Mustard Oils from Nasturtium Influence the Cellular Glucose and Detoxification Metabolism

Nasturtium, which is also known as a medicinal plant, contains mustard oil compounds which are noticeable when eaten by their sharp taste. As a joint study by the DZD partner the German Institute of Human Nutrition (DIfE) and the Leibniz Institute of Vegetable and Ornamental Crops (IGZ) suggests, mustard oil from nasturtium has an anti-diabetic effect and activates enzymes of the detoxification metabolism.

The research team led by Valentina Guzmàn-Pérez, Christiane Bumke-Vogt and Andreas Pfeiffer of DIfE and Monika Schreiner of IGZ recently published its results in the open access journal PLOS ONE (Guzmàn-Pérez et al. 2016, DOI:10.1371/journal.pone.0162397).

Mustard oils mainly occur in nature in a chemically bound form as so-called "mustard oil glycosides" (glucosinolates) in cruciferous plants. These plants include, for example, mustard, broccoli, pak choi, radish, horseradish, garden cress and nasturtium. It has long been known from natural medicine that mustard oil compounds from horseradish and the edible nasturtium (Tropaeolum majus) have antibacterial properties. Moreover, recent  clinical studies have shown that these bioactive plant ingredients also have anti-diabetic properties. For example, mustard oil-containing extracts from broccoli sprouts not only beneficially influence the cholesterol and inflammation marker values of patients with type 2 diabetes but also their glucose metabolism. Similarly, in other studies, horseradish extracts had positive impact on the effect of the messenger substance insulin. But which cellular and molecular mechanisms underlie this antidiabetic effect? To find an answer to this question, the researchers investigated the metabolic effects of mustard oil from nasturtium using test systems based on human cell cultures.

To this end, the scientists gave different concentrations of a mustard oil compound (aromatic benzyl glucosinolate) isolated from nasturtium into the nutrient medium of the test cells and simultaneously added the plant enzyme myrosinase *, which converts the compound into the mustard oil benzyl isothiocyanate. As the researchers observed, depending on the dose, the mustard oil released in the cell culture medium modulated the intracellular signaling pathways of the messenger substance insulin.
It also reduced the production of enzymes necessary for glucose regeneration in the investigated human liver cells.

“From this, we conclude that mustard oil also reduces glucose synthesis in the liver. This is a very important finding, since with respect to diabetes an excessive, endogenous glucose production can lead to elevated blood glucose levels. Our results may also explain the positive results of the clinical studies investigating, the effect of broccoli or horseradish extract on the human glucose metabolism,” said first author Guzmàn-Pérez. "Another interesting result is that the mustard oil also activates protective mechanisms against oxidative stress by stimulating the production of enzymes of the cellular detoxification metabolism," the scientist added.

“It is certainly too early to say to what extent the consumption of nasturtium can help to improve the glucose metabolism of people with type 2 diabetes or to prevent the disease,” said Andreas Pfeiffer, the diabetologist who led the study. “Nevertheless, our results are already helping to better understand the molecular mechanisms underlying the potentially anti-diabetogenic effects of mustard oils,” said Christiane Bumke-Vogt, who coordinated the study. “This is an important prerequisite for developing new nutritional strategies and possibly also diabetes medication,” added Pfeiffer. “In the future, we want to continue our joint investigations by isolating sufficient amounts of the mustard oil compounds from nasturtium and investigating their effects further in nutritional studies," said Monika Schreiner, whose research focuses on secondary plant substances.

Background Information
The substances of the nasturtium act, among other things, against certain viruses, bacteria and yeast fungi. The nasturtium can be used for pain, for improving wound healing, for digestive disorders, as well as against bladder infections and upper respiratory tract infections. The Brassicales species of nasturtium (Tropaeolum majus) was selected by scientists from the University of Würzburg (i.e. the study group for the developmental history of medicinal plants) as "Medicinal Plant of the Year 2013" with reference to the antibiotically active mustard oils contained in it (Source: Wikipedia).

* Myrosinase is an enzyme of vegetable origin that cleaves mustard oil glycosides into glucose and mustard oils. Thus the plant defends itself against predators, because mustard oils are generally sharp-smelling or tasting. The mustard oil glycoside thus represents the safe and thus storable precursor of these aggressive substances. Myrosinase is predominantly found in cruciferous plants, which are characterized by a sharp taste because of the mustard oil glycosides present in them. In the plant, myrosinase and its substrates (mustard oil glycosides) are stored separately in different cells. Only when the plant is injured, for example, by the mouthparts of an insect, are the two components mixed. The myrosinase then cleaves the mustard oil glycosides so that mustard oils are formed. The mustard oils include isothiocyanates (such as allyl mustard oil), thiocyanates, nitriles and epithionitriles. Some of these substances are highly volatile and smell pungent; others are non-volatile and taste sharp. Together, they serve to ward off hostile enemies such as herbivorous insects. Some plants, such as cabbage, accelerate the myrosinase reaction by storing vitamin C. In fact, cabbage has higher vitamin C content than oranges. The reaction of the myrosinase is used by man to season food. If horseradish is rubbed, the storage cells of myrosinase and mustard oil glycoside are injured so that both components come together and mustard oils are produced, which cause the characteristic sharp taste. When, on the other hand, the horseradish is cooked, no tissue injury occurs, so the sharpness does not occur (Source: Wikipedia).