γ-tocotrienol regulates gastric cancer by targeting notch signaling pathway

BACKGROUND

Gastric cancer is a common cause of death from cancer and an important global health care issue. Consequently, there is an urgent need to find new drugs and therapeutic targets for the treatment of gastric cancer. Recent studies have shown that tocotrienols (T3) have significant anticancer ability in cancer cell lines. Our previous study found that γ-tocotrienol (γ-T3) induced apoptosis in gastric cancer cells. We further explored the possible mechanisms of γ-T3 therapy for gastric cancer.

METHODS

In this study, we treated gastric cancer cells with γ-T3, collect and deposit the cells. γ-T3-treated gastric cancer cells group and untreated group were subjected to RNA-seq assay, and analysis of sequencing results.

RESULTS

Consistent with our previous findings, the results suggest that γ-T3 can inhibit mitochondrial complexes and oxidative phosphorylation. Analysis reveals that γ-T3 has altered mRNA and ncRNA in gastric cancer cells. Significantly altered signaling pathways after γ-T3 treatment were enriched for human papillomavirus infection (HPV) pathway and notch signaling pathway. The same significantly down-regulated genes notch1 and notch2 were present in both pathways in γ-T3-treated gastric cancer cells compared to controls.

CONCLUSIONS

It is indicated that γ-T3 may cure gastric cancer by inhibiting the notch signaling pathway. To provide a new and powerful basis for the clinical treatment of gastric cancer.

Lung transcriptome of nonhuman primates exposed to total- and partial-body irradiation

The focus of radiation biodosimetry has changed recently, and a paradigm shift for using molecular technologies of omic platforms in addition to cytogenetic techniques has been observed. In our study, we have used a nonhuman primate model to investigate the impact of a supralethal dose of 12 Gy radiation on alterations in the lung transcriptome. We used 6 healthy and 32 irradiated animal samples to delineate radiation-induced changes. We also used a medical countermeasure, γ-tocotrienol (GT3), to observe any changes. We demonstrate significant radiation-induced changes in the lung transcriptome for total-body irradiation (TBI) and partial-body irradiation (PBI). However, no major influence of GT3 on radiation was noted in either comparison. Several common signaling pathways, including PI3K/AKT, GADD45, and p53, were upregulated in both exposures. TBI activated DNA-damage-related pathways in the lungs, whereas PTEN signaling was activated after PBI. Our study highlights the various transcriptional profiles associated with γ- and X-ray exposures, and the associated pathways include LXR/RXR activation in TBI, whereas pulmonary wound-healing and pulmonary fibrosis signaling was repressed in PBI. Our study provides important insights into the molecular pathways associated with irradiation that can be further investigated for biomarker discovery.

γ-Tocotrienol Protects against Mitochondrial Dysfunction, Energy Deficits, Morphological Damage, and Decreases in Renal Functions after Renal Ischemia

Ischemia-induced mitochondrial dysfunction and ATP depletion in the kidney result in disruption of primary functions and acute injury of the kidney. This study tested whether γ-tocotrienol (GTT), a member of the vitamin E family, protects mitochondrial function, reduces ATP deficits, and improves renal functions and survival after ischemia/reperfusion injury. Vehicle or GTT (200 mg/kg) were administered to mice 12 h before bilateral kidney ischemia, and endpoints were assessed at different timepoints of reperfusion. GTT treatment reduced decreases in state 3 respiration and accelerated recovery of this function after ischemia. GTT prevented decreases in activities of complexes I and III of the respiratory chain, and blocked ischemia-induced decreases in F₀F₁-ATPase activity and ATP content in renal cortical tissue. GTT improved renal morphology at 72 h after ischemia, reduced numbers of necrotic proximal tubular and inflammatory cells, and enhanced tubular regeneration. GTT treatment ameliorated increases in plasma creatinine levels and accelerated recovery of creatinine levels after ischemia. Lastly, 89% of mice receiving GTT and 70% of those receiving vehicle survived ischemia. Conclusions: Our data show novel observations that GTT administration improves mitochondrial respiration, prevents ATP deficits, promotes tubular regeneration, ameliorates decreases in renal functions, and increases survival after acute kidney injury in mice.

Tocotrienols as an Anti-Breast Cancer Agent

In the past few years, breast cancer has become the most prevalent type of cancer. The majority of patients receive combinatorial chemotherapy treatments, which may result in increased risk of developing drug resistance, a reduced quality of life, and substantial side effects. Treatment modalities that could lessen the physical toll of standard treatments or act in synergy with chemotherapeutic treatments would benefit women worldwide. Research into tocotrienols has thus far demonstrated their potential to be such an agent, with tocotrienols surpassing the pharmacological potential of tocopherols. Further research using in vitro and preclinical breast cancer models to support clinical trials is needed. This review uses bibliometric analysis to highlight this gap in research and summarizes the current and future landscape of tocotrienols as an anti-breast cancer agent.

γ-Tocotrienol reverses multidrug resistance of breast cancer cells through the regulation of the γ-Tocotrienol-NF-κB-P-gp axis

The problem of multidrug resistance (MDR) presents a major obstacle in the chemotherapy of cancer. The MDR phenotype is often linked to the overexpression of ATP-binding cassette (ABC) transporters, that pumps out and decreased intracellular drug accumulation. γ-Tocotrienol, an unsaturated tocopherol belonging to the vitamin E family, has been shown to reverse the MDR of MCF-7/Adr cell. To reveal the role of γ-tocotrienol-NF-κB-P-gp axis in the reversal process, the expression level of mdr1/P-gp was determined by real-time PCR and western blot, while NF-κB activity was detected by immunofluorescence and NF-κB transcriptional activity reporter assay. Besides, mdr1 promoter activity and P-gp transport capacity were measured with the effect of γ-tocotrienol and NF-κB agonist/antagonist. Results showed that γ-tocotrienol effectively inhibited the expression levels of mdr1 mRNA and P-gp protein. It is demonstrated that γ-tocotrienol also suppressed mdr1 promoter activity and the efflux activity of P-gp. In addition, the activation of NF-κB signaling pathway and the transcriptional activity of NF-κB were both reduced by γ-tocotrienol. Evidences also showed that the NF-κB pathway is really involved in the regulation of the expression and function of mdr1/P-gp. Taken together, we confirmed that γ-tocotrienol reversed the MDR of MCF-7/Adr through the signaling pathway of NF-κB and P-gp.

γ-Tocotrienol-Loaded Liposomes for Radioprotection from Hematopoietic Side Effects Caused by Radiotherapeutic Drugs

With the successful development and increased use of targeted radionuclide therapy for treating cancer comes the increased risk of radiation injury to bone marrow—both direct suppression and stochastic effects, leading to neoplasia. Herein, we report a novel radioprotector drug, a liposomal formulation of γ-tocotrienol (GT3), or GT3-Nano for short, to mitigate bone marrow radiation damage during targeted radionuclide therapy. Methods: GT3 was loaded into liposomes using passive loading. ⁶⁴Cu-GT3-Nano and ³H-GT3-Nano were synthesized to study the in vivo biodistribution profile of the liposome and GT3 individually. The radioprotection efficacy of GT3-Nano was assessed after acute ¹³⁷Cs whole-body irradiation at a sublethal (4 Gy), a lethal (9 Gy), or a single high-dose administration of ¹⁵³Sm-ethylenediamine-N,N,N′,N′-tetrakis(methylene phosphonic acid) (EDTMP). Flow cytometry and fluorescence microscopy were used to analyze hematopoietic cell population dynamics and the cellular site of GT3-Nano localization in the spleen and bone marrow, respectively. Results: Bone marrow uptake and retention (percentage injected dose per gram of tissue) at 24 h was 6.98 ± 2.34 for ⁶⁴Cu-GT3-Nano and 7.44 ± 2.52 for ³H-GT3-Nano. GT3-Nano administered 24 h before or after 4 Gy of total-body irradiation (TBI) promoted rapid and complete hematopoietic recovery, whereas recovery of controls stalled at 60%. GT3-Nano demonstrated dose-dependent radioprotection, achieving 90% survival at 50 mg/kg against lethal 9-Gy TBI. Flow cytometry of the bone marrow indicated that progenitor bone marrow cells MPP2 and CMP were upregulated in GT3-Nano–treated mice. Immunohistochemistry showed that GT3-Nano accumulates in CD105-positive sinusoid epithelial cells. Conclusion: GT3-Nano is highly effective in mitigating the marrow-suppressive effects of sublethal and lethal TBI in mice. GT3-Nano can facilitate rapid recovery of hematopoietic components in mice treated with the endoradiotherapeutic agent ¹⁵³Sm-EDTMP.

γ-Tocotrienol-Inhibited Cell Proliferation of Human Gastric Cancer by Regulation of Nuclear Factor-κB Activity

γ-Tocotrienol (γ-T3) exhibits the activity of anticancer via regulating cell signaling pathways. Nuclear factor-κB (NF-κB), one of the crucial pro-inflammatory factors, is involved in the regulation of cell proliferation, apoptosis, invasion, and migration of tumor. In the present study, NF-κB activity inhibited by γ-T3 was investigated in gastric cancer cells. Cell proliferation, NF-κB activity, active protein phosphatase type 2A (PP2A), and ataxia-telangiectasia mutated (ATM) protein were explored using 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT), methylene blue, enzyme-linked immunosorbent assay (ELISA), malachite green, luciferase, and Western blotting assays. The effects of γ-T3 on tumor growth and the expression of NF-κB and PP2A proteins were also further examined by implanting human gastric cancer cells in a BALB/c nude mouse model. The results showed that γ-T3 significantly inhibited the cell proliferation and attenuated the NF-κB activity in vitro and in vivo. γ-T3 dramatically increased PP2A activity and protein expression, which suppressed ATM phosphorylation and its translocation to the cytoplasm in gastric cancer cells. Thus, our findings may provide mechanistic insight into effects of γ-T3 on the regulation of NF-κB activity by a PP2A-dependent mechanism and suggest that PP2A may serve as a molecular target for a potential chemopreventive agent.

γ-Tocotrienol Inhibits Proliferation and Induces Apoptosis Via the Mitochondrial Pathway in Human Cervical Cancer HeLa Cells

γ-Tocotrienol, a kind of isoprenoid phytochemical, has antitumor activity. However, there is limited evidence that it has an effect on cervical cancer. In this study, the capacity to inhibit proliferation and induce apoptosis in human cervical cancer HeLa cells and the mechanism underlying these effects were examined. The results indicated that a γ-tocotrienol concentration over 30 μM inhibited the growth of HeLa cells with a 50% inhibitory concentration (IC₅₀) of 46.90 ± 3.50 μM at 24 h, and significantly down-regulated the expression of proliferative cell nuclear antigen (PCNA) and Ki-67. DNA flow cytometric analysis indicated that γ-tocotrienol arrested the cell cycle at G0/G1 phase and reduced the S phase in HeLa cells. γ-tocotrienol induced apoptosis of HeLa cells in a time- and dose-dependent manner. γ-tocotrienol-induced apoptosis in HeLa cells was accompanied by down-regulation of Bcl-2, up-regulation of Bax, release of cytochrome from mitochondria, activation of caspase-9 and caspase-3, and subsequent poly (ADP-ribose) polymerase (PARP) cleavage. These results suggested that γ-tocotrienol could significantly inhibit cell proliferation through G0/G1 cell cycle arrest, and induce apoptosis via the mitochondrial apoptotic pathway in human cervical cancer HeLa cells. Thus, our findings revealed that γ-tocotrienol may be considered as a potential agent for cervical cancer therapy.

Gamma-tocotrienol reverses multidrug resistance of breast cancer cells with a mechanism distinct from that of atorvastatin

In addition to its antioxidant properties, γ-tocotrienol also has the ability to inhibit HMG-CoA reductase, which is the key enzyme in the mevalonate pathway for cholesterol biosynthesis. Statins, the competitive inhibitors of HMG-CoA reductase, display potent anticancer activity and reversal ability of multidrug resistance in a variety of tumor cells, which is believed to be due to their inhibition of HMG-CoA reductase. Here, we determined the role of the mevalonate pathway in γ-tocotrienol-mediated reversal of multidrug resistance in cancer cells. We found both γ-tocotrienol and atorvastatin effectively reversed multidrug resistance of MCF-7/Adr and markedly inhibited the intracellular levels of FPP and GGPP. Exogenous addition of mevalonate or FPP and GGPP almost completely prevented the reversal ability of atorvastatin but only partly attenuated the reversal effect of γ-tocotrienol on doxorubicin resistance. In addition, γ-tocotrienol actively inhibited the expression of P-gp and increased the accumulation of doxorubicin in cells, which led to the enhanced G2/M arrest and cell apoptosis. Taken together, γ-tocotrienol reversed the multidrug resistance of MCF-7/Adr with a mechanism distinct from that of atorvastatin. Instead of the mevalonate pathway, the inhibition of P-gp expression is a potential mechanism by which γ-tocotrienol reverses multidrug resistance in MCF-7/Adr.

Development of Orally Administered γ-Tocotrienol (GT3) Nanoemulsion for Radioprotection

The purpose of this study was two-fold: (1) to formulate γ-tocotrienol (GT3) in a nanoemulsion formulation as a prophylactic orally administered radioprotective agent; and (2) to optimize the storage conditions to preserve the structural integrity of both the formulation and the compound. γ-tocotrienol was incorporated into a nanoemulsion and lyophilized with lactose. Ultra performance liquid chromatography–mass spectroscopy (UPLC–MS) was used to monitor the chemical stability of GT3 over time, the particle size and ζ potential, and scanning electron microscopy (SEM) were used to study the physical stability of the nanoemulsion. Radioprotective and toxicity studies were performed in mice. The liquid formulation exhibited GT3 degradation at all storage temperatures. Lyophilization, in the presence of lactose, significantly reduced GT3 degradation. Both the liquid and lyophilized nanoemulsions had stable particle size and ζ potential when stored at 4 °C. Toxicity studies of the nanoemulsion resulted in no observable toxicity in mice at an oral dose of 600 mg/kg GT3. The nano-formulated GT3 (300 mg/kg) demonstrated enhanced survival efficacy compared to GT3 alone (200 and 400 mg/kg) in CD2F1 mice exposed to total body gamma radiation. The optimal long-term storage of formulated GT3 is as a powder at −20 °C to preserve drug and formulation integrity. Formulation of GT3 as a nanoemulsion for oral delivery as a prophylactic radioprotectant shows promise and warrants further investigation.

γ-Tocotrienol as a Promising Countermeasure for Acute Radiation Syndrome: Current Status

The hazard of ionizing radiation exposure due to nuclear accidents or terrorist attacks is ever increasing. Despite decades of research, still, there is a shortage of non-toxic, safe and effective medical countermeasures for radiological and nuclear emergency. To date, the U.S. Food and Drug Administration (U.S. FDA) has approved only two growth factors, Neupogen (granulocyte colony-stimulating factor (G-CSF), filgrastim) and Neulasta (PEGylated G-CSF, pegfilgrastim) for the treatment of hematopoietic acute radiation syndrome (H-ARS) following the Animal Efficacy Rule. Promising radioprotective efficacy results of γ-tocotrienol (GT3; a member of the vitamin E family) in the mouse model encouraged its further evaluation in the nonhuman primate (NHP) model. These studies demonstrated that GT3 significantly aided the recovery of radiation-induced neutropenia and thrombocytopenia compared to the vehicle controls; these results particularly significant after exposure to 5.8 or 6.5 Gray (Gy) whole body γ-irradiation. The stimulatory effect of GT3 on neutrophils and thrombocytes (platelets) was directly and positively correlated with dose; a 75 mg/kg dose was more effective compared to 37.5 mg/kg. GT3 was also effective against 6.5 Gy whole body γ-irradiation for improving neutrophils and thrombocytes. Moreover, a single administration of GT3 without any supportive care was equivalent, in terms of improving hematopoietic recovery, to multiple doses of Neupogen and two doses of Neulasta with full supportive care (including blood products) in the NHP model. GT3 may serve as an ultimate radioprotector for use in humans, particularly for military personnel and first responders. In brief, GT3 is a promising radiation countermeasure that ought to be further developed for U.S. FDA approval for the ARS indication.

γ-Tocotrienol-induced endoplasmic reticulum stress and autophagy act concurrently to promote breast cancer cell death

The anticancer effects of γ-tocotrienol are associated with the induction of autophagy and endoplasmic reticulum (ER) stress-mediated apoptosis, but a direct relationship between these events has not been established. Treatment with 40 μmol/L of γ-tocotrienol caused a time-dependent decrease in cancer cell viability that corresponds to a concurrent increase in autophagic and endoplasmic reticulum (ER) stress markers in MCF-7 and MDA-MB-231 human breast cancer cells. γ-Tocotrienol treatment was found to cause a time-dependent increase in early phase (Beclin-1, LC3B-II) and late phase (LAMP-1 and cathepsin-D) autophagy markers, and pretreatment with autophagy inhibitors Beclin-1 siRNA, 3-MA or Baf1 blocked these effects. Furthermore, blockage of γ-tocotrienol-induced autophagy with Beclin-1 siRNA, 3-MA, or Baf1 induced a modest, but significant, reduction in γ-tocotrienol-induced cytotoxicity. γ-Tocotrienol treatment was also found to cause a decrease in mitogenic Erk1/2 signaling, an increase in stress-dependent p38 and JNK1/2 signaling, as well as an increase in ER stress apoptotic markers, including phospho-PERK, phospho-eIF2α, Bip, IRE1α, ATF-4, CHOP, and TRB3. In summary, these finding demonstrate that γ-tocotrienol-induced ER stress and autophagy occur concurrently, and together act to promote human breast cancer cell death.

Gamma tocotrienol, a potent radioprotector, preferentially upregulates expression of anti-apoptotic genes to promote intestinal cell survival. Food Chem Toxicol. 2013;60:488-496. [PMID: 23941772 DOI: 10.1016/j.fct.2013.08.011]

Gamma tocotrienol (GT3) has been reported as a potent ameliorator of radiation-induced gastrointestinal (GI) toxicity when administered prophylactically. This study aimed to evaluate the role of GT3 mediated pro- and anti-apoptotic gene regulation in protecting mice from radiation-induced GI damage. Male 10- to 12-weeks-old CD2F1 mice were administered with a single dose of 200 mg/kg of GT3 or equal volume of vehicle (5% Tween-80) 24 h before exposure to 11 Gy of whole-body γ-radiation. Mouse jejunum was surgically removed 4 and 24h after radiation exposure, and was used for PCR array, histology, immunohistochemistry, and immunoblot analysis. Results were compared among vehicle pre-treated no radiation, vehicle pre-treated irradiated, and GT3 pre-treated irradiated groups. GT3 pretreated irradiated groups, both 4h and 24h after radiation, showed greater upregulation of anti-apoptotic gene expression than vehicle pretreated irradiated groups. TUNEL staining and intestinal crypt analysis showed protection of jejunum after GT3 pre-treatment and immunoblot results were supportive of PCR data. Our study demonstrated that GT3-mediated protection of intestinal cells from a GI-toxic dose of radiation occurred via upregulation of antiapoptotic and downregulation of pro-apoptotic factors, both at the transcript as well as at the protein levels.

Nicotine-induced cessation of embryonic development is reversed by γ-tocotrienol in mice

BACKGROUND

This study aimed to evaluate the adverse effects of various doses of nicotine and protective effects of different concentrations of gamma-tocotrienol (gamma-TCT) on in vitro embryonic development and lipid peroxidation in mice.

MATERIAL AND METHODS

A) Effects of various doses of nicotine on in vitro embryonic development: Female mice were treated with 1.0, 3.0, or 5.0 mg/kg/day nicotine for 7 consecutive days. Animals were superovulated, cohabited overnight, and sacrificed. Embryos were cultured in vitro. Plasma was assayed. B) Effects of concomitant treatment of nicotine concurrently with various doses of gamma-TCT on in vitro embryonic development: Female mice were treated with nicotine (5.0 mg/kg/day), gavaged gamma-TCT of 30, 60, or 90 mg/kg/day or nicotine concurrently with gamma-TCT of 3 different doses for 7 consecutive days. Animals were superovulated, cohabited overnight, and sacrificed. Embryos were cultured and plasma was assayed.

RESULTS

A) Effects of various doses of nicotine on in vitro embryonic development: Number of hatched blastocysts decreased in 1.0 and 3.0 mg/kg/day nicotine groups. Nicotine at 5.0 mg/kg/day stopped embryo development at morula. MDA concentrations increased following all nicotine doses. B) Effects of concomitant treatment of nicotine concurrently with various doses of gamma-TCT on in vitro embryonic development: Embryo development was completed in all groups. MDA concentration increased only in the group treated with nicotine concurrently with 30 mg/kg/day gamma-TCT.

CONCLUSIONS

Nicotine impairs in vitro embryo development and increases MDA in plasma. The deleterious impact of nicotine on embryo development is reversed by supplementing gamma-TCT concurrently with nicotine.

Novel drugs to ameliorate gastrointestinal normal tissue radiation toxicity in clinical practice: what is emerging from the laboratory?

PURPOSE OF REVIEW

To give an overview of promising novel agents under development for the prevention and reduction of gastrointestinal radiation injury.

RECENT FINDINGS

Currently, several novel agents are being tested as drugs to prevent or reduce gastrointestinal radiation injury. These drugs may not only prevent injury, but also mitigate toxicity, that is, reduce injury after radiation exposure has occurred. Promising novel agents include the somatostatin analogue SOM230, growth factors, agents acting on the toll-like receptor 5 pathway, endothelial protectants, and the vitamin E analogue γ-tocotrienol.

SUMMARY

Gastrointestinal radiation injury is the most important dose-limiting factor during radiotherapy of the abdomen or pelvis. It may severely affect the quality of life both during radiotherapy treatment and in cancer survivors. To date, there are no agents that can prevent or reduce intestinal radiation injury. Hence, there is an urgent need for the development of novel drugs to ameliorate intestinal toxicity during and after radiotherapy. This review summarizes the several agents that have been shown to reduce intestinal radiation injury in animals. Further research is needed to investigate their safety and efficacy in patients receiving radiotherapy for abdominal or pelvic tumours.

Novel strategies to ameliorate radiation injury: a possible role for tetrahydrobiopterin

Novel pharmacological strategies are urgently needed to prevent or reduce radiation-induced tissue injury. Microvascular injury is a prominent feature of both early and delayed radiation injury. Radiation-induced endothelial dysfunction is believed to play a key role in the pathogenesis of post-irradiation tissue injury. Hence, strategies that could prevent or improve endothelial malfunction are expected to ameliorate the severity of radiation injury. This review focuses on the therapeutic potential of the nitric oxide synthase (NOS) cofactor 5,6,7,8-tetrahydrobiopterin (BH4) as an agent to reduce radiation toxicity. BH4 is an essential cofactor for all NOS enzymes and a critical determinant of NOS function. Inadequate availability of BH4 leads to uncoupling of the NOS enzyme. In an uncoupled state, NOS produces the highly oxidative radicals superoxide and peroxynitrite at the cost of NO. Under conditions of oxidative stress, such as after radiation exposure, BH4 availability might be reduced due to the rapid oxidation of BH4 to 7,8-dihydrobiopterin (7,8-BH2). As a result, free radical-induced BH4 insufficiency may increase the oxidative burden and hamper NO-dependent endothelial function. Given the growing evidence that BH4 depletion and subsequent endothelial NOS uncoupling play a major role in the pathogenesis of endothelial dysfunction in various diseases, there is substantial reason to believe that improving post-irradiation BH4 availability, by either supplementation with it or modulation of its metabolism, might be a novel strategy to reduce radiation-induced endothelial dysfunction and subsequent tissue injury.

A rice bran oil diet improves lipid abnormalities and suppress hyperinsulinemic responses in rats with streptozotocin/nicotinamide-induced type 2 diabetes

The aim of this study was to determine the effects of rice bran oil (RBO) on lipid metabolism and insulin resistance in rats with streptozotocin/nicotinamide-induced type 2 diabetes mellitus (T2DM). Rats were divided into two groups: the control group (15% soybean oil, contains 0 g γ-oryzanol and 0 g γ-tocotrienol/150 g oil for 5 weeks) and the RBO group (15% RBO, contains 5.25 g γ-oryzanol and 0.9 g γ-tocotrienol/150 g oil for 5 weeks). Compared with the control group, the RBO group had a lower plasma nonesterified fatty acid concentration, ratio of total to high-density-lipoprotein cholesterol, hepatic cholesterol concentration, and area under the curve for insulin. The RBO group had a higher high-density-lipoprotein cholesterol concentration and greater excretion of fecal neutral sterols and bile acid than did the control group. RBO may improve lipid abnormalities, reduce the atherogenic index, and suppress the hyperinsulinemic response in rats with streptozotocin/nicotinamide-induced T2DM. In addition, RBO can lead to increased fecal neutral sterol and bile acid excretion.