Concurrent GBT1118 & Losartan Treatment Improves Sickle Cell Nephropathy

Chronic kidney disease (CKD) is a common complication that leads to substantial morbidity and early mortality in sickle cell anemia (SCA). Renin-angiotensin-aldosterone system (RAAS) inhibitors, such as losartan, are recommended to treat SCA-related CKD although these guidelines are based on small studies with short follow-up. The pathophysiology of SCA-related CKD is complex with increased hemolysis and hemoglobinuria identified as risk factors for the development and progression of CKD (PMID 24329963). GBT1118, a mouse analogue of voxelotor, reduces intravascular hemolysis and hemoglobinuria thereby protecting the kidneys from damage if started early (12 weeks of age) before CKD has developed in SCA mice (PMID 35759756).

We investigated whether concurrent GBT1118 + losartan treatment would improve biomarkers of kidney damage and kidney function in older SCA mice starting at 24 weeks of age when CKD is evident. Transgenic sickle mice (Hb SS; Townes model, Jackson Laboratory) were treated as follows: A) GBT1118 + losartan, B) losartan-only, C) control chow (n = 10; 5 male and 5 female mice in each arm). Losartan treatment was started at 21 weeks (groups A & B), GBT1118 at 24 weeks (group A), and both treatments continued until 36 weeks of age. Urine was collected for 24 hours using metabolic cages. We compared markers of hemolysis (hemoglobin, reticulocyte %, hemoglobinuria), reactive oxygen species (thiobarbituric acid reactive substances [TBARS]), kidney injury (kidney injury molecule-1 [KIM-1], nephrin), and kidney function (albuminuria, proteinuria; serum cystatin C and BUN) using ANOVA adjusting for sex. Mean ± standard error values are provided.

At 36 weeks of age, SCA mice treated with GBT1118 + losartan (Group A) had higher hemoglobin concentrations (A: 6.9 ± 0.3 g/dL, B: 5.2 ± 0.4 g/dL, C: 6.5 ± 0.1 g/dL; P = 0.0017), lower reticulocyte % (A: 23 ± 1%, B: 33 ± 1%, C: 38 ± 1%; P < 0.0001), and lower urine hemoglobin concentrations (A: 0.3 ± 0.1 ng/24h, B: 1.7 ± 0.2 ng/24h, C: 1.7 ± 0.3 ng/24h; P = 0.0001) compared to the losartan-only (Group B) and control (Group C) mice. The hemoglobin concentrations and reticulocyte % were significantly lower in the losartan-only versus control mice (P ≤ 0.002).

Urinary biomarkers of oxidant injury (TBARS; A: 43.2 ± 4.5 nmol/24h, B: 80.9 ± 8.1 nmol/24h, C: 87.0 ± 5.9 nmol/24h; P = < 0.0001) and tubular injury (KIM-1; A: 163 ± 13 pg/24h, B: 219 ± 21 pg/24h, C: 307 ± 24 pg/24h; P = 0.0002) were lowest in SCA mice receiving GBT1118 + losartan. Urinary nephrin concentrations, a biomarker of glomerular injury, were similar in the GBT1118 + losartan and losartan-only treated mice and trended lower compared to control mice (A: 8.1 ± 0.9 ng/24h, B: 8.0 ± 1.1 ng/24h, C: 9.8 ± 0.9 ng/24h; P = 0.2).

We observed significant improvements in albuminuria (A: 22 ± 2 µg/24h, B: 37 ± 6 µg/24h, C: 115 ± 15 µg/24h; P < 0.0001) and proteinuria (A: 1.0 ± 0.2 mg/24h, B: 1.5 ± 0.2 mg/24h, C: 4.2 ± 0.5 mg/24h; P < 0.0001) in the GBT1118 + losartan treated mice. Serum cystatin C and BUN increased in the losartan-only treated mice compared to control mice (P≤ 0.004) while remaining stable in the GBT1118 + losartan treated mice (cystatin C; A: 606 ± 15 ng/mL, B: 667 ± 19 ng/dL, C: 586 ± 14 ng/dL) (BUN; A: 26 ± 1 mg/dL, B: 32 ± 2 mg/dL, C: 24 ± 2 mg/dL). Studies are ongoing to evaluate histopathologic and ultrastructural kidney changes across the three treatment groups.

In conclusion, the combination of GBT1118 + losartan improves hemolysis as well as several biomarkers of kidney injury and function in older SCA mice after CKD has developed. Losartan reduces intraglomerular pressure and we observed that losartan-only treated mice had lower urine nephrin, albumin and protein concentrations compared to control SCA mice. RAAS inhibitors have been shown to reduce erythropoietin levels and decrease kidney perfusion pressures in some studies of non-SCA related CKD. Consistent with this, losartan-only treated SCA mice developed more severe anemia and increased serum cystatin C and BUN concentrations compared to control SCA mice. Adding GBT1118 to losartan provided additional protection to the kidney, based upon further improvements in urine TBARS, KIM-1, albumin and protein concentrations, while improving the hemoglobin concentration and maintaining stable serum cystatin C and BUN levels. Our results provide support for developing multimodal strategies, such as the combination of voxelotor + losartan, to treat SCA-related CKD in humans.