Stearidonic acid, a plant-based dietary fatty acid, enhances the chemosensitivity of canine lymphoid tumor cells.

Lymphoma is the most common hematopoietic tumor in dogs and humans, with similar pathogenesis and therapeutic responses. Anticancer drugs like vincristine (VCR) and doxorubicin (DOX) are often used in treating lymphoma. However, the cure rate is generally poor due to chemoresistance. Here, we sought to determine whether stearidonic acid (SDA), a plant-based dietary fatty acid, sensitizes chemoresistant canine lymphoid-tumor cells. GL-1 B-cell lymphoid-tumor cells were found to be highly sensitive to the antitumor-activity of VCR and DOX, while OSW T-cell and 17-71 B-cell lymphoid-tumor cells were moderately and fully resistant, respectively. SDA, at its non-toxic concentrations, significantly promoted the antitumor action of VCR and DOX in both OSW and 17-71 cells. SDA-mediated chemosensitization was associated with SDA inhibition of P-glycoprotein (P-gp) function. This was confirmed in HEK293 cells stably expressing P-gp as well as by increased binding-affinity of SDA to P-gp in P-gp docking analysis. SDA at its chemosensitizing concentrations did not affect the viability of healthy dog peripheral blood mononuclear cells, suggesting that SDA is non-toxic to normal dog peripheral blood leucocytes at its chemosensitizing concentrations. Our study identifies a novel dietary fatty acid that may be used as a dietary supplement in combination with chemotherapy to promote the antitumor efficacy of the chemotherapy drugs in dogs and possibly in humans with chemoresistant lymphoma.

Diindolylmethane, a naturally occurring compound, induces CYP3A4 and MDR1 gene expression by activating human PXR.

Activation of human pregnane X receptor (hPXR)-regulated expression of cytochrome P450 3A4 (CYP3A4) and multidrug resistance protein 1 (MDR1) plays an important role in mediating adverse drug interactions. Given the common use of natural products as part of adjunct human health behavior, there is a growing concern about natural products for their potential to induce undesired drug interactions through the activation of hPXR-regulated CYP3A4 and MDR1. Here, we studied whether 3,3'-diindolylmethane (DIM), a natural health supplement, could induce hPXR-mediated regulation of CYP3A4 and MDR1 in human hepatocytes and intestinal cells. DIM, at its physiologically relevant concentrations, not only induced hPXR transactivation of CYP3A4 promoter activity but also induced gene expression of CYP3A4 and MDR1. DIM decreased intracellular accumulation of MDR1 substrate rhodamine 123, suggesting that DIM induces the functional expression of MDR1. Pharmacologic inhibition or genetic knockdown of hPXR resulted in attenuation of DIM induced CYP3A4 and MDR1 gene expression, suggesting that DIM induces CYP3A4 and MDR1 in an hPXR-dependent manner. Together, these results support our conclusion that DIM induces hPXR-regulated CYP3A4 and MDR1 gene expression. The inductive effects of DIM on CYP3A4 and MDR1 expression caution the use of DIM in conjunction with other medications metabolized and transported via CYP3A4 and MDR1, respectively.

Bisphenol A regulation of testicular endocrine function in male rats is affected by diet.

There is concern that early-life exposure to bisphenol A (BPA) may alter developmental programming and predispose individuals to obesity and reproductive anomalies. The present study was designed to determine if a high fat diet at sexual maturation moderates testicular toxicity occasioned by exposure to BPA during reproductive development. Therefore, male rats were exposed to BPA by maternal gavage (0, 2.5 or 25 µg/kg body weight/day) from gestational day 12 to postnatal day 21. At weaning, control and BPA-exposed animals were placed on a regular normal fat diet (NFD) until 70 days of age when they were continued on the NFD or were maintained on a high fat diet (HFD) until euthanasia at 98 days. Adult male rats maintained on HFD were generally heavier than NFD animals due to greater energy intake but energy intake per unit body weight gain was similar in all animals. However, perinatal exposure to BPA decreased (P<0.05) serum adiponectin as well as adiponectin and AdipoR2 protein expression levels in Leydig cells. Importantly, the combination of BPA exposure and HFD consumption promoted lipid peroxidation evidenced by elevated serum thiobarbituric acid reactive substances and glutathione concentrations. These findings imply that interaction between BPA and HFD potentially causes testicular dysfunction to a greater degree than would be due to BPA exposure or HFD consumption. Given the relationship that exists between energy homeostasis and reproductive activity, additional studies are warranted to investigate the consequences of BPA-diet interactions on testicular function.

Regulation of adiponectin secretion by soy isoflavones has implication for endocrine function of the testis.

Testicular Leydig cells are the predominant source of the male sex steroid hormone testosterone (T), which is required to maintain male fertility. There is now growing evidence that environmental stressors, including chemicals present in food, air and water, may affect energy balance. A relationship between energy balance and reproductive capacity has been proposed for a long time. In the present study, developmental exposures of male rats to soy isoflavones in the maternal diet from gestational day 12 to day 21 post-partum enhanced adiponectin expression in adipose tissue and increased serum adiponectin concentrations in adulthood. However, exposure to soy isoflavones caused a decrease in T production and expression of adiponectin and its receptor (adipoR2) in Leydig cells. In separate experiments, incubation of Leydig cells with recombinant adiponectin in the absence of isoflavones caused a decrease in T biosynthesis associated with diminished expression of the cholesterol transporter steroidogenic acute regulatory protein (StAR). Thus, chemical-induced alterations in serum adiponectin concentrations have implication for steroid hormone secretion. The results also imply that changes in adipose tissue metabolism occasioned by exposure to dietary estrogens, and perhaps other estrogenic agents, possibly contribute to deficiencies in reproductive capacity attributed to these compounds.

Insulin treatment prevents diabetes-induced alterations in astrocyte glutamate uptake and GFAP content in rats at 4 and 8 weeks of diabetes duration.

Rat astrocyte function is changed by diabetes mellitus relative to the nondiabetic state and we believe that altered function contributes to the central nervous system symptoms manifested by individuals with diabetes. We report here a comparison of astrocyte glutamate uptake and GFAP expression in streptozotocin-induced type 1 diabetic rats and insulin-treated diabetic rats at 4 and 8 weeks following diabetes onset. In glial plasmalemmal vesicle (GPV) preparations from treated rats, insulin prevented the increase observed in untreated, diabetic rats of both sodium-dependent and sodium-independent glutamate uptake. We determined by immunoblotting and immunohistochemistry that insulin treatment prevented the decrease of GFAP expression detected in the cerebral cortex, hippocampus, and cerebellum of untreated, diabetic rats. These observations indicate that insulin effects on astrocyte function are significant in managing diabetes-induced central nervous system pathology.

Genistein decreases androgen biosynthesis in rat Leydig cells by interference with luteinizing hormone-dependent signaling.

Testicular Leydig cells express estrogen receptors and are the predominant source of the male sex steroid hormone testosterone (T). Previous studies demonstrated that genistein acts through estrogen receptors in Leydig cells. In the present study, pre-treatment of Leydig cells isolated from 35 day-old male Long Evans rats with the epidermal growth factor receptor (EGFR) kinase inhibitor AG 1478 abrogated genistein inhibition of T biosynthesis. Also, incubation of Leydig cells in culture medium containing epidermal growth factor (EGF) decreased T secretion (control: 255+/-16; EGF: 190+/-17ng/10(6) cells, 24h) (P<0.05). However, T secretion by genistein-treated Leydig cells (0.1nM, 10muM; 24h) was rescued by post-treatment incubation with forskolin (control: 275+/-28 versus 325+/-35; 780+/-85; ng/10(6) cells, 3h) and dibutyryl cyclic adenosine 3'-5'-monophosphate (dbcAMP) (control: 370+/-65 versus 580+/-75; 2500+/-200; ng/10(6) cells, 3h) (P>0.05). Furthermore, post-treatment incubation with cholera toxin, an activator of G proteins, caused genistein-treated Leydig cells to produce similar T amounts as untreated control (control: 55+/-5 versus 52+/-2 and 47+/-4; ng/10(6) cells, 3h) (P>0.05). These observations imply that genistein action interferes with coupling of transmembrane luteinizing hormone receptors (LHR) with G proteins. Uncoupling of LHR from G proteins adversely affects adenylate cyclase function and impacts LH-dependent stimulation of Leydig cells. These findings have implications for testicular steroidogenesis in individuals exposed to genistein and soy-based products.

Activation of Penile Proadipogenic Peroxisome Proliferator-Activated Receptor gamma with an Estrogen: Interaction with Estrogen Receptor Alpha during Postnatal Development.

Exposure to the estrogen receptor alpha (ERalpha) ligand diethylstilbesterol (DES) between neonatal days 2 to 12 induces penile adipogenesis and adult infertility in rats. The objective of this study was to investigate the in vivo interaction between DES-activated ERalpha and the proadipogenic transcription factor peroxisome proliferator-activated receptor gamma (PPARgamma). Transcripts for PPARs alpha, beta, and gamma and gamma1a splice variant were detected in Sprague-Dawley normal rat penis with PPARgamma predominating. In addition, PPARgamma1b and PPARgamma2 were newly induced by DES. The PPARgamma transcripts were significantly upregulated with DES and reduced by antiestrogen ICI 182, 780. At the cellular level, PPARgamma protein was detected in urethral transitional epithelium and stromal, endothelial, neuronal, and smooth muscular cells. Treatment with DES activated ERalpha and induced adipocyte differentiation in corpus cavernosum penis. Those adipocytes exhibited strong nuclear PPARgamma expression. These results suggest a biological overlap between PPARgamma and ERalpha and highlight a mechanism for endocrine disruption.

Regulation of adiponectin secretion by endothelin-1.

Adiponectin is an adipocyte-derived hormone best known for its insulin-sensitizing ability. The expression and circulating concentration of adiponectin are decreased in type 2 diabetics and increase following treatment with thiazolidinediones. Endothelin-1 (ET-1) is a potent vasoconstrictor peptide whose levels are elevated in numerous disease states, including obesity and diabetes. ET-1 has profound effects on adipose tissue metabolism and alters the release of adipose-derived factors such as leptin and resistin, therefore we investigated the role of ET-1 in adiponectin secretion. 3T3-L1 adipocytes were treated with insulin (100 nM), ET-1 (100 nM), or the appropriate vehicle and adiponectin secretion into the media was determined by immunoblotting and densitometric analysis. Adiponectin secretion significantly increased 1h following insulin or ET-1 treatment, respectively. Pretreatment with ET-1 for 24h significantly inhibited the ability of insulin or ET-1 to acutely stimulate adiponectin secretion. The specific ET(A) receptor antagonist, BQ-610 (1 microM), significantly inhibited ET-1-stimulated adiponectin secretion. In summary, ET-1 acutely stimulates adiponectin secretion through the ET(A) receptor. Chronic exposure to ET-1 dramatically decreases the stimulatory effect of insulin and ET-1 on adiponectin secretion. Our findings suggest vascular factors such as ET-1 may play a role in the regulation of adiponectin secretion and whole body energy metabolism.