Direct causal relationship between intestinal microbiota and Alzheimer’s, the study

Alzheimer’s disease it is a complex neurodegenerative pathology that leads to a decline in cognitive functions and mental health. ‘It is increasingly recognized that Alzheimer’s is a multifactorial disease, influenced substantially by genetic, lifestyle and environmental factors.

‘The alterations of the systemic circulatory environment may accelerate the development of Alzheimer’s disease, but the gut microbiome is emerging as a key element to investigate in Alzheimer’s disease, due to its particular susceptibility to lifestyle and environmental influences. (1)

Recent research have identified specific alterations in the composition of the gut microbiome of Alzheimer’s patients. The intestinal microbiota was therefore considered as ‘an important susceptibility factor in Alzheimer’s disease, without however deducing a direct causal relationship between its alterations and the pathology.

Researchers Irish, British and Italians – to understand the role of the microbiome on behavior, metabolism and neurogenesis – transplanted the fecal microbiota of 69 Alzheimer’s patients into young adult rats. After having ‘demolished’ the microbiota of the rats, by administering a mix of antibiotics for seven days.

AntibioticsIt should be remembered that in fighting pathogenic bacteria they demolish the intestinal microbiome. As well as being able to trigger antibiotic resistance phenomena. (3) And the drugs used in the current study to ‘sterilize’ the bacterial flora of guinea pigs are the same ones taken, often in excess, by humans. (4)

Guinea pigs who received the microbiota of Alzheimer’s patients, during a follow-up examination, revealed:

– alteration of the intestinal microbiota and the intestinal epithelium. As already described in scientific literature, the intestinal bacterial heritage of people suffering from Alzheimer’s is characterized by a specific profile, with an abundance of certain categories of bacteria (Bacteroidetes) and reduction of others (firmicutes), deficiency of some genera of bacteria (i.e. Clostridium, Cocoproccus) and increase in others (e.g. Desulfovibrio);

– manifestation of cognitive deficits in behaviors that depend on hippocampal neurogenesis. That is, by the (defective) production of new neurons in the area of ​​the brain that contributes to short- and long-term memory, spatial memory and orientation. The different severity of these deficits, it should be noted, was correlated with the scores on the cognitive status of the donors.

This approach was extended to an in vitro study to measure the impact of the microbiota, through the plasma metabolites on which it influences, on hippocampal neurogenesis.

The serum of Alzheimer’s patients has been shown to decrease the proliferative capacity to differentiate the embryonic progenitor cells of the human hippocampus.

The complete reproduction of neurons, essentially, is inhibited by the systemic decompensation triggered by an unbalanced intestinal microbiota.

‘Our findings reveal that Alzheimer’s symptoms can be transferred to a young and healthy organism via the gut microbiota, confirming a causal role of the microbiota intestinal in Alzheimer’s disease. 

Adult hippocampal neurogenesis (AHN) has also been established as a central cellular process convergent for cognitive changes, influenced by both systemic circulatory factors and gut-mediated factors in Alzheimer’s disease‘, the researchers conclude.

6) Microbiota and health

The microbiota intestinal continues to emerge as a determining element in human, physical and mental health. Maintaining the balance of this community of microorganisms requires an adequate lifestyle, starting with nutrition. The Mediterranean diet and ultra-processed foods, as we have seen, can produce antithetical effects (5,6,7).

Attention must also be paid to adverse effects on the intestinal microbiota related to exposure to pesticides, herbicides and other agrotoxicants. In this regard, we recall the studies on the damage caused by glyphosate, the best-selling herbicide in the world, and the concrete doubts about its neurotoxicity (8,9).

Marta Strinati and Dario Dongo

(1) Stefanie Grabrucker, Moira Marizzoni, Edina Silajdžić, Nicola Lopizzo, Elisa Mombelli, Sarah Nicolas, Sebastian Dohm-Hansen, Catia Scassellati, Davide Vito Moretti, Melissa Rosa, Karina Hoffmann, John F Cryan, Olivia F O’Leary, Jane A English, Aonghus Lavelle, Cora O’Neill, Sandrine Thuret, Annamaria Cattaneo, Yvonne M Nolan, Microbiota from Alzheimer’s patients induces deficits in cognition and hippocampal neurogenesis, Brain, Volume 146, Issue 12, December 2023, Pages 4916–4934, https://doi.org/10.1093/brain/awad303

(2) Giulia Pietrollini. Probiotics, prebiotics and psychobiotics, a revolution for mental health? GIFT (Great Italian Food Trade). 14.2.23 /

(3) Dario Dongo, Sabrina Bergamini. Antibiotic resistance, the silent pandemic. Egalité. 15.12.23

(4) Active substances Ampicillin, Vancomycin, Ciprofloxacin HCL, Imipenem. Trade names Amplital, Levovanox, Ciproxin, Tienam

(5) Dario Dongo, Andrea Adelmo Della Penna. Gut microbiota, diet and health. GIFT (Great Italian Food Trade).

(6) Marta Strinati. Alzheimer, the consumption of dietary fiber reduces the risk and protects the brain of the elderly. GIFT (Great Italian Food Trade).

(7) Marta Strinati. Mediterranean diet and immune system, new scientific evidence. GIFT (Great Italian Food Trade).

(8) Dario Dongo. Pesticides and microbiome, interview with Prof. Alberto Mantovani. GIFT (Great Italian Food Trade).

(9) Dario Dongo. Glyphosate and neurotoxicity, doubts and questions from a toxicologist. GIFT (Great Italian Food Trade).