Exogenous Lipocalin 2 Ameliorates Acute Rejection in a Mouse Model of Renal Transplantation.

Lipocalin 2 (Lcn2) is rapidly produced by damaged nephron epithelia and is one of the most promising new markers of renal injury, delayed graft function and acute allograft rejection (AR); however, the functional importance of Lcn2 in renal transplantation is largely unknown. To understand the role of Lcn2 in renal AR, kidneys from Balb/c mice were transplanted into C57Bl/6 mice and vice versa and analyzed for morphological and physiological outcomes of AR at posttransplantation days 3, 5, and 7. The allografts showed a steady increase in intensity of interstitial infiltration, tubulitis and periarterial aggregation of lymphocytes associated with a substantial elevation in serum levels of creatinine, urea and Lcn2. Perioperative administration of recombinant Lcn2:siderophore:Fe complex (rLcn2) to recipients resulted in functional and morphological amelioration of the allograft at day 7 almost as efficiently as daily immunosuppression with cyclosporine A (CsA). No significant differences were observed in various donor-recipient combinations (C57Bl/6 wild-type and Lcn2(-/-) , Balb/c donors and recipients). Histochemical analyses of the allografts showed reduced cell death in recipients treated with rLcn2 or CsA. These results demonstrate that Lcn2 plays an important role in reducing the extent of kidney AR and indicate the therapeutic potential of Lcn2 in transplantation.

Effects of high levels of dietary zinc oxide on ex vivo epithelial histamine response and investigations on histamine receptor action in the proximal colon of weaned piglets.

The aim of the study was to identify the effect of high dietary zinc oxide (ZnO) levels on the histamine-induced secretory-type response and histamine metabolism in the porcine proximal colon. After weaning at d 26, 3 diets with low (LZn), normal (NZn), and high (HZn) concentrations of zinc (57, 164, or 2,425 mg/kg) were fed to a total of 120 piglets. Digesta and tissue samples were taken from the ascending colon after 7 ± 1, 14 ± 1, 21 ± 1, and 28 ± 1 d. Partially stripped tissue was mounted in Ussing chambers, and histamine was applied either to the serosal or mucosal compartments. Tissue was pretreated with or without aminoguanidine and amodiaquine to block the histamine-degrading enzymes diamine oxidase (DAO) and histamine -methyltransferase (HMT), respectively. Gene expression and catalytic activity of DAO and HMT in the tissue were analyzed. The numbers of mast cells were determined in tissue samples, and histamine concentration was measured in the colon digesta. Colon tissue from another 12 piglets was used for functional studies on histamine H and H receptors by using the neuronal conduction blocker tetrodotoxin (TTX) and the H and H receptor blocker chloropyramine and famotidine, respectively. After serosal histamine application to colonic tissue in Ussing chambers, the change of short-circuit current (Δ) was not affected by pretreatment and was not different between Zn feeding groups. The Δ after mucosal histamine application was numerically lower ( = 0.168) in HZn compared to LZn and NZn pigs. Mast cell numbers increased from 32 to 46 d of life ( < 0.05). Further studies elucidated that the serosal histamine response was partly inhibited by chloropyramine or famotidine ( < 0.01). The response to mucosal histamine tended to be decreased when chloropyramine but not famotidine was applied from either the serosal or the mucosal side ( = 0.055). Tetrodotoxin alone or in combination with chloropyramine resulted in a similar reduction in the mucosal histamine response ( < 0.01). In conclusion, the present study could not identify marked changes in colonic histamine metabolism on dietary ZnO oversupplementation. For the first time, however, H receptors were functionally identified in the pig colon that are localized either on neurons or on cells that activate secretion via neurons. Luminal histamine can elicit a secretory-type response via these receptors.

Influence of iodinated contrast media on the activities of histamine inactivating enzymes diamine oxidase and histamine N-methyltransferase in vitro.

BACKGROUND: Iodinated contrast media can cause pseudoallergic reactions associated with histamine release in significant numbers of patients. To clarify whether these adverse reactions may be aggravated by a compromised histamine catabolism we asked if radiographic contrast agents in vitro inhibit the histamine inactivating enzymes diamine oxidase (DAO) and histamine N-methyltransferase (HMT). METHODS: Nine iodinated contrast agents were tested in vitro. Following pre-incubation of purified porcine kidney DAO and recombinant human HMT with 0.1-10mM of the respective contrast medium (H2O and specific inhibitors of DAO and HMT as controls) enzyme activities were determined by using radiometric micro assays. RESULTS: None of the contrast media irrespective of their structure showed significant inhibition of the activities of DAO and HMT. Pre-incubation of the enzymes with specific inhibitors led to complete inhibition of the respective enzymatic activity. CONCLUSIONS: The iodinated contrast media tested in vitro did not exhibit inhibition of histamine converting enzymes at physiologically relevant concentrations. However due to the in vitro character of this study these results do not directly reflect the in vivo situation.

Histamine intolerance: a metabolic disease?

OBJECTIVE: To evaluate the evidence regarding the disease concept of histamine intolerance as a state of inadequate histamine inactivation. METHODS: Keyword-based systematic screening of the scientific literature and of public websites focusing on diagnostic and therapeutic procedures. RESULTS: Histamine intolerance is commonly diagnosed based solely on subjective reporting of symptoms instead of following systematic diagnostic procedures based on objective laboratory and physical parameters. The only effective long-term therapy is avoidance of histamine-containing food. CONCLUSIONS: The concept of histamine intolerance as a metabolic disease is in need of more experimental and clinical evidence and affected patients will benefit from a clear, evidence-based diagnostic and therapeutic regime.

Structural organization of mammalian copper-containing amine oxidase genes.

OBJECTIVE: Analysis of sequence conservation and structural organization of mammalian genes encoding copper-containing amine oxidases (CAO). METHODS: Sequences of previously characterized genes encoding CAO proteins were used to identify homologous mammalian genes in the NCBI genome sequence databases and to analyze sequence and structural conservation of these genes. RESULTS: Mammals possess four AOC genes encoding diamine oxidase (AOC1), retina-specific amine oxidase (AOC2), vascular adhesion protein-1 (AOC3), and serum amine oxidase (AOC4), with a defective AOC4 gene present in humans, mice, and rats. In addition to the common structure of all AOC genes, there is a high degree of interspecies sequence conservation for each of the four genes. CONCLUSIONS: Sequence and structural conservation of mammalian AOC genes implies a common evolutionary origin and functional diversification after gene duplication events.

Lipocalin-2 regulates the inflammatory response during ischemia and reperfusion of the transplanted heart.

Ischemia and reperfusion (IR) are known to negatively affect early allograft function following solid organ transplantation. Lipocalin-2 (Lcn-2) has been described as a marker and potential positive modulator of acute inflammation during these processes. Using a heterotopic murine heart transplant model we previously found that IR resulted in a pronounced upregulation of Lcn-2 mRNA in the heart at 12 (22.7-fold increase) and 24 h (9.8-fold increase) of reperfusion. We now confirm this increase at the protein level and provide evidence for infiltrating polymorphonuclear cells as the primary source of Lcn-2 protein. Lcn-2 levels are increased 6.6-fold at 12 h, 11.4-fold at 24 h and 6.4 fold at 48 h after reperfusion. In Lcn-2(-/-) grafts the number of infiltrating granulocytes is reduced by 54% (p < 0.05) at 2 h, 79% (p < 0.01) at 12 h, 72% (p < 0.01) at 24 h and 52% (p < 0.01) at 48 h after reperfusion compared to Lcn-2(+/+) grafts, without any differences in cardiomyocyte apoptosis. These data suggest a function of Lcn-2 in the initiation of the inflammatory response. Moreover, an increase in Lcn-2 is not only restricted to the transplanted heart, but is also observed in the kidney, hinting at a possible involvement of Lcn-2 in the systemic response to IR.

The origin of mammalian plasma amine oxidases.

Mammalian blood plasma contains considerable activity of soluble copper-containing amine oxidase (AOC) referred to as plasma or serum amine oxidase (SAO). The identity and origin of SAO was investigated based on the recent characterization of four porcine AOC genes with AOC1 encoding diamine oxidase (DAO), AOC2 retina-specific amine oxidase (RAO), AOC3 vascular adhesion protein-1 (VAP-1), and AOC4 a VAP-1 homologue that is expressed mainly in the liver and has a signal peptide sequence instead of a transmembrane domain at its N-terminus. Purification and characterization of the major amine oxidase activity from porcine serum showed that it is the product of the AOC4 gene. Intriguingly, all mammals possessing a functional AOC4 gene exhibit high plasma amine oxidase activity. Humans and rodents lack a functional AOC4 gene and have comparably low plasma amine oxidase activity that is probably derived from partial proteolytic release of the membrane-associated AOC3 gene product VAP-1.

Plasma amine oxidase: a postulated cardiovascular risk factor in nondiabetic obese patients.

Increased activity of semicarbazide-sensitive plasma amine oxidase (SSAO), an enzyme converting various amines, has been implicated in the generation of endothelial damage through formation of cytotoxic reaction products. We investigated if SSAO activity is elevated in morbidly obese patients, which might contribute to the increased cardiovascular risk associated with obesity. SSAO activity was determined in 74 nondiabetic, obese patients (median body mass index [BMI]: 42.9 kg/m(2)) and in 32 healthy, non-obese controls (median BMI: 23.3 kg/m(2)) using a radiometric assay based on the conversion of [(14)C]benzylamine. SSAO and parameters of glucose and lipid metabolism were compared for subgroups of obese patients with normal (n = 49) and impaired (n = 25) glucose tolerance using nonparametric statistical tests. Median SSAO activity was 434 microU/mL in obese patients, which was significantly higher than in healthy, non-obese controls (median SSAO activity: 361 microU/mL). Median SSAO activity in patients with normal and impaired glucose tolerance was 423 and 464 microU/mL, respectively. SSAO activity was not correlated with any other clinical or laboratory parameters characteristic of the metabolic alterations associated with obesity. Elevated SSAO activity is found in nondiabetic, morbidly obese patients and might be an interesting independent risk factor for obesity-related cardiovascular morbidity. Long-term follow-up of SSAO and its possible role in pathogenic events is warranted since intervention with specific SSAO inhibitors is available.