The mixed lipoxygenase/cyclooxygenase inhibitor SK&F 105809 reduces cerebral edema after closed head injury in rat

A Systematic Review of Closed Head Injury Models of Mild Traumatic Brain Injury in Mice and Rats

Mild TBI (mTBI) is a significant health concern. Animal models of mTBI are essential for understanding mechanisms, and pathological outcomes, as well as to test therapeutic interventions. A variety of closed head models of mTBI that incorporate different aspects (i.e., biomechanics) of the mTBI have been reported. The aim of the current review was to compile a comprehensive list of the closed head mTBI rodent models, along with the common data elements, and outcomes, with the goal to summarize the current state of the field. Publications were identified from a search of PubMed and Web of Science and screened for eligibility following PRISMA guidelines. Articles were included that were closed head injuries in which the authors classified the injury as mild in rats or mice. Injury model and animal-specific common data elements, as well as behavioral and histological outcomes, were collected and compiled from a total of 402 articles. Our results outline the wide variety of methods used to model mTBI. We also discovered that female rodents and both young and aged animals are under-represented in experimental mTBI studies. Our findings will aid in providing context comparing the injury models and provide a starting point for the selection of the most appropriate model of mTBI to address a specific hypothesis. We believe this review will be a useful starting place for determining what has been done and what knowledge is missing in the field to reduce the burden of mTBI.

Therapies targeting lipid peroxidation in traumatic brain injury

Lipid peroxidation can be broadly defined as the process of inserting a hydroperoxy group into a lipid. Polyunsaturated fatty acids present in the phospholipids are often the targets for peroxidation. Phospholipids are indispensable for normal structure of membranes. The other important function of phospholipids stems from their role as a source of lipid mediators - oxygenated free fatty acids that are derived from lipid peroxidation. In the CNS, excessive accumulation of either oxidized phospholipids or oxygenated free fatty acids may be associated with damage occurring during acute brain injury and subsequent inflammatory responses. There is a growing body of evidence that lipid peroxidation occurs after severe traumatic brain injury in humans and correlates with the injury severity and mortality. Identification of the products and sources of lipid peroxidation and its enzymatic or non-enzymatic nature is essential for the design of mechanism-based therapies. Recent progress in mass spectrometry-based lipidomics/oxidative lipidomics offers remarkable opportunities for quantitative characterization of lipid peroxidation products, providing guidance for targeted development of specific therapeutic modalities. In this review, we critically evaluate previous attempts to use non-specific antioxidants as neuroprotectors and emphasize new approaches based on recent breakthroughs in understanding of enzymatic mechanisms of lipid peroxidation associated with specific death pathways, particularly apoptosis. We also emphasize the role of different phospholipases (calcium-dependent and -independent) in hydrolysis of peroxidized phospholipids and generation of pro- and anti-inflammatory lipid mediators. This article is part of a Special Issue entitled SI:Brain injury and recovery.

Tocotrienols in health and disease: the other half of the natural vitamin E family

Tocochromanols encompass a group of compounds with vitamin E activity essential for human nutrition. Structurally, natural vitamin E includes eight chemically distinct molecules: alpha-, beta-, gamma- and delta-tocopherol; and alpha-, beta-, gamma- and delta-tocotrienol. Symptoms caused by alpha-tocopherol deficiency can be alleviated by tocotrienols. Thus, tocotrienols may be viewed as being members of the natural vitamin E family not only structurally but also functionally. Palm oil and rice bran oil represent two major nutritional sources of natural tocotrienol. Taken orally, tocotrienols are bioavailable to all vital organs. The tocotrienol forms of natural vitamin E possesses powerful hypocholesterolemic, anti-cancer and neuroprotective properties that are often not exhibited by tocopherols. Oral tocotrienol protects against stroke-associated brain damage in vivo. Disappointments with outcomes-based clinical studies testing the efficacy of alpha-tocopherol need to be handled with caution and prudence recognizing the untapped opportunities offered by the other forms of natural vitamin E. Although tocotrienols represent half of the natural vitamin E family, work on tocotrienols account for roughly 1% of the total literature on vitamin E. The current state of knowledge warrants strategic investment into investigating the lesser known forms of vitamin E.

Tocotrienols: the emerging face of natural vitamin E

Natural vitamin E includes eight chemically distinct molecules: alpha-, beta-, gamma-, and delta-tocopherols and alpha-, beta-, gamma-, and delta-tocotrienols. More than 95% of all studies on vitamin E are directed toward the specific study of alpha-tocopherol. The other forms of natural vitamin E remain poorly understood. The abundance of alpha-tocopherol in the human body and the comparable efficiency of all vitamin E molecules as antioxidants led biologists to neglect the non-tocopherol vitamin E molecules as topics for basic and clinical research. Recent developments warrant a serious reconsideration of this conventional wisdom. The tocotrienol subfamily of natural vitamin E possesses powerful neuroprotective, anticancer, and cholesterol-lowering properties that are often not exhibited by tocopherols. Current developments in vitamin E research clearly indicate that members of the vitamin E family are not redundant with respect to their biological functions. alpha-Tocotrienol, gamma-tocopherol, and delta-tocotrienol have emerged as vitamin E molecules with functions in health and disease that are clearly distinct from that of alpha-tocopherol. At nanomolar concentration, alpha-tocotrienol, not alpha-tocopherol, prevents neurodegeneration. On a concentration basis, this finding represents the most potent of all biological functions exhibited by any natural vitamin E molecule. Recently, it has been suggested that the safe dose of various tocotrienols for human consumption is 200-1000/day. A rapidly expanding body of evidence supports that members of the vitamin E family are functionally unique. In recognition of this fact, title claims in publications should be limited to the specific form of vitamin E studied. For example, evidence for toxicity of a specific form of tocopherol in excess may not be used to conclude that high-dosage "vitamin E" supplementation may increase all-cause mortality. Such conclusion incorrectly implies that tocotrienols are toxic as well under conditions where tocotrienols were not even considered. The current state of knowledge warrants strategic investment into the lesser known forms of vitamin E. This will enable prudent selection of the appropriate vitamin E molecule for studies addressing a specific health need.

A hypothesis accounting for the inconsistent benefit of glucocorticoid therapy in closed head trauma

Because of disagreement between clinical studies, the American College of Neurological Surgeons (ACNS) most recent recommendation (1996) is that glucocorticoids should not be used in the treatment of closed head trauma (CHT). The current paper reviews clinical studies of glucocorticoids and CHT in order to examine what factors might have accounted for the inconsistent results leading to the ACNS's recommendation. A careful analysIs of these studies reveals that, contrary to the ACNS's sweeping conclusion, the available data support the use of glucocorticoids for patients with CHT, but only in specific cases. Glucocorticoids may be beneficial in the treatment of CHT uncomplicated by intracranial hemorrhage; in situations where intracranial hemorrhage accompanies CHT, glucocorticoid treatment appears detrimental. The second part of this paper examines possible mechanisms accounting for the differential effectiveness of glucocorticoids in CHT patients with and without intracranial hemorrhage. These mechanisms include vasospasm, free radical damage, blood-borne factors, and glutamate neurotoxicity.

New anti-inflammatory treatment strategy in Alzheimer's disease

Numerous reports have indicated that patients suffering from inflammatory diseases (e.g., arthritis) who take anti-inflammatory medication have a reduced risk of developing Alzheimer's disease (AD). Thus, the first generation of anti-inflammatory cyclooxygenase (COX) inhibitors, such as aspirin and indomethacin, have been tested as potential therapeutics in AD. Because the inhibition of COX-1 is also known to cause tissue damage in the gastrointestinal system from the resultant reduced cytoprotection, selective COX-2 inhibitors are being investigated and tested clinically as potentially better therapeutics for AD patients. However, such drugs may also trigger unwanted effects; for example, the COX-2 inhibitors, which reduce the production of one type of eicosanoids, the prostaglandins, may increase the production of other eicosanoids; i.e., the leukotriene B4 (LTB4), which is one of the most potent endogenous chemotactic/inflammatory factors. LTB4 production is initiated by the enzyme 5-lipoxygenase (5-LOX). The expression of the 5-LOX gene is upregulated during neurodegeneration and with aging. In spite of the fact that 5-LOX and leukotrienes are major players in the inflammation cascade, their role in AD pathobiology/therapy has not been extensively investigated. We propose that the 5-LOX inflammatory cascade may take part in the process of aging-associated neurodegenerative diseases, and we point to the role of 5-LOX in neurodegeneration and discuss its relevance for anti-inflammatory therapy of AD.

Determination and clinical significance of plasma levels of prostaglandins in patients with acute brain injury

BACKGROUND

Models of brain injury in experimental animals have shown that the level of prostaglandins (PGs) is increased in damage brain tissue, and that PGs play an important role in secondary brain damage. Almost all previous studies of the relationship between PGs and brain injury have been carried out in animals. In the present study we show that the PGs change in humans with brain injury.

METHODS

The plasma levels of thromboxane B2, 6-Keto-PGF2alpha, prostaglandin F2alpha, and prostaglandin E2 were measured by radioimmunoassay on the 1st, 3rd, 7th, and 14th days after brain injury. The same measurements were made on a control group of 26 healthy volunteers.

RESULTS

The levels of all four PGs were elevated, most markedly in the first week, with levels remaining high in the second week in the severely injured. On the first day levels were, on average, three times those found in the controls, with a seven-fold rise in some of the severely injured patients. Dividing the patients into three groups according to outcome, it was found that if the PGs were markedly increased to begin with and remained high, death or permanent disability was likely. In the group with good outcome, the levels dropped steadily from the initial high levels. The T/K ratio was studied. It related closely to the severity of injury, being higher in more severe injuries and decreasing with recovery. In patients who did not recover, the ratio increased steadily to its highest value on the 7th day, and remained high at the 14th.

CONCLUSION

Changes in PGs levels were closely related to the brain injury severity and its outcome, and there was a marked disturbance of the levels of PGs, which therefore appears to be an important indicator of secondary brain damage.

Biphasic edema development after experimental brain contusion in rat

The time course of edema development following experimental brain contusion was studied by measuring cortex specific gravity 1 and 12 h after the trauma, and thereafter once daily until 7 days after the trauma. A biphasic development of edema was observed; the specific gravity decreased to a minimum on day 2 (P < 0.001), increased to an almost normal level on day 4 and thereafter decreased again to a second minimum 6 days after the trauma (P < 0.01). Delayed edema formation has been recognized in clinical settings, but has not been described in experimental studies. This study, with a prolonged daily follow-up, clearly demonstrates that a secondary phase of edema is an experimentally reproducible entity. The model will enable study of the pathogenetic mechanisms.

Concussion-induced retrograde amnesia in rats

Three experiments were conducted to investigate the characteristics of retrograde amnesia (RA) induced by concussion in rats. In Experiment 1, rats receiving experimental concussion shortly after training in a single punishment trial exhibited severe forgetting on a retention test 48 h later. In the second experiment, rats receiving a concussion within 6 h after training showed severe RA, while those receiving concussion one day to five days after training exhibited progressively weaker amnesia. In Experiment 3, amnesic animals in one group received pretest noncontingent foot shock as a reminder treatment. This pretest cue significantly increased the cross-through latency, thus indicating a reduction in the memory deficit resulting from concussion. These results suggest that experimental concussion can be an effective method to induce retrograde memory loss in rats; that the RA caused by concussion is time-dependent; and that concussion-induced RA can be alleviated by a pretest cue indicating that the underlying mechanism of concussion-induced RA is more likely to be a retrieval deficit than a consolidation failure.