Cardiomyopathy in 2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) Treated Donryu Rats

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine(PhIP)は加熱食品に由来するへテロサイクリックアミンであり, ラット大腸, 前立腺及び乳腺に対する強力な環境発癌物質の1つである。PhIPの75 mg/kg/dayを18週齢の雄Crj : Donryuラットに隔日10回強制経口投与した。52週の試験期間における死亡率が40%と, 対照群及び2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline(MeIQx)群(20及び15%)に比べ高値を示した。この死亡例の75%が心肥大を示し, 拡張型心筋症の特徴を示していた。超微形態的に心筋細胞で筋原線維の減少, ミトコンドリア数の増加及び変性, 筋小胞体の拡張等が認められた。次に, PhIPの20,40及び75 mg/kg/dayを同様に投与し, 心臓の変化を経時的に検討した。試験期間中に40 mg/kg群の1例及び75 mg/kg群の4例が死亡し, 心臓重量は対照動物を含む生存例に比較して高値を示し, 心肥大を呈した。死亡例の75 mg/kg群の投与開始後4週から左心室の炎症性細胞浸潤, 心筋細胞の空胞化/壊死, 線維化が認められ, 投与開始後26週まで観察された。死亡例ではさらに心房内血栓形成や右心室拡張も認められた。40 mg/kg群では投与開始後4週に, 少数例で心筋細胞の空胞化がみられた。投与開始後26週以降に心筋細胞の変性/壊死, 炎症性細胞浸潤や線維化が認められた。超微形態的には筋原線維の減少, 筋小胞体の拡張, ミトコンドリア数の増加, 筋形質の腫脹が40 mg/kg以上の群で認められた。20 mg/kg群では4週後に, 炎症性細胞浸潤や心筋細胞の空胞化が少数例にみられた。投与開始4週後に投薬各群の血圧が一時的に有意な低値を示した。投与開始4週後にPhIP-DNA adductレベルの増加が用量依存的に認められたが, 投与開始13週後(75 mg/kg群)では低値を示した。以上から, PhIPの高用量投与によりDonryuラットにみられた心肥大を伴う死亡例の増加は, PhIPによる心筋障害に起因する拡張型心筋症に起因するものであり, その原因に心筋細胞におけるPhIP-DNA adductの形成が関与していると考えられた。2-Amino-1-methyl-6-phenylimidazo [4,5-b] pyridine (PhIP) is a heterocyclic amine derived from cooked meat and a potent environmental carcinogen for rat colon, prostate and mammary glands. PhIP (75 mg/kg/day) treatment by gavage ten times on alternate days caused increases in mortality and incidence of dilated cardiomyopathy in Crj : Donryu rats after the 52-week study period. Microscopically, vacuolization/necrosis of the cardiac muscle, inflammatory cell infiltration and fibrosis in the left ventricle, atrial thrombosis and left ventricular dilatation were observed in the heart from Week 4 of the study period. Electoronmicroscopically, decrease of myofibrils, increase of mitochondria and dilatation of sarcoplasmic reticulum were observed. PhIP (20,40 and 75 mg/kg/day) treatments decreased blood pressures temporarily in Week 4. PhIP-DNA adduct levels increased in Week 4 of PhIP (20,40 and 75 mg/kg/day) treatments and decreased in Week 13 of PhIP (75 mg/kg/day) treatment. These results suggest that the increases in mortality and incidences of dilated cardiomyopathy in Crj : Donryu rats by high dose of PhIP treatment were caused by the action of PhIP against the cardiac muscle, which may be related to PhIP-DNA adduct formation in the cardiac muscle cells

Salivary Mucocele in a Laboratory Beagle

The histologic characteristics of a salivary mucocele in a beagle used in a toxicity study are described in this report. A pale yellowish cyst under the mandibular skin containing frothy mucus was observed at necropsy. Microscopically, numerous villous projections arose from the internal surface of the cyst and were lined by stratified epithelial-like macrophages, which were immunopositive for macrophage scavenger receptor A. A ruptured sublingual interlobar duct connected to the lumen was observed near the cyst. Luminal amorphous material showed a positive reaction with Alcian blue and periodic acid-Schiff staining as did mucin in the sublingual gland. Ultrastructurally, the epithelial-like macrophages had numerous vacuoles containing electron-lucent material, which was presumed to be lysosomal in origin, and had pseudopods on their cell surfaces interdigitating with those on the adjacent cells. This case report helps to understand the diversity of the background findings in beagles used in toxicity studies

Contribution of renal angiotensin II type I receptor to gene expressions in hypertension-induced renal injury

Contribution of renal angiotensin II type I receptor to gene expressions in hypertension-induced renal injury. Recent evidence indicates that transforming growth factor-β1 (TGF-β1) plays an important role in renal fibrosis via stimulation of extracellular matrix synthesis. The present study was undertaken to investigate the role of angiotensin II type I receptor (AT1 receptor) in hypertension-induced renal injury. Twenty-two-week-old stroke-prone spontaneously hypertensive rats (SHRSP), which had established hypertension and moderate renal damage, were orally given TCV-116, a selective non-peptide AT1 receptor antagonist (0.1, 1 or 10 mg/kg/day), enalapril (10 mg/kg/day) or vehicle once a day for 10 weeks. At the end point of the treatment, we examined renal function, the gene expressions of TGF-β1 and extracellular matrix components in the interstitium [collagen types I (COI) and III (COIII), fibronectin (FN)] and the basement membrane (COIV and laminin), and renal microscopic morphology in rats aged 32 weeks. In vehicle-treated 32 week-old SHRSP with renal dysfunction and nephrosclerosis, renal mRNA levels for TGF-β1, COI, COIII, FN, COIV were all several-fold higher than in WKY. Thus, renal TGF-β1 gene expression was enhanced in SHRSP, which may contribute to the increased renal expressions of COI, COIII, FN, COIV in SHRSP. Treatment with TCV-116 (0.1 mg/kg/day) in SHRSP, in spite of no reduction of blood pressure, decreased renal mRNA levels for TGF-β1, COI, COIII, FN, COIV, being accompanied by the significant decrease in urinary protein and albumin excretion, blood urea nitrogen and plasma creatinine. Treatment with TCV-116 (10 mg/kg/day) in SHRSP decreased mRNAs for TGF-β1, COI, COIII, FN and COIV to almost the same levels as WKY, being associated with normalization of urinary protein and albumin excretion and the prevention of nephrosclerosis, as judged by microscopic histological observations. On the other hand, the effects of enalapril (10 mg/kg/day) on the above mentioned mRNA levels, renal function and renal morphology were weaker than those of TCV-116 (10 mg/kg/day) and were as much as TCV-116 (1 mg/kg/day). These results suggest that independently of hypotensive action, AT1 receptor antagonist has a potent renal protective effect by inhibiting the gene expression of renal TGF-β1 and extracellular matrix components

Effects of Weaning by Surrogate Mothers (ACI) on Tumor Development in SD Rats Treatedwith Methylnitrosourea (MNU) and/or N-Methyl-N-nitro-N-nitrosoguanidine (MNNG)

In this experiment, MNU was administered, followed by MNNG, to assess effects ofsurrogate mothering on tumor. One or two day old male SD pups were treated with or without30mg/kg body weight of methylnitrosourea (MNU) and nursed by SD or ACI surrogate mothersfor 5 weeks. When 6-weeks-old they were then treated with 100ppmN-methyl-N-nitro-N-nitrosoguanidine (MNNG) or tap water for 16 weeks. The tumor incidencein the MNNG alone group was significantly lower than with MNU alone or MNU+MNNG (p<0.01).Kidney or nerve tumors mainly developed in the MNU group, gastric tumors in the MNNG group,and the two combined in the MNU+MNNG group. The incidence and mean number of tumors didnot significantly differ between the two weaning groups. However, mean survival time withthe ACI surrogate mothers after treatment with MNU was increased as compared with the SDmother group. Cumulative development of tumors in the ACI surrogate mother group was alsodelayed (p<0.05). Similar results were obtained with MNU+MNNG and MNNG alone. The presentexperiment suggested that tumor induction might be effected by components of the mother'smilk

Radioprotective Effects of Miso (Fermented Soy Bean Paste) Against Radiation in B6C3Fl Mice : Increased Small Intestinal Crypt Survival, Crypt Lengths and Prolongation of Average Time to Death

The radioprotective effect of miso, a fermentation product from soy bean, was investigated with reference to the survival time, crypt survival and jejunum crypt length in male B6C3F1 mice. Miso at three different fermentation stages (early-, medium- and long-term fermented miso) was mixed in MF diet into biscuits at 10% and was administered from 1 week before irradiation. Animal survival in the long-term fermented miso group was significantly prolonged as compared with the short-term fermented miso and MF cases after 8 Gy of 60Co-γ-ray irradiation at a dose rate of 2Gy min-1. Delay in mortality was evident in all three miso groups, with significantly increased survival. At doses of 10 and 12 Gy X-irradiation at a dose rate of 4 Gy min-1 the treatment with long-term fermented miso significantly increased crypt survival. Also the protective influence against irradiation in terms of crypt lengths in the long-term fermented miso group was significantly greater than in the short-term or medium-term fermented miso and MF diet groups. Thus, prolonged fermentation appears to be very important for protection against radiation effects