Gut microbiota therapy

This June 2022 review cited twenty 2022 papers for relationships between Parkinson’s disease and gut microbiota:

“Clinical diagnosis of PD is based on typical motor symptoms, and novel diagnostic biomarkers have been developed such as imaging markers, and α-synuclein fluid and tissue markers. Multimorbidity of non-motor disorders heighten the risk of adverse outcomes for patients with PD, which usually appear 20 years before onset of motor symptoms.

The gut microbiota is intimately connected to occurrence, development, and progression of PD, especially in early stages. A better understanding of the microbiota–gut–brain axis in PD can provide an opportunity to monitor an individual’s health by manipulating gut microbiota composition.

Several approaches like administration of probiotics, psychobiotics, prebiotics, synbiotics, postbiotics, FMT, and dietary modifications have been tried to mitigate dysbiosis-induced ill effects and alleviate PD progression.

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Epidemiological studies have reported that diet affects (positively or negatively) onset of neurodegenerative disorders. Evidence suggests that diet composition’s effects on brain health is not due to diet-induced inflammatory response, but because of its effects on the gut microbiome.

Dysbiotic gut microbiota (including altered microbial metabolites) may play crucial roles in PD via various mechanisms, such as:

  • Increased intestinal permeability;
  • Aggravated intestinal inflammation and neuroinflammation;
  • Abnormal aggregation of α-synuclein fibrils;
  • Imbalanced oxidative stress; and
  • Decreased neurotransmitters production.

Future studies are essential to further elucidate cause-effect relationships between gut microbiota and PD, improved PD therapeutic and diagnostic options, disease progression tracking, and patient stratification capabilities to deliver personalized treatment and optimize clinical trial designs.”

https://www.frontiersin.org/articles/10.3389/fimmu.2022.937555/full “Gut Microbiota: A Novel Therapeutic Target for Parkinson’s Disease”


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Taurine week #6: Stress

Two 2022 rodent studies of taurine’s associations with long-term stress, starting with a chronic restraint stress model:

“We show that chronic restraint stress can lead to hyperalgesia accompanied by changes in gut microbiota that have significant gender differences. Corresponding changes of bacteria can further induce hyperalgesia and affect different serum metabolism in mice of the corresponding sex.

Different serum metabolites between pseudo-germ-free mice receiving fecal microbiota transplantation from the chronic restraint stress group and those from the control group were mainly involved in bile secretion and steroid hormone biosynthesis for male mice, and in taurine and hypotaurine metabolism and tryptophan metabolism for female mice.

Effects of gut microbiota transplantation on serum metabolomics of female host: Taurine and hypotaurine metabolism, tryptophan metabolism, serotonergic synapse, arachidonic acid metabolism, and choline metabolism in cancer were the five identified pathways in which these different metabolites were enriched.

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Taurine and hypotaurine play essential roles in anti-inflammation, anti-hypertension, anti-hyperglycemia, and analgesia. Taurine can be used as a diagnostic index for fibromyalgia syndrome and neuropathic pain.

These findings improve our understanding of sexual dimorphism in gut microbiota in stress-induced hyperalgesia and the effect of gut microbiota on blood metabolic traits. Follow-up research will investigate causal relationships between them.”

https://www.sciencedirect.com/science/article/pii/S1043661822000743 “Gut microbiota and its role in stress-induced hyperalgesia: Gender-specific responses linked to different changes in serum metabolites”

Human equivalents:

  • A 7-8 month-old mouse would be a 38-42 year-old human.
  • A 14-day stress period is about two years for humans.

A second study used a chronic social defeat stress model:

“The level of taurine in extracellular fluid of the cerebral medial prefrontal cortex (mPFC) was significantly reduced in mice with chronic social defeat stress (CSDS)-induced depression. We found that taurine supplementation effectively rescued immobility time during a tail suspension assay and improved social avoidance behaviors in CSDS mice.

Male C57BL/6 J mice (∼ 23 g) and male CD-1 mice aged 7–8 months (∼ 45 g) were used. CD-1 mice were screened for aggressive behavior during social interactions for three consecutive days before the start of the social defeat sessions. Experimental C57BL/6 J mice were subjected to physical interactions with a novel CD-1 mouse for 10 min once per day over 10 consecutive days.

We found significant reductions in taurine and betaine levels in mPFC interstitial fluid of CSDS mice compared with control mice.

csds taurine betaine

We additionally investigated levels of interstitial taurine in chronic restraint stress (CRS) mice, another depressive animal model. After 14 days of CRS treatment, mice showed typical depression-like behaviors, including decreased sucrose preference and increased immobility time. mPFC levels of interstitial taurine were also significantly decreased in CRS mice.

Taurine treatment protected CSDS mice from impairments in dendritic complexity, spine density, and proportions of different types of spines. Expression of N-methyl D-aspartate receptor subunit 2A, an important synaptic receptor, was largely restored in the mPFC of these mice after taurine supplementation.

These results demonstrated that taurine exerted an antidepressive effect by protecting cortical neurons from dendritic spine loss and synaptic protein deficits.”

https://link.springer.com/article/10.1007/s10571-022-01218-3 “Taurine Alleviates Chronic Social Defeat Stress-Induced Depression by Protecting Cortical Neurons from Dendritic Spine Loss”

Human equivalents:

  • A 7-8 month-old mouse would be a 38-42 year-old human.
  • A 500 mg/kg taurine dose injected intraperitoneally is (.081 x 500 mg) x 70KG = 2.835 g.
  • A 10-day stress period is about a year and a half for humans.

Don’t think aggressive humans would have to be twice as large to stress those around them. There may be choices other than enduring a year and a half of that.

Taurine week #5: Blood

Two 2022 papers investigated taurine’s effects in blood, starting with a review of platelets:

“Taurine is the most abundant free amino acid in the human body, with a six times higher concentration in platelets than any other amino acid. It is highly beneficial for the organism, has many therapeutic actions, and is currently approved for heart failure treatment in Japan. Only the lack of large-scale phase 3 clinical trials restricts taurine use as a therapeutic agent in several other pathologies for treatment of which it has been shown to be effective (hypertension, atherosclerosis, stroke, neurodegenerative diseases, metabolic diseases, e.g., diabetes mellitus, and others).

Because taurine was seen as a non-patentable nutrient, the pharmaceutical industry has not shown much interest in its research. Considering that taurine and its analogues display permissible side effects, along with the need of finding new, alternative antithrombotic drugs with minimal side effects and long-term action, the potential clinical relevance of this fascinating nutrient and its derivatives requires further consideration.”

https://www.mdpi.com/2077-0383/11/3/666/htm “Taurine and Its Derivatives: Analysis of the Inhibitory Effect on Platelet Function and Their Antithrombotic Potential”

Figure 1 provided details of taurine and its derivatives’ effects on various processes involved in platelet activation and aggregation.


A second paper was a rodent study:

“To evaluate chronic effects of taurine on cholesterol levels, we analyzed mice fed a taurine-rich diet for 14–16 weeks. Long-term feeding of taurine lowered plasma cholesterol and bile acids without significantly changing other metabolic parameters, but hardly affected these levels in the liver.

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Taurine upregulates transcriptional activity of Cyp7a1 by suppressing FGF21 production in the liver. Bile acids are converted from blood cholesterol by CYP7A1, and more efficiently enter enterohepatic circulation via taurine conjugation.

This study shows that long-term feeding of taurine lowers both plasma cholesterol and bile acids, reinforcing that taurine effectively prevents hypercholesterolemia.”

https://www.mdpi.com/1422-0067/23/3/1793/htm “Long-Term Dietary Taurine Lowers Plasma Levels of Cholesterol and Bile Acids”

A human equivalent of this male C57BL/6J mouse 16-week taurine intervention is roughly 17 years. That strain’s male maximum lifespan is around 800 days, and human maximum lifespan is currently 122.5 years.


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All about AGEs

My 900th curation is a 2022 review by the lead author of Reversibility of AGEs concentrations that fleshed out details of advanced glycation end products (AGEs) topics:

“This review aims to provide a state-of-the-art overview of the toxicokinetics and toxicodynamics of endogenously formed and exogenous dietary AGEs and their precursors. AGEs are a heterogenous group of:

  • Low molecular mass (LMM) glycation products formed by reaction with a free amino acid residue and/or to dicarbonyl precursors; and
  • High molecular mass (HMM) glycation products formed by reaction with a protein-bound amino acid residue, including cross-linked products (i.e. when two amino acid residues are involved instead of one).

Cross-linking of body proteins results in:

  • Altered structure and function of the proteins;
  • Proteins are less easily degraded;
  • An increase in stiffness in tissues that are rich in these proteins, including arterial, lung tissue, joints, and extracellular matrix. Stiffness in these tissues has been associated with diseases including hypertension, cataracts, dementia, atherosclerosis, glomerulosclerosis, emphysema, and joint pain.

In endogenous formation of AGEs and their precursors, the same pathways as exogenous proceed via non-enzymatic reactions, although they occur at lower rates due to the lower physiological temperatures. In addition, specific endogenous AGE formation pathways include glycolysis and the polyol pathway active under hyperglycemic conditions.

Considering heterogeneity of glycation products, as also reflected in different ADME outcomes, AGEs and their precursors cannot be grouped together. Specific, individual information is required for a proper evaluation, especially considering ADME properties.

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The role of exogenous HMM AGEs and precursors seems to be restricted by limited bioavailability to local effects on the intestine including its microbiota, unless being degraded to their LMM form. An important role is probably left for reactive (endogenously formed) dicarbonyl AGE precursors and as a consequence the endogenously formed AGEs.

The direct contribution of reactive dicarbonyl precursors to dicarbonyl stress and their indirect contribution to endogenous HMM AGE formation and subsequent AGE receptor activation remain to be further studied.”

https://www.sciencedirect.com/science/article/pii/S0278691522001855 “Differences in kinetics and dynamics of endogenous versus exogenous advanced glycation end products (AGEs) and their precursors”

Gut microbiota knowledge through 2021

I’ll curate this 2022 review of what’s known and unknown about our trillions of gut microbiota through its topic headings:

“Most microbial taxa and species of the human microbiome are still unknown. Without revealing the identity of these microbes as a first step, we cannot appreciate their role in human health and diseases.

A. Understanding the Microbiome Composition and Factors That Shape Its Diversity
Effect of Diet Composition on the Microbiome Diversity

  • Macronutrients and Microbiome Diversity
  • Nutrient and Mineral Supplements and Microbiome Diversity

Stress

Drugs

Race and Host Genetics

Aging

Lifestyle

  • Exercise
  • Smoking
  • Urbanization

B. Understanding the Microbiome Function and Its Association With Onset and Progression of Many Diseases

Microbiome Association With Inflammatory and Metabolic Disorders

  • Chronic Inflammation in GIT and Beyond
  • Development of Malignant Tumors
  • Obesity
  • Coronary Artery Disease
  • Respiratory Diseases

Microbiome Role in Psychiatric, Behavioral, and Emotional Disorders

C. Understanding the Microbiome Function as Mediated by Secreted Molecules

D. Conclusion and Future Directions – A pioneering study aimed to computationally predict functions of microbes on earth estimates the presence of 35.5 million functions in bacteria of which only 0.02% are known. Our knowledge of its functions and how they mediate health and diseases is preliminary.”

https://www.frontiersin.org/articles/10.3389/fmicb.2022.825338 “Recent Advances in Understanding the Structure and Function of the Human Microbiome”


I took another test last month at the 14-month point of treating my gut microbiota better. Compared with the 7-month top level measurements, what stood out was an increase in relative abundance from 1% to 7% in the Verrucomicrophia phylum that pretty much exclusively comprises species Akkermansia muciniphilia in humans:

top 5 phylum 2-2022

This review termed Akkermansia muciniphilia relative increases as beneficial. Go with the Alzheimer’s Disease evidence didn’t.

Preventing human infections with dietary fibers inferred that insufficient dietary fiber may disproportionately increase abundance of this species. But I already eat much more fiber than our human ancestors’ estimated 100 grams of fiber every day, so lack of fiber definitely didn’t cause this relative increase.

Resistant starch therapy observed:

“Relative abundances of smaller keystone communities (e.g. primary degraders) may increase, but appear to decrease simply because cross-feeders increase in relative abundance to a greater extent.”

I’ll wait for further evidence while taking responsibility for my own one precious life.

Didn’t agree with this review’s statements regarding microbial associations with fear. These reviewers framed such associations as if gut microbiota in the present had stronger influences on an individual’s fear responses than did any of the individual’s earlier experiences. No way.

I came across this review by it citing The microbiome: An emerging key player in aging and longevity, which was Reference 25 of Dr. Paul Clayton’s blog post What are You Thinking?

Also didn’t agree with some of the doctor’s post:

  • Heterochronic parabiosis of young and old animals is wildly different from fecal transfer. Can’t really compare them to any level of detail.
  • Using a rodent young-to-old fecal microbiota transplant study to imply the same effects would happen in humans? Humans don’t live in controlled environments, so why would a young human individual’s gut microbiota necessarily have healthier effects than an old individual’s?
  • Another example was the penultimate paragraph: “By adding a mix of prebiotic fibers to your diet and maintaining a more youthful and less inflammatory microbiome you will have less inflammation, less endotoxaemia and less inflammageing. You will therefore live healthier and longer.” I’m okay with the first sentence. Equivalating the first sentence to both healthspan and lifespan increases in the second sentence wasn’t supported by any of the 45 cited references.

Eat broccoli sprouts for depression, Part 2

Here are three papers that cited last year’s Part 1. First is a 2021 rodent study investigating a microRNA’s pro-depressive effects:

“Depressive rat models were established via chronic unpredicted mild stress (CUMS) treatment. Cognitive function of rats was assessed by a series of behavioral tests.

Nrf2 CUMS

Nrf2 was weakly expressed in CUMS-treated rats, whereas Nrf2 upregulation alleviated cognitive dysfunction and brain inflammatory injury.

Nrf2 inhibited miR-17-5p expression via binding to the miR-17-5p promoter. miR-17-5p was also found to limit wolfram syndrome 1 (Wfs1) transcription.

We found that Nrf2 inhibited miR-17-5p expression and promoted Wfs1 transcription, thereby alleviating cognitive dysfunction and inflammatory injury in rats with depression-like behaviors. We didn’t investigate the role of Nrf2 in other depression models (chronic social stress model and chronic restraint stress model) and important brain regions other than hippocampus, such as prefrontal cortex and nucleus accumbens. Accordingly, other depression models and brain regions need to be designed and explored to further validate the role of Nrf2 in depression in future studies.”

https://link.springer.com/article/10.1007/s10753-021-01554-4 “Nrf2 Alleviates Cognitive Dysfunction and Brain Inflammatory Injury via Mediating Wfs1 in Rats with Depression‑Like Behaviors” (not freely available)

This study demonstrated that activating the Nrf2 pathway inhibited brain inflammation, cognitive dysfunction, and depression. Would modulating one microRNA and one gene in vivo without Nrf2 activation achieve similar results?


A 2021 review focused on the immune system’s role in depression:

“Major depressive disorder is one of the most common psychiatric illnesses. The mean age of patients with this disorder is 30.4 years, and the prevalence is twice higher in women than in men.

Activation of inflammatory pathways in the brain is considered to be an important producer of excitotoxicity and oxidative stress inducer that contributes to neuronal damage seen in the disorder. This activation is mainly due to pro-inflammatory cytokines activating the tryptophan-kynurenine (KP) pathway in microglial cells and astrocytes.

Elevated levels of cortisol exert an inhibitory feedback mechanism on its receptors in the hippocampus and hypothalamus, stopping stimulation of these structures to restore balance. When this balance is disrupted, hypercortisolemia directly stimulates extrahepatic enzyme 2,3-indolimine dioxygenase (IDO) located in various tissues (intestine, placenta, liver, and brain) and immune system macrophages and dendritic cells.

Elevation of IDO activities causes metabolism of 99% of available tryptophan in the KP pathway, substantially reducing serotonin synthesis, and producing reactive oxygen species and nitrogen radicals. The excitotoxicity generated produces tissue lesions, and activates the inflammatory response.”

https://academic.oup.com/ijnp/article/25/1/46/6415265 “Inflammatory Process and Immune System in Major Depressive Disorder”

This review highlighted that stress via cortisol and IDO may affect the brain and other parts of the body.


A 2022 review elaborated on Part 1’s findings of MeCP2 as a BDNF inhibitor:

“Methyl-CpG-binding protein 2 (MeCP2) is a transcriptional regulator that is highly abundant in the brain. It binds to methylated genomic DNA to regulate a range of physiological functions implicated in neuronal development and adult synaptic plasticity.

Ability to cope with stressors relies upon activation of the hypothalamic–pituitary–adrenal (HPA) axis. MeCP2 has been shown to contribute to early life stress-dependent epigenetic programming of genes that enhance HPA-axis activity.

We describe known functions of MeCP2 as an epigenetic regulator, and provide evidence for its role in modulating synaptic plasticity via transcriptional regulation of BDNF or other proteins involved in synaptogenesis and synaptic strength like reelin. We conclude that MeCP2 is a promising target for development of novel, more efficacious therapeutics for treatment of stress-related disorders such as depression.”

https://www.mdpi.com/2073-4409/11/4/748/htm “The Role of MeCP2 in Regulating Synaptic Plasticity in the Context of Stress and Depression”


Osprey lunch

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The aryl hydrocarbon signaling pathway

I’ll emphasize this densely packed 2021 review’s broccoli sprout compounds / gut microbiota / health interactions:

“The aryl hydrocarbon receptor (AhR) senses cues from environmental toxicants and physiologically relevant dietary/microbiota-derived ligands. AhR signaling mediates bidirectional host-microbiome interactions in a wide range of cellular functions in a ligand-, cell type-, species-, and context-specific manner.

Brassicaceae family plants are rich sources of glucobrassicin, the glucosinolate precursor of indole-3-carbinol (I3C). Glucobrassicin can be enzymatically hydrolyzed and converted into I3C by myrosinase, which is present in intact plant cells and gut microbiota.

I3C activates AhR but exhibits low binding affinity. However, in acidic conditions found in the stomach, I3C undergoes acid condensation reaction to generate a variety of more potent AhR ligands, such as 3,3′-diindolylmethane (DIM).

AhR activation by natural AhR ligands (e.g., I3C) has been shown to prevent pathogenic gut microbial dysbiosis by altering gut microbiome composition in mice with colitis. Depletion of AhR ligands in the diet decreased α diversity of gut microbiota, while I3C supplementation restored microbiota composition.

I3C treatment is effective for treating IBD patients, partly by upregulating IL-22. Targeting AhR could modulate the amplitude and duration of IL-22 signaling to treat IBD patients.

Administration of I3C or DIM significantly reduced the number of tumors in the cecum and small intestine. Supplementation of I3C reduces the number of colorectal tumors in WT, but not in AhR null mice.

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Gut microbiota and diet are major sources of AhR ligands that influence the whole body, including gut, liver, brain, and the immune system. Many human diseases are associated with decreased circulating levels of AhR ligands, partly due to dysbiosis.

The ability of AhR signaling to regulate self-renewal and differentiation of intestinal stem cells intrinsically or extrinsically has recently been brought into the spotlight.”

https://www.ncbi.nlm.nih.gov/labs/pmc/articles/PMC8667662/ “Diet–Host–Microbiota Interactions Shape Aryl Hydrocarbon Receptor Ligand Production to Modulate Intestinal Homeostasis”


Young hawk

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Gut microbiota vs. disease risks

This 2021 review subject was risk relationships between diseases from the perspective of gut microbiota:

“There is a significant inverse relationship between the onset of Alzheimer’s disease/Parkinson’s disease (AD/PD) and cancer, but the mechanism is still unclear. Considering that intestinal flora can connect them, we briefly introduced the relationship among AD/PD, cancer, and intestinal flora, studied metabolites or components of the intestinal flora, and the role of intestinal barriers and intestinal hormones in AD/PD and cancer.

According to existing evidence:

  • Bifidobacterium and Lactobacillus positively affect AD/PD and cancer;
  • Ruminococcaceae, Prevotellaceae, and Prevotella significantly improve on AD/PD but harm cancer; and
  • Blautia has universal anticancer ability, but it may aggravate AD pathology.

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This may partially explain the antagonistic relationship between neurodegenerative diseases and cancer. When some individuals suffer from one disease, their intestinal flora change to obtain a stronger resistance to the other disease than healthy individuals, which is consistent with statistical data.”

https://www.sciencedirect.com/science/article/pii/S0753332221011276 “Composition of intestinal flora affects the risk relationship between Alzheimer’s disease/Parkinson’s disease and cancer”


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Inevitable individual differences

This 2021 review subject was individual differences:

“We will focus on recent findings that try to shed light on the emergence of individuality, with a particular interest in Drosophila melanogaster.

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Another possible source of potential behavioral variability might come from the interaction of individuals with environmental microbes, from Wolbachia infections to changes in the gut microbiome. In this particular case, no genetic variation or neural circuit alteration would be responsible for the change in behavior.

Finally, from an evolutionary point of view, individuality might play an essential role in providing an adaptive advantage. For example, we have described that animals might use diversified bet-hedging as a mechanism to produce high levels of variation within a population to ensure that at least some individuals will be well-adapted when facing unpredictable environments.”

https://www.frontiersin.org/articles/10.3389/fphys.2021.719038/full “Behavior Individuality: A Focus on Drosophila melanogaster


Other papers on this subject include:

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Immune system aging

This 2021 review by three coauthors of Take responsibility for your one precious life – Trained innate immunity cast a wide net:

“Non-specific innate and antigen-specific adaptive immunological memories are vital evolutionary adaptations that confer long-lasting protection against a wide range of pathogens. However, these mechanisms of memory generation and maintenance are compromised as organisms age.

This review discusses how immune function regulates and is regulated by epigenetics, metabolic processes, gut microbiota, and the central nervous system throughout life. We aimed to present a comprehensive view of the aging immune system and its consequences, especially in terms of immunological memory.

aging immune system

A comprehensive strategy is essential for human beings striving to lead long lives with healthy guts, functional brains, and free of severe infections.”

https://link.springer.com/article/10.1007/s12016-021-08905-x “Immune Memory in Aging: a Wide Perspective Covering Microbiota, Brain, Metabolism, and Epigenetics”


Attempts to cover a wide range of topics well are usually uneven. For example, older information in the DNA Methylation In Adaptive Immunity section was followed by a more recent Histone Modifications in Adaptive Immunity section.

This group specializes in tuberculosis vaccine trained immunity studies, and much of what they presented also applied to β-glucan trained immunity. A dozen previously curated papers were cited.

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Natural products vs. neurodegenerative diseases

I was recently asked about taking rapamycin for its effects on mTOR. I replied that diet could do the same thing. Here’s a 2021 review outlining such effects:

“As common, progressive, and chronic causes of disability and death, neurodegenerative diseases (NDDs) significantly threaten human health, while no effective treatment is available. Recent studies have revealed the role of phosphoinositide 3-kinase (PI3K)/Akt (Protein kinase B)/mammalian target of rapamycin (mTOR) in some diseases and natural products with therapeutic potentials.

Growing evidence highlights the dysregulated PI3K/Akt/mTOR pathway and interconnected mediators in pathogenesis of NDDs. Side effects and drug-resistance of conventional neuroprotective agents urge the need for providing alternative therapies.

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Polyphenols, alkaloids, carotenoids, and terpenoids have shown to be capable of a great modulation of PI3K/Akt/mTOR in NDDs. Natural products potentially target various important oxidative/inflammatory/apoptotic/autophagic molecules/mediators, such as Bax, Bcl-2, p53, caspase-3, caspase-9, NF-κB, TNF-α, GSH, SOD, MAPK, GSK-3β, Nrf2/HO-1, JAK/STAT, CREB/BDNF, ERK1/2, and LC3 towards neuroprotection.

This is the first systematic and comprehensive review with a simultaneous focus on the critical role of PI3K/Akt/mTOR in NDDs and associated targeting by natural products.”

https://www.sciencedirect.com/science/article/abs/pii/S0944711321002075 “Natural products attenuate PI3K/Akt/mTOR signaling pathway: A promising strategy in regulating neurodegeneration” (not freely available) Thanks to Dr. Sajad Fakhri for providing a copy.


Natural products mentioned in this review that I eat in everyday foods are listed below. The most effective ones are broccoli and red cabbage sprouts, and oats and oat sprouts:

  • Artichokes – luteolin;
  • Blackberries – anthocyanins;
  • Blueberries – anthocyanins, gallic acid, pterostilbene;
  • Broccoli and red cabbage sprouts – anthocyanins, kaempferol, luteolin, quercetin, sulforaphane;
  • Carrots – carotenoids;
  • Celery – apigenin, luteolin;
  • Green tea – epigallocatechin gallate;
  • Oats and oat sprouts – avenanthramides;
  • Strawberries – anthocyanins, fisetin;
  • Tomatoes – fisetin.

Four humpback whales

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Blood pressure and pain

A trio of papers, with the second and third citing a 2013 review:

“The relationship between pain and hypertension is potentially of great pathophysiological and clinical interest, but is poorly understood. Perception of acute pain initially plays an adaptive role, which results in prevention of tissue damage.

The consequence of ascending nociception is recruitment of segmental spinal reflexes through physiological neuronal connections:

  • In proportion to magnitude and duration of the stimulus, these spinal reflexes cause sympathetic nervous system activation, which increases peripheral resistances, heart rate, and stroke volume; and
  • The response also involves the neuroendocrine system, in particular, the hypothalamic-pituitary-adrenal axis, in addition to further activation of the sympathetic system by adrenal glands.

Persistent pain tends to become chronic and to increase BP values. After a long time, dysfunction of release of endogenous opioids results in a reduction of their analgesic effect. A vicious circle is established, where further pain leads to a reduction in pain tolerance, associated with decreased analgesia mediated by baroreceptors, in a kind of process of exhaustion.”

https://onlinelibrary.wiley.com/doi/epdf/10.1111/jch.12145 “The Relationship Between Blood Pressure and Pain”


A second paper was a 2021 human experimental pain study:

“We investigated the effectiveness of physiological signals for automatic pain intensity estimation that can either substitute for, or complement patients’ self-reported information. Results indicate that for both subject-independent and subject-dependent scenarios, electrodermal activity (EDA) – which is also referred to as skin conductance (SC) or galvanic skin response – was the best signal for pain intensity estimation.

EDA gave mean absolute error (MAE) = 0.93 using only 3 time-series features:

  1. Time intervals between successive extreme events above the mean;
  2. Time intervals between successive extreme events below the mean; and
  3. Exponential fit to successive distances in 2-dimensional embedding space.

Although we obtained good results using 22 EDA features, we further explored to see if we could reach similar or better results with fewer EDA features. This plot highlights that by considering only the top 3 features, we obtained the same level of performance given by all 22 features together.

journal.pone.0254108.g002

This is the first study that achieved less than 1-unit error for continuous pain intensity estimation using only one physiological sensor’s 3 time-series feature, and a Support Vector Regression machine learning model. Considering that this is an encouraging result, we can estimate objective pain using only the EDA sensor, which needs neither a complex setup nor a complex computationally intense machine learning algorithm.

This study paves the way for developing a smart pain measurement wearable device that can change the quality of pain management significantly.”

https://doi.org/10.1371/journal.pone.0254108 “Exploration of physiological sensors, features, and machine learning models for pain intensity estimation”


A third paper was a 2020 human rotator cuff surgery study:

“Results of our study demonstrated that:

  • Pain during the early postoperative period;
  • Time until occurrence of a retear; and
  • Existence of hypertension

were correlated with severity of pain in patients with a retorn rotator cuff.

Pain was selected as the sole outcome parameter of this study because:

  • Pain is an important factor that compels patients to seek treatment for rotator cuff tears, along with functional disability;
  • Pain and subjective functional deficits are important factors that influence a surgeon’s decision to continue with treatment in cases of retearing; and
  • Analyzing pain severity can be a good way to determine patients’ overall satisfaction after rotator cuff repair.

However, pain is not always correlated with disease severity or tear size and vice versa. A lack of pain does not necessarily depend on integrity of the repaired tendon or constitute a good prognosis. In fact, patients with partial-thickness rotator cuff tears showed more pain than did those with full-thickness tears.

Existence of hypertension had a proportional relationship with pain at 12 months postoperatively in patients with retears. This can be interpreted as a suggestion that pain in patients with retears is not acute, but rather chronic, and may be connected to pain in the early postoperative period at 3 months. However, results of this study cannot explain benefits of controlling hypertension in alleviating pain in patients with retears.”

https://journals.sagepub.com/doi/10.1177/2325967120947414 “Factors Related to Pain in Patients With Retorn Rotator Cuffs: Early Postoperative Pain Predicts Pain at 12 Months Postoperatively”


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Gut and brain health

This 2021 human review subject was interactions of gut health and disease with brain health and disease:

“Actions of microbial metabolites are key for appropriate gut-brain communication in humans. Among these metabolites, short-chain fatty acids (SCFAs), tryptophan, and bile acid metabolites / pathways show strong preclinical evidence for involvement in various aspects of brain function and behaviour.

Dietary fibres, proteins, and fats ingested by the host contain components which are metabolized by microbiota. SCFAs are produced from fermentation of fibres, and tryptophan-kynurenine (TRP-KYN) metabolites from dietary proteins. Primary bile acids derived from liver metabolism aid in lipid digestion, but can be deconjugated and bio-transformed into secondary bile acids.

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One of the greatest challenges with human microbiota studies is making inferences about composition of colonic microbiota from faeces. There are known differences between faecal and caecal microbiota composition in humans along with spatial variation across the gastrointestinal tract.

It is difficult to interpret microbiome-host associations without identifying the driving influence in such an interaction. Large cohort studies may require thousands of participants on order to reach 20 % explanatory power for a certain host-trait with specific microbiota-associated metrics (Shannon diversity, relative microbial abundance). Collection of metadata is important to allow for a better comparison between studies, and to identify differentially abundant microbes arising from confounding variables.”

https://www.sciencedirect.com/science/article/pii/S0149763421001032 “Mining Microbes for Mental Health: Determining the Role of Microbial Metabolic Pathways in Human Brain Health and Disease”


Don’t understand why these researchers handcuffed themselves by only using PubMed searches. For example, two papers were cited for:

“Conjugated and unconjugated bile acids, as well as taurine or glycine alone, are potential neuroactive ligands in humans.”

Compare scientific coverage of PubMed with Scopus:

  • 2017 paper: PubMed citations 39; Scopus citations 69.
  • 2019 paper: PubMed citations 69; Scopus citations 102.

Large numbers of papers intentionally missing from PubMed probably influenced this review’s findings, such as:

  1. “There are too few fibromyalgia and migraine microbiome-related studies to make definitive conclusions. However, one fibromyalgia study found altered microbial species associated with SCFA and tryptophan metabolism, as well as changes in serum levels of SCFAs. Similarly, the sole migraine-microbiota study reported an increased abundance of the kynurenine synthesis GBM (gut-brain module).
  2. Due to heterogeneity of stroke and vascular disease conditions, it is difficult to make substantial comparisons between studies. There is convincing evidence for involvement of specific microbial genera / species and a neurovascular condition in humans. However, taxa were linked to LPS biosynthesis rather than SCFA production.
  3. Several studies suggest lasting microbial changes in response to prenatal or postnatal stress, though these do not provide evidence for involvement of SCFA, tryptophan, or bile-acid modifying bacteria. Similar to stress, there are very few studies assessing impact of post-traumatic stress disorder on microbiota.”

These researchers took on a difficult task. Their study design could have been better.


PXL_20210628_095746132

Wildlife

PXL_20210710_100826663

Take acetyl-L-carnitine for early-life trauma

This 2021 rodent study traumatized female mice during their last 20% of pregnancy, with effects that included:

  • Prenatally stressed pups raised by stressed mothers had normal cognitive function, but depressive-like behavior and social impairment;
  • Prenatally stressed pups raised by control mothers did not reverse behavioral deficits; and
  • Control pups raised by stressed mothers displayed prenatally stressed pups’ behavioral phenotypes.

Acetyl-L-carnitine (ALCAR) protected against and reversed depressive-like behavior induced by prenatal trauma:

alcar regime

ALCAR was supplemented in drinking water of s → S mice either from weaning to adulthood (3–8 weeks), or for one week in adulthood (7–8 weeks). ALCAR supplementation from weaning rendered s → S mice resistant to developing depressive-like behavior.

ALCAR supplementation for 1 week during adulthood rescued depressive-like behavior. One week after ALCAR cessation, however, the anti-depressant effect of ALCAR was diminished.

Intergenerational trauma induces social deficits and depressive-like behavior through divergent and convergent mechanisms of both in utero and early-life parenting environments:

  • We establish 2-HG [2-hydroxyglutaric acid, a hypoxia and mitochondrial dysfunction marker, and an epigenetic modifier] as an early predictive biomarker for trauma-induced behavioral deficits; and
  • Demonstrate that early pharmacological correction of mitochondria metabolism dysfunction by ALCAR can permanently reverse behavioral deficits.”

https://www.nature.com/articles/s42003-021-02255-2 “Intergenerational trauma transmission is associated with brain metabotranscriptome remodeling and mitochondrial dysfunction”


Previously curated studies cited were:

This study had an effusive endorsement of acetyl-L-carnitine in its Discussion section, ending with:

“This has the potential to change lives of millions of people who suffer from major depression or have risk of developing this disabling disorder, particularly those in which depression arose from prenatal traumatic stress.”

I take a gram daily. Don’t know about prenatal trauma, but I’m certain what happened during my early childhood.

I asked both these researchers and those of Reference 70 for their estimates of a human equivalent to “0.3% ALCAR in drinking water.” Will update with their replies.


PXL_20210704_095621886

Treat your gut microbiota as one of your organs

Two 2021 reviews covered gut microbiota. The first was gut microbial origins of metabolites produced from our diets, and mutual effects:

“Gut microbiota has emerged as a virtual endocrine organ, producing multiple compounds that maintain homeostasis and influence function of the human body. Host diets regulate composition of gut microbiota and microbiota-derived metabolites, which causes a crosstalk between host and microbiome.

There are bacteria with different functions in the intestinal tract, and they perform their own duties. Some of them provide specialized support for other functional bacteria or intestinal cells.

Short-chain fatty acids (SCFAs) are metabolites of dietary fibers metabolized by intestinal microorganisms. Acetate, propionate, and butyrate are the most abundant (≥95%) SCFAs. They are present in an approximate molar ratio of 3 : 1 : 1 in the colon.

95% of produced SCFAs are rapidly absorbed by colonocytes. SCFAs are not distributed evenly; they are decreased from proximal to distal colon.

Changing the distribution of intestinal flora and thus distribution of metabolites may have a great effect in treatment of diseases because there is a concentration threshold for acetate’s different impacts on the host. Butyrate has a particularly important role as the preferred energy source for the colonic epithelium, and a proposed role in providing protection against colon cancer and colitis.

There is a connection between acetate and butyrate distinctly, which suggests significance of this metabolite transformation for microbiota survival. The significance may even play an important role in disease development.

  • SCFAs can modulate progression of inflammatory diseases by inhibiting HDAC activity.
  • They decrease cytokines such as IL-6 and TNF-α.
  • Their inhibition of HDAC may work through modulating NF-κB activity via controlling DNA transcription.”

https://www.hindawi.com/journals/cjidmm/2021/6658674/ “Gut Microbiota-Derived Metabolites in the Development of Diseases”


A second paper provided more details about SCFAs:

“SCFAs not only have an essential role in intestinal health, but also enter systemic circulation as signaling molecules affecting host metabolism. We summarize effects of SCFAs on glucose and energy homeostasis, and mechanisms through which SCFAs regulate function of metabolically active organs.

Butyrate is the primary energy source for colonocytes, and propionate is a gluconeogenic substrate. After being absorbed by colonocytes, SCFAs are used as substrates in mitochondrial β-oxidation and the citric acid cycle to generate energy. SCFAs that are not metabolized in colonocytes are transported to the liver.

  • Uptake of propionate and butyrate in the liver is significant, whereas acetate uptake in the liver is negligible.
  • Only 40%, 10%, and 5% of microbial acetate, propionate, and butyrate, respectively, reach systemic circulation.
  • In the brain, acetate is used as an important energy source for astrocytes.

Butyrate-mediated inhibition of HDAC increases Nrf2 expression, which has been shown to lead to an increase of its downstream targets to protect against oxidative stress and inflammation. Deacetylase inhibition induced by butyrate also enhances mitochondrial activity.

SCFAs affect the gut-brain axis by regulating secretion of metabolic hormones, induction of intestinal gluconeogenesis (IGN), stimulation of vagal afferent neurons, and regulation of the central nervous system. The hunger-curbing effect of the portal glucose signal induced by IGN involves activation of afferents from the spinal cord and specific neurons in the parabrachial nucleus, rather than afferents from vagal nerves.

Clinical studies have indicated a causal role for SCFAs in metabolic health. A novel targeting method for colonic delivery of SCFAs should be developed to achieve more consistent and reliable dosing.

The gut-host signal axis may be more resistant to such intervention by microbial SCFAs, so this method should be tested for ≥3 months. In addition, due to inter-individual variability in microbiota and metabolism, factors that may directly affect host substrate and energy metabolism, such as diet and physical activity, should be standardized or at least assessed.”

https://www.hindawi.com/journals/cjidmm/2021/6632266/ “Modulation of Short-Chain Fatty Acids as Potential Therapy Method for Type 2 Diabetes Mellitus”