Clozapine-laden carbon dots delivered to the brain via an intranasal pathway: Synthesis, characterization, ex vivo, and in vivo studies

Clozapine, which is widely used to treat schizophrenia, shows low bioavailability due to poor solubility and high first-pass metabolism. The study aimed to design clozapine-loaded carbon dots (CDs) to enhance availability of the clozapine to the brain via intranasal pathway. The CDs were synthesized by pyrolysis of citric acid and urea at 200 °C by hydrothermal technique and characterized by photoluminescence, transmission electron microscopy (TEM), X-ray Photoelectron Spectrometer (XPS), and Fourier transform infrared spectrum (FTIR). The optimized clozapine-loaded CDs (CLZ-CDs-1:3-200) showed a quasi-spherical shape (9-12 nm) with stable blue fluorescence. The CDs showed high drug solubilization capacity (1.5 mg drug in 1 mg/ml CDs) with strong electrostatic interaction with clozapine (drug loading efficiency = 94.74%). The ex vivo release study performed using nasal goat mucosa showed sustained release of clozapine (43.89%) from CLZ-CDs-1:3-200 for 30 h. The ciliotoxicity study (histopathology) confirmed no toxicity to the nasal mucosal tissues using CDs. In the rat model (in vivo pharmacokinetic study), when CDs were administrated by the intranasal route, a significantly higher concentration of clozapine in the brain tissue (Cmax = 58.07 ± 5.36 μg/g and AUCt (µg/h*g) = 105.76 ± 12.31) was noted within a short time (tmax = 1 h) compared to clozapine suspension administered by intravenous route (Cmax = 20.99 ± 3.91 μg/g, AUC t (µg/h*g) = 56.89 ± 12.31, and tmax = 4 h). The high value of drug targeting efficiency (DTE, 486%) index and direct transport percentage (DTP, 58%) indicates the direct entry of clozapine-CDs in the brain via the olfactory route. In conclusion, designed CDs demonstrated a promising dosage form for targeted nose-to-brain delivery of clozapine for the effective treatment of schizophrenia.

Nose to brain delivery of tailored clozapine nanosuspension stabilized using (+)-alpha-tocopherol polyethylene glycol 1000 succinate: Optimization and in vivo pharmacokinetic studies

Clozapine is widely used to treat schizophrenia as an atypical antipsychotic. Low solubility, poor dissolution rate, degradation in the gastrointestinal tract, high hepatic first-pass metabolism, and eventually less drug transfer in the brain are all issues with oral clozapine administration. On account of this poor pharmacokinetic parameters, the authors aimed to develop clozapine nanosuspension using (+)-alpha-tocopherol polyethylene glycol 1000 succinate (TPGS) and polyvinylpyrrolidone K-30 (PVP K-30) and deliver it through the intranasal route. The nanosuspension was prepared by the high-speed homogenization method with 3² full factorial design for optimization of the product. Quality Target Product Profile (QTPP) was enlisted before the product development. The amount of TPGS and speed of homogenizer were selected as independent variables whereas, particle size and drug permeation profile after 24 h (Y₂, %) were selected as dependent variables. As per the results of optimization, amount of TPGS and speed of homogenizer were chosen as 0.1% and 7000 rpm, respectively. The particle size of the optimized nanosuspension of clozapine was found to be 281 nm. The conversion of clozapine crystals to an amorphous form was verified by characterization studies (XRD and DSC). The drug permeability study showed 96.15% and 41.12% clozapine release after 24 h from nanosuspension and conventional suspension, respectively. The study of nasal cilio-toxicity (histopathological studies) demonstrated the appropriateness of nanosuspension for intranasal purposes. The single-dose in vivo pharmacokinetic analysis in the rat model showed a substantial increase in the therapeutic concentration of clozapine in the brain tissue in the case of intranasal nanosuspension (dose = 0.05 mg drug/0.1 mL, C_max = 8.62 ± 0.45 μg/g, t_max = 1 h) compared to conventional oral clozapine suspension (dose = 26.43 mg drug/0.158 mL, C_max = 1.14 ± 0.12 μg/g, t_max = 1 h).Ultimately, in the case of an intranasal route, a 3.56-fold increase in brain drug concentration was observed with a 528-fold lower drug dose compared with oral administration. The results suggest that clozapine nanosuspension may be used for successful nose-to-brain delivery.

Antigenic specificity of rheumatoid synovial fluid lymphocytes

The majority of rheumatoid arthritis (RA) synovial fluid lymphocytes (SFL) demonstrate markers that are suggestive of prior activation. While the mechanism(s) responsible is unknown, prior studies have suggested that certain Mycobacterium tuberculosis (MT) antigens may preferentially activate SFL in vitro. We therefore examined the ability of RA SFL to respond to purified protein derivative and an acetone-precipitable MT antigenic complex (AP-MT) and compared this with the responses by peripheral blood lymphocytes (PBL). The responses were contrasted with those elicited with tetanus toxoid (TT) and mitogenic anti-CD3. In patients with RA, the SF proliferative responses to both TT and anti-CD3 were reduced compared with responses by PB. In contrast, the SF response to purified protein derivative was maintained, and that to AP-MT was significantly increased, compared with PB. SF responses to AP-MT antigens were significantly greater than those to TT. The AP-MT activation of T lymphocytes from RA SF was characterized by an earlier peak proliferative response than that noted with matched PB. AP-MT responsiveness was not restricted to HLA-DR4 positive patients. These observations suggest that an epitope(s) contained within the MT complex of antigens, and enriched in the AP-MT complex, may be important in maintaining the chronic inflammation in at least some patients with RA.

Limited proliferative response to type II collagen in rheumatoid arthritis

In order to define the potential importance of type II collagen in the activation of rheumatoid arthritis (RA) synovial fluid (SF) lymphocytes, we examined the proliferative response of matched peripheral blood and SF lymphocytes to type II collagen. The mean proliferative response to the collagen was somewhat greater (p less than 0.05) with SF, compared to peripheral blood lymphocytes. However, the magnitude of this response was relatively weak as determined by stimulation indices, and it did not approach that observed with peripheral blood lymphocytes in response to tetanus toxoid. Sixty-seven percent of peripheral bloods and 50% of SF demonstrated positive responses to the control antigen, tetanus toxoid. In contrast, only 6 and 28%, respectively, were positive in response to type II collagen. The addition of exogenous interleukin 2 augmented responses to the tetanus toxoid, however, no such enhancement with type II collagen was noted in our patients. Our collagen was arthritogenic in experimental animals. These observations do not support the existence of T cell specificity toward type II collagen as a common mechanism for the expansion of synovial lymphocytes in RA.