Alpha-methyltyrosine reduces the acute cardiovascular and behavioral sequelae in a murine model of traumatic brain injury.

BACKGROUND: Increased catecholamines contribute to heightened cardiovascular reactivity and behavioral deficits after traumatic brain injury (TBI); adrenergic receptor blockade has limited success in reducing adverse sequelae of TBI. Injury-induced increases in the synthesis of catecholamines could contribute to adverse outcomes in TBI. Inhibition of catecholamine synthesis with alpha-methyltyrosine (αMT) could offer a benefit after TBI. METHODS: Original research trial in mice randomized to αMT (50 mg·kg -1 ·d -1 ) or vehicle for 1 week after TBI induced by controlled cortical impact. Primary outcomes of cardiovascular reactivity and behavioral deficits were assessed after 1 week. Secondary outcomes included blood brain barrier permeability and quantification of gene transcription whose products determine intraneuronal chloride concentrations, the release of catecholamines, and activation of the sympathetic nervous system. These genes were the alpha-2 adrenergic receptor ("Adra2c"), the sodium-potassium-chloride cotransporter ("Nkcc1"), and the potassium chloride cotransporter ("Kcc2"). We also assessed the effect of TBI and αMT on the neuronal chloride/bicarbonate exchanger ("Ae3"). RESULTS: Traumatic brain injury-induced increases in blood pressure and cardiac reactivity were blocked by αMT. Inhibition of catecholamine synthesis decreased blood brain barrier leakage and improved behavioral outcomes after TBI. Traumatic brain injury diminished the transcription of Adra2c and enhanced expression of Nkcc1 while reducing Kcc2 transcription; αMT prevented the induction of the Nkcc1 by TBI without reversing the effects of TBI on Kcc2 expression; αMT also diminished Ae3 transcription. CONCLUSION: Traumatic brain injury acutely increases cardiovascular reactivity and induces behavioral deficits in an αMT-sensitive manner, most likely by inducing Nkcc1 gene transcription. Alpha-methyltyrosine may prove salutary in the treatment of TBI by attenuating the enhanced expression of Nkcc1, minimizing blood brain barrier leakage, and diminishing central catecholamine and sympathetic output. We also found an unreported relationship between Kcc2 and the chloride/bicarbonate exchanger, which should be considered in the design of trials planned to manipulate central intraneuronal chloride concentrations following acute brain injury.

Ivabradine-Induced Bradycardia is Accompanied by Reduced Stress-Related Anxiety.

BACKGROUND: Hypertensive individuals with higher heart rates and anxiety have greater cardiovascular morbidity and mortality. Despite the correlation between hypertension, heart rate, and anxiety, scant attention has been paid to the effect of hypertension drug therapy on behavioral outcomes in cardiovascular disease. Ivabradine, an inhibitor of hyperpolarization-activated, cyclic nucleotide-gated funny channels (HCNs), has been used clinically to reduce heart rates and has been shown to improve quality of life in patients with angina and heart failure. We postulated that in addition to lowering heart rate, ivabradine could reduce anxiety in mice exposed to a significant stress paradigm. METHODS: Mice underwent a stress induction protocol, subsequently they received either vehicle or ivabradine (10 mg/kg) via osmotic minipumps. Blood pressure and heart rates were measured with tail cuff photoplethysmography. Anxiety was assessed quantitatively through the open field test (OFT) and the elevated plus maze (EPM). Cognition was assessed with an object recognition test (ORT). Pain tolerance was measured by the hot plate test or subcutaneous injection of formalin. HCN gene expression was measured with RT-PCR. RESULTS: Ivabradine reduced resting heart rate in the stressed mice by 22%. Stressed mice treated with ivabradine displayed significantly greater exploratory behavior in the OFT, EPM, and ORT. The expression of central HCN channels was significantly reduced following stress. CONCLUSION: It is suggested from our findings that ivabradine can reduce anxiety following significant psychological stress. Reductions in heart rate may directly improve quality of life by reducing anxiety in patients with hypertension and high heart rates.

THIRSTY FOR FRUCTOSE: Arginine Vasopressin, Fructose, and the Pathogenesis of Metabolic and Renal Disease.

We review the pathways by which arginine vasopressin (AVP) and hydration influence the sequelae of the metabolic syndrome induced by high fructose consumption. AVP and inadequate hydration have been shown to worsen the severity of two phenotypes associated with metabolic syndrome induced by high fructose intake-enhanced lipogenesis and insulin resistance. These findings have implications for those who frequently consume sweeteners such as high fructose corn syrup (HFCS). Patients with metabolic syndrome are at higher risk for microalbuminuria and/or chronic kidney disease; however, it is difficult to discriminate the detrimental renal effects of the metabolic syndrome from those of hypertension, impaired glucose metabolism, and obesity. It is not surprising the prevalence of chronic renal insufficiency is growing hand in hand with obesity, insulin resistance, and metabolic syndrome in those who consume large amounts of fructose. Higher AVP levels and low hydration status worsen the renal insufficiency found in patients with metabolic syndrome. This inter-relationship has public health consequences, especially among underserved populations who perform physical labor in environments that place them at risk for dehydration. MesoAmerican endemic nephropathy is a type of chronic kidney disease highly prevalent in hot ambient climates from southwest Mexico through Latin America. There is growing evidence that this public health crisis is being spurred by greater fructose consumption in the face of dehydration and increased dehydration-dependent vasopressin secretion. Work is needed at unraveling the mechanism(s) by which fructose consumption and increased AVP levels can worsen the renal disease associated with components of the metabolic syndrome.

Acetazolamide increases locomotion, exploratory behavior, and weight loss following social stress: A treatment for emotional eating?

Sympathomimetics are effective, centrally acting drugs that induce weight loss through their potent anorexic and locomotor properties. We reported that sympathomimetics antagonize catecholamine-dependent, alpha-2 adrenergic receptor-dependent signal transduction mediated by chloride/bicarbonate transport. We posit that other drugs that target cellular chloride/bicarbonate antiport would similarly demonstrate anorectic properties, induce locomotion, and diminish weight gain. Male and female inbred mice were housed in groups or stressed by prolonged social isolation. Mice consumed either normal chow or a high fat, high fructose corn syrup, (i.e. "Western") diet. To inhibit chloride/bicarbonate transport, acetazolamide (ACT, 3 mM) was added to the drinking water. Rodents underwent evaluations of exploratory locomotion and learning with the object recognition test. Mice consuming a "Western" diet gain more weight compared to mice given a normal diet. When placed on a "Western" diet, stressed mice gained weight more rapidly than unstressed. The body weight of mice fed a normal diet with ACT was significantly reduced compared to control mice not given ACT (weight, g ± SEM), 23.7 ± 0.8 v. 21.0 ± 0.5, p = 0.02. ACT did not reduce weight gain in animals chronically maintained on a "Western" diet. Compared to unstressed mice, living in social isolation reduced spontaneous exploratory locomotion time, an indicator of anxiety, in male mice (sec +SEM) from 22.8 ± 3.5 to 12.2 ± 2.1 (p < 0.001), and in female mice, from 47 ± 5.7 to 19.6 ± 2.3 (p < 0.001). ACT had no effect on exploration time in unstressed mice, but ACT completely restored the diminished exploratory locomotion time found in stressed mice compared to unstressed mice. The ratio of time spent exploring new objects compared to familiar items (discrimination ratio [DR]) was reduced following social isolation in males from 2.6 ± 0.5 to 1.2 ± 0.2 (p < 0.05) and in females from 3.8 ± 0.6 to 1.5 ± 0.2 (p < 0.01). ACT normalized the DR ratio of the stressed mice. Decreased food consumption and greater locomotor activity induced by ACT may contribute to acute weight loss; this effect is diminished when rodents were maintained on an unhealthful Western diet. Inhibition of chloride/bicarbonate transport through agents such as acetazolamide could offer a safe, new approach to achieving weight loss.

Canine neuronal ceroid lipofuscinoses: Promising models for preclinical testing of therapeutic interventions.

The neuronal ceroid lipofuscinoses (NCLs) are devastating inherited progressive neurodegenerative diseases, with most forms having a childhood onset of clinical signs. The NCLs are characterized by progressive cognitive and motor decline, vision loss, seizures, respiratory and swallowing impairment, and ultimately premature death. Different forms of NCL result from mutations in at least 13 genes. The clinical signs of some forms overlap significantly, so genetic testing is the only way to definitively determine which form an individual patient suffers from. At present, an effective treatment is available for only one form of NCL. Evidence of NCL has been documented in over 20 canine breeds and in mixed-breed dogs. To date, 12 mutations in 8 different genes orthologous to the human NCL genes have been found to underlie NCL in a variety of dog breeds. A Dachshund model with a null mutation in one of these genes is being utilized to investigate potential therapeutic interventions, including enzyme replacement and gene therapies. Demonstration of the efficacy of enzyme replacement therapy in this model led to successful completion of human clinical trials of this treatment. Further research into the other canine NCLs, with in-depth characterization and understanding of the disease processes, will likely lead to the development of successful therapeutic interventions for additional forms of NCL, for both human patients and animals with these disorders.

Cervical spinal cord and motor unit pathology in a canine model of SOD1-associated amyotrophic lateral sclerosis.

Development of effective treatments for amyotrophic lateral sclerosis (ALS) would be facilitated by identification of early events in the pathological cascade of disease progression. Degenerative myelopathy (DM), a naturally occurring disease in dogs, is quite similar to forms of ALS associated with SOD1 mutations and is likely to be a good model for these forms of the human disease. The sequence of histopathological changes that occur in DM was characterized by analyzing tissue samples obtained from affected dogs euthanized at various stages of disease progression. Cervical spinal cord and the associated spinal nerve roots, ulnar nerve, and the extensor carpi radialis (ECR) muscle were obtained from Pembroke Welsh Corgi dogs (PWCs) with early and late stage DM and from age-matched unaffected PWCs. In early stage disease there was a substantial change in the ratio of the two main muscle fiber types and an increase in mean muscle fiber area in the ECR. DM, even in late stage disease, was not accompanied by changes in the number of motor neuron cell bodies, in the number of axons in the motor or sensory nerve roots, or in the ulnar nerve. In addition, no disease-related denervation of the acetylcholine receptors of the ECR was observed at any stage of the disease. On the other hand, axon densities in both motor and sensory nerve tracts in the cervical cord were reduced in affected dogs. SOD1-immunoreactive aggregates were observed in spinal cord motor neuron cell bodies only in late stage disease. These findings suggest that some of the earliest pathological changes in DM occur in the muscle fibers and upper motor and sensory neuron tracts in the spinal cord. Targeting therapeutic interventions to these early events in the disease are most likely to be effective in slowing disease progression for DM and may translate to therapy of SOD1-related forms of ALS.