Literature Review | June 2018

Select a topic from the list below:

• Evaluation studies of persimmon plant (Diospyros kaki) for physiological benefits and bioaccessibility of antioxidants by in vitro simulated gastrointestinal digestion

• Pharmacological activation of REV-ERBs is lethal in cancer and oncogene-induced senescence

• The NADPH organizers NoxO1 and p47phox are both mediators of diabetes-induced vascular dysfunction in mice

Evaluation studies of persimmon plant (Diospyros kaki) for physiological benefits and bioaccessibility of antioxidants by in vitro simulated gastrointestinal digestion

Ruth Martínez-Las Heras, Alicia Pinazo, Ana Heredia, Ana Andrés, Food Chemistry 214 (2017) 478–485; DOI: 10.1016/j.foodchem.2016.07.104

Bioaccessibility refers to the amount of antioxidants released from a food matrix into the intestinal brush border for transport into the cell (Wootton-Beard et al., 2010). This differs from the more prevalent term – bioavailability, which refers to the quantity of antioxidants which pass through the cell membrane and are available for use within the cell. Thus, in terms of sequence, bioaccessibility is a phase of assessment prior to bioavailability. There are many models which can be used to evaluate the bioaccessibility of antioxidants, where in vivo assessments are deemed as the best. Nevertheless, this is an expensive option and therefore, it is generally advisable to carry out an in vitro evaluation prior to adoption of an in vivo methodology. Vegetables and fruits are known to possess valuable antioxidant compounds which are able to mediate many disease conditions related to the flux of free radicals and oxidative stress. In this respect, it is imperative to assess whether these plant-based antioxidants do survive the complex digestive process through exposure to oral, gastric and intestinal digestive enzymes.

The study by Heras et al (2016), evaluated the bioaccessibility of antioxidants of persimmon plant (Diospyros kaki), more specifically to determine the changes undergone by total polyphenols, flavonoids and the total antioxidant (TAC) capacity of the aqueous leaf extract, fruit and fibre, extracted from the pulp and peel of persimmon fruit and stabilized by hot air drying or freeze-drying. A harmonized INFOGEST protocol published by Minekus et al. (2014) was followed in this study, while the TAC was estimated on the basis of the scavenging activity of the 2,2-diphenyl-1- picrylhydrazyl (DPPH) free radical (Brand-Williams, Cuvelier, & Berset, 1995; Shahidi, Liyana-Pathirana, & Wall, 2006). The total phenolic content of different samples was spectrophotometrically determined by a modified Folin-Ciocalteu method (Sakanaka, Tachibana, & Okada, 2005). The total flavonoid content was measured according to the colorimetric method described by Zhishen, Mengcheng, & Jianming (1999). The in vitro digestion was carried out in the absence of the digestive enzymes as a control. To evaluate the effect of the food matrix on the changes undergone by the polyphenols, flavonoids and TAC along gastrointestinal in vitro digestion, the recovery and bioaccessibility indexes were calculated.

It was observed that the polyphenols, flavonoid and total antioxidant capacity of persimmon leaf aqueous extract were more sensitive to the biochemical conditions of the gastrointestinal environment than those coming from persimmon fruit or fibres, despite being the richest source of the antioxidant compounds. The duodenal pH and the presence of pancreatin and bile salts increased the solubility and release of polyphenols as well as improved the final bioaccessibility of flavonoids in all digestive matrices. It was also concluded that, although the bioaccessibility of TAC in the fruit of persimmon and its fibres was higher than in the aqueous extract of persimmon leaves, a serving of persimmon leaf infusion (1.5 g in 110 mL of water) and a persimmon fruit (200 g) would provide similar bioaccessible antioxidant activity at the end of digestion, whereas a serving of fruit would provide twice total polyphenols than a persimmon leaf infusion. These findings of this study in particular, were of importance since the behavior of the antioxidant compounds present in similar fruits could be expected to be of the same manner. Thus, the study could be used as a platform to conduct evaluations of similar extent on other fruits which are known to be a significant source of antioxidant compounds. (Prepared by Viduranga Waisundara, Department of Food Technology, Faculty of Technology, Rajarata University of Sri Lanka, Mihintale, Sri Lanka)

Pharmacological activation of REV-ERBs is lethal in cancer and oncogene-induced senescence

Sulli G, Rommel A, Wang X, Kolar MJ, Puca F, Saghatelian A, Plikus MV, Verma IM, Nature. 2018 Jan 18;  553 (7688) :351-355

Circadian machinery is the cell autonomous clock that coordinates a complex network of physiological processes such as cell proliferation, metabolism, inflammation and DNA damage response. The disturbance of such machinery predisposes individuals to cancer development. Authors have shown that pharmacological modulation of circadian clock may be an innovative and selective cancer treatment. The authors targeted REV-ERBs, which are essential component of circadian clock which. Viaheme binding, these proteins act as repressors of processes involved in tumorigenesis. Pyrrole derivative SR9009 and SR9011 act as their agonists and selectively target malignant and neoplasms. Authors showed that oxidative stress (excessive production of reactive species in cancer cells) targeting is not the reason for their selectivity to cancer vs normal cells, but it is the action on lipogenesis and regulation of autophagy. These compounds suppressed glioma growth in vivowithout causing toxicity to mice. They also act on numerous other cancer cell types, such as leukemia, breast cancer, colon cancer and melanoma which harbor a range of oncogenic drivers such as HRAS, KRAS, BRAF, PTEN deficiency and β catenin but are not toxic to normal cells at comparable concentrations (Prepared by Ines Batinic-Haberle, Duke University School of Medicine, Durham, NC, USA)

The NADPH organizers NoxO1 and p47phox are both mediators of diabetes-induced vascular dysfunction in mice

Rezende F, Moll F, Walter M, Helfinger V, Hahner F, Janetzko P, Ringel C, Weigert A, Fleming I, Weissmann N, Kuenne C, Looso M, Rieger MA, Nawroth P, Fleming T, Brandes RP, Schröder K. Redox Biology, 15, 12-21. doi:10.1016/j.redox.2017.11.014

The NADPH Oxidases (Nox) are a family of enzymes that generate superoxide or hydrogen peroxide by passing electrons across two heme groups to molecular oxygen. Nox1, one of the seven Nox family members requires complex assembly for its activity. The Nox1 complex is comprised of Nox1, p22phox, Rac1, the activator NoxA1 and the organizer NoxO1. Homologs of NoxA1 and NoxO1, p67phox and p47phox respectively, have been shown to be somewhat interchangeable in the assembled complex. One of the major differences in these mixed complexes is the organizing protein. P47phox, but not NoxO1, has an autoinhibitory domain that is disengaged upon phosphorylation.

The artery is comprised of endothelial, smooth muscle and adventitial cell layers. Nox1 has been found in each of these cell types. P47phox has been shown to be expressed in smooth muscle cells while NoxO1 expression has been shown to be in endothelial cells. Increased Nox1 expression and complex assembly are associated with vascular disease pathogenesis including diabetes induced vascular diseases. What is unclear about this process is if the mixed complexes are cell specific and if they elicit similar responses in differing cell types.

In Rezende et al the authors demonstrate that Nox1 complexes comprised of NoxA1 and NoxO1 had higher basal levels of ROS production as compared to complexes containing NoxA1 and p47phox. This was consistent with the literature demonstrating the need for disengagement of the autoinhibitory domain in p47phox prior to complex formation. The authors found that p47phox was located in primarily in the adventitial cells and localized with macrophages while NoxO1 was in the medial, smooth muscle cells. Given there distinct locations of the organizing proteins within the vasculature, the authors utilized NoxO1 and p47phox knockout mice to determine the role of each in protein in vascular physiology. The authors demonstrate a reduction in systolic blood pressure in the single knockouts alone and double knockouts. However, only in p47phox knockouts was the diastolic pressure reduced. This coincided with increased sensitivity to acetylcholine, endothelium dependent vasorelaxation, in p47phox knockouts. In mice given steptozotocin to mimic type I diabetes, knockdown of either of the organizing proteins protected against diabetes induced endothelial dysfunction. Importantly this observation was not due to an induction in the organizing protein homolog. Non-diabetic and diabetic animal models showed distinct mRNA expression profiles for the p47phox and NoxO1 knockouts. P47phox knockout mice showed induction of inflammatory genes after steptozotocin administration whereas NoxO1 had some overlap in induction of similar inflammatory genes but also some that were specific to the NoxO1 knockout. This was highlighted by the authors by measuring IFNγ levels. NoxO1 knockout mice had reduced IFNγ levels after steptozotocin, however, the p47phox knockout animals had increased levels of IFNγ, after steptozotocin.

The results from this study highlights the importance of cellular distribution of the Nox cytosolic subunits and how that distribution effects vascular homeostasis. It also demonstrates a role for NoxO1 in vascular dysfunction. While the authors focused on diabetes induced vascular dysfunction it is likely that there are other conditions that may rely on distinct roles of these proteins for Nox enzyme complex formation. (Prepared by Brandon Schickling, Duke University, Durham, NC, USA)