Enhancement of autophagy is a potential modality for tumors refractory to radiotherapy

Radiotherapy is a well-established treatment for cancer. However, the existence of radioresistant cells is one of the major obstacles in radiotherapy. In order to understand the mechanism of cellular radioresistance and develop more effective radiotherapy, we have established clinically relevant radioresistant (CRR) cell lines, which continue to proliferate under daily exposure to 2 Gray (Gy) of X-rays for >30 days. X-ray irradiation significantly induced autophagic cells in parental cells, which was exiguous in CRR cells, suggesting that autophagic cell death is involved in cellular radiosensitivity. An autophagy inducer, rapamycin sensitized CRR cells to the level of parental cells and suppressed cell growth. An autophagy inhibitor, 3-methyladenine induced radioresistance of parental cells. Furthermore, inhibition of autophagy by knockdown of Beclin-1 made parental cells radioresistant to acute radiation. These suggest that the suppression of autophagic cell death but not apoptosis is mainly involved in cellular radioresistance. Therefore, the enhancement of autophagy may have a considerable impact on the treatment of radioresistant tumor.     

Oxidized but not acetylated low-density lipoprotein reduces preproinsulin mRNA expression and secretion of insulin from HIT-T15 cells

We examined the effect of oxidized low-density lipoprotein (oxLDL) on the insulin secretion in the culture of HIT-T15 cell line, an islet beta-cell line derived from a hamster pancreatic tumor. In order to check the uptake of modified LDL by HIT-T15 cells, we prepared DiI-labeled native LDL (nLDL), acetylated LDL (AcLDL), and oxLDL. After the addition of each LDL into the cultures of HIT-T15 cells, fluorescence microscopic study was done. It was suggested that AcLDL and oxLDL were taken up by HIT-T15 cells, as well as nLDL. mRNA expression of the LDL receptor, CD36, and SR-B1 was detected in HIT-T15 by RT-PCR. The medium insulin level was measured in the culture of HIT-T15 cells with each LDL. oxLDL significantly reduced the insulin secretion stimulated by various concentrations of glucose, the intracellular content of insulin, and the expression of preproinsulin mRNA compared to the control cultures without LDL addition. In contrast, nLDL and AcLDL had no effect on the insulin secretion, the intracellular insulin level, or the expression of preproinsulin mRNA. MTT assay findings (reflecting cell numbers) were not different between cultures with and without LDLs. These results indicated that oxLDL disturbed the insulin metabolism of HIT-T15 cells.     

Ion-trap tandem mass spectrometric analysis of Amadori-glycated phosphatidylethanolamine in human plasma with or without diabetes

Peroxidized phospholipid-mediated cytotoxicity is involved in the pathophysiology of diseases [i.e., an abnormal increase of phosphatidylcholine hydroperoxide (PCOOH) in plasma of type 2 diabetic patients]. The PCOOH accumulation may relate to Amadori-glycated phosphatidylethanolamine (Amadori-PE; deoxy-D-fructosyl phosphatidylethanolamine), because Amadori-PE causes oxidative stress. However, the occurrence of lipid glycation products, including Amadori-PE, in vivo is still unclear. Consequently, we developed an analysis method of Amadori-PE using a quadrupole/linear ion-trap mass spectrometer, the Applied Biosystems QTRAP. In positive ion mode, collision-induced dissociation of Amadori-PE produced a well-characterized diglyceride ion ([M+H-303]+) permitting neutral loss scanning and multiple reaction monitoring (MRM). When lipid extract from diabetic plasma was infused directly into the QTRAP, Amadori-PE molecular species could be screened out by neutral loss scanning. Interfacing liquid chromatography with QTRAP mass spectrometry enabled the separation and determination of predominant plasma Amadori-PE species with sensitivity of approximately 0.1 pmol/injection in MRM. The plasma Amadori-PE level was 0.08 mol% of total PE in healthy subjects and 0.15-0.29 mol% in diabetic patients. Furthermore, plasma Amadori-PE levels were positively correlated with PCOOH (a maker for oxidative stress). These results show the involvement between lipid glycation and lipid peroxidation in diabetes pathogenesis.     

A role for BiP as an adjustor for the endoplasmic reticulum stress-sensing protein Ire1

In the unfolded protein response, the type I transmembrane protein Ire1 transmits an endoplasmic reticulum (ER) stress signal to the cytoplasm. We previously reported that under nonstressed conditions, the ER chaperone BiP binds and represses Ire1. It is still unclear how this event contributes to the overall regulation of Ire1. The present Ire1 mutation study shows that the luminal domain possesses two subregions that seem indispensable for activity. The BiP-binding site was assigned not to these subregions, but to a region neighboring the transmembrane domain. Phenotypic comparison of several Ire1 mutants carrying deletions in the indispensable subregions suggests these subregions are responsible for multiple events that are prerequisites for activation of the overall Ire1 proteins. Unexpectedly, deletion of the BiP-binding site rendered Ire1 unaltered in ER stress inducibility, but hypersensitive to ethanol and high temperature. We conclude that in the ER stress-sensory system BiP is not the principal determinant of Ire1 activity, but an adjustor for sensitivity to various stresses.     

Mechanism of DNA Damage and Apoptosis Induced by Tetrahydropapaveroline, a Metabolite of Dopamine

Tetrahydropapaveroline (THP), a metabolite of dopamine, has been suspected to be associated with dopaminergic neurotoxicity of L-DOPA. THP induced apoptosis in human leukemia cell line HL-60 cells, but did not in its hydrogen peroxide (H₂O₂)-resistant clone HP100. THP-induced DNA ladder formation in HL-60 cells was inhibited by a metal chelator. THP induced damage to ³²P-labeled DNA fragments in the presence of metals. In the presence of Fe(III)EDTA, THP caused DNA damage at every nucleotide. The DNA damage was inhibited by free hydroxy radical (^·OH) scavengers and catalase, suggesting that the Fe(III)EDTA-mediated DNA damage is mainly due to ^·OH generation. In the presence of Cu(II), THP caused DNA damage mainly at T and G of 5′-TG-3′ sequence. The inhibitive effect of catalase and bathocuproine on Cu(II)-mediated DNA damage suggested that H₂O₂ and Cu(I) participate in the DNA damage. This study demonstrated that THP-induced apoptosis via reactive oxygen species generated from reaction of H₂O₂ and metals plays an important role in cytotoxicity of L-DOPA.     

Aminophospholipid glycation and its inhibitor screening system: a new role of pyridoxal 5'-phosphate as the inhibitor

Peroxidized phospholipid-mediated cytotoxity is involved in the pathophysiology of a number of diseases [i.e., the abnormal increase of phosphatidylcholine hydroperoxide (PCOOH) found in the plasma of type 2 diabetic patients]. The PCOOH accumulation may relate to Amadori-glycated phosphatidylethanolamine (deoxy-D-fructosyl PE, or Amadori-PE), because Amadori-PE causes oxidative stress. However, lipid glycation inhibitor has not been discovered yet because of the lack of a lipid glycation model useful for inhibitor screening. We optimized and developed a lipid glycation model considering various reaction conditions (glucose concentration, temperature, buffer type, and pH) between PE and glucose. Using the developed model, various protein glycation inhibitors (aminoguanidine, pyridoxamine, and carnosine), antioxidants (ascorbic acid, alpha-tocopherol, quercetin, and rutin), and other food compounds (L-lysine, L-cysteine, pyridoxine, pyridoxal, and pyridoxal 5'-phosphate) were evaluated for their antiglycative properties. Pyridoxal 5'-phosphate and pyridoxal (vitamin B(6) derivatives) were the most effective antiglycative compounds. These pyridoxals could easily be condensed with PE before the glucose/PE reaction occurred. Because PE-pyridoxal 5'-phosphate adduct was detectable in human red blood cells and the increased plasma Amadori-PE concentration in streptozotocin-induced diabetic rats was decreased by dietary supplementation of pyridoxal 5'-phosphate, it is likely that pyridoxal 5'-phosphate acts as a lipid glycation inhibitor in vivo, which possibly contributes to diabetes prevention.