Blood Transfusion: When Aged Blood Accelerates Alzheimer's and Young Blood Protects The Brain

Alzheimer's disease doesn't just affect the brain in isolation; it can be influenced by factors present throughout the body, especially in the blood. This study showed that the blood of elderly individuals can accelerate memory loss and the accumulation of toxic proteins in the brain, while young blood can help protect neurons and improve communication between them. These findings suggest that future Alzheimer's treatment may go beyond the brain and consider the organism as a whole.

Alzheimer's disease is the most common form of dementia in the world and affects millions of people, especially those over sixty-five years old. It is a neurodegenerative disease, meaning a condition in which brain cells, called neurons, progressively lose their function and die.

This process occurs slowly and silently over many years, usually beginning with difficulties in recent memory and evolving into problems with language, reasoning, spatial orientation, and autonomy.

The most affected areas of the brain include the hippocampus, essential for memory formation, and regions of the cerebral cortex, responsible for more complex cognitive functions such as planning, decision-making, and social behavior.

One of the main biological mechanisms associated with the disease is the abnormal accumulation of misfolded proteins in the brain, especially beta-amyloid protein, which forms plaques between neurons and impairs communication between them, leading to inflammation and neural degeneration.

Traditionally, Alzheimer's disease has been studied as a problem originating exclusively in the brain. However, recent research has shown that the entire body, and not just the nervous system, can influence the development and progression of the disease.

In this context, blood has come to be seen as a potentially important mediator, as it transports hormones, proteins, inflammatory molecules, and chemical signals capable of affecting brain function.

Previous studies had already suggested that the aging of the organism as a whole could accelerate neurodegenerative processes, but there was still little direct experimental evidence showing how factors present in the blood could interfere with Alzheimer's.

It was with this objective that researchers from different international institutions conducted an experimental study using genetically modified mice to develop brain alterations similar to those observed in human Alzheimer's disease. These animals exhibit, over time, an accumulation of beta-amyloid protein in the brain and memory impairments, and are widely used as a model to study the mechanisms of the disease.

In the experiment, these mice received regular blood infusions from other healthy mice, some young and some old, over thirty weeks. The idea was simple but powerful: to observe whether the “biological environment” created by young or aged blood could accelerate or delay the signs of the disease in the brain.

To make this possible, the researchers performed controlled transfusions, similar to a blood donation in humans, but adapted for laboratory animals. The mice with Alzheimer's received small amounts of blood weekly from young or old donors.

Throughout the experiment, the scientists carefully monitored the animals' behavior and health, ensuring that the observed differences were related to factors present in the blood and not to other external aspects.

At the end of the experimental period, the researchers assessed the mice's memory and learning capacity using a behavioral test called the circular maze test. In this test, the animal needs to learn and remember the location of an exit on a circular platform, using visual cues around it. Animals with preserved memory learn faster and make fewer mistakes, while those with cognitive impairment have greater difficulty.

The results showed that mice that received blood from older animals performed significantly worse, indicating a worsening of memory problems. In contrast, mice that received young blood performed better, suggesting a protective effect on cognitive function.

In addition to behavior, the scientists directly analyzed the animals' brains. To do this, they used techniques that allow visualization and measurement of the accumulation of beta-amyloid protein plaques in brain tissues.

These analyses showed that mice exposed to aged blood had a greater quantity of these plaques, while those that received young blood had less accumulation. This indicates that factors present in the blood can directly influence the mechanisms that lead to the formation of these toxic structures in the brain.

The researchers also conducted an in-depth analysis of the proteins present in the mice's brains, a type of study known as protein analysis. This method allows identifying which proteins are more or less active in a given tissue, offering clues about which cellular processes are being affected.

Alterations were identified in hundreds of proteins, many of them related to communication between neurons, the formation of new synaptic connections, and the control of the electrical activity of brain cells. In particular, a protein involved in controlling calcium entry into neurons stood out, a process essential for the proper functioning of nerve cells. Alterations in this mechanism can lead to both failures in neuronal communication and cell death.

Another relevant finding was the alteration in proteins linked to the endocannabinoid system, a signaling system of the body itself that regulates functions such as memory, mood, and brain inflammation. Changes in this system may contribute to the neural imbalance observed in Alzheimer's disease.

These results help explain why young blood seems to favor a healthier brain environment, while aged blood promotes conditions that accelerate degeneration.

In general, the study demonstrates that blood is not merely a passive transporter of nutrients, but an active agent capable of profoundly influencing brain function. By showing that factors present in aged blood can accelerate the accumulation of toxic proteins and cognitive decline, while components of young blood may have protective effects, the research opens new perspectives for the development of therapies.

Instead of focusing solely on the brain, future strategies could seek to modify the body's systemic environment, either through treatments that alter blood composition or by identifying specific molecules that can be used as medications.

READ MORE:

Infusion of blood from young and old mice modulates amyloid pathology

Matias Pizarro, Ruben Gomez-Gutierrez, Ariel Caviedes, Catalina Valdes, Ute Woehlbier, Cristian Vargas, Mauricio Hernandez, Claudia Duran-Aniotz, Rodrigo Morales

Aging (Albany NY). 2025 Sep 12;17(11):2664-2687. 

doi: 10.18632/aging.206319

Abstract:

Alzheimer's disease (AD) is a neurodegenerative disease characterized by the accumulation of misfolded proteins in the brain. Recently, the impact of blood components in the progression of this disease has come to attention. This study investigates the effects of infusing blood from young and old wild-type mice into transgenic mice that model AD brain amyloidosis. Impaired memory and Aβ accumulation were observed in mice infused with blood from old donors. A proteomic analysis in the brain of these mice identified alterations in components related to synaptogenesis and the endocannabinoid system. The α2δ2 protein, associated with neuronal calcium regulation, was validated as a possible mediator of the observed effects. This study highlights the influence of blood in AD pathology and the identification of potential therapeutic targets.