Chemical and enzymatic stability evaluation of lipoamino acid esters of idebenone

Does hydrophobicity always enhance antioxidant drugs? A cut-off effect of the chain length of functionalized chlorogenate esters on ROS-overexpressing fibroblasts

OBJECTIVES

Phenolic antioxidants are currently attracting a growing interest as potential therapeutic agents to counteract diseases associated with oxidative stress. However, their high hydrophilicity results in a poor bioavailability hindering the development of efficient antioxidant strategies. A promising way to overcome this is to increase their hydrophobicity by lipophilic moiety grafting to form the newly coined 'phenolipids'. Although hydrophobicity is generally considered as advantageous regarding antioxidant properties, it is nevertheless worth investigating whether increasing hydrophobicity necessarily leads to a more efficient antioxidant drug.

METHODS

To answer this question, the antioxidant capacity of a homologous series of phenolics (chlorogenic acid and its methyl, butyl, octyl, dodecyl and hexadecyl esters) toward mitochondrial reactive oxygen species (ROS) generated in a ROS-overexpressing fibroblast cell line was investigated using 2',7'-dichlorodihydrofluorescein.

KEY FINDINGS

Overall, the long chain esters (dodecyl and hexadecyl esters) were more active than the short ones (methyl, butyl, and octyl esters), with an optimal activity for dodecyl chlorogenate. Moreover, dodecyl chlorogenate exerted a strong antioxidant capacity, for concentration and incubation time below the cytotoxicity threshold, making it a promising candidate for further in-vivo studies. More importantly, we found that the elongation of the chain length from 12 to 16 carbons led unexpectedly to a 45% decrease of antioxidant capacity.

CONCLUSION

The understanding of this sudden collapse of the antioxidant capacity through the cut-off theory will be discussed in this article, and may contribute towards development of a rational approach to design novel amphiphilic antioxidant drugs, especially phenolipids with medium fatty chain.

Role of antioxidants in prophylaxis and therapy: A pharmaceutical perspective

Antioxidants are emerging as prophylactic and therapeutic agents. These are the agents, which scavenge free radicals otherwise reactive oxygen species and prevent the damage caused by them. Free radicals have been associated with pathogenesis of various disorders like cancer, diabetes, cardiovascular diseases, autoimmune diseases, neurodegenerative disorders and are implicated in aging. Several antioxidants like SOD, CAT, epigallocatechin-3-O-gallate, lycopene, ellagic acid, coenzyme Q10, indole-3-carbinol, genistein, quercetin, vitamin C and vitamin E have been found to be pharmacologically active as prophylactic and therapeutic agents for above mentioned diseases. Antioxidants are part of diet but their bioavailability through dietary supplementation depends on several factors. This major drawback of dietary agents may be due to one or many of the several factors like poor solubility, inefficient permeability, instability due to storage of food, first pass effect and GI degradation. Conventional dosage forms may not result in efficient formulation owing to their poor biopharmaceutical properties. Principles of novel drug delivery systems need to be applied to significantly improve the performance of antioxidants. Novel drug delivery systems (NDDS) would also help in delivery of these antioxidants by oral route, as this route is of prime importance when antioxidants are intended for prophylactic purpose. Implication of NDDS for the delivery of antioxidants is largely governed by physicochemical characteristics, biopharmaceutical properties and pharmacokinetic parameters of the antioxidant to be formulated. Recently, chemical modifications, coupling agents, liposomes, microparticles, nanoparticles and gel-based systems have been explored for the delivery of these difficult to deliver molecules. Results from several studies conducted across the globe are positive and provided us with new anticipation for the improvement of human healthcare.

A calorimetric evaluation of the interaction of amphiphilic prodrugs of idebenone with a biomembrane model

Lipoamino acids (LAA) are useful promoieties to modify physicochemical properties of drugs, namely lipophilicity and amphiphilicity. The resulting membrane-like character of drug-LAA conjugates can increase the absorption profile of drugs through cell membranes and biological barriers. To show the role of amphiphilicity with respect to lipophilicity in the interaction of drugs with biomembranes, in the present study we evaluated the mode of such an interaction of lipophilic conjugates of LAA with the antioxidant drug idebenone (IDE). DSC analysis and transfer kinetic studies were carried out using dimyristoylphosphatidylcholine (DMPC) multilamellar liposomes (MLVs) as a model. For comparison, two esters of IDE with alkanoic acids were synthesized and included in the analysis. The experimental results indicate that based on their different structure, IDE-LAA conjugates interacted at different levels with respect to pure IDE with DMPC bilayers. In particular, a progressive penetration inside the vesicles was observed upon incubation of IDE-LAA compounds with empty liposomes. The enhanced amphiphilicity of the drug due to the LAA moieties caused more complex interactions with DMPC bilayers, compared to those registered with the native drug or IDE alkanoate esters.