Mitochondrial uptake of aristolactam I plays a critical role in its toxicity

Aristolochic acid I (AAI), a component of aristolochic acids, can be converted to the toxic metabolite Aristolactam I (ALI) in vivo which forms aristolactam-nitrenium with delocalized positive charges. It is widely accepted that delocalized lipophilic cations can accumulate in mitochondria due to the highly negatively charged microenvironment of the mitochondrial matrix, but the uptake of ALI by mitochondria is not known. In this study, the cell uptake and mitochondrial localization of ALI, and its subsequent impact on mitochondrial function were investigated. Results show that ALI can rapidly penetrate HK-2 cells without relying on organic anion transporters 1/3 (OAT1/3). The cellular distribution of ALI was found to align with the observed distribution of a mitochondria-selective dye in HK-2 cells. Furthermore, the cell uptake and mitochondrial uptake of ALI were both inhibited by carbonyl cyanide 4-(trifluoromethoxy) phenylhydrazone, which induces mitochondrial membrane depolarization. These results suggest that ALI is selectively taken up by mitochondria. Consequently, mitochondrial dysfunction was observed after treatment with ALI. It should be noted that inhibiting OAT1/3 could result in an increased exposure of ALI in vivo and cause more seriously nephrotoxicity. In conclusion, this research reports the mitochondrial uptake of ALI and provides new insight on potential strategies for protection against AAI-induced nephrotoxicity.

Oral subacute nephrotoxicity of aristololactam I in rats

Aristolactams (ALs) have been recognized as one kind of metabolites of aristolochic acids (AAs), the nephrotoxic components of Aristolochiaceae plants, and are more widely distributed than AAs in herbal medicines. This study evaluated the oral subacute nephrotoxicity of aristolactam I (AL I), a representative compound of ALs. AL I was intragastrically administered to rats at 20 mg·kg^-1·d^-1 for 10 or 20 days, with aristolochic acid I (AA I) used as positive control at the same dose. After 10-day treatment, AL I led to a significant increase in early renal injury-related indices in urine and obvious histopathological lesions in kidneys, including degeneration of tubular epithelial cells, inflammatory cell infiltration and fibrosis. The lesions induced by AL I were significantly aggravated after 20-day exposure. However, AL I induced less histopathological damage in kidneys than AA I in both 10- and 20-day groups. Our results indicated that oral AL I caused nephrotoxicity by inducing oxidative stress, inflammation, and overactivation of the complement system as AA I did. Three detected apoptosis-associated indicators were not affected by AL I but remarkably increased by AA I. In summary, oral AL I induced evident renal damage in rats after only 10 days of treatment, and the damage was aggravated after 20 days. However, AL I was obviously less nephrotoxic than AA I via oral gavage.

An investigation on nephrotoxicity of Aristolactam I induced epithelial-mesenchymal transition on HK-2 cells

Aristolactam I (AL-I) is the main active ingredient in the Aristolochia plant species, which have been associated with severe nephrotoxicity. In order to investigate the mechanism of AL-I induced renal epithelial-mesenchymal transition (EMT), we established an AL-I induced EMT model in human proximal tubular epithelial cells (HK-2 cells). Biochemical analysis experiment including Morphological examination, 3-(4,5-dimethylthiazol-2-Yl)-2,5-diphenyltetrazolium bromide assay, and Western blot analysis were performed. The results showed that AL-I accumulates in the cytosol causing cytotoxicity and inhibition of proliferation in a concentration- and time-dependent manner. Morphological examination showed that with the increasing concentration of AL-I, the tendency of HK-2 cells transform form epithelial cell to fibroblast cells was stronger. In the Western blot analysis, the expression of α-Smooth muscle actin (α-SMA) and Transforming Growth Factor β1 (TGF-β1) were significantly up-regulated, the expression of E-cadherin was significantly down-regulated after administrating. The ratio of the expression of P-Smad2/3 and Smad2/3 was significantly up-regulated, suggested that TGF-β/Smad-dependent signaling pathway was activated in this process. With presence of TGF-β receptor inhibitor (LY364947), we found that the expressions of three EMT related proteins (E-cadherin, α-SMA and TGF-β1) were obviously reversed. In conclusion, we acknowledge that AL-I can induce renal EMT process in HK-2 cell, which is triggered by the activation of TGF-β/Smad-dependent signaling pathway.