Background: Bilosomes are lipid vesicles that exhibit flexibility and deformability. They consist of phospholipids and amphiphilic bile salts. Compared to the normal vesicular systems such as liposomes and niosomes, bilosomes provide several notable advantages, including simplified manufacturing, cost-effectiveness, and enhanced stability.

Aim: The main objective of the present work was to evaluate the effect of different bile salts on the physical properties that include entrapment efficiency, vesicle size, and polydispersity index(PDI). In addition, in vitro drug release for nisoldipine (NSD) loaded bilosomes was evaluated.

Methods: Nisoldipine-loaded bilosomes were made using a thin film hydration technique. Cholesterol along with surfactant (span 60) was employed, and the formulation also contained several different bile salts, including sodium deoxycholate (SDC), sodium glycocholate (SGC), and sodium taurocholate (STC).

Results: The developed NSD bilosomes exhibited an entrapment efficiency ranging from 44.2 ± 0.3 to 82.36 ± 0.80% and a vesicle size diameter in the nanometric dimensions (166 ± 1.83 to 237.8 ± 3.3 nm). An in-vitro release study revealed that formulas prepared with SDC bile salts showed higher drug release than SGC and STC formulas.

Increasing the bile salt amount from 5 mg to 10 mg increases entrapment efficiency with increasing vesicle size. Further increase in bile salt led to decreased entrapment efficiency with increased vesicle size. SDC gives the best result in terms of entrapment efficiency and acceptable size. STC provides the largest particle size due to its high molecular weight compared to SGC and SDC.

Conclusion: The SDC bile salt component is better suited for manufacturing NSD bilosomes. This is because this component yields the best results regarding high entrapment efficiency, nano size, and prolonged drug release.

Bilosomes, entrapment efficiency, sodium deoxycholate, sodium taurocholate, thin film hydration

Drugs are ineffective until a safe method of delivering them to the circulatory system or a site-specific delivery system is discovered, despite the many advances in pharmaceutical research (Drais and Hussein 2022).

Due to their diverse advantages, lipid-based vesicular systems play a crucial role in pharmaceutical delivery. The advantages encompass the ability to encapsulate both lipophilic and hydrophilic molecules, along with the capability to overcome various challenges such as drug insolubility and drug loading, so bilosomes are preferred over another lipid-based vesicular system (Kharouba et al. 2022).

Bilosomes refer to lipid vesicles that exhibit flexibility and deformability, mostly comprised of phospholipids and amphiphilic bile salts. In contrast to typical vesicular systems such as liposomes and niosomes, bilosomes provide several notable advantages, including simplified manufacturing processes, cost-effectiveness, and enhanced stability (Khafagy et al. 2023).

They resist degradation by enzymatic GIT due to the presence of bile salt in the vesicle membrane, which enhances penetration and makes oral delivery more effective (Anon 2020; Waglewska et al. 2020).

Bilosome formulations frequently use non-ionic surfactants, such as span series, bile salts, and cholesterol. These materials are widely regarded as harmless and have been demonstrated to be fully biocompatible and biodegradable when used to create bilosomes. (Binsuwaidan et al. 2022).

Bile salts are chemicals that can solubilize and enhance the penetration of substances. They are utilized extensively because they are not toxic and are therefore compatible with biological systems (Zafar et al. 2021).

Bile salt gives the vesicles a negative charge, increasing their storage stability and encouraging drug absorption through the M-cells in the Peyer’s patch. After that, cellular activities continue into the underlying lymphoid tissue, preventing hepatic first-pass metabolism and facilitating drug transport into the intestinal lymphatic system (Ismail et al. 2022). Patient compliance and adherence improved due to reduced frequent doses (Kadhim and Rajab 2022).

Different types of bile salts can be used to prepare bilosomes. Some examples include sodium glycocholate (SGC), sodium deoxycholate (SDC), sodium taurocholate (STC), and sodium taurodeoxycholate (STDC) (Palekar-Shanbhag et al. 2020).

Nisoldipine (NSD) (C20H24N2O6) is a calcium channel blocker belonging to the dihydropyridine family that stops calcium from entering cardiac and vascular smooth muscle transmembrane. When calcium ions pass through certain ion channels, the heart contracts. So if this channel (Ca⁺⁺ channel) is blocked this leads to arterioles dilation (Chaudhari et al. 2019) and decreases the contraction of cardiac muscles. For that reason it is primarily employed in the management of cardiovascular disorders, such as the treatment of hypertension, cardiovascular disease, and several types of angina, such as prinzmetal or variant angina. The half-life is seen to be long, between 7 and 12 hours.

The average duration required to reach the highest levels of the drug in the bloodstream has been documented as 9.2 ± 5.1 hours (Nekkanti et al. 2016).

The drug Nisoldipine belongs to Biopharmaceutical classification system (BCS) as (class II drug;that means that it has low solubility and high permeability properties. Furthermore, nisoldipine undergoes first-pass metabolism, before reaching the site of drug action and only 5% of it is used by the body (Al-Edhari and Al Gawhari 2023). Furthermore, NSD’s low water solubility (5.77 × 10−3 g/L) led to poor dissolution and low bioavailability (Chavan et al. 2020; Gasmi et al. 2023).

The present work was designed to develop and formulate NSD bilosomes using different types of bile salts and assess the effect of these salts on bilosomes properties, including entrapment efficiency, particle size, PDI, and drug release.

The NSD loaded bilosomes that had already been made were analyzed for their entrapment efficiency. Results in Table 2 revealed that entrapment efficiency increases significantly from 60.68% in F5 (SGC) into 73.22% and 82.36% in F8 (STC) and F2 (SDC) respectively.

This could be due to lower HLB value (higher hydrophobicity) of SDC (HLB=16) compared to that of SGC and STC possessing higher HLB values (23.1) and (22.1) respectively. The higher hydrophobicity made it easier for the hydrophobic drug NSD to get into the core of the bilayer, which led to a higher EE (El-Nabarawi et al. 2020), as seen in Fig. 1.

Figure 1. 

Effect of type of bile salts on entrapment efficiency (p < 0.05).

Increasing bile salts from 5 to 10 mg Fig. 2, entrapment efficiency increase significantly from 71% to 82% in F1 and F2 respectively. SDC has surface active property and is integrated into bilayer membrane surfaces, enhancing lipid membrane flexibility and drug solubility, increasing entrapment efficiency (Zafar et al. 2021).

Figure 2. 

Effect of Bile salt concentration on Entrapment Efficiency (p < 0.05).

Further increase of bile salt concentration leads to significant decrease in EE from 82.36% in F2 into 60.13% in F3 because high bile salt content enhances the possibility of acting as a solubilizing surfactant and lowers vesicle compactness, facilitating drug leakage and decreasing EE% (Zakaria et al. 2021).

According to the data in Table 2, the bilosomes’ particle size distribution index (PDI) ranged from 0.16 ± 0.037 to 0.33 ± 0.3 (for formulations F8 and F1), indicating a limited size distribution. According to the results of an ANOVA test, the PDI of the produced vesicles was not substantially (p > 0.05) affected by the conditions that were investigated.

Increasing the concentration of bile salt from 5 mg to 10 mg and to 20 mg leads to a significant increase in vesicle size for all types of bile salts (p < 0.05) as seen in Fig. 3.

Figure 3. 

Effect of different concentrations of different bile salts on vesicle size (p < 0.05).

That’s because bile salt, when concentrated to a high level, tends to agglomerate, and that’s exactly what happened here. Anionic bile salts and their steroid structure increase vesicle size in two ways: (i) by increasing the volume of the aqueous core and (ii) by increasing the steric repulsive power among bilosome bilayers, which may increase bilosome bulkiness (Mahmoud et al. 2022).

The increase in vesicle size was determined to be as follows, based on the bile salts that were investigated: STC > SGC > SDC. It’s possible that the variation in vesicle size is caused by a difference in the structure of the bile salt that was used (Abdelbary et al. 2016). SGC (487.6 g/mol) and SDC (414.56 g/mol) based bilosomal vesicles may have created smaller vesicle size when compared to the bulkier STC (537.69 g/mol), which may have resulted in a larger size (Mohsen et al. 2020), Fig. 4 showed that (F7–F9) prepared with STC give significantly larger vesicle size as compared with (F4–F6) and (F1–F3) prepared with SGC and SDC respectively.

Figure 4. 

Effect of bile salts kinds on vesicle dimensions (p < 0.05).

Three formulas, F2, F5, and F8 were selected to do in vitro drug release according to EE% and types of bile salt, to determine the effect of types of bile salt on the drug release percentage of NSD from bilosomes.

The bilosome formulas prepared using SDC F3 showed a higher % drug release (97%) compared to the corresponding bilosome formulas F5 (93.5%) and F8 (87.45%) prepared with SGC and STC, respectively at the end of 24 hr, Fig. 5.

Figure 5. 

In vitro release profile of NSD from different formulas (F2, F5 and F8) along with pure drug suspension.

Release studies show biphasic drug efflux from bilosomal preparations. The initial phase exhibited a prompt and intense release of the drug, primarily resulting from the detachment of the drug molecules that were adsorbed onto the outer surface of the bilosome vesicles. This was followed by a subsequent phase characterized by a gradual and prolonged release of the drug over an extended duration. This sustained release is attributed to the bilosomes’ ability to function as a reservoir for the drug, facilitating its controlled and continuous release (Salim et al. 2022; Kumar et al. 2023).

In addition to improving penetration by integrating itself into the bilayer membrane, SDC is able to increase the fluidity and flexibility of the vesicle bilayer, which in turn makes drug seepage simpler (Salem et al. 2022).

The drug release from bilosomes containing STC was lower than that of SGC-containing bilosomes. The numerous hydrophobic methylene groups on the bilosome side chains during the STC’s conjugation with taurine account for this action, delaying medication release (Ali and Al-Akkam 2023).

Since NSD is highly lipophilic, it would prefer to remain within the lipophilic system than release medium. Increased bile salt concentration had a positive effect on drug release which means increased drug release because it could enhance the fluidity of the bilayer and penetration enhancer effect (Ahmed et al. 2020; Rana et al. 2023).

From the above results, F2 was the optimum formula in terms of small vesicle size with the higher entrapment efficiency along with best drug release, so FTIR was done to determine if there is a chemical interaction between their components.

Fig. 6A displayed the FTIR for a physical combination, a pure medication, and a chosen formula. In the pure NSD spectra, the N-H stretching peak was located at 3318.40 cm^−1, the C-O stretching peak at 1650.01 cm⁻¹, the N-O stretching peak at 1526.25 cm⁻¹, and the C=O stretching peak at 1211.37 cm^−1. (Fu et al. 2017) .

Figure 6. 

FTIR for A. Pure NSD; B. Physical Mixture; C. F2 NSD bilosome formula.

The physical mixture’s FTIR spectrum shows that the (C-O stretching vibration) has slightly shifted from 1650.01 cm^-1 to 1648.71 cm^-1, while the other primary peaks have not altered. This suggests that NSD and the other ingredients needed to create bilosomes do not interact. There is no superimposition between fingerprint regions, which is evidence that there have been modifications in the physical character (Fig. 6) (Kadhim et al. 2020).

The bilosomal formulations effectively entrapped NSD. The physical features of NSD loading bilosomes were affected by the type and amount of bile salts used, including entrapment efficiency, vesicle size, polydispersity index, and in vitro drug release. SDC was found to be better suited for the preparation of NSD-loading bilosomes. The FTIR analyses revealed no incompatibility between the medication and the other excipients in the mixture.

The study’s results are encouraging since the NSD-BS results were in the nanosize range, allowing for optimal NSD delivery through excellent trapping and prolonged drug release.

The authors did not receive any source of funds.

Ghada Hamid Naji: conduct the research, draft writing, and experimental analysis; Fatima J. Al_Gawhari: supervision, revision, and proofreading.

The authors express their gratitude to the College of Pharmacy at the University of Baghdad for supporting the project.