Soy protein isolate induces CYP3A1 and CYP3A2 in prepubertal rats

Effects of soy containing diet and isoflavones on cytochrome P450 enzyme expression and activity

Cytochromes P450 (CYPs) play an important role in metabolism and clearance of most clinically utilized drugs and other xenobiotics. They are important in metabolism of endogenous compounds including fatty acids, sterols, steroids and lipid-soluble vitamins. Dietary factors such as phytochemicals are capable of affecting CYP expression and activity, which may be important in diet-drug interactions and in the development of fatty liver disease, cardiovascular disease and cancer. One important diet-CYP interaction is with diets containing plant proteins, particularly soy protein. Soy diets are traditionally consumed in Asian countries and are linked to lower incidence of several cancers and of cardiovascular disease in Asian populations. Soy is also an important protein source in vegetarian and vegan diets and the sole protein source in soy infant formulas. Recent studies suggest that consumption of soy can inhibit induction of CY1 enzymes by polycyclic aromatic hydrocarbons (PAHs) which may contribute to cancer prevention. In addition, there are data to suggest that soy components promiscuously activate several nuclear receptors including PXR, PPAR and LXR resulting in increased expression of CYP3As, CYP4As and CYPs involved in metabolism of cholesterol to bile acids. Such soy-CYP interactions may alter drug pharmacokinetics and therapeutic efficacy and are associated with improved lipid homeostasis and reduced risk of cardiovascular disease. The current review summarizes results from in vitro; in vivo and clinical studies of soy-CYP interactions and examines the evidence linking the effects of soy diets on CYP expression to isoflavone phytoestrogens, particularly, genistein and daidzein that are associated with soy protein.

Biotransformation and Oxidative Stress Responses in Captive Nile Crocodile (Crocodylus niloticus) Exposed to Organic Contaminants from the Natural Environment in South Africa

In the present study, the biotransformation and oxidative stress responses in relation to chemical burden in the liver of male and female Nile crocodiles--Crocodylus niloticus--from a commercial crocodile farm passively exposed to various anthropogenic aquatic pollutants was investigated. In general, the data showed that male crocodiles consistently produced higher biotransformation and oxidative stress responses compared to females. Relationships between these responses and concentrations of aliphatic hydrocarbons and polycyclic aromatic hydrocarbons (PAHs) were also observed. Specifically, the catalytic assays for EROD and BROD (not PROD and MROD) showed sex-differences between male and female crocodiles and paralleled immunochemically determined CYP1A and CYP3A protein levels; the relatively similar levels of PAHs in both sexes suggest an estrogen-mediated reduction of this pathway in females. The antioxidant system exhibited higher levels in male crocodiles with slight or significant higher values for catalase (CAT), glutathione reductase (GR), glutathione peroxidases-H2O2 (GPx-H2O2), glutathione peroxidases-Cu (GPx-Cu), total antioxidant capacity towards peroxyl radicals (TOSC-ROO) and hydroxyl radicals (TOSC-HO), total glutathione (GSH) and malondialdehyde (MDA). On the other hand, the activities of acyl-CoA oxidase (AOX) and glutathione S-transferases (GST) were significantly higher in females. Principal component analysis (PCA) produced significant groupings that revealed correlative relationships (both positive and negative) between biotransformation/oxidative stress variables and liver PAHs and aliphatic hydrocarbon burden. The overall results suggest that these captive pre-slaughter crocodiles exhibited adverse exposure responses to anthropogenic aquatic contaminants with potentially relevant effects on key cellular pathways, and these responses may be established as relevant species biomarkers of exposure and effects in this endangered species.

Effect of phytochemicals on phase II enzyme expression in infant human primary skin fibroblast cells

Phase II metabolising enzymes enable the metabolism and excretion of potentially harmful substances in adults, but to date it is unclear whether dietary phytochemicals can induce phase II enzymes differently between adults and infants. We investigated the expression of phase II enzymes in an in vitro model of primary skin fibroblasts at three different developmental stages, 1 month, 2 years and adult, to examine potential differences in age-related phase II enzymes in response to different phytochemicals (5-20 μm) including sulphoraphane, quercetin and catechin. Following phytochemical treatment, a significant increase in mRNA of glutathione S-transferase A1 (GSTA1) and NAD(P)H:quinone oxidoreductase 1 (NQO1) was observed, with the most marked increases seen in response to sulphoraphane (3-10-fold for GSTA1, P = 0·001, and 6-35-fold for NQO1, P = 0·001-0·017). Catechin also induced 3-5-fold changes in NQO1 transcription, whereas quercetin had less effect on NQO1 mRNA induction in infant cells. Moreover, NQO1 protein levels were significantly increased in 2-year-old and adult cell models in response to sulphoraphane treatment. These results suggest that metabolic plasticity and response to xenobiotics may be different in infants and adults; and therefore the inclusion of phytochemicals in the infant diet may modulate their induction of phase II metabolism, thereby providing increased protection from potentially harmful xenobiotics in later life.

Formula feeding alters hepatic gene expression signature, iron and cholesterol homeostasis in the neonatal pig

In the U.S. formula feeding remains more popular than breast-feeding. In the current study, neonatal piglets were breast fed and compared with those fed commercially available milk-based formula (milk) or soy-based formula (soy) from postnatal day 2 (PND2) until death at PND21 (the usual age of weaning). Liver weights were greater in formula-fed piglets ( P < 0.05) than in breast-fed piglets ( P < 0.05). Affymetrix array analysis revealed significant differences in hepatic gene expression signatures between piglets fed breast milk or formula, as well as between piglets fed milk or soy. In males, expression of 346 hepatic genes differed between formula-fed and breast-fed piglets, and soy-fed differed from milk-fed piglets in 277 genes. Furthermore, gene expression profiles of males differed from females, even when the same diet was consumed. Serum cholesterol was lower in piglets fed formula relative to breast-fed piglets ( P < 0.05), and this was associated with elevations in mRNA encoding cholesterol 7α-hydroxylase (CYP7A1). Consistent with the human literature, breast-fed piglets had lower hepatic iron accumulation than formula-fed piglets. Hepcidin, a major regulator of hepatic iron trafficking, was elevated in piglets fed formula relative to breast-fed piglets ( P < 0.05). Female piglets fed soy formula had increased expression of CYP3A enzymes ( P < 0.05), and soy formula feeding decreased expression of several hepatic genes considered estrogen inducible. These data suggest that: 1) gene expression profiles in neonates differ significantly depending on the diet consumed, 2) hepatic iron storage and cholesterol metabolism clearly differ between breast and formula feeding in piglets, 3) there is no evidence that soy is estrogenic in neonatal pig liver.

Enhanced expression and glucocorticoid-inducibility of hepatic cytochrome P450 3A involve recruitment of the pregnane-X-receptor to promoter elements in rats fed soy protein isolate

Previous studies and Expt. 1 of the current study demonstrate that diets made with soy protein isolate (SPI) enhance the glucocorticoid-inducibility of hepatic cytochrome P450 (CYP)3A-dependent monooxygenase activities (P < 0.05) compared with diets made with casein (CAS). To determine the underlying molecular mechanism, in a second experiment, we analyzed the time course of dexamethasone (DEX)-induction of hepatic CYP3A mRNA expression on postnatal d (PND) 25 and PND60 in male and female rats fed SPI- or CAS-based diets. After 50 mg(/)kg DEX, CYP3A1 mRNA expression increased >200-fold in SPI-fed males and females at PND25 compared with a 100-fold increase in CAS-fed rats (P < 0.05). The DEX-induced increase in CYP3A1 mRNA in SPI-fed rats on PND60 was also greater than that in CAS-fed rats. The induction by DEX of CYP3A2 mRNA was 1- to 3-fold greater in rats fed SPI compared with those fed CAS on PND25 (P < 0.05). Quantitation of newly synthesized CYP3A1 RNA transcripts by nuclear run-on analysis demonstrated a greater rate of basal transcription in SPI-fed compared with CAS-fed rats on PND60 accompanied by greater binding of the pregnane X receptor (PXR) to a response element on the CYP3A1 promoter in SPI-fed compared with CAS-fed rats (P < 0.05). These data suggest that increased hepatic CYP3A expression and inducibility following SPI feeding involves recruitment of PXR to its response element and suggests that soy consumption has potential effects on metabolism and transport of a wide variety of drugs and on bile acid homeostasis via proteins regulated by this transcription factor.

Anti-anxiety, cognitive, and steroid biosynthetic effects of an isoflavone-based dietary supplement are gonad and sex-dependent in rats

Isoflavone-rich diets are associated with reduced menopausal symptoms and lowered risk of cancers of reproductive tissues. Isoflavones may mimic some effects of estrogen by binding to estrogen receptors, and/or altering steroid availability. Despite their potential health benefits, neither the effects, nor mechanisms, of isoflavones are well understood. We hypothesized that isoflavones would alter behavior and physiology of rats in sex and/or gonad-dependent manner. An isoflavone-based, commercially-available, dietary supplement was administered via subcutaneous implantation to female and male, intact and gonadectomized Long-Evans rats. Affective (elevated plus-maze), cognitive (water-maze), and reproductive (sexual) behavior was examined. Weights of reproductive structures were measured, as an index of trophic effects. Steroid levels in circulation and brain regions associated with behavioral measures were evaluated by radioimmunoassay. The supplement increased anti-anxiety behavior of intact, but not gonadectomized, rats. The supplement enhanced visual-spatial performance of all rats, but this effect was most evident among proestrous female rats, which had the poorest spatial performance. There were neither effects of the supplement on sexual behavior, mass of reproductive tissues, nor plasma steroid levels. The supplement increased levels of 5α-androstane,17ß-diol-3α-diol (3α-diol) in the hippocampus (but not other brain regions) of gonadectomized females. Thus, the supplement altered anxiety and cognitive behavior and brain production of steroids; however, the anti-anxiety effects were limited to rats with an intact reproductive axis and effects on cognitive performance and neurosteriodogenesis were most evident among intact and gonadectomized, female rats respectively.

Non-isoflavone phytochemicals in soy and their health effects

Epidemiological and clinical studies have linked consumption of soy foods with low incidences of a number of chronic diseases, such as cardiovascular diseases, cancer, and osteoporosis. Over the past decades, enormous research efforts have been made to identify bioactive components in soy. Isoflavones and soy protein have been suggested as the major bioactive components in soy and have received considerable attention. However, there are hundreds of phytochemical components in soybeans and soy-based foods. In recent years, accumulating evidence has suggested that the isoflavones or soy proteins stripped of phytochemicals only reflect certain aspects of health effects associated with soy consumption. Other phytochemicals, either alone or in combination with isoflavones or soy protein, may be involved in the health effects of soy. This review attempts to summarize major non-isoflavone phytochemicals in soy, as well as their bioavailability and health effects. In addition, a brief discussion of components formed during food processing is also included.

Guidance from an NIH workshop on designing, implementing, and reporting clinical studies of soy interventions

The NIH sponsored a scientific workshop, "Soy Protein/Isoflavone Research: Challenges in Designing and Evaluating Intervention Studies," July 28-29, 2009. The workshop goal was to provide guidance for the next generation of soy protein/isoflavone human research. Session topics included population exposure to soy; the variability of the human response to soy; product composition; methods, tools, and resources available to estimate exposure and protocol adherence; and analytical methods to assess soy in foods and supplements and analytes in biologic fluids and other tissues. The intent of the workshop was to address the quality of soy studies, not the efficacy or safety of soy. Prior NIH workshops and an evidence-based review questioned the quality of data from human soy studies. If clinical studies are pursued, investigators need to ensure that the experimental designs are optimal and the studies properly executed. The workshop participants identified methodological issues that may confound study results and interpretation. Scientifically sound and useful options for dealing with these issues were discussed. The resulting guidance is presented in this document with a brief rationale. The guidance is specific to soy clinical research and does not address nonsoy-related factors that should also be considered in designing and reporting clinical studies. This guidance may be used by investigators, journal editors, study sponsors, and protocol reviewers for a variety of purposes, including designing and implementing trials, reporting results, and interpreting published epidemiological and clinical studies.

Soy protein isolate reduces hepatosteatosis in yellow Avy/a mice without altering coat color phenotype

Agouti (A(vy)/a) mice fed an AIN-93G diet containing the soy isoflavone genistein (GEN) prior to and during pregnancy were reported to shift coat color and body composition phenotypes from obese-yellow towards lean pseudoagouti, suggesting epigenetic programming. Human consumption of purified GEN is rare and soy protein is the primary source of GEN. Virgin a/a female and A(vy)/a male mice were fed AIN-93G diets made with casein (CAS) or soy protein isolate (SPI) (the same approximate GEN levels as in the above mentioned study) for 2 wks prior to mating. A(vy)/a offspring were weaned to the same diets and studied at age 75 d. Coat color distribution did not differ among diets, but SPI-fed, obese A(vy)/a offspring had lower hepatosteatosis (P < 0.05) and increased (P < 0.05) expression of CYP4a 14, a PPARalpha-regulated gene compared to CAS controls. Similarly, weanling male Sprague-Dawley (SD) rats fed SPI had elevated hepatic Acyl Co-A Oxidase (ACO) mRNA levels and increased in vitro binding of PPARalpha to the PPRE promoter response element. In another hepatosteatosis model, adult SD rats fed a high fat/cholesterol diet, SPI reduced (P < 0.05) steatosis. Thus, 1) consumption of diets made with SPI partially protected against hepatosteatosis in yellow mice and in SD rats, and this may involve induction of PPARalpha-regulated genes; and 2) the lifetime (in utero, neonatal and adult) exposure to dietary soy protein did not result in a shift in coat color phenotype of A(vy)/a mice. These findings, when compared with those of previously published studies of A(vy)/a mice, lead us to conclude that: 1) the effects of purified GEN differ from those of SPI when GEN equivalents are closely matched; 2) SPI does not epigenetically regulate the agouti locus to shift the coat color phenotype in the same fashion as GEN alone; and 3) SPI may be beneficial in management of non-alcoholic fatty liver disease.