How does iron overload increase the risk of infection?

Iron overload, either primary (eg, hereditary hemochromatosis) or secondary (eg, hemolysis/frequent transfusion states), may increase the risk of infections through at least 2 mechanisms: 1. Enhancement of the virulence of the pathogen; and 2. Interference with the body’s normal defense system.1-7

Excess iron has been reported to enhance the growth of numerous organisms, ranging from bacteria (eg, Yersinia, Shigella, Vibrio, Listeria, Legionella, Ehrlichia, many other Gram-negative bacteria, staphylococci, streptococci), mycobacteria, fungi (eg, Aspergillus, Rhizopus/Mucor, Cryptococcus, Pneumocystis), protozoa (eg, Entamaeba, Plasmodium, Toxoplasma) and viruses (HIV, hepatitis B/C, cytomegalovirus, parvovirus). 1-7

In addition to enhancing the growth of many pathogens, excess iron may also inhibit macrophage and lymphocyte function and neutrophil chemotaxis .1,2 Iron loading of macrophages results in the inhibition of interferon-gamma mediated pathways and loss of their ability to kill intracellular pathogens such as Legionella, Listeria and Ehrlichia. 2

Not surprisingly, there are numerous reports in the literature of infections in hemochromatosis, including Listeria monocytogenes meningitis, E. Coli septic shock, Yersinia enterocolitica sepsis/liver abscess, Vibrio vulnificus shock (attributed to ingestion of raw oysters) and mucormycosis causing periorbital cellulitis. 2

Bonus pearl: Did you know that the ascitic fluid of patients with cirrhosis has low transferrin levels compared to those with malignancy, potentially enhancing bacterial growth and increasing their susceptibility to spontaneous bacterial peritonitis? 8

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 References

  1. Weinberg ED, Weinberg GA. The role of iron in infection. Curr Opin Infect Dis 1995;8:164-69. https://journals.lww.com/co-infectiousdiseases/abstract/1995/06000/the_role_of_iron_in_infection.4.aspx
  2. Khan FA, Fisher MA, Khakoo RA. Association of hemochromatosis with infectious diseases: expanding spectrum. Intern J Infect Dis 2007;11:482-87. https://www.sciencedirect.com/science/article/pii/S1201971207000811
  3. Thwaites PA, Woods ML. Sepsis and siderosis, Yersinia enterocolitica and hereditary haemochromatosis. BMJ Case Rep 2017. Doi:10.11336/bvr-206-218185. https://casereports.bmj.com/content/2017/bcr-2016-218185
  4. Weinberg ED. Iron loading and disease surveillance. Emerg Infect Dis 1999;5:346-52. https://wwwnc.cdc.gov/eid/article/5/3/99-0305-t3
  5. Matthaiou EI, Sass G, Stevens DA, et al. Iron: an essential nutrient for Aspergillus fumigatus and a fulcrum for pathogenesis. Curr Opin Infect Dis 2018;31:506-11. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6579532/
  6. Alexander J, Limaye AP, Ko CW, et al. Association of hepatic iron overload with invasive fungal infection in liver transplant recipients. Liver Transpl 12:1799-1804. https://aasldpubs.onlinelibrary.wiley.com/doi/full/10.1002/lt.20827
  7. Schmidt SM. The role of iron in viral infections. Front Biosci (Landmark Ed) 2020;25:893-911. https://pubmed.ncbi.nlm.nih.gov/31585922/
  8. Romero A, Perez-Aurellao JL, Gonzalez-Villaron L et al. Effect of transferrin concentration on bacterial growth in human ascetic fluid from cirrhotic and neoplastic patients. J Clin Invest 1993;23:699-705. https://onlinelibrary.wiley.com/doi/epdf/10.1111/j.1365-2362.1993.tb01289.x

Disclosures: The listed questions and answers are solely the responsibility of the author and do not necessarily represent the official views of Massachusetts General Hospital, Harvard Catalyst, Harvard University, its affiliate academic healthcare centers, or its contributors. Although every effort has been made to provide accurate information, the author is far from being perfect. The reader is urged to verify the content of the material with other sources as deemed appropriate and exercise clinical judgment in the interpretation and application of the information provided herein. No responsibility for an adverse outcome or guarantees for a favorable clinical result is assumed by the author. Thank you!

How does iron overload increase the risk of infection?

Do statins have a role in treating novel Coronavirus infection, COVID-19?

There is currently no firm clinical evidence that statins improve the outcome of COVID-19. However, there are some theoretical reasons for believing that statins may have a role in the treatment of COVID-19.  That’s because beyond their cholesterol lowering action, statins may also have clinically relevant anti-inflammatory and antiviral (pleotropic) properties.  

Anti-inflammatory: Anti-inflammatory effect of statins is well known and is thought to occur through a variety of molecular pathways of the innate and adaptive immune systems as well as attenuation of several circulating proinflammatory cytokines.1 Although observational studies have suggested that statins lower hospitalization and mortality among outpatients hospitalized with infection, pneumonia or sepsis, several randomized controlled trials (RCTs) have failed to show any mortality benefit among ICU patients with sepsis and ARDS treated with statins.2

In contrast, an RCT involving patients with sepsis (majority with pneumonia, mean CRP 195 mg/dL) reported significant reduction in progression to severe sepsis among statin-naïve patients  placed on atorvastatin 40 mg/day at the time of hospitalization.3 So, perhaps timing of statin therapy before florid sepsis and ARDS is an important factor.  

Some have suggested that statins may decrease the fatality rate of a related Coronavirus, Middle East Respiratory Syndrome (MERS) virus, by blunting exuberant inflammatory response that may result in a fatal outcome. 4

Antiviral: Statins may also have antiviral properties, including activity against influenza, hepatitis C virus, Zika and dengue viruses.2,5 Whether statins have activity against coronaviruses such as the agent of COVID-19 is unclear at this time.

It’s interesting to note that cholesterol may have an important role in the membrane attachment, fusion and replication of many enveloped viruses, including influenza.5 Covid-19 is also an enveloped virus.

So what do we do? Based on the current data, it makes sense to continue statins in patients who have known clinical indications for their use and no obvious contraindications because of COVID-19 (eg. rhabdomyolysis).6 As for statin-naïve patients, particularly those in early stages of sepsis and increased risk of cardiovascular events, benefit may outweigh the risk.  Only proper clinical studies will give us more definitive answers.

Bonus Pearl: Did you know that lipids make up a major component of the envelope in enveloped viruses and that cholesterol makes up nearly one-half of total lipid and over 10% the total mass of influenza viruses?

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References

  1. Tousoulis D, Psarros C, Demosthenous M, et al. Innate and adaptive inflammation as a therapeutic target in vascular diseae: The emerging role of statins. J Am Coll Cardiol 2014;63:2491-2502. https://www.sciencedirect.com/science/article/pii/S0735109714011553?via%3Dihub
  2. Fedson DS. Treating the host response to emerging virus diseases: lessons learned from sepsis, pneumonia, influenza and Ebola. Ann Transl Med 2016;4:421. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5124618/pdf/atm-04-21-421.pdf
  3. Patel JM, Snaith C, Thickette DR. Randomized double-blind placebo-controlled trial of 40 mg/day of atorvastatin in reducing the severity of sepsis in ward patients (ASEPSIS Trial) Critical Care 2012;16:R231. https://ccforum.biomedcentral.com/track/pdf/10.1186/cc11895
  4. Espano E, Nam JH, Song EJ, et al. Lipophilic statins inhibit Zika virus production in Vero cells. Scientific Reports 2019;9:11461. https://www.nature.com/articles/s41598-019-47956-1
  5. Sun X, Whittaker GR. Role for influenza virus envelope cholesterol in virus entry and infection. J Virol 2003;77:12543-12551. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC262566/
  6. Virani SS. Is there a role for statin therapy in acute viral infections. Am Coll Cardiol March 18, 2020. https://www.acc.org/latest-in-cardiology/articles/2020/03/18/15/09/is-there-a-role-for-statin-therapy-in-acute-viral-infections-covid-19

Disclosures: The listed questions and answers are solely the responsibility of the author and do not necessarily represent the official views of Massachusetts General Hospital, Harvard Catalyst, Harvard University, its affiliate academic healthcare centers, or its contributors. Although every effort has been made to provide accurate information, the author is far from being perfect. The reader is urged to verify the content of the material with other sources as deemed appropriate and exercise clinical judgment in the interpretation and application of the information provided herein. No responsibility for an adverse outcome or guarantees for a favorable clinical result is assumed by the author. Thank you!

Do statins have a role in treating novel Coronavirus infection, COVID-19?