Mortality, incidence and seasonality of canine and feline patients treated with tick antiserum in three far North Queensland veterinary clinics from 2000 to 2020

Tick paralysis is a paralysis caused by bites from Ixodes holocyclus, affecting an estimated 10,000 companion animals in Australia annually. Despite tick antiserum being the cornerstone of treatment, there are no large-scale general practice studies that examine survival outcomes in tick antiserum-treated animals. In this retrospective study, clinical records from three far north Queensland general practice veterinary clinics were searched for tick antiserum-treated canine and feline patients were seen between 2000 and 2020. Patient records were assessed for survival outcomes, then logistic regression and Bayesian structural time-series model were used to assess trends in incidence and mortality and the relationship between these and time of year, rainfall, and species. The study included 2019 dog and 953 cat records. When patients with unknown outcomes were removed, canine mortality was 11.8% (213/1799) and feline mortality was 5.3% (46/872). Dogs were found to have 2.41 odds of dying following treatment than cats. August and September had the highest mean number of monthly treatments, and rainfall in the previous 5-8 months was positively correlated with the number of patients treated in each month. The odds of mortality did not vary significantly by month or season, and from 2015 onwards, there was a significant decrease in the proportion of dogs treated by the clinics. Overall, this study provides new information on tick antiserum treatment outcomes in general practice as well as new information on tick paralysis incidence in far north Queensland.

Colonic Epithelial-Derived Selenoprotein P Is the Source for Antioxidant-Mediated Protection in Colitis-Associated Cancer

BACKGROUND & AIMS

Patients with inflammatory bowel disease (IBD) demonstrate nutritional selenium deficiencies and are at greater risk of developing colon cancer. Previously, we determined that global reduction of the secreted antioxidant selenium-containing protein, selenoprotein P (SELENOP), substantially increased tumor development in an experimental colitis-associated cancer (CAC) model. We next sought to delineate tissue-specific contributions of SELENOP to intestinal inflammatory carcinogenesis and define clinical context.

METHODS

Selenop floxed mice crossed with Cre driver lines to delete Selenop from the liver, myeloid lineages, or intestinal epithelium were placed on an azoxymethane/dextran sodium sulfate experimental CAC protocol. SELENOP loss was assessed in human ulcerative colitis (UC) organoids, and expression was queried in human and adult UC samples.

RESULTS

Although large sources of SELENOP, both liver- and myeloid-specific Selenop deletion failed to modify azoxymethane/dextran sodium sulfate-mediated tumorigenesis. Instead, epithelial-specific deletion increased CAC tumorigenesis, likely due to elevated oxidative stress with a resulting increase in genomic instability and augmented tumor initiation. SELENOP was down-regulated in UC colon biopsies and levels were inversely correlated with endoscopic disease severity and tissue S100A8 (calprotectin) gene expression.

CONCLUSIONS

Although global selenium status is typically assessed by measuring liver-derived plasma SELENOP levels, our results indicate that the peripheral SELENOP pool is dispensable for CAC. Colonic epithelial SELENOP is the main contributor to local antioxidant capabilities. Thus, colonic SELENOP is the most informative means to assess selenium levels and activity in IBD patients and may serve as a novel biomarker for UC disease severity and identify patients most predisposed to CAC development.

Plasma selenoprotein P concentration and lung cancer risk: results from a case-control study nested within the Shanghai Men's Health Study

Selenoprotein P (SELENOP) is a major selenoenzyme in plasma and linked to antioxidant properties and possibly to lung cancer; however, supporting evidence is limited. We investigated the association between pre-diagnostic plasma SELENOP concentration and lung cancer risk in a case-control study of 403 cases and 403 individually matched controls nested within the Shanghai Men's Health Study. SELENOP concentration in pre-diagnostic plasma samples was measured by a sandwich enzyme-linked immunosorbent assay. Cases were diagnosed with lung cancer between 2003 and 2010. Multivariate conditional logistic regression was used to estimate odds ratios (OR) and the corresponding 95% confidence intervals (CI) for studying the association between plasma SELENOP concentration and lung cancer risk. Cases had slightly lower plasma SELENOP concentration than controls (4.3 ± 1.2 versus 4.4 ± 1.1 mg/l, P difference = 0.09). However, the multivariate analysis showed no association between plasma SELENOP concentration and lung cancer risk among all participants (OR = 1.08, 95% CI = 0.54-2.14 for quartile 4 versus quartile 1), or by smoking status or tumor aggressiveness. In contrast, although the number of cases was limited, plasma SELENOP concentration was positively associated with lung adenocarcinoma risk (OR = 5.38, 95% CI = 1.89-15.35 for tertile 3 versus tertile 1), but not with squamous cell lung carcinoma (OR = 1.69, 95% CI = 0.43-6.70). Our study of adult men living in selenium non-deficient areas in China provides little support for the inverse association between pre-diagnostic plasma SELENOP concentration and lung cancer risk. Our finding of a positive association with risk of lung adenocarcinoma needs to be interpreted with caution.

Cross-sectional survey of health management and prevalence of vector-borne diseases, endoparasites and ectoparasites in Samoan dogs

OBJECTIVE

To determine the prevalence of selected canine vector-borne diseases (Leishmania infantum, Anaplasma spp., Ehrlichia canis, Borrelia burgdorferi and Dirofilaria immitis) and endo- and ectoparasites in Samoan dogs presenting for surgical sterilisation and to report on the general health management of the dogs.

METHODS

This study was a prospective serological cross-sectional survey. Management data were obtained for 242 dogs by interview with their owners. Blood samples were collected from 237 dogs and screened for the canine vector-borne diseases using point-of-care qualitative ELISA assays. Anaplasma spp. positive samples were screened by PCR and sequenced for species identification. Rectal faecal samples were collected from 204 dogs for faecal flotation and immunofluorescent antibody tests were performed for Giardia and Cryptosporidium spp. on a subset of 93 faecal samples. The skin and coat of 221 dogs were examined for presence of ectoparasites.

RESULTS

The D. immitis antigen was detected in 46.8% (111/237) of dogs. Seroprevalence of Anaplasma spp. was 8.4% (20/237); A. platys was confirmed by PCR. Prevalence of hookworm was 92.6% (185/205) and Giardia was 29.0% (27/93). Ectoparasites were detected on 210/221 (95.0%) of dogs examined and 228/242 dogs (94.2%) had previously never received any preventative medication.

CONCLUSIONS

There was a very high prevalence of D. immitis, hookworm and external parasites in Samoan dogs, and prophylactic medication is rarely administered. This is the first report confirming A. platys in Samoa and the South Pacific islands. The public health implications of poor management of the dogs should be considered and investigated further.

Human selenoprotein P and S variant mRNAs with different numbers of SECIS elements and inferences from mutant mice of the roles of multiple SECIS elements

Dynamic redefinition of the 10 UGAs in human and mouse selenoprotein P (Sepp1) mRNAs to specify selenocysteine instead of termination involves two 3' UTR structural elements (SECIS) and is regulated by selenium availability. In addition to the previously known human Sepp1 mRNA poly(A) addition site just 3' of SECIS 2, two further sites were identified with one resulting in 10-25% of the mRNA lacking SECIS 2. To address function, mutant mice were generated with either SECIS 1 or SECIS 2 deleted or with the first UGA substituted with a serine codon. They were fed on either high or selenium-deficient diets. The mutants had very different effects on the proportions of shorter and longer product Sepp1 protein isoforms isolated from plasma, and on viability. Spatially and functionally distinctive effects of the two SECIS elements on UGA decoding were inferred. We also bioinformatically identify two selenoprotein S mRNAs with different 5' sequences predicted to yield products with different N-termini. These results provide insights into SECIS function and mRNA processing in selenoprotein isoform diversity.

Selenomethionine and methyl selenocysteine: multiple-dose pharmacokinetics in selenium-replete men

According to the Nutritional Prevention of Cancer (NPC) trial, a selenized yeast supplement containing selenium, 200 mcg/day, decreased the incidence of total cancer, cancers of the prostate, colon and lung, and cancer mortality. The active agent in the selenized yeast supplement was assumed to be selenomethionine (SEMET), although the supplement had not been well speciated. The SELECT study, largely motivated by the NPC trial, enrolling nearly 40 times as many subjects, showed unequivocally that selenium 200 mcg/day, with selenium in the form of SEMET, does not protect selenium-replete men against prostate or other major cancer. The agent tested by SELECT, pure SEMET, could have been different from the selenized yeast tested in NPC. One of the selenium forms suspected of having chemopreventive effects, and which may have been present in the NPC agent, is methyl selenocysteine (MSC). This study, with 29 selenium-replete patients enrolled in a randomized, double-blind trial, compared the multiple-dose toxicity, pharmacokinetics and pharmacodynamics of MSC and SEMET. Patients were on trial for 84 days. No toxicity was observed. Although SEMET supplementation increased blood selenium concentration more than MSC did, neither form had a more than minimal impact on the two major selenoproteins: selenoprotein P(SEPP1) and glutathione peroxidase(GPX).

Characterisation of methicillin-resistant Staphylococcus aureus clinical isolates from animals in New Zealand, 2012-2013, and subclinical colonisation in dogs and cats in Auckland

AIMS

To characterise methicillin-resistant Staphylococcus aureus (MRSA) isolates from infection sites in animals in New Zealand and assess the prevalence of subclinical MRSA colonisation in dogs and cats attending veterinary clinics in Auckland.

METHODS

MRSA isolates from clinical specimens obtained by the main New Zealand veterinary diagnostic laboratories between June 2012 and June 2013, were genotypically characterised by DNA microarray hybridisation analysis and spa typing. In addition, nasal or perineal skin swabs collected from a cross-sectional sample of dogs (n=361) and cats (n=225) attending 29 veterinary clinics in Auckland during the same period were analysed for MRSA by culture.

RESULTS

Eight MRSA clinical isolates were submitted for characterisation by the participating laboratories. The isolates originated from five dogs, including two isolates from the same dog, one foal, and one isolate had no identification of the source. The strain-types identified were AK3 (ST-5 SCCmecIV t045; n=1), USA500 (ST8 SCCmecIV t064; n=1), WSPP (ST30 SCCmecIV t019; n=1), Rhine Hesse (ST5 SCCmecII t002; n=2), and EMRSA-15 (ST22 SCCmecIV t032; n=3). No MRSA were isolated from 586 cultured swabs. Methicillin-susceptible S. aureus were detected in 9/257 (3.5%) swabs and non-aureus staphylococci in 22/257 (8.5%) swabs. The estimated true MRSA subclinical colonisation prevalence was 0%, with an upper 95% CI boundary of 1.9% for cats and 1.4% for dogs.

CONCLUSIONS

The modest number of MRSA isolates submitted for this study by the participating laboratories suggests clinical MRSA infection in animals in New Zealand continues to be sporadic. The wide variety of strain-types found mirrored the evolving strain-type diversity observed in humans. We cannot rule out bias due to the non-random sampling of dogs and cats, but the apparent colonisation prevalence of 0% was consistent with the low prevalence of subclinical colonisation in humans in New Zealand. These similarities indicate the epidemiology of animal and human MRSA infections are linked.

CLINICAL RELEVANCE

In the last decade, the prevalence of human MRSA infections in New Zealand has steadily increased. This is the second published study of MRSA in animals in New Zealand. The results indicate clinical MRSA infection in animals remains sporadic, but the diversification of the strain-types may pose new therapeutic challenges to veterinarians, due to their diverse resistome.

Brainstem Axonal Degeneration in Mice with Deletion of Selenoprotein P

Selenoprotein P is an abundant extracellular protein that is expressed in liver, brain, and other tissues. Studies in mice with the selenoprotein P gene deleted ( Sepp−/− mice) have implicated the protein in maintaining brain selenium. Sepp−/− mice fed a normal or low selenium diet develop severe motor impairment and die, but Sepp−/− mice fed a high selenium diet remain clinically unimpaired. As an initial step to evaluate the effect of selenoprotein P deletion on central nervous system architecture, the brains and cervical spinal cords of Sepp−/− and Sepp+ /+ mice fed low or high selenium diets were examined by light and electron microscopy. Brains of Sepp−/− mice demonstrated no gross abnormalities. At the light microscopic level, however, Sepp−/− mice fed either the selenium deficient diet or the high selenium diet had enlarged dystrophic axons and degenerated axons in their brainstems and cervical spinal cords. No axonal lesions were observed in the Sepp+ /+ mice fed either diet. Electron microscopy demonstrated that the enlarged axons in the Sepp−/− mice were packed with organelles, suggesting a deficit in fast axonal transport. The similar severity of axonal lesions observed in Sepp−/− mice fed the 2 diets suggests that axonal dystrophy is a common phenotype for deletion of selenoprotein P regardless of selenium intake and that additional studies will be required to determine the pathogenesis of the neurological signs and mortality observed in Sepp−/−mice fed a low selenium diet.

The Effect of the Canine ABCB1-1Δ Mutation on Sedation after Intravenous Administration of Acepromazine

BACKGROUND

Dog breeds with the ABCB1-1Δ mutation have substantially truncated nonfunctional P-glycoprotein. Dogs homozygous for this mutation (mut/mut) are susceptible to the toxic adverse effects of ivermectin, loperamide, and vincristine. Anecdotal reports suggested ABCB1 mut/mut dogs showed increased depth and duration of acepromazine sedation.

HYPOTHESIS/OBJECTIVES

That ABCB1 mut/mut dogs have increased depth and duration of sedation after acepromazine IV compared to normal dogs (nor/nor).

ANIMALS

Twenty-nine rough-coated collies were divided into 3 groups of dogs based on their ABCB1 genotype: 10 mut/mut, 10 mut/nor, and 9 nor/nor.

METHODS

Dogs were given 0.04 mg/kg of acepromazine IV. Level of sedation, heart rate, respiratory rate, and blood pressure were recorded for 6 hours after acepromazine administration. Area under the curves (AUCs) of the normalized sedation score results were calculated and compared.

RESULTS

The median sedation scores for ABCB1 mut/mut dogs were higher than nor/nor dogs at all time points and were higher in mut/nor dogs for the first 2 hours. These differences were not found to be significant for any individual time point (P > .05). The median sedation score AUC for mut/mut dogs was significantly higher than nor/nor dogs (P = .028), but the AUC for mut/nor dogs was not (P = .45). There were no significant differences between groups for heart rate, respiratory rate, and blood pressure (P > .05).

CONCLUSIONS AND CLINICAL IMPORTANCE

In ABCB1 mut/mut dogs acepromazine dose rates should be reduced and careful monitoring performed during sedation.

Selenium deficiency occurs in some patients with moderate-to-severe cirrhosis and can be corrected by administration of selenate but not selenomethionine: a randomized controlled trial

BACKGROUND

Selenomethionine, which is the principal dietary form of selenium, is metabolized by the liver to selenide, which is the form of the element required for the synthesis of selenoproteins. The liver synthesizes selenium-rich selenoprotein P (SEPP1) and secretes it into the plasma to supply extrahepatic tissues with selenium.

OBJECTIVES

We conducted a randomized controlled trial to determine whether cirrhosis is associated with functional selenium deficiency (the lack of selenium for the process of selenoprotein synthesis even though selenium intake is not limited) and, if it is, whether the deficiency is associated with impairment of selenomethionine metabolism.

DESIGN

Patients with Child-Pugh (C-P) classes A, B, and C (mild, moderate, and severe, respectively) cirrhosis were supplemented with a placebo or supranutritional amounts of selenium as selenate (200 or 400 μg/d) or as selenomethionine (200 μg/d) for 4 wk. Plasma SEPP1 concentration and glutathione peroxidase (GPX) activity, the latter due largely to the selenoprotein GPX3 secreted by the kidneys, were measured before and after supplementation.

RESULTS

GPX activity was increased more by both doses of selenate than by the placebo in C-P class B patients. The activity was not increased more by selenomethionine supplementation than by the placebo in C-P class B patients. Plasma selenium was increased more by 400 μg Se as selenate than by the placebo in C-P class C patients. Within the groups who responded to selenate, there was a considerable variation in responses.

CONCLUSION

These results indicate that severe cirrhosis causes mild functional selenium deficiency in some patients that is associated with impaired metabolism of selenomethionine. This trial was registered at clinicaltrials.gov as NCT00271245.

A prospective observational study of needle-handling practices at a University Veterinary Teaching Hospital

AIM

To determine the period prevalence of needlestick injury (NSI) at the Massey University Veterinary Teaching Hospital (VTH) and to identify handling and disposal practices that may contribute to the risk of NSI.

METHODS

Observations of personnel were conducted in the equine (EVH) and companion animal (CAH) clinics of the VTH during scheduled clinical activities over 9- and 10-day periods, respectively. The number and type of NSI incidents, needle uncapping, capping and disposal events were recorded for veterinarians, nurses and other personnel (visitors and students). The number of needle-related practices, as a proportion of observations, were compared between CAH and EVH, and veterinarians, nurses and others using χ(2) tests.

RESULTS

Needlestick injury was not observed during 190 and 163 needle handling and disposal observations in the CAH and EVH, respectively. Uncapping of needles by mouth was observed and was practised more by veterinarians (15/119; 13%) than nurses (2/42; 5%) and others (6/193; 3%) (p=0.001). Two-handed needle recapping after use was observed 265/354 times, and the one handed scooping technique was rarely observed (8/352). In the case of needle disposal, EVH workers used a container that was not purpose built for disposal more than CAH staff (p=0.02), or placed them in a pocket more frequently (p=0.003). Needle disposal containers were available on adjacent bench tops for 65/190 (34%) CAH observations, but no EVH observations. For 51/163 (31%) EVH observations the needle disposal containers were located on the ground, whereas none were observed there in the CAH. No approved sharps containers were observed in the immediate EVH and CAH work areas for 47/163 (28.8%) and 1/191 (0.5%) needle-handling activities, respectively.

CONCLUSIONS

Unsafe needle-handling practices must be reduced by policies and training programmes to encourage safe needle-related practices, and ensuring that approved sharps containers are available in close proximity to where needles are used.

Does exposure to thyroxine-mimics cause feline thyroid hyperplasia?

Over the past four decades, the incidence of feline thyroid hyperplasia (FTH) has steadily increased. Concomitantly, cats' exposure to thyroxine (T4)-mimicking environmental contaminants and food additives has also increased.

KATE HILL

and IAN SHAW: hypothesise that the two could be linked.

Selenoprotein P influences colitis-induced tumorigenesis by mediating stemness and oxidative damage

Patients with inflammatory bowel disease are at increased risk for colon cancer due to augmented oxidative stress. These patients also have compromised antioxidant defenses as the result of nutritional deficiencies. The micronutrient selenium is essential for selenoprotein production and is transported from the liver to target tissues via selenoprotein P (SEPP1). Target tissues also produce SEPP1, which is thought to possess an endogenous antioxidant function. Here, we have shown that mice with Sepp1 haploinsufficiency or mutations that disrupt either the selenium transport or the enzymatic domain of SEPP1 exhibit increased colitis-associated carcinogenesis as the result of increased genomic instability and promotion of a protumorigenic microenvironment. Reduced SEPP1 function markedly increased M2-polarized macrophages, indicating a role for SEPP1 in macrophage polarization and immune function. Furthermore, compared with partial loss, complete loss of SEPP1 substantially reduced tumor burden, in part due to increased apoptosis. Using intestinal organoid cultures, we found that, compared with those from WT animals, Sepp1-null cultures display increased stem cell characteristics that are coupled with increased ROS production, DNA damage, proliferation, decreased cell survival, and modulation of WNT signaling in response to H2O2-mediated oxidative stress. Together, these data demonstrate that SEPP1 influences inflammatory tumorigenesis by affecting genomic stability, the inflammatory microenvironment, and epithelial stem cell functions.

Regulation of Selenium Metabolism and Transport

Selenium is regulated in the body to maintain vital selenoproteins and to avoid toxicity. When selenium is limiting, cells utilize it to synthesize the selenoproteins most important to them, creating a selenoprotein hierarchy in the cell. The liver is the central organ for selenium regulation and produces excretory selenium forms to regulate whole-body selenium. It responds to selenium deficiency by curtailing excretion and secreting selenoprotein P (Sepp1) into the plasma at the expense of its intracellular selenoproteins. Plasma Sepp1 is distributed to tissues in relation to their expression of the Sepp1 receptor apolipoprotein E receptor-2, creating a tissue selenium hierarchy. N-terminal Sepp1 forms are taken up in the renal proximal tubule by another receptor, megalin. Thus, the regulated whole-body pool of selenium is shifted to needy cells and then to vital selenoproteins in them to supply selenium where it is needed, creating a whole-body selenoprotein hierarchy.

Regional variations in percutaneous absorption of methimazole: an in vitro study on cat skin

The use of transdermal gel medications in cats has become popular in veterinary medicine due to the ease of administration compared to oral medication. The research to support systemic absorption of drugs after transdermal gel administration and the preferred skin region to apply these drugs in cats is limited. The aim of this study was to characterize the effect of different skin regions on the percutaneous absorption pharmacokinetics of a commercially available transdermal methimazole after a finite dose was applied to feline skin in vitro. A commercial formulation of methimazole (10 mg) was applied to four skin regions (the inner stratum corneum of the ear, groin, neck, and thorax regions) from six cats. The receptor medium was sampled up to 36 h postapplication, and methimazole concentrations were measured using high-performance liquid chromatography. Methimazole was absorbed more completely across the pinnal skin, compared to the groin, neck, and thorax (P < 0.001), which justifies application to the pinna to maximize efficacy and also to minimize the effects of grooming.

Percutaneous absorption of methimazole: an in vitro study of the absorption pharmacokinetics for two different vehicles

The use of transdermal medications in cats has become popular in veterinary medicine due to the ease of administration compared to oral medication. However, the research to support systemic absorption of drugs applied to the pinna after transdermal administration in cats is limited. The aim of this study was to characterize the percutaneous absorption pharmacokinetics of methimazole in a lipophilic vehicle compared to methimazole in Pluronic(®) lecithin organogel (PLO) using a finite dose applied to feline ear skin in an in vitro Franz cell model. The two formulations of methimazole (10 mg) were applied to the inner stratum corneum of six pairs of feline ears. The receptor medium was sampled up to 30 h post-administration, and methimazole concentrations were measured using high-performance liquid chromatography (HPLC). Histological examination of all ears was undertaken as small differences in the thickness of ear skin may have contributed to inter-individual differences in methimazole absorption between six cats. Methimazole was absorbed more completely across the pinnal skin when administered in the lipophilic vehicle compared to administration in the PLO gel (P < 0.001).

Selenoprotein P is the major selenium transport protein in mouse milk

Selenium is transferred from the mouse dam to its neonate via milk. Milk contains selenium in selenoprotein form as selenoprotein P (Sepp1) and glutathione peroxidase-3 (Gpx3) as well as in non-specific protein form as selenomethionine. Selenium is also present in milk in uncharacterized small-molecule form. We eliminated selenomethionine from the mice in these experiments by feeding a diet that contained sodium selenite as the source of selenium. Selenium-replete dams with deletion of Sepp1 or Gpx3 were studied to assess the effects of these genes on selenium transfer to the neonate. Sepp1 knockout caused a drop in milk selenium to 27% of the value in wild-type milk and a drop in selenium acquisition by the neonates to 35%. In addition to decreasing milk selenium by eliminating Sepp1, deletion of Sepp1 causes a decline in whole-body selenium, which likely also contributes to the decreased transfer of selenium to the neonate. Deletion of Gpx3 did not decrease milk selenium content or neonate selenium acquisition by measurable amounts. Thus, when the dam is fed selenium-adequate diet (0.25 mg selenium/kg diet), milk Sepp1 transfers a large amount of selenium to neonates but the transfer of selenium by Gpx3 is below detection by our methods.

Selenoprotein P and apolipoprotein E receptor-2 interact at the blood-brain barrier and also within the brain to maintain an essential selenium pool that protects against neurodegeneration

Selenoprotein P (Sepp1) and its receptor, apolipoprotein E receptor 2 (apoER2), account for brain retaining selenium better than other tissues. The primary sources of Sepp1 in plasma and brain are hepatocytes and astrocytes, respectively. ApoER2 is expressed in varying amounts by tissues; within the brain it is expressed primarily by neurons. Knockout of Sepp1 or apoER2 lowers brain selenium from ∼120 to ∼50 ng/g and leads to severe neurodegeneration and death in mild selenium deficiency. Interactions of Sepp1 and apoER2 that protect against this injury have not been characterized. We studied Sepp1, apoER2, and brain selenium in knockout mice. Immunocytochemistry showed that apoER2 mediates Sepp1 uptake at the blood-brain barrier. When Sepp1(-/-) or apoER2(-/-) mice developed severe neurodegeneration caused by mild selenium deficiency, brain selenium was ∼35 ng/g. In extreme selenium deficiency, however, brain selenium of ∼12 ng/g was tolerated when both Sepp1 and apoER2 were intact in the brain. These findings indicate that tandem Sepp1-apoER2 interactions supply selenium for maintenance of brain neurons. One interaction is at the blood-brain barrier, and the other is within the brain. We postulate that Sepp1 inside the blood-brain barrier is taken up by neurons via apoER2, concentrating brain selenium in them.

Sepp1(UF) forms are N-terminal selenoprotein P truncations that have peroxidase activity when coupled with thioredoxin reductase-1

Mouse selenoprotein P (Sepp1) consists of an N-terminal domain (residues 1-239) that contains one selenocysteine (U) as residue 40 in a proposed redox-active motif (-UYLC-) and a C-terminal domain (residues 240-361) that contains nine selenocysteines. Sepp1 transports selenium from the liver to other tissues by receptor-mediated endocytosis. It also reduces oxidative stress in vivo by an unknown mechanism. A previously uncharacterized plasma form of Sepp1 is filtered in the glomerulus and taken up by renal proximal convoluted tubule (PCT) cells via megalin-mediated endocytosis. We purified Sepp1 forms from the urine of megalin(-/-) mice using a monoclonal antibody to the N-terminal domain. Mass spectrometry revealed that the purified urinary Sepp1 consisted of N-terminal fragments terminating at 11 sites between residues 183 and 208. They were therefore designated Sepp1(UF). Because the N-terminal domain of Sepp1 has a thioredoxin fold, Sepp1(UF) were compared with full-length Sepp1, Sepp1(Δ240-361), and Sepp1(U40S) as a substrate of thioredoxin reductase-1 (TrxR1). All forms of Sepp1 except Sepp1(U40S), which contains serine in place of the selenocysteine, were TrxR1 substrates, catalyzing NADPH oxidation when coupled with H2O2 or tert-butylhydroperoxide as the terminal electron acceptor. These results are compatible with proteolytic cleavage freeing Sepp1(UF) from full-length Sepp1, the form that has the role of selenium transport, allowing Sepp1(UF) to function by itself as a peroxidase. Ultimately, plasma Sepp1(UF) and small selenium-containing proteins are filtered by the glomerulus and taken up by PCT cells via megalin-mediated endocytosis, preventing loss of selenium in the urine and providing selenium for the synthesis of glutathione peroxidase-3.

Isoform-specific binding of selenoprotein P to the β-propeller domain of apolipoprotein E receptor 2 mediates selenium supply

Sepp1 supplies selenium to tissues via receptor-mediated endocytosis. Mice, rats, and humans have 10 selenocysteines in Sepp1, which are incorporated via recoding of the stop codon, UGA. Four isoforms of rat Sepp1 have been identified, including full-length Sepp1 and three others, which terminate at the second, third, and seventh UGA codons. Previous studies have shown that the longer Sepp1 isoforms bind to the low density lipoprotein receptor apoER2, but the mechanism remains unclear. To identify the essential residues for apoER2 binding, an in vitro Sepp1 binding assay was developed using different Sec to Cys substituted variants of Sepp1 produced in HEK293T cells. ApoER2 was found to bind the two longest isoforms. These results suggest that Sepp1 isoforms with six or more selenocysteines are taken up by apoER2. Furthermore, the C-terminal domain of Sepp1 alone can bind to apoER2. These results indicate that apoER2 binds to the Sepp1 C-terminal domain and does not require the heparin-binding site, which is located in the N-terminal domain. Site-directed mutagenesis identified three residues of Sepp1 that are necessary for apoER2 binding. Sequential deletion of extracellular domains of apoER2 surprisingly identified the YWTD β-propeller domain as the Sepp1 binding site. Finally, we show that apoER2 missing the ligand-binding repeat region, which can result from cleavage at a furin cleavage site present in some apoER2 isoforms, can act as a receptor for Sepp1. Thus, longer isoforms of Sepp1 with high selenium content interact with a binding site distinct from the ligand-binding domain of apoER2 for selenium delivery.

Plasma selenium biomarkers in low income black and white americans from the southeastern United States

Biomarkers of selenium are necessary for assessing selenium status in humans, since soil variation hinders estimation of selenium intake from foods. In this study, we measured the concentration of plasma selenium, selenoprotein P (SEPP1), and glutathione peroxidase (GPX3) activity and their interindividual differences in 383 low-income blacks and whites selected from a stratified random sample of adults aged 40-79 years, who were participating in a long-term cohort study in the southeastern United States (US). We assessed the utility of these biomarkers to determine differences in selenium status and their association with demographic, socio-economic, dietary, and other indicators. Dietary selenium intake was assessed using a validated food frequency questionnaire designed for the cohort, matched with region-specific food selenium content, and compared with the US Recommended Dietary Allowances (RDA) set at 55 µg/day. We found that SEPP1, a sensitive biomarker of selenium nutritional status, was significantly lower among blacks than whites (mean 4.4 ± 1.1 vs. 4.7 ± 1.0 mg/L, p = 0.006), with blacks less than half as likely to have highest vs. lowest quartile SEPP1 concentration (Odds Ratio (OR) 0.4, 95% Confidence Interval (CI) 0.2-0.8). The trend in a similar direction was observed for plasma selenium among blacks and whites, (mean 115 ± 15.1 vs. 118 ± 17.7 µg/L, p = 0.08), while GPX3 activity did not differ between blacks and whites (136 ± 33.3 vs. 132 ± 33.5 U/L, p = 0.320). Levels of the three biomarkers were not correlated with estimated dietary selenium intake, except for SEPP1 among 10% of participants with the lowest selenium intake (≤ 57 µg/day). The findings suggest that SEPP1 may be an effective biomarker of selenium status and disease risk in adults and that low selenium status may disproportionately affect black and white cohort participants.

An in vitro study of alginate oligomer therapies on oral biofilms

OBJECTIVES

The in vitro effect of a novel, oligosaccharide nanomedicine OligoG against oral pathogen-related biofilms, both alone and in the presence of the conventional anti-bacterial agent triclosan, was evaluated.

METHODS

The effect of OligoG±triclosan was assessed against established Streptococcus mutans and Porphyromonas gingivalis biofilms by bacterial counts and image analysis using LIVE/DEAD(®) staining and atomic force microscopy (AFM). The effect of triclosan and OligoG surface pre-treatments on bacterial attachment to titanium and polymethylmethacrylate was also studied.

RESULTS

OligoG potentiated the antimicrobial effect of triclosan, particularly when used in combination at 0.3% against S. mutans grown in artificial saliva. OligoG was less effective against established P. gingivalis biofilms. However, attachment of P. gingivalis, to titanium in particular, was significantly reduced after surface pre-treatment with OligoG and triclosan at 0.01% when compared to controls. Light microscopy and AFM showed that OligoG was biocidal to P. gingivalis, but not S. mutans.

CONCLUSIONS

OligoG and triclosan when used in combination produced an enhanced antimicrobial effect against two important oral pathogens and reduced bacterial attachment to dental materials such as titanium, even at reduced triclosan concentrations. Whilst the use of triclosan against oral bacteria has been widely documented, its synergistic use with OligoG described here, has not previously been reported. The use of lower concentrations of triclosan, if used in combination therapy with OligoG, could have environmental benefits.

CLINICAL IMPORTANCE

The potentiation of antimicrobial agents by naturally occurring oligomers such as OligoG may represent a novel, safe adjunct to conventional oral hygiene and periodontal therapy. The ability of OligoG to inhibit the growth and impair bacterial adherence highlights its potential in the management of peri-implantitis.

Dietary selenium deficiency exacerbates DSS-induced epithelial injury and AOM/DSS-induced tumorigenesis

Selenium (Se) is an essential micronutrient that exerts its functions via selenoproteins. Little is known about the role of Se in inflammatory bowel disease (IBD). Epidemiological studies have inversely correlated nutritional Se status with IBD severity and colon cancer risk. Moreover, molecular studies have revealed that Se deficiency activates WNT signaling, a pathway essential to intestinal stem cell programs and pivotal to injury recovery processes in IBD that is also activated in inflammatory neoplastic transformation. In order to better understand the role of Se in epithelial injury and tumorigenesis resulting from inflammatory stimuli, we examined colonic phenotypes in Se-deficient or -sufficient mice in response to dextran sodium sulfate (DSS)-induced colitis, and azoxymethane (AOM) followed by cyclical administration of DSS, respectively. In response to DSS alone, Se-deficient mice demonstrated increased morbidity, weight loss, stool scores, and colonic injury with a concomitant increase in DNA damage and increases in inflammation-related cytokines. As there was an increase in DNA damage as well as expression of several EGF and TGF-β pathway genes in response to inflammatory injury, we sought to determine if tumorigenesis was altered in the setting of inflammatory carcinogenesis. Se-deficient mice subjected to AOM/DSS treatment to model colitis-associated cancer (CAC) had increased tumor number, though not size, as well as increased incidence of high grade dysplasia. This increase in tumor initiation was likely due to a general increase in colonic DNA damage, as increased 8-OHdG staining was seen in Se-deficient tumors and adjacent, non-tumor mucosa. Taken together, our results indicate that Se deficiency worsens experimental colitis and promotes tumor development and progression in inflammatory carcinogenesis.

Maternal-fetal transfer of selenium in the mouse

Selenoprotein P (Sepp1) is taken up by receptor-mediated endocytosis for its selenium. The other extracellular selenoprotein, glutathione peroxidase-3 (Gpx3), has not been shown to transport selenium. Mice with genetic alterations of Sepp1, the Sepp1 receptors apolipoprotein E receptor-2 (apoER2) and megalin, and Gpx3 were used to investigate maternal-fetal selenium transfer. Immunocytochemistry (ICC) showed receptor-independent uptake of Sepp1 and Gpx3 in the same vesicles of d-13 visceral yolk sac cells, suggesting uptake by pinocytosis. ICC also showed apoER2-mediated uptake of maternal Sepp1 in the d-18 placenta. Thus, two selenoprotein-dependent maternal-fetal selenium transfer mechanisms were identified. Selenium was quantified in d-18 fetuses with the mechanisms disrupted. Maternal Sepp1 deletion, which lowers maternal whole-body selenium, decreased fetal selenium under selenium-adequate conditions but deletion of fetal apoER2 did not. Fetal apoER2 deletion did decrease fetal selenium, by 51%, under selenium-deficient conditions, verifying function of the placental Sepp1-apoER2 mechanism. Maternal Gpx3 deletion decreased fetal selenium, by 13%, but only under selenium-deficient conditions. These findings indicate that the selenoprotein uptake mechanisms ensure selenium transfer to the fetus under selenium-deficient conditions. The failure of their disruptions (apoER2 deletion, Gpx3 deletion) to affect fetal selenium under selenium-adequate conditions indicates the existence of an additional maternal-fetal selenium transfer mechanism.

Choanal atresia in a cat

CASE HISTORY

A 5-month-old domestic shorthair kitten with a history of chronic left unilateral nasal discharge was examined.

CLINICAL FINDINGS

Endoscopy and computed tomography (CT) demonstrated a complete membranous obstruction of the left nasal choana, confirming congenital unilateral choanal atresia. In addition, congenital hydrocephalus was detected on CT. Nasopharyngoscopy was performed for confirmation and treatment of choanal atresia.

DIAGNOSIS

Unilateral membranous choanal atresia associated with congenital hydrocephalus.

CLINICAL RELEVANCE

This report describes a rare congenital condition and for the first time, CT imaging provided an accurate diagnosis and allowed planning for the successful treatment of unilateral membranous choanal atresia. In addition, concurrent congenital hydrocephalus was diagnosed.

Tumor suppressor function of the plasma glutathione peroxidase gpx3 in colitis-associated carcinoma

The glutathione peroxidases, a family of selenocysteine-containing redox enzymes, play pivotal roles in balancing the signaling, immunomodulatory, and deleterious effects of reactive oxygen species (ROS). The glutathione peroxidase GPX3 is the only extracellular member of this family, suggesting it may defend cells against ROS in the extracellular environment. Notably, GPX3 hypermethylation and underexpression occur commonly in prostate, gastric, cervical, thyroid, and colon cancers. We took a reverse genetics approach to investigate whether GPX3 would augment inflammatory colonic tumorigenesis, a process characterized by oxidative stress and inflammation, comparing Gpx3(-/-) mice in an established two-stage model of inflammatory colon carcinogenesis. Gpx3-deficient mice exhibited an increased tumor number, though not size, along with a higher degree of dysplasia. In addition, they exhibited increased inflammation with redistribution toward protumorigenic M2 macrophage subsets, increased proliferation, hyperactive WNT signaling, and increased DNA damage. To determine the impact of acute gene loss in an established colon cancer line, we silenced GPX3 in human Caco2 cells, resulting in increased ROS production, DNA damage and apoptosis in response to oxidative stress, combined with decreased contact-independent growth. Taken together, our results suggested an immunomodulatory role for GPX3 that limits the development of colitis-associated carcinoma.

Fecal selenium excretion is regulated by dietary selenium intake

Whole-body selenium is regulated by excretion of the element. Reports of studies carried out using isotopic tracers have led to the conclusion that urinary selenium excretion is regulated by selenium intake but that fecal excretion is not. Because of the limitations of tracer studies, we measured urinary and fecal selenium excretion by mice with selenium intakes in the form of sodium selenite ranging from deficient to almost toxic. Tissue and whole-body selenium concentrations increased sharply between deficient and adequate selenium intakes, reflecting tissue accumulation of selenium in the form of selenoproteins. Once the requirement for selenium had been satisfied, a 31-fold further increase in intake resulted in less than doubling of tissue and whole-body selenium, demonstrating the effectiveness of selenium excretion by the mouse. Urinary selenium excretion increased with increases in dietary selenium intake. Fecal selenium excretion, which was 20 to 30 % of the selenium excreted in the physiological range, responded to moderately high selenium intake but did not increase further when selenium intake was increased to even higher levels. Thus, fecal selenium excretion contributes to regulation of whole-body selenium at physiological selenium intakes. The pattern of its response to the full spectrum of selenium intakes was different from the urinary excretion response, suggesting that the mechanisms of fecal and urinary routes of excretion are different.

Production of selenoprotein P (Sepp1) by hepatocytes is central to selenium homeostasis

BACKGROUND

Sepp1 transports selenium, but its complete role in selenium homeostasis is not known.

RESULTS

Deletion of Sepp1 in hepatocytes increases liver selenium at the expense of other tissues and decreases whole-body selenium by increasing excretion.

CONCLUSION

Sepp1 production by hepatocytes retains selenium in the organism and distributes it from the liver to peripheral tissues.

SIGNIFICANCE

Sepp1 is central to selenium homeostasis. Sepp1 is a widely expressed extracellular protein that in humans and mice contains 10 selenocysteine residues in its primary structure. Extra-hepatic tissues take up plasma Sepp1 for its selenium via apolipoprotein E receptor-2 (apoER2)-mediated endocytosis. The role of Sepp1 in the transport of selenium from liver, a rich source of the element, to peripheral tissues was studied using mice with selective deletion of Sepp1 in hepatocytes (Sepp1(c/c)/alb-cre(+/-) mice). Deletion of Sepp1 in hepatocytes lowered plasma Sepp1 concentration to 10% of that in Sepp1(c/c) mice (controls) and increased urinary selenium excretion, decreasing whole-body and tissue selenium concentrations. Under selenium-deficient conditions, Sepp1(c/c)/alb-cre(+/-) mice accumulated selenium in the liver at the expense of extra-hepatic tissues, severely worsening clinical manifestations of dietary selenium deficiency. These findings are consistent with there being competition for metabolically available hepatocyte selenium between the synthesis of selenoproteins and the synthesis of selenium excretory metabolites. In addition, selenium deficiency down-regulated the mRNA of the most abundant hepatic selenoprotein, glutathione peroxidase-1 (Gpx1), to 15% of the selenium-replete value, while reducing Sepp1 mRNA, the most abundant hepatic selenoprotein mRNA, only to 61%. This strongly suggests that Sepp1 synthesis is favored in the liver over Gpx1 synthesis when selenium supply is limited, directing hepatocyte selenium to peripheral tissues in selenium deficiency. We conclude that production of Sepp1 by hepatocytes is central to selenium homeostasis in the organism because it promotes retention of selenium in the body and effects selenium distribution from the liver to extra-hepatic tissues, especially under selenium-deficient conditions.

Long isoform mouse selenoprotein P (Sepp1) supplies rat myoblast L8 cells with selenium via endocytosis mediated by heparin binding properties and apolipoprotein E receptor-2 (ApoER2)

In vivo studies have shown that selenium is supplied to testis and brain by apoER2-mediated endocytosis of Sepp1. Although cultured cell lines have been shown to utilize selenium from Sepp1 added to the medium, the mechanism of uptake and utilization has not been characterized. Rat L8 myoblast cells were studied. They took up mouse Sepp1 from the medium and used its selenium to increase their glutathione peroxidase (Gpx) activity. L8 cells did not utilize selenium from Gpx3, the other plasma selenoprotein. Neither did they utilize it from Sepp1(Δ240-361), the isoform of Sepp1 that lacks the selenium-rich C-terminal domain. To identify Sepp1 receptors, a solubilized membrane fraction was passed over a Sepp1 column. The receptors apoER2 and Lrp1 were identified in the eluate by mass spectrometry. siRNA experiments showed that knockdown of apoER2, but not of Lrp1, inhibited (75)Se uptake from (75)Se-labeled Sepp1. The addition of protamine to the medium or treatment of the cells with chlorate also inhibited (75)Se uptake. Blockage of lysosome acidification did not inhibit uptake of Sepp1 but did prevent its digestion and thereby utilization of its selenium. These results indicate that L8 cells take up Sepp1 by an apoER2-mediated mechanism requiring binding to heparin sulfate proteoglycans. The presence of at least part of the selenium-rich C-terminal domain of Sepp1 is required for uptake. RT-PCR showed that mouse tissues express apoER2 in varying amounts. It is postulated that apoER2-mediated uptake of long isoform Sepp1 is responsible for selenium distribution to tissues throughout the body.

A retrospective study of gastric dilatation and gastric dilatation and volvulus in working farm dogs in New Zealand

AIMS

To present findings from a case series of gastric dilatation (GD) or gastric dilatation and volvulus (GDV) in working farm dogs in New Zealand that were examined at veterinary clinics, and to identify possible risk factors for GD or GDV in working farm dogs in New Zealand using a case-control study.

METHODS

This retrospective study included a case-series and a case-control study. The case series analysed information from 62 case records of GD or GDV in working farm dogs seen between August 2004 and September 2009 at 13 veterinary clinics throughout New Zealand. Cases were classified as GD or GDV if the diagnosis was confirmed by radiography, surgery or post-mortem examination. Details of history and treatment, as well as outcomes, were obtained for each case. For the case-control study, records of 41 working farm dogs with GD or GDV (cases) seen between April 2008 and April 2009, and 82 working farm dogs examined because of trauma over the same period and in the same 13 clinics (controls), were used to model the risk factors for GD or GDV.

RESULTS

From the case-series study, 40/62 (65%) cases of GD or GDV that were examined and treated at the veterinary clinics returned to work. Of the 41 dogs where the gastric contents were recorded, 25 (61%) had predominantly food or bones in the stomach, and 26/27 dogs had a history of having eaten meat, bones or scavenged a carcass. The case-control study showed that the significant risk factors for GD or GDV, compared with control dogs presenting with trauma, were breed, age and season. The odds that a case of GD or GDV was a Huntaway, after adjusting for age and season, was 19 times higher than the odds a control was a Huntaway. Gender and bodyweight were not identified as risk factors.

CONCLUSIONS AND CLINICAL RELEVANCE

A high proportion of farm working dogs with GD or GDV were successfully treated by veterinarians. The risk of a case of GD or GDV being a Huntaway was significantly higher than for a dog presenting as a trauma case. However the influences of the season of the year, climatic factors and nutritional factors on the pathogenesis need to be identified before adequate preventative measures can be recommended.

Genetic variation in GPX1 is associated with GPX1 activity in a comprehensive analysis of genetic variations in selenoenzyme genes and their activity and oxidative stress in humans

Previous studies suggest some effects of selenium on risk of several chronic diseases, which may be mediated through a small number of selenoenzymes with antioxidant properties. In this cross-sectional analysis of 195 participants from the Seattle Barrett's Esophagus Study who were free of esophageal cancer at the time of blood draw, we examined whether the number of the minor alleles in 26 tagging single nucleotide polymorphisms (SNP) of five selenoenzyme genes [i.e., glutathione peroxidase 1-4 (GPX1-4) and selenoprotein P (SEPP1)] was associated with activity of GPX1 in white blood cells and GPX3 in plasma, and concentrations of SEPP1 and markers of oxidative stress [malondialdehyde (MDA) and protein carbonyl content] in plasma. At the gene level, associations were observed between overall variation in GPX1 and GPX1 activity (P = 0.02) as well as between overall variation in GPX2 and SEPP1 concentrations (P = 0.03). By individual SNP, two variants in GPX1 (rs8179164 and rs1987628) showed a suggestive association with GPX1 activity (P = 0.10 and 0.08, respectively) and two GPX2 variants (rs4902346 and rs2071566) were associated with SEPP1 concentration (P = 0.004 and 0.002, respectively). Furthermore, two SNP in the SEPP1 gene (rs230813 and rs230819) were associated with MDA concentrations (P = 0.03 and 0.02, respectively). Overall, our study supports the hypothesis that common genetic variants in selenoenzymes affect their activity.

Glutathione peroxidase-3 produced by the kidney binds to a population of basement membranes in the gastrointestinal tract and in other tissues

Glutathione peroxidase-3 (Gpx3), the extracellular glutathione peroxidase synthesized largely in the kidney, binds to basement membranes of renal cortical epithelial cells. The present study assessed extrarenal expression of Gpx3 using RT-PCR and presence of Gpx3 protein using immunocytochemistry. Gpx3 expression was higher in kidney and epididymis than in other tissues. Gpx3 bound to basement membranes of epithelial cells in the gastrointestinal tract, the efferent ducts connecting the seminiferous tubules with the epididymis, the bronchi, and type II pneumocytes. It was not detected on the basement membrane of type I pneumocytes. Gpx3 was also present in the lumen of the epididymis. Transplantation of Gpx3(+/+) kidneys into Gpx3(-/-) mice led to Gpx3 binding to the same basement membranes to which it bound in Gpx3(+/+) mice but not to its presence in the epididymal lumen. These results show that Gpx3 from the blood binds to basement membranes of specific epithelial cells and indicate that the cells modify their basement membranes to cause the binding. They further indicate that at least two Gpx3 compartments exist in the organism. In one compartment, kidney supplies Gpx3 through the blood to specific basement membranes in a number of tissues. In the other compartment, the epididymis provides Gpx3 to its own lumen. Tissues other than kidney and epididymis express Gpx3 at lower levels and may supply Gpx3 to other compartments.

Estrogen status alters tissue distribution and metabolism of selenium in female rats

A reported association between estrogen and selenium status may be important in the regulation of selenium metabolism. In this study, the effect of estrogen status on the metabolism of orally administered (75)Se-selenite and tissue selenium status was investigated. Female Sprague-Dawley rats were bilaterally ovariectomized at 7 weeks of age and implanted with either a placebo pellet (OVX) or pellet containing estradiol (OVX+E2), or were sham operated (Sham). At 12 weeks of age, 60 µCi of (75)Se as selenite was orally administered to OVX and OVX+E2 rats. Blood and organs were collected 1, 3, 6 and 24 h after dosing. Estrogen status was associated with time-dependent differences in distribution of (75)Se in plasma, red blood cell (RBC), liver, heart, kidney, spleen, brain and thymus and incorporation of (75)Se into plasma selenoprotein P (Sepp1) and glutathione peroxidase (GPx). Estrogen treatment also significantly increased selenium concentration and GPx activity in plasma, liver and brain, selenium concentration in RBC and hepatic Sepp1 and GPx1 messenger RNA. These results suggest that estrogen status affects tissue distribution of selenium by modulating Sepp1, as this protein plays a central role in selenium transport.

Progression of neurodegeneration and morphologic changes in the brains of juvenile mice with selenoprotein P deleted

Selenoprotein P (Sepp1) is an important protein involved in selenium (Se) transport and homeostasis. Severe neurologic dysfunction develops in Sepp1 null mice (Sepp1(-/-)) fed a selenium-deficient diet. Sepp1(-/-) mice fed a selenium-deficient diet have extensive degeneration of the brainstem and thalamus, and even when supplemented with selenium exhibit subtle learning deficits and altered basal synaptic transmission and short-term plasticity in the CA1 region of the hippocampus. The goal of this study was to delineate the regional progression of neurodegeneration in the brain, determine the extent of neuronal cell death, and evaluate neurite structural changes within the hippocampus of Sepp1(-/-) mice. Whole brain serial sections of wild-type and Sepp1(-/-) mice maintained on selenium-deficient or supplemented diets over the course of 12 days from weaning were evaluated with amino cupric silver neurodegeneration stain. The neurodegeneration was present in all regions upon weaning and progressed over 12 days in Sepp1(-/-) mice fed selenium-deficient diet, except in the medial forebrain bundle and somatosensory cortex where the neurodegeneration developed post-weaning. The neurodegeneration was predominantly axonal, however the somatosensory cortex and lateral striatum showed silver-stained neurons. Morphologic analysis of the hippocampus revealed decreased dendritic length and spine density, suggesting that loss of Sepp1 also causes subtle changes in the brain that can contribute to functional deficits. These data illustrate that deletion of Sepp1, and presumably selenium deficiency in the brain, produce both neuronal and axonal degeneration as well as more moderate and potentially reversible neurite changes in the developing brain.

Optimization of selenoprotein P and other plasma selenium biomarkers for the assessment of the selenium nutritional requirement: a placebo-controlled, double-blind study of selenomethionine supplementation in selenium-deficient Chinese subjects

BACKGROUND

The intake of selenium needed for optimal health has not been established. Selenoproteins perform the functions of selenium, and the selenium intake needed for their full expression is not known.

OBJECTIVE

This study sought to determine the intake of selenium required to optimize plasma selenoprotein P (SEPP1) and to compare SEPP1 with other plasma selenium biomarkers.

DESIGN

A 40-wk placebo-controlled, double-blind study of selenium repletion was carried out in 98 healthy Chinese subjects who had a daily dietary selenium intake of 14 micro g. Fourteen subjects each were assigned randomly to daily dose groups of 0, 21, 35, 55, 79, 102, and 125 micro g Se as l-selenomethionine. Plasma glutathione peroxidase (GPX) activity, SEPP1, and selenium were measured. A biomarker was considered to be optimized when its value was not different from the mean value of the subjects receiving larger supplements.

RESULTS

The SEPP1 concentration was optimized at 40 wk by the 35- micro g supplement, which indicated that 49 micro g/d could optimize it. GPX activity was optimized by 21 micro g (total ingestion: 35 micro g/d). The selenium concentration showed no tendency to become optimized.

CONCLUSIONS

The present results indicate that SEPP1 concentration is the best plasma biomarker studied for assessing optimal expression of all selenoproteins, because its optimization required a larger intake of selenium than did GPX activity. On the basis of the selenium intake needed for SEPP1 optimization with adjustments for body weight and individual variation, ap 75 micro g Se/d as selenomethionine is postulated to allow full expression of selenoproteins in US residents. This trial was registered at clinicaltrials.gov as NCT00428649.

Extracellular glutathione peroxidase (Gpx3) binds specifically to basement membranes of mouse renal cortex tubule cells

Glutathione peroxidase-3 (Gpx3), also known as plasma or extracellular glutathione peroxidase, is a selenoprotein secreted primarily by kidney proximal convoluted tubule cells. In this study Gpx3(-/-) mice have been produced and immunocytochemical techniques have been developed to investigate Gpx3 metabolism. Gpx3(-/-) mice maintained the same whole-body content and urinary excretion of selenium as did Gpx3(+/+) mice. They tolerated selenium deficiency without observable ill effects. The simultaneous knockout of Gpx3 and selenoprotein P revealed that these two selenoproteins account for >97% of plasma selenium. Immunocytochemistry experiments demonstrated that Gpx3 binds selectively, both in vivo and in vitro, to basement membranes of renal cortical proximal and distal convoluted tubules. Based on calculations using selenium content, the kidney pool of Gpx3 is over twice as large as the plasma pool. These data indicate that Gpx3 does not serve in the regulation of selenium metabolism. The specific binding of a large pool of Gpx3 to basement membranes in the kidney cortex strongly suggests a need for glutathione peroxidase activity in the cortical peritubular space.

Penultimate selenocysteine residue replaced by cysteine in thioredoxin reductase from selenium-deficient rat liver

Selenium is an essential micronutrient for humans and animals, and its deficiency can predispose to the development of pathological conditions. This study evaluates the effect of selenium deficiency on the thioredoxin system, consisting of NADPH, selenoprotein thioredoxin reductase (TrxR), and thioredoxin (Trx); and the glutathione system, including NADPH, glutathione reductase, glutathione, and glutaredoxin coupled with selenoprotein glutathione peroxidase (GPx). We particularly investigate whether inactive truncated TrxR is present under selenium-starvation conditions due to reading of the UGA codon as stop. Feeding rats a selenium-deficient diet resulted in a large decrease in activity of TrxR and GPx in rat liver but not in the levels of Trx1 and Grx1. However, selenium deficiency induced mitochondrial Grx2 10-fold and markedly changed the expression of some flavoproteins that are involved in the cellular folate, glucose, and lipid metabolism. Liver TrxR mRNA was nearly unchanged, but no truncated enzyme was found. Instead, a low-activity form of TrxR with a cysteine substituted for the penultimate selenocysteine in the C-terminal active site was identified in selenium-deficient rat liver. These results show a novel mechanism for decoding the UGA stop codon, inserting cysteine to make a full-length enzyme that may be required for selenium assimilation.

Serum Iron Increases with Acute Inductionof Hepatic Heme Oxygenase-1 in Mice

Heme oxygenase (HO)-1 is induced by oxidative stress and protects against oxidant injury. We examined the effect of rapid induction of hepatic HO-1 on serum iron level. Serum iron was approximately doubled within 6 h when HO-1 was induced by phenobarbital treatment of selenium-deficient mice. Blocking heme synthesis with diethyl 1,4-dihydro-2,4,6-trimethyl-3,5-pyridinedicarboxylate (DDC) prevented the induction of HO-1 and the rise in serum iron. DDC did not block HO-1 induction by hemin. Inhibition of HO activity by tin protoporphyrin prevented a rise in serum iron that occurred following phorone treatment. These results indicate that heme synthesis or an exogenous source of heme is needed to allow induction of HO-1. Further, they link HO-1 induction with a rise in serum iron, suggesting that the iron resulting from catabolism of heme by HO-1 is released by the liver.