Intra- and extrarenal vascular changes in the acute renal failure of the rat caused by high-dose folic acid injection

A novel method for automated crystal visualization and quantification in murine folic acid-induced acute kidney injury

Folic acid (FA)-induced acute kidney injury (FA-AKI) is an increasingly prevalent rodent disease model involving the injection of a high dose of FA that culminates in renal FA crystal deposition and injury. However, the literature characterizing the FA-AKI model is sparse and dated in part due to the absence of a well-described methodology for the visualization and quantification of renal FA crystals. Using widely available materials and tools, we developed a straightforward and crystal-preserving histological protocol that can be coupled with automated imaging for renal FA crystal visualization and generated an automated macro for downstream crystal content quantification. The applicability of the method was demonstrated by characterizing the model in male and female C57BL6/JRj mice after 3 and 30 h of FA treatment. Kidneys from both sexes and timepoints showed a bimodal distribution of FA crystal deposition in the cortical and medullary regions while, compared with males, females exhibited higher renal FA crystal content at the 30-h timepoint accompanied by greater kidney weight and higher plasma urea. Despite comparable plasma phosphate concentrations, FA-AKI resulted in a substantially more elevated plasma intact fibroblast growth factor 23 (FGF23) in females, reflected by a similar pattern in osseous Fgf23 mRNA expression. Therefore, the presented method constitutes a valuable tool for the quantification of renal FA crystals, which can aid the mechanistic characterization of the FA-AKI model and serves as a means to control for confounding changes in FA crystallization when using the model for investigating early and prophylactic AKI therapeutic interventions.NEW & NOTEWORTHY Here, we describe a novel method for the visualization and quantification of renal folic acid (FA) crystals in the rodent FA-induced acute kidney injury (FA-AKI) model. The protocol involves a straightforward histological approach followed by fully automated imaging and quantification steps. Applicability was confirmed by showing that the FA-AKI model is sex-dependent. The method can serve as a tool to aid in characterizing FA-AKI and to control for studies investigating prophylactic therapeutic avenues using FA-AKI.

Aristolochic acid I determine the phenotype and activation of macrophages in acute and chronic kidney disease

Acute and chronic kidney injuries are multifactorial traits that involve various risk factors. Experimental animal models are crucial to unravel important aspects of injury and its pathophysiological mechanisms. Translating knowledge obtained from experimental approaches into clinically useful information is difficult; therefore, significant attention needs to be paid to experimental procedures that mimic human disease. Herein, we compared aristolochic acid I (AAI) acute and chronic kidney injury model with unilateral ischemic-reperfusion injury (uIRI), cisplatin (CP)- or folic acid (FA)-induced renal damage. The administration of AAI showed significant changes in serum creatinine and BUN upon CKD. The number of neutrophils and macrophages were highly increased as well as AAI-induced CKD characterized by loss of tubular epithelial cells and fibrosis. The in vitro and in vivo data indicated that macrophages play an important role in the pathogenesis of AA-induced nephropathy (AAN) associated with an excessive macrophage accumulation and an alternative activated macrophage phenotype. Taken together, we conclude that AA-induced injury represents a suitable and relatively easy model to induce acute and chronic kidney injury. Moreover, our data indicate that this model is appropriate and superior to study detailed questions associated with renal macrophage phenotypes.

Morphological and functional aspects of acute kidney injury after fetal programing in the offspring of diabetic rats

OBJECTIVE

To evaluate the effects of folic acid (FA)-induced renal failure in young offspring of diabetic mothers.

METHODS

The offspring of streptozotocin-induced diabetic dams were divided into four groups: CC (controls receiving vehicle); DC (diabetics receiving vehicle); CA (controls receiving FA solution, 250 mg/kg) and DA (diabetics receiving FA solution, 250 mg/kg). Renal function tests and morphometry results were analyzed.

RESULTS

An increase in creatinine and urea levels was observed in CA and DA groups at two and five months. FA administration caused a significant reduction in the number of glomeruli in the offspring of diabetic dams. The diabetes group treated with FA had fewer glomeruli compared to controls at two and five months. FA caused an increase in the area of the urinary space both in controls and offspring of diabetic dams at two and five months. The number of glomeruli and area of the urinary space at two months were negatively correlated.

CONCLUSIONS

Fetal programing promotes remarkable changes in kidney morphology and function in offspring. We suggest that the morphological changes in the kidneys are more pronounced when fetal programing is associated with newly acquired diseases, e.g. renal failure induced by FA.

Magnetic resonance imaging with hyperpolarized [1,4-(13)C2]fumarate allows detection of early renal acute tubular necrosis

Acute kidney injury (AKI) is a common and important medical problem, affecting 10% of hospitalized patients, and it is associated with significant morbidity and mortality. The most frequent cause of AKI is acute tubular necrosis (ATN). Current imaging techniques and biomarkers do not allow ATN to be reliably differentiated from important differential diagnoses, such as acute glomerulonephritis (GN). We investigated whether (13)C magnetic resonance spectroscopic imaging (MRSI) might allow the noninvasive diagnosis of ATN. (13)C MRSI of hyperpolarized [1,4-(13)C(2)]fumarate and pyruvate was used in murine models of ATN and acute GN (NZM2410 mice with lupus nephritis). A significant increase in [1,4-(13)C(2)]malate signal was identified in the kidneys of mice with ATN early in the disease course before the onset of severe histological changes. No such increase in renal [1,4-(13)C(2)]malate was observed in mice with acute GN. The kidney [1-(13)C]pyruvate/[1-(13)C]lactate ratio showed substantial variability and was not significantly decreased in animals with ATN or increased in animals with GN. In conclusion, MRSI of hyperpolarized [1,4-(13)C(2)]fumarate allows the detection of early tubular necrosis and its distinction from glomerular inflammation in murine models. This technique may have the potential to identify a window of therapeutic opportunity in which emerging therapies might be applied to patients with ATN, reducing the need for acute dialysis with its attendant morbidity and cost.

Modified citrus pectin reduces galectin-3 expression and disease severity in experimental acute kidney injury

Galectin-3 is a β-galactoside binding lectin with roles in diverse processes including proliferation, apoptosis, inflammation and fibrosis which are dependent on different domains of the molecule and subcellular distribution. Although galectin-3 is known to be upregulated in acute kidney injury, the relative importance of its different domains and functions are poorly understood in the underlying pathogenesis. Therefore we experimentally modulated galectin-3 in folic acid (FA)-induced acute kidney injury utilising modified citrus pectin (MCP), a derivative of pectin which can bind to the galectin-3 carbohydrate recognition domain thereby predominantly antagonising functions linked to this role. Mice were pre-treated with normal or 1% MCP-supplemented drinking water one week before FA injection. During the initial injury phase, all FA-treated mice lost weight whilst their kidneys enlarged secondary to the renal insult; these gross changes were significantly lessened in the MCP group but this was not associated with significant changes in galectin-3 expression. At a histological level, MCP clearly reduced renal cell proliferation but did not affect apoptosis. Later, during the recovery phase at two weeks, MCP-treated mice demonstrated reduced galectin-3 in association with decreased renal fibrosis, macrophages, pro-inflammatory cytokine expression and apoptosis. Other renal galectins, galectin-1 and -9, were unchanged. Our data indicates that MCP is protective in experimental nephropathy with modulation of early proliferation and later galectin-3 expression, apoptosis and fibrosis. This raises the possibility that MCP may be a novel strategy to reduce renal injury in the long term, perhaps via carbohydrate binding-related functions of galectin-3.

Angiopoietin-1 therapy enhances fibrosis and inflammation following folic acid-induced acute renal injury

The loss of interstitial capillaries is a feature of several experimental models of renal disease and this contributes to secondary kidney injury. Angiopoietin-1 is a secreted growth factor which binds to Tie-2 present on endothelia to enhance cell survival thereby stabilizing capillary architecture in-vitro. Previous studies showed that angiopoietin-1 prevented renal capillary and interstitial lesions following experimental ureteric obstruction. We tested here the effect of angiopoietin-1 treatment on capillary loss and associated tubulointerstitial damage known to follow recovery from folic acid-induced tubular necrosis and acute renal injury. We found that delivery of angiopoietin-1 by adenoviral vectors stabilized peritubular capillaries in folic acid nephropathy but this was accompanied by profibrotic and inflammatory effects. These results suggest that the use of endothelial growth factor therapy for kidney disease may have varying outcomes that depend on the disease model tested.

Blocking tumor necrosis factor-α inhibits folic acid-induced acute renal failure

Systemic administration of mice with folic acid (FA) has been used for studying the pathogenesis of acute renal failure. However, the molecular mechanisms by which FA induces acute renal failure remain poorly understood. We found that CD-1 mice treated with FA developed acute renal failure characterized by increased blood urea nitrogen, necrosis, and apoptosis of tubular epithelial cells. Compared to control mice, tumor necrosis factor-alpha (TNF-alpha) was markedly elevated in blood and kidneys of these FA-treated mice, accompanied by markedly reduced expression of anti-apoptotic protein BclxL in their kidneys. In vivo administration of FA-treated CD-1 mice with neutralizing anti-TNF-alpha antibody restored the expression of BclxL in kidneys and inhibited the necrosis and apoptosis of renal tubular epithelial cells, leading to the amelioration of acute renal failure. In ex vivo cultures, we found that FA enhanced production of TNF-alpha, decreased expression of BclxL protein, and induced apoptosis of mouse cortical tubule (MCT) cells. Addition of neutralizing anti-TNF-alpha antibody, but not control IgG, in the cultures markedly blocked the apoptotic death of FA-treated MCT cells and restored expression of BclxL to the same levels as those MCT cells cultured in the absence of FA. All these results suggest that TNF-alpha is a critical inflammatory cytokine responsible for FA-mediated acute renal failure. Furthermore, in vivo administration of anti-TNF-alpha antibody may be proved as an effective approach for acute renal failure prevention and treatment.

Increased renal angiopoietin-1 expression in folic acid-induced nephrotoxicity in mice

Growth factors affect epithelial regeneration after acute renal injury, but less is known regarding the expression of vascular growth factors in this setting. A mouse model of folic acid (FA)-induced nephrotoxicity was used to study the expression of angiopoietins (Ang), factors that bind the Tie-2 receptor and modulate endothelial growth. Tubular damage was detected 1 d after FA administration; in the next 14 d, most tubules regenerated but patchy atrophy, with interstitial fibrosis, was also observed. Ang-1 immunostaining was detected between cortical tubules and in the vasa rectae of vehicle-treated animals. FA-induced nephropathy was associated with the acquisition of Ang-1 immunostaining in renal arterial walls and in a subset of injured cortical tubules that failed to stain with periodic acid-Schiff stain, which indicated that they were distal tubules. Renal Ang-1 protein levels were significantly increased after FA administration, compared with time-matched control values, as assessed by Western blotting. Capillaries between regenerating tubules expressed both Tie-2 and platelet-endothelial cell adhesion molecule. A subset of these endothelia expressed proliferating cell nuclear antigen, whereas capillary proliferation was absent in control samples. Therefore, FA-induced nephropathy is associated with increased Ang-1 protein expression in renal epithelia and arteries. In addition, Tie-2-expressing capillaries near damaged cortical tubules undergo proliferation. Further experiments are required to establish whether these events are functionally related.

Vasoconstriction and increased blood pressure in the development of accelerated vascular disease

The pathogenesis of acute vascular lesions has been studied in two types of accelerated vascular disease. Firstly, vascular lesions were induced by a short-term (2 h) infusion of angiotensin II. Low doses of angiotensin II caused only a slight increase in blood pressure and non-destructive lesions. High doses caused a significant elevation of blood pressure and destructive vascular lesions. Secondly, in renovascular hypertension, renal vascular disease was induced by the removal of the stenosing clip from the renal artery. Incidence and severity of destructive vascular lesions were correlated with the calculated gradient between the pressure before and beyond the stenosis. Anaesthesia had a protective effect on the development of destructive vascular lesions in both models. Obviously, this effect is not related to a reduction of the systemic pressure, but rather to the suppression of abnormal vascular tone, characterized by focal constriction alternating with overdilation. Vasomotor changes, which cause a local overdilation, may be responsible for destructive vascular lesions even at normal to subnormal blood-pressure values. Destructive vascular lesions occur as a result of the exceeding of a critical wall tension. The necrosis of medial smooth-muscle cells in non-destructive lesions may be explained by an excessive contraction, which "surpasses" the metabolic capacity of the cells.