Reduction of beta cell mass: partial insulin secretory compensation from the residual beta cell population in the nicotinamide–streptozotocin Göttingen minipig after oral glucose in vivo and in the perfused pancreas

Aims/hypothesis A progressive loss of beta cell function and mass are important contributory factors in the development and progression of type 2 diabetes. The aim of this study was to evaluate the effects of a primary reduction in beta cell mass on beta cell function in vivo and in the perfused pancreas and to relate these characteristics to beta cell mass.Methods The beta cell mass of six Göttingen minipigs was reduced chemically (using 67 mg/kg nicotinamide and 125 mg/kg streptozotocin). Six untreated minipigs were kept as control animals. Insulin responses were evaluated in vivo using the mixed meal tolerance test (2 g/kg oral glucose) and in the isolated perfused pancreata from the same animals by stimulation with glucose, glucagon-like peptide-1 or arginine.Results Beta cell mass was reduced in the beta-cell-reduced animals compared with the control minipigs (182±76 vs 464±156 mg, p<0.01). AUC_glucose was increased in the beta-cell-reduced animals (1383±385 vs 853±113 mmol·l^–1·min in control minipigs, p<0.01), as was the insulin response to oral glucose per unit of beta cell mass (123±84 vs 56±24 pmol·l^–1·min·mg^–1, p<0.05). Total in vitro insulin secretion was increased per unit of beta cell mass in nicotinamide + streptozotocin pancreata compared to controls (83.7±45.9 vs 34.6±14.4 nmol/mg beta cells, p<0.05) with responses to glucose and glucagon-like peptide-1 showing a partial compensation for reduced beta cell mass, whereas no compensation was seen in response to arginine.Conclusions/interpretation A primary reduction in beta cell mass impairs glucose tolerance and leads to a compensatory increase in insulin secretion from the remaining beta cells after oral glucose in vivo, which is even more apparent in the perfused pancreas. It remains to be determined whether this compensation can be maintained in the long term.Conflict of interest statement: M.O. Larsen, B. Rolin, C.F. Gotfredsen and R.D. Carr are all employees and shareholders at Novo Nordisk. J.J. Holst has been on advisory boards for Novo Nordisk.     

Inhibitory effect of clofibrate on arginine-induced insulin secretion in chemical diabetes

Summary Clofibrate, 3g/die for 10 consecutive days, significantly reduced arginine-induced IRI release in chemical diabetics and in normal controls, whether of normal body weight or obese. Blood glucose levels were not affected by clofibrate. In agreement with previous findings, it would appear that clofibrate, administered for short periods, does not lead to a decrease in glucose tolerance. However, studies relating to the effect of chronic clofibrate administration in chemical diabetes are needed in order to be sure that prolonged inhibition of IRI secretion does not lead to overt diabetes.     

Immunohistochemical detection of arginase-I expression in formalin-fixed lung and other tissues

Abstract

Arginases are a family of enzymes that convert l-arginine to l-ornithine and urea. Alterations in expression of the isoform arginase-I are increasingly recognized in lung diseases such as asthma and cystic fibrosis. To define expression of murine arginase-I in formalin-fixed tissues, including lung, an immunohistochemical protocol was validated in murine liver, a tissue that has distinct zonal arginase-I expression, making it a useful control. In the lung, arginase-I immunostaining was observed in airway surface epithelium and this decreased from large to small airways, with a preferential staining of ciliated epithelium versus Clara cells and alveolar epithelia. In submucosal glands, the ducts and serous acini had moderate immunostaining, which was absent in mucous cells. Focal immunostaining was observed in alveolar macrophages, endothelial cells, pulmonary vein cardiomyocytes, pulmonary artery smooth muscle, airway smooth muscle, and neurons of ganglia of the lung. Arginase-I immunostaining was also detected in other tissues including salivary glands, pancreas, liver, skin, and intestine. Differential immunostaining was observed between sexes in submandibular salivary glands; arginase-I was diffusely expressed in the convoluted granular duct cells of females, but was rarely noted in males. Strain specific differences were not detected. In a mouse with an incidental case of lymphoma, neoplastic lymphocytes lacked arginase-I immunostaining, in contrast to immunostaining detected in non-neoplastic lymphocytes of lymphoid tissues. The use of liver tissue to validate arginase-I immunohistochemistry produced consistent expression patterns in mice, and this approach can be useful to enhance consistency of arginase-I immunohistochemical studies.     

Effects of glutamine on wound healing

Studies reporting the need for replacing amino acids such as glutamine (Gln), hydroxymethyl butyrate (HMB) and arginine (Arg) to accelerate wound healing are available in the literature. The primary objective of this study was to present the effects of Gln on tissue hydroxyproline (OHP) levels in wound healing. This study was conducted on 30 female Sprague Dawley rats with a mean weight of 230 ± 20 g. Secondary wounds were formed by excising 2 × 1 cm skin subcutaneous tissue on the back of the rats. The rats were divided into three equal groups. Group C (Control): the group received 1 ml/day isotonic solution by gastric gavage after secondary wound was formed. Group A (Abound): the group received 0·3 g/kg/day/ml Gln, 0·052 g/kg/day/ml HMB and 0·3 g/kg/day/ml Arg by gastric gavage after secondary wound was formed. Group R (Resource): the group received 0·3 g/kg/day/ml Gln by gastric gavage after secondary wound was formed. The OHP levels of the tissues obtained from the upper half region on the 8th day and the lower half region on the 21st day from the same rats in the groups were examined. Statistical analysis was performed using the statistics program SPSS version 17.0. No statistically significant differences were reported with regard to the OHP measurements on the 8th and 21st days (8th day: F = 0·068, P = 0·935 > 0·05; 21st day: F = 0·018, P = 0·983 > 0·05). The increase in mean OHP levels on the 8th and 21st days within each group was found to be statistically significant (F = 1146·34, P = 0·000 < 0·001). We conclude that in adults who eat healthy food, who do not have any factor that can affect wound healing negatively and who do not have large tissue loss at critical level, Gln, Arg and HMB support would not be required to accelerate secondary wound healing.     

蛋白质精氨酸甲基转移酶与肿瘤干预治疗

寻找有效的肿瘤干预靶点对肿瘤患者具有重要意义。蛋白质精氨酸甲基转移酶(PRMTs)是催化蛋白质底物精氨酸残基甲基化的唯一关键酶,参与多种重要的基础细胞代谢过程。近年来的研究发现,异常表达的PRMTs可以通过促进催化精氨酸残基甲基化的过程参与肿瘤的发生与发展;PRMTs表达的高低可以作为判断肿瘤预后的因子。这些结果提示,如果针对性干预PRMTs或许可以给肿瘤患者带来临床获益。     

Effectiveness of arginine-containing toothpastes in treating dentine hypersensitivity: A systematic review

Objectives

To evaluate by way of a systematic review the effectiveness of arginine-containing desensitising toothpastes in comparison to control agents in reducing dentine hypersensitivity.

Data sources

Electronic databases were searched including: Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE, LILACS (30/03/2012). Reference lists of eligible studies and systematic reviews were cross-checked in an attempt to identify additional studies. Strategies to identify grey literature were employed.

Study selection inclusion criteria

Controlled Clinical Trials (CCTs) and Randomised Controlled Trials (RCTs) comparing arginine-containing desensitising toothpastes to non-arginine-containing control toothpastes.Two review authors independently screened the titles and abstracts of studies identified. Data collection forms were completed for included studies.

Outcomes

Changes in sensitivity to tactile and air-blast stimuli. A subjective assessment of sensitivity was also sought.

Conclusion

Data identified indicates a potential role for arginine-containing toothpastes in managing dentine hypersensitivity. However, this conclusion is based on small sample sizes and the studies identified did not follow patients up in the medium to long term. The authors recommend that there is a need for well-designed RCTs to be conducted prior to any definitive recommendations being made.

Clinical significance

Dentine hypersensitivity is a common condition. Its multi-factorial aetiology has led to several treatment modalities being advocated. The continued introduction of new desensitising agents suggests that no product has yet proven ultimately successful. Arginine-containing toothpastes have recently been introduced, this article systematically reviews the evidence relating to their effectiveness.     

Inborn errors of creatine metabolism and epilepsy

Creatine metabolism disorders include guanidinoacetate methyltransferase (GAMT) deficiency, arginine:glycine amidinotransferase (AGAT) deficiency, and the creatine transporter (CT1‐encoded by SLC6A8 gene) deficiency. Epilepsy is one of the main symptoms in GAMT and CT1 deficiency, whereas the occurrence of febrile convulsions in infancy is a relatively common presenting symptom in all the three above‐mentioned diseases. GAMT deficiency results in a severe early onset epileptic encephalopathy with development arrest, neurologic deterioration, drug‐resistant seizures, movement disorders, mental disability, and autistic‐like behavior. In this disorder, epilepsy and associated abnormalities on electroencephalography (EEG) are more responsive to substitutive treatment with creatine monohydrate than to conventional antiepileptic drugs. AGAT deficiency is mainly characterized by mental retardation and severe language disorder without epilepsy. In CT1 deficiency epilepsy is generally less severe than in GAMT deficiency. All creatine disorders can be investigated through measurement of creatine metabolites in body fluids, brain proton magnetic resonance spectroscopy (¹H‐MRS), and molecular genetic techniques. Blood guanidinoacetic acid (GAA) assessment and brain H‐MRS examination should be part of diagnostic workup for all patients presenting with epileptic encephalopathy of unknown origin. In girls with learning and/or intellectual disabilities with or without epilepsy, SLC6A8 gene assessment should be part of the diagnostic procedures. The aims of this review are the following: (1) to describe the electroclinical features of epilepsy occurring in inborn errors of creatine metabolism; and (2) to delineate the metabolic alterations associated with GAMT, AGAT, and CT1 deficiency and the role of a substitutive therapeutic approach on their clinical and electroencephalographic epileptic patterns.     

Arginine metabolism in tumor-associated macrophages in cutaneous malignant melanoma: evidence from human and experimental tumors

Tumor-associated macrophages (TAMs) may elicit contrasting effects on tumor growth, depending on their biological activities. Macrophages use arginine either to synthesize nitric oxide (NO) through the inducible NO synthase (iNOS) or to produce ornithine through arginase activity. Although the effects of NO are primarily cytotoxic, production of ornithine may promote tumor cell proliferation. Thus, iNOS/arginase balance in TAMs may be crucial in tumor progression. The aim of this study was (a) to explore iNOS and arginase expression in TAMs associated with human melanoma at different stages of tumor progression and (b) to explore whether melanoma cells influence iNOS and/or arginase expression in TAMs under basal condition and in the presence of interferon gamma and/or lipopolysaccharide. Immunohistochemical analyses performed on tissue sections from in situ melanoma, invasive melanoma of different pT categories, and metastatic melanoma revealed that (a) the percentage of iNOS-positive TAMs was significantly higher in in situ and thin melanomas in comparison with more advanced, thicker tumors; (b) the percentage of arginase-positive TAMs did not change among the pT categories analyzed; and (c) the percentage of iNOS-positive TAMs was greater than that of arginase-positive TAMs in peritumoral and intratumoral locations of thin melanomas (pT1). Moreover, by the use of an in vitro experimental protocol represented by B16 murine melanoma cells cocultivated with inflammatory macrophages, we found that melanoma cells stimulate iNOS expression and NO production in macrophages. In conclusion, our in vivo and in vitro results suggest that, mainly in early melanoma lesions, iNOS prevails over arginase in TAMs, a phenomenon possibly stimulated by contact with tumor cells. However, macrophages stimulated by murine melanoma cells secreted a level of NO compatible with an antitumor activity only in the presence of interferon gamma.     

Arginase activity mediates reversible T cell hyporesponsiveness in human pregnancy

Complex regulation of T cell functions during pregnancy is required to ensure materno-fetal tolerance. Here we reveal a novel pathway for the temporary suppression of maternal T cell responses in uncomplicated human pregnancies. Our results show that arginase activity is significantly increased in the peripheral blood of pregnant women and remarkably high arginase activities are expressed in term placentae. High enzymatic activity results in high turnover of its substrate L-arginine and concomitant reduction of this amino acid in the microenvironment. Amino acid deprivation is emerging as a regulatory pathway of lymphocyte responses and we assessed the consequences of this enhanced arginase activity on T cell responses. Arginase-mediated L-arginine depletion induces down-regulation of CD3 zeta, the main signalling chain of the TCR, and functional T cell hyporesponsiveness. Importantly, this arginase-mediated T cell suppression was reversible, as inhibition of arginase activity or addition of exogenous L-arginine restored CD3 zeta chain expression and T cell proliferation. Thus, L-arginine metabolism constitutes a novel physiological mechanism contributing to the temporary suppression of the maternal immune response during human pregnancy.