Metformin attenuates Alzheimer's disease-like neuropathology in obese, leptin-resistant mice

https://doi.org/10.1016/j.pbb.2012.03.002Get rights and content

Abstract

Diabetes increases the risk of Alzheimer's disease (AD). The pathological hallmarks for AD brains are extracellular amyloid plaques formed by β-amyloid peptide (Aβ) and intracellular neurofibrillary tangles consisting of hyperphosphorylated tau protein. This study was designed to determine AD-like brain changes in mice modeling for type 2 diabetes. The effects of metformin on these changes also were studied. Seven-week old male db/db mice received intraperitoneal injection of 200 mg kg 1 d 1 metformin for 18 weeks. They were subjected to Barnes maze at an age of 21 weeks and fear conditioning at an age of 24 weeks to assess their cognitive functions. Hippocampus was harvested after these tests for biochemical evaluation. The db/db mice had more tau phosphorylated at S396 and total tau in their hippocampi than their non-diabetic control db + mice. Activated/phosphorylated c-jun N-terminal kinase (JNK), a tau kinase, was increased in the db/db mouse hippocampus. Metformin attenuated the increase of total tau, phospho-tau and activated JNK. The db/db mice had increased Aβ levels. Metformin attenuated the reduction of synaptophysin, a synaptic protein, in the db/db mouse hippocampus. Metformin did not attenuate the impairments of spatial learning and memory as well as long-term hyperglycemia in the db/db mice. Our results suggest that the db/db mice have multiple AD-like brain changes including impaired cognitive functions, increased phospho-tau and Aβ as well as decreased synaptic proteins. Activation of JNK may contribute to the increased phospho-tau in the db/db mice. Metformin attenuates AD-like biochemical changes in the brain of these mice.

Highlights

► The db/db mice have Alzheimer's disease-like brain changes. ► The increased phospho-tau at 396 may be due to JNK activation in the db/db mouse brain. ► Metformin attenuates the Alzheimer's disease-like brain biochemical changes in the db/db mice.

Introduction

Diabetes mellitus (DM) affects more than 20 million Americans (Cherian et al., 2009, Kim et al., 2009). Studies have shown that DM increases the risk for Alzheimer's disease (AD) (Brands et al., 2005, Ott et al., 1999, Strachan et al., 1997), the most common form of dementia in the elderly (Berg and Morris, 1994). The pathological hallmarks in the brain of a patient with AD are extracellular amyloid plaques formed by β-amyloid peptide (Aβ), an enzymatic product of amyloid precursor protein (APP) by β-secretase/β-amyloid converting enzyme 1 (BACE1) and γ-secretase (Vassar, 2004, Vassar and Citron, 2000), and intracellular neurofibrillary tangles consisting of hyperphosphorylated tau proteins (Selkoe, 2001). It has been suggested that Aβ and hyperphosphorylated tau proteins induce local neurotoxicity that ultimately results in AD.

There are at least two types of DM: type 1 and type 2. More patients suffer from type 2 DM (Cherian et al., 2009). Multiple animal models have been developed to facilitate DM research. It has been shown that animals with type 1 and type 2 DM have an increased phospho-tau expression in their brains (Jolivalt et al., 2008, Kim et al., 2009, Li et al., 2007, Planel et al., 2007b). These animals also have increased Aβ expression in the brains (Jolivalt et al., 2008, Li et al., 2007). Among animal models for DM, the db/db (BKS.Cg-Dock7m +/+ Leprdb/J) mice are a common model for type 2 DM. These mice develop hyperglycemia and hyperinsulinemia and are obese, polyphagic, polydipsic and polyuric (Fujita et al., 2002, Kim et al., 2009).

Various treatments for DM have been developed. Many of them aim to control blood glucose levels (Del Prato, 2009). Oral hypoglycemic agents are often used in patients with type 2 DM. Glucophage (metformin) is the most commonly used oral hypoglycemic agent (Kirpichnikov et al., 2002, Knowler et al., 2002). Interestingly, it has been shown recently that metformin increases Aβ expression in neuronal cultures (Chen et al., 2009). However, the effects of metformin on Aβ expression in diabetic mice are not reported. Its effects on other AD-like brain features, such as tau phosphorylation as well as learning and memory functions, in diabetic animals are not known. Thus, we designed this study to evaluate the AD-like brain functional and pathological changes and the effects of metformin on these changes in the db/db mice.

Section snippets

Materials and methods

The animal protocol was approved by the institutional Animal Care and Use Committee of the University of Virginia (Charlottesville, VA). All animal experiments were carried out in accordance with the National Institutes of Health Guide for the Care and Use of Laboratory Animals (NIH publications number 80–23) revised in 1996.

Effects of metformin on the characteristics of type 2 DM in the db/db mice

The db/db mice start to have hyperglycemia at 3–4 weeks of age and develop a full spectrum of type 2 DM characteristics including obesity, hyperglycemia, hyperinsulinemia and insulin resistance by 8 weeks of age (Kim et al., 2009, Lin et al., 2000). As shown in Table 1, the db/db mice had a higher fasting blood glucose level and were heavier than the lean control mice when they were 6 weeks old (P < 0.001 and t(33) = 12.227 for the body weight comparison, P = 0.025 and t(44) = 2.326 for blood glucose

Discussion

It has been shown that there is a significant increase in the phospho-tau in the brains of mice and rats with type 1 and type 2 DM (Clodfelder-Miller et al., 2006, Kim et al., 2009, Li et al., 2007, Planel et al., 2007b). This phosphorylation occurs at multiple sites including Ser199, Ser202, Thr212, Thr231, Ser262 and Ser396 (Clodfelder-Miller et al., 2006, Kim et al., 2009, Li et al., 2007, Planel et al., 2007b). Obvious phosphorylation of tau starts as early as 10 days after streptozotocin

Duality of interest

The authors declare that there is no duality of interest associated with this manuscript.

Acknowledgement

This study was supported by a grant (R01 GM065211 to Z Zuo) from the National Institutes of Health, Bethesda, Maryland, by a grant from the International Anesthesia Research Society (2007 Frontiers in Anesthesia Research Award to Z Zuo), Cleveland, Ohio, by a Grant-in-Aid from the American Heart Association Mid-Atlantic Affiliate (10GRNT3900019 to Z Zuo), Baltimore, Maryland, the Robert M. Epstein Professorship endowment, University of Virginia and a grant (81070912 to W Sheng) from National

References (57)

  • G. Price

    Metformin lactic acidosis, acute renal failure and rofecoxib

    Br J Anaesth

    (2003)
  • R. Vassar et al.

    Abeta-generating enzymes: recent advances in beta- and gamma-secretase research

    Neuron

    (2000)
  • S.Y. Yoon et al.

    Rosiglitazone reduces tau phosphorylation via JNK inhibition in the hippocampus of rats with type 2 diabetes and tau transfected SH-SY5Y cells

    Neurobiol Dis

    (2010)
  • W.Q. Zhao et al.

    Insulin resistance and amyloidogenesis as common molecular foundation for type 2 diabetes and Alzheimer's disease

    Biochim Biophys Acta

    (2009)
  • J. Avila et al.

    Tangling with hypothermia

    Nat Med

    (2004)
  • L. Berg et al.

    Diagnosis

  • M. Bodmer et al.

    Metformin, sulfonylureas, or other antidiabetes drugs and the risk of lactic acidosis or hypoglycemia: a nested case–control analysis

    Diabetes Care

    (2008)
  • A.M. Brands et al.

    The effects of type 1 diabetes on cognitive performance: a meta-analysis

    Diabetes Care

    (2005)
  • Y. Chen et al.

    Antidiabetic drug metformin (GlucophageR) increases biogenesis of Alzheimer's amyloid peptides via up-regulating BACE1 transcription

    Proc Natl Acad Sci USA

    (2009)
  • B. Cherian et al.

    Therapeutic implications of diabetes in cardiovascular disease

    Am J Ther

    (2009)
  • B.J. Clodfelder-Miller et al.

    Tau is hyperphosphorylated at multiple sites in mouse brain in vivo after streptozotocin-induced insulin deficiency

    Diabetes

    (2006)
  • S. Del Prato

    Megatrials in type 2 diabetes. From excitement to frustration?

    Diabetologia

    (2009)
  • H. Fujita et al.

    Effects of antidiabetic treatment with metformin and insulin on serum and adipose tissue adiponectin levels in db/db mice

    Endocr J

    (2005)
  • M. Heishi et al.

    Comparison of gene expression changes induced by biguanides in db/db mice liver

    J Toxicol Sci

    (2008)
  • N. Hirokawa et al.

    Tau proteins: the molecular structure and mode of binding on microtubules

    J Cell Biol

    (1988)
  • Y. Huang et al.

    Isoflurane induces a protein kinase C alpha-dependent increase in cell surface protein level and activity of glutamate transporter type 3

    Mol Pharmacol

    (2005)
  • J. Janson et al.

    Increased risk of type 2 diabetes in Alzheimer disease

    Diabetes

    (2004)
  • G.V. Johnson et al.

    Tau phosphorylation in neuronal cell function and dysfunction

    J Cell Sci

    (2004)
  • Cited by (224)

    • Insulin and disorders of behavioural flexibility

      2023, Neuroscience and Biobehavioral Reviews
    • Novel therapeutic mechanism of action of metformin and its nanoformulation in Alzheimer's disease and role of AKT/ERK/GSK pathway

      2023, European Journal of Pharmaceutical Sciences
      Citation Excerpt :

      So it can have a disease modifying effect in reversing AD pathology (Kasza et al., 2017). Similar to our study, Li et al., demonstrated that treatment with Metformin attenuated the increase in total tau and phosphorylated tau which are hallmarks of AD pathogenesis (Li et al., 2012). In primary neuronal culture obtained from tau transgenic mouse also, treatment with metformin decreased tau phosphorylation indicating its possible use as a disease modifying agent (Kickstein et al., 2010).

    View all citing articles on Scopus

    The research work was performed in and should be attributed to the Department of Anesthesiology, University of Virginia, Charlottesville, VA22908, USA.

    View full text