Effects of starvation on the urinary contents of primary thromboxane and prostacyclin metabolites and a possible selenium-dependent role of prostacyclin in the renal handling of ketone bodies

Differences in Small Molecule Neurotransmitter Profiles From the Crown-of-Thorns Seastar Radial Nerve Revealed Between Sexes and Following Food-Deprivation

Neurotransmitters serve as chemical mediators of cell communication, and are known to have important roles in regulating numerous physiological and metabolic events in eumetazoans. The Crown-of-Thorns Seastar (COTS) is an asteroid echinoderm that has been the focus of numerous ecological studies due to its negative impact on coral reefs when in large numbers. Research devoted to its neural signaling, from basic anatomy to the key small neurotransmitters, would expand our current understanding of neural-driven biological processes, such as growth and reproduction, and offers a new approach to exploring the propensity for COTS population explosions and subsequent collapse. In this study we investigated the metabolomic profiles of small molecule neurotransmitters in the COTS radial nerve cord. Multivariate analysis shows differential abundance of small molecule neurotransmitters in male and female COTS, and in food-deprived individuals with significant differences between sexes in gamma-aminobutyric acid (GABA), histamine and serotonin, and significant differences in histamine and serotonin between satiation states. Annotation established that the majority of biosynthesis enzyme genes are present in the COTS genome. The spatial distribution of GABA, histamine and serotonin in the radial nerve cord was subsequently confirmed by immunolocalization; serotonin is most prominent within the ectoneural regions, including unique neural bulbs, while GABA and histamine localize primarily within neuropil fibers. Glutamic acid, which was also found in high relative abundance and is a precursor of GABA, is known as a spawning inhibitor in seastars, and as such was tested for inhibition of ovulation ex-vivo which resulted in complete inhibition of oocyte maturation and ovulation induced by 1-Methyladenine. These findings not only advance our knowledge of echinoderm neural signaling processes but also identify potential targets for developing novel approaches for COTS biocontrol.

Correlation between Keton Body Level in Selenium-Deficient Rats and Oxidative Damages

The age dependence of ketone body levels (KBLs) and oxidative damages in selenium-deficient (SeD) and normal rats were compared. The feeding SeD diets gave ketogenesis and higher KBLs especially in younger rats. However, KBLs in SeD rats seemed to decrease with their age. Feeding 0.1 mg/kg Se in water with SeD diet did not affect the KBLs in young (8 week old) rats, whereas the addition of Se reduced the KBLs in older (20 week old) rats. Blood KBLs showed some correlations with tissue damage. TBARSs showed no correlations with the tissue damages and KBLs when the values were compared between the same age, while better correlation was obtained between urinary KBLs of 6-20 week old normal rats and the liver TBARSs of 4-16 week old normal rats. The oxidative injury might induce liver damage with some delay. SeD rat kidney TBARS levels normalized by protein had some correlations with BUN and blood KBL. Kidney may be sensitive to the oxidative stresses and/or injuries. Tissue damages of SeD rats decreased with age. In contrast, oxidative injuries might be gradually accumulated in normal rat tissue. Oxidative stress can be visible by gradual accumulation of small damages during the aging, while large stress in young rats can be buffered and masked. The aging based accumulation of oxidative injuries might also be correlated with KBLs, while it might not give notable tissue damages.

Effects of selenium deficiency on the formation and detoxification of endogenous electrophiles in rats

Selenium deficiency could be expected to lead to enhanced lipid peroxidation through loss of selenium-dependent glutathione peroxidase activity. Such a relation has, however, been difficult to verify. In the present study, the influence of selenium deficiency in rats on in vivo doses of some endogenously occurring low-molecular mass aldehydes and epoxides was determined. In vivo doses were measured by mass-spectrometric analysis according the N-alkyl Edman method of reaction products (adducts) with N-terminal valines in hemoglobin. Despite variations between experiments, the adduct levels of acetaldehyde and malonaldehyde were shown to be significantly higher in rats fed a selenium-deficient diet than in controls fed a selenium-adequate diet. No significant effect was found for the other aldehydes measured. In contrast, the in vivo doses of endogenous ethylene oxide and propylene oxide were lowered in selenium-deficient rats, indicating a 1.7-times faster detoxification rate. This was verified by the lower adduct levels in selenium-deficient rats following intraperitoneal administration of these epoxides at moderate doses. In conclusion, the results seem to reflect the complex changes of induced and reduced enzyme activities in response to selenium deficiency. Measurement of reactive compounds through their adducts to hemoglobin has shown its ability to elucidate the effects of selenium deficiency per se.

Developmental expression of extracellular glutathione peroxidase suggests antioxidant roles in deciduum, visceral yolk sac, and skin

Extracellular glutathione peroxidase (EGPx) is a secreted selenium-dependent enzyme that reduces hydroperoxides and organic hydroperoxides. Selenium deficiency in females is associated with infertility and spontaneous abortion, suggesting a role for selenium-requiring proteins during embryonic development. To gain insight into functions of EGPx in vivo, we determined sites of murine EGPx synthesis by in situ hybridization during embryogenesis and in adult tissues. At E7.5 of development, high EGPx expression was found in the maternally derived deciduum, with lower levels of accumulation in the embryonic visceral endoderm. At E9.5, the major sites of expression were the yolk sac endoderm and heart musculature. By E16.5, EGPx mRNA expression persisted in yolk sac endoderm but also accumulated significantly in atrially derived myocytes, ossification centers, adipose tissue, intestinal epithelium, and in a ventral-to-dorsal gradient in developing skin. Glutathione peroxidase activity due to EGPx protein was identified in the fluids surrounding the developing mouse embryo at midgestation. The expression of EGPx in tissues at the maternal-fetal interface--deciduum, visceral yolk sac, and skin--suggests that EGPx may serve to protect the embryo from oxidant damage. In adult mice, we identified the S1 segment of the kidney proximal tubules as the primary site of EGPx mRNA accumulation, with lower EGPx levels in atrial cardiac muscle, intestine, skin, and adipose tissue. These findings suggest that EGPx may serve a wider antioxidant role than previously recognized in the interstitium of multiple localized tissues, particularly those associated with the active transport of lipids.

Effects of starvation and of selenium deficiency on the urinary excretion of electrolytes, ketone bodies, creatinine, urea and uric acid

The aim of this study was to investigate whether urinary excretion of other compounds than ketone bodies are also increased in starved, selenium (Se)-deficient rats. Two groups of male rats were fed an Se-deficient diet with 0.009 mg Se/kg, ("Se-deficient" and "Se-repleted") and one group was fed the same diet with 0.23 mg Se/kg as control for eleven weeks. The urinary excretion of ketone bodies was highly enhanced in Se deficiency, with a 7-fold increase in 3-hydroxybutyrate and an 18-fold increase in acetoacetate. Despite this, the plasma concentration of ketone bodies and the glomerular filtration rate were unaffected in the Se-deficient rats. Starvation resulted in a significant decrease in the urinary content of potassium, magnesium and calcium, in both dietary groups of rats and of urea in the Se-adequate group. No Se-dependent difference was noted for the urinary excretion of these compounds or of sodium, phosphate, creatinine and uric acid in any of the groups. This was unexpected in view of certain previous results and indicates that disturbances in the renal handling of compounds are progressive in Se deficiency, with increased excretion of ketone bodies being an early event while more severe deficiency is required to impair the renal handling of electrolytes and other compounds studied.