Safety and efficacy of upadacitinib in combination with topical corticosteroids in adolescents and adults with moderate-to-severe atopic dermatitis (AD Up): results from a randomised, double-blind, placebo-controlled, phase 3 trial.

BACKGROUND: Systemic therapies are typically combined with topical corticosteroids for the management of moderate-to-severe atopic dermatitis. Upadacitinib is an oral Janus kinase (JAK) inhibitor with greater inhibitory potency for JAK1 than JAK2, JAK3, or tyrosine kinase 2 that is being tested for atopic dermatitis. We aimed to assess the efficacy and safety of upadacitinib plus topical corticosteroids compared with placebo for the treatment of moderate-to-severe atopic dermatitis. METHODS: In this randomised, double-blind, placebo-controlled, phase 3 trial (AD Up) adults (aged 18-75 years) and adolescents (aged 12-17 years) with chronic atopic dermatitis that was moderate to severe (≥10% of body surface area affected, Eczema Area and Severity Index [EASI] score of ≥16, validated Investigator's Global Assessment for atopic dermatitis [vIGA-AD] score of ≥3, and weekly average Worst Pruritus Numerical Rating Scale score of ≥4 at baseline) were enrolled at 171 clinical centres across 22 countries in the Asia-Pacific region, Europe, the Middle East, North America, and Oceania. Patients were randomly assigned (1:1:1) to receive upadacitinib 15 mg, upadacitinib 30 mg, or placebo once daily, all in combination with topical corticosteroids for 16 weeks. Randomisation was done using an interactive response technology system, stratified by baseline disease severity, geographical region, and age. Study investigators, study site personnel, and patients were masked to study treatment. The coprimary endpoints were the proportion of patients who had achieved at least a 75% reduction in EASI score from baseline (EASI-75) and the proportion of patients who had achieved a vIGA-AD response (defined as a vIGA-AD score of 0 [clear] or 1 [almost clear] with ≥2 grades of improvement from baseline) at week 16. Efficacy was analysed in the intention-to-treat population and safety was analysed in all patients who received at least one dose of study drug. This study is registered with ClinicalTrials.gov, NCT03568318, and is active, but not recruiting. FINDINGS: Between Aug 9, 2018, and Dec 20, 2019, 901 patients were randomly assigned to receive upadacitinib 15 mg plus topical corticosteroids (n=300), upadacitinib 30 mg plus topical corticosteroids (n=297), or placebo plus topical corticosteroids (n=304). At week 16, the proportion of patients who had achieved EASI-75 was significantly higher in the upadacitinib 15 mg plus topical corticosteroid group (194 [65%] of 300 patients) and the upadacitinib 30 mg plus topical corticosteroids group (229 [77%] of 297 patients) than the placebo group (80 [26%] of 304 patients; adjusted difference in EASI-75 response rate vs placebo, 38·1% [95% CI 30·8-45·4] for the upadacitinib 15 mg group and 50·6% [43·8-57·4] for the upadacitinib 30 mg group; p<0·0001 for both doses). The proportion of patients who had achieved a vIGA-AD response at week 16 was significantly higher in the upadacitinib 15 mg plus topical corticosteroid group (119 [40%] patients) and upadacitinib 30 mg plus topical corticosteroid group (174 [59%] patients) than the placebo group (33 [11%] patients; adjusted difference in vIGA-AD response vs placebo, 28·5% [22·1-34·9] for the upadacitinib 15 mg group and 47·6% [41·1-54·0] for the upadacitinib 30 mg group; p<0·0001 for both doses). During the double-blind period, upadacitinib 15 and 30 mg were well tolerated in combination with topical corticosteroids. The most frequently reported treatment-emergent adverse events (≥5% in any treatment group) were acne, nasopharyngitis, upper respiratory tract infection, oral herpes, elevation of blood creatine phosphokinase levels, headache, and atopic dermatitis. The incidence of acne was higher in the upadacitinib 15 mg (30 [10%] of 300 patients) and upadacitinib 30 mg (41 [14%] of 297 patients) groups than the placebo group (six [2%] of 304 patients). The incidence of adverse events leading to discontinuation of study drug (four [1%] patients in the upadacitinib 15 mg plus topical corticosteroids group, four [1%] patients in the upadacitinib 30 mg plus topical corticosteroids group, and seven [2%] patients in the placebo plus topical corticosteroids group) and serious adverse events (seven [2%] patients, four [1%] patients, and nine [3%] patients) were similar among treatment groups. No deaths were reported in any treatment group. INTERPRETATION: Upadacitinib plus topical corticosteroids was well tolerated and superior to placebo plus topical corticosteroids. Upadacitinib as combination therapy had a positive benefit-risk profile in adults and adolescents with moderate-to-severe atopic dermatitis. FUNDING: AbbVie.

Using the Bayesian detection of potential risk using inference on blinded safety data (BDRIBS) method to support the decision to refer an event for unblinded evaluation.

In the Sponsor Responsibilities-Safety Reporting Requirements and Safety Assessment for IND and Bioavailability/Bioequivalence Studies: Draft Guidance for Industry (June 2021) the Food and Drug Administration recommends that sponsors develop a Safety Surveillance Plan as a key element of a systematic approach to safety surveillance and describes two possible approaches to assess the aggregate safety data. One approach regularly analyzes unblinded serious adverse events (SAEs) by treatment group. The alternative approach prespecifies estimated background rates for anticipated SAEs in the study population (e.g., myocardial infarctions in an older adult population). If the event rate in the blinded data from the study population exceeds a "trigger rate," then an unblinded analysis by treatment group is conducted. The Bayesian detection of potential risk using inference on blinded safety data (BDRIBS) method has been previously described and offers a quantitative approach for assessing blinded events. In this article we provide a procedural workflow for blinded review of safety data that is consistent with the unblinding "trigger approach" for aggregate safety review. In addition, this publication contextualizes the use of BDRIBS within the broader safety surveillance framework, extends the method to allow for multiple studies, and offers examples of its use in various settings via an R-Shiny application that allows for dynamic visualization and assessment.

How Aggregate Safety Assessment Planning Supports Investigational New Drug Safety Reporting Decisions.

In June 2021, FDA released a Draft Guidance on Sponsor Responsibilities for IND Safety Reporting and cited components of a recommended Safety Surveillance Plan (SSP). To meet the expectations of the 2021 FDA guidance, sponsors should document their plan for aggregate safety assessment. The Drug Information Association-American Statistical Association Interdisciplinary Safety Evaluation scientific working group has proposed an Aggregate Safety Assessment Plan (ASAP) that addresses this recommendation. The 2021 FDA guidance also discusses potential strategies for unblinded review of safety data from ongoing studies by an independent Assessment Entity, which could occur via planned periodic evaluations or "triggered" reviews based on blinded data assessments. The Assessment Entity reviewing unblinded data makes recommendations as to whether the threshold has been met for submission of an aggregate IND safety report. In this paper, we discuss how the ASAP supports IND aggregate safety reporting decisions, including elements to be included in a proposed SSP appendix to the ASAP. In addition, the authors advocate for the benefits of developing a charter (or specific section of the Data Monitoring Committee charter, if applicable) that describes the responsibilities and conduct of the Assessment Entity. With these components in place, study sponsors will meet the objective of having clearly defined processes for the monitoring of clinical trial safety data in aggregate and making IND safety reporting decisions.

Value and Implementation of the Aggregate Safety Assessment Plan.

Aggregate safety assessment involves evaluation of the totality of safety data to characterize the emerging safety profile of a product. The Drug Information Association-American Statistical Association Interdisciplinary Safety Evaluation scientific working group recently published an approach to developing an Aggregate Safety Assessment Plan (ASAP). Creation of an ASAP facilitates a consistent approach to safety data collection and analysis across studies and minimizes important missing data at the time of regulatory submission. A critical aspect of the ASAP is identification of the Safety Topics of Interest (STOI). The STOI, as defined in the ASAP, comprises adverse events (AEs), which have the potential to impact the benefit: risk profile of a product and typically require specialized data collection or analyses. While there are clear benefits to developing an ASAP for a drug development program, multiple concerns may be encountered with implementation. This article uses the examples of two STOIs to demonstrate the benefits and efficiencies gained with implementation of the ASAP in safety planning as well as in optimally characterizing the emerging safety profile of a product.

Interdisciplinary Safety Evaluation for Learning and Decision-Making.

The FDA IND safety reporting Final Rule (21CFR 312.32) applies to all human drugs and biological products being studied under an Investigational New Drug (IND). A sponsor must file an IND safety report for any serious unexpected suspected adverse reaction (SUSAR) of a medicinal product being investigated. Some events may be obviously drug-related (e.g., agranulocytosis, anaphylactic reaction, drug-induced hepatic injury, Stevens-Johnson Syndrome). For serious adverse events that are not interpretable as individual occurrences, additional processes and procedures need to be employed for identifying and assessing risks in the accumulating safety data. The approaches shared in this manuscript apply principally to safety reporting of events that are anticipated to occur in the patient population-regardless of study participation. For these events, the study sponsor should periodically review the data in the aggregate and make a judgment as to whether there is a reasonable possibility of an event having been caused by the study drug rather than the underlying condition of the patient or a concomitant therapy. Factors cited for consideration are the size and consistency of the difference in event frequency between the test and control groups, supportive preclinical findings, evidence of a dose response relationship, plausible mechanism of action, known class effect and occurrence of other related adverse events. Examples are provided that demonstrate the flexibility sponsors have in meeting the spirit of the Final Rule; some combination and variation of methods from the examples could be employed. The important thing, as expressed by Jacqueline Corrigan-Curay (Director of the Office of Medical Policy, Center for Drug Evaluation and Research, FDA), is to have a thoughtful process; a system in place to look for clinically important imbalances, applying the best clinical and quantitative judgment, while maintaining trial integrity (Ball et al. in Interdisciplinary aggregate assessments for IND safety reporting: a dialogue among colleagues from industry, Academia and the FDA. ASA biopharmaceutical section regulatory-industry statistics workshop, 2018).

Aggregate Safety Assessment Planning for the Drug Development Life-Cycle.

The Program Safety Analysis Plan (PSAP) was proposed previously as a tool to proactively plan for integrated analyses of product safety data. Building on the PSAP and taking into consideration the evolving regulatory landscape, the Drug Information Association-American Statistical Association (DIA-ASA) Interdisciplinary Safety Evaluation scientific working group herein proposes the Aggregate Safety Assessment Plan (ASAP) process. The ASAP evolves over a product's life-cycle and promotes interdisciplinary, systematic safety planning as well as ongoing data review and characterization of the emerging product safety profile. Objectives include alignment on the safety topics of interest, identification of safety knowledge gaps, planning for aggregate safety evaluation of the clinical trial data and preparing for safety communications. The ASAP seeks to tailor the analyses for a drug development program while standardizing the analyses across studies within the program. The document is intended to be modular and flexible in nature, depending on the program complexity, phase of development and existing sponsor processes. Implementation of the ASAP process will facilitate early safety signal detection, improve characterization of product risks, harmonize safety messaging, and inform program decision-making.

A Framework for Safety Evaluation Throughout the Product Development Life-Cycle.

Evaluation of the safety profile of medicines is moving from a more reactive approach, where safety experts and statisticians have been primarily focusing on the review of clinical trial data and spontaneous reports, to a more proactive endeavor with cross-functional teams strategically evolving their understanding of the safety profile. They do this by anticipating the ultimate benefit-risk profile and its related risk management implications from the start of development. The proposed approach is based on assessments of integrated program-level safety data. These data stem from multiple sources such as preclinical information; clinical and spontaneous adverse event reports; epidemiological, real-world, and registry data; as well as, potentially, data from social media. Blended qualitative and quantitative evaluations allow integration of data from diverse sources. Adding to this, a collaborative multidisciplinary view, which is focused on continuous learning and decision-making via diverse safety management teams, ensures that companies look at their growing safety database and associated risk management implications from every relevant perspective. This multifaceted and iterative approach starts early in the development of a new medicine, continues into the post-marketing setting, and wanes as the product matures and the safety profile becomes more well understood. Not only does this satisfy regulatory requirements but, crucially, it provides the healthcare system and treated patients with a better understanding of the drug's safety profile.

Global Regulatory Landscape for Aggregate Safety Assessments: Recent Developments and Future Directions.

Notwithstanding successful harmonization efforts, the global regulatory framework governing product safety is complex and continually evolving, as evidenced by additional regional guidance and regulations. In this regulatory review, we provide an overview from both global and regional perspectives. A historical perspective, with a focus on recent developments, enables identification of important long-term trends, such as a shift from single-case medical review of serious adverse events to an interdisciplinary evaluation of aggregate data for the purpose of judging product causality and informing benefit-risk assessments. We will show how these trends lead to opportunities for closer interdisciplinary collaboration, for bridging the gap between preand postmarketing surveillance, and for a more proactive determination of patient populations with a positive benefit-risk profile for product use. We will conclude by pointing to ongoing and future work that seeks to provide specific solutions for ongoing aggregate safety evaluation.

Monitoring Drug Safety in Rheumatoid Arthritis Prevention Trials.

This commentary discusses issues particular to drug safety monitoring in prevention trials. Although the general approach to safety assessment applies across all clinical trials, prevention trials pose special challenges given that the patient population is currently asymptomatic or experiencing only mild symptoms of the targeted disease. This sways the risk-benefit analysis balance toward minimal acceptable risk. Definition of the predisease state with validated biomarkers or other assessment tools is essential. The timing and required length of exposure to the disease intervention to produce an effect requires special methodologic considerations. In addition, prevention trials generally have a longer duration with higher dropout rates. As a result, there is an enhanced focus on lessening patient burden in regard to data collection and finding ways to minimize the safety signal to noise ratio to enable product causality assessment. To meet these challenges, clinical safety monitoring in prevention trials involves 3 essential steps: safety planning, systematic data collection and evaluation, and transparent communication of safety information. We discuss some of these issues using historical experience with primary prevention cardiovascular trials and then focus on unique issues surrounding patient populations at risk for rheumatoid arthritis.

Safety of Adalimumab Dosed Every Week and Every Other Week: Focus on Patients with Hidradenitis Suppurativa or Psoriasis.

BACKGROUND: Adalimumab is approved for the treatment of hidradenitis suppurativa (HS), plaque psoriasis, and other inflammatory conditions. OBJECTIVE: Our objective was to examine the safety of adalimumab administered every other week (EOW) and every week (EW) in patients with HS and psoriasis and to investigate informative data from non-dermatologic indications. METHODS: The safety of adalimumab 40-mg EOW versus EW dosing was examined during placebo-controlled and open-label study periods in patients with HS (three studies), psoriasis (two studies), Crohn's disease (six studies), ulcerative colitis (three studies), and rheumatoid arthritis (one study). RESULTS: No new safety risks or increased rates of particular adverse events (AEs) were identified with EW dosing. In patients with HS or psoriasis, the overall safety of adalimumab 40-mg EOW and EW was generally comparable. In studies of adalimumab for non-dermatologic indications, including Crohn's disease, ulcerative colitis, and rheumatoid arthritis, the overall AE rates were similar for EW and EOW dosing. CONCLUSION: In patients with HS or psoriasis, the safety of adalimumab EW and EOW was comparable and consistent with the expected adalimumab AE profile. The safety of adalimumab EW dosing in patients with dermatologic conditions is supported by data comparing adalimumab EW and EOW dosing for Crohn's disease, ulcerative colitis, and rheumatoid arthritis. TRIAL REGISTRATION: ClinicalTrials.gov NCT00918255, NCT01468207, NCT01468233, NCT00645814, NCT00077779, NCT00055497, NCT01070303, NCT00195715, NCT00348283, NCT00385736, NCT00408629, and NCT00573794.

RPC4046, A Novel Anti-interleukin-13 Antibody, Blocks IL-13 Binding to IL-13 α1 and α2 Receptors: A Randomized, Double-Blind, Placebo-Controlled, Dose-Escalation First-in-Human Study.

INTRODUCTION: A unique anti-interleukin (IL)-13 monoclonal antibody, RPC4046, was generated on the basis of differential IL-13 receptor (R) blockade as assessed in a murine asthma model; the safety, tolerability, pharmacokinetics, and pharmacodynamics of RPC4046 were evaluated in a first-in-human study. METHODS: Anti-IL-13 antibodies with varying receptor blocking specificity were evaluated in the ovalbumin-induced murine asthma model. A randomized, double-blind, placebo-controlled, dose-escalation first-in-human study (NCT00986037) was conducted with RPC4046 in healthy adults and patients with mild to moderate controlled asthma. RESULTS: In the ovalbumin model, blocking IL-13 binding to both IL-13Rs (IL-13Rα1 and IL-13Rα2) inhibited more asthma phenotypic features and more fully normalized the distinct IL-13 gene transcription associated with asthma compared with blocking IL-13Rα1 alone. In humans, RPC4046 exposure increased dose-dependently; pharmacokinetics were similar in healthy and asthmatic subjects, and blockade of both IL-13Rs uniquely affected IL-13 gene transcription. A minority of participants (28%) had antidrug antibodies, which were transient and appeared not to affect pharmacokinetics. Adverse event profiles were similar in healthy and asthmatic subjects, without dose-related or administration route differences, systemic infusion-related reactions, or asthma symptom worsening. Adverse events were mild to moderate, with none reported as probably related to RPC4046 or leading to discontinuations. Non-serious upper respiratory tract infections were more frequent with RPC4046 versus placebo. CONCLUSION: RPC4046 is a novel anti-IL-13 antibody that blocks IL-13 binding to both receptors and more fully blocks the asthma phenotype. These results support further investigation of RPC4046 for IL-13-related allergic/inflammatory diseases (e.g., asthma and eosinophilic esophagitis). FUNDING: AbbVie Inc. sponsored the studies and contributed to the design and conduct of the studies, data management, data analysis, interpretation of the data, and in the preparation and approval of the manuscript.

Protection against rotavirus shedding after intranasal immunization of mice with a chimeric VP6 protein does not require intestinal IgA.

Intranasal immunization of mice with chimeric VP6 and the adjuvant LT(R192G) consistently elicits >95% reductions in fecal rotavirus shedding following challenge. To determine the association between mucosal antibody and protection, we immunized BALB/c wt and J chain knockout (Jch-/-) mice with VP6 and either LT(R192G) or cholera toxin (CT). Both strains developed nearly equal levels of serum rotavirus IgG, but Jch-/- mice, which cannot transport dimeric IgA across epithelial cell surfaces, developed >4-fold higher levels of serum rotavirus IgA. Stool rotavirus IgA was present in wt but undetectable in Jch-/- mice. When challenged with rotavirus strain EDIM, reductions in rotavirus shedding were nearly identical in VP6-immunized wt and Jch-/- mice (i.e., 97% and 92%, respectively; P > 0.01). Th1 CD4 T cell responses were also detected in VP6-immunized animals based on high levels of IFN-gamma and IL-2 found after in vitro VP6 stimulation of spleen cells. Therefore, protection induced by intranasal immunization of mice with VP6 and adjuvant does not depend on intestinal rotavirus IgA antibody but appears to be associated with CD4 T cells.

Polymeric immunoglobulin receptor in intestinal immune defense against the lumen-dwelling protozoan parasite Giardia.

The polymeric Ig receptor (pIgR) is conserved in mammals and has an avian homologue, suggesting evolutionarily important functions in vertebrates. It transports multimeric IgA and IgM across polarized epithelia and is highly expressed in the intestine, yet little direct evidence exists for its importance in defense against common enteric pathogens. In this study, we demonstrate that pIgR can play a critical role in intestinal defense against the lumen-dwelling protozoan parasite Giardia, a leading cause of diarrheal disease. The receptor was essential for the eradication of Giardia when high luminal IgA levels were required. Clearance of Giardia muris, in which IgA plays a dominant role, was severely compromised in pIgR-deficient mice despite significant fecal IgA output at 10% of normal levels. In contrast, eradication of the human strain Giardia lamblia GS/M, for which adaptive immunity is less IgA dependent in mice, was unaffected by pIgR deficiency, indicating that pIgR had no physiologic role when lower luminal IgA levels were sufficient for parasite elimination. Immune IgA was greatly increased in the serum of pIgR-deficient mice, conferred passive protection against Giardia, and recognized several conserved giardial Ags, including ornithine carbamoyltransferase, arginine deiminase, alpha-enolase, and alpha- and beta-giardins, that are also detected in human giardiasis. Corroborative observations were made in mice lacking the J chain, which is required for pIgR-dependent transepithelial IgA transport. These results, together with prior data on pIgR-mediated immune neutralization of luminal cholera toxin, suggest that pIgR is essential in intestinal defense against pathogenic microbes with high-level and persistent luminal presence.

Clinical aspects and pathophysiology of inflammatory bowel disease.

The chronic inflammatory bowel diseases (IBD), Crohn's disease and ulcerative colitis, are recognized as important causes of gastrointestinal disease in children and adults. In this review we delineate the clinical manifestations and diagnostic features of IBD. In addition, we summarize important recent advances in our understanding of the immune mediators of intestinal inflammation. This information has led to new therapeutic approaches in IBD. Further, we discuss the considerable data that point to the significance of genetic factors in the development of IBD and the genetic loci which have been implicated through genome-wide searches. The commensal bacterial flora also appears to be a critical element, particularly in regards to Crohn's disease, although the precise role of the bacteria in the disease manifestations remains unclear. Current investigations promise to yield fresh insights in these areas.

Heterologous protection induced by the inner capsid proteins of rotavirus requires transcytosis of mucosal immunoglobulins.

Protective immunization against rotavirus (RV) can be achieved with heterologous RV, i.e., virus isolated from another species, and with heterologous inner core VP2 and VP6 proteins assembled as virus-like particles (VLP). Although the antigenically conserved VP6 protein does not induce in vitro-neutralizing antibodies, it may, however, elicit immunoglobulins (Ig) involved in heterologous protection, as some IgA against VP6 prevent RV infection in a backpack mouse model. The protective role of Ig directed to the RV inner core proteins VP2 and VP6 was investigated in J-chain-deficient mice (J chain(-/-)), which have a defect in the polymeric Ig receptor (pIgR)-mediated transcytosis of IgA and IgM. J chain(-/-) mice and wild-type (WT) mice were intranasally vaccinated with bovine RV-derived VLP2/6 and then challenged with highly infectious murine ECw RV. Whereas WT mice were totally protected, immunized J chain(-/-) mice shed RV for several days. In addition, naïve J chain(-/-) mice exhibited a 2-day delay in clearing RV compared with WT mice. The immunized J chain(-/-) mice displayed unaltered VLP2/6-specific B-cell numbers in spleen and in mesenteric nodes and similar levels of serum anti-VLP2/6 Ig, confirming that the adaptive B-cell response is preserved in J chain(-/-) mice. These results indicate that J-chain-mediated transcytosis of Ig participates in the clearance of RV and that epithelial pIgR-mediated transport of Ig is involved in the heterologous protection induced by VLP2/6.

Enteric flora and lymphocyte-derived cytokines determine expression of heat shock proteins in mouse colonic epithelial cells.

BACKGROUND & AIMS: Inducible heat shock proteins (hsps), particularly hsp25 and hsp72, are expressed by surface colonocytes and may have a role in protecting intestinal epithelial cells against injury. This study is aimed at determining if enteric bacteria and/or immune signals regulate their physiologic expression. METHODS: Intestinal hsp25, hsp72, and constitutive hsc73 expression were studied in immunodeficient RAG-1(-/-) mice and in normal mice. Mucosal permeability was measured by mannitol flux and transepithelial resistance. Hsp expression in intestinal YAMC cells was assessed after incubation with recombinant cytokines, activated lamina propria lymphocytes (LPLs), or Bacteroides fragilis. RESULTS: Chronic metronidazole treatment decreases colonic mucosal hsp25 and hsp72 expression, an effect associated with increased susceptibility of mucosal barrier function to C. difficile toxin A. Hsp expression also was increased in YAMC cells incubated with B. fragilis, an effect mediated by lipopolysaccharide and other bacteria-derived factors. Colonic hsp72, but not hsp25 or hsc73, expression is decreased in RAG-1(-/-) mice. Recombinant IL-2 and other cytokines enhance YAMC hsp25 and/or hsp72 expression. Activated LPLs induce YAMC hsp expression, an effect blocked by IL-2 neutralizing antibody. CONCLUSIONS: Enteric flora and mucosal lymphocytes play a role in maintaining physiologic expression of colonocyte hsp25 and hsp72.

Protective role of HSP72 against Clostridium difficile toxin A-induced intestinal epithelial cell dysfunction.

We determined whether the cytoprotective heat shock protein HSP72 protects against the injurious effects of Clostridium difficile toxin A (TxA) on intestinal epithelial cells. Colonic epithelial Caco-2/bbe (C2) cells were stably transfected with HSP72 antisense (C2AS) or vector only (C2VC), resulting in low and high HSP72 expression, respectively. Measurements of epithelial barrier integrity, mitochondrial function, and apoptosis activation were assessed after TxA exposure. HSP72 and RhoA interactions were evaluated with immunoprecipitations. In C2AS cells, TxA was associated with a greater decrease in transepithelial resistance (TER), an increase in [(3)H]mannitol flux, and increased dissociation of perijunctional actin. Although HSP72 binds RhoA, it failed to prevent RhoA glucosylation. TxA caused a more rapid decrease in ATP, release of cytochrome c, and activation of caspase-9 in C2AS cells. To determine whether ATP depletion decreases TER, we treated cells with antimycin A, which caused a decline in TER. We conclude that HSP72 may protect intestinal epithelial cells from TxA-mediated damage through several mechanisms, including actin stabilization, mitochondrial protection, and inhibition of apoptosis activation, but not by prevention of RhoA glucosylation.