Neuroprotection

Combined neuroprotective effect of creatine and hypothermia in hypoxic-ischemic brain injury of neonatal rats.

Neonatal Hypoxia-Ischemia (HI) in the full term infant and can lead to long-term severe neurological deficits. To date there are few therapeutic interventions that have been successful in alleviating the clinical symptoms.

Animal models of HI have been vital for the study of treatment strategies. The neonatal rat model of HI (adapted from Levine’s rat ischemic stroke model) is relatively easy to perform and the progression of developing brain damage can be studied dynamically using magnetic resonance imaging techniques. Postnatal day 7 rats are exposed to a unilateral common carotid artery ligation followed by a period of recovery. The rats then undergo a period of hypoxia. This corresponds to a transient hemispheric insult and can be monitored using both MRI and MR spectroscopy.

MRI is used to visualize ongoing changes within the neonatal brain; cytotoxic edema is visible in diffusion-weighted images, and their corresponding apparent diffusion coefficient maps, shortly after the onset of hypoxia-ischemia. Vasogenic edema starts to be visible in T2-weighted images of neonatal rats within 2 hours of HI as fluids move from the bloodstream into the brain.

Changes in the levels of several metabolites, such as the decrease in ATP and phosphocreatine and concomitant increase in inorganic phosphate and lactate can be measured during this time with MRS. There is a short period of recovery during which time cellular energetics and metabolism approach normality due to the restored blood flow. However, this recovery is short lived and a secondary energy failure is observed.

Creatine, an endogenous guanidino compound, and phosphocreatine are crucial components of energy metabolism. The enzyme, creatine kinase uses ATP to convert Cr into the more stable source of high-energy phosphate, PCr. In times of high-energy requirement CK can carry out the reverse reaction, thus generating ATP from ADP and PCr. Oral supplementation of Cr has been shown to increase the concentration of both Cr and PCr in the brains of humans and animals. Creatine has been used as a putative neuroprotective agent in several models of neurological disease and trauma. Indeed, Cr has been shown to be neuroprotective in the neonatal rat model of HI.

We used the neonatal rat model of HI and evaluated the effect of Cr on cytotoxic and vasogenic lesion development 24 h post injury using a novel, objective method of analysis. In addition, we assessed the progression of the lesion into adulthood using MRI.

Methods

• MR: 3T scanner, T2- and diffusion weighted MRI, MRS
• Subjects: non-sexed Wistar rats.

Comparison of acute and long-term images. One typical image per animal (slice 5 from 8) from each group is shown. Top row, T2WI and middle row ADC maps derived from imaged captured 24 h post HI. Bottom row, adult T2WI of the same rat as at the acute stage. Note all HICon90 rats died within 1 week of HI..

Collaborations

Prof. Jürgen Hennig and Dr. Kamil Il’yasov, Medical Physics, Department of Diagnostic Radiology, University Hospital Freiburg, Germany

Support

Swiss Science Foundation

Contact

Prof. Dr. Ernst Martin
ernst.martinkispi.uzh.ch

Former collaborators

Dr. Thomas Loenneker