# Effects of Ghrelin Hormone on Alzheimer’s and Parkinson’s Disease: A Systematic Review of the Existing Literature

## TL;DR

This paper reviews how ghrelin, a hormone, may help treat Alzheimer’s and Parkinson’s diseases by protecting brain cells.

## Contribution

The study is the first systematic review of preclinical ghrelin research for Alzheimer’s and Parkinson’s diseases.

## Key findings

- Acylated ghrelin improves Alzheimer’s outcomes in animal studies.
- Ghrelin shows neuroprotective effects in early-stage Parkinson’s.
- No clinical trials exist yet, but preclinical results are promising.

## Abstract

Ghrelin is an orexigenic hormone secreted mainly in the
stomach
and small intestine. It has many functions, including appetite stimulation,
growth hormone release triggering, and maintaining glucose and energy
homeostasis. It has also been linked to many neuroregenerative and
neuroprotective activities via its activity on the growth hormone
secretagogue receptor 1a (GHS-R1a). In brain tissues, it has been
revealed that only the acylated ghrelin (AG) but not the unacylated
ghrelin (UAG) has the affinity to GHS-R1a. In addition, AG has been
shown to undergo fast enzymatic conversion into the inactive UAG form
in the serum. Many experimental trials were conducted to study ghrelin’s
effect on Alzheimer’s disease (AD) and Parkinson’s disease
(PD), but there have not been systematic reviews made to date. This
systematic review highlighted the findings from preclinical trials
between 2010 and July 2023, in which ghrelin and/or one of its agonists
have been investigated for their effects in treating AD and PD. The
search databases used were Embase, Cochrane, and Medline. All articles
reviewed were animal studies as there were no clinical trials. The
findings on AD showed that AG has demonstrated improved outcomes histopathologically
and symptomatically. Meanwhile for PD, AG was found to have neuroprotective
effects, especially in the early stage of the disease. This systematic
review paves the way for more studies to be done to ensure the applicability
of ghrelin and/or its agonists in treating and/or slowing the progression
of AD, and early prevention and diagnosis of PD.