Improving safety of oil adjuvant-based vaccines

High adjuvant reactogenicity is the main limitation for increasing the effectiveness of vaccine therapy. The aim was to reduce the immunotoxicity effects of complete Freund’s adjuvant (CFA) in warm-blooded animals. Materials and methods. The study examined Wistar rats by dividing animals into negative control (solvents); positive control (single subcutaneous CFA injection of 0.1 ml/200 g body weight (b.w.)); the “minimum” and “maximum” (per os administration of 1:4 citric and succinic acids in ratio of 17 and 88 mg/kg b.w. during 4 weeks after immunization of CFA) experiment. Body weight, hematological (complete blood count) and biochemical (hydroperoxides, malondialdehyde, catalase activity, mitochondrial dehydrogenase activity) parameters were dynamically investigated. At the end of the experiment, necropsy was performed and the relative internal organ mass coefficients were calculated. The spleen and connective tissue (knee joint) were examined histologically. The median, C₂₅–C₇₅ quartiles, Mann–Whitney U-test were calculated. Results and discussion. it was found that parameters examined were within normal range in animals of negative control group. Immunization of warm-blooded animals with CFA was accompanied by transition of acute-to- chronic inflammatory reaction (week 3 and week 7, respectively). The total leukocyte count increased from 12.5 × 10⁹ (negative control) up to 26.6 × 10⁹/L (P = 0.01) on week 3 followed by its decline down to 19.2 × 10⁹/L (P = 0.01) by week 7. Platelet count also increased significantly: from 506 × 10⁹ (negative control) up to 656 × 10⁹/L (P = 0.01, week 3) followed by decrease down to 610 × 10⁹/L by week 7 (P = 0.01). Activation of lipid peroxidation was manifested by malondialdehyde (MDA) level elevated by 55.8–61.8% (P = 0.01); the general CFA-related toxic effect resulted in 11.7% weight loss (P = 0.01), spleen swelling and thymus reduction. Administration of antioxidant acids led to a dose-dependent decline in inflammation (leukocyte count at the minimum dosage — 19.6 × 10⁹–20.9 × 10⁹/L; at the maximum 16.6 × 10⁹–16.0 × 10⁹/L), as well as normalized the “platelet/leukocyte” index up to 29.5–36.3 (positive control 24.6, negative control 40.5). The acid-related protective effect was also manifested as maintained body weight, activated catalase and inhibited lipid peroxidation. The therapeutic effect in alleviated degenerative changes in the spleen and connective tissue were revealed: reduced hemorrhagic focuses and swelling as well as preserved histoarchitectonics. Conclusion. The use of citric and succinic acids contributes to profoundly lowered CFA toxicity due to increased total antioxidant status, inhibited lipid peroxidation, improved mitochondrial metabolic activity, which ultimately lead to a decline in general systemic inflammation and allows to recommend such acids as immunoprotectors from oil adjuvant-coupled effects.