Chronic Kidney Disease-Induced Cardiac Fibrosis Is Ameliorated by Reducing Circulating Levels of a Non-Dialysable Uremic Toxin, Indoxyl Sulfate

Abstract

Cardiovascular death commonly occurs in patients with chronic kidney disease. Indoxyl sulfate (IS), a uremic toxin, has been demonstrated in vitro as a contributory factor in cardiac fibrosis, a typical pathological finding in uremic cardiomyopathy. This study aimed to determine if cardiac fibrosis is reversible by lowering serum IS levels using an oral charcoal adsorbent, AST-120. Subtotal-nephrectomized (5/6-STNx) Sprague-Dawley rats were randomized to receive either AST-120 (AST-120, n = 13) or no treatment (vehicle, n = 17) for 12 weeks. Sham operated rats (n = 12) were used as controls. Early left ventricular (LV) diastolic dysfunction was demonstrated by an increase in peak velocity of atrial filling [A and A’ waves] and a decrease of E/A and E’/A’ ratios obtained by echocardiography. This was accompanied by a 4.5-fold increase in serum IS (p<0.001) as well as elevated tail-cuff blood pressure (p<0.001) and heart weight (p<0.001). Increased LV fibrosis (p<0.001), gene expression of pro-fibrotic (TGF-β, CTGF) and hypertrophic (ANP, β-MHC and α-skeletal muscle actin) markers, as well as TGF-β and phosphorylated NF-κB protein expression were observed in STNx + vehicle rats. Treatment with AST-120 reduced serum creatinine (by 54%, p<0.05) and urine total protein (by 27%, p<0.05) vs vehicle whilst having no effect on blood pressure (AST-120 = 227±11 vs vehicle = 224±8 mmHg, ns) and heart weight. The increase in serum IS was prevented with AST-120 (by 100%, p<0.001) which was accompanied by reduced LV fibrosis (68%, p<0.01) and TGF-β and phosphorylated NF-κB protein expression (back to sham levels, p<0.05) despite no significant change in LV function. In conclusion, STNx resulted in increased cardiac fibrosis and circulating IS levels. Reduction of IS with AST-120 normalizes cardiac fibrosis, in a blood pressure independent manner.

Role of Indoxyl Sulfate as a Predisposing Factor for Atrial Fibrillation in Renal Dysfunction

“…NADPH oxidases are major sources of reactive oxygen species, and activation of NADPH oxidases was associated with the incidence of AF 29, 30, 31, 32, 33, 34, 35, 36. Furthermore, several studies demonstrated that oxidative stress plays an important role in renal dysfunction–induced cardiac fibrosis, and AST‐120 prevented cardiac damage by alleviating oxidative stress 13, 15. In the present study, expression of NOX2, a membrane‐spanning subunit of NADPH oxidases, and NOX4, which is predominantly localized in the mitochondria, was significantly upregulated in LA tissue isolated from 5/6Nx rats, and the expression of MDA was concomitantly upregulated.…”

“…Rats were assigned randomly to the following groups: sham plus vehicle (VEH), sham plus AST‐120, 5/6Nx plus VEH, and 5/6Nx plus AST‐120. VEH and AST‐120 were administered by mixing in standard rat chow at 8% wt/wt for 4 weeks 15. Rats were anesthetized by intraperitoneal injection of a mixture of ketamine (60 mg/kg) and xylazine (10 mg/kg).…”

“…Indoxyl sulfate (IS) is a poorly dialysable uremic toxin due to its high protein binding, and it has been proposed as a critical factor for the progression of inflammation and fibrosis in various tissues 9, 10, 11, 12. IS has been reported to exaggerate cardiac fibrosis via oxidative stress and inflammation in renal dysfunction, and AST‐120 (commonly used in clinical settings as an absorbent of uremic toxins) has been reported to ameliorate fibrosis by reducing circulating levels of IS 13, 14, 15. Given that atrial interstitial fibrosis is a substrate for the pathogenesis of AF,16, 17, 18 we hypothesized that IS may be a predisposing factor for AF in renal dysfunction mediated by aggravation of oxidative stress, inflammation, and atrial fibrosis.…”

Gut bacteria-derived molecules as mediators and markers in cardiovascular diseases. The role of the gut-blood barrier

“…Indoxyl sulphate has been found to impair antioxidant mechanisms in cells and promote free radical formation in renal tubular cells and glomerular mesangial cells. Orally administered probiotics containing non-indole-producing bacteria as well as AST-120, an indole absorbing compound, were found to be beneficial in the treatment of patients with kidney disease [31].…”

“…Heart failure development [48] Indoles Intracellular signalling, biofilm formation, antibiotic resistance in bacteria [30] Accumulation in patients with CKD [9] Impairment of antioxidation and promotion of free radical formation [9] Promotion of endothelium dysfunction: decreased production of nitric oxide, increased production of reactive oxygen species [9] Hypertrophy of cardiac myocytes and production of collagen by cardiac fibroblasts [32] Decrease of indole concentration is beneficial in CKD [31] Correlation of high concentration of indoxyl sulphate with aortic lesion formation and mortality in CKD [9] Pro-arrhythmogenic potential [9] Association with CV events and mortality in CKD [49] Short-chain fatty acids Energy source of colonic cells and pH regulating agents…”