The Association between Elevated Levels of Peripheral Serotonin and Its Metabolite - 5-Hydroxyindoleacetic Acid and Bone Strength and Metabolism in Growing Rats with Mild Experimental Chronic Kidney Disease.

Chronic kidney disease (CKD) is associated with disturbances in bone strength and metabolism. The alterations of the serotonergic system are also observed in CKD. We used the 5/6 nephrectomy model of CKD to assess the impact of peripheral serotonin and its metabolite- 5-hydroxyindoleacetic acid on bone biomechanical properties and metabolism in growing rats. The animals were sacrificed one and three months after nephrectomy. Biomechanical properties were determined on two different bone types: the cortical bone of the femoral diaphysis using three-point bending test and the mixed cortico-trabecular bone by the bending test of the femoral neck. Biomechanical tests revealed preserved cortical bone strength, whereas work to fracture (W) and yield load (Fy) of mixed cortico-trabecular bone were significantly lower in CKD compared to controls. Serum activity of alkaline phosphatase (ALP), a bone formation marker, and tartrate-resistant acid phosphatase (TRACP 5b) reflecting bone resorption, were similar in CKD and controls. ALP was associated with lower femoral stiffness and strength, and higher displacements and W. TRACP 5b was inversely associated with cortical Fu and W. The elevated peripheral serotonergic system in CKD was: inversely associated with stiffness but positively related to the displacements and W; inversely associated with cortical Fy but positively correlated with this parameter in cortico-trabecular bone; inversely associated with ALP in controls but positively correlated with this biomarker in CKD animals. In conclusion, this study demonstrates the distinct effect of mild degree of CKD on bone strength in rapidly growing rats. The impaired renal function affects the peripheral serotonin metabolism, which in turn may influence the strength and metabolism of bones in these rats. This relationship seems to be beneficial on the biomechanical properties of the cortico-trabecular bone, whereas the cortical bone strength can be potentially reduced

Femoral length and biomechanical properties of the femur of control and chronic kidney disease (CKD) rats evaluated by the three-point bending test (A) and the bending test of the femoral neck (B).

<p>Femoral length and biomechanical properties of the femur of control and chronic kidney disease (CKD) rats evaluated by the three-point bending test (A) and the bending test of the femoral neck (B).</p

Body weight and biochemical parameters in controls and chronic kidney disease (CKD) rats after one and three months of disease progression.

<p>Body weight and biochemical parameters in controls and chronic kidney disease (CKD) rats after one and three months of disease progression.</p

The Association between Elevated Levels of Peripheral Serotonin and Its Metabolite – 5-Hydroxyindoleacetic Acid and Bone Strength and Metabolism in Growing Rats with Mild Experimental Chronic Kidney Disease - Fig 3

<p><b>The changes in 5-HT (panel A), 5-HIAA (panel B) levels, the ratio of 5-HT/TRP (panel C), the ratio of 5-HIAA/5-HT (panel D) and the results of two-way ANOVA with Bonferroni post hoc test (panel E) in controls and appropriate chronic kidney disease (CKD) rats.</b> Data are mean ±SD, n = 11 in each group. Abbreviations: CKD = Chronic Kidney Disease, CON = Controls, 5-HT = serotonin, 5-HIAA = 5-hydroxyindoleacetic acid, TRP = tryptophan; *p<0.05, **p<0.01, *** p<0.001 controls versus appropriate CKD group; #p<0.05 CKD-1 versus CKD-3.</p

Representative images of the proximal tibia of controls and CKD rats after 1 and 3 months of CKD indication.

<p>(A) Spongy bone and (B) compact bone in tibia of the CON-1 rat; (C) Spongy bone of CKD-1 rat. Visible an increase in osteoclast surface and an increase in eroded surface of trabecular bone (arrow); (D) The increase in osteoclasts surface (arrows) in compact bone of CKD-1 rat; (E) Spongy bone and (F) compact bone in tibia of CON-3 rat; (G) The significant increase in the osteoclast surface (arrow) and the erosion of trabecular bone in CKD-3 rat; (H) areas of osteoclastic activity in compact bone (arrows) in CKD-3 rat (HE staining, magnification x200, x400).</p

The correlations between serum alkaline phosphatase (ALP) and tartrate-resistant acid phosphatase form 5b (TRACP 5b) activities and biomechanical parameters of the femur of CKD rats: A–three-point bending test (n = 22), B–bending test of the femoral neck (n = 22).

<p>The correlations between serum alkaline phosphatase (ALP) and tartrate-resistant acid phosphatase form 5b (TRACP 5b) activities and biomechanical parameters of the femur of CKD rats: A–three-point bending test (n = 22), B–bending test of the femoral neck (n = 22).</p

The histological changes in the kidney tissue 4 weeks after subtotal nephrectomy.

<p>(A) The intact kidney from sham-operated rat; (B-E) the renal stump of subtotal nephrectomized rat 4 weeks after CKD induction; (B) moderate glomerulosclerosis (C), strong tubular atrophy (D), focal interstitial fibrosis (E) focal interstitial lymphocytic infiltration (HE staining, magnification x200, x400).</p