Distribution Of Risperidone And Paliperidone In Prefrontal Cortex, Striatum And Nucleus Accumbens Of SD Rat

OBJECTIVESTo study the distribution of risperidone and paliperidone in blood and different brain regions (Medial prefrontal cortex (mPFC), Striatum (STR) and Nucleus accumbens (NAc)) of rat brain after separate administration of the two drugs. Microdialysis was employed aiming to find whether there are regional accumulation of drugs in the brain and seek correlations between drug levels in brain and blood.METHODS1. The building of method for simultaneous determination of risperidone and paliperidone in dialysates.A method was built for simultaneous determination of risperidone and paliperidone in blood and brain dialysates by HPLC-MS/MS coupled by on-line solid phase extraction. The potential difficulties, such as loss from transferring and lack of blank samples, were considered and successfully overcome.2. Sample collection by microdialysis 2.1Relative recovery(RR) of drugs through the probeA series concentrations of RR for risperidone and paliperidone were carried out by gain and by loss. Changes of RR as the continuation of sampling time was also investigated. Finally, according to the results, a plan was made for accurately correction of samples.2.2Microdialysis samplingHealthy male SD rats weighing250-300g were chosen for microdialysis experiments. Blood probe was inserted into the jugular vein/right atrium and brain probe was inserted into mPFC, STR or NAc by stereotaxic apparatus under anesthesia. After a24h post-surgical stabilization period, risperidone or paliperidong (both at4mg/kg) was intraperitoneal injected. Microdialysis samples of blood and brain were collected every20min at the same time for600min.2.3Sample analysis and statisticsMicrodialysis samples of blood and brain were analysed by the method built as above. Drug concentrations were revised by relative recovery in vivo. Corrected results were statistically analysed.RESULTS1. Simultaneous determination of risperidone and paliperidone in dialysates.A method for simultaneous determination of risperidone and paliperidone in dialysates was established. The injection volume was set as30μL and rosiglitazone (3ng/mL) was chosen as the internal standard.With a relatively low concentration, drug loss from transferring was striking (recovery for risperidone and paliperidone were44.51%and50.62%, respectively). To overcome this problem, effect of methanol, ethanediol, propylene glycol, acetonitrile, vitaminC and surfactant (sodium dodecylsulphate)were tried. It turned out that acetonitrile(50%) achieved the best amendment with a recovery for risperidone and paliperidone of93.66%and95.32%. The investigation results support ringer’s solution as a substitute of dialysate in part of the validation of methed. The linearity for both drugs in the range of0.05-100ng/mL was good enough (r2>0.996). Recovery, precision and accuracy were all inspection qualified and results for quality control samples complied with the requirements (RSD within±15%)2. Microdialysis experiment2.1Relative recoveryRR of risperidone and paliperidone were independent of dialyse direction (by gain or by loss) and drug concentrations, and RR in vivo did not change significantly as the continuation of sampling. Based on these findings, in vivo RR of drug at a certain level (25ng/ml for brain and200ng/ml for blood) and time points (after sampling) was carried out for correction of samples during the whole procedure. Data from each rat was corrected by RR of the homologous source. 2.2Distribution of risperidone and paliperidone in blood and different regions of rat brainBoth in blood and brain samples, risperidone reached a higher peak concentration more ealier and was eliminated faster as compared to paliperidone.In blood, after a single administration of risperidone, the metabolite paliperidone was rapidly produced and both level of them reach the peak at0.5-1h. Approximately2h after treatment, the level of paliperidone begin to be higher than risperidone. The area under(the plasma concentration time)curve(AUC) of the two drugs were approximately equal. After paliperidone treatment, peak concentration was reached rapidly (0.5h). The AUC for paliperidone was higher than that of active moiety (sum of plasma risperidoen and paliperidone concentrations).In brain, after treatment of risperidone or paliperidone, peak concentration was reached rapidly (about0.5h). After1.5-3h of treatment, the level of paliperidone begin to be higher than risperidone. The AUC of risperidone, paliperidone or active moiety followed the same order:NAc≥STR≥mPFC. In detail, risperidone accumulated in NAc significately (P=0.042and0.027, respectively for mPFC and STR) while AUC for MPFC and STR were almost the same. For paliperidone, AUC for NAc was higher than mPFC significately (P=0.030), while AUC for STR was not significately different from the other two regions. The ratio of brain concentration and blood concentration had the same pattern with AUC. The ratio of NAc, STR and mPFC for risperidone were (0.37-0.43),(0.30-0.39) and (0.23-0.31) respectively while for paliperidone were (0.20-0.28),(0.24-0.28) and (0.15-0.18) The ratio for risperidone was higher than that of paliperidone (1.34,1.93and1.53times respectively for NAc, STR and mPFC)。 In the process of sampling, the ratio for paliperidone was more steady as compared with risperidone. Correlation was found between blood and brain drug levels (P<0.001for risperidone and paliperidone).CONCLUSIONS1. In the three regions (mPFC、STR and NAc) studied here, risperidone accumulated in NAc significately, while distribution for paliperidone in STR and NAc was more uniform and mPFC had the lowest level of paliperidone.2. As compared to risperidone, paliperidone was penetrated into the brain more steadily. Correlation was found between blood and brain drug levels, and therefore, it is valid in estimating brain drug levels from plasma value.