Testicular Injury to Rats Fed on Soybean Protein-Based Vitamin B12-Deficient Diet Can Be Reduced by Methionine Supplementation

Essential metals in health and disease

In total, twenty elements appear to be essential for the correct functioning of the human body, half of which are metals and half are non-metals. Among those metals that are currently considered to be essential for normal biological functioning are four main group elements, sodium (Na), potassium (K), magnesium (Mg), and calcium (Ca), and six d-block transition metal elements, manganese (Mn), iron (Fe), cobalt (Co), copper (Cu), zinc (Zn) and molybdenum (Mo). Cells have developed various metallo-regulatory mechanisms for maintaining a necessary homeostasis of metal-ions for diverse cellular processes, most importantly in the central nervous system. Since redox active transition metals (for example Fe and Cu) may participate in electron transfer reactions, their homeostasis must be carefully controlled. The catalytic behaviour of redox metals which have escaped control, e.g. via the Fenton reaction, results in the formation of reactive hydroxyl radicals, which may cause damage to DNA, proteins and membranes. Transition metals are integral parts of the active centers of numerous enzymes (e.g. Cu,Zn-SOD, Mn-SOD, Catalase) which catalyze chemical reactions at physiologically compatible rates. Either a deficiency, or an excess of essential metals may result in various disease states arising in an organism. Some typical ailments that are characterized by a disturbed homeostasis of redox active metals include neurological disorders (Alzheimer's, Parkinson's and Huntington's disorders), mental health problems, cardiovascular diseases, cancer, and diabetes. To comprehend more deeply the mechanisms by which essential metals, acting either alone or in combination, and/or through their interaction with non-essential metals (e.g. chromium) function in biological systems will require the application of a broader, more interdisciplinary approach than has mainly been used so far. It is clear that a stronger cooperation between bioinorganic chemists and biophysicists - who have already achieved great success in understanding the structure and role of metalloenzymes in living systems - with biologists, will access new avenues of research in the systems biology of metal ions. With this in mind, the present paper reviews selected chemical and biological aspects of metal ions and their possible interactions in living systems under normal and pathological conditions.

Ameliorative effect of vitamin B12 on seminiferous epithelium of cimetidine-treated rats: a histopathological, immunohistochemical and ultrastructural study

Cimetidine is an H2 receptor antagonist that has an antiandrogenic effect. It intervenes with the conversion of testosterone into estrogen in the Sertoli cells with accompanying testicular structural changes. In the present study, the microscopic and the ultrastructural changes induced by cimetidine and the effect of vitamin B12 as a protective agent on rat testes were studied. Immunoexpression of estrogen receptor β (ERβ) in testes was evaluated. Twenty-four adult male rats were divided into four groups: control, cimetidine-treated, vitamin B12 treated, and combined cimetidine and vitamin B12 treated. The experimental rats were administered with cimetidine and/or vitamin B12 for 52 days. Group II rats showed marked atrophy of the seminiferous tubules with a significant increase in tubular diameter and decrease in the tubular luminal and epithelial areas. Ultrastructure of this group showed irregular Sertoli cells with basal cytoplasmic vacuolation and significantly thickened basement membrane. ERβ immunoexpression was similar to controls. Group III rats showed near normal seminiferous tubular structures with minimal cellular alterations and the immunoreactivity of the testicular sections was very close to normal. However, group IV rats showed markedly immunopositive detached cells, spermatids, and primary spermatocytes. Cimetidine interferes with the control of spermatogenesis as evidenced by microscopic and ultrastructural studies and affection of ERβ receptors and vitamin B12 has a protective action against this harmful effect.

Biochemistry, function, and deficiency of vitamin B12 in Caenorhabditis elegans

Caenorhabditis elegans is a nematode that has been widely used as an animal for investigation of diverse biological phenomena. Vitamin B12 is essential for the growth of this worm, which contains two cobalamin-dependent enzymes, methylmalonyl-CoA mutase and methionine synthase. A full complement of gene homologs encoding the enzymes associated with the mammalian intercellular metabolic processes of vitamin B12 is identified in the genome of C elegans However, this worm has no orthologs of the vitamin B12-binders that participate in human intestinal absorption and blood circulation. When the worm is treated with a vitamin B12-deficient diet for five generations (15 days), it readily develops vitamin B12 deficiency, which induces worm phenotypes (infertility, delayed growth, and shorter lifespan) that resemble the symptoms of mammalian vitamin B12 deficiency. Such phenotypes associated with vitamin B12 deficiency were readily induced in the worm.

MMACHC gene mutation in familial hypogonadism with neurological symptoms

Recent studies have convincingly documented that hypogonadism is a component of various hereditary disorders and is often recognized as an important clinical feature in combination with various neurological symptoms, yet, the causative genes in a few related families are still unknown. High-throughput sequencing has become an efficient method to identify causative genes in related complex hereditary disorders. In this study, we performed exome sequencing in a family presenting hypergonadotropic hypogonadism with neurological presentations of mental retardation, epilepsy, ataxia, and leukodystrophy. After bioinformatic analysis and Sanger sequencing validation, we identified compound heterozygous mutations: c.482G>A (p.R161Q) and c.609G>A (p.W203X) in MMACHC gene in this pedigree. MMACHC was previously confirmed to be responsible for methylmalonic aciduria (MMA) combined with homocystinuria, cblC type (cblC disease), a hereditary vitamin B12 metabolic disorder. Biochemical and gas chromatography-mass spectrometry (GC-MS) examinations in this pedigree further supported the cblC disease diagnosis. These results indicated that hypergonadotropic hypogonadism may be a novel clinical manifestation of cblC disease, but more reports on additional patients are needed to support this hypothesis.

Influences of maternal B₁₂ and methionine intake during gestation and lactation on testicular development of offspring in rats

The influence of maternal vitamin B₁₂ malnutrition on testicular development of offspring was examined using soy protein-based B₁₂-deficient diets with or without 0.5% DL-methionine supplementation. Dams were fed the B₁₂-deficient diet throughout gestation and lactation, whereas dams in a control group were fed a control diet which contained cyanocobalamin in the B₁₂-deficient diet without methionine. Offspring born to dams fed the B₁₂-deficient diet without methionine showed poor testicular development, e.g. decreased numbers of seminiferous tubules containing healthy spermatocytes and a high ratio of apoptotic cells per all germ cells. The abnormality was rarely observed in the group fed the B₁₂-deficient diet with methionine. It was likely that the testicular abnormality of offspring was caused by B₁₂-deficiency post partum and was prevented by the methionine supplementation. These observations suggested that maternal B₁₂ nutritional status during the pre-weaning period is quite important for spermatogenesis of male offspring and that the requirement of B₁₂ for testicular development is to produce active B₁₂-dependent methionine synthase.

Vitamin B12 deficiency in Caenorhabditis elegans results in loss of fertility, extended life cycle, and reduced lifespan

Vitamin B₁₂ (B₁₂) deficiency has been linked to developmental disorders, metabolic abnormalities, and neuropathy; however, the mechanisms involved remain poorly understood. Caenorhabditis elegans grown under B₁₂-deficient conditions for five generations develop severe B₁₂ deficiency associated with various phenotypes that include decreased egg-laying capacity (infertility), prolonged life cycle (growth retardation), and reduced lifespan. These phenotypes resemble the consequences of B₁₂ deficiency in mammals, and can be induced in C. elegans in only 15 days. Thus, C. elegans is a suitable animal model for studying the biological processes induced by vitamin deficiency.

Expression of amnionless in mouse testes and Leydig cells

Vitamin B(12) (cobalamin) deficiency results in atrophy of seminiferous tubules and aplasia of spermatozoa and spermatid. The transmembrane protein amnionless (AMN) directs endocytosis of cubilin with its ligand, contributing to intrinsic factor-vitamin B(12) absorption. To understand vitamin B(12) transport in testis, we analysed AMN expression in developing mouse testes and in Leydig cells and speculated the possible role of AMN in testis. In testes, Amn mRNA levels were low until 14 days post partum (pp) and markedly increased from puberty onwards. In the interstitium, Amn mRNA levels were low at 14 days pp and increased at puberty (28 days pp) together with 3-beta-hydroxysteroid dehydrogenase type 6 mRNA. Strong AMN immunoreactivity was observed in early spermatocytes from 7 days pp, suggesting that AMN participates in meiosis. In Leydig cells, AMN was not observed until 14 days pp but was strongly expressed after 28 days pp, suggesting a positive relationship between AMN expression and functional differentiation of adult Leydig cells. Together, AMN may participate in meiosis in early spermatocytes and in functional differentiation of adult Leydig cells through the mediation of vitamin B(12) transport in the mouse testes. This is the first report on AMN expression in the germ cells and soma of mammalian testes.

Cobalamin deficiency results in an abnormal increase inl-methylmalonyl-co-enzyme-A mutase expression in rat liver and COS-7 cells

The aim of the present study was to examine the effects of cobalamin (Cbl) on the activity and expression ofl-methylmalonyl-CoA mutase (MCM) in rat liver and cultured COS-7 cells. The MCM holoenzyme activity was less than 5 % of the total (holoenzyme+apoenzyme) activity in the liver although rats were fed a diet containing sufficient Cbl. When weanling rats were maintained on a Cbl-deficient diet, the holo-MCM activity became almost undetectable at the age of 10 weeks. In contrast, a marked increase in the total-MCM activity occurred under the Cbl-deficient conditions, and at the age of 20 weeks it was about 3-fold higher in the deficient rats than in the controls (108 (sd14·5)v.35 (sd8·5) nmol/mg protein per min (n5);P < 0·05). Western blot analysis confirmed that the MCM protein level increased significantly in the Cbl-deficient rats. However, the MCM mRNA level, determined by real-time PCR, was rather decreased. When COS-7 cells were cultured in a medium in which 10 % fetal bovine serum was the sole source of Cbl, holo-MCM activity was barely detected. The supplementation of Cbl resulted in a large increase in the holo-MCM activity in the cells, but the activity did not exceed 30 % of the total-MCM activity even in the presence of Cbl at 10 μmol/l. In contrast, the total-MCM activity was significantly decreased by the Cbl supplementation, indicating that Cbl deficiency results in an increase in the MCM protein level in COS-7 cells as well as in rat liver.