Evaluation of retinol binding protein 4 and carbamoylated haemoglobin as potential renal toxicity biomarkers in adult mice treated with (177)Lu-octreotate.

Background: The kidneys are regarded as one of the main dose-limiting organs in the treatment of neuroendocrine tumours with (177)Lu-[DOTA(0), Tyr(3)]-octreotate ((177)Lu-octreotate), despite the successful use of kidney uptake blocking agents such as lysine and arginine. To avoid renal toxicity but still give each patient as high amount of (177)Lu-octreotate as possible, there is a need for methods/biomarkers that indicate renal injury in an early stage of the treatment. The aim of this study was to investigate the potential of using urinary retinol binding protein 4 (RBP4) and carbamoylated haemoglobin (Hb) in blood as biomarkers of nephrotoxic effects on adult mice after (177)Lu-octreotate treatment.

Methods: Adult BALB/c nude mice were injected with 60 MBq or 120 MBq of (177)Lu-octreotate or with saline (control). Urine was collected before injection and concentrations of urinary RBP4 and creatinine were determined 14 to 90 days after injection Blood samples were collected after 90 days, and carbamoylated N-terminal valine in Hb, formed from urea, was measured as valine hydantoin (VH) after detachment from Hb.

Results: The RBP4 values increased with administered activity and time. For the 60 and 120 MBq groups, statistically significantly higher RBP4 levels (p <0.05) were found at day 60 and 90 compared to baseline, also at day 30 for 120 MBq group. For VH, the mean values were similar for the 60 MBq and control groups, while a small increase was observed for the 120 MBq group; but there were no statistically significant differences between any of the groups (p >0.05). No morphological changes in the kidney tissue were found.

Conclusions: Urinary RBP4 is a promising new biomarker for radiation-induced renal toxicity. For the conditions used in this experiment, carbamoylated Hb (from urea) measured as VH may not be a sufficiently sensitive biomarker to be used for renal toxicity.

Trial Registration: ID 326-2008.