Autosomal dominant polycystic kidney disease (ADPKD) is the most common inherited renal disease, affecting approximately 1:500–1:1000 live births.1 , 2 3 4 , 5
Obesity is an established risk factor for the development and progression of CKD.6–9 10 , 11 12 , 13
The Halt Progression of Polycystic Kidney Disease (HALT) Study A was a randomized, double-blind, placebo-controlled study in nondiabetic patients with early-stage ADPKD and is among the largest trials ever conducted in patients with ADPKD.14 total kidney volume [TKV]). We hypothesized that categorization as overweight or obese would be independently associated with a greater rate of progression in early-stage ADPKD, as indicated by greater annual change in TKV. We also evaluated whether overweight and obesity were associated with decline in eGFR.
Results
Participant Characteristics at Baseline
Four hundred forty-one participants with early ADPKD who participated in HALT Study A14 n =426) were white, and the mean±SD annual percent change in TKV was 7.4%±5.1%. Participants were categorized by baseline BMI (calculated from an adjusted weight removing the contribution of weight of the kidney and liver) as normal weight (18.5–24.9 kg/m2 ), overweight (25.0–29.9 kg/m2 ), or obese (≥30 kg/m2 ). The median BMI at baseline was 26.3±4.9 kg/m2 . The median (interquartile range) baseline TKV was 1040 (808, 1552) ml. Individuals with a higher BMI were more likely to be men, had a higher systolic BP (SBP) and fasting serum glucose, and had a larger liver volume at baseline (Table 1 ).
Table 1. -
Baseline characteristics of study participants from HALT Study A according to BMI category
Variable
Normal Weight (BMI 18.5–24.9 kg/m2 ) (n =192)
Overweight (BMI 25–29.9 kg/m2 ) (n =168)
Obese (BMI≥30 kg/m2 ) (n =81)
P Value
Age, yr
37±9
38±7
36±9
0.10
Men, %
40.6
66.1
51.9
<0.001
White race, %
93.2
94.0
95.1
0.84
Study BP Target Randomization Group (low, %)
49.0
50.0
51.9
0.91
Study BP Medication Randomization Group (ACEi + ARB, %)
46.9
50.0
53.1
0.63
CKD-EPI eGFR, ml/min per 1.73 m2
92.6±16.9
88.6±17.3
89.9±18.1
0.09
SBP, mm Hg
124±14
129±13
129±15
<0.001
BMI, kg/m2
22.0±1.7
27.4±1.4
34.1±3.7
<0.001
Urinary albumin, mg/24 h
18.1 (11.8–34.9)
17.5 (12.2–27.4)
19.8 (11.0–33.3)
0.61
Fasting serum glucose, mg/dl
88±10
94±10
92±10
<0.001
TKV, ml
985 (641–1561)
1051 (763, 1689)
1103 (762, 1394)
0.33
Liver volume, ml
1869±911
1974±873
2169±511
0.03
Mutation class, %
PKD1 truncating
52.2
45.1
41.2
0.13
PKD1 nontruncating
20.1
32.3
30.1
PKD2
18.5
17.1
16.0
No mutation detected
9.2
5.5
11.1
Data are mean±SD, %, or median (IQR). BMI is calculated from body weight adjusted to remove the contribution of the liver and kidneys to total weight. Mutation class is unavailable in n =12. ARB, angiotensin receptor blocker; CKD-EPI, CKD-EPI equation.
Relation between Overweight and Obesity and Change in TKV
We first considered the initial and final TKV values from each participant in HALT Study A and calculated annual percent change in TKV. Using this approach, the annual percent change in TKV was greater with increasing BMI category (normal weight: 6.1%±4.7%, overweight: 7.9%±4.8%, obese: 9.4%±6.2%; P <0.001; Figure 1 ), with a mean±SD follow-up period of 4.7±0.8 years. In both unadjusted and adjusted analyses, obesity was associated with increased rate of change in TKV as compared with the normal weight group (Table 2 ). When BMI was considered as a continuous variable, higher BMI was also associated with greater annual percent change in TKV in the fully adjusted model (model 5: β =0.79; 95% confidence interval, 0.18 to 1.39, per 5-unit increase in BMI).
Figure 1.: Annual percent change in TKV is greater with increasing BMI category. Annual percent change in TKV according to classification as normal weight, overweight, and obese. *P <0.001.
Table 2. -
Associations (
β -estimates [95% confidence intervals]) of BMI categories with annual percent change in TKV
Model
Normal Weight (BMI 18.5–24.9 kg/m2 ) (n =192)
Overweight (BMI 25–29.9 kg/m2 ) (n =168)
Obese (BMI>30 kg/m2 ) (n =81)
Unadjusted
Ref
1.84 (0.79 to 2.88)
3.39 (2.08 to 4.71)
Model 1
Ref
1.36 (0.34 to 2.38)
3.05 (1.80 to 4.29)
Model 2
Ref
1.33 (0.30 to 2.35)
3.05 (1.81 to 4.29)
Model 3
Ref
0.93 (−0.11 to 1.96)
2.71 (1.46 to 3.95)
Model 4
Ref
1.05 (0.02 to 2.07)
2.84 (1.59 to 4.08)
Model 5
Ref
0.82 (−0.22 to 1.87)
2.70 (1.45 to 3.95)
Model 1: adjusted for age, sex, and race/ethnicity. Model 2: adjusted for model 1+randomization group and SBP Model 3: model 2+eGFR (CKD-EPI equation), urinary albumin excretion, and serum glucose. Model 4: model 3+baseline TKV and liver volume. Model 5: model 4+mutation class. Mutation class is unavailable in n =12.
Because of a significant interaction term of BMI × sex in the linear regression model with an outcome of annual percent change TKV (P value for interaction=0.03) and previous analysis of baseline HALT Study A data which showed effect modification by sex,15 β =1.71; 0.92 to 2.50; women: β =0.87; 0.34 to 1.39, per 5-unit increase in BMI).
Next, we considered three categories of annual percent change in TKV using the initial and final TKV measurements from each participant (<5% growth, 5%–7% growth, and ≥7% growth). In the fully adjusted model, compared with the normal weight group, the obese group had a 3.76 (1.81 to 7.80) greater odds of progressing at a rate of ≥7% compared with <5% TKV growth (Table 3 ). The odds of progressing at a rate ≥7% compared with <5% were also significantly greater in the overweight compared with normal weight group (odds ratio [OR], 2.02; 1.15 to 3.56). For every 5-unit increase in BMI, the odds of progressing at ≥7% was 1.89 (1.42 to 2.52) in the fully adjusted model.
Table 3. -
Associations (OR [95% confidence interval]) of BMI categories with categories of annual percent change in TKV
End Point (Annual %∆ in htTKV)
Model
Normal Weight (BMI 18.5–24.9 kg/m2 ) (n =192)
Overweight (BMI 25–29.9 kg/m2 ) (n =168)
Obese (BMI ≥30 kg/m2 ) (n =81)
5%–7% versus <5%
Unadjusted
Ref
2.10 (1.12 to 3.93)
2.22 (0.95 to 5.20)
Model 1
Ref
1.92 (1.00 to 3.67)
2.16 (0.92 to 5.12)
Model 2
Ref
2.00 (1.03 to 3.89)
2.26 (0.94 to 5.44)
Model 3
Ref
1.55 (0.79 to 3.07)
1.97 (0.81 to 4.81)
Model 4
Ref
1.62 (0.81 to 3.21)
2.16 (0.87 to 5.38)
Model 5
Ref
1.66 (0.82 to 3.38)
2.32 (0.91 to 5.91)
≥7% versus <5%
Unadjusted
Ref
2.39 (1.50 to 3.83)
3.54 (1.89 to 6.64)
Model 1
Ref
2.20 (1.33 to 3.64)
3.45 (1.80 to 6.63)
Model 2
Ref
2.31 (1.38 to 3.85)
3.72 (1.91 to 7.23)
Model 3
Ref
1.92 (1.11 to 3.07)
3.29 (1.67 to 6.51)
Model 4
Ref
2.03 (1.19 to 3.48)
3.70 (1.84 to 7.45)
Model 5
Ref
2.02 (1.15 to 3.56)
3.76 (1.81 to 7.80)
Model 1: adjusted for age, sex, and race/ethnicity. Model 2: adjusted for model 1+randomization group and SBP. Model 3: model 2+eGFR (CKD-EPI equation), urinary albumin excretion, and serum glucose. Model 4: model 3+baseline TKV and liver volume. Model 5: model 4+mutation class. Mutation class is unavailable in n =12.
As a sensitivity analysis, we also considered a clinically meaningful final TKV end point of >1500 ml. In the fully adjusted model, the odds of reaching the >1500 ml end point were significantly greater in the overweight (OR, 3.33; 1.12 to 9.97) and obese (OR, 3.52; 1.06 to 11.69) compared with normal weight group. For every 5-unit increase in BMI, the odds of reaching a final TKV>1500 ml were 1.89 (1.41 to 4.04) in the fully adjusted model.
Last, in a sensitivity analysis utilizing a linear mixed model approach incorporating all available time points where TKV was measured, there was a significant BMI × time interaction in the fully adjusted model (P <0.01), consistent with the results of the primary analysis. For every 5-unit increase in BMI, TKV increased by 32.0 (12.2, 51.8) ml at month 24, 71.6 (33.3, 109.9) ml at month 48, and 101.8 (50.5, 153.0) ml at month 60.
Relation between Overweight and Obesity and eGFR Slope
Four hundred forty-eight participants with early ADPKD who participated in HALT Study A were included in the analysis of the association of overweight and obesity with slope of eGFR over the study duration. Baseline characteristics were very similar to the cohort included in the analysis of the TKV end point (Supplemental Table 1 2 per year. In the fully adjusted linear regression model incorporating all available measurements >4 months (to eliminate short-term hemodynamic effects), obesity was associated with greater decline in eGFR as compared with the normal weight group (Table 4 ). Results were similar when BMI was considered as a continuous variable (model 4: β =−0.03; −0.05 to 0.00, per 5-unit increase in BMI).
Table 4. -
Associations (
β [95% confidence interval]) of BMI categories with eGFR slope
Variable
Normal Weight (BMI 18.5–24.9 kg/m2 ) (n =206)
Overweight (BMI 25–29.9 kg/m2 ) (n =168)
Obese (BMI≥30 kg/m2 ) (n =81)
Unadjusted
Ref
−0.03 (−0.08 to 0.03)
−0.08 (−0.15 to −0.02)
Model 1
Ref
−0.03 (−0.08 to 0.02)
−0.09 (−0.15 to −0.02)
Model 2
Ref
−0.02 (−0.07 to 0.03)
−0.08 (−0.14 to −0.01)
Model 3
Ref
−0.03 (−0.08 to 0.03)
−0.08 (−0.14 to −0.02)
Model 4
Ref
−0.02 (−0.08 to 0.03)
−0.08 (−0.15 to −0.02)
Model 1: adjusted for age, sex, race/ethnicity, and randomization group. Model 2: adjusted for model 1+randomization group and SBP. Model 3: Model 2+eGFR (CKD-EPI equation), urinary albumin excretion, and serum glucose. Model 4: model 3+mutation class. Mutation class is unavailable in n =11.
In a sensitivity analysis utilizing a linear mixed model approach incorporating all available time points after month 4 where eGFR was measured, there was a significant BMI × time interaction in the fully adjusted model (P =0.03), consistent with the results of the eGFR slope analysis. For every 5-unit increase in BMI, eGFR declined by −0.01 (−0.96, 0.93) ml/min per 1.73 m2 at month 24, −1.60 (−3.02, −0.19) ml/min per 1.73 m2 at month 48, and −1.71 (−3.17, −0.24) ml/min per 1.73 m2 at month 60.
Discussion
We have demonstrated for the first time that overweight, and particularly obesity, are strongly associated with rate of progression of early-stage ADPKD, as measured by annual percent change in TKV and eGFR slope. In early-stage patients in HALT Study A, compared with normal weight individuals, obesity was associated with nearly four times greater adjusted odds of progressing at an annual rate of change in TKV of ≥7% compared with <5%. The annual percent increase in TKV in obese individuals was >50% greater than in normal weight individuals. These findings cannot be accounted for by baseline kidney and liver size, because BMI was calculated after removing the contribution of weight from these organs. Furthermore, baseline TKV and liver volume were included in all final adjusted models. In sensitivity analyses, overweight and obesity were also associated with achieving a clinically meaningful final TKV>1500 ml, a volume at which risk of subsequent decline in eGFR is increased.16
In a previous cross-sectional analysis of the baseline data from HALT, body surface area but not BMI was independently associated with baseline height-adjusted TKV and eGFR.15
It is biologically plausible that common pathways may be implicated in both ADPKD and obesity. Obesity can increase the mechanistic target of rapamycin (mTOR) activity via activation by PI3K/Akt and reduced AMP-activated protein kinase (AMPK) activity.17–19 via elevated cellular amino acid, glucose, and ATP concentrations,20 via AMPK activation in the presence of low glucose, high AMP/ATP ratios, and decreased amino acids.21 , 22 23 , 24 25 , 26 27 , 28 in vitro and ex vivo in models of cystogenesis via inhibition of the mTOR pathway and CFTR.29
It has been proposed that obesity in the setting of a positive energy balance may increase cancer risk, in part due to inhibition of AMPK and activation of mTOR and downstream proliferative pathways.20 18 , 30 , 31 20 , 32 33 12 , 13
Obesity is a well established independent risk factor for incident CKD,6 , 34 , 35 7 , 8 36 8 , 37 38–40 16 14
There are several limitations to this study. We are only able to demonstrate an association of overweight and obesity with ADPKD progression, rather than causation, and there may be residual confounding. Although BMI is commonly used to classify overweight and obesity, it is unable to distinguish between fat and muscle mass. Additionally, only baseline BMI and covariates were used in the statistical models. The major strength of this study is that we demonstrated a strong association of overweight and obesity with ADPKD progression, which is a novel and clinically relevant finding. Our results were consistent across various statistical approaches and accounted for any contribution of baseline kidney and liver weight to BMI classification. Last, progression was evaluated longitudinally with approximately 5 years of follow-up, and covariates were well characterized in the setting of a clinical trial.
These results pose an interesting and clinically relevant question of whether weight loss may be an effective strategy to slow progression in patients with ADPKD. The prevalence of overweight and obesity in the HALT study was over half of participants, thus an effective intervention could affect a large number of individuals. Given well known difficulties with weight loss adherence and the life-long nature of ADPKD, targeting prevention of the development of overweight and obesity early in life could potentially be a novel approach. Future research should evaluate the association of overweight and obesity with ADPKD progression in other cohorts, including late-stage patients, and whether weight loss or prevention of weight gain may slow disease progression.
Concise Methods
Study Design
The design of the HALT PKD Study A has been described in detail previously.14 , 15 , 41 1 ) multilevel renin angiotensin aldosterone system blockade with an angiotensin converting enzyme inhibitor (ACEi) + angiotensin receptor blocker (ARB) compared with ACEi + placebo, and (2 ) low (95–110/60–75 mm Hg) compared with standard (120–130/70–80 mm Hg) BP control.
All participants had a known diagnosis of ADPKD and either hypertension or high-normal BP. All participants were free from diabetes. Participants in HALT Study A were 15–49 years of age with an eGFR>60 ml/min per 1.73 m2 using the four-variable Modification of Diet in Renal Disease equation. The primary outcome in HALT Study A was percent change in TKV assessed by magnetic resonance imaging. TKV was assessed at baseline, 24, 48, and 60 months.
Of the 558 participants randomized in Study A, 487 had at least two measurements of TKV. One was missing data for BMI, 14 were excluded due to classification of BMI as underweight (see below), and an additional 31 were missing covariates (described below), leaving 441 participants for the current analysis. Twenty-four months data were used as baseline for n =2 participants who were missing baseline TKV data. Of the 558 participants in HALT Study A, 529 also had at least two measurements of eGFR, 14 were excluded due to classification of BMI as underweight, and an additional 67 were missing covariates or TKV/liver volume for calculation of adjusted BMI, leaving 448 participants for the analysis of change in eGFR.
Study Variables
An adjusted body weight was calculated by subtracting out kidney and liver weight, assuming a tissue density equal to that of water (1 g/cm3 ),42 2 ), overweight (25.0–29.9 kg/m2 ), or obese (≥30 kg/m2 ) using the National Heart, Lung, and Blood Institute’s criteria.43 2 (i.e., underweight) and were thus excluded from analyses, because underweight individuals may differ physiologically from those of normal weight. Magnetic resonance imaging was performed at each study site using a protocol developed by the HALT PKD Imaging Subcommittee to determine TKV (as well as total liver volume).15 , 41
Baseline and follow-up eGFR were calculated using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation.14 41
Confounders related to BMI and the primary outcomes were selected a priori as potential covariates, and all were measured at baseline. Race was categorized as white or nonwhite, as determined by self-report. SBP was measured in the clinical research clinics with the participant seated quietly in a chair for at least 5 minutes, feet on the floor, and arm supported at heart level. Three measurements were taken with at least 30 seconds between each measurement and the last two readings were repeated if there was a >10 mm Hg difference. The last two readings were averaged and reported.41 41 PKD1 truncating mutations, PKD1 nontruncating mutations, PKD2 mutations, and no mutation detected.44
Statistical Analyses
The association of overweight and obesity with change in TKV was assessed using linear regression and multinomial logistic regression models. Participants were classified into three categories according to BMI as described above (normal weight, overweight, and obese), with the normal weight category serving as the reference group in all analyses. In the linear regression models, the dependent variable was annual percent change in TKV calculated from the first and last available measurements. On the basis of analyses of baseline associations in HALT Study A,15 P <0.05) with BMI as a continuous variable only. There was no significant interaction with study randomization group (ACEi/ angiotensin receptor blocker versus ACEi/placebo or low versus standard BP target).
In the multinomial logistic regression models, the outcome was three categories of annual TKV growth (<5%, 5%–7%, and ≥7%), again calculated from the first and last available measurements. ORs were calculated with the <5% annual TKV growth, normal weight group serving at the reference. There were no significant interaction terms between BMI/BMI category and either sex or randomization group, thus stratified analyses were not performed.
In both approaches, the initial model was unadjusted, then multivariable adjusted models were performed to include age, sex, and race/ethnicity (model 1), model 1 plus randomization group and SBP (model 2), model 2 plus eGFR (CKD-EPI) and urinary albumin excretion (model 3), and model 3 plus baseline TKV, baseline liver volume, and serum glucose (model 4). Mutation class was added to model 4 (model 5) for those with the information available (n =429). We additionally considered BMI as a continuous predictor variable. The interaction term was included in model 2 for the linear regression model, considering BMI as a continuous variable. As a sensitivity analysis, we also evaluated achieving a final TKV>1500 ml as a clinically meaningful end point.16
Linear regression models were also used to evaluate the association of BMI categories with eGFR slope, which was obtained by fitting a linear regression model to all eGFR measurements from an individual participant obtained at >4 months (i.e., long-term phase14 n =437). Annual change in eGFR was calculated using the final and month 5 eGFR values. There were no significant interaction terms between BMI/BMI category and either sex or randomization group, thus stratified analyses were not performed.
Last, as sensitivity analyses, we performed linear mixed model analysis incorporating all available measurements (with the exception of month 90 and 96 eGFR, which caused model failure due to a low number of measurements), with BMI as a continuous predictor variable and (1 ) TKV and (2 ) eGFR as continuous end points. Results were similar when the variable TKV was log-transformed. The same covariates were used as described above.
In all analyses, baseline characteristics were summarized by BMI categories and presented as mean±SD or median (interquartile range) for continuous variables and n (%) for categoric variables. Comparisons across BMI categories were made using a chi-squared or Wilcoxon score test for categoric data and ANOVA for continuous variables.
Two-tailed values of P <0.05 were considered statistically significant for all analyses. All statistical analyses were performed using SAS version 9.4.
Disclosure
None.
K.L.N. is supported by the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), K01 DK103678. The Halt Progression of Polycystic Kidney Disease studies were supported by the NIDDK grants U01 DK062402, U01 DK062410, U01 CK082230, U01 DK062408, and U01 DK062401; the National Center for Research Resources General Clinical Research Centers (RR000039 to Emory University, RR000585 to the Mayo Clinic, RR000054 to Tufts Medical Center, RR000051 to the University of Colorado, RR023940 to the University of Kansas Medical Center, and RR001032 to Beth Israel Deaconess Medical Center); the National Center for Advancing Translational Sciences Clinical and Translational Science Awards (RR025008 and TR000454 to Emory University, RR024150 and TR00135 to the Mayo Clinic, RR025752 and TR001064 to Tufts University, RR025780 and TR001082 to the University of Colorado, RR025758 and TR001102 to Beth Israel Deaconess Medical Center, RR033179 and TR000001 to the University of Kansas Medical Center, and RR024989 and TR000439 to Cleveland Clinic); by funding from the Zell Family Foundation (to the University of Colorado); and by a grant from the Polycystic Kidney Disease Foundation.
The funding agencies had no direct role in the conduct of the study; the collection, management, analyses, and interpretation of the data; or preparation or approval of the manuscript.
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