Where disease pathogenesis meets protein formulation: Renal deposition of immunoglobulin aggregates

Aggregation is one of the important issues encountered during the development of immunoglobulin-based drugs. The aim of the current review is to discuss the causes and consequences of immunoglobulin aggregation as well as the relevance of immunoglobulin aggregation to disease pathogenesis. Extracellular deposition of immunoglobulins, either monoclonal light chains or intact polyclonal antibodies, induces renal failure in various nephropathies. The aggregates can present fibrillar or amorphous structures. In this review, factors known to influence protein aggregation, such as the primary structure of the protein, local environment and glycosylation are assessed, as well as the subsequent altered clearance, fibril formation and toxicity. The role of the protein local environment is emphasized. Even if the local environment causes only minor perturbations in the protein structure, these perturbations might be sufficient to trigger aggregate formation. This fact underlines the importance of choosing appropriate formulations for protein drugs. If the formulation provides a slightly destabilizing environment to the protein, the long-term stability of the drug may be compromised by aggregate formation.

Effect of IgA aggregates on transforming growth factor-beta1 production in human mesangial cells and the intraglomerular expression of transforming growth factor-beta1 in patients with IgA nephropathy

BACKGROUND

Transforming growth factor-beta (TGF-beta) stimulates renal fibrosis in various renal diseases including IgA nephropathy.

METHODS

We examined whether immunoglobulin A (IgA) stimulated TGF-beta1 synthesis in human mesangial cells (MCs), and whether this effect was mediated through the protein kinase C (PKC) pathway. We measured the intraglomerular TGF-beta1 mRNA expression by using competitive RT-PCR, and this was compared with various parameters in IgA nephropathy patients.

RESULTS

The IgA aggregate increased the TGF-beta1 mRNA expression in MCs, while this expression was not affected by the culture media or IgG aggregate. Phorbol 12-myristate 13-acetate and calphostin C did not influence the TGF-beta1 mRNA expression that was increased by the IgA aggregate. Intraglomerular TGF-beta1 mRNA expression was significantly correlated with creatinine clearance (r = -0.764, p = 0.027), daily proteinuria (r = 0.781, p = 0.022), serum creatinine (r = 0.884, p = 0.004), and tubulointerstitial changes (r = 0.809, p = 0.015). Glomerular TGF-beta1 mRNA expression was associated with an increased tendency for glomerulosclerosis (r = 0.646, p = 0.084). After 4 years, patients with a high expression of intraglomerular TGF-beta1 mRNA showed a tendency for an decrease of their renal function.

CONCLUSION

The IgA aggregate increased TGF-beta1 mRNA expression in MCs, and this was independent of the PKC pathway. The evaluation of intraglomerular TGF-beta1 mRNA expression could be useful in predicting the progression of IgA nephropathy.