TRIPASS XR تري باس

 

This article focuses on the recent research for the aetiology, the clinical consequences

and the management of the vitamin B complex deficiencies in patients with inflammatory

bowel disease.

Chapter V - The adenosylcobalamin-dependent CoA-carbonyl mutases catalyze the 1,2-

rearrangement of carbonyl groups reversibly converting branched-chain carbonic acids into

straight-chain ones. Currently, this enzyme group comprises of only two known mutases, the

extensively studied methylmalonyl-CoA mutase (MCM, EC 5.4.99.2) and isobutyryl-CoA

mutase (ICM, EC 5.4.99.13). Whereas MCM is widespread among bacteria and animals ICM

seems to be restricted to bacteria and has thus far only been characterized in Streptomyces

spp. Both enzymes have a rather limited substrate spectrum and function effectively merely

Preface xi

with their natural substrates methylmalonyl-CoA and isobutyryl-CoA, respectively.

Interestingly, we have recently discovered a novel bacterial CoA-carbonyl mutase catalyzing

the conversion of 2-hydroxyisobutyryl-CoA into 3-hydroxybutyryl-CoA (Rohwerder et al.

2006, Appl. Environ. Microbiol. 72:4128). This enzyme plays a central role in the productive

degradation of compounds containing a tert-butyl group such as the common fuel additives

methyl and ethyl tert-butyl ether. Similar enzymes are proposed to be involved in the

conversion of pivalic acid and in the degradation of alkanes and alkylated aromatic

hydrocarbons via anaerobic pathways employing addition to fumarate. Since all these

compounds are important pollutants of water and soil, cobalamin and the new CoA-carbonyl

mutases play a thus far not realized role in natural as well as induced bioremediation

processes. Therefore, the authors summarize in this chapter the known reactions and also

speculate about further pathways which have not yet been associated with CoA-carbonyl

mutase activity. In addition, the enzyme structure and the herewith possibly associated

evolution of substrate specificity are outlined. Finally, energetic and kinetic consequences are

discussed which may result from employing a cobalamin-dependent enzyme for dissimilatory

pathways.

Chapter VI - Pyridoxal 5’-phosphate (PLP) is the catalitically active form of the watersoluble vitamin B6, and hence the cofactor of a number of enzymes essential to the human

body. PLP-dependent enzymes are unique for the variety of reactions on amino acids that

they are able to catalyze (transamination, decarboxylation, racemization, β- or γreplacement/elimination). In the absence of the apoenzyme, different reactions would occur

simultaneously, but the protein moiety drives the catalytic power of the coenzyme toward a

specific reaction. However, this specificity is not absolute; most PLP-enzymes catalyze

indeed side-reactions which can have physiological significance and provide interesting

mechanistic and stereochemical information about the structure of the enzyme active site.

Cystalysin is a PLP-dependent Cβ-Sγ lyase present in Treponema denticola, and its main

reaction is the α,β-elimination of L-cysteine to produce pyruvate, ammonia and H2S. The

latter is probably responsible for the hemolytic and hemoxidative activity associated with the

enzyme catalysis. Cystalysin is one of the most representative examples of the high catalytic

versatility of PLP-dependent enzymes. Recently, indeed, it has been shown that cystalysin is

also able to catalyze the racemization of both enantiomers of alanine, the β-desulfination of

L-cysteine sulfinic acid, and the β-decarboxylation of L-aspartate and oxalacetate with

turnover numbers measured in seconds, and the transamination of L- and D-alanine with

turnover numbers measured in minutes.

Extensive biochemical investigations have uncovered several interesting features of

cystalysin, including the binding mode of the cofactor, its substrate specificity, the formation

of reaction intermediates characteristic of most PLP-enzymes, and the involvement of some

active-site residues in the primary and secondary catalytic reactions.

Chapter VII - High total plasma homocysteine levels are detected not only in patients

with homocystinuria, a recessively inherited disease, but also in patients with renal failure,

hypothyroidism, and methyltetrahydrofolate reductase polymorphism. The most important

clinical signs of high plasma homocysteine values are thromboembolic vascular occlusions of

arteries and veins, cerebral impairment, osteoporosis, and displacement of the lens.

Cardiovascular disease is the primary reason of morbidity and mortality in the general

xii Charlyn M. Elliot

population, and it represents about 50% of the causes of mortality of the patients with chronic

renal failure. Folic acid, vitamin B6 and vitamin B12, lower hyperhomocysteinemia acting on

remethylation and transsulphuration pathway. Vitamin B treatments don't often normalize

plasma homocysteine levels, but long-term effects of vitamin B therapy are effective in

reducing the life-threatening vascular risk of homocystinuric patients.

Hyperhomocysteinemia is detected in patients with chronic renal failure, and especially in

patients with stage 5 of chronic kidney disease. Clinical observational studies have shown

different results about the effects of high plasma homocysteine levels on cardiovascular

disease in dialysis patients. In fact, cardiovascular mortality has been associated not only with

hyperhomocysteinemia, but also in some studies with hypohomocysteinemia. These

contrasting data are probably due to the strict relationship between homocysteine and

malnutrition-inflammation markers. Dialysis patients are frequently affected by malnutritioninflammation-atherosclerosis syndrome, and consequently this severe clinical condition can

interfere with homocysteine levels. I and my coworkers recently observed in a prospective

clinical trial that hemodialysis patients, submitted to vitamin B treatment, with low

homocysteine levels and high protein catabolic rate show a significantly higher survival rate

as compared with the other three subgroups. Prospective clinical studies, evaluating

homocysteine-lowering vitamin B therapy on cardiovascular events in patients with mild

hyperhomocysteinemia, have recently shown no clinical benefits. These results could be

misleading because a part of patients had normal homocysteine levels, follow-up time may

have been too short, and confounding factors has not been considered. To summarize, this

paper shows the hottest news regarding the effects of homocysteine-lowering vitamin B

therapy on cardiovascular events, exploring the intriguing puzzle of homocysteine.

Chapter VIII - Vitamin B12 exerts its physiological effect on two major enzymatic

pathways: the conversion of homocysteine to methionine and the conversion of

methylmalonyl coenzyme A to succinyl coenzyme A. Disruption of either of these pathways

due to vitamin B12 deficiency results in an elevation of both serum homocysteine and

methylmalonic acid. Homocysteine levels are also elevated in the case of folate deficiency.

Serum homocysteine is proposed to be more sensitive for functional intracellular vitamin B12

deficiency than analysis of vitamin B12 in serum. Hence, homocysteine, vitamin B12, and

folate are closely linked together in the so-called one-carbon cycle. The proposed mechanism

relates to the methylation reactions involving homocysteine metabolism in the nervous

system. Vitamin B12 is the necessary co-enzyme, adequate for the correct functioning of the

methyl donation from 5 Methyltethrahydrofolate in tetrhahydrofolate, necessary for

methionine synthetase. On the other hand, folate is a cofactor in one-carbon metabolism,

during which it promotes the remethylation of homocysteine- a cytotoxic sulfur-containing

amino acid that can induce DNA strand breakage, oxidative stress and apoptosis. What

clearly merges from Literature is the general conviction that vitamin B12 and folate, directly

through the maintenance of two functions, nucleic acid synthesis and the methylation

reactions, or indirectly, due to their lack which cause SAM mediated methylation reactions

inhibition by its product SAH, and through the related toxic effects of homcystein which

cause direct damage to the vascular endothelium and inhibition of N-methyl-D-Aspartate

receptors, can cause neuropsychiatric disturbances.

Preface xiii

Chapter IX - Vitamin B6 includes a series of compounds containing the pyridoxal

structure, such as pyridoxol, pyridoxamine, pyridoxaldehyde and their derivatives. The

pyridoxal structure，the catalytically active form of vitamin B6, possesses specific

hepatocyte uptake by the pyridoxine transporter at the sinusoidal pole because the pyridoxine

transporters that exist in hepatocytes can selectively recognize and bind to the pyridoxal

structure, and transport it into the cells via a member transport system. Thus pyridoxine can

be adopted as a liver-targeting group and be incorporated into the low molecular weight

compounds and macromolecules for the use as magnetic resonance imaging (MRI) contrast

agents and anticancer conjugates. The research progress of liver-targeting drug delivery

system is discussed briefly. Previous researches have demonstrated that the incorporation of

pyridoxine into these molecules can increase their uptake by the liver, and that these

molecules containing pyridoxine groups exhibit liver-targeting properties.

Chapter X - Vitamin B12 plays a functional role in a variety of organs and body systems

and the list of these organs and body systems is growing. It affects the peripheral and central

nervous systems, bone marrow, skin and mucous membranes, bones, and vessels, as well as

the normal development of children. Vitamin B12 (cobalamin) is unique among all the

vitamins in that it contains not only a complex organic molecule but also an essential trace

element, cobalt. Vitamin B12 plays an important role in DNA synthesis and has important

immunomodulatory and neurotrophic effects. According to our “working hypothesis” a

vitamin B12 has some unique, but still unrecognized functions.

Multifunctional systems in the human body need to maintain homeostasis. Man is an

ideal example of a system that constantly aspires to attain optimal regulation, even under the

stress of severe pathology. We assume that there are universal, interchangeable (as required)

propose that one of these substances is vitamin B12.Why vitamin B12? It is possible that even

when the serum cobalamin level is normal, treatment with vitamin B12 can correct defects

caused by other biologically active substances. In the authors studies this has been proved

successful in the treatment of recurrent aphthous stomatitis with vitamin B12 (irrespective of

its blood level!). We call this phenomenon the “Master Key” effect.

Vitamin B12 deficiency is a common problem that affects the general population. Early

detection of vitamin B12 deficiency is clinically important, and there is evidence that such

deficiency occurs more frequently than would be expected. Vitamin B12 deficiency can

occur in individuals with dietary patterns that exclude animal foods and patients who are

unable to absorb vitamin B12 in food. In addition there is an overall tendency to avoid eating

those foods which are high in Vitamin B12, such as beef, because of the relationship between

meat, cholesterol and cardiovascular diseases. Also there is a tendency, particularly among

the younger generation, to be vegetarians for ideological motives. Changes in life style

among segments of the population with high socioeconomic level, on one hand, and the

existence of poverty, on the other, are two main factors in the decreasing consumption of

animal products, particularly red meat. Thus, there is a decrease in the level of vitamin B12 in

general population, and as a consequence, an increase in pathology due to vitamin B12

deficiency (such as neurological and hematological disorders). If future research will

corroborate the relationship between vitamin B12 and homocystein, the authors may observe

an increase in cardiovascular disease as well. In lieu of these developments and in order to

xiv Charlyn M. Elliot

prevent serious health problems, vitamin B12 fortification should be seriously considered and

discussed.

In: Vitamin B: New Research ISBN 978-1-60021-782-1

Editor: Charlyn M. Elliot, pp. 1-4 © 2008 Nova Science Publishers, Inc.

Expert Commentary

COBALAMIN COMMUNICATION

CURRENT STATE OF ORAL VITAMIN B12

TREATMENT

Karin Björkegren∗

Department of Public Health and Caring Science, Family Medicine Uppsala Science

Park, SE-751 85 Uppsala, Sweden.

ABSTRACT

Background: In contrast to global traditions, most patients in Sweden with vitamin

B12 deficiency are treated with oral vitamin B12, 1 mg daily.

Objective: Analysis of current state of oral therapy with vitamin B12 in clinical

research and routine.

Material and Methods: Review of basic documentation of oral vitamin B12 therapy

in the period 1950-2005.

Results: In the period 1950-1960, various doses of vitamin B12 below 1 mg daily

were tested and mainly rejected. During the period 1960-1968, the leading research

groups agreed that oral cyanocobalamin, 1 mg daily, is the optimal dose for oral vitamin

B12 prophylaxis and treatment of deficiency states. The efficacy of such regimens varies

between 80-100% in different studies. The regimen has gained widespread clinical use in

Sweden, comprising 2.5 million patient years in the period 1964-2005. Lower doses of

oral vitamin B12 still lack documentation of clinical efficacy and long-term clinical

safety and reliability.

Conclusions: Oral cyanocobalamin, 1 mg daily, is a safe and reliable therapy for

most patients with vitamin B12 deficiency. It is suggested that this regimen is compared

with a generally accepted parenteral regimen in a prospective, randomized, open-labeled

study of adequate size in conclusive patients.

∗