Dementia and the Risk of Periodontitis: A Population-Based Cohort Study.

Dementia and Alzheimer's disease (AD) are proposed to be comorbid with periodontitis (PD). It is unclear whether PD is associated with dementia and AD independent of confounding factors. We aimed at identifying the relationship between the longitudinal risk of developing PD in a cohort of patients with dementia and AD who did not show any signs of PD at baseline. In this retrospective cohort study, 8,640 patients with dementia without prior PD were recruited, and 8,640 individuals without dementia history were selected as propensity score-matched controls. A Cox proportional hazard model was developed to estimate the risk of developing PD over 10 y. Cumulative probability was derived to assess the time-dependent effect of dementia on PD. Of the 8,640 patients, a sensitivity test was conducted on 606 patients with AD-associated dementia and 606 non-AD propensity score-matched controls to identify the impact of AD-associated dementia on the risk for PD. Subgroup analyses on age stratification were included. Overall 2,670 patients with dementia developed PD. The relative risk of PD in these patients was significantly higher than in the nondementia group (1.825, 95% CI = 1.715 to 1.942). Cox proportional hazard models showed that patients with dementia were more likely to have PD than individuals without dementia (adjusted hazard ratio = 1.915, 95% CI = 1.766 to 2.077, P < 0.0001, log-rank test P < 0.0001). The risk of PD in patients with dementia was age dependent (P values for all ages <0.0001); younger patients with dementia were more likely to develop PD. The findings persisted for patients with AD: the relative risk (1.531, 95% CI = 1.209 to 1.939) and adjusted hazard ratio (1.667, 95% CI = 1.244 to 2.232; log-rank test P = 0.0004) of PD in patients with AD were significantly higher than the non-AD cohort. Our findings demonstrated that dementia and AD were associated with a higher risk of PD dependent of age and independent of systemic confounding factors.

Intraperitoneal injection of the pancreatic peptide amylin potently reduces behavioral impairment and brain amyloid pathology in murine models of Alzheimer's disease.

Amylin, a pancreatic peptide, and amyloid-beta peptides (Aß), a major component of Alzheimer's disease (AD) brain, share similar ß-sheet secondary structures, but it is not known whether pancreatic amylin affects amyloid pathogenesis in the AD brain. Using AD mouse models, we investigated the effects of amylin and its clinical analog, pramlintide, on AD pathogenesis. Surprisingly, chronic intraperitoneal (i.p.) injection of AD animals with either amylin or pramlintide reduces the amyloid burden as well as lowers the concentrations of Aß in the brain. These treatments significantly improve their learning and memory assessed by two behavioral tests, Y maze and Morris water maze. Both amylin and pramlintide treatments increase the concentrations of Aß1-42 in cerebral spinal fluid (CSF). A single i.p. injection of either peptide also induces a surge of Aß in the serum, the magnitude of which is proportionate to the amount of Aß in brain tissue. One intracerebroventricular injection of amylin induces a more significant surge in serum Aß than one i.p. injection of the peptide. In 330 human plasma samples, a positive association between amylin and Aß1-42 as well as Aß1-40 is found only in patients with AD or amnestic mild cognitive impairment. As amylin readily crosses the blood-brain barrier, our study demonstrates that peripheral amylin's action on the central nervous system results in translocation of Aß from the brain into the CSF and blood that could be an explanation for a positive relationship between amylin and Aß in blood. As naturally occurring amylin may play a role in regulating Aß in brain, amylin class peptides may provide a new avenue for both treatment and diagnosis of AD.

Increased oxidative damage to DNA in a transgenic mouse model of Huntington's disease.

Mitochondrial dysfunction and oxidative damage may play a role in the pathogenesis of Huntington's disease (HD). We examined concentrations of 8-hydroxy-2-deoxyguanosine (OH(8)dG), a well-established marker of oxidative damage to DNA, in a transgenic mouse model of HD (R6/2). Increased concentrations of OH(8)dG were found in the urine, plasma and striatal microdialysates of the HD mice. Increased concentrations were also observed in isolated brain DNA at 12 and 14 weeks of age. Immunocytochemistry showed increased OH(8)dG staining in late stages of the illness. These results suggest that oxidative damage may play a role in the pathogenesis of neuronal degeneration in the R6/2 transgenic mouse model of HD.

Lipoic acid improves survival in transgenic mouse models of Huntington's disease.

There is substantial evidence implicating excitotoxicity and oxidative damage in the pathogenesis of Huntington's disease (HD). We therefore examined whether the antioxidants 2-sulpho-tert-phenyibutyinitrone (S-PBN) and alpha-lipoic acid could exert neuroprotective effects in transgenic mouse models of HD. S-PBN showed no effects on either weight loss or survival in the R6/2 transgenic HD mice. alpha-Lipoic acid produced significant increases in survival in both R6/2 and N171-82Q transgenic mouse models of HD. These findings suggest that alpha-lipoic acid might have beneficial effects in HD patients.

Therapeutic efficacy of EGb761 (Gingko biloba extract) in a transgenic mouse model of amyotrophic lateral sclerosis.

EGb761 is a standardized extract of green Gingko biloba, which exerts protective effects against mitochondrial damage and oxidative stress. We examined whether oral administration of 0.022% or 0.045% EGb761 in the diet could impart neuroprotective effects in a transgenic mouse model (G93A) of amyotrophic lateral sclerosis (ALS). EGb761 significantly improved motor performance and survival, and protected against a loss of spinal-cord anterior motor horn neurons in male G93A mutant transgenic ALS mice, but not in littermate female mutant transgene mice. While EGb761 extended survival in littermate female G93A mice, significance was not reached. EGb761, however, significantly improved weight loss in both male and female transgenic ALS mice. These findings provide evidence for a gender-specific neuroprotective effect of EGb761 in a transgenic model of ALS and suggest that EGb761 may be a potential effective treatment in patients with ALS.

Creatine increase survival and delays motor symptoms in a transgenic animal model of Huntington's disease.

There is substantial evidence for bioenergetic defects in Huntington's disease (HD). Creatine administration increases brain phosphocreatine levels and it stabilizes the mitochondrial permeability transition. We examined the effects of creatine administration in a transgenic mouse model of HD produced by 82 polyglutamine repeats in a 171 amino acid N-terminal fragment of huntingtin (N171-82Q). Dietary supplementation of 2% creatine significantly improved survival, slowed the development of motor symptoms, and delayed the onset of weight loss. Creatine lessened brain atrophy and the formation of intranuclear inclusions, attenuated reductions in striatal N-acetylaspartate as assessed by NMR spectroscopy, and delayed the development of hyperglycemia. These results are similar to those observed using dietary creatine supplementation in the R6/2 transgenic mouse model of HD and provide further evidence that creatine may exert therapeutic effects in HD.

Dichloroacetate exerts therapeutic effects in transgenic mouse models of Huntington's disease.

Dichloroacetate (DCA) stimulates pyruvate dehydrogenase complex (PDHC) activity and lowers cerebral lactate concentrations. In the R6/2 and N171-82Q transgenic mouse models of Huntington's disease (HD), DCA significantly increased survival, improved motor function, delayed loss of body weight, attenuated the development of striatal neuron atrophy, and prevented diabetes. The percentage of PDHC in the active form was significantly reduced in R6/2 mice at 12 weeks of age, and DCA ameliorated the deficit. These results provide further evidence for a role of energy dysfunction in HD pathogenesis and suggest that DCA may exert therapeutic benefits in HD.

Increases in cortical glutamate concentrations in transgenic amyotrophic lateral sclerosis mice are attenuated by creatine supplementation.

Several lines of evidence implicate excitotoxic mechanisms in the pathogenesis of amyotrophic lateral sclerosis (ALS). Transgenic mice with a superoxide dismutase mutation (G93A) have been utilized as an animal model of familial ALS (FALS). We examined the cortical concentrations of glutamate using in vivo microdialysis and in vivo nuclear magnetic resonance (NMR) spectroscopy, and the effect of long-term creatine supplementation. NMDA-stimulated and Ltrans-pyrrolidine-2,4-dicarboxylate (LTPD)-induced increases in glutamate were significantly higher in G93A mice compared with littermate wild-type mice at 115 days of age. At this age, the tissue concentrations of glutamate were also significantly increased as measured with NMR spectroscopy. Creatine significantly increased longevity and motor performance of the G93A mice, and significantly attenuated the increases in glutamate measured with spectroscopy at 75 days of age, but had no effect at 115 days of age. These results are consistent with impaired glutamate transport in G93A transgenic mice. The beneficial effect of creatine may be partially mediated by improved function of the glutamate transporter, which has a high demand for energy and is susceptible to oxidative stress.

Transgenic ALS mice show increased vulnerability to the mitochondrial toxins MPTP and 3-nitropropionic acid.

The pathogenesis of neurodegenerative diseases may involve a genetic predisposition acting in concert with environmental toxins. To test this hypothesis we examined whether transgenic mice with the G93A mutation in Cu,Zn superoxide dismutase show increased vulnerability to either 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) or 3-nitropropionic acid (3-NP). Compared to littermate controls G93A transgenic mice showed a greater loss of striatal dopamine, DOPAC, and HVA at 50, 70, and 120 days of age following administration of MPTP; however, cell loss in the substantia nigra was not greater. The G93A transgenic mice showed significantly increased vulnerability to striatal lesions produced by 3-NP compared with littermate controls at 120 days of age. The finding that G93A mice show increased vulnerability to mitochondrial toxins further implicates mitochondrial dysfunction in the pathogenesis of neuronal death in these mice. The findings support the hypothesis that a genetic defect can increase susceptibility to environmental toxins and that this may play a role in the pathogenesis of neurodegenerative diseases.

Effects of an inhibitor of poly(ADP-ribose) polymerase, desmethylselegiline, trientine, and lipoic acid in transgenic ALS mice.

The development of transgenic mouse models of amyotrophic lateral sclerosis (ALS) allows the testing of neuroprotective agents. We evaluated the effects of five agents in transgenic mice with the G93A Cu,Zn superoxide dismutase mutation. A novel inhibitor of poly(ADP-ribose) polymerase showed no effects on survival. Desmethylselegiline and CGP3466 are agents that exert antiapoptotic effects in vitro by preventing nuclear translocation of glyceraldehyde-3-phosphate dehydrogenase. They had no significant effects on survival in the G93A mice. Trientine, a copper chelator, produced a modest significant increase in survival. Similarly administration of lipoic acid in the diet produced a significant improvement in survival. These results therefore provide evidence for potential therapeutic effects of copper chelators and lipoic acid in the treatment of ALS.

Mice with a partial deficiency of manganese superoxide dismutase show increased vulnerability to the mitochondrial toxins malonate, 3-nitropropionic acid, and MPTP.

There is substantial evidence implicating mitochondrial dysfunction and free radical generation as major mechanisms of neuronal death in neurodegenerative diseases. The major free radical scavenging enzyme in mitochondria is manganese superoxide dismutase (SOD2). In the present study we investigated the susceptibility of mice with a partial deficiency of SOD2 to the neurotoxins 1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine (MPTP), 3-nitropropionic acid (3-NP), and malonate, which are commonly used animal models of Parkinson's and Huntington's disease. Heterozygous SOD2 knockout (SOD2(+/-)) mice showed no evidence of neuropathological or behavioral abnormalities at 2-4 months of age. Compared to littermate wild-type mice, mice with partial SOD2 deficiency showed increased vulnerability to dopamine depletion after systemic MPTP treatment and significantly larger striatal lesions produced by both 3-NP and malonate. SOD2(+/-) mice also showed an increased production of "hydroxyl" radicals after malonate injection measured with the salicylate hydroxyl radical trapping method. These results provide further evidence that reactive oxygen species play an important role in the neurotoxicity of MPTP, malonate, and 3-NP. These findings show that a subclinical deficiency in a free radical scavenging enzyme may act in concert with environmental toxins to produce selective neurodegeneration.

N-acetyl-L-cysteine improves survival and preserves motor performance in an animal model of familial amyotrophic lateral sclerosis.

Increasing evidence implicates oxidative damage as a major mechanism in the pathogenesis of amyotrophic lateral sclerosis (ALS). We examined the effect of preventative treatment with N-acetyl-L-cysteine (NAC), an agent that reduces free radical damage, in transgenic mice with a superoxide dismutase (SODI) mutation (G93A), used as an animal model of familial ALS. NAC was administered at 1% concentration in the drinking water from 4-5 weeks of age. The treatment caused a significantly prolonged survival and delayed onset of motor impairment in G93A mice treated with NAC compared to control mice. These results provide further evidence for the involvement of free radical damage in the G93A mice, and support the possibility that NAC, an over-the-counter antioxidant, could be explored in clinical trials for ALS.

Malonate and 3-nitropropionic acid neurotoxicity are reduced in transgenic mice expressing a caspase-1 dominant-negative mutant.

Increasing evidence implicates caspase-1-mediated cell death as a major mechanism of neuronal death in neurodegenerative diseases. In the present study we investigated the role of caspase-1 in neurotoxic experimental animal models of Huntington's disease (HD) by examining whether transgenic mice expressing a caspase-1 dominant-negative mutant are resistant to malonate and 3-nitropropionic acid (3-NP) neurotoxicity. Intrastriatal injection of malonate resulted in significantly smaller striatal lesions in mutant caspase-1 mice than those observed in littermate control mice. Caspase-1 was significantly activated following malonate intrastriatal administration in control mice but significantly attenuated in mutant caspase-1 mice. Systemic 3-NP treatment induced selective striatal lesions that were significantly smaller within mutant caspase-1 mice than in littermate control mice. These results provide further evidence of a functional role for caspase-1 in both malonate- and 3-NP-mediated neurotoxin models of HD.

Neuroprotective effects of creatine in a transgenic mouse model of Huntington's disease.

Huntington's disease (HD) is a progressive neurodegenerative illness for which there is no effective therapy. We examined whether creatine, which may exert neuroprotective effects by increasing phosphocreatine levels or by stabilizing the mitochondrial permeability transition, has beneficial effects in a transgenic mouse model of HD (line 6/2). Dietary creatine supplementation significantly improved survival, slowed the development of brain atrophy, and delayed atrophy of striatal neurons and the formation of huntingtin-positive aggregates in R6/2 mice. Body weight and motor performance on the rotarod test were significantly improved in creatine-supplemented R6/2 mice, whereas the onset of diabetes was markedly delayed. Nuclear magnetic resonance spectroscopy showed that creatine supplementation significantly increased brain creatine concentrations and delayed decreases in N-acetylaspartate concentrations. These results support a role of metabolic dysfunction in a transgenic mouse model of HD and suggest a novel therapeutic strategy to slow the pathological process.

Mice deficient in cellular glutathione peroxidase show increased vulnerability to malonate, 3-nitropropionic acid, and 1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine.

Glutathione peroxidase (GSHPx) is a critical intracellular enzyme involved in detoxification of hydrogen peroxide (H(2)O(2)) to water. In the present study we examined the susceptibility of mice with a disruption of the glutathione peroxidase gene to the neurotoxic effects of malonate, 3-nitropropionic acid (3-NP), and 1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine (MPTP). Glutathione peroxidase knock-out mice showed no evidence of neuropathological or behavioral abnormalities at 2-3 months of age. Intrastriatal injections of malonate resulted in a significant twofold increase in lesion volume in homozygote GSHPx knock-out mice as compared to both heterozygote GSHPx knock-out and wild-type control mice. Malonate-induced increases in conversion of salicylate to 2,3- and 2, 5-dihydroxybenzoic acid, an index of hydroxyl radical generation, were greater in homozygote GSHPx knock-out mice as compared with both heterozygote GSHPx knock-out and wild-type control mice. Administration of MPTP resulted in significantly greater depletions of dopamine, 3,4-dihydroxybenzoic acid, and homovanillic acid in GSHPx knock-out mice than those seen in wild-type control mice. Striatal 3-nitrotyrosine (3-NT) concentrations after MPTP were significantly increased in GSHPx knock-out mice as compared with wild-type control mice. Systemic 3-NP administration resulted in significantly greater striatal damage and increases in 3-NT in GSHPx knock-out mice as compared to wild-type control mice. The present results indicate that a knock-out of GSHPx may be adequately compensated under nonstressed conditions, but that after administration of mitochondrial toxins GSHPx plays an important role in detoxifying increases in oxygen radicals.

CNS actions of serotonin on cardiovascular function: nonadrenergic, noncholinergic mechanisms.

The present studies investigated the mechanisms mediating the cardiovascular changes induced by intracerebroventricular injection of serotonin (5-HT; 100 nmol) in conscious rats. At 5 min after 5-HT injection, arterial pressure and plasma levels of epinephrine were elevated and heart rate was reduced. The pressor response was abolished either by bilateral adrenalectomy or by pretreatment with chlorisondamine plus vasopressin V1 receptor antagonist. The bradycardic response was attenuated by pretreatment with chlorisondamine or a combination of methylatropine, propranolol, and vasopressin V1 receptor antagonist. At 20 min postinjection, arterial pressure and heart rate were both decreased. The reduction of heart rate at this time point was not blocked by the following pretreatments given alone or in combination: methylatropine, propranolol, vasopressin V1 and V2 receptor antagonists, adenosine A1 receptor antagonist, angiotensin-converting enzyme inhibitor, and chlorisondamine. These results suggest that immediately after intracerebroventricular injection of 5-HT, arterial pressure is elevated through the release of epinephrine and vasopressin and that heart rate is reduced via reciprocal changes in cardiac parasympathetic and sympathetic tone. In contrast, adrenergic, cholinergic, vasopressinergic, purinergic, and angiotensinergic mechanisms do not mediate the bradycardia observed at 20 min postinjection.

Cardiovascular activation by serotonergic stimulation: role of corticotropin-releasing factor.

Serotonin (5-HT) and serotonergic agonists stimulate the release of corticotropin-releasing factor (CRF) from hypophysiotropic neurons and thereby activate the pituitary-adrenal axis. Studies were performed to test the hypothesis that the release of CRF into central nervous system (CNS) sites where it influences cardiovascular function is likewise stimulated by serotonergic mechanisms. Experiments were thus designed to examine whether the cardiovascular effects of central administration of low doses of 5-HT and the 5-HT1A receptor agonist, 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT), are secondary to the release of CRF. Intracerebroventricular administration of 5-HT (1 nmol) and 8-OH-DPAT (3 nmol) produced cardiovascular responses similar to those evoked by CRF (0.15 nmol), i.e., simultaneous elevations of arterial pressure and heart rate, in conscious unrestrained rats. Coadministration of the CRF receptor antagonist, alpha-helical CRF-(9-41) (9 nmol), significantly attenuated the pressor and tachycardic responses to 5-HT and 8-OH-DPAT as well as those to injection of CRF. In contrast, coadministration of alpha-helical CRF-(9-41) did not alter the pressor and bradycardic responses to a high dose (100 nmol) of serotonin. It is concluded that the cardiovascular effects of low doses of 5-HT and 8-OH-DPAT are mediated in part through the release of CRF within the CNS.

Central and peripheral injections of the 5-HT2 agonist, 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane, modify cardiovascular function through different mechanisms.

The mechanisms underlying the cardiovascular effects of central and peripheral administration of the 5-HT2 (serotonin) receptor agonist (+-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane hydrochloride (DOI) were studied in conscious rats. Intravenous (10-1000 nmol/kg) and i.c.v. (3-300 nmol) administration of DOI produced dose-related elevations of arterial pressure without altering heart rate except after injection of the highest doses. Pretreatment with xylamidine tosylate, a 5-HT2 receptor antagonist that does not cross the blood-brain barrier, blocked the pressor response to i.v., but not i.c.v., administration of equivalent doses of DOI. Pretreatment with the vasopressin receptor antagonist d(CH2)5Tyr(Me)AVP significantly reduced the pressor response to i.c.v., but not i.v., administration of DOI. Prior ganglionic blockade with chlorisondamine amplified the pressor response to both i.v. and i.c.v. administration of DOI. Pretreatment with a combination of chlorisondamine, xylamidine and d(CH2)5Tyr(Me)AVP abolished the pressor response to i.c.v. administration of DOI. Thus, the pressor response to i.v. administration of DOI was mediated at sites outside the blood-brain barrier, most likely at vascular 5-HT2 receptors, and was not secondary to vasopressin release. Inappropriate heart rate changes attended the pressor responses to i.v. administration of DOI, suggesting an action at extravascular sites. The pressor response to i.c.v. administration of DOI resulted from a combination of vasopressin release, modulation of autonomic nervous outflow and some leakage into the periphery.

Central nervous actions of serotonin and a serotonin1A receptor agonist: cardiovascular excitation at low doses.

Studies were performed in conscious unrestrained rats to compare the cardiovascular effects of i.c.v. administration of serotonin (5-HT) and the 5-HT1A receptor agonist, 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT). Low doses (less than 10 nmol) of 5-HT and 8-OH-DPAT elicited significant elevations of arterial pressure and heart rate. At doses greater than 10 nmol, 5-HT produced pressor responses attended by significant reductions of heart rate whereas 8-OH-DPAT produced significant depressor and bradycardiac responses. Concurrent i.c.v. administration of the nonselective 5-HT receptor antagonist, methiothepin, abolished the cardiovascular responses to a low (1 nmol) and a high (100 nmol) dose of 5-HT and a low (3 nmol) dose of 8-OH-DPAT. In contrast, methiothepin cotreatment did not prevent the reductions of arterial pressure and heart rate induced by a high (100 nmol) dose of 8-OH-DPAT. These results suggest that stimulation of central nervous system 5-HT1A receptors with low doses of 8-OH-DPAT produces cardiovascular activation.

Muscarinic receptor subtypes of guinea-pig gallbladder smooth muscle.

The antagonism of acetylcholine-induced contractions of guinea-pig gallbladder and ileum smooth muscle strips via various antagonists has been investigated in order to find out the muscarinic receptor subtype(s) of gallbladder smooth muscle. Atropine, pirenzepine, 4-DAMP and AF-DX 116 were used as nonselective, M1-selective, M1- and smooth muscle M3-selective and cardiac M2-selective muscarinic antagonists, respectively. All the muscarinic antagonists examined displaced the concentration-response curves to the right parallelly in a concentration-dependent manner without affecting the maximum response in both tissues. Schild analysis of data was consistent with competitive antagonism. pA2 values of the antagonists were as follows: a) gallbladder: atropine: 8.43; pirenzepine: 7.81; 4-DAMP: 8.10; AF-DX 116: 6.71; b) ileum: atropine: 9.62; pirenzepine: 6.94; 4-DAMP: 9.41; AF-DX 116: 6.55. It may be concluded that the muscarinic receptors of the guinea-pig gallbladder, which mediate acetylcholine-induced contractions, are not of the cardiac M2-subtype and may be distinguished from ileal smooth muscle M3-receptors because 4-DAMP has a 20.4 times greater affinity for ileal smooth muscle muscarinic receptors.