Abstract Sunlight ultraviolet radiation A and B (UV‐A and UV‐B) affect human skin and may be a cause of cancer. Damage to skin nerve fibers and cell DNA is often observed following excessive unprotected exposure. Plants produce numerous specialized metabolites involved in stress mitigation. Brachycerine, a major leaf glucoside alkaloid from the tree Psychotria brachyceras , absorbs in the UV range and is a powerful antioxidant protecting the photosynthetic machinery against this radiation. Herein, the protective effects of new skincare formulations containing brachycerine or foliar extract were tested on ex vivo human skin exposed to UV. Nerve fibers were identified by immunofluorescence, and UV damage or neuroprotection effects were assessed by image analysis. DNA integrity of UV‐B treated samples was evaluated by comet assays. UV‐A and UV‐B significantly reduced (circa 50%) the measured nerve endings density in the untreated or placebo‐treated samples. Pre‐treatment with tested skincare formulations completely blocked the effects of UV on nerve endings. UV‐B‐induced DNA damage was abolished by both the alkaloid and the extract. Cytotoxicity assays showed that brachycerine was not toxic to mammalian cells. Formulations with brachycerine or leaf extract effectively protected ex vivo human skin exposed to UV, indicating that these phytochemicals are potential candidate components of new broad spectrum natural sunscreens.
Screening for UV-sensitive DNA mutation sites as dosimeters for individual sun exposure, using high-fidelity Duplex Sequencing to reduce false positives and a stringent genome alignment protocol to reduce false negatives, revealed: (i) Sun-exposed human skin contained UV signature mutations (C -> T at a diypyrimidine) >1000-fold more frequently than unexposed neonatal skin, making these mutations sensitive genomic dosimeters for UV exposure. (ii) Tumor suppressor gene hotspot nucleotides (nt) reached variant allele frequency (VAF) 0.1%-10% via 30-3000 fold clonal expansion in occasional biopsies, due to being cancer drivers. (iii) Cyclobutane pyrimidine dimer (CPD) hyperhotspots attained those frequencies in nearly every biopsy, due to profuse creation plus similar to 30-fold clonal expansion. (iv) Neonatal keratinocyte cultures exposed to weeks of low-dose UVB exposure developed mutations at skin cancer tumor suppressor gene hotspot nt rarely and randomly, as expected. (v) CPD hyperhotspots in gene promoters acquired mutations in days at 1000-fold higher frequencies. Sun exposure is the strongest risk factor for skin cancer, so quantifiable UV signature mutations at CPD hyperhotspots in normal skin may make it technically feasible to identify individuals in need of monitoring to ensure early detection.
Photodynamic therapy (PDT) is a clinically established photochemical treatment in which light activation of photosensitizers (PS) generates reactive species, such as reactive oxygen species (ROS), that induce localized cytotoxicity. Beyond direct tumor ablation, PDT can modulate the tumor microenvironment, enhancing antitumor immunity and sensitizing tumors to combination therapies. Related sublethal regimens, termed photodynamic priming (PDP), aim to exploit these immunomodulatory effects. While deep tumors can be accessed using fiber-optic or endoscopic light delivery, extending PDT or PDP to disseminated metastatic disease would require numerous invasive insertions, limiting clinical practicality. Here, we examine immune cell-mediated light delivery, in which luciferase-expressing immune cells infiltrate tumors and act as internal bioluminescent sources for photodynamic activation. Although this strategy could enable PDT and PDP across widespread lesions without external illumination, it remains unclear whether far-field photon emission from luciferase is sufficient to activate PS, or whether near-field mechanisms such as bioluminescence resonance energy transfer are required. Using luciferase-engineered tumor-associated macrophages and verteporfin, we observed no detectable ROS generation or tumor cell cytotoxicity in vitro. Complementary Monte Carlo simulations incorporating tissue scattering and absorption show that achievable photon fluxes are several orders of magnitude below established thresholds for cytotoxic PDT. These findings quantitatively define the limits of far-field bioluminescence and highlight the need for near-field strategies for immune cell mediated PDT and PDP.
5-Aminolevulinic acid (ALA) is administered as a prodrug for tumor fluorescence detection and photodynamic therapy (PDT) after being converted endogenously to the active drug protoporphyrin IX (PpIX). As a substrate of the ABCG2 transporter, PpIX is subject to outward transport in cells with ABCG2 expression, resulting in reduced PpIX fluorescence and PDT effect. Due to the lack of approved ABCG2 inhibitors, lapatinib (Lap), a kinase inhibitor approved for cancer treatment, has been repurposed as an ABCG2 inhibitor for the enhancement of ALA. To provide evidence that Lap enhances ALA by inhibiting ABCG2, we knocked down ABCG2 in four tumor cell lines and evaluated the effects of Lap on enhancing ALA-PpIX fluorescence and PDT in the wild-type and ABCG2-knockdown cell lines. ABCG2 knockdown enhanced ALA-PpIX fluorescence and PDT response, underscoring the importance of ABCG2 in regulating intracellular PpIX accumulation. However, compared with the corresponding wild-type cell lines, Lap induced less enhancement of PpIX fluorescence and PDT in ABCG2-knockdown cell lines, particularly at high concentrations and in cell lines with low ABCG2 activities. By downregulating ABCG2 in tumor cells, we showed that Lap-induced ALA enhancement was reduced, demonstrating that Lap enhances ALA by blocking ABCG2-mediated PpIX efflux.
This work reports the synthesis, physicochemical characterization, and toxicity assessment of bifunctional YVO4:Er,Yb@Fe3O4 nanocomposites designed for optical-magnetic bioapplications. Upconversion nanoparticles (UCNPs) of YVO4:Er,Yb were synthesized and subsequently decorated with Fe3O4 nanoparticles. Nanocomposites exhibit superparamagnetic behavior and efficiently upconvert 980 nm near-infrared radiation (NIR) into visible green emission at 545 nm, making them attractive candidates for multimodal bioimaging. Structural, optical, and magnetic properties were analyzed by X-ray diffraction (XRD), Raman spectroscopy, photoluminescence (PL), transmission electron microscopy (TEM), and vibrating sample magnetometry (VSM). A slight redshift of the characteristic vanadate Raman modes was observed, suggesting interfacial interactions between Fe2+/Fe3+ sites and Y-O or V-O surface groups. Upconversion emission intensity decreased with increasing magnetite content. The lifetime of the green 4S3/2 -> 4I15/2 transition decreased from 5.11 to 4.62 microseconds upon magnetite decoration, indicating enhanced nonradiative relaxation. Toxicity assays using Artemia salina indicated that the nanocomposites are non-toxic, yielding LC50 values of 204 ppm for YVO4:Er,Yb, 698 ppm for Fe3O4, and 345 ppm for the nanocomposite containing 30 wt% Fe3O4. These results demonstrate that Fe3O4 decoration not only imparts magnetic functionality but also reduces the toxicity of UCNPs. The combined optical-magnetic properties and low toxicity support their potential use in photoactive nanomaterial systems.
