Metabolism and disposition of arsenic species from controlled dosing with sodium arsenite in adult female CD-1 mice. III. Toxicokinetic studies following oral and intravenous administration

Survey of arsenic content in edible seaweeds and their health risk assessment

Since humans are especially sensitive to arsenic exposure, predominantly through diet, a strict control of the most widely consumed seaweeds is mandatory. Total arsenic contents and arsenic species in twenty-five different seaweeds from five different origins were studied. Seaweeds selected, included Phaeophyta (brown seaweed), Chlorophyta (green seaweed) and Rhodophyta (red seaweed) genera. The highest arsenic content appears in the Phaeophyta seaweed in the range from 11 to 162 mg kg-1 dried weight. Arsenosugars were found to be the predominant species of arsenic in most seaweeds, being up to 99.7% of total arsenic in some samples. The arsenic dietary intakes for seaweeds studied were assessed and the Target Hazard Quotients (THQ) and the Target Cancer Risk (TCR) were calculated, taking into account inorganic arsenic contents (iAs). iAs species in seaweeds showed low risk of arsenic intake except for Hizikia fusiforme samples.

Arsenic-Containing Medicine Treatment Disturbed the Human Intestinal Microbial Flora

Human intestinal microbiome plays vital role in maintaining intestinal homeostasis and interacting with xenobiotics. Few investigations have been conducted to understand the effect of arsenic-containing medicine exposure on gut microbiome. Most animal experiments are onerous in terms of time and resources and not in line with the international effort to reduce animal experiments. We explored the overall microbial flora by 16S rRNA genes analysis in fecal samples from acute promyelocytic leukemia (APL) patients treated with arsenic trioxide (ATO) plus all-trans retinoic acid (ATRA). Gut microbiomes were found to be overwhelmingly dominated by Firmicutes and Bacteroidetes after taking medicines containing arsenic in APL patients. The fecal microbiota composition of APL patients after treatment showed lower diversity and uniformity shown by the alpha diversity indices of Chao, Shannon, and Simpson. Gut microbiome operational taxonomic unit (OTU) numbers were associated with arsenic in the feces. We evaluated Bifidobacterium adolescentis and Lactobacillus mucosae to be a keystone in APL patients after treatment. Bacteroides at phylum or genus taxonomic levels were consistently affected after treatment. In the most common gut bacteria Bacteroides fragilis, arsenic resistance genes were significantly induced by arsenic exposure in anaerobic pure culture experiments. Without an animal model, without taking arsenicals passively, the results evidence that arsenic exposure by drug treatment is not only associated with alterations in intestinal microbiome development at the abundance and diversity level, but also induced arsenic biotransformation genes (ABGs) at the function levels which may even extend to arsenic-related health outcomes in APL.

Route of Arsenic Exposure Differentially Impacts the Expression of Genes Involved in Gut-Mucosa-Associated Immune Responses and Gastrointestinal Permeability

First-pass metabolism alters arsenic biotransformation and its immunomodulatory activities. This study aims to determine the mRNA expression of intestinal-immunity- and permeability-associated genes, levels of cytokine/chemokines and levels of immunoglobulin isotypes when CD-1 mice were exposed to a single dose of intravenous (IV) sodium arsenite (50 µg/kg body weight (BW)) and to compare these responses to exposure via oral gavage (OG) (50 µg/kg BW). Samples were collected at 1, 4, 24 and 48 h post IV exposure and 24 and 48 h post OG. Sodium arsenite IV exposure led to a transient modulation of mRNA expression and protein levels of immunity-related genes involved in inflammation/apoptotic pathways and production of cytokines/chemokines, whereas it also led to downregulated expression of genes encoding tight junction, focal adhesion, and gap junction proteins, which are responsible for maintaining cell permeability. Oral exposure perturbed fewer cell-permeability-related genes at 24 and 48 h post exposure. At 24 h post exposure, OG decreased IgA and IgG2b levels; however, IV exposure significantly increased IgG2b, IgG3 and IgA in ileal tissue. Earlier, we showed significant downregulation of mRNA expression of genes involved in the immune-related pathways during OG in the intestinal mucosa of the same animals. Cumulatively, these results provide evidence that the exposure route of a xenobiotic can differentially impact the intestinal responses due to the impact of first-pass metabolism.

Inorganic arsenic alters the development of dopaminergic neurons but not serotonergic neurons and induces motor neuron development via Sonic hedgehog pathway in zebrafish

The mechanism of inorganic arsenic-induced neurotoxicity at the cellular level is not known. In zebrafish, teratological effects of inorganic arsenic have been shown at various concentrations. Here, we used similar concentrations of inorganic arsenic to evaluate the effects on specific neuron types. Exposure of zebrafish embryos at 5 h post fertilization (hpf) to sodium arsenite induced developmental toxicity (reduced body length) in 72 hpf larvae, beginning at a concentration of 300 mg/L concentration. Mortality or overt morphological deformity was detected at 500 mg/L sodium arsenite. While 200 mg/L sodium arsenite induced development of tyrosine hydroxylase-positive (dopaminergic) neurons, there was no significant effect on the development of 5-hydroxytryptamine (serotonergic) neurons. Sodium arsenite reduced acetylcholinesterase activity. In the hb9-GFP transgenic larvae, both 200 and 400 mg/L sodium arsenite produced supernumerary motor neurons in the spinal cord. Inhibition of the Sonic hedgehog (Shh) pathway that is essential for motor neuron development, by Gant61, prevented sodium arsenite-induced supernumerary motor neuron development. Inductively coupled plasma mass spectrometry (ICP-MS) revealed that with 200 mg/L and 400 mg/L sodium arsenite treatment, each larva had an average of 387.8 pg and 847.5 pg arsenic, respectively. The data show for the first time that inorganic arsenic alters the development of dopaminergic and motor neurons in the zebrafish larvae and the latter occurs through the Shh pathway. These results may help understand why arsenic-exposed populations suffer from psychiatric disorders and motor neuron disease and Shh may, potentially, serve as a plasma biomarker of arsenic toxicity.

The gut microbiome promotes arsenic metabolism and alleviates the metabolic disorder for their mammal host under arsenic exposure

Gut microbiome can participate in arsenic metabolism. However, its efficacy in the host under arsenic stress is still controversial. To clarify their roles in fecal arsenic excretion, tissue arsenic accumulation, host physiological states and metabolism, in this study, ninety-six C57BL/6 male mice were randomly divided to four groups, groups A and B were given sterile water, and groups C and D were given the third generation of broad-spectrum antibiotic (ceftriaxone) to erase the background gut microbiome. Subsequently, groups B and D were subchronicly exposed to arsenic containing feed prepared by adding arsenical mixture (rice arsenic composition) into control feed. In group D, the fecal total arsenic (C_tAs) decreased by 25.5 %, iAs^III composition increased by 46.9 %, unclarified As (uAs) composition decreased by 92.4 %, and the liver C_tAs increased by 26.7 %; the fecal C_tAs was positively correlated with microbial richness and some metabolites (organic acids, amino acids, carbohydrates, SCFAs, hydrophilic bile acids and their derivatives); and fecal DMA was positively correlated with microbial richness and some metabolites (ferulic acid, benzenepropanoic acid and pentanoic acid); network analysis showed that the numbers of modules, nodes, links were decreased and vulnerability was increased; some SCFAs and hydrophilic bile acid decreased, and hydrophobic bile acids increased (Ps < 0.05). In the tissue samples of group D, Il-18 and Ifn-γ gene expression increased and intestinal barrier-related genes Muc2, Occludin and Zo-1 expression decreased (Ps < 0.05); serum glutathione and urine malondialdehyde significantly increased (Ps < 0.05); urine metabolome significantly changed and the variation was correlated with six SCFAs-producing bacteria, and some SCFAs including isobutyric acid, valeric acid and heptanoic acid decreased (Ps < 0.05). Therefore, the normal gut microbiome increases fecal arsenic excretion and biotransformation, which can maintain a healthier microbiome and metabolic functions, and alleviate the metabolic disorder for their mammal host under arsenic exposure.

Arsenic exposure promotes the emergence of cardiovascular diseases

A large number of studies conducted in the past decade 2010-2020 refer to the impact of arsenic (As) exposure on cardiovascular risk factors. The arsenic effect on humans is complex and mainly depends on the varying individual susceptibilities, its numerous toxic expressions and the variation in arsenic metabolism between individuals. In this review we present relevant data from studies which document the association of arsenic exposure with various biomarkers, the effect of several genome polymorphisms on arsenic methylation and the underling molecular mechanisms influencing the cardiovascular pathology. The corresponding results provide strong evidence that high and moderate-high As intake induce oxidative stress, inflammation and vessel endothelial dysfunction that are associated with increased risk for cardiovascular diseases (CVDs) and in particular hypertension, myocardial infarction, carotid intima-media thickness and stroke, ventricular arrhythmias and peripheral arterial disease. In addition, As exposure during pregnancy implies risks for blood pressure abnormalities among infants and increased mortality rates from acute myocardial infarction during early adulthood. Low water As concentrations are associated with increased systolic, diastolic and pulse pressure, coronary heart disease and incident stroke. For very low As concentrations the relevant studies are few. They predict a risk for myocardial infarction, stroke and ischemic stroke and incident CVD, but they are not in agreement regarding the risk magnitude.

Preclinical In Vitro Model to Assess the Changes in Permeability and Cytotoxicity of Polarized Intestinal Epithelial Cells during Exposure Mimicking Oral or Intravenous Routes: An Example of Arsenite Exposure

The gastrointestinal tract (GIT) is exposed to xenobiotics, including drugs, through both: local (oral) and systemic routes. Despite the advances in drug discovery and in vitro pre-clinical models, there is a lack of appropriate translational models to distinguish the impact of these routes of exposure. Changes in intestinal permeability has been observed in different gastrointestinal and systemic diseases. This study utilized one such xenobiotic, arsenic, to which more than 200 million people around the globe are exposed via their food, drinking water, work environment, soil, and air. The purpose of this study was to establish an in vitro model to mimic gastrointestinal tract exposure to xenobiotics via oral or intravenous routes. To achieve this, we compared the route (mimicking oral and intravenous exposure to GIT and the dose response (using threshold approach) of trivalent and pentavalent inorganic arsenic species on the permeability of in vitro cultured polarized T84 cells, an example of intestinal epithelial cells. Arsenic treatment to polarized T84 cells via the apical and basolateral compartment of the trans-well system reflected oral or intravenous routes of exposure in vivo, respectively. Sodium arsenite, sodium arsenate, dimethyl arsenic acid sodium salt (DMA^V), and disodium methyl arsonate hydrate (MMA^V) were assessed for their effects on intestinal permeability by measuring the change in trans-epithelial electrical resistance (TEER) of T-84 cells. Polarized T-84 cells exposed to 12.8 µM of sodium arsenite from the basolateral side showed a marked reduction in TEER. Cytotoxicity of sodium arsenite, as measured by release of lactate dehydrogenase (LDH), was increased when cells were exposed via the basolateral side. The mRNA expression of genes related to cell junctions in T-84 cells was analyzed after exposure with sodium arsenite for 72 h. Changes in TEER correlated with mRNA expression of focal-adhesion-, tight-junction- and gap-junction-related genes (upregulation of Jam2, Itgb3 and Notch4 genes and downregulation of Cldn2, Cldn3, Gjb1, and Gjb2). Overall, exposure to sodium arsenite from the basolateral side was found to have a differential effect on monolayer permeability and on cell-junction-related genes as compared to apical exposure. Most importantly, this study established a preclinical human-relevant in vitro translational model to assess the changes in permeability and cytotoxicity during exposure, mimicking oral or intravenous routes.

NAC antagonizes arsenic-induced neurotoxicity through TMEM179 by inhibiting oxidative stress in Oli-neu cells

Arsenic is one of the most common environmental pollutants. Neurotoxicity induced by arsenic has become a major public health concern. However, the effects of arsenic-induced neurotoxicity in the brain and the underlying molecular mechanisms are not well understood. N-acetyl-cysteine (NAC) is a thiol-based antioxidant that can antagonize heavy metal-induced neurotoxicity by scavenging reactive oxygen species (ROS). Here, we used the mouse oligodendrocyte precursor cell (OPC) line Oli-neu to explore the neurotoxic effects of arsenic and the protective effects of NAC. We found that arsenic exposure decreased cell viability, increased oxidative stress, caused mitochondrial dysfunction, and led to apoptosis of Oli-neu cells. Furthermore, we revealed that NAC treatment reversed these neurotoxic effects of arsenic. TMEM179, a key membrane protein, was found highly expressed in OPCs and to be an important factor in maintaining mitochondrial functions. We found that TMEM179 played a critical role in mediating the neurotoxic effects of arsenic and the protective role of NAC. PKCβ is a downstream factor through which TMEM179 regulates the expression of apoptosis-related proteins. This study improves our understanding of the neurotoxic effects and mechanisms of arsenic exposure and the protective effects of NAC. It also identifies a potential molecular target, TMEM179, for the treatment of arsenic-induced neurotoxicity.

Single-cell RNA-seq Analysis Reveals That Prenatal Arsenic Exposure Results in Long-term, Adverse Effects on Immune Gene Expression in Response to Influenza A Infection

Arsenic exposure via drinking water is a serious environmental health concern. Epidemiological studies suggest a strong association between prenatal arsenic exposure and subsequent childhood respiratory infections, as well as morbidity from respiratory diseases in adulthood, long after systemic clearance of arsenic. We investigated the impact of exclusive prenatal arsenic exposure on the inflammatory immune response and respiratory health after an adult influenza A virus (IAV) lung infection. C57BL/6J mice were exposed to 100 ppb sodium arsenite in utero, and subsequently infected with IAV (H1N1) after maturation to adulthood. Assessment of lung tissue and bronchoalveolar lavage fluid at various time points post-IAV infection reveals greater lung damage and inflammation in arsenic-exposed mice versus control mice. Single-cell RNA sequencing analysis of immune cells harvested from IAV-infected lungs suggests that the enhanced inflammatory response is mediated by dysregulation of innate immune function of monocyte-derived macrophages, neutrophils, natural killer cells, and alveolar macrophages. Our results suggest that prenatal arsenic exposure results in lasting effects on the adult host innate immune response to IAV infection, long after exposure to arsenic, leading to greater immunopathology. This study provides the first direct evidence that exclusive prenatal exposure to arsenic in drinking water causes predisposition to a hyperinflammatory response to IAV infection in adult mice, which is associated with significant lung damage.

Origins, fate, and actions of methylated trivalent metabolites of inorganic arsenic: progress and prospects

The toxic metalloid inorganic arsenic (iAs) is widely distributed in the environment. Chronic exposure to iAs from environmental sources has been linked to a variety of human diseases. Methylation of iAs is the primary pathway for metabolism of iAs. In humans, methylation of iAs is catalyzed by arsenic (+ 3 oxidation state) methyltransferase (AS3MT). Conversion of iAs to mono- and di-methylated species (MAs and DMAs) detoxifies iAs by increasing the rate of whole body clearance of arsenic. Interindividual differences in iAs metabolism play key roles in pathogenesis of and susceptibility to a range of disease outcomes associated with iAs exposure. These adverse health effects are in part associated with the production of methylated trivalent arsenic species, methylarsonous acid (MAs^III) and dimethylarsinous acid (DMAs^III), during AS3MT-catalyzed methylation of iAs. The formation of these metabolites activates iAs to unique forms that cause disease initiation and progression. Taken together, the current evidence suggests that methylation of iAs is a pathway for detoxification and for activation of the metalloid. Beyond this general understanding of the consequences of iAs methylation, many questions remain unanswered. Our knowledge of metabolic targets for MAs^III and DMAs^III in human cells and mechanisms for interactions between these arsenicals and targets is incomplete. Development of novel analytical methods for quantitation of MAs^III and DMAs^III in biological samples promises to address some of these gaps. Here, we summarize current knowledge of the enzymatic basis of MAs^III and DMAs^III formation, the toxic actions of these metabolites, and methods available for their detection and quantification in biomatrices. Major knowledge gaps and future research directions are also discussed.

Tissue- and Region-Specific Accumulation of Arsenic Species, Especially in the Brain of Mice, After Long-term Arsenite Exposure in Drinking Water

Arsenic is identified as a known carcinogen and ubiquitously exists in nature. It appears that accumulation of inorganic arsenic (iAs) and its methylated metabolites in various tissues is closely correlated with the long-term toxicity and carcinogenicity of this metalloid. In this study, various arsenic species in murine tissues, especially in the cerebral cortex, cerebellum, and hippocampus, were determined after long-term exposure to 25, 50, 100, and 200 mg/L sodium arsenite in drinking water for 1 and 12 months. Our data showed that the amount of total arsenic (TAs) increased in an obvious dose-dependent manner in various tissues, and TAs levels were in the order of urinary bladder > brain > lung > liver > kidney > spleen. Furthermore, iAs^III and DMA could be observed in all tissues and brain regions with DMA being the predominant metabolite. The bladder, brain, and lung orderly contained the higher levels of DMA, while the liver, kidney, and spleen accumulated the higher proportion of iAs^III. MMA was preferentially accumulated in the lung and bladder of mice regardless of arsenic exposure doses or duration. What's more, amazingly higher levels of MMA were observed in the hippocampus, which was distinguished from the cerebral cortex and cerebellum. Together with these results, our study clearly demonstrates that the accumulation of iAs and its methylated metabolites is tissue-specific and even not homogeneous among different brain regions in mice by long-term exposure to arsenite. Our study thus provides crucial information for recognizing arsenical neurotoxicity, and reducing the uncertainty in the risk assessment for this toxic metalloid.

Reduction by, ligand exchange among, and covalent binding to glutathione and cellular thiols link metabolism and disposition of dietary arsenic species with toxicity

Arsenic (As) is a common contaminant in the earth's crust and widely distributed in food and drinking water. As exposures have been associated with human disease, including cancer, diabetes, lung and cardiovascular disorders, and there is accumulating evidence that early life exposures are important in the etiology. Mode-of-action analysis includes a critical role for metabolic activation of As species to reactive trivalent intermediates that disrupt cellular regulatory systems by covalent binding to thiol groups. The central role of glutathione (GSH) in the chemical reactions of metabolism and disposition of arsenic species was investigated here. The chemical kinetics were measured for reactions in which GSH is a ligand for trivalent As complex formation, a reductant for pentavalent As species, and a participant in ligand exchange reactions with other biological As-thiol complexes. The diverse reactions of GSH with As species demonstrate prominent roles in: (1) metabolic activation via reduction; (2) transport from tissues that are the primary sources of reactive trivalent As intermediates following ingestion (intestine and liver) to downstream target organs (e.g., lung, kidney, and bladder); and (3) oxidation to the terminal metabolite, dimethylarsinic acid (DMA^V), which is excreted. Studies of As metabolism and disposition emphasize the link between metabolic activation vs. excretion of As (i.e., internal dosimetry of reactive species) and the disruption of critical cellular thiol-based regulatory processes that define the dose-response characteristics of disease in human epidemiological studies and animal models and underpin risk assessment.

Determination of arsenicals in mouse tissues after simulated exposure to arsenic from rice for sixteen weeks and the effects on histopathological features

The accumulation of arsenic in rice has become a worldwide concern. In this study, dose-dependency in tissues (intestine, liver and kidney) and blood distribution of inorganic arsenicals and their methylated metabolites were investigated in male C57BL/6 mice exposed to four arsenic species (arsenite [iAs]^III, arsenate [iAs]^V, monomethylarsonate [MMA]^V, and dimethylarsinate [DMA]^V) at four doses (control [C]: 0 μg/g, simulation [S]: 0.91 μg/g, medium [M]: 9.1 μg/g and high [H]: 30 μg/g) according to the arsenical composition in rice for 8 and 16 weeks. No adverse effects were observed, while body weight gain decreased in group H. Increases in total arsenic concentrations (C_tAs) and histopathological changes in the tissues occurred in all of the test groups. C_tAs presented a tendency of kidney > intestine > liver > blood and were time-/dose-dependent in the liver and kidney in groups M and H. In the intestine and blood, abundant iAs (23%-28% in blood and 36%-49% in intestine) was detected in groups M and H, and C_tAs decreased in group H from the 8th week to the 16th week. PMI decreased in the liver and SMI decreased in the kidney. These results indicate that the three tissues are injured through food arsenic. The intestine can also accumulate food arsenic, and the high arsenic dose will cause a deficiency in the absorbing function of the intestine. Thus, long-term exposure to arsenic-contaminated rice should be taken seriously attention.

Biotransformation of arsenic and toxicological implication of arsenic metabolites

Arsenic is a well-known environmental carcinogen and chronic exposure to arsenic through drinking water has been reported to cause skin, bladder and lung cancers, with arsenic metabolites being implicated in the pathogenesis. In contrast, arsenic trioxide (As₂O₃) is an effective therapeutic agent for the treatment of acute promyelocytic leukemia, in which the binding of arsenite (iAs^III) to promyelocytic leukemia (PML) protein is the proposed initial step. These findings on the two-edged sword characteristics of arsenic suggest that after entry into cells, arsenic reaches the nucleus and triggers various nuclear events. Arsenic is reduced, conjugated with glutathione, and methylated in the cytosol. These biotransformations, including the production of reactive metabolic intermediates, appear to determine the intracellular dynamics, target organs, and biological functions of arsenic.

SO2 derivatives and As co-exposure promote liver cancer metastasis through integrin αvβ3 activation

Arsenic (As) and sulfur dioxide (SO₂) are two environmental pollutants that have been shown to promote the development of human cancer. In recent years, due to increased pollution, humans are often exposed to SO₂, in addition to As. Despite the development and implementation of standards for environment and air quality, cases of disease caused by As or SO₂ continue to rise alarmingly. It is currently unknown whether simultaneous exposure to As and SO₂ results in increased cancer promoting activity. In this study, concentrations of As and SO₂ below the limits established by the world health organization (WHO) in force environmental standards (concentrations of As should be lower than 1×10^-2 mg/L and SO₂ should be lower than 50 μg/m³), were employed to investigate possible, long-term, synergistic effects of As and SO₂, by using cell-based assays. We found that co-exposure to these pollutants significantly promotes HepG2 cancer cell migration, while As or SO₂ alone have no remarkable effects. Integrins αvβ3 play a key role in this process, as cilengitide, an integrin αvβ3 inhibitor, substantially prevented As and SO₂-induced cell migration. MMPs, IL-8, and TGF-β were also involved in the induced cell migration. In summary, combined exposure to As and SO₂ promotes integrin-dependent cell migration and may be of relevance for the activation of mechanisms underlying liver cancer progression.

Metabolism and disposition of arsenic species from controlled dosing with sodium arsenite in adult and neonatal rhesus monkeys. VI. Toxicokinetic studies following oral administration

Arsenic is a common toxic contaminant in food and drinking water. Metabolic activation of arsenic species produces reactive trivalent intermediates that can disrupt cellular regulatory systems by covalent binding to thiol groups. Arsenic exposures have been associated with human diseases including cancer, diabetes, lung and cardiovascular disorders and there is accumulating evidence that early life exposures are important in the etiology. Previous toxicokinetic studies of arsenite ingestion in neonatal CD-1 mice showed consistent evidence for metabolic and physiologic immaturity that led to elevated internal exposures to trivalent arsenic species in the youngest mice, relative to adults. The current study in rhesus monkeys showed that metabolism and binding of trivalent intermediates after arsenite ingestion were similar between adult monkeys and CD-1 mice. Unlike neonatal mice, monkeys from the age of 5-70 days showed similar metabolism and binding profiles, which were also similar to those in adults. The absence of evidence for metabolic immaturity in monkeys suggests that toxicological effects observed in mice from early postnatal exposures to arsenic could over-predict those possible in primates, based on significantly higher internal exposures.

A single or short time repeated arsenic oral exposure in mice impacts mRNA expression for signaling and immunity related genes in the gut

Arsenic is prevalent in contaminated drinking water and affects more than 140 million people in 50 countries. While the wide-ranging effects of arsenic on neurological development and cancer draw the majority of concern, arsenic's effects on the gut mucosa-associated immune system are often overlooked. In this study, we show that 24 h after a single dose [low dose (50 μg/kg bw), medium dose (100 μg/kg bw) or high dose (200 μg/kg bw)] of arsenic by oral gavage, mice show significantly reduced gut mucosa-associated mRNA expression for the key genes involved in the signaling pathways central to immune responses, such as Nuclear factor κB (NFκB), Extracellular signal-regulated protein kinases 1 and 2 (ERK1/2), p38 and Myeloid differentiation protein 88-dependent (Myd88) pathways. Additionally, mRNA expression of apoptosis, inflammasomes and inflammatory response genes are significantly downregulated in the animals exposed to arsenic. Comparisons of time-dependent effects (24 h vs 48 h) from low dose arsenic exposed animals showed a significant shift in expression of Myd88 alone, suggesting that the down regulation was sustained for the key genes/signaling pathway. An extended eight-day exposure to arsenic showed a decreased state of immune preparedness, though not as diminished as seen in the single dose exposure.