Abstract
Consumption of dietary bioactives is an avenue to enhancing the effective healthiness of diets by attenuating the glycaemic response. The intestinal brush border enzyme sucrase-isomaltase (SI) is the sole enzyme hydrolysing consumed sucrose, and we previously showed the acute effects of olive leaf extract (OLE) on sucrase activity when given together with sugars both in vitro and in vivo. Here we tested whether OLE could affect sucrase expression when pre-incubated chronically, a “priming” effect not dependent on competitive interaction with SI, in both a cell model and a human intervention. Using differentiated Caco-2/TC7 cells, long-term pre-treatment with oleuropein-rich olive leaf extract (OLE) lowered SI mRNA, surface protein and activity, and attenuated subsequent sucrose hydrolysis. Based on these results, a randomised, double-blinded, placebo-controlled, crossover pilot study was conducted. OLE (50 mg oleuropein) was consumed in capsule form 3 times a day for 1 week by 11 healthy young women followed by an oral sucrose tolerance test in the absence of OLE. However this treatment, compared to placebo, did not induce a change in post-prandial blood glucose maximum concentration (Glcmax), time to reach Glcmax and incremental area under the curve. These results indicate that changes in SI mRNA, protein and activity in an intestinal cell model by OLE are not sufficient under these conditions to induce a functional effect in vivo in healthy volunteers.
Highlights
Food components which lower the glycaemic response of carbohydrate-rich meals could help attenuate the overall dietary glycaemic load and potentially decrease the risk of type 2 diabetes [1].We have previously shown an acute activity for pomegranate and for mixed fruit puree with bread [2,3], and others have shown comparable effects for cinnamon on rice [4], for mixed berry puree with sucrose [5], and for apple extract with glucose [6]
We have shown that oleuropein inhibits acutely sucrase activity when
olive leaf extract (OLE) substantially decreased SI mRNA expression by ~78% (p < 0.001) for cells cultured in glucose and by 74% (p < 0.001) for cells cultured in sucrose
Summary
We have previously shown an acute activity for pomegranate and for mixed fruit puree with bread [2,3], and others have shown comparable effects for cinnamon on rice [4], for mixed berry puree with sucrose [5], and for apple extract with glucose [6]. The health benefits of olives and olive oil are well documented, but originally attributed to the constituent oleic acid, the complementary effects of the (poly)phenolic components have been recognized [9,10]. Olive leaves have a higher concentration of oleuropein compared to the olive fruit [11] while an olive leaf extract (OLE) has been reported to have several functional properties [10,12]. We have shown that oleuropein inhibits acutely sucrase activity when
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