The regulation of glucose and lipid homeostasis via PLTP as a mediator of BAT-liver communication

While brown adipose tissue (BAT) is well-recognized for its ability to dissipate energy in the form of heat, recent studies suggest multifaced roles of BAT in the regulation of glucose and lipid homeostasis beyond stimulating thermogenesis. One of the functions involves interorgan communication with metabolic organs, such as the liver, through BAT-derived secretory factors, a.k.a., batokine. However, the identity and the roles of such mediators remain insufficiently understood. Here, we employed proteomics and transcriptomics in human thermogenic adipocytes and identified previously unappreciated batokines, including phospholipid transfer protein (PLTP). We found that increased circulating levels of PLTP, via systemic or BAT-specific overexpression, significantly improve glucose tolerance and insulin sensitivity, increased energy expenditure, and decrease the circulating levels of cholesterol, phospholipids, and sphingolipids. Such changes were accompanied by increased bile acids in the circulation, which in turn enhances glucose uptake and thermogenesis in BAT. Our data suggest that PLTP is a batokine that contributes to the regulation of systemic glucose and lipid homeostasis as a mediator of BAT-liver interorgan communication.

Enzyme promiscuity drives branched-chain fatty acid synthesis in adipose tissues

Fatty acid synthase (FASN) predominantly generates straight-chain fatty acids using acetyl-CoA as the initiating substrate. However, monomethyl branched-chain fatty acids (mmBCFAs) are also present in mammals but are thought to be primarily diet derived. Here we demonstrate that mmBCFAs are de novo synthesized via mitochondrial BCAA catabolism, exported to the cytosol by adipose-specific expression of carnitine acetyltransferase (CrAT), and elongated by FASN. Brown fat exhibits the highest BCAA catabolic and mmBCFA synthesis fluxes, whereas these lipids are largely absent from liver and brain. mmBCFA synthesis is also sustained in the absence of microbiota. We identify hypoxia as a potent suppressor of BCAA catabolism that decreases mmBCFA synthesis in obese adipose tissue, such that mmBCFAs are significantly decreased in obese animals. These results identify adipose tissue mmBCFA synthesis as a novel link between BCAA metabolism and lipogenesis, highlighting roles for CrAT and FASN promiscuity influencing acyl-chain diversity in the lipidome.

The UPR Activator ATF6 Responds to Proteotoxic and Lipotoxic Stress by Distinct Mechanisms

The unfolded protein response (UPR) is induced by proteotoxic stress of the endoplasmic reticulum (ER). Here we report that ATF6, a major mammalian UPR sensor, is also activated by specific sphingolipids, dihydrosphingosine (DHS) and dihydroceramide (DHC). Single mutations in a previously undefined transmembrane domain motif that we identify in ATF6 incapacitate DHS/DHC activation while still allowing proteotoxic stress activation via the luminal domain. ATF6 thus possesses two activation mechanisms: DHS/DHC activation and proteotoxic stress activation. Reporters constructed to monitor each mechanism show that phenobarbital-induced ER membrane expansion depends on transmembrane domain-induced ATF6. DHS/DHC addition preferentially induces transcription of ATF6 target lipid biosynthetic and metabolic genes over target ER chaperone genes. Importantly, ATF6 containing a luminal achromatopsia eye disease mutation, unresponsive to proteotoxic stress, can be activated by fenretinide, a drug that upregulates DHC, suggesting a potential therapy for this and other ATF6-related diseases including heart disease and stroke.

Mapping Novel Metabolic Nodes Targeted by Anti-Cancer Drugs that Impair Triple-Negative Breast Cancer Pathogenicity

Triple-negative breast cancers (TNBCs) are estrogen receptor, progesterone receptor, and HER2 receptor-negative subtypes of breast cancers that show the worst prognoses and lack targeted therapies. Here, we have coupled the screening of ∼400 anticancer agents that are under development or in the clinic with chemoproteomic and metabolomic profiling to identify novel metabolic mechanisms for agents that impair TNBC pathogenicity. We identify 20 anticancer compounds that significantly impaired cell survival across multiple types of TNBC cells. Among these 20 leads, the phytoestrogenic natural product licochalcone A was of interest, since TNBCs are unresponsive to estrogenic therapies, indicating that licochalcone A was likely acting through another target. Using chemoproteomic profiling approaches, we reveal that licochalcone A impairs TNBC pathogenicity, not through modulating estrogen receptor activity but rather through inhibiting prostaglandin reductase 1, a metabolic enzyme involved in leukotriene B4 inactivation. We also more broadly performed metabolomic profiling to map additional metabolic mechanisms of compounds that impair TNBC pathogenicity. Overlaying lipidomic profiling with drug responses, we find that deubiquitinase inhibitors cause dramatic elevations in acyl carnitine levels, which impair mitochondrial respiration and contribute to TNBC pathogenic impairments. We thus put forth two unique metabolic nodes that are targeted by drugs or drug candidates that impair TNBC pathogenicity. Our results also showcase the utility of coupling drug screens with chemoproteomic and metabolomic profiling to uncover unique metabolic drivers of TNBC pathogenicity.

Protein Sialylation Regulates a Gene Expression Signature that Promotes Breast Cancer Cell Pathogenicity

Many mechanisms have been proposed for how heightened aerobic glycolytic metabolism fuels cancer pathogenicity, but there are still many unexplored pathways. Here, we have performed metabolomic profiling to map glucose incorporation into metabolic pathways upon transformation of mammary epithelial cells by 11 commonly mutated human oncogenes. We show that transformation of mammary epithelial cells by oncogenic stimuli commonly shunts glucose-derived carbons into synthesis of sialic acid, a hexosamine pathway metabolite that is converted to CMP-sialic acid by cytidine monophosphate N-acetylneuraminic acid synthase (CMAS) as a precursor to glycoprotein and glycolipid sialylation. We show that CMAS knockdown leads to elevations in intracellular sialic acid levels, a depletion of cellular sialylation, and alterations in the expression of many cancer-relevant genes to impair breast cancer pathogenicity. Our study reveals the heretofore unrecognized role of sialic acid metabolism and protein sialylation in regulating the expression of genes that maintain breast cancer pathogenicity.

Reduced in vivo hepatic proteome replacement rates but not cell proliferation rates predict maximum lifespan extension in mice

Combating the social and economic consequences of a growing elderly population will require the identification of interventions that slow the development of age-related diseases. Preserved cellular homeostasis and delayed aging have been previously linked to reduced cell proliferation and protein synthesis rates. To determine whether changes in these processes may contribute to or predict delayed aging in mammals, we measured cell proliferation rates and the synthesis and replacement rates (RRs) of over a hundred hepatic proteins in vivo in three different mouse models of extended maximum lifespan (maxLS): Snell Dwarf, calorie-restricted (CR), and rapamycin (Rapa)-treated mice. Cell proliferation rates were not consistently reduced across the models. In contrast, reduced hepatic protein RRs (longer half-lives) were observed in all three models compared to controls. Intriguingly, the degree of mean hepatic protein RR reduction was significantly correlated with the degree of maxLS extension across the models and across different Rapa doses. Absolute rates of hepatic protein synthesis were reduced in Snell Dwarf and CR, but not Rapa-treated mice. Hepatic chaperone levels were unchanged or reduced and glutathione S-transferase synthesis was preserved or increased in all three models, suggesting a reduced demand for protein renewal, possibly due to reduced levels of unfolded or damaged proteins. These data demonstrate that maxLS extension in mammals is associated with improved hepatic proteome homeostasis, as reflected by a reduced demand for protein renewal, and that reduced hepatic protein RRs hold promise as an early biomarker and potential target for interventions that delay aging in mammals.

Ether lipid generating enzyme AGPS alters the balance of structural and signaling lipids to fuel cancer pathogenicity

Aberrant lipid metabolism is an established hallmark of cancer cells. In particular, ether lipid levels have been shown to be elevated in tumors, but their specific function in cancer remains elusive. We show here that the metabolic enzyme alkylglyceronephosphate synthase (AGPS), a critical step in the synthesis of ether lipids, is up-regulated across multiple types of aggressive human cancer cells and primary tumors. We demonstrate that ablation of AGPS in cancer cells results in reduced cell survival, cancer aggressiveness, and tumor growth through altering the balance of ether lipid, fatty acid, eicosanoid, and fatty acid-derived glycerophospholipid metabolism, resulting in an overall reduction in the levels of several oncogenic signaling lipids. Taken together, our results reveal that AGPS, in addition to maintaining ether lipids, also controls cellular utilization of fatty acids, favoring the generation of signaling lipids necessary for promoting the aggressive features of cancer.

Cancer cells incorporate and remodel exogenous palmitate into structural and oncogenic signaling lipids

De novo lipogenesis is considered the primary source of fatty acids for lipid synthesis in cancer cells, even in the presence of exogenous fatty acids. Here, we have used an isotopic fatty acid labeling strategy coupled with metabolomic profiling platforms to comprehensively map palmitic acid incorporation into complex lipids in cancer cells. We show that cancer cells and tumors robustly incorporate and remodel exogenous palmitate into structural and oncogenic glycerophospholipids, sphingolipids, and ether lipids. We also find that fatty acid incorporation into oxidative pathways is reduced in aggressive human cancer cells, and instead shunted into pathways for generating structural and signaling lipids. Our results demonstrate that cancer cells do not solely rely on de novo lipogenesis, but also utilize exogenous fatty acids for generating lipids required for proliferation and protumorigenic lipid signaling. This article is part of a special issue entitled Lipid Metabolism in Cancer.

Mechanisms linking obesity and cancer

The incidence of obesity in US adults has been steadily increasing over the past few decades. Many comorbidities associated with obesity have been well-established such as type 2 diabetes and cardiovascular diseases. However, more recently an epidemiological relationship between obesity and the prevalence of a variety of cancers has also been uncovered. The shift of the paradigm surrounding white adipose tissue function from purely an energy storage tissue, to one that has both endocrine and metabolic relevance, has led to several mechanisms implicated in how obesity drives cancer prevalence and cancer deaths. Currently, there are four categories into which these mechanisms fall - increased lipids and lipid signaling, inflammatory responses, insulin resistance, and adipokines. In this review, we examine each of these categories and the mechanisms through which they drive cancer pathogenesis. Understanding the relationship(s) between obesity and cancer and especially the nodal points of control in these cascades will be essential in developing effective therapeutics or interventions for combating this deadly combination. This article is part of a Special Issue entitled Lipid Metabolism in Cancer.

The effect of long term calorie restriction on in vivo hepatic proteostatis: a novel combination of dynamic and quantitative proteomics

Calorie restriction (CR) promotes longevity. A prevalent mechanistic hypothesis explaining this effect suggests that protein degradation, including mitochondrial autophagy, is increased with CR, removing damaged proteins and improving cellular fitness. At steady state, increased catabolism must be balanced by increasing mitochondrial biogenesis and protein synthesis, resulting in faster protein replacement rates. To test this hypothesis, we measured replacement kinetics and relative concentrations of hundreds of proteins in vivo in long-term CR and ad libitum-fed mice using metabolic (2)H(2)O-labeling combined with the Stable Isotope Labeling in Mammals protocol and LC-MS/MS analysis of mass isotopomer abundances in tryptic peptides. CR reduced absolute synthesis and breakdown rates of almost all measured hepatic proteins and prolonged the half-lives of most (≈ 80%), particularly mitochondrial proteins (but not ribosomal subunits). Proteins with related functions exhibited coordinated changes in relative concentration and replacement rates. In silico expression pathway interrogation allowed the testing of potential regulators of altered network dynamics (e.g. peroxisome proliferator-activated receptor gamma coactivator 1-alpha). In summary, our combination of dynamic and quantitative proteomics suggests that long-term CR reduces mitochondrial biogenesis and mitophagy. Our findings contradict the theory that CR increases mitochondrial protein turnover and provide compelling evidence that cellular fitness is accompanied by reduced global protein synthetic burden.

Carbohydrate intake and cardiometabolic risk factors in high BMI African American children

The aim of this study was to evaluate the relationship between intakes of subgroups of energy-providing carbohydrate, and markers of cardiometabolic risk factors in high BMI African American (AA) children.

A cross sectional analysis was performed on data from a sample of 9-11 year old children (n = 95) with BMI greater than the 85^th percentile. Fasting hematological and biochemical values for selected markers of cardiometabolic risk factors were related to intakes of carbohydrates and sugars.

After adjusting for gender, pubertal stage and waist circumference, multivariate regression analysis showed that higher intakes of carbohydrate (with fat and protein held constant) were associated with higher plasma concentrations of triglycerides (TG), VLDL-C, IDL-C, and worse insulin resistance (homeostasis model assessment of insulin resistance, HOMA-IR). After dividing carbohydrate into non-sugar versus sugar fractions, sugars were significantly related to higher TG, VLDL-C, IDL-C, lower adipocyte fatty acid insulin sensitivity (ISI-FFA), and was closely associated with increased HOMA-IR. Similar trends were observed for sugars classified as added sugars, and for sugars included in beverages. Further dividing sugar according to the food group from which it was consumed showed that consuming more sugar from the candy/soda food group was highly significantly associated with increased TG, VLDL-C, IDL-C and closely associated with increased HOMA-IR. Sugars consumed in all fruit-containing foods were significantly associated with lower ISI-FFA. Sugars consumed as fruit beverages was significantly associated with VLDL-C, IDL-C and ISI-FFA whereas sugars consumed as fresh, dried and preserved fruits did not show significant associations with these markers.

Sugars consumed from in all dairy foods were significantly associated with higher TG, VLDL-C and IDL-C, and with significantly lower HDL-C and ISI-FFA. These effects were associated with sugars consumed in sweetened dairy products, but not with sugars consumed in unsweetened dairy products. This analysis suggests that increases in carbohydrate energy, especially in the form of sugar, may be detrimental to cardiometabolic health in high BMI children.

Macronutrient intakes and cardio metabolic risk factors in high BMI African American children

BACKGROUND

The aim of this study was to evaluate the relationship between intakes of energy-providing macronutrients, and markers of cardio metabolic risk factors in high BMI African American (AA) children.

METHODS

A cross sectional analysis of a sample of 9-11 year old children (n = 80) with BMI greater then the 85th percentile. Fasting hematological and biochemical measurements, and blood pressure were measured as selected markers of cardio metabolic risk factors and their relationships to dietary intakes determined.

RESULTS

After adjusting for gender, pubertal stage and waist circumference (WC), multivariate regression analysis showed that higher total energy intakes (when unadjusted for source of energy) were associated with higher plasma concentrations of intermediate density lipoprotein cholesterol (IDL-C) and very low density lipoprotein cholesterol (VLDL-C). Higher intakes of carbohydrate energy (fat and protein held constant) were associated with higher IDL-C, VLDL-C, triglycerides (TG) and homeostasis model assessment of insulin resistance (HOMA-IR). Higher intakes of fat (carbohydrate and protein held constant), however, were associated with lower IDL-C; and higher protein intakes (fat and carbohydrate held constant) were associated with lower HOMA-IR.

CONCLUSION

The specific macronutrients that contribute energy are significantly associated with a wide range of cardio metabolic risk factors in high BMI AA children. Increases in carbohydrate energy were associated with undesirable effects including increases in several classes of plasma lipids and HOMA-IR. Increases in protein energy were associated with the desirable effect of reduced HOMA-IR, and fat energy intakes were associated with the desirable effect of reduced IDL-C. This analysis suggests that the effect of increased energy on risk of developing cardio metabolic risk factors is influenced by the source of that energy.

Sensory experience modifies the short-term dynamics of neocortical synapses

Many representations of sensory stimuli in the neocortex are arranged as topographic maps. These cortical maps are not fixed, but show experience-dependent plasticity. For instance, sensory deprivation causes the cortical area representing the deprived sensory input to shrink, and neighbouring spared representations to enlarge, in somatosensory, auditory or visual cortex. In adolescent and adult animals, changes in cortical maps are most noticeable in the supragranular layers at the junction of deprived and spared cortex. However, the cellular mechanisms of this experience-dependent plasticity are unclear. Long-term potentiation and depression have been implicated, but have not been proven to be necessary or sufficient for cortical map reorganization. Short-term synaptic dynamics have not been considered. We developed a brain slice preparation involving rat whisker barrel cortex in vitro. Here we report that sensory deprivation alters short-term synaptic dynamics in both vertical and horizontal excitatory pathways within the supragranular cortex. Moreover, modifications of horizontal pathways amplify changes in the vertical inputs. Our findings help to explain the functional cortical reorganization that follows persistent changes of sensory experience.

In vivo effects of putative crowding factors on development of Hymenolepis diminuta

During in vitro incubation, Hymenolepsis diminuta secretes substances into the medium that inhibit DNA synthesis in the germinative region of freshly isolated, uncrowded worms. Of the many substances that are released by H. diminuta into the medium, earlier studies indicate that only succinate, acetate, glucosaminic acid, and cGMP are responsible for the inhibition. In the present report, effects of these putative crowding factors on worm development in vivo were examined. At 7 days postinfection the proximal end of the host's intestine was catheterized and perfused with test solution. The test solution contained 28 nM cGMP, 250 microM glucosaminic acid, 120 mM succinate, and 40 mM acetate. The solution was perfused by a peristaltic pump at a rate of 50 ml/day. At 2 wk postinfection, worms were recovered for subsequent analysis. Worms developing in the presence of crowding factors were 53% less in wet weight than control worms. Carbohydrate concentrations in worms from experimental groups were not different from those in control groups; therefore, the inhibition in growth was probably not due to carbohydrate deprivation. Worms from experimental groups had fewer immature, mature, and gravid proglottids than did worms from control groups. The results are consistent with the hypothesis that the tested substances, which inhibit DNA synthesis in H. diminuta in vitro, are a part of the cause of the crowding effect in vivo.

Effect of host feeding and available glucose on glycogen synthase and phosphorylase activities in Hymenolepis diminuta and Vampirolepis microstoma

The influences of host feeding and the availability of glucose in vitro on the activities of glycogen synthase and glycogen phosphorylase in Hymenolepis diminuta and in Vampirolepis microstoma were studied. The worms were recovered from hosts that had been fed ad libitum, starved for 24 hr, or starved 24 hr and then refed for 1 hr immediately prior to worm recovery. The ratios of active to inactive glycogen synthase and phosphorylase were correlated with the host feeding regimen prior to recovery. Glycogen synthase in H. diminuta was predominately in the inactive D form in worms from both fed and fasted hosts. One hour after refeeding, up to 80% of the synthase was in the active I form. Phosphorylase in H. diminuta was predominantly in the active a form in worms from fed and fasted hosts, but activity of this enzyme was suppressed in worms from refed hosts. When H. diminuta from fasted hosts was incubated in a balanced salt solution containing 40 mM glucose, glycogen synthase I increased, and phosphorylase a decreased. Glycogen synthase in V. microstoma was predominantly in the inactive D form in worms from both the fed and fasted hosts, but the proportion in the active I form increased to over half the total synthase by 1 hr of host refeeding. The proportion of glycogen phosphorylase a was high in worms from fed hosts and decreased, but not dramatically, in worms from fasted hosts. The results suggested that the worms had access to another source of glucose, probably from the host bile, and we measured a low but significant concentration of carbohydrate in the gall bladder bile of mice.(ABSTRACT TRUNCATED AT 250 WORDS)

Developmental physiology of cestodes: cyclic nucleotides and the identity of putative crowding factors in Hymenolepis diminuta

Worm-conditioned saline (WCS) was prepared by incubating Hymenolepis diminuta from crowded infections for 12 hr in a balanced salt solution. The effect of the WCS on the incorporation of [3H] thymidine into DNA in the anterior regions of fresh H. diminuta was compared to effects produced by the cyclic nucleotides in the WCS. Cyclic AMP and cGMP were found in the WCS, and cGMP but not cAMP (at the concentration in WCS) caused some inhibition of DNA synthesis. For further study of the effects of cyclic nucleotides, worms were incubated with theophylline, caffeine, 3-isobutyl-1-methyl xanthine, 2-deoxy cGMP, and L-ascorbic acid, all of which produced some inhibition of [3H] thymidine incorporation. Treatment of WCS with 3',5' cyclic nucleotide phosphodiesterase abolished part of its inhibitory activity, i.e., that part presumed to be due to cGMP. When worms were incubated in the presence of succinate, acetate, D-glucosaminic acid, and cGMP simultaneously and in the concentrations each was found in the WCS, DNA synthesis was inhibited to a degree equal to that found in the WCS. Thus these substances apparently represent the putative crowding factors in the WCS. WCS prepared with worms from different population densities contained the same levels of cAMP but varied in content of cGMP, which decreased as the worm density increased. WCS prepared with patent worms contained high levels of cAMP, but the same amounts of cGMP as WCS prepared with 10-day-old worms. At least some inhibitors of cyclic nucleotide phosphodiesterase inhibited the secretion of cGMP by the worms. Levels of cGMP in the host intestine varied with the presence or absence of worms, number of worms, and area of the intestine.

Developmental physiology of cestodes: characterization of putative crowding factors in Hymenolepis diminuta

It was shown previously that worm-conditioned saline (WCS) prepared from crowded 10-day-old H. diminuta inhibited the incorporation of 3H-thymidine into DNA in the anterior regions of uncrowded worms and that the inhibition was partially accounted for by succinate and acetate excreted by the worms. The present study describes further characterization of the active components of WCS. An ultrafiltrate was fully as potent as untreated WCS, indicating that all detectable inhibitory components were less than about 500 daltons in molecular mass. Inhibitory factors in WCS were stable to heat (80 C for 30 min), cold (4 C for 48 hr), drying and reconstitution, alkaline pH (11 to 12 for 3 hr), and ethanolic extraction. Active compounds were probably not lipoidal in nature. Although the acidic ethanol extract of WCS was inhibitory, no activity was observed in fractions of WCS that contained basic, acidic and neutral amino acids. Amino compounds in the WCS were further investigated. Twenty-four amino acids were identified, 3 of which (phosphoserine, 1-methylhistidine, and 3-methylhistidine) have not been reported previously for H. diminuta. On a molar basis, alanine accounted for 40-50% of the amino acids released. The amino sugar, D-glucosaminic acid, was found in the WCS and also has not been heretofore reported from H. diminuta or any other cestode. In concentrations comparable to those in the WCS, D-glucosaminic acid inhibited incorporation of 3H-thymidine into the DNA of the tapeworms by 25-35%, suggesting that D-glucosaminic acid may be one of the crowding factors.

Amino acid metabolism in the rat tapeworm, Hymenolepis diminuta

1. The amino acid metabolism of the rat tapeworm, Hymenolepis diminuta was investigated. 2. In addition to the characteristic end products of helminth metabolism, H. diminuta also forms substantial amounts of 14C-alanine during incubations in 14C-glucose. 3. Of 10 amino acids tested, only 14C-labelled asparate and, to a lesser extent alanine, generated substantial amounts of 14CO2 when incubated with H. diminuta. 4. 14C-aspartate was incorporated into both succinate and acetate, major products of the worms mitochondrial metabolism, but the rates were low when compared to the metabolism of exogenous glycogen. 5. These results suggest that amino acid metabolism in H. diminuta is very limited.

Developmental physiology of cestodes. XVII. Some biological properties of putative "crowding factors" in Hymenolepis diminuta

A "worm conditioned saline" (WCS) was prepared by incubation of 10-day-old Hymenolepis diminuta (Cestoda: Cyclophyllidea) from infections varying in population density (10, 50, 100 worms per host). Upon subsequent testing on 10-day-old worms from uncrowded (10 worms) infections, WCS prepared with worms from more crowded populations inhibited 3H-thymidine incorporation into DNA to a greater degree than did WCS prepared with worms from less crowded populations. WCS prepared with adult worms (20-30 days old) from crowded (50-worm) infections also inhibited DNA synthesis in 10-day-old cestodes from 10-worm infections. WCS from the anterior ends of adult worms was more inhibitory than WCS prepared with gravid proglottids. The time course of the inhibition was consistent with a G1 block in the cell cycle of the stem cells of the germinative area. The experiments lend support to the hypothesis that these cestodes secrete "crowding factors" that inhibit the growth of other H. diminuta in the same rat.

Glycogen synthase in the rat tapeworm, Hymenolepis diminuta--I. Enzyme activity during development and with crowding

1. Activity of glycogen synthase (E.C. 2.4.1.11) in Hymenolepis diminuta (Cestoda: Cyclophyllidea) was investigated as a function of development and with crowding. 2. Synthase activity was low in the anterior and posterior ends of the worms and highest in the pregravid proglottids in the mid-portion of the strobila. 3. The enzyme activity increased during development of the cestode at least up to 15 days postinfection, but the increase in activity apparently was not due to conversion of the inactive to the active form. 4. Mature oncospheres also contained glycogen synthase, but the activity was lower than in strobilar tissues. 5. Synthase I activities and the proportion of total activity in the I form were generally higher in worms from high density (100 worm) infections than in those from low density (10 worm) infections.

Galactose utilization by the rat tapeworm, Hymenolepis diminuta

1. Hymenolepis diminuta incorporated label from 14C-galactose into glycogen, but the sugar would not support net glycogen synthesis. Glucose stimulated the incorporation of label from 14C-galactose into glycogen, while glycerol did not. 2. During incubations in galactose, large internal pools of galactose and galactose 1-P accumulated, while the concentration of glucose 6-phosphate remained unchanged. 3. In vitro culture experiments indicated that galactose would not support worm growth. Therefore, while galactose can be metabolized to a limited extent, it cannot substitute for glucose as a nutrient source.

Glycogen synthase in the rat tapeworm, Hymenolepis diminuta--II. Control of enzyme activity by glucose and glycogen

1. The proportion of activity in the physiologically active I form of glycogen synthase in Hymenolepis diminuta (Cestoda) decreased in the worm when the rat host was fasted and was greatly increased in the cestode 1 hr after a 24 hr fasted rat was refed. 2. The increase in glycogen synthase I activity was due to glucose present in the host gut after feeding, not to other physiological changes in the rat intestine due to meal consumption. 3. Incubation of intact H. diminuta in vitro with glucose also resulted in the conversion of glycogen synthase D to I. 4. Glucose does not appear to affect the glycogen synthase complex directly, because neither the total synthase converted to I nor the rate of conversion was affected by glucose in a partially purified homogenate. 5. High concentrations of glycogen inhibited the synthase D to I conversion and high mol. wt glycogen was a more effective inhibitor than low mol. wt glycogen.

Enzymes of galactose utilization in the rat tapeworm, Hymenolepis diminuta

1. Crude enzyme preparations from Hymenolepis diminuta contained galactokinase, galactose 1-phosphate uridyl transferase and UDPgalactose 4-epimerase activity, although their specific activities were low. 2. Galactose 1-phosphate non-competitively inhibited galactose phosphorylation. This inhibition, together with the low specific activities of the enzymes in the pathway of galactose utilization, probably accounts for the inadequacy of galactose as a main nutritive carbohydrate for development of the worm.

Adsorption of bile salts by the cestodes, Hymenolepis diminuta and H. microstoma

The accumulation of purified sodium taurocholate (NaTC) and sodium glycocholate (NaGC) by Hymenolepis diminuta and Hymenolepis microstoma (Cestoda: Cyclophyllidea) was determined using radioactive bile salts. H. diminuta reached equilibrium levels of approximately 120 nmoles NaTC/g dry wt and 300 nmoles NaGC/g dry wt. Presentation of the bile salts in mixed micelles with 0.35 mM oleic acid did not alter these values. With H. microstoma, the maxima were 195 nmoles NaTC/g dry wt and 614 nmoles NaCG/g dry wt. These values were similarly unaffected by the addition of 0.35 mM oleic acid to the micelles. Equilibrium values of this magnitude, in media containing as much as 25 or 30 mM bile salt, and the maintenance of this level during incubations of 15 to 60 min eliminated the possibility that the accumulation was by diffusion or by any form of mediated transport into the worm. The accumulation on NaTC by H. diminuta was [Na+] independent, and insensitive to ouabain, DNP, and high [K+]. These observations, the maintenance of different levels of NaTC and NaGC, and the failure of the 2 bile salts to compete indicated that there was no active excretion mechanism operating in a fashion similar to the active transport of bile salts in the vertebrate small intestine. It was concluded that the accumulation of NaTC by H. diminuta was actually adsorption to the tegument. Comparable, although more limited, experiments extended this conclusion to the accumulation of NaGC by H. diminuta and of NaTC and NaGC by H. microstoma. It is suggested that bile salt monomers, rather than intact micelles, adsorb to specific loci on the tegument.

Effect of bile salts on the absorption of glucose and oleic acid by the cestodes, Hymenolepis diminuta and H. microstoma

The uptake of 2 mM 14C-glucose by H. diminuta during 1-min incubations was inhibited by addition of 10 mM sodium taurocholate (NaTC) to the incubation media. Preincubation in 10 mM NaTC for 30 min did not increase the inhibition, suggesting that the inhibition was competitive. This was confirmed with a standard Lineweaver-Burk experiment. Addition of 0.35 mM oleic acid to the NaTC micelles did not alter the level of inhibition. Sodium glycocholate (NaGC) did not inhibit the uptake of glucose by H. diminuta. The uptake of glucose by H. microstoma was also inhibited by NaTC, and was not affected by NaGC. H. diminuta absorbed 3.62 mumoles of oleic acid/g dry wt during 15-min incubations in mixed micelles of 10 mM NaTC and 0.35 mM oleic acid. The total uptake was determined as the sum of the ethanol extractable and nonextractable 3H-oleic acid. In 15 mM NaTC, the uptake of oleic acid was reduced by 50%; at 30 mM NaTC the uptake of oleic acid decreased by half again. Substituting NaGC for NaTC, the greatest uptake of oleic acid, 2.63 mumoles/g dry wt, was from mixed micelles of 15 mM NaGC and 0.35 mM oleic acid. Lesser amounts of oleic acid were absorbed from mixed micelles at 5 or 30 mM NaGC. H. microstoma exhibited a similar pattern of oleic acid uptake from mixed micelles with NaTC and NaGC. At all bile salt concentrations tested, H. microstoma absorbed more oleic acid than H. diminuta and incorporated more oleic acid into the nonextractable pool. The possible roles of bile salts in the absorption of oleic acid as indicated by the results herein are discussed.

Developmental physiology of cestodes. XIV. Roughage and carbohydrate content of host diet for optimal growth and development of Hymenolepis diminuta

Diets of rats infected with Hymenolepis diminuta (CESTODA: Cyclophyllidea) were altered with respect to carbohydrate content and to roughage, and the effects on worm growth and development were studied. Compared to worms from rats fed a 56% glucose diet, those on a 56% starch diet were heavier at 10 and 15 days and had more immature proglottids at 5 days, mature prglottids at 10 days, and mature and gravid proglottids at 15 days postinfection. In addition, worms from rats fed the starch diet contained a higher carbohydrate concentration and a lower lipid concentration from those fed the glucose diet. Worms from rats fed diets with combinations of carbohydrates such as 51% starch-5% sucrose and 51% starch-5% lactose were not different from those fed the 56% starch diet. If rats were fed a pellet diet (Purina Laboratory Chow), the worms grew substantially larger than those from rats fed the 56% starch or combination diets. The differences could be overcome if a 6% roughage component were included in the 56% starch diet. Therefore, the starch-roughage diet here presented is recommended as the optimal defined diet for studies of the development of H. diminuta in the definitive host.