Saturday, July 22, 2017

AMPK activators Metformin & CHIR99021 improve gut bacteria in humans, Fragile X, & promote inner ear, dental pulp, & cancer stem cell differentiation

CC BY 2.5 (http://creativecommons.org/licenses/by/2.5)], via Wikimedia Commons; By Peter Saxon (Own work) [CC BY-SA 4.0 (http://creativecommons.org/licenses/by-sa/4.0)], via Wikimedia Commons; Rocky Mountain Laboratories, NIAID, NIH [Public domain]

A recent study published online in the journal Nature Medicine in May of 2017 presented startling evidence that the AMPK activator metformin, which has also recently been shown to alleviate accelerated aging defects in cells derived from Hutchinson-Gilford progeria (HGPS) patients, exerted a significant beneficial effect on the gut microbiome in humans in a randomized double-blind placebo controlled study [1-4]. In treatment-naïve patients with Type 2 diabetes (placebo: n = 18 or 1,700 mg/d of metformin: n = 22), a significant decrease in hemoglobin A1c (HbA1c) levels and fasting blood glucose was observed only in metformin-treated patients during the 4-month study period [1]. HbA1c levels and fasting blood glucose were also significantly reduced in a subset of placebo-treated patients that were switched to metformin after 6 months of treatment. Interestingly, whole-genome shotgun sequencing of fecal samples indicated that metformin treatment for 2 and 4 months significantly altered the relative abundance of 81 and 86 bacterial strains, respectively, with an increase in Bifidobacterium and Akkermansia muciniphila [1]. Metformin also directly promoted the growth of Bifidobacterium adolescentis and A. muciniphila in vitro, both of which have been associated with improved metabolic features in mice [1].

Importantly, fecal samples from humans that had been treated with metformin for 4 months and transferred to germ-free mice (via oral gavage) fed a high-fat diet improved glucose tolerance in mice compared to mice that received fecal samples from humans before treatment with metformin [1]. Intriguingly, metformin treatment was also linked to gene enrichment for bacterial environmental responses, including metabolism of the short-chain fatty acids and AMPK activators butyrate and propionate [1,5]. Fecal propionate and butyrate concentrations were significantly increased after 4 months of metformin treatment in men compared to the placebo group, indicating that metformin also beneficially modulates bacterial secondary metabolite production by inducing a bacterial stress response [1]. Moreover, several environmental stressors, including heat shock/stress, which activates AMPK in human cells, also promotes the production of various bacterial secondary metabolites, indicating that the mechanism of action by which metformin promotes an increase in beneficial human gut bacteria and release of bacterial secondary metabolites is via the induction of a stress response in bacteria [6,7].

Furthermore, the beneficial effects of the induction of a cellular stress response likely crosses species boundaries, as increases in calcium (Ca2+) and reactivate oxygen species (ROS) (mediators of cellular stress induction) also promotes seed germination, root gravitropism, and fertilization in plants [8-13]. Additionally, an increase in the AMP(ADP)/ATP ratio, intracellular Ca2+ increases, or an increase in the levels of ROS have been shown to activate the master metabolic regulator AMPK and promote the differentiation of embryonic, adult, and cancer stem cells [14-18]. Metformin and butyrate have also been shown to synergistically activate AMPK and decrease the cancer stem cell-like population in breast cancer cells, butyrate has been shown to induce pancreatic cancer stem cell differentiation, and metformin induces glioma stem cell differentiation and elimination in an AMPK-dependent manner, indicating that cellular stress-induced AMPK activation is a critical mediator linking cancer, embryonic, and adult stem cell differentiation, as proposed in my recent publication linking cancer stem cell differentiation and/or apoptosis with latent HIV-1 reactivation [19-21].

Indeed, a recent study published in the journal Cell Reports by researchers from Harvard Medical School and MIT showed that the glycogen synthase kinase 3β (GSK3β) inhibitor CHIR99021 (CHIR) and the histone deacetylase (HDAC) inhibitor valproic acid (VPA), both of which activate AMPK, significantly expanded cochlear supporting cells (i.e. “inner ear stem cells”) that expressed and maintained the epithelial stem cell marker Lgr5 [22-24]. Treatment with CHIR and VPA also led to the differentiation of Lgr5-expressing cells into hair cells in high yield, providing additional evidence that AMPK activation promotes differentiation of adult stem cells including inner ear stem cells, possibly leading to treatments for hearing loss [24]. Interestingly, the authors demonstrated in a previous study that CHIR and VPA also promoted the multilineage differentiation of Lgr5+ intestinal stem cells into mature enterocytes, goblet cells and Paneth cells [25]. AMPK activation has also been shown to improve gut epithelial differentiation and metformin increases goblet and Paneth cell differentiation from intestinal epithelial cells, further indicating that AMPK activation likely represents a common mechanism of action linking structurally dissimilar compounds that enhance inner ear and intestinal stem cell maintenance and differentiation [26,27].  

Moreover, a recently published study in the journal Scientific Reports in January of 2017 demonstrated that topical administration of GSK3β inhibitors including the AMPK activator CHIR led to the mobilization of resident mesenchymal stem cells in the tooth pulp that had been exposed via the drilling of holes in mice molars [28]. GSK3β inhibitor-induced stem cell mobilization promoted a natural process of reparative dentin (also spelled dentine) formation that completely restored dentin, leading the authors to conclude that stimulation of mesenchymal stem cell mobilization and differentiation into odontoblast-like cells may represent a novel approach to clinical tooth restoration [28]. AMPK activation has previously been shown to promote osteogenic (i.e. bone forming) differentiation of human adipose tissue-derived mesenchymal stem cells and metformin induces osteoblastic differentiation of human induced pluripotent stem cell-derived mesenchymal stem cells in an AMPK-dependent manner, providing further evidence that structurally diverse compounds including metformin and CHIR that promote adult stem cell differentiation likely do so via a common mechanism of AMPK activation [29,30].

The induction of cellular stress and AMPK activation may also link beneficial modulation of the gut microbiome in humans not only with adult stem cell maintenance and differentiation, but also with the amelioration of pathologies associated with neurological disorders. A study recently published in the journal Clinical Genetics in April of 2017 demonstrated for the first time that metformin consistently improved behavior in several patients diagnosed with Fragile X Syndrome (FXS), a genetic disorder characterized by intellectual disability and significant deficits in neurological function and cognitive development [31]. An improvement in behavior was documented in the Aberrant Behavior Checklist (ABC) for all cases, as evidenced by consistent improvements (i.e. lower scores compared to pre-metformin treatment) in social avoidance, irritability, hyperactivity, and social unresponsiveness as well as improvements in language and conversational skills reported by familial caretakers [31].

Also, metformin has been shown to rescue and restore memory deficits in a Drosophila model of FXS and a recently published study (2017) demonstrated that metformin corrected social novelty impairment, reduced testicular weight, decreased repetitive grooming, rescued excessive long-term depression and dendritic spine abnormalities, restored excitatory synaptic transmission, and acutely activated AMPK in hippocampal pyramidal neurons in an FXS mouse model [32,33]. Interestingly, GSK3β inhibitors including the AMPK activator CHIR have been shown to rescue deficits in long-term potentiation at medial perforant path-dentate granule cells synapses in an FXS mouse model, indicating that cellular stress-induced AMPK activation by metformin and CHIR links the beneficial effects of those compounds in phenomena as disparate as stem cell differentiation, FXS, and long-term potentiation, hypotheses that I initially proposed in 2017 [34-36].

Lastly, as butyrate has been shown to reactivate latent HIV-1, facilitating immune system detection and virus destruction, and metformin when combined with bryostatin-1 (which also activates AMPK) promotes latent HIV-1 reactivation, cellular stress-induced AMPK activation likely also links beneficial modulation of human gut bacteria with latent HIV-1 reactivation [37-39].

AMPK activation also promotes oocyte meiotic induction and maturation (processes that are critical for efficient oocyte activation) and AMPK has recently been found localized across the entire acrosome in human spermatozoa [40-42]. The induction of cellular stress (e.g. increases in ROS, intracellular Ca2+, and/or AMP(ADP)/ATP ratio increase), which activates AMPK, also promotes oocyte meiotic induction/maturation, oocyte activation, and the acrosome reaction in human sperm, processes critical for the creation of all human life [41,43,44]. Indeed, the calcium ionophore ionomycin, which activates AMPK, is commonly used to promote latent HIV-1 reactivation and is extensively used to activate human oocytes, creating normal healthy children [44-46]. Such evidence indicates and further substantiates the novel and provocative assertion that AMPK activation links the amelioration of pathological cellular defects in FXS and Hutchinson-Gilford progeria syndrome with the gut microbiota, HIV-1 latency, adult and cancer stem cells, learning and memory, and the creation of all human life [4,35,36,39,40,47].

https://www.linkedin.com/pulse/ampk-activators-metformin-chir99021-improve-gut-bacteria-finley



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