Effect of bardoxolone methyl on the urine albumin-to-creatinine ratio in patients with type 2 diabetes and stage 4 chronic kidney disease

Bardoxolone methyl attenuates inflammation by inducing nuclear factor erythroid-derived 2-related factor 2 and suppressing nuclear factor κB. The Bardoxolone Methyl Evaluation in Patients With Chronic Kidney Disease and Type 2 Diabetes (BEACON) trial was a phase 3 placebo-controlled, randomized, double-blind, parallel-group, international, multicenter trial in 2185 patients with type 2 diabetes mellitus and stage 4 chronic kidney disease. BEACON was terminated because of safety concerns, largely related to a significant increase in early heart failure events in patients randomized to bardoxolone methyl. Bardoxolone methyl resulted in increased estimated glomerular filtration rate (eGFR) and urine albumin-to-creatinine ratio. Herein, we present post hoc analyses characterizing the relation between the urine albumin-to-creatinine ratio and eGFR. The urine albumin-to-creatinine ratio and eGFR were assessed every four weeks through Week 12, followed by assessments every eight weeks thereafter, and 4 weeks after the last dose of bardoxolone methyl was administered. The initial increases in urine albumin-to-creatinine ratio observed in patients randomized to bardoxolone methyl were attenuated after six months. Multivariable regression analysis identified baseline eGFR and eGFR over time as the dominant factors associated with change in the urine albumin-to-creatinine ratio. Relative to placebo, bardoxolone methyl resulted in a significant decrease in albuminuria when indexed to eGFR (least-squared means: −0.035 [95% confidence interval −0.031 to −0.039]). Thus, among patients with type 2 diabetes mellitus and stage 4 chronic kidney disease treated with bardoxolone methyl, changes in albuminuria are directly related to changes in eGFR, challenging the conventional construct that increases in albuminuria universally reflect kidney injury and denote harm. Bardoxolone methyl attenuates inflammation by inducing nuclear factor erythroid-derived 2-related factor 2 and suppressing nuclear factor κB. The Bardoxolone Methyl Evaluation in Patients With Chronic Kidney Disease and Type 2 Diabetes (BEACON) trial was a phase 3 placebo-controlled, randomized, double-blind, parallel-group, international, multicenter trial in 2185 patients with type 2 diabetes mellitus and stage 4 chronic kidney disease. BEACON was terminated because of safety concerns, largely related to a significant increase in early heart failure events in patients randomized to bardoxolone methyl. Bardoxolone methyl resulted in increased estimated glomerular filtration rate (eGFR) and urine albumin-to-creatinine ratio. Herein, we present post hoc analyses characterizing the relation between the urine albumin-to-creatinine ratio and eGFR. The urine albumin-to-creatinine ratio and eGFR were assessed every four weeks through Week 12, followed by assessments every eight weeks thereafter, and 4 weeks after the last dose of bardoxolone methyl was administered. The initial increases in urine albumin-to-creatinine ratio observed in patients randomized to bardoxolone methyl were attenuated after six months. Multivariable regression analysis identified baseline eGFR and eGFR over time as the dominant factors associated with change in the urine albumin-to-creatinine ratio. Relative to placebo, bardoxolone methyl resulted in a significant decrease in albuminuria when indexed to eGFR (least-squared means: −0.035 [95% confidence interval −0.031 to −0.039]). Thus, among patients with type 2 diabetes mellitus and stage 4 chronic kidney disease treated with bardoxolone methyl, changes in albuminuria are directly related to changes in eGFR, challenging the conventional construct that increases in albuminuria universally reflect kidney injury and denote harm. see commentary on page 823 see commentary on page 823 In chronic kidney disease (CKD), multiple mechanisms regulate urine albumin appearance. Damage to the glomerular barrier can increase permeability or decrease selectivity of the glomerular filtration barrier, thereby increasing the amount of albumin entering the proximal tubule. Because filtered albumin is processed by proximal tubular cells via endocytotic pathways to return albumin to the peritubular blood supply or to degrade albumin to small peptide fragments, saturation of either of these pathways will also increase the amount of albumin that is excreted in the urine.1Comper W.D. Hilliard L.M. Nikolic-Paterson D.J. et al.Disease-dependent mechanisms of albuminuria.Am J Physiol Renal Physiol. 2008; 6: F1589-F1600Crossref Scopus (127) Google Scholar Consequently, albuminuria and reduced glomerular filtration rate (GFR) are markers of structural kidney damage, and are often used to evaluate kidney function in CKD.2Kidney Disease: Improving Global Outcomes (KDIGO) KDIGO 2012 Clinical Practice Guideline for the evaluation and management of chronic kidney disease.Kidney Int Suppl. 2013; 1: S1-S150Google Scholar Albuminuria, defined as the excretion of excess serum albumin in urine (30–300 mg/d in microalbuminuria or moderately increased albuminuria, >300 mg/d in macroalbuminuria or severely increased albuminuria, and >2200 mg/d in nephrotic syndrome),3Keane W.F. Eknoyan G. Proteinuria, albuminuria, risk, assessment, detection, elimination (PARADE): a position paper of the National Kidney Foundation.Am J Kidney Dis. 1999; 5: 1004-1010Abstract Full Text Full Text PDF Scopus (480) Google Scholar is commonly considered a predictor of kidney disease progression. In patients with nondiabetic CKD, lower levels of proteinuria are associated with a lower incidence of glomerular disease,4Ruggenenti P. Perna A. Mosconi L. et al.Urinary protein excretion rate is the best independent predictor of ESRF in non-diabetic proteinuric chronic nephropathies. “Gruppo Italiano di Studi Epidemiologici in Nefrologia” (GISEN).Kidney Int. 1998; 5: 1209-1216Abstract Full Text Full Text PDF Scopus (374) Google Scholar and in diabetic CKD, excess urinary protein (albumin) excretion is a risk factor for kidney disease progression and is associated with a more rapid decline in GFR and progression to end-stage renal disease.5Rossing P. Hommel E. Smidt U.M. et al.Impact of arterial blood pressure and albuminuria on the progression of diabetic nephropathy in IDDM patients.Diabetes. 1993; 5: 715-719Crossref Scopus (147) Google Scholar, 6Breyer J.A. Bain R.P. Evans J.K. et al.Predictors of the progression of renal insufficiency in patients with insulin-dependent diabetes and overt diabetic nephropathy. The Collaborative Study Group.Kidney Int. 1996; 5: 1651-1658Abstract Full Text PDF Scopus (199) Google Scholar, 7Coresh J. Heerspink H.J.L. Sang Y. et al.Change in albuminuria and subsequent risk of end-stage kidney disease: an individual participant-level consortium meta-analysis of observational studies.Lancet Diabetes Endocrinol. 2019; 7: 115-127Abstract Full Text Full Text PDF PubMed Scopus (134) Google Scholar, 8Heerspink H.J.L. Greene T. Tighiouart H. et al.Change in albuminuria as a surrogate endpoint for progression of kidney disease: a meta-analysis of treatment effects in randomised clinical trials.Lancet Diabetes Endocrinol. 2019; 7: 128-139Abstract Full Text Full Text PDF PubMed Scopus (145) Google Scholar Although several interventional trials employing individual inhibitors of the renin-angiotensin-aldosterone system, including Reduction of Endpoints in Non-Insulin-dependent Diabetes Mellitus with the Angiotensin II Antagonist Losartan and Irbesartan Diabetic Nephropathy Trial, have shown that the reduction of proteinuria was associated with delayed progression of diabetic and nondiabetic CKD,9Brenner B.M. Cooper M.E. de Z.D. et al.The losartan renal protection study—rationale, study design and baseline characteristics of RENAAL (Reduction of Endpoints in NIDDM with the Angiotensin II Antagonist Losartan).J Renin Angiotensin Aldosterone Syst. 2000; 4: 328-335Crossref Scopus (116) Google Scholar, 10de Zeeuw D. Remuzzi G. Parving H.H. et al.Proteinuria, a target for renoprotection in patients with type 2 diabetic nephropathy: lessons from RENAAL.Kidney Int. 2004; 6: 2309-2320Abstract Full Text Full Text PDF Scopus (805) Google Scholar, 11Holtkamp F.A. de Z.D. de Graeff P.A. et al.Albuminuria and blood pressure, independent targets for cardioprotective therapy in patients with diabetes and nephropathy: a post hoc analysis of the combined RENAAL and IDNT trials.Eur Heart J. 2011; 12: 1493-1499Crossref Scopus (102) Google Scholar, 12Lewis E.J. Hunsicker L.G. Clarke W.R. et al.Renoprotective effect of the angiotensin-receptor antagonist irbesartan in patients with nephropathy due to type 2 diabetes.N Engl J Med. 2001; 12: 851-860Crossref Scopus (5040) Google Scholar the relation between changes in proteinuria and outcomes in other more complex trials is less clear.13Jamerson K. Weber M.A. Bakris G.L. et al.Benazepril plus amlodipine or hydrochlorothiazide for hypertension in high-risk patients.N Engl J Med. 2008; 23: 2417-2428Crossref Scopus (1753) Google Scholar, 14Bakris G.L. Sarafidis P.A. Weir M.R. et al.Renal outcomes with different fixed-dose combination therapies in patients with hypertension at high risk for cardiovascular events (ACCOMPLISH): a prespecified secondary analysis of a randomised controlled trial.Lancet. 2010; 9721: 1173-1181Abstract Full Text Full Text PDF Scopus (421) Google Scholar, 15Mann J.F. Schmieder R.E. McQueen M. et al.Renal outcomes with telmisartan, ramipril, or both, in people at high vascular risk (the ONTARGET study): a multicentre, randomised, double-blind, controlled trial.Lancet. 2008; 9638: 547-553Abstract Full Text Full Text PDF Scopus (1334) Google Scholar, 16Parving H.H. Brenner B.M. McMurray J.J. et al.Cardiorenal end points in a trial of aliskiren for type 2 diabetes.N Engl J Med. 2012; 23: 2204-2213Crossref Scopus (987) Google Scholar, 17Heerspink H.L. de Z.D. Composite renal endpoints: was ACCOMPLISH accomplished?.Lancet. 2010; 9721: 1140-1142Abstract Full Text Full Text PDF Scopus (17) Google Scholar, 18Ruggenenti P. Remuzzi G. Proteinuria: is the ONTARGET renal substudy actually off target?.Nat Rev Nephrol. 2009; 8: 436-437Crossref Scopus (45) Google Scholar Through activation of nuclear factor erythroid-derived 2-related factor 2 and inhibition of nuclear factor kappa-light-chain-enhancer of activated B-cells, bardoxolone methyl and related semisynthetic triterpenoids upregulate the antioxidant response and suppress proinflammatory signaling to reduce inflammation and improve mitochondrial function.19Sporn M.B. Liby K.T. Yore M.M. et al.New synthetic triterpenoids: potent agents for prevention and treatment of tissue injury caused by inflammatory and oxidative stress.J Nat Prod. 2011; 3: 537-545Crossref Scopus (268) Google Scholar, 20Ruiz S. Pergola P.E. Zager R.A. et al.Targeting the transcription factor Nrf2 to ameliorate oxidative stress and inflammation in chronic kidney disease.Kidney Int. 2013; 6: 1029-1041Abstract Full Text Full Text PDF Scopus (475) Google Scholar Seven clinical trials enrolling approximately 2600 patients with type 2 diabetes mellitus (T2DM) and CKD have studied bardoxolone methyl. Several of these trials have shown bardoxolone methyl treatment is associated with improvements in kidney function assessed by different methods, including inulin clearance (Nangaku et al. J Am Soc Nephrol 2017;28:B1, Abstract SA-OR 122), creatinine clearance, and estimated glomerular filtration rate (eGFR).21Pergola P.E. Raskin P. Toto R.D. et al.Bardoxolone methyl and kidney function in CKD with type 2 diabetes.N Engl J Med. 2011; 4: 327-336Crossref Scopus (711) Google Scholar, 22Pergola P. Krauth M. Huff W. et al.Effect of bardoxolone on kidney function in patients with T2D and stage 3b-4 CKD.Am J Nephrol. 2011; 33: 469-476Crossref PubMed Scopus (201) Google Scholar, 23de Zeeuw D. Akizawa T. Audhya P. et al.Bardoxolone methyl in type 2 diabetes and stage 4 chronic kidney disease.N Engl J Med. 2013; 26: 2492-2503Crossref Scopus (697) Google Scholar In a phase 2, randomized, placebo-controlled, double-blinded clinical trial (BEAM, NCT00811889), patients with T2DM and stage 3 CKD randomly assigned to bardoxolone methyl experienced significantly improved kidney function relative to placebo as assessed by a lower serum creatinine concentration (corresponding to higher eGFR), along with lower serum concentrations of urea nitrogen, uric acid, and phosphorus.21Pergola P.E. Raskin P. Toto R.D. et al.Bardoxolone methyl and kidney function in CKD with type 2 diabetes.N Engl J Med. 2011; 4: 327-336Crossref Scopus (711) Google Scholar However, in concert with improved kidney function, albuminuria was also increased. Similarly, bardoxolone methyl increased eGFR and urine albumin-to-creatinine ratio (UACR) in a larger, phase 3 randomized, placebo-controlled, double-blind study that enrolled patients with T2DM and stage 4 CKD, 90% of whom were receiving inhibitors of the renin-angiotensin-aldosterone system (Bardoxolone Methyl Evaluation in Patients With Chronic Kidney Disease and Type 2 Diabetes [BEACON], NCT01351675).23de Zeeuw D. Akizawa T. Audhya P. et al.Bardoxolone methyl in type 2 diabetes and stage 4 chronic kidney disease.N Engl J Med. 2013; 26: 2492-2503Crossref Scopus (697) Google Scholar Mathematical modeling of albumin in the proximal tubule demonstrates that both the rate of tubular protein reabsorption and the residence time of glomerular filtrate in the proximal tubule can affect urinary albumin excretion. Accordingly, an increase in glomerular filtration, independent of mechanism, would be expected to increase filtration and delivery of albumin to the tubules, reduce albumin reabsorption, and increase albumin excretion. Tubular protein reabsorptive capacity is limited by the availability of the endocytosis and receptor recycling machinery of proximal tubule cells.24Lazzara M.J. Deen W.M. Model of albumin reabsorption in the proximal tubule.Am J Physiol Renal Physiol. 2007; 1: F430-F439Crossref Scopus (60) Google Scholar Preclinical studies demonstrate that bardoxolone methyl downregulates expression of megalin of the megalin-cubilin complex, the primary proteins involved in protein reabsorption in the proximal tubules.25Reisman S.A. Chertow G.M. Hebbar S. et al.Bardoxolone methyl decreases megalin and activates nrf2 in the kidney.J Am Soc Nephrol. 2012; 10: 1663-1673Crossref Scopus (83) Google Scholar In addition, the residence time of the glomerular filtrate in the proximal tubules, as determined by the single nephron GFR (SNGFR), markedly influences the rate of protein uptake. As SNGFR (and the rate of flow) increases, the residence time and amount of protein uptake decrease; a 50% increase in SNGFR is predicted to cause 4- to 5-fold increases in albumin excretion in rats or humans.24Lazzara M.J. Deen W.M. Model of albumin reabsorption in the proximal tubule.Am J Physiol Renal Physiol. 2007; 1: F430-F439Crossref Scopus (60) Google Scholar Thus, increased eGFR together with decreased megalin expression with bardoxolone methyl may result in decreased reabsorption of filtered albumin and may explain the absolute increase in urinary albumin excretion observed in clinical trials. Herein, we report the results of post hoc analyses of the BEACON trial aimed to determine whether the effect of bardoxolone methyl on albuminuria can be attributed to the changes in eGFR. Previous publications describe the demographics and baseline characteristics of patients randomized to bardoxolone methyl and those randomized to placebo in BEACON23de Zeeuw D. Akizawa T. Audhya P. et al.Bardoxolone methyl in type 2 diabetes and stage 4 chronic kidney disease.N Engl J Med. 2013; 26: 2492-2503Crossref Scopus (697) Google Scholar, 26Lambers H.H.J. Chertow G.M. Akizawa T. et al.Baseline characteristics in the Bardoxolone methyl EvAluation in patients with Chronic kidney disease and type 2 diabetes mellitus: the Occurrence of renal eveNts (BEACON) trial.Nephrol Dial Transplant. 2013; 11: 2841-2850Crossref Scopus (17) Google Scholar (see Supplementary Table S1). Baseline geometric mean UACR was 210 mg/g (95% confidence interval [CI]: 188–236 mg/g) and 221 mg/g (95% CI: 196–249 mg/g) for patients randomized to bardoxolone methyl and placebo, respectively. More than half had baseline UACR > 300 mg/g: 540 of 1088 (50%) patients randomized to bardoxolone methyl and 578 of 1097 (53%) patients randomized to placebo. The percentage of patients receiving concomitant renin-angiotensin-aldosterone system blockers at baseline was similar among patients randomized to bardoxolone methyl and placebo. As previously reported, patients in BEACON randomized to bardoxolone methyl experienced a mean increase in eGFR by week 4 of treatment that persisted through week 48.23de Zeeuw D. Akizawa T. Audhya P. et al.Bardoxolone methyl in type 2 diabetes and stage 4 chronic kidney disease.N Engl J Med. 2013; 26: 2492-2503Crossref Scopus (697) Google Scholar Patients randomized to bardoxolone methyl experienced an overall mean increase of 5.5 ml/min per 1.73 m2 (95% CI: 5.2–5.9 ml/min per 1.73 m2; P < 0.001) from a mean baseline of 22.4 ml/min per 1.73 m2. In contrast, placebo-treated patients experienced a mean decline in eGFR (−0.9 ml/min per 1.73 m2, 95% CI: −1.2 to −0.5 ml/min per 1.73 m2; P < 0.001), corresponding to a difference between groups of 6.4 ml/min per 1.73 m2 (95% CI: 5.9–6.9 ml/min per 1.73 m2; P < 0.001).23de Zeeuw D. Akizawa T. Audhya P. et al.Bardoxolone methyl in type 2 diabetes and stage 4 chronic kidney disease.N Engl J Med. 2013; 26: 2492-2503Crossref Scopus (697) Google Scholar As seen in Figure 1, UACR in BEACON increased significantly in the bardoxolone methyl group, as compared with the placebo group, which decreased over time. During the first 12 weeks of treatment, the increase in UACR in the bardoxolone methyl group followed a trajectory similar to that of eGFR (Figure 2). However, after remaining stable for 5 to 6 months, UACR in the bardoxolone methyl group declined toward baseline. Moreover, the increase in UACR observed in the bardoxolone methyl group declined further toward baseline 4 weeks after drug withdrawal. The geometric mean UACR 4 weeks after treatment for patients treated for at least 48 weeks was 206 mg/g (95% CI: 153–277 mg/g; n = 201) and 156 mg/g (95% CI: 119–203 mg/g; n = 255) in patients randomized to bardoxolone methyl and placebo, respectively.Figure 2Urinary albumin-to-creatinine ratio (UACR) and estimated glomerular filtration rate (eGFR) over time in Bardoxolone Methyl Evaluation in Patients With Chronic Kidney Disease and Type 2 Diabetes. Data plotted are geometric mean values of UACR (± 95% confidence intervals; black) and mean eGFR values (± 95% confidence intervals; blue) for patients randomized to bardoxolone methyl (left; n = 1088) or placebo (right; n = 1097).View Large Image Figure ViewerDownload Hi-res image Download (PPT) Table 1 shows changes from baseline in eGFR at week 48 and 4 weeks after treatment in patients stratified by UACR changes at week 12, when increases in albuminuria were near maximal with bardoxolone methyl treatment. Notably, mean increases in eGFR from baseline at both time points were not different among patients in the highest and lowest quartiles of week 12 UACR changes in both treatment groups.Table 1Changes from baseline in eGFR by quartiles of UACR changeTreatmentQuartileNGeometric mean (median) UACRMean eGFR change ± SDBaselineWeek 12Week 12 changeWeek 484 weeks post-withdrawalPlacebo17080 (82)30 (37)−63%−1.4 ± 4.5−0.5 ± 5.2270234 (332)193 (247)−18%−0.7 ± 4.6−0.9 ± 4.6370174 (289203 (356)16%−1.6 ± 4.2−1.6 ± 4.5471100 (164)227 (351)127%−1.2 ± 5.3−0.1 ± 6.9Bardoxolone methyl159115 (116)48 (43)−58%6.4 ± 9.81.5 ± 5.9260216 (375)251 (249)16%4.4 ± 6.10.3 ± 6.336094 (308)392 (687)102%4.0 ± 8.90.4 ± 7.446056 (86)304 (420)440%7.8 ± 10.91.7 ± 8.4eGFR, estimated glomerular filtration rate; UACR, urine albumin-to-creatinine ratio.Patients were analyzed by quartiles of week 12 UACR change (calculated as the logarithm of week 12 UACR/baseline UACR ratios). For each quartile of patients, the percent change was calculated for the geometric mean of UACR (mg/g) at week 12 relative to UACR at baseline, the mean change from baseline in eGFR (ml/min per 1.73 m2) at week 48 and 4 weeks after withdrawal. Only patients with nonmissing baseline, week 12, and week 48 eGFR and UACR values were included. Open table in a new tab eGFR, estimated glomerular filtration rate; UACR, urine albumin-to-creatinine ratio. Patients were analyzed by quartiles of week 12 UACR change (calculated as the logarithm of week 12 UACR/baseline UACR ratios). For each quartile of patients, the percent change was calculated for the geometric mean of UACR (mg/g) at week 12 relative to UACR at baseline, the mean change from baseline in eGFR (ml/min per 1.73 m2) at week 48 and 4 weeks after withdrawal. Only patients with nonmissing baseline, week 12, and week 48 eGFR and UACR values were included. The best-fitting model to explain changes in log(UACR) over time included baseline log(UACR), treatment, time, baseline eGFR, and eGFR as covariates (Table 2). The inclusion of the interaction of the treatment group with time (i.e., testing whether the estimated effect of eGFR on UACR increased or decreased over time) did not improve model fit. The inclusion of eGFR as a covariate for log-UACR demonstrates that independent of treatment group, time, or baseline eGFR and UACR, increases in eGFR are associated with increases in UACR and exponentiation of the coefficients allows us to use the model to estimate the change in UACR. For example, extrapolating from the regression coefficient for eGFR in Table 2 (β = 0.010, 95% CI: 0.0088–0.012), a 5.5 ml/min per 1.73 m2 increase in eGFR for a patient would translate to an approximately 6% increase from baseline in UACR, irrespective of time, treatment, or baseline eGFR or UACR.Table 2Multivariate model of log(UACR) over time in BEACONEffectβ coefficient (95% CI)aFor a positive β coefficient, an increase in the covariate corresponds to increases in UACR, whereas negative β coefficients describe a decrease in UACR with increases in the covariate.P valueTreatment (bardoxolone methyl vs. placebo)0.33 (0.30, 0.36)<0.001Time (wk)0.0068 (0.0058, 0.0078)<0.001Baseline log(UACR)bPer unit increase.0.96 (0.95, 0.96)<0.001Baseline eGFRcPer ml/min per 1.73 m2 increase.−0.013 (−0.017, −0.0099)<0.001eGFRcPer ml/min per 1.73 m2 increase.0.010 (0.0088, 0.012)<0.001BEACON, Bardoxolone Methyl Evaluation in Patients With Chronic Kidney Disease and Type 2 Diabetes; CI, confidence interval; eGFR, estimated glomerular filtration rate; UACR, urine albumin-to-creatinine ratio.a For a positive β coefficient, an increase in the covariate corresponds to increases in UACR, whereas negative β coefficients describe a decrease in UACR with increases in the covariate.b Per unit increase.c Per ml/min per 1.73 m2 increase. Open table in a new tab BEACON, Bardoxolone Methyl Evaluation in Patients With Chronic Kidney Disease and Type 2 Diabetes; CI, confidence interval; eGFR, estimated glomerular filtration rate; UACR, urine albumin-to-creatinine ratio. To provide an alternative and somewhat simplified metric for expressing the excretion of albumin relative to GFR, we normalized log(UACR) values to eGFR and employed mixed effects regression analysis to assess differences in the log(UACR)/eGFR ratio for patients by the randomized group. Treatment with bardoxolone methyl yielded lower log(UACR)/eGFR over time (overall least-squared means: −0.035; 95% CI: −0.031 to −0.039; P < 0.001 vs. placebo; Figure 3). In BEACON, a placebo-controlled randomized trial enrolling patients with T2DM and stage 4 CKD, bardoxolone methyl increased eGFR from baseline and relative to placebo; the increase in eGFR was associated with increased urinary albumin excretion. Preclinical studies demonstrate that bardoxolone methyl downregulates the primary proteins involved in protein reabsorption in the proximal tubules (megalin-cubilin complex).25Reisman S.A. Chertow G.M. Hebbar S. et al.Bardoxolone methyl decreases megalin and activates nrf2 in the kidney.J Am Soc Nephrol. 2012; 10: 1663-1673Crossref Scopus (83) Google Scholar Administration of bardoxolone methyl to cynomolgus monkeys significantly decreased the protein expression of renal tubular megalin, which correlated with increases in UACR. Moreover, the bardoxolone methyl–induced decrease in megalin corresponded with pharmacologic induction of renal nuclear factor erythroid-derived 2-related factor 2 targets, including reduced NAD phosphate:quinone oxidoreductase 1 enzyme activity and glutathione content.25Reisman S.A. Chertow G.M. Hebbar S. et al.Bardoxolone methyl decreases megalin and activates nrf2 in the kidney.J Am Soc Nephrol. 2012; 10: 1663-1673Crossref Scopus (83) Google Scholar These results indicate that nuclear factor erythroid-derived 2-related factor 2 may have a role in megalin regulation and could contribute to the increase in albuminuria that accompanies bardoxolone methyl administration. Mathematical modeling of albumin reabsorption in the proximal tubule also supports the interpretation that increased filtration rates seen with bardoxolone methyl treatment are expected to increase protein delivery and reduce fractional protein reabsorption, therefore resulting in increased urinary protein excretion.24Lazzara M.J. Deen W.M. Model of albumin reabsorption in the proximal tubule.Am J Physiol Renal Physiol. 2007; 1: F430-F439Crossref Scopus (60) Google Scholar These 2 effects may explain the increases in urinary albumin excretion observed in patients treated with bardoxolone methyl.21Pergola P.E. Raskin P. Toto R.D. et al.Bardoxolone methyl and kidney function in CKD with type 2 diabetes.N Engl J Med. 2011; 4: 327-336Crossref Scopus (711) Google Scholar, 23de Zeeuw D. Akizawa T. Audhya P. et al.Bardoxolone methyl in type 2 diabetes and stage 4 chronic kidney disease.N Engl J Med. 2013; 26: 2492-2503Crossref Scopus (697) Google Scholar Post hoc multivariable regression analyses from the BEACON study support the conclusion that independent of treatment group, eGFR is significantly associated with UACR and therefore contributes to the observed increases in urinary albumin excretion. The absence of a significant treatment-by-time interaction term suggests that this finding is consistent across the entire study period (up to 64 weeks of treatment). Moreover, consistent with the multivariable model, when accounting for the change in eGFR, urinary albumin excretion declined in response to bardoxolone methyl relative to placebo in BEACON. Although albuminuria can be evidence of glomerular pathology, it also arises from dysfunction or saturation of the endocytotic pathways within the proximal tubule. Furthermore, albuminuria contributes to kidney injury when there is excessive albumin uptake into the proximal tubules. Recent studies have shown that albumin uptake into the proximal tubules and chronic overload of the albumin endocytosis machinery leads to chronic interstitial inflammation, oxidative stress, infiltration of inflammatory effector cells, and cellular damage and fibrosis.27Tang S. Leung J.C. Abe K. et al.Albumin stimulates interleukin-8 expression in proximal tubular epithelial cells in vitro and in vivo.J Clin Invest. 2003; 4: 515-527Crossref Scopus (232) Google Scholar, 28Hirschberg R. Bioactivity of glomerular ultrafiltrate during heavy proteinuria may contribute to renal tubulo-interstitial lesions: evidence for a role for insulin-like growth factor I.J Clin Invest. 1996; 1: 116-124Crossref Scopus (70) Google Scholar, 29Eddy A.A. McCulloch L. Liu E. et al.A relationship between proteinuria and acute tubulointerstitial disease in rats with experimental nephrotic syndrome.Am J Pathol. 1991; 5: 1111-1123Google Scholar, 30Eddy A.A. Interstitial nephritis induced by protein-overload proteinuria.Am J Pathol. 1989; 4: 719-733Google Scholar In proximal tubule cells, endocytosis of excess albumin activates reduced NAD phosphate oxidase via protein kinase C, resulting in the production of reactive oxygen species.27Tang S. Leung J.C. Abe K. et al.Albumin stimulates interleukin-8 expression in proximal tubular epithelial cells in vitro and in vivo.J Clin Invest. 2003; 4: 515-527Crossref Scopus (232) Google Scholar, 31Morigi M. Macconi D. Zoja C. et al.Protein overload-induced NF-kappaB activation in proximal tubular cells requires H(2)O(2) through a PKC-dependent pathway.J Am Soc Nephrol. 2002; 5: 1179-1189Google Scholar, 32Whaley-Connell A.T. Morris E.M. Rehmer N. et al.Albumin activation of NAD(P)H oxidase activity is mediated via Rac1 in proximal tubule cells.Am J Nephrol. 2007; 1: 15-23Crossref Scopus (59) Google Scholar In addition, excessive protein reabsorption in the proximal tubule induces nuclear factor kappa-light-chain-enhancer of activated B-cell signaling, leading to upregulation of nuclear factor kappa-light-chain-enhancer of activated B-cell target genes, such as proinflammatory cytokines Monocyte chemoattactant protein-1 (MCP-1), Regulated on activation, normal T-cell expressed and secreted (RANTES), and interleukin-8, which recruit monocytes, macrophages, neutrophils, and lymphocytes to the proximal tubule interstitium and promote interstitial inflammation.33Zoja C. Donadelli R. Colleoni S. et al.Protein overload stimulates RANTES production by proximal tubular cells depending on NF-kappa B activation.Kidney Int. 1998; 6: 1608-1615Abstract Full Text Full Text PDF Scopus (394) Google Scholar, 34Wang Y. Chen J. Chen L. et al.Induction