Minori Higashiyama

Association of CTLA-4 polymorphism with positive anti-GAD antibody in Japanese subjects with type 1 diabetes mellitus

CTLA‐4, expressed on activated T cells, is thought to be a negative regulator of T cell function. Its gene (2q33) may confer genetic susceptibility to type 1 diabetes mellitus (IDDM12). The present study was undertaken to clarify the role of CTLA‐4 gene polymorphism in Japanese subjects with type 1 diabetes and its effect on their clinical features.

Association of endogenous insulin secretion and mode of therapy with body fat and serum leptin levels in diabetic subjects

Insulin is one of the hormonal regulators of leptin synthesis and participates in adipose tissue maintenance. The present study was undertaken to clarify the association of endogenous insulin secretion and mode of therapy with body fat and serum leptin levels in diabetic subjects. We measured the fasting serum C-peptide level, as an estimate of endogenous insulin secretion, and the serum leptin level in 176 Japanese diabetic subjects (79 men and 97 women; age, 55.9+/-14.3 years; body mass index [BMI], 23.8+/-4.1 kg/m2 [mean+/-SD]). Thirty-one subjects were treated with diet therapy alone, 66 with sulfonylurea (SU), and 79 with insulin (including 29 with type I diabetes mellitus). Body fat was analyzed by the impedance method. Serum leptin levels significantly correlated with the BMI and body fat and were higher in women, mainly because of their greater body fat. Serum C-peptide concentrations positively correlated with body fat and serum leptin in subjects treated with diet and SU. In insulin-treated type II diabetic subjects, both serum C-peptide and the daily insulin dose were weakly associated with body fat and serum leptin. In those subjects, despite a lower percent body fat and body fat mass, serum leptin concentrations (10.3+/-8.4 ng/mL) were comparable to the levels in subjects treated with diet (8.8+/-8.5 ng/mL). When compared within the same BMI and body fat groups (BMI 20 to 25 and > 25 kg/m2) including the control subjects matched for age and sex, serum leptin levels were higher in insulin-treated type II diabetic subjects versus the control subjects and diabetic patients treated with diet or SU. Stepwise regression analysis for all of the diabetic subjects showed that both the serum C-peptide level and exogenous insulin administration, as well as the BMI, gender, and age, were determinants of the serum leptin level. In conclusion, endogenous insulin secretion is closely associated with body fat and serum leptin in diabetic subjects treated with diet therapy and SU. In Japanese insulin-treated type II diabetic subjects, both endogenous and exogenous insulin are associated with body fat and serum leptin, which is maintained at levels comparable to or somewhat higher than the levels in control subjects and diabetic patients treated without insulin.

Decrease in Urinary Excretion of Aquaporin-2 Associated with Impaired Urinary Concentrating Ability in Diabetic Nephropathy

Aquaporin-2 (AQP-2) is known to be expressed in the renal collecting duct cells and participates in urinary concentration in response to arginine vasopressin (AVP). The present study was undertaken to determine whether progression of renal dysfunction affects urinary excretion of AQP-2 in diabetic nephropathy. The study was composed of 8 control subjects and 14 patients with type 2 diabetes classified into two groups according to serum creatinine level (cut-off point; 1.5 mg/dl). After an 8-hour water deprivation, both urinary osmolality (Uosm) and urinary excretion of AQP-2 significantly decreased in the diabetic patients with chronic renal failure as compared to the control subjects (p < 0.0001, p < 0.05, respectively). After a water load (10 ml/kg), no differences were found in plasma osmolality (Posm), AVP levels and Uosm, whereas urinary excretion of AQP-2 significantly decreased in the patients with chronic renal failure as compared to the control subjects (p < 0.05). These results indicate that the decreased urinary excretion of AQP-2 in diabetic nephropathy is due to the impaired cellular signaling of AVP in collecting duct cells, which may be partly involved in the urinary concentrating defect in renal failure.

Arginine vasopressin inhibits apoptosis of rat glomerular mesangial cells via V1a receptors.

Arginine vasopressin (AVP) promotes proliferation of glomerular mesangial cells. We examined whether AVP modulates an apoptosis of cultured rat glomerular mesangial cells at 3-17th passages. The agarose gel electrophoresis demonstrated that AVP attenuated a ladder formation stimulated by the serum deprivation. The quantitation of oligonucleosomes by ELISA also showed that AVP suppressed the serum deprivation-induced apoptosis. Such an antiapoptotic effect of AVP was dose-dependent. An AVP V1a receptor antagonist, d(CH2)5Tyr(Me)AVP, abolished the antiapoptotic effect of AVP. The inhibitory effect of AVP on the apoptosis was reduced by staurosporine and mimicked by phorbol-12-myristate-13-acetate. These results suggest that AVP inhibits serum deprivation-induced apoptosis of glomerular mesangial cells via V1a receptor-protein kinase C pathway.

Lack of vasopressin-independent upregulation of AQP-2 gene expression in homozygous Brattleboro rats.

Arginine vasopressin (AVP) plays an important role in the expression of aquaporin (AQP-2) in the collecting duct. The present study was undertaken to determine whether there is an AVP-independent regulation of AQP-2 gene expression in homozygous Brattleboro rats in which endogenous AVP is absent. Exogenous administration of 1-deamino-8-d-AVP produced an antidiuresis and expressed AQP-2 mRNA and AQP-2 protein in the renal medulla of the homozygous Brattleboro rats. Twelve hours of water deprivation produced severe dehydration in the homozygous Brattleboro rats, such that urinary osmolality increased from 200 to 649 mosmol/kgH2O. However, no increase in AQP-2 mRNA expression was observed after this dehydration, and the medullary tissue content and urinary excretion of AQP-2 also remained unchanged. Increases in AQP-2 mRNA expression and AQP-2 protein were evident in Long-Evans rats after 64 h of water deprivation, with a severity of dehydration almost equal to the 12-h dehydrated, homozygous Brattleboro rats. These results indicate the lack of an AVP-independent mechanism for upregulating AQP-2 mRNA expression in renal collecting duct cells.Arginine vasopressin (AVP) plays an important role in the expression of aquaporin (AQP-2) in the collecting duct. The present study was undertaken to determine whether there is an AVP-independent regulation of AQP-2 gene expression in homozygous Brattleboro rats in which endogenous AVP is absent. Exogenous administration of 1-deamino-8-D-AVP produced an antidiuresis and expressed AQP-2 mRNA and AQP-2 protein in the renal medulla of the homozygous Brattleboro rats. Twelve hours of water deprivation produced severe dehydration in the homozygous Brattleboro rats, such that urinary osmolality increased from 200 to 649 mosmol/kgH(2)O. However, no increase in AQP-2 mRNA expression was observed after this dehydration, and the medullary tissue content and urinary excretion of AQP-2 also remained unchanged. Increases in AQP-2 mRNA expression and AQP-2 protein were evident in Long-Evans rats after 64 h of water deprivation, with a severity of dehydration almost equal to the 12-h dehydrated, homozygous Brattleboro rats. These results indicate the lack of an AVP-independent mechanism for upregulating AQP-2 mRNA expression in renal collecting duct cells.

Urinary excretion of the aquaporin-2 water channel exaggerated in pathological states of impaired water excretion.

OBJECTIVE The present study was undertaken to determine whether the hydro‐osmotic action of arginine vasopressin (AVP) is exaggerated in pathological states of impaired water excretion by measuring urinary excretion of the aquaporin‐2 (AQP‐2) water channel.

Serum levels of leptin and changes during the course of recovery from diabetic ketoacidosis.

Secretion of leptin, the obese gene product, is stimulated by insulin and glucocorticoids and reduced by fasting. In subjects with diabetic ketoacidosis (DKA), severe insulinopenia and prolonged fasting might cause a decrease in serum leptin levels, and subsequent insulin therapy would reverse the decrease. Otherwise, some other confounding factors, neither insulin nor fasting, might affect serum leptin levels in patients with DKA. The present study was undertaken to address these issues. Eleven patients with type 1 diabetes mellitus (seven males and four females, aged 44+/-6 years, mean +/- SEM), admitted to Jichi Medical School Hospital presenting DKA, were studied during the therapeutic period. Thirty-five sex-, age- and body mass index-matched healthy subjects served as controls. Serum leptin levels at the hospitalization were significantly greater than those of the matched control subjects (5.5+/-1.0 vs. 3.2+/-0.3 microg/l, P < 0.01). After the start of therapy with a small dose of short-acting insulin and a large volume of fluid infusion, serum leptin concentrations further increased to 10.6+/-3.6 microg/l at 24 h, and thereafter the concentrations gradually decreased and normalized at the discharge (3.3+/-0.7 microg/l, day 24+/-4). The peak levels at 24 h were significantly higher than the levels at the discharge (P < 0.05), and also +77+/-34% higher than those at the hospitalization (P < 0.005). Serum cortisol levels (1830+/-200 nmol/l) were markedly elevated at hospitalization. These results indicate that serum leptin levels are increased even under insulinopenia and fasting in the patients with DKA. Such a finding may be associated with marked hyperglycemia or enhanced secretion of glucocorticoid hormone, although the exact mechanisms remain to be elucidated. We speculate that leptin may serve as a stress peptide in DKA, but further analysis is necessary to explore a physiological role of leptin in DKA.

Urinary Excretion of Aquaporin-2 Water Channel is Dominant in Pathological State of Arginine Vasopressin-Induced Impaired Water Excretion

There is impaired water excretion in patients with syndrome of inappropriate secretion of antidiuretic hormone (SIADH), congestive heart failure, liver cirrhosis with ascites and adrenal insufficiency (Bartter and Schwartz 1967, Bichet et al., 1982, Schrier 1988a, b). In these clinical settings there is hyponatremia to a various extent. Non-suppressible release of arginine vasopressin (AVP) is found despite hypoosmolality, which should suppress plasma AVP to undetectable levels (Bartter and Schwartz 1967, Bichet et al., 1982, Schrier 1988a, b, Ishikawa et al., 1982, Ishikawa 1986).

Upregulation of Aquaporin-2 Gene Expression in Pathological State of Impaired Water Excretion in Glucocorticoid-Deficient Rats

Impairment in water excretion occurs in patients with hypopituitarism and adrenal insufficiency (Slessor 1951, Amhed et al., 1967, Ishikawa et al., 1991), and in experimental models of glucocorticoid- and mineralocorticoid-deficiency (Green et al., 1970, Linas et al., 1980, Ishikawa and Schrier 1982, Robinson et al., 1983). There is evidence that arginine vasopressin (AVP) plays a crucial role in impaired water excretion in these pathological states (Amhed et al., 1967, Ishikawa et al., 1991, Linas et al., 1980, Ishikawa and Schrier 1982). We demonstrated the removal of water retention by an AVP V2 receptor antagonist in glucocorticoid-deficient rats (Ishikawa and Schrier 1982).