Dynamic Changes in the Endocannabinoid System during the Aging Process: Focus on the Middle-Age Crisis.

Endocannabinoid (eCB) signaling is markedly decreased in the hippocampus (Hip) of aged mice, and the genetic deletion of the cannabinoid receptor type 1 (CB1) leads to an early onset of cognitive decline and age-related histological changes in the brain. Thus, it is hypothesized that cognitive aging is modulated by eCB signaling through CB1. In the present study, we detailed the changes in the eCB system during the aging process using different complementary techniques in mouse brains of five different age groups, ranging from adolescence to old age. Our findings indicate that the eCB system is most strongly affected in middle-aged mice (between 9 and 12 months of age) in a brain region-specific manner. We show that 2-arachidonoylglycerol (2-AG) was prominently decreased in the Hip and moderately in caudate putamen (CPu), whereas anandamide (AEA) was decreased in both CPu and medial prefrontal cortex along with cingulate cortex (mPFC+Cg), starting from 6 months until 12 months. Consistent with the changes in 2-AG, the 2-AG synthesizing enzyme diacylglycerol lipase α (DAGLα) was also prominently decreased across the sub-regions of the Hip. Interestingly, we found a transient increase in CB1 immunoreactivity across the sub-regions of the Hip at 9 months, a plausible compensation for reduced 2-AG, which ultimately decreased strongly at 12 months. Furthermore, quantitative autoradiography of CB1 revealed that [3H]CP55940 binding markedly increased in the Hip at 9 months. However, unlike the protein levels, CB1 binding density did not drop strongly at 12 months and at old age. Furthermore, [3H]CP55940 binding was significantly increased in the lateral entorhinal cortex (LEnt), starting from the middle age until the old age. Altogether, our findings clearly indicate a middle-age crisis in the eCB system, which could be a potential time window for therapeutic interventions to abrogate the course of cognitive aging.

Efficacy of Δ9 -Tetrahydrocannabinol (THC) Alone or in Combination With a 1:1 Ratio of Cannabidiol (CBD) in Reversing the Spatial Learning Deficits in Old Mice.

Decline in cognitive performance, an aspect of the normal aging process, is influenced by the endocannabinoid system (ECS). Cannabinoid receptor 1 (CB1) signaling diminishes with advancing age in specific brain regions that regulate learning and memory and abolishing CB1 receptor signaling accelerates cognitive aging in mice. We recently demonstrated that prolonged exposure to low dose (3 mg/kg/day) Δ9-tetrahydrocannabinol (THC) improved the cognitive performances in old mice on par with young untreated mice. Here we investigated the potential influence of cannabidiol (CBD) on this THC effect, because preclinical and clinical studies indicate that the combination of THC and CBD often exhibits an enhanced therapeutic effect compared to THC alone. We first tested the effectiveness of a lower dose (1 mg/kg/day) THC, and then the efficacy of the combination of THC and CBD in 1:1 ratio, same as in the clinically approved medicine Sativex®. Our findings reveal that a 1 mg/kg/day THC dose still effectively improved spatial learning in aged mice. However, a 1:1 combination of THC and CBD failed to do so. The presence of CBD induced temporal changes in THC metabolism ensuing in a transient elevation of blood THC levels. However, as CBD metabolizes, the inhibitory effect on THC metabolism was alleviated, causing a rapid clearance of THC. Thus, the beneficial effects of THC seemed to wane off more swiftly in the presence of CBD, due to these metabolic effects. The findings indicate that THC-treatment alone is more efficient to improve spatial learning in aged mice than the 1:1 combination of THC and CBD.

Follow up: palmitic acid ester of tetrahydrocannabinol (THC) and palmitic acid diester of 11-hydroxy-THC - unsuccessful search for additional THC metabolites.

OBJECTIVES: In a previous investigation we searched for the occurrence of palmitic acid ester compounds of delta9-tetrahydrocannabinol (THC) and its primary metabolite 11-hydroxy-delta9-THC (11-OH-THC) in human body fluids and tissues (THC palmitic acid monoester [THC-Pal] and 11-OH-THC palmitic acid diester [11-OH-THC-DiPal]). As those esters could not be detected in various human body fluids (e.g. blood) or tissues (e.g. adipose tissue) we extended the investigation analyzing adipose tissue samples of mice previously given synthetic THC or a cannabis extract. METHODS: In total, 48 adipose tissue samples previously tested positive for THC by means of a liquid chromatographic triple quadrupole mass spectrometric (LC-QQQ-MS) method were analyzed for the presence of THC-Pal and 11-OH-THC-DiPal by means of LC-QQQ-MS. RESULTS: THC-Pal and 11-OH-THC-DiPal were not detected among the adipose tissue samples analyzed despite the presence of high THC concentrations within the adipose tissue. THC concentrations in adipose tissue were in a range of approximately 7-2,595 ng/g (median: 468 ng/g, average: 704 ng/g). CONCLUSIONS: A (site-specific) synthesis of 11-OH-THC palmitic acid monoesters (11-hydroxy-delta9-THC-1-palmitate and 11-palmitoyloxy-delta9-THC) still remains to be done. After synthesis of these monoesters, their presence in the body fluids and tissues after THC administration should be investigated.

Follow up: palmitic acid ester of tetrahydrocannabinol (THC) and palmitic acid diester of 11-hydroxy-THC - unsuccessful search for additional THC metabolites.

OBJECTIVES: In a previous investigation we searched for the occurrence of palmitic acid ester compounds of delta9-tetrahydrocannabinol (THC) and its primary metabolite 11-hydroxy-delta9-THC (11-OH-THC) in human body fluids and tissues (THC palmitic acid monoester [THC-Pal] and 11-OH-THC palmitic acid diester [11-OH-THC-DiPal]). As those esters could not be detected in various human body fluids (e.g. blood) or tissues (e.g. adipose tissue) we extended the investigation analyzing adipose tissue samples of mice previously given synthetic THC or a cannabis extract. METHODS: In total, 48 adipose tissue samples previously tested positive for THC by means of a liquid chromatographic triple quadrupole mass spectrometric (LC-QQQ-MS) method were analyzed for the presence of THC-Pal and 11-OH-THC-DiPal by means of LC-QQQ-MS. RESULTS: THC-Pal and 11-OH-THC-DiPal were not detected among the adipose tissue samples analyzed despite the presence of high THC concentrations within the adipose tissue. THC concentrations in adipose tissue were in a range of approximately 7-2,595 ng/g (median: 468 ng/g, average: 704 ng/g). CONCLUSIONS: A (site-specific) synthesis of 11-OH-THC palmitic acid monoesters (11-hydroxy-delta9-THC-1-palmitate and 11-palmitoyloxy-delta9-THC) still remains to be done. After synthesis of these monoesters, their presence in the body fluids and tissues after THC administration should be investigated.

Parkin cooperates with GDNF/RET signaling to prevent dopaminergic neuron degeneration.

Parkin and the glial cell line-derived neurotrophic factor (GDNF) receptor RET have both been independently linked to the dopaminergic neuron degeneration that underlies Parkinson's disease (PD). In the present study, we demonstrate that there is genetic crosstalk between parkin and the receptor tyrosine kinase RET in two different mouse models of PD. Mice lacking both parkin and RET exhibited accelerated dopaminergic cell and axonal loss compared with parkin-deficient animals, which showed none, and RET-deficient mice, in which we found moderate degeneration. Transgenic expression of parkin protected the dopaminergic systems of aged RET-deficient mice. Downregulation of either parkin or RET in neuronal cells impaired mitochondrial function and morphology. Parkin expression restored mitochondrial function in GDNF/RET-deficient cells, while GDNF stimulation rescued mitochondrial defects in parkin-deficient cells. In both cases, improved mitochondrial function was the result of activation of the prosurvival NF-κB pathway, which was mediated by RET through the phosphoinositide-3-kinase (PI3K) pathway. Taken together, these observations indicate that parkin and the RET signaling cascade converge to control mitochondrial integrity and thereby properly maintain substantia nigra pars compacta dopaminergic neurons and their innervation in the striatum. The demonstration of crosstalk between parkin and RET highlights the interplay in the protein network that is altered in PD and suggests potential therapeutic targets and strategies to treat PD.

Critical cysteines in Akt1 regulate its activity and proteasomal degradation: implications for neurodegenerative diseases.

Impaired Akt1 signaling is observed in neurodegenerative diseases, including Parkinson׳s disease (PD). In PD models oxidative modification of Akt1 leads to its dephosphorylation and consequent loss of its kinase activity. To explore the underlying mechanism we exposed Neuro2A cells to cadmium, a pan inhibitor of protein thiol disulfide oxidoreductases, including glutaredoxin 1 (Grx1), or downregulated Grx1, which led to dephosphorylation of Akt1, loss of its kinase activity, and also decreased Akt1 protein levels. Mutation of cysteines to serines at 296 and 310 in Akt1 did not affect its basal kinase activity but abolished cadmium- and Grx1 downregulation-induced reduction in Akt1 kinase activity, indicating their critical role in redox modulation of Akt1 function and turnover. Cadmium-induced decrease in phosphorylated Akt1 correlated with increased association of wild-type (WT) Akt1 with PP2A, which was absent in the C296-310S Akt1 mutant and was also abolished by N-acetylcysteine treatment. Further, increased proteasomal degradation of Akt1 by cadmium was not seen in the C296-310S Akt1 mutant, indicating that oxidation of cysteine residues facilitates degradation of WT Akt1. Moreover, preventing oxidative modification of Akt1 cysteines 296 and 310 by mutating them to serines increased the cell survival effects of Akt1. Thus, in neurodegenerative states such as PD, maintaining the thiol status of cysteines 296 and 310 in Akt1 would be critical for Akt1 kinase activity and for preventing its degradation by proteasomes. Preventing downregulation of Akt signaling not only has long-range consequences for cell survival but could also affect the multiple roles that Akt plays, including in the Akt-mTOR signaling cascade.

Redox modification of Akt mediated by the dopaminergic neurotoxin MPTP, in mouse midbrain, leads to down-regulation of pAkt.

Impairment of Akt phosphorylation, a critical survival signal, has been implicated in the degeneration of dopaminergic neurons in Parkinson's disease. However, the mechanism underlying pAkt loss is unclear. In the current study, we demonstrate pAkt loss in ventral midbrain of mice treated with dopaminergic neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), when compared to ventral midbrain of control mice treated with vehicle alone. Thiol residues of the critical cysteines in Akt are oxidized to a greater degree in mice treated with MPTP, which is reflected as a 40% loss of reduced Akt. Association of oxidatively modified Akt with the phosphatase PP2A, which can lead to enhanced dephosphorylation of pAkt, was significantly stronger after MPTP treatment. Maintaining the protein thiol homeostasis by thiol antioxidants prevented loss of reduced Akt, decreased association with PP2A, and maintained pAkt levels. Overexpression of glutaredoxin, a protein disulfide oxidoreductase, in human primary neurons helped sustain reduced state of Akt and abolished MPP(+)-mediated pAkt loss. We demonstrate for the first time the selective loss of Akt activity, in vivo, due to oxidative modification of Akt and provide mechanistic insight into oxidative stress-induced down-regulation of cell survival pathway in mouse midbrain following exposure to MPTP.

Redox activated MAP kinase death signaling cascade initiated by ASK1 is not activated in female mice following MPTP: novel mechanism of neuroprotection.

Incidence of Parkinson's disease (PD) is lower in women compared to men (1:1.46), which is reflected in animal models. However, precise mechanisms are unclear. Administration of MPTP (1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine) to female mice does not lead to mitochondrial complex I inhibition as seen in males and the progressive dopaminergic cell loss in substantia nigra (SNpc) is significantly attenuated. Redox driven apoptotic signaling pathways regulated by thiol disulfide oxidoreductase(s) have been implicated in the neurodegeneration seen in PD. Oxidation of thioredoxin leads to activation of apoptosis signal regulating kinase 1 (ASK1; MAPKKK) initiating cell death cascade through MAP kinase(s). Higher constitutive expression of enzymes involved in cellular redox maintenance, such as glutathione reductase, thioredoxin, and thioredoxin reductase is observed in female brain. Exposure to MPTP activates ASK1 in male but not in female mice. Higher expression of Trx in females potentially prevents ASK1 activation. Downstream of ASK1, phosphorylation of p38 MAP kinase is seen in male but not female mice. Expression of DJ-1, the redox sensing protein is higher in females and the loss of nuclear DJ-1, followed by translocation of Daxx (death associated protein) from the nucleus to the cytosol, which promotes ASK1 mediated death cascade is not seen in females. The enzymes involved in redox maintenance potentially could play a crucial role in preventing the activation of redox driven death signaling cascade and offer neuroprotection. Theraupeutic strategies that help maintain redox homeostasis may help prevent the progressive neurodegeneration seen in PD.