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L-Allylglycine is an amino acid derivative that reduces glutamate decarboxylase (GAD) activity by 60% when administered at a dose of 39.8 μmol g per hour ex vivo in mouse brain preparations. L-Allylglycine (1.2 mmol kg, i.p.) induces convulsions and decreases GABA concentration throughout the cerebellum, pons, medulla, striatum, cortex, and hippocampus in mice. Chronic administration (3.2 μg 0.5 μl per hour for 13 days) of L-allylglycine in rats increases locomotor activity in an open field test and impairs attention in the 5-choice serial reaction time task (5CSRTT). In vitro, L-allylglycine inhibits GAD only when used at high concentrations (1-80 mM). The more potent in vivo activity can be attributed to metabolic conversion of L-allylglycine to 2-keto-4-pentanoic acid, a more potent convulsant and GAD inhibitor.

MTP 131 is a mitochondria-targeted peptide antioxidant.1,2It localizes to the mitochondria and reducestert-butyl hydroperoxide-induced lipid peroxidation and apoptosis in SH-SY5Y cells when used at concentrations ranging from 0.001 to 1 nM.1MTP 131 (2 mg kg) reduces infarct volume, hemispheric swelling, and glutathione (GSH) depletion in a mouse model of acute cerebral ischemia induced by middle cerebral artery occlusion (MCAO).2It increases survival, improves motor function, and decreases degeneration of the lumbar spinal cord in a superoxide dismutase 1 mutant (SOD1G93A) transgenic mouse model of amyotrophic lateral sclerosis (ALS) when administered at a dose of 5 mg kg. MTP 131 reduces albuminuria, urinary hydrogen peroxide levels, and mesangial matrix accumulation, as well as preserves superoxide production, in adb dbmouse model of diabetic nephropathy.3 1.Zhao, K., Luo, G., Giannelli, S., et al.Mitochondria-targeted peptide prevents mitochondrial depolarization and apoptosis induced by tert-butyl hydroperoxide in neuronal cell linesBiochem. Pharmacol.70(12)1796-1806(2005) 2.Szeto, H.H.Mitochondria-targeted peptide antioxidants: Novel neuroprotective agentsAAPS J.8(3)E521-E531(2006) 3.Miyamoto, S., Zhang, G., Hall, D., et al.Restoring mitochondrial superoxide levels with elamipretide (MTP-131) protects db db mice against progression of diabetic kidney diseaseJ. Biol. Chem.295(21)7249-7260(2020)

TPP-1, a peptide inhibitor, targets the interaction between programmed cell death protein 1 (PD-1) and its ligand (PD-L1), binding specifically to PD-L1 with a dissociation constant (Kd) of 94.67 nM. At a concentration of 20 µM, TPP-1 effectively counteracts the PD-L1-induced suppression of IFN-γ production in anti-CD3-stimulated isolated human CD4+ T cells. Furthermore, TPP-1 demonstrates significant efficacy in reducing tumor volume in a mouse xenograft model of HL-60 leukemia. This model involved HL-60 cells co-cultured with anti-CD3-activated isolated human CD4+ T cells, with TPP-1 administration at a dosage of 4 mg/kg showing notable antitumor activity.

Gastric inhibitory peptide 1 (GIP-1) (3-42), a fragment of the incretin hormone GIP and antagonist to the GIP receptor, is generated through the action of serum dipeptidyl peptidase 4 (DDP-4). When administered at 25 nmol/kg to an ob/ob mouse diabetes model, GIP-1 (3-42) elevates plasma glucose levels and lowers plasma insulin levels, demonstrating its effect on reducing insulin secretion from BRIN-BD11 pancreatic cells at a concentration of 100 nM.

Gastrin-releasing peptide (GRP) is a neuropeptide that stimulates gastrin release. It binds to (Ki = 300 nM) and stimulates amylase secretion in rat pancreatic AR42J cells (EC50 = 0.3 nM). GRP increases proliferation of human liver carcinoma HepG2 and MHCC97H cells but does not affect the proliferation of normal HL-7702 liver cells at a concentration of 1 nM. In vivo, GRP (0.35 nmol/kg/h) increases both pancreatic exocrine secretion and pancreatic polypeptide (PP) release in rats. It dose-dependently stimulates gastrin, pancreatic amylase, lipase, bilirubin, and acid output and induces gallbladder contraction in humans when administered at doses ranging from 1 to 27 pmol/kg per hour.

Proadrenomedullin N-terminal 12 peptide (PAMP-12), an endogenous fragment originating from the adrenal medulla and spanning amino acids 9-20 of human PAMP-20, plays a role in causing hypotension. It functions as an agonist for the MAS-related G protein-coupled receptor family member X2 (MRGPRX2), inhibiting forskolin-stimulated cAMP accumulation in CHO cells expressing human MRGPRX2 (EC50 = 57.2 nM) and selectively prompting calcium mobilization in these cells (EC50 = 41 nM), but not in cells expressing MRGPRX1, MRGPRX3, or MRGPRX4 at 1 µM. As an antagonist of nicotinic acetylcholine receptors (nAChRs), PAMP-12 obstructs carbachol-triggered catecholamine release and the influx of calcium and sodium (IC50s = 1.3, 0.39, and 0.87 µM, respectively) in primary bovine adrenal chromaffin cells, with no effect on histamine-induced responses (IC50s = >1 µM for all). Additionally, it decreases mean arterial blood pressure in normotensive rats at doses ranging from 10 to 50 nmol/kg.

F1, an anti-inflammatory peptide, incorporates the HIV-1 Tat protein transduction domain linked with a 15-amino acid sequence from residues 46-60 of the inhibitor of NF-κB kinase-interacting peptide (IKIP). It effectively blocks LPS-induced phosphorylation of IκB kinase α (IKKα) and IKKβ, along with the nuclear translocation of NF-κB (p65) in mouse peritoneal macrophages at 5 µM concentration. F1, administered at 5 mg/kg in vivo, significantly reduces IL-6, TNF-α, and IL-1β serum levels and enhances survival in a mouse sepsis model induced by LPS.

Adrenomedullin (22-52) is a C-terminal fragment of adrenomedullin (1-52) . In vitro, adrenomedullin (22-52) reduces basal corticosterone production in a mixture of rat adrenocortical and adrenomedulllary cells. It also reverses increases in ACTH-stimulated corticosterone production induced by adrenomedullin (1-52). Adrenomedulin (22-52) (0.5 and 5 μg/kg/min) has no effect on basal regional cerebral blood flow but reverses increases in regional cerebral blood flow induced by rat adrenomedullin in rats. Unlike adrenomedullin (1-52), adrenomedullin (22-52) has no effect on mesenteric arterial perfusion pressure in cats.

Klotho-derived peptide 1 (KP1) (56-87), a peptide originating from the human Klotho protein, disrupts TGF-β signaling by binding to TGF-β receptor types 1 and 2 (TGFBR1 and TGFBR2; Kds = 1.41 and 14.6 µM, respectively). Preincubation with KP1 at a concentration of 10 µg/ml hinders the TGF-β-induced escalation of fibronectin and α-smooth muscle actin (α-SMA) levels in NRK-49F rat fibroblasts. Furthermore, in vivo studies reveal that KP1, administered at 1 mg/kg per day, preferentially accumulates in damaged kidneys, leading to significant reductions in serum creatinine and blood urea nitrogen levels, indicators of improved kidney function. Additionally, it decreases kidney fibrosis in mouse models of unilateral ureteral obstruction (UUO) and unilateral ischemia-reperfusion injury-induced renal fibrosis.

PAR2 (1-6) amide is a synthetic peptide agonist of proteinase-activated receptor 2 (PAR2) that corresponds to residues 1-6 of the amino terminal tethered ligand sequence of human PAR2 and residues 37-42 of the full-length sequence.1It binds to NCTC 2544 cells expressing human PAR2 (Ki= 9.64 μM in a radioligand binding assay) and induces calcium mobilization in the same cells (EC50= 0.075 μM).2PAR2 (1-6) amide (100 μM) reduces colony formation of A549 lung cancer cells.1It induces superoxide production and degranulation in isolated human eosinophils when used at a concentration of 500 μM.3PAR2 (1-6) amide (5 μmol/kg) induces tear secretion in rats when used in combination with amastatin .4 1.Bohm, S.K., Kong, W., Bromme, D., et al.Molecular cloning, expression and potential functions of the human proteinase-activated receptor-2Biochem. J.314(Pt 3)1009-1016(1996) 2.Kanke, T., Ishiwata, H., Kabeya, M., et al.Binding of a highly potent protease-activated receptor-2 (PAR2) activating peptide, [3H]2-furoyl-LIGRL-NH2, to human PAR2Br. J. Pharmacol.145(2)255-263(2005) 3.Miike, S., McWilliam, A.S., and Kita, H.Trypsin induces activation and inflammatory mediator release from human eosinophils through protease-activated receptor-2J. Immunol.167(11)6615-6622(2001) 4.Nishikawa, H., Kawai, K., Tanaka, M., et al.Protease-activated receptor-2 (PAR-2)-related peptides induce tear secretion in rats: Involvement of PAR-2 and non-PAR-2 mechanismsJ. Pharmacol. Exp. Ther.312(2)324-331(2005)

Bovine Myeloid Antimicrobial Peptide (BMAP) 28, a synthetic peptide derived from bovine cathelicidin-5 (amino acids 132-158), exhibits antimicrobial activity against E. coli, S. aureus, MRSA, S. epidermidis, and the fungus C. albicans, with minimum inhibitory concentrations (MICs) of 2, 2, 4, 1, and 8 µM respectively. At a concentration of 200 nM, BMAP 28 permeabilizes the inner membrane of E. coli, and at 5 µM, it inhibits herpes simplex virus 1 (HSV-1) replication in Vero 76 cells. Furthermore, at 30 µM, it causes hemolysis in human erythrocytes and cytotoxicity in human neutrophils. In vivo, a dose of 0.8 mg/kg enhances survival in mice infected with E. coli or MRSA, but not P. aeruginosa.

Tat-Gap 19, a peptide inhibitor of connexin43 (Cx43) hemichannels, is derived from the HIV-1 Tat protein transduction domain fused with a nine-amino acid sequence from Cx43 residues 128-136. This compound, at a concentration of 10 µM, effectively suppresses glutamate-induced ATP release in primary rat hepatocytes, indicating inhibition of Cx43 hemichannel activity. Furthermore, Tat-Gap 19 demonstrates therapeutic potential by significantly reducing infarct volume in a mouse cerebral ischemia-reperfusion injury model following middle cerebral artery occlusion (MCAO) at a dosage of 25 mg/kg. Moreover, its intraperitoneal administration at 1 mg/kg per day ameliorates fibrosis and decreases the area of hepatic stellate cells, the precursors to myofibroblasts, expressing α-smooth muscle actin (α-SMA), in a model of thioacetamide-induced liver damage. Additionally, it enhances superoxide dismutase (SOD) activity in hepatic cells from the treated mice, indicating its antioxidative benefits.

F9170, an antiviral peptide derived from the HIV-1 envelope glycoprotein (amino acids 789-803), targets the LLP1 domain in the virus's envelope protein cytoplasmic tail. This interaction inhibits HIV-1 IIIB infection in MT-2 cells, evidenced by an EC50 value of 0.19 µM. Additionally, at a dosage of 3 mg/kg, F9170 significantly lowers plasma viral load in rhesus macaques infected with simian HIV (SHIV).

EP4 antagonist 14 is a prostaglandin E2 receptor subtype EP4 antagonist, demonstrating an IC50 of 1.1 nM in a HEK293 human receptor reporter assay and blocking β-arrestin recruitment due to PGE2 with an IC50 of 0.9 nM. At 10 µM, it reduces PGE2-stimulated mRNA levels of Il-4, macrophage mannose receptor 1 (Mrc1), chitinase-like protein 3 (Chil3), chemokine (C-X-C) motif ligand 1 (Cxcl1), triggering receptor expressed on myeloid cells 2 (Trem2), and arginase-1 (Arg1) in RAW 264.7 macrophages. When used at 30 mg/kg per day alongside anti-PD-1 antibodies, it curbs tumor growth and enhances CD8+ T cell infiltration in tumors using a CT26 murine colon cancer model.

The compound 4A7C-301-Nurr1 agonist is a specific agonist for the nuclear receptor-related 1 (Nurr1). By binding to the Nurr1 ligand-binding domain with an IC50 value of 48.22 nM, it enhances the transcriptional activity of both Nurr1-LBD and the full-length Nurr1, as demonstrated in reporter assays using SK-N-BE(2)C human neuroblastoma cells, with EC50 values of 6.53 and 50-70 µM, respectively. Additionally, administration of 4A7C-301-Nurr1 agonist at a dosage of 5 mg/kg per day has been shown to mitigate dopaminergic cell death in the striatum and substantia nigra pars compacta and ameliorate motor and olfactory deficits in mouse models of Parkinson's disease, circumventing the induction of dyskinesia-like behaviors. These models were induced either by the neurotoxin MPTP or by overexpression of α-synuclein.

Obestatin is a 23 amino acid peptide hormone with a conserved C-terminal glycine residue and amidation site that is formed by cleavage of the ghrelin and obestatin prepropeptide.1It binds to the orphan receptor GPR39 (Kd= 1 nM) and stimulates cAMP production in CHO and HEK293 cells overexpressing human GPR39. Obestatin inhibits contraction of isolated mouse jejunum muscle strips induced by ghrelin .In vivo, obestatin (12.5-1,000 nmol/kg) suppresses food intake in a time- and dose-dependent manner and reduces body weight gain and gastric emptying in mice. Obestatin (0.22 g per animal) also reduces food intake and glucose response without affecting plasma insulin responses in fasted high-fat diet fed mice.2 1.Zhang, J.V., Ren, P.C., Avsian-Kretchmer, O., et al.Obestatin, a peptide encoded by the ghrelin gene, opposes ghrelin's effects on food intakeScience310(5750)996-999(2005) 2.Subasinghage, A.P., Green, B.D., Flatt, P.R., et al.Metabolic and structural properties of human obestatin {1-23} and two fragment peptidesPeptides31(9)1697-1705(2010)

CCK (27-33) is a C-terminal fragment of CCK , a peptide hormone found in the intestine and brain that stimulates digestion, mediates satiety, and is involved in anxiety. Non-sulfated CCK (27-33) inhibits binding of [3H]naloxone in rat cerebellum membranes (IC50 = 4 uM) and inhibits electrically-stimulated contraction of isolated guinea pig ileum (IC50 = 17 uM), an effect that can be reversed by naloxone. Unlike sulfated CCK (27-33), the non-sulfated form does not reduce exploratory behavior in mice when administered at doses up to 1 uMol/kg.

Tat-NTS peptide, a cell-penetrating compound, comprises the HIV-1 Tat protein transduction domain fused with a 10-amino acid sequence (residues 228-237) from the repeat III domain of annexin A1, serving as a nuclear translocation signal (NTS). This peptide hinders the interaction between annexin A1 and importin β, obstructing annexin A1's nuclear entry in primary mouse hippocampal neurons. Tat-NTS effectively prevents apoptosis triggered by glucose-oxygen deprivation and reperfusion in these neurons. When administered in vivo at a dosage of 10 mg/kg, it significantly reduces infarct size, minimizes neuronal apoptosis, and improves navigation performance in the Morris water maze test for mice subjected to ischemia-reperfusion injury via middle cerebral artery occlusion (MCAO).

Pap12-6, an antibacterial peptide originating from the first twelve N-terminal amino acids of papiliocin found in P. xuthus larvae, exhibits activity against a range of eight Gram-negative bacteria (e.g., E. coli, P. aeruginosa, S. syphimurium with MIC50s=4-8 µM) and Gram-positive bacteria (e.g., S. aureus, methicillin-resistant S. aureus 3126, B. subtilis, and S. epidermidis with MIC50s=4-8 µM), without compromising the viability of human erythrocytes, mouse RAW 264.7 macrophages, human HaCaT keratinocytes, or human HEK293 kidney cells at 25 µM. It causes membrane depolarization in E. coli at 4 and 8 µM and, upon preincubation at 10 µM, decreases nitrite (NO2-), Tnf-α, and Il-6 secretion in LPS-stimulated RAW 264.7 macrophages. In a murine model, Pap12-6 enhances survival rates and diminishes colony forming units (CFUs) in several organs upon E. coli infection at 10 mg/kg and 1 mg/kg doses, respectively. Additionally, at a 1 mg/kg dose, it lowers serum aspartate aminotransferase (AST) and alanine transaminase (ALT) levels, as well as blood urea nitrogen levels in E. coli-induced sepsis, indicating its therapeutic potential for bacterial infections without affecting host cell viability.

Azurin (50-77) is a peptide fragment derived from the copper-containing bacterial protein azurin, present in P. aeruginosa. It exhibits properties that regulate the cell cycle, inhibit cancer proliferation, and manage angiogenesis, proving its potential as an anticancer agent. Specifically, this compound acts as a VEGFR2 inhibitor with an IC20 of approximately 10.7 µM. At a concentration of 20 µM, it effectively induces cell cycle arrest at the G2/M phase in MCF-7 breast cancer cells, while a higher concentration of 50 µM significantly reduces the proliferation of both MCF-7 and ZR-75-1 breast cancer cell lines. Furthermore, Azurin (50-77) impedes VEGF-A-induced capillary tube formation with an IC50 of 12 µM, and alters the cellular and extracellular levels of critical signaling and structural proteins such as F-actin, focal adhesion kinase (FAK), paxillin, and platelet endothelial cell adhesion molecule-1 (PECAM-1) in human umbilical vein endothelial cells (HUVECs) at a concentration of 25 µM. Demonstrating its efficacy in vivo, Azurin (50-77) administered at 10 mg/kg per day notably reduces tumor volume in an MCF-7 mouse xenograft model, highlighting its therapeutic potential.

R 715, a bradykinin B1 receptor antagonist, inhibits contractions in isolated human umbilical cords that express bradykinin B1 receptors (pA2 = 8.49). When administered at doses of 200, 400, and 600 µg/kg, R 715 enhances latency to tail withdrawal in the tail-flick test for diabetic neuropathy mouse models induced by streptozotocin (STZ), signaling potential analgesic properties. Furthermore, at a 1 mg/kg per day dosage, it mitigates symptoms in a mouse model of experimental autoimmune encephalomyelitis (EAE) induced by MOG35-55 antigen peptide, such as reducing hind limb weakness and paralysis, improving gait symmetry, and decreasing spinal inflammation, neuron demyelination, and lesion monocyte invasion. Additionally, R 715 at 0.01 nmol/animal, administered intracerebroventricularly (i.c.v.), lowers mean arterial blood pressure and increases heart rate in spontaneously hypertensive rats, indicating cardiovascular effects.

Trofinetide, derived from the neuroprotective tripeptide Gly-Pro-Glu (an N-terminal sequence of insulin-like growth factor-1, IGF-1), shows promise in various neuroprotective models. At a concentration of 10 nM, it mitigates cell death in primary rat embryonic striatal neurons caused by okadaic acid. Additionally, Trofinetide reduces the expression of pro-inflammatory markers (IL-1β, TNF-α, IL-6, and E-selectin) in a rat model simulating neuroinflammation from penetrating ballistic-like brain injuries. In cases of brain injury induced by middle cerebral artery occlusion (MCAO), administration of Trofinetide at 30 and 60 mg/kg reduces the area of cortical and striatal infarct. Furthermore, a daily dose of 100 mg/kg reverses social recognition and contextual fear conditioning deficits, diminishes the number of dendritic spines, and decreases testicular weight gain in an fmr1-/- knockout mouse model of fragile X syndrome. Trofinetide formulations have been employed in treating Rett syndrome, highlighting its versatility across various neurological conditions.

Tirzepatide acts as an agonist for both the glucagon-like peptide 1 receptor (GLP-1R) and G protein-coupled receptor 119 (GPR119), effectively inducing cAMP production in HEK293 cells that express either human GLP-1R or GPR119, with EC50 values of 6.54 and 1.01 nM, respectively. Additionally, at a concentration of 100 nM, it triggers receptor internalization in these cells. In vivo studies demonstrate that tirzepatide, administered at 10 nmol/kg per day, significantly reduces body weight, food intake, as well as plasma and hepatic triglyceride levels, free fatty acids (FFAs), leptin, and blood glucose in mice with high-fat diet-induced obesity. Furthermore, a dose of 50 nmol/kg every three days prevents an increase in eosinophils and lymphocytes in the bronchoalveolar lavage fluid (BALF) and inhibits bronchoconstriction prompted by methacholine in mice models of both asthma and diabetes, indicating its potential in treating type 2 diabetes mellitus.

STING agonist 12L is a stimulator of interferon genes (STING) agonist that exhibits binding affinity for both wild-type STING and its variants R232, AQ, and Q with half-maximal inhibitory concentrations (IC50s) of 1.15 µM for wild-type, 1.06 µM for R232, 0.61 µM for AQ, and 1.12 µM for Q. It effectively induces reporter gene expression in THP-1 and RAW 264.7 cells, with half-maximal effective concentrations (EC50s) of 0.38 µM and 12.94 µM, respectively. At a concentration of 5 µM, STING agonist 12L escalates the expression of IFNB1, CXCL10, and IL6 mRNA in THP-1 cells. When administered in vivo at a dose of 10 mg/kg, it enhances plasma IFN-β levels and considerably reduces tumor volume and the number of lung metastases in a B16/F10 murine melanoma model.