-iso-propylmethylphosphonic acid (detection limit, 4 ng/mL), O-pinacolylmethylphosphonic acid (0.6 ng/mL), and O-isobutylmethylphosphonic acid (1 ng/mL), in plasma samples was developed using liquid chromatography-mass spectrometry. The curves of the elutionxcretion of OPA metabolites were obtained for the samples of biological material of rats exposed to toxic substances. Determination was performed by mass spectrometry with electrospray ionization in the negative ion mode, using deprotonated molecules for detection. The biological samples were analyzed by reversed-phase chromatography using hydrophilic end-capped adsorbents. Solid phase extraction on reversed-phase adsorption cartridges containing a copolymer of styrene and divinylbenzene was proposed for sample preparation.     

Characteristics of PLGA-gelatin complex as potential artificial nerve scaffold

The segmentation lesion of peripheral nerve will seriously impair the motion and sensation of the patients, and the satisfactory recovery of segmented peripheral nerve by autograft or allograft is still a great challenge posing to the neurosurgery. Apart from autograft for nerve repair, different allograft has been studying. In this study, a scaffold fabricated with polylactic acid-co-glycolic acid (PLGA) copolymer and gelatin was evaluated to be a potential artificial nerve scaffold in vitro. The effect of different mass ratio between PLGA and gelatin upon the characteristics of PLGA–gelatin scaffolds such as microstructure, mechanical property, degradation behavior in PBS, cell adhesion property were investigated. The results showed the homogeneity and mechanical property of the scaffolds became poor with the increase of gelatin, and the rate of max water-uptake and the mass loss of scaffolds increases with the increase of gelatin, and the cells could adhere to the scaffolds. Those indicated the scaffolds fabricated by the PLGA–gelatin complex had excellent biocompatibility, suitable mechanical property and sustained-release characteristics, which would meet the requirements for artificial nerve scaffold.     

Di-isopropyl fluorophosphate electrode based on squid nerve tissue

Di-isopropyl fluorophosphatase is contained in the giant axon of squid nerve tissue. This tissue can be coupled with a fluoride ion-selective electrode to produce an electrode selective to di-isopropyl fluorophosphate. The semilogarithmic calibration curve at pH 7.1 is linear over the range 2 × 10^?6?7 × 10^?3 M (RSD < 3% ) with a slope of about 44 mV/decade. The detection limit is 8 × 10^?6 M. The electrode lifetime (with constant response characteristics) is about 16 days.     

Immunoaffinity fractionation of neutralizing polyclonal antibodies to nerve growth factors

A method of fractionation according to affinity and specificity of polyclonal antibodies to murine and ovine nerve growth factors (NGFs) has been developed. The antibody preparations obtained neutralize the biological activity of -NGF at a molar ratio of about 1 and recognize the species-specific and conservative epitopes of these NGFs, being valuable probes for two-site immunoanalyses.Institute of Biochemistry, Uzbek Academy of Sciences, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 828–833, November–December, 1991.     

Reaction of nerve agents with phosphate buffer at pH 7

Chemical weapon nerve agents, including isopropyl methylphosphonofluoridate (GB or Sarin), pinacolyl methylphosphonofluoridate (GD or Soman), and S-(2-diisopropylaminoethyl) O-ethyl methylphosphonothioate (VX), are slow to react in aqueous solutions at midrange pH levels. The nerve agent reactivity increases in phosphate buffer at pH 7, relative to distilled water or acetate buffer. Reactions were studied using (31)P NMR. Phosphate causes faster reaction to the corresponding alkyl methylphosphonic acids, and produces a mixed phosphate/phosphonate compound as an intermediate reaction product. GB has the fastest reaction rate, with a bimolecular rate constant of 4.6 × 10(-3) M(-1)s(-1)[PO(4)(3-)]. The molar product branching ratio of GB acid to the pyro product (isopropyl methylphosphonate phosphate anhydride) is 1:1.4, independent of phosphate concentration, and the pyro product continues to react much slower to form GB acid. The pyro product has two doublets in the (31)P NMR spectrum. The rate of reaction for GD is slower than GB, with a rate constant of 1.26 × 10(-3) M(-1)s(-1) [PO(4)(3-)]. The rate for VX is considerably slower, with a rate constant of 1.39 × 10(-5) M(-1)s(-1) [PO(4)(3-)], about 2 orders of magnitude slower than the rate for GD. The rate constant of the reaction of GD with pyrophosphate at pH 8 is 2.04 × 10(-3) min(-1) at a concentration of 0.0145 M. The rate of reaction for diisopropyl fluorophosphate is 2.84 × 10(-3) min(-1) at a concentration of 0.153 M phosphate, a factor of 4 slower than GD and a factor of 15 slower than GB, and there is no detectable pyro product. The half-lives of secondary reaction of the GB pyro product in 0.153 and 0.046 M solution of phosphate are 23.8 and 28.0 h, respectively, which indicates little or no dependence on phosphate.     

New spot test for some phosphorus nerve gases

A new spot test reaction is described for the identification of some phosphorus nerve gases. The reaction is based on peroxidation of the nerve gas with 5% urea peroxide in 3% potassium-sodium carbonate followed by a reaction with thallium(I) sulfate to form a yellow color or precipitate of thallium(III) oxyhydrate. A rapid and sensitive reaction with o-dianisidine is also described. Some nerve gases (0.1–15 μg) are detected by both procedures.     

Facilitating the culture of mammalian nerve cells with polyelectrolyte multilayers

When neuron-like cells (NLCs) derived from pluripotent embryonal carcinoma cells (P19) are cultured on bare tissue culture substrates, they require a monolayer of fibroblast cells to exhibit normal neurite outgrowth, behavior typical of neuronal cultures. However, substrate treatment with polyelectrolyte multilayers (PEMs) composed of poly(allylamine hydrochloride) (PAH) and poly(styrenesulfonic acid) (PSS) significantly improved these cultures. Cell morphology was more spread, indicative of healthy cells, and direct attachment of neuronal cell bodies to the treated surface was observed. Neuronal outgrowth across the surface was not dependent on an underlying fibroblast monolayer with the PEMs surface treatment. Additionally, the PEMs surface treatment can be used to condition various surfaces, facilitating neuronal cultures on surfaces which are natively hydrophilic (tissue culture polystyrene) or hydrophobic (poly(dimethylsiloxane), PDMS). Microfluidic networks were used to micropattern the PEMs onto PDMS, resulting in confined regions of cellular attachment and directed neuronal outgrowth. The ability of PEMs to encourage NLC attachment without supporting cells to a variety of surfaces and surface geometries greatly simplifies neuronal culture methodology and enables neuronal investigations in new environments.     

Analysis of nerve agents using capillary electrophoresis and laboratory-on-a-chip technology

The nerve agents belong among the most toxic compounds produced by human kind. While they have been used very sporadically until now, typically in local conflicts or by local terrorists groups, the global increase in terrorist activity in the recent years has generated tremendous demand for innovative tools capable of detecting nerve agents. Fast, sensitive and reliable detection of nerve agents in the field is very important issue in present days. Capillary electrophoresis (CE) offers great possibilities for sensitive detection of these harmful compounds as well as incorporation in mobile laboratory and it proved to have capability to detect nerve agent breakdown products in real environmental samples. Laboratory-on-a-chip format offers great possibilities to create portable, field deployable, rapidly responding and potentially disposable device, allowing security forces to make the important decision regarding the safety of civilians. This article overviews the conventional capillary electrophoretic and laboratory-on-a-chip techniques for analysis of degradation products of G-type and V-type nerve agents. It discusses diverse strategies of detection of different nerve agents breakdown products, which are corresponding to their parental nerve agents. It also overviews possibilities and challenges for analysis of the real samples.     

A lab-on-a-chip for detection of nerve agent sarin in blood

Sarin (C(4)H(10)FO(2)P,O-isopropyl methylphosphonofluoridate) is a colourless, odourless and highly toxic phosphonate that acts as a cholinesterase inhibitor and disrupts neuromuscular transmission. Sarin and related phosphonates are chemical warfare agents, and there is a possibility of their application in a military or terrorist attack. This paper reports a lab-on-a-chip device for detecting a trace amount of sarin in a small volume of blood. The device should allow early detection of sarin exposure during medical triage to differentiate between those requiring medical treatment from mass psychogenic illness cases. The device is based on continuous-flow microfluidics with sequential stages for lysis of whole blood, regeneration of free nerve agent from its complex with blood cholinesterase, protein precipitation, filtration, enzyme-assisted reaction and optical detection. Whole blood was first mixed with a nerve gas regeneration agent, followed by a protein precipitation step. Subsequently, the lysed product was filtered on the chip in two steps to remove particulates and fluoride ions. The filtered blood sample was then tested for trace levels of regenerated sarin using immobilised cholinesterase on the chip. Activity of immobilised cholinesterase was monitored by the enzyme-assisted reaction of a substrate and reaction of the end-product with a chromophore. Resultant changes in chromophore-induced absorbance were recorded on the chip using a Z-shaped optical window. Loss of enzyme activity obtained prior and after passage of the treated blood sample, as shown by a decrease in recorded absorbance values, indicates the presence of either free or regenerated sarin in the blood sample. The device was fabricated in PMMA (polymethylmethacrylate) using CO(2)-laser micromachining. This paper reports the testing results of the different stages, as well as the whole device with all stages in the required assay sequence. The results demonstrate the potential use of a field-deployable hand-held device for point-of-care triage of suspected nerve agent casualties.     

Immunoaffinity fractionation of neutralizing polyclonal antibodies to nerve growth factors

A method of fractionation according to affinity and specificity of polyclonal antibodies to murine and ovine nerve growth factors (NGFs) has been developed. The antibody preparations obtained neutralize the biological activity of β-NGF at a molar ratio of about 1 and recognize the species-specific and conservative epitopes of these NGFs, being valuable probes for two-site immunoanalyses. Institute of Biochemistry, Uzbek Academy of Sciences, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 828–833, November–December, 1991.     

Theoretical proton affinity and fluoride affinity of nerve agent VX

Proton affinity and fluoride affinity of nerve agent VX at all of its possible sites were calculated at the RI-MP2/cc-pVTZ//B3LYP/6-31G* and RI-MP2/aug-cc-pVTZ//B3LYP/6-31+G* levels, respectively. The protonation leads to various unique structures, with H(+) attached to oxygen, nitrogen, and sulfur atoms; among which the nitrogen site possesses the highest proton affinity of -ΔE ～ 251 kcal/mol, suggesting that this is likely to be the major product. In addition some H(2), CH(4) dissociation as well as destruction channels have been found, among which the CH(4) + [Et-O-P(═O)(Me)-S-(CH(2))(2)-N(+)(iPr)═CHMe] product and the destruction product forming Et-O-P(═O)(Me)-SMe + CH(2)═N(+)(iPr)(2) are only 9 kcal/mol less stable than the most stable N-protonated product. For fluoridization, the S-P destruction channel to give Et-O-P(═O)(Me)(F) + [S-(CH(2))(2)-N-(iPr)(2)](-) is energetically the most favorable, with a fluoride affinity of -ΔE ～ 44 kcal. Various F(-) ion-molecule complexes are also found, with the one having F(-) interacting with two hydrogen atoms in different alkyl groups to be only 9 kcal/mol higher than the above destruction product. These results suggest VX behaves quite differently from surrogate systems.     

Determination of protein adducts of organophosphorus nerve agents in blood plasma

A comparative study of the efficiency of procedures for the determination of the biomarkers of organophosphorus agents (OPAs) in blood plasma was performed. It was found that the gas chromatography–mass spectrometry determination of OPAs reactivated from the composition of protein adducts is a rapid method for the detection of exposure to OPAs. The liquid chromatography–mass spectrometry determination of phosphonylated butyrylcholinesterase and albumin fragments modified with OPA residues provides an opportunity to perform more sensitive and retrospective analysis. The tyrosine adducts of OPAs with serum albumin and other blood plasma proteins are not prone to dealkylation in the course of aging; in the series of the test markers, they possess the greatest diagnostic value because they make it possible to determine the precise structure a toxic agent after the longest time interval after exposure. The tentative limit of detection of OPA markers varies from 0.1 to 1.0 ng/mL.     

Smart hydrogel sensor for detection of organophosphorus chemical warfare nerve agents

A novel “turn-off” fluorescence, smart hydrogel sensor for detection of a nerve agent simulant has been developed and tested. The smart hydrogel chemosensor has demonstrated an extremely fast and select fluorescence quenching detection response to the Sarin simulant diethylchlorophosphate (DCP) in the aqueous and vapor phases. The fluorogenic sensor utilizes 6,7-dihydroxycoumarin embedded in an polyacrylamide hydrogel matrix as the fluorescent sensing material. The rapid fluorescence quenching of the smart hydrogel films could easily be observed with the naked eye using a hand-held UV light at λ = 365 nm which demonstrates their practical application in real-time on-site monitoring.     

Tissue engineering and peripheral nerve regeneration (III)

The biodegradation rate and biocompatibility of poly (d, / -lactide) (PDLLA)in vivo were evaluated. The aim of this study was to establish a nerve guide constructed by the PDLLA with 3-D microenvironment and to repair a 10 mm of sciatic nerve gap in rats. The process of the nerve regeneration was investigated by histological assessment, electrophysiological examination, and determination of wet weight recovery rate of the gastrocnemius muscle. After 3 weeks, the nerve guide had changed from a transparent to an opaque status. The conduit was degraded and absorbed partly and had lost their strength with breakage at the 9th week of postoperation. At the conclusion of 12 weeks, proximal and distal end of nerves were anastomosed by nerve regeneration and the conduit vanished completely. The results suggest that PDLLA conduits may serve for peripheral nerve regeneration and PDLLA is a sort of hopeful candidate for tissue engineering.