Mixed micelles formulation for carvedilol delivery: In-vitro characterization and in-vivo evaluation

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Abstract

Carvedilol (CAR) is a widely studied, beta and alpha-1 blocker, antihypertensive drug due to its poor water solubility and low oral bioavailability (25–35%). The aim of this work is to improve poor water solubility and the pharmacokinetic parameters of carvedilol by using an optimized and self-assembly prepared micelle formulation. Optimized micelle formulation composed of Pluronic® F127, D-α-tocopheryl polyethylene glycol 1000 succinate, L-cysteine HCl in a ratio of 4:3:3. Micellar size, polydispersity index, zeta potential, morphology, critical micelle concentration, thermal behaviors, in-vitro dissolution of micelles and pharmacokinetic parameters in rats were characterized in this study. Carvedilol aqueous solubility increased (up to 271-fold) as a result of its encapsulation within a mixed micelle formulation. The measured micellar sizes of blank and carvedilol loaded mixed micelles are lower than 30 nm with size distributions of 26.69 ± 2.93 nm and 24.16 ± 4.89 nm, respectively. Transmission electron microscopy revealed that the micelles were spherically shaped. There is a significant enhancement of carvedilol dissolution compared to commercially available tablet formulation (f2 < 50). The in-vivo test demonstrated that the t1/2 and AUC0–∞ values of micelles were approximately 10.89- and 2.65-fold greater than that of the commercial tablets, respectively. Based on our study, bring such applications into being may provide effective new drugs for treatment armamentarium of cardiovascular diseases and hypertension in near future.

Introduction

Oral drug administration is the most frequently used drug delivery route due to its easy ingestion, sustained and controllable delivery, avoidance of pain and patient compliance. Orally administered drugs need to be soluble in gastric fluid for proper absorption and have to reach therapeutic concentration to be effective. Absorption of a drug from gastrointestinal tract vitally depends on its water solubility and permeability (Homayun et al., 2019, Arregui et al., 2019). As a scientific framework, the Biopharmaceutical Classification System (BCS) classify drugs in terms of solubility and permeability degrees. Class II and IV contain drugs which have low solubility-high permeability and low solubility-low permeability properties, respectively. These are the most challenging classes for pharmaceutical industry and researchers (Krstić et al., 2020). Drug candidates under discovery and development process have solubility issues since 90% of drugs in the development process are poorly water-soluble. Over the years, different methods and approaches have been developed to enhance water solubility of drugs including micronization and nanonization, particle engineering, amorphization, solid dispersion, salt formation, the use of surfactants “micellization”, cyclodextrins, and polymeric complexes (Khoder et al., 2016).

Cardiovascular diseases, which bring about 31% of global deaths, are the leading cause of death worldwide according to the World Health Organization (WHO). Therefore, effective treatment strategies and new drugs are needed for treatment of cardiovascular diseases. Carvedilol (CAR) is a third-generation, non-selective beta and alpha-1 blocking agent and leads to reduced blood pressure through vasodilatation. CAR, a BCS class II drug, is well absorbed after oral administration but due to its properties such as low and pH dependent solubility in water, narrow absorption window in the upper gastrointestinal tract, slow dissolution rate in the intestinal tract and a significant degree of first-pass metabolism, the oral bioavailability is only 25% to 35% in humans, and it is variable in general. Therefore, in this study we have focused on increasing bioavailability of CAR by using polymeric micellar carriers. As CAR is being a P-glycoprotein substrate, it is actively pumped out of the cells and as a result, its intestinal absorption is reduced (Arregui et al., 2019, Krstić et al., 2020, Liu et al., 2012). It was reported that CAR reduced morbidity and mortality in adults and also better tolerated compared to other beta-blockers (Wegmann et al., 2017). There are numerous strategies to enhance water-solubility and overcome dissolution-related problems of CAR. These approaches may be listed as the use of lipophilic solutions; conversion to salt form; formation of inclusion complex with cyclodextrins (Taveira et al., 2018); the use of a self-emulsifying system, the preparation of solid dispersions with porous silica, nanosuspension formulations (Liu et al., 2012); and micellar solubilization (Wegmann et al., 2017, Kahraman et al., 2015). Due to short biological half-life of CAR; there have been so many attempts for encapsulation of CAR into nanosystems to obtain controlled drug release such as nanoparticles (Sharma et al., 2019); self-nano-emulsifying drug delivery systems (SNEDDS) (Singh et al., 2011); nano-niosomes (Taymouri and Varshosaz, 2016); solid lipid nanoparticles (Venishetty et al., 2012); and micelles (Wegmann et al., 2017) were developed to improve bioavailability of CAR. Micelle formulations gain attention due to their properties such as ease of preparation; applicability of the production methods to scale up, small particle size, solubility enhancing property and providing controlled release. Micelle formulations (10–200 nm) are considered as a promising option for solubilizing hydrophobic compounds. They are self-assembled systems forming above the critical micellar concentration (CMC) of amphiphilic polymers. Hydrophilic and hydrophobic components of amphiphilic polymer create core–shell nanostructures, which provides solubilization of drugs having poor water solubility, controlled drug release, protection of vulnerable molecules and prolonged circulation time in-vivo. As shown in recent studies, polymeric micelles are one of the most efficient nanoparticulate delivery systems to improve the bioavailability of hydrophobic drugs (Piazzini et al., 2019, Li et al., 2017, Bagheri et al., 2021). Genexol®-PM (marketed in Europe and Korea) and Nanoxel® (marketed in India) are clinically approved self-assembled polymeric micelle formulations based on polyethylene glycol-b-poly(D,L-lactic acid) block copolymer. There are numerous micelle formulations (NK105, NK012, NC-6300, NC-6004, NC-4016, CPC-634, AZD2811, ONM-100) that are under clinical investigation (Mi et al., 2021, Varela-Moreira et al., 2017). As a safe micelle base material; Pluronic® F127 (F127) is a poly(oxyethylene)-poly(oxypropylene)-(polyoxyethylene) triblock copolymer with a general formula of PEO100-PPO69-PEO100 and it is commercially available. It is commonly used as an ideal micellar carrier due to its low CMC value, excellent biocompatibility and high safety. In several studies (Lian et al., 2017, Liu et al., 2017, Halder et al., 2018); it was used to increase the bioavailability of drugs in addition to improve stability and circulation time. D-α-tocopheryl polyethylene glycol 1000 succinate (TPGS) is an anionic water-soluble derivative of vitamin E that consists of conjugates of vitamin E succinate and polyethylene glycol (PEG). It is also U.S. Food and Drug Administration (FDA) approved as a safe pharmaceutical adjuvant and it has been used in different drug formulations. Stated advantages of TPGS make it a suitable candidate as a carrier for nanoparticulate drug delivery, especially in applications of poorly water-soluble drug solubilization. Moreover, it enhances the cellular uptake and the blood circulation time of drugs as well. The only disadvantage of TPGS in micelle formulations is that its relatively high CMC value (0.02%, w/w) causing TPGS micelles to dissociate in the plasma easily (Meng et al., 2017). As reported earlier co-administration of TPGS with cyclosporin-A resulted in enhanced oral absorption due to improved solubilization (Sokol et al., 1991). In this work; F127 and TPGS are combined to prepare mixed micellar carriers. Since it is safe; biodegradable, highly soluble and stable pharmaceutical excipient, albumin, was also included into the study due to its solubilizing effects. Albumin has the ability to form reversible complexes with hydrophobic drugs causing enhanced water solubility (Khoder et al., 2016, Khoder et al., 2018). Amorphization (the co-amorphous technique) is among the techniques used to overcome poor aqueous solubility of drugs that are a member of classes II and IV of the BCS (Kasten et al., 2019). Amino acids are promising co-formers for these type of formulations as they are cheap and safe. These compounds are known to improve the physical stability of many amorphous drugs with different interactions like hydrogen bonding; hydrophobic and/or ionic interactions (Huang et al., 2017). In this study; we have additionally used l-cysteine HCl (Cys) amino acid as a low molecular weight excipient to prepare co-amorphous mixtures.

Main purpose of this study is to combine and evaluate different solubilization approaches so as to improve water solubility and oral bioavailability of CAR.

Section snippets

Materials

Pluronic® F68 (F68), Pluronic® F108 (F108), F127, l-cysteine hydrochloride monohydrate, human serum albumin (HSA) (≥96% albumin, essentially fatty acid free), methanol and acetonitrile were purchased from Sigma-Aldrich (St. Louis, MO, USA). All Type I water was of analytical grade (Milli-Q Plus System–Millipore/Millipore Corporation, Burlington, MA, USA). Carvedilol (Mw: 4076.474 g/mol) was a kind gift of Deva Pharmaceuticals, Turkey.

Determination of carvedilol solubility

The equilibrium solubility of CAR was determined by the

Solubility of carvedilol was increased

Equilibrium solubility of CAR was calculated as 17.42 ± 2.11 μg/mL at 25 °C following the measurements using HPLC. Effect of micelle formulation, different excipients and combination of these excipients on the solubility of CAR were evaluated with the same method used in the solubility determination of pure CAR. It is reported that poor water solubility of active substances is one of the most challenging issue during formulation process for optimum bioavailability (Savjani et al., 2012). As

Conclusion

In this study, F127-1/TPGS-1/Cys-1 mixed micelle formulation was designed and prepared to improve the low solubility of carvedilol as a novel drug delivery approach. F127-TPGS mixed micelle formulations have been developed earlier for targeting drug delivery across the blood brain barrier and anticancer drug delivery (Meng et al., 2017, Butt et al., 2012). There are different strategies to enhance solubility and oral bioavailability of CAR in the literature including solid dispersions, micelle

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

The authors kindly acknowledge Prof. Güneş Esendağlı, Department of Basic Oncology, Hacettepe University Cancer Institute, for helpful comments and discussions.

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