Toxic time bombs: Frequent detection of anticoagulant rodenticides in urban reptiles at multiple trophic levels

Anticoagulant rodenticides (ARs) are regularly used around the world to control pest mammals. Second-generation anticoagulant rodenticides (SGARs) are highly persistent in biological tissue and have a high potential for bioaccumulation and biomagnification. Consequently, exposure and poisoning of non-target organisms has been frequently documented, especially in countries with unregulated AR sales and usage. Most of this research has focussed on rodent-predators, usually raptors and predatory mammals, although exposure has also been documented in invertebrates and insectivorous fauna. Few studies have explored non-target exposure in reptiles, despite species sharing similar trophic positions and dietary preferences to other exposed fauna. We tested three abundant urban reptile species in Perth, Western Australia that differ in diet and trophic tiers for multiple AR exposure, the dugite Pseudonaja affinis (rodent-predator), the bobtail Tiliqua rugosa (omnivore) and the tiger snake Notechis scutatus occidentalis (frog-predator). We found frequent exposure in all three species (91% in dugites, 60% in bobtails and 45% in tiger snakes). Mean combined liver concentrations of ARs of exposed individuals were 0.178 mg/kg in dugites, 0.040 mg/kg in bobtails and 0.009 mg/kg in tiger snakes. High exposure frequency and liver concentration was expected for the dugite. Exposure in the other species is more surprising and implies widespread AR contamination of the food web. We discuss the likelihood of global AR exposure of urban reptiles, highlight the potential for reptiles to be important vectors of ARs in the food web and highlight implications for humans consuming wild reptiles.

The plant natural product 2-methoxy-1,4-naphthoquinone stimulates therapeutic neural repair properties of olfactory ensheathing cells

Olfactory ensheathing cells (OECs) are crucial for promoting the regeneration of the primary olfactory nervous system that occurs throughout life. Transplantation of OECs has emerged as a promising therapy for nervous system injuries, in particular for spinal cord injury repair. Functional outcomes in both animals and humans are, however, highly variable, primarily because it is difficult to rapidly obtain enough OECs for transplantation. Compounds which can stimulate OEC proliferation without changing the phenotype of the cells are therefore highly sought after. Additionally, compounds which can stimulate favourable cell behaviours such as migration and phagocytic activity are desirable. We conducted a medium-throughput screen testing the Davis open access natural product-based library (472 compounds) and subsequently identified the known plant natural product 2-methoxy-1,4-naphthoquinone as a stimulant of OEC viability. We showed that 2-methoxy-1,4-naphthoquinone: (i) strongly stimulates proliferation over several weeks in culture whilst maintaining the OEC phenotype; (ii) stimulates the phagocytic activity of OECs, and (iii) modulates the cell cycle. We also identified the transcription factor Nrf2 as the compound’s potential molecular target. From these extensive investigations we conclude that 2-methoxy-1,4-naphthoquinone may enhance the therapeutic potential of OECs by stimulating proliferation prior to transplantation.

Bad news for bobtails: understanding predatory behaviour of a resource-subsidised corvid towards an island endemic reptile

Context Resource subsidisation as a result of urbanisation and other human activity can have positive impacts for some opportunistic predators. Many species of corvid have benefitted from the expansion of human-dominated habitats; however, their impacts on co-occurring prey fauna are generally poorly understood. Aims We aimed to test the hypothesis that urbanisation associated with tourism impacts the predator–prey relationship between Australian ravens, or wardongs (Corvus coronoides), a ubiquitous corvid of southern Australia, and Rottnest Island bobtails (Tiliqua rugosa konowi), a subspecies of bobtail lizard isolated to a small (19km2) island off the coast of Western Australia. Methods Using clay model lizards and camera traps, we assessed the wardongs’ attack rates by distance from the settlement and by whether the model was in closed or open habitat. Key Results We found that while wardongs preyed upon Rottnest Island bobtails, predation was not affected by proximity to human settlement despite the highest number of wardongs being found there. Models in closed vegetation were attacked by wardong significantly more than were those in open vegetation. Implications Increased predation rates in closed vegetation suggests that current revegetation efforts on the island may be increasing the availability of preferred hunting habitat for the wardong. This finding may influence decisions by management on whether to control the large population of wardongs on the island.

Dichloro-naphthoquinone as a non-classical inhibitor of the mycobacterial carbonic anhydrase Rv3588c

The soluble mycobacterial carbonic anhydrases Rv3588c and Rv1284 belong to a different class of carbonic anhydrases than those found in humans, making them attractive drug targets by using the inherent differences in the folds of the different classes. By screening a natural product library, we identified naphthoquinone derivatives as a novel non-classical inhibitor scaffold of mycobacterial carbonic anhydrases that lack the sulfonamide/sulfamate group and thus did not affect human carbonic anhydrase II.

Adapting to suburbia: bird ecology on an urban-bushland interface in Perth, Western Australia

Birds in urban landscapes must contend with fragmented and degraded remnants of native vegetation and their survival may be dependent on factors such as their ability to disperse through and/or utilize the urban matrix. We examined the frequency of occurrence of birds in native bushland in Kings Park, Perth, Western Australia, and in nine adjacent suburban gardens. We quantified dispersal capacity by observing bird crossing frequency and height over a major six-lane road separating the bushland from adjacent gardens. Finally we quantified matrix utilisation by recording foraging behaviour in urban gardens and bushland. Native bushland had a higher species richness than urban gardens (30 versus 17 species) and 18 species were associated more strongly with bushland. Of these 18 species, 61% were never recorded in urban gardens. Gardens were typified by three generalist species, the Singing Honeyeater Lichenostomus virescens and the introduced Laughing Dove Spilopelia senegalensis and Spotted Dove S. chinensis. Three generalist species, the Red Wattlebird Anthochaera carunculata, Rainbow Lorikeet Trichoglossus haematodus, and Brown Honeyeater Lichmera indistincta were equally abundant in all habitats. Four of 18 bird species (Singing Honeyeater Red Wattlebird, Rainbow Lorikeet, and Australian Ringneck Barnardius zonarius) accounted for the majority of road crossing events. Urban gardens provided a rich resource for generalists and urban exploiters, all of which spent significantly more time foraging on nectar in gardens and significantly more time foraging on insects in bushland. We conclude that urban gardens provide habitat for some species that exploit nectar, but most species in bushland, particularly insectivores, do not use gardens. Our results indicate the importance of retaining well-managed bushland for supporting viable urban bird populations.

A rapid LC-MS-MS method for the determination of nicotine and cotinine in serum and saliva samples from smokers: validation and comparison with a radioimmunoassay method

The development and validation of a rapid liquid chromatography (LC)-tandem mass spectrometry (MS-MS) method for determination of nicotine and cotinine in smokers' serum is described. The method is based on solid-phase extraction in a 96-well plate format and requires only 100 microL of serum. Using normal-phase chromatography, both analytes elute in less than 1 min, which permits high sample throughput applications. The calibrated range is 2-100 ng/mL nicotine and 20-1,000 ng/mL cotinine. For known samples, recovery is 95-116% for nicotine and 93-94% for cotinine. The method is extended to rat serum and human saliva (cotinine only) using partial validation techniques. When compared with an existing radioimmunoassay method in our laboratory, the LC-MS-MS method gives improved accuracy, precision, and sample throughput.

A benzylisoquinoline alkaloid from Doryphora sassafras

Chemical investigation of the Australian rainforest plant Doryphora sassafras has resulted in the isolation of a new natural product, 2-methyl-1-(p-methoxybenzyl)-6,7-methylenedioxyisoquinolinium chloride (1). The iodide salt of compound 1 has previously been synthesized but only partially characterized. This paper reports the full spectroscopic characterization of 1 by MS, IR, UV, and NMR data.

Structural analysis of cDNA encoding thymidylate synthase in hepatic metastases of human colorectal tumors

The enzyme thymidylate synthase (TS) is an important target of 5-fluorouracil (FUra) that is utilized for the treatment of disseminated colorectal cancer. One determinant of clinical response to FUra-based therapy is TS expression. with high levels of expression being predictive of poor response. In the present investigation the levels of immunoreactive TS were analyzed in human colon metastases in the liver (n=l1). The levels of TS ranged from 0.30 to 4.60 pmol TS/g tissue. A good correlation was observed between the levels of immunoreactive TS and TS mRNA (n=6, r=0.69). Of the 11 metastases analyzed, 5 exhibited relatively high levels of TS expression. Two metastases with high TS expression were obtained from patients who received adjuvant therapy with FUra. In 4 metastases with relatively high levels of TS expression, TS gene copy number was analyzed. No evidence for amplification of TS gene sequences was observed. The basis for the high levels of TS expression was examined by structural analysis of TS cDNA. No nucleotide sequence differences were detected in the coding regions of the TS genes from the metastases. Mutations were detected at positions 961 and/or 1031 in the 3'-untranslated regions of the TS gene from the metastases; mutations at these sites were also detected in DNA isolated from normal colon mucosa (n=4) and primary colorectal tumors (n=4). No correlation was observed between TS expression and the nucleotide alterations at these positions. Polymorphism was observed in the 5'-untranslated regions of the TS gene in hepatic metastases (n=6). A general trend was observed between the structure of the 5'-untranslated region of the gene and TS expression.

Increased production of apolipoprotein B-containing lipoproteins in the absence of hyperlipidemia in transgenic mice expressing cholesterol 7alpha-hydroxylase

The finding that expression of a cholesterol 7alpha-hydroxylase (CYP7A1) transgene in cultured rat hepatoma cells caused a coordinate increase in lipogenesis and secretion of apoB-containing lipoproteins led to the hypothesis that hepatic production of apoB-containing lipoproteins may be linked to the expression of CYP7A1 (Wang, S.-L., Du, E., Martin, T. D., and Davis, R. A. (1997) J. Biol. Chem. 272, 19351-19358). To examine this hypothesis in vivo, a transgene encoding CYP7A1 driven by the constitutive liver-specific enhancer of the human apoE gene was expressed in C56BL/6 mice. The expression of CYP7A1 mRNA (20-fold), protein ( approximately 10-fold), and enzyme activity (5-fold) was markedly increased in transgenic mice compared with non-transgenic littermates. The bile acid pool of CYP7A1 transgenic mice was doubled mainly due to increased hydrophobic dihydroxy bile acids. In CYP7A1 transgenic mice, livers contained approximately 3-fold more sterol response element-binding protein-2 mRNA. Hepatic expression of mRNAs encoding lipogenic enzymes (i.e. fatty-acid synthase, acetyl-CoA carboxylase, stearoyl-CoA desaturase, squalene synthase, farnesyl-pyrophosphate synthase, 3-hydroxy-3-methylglutaryl-CoA reductase, and low density lipoprotein receptor) as well as microsomal triglyceride transfer protein were elevated approximately 3-5-fold in transgenic mice. CYP7A1 transgenic mice also displayed a >2-fold increase in hepatic production and secretion of triglyceride-rich apoB-containing lipoproteins. Despite the increased hepatic secretion of apoB-containing lipoproteins in CYP7A1 mice, plasma levels of triglycerides and cholesterol were not significantly increased. These data suggest that the 5-fold increased expression of the low density lipoprotein receptor displayed by the livers of CYP7A1 transgenic mice was sufficient to compensate for the 2-fold increase production of apoB-containing lipoproteins. These findings emphasize the important homeostatic role that CYP7A1 plays in balancing the anabolic lipoprotein assembly/secretion pathway with the cholesterol catabolic bile acid synthetic pathway.

2000 George Lyman Duff Memorial Lecture: atherosclerosis is a liver disease of the heart

The production of apolipoprotein B (apoB)-containing lipoproteins by the liver is regulated by a complex series of processes involving apoB being cotranslationally translocated across the endoplasmic reticulum and assembled into a lipoprotein particle. The translocation of apoB across the endoplasmic reticulum is facilitated by the intraluminal chaperone, microsomal triglyceride transfer protein (MTP). MTP facilitates the translocation and folding of apoB, as well as the addition of lipid to lipid-binding domains (which consist of amphipathic beta sheets and alpha helices). In the absence of MTP or sufficient lipid, apoB exhibits translocation arrest. Thus, apoB translation, translocation, and assembly with lipids to form a core-containing lipoprotein particle occur as concerted processes. Abrogation of >/=1 of these processes diverts apoB into a degradation pathway that is dependent on conjugation with ubiquitin and proteolysis by the proteasome. The nascent core-containing lipoprotein particle that forms within the lumen of the endoplasmic reticulum can be "enlarged" to form a mature very low density lipoprotein particle. Additional studies show that the assembly and secretion of apoB-containing lipoproteins are linked to the cholesterol/bile acid synthetic pathway controlled by cholesterol 7alpha-hydroxylase. Studies in cultured cells and transgenic mice indicate that the expression of cholesterol 7alpha-hydroxylase indirectly regulates the expression of lipogenic enzymes through changes in the cellular content of mature sterol response element binding proteins. Oxysterols and bile acids may also act via the ligand-activated nuclear receptors LXR and FXR to link the metabolic pathways controlling energy balance and lipid metabolism to nutritional state.

Cholesterol and hepatic lipoprotein assembly and secretion

The assembly and secretion of apo B100 containing lipoproteins (i.e., VLDL) by the liver and cholesterol metabolism are interrelated on several different levels and for several different physiologic reasons. Firstly, hepatic VLDL is the major precursor for LDL, which in the human is the major vehicle responsible for transporting cholesterol to peripheral tissues. Secondly, cholesterol is supplied to many tissues by a specific uptake of LDL via LDL receptor, which is expressed in a regulated manner by most mammalian tissues. Thirdly, the rate of hepatic cholesterol biosynthesis and metabolism to bile acids correlates with production of VLDL. This apparent coordinate expression of cholesterol biosynthetic/catabolic enzymes and hepatic VLDL assembly/secretion are mediated at least in part through the sterol response element binding protein (SREBP) transcription factor family. Their gene targets include a plethora of enzymes that regulate glycolysis, energy production, lipogenesis and cholesterol catabolism. Studies of hepatoma cells overexpressing CYP7A1, the rate-limiting enzyme controlling bile acid synthesis, show that as a result of increased mature SREBP1, there is a coordinate induction of lipogenesis and the assembly and secretion of VLDL. These and additional studies show that the bile acid synthetic pathway and the VLDL assembly/secretion pathway are coordinately linked through SREBP-dependent transcription. Based on studies showing that within the liver acinus, the expression of CYP7A1 is mainly in the pericentral region while HMG-CoA reductase is mainly periportal, we propose that a 'metabolic zonal segregation' plays an important role in coordinate regulation of cholesterol and VLDL metabolism. This putative 'metabolic zonal segregation' may provide segregation of metabolic functions which may be mutually antagonistic. For example, there may be physiologic states in which the bile acid synthetic pathway may compete with the VLDL assembly/secretion pathway for a limited amount of cholesterol. Metabolic antagonism (e.g., competition for cholesterol) may be avoided via inducing SREBP-mediated transcription. Adaptation of catabolic hepatocytes to accommodate the expression of VLDL assembly/secretion may occur in response to activation of SREBP-mediated transcription. Support for these is discussed.

Minority recruitment and retention in dietetics: issues and interventions

To better understand the reasons why minorities and males are underrepresented among registered dietitians (RDs) and dietetic technicians, registered, (DTRs) and to develop focuses for intervention, the investigators performed a telephone survey of newly credentialed RDs and DTRs and directors of RD and DTR education programs. Using lists of students recruited by the American Dietetic Association for participation in the survey, the investigators interviewed 83 RDs and DTRs and 20 education program directors. RDs and DTRs attributed minority underrepresentation primarily to the field's lack of visibility and underrepresentation of men to the traditional association with women. Education program directors attributed minority underrepresentation to educational disadvantages, particularly in scientific subjects. Findings from this study support program-level interventions such as increasing program flexibility, initiating outreach to K-12 schools and lower-division college students, providing tutoring in a nondemeaning atmosphere, and visibly expressing commitment to minority representation. More fundamental changes in the profession itself appear necessary for large-scale increases in minority representation. These include increasing internship opportunities; raising the profession's level of remuneration, prestige, and independence; increasing scholarship support; and advertising nationally through channels capable of reaching minorities.

In nonhepatic cells, cholesterol 7alpha-hydroxylase induces the expression of genes regulating cholesterol biosynthesis, efflux, and homeostasis

CHO cells expressing the liver-specific gene product cholesterol-7alpha-hydroxylase showed a 6-fold increase in the biosynthesis of [(14)C]cholesterol from [(14)C]acetate, as well as increased enzymatic activities of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase and squalene synthase. Cells expressing cholesterol-7alpha-hydroxylase contained less sterol response element-binding protein 1 (SREBP1) precursor, whereas the cellular content of mature SREBP1, as well as the mRNAs of cholesterol biosynthetic genes (HMG-CoA reductase and squalene synthase), were all increased approximately 3-fold. Cells expressing cholesterol-7alpha-hydroxylase displayed greater activities of luciferase reporters containing the SREBP-dependent promoter elements derived from HMG-CoA reductase and farnesyl diphosphate synthase, in spite of accumulating significantly more free and esterified cholesterol and 7alpha-hydroxycholesterol. While cells expressing cholesterol-7alpha-hydroxylase displayed increased SREBP-dependent transcription, sterol-mediated repression of SREBP-dependent transcription by LDL-cholesterol and exogenous oxysterols was similar in both cell types. Cells expressing cholesterol-7alpha-hydroxylase displayed greater rates of secretion of cholesterol as well as increased expression of the ABC1 cassette protein mRNA. Adding 25-hydroxycholesterol to the culture medium of both cell types increased the expression of ABC1 cassette protein mRNA. The combined data suggest that in nonhepatic CHO cells multiple regulatory processes sensitive to cellular sterols act independently to coordinately maintain cellular cholesterol homeostasis.

Bile acid induction of cytokine expression by macrophages correlates with repression of hepatic cholesterol 7alpha-hydroxylase

In the studies reported herein, we show that two complementary experimental models: inbred strains of mice (i.e. C57BL/6 and C3H/HeJ), and a differentiated line of rat hepatoma cells (i.e. L35 cells), require the activation of cytokines by monocyte/macrophages to display bile acid negative feedback repression of cholesterol 7alpha-hydroxylase (CYP7A1). Feeding a bile acid-containing atherogenic diet for 3 weeks to C57BL/6 mice led to a 70% reduction in the expression of hepatic CYP7A1 mRNA, whereas no reduction was observed in C3H/HeJ mice. The strain-specific response to repression of CYP7A1 paralleled the activation of hepatic cytokine expression. Studies using cultured THP-1 monocyte/macrophages showed that the hydrophobic bile acid chenodeoxycholate, a well established potent repressor of CYP7A1, induced the expression of mRNAs encoding interleukin 1 (IL-1) and tumor necrosis factor alpha (TNFalpha). In contrast, the hydrophilic bile acid ursodeoxycholate, which does not repress CYP7A1, did not induce cytokine mRNA expression by THP-1 cells. Chenodeoxycholate activation of cytokines by THP-1 cells was blocked by the peroxisome proliferator-activated receptor gamma agonist rosiglitazone. The expression of cytokines (e.g. IL-1 and TNFalpha) by THP-1 cells paralleled with the ability of these cells to produce conditioned medium that when added to rat L35 hepatoma cells, repressed CYP7A1. Moreover, rosiglitazone, which blocks cytokine activation by macrophages, also blocked the repression of CYP7A1 normally exhibited by C57BL/6 mice fed the bile acid-containing atherogenic diet. The combined data indicate that the activation of cytokines may mediate CYP7A1 repression caused by feeding mice an atherogenic diet containing bile acids.

Stability of 5-Fluorouracil in an extemporaneously compounded ophthalmic solution

5-Fluorouracil (5-FU) is used in the treatment of a variety of ophthalmic conditions, including glaucoma, pterygium, retinal detachment and premalignant eye lesions. Specifically for the treatment of pterygium, intravitreal injections of 5-FU have been extemporaneously compounded by pharmacists and typically stored in syringes. No data exist concerning the chemical and physical stability of these solutions. With this in mind, the stability of 5-FU (1mg/0.1mL) in 0.9% sodium chloride injection prepared in the hospital pharmacy laboratory at the University of South Carolina was studied with respect to time and temperature. Admixtures of 5-FU were aseptically prepared and stored in 1-mL tuberculin syringes. The stability of these solutions was evaluated in a freezer, in a refrigerator, at room temperature and in an oven set at 40 deg C. Immediately after prepareation, samples were collected to determine initial concentration using a stability-indicating high-performance liquid chromatography method and to assess the pH of the solution. The same tests were repeated after one, three, five and seven days of storage. Samples were also visually inspected at these times for signs of physical incompatibility. Tuberculin syringes stored at each of the temperatures showed no signs of physical incompatibility (precipitate) or loss of drug. There was also no appreciable change in pH of the solution over the study period. This study showed that aseptically prepared 5-FU ophthalmic solutions packaged in tuberculin syringes can be stored safely for up to seven days at temperatures ranging form -10 to 40 deg C/

One or more labile proteins regulate the stability of chimeric mRNAs containing the 3'-untranslated region of cholesterol-7alpha -hydroxylase mRNA

Multiple AUUUA elements similar to those that regulate the degradation of several different mRNAs are conserved in the 3'-untranslated region (3'-UTR) of cholesterol-7alpha-hydroxylase (CYP7A1) mRNAs from several species. We examined if stabilization of mRNA decay could account for the >20-fold increase in the expression of CYP7A1 mRNA without a detectable change in transcription following dexamethasone treatment of rat hepatoma cells (L35 cells). Following RNA polymerase II-dependent transcription block or protein synthesis block, the decay of CYP7A1 mRNA displayed a short half-life ( approximately 30 min). Control experiments showed that in cells pre-treated with a RNA polymerase II inhibitor, dexamethasone had no detectable effect on CYP7A1 mRNA decay. Stable expression of luciferase reporter mRNAs in L35 cells showed that the CYP7A1 3'-UTR was required to observe a dexamethasone induction. To examine the hypothesis that a labile protein is required for dexamethasone-induced mRNA stabilization, cells were stably transfected with a tetracycline-repressible promoter that drives the expression of a green fluorescent protein analogue (ECFP) with or without the 3'-UTR of CYP7A1. Cells expressing ECFP with the 3'-UTR of CYP7A1 displayed a 3-fold dexamethasone induction of ECFP mRNA, whereas cells expressing ECFP without the 3'-UTR did not. Moreover, specific block of the transcription of ECFP containing the 3'-UTR by adding the tetracycline analogue doxycycline clearly displayed dexamethasone-induced stabilization of mRNA decay. These data provide compelling evidence that a putative labile protein and the 3'-UTR of CYP7A1 act together to decrease the rate of CYP7A1 mRNA degradation.

The JNK and P38 MAP kinase signaling pathways in T cell-mediated immune responses

The mitogen-activated protein (MAP) kinase family members, which include the extracellular response kinases (ERK), p38, and c-Jun amino terminal kinases (JNK), play a role in mediating signals triggered by cytokines, growth factors, and environmental stress. JNK and p38 MAP kinases have been involved in inflammatory processes induced by a variety of stimuli, such as oxidative stress. Here, we describe the role of the JNK and p38 MAP kinase signaling pathways in the development of T cells in the thymus, and activation and differentiation of T cells in the peripheral immune system.

10-Hydroxydarlingine, a new tropane alkaloid from the Australian proteaceous plant triunia erythrocarpa

Triunia erythrocarpa was identified as containing alkaloids during chemical screening of Queensland Proteaceae using Dragendorff's reagent. A new tropane, 10-hydroxydarlingine (1), and the known tropane, darlingine (2), were isolated from the leaves of T. erythrocarpa. The absolute stereochemistry of 10-hydroxydarlingine (1) was assigned using the advanced Mosher method. T. erythrocarpa is only the seventh member of the Proteaceae to have been shown to produce alkaloids.

Longithorols C-E. Three new macrocyclic sesquiterpene hydroquinone metabolites from the australian ascidian, aplidium longithorax

Chemical investigation of a Great Barrier Reef ascidian, Aplidium longithorax has resulted in the isolation of two new para-substituted cyclofarnesylated hydroquinone compounds, longithorols C (1) and D (2), and a novel macrocyclic chromenol, longithorol E (3). Longithorol C (1) had its absolute stereochemistry determined by the advanced Mosher method and all compounds had their structures determined by interpretation of spectroscopic data.

Cell and molecular biology of the assembly and secretion of apolipoprotein B-containing lipoproteins by the liver

Triglycerides are one of the most efficient storage forms of free energy. Because of their insolubility in biological fluids, their transport between cells and tissues requires that they be assembled into lipoprotein particles. Genetic disruption of the lipoprotein assembly/secretion pathway leads to several human disorders associated with malnutrition and developmental abnormalities. In contrast, patients displaying inappropriately high rates of lipoprotein production display increased risk for the development of atherosclerotic cardiovascular disease. Insights provided by diverse experimental approaches describe an elegant biological adaptation of basic chemical interactions required to overcome the thermodynamic dilemma of producing a stable emulsion vehicle for the transport and tissue targeting of triglycerides. The mammalian lipoprotein assembly/secretion pathway shows an absolute requirement for: (1) the unique amphipathic protein: apolipoprotein B, in a form that is sufficiently large to assemble a lipoprotein particle containing a neutral lipid core; and, (2) a lipid transfer protein (microsomal triglyceride transfer protein-MTP). In the endoplasmic reticulum apolipoprotein B has two distinct metabolic fates: (1) entrance into the lipoprotein assembly pathway within the lumen of the endoplasmic reticulum; or, (2) degradation in the cytoplasm by the ubiquitin-dependent proteasome. The destiny of apolipoprotein B is determined by the relative availability of individual lipids and level of expression of MTP. The dynamically varied expression of cholesterol-7alpha-hydroxylase indirectly influences the rate of lipid biosynthesis and the assembly and secretion lipoprotein particles by the liver.

Chinese hamster ovary cells require the coexpression of microsomal triglyceride transfer protein and cholesterol 7alpha-hydroxylase for the assembly and secretion of apolipoprotein B-containing lipoproteins

Due to the absence of microsomal triglyceride transfer protein (MTP), Chinese hamster ovary (CHO) cells lack the ability to translocate apoB into the lumen of the endoplasmic reticulum, causing apoB to be rapidly degraded by an N-acetyl-leucyl-leucyl-norleucinal-inhibitable process. The goal of this study was to examine if expression of MTP, whose genetic deletion is responsible for the human recessive disorder abetalipoproteinemia, would recapitulate the lipoprotein assembly pathway in CHO cells. Unexpectedly, expression of MTP mRNA and protein in CHO cells did not allow apoB-containing lipoproteins to be assembled and secreted by CHO cells expressing apoB53. Although expression of MTP in cells allowed apoB to completely enter the endoplasmic reticulum, it was degraded by a proteolytic process that was inhibited by dithiothreitol (1 mM) and chloroquine (100 microM), but resistant to N-acetyl-leucyl-leucyl-norleucinal. In marked contrast, coexpression of the liver-specific gene product cholesterol 7alpha-hydroxylase with MTP resulted in levels of MTP lipid transfer activity that were similar to those in mouse liver and allowed intact apoB53 to be secreted as a lipoprotein particle. These data suggest that, although MTP-facilitated lipid transport is not required for apoB translocation, it is required for the secretion of apoB-containing lipoproteins. We propose that, in CHO cells, MTP plays two roles in the assembly and secretion of apoB-containing lipoproteins: 1) it acts as a chaperone that facilitates apoB53 translocation, and 2) its lipid transfer activity allows apoB-containing lipoproteins to be assembled and secreted. Our results suggest that the phenotype of the cell (e.g. expression of cholesterol 7alpha-hydroxylase by the liver) may profoundly influence the metabolic relationships determining how apoB is processed into lipoproteins and/or degraded.

New lamellarin alkaloids from the australian ascidian, didemnum chartaceum

Five novel lamellarin-class alkaloids have been isolated from a Great Barrier Reef ascidian, Didemnum chartaceum. The structures of the 20-sulfated derivatives of lamellarins B, C, and L (1-3); the 8-sulfated derivative of lamellarin G (4), plus a nonsulfated compound, lamellarin Z (5), were identified by interpretation of spectroscopic data. Lamellarin G 8-sulfate (4) is the first example of this class of compounds sulfated at the C-8 position, while lamellarin Z (5) is the first example of a dimethoxylated lamellarin. The known lamellarins A, B, C, E, G, and L (6-11), plus the triacetate derivatives of lamellarins D (12) and N (13), were also isolated. An aberration in the integration of signals in the 1H NMR spectra of the 20-sulfated derivatives of lamellarins B, C, and L (1-3) led to NMR relaxation studies. T1 values were calculated for all protons in the sulfated lamellarins (1-4) and their corresponding nonsulfated derivatives (7, 8, 10, 11). Interestingly, the protons ortho to the sulfate group in compounds (1-4) had T1 values up to five times larger than the corresponding protons in their nonsulfated derivatives (7, 8, 10, 11).

Translocation-arrested apolipoprotein B evades proteasome degradation via a sterol-sensitive block in ubiquitin conjugation

In this study, we explored how sterol metabolism altered by the expression of cholesterol-7alpha-hydroxylase NADPH:oxygen oxidoreductase (7alpha-hydroxylase) affects the ubiquitin-dependent proteasome degradation of translocation-arrested apoB53 in Chinese hamster ovary cells. Stable expression of two different plasmids that encode either rat or human 7alpha-hydroxylase inhibited the ubiquitin conjugation of apoB and its subsequent degradation by the proteasome. Oxysterols (25-hydroxycholesterol and 7-ketocholesterol) reversed the inhibition of apoB degradation caused by 7alpha-hydroxylase. The combined results suggest that the normally rapid proteasome degradation of translocation-arrested apoB can be regulated by a sterol-sensitive polyubiquitin conjugation step in the endoplasmic reticulum. Blocked ubiquitin-dependent proteasome degradation caused translocation-arrested apoB to become sequestered in segregated membrane domains. Our results described for the first time a novel mechanism through which the "quality control" proteasome endoplasmic reticulum degradative pathway of translocation-arrested apoB is linked to sterol metabolism. Sterol-sensitive blocked ubiquitin conjugation appears to selectively inhibit the proteasome degradation of apoB, but not 7alpha-hydroxylase protein, with no impairment of cell vitality or function. Our findings may help to explain why the hepatic production of lipoproteins is increased when familial hypertriglyceridemic patients are treated with drugs that activate 7alpha-hydroxylase (e.g. bile acid-binding resins).

Longithorones J and K, two new cyclofarnesylated quinone derived metabolites from the australian ascidian aplidium longithorax

Chemical investigation of a Great Barrier Reef ascidian, Aplidium longithorax, has resulted in the isolation of two new cyclofarnesylated quinone-derived compounds, longithorones J (1) and K (2). Longithorone J (1) is the first example of a gamma-hydroxy-cyclohexenone in this structure class. Longithorone K (2) is a dihydro analogue of longithorone B.

A further study of FTC yield and nicotine absorption in smokers

The relationship between nicotine yield as determined by the FTC method and nicotine absorption was examined in 72 smokers in a more rigorous repetition of a previous study of 33 smokers. For this study, 113 smokers evenly distributed across four FTC "tar" yield ranges were recruited, only 72 demonstrated reasonable compliance with the study criteria with regard to sample collections and cigarette brand style consistency. Subjects recorded the number of cigarettes smoked daily and collected a 24-h urine sample and a saliva sample on 3 consecutive days. Nicotine absorption was determined by monitoring urinary excretion of nicotine and its metabolites. In addition, saliva samples were monitored for cotinine using radioimmunoassay (RIA). The correlation of the relationship for nicotine absorbed per cigarette was positive and significant (r = 0.31, P = 0.008) but weaker than in the previous study. Only smokers in the highest yield range showed any statistical difference from smokers in the lower ranges. Our results suggest that FTC nicotine yield is weakly related to nicotine absorption and that smoker-controlled factors exert a great influence on the amount of nicotine absorbed by smokers. Compensation is substantial but incomplete for the minority (by market share) of smokers at the low end of the yield scale. It is uncertain how well any alternative set of machine parameters would predict nicotine absorption for the majority of smokers, even if it were more predictive for the small number of smokers at the lower yield part of the range.

Eudistomin V, a new beta-carboline from the Australian ascidian Pseudodistoma aureum

Chemical investigation of the Australian ascidian Pseudodistoma aureum has resulted in the isolation of a new beta-carboline, eudistomin V (1). The known compounds eudistomin H (2) and I (3) were also isolated, and all compounds had their structures determined by spectroscopic means.

Nitric oxide formation in an iron oxide pellet rotary kiln furnace

A one-dimensional numerical model was developed to simulate the effects of heat and mass transfer on the formation of oxides of nitrogen (NOx) in a rotary kiln furnace for iron oxide pellet induration. The modeled kiln has a length-to-diameter ratio of approximately seven. The principal mechanism of heat transfer is radiation from the flame, which was described by the net radiation method. The well known Zeldovich mechanism was used to predict thermal NOx generation. Temperature fluctuations in the vicinity of the flame were estimated with a clipped Gaussian probability density function. The thermal energy and mass balance model equations were solved numerically. The model is capable of predicting temperature profiles and NOx production rates in agreement with observed plant performance. The model was used to explore the effects of process changes on the total NOx formation in the kiln. It was concluded that the gas temperature as well as the partial pressure of oxygen in the process gases controls the rate of NOx formation. Lowering the temperature of the kiln gases by increasing the secondary air flow rates requires simultaneously decreasing the pellet production rate in order to maintain the pellet temperatures needed for blast furnace conditions.

Coordinate regulation of lipogenesis, the assembly and secretion of apolipoprotein B-containing lipoproteins by sterol response element binding protein 1

Stable plasmid-driven expression of the liver-specific gene product cholesterol 7alpha-hydroxylase (7alpha-hydroxylase) was used to alter the cellular content of transcriptionally active sterol response element binding protein 1 (SREBP1). As a result of stable expression of 7alpha-hydroxylase, individual single cell clones expressed varying amounts of mature SREBP1 protein. These single cell clones provided an opportunity to identify SREBP1-regulated genes that may influence the assembly and secretion of apoB-containing lipoproteins. Our results show that in McArdle rat hepatoma cells, which normally do not express 7alpha-hydroxylase, plasmid-driven expression of 7alpha-hydroxylase results in the following: 1) a linear relationship between (i) the cellular content of mature SREBP1 and 7alpha-hydroxylase protein, (ii) the relative expression of 7alpha-hydroxylase mRNA and the mRNA's encoding the enzymes regulating fatty acid, i.e. acetyl-CoA carboxylase and sterol synthesis, i.e. HMG-CoA reductase, (iii) the relative expression of 7alpha-hydroxylase mRNA and microsomal triglyceride transfer protein mRNA, a gene product that is essential for the assembly and secretion of apoB-containing lipoproteins; 2) increased synthesis of all lipoprotein lipids (cholesterol, cholesterol esters, triglycerides, and phospholipids); and 3) increased secretion of apoB100 without any change in apoB mRNA. Cells expressing 7alpha-hydroxylase contained significantly less cholesterol (both free and esterified). The increased cellular content of mature SREBP1 and increased secretion of apoB100 were concomitantly reversed by 25-hydroxycholesterol, suggesting that the content of mature SREBP1, known to be decreased by 25-hydroxycholesterol, mediates the changes in the lipoprotein assembly and secretion pathway that are caused by 7alpha-hydroxylase. These data suggest that several steps in the assembly and secretion of apoB-containing lipoproteins by McArdle hepatoma cells may be coordinately linked through the cellular content of mature SREBP1.

Clinical evaluation of Acuvue contact lenses with UV blocking characteristics

BACKGROUND

In response to increasing scientific evidence which indicates that ultraviolet radiation (UVR) is a potential threat to ocular health, Acuvue contact lenses (Vistakon, Johnson & Johnson Vision Products Inc., Jacksonville, Florida) have been developed which incorporate an ultraviolet (UV) blocker within the lens polymer. Data are presented for the first clinical evaluation of Acuvue lenses with UV blocking characteristics.

METHOD

A double-masked, multicenter, prospective clinical trial involving 94 subjects was conducted. The study followed a randomized, parallel group design and consisted of 3 months of daily wear with two-weekly lens replacement. Two thirds of the subjects (61) wore the test lenses (Acuvue with UV blocker) and the remaining subjects (33) wore conventional Acuvue lenses (without UV blocker).

RESULTS

Biomicroscopic evaluations indicated that the performance of the test and control lenses was clinically similar. No clinically relevant differences between the test and control lenses were noted in the subjective assessments of vision, comfort, or handling. In addition, no differences were shown for surface deposition, lens durability, visual acuity, and subjective symptoms.

CONCLUSION

The study findings indicate that the addition of a UV blocker to Acuvue contact lenses has been achieved without affecting daily wear clinical performance. Because there is increasing evidence to suggest that the ocular tissues may be damaged by UVR, it is prudent for eye care practitioners to prescribe contact lenses that offer the benefits of both regular replacement and UV protection.

Cholesterol 7alpha-hydroxylase influences the expression of hepatic apoA-I in two inbred mouse strains displaying different susceptibilities to atherosclerosis and in hepatoma cells

C57BL/6 mice are susceptible to diet-induced atherosclerosis, whereas BALB/c mice are resistant. The susceptibility of C57BL/6 mice has been linked to decreased plasma HDL cholesterol in response to a diet containing fat, cholesterol, and cholic acid. Feeding C57BL/6 mice a diet consisting of fat and cholesterol, but no cholic acid, increased plasma high density lipoprotein (HDL) cholesterol. The increase in HDL was associated with increases in both plasma apolipoprotein (apo)A-I and hepatic apoA-I mRNA. Supplementation of the cholesterol-rich diet with cholic acid inhibited the stimulatory effect of cholesterol on hepatic apoA-I mRNA expression, resulting in similar hepatic apoA-I mRNA levels compared to chow-fed mice. Atherosclerosis-resistant BALB/c mice were also resistant to diet-induced changes in plasma HDL, apoA-I, and hepatic apoA-I mRNA levels. Previous studies showed that the diets changed both the activity and mRNA encoding the liver specific enzyme 7alpha-hydroxylase (1993.J. Lipid Res. 34: 923-931). In both strains of mice, hepatic expression of apoA-I and 7alpha-hydroxylase mRNA varied in parallel. Whereas susceptible C57BL/6 mice also showed a significant correlation between HDL cholesterol and expression of 7alpha-hydroxylase, no such correlation was observed in BALB/c mice, suggesting that genetic differences in HDL metabolism, not hepatic apoA-I synthesis, are responsible for the strain specific differences in plasma HDL levels. The finding that lecithin: cholesterol acyltransferase (LCAT) activity was significantly decreased in C57BL/6 mice, but not in BALB/ c mice fed the atherogenic diet, further supports this conclusion. Additional studies show that McArdle hepatoma cells stably expressing plasmid-derived rat 7alpha-hydroxylase recapitulated the parallel linear relationship between 7alpha-hydroxylase and apoA-I mRNA expression observed in both strains of mice. These data link hepatic apoA-I mRNA expression to hepatic cholesterol/bile acid metabolism.

Expression of human cholesterol 7alpha-hydroxylase in atherosclerosis-susceptible mice via adenovirus infection

Adenovirus is a vector for the delivery of genes mainly to the liver. Short-term (approximately 3 days) studies using adenovirus transfection have provided valuable insights into how genes can complement normal and pathological phenotypes. When atherosclerosis-susceptible C57BL/6 mice were infected with an adenovirus vector containing the human 7alpha-hydroxylate cDNA (AV17h1) and fed on a chow diet, human 7alpha-hydroxylase mRNA and enzyme activity doubled compared with that in mice infected with an adenovirus vector (AV1Null) alone. In AV17h1-infected mice fed on a high fat cholic acid (HFCA) diet, mRNA expression and activity of both the endogenous and adenovirus (human) 7alpha-hydroxylase were repressed. AV17h1-infected mice fed on a HFCA diet and killed at mid-light had increased 7alpha-hydroxylase activity and mRNA compared with mice killed at mid-dark. Since expression of AV17h1 is driven by a constitutive Rous sarcoma virus promoter, the repression of human 7alpha-hydroxylase by the HFCA diet was unexpected. In spite of this post-transcriptional repression by the HFCA diet, AV17h1-infected mice expressed the human 7alpha-hydroxylase mRNA, causing its enzyme activity to be 3-fold greater than in AV1Null-infected mice. In AV17h1-infected mice, the 7alpha-hydroxylase enzyme activity varied as a linear function of human mRNA abundance. In conclusion, the accumulation of apolipoprotein B-containing lipoproteins in plasma of C57BL/6 mice fed on the HFCA diet was not reduced by longer-term (2 weeks) 7alpha-hydroxylase expression, probably because of its diminished expression caused by the diet and hepatic inflammation from the adenovirus infection. These results may suggest that adenovirus is effective in promoting longer-term (2 weeks) expression of 7alpha-hydroxylase.

Evolution of processes and regulators of lipoprotein synthesis: from birds to mammals

Mammalian lipoproteins are synthesized in the liver and secreted into the blood plasma where they are targeted to specific tissues. Through specific cell surface receptors, hepatic lipoproteins are taken up and their lipid contents are then used for anabolic and energy requirements. Because of the well-established role that plasma lipoproteins play as risk factors for the development of cardiovascular disease, a great amount of attention has been directed toward understanding their metabolism and biosynthesis. The major focus of this report is to review the evolution of gene products that are essential in regulating, synthesizing, assembling and secreting the lipid and protein components of lipoproteins. Using the primordial vitellogenin lipoprotein system as the paradigm, I show how metabolic signals derived from the sterol biosynthetic pathway provide a coordinate regulation of genes necessary to assemble and secrete mammalian apolipoprotein B-containing lipoproteins. In lower species, estrogen induces the expression of genes required for both vitellogenin synthesis and its tissue targeting (the vitellogenin receptor). This coordinate induction provides lipid to the ovaries for egg development. In mammals, a sterol-derived metabolic signal regulates the expression of genes required for lipoprotein synthesis and for the LDL receptor. The signal is not sex linked, providing an adaptive advantage to changes in nutritional status.

National incidence of smoking and misclassification among the U.S. married female population

Because of a lack of representative data on smoking status misclassification among U.S. married females, a two-part study was conducted. Part I was conducted to obtain nationally representative estimates of the percentage of U.S. women who report themselves to be current, former, and never smokers, to determine the concordance of smoking habits among spouse pairs, and to establish field quotas and probability weightings for Part II. Part II was conducted to determine smoker misclassification rates using salivary cotinine as an indication of active smoking. Part I, conducted in January 25-29, 1992, utilized random-digit dialing telephone interviewing throughout the 48 contiguous United States. Part II, conducted from February 19, 1992 to March 7, 1992, was a mall-intercept study in nine geographically disperse U.S. cities and it involved interviewing and saliva collection. Among married U.S. women, 25% reported they were current smokers, 22% reported they were former smokers, and 53% reported they were never smokers. Using a cotinine concentration of either > 35 ng/ml or > 106 ng/ml to indicate regular smoking, 3.61% and 2.55% of regular smokers, respectively, reported themselves to be never smokers. The concordance ratio, an important parameter in correcting for non-differential misclassification bias, was found to be 5.52. In addition, an indication of substantial differential misclassification was found between exposed and unexposed populations. This type of misclassification bias has previously not been accounted for in the adjustment of epidemiology-based risk assessments of tobacco smoke exposure and lung cancer. Taken together, these data suggest that misclassification bias alone is likely to explain any lung cancer risk elevation observed in the U.S. epidemiology of environmental tobacco smoke exposure among nonsmoking women.

Transcriptional induction of cholesterol 7alpha-hydroxylase by dexamethasone in L35 hepatoma cells requires sulfhydryl reducing agents

It is known that hepatic levels of reduced glutathione correlate with the activity of the liver-specific enzyme cholesterol-7alpha-hydroxylase. We examined the possibility that sulfhydryl reducing agents activate transcription of cholesterol 7alpha-hydroxylase. Adding dithiothreitol (DTT, 1 mM) and dexamethasone to L35 hepatoma cells increased the content of 7alpha-hydroxylase mRNA 3-fold above the levels observed with dexamethasone alone. Without dexamethasone, DTT had no affect. The addition of reduced glutathione to L35 cells demonstrated a similar potentiation of expression dependent on dexamethasone. Nuclear run-on assays showed that in the presence of both dexamethasone and DTT, the transcription of the 7alpha-hydroxylase gene was clearly increased. In contrast, by itself, dexamethasone did not cause a detectable increase in the transcription of the 7alpha-hydroxylase gene. Dexamethasone and DTT did not affect the transcription of beta-actin, suggesting a selective induction of the 7alpha-hydroxylase gene. DTT reversed repression of 7alpha-hydroxylase expression by insulin but not the repression by phorbol ester. Our data show for the first time that the sulfhydryl redox potential of the hepatocyte (i.e. level of reduced glutathione) has a marked influence on the transcription and expression of the liver-specific gene 7alpha-hydroxylase.

A long-term outcome study of 170 surgically treated patients with compressive cervical radiculopathy

BACKGROUND

There is a general impression that publications in neuro-surgical journals have comprehensively evaluated the relative merits of various operative techniques with long-term follow-up in patients treated for compressive cervical radiculopathy. However, in some 20,000 neurosurgical papers over the past 50 years, only 74 (0.3%) have addressed this common surgical problem.

METHODS

Long-term outcome was assessed by the standardized Functional Economic Outcome Rating Scale of Prolo. Information was obtained primarily by telephone interviews and office visits. No patients were operated upon without a confirmatory neuroradiologic study. Single level soft discs were removed through a posterior-lateral foraminotomy with hemilaminectomy or laminectomy the root was decompressed by the same technique with hard discs.

RESULTS

One hundred seventy patients were operated on from 1959-91 with a 96% follow-up. The mean follow-up period was 15 years. Patients who had sedentary occupations and housewives, had statistically higher Economic Prolo scores (p < 0.001) than those who did strenuous work. Of 10 patients with a total Prolo score of 5 or less, seven did strenuous work and had Workers' Compensation claims; the remaining had legal claims or were at psychologic risk for operation. In 86% of patients outcome was good; defined as a Prolo score of 8 in 5%, 9 in 38%, and 10 in 43%. Of 10 recurrences (6%), seven occurred within 3 years after operation and were treated by discectomy and anterior cervical fusion. There were two patients with postoperative deltoid motor weakness who recovered within 1 year.

CONCLUSIONS

Although outcome studies must have subjective criteria, the Prolo Scale is more objective and quantitative than currently used methods. The posterior approach to disc lesions causing compressive cervical radiculopathy should be compared to other techniques using the Prolo Outcome Scale.

Human urine mutagenicity study comparing cigarettes which burn or primarily heat tobacco

Cigarette smokers have been reported to void urine which is more mutagenic, as measured in the Ames assay, than urine voided by non-smokers. Condensate from the mainstream smoke of a cigarette which primarily heats tobacco (test cigarette) has shown significantly reduced mutagenicity in a battery of in vitro genotoxicity assays compared with tobacco-burning cigarettes. The objective of this study was to determine whether the reduction in mutagenic activity observed in the in vitro assays would be reflected in the urine of smokers of the test cigarette. Twenty smokers were enrolled in a 4-week crossover study, with each smoker consuming test cigarettes ad libitum for a week and their usual brand of tobacco-burning cigarettes the other 3 weeks. Diet was strictly controlled throughout the study, and broiled and pan-fried meat was not served to minimize ingestion of mutagenic protein pyrolysis products. There was no statistically significant difference (p = 0.06) in consumption of tobacco-heating and tobacco-burning cigarettes. There were no statistically significant differences (p = 0.22) in salivary cotinine concentrations for smokers when smoking either tobacco-burning or tobacco-heating cigarettes. Urinary nicotine (ng/mg creatinine) was not different (p = 0.31) for smokers when smoking either tobacco-burning or tobacco-heating cigarettes. Urinary cotinine (ng/mg creatinine) was 32% lower (p = 0.0004) when smoking tobacco-heating cigarettes as compared with smoking tobacco-burning cigarettes. Twenty-four-hour urine samples were collected twice weekly, concentrated using XAD-2 resin and tested in Ames strains TA98 and YG1024 with metabolic activation. Tobacco-burning cigarette smokers experienced a 79% reduction in urinary mutagenicity as measured in strain YG1024 and a 72% reduction as measured in strain TA98 during the week that they smoked the tobacco-heating cigarette while maintaining a fixed dietary regimen. The results of this study indicate that smokers of tobacco-heating cigarettes void urine which is significantly less mutagenic than urine voided by smokers of tobacco-burning cigarettes.

Assessing the sensory role of nicotine in cigarette smoking

Thirty-two subjects were tested in five double-blind sessions (16 subjects in the morning following overnight smoking abstention, and 16 in the afternoon following ad-lib smoking). In each session, subjects smoked one of five experimental (EX) cigarettes having the following FTC nicotine/"tar' yields in mg: 0.08/8.5, 0.17/9.1, 0.37/9.8, 0.48/9.8, and 0.74/10.4. In a sixth session, subjects smoked a 0.71/8.6 commercial "light' (CL) cigarette that was their usual brand. Before and after smoking, subjects subjectively rated their desire to smoke a cigarette of their usual brand and had blood samples drawn. Following smoking, subjects rated the cigarette on a variety of sensory dimensions; they also rated smoking satisfaction. Analysis of variance indicated that nicotine played an important sensory role for a variety of dimensions related to cigarette taste and sensory impact but not perceived draw. Principal-components analyses indicated that sensory factors were at least as important as nicotine pharmacology (indirectly indexed by the pre-to post-smoking rise in blood nicotine concentration) when considering smoking's overall effects on satisfaction, product acceptance, and reduction in desire to smoke.

Thermodynamic stabilization of nucleotide binding to thymidylate synthase by a potent benzoquinazoline folate analogue inhibitor

The stabilization of dUMP, FdUMP, and dGMP binding to Escherichia coli thymidylate synthase (TS) in the presence and absence of a folate analogue inhibitor of TS, 1843U, was determined by differential scanning calorimetry. When the enzyme is thermally unfolded in the presence of dUMP, two separate temperature transitions are evident, although only one binding site/dimer was detected in equilibrium dialysis experiments. In the absence of dUMP, TS shows a major peak of unfolding at 45 degrees C with a shoulder at 47 degrees C. In the presence of increasing amounts of dUMP progressive changes in the size of each peak occur, each associated with a higher temperature of unfolding. At a ratio of dUMP/TS of 100, a major peak predominates with an unfolding temperature (Td) of 60 degrees C. FdUMP shows a similar profile, while dGMP does not alter the Td of the enzyme since dGMP alone does not bind to TS. Despite the fact that 1843U binds tightly to TS in the absence of nucleotide ligands [Dev, I. K., Dallas, W.S., Ferone, R., Hanlon, H., McKee, D.D., & Yates, B. B. (1994) J.Biol. Chem. 269, 1873-1882], it exhibits only a small effect on the Td profile of TS. However, when 1843U is present, in addition to the nucleotides (dUMP, FdUMP, or dGMP), a Td of 72 degrees C is achieved and the enthalpy of unfolding is increased by one-third. The stabilizing effect of substrate binding to TS by 1843U examined by thermodynamic parameters can be attributed to the considerable extra amount of free energy released on formation of the ternary complex of TS-1843U-nucleotide. The tightness of this complex is due to the stacking energy that results from Van der Waals contacts between the nucleotide purine or pyrimidine ring and the benzoquinazoline ring of 1843U [Weichsel, A., Montfort, W. R., Cieśla, J., & Maley, F. (1995) Proc. Natl. Acad. Sci. U.S.A. 92, 3493-3497], which induces a local conformational change in the protein. This conformational change is associated with a significant positive entropy change, which suggests that water is expelled from the active site region.

Translocation of apolipoprotein B across the endoplasmic reticulum is blocked in abetalipoproteinemia

Abetalipoproteinemia (ABL) is an autosomal recessive disease characterized by the inability of the liver and intestine to secrete apolipoprotein B (apoB). Mutations in the microsomal triglyceride transfer protein (MTP) gene, but not the apoB gene, are responsible for the ABL phenotype. It is not clear how loss of MTP in ABL patients leads to a complete, but specific, block in the secretion of apoB. It is to this question that our work is directed. In cultured cells lacking MTP, translocation of apoB is completely arrested, leading to the hypothesis that apoB requires MTP in order to completely enter the lumen of the endoplasmic reticulum, the site of lipoprotein assembly. We examined this hypothesis by determining the presence in plasma of distinct N-terminal apoB peptides, produced exclusively from translocation arrested apoB, in the plasma of six ABL patients and six normal subjects. The data show that N-terminal apoB peptides are present in the plasma of six ABL patients, whereas intact apoB-100 was barely detectable. Moreover, the plasma of all six ABL patients displayed a 2000-fold increase in the amount of an 85 kDa N-terminal apoB peptide relative to apoB-100. These data provide the first in vivo data supporting the essential role that MTP plays in apoB translocation. In normal humans, varied expression of MTP may be responsible for the post-transcriptional regulation of apoB secretion.

Rat hepatoma L35 cells, a liver-differentiated cell line, display resistance to bile acid repression of cholesterol 7 alpha-hydroxylase

A stable hepatoma cell line (L35 cells) showing an activation of the cholesterol 7 alpha-hydroxylase gene (CYP7) that had been silent in the parental hepatoma cell line (H35 cells) was used to examine the influence of bile acids on its gene expression and activity. L35 cells were found to concentrate taurocholate from the culture medium, without any significant effect on the expression of 7 alpha-hydroxylase. At physiologic levels (up to 100 microM), CYP7 mRNA expression was not repressed by any bile acid. At supra-physiologic levels (1 mM), the more hydrophobic dihydroxy bile acids, taurodeoxycholate and taurochenodeoxycholate, decreased CYP7 mRNA without decreasing the relative abundance of beta-actin mRNA. Similar results were obtained by culturing cells with sodium dodecylsulfate (50 microM). The medium of L35 cells treated with either taurochenodeoxycholate (1 mM), taurodeoxycholate (1 mM), or sodium dodecylsulfate (50 microM) contained significantly greater activities of two cytosolic enzymes, lactate dehydrogenase and phosphoglucose isomerase, indicating a cytotoxic response. Activation of protein kinase C by phorbol esters decreased the expression of 7 alpha-hydroxylase mRNA without evidence of cytotoxicity; therefore, the inability of L35 cells to show bile acid repression cannot be ascribed to a lack of an effect by this secondary messenger system. In addition, insulin decreased and dexamethasone increased 7 alpha-hydroxylase mRNA without increasing the release of the cytoplasmic enzyme markers. The combined data suggest that L35 cells are resistant to repression of CYP7 gene expression by bile acids, but display physiologic expression to hormones and protein kinase C activation.