Rapid and Efficient Enrichment of Snake Venoms from Human Plasma Using a Strong Cation Exchange Tip Column to Improve Snakebite Diagnosis

Snake envenomation is a serious public health issue in many tropical and subtropical countries. Accurate diagnosis and immediate antivenom treatment are critical for effective management. However, the venom concentration in the victims' plasma is usually low, representing one of the bottlenecks in developing clinically applicable assays for venom detection and snakebite diagnosis. In this study, we attempted to develop a simple method for rapid enrichment of venom proteins from human plasma to facilitate detection. Our experiments showed that several major protein components of both Naja atra (N. atra) and Bungarus multicinctus (B. multicinctus) venoms have higher isoelectric point (pI) values relative to high-abundance human plasma proteins and could be separated via strong cation exchange-high-performance liquid chromatography (SCX-HPLC). Based on this principle, we developed an SCX tip column-based protocol for rapid enrichment of N. atra and B. multicinctus venom proteins from human plasma. Application of liquid chromatography-tandem mass spectrometry (LC-MS/MS) led to the identification of cytotoxin and beta-bungarotoxin as the major proteins enriched by the SCX tip column in each venom sample. The entire process of venom enrichment could be completed within 10-15 min. Combination of this method with our previously developed lateral flow strip assays (rapid test) significantly enhanced the sensitivity of the rapid test, mainly via depletion of the plasma protein background, as well as increase in venom protein concentration. Notably, the SCX tip column-based enrichment method has the potential to efficiently enrich other Elapidae snake venoms containing proteins with higher pI values, thereby facilitating venom detection with other assays. This simple and rapid sample preparation method should aid in improving the clinical utility of diagnostic assays for snakebite.

An ISFET-based immunosensor for the detection of beta-Bungarotoxin

An ion-sensitive field effect transistor (ISFET)-based immunosensor was developed to detect/quantitate beta-Bungarotoxin (beta-BuTx), a potent presynaptic neurotoxin from the venom of Bungarus multicinctus. A murine monoclonal antibody (mAb 15) specific to beta-BuTx was immobilized onto silicon nitride wafers after silanization and activation with glutaraldehyde. A chip based enzyme linked-immunosorbantassay (ELISA) was performed to ascertain antigen binding to the immobilized antibody. To develop an electrochemical immunosensing system for the detection/quantitation of beta-BuTx, an ISFET was used as a solid phase detector. MAb 15 was immobilized on the gate region of the ISFET. The antigen antibody reaction was monitored by the addition of urease conjugated rabbit anti-beta-BuTx antibodies. The sensor can detect toxin level as low as 15.6 ng/ml. The efficacy of the sensor for the determination of beta-BuTx from B. multicinctus venom was demonstrated in mouse model. Toxin concentration was highest at the site of injection (748.0+/-26 ng/ml) and moderate amount was found in the plasma (158.5+/-13 ng/ml).

Saturable binding to cell membranes of the presynaptic neurotoxin, beta-bungarotoxin

Brief exposure to the protein neurotoxin, beta-bungarotoxin, is known to disrupt neuromuscular transmission irreversibly by blocking the release of transmitter from the nerve terminal. This neurotoxin also has a phospholipase A2 activity, although phospholipases in general are not very toxic. To determine if the toxicity of this molecule might result from specific binding to neural tissue, we have looked for high affinity, saturable binding using 125I-labelled toxin. At low membrane protein concentration 125I-labeled toxin binding was directly proportional to the amount of membrane; at fixed membrane concentration 125I-labeled toxin showed saturable binding. It was unlikely that iodination markedly changed the toxin's properties since the iodinated toxin had a comparable binding affinity to that of native toxin as judged by competition experiments. Comparison of toxin binding to brain, liver and red blood cell membranes showed that all had high affinity binding sites with dissociation constants between one and two nanomolar. This is comparable to the concentrations previously shown to inhibit mitochondrial function. However, the density of these sites showed marked variation such that the density of sites was 13.0 pmol/mg protein for a brain membrane preparation, 2.4 pmol/mg for liver and 0.25 pmol/mg for red blood cell membranes. In earlier work we had shown that calcium uptake by brain mitochondria is inhibited at much lower toxin concentrations than is liver mitochondrial uptake. Both liver and brain mitochondria bind toxin specifically, but the density of 125I-labeled toxin binding sites on brain mitochondrial preparations (3.3 +/- 0.3 pmol/mg) exceeded by a factor of ten the density on liver mitochondrial preparations (0.3 +/- 0.05 pmol/mg). It is also shown that labeled toxin does not cross synaptosomal membranes, suggesting that mitochondria may not be the site of action of the toxin in vivo. We conclude that beta-bungarotoxin is an enzyme which can bind specifically with high affinity to cell membranes.