New Gly-Pro-Glu (GPE) analogues: expedite solid-phase synthesis and biological activity

Exploring structural determinants of neuroprotection bias on novel glypromate conjugates with bioactive amines

Neurodegenerative disorders of the central nervous system (CNS) such as Alzheimer's and Parkinson's diseases, afflict millions globally, posing a significant public health challenge. Despite extensive research, a critical hurdle in effectively treating neurodegenerative diseases is the lack of neuroprotective drugs that can halt or reverse the underlying disease processes. In this work, we took advantage of the neuroprotective properties of the neuropeptide glycyl-l-prolyl-l-glutamic acid (Glypromate) for the development of new peptidomimetics using l-pipecolic acid as a proline surrogate and exploring their chemical conjugation with relevant active pharmaceutical ingredients (API) via a peptide bond. Together with prolyl-based Glypromate conjugates, a total of 36 conjugates were toxicologically and biologically evaluated. In this series, the results obtained showed that a constrained ring (l-proline) at the central position of the peptide motif accounts for enhanced toxicological profiles and biological effects using undifferentiated and differentiated human neuroblastoma SH-SY5Y cells. Additionally, it was shown that biased biological responses are API-dependent. Conjugation with (R)-1-aminoindane led to a 38-43% reduction of protein aggregation induced by Aβ25-35 (10 μM), denoting a 3.2-3.6-fold improvement in comparison with the parent neuropeptide, with no significative difference between functionalization at α and γ-carboxyl ends. On the other hand, the best-performing neuroprotective conjugate against the toxicity elicited by 6-hydroxydopamine (6-OHDA, 125 μM) was obtained by conjugation with memantine at the α-carboxyl end, resulting in a 2.3-fold improvement of the neuroprotection capacity in comparison with Glypromate neuropeptide. Altogether, the chemical strategy explored in this work shows that the neuroprotective capacity of Glypromate can be modified and fine-tuned, opening a new avenue for the development of biased neurotherapeutics for CNS-related disorders.

Concise Overview of Glypromate Neuropeptide Research: From Chemistry to Pharmacological Applications in Neurosciences

Neurodegenerative diseases of the central nervous system (CNS) pose a serious health concern worldwide, with a particular incidence in developed countries as a result of life expectancy increase and the absence of restorative treatments. Presently, treatments for these neurological conditions are focused on managing the symptoms and/or slowing down their progression. As so, the research on novel neuroprotective drugs is of high interest. Glypromate (glycyl-l-prolyl-l-glutamic acid, also known as GPE), an endogenous small peptide widespread in the brain, holds great promise to tackle neurodegenerative diseases such as Parkinson's, Alzheimer's, and Huntington's, s well as other CNS-related disorders like Rett and Down's syndromes. However, the limited pharmacokinetic properties of Glypromate hinder its clinical application. As such, intense research has been devoted to leveraging the pharmacokinetic profile of this neuropeptide. This review aims to offer an updated perspective on Glypromate research by exploring the vast array of chemical derivatizations of more than 100 analogs described in the literature over the past two decades. The collection and discussion of the most relevant structure-activity relationships will hopefully guide the discovery of new Glypromate-based neuroprotective drugs.

Toxicity of Glycyl-l-Prolyl-l-Glutamate Pseudotripeptides: Cytotoxic, Oxidative, Genotoxic, and Embryotoxic Perspectives

The tripeptide H-Gly-Pro-Glu-OH (GPE) and its analogs began to take much interest from scientists for developing effective novel molecules in the treatment of several disorders including Alzheimer’s disease, Parkinson’s disease, and stroke. The peptidomimetics of GPEs exerted significant biological properties involving anti-inflammatory, antiapoptotic, and anticancer properties. The assessments of their hematological toxicity potentials are critically required for their possible usage in further preclinical and clinical trials against a wide range of pathological conditions. However, there is so limited information on the safety profiling of GPE and its analogs on human blood tissue from cytotoxic, oxidative, and genotoxic perspectives. And, their embryotoxicity potentials were not investigated yet. Therefore, in this study, measurements of mitochondrial viability (using MTT assay) and lactate dehydrogenase (LDH) release as well as total antioxidant capacity (TAC) assays were performed on cultured human whole blood cells after treatment with GPE and its three novel peptidomimetics for 72 h. Sister chromatid exchange (SCE), micronucleus (MN), and 8-oxo-2-deoxyguanosine (8-OH-dG) assays were performed for determining the genotoxic damage potentials. In addition, the nuclear division index (NDI) was figured out for revealing their cytostatic potentials. Embryotoxicity assessments were performed on cultured human pluripotent NT2 embryonal carcinoma cells by MTT and LDH assays. The present results from cytotoxicity, oxidative, genotoxicity, and embryotoxicity testing clearly propounded that GPEs had good biosafety profiles and were trouble-free from the toxicological point of view. Noncytotoxic, antioxidative, nongenotoxic, noncytostatic, and nonembryotoxic features of GPE analogs are worthwhile exploring further and may exert high potentials for improving the development of novel disease-modifying agents.

Design, Synthesis, and Biological Evaluation of Hybrid Glypromate Analogues Using 2-Azanorbornane as a Prolyl and Pipecolyl Surrogate

Neurodegenerative disorders of the central nervous system are a class of heterogeneous pathologies affecting millions of people worldwide and represent a global health burden in developed and developing countries. Without restorative treatments currently available, research on neuroprotective drugs is considered a health priority. In this study, new analogues of the glycyl-l-prolyl-l-glutamic acid (Glypromate) neuropeptide were designed, synthesized, and biologically evaluated using (1R,3S,4S)-2-azanorbornane-3-carboxylic acid as a hybrid construct of l-proline and l-pipecolic acid. Neuroprotection assays carried out in human neuroblastoma SH-SY5Y cells using 6-hydroxydopamine as a stress inducer showed great percentage of recovery (29.7-40.0%) at 100 μM. Among this series, [(1R,3S,4S)-2-glycyl-2-azanorbornane-3-carbonyl]-l-aspartic acid (2a) stands out with a remarkable percentage of recovery (40.0%, at 100 μM) and safe toxicological profile in SH-SY5Y and human adipose mesenchymal stem cells.

Glycyl-L-Prolyl-L-Glutamate Pseudotripeptides for Treatment of Alzheimer's Disease

So far, there is no effective disease-modifying therapies for Alzheimer’s Disease (AD) in clinical practice. In this context, glycine-L-proline-L-glutamate (GPE) and its analogs may open the way for developing a novel molecule for treating neurodegenerative disorders, including AD. In turn, this study was aimed to investigate the neuroprotective potentials exerted by three novel GPE peptidomimetics (GPE1, GPE2, and GPE3) using an in vitro AD model. Anti-Alzheimer potentials were determined using a wide array of techniques, such as measurements of mitochondrial viability (MTT) and lactate dehydrogenase (LDH) release assays, determination of acetylcholinesterase (AChE), α-secretase and β-secretase activities, comparisons of total antioxidant capacity (TAC) and total oxidative status (TOS) levels, flow cytometric and microscopic detection of apoptotic and necrotic neuronal death, and investigating gene expression responses via PCR arrays involving 64 critical genes related to 10 different pathways. Our analysis showed that GPE peptidomimetics modulate oxidative stress, ACh depletion, α-secretase inactivation, apoptotic, and necrotic cell death. In vitro results suggested that treatments with novel GPE analogs might be promising therapeutic agents for treatment and/or or prevention of AD.

D. dos Santos AC, García-Mera X, Rodríguez-Borges JE, Sampaio-Dias IE. Bioinspired design for the assembly of Glypromate® neuropeptide conjugates with active pharmaceutical ingredients

A robust and bioinspired methodology for the efficient conjugation of Glypromate® with active pharmaceutical ingredients for neurodegenerative diseases.

Highly efficient one-pot assembly of peptides by double chemoselective coupling

An efficient and faster methodology for the assembly of oligopeptides by a three-step one-pot protocol with high yields and virtually no epimerization.

A new constrained proline analogue with an 8-azabicyclo[3.2.1]octane skeleton

A straightforward synthesis of 8-azabicyclo[3.2.1]octane-1-carboxylic acid, a new proline analogue with a bicyclic structure, is described. The procedure makes use of readily available starting materials and involves simple, high-yielding transformations.

The neuroprotective activity of GPE tripeptide analogues does not correlate with glutamate receptor binding affinity

The influence of several modifications on the GPE tripeptide structure upon the binding to GluRs and on their neuroprotective effects has been studied. The results indicated that the prevention of neuronal death showed by GPE and some analogues is not directly related to their affinity at glutamate receptors.

Synthesis of macrocyclic analogues of the neuroprotective agent glycyl-l-prolyl-l-glutamic acid (GPE)

The syntheses of seven macrocyclic analogues of the neuroprotective tripeptide glycyl-L-prolyl-L-glutamic acid (GPE) are described. Macrocycles 6 and 7 mimic the cis conformer of GPE whereas macrocycles 2-5, 8, and 9 mimic the trans conformer of GPE. The macrocyclic peptides of well-defined geometry were prepared via Grubbs ring closing metathesis of an appropriate diene precursor. In turn each of the diene precursors were prepared from the readily available allyl-substituted amino acid building blocks 12, 13, 14, 27, 36 and 51.