Validation of a commercially available immunoassay for the measurement of bovine cardiac troponin I

BACKGROUND

Commercially available cardiac troponin I (cTnI) assays developed for use in humans have not yet been validated for use in cattle.

HYPOTHESES

The ADVIA Centaur TnI-Ultra immunoassay can be used for the detection of bovine cTnI. In healthy cattle, serum cTnI is undetectable or is present only in trace amounts.

METHODS

Purified bovine cTnI and cTnI-free bovine serum were used for the evaluation of assay performance including intra- and inter-assay precision, sensitivity, interference, linearity, and recovery. Effects of storage at 23, 4, -20, and -80 degrees C for 2 days, and at -20 and -80 degrees C for 7 and 14 days and repeated freeze-thaw cycles on recovery of cTnI were analyzed. Serum cTnI concentrations in 30 healthy dairy cows were determined.

RESULTS

Intra- and inter-assay precisions (mean +/- SD) were 4.48 +/- 2.26 and 13.36 +/- 6.59%, respectively. The assay demonstrated linearity at 0.5, 2, 15, and 30 ng/mL cTnI. Mean recovery was 100.81, 85.26, 87.72, and 114.42%, respectively. Skeletal muscle homogenate added to serum of known cTnI concentration did not alter the concentration of the analyte (P > .05). Concentration of cTnI significantly decreased when samples were stored at 4 and 23 degrees C for 2 days (P < .05). Repeated freeze-thaw cycles and storage at -20 degrees C for 7 days had no significant influence on cTnI concentration (P > .05). Serum cTnI concentration in healthy cattle was <or=0.03 ng/mL.

CONCLUSION AND CLINICAL IMPORTANCE

ADVIA Centaur can be used reliably for the detection of serum cTnI concentration in cattle.

Comparison of proteome and antigenic proteome between two Neospora caninum isolates

This study was conducted to explore the relationship between two isolates of Neospora caninum (N. caninum) (KBA-2 and VMDL-1) using proteomics. To achieve the goal, proteins of N. caninum tachyzoite lysates of KBA-2 and VMDL-1 were separated by two-dimensional gel electrophoresis (2-DE), stained with silver-nitrate and analyzed using matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) to compare protein profiles. In addition, proteins separated by 2-DE were transferred to membranes, probed with bovine anti-N. caninum KBA-2 immunoglobulin G, and reactive proteins were visualized and compared between the two isolates. Most spots on 2-DE profiles and antigenic spots on 2-DE immunoblot profiles were located at similar locations in terms of isoelectric point and molecular weight. Proteins common to both isolates included the following: heat shock protein 70, subtilisin-like serine protease, nucleoside triphosphatase, heat shock protein 60, pyruvate kinase, tubulin alpha, tubulin beta, enolase, putative protein disulfide isomerase, actin, fructase-1,6-bisphosphatase, putative ribosomal protein S2, microneme protein Nc-P38, lactate dihydrogenase, fructose-1,6-bisphosphatase aldolase, serine threonine phosphatase 2C, 14-3-3 protein homologue, N. caninum dense granule-1 and NcGRA2. As a consequence, even though N. caninum KBA-2 and VMDL-1 isolates were isolated from geographically distinct locations there were significant homology in the proteome and antigenic proteome profiles. In addition, proteomic approach was verified as a useful tool for understanding of host immune response against different isolates of protozoa.

Pulmonary neoplasia in two llamas (Lama glama)

Two llamas with pulmonary tumors were examined. Llama No. 1 had multiple nodules throughout the lung that consisted histologically of solid clusters of polygonal to spindle cells with rare glandular differentiation. Intravascular emboli were common. Similar neoplastic masses were present in the kidney, heart, and liver. Immunohistochemically, neoplastic cells were positive for broad-spectrum cytokeratins (CKs), high-molecular weight CKs, CKs 5/6, and vimentin. The diagnosis was pulmonary carcinoma. Llama No. 2 had pulmonary nodules without extrapulmonary involvement. Microscopically, neoplastic cells formed acini lined by simple epithelium and solid cords of squamous cells that sometimes surrounded acini. Neoplastic cells were strongly positive for broad-spectrum CKs and weakly positive for thyroid transcription factor-1. The diagnosis was adenosquamous carcinoma. Pulmonary tumors account for 23% of neoplasms in South American camelids in our laboratory, making this the second most common type of neoplasm after lymphosarcoma.

Antigenic evaluation of a recombinant baculovirus-expressed Sarcocystis neurona SAG1 antigen

Sarcocystis neurona is the primary parasite associated with equine protozoal myeloencephalitis (EPM). This is a commonly diagnosed neurological disorder in the Americas that infects the central nervous system of horses. Current serologic assays utilize culture-derived parasites as antigen. This method requires large numbers of parasites to be grown in culture, which is labor intensive and time consuming. Also, a culture-derived whole-parasite preparation contains conserved antigens that could cross-react with antibodies against other Sarcocystis species and members of Sarcocystidae such as Neospora spp., Hammondia spp., and Toxoplasma gondii. Therefore, there is a need to develop an improved method for the detection of S. neurona-specific antibodies. The sera of infected horses react strongly to surface antigen 1 (SnSAG1), an approximately 29-kDa protein, in immunoblot analysis, suggesting that it is an immunodominant antigen. The SnSAG1 gene of S. neurona was cloned, and recombinant S. neurona SAG1 protein (rSnSAG1-Bac) was expressed with the use of a baculovirus system. By immunoblot analysis, the rSnSAG1-Bac antigen detected antibodies to S. neurona from naturally infected and experimentally inoculated equids, cats, rabbit, mice, and skunk. This is the first report of a baculovirus-expressed recombinant S. neurona antigen being used to detect anti-S. neurona antibodies in a variety of host species.

Anti-protozoal efficacy of high performance liquid chromatography fractions of Torilis japonica and Sophora flavescens extracts on Neospora caninum and Toxoplasma gondii

We previously reported that alcoholic extracts of Sophora flavescens and Torilis japonica from South Korea demonstrated good efficacy in reducing replication of Toxoplasma gondii and Neospora caninum. To characterize the chemical component associated with anti-protozoal activity, specific fractions were isolated by high performance liquid chromatography (HPLC) and used for in vitro testing. These fractions were evaluated in vitro against T. gondii and N. caninum. Fractions of the herb extracts were serially diluted to final concentrations of 2.850 to 0.356 ng/ml in medium and added to wells containing replicating T. gondii and N. caninum. To determine the ability of each fraction to inhibit parasite proliferation, 3H-uracil incorporation was used to determine parasite replication. In cultures infected with T. gondii, a fraction of T. japonica (TJ2) inhibited T. gondii proliferation by 99.2, 94.4, 88.6 and 27.0% in the range from 2.850 to 0.356 ng/ml. Four fractions of S. flavescens (SF1-SF4) inhibited T. gondii proliferation by 99.6-60.6, 96.9-48.1, 92.3-68.2 and 95.4-52.9% in the range from 2.850 to 0.356 ng/ml. In cultures infected with N. caninum, a fraction of T. japonica (TJ2) inhibited N. caninum proliferation by 98.3, 95.5, 79.7 and 30.6% in the range from 2.850 to 0.356 ng/ml. Four fractions of S. flavescens (SF1-SF4) inhibited N. caninum proliferation by 97.1-25.9, 94.8-35.5, 95.9-33.7 and 95.4-49.4% in the range from 2.850 to 0.356 ng/ml. These fractions of T. japonica and S. flavescens extracts are currently undergoing in vivo evaluation in experimentally infected mice.

The identification of a sequence related to apicomplexan enolase from Sarcocystis neurona

Equine protozoal myeloencephalitis (EPM) is a neurological disease caused by Sarcocystis neurona, an apicomplexan parasite. S. neurona is also associated with EPM-like diseases in marine and small mammals. The mechanisms of transmission and ability to infect a wide host range remain obscure; therefore, characterization of essential proteins may provide evolutionary information allowing the development of novel chemotherapeutics that target non-mammalian biochemical pathways. In the current study, two-dimensional electrophoresis and matrix-assisted laser desorption ionization-time of flight (MALDI-ToF) mass spectrometry were combined to characterize and identify an enolase protein from S. neurona based on peptide homology to the Toxoplasma gondii protein. Enolase is thought to be a vestigial, non-photosynthetic protein resulting from an evolutionary endosymbiosis event of an apicomplexan ancestor with green algae. Enolase has also been suggested to play a role in parasite stage conversion for T. gondii. Characterization of this protein in S. neurona and comparison to other protozoans indicate a biochemical similarity of S. neurona enolase to other tissue-cyst forming coccidians that cause encephalitis.

Anti-protozoal efficacy of medicinal herb extracts against Toxoplasma gondii and Neospora caninum

The purpose of this study was to determine whether alcohol extracts of herbs (Sophora flavescens Aiton, Sinomenium acutum (Thunb.) Rehder and E.H. Wilson, Pulsatilla koreana (Yabe ex Nakai) Nakai ex T. Mori, Ulmus macrocarpa Hance and Torilis japonica (Houtt.) DC.) from South Korea, possess in vitro anti-protozoal activity against cultures of Toxoplasma gondii and Neospora caninum. These herbs have been used as human anti-parasitics in Asian countries for many years. Alcohol extracts of these herbs were serially diluted to final concentrations ranging from 625 to 19.5 ng/ml in media and added to wells containing either T. gondii or N. caninum tachyzoites in equine dermal (ED) cells. Parasite growth inhibition was measured using 3H-uracil incorporation as compared to untreated controls. T. japonica inhibited T. gondii proliferation by 99.3, 95.5, 73.0 and 54.0% in the range from 156 to 19.5 ng/ml, and S. flavescens inhibited T. gondii proliferation by 98.7, 83.0 and 27.2% in the range from 156 to 39 ng/ml. T. japonica inhibited N. caninum proliferation by 97.8, 97.9, 85.3 and 46.4% in the range from 156 to 19.5 ng/ml. S. flavescens inhibited N. caninum proliferation by 98.6, 97.0, 69.5 and 14.0% in the range from 156 to 19.5 ng/ml. Toxicity to host cells was noted when concentrations of T. japonica and S. flavescens exceeded 625 ng/ml. The herb extracts from S. acutum, Pulsatilla koreana, and U. macrocarpa also showed toxicity at higher levels but did not achieve the same inhibition effects at the lower concentrations against T. gondii and N. caninum as T. japonica and S. flavescens.

Pharmacokinetics and bioavailability of trimethoprim-sulfamethoxazole in alpacas

The pharmacokinetics and bioavailability of trimethoprim-sulfamethoxazole (TMP-SMX) were studied in six healthy male-castrate alpacas (Lama pacos) after intravenous (i.v.) or oral (p.o.) drug administration of 15 mg/kg TMP-SMX using a crossover design with a 2-week washout period. After 90 days one group (n = 3) was given a p.o. dose of 30 mg/kg TMP-SMX and the other group (n = 3) was given a p.o. dose of 60 mg/kg TMP-SMX. After i.v. administration of 15 mg/kg of TMP-SMX the mean initial plasma concentration (C0) was 10.75 +/- 2.12 microg/mL for trimethoprim (TMP) and 158.3 +/- 189.3 microg/mL for sulfamethoxazole (SMX). Elimination half-lives were 0.74 +/- 0.1 h for TMP and 2.2 +/- 0.6 h for SMX. The mean residence times were 1.45 +/- 0.72 h for TMP and 2.8 +/- 0.6 h for SMX. The areas under the respective concentration vs. time curves (AUC) were 2.49 +/- 1.62 microg h/mL for TMP and 124 +/- 60 microg h/mL for SMX. Total clearance (Clt) for TMP was 21.63 +/- 9.85 and 1.90 +/- 0.77 mL/min kg for SMX. The volume of distribution at steady state was 2.32 +/- 1.15 L/kg for TMP and 0.35 +/- 0.09 L/kg for SMX. After intragastric administration of 15, 30 and 60 mg/kg the peak concentration (Cmax) of SMX were 1.9 +/- 0.8, 2.6 +/- 0.4 and 2.8 +/- 0.7 microg/mL, respectively. The AUC was 9.1 +/- 5, 25.9 +/- 3.3 and 39.1 +/- 4.1 microg h/mL, respectively. Based upon these AUC values and correcting for dose, the respective bioavailabilities were 7.7, 10.5 and 7.94%. Trimethoprim was not detected in plasma after intragastric administration. These data demonstrate that therapeutic concentrations of TMP-SMX are not achieved after p.o. administration to alpacas.

Experimental inoculation of domestic cats (Felis domesticus) with Sarcocystis neurona or S. neurona-like merozoites

Sarcocystis neurona is the parasite most commonly associated with equine protozoal myeloencephalitis (EPM). Recently, cats (Felis domesticus) have been demonstrated to be an experimental intermediate host in the life cycle of S. neurona. This study was performed to determine if cats experimentally inoculated with culture-derived S. neurona merozoites develop tissue sarcocysts infectious to opossums (Didelphis virginiana), the definitive host of S. neurona. Four cats were inoculated with S. neurona or S. neurona-like merozoites and all developed antibodies reacting to S. neurona merozoite antigens, but tissue sarcocysts were detected in only two cats. Muscle tissues from the experimentally inoculated cats with and without detectable sarcocysts were fed to laboratory-reared opossums. Sporocysts were detected in gastrointestinal (GI) scrapings of one opossum fed experimentally infected feline tissues. The study results suggest that cats can develop tissue cysts following inoculation with culture-derived Sarcocystis sp. merozoites in which the particular isolate was originally derived from a naturally infected cat with tissue sarcocysts. This is in contrast to cats which did not develop tissue cysts when inoculated with S. neurona merozoites originally derived from a horse with EPM. These results indicate present biological differences between the culture-derived merozoites of two Sarcocystis isolates, Sn-UCD 1 and Sn-Mucat 2.

Seroprevalence of Neospora, Toxoplasma gondii and Sarcocystis neurona antibodies in horses from Jeju island, South Korea

Parasite-specific antibody responses to Neospora spp. and Toxoplasma gondii, antigens were detected using the indirect fluorescent antibody test (IFAT) and immunoblot analysis in a korean equine population located on Jeju island, South Korea (126 degrees 12' E and 33 degrees 34' N). For comparison, a naturally infected Neospora hughesi horse and an experimentally inoculated T. gondii equid (pony) were used. In addition, all samples were tested for antibodies to Sarcocystis neurona by immunoblot analysis. A total of 191 serum samples from clinically normal horses were evaluated. Only 2% (4 out of 191) and 2.6% (5 out of 191) of the samples had showed reactivity at 1:100 using the IFAT for Neospora spp. and T. gondii, respectively. For T. gondii, two samples matched the antigen banding pattern of the positive control by immunoblot analysis. No sample was positive for N. hughesi by immunoblot analysis in this study. Overall, there was a 1% seroprevalence for T. gondii antibodies in the horses tested based on immunoblot analysis. The seroprevalence for S. neurona and N. hughesi antibodies was 0%. We concluded that these horses are either not routinely exposed to these parasites or antibody titers are not sufficiently elevated to be detectable. It is most likely the former explanation since Jeju island equine farms are isolated from the main land, and the horses were all less than 3 years of age. This naïve population of horses could be useful when evaluating S. neurona serodiagnostic tests or evaluating potential S. neurona vaccines since exposure risks to S. neurona and closely related parasites are negligible.

Characterization of monoclonal antibodies developed against Sarcocystis neurona

Equine protozoal myeloencephalitis (EPM), caused by a protozoal parasite infection of the central nervous system, is the most commonly diagnosed neurologic disease of horses in North America. In specific regions of the United States approximately 50% of the horse population is seropositive to Sarcocystis neurona. However, not all seropositive horses develop clinical signs. Detailed clinical examination, along with cerebrospinal fluid antibody evaluation are often used to diagnose EPM. Postmortem evaluation of the brain stem and spinal cord for histopathologic lesions compatible with nonsuppurative meningoencephalomyelitis is used for reaching a diagnosis since organisms are difficult to detect by routine staining methods. Immunohistochemical staining aids detection of organisms; however, the polyclonal antibodies that react with S. neurona may react with merozoites of other closely related Sarcocystis species. In this study, two different monoclonal antibodies, mAb 2A7-18 and mAb 2G5-2, were developed against the merozoite stage of S. neurona UCD-SN1 strain. The antibodies were evaluated by immunoblot, immunofluorescence, immuno-electron microscopy and immunohistochemistry for their ability to react with S. neurona. MAb 2G5-2 reacted with antigenically distinct S. neurona isolates whereas mAb 2A7-18 appeared to be limited in its ability to recognize different isolates. These two monoclonal antibodies recognize protein epitopes of two different immunodominant proteins of S. neurona.

The 14-3-3 cerebrospinal fluid immunoassay lacks utility in the diagnosis of clinical scrapie

This study determined whether the immunoassay for cerebrospinal fluid 14-3-3 protein concentration was sensitive and specific in the diagnosis of naturally occurring clinical scrapie in sheep. Cerebrospinal fluid was collected from 9 sheep with the confirmed diagnosis of scrapie. Additionally, cerebrospinal fluid was collected from 13 clinically normal sheep, which originated from a closely monitored flock with no history of scrapie. Sensitivity and specificity were calculated using standard epidemiological methods. Cerebrospinal fluid immunoassay results did not differ significantly between positive and negative sheep. Test sensitivity varied from 0.55 to 0.66, depending on the choice of test endpoint. Test specificity varied from 0.30 to 0.77, depending on the choice of test endpoint. The 14-3-3 cerebrospinal fluid immunoassay appears to have no value in the diagnosis of clinical scrapie in sheep.

Leukotoxin-diol: a putative toxic mediator involved in acute respiratory distress syndrome

Leukotoxin is clinically associated with acute respiratory distress syndrome (ARDS). Recently, we found that leukotoxin-diol, the hydrated product of leukotoxin, is more toxic than the parent leukotoxin in vitro (Moghaddam and colleagues, Nature Med. 1997;3:562-566). To test if this difference in the toxicity of leukotoxin and leukotoxin-diol exists in vivo, Swiss Webster mice were administered leukotoxin or leukotoxin-diol. All mice treated with leukotoxin-diol died of ARDS-like respiratory distress, whereas the animals exposed to leukotoxin at the same dose survived. Histopathologic evaluation of the lungs revealed massive alveolar edema and hemorrhage with interstitial edema around blood vessels in the lungs of mice treated with leukotoxin-diol, whereas the lungs of mice treated with identical doses of leukotoxin had perivascular edema only and little change in alveolar spaces. Immunohistochemistry showed that the soluble epoxide hydrolase responsible for the hydrolysis of leukotoxin to its diol is concentrated in the vascular smooth muscle of small and medium-sized pulmonary vessels. In addition, 4-phenylchalcone oxide, an inhibitor of soluble epoxide hydrolase, was found to decrease the mortality induced by leukotoxin but had no effect on mortality induced by leukotoxin-diol. These studies provide strong in vivo evidence that leukotoxin may act as a protoxicant and that the corresponding diol is a putative toxic mediator involved in the development of ARDS.

Serum immunoglobulin G concentrations in calves fed fresh and frozen colostrum

OBJECTIVE

To determine whether serum IgG concentrations in neonatal calves are adversely affected by short-term frozen storage of colostrum.

DESIGN

Prospective study.

SAMPLE POPULATION

Experiment 1 consisted of 10 pairs of Holstein calves (n = 20) fed matched aliquots of either fresh (n = 10) or frozen and thawed (10) colostrum. In experiment 2, 26 Holstein calves were fed either fresh (n = 13) or frozen and thawed (n = 13) colostrum.

PROCEDURE

Experiment 1 consisted of calves resulting from observed parturitions; calves were randomly assigned to treatment groups (fresh or frozen and thawed colostrum) in pairs. Calves were fed 4 L aliquots of colostrum via oroesophageal intubation at 3 hours of age. Serum IgG concentrations at 2 days of age were compared between the 2 groups by use of a paired t-test. Experiment 2 consisted of calves resulting from observed parturitions; calves were randomly assigned to treatment groups (fresh or frozen and thawed colostrum). Calves were fed 4 L aliquots of colostrum via oroesophageal intubation at 3 hours of age. Regression analysis was used to determine whether calf serum IgG concentration was a function of colostral IgG concentration and colostrum storage group.

RESULTS

Significant differences were not observed between the 2 groups in experiment 1. No significant relationship was observed between colostrum storage group and serum IgG concentration in experiment 2. The model that best predicted serum IgG concentrations accounted for 20% of the variability in serum IgG concentration.

CONCLUSION AND CLINICAL RELEVANCE

Frozen colostrum is an adequate source of IgG for calves.

Factors modulating the epithelial response to toxicants in tracheobronchial airways

As one of the principal interfaces between the organism and the environment, the respiratory system is a target for a wide variety of toxicants and carcinogens. The cellular and architectural complexity of the respiratory system appears to play a major role in defining the focal nature of the pulmonary response to environmental stressors. This review will address the biological factors that modulate the response of one of the major target compartments within the respiratory system, the tracheobronchial airway tree. Individual airway segments respond uniquely to toxic stress and this response involves not only the target cell population, e.g. epithelium, but also other components of the airway wall suggesting a trophic interaction within all components of the airway wall in maintaining steady state and responding to injury. A number of biological factors modulate the nature of the response, including: (1) metabolic potential at specific sites for activation and detoxification; (2) the nature of the local inflammatory response; (3) age of the organism at the time of exposure; (4) gender of the exposed organism; (5) history of previous exposure; and (6) species and strain of the organism exposed.

Sensitivity and specificity of serum copper determination for detection of copper deficiency in feeder calves

OBJECTIVE

To determine the relationship between serum and liver copper concentrations and evaluate serum copper determination for diagnosis of copper deficiency in juvenile beef calves.

DESIGN

Cross-sectional study.

ANIMALS

105 juvenile beef calves.

PROCEDURE

Copper concentrations were measured in paired liver and serum samples from 6- to 9-month-old beef calves. Regression models that predicted liver copper concentration as a function of serum copper concentration were developed. Sensitivity and specificity of serum copper concentration for detection of low liver copper concentration were determined, using a range of serum copper concentrations as test endpoints. Positive and negative predictive values were calculated.

RESULTS

The association between serum and liver copper concentrations was significant; however, regression models accounted for only a small portion of the variation in liver copper concentrations. For a serum copper concentration endpoint of 0.45 microg/g, sensitivity and specificity for detection of low liver copper concentration were 0.53 and 0.89, respectively. Positive and negative predictive values of serum copper concentration for detection of low liver copper concentration ranged from 0.37 to 0.85 and 0.63 to 0.94, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

Regression models are inappropriate for predicting copper status as a function of serum copper concentration. Serum copper concentration is fairly specific for detection of low liver copper concentration but only marginally sensitive when serum copper concentration of 0.45 microg/g is used as a test endpoint. The value of serum copper concentration as a diagnostic indicator depends on prevalence of copper deficiency.

In vitro quantitative analysis of (3)H-uracil incorporation by Sarcocytis neurona to determine efficacy of anti-protozoal agents

Parasite-specific incorporation of (3)H-uracil was used to assess the replication of Sarcocystis neurona, a protozoal parasite associated with equine protozoal myeloencephalitis (EPM). Anti-protozoal drugs, pyrimethamine (0.01, 0.1 and 1.0microg/ml PYR), sulfadiazine (5microg/ml; SDZ), sulfamethoxazole (5microg/ml; SMZ), diclazuril (100ng/ml; DCZ), atovaquone (0.04ng/ml; ATQ), tetracycline (5microg/ml; TET) and the herbicide glyphosate (1.5 and 4.5mM; GLY) were studied with varying S. neurona parasite densities (2x10(1)-1.2x10(6)merozoites/well). A microtiter plate format was used to test these compounds, and incorporation of (3)H-uracil was determined using a semi-automated plate harvester and liquid scintillation counter. When PYR, DCZ, ATQ, SMZ, SDZ, and TET were tested, the assay was most reliable when parasite densities were greater than 9.0x10(4) individual merozoites per well. When the herbicide GLY was tested, as few as 900 individual merozoites were sufficient to demonstrate reduction in parasite proliferation. Of the anti-protozoal drugs commonly used to treat EPM, PYR was the most potent anti-S. neurona agent tested. The herbicide GLY appears to be more potent than all of the other compounds tested in vitro; however information regarding in vivo use of GLY is not available, and central nervous system penetration by this compound is unlikely. Incorporation of (3)H-uracil by replicating S. neurona is quantitative and can be used in a semi-automated assay. This in vitro assay is capable of high throughput screening of candidate drugs that may have applications in a clinical setting. Further studies using a wider range of drug concentrations with optimal numbers of merozoites are necessary to determine true potency of these agents.

Effect of pasteurization at 76 and 63 degrees C on the absorption of colostral IgG in calves

The timely ingestion and absorption of colostral immunoglobulin is a critical determinant of neonatal calf health. Calves are born without appreciable concentrations of the serum immunoglobulins needed to protect against pathogenic bacteria, viruses and protozoa (Tyler & Parish, 1995). The beneficial effect of passive transfer of colostral immunoglobulin also extends beyond the neonatal period and persists into juvenile and adult life (Robison et al. 1988; Tyler et al. 1998; DeNise et al. 1989). Calves with failure of passive transfer, defined as serum protein < 50 g/l or serum IgG < 10 g/l, have increased mortality risks that persist until 10 weeks of age (Tyler et al. 1998).

Several diseases are potentially spread by the ingestion of colostrum, including bovine leukosis and Johne's disease (Perrin & Polack, 1988; Streeter et al. 1995). In one study 22% of latently infected cows were demonstrated to shed Mycobacterium paratuberculosis in their colostrum (Streeter et al. 1995). Optimal programmes to prevent and eradicate these diseases generally include the provision that calves are given colostrum derived from cows of known negative disease status. Pasteurization or heat treatment of colostrum may provide a mechanism whereby calves are provided with protection against neonatal disease without creating undue potential for infection by chronic, economically relevant diseases.

Attempts to heat disinfect colostrum are common in goat herds (MacKenzie et al. 1987). Pasteurization has been demonstrated to be effective against the caprine arthritis–encephalomyelitis virus (Adams et al. 1983; MacKenzie et al. 1987). Although Myco. paratuberculosis appears to resist pasteurization, this form of processing has been demonstrated to decrease the likelihood of positive colostral cultures for Myco. paratuberculosis under experimental conditions (Meylan et al. 1996). Sterilizing the milk and colostrum given to calves is a logical and reasonable strategy to prevent transmission of infectious microorganisms. The potential disadvantage of heat treating colostrum is that the immunoglobulins in colostrum may become denatured (Smith & Sherman, 1994). Pasteurization causes only a slight decrease in the colostral concentration of IgG in cattle (Meylan et al. 1996); however, the biological behaviour of these pasteurized immunoglobulins has not been critically examined. Therefore, we cannot be completely confident that immunoglobulin absorption, persistence in serum and biological activity are unchanged by this processing.

The goal of this study was to determine the effect of pasteurization at 76 and 63 °C on the absorption of IgG from colostrum. Should these procedures decrease immunoglobulin absorption, the use of pasteurization in disease eradication programmes would require increased efforts to optimize the passive transfer of immunoglobulin.

Effects of pasteurization of colostrum on subsequent serum lactoferrin concentration and neutrophil superoxide production in calves

OBJECTIVE

To determine the effects of pasteurization of colostrum on serum lactoferrin concentration and neutrophil oxidative function by comparing values from calves given pasteurized (76 C, 15 minutes) colostrum versus calves given fresh frozen colostrum.

ANIMALS

8 Holstein bull calves were used to study the effects of pasteurization of colostrum on the absorption of lactoferrin and neutrophil oxidative burst. Three additional calves were used to study the effect of exogenous lactoferrin on neutrophil oxidative burst.

METHODS

Calves were fed fresh frozen or heat pasteurized colostrum (76 C for 15 minutes) via esophageal feeder within 4 hours of birth. Neutrophils were isolated from whole blood samples. Neutrophil oxidative burst was induced by phorbol ester (300 ng/ml) stimulation of cells (1 X 10(6) cells) at 37 C. Serum lactoferrin concentrations were compared, using immunoblot analysis. Serum IgG concentrations were determined by radial immunoassay. Comparisons were made between the use of the 2 types of colostrum in calves by measuring subsequent serum IgG and lactoferrin concentrations and neutrophil superoxide production.

RESULTS

Serum IgG and lactoferrin concentrations increased more in calves receiving fresh frozen colostrum. Neutrophil superoxide production was higher in neutrophils prepared from calves receiving fresh frozen colostrum. Colostral lactoferrin addition to neutrophil incubations resulted in increased oxidative burst.

CONCLUSIONS AND CLINICAL RELEVANCE

Compared with calves given fresh frozen colostrum, calves given pasteurized colostrum had decreased serum IgG and lactoferrin concentrations and neutrophil superoxide production 24 hours after administration. These results suggest that pasteurizing bovine colostrum at 76 C for 15 minutes has substantial effects on passive transfer of proteins and neutrophil function.

Effects of prior feeding on pharmacokinetics and estimated bioavailability after oral administration of a single dose of microencapsulated erythromycin base in healthy foals

OBJECTIVE

To determine effects of prior feeding on pharmacokinetics and estimated bioavailability of orally administered microencapsulated erythromycin base (MEB) in healthy foals.

ANIMALS

6 healthy foals, 3 to 5 months old.

PROCEDURE

Foals were given 2 doses of MEB (25 mg/kg of body weight, PO). One dose was administered after food was withheld overnight, and the other was administered after foals had consumed hay. The study used a crossover design with a 2-week period between doses. Blood was collected via a jugular vein prior to and at specific times after drug administration. Concentrations of erythromycin A and anhydroerythromycin A in plasma were determined, using high-performance liquid chromatography. Results pharmacokinetic analysis of plasma concentration-time data for food-withheld and fed conditions were compared.

RESULTS

Plasma concentrations of erythromycin A for foals were lower after feeding than concentrations when food was withheld. Area under the plasma concentration-time curve, maximum plasma concentration, and estimated bioavailability were greater in foals when food was withheld than when foals were fed. Anhydroerythromycin A was detected in plasma after administration of MEB in all foals.

CONCLUSIONS AND CLINICAL RELEVANCE

Foals should be given MEB before they are fed hay. Administration of MEB to foals from which food was withheld overnight apparently provides plasma concentrations of erythromycin A that exceed the minimum inhibitory concentration of Rhodococcus equi for approximately 5 hours. The dosage of 25 mg/kg every 8 hours, PO, appears appropriate.

Pharmacokinetics of erythromycin estolate and erythromycin phosphate after intragastric administration to healthy foals

OBJECTIVE

To determine pharmacokinetics and plasma concentrations of erythromycin and related compounds after intragastric administration of erythromycin phosphate and erythromycin estolate to healthy foals.

ANIMALS

11 healthy 2- to 6-month-old foals.

PROCEDURE

Food was withheld from foals overnight before intragastric administration of erythromycin estolate (25 mg/kg of body weight; n = 8) and erythromycin phosphate (25 mg/kg; 7). Four foals received both drugs with 2 weeks between treatments. Plasma erythromycin concentrations were determined at various times after drug administration by use of high-performance liquid chromatography. Maximum plasma peak concentrations, time to maximum concentrations, area under plasma concentration versus time curves, half-life of elimination, and mean residence times were determined from concentration versus time curves.

RESULTS

Maximum peak concentration of erythromycin A after administration of erythromycin phosphate was significantly greater than after administration of erythromycin estolate (2.9 +/- 1.1 microg/ml vs 1.0 +/- 0.82 microg/ml). Time to maximum concentration was shorter after administration of erythromycin phosphate than after erythromycin estolate (0.71 +/- 0.29 hours vs 1.7 +/- 1.2 hours). Concentrations of anhydroerythromycin A were significantly less 1 and 3 hours after administration of erythromycin estolate than after administration of erythromycin phosphate.

CONCLUSIONS AND CLINICAL RELEVANCE

Plasma concentrations of erythromycin A remained > 0.25 microg/ml (reported minimum inhibitory concentration for Rhodococcus equi) for at least 4 hours after intragastric administration of erythromycin phosphate or erythromycin estolate, suggesting that the recommended dosage for either formulation (25 mg/kg, q 6 h) should be adequate for treatment of R equi infections in foals.

Quantification of individual glutathione S-transferase isozymes in hepatic and pulmonary tissues of naphthalene-tolerant mice

Acute exposure to naphthalene produces severe bronchiolar epithelial cell necrosis in mice, whereas subchronic exposure to naphthalene (200 mg/kg/7 days) fails to produce epithelial necrosis and renders the animals tolerant to subsequent challenge doses of naphthalene. Mechanisms responsible for the development of tolerance have not been delineated. The few studies exploring naphthalene tolerance focus on expression of microsomal enzymes and have yet to delve into expression of the hepatic detoxification enzymes such as glutathione S-transferases (GSTs; EC 2.5.1.18). Glutathione conjugation catalyzed by GSTs accounts for one of the two primary routes of naphthalene detoxification. In this study, we rigorously quantify levels of individual GST isozymes expressed within the livers and lungs of mice with acquired tolerance to naphthalene. Subchronic exposure to naphthalene increases the abundance of some hepatic GSTs to levels as much as 68% greater than controls. Naphthalene-tolerant mice displayed increases in mGSTM1 (51%), mGSTM2 (58%), and mGSTP1 (66%), whereas no significant difference in mGSTA3 was observed between exposed and control mice. Extracts of pulmonary tissues from naphthalene-tolerant mice showed minor increases in levels of mGSTP1 (7%) and Peak 8 isozyme (27%) and decreases in levels of mGSTM1 (31%), mGSTM2 (17%), and mGSTA3 (8%). The total enzymatic activity for the conjugation of 1-chloro-2,4-dinitrobenzene (CDNB) was 22% lower in lung extracts from naphthalene-tolerant animals than in controls. These results indicate that induction of hepatic GSTs is substantial and may be an important factor in the development of tolerance to naphthalene.

Hepatic and pulmonary enzyme activities in horses

OBJECTIVE

To determine hepatic and pulmonary phase-I and phase-II enzyme activities in horses.

SAMPLE POPULATION

Pulmonary and hepatic tissues from 22 horses that were 4 months to 32 years old.

PROCEDURE

Pulmonary and hepatic tissues from horses were used to prepare cytosolic (glutathione S-transferase and soluble epoxide hydrolase) and microsomal (cytochrome P450 monooxygenases) enzymes. Rates of microsomal metabolism of ethoxyresorufin, pentoxyresorufin, and naphthalene were determined by high-performance liquid chromatography. Activities of glutathione S-transferase and soluble epoxide hydrolase were determined spectrophotometrically. Cytochrome P450 content was determined by carbon monoxide bound-difference spectrum of dithionite-reduced microsomes. Activity was expressed relative to total protein concentration.

RESULTS

Microsomal protein and cytochromeP450 contents were detectable in all horses and did not vary with age. Hepatic ethoxyresorufin metabolism was detected in all horses; by comparison, pulmonary metabolism of ethoxyresorufin and hepatic and pulmonary metabolism of pentoxyresorufin were detected at lower rates. Rate of hepatic naphthalene metabolism remained constant with increasing age, whereas rate of pulmonary naphthalene metabolism was significantly lower in weanlings (ie, horses 4 to 6 months old), compared with adult horses. Hepatic glutathione S-transferase activity (cytosol) increased with age; however, these changes were not significant. Pulmonary glutathione S-transferase activity (cytosol) was significantly lower in weanlings than adult horses. Hepatic and pulmonary soluble epoxide hydrolase did not vary with age of horses.

CONCLUSIONS AND CLINICAL RELEVANCE

Activity of cytochrome P450 isoforms that metabolize naphthalene and glutathione S-transferases in lungs are significantly lower in weanlings than adult horses, which suggests reduced ability of young horses to metabolize xenobiotics by this organ.

Comparison of microbiologic and high-performance liquid chromatography assays to determine plasma concentrations, pharmacokinetics, and bioavailability of erythromycin base in plasma of foals after intravenous or intragastric administration

OBJECTIVE

To determine pharmacokinetics and bioavailability of erythromycin base after intragastric administration and erythromycin lactobionate after IV administration to healthy foals and to compare a microbiologic assay with a high-performance liquid chromatography (HPLC) method to determine plasma concentrations of erythromycin A.

ANIMALS

6 healthy foals that were 2 to 4 months old.

PROCEDURE

Foals were given single doses of erythromycin (10 mg/kg of body weight, IV, and 25 mg/kg, intragastrically) in a crossover study. Venous blood samples were obtained at specific times after drug administration, and plasma was harvested for determination of erythromycin concentrations by microbiologic assay and a HPLC method Pharmacokinetic analysis of plasma concentration-time data was performed, and results derived from each method were compared.

RESULTS

Concentration-time profiles for IV administration were best described by a two-compartment open model. Comparing pharmacokinetic data obtained by the 2 methods revealed substantial differences in results. Values for area under the plasma concentration-time curve and area under the first moment of the curve were substantially higher when determined by the bioassay, indicating overestimation of plasma concentration-time data by this method. The derived rate transfer constants (K21 and K(e)1) and mean residence time were significantly different, when determined by the bioassay. Systemic bioavailability of erythromycin base was low in all foals.

CONCLUSIONS AND CLINICAL RELEVANCE

The bioassay method overestimated plasma concentrations of erythromycin, compared with the HPLC method. Despite low systemic bioavailability of erythromycin base administered intragastrically, plasma concentrations of erythromycin exceeded, for at least 4 hours, the minimum inhibitory concentration of most Rhodococcus equi isolates.

Quantitative profiling of tissue- and gender-related expression of glutathione S-transferase isoenzymes in the mouse

Cytosolic glutathione S-transferase (GST) isoenzymes from brain, heart, lung, liver, kidney and gonads of male and female CD-1 mice were identified and quantified with a combination of affinity purification, electrospray ionization MS, Edman microsequencing, Western blot analysis and reverse-phase HPLC. The three principal hepatic GST subunits, mGSTA3 (25271 Da), mGSTP1 (23478 Da), and mGSTM1 (25839 Da), were isolated from liver, lung, kidney, testes and female heart, whereas brain, ovaries and male heart contained mGSTM1 and mGSTP1. Additional isoenzymes were detected in tissues, including mu class subunits mGSTM2 (25580 Da) and mGSTM3 (25570 Da), an N-terminally blocked Alpha subunit (25480 Da) assigned as mGSTA4, and proteins of molecular masses 25490, 22540, 24493, 24378 and 25383 Da. Distinct gender differences in expression of GST subunits were observed for liver, heart, kidney and gonads, whereas GST expression was similar in brain and lung for both genders. In contrast with patterns of expression in liver (high ratio of mGSTA3 to mGSTP1 in females relative to males), mGSTP1 was the most abundant subunit in female gonads, whereas mGSTA3 was not present in detectable quantities. The profile of GST expression in kidney was similar to that in liver; however, male kidneys expressed 30% more soluble GST than female kidneys. A striking gender-related difference in GST expression was found in cardiac tissue, where female animals expressed 50% more soluble GST than male tissues, and the GST isoenzyme with the greatest documented activity towards lipid hydroperoxides, mGSTA3, was present in female tissue yet absent from male tissue. These results point to complex gender- and tissue-dependent expression of individual mouse GST isoenzymes.