Cardiovascular diseases (CVDs) are considered the leading cause of death worldwide, with an estimated 17.9 million deaths every year, as reported by the World Health Organization [1]. One of the main risk factors for CVD development is hyperlipidaemia [2], which is characterized by an increase in serum total cholesterol (TC), triglycerides (TGs), and low-density lipoprotein (LDL), combined with a reduction in high-density lipoprotein (HDL) serum levels [3], [4].

Statins are one of the most commonly used drugs for the management of hyperlipidaemia and act by inhibiting the 3-hydroxy-3-methylglutaryl coenzyme-A (HMG-CoA) reductase enzyme, which is the rate-controlling enzyme of the mevalonate pathway [5]. Atorvastatin calcium (ATR) is a synthetic statin that works by lowering TGs and LDL and raising HDL levels [6], [7], besides possessing anti-inflammatory and antioxidant properties [8], which makes it one of the most studied drugs in the pharmaceutical field. Nevertheless, the therapeutic efficacy of ATR in many clinical settings is significantly hampered by its poor aqueous solubility. ATR is classified as class II according to the Biopharmaceutical Classification System (BCS) [9]. ATR is practically insoluble in aqueous medium (<0.1 mg/mL), as reported [10], [11], and very slightly soluble in phosphate buffer pH 6.8 (approx. 0.29 mg/mL) [12]. Furthermore, besides its poor solubility, insufficient intestinal absorption and extensive gut wall extraction, collectively, contributed to its poor oral bioavailability (∼ 12–14%) [13], [14], which leads to the administration of large doses of ATR, predisposing the risk of inducing severe adverse effects such as hepatotoxicity and kidney failure [15], [16].

Various pharmaceutical delivery systems have been adopted to enhance the oral bioavailability of atorvastatin via increasing its dissolution, and thereby, oral absorption. These systems included the formulation of nanoparticles [14], [17], [18], solid dispersions [9], [19], [20], [21], floating matrix tablets [13], nanosponges [22], niosomes [23], and co-crystallization [24]. Other techniques include the inclusion of ATR in lipid-based delivery systems such as self-emulsifying drug delivery systems [25], [26], and nano-structured lipid carriers [27], [28], [29].

A promising approach to improving the oral bioavailability of lipophilic drugs and/or BCS Class II drugs is their encapsulation within a lipid-based drug delivery system known as pro-nanolipospheres (PNLs) [30], [31]. PNLs are isotropic, homogenous mixtures of an active lipophilic drug in a combination with lipids, surfactants, phospholipids, and co-solvents. This anhydrous liquid mixture is sometimes referred to as "pre-concentrates”. These pre-concentrates spontaneously constitute drug-entrapped O/W nano-emulsions with a particle diameter of ∼ 200 nm upon mixing with an aqueous phase, such as that in the upper GI lumen content [32], [33]. These self-emulsifying drug delivery systems are designed to overcome the drawbacks associated with traditional colloidal systems such as micro- or nano-emulsions, liposomes and polymeric nanoparticles [34], [35]. They offer the advantages of low cost of ingredients, better physical stability [36], ease of preparation and scale-up, high dispersibility in an aqueous medium [37], high entrapment of hydrophobic drugs, controlled particle size, and extended release of entrapped drug after administration [38].

Recently, studies have affirmed the efficacy of PNL as a delivery vehicle for increasing the oral bioavailability of lipophilic drugs by different mechanisms, including not only enhancing drug solubility but also decreasing intra-enterocyte metabolism by CYP family enzymes and bypassing P-gp efflux mechanisms [31], [36]. For instance, Cherniakov et al. [39] have emphasized that encapsulating cannabidiol (CBD) and delta-9-tetrahydrocannabinol (THC) within PNLs significantly resulted in a 3- and 6-fold rise in their relative bioavailability, respectively, in comparison with CBD or THC solutions. In the same context, Avramoff et al. verified the efficacy of pro-dispersion lipospheres for enhancing the oral bioavailability of the water-insoluble immunosuppressant drug Cyclosporin A [40].

In this study, therefore, we challenged the efficacy of PNLs for enhancing the oral bioavailability of the poorly water-soluble lipid-lowering drug, atorvastatin. A mixture of lipid/lipid combinations, Tween 20, Span 80, and co-surfactant were utilized for the formulation of atorvastatin-loaded pro-nanolipospheres (ATR-loaded PNLs), and the in vivo efficacy of the formulated ATR-loaded PNLs was assessed via pharmacokinetic studies and a pharmacodynamic evaluation of hypo-lipidemic activity in a poloxamer 407-induced hyper-lipidemic rat model.