Abstract
Activity-guided fractionation of Actinidia fruit species, including Kiwifruit, has identified DLGG (dilinolenoyl galactosyl glycerol) as a potent PPARγ (peroxisome-proliferator-activated receptor γ) ligand. DLGG is a type of MGDG (monogalactosyl diacylglycerol) and is present in all chloroplasts, and therefore all green fruits and vegetables. PPARγ is a ligand-activated transcription factor that regulates glucose metabolism and inflammation. An ethyl acetate extract of Actinidia chrysantha was fractionated by HPLC and the PPARγ-binding activity was detected by FP (fluorescence polarization). Linoleic and α-linolenic acids in A. chrysantha were readily detected as PPARγ ligands. Slow-binding PPARγ ligands were detected in several hydrophobic fractions. High-resolution MS identified DLGG as one of these ligands and confirmed that its binding is non-covalent. DLGG is a slow-binding PPARγ ligand with an IC50 of 1.64 μM, ±0.093 achieved after 45 min equilibration. DLGG is the first example of a form of DAG (diacylglycerol) that is a PPARγ ligand. In addition, DLGG is the first reported glycolipid ligand for PPARγ and also the first non-covalent, slow-binding PPARγ ligand.
Highlights
PPARγ is a ligand-activated transcription factor and the target of the thiazolidinedione group of anti-diabetic drugs [1]
Actinidia species were selected as a potential source of new PPARγ ligands because they are rich in α-linolenic acid, a well-known PPARγ ligand, and because they contain a variety of polyunsaturated compounds such as lutein, β-carotene and various other carotenoids [13]
Survey of Actinidia species for PPARγ ligand activity PPARγ -binding activity was detected in all extracts and the activity varied among the different Actinidia species (Figure 1A)
Summary
PPARγ (peroxisome-proliferator-activated receptor γ ) is a ligand-activated transcription factor and the target of the thiazolidinedione group of anti-diabetic drugs [1]. Actinidia species were selected as a potential source of new PPARγ ligands because they are rich in α-linolenic acid, a well-known PPARγ ligand, and because they contain a variety of polyunsaturated compounds such as lutein, β-carotene and various other carotenoids [13]. We have used activity guided fractionation to identify a new PPARγ ligand in ethyl acetate extracts of Actinidia species, of which kiwifruit (A. deliciosa) is a member. PPARγ -binding activity was measured using a FP (fluorescence polarization) assay, and the active molecule was characterized using HPLC and MS. PPARγ binding activity in Actinidia extracts (A) PPARγ binding activity in the ethyl acetate extracts of a panel of Actinidia species fruits measured by FP. Mass spectra were averaged across the protein HPLC peak and the molecular masses of PPARγ and the PPARγ conjugates were calculated using the ‘deconvolute’ function of DataAnalysis (Bruker Daltonics)
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