According to a study published in the journal Science Advances, the brains of women who had Alzheimer’s had higher amounts of complement C3, an inflammatory immune protein, than those of men who had died from the illness. The study also showed that estrogen can prevent the formation of this form of complement C3.

For the study, the researchers used a new method for detecting S-nitrosylation to quantify proteins modified in 40 postmortem human brains. Several studies have shown that the biochemical and molecular mechanisms underlying neurodegenerative diseases include several chemical reactions that form a modified type of complement C3 via a process called protein S-nitrosylation. In the study, the researchers found that S-nitrosylation happened when a nitric oxide (NO)-related molecule was bound to a sulphur atom (S) on a particular amino acid building block of proteins to form a modified "SNO-protein."

The researchers found 1,449 different proteins that had been S-nitrosylated. They also found that the levels of S-nitrosylated C3 (SNO-C3) proteins were six-fold higher in female Alzheimers brains compared to male Alzheimers brains. Furthermore, they discovered that SNO-C3 levels increased as estrogen (b-estradiol) levels decreased with the onset of menopause. This fall in estrogen levels resulted in the activation of an enzyme that makes nitric oxide (NO) in brain cells, which further resulted in SNO-C3 activating microglial destruction of synapses. 

(Source: https://www.tribuneindia.com/news/health/study-explains-why-women-are-at-a-higher-risk-of-alzheimers-disease-than-men-461268 )