What are proven peptides?

What Are Proven Peptides?

Proven peptides are biologically validated protein fragments (typically 2-50 amino acids) that have demonstrated clinical efficacy through rigorous testing, including FDA-approved peptide drugs and clinically validated biomarkers used for diagnosis, risk stratification, and treatment guidance in medical practice. 1, 2

Categories of Proven Peptides

Therapeutic Peptides (FDA-Approved Drugs)

• More than 80 peptide-based drugs have reached the market for conditions including diabetes, cardiovascular diseases, and urological disorders, with approximately 140 additional peptide therapeutics currently in clinical trials 1, 3
• Insulin represents the first commercial peptide drug (introduced in the 1920s), establishing the paradigm for peptide-based therapeutics that has evolved over 100 years 4
• Peptide receptor radionuclide therapy (PRRNT) using radiolabeled somatostatin analogues (DOTATOC and DOTATATE) is proven effective for treating neuroendocrine tumors, with DOTATATE showing 6-9 fold higher affinity for somatostatin receptor subtype 2 compared to DOTATOC 5

Diagnostic and Prognostic Peptide Biomarkers

Natriuretic Peptides (BNP/NT-proBNP):

• BNP and NT-proBNP are the most established biomarkers for heart failure diagnosis, with primary utility in confirming or refuting heart failure and stratifying long-term risk profiles 6
• For chronic heart failure, use BNP ≥35 pg/mL or NT-proBNP ≥125 pg/mL as diagnostic thresholds 5
• For acute heart failure, apply age-adjusted NT-proBNP cutoffs: 450 pg/mL (<50 years), 900 pg/mL (50-75 years), and 1,800 pg/mL (>75 years) with 99% negative predictive value below 300 pg/mL 5
• BNP became clinically validated remarkably rapidly—first reported in human hearts in the early 1990s, then validated in 1,586 patients, and subsequently FDA-approved for point-of-care testing 5

Cardiac Troponin:

• Troponin measurement has become integral to clinical cardiology, with the very definition of myocardial infarction and determination of antithrombotic treatment benefit now resting on serum troponin levels 5
• Even minute troponin elevations identify high-risk patients who derive greater benefit from aggressive interventional strategies 5

C-Reactive Protein:

• High-sensitivity CRP (hs-CRP) should be measured only in patients with intermediate/moderate cardiovascular risk (10-year ASCVD risk), not in low-risk or already high-risk individuals where it adds minimal value 7
• hs-CRP has significant limitations: multiple confounders, narrow diagnostic window, lacks specificity, and shows no dose-effect relationship between CRP changes and cardiovascular disease risk 7

Critical Methodological Considerations

Sample Collection and Processing Requirements

For accurate peptide measurement, adhere to strict protocols 5:

• Collect blood samples in EDTA tubes with validated peptidase inhibitor cocktails
• Store immediately at -80°C or extract peptides immediately
• For urine samples, use acidification or inhibitors
• For tissue samples, rinse blood and rapidly freeze in liquid nitrogen

Analytical Methods

• LC-MS/MS and HPLC-MS/MS represent the gold standard for peptide quantification, though they require substantial expertise and cost 5
• RIA and ELISA can achieve requisite sensitivity and specificity only when validated with HPLC/MS and require optimal conditions with peptide extraction/purification 5
• Standardized methods and centralized specimen analysis are necessary to enable cross-study comparisons and appropriate clinical inferences 5

Common Pitfalls and How to Avoid Them

Commercial Assay Validation Issues

The most critical pitfall: commercially available zonulin ELISA tests are fundamentally flawed—they detect complement proteins instead of true zonulin (pre-haptoglobin-2), rendering results completely unreliable and invalidating any clinical conclusions drawn from these tests 8

Peptide Measurement Challenges

• Low peptide concentrations (~fmol/mL), interfering substances, ongoing metabolism, and sequence homogeneity create significant analytical challenges 5
• Antibodies may cross-react (e.g., Ang III with anti-Ang II antibodies), requiring careful validation 5
• Assays cannot distinguish peptide source (extracellular vs. intracellular in tissue samples, or specific tissue origin in blood samples) 5

Clinical Trial Design Considerations

• Low recruitment and enrollment represent the most common reason for trial termination when using natriuretic peptides as inclusion criteria 5
• Higher BNP/NT-proBNP cutoff values yield more events but reduce eligible patient numbers, creating a trade-off between statistical power and feasibility 5
• Risk exists for enrolling patients without actual heart failure when not using objective biomarker criteria—in TOPCAT, patients enrolled via hospitalization (rather than elevated natriuretic peptides) showed lower event rates and no treatment benefit 5

Emerging Applications

Advanced Peptide Technologies

• Multifunctional and cell-penetrating peptides represent new frontiers beyond traditional peptide design, along with peptide-drug conjugates 1
• Peptides derived from intercellular junction proteins (occludins, claudins, cadherins) show promise for improving drug delivery through the intestinal mucosa barrier and blood-brain barrier via paracellular pathways 9
• Peptides conjugated to drugs can target specific cell types (cancer cells, immune cells) to reduce side effects by directing therapy to diseased cells without affecting normal cells 9

Novel Biomarkers Under Investigation

• Soluble suppressor of tumorigenicity 2 (sST2), galectin-3, and growth differentiation factor 15 (GDF-15) are emerging as additional heart failure biomarkers 6
• Neoantigen peptides for cancer immunotherapy require comprehensive bioinformatic pipelines integrating DNA/RNA sequencing, MHC binding predictions, and immunogenicity assessments 5

Proteomics and Pattern Recognition

An obvious hypothesis: patterns of disease-related peptide changes would provide substantially more clinical information than single markers, justifying aggressive research investment in clinical proteomics 5