Editorial by Sharon Williams March 2021
What do we really know about the safety of gadolinium-based contrast agents? Are researchers looking in the right places for insight into the potential toxic effects of gadolinium? After reading a 1995 paper by Vogler et al., I came away thinking that it may be time to review findings from preclinical animal studies with all gadolinium-based contrast agents (GBCAs) while taking into consideration what is now known about GBCAs and what happens to them after administration into the human body.
When I started my gadolinium-related research in early 2010, it seemed that if you had good kidney function, all the gadolinium would be excreted in a matter of hours, and then that was pushed back to be a few days, and now it seems it could take months and even years to be eliminated. Based on gadolinium being found in various human tissues, I question if all of it will ever get out of the patient’s body. If gadolinium were not a toxic metal, we might be inclined not to worry about it, but it is toxic, and I believe everyone should be worried about the long-term effects of retaining it.
In 2006, the connection was first made between a potentially fatal disease known as nephrogenic systemic fibrosis (NSF) and gadolinium-based contrast agents that are frequently administered for MRIs and MRAs. But NSF involved patients who had severe kidney problems, and most of those patients had received one of the linear GBCAs, which are thought to be more likely to dissociate and leave gadolinium in the patient’s body. What about the patients with normal kidney function who have described the onset of new, unexplained symptoms soon after their MRIs with a GBCA, and who are still excreting gadolinium many years later? When will those patients’ gadolinium-induced symptoms be recognized?
Residual Gadolinium from all GBCAs –
It was not until 2015 that the FDA first acknowledged that gadolinium retention in patients with normal kidney function was happening as well, but the focus continued to be on the linear agents. The published literature has indicated that macrocyclic GBCAs are more stable and less likely to separate and leave residual gadolinium in patients’ bodies. However, recent research has shown that even macrocyclic GBCAs are remaining in the brain, bones, and elsewhere in the body, regardless of the patient’s level of kidney function at the time of his or her MRI. Despite that, the FDA continues to say that it has seen no evidence that retained gadolinium causes harm, even though the FDA and researchers agree that gadolinium is a toxic metal that has no biological use in the human body.
So, how safe is residual gadolinium? And what did preclinical studies show that may have been overlooked or perhaps misinterpreted based on results that were seen in animals? Remember, when GBCAs were first developed, they did not intend that they would be administered multiple times to the same patient. In fact, a 1991 paper by Rocklage et al. said it was “unlikely that MRI contrast agents would be administered repeatedly in patients,” and that was important since the same paper indicated that “minute amounts of chelated or unchelated metals are likely to remain in the body for an extended period and could possibly result in a toxic effect.” The authors acknowledged that this could result in accumulation of metal and that the “long-term effects of such potential deposition have yet to be determined.” Well, here we are 30 years later in 2021, and the long-term effects of gadolinium deposition are still unknown. Why is that?
Macrocyclic GBCAS may be more neurotoxic –
I recently learned of a 1995 preclinical study by Vogler et al. for gadobutrol that may explain some things. Gadobutrol is a macrocyclic gadolinium-based contrast agent that is better known by the brand name Gadovist® or Gadavist®. The title of the paper is “Pre-clinical evaluation of gadobutrol: a new, neural, extracellular contrast agent for magnetic resonance imaging.” The study involved the macrocyclic agents gadobutrol, ProHance®, and Dotarem®, and the linear or open chain agents Magnevist® and Omniscan®. Based on what I have read in numerous published papers, I had expected to find that the two linear agents were found to be less safe. By less safe, I mean that the LD50 for the two linear agents would have been much lower than that of the three macrocyclic agents, but that was not the case.
For those who may not be familiar with what LD50 represents, it is the median lethal dose, or dose at which 50% of the animals die from the administered drug. So, the higher the LD50, the better tolerated by study animals. Table 6 in the paper includes the LD50 and ED50 for each of the 5 GBCAs after the contrast agents were injected into the cisterna cerebellomedullaris in rats, which is a space filled with cerebrospinal fluid or CSF. (ED50 is the median effective dose of the administered drug).
As you can see below, the LD50 for the 3 macrocyclic agents gadobutrol, ProHance, and Dotarem is significantly lower than that for the linear agents Magnevist and Omniscan. According to the authors of the study, “the values of the macrocyclic compounds are lower by a factor of 5-20.”
The results of this study seem to indicate that macrocyclic GBCAS are potentially much more neurotoxic than linear GBCAs. The authors noted that as “cerebral tolerance after intracisternal injection is concerned, it is noticeable that the macrocyclic compounds exhibit side effects in rats after lower doses than the open-chained compounds.” But then they dismissed that finding and said that “it should be noted that this is of no clinical relevance, because the substance was injected directly into the liquor in these experiments and the resulting concentration in the liquor is much higher than concentrations which may occur in the clinical setting”. In plain English, it means, unlike GBCAs that are normally administered intravenously to patients, the GBCAs in the study were injected directly into an area filled with cerebrospinal fluid or CSF, which would result in much more gadolinium getting into the CSF and brain. Vogler and his colleagues did not expect that to occur in patients, especially those who had an intact blood-brain barrier (BBB). However, recent research seems to indicate otherwise.
Are all radiologists aware of the 1995 Vogler study? Was the FDA aware of it? If not, why not?
What we know today –
Remember, that preclinical study was done in 1995, and since then we have learned a lot more about the entry of GBCAs and gadolinium into the CSF and brain. For instance, a 2018 study by Berger et al. found that gadoterate meglumine (Dotarem®) easily penetrates in the CSF regardless of the patient’s level of renal function and in patients with an intact BBB. A 2018 study by Nehra et al. found that gadolinium is present in human CSF almost immediately after intravenous administration of gadobutrol (Gadavist®) in both adult and pediatric patients even in the setting of normal renal function and no dysfunction of the BBB. Interestingly, when comparing their findings to those seen in rats by Jost et al. (2016), the authors noted that “these findings imply significant limitations in the translational potential of the rat model as a surrogate for human gadolinium CSF clearance because substantial levels of gadolinium were detected well beyond 24 hours in the CSF of all human subjects with findings suggestive of an intact BBB.” In fact, gadolinium was detectable in CSF and serum for up to 24 days after intravenous administration of gadobutrol.
Since more radiology departments began using macrocyclic agents, I have told the FDA and several radiologists that we have seen a significant increase in the number of people joining our Gadolinium Toxicity support group who have only received a macrocyclic agent, and the initial symptoms reported by those people seem to be much more intense. I believe the 1995 study by Vogler et al. may provide some explanation as to why that is occurring.
I wonder what else might be learned by carefully reviewing the preclinical findings for all GBCAs while taking into consideration what has been learned about GBCAs and gadolinium’s entry into the CSF and brain, as well as deposition in the brain, bones, skin, and other parts of the human body.
Answers are needed about GBCA Safety –
Once again, we seem to have more questions than answers about GBCAs. I believe that must change before more patients’ lives are adversely affected. Patients who have been affected by retained gadolinium want and deserve answers, and I would expect that the FDA and Radiologists would want answers as well.
We cannot wait another 30 years to determine the long-term effects of gadolinium deposition, and which, if any, GBCAs are safe.
Berger, F., Kubik-Huch, R. A., Niemann, T., Schmid, H. R., Poetzsch, M., Froehlich, J. M., Kraemer, T. (2018). Gadolinium Distribution in Cerebrospinal Fluid after Administration of a Gadolinium-based MR Contrast Agent in Humans. Radiology, 171829. https://doi.org/10.1148/radiol.2018171829
Food & Drug Administration. (2015). FDA Drug Safety Communication, July 27, 2015. Retrieved from https://www.fda.gov/drugs/drug-safety-and-availability/fda-drug-safety-communication-fda-evaluating-risk-brain-deposits-repeated-use-gadolinium-based
Jost, G., Frenzel, T., Lohrke, J., Lenhard, D. C., Naganawa, S., & Pietsch, H. (2017). Penetration and distribution of gadolinium-based contrast agents into the cerebrospinal fluid in healthy rats: a potential pathway of entry into the brain tissue. European Radiology, 27(7), 2877–2885. https://doi.org/10.1007/s00330-016-4654-2
Nehra, A. K., McDonald, R. J., Bluhm, A. M., Gunderson, T. M., Murray, D. L., Jannetto, P. J., McDonald, J. S. (2018). Accumulation of Gadolinium in Human Cerebrospinal Fluid after Gadobutrol-enhanced MR Imaging: A Prospective Observational Cohort Study. Radiology, 171105. https://doi.org/10.1148/radiol.2018171105
Rocklage, S. M., Worah, D., & Kim, S.-H. (1991). Metal ion release from paramagnetic chelates: What is tolerable? Magnetic Resonance in Medicine, 22(2), 216–221. Retrieved from http://doi.wiley.com/10.1002/mrm.1910220211
Vogler, H., Platzek, J., Schuhmann-Giampieri, G., Frenzel, T., Weinmann, H.-J., Radüchel, B., & Press, W.-R. (1995). Pre-clinical evaluation of gadobutrol: a new, neutral, extracellular contrast agent for magnetic resonance imaging. European Journal of Radiology, 21(1), 1–10. https://doi.org/https://doi.org/10.1016/0720-048X(95)00679-K
A recent study by Semelka and Ramalho allowed 9 physicians with self-diagnosed gadolinium deposition disease (GDD) to report their own experience. The physicians included 7 females and 2 males. Symptoms developed after a single injection in one doctor and after multiple injections in the other eight. The precipitating agent included both linear and macrocyclic gadolinium-based contrast agents (GBCAs). Eight of the physicians reported that they were compelled to change their practice of medicine.
The study, Physicians with self-diagnosed gadolinium deposition disease: a case series, found that in various physicians, GDD showed common features and had a substantial impact on daily activity. The most consistent symptoms reported were a burning sensation, brain fog, fatigue, distal paresthesia, fasciculations, headache, and insomnia.
My thoughts –
The symptoms described by the physicians are similar to those reported in our 2014 Symptom Survey, and those symptoms continue to be reported by newly affected people who join our Gadolinium Toxicity support group or one of the other online patient groups.
If we accept that these self-reported cases of gadolinium deposition disease were induced by the toxic effects of retained gadolinium, which I believe that they were, then it seems that the symptoms reported by patients after their MRIs with a GBCA must also be recognized as being gadolinium-induced.
As Drs. Semelka and Ramalho said in their conclusion, “physicians are educated reporters on disease, so their personal descriptions should spark interest in further research.” I agree.
Interestingly, Hubbs Grimm and I concluded our 2014 Symptom Survey paper by saying, “the results of the Symptom Survey and Gadolinium Retention Update presented here should stimulate further professional investigation into gadolinium retention in all patient populations including those with normal renal function.” Here we are 7 years later in 2021 and researchers still have not connected patient symptoms after contrast-enhanced MRIs to the known toxic effects of gadolinium. Why is that?
Semelka, R., & Ramalho, M. (2021). Physicians with self-diagnosed gadolinium deposition disease: a case series. Radiol Bras. Retrieved from http://www.rb.org.br/detalhe_aop.asp?id=3328
Williams, S., & Grimm, H. (2014). Gadolinium Toxicity: A Survey of the Chronic Effects of Retained Gadolinium from Contrast MRIs. Retrieved from https://gdtoxicity.files.wordpress.com/2014/09/gd-symptom-survey.pdf
On August 25, 2020, I wrote an open letter to the FDA, Radiologists and Researchers about the symptoms of gadolinium toxicity that have not, as yet, been recognized by the FDA or medical community as being caused by retained gadolinium (Gd). I believe part of the problem stems from the fact that histopathological examination has not found any evidence that deposited Gd caused “harm” in the brain. However, the lack of physical evidence and abnormal blood tests does not mean that harmful events have not taken place in patients’ bodies. What if gadolinium affected the function of cells, especially nerve cells, and triggered a cascade of adverse events, experienced by the person as decidedly abnormal and unpleasant sensations? Would that be easily detected on histological examination of tissue, or blood tests?
In my letter, I reviewed facts that we already know about Gd from the literature, in terms of both its retention after contrast administration and its effects at a cellular level. Given that Gd has been shown to induce mitochondrial toxicity, interfere with ion channels, create neuronal hyperexcitability, and affect inflammatory processes, could Gd be affecting not only the part of the brain that controls many processes, but also peripheral and autonomic nerve endings, as well as dorsal root ganglia, to produce the many and varied symptoms that patients are experiencing?
We know that retention of Gd has been demonstrated in humans, that unexplained symptoms are occurring, and the neuronal effects of Gd have been demonstrated experimentally. Could it just be that the connection has not yet been made, and when considered together, all these facts might explain how patients’ symptoms are being caused by retained Gd from gadolinium-based contrast agents (GBCAs)?
I believe many symptoms of gadolinium toxicity can be explained by Gd-induced small fiber neuropathy (SFN) and long-standing neuropathic pain. Interestingly, as you will see in my letter, many symptoms of SFN are the same as the clinical symptoms associated with nephrogenic systemic fibrosis (NSF), which makes sense to me since the cause is the same.
Symptoms of Gadolinium Toxicity: Can their cause be explained? is available for download as a PDF and it will be posted in Our Research in the Research section of our website. The reason for making my letter available to the public now is to inform doctors, researchers, and affected patients about gadolinium-related facts that do not seem to be widely recognized. My hope is that more research will be conducted that involves evaluation and testing of patients who have retained gadolinium and are experiencing SFN-like symptoms, which, until now, have been unexplained and perplexing to clinicians who are not familiar with the potential toxic effects of retained gadolinium.
A recent study by Alkhunizi et al., Gadolinium Retention in the Central and Peripheral Nervous System: Implications for Pain, Cognition, and Neurogenesis, found that gadolinium was retained, not only in the cerebrum, but also in the spinal cord and peripheral nerves of rats exposed to multiple administrations of linear and macrocyclic agents. Healthy rats were injected daily for 20 days with the linear gadolinium-based contrast agent (GBCA) gadodiamide or the macrocyclic agent gadoterate meglumine. Gadolinium (Gd) retention in the cerebrum, spinal cord, and peripheral nerves occurred with both agents; however, significantly more was retained from the linear agent gadodiamide.
The study also assessed the functional implications of Gd retention on hippocampal neurogenesis and sensory and cognitive processing. In rats, gadodiamide, but not gadoterate meglumine, led to pain hypersensitivity. The authors said their results show that repeat administration of gadodiamide leads to heat and mechanical hyperalgesia in rats, suggesting that the linear GBCA might have triggered the sensitization of spinal cord nociceptive neurons. Neither agent was found to affect spatial working memory performance, hippocampal cellular proliferation, or hippocampal neurogenesis.
Interestingly, the authors commented that “retention of gadolinium in the spinal cord and peripheral nerves might contribute to sensory symptoms and burning pain in the torso and extremities described by some patients after GBCA administration.” They also said, “eventually, attention must be drawn to the long-term effects of such metal retention in the central and peripheral nervous system, especially in children and adults with medical conditions necessitating multiple MRI examinations, such as brain tumors, spinal cord abnormalities, or multiple sclerosis.”
I agree that attention must be drawn to the long-term effects of metal retention in the body, but not eventually, it needs to happen now.
I think this is an important study because the focus is not just on the gadolinium that was retained in brain tissue. While the brain is vital to our survival, it is important to investigate where else it is being retained and to consider what adverse effects that might have on the human body. In the study by Alkhunizi et al., the results show that Gd retained in the spinal cord and peripheral nervous system can adversely affect nociceptive neurons. According to Krames (2014), nociceptive pain is the most common type of pain and results from signaling of noxious or potentially harmful stimuli by nociceptors around the body. Could that explain many of the neuropathic symptoms that patients have described after their MRIs with a gadolinium-based contrast agent?
Alkhunizi, S. M., Fakhoury, M., Abou-Kheir, W., & Lawand, N. (2020). Gadolinium Retention in the Central and Peripheral Nervous System: Implications for Pain, Cognition, and Neurogenesis. Radiology, 192645. https://doi.org/10.1148/radiol.2020192645
Krames, E. S. (2014). The Role of the Dorsal Root Ganglion in the Development of Neuropathic Pain. Pain Medicine, 15(10), 1669–1685. https://doi.org/10.1111/pme.12413