Plant species have developed effective defense strategies for colonizing diverse habitats and protecting themselves from numerous attacks from a wide range of organisms, including insects, vertebrates, fungi, and bacteria. The bark of trees in particular constitutes a number of components that protect against unwanted intruders. This review focuses on the antioxidative, dermal immunomodulatory, and antimicrobial properties of bark extracts from European common temperate trees in light of various skin pathogens, wound healing, and the maintenance of skin health. The sustainability aspect, achieved by utilizing the bark, which is considered a byproduct in the forest industry, is addressed, as are various extraction methods applied to retrieve extracts from bark.

Bark is a major by-product of woodworking industries. The contents of several wood species are known to harbor antimicrobial, antiviral, anti-inflammatory and wound-healing capacities. The aim of this work was to identify beneficial properties of Austrian larch, birch and beech bark extracts for their potential usage as additives or active ingredients in dermatological applications. Bacterial agar diffusion assay and resazurin-based broth microdilution assay were used to evaluate anti-bacterial activity. To gain more insight into the cellular response to bark extracts, viability-, scratch-assays and ELISAs were performed. Birch and beech extracts showed strong antimicrobial activities against Gram-positive bacteria, including Cutibacterium acnes, Staphylococcus epidermidis and MRSA. Wound closure was enhanced with birch and beech extracts as compared to controls in the scratch-assays. Whereas beneficial properties of birch bark components have previously been described, the similar effects of beech extracts are novel. The combined positive effect on wound-healing and antimicrobial activity has great potential for the treatment of various skin diseases, including acne in future dermal applications.

This study aimed at identifying factors influencing SARS-CoV-2-specific IgG antibody levels after vaccination and/or infection. Between January 2022 and March 2023, 2000 adults (≥18 years, Salzburg, Austria) participated in this population-based seroprevalence study by providing 3 mL of blood to detect SARS-CoV-2-specific IgG antibodies using an anti-SARS-CoV-2 IgG quantitative assay and by completing a self-designed questionnaire including anthropometric factors, vaccination information, and medical history. For 77 of the participants, a time-course study up to 24 weeks post vaccination or quarantine end was performed. Convalescent-only subjects had the lowest median antibody titer (65.6 BAU/mL) compared to vaccinated and hybrid immunized subjects (p-value < 0.0001) The type of vaccine as well as vaccine combinations significantly influenced the levels of SARS-CoV-2 spike-protein-specific IgG, ranging from a median antibody level of 770.5 BAU/mL in subjects who were vaccinated only to 3020.0 BAU/mL in hybrid immunized subjects (p-value < 0.0001). Over time, a significant decline in the levels of neutralizing antibodies was found. Depending on the subpopulation analyzed, further significant influencing factors included sex assigned at birth, disease severity, chronic diseases, and medication. A hybrid immunization resulted in more robust immune responses. Nevertheless, there were multiple other factors impacting these responses. This knowledge should be included in future vaccination strategies and serve as a guide in the development of personalized medicine.

Raspberry ( Rubus idaeus L.) leaves are an abundant agri‐food by‐product with high potential as a source of natural bioactive compounds. In this study, ultrasound‐assisted extraction (UAE) was applied as a green approach to recover phenolic‐rich extracts, which were subsequently characterized by HPLC–DAD and high‐resolution mass spectrometry (HPLC–HRMS). To elucidate structure–activity relationships, the extract was fractionated by preparative HPLC into phenolic acid/catechin‐, ellagitannin‐, and flavonoid‐rich fractions. Antioxidant activity was evaluated using conventional spectrophotometric assays, kinetic stopped‐flow DPPH measurements, and isothermal calorimetry in bulk sunflower oil and Pickering emulsions stabilized by zein nanoparticles. The ellagitannin‐rich fraction, dominated by sanguiin H‐6, exhibited the highest radical scavenging activity and largely accounted for the antioxidant behavior of the whole extract. While moderate inhibition of lipid oxidation was observed in bulk oil, a marked enhancement of antioxidant efficiency and induction time was achieved in Pickering emulsions, highlighting the importance of interfacial localization effects. Antimicrobial activity tests showed significant inhibition of Gram‐positive foodborne pathogens, particularly Bacillus cereus and Staphylococcus aureus . Overall, this work demonstrates the potential of raspberry leaves as a sustainable source of multifunctional bioactives and underscores the role of green extraction, fractionation, and appropriate delivery systems in maximizing their effectiveness for food applications.

Tree bark is a complex protective tissue that serves both physiological and defensive functions and is particularly rich in phenolic compounds bearing antioxidant, antimicrobial, anti-inflammatory and wound healing properties. The aim of this study was to investigate the antioxidant activity of aqueous bark extracts from 6 European tree species, namely black alder, common beech, silver birch, bird cherry, oak and scots pine using the antioxidant assay Antioxidant Power 1 (AOP1) on a keratinocyte cell line in the light of dermatological applications. The AOP1 assay relies on light-induced intracellular reactive oxygen species (ROS) production that disrupts efflux transport, enabling the accumulation of fluorescent cyanine dyes which can be quantitatively detected by increased fluorescence. Particular attention was placed on the multi-level output provided by AOP1, which includes information on the intracellular antioxidant as well as prooxidative effects of specific compounds and insight into the ground stress level of cells. The results showed that tree bark extracts exhibit a different antioxidant mechanism compared to the well-known antioxidative substance resveratrol. Bark extracts limit the total amount of ROS produced over the duration of the assay, with oak, beech and pine bark extracts showing the highest antioxidant capacity. In contrast, resveratrol delays ROS production over several illumination cycles before levels reach those of untreated cells. Cellular ground stress level was elevated by alder and birch whereas oak, beech and pine reduced the ground stress level similar to that of resveratrol. Results of AOP1 were linked to the constituents of the tree bark extracts derived by Soxhlet extraction, determined by HPLC-DAD analysis. The results highlight the potential of AOP1 as a screening tool with multi-level output and demonstrate the antioxidative potential of six European tree bark extracts, underscoring their promise as sustainable, value-added resources for the development of dermatological therapies targeting oxidative stress–related skin disorders.