Detailed glomerular ultrastructure in Japanese type 2 diabetic patients by the quick-freezing and deep-etching method

Mesangial expansion and glomerular basement membrane (GBM) thickening did not correlate with urinary albumin excretion (UAE) in type 2 diabetic patients in our previous studies; therefore, it was necessary to elucidate more detailed ultrastructural changes in the early stages of diabetic nephropathy (DN) in type 2 diabetic patients. The quick-freezing and deep-etching (QF-DE) method allows us to examine three-dimensional ultrastructures of human renal glomeruli in vivo at high resolution. The QF-DE method was applied to six type 2 diabetic patients without definable renal diseases other than DN. Four patients were normoalbuminuric (NA) and the other two were microalbuminuria (MA). Three control specimens were the normal parts from nephrectomies due to renal cell carcinomas. Electron microscopic morphometric analyses provided quantitative glomerular structural changes. Replica membranes were prepared by the QF-DE method, and diameters of mesh structures at the GBM and mesangial matrix (MM) were measured on electron micrographs as previously described. By the QF-DE method, both the GBM middle layer and MM were composed of polygonal meshwork structures. The mesh pores of the GBM and MM were more enlarged and irregular in shape in NA diabetic patients than those of the controls, and these ultrastructural changes became more obvious in MA patients. The mesh diameters of the GBM and MM in the diabetic patients were also larger than those of the controls. Such a mesh diameter of the GBM was well correlated with the amount of UAE, while the mesh diameter of MM showed a slight correlation with UAE. Although there were small number of subjects in the present study, the detailed ultrastructural changes in NA and MA type 2 diabetic patients, which had not been disclosed by conventional electron microscopy, were revealed by the QF-DE method. Increased mesh diameters of GBM might be related with the increase of UAE.