Antimicrobial susceptibility patterns of aerobic bacteria isolated from canine urinary samples in South East Queensland, 2013 to 2018

Urinary tract infections are a common diagnosis in dogs presenting to veterinary practice. Veterinarians often treat suspected infections empirically, either in the absence of culture and susceptibility testing results or whilst waiting for them. This study aimed to identify the bacteria most frequently isolated from canine urinary samples and their antimicrobial susceptibility patterns in South East Queensland (SEQ) to help guide responsible empirical antimicrobial prescription by the veterinary community in this geographical location. Cumulative antibiograms were generated from the results of 1284 culture-positive urinary samples in SEQ, obtained from a commercial veterinary laboratory over a 5-year period. Escherichia coli was the most commonly isolated bacterial species (43%), followed by Staphylococcus spp. (23%), Proteus spp. (21%) and Enterococcus spp. (10%). Of the six most common isolates, 97% had susceptibility to at least one low-importance antimicrobial. Susceptibility to the low-importance and first-line antimicrobial recommendation, amoxicillin, was 81% for E. coli and 24% for Staphylococcus spp. Susceptibility of both E. coli and Staphylococcus spp. to medium-importance and commonly recommended empirical antimicrobials, trimethoprim sulphonamides and amoxicillin-clavulanic acid was ≥85% and >92% for high-importance antimicrobials enrofloxacin and ceftiofur. Of the E. coli and Staphylococcus spp. isolates, 8.8% and 4%, respectively, were considered multidrug resistant. There was no increase in resistance to antimicrobials detected over the study period. Susceptibilities suggest low- and medium-importance antimicrobials remain acceptable first-line empirical treatments. However, this should be continually assessed and updated using local surveillance data.

Understanding barriers to reducing antimicrobials on Australian dairy farms: A qualitative analysis

INTRODUCTION

Reducing antibiotic use in production animal systems is one strategy which may help to limit the development of antimicrobial resistance. To reduce antimicrobial use in food-producing animals, it is important to first understand how antibiotics are used on farm and what barriers exist to decreasing their use. In dairy production systems, mastitis is one of the most common reasons for administering antimicrobials. Therefore, it is important to understand the motivations and behaviours of dairy farmers in relation to the diagnosis, treatment and prevention of mastitis.

MATERIALS AND METHODS

In this study, we interviewed a sample of dairy farmers and dairy industry professionals from the major dairying regions of eastern Australia regarding their current practices used to diagnose, treat, and control subclinical and clinical mastitis. Inductive thematic analysis was used to code interview transcripts and identify the recurrent themes.

RESULTS

Four overarching themes were identified: (1) the challenges associated with the detection and diagnosis of clinical mastitis, including with laboratory culture, (2) the motivations behind treatment decisions for different cases, (3) decisions around dry cow therapy and the role of herd recording, and (4) concerns regarding the development of antimicrobial resistance.

DISCUSSION

This study identifies several challenges which may limit the ability of Australian dairy farmers to reduce antimicrobial use on farm, such as the need for rapid and reliable diagnostic tests capable of identifying the pathogenic causes of mastitis and the difficulties associated with conducting herd recording for the implementation of selective dry cow therapy. Industry professionals were concerned that farmers were not using individual cow records to aid in treatment decisions, which could result in unnecessary antimicrobial use. The results of this study can act as the basis for future research aimed at assessing these issues across the broader Australian dairy industry.

Males with sickle cell disease have higher risks of cerebrovascular disease, increased inflammation, and a reduced response to hydroxyurea

Biological sex is important. Male sex is associated with worse outcomes in most measures, including cerebrovascular disease, hospital admissions, and blood transfusions, but not survival. Females also appear to have a better response to hydroxyurea therapy, reduced markers of inflammation, and better liver function.

The cation-leaky hereditary stomatocytosis syndromes: A tale of six proteins

This review concerns a series of dominantly inherited haemolytic anaemias in which the membrane of the erythrocyte 'leaks' the univalent cations, compromising the osmotic stability of the cell. The majority of the conditions are explained by mutations in one of six genes, coding for multispanning membrane proteins of different structure and function. These are: RhAG, coding for an ammonium carrier; SLC4A1, coding for the band 3 anion exchanger; PIEZO1, coding for a mechanosensitive cation channel; GLUT1, coding for a glucose transporter; KCNN4, coding for an internal-calcium-activated potassium channel; and ABCB6, coding for a porphyrin transporter. This review describes the five clinical syndromes associated with genetic defects in these genes and their variable genotype/phenotype relationships.

A critical role for altered red cell cation permeability in pathogenesis of sickle cell disease and other haemolytic anaemias

The aetiology of sickle cell disease is well known, but pathogenesis is complicated and details remain uncertain. A thorough understanding may suggest novel ways for designing more effective therapies. One area of importance, covered here in Nader et al., is the altered cation permeability of sickle cells and how the co-ordinated operation of a number of membrane transport proteins contributes to disease progression, all driven by the initial event of HbS polymerisation. There are echoes here of the cation leaks of hereditary stomatocytosis. Nader et al. propose a central role for PIEZO1, a novel mechanosensitive channel found in red cells, which may be aberrantly activated in sickle cells following HbS polymerisation and which may have potential as a novel target for future chemotherapies. Commentary on: Nader et al. Piezo1 activation augments sickling propensity and the adhesive properties of sickle red blood cells in a calcium-dependent manner. Br J Haematol 2023;202:657-668.

Emerging drug targets for sickle cell disease: shedding light on new knowledge and advances at the molecular level

INTRODUCTION

In sickle cell disease (SCD), a single amino acid substitution at β6 of the hemoglobin (Hb) chain replaces glutamate with valine, forming HbS instead of the normal adult HbA. Loss of a negative charge, and the conformational change in deoxygenated HbS molecules, enables formation of HbS polymers. These not only distort red cell morphology but also have other profound effects so that this simple etiology belies a complex pathogenesis with multiple complications. Although SCD represents a common severe inherited disorder with life-long consequences, approved treatments remain inadequate. Hydroxyurea is currently the most effective, with a handful of newer treatments, but there remains a real need for novel, efficacious therapies.

AREAS COVERED

This review summarizes important early events in pathogenesis to highlight key targets for novel treatments.

EXPERT OPINION

A thorough understanding of early events in pathogenesis closely associated with the presence of HbS is the logical starting point for identification of new targets rather than concentrating on more downstream effects. We discuss ways of reducing HbS levels, reducing the impact of HbS polymers, and of membrane events perturbing cell function, and suggest using the unique permeability of sickle cells to target drugs specifically into those more severely compromised.

The pleiotropic effects of α-thalassemia on HbSS and HbSC sickle cell disease: Reduced erythrocyte cation co-transport activity, serum erythropoietin, and transfusion burden, do not translate into increased survival

α-Thalassemia is one of the most important genetic modulators of sickle cell disease (SCD). Both beneficial and detrimental effects have been described previously. We use a 12-year data set on a large cohort of patients with HbSS (n = 411) and HbSC (n = 146) to examine a wide range of these clinical and laboratory associations. Our novel findings are that α-thalassemia strongly reduces erythrocyte potassium chloride co-transporter (KCC) activity in both HbSS and HbSC (p = .035 and p = .00045 respectively), suggesting a novel mechanism through which α-thalassemia induces a milder phenotype by reducing red cell cation loss. This may be particularly important in HbSC where reduction in mean cell hemoglobin concentration is not seen and where KCC activity has previously been found to correlate with disease severity. Additionally, we show that α-thalassemia not only increases hemoglobin in patients with HbSS (p = .0009) but also reduces erythropoietin values (p = .0005), demonstrating a measurable response to improved tissue oxygenation. We confirm the reno-protective effect of α-thalassemia in patients with HbSS, with reduced proteinuria (p = .003) and demonstrate a novel association with increased serum sodium (p = .0004) and reduced serum potassium values (p = 5.74 × 10^-10 ). We found patients with α-thalassemia had a reduced annualized transfusion burden in both HbSS and HbSC, but α-thalassemia had no impact on annualized admission rates in either group. Finally, in a larger cohort, we report a median survival of 62 years in patients with HbSS (n = 899) and 80 years in those with HbSC (n = 240). α-thalassemia did not influence survival in HbSS, but a nonsignificant trend was seen in those with HbSC.

Antimicrobial susceptibility, plasmid replicon typing, phylogenetic grouping, and virulence potential of avian pathogenic and faecal Escherichia coli isolated from meat chickens in Australia

Globally, avian colibacillosis is a leading cause of morbidity and mortality in poultry, associated with economic losses and welfare problems. Here, clinical avian pathogenic E. coli isolates (CEC; n=50) and faecal E. coli isolates from healthy (FEC; n=187) Australian meat chickens collected between 2006 and 2014 were subjected to antimicrobial susceptibility testing, phylogenetic grouping, plasmid replicon (PR) typing, multilocus sequence typing, and virulence gene (VG) profiling. Extended-spectrum cephalosporin (ESC)- and fluoroquinolone (FQ)-resistant E. coli isolates underwent further genetic characterisation. Significant proportions of CEC and FEC were respectively susceptible (13/50 [26%]; 48/187 [26%],) or MDR (9/50 [18%]; 26/187 [14%]) to 20 tested antimicrobials. Phylogenetic groups A and C, and PR types IncFIB and IncFrep were most commonly represented. Five tested CEC-associated VGs were more prevalent in CEC (≥90%) compared to FEC isolates (≤58%). Some isolates (CEC n=3; FEC n=7) were resistant to ESCs and/or FQs and possessed signature mutations in chromosomal FQ target genes and plasmid-mediated qnrS, bla_CMY-2, and bla_DHA-1 genes. Sequence type 354 (n=4), associated with extraintestinal infections in a broad range of hosts, was prevalent among the ESC- and/or FQ-resistant FEC.This study confirmed the existence of a small reservoir of ESC- and FQ-resistant E. coli in Australian commercial meat chickens despite the absence of use in the industry of these drug classes. Otherwise, a diversity of VGs and PR types in both faecal and clinical E. coli populations were identified. It's hypothesised that the source of ESC- and FQ-resistant E. coli may be external to poultry production facilities.Highlights1. Low-level resistance to older and newer generation antimicrobial drugs detected2. The most common sequence type (ST) associated with FQ resistance was ST354 (4/10)3. A small proportion of CEC (n=3) and FEC (n=7) were resistant to ESCs and/or FQs.

Does Plasma Inhibit the Activity of KCl Cotransport in Red Cells From LK Sheep?

Red cells from LK sheep represent an important paradigm for control of KCl cotransport activity, as well as being important to sheep erythroid function. A previous report (Godart et al., 1997) suggested that autologous plasma markedly inhibits red cell KCC activity and identified the presence of the bicarbonate/CO₂ buffer system as the probable cause. Findings were restricted, however, to red cells from patients with sickle cell disease (SCD) swollen anisotonically and carried out at a very high O₂ tension (c.700 mmHg). It was therefore important to investigate the generality of the effect described and whether it was also relevant to the two main stimuli for KCC activity encountered most often by circulating red cells in vivo - low pH in active muscle beds during exercise and high urea concentrations in the renal medulla during antidiuresis. Results confirm that inhibition was significant in response to anisotonic swelling with KCC activity in MOPS-buffered saline (MBS) vs. bicarbonate-buffered saline (BBS) and in MBS vs. plasma both reduced (by about 25 and 50%, respectively). By contrast, however, inhibition was absent at low pH and in high concentrations of urea. These findings suggest therefore that red cell KCC activity represents an important membrane permeability in vivo in red cells suspended in plasma. They are relevant, in particular, to sheep red cells, and may also be important by extension to those of other species and to the abnormal red cells found in human patients with SCD.

Successful treatment of a chronic oroantral fistula infected with extensively drug resistant bacteria using long-term oesophageal tube feeding and several non-conventional treatments in a horse

BACKGROUND

Chronic oroantral fistulae (OAF) with secondary sinusitis can occur following repulsion of cheek teeth in horses.

CASE REPORT

An 8-year-old Andalusian cross gelding presented with an iatrogenic clinical crown fracture of tooth 209, which underwent repulsion of its apical portion (day 0). The horse was treated with intramuscular penicillin and intravenous gentamicin (5 days), followed by oral trimethoprim-sulphonamide (10 days) and then oral doxycycline (14 days). The acute iatrogenic OAF created during the initial repulsion persisted; a chronic OAF was identified on day 24. On day 48, septic sinusitis with multidrug-resistant (MDR) Escherichia coli was confirmed. Although susceptible to enrofloxacin in vitro, 30 days of therapy was unsuccessful. Subsequent serial cultures grew multiple MDR and extensively drug-resistant (XDR) gram-negative microorganisms. Whole-genome sequencing (WGS) revealed multiple sequence types of E. coli, with a range of resistance and virulence genes. The orientation of the OAF, regional osteomyelitis and septic sinusitis were confirmed with computed tomography on day 70. On day 74, enteral nutrition was provided through a cervical oesophagostomy tube for 3 months for prevention of oral feed contamination. The OAF was treated with various alternative therapeutics, including apple cider vinegar, propolis and amikacin impregnated products, until resolution on day 116.

CONCLUSION

These non-conventional therapeutics, antimicrobials and long-term oesophagostomy contributed to the successful treatment of a complicated OAF. In the future, WGS may be useful to inform antimicrobial selection when MDR or XDR organisms are identified.

Treatment of moderate grade dog bite wounds using amoxicillin-clavulanic acid with and without enrofloxacin: a randomised non-inferiority trial

BACKGROUND

Dog-to-dog bite wounds are a common veterinary emergency presentation: despite this, there is insufficient information to guide veterinarians on appropriate empirical antimicrobial management.

OBJECTIVES

Investigate the effectiveness of amoxicillin-clavulanic acid with and without enrofloxacin in the treatment of moderate grade dog bite wounds (DBW). To describe common pathogens and their antimicrobial susceptibility patterns.

MATERIALS AND METHODS

In a single-centre parallel group pragmatic trial, 50 dogs presenting with moderate grade DBW were prospectively randomised to receive amoxicillin-clavulanic acid (group A) or amoxicillin-clavulanic acid and enrofloxacin (group B). Swabs were taken for culture and susceptibility testing at admission. Stabilisation, wound care and surgical debridement were performed at the discretion of admitting clinicians. The primary outcome was complication due to infection at 10 days, with Bayesian inference used to estimate the difference in proportions between treatment groups.

RESULTS

Of the 24 dogs in treatment group A, 1 required the addition of enrofloxacin at re-examination. None of the 26 dogs in group B required alteration of antimicrobial coverage. The difference in complication rate due to infection between treatment groups was 4.2%. Twenty-one different organisms were identified: Staphylococcus pseudintermedius, Neisseria spp., Pasteurella multocida and P. canis were the most common. Over 90% of gram-negative and gram-positive isolates were susceptible to amoxicillin-clavulanic acid. Ninety-six percent of gram-negative and 86% of gram-positive isolates were susceptible to enrofloxacin.

CONCLUSION AND CLINICAL SIGNIFICANCE

Amoxicillin-clavulanic acid is an appropriate empirical antimicrobial choice for moderate DBW in South East Queensland. Reduced empirical enrofloxacin use will promote antimicrobial stewardship and potentially antimicrobial resistance.

Prevalence and spatial distribution of Coxiella burnetii seropositivity in northern Australian beef cattle adjusted for diagnostic test uncertainty

Q fever is a zoonotic disease caused by infection with Coxiella burnetii transmitted from animals including, but not limited to, cattle, sheep and goats. The infection in cattle is typically sub-clinical with some evidence suggesting associated reproductive loss. There is currently limited data on the true prevalence and distribution of coxiellosis in beef cattle across northern Australia. During this study, 2,012 sera samples from beef cattle managed on commercial farms located in Queensland and the Northern Territory were tested using an indirect immunofluorescent assay (IFA) for serological evidence of IgG antibodies against C. burnetii. Bayesian latent class models were used to estimate the true prevalence, adjusted for diagnostic test sensitivity and specificity and incorporating the hierarchical structure of the cattle within farms and regions. In this study, cattle in the Northern Territory had lower estimated true prevalence than cattle within most regions of Queensland with the exception of south-east Queensland. Results from this study have described the geographic distribution and estimated the true prevalence of antibodies to C. burnetii in a sample of extensively managed beef cattle located across the tropical grazing regions of northern Australia.

Yoda1 and phosphatidylserine exposure in red cells from patients with sickle cell anaemia

Phosphatidylserine (PS) exposure is increased in red cells from sickle cell anaemia (SCA) patients. Externalised PS is prothrombotic and attractive to phagocytes and activated endothelial cells and thus contributes to the anaemic and ischaemic complications of SCA. The mechanism of PS exposure remains uncertain but it can follow increased intracellular Ca²⁺ concentration ([Ca²⁺]_i). Normally, [Ca²⁺]_i is maintained at very low levels but in sickle cells, Ca²⁺ permeability is increased, especially following deoxygenation and sickling, mediated by a pathway sometimes called P_sickle. The molecular identity of P_sickle is also unclear but recent work has implicated the mechanosensitive channel, PIEZO1. We used Yoda1, an PIEZO1 agonist, to investigate its role in sickle cells. Yoda1 caused an increase in [Ca²⁺]_i and PS exposure, which was inhibited by its antagonist Dooku1 and the PIEZO1 inhibitor GsMTx4, consistent with functional PIEZO1. However, PS exposure did not necessitate an increase in [Ca²⁺]_i. Two PKC inhibitors were also tested, chelerytherine chloride and calphostin C. Both reduced PS exposure whilst chelerytherine chloride also reduced Yoda1-induced increases in [Ca²⁺]_i. Findings are therefore consistent with the presence of PIEZO1 in sickle cells, able to mediate Ca²⁺ entry but that PKC was also involved in both Ca²⁺ entry and PS exposure.

Nanoscale adhesion profiling and membrane characterisation in sickle cell disease using hybrid atomic force microscopy-IR spectroscopy

Sickle cell disease (SCD) presents a significant global health problem. At present there is no effective treatment, with most being supportive for its associated complications such as the vaso-occlusive crises that result from increased cell adhesion. Hypoxic sickle cells have previously shown greater phosphatidylserine (PS) exposure and oxidative damage, as well as being notably "stickier" suggesting that increased cell cohesion and adhesion to the blood vessel endothelium is a possible mechanism for vaso-occlusion. The present work uses the hybrid technique of atomic force microscopy nano-infrared spectroscopy (AFM-IR) to probe changes to the coefficient of friction and C-O IR intensity in SCD on a nanoscale for dried red blood cells (RBCs) fixed under conditions of hypoxia and correlates these observations with adhesive interactions at the membrane. Using functionalised AFM tips, it has been possible to probe adhesive interactions between hydrophilic and hydrophobic moieties exposed at the surface of the dried RBCs fixed under different oxygenation states and for different cell genotypes. The results are consistent with greater PS-exposure and oxidative damage in hypoxic sickle cells, as previously proposed, and also show strong correlation between localised oxidative damage and increased adhesion. A mechanistic explanation involving significant lipid tail disruption as a result of oxidative action, in combination with differing concentrations of externalised PS lipids, is proposed to explain the observed adhesion behaviour of each type of cell.

The role of WNK in modulation of KCl cotransport activity in red cells from normal individuals and patients with sickle cell anaemia

Abnormal activity of red cell KCl cotransport (KCC) is involved in pathogenesis of sickle cell anaemia (SCA). KCC-mediated solute loss causes shrinkage, concentrates HbS, and promotes HbS polymerisation. Red cell KCC also responds to various stimuli including pH, volume, urea, and oxygen tension, and regulation involves protein phosphorylation. The main aim of this study was to investigate the role of the WNK/SPAK/OSR1 pathway in sickle cells. The pan WNK inhibitor WNK463 stimulated KCC with an EC₅₀ of 10.9 ± 1.1 nM and 7.9 ± 1.2 nM in sickle and normal red cells, respectively. SPAK/OSR1 inhibitors had little effect. The action of WNK463 was not additive with other kinase inhibitors (staurosporine and N-ethylmaleimide). Its effects were largely abrogated by pre-treatment with the phosphatase inhibitor calyculin A. WNK463 also reduced the effects of physiological KCC stimuli (pH, volume, urea) and abolished any response of KCC to changes in oxygen tension. Finally, although protein kinases have been implicated in regulation of phosphatidylserine exposure, WNK463 had no effect. Findings indicate a predominant role for WNKs in control of KCC in sickle cells but an apparent absence of downstream involvement of SPAK/OSR1. A more complete understanding of the mechanisms will inform pathogenesis whilst manipulation of WNK activity represents a potential therapeutic approach.

The effect of the antisickling compound GBT1118 on the permeability of red blood cells from patients with sickle cell anemia

Sickle cell anemia (SCA) is one of the commonest severe inherited disorders. Nevertheless, effective treatments remain inadequate and novel ones are avidly sought. A promising advance has been the design of novel compounds which react with hemoglobin S (HbS) to increase oxygen (O2 ) affinity and reduce sickling. One of these, voxelotor (GBT440), is currently in advanced clinical trials. A structural analogue, GBT1118, was investigated in the current work. As RBC dehydration is important in pathogenesis of SCA, the effect of GBT1118 on RBC cation permeability was also studied. Activities of Psickle , the Gardos channel and the KCl cotransporter (KCC) were all reduced. Gardos channel and KCC activities were also inhibited in RBCs treated with Ca2+ ionophore or the thiol reagent N-ethylmaleimide, indicative of direct effects on these two transport systems. Consistent with its action on RBC membrane transporters, GBT1118 significantly increased RBC hydration. RBC hemolysis was reduced in a nonelectrolyte lysis assay. Further to its direct effects on O2 affinity, GBT1118 was therefore found to reduce RBC shrinkage and fragility. Findings reveal important effects of GBT1118 on protecting sickle cells and suggest that this is approach may represent a useful therapy for amelioration of the clinical complications of SCA.

Regulation of erythrocyte Na+/K+/2Cl- cotransport by an oxygen-switched kinase cascade

Many erythrocyte processes and pathways, including glycolysis, the pentose phosphate pathway (PPP), KCl cotransport, ATP release, Na⁺/K⁺-ATPase activity, ankyrin-band 3 interactions, and nitric oxide (NO) release, are regulated by changes in O₂ pressure that occur as a red blood cell (RBC) transits between the lungs and tissues. The O₂ dependence of glycolysis, PPP, and ankyrin-band 3 interactions (affecting RBC rheology) are controlled by O₂-dependent competition between deoxyhemoglobin (deoxyHb), but not oxyhemoglobin (oxyHb), and other proteins for band 3. We undertook the present study to determine whether the O₂ dependence of Na⁺/K⁺/2Cl^- cotransport (catalyzed by Na⁺/K⁺/2Cl^- cotransporter 1 [NKCC1]) might similarly originate from competition between deoxyHb and a protein involved in NKCC1 regulation for a common binding site on band 3. Using three transgenic mouse strains having mutated deoxyhemoglobin-binding sites on band 3, we found that docking of deoxyhemoglobin at the N terminus of band 3 displaces the protein with no lysine kinase 1 (WNK1) from its overlapping binding site on band 3. This displacement enabled WNK1 to phosphorylate oxidative stress-responsive kinase 1 (OSR1), which, in turn, phosphorylated and activated NKCC1. Under normal solution conditions, the NKCC1 activation increased RBC volume and thereby induced changes in RBC rheology. Because the deoxyhemoglobin-mediated WNK1 displacement from band 3 in this O₂ regulation pathway may also occur in the regulation of other O₂-regulated ion transporters, we hypothesize that the NKCC1-mediated regulatory mechanism may represent a general pattern of O₂ modulation of ion transporters in erythrocytes.

Oxidative stress and phosphatidylserine exposure in red cells from patients with sickle cell anaemia

Phosphatidylserine (PS) exposure increases as red cells age, and is an important signal for the removal of senescent cells from the circulation. PS exposure is elevated in red cells from sickle cell anaemia (SCA) patients and is thought to enhance haemolysis and vaso-occlusion. Although precise conditions leading to its externalisation are unclear, high intracellular Ca2+ has been implicated. Red cells from SCA patients are also exposed to an increased oxidative challenge, and we postulated that this stimulates PS exposure, through increased Ca2+ levels. We tested four different ways of generating oxidative stress: hypoxanthine and xanthine oxidase, phenazine methosulphate, nitrite and tert-butyl hydroperoxide, together with thiol modification with N-ethylmaleimide (NEM), dithiothreitol and hypochlorous acid (HOCl), in red cells permeabilised to Ca2+ using bromo-A23187. Unexpectedly, our findings showed that the four oxidants significantly reduced Ca2+ -induced PS exposure (by 40-60%) with no appreciable effect on Ca2+ affinity. By contrast, NEM markedly increased PS exposure (by about 400%) and slightly but significantly increased the affinity for Ca2+ . Dithiothreitol modestly reduced PS exposure (by 25%) and HOCl had no effect. These findings emphasise the importance of thiol modification for PS exposure in sickle cells but suggest that increased oxidant stress alone is not important.

The effect of xanthine oxidase and hypoxanthine on the permeability of red cells from patients with sickle cell anemia

Red cells from patients with sickle cell anemia (SCA) are under greater oxidative challenge than those from normal individuals. We postulated that oxidants generated by xanthine oxidase (XO) and hypoxanthine (HO) contribute to the pathogenesis of SCA through altering solute permeability. Sickling, activities of the main red cell dehydration pathways (Psickle , Gardos channel, and KCl cotransporter [KCC]), and cell volume were measured at 100, 30, and 0 mmHg O2 , together with deoxygenation-induced nonelectrolyte hemolysis. Unexpectedly, XO/HO mixtures had mainly inhibitory effects on sickling, Psickle , and Gardos channel activities, while KCC activity and nonelectrolyte hemolysis were increased. Gardos channel activity was significantly elevated in red cells pharmacologically loaded with Ca2+ using the ionophore A23187, consistent with an effect on the transport system per se as well as via Ca2+ entry likely via the Psickle pathway. KCC activity is controlled by several pairs of conjugate protein kinases and phosphatases. Its activity, however, was also stimulated by XO/HO mixtures in red cells pretreated with N-ethylmaleimide (NEM), which is thought to prevent regulation via changes in protein phosphorylation, suggesting that the oxidants formed could also have direct effects on this transporter. In the presence of XO/HO, red cell volume was better maintained in deoxygenated red cells. Overall, the most notable effect of XO/HO mixtures was an increase in red cell fragility. These findings increase our understanding of the effects of oxidative challenge in SCA patients and are relevant to the behavior of red cells in vivo.

Phenotypic and genotypic profiling of antimicrobial resistance in enteric Escherichia coli communities isolated from finisher pigs in Australia

OBJECTIVE

To assess herd-to-herd variation in antimicrobial resistance phenotypes and associated antimicrobial resistance genes (ARGs) in faecal commensal Escherichia coli communities isolated from Australian slaughter-age pigs.

METHODS

Hydrophobic grid-membrane filtration (HGMF) was used to screen populations of E. coli isolated from faecal samples obtained from pigs prior to or at slaughter. Multiplex PCRs were applied to the pooled DNA extracted from the samples to identify specific ARGs.

METHODS

Pooled faecal samples from 30 finishers, from 72 different Australian pig farms, produced 5003 isolates for screening. HGMF techniques and image analysis were used to confirm E. coli resistance phenotypes to four antimicrobial agents (ampicillin, gentamicin, florfenicol and ceftiofur) using selective agars. Multiplex PCRs were performed on DNA from pooled samples for 35 ARGs associated with seven chemical classes.

RESULTS

The prevalence of E. coli isolates showing no resistance to any of the drugs was 50.2% (95% confidence interval (CI) 41.8-58.6%). Ceftiofur resistance was very low (1.8%; CI 0.8-3.9%) and no ARGs associated with 3rd-generation cephalosporin resistance were detected. By contrast, ampicillin (29.4%, CI 22.8-37.0%), florfenicol (24.3%, CI 17.8-32.3%) and gentamicin (CI 17.5%, 10.7-27.2%) resistance prevalence varied greatly between farms and associated ARGs were common. The most common combined resistance phenotype was ampicillin-florfenicol.

CONCLUSION

The use of registered antimicrobials in Australian pigs leads to the enteric commensal populations acquiring associated ARGs. However, despite a high intensity of sampling, ARGs imparting resistance to the critically important 3rd-generation cephalosporins were not detected.

The super sickling haemoglobin HbS-Oman: a study of red cell sickling, K+ permeability and associations with disease severity in patients heterozygous for HbA and HbS-Oman (HbA/S-Oman genotype)

Studying different sickle cell genotypes may throw light on the pathogenesis of sickle cell disease (SCD). Here, the clinical profile, red cell sickling and K⁺ permeability in 29 SCD patients (15 patients with severe disease and 14 with a milder form) of HbA/S-Oman genotype were analysed. The super sickling nature of this Hb variant was confirmed. The red cell membrane permeability to K⁺ was markedly abnormal with elevated activities of P_sickle , Gardos channel and KCl cotransporter (KCC). Results were consistent with Ca²⁺ entry and Mg²⁺ loss via P_sickle stimulating Gardos channel and KCC activities. The abnormal red cell behaviour was similar to that in the commonest genotype of SCD, HbSS, in which the level of mutated Hb is considerably higher. Although activities of all three K⁺ transporters also correlated with the level of HbS-Oman, there was no association between transport phenotype and disease severity. The super sickling behaviour of HbS-Oman may obviate the need for solute loss and red cell dehydration to encourage Hb polymerisation, required in other SCD genotypes. Disease severity was reduced by concurrent α thalassaemia, as observed in other SCD genotypes, and represents an obvious genetic marker for prognostic tests of severity in young SCD patients of the HbA/S-Oman genotype.

Isolation of Nocardia mexicana from focal proliferative tenosynovitis and arthritis in a steer

CASE REPORT

An 18-month-old Charolais steer was presented with lameness and fluctuant swelling of the right stifle joint, which yielded neutrophils on fine-needle aspiration. A diagnosis of bacterial proliferative tenosynovitis and arthritis was made on postmortem and histological examination. Culture and 16S rRNA sequencing identified a Nocardia sp. with 99% homology with the corresponding DNA fragment of N. mexicana DSM 44952. Antimicrobial susceptibility testing revealed the isolate was susceptible to co-trimoxazole and third-generation cephalosporins.

CONCLUSION

We report the first case, both in Australia and internationally, of proliferative tenosynovitis and arthritis caused by Nocardia spp. infection in a bovine and the first report of pathology attributed to N. mexicana in a veterinary patient. Given the limited susceptibility of the bacteria, the poor antimicrobial penetration that would be expected and the morphological changes that had taken place in the joint; the steer would have required protracted antimicrobial treatment in addition to invasive debridement of the lesion. This case emphasises the importance of routinely performing cytology and extended incubation of cultures in cases of arthritis in order to make ethical and economically viable treatment decisions.

The clinical significance of K-Cl cotransport activity in red cells of patients with HbSC disease

HbSC disease is the second commonest form of sickle cell disease, with poorly understood pathophysiology and few treatments. We studied the role of K-Cl cotransport activity in determining clinical and laboratory features, and investigated its potential role as a biomarker. Samples were collected from 110 patients with HbSC disease and 41 with sickle cell anemia (HbSS). K-Cl cotransport activity was measured in the oxygenated (K-Cl cotransport(100)) and deoxygenated (K-Cl cotransport(0)) states, using radioactive tracer studies. K-Cl cotransport activity was high in HbSC and decreased significantly on deoxygenation. K-Cl cotransport activity correlated significantly and positively with the formation of sickle cells. On multiple regression analysis, K-Cl cotransport increased significantly and independently with increasing reticulocyte count and age. K-Cl cotransport activity was increased in patients who attended hospital with acute pain in 2011 compared to those who did not (K-Cl cotransport(100): mean 3.87 versus 3.20, P=0.009, independent samples T-test; K-Cl cotransport(0): mean 0.96 versus 0.68, P=0.037). On logistic regression only K-Cl cotransport was associated with hospital attendance. Increased K-Cl cotransport activity was associated with the presence of retinopathy, but this effect was confounded by age. This study links variability in a fundamental aspect of cellular pathology with a clinical outcome, suggesting that K-Cl cotransport is central to the pathology of HbSC disease. Increased K-Cl cotransport activity is associated with increasing age, which may be of pathophysiological significance. Effective inhibition of K-Cl cotransport activity is likely to be of therapeutic benefit.

Effects of 5-hydroxymethyl-2-furfural on the volume and membrane permeability of red blood cells from patients with sickle cell disease

The heterocyclic aldehyde 5-hydroxymethyl-2-furfural (5HMF) interacts allosterically with the abnormal form of haemoglobin (Hb), HbS, in red blood cells (RBCs) from patients with sickle cell disease (SCD), thereby increasing oxygen affinity and decreasing HbS polymerization and RBC sickling during hypoxia. We hypothesized that should 5HMF also inhibit the main cation pathways implicated in the dehydration of RBCs from SCD patients - the deoxygenation-induced cation pathway (Psickle), the Ca(2+)-activated K(+) channel (the Gardos channel) and the K(+)-Cl(-) cotransporter (KCC) - it would have a synergistic effect in protection against sickling, directly through interacting with HbS, and indirectly through maintaining hydration and reducing [HbS]. This study was therefore designed to investigate the effects of 5HMF on RBC volume and K(+) permeability in vitro. 5HMF markedly reduced the deoxygenation-induced dehydration of RBCs whether in response to maintained deoxygenation or to cyclical deoxygenation/re-oxygenation. 5HMF was found to inhibit Psickle, an effect which correlated with its effects on sickling. Deoxygenation-induced activation of the Gardos channel and exposure of phosphatidylserine were also inhibited, probably indirectly via reduced entry of Ca(2+) through the Psickle pathway. Effects of 5HMF on KCC were more modest with a slight inhibition in N-ethylmaleimide (NEM, 1 mm)-treated RBCs and stimulation in RBCs untreated with NEM. These findings support the hypothesis that 5HMF may also be beneficial through effects on RBC ion and water homeostasis.

Effects of o-vanillin on K⁺ transport of red blood cells from patients with sickle cell disease

Aromatic aldehydes like o-vanillin were designed to reduce the complications of sickle cell disease (SCD) by interaction with HbS, to reduce polymerisation and RBC sickling. Present results show that o-vanillin also directly affects RBC membrane permeability. Both the K(+)-Cl(-) cotransporter (KCC) and the Ca(2+)-activated K(+) channel (or Gardos channel) were inhibited with IC50 of about 0.3 and 1 mM, respectively, with activities almost completely abolished by 5 mM. Similar effects were observed in RBCs treated with the thiol reacting reagent N-ethylmaleimide or with the Ca(2+) ionophore A23187, to circumvent any action via HbS polymerisation. The deoxygenation-induced cation conductance (sometimes termed P(sickle)) was partially inhibited, whilst deoxygenation-induced exposure of phosphatidylserine was completely abrogated. Na(+)/K(+) pump activity was also reduced. Notwithstanding, o-vanillin stimulated K(+) efflux through an unidentified pathway and resulted in reduction in cell volume (as measured by wet weight-dry weight). These actions are relevant to understanding how aromatic aldehydes may affect RBC membrane permeability per se as well as HbS polymerisation and thereby inform design of compounds most efficacious in ameliorating the complications of SCD.

Comparison of antimicrobial resistance phenotypes and genotypes in enterotoxigenic Escherichia coli isolated from Australian and Vietnamese pigs

This study aimed to compare the antibiogram phenotype and carriage of antimicrobial resistance genes (ARGs) of 97 porcine multidrug-resistant (MDR) enterotoxigenic Escherichia coli (ETEC) isolates obtained from Vietnam and 117 porcine MDR-ETEC obtained from Australia, two countries with different antimicrobial regulation systems. An antimicrobial resistance index (ARI) was calculated to quantify their potential significance to public health. Both Vietnamese and Australian isolates had moderate to high levels of resistance to commonly used antibiotics (ampicillin, tetracycline and sulphonamides). None of the Australian isolates were resistant to fluoroquinolones or third-generation cephalosporins and none possessed associated plasmid-mediated ARGs. However, 23.1% of Australian isolates were resistant to gentamicin owing to ARGs associated with apramycin or neomycin resistance [e.g. aac(3)-IV] that impart cross-resistance to gentamicin. Whilst Vietnamese isolates carried aminoglycoside ARGs, 44.4% of commercial pig isolates were resistant to gentamicin in comparison with 0% of village pig isolates. The plasmid-mediated fluoroquinolone ARG qnrB was commonly detected in Vietnamese isolates (52.3% commercial, 44.1% village), but phenotypic resistance was low (3.2% and 11.8%, respectively). The mean ARI for Vietnamese isolates (26.0) was significantly different (P<0.001) from the mean ARI for Australian isolates (19.8), primarily reflecting fluoroquinolone resistance in the former collection. This comparison suggests the effectiveness of regulations that slow the dissemination of 'critical' resistance by restricting the availability of important classes of antimicrobials.

Identification of the Ca²⁺ entry pathway involved in deoxygenation-induced phosphatidylserine exposure in red blood cells from patients with sickle cell disease

Phosphatidylserine (PS) exposure in red blood cells (RBCs) from sickle cell disease (SCD) patients is increased compared to levels in normal individuals and may participate in the anaemic and ischaemic complications of SCD. Exposure is increased by deoxygenation and occurs with elevation of intracellular Ca²⁺ to low micromolar levels. The Ca²⁺ entry step has not been defined but a role for the deoxygenation-induced pathway, P_sickle, is postulated. Partial P_sickle inhibitors 4-acetamido-4′-isothiocyanostilbene-2,2′-disulphonic acid (SITS), 4,4′-dithiocyano-2,2′-stilbene-disulphonic acid (DIDS) and dipyridamole inhibited deoxygenation-induced PS exposure (DIDS IC₅₀, 118 nM). Inhibitors and activators of other pathways (including these stimulated by depolarisation, benzodiazepines, glutamate and stretch) were without effect. Zn²⁺ and Gd³⁺ stimulated PS exposure to high levels. In the case of Zn²⁺, this effect was independent of oxygen (and hence HbS polymerisation and RBC sickling) but required extracellular Ca²⁺. The effect was completely abolished when Zn²⁺ (100 μM) was added to RBCs suspended in autologous plasma, implying a requirement of high levels of free Zn²⁺.

Growth factor regulation of intracellular pH homeostasis under hypoxic conditions in isolated equine articular chondrocytes

Hypoxia and acidosis are recognized features of inflammatory arthroses. This study describes the effects of IGF-1 and TGF-β(1) on pH regulatory mechanisms in articular cartilage under hypoxic conditions. Acid efflux, reactive oxygen species (ROS), and mitochondrial membrane potential were measured in equine articular chondrocytes isolated in the presence of serum (10% fetal calf serum), IGF-1 (1, 10, 50, 100 ng/ml) or TGF-β(1) (0.1, 1, 10 ng/ml) and then exposed to a short-term (3 h) hypoxic insult (1% O(2)). Serum and 100 ng/ml IGF-1 but not TGF-β(1) attenuated hypoxic regulation of pH homeostasis. IGF-1 appeared to act through mitochondrial membrane potential stabilization and maintenance of intracellular ROS levels in very low levels of oxygen. Using protein phosphorylation inhibitors PD98059 (25 µM) and wortmannin (200 nM) and Western blotting, ERK1/2 and PI-3 kinase pathways are important for the effect of IGF-1 downstream to ROS generation in normoxia but only PI-3 kinase is implicated in hypoxia. These results show that oxygen and growth factors interact to regulate pH recovery in articular chondrocytes by modulating intracellular oxygen metabolites.

A non-electrolyte haemolysis assay for diagnosis and prognosis of sickle cell disease

Red blood cells (RBCs) from patients with sickle cell disease (SCD) lyse in deoxygenated isosmotic non-electrolyte solutions. Haemolysis has features which suggest that it is linked to activation of the pathway termed P_sickle. This pathway is usually described as a non-specific cationic conductance activated by deoxygenation, HbS polymerisation and RBC sickling. The current work addresses the hypothesis that this haemolysis will provide a novel diagnostic and prognostic test for SCD, dependent on the altered properties of the RBC membrane resulting from HbS polymerisation. A simple test represented by this haemolysis assay would be useful especially in less affluent deprived areas of the world where SCD is most prevalent. RBCs from HbSS and most HbSC individuals showed progressive lysis in deoxygenated isosmotic sucrose solution at pH 7.4 to a level greater than that observed with RBCs from HbAS or HbAA individuals. Cytochalasin B prevented haemolysis. Haemolysis was temperature- and pH-dependent. It required near physiological temperatures to occur in deoxygenated sucrose solutions at pH 7.4. At pH 6, haemolysis occurred even in oxygenated samples. Haemolysis was reduced in patients on long-term (>5 months) hydroxyurea treatment. Several manoeuvres which stabilise soluble HbS (aromatic aldehydes o-vanillin or 5-hydroxymethyl, and urea) reduced haemolysis, an effect not due to increased oxygen affinity. Conditions designed to elicit HbS polymerisation in cells from sickle trait patients (deoxygenated hyperosmotic sucrose solutions at pH 6) supported their haemolysis. These findings are consistent with haemolysis requiring HbS polymerisation and support the hypothesis that this may be used as a test for SCD.

The conductance of red blood cells from sickle cell patients: ion selectivity and inhibitors

The abnormally high cation permeability in red blood cells (RBCs) from patients with sickle cell disease (SCD) occupies a central role in pathogenesis. Sickle RBC properties are notably heterogeneous, however, thus limiting conventional flux techniques that necessarily average out the behaviour of millions of cells. Here we use the whole-cell patch configuration to characterise the permeability of single RBCs from patients with SCD in more detail. A non-specific cation conductance was reversibly induced upon deoxygenation and was permeable to both univalent (Na+, K+, Rb+) and also divalent (Ca2+, Mg2+) cations. It was sensitive to the tarantula spider toxin GsMTx-4. Mn2+ caused partial, reversible inhibition. The aromatic aldehyde o-vanillin also irreversibly inhibited the deoxygenation-induced conductance, partially at 1mM and almost completely at 5mM. Nifedipine, amiloride and ethylisopropylamiloride were ineffective. In oxygenated RBCs, the current was pH sensitive showing a marked increase as pH fell from 7.4 to 6, with no change apparent when pH was raised from 7.4 to 8. The effects of acidification and deoxygenation together were not additive. Many features of this deoxygenation-induced conductance (non-specificity for cations, permeability toCa2+ andMg2+, pH sensitivity, reversibility, partial inhibition by DIDS and Mn2+) are shared with the flux pathway sometimes referred to as Psickle. Sensitivity to GsMTx-4 indicates its possible identity as a stretch-activated channel. Sensitivity to o-vanillin implies that activation requires HbS polymerisation but since the conductance was observed in whole-cell patches, results suggest that bulk intracellular Hb is not involved; rather a membrane-bound subfraction is responsible for channel activation. The ability to record P(sickle)-like activity in single RBCs will facilitate further studies and eventual molecular identification of the pathway involved.

Deoxygenation-induced and Ca(2+) dependent phosphatidylserine externalisation in red blood cells from normal individuals and sickle cell patients

Phosphatidylserine (PS) is usually confined to the inner leaflet of the red blood cell (RBC) membrane. It may become externalised in various conditions, however, notably in RBCs from patients with sickle cell disease (SCD) where exposed PS may contribute to anaemic and ischaemic complications. PS externalisation requires both inhibition of the aminophospholipid translocase (or flippase) and activation of the scramblase. Both may follow from elevation of intracellular Ca(2+). Flippase inhibition occurs at low [Ca(2+)](i), about 1μM, but [Ca(2+)](i) required for scrambling is reported to be much higher (around 100μM). In this work, FITC-labelled lactadherin and FACS were used to measure externalised PS, with [Ca(2+)](i) altered using bromo-A23187 and EGTA/Ca(2+) mixtures. Two components of Ca(2+)-induced scrambling were apparent, of high (EC(50) 1.8±0.3μM) and low (306±123μM) affinity, in RBCs from normal individuals and the commonest SCD genotypes, HbSS and HbSC. The high affinity component was lost in the presence of unphysiologically high [Mg(2+)] but was unaffected by high K(+) (90mM) or vanadate (1mM). The high affinity component accounted for PS scrambling in ≥2/3rd RBCs. It is likely to be most significant in vivo and may be involved in the pathophysiology of SCD or other conditions involving eryptosis.

Pathophysiology of red cell volume

In the current work, we review three situations where red cell volume changes are important. Red cell apoptosis (eryptosis) accounts for the removal of ageing and damaged erythrocytes from the circulation by macrophages. Amongst other cellular responses, eryptosis is associated with net cytosolic KCl loss and concomitant cell shrinkage. KCl efflux is mediated by activation of Ca(2+)-activated K(+) (Gardos) channels, permitting downhill movement of K(+) and electrically obliged Cl(-) through, as yet, incompletely described pathways. Red cells from patients suffering from sickle cell disease demonstrate progressive dehydration. Osmolyte loss is accounted for by the activation of two separate pathways. KCl cotransport, normally quiescent in red cells from HbA individuals, is activated under deoxygenated conditions and mediates net KCl efflux. Furthermore, intracellular Ca(2+) is elevated, probably as a result of Ca(2+) influx through a deoxygenation induced non-selective cation pathway termed P(sickle). This results in Gardos channel activation coupled indirectly with Cl(-) loss. Finally, a number of red cell stomatocytoses have been described where alterations to erythrocyte volume are the result of increased membrane cation permeability, in particular to Na(+) and K(+). The emerging significance of non-selective cation pathways is common to each of these conditions, and, although differences exist between their properties, particularly with regard to activation and ion selectivity, it is conceivable that they represent activation of closely related pathways. The recent finding that many hereditary stomatocytoses are caused by mutations to band 3 (AE-1) raises the possibility that modifications to this transporter could account for altered cation fluxes under different conditions.

The effect of oxygen tension on calcium homeostasis in bovine articular chondrocytes

Background

Articular chondrocytes normally experience a lower O₂ tension compared to that seen by many other tissues. This level may fall further in joint disease. Ionic homeostasis is essential for chondrocyte function but, at least in the case of H⁺ ions, it is sensitive to changes in O₂ levels. Ca²⁺ homeostasis is also critical but the effect of changes in O₂ tension has not been investigated on this parameter. Here we define the effect of hypoxia on Ca²⁺ homeostasis in bovine articular chondrocytes.

Methods

Chondrocytes from articular cartilage slices were isolated enzymatically using collagenase. Cytoplasmic Ca²⁺ levels ([Ca²⁺]_i) were followed fluorimetrically using Fura-2 to determine the effect of changes in O₂ tension. The effects of ion substitution (replacing extracellular Na⁺ with NMDG⁺ and chelating Ca²⁺ with EGTA) were tested. Levels of reactive oxygen species (ROS) and the mitochondrial membrane potential were measured and correlated with [Ca²⁺]_i.

Results

A reduction in O₂ tension from 20% to 1% for 16-18 h caused [Ca²⁺]_i to approximately double, reaching 105 ± 23 nM (p < 0.001). Ion substitutions indicated that Na⁺/Ca²⁺ exchange activity was not inhibited at low O₂ levels. At 1% O₂, ROS levels fell and mitochondria depolarised. Restoring ROS levels (with an oxidant H₂O₂, a non-specific ROS generator Co²⁺ or the mitochondrial complex II inhibitor antimycin A) concomitantly reduced [Ca²⁺]_i.

Conclusions

O₂ tension exerts a significant effect on [Ca²⁺]_i. The proposed mechanism involves ROS from mitochondria. Findings emphasise the importance of using realistic O₂ tensions when studying the physiology and pathology of articular cartilage and the potential interactions between O₂, ROS and Ca²⁺.

Novel permeability characteristics of red blood cells from sickle cell patients heterozygous for HbS and HbC (HbSC genotype)

Individuals heterozygous for HbS and HbC (HbSC) represent about 1/3(rd) of sickle cell disease (SCD) patients. Whilst HbSC disease is generally milder, there is considerable overlap in symptoms with HbSS disease. HbSC patients, as well as HbSS ones, present with the chronic anaemia and panoply of acute vaso-occlusive complications that characterize SCD. However, there are important clinical and haematological differences. Certain complications occur with greater frequency in HbSC patients (like proliferative retinopathy and osteonecrosis) whilst intravascular haemolysis is reduced. Patients with HbSC disease can be considered as a discrete subset of SCD cases. Although much work has been carried out on understanding the pathogenesis of SCD in HbSS homozygotes, including the contribution of altered red blood cell permeability, relatively little pertains directly to HbSC individuals. Results reported in the literature suggest that HbSC cells, and particularly certain subpopulations, present with similar permeability to HbSS cells but there are also important differences - these have not been well characterized. We hypothesise that their unique cell transport properties accounts for the different pattern of disease in HbSC patients and represents a potential chemotherapeutic target not shared in red blood cells from HbSS patients. The distinct pattern of clinical haematology in HbSC disease is emphasised here. We analyse some of the electrophysiological properties of single red blood cells from HbSC patients, comparing them with those from HbSS patients and normal HbAA individuals. We also use the isosmotic haemolysis technique to investigate the behaviour of total red blood cell populations. Whilst both HbSS and HbSC cells show increased monovalent and divalent (Ca(2+)) cation conductance further elevated upon deoxygenation, the distribution of current magnitudes differs, and outward rectification is greatest for HbSC cells. In addition, although Gd(3+) largely abolishes the cation conductance of both HbSS and HbSC cells, only in HbSS ones are currents inhibited by the aminoglycosides like streptomycin. This distinction is retained in isosmotic lysis experiments where both HbSS and HbSC cells undergo haemolysis in sucrose solutions but streptomycin significantly inhibits lysis only in HbSS cells. These findings emphasise similarities but also differences in the permeability properties of HbSS and HbSC cells, which may be important in pathogenesis.

Rapid effects of hypoxia on H+ homeostasis in articular chondrocytes

Articular chondrocytes experience low oxygen (O(2)) levels compared with many other tissues, and values fall further in disease states. Chondrocyte intracellular pH (pH(i)) is a powerful modulator of matrix synthesis and is principally regulated by Na(+)-H(+) exchange (NHE). In equine chondrocytes, NHE is inhibited when cells are incubated for 3 h at low O(2), leading to intracellular acidosis. O(2)-dependent changes in reactive oxygen species (ROS) levels appear to underlie this effect. The present study examines whether hypoxia can influence chondrocyte NHE activity and pH(i) over shorter timescales using the pH-sensitive fluoroprobe BCECF in cells isolated not only from equine cartilage but also from bovine tissue. O(2) levels in initially oxygenated solutions gassed with N(2) fell to approximately 1% within 2 h. A progressive fall in pH(i) and acid extrusion capacity was observed, with statistically significant effects (P < 0.05) apparent within 3 h. For equine and bovine cell populations subjected to step change in O(2) by resuspension in hypoxic (1%) solutions, a decline in acid extrusion and pH(i) was observed within 10 min and continued throughout the recording period. This effect represented inhibition of the NHE-mediated fraction of acid extrusion. Cells subjected to hypoxic solutions supplemented with CoCl(2) (100 microM) or antimycin A (100 microM) to raise levels of ROS did not acidify. The conserved nature and rapidity of the response to hypoxia has considerable implications for chondrocyte homeostasis and potentially for the maintenance of cartilage integrity.

Non-electrolyte permeability of deoxygenated sickle cells compared

The passive permeability pathways of red cells are poorly defined, with the exception of the Gardos channel. Several cation and anion pathways can be induced by a variety of manoeuvres, however, including treatment with oxidants, low ionic strength (LIS), shrinkage, swelling and also infection with the intra-erythrocytic malaria parasite. Several of these stimuli (malaria, swelling, LIS), in addition, also activate a non-electrolyte this permeability. Sickle cells uniquely show a deoxygenation-induced pathway, which is termed P(sickle) and is usually considered to be a conductive cationic pathway. In this report, we explore further the extent to which this permeability pathway of deoxygenated sickle cells is available for non-electrolyte transport. We show that a number of solutes are permeable, with greater permeability to sugars (notably lactose and maltose) and smaller molecules, and less to charged or zwitterionic species. Red cells from heterozygous HbSC patients also showed deoxygenation-induced haemolysis in isosmotic sucrose solution, though to a slightly lesser extent than for red cells from homozygous sickle cell patients. In contrast to sickle cells, red cells from beta-thalassaemic patients did not show haemolysis in isosmotic sucrose solutions, regardless of the O(2) tension. Of the secondary cellular changes resulting from incubation in non-electrolyte solutions (which include imposition of a highly positive membrane potential, marked intracellular alkalinisation and cell shrinkage), none appear to correlate with activation of the non-electrolyte permeability. Rather, findings indicate that it is low ionic strength per se that is responsible. Normal red cells also show changes in ionic and non-electrolyte permeability in low ionic strength media, and these permeabilities are compared to those found in deoxygenated sickle cells. The extent to which these different permeabilities in normal and sickle red cells can be ascribed to one or more common pathways remains to be determined.

Oxygen and reactive oxygen species in articular cartilage: modulators of ionic homeostasis

Articular cartilage is an avascular tissue dependent on diffusion mainly from synovial fluid to service its metabolic requirements. Levels of oxygen (O(2)) in the tissue are low, with estimates of between 1 and 6%. Metabolism is largely, if not entirely, glycolytic, with little capacity for oxidative phosphorylation. Notwithstanding, the tissue requires O(2) and consumes it, albeit at low rates. Changes in O(2) tension also have profound effects on chondrocytes affecting phenotype, gene expression, and morphology, as well as response to, and production of, cytokines. Although chondrocytes can survive prolonged anoxia, low O(2) levels have significant metabolic effects, inhibiting glycolysis (the negative Pasteur effect), and also notably matrix production. Why this tissue should respond so markedly to reduction in O(2) tension remains a paradox. Ion homeostasis in articular chondrocytes is also markedly affected by the extracellular matrix in which the cells reside. Recent work has shown that ion homeostasis also responds to changes in O(2) tension, in such a way as to produce significant effects on cell function. For this purpose, O(2) probably acts via alteration in levels of reactive oxygen species. We discuss the possibility that O(2) consumption by this tissue is required to maintain levels of ROS, which are then used physiologically as an intracellular signalling device. This postulate may go some way towards explaining why the tissue is dependent on O(2) and why its removal has such marked effects. Understanding the role of oxygen has implications for disease states in which O(2) or ROS levels may be perturbed.

Abnormal permeability pathways in human red blood cells

A number of situations that result in abnormal permeability pathways in human red blood cells (RBCs) have been investigated. In sickle cell disease (SCD), RBCs contain HbS, rather than the normal HbA. When deoxygenated, an abnormal conductance pathway, termed P(sickle), is activated, which contributes to cell dehydration, largely through allowing Ca(2+) entry and subsequent activation of the Gardos channel. Whole-cell patch-clamp recordings from sickle RBCs show a deoxygenated-induced conductance, absent from normal RBCs, which shares some of the properties of P(sickle): equivalent Na(+) and K(+) permeability, significant Ca(2+) conductance, partial inhibition by DIDS and also Zn(2+). Gd(3+) markedly attenuates conductance in both normal and sickle RBCs. In addition, deoxygenated sickle cells, but not oxygenated ones or normal RBCs regardless of the oxygen tension, undergo haemolysis in isosmotic non-electrolyte solutions. Non-electrolyte entry was confirmed radioisotopically whilst haemolysis was inhibited by DIDS. These findings suggest that under certain circumstances P(sickle) may also be permeable to non-electrolytes. Finally, RBCs from certain patients with hereditary stomatocytosis have a mutated band 3, which appears able to act as a conductance pathway for univalent cations. These results extend our understanding of the abnormal permeability pathways of RBCs.

The role of mitochondrial reactive oxygen species in pH regulation in articular chondrocytes

OBJECTIVE

To examine the effect of O(2) and the role, and source, of reactive oxygen species (ROS) on pH regulation in articular chondrocytes.

METHODS

Cartilage from equine metacarpo/tarsophalangeal joints was digested (collagenase) to isolate chondrocytes and loaded with 2',7'-bis-2-(carboxyethyl)-5(6)-carboxylfluorescein, a pH-sensitive fluorophore. O(2) tension was maintained using Eschweiler tonometers and a Wosthoff gas mixer. Cells were exposed to agents which alter ROS levels, mitochondrial inhibitors and/or inhibitors of protein phosphorylation. ROS levels were determined by dichlorofluorescein and mitochondrial membrane potential measured using JC-1.

RESULTS

pH homeostasis was dependent on ROS. Na(+)/H(+) exchanger (NHE) activity was inhibited at low O(2) tension (acid efflux reducing from 2.30+/-0.05 to 1.27+/-0.11mMmin(-1) at 1%). NHE activity correlated with ROS levels (r(2)=0.65). ROS levels were increased by antimycin A (with levels at 1% O(2) tension increasing from 59+/-9% of the value at 20% to 87+/-7%), but reduced by rotenone, myxothiazol and diphenyleneiodonium. Hypoxia induced depolarisation of the mitochondrial membrane potential (with JC-1 red-green fluorescence ratio at 1% O(2) tension decreasing to 40+/-10% of the value at 20%). The response to changes in O(2) and to antimycin A was inhibited by staurosporine, wortmanin and calyculin A.

CONCLUSION

The fall in ROS levels in hypoxia reduces the ability of articular chondrocytes to regulate pH, inhibiting NHE activity via changes in protein phosphorylation. The site of ROS generation is likely to be mitochondrial electron transport chain complex III. These effects are important to understanding normal chondrocyte function and response to altered O(2) tension.

Deoxygenation-induced non-electrolyte pathway in red cells from sickle cell patients

Red cells from patients with sickle cell disease contain HbS rather than the normal HbA (here termed HbS cells). On deoxygenation, HbS cells exhibit a distinctive solute permeability pathway, P(sickle), activated stochastically, and partially inhibited by DIDS and dipyridamole. It is often referred to as a cation channel although its permeability characteristics remain vague and its molecular identity is unknown. We show that, in contrast to normal red cells, a proportion of HbS cells underwent haemolysis when deoxygenated in isosmotic non-electrolyte solutions. Haemolysis was stochastic: cells unlysed after an initial deoxygenation pulse showed lysis when harvested, reoxygenated and subsequently exposed to a second period of deoxygenation. O(2) dependence of haemolysis was similar to that of P(sickle) activation. Haemolysis was accompanied by high rates of sucrose influx, and both haemolysis and sucrose influx were inhibited by DIDS and dipyridamole. Sucrose influx was only detected as ionic strength was reduced below 80 mM. These findings are consistent with the postulate that deoxygenation of HbS cells, under certain conditions, activates a novel non-electrolyte pathway. Their significance lies in understanding the nature of the deoxygenation-induced permeability in HbS cells, together with its relationship with novel pathways induced by a variety of manipulations in normal red cells.

The effect of deoxygenation on whole-cell conductance of red blood cells from healthy individuals and patients with sickle cell disease

Red blood cells from patients with sickle cell disease (SCD) exhibit increased electrogenic cation permeability, particularly following deoxygenation and hemoglobin (Hb) polymerisation. This cation permeability, termed P(sickle), contributes to cellular dehydration and sickling, and its inhibition remains a major goal for SCD treatment. Nevertheless, its characteristics remain poorly defined, its molecular identity is unknown, and effective inhibitors have not been established. Here, patch-clamp methodology was used to record whole-cell currents in single red blood cells from healthy individuals and patients with SCD. Oxygenated normal red blood cells had a low membrane conductance, unaffected by deoxygenation. Oxygenated HbS cells had significantly increased conductance and, on deoxygenation, showed a further rise in membrane conductance. The deoxygenation-induced pathway was variable in magnitude. It had equal permeability to Na(+) and K(+), but was less permeable to NMDG(+) and Cl(-). Conductance to Ca(2+) was also of a similar magnitude to that of monovalent cations. It was inhibited by DIDS (100 microM), Zn(2+) (100 microM), and by Gd(3+) (IC(50) of approximately 2 microM). It therefore shares some properties with P(sickle). These findings represent the first electrical recordings of single HbS cells and will facilitate progress in understanding altered red blood cell cation transport characteristics of SCD.

Haematology and biochemistry in healthy young pheasants and red-legged partridges and effects of spironucleosis on these parameters

Plasma biochemical and haematological parameters were examined in 4-week-old to 12-week-old game birds. Healthy, uninfected pheasants and partridges had similar levels of total protein, albumin, osmolality, Na+, Cl-, K+, Mg2+ and glucose. Triglyceride, globulin and Ca2+ were significantly higher and PO43- was lower in the partridges. Pheasants carrying a light to moderate infection with Spironucleus had significantly lower total protein, albumin, osmolality, Na+, Cl-, Ca2+ and PO43-. In severely affected pheasants, the osmolality, Na+ and Cl- fell further. Triglyceride and glucose were significantly lower than in healthy birds, and Mg2+ was higher. Similar data were obtained from infected partridges. Red cell parameters rose significantly in pheasants severely affected by spironucleosis, and the percent of heterophils was significantly higher and lymphocytes and basophils lower in their blood smears. The breast and leg muscle wet weight from severely affected pheasants was 22.2 and 37.7% that of uninfected birds, although the water content of the breast muscle was significantly higher.

The effect of O2 tension on pH homeostasis in equine articular chondrocytes

OBJECTIVE

To determine the effects of varying O(2) on pH homeostasis, based on the hypothesis that the function of articular chondrocytes is best understood at realistic O(2) tensions.

METHODS

Cartilage from equine metacarpophalangeal/tarsophalangeal joints was digested with collagenase to isolate chondrocytes, and then loaded with the pH-sensitive fluorophore 2',7'-bis-2-(carboxyethyl)-5(6)-carboxylfluorescein. The radioisotope(22)Na(+) was used to determine the kinetics of Na(+)/H(+) exchange (NHE) and the activity of the Na(+)/K(+) pump, and ATP levels were assessed with luciferin assays. Levels of reactive oxygen species (ROS) were determined using 2',7'-dichlorofluorescein diacetate.

RESULTS

The pH homeostasis was unaffected when comparing tissue maintained at 20% O(2) (the level in water-saturated air at 37 degrees C) with that at 5% O(2) (which approximates the normal level in healthy cartilage); however, an O(2) tension of <5% caused a fall in intracellular pH (pH(i)) and slowed pH(i) recovery following acidification, an effect mediated via inhibition of NHE activity (likely through acid extrusion by NHE isoform 1). The Na(+)/K(+) pump activity and intracellular ATP concentration were unaffected by hypoxia, but the levels of ROS were reduced. Hypoxic inhibition of NHE activity and the reduction in ROS levels were reversed by treatment with H(2)O(2), Co(2+), or antimycin A. Treatment with calyculin A also prevented hypoxic inhibition of NHE activity.

CONCLUSION

The ability of articular chondrocytes to carry out pH homeostasis is compromised when O(2) tensions fall below those normally experienced, via inhibition of NHE. The putative signal is a reduction in levels of ROS derived from mitochondria, acting via altered protein phosphorylation. This effect is relevant to both physiologic and pathologic states of lowered O(2), such as in chronic inflammation.