Amyloid in the retina
Beta-amyloids in the retina indicated cognitive deficits and a decrease in the volume of the hippocampus
Ekaterina Roshchina, N+1
American scientists have shown that the detection of amyloid plaques in the retina is associated with an increase in cognitive deficits and a decrease in the volume of the hippocampus, characteristic of Alzheimer's disease, long before the clinical manifestation of symptoms. The article was published in the journal Alzheimer's & Dementia: Diagnosis, Assessment & Disease Monitoring (Dumitrascu et al., Sectoral segmentation of retinal amyloid imaging in subjects with cognitive decline).
Alzheimer's disease (AD) is the most common form of neurodegenerative brain diseases characterized by behavioral changes, disorientation, memory disorders and cognitive deficits up to the loss of basic skills. Patients have difficulty washing, dressing and using cutlery, and in the later stages, patients have difficulty even walking and swallowing. Unfortunately, by the time symptoms indicating a diagnosis appear, the damage may be too extensive for effective treatment, so the issue of early diagnosis of AD is quite acute.
Final diagnosis BA is confirmed after an autopsy if an accumulation of improperly folded proteins – beta-amyloids, which cause the death of neurons, is detected in the brain tissues. But in 2010, Maya Koronyo-Hamaoui from Cedars-Sinai Medical Center and her colleagues determined that the deposition of beta-amyloids in AD is also observed in the retina of deceased patients, and there they can form several decades before the onset of symptoms.
The retina is the only tissue of the central nervous system that is not protected by bone and is most accessible for high–resolution imaging. In 2017, the Coronio-Hamawi team developed a method for detecting amyloid plaques in the retina of living patients with AD: scientists used laser ophthalmoscopy with the introduction of a fluorescent compound (fluorophore curcumin), which bound to beta-amyloids. Nevertheless, the question remains open whether the detection of amyloid plaques in the retina will allow predicting a decrease in cognitive abilities and brain volume long before the appearance of a clinical picture of AD.
In a new study led by Coronio-Hamawi, scientists using the developed imaging method looked for correlations between amyloid plaques in the retina, cognitive decline and a decrease in brain volume in 34 patients over 40 years old who went to the clinic complaining of a decrease in mental skills. The researchers measured the total intracranial volume and the volume of the hippocampus and lateral ventricles in the participants, and also suggested that they undergo The Montreal Cognitive Test (MOCA), which showed mental decline if the result was 26 points or lower, and the Clinical Dementia Rating Scale (CDR), according to which a score of 0.5 points indicates a normal cognitive decline, 1 – mild cognitive deficit (MCI), which does not complicate daily activities, 2 – moderate dementia.
According to the MOCA test, 23.5 percent of the subjects had normal cognitive indicators, 64.7 percent had a decrease in memory, and 11.8 percent of the researchers assumed dementia. According to CDR, 32.2 percent of patients had normal cognitive decline, 50 percent had mild cognitive deficits and 11.8 percent had moderate dementia.
The accumulation of amyloid plaques is not associated with gender, age and the leading eye (p>0.05), but the number of beta-amyloids and their distribution area were significantly higher in participants with a higher CDR and a lower MOCA score, and they are also associated with a decrease in hippocampal volume (p<0.05). In addition, the amount of beta-amyloids differed significantly between the three CDR groups, increasing with increasing mental deficits (p<0.05).
The authors concluded that the detection of amyloid plaques in the retina is associated with the development of cognitive deficits and a decrease in the volume of the hippocampus, characteristic of AD. The researchers noted that further study may help develop a method for early diagnosis of AD, and suggested that beta-amyloid deposits in the retina may become a target for the treatment of the disease in the initial stages.
Another biomarker of AD is tau protein, which accumulates inside neurons and leads to their death. It turned out that the aggregation of tau protein inside neurons is caused by the accumulation of beta-amyloids outside, and norepinephrine receptors act as intermediaries in this process.
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