Thermal Reaction Behavior of Triphenylimidazolyl Radical with a Bulky Substituent.

The triphenylimidazolyl radical (TPIR) is generated by the irradiation of the photochromic molecule hexaarylbiimidazole (1,2'-HABI). Usually, the unsubstituted TPIRs form 1,2'-HABI thermally at room temperature. In this study, we report the thermal reaction behavior of TPIR with a tBu group (tBu-TPIR) under N2 atmosphere and the novel reactivities of TPIRs. Under N2 atmosphere at room temperature, tBu-TPIRs form SpI with a spiro carbon and a novel HABI isomer tBu-1,4'-HABI, whose bonding pattern is different from that of the original unsubstituted HABI (1,2'-HABI). The results of 1H NMR spectroscopy, EPR measurements, and DFT calculations revealed that SpI is generated via three steps: (1) intramolecular hydrogen transfer from the tBu group to the nitrogen atom of the imidazole ring, (2) intramolecular cyclization of alkyl radicals, and (3) intermolecular hydrogen transfer with another tBu-TPIR. Furthermore, we found that the thermal reaction of tBu-TPIR at a low temperature affords the diastereomers of other isomers (tBu-4,4'-HABI_RS and tBu-4,4'-HABI_RR); in other words, the thermal reaction of tBu-TPIR depends on temperature.

Enhanced TGF-beta/Smad signaling in the early stage of diabetic nephropathy is independent of the AT1a receptor.

BACKGROUND: Angiotensin II (AII) and transforming growth factor-beta (TGF-beta) are closely involved in the pathogenesis of diabetic nephropathy (DN). AII is known to induce TGF-beta production in resident renal cells, including glomerular mesangial cells and tubular epithelial cells. TGF-beta receptor types I and II (TGF-betaRI, II) are up-regulated in the diabetic kidney. The aim of this study was to clarify the role of AII in the regulation of the TGF-beta system in the early stage of DN using AII type1a receptor-deficient(AT1a(-/-)) mice. METHODS: We investigated the expression of TGF-beta1, TGF-betaRI, II, and Smad signaling in AT1a(-/-) mice with streptozotocin (STZ)-induced DN. Mice were killed 10 and 20 days after the induction of hyperglycemia. The expression of TGF-beta receptors was analyzed by immunohistochemical staining and reverse transcriptase-polymerase chain reaction (RT-PCR). TGF-beta-specific Smad signaling was analyzed by electrophoretic mobility shift assay and Western blotting. RESULTS: The expression of both TGF-betaRI and RII was up-regulated in the glomerular tufts and vasculature in diabetic AT1a(+/+) mice kidney by immunohistochemistry. RT-PCR revealed that mRNAs for TGF-betaRI and RII were also up-regulated. Smad2 and 4 protein levels were reduced in the renal cortex after the induction of diabetes, with an increase of Smad 3/4 complex in the nucleus. The expression of TGF-beta receptors increased in both diabetic AT1a(-/-) and AT1a(+/+) mice. Smad signaling in AT1a(-/-) mice was also enhanced. CONCLUSIONS: Our results suggest that the complete blockade of the AT1a-mediated pathway has a minimal effect on the enhanced TGF-beta/Smad signaling in the early stage of DN, at least in the AT1a(-/-) model.

Renal interstitial fibrosis is reduced in angiotensin II type 1a receptor-deficient mice.

Unilateral ureteral obstruction (UUO) results in tubulointerstitial fibrosis of the affected kidney by stimulating the renin-angiotensin system. This study established a UUO model in angiotensin type 1a receptor (AT1a) deficient (mutant) mice to elucidate the role of angiotensin II through AT1a on the fibrosis of the obstructed kidney (OBK). The relative volume of the tubulointerstitium was measured by an image analyzer; deposition of collagen types III and IV and monocyte/macrophage infiltration were histologically examined using specific antibodies. Also determined were the mRNA levels of transforming growth factor-beta by Northern blot analysis. Nuclear factor-kappaB activity was assessed by gel shift assay. UUO in wild mice resulted in a marked expansion of relative volume of the tubulointerstitium, together with increased deposition of collagen types III and IV and number of infiltrated monocytes/macrophages in the interstitium, relative to sham-operated mice. In comparison, these changes were significantly lower in mutant mice with UUO. The mRNA level of transforming growth factor-beta was significantly higher in the OBK of wild mice with UUO compared with sham-operated mice. In contrast, the increase in mRNA level in the OBK of mutant mice was significantly less than in wild mice. Finally, UUO resulted in activation of nuclear factor-kappaB in wild mice but was inhibited in the OBK of mutant mice. The results provide direct evidence that angiotensin II acting via the AT1a plays a pivotal role in the development of tubulointerstitial fibrosis in UUO.