Synergy quantifications to identify individual contributions of combination partners to the overall activity - The example of STW 5

Abstract

Background: The rationale of combinations of plant extracts is often questioned. The common argument for combinations is a higher efficacy of the combination partners by multitargeting and the elimination of adverse events.

Aim: STW5, a well-known fixed herbal multicomponent preparation, is recommended in the German treatment guidelines for functional gastrointestinal diseases. The study assessed effects of STW5, its single plant components and combinations thereof on different targets to identify synergistic, additive or antagonistic effects of the combination partners.

Study design/methods: STW5, its nine components and triple combinations thereof were investigated in two in vitro models - human esophageal epithelial cells (Het1A) and intestinal smooth muscle cells (HISMC) - in comparison to Omeprazole (OM) for the release of interleukin 8 (IL-8) as surrogate for inflammation and of Ca²⁺ as surrogate for motion, under non-inflammatory and inflammatory (Capsaicin 80 µM (CAP)) conditions. The combination index (CI) of triple combinations was calculated to assess synergistic, antagonistic and additive effects.

Results: In Het-1A cells, STW5 showed, under non-inflammatory as well as inflammatory conditions, releases of IL-8 (49.3 ± 4.2 pg/ml, 33.7 ± 2 pg/ml) comparable to the untreated control (46.3 ± 4.8 pg/ml). CAP increased IL-8 releases to 85.8 ± 14 pg/ml (p < 0.005). Among the single plant extracts the Iberis amara extract (IBE) induced high IL-8 releases under non-inflammatory (441 ± 177 pg/ml) and inflammatory (625± 121 pg/ml) conditions. The Silybum marianum (L.) extract (SM) reduced releases up to 20.1 ± 8 pg/ml (inflammation). The CI-values of triple combinations with IBE ranged from high synergy (CI<0.03) to antagonism (CI:480). Within the triple combinations SM was the most effective combination partner to reduce IL-8. The combination of Angelica archangelica (L.)/Carum carvi (L.) was also effective. In HISMCs, STW5 induced concentration dependent higher Ca²⁺-releases. Only Melissa officinalis (L.) (MO) induced high Ca²⁺- releases in HISMCs.

Conclusion: In Het-1A, STW5 inhibited Il-8 releases, although one of its components (IBE) stimulated IL-8 strongly. The combination partners in STW5 assured an overall marked anti-inflammatory action. In the triple combinations SM was identified as most important combination partner for the IL-8 reduction. CI-measurements can support the identification of active combination partners in a multicomponent preparation and can give directions towards the search for multitarget effects.

Keywords: Ca(2+); Combination index; Functional gastrointestinal diseases; IL-8; Multitargeting; Reflux-esophagitis; Synergy.