Multifaceted roles for STAT3 in gammaherpesvirus latency revealed through in vivo B cell knockout models

Cancers associated with the oncogenic gammaherpesviruses, Epstein-Barr virus and Kaposi sarcoma herpesvirus, are notable for their constitutive activation of the transcription factor signal transducer and activator of transcription 3 (STAT3). To better understand the role of STAT3 during gammaherpesvirus latency and the B cell response to infection, we used the model pathogen murine gammaherpesvirus 68 (MHV68). Genetic deletion of STAT3 in B cells of CD19cre/+Stat3f/f mice reduced peak MHV68 latency approximately sevenfold. However, infected CD19cre/+Stat3f/f mice exhibited disordered germinal centers and heightened virus-specific CD8 T cell responses compared to wild-type (WT) littermates. To circumvent the systemic immune alterations observed in the B cell-STAT3 knockout mice and more directly evaluate intrinsic roles for STAT3, we generated mixed bone marrow chimeric mice consisting of WT and STAT3 knockout B cells. We discovered a dramatic reduction in latency in STAT3 knockout B cells compared to their WT B cell counterparts in the same lymphoid organ. RNA sequencing of sorted germinal center B cells revealed that MHV68 infection shifts the gene signature toward proliferation and away from type I and type II IFN responses. Loss of STAT3 largely reversed the virus-driven transcriptional shift without impacting the viral gene expression program. STAT3 promoted B cell processes of the germinal center, including IL-21-stimulated downregulation of surface CD23 on B cells infected with MHV68 or EBV. Together, our data provide mechanistic insights into the role of STAT3 as a latency determinant in B cells for oncogenic gammaherpesviruses.IMPORTANCEThere are no directed therapies to the latency program of the human gammaherpesviruses, Epstein-Barr virus and Kaposi sarcoma herpesvirus. Activated host factor signal transducer and activator of transcription 3 (STAT3) is a hallmark of cancers caused by these viruses. We applied the murine gammaherpesvirus pathogen system to explore STAT3 function upon primary B cell infection in the host. Since STAT3 deletion in all CD19+ B cells of infected mice led to altered B and T cell responses, we generated chimeric mice with both normal and STAT3-deleted B cells. B cells lacking STAT3 failed to support virus latency compared to normal B cells from the same infected animal. Loss of STAT3 impaired B cell proliferation and differentiation and led to a striking upregulation of interferon-stimulated genes. These findings expand our understanding of STAT3-dependent processes that are key to its function as a pro-viral latency determinant for oncogenic gammaherpesviruses in B cells and may provide novel therapeutic targets.

Intrinsic p53 Activation Restricts Gammaherpesvirus-Driven Germinal Center B Cell Expansion during Latency Establishment

Gammaherpesviruses (GHV) are DNA tumor viruses that establish lifelong latent infections in lymphocytes. For viruses such as Epstein-Barr virus (EBV) and murine gammaherpesvirus 68 (MHV68), this is accomplished through a viral gene-expression program that promotes cellular proliferation and differentiation, especially of germinal center (GC) B cells. Intrinsic host mechanisms that control virus-driven cellular expansion are incompletely defined. Using a small-animal model of GHV pathogenesis, we demonstrate in vivo that tumor suppressor p53 is activated specifically in B cells that are latently infected by MHV68. In the absence of p53, the early expansion of MHV68 latency was greatly increased, especially in GC B cells, a cell-type whose proliferation was conversely restricted by p53. We identify the B cell-specific latency gene M2, a viral promoter of GC B cell differentiation, as a viral protein sufficient to elicit a p53-dependent anti-proliferative response caused by Src-family kinase activation. We further demonstrate that EBV-encoded latent membrane protein 1 (LMP1) similarly triggers a p53 response in primary B cells. Our data highlight a model in which GHV latency gene-expression programs that promote B cell proliferation and differentiation to facilitate viral colonization of the host trigger aberrant cellular proliferation that is controlled by p53.

IMPORTANCE

Gammaherpesviruses cause lifelong infections of their hosts, commonly referred to as latency, that can lead to cancer. Latency establishment benefits from the functions of viral proteins that augment and amplify B cell activation, proliferation, and differentiation signals. In uninfected cells, off-schedule cellular differentiation would typically trigger anti-proliferative responses by effector proteins known as tumor suppressors. However, tumor suppressor responses to gammaherpesvirus manipulation of cellular processes remain understudied, especially those that occur during latency establishment in a living organism. Here we identify p53, a tumor suppressor commonly mutated in cancer, as a host factor that limits virus-driven B cell proliferation and differentiation, and thus, viral colonization of a host. We demonstrate that p53 activation occurs in response to viral latency proteins that induce B cell activation. This work informs a gap in our understanding of intrinsic cellular defense mechanisms that restrict lifelong GHV infection.

B cell-intrinsic STAT3-mediated support of latency and interferon suppression during murine gammaherpesvirus 68 infection revealed through an in vivo competition model

Cancers associated with the oncogenic gammaherpesviruses, Epstein-Barr virus and Kaposi sarcoma herpesvirus, are notable for their constitutive activation of the transcription factor STAT3. To better understand the role of STAT3 during gammaherpesvirus latency and immune control, we utilized murine gammaherpesvirus 68 (MHV68) infection. Genetic deletion of STAT3 in B cells of CD19cre/+Stat3f/f mice reduced peak latency approximately 7-fold. However, infected CD19cre/+Stat3f/f mice exhibited disordered germinal centers and heightened virus-specific CD8 T cell responses compared to WT littermates. To circumvent the systemic immune alterations observed in the B cell-STAT3 knockout mice and more directly evaluate intrinsic roles for STAT3, we generated mixed bone marrow chimeras consisting of WT and STAT3-knockout B cells. Using a competitive model of infection, we discovered a dramatic reduction in latency in STAT3-knockout B cells compared to their WT B cell counterparts in the same lymphoid organ. RNA sequencing of sorted germinal center B cells revealed that STAT3 promotes proliferation and B cell processes of the germinal center but does not directly regulate viral gene expression. Last, this analysis uncovered a STAT3-dependent role for dampening type I IFN responses in newly infected B cells. Together, our data provide mechanistic insight into the role of STAT3 as a latency determinant in B cells for oncogenic gammaherpesviruses.

Pediatric SARS-CoV-2 Seroprevalence in Arkansas Over the First Year of the COVID-19 Pandemic

BACKGROUND

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) seroprevalence studies largely focus on adults, but little is known about spread in children. We determined SARS-CoV-2 seroprevalence in children and adolescents from Arkansas over the first year of the coronavirus disease of 2019 (COVID-19) pandemic.

METHODS

We tested remnant serum samples from children ages 1-18 years who visited Arkansas hospitals or clinics for non-COVID-19-related reasons from April 2020 through April 2021 for SARS-CoV-2 antibodies. We used univariable and multivariable regression models to determine the association between seropositivity and participant characteristics.

RESULTS

Among 2357 participants, seroprevalence rose from 7.9% in April/May 2020 (95% CI, 4.9-10.9) to 25.0% in April 2021 (95% CI, 21.5-28.5). Hispanic and black children had a higher association with antibody positivity than non-Hispanic and white children, respectively, in multiple sampling periods.

CONCLUSIONS

By spring 2021, most children in Arkansas were not infected with SARS-CoV-2. With the emergence of SARS-CoV-2 variants, recognition of long-term effects of COVID-19, and the lack of an authorized pediatric SARS-CoV-2 vaccine at the time, these results highlight the importance of including children in SARS-CoV-2 public health, clinical care, and research strategies.

Chronic anti-phencyclidine monoclonal antibody therapy decreases phencyclidine-induced in utero fetal mortality in pregnant rats

Illicit drug use during pregnancy is a serious social and public health problem inflicting an array of deleterious effects on both mother and offspring. We investigated the hypothesis that a murine anti-phencyclidine (PCP) monoclonal antibody (mAb6B5; K(D)=1.3 nM) can safely protect mother and fetus from PCP-induced adverse health effects in pregnant rats. Pregnant Sprague-Dawley rats (n=4-5) were intravenously administered bolus injections of PCP (1mg/kg) on multiple days during pregnancy. They were also chronically treated with anti-PCP mAb6B5 at 45 mg/kg as a PCP antagonist. This dose provided one mAb-PCP binding site for every four PCP molecules. Therapeutic and safety study endpoints included pregnancy outcome (litter size, number of live vs. dead pups), maternal hemodynamic status and locomotor activity. Maternal hemodynamic changes (i.e., blood pressure and heart rate) and locomotor activity were measured in dams from gestation days 6-21 (one day antepartum) using a radiotelemetry-tracking device with a femoral arterial pressure catheter. This mAb6B5 treatment regimen significantly (p=0.008) reduced the number of PCP-induced in utero fetal deaths (odds ratio=3.2; 95%CI 1.3 to 7.9) and significantly (p<0.05) reduced acute PCP-induced maternal locomotor effects in the second trimester. Maternal hemodynamic responses to PCP were not significantly affected by mAb6B5 treatment. In conclusion, these data suggest that anti-PCP mAb treatments administered during pregnancy can safely protect a mother and her fetus(es) from PCP-related morbidity and mortality even when the mAb dose is too low to significantly prevent other PCP-induced maternal pharmacological effects.

Interviewing witnesses: the effect of forced confabulation on event memory

After viewing a crime video, participants answered 16 answerable and 6 unanswerable questions. Those in the "voluntary guess" condition had a "don't know" response option; those in the "forced guess" condition did not. One week later the same questions were answered with a "don't know" option. In both experiments, information generated from forced confabulation was less likely remembered than information voluntarily self-generated. Further, when the same answer was given to an unanswerable question both times, the confidence expressed in the answer increased over time in both the forced and the voluntary guess conditions. Pressing eyewitnesses to answer questions, especially questions repeated thrice (Experiment 2), may not be an effective practice because it reliably increases intrusion errors but not correct recall.

Effects of anti-phencyclidine and anti-(+)-methamphetamine monoclonal antibodies alone and in combination on the discrimination of phencyclidine and (+)-methamphetamine by pigeons

RATIONALE

Drug-specific monoclonal antibodies against phencyclidine (PCP) and (+)-methamphetamine [(+)-METH] should bind to these drugs to block their discriminative stimulus effects.

OBJECTIVES

To determine if mouse monoclonal antibodies against PCP and (+)-METH can block the discriminative stimulus effects of the drugs in pigeons.

MATERIALS AND METHODS

Pigeons were trained to discriminate among intramuscular injections of saline, 1 mg/kg PCP, and 2 mg/kg (+)-METH. After responding stabilized, cumulative dose-response curves were obtained for PCP and (+)-METH. Doses of an anti-PCP antibody at 620 mg/kg (anti-PCP mAb6B5) with a K (D) of 1.3 nM for PCP and no measurable affinity for (+)-METH and 1,000 mg/kg doses of anti-(+)-METH antibody (anti-METH mAb6H7) with a K (D) of 41 nM for (+)-METH and no measurable affinity for PCP were subsequently administered, first alone and later in combination after which the dose-response curves were redetermined.

RESULTS

When the antibodies were given alone, the anti-PCP antibody blocked the discriminative stimulus effects of PCP, but not those of (+)-METH, and the anti-(+)-METH antibody blocked the discriminative stimulus effects of (+)-METH, but not those of PCP. The anti-PCP antibody shifted the PCP dose-response curve further to the right and for a longer time than the anti-(+)-METH antibody shifted the dose response curve for (+)-METH. When the anti-PCP and anti-(+)-METH antibodies were administered on the same day, the discriminative stimulus effects of both drugs were completely blocked 1 day after antibody administration.

CONCLUSIONS

These experiments demonstrate the high specificity of the antibodies for the drugs to which they bind and show that monoclonal antibodies can be combined to antagonize the effects of more than one drug.

Development of a liquid chromatography–tandem mass spectrometric method for the determination of methamphetamine and amphetamine using small volumes of rat serum

The aim of this paper was to develop LC/MS/MS methodology for the determination of methamphetamine (METH) and amphetamine (AMP) using low microliter volumes (20-150 microl) of rat serum and demonstrate the use of this method for the study of serum pharmacokinetics in the rat. The analytes were extracted from rat serum using solid-phase extraction followed by an isocratic separation on a narrow-bore Hypersil C(18) column. Lower limits of quantitation for METH and AMP were 0.3 ng/ml using positive ion electrospray tandem mass spectrometry. The accuracy of the method was within 20% of the actual values over a wide range of serum concentrations. The within-day and between-day precision was better than 20% (R.S.D.). Ion-suppression matrix effects on electrospray ionization were evaluated for extracted rat serum. The LC/MS/MS method was further validated by comparing serum concentrations of METH and AMP to serum concentrations previously determined using an LC/[ (3)H]-METH assay with radiochemical detection. Finally, the LC/MS/MS method was used to study the pharmacokinetics of METH and AMP after a 1mg/kg intravenous bolus dose of METH to female Sprague-Dawley rats.

Effects of murine-derived anti-methamphetamine monoclonal antibodies on (+)-methamphetamine self-administration in the rat

Two murine-derived anti-methamphetamine monoclonal antibodies were studied as potential pharmacokinetic antagonists of (+)-methamphetamine self-administration by rats. Intravenous administration of a 1 g/kg dose of the lower affinity [antibody equilibrium dissociation constant (K(d)) = 250 nM] monoclonal antibody (mAb) designated mAb6H8, 1 day before the start of several daily 2-h self-administration sessions produced effects that depended on the dose of (+)-methamphetamine. mAb6H8 increased the rate of self-administration of a unit dose of 0.06 mg/kg (+)-methamphetamine, had little effect on the rate of self-administration of a unit dose of 0.03 mg/kg (+)methamphetamine, and lowered the rate of self-administration of a unit dose of 0.01 mg/kg (+)-methamphetamine to a level similar to that after saline substitution. mAb-induced changes in rates of self-administration occurred very early in self-administration sessions and lasted for 3 to 7 days. Intravenous administration of a 1 or a 0.6 g/kg dose of a higher affinity (K(d) = 11 nM) mAb designated mAb6H4, 24 h before the first of several self-administration sessions, produced very similar effects to the lower affinity mAb, despite the more than 20-fold greater affinity for (+)-methamphetamine. It is proposed that these anti-methamphetamine antibodies bind some of the self-administered (+)-methamphetamine before it can penetrate into brain, thereby reducing the amount of free drug available to function as a reinforcer. Although neither of these mAb medications are optimal antibodies for treating (+)-methamphetamine abuse, the experiments demonstrate that anti-(+)-methamphetamine monoclonal antibodies can attenuate the self-administration of the drug and suggest the potential of using monoclonal antibodies as pharmacokinetic antagonists of (+)-methamphetamine.

Pharmacokinetic antagonism of (+)-methamphetamine discrimination by a low-affinity monoclonal anti-methamphetamine antibody

Animals were trained to discriminate 5 or 10 mg/kg cocaine (rats), or 3 mg/kg (+)-amphetamine (pigeons) from saline, after which dose-response curves were determined for (+)-methamphetamine and other drugs before and after administration of a (+)-methamphetamine-specific monoclonal antibody (K(D) =250 nM). In rats trained to discriminate 10 mg/kg cocaine from saline, intravenous (+)-methamphetamine was about three times more potent as a discriminative stimulus than intraperitoneal (+)-methamphetamine. Also in these rats, intraperitoneal (+)-methamphetamine and (+)-amphetamine were about equipotent as discriminative stimuli, and were about three times more potent than intraperitoneal cocaine. In pigeons trained to discriminate 3 mg/kg intramuscular (i.m.) (+)-amphetamine from saline, (+)-methamphetamine and (+)-amphetamine were nearly equipotent, while cocaine was slightly less potent. In rats trained to discriminate 5 or 10 mg/kg cocaine from saline, intravenous administration of 1 g/kg of the antibody shifted both intravenous and intraperitoneal dose-response curves for (+)-methamphetamine discrimination approximately threefold to the right at 1 or 4 days after administration of the antibody. In pigeons trained to discriminate 3 mg/kg intramuscular (+)-amphetamine from saline, a similar shift of the (+)-methamphetamine dose-response curve to the right also lasted for 4-7 days. However, the antibody did not affect the (+)-amphetamine dose-response curve (pigeons), or the cocaine (rats) dose-response curve. The data show that a low affinity anti-(+)-methamphetamine-specific antibody can produce a specific antagonism of an effect of (+)-methamphetamine that is closely associated with its abuse.

Intravenous (+)-methamphetamine causes complex dose-dependent physiologic changes in awake rats

Hemodynamic and temperature dose-response relationships were characterized in freely moving rats following i.v. (+)-methamphetamine administration to mimic the rapid onset of effects experienced by many human users. Rats received saline and (+)-methamphetamine in a repeated-measures, mixed-sequence design at 22+/-1 degrees C. Significantly greater blood pressure and heart rate elevations were observed after 1.0 and 3.0 mg/kg (+)-methamphetamine vs. 0.1 and 0.3 mg/kg. The time to peak hemodynamic values and the duration of effects were significantly greater after 3.0 mg/kg vs. the lower doses. The time to peak temperatures was significantly longer after 1.0 mg/kg vs. the lower doses. Following 3.0 mg/kg, all rats experienced temperature decreases before having elevated temperatures. The duration and magnitude of the delayed temperature elevations were significantly greater after 3.0 mg/kg vs. the lower doses. In conclusion, the (+)-methamphetamine-induced hemodynamic and temperature effects were not temporally synchronized, and the complex responses were not linearly related to dose.

Differential and region-specific activation of mitogen-activated protein kinases following chronic administration of phencyclidine in rat brain

We have previously demonstrated elevation of the extracellular signal-regulated kinase (ERK) pathway in the cerebellum from patients with schizophrenia, an illness that may involve dysfunction of the N-methyl-D-aspartate (NMDA) receptor. Since the NMDA antagonist, phencyclidine (PCP), produces schizophrenic-like symptoms in humans, and abnormal behavior in animals, we examined the effects of chronic PCP administration in time- and dose-dependent manner on ERK and two other members of mitogen-activated protein kinase family, c-Jun N-terminal protein kinase (JNK) and p38, in rat brain. Osmotic pumps for PCP (18 mg/kg/day) and saline (controls) were implanted subcutaneously in rats for three, 10, and 20 days. Using Western blot analysis, we found no change at three days, but a significant increase in the phosphorylation of ERK1, ERK2 and MEK in the cerebellum at 10- and 20-days of continuous PCP infusion. For the experiments involving various doses of PCP, rats were infused with PCP at concentrations of 2.5, 10, 18, or 25 mg/kg/day, or saline for 10 days. We observed a dose-dependent elevation in the phosphorylation of ERK1 and ERK2 only in the cerebellum but not in brainstem, frontal cortex or hippocampus. The activities of JNK and p38 were unchanged in all investigated brain regions including cerebellum. These results demonstrate that chronic infusion of PCP in rats produces a differential and brain region-specific activation of MAP kinases, suggesting a role for the ERK signaling pathway in PCP abuse and perhaps in schizophrenia.

Generation of anti-(+)methamphetamine antibodies is not impeded by (+)methamphetamine administration during active immunization of rats

The goal of these studies was to determine if chronic (+)methamphetamine ((+)METH) administration affects the production of anti-(+)METH antibodies during active immunization of rats. Active immunization for the treatment of chronic drug abuse has been proposed for drugs such as cocaine and nicotine. However, studies have not adequately addressed whether continual drug use during treatment would affect the development of an immune response. For the current studies, male Sprague-Dawley rats were immunized with either keyhole limpet hemocyanin (KLH; control group) or a (+)METH hapten ((+)METH with a six carbon spacer group at the para position of the ring structure)-KLH conjugate. The (+)METH-KLH animals were further divided into two groups. One group was immunized with no subsequent administration of (+)METH, while the other group was immunized and repeatedly challenged (twice a week throughout the study) with an i.p. dose of 3 mg/kg (+)METH. The results showed that the two groups of (+)METH-KLH immunized rats developed and maintained anti-(+)METH antibody titers. The anti-(+)METH immune responses of the two groups were not statistically different (P < 0.05) as measured by serum titers and the relative antibody affinities. These data suggest that repeated administration of (+)METH does not affect the generation of an anti-(+)METH antibody response in actively immunized rats.

The effect of rate of drug administration on the extent and time course of phencyclidine distribution in rat brain, testis, and serum

The goal of these studies was to examine the relationship between the rate of phencyclidine (PCP) administration and PCP tissue distribution. The time course of PCP distribution in serum, brain, and testis after rapid (i.v.) and slow (s.c.) administration was studied. Brain and serum PCP concentrations after an i.v. bolus dose (1 mg/kg at 900 microg/min) were highest at 30 s and decreased biphasically, with serum concentrations decreasing 30 times faster than brain concentrations during the early phase. Consequently, the brain-to-serum PCP concentration ratio increased from 8:1 at 30 s to 14:1 at 20 min before equilibrating at a ratio of 3:1 that remained constant from 1 to 8 h. In contrast, the testis-to-serum ratio increased slowly from 1:1 to 12:1 over 4 h, and then remained constant. In a separate group of animals, an s.c. infusion of PCP (18 mg/kg/day or 3.6 microg/min) produced a brain-to-serum ratio (6:1) that remained constant throughout the 96-h infusion. Testis-to-serum ratios increased from 4:1 at 1 h to 12:1 at 8 h and then remained constant for 96 h. Steady-state infusion of a pharmacologically inactive dose (2.5 mg/kg/day) produced a brain-to-serum ratio (3:1) that was significantly lower than the ratio (6:1) after infusion of the three pharmacologically active doses (10-25 mg/kg/day). The temporary high brain PCP concentrations and the dynamic disequilibrium between brain and serum concentrations after rapid i.v. administration could provide a better understanding of the preference of the human drug abuser for rapid rates (e.g., i.v. or smoking) of drug administration.

Disposition of methamphetamine and its metabolite amphetamine in brain and other tissues in rats after intravenous administration

These studies characterized the concentration-time profile of (+)-methamphetamine [(+)-METH] and its metabolite (+)-amphetamine [(+)-AMP] in the brain and five other tissues after (+)-METH administration. Male Sprague-Dawley rats received a pharmacologically active (+)-METH i.v. bolus dose (1.0 mg/kg) or a nonpharmacologically active s.c. infusion (20 h at 1.2 mg/kg/day). Tissues (n = 3 per time point) were collected for more than four elimination half-lives in the i.v. group, or at a single steady-state time point (20 h) in the s.c. group. Based on data from the area under the concentration-time curves after i.v. dosing, the rank order of (+)-METH tissue accumulation was kidney > spleen > brain > liver > heart > serum with terminal elimination half-life values ranging from 53 to 66 min. (+)-METH concentrations were highest at the first measured time point (2 min) in all tissues except the spleen, which peaked at 10 min. The brain-to-serum concentration ratio rose from 7:1 at 2 min to a peak of 13:1 at 20 min before equilibrating to a constant value of 8:1 at 2 h. Following s.c. (+)-METH dosing, the (+)-METH brain-to-serum concentration ratio was the same as the equilibrated ratio following i.v. dosing. (+)-AMP concentrations peaked at 20 min in all tissues before decaying with terminal elimination half-life values ranging from 68 to 75 min. Analysis of the area under the concentration-time curve molar amounts of (+)-AMP and (+)-METH showed that (+)-AMP accounted for approximately one-third of the drug tissue exposure over time. Thus, these data indicate the importance of both (+)-METH and (+)-AMP in pharmacological effects following i.v. (+)-METH administration.

Anti-phencyclidine monoclonal antibodies provide long-term reductions in brain phencyclidine concentrations during chronic phencyclidine administration in rats

These studies examined the hypothesis that a single large dose of monoclonal anti-phencyclidine (PCP) antibody could provide long-term reductions in brain PCP concentrations despite continuous PCP administration. PCP (18 mg/kg/day, s.c.) was infused to steady-state (24 h) and then a mole-equivalent dose of a short-acting anti-PCP antigen-binding fragment (Fab) or a long-acting anti-PCP IgG was administered i.v. The PCP infusion continued for up to 27 days, even though the binding capacity of the single dose of antibody used should have been saturated within the first day. At selected time points after antibody administration, brain, testis, and serum PCP concentrations were measured. Serum PCP concentrations rapidly increased approximately 100- and 300-fold after Fab or IgG administration, respectively. Based on the antibody-bound PCP concentrations in serum, the functional elimination half-life (t(1/2lambdaZ)) values for PCP-Fab and PCP-IgG complexes were 9.4 h and 15.4 days, respectively. Fab and IgG administration produced a complete removal of PCP from the brain within 15 min. Although brain PCP concentrations were significantly decreased for only 4 h in Fab-treated animals, IgG administration resulted in significant decreases in brain PCP concentrations lasting for at least 27 days. In contrast, testis PCP concentrations were not substantially affected by antibody administration, suggesting that redistribution of PCP from the testis is too slow to benefit from a limited dose of antibody. These results indicate that anti-PCP IgG can preferentially protect the brain for approximately 4 weeks after IgG administration, even when the antibody binding capacity should have been saturated with continuously administered PCP.

Spontaneous locomotor activity and pharmacokinetics of intravenous methamphetamine and its metabolite amphetamine in the rat

The purpose of these studies was to better understand the behavioral effects and pharmacokinetics of an i.v. bolus dose of (+)-methamphetamine [(+)-METH] in a rat model of (+)-METH abuse. We characterized the behavioral effects after increasing (+)-METH doses (0.1, 0.3, and 1.0 mg/kg) and the pharmacokinetics of (+)-METH (and its metabolite (+)-amphetamine [(+)-AMP)]) at the lowest and highest of these doses in adult male Sprague-Dawley rats. The doses and route of administration were selected to mimic aspects of human use on a dose/body weight basis. Although the 0.1 mg/kg dose did not cause statistically significant increases in locomotor activity compared with saline controls, the higher doses (0.3 and 1.0 mg/kg) caused statistically significant increases in locomotor activity (p <.05), which lasted for up to 3 h at the highest dose. After the 1.0 mg/kg dose, the volume of distribution at steady state was 9.0 liters/kg, the total clearance was 126 ml/min/kg, and the average distribution and elimination half-lives were 9.2 and 63.0 min, respectively. Because the pharmacokinetic values after the 0.1 mg/kg dose were not different from those after the 1.0 mg/kg dose, the pharmacokinetics of (+)-METH were considered to be independent of the dose over this 10-fold range. (+)-AMP serum concentrations after the 1.0 mg/kg dose peaked from 10 to 30 min, and exhibited a T(1/2lambdaz) of 98.5 min. The statistically longer T(1/2lambdaz) of (+)-AMP (p <.05) suggested that the (+)-AMP terminal elimination rate and not the (+)-AMP metabolic formation rate is the rate-limiting step in (+)-AMP elimination following i.v. (+)-METH dosing.

Sexual dimorphism in phencyclidine in vitro metabolism and pharmacokinetics in rats

Studies were conducted to determine the differences in phencyclidine (PCP) in vitro metabolism and pharmacokinetics in female and male Sprague-Dawley (SD) rats. Formation rates of five major PCP metabolites in liver microsomes were significantly higher (p <.05) in males compared with females in three different rat strains (SD, Fischer 344, and Dark Agouti). In addition, the formation rate for an irreversibly bound PCP metabolite in males was the second highest of the six metabolites measured in these studies. However, the liver microsomes from the females produced essentially no metabolite binding in any strain. To determine the in vivo consequences of these in vitro metabolism results, we determined PCP's pharmacokinetic profile in female SD rats after a pharmacologically active i.v. dose of PCP (1 mg/kg) and then compared these data with the pharmacokinetic profile in male SD rats. The value for PCP systemic (and nonrenal) clearance was more than 45% lower (p <.05) in female rats. In addition, the terminal elimination T(1/2) was significantly longer (p <.05) in the female rats (5.5 versus 3.4 h, respectively). Because the initial serum concentration, volume of distribution at steady state, and renal clearance were not significantly different between the sexes, the longer half-life was attributed directly to a decreased ability of females to metabolize the drug. Consequently, these pharmacokinetic data suggest pharmacological differences in PCP effects between female and male rats are due primarily to a decreased ability of female rats to metabolize the drug.

Pharmacokinetic mechanisms for obtaining high renal coelimination of phencyclidine and a monoclonal antiphencyclidine antigen-binding fragment of immunoglobulin G in the rat

Our purpose was to determine mechanisms and methods for significantly increasing the renal coelimination of phencyclidine (PCP) and an anti-PCP monoclonal antibody binding fragment (anti-PCP Fab). To accomplish this goal, we performed a series of experiments to examine the dose-dependence of Fab elimination, mechanisms for enhancing PCP and Fab urinary coelimination and the antigenicity of repeated Fab administration. The results showed that urinary elimination of PCP and anti-PCP Fab was linear over a 30-fold range of doses. Anti-PCP Fab serum pharmacokinetics were best described using bi- or tri-exponential curves with a terminal elimination half-life of approximately 8 hr. Nevertheless, under all experimental conditions the early, nonterminal phase(s) were responsible for the majority (60%) of intact Fab elimination, with only 40% of the Fab eliminated during the terminal phase. These data suggest that the early rapid decline in Fab serum concentrations was primarily due to passive filtration and excretion of intact Fab, and not due to extravascular distribution as previously described. In comparison of methods for enhancing renal coelimination of Fab and PCP, systemic alkalinization produced a significant increase in Fab urinary elimination, with 69% of the Fab dose and 41% of the PCP dose recovered intact in the urine. Finally, in studies of the antigenicity of Fab, repeated administration of Fab produced no significant immune response or renal impairment. Overall, these experiments suggest that careful attention to the physiological status of the kidney during early time periods is essential for maximum coelimination of Fab and bound chemicals.

Crystal structure of monoclonal 6B5 Fab complexed with phencyclidine

The crystal structure of monoclonal antibody (mAb) 6B5 Fab fragment complexed with 1-(1-phenylcyclohexyl)piperidine (PCP or phencyclidine) was determined at 2.2-A resolution. 6B5 was originally produced from a mouse immunized with a phencyclidine analogue hapten 5-[N-(1'phenylcyclohexyl)amino]pentanoic acid conjugated to bovine serum albumin. This mAb was selected for further study because of its high affinity (Kd = 2 x 10(-9) M/liter) for PCP and usefulness in reversing PCP-induced central nervous system toxicity in laboratory animals. The dominant feature of the 6B5 Fab.PCP complex is the deep binding site and hydrophobic nature of the interaction. The ligand binding pocket of 6B5 Fab has numerous aromatic side chains, as compared with other known Fab structures. The most notable feature of the binding site is a Trp at position 97H (H-chain), and the side chain of this residue appears to act as a hydrophobic umbrella on the ligand in the antigen binding pocket. There are only two other known Fabs found with a Trp at the 97H position in complementarity determining region (CDR) H3, but they do not play a major role in the interaction with their respective antigens; in both Fab TE33 and R6.5 the Trp 97H side chain is positioned away from the bound antigen. Comparison of the CDR residues of 6B5 with other Fab structures with similar CDR sizes and amino acid compositions reveals a number of important patterns of residue substitutions that appear to be critical for specific PCP ligand interactions.

Pharmacodynamics of a monoclonal antiphencyclidine Fab with broad selectivity for phencyclidine-like drugs

The development of treatment strategies for drug intoxication has been hindered in part by the lack of clinically useful antagonists. Consequently, the major goal of these studies was to determine whether a monoclonal antibody Fab fragment (of IgG) could be used as an effective drug class-selective antagonist and to understand better the dose-response relationships for reversing CNS drug toxicity. Changes in drug-induced locomotor effects in a rat model were used to assess the ability of the antiphencyclidine (anti-PCP) Fab to reverse the behavioral effects of PCP and other potent arylcyclohexylamines. In experiments to determine the pharmacodynamics of Fabinduced antagonism of behavioral effects, the Fab completely reversed all PCP-induced locomotor effects in a Fab dose-dependent manner with a minimal effective dose of 0.18 mole-equivalents of Fab and an ED50 value of about one-third mole-equivalent. The anti-PCP Fab also completely reversed the locomotor effects induced by two other structurally related potent analogs of PCP: 1-[1-(2-thienyl)cyclohexyl]piperidine and N-ethyl-1-phenylcyclohexylamine. In addition, pharmacological and immunological selectivity was further tested by treatment of the behavioral effects induced by the structurally unrelated locomotor stimulant (+)methamphetamine. The antibody did not effectively reverse the effects of methamphetamine-induced locomotor activity. These results indicate that antibody-based medications can be developed to treat toxicity caused by classes of drugs as well as by individual drugs.

Exposure to acute stress induces brain interleukin-1beta protein in the rat

Peripheral immune stimulation such as that provided by lipopolysaccharide (LPS) has been reported to increase brain levels of IL-1beta mRNA, immunoreactivity, and bioactivity. Stressors produce many of the same neural and endocrine responses as those that follow LPS, but the impact of stressors on brain interleukin-1beta (IL-1beta) has not been systematically explored. An ELISA designed to detect IL-1beta was used to measure levels of IL-1beta protein in rat brain. Brain IL-1beta was explored after exposure to inescapable shock (IS; 100 1.6 mA tail shocks for 5 sec each) and LPS (1 mg/kg) as a positive control. Rats were killed either immediately or 2, 7, 24, or 48 hr after IS. Brains were dissected into hypothalamus, hippocampus, cerebellum, posterior cortex, and nucleus tractus solitarius regions. LPS produced widespread increases in brain IL-1beta, but IS did not. Adrenal glucocorticoids are known to suppress IL-1beta production in both the periphery and brain. Thus, it was possible that the stressor did provide stimulus input to the brain IL-1beta system(s), but that the production of IL-1beta protein was suppressed by the rapid and prolonged high levels of glucocorticoids produced by IS. To test this possibility rats were adrenalectomized or given sham surgery, with half of the adrenalectomized rats receiving corticosterone replacement to maintain basal corticosterone levels. IS produced large increases in brain IL-1beta protein in the adrenalectomized subjects 2 hr after stress, whether basal corticosterone levels had been maintained. Thus elimination of the stress-induced rise in corticosterone unmasked a robust and widespread increase in brain IL-1beta.

Stationary crystal diffraction with a monochromatic convergent X-ray source and application for macromolecular crystal data collection

A diffraction geometry utilizing convergent X-rays from a polycapillary optic incident on a stationary crystal is described. A mathematical simulation of the resulting diffraction pattern (in terms of spot shape, position and intensity) is presented along with preliminary experimental results recorded from a lysozyme crystal. The effective source coverage factor is introduced to bring the reflection intensities onto the same scale. The feasibility of its application to macromolecular crystal data collection is discussed.

Brain microsomal metabolism of phencyclidine in male and female rats

These studies examined the microsomal brain metabolism of phencyclidine (PCP) in male and female Sprague-Dawley rats. Several monohydroxylated metabolites of PCP were detected including cis- and trans-1-(1-phenyl-4-hydroxycyclohexyl)piperidine (c-PPC and t-PPC) and 1-(1-phenylcyclohexyl)-4-hydroxypiperidine (PCHP). The in vitro formation of these metabolites required NADPH and was inhibited by carbon monoxide. c-PPC was formed in the male and female brain microsomes at rates of 7.1 +/- 1.3 and 5.7 +/- 1.1 fmol/min per mg, respectively, while t-PPC was formed at rates of 16.2 +/- 3.3 and 16.5 +/- 4.2 fmol/min per mg. PCHP had the highest formation rate at 50.7 +/- 8.9 and 48.2 +/- 8.8 fmol/min per mg, respectively. Although previous studies with rat liver microsomes find higher levels of PCP metabolism in male rats and the formation of an irreversibly bound metabolite in male rats, the present study of brain metabolism found no sex differences in brain metabolism. The formation of PCP metabolites in male rat livers is at least partially mediated by the male-specific isozyme CYP2C11, and possibly CYP2D1. Nevertheless, the formation of the major brain metabolite, PCHP, was not inhibited by an anti-CYP2C11 or an anti-CYP2D6 antibody. However, PCHP formation was inhibited by drug inhibitors of CYP2D1-mediated metabolism, suggesting the involvement of a CYP2D isoform. These data indicate brain metabolism of PCP is significant, but unlike the liver it is not sexually dimorphic.

Metabolism of phencyclidine by human liver microsomes

These studies examined in vitro metabolism of phencyclidine (PCP) in a series of human liver microsomes (N = 10). Each sample was characterized for cytochrome P450 (CYP) content and for CYP1A, CYP2A, CYP2C, CYP2D, CYP2E, CYP3A, CYP4A, and lauric acid 11-hydroxylation metabolic activities. At least five PCP metabolites (c-PPC, t-PPC, PCHP, an unknown metabolite, and an irreversibly bound metabolite) were formed by the various human liver microsomes. Nevertheless, there was a large degree of inter-individual variation in the metabolite formation. For example, the irreversibly bound metabolite was formed in detectable amounts in only four of the ten samples. c-PPC, t-PPC and the irreversibly bound PCP metabolite formation rates significantly correlated with CYP3A activity. The CYP3A inhibitor troleandomycin was used to inhibit the formation of PCP metabolites. Troleandomycin inhibition was dose dependent with the highest dose producing complete inhibition of the formation of c-PPC, t-PPC, PCHP, and the irreversibly bound metabolite. In addition, PCP inhibited CYP3A-mediated testosterone 6 beta-hydroxylation by 50%. Furthermore, the relative intensity of CYP3A immunoreactive proteins significantly correlated with testosterone 6 beta-hydroxylation and with PCP metabolite formation (except for the unknown metabolite). PCHP formation also correlated with CYP1A activity, while the formation of the unknown PCP metabolite correlated with CYP2A activity. These studies suggest that several CYP isoforms contribute to PCP metabolism and that CYP3A plays a major role in PCP biotransformation in human liver microsomes.

Phencyclidine continuous dosing produces a treatment time-dependent regulation of rat CYP2C11 function, protein expression and mRNA levels

These studies determined the effects of continuous phencyclidine (PCP) administration on cytochrome P450 2C11 (CYP2C11) function, protein expression and mRNA levels. Male Sprague-Dawley rats received s.c. PCP infusions (18 mg/kg/day) for 1, 3, 10 or 20 days (n = 4 per group). Control animals received saline infusions for 3 or 20 days. Livers were collected 24 hr postinfusion, a time when PCP was completely cleared from the animals. In microsomes from the 1- and 3-day PCP infusions, there was a significant decrease (P < .05) in CYP2C11 protein expression (61 and 46% of control values, respectively) and in CYP2C11-mediated metabolism of PCP to a reactive metabolite (36 and 41% of control values). Both protein expression and PCP metabolite formation had returned to normal by 10 days of continuous PCP infusion. CYP2C11 function (as measured by 2alpha-OH testosterone formation) was decreased in the 1-, 3- and 10-day infused rats to 46, 28 and 45% of control values (P < .05). CYP2C11 function, expression and reactive PCP metabolite formation returned to normal after 20 days of PCP infusion. In contrast, CYP2C11 mRNA levels were decreased (P < .05) in liver tissue in PCP-treated rats from 1 to 20 days (43, 31, 37 and 47%, respectively). These data suggest that continuous PCP infusions initially decrease CYP2C11 function and protein expression by a pretranslational mechanism, but continued exposure to PCP leads to metabolic adaptation without the recovery of mRNA levels. Thus, chronic exposure to PCP can produce time-dependent regulation of CYP2C11-mediated metabolism of endogenous and exogenous compounds.

Metabolic inactivation of cytochrome P4502B1 by phencyclidine: immunochemical and radiochemical analyses of the protective effects of glutathione

Phencyclidine (PCP) inactivates the 7-ethoxy-4-trifluoromethylcoumarin O-deethylase activity of P4502B1 in a reconstituted system containing NADPH-cytochrome P450 (P450) reductase (reductase) and L-alpha-phosphatidylcholine, dilauroyl in a time-, concentration-, and NADPH-dependent manner. Catalytic activity of the enzyme could not be restored upon reconstitution with fresh reductase, indicating that the effect was on the P450 and not on the reductase. Although the kinetics suggested that PCP would be classified as a classical mechanism-based inactivator, protection against inactivation of P450 by PCP by the presence of an exogenous nucleophile, such as glutathione (GSH), indicated otherwise. There was no loss of spectrally detectable P450 associated with inactivation either in the presence or absence of GSH. When radiolabeled PCP was used to inactivate the enzyme and the reaction mixture analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, radioactivity was found to be associated with P450, reductase, and catalase that had been added to protect against oxidative damage. When GSH was included in the reaction mixtures, analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis demonstrated a marked decrease in the binding to all three proteins. Correspondingly, analysis of the components of the inactivated sample by reversed-phase HPLC demonstrated that radioactivity was associated with P450, reductase, and catalase, and that there was a marked decrease in the labeling of all three proteins in the presence of GSH. The stoichiometry of binding of radiolabeled PCP to the proteins in the incubation mixture in the absence of GSH was 4:1. In the presence of GSH, no significant amount of radioactivity was incorporated into the proteins. An anti-PCP metabolite antibody was used to detect PCP metabolite adducts bound to the inactivated enzyme by Western blot analysis. The antibody recognized adducts bound to P450, reductase, and catalase. In the presence of GSH, there was a decrease in immunoreactivity, although binding of PCP to all three proteins was still detected. Because the added nucleophile protects against inactivation and protein labeling by PCP, these data suggest that the reactive intermediate may escape from the active site and attack other sites on the P450, as well as other proteins in the milieu.

Antiphencyclidine monoclonal Fab fragments reverse phencyclidine-induced behavioral effects and ataxia in rats

Antiphencyclidine monoclonal antibody binding fragments (anti-PCP Fab) were studied in rats as a possible treatment for phencyclidine (PCP) overdose. Each male Sprague-Dawley rat (n = 4 per group) received an i.v. dose of 1 mg/kg of PCP followed 5 min later (as toxicity maximized) by one of three treatments in a random cross-over design. The treatments were 1 ml of saline, a nonspecific polyclonal human Fab, or a high affinity (Kd = 1.8 nM) anti-PCP monoclonal Fab. The doses of the nonspecific and anti-PCP Fab were 0.3, 1.0 and 3.0 times the mole equivalent (mol-eq) dose of PCP. Changes in locomotor activity and ataxia were the best indicators of PCP-induced behaviors among several time-dependent behavioral changes that were evaluated. PCP administration followed by saline treatment resulted in increases in locomotor activity and ataxia that declined to base line after 35 to 40 min. Anti-PCP Fab at 1.0 and 3.0 times the mol-eq dose of PCP significantly (P < .05) and rapidly reversed PCP-induced behaviors to base-line values. Although the 0.3 mol-eq dose of Fab appeared to slightly decrease the behavioral toxicity, the effects were not statistically different from controls in most cases. No significant effects on PCP-induced behaviors were observed after any dose of the nonspecific Fab. In addition, pharmacological and immunological specificity were tested further by treatment of MK-801 {(+)-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5, 10-imine-}-induced behavioral effects. MK-801 is a PCP-like, noncompetitive N-methyl-D-aspartate receptor antagonist which is structurally unrelated to PCP. The anti-PCP Fab treatment had no effect on MK-801-induced locomotor activity. These data clearly show that anti-PCP Fab is a specific PCP antagonist that can rapidly reverse PCP-induced behavioral toxicity in the rat.

Antiphencyclidine monoclonal antibody therapy significantly changes phencyclidine concentrations in brain and other tissues in rats

These studies determined how high-affinity monoclonal antiphencyclidine (PCP) antigen binding fragments of immunoglobulin G (Fab) affects PCP tissue concentrations and serum protein binding in male rats. Animals received an i.v. bolus dose of 1.0 mg/kg of PCP, followed at 2 hr when distribution was complete (but about 70% of the dose remained) by either saline (for controls) or an equimolar dose of anti-PCP Fab. This dose of PCP was chosen because it produces behavioral effects and ataxia for about 40 min. The rats were sacrificed over the next 16 hr (n = 3 per time point) and blood, brain, fat, heart, kidney, liver, lung, muscle and testis were collected. After anti-PCP Fab treatment, serum PCP concentrations increased significantly (P < .05) for the duration of the experiment. This resulted in a decrease in the PCP volume of distribution and systemic clearance to 11 and 12% of controls, respectively. Because these parameters decreased to a similar degree, the terminal elimination half-life was unaltered after Fab treatment. The percentage of unbound PCP in serum averaged 47 +/- 15% (mean +/- S.D.) in controls and 3 +/- 2% in Fab-treated animals for the duration of sampling. The area under the tissue concentration vs. time curves after anti-PCP Fab administration were decreased substantially in the brain (23% of controls), fat (24%), heart (52%), lung (74%) and testis (12%), but increased in the liver (137%). Because of anti-PCP Fab renal elimination, kidney PCP concentrations were significantly increased at all time points after Fab treatment (P < .05), which resulted in an 18-fold increase in the PCP area under the curve. These studies show anti-PCP Fab can rapidly remove PCP from the brain and maintain it in a highly bound form for a significant time.

Phencyclidine metabolite irreversible binding in the rat: gonadal steroid regulation and CYP2C11

These studies were conducted to determine the effect of hormones on sex-related differences in phencyclidine (PCP) metabolite irreversible binding and to determine the cytochrome P450 isoform(s) involved in this process. Sprague-Dawley male rats were castrated or administered estradiol and Sprague-Dawley female rats were ovarectomized or ovarectomized and given testosterone. Liver microsomal metabolism studies demonstrated that PCP metabolite binding to proteins was significantly altered by testosterone and estrogen administration. Castration of male rats decreased metabolite binding to 57% of sham-operated male levels, and administration of testosterone to ovarectomized female rats increased metabolite binding to 41 % of normal male levels. No metabolite adducts could be detected in microsomes from male rats administered estradiol or from sham-operated females given vehicle. These hormone-induced changes in metabolite binding closely matched the hormone-induced changes in CYP2C11 function and expression in these same microsomes. PCP metabolite irreversible binding to microsomal proteins was highly correlated with CYP2C11 function (as assessed by the formation of 2alpha-OH-testosterone, r = 0.91) and with CYP2C11 expression (as assessed by Western blot analysis, r = 0.95). In addition, an anti-CYP2C11 monoclonal antibody almost completely inhibited PCP metabolite binding (down to 7% of control male values) in an antibody concentration-dependent manner. These data strongly implicate CYP2C11 as an isoform involved in PCP metabolism and the formation and/or binding of a reactive PCP metabolite to microsomal proteins.

Antipeptide antibodies targeted against specific regions of rat CYP2D1 and human CYP2D6

Four peptides (pep23-33, pep26-38, pep283-297, and pep409-419) corresponding to unique sequences in rat cytochrome P450 (CYP) 2D1 and/or human CYP2D6 were selected for production of antipeptide antibodies. Rat liver microsomal protein was recognized by anti-serum to all four peptides in ELISAs; however, antisera against pep23-33 and pep26-36 proved not usable for any other applications. Western blots of microsomal protein from a cell line specifically expressing human CYP2D6 revealed that antisera to pep283-297 and pep409-419 recognized a single protein band of the same molecular size as CYP2D6. Antisera to pep283-297 and pep409-419 recognized a rat microsomal protein presumed to be CYP2D1, because it comigrated with human CYP2D6 and had an apparent molecular size of 52 kDa. An unknown protein of approximately 85 kDa was also recognized by pep409-419. Recognition of microsomal protein(s) by antisera to pep283-297 and pep409-419 was blocked by pep283-297 or a bovine serum albumin-pep409-419 conjugate, respectively. Antiserum to pep283-297 was used to analyze sex and strain differences in liver microsomes prepared from Sprague-Dawley, Fischer 344, and Dark Agouti male and female rats. Sprague-Dawley and Fischer 344 rats expressed similar amounts of CYP2D1, but expression in Dark Agouti rats was significantly lower. The antiserum did not detect a sexual dimorphism in any of the strains. A significant correlation between antipeptide283-297 immunoreactivity and Vmax for dextromethorphan O-demethylation existed in female rat strains; however, this relationship did not exist in male rat strains.(ABSTRACT TRUNCATED AT 250 WORDS)

Anti-phencyclidine monoclonal Fab fragments markedly alter phencyclidine pharmacokinetics in rats

The purpose of these studies was to explore the use of phencyclidine (PCP)-specific high affinity antibodies as a possible treatment for phencyclidine toxicity. High affinity (Kd = 1.8 nM) anti-PCP monoclonal Fab fragments were purified from papain digested anti-PCP immunoglobulin produced in mouse ascites. Control animals (n = 5) received an i.v. bolus dose of 1 mg/kg of PCP, along with a tracer dose of 250 microCi of [3H]PCP. Fab-treated rats (n = 5) also received this PCP dose, but at 2 hr after dosing (when PCP distribution was complete) they received an equimolar dose of anti-PCP Fab (50 mg). Within 5 min after the anti-PCP Fab administration, serum [3H]PCP concentrations increased approximately 60- to 100-fold. Fab treatment caused the [3H]PCP volume of distribution at steady state to decrease from 12.6 +/- 3.0 liters/kg (mean +/- S.D.) in control animals to 0.6 +/- 0.2 liters/kg in the Fab-treated animals (about 5% of control values). Systemic clearance changed from 66.3 +/- 16.9 to 6.8 +/- 2.8 ml/min/kg (about 10% of control values). Because both volume of distribution and systemic clearance decreased to a similar degree, the terminal elimination half-life did not change significantly (3.9 hr in controls vs. 4.9 hr in treated animals, harmonic means). Renal clearance decreased from 1.8 +/- 0.6 to 0.62 +/- 0.17 ml/min/kg after Fab treatment. The anti-PCP Fab caused the percentage of PCP recovered in urine to increase from 2.5 +/- 0.5 to 10.3 +/- 4.7%.(ABSTRACT TRUNCATED AT 250 WORDS)

Disposition of a monoclonal anti-phencyclidine Fab fragment of immunoglobulin G in rats

Treatment of drug toxicity is problematic for compounds like phencyclidine (PCP) which have no known antagonists. With the advent of technology for production of large amounts of monoclonal antibody, it is now possible to explore the use of these antibodies as high affinity in vivo antagonists for treatment of PCP overdose. In the current study, the pharmacokinetics of an anti-PCP monoclonal antibody Fab (antigen binding fragment of immunoglobulin G) were determined in adult male Sprague-Dawley rats (n = 5). Each animal was cannulated and dosed with approximately 0.12 g/kg of unlabeled anti-PCP Fab fragments (Kd for PCP = 1.8 +/- 0.27 nM) along with a tracer dose of anti-PCP [3H]Fab. Blood was drawn at predetermined intervals and serum was analyzed for total radioactivity by liquid scintillation spectrometry. Serum and urine were analyzed for intact anti-PCP [3H]Fab after fractionation on a high-performance liquid chromatography molecular weight sizing column followed by quantitation by liquid scintillation spectrometry. The pharmacokinetic parameters for the [3H]Fab in rat serum were a terminal elimination T1/2 of 7.5 hr (harmonic mean), a volume of the central compartment of 0.17 +/- 0.026 liters/kg and a steady-state volume of distribution of 0.55 +/- 0.15 liters/kg (mean +/- S.D.). Systemic and renal clearances were 2.7 +/- 0.9 and 0.47 +/- 0.24 ml/min/kg, respectively. The total amount of the radioactive dose ([3H] Fab plus radioactive catabolic products) appearing in the urine was 51 +/- 11%, whereas urinary excretion of intact [3H]Fab accounted for 21 +/- 15% of the total dose. All animals tolerated the Fab infusion without adverse effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Dose- and time-dependent changes in phencyclidine metabolite covalent binding in rats and the possible role of CYP2D1

We determined whether chronic dosing with phencyclidine (PCP) could affect the in vitro function of liver microsomal enzymes in male Sprague-Dawley rats. PCP chronic dosing of rats (n = 3 per group) for 3 days with 2.5, 10 and 18 mg/kg/day caused a dose-dependent decrease (23, 36 and 53%, respectively) in the ability of the microsomal enzymes to bind covalently PCP metabolites. The 10- and 18-mg/kg/day dosing groups were significantly different from the 3-day saline-infused control group (P < .05). The results from time-dependent dosing studies indicated PCP covalent binding was significantly reduced (P < .05) in rats (n = 3 per group) infused with 18 mg/kg/day of PCP for 1, 2, 3, 4 and 10 days. Subsequently, it returned to near control values in rats infused for 20 days. In parallel with the time-dependent decreases in covalent binding, the concentrations of at least three phase I PCP mono- and dihydroxylated metabolites were also significantly reduced (P < .05) at the earlier time periods of dosing (3 and 10 days), but the rate of their formation returned to near normal values by 20 days of dosing. Total cytochrome P450 content did not differ from the control groups at any of the doses or time points. As dose- and time-dependent decreases in covalent binding suggested a specific metabolic pathway or isoenzyme was affected, we studied the affect on specific isoenzyme pathways. For these studies a series of cytochrome P450 inhibitors were used.(ABSTRACT TRUNCATED AT 250 WORDS)

Phencyclidine dependence: the relationship of dose and serum concentrations to operant behavioral effects

The dependence-producing properties of 10 days of chronic i.v. infusions of phencyclidine (PCP) and the relationship between PCP serum concentrations and behavioral effects were studied in Sprague-Dawley rats. For dependence studies, rats were trained to respond for food under a fixed-ratio 30 schedule during half-hour response periods every 6 hr. After training, implantation of jugular catheters, and restabilization of behavior, the rats were infused with PCP.HCl at 3.2, 5.6, 10.0 or 17.8 mg/kg/day (n = 5 or 6 per dose). The two higher doses initially decreased response rates, but tolerance developed within 4 to 5 days. When PCP infusions were terminated, dose-dependent decreases in session response rate occurred in the three highest dose groups (P less than .05). Mild, overt signs of abstinence were observed only in the highest dose group. Response rates returned to base line within 2 to 3 days after stopping PCP infusions. PCP serum concentrations in rats infused with 10 mg of PCP.HCl/kg/day for 10 days were stable from hour 24 to day 10 (mean steady-state concentration (+/- S.D.) = 97 (+/- 20) ng of PCP/ml; n = 4). The average terminal elimination half-life after stopping infusions on day 10 was 4.6 hr. Comparison of the average response rates with the average serum concentrations showed that during the first 24 hr of infusions, the rate of responding for food decreased as PCP concentrations increased; however, once the animals became tolerant to PCP there was no relationship. In contrast, during the first 24 hr after stopping infusions, response rates decreased as serum concentrations decreased.

Effects of gonadal steroids on clearance of growth hormone at steady state in the rat

Gonadal steroids have been implicated in the modulation of GH secretory patterns in the rat. We have studied the effects of testosterone (T) or estradiol (E2) on the steady state clearance (Clss) and plasma half-life (t1/2) of GH in male and female rats (n = 4-6/group). A femoral and a jugular cannula were surgically implanted into adult Sprague-Dawley rats. At the time of cannulation some rats were orchidectomized, and a Silastic capsule containing E2, T, or nothing was implanted sc. After recovery from surgery, either purified rat GH or a crude extract of rat pituitary was infused iv to attain steady state plasma GH concentrations. Blood samples were taken every 30 min for 4 h during the infusion, and nine samples were taken at 2.5-min intervals immediately after stopping the infusion. The mean Clss for GH in female rats were significantly (P less than or equal to 0.001) less than that in males, whereas the t1/2 did not differ between the two groups. Neither the Clss nor the t1/2 was affected by castration in males or females. The Clss of GH in E2-treated castrated males was significantly less (P less than 0.001) than that for intact males, but the t1/2 did not differ between the two groups. The Clss for GH was greater in T-treated ovariectomized rats than in intact females, but the t1/2 did not differ with T treatment. These results suggest that 1) the Clss for GH is lower in female rats than in males; 2) 4 weeks of gonadectomy has no effect on the Clss in males or females; 3) under experimental conditions, E2 decreases and T increases the Clss for GH; and 4) the t1/2 for GH is not different in males or females. The steroid-induced changes in Clss in the absence of detectable effects on t1/2 suggest that factors affecting the volume of distribution at steady state (i.e. plasma GH-binding proteins or GH heterogeneity) are involved in the effects of gonadal steroids on GH clearance in the rat.

Phencyclidine pharmacokinetics and concentration-response relationships in the pigeon

Phencyclidine (PCP) pharmacokinetics and drug discrimination were examined in pigeons (n = 6 in both groups) after intramuscular doses of 1.48 mg/kg. PCP absorption was rapid with maximum measured plasma concentrations ranging from 559 to 1450 ng/ml at 10-30 min after dosing, which corresponded to the time of maximum PCP stimulus effects in the drug discrimination studies. The terminal elimination half-life was 0.88 hr (harmonic mean). Average values for the volume of distribution and total body clearance were 1.6 l/kg and 18.2 ml/min/kg, respectively. In the behavioral studies, pigeons discriminated PCP-like effects from about 2 min to 2 hr after dosing. An average value for response on the PCP-appropriate key and for PCP concentration at each time point from 2 min to 2 hr was calculated from the individual subject data. Least-squares linear regression analysis of these data showed a highly significant relationship between the ability to discriminate PCP and log PCP concentration (y = 103x - 219, r2 = .810, p less than 0.005). This analysis suggests PCP concentration is a good predictor of behavioral efficacy.

The effect of age on digoxin pharmacokinetics in Fischer-344 rats

Digoxin protein binding and pharmacokinetics were studied in 4-, 14-, and 25-month-old male Fischer-344 rats to determine if there were age-dependent changes in digoxin disposition. Serum protein binding did not differ among age groups. The average percentage unbound digoxin for all animals was 61.3 +/- 5.3% (means +/- SD, n = 15). For pharmacokinetic studies, [3H]digoxin and 1 mg/kg unlabeled digoxin were administered as an intravenous bolus dose to animals from each age group. The [3H]digoxin terminal elimination half-life was 2.0, 2.3, and 2.5 hr, respectively. The steady-state volume of distribution in the three age groups was 1.51, 1.49, and 1.27 liters/kg, respectively. Total body clearance for the three age groups was 14.2, 12.1, and 7.5 ml/min/kg, respectively. Analysis of variance of these data followed by Duncan's multiple range test indicated a significant decrease in clearance in the aged rats (25-month-old, p less than 0.05). This age-dependent decrease in clearance suggested that digoxin pharmacokinetics could be a significant factor in age-related alterations in digoxin cardiotoxicity in the rat, as it is in humans, and that the Fischer-344 rat could be a useful model for studies of digoxin pharmacokinetic changes with age.

The pharmacokinetics of [3H]1-[1-(2-thienyl)cyclohexyl]piperidine (TCP) in Sprague-Dawley rats

Using adult male Sprague-Dawley rats, we examined the blood protein binding and pharmacokinetics of the potent phencyclidine (PCP) receptor ligand 1-[1-(2-thienyl)cyclohexyl]piperidine (TCP). The average percentage of unbound [3H]TCP in rat serum was 42 +/- 6% and the [3H]TCP blood to plasma ratio was 0.98 +/- 0.03 (mean +/- SD, n = 5 in both studies). For the pharmacokinetic studies, [3H]TCP and 1 mg/kg unlabeled TCP were administered as an iv bolus dose. The average [3H]TCP elimination half-life was 2.1 hr. In contrast, total radioactivity in the plasma had a much longer half-life, suggesting much slower metabolite elimination. The average distribution volumes were 27 +/- 17, 15.6 +/- 6.2, and 5.6 +/- 3.0 liters/kg for V beta, Vss, and Vc, respectively. Total body and renal clearance values were 132 +/- 45 and 1.1 +/- 0.4 ml/min/kg, respectively. When TCP pharmacokinetic parameters were compared to PCP pharmacokinetic data in rats from a previous study, a strikingly similar pharmacokinetic profile was found. These data indicated that TCP and PCP are equivalent, from a pharmacokinetic point of view, and that the higher pharmacological potency of TCP over PCP is probably due to receptor-mediated differences.

Structure-activity relationships of arylcyclohexylamines as discriminative stimuli in pigeons

The effects of a variety of arylcyclohexylamines, opioid drugs and other drugs were studied for phencyclidine-like effects in pigeons trained to discriminate phencyclidine (PCP) from saline. There was a good correlation between the relative potency of arylcyclohexylamines as PCP-like discriminative stimuli in pigeons and these drugs as discriminative stimuli in rats. Substitution of methyl groups on the piperidine or cyclohexyl rings of PCP reduced potency, but not efficacy, whereas substitution of hydroxyl groups decreased both potency and efficacy. Replacement of the phenyl ring with a thienyl ring increased PCP-like activity, but replacement of the piperidine ring with a pyrrolidine ring or a morpholine ring decreased potency. Compounds with methyl or ethyl groups on the nitrogen atom replacing the piperidine ring also were active. These data suggest that N-alkyl substitutions decrease potency but not efficacy, whereas hydroxylation of the cyclohexyl ring decreases efficacy as well. The data also support the suggestion that size of the aromatic ring is also a determinant of PCP-like activity. Both optical isomers of cyclazocine and N-allylnormetazocine were active as PCP-like discriminative stimuli, although the (-)-isomer was more potent than the (+)-isomer for cyclazocine and the reverse was true for N-allylnormetazocine. The pigeon shows less stereospecific activity with these drugs than the rat and especially the squirrel monkey. A variety of other opioid-like chemical structures, as well as other drugs such as d-amphetamine and pentobarbital, were inactive as PCP-like discriminative stimuli.

Isolation of monoclonal antibodies to phencyclidine from ascites fluid by preparative isoelectric focusing in the Rotofor

A monoclonal antibody to phencyclidine was developed, produced in mouse ascites fluid, and purified. The purification used only preparative-scale isoelectric focusing in the Rotofor and dialysis. In 4 h, 25% (4 mg) of the antibody from 10 ml of ascites fluid was purified to homogeneity while 63% of the total antibody was recovered.

Antibodies against arylcyclohexylamines and their similarities in binding specificity with the phencyclidine receptor

Rabbit antibodies were generated against five unique epitopes of phencyclidine (PCP)-like molecules to determine the molecular requirements for arylcyclohexylamine binding to the PCP receptor. Three of the haptens contained the three ring structures of PCP. A fourth hapten was synthesized from a derivative of the highly potent PCP analog, 1-[1-(2-thienyl)cyclohexyl]piperidine. The fifth hapten, 5-[N-(1'-phenylcyclohexyl)amino]pentanoic acid, was used as a haptenic model for N-ethyl-1-phenylcyclohexylamine, one of the most potent arylcyclohexylamines. These haptens were bound covalently to bovine serum albumin and were then used as antigens to immunize rabbits. The affinities and cross-reactivity patterns of the resulting five antibodies were studied in a [3H]PCP radioimmunoassay using standard curves of various arylcyclohexylamines. The dissociation constants ranged from 1.9 to 51.6 nM. From the average IC50 values of the radioimmunoassay dose-response curves, the relative potency of each ligand to PCP was determined. Least-squares linear regression was used to correlate these data with relative potency data from two [3H]PCP receptor binding assays and a PCP drug discrimination assay in the rat. Only relative potency data from the anti-5[N-(1'-phenylcyclohexyl)amino]pentanoic acid antibody showed a significant correlation with data from the three pharmacological studies (r2 = 0.80, 0.57 and 0.78, respectively; p less than .05 in all cases). These data indicated the 5-[N-(1'-phenylcyclohexyl)amino]pentanoic acid hapten contained the pharmacologically active features needed for arylcyclohexylamine binding to the PCP receptor.

Phencyclidine pharmacokinetic scaling among species

Interspecies pharmacokinetic parameters (y) for phencyclidine [1-(1-phenylcyclohexyl)piperidine] were correlated with body weight (B) using linear regression and the allometric equation of the form y = aBx (which also may be written as the linear regression equation, log y = x log B + log a). The data were obtained from previously reported pharmacokinetic studies in mammals (i.e., humans, monkey, dog, rat and mouse) and new pharmacokinetic data for the pigeon. The animal body weights ranged from 32.5 to 77,000 g and included 6 animal species from 2 vertebrate classes. The pharmacokinetic parameters correlated with body weight were T1/2 (T1/2 = 126B0.32, r2 = 0.799), volume of distribution (V beta = 10B0.96, r2 = 0.966) and systemic clearance (CLs = 50B0.64, r2 = 0.891). In addition, clearance values were multiplied by the maximum lifespan potential (MLP) of each animal and correlated with body weight [CLs X MLP = (3.3 X 10(5))B1.0, r2 = 0.991]. This helped normalize for species differences in systemic clearance, which correlated with species longevity. These allometric equations should provide the information for scaling phencyclidine pharmacokinetic data among diverse species.

Disposition kinetics of the monohydroxy metabolites of phencyclidine in the dog

The monohydroxy metabolites of phencyclidine (PCP) have been suggested to contribute to the pharmacologic activity of PCP, and perhaps account for its prolonged action. The disposition kinetics of the monohydroxy metabolites of PCP were examined in dogs. Intravenous doses of the piperidine-hydroxylated metabolite (PCHP) and the trans- and cis-forms of the cyclohexyl-hydroxylated metabolite (trans-PPC and cis-PPC) were each administered to three dogs. The elimination half-life of each metabolite was short, with harmonic mean values of 1.29, 0.98 and 0.92 hr for PCHP, trans-PPC and cis-PPC, respectively. The compounds had large volumes of distribution, with average values of 6.7, 4.7 and 4.4 liters/kg for PCHP, trans-PPC and cis-PPC, respectively. Systemic clearances were high for each compound (51.9, 50.9 and 54.2 ml/min/kg for PCHP, trans-PPC and cis-PPC, respectively), but renal clearances were low (average values ranged from 2 to 8% of systemic clearance), suggesting that these metabolites undergo further metabolism. Analysis of acid-hydrolyzed serum and urine samples indicated that all three compounds were conjugated and that these conjugates were the primary metabolites. The conjugated metabolites exhibited elimination half-lives longer than the parent compounds after administration of the monohydroxy forms and after PCP dosing. The disposition of these metabolites suggest that these compounds are not produced in sufficient quantities or do they exhibit pharmacokinetic behavior which would be consistent with the prolonged effects from PCP.

Amitriptyline plasma protein binding: effect of plasma pH and relevance to clinical overdose

Reversing ventricular ectopy with plasma alkalinization following acute tricyclic antidepressant overdose is a recognized mode of therapy. The mechanism responsible for this effect is unclear. Changes in plasma protein binding of free drug, effects of the sodium ion on the myocardium, and alterations of plasma concentrations of alpha-1-acid glycoprotein may all interact to alter toxicity of tricyclics in overdose. An in vitro investigation using equilibrium dialysis was designed to examine the effect of altering plasma pH on percentage of free amitriptyline at clinical overdose plasma concentrations. A 1973 report on this effect lacked adequate controls and was faulty in experimental protocol. The current investigation used plasma concentrations typically present in amitriptyline overdose, a sensitive gas liquid chromatographic assay to detect total and free drug, and adequate control of plasma pH. The results of two separate experiments demonstrated a significant decrease in percentage of free amitriptyline of 20% over a pH range of 7.0-7.4 (P less than 0.05) and 42% over a pH range of 7.4-7.8 (P less than 0.05). The rate of change in slope in both experiments was not significantly different (P less than 0.01) indicating similar effects of pH change on plasma protein binding of amitriptyline within the two groups.

Phencyclidine-specific Fab fragments alter phencyclidine disposition in dogs

High affinity antibodies (K0 = 3 X 10(9) M-1) against the widely abused drug phencyclidine (PCP) were produced in goats and then purified and extensively characterized for use in in vivo pharmacokinetic studies. An iv dose of 3H-PCP was administered to three dogs, followed 2 hr later by an equimolar dose of PCP-specific antigen-binding fragments (Fab). Within 10 min after Fab administration, the concentration of PCP in the serum had increased 17-56-fold in the three dogs. The Fab administration also produced a 10-fold decrease in volume of distribution and in systemic and renal clearances. The concentration of PCP metabolites decreased for a period of time after Fab administration. Equilibrium dialysis studies showed that the percentage of unbound PCP changed from about 50% before Fab administration to less than 1% unbound after Fab. In addition, the blood/plasma ratio of PCP changed from a near-equal distribution between red blood cells and plasma before Fab to virtually all of the drug being confined to the plasma fraction after Fab administration. Although Fab produced a dramatic redistribution and extensive protein binding of PCP, the route of elimination of PCP was not altered. These data suggest that high affinity anti-PCP Fab could reverse the toxicity of PCP.

Phencyclidine (PCP) disposition kinetics in dogs as a function of dose and route of administration

Phencyclidine (PCP) disposition kinetics has been examined in dogs as a function of dose and after i.v. and p.o. administration. Intravenous doses ranged from a tracer quantity of [3H]PCP to 5 mg/kg of unlabeled PCP. The elimination half-life of intact PCP was relatively short with harmonic mean values of 2.7, 5.4 and 3.9 hr for the tracer, 1- and 5-mg/kg doses, respectively. In contrast, measurement of total radioactivity gave a much longer half-life (35-52 hr) suggesting slower metabolite elimination. The drug has a large apparent volume of distribution (weighted mean of 20 liters/kg) and a systemic clearance (which is primarily metabolic) that approaches estimates of liver blood flow in the dog. Renal clearance of intact PCP represents a small fraction of total clearance. Percentage of the [3H]PCP dose recovered as total radioactivity was 49% in urine and 12% in feces. Several metabolites of PCP were determined in urine and they account for about 30% of the dose with the aminopentanoic acid derivative being present in the greatest amount. One of the hydroxylated metabolites is present in cis- and trans-forms, with the latter predominating. Three animals received an i.v. dose of [3H] PCP and a p.o. dose of unlabeled PCP at the same time to determine absolute bioavailability. Approximately 25% of the dose is absorbed intact. The p.o. (intrinsic) clearance of PCP is about four times greater than systemic clearance suggesting a blood flow-dependence in clearance and substantial first-pass hepatic metabolism.