BioChem

Background: The root extracts of Waltheria indica L. (Malvaceae) are used in African traditional medicine to treat erectile dysfunction (ED). This use, however, is not supported by compelling scientific data or linked to any characterized active constituent(s). Therefore, our aim was to determine the major active compound(s) in the ethanol root extract of Waltheria indica (EEWI) responsible for the possible aphrodisiac action and the probable mechanism(s) involved. Methods: Unbiased screening by high-performance liquid chromatography was used to identify the phenolic compounds in the EEWI. These compounds were docked with phosphodiesterase-5 (PDE-5), arginase II, and aromatase to predict aphrodisiac-related mechanisms of action. Rutin (15, 30, and 60 mg/kg), the top in silico hit, was evaluated, along with EEWI (100, 200, and 400 mg/kg), for aphrodisiac properties in rats in vivo and the possible mechanisms underlying its actions. Results: Rutin demonstrated strong PDE-5 binding affinity (docking score: −11.048 kcal/mol). EEWI and rutin significantly reduced mount latency and increased mount frequency, intromission latency, intromission frequency, ejaculatory latency, and post-ejaculatory interval. Rutin but not EEWI significantly reduced penile PDE-5 levels. EEWI and rutin both significantly increased penile cGMP levels. EEWI (400 mg/kg) and all doses of rutin significantly increased testicular and plasma testosterone levels. All doses of EEWI and rutin reduced plasma prolactin levels but did not affect testicular cholesterol levels. Neither whole-body weight nor penile or testicular weights were affected by the treatment. Conclusions: EEWI and its rutin constituent possess aphrodisiac properties. As a mechanism, rutin lowers penile PDE-5 levels, and both rutin and EEWI increase cGMP and testosterone levels but reduce prolactin levels. Therefore, our study offers empirical evidence that highlights the potential aphrodisiac effect of EEWI.

Background/Objectives: Reversible thylakoid protein phosphorylation regulates photosynthetic acclimation by coordinating light harvesting, electron transport, and photoprotection. This review examines STN7/STN8 kinases, their counteracting phosphatases, and their established and emerging substrates in response to abiotic stress. Methods: This narrative review synthesizes literature retrieved from Web of Science, Scopus, PubMed, and Google Scholar, focusing on kinase–phosphatase regulation, substrate specificity, phosphoproteomics, and photosynthetic acclimation. Results: STN7 and STN8 regulate complementary but partially overlapping phosphorylation networks. STN7 mediates light-harvesting complex II (LHCII) phosphorylation, state transitions, and excitation-energy redistribution, whereas STN8 phosphorylates photosystem II (PSII) core proteins involved in PSII repair and recovery. Their regulation is linked to the photosynthetic electron transport chain; the redox state of plastoquinone (PQ) promotes STN7 activation via cytochrome b₆f, while the upstream regulation of STN8 remains unclear. Abiotic stresses disrupt electron transport and PQ redox homeostasis in stress- and time-dependent ways that may shape phosphorylation responses. Beyond canonical substrates, phosphoproteomic and genetic studies extend the STN7/STN8-associated network to calcium signaling, electron partitioning, thylakoid architecture, metabolism, and chloroplast gene regulation. However, the kinase dependence and physiological significance of many emerging targets remain unresolved and may differ among species and lineages. Conclusions: STN7/STN8-mediated thylakoid protein phosphorylation links chloroplast redox signaling with photosynthetic acclimation under abiotic stress. Future studies combining direct substrate validation, kinase–phosphatase genetics, redox measurements, and comparative analyses across photosynthetic lineages are needed to distinguish conserved mechanisms from stress- and species-dependent responses.

Background/Objectives: Carbon dots (CDs) are fluorescent carbon-based nanomaterials attracting considerable attention recently because of their high photostability, tunable luminescence characteristics, low toxicity, and versatile surface chemistry. In this study, Hematoxylin (HT), a naturally occurring phenolic aromatic compound used as a histological staining dye, abundant in hydroxyl functional groups, was selected as a sustainable precursor for CD synthesis. The intrinsic fluorescence and favorable carbonization characteristics of HT are also value-added advantages for CDs. Methods: The use of citric acid (CA) during synthesis improves fluorescence behavior, colloidal stability, and biological performance of CDs. HT-based CDs prepared via the bottom-up synthesis method employing the hydrothermal technique as multifunctional fluorescent materials were also evaluated for potential bioimaging and light-activated antimicrobial applications. Results: The obtained HT-based CDs displayed good aqueous dispersion properties. HT CDs had a hydrodynamic diameter of 115 ± 1 nm and showed a fluorescence emission intensity of 5181 a.u. at λ_em = 329 nm when excited at λ_ex = 300 nm. In contrast, HT:CA CDs prepared at a 1:1 HT-CA weight ratio had a hydrodynamic diameter of 310 ± 19 nm and exhibited a significantly higher fluorescence emission intensity, e.g., 31,840 a.u. at λ_em = 332 nm when excited at λ_ex = 300 nm. Antioxidant studies of HT CDs and HT CDs using four different assays revealed that the antioxidant capacity of HT was partially retained and exhibited a concentration-dependent response. Notably, HT:CA CDs demonstrated significantly enhanced antimicrobial performance under UV-A irradiation compared to HT CDs, with bacterial cell viability calculated as 13 ± 4% for HT:CA CDs and 59 ± 2% for HT CDs. Moreover, HT CDs and HT:CA CDs demonstrated significantly enhanced cytocompatibility on the L929 fibroblast cell line, high cell viability up to 200 μg/mL, versus toxic HT molecules even at 100 μg/mL. Conclusions: HT-based CDs, particularly HT:CA CDs, demonstrated favorable fluorescence, antioxidant, antimicrobial, and cytocompatibility properties, supporting their potential application as multifunctional fluorescent materials for bioimaging and light-activated antimicrobial applications.