Factors affecting the content of the ursolic and oleanolic acid in apple peel: influence of cultivars, sun exposure, storage conditions, bruising and Penicillium expansum infection

Promising Ursolic Acid as a Novel Antituberculosis Agent: Current Progress and Challenges

Tuberculosis (TB) stands as the second most prevalent cause of global human mortality from infectious diseases. In 2022, the World Health Organization documented an estimated number of global TB cases reaching 7.5 million, which causes death for 1.13 million patients. The continuous growth of drug-resistant TB cases due to various mutations in the Mycobacterium tuberculosis (MTB) strain, raises the urgency of the exploration of novel anti-TB treatments. Ursolic acid (UA) is a natural pentacyclic triterpene found in various plants that has shown potential as a novel anti-TB agent. This review aims to provide an overview of the therapeutic prospects of UA against MTB, with a particular emphasis on in silico, in vitro, and in vivo studies. Various mechanisms of action of UA against MTB are briefly recapped from in silico studies, such as enoyl acyl carrier protein reductase inhibitors, FadA5 (Acetyl-CoA acetyltransferase) inhibitors, tuberculosinyl adenosine transferase inhibitors, and small heat shock protein 16.3 inhibitor. The potential of UA to overcome drug resistance and its synergistic effects with existing antituberculosis drugs are briefly explained from in vitro studies using a variety of methods, such as Microplate Alamar Blue Assay, Mycobacteria Growth Indicator Tube 960 and Resazurin Assays, morphological change evaluation using transmission electron microscopy, and in vivo studies using BALB/C infected with multi drug resistant clinical isolates. Besides its promising mechanism as an antituberculosis drug, its complex chemical composition, limited availability and supply, and lack of intellectual property are also reviewed as those are the most frequently occurring challenges that need to be addressed for the successful development of UA as novel anti-TB agent.

Oleanolic acid alleviate intestinal inflammation by inhibiting Takeda G-coupled protein receptor (TGR) 5 mediated cell apoptosis

Oleanolic acid (OA) is a bioactive compound present in plant-based foods known for its beneficial impact on gastrointestinal health, specifically in alleviating diarrhea. Nonetheless, the underlying mechanisms by which OA mitigates gut epithelial damage have yet to be elucidated. In this study, OA significantly markedly ameliorated adverse effects induced by Dextran Sulfate Sodium (DSS), including weight loss and epithelial morphological damage in a murine model. Remarkably, compared to normal mice, standalone administration of OA had no discernible impact on the animals. Concurrently, we identified a significant up-regulation in the expression levels of TGR5 and BAX in the intestines of DSS-exposed mice, coupled with a decline in Bcl2 expression. Correlation analyses revealed a robust association between TGR5 and BAX expression. Oral administration of OA efficaciously counteracted these alterations. To probe the role of TGR5 in cellular apoptosis, further, a lentivirus transfection approach was utilized to induce TGR5 overexpression in intestinal epithelial cells (IPEC-J2). RNA sequencing indicated that TGR5 overexpression significantly influenced biological processes, particularly in modulating cellular activation and intercellular adhesion, in contrast to the control group cells. Functional assays substantiated that TGR5 overexpression compromised cell viability and accelerated apoptosis. Notably, OA treatment in TGR5-overexpressed cells restored cell viability, suppressed TGR5 and BAX expression, and augmented Bcl2 expression. In sum, our data suggest that OA mitigates intestinal epithelial apoptosis and bolsters cellular proliferation by downregulating TGR5. This research provides valuable insights into the prospective utility of OA as a functional food supplement or adjunctive therapeutic agent for enhancing gastrointestinal health.

Triterpenoids of Three Apple Cultivars—Biosynthesis, Antioxidative and Anti-Inflammatory Properties, and Fate during Processing

Triterpenoids are a group of secondary plant metabolites, with a remarkable pharmacological potential, occurring in the cuticular waxes of the aerial parts of plants. The aim of this study was to analyze triterpenoid variability in the fruits and leaves of three apple cultivars during the growing season and gain new insights into their health-promoting properties and fate during juice and purée production. The identification and quantification of the compounds of interest were conducted using gas chromatography coupled with mass spectrometry. The waxes of both matrices contained similar analytes; however, their quantitative patterns varied: triterpenic acids prevailed in the fruits, while higher contents of steroids and esterified forms were observed in the leaves. The total triterpenoid content per unit area was stable during the growing season; the percentage of esters increased in the later phases of growth. Antioxidative and anti-inflammatory properties were evaluated with a series of in vitro assays. Triterpenoids were found to be the main anti-inflammatory compounds in the apples, while their impact on antioxidant capacity was minor. The apples were processed on a lab scale to obtain juices and purées. The apple purée and cloudy juice contained only some of the triterpenoids present in the raw fruit, while the clear juices were virtually free of those lipophilic compounds.

Phytochemical and Antioxidant Profile of the Medicinal Plant Melia azedarach Subjected to Water Deficit Conditions

Environmental stress triggered by climate change can alter the plant’s metabolite profile, which affects its physiology and performance. This is particularly important in medicinal species because their economic value depends on the richness of their phytocompounds. We aimed to characterize how water deficit modulated the medicinal species Melia azedarach’s lipophilic profile and antioxidant status. Young plants were exposed to water deficit for 20 days, and lipophilic metabolite profile and the antioxidant capacity were evaluated. Leaves of M. azedarach are rich in important fatty acids and oleamide. Water deficit increased the radical scavenging capacity, total phenol, flavonoids, and catechol pools, and the accumulation of β-sitosterol, myo-inositol, succinic acid, sucrose, d-glucose and derivatives, d-psicofuranose, d-(+)-fructofuranose, and the fatty acids stearic, α-linolenic, linoleic and palmitic acids. These responses are relevant to protecting the plant against climate change-related stress and also increase the nutritional and antioxidant quality of M. azedarach leaves.

Determination of the ursolic and oleanolic acids content with the antioxidant capacity in apple peel extract of various cultivars

Apples are rich sources of ursolic acid (UA) and oleanolic acid (OA) which are the major and most prominent triterpenes in the peel of an apple. Pentacyclic triterpenes are ideal nutraceuticals due to their ability to reduce the risk of many life-threatening diseases such as cancer, cardiovascular and diabetes. This study was to determine the content of UA and OA in the apple peel extract from different cultivars grown in South Africa as well as the correlation of their content level with antioxidant capacity. Quantitative analysis of UA and OA in apple peels from three cultivars; red delicious (RD), royal gala (RG) and granny smith (GS) apples was carried out using HPLC and their antioxidant capacity was analyzed using the DPPH assay. The RD showed the highest content of UA and OA (248.02 ± 0.08 µg/ml and 110.00 ± 0.08 µg/ml respectively) in the apple peel extract and also displayed a significantly high level of antioxidant capacity (97.3 ± 0.40%; p < 0.0001) compared to the RG and GS cultivars. A strong positive correlation was noted between the UA, OA and antioxidant capacities of all the cultivars. Only the RD cultivar showed a significant correlation though; UA (r = 0.9570; p = 0.0027) and OA (r = 0.8503; p = 0.0319). This study demonstrated that the RD and RG apple peels possess the highest UA and OA content which invariably increases their antioxidant activities compared to GS apple. Thus, both apple cultivars would be useful and recommended for food consumption and nutraceuticals values to improve human health.

Chemical Profiling of Two Italian Olea europaea (L.) Varieties Subjected to UV-B Stress

The depletion of the stratospheric ozone layer due to natural and/or anthropogenic causes decreases the amount of UV-B radiation filtered, and consequently increases the risk of potential damage to organisms. In the Mediterranean region, high UV-B indices are frequent. Even for species typical of this region, such as the olive tree, the progressive increase in UV-B radiation represents a threat. This work aimed to understand how high UV-B radiation modulates the phenolic and lipophilic profile of olive varieties, and identify metabolites that enhance olive stress tolerance. Two Italian olive varieties were subjected to chronic UV-B stress, and leaves were analyzed by gas and liquid chromatography. The results indicated that the most representative phenolic and lipophilic compounds of Giarraffa and Olivastra Seggianese were readjusted in response to UV-B stress. The Giarraffa variety seemed better suited to prolonged UV-B stress, possibly due to the higher availability of flavonoids that could help control oxidative damage, and the accumulation of hydroxycinnamic acid derivatives that could provide strong UV-B shield protection. In addition, this variety contained higher levels of fatty acids (e.g., palmitic, α-linolenic, and stearic acids), which can help to maintain membrane integrity and accumulate more sorbitol (which may serve as an osmoprotectant or act a free-radical scavenger), terpenes, and long-chain alkanes, providing higher protection against UV-B stress.

Phenolic and lipophilic metabolite adjustments in Olea europaea (olive) trees during drought stress and recovery

The frequency of combined stress events is increasing due to climate change and represents a new threat to olive (Olea europaea) culture. How olive plants modulate their profile of metabolites under multiple stressing agents remains to unveil, although several metabolites affect plants' resilience, and olive production and quality. Young olive plants were exposed to a water deficit (WD) for 30 days and then exposed to a shock of heat and high UVB-radiation (WD^HS+UVB treatment) for 2 days. Then, plants were re-watered and grown under optimal conditions (recovery) for 30 days. Leaves were collected after stress and recovery, analysed by liquid and gas chromatography, and the lipophilic and phenolic profiles were characterized. Except for the oleuropein derivatives, the qualitative metabolite profile was similar during stress and recovery. Metabolite increases or decreases in response to stress were stronger when WD was followed by WD^HS+UVB treatment. Phenolic compounds (luteolin-7-O-glucoside, quercetin-3-O-rutinoside, apigenin-7-O-glucoside, chrysoeriol-7-O-glucoside, kaempferol derivatives, oleuropein, and lucidumoside C) were the most involved after WD and WD^HS+UVB, possibly acting as reactive oxygen species (ROS) scavengers. Lipophilic compounds were more relevant during the recovery period. The catabolism of fatty acids and carbohydrates may provide the necessary energy for plant performance reestablishment, and sterols, long-chain alkanes, and terpenes metabolic pathways may be shifted for the production of compounds with a more important stress protection role. This work highlights for the first time that tolerance mechanisms activated by WD in olive plants are related to metabolite changes, that are adjusted when other stressors are overlapped (WD^HS+UVB), and also help the plants recover. This metabolites' plasticity represents an essential contribution to understanding how dry-farming olive orchards may deal with drought combined with high UV-B or heat.

Physiological and Metabolite Reconfiguration of Olea europaea to Cope and Recover from a Heat or High UV-B Shock

To understand how olives reconfigure their metabolism to face stress shock episodes, plants from the economically relevant olive (Olea europaea cv. Cobrançosa) were exposed to high UV-B radiation (UV-B, 12 kJ m^-2 d^-1) or heat shock (HS, 40 °C) for two consecutive days. The physiological responses and some important lipophilic compounds were evaluated immediately (day 0) and 30 days after UV-B or HS episodes. Both treatments induced a reduction of the olive physiological performance, particularly increasing cell membrane damages and proline pool and at the same time reducing chlorophyll levels, the quantum yield of photosystem II (Φ_PSII), and the efficiency of excitation energy capture by open photosystem II (PSII) reaction centers (F'_v/F'_m). Nevertheless, the HS episode caused more adverse effects, additionally reducing the pool of protective pigments (carotenoids) and the maximum efficiency of PSII (with F₀ increase). In the UV-B treatment, despite the higher lipid peroxidation, the activation of some stress protective mechanisms (e.g., increase of NPQ and carotenoids and remobilization of some metabolites, such as phytol and proline) might have contributed to avoiding photoinhibition. Thirty days after stress relief, the performance of olives from both treatments recovered similarly, in part due to the metabolites' adjustments that contributed to strengthened stress protection (an increase of long-chain alkanes) and provided energy (through the use of soluble sugars, mannitol, and myo-inositol) for re-establishment. Other metabolites, like anthocyanins and squalene, also have an important role in responding specifically to HS or UV-B recovery for helping in the oxidative damage control. These data contribute to understanding how young olive plants may deal with climatic episodes when being transferred from nurseries to field orchards, under the actual context of climate change.

Cuticular waxes of nectarines during fruit development in relation to surface conductance and susceptibility to Monilinia laxa

The cuticle is composed of cutin and cuticular waxes, and it is the first protective barrier to abiotic and biotic stresses in fruit. In this study, we analysed the composition of and changes in cuticular waxes during fruit development in nectarine (Prunus persica L. Batsch) cultivars, in parallel with their conductance and their susceptibility to Monilinia laxa. The nectarine waxes were composed of triterpenoids, mostly ursolic and oleanolic acids, phytosterols, and very-long-chain aliphatics. In addition, we detected phenolic compounds that were esterified with sugars or with triterpenoids, which are newly described in cuticular waxes. We quantified 42 compounds and found that they changed markedly during fruit development, with an intense accumulation of triterpenoids during initial fruit growth followed by their decrease at the end of endocarp lignification and a final increase in very-long-chain alkanes and hydroxylated triterpenoids until maturity. The surface conductance and susceptibility to Monilinia decreased sharply at the beginning of endocarp lignification, suggesting that triterpenoid deposition could play a major role in regulating fruit permeability and susceptibility to brown rot. Our results provide new insights into the composition of cuticular waxes of nectarines and their changes during fruit development, opening new avenues of research to explore brown rot resistance factors in stone fruit.

Canopy attachment position influences metabolism and peel constituency of European pear fruit

BACKGROUND

Inconsistent pear fruit ripening resulting from variable harvest maturity within tree canopies can contribute to postharvest losses through senescence and spoilage that would otherwise be effectively managed using crop protectant and storage regimes. Because those inconsistencies are likely based on metabolic differences, non-targeted metabolic profiling peel of 'd'Anjou' pears harvested from the external or internal canopy was used to determine the breadth of difference and link metabolites with canopy position during long-term controlled atmosphere storage.

RESULTS

Differences were widespread, encompassing everything from expected distinctions in flavonol glycoside levels between peel of fruit from external and internal canopy positions to increased aroma volatile production and sucrose hydrolysis with ripening. Some of the most substantial differences were in levels of triterpene and phenolic peel cuticle components among which acyl esters of ursolic acid and fatty acyl esters of p-coumaryl alcohol were higher in the cuticle of fruit from external tree positions, and acyl esters of α-amyrin were elevated in peel of fruit from internal positions. Possibly the most substantial dissimilarities were those that were directly related to fruit quality. Phytosterol conjugates and sesquiterpenes related to elevated superficial scald risk were higher in pears from external positions which were to be potentially rendered unmarketable by superficial scald. Other metabolites associated with fruit aroma and flavor became more prevalent in external fruit peel as ripening progressed and, likewise, with differential soluble solids and ethylene levels, suggesting the final product not only ripens differentially but the final fruit quality following ripening is actually different based on the tree position.

CONCLUSIONS

Given the impact tree position appears to have on the most intrinsic aspects of ripening and quality, every supply chain management strategy would likely lead to diverse storage outcomes among fruit from most orchards, especially those with large canopies. Metabolites consistently associated with peel of fruit from a particular canopy position may provide targets for non-destructive pre-storage sorting used to reduce losses contributed by this inconsistency.

Fragmentation of the main triterpene acids of apple by LC-APCI-MSn

In this paper, we investigated the fragmentation of the main triterpene acids of apple using an liquid chromatography atmospheric pressure chemical ionization mass spectrometry (LC-APCI-MSⁿ ) approach and high-resolution mass spectrometry (HR-MS) (Q-TOF). Triterpenes were isolated using semipreparative high-performance liquid chromatography, and chemical structures were elucidated by HR-MS and nuclear magnetic resonance spectroscopy. Finally, compounds were used to study MSⁿ behavior in ion trap. Isolated triterpenes present similar structures, bearing carboxyl group linked to C-17 and different substitutions. We observed significant changes in MS² spectra, which were useful for further compound identification. The observed fragments allowed the discrimination of different derivatives, namely, pomaceic, annurcoic, euscaphic, pomolic, corosolic, maslinic, betulinic, oleanolic, and ursolic acids. The proposed method allows a rapid identification of triterpene acids, and it could be useful for the analysis of these compounds in apple fruits and in other natural sources.

UV-B radiation modulates physiology and lipophilic metabolite profile in Olea europaea

Ultraviolet-B (UV-B) radiation plays an important role in plant photomorphogenesis. Whilst the morpho-functional disorders induced by excessive UV irradiation are well-known, it remains unclear how this irradiation modulates the metabolome, and which metabolic shifts improve plants' tolerance to UV-B. In this study, we use an important Mediterranean crop, Olea europaea, to decipher the impacts of enhanced UV-B radiation on the physiological performance and lipophilic metabolite profile. Young olive plants (cv. 'Galega Vulgar') were exposed for five days to UV-B biologically effective doses of 6.5 kJ m^-2 d^-1 and 12.4 kJ m^-2 d^-1. Cell cycle/ploidy, photosynthesis and oxidative stress, as well as GC-MS metabolites were assessed. Both UV-B treatments impaired net CO₂ assimilation rate, transpiration rate, photosynthetic pigments, and RuBisCO activity, but 12.4 kJ m^-2 d^-1 also decreased the photochemical quenching (qP) and the effective efficiency of PSII (Φ_PSII). UV-B treatments promoted mono/triperpene pathways, while only 12.4 kJ m^-2 d^-1 increased fatty acids and alkanes, and decreased geranylgeranyl-diphosphate. The interplay between physiology and metabolomics suggests some innate ability of these plants to tolerate moderate UV-B doses (6.5 kJ m^-2 d^-1). Also their tolerance to higher doses (12.4 kJ m^-2 d^-1) relies on plants' metabolic adjustments, where the accumulation of specific compounds such as long-chain alkanes, palmitic acid, oleic acid and particularly oleamide (which is described for the first time in olive leaves) play an important protective role. This is the first study demonstrating photosynthetic changes and lipophilic metabolite adjustments in olive leaves under moderate and high UV-B doses.

Methyl Jasmonate and Salicylic Acid Enhanced the Production of Ursolic and Oleanolic Acid in Callus Cultures of Lepechinia Caulescens

Background

The production of triterpenes from plants for pharmacological purposes varies in concentration, due to genetic and environmental factors. In vitro culture enables the control and increase of these bioactive molecules.

Objective

To evaluate the effect of plant growth regulators and elicitors in the induction of calli and the production of ursolic acid (UA) and oleanolic acid (OA) in Lepechinia caulescens.

Materials and Methods

Leaf explants were exposed for the induction of calli at different concentrations and combinations of 2,4-dichlorophenoxyacetic acid (2,4-D) and 6-benzylaminopurine (BAP). Methyl jasmonate (MJ) and salicylic acid were used as elicitors. High-performance liquid chromatography method was used to quantify UA and OA content in each treatment.

Results

Treatment with 3.0 mg/L of 2,4-D and 0.1 mg/L of BAP produced the best results for calli induction and production of UA (1.57 mg/g dry weight [DW]) and OA (1.13 mg/g DW). Both elicitors facilitated the accumulation of triterpenes.

Conclusion

The combination of auxins and cytokinins showed favorable results for the induction of calli. Variation concerning the accumulation of UA and OA was observed between treatments. MJ increased the production of triterpenes five times after 8 h of exposure, compared to control treatment. There is a greater accumulation of UA (16.58 mg/g DW) and OA (1.94 mg/g DW) in leaves of wild plants.

SUMMARY

Callus cultures of Lepechinia caulescens were obtained from leaf explants treated with 2,4-dichlorophenoxyacetic acid and 6-bencylaminopurineResulting cultures were elicited with methyl jasmonate (MJ) and salicylic acid to increase the production of the triterpenes, ursolic acid (UA), and oleanolic acid (OA)The cultures elicited with MJ increased the production of UA and OA five times, as compared to the control. Abbreviations used: 2,4-D: 2,4-dichlorophenoxyacetic acid, BAP: 6-benzylaminopurine, DW: Dry weight, MJ: Methyl jasmonate, OA: Oleanolic acid, PGRs: Plant growth regulators, UA: Ursolic acid, SA: Salicylic acid.

Recent developments on the extraction and application of ursolic acid. A review

Ursolic acid (UA) is a pentacyclic triterpenoid widely found in herbs, leaves, flowers and fruits; update information on the major natural sources or agro-industrial wastes is presented. Traditional (maceration, Soxhlet and heat reflux) and modern (microwave-, ultrasound-, accelerated solvent- and supercritical fluid) extraction and purification technologies of UA, as well as some patented process, are summarized. The great interest in this bioactive compound is related to the beneficial effects in human health due to antioxidant, antimicrobial, anti-inflammatory, hepatoprotective, immunomodulatory, anti-tumor, chemopreventive, cardioprotective, antihyperlipidemic and hypoglycemic activities, and others. UA may augment the resistance of the skin barrier to irritants, prevent dry skin and could be suitable to develop antiaging products. The development of nanocrystals and nanoparticle-based drugs could reduce the side effects of high doses of UA in organisms, and increase its limited solubility and poor bioavailability of UA which limit the potential of this bioactive and the further applications. Commercial patented applications in relation to cosmetical and pharmaceutical uses of UA and its derivatives are surveyed.