Parkinson's disease (PD) is the second most common neurodegenerative disorder and its main pathological feature is the degeneration of dopaminergic neurons on the Substantia Nigra (SN) (Poewe et al., 2017), All the current existing therapies just provide a temporary symptomatic relief and can't stop the progression of the disease. At present, there is no cure for PD because its etiopathology and the molecular mechanism is still not completely understood, with hypotheses involving several factors, such as: environmental neurotoxins, protein misfolding and aggregation, mitochondrial abnormalities, genetic predisposition, and gut microbiota (Klingelhoefer and Reichmann, 2015; Olanow and Tatton, 1999; Vila and Przedborski, 2004; Bloem et al., 2021).

One of the main hypotheses for the relentless progression of the disease is the vicious cycle between activation of microglia and damage to dopaminergic neurons (Gentleman, 2013; Whitton, 2007; Badanjak et al., 2021). The activation of microglia in the PD brain upregulates the production of proinflammatory cytokines that damages the neurons, when in excess (Doorn et al., 2012; Ransohoff, 2016; Marogianni et al., 2020). This leads to neuronal degeneration releasing cellular debris and apoptotic molecules that further activates the microglia. As a result of this process, a patient with PD has overall higher peripheral levels of cytokines and chemokines (Reale et al., 2009). Hence, the regulation of proinflammatory cytokines in the brain has been pointed as a viable target for halting the progression of the disease (Li et al., 2022).

Animal venoms are a rich source of pharmacologically active peptides that evolved to interact with diverse parts of the cardiovascular and nervous systems as tools for predation and defense (Fry et al., 2009; Zambelli et al., 2016). The peptide Exendin-4, isolated from the venom of Heloderma suspectum, known as the Gila monster, has demonstrated neuroprotective effects in different parkinsonian models by inhibiting microglia activation (Bertilsson et al., 2008; Harkavyi et al., 2008a; Kim et al., 2009) This peptide has shown promising effects on human PD patients and is undergoing a phase 3 multicenter study to assert its effectiveness as a medicine (Vijiaratnam et al., 2021). Crude bee venom administered via acupuncture has also been reported to have a promising effect in slowing the progression of PD by modulating the microglia activation (Doo et al., 2010; Kim et al., 2011). However, this effect could be only due to acupuncture since it alone can reduce neuroinflammation and regulate gut microbiota in a mouse model of PD (Jang et al., 2020).

Wasp venoms have been shown to exert a range of pharmacological effects, such as: antinociceptive, anxiolytic, anti-inflammatory, and antiepileptic (Do Couto et al., 2012; Monge-Fuentes et al., 2015; Silva et al., 2015; de Castro et al., 2020; Lopes et al., 2021). Specifically, bradykinin is considered an anti-inflammatory wasp peptide that downregulates the production of TNF-α and IL-1β and can have an important activity on acute brain inflammation, like ischemic stroke (Silva et al., 2015; Thornton et al., 2010). A peptide described from the Parachartergus fraternus's venom, fraternine, is able to protect against 6-OHDA dopaminergic lesion on the SN and alleviate motor impairments (Biolchi et al., 2020).

Rational design of the amino acid sequence and size of the peptide can make it more available to the organism, requiring a lower dose to exert activity. A common modification that is usually capable of producing more potent peptides are the addition of an amide group on the C-terminal of the compound (Merkler, 1994). Secondary structures such as disulfide bonds and a reduction in molecular weight can make the compound more resistant to enzymes in the body and thus making it more bioavailable (Wang et al., 2019; Wang and Craik, 2016; Siedhoff et al., 2020). Thus, many studies have sought to develop new therapies by changing compounds isolated from animal venoms as a way of enhancing an existing activity to alter the course of a disease and avoid the death of remaining neurons (Silva et al., 2015).

In this study, we tested three synthetic peptides analogs of fraternine in a 6-OHDA mouse model of PD to test for its potential neuroprotective effect on dopaminergic neurons of SN. The proposed modification aimed to produce an amidated smaller drug, capable of also producing antiparkinsonian responses and neuroprotection against neuronal death. We also tested for their effect on immunomodulation via a cytokine dosage of brain cells.