Risk Factors in Patients Who Had Prior Renal or Liver Transplant Undergoing Primary Total Knee Arthroplasty.

BACKGROUND: More solid organ transplant (SOT) patients are undergoing total knee arthroplasty (TKA). This study identifies risk factors for complications, implant survivorship, and mortality in TKA patients who had prior SOT. METHODS: We identified 176 TKAs in patients who had prior SOT. Of these, 77 had a prior renal (RT), 77 had a prior liver (LT) transplant, and 22 had multiple prior transplants (MT). Median survival was estimated using Kaplan-Meier. Univariate analyses were assessed with mixed-effects logistic regressions for complications and Cox-regressions for mortality. Median follow-up was 63 months (range, 24 to 109). RESULTS: At least one acute medical complication occurred in 25, 13, and 27% of cases with prior RT, LT, and MT, respectively (P = .12). None of the variables were significantly associated with acute medical complications. At least one surgical complication occurred in 14, 13 and 14% of cases with prior RT, LT, and MT, respectively (P = 1). Vitamin D supplementation (Odds Ratio [OR] = 0.38, P < .03) was associated with lower risk of surgical complications. Reoperation and revision rates were 5 and 3%, respectively. Older age at time of transplantation and greater level of serum creatinine at time of TKA were associated with lower risk (OR = 0.96, P = .01), and higher risk of reoperation (OR = 4.9, P = .01), respectively. Coronary artery disease was associated with higher mortality (Hazard Ratio = 2.35, P = .01). CONCLUSIONS: Vitamin D was associated with lower surgical complications, whereas a younger age at time of transplantation increased the risk of reoperation. Additionally, SOT patients with coronary artery disease demonstrated higher mortality after TKA.

Case report: JC polyomavirus nephropathy in simultaneous heart-kidney transplantation: the role of viral-specific in situ hybridization staining.

Introduction: JC polyomavirus (JCPyV) is a ubiquitous virus that can be latent in the brain and the kidney. It is the etiologic agent responsible for progressive multifocal leukoencephalopathy, a fatal, demyelinating disease of the central nervous system, and rarely causes polyomavirus nephropathy in immunocompromised kidney transplant recipients. Case description: We present the first case of JCPyV nephropathy in a simultaneous heart-kidney transplant patient, where viral-specific in situ hybridization staining of the kidney tissue was utilized to confirm the diagnosis. The patient was diagnosed 6 years after simultaneous heart-kidney transplantation and was treated with immunosuppression reduction and intravenous immunoglobulin. Discussion: JCPyV nephropathy should be considered in the differential diagnosis of kidney allograft injury, particularly, with suggestive light microscopy histologic features in the absence of BK polyomavirus viremia and/or viruria. In addition to obtaining JCPyV PCR in the blood, in situ hybridization staining may have a utility in confirming the diagnosis. To date, we lack effective JCPyV-specific therapies, and prompt initiation of immunosuppression reduction remains the mainstay of treatment.

A single-center experience of post-transplant atypical hemolytic uremic syndrome.

PURPOSE: Atypical hemolytic uremic syndrome (aHUS) is a genetic-based thrombotic microangiopathy (TMA) that is mediated by the activation of the alternative complement pathway. Heterozygous deletion in CFHR3-CFHR1 occurs in 30% of the general population and has not been classically linked to aHUS. Post-transplant aHUS has been associated with a high rate of graft loss. Herein, we report our case series of patients who developed aHUS after solid-organ transplantation. MATERIALS AND METHODS: Five consecutive cases of post-transplant aHUS were identified at our center. Genetic testing was performed in all but one. RESULTS: One patient had a presumed TMA diagnosis before transplant. One heart and 4 kidney (KTx) transplant recipients were diagnosed with aHUS based on the clinical picture of TMA, acute kidney injury, and normal ADAMTS13 activity. Genetic mutation testing revealed heterozygous deletion in CFHR3-CFHR1 in 2 patients and a heterozygous complement factor I (CFI) variant of uncertain clinical significance (VUCS) (Ile416Leu) in a third. Four patients were on tacrolimus, 1 had anti-HLA-A68 donor-specific antibody (DSA), and another had borderline acute cellular rejection at the time of aHUS diagnosis. Four responded to eculizumab, and 1 out of 2 patients came off renal replacement therapy. One KTx recipient died from severe bowel necrosis in the setting of early post-transplant aHUS. CONCLUSION: Calcineurin inhibitors, rejection, DSA, infections, surgery, and ischemia-reperfusion injury are common triggers that could unmask aHUS in solid-organ transplant recipients. Heterozygous deletion in CFHR3-CFHR1 and CFI VUCS may be important susceptibility factors acting as the first hit for alternative complement pathway dysregulation.

Characteristics and Graft Outcomes of Kidney Transplant Candidates with Enteric Risk Factors and Elevated Plasma Oxalate Levels.

INTRODUCTION: This study describes patient characteristics and examines graft function of kidney transplant recipients (without primary hyperoxaluria) with elevated plasma oxalate (POx) and enteric risk factors prior to transplant at our institution. METHODS: Kidney transplant recipients between 2012 and 2020 with elevated POx at the time of kidney transplant evaluation were included. A matched control cohort was gathered using patient/donor age, living/deceased donor type, panel reactive antibody, kidney donor profile index, and human leukocyte antigen mismatch as matching variables. Graft function at 1 year and at last follow-up was reported. RESULTS: A total of 106 patients with elevated POx were identified. A third of the patients had Roux-en-Y gastric bypass, a third had other enteric risks, and a third did not have an identifiable enteric risk. Median eGFR (estimated glomerular filtration rate) at 1 year and at last follow-up was similar between cases and controls except for subgroup of patients with pre-transplant POx >30 µmol/L where 1-year eGFR was lower compared to controls. Across eGFR categories, more cases were in eGFR category <30 mL/min/1.73 m2 compared to controls. CONCLUSION: Roux-en-Y gastric bypass is the most common identifiable risk for elevated POx in kidney transplant candidates. 1-year graft function was not inferior in cases compared to matched controls except for subgroup with POx >30 µmol/L pre-transplant.

The Role of Complement Split-products as Biomarkers for Acute Antibody-mediated Rejection of Kidney Allografts.

Acute antibody-mediated rejection (AMR) is mediated by the activation of the classical complement system in addition to noncomplement-dependent inflammatory pathways. Complement fixation by donor-specific antibodies leads to cleavage of the complement proteins C4, C3, and C5 to produce multiple complement split-products (CSP) and the end-effector membrane attack complex, C5b-9. In this study, we investigate CSP as potential biomarkers for AMR. Methods: In an Institutional Review Board-approved, prospective, controlled study, CSP levels were measured in blood and urine samples from consecutive kidney transplant recipients with biopsy-proven AMR (n = 10), acute cellular rejection (ACR) (n = 5), or no rejection (n = 5). After obtaining informed consent, samples were collected at the time of biopsy (day 0) and days 15 (end of rejection treatment) and 30 postbiopsy for AMR and ACR patients. ELISA was used to measure C5a, C4d, and soluble C5b-9 concentrations in blood and urine, in addition to factor Bb (Bb) concentration in blood only. Kidney transplant histopathology was evaluated using the Banff 2013 classification. Rejection treatment and follow-up were performed per standard of care. Results: Blood and urine CSP levels adjusted to urine creatinine were not elevated in AMR compared to no rejection and ACR arms. There was significant variability in CSP concentration within each of the study groups. Conclusion: Our study does not support the utility of CSP as surrogate biomarkers of AMR; however, it is limited by the small sample size and larger studies may be warranted.

Case report: Emphysematous pyelonephritis associated with kidney allograft abscess formation.

Emphysematous pyelonephritis (EPN) is a severe, acute necrotizing infection that is defined by the presence of gas in the kidney parenchyma. Multiple case reports have described the radiological findings and clinical course of EPN. Herein, we report on EPN including the histopathological findings in a kidney transplant recipient. Our patient presented with EPN complicated by multiorgan failure and was successfully managed with transplant nephrectomy.

COVID-19 in Kidney Transplantation: Outcomes, Immunosuppression Management, and Operational Challenges.

The coronavirus disease 2019 (COVID-19) pandemic, caused by the severe acute respiratory syndrome coronavirus 2, has led to the death of hundreds of thousands of people worldwide. If infected, older individuals and those with diabetes, hypertension, cardiovascular disease, and compromised immune systems are at higher risk for unfavorable outcomes. These comorbidities are prevalent in patients with kidney disease, hence the significant burden of COVID-19 on kidney transplant programs. Multiple case series of kidney transplant recipients with COVID-19 have shown increased mortality compared to nontransplant patients. To date, we do not have high-level evidence to inform immunosuppression minimization strategies in infected transplant recipients. Most centers however have adopted early antimetabolite withdrawal in addition to other interventions. This review summarizes the published COVID-19 literature as it relates to outcomes and immunosuppression management in kidney transplant recipients. It also discusses challenges pertaining to pretransplant evaluation and wait-listed patients.

APOL1 Genotyping in Potential African American Living Kidney Donors: Utility and Cost-Effectiveness.

BACKGROUND: Apolipoprotein L1 gene (APOL1) variants predispose to nondiabetic kidney disease in African American (AA) patients. Here, we share our experience with APOL1 genotyping of AA potential living kidney donors and offer a perspective on its utility and cost-effectiveness in this population. METHODS: Since May 2017, all potential AA living kidney donors at our center underwent APOL1 genotyping early in the donor evaluation process. APOL1 high-risk individuals were declined, whereas those with low-risk genotype continued with further evaluation and testing. RESULTS: One out of 26 potential donors had high-risk genotype and was therefore declined. The rest were eligible to continue the donor evaluation process and 7 of them underwent donor nephrectomy without any complications. A crude cost analysis utilizing our sample suggested probable cost-effectiveness of APOL1 genotyping as it can prevent earlier onset of chronic kidney disease in AA donors. CONCLUSION: We propose a role for systematically incorporating APOL1 genotyping in the evaluation and informed consent process of potential AA donors while acknowledging the controversial considerations associated with it.

Reducing Donor-specific Antibody During Acute Rejection Diminishes Long-term Renal Allograft Loss: Comparison of Early and Late Rejection.

BACKGROUND: Reduction in donor-specific antibody (DSA) has been associated with improved renal allograft survival after antibody-mediated rejection (AMR). These observations have not been separately analyzed for early and late AMR and mixed acute rejection (MAR). The purpose of this study was to evaluate long-term responses to proteasome inhibitor-based therapy for 4 rejection phenotypes and to determine factors that predict allograft survival. METHODS: Retrospective cohort study evaluating renal transplant recipients with first AMR episodes treated with proteasome inhibitor-based therapy from January 2005 to July 2015. RESULTS: A total of 108 patients were included in the analysis. Immunodominant DSA reduction at 14 days differed significantly (early AMR 79.6%, early MAR 54.7%, late AMR 23.4%, late MAR 21.1%, P < 0.001). Death-censored graft survival (DCGS) differed at 3 years postrejection (early AMR 88.3% versus early MAR 77.8% versus late AMR 56.7% versus late MAR 54.9%, P = 0.02). Multivariate analysis revealed that immunodominant DSA reduction > 50% at 14 days was associated with improved DCGS (odds ratio, 0.12, 95% CI, 0.02-0.52, P = 0.01). CONCLUSIONS: In summary, significant differences exist across rejection phenotypes with respect to histological and DSA responses. The data suggest that DSA reduction may be associated with improved DCGS in both early and late AMR.

A phase Ib, open-label, single arm study to assess the safety, pharmacokinetics, and impact on humoral sensitization of SANGUINATE infusion in patients with end-stage renal disease.

The endeavor to study desensitization in kidney transplantation has not been matched by an effort to investigate strategies to prevent sensitization. In this study (NCT02437422), we investigated the safety, impact on sensitization, and pharmacokinetics of SANGUINATE (SG), a hemoglobin-based oxygen carrier, as a potential alternative to packed red blood cells (PRBC) in transplant candidates with end-stage renal disease (ESRD). Ten ESRD subjects meeting inclusion/exclusion (I/E) criteria were planned to receive three weekly infusions of SG (320 mg/kg). The study was stopped after five subjects were enrolled, and their data were analyzed after completing a follow-up period of 90 days. Two subjects had elevated troponin I levels in setting of SG infusion, one of which was interpreted as a non-ST elevation myocardial infarction. All other adverse events were transient. SG pharmacokinetic analysis showed mean (SD) Cmax , Tmax , AUC, and half-life of 4.39 (0.69) mg/mL, 2.42 (0.91) hours, 171.86 (52.35) mg h/mL, and 40.60 (11.96) hours, respectively. None of the subjects developed new anti-HLA antibodies following SG infusion and throughout the study period. In conclusion, SG is a potential alternative to PRBCs in ESRD patients considered for kidney transplantation as it was not associated with humoral sensitization. Larger studies in highly sensitized patients are required to further evaluate for potential safety signals.

Severe BK polyomavirus-induced hemorrhagic cystitis in a kidney transplant recipient with the absence of renal allograft involvement.

BK polyomavirus mostly manifests as polyomavirus-associated nephropathy (PyVAN) in kidney transplant patients and polyoma virus-associated hemorrhagic cystitis (PyVHC) in bone marrow transplant patients. PyVHC in kidney transplant patients is only reported in four cases in the literature. Our patient had severe hemorrhagic cystitis without renal involvement. We postulate that our patient's exposure to ifosfamide and radiation 8 years prior transplantation might predispose him to this disease.

Acute Kidney Injury in Transplant Setting: Differential Diagnosis and Impact on Health and Health Care.

Acute kidney injury (AKI) is common in kidney transplant recipients. In addition to the usual causes of AKI in native kidneys, certain features and risk factors are unique to kidney allografts. In this article, we will present an overview of the common transplant-specific AKI etiologies that include increased susceptibility to hemodynamic-mediated AKI, acute rejection, medication-induced AKI, recurrence of native kidney disease, infections, urinary tract obstruction, vascular thrombosis and post-transplant lymphoproliferative disorder. AKI is independently associated with allograft loss and patient mortality. It is, therefore, prudent for transplant centers to address it as a major quality measure.

Contrast-Induced Nephropathy in Renal Transplant Recipients: A Single Center Experience.

BACKGROUND: Contrast-induced nephropathy (CIN) in native kidneys is associated with a significant increase in mortality and morbidity. Data regarding CIN in renal allografts are limited, however. We retrospectively studied CIN in renal allografts at our institution: its incidence, risk factors, and effect on long-term outcomes including allograft loss and death. METHODS: One hundred thirty-five renal transplant recipients undergoing 161 contrast-enhanced computed tomography (CT) scans or coronary angiograms (Cath) between years 2000 and 2014 were identified. Contrast agents were iso- or low osmolar. CIN was defined as a rise in serum creatinine (SCr) by >0.3 mg/dl or 25% from baseline within 4 days of contrast exposure. After excluding 85 contrast exposures where patients had no SCr within 4 days of contrast administration, 76 exposures (CT: n = 45; Cath: n = 31) in 50 eligible patients were analyzed. Risk factors assessed included demographics, comorbid conditions, type/volume of contrast agent used, IV fluids, N-acetylcysteine administration, and calcineurin inhibitor use. Bivariate and multivariable analyses were used to assess the risk of CIN. RESULTS: Incidence of CIN was 13% following both, CT (6 out of 45) and Cath (4 out of 31). Significant bivariate predictors of CIN were IV fluid administration (p = 0.05), lower hemoglobin (p = 0.03), and lower albumin (p = 0.02). In a multivariable model, CIN was predicted by N-acetylcysteine (p = 0.03) and lower hemoglobin (p = 0.01). Calcineurin inhibitor use was not associated with CIN. At last follow-up, CIN did not affect allograft or patient survival. CONCLUSION: CIN is common in kidney transplant recipients, and there is room for quality improvement with regards to careful renal function monitoring post-contrast exposure. In our study, N-acetylcysteine exposure and lower hemoglobin were associated with CIN. Calcineurin inhibitor use was not associated with CIN. Our sample size is small, however, and larger prospective studies of CIN in renal allografts are needed.

Acute Rejection Clinically Defined Phenotypes Correlate With Long-term Renal Allograft Survival.

BACKGROUND: Classification of acute rejection (AR) based on etiology and timing may provide a means for enhancing therapeutic results and allograft survival. This study evaluated graft and patient survival after the first AR episodes among kidney transplant recipients with an early or late antibody-mediated rejection (AMR), acute cellular rejection (ACR) or mixed AR (MAR). METHODS: A prospective institutional review board-approved database was queried to identify biopsy-proven first AR episodes occurring from January 2005 to October 2012. The ACR was defined by Banff criteria; borderline AR was excluded. The AMR was defined as 3 of 4 criteria: renal dysfunction, donor specific antibody, C4d positivity on biopsy, and histological changes. The MAR met criteria for both ACR and AMR. Early AR occurred within six months post-transplant. AR episodes were then assigned to 1 of the 6 categories--early AMR, early ACR, early MAR, late AMR, late ACR, and late MAR. RESULTS: One hundred eighty-two kidney transplant recipients identified with a first AR episode. Mean follow-up was 773 days (± 715 days). No difference was observed in patient survival. Death-censored graft survival was 84%. Death-censored graft loss was higher with late versus early AMR (P = 0.01) and late versus early ACR (P = 0.03), but not late versus early MAR (P = 0.3). CONCLUSIONS: The AR type demonstrated a hierarchy for graft survival with ACR better than MAR better than AMR, which persisted for both early and late AR. Improvement in long-term results of AR may require development of specific treatment for individual AR types.

A Banff Component Scoring-based Histologic Assessment of Bortezomib-based Antibody-mediated Rejection Therapy.

BACKGROUND: Histology remains a cornerstone for antibody-mediated rejection (AMR) diagnosis. Little data exist supporting histology for assessing therapeutic responses. This study evaluates histologic components in assessing AMR therapeutic responses. METHODS: Antibody-mediated rejection was diagnosed using Antibody Working Group criteria and Banff component scoring, and C4d staining data were analyzed. Statistics included independent and paired samples t test, χ(2), Fisher exact, or the Wilcoxon-signed rank test. Fifty-five AMR patients were analyzed. Early AMR was defined as occurring within 6 months after transplantation and treated with a single rituximab dose and 4 bortezomib doses preceded by plasmapheresis. Allograft biopsies were performed within 48 hours of treatment; repeat biopsy was performed 14 to 21 days later. RESULTS: Early AMR demonstrated histologic improvement in mean scores for acute Banff components glomerulitis (g), C4d, g+ peritubular capillaritis (ptc) and acute composite score, but showed deterioration in chronic Banff components tubular atrophy and interstitial fibrosis. Late AMR showed improved mean scores for acute Banff components tubulitis, interstitial inflammation, g, ptc, g + ptc, C4d, and acute composite score, but chronic scores did not change. Significant changes in distribution of Banff scores after treatment were observed for g, C4d, tubular atrophy, and interstitial fibrosis scores in early AMR patients and tubulitis, interstitial inflammation, g, ptc, and C4d in late AMR. CONCLUSIONS: These results show that: (1) Banff component scoring provides insights into histologic responses to AMR therapy and may provide a potential endpoint for clinical AMR trials. (2) Early and late AMR demonstrate differences in acute and chronic Banff components at the time of the AMR diagnostic biopsy, as well as differential responses to AMR therapy.

Late antibody-mediated rejection in renal allografts: outcome after conventional and novel therapies.

BACKGROUND: Although several strategies for treating early antibody-mediated rejection (AMR) in kidney transplants have been investigated, evidence on treatment of late AMR manifesting after 6 months is sparse. In this single-center series, we present data on 23 consecutive patients treated for late AMR. METHODS: Late AMR was diagnosed using Banff 2007 criteria along with presence of donor-specific antibodies (DSA) and acute rise in serum creatinine (SCr). Response to therapy was assessed by improvement in SCr, histologic improvement, and decline in DSA strength. RESULTS: Overall, 17% (4/23) had documented nonadherence while 69% (16/23) had physician-recommended reduction in immunosuppression before AMR. Eighteen patients (78%) were treated with plasmapheresis or low-dose IVIg+rituximab; 11 (49%) with refractory AMR also received one to three cycles of bortezomib. While there was an improvement (P=0.02) in mean SCr (2.4 mg/dL) at the end of therapy compared with SCr at the time of diagnosis (2.9 mg/dL), this improvement was not sustained at most recent follow-up. Eleven (48%) patients had no histologic resolution on follow-up biopsy. Lack of histologic response was associated with older patients (odds ratio [OR]=3.17; P=0.04), presence of cytotoxic DSA at time of diagnosis (OR=200; P=0.04), and severe chronic vasculopathy (cv≥2) on index biopsy (OR=50; P=0.06). CONCLUSIONS: A major setting in which late AMR occurred in our cohort was reduction or change in immunosuppression. Our data demonstrate an inadequate response of late AMR to current and novel (bortezomib) therapies. The benefits of therapy need to be counterweighed with potential adverse effects especially in older patients, large antibody loads, and chronic allograft vasculopathy.

Desensitization in kidney transplantation: review and future perspectives.

More than half of the kidney transplant candidates awaiting transplantation are sensitized to human leukocyte antigens (HLAs). Desensitization to HLAs involves treatment with immunomodulating therapies designed to reduce levels of anti-HLA antibodies in order to make kidney transplantation possible. Over the last two decades, desensitization therapies have been limited to plasmapheresis (PP), immunoadsorption (IA), intravenous immunoglobulins (IVIg), and rituximab. Review of reported experiences with desensitization in kidney transplant candidates revealed that PP or IA alone is inadequate to achieve durable reductions in HLA antibodies. Increasing evidence has accumulated indicating that high-dose IVIg has limited ability to reduce HLA antibodies, but a few centers have reported success with high-dose IVIg+rituximab in non-randomized trials. Overall experience in multiple centers, however, has shown high antibody-mediated rejection (AMR) rates, particularly in patients with the highest degrees of HLA sensitization. Low-dose IVIg combined with alternate day PP in living donor transplant candidates has been shown to provide enhanced survival over dialysis. However, low-dose IVIg/PP regimens also continue to be associated with unacceptable AMR rates. Recent experiences with plasma cell-targeted therapies based on the proteasome inhibitor bortezomib are relatively small but may represent an important alternative to non-deletional strategies with IVIg.

Lipotoxic disruption of NHE1 interaction with PI(4,5)P2 expedites proximal tubule apoptosis.

Chronic kidney disease progression can be predicted based on the degree of tubular atrophy, which is the result of proximal tubule apoptosis. The Na+/H+ exchanger NHE1 regulates proximal tubule cell survival through interaction with phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2], but pathophysiologic triggers for NHE1 inactivation are unknown. Because glomerular injury permits proximal tubule luminal exposure and reabsorption of fatty acid/albumin complexes, we hypothesized that accumulation of amphipathic, long-chain acyl-CoA (LC-CoA) metabolites stimulates lipoapoptosis by competing with the structurally similar PI(4,5)P2 for NHE1 binding. Kidneys from mouse models of progressive, albuminuric kidney disease exhibited increased fatty acids, LC-CoAs, and caspase-2-dependent proximal tubule lipoapoptosis. LC-CoAs and the cytosolic domain of NHE1 directly interacted, with an affinity comparable to that of the PI(4,5)P2-NHE1 interaction, and competing LC-CoAs disrupted binding of the NHE1 cytosolic tail to PI(4,5)P2. Inhibition of LC-CoA catabolism reduced NHE1 activity and enhanced apoptosis, whereas inhibition of proximal tubule LC-CoA generation preserved NHE1 activity and protected against apoptosis. Our data indicate that albuminuria/lipiduria enhances lipotoxin delivery to the proximal tubule and accumulation of LC-CoAs contributes to tubular atrophy by severing the NHE1-PI(4,5)P2 interaction, thereby lowering the apoptotic threshold. Furthermore, these data suggest that NHE1 functions as a metabolic sensor for lipotoxicity.

Phosphoinositide binding differentially regulates NHE1 Na+/H+ exchanger-dependent proximal tubule cell survival.

Tubular atrophy predicts chronic kidney disease progression, and is caused by proximal tubular epithelial cellcaused by proximal tubular epithelial cell (PTC) apoptosis. The normally quiescent Na(+)/H(+) exchanger-1 (NHE1) defends against PTC apoptosis, and is regulated by PI(4,5)P(2) binding. Because of the vast array of plasma membrane lipids, we hypothesized that NHE1-mediated cell survival is dynamically regulated by multiple anionic inner leaflet phospholipids. In membrane overlay and surface plasmon resonance assays, the NHE1 C terminus bound phospholipids with low affinity and according to valence (PIP(3) > PIP(2) > PIP = PA > PS). NHE1-phosphoinositide binding was enhanced by acidic pH, and abolished by NHE1 Arg/Lys to Ala mutations within two juxtamembrane domains, consistent with electrostatic interactions. PI(4,5)P(2)-incorporated vesicles were distributed to apical and lateral PTC domains, increased NHE1-regulated Na(+)/H(+) exchange, and blunted apoptosis, whereas NHE1 activity was decreased in cells enriched with PI(3,4,5)P(3), which localized to basolateral membranes. Divergent PI(4,5)P(2) and PI(3,4,5)P(3) effects on NHE1-dependent Na(+)/H(+) exchange and apoptosis were confirmed by selective phosphoinositide sequestration with pleckstrin homology domain-containing phospholipase Cδ and Akt peptides, PI 3-kinase, and Akt inhibition in wild-type and NHE1-null PTCs. The results reveal an on-off switch model, whereby NHE1 toggles between weak interactions with PI(4,5)P(2) and PI(3,4,5)P(3). In response to apoptotic stress, NHE1 is stimulated by PI(4,5)P(2), which leads to PI 3-kinase activation, and PI(4,5)P(2) phosphorylation. The resulting PI(3,4,5)P(3) dually stimulates sustained, downstream Akt survival signaling, and dampens NHE1 activity through competitive inhibition and depletion of PI(4,5)P(2).