Biomedical subjects

Sharon Moalem

Publications and source records attributed to Sharon Moalem.

5 recordsLinked to original sources

PubMed2006

Aluminum and Alzheimer's disease, a personal perspective after 25 years.

It is now 25 years since the publication of our original paper investigating the association aluminum with Alzheimer's disease. This publication reported on the results of scanning electron microscopy coupled x-ray spectrometry microprobe elemental studies of both neurofibrillary tangle-bearing and tangle-free neurons in the hippocampus of cases of Alzheimer's disease and controls. Peaks related to the presence of aluminum were consistently detected within the tangle-bearing neurons. This paper supported the association of aluminum and Alzheimer's disease on the cellular level of resolution and caused considerable interest and discussion. Subsequent work demonstrated prominent evidence of aluminum accumulation in the tangle-bearing neurons of cases of amyotrophic lateral sclerosis/parkinsonism-dementia complex of Guam. This latter observation has now been replicated using five different forms of microanalysis. Finally, using laser microprobe mass analysis, we demonstrated that the abnormally high aluminum-related signal which we originally detected was actually located within the neurofibrillary tangle, itself, and was accompanied by excess concentrations of iron. Although it is unlikely that aluminum represents an etiologic cause of Alzheimer's disease, we believe that this highly reactive element, known to cross-link hyperphosphorylated proteins, may play an active role in the pathogenesis of critical neuropathologic lesion in Alzheimer's disease and other related disorders.

Aluminum↗

PubMed2004

Hemochromatosis and the enigma of misplaced iron: implications for infectious disease and survival.

The mystery surrounding the apparent lack of iron within the macrophages of individuals with hereditary hemochromatosis, a condition of excessive uptake of dietary iron, has yet to be fully explained. We have suggested that iron deficiency of macrophages in people with hereditary hemochromatosis mutations is associated with increased resistance to infection by Yersinia and other intracellular pathogens, a selection pressure resulting in unusually high current population frequencies of hereditary hemochromatosis mutations. Such selection pressure has been called Epidemic Pathogenic Selection (EPS). In support of the theory of EPS, a considerable number of virulent species of bacteria multiply mainly in iron-rich macrophages of their mammalian hosts. Among these fastidious pathogens are strains of Chlamydia, Coxiella, Francisella, Legionella, Mycobacterium, Salmonella and Yersinia. Iron deficiency of macrophages of persons with hereditary hemochromatosis gene mutations may result in increased resistance to members of these bacterial pathogens. People with genes that result in hereditary hemochromatosis may be protected against coronary artery disease associated with Chlamydia and Coxiella infection in the absence of iron overload. In the clinical setting, when a patient appears to be iron deficient, the reason for this should be carefully evaluated. Iron supplementation may adversely affect the health of individuals who have mounted an acute phase response to infection, injury or stress, or who carry genes predisposing them to iron overload disorders.

Bacterial Infections↗

PubMed2003

Relation between apolipoprotein E genotype, hepatitis B virus status, and thyroid status in a sample of older persons with Down syndrome.

Dementia of the Alzheimer type (DAT) is common in older persons with Down syndrome (DS). There are three common alleles of the apolipoprotein E (ApoE) gene (Sigma 2, Sigma 3, and Sigma 4) resulting in three different isoforms (E2, E3, and E4) and six different genotypes (2,2; 2,3; 2,4; 3,3; 3,4; and 4,4). Sigma 4 is a risk factor for DAT whereas Sigma 2 appears prophylactic. As hepatitis B virus (HBV) infection and hypothyroidism also are common in DS, we evaluated associations between ApoE type, HBV status, and thyroid status in a sample of older persons with DS (n = 55; mean age, 44.3 +/- 10.8 years) using chi-squared analysis. Participants were classified as E2 (2,2 or 2,3), E3 (3,3), or E4 (3,4 or 4,4); positive for markers of HBV infection in the present or past (i.e., total HBcAb+ and/or HBsAg+ with or without infectivity, defined as HBV+) or negative for markers of HBV infection (defined as HBV-) and, currently receiving thyroid hormone supplement (defined as "hypothyroidism") or having normal thyroid function. The majority of the HBV+ were currently HBcAb+ and HBsAb+, but not HBsAg+. In females, there was an ApoE allele effect on thyroid status (P < or = 0.01), E2 being negatively (P < or = 0.01) and E4 being positively (P < or = 0.05) associated with "hypothyroidism". There was no evidence for an ApoE allele effect on thyroid status in males. There was no evidence for an ApoE allele effect on HBV status, or for an HBV status effect on thyroid status. As thyroid status can affect cognitive function, ApoE allele effects in DAT may, in part, be thyroid effects.

Adult↗

PubMed2002

Epidemic pathogenic selection: an explanation for hereditary hemochromatosis?

Hereditary hemochromatosis (HH) is a disorder associated with progressive iron overload and deposition in multiple organs. It is the most common inherited single gene disorder in people of Northern and Western European descent. About 80% of individuals of European descent with HH are homozygous for a cysteine-to-tyrosine substitution (C282Y) in the gene now called HFE. The function of HFE protein, a major histocompatibility class I-like transmembrane protein, has not been fully elucidated. Three consequences of the C282Y mutation are lack of expression of HFE on the cellular surface, a lowered iron level in macrophages, and an increased rate of clearance of iron from the intestinal lumen. These changes could confer protection against certain pathogens early in life before iron overload occurs. Furthermore, the C282Y mutation might have been selected for during the European plagues caused by Yersinia spp. and other pathogens because of the conferred resistance to infection, i.e., by epidemic pathogenic selection.

Amino Acid Substitution↗

PubMed2002

The quandary of reductionism: relevance to Alzheimer disease research.

Modern science has embraced reductionism, seeking ever-smaller parts to explain the whole. Although reductionistic approaches are successful in very simple biological modelling, they are not necessarily appropriate for systems of increasing complexity. Drawing on famous historical examples of how non-reductionist thinking has benefited mankind, and of how reductionism has sometimes led to erroneous conclusions, we call attention to the need to move away from purely linear reasoning in order to succeed in addressing many of the problems we face with the predicted demographic increase in seniors, and the increase in numbers of those afflicted with Alzheimer disease. The time has come to reconsider and seriously question our most basic assumptions and beliefs surrounding what we believe Alzheimer disease to be, without which we run the risk of missed opportunities and failure.

Alzheimer Disease↗