Bioinformatics inspiring peptides from toxins as a new alternative in obesity treatment

Obesity is a nutritional disorder caused by the excessive accumulation of white adipose tissue (WAT) in the body, which is characterized by a high body mass index and interferes with the body's energy balance. Obesity is a major risk factor for a number of different diseases, such as type 2 diabetes, cardiovascular disease, hypertension, fatty liver disease and some malignant tumors. The treatment of obesity primarily focuses on diet and physical exercise; when lifestyle changes fail, drugs and surgery will be considered as treatment options. At present, a number of so-called anti-obesity drugs have been developed, which affect digestion and absorption. These drugs can produce significant weight loss in the individual; however, some patients are unwilling to receive this type of treatment, due to side effects such as insomnia, hypertension and dizziness. This perspective shows that rational design is an alternative methodology based on native bioactive molecules for the development of analogous compounds, improved from the point of view of efficiency and side effects. We also show that the modification of peptides from animal toxins can be an interesting alternative in the treatment of obesity, since peptides from toxins have already shown significant antiinflammatory effects.


Perspective
Obesity is a clinical condition defined by the accumulation of excess body fat and an increased risk of developing other diseases, as indicated by the Body Mass Index (BMI) ≥ 30 kg.m -2 (Schütz, et al., 2021). According to the World Health Organization (WHO), it is estimated that in 2035 about 39% of the world's population will suffer from obesity, a disease capable of causing or aggravating more than 200 clinical conditions (Srivastava & Apovian, 2018;Al-Goblan, et al., 2014).
The clinical condition is linked to type 2 diabetes mellitus (DM2) and is associated with the development of insulin resistance (Al-Goblan, et al., 2014).
The increase in adipose tissue causes the release of free fatty acids, which activate nuclear factor7 Kappa B (NF-kB) and signaling pathway P38 Mitogen-Activated Protein Kinases (MAPK), which signal between the primary response proteins of myeloid differentiation 88 (MyD88) and TIR-domain-containing adapter-inducing interferon-β (TRIF), mediating the Toll type 4 (TLR4) receptor expression activation cascade in adipocytes and macrophages. This process increases the stress of the endoplasmic reticulum (ER), producing reactive oxygen species, in addition to promoting the secretion of pro-inflammatory cytokines, such as chemotactic monocytic protein-1, tumor necrosis factor α (TNF-α), interleukin (IL) -1β and IL-6 (Ahmed, et al., 2021).
Other studies demonstrate the relationship between the secretion of pro-inflammatory cytokines related to insulin resistance and the high production and deposition of free fatty acids and dietary lipids, which cause lipotoxicity in muscle cells and other organs. These fats are deposited in abnormal locations, causing the secretion of toxic lipids, such as ceramides and diacylglycerides, to alter the phosphatidylinositol 3-kinase (PI3K) pathway, and activate protein kinase C (PKC), CJun N-Terminal kinase (JNK) and IkB kinase complex (IKK), generating stress in the ER and membrane stiffening, which induces inflammation and the onset of apoptosis (Ahmed et al., 2021). Other factors, such as the individual's reduction of physical activity and eating habits with high caloric density, contribute to the worsening of this condition. In contrast, carrying out physical exercises contributes to reducing the secretion of pro-inflammatory cytokines (Elias & Vancea, 2019;Lopes, et al., 2017).
Appetite is a phenomenon that is highly regulated by a coordinated interaction between the central and peripheral nervous systems. Two signals inform the brain about the body's energy expenditure: these are short and long-term signals Research, Society and Development, v. 10, n. 14, e432101422057, 2021 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org /10.33448/rsd-v10i14.22057 3 produced, respectively, by the gastrointestinal system and adipose tissue (Gao, et al., 2020). GLP-1 has many results for obesity treatments. In a three-month randomized phase 1 case study involving 22 obese patients with a percentage of BMI ≥ 35 kg.m², exanatide, a GLP-1 receptor agonist, was administered subcutaneously. In the first month, the dose was initially 5 µM twice a day, and in the following two months the dose was 10 µM twice a day. The treatment provided a decrease in the BMI rate equivalent to -1.13 kg.m² (4%), which may be effective for weight reduction in cases of obesity (Kelly, et al., 2013).
Leptin is another protein hormone secreted mainly by adipocytes that can act on hypothalamus neuronal cells, promoting hunger inhibition and increased energy expenditure. This protein decreases appetite by inhibiting neuropeptide Y (NPY) and increasing anorectic neuropeptides (Gao, et al., 2020). In addition to adipocytes, leptin can be secreted by the stomach when stimulated by intestinal peptides such as ghrelin, and insulin hormone after food intake (Figure 1). Similar to type 2 diabetes insulin resistance in patients, obese individuals may have resistance to leptin due to changes in the leptin receptor or deficiency in the transport system in the blood-brain barrier (Friedman, 2016). Leptin has also shown extensive regulatory activity in insulin signaling (Friedman, 2016). The current pharmacological options are not sufficient to address the clinical heterogeneity of obesity treatment due to the various related diseases and the treatment's high cost (Srivastava & Apovian, 2018). Thus, new strategies are needed to solve this problem, and the use of bioactive or synthetic peptides becomes a promising strategy. Several companies focus on the production of double or triple GLP-1 agonists, which are noted for DM2 and obesity treatment. Among the clinical-phase peptides, the GLP-1-glucose-dependent insulinotropic peptide (GIP) and GLP-1-glucagon double-agonist peptides, which are used in proof of concept in overweight and DM2 patients, stand out (Fosgerau & Hoffmann, 2014). Research, Society andDevelopment, v. 10, n. 14, e432101422057, 2021 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v10i14.22057 4 Given this interest, animal toxins represent a source of active biomolecules to be explored, having registered peptides with antibacterial, antiparasitic, antiviral, antifungal, antifreeze, antitumor, immunomodulatory and anti-inflammatory activity (Migliolo, et al., 2016;Yacoub, et al., 2020). In association with bioactive peptides, rational design methodology appears as the first analysis for the development of bio-inspired therapeutic molecules based on function-structure (Irazazabal, 2016).
Rational design is the in silico technique which, by modifications in the native peptide, promotes the construction of analogues. These can be explored through molecular modeling and molecular dynamics, in order to decrease the cost in bioprospection, optimizing the success of a synthetic peptide in the interaction with the target, in addition to lowering the cost of production by organic chemical synthesis (Figure 2). The method of comparative homology uses knowledge about native proteins with similarity to the primary sequence as a basis for a 3D construction model. Figure 2. Process of peptide rational design using bioinformatic tools. Firstly, a target sequence such as a toxin is selected and the models are identified; then sequence alignments are made to start comparative homology modeling. This uses as a basis the knowledge of target sequences' template-based modeling, which seeks to construct a three-dimensional model with resemblance to the original primary sequence. The three-dimensional models are provided and validated by means of prediction servers and high confidence score averages, such as the Ramachandran Plot, which define the final model as reliable. When they are considered satisfactory, models undergo molecular dynamics and other in silico studies to understand the likely molecular behavior in different environments.
So, the rational design technique can therefore be used for complementary studies with peptides from toxins that are deposited in databases to improve their pharmacological potential. Classic peptides have already been described in the literature showing a potential anti-inflammatory effect. Mastoparan peptide derived from Vespa simillima toxin, for example, with a sequence of just 14 amino acids (NH2-INLKALAALAKKIL-NH2), +4 charge and 71% hydrophobicity, has shown antiinflammatory activity in reducing the release of pro-inflammatory cytokines and the expression of TLR4. This peptide dramatically reduces the expression of TNFα and IL-6 mRNA at a concentration of 40 µM (Moreno & Giralt, 2015;Hochberg, et al., 2021).
Other peptides, such as cathelidicin, have already been well described for their anti-inflammatory and anti-obesity properties. Cathelicidin-PY, derived from skin secretions of the frog Paa yunnanensis, for example, is a peptide with 29 amino acid residues (NH2-RKCNFLCKLKEKLRTVITSHIDKVLRPQG-COOH), +6 charge and 37% hydrophobicity. This peptide is capable of inhibiting the production inflammatory cytokines such as TNF-α, IL-6, nitric oxide (NO) and monocyte chemoattractant protein-1 (MCP-1) at low concentrations (5.8 nM), inhibiting the activation of TLR4 inflammatory response pathways induced by LPS. In addition, a recent clinical study suggested that the regulation of human cathelicidin expression in obese patients may be associated with bile acids, incretins or metabolic factors, and that cathelicidins may be adipokines at the interface between metabolism and the innate immune response (Hochberg, et al., 2021). Thus, Cathelicidin-PY becomes an interesting candidate for the development of peptide drugs to treat obesity and its comorbidities (Wei, et al., 2013).
Modifying these peptides could increase their anti-inflammatory activity and make them better candidates for obesity therapy. Studies with bioinspired peptides from toxins, with anti-obesity effects, are still lacking. Thus, it is suggested that rational design is a biotechnological tool that can benefit a number of patients through rational planning for peptide drugs, in the fight against inflammation and obesity, presenting potentially more effective and specific pharmacological alternatives to improve the chances of treatment success.

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Disclosure
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