Carcinogenic risk of heterocyclic amines in combination – Assessment with a liver initiation model

Carcinogenic potential of heterocyclic amines (HCAs) was investigated using an in vivo 5-week initiation assay with quantitative evaluation of glutathione S-transferase placental form (GST-P) positive foci in rat liver. Numbers of GST-P positive foci were significantly increased with individual administration of six different HCAs, indicating utility of the assay. It was therefore applied to investigate risk with multiple HCAs in combination. Unexpectedly, concomitant treatment with 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) did not result in any additive carcinogenicity. In the rats taking MeIQx prior to PhIP the value was almost equal to the sum total of individual data, indicating additive initiation activities. In contrast, simultaneous or prior administration of PhIP rather exerted inhibitory effects on the carcinogenic potential of MeIQx. Moreover, microarray and quantitative RT-PCR assessment revealed that PhIP induced cytochrome P450 1A1, responsible for both activation and detoxification of HCAs, more strongly than MeIQx. It is noteworthy that complex exposure to multiple HCAs is not necessarily associated with increased risk of carcinogenesis because they are simultaneously and continuously ingested under normal circumstances.     

Effect of diet type on enhanced intestinal protein synthesis by the gut microflora in the chick

An experiment was conducted to investigate the effect of diet type on enhanced protein synthesis by the gut microflora in the chick intestine. Both germ-free (GF) and conventional (CV) White Leghorn chicks were fed ad libitum from 4 to 14 d of age either a nonpurified diet or a purified diet having 19% crude protein and 12.1 kJ/g metabolizable energy value. At 14 d of age, protein synthesis was measured in duodenum, jejunoileum and ceca after a large dose of L-[4-3H]phenylalanine injected intravenously via a wing vein. The results showed that wet tissue weights for all intestinal sections were significantly greater in CV birds than in GF counterparts with consistently larger differences between the two environments in chicks fed the nonpurified diet than in those fed the purified diet. Protein synthesis in all intestinal sections was significantly enhanced by the presence of gut microflora in terms of both fractional rate (%/d) and absolute rate [mg/(100 g BW.d)]. The effect of diet type on fractional and absolute rates of protein synthesis was most remarkable in ceca where the significant difference between GF and CV states was found only in chicks fed the nonpurified diet but not in those fed the purified diet.     

Effect of renal impairment on the pharmacokinetics of memantine

The effect of renal impairment on the pharmacokinetics of a single oral dose of memantine (10 mg) was determined in Japanese subjects. Subjects were assigned to four groups based on baseline creatinine clearance (CL(CR)): normal renal function (> 80 mL/min, n = 6), and mild (50 to ≤ 80 mL/min, n = 6), moderate (30 to < 50 mL/min, n = 6), and severe renal impairment (5 to < 30 mL/min, n = 7). Mean memantine maximum plasma concentration (C(max)) was similar in the groups (12.66, 17.25, 15.75, and 15.83 ng/mL, respectively), as was mean time to C(max) (6.2, 5.2, 4.3, and 5.4 h, respectively). However, exposure to memantine determined from mean area under the plasma concentration-time curve was 1.62-, 1.97-, and 2.33-times higher in subjects with mild, moderate, and severe renal impairment, respectively, as compared to controls with normal renal function. Mean memantine plasma elimination half-life increased according to increasing renal impairment (61.15, 83.00, 100.13, and 124.31 h, respectively), while mean cumulative urinary recovery of unchanged memantine in 72 h after dosing decreased according to increasing renal impairment (33.68%, 33.47%, 23.60%, and 16.17%, respectively). These results are the same as those in the previous study on caucasian individuals, when compared per body weight. It is suggested that the dose of memantine should be halved in patients with renal impairment.     

Effects of the combination of SGLT2 selective inhibitor ipragliflozin and various antidiabetic drugs in type 2 diabetic mice

The sodium-glucose cotransporter 2 (SGLT2) is responsible for most glucose reabsorption in the kidney and has been proposed as a novel therapeutic target for the treatment of type 2 diabetes. In the present study, the combinatory effects of SGLT2 selective inhibitor ipragliflozin and various antidiabetic drugs in high-fat diet and streptozotocin-nicotinamide-induced type 2 diabetic mice were investigated. Ipragliflozin dose-dependently increased urinary glucose excretion and improved glucose tolerance. In addition, each antidiabetic drug (mitiglinide, glibenclamide, sitagliptin, insulin, metformin, voglibose, or rosiglitazone) also significantly improved glucose tolerance without affecting urinary glucose excretion. Combination treatment of ipragliflozin with each antidiabetic drug additively improved glucose tolerance. In these experiments, ipragliflozin-induced increases in urinary glucose excretion were not influenced by combination treatment with antidiabetic drugs. Further, ipragliflozin did not affect antidiabetic drug-induced insulinotropic action (mitiglinide and glibenclamide), increases in plasma glucagon-like peptide-1 and insulin levels via inhibition of dipeptidyl peptidase 4 activity (sitagliptin), increases in plasma insulin level (insulin), decreases in hepatic phosphoenolpyruvate carboxykinase activity (metformin), inhibition of small intestinal disaccharidase activity (voglibose), or improvement of impaired insulin secretion (rosiglitazone). These results suggest that combination treatment of ipragliflozin with various antidiabetic drugs additively enhances the improvement in glucose tolerance without affecting each drug’s unique pharmacological effects. Ipragliflozin may therefore be expected to be effective when administered as part of a combination regimen in the treatment of type 2 diabetes.     

Comparison of effects of xenobiotics on extrahepatic and hepatic microsomal drug-metabolizing enzymes in mice

The content of microsomal protein is the same in both kidneys and small intestine, corresponding to 57% of the control value expressed as 100% in the untreated liver. The contents of P450 and cytochrome b(5), and the activity of NADPH-cytochrome c reductase in the kidney were higher than those in the small intestine, which were 17%, 22% and 41% of controls, respectively, in the former and 5%, 11% and 22% of controls in the latter. As compared with similar measurements made in the liver, the activities of substrate-metabolizing enzymes in these extrahepatic organs were very low. The activities of renal aniline hydroxylase, aminopyrine N-demethylase, 7-ethoxycoumarin O-deethylase, 7-methoxycoumarin O-demethylase and benzo(a)pyrene hydroxylase were 6%, 5%, 3%, 0.6% and 0.2% of controls, respectively. The activities of these enzymes in the small intestine were lower than those in the kidney or below the limits of detection. These results suggested that isoforms or their contents of P450 responsible for these substrate biotransformations are different among liver, kidneys and small intestine. Meantime, this study showed similar significant inductions by phenobarbital and rifampin of small intestinal and hepatic microsomal drug-metabolizing enzymes. In contrast, neither phenobarbital nor rifampin was capable of increasing renal microsomal enzymes, with the exception of benzo(a)pyrene hydroxylase which was induced by rifampin. These findings indicated that both liver and small intestine, but not kidneys contain the same phenobarbital- and rifampin-inducible P450 isoforms, cytochrome b(5) and NADPH-cytochrome c reductase. In addition, CCl(4) could be bioactivated by CYP2E1 to free radicals in the kidney which caused destruction of microsomal enzymes. In mice pretreated with phenobarbital, CCl(4) also attenuated the increase in content of P450 in the small intestine, which appeared to be a result of induction by phenobarbital of CYP2E1.     

Human group IIA secretory phospholipase A2 induces neuronal cell death via apoptosis.

Expression of group IIA secretory phospholipase A2 (sPLA2-IIA) is documented in the cerebral cortex (CTX) after ischemia, suggesting that sPLA2-IIA is associated with neurodegeneration. However, how sPLA2-IIA is involved in the neurodegeneration remains obscure. To clarify the pathologic role of sPLA2-IIA, we examined its neurotoxicity in rats that had the middle cerebral artery occluded and in primary cultures of cortical neurons. After occlusion, sPLA2 activity was increased in the CTX. An sPLA2 inhibitor, indoxam, significantly ameliorated not only the elevated activity of the sPLA2 but also the neurodegeneration in the CTX. The neuroprotective effect of indoxam was observed even when it was administered after occlusion. In primary cultures, sPLA2-IIA caused marked neuronal cell death. Morphologic and ultrastructural characteristics of neuronal cell death by sPLA2-IIA were apoptotic, as evidenced by condensed chromatin and fragmented DNA. Before apoptosis, sPLA2-IIA liberated arachidonic acid (AA) and generated prostaglandin D2 (PGD2), an AA metabolite, from neurons. Indoxam significantly suppressed not only AA release, but also PGD2 generation. Indoxam prevented neurons from sPLA2-IIA-induced neuronal cell death. The neuroprotective effect of indoxam was observed even when it was administered after sPLA2-IIA treatment. Furthermore, a cyclooxygenase-2 inhibitor significantly prevented neurons from sPLA2-IIA-induced PGD2 generation and neuronal cell death. In conclusion, sPLA2-IIA induces neuronal cell death via apoptosis, which might be associated with AA metabolites, especially PGD2. Furthermore, sPLA2 contributes to neurodegeneration in the ischemic brain, highlighting the therapeutic potential of sPLA2-IIA inhibitors for stroke.     

A quantitative evaluation of pontine volume by computed tomography in patients with cerebellar degeneration

We used CT to make a quantitative evaluation of the pontine volumes of 55 patients with adult-onset cerebellar degeneration and compared the results with their clinical records. Patients with pontine atrophy showed significantly more autonomic dysfunction and extrapyramidal signs; their other clinical features did not differ from patients without pontine atrophy. After dividing the patients into 2 groups, those with and without autonomic dysfunction or extrapyramidal signs, we found that those with these manifestations also had pontine atrophy, a later onset and shorter duration of the disease, and impairment of higher brain functions. The group without these manifestations had relatively normal pontine volume, a greater familial tendency for cerebellar degeneration, and longer duration of the disease. Our results suggest that quantitative volume evaluation of the pons by CT is important for the clinical categorization of cerebellar degeneration.     

Effect of Euro-Collins' or UW solution on the early graft function following cadaveric kidney transplantation

From November 1985 to March 1990, 55 cadaveric kidney transplants were performed under cyclosporine therapy. All kidneys were harvested from non-heart beating donors and cold stored after being flushed with EC solution (Group I, n = 27) or UW solution (Group II, n = 28). Warm ischemic time (min) in groups I and II were 7.1 +/- 3.3 and 6.9 +/- 2.3, respectively. Cold ischemic times (hr) in groups I and II were 6.9 +/- 2.4 and 8.4 +/- 2.8, respectively. Mean numbers of days for postoperative dialysis were 14.0 +/- 7.9 in group I and 7.9 +/- 5.8 in group II (p less than 0.05). One-month creatinine (mg/dl) was 2.9 +/- 2.8 in group I and 1.75 +/- 1.0 in group II (NS). One-month graft survivals (%) in groups I and II were 81.4% and 92.8%, respectively. In conclusion, UW solution has provided beneficial effect of preservation on ischemic damaged kidney and appears to be method of choice in non-heart beating cadaveric kidney transplantation.