INTRODUCTION:

BCSis a scientific categorization of a drug substance on the basis of its water solubility and intestinal permeability. After oral administration of a drug, it gets dissolved into the gastric (hydrophilic) fluid initially, and then permeated across the biological membranes (lipophilic) and finally reaches in the blood. Many synthetic and natural medications have limited absorption or penetration through the biological membrane, which limits their absorption and total availability to the body system¹.

Poor absorption may be due to their poor water solubility, whereas poor permeation may be due to the poor miscibility with the lipids, thereby severely limiting their capability to pass over the lipid-rich cell membranes of the small intestine.

Therefore, a greater no. of strategies including soluble pro-drug, solid dispersions, cyclodextrin and phospholipids, and vesicular drug delivery systems, etc have been investigated to improve the absorption and penetration of biologically active molecules^2-4.

Vesicular drug delivery systems (VDDS) are important systems used for drug targeting, increasing the bioavailability and stability. These systems have an aqueous core normally adjoining by a lipid bilayer. The system is used as vehicle for the delivery of both water soluble and water insoluble types of drugs. The hydrophilic drugs are entrapped in the inner aqueous core, while hydrophobic drugs are encapsulated in a lipid bilayer. The various advantages offered by VDDS are tissue targeting, high drug entrapment, long retention time, reduced side effects, and increased bioavailability. Furthermore, the system can deliver a drug to the site of action at predetermined rate^5-7.

However, beneficial VDDS have certain limitations. The chief limitations of VDDS are linked to their preparation method, stability, scale-up, loading efficacy, cost-effectiveness, sterilization, burst release, and short half-life. Therefore, the pharmacosomes were developed to reduce various defect associated with the conventional vesicular delivery systems. The pharmacosomes are reported as lipophilic prodrug conjugates that self-assemble.

In this review, overview in a very comprehensive manner, the pharmacosomes as an important vesicular delivery system, different components and techniques of preparation and characterization of pharmacosomes, and their applications. In addition, we have analysed the pharmacosomes of different drugs prepared using variety of lipids and their effects on physicochemical properties and pharmacokinetic performance of the drugs. Finally, we conclude by outlining future outcome for the development of pharmacosomes drug delivery.

Pharmacosomes:

Pharmacosomes are colloidal dispersions where the active medicament is covalently bound to the lipid which gives rise to an amphiphilic block. Based on chemical arrangement of drug lipid complex, they reside as fine to an extreme degree of vesicular, micellar, and hexagonal aggregates. The development of vesicular pharmacosomes originates from the surface and bulk interlinking of drugs and lipids. The drug possessing the active functional groups (–COOH, -OH, -NH2) can be covalently linked to lipids with or without spacer chain by esterification or any other suitable conjugation strategy leads to formation of prodrugs. These prodrugs behave like amphiphilic molecules and get self-assembled in one or more layers in contact with the aq. medium. These layers further self-assembled inform of vesicles which resulting in formation of pharmacosomes. In pharmacosomes the drug molecules act as polar head and attached lipids as a non-polar tail. Pharmacosomes avoid problems such as drug leakage, drug incorporation, and reduced shelf life. They can improve bioavailability of drug due to the depletion of interfacial tension, increased area of contact. Pharmacosomes stability is depends on the physical and chemical characteristics of the conjugate system. It possesses several advantages above other vesicular systems such as transferosomes, niosomes, liposomes and hence serves as an alternative to this vesicular systems⁸.

Pharmacosomes plays a vital role in the improvement of the drugs dissolution in gastrointestinal fluid and enhancement of their permeation through the lipophilic membrane. Besides, they can enhancedrugs bioavailabilityhaving either low lipid or/and water solubility. The prodrug approach has a high drug trapping efficacy and effectively avoids vesicle leakage and bursts release. As a result, the step of removing the unbound or unentrapped medication from the process of formulation can be skipped, which is a major restriction of liposomes. Pharmacosomes stability is mainly depends on the physiochemical properties of drug-phospholipid complex like solubility, melting point, phase transition temperature, and lipid composition^9-10. The types of functional groups present in the drug molecule, the length of fatty acid chains in lipids, and the presence or lack of spacer groups all affect the rate of pharmacosome breakdown into active drug molecules. To achieve the desired in vivo pharmacokinetic behaviour, all of these parameters can be tweaked individually. It is reported that a lot of drugs including anti-cancer, cardiovascular drugs, non-steroidal anti-inflammatory drugs (NSAIDS), proteins, and herbal products are delivered through pharmacosomes. Pharmacosomes can be given through different routes like topical, oral and extra vascular routes^11,12.

Fig. 1. Structure of pharmacosome

Advantages^13,14:

1. Drug can be delivered to the active site of infection.

2. Improve bioavailability especially in the case of hydrophobic drug.

3. Reduction in adverse effect and toxicity.

4. Drug carriers like liposomes, nanoparticles, micro emulsions which lead to low physical stability and low drug-loading efficiencysuch as sedimentation, aggregation, and drug leakage during preparation, etc is not present in pharmacosomes.

5. Easily incorporate the drug.

6. Entrapment efficiency is high and predefined since the medication and carrier are covalently bonded and form a stoichiometrically specified unit.

Disadvantage¹⁵:

1. It requires surface and bulk interactivity of lipids with drugs.

2. To protect the leakage of drugs it requires covalent bonding

Application^16-18:

1. Pharmacosomes show wider stability profile and longer shelf life.

2. Pharmacosomes has capacity to increase drug absorption and conveyance. Using response surface design, the formulated pharmacosomes were optimized and their attributes examined by colleagues.

3. Pharmacosomes can increase the permeation rate by improving the fluidity ofmembranes. The approaches have successfully improved therapy, performance, and various drugs such as pindolol diglyceride, amoxicillin, Taxol, cytarabine, dermatansulfate, bupranolol hydrochloride, and so on.

4. Pharmacosomes have a greater degree of selectivity for targeted drug delivery.

5. Pharmacosomes have reach a new level by amplifying therapeutic effects of many drugs like cytarabine, Taxol, dermatan sulphate, pindolol derivative, amoxicillin and so forth.

Component of Pharmacosomes:

The three main components of pharmacosomes are drug, lipid and solvents.

Drug:

A drug having active hydrogen atom (-OH, -NH_{2, -}COOH,) esterified with a lipid moiety to get amphiphilic block. This amphiphilic block facilitates drug transport via cell membrane, tissue and cell wall. Pharmacosomes of several drugs such as diclofenac, aceclofenac, geniposide, aspirin etc were prepared.

Solvent¹⁹:

Solvents with high polarity and solubility used for preparation of pharmacosomes. Highly purified and volatile solvent must be used. Generally solvents with intermediate polarity such as acetone, dichloromethane, ethanol, methanol, tetrahydrofuran etc. were preferred for preparation of pharmacosomes.

Lipid^20,21:

The basic component of a biological membrane is phospholipids. Thephospholipids are of 2 types such as sphingolipidsandphosphoglycerates which are majorly used. Phosphatidylcholine is commonly used lipid for the pharmacosome preparation. It is an amphiphilic block in which hydrophobic acyl hydrocarbon chains pair binds with a water-soluble polar head group of phosphocholine with glycerol bridge. Phosphatidylcholine helps to maintain purity of cell membrane and involved in various biological processes. It acts as source of protein and hepatoprotective agent and utilize in the control of liver disorders. Besides, it prevents fibrosis and also the cirrhosis by enhancing collagen breakdown. Furthermore, it is used to treat different brain conditions such as memory loss, Alzheimer disease, and tardive dyskinesia, and in cancer management. The chemical structure of different lipids used for pharmacosomes preparation.

Table no. 1. Difference between pharmacosomes and liposomes¹⁷:

Liposomes		Pharmacosomes
Principle	Incorporation of drug in the aq. or lipid phase ofmixture of lipid where the physicochemical properties of the carrier and release of drug will be functions of different lipids used.	The covalent binding of a medication to a lipid results in a molecule that serves as both a carrier and an active agent. The physicochemical properties depend on drug as well as the lipid.
Loss of drug	Through leakage	No leakage, since drug is covalently bound but loss of drug by hydrolysis is possible.
Manufacturing	Cast fill method Extrusion/sonication Injectable method Reverse phase evaporation etc.	Self- dispersion through moderate mixing and sonication.
Separation of free drug	By gel filtration, dialysis, ultrafiltration, ultracentrifugation.	Not necessary since the drug covalently linked.
Volume of inclusion	Decisive in incorporation of drug molecules.	Irrelevant, since the drug is covalently bound
Surface charge	Achieved through lipid combination.	Depends on the physicochemical structure of complex.
Membrane fluidity	Depends on lipid combination and presence of cholesterol fluidity influences the rate of drug release and physical stability of system.	Depends on drug lipid complex phase transition temp. The drug is covalently bound, hence there is zero effect on release rate.
Release of drug	Diffusion through the bilayer, desorption from the surface or release through degradation of liposomes.	Hydrolysis (including enzymatic).
Physical stability	Relatively good Aggregation through double valanced cation.	Depends on physicochemical properties of drug and lipid complex.

Methods of Pharmacosomes Preparation^22-25:

The pharmacosomes can be prepared by different methods. The methods of pharmacosomes preparation are discussed below.

1. Hand shaking method:

It is one of the simple methods of pharmacosomes preparation where the drug lipid mixture is dissolved in an organic solvent which is volatile in nature in a RBF. Then, the solvent is permit to evaporate utilizing a rotary vacuum evaporator that leads the formation of a thin film in a flask. Finally, the thin film is hydrated using an aqueous medium which offer a vesicular suspension.

2. Ether injection method:

Thecomplex of drug and lipid is dissolved in a definite quantity of ether. This ether solution is then injected in hot buffer or aqueous medium, where vesicles get formed. Vesicles may be in different forms such as round, cylindrical, cubic, or hexagonal type. The shape of vesicles depends on the amphiphilic nature of compound and its concentration.

3. Anhydrous co-solvent lyophilization method:

The drug and phospholipid are dissolved in solution of DMSO and glacial acetic acid. Then, this mixture is blend to form a clear liquid solution and freeze-dried at whole night at condenser temperature. The complex obtained is flushed with nitrogen. Then stored at 4⁰C.

4. Solvent evaporation method:

It is a conventional method of pharmacosomes preparation where the drug is firstly acidified to get reactive hydrogen atom which is necessary for complexation. An acid solution of drug extracted with chloroform then recrystallized. The drug lipid complex is dissolved in the organic solvents in an RBF at different ratios. The resultant mixture then refluxed for 1 or 2 hours. Then dried under vacuum evaporator at 40⁰C. This dried residue placed in a vacuum desiccator for complete drying. It is time-consuming and involves multistage processing.

5. Supercritical fluid process:

This method is used to overcome shortcomings related with the solvent evaporation technique. The main drawbacks of solvent evaporation technique, time-consuming and involve multistage processing. Besides, the dissolution of pharmacosomes does not improve ideally. Parameters allied to solid morphology, including thecrystal pattern, crystal habit, and particle size, affect the dissolution rate of a compound hence affect bioavailability. The two main techniques used in the supercritical process are gas anti-solvent and solution improve dispersion by supercritical fluid. In this method drug lipid complex is dissolved into supercritical fluid of CO₂ and mixed by using a nozzle mixing chamber. Pharmacosomes formed by fast mixing of dispersion due to the turbulent flow of carbon dioxideandsolvent.

Characterization of Pharmacosomes:

Characterization of drug-lipid complex (prodrug):

1. Chromatography²⁶:

The simple chromatographic technique like TLC is primarily used for the confirmation of prodrug. The purity of starting materials and product as well as the progress of drug-phospholipid conjugate synthesis is confirmed by this technique. Nowadays, advanced techniques such as HPTLCand HPLCare widely used over TLC due to higher sensitivity, rapid separation and better resolution.

2. Melting point²⁷:

The melting point (MP) is an important parameter that gives information regarding any structural changes in the organic compound. The prodrug formation is characterized by a change in melting point which is normally notably different from that of either pure drug or lipid. The MP of drug will be increased or decreased due to incorporation of lipid moiety. A technique like DSCis widely used to determine the MP of compounds.

3. Ultraviolet spectroscopy:

It is one of the preliminary spectroscopy techniques used to identify the changes in the absorption peaks that occur due to a change in molecular structure. The UV-visible spectrum for pure drug, phospholipid, physical mixture, and prodrug is recorded. The absorption peaks in physical mixtures usually appear at the same wavelength as observed in pure drug and phospholipid. The production of new bonds and recently launched neighbouring groups can be verified by changing peaks, which can be attributable to prodrug synthesis.

4. Fourier transform infrared spectroscopy (FTIR)²⁸:

The prodrug formation is confirmed using FTIR by comparing theIRspectrum of prodrug with individual components and physical mixture. The spectrum of a prodrug is commonly different from particular components or physical mixture due to chemical interactions between drug and phospholipid which leads to the generation of new bonds^.

5. X-ray diffraction (XRD)²⁹:

X-ray diffraction analysis is also performed to confirm the formation of the drug-phospholipid conjugate. In X-ray diffraction pattern the crystalline drugs demonstrate characteristic intense peaks while phospholipid which is amorphous, shows wide peaks.Due to the prevalence of the both free drug as well as phospholipids, the physical mixtures get both sharp as well as wide peaks. The production of a drug-phospholipid conjugate is indicated by the absence or depletion in the intensity of sharp peaks.

6. Solubility studies:

The solubility is again one of the criteria used in the characterization of drug-phospholipid conjugate. The former drug-phospholipid conjugate will affect the solubility profile of the drug. The conjugation of drug with lipophilic moieties decreases solubility and increases the membrane permeability. The solubility studies are performed in water and buffer solutions of different pH values. An excessive amount of sample beyond saturation is added in vials containing different solvents and equilibrated in shaker bath at 37⁰C for 24 hrs at controlled rpm. After completion of 24 hrs, a known volume of sample is withdrawn and the amt. of drug solubilized is determined by UV-visible spectroscopy.

Characterization of vesicles^30-34:

1. Surface morphology:

The shape and size of pharmacosomes are altered by certain parameters such as purity of phospholipids, speed of rotation, method of preparation. Surface morphology can be studied by using SEM and TEM, etc technique.

2. Drug content:

Fordrug content determination an equivalent amount of drug-lipid complex is measured and transferred to volumetric flask which containing solvent. Then flask is sonicated to achieve solubilization for 24 hrs. Finally, the solutions are diluted and drug content is determined using UV-visible spectroscopy or HPLC.

3. In vitro drug release study:

The equilibrium reverse dialysis bag technique is used to perform in vitro drug release study. Dialysis bag containing donor phase (an emulsion of drug, drug lipid complex) suspended in a vessel comprising of continuous phase outside and stirred. At definite time interval dialysis bag is removed and analysed for drug release. This method has certain advantages as the rise surface area available for donor and receiver phase and increased efficiency due to reduction in the number of steps.

4. In vivo characterization:

Specific study models were selected based on the expected pharmacological action of the drug in the pharmacosomes. For evaluating in vivo hepatoprotective activity, the effect of test pharmacosomes on animals against alcohol or paracetamol-induced hepatotoxicity can be observed.

5. Stability:

FTIR spectrum of drug lipid complex in solidified form is compared with FTIR spectrum of its micro-dispersion in water later lyophilization at different time intervals. This spectrum data tells about the stability of pharmacosomes.

Table no 2: Pharmacosomes prepared using different drugs, lipids and preparation method with comments¹:

Drug	Lipid	Preparation method	Comments
Aceclofenac	Soya phosphatidylcholine	Solvent evaporation	Improved bioavailability of Aceclofenac
Diclofenac	Soya phosphatidylcholine	Solvent evaporation	Improved solubility of diclofenac
Aspirin	Soya phosphatidylcholine	Solvent evaporation	Controlled release of Aspirin
Rosuvastatin	Soya lecithin	Hand shaking	improved bioavailability of Rosuvastatin
Acyclovir	Phosphatidylcholine	Tetrahydrofuran injection	Improved solubility of Acyclovir
Ketoprofen	Soya phosphatidylcholine	Solvent evaporation	Increased solubility and dissolution of Ketoprofen
Ornidazole	Soya lecithin	Solvent evaporation	Showed sustained release of Ornidazole
Losartan	Losartan	Solvent evaporation	Improved bioavailability of
Furosemide	Soya phosphatidylcholine	Solvent evaporation	sustained release of
Geniposide	Phospholipid	Solvent evaporation	Improved lipophilicity, absorption and permeation of Geniposide

CONCLUSION:

Pharmacosomes is a stepping stone to improve delivery of drugs containing active hydrogen atom (-OH, -NH_{2, -}COOH,). In Pharmacosomes drug is bound to the lipid by covalent, van der Waal and hydrogen bonding. The drug-lipid conjugate (prodrug) is amphiphilic in nature and get self-assembled in vesicles in an aqueous medium. In contrast to conventional liposomes, Pharmacosomes are characterized by an unusually high drug loading, amenability to sterilization, higher in-vitro stability, and a low burst release. A large variety of drugs formulated as Pharmacosomes using different lipids and preparation techniques have shown improved physicochemical properties and pharmacokinetic performance of the drug.

REFERENCES:

1. Kumbhar P, Shinde T, Jadhav T, Gavade T, Sorate T, Mali U, Disouza J, Manjappa A. Pharmacosomes: An approach to improve biopharmaceutical properties of drugs basic considerations in development. Research J. Pharm. and Tech.2021;14(8):4485-4490.

2. Mukherjee PK, Maiti K, Kumar V. Value added drug delivery systems with botanicals: Approach for dosagedevelopment from natural resources. Pharm Rev. 2007;6:57-60.

3. Samuni A, Chong P, Barenholz LGY, Thompson TE. Physical and chemical modifications of adriamycirdroncomplex by phospholipid bilayers. Cancer Res.1986;46:594-599.

4. Tanhuanpaa K, Cheng KH, Anttonen K. Characteristics of pyrene phospholipid/g-cyclodextrin complex. Biophys J. 2001;81(9):1501-1510.

5. RoohiK, DilipKP, Anupam S, Vikas K, Bhaskar M. Ethosomes: A novel approach for transdermal and topical drug delivery. Research J. Topical and Cosmetic Sci.2015;6(1):15-20.

6. Kshitij BM, Suraj RW. Niosomes: A novel drug delivery system. Asian J. Pharm. Res. 2013;3(1):15-19.

7. Nilesh VK, Vijay RM. Ethosomes: A novel drug carrier. Res. J. Topical and Cosmetic Sci. 2013;4(1):84-91.

8. Gondkar SB, Nikita SM, Saudagar RB. An overview on trends and development of niosomes as drug delivery. Research J. Topical and Cosmetic Sci. 2016;7(2):79-85.

9. Semalty A, Semalty M, Rawat BS, Singh D, Rawat MS. Pharmacosomes: the lipid-based new drug delivery system. Expert Opin. Drug Delivery. 2009;6:599-612.

10. Pathak K, Keshri L, Shah M. Lipid nanocarriers: influence of lipids on product development and pharmacokinetics. Crit. Rev. Ther. Drug Carrier Syst.2011;28:357-393.

11. Selvaraju K, Vengadesh PK, Karthick K, Padma Preetha J, Arul Kumaran K.S.G. Pharmacosomes: An Immense Potential Vesicular Constructs. Research J. Pharma. Dosage Forms and Tech. 2011;3(3):84-86.

12. Nilesh V.K, Vijay RM. Ethosomes: A novel drug carrier. Res. J. Topical and Cosmetic Sci. 2013;4(1):84-91.

13. Singh VK,Patel A, Chandra D, Yadav KK, pharmacosomes: a novel carrier for targeted and controlled vesicular drug delivery system. World Journal of Pharmaceutical Research 2014;(3)5:1221-1238.

14. Sultana SK,Sindhuri TK,Parveen P,Mahathi K. An updated overview on pharmacosomes. International journal of Universal pharmacy and Bio Science. 2014;3(3):710-731.

15. Ali Gamal Ahmed Al-kaf, Ahmad Mohammed Othman. A review on pharmacosomes: an emerging novel vesicular drug delivery system. Universal Journal of Pharmaceutical Research. 2017; 2(1):33-36.

16. Nikita D.Raut I, NitalikarM, Shrinivas K. Mohite C, Magdum S. Pharmacosomes as Drug Delivery System: An Overview. Asian Journal of Pharmaceutical Research. 2011;11(2):122-127.

17. Negi K,Kumar K, Teotia T. Pharmacosomes: a novel drug delivery system. Ijmpr. 2020;4(5):75-79.

18. Pandita A, Sharma P. Pharmacosomes: An Emerging Novel Vesicular Drug DeliverySystem for Poorly Soluble Synthetic and Herbal Drugs. Hindawi Publishing Corporation. 2013;1-10

19. Soniya L, Kattyar , Pravin SP, Sachin VP, Satwashila SK. Phytosomes and Recent research on Phytosomal Drugs. Asian Journal Pharmaceutical Analysis.2022;12(1):61-69.

20. Tabasum SM, Monika ST, Yogita R, Manoj N. Liposomes as a Drug carrier. Asian Journal of Research in Pharmaceutical science. 2019;9(2):141-147.

21. Little A, Levy R, Chuaqui-kidd P, Hand D. Double-blind, placebo-controlled trial of high-dose lecithin in Alzheimer’s disease. J Neurol Neurosurg Psychiatary 1985;48:736-742.

22. Selvaraju K, Vengadesh PK, Karthick K, Padma Preetha J, Arul Kumaran K.S.G. Pharmacosomes: An Immense Potential Vesicular Constructs. Research J. Pharma. Dosage Forms and Tech. 2011;3(3):84-86.

23. Nilesh V.K, Vijay RM. Ethosomes: A novel drug carrier. Res. J. Topical and Cosmetic Sci. 2013;4(1):84-91.

24. Saha D, Mridha D, Kayal S, Beura S. Overview on Liposomes as Drugs Carrier. Research Journal of Pharmaceutical Dosage Forms and Technology.2010;2(6):370-373.

25. Suraj RW, Abhishek DD, Mohan AU, Rahul MB, Dhaval PG, Rinkesh RM, Syed MF. Liposome as a drug delivery system: A review. Research J. Pharma. Dosage Forms and Tech. 2012;4(2):104-112.

26. Yogita R, Shital S, Aishwarya P, Manojkumar N, Shrinivas M. Phytosomes: A novel approach in herbal drug delivery system. Asian J. Res. Pharm. Sci. 2018;8(3):151-154.

27. Shepherd RW, Bunting PS, Khan M, Hill JG, Soldin SJ, Gall DG. A rapid, sensitive method for accurate analysis of individual bile acids in biological fluids by high performance thin layer chromatography and densitometry. Clin. Biochem. 1978;11:106-111.

28. Chirag PJ, Satyanand T, Pinkesh P, Alpesh Y. Phytosomes: A Current Trend for Enhancement of Bioavailability of Polar Phytoconstituents.Research Journal of Pharmaceutical Dosage Forms and Technology. 2014;6(1):44-49.

29. Song Y, Zhuang J, Guo J, Xiao Y, Ping Q. Preparation and properties of a silybinphospholipid complex. Die Pharmazie- An Int. J. Pharm. Sci. 2008;63:35-42.

30. Xia HJ, Zhang ZH, Jin X, Hu Q, Chen XY, Jia XB. A novel drug–phospholipid complex enriched with micelles: Preparation and evaluation in vitro and in vivo. Int. J. Nanomed. 2013;545-54.

31. Supraja B, Mulangi S. An updated review on pharmacosomes, a vesicular drug delivery system. J Drug Delivery Ther 2019;9:393-402.

32. Saudagar RB, Samuel S. Ethosomes: Novel noninvasive Carrier for Transdermal Drug Delivery. Asian Journal of Pharmacy and Technology.2016;6(2):135-138.

33. Hada NK, Ashawat MS. Aquasome: A Self Assembling Supramolecular and Nanoparticulate Carrier System for Bio-Actives. Research Journal of Pharmaceutical Dosage Forms and Technology.2014;6(1):50-53.

34. Aishwarya CP, Shital SS, Yogita TR, Manojkumar MN, Shreenivas KM. Review on Aquasome novel Drug delivery System. Research Journal of Topical and Cosmetics Sciences. 2018;9(1):19-24.

Received on 20.06.2022 Modified on 14.07.2022

Asian J. Res. Pharm. Sci. 2022; 12(4):291-296.

DOI: 10.52711/2231-5659.2022.00050