BackgroundEarly cognitive impairment in Alzheimer Disease (AD) is thought to result from the dysfunctional effect of amyloid beta (Aβ) oligomers targeting the synapses. Some individuals, however, escape cognitive decline despite the presence of the neuropathologic features of AD (Aβ plaques and neurofibrillary tangles). We term this group Non-Demented with AD Neuropathology or NDAN. The present study illustrates one putative resistance mechanism involved in NDAN cases which may suggest targets for the effective treatment of AD.ResultsHere we describe the localization of Aβ oligomers at the postsynapse in hippocampi from AD cases. Notably, however, we also found that while present in soluble fractions, Aβ oligomers are absent from hippocampal postsynapses in NDAN cases. In addition, levels of phosphorylated (active) CREB, a transcription factor important for synaptic plasticity, are normal in NDAN individuals, suggesting that their synapses are functionally intact. Analysis of Zn2+ showed that levels were increased in both soluble fractions and synaptic vesicles in AD hippocampi, paralleled by a decrease of expression of the synaptic vesicle Zn2+ transporter, ZnT3. Conversely, in NDAN individuals, levels of Zn2+ in soluble fractions were significantly lower than in AD, whereas in synaptic vesicles the levels of Zn2+ were similar to AD, but accompanied by preserved expression of the ZnT3.ConclusionsTaken together, these data illustrate that despite substantial AD neuropathology, Aβ oligomers, and increased synaptic vesicle Zn2+, susceptible brain tissue in these aged NDAN individuals features, as compared to symptomatic AD subjects, significantly lower total Zn2+ levels and no association of Aβ oligomers with the postsynapse, which collectively may promote the maintenance of intact cognitive function.
Background & Aims Porphyria cutanea tarda (PCT) is an iron-related disorder caused by reduced activity of hepatic uroporphyrinogen decarboxylase (UROD); it can be treated by phlebotomy or low doses of hydroxychloroquine. We performed a prospective pilot study to compare the efficacy and safety of these therapies. Methods We analyzed data from 48 consecutive patients with well-documented PCT to characterize susceptibility factors; patients were treated with phlebotomy (450 mL, every 2 weeks until they had serum ferritin levels of 20 ng/mL) or low-dose hydroxychloroquine (100 mg orally, twice weekly, until at least 1 month after they had normal plasma levels of porphyrin). We compared the time required to achieve a normal plasma porphyrin concentration (remission, the primary outcome) for 17 patients treated with phlebotomy and 13 treated with hydroxychloroquine. Results The time to remission was a median 6.9 months for patients that received phlebotomy and 6.1 months for patients treated with hydroxychloroquine treatment (6.7 and 6.5 months for randomized patients), a difference that was not significant (Log Rank P=.06 and P=.95, respectively). The sample size was insufficient to confirm noninferiority of hydroxychloroquine treatment (hazard ratio [HR], 2.19; 95% confidence interval [CI], 0.95–5.06) for all patients. Patients that received hydroxychloroquine had substantially better compliance. There were no significant side effects of either treatment. Conclusions Hydroxychloroquine, 100 mg twice weekly, is as effective and safe as phlebotomy in patients with PCT, although noninferiority was not established. Given these results, higher-dose regimens of hydroxychloroquine, which have more side effects, do not seem justified. Compliance was better and projected costs were lower for hydroxychloroquine than phlebotomy treatment. Long-term studies are needed to compare durability of response.
Acute intermittent porphyria (AIP), the most common acute hepatic porphyria, is an autosomal-dominant disorder due to the half-normal activity of the heme biosynthetic enzyme, hydroxymethylbilane (HMB) synthase (1). Symptomatic heterozygotes, most (~90%) of which are women, experience episodic life-threatening acute neurovisceral attacks that typically begin with severe abdominal pain and may include hypertension, tachycardia, constipation, motor weakness and seizures. These attacks are precipitated by certain drugs, dieting and hormonal factors that increase the hepatic expression of 5-aminolevulinic acid synthase 1 (ALAS1) (1). When hepatic ALAS1 is induced, the half-normal activity of HMB synthase becomes ratelimiting, leading to decreased heme biosynthesis and depletion of the hepatic "free" heme pool. Depletion of the"free" heme pool leads to further induction of Acute intermittent porphyria (AIP) is an autosomal-dominant hepatic disorder caused by the half-normal activity of hydroxymethylbilane (HMB) synthase. Symptomatic individuals experience life-threatening acute neurovisceral attacks that are precipitated by factors that induce the hepatic expression of 5-aminolevulinic acid synthase 1 (ALAS1), resulting in the marked accumulation of the putative neurotoxic porphyrin precursors 5-aminolevulinic acid (ALA) and porphobilinogen (PBG). Here, we provide the first detailed description of the biochemical and pathologic alterations in the explanted liver of an AIP patient who underwent orthotopic liver transplantation (OLT) due to untreatable and debilitating chronic attacks. After OLT, the recipient's plasma and urinary ALA and PBG rapidly normalized, and her attacks immediately stopped. In the explanted liver, (a) ALAS1 mRNA and activity were elevated approximately ~3-and 5-fold, and ALA and PBG concentrations were increased ~3-and 1,760-fold, respectively; (b) uroporphyrin III concentration was elevated; (c) microsomal heme content was sufficient, and representative cytochrome P450 activities were essentially normal; (d) HMB synthase activity was approximately half-normal (~42%); (e) iron concentration was slightly elevated; and (f) heme oxygenase I mRNA was increased approximately three-fold. Notable pathologic findings included nodular regenerative hyperplasia, previously not reported in AIP livers, and minimal iron deposition, despite the large number of hemin infusions received before OLT. These findings suggest that the neurovisceral symptoms of AIP are not associated with generalized hepatic heme deficiency and support the neurotoxicity of ALA and/or PBG. Additionally, they indicate that substrate inhibition of hepatic HMB synthase activity by PBG is not a pathogenic mechanism in acute attacks.
Aberrant central nervous system zinc homeostasis has been reported in Alzheimer’s disease (AD). However, there are conflicting reports describing zinc concentration either increased or decreased in the brain of AD patients. Such discrepancies may be due to differences in the brain area examined, zinc detection method, and/or tissue composition. Furthermore, detection and measurement of the releasable zinc pool in autopsy tissue is difficult and usually unreliable. Obtaining an adequate assessment of this releasable zinc pool is of particular significance in AD research in that zinc can coordinate with and stabilize toxic amyloid beta oligomers, which are believed to play a key role in AD neuropathology. In addition, zinc released into the synaptic cleft can interact with the postsynaptic neurons causing altered signaling and synaptic dysfunction, which is a well established event in AD. The method presented here combines two approaches, biochemical fractionation and atomic absorption spectrophotometry, to allow, in addition to extracellular zinc concentration, the reliable and quantitative measurement of zinc specifically localized in synaptic vesicles, which contain the majority of the neuronal releasable zinc. Using this methodology, we found that synaptic vesicle zinc concentrations were increased in AD hippocampi compared to age-matched controls and that this increase in releasable zinc matched increased concentration of zinc in the extracellular space.
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