Fatty acids bound to albumin are filtered through glomeruli, reabsorbed by proximal tubular epithelial cells, and metabolized. Because albumin serves as a carrier, an increase in delivery of fatty acids to the proximal tubule may occur in proteinuric states, possibly leading to toxic effects. At present, the contribution of fatty acids to tubulointerstitial damage and the mechanisms underlying this toxicity remain unclear. We recently found that the transcription factor peroxisome proliferator-activated receptor ␣ (PPAR␣) regulates fatty acid metabolism in proximal tubules, so we tested its role in tubular damage under proteinuric conditions. We induced protein-overload nephropathy in Ppara-null or wildtype (WT) mice by injecting fatty acids bound to BSA. Ppara-null mice exhibited greater renal dysfunction from severe proximal tubular injury than WT mice. Kidneys from Ppara-null mice injected with albumin alone showed little injury. Acute tubular injury was associated with deranged fatty acid homeostasis, increased oxidative stress, increased apoptosis, and activation of NFB signaling. These results suggest a role for fatty acids in proteinuria-associated tubular toxicity, as well as a protective role for PPAR␣. Modulation of PPAR␣ may be a future therapeutic option for tubular toxicity from fatty acids.

A retrospective study of 166 patients with IgA nephropathy was undertaken to clarify possible correlations between clinical and histological features, and the severity and prognosis of the disease. At the time of biopsy, impaired renal function, with creatinine clearance (C_cr) below 90 ml/min was found in 61 cases. At the final examination, after a mean follow-up period of 34 months, 82 patients had impaired renal function, 12 of these patients went into terminal renal failure requiring hemodialysis treatment. The presence of proteinuria of more than 1.0 g/day was closely correlated with impairment of renal function both at the time of biopsy and at the final observation. An unfavorable outcome was also anticipated in the presence of hypertension. In contrast, microhematuria, macrohematuria or high serum IgA levels did not appear to be related to the outcome. Histologically, sclerotic lesions such as mesangial or global sclerosis, interstitial fibrosis and tubular atrophy, and some active changes such as mesangial hypercellularity and tuft adhesion were more frequent and severe in patients with impaired renal function. Impressive localization of IgA and C3 in the mesangium as well as in capillary loops was observed more often in these patients. These results clearly indicate that IgA nephropathy may follow a slowly progressive course in about half of the patients, and that marked proteinuria and severe histological changes appear to correlate closely with an unfavorable course.

Early diagnosis was the most important factor for improving the prognosis of RPGN patients. To avoid early death due to opportunistic infection in older patients, a milder immunosuppressive treatment such as an initial oral prednisolone dose reduction with or without immunosuppressant is recommended.

Mast cells are one of the constitutive cells in the interstitium of IgA nephritis patients and affect renal function by contributing to the interstitial fibrosis.