Carnosic Acid and Carnosol, Two Major Antioxidants of Rosemary, Act through Different Mechanisms

Carnosic acid, a phenolic diterpene specific to the Lamiaceae family, is highly abundant in rosemary (Rosmarinus officinalis). Despite numerous industrial and medicinal/pharmaceutical applications of its antioxidative features, this compound in planta and its antioxidant mechanism have received little attention, except a few studies of rosemary plants under natural conditions. In vitro analyses, using high-performance liquid chromatography-ultraviolet and luminescence imaging, revealed that carnosic acid and its major oxidized derivative, carnosol, protect lipids from oxidation. Both compounds preserved linolenic acid and monogalactosyldiacylglycerol from singlet oxygen and from hydroxyl radical. When applied exogenously, they were both able to protect thylakoid membranes prepared from Arabidopsis (Arabidopsis thaliana) leaves against lipid peroxidation. Different levels of carnosic acid and carnosol in two contrasting rosemary varieties correlated with tolerance to lipid peroxidation. Upon reactive oxygen species (ROS) oxidation of lipids, carnosic acid was consumed and oxidized into various derivatives, including into carnosol, while carnosol resisted, suggesting that carnosic acid is a chemical quencher of ROS. The antioxidative function of carnosol relies on another mechanism, occurring directly in the lipid oxidation process. Under oxidative conditions that did not involve ROS generation, carnosol inhibited lipid peroxidation, contrary to carnosic acid. Using spin probes and electron paramagnetic resonance detection, we confirmed that carnosic acid, rather than carnosol, is a ROS quencher. Various oxidized derivatives of carnosic acid were detected in rosemary leaves in low light, indicating chronic oxidation of this compound, and accumulated in plants exposed to stress conditions, in parallel with a loss of carnosic acid, confirming that chemical quenching of ROS by carnosic acid takes place in planta.

Mass Transport Phenomena in Lipid Oxidation and Antioxidation

In lipid dispersions, the ability of reactants to move from one lipid particle to another is an important, yet often ignored, determinant of lipid oxidation and its inhibition by antioxidants. This review describes three putative interparticle transfer mechanisms for oxidants and antioxidants: (a) diffusion, (b) collision-exchange-separation, and (c) micelle-assisted transfer. Mechanism a involves the diffusion of molecules from one particle to another through the intervening aqueous phase. Mechanism b involves the transfer of molecules from one particle to another when the particles collide with each other. Mechanism c involves the solubilization of molecules in micelles within the aqueous phase and then their transfer between particles. During lipid oxidation, the accumulation of surface-active lipid hydroperoxides (LOOHs) beyond their critical micelle concentration may shift their mass transport from the collision-exchange-separation pathway (slow transfer) to the micelle-assisted mechanism (fast transfer), which may account for the transition from the initiation to the propagation phase. Similarly, the cut-off effect governing antioxidant activity in lipid dispersions may be due to the fact that above a certain hydrophobicity, the transfer mechanism for antioxidants changes from diffusion to collision-exchange-separation. This hypothesis provides a simple model to rationalize the design and formulation of antioxidants and dispersed lipids.

Rapid, cost-effective and accurate quantification of Yucca schidigera Roezl. steroidal saponins using HPLC-ELSD method

Yucca GRAS-labelled saponins have been and are increasingly used in food/feed, pharmaceutical or cosmetic industries. Existing techniques presently used for Yucca steroidal saponin quantification remain either inaccurate and misleading or accurate but time consuming and cost prohibitive. The method reported here addresses all of the above challenges. HPLC/ELSD technique is an accurate and reliable method that yields results of appropriate repeatability and reproducibility. This method does not over- or under-estimate levels of steroidal saponins. HPLC/ELSD method does not require each and every pure standard of saponins, to quantify the group of steroidal saponins. The method is a time- and cost-effective technique that is suitable for routine industrial analyses. HPLC/ELSD methods yield a saponin fingerprints specific to the plant species. As the method is capable of distinguishing saponin profiles from taxonomically distant species, it can unravel plant adulteration issues.

Carnosic acid

Carnosic acid (salvin), which possesses antioxidative and antimicrobial properties, is increasingly exploited within the food, nutritional health and cosmetics industries. Since its first extraction from a Salvia species (∼70 years ago) and its identification (∼50 years ago), numerous articles and patents (∼400) have been published on specific food and medicinal applications of Rosmarinus and Salvia plant extracts abundant in carnosic acid. In contrast, relevant biochemical, physiological or molecular studies in planta have remained rare. In this overview, recent advances in understanding of carnosic acid distribution, biosynthesis, accumulation and role in planta, and its applications are summarised. We also discuss the deficiencies in our understanding of the relevant biochemical processes, and suggest the molecular targets of carnosic acid. Finally, future perspectives and studies related to its potential roles are highlighted.

Mathematically combined half-cell reduction potentials of low-molecular-weight thiols as markers of seed ageing

The half-cell reduction potential of the glutathione disulphide (GSSG)/glutathione (GSH) redox couple appears to correlate with cell viability and has been proposed to be a marker of seed viability and ageing. This study investigated the relationship between seed viability and the individual half-cell reduction potentials (E(i)s) of four low-molecular-weight (LMW) thiols in Lathyrus pratensis seeds subjected to artificial ageing: GSH, cysteine (Cys), cysteinyl-glycine (Cys-Gly) and γ-glutamyl-cysteine (γ-Glu-Cys). The standard redox potential of γ-Glu-Cys was previously unknown and was experimentally determined. The E(i)s were mathematically combined to define a LMW thiol-disulphide based redox environment (E(thiol-disulphide)). Loss of seed viability correlated with a shift in E(thiol-disulphide) towards more positive values, with a LD(50) value of -0.90 ± 0.093 mV M (mean ± SD). The mathematical definition of E(thiol-disulphide) is envisaged as a step towards the definition of the overall cellular redox environment, which will need to include all known redox-couples.

Changes in volatiles and glycosides during fruit maturation of two contrasted tomato ( Solanum lycopersicum ) lines

The relationship between fruit maturation and volatile contents was investigated in two contrasted Cervil (CER) and Levovil (LEV) tomato ( Solanum lycopersicum ) lines. As fruits ripened, their volatile contents mainly increased. Although some compounds displayed contrasting patterns, overall, volatiles were clearly more abundant and conferred stronger aromas to CER than to LEV fruits. This intervarietal difference in volatile contents yielding much lower volatile contents in LEV was further investigated to determine whether it is due to a higher capacity of volatile glycosylation within LEV as compared to CER. Again, glycosides mainly increased during fruit maturation and were more abundant within CER than within LEV. Overall glycoside findings were indicative of a superior capacity to biosynthesize rather than an inferior capacity to glycosylate volatiles of CER. Eugenol and 2-methoxyphenol volatiles were exceptional compounds as they remained at higher levels in maturing LEV than in CER. 2-Methylthioacetaldehyde was for the first time identified as putatively related to differences of aroma between lines, as it was abundant in Cervil but absent in Levovil. Considering the described odor value of these three products, they should contribute differently to the particular olfactive features of LEV and CER fruits.

Glutathione half-cell reduction potential: a universal stress marker and modulator of programmed cell death?

The elucidation of factors that contribute to cell viability loss is presently compromised by the lack of a universal measure that quantifies "stress." We have investigated mechanisms of viability loss in plant seeds to find a reliable marker of stress response. Oxidative damage has previously been correlated with degenerative processes and death, but how exactly this contributes to viability loss is unknown. We show in four species subjected to ageing or desiccation that seed viability decreased by 50% when the half-cell reduction potential of glutathione (E(GSSG/2GSH)), a major cellular antioxidant and redox buffer, increased to -180 to -160 mV. We then conducted a metaanalysis of data representative of 13 plant and fungal orders to show that plant stress generally becomes lethal when E(GSSG/2GSH) exceeds -160 mV. We put forward that this change in E(GSSG/2GSH) is part of the signaling cascade that initiates programmed cell death (PCD), finally causing internucleosomal DNA fragmentation in the final, or execution phase, of PCD. E(GSSG/2GSH) is therefore a universal marker of plant cell viability and allows us to predict whether a seed will live, germinate, and produce a new plant, or if it will die.

Isolation of high-quality RNA from polyphenol-, polysaccharide- and lipid-rich seeds

Seed polyphenols, polysaccharides and lipids often interfere with or degrade RNA, restricting its yield and quality. Existing RNA isolation methods specifically alleviate one or two of these challenges, but are usually designed for a single species rather than for a broad biodiversity. Many protocols also do not eliminate chromosomal DNA, which causes false positives in gene expression studies. The method reported here addresses all of the above challenges. The concentration of the phenol blocker polyvinylpyrrolidone in the extraction buffer was optimised for use on a broader range of species. DNase I was added to eliminate chromosomal DNA and the timing of this step was optimised. Lipids were removed by centrifugation. Polysaccharides and proteins, including excess DNase I, were separated from RNA during ethanol precipitation of nucleic acids. In seeds of five plant species from four taxonomically distant families, significant amounts of RNA were isolated in less than half the time typically required by previously reported methods. Colorimetric tests showed that the isolated RNA was free from interfering contaminants. In addition, reverse transcription-PCR confirmed that the isolated RNA was of appropriate quality and integrity for gene expression studies.