Oxidative Stability in Lipid Formulations: a Review of the Mechanisms, Drivers, and Inhibitors of Oxidation.

The importance of lipid-based formulations in addressing solubility and ultimately the bioavailability issues of the emerging drug entities is undeniable. Yet, there is scarcity of literature on lipid excipient chemistry and performance, notably in relation to oxidative stability. While not all lipid excipients are prone to oxidation, those with sensitive moieties offer drug delivery solutions that outweigh the manageable oxidative challenges they may present. For example, caprylocaproyl polyoxylglycerides help solubilize and deliver cancer drug to patients, lauroyl polyoxylglycerides enhance the delivery of cholesterol lowering drug, and sesame/soybean oils are critical part of parenteral nutrition. Ironically, excipients with far greater oxidative propensity are omnipresent in pharmaceutical products, a testament to the manageability of oxidative challenges in drug development. Successful formulation development requires awareness of what, where, and how formulation stability may be impacted, and accordingly taking appropriate steps to circumvent or meet the challenges ahead. Aiming to fill the information gap from a drug delivery scientist perspective, this review discusses oxidation pathways, prooxidants, antioxidants, and their complex interplay, which can paradoxically take opposite directions depending on the drug delivery system.

A rapid and sensitive method for characterization and quantification of polyglycerol esters by supercritical fluid chromatography coupled to high-resolution mass spectrometry (SFC-HRMS).

Polyglycerol esters of fatty acids (PGEs), a very complex mixture of various isomers, are widely used as green surfactants in different industrial fields such as in cosmetic, pharmaceutic and food industries. However, no study related to the purification and the absolute quantification of these compounds has been described yet. In this study, we developed a rapid and efficient method for characterization and quantification of PGEs using Supercritical Fluid CO2 coupled to High-Resolution Mass Spectrometry (SFC-HRMS). The SFC conditions were first considered including the stationary phase, the nature of mobile phase, the column temperature, the back-pressure regulator. The MS parameters (drying-gas temperature, capillary voltage, nozzle voltage, fragmentor voltage) were then investigated to get the best sensitivity for the PGE analysis. The MS/MS-based structural characterization of targeted PGE, triglycerol mono-oleate (PG3+1C18:1), was established and is helpful to study complex mixtures of PGEs with numerous isobaric PGEs. PG3+1C18:1 was then purified at lab scale and used as standard for quantification. This enabled to develop a rapid quantification method for PG3+1C18:1 within 12 min with good linearity (R2 = 0.9997) as well as sensitivity (picogram level). The validated method was then successfully applied to quantify PG3+1C18:1 in commercial products in order to evaluate their composition.

Quantitative monitoring of galactolipid hydrolysis by pancreatic lipase-related protein 2 using thin layer chromatography and thymol-sulfuric acid derivatization.

Galactolipids are the most abundant lipids on earth where they are mainly found in photosynthetic membranes of plant, algae, and cyanobacteria. Pancreatic lipase-related protein 2 (PLRP2) is an enzyme with galactolipase activity allowing mammals, especially herbivores, to digest this important source of fatty acids. We present a method for the quantitative analysis of galactolipids and galactosylated products resulting from their digestion by guinea pig PLRP2 (GPLRP2), using thin-layer-chromatography (TLC), thymol-sulfuric acid as derivatization reagent and scanning densitometry for detection. Thymol-sulfuric acid reagent has been used for the colorimetric detection of carbohydrates. It is shown here that the derivatization of galactosyl group from galactolipids by this reagent is not affected by the bound acyl glycerol, acyl chains length and number of galactose residues in the polar head. This allowed quantifying simultaneously the initial substrate and all galactosylated products generated upon the hydrolysis of monogalactosyl di-octanoylglycerol (C8-MGDG) by GPLRP2 using a single calibration with C8-MGDG as reference standard. The reaction products, monogalactosyl monooctanoyl glycerol (C8-MGMG) and monogalactosyl glycerol (MGG), were identified and quantified, MGG being recovered from the aqueous phase and analyzed by a separate TLC analysis. This method is therefore suitable to quantify the products resulting from the release of both fatty acids present in MGDG and thereby shows that PLRP2 can contribute to the complete digestion of galactolipids and further intestinal absorption of their fatty acids.

Polyoxylglycerides and glycerides: effects of manufacturing parameters on API stability, excipient functionality and processing.

Lipid-based formulations are a viable option to address modern drug delivery challenges such as increasing the oral bioavailability of poorly water-soluble active pharmaceutical ingredients (APIs), or sustaining the drug release of molecules intended for chronic diseases. Esters of fatty acids and glycerol (glycerides) and polyethylene-glycols (polyoxylglycerides) are two main classes of lipid-based excipients used by oral, dermal, rectal, vaginal or parenteral routes. These lipid-based materials are more and more commonly used in pharmaceutical drug products but there is still a lack of understanding of how the manufacturing processes, processing aids, or additives can impact the chemical stability of APIs within the drug product. In that regard, this review summarizes the key parameters to look at when formulating with lipid-based excipients in order to anticipate a possible impact on drug stability or variation of excipient functionality. The introduction presents the chemistry of natural lipids, fatty acids and their properties in relation to the extraction and refinement processes. Then, the key parameters during the manufacturing process influencing the quality of lipid-based excipients are provided. Finally, their critical characteristics are discussed in relation with their intended functionality and ability to interact with APIs and others excipients within the formulation.

Lipolysis of the semi-solid self-emulsifying excipient Gelucire 44/14 by digestive lipases.

Gelucire 44/14 is a semi-solid self-emulsifying excipient used for the oral delivery of poorly water-soluble drugs. It is composed of C8-C18 acylglycerols and PEG-32 esters, all of which are potential substrates for digestive lipases. Here we studied the lipolysis of Gelucire 44/14 by porcine pancreatic extracts, human pancreatic juice and several purified digestive lipases. Human pancreatic lipase (HPL), the main lipase involved in the digestion of triacylglycerols, did not show any significant activity on Gelucire 44/14 or on either of its individual compounds, C8-C18 acylglycerols and PEG-32 esters. Other pancreatic lipases such as human pancreatic lipase-related protein 2 (HPLRP2) showed low activity on Gelucire 44/14 although the highest activity of HPLRP2 was that observed on the C8-C18 acylglycerol fraction, which accounts for 20% (w/w) of Gelucire 44/14. In addition, HPLRP2 showed low activities on the PEG-32 esters, whether these were tested individually or mixed together. Carboxyl ester hydrolase (CEH) showed high activity on Gelucire 44/14, and the highest activities of CEH were those recorded on the total PEG-32 ester fraction and on each individual PEG-32 ester, except for PEG-32 monostearate. The highest activity of all the enzymes tested was that of dog gastric lipase (DGL) on Gelucire 44/14, although DGL showed low activity on the PEG-32 ester fraction and on each individual PEG-32 ester. We compared the lipolysis of Gelucire 44/14 with that of Labrasol, another self-emulsifying excipient, which is liquid at room temperature. Human pancreatic juice showed similar rates of activity on both Gelucire 44/14 and Labrasol. This finding means that these excipients are hydrolyzed in vivo during pancreatic digestion, mainly by CEH in the case of Gelucire 44/14 and by both HPLRP2 and CEH in that of Labrasol, whereas HPL showed very low activities on each of these two excipients. This is the first time the effects of PEG and acyl chain length on the lipolytic activity of digestive lipases on PEG esters have been investigated.

Comparative study on digestive lipase activities on the self emulsifying excipient Labrasol, medium chain glycerides and PEG esters.

Labrasol is a lipid-based self-emulsifying excipient used in the preparation of lipophilic drugs intended for oral delivery. It is mainly composed of PEG esters and glycerides with medium acyl chains, which are potential substrates for digestive lipases. The hydrolysis of Labrasol by porcine pancreatic extracts, human pancreatic juice and several purified digestive lipases was investigated in the present study. Classical human pancreatic lipase (HPL) and porcine pancreatic lipase, which are the main lipases involved in the digestion of dietary triglycerides, showed very low levels of activity on the entire Labrasol excipient as well as on separated fractions of glycerides and PEG esters. On the other hand, gastric lipase, pancreatic lipase-related protein 2 (PLRP2) and carboxyl ester hydrolase (CEH) showed high specific activities on Labrasol. These lipases were found to hydrolyze the main components of Labrasol (PEG esters and monoglycerides) used as individual substrates, whereas these esters were found to be poor substrates for HPL. The lipolytic activity of pancreatic extracts and human pancreatic juice on Labrasol(R) is therefore mainly due to the combined action of CEH and PLRP2. These two pancreatic enzymes, together with gastric lipase, are probably the main enzymes involved in the in vivo lipolysis of Labrasol taken orally.