Effects of diosgenin, a plant-derived steroid, on bile secretion and hepatocellular cholestasis induced by estrogens in the rat

Diosgenin alleviates nonalcoholic steatohepatitis through affecting liver-gut circulation

Nonalcoholic steatohepatitis (NASH), as the aggressive form of nonalcoholic fatty liver disease (NAFLD), rapidly becomes the leading cause of end-stage liver disease or liver transplantation. Nowadays, there has no approved drug for NASH treatment. Diosgenin possesses multiple beneficial effects towards inhibition of lipid accumulation, cholesterol metabolism, fibrotic progression and inflammatory response. However, there has been no report concerning its effects on NASH so far. Using methionine and choline-deficient (MCD) feeding mice, we evaluated the anti-NASH effects of diosgenin. 16 S rDNA was used to investigate gut microbiota composition. Transcriptome sequencing, LC/MS and GC/MS analysis were used to evaluate bile acids (BAs) metabolism and their related pathway. Compared with the MCD group, diosgenin treatment improved the hepatic dysfunction, especially decreased the serum and hepatic TC, TG, ALT, AST and TBA to nearly 50%. Content of BAs, especially CA and TCA, were decreased from 59.30 and 26.00-39.71 and 11.48 ng/mg in liver and from 0.96 and 2.1-0.47 and 1.13 μg/mL in serum, and increased from 7.01 and 11.08-3.278 and 5.11 ng/mg in feces, respectively. Antibiotic and fecal microbiota transplantation (FMT) treatment further confirmed the therapeutic effect of diosgenin on gut microbiota, especially Clostridia (LDA score of 4.94), which regulated BAs metabolism through the hepatic FXR-SHP and intestinal FXR-FGF15 pathways. These data indicate that diosgenin prevents NASH by altering Clostridia and BAs metabolism. Our results shed light on the mechanisms of diosgenin in treating NASH, which pave way for the design of novel clinical therapeutic strategies.

Therapeutic potential and research progress of diosgenin for lipid metabolism diseases

Diosgenin, a steroidal saponin, is a natural product found in many plants. Diosgenin has a wide range of pharmacological activities, and has been used to treat cancer, nervous system diseases, inflammation, and infections. Numerous studies have shown that diosgenin has potential therapeutic value for lipid metabolism diseases via various pathways and mechanisms, such as controlling lipid synthesis, absorption, and inhibition of oxidative stress. These mechanisms and pathways have provided ideas for researchers to develop related drugs. In this review, we focus on data from animal and clinical studies, summarizing the toxicity of diosgenin, its pharmacological mechanism, recent research advances, and the related mechanisms of diosgenin as a drug for the treatment of lipid metabolism, especially in obesity, hyperlipidemia, nonalcoholic fatty liver disease, atherosclerosis, and diabetes. This systematic review will briefly describe the advantages of diosgenin as a potential therapeutic drug and seek to enhance our understanding of the pharmacological mechanism, recipe-construction, and the development of novel therapeutics against lipid metabolism diseases.

Diosgenin and Its Analogs: Potential Protective Agents Against Atherosclerosis

Atherosclerosis is a chronic inflammatory disease of the artery wall associated with lipid metabolism imbalance and maladaptive immune response, which mediates most cardiovascular events. First-line drugs such as statins and antiplatelet drug aspirin have shown good effects against atherosclerosis but may lead to certain side effects. Thus, the development of new, safer, and less toxic agents for atherosclerosis is urgently needed. Diosgenin and its analogs have gained importance for their efficacy against life-threatening diseases, including cardiovascular, endocrine, nervous system diseases, and cancer. Diosgenin and its analogs are widely found in the rhizomes of Dioscore, Solanum, and other species and share similar chemical structures and pharmacological effects. Recent data suggested diosgenin plays an anti-atherosclerosis role through its anti-inflammatory, antioxidant, plasma cholesterol-lowering, anti-proliferation, and anti-thrombotic effects. However, a review of the effects of diosgenin and its natural structure analogs on AS is still lacking. This review summarizes the effects of diosgenin and its analogs on vascular endothelial dysfunction, vascular smooth muscle cell (VSMC) proliferation, migration and calcification, lipid metabolism, and inflammation, and provides a new overview of its anti-atherosclerosis mechanism. Besides, the structures, sources, safety, pharmacokinetic characteristics, and biological availability are introduced to reveal the limitations and challenges of current studies, hoping to provide a theoretical basis for the clinical application of diosgenin and its analogs and provide a new idea for developing new agents for atherosclerosis.

The role of diosgenin in crohn’s disease

Inflammatory bowel disease (IBD) is a chronic idiopathic inflammation that can grossly affect the entire gastrointestinal tract (GIT) from the mouth to the anus. Crohn’s disease is the most known type of IBD and has been the focus of attention due to its increase in prevalence worldwide. Although the etiology is yet to be elucidated, recent studies have pointed out Crohn’s disease to arise from a complex interaction between environmental influences, genetic predisposition, and altered gut microbiota, resulting in dysregulated adaptive and innate responses. The presenting hallmarks of Crohn’s disease may include weight loss, nausea, vomiting, abdominal pain, diarrhea, fever, or chills. Treatment is usually done with many approved immunosuppressive drugs and surgery. However, a promising avenue from natural compounds is a safer therapy due to its safe natural active ingredients and the strong activity it shows in the treatment and management of diseases. Diosgenin, “a major biologically active natural steroidal sapogenin found in Chinese yam,” has been widely reported as a therapeutic agent in the treatment of various classes of disorders such as hyperlipidemia, inflammation, diabetes, cancer, infection, and immunoregulation. In this review, an analysis of literature data on diosgenin employed as a therapeutic agent for the treatment of Crohn’s disease is approached, to strengthen the scientific database and curtail the dreadful impact of Crohn’s disease.

Hypothalamus-pituitary-adrenal Axis in Glucolipid metabolic disorders

With the change of life style, glucolipid metabolic disorders (GLMD) has become one of the major chronic disorders causing public health and clinical problems worldwide. Previous studies on GLMD pay more attention to peripheral tissues. In fact, the central nervous system (CNS) plays an important role in controlling the overall metabolic balance. With the development of technology and the in-depth understanding of the CNS, the relationship between neuro-endocrine-immunoregulatory (NEI) network and metabolism had been gradually illustrated. As the hub of NEI network, hypothalamus-pituitary-adrenal (HPA) axis is important for maintaining the balance of internal environment in the body. The relationship between HPA axis and GLMD needs to be further studied. This review focuses on the role of HPA axis in GLMD and reviews the research progress on drugs for GLMD, with the hope to provide the direction for exploring new drugs to treat GLMD by taking the HPA axis as the target and improve the level of prevention and control of GLMD.

Preparation and Evaluation of Diosgenin Nanocrystals to Improve Oral Bioavailability

Diosgenin (DSG), a well-known steroid sapogenin derived from Dioscorea nipponica Makino and Dioscorea zingiberensis Wright, has a variety of bioactivities. However, it shows low oral bioavailability due to poor aqueous solubility and strong hydrophobicity. The present study aimed to develop DSG nanocrystals to increase the dissolution and then improve the oral bioavailability and biopharmaceutical properties of DSG. DSG nanocrystals were prepared by the media milling method using a combination of pluronic F127 and sodium dodecyl sulfate as surface stabilizers. The physicochemical properties of the optimal DSG nanocrystals were characterized using their particle size distribution, morphology, differential scanning calorimetry, powder X-ray diffraction, Fourier transform infrared spectroscopy data, and solubility and dissolution test results. Pharmacokinetic studies of the DSG coarse suspension and its nanocrystals were performed in rats. The particle size and polydispersity index of DSG nanocrystals were 229.0 ± 3.7 nm and 0.163 ± 0.064, respectively. DSG retained its original crystalline state during the manufacturing process, and its chemical structure was not compromised by the nanonizing process. The dissolution rate of the freeze-dried DSG nanocrystals was significantly improved in comparison with the original DSG. The pharmacokinetic studies showed that the AUC_0-72h and C _max of DSG nanocrystals increased markedly (p < 0.01) in comparison with the DSG coarse suspension by about 2.55- and 2.01-fold, respectively. The use of optimized nanocrystals is a good and efficient strategy for oral administration of DSG due to the increased dissolution rate and oral bioavailability of DSG nanocrystals.

Persistent organic pollutants in adipose tissue should be considered in obesity research

Although low doses of persistent organic pollutants (POPs), strong lipophilic chemicals with long half-lives, have been linked to various endocrine, immune, nervous and reproductive system diseases, few obesity studies have considered adipose tissue as an important POPs exposure source. Because the toxicodynamics of POPs relate directly to the dynamics of adiposity, POPs might explain puzzling findings in obesity research. In two people exposed to the same amounts of environmental POPs, the one having more adipose tissue may be advantaged because POPs storage in adipose tissue can reduce burden on other critical organs. Therefore, adipose tissue can play a protective role against the POPs effects. However, two situations increase the POPs release from adipose tissue into the circulation, thereby increasing the risk that they will reach critical organs: (i) weight loss and (ii) insulin resistance. In contrast, weight gain reduces this possibility. Therefore, avoiding harmful health effects of POPs may mostly contradict conventional judgments about obesity and weight change. These contradictory situations can explain the obesity paradox, the adverse effects of intensive intentional weight loss and the protective effects of obesity against dementia. Future studies should consider that adipose tissue is widely contaminated with POPs in modern society.

Diosgenin-caused changes of the adrenal gland histological parameters in a rat model of the menopause

Diosgenin, a steroidal sapogenin of natural origin, has demonstrated benefits when it comes to the treatment of malignancies, cardiovascular issues and menopausal symptoms. In this study, we investigated the histological changes of the adrenal gland after diosgenin application in a rat model of the menopause. Middle-aged, acyclic female Wistar rats were divided into control (C; n=6) and diosgenin treated (D; n=6) groups. Diosgenin (100mg/kg b.w./day) was orally administered for four weeks, while C group received the vehicle alone. A histological approach included design-based stereology, histochemistry and immunohistochemistry. The adrenal cortex volume decreased in D females by 15% (p<0.05) while the volume of adrenal medulla increased (p<0.05) by 64%, compared to the same parameters in C group. Volume density of the zona glomerulosa (expressed per absolute adrenal gland volume) in D rats increased (p<0.05) by 22% in comparison with C animals. Diosgenin treatment decreased (p<0.05) the volume density of the zona fasciculata (expressed per volume of adrenal cortex) by 15% when compared to C females. Absolute volume of the zona reticularis in D group decreased (p<0.05) by 38% in comparison with the same parameter in C rats. Also, after diosgenin application, the volume density of the zona reticularis (expressed per volume of adrenal cortex) and the zona reticularis cell volume were decreased by 51% and 20% (p<0.05) respectively, compared to C animals. Our results, reflecting a decrease in many stereological parameters of the adrenal cortex, indicate that diosgenin took over the role of corticosteroid precursors and became incorporated into steroidogenesis.

Anticancer and apoptotic effects on cell proliferation of diosgenin isolated from Costus speciosus (Koen.) Sm

Background

Diosgenin, a naturally occurring steroid saponin found abundantly in C. speciosus, is a well-known precursor of various synthetic steroidal drugs that are extensively used in the pharmaceutical industry.

Methods

The present study was conducted to evaluate the in vitro anticancer and apoptotic effects on cell proliferation of diosgenin isolated from C. speciosus (Koen.) Sm.

Results

The results indicated that the treatment of HepG2 cells with the sample resulted in a cytotoxic effect as concluded from the IC₅₀ value 32.62 μg/ml, while the treatment of HepG2 cells with paclitaxel, a known anti-cancer drug, resulted in an IC₅₀ value of 0.48 μg/ml. The treatment of MCF-7 cells with the tested sample resulted in high inhibition in the cell viability, and resulted in an IC₅₀ value of 11.03 μg/ml, while the treatment of MCF-7 cells with paclitaxel resulted in an IC₅₀ value of 0.61 μg/ml. The levels of DR4 and caspase-3 were significantly increased (P < 0.01) in MCF-7 cells treated with the tested sample compared to untreated cells and possessed a similar activity of paclitaxel in DR4 induction but lower induction in caspase-3. On the other hand the treatment of macrophages or lymphocytes with diosgenin (250 μg/ml) resulted in an induction in the cell proliferation up to 3.2-fold and 2.1-fold of control, respectively.

Conclusions

The results presented here may suggest that diosgenin isolated from C. speciosus possess anticancer and apoptotic effects on cell proliferation, and therefore, can be used as pharmaceuticals drugs.

Influence of different particle processing on hypocholesterolemic and antiatherogenic activities of yam (Dioscorea pseudojaponica) in cholesterol-fed rabbit model

BACKGROUND

Nanoparticle processing is implicated in enhancing bioactive or nutritional compound release from raw foods. The aim of the present study was to evaluate whether different particle processing might affect the lipid-lowering activity of Dioscorea pseudojaponica (DP) and to investigate whether DP could be a potential functional food for prevention of atherogenesis. Its possible molecular mechanisms were also evaluated.

RESULTS

The results indicated that 50 mesh-size DP (50 mesh DP) particles exhibited stronger effects than nanoscale DP (nano DP) particles in terms of lowering the level of serum cholesterol as well as reducing the extent of fatty liver and aortic fatty streak. Moreover, both DP particle types, particularly 50 mesh DP, significantly activated AMPK (5'-adenosine monophosphate-activated protein kinase) and deactivated ACC (acetyl-CoA carboxylase), as demonstrated by the increased levels of both enzymes in their phosphorylated form. Coincidently, high-performance liquid chromatography (HPLC) analysis showed a higher content (P < 0.01) of dioscin, a known lipid-lowering compound, in 50 mesh DP than in nano DP.

CONCLUSION

These results suggest that improper processing conditions will lead to the decomposition of bioactive components in yam. They also demonstrate for the first time that the lipid-lowering mechanisms of DP may occur through the AMPK-ACC pathway.

Diosgenin Induces Apoptosis in HepG2 Cells through Generation of Reactive Oxygen Species and Mitochondrial Pathway

Diosgenin, a naturally occurring steroid saponin found abundantly in legumes and yams, is a precursor of various synthetic steroidal drugs. Diosgenin is studied for the mechanism of its action in apoptotic pathway in human hepatocellular carcinoma cells. Based on DAPI staining, diosgenin-treated cells manifested nuclear shrinkage, condensation, and fragmentation. Treatment of HepG2 cells with 40 μM diosgenin resulted in activation of the caspase-3, -8, -9 and cleavage of poly-ADP-ribose polymerase (PARP) and the release of cytochrome c. In the upstream, diosgenin increased the expression of Bax, decreased the expression of Bid and Bcl-2, and augmented the Bax/Bcl-2 ratio. Diosgenin-induced, dose-dependent induction of apoptosis was accompanied by sustained phosphorylation of JNK, p38 MAPK and apoptosis signal-regulating kinase (ASK)-1, as well as generation of the ROS. NAC administration, a scavenger of ROS, reversed diosgene-induced cell death. These results suggest that diosgenin-induced apoptosis in HepG2 cells through Bcl-2 protein family-mediated mitochndria/caspase-3-dependent pathway. Also, diosgenin strongly generated ROS and this oxidative stress might induce apoptosis through activation of ASK1, which are critical upstream signals for JNK/p38 MAPK activation in HepG2 cancer cells.

Diosgenin ameliorates cognition deficit and attenuates oxidative damage in senescent mice induced by D-galactose

This study attempted to access the neuroprotective effect of diosgenin on the senescent mice induced by d-galactose (D-gal). The mice in the experiments were orally administered with diosgenin (1, 5, 25 and 125 mg/kg), for four weeks from the sixth week. The learning and memory abilities of the mice in Morris water maze test and the mechanism involved in the neuroprotective effect of diosgenin on the mice brain tissue were investigated. Diosgenin (5, 25 and 125 mg/kg, p.o.) showed significantly improved learning and memory abilities in Morris water maze test compared to D-gal treated mice (200 mg/kg, ten weeks). Diosgenin also increased the activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px), and decreased the malondialdehyde (MDA) level in the brain of D-gal treated mice. These results indicated that diosgenin has the potential to be a useful treatment for cognitive impairment. In addition, the memory enhancing effect of diosgenin may be partly mediated via enhancing endogenous antioxidant enzymatic activities.

Phloracetophenone-induced choleresis in rats is mediated through Mrp2

Phloracetophenone (2,4,6-trihydroxyacetophenone, THA) is a potent choleretic in the bile fistula rat, although the mechanism is unknown. In the present study, we examined how THA enhances bile secretion. Stepwise infusions of THA (1-4 micromol/min) in the isolated perfused rat liver resulted in an immediate and dose-dependent increase in bile flow (BF), which reached saturation. The increase in BF was not associated with a change in the excretion of bile acids, suggesting that THA stimulated bile acid-independent bile flow. To further define the mechanism, the effect of THA on the excretion of sulfobromophthalein (BSP) and disulfobromophthalein (DBSP), typical multidrug resistance protein-2 (Mrp2) substrates was examined. THA inhibited the biliary excretion of both substrates. Because DBSP is excreted without conjugation to glutathione, in contrast to BSP, the findings suggest that THA might compete with DBSP and BSP metabolites at a common canalicular transport site, presumably Mrp2. THA infusions had no effect on the subcellular localization and distribution of either Mrp2 or the bile salt export pump (Bsep), nor the integrity of the tight junction. In contrast, the choleretic activity of THA was completely absent in the TR(-) rat, an animal model that lacks Mrp2, directly implicating this canalicular export pump as the mechanisms by which THA is excreted in bile. THA also partially reversed the cholestatic effects of estradiol-17beta-D-glucuronide, a process also dependent on Mrp2. In conclusion, the choleretic activity of THA and its possible metabolites is dependent on Mrp2. THA appears to stimulate BF by its osmotic effects and may attenuate the cholestatic effects of hepatotoxins undergoing biotransformation and excretion via similar pathways.

3α-6α-Dihydroxy-7α-fluoro-5β-cholanoate (UPF-680), physicochemical and physiological properties of a new fluorinated bile acid that prevents 17α-ethynyl-estradiol-induced cholestasis in rats

3alpha-6alpha-Dihydroxy-7alpha-fluoro-5beta-cholanoate (UPF-680), the 7alpha-fluorine analog of hyodeoxycholic acid (HDCA), was synthesized to improve bioavailability and stability of ursodeoxycholic acid (UDCA). Acute rat biliary fistula and chronic cholestasis induced by 17alpha-ethynyl-estradiol (17EE) models were used to study and compare the effects of UPF-680 (dose range 0.6-6.0 micromol/kg min) with UDCA on bile flow, biliary bicarbonate (HCO(3)(-)), lipid output, biliary bile acid composition, hepatic enzymes and organic anion pumps. In acute infusion, UPF-680 increased bile flow in a dose-related manner, by up to 40.9%. Biliary HCO(3)(-) output was similarly increased. Changes were observed in phospholipid secretion only at the highest doses. Treatment with UDCA and UPF-680 reversed chronic cholestasis induced by 17EE; in this model, UDCA had no effect on bile flow in contrast to UPF-680, which significantly increased bile flow. With acute administration of UPF-680, the biliary bile acid pool became enriched with unconjugated and conjugated UPF-680 (71.7%) at the expense of endogenous cholic acid and muricholic isomers. With chronic administration of UPF-680 or UDCA, the main biliary bile acids were tauro conjugates, but modification of biliary bile acid pool was greater with UPF-680. UPF-680 increased the mRNA for cytochrome P450 7A1 (CYP7A1) and cytochrome P450 8B (CYP8B). Both UDCA and UPF-680 increased the mRNA for Na(+) taurocholate co-transporting polypeptide (NCTP). In conclusion, UPF-680 prevented 17EE-induced cholestasis and enriched the biliary bile acid pool with less detergent and cytotoxic bile acids. This novel fluorinated bile acid may have potential in the treatment of cholestatic liver disease.

Hypoglycemic effects of steroidal sapogenins isolated from Jamaican bitter yam, Dioscorea polygonoides

In this study, three steroidal sapogenins (Delta3 diosgenin, diosgenin, and pennogenin) and the phytosterols, stigmasterol and beta-sitosterol were isolated from Jamaican bitter yam, Dioscorea polygonoides. Their effects on fasting blood glucose and intestinal amylase and ATPases in streptozotocin-induced diabetic rats were studied. The diabetic rats (fed supplemented and unsupplemented diets) lost weight significantly compared to the normal group. There was a significant increase in the activity of alpha-amylase in the proximal region of the small intestinal mucosa of diabetic rats fed sapogenin extract or commercial diosgenin. However, this did not result in increased fasting blood glucose. Instead, supplementation of the diet with bitter yam sapogenin extract significantly decreased fasting blood glucose compared to the diabetic group. Supplementation of the diet with bitter yam sapogenin extract or commercial diosgenin significantly reduced Na+-K+-ATPase activity in all three regions compared to the diabetic control group. Commercial diosgenin supplementation resulted in a significant increase in Ca2+ ATPase activity in proximal region compared to the diabetic control and bitter yam sapogenin extract groups. The effect of bitter yam sapogenin extract or commercial diosgenin on intestinal Na+-K+-ATPase activity could account for their hypoglycemic properties. However, there was adverse effect on the body weight.

Alteration of the expression of adenosine triphosphate-binding cassette transporters associated with bile acid and cholesterol transport in the rat liver and intestine during cholestasis

BACKGROUND AND AIM

Multidrug resistance protein 2 (Mrp2), Mrp3, adenosine triphosphate-binding cassette transporter g5 (Abcg5) and adenosine triphosphate-binding cassette transporter g8 (Abcg8) have been identified as bile acid or cholesterol transporter in the enterocytes as well as hepatocytes. The purpose of the present study was to evaluate intestinal and hepatic adenosine triphosphate-binding cassette transporter expressions during cholestasis.

METHODS

Experiment 1: Rats were subjected to bile duct ligation or sham operation. Blood, liver and small intestines were obtained 24 and 72 h after operation. Experiment 2: Rats were divided into four groups as follows: (i) control group; (ii) diosgenin group (fed with diosgenin in diet [1%(wt/wt)] for 7 days); (iii) ethinyl estradiol group (received ethinyl estradiol [5 mg/kg daily] for 5 days); and (iv) diosgenin-ethinyl estradiol group (received ethinyl estradiol and diosgenin). After treatment, blood, bile, liver and intestines were obtained. The mRNA related to lipid and bile acid metabolism was analyzed by reverse transcription polymerase chain reaction.

RESULTS

Intestinal Mrp2 and Abcg5/Abcg8 mRNA expression remarkably decreased 24 h after bile duct ligation (43% and 61%/54% of sham operation) and recovered 72 h after bile duct ligation (103% and 95%/83% of sham operation). Intestinal Mrp3 mRNA expression did not change after bile duct ligation. Intestinal Mrp2 mRNA expression was remarkably increased in diosgenin and diosgenin-ethinyl estradiol groups in comparison with the control group. There were no significant differences in intestinal Mrp3 mRNA expression among the four groups. Hepatic Mrp3 mRNA expression was remarkably increased in the D, EE and DE groups in comparison with the control group (531%, 321% and 1160% of control, respectively, P < 0.01). Hepatic Abcg5 and Abcg8 mRNA expression decreased in ethinyl estradiol and diosgenin-ethinyl estradiol groups compared with the control group and there were no differences in intestinal Abcg5 and Abcg8 mRNA expressions among the four groups.

CONCLUSION

Bile duct ligation affects not only hepatic but also the intestinal Mrp2 and Abcg5 and Abcg8 expressions. Intestinal Mrp2 mRNA level was regulated by factor in the lumen (e.g. diosgenin feeding). Cholestasis by ethinyl estradiol treatment was enhanced by diosgenin and the increase in hepatic Mrp3 mRNA level might affect the enhancement.

Diosgenin, a plant steroid, induces apoptosis in human rheumatoid arthritis synoviocytes with cyclooxygenase-2 overexpression

In the present study, we have shown for the first time that a plant steroid, diosgenin, causes an inhibition of the growth of fibroblast-like synoviocytes from human rheumatoid arthritis, with apoptosis induction associated with cyclooxygenase-2 (COX-2) up-regulation. Celecoxib, a selective COX-2 inhibitor, provoked a large decrease in diosgenin-induced apoptosis even in the presence of exogenous prostaglandin E₂, whereas interleukin-1β, a COX-2 inducer, strongly increased diosgenin-induced apoptosis of these synoviocytes. These findings suggest that the proapoptotic effect of diosgenin is associated with overexpression of COX-2 correlated with overproduction of endogenous prostaglandin E₂. We also observed a loss of mitochondrial membrane potential, caspase-3 activation, and DNA fragmentation after diosgenin treatment.

Hepatic canalicular membrane transport of bile salt in C57L/J and AKR/J mice: implications for cholesterol gallstone formation

C57L/J (gallstone-susceptible) and AKR/J (gallstone-resistant) mice have been utilized for quantitative trait loci (QTL) analysis to identify the Lith 1 locus for cholelithiasis. Abcb11 encodes for the liver canalicular membrane bile salt export pump (BSEP), which maps to this QTL and is a candidate gene for Lith 1. We investigated the transmembrane transport of taurocholate in canalicular liver membrane vesicles isolated from these murine strains. Canalicular liver plasma membranes (cLPM) and RNA were isolated from C57L/J and AKR/J mice livers, and were utilized for Northern and Western blot analysis and functional (3)H-taurocholate uptake studies. ATP-dependent (3)H-taurocholate uptake was significantly higher in AKR/J, compared to C57L/J mice. V(max) was 127 vs. 42 pmol TC/mg/s in the murine strains, respectively, while K(m) was unchanged. In contrast, gene and protein expression of hepatic Abcb11 was increased three-fold in C57L/J, compared to AKR/J mice. Thus, Abcb11 bile salt transport activity per unit protein was reduced nine-fold in the C57L/J, compared to AKR/J mice. In contrast, canalicular membrane cholesterol:phospholipid content was also significantly higher in the C57L/J mice. We conclude that gallstone-susceptible C57L/J mice demonstrate increased gene and canalicular membrane expression of Abcb11, however, taurocholate transport is functionally diminished. The latter may be due to the increased cholesterol membrane content of the cLPM in C57L/J mice. These findings may be important for the pathogenesis of gallstone formation.

Epoxidation of Diosgenin, 25(R)-1,4,6-Spirostatrien-3-one and 25(R)-4,6-Spirostadien-3β-ol

Upon treatment of 25(R)-spirost-5-en-3β-ol (diosgenin), 25(R)-1,4,6-spirostatrien-3-one and 25(R)-4,6-spirostadien-3β-ol with 30% H₂O₂ and 5% NaOH in methanol, diosgenin did not react, 25(R)-1,4,6-spirostatrien-3-one was converted to 25(R)-1α,2α-epoxy-4,6-spirostadien-3-one and 25(R)-4,6-spirostadien-3β-ol was oxidized to give a small amount of 25(R)-4,6-spirostadien-3-one, while most of the original starting material remained unchanged. On the other hand, reactions of diosgenin, 25(R)-1,4,6-spirostatrien-3-one and 25(R)-4,6-spirostadien-3β-ol with m-chloroperoxy-benzoic acid in chloroform yielded 25(R)-5α,6α-epoxyspirostan-3β-ol, 25(R)-6α,7α-epoxy-1,4-spirostadien-3-one and 25(R)-4β,5β-epoxy-6-spirosten-3β-ol, respectively.

Genetic background of cholesterol gallstone disease

Cholesterol gallstone formation is a multifactorial process involving a multitude of metabolic pathways. The primary pathogenic factor is hypersecretion of free cholesterol into bile. For people living in the Western Hemisphere, this is almost a normal condition, certainly in the elderly, which explains the very high incidence of gallstone disease. It is probably because the multifactorial background genes responsible for the high incidence have not yet been identified, despite the fact that genetic factors clearly play a role. Analysis of the many pathways involved in biliary cholesterol secretion reveals many potential candidates and considering the progress in unraveling the regulatory mechanisms of the responsible genes, identification of the primary gallstone genes will be successful in the near future.

Human immunodeficiency virus-1 Tat protein and methamphetamine interact synergistically to impair striatal dopaminergic function

The human immunodeficiency virus (HIV)-1 transactivating protein Tat may be pathogenically relevant in HIV-1-induced neuronal injury. The abuse of methamphetamine (MA), which is associated with behaviors that may transmit HIV-1, may damage dopaminergic afferents to the striatum. Since Tat and MA share common mechanisms of injury, we examined whether co-exposure to these toxins would lead to enhanced dopaminergic toxicity. Animals were treated with either saline, a threshold dose of MA, a threshold concentration of Tat injected directly into the striatum, or striatal injections of Tat followed by exposure to MA. Threshold was defined as the highest concentration of toxin that would not result in a significant loss of striatal dopamine levels. One week later, MA-treated animals demonstrated a 7% decline in striatal dopamine levels while Tat-treated animals showed an 8% reduction. Exposure to both MA + Tat caused an almost 65% reduction in striatal dopamine. This same treatment caused a 56% reduction in the binding capacity to the dopamine transporter. Using human fetal neurons, enhanced toxicity was also observed when cells were exposed to both Tat and MA. Mitochondrial membrane potential was disrupted and could be prevented by treatment with antioxidants. This study demonstrates that the HIV-1 'virotoxin' Tat enhances MA-induced striatal damage and suggests that HIV-1-infected individuals who abuse MA may be at increased risk of basal ganglia dysfunction.

Regulation of biliary cholesterol secretion is independent of hepatocyte canalicular membrane lipid composition: a study in the diosgenin-fed rat model

BACKGROUND/AIMS

Phosphatidylcholine (PC) and sphingomyelin (SM) are the major phospholipids on the outer leaflet of the hepatocyte canalicular membrane. Since cholesterol preferentially associates with SM in detergent-resistant microdomains, we hypothesized that canalicular membrane lipid composition could modulate secretion of the sterol into bile.

METHODS

Male Wistar rats were fed for 10 days with a control diet with or without the plant sterol diosgenin (1% w/w) to induce biliary cholesterol hypersecretion. Thereafter, lipid compositions and phospholipid molecular species were determined in fistula bile and highly enriched canalicular membrane fractions.

RESULTS

Despite four-fold higher biliary cholesterol output in diosgenin-fed rats, no differences were observed between canalicular membranes of diosgenin and control groups with respect to cholesterol/phospholipid ratios (0.58 vs 0.62), phospholipid classes and acyl chain compositions of SMs (16:0 > 24:1 > 24:0 > 22:0 > 18:0 > 23:0 > 20:0 > 24:2), or PCs (mainly diacyl 16:0-18:2, 16:0-20:4, 18:0-20:4, and 18:0-18:2). In contrast to canalicular PCs, bile contained more hydrophilic species (mainly diacyl 16:0-18:2 and 16:0-20:4), without differences between both groups. In vitro resistance of purified canalicular membrane fractions against detergents such as Triton X-100 and taurocholate was also similar in both groups.

CONCLUSIONS

Diosgenin-induced biliary cholesterol hypersecretion occurs in the absence of changes of canalicular membrane lipids. Our data therefore do not support a major role of canalicular membrane lipid composition in regulation of biliary cholesterol secretion.

Differential expression of canalicular membrane Ca2+/Mg(2+)-ecto-ATPase in estrogen-induced and obstructive cholestasis in the rat

Extracellular adenosine triphosphate (ATP) may regulate hepatocyte and cholangiocyte functions, and under some conditions it may have deleterious effects on bile secretion and cause cholestasis. The canalicular membrane enzyme Ca2+/Mg2+-ecto-ATPase (ecto-ATPase) hydrolyzes ATP/adenosine diphosphate (ATP/ADP) and regulates hepatic extracellular ATP concentration. Changes in liver ecto-ATPase in estrogen-induced cholestasis were examined in male rats receiving 17alpha-ethinylestradiol (E groups) for 1, 3, or 5 days (5 mg/kg/day, sc) and compared with changes in rats subjected to obstructive cholestasis (O groups) for 1, 3, or 8 days. Activity of ecto-ATPase, protein mass in canalicular membranes and bile (estimated by Western blotting), steady state mRNA levels (by Northern blotting), and cellular and acinar distributions of the enzyme (histochemistry and immunocytochemistry) were assessed in these groups. Activity of ecto-ATPase, protein mass in isolated canalicular membranes, and enzyme mRNA levels were significantly increased in E group rats as compared with controls. In contrast, these parameters were markedly decreased in O group rats, and the enzyme protein was undetectable in bile. The ecto-ATPase histochemical reaction was markedly increased in the canalicular membrane of E group rats, extending from acinar zone 2 to zone 1, whereas it decreased in the O group. The ecto-ATPase immunocytochemical reaction was present in the canalicular membrane and pericanalicular vesicles in control and E group hepatocytes, but it decreased in obstructive cholestasis and was localized only to the canalicular membrane. Thus, significant changes in liver ecto-ATPase were apparent in 17alpha-ethinylestradiol-induced cholestasis that were opposite to those observed in obstructive cholestasis. Assuming that the alterations observed in obstructive cholestasis are the result of the cholestatic phenomenon, we conclude that changes in ecto-ATPase in 17alpha-ethinylestradiol-treated rats might be either primary events or part of an adaptive response in 17alpha-ethinylestradiol-induced cholestasis.