Modulators of diabetic neuropathy and inflammation from Saponaria officinalis: Isolation of active phytochemicals and potential mechanisms of action.

Abstract

Natural metabolites are rich in neuroactive and anti-inflammatory phytochemicals. Soapwort or Saponaria officinalis (Sap) has been utilized for its immunomodulatory and ant-rheumatic properties. Thus, the aim is to exploit Sap phytochemically and to investigate Sap isolated active phytochemicals effect to modulate diabetic neuropathy and inflammation, and their possible mechanisms of action. Bio-guided chromatographic fractionation and phytochemical isolation of the most abundant Sap phytochemicals utilizing RP-HPLC, 13C, and 1H NMR, in-vivo models of diabetes, diabetic neuropathy, and inflammation were used. Glucometers, HbA1c micro-columns, in-vivo hind-paw edema, tail-flick, hot plate, and Von-Frey filaments methods were utilized to investigate the acute, subchronic, and long term diabetes, inflammation, hyperalgesia, and mechanical allodynia. In-vivo antioxidant, inhibitory alpha-amylase, and alpha-glucosidase, and serum insulin levels, IL-6, IL-10, and TNF-alpha cytokines levels were utilized to investigate Sap mechanisms of action. The phytochemical post-hydrolysis RP-HPLC investigation results show six major peaks; Quillaic acid (12.5%), Quillaic acid 22 β-OH (11.25%), Gypsogenin (21.25%), Phytolaccinic acid (18.75%), Phytolaccinic acid (17.50%), and Echynocystic acid (15.10%). The bio-guided chromatographic fractionation investigation utilizing reversed phase HPLC, 13C and 1H NMR has shown that Quillaic acid (QA) is the most abundant and biologically active compound. Sap 20mg/kg has shown the highest potency in normalization of blood glucose level (BGL) acutely (6-h), subchronically (eight-days), and longer-term (eight-weeks) correlated to Sap 10 and 7mg/kg, and QA 0.7, 1.0, 2.0mg/kg. The highest amelioration of diabetic neuropathy (thermal hyperalgesia and mechanical allodynia) was Sap 20mg/kg. The anti-inflammatory potentials of Sap 20mg/kg have shown dominance in decreasing carrageenan-induced in-vivo hind-paw edema. The anti-nociceptive mechanism of action might be due to Sap insulin secretagogue and the in-vivo antioxidant potentials. The reduction of IL-6 cytokines and TNF-alpha, along with the elevation of the IL-10 cytokine level might be the underlying Sap anti-inflammatory mechanism. Phytochemically, QA has shown to be the most abundant and biologically active compound in Sap extract. Sap has shown significant (p<0.05) anti-diabetic, anti-diabetic neuropathy, and anti-inflammatory effects. Our results provide new insights into the potential effects of Saponaria and Quillaic acid as future alternative therapies against diabetic neuropathy and inflammation.