添田 聡

OBJECTIVES: Histidine decarboxylase (HDC), a histamine synthase, is expressed in various tissues and is induced by proinflammatory cytokines such as TNFα. As they age, C57BL/6 mice show auto-antibody deposition and lymphocyte infiltration into various tissues, including salivary glands. However, the mechanism underlying cell infiltration and the change in HDC expression in salivary glands with aging remain unclear. Thus, we aimed to elucidate the relationship between histamine and inflammaging. METHODS: We investigated the change in histology and HDC expression in the major salivary glands (parotid, submandibular, and sublingual) of 6-week- and 9-month-old wild-type mice. We also determined the histological changes, cytokine expression, and anti-aging factor Klotho in the salivary glands of 9-month-old wild-type and HDC-deficient (HDC-KO) mice. RESULTS: Cell infiltration was observed in the submandibular gland of 9-month-old wild-type mice. Although most cells infiltrating the submandibular glands were CD3-positive and B220-positive lymphocytes, CD11c-positive and F4/80-positive monocyte lineages were also detected. HDC, TNFα, and IL-1β mRNA expression increased in the submandibular gland of 9-month-old wild-type mice. The expression of PPARγ, an anti-inflammatory protein, declined in 9-month-old wild-type mice, and Klotho expression increased in 9-month-old HDC-KO mice. Immunohistochemistry showed that Klotho-positive cells disappeared in the submandibular gland of 9-month-old wild-type mice, while Klotho was detected in all salivary glands in HDC-KO mice of the same age. CONCLUSION: Our findings demonstrate the multifunctionality of histamine and can aid in the development of novel therapeutic methods for inflammatory diseases such as Sjogren's syndrome and age-related dysfunctions.

Background: We previously reported that myocardial fibrosis may be one of the causes of left ventricular hypertrophy and cardiac dysfunction in dogs with hyperglucocorticism (HGC). The detailed mechanism by which myocardial fibrosis of the left ventricle occurs in dogs with hyperglucocorticism (HGC) remains unclear. Aim: This study investigated the mechanism by which HGC causes fibrosis of the left ventricle.Methods: The impacts of HGC on the heart by comparing samples obtained from high-dose glucocorticoid-treated (P) and untreated (C) dogs. The P group included healthy Beagle dogs (n=6) treated with prednisolone (2 mg/kg, bid, po) for 84 days, and the C group included healthy Beagle dogs (n=6) euthanized for unrelated reasons. In three of the P group dogs, serum was collected before the start of administration (Day 0) and on Day 84 to measure angiotensin II concentrations and oxidative stress markers (8-hydroxy-2’-deoxyguanosine (8OHdG), NADPH oxidase, and superoxide levels). Samples of the left ventricular free wall (LVFW), right ventricular free wall (RVFW), interventricular septum (IVS), and aortic root were harvested from both groups (n = 6 for each group). Using these tissue samples, angiotensin II type 1 receptor (AT1R), 8OHdG, and transforming growth factor β1 (TGFβ1) immunohistochemical stains were performed.Results: The blood NADPH oxidase concentration was significantly higher (P=0.027) in the P group 84 days after initiation of the medication compared to that before prednisolone treatment. By contrast, there was no significant difference in serum angiotensin II (P=0.450), 8OHdG (P=0.068), and superoxide (P=0.057) concentrations. The positive staining rates of AT1R, 8OHdG, and TGFβ1 in the heart (LVFW, RVFW, IVS, and aortic root) were significantly higher in the P group than those in the C group.Conclusion: Angiotensin II and oxidative stress in HGC may cause left ventricular fibrosis in dogs.

Background: In recent years, left ventricular hypertrophy and cardiac dysfunction have been reported in human and canine patients with hypercortisolism (HAC) and in dogs treated experimentally with high-dose prednisolone. However, to our knowledge, there have been no reports on the effects of hyperglucocorticism (HGC) on the mitral valve (MV). Aim: This study aimed to compare the MV in dogs treated with high-dose prednisolone with that in healthy dogs to investigate the effects of HGC on the MV.Methods: We investigated the effects of HGC on the MV by comparing samples obtained from high-dose glucocorticoid-treated (P) and healthy (C) dogs. The P group included healthy Beagle dogs (n = 6) treated with prednisolone (2 mg/kg, bid, po) for 84 days and the C group included healthy Beagle dogs (n = 6) euthanized for unrelated reasons. The anterior and posterior mitral leaflets (AML and PML, respectively) from both groups were harvested and stained with hematoxylin–eosin, Alcian blue, and Masson trichome. Additionally, adiponectin (ADN) and glucocorticoid receptor immunohistochemistry were performed. Histological evaluation was performed in the atrialis, spongiosa, fibrosa, and all layers of the proximal, middle, and distal regions of the AML and PML. Results: The proportion of the spongiosa layer thickness to the total thickness was higher in the P than in the C group (proximal and middle AML). However, the proportion of the fibrosa layer thickness to the total thickness was lower in the P than in the C group (middle PML). Areas of acidic sulfated mucosubstance deposition were smaller in the fibrosa layer and all layers (middle AML), while those of collagen deposition were smaller in the spongiosa and total layers (proximal and middle AML), in the P than in the C group. Additionally, ADN expression in the spongiosa layer was higher in the P than in the C group (middle AML). Conclusion: These findings suggest that long-term administration of synthetic glucocorticoids induces histological changes in the MV. These changes may lead to MV dysfunction in dogs with HGC.