Leslie P. Weiner, MD proposed in 1980 that the mechanism of motor neuron death is sometimes related to the loss of androgen receptors.

(doi:10.1001/archneur.1980.00500520027002)

A recently published article brings some substance to his hypothesis.

Weiner based his hypothesis on characteristic of ALS.

1. Male-to-female ratio. There have been frequent reports of preponderance of male to female patients with ALS. The ratio of 1.5 to 2.5 has been reported. A 1:1 ratio has been calculated for patients over the age of 65.

2. Age. The average age of ALS patients is 55 to 60 years.

3. Sparing of neuronal populations. In almost all cases of ALS, the extraocular muscles are not involved. The urinary and anal sphincters are also spared. The neurons of cranial nerves III, IV, and VI and sacral spinal cord motor neurons (S-2) are left intact even in far advanced cases of ALS.

4. Axonal changes. There are changes in ALS that suggest axonal involvement.

5. Certain types of axonal injury and axonal repair.

Leslie P. Weiner hypothesis:

1. Could androgen receptors, and hence, androgens themselves, be important in motor neuron function?
2. Could the sparing of cranial nerves in ALS be due to the lack of dependence of these neurons on androgens?
3. Could the role of androgens be important in repair processes following axonal injury?

One could postulate that normal people have insults to their nerves and muscles hundreds of times in a life time. The neuron, with the "anabolic" help of androgen, can repair its axon. In ALS, whether due to toxins, viruses, trauma, or an accelerating "aging" process, androgen receptors are lost and axonal changes result in the death of the motor neuron.

What about dihydrotestosterone in ALS?

Fast forward in 2020, dr Nishit Sawal and colleagues aimed at testing Cerebrospinal fluid (CSF) levels of free testosterone and dihydrotestosterone in 13 ALS patients [7 males, 6 females] and 22 controls [12 males, 10 females].

While testosterone is well known for its role in sexual development, it does not stop here. Androgen including testosterone enhances muscle growth. Testosterone also regulates platelet aggregation in humans. It has been correlated with health deterioration in several neurodegenerative diseases, including Alzheimer.

Adult testosterone effects are more clearly demonstrable in males than in females, but are likely important to both sexes. Some of these effects may decline as testosterone levels might decrease in the later decades of adult life.

Androgens affect the cerebral vasculature and may contribute to sex differences in cerebrovascular diseases. Men are at a greater risk for stroke and vascular contributions to cognitive impairment and dementia (VCID) compared to women throughout much of the lifespan. In men, low androgen levels have been linked to metabolic and cardiovascular diseases including hypertension, diabetes, hyperlipidemia, and obesity, which greatly increase the risk of stroke and VCID.

Dihydrotestosterone (DHT) is the most potent natural androgen in humans. There has been an increasing interest in this androgen and its role in the development of primary and secondary sexual characteristics as well as its potential roles in diseases ranging from prostate and breast cancer to Alzheimer's disease. Dihydrotestosterone is created when testosterone is converted into a new form, dihydrotestosterone. About 10% of the testosterone in the bodies of both men and women is converted into dihydrotestosterone in adults, with a much higher amount in puberty. This may be why it is so closely related to the triggering of puberty. The dihydrotestosterone hormone is much more powerful than testosterone.

What the scientists found

What they found was that CSF free testosterone levels did not show any significant differences but CSF dihydrotestosterone levels were significantly decreased in all male and female ALS patients.

What did the scientists conclude?

They concluded that dihydrotestosterone is probably integral to survival of motor neurons. In patients predisposed to develop ALS, there is possibly a sort of “testosterone resistance” at level of blood–brain barrier [BBB] existing right from birth and is likely the result of dysfunctional transport protein involved in testosterone transfer across the BBB. In these patients, lesser amount of testosterone is able to breach the BBB and enter the central neural axis.

Lesser amount of testosterone is available to dihydrotestosterone and so fewer dihydrotestosterone is generated. There is inadequate negative feedback suppression of Luteinizing hormone at the level of anterior pituitary by dihydrotestosterone. As a result of higher Luteinizing hormone levels, testosterone levels rise in the peripheral testosterone fraction [the fraction outside the BBB] and this explains the various physical attributes of ALS patients like lower Ratio of the index and ring finger lengths (2D:4D ratio), increased incidence of early onset alopecia etc.

This deficiency of dihydrotestosterone leads to motor neuron death causing ALS.

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La maladie d'Alzheimer est une maladie neurodégénérative chronique qui commence généralement lentement et accélère progressivement. Bien qu'elle soit variable, l'espérance de vie typique après le diagnostic est de trois à neuf ans.

Source Alzforum

Les deux principales hypothèses sur l’origine de cette maladie, affirment que des quantités anormales de protéines amyloïdes ou encore de protéines tau s’agglomèrent dans le cerveau. Les plaques issues de l’agglomération de protéines, entraîneraient une perte progressive de la fonction cérébrale.

On ne sait pas pourquoi ces dysfonctionnements protéiques se produisent. De nombreux essais cliniques ayant pour but de réduire ces plaques, n’ont jamais réussi à améliorer la condition des patients, aussi les scientifiques se tournent petit à petit vers des hypothèses concurrentes.

D’après une nouvelle étude publiée le 12 Octobre 2020 dans le Journal of Neuroscience, au cours de la maladie d'Alzheimer une altération du flux sanguin vers les régions du cerveau coïncide avec l'accumulation de protéines tau et β amyloïde. Cette relation se renforce à mesure que la cognition diminue. Les chercheurs ont aussi testé l’hypothèse selon laquelle un mauvais fonctionnement de la barrière hémato-encéphalique peut être impliqué et leurs résultats semblent la confirmer. Albrecht et ses collègues de la Keck School of Medicine of the University of Southern California ont utilisé l'IRM et la TEP pour comparer le flux sanguin et l'accumulation de protéine tau dans le cerveau des personnes âgées.

Cette corrélation concerne de plus en plus de régions du cerveau au fur et à mesure que la maladie progresse en gravité. Ces résultats suggèrent que le ciblage de la fonction vasculaire pourrait être essentiel pour prévenir et traiter la démence d'Alzheimer.

Dr. Silvia Pozzi, Jean-Pierre Julien and colleagues have designed a second antibody therapy against misplaced TDP-43, the most obvious cellular problem in ALS.

2020 has seen several announcements in this area, which could create a vaccine against ALS. Penetrating the cell is a challenge. Promis neurosciences had announced that they designed a peptide (a tiny protein) targeting TDP-43, and JP Julien's lab worked on single chain antibodies. Single chain antibodies are miniaturized antibodies, their size is roughly half of a normal antibody.

Now JP Julien's team now announced that they successfully designed and tested a monoclonal antibody on a mice model of the disease. Some signs that they have hope it may progress towards clinical trials is that they tested several administration modes and applied for a patent (US 15/532,909).

This is great news and a further step toward a vaccine, as monoclonal antibodies production is well controlled.

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This book retraces the main achievements of ALS research over the last 30 years, presents the drugs under clinical trial, as well as ongoing research on future treatments likely to be able stop the disease in a few years and to provide a complete cure in a decade or two.

A hypothesis describing a mechanism leading to Alzheimer's disease.

Scientists in an interdisciplinary team, have developed a hypothesis that the disease begins when we ingest excess fructose, this phenomenon would be accentuated if there is concomitant consumption of salt and /or alcohol. This excess fructose induces behavioral and metabolic changes, which ultimately lead to Alhzeimer's disease.

The study was published in Frontiers in Aging Neuroscience, it brought together an interdisciplinary team of neurologists, neuroscientists and experts on sugar metabolism

Behavioral and metabolic changes

In the wild, starving animals activate behavioral and metabolic changes to aid their survival once fat stores are depleted. This includes the development of foraging behavior, reduced energy production, and the development of insulin resistance which reduces the uptake of glucose into muscle, thereby promoting preferential uptake by the brain (Koffler and Kisch, 1996; Cahill, 2006).

Studies in humans have largely confirmed these results. The administration of fructose has unique effects on the attention and reward centers, resulting in more hunger and desire for sugary foods than glucose and which is linked to reduced cortical activity (Purnell et al., 2011).

In addition to stimulating hunger, thirst and the search for food, fructose increases the storage of fats, including in the liver, blood (triglycerides) and adipose tissue, thus providing stored energy as well as metabolic water when needed (Johnson et al., 2016).

Deleterious effects of uric acid. Uric acid, generated by fructose, increases blood pressure responses by reducing endothelial nitric oxide, stimulating oxidative stress, and activating the renin-angiotensin system. There is also a very active stimulation of innate immunity, probably mediated by uric acid. These are all protective systems to help survive extreme conditions like famine.

But it is speculated that if it lasts too long, chronic mitochondrial oxidative stress results in impaired mitophagy with the buildup of damaged mitochondria and fewer functioning mitochondria (Shefa et al., 2019), thus affecting overall energy production. and metabolism and resulting in increased dependence on glycolysis.

Generation of fructose in the body Certain foods that do not contain fructose also activate aldose reductase (AR) and stimulate endogenous fructose production, including high glycemic carbohydrates, salty foods, and alcohol (Lanaspa et al., 2013, 2018 ; Wang et al., 2020).

Aldose reductase is expressed in neurons, including the hippocampus (Picklo et al., 2001; Hwang et al., 2017). The activation of aldose reductase leading to the generation of fructose has been shown in the brain after dehydration in rats (Song et al., 2017) as well as after glucose loading in humans (Hwang et al. , 2017). Importantly, there is evidence of endogenous fructose production in patients with Alzheimer's disease, with intracerebral sorbitol and fructose levels 3-5 times higher than normal (Xu et al., 2016) .

Conclusion In one of the scenarios described by Johnson and colleagues, glucose hypometabolism increases oxidative stress and induces progressive loss of mitochondria, ultimately leading to neuronal dysfunction and death. In this scenario, the amyloid plaques and neurofibrillary tangles are part of the inflammatory response and participate in the injury, but are not the central factors of the disease.

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Une hypothèse décrivant un mécanisme aboutissant à la maladie d’Alzheimer.

Des scientifiques dans une équipe interdisciplinaire, ont développé une hypothèse selon laquelle la maladie commence lorsque nous ingérons un excès de fructose, ce phénomène serait accentué s’il y a une consommation concomitante de sel et/ou d’alcool. Cet excès de fructose induit des changements comportementaux et métaboliques, qui à terme induisent la maladie d’Alhzeimer.

L'étude a été publiée dans les Frontiers in Aging Neuroscience, elle a réuni une équipe interdisciplinaire de neurologues, de neuroscientifiques et d'experts sur le métabolisme du sucre

Changements comportementaux et métaboliques

Dans la nature, les animaux qui meurent de faim activent des changements comportementaux et métaboliques pour favoriser leur survie une fois que les réserves de graisse sont épuisées. Cela comprend le développement d’un comportement de recherche de nourriture, une réduction de la production d'énergie et le développement d'une résistance à l'insuline qui réduit l'absorption du glucose dans le muscle, favorisant ainsi l'absorption préférentielle par le cerveau (Koffler et Kisch, 1996; Cahill, 2006).

Pour éviter la famine, les animaux stockent de la graisse en prévision des périodes de pénurie alimentaire, comme avant l'hibernation, la migration sur de longues distances ou la nidification. Une approche utilisée par de nombreux animaux consiste à ingérer des aliments riches en fructose, tels que des fruits et du miel.

Au fil du temps, les animaux développent une résistance à la leptine qui entraîne une consommation excessive de nourriture tout en réduisant l'oxydation des graisses (Shapiro et al., 2008).

Des études chez l'homme ont largement confirmé ces résultats. L'administration de fructose a des effets uniques sur les centres d'attention et de récompense, ce qui entraîne plus de faim et de désir d'aliments sucrés que le glucose et qui est lié à une activité corticale réduite (Purnell et al., 2011).

En plus de stimuler la faim, la soif et la recherche de nourriture, le fructose augmente préférentiellement le stockage des graisses, y compris dans le foie, le sang (triglycérides) et les tissus adipeux, fournissant ainsi de l'énergie stockée ainsi que de l'eau métabolique en cas de besoin (Johnson et al. ., 2016).

Effets délétères de l'acide urique. L'acide urique, généré par le fructose, augmente les réponses de la pression artérielle en réduisant l'oxyde nitrique endothélial, en stimulant le stress oxydatif et en activant le système rénine-angiotensine. Il existe également une stimulation très active de l'immunité innée probablement médiée par l'acide urique. Ce sont tous des systèmes de protection pour aider à survivre dans des conditions extrêmes comme une famine.

Mais il est spéculé que s'il dure trop longtemps, le stress oxydatif mitochondrial chronique entraîne une mitophagie altérée avec l'accumulation de mitochondries endommagées et moins de mitochondries fonctionnelles (Shefa et al., 2019), affectant ainsi la production d'énergie globale et le métabolisme et entraînant une dépendance accrue à la glycolyse.

Génération de fructose dans l'organisme Certains aliments qui ne contiennent pas de fructose activent également l'aldose réductase (AR) et stimulent la production endogène de fructose, y compris les glucides à indice glycémique élevé, les aliments salés et l'alcool (Lanaspa et al., 2013, 2018; Wang et al., 2020).

L'aldose réductase est exprimée dans les neurones, y compris dans l'hippocampe (Picklo et al., 2001; Hwang et al., 2017). L'activation de l’aldose réductase entrainant la génération de fructose a été montrée dans le cerveau après une déshydratation chez le rat (Song et al., 2017) ainsi qu'après une charge en glucose chez l'homme (Hwang et al., 2017). Surtout, il existe des preuves d'une production endogène de fructose chez les patients atteints de la maladie d'Alzheimer, avec des niveaux intracérébraux de sorbitol et de fructose 3 à 5 fois plus élevés que la normale (Xu et al., 2016).

Conclusion Dans l'un des scénarios décrits par Johnson et ses collaborateurs, l'hypométabolisme du glucose augmente le stress oxydatif et induit une perte progressive des mitochondries , conduisant finalement à un dysfonctionnement neuronal et à la mort. Dans ce scénario, les plaques amyloïdes et les enchevêtrements neurofibrillaires font partie de la réponse inflammatoire et participent à la blessure, mais ne sont pas les facteurs centraux de la maladie.