Toxicity analysis of Nisin

As a widely used natural food preservative, toxicity research on Nisin is central to its safety assessment. The following analysis covers acute toxicity, subchronic toxicity through experimental models, data characteristics, and mechanism of action:

I. Acute Toxicity Studies: Safety Boundaries for Short-Term High-Dose Exposure

1. Animal Models and Dosage Design

Experimental Subjects: Mammals such as rats, mice, and rabbits are commonly used, administered via oral gavage, intraperitoneal injection, or intravenous injection to simulate different exposure routes.

Dosage Range: In oral acute toxicity tests, the median lethal dose (LD₅₀) of Nisin in rats typically exceeds 2000 mg/kg body weight (classified as "practically non-toxic" per FDA toxicity grading standards). For example, the oral LD₅₀ in mice reaches 4000–6000 mg/kg, far higher than that of table salt (LD₅₀ ≈ 3000 mg/kg).

2. Toxicity Manifestations and Mechanisms

Acute Exposure Reactions: High doses may cause transient gastrointestinal irritation (e.g., vomiting, diarrhea) without organ-specific damage. In intraperitoneal injection experiments, rats may exhibit temporary immune cell activation, but no pathological changes in vital organs like the liver or kidneys are observed.

Mechanism of Action: Nisin’s low acute toxicity relates to its target— as a bacterial cell membrane disruptor, it shows no significant damage to eukaryotic cell membranes (due to major compositional differences from bacterial membranes, lacking peptidoglycan precursors for Nisin binding), resulting in extremely low toxicity to mammalian cells.

II. Subchronic Toxicity Studies: Assessment of Potential Risks from Long-Term Low-Dose Exposure

1. Experimental Design and Observation Period

Duration and Dosage: Typically lasting 90 days (rodents) or 6 months (non-rodents), with dosages set at 100–1000 times the expected human intake (e.g., 50–2000 mg/kg/day in rat experiments).

Observation Indicators:

Macro Indicators: Body weight gain, food intake, blood biochemistry (liver and kidney function markers like ALT, creatinine), urine analysis;

Micro Indicators: Histopathological examination of major organs (liver, kidney, spleen, thymus), immune function (e.g., lymphocyte subsets), and genotoxicity testing.

2. Key Research Findings

No-Observed-Adverse-Effect Level (NOAEL): In 90-day rat subchronic experiments, NOAEL is usually ≥200 mg/kg/day. At 1000 mg/kg/day, some rats may exhibit mild intestinal flora disturbance (e.g., reduced Bifidobacterium count) without tissue damage or systemic toxicity.

Impact on the Immune System: High-dose Nisin may cause mild thymic atrophy in rats (dosage ≥500 mg/kg/day), but lymphocyte counts and immunoglobulin levels remain unchanged, indicating extremely weak immunotoxicity.

Metabolism and Excretion: Orally ingested Nisin is rapidly degraded into amino acids by proteases in the gastrointestinal tract. Intact molecules are undetectable in blood, and urinary excretion rate is <1%, confirming no body accumulation.

III. Toxicity Considerations for Special Populations and Sensitive Groups

Infants, Toddlers, and Pregnant Women

Trace amounts of Nisin naturally exist in breast milk (≈0.1–1 μg/L), with no reported adverse effects on infant development.

Rat teratogenicity tests (dosage up to 1000 mg/kg/day) show no fetal structural abnormalities or growth retardation, indicating no teratogenicity.

Immunocompromised Individuals

In vitro experiments show Nisin does not inhibit the activity of human immune cells (e.g., T cells, macrophages). Even in immunosuppressed models (e.g., nude mice), high-dose exposure does not increase infection risk.

IV. Safety Conclusions from Toxicity Studies and International Recognition

Assessments by Authoritative Agencies

The Joint FAO/WHO Expert Committee on Food Additives (JECFA) has established an acceptable daily intake (ADI) for Nisin of 0–33,000 IU/kg (≈5 mg/kg), far higher than actual dietary exposure (adult daily intake ≈0.1–0.5 mg).

Both the EU’s EFSA and the US FDA have approved Nisin as a safe preservative for use in dairy products, meats, and other foods.

Comparison with Chemical Preservatives

Compared to potassium sorbate (ADI 0–25 mg/kg) and sodium benzoate (ADI 0–5 mg/kg), Nisin has a higher safety threshold and advantages in toxicity risk due to its natural origin.

V. Research Limitations and Future Directions

Current Gaps

Subchronic studies primarily focus on rodents, with limited data from non-human primate models.

The dynamic impact of long-term exposure on intestinal flora (e.g., drug resistance gene transfer) requires further investigation.

Frontier Explorations

Using single-cell sequencing to analyze Nisin’s effects on intestinal immune cells.

Employing organoid models to study Nisin’s potential toxic effects on human organs (e.g., intestine, liver), enhancing the precision of risk assessment.

Acute and subchronic toxicity studies of Nisin demonstrate its extremely high safety for mammals, with no risks of accumulation, teratogenicity, or immunotoxicity. This property not only supports its widespread use in the food industry but also provides toxicological evidence for development in biomedical fields (e.g., topical antibacterial formulations). Future research should integrate emerging toxicological technologies to further improve safety data on long-term exposure and expand its applications in broader scenarios.