Progesterone in the Experimental Treatment of Brain Injury: a Personal Respective

By: Donald G. Stein, Ph.D. Department of Emergency Medicine, Emory University, Atlanta, Georgia, USA

Despite the hundreds of millions of dollars spent by pharmaceutical companies and the National Institutes of Health (NIH) in recent decades, no safe and effective treatment for the acute stages of traumatic brain injury (TBI) or stroke is currently available. In the case of TBI, several approaches have been tested (barbiturate coma, hypothermia, magnesium sulfate, mannitol, glucocorticosteroids, dexanabinol, human serum albumin, and hyperbaric oxygen, among others), but none have been proven safe and effective in clinical trials (Roberts et al., 1998). In fact, recently a major trial (CRASH) of intravenous corticosteroids in adults (n=10,008) with TBI reported a highly significant increase in death rates six months after injury (3.4% over controls) following methylprednisolone treatment (Edwards et al., 2005). Similarly, an NIH-funded clinical trial with 184 patients treated with magnesium sulfate was terminated because of an increase of almost 25% in mortality in treated patients compared to controls (Temkin et al., 2005). 

According to the Centers for Disease Control, every 15 seconds, in the United States alone, someone suffers a TBI. About 80% of the victims survive, but with varying degrees of impairment that prevent them from returning to their work or lifestyle. The Federal Agency for Healthcare Research and Quality reports that TBI is the most frequent cause of death in the hospital among Americans 44 years and younger, and the war in Iraq has added to the tragic statistics for TBI repair. “Nearly two-thirds of injured U.S. soldiers sent from Iraq to Walter Reed Army Medical Center have been diagnosed with traumatic brain injuries—a percentage thought to be higher than any other past U.S. conflict.” Of 1116 soldiers treated for battle injuries at Walter Reed Army Medical Center between January 2003 and April 2005, almost one-third had a TBI.

Progesterone and Recovery from Traumatic Brain Injury

Almost all of my 40-plus years of research has focused on the search for a safe and effective acute-stage treatment to reduce the toxic processes that continue to kill nerve cells long after the initial traumatic event has occurred. Like most neuroscience research in laboratory rats, virtually all of my studies used male subjects. This was, and continues to be, the standard of practice despite an extensive literature showing that gender plays an important role in many diseases and their management (see for example, Jensvold, 1996 and Legato, 2005). About 20 years ago I thought it was time for our laboratory to examine whether female laboratory rats would recover better than males after extensive bilateral damage to the medial frontal cortex. We developed a rat model of cortical injury because this is the part of the brain most often injured in humans, and because a small number of anecdotal but somewhat conflicting clinical reports (e.g., Farace and Alves, 2000) indicated that females tend to recover better than males after a brain injury (Groswasser et al., 1998; see also Stein, 2004), and that there were important gender differences in cerebral organization that might account for the differing patterns of recovery (Kimura, 1992, 1996).

Sex differences observed in the performance of cognitive tasks were often attributed to differences in the morphological and functional organization of the brain. For example, Shaywitz et al. (1995) used imaging techniques to demonstrate that during certain language based tasks, the brain activation of normal male adults was much more lateralized to the left inferior frontal gyrus regions, whereas in females the pattern of activation was much more diffuse and involved both the left and right hemispheres. Similar results were obtained by Baxter et al. (2003), who showed that females had more bilateral activation of the inferior frontal gyrus and superior temporal gyrus than males. What does this have to do with the outcome of brain injury? One explanation for apparently better recovery from stroke and TBI in females is that, since they have more bilateral and distributed representation of language and cognitive function, they are better able to compensate for damage than males, where the localized damage would lead to more profound deficits and less ‘recoverable’ function.

Of course, we did not have these data available to us when we started our work. We developed a simpler hypothesis to account for the better recovery. Since a substantial literature already showed that sex hormones such as estrogen, progesterone, and testosterone could affect morphological development, we hypothesized that the hormonal status of the female at the time of injury would significantly affect the outcome of brain injury. However, we were not certain whether estrogen or progesterone would have a greater effect on recovery from cerebral damage (Djebaili et al., 2004). Colleagues at the Worcester (MA) Foundation for Experimental Biology (then a major center for reproductive biology research) suggested that we test the females by making them pseudopregnant. This turned out to be a relatively simple matter of manipulating the rats’ hormonal status by mild mechanical stimulation of the cervix, taking vaginal smears to determine the stage of estrus when estrogen and progesterone were at their respective peaks, and then administering the cortical injury when the animals were either high in estrogen or high in progesterone. After injury, the animals were allowed to recover for a week and then tested on a spatial learning task to measure cognitive functional recovery. It is important to emphasize that this experiment used no hormonal injections or other treatments. Here we studied only whether endogenous levels of circulating hormones in females could influence the outcome of their extensive brain injuries.  

We expected the females to show better recovery than male rats, but we were surprised to find that the extent of the females’ functional recovery was dependent on where they were in their cycle at the time they received their brain injury. Females high in progesterone relative to estrogen at the time of injury had much better functional recovery in spatial learning tasks and less brain swelling than females higher in estrogen than progesterone (Attella et al., 1987). When we measured the extent of the injury we found that the rats higher in PROG at the time of injury had significantly less ventricular dilation (ventriculomegaly) than animals injured when estrogen was at its peak. We attributed this finding to progesterone-induced reductions in cerebral edema, but needed to test this idea more directly. The important point from this study is that morphological and behavioral recovery was directly affected by the naturally circulating levels of hormone at the time of injury, with higher levels of progesterone producing the best outcome.

We next tested male and female rats with bilateral lesions of the frontal cortex given post-TBI injections of progesterone (4mg/kg for 5 days). Here, both the males and females showed very significant decreases in direct measurements of cerebral edema, improved recovery on spatial navigation, and reduction in sensory neglect, even when treatment was delayed up to 24 hours (Hoffman et al., 1996; Roof, 1992). This indicated that progesterone has a relatively large window of opportunity for treatment, but the most substantial reductions in cerebral edema were observed in subjects treated within the first 6 hours after injury. 

From these encouraging studies we went on to explore how progesterone works to enhance recovery at the molecular level. We found that, for the most part, the hormone reduces cerebral edema by dramatically downregulating the expression of injury-induced inflammatory factors that cause the destruction of vulnerable nerve cells. Through other molecular pathways, progesterone works to reduce programmed cell death (apoptosis) which can occur weeks to months after the initial injury cascade has subsided, and stimulates glial cells such as oligodendrocytes in the brain and Schwann cells in the peripheral nervous system to make more myelin and restore more normal nerve conduction.

The most important outcome of this research to date has been support from the National Institute of Neurological Disorders and Stroke for a Phase IIa, double-blind, randomized trial to test progesterone in 100 patients with moderate to severe TBI. Phase II trials are primarily concerned with whether or not a new treatment is safe, and secondarily with whether there is evidence of functional benefit. Safety was monitored by an NIH-selected Data Safety Monitoring Board, who found no evidence of serious adverse events attributable to the treatment (4 days of intravenously administered progesterone). This was gratifying, to say the least, but the study also revealed that progesterone treatment reduced mortality by almost 60% compared to state-of-the-art treatment without progesterone. Much more clinical work in a multi-center setting needs to be done before any firm conclusions can be drawn, but we do know that to date this is the only successful outcome for a clinical trial in TBI. It is exciting to see the laboratory research brought to the clinic, where a multi-disciplinary team of clinicians and scientists has been able to work closely to offer real hope to the victims of TBI. Both basic and clinical research must continue, to see whether the same benefits might be available to stroke patients, and to patients with either disorder at all age levels from pediatric injury through old age.


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Baxter, L. C., Saykin, A. J., Flashman, L. A., Johnson, S. C., Guerin, S. J., Babcock, D. R., Wishart, H. A., 2003. Sex differences in semantic language processing: a functional MRI study. Brain Lang 84, 264-272.

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Roof, R. L., Stein, D. G., 1992. Progesterone treatment attenuates brain edema following contusion injury in male and female rats. Restor. Neurol. Neurosc 4, 425-427.

Shaywitz, B. A., Shaywitz, S. E., Pugh, K. R., Constable, R. T., Skudlarski, P., Fulbright, R. K., Bronen, R. A., Fletcher, J. M., Shankweiler, D. P., Katz, L., et al., 1995. Sex differences in the functional organization of the brain for language [see comments]. Nature 373, 607-609.

Stein, D. G., 2004. Brain Trauma, Sex Hormones, Neuronal Survival and Recovery of Function. In: Legato, M. (ed.), Principles Of Gender-Specific Medicine. Academic Press, New York, pp. 104-115.

Temkin, N.R., Anderson, G.D. Winn, H.R., Britz, G., Schuster, J., Lucas, Y., Newell, D.W., Nelson, P., Machamer, J., Barber, J., Dikmen, S.S., 2005. Magnesium sulfate for neuorprotection after traumatic brain injury: a randomized trial.  23rd Annual National Neurotrauma symposium, Washington, D.C.