Ear To The Ground

Are animal models a good analogy for humans? A recently published study of mice suggests that there may be problems

To set standards, animal models are frequently used.  Such use allows researchers to investigate disease and injury states in ways which would be considered unethical to inflict on humans.  For example, to determine some threshold injury or disease state, various groups of animals may be exposed to widely varying concentrations of the particular molecule being assessed.  It is assumed that because the animal commonly used is a mammal, as are we, that the biochemical and metabolic processes of the two different species have enough in common that useful data will be generated to, say, set standards of some sort (e.g., "no effects" levels, exposures that impact fertility or birth defects or cause cancer) or show the effectiveness of drugs.  But, is such data valid?  Recently published work on mice suggest there may be problems.

The study discussed in this blog grew out of a much larger effort to understand why nearly 150 clinical trials of drugs targeted at sepsis in humans failed.  Sepsis, a potentially deadly reaction that occurs as the body tries to fight an infection, afflicts 750,000 patients a year in the United States, kills one-fourth to one-half of them, and costs the nation $17 billion a year.  It is the leading cause of death in intensive-care units. 

These drugs were developed using mouse models and the drugs were all intended to control excessive immune responses.  Potentially deadly immune responses occur when a person’s immune system overreacts to what it perceives as danger signals, including toxic molecules from bacteria, viruses, fungi, or proteins released from cells damaged by trauma or burns.  Such immune system responses may also play a role in heart disease and cancer. 

The new study indicates that mouse models do not accurately reflect the genetic and proteomic responses to acute inflammatory stress in humans.  As noted, the research grew out of a larger project to characterize human inflammatory response to serious trauma (e.g., burns, car accidents, infection). The project was aimed at studying the multitude of genetic responses that result from these acute inflammatory stimuli in humans to ascertain the key biophysiologic response to such inflammation.  As often happens in science, serendipity intervened.

When reviewers rejected one of the group's papers because it failed to show that events in humans were reproduced in mice, the researchers began to question the relevance of mouse models.  So they decided to compare their data about human responses to that from corresponding murine (rodent) model systems.  The researchers compared changes in the expression of thousands of genes, the time course of those changes (using software designed to normalize the different time frames in which responses occur in mice and humans), and the regulation of major signaling pathways involved.

In humans, the genetic response was highly consistent even though patients were subjected to different inflammatory stimuli and different subsequent treatments, suggesting that the drugs targeting these molecular mechanisms could work for multiple inflammatory diseases. The common patterns seen in humans were not reproduced in mouse models, and the responses among the various mouse models varied widely.  The researchers also compared existing gene expression data from human patients and corresponding mouse models for several acute inflammatory diseases, including sepsis and acute respiratory distress syndrome, as well as response to injury.  Again, mouse models poorly mimicked the response among humans, which were highly consistent.  What was seen was that different conditions in mice — burns, trauma, sepsis — did not engender the same response.  Each condition used different groups of genes. In humans, though, similar genes were used in all three conditions. 

Learned commentary on the study were highly varied.  Some noted that the "commonality" alleged in various mouse models of humans was set too low, that there needs to be a higher degree to which a model reproduces human disease in terms of molecular mechanisms, rather than just phenotype (the observable physical or biochemical characteristics of an organism).  Critics noted that the research focused on one strain of mice, and that until data was in on other strains, it was too early to draw sweeping conclusions.  Other critics noted that the paper was correct insofar as the behavior of white blood cells goes, but that it was improper to draw any sweeping conclusions about other bodily organs (e.g., lungs, liver, heart, brain).

What does this mean, then, if anything, for litigators?  Now that Daubert has come to California, one has to think in terms of genes, RNA, molecular pathways etc.  It is not enough to allow an expert to waive his/her hands and say X causes Y without asking --- why is that?  Explain to me exactly how disease Z comes about in terms of genes being utilized or blocked, molecules conveying messages, modifications happening to normal pathways. 

The study can be found at http://www.pnas.org/content/110/9/3507.   

Have past blood tests for BPA been faulty? Recently published study so claims

Prior posts have noted in detail the results of various studies of the impacts of BPA on various test media (e.g., animals).  Prior posts have described the ongoing public debate over BPA and its listing and then delisting as a reproductive toxicant under California's Proposition 65.  A recent post described testing done on newborns in a neonatal ICU, and their substantially large exposure to BPA, as demonstrated by the sampling of urine.  Now a study challenges the accuracy of past human blood samples for BPA.  The study indicates that the amount attributed to the average general population is in error by perhaps three orders of magnitude.

In experiments rodents received 7 doses of BPA daily from conception through birth and subsequently into early adulthood.  Amounts ranged from "very low" (2.5 micrograms per kilogram of body weight, in the range of probable human exposure) to doses 100-times higher.  The researchers reported not seeing adverse effects in the low range, and that they detected none of the active form of the chemical in animals receiving less than 80 micrograms per kilogram of body weight per day.  Blood levels were below the limits of detection.

As yet unpublished studies have indicated that studies in rodents and monkeys demonstrate the rapid breakdown of ingested BPA into inactive substances.  However, as recently reported, infants have been shown to be much less efficient are breaking down BPA than adults. 

Researchers argue that because urine levels were at a particular point in the 28 thousand individuals sampled, the corresponding blood levels should be in the parts per trillion range.  Such levels are not detectable given current analytical capabilities.  Since they were not undetectable in various studies, the researchers state that the sampled population must have been exposed to unusually high amounts, or that the samples were contaminated during the sampling or analytical process. 

Critics point out that more than 25 studies have measured blood BPA levels, and thus it is unlikely all were wrong.  They state that just because the researchers state that urine/blood relationship must be of a particular sort does not mean that such an assertion is scientifically correct.

This debate will continue.  Stay tuned.

Studies and conference reports relevant to this issue can be found at:  http://aaas.confex.com/aaas/2013/webprogram/Paper8721.html; http://aaas.confex.com/aaas/2013/webprogram/Paper8728.html; http://aaas.confex.com/aaas/2013/webprogram/Paper8725.html; http://aaas.confex.com/aaas/2013/webprogram/Paper8720.html; http://toxsci.oxfordjournals.org/content/85/2/823.full; http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2944084/; http://endo.endojournals.org/content/early/2011/12/07/en.2011-1772.abstract; http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2920080/.

Neonatal intensive care appears to expose babies to significant levels of BPA

Although the level of BPA that may be toxic to humans has not been quantified, babies treated in neonatal intensive care appear to be exposed to relatively larger doses of BPA, according to an interesting, but small study.  This exposure may be more harmful due to the limited ability of neonates to detoxify BPA.

A recent study found that newborns in intensive care excrete 17.8 micrograms per liter of BPA, significantly more than the 0.45 microgram/l of healthy infants.  The researchers found the level of care afforded neonates indicated the level of BPA exposure.  Thus, four or more ICU devices resulted in neonatal urine showing BPA at 36.6 microgram/l.  It is of significance that the neonatal ICU unit where the study was done had taken care to avoid BPA containing products whenever possible. 

Breathing tubes, intravenous drug delivery lines, and enclosed incubators are plastic, and some types of plastic contain BPA.  Several studies have indicated that elevated BPA exposure of neonates can result in behavioral problems and moodiness.  Animal studies have linked BPA to the development of feminization in males and the later development of hypertension and diabetes.

Another statistical surprise was that prematurity accounted for 30% of the variability in urinary BPA.  One possible explanation may be, as shown in animal studies, youngsters break down BPA very slowly.  Thus, if this trait holds for humans, then exposure at a very young age may be more harmful than at an older age.

Studies and conference reports that address these and other potentially adverse impacts from BPA can be found at:  http://pediatrics.aappublications.org/content/131/3/483; http://aaas.confex.com/aaas/2013/webprogram/Paper8721.html; http://edrv.endojournals.org/content/33/3/378; http://jama.jamanetwork.com/article.aspx?articleid=182571; http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2799471/.

Why is beef bad for your heart and arteries? Only your GI bacteria know for sure

Prior posts have noted the extent to which the makeup of the bacteria in one's GI tract can be critically important.  The wrong mix, which apparently arises from the nature of one's diet, can lead to a wide variety of unfortunately ugly diseases and adverse conditions.  Research now indicates that the makeup of one's GI "flora" explains a lot about why meat poses a potential risk of heart disease and atherosclerosis. 

Previous research has shown that high levels of meat-eating are linked to cardiovascular risk, partly because of the saturated fats and cholesterol in meat.  However, the higher levels of these ingredients is not sufficient to explain the difference in heart disease between meat eaters and vegans or vegetarians.  The study demonstrates that differences in the bacterial colony of one's GI tract explains why.

The study followed 2,595 people and measured carnitine levels, as well as those of its byproduct, TMAO. Omnivores produced more TMAO than vegetarians and vegans after eating carnitine, the researchers found.  Although carnitine is also found in fish, poultry, wheat, and some vegetables, its main food source is red meat, especially lamb, according to the study.  Because vegetarians and vegans eat fewer foods that contain it, their gut bacteria does not process carnitine as easily, which may explain some of the health benefits of meatless diets.

The researchers also feed mice diets that would produce high levels of TMAO; this aspect of the study showed that the animals had higher levels of hardened arteries.  However, if the researchers suppressed the bacteria living in the mouse’s guts, the effects dissipated.

Carnitine is also an ingredient in many dietary supplements which are taken to increase muscle mass.  The authors have noted that the safety of such supplements needs to be studied in light of the results from their work.

The study can be found at:  http://www.nature.com/nm/journal/vaop/ncurrent/full/nm.3145.html.

The never ending story of BPA

As noted in prior posts, the Office of Health Hazard Assessment ("OEHHA", pronounced oh we hah) added BPA to the Proposition 65 list of reproductive toxicants on April 11, 2013.  The basis was the authoritative source mechanism.  [See http://www.rmkb.com/tasks/sites/rmkb/assets/image/253.pdf for an overview of Prop. 65.]  As noted in prior post, the American Chemistry Council sued OEHHA on the grounds that the authoritative source's evaluation of BPA did not meet the statutory standards for listing.

On April 19, 2013, the Superior Court issued a preliminary injunction in the lawsuit mandating that OEHHA delist BPA, at least for now.  The order can be found at http://www.oehha.ca.gov/prop65/law/pdf_zip/041913PIOrderBPA.pdf. 

Stay tuned for more thrilling episodes.

California adds BPA to the Proposition 65 List of Chemicals

Numerous prior posts have dealt with the controversy over BPA.  Besides the numerous animal and other non-human studies, prior posts have noted that the primary route of exposure appears to be thermal cash register receipts, not merely the plastic water bottles, can liners, and medical tubing that until the link with receipts was found were assumed to be the route of exposure. 

Prior posts also noted that litigation had been filed attacking the basis for the proposed listing.  [An overview of Prop. 65 and the various listing mechanisms can be found at http://www.rmkb.com/index.cfm/publications/publication-details/?pkid=253.  A review of a major flaw in the Prop. 65, the failure to have a standard by which to measure exposure, can be found at http://www.rmkb.com/index.cfm/publications/publication-details/?pkid=965.] 

On April 11, 2013, the Office of Health Hazard Assessment ("OEHHA") listed BPA as a developmental toxicant.  What this means is that after one year a warning will be required on products that expose consumers to more than 1/1000 of the "no effects" level of BPA.  What is interesting is that OEHHA only cites to the can liners and water bottles as a route of exposure, which seems rather limited. 

One can anticipate a most interesting trial on the issue of using the authoritative body mechanism in this matter when the language from the authoritative body seems qualified in such a manner that the listing would not be supported by this mechanism.

OEHHA also lists those studies cited by National Toxicology Program to support its conclusion about the nature of BPA.  Those studies can be found listed at http://oehha.ca.gov/prop65/CRNR_notices/admin_listing/intent_to_list/NOILABpkg42BPA.html.

Can addressing air pollution decrease global warming? You betcha

Prior posts have noted the adverse health impacts from small particles, often referred to generally as PM10 and/or PM2.5.  Prior posts have also noted the adverse impact of soot on global warming, which because it is black and absorbs heat warms up the atmosphere and whatever it is coating (e.g., glaciers).  Yet addressing this problem can both improve public health and decrease global warming.

To date, strategies to address global warming have focused on gases that stay in the atmosphere from medium- to long-term (e.g., methane [half life, 7 years] and carbon dioxide [half life, 19 to 49 years, without getting into the complexities of the CO2 cycling between atmosphere, ocean, plants etc., which could drive the half-life to a 5-100 year "bracket"]).  [Regarding impacts of methane, see http://epa.gov/climatechange/ghgemissions/gases/ch4.html.  Regarding impacts of CO2, see http://epa.gov/climatechange/ghgemissions/gases/co2.html.] 

In contrast, soot stays in the atmosphere for a much shorter period of time.  A recent study suggests a serious re-think may be needed because soot is the second most damaging greehouse agent after CO2 and twice as bad as previously believed.

The study found that the soot that is currently present has a warming effect of 1.1 watts per square meter of the Earth's surface.  This is greater than methane (a greenhouse gas that I have noted in prior posts is often ignored or downplayed in the discussion of strategy to address global warming) and second only to CO2 at 1.7 watts per square meter.  The prior UNEP estimate for soot was 0.3-0.6.

The study argues that the warming from soot will be especially significant in the Northern latitudes (e.g., glaciers, snowpacks).  Also, it sees a potential threat to regional precipitation patterns, such as the Asian monsoons.  Now, let's turn to the other side of soot.  The UNEP attributes 2.4 million deaths per year due to the adverse effect of such particulates on lungs, an issue noted in numerous prior posts.  [See http://www.unep.org/ccac/ShortLivedClimatePollutants/tabid/101650/Default.aspx.]

As noted, CO2 lasts a long time in the atmosphere.  In contrast, soot drops out within weeks.  Controlling soot means that it goes away relatively quickly.  In Europe and America, 70% of soot comes fro diesel engines, which may be the more harmful form of such airborne particulates (see http://www.ncbi.nlm.nih.gov/pubmed/21810552).  Better exhaust controls and the scrapping of old, high pollution cars would have a major beneficial effect.  In the LDC's, the problem also includes inefficient stoves and dirty fuel; these are problems that should be easy to address if well understood and simple technologies are provided to replace the current processes. 

The benefits of reducing soot is that it has immediate, local health benefits and is cheaper than addressing CO2 emissions.  No global treaty is needed, and there are no free rides; benefits are local with improved health.  Such controls may reduce by half a degree the temperature rise projected for global warming, buying politicans and world leaders roughly two additional decades to address controls on methane and CO2.

The study can be found at:  http://onlinelibrary.wiley.com/doi/10.1002/jgrd.50171/abstract. 

Another maxim bites the dust: Isolated coral reefs can recover from bleaching

Stony corals that are reef-building corals (also known as Hermtypic corals [see http://en.wikipedia.org/wiki/Hermatypic_coral]) require algae from the genus Symbiodinium [see http://en.wikipedia.org/wiki/Symbiodinium] to be in a healthy condition.  The loss of these intracellular Symbiodinium from the host coral is known as bleaching, a condition which leads to the deterioration of a reef.  The loss arises when the conditions necessary to sustain the Symbiodinium cannot be maintained.  Anything that impacts the coral's ability to supply the Symbiodinium with nutrients for photosynthesis (e.g., carbon dioxide, ammonium) will result in the expulsion of the Symbiodinium.  As noted in http://en.wikipedia.org/wiki/Coral_bleaching#Great_Barrier_Reef:  "This process is a 'downward spiral', whereby the coral's failure to prevent the division of zooxanthellae leads to ever-greater amounts of the photosynthesis-derived carbon to be diverted into the algae rather than the coral. This makes the energy balance required for the coral to continue sustaining its algae more fragile, and hence the coral loses the ability to maintain its parasitic control on its zooxanthellae."

The loss of such microalgae leaves the coral vulnerable to invasive algae and death.  One of the maxims of bleaching has been that reefs could recover only after young new corals from neighboring, healthy reefs settle into the bleached reef.  Now this maxim appears to be of questionable validity.

Researchers in Australia studied Scott Reef, which suffered a bleaching in 1998 and is more than 150 miles from other reefs, seemingly a kiss of death.  However, the researchers found that the corals have grown back.  The coral cover increased from 9% to 44% within 12 years of the coral bleaching event despite a 94% reduction in larval supply for 6 years after the bleaching.  The initial increase in coral cover was the result of high rates of growth and survival of remnant colonies, followed by a rapid increase in juvenile "recruitment" as colonies matured.

The researchers concluded that, contrary to the maxim, the benefit of isolation insulated the reef from chronic anthropogenic (human induced) pressures, which greatly enhanced its ability to recover.

The report can be found at: http://www.sciencemag.org/content/340/6128/69.       

Mistletoe can be a keystone species for birds in a wooded environment

A keystone species is one that "influences the ecological composition, structure, or functioning of its community far more than its abundance would suggest."  (See http://glossary.eea.europa.eu/terminology/concept_html?term=keystone%20species.)  Although the term is often thrown about, demonstrating that a keystone species really exists by a controlled experiment was only first shown in a paper published in 2012.

Researchers in Australia for two years surveyed the bird population of every patch of woodland to be used in an experiment.  They then sorted woodland into two groups: those with and those without mistletoe.  They further divided the former in two; half the patches had the mistletoe removed and half had it left alone.  Then three years following the removal of the mistletoe from some of the patches of woodland they undertook another bird survey [in those patches with mistletoe removed, ongoing activities were undertaken to cull any mistletoe regrowth].

As one would expect, in patches in which the mistletoe was removed/culled, species that feed on mistletoe berries or nested in mistletoe plants disappeared.  No surprise.  But, the survey found that around 1/4 of other bird species disappeared from the removed/culled patches of woodland.  In patches in which the mistletoe was left in place, the number of bird species actually increased.  At least part of the increase was attributed to the end of a period of drought.  So, mistletoe was acting as a keystone species, but by what mechanism?

The researchers concluded that mistletoe was enhancing the food supply, but not merely by providing berries.  First, mistletoe weakens or kills the host trees, opening them to infestation by various insects etc.  Second, mistletoe sheds a lot of leaves, which added to the depth of leaf litter in the woods.  Deep litter favors insects.  In either case, an enhanced food supply was provided for insectivorous birds.

The study can be found at:  http://rspb.royalsocietypublishing.org/content/early/2012/07/03/rspb.2012.0856.