Kidney stone formers have more renal parenchymal crystals than non-stone formers, particularly in the papilla region

Abstract

Background: We investigated the renoprotective ability of healthy people against kidney stone formation. To clarify intratubular crystal kinetics and processing in human kidneys, we performed a quantitative and morphological observation of nephrectomized renal parenchyma tissues.

Methods: Clinical data and pathological samples from 60 patients who underwent radical nephrectomy for renal cancer were collected from June 2004 to June 2010. The patients were retrospectively classified as stone formers (SFs; n = 30, kidney stones detected by preoperative computed tomography) and non-stone formers (NSFs; n = 30, no kidney stone history). The morphology of parenchymal intratubular crystals and kidney stone-related gene and protein expression levels were examined in noncancerous renal sections from both groups.

Results: SFs had a higher smoking rate (P = 0.0097); lower red blood cell, hemoglobin, and hematocrit values; and higher urinary red blood cell, white blood cell, and bacterial counts than NSFs. Scanning electron microscopy revealed calcium-containing crystal deposits and crystal attachment to the renal tubular lumen in both groups. Both groups demonstrated crystal transmigration from the tubular lumen to the interstitium. The crystal diffusion analysis indicated a significantly higher crystal existing ratio in the medulla and papilla of SFs and a significantly higher number of papillary crystal deposits in SFs than NSFs. The expression analysis indicated relatively high osteopontin and CD68, low superoxide dismutase, and significantly lower Tamm-Horsfall protein expression levels in SFs. Multivariate logistic regression analysis involving the above factors found the presence of renal papillary crystals as a significant independent factor related to SFs (odds ratio 5.55, 95% confidence interval 1.08-37.18, P = 0.0395).

Conclusions: Regardless of stone formation, intratubular crystals in the renal parenchyma seem to transmigrate to the interstitium. SFs may have reduced ability to eliminate renal parenchymal crystals, particularly those in the papilla region, than NSFs with associated gene expression profiles.

Keywords: Kidney stones; Macrophages; Osteopontin; Oxidative stress; Tamm-Horsfall protein.

Fig. 1

Morphology and composition of renal tubular crystal deposits in stone formers (SFs) and non-stone formers (NSFs). a Crystal attachment to the tubular walls detected by polarized light optical microphotography of hematoxylin and eosin-stained renal cortex sections (magnification, × 800). b Crystal attachment to the tubular walls detected by scanning electron microscopy (SEM) of the crystal ultrastructure. c Energy-dispersive X-ray spectroscopy (EDX) of the mineral components on the surface of SEM-detected crystal deposits. The EDX spectrum shows calcium as the main component of the deposits

Fig. 2

Microscopic observation of Pizzolato-stained calcium oxalate crystal deposits in the renal cortex, medulla, and papilla of stone formers (SFs) and non-stone formers (NSFs). a In the renal cortex, the crystals were located in the tubular lumen and attached to the walls. b In the medullary region, the crystal-attached tubular epithelial cells were abraded and crystal transmigration into the interstitium was observed. (c) In the papillary region, almost all the crystals were detected in the interstitium. Arrows indicate tubules with crystal deposits

Fig. 3

Comparison of the crystal distribution in the renal cortex, medulla, and papilla between stone formers (SFs) and non-stone formers (NSFs). a The existing ratios (number of kidneys with crystal formation/whole kidneys). b The crystal numbers per 100 visual fields (magnification, × 100). Data represent means (standard deviation); *P < 0.05 and **P < 0.01 indicates statistically significant differences by repeated-measures analysis of variance

Fig. 4

Kidney stone-related gene and protein expressions in stone formers (SFs) and non-stone formers (NSFs). a Immunohistochemistry (magnification, × 100) for osteopontin (OPN), superoxide dismutase (SOD), CD68, and Tamm–Horsfall protein (THP). b mRNA expression levels of the secreted phosphoprotein-1 gene (SPP1), SOD1, CD68, and uromodulin gene (UMOD) detected by quantitative polymerase chain reaction (qPCR). The glyceraldehyde 3-phosphate dehydrogenase gene was used as the internal control. Data represent means (standard deviation). *P < 0.05 indicates statistically significant differences by the Mann-Whitney U-test