Anti-inflammatory activity of seven plant species with potential use as livestock feed additives

Abstract

Inflammatory conditions and associated oxidative stress are common in livestock. The present study aimed to investigate in depth the anti-inflammatory activity of seven medicinal plants (Dichrostachys cinerea, Ehretia rigida, Salix babylonica, Vachellia erioloba, V. gerrardii, V. sieberiana and V. tortilis) traditionally used to treat inflammatory disorders in South Africa. These plants are being investigated for possible inclusion in animal feed as additives to support health and promote growth. The anti-inflammatory potential of plant extracts was evaluated in terms of inhibition of the 15-lipoxygenase (15-LOX) enzyme and nitric oxide (NO) release in LPS-induced RAW 264.7 macrophages, together with cytotoxicity studies. The effect of plant extracts in modulating the expression of pro-inflammatory mediators including cyclooxygenase (COX), inducible nitric oxide synthase (iNOS), and the cytokine interleukin-6 (IL-6) was evaluated using quantitative reverse transcription polymerase chain reaction (qRT-PCR). In vitro antioxidant activity was investigated using chemical assays. ULPC-MS and ICP-MS were used to detect potentially bioactive phytochemicals and concentrations of essential elements respectively. Methanol and acetone extracts of D. cinerea had the best activity against 15-LOX (IC50 values of 0.80 and 0.64 mg/ml, respectively). The methanol extracts of E. rigida, V. tortilis and V. sieberiana inhibited NO with IC50 of 90.11, 101.52 and 94.11 µg/ml respectively, higher than that of the positive control (IC50 = 30.00 µg/ml). Furthermore, these plants had low cytotoxicity (LC50 ≥ 70 µg/ml) against RAW 264.7 macrophages. Interestingly, E. rigida, V. sieberiana and V. tortilis extracts decreased the expression of iNOS, COX and IL-6. There was a positive correlation between the inhibition of NO release from macrophages by plant extracts and the downregulation of iNOS mRNA levels. There was no significant difference in the antioxidant activity (ABTS) of D. cinerea methanolic extract with IC50 = 5.37 µg/ml compared to the positive controls, Trolox (IC50 = 4.42 µg/ml) and ascorbic acid (IC50 = 4.43 µg/ml). Flavonoids, fatty acids and essential trace elements such as Fe, Zn and Mn were detected in E. rigida, and these are likely to be responsible for the good anti-inflammatory effect of the extracts. This study provides the first evidence of the regulation of pro-inflammatory mediator and cytokine genes by the selected plant extracts. These results support the use of the plants, in particular E. rigida, as potential feed additives to reduce inflammation associated with many diseases.