Ramón Cacabelos

Celastrol, a potent antioxidant and anti-inflammatory drug, as a possible treatment for Alzheimer's disease

In the brains of patients with Alzheimers disease (AD) signs of neuronal degeneration are accompanied by markers of microglial activation, inflammation, and oxidant damage. The presence of nitrotyrosine in the cell bodies of neurons in AD suggests that peroxynitrite contributes to the pathogenesis of the disease. A drug with antioxidant and anti-inflammatory activity may prevent neuronal degeneration in AD. Celastrol, a plant-derived triterpene, has these effects. In low nanomolar concentrations celastrol was found to suppress the production by human monocytes and macrophages of the pro-inflammatory cytokines TNF-alpha and IL-1beta. Celastrol also decreased the induced expression of class II MHC molecules by microglia. In macrophage lineage cells and endothelial cells celastrol decreased induced but not constitutive NO production. Celastrol suppressed adjuvant arthritis in the rat, demonstrating in vivo anti-inflammatory activity. Low doses of celastrol administered to rats significantly improved their performance in memory, learning and psychomotor activity tests. The potent antioxidant and anti-inflammatory activities of celastrol, and its effects on cognitive functions, suggest that the drug may be useful to treat neurodegenerative diseases accompanied by inflammation, such as AD.

Serum TNF-alpha levels are increased and correlate negatively with free IGF-I in Alzheimer disease

Tumor necrosis factor-alpha (TNF-alpha) and insulin-like growth factor-I (IGF-I) have been involved in the pathogenesis of Alzheimers disease (AD) as neurotoxic and survival factors, respectively. Recent experimental studies suggest that the signalling pathways of TNF-alpha and IGF-I are functionally interrelated. In order to investigate the possible interaction of TNF-alpha and IGF-I in AD and mild cognitive impairment (MCI), the serum levels of total IGF-I, free IGF-I and TNF-alpha were determined in 141 AD patients, 56 MCI cases and 30 controls. As compared with controls, AD patients showed increased TNF-alpha and decreased IGF-I levels in serum, as well as a significant negative correlation between TNF-alpha and free IGF-I values. MCI patients also exhibited significantly higher TNF-alpha levels than controls. The present results suggest that increased TNF-alpha levels are involved in the pathogenesis of AD and MCI, and might antagonize the neurotrophic activity of IGF-I in these medical conditions. In addition, the combined determination of TNF-alpha and IGF-I might be useful to monitor anti-inflammatory and/or neurotrophic drug effects in AD.

Blood levels of histamine, IL-1β, and TNF-α in patients with mild to moderate alzheimer disease

In this study, we have evaluated the levels of blood histamine, serum interleukin-1 beta (IL-1β), and plasma tumor necrosis factor-alpha (TNF-α) in 20 patients with mild to moderate Alzheimer disease (AD; 13 early onset and 7 late-onset AD subjects) and in 20 agematched control subjects (C). AD patients showed higher concentrations of histamine (AD=452.9±237.9 pmol/mL; C=275.3±151.5 pmol/mL;p<0.05) and IL-1β (AD=211.2±31.1 pg/mL; C=183.4±24.4 pg/mL;p<0.01), and lower values of TNF-α (AD=3.59±2.02 pg/mL; C=9.47±2.64 pg/mL;p<0.001) than elderly controls. Increased levels of histamine and decreased levels of TNF-α were observed in both early onset AD (EOAD) and late-onset AD (LOAD) patients, but only EOAD subjects had elevated serum IL-1β values compared with age-matched controls. Age negatively correlated with histamine (r=−0.57;p<0.05) and positively with IL-1β levels (r=0.48;p<0.05) in healthy subjects, but not in AD, whereas a positive correlation between TNF-α scores and age was only found in AD patients (r=0.46;p<0.05). Furthermore, histamine and TNF-α values correlated negatively in AD (r=−0.50,p<0.05). In addition, cognitive impairment increased in patients with lower TNF-α and higher histamine and IL-1β levels, as indicated by the correlations between mental performance scores and histamine (r=−0.37, ns), IL-1β (r=−0.33, ns) and TNF-α levels (r=0.42,p<0.05). Finally, histamine concentrations decreased as depression scores increased in AD (r=−0.63,p<0.01). These data suggest a dysfunction in cytokine and histamine regulation in AD, probably indicating changes associated with inflammatory processes.

Histamine function in brain disorders

The neurotransmitter histamine (HA) has been implicated in the regulation of numerous and important activities of the central nervous system as arousal, cognition, circadian rhythms and neuroendocrine regulation. The data presented here indicate the participation of the histaminergic system in central nervous system disorders, such as Alzheimers disease and schizophrenia. We also present experimental data on histamine in an animal model of neurodegeneration and the cytotoxic effects of histamine on cultured rat endothelial cells. More studies are needed to investigate the role of the histaminergic system in central nervous system disorders. Peripheral cellular studies in health and disease, molecular studies on receptors and in vivo pharmacological studies may help us to better understand the function of the histaminergic system in health and disease.

Oxidative Stress Mediated Mitochondrial and Vascular Lesions as Markers in the Pathogenesis of Alzheimer Disease

Mitochondrial dysfunction plausibly underlies the aging-associated brain degeneration. Mitochondria play a pivotal role in cellular bioenergetics and cell-survival. Oxidative stress consequent to chronic hypoperfusion induces mitochondrial damage, which is implicated as the primary cause of cerebrovascular accidents (CVA) mediated Alzheimers disease (AD). The mitochondrial function deteriorates with aging, and the mitochondrial damage correlates with increased intracellular production of oxidants and pro-oxidants. The prolonged oxidative stress and the resultant hypoperfusion in the brain tissues stimulate the expression of nitric oxide synthase (NOS) enzymes, which further drives the formation of reactive oxygen species (ROS) and reactive nitrogen species (RNS). The ROS and RNS collectively contributes to the dysfunction of the blood-brain barrier (BBB) and damage to the brain parenchymal cells. Delineating the molecular mechanisms of these processes may provide clues for the novel therapeutic targets for CVA and AD patients.

Therapeutic Effects of CDP-Choline in Alzheimer's Disease-Cognition, Brain Mapping, Cerebrovascular Hemodynamics, and Immune Factorsa

CDP‐choline was given to patients with Alzheimers disease (AD) at a daily dose of 1000 mg/day p.o. for one month. This compound slightly improved mental performance, tended to reduce theta activity in fronto‐temporal regions, increasing alpha power in occipital areas, and enhanced cerebrovascular perfusion by increasing blood flow velocity and reducing pulsatility and resistance indexes. In addition, CDP‐choline diminished histamine and interleukin‐l levels in blood and serum, respectively, and increased plasma TNF.

Cerebrovascular risk factors in Alzheimer's disease: Brain hemodynamics and pharmacogenomic implications

Abstract Recent evidence indicates that different vascular risk factors are present in Alzheimers disease (AD) and other prevalent dementia types probably contributing to deterioration of cerebrovascular function, thus enhancing neurodegeneration and premature neuronal death due to a reduction in brain perfusion. Brain blood flow shows a reduced velocity and increased pulsatility (PI) and resistance indices (RI) in different types of dementia and in diabetes and hypertension, as well. High levels of diastolic blood pressure correlate with diminished brain blood flow and elevated PI and RI, accompanied by cognitive deterioration. Nitric oxide (NO) levels are found increased in the sera and brain tissue of AD patients. Vascular risk factors (hyperglycemia, LDL-cholesterol, triglycerides, hypertension) and altered brain hemodynamic parameters correlate with APOE genotypes of which APOE-4/4 carriers represent the AD population with the highest cerebrovascular risk. In addition, the genomic profiles of patients with dementia integrating AD-related genes (APOE, PS1, PS2, cFOS) in a mini-tetragenic haplotype significantly differ from controls with an absolute genetic variation of about 50%-60%. Cerebrovascular dysfunction is a factor common to most types of dementia; however, genetic variation among different dementia types might be determinant for the activation of early vascular events inducing or accelerating neurodegeneration. In this regard, cerebrovascular dysfunction should be considered a potential therapeutic target in dementia.

Pharmacogenetic Aspects of Therapy with Cholinesterase Inhibitors: The Role of CYP2D6 in Alzheimers Disease Pharmacogenetics

Recent studies demonstrate that the therapeutic response in Alzheimers disease (AD) is genotype-specific. More than 200 genes are potentially associated with AD pathogenesis and neurodegeneration, and approximately 1,400 genes distributed across the human genome account for 20 to 95% of variability in drug disposition and pharmacodynamics. Cytochrome P450 enzymes encoded by genes of the CYP superfamily, such as CYP1A1 (15q22-q24), CYP2A6 (19q13.2), CYP2C8 (10q24), CYP2C9 (10q24), CYP2C19 (10q24.1-q24.3), CYP2D6 (22q13.1), CYP2E1 (10q24.3-qter), and CYP3A5 (7q22.1), acting as terminal oxidases in multicomponent electron transfer chains which are called P450-containing monooxygenase systems, metabolize more than 90% of drugs. Some of the enzymatic products of the CYP gene superfamily can share substrates, inhibitors and inducers whereas others are quite specific for their substrates and interacting drugs. Some cholinesterase inhibitors (tacrine, donepezil, galantamine) are metabolized via CYP-related enzymes, especially CYP2D6, CYP3A4, and CYP1A2. The distribution of CYP2D6 genotypes in the Spanish population is the following: (a) Extensive Metabolizers (EM)(51.61%): *1/*1, 47.10%; and *1/*10, 4.52%; (b) Intermediate Metabolizers (IM)(32.26%): *1/*3, 1.95%; *1/*4, 17.42%; *1/*5, 3.87%; *1/*6, 2.58%; *1/*7, 0.75%; *10/*10, 1.30%; *4/*10, 3.23%; *6/*10, 0.65%; and *7/*10, 0.65%; (b) Poor Metabolizers (PM)(9.03%): *4/*4, 8.37%; and *5/*5, 0.65%; and (c) Ultrarapid Metabolizers (UM)(7.10%): *1xN/*1, 4.52%; *1xN/*4, 1.95%; and CYP2D6 gene duplications, 0.65%. PMs and UMs also accumulate genotypes of risk associated with APOE-, PS-, ACE-, and PRNP-related genes. Approximately, 15% of the AD population may exhibit an abnormal metabolism of cholinesterase inhibitors; about 50% of this population cluster would show an ultrarapid metabolism, requiring higher doses of cholinesterase inhibitors to reach a therapeutic threshold, whereas the other 50% of the cluster would exhibit a poor metabolism, displaying potential adverse events at low doses. In AD patients treated with a multifactorial therapy, including cholinesterase inhibitors (e.g., donepezil), the best responders are the CYP2D6-related EMs and IMs, and the worst responders are PMs and UMs. In addition, the presence of the APOE-4 allele in genetic clusters integrating CYP2D6 and APOE genotypes contributes to deteriorate the therapeutic outcome. From these data, it can be postulated that pharmacogenetic and pharmacogenomic factors are responsible for 75-85% of the therapeutic response in AD patients treated with conventional drugs.

β-Amyloid(1–40)-induced neurodegeneration in the rat hippocampal neurons of the CA1 subfield

Abstract Small volumes of solutions injected into the hippocampus produce dramatic degeneration in dentate gyrus neurons, but not in neurons of the CA1 subfield. The aim of the present study was to ascertain whether solutions with different fragments of the β-amyloid protein (Aβ) could produce further degeneration in areas beyond the dentate gyrus. It was found that 5 days after injection of an aqueous solution containing the Aβ 1–40 fragment into the hippocampus, long stretches of the CA1 subfield were either deprived of neurons or most of the neurons were degenerating. By contrast, in animals with deposits containing Aβ 1–28, Aβ 1–42 or water, neuronal degeneration or depletion only occurred in a reduced area around the place where the implant needle penetrated the CA1 subfield. In animals injected with Aβ 1–40, many profiles in the CA1 subfield and dentate gyrus were undergoing apoptosis, as seen using preparations processed by routine histology or the TUNEL technique for detection of fragmented DNA. In addition, there was higher infiltration by ED1-positive, activated microglia-macrophagic cells in Aβ 1–42 deposits than in deposits of Aβ 1–40. The present results suggest that the intrahippocampal injection of toxic Aβ fragments produces neuronal degeneration in the rat CA1 subfield when using the appropriate protocol, and, thus, can provide an in vivo model to investigate the neurotoxic effects of Aβ and for the evaluation of drugs with potential anti-neurodegenerative activity.

Parkinson's Disease: From Pathogenesis to Pharmacogenomics.

Parkinson’s disease (PD) is the second most important age-related neurodegenerative disorder in developed societies, after Alzheimer’s disease, with a prevalence ranging from 41 per 100,000 in the fourth decade of life to over 1900 per 100,000 in people over 80 years of age. As a movement disorder, the PD phenotype is characterized by rigidity, resting tremor, and bradykinesia. Parkinson’s disease -related neurodegeneration is likely to occur several decades before the onset of the motor symptoms. Potential risk factors include environmental toxins, drugs, pesticides, brain microtrauma, focal cerebrovascular damage, and genomic defects. Parkinson’s disease neuropathology is characterized by a selective loss of dopaminergic neurons in the substantia nigra pars compacta, with widespread involvement of other central nervous system (CNS) structures and peripheral tissues. Pathogenic mechanisms associated with genomic, epigenetic and environmental factors lead to conformational changes and deposits of key proteins due to abnormalities in the ubiquitin–proteasome system together with dysregulation of mitochondrial function and oxidative stress. Conventional pharmacological treatments for PD are dopamine precursors (levodopa, l-DOPA, l-3,4 dihidroxifenilalanina), and other symptomatic treatments including dopamine agonists (amantadine, apomorphine, bromocriptine, cabergoline, lisuride, pergolide, pramipexole, ropinirole, rotigotine), monoamine oxidase (MAO) inhibitors (selegiline, rasagiline), and catechol-O-methyltransferase (COMT) inhibitors (entacapone, tolcapone). The chronic administration of antiparkinsonian drugs currently induces the “wearing-off phenomenon”, with additional psychomotor and autonomic complications. In order to minimize these clinical complications, novel compounds have been developed. Novel drugs and bioproducts for the treatment of PD should address dopaminergic neuroprotection to reduce premature neurodegeneration in addition to enhancing dopaminergic neurotransmission. Since biochemical changes and therapeutic outcomes are highly dependent upon the genomic profiles of PD patients, personalized treatments should rely on pharmacogenetic procedures to optimize therapeutics.