Kalpana Parikh

Gene-Delivered Butyrylcholinesterase Is Prophylactic against the Toxicity of Chemical Warfare Nerve Agents and Organophosphorus Compounds

Gene delivery using an adenoviral system has been effective in introducing therapeutic proteins in vitro and in vivo. This study tested the feasibility of using adenovirus to deliver clinically relevant amounts of butyrylcholinesterase (BChE), a proven bioscavenger of nerve agents. The adenovirus construct expressed full-length mouse BChE. Mice were injected with a single dose of adenovirus (1.5 × 1010 infectious units) in the tail vein; plasma was collected through day 11 and assayed for BChE activity. Maximum activity, representing a 300- to 3400-fold increase over baseline, was found on day 4. Expression levels returned to baseline by day 10. Nondenaturing gel electrophoresis showed the recombinant BChE was a dimer that could be converted to tetramers by addition of polyproline. The toxic compounds chosen for protection studies were positively charged organophosphorus agents, echothiophate, and O-ethyl-S-2-N,N-diisopropylaminoethyl methylphosphonothiolate (VX). Mice containing elevated blood levels of BChE (300- to 3,000-fold over the control mice) were challenged with incremental doses of echothiophate or VX. Mice showed no signs of toxicity and were protected from up to 30× LD50 dose of echothiophate and 5× LD50 dose of VX. A good correlation was observed between tolerated echothiophate dose and plasma BChE levels at time of challenge. The absolute increases in levels of circulating BChE and the sustained nature of the response resulted in a very high enzyme concentration, deemed critical in acute toxicity (5× LD50 or more) scenarios. These results suggest that gene-delivered BChE is a prophylactic and affords protection equivalent to that of a multimilligram injection of the same.

Adenovirus-mediated human paraoxonase1 gene transfer to provide protection against the toxicity of the organophosphorus pesticide toxicant diazoxon

Human paraoxonase1 (hPON1) is a potential therapeutic against the toxicity of organophosphorus (OP) pesticides and chemical warfare nerve agents. We tested whether PON1 gene transfer using adenovirus provides protection against the toxicity of the OP diazoxon. Using an adenovirus construct containing hPON1 gene, we showed elevated levels of recombinant hPON1 in vitro in 293A cells and in vivo in mice. The recombinant enzyme was secreted by 293A cells into culture medium and into the systemic circulation of mice. Western blotting revealed that the virally expressed hPON1 had the expected molecular weight of 45 kDa. Recombinant hPON1 in mice was in complex with mouse high-density lipoprotein (HDL) and migrated more slowly than endogenous hPON1 in the human HDL complex. Mice injected with adenovirus expressed PON1 at 600–3480 U ml–1 on day 5 post-treatment, which is 8–50-fold above endogenous. Six mice expressing hPON1 survived 2LD50 doses of diazoxon. Four of the six mice survived a second dose of diazoxon (for a total of 4LD50) administered 24 h later. In contrast, none of the three mice in the control group survived one 2LD50 dose. These results show that hPON1 in mice functions as a prophylactic and offers significant protection against lethal doses of diazoxon.

Senescence Marker Protein 30 (SMP30) Expression in Eukaryotic Cells: Existence of Multiple Species and Membrane Localization

Senescence marker protein (SMP30), also known as regucalcin, is a 34 kDa cytosolic marker protein of aging which plays an important role in intracellular Ca2+ homeostasis, ascorbic acid biosynthesis, oxidative stress, and detoxification of chemical warfare nerve agents. In our goal to investigate the activity of SMP30 for the detoxification of nerve agents, we have produced a recombinant adenovirus expressing human SMP30 as a fusion protein with a hemaglutinin tag (Ad-SMP30-HA). Ad-SMP30-HA transduced the expression of SMP30-HA and two additional forms of SMP30 with molecular sizes ∼28 kDa and 24 kDa in HEK-293A and C3A liver cells in a dose and time-dependent manner. Intravenous administration of Ad-SMP30-HA in mice results in the expression of all the three forms of SMP30 in the liver and diaphragm. LC-MS/MS results confirmed that the lower molecular weight 28 kDa and 24 kDa proteins are related to the 34 kDa SMP30. The 28 kDa and 24 kDa SMP30 forms were also detected in normal rat liver and mice injected with Ad-SMP30-HA suggesting that SMP30 does exist in multiple forms under physiological conditions. Time course experiments in both cell lines suggest that the 28 kDa and 24 kDa SMP30 forms are likely generated from the 34 kDa SMP30. Interestingly, the 28 kDa and 24 kDa SMP30 forms appeared initially in the cytosol and shifted to the particulate fraction. Studies using small molecule inhibitors of proteolytic pathways revealed the potential involvement of β and γ-secretases but not calpains, lysosomal proteases, proteasome and caspases. This is the first report describing the existence of multiple forms of SMP30, their preferential distribution to membranes and their generation through proteolysis possibly mediated by secretase enzymes.

Effect of polyethylene glycol modification on the circulatory stability and immunogenicity of recombinant human butyrylcholinesterase

The therapeutic value of human serum butyrylcholinesterase (Hu BChE) as a bioscavenger of chemical warfare agents is due to its high reactivity with organophosphorus compounds and prolonged circulatory stability. Native Hu BChE is mostly tetrameric in form while the enzyme produced using molecular cloning technology is a mixture of tetramers, dimers, and monomers. Previous studies revealed that monomers and dimers of recombinant human (rHu) BChE cleared rapidly from the circulation of mice compared to tetrameric rHu BChE and native Hu BChE, which have mean residence times (MRTs) of 18h and 45h, respectively. It was also shown that polyethylene glycol-20K (PEG) modification of tetrameric rHu BChE prolonged its circulatory stability and bioavailability in vivo. The goal of this study was to determine if modification with PEG could prolong the circulatory stability and eliminate the immunogenicity of monomeric rHu BChE. Monomeric rHu BChE was expressed in human 293A cells using a cDNA lacking the 45 amino acid tetramerization domain from the carboxyl terminus and the adenovirus expression system. The catalytic and inhibitory properties of purified monomeric rHu BChE were similar to those for native Hu BChE and were not affected by PEG modification. As expected, monomeric rHu BChE rapidly cleared from the circulation of mice (MRT=3.2+/-0.3h) while monomeric PEG-rHu BChE demonstrated significant improvement in its bioavailability and circulatory stability in blood (MRT=31.4+/-5.4h). However, a second injection of monomeric PEG-rHu BChE, 28 days after the first, displayed a much shorter MRT=11.6+/-0.4h, and circulating anti-monomeric PEG-rHu BChE antibodies were detected in the blood of mice. These results suggest that PEG modification increased the circulatory stability of monomeric rHu BChE but failed to reduce or eliminate its immunogenicity.

Adenovirus-mediated gene transfer of human butyrylcholinesterase results in persistent high-level transgene expression in vivo.

Human serum butyrylcholinesterase (Hu BChE) is a promising therapeutic against the toxicity of chemical warfare nerve agents, pesticide intoxication, and cocaine overdose. However, its widespread application is hampered by difficulties in large-scale production of the native protein from human plasma and/or availability as a recombinant protein suitable for use in vivo. This limitation may be resolved by in vivo delivery and expression of the Hu BChE gene. In this study, recombinant (r) adenoviruses (Ads) encoding full-length and truncated rHu BChEs were tested for in vivo expression in mice. Mice injected with these rAds intraperitoneally failed to express rHu BChE. However, a single tail vein injection of both rAds resulted in persistent high serum levels of rHu BChE in BChE knockout mice, which peaked on days 4/5 at 377+/-162U/ml for full-length rHu BChE and 574+/-143U/ml for truncated rHu BChE. These activity levels are orders of magnitude higher than 1.9U/ml of mouse BChE present in wild-type mouse serum. Thereafter, rHu BChE levels dropped rapidly and very little or no activity was detected in the serum 10 days post-virus administration. In conclusion, the present study demonstrates the potential of rAd-mediated Hu BChE gene therapy to counteract multiple lethal doses of chemical warfare nerve agent toxicity.

Adenovirus-transduced human butyrylcholinesterase in mouse blood functions as a bioscavenger of chemical warfare nerve agents.

Human serum butyrylcholinesterase (Hu BChE) is a promising therapeutic against the toxicity of chemical warfare nerve agents. We have showed previously that recombinant (r) Hu BChE can be expressed at very high levels, 400 to 600 U/ml in mouse blood, by delivering the Hu BChE gene using adenovirus (Ad). Here, we report the biochemical properties of the Ad-expressed full-length and truncated rHu BChE in mouse blood. The molecular sizes of the full-length rHu BChE subunit and its oligomers were similar to those of native Hu BChE, although only a small portion of the full-length rHu BChE subunit underwent assembly into dimers and tetramers. As expected, Ad containing the truncated Hu BChE gene transduced the expression of monomeric rHu BChE only. Compared with 415 U of rHu BChE per milliliter in blood, tissues including liver, lung, heart, brain, kidney, muscle, intestine, diaphragm, salivary gland, and fat expressed <10 U/g of rHu BChE activity. Ad-expressed rHu BChE in mouse blood neutralized soman and O-ethyl S-2-N,N-diisopropylaminoethyl methylphosphonothiolate at rates similar to those of native Hu BChE and rHu BChE expressed in vitro. Because the expression of rHu BChE rapidly decreased 6 days after virus administration, sera were assayed for the presence of anti-Hu BChE antibodies. Anti-Hu BChE antibodies were detected on day 7 and in increased amounts thereafter, which coincided with the loss of Hu BChE expression in sera. In conclusion, the delivery of Hu BChE gene using Ad can be a promising strategy that can provide protection against multiple lethal doses of chemical warfare nerve agents in vivo.

A repeated injection of polyethyleneglycol-conjugated recombinant human butyrylcholinesterase elicits immune response in mice

Human serum butyrylcholinesterase (Hu BChE) serves as an efficacious bioscavenger of highly toxic organophosphorus (OP) compounds. Since there is a concern that the supply of native Hu BChE may be limited, monomeric and tetrameric forms of recombinant Hu BChE (rHu BChE) were evaluated as replacements and found that they lacked sufficient stability in vivo. However, their in vivo stability could be significantly prolonged by conjugation with polyethyleneglycol-20K (PEG) suggesting that monomeric and tetrameric PEG-rHu BChE could function as bioscavengers. Here, the immunogenicity of PEG-rHu BChE was evaluated in mice following two injections given four weeks apart. In addition to pharmacokinetic parameters, such as mean residence time, maximal concentration, time to reach the maximal concentration, elimination half-life and area under the plasma concentration-time curve extrapolated to infinity, the presence of circulating anti-rHu BChE antibodies was also determined. Although the pharmacokinetic parameters were significantly improved for the first injection of monomeric and tetrameric PEG-rHu BChEs, they were much lower for the second injection. Anti-rHu BChE antibodies were detected in the blood of mice following the first and second enzyme injections and their levels were approximately higher by 5-fold and 2-fold in mice injected with monomeric and tetrameric PEG-rHu BChEs as compared to mice injected with unconjugated enzymes. The findings that the rapid clearance of a repeat injection of PEG-rHu BChEs in mice which coincides with the presence of circulating anti-rHu BChE antibodies suggest that PEG conjugation prolonged the circulatory stability of rHu BChE but failed to eliminate its immunogenicity in mice.

Persistent and high-level expression of human liver prolidase in vivo in mice using adenovirus

Human liver prolidase, a metal-dependent dipeptidase, is being tested as a potential catalytic bioscavenger against organophosphorus (OP) chemical warfare nerve agents. The purpose of this study was to determine whether persistent and high-levels of biologically active and intact recombinant human (rHu) prolidase could be introduced in vivo in mice using adenovirus (Ad). Here, we report that a single intravenous injection of Ad containing the prolidase gene with a 6× histidine-tag (Ad-prolidase) introduced high-levels of rHu prolidase in the circulation of mice which peaked on days 5-7 at 159 ± 129 U/mL. This level of prolidase is ~120 times greater than that of the enzyme level in mice injected with Ad-null virus. To determine if all of Ad-prolidase-produced rHu prolidase was exported into the circulation, enzyme activity was measured in a variety of tissues. Liver contained the highest levels of rHu prolidase on day 7 (5647 ± 454 U/g) compared to blood or any other tissue. Recombinant Hu prolidase hydrolyzed DFP, a simulant of OP nerve agents, in vitro. In vivo, prolidase overexpression extended the survival of 4 out of 6 mice by 4-8h against exposure to two 1× LD(50) doses of DFP. In contrast, overexpression of mouse butyrylcholinesterase (BChE), a proven stoichiometric bioscavenger of OP compounds, protected 5 out of 6 mice from DFP lethality and surviving mice showed no symptoms of DFP toxicity. In conclusion, the results suggest that gene delivery using Ad is capable of introducing persistent and high levels of human liver prolidase in vivo. The gene-delivered prolidase hydrolyzed DFP in vitro but provided only modest protection in vivo in mice, delaying the death of the animals by only 4-8h.