03 May, 2014

Game Changers for ATTR Amyloidosis?

I originally started this entry a year ago, having recently attended the huge weekend symposium for patients with familial amyloidosis in Chicago (here are the details) with a planned trip to Rio for the International Symposium on Familial Amyloidotic Polyneuropathy.  Maybe it was the easy lure of Twitter. Maybe it was too many caiparinhas in Rio. Whatever the reason, I lost my blogging mojo, and put it away until now. Despite this, internet-trolling 'bots have remained extremely interested in my blog, with over 15K hits originating in Russia, Ukraine, and China alone during this year-long absence. Hopefully I can lure some amyloidosis-interested humans back to the site with insightful analysis and witty banter.

I just attended the International Amyloidosis Society's XIV Symposium taking place in Indianapolis. Tuesday, April 29th, was largely dedicated to ATTR (transthyretin) amyloidosis, so it seems timely to discuss an important publication describing a novel new therapy for ATTR amyloidosis. I hope to briefly discuss some of my favorite oral and poster presentations from the symposium in the near future. Here is a link to the abstract book for those of you who just cannot wait.  

The paper, published in the New England Journal of Medicine at the end of August, describes the use of RNAi (RNA interference) as a means of selectively inhibiting production of transthyretin (TTR) but not other proteins. 

Before discussing the paper, some background on the biology of protein synthesis. Cells make proteins in a multi-step process. The coded template (the gene) for each protein is found in your DNA in the nucleus of each cell. When the cell wants to make a protein, the gene for that specific protein is copied as messenger RNA (mRNA). This is called transcription. The mRNA leaves the nucleus, and then is translated into protein in the cytoplasm (the part of the cell outside of the nucleus). In ATTR amyloidosis, misfolded transthyretin produced predominantly by liver cells (hepatocytes) aggregates into larger insoluble fibrils of amyloid which deposit in various organs, injuring them.  Protein synthesis is summarized below. 

If You are interested in a more in-depth discussion of this, click here.  

Dr. Coelho and colleagues conducted two sequential Phase 1 studies evaluating siRNA targeting ATTR synthesis. "siRNA" stands for small interfering RNA, which (together with a multi-protein cluster called RISC) finds, binds, and grinds a specific mRNA, thereby selectively shutting down production of the protein the mRNA encodes. Your basic silver bullet. The siRNA was packaged for delivery to liver cells (where transthyretin is produced) in lipid nanoparticles.  The two studies reported by Coelho look at two different nanoparticle preparations to deliver the same siRNA payload. The two preparations are called ALN-TTR01 and ALN-TTR02. The second one (ALN-TTR02) has since moved forward into clinical studies as the I.V. drug patisiran. There is also a subcutaneous formulation in development. 

Unwind, Find, Bind, Grind. Repeat as necessary. 

In the NEJM article, the authors showed that even a single dose of ALN-TTR02 could induce >85% knockdown of transthyretin levels. Even 4 weeks after the dose, TTR levels were still partially knocked down (albeit less so). The trials included patients with ATTR amyloidosis (the ALN-TTR01 trial) and healthy volunteers (the ALN-TTR02 trial). Side effects were manageable, with about 20% of patients experiencing infusion reactions that could be handled with steroids, temporary interruption of the infusion, and resumption of the drug at a slower infusion rate. 

Reliable reduction in TTR levels after ALN-TTR02 administration.

This week, at the ISA symposium, Dr Ole Suhr and colleagues (including Dr. Coelho) presented some data from a Phase II study of ALN-TTR02 in patients with Familial Amyloidotic Polyneuropathy, an inherited form of ATTR. Here is a copy of the abstract:

Note: Alnylam is the pharmaceutical company that makes ALN-TTR02 (patisiran)

Analysts ponder whether 85% reduction in TTR production is adequate to alter the clinical course of FAP, and that of course remains to be determined. Here is a link to an insightful blog discussing the implications of this in terms of drug development. 

Also presented at the mtg in Indy was an update regarding the status of ISIS-TTrx, another transthyretin mRNA-targeting agent using a different platform (its an antisense molecule). Here is the abstract:

ISIS-TTRx is a product of ISIS Pharmaceuticals
The actual oral presentation made by Dr. Ackermann focused on her company and the general technology of antisense therapy.  

As more information regarding both patisiran and ISIS-TTRx enters the public domain, I'll update this topic. 

16 June, 2013

Japanese Scientists Debunk Longstanding Avian Behavioral Theory

Recent research published in the Journal Amyloid casts doubt on the widely accepted concept that chickens cross the road merely to get to the other side. It appears that at least some of them may actually be searching for an amyloidosis specialist. 

Tomoaki Murakami and colleagues describe their research related to an outbreak of AA amyloidosis occurring at a Japanese poultry farm. Avian AA amyloidosis is well characterized (as indicated by its inclusion in Table II from the most recent amyloid fibril nomenclature committee guidelines). AA amyloidosis has been described in waterfowl (due to chronic inflammatory conditions) and chickens (due to bacterial infections or repeated vaccinations). AA amyloid has also been detected in the livers of force-fed ducks and geese used for foie gras. 

A photomicrograph of a hepatic venule from a sample of commercially-available foie gras
(top panel, h/e stain; middle, congo red stain under polarized light; bottom IHC confirming AA amyloid).
Ref: http://www.ncbi.nlm.nih.gov/pubmed/17578924
The authors studied four breeds of chickens, one of which has previously been shown to have a propensity for developing systemic AA amyloidosis after repeated vaccinations for Salmonella enteritidis (SE) and/or Mycoplasma gallisepticum (MG). In this study, chickens were inoculated with a single dose of one of two SE vaccines ("SE(a)" or "SE(b)") or an MG vaccine. Then some of the chickens were also given a dose of an AA amyloid fibril solution which the authors had prepared from the livers of other chickens with AA amyloidosis. Additionally, there were some chickens who received only vaccine without AA fibrils, only fibrils without vaccine, or neither.

The findings: 

  • 29 out of 38 chickens (all breeds studied) who got both vaccine SE(a) and a dose of AA fibrils (either orally or intravenously) developed AA amyloidosis. If the AA fibrils were administered orally, then the amyloidosis tended to develop in the chickens' spleens; the chickens who got the AA fibrils intravenously developed more widespread systemic amyloidosis (including the birds' intestines). 
  • ZERO out of 113 other chickens developed systemic AA amyloidosis.
  • Serum AA precursor protein levels (SAA levels) did not correlate with risk of developing systemic AA amyloidosis. The SE(a) vaccine did not induce an increase in SAA in any subgroup of chickens (including those who developed amyloidosis) and the MG vaccine did induce a rise in SAA (with no cases of associated amyloidosis).
The scientists (and another author providing commentary in the same issue of the journal) concluded that the outbreak of avian AA amyloidosis was likely the result of chickens ingesting amyloid-contaminated feed and/or droppings after having had industry-standard vaccinations which may have pre-disposed them to developing amyloidosis. 

Not an unprecedented finding. Fecal transmission is suspected to contribute to the high incidence of systemic AA amyloidosis in captive cheetahs (like cheetahs don't have enough problems). Also, the same scientists who discovered amyloidosis in foie gras fed it to amyloid-susceptible mice and found it accelerated the rate at which systemic AA amyloidosis developed. They concluded foie gras was a potential Amyloid Enhancing Factor (AEF), and that 
"It would seem prudent for children and adults with rheumatoid arthritis or other diseases who are at risk for [AA amyloidosis] to avoid foods that may be contaminated with AA fibrils." 
Then, citing studies such as one in which formation of a specific type of amyloidosis (AApoAII) could be accelerated in predisposed experimental mice by intravenous injection of any of several different types of human amyloid fibrils (AL, ATTR, Abeta2-MG, and others), they suggest
"...that it may be hazardous for individuals who are prone to develop other types of amyloid-associated disorders, e.g., Alzheimer's disease or type II diabetes, to consume such products."
Which nags at me. I don't so much wonder about whether my father, the son of a woman who died of Alzheimer's disease, should enjoy foie gras as much as he does (though maybe I should - it's Fathers' Day). I worry a little bit about whether diet could be affecting the outcome of my patients with documented systemic amyloidosis. Is our carnivorous American diet full of AEFs? Possibly. An examination of the kidneys and other organs from 302 apparently healthy cattle slaughtered for meat revealed AA amyloidosis in 5% of the animals (take a look). The incidence was lower (0.4% - 2%) in other studies. A largely vegetarian diet has been cited as a possible explanation for the virtual absence of secondary amyloidosis in leprosy patients in India compared to the fairly high incidence amongst leprosy patients in the United States, Malaysia, Brazil, and other countries.  Check out this 1965 article by Amyloid Guru Alan S. Cohen and colleagues which explores this very topic.  At this time, though, there is no compelling evidence for transmission or acceleration of amyloidosis (AA or any other type) in humans from ingestion of AA-containing bovine meat or organs.  Additionally, a search of the medical literature did not turn up any studies looking at the impact of diet on prognosis in AL amyloidosis. So for now, I'll just worry a little bit. Comments welcome. 

19 May, 2013

Digoxin Sensitivity and AL #Amyloidosis

Last week, I learned something. Since learning new things is a good habit to get into, I thought I'd share - especially since the pertinent data were actually a little difficult to track down. 

A patient of mine with long-standing AL amyloidosis was admitted to the hospital with congestive heart failure occurring in the setting of rapid atrial fibrillation ("AFib"). For non-medical folks, this means the top chambers of the heart  (the atria) were beating extremely fast and irregularly, driving the bottom part of the heart (the ventricles) to do the same. This is not a kind thing of the atria to ask of the stiff, thick, amyloid-filled ventricles. 

The situation was particularly difficult because of the patient's chronically low blood pressure.  His typical BP of 90/50 was running even lower due to the abnormal heart rhythm.  Some of the medications one might normally employ to control the Afib - like beta-blockers or calcium channel blockers - could not be used here because of the BP.  I suggested to the medical residents that we try using digoxin, which would not be expected to lower the blood pressure.  An hour later, the team called me back to let me know they had decided against that because the risk of digoxin toxicity was too high in this patient. I asked why they felt he was at risk for this, and the answer surprised me.

"His amyloidosis."

A search of PubMed using the search terms "digoxin" and "amyloidosis" yields only 8 references, at least as of the afternoon of May 18th, 2013. Of these, one of them was a case report of a person who was diagnosed with cardiac amyloidosis after developing fainting spells on digoxin.  Another article describing two cases of familial transthyretin (ATTR) mentions in the abstract that such patients are prone to digoxin toxicity, but does not state that the patients in that report experienced this. I have thus far not been able to track don a copy of the actual article text. The other 6 references that came up were not relevant to my specific patient's case. 

I tried another strategy and pulled up a review from cardiac amyloidosis guru Dr. Rodney Falk. Here is his commentary on the use of digoxin in AL amyloidosis patients: 
"There is no role for digoxin in patients with cardiac amyloidosis who are in sinus rhythm. However, for patients with atrial fibrillation, cautious use of digoxin may aid in heart rate control although the risk of digoxin toxicity may be increased, possibly related to abnormal binding of the drug to amyloid fibrils."
A reference for last statement not provided, so more digging was needed.  Turned up the following additional references, not identified by original search:

A 1961 article from one of Michigan's own in the Annals of Internal Medicine which described two amyloidosis patients who seemed to have problems stemming from digitalis (a drug structurally related to digoxin, but with a longer half-life in the blood: 5-7 days, compared to 1.5-2 days). Pt #1 was a 58-yo farmer with jaundice and hypoalbuminemia (low serum protein levels) and atrial fibrillation who developed severe bradycardia (slow heart rate) of approximately 30 beats per minute after a 0.8 mg loading dose of digitalis followed a couple of days later by a 0.1 mg dose. Although it is not entirely clear from the text, it appears the patient had a liver biopsy proving he had systemic amyloidosis a few days before dying of liver failure.  No information was provided regarding kidney function. On autopsy, multiple organs were confirmed to be infiltrated with amyloid, including the heart. Amyloid fibril typing was not performed.  Pt #2, on the other hand, almost definitely had AL amyloidosis complicating a plasmacytoma. She was in sinus rhythm but had symptoms of congestive heart failure and exam findings suggesting cardiac tamponade (compressive fluid around the heart). She was treated with 1.3 grams of an older digitalis preparation (digitalis folia) over 60 hours. I cannot find a good reference with a dosage equivalency table to put this into current medical context. Also, again, no information on kidney function was provided. After dosing, the patient developed cardiac bigeminy (paired heart beats) with a rate of 70 beats per minute. The patient then developed severe hyperkalemia (high serum potassium levels - 8.3 mEq/L in this case, or about twice the normal level, after originally starting in the normal range). The patient suffered heart rhythm disturbances typical of this potassium level, and she died. On autopsy, the patient was found to have cardiac amyloidosis and a pericardial effusion (fluid around the heart) was confirmed. In 1961, serum digitalis levels were not obtainable.

A second article from A. Pomerance of London's Central Middlesex Hospital's Department of Morbid Anatomy and Histology was received at the British Heart Journal on Aug 17th, 1964, and was ultimately published in 1965. It turns out that at the exact same time, the Beatles were at work trying to get the tracks for Beatles for Sale! recorded and mixed. Busy time for the British. Pomerance's article is an autopsy series of 21 elderly patients with "senile amyloidosis."  At the time, the composition of the fibrils had not been characterized; today we know that most if not all of these cases were likely ATTR (wild type) amyloid.  The report is actually pretty fascinating from a historical standpoint, and it summarizes what was known at the time about systemic amyloidosis citing even older literature. As far as the cases, 3 of 21 patients were reported to have been "sensitive to digitalis" during hospital admissions prior to the terminal ones. No information about digitalis dosing, serum levels, or kidney function was provided. Two of the three patients had had prior myocardial infarctions. 

So, 6 total cases of amyloidosis patients experiencing "digitalis sensitivity." One of the cases provides sufficient detail to justify this diagnosis.  One (pt #2 from the 1961 Cassidy article) almost certainly did not experience digitalis sensitivity but died of hyperkalemia-induced arrhythmia in the setting of pre-existing cardiac tamponade. There is insufficient data on the other four patients (from Pomerance's report, and from the original PubMed search I did) to reach any conclusions one way or the other. 

What about the last part of the cited text from the Falk article? The best support for this was a brief report by Dr A. Rubinow, Martha Skinner, and Alan Cohen from Boston University published in 1981. They describe a laboratory experiment in which they added digoxin to pellets of amyloid fibrils isolated from the spleens of three patients with amyloidosis, and also to samples of ground up tissues: normal human liver, normal human heart, and human heart affected by amyloidosis.  They demonstrated that both pellets of pure amyloid fibrils or heart tissue from a patient with amyloidotic cardiomyopathy bound digoxin, whereas the control tissues (the ones without amyloid) did not. 

Ref: http://circ.ahajournals.org/content/63/6/1285.long
The authors discuss cardiac glycosides' mechanism of action, and - citing the relevance of cardiac tissue levels of the drugs rather than serum levels - postulate that binding of digoxin by amyloid-laden cardiac tissue may increase effective drug levels where it counts. However, they (correctly) point out that it is unknown whether amyloid-bound digoxin retains its pharmacologic activity. Their conclusions? 
"Therapeutic judgement regarding the cautious administration of digoxin in patients with cardiac amyloidosis still rests on clinical grounds."
My conclusions? The same. Patients with amyloid cardiomyopathy are known to be at risk for potentially fatal arrhythmias - its what accounts for the dismal outcomes seen in patients with cardiac stage 3 AL amyloidosis.  It is also clear that patients with structural heart injury from any cause may be at risk for digoxin-induced arrhythmias. So caution is warranted.  A critical review of the literature, however, does not make the case that digoxin can never be used in patients with systemic amyloidosis.