Inhibition of MMP-9 activity following hypoxic ischemia in the developing brain using a highly specific inhibitor.

Perinatal hypoxic ischemic (HI) brain injury is a leading cause of long-term neurological handicap in newborn babies. Recently, excessive activity of matrix metalloproteinases (MMPs), and in particular MMP-9, has been implicated in the aetiology of HI injuries to the immature brain. Our previous study suggested that MMP-9 may be involved in the development of the delayed injury processes following HI injury to the developing brain. Given this, we therefore propose that MMP-9 may be a useful target for rescue therapies in the injured developing brain. To address this, we chose to use SB-3CT, a highly selective inhibitor that is known to target only MMP-2 and MMP-9, to attenuate the elevated MMP-9 activity seen following HI injury to the developing brain. Twenty-one-day-old postnatal Wistar rats were subjected to unilateral carotid artery occlusion followed by exposure to hypoxia (8% oxygen for 1 h). SB-3CT (50 mg/kg body weight in 25% dimethyl sulphoxide/75% polyethylene glycol) or an equal volume of vehicle or saline diluent was then administered intraperitoneally at 2, 5 and 14 h following the insult. Gelatin zymography revealed that pro-MMP-9 levels were significantly reduced at 6 h following hypoxic ischaemia (p ≤ 0.05). However, our results showed that despite significantly inhibiting brain pro-MMP-9 activity after hypoxic ischaemia, SB-3CT failed to confer significant neuroprotection in postnatal day 21 rats 3 days after an HI insult. Further investigations are warranted using a recently reported selective water-soluble version of SB-3CT or another MMP-9 selective inhibitor to resolve the role of MMP-9 in the aetiology of HI injury in the developing brain.

Age-related memory decline is associated with vascular and microglial degeneration in aged rats.

The hippocampus processes memory is an early target of aging-related biological and structural lesions, leading to memory decline. With absent neurodegeneration in the hippocampus, which identified in rodent model of normal aging the pathology underlying age-related memory impairment is not complete. The effective glial-vascular networks are the key for maintaining neuronal functions. The changes of glial cells and cerebral capillaries with age may contribute to memory decline. Thus we examined age associated changes in neurons, glial phenotypes and microvasculature in the hippocampus of aged rats with memory decline. Young adult (6 months) and aged (35 months) male rats (Fisher/Norway-Brown) were used. To evaluate memory, four days of acquisition phase of Morris water maze tasks were carried out in both age groups and followed by a probe trial 2 h after the acquisition. The brains were then collected for analysis using immunochemistry. The aged rats showed a delayed latency (p<0.001) and longer swimming path (p<0.001) to locate a hidden platform. They also spent less time in and made delayed and fewer entries into the correct quadrant during the probe trial. Without seen neuronal degeneration, the aged rats with memory impairments have displayed dopamine depletion, profound vascular and microglial degeneration with reduced vascular endothelial growth factor and elevated GFAP expression in the hippocampus. The data indicate the memory decline with age is associated with neuronal dysfunction, possibly due to impaired glial-vascular-neuronal networks, but not neuronal degeneration. Glial and vascular degeneration found in aged rats may represent early event of aging pathology prior to neuronal degeneration.

NNZ-2566: a Gly-Pro-Glu analogue with neuroprotective efficacy in a rat model of acute focal stroke.

The N-terminal cleavage product of human insulin-like growth factor-1 (IGF-1) in the brain is the tripeptide molecule Glypromate (Gly-Pro-Glu). Glypromate has demonstrated neuroprotective effects in numerous in vitro and in vivo models of brain injury and is in clinical trials for the prevention of cognitive impairment following cardiac surgery. NNZ-2566 is a structural analogue of Glypromate, resulting from alpha-methylation of the proline moiety, which has improved the elimination half-life and oral bioavailability over the parent peptide. In vivo, NNZ-2566 reduces injury size in rats subjected to focal stroke. An intravenous infusion of NNZ-2566 of 4 h duration (3-10 mg/kg/h), initiated 3 h after endothelin-induced middle-cerebral artery constriction, significantly reduced infarct area as assessed on day 5. Neuroprotective efficacy in the MCAO model was also observed following oral administration of the drug (30-60 mg/kg), when formulated as a microemulsion. In vitro, NNZ-2566 significantly attenuates apoptotic cell death in primary striatal cultures, suggesting attenuation of apoptosis is one mechanism of action underlying its neuroprotective effects. NNZ-2566 is currently in clinical trials for the treatment of cognitive deficits following traumatic brain injury, and these data further support the development of the drug as a neuroprotective agent for acute brain injury.

Selective cortical alteration after hypoxic-ischemic injury in the very immature rat brain.

Distinctive cerebral lesions with disruptions to the developing white matter are found in very low birth weight (VLBW) infants. Although hypoxia-ischemia (HI) is a causal pathway, the pathogenesis of cerebral white matter injury in the VLBW infant is not fully understood. Pertinent murine models would facilitate the investigation of the processes leading to these cerebral lesions and enable the evaluation of therapeutic strategies. Postnatal d 3 (P3) rats are at a stage of cortical oligodendroglial maturation and axonal outgrowth similar to very preterm infants. Our aim was to characterize the effects of a focal hypoxic-ischemic injury at P3 on subsequent cerebral development. Three groups of P3 Wistar rats were investigated: group I underwent right carotid ligation followed by 6% hypoxia for 30 min (HI), group 2 had carotid ligation only, and group 3 had no intervention. At P21, in the HI group, the right cortical area was reduced compared with controls (p < 0.01). There were no significant alterations in the size of the dorsal hippocampus, striatum, and thalamus. The cortical myelinated area was reduced in the HI animals compared with controls (p < 0.01). There was a corresponding loss of myelinated axons extending up into the cortex, with deep cortical neuronal and axonal architecture markedly disrupted. Glial fibrillary acidic protein immunohistology showed a reactive gliosis in the deep parietal cortex (p < 0.01). Moderate HI injury in the immature rat brain compromised cortical growth and led to a selective alteration of cortical myelinated axons with persistent gliosis. These alterations induced at P3 by unilateral HI share neuropathological similarities with the diffuse white matter lesions found in VLBW infants.