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Inflammation and Metabolism

Inflammation is an integral component of the normal immune response that occurs when cells encounter harmful stimuli, such as invading pathogens, damaged cells, or irritants. During inflammation, cells activate inflammatory processes and complexes that increase the production of cytokines—proteins that recruit and activate immune cells.

Inflammation and mitochondrial metabolism are closely associated. The mitochondria are often called the “powerhouses” of the cell as they produce the energy that the cell needs to function. This energy is produced by converting fatty acids and glucose into adenosine triphosphate (ATP) by a process called oxidative phosphorylation. During inflammation, mitochondrial metabolism is temporarily reprogrammed to suppress oxidative phosphorylation.1,2 Instead of making ATP, fatty acids and glucose are diverted to increase the production of proinflammatory mediators.3 Because oxidative phosphorylation is suppressed, the mitochondria release chemically-reactive molecules called “reactive oxygen species,” or ROS, which can directly attack harmful stimuli and amplify the production of cytokines.4

Resolution of Inflammation

In the normal immune response, the resolution phase of inflammation begins after the harmful stimuli have been eliminated. During this phase, cytokine production is turned off, ROS are neutralized, and mitochondrial metabolism returns to its normal state.

However, in many chronic and genetic diseases, the resolution phase of inflammation fails to occur or is inadequate, leading to the persistent production of cytokines, ROS, and mitochondrial dysfunction. These processes cause chronic inflammation, which can ultimately lead to tissue damage and loss of organ function.5

Nrf2 Activators

Nrf2 is a protein that plays a key role in the resolution phase of inflammation by regulating the expression of specific genes that are involved in mitochondrial metabolism, redox balance, and cytokine production.6 In chronic disease, the activity of Nrf2 is often inadequate, which renders the cell unable to turn off the processes that lead to chronic inflammation.7-9

Our two lead product candidates, bardoxolone methyl and omaveloxolone, are Nrf2 activators that promote the resolution of inflammation. Bardoxolone methyl and omaveloxolone selectively bind to Keap1, a protein that governs the activity of Nrf2 in response to cellular stress. By binding to Keap1, bardoxolone methyl and omaveloxolone stabilize Nrf2 and increase its activity.

When activated, Nrf2 promotes the resolution of inflammation by:

  1. Normalizing mitochondrial metabolism
    Nrf2 activation can normalize mitochondrial metabolism and increase ATP production by increasing the availability of NADH and FADH2 – two important mitochondrial molecules required for efficient oxidative phosphorylation; promoting glucose uptake and fatty acid oxidation, and increasing factors that control mitochondrial biogenesis.10

    Mitochondria can reprogram their metabolism according to the energetic demands placed on the cell. Once the demand is met, metabolism shifts back to its normal state. Mitochondrial dysfunction, a key feature of a variety of diseases, occurs when metabolism does not return to its normal state and leads to the persistent production of ROS and other inflammatory mediators. Nrf2 activation can potentially normalize mitochondrial function in several ways:

    • Nrf2 increases the availability of NADH and FADH2, two molecules that are necessary for efficient oxidative phosphorylation and ATP production. NADH and FADH2 are called “reducing equivalents,” as mitochondria can harness their “reducing” power to make the process of oxidative phosphorylation efficient. The management of these reducing equivalents is a constant and critical balancing act within the mitochondria10
    • Nrf2 ensures the efficient consumption of fats and sugars as fuel sources for ATP production. Nrf2 promotes the transport of fatty acids to the mitochondria and promotes the transport of glucose from the bloodstream into cells11,12
    • Nrf2 may also be involved in mitochondrial biogenesis. PGC1α is a protein that increases the number of mitochondria in a cell. Activation of Nrf2 has been shown to increase PGC1α expression in skeletal muscle, which may increase ATP production13
    • Nrf2 activation may improve the efficiency of oxidative phosphorylation by preventing mitochondrial DNA damage caused by ROS. Nrf2 increases the antioxidant capacity of the cell14

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  2. Restoring redox balance
    Nrf2 increases the expression of antioxidant enzymes and systems that work together to reduce the levels of ROS and restore redox balance.
    Redox balance is altered when mitochondria reprogram their metabolism to increase ROS production and amplify the inflammatory response. ROS (eg, hydrogen peroxide and superoxide) are chemically-reactive molecules that increase inflammatory signaling by activating NF-κB and the NLRP3 inflammasome. ROS production is a critical component of the normal inflammatory response as it enables affected cells to kill harmful stimuli. However, when not carefully regulated, ROS can injure normal healthy tissue. Excessive ROS, as seen in chronic inflammation, can cause cellular damage in critical organs including muscle, lung, heart, liver, brain, and the eyes.4

    Nrf2 restores redox balance and lowers ROS levels by increasing the transcription of many genes, including those that encode components of the glutathione and thioredoxin systems, antioxidant enzymes, and proteins that regulate iron metabolism.15,16

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  3. Suppressing cytokine production
    In addition to suppressing inflammation by normalizing mitochondrial metabolism and restoring redox balance, Nrf2 directly suppresses the expression of proinflammatory cytokine genes by binding to their promoters and inhibiting transcription.
    Nrf2 activity reduces inflammation and suppresses the production of many proinflammatory mediators including nitric oxide (NO), TNF-α, MCP-1 (CCL2), IL-1β, IL-6, and RANTES (CCL5) in vitro and in preclinical models of disease.17-19 Nrf2 has been shown to directly suppress the transcription of many proinflammatory genes.20 In addition, Nrf2 indirectly inhibits inflammation by reducing ROS and normalizing mitochondrial function, resulting in the suppression of NF-κB and NLRP3 inflammasome signaling.
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Bardoxolone methyl and omaveloxolone have been extensively studied by many investigators. Their cytoprotective and therapeutic effects have been observed in many preclinical models and associated with meaningful improvements in disease symptoms, such as inflammation, tissue remodeling, and fibrosis.

Nrf2 activators have been shown to improve disease symptoms and reduce inflammation and fibrosis in several disease models, including:

  • Chronic kidney disease21-26
  • Acute kidney injury27,28
  • Pulmonary inflammation and fibrosis19,29-32
  • Maladaptive cardiac remodeling33,34
  • Friedreich’s ataxia35

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References
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  17. Probst BL, Trevino I, McCauley L, et al. RTA 408, a novel synthetic triterpenoid with broad anticancer and anti-inflammatory activity. PLoS One. 2015;10(4):e0122942.
  18. Dinkova-Kostova AT, Liby KT, Stephenson KK, et al. Extremely potent triterpenoid inducers of the phase 2 response: correlations of protection against oxidant and inflammatory stress. Proc Natl Acad Sci U S A. 2005;102(12):4584-4589.
  19. Thimmulappa RK, Scollick C, Traore K, et al. Nrf2-dependent protection from LPS induced inflammatory response and mortality by CDDO-imidazolide. Biochem Biophys Res Commun. 2006;351(4):883-889.
  20. Kobayashi EH, Suzuki T, Funayama R, et al. Nrf2 suppresses macrophage inflammatory response by blocking proinflammatory cytokine transcription. Nat Commun. 2016;7:11624.
  21. Chin M, Lee CY, Chuang JC, et al. Bardoxolone methyl analogs RTA 405 and dh404 are well tolerated and exhibit efficacy in rodent models of type 2 diabetes and obesity. Am J Physiol Renal Physiol. 2013;304(12):F1438-F1446.
  22. Tan SM, Sharma A, Stefanovic N, et al. Derivative of bardoxolone methyl, dh404, in an inverse dose-dependent manner lessens diabetes-associated atherosclerosis and improves diabetic kidney disease. Diabetes. 2014;63(9):3091-3103.
  23. Camer D, Yu Y, Szabo A, Wang H, Dinh CH, Huang XF. Bardoxolone methyl prevents the development and progression of cardiac and renal pathophysiologies in mice fed a high-fat diet. Chem Biol Interact. 2016;243:10-18.
  24. Hisamichi M, Kamijo-Ikemori A, Sugaya T, Hoshino S, Kimura K, Shibagaki Y. Role of bardoxolone methyl, a nuclear factor erythroid 2-related factor 2 activator, in aldosterone- and salt-induced renal injury. Hypertens Res. 2018;41(1)8-17.
  25. Aminzadeh MA, Resiman SA, Vaziri ND, Khazaeli M, Yuan J, Meyer CJ. The synthetic triterpenoid RTA dh404 (CDDO-dhTFEA) restores Nrf2 activity and attenuates oxidative stress, inflammation, and fibrosis in rats with chronic kidney disease. Xenobiotica. 2014;44(6):570-578.
  26. Wu T, Ye Y, Min SY, et al. Prevention of murine lupus nephritis by targeting multiple signaling axes and oxidative stress using a synthetic triterpenoid. Arthritis Rheumatol. 2014;66(11):3129-3139.
  27. Liu M, Reddy NM, Higbee EM, et al. The Nrf2 triterpenoid activator, CDDO-imidazolide, protects kidneys from ischemia-reperfusion injury in mice. Kidney Int. 2014;85(1):134-141.
  28. Kocak C, Kocak FE, Akcilar R, et al. Effects of captopril, telmisartan and bardoxolone methyl (CDDO-Me) in ischemia-reperfusion-induced acute kidney injury in rats: an experimental comparative study. Clin Exp Pharmacol Physiol. 2016;43(2):230-241.
  29. Uchida M, Anderson EL, Squillace DL, et al. Oxidative stress serves as a key checkpoint for IL-33 release by airway epithelium. Allergy. 2017;72(10):1521-1531.
  30. Wang YY, Zhang CY, Ma YQ, He ZX, Zhe H, Zhou SF. Therapeutic effects of C-28 methyl ester of 2-cyano-3,12-dioxoolean-1,9-dien-28-oic acid (CDDO-Me; bardoxolone methyl) on radiation-induced lung inflammation and fibrosis in mice. Drug Des Devel Ther. 2015;9:3163-3178.
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  32. Kulkarni AA, Thatcher TH, Hsiao HM, et al. The triterpenoid CDDO-Me inhibits bleomycin-induced lung inflammation and fibrosis. PLoS One. 2013;8(5):e63798.
  33. Bubb KJ, Kok C, Tang O, et al. The NRF2 activator DH404 attenuates adverse ventricular remodeling post-myocardial infarction by modifying redox signaling. Free Radic Biol Med. 2017;108:585-594.
  34. Xing Y, Niu T, Wang W, et al. Triterpenoid dihydro-CDDO-trifluoroethyl amide protects against maladaptive cardiac remodeling and dysfunction in mice: a critical role of Nrf2. PLoS One. 2012;7(9):e44899.
  35. Abeti R, Baccaro A, Esteras N, Giunti P. Novel Nrf2-inducer prevents mitochondrial defects and oxidative stress in Friedreich’s ataxia models. Front Cell Neurosci. 2018;12:188.
View References
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