Development And Optimization of Candesartan Cilexetil Loaded Nanostructured Lipid Carriers Based Intranasal in Situ Gel for Targeted Brain Delivery in Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by memory loss and cognitive impairment. Current therapeutic approaches suffer from poor brain bioavailability due to the blood-brain barrier (BBB) and extensive first-pass metabolism. Intranasal drug delivery offers a promising alternative route by bypassing the BBB and delivering drugs directly to the brain through olfactory and trigeminal pathways [11, 12, 13]. Nanostructured lipid carriers (NLCs) provide advantages such as improved drug loading, enhanced stability, and controlled drug release, while in situ gels improve nasal residence time and mucoadhesion. Therefore, the present study focused on the development and optimization of Candesartan Cilexetil loaded NLC-based intranasal in situ gel for targeted brain delivery in Alzheimer's disease [14, 15].

Intranasal administration has emerged as a promising non-invasive approach for direct nose-to-brain drug delivery. This route bypasses the blood-brain barrier and hepatic first-pass metabolism, thereby improving drug bioavailability and enhancing therapeutic efficacy[16]. Among various advanced drug delivery systems, nanocarrier-based formulations have gained considerable attention due to their ability to improve drug solubility, stability, controlled release, and targeted delivery[17]. Nanostructured lipid carriers (NLCs), in particular, offer several advantages, including high drug-loading capacity, biocompatibility, and enhanced permeability across biological membranes. There are several types of the In situ gelling systems based on the triggering factors which are mentioned below[18].

1. Temperature sensitive In situ gel.
2. pH sensitive In situ gel.
3. Ion activated In situ gel [19].

Fig 1. CMC formation in temperature sensitive In situ gel.                  Fig 2. Ion activated In situ gel

"Candesartan Cilexetil, an angiotensin II receptor blocker, has demonstrated potential neuroprotective effects through anti-inflammatory, antioxidant, and neurovascular protective mechanisms [20]. Emerging evidence suggests that modulation of the brain renin-angiotensin system (RAS) plays a significant role in the pathogenesis and management of Alzheimer's disease. Therefore, the development of a nanocarrier-based intranasal formulation of Candesartan Cilexetil represents a promising strategy for targeted brain delivery, with the potential to improve therapeutic outcomes and overcome the limitations associated with conventional treatment approaches for Alzheimer’s disease”[ 21, 22].

Fig 3. Structure of Candesartan Cilexetil

Advantages of Intranasal NLC-Based In Situ Gel Delivery System[23, 24]

• Direct Nose-to-Brain Delivery
• Avoidance of First-Pass Metabolism
• Non-Invasive Administration
• Enhanced Drug Loading: Nanostructured lipid carriers (NLCs) possess high drug-loading capacity and encapsulation efficiency.
• Controlled Drug Release
• Improved Stability
• Biocompatibility and Biodegradability
• Increased Nasal Residence Time
• Enhanced Mucoadhesion
• Potential Neuroprotective Effect

Disadvantages of Intranasal NLC-Based In Situ Gel Delivery System [25]

• Limited Drug Dose Capacity
• Mucociliary Clearance
• Formulation Complexity.
• Stability
• Variability in Nasal Physiology
• Potential Nasal Irritation
• High Manufacturing Cost
• Scale-Up Challenges
• Regulatory Challenges
• Limited Clinical Data

MATERIALS AND METHODS

Chemicals and Reagents

Candesartan Cilexetil was used as the active pharmaceutical ingredient. Various lipids, surfactants, co-surfactants, polymers, and solvents, including Caprylic Capric Triglyceride, Tween 80, Span 80, Labrasol, Poloxamer 407, Carbopol 934, HPMC, and Methanol, were procured from reputed suppliers. These materials were used for the preparation, optimization, and evaluation of the nanocarrier-based intranasal formulation for targeted brain delivery in Alzheimer's disease.

Preformulation studies

"Preformulation research comprises a group of pharmaceutical and analytical investigations that precede and support formulation development. It represents the first step in the rational development of dosage forms. Preformulation studies are designed primarily to determine the physicochemical properties of the drug substance and its compatibility with selected excipients, which may influence the performance, stability, and efficacy of the final formulation. These studies provide essential information that guides formulators in the development of an elegant, stable, safe, and effective dosage form with optimized performance characteristics [26,27].

Preparation of Candesartan Cilexetil loaded nanostructured lipid carrier (NLCs) Preparation of trial batches of NLCs by Hot emulsification followed by probe sonication method.

Candesartan Cilexetil-loaded Nanostructured Lipid Carriers (NLCs) were prepared using the hot emulsification followed by probe sonication method. The lipid phase, containing the drug, solid lipid, liquid lipid, and surfactant, was melted at a temperature 10°C above the melting point of the solid lipid. This lipid phase was then added to the aqueous phase maintained at the same temperature to form a pre-emulsion [28]. The resulting mixture was stirred at 1000 rpm for 10 minutes at 65–70°C to obtain a homogeneous emulsion. Subsequently, the pre-emulsion was subjected to probe sonication and cooled to room temperature to form the NLC dispersion. Various formulations were prepared by altering the drug-to-lipid ratio, solid lipid-to-liquid lipid ratio, and surfactant concentration to evaluate their effects on the physicochemical properties and optimize the formulation for targeted brain delivery of Candesartan Cilexetil [29, 30].

Table 1. Composition of trial batches of Candesartan Cilexetil NLCs

RESULTS AND DISCUSSION

PREFORMULATION STUDIE

Identification

1. Organoleptic characterization:

• Color: White
• Taste: Tasteless
• Odour: Odourless

2. Melting point of Candesartan Cilexetil

Table 2 –Melting point of Drug

3. DSC study

4. FT – IR spectroscopy

Fig.5. FT-IR spectrum of CND

Table-2. IR frequencies of CND functional group

5. XRPD

Fig.6. X-ray diffraction pattern of CND

XRD patterns of pure CND exhibited sharp at a diffraction angle of 2θ   13°, 18°, 20°, 23° and 26° with the peak intensity 4371, 8142, 5248, 9396 and 5638. This indicates that the drug was present as crystalline form.

Table 3. Data for evaluation of trial batches for particle size

*Mean ± S.D (n=3

Table 4. Trial batches of In situ gel:

6. Evaluation of CND loaded In situ gel:

1. Physical evaluation

Table 5.Physical evaluation of CND-NLC In situ gel

The appearance, colour, and homogeneity of the gel were observed visually. The pH of the gel was measured by pH meter (n = 3)

Table 6. Characterization of In situ gel batches (Mean±SD, n=3)

2. In Vitro drug release study

The CND release study from optimized NLC formulation was performed through dialysis membrane (Mol. Wt. 12,000 Da) using vertical Franz diffusion cell at 34.5°C± 0.5°C for 8hrs. The membrane was stabilized in a simulated nasal electrolyte solution (SNES, pH 6.4) for 15 min. The NLC (1 mL) were uniformly distributed in the donor chamber, and the SNES was continuously stirred by a magnetic stirrer. Aliquots (0.1 mL) were withdrawn from the receiver compartment at predefined time intervals (1hr), and the same amount of fresh SNES was used for refilling the volume of a cell. The validated UV method was used for determination of the percentage of drug release through the dialysis membrane. Simultaneously, the NLC was checked for different release kinetic models such as zero-order, first-order, Higuchi, Hixon– Crowell cube root, and Korsmeyer– Peppas models, and a best-fitted model was selected (Madane et al.,2016).

Table7. In vitro drug release study for CND- NLC simple solution and CND- NLC

In situ gel.

(Mean±SD, n=3

Fig.7 Cumulative drug release from CND dispersion, CND- NLC and CND-In situ gel TMZ

3. Release kinetics

The release data of CND-NLC In situ gel and CND simple solution were fitted to different kinetic mathematical models: Zero order which describes the release rate as independent of drug concentration, first order which describes that the release rate is dependent on drug concentration; Higuchi which is based on the Fick’s law of diffusion and Korsemeyer-Peppas which is based on Quasi Fickian diffusion mechanism.

System follows Higuchi model with the highest R ² values which is 0.9981.

Table 8. Data for kinetic models for CND dispersion, CND-NLC and CND-In situ gel

The values obtained are in the table which is mentioned below.

4. Ex Vivo permeation study

Ex vivo permeation studies of Candesartan Cilexetil (CND) were performed using sheep nasal mucosa, which closely resembles human nasal mucosa in anatomy and histology. The study demonstrated that approximately 90% of CND permeated from the simple drug solution within 4 hours, whereas only 39.5% permeated from the in situ gel, indicating sustained and controlled drug release. The in situ gel formulation exhibited prolonged drug permeation, with 66.5% drug release observed over 8 hours. The permeability parameters, including apparent permeability coefficient (Papp), steady-state flux (Jss), and diffusion coefficient (D), confirmed efficient transport of CND through the nasal mucosa. These findings suggest that the developed intranasal formulation provides sustained drug delivery and effective permeation through the nasal route.

Table 28. Ex vivo % drug release for CND- NLC simple solution and CND- NLC In situ gel

Mean ± S.D (n=3)

Fig 8. Ex vivo % drug release for CND- NLC simple solution and CND- NLC In situ gel