Glycohemoglobin: a primary predictor of the development or reversal of complications of diabetes mellitus.

BACKGROUND: Diabetes mellitus is a major health problem worldwide with long-term micro- and macrovascular complications responsible for a majority of its morbidity and mortality. The development and progression of these complications relate strongly to glycemic control. METHODS: We reviewed the literature extensively for studies that relate glycemic control to the development and progression of diabetic complications. We discuss the problems of standardizing glycohemoglobin measurements for monitoring diabetic therapy and also consider recently developed electrospray ionization mass spectrometry methods that have been considered as candidate reference methods for estimation of glycohemoglobin. RESULTS: Several clinical trials and studies have clearly shown that improved glycemic control is strongly associated with decreased development and/or progression of complications in both type 1 and type 2 diabetes mellitus. Irrespective of the methods used for estimating glycohemoglobin, these results underline the importance of glycohemoglobin for guiding therapy of diabetes mellitus. Recently developed candidate reference methods promise to yield greatly improved standardization for the measurement of glycohemoglobin. CONCLUSIONS: Glycohemoglobin measurement remains the optimal indicator of glycemic control in diabetic patients, but translation of findings from clinical trials to clinical practice worldwide demands consistent values across all assays. To ensure that the important prognostic information still applies to all diabetic patients with the application of the reference method(s), the hemoglobin A(1c) values reported in the major clinical trials will have to be translated into statistically and computationally compatible values based on the new reference system(s).

Alterations in human glomerular epithelial cells interacting with nonenzymatically glycosylated matrix.

The glomerular epithelial cells and the glomerular basement membrane are important constituents of the permselective barrier in the kidney. These are affected in diabetic nephropathy, one of the long-term complications in diabetic patients. Nonenzymatic glycosylation resulting in the accumulation of advanced glycosylation end products correlates with the development of long-term complications in diabetes. The interaction of cells with extracellular matrix proteins plays a critical role in a variety of biological processes. Recent studies show that cell-matrix interactions mediated by integrins can transduce biochemical signals to the cell interior and regulate cell behavior. In this paper we demonstrate that interactions of human glomerular epithelial cells with a nonenzymatically glycated matrix are altered with defective cell spreading, reduced phosphorylation of focal adhesion kinase and reduced activity of mitogen-activated protein kinase. These data suggest that matrix glycation interferes with normal cell-matrix interactions and intracellular signaling that can potentially result in differential gene expression contributing to the changes seen in diabetic nephropathy.

Integrin-mediated interactions between primary/T-sv40 immortalized human glomerular epithelial cells and type IV collagen.

The use of human glomerular epithelial cells (HGEC) in research has been severely restricted by several obstacles, which have been circumvented by the generation of T-SV40 immortalized human visceral glomerular epithelial cells (Delarue et al, 1991). In this work, we compared the primary and immortalized HGEC for expression of integrin and some nonintegrin surface receptors. We also studied the adhesion of both types of HGEC to glomerular basement membrane (GBM), type IV collagen (tIV), and its major noncollagenous NC1 domain. The integrins mediating adhesion of HGEC to tIV were also examined. Expression of integrin and some nonintegrin cell surface receptors was analyzed by flow cytometry. Adhesion to GBM, tIV, and its major noncollagenous NC1 domain was studied by direct solid phase cell adhesion assays. Identification of integrins mediating adhesion of HGEC to tIV was achieved by inhibition of cell adhesion using monoclonal antibodies to integrin subunits. The primary and immortalized HGEC share phenotypic characteristics, and alpha3beta1 appeared to be the major integrin present on both HGEC types. The kinetics of binding to GBM, tIV, and its noncollagenous NCI domain were similar in both the primary and immortalized HGEC, although the latter displayed a somewhat weaker binding. Both the primary and immortalized HGEC displayed significantly better adhesion to NC1-alpha3 compared with NC1-alpha1, alpha3beta1 appears to be the major integrin mediating the adhesion of HGEC to tIV. Our studies suggest that alpha3beta1 is the major integrin present on HGEC. This has been confirmed by flow cytometric analysis. In addition, we demonstrated a functional role for this integrin in mediating attachment of HGEC to tIV. Our data also demonstrate a preference in binding of HGEC to alpha3 chains of NC1 compared with alpha1 chains of NC1. These findings were seen in both the primary and immortalized HGEC. The T-SV40 immortalized HGEC can therefore serve as a very useful tool to study glomerular visceral cell biology.

REceptors in proximal tubular epithelial cells for tubulointerstitial nephritis antigen.

Tubulointerstitial nephritis antigen (TIN-ag) is a novel basement membrane macromolecule that is involved in human antitubular-basement-membrane-mediated tubulointerstitial nephritis. The presence of antibodies to TIN-ag may result in an alteration of proximal tubule epithelial cell interaction with surrounding matrix and contribute to the pathogenesis of immune-mediated tubulointerstitial disease. To study the adhesive interactions between TIN-ag and proximal tubule epithelial cells and the macromolecules that mediate these interactions, an immortalized proximal tubular epithelial cell line from normal adult human kidney (HK-2) was used. Plastic-coated TIN-ag was able to promote adhesion of HK-2 cells in a concentration-dependent manner. the strength of the adhesive interaction was comparable to that of type IV collagen or laminin. to explore which members of the integrin family of cell surface receptors were involved in this interaction, we performed fluorescence activated cell sorting (FACS) analysis and adhesion-inhibition studies using monoclonal antibodies against various integrins. Both approaches suggested that integrins alpha 3 beta 1 and alpha 5 beta 3 are crucial for the adhesion of proximal tubule epithelial cells on TIN-ag, and that they are probably using independent domains of TIN-ag for their action. These data will help us to understand the interactions between proximal tubule epithelial cells and the underlying basement membrane, and will provide tubule clues to the pathogenesis of kidney tubular diseases at the molecular level.