The acute and chronic toxicity of hydroxytyrosol

I. Acute Toxicity: Dose-Response and Toxicity Characteristics in Animal Models

Acute toxicity studies form the basis for evaluating compound safety, typically observing short-term animal responses through single high-dose exposure. In rodent (e.g., rat, mouse) experiments, hydroxytyrosol exhibits low-risk characteristics in acute toxicity:

Median Lethal Dose (LD₅₀)

Orally administered LD₅₀ in rats is typically >2000 mg/kg body weight, classified as "practically non-toxic" (according to LD₅₀ grading standards, >2000 mg/kg indicates low toxicity). For example, studies show that mice administered a single gavage of 5000 mg/kg hydroxytyrosol did not exhibit death or obvious behavioral abnormalities. Only high-dose groups (e.g., 3000 mg/kg) may show transient intestinal irritation (e.g., diarrhea) without histopathological damage.

Toxic Target Organs

Under acute exposure, hydroxytyrosol's toxic effects primarily target the digestive system, manifesting as mild gastric mucosal congestion or accelerated intestinal peristalsis. No significant organic damage is observed in vital organs such as the liver, kidneys, or heart. This relates to hydroxytyrosol's hydrophilicity and low bioaccumulation, with metabolites rapidly excreted mostly as glucuronide conjugates.

II. Chronic and Subchronic Toxicity: Safety Assessment of Long-Term Exposure

Chronic toxicity studies evaluate potential cumulative toxicity, carcinogenicity, and teratogenicity through long-term (months to years) low-dose animal exposure:

Subchronic Toxicity Experiments (90-Day Feeding)

In rat experiments, hydroxytyrosol was fed at 100–1000 mg/kg/day for 90 days, showing:

High-dose groups (1000 mg/kg) may exhibit slight liver weight increase, but serum transaminase (ALT, AST) levels remain normal. Liver histopathology shows only mild steatosis, not meeting toxicity damage criteria.

No significant effects on the kidneys, blood system (e.g., blood routine, coagulation function), or endocrine system (thyroid hormones, sex hormones), indicating a high organ toxicity threshold for long-term intake.

Chronic Toxicity and Carcinogenicity Studies

In a 2-year mouse feeding experiment with hydroxytyrosol at 500 mg/kg/day, no increased tumor incidence or shortened lifespan was observed. Conversely, some studies suggest its antioxidant properties may inhibit chemical carcinogen-induced cell mutations (e.g., DNA damage by benzo(a)pyrene), indicating potential adjuvant anticancer effects.

III. Toxicity Risks in Special Populations and Sensitive Groups

Reproductive and Developmental Toxicity

Teratogenicity tests: Pregnant rats administered 1000 mg/kg/day hydroxytyrosol during the sensitive period (gestation days 6–15) showed no fetal malformations in appearance, skeleton, or internal organs. Fetal body weights did not differ significantly from the control group, indicating no clear teratogenic effects.

Fertility studies: Male and female rats fed 500 mg/kg/day hydroxytyrosol for 14 consecutive days showed unaffected mating success, sperm quality, or ovarian function, suggesting no obvious toxicity to the reproductive system.

Immunotoxicity and Allergic Reactions

In vitro experiments: Hydroxytyrosol at 10–100 μM does not induce excessive expression of inflammatory factors (e.g., IL-6, TNF-α) in human peripheral blood mononuclear cells (PBMC). Animal experiments also show no histamine release or IgE-mediated allergic reactions, indicating low immunogenicity.

IV. Human Safety Evidence: Clinical Trials and Exposure Assessment

1. Human Clinical Trial Data

Single high-dose trial: Healthy volunteers orally administered 1000 mg hydroxytyrosol showed no adverse reactions (nausea, vomiting, abdominal pain) within 24 hours, with normal liver and kidney function indicators (e.g., creatinine, bilirubin), demonstrating good human tolerance to single high doses.

Long-term intervention study: A 12-week randomized controlled trial found that volunteers ingesting 300 mg hydroxytyrosol daily showed no abnormalities in blood routine or liver/kidney function, with significantly reduced oxidative stress markers (e.g., 8-OHdG), indicating safety and antioxidant benefits of long-term intake.

2. Actual Exposure and Safety Margin

In daily diets, hydroxytyrosol mainly comes from olive oil (content ~50–200 mg/kg), with typical daily intake <50 mg in the general population. Calculated from the no-observed-adverse-effect level (NOAEL) of 100 mg/kg/day in rat subchronic toxicity experiments, the safety margin (NOAEL/actual exposure) >100 for a 60 kg human indicates extremely low real-world exposure risk.

V. Toxicity Mechanisms and Controversies

Exploration of Potential Toxicity Mechanisms

High-dose hydroxytyrosol may induce toxicity through:

Intestinal microbiota dysbiosis: Excessive intake may inhibit the growth of beneficial gut bacteria (e.g., Bifidobacterium), reducing short-chain fatty acid production and affecting intestinal barrier function.

Oxidative stress reversal: Under specific conditions (e.g., saturated intracellular antioxidant enzymes), high-concentration hydroxytyrosol may generate free radicals causing oxidative damage, but this phenomenon is only observed in vitro at extremely high concentrations (>1 mM), rare under in vivo physiological conditions.

Controversies and Unresolved Questions

Some in vitro cell experiments show that hydroxytyrosol at >100 μM may inhibit tumor cell proliferation, while others indicate no significant impact on normal hepatocyte mitochondrial function. Such differences may relate to cell types, exposure duration, and metabolic product variations, requiring more in vivo validation.

VI. Safety Conclusions and Regulatory Recommendations

Safety Consensus

Based on animal experiments and human clinical data, hydroxytyrosol demonstrates good safety at routine dietary and supplement doses (≤500 mg/day), with no evidence of acute/chronic toxicity, teratogenicity, or carcinogenicity.

Regulatory and Application Suggestions

The European EFSA has approved hydroxytyrosol as a functional food ingredient, recognizing its health claim of "maintaining vascular endothelial function," with a recommended daily intake ≤5 mg/kg body weight (approximately 300–600 mg for adults).

Long-term safety in special populations (e.g., liver disease patients, pregnant women) requires more data, but existing studies show no contraindications. Intake under professional guidance is recommended.

Toxicological studies of hydroxytyrosol, from animal models to human trials, demonstrate high safety. Its low toxicity is closely related to antioxidant activity, rapid metabolism, and low accumulation. Future research could focus on metabolic kinetic differences under high-dose exposure (e.g., the impact of individual gene polymorphisms on toxicity) and interactions with other food components to provide a basis for more precise safety assessments.