# Nanoformulation of Peptides for Pharmaceutical Applications: In Vitro and In Vivo Perspectives
## 2 Overview of Peptides  
Peptides are specific protein fragments that possess beneficial effects for the functions of living organisms [12]. They can be synthesized via amino acids linked by covalent bonds called peptide or amide bonds [13]. Proteins and peptides play vital roles in the metabolic activities of live cells. They can exhibit antihypertensive, mineral binding, antimicrobial, immunomododulatory, antioxidant, and antithrombotic activities [13]. The amino acid constituents and arrangements are responsible for the activities of the peptides. The interplay of amino acid sequences regulates biological processes in the cells of living organisms [14]. Proteins obtained from animals and plant sources are utilized as precursors to synthesize peptides with distinct structures [13; 15; 16]. Several peptides display structural and functional characteristics similar to proteins, particularly peptide residues of 2 to 20 amino acid lengths with arginine, proline, or lysine amino acid groups as well as hydrophobic properties [17; 18]. Recently, peptides were employed in organic transformation that occurred in the storing and processing of foods and significantly contributed to their sensory features. They are documented as a group of bioactive molecules with a wide range of biological properties in addition to their nutritional functions. Lately, nutraceuticals and functional foods with peptides have gained attention, specifically for their influence on the health of humans and their actions in the prevention of certain ailments [13; 19; 20]. Peptides are present in bovine milk [21], cheese, and dairy foods [21; 22; 23] as proteins. Moreover, they exist in the blood of bovine [24], meat, gelatin, fish, and eggs [13]. Peptides obtained from the proteins of animals are shown to exhibit several beneficial functionalities [25]. Recently, albumin obtained from animal blood was hydrolyzed via several trypsin concentrations and the sequence of peptides from the hydrolyses showed several properties, such as blood glucose control (inhibition of dipeptidyl peptidase-4), attenuation of hypertension (angiotensin-converting enzyme inhibition), and abrogation of oxidative stress [26]. Similarly, peptides derived from milk were reported to display antioxidant actions by preventing essential fatty acids peroxidation. Consistently, peptides liberated via hydrolysis of casein possess lipophilic and hydrophilic antioxidant activities against reactive oxygen species (ROS) and sequestering of metal ions [13; 27]. Protein hydrolyses obtained from fish are treated to enzymes and improve the value of underutilized fish species and by-products of fish products. These protein hydrolyses contain peptides with distinct sequences [28]. Extracts of dry-cured ham from Spain were reported to exhibit antioxidant activities against the 1,1-diphenyl-2-picrylhydrazyl radical and superoxide ion, depending on their peptide compositions. Consistently, peptides such as Leu-Ala-Arg-Leu, Gly-Ala-Leu-Ala-Ala-His, Leu-His-Tyr, Pro-His-Tyr-Leu, GlyGly-Glu, and Gly-Ala-His isolated from _Sardinella_ showed antioxidant activities against 2,2-diphenyl-1-picrylhydrazyl radical [29]. In addition, \(\alpha\)- and \(\beta\)-lactoglobulin, as well as enzymatic hydrolysate, displayed enhanced free radical scavenging activities. Further, peptides and proteins isolated from eggs, gelatins, and potatoes were reported to exhibit antioxidant activities [30; 31; 32]. Leu-Lys-Gln-Clu-Leu-Glu-Asp-Leu-LeuGlu-Lys-Gln-Glu peptides (1.6 kDa) obtained from the hydrolysis of _Crassostra gigas_ (oyster) were identified to nullify lipid peroxidation, scavenged superoxide, and hydroxyl radical [33]. Moreover, the hydrolysis of bivalve mollusks (_Mactra veneriformis_) produced 21 peptides, which displayed antioxidant activities [34]. Another study showed that whey proteins, caseins, and protein fractions obtained from the digestion of goat milk by pepsin contain peptides with allergenic properties. These peptides also possess antioxidant activities against superoxide anion radicals [35].