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Received for publication April 27, 2004.
Revised June 9, 2004.
Accepted for publication June 14, 2004.
Tubular dysfunction is an important early manifestation of diabetic nephropathy. Reduced renal expression of organic cation transporters (OCTs) potentially contributes to impaired cation clearance in diabetes. This study examines the role of advanced glycation end-products (AGEs) in mediating these changes. Experimental diabetes was induced with streptozotocin (55mg/kg). Rats were randomly treated with the AGE inhibitor, aminoguanidine, for 32-weeks. In a second protocol, diabetic rats were followed with and without low dose insulin therapy (2U/day) for 4-weeks. Expression of OCTs was determined by real time RT-PCR and western blotting. As a marker of cation transport, the fractional clearance of endogenous N-methyl-nicotinamide (NMN) was determined by HPLC. Both short- and long-term diabetes was associated with reduced gene and protein expression of the three renal OCT isotypes. This was associated with a reduction in the fractional clearance of NMN compared to control animals by over 50%. These changes correlated with the accumulation of renal and plasma AGEs. Treatment with the AGE inhibitor, aminoguanidine, restored the expression of OCT-2 and OCT-3 in diabetic animals and normalised renal NMN clearance. NMN clearance was also improved in diabetic animals receiving low-dose insulin, correlating with a reduction in AGEs and improvement in effective renal plasma flow. These studies demonstrate an early impairment of expression of OCTs and cation clearance associated with diabetes. These changes correlate with the accumulation of AGEs and may be partly attenuated by an AGE-inhibitor, implicating a role for AGEs in organic cation transport.
Key words:
Advanced glycation, Diabetes, N-methylnicotinamide, Organic cation, Proximal tubule, Renal clearance
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