## 2 Results and Discussion
### In Silico Simulated Gastrointestinal (GI) Digestion of Bioactive Peptides
Evaluation of ADME parameters at the initial stage mitigates the pharmacokinetics (i.e., the fate of a therapeutic compound in the organism) related failures in the clinical phase. SwissADME evaluation methods include the analysis of drug-likeness which investigates the probability to be an oral drug [44]. One of the most common and convenient delivery methods of peptide therapeutics is oral administration [45]. The selected criteria in the present study focused on the crucial physicochemical parameters used for drug designing, including number of rotatable bonds (ROTB), number of hydrogen bond acceptors, number of hydrogen bond \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Active** & **Prediction** & **Hydrophobicity** & **Hydrophilicity** & **Charge** & **pI** & **Molecular Weight (Da)** \\ \hline PL & Non-toxic & \(0.23\) & \(-0.9\) & \(0\) & \(5.88\) & \(228.31\) \\ DF & Non-toxic & \(-0.05\) & \(0.25\) & \(-1\) & \(3.8\) & \(280.29\) \\ GP & Non-toxic & \(0.04\) & \(0\) & \(0\) & \(5.88\) & \(172.20\) \\ AF & Non-toxic & \(0.43\) & \(-1.5\) & \(0\) & \(5.88\) & \(236.28\) \\ PR & Non-toxic & \(-0.92\) & \(1.5\) & \(1\) & \(10.11\) & \(271.33\) \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Physicochemical properties and toxicity of bioactive fragments releasing after the simulation in silico digestion. donors and water solubility. Furthermore, polarity of the molecule was evaluated using topological polar surface area (TPSA) technique considering sulfur and phosphorus as polar atoms. TPSA is one of the key parameters to estimate the ADME properties [44]. Lipophilicity was analyzed based on the partition coefficient between octanol and water (log Po/w) and it has a vital impact on pharmacokinetics in drug discovery process. Bioavailability score and Lipinski filter were evaluated to assess the qualitative chance for sea cucumber derived peptides to become oral drugs with emphasis on bioavailability and structural characteristics. Lipinski filter is developed on the Lipinski ([PERSON]'s) rule of five which is known as the rule of thumb to determine the drug-likeness of a molecule [42]. The main criteria of the rule include less than five hydrogen bond donors (the total number of nitrogen-hydrogen and oxygen-hydrogen bonds), no more than 10 hydrogen bond acceptors (all nitrogen or oxygen atoms), molecular mass of less than 500 Da, and an octanol-water partition coefficient (log P) greater than or equal to five. In general, orally active drugs can have only one exemption/violation of these criteria. All these parameters were evaluated on par with the standard captopril. As shown in Table 10, four of the five predicted dipeptides from sea cucumber protein hydrolysates were in accordance with all Lipinski criteria. The remaining dipeptide PR was also in agreement with Lipinski filter criteria with one violation (exceeded the maximum number of hydrogen bond donors (HBD)). Moreover, it has been suggested that compounds with more than 10 rotatable bonds show poor oral bioavailability whereas TPSA value ranging from 20 to 130A2 are suitable for providing high oral bioavailability [42]. All peptides, except PR, exhibited low TPSA values and high gastrointestinal absorbance ability. Lipophilicity and polarity of compounds are crucial to determine the passive gastrointestinal digestion [46]. Furthermore, bioavailability scores of all the identified peptides were similar to that of standard inhibitory drug captopril. Bioavailability radar, a graphical representation of most of the above-mentioned parameters with some additional properties simplifies the evaluation of drug-likeness of a molecule. Six physicochemical properties, including lipophilic, molecular weight/size, polarity, solubility, saturation, and flexibility of the molecule were displayed in the radar (Figure 1). LIPO, Lipophilicity: \(-0.7<\) XLOGP3 \(<\) +5.0; SIZE, Molecular size: 150 g/mol \(<\) mol. wt.