SARS-CoV-2 Main Protease Inhibitors from Natural Product Repository as Therapeutic Candidates for the Treatment of Coronaviridae Infections

BACKGROUND

The main protease (Mpro) is a crucial enzyme for the life cycle of SARS-CoV-2 and a validated target for the treatment of COVID-19 infection. Natural products have been a proper alternative for treating viral diseases by modulating different steps of the life cycle of many viruses.

OBJECTIVE

This review article is designed to summarize the cumulative information of natural-derived Mpro inhibitors that are validated by experimental biological testing.

METHODS

The natural-derived Mpro inhibitors of SARS-CoV-2 that have been discovered since the emergence of the COVID-19 pandemic are reviewed in this article. Only natural products with experimental validation are reported in this article. Collected compounds are classified according to their chemical identity into flavonoids, phenolic acids, quinones, alkaloids, chromones, stilbenes, tannins, lignans, terpenes, and other polyphenolic and miscellaneous natural-derived Mpro inhibitors.

CONCLUSION

These compounds could serve as scaffolds for further lead-structure optimization for desirable potency, a larger margin of safety, and better oral activity.

Population Pharmacokinetics Modeling of Lamotrigine in Jordanian Epileptic Patients Using Dried Blood Spot Sampling

AIMS

To characterize the population pharmacokinetics of lamotrigine in Jordanian epileptic patients and to identify factors affecting therapeutic parameters.

PATIENTS AND METHODS

A population pharmacokinetics model for lamotrigine was established based on a prospectively collected data of 52 steady-state concentrations from 38 adult and pediatric patients with epilepsy. Lamotrigine concentrations were determined by a dried blood spot liquid chromatography method. Data were analyzed according to a one-compartment model with first-order absorption and elimination using the nonlinear mixed effect modeling program. The covariates effect of total body weight, gender, age, and co-medication with topiramate, carbamazepine, phenytoin, phenobarbital, and valproic acid on lamotrigine clearance were investigated using a stepwise forward addition followed by a stepwise backward elimination.

RESULTS

The final population pharmacokinetics model for lamotrigine clearance was as follows: CL/F_pop=θ₁*exp ^(θ3*age)*exp ^{(θ5*carbamazepine)}*exp ^{(θ6*valproic acid)} , where θ₁ is the relative clearance (L/hr) estimated, and θ₃, θ₅, and θ₆ are the fixed parameters relating to age and co-medication with carbamazepine and valproic acid, respectively.The population mean value of lamotrigine total clearance generated in the final model (with covariates) was 2.12 L/hr. Inter-individual variability and residual unexplained variability expressed as the coefficient of variation was 37.1 and 26.1%, respectively.

CONCLUSION

Lamotrigine total clearance in the Jordanian patients is comparable to that reported by others for Caucasian patients. Age and concomitant therapy with carbamazepine and valproic acid significantly affected lamotrigine clearance, and accounted for 48% of its inter-individual variability.

Bayesian Population Pharmacokinetic Modeling of Eltrombopag in Chronic Hepatitis C Patients

BACKGROUND AND OBJECTIVES

Eltrombopag is a thrombopoietic growth factor that is approved for the treatment of thrombocytopenia in chronic hepatitis C virus (HCV) patients. We aimed to describe eltrombopag population pharmacokinetics in hepatitis C patients. Bayesian statistical approach will be applied to screen for patients' characteristics associated with eltrombopag pharmacokinetic parameters.

METHODS

A population pharmacokinetic analysis was conducted using WinBUGS version 1.4.3. Data from 483 individuals with chronic HCV infection were analyzed. This analysis is a secondary analysis of two clinical studies (ENABLE1 and ENABLE2) sponsored by GlaxoSmithKline. Several patients' characteristics were examined as possible covariates of the population pharmacokinetic model. Prior information from previous studies was incorporated in the bayesian model as prior distribution to estimate pharmacokinetic parameters.

RESULTS

A two-compartment pharmacokinetic model with first-order absorption with exponential error model best fit the data. We identified East Asian race and total bilirubin level as predictors of eltrombopag clearance. Typical value for distributional clearance was 0.762 L/h (95% Bayesian credible set, 0.703-0.826), for volume of distribution of the central and peripheral compartments were 12 L (10.9-13.4) and 10.9 L (10.4-11.5), and for absorption lag time was 0.947 h (0.918-0.977). Assuming an average total bilirubin of 21.7 µmol/L, the typical elimination clearance value for an East Asian patient was 0.14 L/h and for other races was 0.20 L/h.

CONCLUSIONS

Eltrombopag pharmacokinetic behavior was described using population bayesian approach. This model can be applied to optimize eltrombopag dosing in order to reduce the incidence of thrombocytopenia in HCV-infected patient receiving interferon-based therapy.

A time-to-event analysis describing virologic response in patients with chronic hepatitis C infection

The objective of this project was to describe longitudinal change in chronic hepatitis C virologic reponse using time-to-event (TTE) analysis and to identify patient characteristics that determine the dynamics of this change. We compiled demographic, clinical, and genetic data from 715 chronic hepatitis C virus (HCV) patients treated with pegylated interferon (PEG-IFN) alfa-2a and ribavirin. TTE modelling described the time between antiviral treatment initiation and the first observation of undetectable HCV RNA. A lognormal TTE model was selected to describe time to first undetectable HCV RNA. The identified predictors of prolonged time to achieve undetectable HCV RNA include HCV genotype 1, low pre-treatment ALT level, older age, or with elevated baseline haemoglobin level. In conclusion, a cohort of patients with low probability of achieving SVR can be identified. This project identifies patients with a low risk of responding to PEG-IFN alfa-2a and ribavirin combination.

Evaluation of the impact of waterpipe tobacco smoke exposure on the activity and expression of rat hepatic CYP450: a pharmacokinetic study

Waterpipe smoke contains many toxic constituents that can alter drug pharmacokinetics. This study assessed the effect of waterpipe smoke exposure on the activity and expression of CYP450 enzymes in rats. Animals (n = 10/group) were exposed to either waterpipe smoke or side-stream cigarette smoke for 1 h/day (6 days/week) for 31 days, or fresh air (control). An intragastric cocktail solution containing three probe drugs, phenacetin, chlorzoxazone and testosterone was administered to assess the activity of CYP1A2, CYP2E1 and CYP3A, respectively. Serum concentrations were determined using LC-MS/MS and the pharmacokinetic parameters were calculated. The mRNA expression of hepatic enzymes was also quantified. Waterpipe and cigarette smoke exposure did not significantly alter the pharmacokinetics of phenacetin, chlorzoxazone and testosterone. For example, the clearance and drug exposure values were comparable among groups for all probe drugs. Additionally, there was no significant effect of waterpipe and cigarette smoke on mRNA expression of hepatic CYP1A2, CYP2E1 and CYP3A2. The results demonstrate that waterpipe smoke exposure had no effect on the functional expression of three key CYP450 isoforms in rats. Future research is required with longer exposure periods to waterpipe smoke. Such work serves to enhance current understanding of effect of waterpipe smoke exposure on pharmacokinetics.

A population pharmacodynamic model characterizing neutropenia associated with pegylated interferon alpha 2-a therapy in patients with chronic hepatitis C viral infection

Neutropenia is a hematologic disorder commonly reported in patients with chronic hepatitis C viral (HCV) infection. The objective of the present analysis is to describe the change in neutrophil count resulting from peglated interferon alpha 2-a (PEG-IFN α-2a) therapy in HCV-infected patients. A population pharmacodynamic model will be developed. We also plan to identify patient characteristics that contribute to the development of PEG-IFN α-2a-induced neutropenia in hepatitis C patients. A population pharmacodynamic modeling approach was applied to a cohort of patients (n = 292) with chronic HCV infection. Modeling was performed using NONMEM 6. Data was obtained from two phases III studies sponsored by Hoffmann-La Roche. Covariate screening was applied to evaluate various demographic and clinical characteristics as possible predictors of pharmacodynamic parameter during model development. A total of 4517 neutrophil counts from 292 subjects were analyzed by the proposed population pharmacodynamic model. A constant residual error model was used to the log-transformed neutrophil count. Platelet baseline count and uric acid level were identified as predictors of neutrophil pharmacodynamic model. Increased baseline platelet count is expected to result in higher neutrophil baseline. A higher neutrophil baseline is also expected in patients with increased uric acid level. In conclusion, a mechanistic pharmacodynamic model was developed. The effect of various covariates was included in the model. This allows the prediction of neutrophil count following antiviral therapy in patients with hepatitis C infection. Clinical studies: NV15942 and NV15801.

Patient characteristics associated with peglyated interferon alfa-2a induced neutropenia in chronic hepatitis C patients

Neutropenia is a haematologic disorder commonly reported in patients with chronic hepatitis C virus (HCV) infection treated with pegylated interferon alfa-2a (PEG-IFN α-2a). The objective of the present project is to identify patient characteristics associated with neutropenia in hepatitis C patients. Demographic, clinical, and genetic data from 715 patients with chronic HCV infection treated with PEG-IFN α-2a and ribavirin. The outcome variable was the development of grade 3 or 4 neutropenia, defined as the decrease in neutrophil counts below 1 10⁹ /L anytime during study. Predictors of neutropenia were identified using a 2-stage approach. First, univariate analysis was performed to identify possible predictors of neutropenia. T test was used for continuous variables and Fisher's exact test was used for categorical variables. Second, multiple logistic regression with stepwise addition was then performed using predictors identified in the univariate analysis step to produce final model containing independent predictors at P < .05. Logistic regression identified female gender, absolute neutrophils counts, and cholesterol level as the main predictors of neutropenia. Female gender increases the odds of experiencing neutropenia by 86% compared to male gender. A 1 unit (mmol/L) increase in cholesterol level decreases the odds of developing neutropenia by 13%. A 55% reduction in the likelihood of developing neutropenia for a 1 unit (10⁹ /L) increase in the absolute neutrophils counts. Patients with high risk of developing neutropenia can be identified. Identification of this cohort allows early intervention to prevent neutropenia. Possible intervention is to administer drugs that raise neutrophil count such as filgrastim before neutropenia occurs.

Modeling longitudinal changes in buprenorphine treatment outcome for opioid dependence

INTRODUCTION

The present analysis describes the longitudinal change in buprenorphine treatment outcome. It also examines several participant characteristics to predict response to buprenorphine.

METHODS

Participants (n=501, age>15 years) received buprenorphine/naloxone treatment for 4 weeks, and then were randomly assigned to undergo dose tapering over either 7 days or 28 days. An empirical model was developed to describe the longitudinal changes in treatment outcome. Several patient characteristics were also examined as possible factors influencing treatment outcome.

RESULTS

We have developed a model that captures the general behavior of the longitudinal change in the probability of having an opioid-negative urine sample following buprenorphine treatment. The model captures both the initial increase (i. e., initial response) and the subsequent decrease (i. e., relapse to opioid) in the likelihood of providing an opioid-negative urine sample. Characteristics associated with successful buprenorphine treatment outcome include: having a negative urine test for drugs, having alcohol problems [assessed using alcohol domain of addiction severity index (ASI-alcohol)] at screening, being older, and receiving low cumulative buprenorphine dose. However, ASI-alcohol values were generally low which make the application of the proposed alcohol effect for patients with more severe alcohol problems questionable.

CONCLUSIONS

A novel approach for analyzing buprenorphine treatment outcome is presented in this manuscript. This approach describes the longitudinal change in the probability of providing an opioid-free urine sample instead of considering opioid use outcome at a single time point. Additionally, this model successfully describes relapse to opioid. Finally, several patient characteristics are identified as predictors of treatment outcome.

Predictors of long term opioid withdrawal outcome after short-term stabilization with buprenorphine

OBJECTIVE

We aim to examine predictors of opiate abstinence status 3 months after the end of buprenorphine/naloxone treatment for opioid-dependent participants.

PATIENTS AND METHODS

Participants (n= 516, age > 15 years) received buprenorphine/ naloxone treatment for 4 weeks and then randomly assigned to undergo dose tapering over either 7 days or 28 days. Bivariate analysis was performed to identify possible predictors of successful opiate abstinence outome (p-value < 0.10). Logistic regression analysis with backward stepwise selection was, then, performed to produce final model containing independent predictors at p-value < 0.05.

RESULTS

Bivariate analysis identified several possible predictors including: opioid and drug urine tests result at the end taper; employment status, family problems, and alcohol use domains of addiction severity index (ASI) score; and clinical opiate withdrawal scale (COWS) at the end of stabilization. Final predictor list identified by logistic regression include: ASI score for family and alcohol problems, COWS at the end of stabilization and opiate urine test at the end of taper.

CONCLUSIONS

Participants presenting with a negative urine test for opiate, more severe alcohol, more severe family problems, or more symptoms of opiate withdrawal at the end of stabilization were more likely to have a successful opiate abstinence.

Population pharmacodynamic analysis of erythropoiesis in preterm infants for determining the anemia treatment potential of erythropoietin

A population pharmacokinetics/pharmacodynamic (PK/PD) model was developed to describe changes in erythropoiesis as a function of plasma erythropoietin (EPO) concentration over the first 30 days of life in preterm infants who developed severe anemia requiring red blood cell (RBC) transfusion. Several covariates were tested as possible factors influencing the responsiveness to EPO. Discarded blood samples in 27 ventilated preterm infants born at 24-29 wk of gestation were used to construct plasma EPO, hemoglobin (Hb), and RBC concentration-time profiles. The amount of Hb removed for laboratory testing and that transfused throughout the study period were recorded. A population PK/PD model accounting for the dynamic Hb changes experienced by these infants was simultaneously fitted to plasma EPO, Hb, and RBC concentrations. A covariate analysis suggested that the erythropoietic efficacy of EPO is increased for preterm infants at later gestational ages. The PD analysis showed a sevenfold difference in maximum Hb production rate dependent on gestational age and indicated that preterm infants, when stimulated by EPO, have the capacity to produce additional Hb that may result in a decrease in RBC transfusions. The present model has utility in clinical trial simulations investigating the treatment potential of erythropoietic stimulating agents in the treatment of anemia of prematurity.

Pharmacodynamic analysis of stress erythropoiesis: change in erythropoietin receptor pool size following double phlebotomies in sheep

A feedback receptor regulation model was incorporated into a pharmacodynamic model to describe the stimulation of hemoglobin (Hb) production by endogenous erythropoietin (EPO). The model considers the dynamic changes that take place in the EPO receptor (EPOR) pool under phlebotomy-induced anemia. Using a (125)I-rhEPO tracer the EPO clearance changes are evaluated longitudinally prior to and following phlebotomy-induced anemia indirectly to evaluate changes in the EPOR pool size, which has been shown to be linearly related to the clearance. The proposed model simultaneously captures the general behavior of temporal changes in Hb relative to EPO plasma clearance in five lambs (r = 0.95), while accounting for the confounding variables of phlebotomy and changes in the blood volume in the growing animals. The results indicate that under anemia the EPOR pool size is up-regulated by a factor of nearly two over baseline and that the lowest and highest EPOR pool sizes differ by a factor of approximately four. The kinetic model developed and the data-driven mechanism proposed serves as a starting point for developing an optimal EPO dosing algorithm for the treatment of neonatal anemia.

Selective extraction of salbutamol from human plasma with the use of phenylboronic acid

An investigation was conducted on the usage of a single-step extraction procedure involving the retention of a phenylboronate-salbutamol complex on an end-capped C18 solid-phase sorbent to determine the level of salbutamol in human plasma samples. Propranolol, a beta-blocker, was chosen as the internal standard for this assay. In this solid-phase clean-up method, 50 mM sodium carbonate buffer, pH 9.60, was used for conditioning the column as well as washing the endogenous interference. Under the optimal conditions, the recovery of salbutamol from spiked plasma samples was found to be high and reproducible with mean recoveries (n = 3) of more than 90% after elution by using 50% 1 M trifluoroacetic acid in methanol. This sample clean-up step was effectively analyzed under reversed-phase high-performance liquid chromatography with fluorimetric detection. The method was successfully applied to the routine measurement of salbutamol in human plasma from the bioequivalence study on the different administration route of salbutamol. Quantification of salbutamol was convincingly reported with the correlation of coefficient of 0.9980 for the concentration range from 0 to 1000 ng ml(-1). An adequate precision was achieved with both between- and within-day precisions of less than 10% (n = 6) for 100 and 1000 ng ml(-1) and less than 15% (n = 6) for 10 ng ml(-1).

Polyphenolic constituents of Callistemon lanceolatus leaves

Two new flavonol glycosides, kaempferol 3-O-beta-D-galacturonopyranoside and quercetin 3-O-(2"-O-galloyl)-beta-D-glucoronopyranoside, were isolated, from leaves of Callistemon lanceolatus DC, as well as eighteen known polyphenols (phenolic acids, flavonoids and three tannins). All structures were established mainly on the basis of chemical and spectroscopic analysis (UV, 1D NMR and negative ESI-MS) and finally confirmed by 2D NMR experiments (HMQC and HMBC), in the case of flavonoid glycosides and tannins.

Polyvinyl chloride-based membranes for flow injection analysis of quinine in beverages

Potentiometric response characteristics were evaluated for quinine selective sensors based on a lipophilic ion-exchanger potassium tetrakis[3,5-bis(trifluoromethylphenyl)]borate (PTFB) immobilized together with plasticizing solvents in polyvinyl chloride membranes. The use of dioctyl phthalate (DOP), 2-nitrophenyl phenyl ether (NPPE), and bis(2-ethylhexyl)adipate (BEHA) plasticizers produced good quality quinine sensors that were sensitive and fast responding, and exhibited near Nernstian responses when used as batch-sensors. These membranes were further tested in a wall-jet flow-through potentiometric flow injection analysis (FIA) detector. Quinine sensors containing BEHA were the most suitable membrane, with no noticeable differences in sensitivity even after 5 h of continuous exposure to solutions. Interference by foreign species such as alkali, alkaline earth metal ions, sugars, and sodium benzoate was minimal in either the batch-mode (log selectivity coefficients <-2.60) or as FIA detector. When the FIA method was used, recoveries averaged 99.70% from mineral water samples spiked with 16.22 and 162.20 ppm quinine. Results for determination of quinine in other drinks such as carbonated (64.88 and 71.37 ppm) and bitter lemon drinks (55.15 ppm) agreed with those of the manufacturer's claimed values of <68, <81, and 51 ppm, respectively. With a sample throughput of 50 samples/h under optimized flow conditions, the method can be routinely used to monitor quinine in such samples.

Clean-up, detection and determination of salbutamol in human urine and serum

Salbutamol ¿2-(tert-butylamino)-1-[4-hydroxy-3- (hydroxymethyl)phenyl]ethanol¿, also known as albuterol, is clinically the most widely used beta 2-adrenoceptor agonist in the treatment of bronchial asthma. During this study, we evaluated liquid-liquid extraction (LLE) and solid-phase extraction (SPE) in order to develop a reliable extraction method followed by analysis using liquid chromatography and gas chromatography. An assay is described which involves SPE as the clean-up method followed by gas chromatography-mass spectrometry to determine salbutamol levels in human serum after oral administration. The SPE method requires the use of a hyper-cross-linked styrene-divinylbenzene bonded phase (ENV+) without involving any sample pre-treatment to obtain 60-65% recoveries for salbutamol and terbutaline as the internal standard. Distilled water and 1% trifluoroacetic acid in methanol were found to be the most suitable washing solvent and eluting solvent, respectively. A detection limit of 2 ng mL-1 was achieved by derivatization with N-methyl-N-trimethylsilyltrifluoroacetamide to form trimethylsilyl (TMS)-salbutamol (m/z 369) and TMS-terbutaline (m/z 356). The relationship between the ratio of the peak area of salbutamol to that of the internal standard and concentration was linear for the range tested (2-200 ng mL-1) and the correlation of coefficient was 0.9999 with a y-intercept not significantly different from zero. The inter-day relative standard deviation (RSD) was < 10% for all three concentrations. The intra-day RSD was 14% for 2 ng mL-1. This assay was then successfully applied to human serum samples obtained from clinical trials after oral administration of salbutamol.

A light microscopical morphometric study of the luminal epithelium of human endometrium during the peri-implantation period

Different aspects of the histology of luminal epithelial cells were examined quantitatively at the light microscopical level. For the first time, using a variety of morphometric indices, an attempt was made to quantify and compare the cellular events in a group of well defined fertile controls and infertile subjects during the peri-implantation period. The most striking observation was that the majority of the features examined, including all nuclear parameters and most cell dimensions, were similar and did not differ significantly between the fertile controls and the infertile subjects over the period of study. The coefficients of variation of most of the parameters investigated were similar and within a narrow range in both the fertile and infertile population, indicating little variation either between individuals at a particular stage or between subjects on different days. This low inter-subject variability may suggest that the cellular events which we have been able to quantify at the light microscope level in the uterine surface epithelium around the anticipated time of implantation are precisely regulated. Such precise regulation does not mean that changes do not occur in luminal epithelial cells during this time, but that those which do occur are well controlled and co-ordinated. Possible changes in biochemistry, physiology and ultrastructure of these cells remain to be determined.

Attenuation of SCH 23390-induced alteration of striatal dopamine D1 receptor ontogeny by prolyl-leucyl-glycinamide in the rat

Long-term postnatal treatment of rats with SCH 23390 is associated with a reduction in the development of dopamine D1 receptors in the striatum. Because the tripeptide, L-prolyl-L-leucyl-glycinamide (PLG) attenuates the neuroleptic-induced increase in D2 receptors in the striatum in adult rats, this study was undertaken with the objective of determining whether PLG could modulate a developmental alteration in the D1 subtype of receptor. Rats were treated with the dopamine D1 receptor antagonist, SCH 23390 (R[+]-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1-H-3- benzazepine) (0.30 mg/kg/d i.p.) for 32 successive days from birth, while D1 receptors in the striatum were assessed at 5 and 8 weeks from birth. Postnatal treatment with SCH 23390 reduced in vitro binding of [3H]SCH 23390 to homogenates in the striatum by 70% at 8 weeks. Scatchard analysis at 5 weeks determined that the Bmax for the binding of [3H]SCH 23390 was reduced by 78%, while the Kd was unaltered. When PLG (1.0 mg/kg/d.i.p.) was administered together with SCH 23390 for the initial 32 days from birth, the binding of [3H]SCH 23390 to homogenates of the striatum was unchanged from that of the control group at 8 weeks. Also, at 5 weeks the Bmax and Kd were unaltered from control in the group that was treated with both SCH 23390 and PLG. The binding of [3H]SCH 23390 was not altered from control in the group treated with PLG alone. Also, PLG given in vitro did not alter the binding of [3H]SCH 23390 to control homogenates of the striatum. These findings indicate that PLG is able to attenuate neuroleptic-induced alterations in dopamine D1 receptors in the striatum.

MIF-1 attenuates spiroperidol alteration of striatal dopamine D2 receptor ontogeny

Long-term postnatal treatment of rats with the dopamine D2 receptor antagonist, spiroperidol, results in the impaired development of striatal D2 receptors. Because the tripeptide prolyl-leucyl-glycinamide (MIF-1) attenuates haloperidol-induced up-regulation of striatal dopamine D2 receptors in adult rats, we studied the effect of MIF-1 on the spiroperidol-induced alteration of striatal D2 ontogeny. Postnatal treatment of rats with spiroperidol (1.0 mg/kg/day, IP, x32 days from birth) resulted in a 74% decrease in the Bmax for [3H]spiroperidol binding with no change in the Kd at 5 weeks. When rats were studied at 8 weeks, in the absence of additional treatment, total specific [3H]spiroperidol binding was reduced by 59%. While MIF-1 alone (1.0 mg/kg/day, IP, x32 days from birth) had no effect on [3H]spiroperidol binding, MIF-1 completely attenuated the ontogenic impairment of striatal D2 receptors that was produced by spiroperidol treatment. At 5 weeks the Bmax for [3H]spiroperidol binding was at the saline control level in the group of rats cotreated with spiroperidol and MIF-1. At 8 weeks, with no additional treatments, the specific binding of [3H]spiroperidol to striatum was also at control levels in the group cotreated with spiroperidol and MIF-1. These findings demonstrate that MIF-1 attenuates spiroperidol-induced impairment of development of striatal dopamine D2 receptors in rats.

Impaired ontogeny of striatal dopamine D1 and D2 binding sites after postnatal treatment of rats with SCH-23390 and spiroperidol

The effect of chronic postnatal treatment of rats with selective D1- and/or D2-receptor antagonists on the development of D1- and D2-receptors in the striatum was studied. When neonatal rats were treated postnatally from the day of birth for 32 successive days with the D1-receptor antagonist, SCH-23390 (0.30 mg/kg i.p.), the development of striatal dopamine D1-receptors was markedly impaired, and the development of striatal D2-receptors was slightly impaired. Alternatively, chronic treatment with the D2-receptor antagonist, spiroperidol (1.0 mg/kg i.p.), resulted in a markedly impaired development of striatal dopamine D2-receptors, and a slightly impaired development of striatal D1-receptors. Scatchard analysis revealed that chronic SCH-23390 treatment during development resulted in a 78% decrease in the Bmax for in vitro binding of [3H]SCH-23390 to striatal homogenates, while the Kd was unaltered. Similarly, chronic postnatal treatment with spiroperidol was associated with a 74% reduction in the Bmax, while the Kd for in vitro binding of [3H]spiroperidol to striatal homogenates was unchanged. These findings demonstrate that chronic selective dopamine receptor antagonism affects development of both striatal D1- and D2-receptor types. The critical period during which striatal dopamine receptor ontogeny can be altered is not restricted to prenatal periods, since suitable postnatal challenge will alter striatal dopamine-receptor development.

Impaired striatal dopamine receptor development: differential D-1 regulation in adults

Previous reports have indicated that prenatal, but not postnatal, haloperidol impairs the ontogenic development of striatal dopamine D-2 receptors. In the present study a specific D-2 receptor antagonist, spiroperidol (1.0 mg/kg i.p.) and/or a specific D-1 receptor antagonist, SCH 23390 (0.30 mg/kg i.p.), was administered to rats for 32 successive days from birth. Postnatal spiroperidol and SCH 23390 treatments markedly impaired the development of striatal dopamine D-2 and D-1 receptors, respectively, at 12 weeks after birth. Spiroperidol did not affect D-1 receptor development and did not modify the effect of SCH 23390 treatment. Also, SCH 23390 did not affect D-2 receptor development and did not modify the effect of spiroperidol treatment. When rats with impaired development of striatal D-2 receptors were challenged at 12 weeks with spiroperidol (1.0 mg/kg per day i.p. x 17 days) D-2 receptors did not up-regulate. However, when rats with impaired development of striatal D-1 receptors were challenged at 12 weeks with SCH 23390 (0.30 mg/kg per day i.p. x 17 days) D-1 receptors did up-regulate. These findings demonstrate that postnatal treatment with D-1 and D-2 receptor antagonists can permanently impair the development of striatal D-1 and D-2 receptors. Moreover, the ability of developmentally impaired striatal D-1 receptors to up-regulate in adulthood appears to be greater than that for the developmentally impaired striatal D-2 receptors.