Light vs. Brain Cells: How Photodynamic Therapy Impacts Neurons & Astrocytes
"Uncover the surprising effects of photodynamic therapy (PDT) on brain cells and learn how this cancer treatment can trigger calcium signals and lipid peroxidation in neurons and astrocytes."
Photodynamic therapy (PDT) is a powerful method for destroying brain tumors by producing reactive oxygen species (ROS), leading to oxidative stress and the death of cancerous cells. Radachlorin, a chlorine derivative photosensitizer, is often used in PDT due to its ability to quickly accumulate in tumor tissue and rapidly clear from the body. However, the effects of radachlorin on healthy brain cells remain unclear.
One major effect of PDT is the induction of reactive oxygen species (ROS). While excessive ROS production can trigger cell death, smaller amounts can play a physiological role, including acting as stimuli for calcium signaling. Calcium ions are vital for regulating intracellular processes and cell-to-cell communication, especially in excitable cells like neurons and astrocytes.
Research has shown that PDT can increase intracellular calcium levels by activating calcium channels or releasing calcium from internal stores. Given the importance of understanding how PDT impacts healthy brain cells, this article delves into the specific effects of radachlorin on calcium signaling and lipid peroxidation in neurons and astrocytes.
Current Evidence in Brain Tumors
Photodynamic therapy has been investigated for malignant brain tumors, including surgically unresectable gliomas. One study examined the safety and efficacy of Talaporfin sodium in patients whose tumors invaded brain areas associated with language and motor functions. Reviews also describe PDT as an emerging treatment modality and report that it has been used for more than 30 years in patients with brain cancer. Publication tracking shows continued research activity in photodynamic therapy applications for malignant brain tumors.
Practical Limits of PDT
Photodynamic therapy combines a photosensitizer, light, and tissue oxygen, but several factors can limit its performance. Reviews identify challenges involving light delivery, tissue oxygenation, and the inherent properties of photosensitizers. Researchers have designed and synthesized different photosensitizers to address these limitations. Another reported concern is that PDT may not eliminate every abnormal cell, potentially leaving residual disease and contributing to incomplete responses or recurrence.
From Heliotherapy to PDT
The historical development of photodynamic therapy includes photodynamic reactions first observed by scientists from three countries in the early twentieth century. The treatment's distant origins are also associated with heliotherapy, which was practiced in ancient civilizations including Egypt, China, India, Greece, and Rome. Modern PDT uses photosensitizers activated by light at an absorbance wavelength, in either the visible or near-infrared range. The resulting reactions can produce reactive oxygen species in the presence of molecular oxygen.
Calcium Signals and Brain Cell Response: What Happens?
Researchers investigated how radachlorin affects primary cultures of cortical neurons and astrocytes using live cell imaging. They found that irradiation in the presence of radachlorin induced calcium signals in both neurons and astrocytes, indicating a direct impact on these brain cells.
- Internal Calcium Stores: The calcium signal depended on internal calcium stores within the cells. Even in a calcium-free environment, the signal persisted.
- Endoplasmic Reticulum (ER): Blocking the ER's calcium stores with thapsigargin (an inhibitor of SERCA) eliminated the calcium response.
- Phospholipase C (PLC): Inhibitors of phospholipase C (U73122 and Trolox) suppressed the calcium response, indicating PLC's involvement.
- Lipid Peroxidation: Radachlorin induced lipid peroxidation in both neurons and astrocytes.
Mapping Neural Effects
Recent research is examining how photodynamic therapy affects healthy brain tissue, rather than focusing only on clinical outcomes. A 2025 review notes that the molecular mechanisms underlying PDT effects on the healthy brain have not yet been thoroughly characterized. It summarizes potential effects involving neural tissue, brain vasculature, and the blood-brain barrier. Other recent reviews address nanotechnology-assisted PDT, its mechanisms in brain-related pathologies, and technological advances and challenges.
Unresolved Risks
PDT is not uniformly effective, and its results may depend on how well light reaches the target, how much oxygen is available, and how the photosensitizer behaves. Because abnormal cells may survive treatment, an incomplete response or recurrence remains possible. Evidence concerning effects on healthy neural cells is still developing, so conclusions about long-term neuronal or astrocyte outcomes should remain cautious.
PDT Among Light-Based Approaches
Photodynamic therapy is described as a minimally invasive cancer treatment that uses a photosensitizer activated by light at a specific wavelength. The activated photosensitizer produces reactive oxygen species, distinguishing PDT from broader phototherapy approaches. Phototherapy has also been reviewed as a promising non-invasive modality for age-related brain disorders such as stroke, Alzheimer's disease, and Parkinson's disease. These approaches share the use of light but are discussed in different therapeutic contexts.
Protecting the Brain: Implications of PDT on Healthy Tissue
The study highlights that irradiation with radachlorin induces lipid peroxidation in neurons and astrocytes, either directly or indirectly through ROS production. The fact that Trolox, an antioxidant, blocked the effect of radachlorin irradiation further supports the role of ROS.
A Promising but Developing Field
Taken together, the available material presents PDT as a selective and potentially useful treatment approach, but not as a fully resolved technology. Its effects depend on the interaction among light, photosensitizers, and oxygen. Research on healthy brain tissue and neural mechanisms remains incomplete. Interpretations about neurons and astrocytes should therefore distinguish established treatment principles from findings that are still under investigation.
AI-Enabled Personalization
Future PDT research is expected to explore artificial intelligence as a tool for improving patient outcomes. Recent reviews identify federated learning and explainable AI among the field's future directions. They also emphasize regulatory considerations, reflecting the need to connect technical development with clinical implementation. These priorities are presented as a roadmap for closer collaboration between AI and PDT research communities.
Translation into Care
PDT's broader development must account for technical, biological, and clinical constraints. Light delivery, tissue oxygenation, photosensitizer properties, and incomplete treatment responses can all complicate translation into routine care. Research on brain applications also needs to clarify how treatment interacts with healthy neural tissue and the blood-brain barrier. These unresolved issues suggest that progress will require coordinated work across laboratory, clinical, and regulatory settings.
Patient-Centered Applications
PDT has been investigated in real clinical settings, including treatment of surgically difficult tumors and combined therapy for eye disease. One reported study included 61 patients with polypoidal choroidal vasculopathy treated with PDT and anti-VEGF intravitreal injection. In cancer research, PDT is described as using specific light wavelengths to generate reactive oxygen species that can target tumor cells, damage tumor vasculature, and activate antitumor immunity. These applications illustrate both the clinical reach of PDT and the importance of evaluating benefits and risks for individual patients.
The photodynamic effect of radachlorin may induce ROS production that triggers lipid peroxidation. Oxidized lipids then stimulate phospholipase C, leading to IP3 production and calcium release from the ER.
While PDT is valuable for cancer treatment, this research underscores the importance of considering its effects on healthy brain tissue. Photo-induced calcium signals in neurons and astrocytes could be protective, stimulating processes for cell protection or utilizing oxidized lipids. However, in certain brain areas, this signal might interfere with normal regulatory processes within the central nervous system. Since calcium signaling is energy-intensive, prolonged elevations in calcium, combined with disrupted energy metabolism from PDT, could potentially damage healthy tissue.