Effect of oral antidiabetic agents on plasma amylin level in patients with non-insulin-dependent diabetes mellitus (type 2)

Effect of amylin on memory and central insulin resistance in a rat model of Alzheimer's disease

Context: Alzheimer's disease is strongly associated with brain insulin signalling.Objective: Investigating the effect of amylin as a novel treatment in streptozotocin (STZ) rat model of AD.Materials and methods: Alzheimer's disease (AD) was induced in albino rats by intracerebroventricular injection of STZ (3 mg/kg). Rats received either amylin analogue (Pramlintide 200 μg/kg/day) or Metformin (30 mg/kg/day) for 5 weeks.Results: Both Pramlintide and Metformin improve learning and memory through enhancing insulin signalling (p-IR and p-PI3K) which lead to lowering level of CSF glucose, phosphorylated tau proteins, and amyloid-β peptide (Aβ) in hippocampus.Conclusions: Insulin sensitisers as Metformin and Pramlintide can improve learning and memory and decrease the pathological changes in STZ induced rat model of AD. However, Pramlintide is superior to Metformin in some memory tests which related to its action as an amylin analogue. Amylin improves learning and memory through an independent effect other than insulin sensitisation.

Amylin and its analogs: a friend or foe for the treatment of Alzheimer's disease?

Amylin, a gut-brain axis hormone, and amyloid-beta peptides (Aβ), a major component of the Alzheimer's disease (AD) brain, share several features, including similar β-sheet secondary structures, binding to the same receptor and being degraded by the same protease, insulin degrading enzyme (IDE). However, while amylin readily crosses the blood brain barrier (BBB) and mediates several activities including improving glucose metabolism, relaxing cerebrovascular structure, modulating inflammatory reaction and perhaps enhancing neural regeneration, Aβ has no known physiological functions. Thus, abundant Aβ in the AD brain could block or interfere with the binding of amylin to its receptor and hinder its functions. Recent studies using animal models for AD demonstrate that amylin and its analog reduce the AD pathology in the brain and improve cognitive impairment in AD. Given that, in addition to amyloid plaques and neurofibrillary tangles, perturbed cerebral glucose metabolism and cerebrovascular damage are the hallmarks of the AD brain, we propose that giving exogenous amylin type peptides have the potential to become a new avenue for the diagnosis and therapeutic of AD. Although amylin's property of self-aggregation may be a limitation to developing it as a therapeutic for AD, its clinical analog, pramlintide containing 3 amino acid differences from amylin, does not aggregate like human amylin, but more potently mediates amylin's activities in the brain. Pramlintide is an effective drug for diabetes with a favorable profile of safety. Thus a randomized, double-blind, placebo-controlled clinical trial should be conducted to examine the efficacy of pramlintide for AD. This review summarizes the knowledge and findings on amylin type peptides and discuss pros and cons for their potential for AD.

Daily exercise training protects against albuminuria and angiotensin converting enzyme 2 shedding in db/db diabetic mice

Angiotensin II (Ang II) is involved in induction and progression of renal damage in diabetes. Angiotensin converting enzyme 2 (ACE2) is highly expressed in the kidney and has been shown to be renoprotective by degrading Ang II to Ang-(1-7). A disintegrin and metalloproteinase 17 (ADAM17)-mediated shedding of renal ACE2 contribute to diabetic nephropathy pathogenesis. Lifestyle modification and metformin are recommended as initial therapies for most patients with type 2 diabetes. The aim of this study was to investigate whether exercise training and/or metformin improve glucose homeostasis and albuminuria and downregulate renal ADAM17 and ACE2 shedding in db/db mice. Seven-week-old normal and db/db mice were subjected either to a sedentary existence or exercise training with and without metformin (150 mg/kg per day) for 10 weeks. Exercise training significantly lowered blood glucose, urinary albumin and ACE2 excretion in db/db mice. ADAM17 and ACE2 proteins were co-localized in cortical tubules of the kidney, indicating a possible interaction. Metformin treatment was effective in lowering hyperglycemia only during the first 2 weeks of treatment. Increased renal ADAM17 in 17-week-old db/db mice was corrected by physical exercise but not metformin. In addition, exercise training reduced plasma triglycerides and enhanced insulin levels of db/db mice. In conclusion, exercise training alone and in combination with metformin prevented shedding of renal ACE2 by decreasing ADAM17 protein. Urinary ACE2 could serve as a prognostic tool for the progression of kidney damage and its attenuation by exercise may partially contribute to its renal protection.

Positive association between plasma amylin and cognition in a homebound elderly population

Our recent study reported that amylin, a pancreatic peptide that readily crosses the blood-brain barrier, improves learning and memory in Alzheimer's disease mouse models. However, the relationship between peripheral amylin and cognition in humans is unknown. In this follow-up study, using a cross-sectional, homebound elderly population, improvement in cognitive function with increasing quartiles of plasma amylin was suggested by positive association with verbal memory (p = 0.0002) and visuoconstruction tasks (p = 0.004), and inverse association with timed measures of attention (p < 0.0001) and executive function (p = 0.04). After adjusting for demographic information, apolipoprotein E4 allele, diabetes, stroke, kidney function, and lipid profile, log10 of plasma amylin remained associated with these cognitive domains. In contrast, plasma amyloid-β peptide was not associated with these specific cognitive domains. Our study suggests that peripheral amylin may be protective for cognitive decline, especially in the domains affected by Alzheimer's disease.