Robert Naviaux, at researcher at University of California, San Diego, published a landmark paper yesterday on the metabolites of patients with ME/CFS. It made news around the world. Below, an in-depth analysis of the paper’s findings and its implications.
Note: some of the information below is speculative, linking Naviaux’s findings to other research. Findings not explicitly indicated by the study are summarized at the end of the article.
For those who are wondering at the results and their implications, Naviaux’s study in a nutshell states that the cells of ME patients are in a sort of protective hibernation, limiting their consumption of resources and engaging in a hypometabolic state as a response to infection or other stressors. By examining patients’ metabolites in detail, it was found that this degree of protective hibernation correlates directly to clinical severity.
Naviaux also posits that cells in ME/CFS are cells under enormous stress, for which they create a series of defenses, metaphorically installing a superior lock and alarm system and hiding all the valuables. However, some pathogens know the code to get in, and when the resources are hidden, the host can’t use them, either. Both of these aspects of this mode of cellular defense have profound implications for symptomology.
Naviaux’s study featured differences between male and female patients that have not been described in other studies before:
- Women, but not men, generally had disturbed fatty acid and endocannabinoid metabolism
- Men, but not women, generally showed increased serine and threonine concentrations
Glycospingolipids, spingolipids, and cholesterol synthesis low – and that’s a huge deal
Sphingolipid depletion would go a long way to explaining some of the abnormalities seen in CFS patients. Ceramides, a product of spingolipids, are responsible for the creation of ‘lipid rafts’, which mobilize and aggregate during infection. Lipid rafts also require cholesterol and other fatty molecules to function properly.
At one time, it was believed that membrane proteins and fats were always scattered haphazardly throughout the lipid bilayer that makes up the cell membrane.
However, now there is a theory that there are lipid-rich areas of the membrane, full of glycosphingolipids (sugar-amino alcohol-fatty bits), cholesterol, gangliosides, and proteins. These exist as little ‘pockets’, though they may be linear as well; and they tend to cluster in this manner when the cell is stressed. Stress here signifies anything that has the potential to cause cell damage, rather than to intimate that these cells are frightened or upset. (Last we checked, cells didn’t get very emotional.)
The way they function together in these situations is complex, and might require a bunch of proteins and fats all acting in a little network, pulled along by actin. If any of these proteins or fats are disrupted, the membrane rafts lose functionality. And what they do is very important: they help maintain the structural integrity of the cell, while also playing an immune role. Calveolins and cavins, chemicals that are part of lipid rafts, may promote or inhibit immune activation, and are also involved in neuronal signalling; and the calveolin to cavin relationship often governs inflammatory signalling pathways.
In order to defend the cell, lipid rafts aggregate, making it more challenging for a pathogen to enter. However, some bacterial and viral pathogens have evolved to not only get around this defense technique, but exploit it. By ‘sneaking in’ the cellular back-door, these pathogens also escape being sent to the lysosome for disposal, and may therefore survive longer than their traditionally-infectious counterparts.
Pathogens that have evolved to enter the cell via lipid rafts
|Pseudomonas aeruginosa  and ||HIV-1|
|Escherichia. coli  and ||Species C human adenovirus (HadV)|
|Camylobacter jejuni  and ||Rhinovirus|
|Chlamydia species  and ||Enterovirus|
|Mycobacteria species ,  and ||Echovirus|
|Brucella species ,  and ||Simian virus|
|Shigella flexneri||Epstein-Barr Virus|
|Ehrlichia chaffeensis  and ||Ebola|
|Anaplasma phagocytophilum  and ||HSV-1|
|Group A Streptococci|
|(Zaas et al, 2005)||(Suzuki, 2006)|
It appears as though certain fungi utilize this mechanism as well, although fungal pathogens are the least studied of the three pathogen-types in terms of their lipid raft interactions.
Downregulating sphingolipid synthesis in general, and ceramide synthesis in particular, could well be part of a host-defense response in the presence of these pathogens to prevent their entry, to decrease the risk of cellular apoptosis in response to infection. It’s also possible that the cells upregulate the creation of lipid rafts as a continued protective measure, resulting in the presence of fewer free lipids involved in this process.
The lipid raft-Rituximab connection
Fluge and Mella recently released a study stating that B-cell survival factors APRIL and BAFF were likely not the cause of the success of Rituximab in abating symptoms in ME patients. If Naviaux et al.’s research turns out to be replicable, his findings may both explain why the incidence of cancer is higher in ME patients and why Rituximab works for some. From George and Wu (2012),
Rituxan/Rituximab, an anti-CD20 antibody used clinically to initiate CD20-mediated apoptosis, was used for the study of the activation mechanism of CD20. Upon activation, CD20 translocated to the lipid rafts domains of the cell where they were activated to initiate apoptosis.
In other words, Rituximab may work in ME by creating the necessary disruption in lipid rafts to prevent pathogens from using this ‘back door’ to creep into the cell, in the case of an active infection; or it may force the destruction of only cells that exist in this defensive state, causing a cascade of metabolic events that eventually results in the majority of cells no longer in metabolic hibernation. This may in part explain the lag in efficacy in Rituximab, if the process involves slowly but steadily replacing cells stuck in hibernation with healthier ones, and those cells replicating. This would be a gradual process rather than an instant one.
This lipid-disrupting property is also what makes Rituximab effective against cancer, an illness which, in and of itself may itself be profoundly affected by lipid raft dysregulation, which may in turn help explain the increased incidence of cancer in ME.
The most ‘diagnostic’ metabolites:
Out of all the metabolic pathways that Naviaux’s team measured, the following were most often irregular in male and female subjects:
Generally, these patterns were the opposite of the patterns seen in acute inflammation and infection: rather than a knock-down, drag-out fight, cells appear to be hunkering down, trying to make as little metabolic ‘noise’ as possible. Naviaux’s team noted that the pattern in ME patients was almost the exact opposite of that found in systemic inflammatory conditions such as metabolic syndrome and heart disease.
Moreover, Naviaux’s team found that analysis of several of these metabolites could be diagnostic, such that even one metabolite could be predictive of illness; however, Naviaux’s team notes that their small sample size and localized population makes a one-metabolite test too unrealistic, and recommends the study of 8 metabolites for men and 13 in women to make an accurate diagnosis.
Finally, Naviaux’s team found that the metabolic abnormalities observed were directly related to redox or to the availability of NADPH, a high-energy molecule necessary to fuel the reactions of cellular respiration, which was found to be depleted in patients.
Provided Naviaux’s work is replicable, and his interpretations are correct, the findings would have enormous implications.
- We have a reasonable set of biomarkers that would produce a viable diagnostic test.
- We may understand better why ME is associated with illnesses such as cancer and autoimmunity
- We may understand better why a chemotherapeutic agent such as Rituximab should improve symptoms in ME.
- We may have an explanation for the ‘sick but never sick’ state experienced by many patients: in cells overutilizing lipid rafts to prevent infection, only a select few pathogens ‘know’ how to still enter the cell, and hypometabolic changes create less ‘food’ (metabolites tasty to pathogens) as a result, further preventing the growth of pathogens who do not favor lipid raft-assisted infection.
- The sequestering of resources and hypometabolism would explain why patients are so profoundly fatigued, and provide a rationale for PEM: the resources simply aren’t there.
- Finally, errors in the makeup or metabolism of lipid rafts would have a profound effect on the biology of every system, since lipid rafts are directly involved in cell recognition (errors would cause autoimmunity), other kinds of cell signalling including neuronal signalling, and general immune function as well as the physical integrity of the cell.
What we do not yet understand is how this will affect potential treatment avenues. If this ‘hibernation state’ – that Naviaux calls ‘dauer’ – is a protective response, ‘turning it off’ may not be in our best interest, especially if the initial insult lingers. We remain faced with one of the biggest and most persistent questions in ME research: is the initial-insult pathogen / stressor still there, or not?
Patients experiencing fewer symptoms from taking an antifungal, antibiotic, or antiviral in this case would not necessarily indicate the presence of an active infection. Some antimicrobial agents disrupt lipid rafts, and aren’t as picky about targeting pathogens as we’d like to think. Therefore, the effectiveness of antimicrobial therapies in an ME patient would not necessarily indicate the presence of a currently-active infection.
Unfortunately, it may not be a simple yes-or-no answer. The presence or absence of a systemic pathogen may in fact be a source of patient subsets, with a group of patients still experiencing active or latent infection, and another stuck in an autoimmune-type symptom picture in which the initial-insult pathogen is no longer active, but the system is unable to come unstuck from protective-hibernation mode.
There are still many questions to answer, and replication studies ahead; however, this is likely the most promising research into ME since Lipkin and Hornig‘s landmark cytokine study, with real, positive implications for the ME community.
Access Naviaux et al’s paper here.
Access the supplementary materials here.
Access the Q & A Session on the paper here.
Note: The paper created by Dr Naviaux’s research team is more circumspect about implications of the study. Therefore, I would like to make a clear-cut distinction between my own suppositions and that of Naviaux’s paper:
It is my hypothesis that lipid raft metabolism has implications for the mechanism via which Rituximab improves symptoms in ME patients.
It is my hypothesis that lipid raft disruption is why certain antimicrobial agents may be effective treatments for ME even in the absence of a pathogen.
While it is not my hypothesis that lipid raft aggregation would create an advantage for some pathogens over others, it is my hypothesis that this is what makes certain infections more common in ME patients.
It is my hypothesis that lipid raft dysregulation might create an advantage for some pathogens while inhibiting others, creating the ‘sick but never sick’ patient symptom-picture.
It is my hypothesis that lipid raft dysregulation is what ME and cancer have in common, which may have implications for their increased co-incidence.