Škrlec et al. (Applied Microbiology and Biotechnology, 2018) engineered Lactococcus lactis — a GRAS-status lactic acid bacterium — to produce and deliver BPC-157 via two strategies: cell-surface display with trypsin-mediated shedding, and direct secretion into the growth medium. The secretion strategy yielded superior antioxidant activity in cell-free supernatants, establishing L. lactis as a viable microbial chassis for oral BPC-157 delivery.
Why Was Lactococcus lactis Selected as the Microbial Chassis for BPC-157 Delivery?
Lactococcus lactis carries GRAS (Generally Recognised As Safe) status, lacks endotoxins, and has a well-characterised genetic toolkit including the nisin-controlled expression (NICE) system. These properties make it a preferred host for oral delivery of therapeutic peptides, where safety, mucosal compatibility, and inducible expression control are all required simultaneously.
Unlike Escherichia coli-based expression systems, L. lactis does not produce lipopolysaccharide endotoxins, eliminating a major safety concern for mucosal applications. Its gram-positive cell wall architecture also provides a stable scaffold for surface-anchored protein display, a property exploited directly in the Škrlec study.
The NICE system uses nisin — a bacteriocin produced by L. lactis itself — as an inducer of the nisA promoter. This allows tight, dose-dependent control of recombinant gene expression, which is critical when producing a bioactive peptide that must be expressed at sufficient yield without metabolic burden overwhelming the host cell.
Previous work had established L. lactis as a delivery platform for cytokines, antigens, and anti-inflammatory proteins in gastrointestinal disease models. The Škrlec study extended this precedent to a short therapeutic peptide — BPC-157 — whose gastric stability and oral bioavailability made it a logical candidate for a bacterium-based oral delivery approach.
What Is the Antioxidant Basis of BPC-157 That Makes Delivery Engineering Relevant?
BPC-157 (sequence: Gly-Glu-Pro-Pro-Pro-Gly-Lys-Pro-Ala-Asp-Asp-Ala-Gly-Leu-Val; MW ≈ 1,419 Da) scavenges reactive oxygen species and upregulates endogenous antioxidant enzymes including heme oxygenase-1 (HO-1) via nitric oxide synthase interaction. Its three consecutive proline residues confer conformational rigidity that may contribute to radical-scavenging geometry, and its antioxidant activity has been confirmed in DPPH and ABTS assay systems.
The peptide's antioxidant profile is mechanistically distinct from simple radical scavengers such as ascorbate. BPC-157 appears to act upstream by modulating NOS activity and downstream antioxidant gene expression, rather than directly quenching radicals through electron donation alone. This positions it as a regulator of oxidative tone rather than a stoichiometric antioxidant.
Free radical scavenging by BPC-157 has been documented in gastric mucosal injury models where oxidative stress is a primary driver of tissue damage. Normalisation of malondialdehyde (MDA) levels — a lipid peroxidation marker — in BPC-157-treated animals is consistent with meaningful in vivo antioxidant activity beyond what in vitro assays alone can confirm.
The relevance to delivery engineering is direct: if BPC-157's antioxidant activity is to be exploited therapeutically at mucosal surfaces, the peptide must reach those surfaces in a biologically active form. Conventional oral peptide delivery is hampered by proteolytic degradation; a living bacterial vehicle that produces BPC-157 locally within the gastrointestinal lumen addresses this barrier at its source.
How Does the Surface Display and Trypsin-Shedding Strategy Work?
In the surface display approach, BPC-157 was fused to a cell-wall-anchoring domain derived from a lactococcal surface protein, directing the peptide to the outer face of the bacterial cell wall. Trypsin was then applied to cleave the peptide from its anchor, releasing soluble BPC-157 — a strategy designed to mimic protease-mediated release in the gastrointestinal environment.
The construct used the Usp45 signal peptide to direct the fusion protein through the secretory pathway to the cell surface. The anchor domain retains the fusion protein at the cell wall until proteolytic cleavage occurs. Flow cytometric analysis confirmed surface localisation of the BPC-157 fusion, and trypsin treatment produced detectable released peptide.
The biological rationale for trypsin-mediated shedding is that the gastrointestinal tract contains endogenous serine proteases — including trypsin secreted by the pancreas — that could serve as natural release triggers in vivo. This would theoretically allow the bacterium to act as a depot, releasing BPC-157 progressively as it transits the small intestine where pancreatic proteases are most active.
However, the Škrlec study found that the surface-display strategy produced lower antioxidant activity in the released fraction compared with the secretion approach. This outcome suggests that trypsin cleavage efficiency, peptide folding after anchor release, or recovery yield may limit the practical utility of surface display for this particular peptide.
What Did the Secretion Strategy Achieve and Why Did It Outperform Surface Display?
The secretion strategy directed BPC-157 — fused to the Usp45 signal peptide without a cell-wall anchor — into the extracellular growth medium. Cell-free supernatants from secreting L. lactis strains demonstrated measurable radical-scavenging activity in antioxidant assays, and this activity exceeded that recovered from the trypsin-shedding surface-display approach, establishing secretion as the superior delivery configuration.
The Usp45 signal peptide is the most widely used secretion signal in L. lactis engineering. It directs proteins through the Sec translocon into the extracellular space without retaining them at the cell wall. For a 15-amino-acid peptide like BPC-157, this pathway is particularly efficient because the small cargo imposes minimal translocation burden.
The superior antioxidant performance of secreted BPC-157 likely reflects higher effective concentration of free, correctly folded peptide in the assay medium. Surface-anchored peptide must undergo proteolytic release before it can act in solution, introducing a yield-limiting step. Secreted peptide is immediately available in its active form without requiring an additional enzymatic processing event.
From a translational perspective, secretion into the gastrointestinal lumen would allow BPC-157 to interact directly with mucosal epithelial cells and luminal reactive oxygen species without dependence on local protease activity. This is mechanistically advantageous in conditions such as inflammatory bowel disease, where mucosal protease profiles are dysregulated.
How Does the NICE Expression System Enable Controlled BPC-157 Production in L. lactis?
The nisin-controlled expression (NICE) system places BPC-157 gene constructs under the nisA promoter, which is activated by sub-inhibitory concentrations of exogenous nisin. This allows researchers to induce BPC-157 production on demand, titrate expression level by adjusting nisin concentration, and avoid constitutive expression that could impose metabolic stress or select for loss-of-function mutations in the producing strain.
Inducibility is a critical feature for therapeutic applications. A constitutively expressing strain would produce BPC-157 throughout its growth cycle, including during manufacturing and storage phases where uncontrolled peptide accumulation could affect strain stability. The NICE system decouples growth from production, allowing biomass to accumulate before induction.
The NICE system has been validated across a wide range of heterologous proteins in L. lactis, with expression levels spanning several orders of magnitude depending on construct design and induction conditions. For a short peptide like BPC-157, optimising codon usage for lactococcal codon preferences and minimising secondary structure in the mRNA 5′ UTR are key determinants of yield.
What Is the Broader Context for Bacterial Oral Peptide Delivery in 2026?
Oral delivery of therapeutic peptides remains a major pharmaceutical challenge in 2026. The GI tract's extreme pH range, mucus barrier, and dense protease environment degrade most peptides before absorption. Recombinant lactic acid bacteria represent one active strategy — alongside lipid nanoparticles and permeation enhancers — being investigated to overcome these barriers for locally acting peptides like BPC-157.
The L. lactis approach offers a distinctive advantage: the bacterium itself is the protective matrix. BPC-157 is not exposed to the gastric environment until it is secreted or shed within the intestinal lumen, where conditions are more favourable for peptide stability. This is mechanistically different from encapsulating pre-formed peptide in a nanoparticle, where barrier integrity depends on the physical properties of the carrier material.
A 2025 study in ASM Spectrum demonstrated analogous success engineering Lactobacillus gasseri to secrete GLP-1 for oral delivery, achieving measurable glycaemic effects in animal models. This parallel work validates the broader lactic acid bacteria secretion platform and suggests that the Škrlec BPC-157 approach is part of a convergent research trajectory rather than an isolated proof of concept.
A 2026 review by Wang et al. further catalogues the biochemical barriers to oral peptide delivery and identifies living bacterial secretion systems as among the most promising emerging strategies, particularly for peptides with local gastrointestinal targets — a category that includes BPC-157's established mucosal healing indications.
What Are the Key Limitations and Translational Gaps of This Approach?
The Škrlec study was conducted entirely in vitro. Antioxidant activity was measured in cell-free supernatants using chemical assays (DPPH, ABTS), not in cell-based or animal models. No in vivo data on BPC-157 delivery efficiency, mucosal bioavailability, or therapeutic outcome from the recombinant L. lactis system have been published, representing a substantial translational gap as of 2026.
Regulatory pathways for live recombinant bacterial therapeutics are complex. A genetically modified L. lactis strain expressing a foreign peptide would be classified as a genetically modified organism (GMO) in most jurisdictions, requiring containment strategies, environmental risk assessment, and clinical trial authorisation distinct from conventional drug development. These regulatory hurdles add significant time and cost to translation.
Strain stability over multiple generations is a further concern. Selection pressure against metabolically costly transgene expression can drive loss of the expression plasmid or promoter mutations in the producing strain during large-scale fermentation. Chromosomal integration of the BPC-157 construct, rather than plasmid-based expression, would improve stability but requires additional engineering effort.
Finally, the antioxidant assays used — DPPH and ABTS radical scavenging — measure chemical reducing capacity rather than biological antioxidant activity in a cellular context. Confirmation that secreted BPC-157 from L. lactis retains the same HO-1 upregulation, MDA normalisation, and cytoprotective activity observed with chemically synthesised BPC-157 in animal models remains an essential next experimental step.
What Safety Considerations Apply to Recombinant L. lactis BPC-157 Delivery?
Safety evaluation of a recombinant L. lactis BPC-157 system must address three layers: the safety profile of BPC-157 itself, the safety of the L. lactis host, and risks introduced by genetic modification. Each layer carries a different evidence base and regulatory burden, and none is fully resolved by existing literature as of 2026.
BPC-157 as a synthesised peptide has demonstrated no established lethal dose in rodent acute toxicity studies and was well-tolerated in a human pilot trial for ulcerative colitis. However, its pro-angiogenic activity via VEGFR2 upregulation raises a theoretical oncological concern that has not been formally evaluated in long-term studies. Any delivery system that increases mucosal BPC-157 exposure must account for this risk in its safety dossier.
Lactococcus lactis has an extensive human safety record as a food organism and has been used in Phase I/II clinical trials for cytokine delivery in Crohn's disease without serious adverse events. The wild-type organism is non-pathogenic and non-colonising, which limits environmental persistence after oral administration. Recombinant strains carrying antibiotic resistance markers — commonly used in laboratory constructs — would require replacement with food-grade selection systems before any clinical use.
Practitioners and researchers should note that no recombinant L. lactis BPC-157 product has received regulatory approval or entered clinical trials as of 2026. All available data are preclinical and in vitro. This system should be regarded as a research-stage platform with significant development work required before human application can be responsibly considered. Does BPC-157 Stimulate Nitric Oxide While Simultaneously Generating Oxidative Stress in 2026? What Does 2026 Research Reveal About BPC-157's Biopharmaceutical Challenges, Formulation Strategies, and Translational Development Barriers? What Does 2026 Research Reveal About BPC-157 for Musculoskeletal Healing — Regeneration or Risk?