The Toxicologist - Society of Toxicology

2042 MECHANISTICALLY-BASED COMPUTATIONAL
MODEL OF THE HOST IMMUNE RESPONSE TO
BIOLOGICAL WARFARE AGENTS: APPLICATION TO
TULAREMIA.
C. Hack, E. J. Fleming, P. E. Anderson and J. M. Gearhart. AFRL/711
HPW/RHPB, Wright-Patterson Air Force Base, OH.
Category A pathogens are highly virulent, top priority threat agents, yet there is no
effective vaccine for several, and the best animal model remains to be determined
for some. There is a clear need for tools for investigating mechanisms of pathogenesis
in multiple species and exploring intervention strategies. We are developing a
mechanistically-based computational model of the interactions between pathogens
and the host immune system. The model structure incorporates cellular members
of innate and adaptive immunity as well as cytokines to orchestrate their actions.
Our computational approach allows various steps in immune response to be turned
up or down, to simulate pathogen-specific mechanisms of immune subversion. In
applying the model to tularemia, simulated production of pro-inflammatory cytokines
by infected macrophages and dendritic cells was reduced by strain-dependent
amounts. The resulting time course profiles of neutrophils, macrophages, dendritic
cells, helper T cells, B cells, cytotoxic T lymphocytes, natural killer cells, and
bacterial cells were compared with data from experimental mouse models of tularemia.
The results show successful simulation of pathogen-host response dynamics,
and suggest the present research could be used to help identify and develop
novel interventions that focus on interrupting the disease cycle through incorporation
of prophylactic and therapeutic agents into the model. Ultimately, this work
will provide useful decision-making tools and answers to biodefense questions, particularly
those that are difficult to answer using other approaches such as risk to humans
and enhanced virulence of genetically altered pathogens.
2043 ABSORPTION, DISPOSITION ELIMINATION
KINETICS OF THE BIOLOGICAL TOXIN
MYCROCYSTIN LR.
D. Kracko, K. Turteltaub, R. Harris, M. Doyle-Eisele and J. McDonald.
Lovelace, Albuqueruque, NM.
The objective of this research is to define elimination kinetics/disposition of biomarkers
of exposure to Microcystin LR. This is conducted through tissue distribution
and pharmacokinetic studies in rodents and non-human primates (NHP),
modeling of disposition and elimination characteristics, selection of optimal excretion
matrix to utilize for biomarker targeting, and identification of biomarkers that
can be used to link to toxin exposure. The rodent data are described here. Custom
14C labeled toxin was developed that allows disposition and excreta analysis. Both
radioactivity and ELISA analysis of parent compound were conducted. Sprague-
Dawley rats were observed up to 72 hf post oral dose administration. Tissues and
blood were collected at 0.25, 1, 4, 8, 12, 24, 48, 72 hr. Urine and feces were collected
for 72 h. SEB showed rapid absorption from the GI tract, and metabolism of
the parent compound within 1-2 hours after dose administration. The metabolism
was confirmed by the absence of parent compound coupled to the presence of radioactivity
remaining in tissues, plasma and excreta. Microcystin LR showed concentrations
of parent compound in excreta and peripheral organs. It was detected in
both urine and feces 24-72 hr after dose administration. Interestingly, the radioactivity
did show excretion at earlier time points. These results may suggest kidney
malfunction, organ overload, or some other compromise of the endogenous proteolytic
degradation mechanism. The intact or fragmented Microcystin was observed
in the GI and peripheral organs, especially the kidney and liver. Urine samples
showed high concentrations of intact Microcystin LR, and thus may be an appropriate
matrix to assess for biomarkers. High levels of Microcystin LR metabolites
were observed in feces samples, allowing it to be another appropriate matrix to assess
for potential biomarkers.
2044 ABSORPTION, DISPOSITION ELIMINATION
KINETICS OF THE BIOLOGICAL TOXIN SEB.
R. Harris, M. Doyle-Eisele, J. McDonald and K. Turteltaub. Lovelace,
Albuqueruque, NM.
The objective of this research is to define elimination kinetics/disposition of biomarkers
of exposure to Staphylocollal Enterotoxin B (SEB). This is conducted
through tissue distribution and pharmacokinetic studies in rodents and nonhuman
primates (NHP), modeling of disposition and elimination characteristics,
selection of optimal excretion matrix to utilize for biomarker targeting, and identi-
438 SOT 2011 ANNUAL MEETING
fication of biomarkers that can be used to link to toxin exposure. The rodent data
are described here. Custom 14C labeled toxin was developed that allows disposition
and excreta analysis. Both radioactivity and ELISA analysis of parent compound
were conducted. Sprague-Dawley rats were observed up to 72 h post oral dose administration.
Tissues and blood were collected at 0.25, 1, 4, 8, 12, 24, 48, 72 hr.
Urine and feces were collected for 72 h. SEB showed rapid absorption from the GI
tract, and metabolism of the parent compound within 1-2 hours after dose administration.
The metabolism was confirmed by the absence of parent compound coupled
to the presence of radioactivity remaining in tissues, plasma and excreta.
Radioactivity from SEB metabolites spiked in plasma and urine at approximately 6-
10 hours after dosing. By 72 hours post dose, urine and plasma concentrations were
near zero. Tissue uptake was observed early (3 hr) in liver, followed by an increase in
kidney. In all cases the absorption from the stomach was followed by a peak in concentration
within the first 12 hours that was then followed by a in tissue concentration
and excretion. For evaluation of biomarkers, the peak concentration would be
obtained within the first 12 hrs after dosing. However, it appears that metabolites
from SEB exposure may be detectable out to 72 hr post exposure. Based on these
results, biomarkers of exposure focused on the measurement of intact SEB would
not be feasible. However, detection of metabolites may offer a unique opportunity
to assess exposure.
2045 CORRELATION OF LD50 AND CYTOCHROME C
OXIDASE ACTIVITY IN MITOCHRONDRIA FROM
BRAINS OF RODENTS TREATED WITH CYANIDE AND
CYANIDE POISONING ANTIDOTES.
D. Haines, I. Petrikovics, P. Guidry and M. Marziaz. Department of Chemistry,
Sam Houston State University, Huntsville, TX.
The mechanism of cyanide’s toxicity remains an active area of study despite many
years of intense research. It has been well established that this small toxin inhibits
mitochondrial electron transport by inhibiting cytochrome c oxidase, but additional
and more subtle targets appear to exist that contribute to toxicity as well. We
have measured cytochrome c oxidase activity in the brains of mice and rats given
lethal or sub-lethal cyanide doses, either alone or in the presence of potential therapeutic
and prophylactic agents. The results support earlier claims that cytochrome c
oxidase is inhibited but that maximal inhibition is less than 80% of the total cytochrome
c oxidase activity. Although the data for individual rodents varies significantly
as is normal for animal studies, we observe excellent correlation between the
EC75 for cytochrome c oxidase inhibition determined for each treatment regimen
with the corresponding LD50 values determined from rodent survival for the the
same regimen. These studies were supported by the ARMY MEDICAL RE-
SEARCH INSTITUTE OF CHEMICAL DEFENSE under the auspices of the
U.S. Army Research Office Scientific Services Program and the Welch Foundation.
2046 NOVEL SULFUR DONOR FORMULATIONS FOR
CYANIDE ANTAGONISM.
P. K. Jayanna 1 , I. Petrikovics 1 , J. C. Yu 2 , M. Zottola 3 , M. Ancha 1 and G. A.
Rockwood 3 . 1 Chemistry, Sam Houston State University, Huntsville, TX, 2 Forensic
Science, Sam Houston State University, Huntsville, TX and 3 Analitical Toxicology,
U.S. AMRICD, Aberdeen Proving Ground, MD.
The major mechanism to detoxifying cyanide in the body is through the formation
of thiocyanate, which is then readily excreted in urine. Our antidotal approach is
based on the utilization of exogenously administered sulfur donors and sulfurtransferases,
e.g. rhodanese. Sulfur donors with better lipophilicities (better membrane
penetration capabilities) can utilize the endogenous rhodanese localized within the
mitochondria. Dimethyltrisulfate (DMTS) reacts effectively with cyanide to yield
thiocyanate. Earlier studies reported the liposomal encapsulations of DMTS with
exogenous rhodanese, and their in vivo antidotal efficacy. The present research was
directed towards evaluating the hypothesis that micellar incorporation of DMTS
alone would also be advantageous: namely by enhancing the membrane penetrating
ability of the DMTS and by increasing the pre-administration stability by mitigating
the volatility of DMTS in solution. Accordingly, we prepared and characterized
PEG-PE micellar DMTS, an appropriate formulation for intramuscular administration
in vivo. The micelles were characterized by cryo-electron microscopy. Due
to the fact that in micelles DMTS molecules are completely immersed the hydrophobic
lipid core, a high encapsulation (70-85%) efficiency was achieved. Head
Space GC-MS experiments demonstrate that the micellar DMTS is significantly
more stable than DMTS by itself. We propose that micellar DMTS represents a feasible
sulfur donor formulation with in vivo applicability.