smoking good?... or smoking bad?

The relationship between smoking and the form of IBD that was manifested in siblings with a genetic predisposition was determined and explained in the article entitled “In siblings with similar genetic susceptibility for inflammatory bowel disease, smokers tend to develop Crohn’s Disease and non-smokers develop ulcerative colitis” by S Bridger, J C W Lee, I Bjarnason, J E Lennard Jones, and A J Macpherson. It was found that CD was more commonly developed in the siblings that smoke, especially in women. Furthermore, it was also determined that the smokers in the study had less of a chance of developing UC. I found this article interesting because it shows an extreme link between “tobacco usage inhibiting UC and enhancing CD pathogenic mechanisms.” It was also stated that “the influences of tobacco on disease pathogenesis are on the immunopathogenic mechanisms at disease onset as opposed to cumulative damage” due to the fact that the manifestation was effectively reversed when the subjects were no longer smoking for a year. Also, it was discussed that there are many diseases that are associated with tobacco smoke, however the mechanisms are not known. It is known that smoking has “multiple effects on many immune and inflammatory functions.” The need for further studies such as the rodent model presented in this article is evident.

More Bad News About Sugars...?

The pathology of IBD links both UC and CD with the degradation of the mucus lining the epithelium of the gut (specifically the large bowel). What I have found interesting is theories suggesting the link between diet and IBD that focuses on the role of carbohydrates. Simple sugars are absorbed into the bloodstream, whereas the more complex sugars require further digestion via intestinal enzymes. When these sugars are not fully digested, the undigested remnants can ferment through bacterial action, serving as an energy source for bacterial replication. Enzymes are soon destroyed, and the mucus-producing cells of the small intestine, the goblet cells, begin to secrete mucus to protect the intestinal wall against microbial toxins and undigested carbohydrates. This mucus-coating prevents sugars and starches needing digestion from reaching the enzyme cells, and fermentation and damage escalate as the cycle continues.

I then linked this information to what we know about the appendix. From prior reading, we now know that the appendix is dependent on the mucus that lines the epithelium of the bowel. We also know that diet may well account for the incidence of appendicitis. So, is it possible that the sugary diet of modern society is damaging the role of the appendix to regulate immune system function, and that this, coupled with the damage to the GI tract by bacteria feeding on these sugars, could be one way of inducing IBD?

Talks about a book on carbohydrates and intestinal health: http://www.sheilashea.com/ibd.html

huOKT3gamma in T1DM

Diabetes Mellitus, or Type 1 Diabetes (T1DM), is an autoimmune disorder in which one’s T cells destroy the insulin-producing pancreatic b cells. (5) Insulin is necessary for the metabolism of glucose and a balance between insulin and glucose must be maintained to avoid either hyperglycemia or hypoglycemia.
b cells account for about 60% of the cells are produced in the islets of the pancreas. The onset of T1DM occurs when one’s b cells have nearly all been destroyed. Once this occurs treatment with exogenous insulin to maintain the proper insulin-glucose balance is required. Food intake must be carefully monitored carefully as is affects this balance.
The monitoring devices, delivery methods and the daily management of T1DM has become more streamlined and convenient, it still requires insulin in the right amounts at the right intervals. The advent of “closed loop” systems would, in essence, act as an artificial pancreas but would still require exogenous insulin. There are two other options that offer promise of dramatically changing treatment. One is islet cell transplantation which restores the pancreas’s ability to produce b cells and thereby endogenous insulin. A second option, and the focus here, is the preservation of islet cell function – the production of b cells which produce insulin. This necessitates interfering in the process that results in b cell destruction as close to onset of frank diabetes as possible.
Anti-rejection therapies used in organ transplantation are a possibility because of their effect on autoimmune responses. One agent with promise has been used in renal and renal-pancreatic transplants: huOKT3g which interferes in the events leading to autoimmune destruction of b cells. (3) huOKT3g is an ati-CD3 antibody; CD 3 is a group of proteins that associates with T-cell receptors to generate an activation signal in T lymphocytes that results in the destruction of b cells. huOKT3g is a humanized, nonmitogenic, Fc receptor non-binding OKT3 antibody. (3) This means that it is an antibody derived from a mouse in which the genetic information for six complimentarity determining regions (CDRs) has been grafted within a human IgG1 monoclonal antibody. (1) This reduces the amount of mouse material to £ 10%. The antibody is nonmitogenic because it contains no substances that signal a cell to divide which would trigger mitosis. (1) In addition, the CH2 region of the IgG1 has been altered by site-directed mutagenesis which changes Fc receptor binding activity which also eliminates T cell activation. Studies have shown that these manipulations of the antibody result in it retaining its immunosuppressive properties, but not its immune activating properties.(1) The most encouraging thing about huOKT3g treatment (by infusion) is that its effect on b cell preservation persists for at least a year post-infusion. Current trials are testing whether reinfusion at 1 year can further extend the preservation of b cells.

References:
Woodle ES, Bluestone JA, Zivin RA, Jolliffe LK, Auger j, Xu D, Thistlethwaite JR, Humanized, Nonmitogenic OKT3 Antibody, huOKT3g (Ala-Ala): Initial clinical Experience, Transplantation Proceedings, 30, 1369-1370, 1998.
Seegan GW, Smith CA, Schumaker VN, Changes in quaternary structure of IgG upon reduction of the interheavy-chain disulfide bond, Proceedings National Academy of Sciences, Vol. 76, No 2. 907-911, February 1979.
Woodle ES, Xu D, Zivin RA, Auger J, Charette J, Olaughlin R, Peace D, Jolliffe LK, Haverty T, Bluestone JA, Thistlethwaited JR, Phase I Trial of Humanized, Fc Receptor Nonbinding OHT3 Antibody, huOKT3[gamma[ in the Treatment of Acute Renal Allograft Rejection, Transplantation, Vol. 68(5), 608-616, 15 September 1999
Chatenoud L, Primo J, Bach, JF, CD3 Antibody-Induced Dominant Self Tolerance in Overtly Diabetic NOD Mice, The Journal of Immunology, 22-1767, 2947-2954, 1997.
Herold KC, Hagopian W, Auger JA, Poumian E, Taylor L, Donaldson D, Gitelman SE, Harlan DM, Xu D, Zivin RA, Bluestone JA, Anti-CD3 Monoclonal Antibody in New-Onset Type 1 Diabetes Mellitus, NEJM, 346, No 22, May 30, 2002.

The clinical trial of TGN1412 and an unexpected outcome

Just when one thought in the 21st century that it is certainly safe to participate in the trial of a new and promising drug, something goes terribly wrong! On March 13, 2006, six healthy male volunteers at St. Mark’s Hospital experienced symptoms ranging from headache, nausea, diarrhea, to peripheral vasodilatation, hypotension, tachycardia, to adult respiratory distress syndrome and multiple organ failure, resulting from the administration of what was considered a low dose of a new monoclonal antibody, TGN1412 (1). The use of monoclonal antibodies in the treatment of diseases such as lymphoma is common place in medicine today (2). These antibodies are clones of a single parent B cell, specific to one antigen, and when, in production, they are fused to a substance of interest, they can be used to identify and purify that substance (4). They have thus been used in the treatment of various cancers and, recently, this monoclonal antibody was hoped to be promising in the treatment of leukemia and auto-immune diseases such as rheumatoid arthritis (2).
TGN1412, developed by TeGenero Immuno Therapeutics and tested initially on mice by Parexel, is one such humanized (as opposed to murine or mouse) monoclonal antibody (2). It is unique both because it is a “super-agonist” of the T cell surface receptor CD28 and because normally this trigger would require that the T cell were also attached to a co-stimulator antigen for significant response (3). For TGN1412 this is not the case and given a much greater expected immune system response, it would seem that this antibody would be geared towards patients with a suppressed immune system. Instead, it was found that TGN1412 preferentially activated regulatory T cells and a net suppression of the immune response. This was the thinking in utilizing the drug for patients with conditions like rheumatoid arthritis, where the immune system is hard at work attacking the body’s joints.
Many are calling what occurred in this first human trial with TGN1412 the result of a cytokine storm, characterized by, and evidenced in all six of the volunteers in this clinical trial, the presence of multiple inflammatory mediators in the patient’s serum (1). All six men also suffered early acute lung injury and lymphopenia, (low numbers of lymphocytes) which is not characteristic of cytokine storm (1). All six men survived after extensive treatment, complication, and stay, ranging from 30 to 45 days, in the Intensive Care Unit of the National Health Service hospital in London and an intensive inquiry into the events was immediately underway by the Medicines and Healthcare products Regulatory Agency in the United Kingdom (2). There remain questions related to the after-effects to the six volunteers, including lower than normal numbers of functioning T cells and the development of cancer in one participant (3). TeGenero maintains that all earlier animal testing produced dramatically different results with the clinical trial producing completely unexpected results. The clinical study was approved by the MHRA and according to their reports, protocols were followed, with no deficiencies identified in the manufacture and storage of TGN1412 (3). The conclusion remains that the outcome was the result of an “unpredicted biological action of the drug in humans” and much further monoclonal antibody research has been stunted in the UK (3). While certainly oftentimes the benefits outweigh the negatives of medical research, this example certainly does little to bolster the public’s confidence in placing their safety in our hands.

References:
(1) “Cytokine Storm in a Phase 1 Trial of the Anti-CD28 Monoclonal Antibody TGN1412.” The New England Journal of Medicine, Volume 355:1018-1028, September 7, 2006.
(2) “Catastrophic Immune Response may have caused drug trial horror.” New Scientist, 14:22, March 17, 2006.
(3) “TGN1412.” http://en.wikipedia.org/wiki/TGN1412, 10/2/2007.
(4) “Monoclonal antibodies.” http://en.wikipedia.org/wiki/Monoclonal_antibodies, 10/2/2007.

Appendicectomy: no beneficial effect in subjects with UC

In a study done by a group of Danish researchers on subjects who were admitted for ulcerative colitis there was no evidence for beneficial effects of appendictomy on admission rates in nationwide Danish hospitals in patients with UC. A cohort of patients who had an appendicectomy and their repeat admission for UC was studied. From 1981 to 1999, 202 subjects were identified as having an appendicectomy after their onset of UC. In this population based nationwide study with complete follow up, it was discovered that there was a moderate decline in hospital admission rates for UC after appendicectomy as compared to those who already had UC before their appendicectomy. The decline is not attributed to appendicectomy though because of the reference cohort showing a larger decline in admission rate.
Reference: Appendicectomy has no beneficial effect on admission rates in patients with ulcerative colitis; J Hallas, D Gaist, W Vach and H T Sørensen.
Furthermore, there is evidence released this week about the purpose of the appendix. An article published in the Journal of Theoretical Biology this week was referred to by the Associated Press. (http://news.yahoo.com/s/ap/20071006/ap_on_he_me/appendix_s_purpose) The article summarizes the work done by the researchers at Duke. It states that the purpose of the appendix (remember theoretically, unproven) is to act as a producer and store of good bacteria important in GI homeostasis. The article also goes on to describe the appendix as an outdated organ in the evolutionary timeline. The need for bacteria for the digestive system is not available to people from modern environments.
In conclusion, the study about the purpose of the appendix reinforces the study that an appendicectomy is not beneficial for patients with UC.

Genetics and IBD

I found the genetic aspect of CD (Crohn’s Disease) and UC (ulcerative colitis) that was explored in the articles entitled Inflammatory Bowel Disease: Cause and Immunology, Inflammatory Bowel Disease: Past, Present, and Future, as well as Translational Research in Inflammatory Bowel Disease to be interesting. Each of these three articles explored the genetics behind the susceptibility to IBD. Some genetic facts that were listed include: “Approximately 10-15% of IBD cases are familial, with familial clustering of CD and UC families occurring such that 75% of families are concordant for disease type, and 25% have both CD and UC within the same family” (Translational Research in Inflammatory Bowel Disease, Abreu, M., Sparrow, M.). Also, The research conducted with monozygotic twins revealed that there is a “pooled concordance in monozygotic twins of 37.3% for CD and 10% for UC” (Inflammatory Bowel Disease: Cause and Immunology, Baumgart, D., Carding, S.). It was also interesting to see that there was a less significant link between dizygotic twins (7% for CD and 3% for UC, according the same article). Furthermore, the linkage of genetic predisposition to CD was found to be stronger than that of UC. It was found that UC and CD have susceptibility regions on 12 chromosomes labeled as IBD1-9 and CARD15 (NOD2). Genetics appears to play a large role in susceptibility to IBD, however there are also links to environmental factors. The article Inflammatory Bowel Disease: Cause and Immunology mentions many environmental factors that have been shown to contribute to IBD, however it would be interesting to further understand why these factors increase risk. Also, for further research, I found an article entitled “Clinical Aspects and Pathophysiology of Inflammatory Bowel Disease” by Hendrickson, B., Gokhale, R., and Cho, J. from the Clinical Microbial Reviews. http://cmr.asm.org/cgi/content/full/15/1/79

Oral Tolerance and Retinoic Acid

Oral tolerance is defined as the induction of antigen specific immunological tolerance brought about by ingesting protein antigens(1). Ingested foods have unique antigenic characteristics the immune system is programmed to ignore, thereby allowing the body to tolerate the antigens found in food. In order to properly maintain immunologic homeostasis, oral tolerance is essential. Recently evidence has been published that identified a role for retinoic acid in oral tolerance(2-4). Retinoic acid is the physiologically active metabolite of vitamin A, retinol, and beta carotene found in the diet.
Two major players in oral tolerance are dendritic cells (DC) and T regulatory cells (T reg)(5). DC are responsible for antigen presentation, T reg cells are responsible for suppression of Th1, Th2, and Th17 (6) and thus are anti-inflammatory (the voice of reason in an otherwise reactionary society). Because of their function as immune suppressors, it stands to reason that T reg cells should play a pivotal role in any process of tolerization, including oral tolerance. Here are a few other details about T reg cells that are important for the rest of this summary to make sense: they need Transforming growth factor beta (TGF-b) to become a T reg cell from a naïve T cell, they primarily come from the thymus but they can also be produced peripherally, including the Gut Associated Lymphoid Tissue (GALT), and there is an integrin called a4b7 that helps them home to the GALT(5).
So here is what scientists have recently found: there is a specific population of DC (CD103+) in the GALT that makes TGF-b so that the naïve T cell that binds the antigens that it found in the intestinal lumen is stimulated to become a T-reg cell. The same DC’s also make retinoic acid and when these cells are treated such that they can no longer make retinoic acid, their capacity to induce differentiation into a T reg cell is diminished (3;4). In addition, a4b7 expression in T reg cells that were made in the thymus is dependent upon retinoic acid so it plays a role in the efficient trafficking to the GALT(2). Both of these findings, when taken together provide evidence that retinoic acid could play an important role in oral tolerance. What remains to be defined is whether it is necessary (meaning oral tolerance can not proceed in its absence); we know it is not sufficient (it alone can not induce oral tolerance).
Now to the part about why I care: disturbances in oral tolerance have been implicated as a possible mechanism in the pathogenesis of type 1 diabetes (T1D).* Some scientists have postulated that there are proteins in common foods that share antigenic determinants with the beta cells (bovine insulin is regularly vilified in the court of scientific opinion) and, when the very important process of oral tolerance is disturbed, the immune system becomes ‘confused’ and starts attacking beta cells(7). So could retinoic acid play a role? Before we can answer this question there are a number others that need to be answered first, I will introduce a few of them. First: is abnormal oral tolerance really the pathogenic mechanism in the auto-immune process that leads to T1D? Second: is retinoic acid necessary to the process of oral tolerance? Third: how are people with beta cell autoimmunity different with respect to their cells’ ability to utilize the dietary precursors of retinoic acid?
What other questions do you think are important when piecing this puzzle together?


* Type 1 diabetes is an absolute lack of insulin due to the immune mediated destruction of the beta cells (the insulin producers) in the pancreas.

Reference List

(1) Faria AM, Weiner HL, Faria AMC, Weiner HL. Oral tolerance. [Review] [321 refs]. Immunological Reviews 2005; 206:232-259.
(2) Benson MJ, Pino-Lagos K, Rosemblatt M, Noelle RJ, Benson MJ, Pino-Lagos K et al. All-trans retinoic acid mediates enhanced T reg cell growth, differentiation, and gut homing in the face of high levels of co-stimulation.[see comment]. Journal of Experimental Medicine 2007; 204(8):1765-1774.
(3) Coombes JL, Siddiqui KR, rancibia-Carcamo CV, Hall J, Sun CM, Belkaid Y et al. A functionally specialized population of mucosal CD103+ DCs induces Foxp3+ regulatory T cells via a TGF-beta and retinoic acid-dependent mechanism.[see comment]. Journal of Experimental Medicine 2007; 204(8):1757-1764.
(4) Sun CM, Hall JA, Blank RB, Bouladoux N, Oukka M, Mora JR et al. Small intestine lamina propria dendritic cells promote de novo generation of Foxp3 T reg cells via retinoic acid.[see comment]. Journal of Experimental Medicine 2007; 204(8):1775-1785.
(5) von BH, von Boehmer H. Oral tolerance: is it all retinoic acid?[comment]. Journal of Experimental Medicine 2007; 204(8):1737-1739.
(6) Cohen JJ. JJ Cohen's IMMU 7630 Class Notes. Ref Type: Generic
(7) Vaarala O, Vaarala O. Is it dietary insulin?. [Review] [50 refs]. Annals of the New York Academy of Sciences 2006; 1079:350-359.

Dendritic cells and T-cell responses in IBD

In reading several articles on the pathology of Inflammatory Bowel Disease (IBD), it appears that there are a few common understandings and possible avenues for therapeutics for both Crohn’s disease and Ulcerative colitis. Firstly, IBD typically manifests following an abnormal immune response to luminal (gut) flora. While the cause of this reaction has recently been linked to one or more genetic abnormalities, many researchers are focusing more on what occurs in the induced response, and how such a pathway can be halted before damage to tissue occurs. What appears to be common in both CD and UC is the activation of a T-cell mediated inflammatory response that results in the predomination of effector T-cells over regulatory T-cells, escalating the damaging inflammatory process. What also appears to play a part in both diseases is the presence and activation of dendritic cells. The dendritic cells of the gut reside just beneath the epithelial cells, and through the interstices of the intestinal epithelial cells, project long podocytes into the intestinal lumen for sampling of luminal antigens. After processing and presenting this data, either activation or tolerization results. Since it would be difficult to alter this sampling process, perhaps targeting the process following T-cell activation would be more feasible. In both forms of IBD, the expression of TLR-4 (toll-like receptor 4) is increased by dendritic cells following a helper T-cell response. This receptor, however, is distinct in its association with CD14, enabling presentation of lipopolysaccharide, which thereby induces influx of pro-inflammatory cytokines. If the expression of TLR-4 is common and frequent in both CD and UC, could the complex of this receptor with CD14 somehow be prevented? If so, could this lead to perhaps one method for disabling pro-inflammatory cytokine recruitment?

The Link Between Smoking and IBD

Inflammatory bowel disease is actually two different but similar diseases, Crohn's disease and ulcerative colitis. As said in the previous blog Crohn's disease generally tends to involve the entire bowel wall, whereas ulcerative colitis affects only the lining of the bowel. Even though it is still unknown what causes this uncomfortable disease, researchers have found that a number of factors such as environment, diet, and genetics can lead to this two diseases. While reading the article Inflammatory bowel disease: cause and immunobiology, I was surprised in discovering an interesting fact linking smoking and inflammatory bowel disease. It turns out that studies have shown that people who smoke are more likely to develop Crohn's disease than non-smokers. Smoker's tend to have a more aggressive form of Crohn's disease. However, when associated with ulcerative colitis it was shown that those who smoked were less likely to develop ulcerative colitis and tend to have a less severe course than those who do not smoke. Trials have shown that nicotine is of some benefit in ulcerative colitis due to increased mucus production and decreased cytokines. The article Smoking and inflammatory bowel disease. A case control study on gut.bmj.com goes into great detail about the results and statistics that they found when comparing smokers and non-smokers to UC and CD. They took non-smokers, ex-smokers and smokers and found that with heavy smokers, the risk of acquiring UC was lower than the non-smokers. Little is known on how smoking effects the location and the course of this disease. Although these studies have shown that smokers are less likely to have ulcerative colitis, smoking can lead to many other deadly diseases and is not advised as a therapeutic method for those who develop UC.

What is Inflammatory Bowel Disease?

That is was my first question when divulging into this week. The lay article from the Saturday Evening Post was a nice introduction. Not to be confused with irritable bowel syndrome, IBD is a fairly severe but typically non-fatal disease(such exceptions include a ruptured colon). Symptoms include upset stomach, diharrea, vomiting and nasuea. There are two types of IDB, ulcerative colitis and Crohn’s Disease. The differences are that UC affects the only the mucosa in the colon whereas Crohn’s has the potential to affect any and/or all of GI tract including the entire wall of the GI. The actual cause of the disease is unknown but it has a genetic trace in 10-15% of subjects with familial clustering of CD and UC families occurring such that 75% of families are concordant for disease type, and 25% have both CD and UC within the same family. (Abreu et al. Translational Research in Inflammatory Bowel Disease) Treatments are somewhat limited, typical anti-inflammatory protocol such as the use of prednisone is used often. However there has been some break through with the use of cyclosporine, a drug used in organ transplants as mentioned by the Saturday Evening Post. Overall, this disease is somewhat of a quandry. Hopefully a cure is in sight!