Plasmalogen Deficiency: A Risk Factor for Dementias and Potential Treatment Target

Altered lipid metabolism is implicated in the risk of sporadic Alzheimer’s disease (AD) and related dementias (ADRD); however, the precise mechanisms accounting for findings from observational studies remains to be fully elucidated. Plasmalogens are a subclass of integral membrane phospholipids with unique properties that appear to play important roles relevant to the pathophysiology of AD and ADRD, including vesicle fusion necessary for synaptic neurotransmitter release, modulation of membrane fluidity and microdomain dynamics, membrane antioxidant functions, and neuroprotection. Like the more familiar phosphatides, plasmalogens are synthesized on a 3-carbon glycerol backbone; however, they differ from phosphatides by the presence of a vinyl ether linkage at the 1st (sn1) glycerol carbon atom in place of the acyl ester linkage present at sn1 in phosphatides, and at sn2 in both lipid subclasses. Plasmalogens bearing the omega-3 fatty acid docosahexaenoic acid (DHA), a key component of fish oils, are the most abundant plasmalogen species in cerebral cortex membranes. Circulating plasmalogen levels are decreased in older individuals, and are further decreased in AD and Mild Cognitive Impairment (MCI). In addition, reduced indices of plasmalogen biosynthesis and/or remodeling are significantly correlated with elevated cerebrospinal fluid (CSF) concentrations of total tau, which is a biomarker of AD and certain other neurodegenerative diseases. This correlation suggests a functional relationship between reduced plasmalogen availability and neurodegeneration. Endogenous plasmalogen synthesis requires the integrity of peroxisomes for the attachment of an alkyl side chain to the sn1 glycerol carbon. Decreased peroxisome function may be a key factor underlying the decrease in circulating plasmalogens with aging and with neurodegenerative diseases such as AD and ADRD. Preclinical data indicate that oral administration of a precursor phospholipid compound, DHA-containing alkyl-diacylglycerol, or DHA-AAG, can increase circulating DHA-containing plasmalogens in a peroxisome-independent manner, as conversion to plasmalogens from this precursor requires only the endoplasmic reticulum. We present here data showing that: 1) oral administration of a single dose of DHA-AAG at 100mg/kg to 6 (4M/2F) healthy subjects aged 23-56 increased circulating plasmalogen levels by 80% within 24 hours; and 2) daily oral administration of DHA-AAG to 22 persons (11M/11F), aged 37-84 (mean= 69) yr, with mild to moderate cognitive impairment [CDR: 0.5 (N=14); 1 (N=4); 2 (N = 4)] on an ascending-dose schedule of 1.0 ml/day for 30 days, followed by 2.0 ml/day for 60 days, followed by 4.0 ml for 30 days, increased serum DHA plasmalogens by \u3e 2-fold by the end of the treatment period. DHA-AAG was well-tolerated by both groups of individuals in these 2 studies. These findings suggest that DHA-AAG may be a useful agent for correcting plasmalogen deficiency associated with aging and aging-associated cognitive disorders. Future studies will examine the effect of plasmalogen repletion with DHA-AAG on cerebrospinal fluid plasmalogen concentrations, and effects on cognitive function and other clinical outcomes

Number of risk genotypes is a risk factor for major depressive disorder: a case control study

BACKGROUND: The objective of the study was to determine the genetic basis of Major Depressive Disorder, and the capacity to respond to antidepressant treatment. An association study of 21 candidate polymorphisms relevant to monoamine function and the mechanism of antidepressant response was conducted in 3 phenotypically distinct samples: a group with chronic or recurrent depression unable to respond to antidepressants (non-responders) (n = 58), a group capable of symptomatic improvement with or without treatment (responders) (n = 39), and volunteer controls (n = 85). The responders and non-responders constituted a larger group of depressed subjects. METHODS: A candidate gene approach was employed to asses the genetics basis of Major Depressive Disorder. The genotypic frequencies of selected polymorphisms were compared between the controls and depressed subjects. To asses the genetics basis of the capacity to respond to antidepressant treatment, the responders were compared to the non-responders. Candidate genes were chosen based on functional studies and proximity to whole genome linkage findings in the literature. Risk genotypes were identified by previous functional studies and association studies. RESULTS: A statistically significant difference in genotype frequency for the SLC6A4 intron 2 VNTR was detected between the subjects with a history of depression and controls (p = 0.004). Surprisingly, a statistically significant difference was detected between responders and non-responders for the DRD4 exon III VNTR genotype frequencies (p = 0.009). Furthermore, a difference between the controls and depressed subjects as well as between the controls and non-responders was detected for the number and distribution of risk genotypes in each group. CONCLUSION: An association between several monoamine-related genes and Major Depressive Disorder is supported. The data suggest that the two depressive phenotypes are genetically different, inferring that the genetic basis for the capacity to respond to standard antidepressant treatment, and the genetic susceptibility to Major Depressive Disorder may be independent. In addition, a proof of concept is provided demonstrating that the number of risk genotypes may be an indication of susceptibility of major depressive disorder and the severity of the disorder

Plasma and cerebrospinal fluid monoamine metabolism in patients with chronic fatigue syndrome: Preliminary findings

The syndrome of chronic fatigue, feverishness, diffuse pains, and other constitutional complaints, often precipitated by an acute infectious illness and aggravated by physical and emotional stressors, has a lengthy history in the medical literature. The Centers for Disease Control (CDC) recently formulated a case definition, renaming the illness "chronic fatigue syndrome". Nevertheless, there remain few biological data that can validate the existence of this syndrome as distinct from a wide variety of other, largely psychiatric disorders, and little understanding of its pathogenesis. In the present study, basal plasma and cerebrospinal fluid levels of the monoamine metabolites, 3-methoxy-4-hydroxyphenylglycol (MHPG), 5-hydroxyindoleacetic acid (5-HIAA), and homovanillic acid (HVA) were determined in 19 patients meeting CDC research case criteria for chronic fatigue syndrome and in 17 normal individuals. Patients with chronic fatigue syndrome showed a significant reduction in basal plasma levels of MHPG and a significant increase in basal plasma levels of 5-HIAA. Although the functional significance of these findings has not been definitively elucidated, they are compatible with the clinical presentation of a syndrome associated with chronic lethargy and fatigue, and with evidence of persistent immune stimulation, and lend support to the idea that chronic fatigue syndrome represents a clinical entity with potential biological specificity.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29681/1/0000008.pd

Effects of 12 Months of Vagus Nerve Stimulation in Treatment-Resistant Depression: A Naturalistic Study

Background: The need for effective, long-term treatment for recurrent or chronic, treatment-resistant depression is well established. Methods: This naturalistic follow-up describes outpatients with nonpsychotic major depressive (n = 185) or bipolar (I or II) disorder, depressed phase (n = 20) who initially received 10 weeks of active (n = 110) or sham vagus nerve stimulation (VNS) (n = 95). The initial active group received another 9 months, while the initial sham group received 12 months of VNS. Participants received antidepressant treatments and VNS, both of which could be adjusted. Results: The primary analysis (repeated measures linear regression) revealed a significant reduction in 24-item Hamilton Rating Scale for Depression (HRSD24) scores (average improvement, .45 points [SE = .05] per month (p \u3c .001). At exit, HRSD24 response rate was 27.2% (55/202); remission rate (HRSD24 ≤ 9) was 15.8% (32/202). Montgomery Asberg Depression Rating Scale (28.2% [57/202]) and Clinical Global Impression-Improvement (34.0% [68/200]) showed similar response rates. Voice alteration, dyspnea, and neck pain were the most frequently reported adverse events. Conclusions: These 1-year open trial data found VNS to be well tolerated, suggesting a potential long-term, growing benefit in treatment-resistant depression, albeit in the context of changes in depression treatments. Comparative long-term data are needed to determine whether these benefits can be attributed to VNS

Effects of 12 Months of Vagus Nerve Stimulation in Treatment-Resistant Depression: A Naturalistic Study

Background: The need for effective, long-term treatment for recurrent or chronic, treatment-resistant depression is well established. Methods: This naturalistic follow-up describes outpatients with nonpsychotic major depressive (n = 185) or bipolar (I or II) disorder, depressed phase (n = 20) who initially received 10 weeks of active (n = 110) or sham vagus nerve stimulation (VNS) (n = 95). The initial active group received another 9 months, while the initial sham group received 12 months of VNS. Participants received antidepressant treatments and VNS, both of which could be adjusted. Results: The primary analysis (repeated measures linear regression) revealed a significant reduction in 24-item Hamilton Rating Scale for Depression (HRSD24) scores (average improvement, .45 points [SE = .05] per month (p \u3c .001). At exit, HRSD24 response rate was 27.2% (55/202); remission rate (HRSD24 ≤ 9) was 15.8% (32/202). Montgomery Asberg Depression Rating Scale (28.2% [57/202]) and Clinical Global Impression-Improvement (34.0% [68/200]) showed similar response rates. Voice alteration, dyspnea, and neck pain were the most frequently reported adverse events. Conclusions: These 1-year open trial data found VNS to be well tolerated, suggesting a potential long-term, growing benefit in treatment-resistant depression, albeit in the context of changes in depression treatments. Comparative long-term data are needed to determine whether these benefits can be attributed to VNS

Comparing biological markers of Alzheimer\u27s disease across blood fraction and platforms: Comparing apples to oranges

Introduction: This study investigated the comparability of potential Alzheimer\u27s disease (AD) biomarkers across blood fractions and assay platforms. Methods: Nonfasting serum and plasma samples from 300 participants (150 AD patients and 150 controls) were analyzed. Proteomic markers were obtained via electrochemiluminescence or Luminex technology. Comparisons were conducted via Pearson correlations. The relative importance of proteins within an AD diagnostic profile was examined using random forest importance plots. Results: On the Meso Scale Discovery multiplex platform, 10 of the 21 markers shared \u3e50% of the variance across blood fractions (serum amyloid A R2 = 0.99, interleukin (IL)10 R2 = 0.95, fatty acid-binding protein (FABP) R2 = 0.94, I309 R2 = 0.94, IL-5 R2 = 0.94, IL-6 R2 = 0.94, eotaxin3 R2 = 0.91, IL-18 R2 = 0.87, soluble tumor necrosis factor receptor 1 R2 = 0.85, and pancreatic polypeptide R2 = 0.81). When examining protein concentrations across platforms, only five markers shared \u3e50% of the variance (beta 2 microglobulin R2 = 0.92, IL-18 R2 = 0.80, factor VII R2 = 0.78, CRP R2 = 0.74, and FABP R2 = 0.70). Discussion: The current findings highlight the importance of considering blood fractions and assay platforms when searching for AD relevant biomarkers

Genetic Influences on Plasma Homocysteine Levels in African Americans and Yoruba Nigerians.

Plasma homocysteine, a metabolite involved in key cellular methylation processes seems to be implicated in cognitive functions and cardiovascular health with its high levels representing a potential modifiable risk factor for Alzheimer’s disease (AD) and other dementias. A better understanding of the genetic factors regulating homocysteine levels, particularly in non-white populations, may help in risk stratification analyses of existing clinical trials and may point to novel targets for homocysteine-lowering therapy. To identify genetic influences on plasma homocysteine levels in individuals with African ancestry, we performed a targeted gene and pathway-based analysis using a priori biological information and then to identify new association performed a genome-wide association study. All analyses used combined data from the African American and Yoruba cohorts from the Indianapolis-Ibadan Dementia Project. Targeted analyses demonstrated significant associations of homocysteine and variants within the CBS (Cystathionine beta-Synthase) gene. We identified a novel genome-wide significant association of the AD risk gene CD2AP (CD2-associated protein) with plasma homocysteine levels in both cohorts. Minor allele (T) carriers of identified CD2AP variant (rs6940729) exhibited decreased homocysteine level. Pathway enrichment analysis identified several interesting pathways including the GABA receptor activation pathway. This is noteworthy given the known antagonistic effect of homocysteine on GABA receptors. These findings identify several new targets warranting further investigation in relation to the role of homocysteine in neurodegeneration

Altered bile acid profile associates with cognitive impairment in Alzheimer's disease—An emerging role for gut microbiome

Introduction Increasing evidence suggests a role for the gut microbiome in central nervous system disorders and a specific role for the gut‐brain axis in neurodegeneration. Bile acids (BAs), products of cholesterol metabolism and clearance, are produced in the liver and are further metabolized by gut bacteria. They have major regulatory and signaling functions and seem dysregulated in Alzheimer's disease (AD). Methods Serum levels of 15 primary and secondary BAs and their conjugated forms were measured in 1464 subjects including 370 cognitively normal older adults, 284 with early mild cognitive impairment, 505 with late mild cognitive impairment, and 305 AD cases enrolled in the AD Neuroimaging Initiative. We assessed associations of BA profiles including selected ratios with diagnosis, cognition, and AD‐related genetic variants, adjusting for confounders and multiple testing. Results In AD compared to cognitively normal older adults, we observed significantly lower serum concentrations of a primary BA (cholic acid [CA]) and increased levels of the bacterially produced, secondary BA, deoxycholic acid, and its glycine and taurine conjugated forms. An increased ratio of deoxycholic acid:CA, which reflects 7α‐dehydroxylation of CA by gut bacteria, strongly associated with cognitive decline, a finding replicated in serum and brain samples in the Rush Religious Orders and Memory and Aging Project. Several genetic variants in immune response–related genes implicated in AD showed associations with BA profiles. Discussion We report for the first time an association between altered BA profile, genetic variants implicated in AD, and cognitive changes in disease using a large multicenter study. These findings warrant further investigation of gut dysbiosis and possible role of gut‐liver‐brain axis in the pathogenesis of AD

Vagus Nerve Stimulation for Treatment-Resistant Depression: A Randomized, Controlled Acute Phase Trial

Background: Vagus nerve stimulation (VNS) alters both concentrations of neurotransmitters or their metabolites and functional activity of central nervous system regions dysregulated in mood disorders. An open trial has suggested efficacy. Methods: This 10-week, acute, randomized, controlled, masked trial compared adjunctive VNS with sham treatment in 235 outpatients with nonpsychotic major depressive disorder (n = 210) or nonpsychotic, depressed phase, bipolar disorder (n = 25). In the current episode, participants had not responded adequately to between two and six research-qualified medication trials. A two-week, single-blind recovery period (no stimulation) and then 10 weeks of masked active or sham VNS followed implantation. Medications were kept stable. Primary efficacy outcome among 222 evaluable participants was based on response rates (≥ 50% reduction from baseline on the 24-item Hamilton Rating Scale for Depression [HRSD24]). Results: At 10-weeks, HRSD24 response rates were 15.2% for the active (n = 112) and 10.0% for the sham (n = 110) groups (p = .251, last observation carried forward [LOCF]). Response rates with a secondary outcome, the Inventory of Depressive Symptomatology – Self-Report (IDS-SR30), were 17.0% (active) and 7.3% (sham) (p = .032, LOCF). VNS was well tolerated; 1% (3/235) left the study because of adverse events. Conclusions: This study did not yield definitive evidence of short-term efficacy for adjunctive VNS in treatment-resistant depression