HHS Public Access Author manuscript Author Manuscript
Kidney Int. Author manuscript; available in PMC 2017 August 01. Published in final edited form as: Kidney Int. 2016 August ; 90(2): 440–449. doi:10.1016/j.kint.2016.04.027.
APOL1 renal-risk variants associate with reduced cerebral white matter lesion volume and increased gray matter volume
Author Manuscript
Barry I. Freedman, MD#1,2, Crystal A. Gadegbeku, MD#3, R. Nick Bryan, MD, PhD#4, Nicholette D. Palmer, PhD2,5, Pamela J. Hicks, BS5, Lijun Ma, MD, PhD1, Michael V. Rocco, MD1, S. Carrie Smith, BS5, Jianzhao Xu, BS5, Christopher T. Whitlow, MD, PhD6, Benjamin C. Wagner, BME6, Carl D. Langefeld, PhD7, Amret T. Hawfield, MD1, Jeffrey T. Bates, MD8, Alan J. Lerner, MD9, Dominic S. Raj, MD10, Mohammad S. Sadaghiani, MD, MPH3, Robert D. Toto, MD11, Jackson T. Wright Jr., MD, PhD12, Donald W. Bowden, PhD2,4, Jeff D. Williamson, MD13, Kaycee M. Sink, MD, MAS13, Joseph A. Maldjian, MD6,14, Nicholas M. Pajewski, PhD#7, and Jasmin Divers, PhD#7 for the African American-Diabetes Heart Study MIND (AA-DHS MIND) and Systolic Blood Pressure Intervention Trial (SPRINT) Research Groups 1
Department of Internal Medicine, Section on Nephrology; Wake Forest School of Medicine, Winston-Salem, NC
2
Centers for Diabetes Research and Genomics and Personalized Medicine Research; Wake Forest School of Medicine, Winston-Salem, NC
Author Manuscript
3Department
of Medicine, Temple University School of Medicine, Philadelphia, PA
4Department
of Radiology, University of Pennsylvania, Philadelphia, PA
5
Department of Biochemistry; Wake Forest School of Medicine, Winston-Salem, NC
6
Department of Radiologic Sciences, Advanced Neuroscience Imaging Research (ANSIR) Laboratory; Wake Forest School of Medicine, Winston-Salem, NC 7Division
of Public Health Sciences, Department of Biostatistical Sciences; Wake Forest School of Medicine, Winston-Salem, NC
8Michael
E. DeBakey Veterans Administration Medical Center and Baylor College of Medicine, Houston, TX 9Department
of Neurology, Case Western Reserve University School of Medicine, Cleveland, OH
Author Manuscript
10
Department of Medicine, George Washington University, Washington, DC
11
Department of Internal Medicine, University of Texas, Southwestern Medical Center, Dallas, TX
12Department
of Medicine, Case Western Reserve University School of Medicine, Cleveland, OH
Correspondence: Barry I. Freedman, M.D., Section on Nephrology, Wake Forest School of Medicine, Medical Center Boulevard, Winston-Salem, NC 27157-1053, U.S.A., Phone: 336-716-6192, Fax: 336-716-4318, [email protected]. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Freedman et al.
Page 2
13
Author Manuscript
Department of Internal Medicine, Section on Gerontology and Geriatric Medicine; Wake Forest School of Medicine, Winston-Salem, NC 14
Department of Radiology, Advanced Neuroscience Imaging Research (ANSIR) Laboratory; University of Texas Southwestern Medical Center, Dallas, TX #
These authors contributed equally to this work.
Abstract
Author Manuscript Author Manuscript
To assess apolipoprotein L1 gene (APOL1) renal-risk-variant effects on the brain, magnetic resonance imaging (MRI)-based cerebral volumes and cognitive function were assessed in 517 African American-Diabetes Heart Study (AA-DHS) MIND and 2,568 hypertensive African American Systolic Blood Pressure Intervention Trial (SPRINT) participants without diabetes. Within these cohorts, 483 and 197 had cerebral MRI, respectively. AA-DHS participants were 60.9% female, mean age of 58.6 years, diabetes duration 13.1 years, estimated glomerular filtration rate of 88.2 ml/min/1.73m2, and a median spot urine albumin to creatinine ratio of 10.0 mg/g. In additive genetic models adjusting for age, sex, ancestry, scanner, intracranial volume, body mass index, hemoglobin A1c, statins, nephropathy, smoking, hypertension, and cardiovascular disease, APOL1 renal-risk-variants were positively associated with gray matter volume (β 3.4×10−3) and negatively associated with white matter lesion volume (β −0.303) (an indicator of cerebral small vessel disease) and cerebrospinal fluid volume (β −30707) (all significant), but not with white matter volume or cognitive function. Significant associations corresponding to adjusted effect sizes (β/standard error) were observed with gray matter volume (0.16) and white matter lesion volume (−0.208), but not with cerebrospinal fluid volume (−0.251). Meta-analysis results with SPRINT MIND participants who had cerebral MRI were confirmatory. Thus, APOL1 renal-risk-variants are associated with larger gray matter volume and lower white matter lesion volume suggesting lower intracranial small vessel disease.
Keywords African Americans; APOL1; brain; cognition; hypertension; MRI; type 2 diabetes mellitus
Introduction
Author Manuscript
The apolipoprotein L1 gene (APOL1) G1 and G2 renal-risk-variants (RRVs) are strongly associated with a spectrum of non-diabetic kidney diseases in African Americans (AAs).1-3 Whether APOL1 RRVs also associate with altered risk for cardiovascular disease (CVD) remains controversial.4 APOL1 G1 and G2 variants are associated with lower levels of calcified atherosclerotic plaque (CP) in coronary and carotid arteries.5;6 CP is a measure of subclinical CVD and an important predictor of CVD events and mortality.7 The African American-Diabetes Heart Study (AA-DHS) and the Jackson Heart Study (JHS) both detected lower levels of CP in AAs with increasing numbers of APOL1 RRVs.5;6 However, observations linking APOL1 RRVs with outcomes in these cohorts yield opposing results. AA-DHS identified improved survival with increasing numbers of APOL1 RRVs.6 In contrast, JHS (validated in the Women’s Health Initiative [WHI]) observed increased risk for myocardial infarction and CVD events in those with two APOL1 RRVs.4;5 The
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paradoxically higher CVD risk with APOL1 in JHS and WHI could relate to confounding from APOL1 association with nephropathy. APOL1 was not associated with chronic kidney disease (CKD) in the type 2 diabetes (T2D)-affected AA-DHS cohort, thereby minimizing the potential for nephropathy-related CVD confounding effects.6 Nonetheless, the impact of APOL1 RRVs on the extra-renal vasculature requires additional study.
Author Manuscript
Cerebral structure can be accurately assessed using magnetic resonance imaging (MRI).8 Therefore, the AA-DHS MIND and the Systolic Blood Pressure Intervention Trial (SPRINT) MIND studies were initiated to improve understanding of environmental and inherited risk factors for subclinical cerebrovascular disease and cognitive performance.9-11 AA-DHS further aimed to assess relationships between conventional and non-conventional CVD risk factors with cerebral volumes and cognitive performance in the understudied AA population.12 Based on potential systemic vascular effects of APOL1, the G1 and G2 RRVs were tested for association with cerebral structure and cognitive function in AA-DHS MIND participants with T2D and hypertensive AA SPRINT MIND participants without diabetes.
Results
Author Manuscript
Demographic, clinical and imaging data in 517 AA-DHS MIND participants is displayed in Table 1. Of the total, 483 completed laboratory analysis, MRI scans, and cognitive testing (34 completed cognitive testing and laboratory analysis, but not the MRI due to claustrophobic symptoms). As in general populations, 13.9% of all AA-DHS MIND participants had two APOL1 RRVs; this group also had significantly higher overall African ancestry proportion, more kidney disease, and greater percentages of high school and college graduates. Although TICV was similar across the three genotype groups, significantly lower unadjusted WMLV was seen in those with two APOL1 RRVs. The APOL1 renal-risk genotype association with nephropathy in AA-DHS MIND differs from the lack of nephropathy association in a prior AA-DHS report, because 220 new participants were recruited for MRI scans.6 AA SPRINT (and SPRINT MIND MRI) participant demographic, clinical and MRI imaging data are presented in Table 2; 14% of the 2,568 AA SPRINT participants had two APOL1 RRVs. As in AA-DHS MIND, these individuals had higher overall African ancestry proportion; they also had a lower estimated glomerular filtration rate (eGFR) and higher urine albumin:creatinine ratio (UACR).
Author Manuscript
Table 3 displays adjusted AA-DHS MIND association results between APOL1 RRVs with MRI volumes and cognitive testing results in additive genetic models (Supplementary Table S1 displays recessive genetic models). As seen with CP associations in AA-DHS, APOL1 RRV associations with gray matter volume (GMV), cerebrospinal fluid volume (CSFV), and white matter lesion volume (WMLV) were stronger in additive models. In fully-adjusted models, APOL1 RRVs were significantly and positively associated with GMV (parameter estimate [β] 3.50×10−3 standard error [SE] 1.48×10−3; p=0.018) and negatively associated with WMLV (β −0.303, SE 0.099; p=2.33×10−3) and CSFV (β −30707, SE 8264; p=2.28×10−4), but not with white matter volume (WMV), Montreal Cognitive Assessment (MoCA), or modified mini-mental status examination (3MS) cognitive test performance. These associations were observed with Box-Cox transformed outcomes and correspond to adjusted effect sizes (β/SE) of 0.16 GMV, −1.208 WMLV, and −0.251 CSFV (p-values
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0.028, 0.01 and 0.93, respectively). The significant association observed with the transformed CSFV outcome and APOL1 was no longer significant after applying the inverse of the transformation.
Author Manuscript
Cognitive testing was performed in 2,568 AA SPRINT participants who also had APOL1 and ancestry informative marker genotypes; MRIs were performed in 197. Among the 197 AA SPRINT participants with an MRI, 10.2% (N=20) had two APOL1 RRVs. APOL1 RRV associations with cerebral volumes in the smaller number of non-diabetic SPRINT MIND participants were non-significant but trended in the same directions as in AA-DHS MIND (Table 4). In the fully-adjusted additive genetic models, APOL1 RRVs had a non-significant positive relationship with GMV (p=0.16) and negative relationships with both WMLV (p=0.54) and CSFV (p=0.29). Supplementary Table S2 displays results with the recessive genetic model. As in AA-DHS MIND, significant associations were not observed between APOL1 RRVs and cognitive performance in SPRINT. A meta-analysis was performed in the full sample of AA-DHS MIND and SPRINT participants (Table 5). Significant associations were again observed between APOL1 renalrisk variants with lower WMLV and higher GMV in this well-powered analysis.
Author Manuscript
Finally, associations between hypertension (defined as systolic blood pressure >140 mmHg, physician report, or taking anti-hypertensive medications), eGFR, and UACR with WMLV and GMV were assessed in AA-DHS MIND. Supplementary Table S3 reveals that hypertension and albuminuria were positively associated with WMLV; eGFR was negatively associated with WMLV. In contrast, hypertension did not significantly impact GMV; eGFR and UACR were positively and negatively associated, respectively, with GMV. This is consistent with findings in a prior AA-DHS MIND report containing approximately half of the cohort.13 While not specific to African Americans, a recently published study of brain perfusion in SPRINT MRI participants also indicated a positive association between albuminuria and WMLV, with the highest WMLV seen in individuals with UACR >30 mg/g and eGFR 30 mg/g and/or eGFR 30 years in the absence of diabetic ketoacidosis, with either active diabetes treatment (insulin and/or oral hypoglycemic agents), fasting blood sugar ≥126 mg/dL, non-fasting blood sugar ≥200 mg/dL, or hemoglobin A1c (HbA1c) ≥6.5%. Hypertension was considered present if diagnosed by a physician, anti-hypertensive medications were prescribed, or clinic blood pressures were >140/90 mmHg. The study was approved by the WFSM Institutional Review Board and all participants provided written informed consent. Individuals with a known serum creatinine concentration >2 mg/dl were not recruited. Examinations were performed in the WFSM Clinical Research Unit. Subjects had fasting blood work for measurement of chemistries, HbA1c, lipid profiles, high sensitivity Creactive protein, and a spot urine albumin and creatinine concentration for UACR (LabCorp, Burlington, NC). Estimated GFR was computed using the Chronic Kidney DiseaseEpidemiology Collaboration (CKD-EPI) equation.38 After a morning snack, cognitive testing and cerebral MRI were performed.13;39
Author Manuscript Author Manuscript
African American SPRINT participants—SPRINT is a two-armed, multicenter, randomized, open label, clinical trial including 9,361 participants designed to test whether a strategy to treat systolic blood pressure (SBP) to 300 mg/g, %
Serum creatinine, mg/dl
Estimated GFR, ml/min/1.73m2
Kidney Int. Author manuscript; available in PMC 2017 August 01. 210 212 212 212 212 212 207
Hemoglobin A1c, %
High School or less, %
Technical/AS degree, %
College graduate, %
Modified Mini Mental State (0-100)
Montreal Cognitive Assessment (0-30)
Digit Symbol Coding (0-135)
MRI Variables
211
Fasting glucose, mg/dl
Kidney disease , %
2
89.2 (23.4) 90.0
212
Current/former smoker, %
49.0 (17.1) 50.0
19.3 (3.9) 19.0
85.6 (9.0) 87.0
[12.7%]
[42.0%]
[45.3%]
8.1 (2.1) 7.4
154.8 (64.3) 141.0
0.98 (0.3) 0.91
[10.0%]
157.1 (539.3) 10.2
[42.0%]
77.8 (11.5) 78.5
132.9 (17.8) 132.8
[55.7%]
[84.1%]
207
Hypertension, %
[22.2%]
212
35.2 (9.0) 33.6
13.4 (8.2) 11.7
0.78 (0.14) 0.8
[57.5%]
58.4 (10.2) 57.1
Mean (SD) median
History of cardiovascular disease, %
Body mass index,
211
212
African ancestry proportion, %
kg/m2
212
Diabetes duration, years
212
Female, %
N
APOL1 0 risk alleles
Age, years
Variables
231
235
235
235
235
235
233
233
233
233
233
231
231
234
235
235
232
231
234
235
233
235
235
234
N
50.0 (16.0) 49.0
19.3 (4.0) 19.0
85.5 (10.1) 87.0
[20.4%]
[40.9%]
[38.7%]
7.9 (1.9) 7.4
142.4 (60.4) 127.0
[59.2%]
89.0 (23.9) 91.0
0.97 (0.3) 0.89
[9.1%]
148.5 (549.1) 9.1
[37.2%]
76.1 (10.9) 76.0
130.1 (17.3) 129.0
[53.9%]
[88.7%]
[22.6%]
35.5 (8.5) 34.0
13.0 (7.3) 11.8
0.78 (0.15) 0.81
[64.3%]
58.8 (9.1) 58.0
Mean (SD) median
APOL1 1 risk allele
70
70
70
70
70
70
70
70
70
70
70
70
70
70
70
70
70
69
70
70
70
70
70
70
N
52.2 (15.7) 49.5
19.3 (4.1) 19.5
86.2 (8.3) 87.5
[22.9%]
[52.9%]
[24.3%]
8.4 (2.2) 7.8
161.4 (70.3) 146.5
[77.1%]
82.4 (21.3) 82.0
1.0 (0.23) 1.0
[14.3%]
301.7 (944.3) 17.3
[35.7%]
77.0 (12.1) 76.0
131.4 (20.5) 130.5
[55.7%]
[82.6%]
[24.3%]
34.6 (7.0) 33.9
12.3 (7.1) 11.2
0.83 (0.11) 0.84
[60.0%]
58.6 (9.6) 58.9
Mean (SD) median
APOL1 2 risk alleles
Baseline demographic, laboratory, neuropsychological testing, and MRI data in the AA-DHS MIND
0.32
0.91
0.8
1.2×10−3
1.2×10−3
1.2×10−3
0.83
0.39
0.02
0.09
0.18
0.57
0.33
0.24
0.18
0.1
0.85
0.61
0.75
0.74
0.41
0.02
0.32
0.43
1
P-value
Author Manuscript
Table 1 Freedman et al. Page 14
Author Manuscript 196 196 194
Gray Matter Volume, cm3 Cerebrospinal Fluid Volume, cm3 White Matter Lesion Volume, cm3 8.6 (16.3) 2.8
253.8 (53.9) 240.8
564.0 (58.7) 564.0
494.7 (68.4) 491.2
1305 (141) 1302
Mean (SD) median
217
220
220
220
220
N
6.3 (11.1) 1.1
242.8 (46.3) 236.4
563.1 (58.9) 557.7
493.0 (62.6) 486.1
1292 (132) 1271
Mean (SD) median
APOL1 1 risk allele
kidney disease defined as eGFR 30 mg/g;
Based on the Cochran-Armitage trend test;
2
1
ACR – albumin:creatinine ratio; GFR – glomerular filtration rate.
White Matter Volume,
196
196
cm3
Total Intracranial Volume, cm3
N
Author Manuscript APOL1 0 risk alleles
67
67
67
67
67
N
4.7 (9.7) 1.2
240.3 (35.0) 241.2
569.3 (60.9) 563.9
488.0 (62.2) 476.8
1292 (130) 1280
Mean (SD) median
APOL1 2 risk alleles
Author Manuscript
Variables
6.6×10−3
0.11
0.98
0.47
0.28
1
P-value
Freedman et al. Page 15
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Kidney Int. Author manuscript; available in PMC 2017 August 01.
Author Manuscript
Author Manuscript
Author Manuscript 139.8 ± 16.5 80.9 ± 12.3 366 (34.7)
Systolic blood pressure, mmHg
Diastolic blood pressure, mmHg
Statin medications
Kidney Int. Author manuscript; available in PMC 2017 August 01. 102 (9.6) 135 (12.7) 22 (19-25) 46 (37-56)
College graduate
Some training beyond college degree
Montreal Cognitive Assessment (0-30)
Digit Symbol Coding (0-135)
Total Intracranial Volume, cm3
1356.3 (1230.4-1442.1)
(N=83)
449 (42.2)
Some training beyond HS, but no college degree
MRI Variables
222 (20.8)
HS graduate or GED
96 (89-104)
366 (35.5)
76.6 ± 22.7
1.06 (0.89-1.25)
157 (14.7)
ml/min/1.73m2
37 (3.6)
< High School (HS) education
Education
Fasting glucose, mg/dL
Kidney Disease
1
Estimated glomerular filtration rate,
Serum creatinine, mg/dL
Urine albumin:creatinine ratio >300 mg/g, %
8.7 (4.9-21.7)
823 (77.3)
Urine albumin:creatinine ratio, mg/g
181 (17.0)
Current/Former smoker
31 ± 6.5
0.79 (0.71-0.86)
History of cardiovascular disease
Body mass index,
kg/m2
African ancestry proportion, %
64.4 ± 9.1 482 (45.3)
Female, %
(N=1,065)
APOL1 0 risk alleles
Age, years
Variables
1349.0 (1278.6-1444.5)
(N=94)
46 (36-57)
22 (19-25)
164 (14.3)
115 (10.1)
460 (40.2)
241 (21.1)
163 (14.3)
96 (88-104)
377 (34.6)
76.9 ± 22.5
1.05 (0.88-1.27)
29 (2.7)
8.8 (5.1-21.2)
378 (33.2)
81.2 ± 12.5
139.7 ± 16.3
881(77.1)
178 (15.6)
30.7 ± 6.2
0.81 (0.73-0.87)
515 (45.1)
64.5 ± 9.0
(N=1,143)
APOL1 1 risk alleles
1350.3 (1279.4-1399.7)
(N=20)
45 (36-56.8)
22 (19-25)
36 (10.0)
30 (8.3)
149 (41.4)
79 (21.9)
66 (18.3)
95 (88-102)
145 (41.4)
73.3 ± 24.6
1.09 (0.89-1.38)
24 (6.9)
12.2 (6.5-32.8)
123 (34.3)
82.3 ± 12.6
139.4 ± 15.8
274(76.1)
60 (16.7)
31.5 ± 6.7
0.84 (0.77-0.88)
169 (46.9)
63.5 ± 9.0
(N=360)
APOL1 2 risk alleles
0.742
0.9476
0.9132
0.3658
0.3234
0.0616
0.0283
0.0268
Kidney Int. Author manuscript; available in PMC 2017 August 01. Published in final edited form as: Kidney Int. 2016 August ; 90(2): 440–449. doi:10.1016/j.kint.2016.04.027.
APOL1 renal-risk variants associate with reduced cerebral white matter lesion volume and increased gray matter volume
Author Manuscript
Barry I. Freedman, MD#1,2, Crystal A. Gadegbeku, MD#3, R. Nick Bryan, MD, PhD#4, Nicholette D. Palmer, PhD2,5, Pamela J. Hicks, BS5, Lijun Ma, MD, PhD1, Michael V. Rocco, MD1, S. Carrie Smith, BS5, Jianzhao Xu, BS5, Christopher T. Whitlow, MD, PhD6, Benjamin C. Wagner, BME6, Carl D. Langefeld, PhD7, Amret T. Hawfield, MD1, Jeffrey T. Bates, MD8, Alan J. Lerner, MD9, Dominic S. Raj, MD10, Mohammad S. Sadaghiani, MD, MPH3, Robert D. Toto, MD11, Jackson T. Wright Jr., MD, PhD12, Donald W. Bowden, PhD2,4, Jeff D. Williamson, MD13, Kaycee M. Sink, MD, MAS13, Joseph A. Maldjian, MD6,14, Nicholas M. Pajewski, PhD#7, and Jasmin Divers, PhD#7 for the African American-Diabetes Heart Study MIND (AA-DHS MIND) and Systolic Blood Pressure Intervention Trial (SPRINT) Research Groups 1
Department of Internal Medicine, Section on Nephrology; Wake Forest School of Medicine, Winston-Salem, NC
2
Centers for Diabetes Research and Genomics and Personalized Medicine Research; Wake Forest School of Medicine, Winston-Salem, NC
Author Manuscript
3Department
of Medicine, Temple University School of Medicine, Philadelphia, PA
4Department
of Radiology, University of Pennsylvania, Philadelphia, PA
5
Department of Biochemistry; Wake Forest School of Medicine, Winston-Salem, NC
6
Department of Radiologic Sciences, Advanced Neuroscience Imaging Research (ANSIR) Laboratory; Wake Forest School of Medicine, Winston-Salem, NC 7Division
of Public Health Sciences, Department of Biostatistical Sciences; Wake Forest School of Medicine, Winston-Salem, NC
8Michael
E. DeBakey Veterans Administration Medical Center and Baylor College of Medicine, Houston, TX 9Department
of Neurology, Case Western Reserve University School of Medicine, Cleveland, OH
Author Manuscript
10
Department of Medicine, George Washington University, Washington, DC
11
Department of Internal Medicine, University of Texas, Southwestern Medical Center, Dallas, TX
12Department
of Medicine, Case Western Reserve University School of Medicine, Cleveland, OH
Correspondence: Barry I. Freedman, M.D., Section on Nephrology, Wake Forest School of Medicine, Medical Center Boulevard, Winston-Salem, NC 27157-1053, U.S.A., Phone: 336-716-6192, Fax: 336-716-4318, [email protected]. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Freedman et al.
Page 2
13
Author Manuscript
Department of Internal Medicine, Section on Gerontology and Geriatric Medicine; Wake Forest School of Medicine, Winston-Salem, NC 14
Department of Radiology, Advanced Neuroscience Imaging Research (ANSIR) Laboratory; University of Texas Southwestern Medical Center, Dallas, TX #
These authors contributed equally to this work.
Abstract
Author Manuscript Author Manuscript
To assess apolipoprotein L1 gene (APOL1) renal-risk-variant effects on the brain, magnetic resonance imaging (MRI)-based cerebral volumes and cognitive function were assessed in 517 African American-Diabetes Heart Study (AA-DHS) MIND and 2,568 hypertensive African American Systolic Blood Pressure Intervention Trial (SPRINT) participants without diabetes. Within these cohorts, 483 and 197 had cerebral MRI, respectively. AA-DHS participants were 60.9% female, mean age of 58.6 years, diabetes duration 13.1 years, estimated glomerular filtration rate of 88.2 ml/min/1.73m2, and a median spot urine albumin to creatinine ratio of 10.0 mg/g. In additive genetic models adjusting for age, sex, ancestry, scanner, intracranial volume, body mass index, hemoglobin A1c, statins, nephropathy, smoking, hypertension, and cardiovascular disease, APOL1 renal-risk-variants were positively associated with gray matter volume (β 3.4×10−3) and negatively associated with white matter lesion volume (β −0.303) (an indicator of cerebral small vessel disease) and cerebrospinal fluid volume (β −30707) (all significant), but not with white matter volume or cognitive function. Significant associations corresponding to adjusted effect sizes (β/standard error) were observed with gray matter volume (0.16) and white matter lesion volume (−0.208), but not with cerebrospinal fluid volume (−0.251). Meta-analysis results with SPRINT MIND participants who had cerebral MRI were confirmatory. Thus, APOL1 renal-risk-variants are associated with larger gray matter volume and lower white matter lesion volume suggesting lower intracranial small vessel disease.
Keywords African Americans; APOL1; brain; cognition; hypertension; MRI; type 2 diabetes mellitus
Introduction
Author Manuscript
The apolipoprotein L1 gene (APOL1) G1 and G2 renal-risk-variants (RRVs) are strongly associated with a spectrum of non-diabetic kidney diseases in African Americans (AAs).1-3 Whether APOL1 RRVs also associate with altered risk for cardiovascular disease (CVD) remains controversial.4 APOL1 G1 and G2 variants are associated with lower levels of calcified atherosclerotic plaque (CP) in coronary and carotid arteries.5;6 CP is a measure of subclinical CVD and an important predictor of CVD events and mortality.7 The African American-Diabetes Heart Study (AA-DHS) and the Jackson Heart Study (JHS) both detected lower levels of CP in AAs with increasing numbers of APOL1 RRVs.5;6 However, observations linking APOL1 RRVs with outcomes in these cohorts yield opposing results. AA-DHS identified improved survival with increasing numbers of APOL1 RRVs.6 In contrast, JHS (validated in the Women’s Health Initiative [WHI]) observed increased risk for myocardial infarction and CVD events in those with two APOL1 RRVs.4;5 The
Kidney Int. Author manuscript; available in PMC 2017 August 01.
Freedman et al.
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Author Manuscript
paradoxically higher CVD risk with APOL1 in JHS and WHI could relate to confounding from APOL1 association with nephropathy. APOL1 was not associated with chronic kidney disease (CKD) in the type 2 diabetes (T2D)-affected AA-DHS cohort, thereby minimizing the potential for nephropathy-related CVD confounding effects.6 Nonetheless, the impact of APOL1 RRVs on the extra-renal vasculature requires additional study.
Author Manuscript
Cerebral structure can be accurately assessed using magnetic resonance imaging (MRI).8 Therefore, the AA-DHS MIND and the Systolic Blood Pressure Intervention Trial (SPRINT) MIND studies were initiated to improve understanding of environmental and inherited risk factors for subclinical cerebrovascular disease and cognitive performance.9-11 AA-DHS further aimed to assess relationships between conventional and non-conventional CVD risk factors with cerebral volumes and cognitive performance in the understudied AA population.12 Based on potential systemic vascular effects of APOL1, the G1 and G2 RRVs were tested for association with cerebral structure and cognitive function in AA-DHS MIND participants with T2D and hypertensive AA SPRINT MIND participants without diabetes.
Results
Author Manuscript
Demographic, clinical and imaging data in 517 AA-DHS MIND participants is displayed in Table 1. Of the total, 483 completed laboratory analysis, MRI scans, and cognitive testing (34 completed cognitive testing and laboratory analysis, but not the MRI due to claustrophobic symptoms). As in general populations, 13.9% of all AA-DHS MIND participants had two APOL1 RRVs; this group also had significantly higher overall African ancestry proportion, more kidney disease, and greater percentages of high school and college graduates. Although TICV was similar across the three genotype groups, significantly lower unadjusted WMLV was seen in those with two APOL1 RRVs. The APOL1 renal-risk genotype association with nephropathy in AA-DHS MIND differs from the lack of nephropathy association in a prior AA-DHS report, because 220 new participants were recruited for MRI scans.6 AA SPRINT (and SPRINT MIND MRI) participant demographic, clinical and MRI imaging data are presented in Table 2; 14% of the 2,568 AA SPRINT participants had two APOL1 RRVs. As in AA-DHS MIND, these individuals had higher overall African ancestry proportion; they also had a lower estimated glomerular filtration rate (eGFR) and higher urine albumin:creatinine ratio (UACR).
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Table 3 displays adjusted AA-DHS MIND association results between APOL1 RRVs with MRI volumes and cognitive testing results in additive genetic models (Supplementary Table S1 displays recessive genetic models). As seen with CP associations in AA-DHS, APOL1 RRV associations with gray matter volume (GMV), cerebrospinal fluid volume (CSFV), and white matter lesion volume (WMLV) were stronger in additive models. In fully-adjusted models, APOL1 RRVs were significantly and positively associated with GMV (parameter estimate [β] 3.50×10−3 standard error [SE] 1.48×10−3; p=0.018) and negatively associated with WMLV (β −0.303, SE 0.099; p=2.33×10−3) and CSFV (β −30707, SE 8264; p=2.28×10−4), but not with white matter volume (WMV), Montreal Cognitive Assessment (MoCA), or modified mini-mental status examination (3MS) cognitive test performance. These associations were observed with Box-Cox transformed outcomes and correspond to adjusted effect sizes (β/SE) of 0.16 GMV, −1.208 WMLV, and −0.251 CSFV (p-values
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0.028, 0.01 and 0.93, respectively). The significant association observed with the transformed CSFV outcome and APOL1 was no longer significant after applying the inverse of the transformation.
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Cognitive testing was performed in 2,568 AA SPRINT participants who also had APOL1 and ancestry informative marker genotypes; MRIs were performed in 197. Among the 197 AA SPRINT participants with an MRI, 10.2% (N=20) had two APOL1 RRVs. APOL1 RRV associations with cerebral volumes in the smaller number of non-diabetic SPRINT MIND participants were non-significant but trended in the same directions as in AA-DHS MIND (Table 4). In the fully-adjusted additive genetic models, APOL1 RRVs had a non-significant positive relationship with GMV (p=0.16) and negative relationships with both WMLV (p=0.54) and CSFV (p=0.29). Supplementary Table S2 displays results with the recessive genetic model. As in AA-DHS MIND, significant associations were not observed between APOL1 RRVs and cognitive performance in SPRINT. A meta-analysis was performed in the full sample of AA-DHS MIND and SPRINT participants (Table 5). Significant associations were again observed between APOL1 renalrisk variants with lower WMLV and higher GMV in this well-powered analysis.
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Finally, associations between hypertension (defined as systolic blood pressure >140 mmHg, physician report, or taking anti-hypertensive medications), eGFR, and UACR with WMLV and GMV were assessed in AA-DHS MIND. Supplementary Table S3 reveals that hypertension and albuminuria were positively associated with WMLV; eGFR was negatively associated with WMLV. In contrast, hypertension did not significantly impact GMV; eGFR and UACR were positively and negatively associated, respectively, with GMV. This is consistent with findings in a prior AA-DHS MIND report containing approximately half of the cohort.13 While not specific to African Americans, a recently published study of brain perfusion in SPRINT MRI participants also indicated a positive association between albuminuria and WMLV, with the highest WMLV seen in individuals with UACR >30 mg/g and eGFR 30 mg/g and/or eGFR 30 years in the absence of diabetic ketoacidosis, with either active diabetes treatment (insulin and/or oral hypoglycemic agents), fasting blood sugar ≥126 mg/dL, non-fasting blood sugar ≥200 mg/dL, or hemoglobin A1c (HbA1c) ≥6.5%. Hypertension was considered present if diagnosed by a physician, anti-hypertensive medications were prescribed, or clinic blood pressures were >140/90 mmHg. The study was approved by the WFSM Institutional Review Board and all participants provided written informed consent. Individuals with a known serum creatinine concentration >2 mg/dl were not recruited. Examinations were performed in the WFSM Clinical Research Unit. Subjects had fasting blood work for measurement of chemistries, HbA1c, lipid profiles, high sensitivity Creactive protein, and a spot urine albumin and creatinine concentration for UACR (LabCorp, Burlington, NC). Estimated GFR was computed using the Chronic Kidney DiseaseEpidemiology Collaboration (CKD-EPI) equation.38 After a morning snack, cognitive testing and cerebral MRI were performed.13;39
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African American SPRINT participants—SPRINT is a two-armed, multicenter, randomized, open label, clinical trial including 9,361 participants designed to test whether a strategy to treat systolic blood pressure (SBP) to 300 mg/g, %
Serum creatinine, mg/dl
Estimated GFR, ml/min/1.73m2
Kidney Int. Author manuscript; available in PMC 2017 August 01. 210 212 212 212 212 212 207
Hemoglobin A1c, %
High School or less, %
Technical/AS degree, %
College graduate, %
Modified Mini Mental State (0-100)
Montreal Cognitive Assessment (0-30)
Digit Symbol Coding (0-135)
MRI Variables
211
Fasting glucose, mg/dl
Kidney disease , %
2
89.2 (23.4) 90.0
212
Current/former smoker, %
49.0 (17.1) 50.0
19.3 (3.9) 19.0
85.6 (9.0) 87.0
[12.7%]
[42.0%]
[45.3%]
8.1 (2.1) 7.4
154.8 (64.3) 141.0
0.98 (0.3) 0.91
[10.0%]
157.1 (539.3) 10.2
[42.0%]
77.8 (11.5) 78.5
132.9 (17.8) 132.8
[55.7%]
[84.1%]
207
Hypertension, %
[22.2%]
212
35.2 (9.0) 33.6
13.4 (8.2) 11.7
0.78 (0.14) 0.8
[57.5%]
58.4 (10.2) 57.1
Mean (SD) median
History of cardiovascular disease, %
Body mass index,
211
212
African ancestry proportion, %
kg/m2
212
Diabetes duration, years
212
Female, %
N
APOL1 0 risk alleles
Age, years
Variables
231
235
235
235
235
235
233
233
233
233
233
231
231
234
235
235
232
231
234
235
233
235
235
234
N
50.0 (16.0) 49.0
19.3 (4.0) 19.0
85.5 (10.1) 87.0
[20.4%]
[40.9%]
[38.7%]
7.9 (1.9) 7.4
142.4 (60.4) 127.0
[59.2%]
89.0 (23.9) 91.0
0.97 (0.3) 0.89
[9.1%]
148.5 (549.1) 9.1
[37.2%]
76.1 (10.9) 76.0
130.1 (17.3) 129.0
[53.9%]
[88.7%]
[22.6%]
35.5 (8.5) 34.0
13.0 (7.3) 11.8
0.78 (0.15) 0.81
[64.3%]
58.8 (9.1) 58.0
Mean (SD) median
APOL1 1 risk allele
70
70
70
70
70
70
70
70
70
70
70
70
70
70
70
70
70
69
70
70
70
70
70
70
N
52.2 (15.7) 49.5
19.3 (4.1) 19.5
86.2 (8.3) 87.5
[22.9%]
[52.9%]
[24.3%]
8.4 (2.2) 7.8
161.4 (70.3) 146.5
[77.1%]
82.4 (21.3) 82.0
1.0 (0.23) 1.0
[14.3%]
301.7 (944.3) 17.3
[35.7%]
77.0 (12.1) 76.0
131.4 (20.5) 130.5
[55.7%]
[82.6%]
[24.3%]
34.6 (7.0) 33.9
12.3 (7.1) 11.2
0.83 (0.11) 0.84
[60.0%]
58.6 (9.6) 58.9
Mean (SD) median
APOL1 2 risk alleles
Baseline demographic, laboratory, neuropsychological testing, and MRI data in the AA-DHS MIND
0.32
0.91
0.8
1.2×10−3
1.2×10−3
1.2×10−3
0.83
0.39
0.02
0.09
0.18
0.57
0.33
0.24
0.18
0.1
0.85
0.61
0.75
0.74
0.41
0.02
0.32
0.43
1
P-value
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Table 1 Freedman et al. Page 14
Author Manuscript 196 196 194
Gray Matter Volume, cm3 Cerebrospinal Fluid Volume, cm3 White Matter Lesion Volume, cm3 8.6 (16.3) 2.8
253.8 (53.9) 240.8
564.0 (58.7) 564.0
494.7 (68.4) 491.2
1305 (141) 1302
Mean (SD) median
217
220
220
220
220
N
6.3 (11.1) 1.1
242.8 (46.3) 236.4
563.1 (58.9) 557.7
493.0 (62.6) 486.1
1292 (132) 1271
Mean (SD) median
APOL1 1 risk allele
kidney disease defined as eGFR 30 mg/g;
Based on the Cochran-Armitage trend test;
2
1
ACR – albumin:creatinine ratio; GFR – glomerular filtration rate.
White Matter Volume,
196
196
cm3
Total Intracranial Volume, cm3
N
Author Manuscript APOL1 0 risk alleles
67
67
67
67
67
N
4.7 (9.7) 1.2
240.3 (35.0) 241.2
569.3 (60.9) 563.9
488.0 (62.2) 476.8
1292 (130) 1280
Mean (SD) median
APOL1 2 risk alleles
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Variables
6.6×10−3
0.11
0.98
0.47
0.28
1
P-value
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Author Manuscript 139.8 ± 16.5 80.9 ± 12.3 366 (34.7)
Systolic blood pressure, mmHg
Diastolic blood pressure, mmHg
Statin medications
Kidney Int. Author manuscript; available in PMC 2017 August 01. 102 (9.6) 135 (12.7) 22 (19-25) 46 (37-56)
College graduate
Some training beyond college degree
Montreal Cognitive Assessment (0-30)
Digit Symbol Coding (0-135)
Total Intracranial Volume, cm3
1356.3 (1230.4-1442.1)
(N=83)
449 (42.2)
Some training beyond HS, but no college degree
MRI Variables
222 (20.8)
HS graduate or GED
96 (89-104)
366 (35.5)
76.6 ± 22.7
1.06 (0.89-1.25)
157 (14.7)
ml/min/1.73m2
37 (3.6)
< High School (HS) education
Education
Fasting glucose, mg/dL
Kidney Disease
1
Estimated glomerular filtration rate,
Serum creatinine, mg/dL
Urine albumin:creatinine ratio >300 mg/g, %
8.7 (4.9-21.7)
823 (77.3)
Urine albumin:creatinine ratio, mg/g
181 (17.0)
Current/Former smoker
31 ± 6.5
0.79 (0.71-0.86)
History of cardiovascular disease
Body mass index,
kg/m2
African ancestry proportion, %
64.4 ± 9.1 482 (45.3)
Female, %
(N=1,065)
APOL1 0 risk alleles
Age, years
Variables
1349.0 (1278.6-1444.5)
(N=94)
46 (36-57)
22 (19-25)
164 (14.3)
115 (10.1)
460 (40.2)
241 (21.1)
163 (14.3)
96 (88-104)
377 (34.6)
76.9 ± 22.5
1.05 (0.88-1.27)
29 (2.7)
8.8 (5.1-21.2)
378 (33.2)
81.2 ± 12.5
139.7 ± 16.3
881(77.1)
178 (15.6)
30.7 ± 6.2
0.81 (0.73-0.87)
515 (45.1)
64.5 ± 9.0
(N=1,143)
APOL1 1 risk alleles
1350.3 (1279.4-1399.7)
(N=20)
45 (36-56.8)
22 (19-25)
36 (10.0)
30 (8.3)
149 (41.4)
79 (21.9)
66 (18.3)
95 (88-102)
145 (41.4)
73.3 ± 24.6
1.09 (0.89-1.38)
24 (6.9)
12.2 (6.5-32.8)
123 (34.3)
82.3 ± 12.6
139.4 ± 15.8
274(76.1)
60 (16.7)
31.5 ± 6.7
0.84 (0.77-0.88)
169 (46.9)
63.5 ± 9.0
(N=360)
APOL1 2 risk alleles
0.742
0.9476
0.9132
0.3658
0.3234
0.0616
0.0283
0.0268
