LAT1 inhibitor JPH203 sensitizes cancer cells to radiation by enhancing radiation-induced cellular senescence.

L-type amino acid transporter 1 (LAT1) is important for transporting neutral amino acids into cells. LAT1 expression is correlated with cancer malignancy, suggesting that LAT1 is a promising target for cancer therapy. JPH203, a potential novel drug targeting LAT1, has been shown to suppress tumor growth in various cancer cell lines. However, a combination study of JPH203 and radiation therapy has not been reported. Here, we examined the effects of JPH203 on radiosensitivity after irradiation in A549 and MIA Paca-2 cells. We showed that X-irradiation increased cellular neutral amino acid uptake via LAT1 in both cell lines. JPH203 inhibited the radiation-induced increase in neutral amino acid uptake. We demonstrated that JPH203, at minimally toxic concentrations, significantly sensitized cancer cells to radiation. JPH203 significantly downregulated mTOR activity and enhanced cellular senescence post-irradiation without reducing ATP and GSH levels. These results indicate that LAT1 inhibition by JPH203 sensitizes cancer cells to radiation by enhancing cellular senescence via mTOR downregulation. Thus, JPH203 may be a potent anti-cancer drug in combination with radiation therapy.

Upregulation of fatty acid synthesis and the suppression of hepatic triglyceride lipase as a direct cause of hereditary postprandial hypertriglyceridemia in rabbits.

Rabbits with hereditary postprandial hypertriglyceridemia exhibit central obesity and are regarded as a reliable model for metabolic syndrome. This study was performed to gain insight into the affected process of lipid metabolism and into the causative genes of the postprandial hypertriglyceridemia rabbits. Eleven genes that play key roles in lipid metabolism were selected, their mRNA levels were assessed by quantitative PCR, and their expressions were compared among postprandial hypertriglyceridemia rabbits using Japanese white rabbits as the control. Two genes appeared to be in causal connection with postprandial hypertriglyceridemia, and these were regarded as likely candidates for the pathogenesis. One was the fatty acid synthase gene, which had an expression constitutively higher in postprandial hypertriglyceridemia rabbits than in Japanese white rabbits during the fasting state and reached quite high levels after feeding. The other was the gene for hepatic triglyceride lipase with an expression that was approximately one order lower than that found in the Japanese white rabbits. The low plasma hepatic triglyceride lipase activities were consistent with the low levels of the transcript in the livers of the postprandial hypertriglyceridemia rabbits. Thus, elevated fatty acid synthesis and defected lipid hydrolysis together would cause the postprandial hypertriglyceridemia in postprandial hypertriglyceridemia rabbits.

Hypertriglyceridemia in Watanabe heritable hyperlipidemic rabbits was associated with increased production and reduced catabolism of very-low-density lipoproteins.

Watanabe heritable hyperlipidemic (WHHL) rabbit is an animal model for human familial hypercholesterolemia. Recently, we segregated a new mutant of WHHL rabbits with plasma levels of triglycerides (TG) >500 mg/dl (designated as TGH-WHHL). To investigate the underlying mechanisms for hypertriglyceridemia, we compared TGH-WHHL with WHHL rabbits with lower plasma TG levels (<250 mg/dl, designated as TGL-WHHL). A Triton WR-1339 injection experiment revealed that TGH-WHHL rabbits had increased secretion and decreased clearance of TG-rich lipoproteins. Furthermore, TGH-WHHL rabbits had lower a post-heparin activity of lipoprotein lipase and a higher cholesterol ester transfer protein activity than TGL-WHHL rabbits. Cultured hepatocytes isolated from TGH-WHHL rabbits showed a higher secretion rate of TG and cholesterol than those of TGL-WHHL rabbits. In addition, TGH-WHHL rabbits exhibited marked insulin resistance. These data suggest that hypertriglyceridemia exhibited by WHHL rabbits is caused by both increased production and impaired catabolism of TG-rich lipoproteins and associated with insulin resistance.

Pathologic findings in rabbit models of hereditary hypertriglyceridemia and hereditary postprandial hypertriglyceridemia.

In recent years, the association between hyperlipidemia and the development of arteriosclerosis has been addressed in several studies. Rabbit models of hypertriglyceridemia (TGH) and postprandial hypertriglyceridemia (PHT) have been developed at the authors' institute. TGH rabbits manifest pathology similar to that of humans with TGH, such as xanthoma, in addition to atherosclerosis of arterioles. Furthermore, PHT rabbits show visceral obesity, insulin resistance, and impaired glucose tolerance, with pathologic features similar to those of the metabolic syndrome assumed to be the cause of human ischemic heart disease. This study was designed to investigate the histopathologic features of TGH and PHT rabbits. TGH rabbits showed advanced aortic atherosclerosis, accompanied by intimal thickening of coronary and renal arteries, fatty liver changes, and xanthoma. PHT rabbits demonstrated aortic intimal thickening and hepatic fatty degeneration. The results of this study suggest that TGH and PHT rabbits are useful animal models for studying human hyperlipidemia and metabolic syndrome and the cardiovascular diseases that result from these conditions.

Hereditary postprandial hypertriglyceridemic rabbit exhibits insulin resistance and central obesity: a novel model of metabolic syndrome.

OBJECTIVE: We have established a hereditary postprandial hypertriglyceridemic (PHT) rabbit. The present study was designed to define whether this rabbit model represents both insulin resistance and central obesity. METHODS AND RESULTS: Body weight, abdominal circumference, visceral fat weight, and glucose tolerance were compared between PHT and Japanese white (JW) rabbit. Plasma levels of triglycerides (TG), total cholesterol (TC), glucose, and insulin were measured before and after feeding. Abdominal circumference of PHT rabbit was larger than that of JW rabbit, with no difference in body mass index. Visceral fat accumulation was noted as obvious in mesenterium, retroperitoneal space, and epididymal area. Plasma TG and TC levels were high preprandially and markedly increased postprandially in PHT rabbit compared with JW rabbit. Although plasma glucose levels were comparable in both groups, plasma insulin levels were elevated in PHT rabbit. Glucose tolerance tests indicated that plasma insulin levels in PHT rabbit were consistently higher than in JW rabbit. A positive correlation was observed between plasma insulin levels and visceral fat weight in PHT rabbit. CONCLUSIONS: PHT rabbit shows insulin resistance along with central obesity. PHT rabbit will serve as a model for elucidating genetic predisposition and pathophysiology in metabolic syndrome.

Progression of severe atherosclerosis and increased arterial pulse pressure in the newly developed heritable mixed hyperlipidaemic rabbits.

We have recently segregated a new line of rabbit, named TGH, with severely high levels of plasma triglyceride and cholesterol. The aim of the present study was to investigate the progression of atherosclerosis and haemodynamic parameters in TGH rabbits. 2. Japanese white (JW) and TGH rabbits (24-27 months old) were anaesthetized with ketamine and xylazine. Plasma concentrations of triglyceride were 63.1 8.0 and 446.0 35.2 mg/dL in JW and TGH rabbits, respectively. Blood pressure was measured by a catheter implanted in the femoral artery. Histological examinations were performed using haematoxylin-eosin and elastica-Masson trichrome staining to detect atherosclerotic lesions. 3. The JW rabbits had no atherosclerotic lesions. In TGH rabbits, severe atherosclerotic lesions were observed throughout the aorta, especially in the aortic arch. Basal femoral arterial pressure was not significantly different between JW and TGH rabbits. However, the basal pulse pressure in TGH rabbits (48.3 4.5 mmHg) was significantly greater than that of JW rabbits (28.0 5.6 mmHg). Intravenous infusion of N(G)-nitro-L-arginine methyl ester (L-NAME; 26.9 mg/kg) increased the blood pressure of TGH and JW rabbits. There was no significant difference in the response to L-NAME between the two rabbit strains. 4. The present study shows that severe atherosclerotic changes develop in TGH rabbits and suggests that the hyperlipidaemia combined with hypercholesterolaemia and hypertriglyceridaemia is an important factor for promoting atherosclerosis in TGH rabbits. The greater pulse pressure in TGH rabbits may be due to the increased vascular stiffness with atherosclerosis. 5. This newly developed TGH rabbit line of heritable hypertriglyceridaemia with hypercholesterolaemia will become a useful animal model for studies on the role of hyperlipidaemia in the progression of atherosclerosis and in many atherosclerosis-related diseases.

Diminution of angiotensin II-induced contraction of the abdominal aorta isolated from Watanabe heritable hyperlipidemic rabbits.

The purpose of this study was to investigate the changes in vasocontractile responses in atherosclerosis, using abdominal aortic strips isolated from Watanabe heritable hyperlipidemic (WHHL) rabbits and Japanese White (control) rabbits. The aortic strips from WHHL rabbits showed a significantly lower contractile response to angiotensin II than that in strips from control rabbits. The contractile responses to phenylephrine and 5-hydroxytryptamine were not different in WHHL and control groups. The contractile response to angiotensin II was higher in endothelium-denuded aortic strips than in endothelium-intact strips, but to a greater extent in the control group than in the WHHL group. The contractile response to angiotensin II in the absence of the endothelium was also lower in the WHHL group than in the control group. Pretreatment with N(G)-nitro-L-arginine significantly increased the contractile response to angiotensin II in the endothelium-intact aortic strips in both the WHHL and control groups, while pretreatment with diclofenac did not affects the aortic contractile response to angiotensin II. The contractile responses to angiotensin II in the presence of N(G)-nitro-L-arginine and diclofenac were lower in the WHHL group than in the control group. The contractile response to angiotensin II in the presence of PD123319 was also lower in the WHHL group than in the control group. Endothelium-dependent relaxation by acetylcholine occurred to the some extent in the WHHL and control groups. These results suggest that the WHHL rabbit abdominal aorta displays attenuated angiotensin II-induced contraction, mainly due to an abnormality in the angiotensin II-specific contractile pathway of the medial smooth muscle.

Chronic hypertriglyceridemia in young watanabe heritable hyperlipidemic rabbits impairs endothelial and medial smooth muscle function.

Several studies have suggested that hypertriglyceridemia is a common risk factor for coronary heart disease. Although increasing serum levels of triglyceride correlate with hypercoagulability, little is known about the contribution of hypertriglyceridemia to vascular function. We successfully segregated two lines of rabbits with genetically-determined severely high (TGH; 2764 +/- 413 mg/dl) and moderately high (TGL; 191 +/- 12 mg/dl) levels of triglyceride, but with comparable levels of total cholesterol, from Watanabe heritable hyperlipidemic rabbits. To determine whether hypertriglyceridemia was involved in alterations of vascular function, we conducted isometric tension studies and analyzed protein expression on thoracic aortic rings isolated from young (3-4 month) TGH, TGL and Japanese White rabbit (JW). No difference in percentage of plaque area in the thoracic aorta was found between TGH and TGL. Relaxing responses, evoked by sodium nitroprusside were similar in JW, TGL and TGH, but endothelium-dependent relaxation to acetylcholine was impaired in TGH compared with JW or TGL (maximal relaxation in JW; 83.5 +/- 2.7%, TGL; 79.9 +/- 5.3%, TGH; 59.1 +/- 5.7%, p<0.05). Relaxation to A23187 was also attenuated in TGH compared with JW, but not significantly different between TGL and JW. Endothelium-independent relaxation elicited by isoproterenol in TGH was significantly decreased compared with JW or TGL (maximal relaxation in JW; 95.2 +/- 2.6% TGL; 91.0 +/- 4.9%, TGH; 75.1 +/- 5.2%, p<0.05). Protein expression of angiotensin II type-1 receptor was increased in TGH and that of nitric oxide synthases-3 was attenuated in TGH compared with TGL. This is the first study showing that endothelium-dependent and -independent vascular relaxation under the condition of combined hyperlipidemia was severely impaired as compared to that under only hypercholesterolemia. These results suggest that hypertriglyceridemia aggravates functional impairment induced by hypercholesterolemia in endothelial and smooth muscle cells.