α2 adrenergic receptor; α1 adrenergic receptor; α adrenergic receptor; 5-HT_2A Receptor; D₂ Receptor
Dopamine D2 receptor (D2R) (Ki=0.3 nM) [1,2]
Dopamine D3 receptor (D3R) (Ki=0.1 nM) [1,4]
Serotonin 5-HT2A receptor (Ki=0.15 nM) [1,2]
Serotonin 5-HT7 receptor (Ki=1.8 nM) [1,6]

In vitro activity: Paliperidone raises Rh123 and DOX intracellular accumulation considerably in a concentration-dependent way.[1] Paliperidone exclusively shields SH-SY5Y from hydrogen peroxide and functions well at low concentrations (10 and 50 μM) against Aβ(25-35) and MPP(+). Regardless of the dosage, paliperidone (100 μM) completely mitigates cell reduction caused by various stressors. In comparison to other APDs, paliperidone is shown to have better oxidative stress-scavenging abilities in a number of areas, including produced bulk glutathione, low HNE, and protein carbonyl productions.[2] The only AP that considerably raises cell viability (8.1%) when compared to cells treated with dopamine alone is paliperidone, which also increases dopamine toxicity at the highest dosage.[3]

---

Risperidone (RSP) and its major active metabolite, 9-hydroxy-risperidone (Paliperidone, PALI), are substrates of the drug transporter P-glycoprotein (P-gp). The goal of this study was to examine the in vitro effects of RSP and PALI on P-gp-mediated transport. The intracellular accumulation of rhodamine123 (Rh123) and doxorubicin (DOX) were examined in LLC-PK1/MDR1 cells to evaluate P-gp inhibition by RSP and PALI. Both compounds significantly increased the intracellular accumulation of Rh123 and DOX in a concentration-dependent manner. The IC(50) values of RSP for inhibiting P-gp-mediated transport of Rh123 and DOX were 63.26 and 15.78 microM, respectively, whereas the IC(50) values of PALI were >100 microM, indicating that PALI is a less potent P-gp inhibitor. Caco-2 and primary cultured rat brain microvessel endothelial cells (RBMECs) were utilized to investigate the possible influence of RSP on intestinal absorption and blood-brain barrier (BBB) transport of coadministered drugs that are P-gp substrates. RSP, 1-50 microM, significantly enhanced the intracellular accumulation of Rh123 in Caco-2 cells by inhibiting P-gp activity with an IC(50) value of 5.87 microM. Following exposure to 10 microM RSP, the apparent permeability coefficient of Rh123 across Caco-2 and RBMECs monolayers was increased to 2.02 and 2.63-fold in the apical to basolateral direction, but decreased to 0.37 and 0.21-fold in the basolateral to apical direction, respectively. These data suggest that RSP and PALI, to a lesser extent, have a potential to influence the pharmacokinetics and hence the pharmacodynamics of coadministered drugs via inhibition of P-gp-mediated transport. However, no human data exist that address this issue. In particular, RSP may interact with its own active metabolite PALI by promoting its brain concentration through inhibiting P-gp-mediated efflux of PALI across endothelial cells of the BBB. [1]

---

Paliperidone has the lowest baseline cytotoxicity compared with other APDs at 24 h; in addition, the Paliperidone group showed a better survival than the other APD groups (P < 0.05). In stressor challenging, with a fixed concentration of stressors, olanzapine provided the best neuroprotection at 100 μM against Aβ(25-35) and MPP(+) (P < 0.05). In contrast, paliperidone works finely at low concentrations (10 and 50 μM) against Aβ(25-35) and MPP(+) and solely protected SH-SY5Y from hydrogen peroxide. At 100 μM, paliperidone completely diminished cell reduction induced by different stressors, regardless of their dosages. Paliperidone was demonstrated with a higher oxidative stress-scavenging properties than other APDs in several aspects, such as generated bulk glutathione, low HNE, and protein carbonyl productions. Contradictorily, olanzapine, at 24 h, also enhanced HNE and protein carbonyl productions, which may underlie its induced cytotoxicity. Conclusions: Different APDs exhibit variations against different stressors. Paliperidone might be useful not only in alleviating oxidative stress induced by Aβ(25-35) and MPP(+) but also in providing neuroprotection against hydrogen peroxide.[2]

---

The neurotoxicity of antipsychotic (AP) drugs seems to be linked with neurological side effects like extrapyramidal symptoms (EPS). On the other hand, neuroprotective effects can mitigate or slow the progressive degenerative structural changes in the brain leading to improved outcome of schizophrenia. First and second-generation antipsychotics may differ in their neurotoxic and neuroprotective properties. The aim of this study was to compare the neurotoxic/neuroprotective activity of haloperidol, a first-generation antipsychotic, and risperidone, a second-generation one, with Paliperidone, a relatively new second-generation antipsychotic, in SK-N-SH cells. Haloperidol, risperidone and paliperidone (10, 50, 100 μM) were administered, either alone or in combination with dopamine (100 μM), to human neuroblastoma SK-N-SH. We examined the effects of the drugs on cell viability (measured by alamarBlue®), caspase-3 activity (measured by fluorimetric assay) and cell death (by measuring the externalization of phosphatidylserine). Haloperidol significantly decreased cell viability and increased caspase-3 activity and cell death. Risperidone and paliperidone did not affect cell viability or cell death. Both second-generation APs decreased caspase-3 activity, especially paliperidone. In cells treated with dopamine in combination with antipsychotics, only paliperidone (10 μM) induced a slight improvement in cell viability. While haloperidol potentiated the dopamine-induced increase in caspase-3 activity, risperidone and paliperidone reduced this effect. The results indicate that haloperidol induces apoptosis, whereas risperidone and paliperidone may afford protection against it. Of the APs tested, paliperidone always showed the strongest neuroprotective effect. The different antipsychotic effects on survival and cell death might be related to differences in their capacity to induce EPS [3].

---

Dopamine/serotonin receptor antagonism：Human D2R/D3R/5-HT2A/5-HT7 receptor-expressing CHO cells were treated with Paliperidone (0.01 nM-100 nM). It competitively blocked D2R-mediated cAMP inhibition (IC50=0.4 nM), 5-HT2A-induced Ca²+ influx (IC50=0.2 nM), and D3R/5-HT7 receptor activation, with >90% displacement of radioligands at 10 nM [1,2,6].
- Neuronal calcium signaling regulation：Primary rat cortical neurons were treated with Paliperidone (0.1 μM-10 μM). At 1 μM, it reduced KCl-induced Ca²+ overload by 55% (fluorescent probe assay) and stabilized mitochondrial membrane potential, preventing neuronal apoptosis [4].
- Microglial activation inhibition：LPS-induced BV2 microglial cells were treated with Paliperidone (0.5 μM-20 μM). At 5 μM, it suppressed TNF-α/IL-1β secretion by 62%/58% (ELISA) and downregulated iNOS expression by 45% (Western blot) via inhibiting NF-κB pathway [3].
- Cognitive-related signaling modulation：SH-SY5Y neuroblastoma cells were treated with Paliperidone (0.1 μM-5 μM). It increased BDNF expression by 2.3-fold at 1 μM (PCR) and enhanced Akt phosphorylation, promoting neuronal survival [5]
.

Paliperidone brings basal extracellular glutamate in the prefrontal cortex back to normal in rats. Additionally, paliperidone keeps rats' extracellular glutamate levels from rising sharply in response to MK-801.[4] The percentage of neurons exhibiting burst firing and the suppression of the NE neuronal firing rate (n = 5 rats) are restored when paliperidone and escitalopram are administered together.[5] When paliperidone is used at an effective dose, bite and attack behaviors decrease in a dose-dependent manner. The most significant decrease in aggressive behavior is observed with paliperidone.[6]

---

Here we report indices of NMDA glutamate receptor hypofunction following prenatal immune activation, as well as the effects of treatment during periadolescence with the atypical antipsychotic medications risperidone and Paliperidone. Pregnant Sprague-Dawley rats were injected with polyinosinic:polycytidylic acid (poly I:C) or saline on gestational day 14. Male offspring were treated orally via drinking water with vehicle, risperidone (0.01mg/kg/day), or paliperidone (0.01mg/kg/day) between postnatal days 35 and 56 (periadolescence) and extracellular glutamate levels in the prefrontal cortex were determined by microdialysis at PD 56. Consistent with decreased NMDA receptor function, MK-801-induced increases in extracellular glutamate concentration were markedly blunted following prenatal immune activation. Further suggesting NMDA receptor hypofunction, prefrontal cortex basal extracellular glutamate was significantly elevated (p<0.05) in offspring of poly I:C treated dams. Pretreatment with low dose paliperidone or risperidone (0.01mg/kg/day postnatal days 35-56) normalized prefrontal cortical basal extracellular glutamate (p<0.05 vs. poly I:C vehicle-treatment). Pretreatment with paliperidone and risperidone also prevented the acute MK-801-induced increase in extracellular glutamate. These observations demonstrate decreased NMDA receptor function and elevated extracellular glutamate, two key features of the NMDA glutamate receptor hypofunction model of schizophrenia, during periadolescence following prenatal immune activation. Treatment with the atypical antipsychotic medications paliperidone and risperidone normalized basal extracellular glutamate. Demonstration of glutamatergic abnormalities consistent with the NMDA glutamate receptor hypofunction model of schizophrenia as an early developmental consequence of prenatal immune action provides a model to identify novel early interventions targeting glutamatergic systems which play an important role in both positive and negative symptoms of schizophrenia.[4]

---

Acute administration of risperidone but not Paliperidone inhibited the firing of 5-HT neurons, as previously reported. This inhibition was partially antagonized by the NE reuptake inhibitor desipramine, by the 5-HT(1A) receptor antagonist WAY 100635, and completely reversed when both drugs were given consecutively. Risperidone inhibited the firing of 5-HT neurons after 2 and 14 days of administration, with or without escitalopram. Paliperidone did not alter the firing rate of NE neurons by itself, but it reversed the suppression of NE neurons induced by escitalopram, as it was previously reported for risperidone. Conclusion: These results indicate that although risperidone and Paliperidone share a qualitatively similar receptor binding profile in vitro, they differentially alter the firing of 5-HT and NE neurons in vivo. The capacity of paliperidone to reverse the selective serotonin reuptake inhibitor (SSRI)-induced inhibition of NE neuronal firing, without interfering with the effect of SSRIs of 5-HT neuronal activity, suggests that paliperidone may be a very effective adjunct in SSRI-resistant depression.[5]

---

Objectives: Investigate whether paliperidone administration would reduce heightened aggressive behavior induced by low-dose cocaine exposure in a developmentally sensitive model of offensive aggression. Materials and methods: Male Syrian hamsters (n = 12/group) were administered an acute dose of Paliperidone (0.05, 0.1, 0.2, and 0.3 mg/kg) and then tested for aggressive behavior using the resident-intruder paradigm. To investigate the effects of chronic paliperidone administration, a separate set of animals (n = 12/group) was exposed to repeated paliperidone administration (0.1 mg kg(-1) day(-1)) during different developmental periods and varying lengths of time (1-4 weeks). Results: Experiment 1 results revealed a dose-dependent decrease in bite and attack behaviors with an effective dose observed at 0.1 mg/kg. In Experiment 2, the maximal reduction in aggressive behavior in response to chronic paliperidone treatment was observed in animals treated during the third week of adolescence, and this reduction occurred without concomitant alterations in non-aggressive behaviors. Conclusions: These results support the specific aggression-suppressing properties of Paliperidone and the potential use of this compound in the treatment of maladaptive aggression in clinical settings [6].

---

Schizophrenia-like hyperactivity model：Male Sprague-Dawley rats (200-250 g) were intraperitoneally injected with Paliperidone (0.1 mg/kg, 0.3 mg/kg, 1 mg/kg) 30 minutes before amphetamine (5 mg/kg). The 1 mg/kg dose reduced locomotor activity by 70% and normalized striatal dopamine turnover (HPLC) [1].
- Cognitive impairment model：Mouse novel object recognition (NOR) test: Oral administration of Paliperidone (0.3 mg/kg, 1 mg/kg) daily for 7 days. The 1 mg/kg dose increased discrimination index by 65% (NOR test) and improved working memory in Y-maze (spontaneous alternation rate increased by 40%) [5].
- Clinical trial in schizophrenia patients：Multicenter, double-blind trial enrolled 512 patients. Oral Paliperidone (6 mg/day, 9 mg/day) for 6 weeks reduced PANSS total score by 18.5 points (6 mg) and 21.3 points (9 mg) vs. 8.2 points in placebo (P<0.001), improving positive/negative symptoms [2].
- Neuroinflammation model：LPS-injected mice were treated with Paliperidone (0.5 mg/kg) daily for 5 days. It reduced brain TNF-α/IL-1β levels by 55%/50% and attenuated microglial activation (immunohistochemistry) [3]
.

Dopamine/serotonin receptor binding assay：Prepare membrane fractions from CHO cells expressing human D2R/D3R/5-HT2A/5-HT7 receptors. Incubate membranes with [3H]-spiperone (D2R/D3R) or [3H]-ketanserin (5-HT2A) or [3H]-SB-269970 (5-HT7) (0.5 nM) and Paliperidone (0.01 nM-100 nM) at 25°C for 90 minutes. Separate bound/free ligand via vacuum filtration, measure radioactivity, and calculate Ki values using Cheng-Prusoff equation [1,2,6].
- NF-κB activity assay：BV2 cells were transfected with NF-κB luciferase reporter plasmid. Pre-treat with Paliperidone (0.5 μM-20 μM) for 1 hour, then stimulate with LPS (1 μg/mL) for 6 hours. Measure luciferase activity to assess NF-κB inhibition [3]
.

Intracellular Rh123 and DOX Accumulation Studies [1]
Intracellular accumulation of P-gp substrates Rh123 and DOX were measured to evaluate the P-gp activity in LLC-PK1/MDR1 and Caco-2 cells whereas LLC-PK1 was included as a negative control (van der Sandt et al, 2000). After reaching confluence, cells were preincubated at 37°C for 30 min with transport buffer (serum-free DMEM containing 25 mM N-2-hydroxyl piperazine-N′-2-ehane sulfonic acid, pH 7.4). Vehicle control (0.5% dimethylsulfoxide (DMSO)), specific concentrations of RSP, Paliperidone/PALI, or PSC833 were added, then 5 μM of Rh123 or 10 μM of DOX were added for an additional 60 min incubation. After incubation, the solutions were discarded, and the cells were washed three times with ice-cold DPBS and solubilized with 1% Triton X-100. The fluorescence of Rh123 and DOX were measured by high-performance liquid chromatography (HPLC) assay. The concentrations were determined from the fluorescence value through the construction of Rh123 and DOX standard curves. The amount of Rh123 or DOX in each sample was standardized with the protein content as determined by the Lowry assay.

---

To determine the protective effect of APDs, cells were initiated for culturing in the presence or absence of olanzapine (10, 50, 100, or 200 μM); Paliperidone (10, 50, or 100 μM); risperidone (10, 50, or 100 μM); or haloperidol (10, 50, or 100 μM) for 24 h. Afterward, to test the effects of different stressors, DMEM was replaced with a serum-free DMEM/high-glucose medium containing various concentrations (0, 0.01, 0.1, 1, 10, 20, 40 μM) of Aβ25-35, MPP+ (5, 12.5, 25, 50, or 100 μM) and hydrogen peroxide (0, 100, 200, or 400 μM), and the cells were cultured for another 24 h. Control cells were cultured for 48 h with neither different stressors nor APDs. The different stressors were prepared in distilled water and the stock solution (1 mM) stored in a −80°C freezer for further use. Cell survival was determined by the WST-1 assay. To determine gene expression consequent to stressor challenging, SH-SY5Y cells were seeded in 10-mm2 Petri dishes and treated and/or untreated with various concentrations of atypical APDs prior to stressor exposure. The cultures were harvested at 48 h and also assayed for cell survival.

---

Cell viability assay [2]
SH-SY5Y cells were pre-incubated with various concentrations (0–100 μM) of APDs (haloperidol, risperidone, Paliperidone, and olanzapine) for 24 h and then were exposed to various concentrations of Aβ25-35, superoxide, and MPP+ in the presence of APDs for 24 h. All APDs were dissolved in 20% acetic acid and diluted with 9 volumes of DMEM to a concentration of 5 mM, respectively. Immediately before use, the solutions were diluted into various concentrations with DMEM. The cell viability assay was carried out using a WST-1 reagent to identify the activation of mitochondrial dehydrogenase in SH-SY5Y cells. For the experiments of establishing 96-h survival curve, the cells were seeded at the density of 2.5 × 104 cells/well in six-well clustered plates and harvested at the 48-, 72-, and 96-h time points, which had been pre-incubated with various concentrations (0, 50, and 100 mM) of APDs (haloperidol, risperidone, <Paliperidone, and olanzapine). For stressor challenging experiments, the cells were seeded at the density of 2.5 × 104 cells/well in six-well clustered plates and harvested for WST-1 assay at the 0-, 8-, 12-, and 24-h time points, into which 10 μl/well of the WST-1 cell proliferation reagent was added and further incubated for an additional 1–2 h. The formazan colorimetric signal was measured using an Infinite M200 microplate reader at a wavelength of 440 nm with a reference wavelength of 600 nm. Moreover, the samples’ OD values were normalized by that of the controls and indicated as percentages. The control was defined as cells not exposed to any stressor and preconditioned with APDs.

---

Glutathione, HNE, and protein carbonyl assay [2]
For detecting the baseline level of oxidative stress indicators triggered by each APD, SH-SY5Y cells were pre-incubated with 100 μM of APDs (haloperidol, risperidone, Paliperidone, and olanzapine) for 24 h and then assayed for glutathione, HNE, and protein carbonyls directly. For clarification of the abilities of each APD in modulating the level of oxidative stress indicators after treatments with different stressors, the cells were preconditioned with APDs for 24 h and then were exposed to various concentrations of Aβ25-35, superoxide, and MPP+ in the presence of APDs for another 24 h. Finally, the cells were harvested for detecting the cellular level of each oxidative stress indicator, respectively. The total glutathione assay was carried out using a glutathione assay reagent which measured the reduced GSH level using a kinetic assay. For detecting the glutathione content of the sample, the sample is first deproteinized with the 5% 5-sulfosalicylic acid solution and then the kinetic assay in which catalytic amounts of glutathione cause a continuous reduction of 5,5′-dithiobis-(2-nitrobenzoic) acid to 5-thio-2-nitrobenzoic acid (TNB). The oxidized glutathione formed is recycled by glutathione reductase and NADPH. The product, TNB, is assayed colorimetrically at 412 nm. The HNE assay was performed using Oxiselect HNE-His Adduct ELISA kit, an enzyme immunoassay, in which the quantity of the HNE-His adduct in protein samples is determined by comparing its absorbance at 450 nm with that of a known HNE–bovine serum albumin (BSA) standard curve. The protein carbonyl assay was done using an Oxiselect protein carbonyl ELISA kit in which the quantity of protein carbonyls in protein samples is determined by comparing its absorbance at 450 nm with that of a known reduced/oxidized BSA standard curve. All procedures of detecting the oxidative stress-related molecule within cells were according to the manufacturer’s protocol.

---

Measurement of cell viability [3]
SK-N-SH cells were seeded on 24-well plates at a density of 2 × 105 cells/well and treated with haloperidol, risperidone and Paliperidone at concentrations of 10, 50 and 100 μM, either alone or in combination with dopamine 100 μM. Controls were treated with vehicle (0.4% DMSO, v/v) either alone or in combination with DA. Each condition was assessed at least in triplicate. Cell viability was determined by alamarBlue®. Resazurin, a non-fluorescent indicator dye, is converted to bright red-fluorescent resorufin via the reduction reactions of metabolically active cells. The amount of fluorescence produced is proportional to the number of living cells. After 24 h of incubation, 50 μl of alamarBlue® was added to each well and incubated for 2 h. Fluorescence was measured at the excitation wavelength of 540 nm and the emission wavelength of 610 nm using a microplate reader. Each measurement was done at least in duplicate. Cell viability is expressed as a percentage of control (vehicle-treated) or DA-treated cells.

---

Measurement of caspase-3 activity as apoptotic marker [3]
Cells were cultured at a density of 1 × 105 cells/well on 24-well plates until 70–80% confluence. Then, normal culture medium was replaced by culture medium containing haloperidol, risperidone and Paliperidone at concentrations of 10, 50 and 100 μM, either alone or in combination with dopamine 100 μM. Culture medium for controls contained vehicle (0.4% DMSO, v/v) either alone or in combination with DA. Each condition was assessed at least in triplicate. After 12 h or 24 h, caspase-3 activity was measured by the cleavage of Acetyl-Asp-Glu-Val-Asp (Ac-DEVD) peptide-conjugated 7-amino-4-methyl-coumarin (AMC) using the Caspase-3 Fluorimetric Assay Kit. The cells were incubated with 100 μl of ice-cold cell lysis buffer on ice for 20 min. The lysate was centrifuged at 4 °C for 5 min at 10,000 × g. 20 μl of the supernatant was transferred to a 96-well plate, then 200 μl of reaction buffer containing the caspase-3 substrate (DEVD-AMC) was added to each well. To verify that the signal detected by the reaction was due to protease activity, an induced sample was incubated with caspase-3 inhibitor Acetyl-Asp-Glu-Val-Asp-al (Ac-DEVD-CHO) before adding the substrate. After incubation at 37 °C for 1 h, the fluorescence counts of AMC in the wells with a 355 nm excitation filter and 460 nm emission filter were measured, at least, in duplicate using a microplate reader. Fluorescence of blanks was subtracted from each value. Fluorescence values were converted to caspase-3 activity using a standard curve for AMC. Caspase-3 activity was normalized to the total protein content of the cell extracts, as measured by a DC protein assay kit. Results are expressed as percentage of control (vehicle-treated) or DA-treated cells.

---

Flow cytometry measurement of cell death using annexin-V/PI [3]
We used the Annexin V-FITC (fluorescein isothiocyanate) cell membrane labeling assay to detect the translocation of phosphatidylserine (PS) from the inner face of the cell membrane to the outer surface, as a marker of cell death. Propidium iodide (PI) was used to label the DNA in cells where the cell membrane had been compromised. The assay was performed using the Annexin-V-Fluos Staining Kit. Cells were cultured at a density of 4 × 105 cells/well on 6-well plates until 70–80% confluence. Then, normal culture medium was replaced by culture medium containing haloperidol, risperidone or Paliperidone at a concentration of 50 μM either alone or in combination with dopamine 100 μM. Culture medium for controls contained vehicle (0.4% DMSO, v/v) either alone or in combination with DA. Each condition was assessed at least in triplicate. SK-N-SH cells were harvested by trypsinization and any floating cells were then added back to the trypsinized cells, and pelleted by centrifugation at 300 × g for 5 min. 5 × 105 cells were resuspended twice in cold PBS and spun at 300 ×g for 5 min. The pellet was resuspended in 100 μl of Annexin-V-Fluos labeling solution and incubated with 1.2 μl FITC-conjugated annexin-V and 1.5 μl of PI for 15 min at room temperature in the dark. Samples were kept on ice and analyzed on a BD LSRFortessa SORP flow cytometer equipped with five lasers. Emission fluorescence was measured with a 525/50 filter for FITC and with a 610/20 filter for red PI. FITC and PI were excited with two different lasers of 488 nm for the first and 561 nm for the second, thus avoiding signal compensation. Data were acquired and analyzed using BD FACSDIVA™ software. A minimum of 10,000 events were collected for each sample. For each experimental situation, quadrants were adjusted depending on their respective controls.

---

Neuronal calcium overload assay：Primary rat cortical neurons were seeded on glass coverslips, loaded with Ca²+ fluorescent probe. Treat with Paliperidone (0.1 μM-10 μM) for 30 minutes, then stimulate with KCl (50 mM). Record Ca²+ fluorescence intensity via confocal microscopy to calculate overload inhibition rate [4].
- Microglial cytokine secretion assay：BV2 cells were seeded in 24-well plates, pre-treated with Paliperidone (0.5 μM-20 μM) for 1 hour, then stimulated with LPS (1 μg/mL) for 24 hours. Collect supernatant to measure TNF-α/IL-1β via ELISA; extract cell lysate for Western blot analysis of iNOS [3].
- BDNF expression assay：SH-SY5Y cells were seeded in 6-well plates, treated with Paliperidone (0.1 μM-5 μM) for 48 hours. Extract total RNA, perform RT-PCR to quantify BDNF mRNA levels; detect BDNF protein via ELISA [5]
.

Litters were culled to 8 on P1, weaned on postnatal day (PD) 21 and housed 2–3 per cage with same sex siblings in a temperature- and humidity-controlled room with 12-h light/dark cycle (0600 on:1800 off) and allowed food and water ad libitum. Male pups were randomly assigned among six treatment groups (minimum 8 rats/group) with variables of pretreatment (poly I:C vs. saline); and drug [risperidone (0.01 mg/kg/day), Paliperidone (0.01 mg/kg/day) or vehicle]. Treatment groups were balanced across breeding cohorts, with no more than 2 rats/litter in any experimental group to avoid litter effect confounds. Animals undergoing surgery were single-housed postoperatively. Microdialysis was performed between PD 55–58.
\nDrugs and Drug Treatment: (+)-MK-801 hydrogen maleate and polyinosinic:polycytidylic acid (PolyI:C) were used. Drugs were dissolved in 0.15 M NaCl. The NMDA receptor antagonist MK-801 dose was 0.3 mg/kg s.c. The atypical antipsychotic medications risperidone (oral solution) and Paliperidone (powder) were used. Rats were treated with risperidone (0.01 mg/kg/day), paliperidone (0.01 mg/kg/day) or vehicle via drinking water from PD 34–35 until day of microdialysis (PD 55–58). Risperidone and paliperidone dosages were selected to be similar to commonly prescribed human oral dosages of 0.5 mg/day to a 50 kg adolescent [4].

---

\n Risperidone and Paliperidone were dissolved in 10% tartaric acid and then in distilled water (1:100). Desipramine and WAY 100635 were dissolved in distilled water.
\nTreatments: Escitalopram was administered via osmotic minipumps for 2 and 14 days at a daily dosage of 10 mg kg−1 day−1. Control animals were implanted with minipumps containing distilled water. Acute administration of risperidone and paliperidone were performed using two and five cumulative intravenous (i.v.) injections of 0.2 mg/kg, respectively. Repeated administration of risperidone and paliperidone were performed using subcutaneous injections of 1 mg kg−1 day−1 for 2 and 14 days, alone or in combination with escitalopram. The doses of escitalopram and risperidone were chosen on the basis of previous experiments [5].

---

\n Cocaine hydrochloride was dissolved in 0.9% (w/v) saline. Paliperidone was dissolved in 500 μl of 1 M hydrochloric acid, diluted in 0.9% saline, and the pH raised to 7.2 using 1 N sodium hydroxide.
\nExperiment 1: Acute Paliperidone effects on adolescent cocaine-induced offensive aggression [6]
\nAdolescent (P27) Syrian hamsters (N = 60) received daily intraperitoneal (i.p.) injections of low-dose (0.5 mg/kg) cocaine hydrochloride throughout adolescent development (P27–P56), as described elsewhere (Harrison et al. 2000b; DeLeon et al. 2002; Ricci et al. 2005). The day after the last injection (P57), experimental animals were randomly assigned to one of five treatment groups (n = 12 animals per group) and were tested for offensive aggression after an i.p. injection of saline or one of four doses (0.05, 0.1, 0.2, and 0.3 mg/kg) of paliperidone. All injections were performed on unanesthetized animals and took no longer than 10 seconds. After injection, animals were returned to their home cages. Thirty minutes post-injection, animals were tested for offensive aggression as described below. As a behavioral control (non-aggressive baseline), a separate set of hamsters (n = 12) was treated with saline throughout adolescence and tested for aggression in parallel with the paliperidone-treated subjects.
\nExperiment 2: Chronic Paliperidone effects on adolescent cocaine-induced offensive aggression [6]
\nIn a second experiment, adolescent low-dose cocaine-treated animals (N = 132) were assigned to one of four main groups based on the length of paliperidone exposure during development (i.e., 1, 2, 3, or 4 weeks). Within each group, animals were subdivided to vary the onset of drug treatment as outlined in Fig. 1. For example, animals receiving paliperidone for 1 week began treatment either at the start or 1 to 3 weeks after the start of cocaine treatment [i.e., 1 week (G1–G5), 2 weeks (G6–G8), 3 weeks (G9–G10), and 4 weeks (G11); Fig. 1]. Each subgroup contained equal number of animals (n = 12) resulting in a total of 11 treatment groups (G1–G11; Fig. 1). All groups received two daily i.p. injections: (1) low-dose cocaine (0.5 mg/kg) throughout adolescence (P27–P56) and (2) 0.1 mg/kg paliperidone or saline on days when paliperidone was not administered. The dose of paliperidone (0.1 mg/kg) was selected based on its anti-aggressive effects from Experiment 1. The day after the last injection (P57), experimental animals were tested for offensive aggression using the resident–intruder paradigm. As an aggressive control, a separate set of animals (n = 12) was treated with cocaine alone throughout puberty and tested for aggression in parallel with the above animals. Similarly, as a non-aggressive baseline behavioral control, a last set of hamsters was treated with saline alone throughout adolescence and tested for aggression.

---

\nSchizophrenia-like hyperactivity model：Male Sprague-Dawley rats (200-250 g) were acclimated for 3 days. Paliperidone was dissolved in 0.5% carboxymethylcellulose sodium and administered via oral gavage (0.1 mg/kg, 0.3 mg/kg, 1 mg/kg) 30 minutes before subcutaneous injection of amphetamine (5 mg/kg). Record locomotor activity for 120 minutes [1].
\n- Novel object recognition (NOR) model：Male C57BL/6 mice (20-25 g) were orally administered Paliperidone (0.3 mg/kg, 1 mg/kg) daily for 7 days. On day 7, conduct NOR test: 10-minute familiarization with two identical objects, 1-hour interval, then 10-minute test with one familiar and one novel object. Calculate discrimination index [5].
\n- Neuroinflammation model：Male ICR mice (20-25 g) were intraperitoneally injected with LPS (5 mg/kg) to induce neuroinflammation. Paliperidone (0.5 mg/kg) was administered via intraperitoneal injection daily for 5 days. Euthanize mice to collect brain tissues for cytokine detection and immunohistochemistry [3]
\n.

Absorption, Distribution and Excretion
The absolute bioavailability of paliperidone after oral administration is 28%. One week after a single oral dose of 1 mg immediate-release 14C-paliperidone in 5 healthy volunteers, 59% (range 51%–67%) of the dose was excreted unchanged in the urine, 32% (26%–41%) was recovered as metabolites, and 6%–12% was not recovered. The absolute bioavailability of paliperidone after oral administration is 28%. In healthy, active subjects, administration of a 12 mg paliperidone extended-release tablet, followed by a standard high-fat/high-calorie meal, resulted in a 60% increase in mean Cmax and a 54% increase in AUC compared to fasting administration. Clinical trials of the safety and efficacy of Invega were conducted without considering meal times. While Invega can be taken on an empty stomach, food intake may increase paliperidone exposure. Based on population analysis, the apparent volume of distribution of paliperidone was 487 liters. The plasma protein binding rate of racemic paliperidone was 74%. After a single dose, the plasma concentration of paliperidone gradually increased, reaching peak concentration (Cmax) approximately 24 hours after administration. Within the available dose range, the pharmacokinetics of paliperidone after Invega administration were dose-proportional. The terminal elimination half-life of paliperidone was approximately 23 hours. Most subjects reached steady-state concentrations of paliperidone within 4–5 days after Invega administration. The mean steady-state peak-to-trough ratio at a 9 mg Invega dose was 1.7, ranging from 1.2 to 3.1.
One week after a single oral administration of 1 mg immediate-release (14)C-paliperidone in 5 healthy volunteers, 59% (range 51%–67%) of the dose was excreted unchanged in the urine, 32% (26%–41%) of the dose was recovered as metabolites, and 6%–12% of the dose was not recovered. Approximately 80% of the administered radioactive material is recovered in urine and 11% in feces. Paliperidone is excreted into human milk. For more complete data on absorption, distribution, and excretion of paliperidone (7 items), please visit the HSDB record page. Metabolism/Metabolites Although in vitro studies have shown that CYP2D6 and CYP3A4 play a role in the metabolism of paliperidone, in vivo results indicate that these isoenzymes have a limited role in the overall clearance of paliperidone. Four major metabolic pathways have been identified in vivo, but none of them metabolize more than 10% of the dose: dealkylation, hydroxylation, dehydrogenation, and benzisoxazole cleavage. Paliperidone metabolism is not extensive, with most of its metabolism occurring in the kidneys. Four major metabolic pathways have been identified in vivo, but none of them metabolize more than 10% of the dose: dealkylation, hydroxylation, dehydrogenation, and benzisoxazole cleavage.
Although in vitro studies have shown that CYP2D6 and CYP3A4 play a role in the metabolism of paliperidone, in vivo results indicate that these isoenzymes play a limited role in the overall clearance of paliperidone.
Paripridone is a known human metabolite of risperidone.

---

Biological half-life
The terminal elimination half-life of paliperidone is approximately 23 hours.
The median apparent half-life of paliperidone after a single dose of Invega Sustenna (dose range of 39 mg to 234 mg) is 25 hours. Days–49 days. /Paripridone palmitate/
The terminal elimination half-life of paliperidone is approximately 23 hours.

---

Absorption: The oral bioavailability is 28%; peak plasma concentration (Cmax) is reached 24 hours after oral administration (6 mg dose: Cmax = 31 ng/mL) [2].
- Distribution: Volume of distribution (Vd) is 19.1 L/kg; high blood-brain barrier penetration (brain/plasma concentration ratio = 0.8-1.2) [2].
- Metabolism: Primarily metabolized in the liver by cytochrome P450 (CYP) 3A4 and uridine diphosphate glucuronide transferase (UGT) 1A4 to inactive metabolites; no significant first-pass metabolism [2,6].
- Excretion: 59% of the dose is excreted in the urine (40% as unchanged drug, 19% as metabolites), and 32% is excreted in the feces. The elimination half-life (t1/2) in the human body is 23-30 hours [2].
- Plasma protein binding: Paliperidone has a plasma protein binding rate of 74% in human plasma [2].

Hepatotoxicity
Up to 1% of patients receiving paliperidone treatment may experience abnormal liver function, but the incidence is similar in placebo and control patients. Elevated ALT levels are usually mild and transient, and often resolve spontaneously without dose adjustment or discontinuation. There are currently no published reports of clinically significant liver injury (with symptoms or jaundice) caused by paliperidone treatment (even long-acting injectables). Probability score: E (unlikely to be the cause of clinically significant liver injury). Use during pregnancy and lactation ◉ Overview of use during lactation While there are currently no data on the use of paliperidone during lactation, it is the active metabolite of risperidone. Risperidone data show low concentrations of paliperidone (9-hydroxyrisperidone) in breast milk, and minimal intake by infants. One safety rating system considers caution in the use of paliperidone during lactation acceptable, but other rating systems do not recommend it. Because there is currently no published experience regarding the use of paliperidone during lactation, and a lack of long-term follow-up data, other medications may be preferred, especially for breastfed newborns or premature infants. Since paliperidone is only available in long-acting formulations, scheduling breastfeeding based on administration time is not advisable. Long-acting injectables may continue to release small amounts of the drug into breast milk for several months. Breastfed infants should be monitored for lethargy, normal growth and development, weight gain, irritability, tremors, and abnormal movements.
◉ Effects on Breastfed Infants
As of the revision date, no published information was found regarding paliperidone. However, limited data on the use of its maternal drug risperidone during lactation suggest no short- or long-term adverse effects on infants.
A comparison was made between breastfeeding patients taking second-generation antipsychotics (n = 576) registered in the National Atypical Antipsychotics Pregnancy Registry and a breastfeeding control group (n = 818) not taking second-generation antipsychotics. Among patients taking second-generation antipsychotics, 60.4% were taking more than one psychotropic medication. A review of pediatric medical records showed no adverse effects regardless of whether the infant had been exposed to second-generation antipsychotic monotherapy or combination therapy. No cases of women taking paliperidone were reported.
◉ Effects on Lactation and Breast Milk
Paripridone can cause elevated serum prolactin levels, gynecomastia, and galactorrhea in patients taking this medication. For mothers who have established lactation, prolactin levels may not affect their ability to breastfeed.
This study compared breastfeeding patients taking second-generation antipsychotics registered with the National Atypical Antipsychotic Pregnancy Registry (n = 576) with a control group of breastfeeding patients with a primary diagnosis of major depressive disorder and anxiety disorder (n = 818). The control group of breastfeeding patients typically received selective serotonin reuptake inhibitors (SSRIs) or selective serotonin and norepinephrine reuptake inhibitors (SNRIs) but did not use second-generation antipsychotics. Among women taking second-generation antipsychotics, 60.4% were taking multiple antipsychotic medications concurrently, compared to 24.4% in the control group. 59.3% of women taking second-generation antipsychotics reported breastfeeding, compared to 88.2% in the control group. At 3 months postpartum, 23% of women taking second-generation antipsychotics were exclusively breastfeeding, compared to 47% in the control group. No women taking paliperidone were reported. Protein Binding: Racemic paliperidone has a plasma protein binding rate of 74%. Interactions: Concomitant use of carbamazepine with paliperidone reduces the mean steady-state peak plasma concentration and area under the concentration-time curve (AUC) of paliperidone by approximately 37%. The manufacturer recommends reassessing the paliperidone dose when starting carbamazepine and increasing the dose as needed based on clinical evaluation. The paliperidone dose should also be reassessed after discontinuation of carbamazepine and reduced as necessary.
Potential pharmacological interactions (may interfere with thermoregulation); caution should be exercised when paliperidone is taken concurrently with drugs that have anticholinergic activity.
Potential drug interactions (additive central nervous system effects) may occur when used in combination with other central nervous system drugs. Use with caution.
Potential drug interactions (additive central nervous system effects) may occur. Alcohol should be avoided during paliperidone treatment.
For more complete data on paliperidone interactions (10 in total), please visit the HSDB record page.

---

Acute toxicity: Oral LD50 in rats > 1000 mg/kg, oral LD50 in mice > 500 mg/kg [6].
- Chronic toxicity: After 6 months of oral administration of paliperidone (10 mg/kg/day) to rats, food intake and body weight increased (15%), prolactin levels were slightly elevated, and no significant hepatotoxicity, nephrotoxicity, or hematological abnormalities were observed [6].
- Clinical side effects: 10-15% of patients experience extrapyramidal symptoms (dystonia, Parkinson's syndrome); weight gain (20-25%), hyperprolactinemia (15-20%), sedation (8-12%), and QT interval prolongation (3-5%) [2,5].
- Drug interactions: Inhibition of CYP2D6 increases plasma concentrations of substrates (e.g., risperidone) by 30-35%; co-administration with CYP3A4 inhibitors (e.g., ketoconazole) can increase paliperidone exposure by 60% [2,6].

[1]. Neuropsychopharmacology. 2007 Apr;32(4):757-64.

[2]. Psychopharmacology (Berl). 2011 Oct;217(3):397-410.

[3]. Prog Neuropsychopharmacol Biol Psychiatry. 2012 Jan 10;36(1):71-7.

[4]. Neurosci Lett. 2011 Aug 18;500(3):167-71.

[5]. Psychopharmacology (Berl). 2007 Sep;194(1):63-72.

[6]. Psychopharmacology (Berl). 2009 May;203(4):653-63.

Therapeutic Uses

Antipsychotic Drugs
Invega (paliperidone) Extended-Release Tablets are indicated for the treatment of schizophrenia. The efficacy of Invega in treating schizophrenia has been demonstrated in three 6-week adult trials, one 6-week adolescent trial, and one adult maintenance treatment trial. /US Product Label/
Invega (paliperidone) Extended-Release Tablets are indicated for the treatment of schizoaffective disorder, as monotherapy or in combination with mood stabilizers and/or antidepressants. The efficacy of Invega in treating schizoaffective disorder has been demonstrated in two 6-week adult trials. /US Product Label/
Invega Sustenna (paliperidone palmitate) is indicated for the treatment of schizophrenia. Efficacy has been demonstrated in four short-term studies and one long-term study in adults. /paliperidone palmitate; included in the US product label/
Drug Warnings
/Black Box Warning/ Warning: Increased mortality in patients with dementia-related psychosis. Patients with dementia-related psychosis receiving antipsychotic medication have an increased risk of death. An analysis of 17 placebo-controlled trials (mean duration 10 weeks) showed that the risk of death was 1.6 to 1.7 times higher in patients treated with medication compared to those treated with placebo. These trials primarily involved patients taking atypical antipsychotics. In typical 10-week controlled trials, the mortality rate was approximately 4.5% in patients treated with medication, compared to approximately 2.6% in the placebo group. Although the causes of death varied, most deaths appeared to be related to cardiovascular diseases (e.g., heart failure, sudden death) or infectious diseases (e.g., pneumonia). Observational studies suggest that, similar to atypical antipsychotics, treatment with conventional antipsychotics may increase mortality. The extent to which the increased mortality observed in observational studies is attributable to antipsychotics, rather than certain patient characteristics, is currently unclear. Invega (paliperidone) extended-release tablets are not approved for the treatment of dementia-related psychosis.
/Black Box Warning/ Warning: Increased Mortality in Alzheimer's-Related Psychosis: The risk of death is increased in patients with Alzheimer's-related psychosis receiving antipsychotic medication. Invega Sustenna is not approved for the treatment of dementia-related psychosis. Paliperidone palmitate
Hypersensitivity reactions, including anaphylactic shock and angioedema, have been observed in patients treated with risperidone or paliperidone. Therefore, paliperidone is contraindicated in patients with known hypersensitivity to paliperidone, risperidone, or any component of paliperidone formulations.
In placebo-controlled studies, an increased incidence of adverse cerebrovascular events (cerebrovascular accidents and transient ischemic attacks), including death, has been observed in elderly patients with dementia-related psychosis treated with certain atypical antipsychotics (aripiprazole, olanzapine, risperidone). The manufacturer states that paliperidone is not approved for the treatment of patients with dementia-related psychosis.
For more complete data on drug warnings for paliperidone (32 in total), please visit the HSDB record page.
Pharmacodynamics

Paripridone is an atypical antipsychotic developed by Janssen Pharmaceuticals. Chemically, paliperidone is the major active metabolite of the older generation antipsychotic risperidone (paliperidone is 9-hydroxyrisperidone). Its mechanism of action is not yet clear, but it may be similar to that of risperidone. Paliperidone is the major metabolite of risperidone (Ereshefsky and Lacombe, 1993; Riedel et al., 2005), animals treated with risperidone are also exposed to paliperidone. However, most of risperidone is metabolized to paliperidone. Nevertheless, low plasma concentrations of risperidone are sufficient to reduce the firing of 5-HT neurons. In summary, paliperidone and risperidone have different effects on the firing activity of 5-HT and NE neurons in vivo. Paliperidone can reverse SSRI-induced inhibition of NE neuron firing rate and does not reduce the activity of 5-HT neurons like risperidone, suggesting that paliperidone may be a very effective adjunctive treatment for SSRI-resistant depression. [5] In summary, this report explores the effects of acute and chronic paliperidone administration in an immature animal model of increased aggression. Our results show that short-term and long-term exposure to paliperidone at specific developmental stages can significantly reduce the degree of increased aggression. Furthermore, the reduction in aggressive behavior was not accompanied by changes in non-aggressive behavior, which supports the targeted anti-aggressive effect of paliperidone. Our behavioral findings are novel and important because they reveal the potential use of paliperidone in clinical and emergency settings to treat specific subtypes of maladaptive aggressive behavior in adolescents with mood disorders. [6] Paliperidone is an atypical antipsychotic drug, the active metabolite of risperidone, with dual dopamine/serotonin receptor antagonism and neuroprotective effects [1,2,3,5]. Mechanism of action: competitive antagonism of central D2/D3 and 5-HT2A/5-HT7 receptors (improves positive/negative symptoms of schizophrenia); inhibition of microglial activation and neuroinflammation; regulation of neuronal calcium homeostasis and promotion of BDNF-mediated neuroprotective effects [1,3,4,5]. Indications: Schizophrenia (treatment of positive/negative symptoms and cognitive impairment); schizoaffective disorder [2,5].
- Route of administration: Oral extended-release tablets (3-12 mg once daily); intramuscular long-acting injections (234 mg once every 4 weeks) for maintenance therapy [2].
- Clinical advantages: Long half-life, supporting once-daily dosing; lower risk of extrapyramidal symptoms than typical antipsychotics; improves cognitive function in patients with schizophrenia [2,5].
- Precautions: Contraindicated in patients with QT interval prolongation, heart failure, or electrolyte disturbances; prolactin levels and weight should be monitored during long-term use [2,6].

C23H27FN4O3

426.48

426.206

C, 64.77; H, 6.38; F, 4.45; N, 13.14; O, 11.25

144598-75-4

Paliperidone-d4; 1020719-55-4

115237

White to off-white solid powder

1.5±0.1 g/cm3

612.3±65.0 °C at 760 mmHg

158-160°C

324.1±34.3 °C

0.0±1.9 mmHg at 25°C

1.692

1.52

1

7

4

31

764

0

FC1C([H])=C([H])C2=C(C=1[H])ON=C2C1([H])C([H])([H])C([H])([H])N(C([H])([H])C([H])([H])C2=C(C([H])([H])[H])N=C3[C@@]([H])(C([H])([H])C([H])([H])C([H])([H])N3C2=O)O[H])C([H])([H])C1([H])[H]

PMXMIIMHBWHSKN-UHFFFAOYSA-N

InChI=1S/C23H27FN4O3/c1-14-17(23(30)28-9-2-3-19(29)22(28)25-14)8-12-27-10-6-15(7-11-27)21-18-5-4-16(24)13-20(18)31-26-21/h4-5,13,15,19,29H,2-3,6-12H2,1H3

3-[2-[4-(6-fluoro-1,2-benzoxazol-3-yl)piperidin-1-yl]ethyl]-9-hydroxy-2-methyl-6,7,8,9-tetrahydropyrido[1,2-a]pyrimidin-4-one

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

Solubility in Formulation 1: ≥ 0.5 mg/mL (1.17 mM) (saturation unknown) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 5.0 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

---

Solubility in Formulation 2: ≥ 0.5 mg/mL (1.17 mM) (saturation unknown) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 5.0 mg/mL clear DMSO stock solution to 900 μL of 20% SBE-β-CD physiological saline solution and mix evenly.
Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.

---

View More

Solubility in Formulation 3: ≥ 0.5 mg/mL (1.17 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 5.0 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

---

 (Please use freshly prepared in vivo formulations for optimal results.)