Effects of proton and oxygen ion irradiation on cardiovascular function and structure in a rabbit model.

PURPOSE: Astronauts on missions beyond low Earth orbit will be exposed to galactic cosmic radiation, and there is concern about potential adverse cardiovascular effects. Most of the research to identify cardiovascular risk of space radiation has been performed in rodent models. To aid in the translation of research results to humans, the current study identified long-term effects of high-energy charged particle irradiation on cardiovascular function and structure in a larger non-rodent animal model. MATERIALS AND METHODS: At the age of 12 months, male New Zealand white rabbits were exposed to whole-body protons (250 MeV) or oxygen ions (16O, 600 MeV/n) at a dose of 0 or 0.5 Gy and were followed for 12 months after irradiation. Ultrasonography was used to measure in vivo cardiac function and blood flow parameters at 10- and 12-months post-irradiation. At 12 months after irradiation, blood cell counts and blood chemistry values were assessed, and cardiac tissue and aorta were collected for histological as well as molecular and biochemical analyses. Plasma was used for metabolomic analysis and to quantify common markers of cardiac injury. RESULTS: A small but significant decrease in the percentage of circulating lymphocytes and an increase in neutrophil percentage was seen 12 months after 0.5 Gy protons, while 16O exposure resulted in an increase in monocyte percentage. Markers of cardiac injury, cardiac troponin I (cTnI) and N-Terminal pro-B-type Natriuretic Peptide were modestly increased in the proton group, and cTnI was also increased after 16O. On the other hand, metabolomics on plasma at 12 months revealed no changes. Both types of irradiation demonstrated alterations in cardiac mitochondrial morphology and an increase in left ventricular protein levels of inflammatory cell marker CD68. However, changes in cardiac function were only mild. CONCLUSION: Low dose charged particle irradiation caused mild long-term changes in inflammatory markers, cardiac function, and structure in the rabbit heart, in line with previous studies in mouse and rat models.

Cytogenetic and epigenetic aberrations in peripheral lymphocytes of northwest Arkansas Marshallese.

PURPOSE: Nuclear weapons testing in the northern Marshall Islands between 1946 and 1958 resulted in ionizing radiation (IR) exposure of the thousands of Marshallese. Furthermore, numerous islands were contaminated by radioactive fallout. Significant increases in cancer and metabolic syndrome incidences have been reported among Marshallese, and potential for further increases looms due to the latency of radiation-induced health effects. The purpose of this study was to investigate the genetic and epigenetic effects of exposure to IR that could be associated with radiation-induced disease among the Northwest Arkansas (NWA) Marshallese. MATERIALS AND METHODS: We performed analysis of chromosomal aberrations and DNA methylation based on residential and exposure history of NWA Marshallese. RESULTS: Analysis of chromosomal aberrations demonstrated higher incidence of genetic rearrangements in women with self-reported history of radiation exposure (95% CI: 0.10, 1.22; p=.022). Further clustering of study participants based on their residential history demonstrated that participants who spent substantial amounts of time (≥6 months) in the northern atolls (thus, in the proximity of nuclear tests) before 1980 had more chromosomal aberrations than their peers who lived only in the southern atolls (95% CI: 0.08, -0.95; p=.021), and that this difference was driven by women. A relationship between the time spent in the northern atolls and increase in chromosomal aberrations was observed: 0.31 increase in chromosomal aberrations for every 10 years spent at northern atolls (95% CI: 0.06, 0.57; p=.020). Finally, significant inverse correlations between the chromosomal aberrations and the extent of DNA methylation of four LINE-1 elements L1PA2, L1PA16, L1PREC1, and L1P4B were identified. CONCLUSIONS: The results of this study provide first evidence of the presence of stable genetic and epigenetic rearrangements in peripheral lymphocytes of NWA Marshallese and warrant further studies to analyze the role of radiation exposure in health disparities experienced by this Pacific Island nation.

Methods for induction and assessment of intestinal permeability in rodent models of radiation injury.

Ionizing radiation (IR) is a significant contributor to the contemporary market of energy production and an important diagnostic and treatment modality. Besides having numerous useful applications, it is also a ubiquitous environmental stressor and a potent genotoxic and epigenotoxic agent, capable of causing substantial damage to organs and tissues of living organisms. The gastrointestinal (GI) tract is highly sensitive to IR. This problem is further compounded by the fact that there is no FDA-approved medication to mitigate acute radiation-induced GI syndrome. Therefore, establishing the animal model for studying IR-induced GI-injury is crucially important to understand the harmful consequences of intestinal radiation damage. Here, we discuss two different animal models of IR-induced acute gastrointestinal syndrome and two separate methods for measuring the magnitude of intestinal radiation damage.

Dietary Methionine Supplementation Exacerbates Gastrointestinal Toxicity in a Mouse Model of Abdominal Irradiation.

BACKGROUND AND PURPOSE: Identification of appropriate dietary strategies for prevention of weight and muscle loss in cancer patients is crucial for successful treatment and prolonged patient survival. High-protein oral nutritional supplements decrease mortality and improve indices of nutritional status in cancer patients; however, high-protein diets are often rich in methionine, and experimental evidence indicates that a methionine-supplemented diet (MSD) exacerbates gastrointestinal toxicity after total body irradiation. Here, we sought to investigate whether MSD can exacerbate gastrointestinal toxicity after local abdominal irradiation, an exposure regimen more relevant to clinical settings. MATERIALS AND METHODS: Male CBA/CaJ mice fed either a methionine-adequate diet or MSD (6.5 mg methionine/kg diet vs 19.5 mg/kg) received localized abdominal X-irradiation (220 kV, 13 mA) using the Small Animal Radiation Research Platform, and tissues were harvested 4, 7, and 10 days after irradiation. RESULTS: MSD exacerbated gastrointestinal toxicity after local abdominal irradiation with 12.5 Gy. This was evident as impaired nutrient absorption was paralleled by reduced body weight recovery. Mechanistically, significant shifts in the gut ecology, evident as decreased microbiome diversity, and substantially increased bacterial species that belong to the genus Bacteroides triggered proinflammatory responses. The latter were evident as increases in circulating neutrophils with corresponding decreases in lymphocytes and associated molecular alterations, exhibited as increases in mRNA levels of proinflammatory genes Icam1, Casp1, Cd14, and Myd88. Altered expression of the tight junction-related proteins Cldn2, Cldn5, and Cldn6 indicated a possible increase in intestinal permeability and bacterial translocation to the liver. CONCLUSIONS: We report that dietary supplementation with methionine exacerbates gastrointestinal syndrome in locally irradiated mice. This study demonstrates the important roles registered dieticians should play in clinical oncology and further underlines the necessity of preclinical and clinical investigations in the role of diet in the success of cancer therapy.

Safety and Molecular-Toxicological Implications of Cannabidiol-Rich Cannabis Extract and Methylsulfonylmethane Co-Administration.

Cannabidiol (CBD) is a biologically active, non-psychotropic component of Cannabis sativa whose popularity has grown exponentially in recent years. Besides a wealth of potential health benefits, ingestion of CBD poses risks for a number of side effects, of which hepatotoxicity and CBD/herb-drug interactions are of particular concern. Here, we investigated the interaction potential between the cannabidiol-rich cannabis extract (CRCE) and methylsulfonylmethane (MSM), a popular dietary supplement, in the mouse model. For this purpose, 8-week-old male C57BL6/J mice received MSM-containing water (80 mg/100 mL) ad libitum for 17 days. During the last three days of treatment, mice received three doses of CRCE administered in sesame oil via oral gavage (123 mg/kg/day). Administration of MSM alone did not result in any evidence of liver toxicity and did not induce expression of mouse cytochrome P450 (CYP) enzymes. Administration of CRCE did produce significant (p < 0.05) increases in Cyp1a2, Cyp2b10, Cyp2c29, Cyp3a4, Cyp3a11, Cyp2c65, and Cyp2c66 messenger RNA, however, this effect was not amplified by MSM/CRCE co-treatment. Similarly, no evidence of liver toxicity was observed in MSM/CRCE dosed mice. In conclusion, short-term MSM/CRCE co-administration did not demonstrate any evidence of hepatotoxicity in the mouse model.

Potential Probiotic or Trigger of Gut Inflammation - The Janus-Faced Nature of Cannabidiol-Rich Cannabis Extract.

Cannabidiol (CBD) is the major non-psychotropic phytocannabinoid present in Cannabis sativa. In 2018, Congress designated certain C. sativa plant material as "hemp," thus removing it from the DEA's list of controlled substances. As a result, CBD-containing hemp extracts and other CBD products are now widely available and heavily marketed, yet their FDA regulatory status is still hotly debated. The goal of this study was to investigate the effects of a cannabidiol-rich cannabis extract (CRCE) on the gut microbiome and associated histomorphological and molecular changes in the mouse gut mucosa. Male C57BL6/J mice were gavaged with either 0, 61.5, 184.5, or 615 mg/kg/bw of CRCE in sesame oil for 2 weeks (Mon-Fri). Substantial CRCE-induced increases in the relative abundance of A. muciniphila, a bacterial species currently accepted as probiotic, was observed in fecal samples at all doses. This was paralleled by decreases in the relative abundance of other gut bacterial species. Coincident with the observed changes in gut ecology were multiple pro-inflammatory responses, including increased expression of cytokines and chemokines-Il1ß, Cxcl1, and Cxcl2 in the colon tissue. Furthermore, dramatic increases in the relative abundance of A. muciniphila significantly decreased expression of Muc2-a gene intimately associated with gut integrity. Taken together, these findings raise concerns about the safety of long-term CBD usage and underline the need for additional well-designed studies into its tolerability and efficacy.

The Development and Characterization of an scFv-Fc Fusion-Based Gene Therapy to Reduce the Psychostimulant Effects of Methamphetamine Abuse.

Methamphetamine (METH) continues to be among the most addictive and abused drugs in the United States. Unfortunately, there are currently no Food and Drug Administration-approved pharmacological treatments for METH-use disorder. We have previously explored the use of adeno-associated viral (AAV)-mediated gene transfer of an anti-METH monoclonal antibody. Here, we advance our approach by generating a novel anti-METH single-chain variable fragment (scFv)-Fc fusion construct (termed 7F9-Fc) packaged into AAV serotype 8 vector (called AAV-scFv-Fc) and tested in vivo and ex vivo. A range of doses [1 × 1010, 1 × 1011, and 1 × 1012 vector copies (vcs)/mouse] were administered to mice, eliciting a dose-dependent expression of 7F9-Fc in serum with peak circulating concentrations of 48, 1785, and 3831 µg/ml, respectively. Expressed 7F9-Fc exhibited high-affinity METH binding, IC50 = 17 nM. Between days 21 and 35 after vector administration, at both 1 × 1011 vc/mouse and 1 × 1012 vc/mouse doses, the AAV-7F9-Fc gene therapy significantly decreased the potency of METH in locomotor assays. On day 116 post-AAV administration, mice expressing 7F9-Fc sequestered over 2.5 times more METH in the serum than vehicle-treated mice, and METH concentrations in the brain were reduced by 1.2 times the value for vehicle mice. These data suggest that an AAV-delivered anti-METH Fc fusion antibody could be used to persistently reduce concentrations of METH in the central nervous system. SIGNIFICANCE STATEMENT: In this manuscript, we describe the testing of a novel antimethamphetamine (METH) single-chain variable fragment-Fc fusion protein delivered in mice using gene therapy. The results suggest that the gene therapy delivery system can lead to the production of significant antibody concentrations that mitigate METH's psychostimulant effects in mice over an extended time period.

Methionine dietary supplementation potentiates ionizing radiation-induced gastrointestinal syndrome.

Methionine is an essential amino acid needed for a variety of processes in living organisms. Ionizing radiation depletes tissue methionine concentrations and leads to the loss of DNA methylation and decreased synthesis of glutathione. In this study, we aimed to investigate the effects of methionine dietary supplementation in CBA/CaJ mice after exposure to doses ranging from 3 to 8.5 Gy of 137Cs of total body irradiation. We report that mice fed a methionine-supplemented diet (MSD; 19.5 vs. 6.5 mg/kg in a methionine-adequate diet, MAD) developed acute radiation toxicity at doses as low as 3 Gy. Partial body irradiation performed with hindlimb shielding resulted in a 50% mortality rate in MSD-fed mice exposed to 8.5 Gy, suggesting prevalence of radiation-induced gastrointestinal syndrome in the development of acute radiation toxicity. Analysis of the intestinal microbiome demonstrated shifts in the gut ecology, observed along with the development of leaky gut syndrome and bacterial translocation into the liver. Normal gut physiology impairment was facilitated by alterations in the one-carbon metabolism pathway and was exhibited as decreases in circulating citrulline levels mirrored by decreased intestinal mucosal surface area and the number of surviving crypts. In conclusion, we demonstrate that a relevant excess of methionine dietary intake exacerbates the detrimental effects of exposure to ionizing radiation in the small intestine.NEW & NOTEWORTHY Methionine supplementation, instead of an anticipated health-promoting effect, sensitizes mice to gastrointestinal radiation syndrome. Mechanistically, excess of methionine negatively affects intestinal ecology, leading to a cascade of physiological, biochemical, and molecular alterations that impair normal gut response to a clinically relevant genotoxic stressor. These findings speak toward increasing the role of registered dietitians during cancer therapy and the necessity of a solid scientific background behind the sales of dietary supplements and claims regarding their benefits.

NZO/HlLtJ as a novel model for the studies on the role of metabolic syndrome in acute radiation toxicity.

Purpose: Growing rates of metabolic syndrome and associated obesity warrant the development of appropriate animal models for better understanding of how those conditions may affect sensitivity to IR exposure.Materials and methods: We subjected male NZO/HlLtJ mice, a strain prone to spontaneous obesity and diabetes, to 0, 5.5, 6.37, 7.4 or 8.5 Gy (137Cs) of total body irradiation (TBI). Mice were monitored for 30 days, after which proximal jejunum and colon tissues were collected for further histological and molecular analysis.Results: Obese NZO/HlLtJ male mice are characterized by their lower sensitivity to IR at doses of 6.37 Gy and under, compared to other strains. Further escalation of the dose, however, results in a steep survival curve, reaching LD100/30 values at a dose of 8.5 Gy. Alterations in the expression of various tight junction-related proteins coupled with activation of inflammatory responses and cell death were the main contributors to the gastrointestinal syndrome.Conclusions: We demonstrate that metabolic syndrome with exhibited hyperglycemia but without alterations to the microvasculature is not a pre-requisite of the increased sensitivity to TBI at high doses. Our studies indicate the potential of NZO/HlLtJ mice for the studies on the role of metabolic syndrome in acute radiation toxicity.

Paradoxical Patterns of Sinusoidal Obstruction Syndrome-Like Liver Injury in Aged Female CD-1 Mice Triggered by Cannabidiol-Rich Cannabis Extract and Acetaminophen Co-Administration.

The goal of this study was to investigate the potential for a cannabidiol-rich cannabis extract (CRCE) to interact with the most common over-the-counter drug and the major known cause of drug-induced liver injury-acetaminophen (APAP)-in aged female CD-1 mice. Gavaging mice with 116 mg/kg of cannabidiol (CBD) [mouse equivalent dose (MED) of 10 mg/kg of CBD] in CRCE delivered with sesame oil for three consecutive days followed by intraperitoneally (i.p.) acetaminophen (APAP) administration (400 mg/kg) on day 4 resulted in overt toxicity with 37.5% mortality. No mortality was observed in mice treated with 290 mg/kg of CBD+APAP (MED of 25 mg/kg of CBD) or APAP alone. Following CRCE/APAP co-administration, microscopic examination revealed a sinusoidal obstruction syndrome-like liver injury-the severity of which correlated with the degree of alterations in physiological and clinical biochemistry end points. Mechanistically, glutathione depletion and oxidative stress were observed between the APAP-only and co-administration groups, but co-administration resulted in much greater activation of c-Jun N-terminal kinase (JNK). Strikingly, these effects were not observed in mice gavaged with 290 mg/kg CBD in CRCE followed by APAP administration. These findings highlight the potential for CBD/drug interactions, and reveal an interesting paradoxical effect of CBD/APAP-induced hepatotoxicity.

Hepatotoxicity of a Cannabidiol-Rich Cannabis Extract in the Mouse Model.

The goal of this study was to investigate Cannabidiol (CBD) hepatotoxicity in 8-week-old male B6C3F1 mice. Animals were gavaged with either 0, 246, 738, or 2460 mg/kg of CBD (acute toxicity, 24 h) or with daily doses of 0, 61.5, 184.5, or 615 mg/kg for 10 days (sub-acute toxicity). These doses were the allometrically scaled mouse equivalent doses (MED) of the maximum recommended human maintenance dose of CBD in EPIDIOLEX® (20 mg/kg). In the acute study, significant increases in liver-to-body weight (LBW) ratios, plasma ALT, AST, and total bilirubin were observed for the 2460 mg/kg dose. In the sub-acute study, 75% of mice gavaged with 615 mg/kg developed a moribund condition between days three and four. As in the acute phase, 615 mg/kg CBD increased LBW ratios, ALT, AST, and total bilirubin. Hepatotoxicity gene expression arrays revealed that CBD differentially regulated more than 50 genes, many of which were linked to oxidative stress responses, lipid metabolism pathways and drug metabolizing enzymes. In conclusion, CBD exhibited clear signs of hepatotoxicity, possibly of a cholestatic nature. The involvement of numerous pathways associated with lipid and xenobiotic metabolism raises serious concerns about potential drug interactions as well as the safety of CBD.

Decaffeinated Green Tea Extract Does Not Elicit Hepatotoxic Effects and Modulates the Gut Microbiome in Lean B6C3F1 Mice.

The main purpose of this study was to investigate the hepatotoxic potential and effects on the gut microbiome of decaffeinated green tea extract (dGTE) in lean B6C3F1 mice. Gavaging dGTE over a range of 1X-10X mouse equivalent doses (MED) for up to two weeks did not elicit significant histomorphological, physiological, biochemical or molecular alterations in mouse livers. At the same time, administration of dGTE at MED comparable to those consumed by humans resulted in significant modulation of gut microflora, with increases in Akkermansia sp. being most pronounced. Results of this study demonstrate that administration of relevant-to-human-consumption MED of dGTE to non-fasting mice does not lead to hepatotoxicity. Furthermore, dGTE administered to lean mice, caused changes in gut microflora comparable to those observed in obese mice. This study provides further insight into the previously reported weight management properties of dGTE; however, future studies are needed to fully evaluate and understand this effect.

Impact of obesity on the toxicity of a multi-ingredient dietary supplement, OxyELITE Pro™ (New Formula), using the novel NZO/HILtJ obese mouse model: Physiological and mechanistic assessments.

Herbal dietary supplement (HDS)-induced hepato- and cardiotoxicity is an emerging clinical problem. In this study, we investigated the liver and heart toxicity of HDS OxyELITE-PRO™ New Formula (OEP-NF), a dietary supplement marketed for weight loss and performance enhancement that was recently withdrawn from the market. Using a novel NZO/HlLtJ obese mouse model, we demonstrated that administration of clinically relevant mouse equivalent doses (MED) of OEP-NF produced cardio- and hepatotoxic risks following both short- and long-term administration schedules. Specifically, gavaging female NZO/HlLtJ with up to 2X MED of OEP-NF resulted in 40% mortality within two weeks. Feeding mice with either 1X or 3X MED of OEP-NF for eight weeks, while not exhibiting significant effects on body weights, significantly altered hepatic gene expression, increased the number of apoptotic and mast cells in the heart and affected cardiac function. The degree of toxicity in NZO/HlLtJ mice was higher than that observed previously in non-obese CD-1 and B6C3F1 strains, suggesting that an overweight/obese condition can sensitize mice to OEP-NF. Adverse health effects linked to OEP-NF, together with a number of other hepato- and cardiotoxicity cases associated with HDS ingestion, argue strongly for introduction of quality standards and pre-marketing safety assessments for multi-ingredient HDS.

Development and testing of AAV-delivered single-chain variable fragments for the treatment of methamphetamine abuse.

Methamphetamine (METH) substance abuse disorders have major impact on society, yet no medications have proven successful at preventing METH relapse or cravings. Anti-METH monoclonal antibodies can reduce METH brain concentrations; however, this therapy has limitations, including the need for repeated dosing throughout the course of addiction recovery. An adeno-associated viral (AAV)-delivered DNA sequence for a single-chain variable fragment could offer long-term, continuous expression of anti-METH antibody fragments. For these studies, we injected mice via tail vein with 1 x 10(12) vector genomes of two AAV8 scFv constructs and measured long-term expression of the antibody fragments. Mice expressed each scFv for at least 212 days, achieving micromolar scFv concentrations in serum. In separate experiments 21 days and 50 days after injecting mice with AAV-scFvs mice were challenged with METH in vivo. The circulating scFvs were capable of decreasing brain METH concentrations by up to 60% and sequestering METH in serum for 2 to 3 hrs. These results suggest that AAV-delivered scFv could be a promising therapy to treat methamphetamine abuse.

DNA Methylation in Radiation-Induced Carcinogenesis: Experimental Evidence and Clinical Perspectives.

Ionizing radiation is a valuable tool in many spheres of human life. At the same time, it is a genotoxic agent with a well-established carcinogenic potential. Progress achieved in the last two decades has demonstrated convincingly that ionizing radiation can also target the cellular epigenome. Epigenetics is defined as heritable changes in the expression of genes that are not due to alterations of DNA sequence but consist of specific covalent modifications of chromatin components, such as methylation of DNA, histone modifications, and control performed by non-coding RNAs. Accumulating evidence suggests that DNA methylation, a key epigenetic mechanism involved in the control of expression of genetic information, may serve as one of the driving mechanisms of radiation-induced carcinogenesis. Here, we review the literature on the effects of ionizing radiation on DNA methylation in various biological systems, discuss the role of DNA methylation in radiation carcinogenesis, and provide our opinion on the potential utilization of this knowledge in radiation oncology.

MicroRNAs as biomarkers for liver injury: Current knowledge, challenges and future prospects.

MicroRNAs (miRNAs) are short regulatory RNAs that are involved in various biological processes that regulate gene expression posttranscriptionally. Changes in miRNA expression can be detected in many physiological and pathological events, such as liver injury. Drug induced liver injury is a life threatening condition that frequently requires organ transplantation. Hepatotoxicity is also one of the major causes of drug failure in clinical trials and of drug withdrawal from the market. The profiling of miRNA expression shows great promise in monitoring liver injury, in the prediction of outcome in patients, and in the identification of liver-reactive compounds in toxicological assessment. Recent studies have demonstrated organ-specificity of some miRNAs (i.e., miR-122), which are released into biological fluids as a result of hepatocyte damage. This attests to the potential of miRNAs as noninvasive biomarkers to detect liver toxicity. This review presents information on miRNA signatures of hepatotoxicity and on the application of promising miRNA biomarkers in preclinical safety assessment. We further discuss the technical challenges associated with these emerging biomarkers for early diagnosis and detection of hepatotoxicity.

Safety assessment of the dietary supplement OxyELITE™ Pro (New Formula) in inbred and outbred mouse strains.

Herbal dietary supplements have gained wide acceptance as alternatives to conventional therapeutic agents despite concerns regarding their efficacy and safety. In 2013, a spate of severe liver injuries across the United States was linked to the dietary supplement OxyELITE Pro-New Formula (OEP-NF), a multi-ingredient product marketed for weight loss and exercise performance enhancement. The principal goal of this study was to assess the hepatotoxic potential of OEP-NF in outbred and inbred mouse models. In an acute toxicity study, significant mortality was observed after administering 10X and 3X mouse-equivalent doses (MED) of OEP-NF, respectively. Increases in liver/body weight ratio, ALT and AST were observed in female B6C3F1 mice after gavaging 2X and 1.5X MED of OEP-NF. Similar findings were observed in a 90-day feeding study. These alterations were paralleled by altered expression of gene- and microRNA-signatures of hepatotoxicity, including Cd36, Nqo1, Aldoa, Txnrd1, Scd1 and Ccng1, as well as miR-192, miR-193a and miR-125b and were most pronounced in female B6C3F1 mice. Body weight loss, observed at week 1, was followed by weight gain throughout the feeding studies. These findings bolster safety and efficacy concerns for OEP-NF, and argue strongly for implementation of pre-market toxicity studies within the dietary supplement industry.

The pharmacokinetics of racemic MDPV and its (R) and (S) enantiomers in female and male rats.

BACKGROUND: These studies investigated the serum pharmacokinetic (PK) profile of racemic (3,4)-methylenedioxypyrovalerone [(R,S)-MDPV)] and its (R)- and (S)-enantiomers in female and male Sprague Dawley rats. METHODS: Intravenous (R,S)-MDPV (3 and 5.6mg/kg) and single enantiomer of (R)- and (S)-MDPV (1.5mg/kg) were administered to both sexes for PK studies. Intraperitoneal (ip) bioavailability was determined at 3mg/kg (R,S)-MDPV. Locomotor activity studies were conducted after ip treatment with saline and 0.3-5.6mg/kg of (R,S)-MDPV. RESULTS: PK values after iv (R,S)-MDPV showed a significant (p<0.05) sex-dependent differences in the volume of distribution at steady state (Vdss) for (R)- and (R,S)-MDPV at both (R,S)-MDPV doses. The female S/R enantiomeric ratios for area under the concentration time curve (AUCinf) and clearance were significantly lower and higher, respectively, than values determined in males. Importantly, there was no evidence of in vivo inversion of (R)-MDPV or (S)-MDPV to its antipode. There were, however, significant sex-dependent differences in volume of distribution after administration of the (R)-enantiomer. Bioavailability studies of ip (R,S)-MDPV showed greater variability and significantly greater bioavailability in male rats. Accordingly, there was a significantly greater maximal distance traveled measurement in male rats at a 3.0mg/kg dose. CONCLUSION: PK sex differences in (R,S)-MDPV and enantiomers were most apparent in volume of distribution, which could be caused by differences in drug blood and tissue protein binding. The increased magnitude and variance in ip bioavailability in male compared to female rats could lead to sex-dependent differences in the pharmacological action caused by active enantiomer (S)-MDPV.