Cabbage and fermented vegetables : From death rate heterogeneity in countries to candidates for mitigation strategies of severe COVID-19

Large differences in COVID-19 death rates exist between countries and between regions of the same country. Some very low death rate countries such as Eastern Asia, Central Europe, or the Balkans have a common feature of eating large quantities of fermented foods. Although biases exist when examining ecological studies, fermented vegetables or cabbage have been associated with low death rates in European countries. SARS-CoV-2 binds to its receptor, the angiotensin-converting enzyme 2 (ACE2). As a result of SARS-CoV-2 binding, ACE2 downregulation enhances the angiotensin II receptor type 1 (AT(1)R) axis associated with oxidative stress. This leads to insulin resistance as well as lung and endothelial damage, two severe outcomes of COVID-19. The nuclear factor (erythroid-derived 2)-like 2 (Nrf2) is the most potent antioxidant in humans and can block in particular the AT(1)R axis. Cabbage contains precursors of sulforaphane, the most active natural activator of Nrf2. Fermented vegetables contain many lactobacilli, which are also potent Nrf2 activators. Three examples are: kimchi in Korea, westernized foods, and the slum paradox. It is proposed that fermented cabbage is a proof-of-concept of dietary manipulations that may enhance Nrf2-associated antioxidant effects, helpful in mitigating COVID-19 severity.Peer reviewe

Nrf2-interacting nutrients and COVID-19 : time for research to develop adaptation strategies

There are large between- and within-country variations in COVID-19 death rates. Some very low death rate settings such as Eastern Asia, Central Europe, the Balkans and Africa have a common feature of eating large quantities of fermented foods whose intake is associated with the activation of the Nrf2 (Nuclear factor (erythroid-derived 2)-like 2) anti-oxidant transcription factor. There are many Nrf2-interacting nutrients (berberine, curcumin, epigallocatechin gallate, genistein, quercetin, resveratrol, sulforaphane) that all act similarly to reduce insulin resistance, endothelial damage, lung injury and cytokine storm. They also act on the same mechanisms (mTOR: Mammalian target of rapamycin, PPAR gamma:Peroxisome proliferator-activated receptor, NF kappa B: Nuclear factor kappa B, ERK: Extracellular signal-regulated kinases and eIF2 alpha:Elongation initiation factor 2 alpha). They may as a result be important in mitigating the severity of COVID-19, acting through the endoplasmic reticulum stress or ACE-Angiotensin-II-AT(1)R axis (AT(1)R) pathway. Many Nrf2-interacting nutrients are also interacting with TRPA1 and/or TRPV1. Interestingly, geographical areas with very low COVID-19 mortality are those with the lowest prevalence of obesity (Sub-Saharan Africa and Asia). It is tempting to propose that Nrf2-interacting foods and nutrients can re-balance insulin resistance and have a significant effect on COVID-19 severity. It is therefore possible that the intake of these foods may restore an optimal natural balance for the Nrf2 pathway and may be of interest in the mitigation of COVID-19 severity

The Direct Actions of GABA, 2'-Methoxy-6-Methylflavone and General Anaesthetics at β3γ2L GABAA Receptors: Evidence for Receptors with Different Subunit Stoichiometries.

2'-Methoxy-6-methylflavone (2'MeO6MF) is an anxiolytic flavonoid which has been shown to display GABAA receptor (GABAAR) β2/3-subunit selectivity, a pharmacological profile similar to that of the general anaesthetic etomidate. Electrophysiological studies suggest that the full agonist action of 2'MeO6MF at α2β3γ2L GABAARs may mediate the flavonoid's in vivo effects. However, we found variations in the relative efficacy of 2'MeO6MF (2'MeO6MF-elicited current responses normalised to the maximal GABA response) at α2β3γ2L GABAARs due to the presence of mixed receptor populations. To understand which receptor subpopulation(s) underlie the variations observed, we conducted a systematic investigation of 2'MeO6MF activity at all receptor combinations that could theoretically form (α2, β3, γ2L, α2β3, α2γ2L, β3γ2L and α2β3γ2L) in Xenopus oocytes using the two-electrode voltage clamp technique. We found that 2'MeO6MF activated non-α-containing β3γ2L receptors. In an attempt to establish the optimal conditions to express a uniform population of these receptors, we found that varying the relative amounts of β3:γ2L subunit mRNAs resulted in differences in the level of constitutive activity, the GABA concentration-response relationships, and the relative efficacy of 2'MeO6MF activation. Like 2'MeO6MF, general anaesthetics such as etomidate and propofol also showed distinct levels of relative efficacy across different injection ratios. Based on these results, we infer that β3γ2L receptors may form with different subunit stoichiometries, resulting in the complex pharmacology observed across different injection ratios. Moreover, the discovery that GABA and etomidate have direct actions at the α-lacking β3γ2L receptors raises questions about the structural requirements for their respective binding sites at GABAARs

The Direct Actions of GABA, 2'-Methoxy-6-Methylflavone and General Anaesthetics at β3γ2L GABAA Receptors: Evidence for Receptors with Different Subunit Stoichiometries.

2'-Methoxy-6-methylflavone (2'MeO6MF) is an anxiolytic flavonoid which has been shown to display GABAA receptor (GABAAR) β2/3-subunit selectivity, a pharmacological profile similar to that of the general anaesthetic etomidate. Electrophysiological studies suggest that the full agonist action of 2'MeO6MF at α2β3γ2L GABAARs may mediate the flavonoid's in vivo effects. However, we found variations in the relative efficacy of 2'MeO6MF (2'MeO6MF-elicited current responses normalised to the maximal GABA response) at α2β3γ2L GABAARs due to the presence of mixed receptor populations. To understand which receptor subpopulation(s) underlie the variations observed, we conducted a systematic investigation of 2'MeO6MF activity at all receptor combinations that could theoretically form (α2, β3, γ2L, α2β3, α2γ2L, β3γ2L and α2β3γ2L) in Xenopus oocytes using the two-electrode voltage clamp technique. We found that 2'MeO6MF activated non-α-containing β3γ2L receptors. In an attempt to establish the optimal conditions to express a uniform population of these receptors, we found that varying the relative amounts of β3:γ2L subunit mRNAs resulted in differences in the level of constitutive activity, the GABA concentration-response relationships, and the relative efficacy of 2'MeO6MF activation. Like 2'MeO6MF, general anaesthetics such as etomidate and propofol also showed distinct levels of relative efficacy across different injection ratios. Based on these results, we infer that β3γ2L receptors may form with different subunit stoichiometries, resulting in the complex pharmacology observed across different injection ratios. Moreover, the discovery that GABA and etomidate have direct actions at the α-lacking β3γ2L receptors raises questions about the structural requirements for their respective binding sites at GABAARs

Propofol activates β3γ2L (1:15) and (1:100) receptors with different relative efficacies.

<p>(A) Representative traces of propofol (1–300 μM) direct activation in comparison to 3 mM GABA at β3γ2L (1:15) and (1:100) GABA_ARs. (B) Concentration-response curves of propofol activation at β3γ2L receptors expressed at 1:15 (<i>n</i> = 4) and 1:100 (<i>n</i> = 4) ratios. Data are normalised to the 3 mM GABA response.</p

Characteristics of receptors expressed in various combinations of α2, β3 and γ2L GABA_AR subunits.

<p>^<i>a</i> Expression level is expressed as the current responses ± SEM (nA) elicited by 3 mM GABA, except for homomeric and α2γ2L receptors (60 mM GABA).</p><p>Characteristics of receptors expressed in various combinations of α2, β3 and γ2L GABA_AR subunits.</p

Characterisation of β3γ2L GABA_ARs expressed at 1:15, 1:50 and 1:100 ratios.

<p>The level of constitutive activity is indicated by (A) holding current of injected oocytes and (B) the inhibition of baseline current by 100 μM Zn²⁺. (A) β3γ2L GABA_ARs expressed at 1:15 ratio showed significantly larger holding current (-260 ± 40 nA; <i>n</i> = 30) than at 1:50 (-28 ± 6.0 nA; <i>n</i> = 15) and 1:100 (-15 ± 5.0 nA; <i>n</i> = 21) ratios (<i>p</i> ≤ 0.001; Tukey’s test). (B<b>)</b> Representative traces demonstrating current responses of 3 mM GABA, 100 μM 2’MeO6MF and 100 μM Zn²⁺. At 1:15 ratio, receptors were sensitive to the inhibition of 100 μM Zn²⁺ (reduction in inward current; <i>n</i> = 10). Zn²⁺ did not have any effects at 1:50 (<i>n</i> = 7) and 1:100 (<i>n</i> = 8) ratios. (C) Representative traces demonstrating 2’MeO6MF’s direct activation from 1 to 300 μM in comparison to 3 mM GABA response. (D) 2’MeO6MF concentration-response curves of β3γ2L (1:15; <i>n</i> = 8), (1:50; <i>n</i> = 7) and (1:100; <i>n</i> = 6) GABA_ARs. Data are normalised to the 3 mM GABA response. (E) Representative traces of GABA current responses from 1 μM to 30 mM at β3γ2L (1:15), (1:50) and (1:100) GABA_ARs. (F) GABA concentration-response curves of β3γ2L (1:15; <i>n</i> = 6), (1:50; <i>n</i> = 8) and (1:100; <i>n</i> = 9) GABA_ARs. Data are presented as mean ± SEM. Bars indicate durations of drug application. The holding current values are represented by the dotted lines.</p