A TNF inhibitor is a pharmaceutical drug that suppresses response to tumor necrosis factor (TNF), which is part of the inflammatory response. TNF is involved in clinical problems associated with autoimmune disorders such as rheumatoid arthritis, ankylosing spondylitis, Crohn's disease, psoriasis, hidradenitis suppurativa and refractory asthma, so a TNF inhibitor may be used in their treatment. The important side effects that have been most extensively related to TNF inhibitors include: lymphoma, infections (especially - Tuberculosis reactivation), congestive heart failure, demyelinating disease, a lupus-like syndrome, induction of auto-antibodies, injection site reactions, and systemic side effects.
History of anti-TNF treatments
Early experiments associated TNF function with the pathogenesis of bacterial sepsis, thus the first preclinical studies using anti-TNF antibodies were performed in animal models of sepsis  and showed that anti-TNF antibodies protected mice from sepsis. However, subsequent clinical trials in sepsis patients showed no significant benefit upon anti-TNF treatment. It wasn't until 1991 that studies in more physiological animal models of TNF overexpression, namely the human TNF transgenic mouse model, provided the pre-clinical rational for a unique role of TNF in the development of polyarthritis and that anti-TNF treatments could be effective against human arthritides. This was later confirmed in clinical trials  and led to the development of the highly successful first biological therapies for RA.
This inhibition can be achieved with a monoclonal antibody such as infliximab (Remicade), adalimumab (Humira), certolizumab pegol (Cimzia), and golimumab (Simponi), or with a circulating receptor fusion protein such as etanercept (Enbrel).
While most clinically useful TNF inhibitors are monoclonal antibodies, some are simple molecules such as xanthine derivatives (e.g. pentoxifylline) and Bupropion. Bupropion is the active ingredient in the smoking cessation aid Zyban and the antidepressant Wellbutrin.
Several 5-HT2A agonist hallucinogens including (R)-DOI, TCB-2, LSD and LA-SS-Az have unexpectedly also been found to act as potent inhibitors of TNF, with DOI being the most active, showing TNF inhibition in the picomolar range, an order of magnitude more potent than its action as a hallucinogen.
Clinical application of anti-TNF drugs in rheumatoid arthritis was demonstrated by Marc Feldmann and Ravinder N. Maini, who won the 2003 Lasker Award for their work. Anti-TNF compounds help eliminate abnormal B cell activity.
The FDA continues to receive reports of a rare cancer of white blood cells (known as Hepatosplenic T-Cell Lymphoma or HSTCL), primarily in adolescents and young adults being treated for Crohn’s disease and ulcerative colitis with medicines known as tumor necrosis factors (TNF) blockers, as well as with azathioprine, and/or mercaptopurine.
Starting TNF inhibition puts patients at increased risk of opportunistic infections. FDA has warned about the risk of infection from two bacterial pathogens, Legionella and Listeria. People taking TNF blockers are at increased risk for developing serious infections that may lead to hospitalization or death due to bacterial, mycobacterial, fungal, viral, parasitic, and other opportunistic pathogens.
In patients with latent Mycobacterium tuberculosis infection, active tuberculosis (TB) may develop soon after the initiation of treatment with infliximab. Before prescribing the drug, physicians should screen patients for latent TB infection or disease. The anti-TNF monoclonal antibody biologics, Infliximab and adalimumab, and the fusion protein etanercept which are all currently approved by the U.S. Food and Drug Administration (FDA) for human use, have label warnings which state that patients should be evaluated for latent TB infection and treatment should be initiated prior to starting therapy with these medications.
The U.S. Food and Drug Administration (FDA) issued a warning on September 4, 2008, that patients on TNF inhibitors are at increased risk of opportunistic fungal infections, such as pulmonary and disseminated histoplasmosis, coccidioidomycosis, and blastomycosis. They encourage clinicians to consider empiric antifungal therapy in all patients at risk until the pathogen is identified.
Anti-TNF agents in nature
TNF or the effects of TNF are also inhibited by a number of natural compounds, including curcumin (a compound present in turmeric), and catechins (in green tea). Also activation of cannabinoid CB1 or CB2 receptors by cannabis or Echinacea purpurea seem to have anti-inflammatory properties through TNF inhibition.
- Scheinfeld N (September 2004). "A comprehensive review and evaluation of the side effects of the tumor necrosis factor blockers etanercept, infliximab and adalimumab". J Dermatolog Treat 15 (5): 280–94. doi:10.1080/09546630410017275. PMID 15370396.
- Pappas DA, Bathon JM, Hanicq D, Yasothan U, Kirkpatrick P (September 2009). "Golimumab". Nat Rev Drug Discov 8 (9): 695–6. doi:10.1038/nrd2982. PMID 19721444.
- Beutler B, Milsark IW, Cerami AC (August 1985). "Passive immunization against cachectin/tumor necrosis factor protects mice from lethal effect of endotoxin.". Science 229 (4716): 869–71. PMID 3895437.
- Keffer J, Probert L, Cazlaris H, Georgopoulos S, Kaslaris E, Kioussis D, Kollias G (December 1991). "Transgenic mice expressing human tumour necrosis factor: a predictive genetic model of arthritis.". EMBO J. 10 (13): 4025–31. PMID 1721867.
- Elliott MJ, Maini RN, Feldmann M, Kalden JR, Antoni C, Smolen JS, Leeb B, Breedveld FC, Macfarlane JD, Bijl H, et al. (October 1994). "Randomised double-blind comparison of chimeric monoclonal antibody to tumour necrosis factor alpha (cA2) versus placebo in rheumatoid arthritis.". Lancet. 344 (8930): 1105–10. PMID 7934491.
- doi: 10.1124/jpet.301.2.418 JPET May 1, 2002 vol. 301 no. 2 418-426
- Essayan DM (November 2001). "Cyclic nucleotide phosphodiesterases". J. Allergy Clin. Immunol. 108 (5): 671–80. doi:10.1067/mai.2001.119555. PMID 11692087.
- Marques LJ, Zheng L, Poulakis N, Guzman J, Costabel U (February 1999). "Pentoxifylline inhibits TNF-alpha production from human alveolar macrophages". Am. J. Respir. Crit. Care Med. 159 (2): 508–11. PMID 9927365.
- Brustolim D, Ribeiro-dos-Santos R, Kast RE, Altschuler EL, Soares MB (June 2006). "A new chapter opens in anti-inflammatory treatments: the antidepressant bupropion lowers production of tumor necrosis factor-alpha and interferon-gamma in mice". Int. Immunopharmacol. 6 (6): 903–7. doi:10.1016/j.intimp.2005.12.007. PMID 16644475.
- Miller KJ, Gonzalez HA (December 1998). "Serotonin 5-HT2A receptor activation inhibits cytokine-stimulated inducible nitric oxide synthase in C6 glioma cells". Ann. N. Y. Acad. Sci. 861: 169–73. Bibcode:1998NYASA.861..169M. doi:10.1111/j.1749-6632.1998.tb10188.x. PMID 9928254.
- Yu B, Becnel J, Zerfaoui M, Rohatgi R, Boulares AH, Nichols CD (November 2008). "Serotonin 5-hydroxytryptamine(2A) receptor activation suppresses tumor necrosis factor-alpha-induced inflammation with extraordinary potency". J. Pharmacol. Exp. Ther. 327 (2): 316–23. doi:10.1124/jpet.108.143461. PMID 18708586.
- Pelletier M, Siegel RM (December 2009). "Wishing away inflammation? New links between serotonin and TNF signaling". Mol. Interv. 9 (6): 299–301. doi:10.1124/mi.9.6.5. PMC 2861806. PMID 20048135.
- Keffer J, Probert L, Cazlaris H, Georgopoulos S, Kaslaris E, Kioussis D, Kollias G (December 1991). "Transgenic mice expressing human tumour necrosis factor: a predictive genetic model of arthritis". The EMBO Journal 10 (13): 4025–31. PMC 453150. PMID 1721867.
- Feldmann M, Maini RN (October 2003). "Lasker Clinical Medical Research Award. TNF defined as a therapeutic target for rheumatoid arthritis and other autoimmune diseases". Nat. Med. 9 (10): 1245–50. doi:10.1038/nm939. PMID 14520364.
- Anolik JH, Ravikumar R, Barnard J, Owen T, Almudevar A, Milner EC, Miller CH, Dutcher PO, Hadley JA, Sanz I (January 2008). "Cutting edge: anti-tumor necrosis factor therapy in rheumatoid arthritis inhibits memory B lymphocytes via effects on lymphoid germinal centers and follicular dendritic cell networks". J. Immunol. 180 (2): 688–92. PMID 18178805.
- A new view of drugs used to treat rheumatoid arthritis
- Haslund P, Lee RA, Jemec GB (November 2009). "Treatment of hidradenitis suppurativa with tumour necrosis factor-alpha inhibitors". Acta Derm. Venereol. 89 (6): 595–600. doi:10.2340/00015555-0747. PMID 19997689.
- Keane J, Gershon S, Wise RP, Mirabile-Levens E, Kasznica J, Schwieterman WD, Siegel JN, Braun MM (October 2001). "Tuberculosis associated with infliximab, a tumor necrosis factor alpha-neutralizing agent". N. Engl. J. Med. 345 (15): 1098–104. doi:10.1056/NEJMoa011110. PMID 11596589.
- "FDA: Manufacturers of TNF-Blocker Drugs Must Highlight Risk of Fungal Infections" (Press release). U.S. Food and Drug Administration (FDA). September 4, 2008. Retrieved 2009-11-15.
- Siddiqui AM, Cui X, Wu R, Dong W, Zhou M, Hu M, Simms HH, Wang P (July 2006). "The anti-inflammatory effect of curcumin in an experimental model of sepsis is mediated by up-regulation of peroxisome proliferator-activated receptor-gamma". Crit. Care Med. 34 (7): 1874–82. doi:10.1097/01.CCM.0000221921.71300.BF. PMID 16715036.
- Okunieff P, Xu J, Hu D, Liu W, Zhang L, Morrow G, Pentland A, Ryan JL, Ding I (July 2006). "Curcumin protects against radiation-induced acute and chronic cutaneous toxicity in mice and decreases mRNA expression of inflammatory and fibrogenic cytokines". Int. J. Radiat. Oncol. Biol. Phys. 65 (3): 890–8. doi:10.1016/j.ijrobp.2006.03.025. PMID 16751071.
- Gulcubuk A, Altunatmaz K, Sonmez K, Haktanir-Yatkin D, Uzun H, Gurel A, Aydin S (February 2006). "Effects of curcumin on tumour necrosis factor-alpha and interleukin-6 in the late phase of experimental acute pancreatitis". J Vet Med a Physiol Pathol Clin Med 53 (1): 49–54. doi:10.1111/j.1439-0442.2006.00786.x. PMID 16411910.
- Lantz RC, Chen GJ, Solyom AM, Jolad SD, Timmermann BN (June 2005). "The effect of turmeric extracts on inflammatory mediator production". Phytomedicine 12 (6–7): 445–52. doi:10.1016/j.phymed.2003.12.011. PMID 16008121.
- Raduner S, Majewska A, Chen JZ, Xie XQ, Hamon J, Faller B, Altmann KH, Gertsch J (May 2006). "Alkylamides from Echinacea are a new class of cannabinomimetics. Cannabinoid type 2 receptor-dependent and -independent immunomodulatory effects". J. Biol. Chem. 281 (20): 14192–206. doi:10.1074/jbc.M601074200. PMID 16547349.