Complement Activation in Patients With Diabetic Nephropathy.

INTRODUCTION: Complement activation plays a role in various organs in patients with diabetes. However, in diabetic nephropathy (DN), the role of complement activation is poorly understood. We examined the prevalence and clinical significance of complement deposits in the renal tissue of cases with type 1 and type 2 diabetes with and without DN. METHODS: We measured the prevalence of glomerular C4d, C1q, mannose-binding lectin (MBL), and C5b-9 deposits in 101 autopsied diabetic cases with DN, 59 autopsied diabetic cases without DN, and 41 autopsied cases without diabetes or kidney disease. The presence of complement deposits was scored by researchers who were blinded with respect to the clinical and histological data. RESULTS: C4d deposits were more prevalent in cases with DN than in cases without DN in both the glomeruli (46% vs. 26%) and the arterioles (28% vs. 12%). C1q deposits were also increased in the glomerular hili (77% vs. 55%) and arterioles (33% vs.14%), and were correlated with DN (P < 0.01). MBL deposits were only rarely observed. C5b-9 deposits were more prevalent in the cases with diabetes mellitus (DM) than in the cases without DM (69% vs. 32%; P < 0.001). Finally, glomerular C4d and C5b-9 deposits were correlated with the severity of DN (ρ = 0.341 and 0.259, respectively; P < 0.001). CONCLUSION: Complement activation is correlated with both the presence and severity of DN, suggesting that the complement system is involved in the development of renal pathology in patients with diabetes and is a promising target for inhibiting and/or preventing DN in these patients.

Metabolic imaging of fatty kidney in diabesity: validation and dietary intervention.

Background: Obesity and type 2 diabetes have not only been linked to fatty liver, but also to fatty kidney and chronic kidney disease. Since non-invasive tools are lacking to study fatty kidney in clinical studies, we explored agreement between proton magnetic resonance spectroscopy (1H-MRS) and enzymatic assessment of renal triglyceride content (without and with dietary intervention). We further studied the correlation between fatty kidney and fatty liver. Methods: Triglyceride content in the renal cortex was measured by 1H-MRS on a 7-Tesla scanner in 27 pigs, among which 15 minipigs had been randomized to a 7-month control diet, cafeteria diet (CAF) or CAF with low-dose streptozocin (CAF-S) to induce insulin-independent diabetes. Renal biopsies were taken from corresponding MRS-voxel locations. Additionally, liver biopsies were taken and triglyceride content in all biopsies was measured by enzymatic assay. Results: Renal triglyceride content measured by 1H-MRS and enzymatic assay correlated positively (r = 0.86, P < 0.0001). Compared with control diet-fed minipigs, renal triglyceride content was higher in CAF-S-fed minipigs (137 ± 51 nmol/mg protein, mean ± standard error of the mean, P < 0.05), but not in CAF-fed minipigs (60 ± 10 nmol/mg protein) compared with controls (40 ± 6 nmol/mg protein). Triglyceride contents in liver and kidney biopsies were strongly correlated (r = 0.97, P < 0.001). Conclusions: Non-invasive measurement of renal triglyceride content by 1H-MRS closely predicts triglyceride content as measured enzymatically in biopsies, and fatty kidney appears to develop parallel to fatty liver. 1H-MRS may be a valuable tool to explore the role of fatty kidney in obesity and type 2 diabetic nephropathy in humans in vivo.

Macrophages in diabetic nephropathy in patients with type 2 diabetes.

BACKGROUND: Inflammation plays a role in the development of diabetic nephropathy (DN) in type 2 diabetes. Although macrophages have been found in experimental models of DN, little is known regarding the presence of macrophages in patients with DN. Therefore, we investigated the presence and phenotype of glomerular and interstitial macrophages in relation to clinical and histopathological parameters in patients with DN. METHODS: Renal autopsy samples were obtained from 88 type 2 diabetic patients with histologically proven DN and stained for CD68 and CD163 as general and M2/anti-inflammatory markers of macrophages. Renal damage was scored based on histopathological classification of DN. Control renal autopsy samples were obtained from patients without renal abnormalities and from diabetic patients without DN. Positive cells per glomerulus were counted. Interstitial macrophages were counted semi-quantitatively. RESULTS: Macrophages were present in all groups. In the DN group, the mean number of CD68+ cells per glomerulus and CD163+ cells per glomerulus was 4.2 (range 0-19) and 2.1 (range 0-14.47), respectively. The distribution was similar between all histopathological classes. Glomerular CD163+ macrophages were positively associated with DN class, interstitial fibrosis and tubular atrophy, and glomerulosclerosis. Interstitial CD68+ macrophages were correlated with glomerular filtration rate stage and albuminuria. CONCLUSIONS: Our results demonstrate that macrophages are present in the glomeruli and interstitium of type 2 diabetic patients with DN and of controls. Although patients and controls had similar numbers of glomerular macrophages, glomerular anti-inflammatory CD163+ macrophages were associated with pathological lesions in DN. Taken together with the correlation between interstitial macrophages and interstitial fibrosis and tubular atrophy, DN class, and renal function, this finding suggests that macrophages may play a role in DN progression. Therefore, targeting macrophages may be a promising new therapy for inhibiting the progression of DN.

An autopsy study suggests that diabetic nephropathy is underdiagnosed.

The reported prevalence of diabetic nephropathy (DN) among patients with diabetes varies widely. Most studies use the presence of microalbuminuria for clinical onset of DN in the absence of a histopathologic evaluation. In this autopsy study, we collected and analyzed data from a cohort of patients with type 1 or 2 diabetes and determined the prevalence of histologically proven DN in patients with or without clinical manifestations of renal disease. We also examined the distribution among histopathologic classes with respect to clinical parameters. Renal tissue specimens from autopsies and clinical data were collected retrospectively from 168 patients with diabetes. The histopathologic classification for DN was scored as were interstitial and vascular parameters. In this cohort, 106 of 168 patients had histopathologic changes in the kidney characteristic of DN. Twenty of the 106 histologically proven DN cases did not present with DN-associated clinical manifestations within their lifetime. Glomerular and interstitial lesions were associated with renal function but not with proteinuria. We also found that underdiagnosed DN may encompass all histopathologic classes except the sclerotic class. Thus, the prevalence of histologically proven DN was higher than previously appreciated, and we found a relatively high proportion of DN that was clinically underdiagnosed yet histologically proven, suggesting that DN lesions may develop before the onset of clinical findings.

Intrinsic carnosine metabolism in the human kidney.

Histidine-containing dipeptides like carnosine and anserine have protective functions in both health and disease. Animal studies suggest that carnosine can be metabolized within the kidney. The goal of this study was to obtain evidence of carnosine metabolism in the human kidney and to provide insight with regards to diabetic nephropathy. Expression, distribution, and localization of carnosinase-1 (CNDP1), carnosine synthase (CARNS), and taurine transporters (TauT) were measured in human kidneys. CNDP1 and CARNS activities were measured in vitro. CNDP1 and CARNS were located primarily in distal and proximal tubules, respectively. Specifically, CNDP1 levels were high in tubular cells and podocytes (20.3 ± 3.4 and 15 ± 3.2 ng/mg, respectively) and considerably lower in endothelial cells (0.5 ± 0.1 ng/mg). CNDP1 expression was correlated with the degradation of carnosine and anserine (r = 0.88 and 0.81, respectively). Anserine and carnosine were also detectable by HPLC in the renal cortex. Finally, TauT mRNA and protein were found in all renal epithelial cells. In diabetic patients, CNDP1 seemed to be reallocated to proximal tubules. We report compelling evidence that the kidney has an intrinsic capacity to metabolize carnosine. Both CNDP1 and CARNS are expressed in glomeruli and tubular cells. Carnosine-synthesizing and carnosine-hydrolyzing enzymes are localized in distinct compartments in the nephron and increased CNDP1 levels suggest a higher CNDP1 activity in diabetic kidneys.