Dosing Recommendation Based on the Effects of Different Meal Types on Pexidartinib Pharmacokinetics in Healthy Subjects: Implementation of Model-informed Drug Development Strategy

Pexidartinib, an oral small molecule inhibitor of the colony-stimulating factor 1 receptor, is approved for treatment of adults with symptomatic tenosynovial giant cell tumor associated with severe morbidity or functional limitations and not amenable to improvement with surgery. The original dosing regimen is 400 mg of pexidartinib (2 × 200-mg capsules) twice daily, administered on an empty stomach at least 1 hour before or 2 hours after a meal or snack. Because pexidartinib is likely to be taken over an extended period of time, the ability to take pexidartinib with a meal would simplify timing of administration and potentially improve compliance. Since administering 400 mg of pexidartinib with a low-fat meal increases exposure by ≈60% relative to the fasted state, administering 250 mg of pexidartinib with a low-fat meal (low-fat meal dosing regimen) was predicted to achieve an exposure similar to 400 mg administered during a fasted state (original dosing regimen). Based on clinical trial simulations with two one-sided t-tests and bootstrapping (ie, resampling) analyses, a bioequivalence study (n = 24) would have >90% power to conclude that the original dosing regimen (400 mg fasted twice daily) and the low-fat meal dosing regimen (250 mg with a low-fat meal twice daily) are bioequivalent. This report provides the outcome of the implementation of the model-informed drug development strategy to recommend and justify a low-fat meal dosing regimen for pexidartinib that has the potential to improve patient compliance while maintaining drug exposure.

Pexidartinib Long-Term Hepatic Safety Profile in Patients with Tenosynovial Giant Cell Tumors

Background

Pexidartinib is approved in the U.S. for tenosynovial giant cell tumors (TGCTs). Herein, we assessed the hepatic safety profile of pexidartinib across patients with TGCTs receiving pexidartinib.

Materials, and Methods

Hepatic adverse reactions (ARs) were assessed by type and magnitude of liver test abnormalities, classified as (a) isolated aminotransferase elevations (alanine [ALT] or aspartate [AST], without significant alkaline phosphatase [ALP] or bilirubin elevations), or (b) mixed or cholestatic hepatotoxicity (increase in ALP with or without ALT/AST and bilirubin elevations, based on adjudication). Median follow‐up from initial pexidartinib treatment was 39 months (range, 32–82) in 140 patients with TGCTs across clinical studies NCT01004861, NCT02371369, NCT02734433, and NCT03291288.

Results

In total, 95% of patients with TGCTs (133/140) treated with pexidartinib (median duration of exposure, 19 months [range, 1–76]), experienced a hepatic AR. A total of 128 patients (91%) had reversible, low‐grade dose‐dependent isolated AST/ALT elevations without significant ALP elevations. Five patients (4%) experienced serious mixed or cholestatic injury. No case met Hy's law criteria. Onset of hepatic ARs was predominantly in the first 2 months. All five serious hepatic AR cases recovered 1–7 months following pexidartinib discontinuation. Five patients from the non‐TGCT population (N = 658) experienced serious hepatic ARs, two irreversible cases.

Conclusion

This pooled analysis provides information to help form the basis for the treating physician's risk assessment for patients with TCGTs, a locally aggressive but typically nonmetastatic tumor. In particular, long‐term treatment with pexidartinib has a predictable effect on hepatic aminotransferases and unpredictable risk of serious cholestatic or mixed liver injury.

Implications for Practice

This is the first long‐term pooled analysis to report on the long‐term hepatic safety of pexidartinib in patients with tenosynovial giant cell tumors associated with severe morbidity or functional limitations and not amenable to improvement with surgery. These findings extend beyond what has been previously published, describing the observed instances of hepatic toxicity following pexidartinib treatment across the clinical development program. This information is highly relevant for medical oncologists and orthopedic oncologists and provides guidance for its proper use for appropriate patients within the Pexidartinib Risk Evaluation and Mitigation Safety program.

Pexidartinib is approved in the U.S. for treatment of tenosynovial giant cell tumors (TGCT). This article assesses the hepatic safety profile of pexidartinib in TGCT cases and describes risk mitigation procedures designed to identify any instances of serious liver injury as early as possible to better inform prescribers and patients about this drug.

Long-term outcomes of pexidartinib in tenosynovial giant cell tumors

Background

The objective of this study was to report on the long‐term effects of pexidartinib on tenosynovial giant cell tumor (TGCT).

Methods

This was a pooled analysis encompassing 3 pexidartinib‐treated TGCT cohorts: 1) a phase 1 extension study (NCT01004861; 1000 mg/d; n = 39), 2) ENLIVEN patients randomized to pexidartinib (1000 mg/d for 2 weeks and then 800 mg/d; n = 61), and 3) ENLIVEN crossover patients (NCT02371369; 800 mg/d; n = 30). Eligible patients were 18 years old or older and had a histologically confirmed TGCT that was unresectable and symptomatic. Efficacy endpoints included the best overall response (complete or partial response) and the duration of response (DOR) by the Response Evaluation Criteria in Solid Tumors (RECIST) and the tumor volume score (TVS). The safety assessment included the frequency of treatment‐emergent adverse events (TEAEs) and hepatic laboratory abnormalities (aminotransferase elevations and mixed/cholestatic hepatotoxicity). The data cutoff was May 31, 2019.

Results

One hundred thirty patients with TGCT received pexidartinib (median treatment duration, 19 months; range, 1 to 76+ months); 54 (42%) remained on treatment at the end of the analysis (26 months after initial data cut of March 2017). The RECIST overall response rate (ORR) was 60%; the TVS ORR was 65%. The median times to response were 3.4 (RECIST) and 2.8 months (TVS), with 48 of the responding patients (62%) achieving a RECIST partial response by 6 months and with 72 (92%) doing so by 18 months. The median DOR was reached for TVS (46.8 months). Reported TEAEs were mostly low‐grade, with hair color changes being most frequent (75%). Most liver abnormalities (92%) were aminotransferase elevations; 4 patients (3%) experienced mixed/cholestatic hepatotoxicity (all within the first 2 months of treatment), which was reversible in all cases (recovery spanned 1‐7 months).

Conclusions

This study demonstrates the prolonged efficacy and tolerability of long‐term pexidartinib treatment for TGCT.

This analysis further illustrates that systemic therapy targeting the CSF1/CSF1R pathway is an effective therapeutic strategy in patients with tenosynovial giant cell tumor. Because of the limited availability of long‐term prospective data for tenosynovial giant cell tumor, these findings are encouraging and demonstrate the overall long‐term benefit of continued treatment with pexidartinib.

Pexidartinib versus placebo for advanced tenosynovial giant cell tumour (ENLIVEN): a randomised phase 3 trial

BACKGROUND

Tenosynovial giant cell tumour (TGCT), a rare, locally aggressive neoplasm, overexpresses colony-stimulating factor 1 (CSF1). Surgery is standard with no approved systemic therapy. We aimed to evaluate pexidartinib, a CSF1 receptor inhibitor, in patients with TGCT to provide them with a viable systemic treatment option, especially in cases that are not amenable to surgical resection.

METHODS

This phase 3 randomised trial had two parts. Part one was a double-blind study in which patients with symptomatic, advanced TGCT for whom surgery was not recommended were randomly assigned via an integrated web response system (1:1) to the pexidartinib or placebo group. Individuals in the pexidartinib group received a loading dose of 1000 mg pexidartinib per day orally (400 mg morning; 600 mg evening) for the first 2 weeks, followed by 800 mg per day (400 mg twice a day) for 22 weeks. Part two was an open-label study of pexidartinib for all patients. The primary endpoint, assessed in all intention-to-treat patients, was overall response at week 25, and was centrally reviewed by RECIST, version 1.1. Safety was analysed in all patients who received at least one dose of the study drug. This study is registered with ClinicalTrials.gov, number NCT02371369.

FINDINGS

Between May 11, 2015, and Sept 30, 2016, of 174 patients assessed for eligibility, 120 patients were randomly assigned to, and received, pexidartinib (n=61) or placebo (n=59). There were 11 dropouts in the placebo group and nine in the pexidartinib group. Emergence of mixed or cholestatic hepatotoxicity caused the data monitoring committee to stop enrolment six patients short of target. The proportion of patients who achieved overall response was higher for pexidartinib than placebo at week 25 by RECIST (24 [39%] of 61 vs none of 59; absolute difference 39% [95% CI 27-53]; p<0·0001). Serious adverse events occurred in eight (13%) of 61 patients in the pexidartinib group and one (2%) of 59 patients in the placebo group. Hair colour changes (67%), fatigue (54%), aspartate aminotransferase increase (39%), nausea (38%), alanine aminotransferase increase (28%), and dysgeusia (25%) were the most frequent pexidartinib-associated adverse events. Three patients given pexidartinib had aminotransferase elevations three or more times the upper limit of normal with total bilirubin and alkaline phosphatase two or more times the upper limit of normal indicative of mixed or cholestatic hepatotoxicity, one lasting 7 months and confirmed by biopsy.

INTERPRETATION

Pexidartinib is the first systemic therapy to show a robust tumour response in TGCT with improved patient symptoms and functional outcomes; mixed or cholestatic hepatotoxicity is an identified risk. Pexidartinib could be considered as a potential treatment for TGCT associated with severe morbidity or functional limitations in cases not amenable to improvement with surgery.

FUNDING

Daiichi Sankyo.

Phase II study of the halichondrin B analog eribulin mesylate in patients with locally advanced or metastatic breast cancer previously treated with an anthracycline, a taxane, and capecitabine

PURPOSE

The activity and safety of eribulin mesylate (E7389), a nontaxane microtubule dynamics inhibitor with a novel mechanism of action, were evaluated in patients with locally advanced or metastatic breast cancer previously treated with an anthracycline, taxane, and capecitabine.

PATIENTS AND METHODS

Eligible patients in this single-arm, open-label phase II study received eribulin mesylate (1.4 mg/m(2)) administered as a 2- to 5-minute intravenous infusion on days 1 and 8 of a 21-day cycle. The primary end point was objective response rate (ORR) assessed by independent review.

RESULTS

Of 299 enrolled patients who had received a median of four prior chemotherapy regimens, 291 received eribulin (for a median of four cycles). Of these, 269 patients met key inclusion criteria for the primary efficacy analysis. The primary end point of ORR by independent review was 9.3% (95% CI, 6.1% to 13.4%; all partial responses [PRs]), the stable disease (SD) rate was 46.5%, and clinical benefit rate (complete response + PR + SD > or = 6 months) was 17.1%. The investigator-reported ORR was 14.1% (95% CI, 10.2% to 18.9%). Median duration of response was 4.1 months, and progression-free survival was 2.6 months. Median overall survival was 10.4 months. The most common treatment-related grade 3 or 4 toxicities were neutropenia (54%; febrile neutropenia, 5.5%), leukopenia (14%), and asthenia/fatigue (10%; no grade 4); grade 3 neuropathy occurred in 6.9% of patients (no grade 4).

CONCLUSION

Eribulin demonstrated antitumor activity in extensively pretreated patients who had previously received an anthracycline, taxane, and capecitabine, with a manageable tolerability profile.

Phase I study of eribulin mesylate administered once every 21 days in patients with advanced solid tumors

PURPOSE

To evaluate the maximum tolerated dose (MTD), dose-limiting toxicities (DLT), and pharmacokinetics of eribulin mesylate (E7389), a halichondrin B analogue, administered every 21 days in patients with advanced solid tumors.

EXPERIMENTAL DESIGN

Eribulin mesylate was given as a 1-hour infusion every 21 days at doses of 0.25, 0.5, 1, 2, 2.8, and 4 mg/m(2). The MTD was identified using an accelerated titration design. The pharmacokinetics of eribulin were evaluated in the plasma and urine with the first dose.

RESULTS

Twenty-one patients were enrolled. At 4 mg/m(2), three patients experienced a DLT of febrile neutropenia on day 7. The dose level was reduced to 2.8 mg/m(2) where two of three patients experienced dose-limiting febrile neutropenia. Six additional patients were enrolled at 2 mg/m(2) (seven patients in total received this dose) and one of these patients experienced a neutropenic DLT. The MTD of eribulin mesylate was therefore 2 mg/m(2). Nonhematologic toxicities included alopecia, fatigue, anorexia, and nausea. Pharmacokinetic analysis showed linear kinetics for eribulin over the dose range studied and a terminal half-life of 2 days. The plasma-concentration-time profile exhibited a rapid distribution phase followed by a slow elimination phase. Drug clearance was nonrenal. One patient with non-small cell lung cancer achieved an unconfirmed partial response and 12 patients had stable disease.

CONCLUSIONS

Eribulin mesylate administered as a 1-hour infusion every 21 days has a manageable toxicity profile at 2 mg/m(2), with further dose escalation limited by neutropenia.

Phase II study of eribulin mesylate, a halichondrin B analog, in patients with metastatic breast cancer previously treated with an anthracycline and a taxane

PURPOSE

Eribulin mesylate (E7389), a nontaxane microtubule dynamics inhibitor, is a structurally simplified, synthetic analog of the marine natural product halichondrin B. This open-label, single-arm, phase II study evaluated efficacy and tolerability of eribulin in heavily pretreated patients with metastatic breast cancer (MBC).

METHODS

MBC patients who were previously treated with an anthracycline and a taxane received eribulin mesylate (1.4 mg/m(2)) as a 2- to 5-minute intravenous (IV) infusion on days 1, 8, and 15 of a 28-day cycle. Because of neutropenia (at day 15), an alternative regimen of eribulin on days 1 and 8 of a 21-day cycle was administered. The primary end point was overall response rate.

RESULTS

Of the 103 patients treated, the median number of prior chemotherapy regimens was four (range, one to 11 regimens). In the per-protocol population (n = 87), eribulin achieved an independently reviewed objective response rate (all partial responses [PRs]) of 11.5% (95% CI, 5.7 to 20.1) and a clinical benefit rate (PR plus stable disease > or = 6 months) of 17.2% (95% CI, 10.0 to 26.8). The median duration of response was 171 days (5.6 months; range, 44 to 363 days), the median progression-free survival was 79 days (2.6 months; range, 1 to 453 days), and the median overall survival was 275 days (9.0 months; range, 15 to 826 days). The most common drug-related grades 3 to 4 toxicities were as follows: neutropenia, 64%; leukopenia, 18%; fatigue, 5%; peripheral neuropathy, 5%; and febrile neutropenia, 4%.

CONCLUSION

Eribulin demonstrated activity with manageable tolerability (including infrequent grade 3 and no grade 4 neuropathy) in heavily pretreated patients with MBC when dosed as a short IV infusion on days 1 and 8 of a 21-day cycle.

Complement fragment C5a and inflammatory cytokines in neutrophil recruitment during intramammary infection with Escherichia coli

Generation of inflammatory mediators and leukocyte recruitment to infection at an epithelial surface were studied during Escherichia coli-induced mastitis. One uninfected gland of each of eight midlactation cows was challenged with only 30 CFU of E. coli McDonald strain 487, a serum-resistant isolate from a cow with mastitis. Bacteria grew logarithmically during the first 10 to 12 h after challenge, reaching concentrations of more than 10(5) CFU/ml with no detectable host response during this time. An intense inflammatory reaction began approximately 12 h after the challenge and was characterized by a breakdown in the blood-milk permeability barrier followed by pyrexia and a pronounced leukocytic influx. Coincident with the onset of mammary inflammation was the appearance of neutrophil chemotactic activity in the milk from infected glands. Factors able to upregulate CD18 expression on peripheral blood neutrophils also appeared in milk at this time. The lack of appearance of chemotactic and CD18-upregulating activities until 12 h after challenge indicated that delays in neutrophil recruitment resulted from an initial lack of bacterial recognition and inflammatory mediator production. Production of complement fragment C5a, tumor necrosis factor, and interleukin-1 (IL-1) occurred earlier than production of IL-6 or IL-8. The early and intense production of C5a indicates that this chemoattractant may be more important than IL-8 during the initial recruitment and activation of neutrophils to a developing E. coli infection.

Effect of recombinant bovine interleukin-1 beta in normal calves and in calves infected with bovine herpesvirus type 1

Bovine herpesvirus-1 (BHV-1) is an important pathogen of respiratory infections in cattle. Its continuing importance lies in its ability to predispose infected hosts to bacterial infections. In this present study, we determined whether the immunoregulatory effects induced by interleukin-1 (IL-1) could stimulate appropriate host defense mechanisms to influence the course of BHV-1 infection in cattle. We first evaluated the effect of different doses (10-1000 ng/kg) of IL-1 in normal cattle. A single administration of IL-1 was able to induce a dose-dependent increase in polymorphonuclear (PMN) cells as well as monocytes in peripheral blood. The number of CD3+ lymphocytes and gamma/delta T cells in peripheral circulation decreased transiently in a dose-dependent manner. In the disease model, the effect of IL-1 administration (300 ng/kg) 24 h before, at the time of, and 24 h after the BHV-1 challenge was assessed. As a single therapeutic modality, IL-1 did not significantly reduce the establishment or progression of BHV-1-induced disease. Nevertheless, our results demonstrated that the significant modulation of diverse immune parameters did not exacerbate disease. Thus, the use of IL-1 as an adjunct therapy or as a vaccine adjuvant in cattle can be safely considered in situations where BHV-1 infection is likely to occur.

Bacterial growth, inflammatory cytokine production, and neutrophil recruitment during coliform mastitis in cows within ten days after calving, compared with cows at midlactation

OBJECTIVE

To define causes of increased susceptibility to coliform mastitis after parturition.

ANIMALS

12 healthy Holstein cows assigned to 2 groups. Group-1 cows (n = 6) had calved between 6 and 10 days earlier. Group-2 cows (n = 6) were in midlactation.

PROCEDURE

Cows from each group were paired and challenge exposed with Escherichia coli in 1 mammary gland. Mastitis severity was determined by bacterial concentration in milk, pyrexia, and milk production. Measures of host defense were neutrophil chemotaxis, adhesion molecule expression, leukocyte recruitment, and cytokine production.

RESULTS

After challenge exposure, group-1 cows had more rapid E coli growth, higher peak bacterial concentration, and higher fever. Leukocyte recruitment was poor in 1 group-1 cow that had peracute mastitis. In contrast, leukocyte recruitment in 5 other group-1 cows began sooner than that in group-2 cows. In these group-1 cows, prechallenge-exposure milk somatic cell counts (SCC) were significantly lower than those in group-2 cows. Prechallenge-exposure SCC were correlated to stimulated CD18 expression (R2 = 0.79), and both measures correlated inversely with bacterial growth rate (R2 = -0.75). Values for tumor necrosis factor alpha, interleukin 1, and interleukin 8 in group-1 cows after challenge exposure were greater than or equal to those in group-2 cows.

CONCLUSIONS

Weak leukocyte recruitment to the mammary gland is associated with increased severity of coliform mastitis. Impaired production of cytokines measured is not a cause of increased susceptibility to coliform mastitis in early lactation.

CLINICAL RELEVANCE

Low milk SCC after calving may increase susceptibility to severe coliform mastitis.

Relationship of inflammatory cytokines, growth hormone, and insulin-like growth factor-I to reduced performance during infectious disease

Production of inflammatory cytokines and concentrations of growth hormone and insulin-like growth factor-I (IGF-I) were studied during experimental Escherichia coli mastitis to determine their potential involvement in reduced animal performance during infectious disease. During the first 10 to 14 hr after intramammary infusion of E. coli, bacteria multiplied to maximum levels of 10(4)-10(9) cfu/ml of milk with no clinical signs of mastitis. A rapid and intense inflammatory response, characterized by udder swelling, increased bovine serum albumin (BSA) and somatic cell count (SCC) in milk of infected glands, and elevated rectal temperature and serum cortisol concentration, began at approximately 12 hr after challenge. Lactational performance was reduced greatly at 24 hr, and the maximal decrease averaged 76% and 63% among infected and uninfected glands, respectively, of challenged cows; three cows became temporarily agalactic in all glands. By 6 days, all cows had nearly or completely eliminated the E. coli, and milk production had partially recovered. Milk composition showed an initial decrease in fat percentage followed by an increase thereafter. Protein percentage was increased and lactose content was reduced during most of the mastitic episode. High concentrations of tumor necrosis factor (TNF) and interleukin-1 (IL-1) were detected in milk of infected glands, and their appearance preceded or coincided with development of the mammary inflammation, systemic reaction, and hypogalactia. Serum growth hormone concentration was higher among challenged cows, whereas serum IGF-I concentrations changed little during the mastitic episode. Concentrations of IGF-I in milk whey increased from 5.0 to 12.2 ng/ml among infected glands and from 4.4 to 8.5 ng/ml among contralateral, uninfected glands; IGF binding proteins also increased in the milk of infected glands. These data demonstrate that (i) reduced lactational performance is not caused by reduced concentrations of growth hormone or IGF-I and (ii) inflammatory cytokines are produced at a time consistent with a possible role in the inhibition of milk synthesis.

Regulation of bovine acute phase responses by recombinant interleukin-1 beta

The acute phase response is a collection of physiologic changes initiated early in the inflammatory process. This response is comprised of both localized changes at the site of infection or injury and the initiation of systemic responses, such as the increase in production of acute phase proteins. Cytokines such as interleukin (IL)-1, IL-6, and tumor necrosis factor (TNF) play key roles in the regulation of acute phase response in the species studied to date. To better characterize the acute phase response of cattle, recombinant bovine (rBo). IL-1 beta was administered to cattle. A single administration of rBoIL-1 beta was able to induce a dose dependent increase in body temperature, circulating leukocytes, and serum haptoglobin and fibrinogen concentrations, as well as a decrease in plasma zinc concentration. Five daily administrations of rBoIL-1 beta resulted in heightened and prolonged elevations of haptoglobin and fibrinogen. In addition, alpha 1-acid glycoprotein levels were increased, a response not seen after a single administration of rBoIL-1 beta. These results indicate that IL-1 is an important regulator of the acute phase response in cattle.

Effect of recombinant bovine interleukin-1 beta on viral/bacterial pneumonia in cattle

Bovine herpesvirus-1 (BHV-1) is an important pathogen of respiratory infections in cattle. Its continuing importance lies in its ability to predispose infected hosts to bacterial infections (e.g., Pasteurella haemolytica). In this study we determined whether the immunoregulatory effects induced by recombinant bovine interleukin-1 (rbIL-1) could stimulate appropriate host defense mechanisms to influence the course of BHV-1 and P. haemolytica infection in cattle. We first evaluated the effect of multiple doses (5 doses of 300 ng/kg) of rbIL-1 in normal cattle. An increase in polymorphonuclear (PMN) cells, as well as monocytes, in peripheral blood was observed during the course of IL-1 administration. In addition, the phagocytic activity of monocytes was increased. Although the phagocytic and oxidative burst activities in PMN decreased during the course of rbIL-1 treatment, no changes were observed in the bactericidal capacity of these cells. Lymphocyte numbers in peripheral blood remained unchanged; however, the functional activity of these cells, as measured by IFN-gamma production upon in vitro stimulation, was decreased. In the bovine respiratory disease model, multiple administration of IL-1 did not influence significantly the progression of BHV-1/P. haemolytica infection in cattle. Thus, our results demonstrated that IL-1, although not therapeutically effective, could be administered safely as an adjuvant, even during the course of BHV-1/P. haemolytica infection.

Administration of recombinant human interleukin 1 receptor antagonist during endotoxin-induced mastitis in cows

The role of interleukin 1 (IL-1) as an inflammatory mediator during mastitis and the therapeutic effect of recombinant human IL-1 receptor antagonist (IL-1ra) for bovine mastitis was studied. Cows were intramammarily infused with lipopolysaccharide (25 micrograms) in 1 mammary gland. Half the cows also received infusions of 5 mg of IL-1ra into the same mammary gland just prior to endotoxin infusion and 4, 8, and 12 hours later. After endotoxin infusion, tumor necrosis factor and high IL-1 bioactivity were detected in whey from infused glands. Vascular permeability changes and neutrophil accumulation in milk paralleled the appearance of cytokines. A systemic reaction, characterized by pyrexia and an increase in blood cortisol concentration, also were observed. Milk yield was inhibited and milk composition was altered in infused and noninfused glands. The increase in IL-1 bioactivity in milk after endotoxin infusion was almost completely prevented in glands receiving IL-1ra. However, IL-1ra had no effect on local inflammation, systemic reaction, or impairment in productive performance. These results indicate that IL-1 does not mediate its effect within the milk compartment, and suggest either that IL-1 is not critical to the mastitic response or that intramammary infusion of IL-1ra does not place the antagonist where IL-1 interacts with its receptor.

Factors affecting milk somatic cells and their role in health of the bovine mammary gland

Milk somatic cells play a protective role against infectious disease in the bovine mammary gland. Many genetic and environmental factors affect the number and kinds of leukocytes that account for the vast majority of somatic cells in milk. Neutrophils constitute the vast majority of somatic cells in mammary glands that are infected with mastitis pathogens. The recruitment of neutrophils into the infected mammary gland is a normal part of the cow's defense mechanisms that is very effective for eradicating the majority of infections that occur. For many reasons, milk production and milk quality are negatively impacted by the presence of inflammation in infected glands. Because of the negative effects of high SCC in milk, various approaches are needed to reduce milk SCC. In the future, genetic gains for milk quality and mastitis resistance may be made by removing bulls from breeding programs when their daughters are predisposed to high SCC.

Bovine L-selectin: a peripheral lymphocyte homing receptor

The cDNA clone encoding for the bovine peripheral lymph node homing receptor (L-selectin) was isolated and sequenced. The predicted amino acid sequence of bovine L-selectin showed an overall high identity with that of human and murine L-selectin. However, the cytoplasmic tail of bovine L-selectin showed little similarity to that of human and murine L-selectin. The monoclonal antibody DREG-56, which recognizes human L-selectin, blocked the binding of bovine peripheral blood lymphocytes to high-walled endothelial venules in murine peripheral lymph nodes. Surface expression of bovine L-selectin was high in lymphocytes isolated from peripheral lymph nodes and low in lymphocytes isolated from Peyer's patches. This evidence strongly suggests that bovine L-selectin is a peripheral lymphocyte homing receptor.

Clinical manifestations of leukocyte adhesion deficiency in cattle: 14 cases (1977-1991)

In Holstein cattle, an inherited disease has been recognized recently in which leukocytes lack surface glycoproteins termed beta 2 integrins, which are important in cell adhesion processes. This disease is the homologue of leukocyte adhesion deficiency in human beings and has been termed bovine leukocyte adhesion deficiency. The molecular basis of this disease is failure to produce normal CD18. The gene encoding bovine CD18 and its abnormal mutation have been sequenced, allowing specific diagnosis of the condition by DNA amplification by polymerase chain reaction followed by specific endonuclease digestion. This test was applied to formalin-fixed archival tissues from 18 cattle that had been admitted to the veterinary medical teaching hospital between 1975 and 1991 and that had had persistent and severe neutrophilia. Blood samples were collected from 2 additional cattle, and leukocytes from these samples also were tested. Fourteen cattle were confirmed to have been homozygous for the bovine leukocyte adhesion deficiency gene. Cattle with this condition had ranged in age from 2 weeks to 8 months at admission. They typically had had chronic bacterial infections that had failed to respond to or had recurred after conventional treatment. Consistent findings in these cattle included signs of bronchopneumonia, gingivitis, periodontitis, and peripheral lymphadenopathy. Severe neutrophilia, usually without a left shift, was a hallmark of the disease; consistent clinical biochemical findings included hypoalbuminemia, hyperglobulinemia, and hypoglycemia. This disease is important because it mimics common calfhood diseases such as pneumonia and diarrhea, but is ultimately consistently fatal before adulthood.

Cytokine production during endotoxin-induced mastitis in lactating dairy cows

The role of interleukin-1 (IL-1), interleukin-6 (IL-6), and tumor necrosis factor alpha during endotoxin-induced mastitis in cows was characterized. Six cows had 10 micrograms of Escherichia coli lipopolysaccharide infused into 1 mammary gland. Three other cows served as nontreated controls. Within 1.5 to 2.5 hours after infusion, endotoxin caused obvious edema of the mammary gland and increased serum albumin concentration in milk of infused glands 6 times. Milk somatic cell count began to increase 3 to 5 hours after infusion in all treated glands. At 7 hours after infusion, somatic cell counts were increased > 10 times, compared with counts in milk from control cows. Pyrexia of > 1 C developed in only 1 cow, but all treated cows had serum cortisol concentrations > 50 ng/ml in response to endotoxin treatment. High concentrations of IL-1 (10 to 600 U/ml) and IL-6 (2 to 22 U/ml) were detected in milk of infused glands beginning 2.5 to 4 hours after infusion. Endotoxin did not induce detectable amounts of tumor necrosis factor activity in milk or serum. Swelling and mammary gland permeability changes preceded any detectable increase in IL-1 and IL-6 activity, indicating that these clinical signs of inflammation were not mediated by these cytokines. Systemic responses and the leukocytic influx into endotoxin-infused glands developed after or concurrently with initial increases in IL-1 and IL-6 activities in milk. These results suggested that IL-1 and IL-6 may have a role in mammary gland defenses and in the pathophysiologic changes during endotoxin-induced mastitis.

Identification and prevalence of a genetic defect that causes leukocyte adhesion deficiency in Holstein cattle

Two point mutations were identified within the gene encoding bovine CD18 in a Holstein calf afflicted with leukocyte adhesion deficiency (LAD). One mutation causes an aspartic acid to glycine substitution at amino acid 128 (D128G) in the highly conserved extracellular region of this adhesion glycoprotein, a region where several mutations have been found to cause human LAD. The other mutation is silent. Twenty calves with clinical symptoms of LAD were tested, and all were homozygous for the D128G allele. In addition, two calves homozygous for the D128G allele were identified during widespread DNA testing, and both were subsequently found to exhibit symptoms of LAD. The carrier frequency for the D128G allele among Holstein cattle in the United States is approximately 15% among bulls and 6% among cows. This mutation is also prevalent among Holstein cattle throughout the world, placing this disorder among the most common genetic diseases known in animal agriculture. All cattle with the mutant allele are related to one bull, who through the use of artificial insemination sired many calves in the 1950s and 1960s. The organization of the dairy industry and the diagnostic test described herein will enable nearly complete eradication of bovine LAD within 1 year. These results also demonstrate that bovine LAD is genetically homologous and phenotypically similar to human LAD, thus providing a useful animal model for studies of LAD and beta 2 integrin function.

Bovine leukocyte adhesion deficiency. Beta 2 integrin deficiency in young Holstein cattle

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Sequence of the bovine CD18-encoding cDNA: comparison with the human and murine glycoproteins

The bovine cDNA (CD18) encoding CD18, a cell-surface glycoprotein involved in multiple leukocyte functions, was sequenced and compared with the human and murine sequences. Portions of the 5'- and 3'-untranslated regions of the nucleotide sequences are conserved among the three species, including a 3' A+T-rich region believed to regulate mRNA stability and translational efficiency. The 2833-bp bovine sequence coded for a protein of 769 amino acids (aa). Overall, the deduced aa sequences were greater than 80% identical among the three species. The aa 96-389 and those in the cytoplasmic domain were very highly conserved with approx. 95% aa identity. All Cys residues and potential Asn-glycosylation sites present in the bovine sequence were also present in the human and murine sequences. The aa identity was also found in those regions where mutations were found to cause the genetic disease, leukocyte adhesion deficiency. These data identify functionally important regions of the CD18 mRNA and protein.

High cortisol concentrations and mediation of the hypogalactia during endotoxin-induced mastitis

A series of experiments was conducted to define the role of cortisol in the hypogalactia during endotoxin-induced mastitis. In the first experiment, three of six nonmastitic cows were given a continuous infusion of trilostane, a 3 beta-hydroxysteroid dehydrogenase inhibitor that blocks enhanced cortisol synthesis. Trilostane had no effect in these cows. In the second experiment, six midlactation cows were given 10 micrograms of endotoxin in each of two homolateral quarters to induce mastitis. Three of these cows also received trilostane. Increased serum cortisol following endotoxin infusion was blocked by trilostane treatment, whereas serum glucose and rectal temperatures were unaffected. Preventing the cortisol increase failed to reduce hypogalactia in endotoxin-infused or uninfused quarters. Decreases in milk production and increases in measures of mammary inflammation were greater in trilostane-treated cows, indicating that endogenous cortisol may moderate the cow's inflammatory response. In the third experiment, three of six nonmastitic cows were injected intramuscularly with 150 IU of ACTH. Serum cortisol concentration exceeded 70 ng/ml for at least 3 h in cows receiving ACTH. This cortisol concentration, comparable with concentrations found during endotoxin mastitis, did not inhibit milk production. Together, these data demonstrate that the acute cortisol increase does not mediate the hypogalactia associated with endotoxin-induced mastitis.

Light microscopic and ultrastructural pathology of seminiferous tubules of rats given multiple doses of Pasteurella multocida group D protein toxin

Male Holtzman rats were given subcutaneous doses of a purified Pasteurella multocida group D heat-labile toxin on alternate days for up to 22 days. Rats were necropsied at 18 days or 36 days (14 days after last dose of toxin) or when moribund, and testicles were taken for histologic and ultrastructural examination. Other selected tissues, including liver and spleen, were taken for histologic examination. Histologically, testicular and splenic lesions occurred more consistently and at much smaller doses when compared with lesions in other target organs such as liver. Testicular and splenic lesions were present in all rats (6/6) given 0.8 micrograms/kg toxin and were seen in some rats (1/6) given as little as 0.2 micrograms/kg toxin. Only 3/6 rats given 0.8 micrograms/kg toxin had hepatic lesions; no hepatic lesions were seen at doses of 0.2 micrograms/kg. Testicles from toxin-treated rats were smaller and weighed less than controls. Seminiferous tubules were moderately dilated and lined by polygonal sertoli cells. The normal spermatogenic maturation sequence and mature spermatids were absent, and many tubules contained multinucleate spermatocytes. Severely affected tubules were necrotic and mineralized. Ultrastructurally, there was necrosis of adluminal spermatocytes, multinucleate cell formation, and spaces between Sertoli cell plasma membranes. Testicular lesions were similar to those described for vitamin D-deficient rats, vitamin A-deficient rats, vasectomized rats, and rats given intravenous tumor necrosis factor; however, rats given lethal doses of toxin did not have elevated levels of TNF alpha activity.

Lactating cows become partially refractory to frequent intramammary endotoxin infusions: recovery of milk yield despite a persistently high somatic cell count

Midlactation cows were infused with 10 micrograms endotoxin in the same two homolateral quarters after each of several consecutive milkings to study the effect of prolonged, endotoxin-induced mastitis on lactational performance. The initial infusion induced an acute response with systemic involvement. Inflammation developed in infused quarters, and milk production declined and milk composition was altered in all quarters. Subsequent infusions failed to induce systemic responses. Furthermore, milk yield and composition in uninfused quarters returned to pre-treatment levels despite further infusions. In infused quarters, milk yield, protein percentage and serum albumin concentration showed partial recovery during the endotoxin infusion period. In contrast, decreased lactose concentration, and increased cell count, N-acetyl-beta-D-glucosaminidase and lactoferrin levels persisted throughout the infusion period. After infusions were stopped, all measurements returned to near pretreatment levels. These data demonstrate that systemic, but not local, responses become refractory to multiple intramammary endotoxin infusions, and that multiple infusions have continued but little progressive or permanent, inhibitory effects on lactational performance despite a persistent mammary leucocytosis.

Suppression of milk production during endotoxin-induced mastitis

Healthy, midlactation cows were given intramammary infusions of 10 micrograms of endotoxin in two homolateral quarters. Productive, inflammatory, and systemic responses were studied to investigate the pathophysiological effects of mastitis on lactational performance. Endotoxin suppressed milk yield in all quarters of treated cows. A more severe and prolonged suppression occurred in infused quarters compared with uninfused quarters. The fat percentage of milk from all quarters was increased with a greater increase occurring in infused quarters. The protein composition of milk was elevated, and the lactose concentration was depressed in infused quarters. Mammary inflammation--as measured by milk SCC, NAGase, serum albumin, and lactoferrin--was limited to infused quarters. Changes in milk NAGase closely paralleled changes in milk SCC. Daily feed intake was unaffected, and serum glucose levels did not decline following infusion. The lactose concentration of urine increased rapidly after infusion. Reduction in milk yield in all quarters, but varying changes in milk composition in infused versus uninfused quarters suggest that mastitic hypogalactia is mediated by multiple pathophysiological events and is not solely due to inflammatory damage to the mammary epithelium. Part of the reduced lactational performance may result from escape of milk components from the udder into the circulation.

Reduced lactational performance following intravenous endotoxin administration to dairy cows

Nonpregnant lactating cows were given 100 micrograms of endotoxin via the jugular vein to determine effects of intravenous endotoxin administration on mammary inflammation and lactational performance. At the first milking (11 h) posttreatment, milk yield was reduced 33%. Milk fat percentage was elevated at this time, but lactose concentration was decreased. Milk yield and composition returned to pretreatment levels within 2 d. Clinical mastitis was not induced by endotoxin treatment, but milk SCC, NAGase, serum albumin, and lactoferrin were increased by 50%. This increase was small compared with increases during mastitis and may have resulted from lower milk volume. These results support the hypothesis that part of the reduced lactational performance during endotoxin mastitis is mediated by systemic pathophysiological responses and indicate that intravenous endotoxin administration may be a useful model to study adverse effects of infectious disease on lactational performance.

Endotoxin mastitis in cows milked four times daily

As part of a project to identify the pathophysiological cause or causes of mastitic hypogalactia, midlactation cows were infused in two homolateral quarters with 10 micrograms of endotoxin while being milked four times daily to resolve better the temporal changes in mammary synthetic activity during endotoxin mastitis. Milk fat was decreased by the first milking (5 h) postinfusion and then recovered rapidly. In contrast, milk yield and the yields of protein and lactose were not significantly inhibited until the second milking, and these yields recovered slowly thereafter. The decline in milk yield by infused quarters was only 20% greater than the decline by uninfused quarters in this experiment. Mammary inflammation developed rapidly in infused quarters as milk serum albumin concentration was maximal at the first milking. Milk SCC and NAGase were also elevated at this time, and maximal levels occurred at milkings 2 to 4. Increased temperature, increased cortisol, and a mild anorexia were apparent at the first milking only. Endotoxin treatment had no effect on serum prolactin or glucose. These data suggest that the delayed hypogalactia is consequent to the mammary inflammation and systemic responses following endotoxin infusion. The results indicate that different pathophysiological events may inhibit synthesis of the different milk components.

Physiological responses to intramammary or intravenous treatment with endotoxin in lactating dairy cows

Twenty-one, middle to late lactation Holstein cows were assigned to one of three treatments in a completely randomized design to examine physiological changes associated with intramammary or intravenous administration of Escherichia coli endotoxin. Treatments were 1) Hank's balanced salt solution infusion in two contralateral quarters (control), 2) E. coli endotoxin infusion in two contralateral quarters, and 3) intravenous infusion of E. coli endotoxin. Blood was sampled and rectal temperature was measured at 30-min intervals. Endotoxin treatment was at 0900 h and sampling continued until 1700 h. Serum prolactin, cortisol, and 13,14-dihydro-15-keto-prostaglandin F2 alpha were measured. A pyretic response was observed in intravenous and intramammary treatment groups after endotoxin treatment. Response peak was higher (41.1 vs. 40.3 degrees C) and occurred later (6 vs. 4.5 h posttreatment) in the intramammary than the intravenous treatment group. Significant prolactin peaks were observed also in intravenous and intramammary endotoxin treatment groups. Prolactin peaked higher (288 vs. 112 ng/ml) and occurred sooner (1 vs. 4 h posttreatment) in the intravenous than in the intramammary treatment group. Cortisol followed a trend similar to prolactin. Cortisol peaked higher (100 vs. 82 ng/ml) and sooner (2.5 vs. 4.5 h posttreatment) in the intravenous than in the intramammary treatment group. Concentrations of 13,14-dihydro-15-keto-prostaglandin F2 alpha increased rapidly posttreatment in the intravenous group only.

Effects of premilking udder preparation on bacterial population, sediment, and iodine residue in milk

Udder preparations that wet both udder surfaces and teats had the highest standard plate count in milk compared with methods that wet teats only. Physical action of cleaning teats with a dry towel lowered bacterial count compared with preparations wetting both udder surfaces and teats. Methods resulting in lowest bacterial counts were the use of water hose, wet towel, or premilking disinfectant teat dip followed by drying with paper towels. Counts of coliform and Staphylococcus sp. followed similar trends. In most comparisons, addition of udder wash sanitizer was of marginal or no benefit. Standard plate count of teat rinses after udder preparation confirmed the benefit of cleaning and drying teats. Physical manipulation of teats during cleaning was essential for lowering sediment in milk. Drying of teats with a paper towel for at least 10 s after dipping with a 1% iodophor disinfectant dip was essential for reducing iodine residue. Both premilking and postmilking disinfectant teat dipping with a 1% iodophor teat dip caused higher iodine residue in milk than premilking disinfectant dip with subsequent drying. A .5% iodophor teat dip contributed less iodine in milk than a 1% iodophor teat dip. Premilking udder preparation affects bacterial count, sediment, and iodine residue in milk.