AST-120 Protects Cognitive and Emotional Impairment in Chronic Kidney Disease Induced by 5/6 Nephrectomy

Abstract

Background: Uremic toxins resulting from chronic kidney disease (CKD) can cause cognitive and emotional disorders, as well as cardiovascular diseases. Indoxyl sulfate (IS) and p-cresol are notable uremic toxins found in patients with CKD. However, few studies have investigated whether reducing uremic toxins can alleviate cognitive and emotional disorders associated with CKD.

Methods: We studied the effects of AST-120, which lowers IS levels, through behavioral tests, local field potentials, field excitatory postsynaptic potentials, and histological experiments in a 5/6 nephrectomy CKD model.

Results: We confirmed AST-120's effectiveness in CKD by measuring serum creatinine, blood urea nitrogen, and IS levels and performing renal tissue staining. Behavioral phenotypes indicated an alleviation of cognitive and anxiety disorders following AST-120 treatment in CKD-induced rats, which was further validated through local field potentials and field excitatory postsynaptic potential recordings. Double immunofluorescence staining for aquaporin-4 and glial fibrillary acidic protein in the hippocampus of CKD rats treated with AST-120 showed reduced coexpression.

Conclusions: Our findings demonstrate the potential therapeutic effects of AST-120 in lowering IS levels and improving cognitive and emotional impairments associated with CKD.

Keywords: AST-120; blood–brain barrier; chronic kidney disease; cognitive phenotypes; indoxyl sulfate.

Figure 1

The effect of AST-120 treatment on body weight and blood analysis in the CKD group. Body weight and food intake in the CKD + AST-120 group were significantly restored to control levels (A,B). * p < 0.05 and *** p < 0.001, control group vs. CKD group; $ p < 0.05, $$ p < 0.01 and $$$ p < 0.001, control group vs. CKD + AST-120 group; # p < 0.05, ## p < 0.01 and ### p < 0.001, CKD group vs. CKD + AST-120 group. Serum BUN and creatinine levels were significantly decreased in the CKD + AST-120 group compared to the CKD group (C,D). Additionally, serum IS levels were significantly reduced in the CKD + AST-120 group compared to the CKD group (E). Data are presented as means ± standard errors of the mean (SEM). * p < 0.05, ** p < 0.01, *** p < 0.001, one-way analysis of variance (ANOVA) followed by Tukey’s post hoc multiple comparisons test. Body weight and food intake: n = 10/group.

Figure 2

The effect of AST-120 treatment on renal fibrosis in CKD rats. Representative images of the cortex (A1–C1) and medulla (A2–C2) of the kidney in the control, CKD, and CKD + AST-120 groups. Masson’s trichrome staining revealed progressive interstitial fibrosis in the CKD group, which significantly decreased in the CKD + AST-120 group (A–E). Notably, the CKD group exhibited glomerulosclerosis (arrow) and injured tubules (*) (B1,B2). Glomerulosclerosis in the CKD + AST-120 group was significantly reduced compared to that in the CKD group (C1). However, injured tubules in the CKD + AST-120 group did not show recovery (*) (C1,C2). Data are presented as means ± SEM. ** p < 0.01, *** p < 0.001, one-way ANOVA followed by Tukey’s post hoc multiple comparisons test. n = 5/group.

Figure 3

The impact of AST-120 treatment on anxiogenic phenotypes in the CKD group. Representative cumulative traces of navigational pathways for the control, CKD, and CKD + AST-120 groups during exploratory behavior in the open field (A). Locomotor activity and time spent in the central sector by the CKD + AST-120 group were higher compared to the CKD group (B,C). Light/dark transition counts and total duration in the light box were greater in the CKD + AST-120 group than in the CKD group (D,E). The total number of entries and the percentage of entries into the open arms of the elevated plus maze were markedly enhanced in the CKD + AST-120 group compared to the CKD group (F,G). Data are presented as means ± SEM. ** p < 0.01, and *** p < 0.001, one-way ANOVA followed by Tukey’s post hoc multiple comparisons test.

Figure 4

The effect of AST-120 treatment on novel object recognition memory in the CKD group. During the habituation period, the frequency and exploration time for the same objects were similar among the control, CKD, and CKD + AST-120 groups (A1,A2). The total object exploration times were significantly restored in the CKD + AST-120 group compared to the CKD group (A3). Additionally, the CKD + AST-120 group exhibited significantly increased frequency and time spent on novel objects, comparable to the control group (B1,B2). Specifically, the discrimination index for novel objects in the CKD + AST-120 group was notably higher compared to the CKD group (B3). Data are presented as means ± SEM. * p < 0.05 and *** p < 0.001, one-way ANOVA followed by Tukey’s post hoc multiple comparisons test.

Figure 5

The effect of AST-120 treatment on spatial working and learning memory in the CKD group. In the CKD + AST-120 group, the average percentage of spontaneous movement was markedly reduced compared with the CKD group (A). The CKD + AST-120 group demonstrated fewer errors on the second and fifth days of testing (probe test) compared to the CKD group (B1). ** p < 0.01, control group vs. CKD group; # p < 0.05 and ## p < 0.01, CKD group vs. CKD + AST-120 group. Notably, in the CKD + AST-120 group, latency times during the probe trials to find the target hole were restored to control group levels (B2). Data are presented as means ± SEM. * p < 0.05, ** p < 0.01, and *** p < 0.001, one-way ANOVA followed by Tukey’s post hoc multiple comparisons test.

Figure 6

The effect of AST-120 treatment on theta-frequency oscillations in the CKD group. Representative raw traces of LFP signals in the CA1 region of the hippocampus (A). Power spectral analysis of the CKD + AST-120 group showed significant reductions in power at lower frequencies compared to the CKD group (B). Hippocampal delta, theta, and alpha oscillations were significantly decreased in the CKD + AST-120 group, approximating levels seen in the control group (C–E). The average normalized power of the CKD + AST-120 group was notably lower compared to the CKD group (F). Data are presented as means ± SEM. * p < 0.05, ** p < 0.01 and *** p < 0.001, one-way ANOVA followed by Tukey’s post hoc multiple comparisons test. Control: n = 5; CKD: n = 5; CKD + AST-120: n = 4.

Figure 7

The effect of AST-120 treatment on fEPSP in the CKD group. Representative traces for fEPSP in the hippocampal CA1 region before and after sTPS in the control, CKD, and CKD + AST-120 groups (A). The amplitude of evoked fEPSP (B) and the slope changes (C) following LTP in the CKD + AST-120 group was significantly increased compared with the CKD group. The arrows in panel B indicate the time point of the sTPS application for LTP. Data are presented as means ± SEM. * p < 0.05, ** p < 0.01, and *** p < 0.001, one-way ANOVA followed by Tukey’s post hoc multiple comparisons test, n = 3/group.

Figure 8

The effect of AST-120 treatment on cerebral edema in the hippocampus in the CKD group. The double labeling of GFAP and AQP-4 in the hippocampal CA1 (A1–A4) and DG (A5–A8) regions of the control group revealed significantly reduced GFAP immunoreactivity in the hippocampus of the CKD + AST-120 group in the CA1 (B1–C2) and DG (B5–C6) regions compared to the CKD group. Furthermore, double labeling of GFAP and AQP-4 was markedly decreased in the hippocampal CA1 (arrows, B3–C4) and DG (arrows, B7–C8) regions of the CKD + AST-120 group relative to the CKD group. GFAP (green); AQP-4 (red); merged images (yellow); scale bar = 10 μm. A diagram of the hippocampal CA1 and DG (D) regions. There was a significant difference in quantification between the CKD + AST-120 group and the CKD group (E,F). A.U.—arbitrary unit. Data are presented as means ± SEM. *** p < 0.001, one-way ANOVA followed by Tukey’s post hoc multiple comparisons test, n = 5/group.