Obesity-induced diabetes in mouse strains treated with gold thioglucose: a novel animal model for studying ß-cell dysfunction.

An obesity-induced diabetes model using genetically normal mouse strains would be invaluable but remains to be established. One reason is that several normal mouse strains are resistant to high-fat diet-induced obesity. In the present study, we show the effectiveness of gold thioglucose (GTG) in inducing hyperphagia and severe obesity in mice, and demonstrate the development of obesity-induced diabetes in genetically normal mouse strains. GTG treated DBA/2, C57BLKs, and BDF1 mice gained weight rapidly and exhibited significant increases in nonfasting plasma glucose levels 8-12 weeks after GTG treatment. These mice showed significantly impaired insulin secretion, particularly in the early phase after glucose load, and reduced insulin content in pancreatic islets. Interestingly, GTG treated C57BL/6 mice did not become diabetic and retained normal early insulin secretion and islet insulin content despite being as severely obese and insulin resistant as the other mice. These results suggest that the pathogenesis of obesity-induced diabetes in GTG-treated mice is attributable to the inability of their pancreatic ß-cells to secrete enough insulin to compensate for insulin resistance. Mice developing obesity-induced diabetes after GTG treatment might be a valuable tool for investigating obesity-induced diabetes. Furthermore, comparing the genetic backgrounds of mice with different susceptibilities to diabetes may lead to the identification of novel genetic factors influencing the ability of pancreatic ß-cells to secrete insulin.

A novel model of type 2 diabetes mellitus based on obesity induced by high-fat diet in BDF1 mice.

For experimental research on type 2 diabetes mellitus, a diet-induced obesity-dependent diabetes model developed using genetically normal animals is essential. However, attempts at feeding a high-fat diet (HFD) to major inbred strains of mice have not resulted in the establishment of an ideal model. Here, we show that BDF1 mice, the F(1) hybrids of C57BL/6 and DBA/2 normal strains, develop HFD-induced obesity-dependent diabetes. BDF1 mice fed a HFD gained weight rapidly and developed severe diabetes characterized by hyperglycemia, glucosuria, and elevation of hemoglobin A(1C) levels in 3 to 4 months. The glucose tolerance of the diabetic mice was significantly impaired, and the elevation of plasma insulin after a glucose load was significantly reduced. Isolated pancreatic islets of HFD-fed BDF1 mice showed decreased insulin content and a reduced insulin secretory response to higher concentrations of glucose. Immunohistochemical analysis of the pancreas showed reduced staining intensity to insulin and aberrant distribution of glucagon-positive cells in diabetic BDF1 mice. These observations suggest the cause of the diabetes in HFD-fed BDF1 mice to be dysfunction of the pancreatic beta-cells, which do not produce or secrete enough insulin to compensate for insulin resistance. BDF1 mice fed a HFD showing obesity-dependent diabetes are suggested to be an appropriate animal model of type 2 diabetes mellitus. This model would be useful for exploring the mechanism of obesity-dependent type 2 diabetes mellitus and evaluating antiobesity and antidiabetic drugs.

Pharmacological characterization of RS-1259, an orally active dual inhibitor of acetylcholinesterase and serotonin transporter, in rodents: possible treatment of Alzheimer's disease.

A dual inhibitor of acetylcholinesterase (AChE) and serotonin transporter (SERT), RS-1259 (4-[1S)-methylamino-3-(4-nitrophenoxy)]propylphenyl N,N-dimethylcarbamate (fumaric acid)(1/2)salt), was newly synthesized. RS-1259 simultaneously inhibited AChE and SERT in the brain following an oral administration in mice and rats. Actual simultaneous elevation of extracellular levels of 5-HT and ACh in the rat hippocampus was confirmed by microdialysis. The compound was as effective as SERT inhibitors such as fluoxetine and fluvoxamine in a 5-hydroxytryptophan-enhancing test in mice. Spatial memory deficits in the two-platform task of a water maze in aged rats were ameliorated by RS-1259 as well as donepezil. Both RS-1259 and donepezil increased the awake episodes in the daytime electroencephalogram of rats. Although RS-1259 was weaker than donepezil in enhancing central cholinergic transmission, as observed by ACh elevation in the hippocampus and memory enhancement in aged rats, the efficacy of RS-1259 on the consciousness level, which reflects the whole activity in the brain, was almost the same as that of donepezil. These results suggest that both cholinergic and serotonergic systems are involved in maintaining brain arousal and that a dual inhibitor of AChE and SERT may be useful for the treatment of cognitive disorders associated with reduced brain activity such as in Alzheimer's disease.

Beta-amyloid racemized at the Ser26 residue in the brains of patients with Alzheimer disease: implications in the pathogenesis of Alzheimer disease.

Oligomeric and fibrillar beta-amyloid (Abeta) may be toxic in Alzheimer disease (AD), especially after post-translation modification cumulative over time. Racemization of Ser and Asp residues of Abeta in senile plaques (SPs) occurs as an age-dependent process in AD. We previously reported that Abeta1-40 racemized at Ser26 is soluble and susceptible to proteolysis yielding toxic [D-Ser26]Abeta25-35/40 fragments in vitro and in vivo. Here, we focus on the localization of racemized Ser26 residues in AD brains within the limbic system, the earliest site of AD histopathology. We developed antisera (20.1 and 22.7). each with epitopes within [D-Ser26]Abeta25-40. Two forms of truncated [D-Ser26]Abeta were detected either in SPs or within neurons in all 11 AD-affected brains, but not in age-matched controls. [D-Ser26]Abeta25/26-35 (detected by 20.1) was localized to plaque cores, extracellular neurofibrillary "ghost" tangles and vascular amyloid deposits. In contrast, [D-Ser26]Abeta25-40 (detected by 22.7) was observed in most neurons containing intracellular neurofibrillary tangles, but not in SPs. These results suggest [D-Ser26]Abeta]1-40, formed during aging, becomes soluble and diffuses from SPs. It is then proteolyzed to [D-Ser26]Abeta25-35/40, which is toxic and may contribute to the neurodegeneration. This hypothesis may explain the long lag between SP formation and neurofibrillary degeneration in AD brains.

In vivo conversion of racemized beta-amyloid ([D-Ser 26]A beta 1-40) to truncated and toxic fragments ([D-Ser 26]A beta 25-35/40) and fragment presence in the brains of Alzheimer's patients.

The lag between beta-amyloid (A beta) deposition and neurodegeneration in Alzheimer's disease (AD) suggests that age-dependent factors are involved in the pathogenesis. Racemization of Ser and Asp in A beta is a typical age-dependent modification in AD. We have shown recently that A beta1-40 racemized at Ser(26) ([D-Ser(26)]A beta 1-40) is soluble and non-toxic to neuronal cells, but is easily converted by brain proteases to truncated toxic fragments, [D-Ser(26)]A beta 25-35/40. Furthermore, [D-Ser(26)]A beta1-40 in vivo, produced a drastic and synergistic neuronal loss by enhancing the excitotoxicity when co-injected into rat hippocampus with ibotenic acid, an excitatory amino acid, suggesting an in vivo conversion of non-toxic [D-Ser(26)]A beta1-40 to toxic fragments including [D-Ser(26)]A beta 25-35/40. In this study, we further investigated the mechanism behind the in vivo neuronal loss by [D-Ser(26)]A beta1-40 and ibotenic acid in rats, and also searched for the presence of [D-Ser(26)]A beta 25-35/40 antigens in AD brains. Quantitative analyses of the damaged area indicate clearly that non-toxic [D-Ser(26)]A beta 1-40 caused as much neurodegeneration as toxic [D-Ser(26)]A beta 25-35/40. MK-801, an NMDA receptor antagonist, completely inhibited the neurodegeneration. The immunohistochemical analyses using anti-[D-Ser(26)]A beta 25-35/40-specific antibodies demonstrated the presence of [D-Ser(26)]A beta 25-35/40 antigens in senile plaques and in degenerating hippocampal CA1 neurons in AD brains, but not in age-matched control brains. These results strengthen our hypothesis that soluble [D-Ser(26)]A beta1-40, possibly produced during aging, is released from plaques and converted by proteolysis to toxic [D-Ser(26)]A beta 25-35/40, which damage hippocampal CA1 neurons by enhancing excitotoxicity in AD. This may account for the lag between A beta deposition and neurodegeneration in AD.