Skin defences boosted by grapefruit extract

 This clears the cell of molecular rubbish, thereby preventing molecular damage, and ageing.2 According to the literature, citrus fruits rich in bioflavonoids such as naringin and hesperidin3 can help to protect the body against toxin overload when taken orally.4 The use of such natural actives is continuously increasing as the understanding of their ability to slow the ageing process improves. One of the most powerful detoxification mechanisms is centred on the phase I and phase II enzymes. Phase I activation of lipophilic compounds is carried out by enzymes of the CYP450 family.5 This phase I biotransformation creates an activated intermediate that is either directly eliminated from the body, or more commonly becomes a substrate for one of the phase II conjugation enzymes prior to elimination from the cell. Phase II enzymes, such as quinone reductase, perform a broad variety of detoxification reactions. Quinone reductase is able to detoxify a broad range of quinones produced by oxidative metabolism and is known to be expressed in human keratinocytes. Here we summarise two in vitro studies which show that a standardised grapefruit extract rich in naringin and hesperidin3 significantly induces the activity of both phase I and phase II enzymes in primary human keratinocytes.

 Citrus fruits are commonly used in commercial juice preparations for human consumption. Fruits from citrus species are widely used in traditional medicine, reflecting the particularly high abundance of bioactive compounds in the peel of the fruit. Many active components of medicinal value have been isolated from citrus species, including anti-allergic, antioxidant, anti-tumor and immunomodulating agents.6 Citrus fruits contain a wide variety of phytochemicals, including flavonoids, such as hesperetin, hesperidin, naringin and narirutin (Fig. 1). The biological action of these flavonoids is possibly linked to their interactions with key regulatory enzymes involved in cell activation and receptor binding.6 In addition, these flavonoids function as antioxidants. Polyphenols (such as the flavonoids) may be regarded as xenobiotics by animal cells, and are known to interact with the phase I and phase II enzyme systems. It has also been shown that flavonoids modulate the expression of glutathione, an important enzyme in both cellular antioxidant defences and detoxification of xenobiotics.4 One important task for cellular glutathione is to scavenge free radicals and peroxides produced during normal cellular respiration, which would otherwise oxidise proteins, lipids, and nucleic acids. One mechanism operating to counteract oxidative damage involves transactivation of genes encoding enzymes that participate in glutathione metabolism and synthesis. Typically, these enzymes belong to the phase I and II families of detoxification genes.4 Through both routine metabolism and environmental exposure, the skin continuously accumulates a variety of endogenous and exogenous metabolites. Without prompt detoxification, these compounds can accelerate the ageing process (Fig. 2).7 The natural defence mechanisms of the skin cells are centered on detoxifying phase I and phase II enzymes that transform the waste molecules prior to excretion from the cell.1 Phase I and phase II enzymes may be either constitutively expressed or inducible. Importantly, certain environmental and nutritional agents have been found to influence the induction and activities of specific phase I and phase II enzymes. In these studies, phase I and phase II enzymes were evaluated in the presence and absence of a standardised grapefruit extract (GE).

Materials and methods