Cerebral PET imaging and histological evidence of transglutaminase inhibitor cystamine induced neuroprotection in transgenic R6/2 mouse model of Huntington's disease

To investigate efficacy of cystamine induced neuroprotection, we conducted PET imaging studies of cerebral glucose metabolism with [¹⁸F]FDG (2-deoxy-2-[¹⁸F]fluoro-d-glucose) and striatal dopamine D2 receptor function with [¹¹C]raclopride in R6/2 transgenic Huntington mice. In the control mice, exponentially decreasing glucose utilization was observed in the striatum N_str [SUV]=(41.75±11.80) _58,str*exp(-(0.041±0.007)*t [days]); cortex N _cort [SUV]=24.14±3.66)_58,cort*exp(-(0. 043±0.007)*t [days]); and cerebellum N_cer [SUV]=(34.97±10.58)_58,cer*exp(-(0.037±0.008) *t [days]) as a function of age starting at 58 days. Given that the underlying degeneration rate in the cystamine treated mice is similar to that observed in control animals, the protection coefficient (β) calculated from the equation N_t=N₅₈*exp(-(1-β) *k*t) was 0.133±0.035 for the striatum; 0.122±0.028 for the cortex and 0.224±00.042 for the cerebellum with a dose of 100 mg/kg. The 50 mg/kg cystamine dose provided significant protection only for the striatum and only minor protection was obtained using lower doses. Striatal binding potential of [¹¹C]raclopride was 1.059±0.030 in the control mice, and enhanced in the cystamine treated animals in a dose dependent manner up to 1.245±0.063 using the 100 mg/kg dose. Histological analysis confirmed cystamine induced neuroprotection of striatal and cortical neurons and Nissl staining revealed that formation of cellular inclusions was reversed in a dose dependent manner. Cerebral imaging and histological evidence support the use of cystamine as a neuroprotective agent for Huntington's disease (HD) pathology.