Secretion of chemokines and cytokines by human tubular epithelial cells in response to proteins

Differences in the modulating potential of advanced glycation end product (AGE) peptides versus AGE proteins

Differences in the modulating potential of advanced glycation end product (AGE) peptides versus AGE proteins. Advanced glycation end products (AGEs), identified as irreversible products of a complex reaction of carbonyl groups of reducing sugars with free protein amino groups, are characterized by resistance to proteolytic degradation. The incomplete digestion of AGEs results in low molecular weight AGEs accumulating in the blood of diabetic and uremic patients. We hypothesized that the accumulation of these compounds may contribute to the dysfunction and/or degeneration of tubular epithelial cells. Our study examined whether low-molecular-weight AGE peptides and high-molecular-weight AGE proteins affect the functional cellular properties of two tubular epithelial cell lines: immortalized human kidney tubular epithelial (IHKE) and immortalized rat renal proximal tubular cells (IRPTCs). Parameters of cellular damage and growth behavior were cell counting, analysis of the cellular metabolic activity (MTT assay), as well as cellular proliferation (3[H]-thymidine-incorporation). IHKE treated with bovine serum albumin-AGE (BSA-AGE 50) or BSA-AGE-Pep 50 revealed a decrease in cellular metabolic activity as compared with controls after 48 hours of incubation (73 +/- 9% for BSA-AGE 50 and 62 +/- 11% for BSA-AGE-Pep 50 vs. 89 +/- 8% for BSA Co 50). Low molecular weight BSA-AGE-Pep 50 induced a significantly greater cellular damage in IRPTCs as compared with high molecular weight BSA-AGE 50 after 144 hours of incubation (59 +/- 15% for BSA-AGE 50 vs. 31 +/- 13% for BSA-AGE-Pep 50). The decrease in metabolic activity correlated well with a decrease in cellular proliferation. The results suggest a higher toxic potential of low molecular weight AGE peptides compared with high molecular weight AGE proteins in IRPTC and IHKE. This may provide evidence that low molecular weight degradation products of AGE-modified proteins have an important risk potential.

Follow-up study of glomerular dimensions and cortical interstitium in microalbuminuric type 1 diabetic patients with or without antihypertensive treatment

BACKGROUND

A decrease in urinary albumin excretion is regularly seen with antihypertensive treatment in patients with diabetic nephropathy. Our study concerns structural data obtained by light microscopy in baseline and follow-up biopsies in antihypertensive treated patients and in a reference group.

METHODS

Microalbuminuric type 1 diabetic patients with diabetes duration of 6-16 years were studied. Two groups, allocated to treatment with either angiotensin-converting enzyme-inhibitor (group 1, n=6) or beta-blocker (group 2, n=6) after the baseline biopsy, were studied in parallel, whereas the reference group (group 3, n=9), without antihypertensive treatment, was part of a previously completed study. The renal plastic-embedded biopsies were serially sectioned (1 microm), the sections being used for determining glomerular volume, vascular pole area, and interstitial space expressed as fraction of tubular cortex.

RESULTS

A significant increase in glomerular volume (P=0.04) was seen in group 3 only. Vascular pole area (VPA) and VPA relative to calculated glomerular surface did not show significant changes in any of the groups, only a tendency to increase in VPA in group 3 (P=0.051). The increase in VPA correlated with systolic blood pressure during the study period (r=0.49, P=0.03). Glomerular volume did not correlate with HbA(1C), current diabetic glomerulopathy, or ensuing worsening of glomerulopathy. In group 3 every case showed an increase in interstitium (P=0.0009), group 2 showed a decrease (P=0.03), and group 1 showed no change. Increase in interstitial fractional volume correlated with diastolic blood pressure during the study (r=0.54, P=0.01).

CONCLUSIONS

In early microalbuminuria, type 1 diabetic patients show glomerular growth, probably compensatory to the developing glomerulopathy. The increase in interstitial volume fraction, demonstrable in early nephropathy, is further augmented over a few years, but is arrested by antihypertensive treatment.

Chemokines as therapeutic targets in renal disease

Increased understanding of the fundamental importance of the role of chemokines and their receptors in inflammation, together with the demonstration of their involvement in human and experimental inflammatory renal disease, make these molecules potential therapeutic targets. A number of recent studies using genetically deficient mice and chemokine receptor antagonists in animal models have demonstrated that chemokine inhibition can attenuate experimental renal injury. Because there is simultaneous expression of multiple chemokines and receptors in disease, strategies that are aimed at antagonizing multiple chemokines receptor interactions are likely to be more effective than therapies that target a single chemokine. It is also now recognized that chemokines are involved in normal immune development and immune regulation. These observations, together with the results of studies that have demonstrated deleterious effects of chemokine receptor antagonism in experimental renal disease, highlight the need for thorough understanding of the role of individual chemokines in the pathogenesis of different types of renal disease before optimal therapeutic interventions may be achieved.

The role of tubulointerstitial injury in chronic renal failure

Progressive renal failure results from a triad of glomerulosclerosis, tubulointerstitial fibrosis and vascular sclerosis. The mechanisms by which tubules are injured, and by which the tubular epithelial cell then excites interstitial inflammation culminating in fibroblast activation and fibrosis have become increasingly understood. Most current methods to prevent progressive glomerulosclerosis would inherently prevent tubular injury and interstitial fibrosis. The behaviour and control of the renal fibroblast is being investigated, with the potential for direct interference with its functions.