Evidence of a sudden increase in α-chloralose poisoning in dogs and cats in the Netherlands between 2018 and 2021

BACKGROUND

After changes in European Union biocide legislation, the Dutch Poisons Information Center observed a strong increase in information requests concerning dogs and cats exposed to α-chloralose. To investigate whether α-chloralose-based rodenticides are safe for non-professional use, additional information regarding poisoning scenarios and clinical course was collected.

METHODS

Veterinarians reporting α-chloralose exposure over a 2.5-year period were contacted by mail for follow-up information concerning exposure scenario, product formulation, clinical course and treatment, and outcome. In total, information was collected for 96 dogs and 41 cats.

RESULTS

Fifty-three of 96 dogs and 17 of 19 cats known to have been exposed to α-chloralose-based rodenticides developed signs of central nervous system (CNS) depression or sensory-induced CNS excitation. Mortality in dogs and cats following exposure was 1% and 18%, respectively. An additional 22 cats presented with clinical signs suggestive of α-chloralose poisoning, with a mortality of 5%.

LIMITATIONS

Exposure to α-chloralose was not confirmed by biochemical analyses.

CONCLUSION

Dogs and especially cats were at risk of poisoning from α-chloralose. If criteria such as acute toxicity and risk of (secondary) poisoning are applied during the approval of α-chloralose-based rodenticides, similar to anticoagulant-based rodenticides, it can be concluded that α-chloralose is also not safe for non-professional use.

Incidence of Vitis fruit-induced clinical signs and acute kidney injury in dogs and cats

OBJECTIVES

To determine the incidence of clinical signs and Vitis fruit-induced acute kidney injury in dogs and cats with a Vitis fruit ingestion reported to the Dutch Poisons Information Center, and a description of the therapies instituted by the veterinarians.

MATERIALS AND METHODS

A prospective surveillance study, data were obtained from veterinarians and pet owners.

RESULTS

Ninety-five dogs and 13 cats with proven Vitis fruit ingestion were included. Fourteen dogs and two cats developed clinical signs: emesis (11/16, 68.8%), lethargy (5/16, 31.3%), diarrhoea (3/16, 18.8%), anorexia (3/16, 18.8%), tremor (2/16, 12.5%) and restlessness (1/16, 6.3%). The overall incidence for developing clinical signs was 14.7% in dogs and 15.4% in cats. One (1/95, 1%) dog developed acute kidney injury after ingestion of Vitis fruit. No cats developed acute kidney injury. Induction of emesis and/or administration of activated charcoal was instituted in 72 of 82 (88%) and eight of 11 (73%) of asymptomatic dogs and cats and six of 14 (43%) and two of two (100%) of symptomatic dogs and cats, respectively. Overall, emesis was induced in 72 of 95 (76%) dogs (100% success rate) and removed Vitis fruits in the majority of cases (98% when induced <4 hours after ingestion and 83% when induced 4 to 12 hours after ingestion). Emesis was induced in seven of 13 (54%) cats (86% success rate) and removed Vitis fruits in 83% of the cases.

CLINICAL SIGNIFICANCE

In this study, a significant proportion (around 15%) of dogs and cats developed clinical signs after ingestion of Vitis fruits, which were predominantly related to the gastrointestinal tract. Symptomatic acute kidney injury was rare. Our findings suggest the use of decontamination measures, i.e. induction of emesis, may be warranted up to 12 hours after ingestion.

Genomic Investigation of Two Acinetobacter baumannii Outbreaks in a Veterinary Intensive Care Unit in The Netherlands

Acinetobacter baumannii is a nosocomial pathogen that frequently causes healthcare-acquired infections. The global spread of multidrug-resistant (MDR) strains with its ability to survive in the environment for extended periods imposes a pressing public health threat. Two MDR A. baumannii outbreaks occurred in 2012 and 2014 in a companion animal intensive care unit (caICU) in the Netherlands. Whole-genome sequencing (WGS) was performed on dog clinical isolates (n = 6), environmental isolates (n = 5), and human reference strains (n = 3) to investigate if the isolates of the two outbreaks were related. All clinical isolates shared identical resistance phenotypes displaying multidrug resistance. Multi-locus Sequence Typing (MLST) revealed that all clinical isolates belonged to sequence type ST2. The core genome MLST (cgMLST) results confirmed that the isolates of the two outbreaks were not related. Comparative genome analysis showed that the outbreak isolates contained different gene contents, including mobile genetic elements associated with antimicrobial resistance genes (ARGs). The time-measured phylogenetic reconstruction revealed that the outbreak isolates diverged approximately 30 years before 2014. Our study shows the importance of WGS analyses combined with molecular clock investigations to reduce transmission of MDR A. baumannii infections in companion animal clinics.

The Effect of the Preoperative Fasting Regimen on the Incidence of Gastro-Oesophageal Reflux in 90 Dogs

Simple Summary

Gastro-oesophageal reflux (GOR), a potential risk during anaesthesia, happens when the stomach contents move up into the oesophagus. The refluxed contents can damage the lining of the oesophagus or the respiratory tract. For many years it was believed that an increase in the stomach contents’ volume increases the risk of GOR. However, more recent studies have demonstrated this to be incorrect. The objective of this study was to compare the effects of three different pre-anaesthetic fasting regimens on the frequency of GOR in dogs under anaesthesia. Ninety dogs undergoing non-abdominal and non-thoracic elective surgery were included in the study and equally allocated to three groups. The results of this study suggest that the administration of a meal 3 h before anaesthesia does not have any beneficial effect in the reduction of GOR incidence in dogs compared to the administration of a meal 12 h before anaesthesia.

Abstract

This study aimed to investigate the effect of three different preoperative fasting regimens on the incidence of gastro-oesophageal reflux (GOR) in dogs under general anaesthesia. Ninety dogs undergoing non-abdominal and non-thoracic elective surgery were included in the study and equally allocated to three groups. Dogs received canned food providing half the daily resting energy requirements (RER) 3 h prior to premedication (group 3H), a quarter of the daily RER 3 h before premedication (group 3Q), and half the daily RER 12 h before premedication (group 12H). The animals were premedicated with acepromazine and pethidine, anaesthesia was induced with propofol and maintained with isoflurane vaporised in oxygen. Oesophageal pH was monitored throughout anaesthesia. Demographic and surgery-related parameters were not different among groups. The incidence of GOR was 11/30 in group 3H (36.7%), 9/30 in group 3Q (30.0%) and 5/30 in group 12H (16.7%), which was not statistically different (p = 0.262). Reduction of the amount of the preoperative meal from half to a quarter of the daily RER did not reduce the incidence of GOR but resulted in a lower oesophageal pH (p = 0.003). The results of this study suggest that the administration of a meal 3 h before anaesthesia does not have any beneficial effect in the reduction of GOR incidence in dogs compared to the administration of a meal 12 h before anaesthesia.

A novel insertion technique for urinary catheters in female dogs with the use of a guidewire

BACKGROUND

Complicated transurethral urinary bladder catheterization in female dogs is a commonly encountered urologic problem, often causing inadvertent trauma to the lower urinary tract and breach in aseptic technique.

KEY CONCEPTS

A novel method for transurethral insertion of urinary catheters in female dogs is described. The main variation from current procedures involves the application of the Seldinger technique with the use of an introduction catheter that is specifically designed to feed into the urethra, and the use of a guidewire to replace the introducer with an indwelling balloon catheter.

SIGNIFICANCE

The technique presented offers a step-by-step approach that could improve success in urinary catheter placement. This modification may facilitate catheter insertion, be less traumatic, and offer better control of asepsis, especially with challenging urethral catheterization. The technique also offers an easy method to replace the catheter. Application of the technique may reduce catheter-associated urinary tract infections as it addresses certain infection-related risk factors. Prospective validation studies are needed to support its advantages over current urinary catheter placement techniques.

Gene expressions of de novo hepatic lipogenesis in feline hepatic lipidosis

Objectives

The aim of this study was to evaluate if de novo hepatic lipid synthesis contributes to fatty acid overload in the liver of cats with feline hepatic lipidosis (FHL).

Methods

Lipogenic gene expression of peroxisome proliferator-activated receptor-alpha (PPAR-α), peroxisome proliferator-activated receptor-gamma (PPAR-γ), fatty acid synthase (FASN) and sterol regulatory element-binding factor (SREBF1) were evaluated using quantitative RT-PCR in liver tissue of six cats with FHL and compared with the liver tissue of eight healthy cats.

Results

In liver tissue, PPAR-α, PPAR-γ and FASN mRNA expression levels were not significantly different (P >0.12, P >0.89 and P >0.5, respectively) in the FHL group compared with the control group. SREBF1 gene expression was downregulated around 10-fold in the FHL group vs the control group (P = 0.039).

Conclusions and relevance

The downregulation of SREBF1 in the liver tissue of cats with FHL does not support the hypothesis that de novo lipogenesis in the liver is an important pathway of fatty acid accumulation in FHL.

Immunohistochemical characterisation of the hepatic stem cell niche in feline hepatic lipidosis: a preliminary morphological study

OBJECTIVES

The aim of this study was to describe the cellular and stromal components of the hepatic progenitor cell niche in feline hepatic lipidosis (FHL).

METHODS

Immunohistochemical staining for the progenitor/bile duct marker (K19), activated Kupffer cells (MAC387), myofibroblasts (alpha-smooth muscle actin [α-SMA]) and the extracellular matrix component laminin were used on seven liver biopsies of cats with FHL and three healthy cats. Double immunofluorescence stainings were performed to investigate co-localisation of different cell types in the hepatic progenitor cell (HPC) niche.

RESULTS

HPCs, Kupffer cells, myofibroblasts and laminin deposition were observed in the liver samples of FHL, although with variability in the expression and positivity of the different immunostainings between different samples. When compared with the unaffected cats where K19 positivity and minimal α-SMA and laminin positivity were seen mainly in the portal area, in the majority of FHL samples K19 and α-SMA-positive cells and laminin positivity were seen also in the periportal and parenchymatous area. MAC387-positive cells were present throughout the parenchyma.

CONCLUSIONS AND RELEVANCE

This is a preliminary morphological study to describe the activation and co-localisation of components of the HPC niche in FHL. Although the HPC niche in FHL resembles that described in hepatopathies in dogs and in feline lymphocytic cholangitis, the expression of K19, α-SMA, MAC387 and lamin is more variable in FHL, and a common pattern of activation could not be established. Nevertheless, when HPCs were activated, a spatial association between HPCs and their niche could be demonstrated.

Negative pressure therapy versus passive open abdominal drainage for the treatment of septic peritonitis in dogs: A randomized, prospective study

OBJECTIVE

To compare passive open abdominal drainage (POAD) and negative-pressure abdominal drainage (NPAD) using the ABThera™ system in the treatment of septic peritonitis.

STUDY DESIGN

Randomized prospective clinical trial.

ANIMALS

Dogs (n = 16) with septic peritonitis.

METHODS

Dogs with septic peritonitis were randomly assigned to one of two treatment protocols: NPAD versus POAD. Anesthesia time, operating time, duration of drainage, costs, survival, and complications were compared between techniques. Hematological and biochemical parameters in blood and abdominal fluid, and histopathological findings of omentum and abdominal wall tissue samples were compared between NPAD and POAD at time of initial surgery and at time of closure.

RESULTS

Overall survival was 81%. Treatment costs, anesthesia and operating time, drainage time, survival, and postoperative complications were similar between techniques. Loss of total plasma protein and decreased inflammation-related factors in abdominal fluid at time of closure were noted in all patients. Neutrophilic inflammation was greater in abdominal wall samples after NPAD. POAD patients showed discomfort during bandage changes and had frequent leakage of abdominal fluid outside of the bandage.

CONCLUSION

NPAD is an effective alternative to POAD for treatment of septic peritonitis, based on costs and survival. NPAD resulted in less abdominal fluid leakage, and evidence of superior healing on histological evaluation of abdominal tissues.

Sex specific differences in hepatic and plasma lipid profiles in healthy cats pre and post spaying and neutering: relationship with feline hepatic lipidosis

BACKGROUND

A link between lipid metabolism and disease has been recognized in cats. Since hepatic lipidosis is a frequent disorder in cats, the aim of the current study was to evaluate liver and plasma lipid dimorphism in healthy cats and the effects of gonadectomy on lipid profiling. From six female and six male cats plasma and liver lipid profiles before and after spaying/neutering were assessed and compared to five cats (three neutered male and two spayed female) diagnosed with hepatic lipidosis.

RESULTS

Intact female cats had a significantly lower level of plasma triacylglycerides (TAG) and a higher liver level of the long chain polyunsaturated fatty acid arachidonic acid (AA) compared to their neutered state. Both male and female cats with lipidosis had a higher liver, but not plasma TAG level and an increased level of plasma and liver sphingomyelin compared to the healthy cats.

CONCLUSION

Although lipid dimorphism in healthy cats resembles that of other species, intact female cats show differences in metabolic configuration that could predispose them to develop hepatic lipidosis. The increased sphingomyelin levels in cats with lipidosis could suggest a potential role in the pathogenesis of hepatic lipidosis in cats.

SUCNR1-mediated chemotaxis of macrophages aggravates obesity-induced inflammation and diabetes

AIMS/HYPOTHESIS

Obesity induces macrophages to drive inflammation in adipose tissue, a crucial step towards the development of type 2 diabetes. The tricarboxylic acid (TCA) cycle intermediate succinate is released from cells under metabolic stress and has recently emerged as a metabolic signal induced by proinflammatory stimuli. We therefore investigated whether succinate receptor 1 (SUCNR1) could play a role in the development of adipose tissue inflammation and type 2 diabetes.

METHODS

Succinate levels were determined in human plasma samples from individuals with type 2 diabetes and non-diabetic participants. Succinate release from adipose tissue explants was studied. Sucnr1 ^-/- and wild-type (WT) littermate mice were fed a high-fat diet (HFD) or low-fat diet (LFD) for 16 weeks. Serum metabolic variables, adipose tissue inflammation, macrophage migration and glucose tolerance were determined.

RESULTS

We show that hypoxia and hyperglycaemia independently drive the release of succinate from mouse adipose tissue (17-fold and up to 18-fold, respectively) and that plasma levels of succinate were higher in participants with type 2 diabetes compared with non-diabetic individuals (+53%; p < 0.01). Sucnr1 ^-/- mice had significantly reduced numbers of macrophages (0.56 ± 0.07 vs 0.92 ± 0.15 F4/80 cells/adipocytes, p < 0.05) and crown-like structures (0.06 ± 0.02 vs 0.14 ± 0.02, CLS/adipocytes p < 0.01) in adipose tissue and significantly improved glucose tolerance (p < 0.001) compared with WT mice fed an HFD, despite similarly increased body weights. Consistently, macrophages from Sucnr1 ^-/- mice showed reduced chemotaxis towards medium collected from apoptotic and hypoxic adipocytes (-59%; p < 0.05).

CONCLUSIONS/INTERPRETATION

Our results reveal that activation of SUCNR1 in macrophages is important for both infiltration and inflammation of adipose tissue in obesity, and suggest that SUCNR1 is a promising therapeutic target in obesity-induced type 2 diabetes.

DATA AVAILABILITY

The dataset generated and analysed during the current study is available in GEO with the accession number GSE64104, www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE64104 .

Evaluation of a virtual pet visit system with live video streaming of patient images over the Internet in a companion animal intensive care unit in the Netherlands

OBJECTIVE

To evaluate the impact of a virtual pet visit system ("TelePet" System, TPS) on owners and staff of a companion animal ICU.

DESIGN

Longitudinal interventional study (2010-2013).

SETTING

Companion animal ICU at a university veterinary medical teaching hospital.

STUDY POPULATIONS

Pet owners, ICU technicians.

INTERVENTIONS

The introduction of the TPS, with live video streaming of patient images over the Internet, in a companion animal ICU.

MEASUREMENTS AND MAIN RESULTS

Pet owners experienced TPS as a valuable extra service. Most TPS users (72.4%) experienced less anxiety and felt less need (40.4% of TPS users) to visit their hospitalized pet in person. Most users (83.5%) shared TPS access with their family. The introduction of the TPS did not improve overall owner satisfaction, except for the score on "quality of medical treatment." Seven of 26 indicators of owner satisfaction were awarded higher scores by TPS users than by TPS nonusers in the survey after the introduction of the system. However, the lack of randomization of owners might have influenced findings. The enthusiasm of the ICU technicians for the system was tempered by the negative feedback from a small number of owners. Nevertheless they recognized the value of the system for owners. The system was user friendly and ICU staff and TPS users experienced few technical problems.

CONCLUSIONS

As veterinary healthcare is moving toward a more client-centered approach, a virtual pet visit system, such as TPS, is a relatively simple application that may improve the well-being of most owners during the hospitalization of their pet.

No up-regulation of the phosphatidylethanolamine N-methyltransferase pathway and choline production by sex hormones in cats

BACKGROUND

Feline hepatic lipidosis (FHL) is a common cholestatic disease affecting cats of any breed, age and sex. Both choline deficiency and low hepatic phosphatidylethanolamine N-methyltransferase (PEMT) activity are associated with hepatic lipidosis (HL) in humans, mice and rats. The PEMT expression is known to be upregulated by oestrogens, protecting the females in these species from the development of HL when exposed to choline deficient diets. The aim of the present study was to evaluate the influence of sex hormones on choline synthesis via the PEMT pathway in healthy male and female cats before and after spaying/neutering, when fed a diet with recommended dietary choline content.

RESULTS

From six female and six male cats PEMT activity was assayed directly in liver biopsies taken before and after spaying/neutering, and assessed indirectly by analyses of PEMT-specific hepatic phosphatidylcholine (PC) species and plasma choline levels. Hepatic PEMT activity did not differ between intact female and male cats and no changes upon spaying/neutering were observed. Likewise, no significant differences in liver PC content and PEMT-specific polyunsaturated PC species were found between the sexes and before or after spaying/neutering.

CONCLUSION

These results suggest that choline synthesis in cats differs from what is observed in humans, mice and rats. The lack of evident influence of sex hormones on the PEMT pathway makes it unlikely that spaying/neutering predisposes cats for HL by causing PC deficiency as suggested in other species.

Intellectual disability and bleeding diathesis due to deficient CMP--sialic acid transport

OBJECTIVE

To identify the underlying genetic defect in a patient with intellectual disability, seizures, ataxia, macrothrombocytopenia, renal and cardiac involvement, and abnormal protein glycosylation.

METHODS

Genetic studies involved homozygosity mapping by 250K single nucleotide polymorphism array and SLC35A1 sequencing. Functional studies included biochemical assays for N-glycosylation and mucin-type O-glycosylation and SLC35A1-encoded cytidine 5'-monophosphosialic acid (CMP-sialic acid) transport after heterologous expression in yeast.

RESULTS

We performed biochemical analysis and found combined N- and O-glycosylation abnormalities and specific reduction in sialylation in this patient. Homozygosity mapping revealed homozygosity for the CMP-sialic acid transporter SLC35A1. Mutation analysis identified a homozygous c.303G > C (p.Gln101His) missense mutation that was heterozygous in both parents. Functional analysis of mutant SLC35A1 showed normal Golgi localization but 50% reduction in transport activity of CMP-sialic acid in vitro.

CONCLUSION

We confirm an autosomal recessive, generalized sialylation defect due to mutations in SLC35A1. The primary neurologic presentation consisting of ataxia, intellectual disability, and seizures, in combination with bleeding diathesis and proteinuria, is discriminative from a previous case described with deficient sialic acid transporter. Our study underlines the importance of sialylation for normal CNS development and regular organ function.

Mechanism and function of Drosophila capa GPCR: a desiccation stress-responsive receptor with functional homology to human neuromedinU receptor

The capa peptide receptor, capaR (CG14575), is a G-protein coupled receptor (GPCR) for the D. melanogaster capa neuropeptides, Drm-capa-1 and -2 (capa-1 and -2). To date, the capa peptide family constitutes the only known nitridergic peptides in insects, so the mechanisms and physiological function of ligand-receptor signalling of this peptide family are of interest. Capa peptide induces calcium signaling via capaR with EC₅₀ values for capa-1 = 3.06 nM and capa-2 = 4.32 nM. capaR undergoes rapid desensitization, with internalization via a b-arrestin-2 mediated mechanism but is rapidly re-sensitized in the absence of capa-1. Drosophila capa peptides have a C-terminal -FPRXamide motif and insect-PRXamide peptides are evolutionarily related to vertebrate peptide neuromedinU (NMU). Potential agonist effects of human NMU-25 and the insect -PRLamides [Drosophila pyrokinins Drm-PK-1 (capa-3), Drm-PK-2 and hugin-gamma [hugg]] against capaR were investigated. NMU-25, but not hugg nor Drm-PK-2, increases intracellular calcium ([Ca²⁺]i) levels via capaR. In vivo, NMU-25 increases [Ca²⁺]i and fluid transport by the Drosophila Malpighian (renal) tubule. Ectopic expression of human NMU receptor 2 in tubules of transgenic flies results in increased [Ca²⁺]i and fluid transport. Finally, anti-porcine NMU-8 staining of larval CNS shows that the most highly immunoreactive cells are capa-producing neurons. These structural and functional data suggest that vertebrate NMU is a putative functional homolog of Drm-capa-1 and -2. capaR is almost exclusively expressed in tubule principal cells; cell-specific targeted capaR RNAi significantly reduces capa-1 stimulated [Ca²⁺]i and fluid transport. Adult capaR RNAi transgenic flies also display resistance to desiccation. Thus, capaR acts in the key fluid-transporting tissue to regulate responses to desiccation stress in the fly.

Succinate receptors in the kidney

The G protein-coupled succinate and α-ketoglutarate receptors are closely related to the family of P2Y purinoreceptors. Although the α-ketoglutarate receptor is almost exclusively expressed in the kidney, its function is unknown. In contrast, the succinate receptor, SUCRN1, is expressed in a variety of tissues, including blood cells, adipose tissue, liver, retina, and the kidney. Recent evidence suggests SUCRN1 and its succinate ligand are novel detectors of local stress, including ischemia, hypoxia, toxicity, and hyperglycemia. Local levels of succinate in the kidney also activate the renin-angiotensin system and together with SUCRN1 may play a key role in the development of hypertension and the complications of diabetes mellitus, metabolic disease, and liver damage. This makes the succinate receptor a promising drug target to counteract an expanding number of interrelated disorders.

Novel mutation in the AVPR2 gene in a Danish male with nephrogenic diabetes insipidus caused by ER retention and subsequent lysosomal degradation of the mutant receptor

Mutations in the arginine vasopressin receptor 2 (AVPR2) gene can cause X-linked nephrogenic diabetes insipidus (NDI) characterized by the production of large amounts of urine and an inability to concentrate urine in response to the antidiuretic hormone vasopressin. We have identified a novel mutation in the AVPR2 gene (L170P) located in the fourth transmembrane domain in a Danish NDI male. Analysis of the mutant receptor in Madin-Darby Canine Kidney cell culture revealed that AVPR2-L170P was retained in the endoplasmic reticulum, and the expression was dramatically downregulated compared to wild-type AVPR2. Inhibition of the lysosome resulted in increased intracellular accumulation of AVPR2-L170P, indicating that AVPR2-L170P is downregulated via the lysosome. Inhibition of the proteasome resulted in plasma membrane localization of AVPR2-L170P, although the overall levels of AVPR2-L170P were unchanged.

Counteracting vasopressin-mediated water reabsorption by ATP, dopamine, and phorbol esters: mechanisms of action

Water homeostasis is regulated by a wide variety of hormones. When in need for water conservation, vasopressin, released from the brain, binds renal principal cells and initiates a signaling cascade resulting in the insertion of aquaporin-2 (AQP2) water channels in the apical membrane and water reabsorption. Conversely, hormones, including extracellular purines and dopamine, antagonize AVP-induced water permeability, but their mechanism of action is largely unknown, which was investigated here. Addition of these hormones to mpkCCD cells decreased total and plasma membrane abundance of AVP-induced AQP2, partly by increasing its internalization to vesicles and lysosomal degradation. This internalization was ubiquitin dependent, because the hormones increased AQP2 ubiquitination, and the plasma membrane localization of AQP2-K270R, which cannot be monoubiquitinated, was unaffected by these hormones. Both hormones also increased AQP2 phosphorylation at S261, which followed ubiquitination, but was not essential for hormone-induced AQP2 degradation. A similar process occurs in vivo, as incubation of dDAVP-treated kidney slices with both hormones also resulted in the internalization and S261 phosphorylation of AQP2. Both hormones also reduced cAMP and AQP2 mRNA levels, suggesting an additional effect on AQP2 gene transcription. Interestingly, phorbol esters only reduced AQP2 through the first pathway. Together, our results indicate that ATP and dopamine counteract AVP-induced water permeability by increasing AQP2 degradation in lysosomes, preceded by ubiquitin-dependent internalization, and by decreasing AQP2 gene transcription by reducing the AVP-induced cAMP levels.

Autosomal recessive mental retardation, deafness, ankylosis, and mild hypophosphatemia associated with a novel ANKH mutation in a consanguineous family

CONTEXT

Mutations in ANKH cause the highly divergent conditions familial chondrocalcinosis and craniometaphyseal dysplasia. The gene product ANK is supposed to regulate tissue mineralization by transporting pyrophosphate to the extracellular space.

OBJECTIVE

We evaluated several family members of a large consanguineous family with mental retardation, deafness, and ankylosis. We compared their skeletal, metabolic, and serological parameters to that of the autosomal recessive progressive ankylosis (ank) mouse mutant, caused by a loss-of-function mutation in the murine ortholog Ank.

PARTICIPANTS

The studied patients had painful small joint soft-tissue calcifications, progressive spondylarthropathy, osteopenia, mild hypophosphatemia, mixed hearing loss, and mental retardation.

RESULTS

After mapping the disease gene to 5p15, we identified the novel homozygous ANK missense mutation L244S in all patients. Although L244 is a highly conserved amino acid, the mutated ANK protein was detected at normal levels at the plasma membrane in primary patient fibroblasts. The phenotype was highly congruent with the autosomal recessive progressive ankylosis (ank) mouse mutant. This indicates a loss-of-function effect of the L244S mutation despite normal ANK protein expression. Interestingly, our analyses revealed that the primary step of joint degeneration is fibrosis and mineralization of articular soft tissues. Moreover, heterozygous carriers of the L244S mutation showed mild osteoarthritis without metabolic alterations, pathological calcifications, or central nervous system involvement.

CONCLUSION

Beyond the description of the first human progressive ankylosis phenotype, our results indicate that ANK influences articular soft tissues commonly involved in degenerative joint disorders. Furthermore, this human disorder provides the first direct evidence for a role of ANK in the central nervous system.

Regulation of AQP2 localization by S256 and S261 phosphorylation and ubiquitination

Vasopressin-induced water reabsorption coincides with phosphorylation of aquaporin-2 (AQP2) at S256 (pS256), dephosphorylation at S261, and its translocation to the apical membrane, whereas treatment with the phorbol ester 12-tetradecanoylphorbol-13-acetate (TPA) induces AQP2 ubiquitination at K270, its internalization, and lysosomal degradation. In this study we investigated the relationship between S256 and S261 phosphorylation in AQP2 and its ubiquitination and trafficking in MDCK cells. Forskolin stimulation associated with increased pS256 and decreased pS261 AQP2, indicating that MDCK cells are a good model. After forskolin stimulation, TPA-induced ubiquitination of AQP2 preceded phosphorylation of AQP2 at S261, which in the first instance occurred predominantly on ubiquitinated AQP2. Forskolin-induced changes in pS261 were also observed for AQP2-S256A and AQP2-S256D, which constitutively localize in vesicles and the apical membrane, respectively. Although pS261 varies with forskolin as with wild-type AQP2, AQP2-S256A is not increased in its ubiquitination. Our data reveal that pS261 occurred independently of AQP2 localization and suggest that pS261 follows ubiquitination and endocytosis and may stabilize AQP2 ubiquitination and intracellular localization. The absence of increased ubiquitination of AQP2-S256A indicates that its intracellular location is due to the lack of pS256. Furthermore, AQP2-S261A and AQP2-S261D localized to vesicles, which was due to their increased ubiquitination, because changing K270 into Arg in both mutants resulted in their localization in the apical membrane. Although still increased in its ubiquitination, AQP2-S256D-S261D localized in the apical membrane. AQP2-S256D-K270R-Ub, however, localized to intracellular vesicles. Although our localization of AQP2-S261A/D is different from that of others, these data indicate that constitutive S256 phosphorylation counterbalances S261D-induced ubiquitination and internalization or changes its structure to allow distribution to the apical membrane. The vesicular localization of AQP2-S256D-K270R-Ub, however, indicates that the dominant apical sorting of S256D can again be overruled by constitutive ubiquitination. These data indicate that the membrane localization of AQP2 is determined by the balance of the extents of phosphorylation and ubiquitination.

Functional variation in the arginine vasopressin 2 receptor as a modifier of human plasma von Willebrand factor levels

SUMMARY OBJECTIVES

Stimulation of arginine vasopressin 2 receptor (V2R) with arginine vasopressin (AVP) results in a rise in von Willebrand factor (VWF) and factor VIII plasma levels. We hypothesized that gain-of-function variations in the V2R gene (AVPR2) would lead to higher plasma levels of VWF and FVIII.

METHODS AND RESULTS

We genotyped the control populations of two population-based studies for four AVPR2 variations: a-245c, G12E, L309L, and S331S. Rare alleles of a-245c, G12E, and S331S, which were in linkage disequilibrium, were associated with higher VWF propeptide, VWF and FVIII levels. The functionality of the G12E variant was studied in stably transfected MDCKII cells, expressing constructs of either 12G-V2R or 12E-V2R. Both V2R variants were fully glycosylated and expressed on the basolateral membrane. The binding affinity of V2R for AVP was increased three-fold in 12E-V2R-green fluorescent protein (GFP) cells, which is in accordance with increased levels of VWF propeptide associated with the 12E variant. The dissociation constant (K(D)) was 4.5 nm [95% confidence interval (CI) 3.6-5.4] for 12E-V2R-GFP and 16.5 nm (95% CI 10.1-22.9) for 12G-V2R-GFP. AVP-induced cAMP generation was enhanced in 12E-V2R-GFP cells.

CONCLUSIONS

The 12E-V2R variant has increased binding affinity for AVP, resulting in increased signal transduction, and is associated with increased levels of VWF propeptide, VWF, and FVIII.

Potential of nonpeptide (ant)agonists to rescue vasopressin V2 receptor mutants for the treatment of X-linked nephrogenic diabetes insipidus

According to the body's need, water is reabsorbed from the pro-urine that is formed by ultrafiltration in the kidney. This process is regulated by the antidiuretic hormone arginine-vasopressin (AVP), which binds to its type 2 receptor (V2R) in the kidney. Mutations in the gene encoding the V2R often lead to the X-linked inheritable form of nephrogenic diabetes insipidus (NDI), a disorder in which patients are unable to concentrate their urine despite the presence of AVP. Many of these mutations are missense mutations that do not interfere with the intrinsic functionality of V2R, but cause its retention in the endoplasmic reticulum (ER), making it unavailable for AVP binding. Because the current treatments for NDI relieve its symptoms to some extent, but do not cure the disorder, cell-permeable antagonists (pharmacological chaperones) have been successfully used to stabilise the mutant receptors and restore their plasma membrane localisation. Recently, cell-permeable agonists also were shown to rescue ER-retained V2R mutants, leading to increased cAMP levels and translocation of aquaporin-2 to the apical membrane. This makes V2R-specific cell-permeable agonists very promising therapeutics for NDI as a result of misfolded V2R receptors.

Effect of the cGMP pathway on AQP2 expression and translocation: potential implications for nephrogenic diabetes insipidus

BACKGROUND

Arginine vasopressin (AVP) binding to the V2 receptor (V2R) in renal collecting duct principal cells induces a cAMP signalling cascade resulting in the activation of protein kinase A (PKA), translocation of aquaporin-2 (AQP2) to the apical membrane and an increase in AQP2 expression. Consequently, concentration of urine is initiated. X-linked nephrogenic diabetes insipidus (NDI), characterized by the inability to concentrate urine in response to AVP, is caused by mutations in the V2R gene. Initiation of AQP2 translocation, while circumventing the V2R-cAMP-PKA pathway has been suggested as a putative therapy for these patients. In this respect, the activation of a cAMP-independent and cGMP-dependent pathway for AQP2 membrane insertion by different cyclic guanosine monophosphate (cGMP) pathway activators, such as atrial natriuretic peptide (ANP), l-arginine and 8-bromoguanosine 3',5'-cyclic monophosphate (8-Br-cGMP), has been put forward. However, it is unclear whether they can increase AQP2 expression.

METHODS

Mouse cortical collecting duct (mpkCCD) cells were incubated with ANP, l-arginine and 8-Br-cGMP for 2 h and subjected to immunocytochemistry and cell surface biotinylation assays to examine their effect on AQP2 translocation. To test the effect of cGMP pathway activators on AQP2 expression, the mpkCCD cells were treated with dDAVP, ANP and l-arginine for 4 days, or with 8-Br-cGMP for the last day. AQP2 protein levels were determined by immunoblotting.

RESULTS

ANP, l-arginine and 8-Br-cGMP induced the translocation of AQP2 in the mpkCCD cells. However, in contrast to dDAVP, ANP, l-arginine and 8-Br-cGMP did not increase the expression of AQP2.

CONCLUSIONS

Our results suggest that while activators of the cGMP pathway are likely beneficial in the treatment of X-linked NDI, their ability to relieve NDI in the patients may be improved when combined with agents stimulating AQP2 expression.

Clinical evaluation of the efficacy and safety of a constant rate infusion of dexmedetomidine for postoperative pain management in dogs

OBJECTIVE

To compare postoperative analgesia provided by a constant rate infusion (CRI) of dexmedetomidine (DMED) to that of a well-established positive control [morphine (MOR)] in critically ill dogs. The sedative, cardiorespiratory effects and clinical safety of a 24-hour DMED CRI were also evaluated.

STUDY DESIGN

Prospective, randomised, blinded, positive-controlled parallel-group clinical study.

ANIMALS

Forty hospitalised, client-owned dogs requiring post-operative pain management after invasive surgery.

METHODS

After surgery, a loading dose of either DMED (25 microg m(-2)) or MOR (2500 microg m(-2)) followed by a 24-hour CRI of DMED (25 microg m(-2) hour(-1)) or MOR (2500 microg m(-2) hour(-1)) was administered. Pain was measured using the Short Form of the Glasgow Composite Measure Pain Scale, sedation and physiological variables were scored at regular intervals. Animals considered to be painful received rescue analgesia and were allocated to a post-rescue protocol; animals which were unresponsive to rescue analgesia were removed from the study. Data were analysed with anova, two-sample t-tests or Chi-square tests. Time to intervention was analysed with Kaplan-Meier methodology.

RESULTS

Forty dogs were enrolled. Twenty dogs (9 DMED and 11 MOR) did not require rescue analgesia. Eleven DMED and eight MOR dogs were allocated to the post-rescue protocol and seven of these removed from the study. Significant differences in pain scores between groups were not observed during the first 12 hours, however, DMED dogs were less (p = 0.009) painful during the last 12 hours. Sedation score over the entire 24-hour study was not significantly different between groups. CONCLUSION / CLINICAL RELEVANCE: Dexmedetomidine CRI was equally effective as MOR CRI at providing postoperative analgesia and no clinically significant adverse reactions were noted. This study shows the potential of DMED to contribute to a balanced postoperative analgesia regimen in dogs.

LIP5 interacts with aquaporin 2 and facilitates its lysosomal degradation

Vasopressin binding to the V2 receptor in renal principal cells leads to activation of protein kinase A, phosphorylation of aquaporin 2 (AQP2) at Ser256, and the translocation of AQP2 to the apical membrane, resulting in concentration of the urine. In contrast, phorbol ester-induced activation of protein kinase C pathway leads to ubiquitination of AQP2 at Lys270 and its internalization to multivesicular bodies, where it is targeted for lysosomal degradation or stored for recycling. Because little is known about the regulation of AQP2 trafficking, we used the carboxy-terminal tail of constitutively nonphosphorylated AQP2 (S256A) as a bait for interacting proteins in a yeast two-hybrid assay. We isolated lysosomal trafficking regulator-interacting protein 5 (LIP5) and found that LIP5 interacted with the proximal carboxy-terminal tail (L230-D243) of AQP2 in vitro but not with AQP3 or AQP4, which are also expressed in principal cells. Immunohistochemistry revealed that LIP5 co-localized with AQP2 in principal cells. LIP5 binding occurred independent of the state of Ser256 phosphorylation or Lys270 ubiquitination. LIP5 has been shown to facilitate degradation of the EGF receptor; here, LIP5 seemed to bind this receptor. Knockdown of LIP5 in mouse renal cells (mpkCCD) reduced the phorbol ester-induced degradation of AQP2 approximately two-fold. In summary, LIP5 binds cargo proteins and, considering the role of LIP5 in protein sorting to multivesicular bodies, plays a role in the degradation of AQP2, possibly by reducing the formation of late endosomes.

SLC29A3 gene is mutated in pigmented hypertrichosis with insulin-dependent diabetes mellitus syndrome and interacts with the insulin signaling pathway

Pigmented hypertrichotic dermatosis with insulin-dependent diabetes (PHID) syndrome is a recently described autosomal recessive disorder associated with predominantly antibody negative, insulin-dependent diabetes mellitus. In order to identify the genetic basis of PHID and study its relationship with glucose metabolism, we performed homozygosity mapping in five unrelated families followed by candidate gene sequencing. Five loss-of-function mutations were identified in the SLC29A3 gene which encodes a member of a highly conserved protein family that transports nucleosides, nucleobases and nucleoside analogue drugs, hENT3. We show that PHID is allelic with a related syndrome without diabetes mellitus, H syndrome. The interaction of SLC29A3 with insulin signaling pathways was then studied using an established model in Drosophila melanogaster. Ubiquitous knockdown of the Drosophila ortholog of hENT3, dENT1 is lethal under stringent conditions; whereas milder knockdown induced scutellar bristle phenotypes similar to those previously reported in the knockdown of the Drosophila ortholog of the Islet gene. A cellular growth assay showed a reduction of cell size/number which could be rescued or enhanced by manipulation of the Drosophila insulin receptor and its downstream signaling effectors, dPI3K and dAkt. In summary, inactivating mutations in SLC29A3 cause a syndromic form of insulin-dependent diabetes in humans and in Drosophila profoundly affect cell size/number through interactions with the insulin signaling pathway. These data suggest that further investigation of the role of SLC29A3 in glucose metabolism is a priority for diabetes research.

Water in health and disease: new aspects of disturbances in water metabolism

Vasopressin is a critical regulator of water homeostasis. There are two major receptors for vasopressin: V1 and V2 receptors. Disturbances in water balance are commonly encountered in clinical practice and can be divided into disorders of urinary dilution and concentration. The major representatives of such disorders are diabetes insipidus and the syndrome of inappropriate secretion of antidiuretic hormone (SI ADH). Recent studies show that genetic forms of nephrogenic diabetes insipidus are due to mutations in the genes coding for the vasopressin V2 receptor (V2R) or aquaporin-2 (AQP2). Identification of the genes involved and analysis of the cellular fate of the V2R and AQP2 mutants are relevant for understanding the functioning of the V2R and AQP2 protein. These developments also have implications for future therapeutic options. The development of nonpeptide vasopressin receptor antagonists (VRAs) offers prospects for the treatment of euvolaemic (SI ADH) or hypervolaemic hyponatraemia (congestive heart failure or cirrhosis). Several nonpeptide VRAs are now in various stages of clinical trials. At present, only conivaptan is registered by the FD A for intravenous treatment of euvolaemic and hypervolaemic hyponatremia. A recent long-term study comparing tolvaptan with placebo in patients with chronic heart failure showed no reduction in risk of death and hospitalisation.

Pharmacological chaperones in nephrogenic diabetes insipidus: possibilities for clinical application

The antidiuretic hormone arginine-vasopressin regulates water homeostasis in the human body by binding to its vasopressin type 2 receptor (V2R). Mutations in AVPR2, the gene encoding V2R, lead to the X-linked congenital form of nephrogenic diabetes insipidus (NDI), a disease characterized by the inability to concentrate urine in response to vasopressin; often this involves missense mutations or deletion of one or a few amino acids. In vitro V2R expression studies revealed that the function of most of these receptors is not disturbed, but due to their misfolding, the quality control mechanism of the endoplasmic reticulum (ER) retains these receptors inside the cell, thereby preventing their functioning at the plasma membrane. This review summarizes our current knowledge on ER retention of V2R mutants, and describes the different approaches that have been undertaken to restore the plasma membrane expression and function of V2R mutants in NDI in vitro and in vivo. The use of cell permeable receptor ligands (called 'pharmacological chaperones') appears promising for the treatment of NDI in a subset of patients.

Insulin sensitivity and beta-cell function in healthy cats: assessment with the use of the hyperglycemic glucose clamp

A hyperglycemic clamp (HGC) was developed for use in conscious cats. In 21 healthy, normal glucose tolerant cats glucose disposal rate (M), insulin sensitivity (ISI (HGC)), and beta-cell response (I) at arterial plasma glucose of 9 mmol.l (-1) were measured. The HGC was tolerated well and steady state glucose infusion was achieved. Compared to values reported for humans, M values for the cats were low, which appeared to relate to both a low ISI (HGC) and a low I. HGC measures correlated with fasting plasma glucose and insulin concentrations as well as with their HOMA (homeostasis model assessment) and QUICKI (quantitative insulin sensitivity check index) counterparts. Also, I and ISI (HGC) correlated with their counterparts derived from intravenous glucose tolerance tests. In conclusion, this is the first report of hyperglycemic glucose clamping in cats. The procedure (HGC) allows for measurements of glucose disposal, beta-cell response and insulin sensitivity. Compared to human data, both insulin sensitivity and insulin secretion appeared to be low in cats. This is compatible with the carnivorous nature of this species, for which insulin resistance would be advantageous during periods of restricted food availability.

Relief of Nocturnal Enuresis by Desmopressin Is Kidney and Vasopressin Type 2 Receptor Independent

Primary nocturnal enuresis (PNE) is a common problem in childhood and adolescence. Although various treatments are highly effective, a common underlying hypothesis on the pathogenesis is lacking. The success of desmopressin, a synthetic analogue of the antidiuretic hormone vasopressin, has been attributed to increased renal water reabsorption that is mediated by activation of the renal vasopressin V2 receptor (V2R). However, this effect does not explain other symptoms of PNE, such as the failure to arouse upon bladder distension. This study identified a family in which one child displayed PNE and coexisting nephrogenic diabetes insipidus, as a result of a novel nonsense mutation in the V2R gene (C358X). Cell-biologic investigations revealed that V2R-C358X is retained in the endoplasmic reticulum and is unstable, which explains his nephrogenic diabetes insipidus. Consistently, extrarenal V2R-mediated responses were absent in the patient who was treated with desmopressin. Administration of desmopressin, however, changed his PNE into nocturia, because he now still voided unchanged high urinary volumes at night but woke up and went to the bathroom. Withdrawal of desmopressin was accompanied by bedwetting, whereas reintroduction again relieved the symptoms. Therefore, these data indicate that neither a functioning renal concentration system nor a functional V2R is needed for the therapeutic benefit of desmopressin in PNE. Rather, it suggests that another vasopressin receptor and other organ(s) is the target for desmopressin to relieve PNE.

Cell biological aspects of the vasopressin type-2 receptor and aquaporin 2 water channel in nephrogenic diabetes insipidus

In the renal collecting duct, water reabsorption is regulated by the antidiuretic hormone vasopressin (AVP). Binding of this hormone to the vasopressin V2 receptor (V2R) leads to insertion of aquaporin-2 (AQP2) water channels in the apical membrane, thereby allowing water reabsorption from the pro-urine to the interstitium. The disorder nephrogenic diabetes insipidus (NDI) is characterized by the kidney's inability to concentrate pro-urine in response to AVP, which is mostly acquired due to electrolyte disturbances or lithium therapy. Alternatively, NDI is inherited in an X-linked or autosomal fashion due to mutations in the genes encoding V2R or AQP2, respectively. This review describes the current knowledge of the cell biological causes of NDI and how these defects may explain the patients' phenotypes. Also, the increased understanding of these cellular defects in NDI has opened exciting initiatives in the development of novel therapies for NDI, which are extensively discussed in this review.

Functional rescue of vasopressin V2 receptor mutants in MDCK cells by pharmacochaperones: relevance to therapy of nephrogenic diabetes insipidus

Intracellular retention of a functional vasopressin V2 receptor (V2R) is a major cause of congenital nephrogenic diabetes insipidus (NDI) and rescue of V2R mutants by nonpeptide antagonists may restore their basolateral membrane (BM) localization and function. However, the criteria for efficient functional rescue of G protein-coupled receptor (GPCR) mutants at clinically feasible antagonist concentrations are unknown. We found that the four nonpeptide antagonists SR49059, OPC31260, OPC41061, and SR121463B induced maturation and rescued the BM expression of eight of nine different V2R mutants, stably expressed in physiologically relevant polarized cells. The extent of maturation and rescued BM expression correlated with the antagonists' concentration and affinity for the V2R. Displacement of the antagonists by AVP and subsequent cAMP generation inversely correlated with the antagonists' affinities for the V2R but is partially influenced by antagonist-specific aspects. Despite limited increases in maturation and cell-surface expression of V2R mutants, the low-affinity SR49059 optimally induced functional rescue at high concentrations, due to its easy displacement by vasopressin. At clinically feasible antagonist concentrations, however, only the high-affinity antagonists OPC31260 and OPC41061 induced functional rescue, as at these concentrations the extent of BM expression became limited. In conclusion, functional rescue of mutant V2Rs at clinically feasible concentrations is most effective with high-affinity antagonists. As OPC31260 and OPC41061 are clinically safe, they are promising candidates to relieve NDI. Moreover, as numerous other diseases are caused by endoplasmic reticulum-retained GPCRs for which cell-permeable antagonists become available, our finding that high-affinity antagonists are superior is anticipated to be important for pharmacotherapy development of these diseases.

Aldosterone-to-renin and cortisol-to-adrenocorticotropic hormone ratios in healthy dogs and dogs with primary hypoadrenocorticism

In dogs with primary hypoadrenocorticism, hypocortisolism and hypoaldosteronism usually are present, but these deficiencies also may occur in isolated forms. The diagnosis is commonly made by measuring plasma cortisol concentration before and after stimulation with ACTH, thereby ignoring aldosterone. In search of an alternative approach that would include assessment of glucocorticoid and mineralocorticoid production, 2 pairs of endocrine variables were measured: (1) plasma concentration of cortisol and ACTH, and (2) plasma aldosterone concentration and plasma renin activity. In addition, the cortisol-to-ACTH ratio (CAR) and the aldosterone-to-renin ratio (ARR) were calculated. Reference intervals were established in a population of 60 healthy dogs. In these dogs, CAR ranged from 1.1 to 26.1 and ARR ranged from 0.1 to 1.5. The variables were compared with those of 22 dogs with spontaneous primary hypoadrenocorticism. Plasma concentration of cortisol and ACTH in both groups of dogs overlapped, whereas CAR did not. Similarly, plasma aldosterone concentration and plasma renin activity overlapped, whereas ARR did not. These observations indicate that measurement of these endogenous variables (in one blood sample) allows the specific diagnoses of primary hypocortisolism and primary hypoaldosteronism.

Polarisation, key to good localisation

Polarisation of cells is crucial for vectorial transport of ions and solutes. In literature, however, proteins specifically targeted to the apical or basolateral membrane are often studied in non-polarised cells. To investigate whether these data can be extrapolated to expression in polarised cells, we studied several membrane-specific proteins. In polarised MDCK cells, the Aquaporin-2 water channel resides in intracellular vesicles and apical membrane, while the vasopressin-type 2 receptor, anion-exchanger 1 (AE1) protein and E-Cadherin mainly localise to the basolateral membrane. In non-polarised MDCK cells, however, Aquaporin-2 localises, besides plasma membrane, mainly in the Golgi complex, while the others show a dispersed staining throughout the cell. Moreover, while AQP2 mutants in dominant nephrogenic diabetes insipidus are missorted to different organelles in polarised cells, they all predominantly localise to the Golgi complex in non-polarised MDCK cells. Additionally, the maturation of V2R, and likely its missorting, is affected in transiently-transfected compared to stably-transfected cells. In conclusion, we show that the use of stably-transfected polarised cells is crucial in interpreting the processing and the localisation of membrane targeted proteins.

Effect of octreotide on plasma concentrations of glucose, insulin, glucagon, growth hormone, and cortisol in healthy dogs and dogs with insulinoma

The inhibitory effect of the somatostatin analogue octreotide on the secretion of insulin could be used in the treatment of insulinoma. However, current information on the effectiveness of octreotide in dogs is conflicting. Therefore, the endocrine effects of a single subcutaneous dose of 50 microg octreotide were studied in healthy dogs in the fasting state (n=7) and in dogs with insulinoma (n=12). Octreotide did not cause any adverse effects. In healthy dogs in the fasting state, both plasma insulin and glucagon concentrations declined significantly. Basal (non-pulse related) GH and ACTH concentrations were not affected. A slight but significant decrease in the plasma glucose concentrations occurred. Dogs with insulinoma had significantly higher baseline insulin concentrations and lower baseline glucose concentrations than healthy dogs in the fasting state. Plasma glucagon, GH, ACTH, and cortisol concentrations did not differ from those in healthy dogs. Baseline plasma insulin concentrations decreased significantly in dogs with insulinoma after octreotide administration, whereas plasma concentrations of glucagon, GH, ACTH, and cortisol did not change. In contrast to the effects in the healthy dogs, in the dogs with insulinoma plasma glucose concentrations increased. Thus, the consistent suppression of plasma insulin concentrations in dogs with insulinoma, in the absence of an suppressive effect on counter-regulatory hormones, suggests that further studies on the effectiveness of slow-release preparations in the long-term medical treatment of dogs with insulinoma are warranted.

Rescue of vasopressin V2 receptor mutants by chemical chaperones: specificity and mechanism

Because missense mutations in genetic diseases of membrane proteins often result in endoplasmic reticulum (ER) retention of functional proteins, drug-induced rescue of their cell surface expression and understanding the underlying mechanism are of clinical value. To study this, we tested chemical chaperones and sarco(endo)plasmic reticulum Ca2+ ATPase pump inhibitors on Madin-Darby canine kidney cells expressing nine ER-retained vasopressin type-2 receptor (V2R) mutants involved in nephrogenic diabetes insipidus. Of these nine, only V2R-V206D showed improved maturation and plasma membrane rescue with glycerol, dimethyl sulfoxide (DMSO), thapsigargin/curcumin, and ionomycin but not with other osmolytes or growth at 27 degrees C. This revealed that rescue is mutant specific and that this mutant is prone to rescue by multiple compounds. Rescue did not involve changed expression of molecular chaperones calnexin, heat-shock protein (HSP) 70, or HSP90. V2R antagonist SR121463B treatment revealed that V2R-V206D and V2R-S167T were rescued and matured to a greater extent, suggesting that the rescuing activity of a pharmacological versus chemical chaperone is broader and stronger. Calcium measurements showed that rescue of V2R-V206D by thapsigargin, curcumin, and ionomycin was because of increased cytosolic calcium level, rather than decreased endoplasmic reticulum calcium level. The molecular mechanism underlying rescue by DMSO, glycerol, and SR121463B is different, because with these compounds intracellular calcium levels were unaffected.

Characterization of vasopressin V2 receptor mutants in nephrogenic diabetes insipidus in a polarized cell model

X-linked nephrogenic diabetes insipidus (NDI) is caused by mutations in the gene encoding the vasopressin V2 receptor (V2R). For the development of a tailored therapy for NDI, knowledge of the cellular fate of V2R mutants is needed. It would be useful when this fate could be predicted from the location and type of mutation. To identify similarities and differences in localization, maturation, stability, and degradation of COOH-terminal GFP-tagged V2R mutants, we stably expressed nine mutants in polarized Madin-Darby canine kidney cells. The mutants V2R-L44P, -Delta62-64, -I130F, -S167T, -S167L, and -V206D were mainly expressed in the endoplasmic reticulum (ER) as immature proteins. These mutants had relatively short half-lives due to proteasomal degradation, except for V2R-Delta62-64. In contrast, V2R-R113W, -G201D, and -T204N were expressed in the ER and in the basolateral membrane as immature, high-mannose glycosylated, and mature complex-glycosylated proteins. The immature forms of V2R-R113W and -T204N, but not V2R-G201D, were rapidly degraded. The mature forms varied extensively in their stability and were degraded by only lysosomes (V2R-T204N and wild-type V2R) or lysosomes and proteasomes (V2R-G201D, -R113W). These data reveal that most missense V2R mutations lead to retention in the ER and suggest that mutations that likely distort a transmembrane domain or introduce a charged amino acid close to it make a V2R mutant more prone to ER retention. Because six of the mutants tested showed significant increases in intracellular cAMP levels on transient expression in COS cells, activation of these six receptors following rescue of cell-surface expression might provide a cure for NDI patients.

Comparison of ultrasonography, computed tomography, and single-photon emission computed tomography for the detection and localization of canine insulinoma

Accurate preoperative detection, localization, and staging of the primary tumor and metastases are essential for the selection of appropriate candidates for surgery. In dogs with insulinoma, preoperative assessment usually is performed with transabdominal ultrasonography (US). There are no reports on the use of computed tomography (CT) for this purpose. The preoperative use of somatostatin receptor scintigraphy (SRS) recently has been advocated for the identification of insulinoma and gastrinoma in dogs, but its accuracy remains to be established. In this report US, CT, and single-photon emission computed tomography (SPECT) with [111In-DTPA-D-Phe1]-octreotide (a specific form of SRS) were compared for their effectiveness in detecting and localizing primary and metastatic insulinoma in dogs. Findings at surgery or postmortem examination served as control. Of 14 primary insulinomas, 5, 10, and 6 were correctly identified by US, CT, and SPECT, respectively. No lymph node metastases were detected by US or SPECT. CT identified 2 of 5 lymph node metastases but also identified 28 false-positive lesions. Two of 4 livers were found to be positive for metastases by 1 of the imaging techniques. US can be used for the initial evaluation of dogs with hypoglycemia. Although CT identifies most primary tumors, intraoperative inspection and palpation of the pancreas is still superior. SPECT appears as effective as US and CT in detecting insulinomas. Future developments in preoperative imaging techniques might improve current methods of canine insulinoma detection.

Regulation of the vasopressin V2 receptor by vasopressin in polarized renal collecting duct cells

Binding of arginine-vasopressin (AVP) to its V2 receptor (V2R) in the basolateral membrane of principal cells induces Aquaporin-2-mediated water reabsorption in the kidney. To study the regulation of the V2R by dDAVP in a proper model, a polarized renal cell line stably-expressing V2R-GFP was generated. Labeled AVP-binding studies revealed an equal basolateral vs. apical membrane distribution for V2R-GFP and endogenous V2R. In these cells, GFP-V2R was expressed in its mature form and localized for 75% in the basolateral membrane and for 25% to late endosomes/lysosomes. dDAVP caused a dose- and time-dependent internalization of V2R-GFP, which was completed within 1 h with 100 nM dDAVP, was prevented by coincubation with a V2R antagonist, and which reduced its half-life from 11.5 to 2.8 h. Semiquantification of the V2R-GFP colocalization with E-cadherin (basolateral membrane), early endosomal antigen-1 (EEA-1) and lysosome-associated membrane protein-2 (LAMP-2) in time revealed that most dDAVP-bound V2R was internalized via early endosomes to late endosomes/lysosomes, where it was degraded. The dDAVP-internalized V2R did not recycle to the basolateral membrane. In conclusion, we established the itinerary of the V2R in a polarized cell model that likely resembles the in vivo V2R localization and regulation by AVP to a great extent.

Locally produced growth hormone in canine insulinomas

The production and release of GH has been demonstrated in a variety of extra-pituitary tissues. In this respect insulin-producing pancreatic tumours are also of interest because it has been observed that GH may promote islet cell proliferation. However, these effects have only been related to GH of pituitary origin and the possibility of local production of GH with autocrine-/paracrine effects has not been considered. In this study, a reverse transcriptase polymerase chain reaction (RT-PCR) was used to demonstrate the presence of GH mRNA in pancreatic tissue of five healthy dogs and insulinomas of 14 dogs. After Southern blotting of the RT-PCR products, blots were hybridized using a canine-specific GH-probe and quantified using phosphor imaging. GH gene expression was further demonstrated by in situ hybridization using a canine digoxigenin-labelled GH-specific cDNA probe. In addition, GH immunohistochemistry was performed. In five samples of normal pancreatic tissue a weak hybridization signal was found. This signal was significantly higher in nine of 12 primary tumours. In ten of 11 metastases there was a positive hybridization signal, and this signal was also significantly higher than in the primary tumours. In situ hybridization in one sample demonstrated that GH mRNA was only produced in the tumour cells. The local production of GH was confirmed by positive staining of tumour tissue with anti-GH antibodies in ten of 12 samples. It is concluded that canine insulinomas express the gene encoding GH mRNA. The locally produced GH may have an autocrine/paracrine effect on tumour progression. The relatively high expression levels in metastases of these tumours may be related to the low inhibitory influence of somatostatin outside the pancreas.

Pyothorax in nine dogs

The results of treatment of pyothorax using systemic antibiotics, drainage, and lavage of the pleural space, are reported for 9 dogs. All 9 dogs recovered completely. In 8 of the 9 dogs the follow-up period was at least 6 months and in none was there a relapse. The results obtained with this treatment are excellent in comparison with the results that have been reported for treatment with systemic antibiotics and drainage of the pleural space but without lavage. Apart from the addition of pleural lavage to the treatment protocol, the better result might be because migrating plant related foreign bodies did not seem to play an important role in the pathogenesis of pyothorax in this group of dogs.

[Enteral, nutritional support for critically ill patients]

Critically ill patients are characterized by acute changes in their metabolism, which are described by the term 'hypermetabolism'. In combination with anorexia, hypermetabolism leads to a negative energy and nitrogen balance. Consequently, wound healing can be inhibited, resistance is reduced, and (multiple) organ failure can occur. With the aid of nutritional support these consequences can be counteracted. During hypermetabolism protein breakdown is increased, and it is necessary to supply extra protein in the diet of critically ill patients. The amino acid glutamine is an important source of energy for enterocytes, and extra glutamine can improve the protective function of the intestinal mucosa. Branched amino acids serve as energy source during the acute phase. Arginine can reduce symptoms of encephalopathy by improving the conversion of ammonia to urea. Extra arginine in the diet also improves resistance. Because of the increased energy demand, diets for critically ill patients should be rich in fat. Moreover, extra n-3 fatty acids can improve immune function. A diet supplemented with extra zinc seems warranted because of its beneficial effect on wound healing and its inhibitory effect on protein breakdown. The enteral route is preferred because it protects the mucosal barrier of the gut, and it is less expensive and easier than the parenteral route. An enteral diet for critically ill patients is presented. Various factors that determine the choice of technique for enteral feeding are discussed.

[Pyothorax in nine dogs]

Nine dogs with pyothorax were treated with systemic antibiotics, and drainage and lavage of the pleural space. All nine dogs recovered completely. Eight dogs were followed up for 6 months or longer and none showed signs of relapse. The results of this treatment are excellent compared with those for treatment with systemic antibiotics and drainage of the pleural space but without lavage. Apart from the addition of pleural lavage to the treatment protocol, this difference in efficacy may be due to the fact that migrating grass seed awns do not seem to play an important role in the pathogenesis of pyothorax in dogs in the Netherlands.