Clearance Ratios of Amylase Isoenzymes and IgG Subclasses: Do They Reflect Glomerular Charge Selectivity?

Abstract

The clearance ratios of endogenous plasma proteins with the same size but a different charge, such as the amylase isoenzymes and the immunoglobulin (Ig) G subclasses, have been used to assess glomerular charge selectivity in man. These proteins are, however, subject to tubular reabsorption. In this study we measured the IgG subclass/IgG clearance ratios for IgG1 (pi 8.0-9.5), IgG2 (pI 7.0-7.5) and IgG4 (pI < 6) in 6 healthy volunteers. Our results suggested a selective influence of tubular reabsorption: the IgG1/IgG clearance ratio was 0.68 ± 0.14 (mean ± SD) and lower than IgG2/IgG (2.02 ± 1.06, p ≤ 0.01). IgG4/IgG was 0.89 ± 0.39. In addition, we studied the clearance ratios of pancreatic (PA, pI 7.0) and salivary amylase (SA, pI 5.9-6.4) and of IgGl and IgG2 in 8 patients with minimal change nephrotic syndrome (MCNS), 11 patients recovering from acute tubular necrosis (ATN) and 9 healthy volunteers (controls). In MCNS glomerular charge selectivity is lost, while in recovering ATN tubular function is severely disturbed. The PA/SA clearance ratio was 3.25 ± 0.89 in controls, reflecting intact glomerular charge selectivity. In MCNS patients the PA/SA clearance ratio had decreased to 1.21 ± 0.23 (p ≤ 0.001). In ATN patients the PA/SA clearance ratio was reduced as well: 1.55 ± 0.41 (p < 0.001), although the aselective nature of the proteinuria and the modest albuminuria indicated intact glomerular charge selectivity. The IgGl/ IgG2 clearance ratio was 0.54 ± 0.15 in controls, again suggesting preferential tubular reabsorption of IgGl. In MCNS patients the IgG1/IgG2 clearance ratio was 0.16 ± 0.10 (p ≤ 0.001); this probably reflects the relatively increased glomerular sieving of IgG2 when glomerular charge selectivity is lost. In ATN patients the IgGl/IgG2 clearance ratio was 1.07 ± 0.47 (p ≤ 0.001), which suggests a partial loss of preferential reabsorption of IgGl. It was concluded that the PA/SA clearance ratio is influenced by loss of tubular function and therefore does not reflect glomerular charge selectivity specifically. The IgG1/IgG2 ratio cannot be used to assess glomerular charge selectivity either because of the interference of selective tubular reabsorption of the subclasses. These findings put the assessment of glomerular charge using endogenous proteins in a new light and bring forward the necessity to interpret these ratios with the outmost cautiousness.

Broad-spectrum Four-dimensional Orthogonal Electrophoresis: A Novel Comprehensively Feasible System for Protein Complexomics Investigation

“…Actually, previous study suggested that pI of IgG2 is 7.0 -7.5 (33), which was in accordance with VIII spot position (pI, ϳ7.3). The glycopeptide peak at m/z 2805.1, termed as IgG2 G0F1N (N, bisecting GlcNAc), in the GVIII spot spectrum, and peaks at m/z 2796.1 (IgG1 G1F1) and m/z 2805.2 (IgG2 G0F1N) in the LVIII spot spectrum, were higher than their corresponding peaks in NVIII spot spectrum, suggesting that part I may be a convenient approach for simplifying protein PTM study, attributed to the high-performance separation.…”

Considerations for extraction of monoclonal antibodies targeted to different subcellular compartments in transgenic tobacco plants

“…However, a range of pH values (pH 5–7) was found to be suitable. When the extraction buffer approached the p I value of IgG1 (8–9.5; Buis et al ., 1997), less mAb was extractable. Interestingly, when the tobacco TSP levels were measured, the amount of TSP released at pH 7.4 was significantly higher than that at pH 6 ( P = 0.017) (Figure 8b).…”

Antiphospholipase A2 Receptor Antibody Titer and Subclass in Idiopathic Membranous Nephropathy

“…Indeed, the ratio of the clearance of IgG and IgG4 decreased in patients with minimal change disease, compatible with increased filtration of IgG4. 17 Still, we cannot exclude that these adjustments may cause an artificial correlation. We did, however, find a significant correlation between IgG4, but not IgG1 and IgG3, titers and the occurrence of spontaneous remissions.…”