Homocysteine Hypothesis on the Impaired Peripheral but Not Central Nervous System Oxytocin Responses in Cystathionine γ-Lyase-Deficient Dam Mice.

An elevated plasma homocysteine level is an independent risk factor for cardiovascular diseases, neurological disorders, and pregnancy complications. We recently demonstrated partial lactation failure in cystathionine γ-lyase-deficient (Cth-/-) dam mice and their defective oxytocin responses in peripheral tissues: uterine (ex vivo) and mammary gland (in vivo). We reasoned that elevated levels of circulatory homocysteine in Cth-/- dam mice counteract with oxytocin-dependent milk ejection from the mammary gland. Based on our observation that those mice displayed normal maternal behaviors against their pups and adult Cth-/- male mice exhibited normal social behaviors against adult wild-type female mice, both of which are regulated by oxytocin in the central nervous system (CNS), we conducted the present study to investigate the amino acid profiles, including total homocysteine, in both blood and cerebrospinal fluid (CSF) of wild-type and Cth-/- female mice before pregnancy and at day 1 of lactation (L1). Serum levels of total homocysteine in wild-type and Cth-/- L1 dam mice were 9.44 and 188 µmol/L, respectively, whereas their CSF levels were below 0.21 (limit of quantification) and 3.62 µmol/L, respectively. Their CSF/serum level ratio was the lowest (1/51.9) among all 20 proteinogenic amino acids, sulfur-containing amino acids, and citrulline/ornithine in Cth-/- mice. Therefore, we hypothesize that the blood-brain barrier protects the CNS from high levels of circulatory homocysteine in Cth-/- dam mice, thereby conferring normal oxytocin-dependent maternal behaviors.

Abnormal Amino Acid Profiles of Blood and Cerebrospinal Fluid from Cystathionine ß-Synthase-Deficient Mice, an Animal Model of Homocystinuria.

Mental retardation is the most common feature among inborn errors of amino acid metabolism. Patients with homocystinuria/homocysteinemia caused by cystathionine ß-synthase (CBS) deficiency suffer from thromboembolism and mental retardation from early ages; therefore, detection by newborn screening is performed. Furthermore, elevated levels of serum homocysteine during pregnancy are associated with the occurrence of neural tube defects (NTDs) in newborns. However, the causes of such central nervous system (CNS) defects are unknown. We found previously impaired learning abilities in Cbs-deficient (Cbs-/-) mice (but not NTD births). Here, we investigated the amino acid profiles of serum and cerebrospinal fluid (CSF) from Cbs-/- mice. Mice deficient in cystathionine γ-lyase (Cth), a downstream enzyme of CBS in transsulfuration, as well as wild-type mice, were analyzed as controls. Cbs-/- and Cth-/- mice were smaller than wild-type mice, and CSF yields in Cbs-/- mice were lower than the others. CSF amino acid levels were generally lower than those in serum, and compared with the dramatic amino acid level alterations in Cbs-/- mouse serum, alterations in CSF were less apparent. However, marked upregulation (versus wild-type) of aspartic acid/asparagine (Asp/Asn), glutamine (Gln), serine (Ser), threonine (Thr), phenylalanine (Phe), tyrosine (Tyr), methionine (Met), total homocysteine, and citrulline, and downregulation of lysine (Lys) were found in Cbs-/- mouse CSF. Because similar regulation of total homocysteine/citrulline/Lys was observed in the CSF of Cth-/- mice, which are free of CNS dysfunction, the reduced CSF volumes and the level changes of other amino acids could be relevant to Cbs-/--specific CNS defects.

Homocysteine, another risk factor for Alzheimer disease, impairs apolipoprotein E3 function.

Apolipoprotein E (apoE) ε4 and hyperhomocysteinemia are risk factors for Alzheimer disease (AD). The dimerization of apoE3 by disulfide bonds between cysteine residues enhances apoE3 function to generate HDL. Because homocysteine (Hcy) harbors a thiol group, we examined whether Hcy interferes with the dimerization of apoE3 and thereby impairs apoE3 function. We found that Hcy inhibits the dimerization of apoE3 and reduces apoE3-mediated HDL generation to a level similar to that by apoE4, whereas Hcy does not affect apoE4 function. Western blot analysis of cerebrospinal fluid showed that the ratio of apoE3 dimers was significantly lower in the samples from the patients with hyperhomocysteinemia than in those that from control subjects. Hyperhomocysteinemia induced by subcutaneous injection of Hcy to apoE3 knock-in mice decreased the level of the apoE3 dimer in the brain homogenate. Because apoE-HDL plays a role in amyloid ß-protein clearance, these results suggest that two different risk factors, apoE4 and hyperhomocysteinemia, may share a common mechanism that accelerates the pathogenesis of AD in terms of reduced HDL generation.

Elevated cerebrospinal fluid and plasma homocysteine levels in ALS.

BACKGROUND: High cerebrospinal fluid (CSF) and plasma levels of homocysteine (HC) have been reported in certain neurodegenerative disorders, such as Alzheimer's, Parkinson's diseases and, recently, amyotrophic lateral sclerosis (ALS). OBJECTIVES: To assay the CSF and plasma levels of HC in ALS patients and controls, and to evaluate the relationship between HC levels and clinical variables of the disease. METHODS: Cerebrospinal fluid from sixty-nine (M/F 1.87) and plasma from sixty-five ALS patients (M/F 1.83) were taken and stored at -80 degrees C until use. Controls (CSF = 55; plasma = 67) were patients admitted to our hospital for neurological disorders with no known relationship to HC changes. CSF and plasma from ALS patients and controls were obtained as a necessary step of the diagnostic workup. HC levels in CSF and plasma were assayed using a high performance liquid chromatograph (HPLC) and a fluorimeter detector. RESULTS: The median level of total HC in the CSF of ALS patients was 0.46( )microM, significantly higher than that of the controls (0.24 microM, +91.6%, P < 0.001). A similar trend was observed when HC was assayed in plasma (ALS, 12.4 microM vs. controls, 7.26 microM, +70.8%, P < 0.001). The CSF and plasma HC levels showed no relationship with the disease progression, age at onset, and the site of onset. CONCLUSIONS: Homocysteine is a biochemical marker in ALS, and it might be related to the pathophysiology of the disease.