Myoadenylate deaminase deficiency: successful symptomatic therapy by high dose oral administration of ribose

Inborn Errors of Purine Salvage and Catabolism

Cellular purine nucleotides derive mainly from de novo synthesis or nucleic acid turnover and, only marginally, from dietary intake. They are subjected to catabolism, eventually forming uric acid in humans, while bases and nucleosides may be converted back to nucleotides through the salvage pathways. Inborn errors of the purine salvage pathway and catabolism have been described by several researchers and are usually referred to as rare diseases. Since purine compounds play a fundamental role, it is not surprising that their dysmetabolism is accompanied by devastating symptoms. Nevertheless, some of these manifestations are unexpected and, so far, have no explanation or therapy. Herein, we describe several known inborn errors of purine metabolism, highlighting their unexplained pathological aspects. Our intent is to offer new points of view on this topic and suggest diagnostic tools that may possibly indicate to clinicians that the inborn errors of purine metabolism may not be very rare diseases after all.

A Randomized, Double-Blind, Placebo-Controlled Study to Evaluate the Effectiveness of a Food Supplement Containing Creatine and D-Ribose Combined with a Physical Exercise Program in Increasing Stress Tolerance in Patients with Ischemic Heart Disease

The aim of this study is to establish whether a supplement of creatine and ribose combined with a physical exercise program can improve the total work capacity during exercise in a population of patients with known ischemic heart disease. A double-blind, six-month study was designed in which 53 patients were enrolled and randomized to take either a nutraceutical composition containing creatine, D-ribose, vitamin B₁, and vitamin B₆ (active treatment) or the placebo. Both the nutraceutical supplement and the placebo were supplied by Giellepi S.p.A. Health Science in Lissone, Italy. After six months of study, the cardiac double product at the peak of the load, the delta double product, and the chronotropic index were higher in the active treatment group than in the placebo group. We can conclude that a supplementation with creatine, D-ribose, vitamin B₁, and vitamin B₆, in addition to standard therapy and a physical exercise program, seems to be helpful in improving exercise tolerance compared to the placebo in a population with cardiovascular disease. However, this needs to be further studied, given that there is no clear evidence that the double product can be used as a surrogate measure of exercise tolerance.

Formaldehyde produced from d-ribose under neutral and alkaline conditions

Formaldehyde is toxic and has been implicated in the pathologies of various diseases, such as cognitive impairment and cancer. Though d-ribose is widely studied and provided as a supplement to food such as flavor and drinks, no laboratories have reported that d-ribose is involved in the formaldehyde production. Here, we show that formaldehyde is produced from d-ribose in lysine or glycine solution and Tris-HCl buffer under neutral and alkaline conditions. Intraperitoneal injection of C57BL/6J mice with d-ribose significantly increased the concentration of brain formaldehyde, compared to the injection with d-glucose or saline. These data suggest that formaldehyde levels should be monitored for the people who take d-ribose as a supplement.

Safety of d-ribose as a novel food pursuant to Regulation (EU) 2015/2283

Following a request from the European Commission, the EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA) was asked to deliver an opinion on D-ribose as a novel food (NF) pursuant to Regulation (EU) 2015/2283. The applicant intends to market the NF as ingredient in a variety of foods, food supplements and in certain foods for specific groups. The NF is produced by fermentation using a transketolase-deficient strain of Bacillus subtilis and marketed as Bioenergy Ribose™. The information provided on the batch-to-batch variability, specifications, stability, production process and history of the organism used as a source of the NF is sufficient and does not raise safety concerns. The Panel considers that the effects observed in a subchronic toxicity study in rats could be the consequence of nutritional imbalances, but toxicological effects could not be ruled out; from this study, the Panel derived a No observed adverse effect level (NOAEL) of 3.6 g/kg body weight (bw) per day. From the human studies indicating a potential decrease in glucose levels and/or the occurrence of transient symptomatic hypoglycaemia at intakes of 10 g of d-ribose, the Panel defined 70 mg/kg bw per day as the NOAEL with respect to hypoglycaemia that can be considered applicable for adults. For children, the Panel acknowledges the lack of human data directly relevant for this population group. Based on the NOAEL derived from the subchronic toxicity study in rats, an acceptable level of intake of 36 mg/kg bw per day was defined that would also take into account the potentially increased sensitivity of certain population groups to hypoglycaemia. The Panel concludes that the NF is safe for the general population at intake levels up to 36 mg/kg bw per day and considers that the safety of the NF at the intended uses and use levels as proposed by the applicant has not been established.

Normal activities of AMP-deaminase and adenylate kinase in patients with McArdle disease

During physical activity in McArdle patients, little or no lactate is released in the skeletal muscle. However, excessive ammonia production has frequently been reported in these patients. Production of ammonia is catalysed by AMP deaminase (AMPD) and adenylate kinase (AK). The activities of AMPD and AK along with housekeeping enzyme phosphoglucoisomerase (PGI) were measured in 11 genetically confirmed McArdle patients and compared with 27 healthy controls. The AMPD and AK activities were not significantly different in patients and controls. The activity of PGI was significantly higher in patients than in controls suggesting compensation of the impaired glycogenolysis in McArdle. The ratios of activities of AMPD and AK over PGI were significantly lower in patients than in controls. High ammonia production in McArdle patients is not based on enzyme induction of AMPD and AK but possibly due to kinetic activation of the enzyme AMPD by increased concentration of the substrate AMP.

Ribose Accelerates Gut Motility and Suppresses Mouse Body Weight Gaining

The increasing prevalence of obesity is closely related to excessive energy consumption. Clinical intervention of energy intake is an attractive strategy to fight obesity. However, the current FDA-approved weight-loss drugs all have significant side effects. Here we show that ribose upregulates gut motility and suppresses mice body weight gain. Ribokinase, which is encoded by Rbks gene, is the first enzyme for ribose metabolism in vivo. Rbks mutation resulted in ribose accumulation in the small intestine, which accelerated gut movement. Ribose oral treatment in wild type mice also enhanced bowel motility and rendered mice resistance to high fat diets. The suppressed weight gain was resulted from enhanced ingested food excretion. In addition, the effective dose of ribose didn't cause any known side effects (i.e. diarrhea and hypoglycemia). Overall, our results show that ribose can regulate gut motility and energy homeostasis in mice, and suggest that administration of ribose and its analogs could regulate gastrointestinal motility, providing a novel therapeutic approach for gastrointestinal dysfunction and weight control.

Metabogenic and Nutriceutical Approaches to Address Energy Dysregulation and Skeletal Muscle Wasting in Duchenne Muscular Dystrophy

Duchenne Muscular Dystrophy (DMD) is a fatal genetic muscle wasting disease with no current cure. A prominent, yet poorly treated feature of dystrophic muscle is the dysregulation of energy homeostasis which may be associated with intrinsic defects in key energy systems and promote muscle wasting. As such, supplementative nutriceuticals that target and augment the bioenergetical expansion of the metabolic pathways involved in cellular energy production have been widely investigated for their therapeutic efficacy in the treatment of DMD. We describe the metabolic nuances of dystrophin-deficient skeletal muscle and review the potential of various metabogenic and nutriceutical compounds to ameliorate the pathological and clinical progression of the disease.

Inborn errors of purine metabolism: clinical update and therapies

Inborn errors of purine metabolism exhibit broad neurological, immunological, haematological and renal manifestations. Limited awareness of the phenotypic spectrum, the recent descriptions of newer disorders and considerable genetic heterogeneity, have contributed to long diagnostic odysseys for affected individuals. These enzymes are widely but not ubiquitously distributed in human tissues and are crucial for synthesis of essential nucleotides, such as ATP, which form the basis of DNA and RNA, oxidative phosphorylation, signal transduction and a range of molecular synthetic processes. Depletion of nucleotides or accumulation of toxic intermediates contributes to the pathogenesis of these disorders. Maintenance of cellular nucleotides depends on the three aspects of metabolism of purines (and related pyrimidines): de novo synthesis, catabolism and recycling of these metabolites. At present, treatments for the clinically significant defects of the purine pathway are restricted: purine 5'-nucleotidase deficiency with uridine; familial juvenile hyperuricaemic nephropathy (FJHN), adenine phosphoribosyl transferase (APRT) deficiency, hypoxanthine phosphoribosyl transferase (HPRT) deficiency and phosphoribosyl-pyrophosphate synthetase superactivity (PRPS) with allopurinol; adenosine deaminase (ADA) and purine nucleoside phosphorylase (PNP) deficiencies have been treated by bone marrow transplantation (BMT), and ADA deficiency with enzyme replacement with polyethylene glycol (PEG)-ADA, or erythrocyte-encapsulated ADA; myeloadenylate deaminase (MADA) and adenylosuccinate lyase (ADSL) deficiencies have had trials of oral ribose; PRPS, HPRT and adenosine kinase (ADK) deficiencies with S-adenosylmethionine; and molybdenum cofactor deficiency of complementation group A (MOCODA) with cyclic pyranopterin monophosphate (cPMP). In this review we describe the known inborn errors of purine metabolism, their phenotypic presentations, established diagnostic methodology and recognised treatment options.

Daily supplementation of D-ribose shows no therapeutic benefits in the MHC-I transgenic mouse model of inflammatory myositis

Background

Current treatments for idiopathic inflammatory myopathies (collectively called myositis) focus on the suppression of an autoimmune inflammatory response within the skeletal muscle. However, it has been observed that there is a poor correlation between the successful suppression of muscle inflammation and an improvement in muscle function. Some evidence in the literature suggests that metabolic abnormalities in the skeletal muscle underlie the weakness that continues despite successful immunosuppression. We have previously shown that decreased expression of a purine nucleotide cycle enzyme, adenosine monophosphate deaminase (AMPD1), leads to muscle weakness in a mouse model of myositis and may provide a mechanistic basis for muscle weakness. One of the downstream metabolites of this pathway, D-ribose, has been reported to alleviate symptoms of myalgia in patients with a congenital loss of AMPD1. Therefore, we hypothesized that supplementing exogenous D-ribose would improve muscle function in the mouse model of myositis. We treated normal and myositis mice with daily doses of D-ribose (4 mg/kg) over a 6-week time period and assessed its effects using a battery of behavioral, functional, histological and molecular measures.

Results

Treatment with D-ribose was found to have no statistically significant effects on body weight, grip strength, open field behavioral activity, maximal and specific forces of EDL, soleus muscles, or histological features. Histological and gene expression analysis indicated that muscle tissues remained inflamed despite treatment. Gene expression analysis also suggested that low levels of the ribokinase enzyme in the skeletal muscle might prevent skeletal muscle tissue from effectively utilizing D-ribose.

Conclusions

Treatment with daily oral doses of D-ribose showed no significant effect on either disease progression or muscle function in the mouse model of myositis.

Purine metabolites in fibromyalgia syndrome

OBJECTIVE

To evaluate serum purine metabolite concentrations in patients affected by fibromyalgia syndrome (FMS) and the relationships between their levels and FM clinical parameters.

DESIGN AND METHODS

Serum purine levels were quantified using LC/UV-vis in 22 fibromyalgic females (according to the American College of Rheumatology classification criteria) and 22 healthy females.

RESULTS

Significantly higher serum inosine, hypoxanthine and xanthine levels (p<0.001) and significantly lower serum adenosine (p<0.05) were detected in the FMS patients vs healthy controls. Our data show a negative correlation between adenosine and Fibromyalgia Impact Questionnaire (FIQ).

CONCLUSIONS

Study results suggest that purines, in particular adenosine and inosine, may be involved in pain transmission in fibromyalgia.

Primary adenosine monophosphate (AMP) deaminase deficiency in a hypotonic infant

The spectrum of the adenosine monophosphate (AMP) deaminase deficiency ranges from asymptomatic carriers to patients who manifest exercise-induced muscle pain, occasionally rhabdomyolysis, and idiopathic hyperCKemia. However, previous to the introduction of molecular techniques, rare cases with congenital weakness and hypotonia have also been reported. We report a 6-month-old girl with the association of congenital muscle weakness and hypotonia, muscle deficiency of adenosine monophosphate deaminase, and the homozygous C to T mutation at nucleotide 34 of the adenosine monophosphate deaminase-1 gene. This observation indicates the possible existence of a primary adenosine monophosphate deaminase deficiency manifested by congenital muscle weakness and hypotonia.

Ecto- and cytosolic 5′-nucleotidases in normal and AMP deaminase-deficient human skeletal muscle

In skeletal muscle, adenosine monophosphate (AMP) is mainly deaminated by AMP deaminase. However, the C34T mutation in the AMPD1 gene severely reduces AMP deaminase activity. Alternatively, intracellular AMP is dephosphorylated to adenosine via cytosolic AMP 5'-nucleotidase (cN-I). In individuals with a homozygous C34T mutation, cN-I might be a more important pathway for AMP removal. We determined activities of AMP deaminase, cN-I, total cytosolic 5'-nucleotidase (total cN), ecto-5'-nucleotidase (ectoN) and whole homogenate 5'-nucleotidase activity in skeletal muscle biopsies from patients with different AMPD1 genotypes [homozygotes for C34T mutation (TT); heterozygotes for C34T mutation (CT); and homozygotes for wild type (CC): diseased controls CC; and normal controls CC]. AMP deaminase activity showed genotype-dependent differences. Total cN activity in normal controls accounted for 57+/-22% of whole homogenate 5'-nucleotidase activity and was not significantly different from the other groups. A weak inverse correlation was found between AMP deaminase and cN-I activities (r2=0.18, p<0.01). There were no significant differences between different groups in the activities of cN-I, whole homogenate 5'-nucleotidase and ectoN, or in cN-I expression on Western blots. No correlation for age, fibre type distribution and AMPD1 genotype was found for whole homogenate nucleotidase, total cN and cN-I using multiple linear regression analysis. There was no gender-specific difference in the activities of whole homogenate nucleotidase, total cN and cN-I. The results indicate no changes in the relative expression or catalytic behaviour of cN-I in AMP deaminase-deficient human skeletal muscle, but suggest that increased turnover of AMP by cN-I in working skeletal muscle is due to higher substrate availability of AMP.

The role of ribose in human skeletal muscle metabolism

Bioenergetic pathways in muscle provide high-energy compounds that are required for cellular integrity and function. Increased cellular demand for adenosine triphosphate (ATP) or limitations in the rephosphorylation rate of adenosine diphosphate (ADP) can decrease the total adenine nucleotide (TAN) pool, which may take several days to recover or may not recover at all in cases of chronic ischemia. Total adenine nucleotide levels may be significantly decreased as a result of myocardial or skeletal muscle ischemia, certain metabolic diseases, repeated intense skeletal muscle contractions or in repetitive high-intensity exercise. Ribose, a naturally occurring pentose sugar, has been shown to enhance the recovery of myocardial or skeletal muscle ATP and TAN levels following ischemia or high-intensity exercise. Furthermore, ribose has been demonstrated to modulate the production of oxygen free radicals during and following exercise. The following paper reviews skeletal muscle energetics and the potential role of ribose during and following exercise.

A G468-T AMPD1 mutant allele contributes to the high incidence of myoadenylate deaminase deficiency in the Caucasian population

Myoadenylate deaminase deficiency is the most common metabolic disorder of skeletal muscle in the Caucasian population, affecting approximately 2% of all individuals. Although most deficient subjects are asymptomatic, some suffer from exercise-induced myalgia suggesting a causal relationship between a lack of enzyme activity and muscle function. In addition, carriers of this derangement in purine nucleotide catabolism may have an adaptive advantage related to clinical outcome in heart disease. The molecular basis of myoadenylate deaminase deficiency in Caucasians has been attributed to a single mutant allele characterized by double C to T transitions at nucleotides +34 and +143 in mRNA encoded by the AMPD1 gene. Polymerase chain reaction-based strategies have been developed to specifically identify this common mutant allele and are considered highly sensitive. Consequently, some laboratories preferentially use this technique over other available diagnostic tests for myoadenylate deaminase deficiency. We previously identified a G468-T mutation in one symptomatic patient who was only heterozygous for the common AMPD1 mutant allele. In this report, nine additional individuals with this compound heterozygous genotype are revealed in a survey of 48 patients with documented deficiency of skeletal muscle adenosine monophosphate deaminase and exercise-induced myalgia. Western blot analysis of leftover biopsy material from one of these individuals does not detect any immunoreactive myoadenylate deaminase polypeptide. Baculoviral expression of the G468-T mutant allele produces a Q156H substitution enzyme exhibiting labile catalytic activity. These combined results demonstrate that the G468-T transversion is dysfunctional and further indicate that AMPD1 alleles harboring this mutation contribute to the high incidence of partial and complete myoadenylate deaminase deficiency in the Caucasian population. Consequently, genetic tests for abnormal AMPD1 expression designed to diagnose patients with metabolic myopathy, and to evaluate genetic markers for clinical outcome in heart disease should not be based solely on the detection of a single mutant allele.

Rhabdomyolysis: a review

Rhabdomyolysis, a syndrome of skeletal muscle breakdown with leakage of muscle contents, is frequently accompanied by myoglobinuria, and if sufficiently severe, acute renal failure with potentially life-threatening metabolic derangements may ensue. A diverse spectrum of inherited and acquired disorders affecting muscle membranes, membrane ion channels, and muscle energy supply causes rhabdomyolysis. Common final pathophysiological mechanisms among these causes of rhabdomyolysis include an uncontrolled rise in free intracellular calcium and activation of calcium-dependent proteases, which lead to destruction of myofibrils and lysosomal digestion of muscle fiber contents. Recent advances in molecular genetics and muscle enzyme histochemistry may enable a specific metabolic diagnosis in many patients with idiopathic recurrent rhabdomyolysis.

No effects of oral ribose supplementation on repeated maximal exercise and de novo ATP resynthesis

A double-blind randomized study was performed to evaluate the effect of oral ribose supplementation on repeated maximal exercise and ATP recovery after intermittent maximal muscle contractions. Muscle power output was measured during dynamic knee extensions with the right leg on an isokinetic dynamometer before (pretest) and after (posttest) a 6-day training period in conjunction with ribose (R, 4 doses/day at 4 g/dose, n = 10) or placebo (P, n = 9) intake. The exercise protocol consisted of two bouts (A and B) of maximal contractions, separated by 15 s of rest. Bouts A and B consisted of 15 series of 12 contractions each, separated by a 60-min rest period. During the training period, the subjects performed the same exercise protocol twice per day, with 3-5 h of rest between exercise sessions. Blood samples were collected before and after bouts A and B and 24 h after bout B. Knee-extension power outputs were approximately 10% higher in the posttest than in the pretest but were similar between P and R for all contraction series. The exercise increased blood lactate and plasma ammonia concentrations (P < 0.05), with no significant differences between P and R at any time. After a 6-wk washout period, in a subgroup of subjects (n = 8), needle-biopsy samples were taken from the vastus lateralis before, immediately after, and 24 h after an exercise bout similar to the pretest. ATP and total adenine nucleotide content were decreased by approximately 25 and 20% immediately after and 24 h after exercise in P and R. Oral ribose supplementation with 4-g doses four times a day does not beneficially impact on postexercise muscle ATP recovery and maximal intermittent exercise performance.

Can the pentitol-hexitol theory explain the clinical observations made with xylitol?

The natural dietary carbohydrate xylitol has been used as a source of energy in infusion therapy and found to act curatively in certain clinical situations. Xylitol has also been used as a sweetener in the diabetic diet and as a non- or anticariogenic agent. Xylitol is a sugar alcohol (polyhydric alcohol) of the pentitol type. The various advantageous clinical effects associated with enteral and parenteral administration of xylitol can be considered to result from the five-carbon (pentitol) nature of the molecule and from the molecule's special configuration even when compared with other pentitols. Such effects may be regarded as simple consequences of evolutionary expediency in a situation where human nutrition and man's significant energy-yielding metabolic pathways are associated with the six-carbon nature of D-glucose and the close derivatives and polymers of D-glucose and related sugars, and the physiologic involvement of the five-carbon xylitol in several ancillary pathways. Consequently, most clinical effects occasioned by xylitol cannot be expected to be caused by six-carbon hexitols such as D-mannitol and D-glucitol. A simple pentitol-hexitol theory seems to explain most of the clinical effects associated with the administration of xylitol. This theory is in congruence with the general evolutionary development in which the metabolism of C(6)-based carbohydrates is often inhibited by C(5)-based ones (as manifested in certain bacterial infections in man), or where the presence of the C(5)-based xylitol forwards therapeutically significant metabolic pathways (as observed in parenteral nutrition and treatment of certain enzyme deficiencies). The validity of the theory can be verified in controlled clinical trials.

Myoadenylate deaminase deficiency. A common inherited defect with heterogeneous clinical presentation

Myoadenylate deaminase deficiency is a clinically heterogeneous metabolic disorder that is commonly diagnosed in a variety of neurologic settings. Although the molecular basis for this purine nucleotide catabolic derangement may typically be attributed to the inheritance of a single prevalent mutant allele, the clinical spectrum in the absence of other definable abnormalities can range from asymptomatic to mild exercise-induced myalgia. Moreover, myoadenylate deaminase deficiency is also found associated with other definable neuromuscular disorders. The myoadenylate deaminase deficiency in these latter cases may, in part, be precipitated by pathologic change or act synergistically in combination with another metabolic disease.

Effect of D-ribose on purine synthesis and neurological symptoms in a patient with adenylosuccinase deficiency

Oral supplementation of 10 mmol/kg/day of D-ribose to a patient with an inherited deficit of adenylosuccinase, severe psychomotor retardation, and epilepsy caused a marked increase in plasma concentration and urinary excretion of urate, while minor changes in succinylpurine levels were observed. D-Ribose administration was accompanied by a slight improvement of behaviour and a progressive reduction of seizure frequency, which increased dramatically upon two attempts to withdraw the drug. Substitution of D-ribose with an equivalent amount of D-glucose did not result in an increase of seizure frequency.

Myoadenylate deaminase deficiency, hypertrophic cardiomyopathy and gigantism syndrome

We report a 20-year-old man with gigantism syndrome, hypertrophic cardiomyopathy, muscle weakness, exercise intolerance, and severe psychomotor retardation since childhood. Histochemical and biochemical analysis of skeletal muscle biopsy revealed myoadenylate deaminase deficiency; molecular genetic analysis confirmed the diagnosis of primary (inherited) myoadenylate deaminase deficiency. Plasma, urine, and muscle carnitine concentrations were reduced. L-Carnitine treatment led to gradual improvement in exercise tolerance and cognitive performance; plasma and tissue carnitine levels returned to normal, and echocardiographic evidence of left ventricular hypertrophy disappeared. The combination of inherited myoadenylate deaminase deficiency, gigantism syndrome and carnitine deficiency has not previously been described.

Clinical heterogeneity and molecular mechanisms in inborn muscle AMP deaminase deficiency

Lack of the muscle-specific isoform of AMP deaminase (myoadenylate deaminase deficiency) can cause a metabolic myopathy, with exercise-induced muscle symptoms such as early fatigue, cramps and/or myalgia. It is the most common muscle enzyme defect in man, found in about 2-3% of all muscle biopsies. The genetic basis of the inherited defect is the nonsense mutation C34-T in the AMPD1 gene encoding myoadenylate deaminase. The mutation results in a premature stop of the enzyme synthesis. In a healthy German population, the frequency of the mutant allele was 0.1, and 1% of this population is expected to be homozygous for the mutation. In people with muscle symptoms, the allele frequency was significantly higher (0.145). The correlation between allele frequency and muscle symptoms underscores the clinical significance of this defect. However, the vast majority of homozygous subjects do not develop a metabolic myopathy. This clinical heterogeneity may be due to molecular genetic factors such as alternative splicing of the exon harbouring the mutation, or due to metabolic conditions such as pathways compensating for the defect. The real basis for the high percentage of asymptomatic homozygous subjects remains to be revealed.

Tension myalgia versus myoadenylate deaminase deficiency: a case report

Myalgia is a complaint associated with numerous medical conditions such as metabolic or hormonal abnormalities, toxic myopathies, tetanus, electrolyte disturbances, inflammatory diseases, and exertion-related pain. A diagnosis of tension myalgia or myofascial-type pain is often considered when no objective findings are seen in the evaluation. This is a report of a patient who was treated unsuccessfully for fibromyalgia for many years and who ultimately was diagnosed with a rare benign skeletal muscle metabolic disorder caused by myoadenylate deaminase deficiency. We discuss this enzyme deficiency and its importance for the physiatric community.

A double blind, placebo controlled, crossover trial of D-ribose in McArdle's disease

To determine whether seven days oral D-ribose would improve exercise tolerance in a group of 5 patients with McArdle's disease, we performed a double blind placebo controlled crossover trial. Subjects performed weekly treadmill exercise tests with expired gas analysis until their times were reproducible. They then received 60 g D-ribose daily or placebo for seven days. Exercise testing was repeated on completion of this period. A seven day washout period then followed. Subjects then performed a new baseline exercise test prior to starting the other solution. Again after seven days the exercise test was repeated. There was no significant difference between pre-treatment exercise tests for peak oxygen consumption or level of leg fatigue. Patients did not like taking the ribose and D-Ribose does not appear to be of benefit to patients with McArdle's disease.

Molecular biology of AMP deaminase deficiency

In man, there are at least four isoforms of adenosine monophosphate deaminase (AMPD): myoadenylate deaminase in skeletal muscle, the L isoform in liver, and the E1 and E2 isoforms in erythrocytes. Myoadenylate deaminase is encoded by the AMPD1 gene located on chromosome 1 p13-p21, the L isoform by the AMPD2 gene, and both isoforms in erythrocytes by the AMPD3 gene. Myoadenylate deaminase deficiency is found in 2-3% of all muscle biopsies. The inborn type of myoadenylate deaminase deficiency is caused by a single mutant allele harbouring two mutations: C34-->T (Gln-->Stop) and C143-->T (Pro-48-->Leu). Population studies revealed a frequency of the mutant allele of 0.12 in Caucasian Americans and Germans. The C34-->T mutation is located in exon 2, which is alternatively spliced in part of the AMPD1 transcript in human muscle. Since the second mutation does not affect enzyme function, alternatively spliced mRNA encodes a catalytically active enzyme. Only one patient with a disorder linked to liver AMPD has been described so far. In this patient the decreased inhibition of this enzyme by GTP resulted in uric acid overproduction and gout. A complete lack of erythroyte AMPD activity is found in asymptomatic subjects. The molecular basis of both disorders is not yet known.

Effects of therapeutic ribose levels on human lymphocyte proliferation in vitro

Ribose has been used successfully in the treatment of ischemic heart disease and muscular enzyme deficiencies, and its administration also facilitates the diagnosis of coronary artery disease by influencing thallium-201 scintigraphy. Concerns about the safety of ribose therapy have been triggered by reports about inhibitory effects of ribose on cell proliferation in vitro. This study examines possible side effects of ribose on human lymphocytes. Unstimulated and mitogen-stimulated human lymphocytes were incubated with ribose concentrations associated with high-dose oral administration, i.e., 3.5 mM, and with two- (7 mM) and tenfold (35 mM) higher concentrations. Cell cultures with matching glucose concentrations served as controls. Incorporation of [3H]thymidine into cells was used to measure cell proliferation. No significant inhibition of human lymphocyte proliferation in vitro was observed in mitogen-stimulated cells. Unstimulated cultures showed significant inhibition only at 35 mM ribose. It is concluded that ribose plasma levels associated with high-dose oral administration do not inhibit human lymphocyte proliferation in vitro. No evidence was found that short-term ribose therapy is harmful to human lymphocytes.

Myoadenylate deaminase deficiency with severe rhabdomyolysis

A 13-year-old Turkish girl was admitted because of recurrent episodes of muscle pain and weakness since the age of 5 years. As an outpatient she developed severe acute rhabdomyolysis (myoglobinuria and increased serum creatine kinase level of 19,000 units/l). The acute rhabdomyolysis and the preceding episodes of muscle pain and weakness had been induced by exercise. There was no increase in plasma ammonia level during ischaemic forearm exercise test and bicycle ergometry. Myoadenylate deaminase deficiency was proven both histochemically and biochemically. The girl was found to be homozygous for the C 34-T mutation of the AMPD1 gene causing primary myoadenylate deaminase deficiency in skeletal muscle. Both parents and her brother were heterozygous for that mutation. Myoadenylate deaminase deficiency has to be considered as a cause of severe rhabdomyolysis.

Ergometer exercise in myoadenylate deaminase deficient patients

Three patients with primary myoadenylate deaminase deficiency were subjected to exercise on a bicycle ergometer at 125 W for 30 minutes. Blood samples prior to, during, and at the end of exercise were analyzed for lactate, ammonia, and hypoxanthine. In addition, urinary hypoxanthine excretion was measured. In these patients the serum lactate level increased to concentrations between 7.9 and 9.0 mmol/l at the end of exercise whereas the mean lactate level in nine control subjects at the end of exercise was 3.3 mmol/l (range 1.1-8.1 mmol/l). There was no difference to control subjects in the exercise-induced increase in plasma levels of ammonia and hypoxanthine or in the increase in urinary hypoxanthine excretion. The findings support the hypothesis of a reduced substrate supply to the citric acid cycle in myoadenylate deaminase deficiency. The normal formation of ammonia and hypoxanthine excludes a marked loss of adenine nucleotides in working muscles in these patients.

The purine nucleotide cycle and its molecular defects

Three enzymes of purine metabolism, adenylosuccinate synthetase, adenylosuccinate lyase and AMP deaminase, have been proposed to form a functional unit, termed the purine nucleotide cycle. This cycle converts AMP into IMP and reconverts IMP into AMP via adenylosuccinate, thereby producing NH3 and forming fumarate from aspartate. In muscle, the purine nucleotide cycle has been shown to function during intense exercise; the metabolic flux through the cycle has been proposed to play a role in the regeneration of ATP by pulling the adenylate kinase reaction in the direction of formation of ATP, and by providing Krebs cycle intermediates. In kidney, the purine nucleotide cycle was shown to account for the release of NH3 under the normal acid-base status, but not under acidotic conditions. In brain, the purine nucleotide cycle might function under conditions that induce a loss of ATP, and thereby contribute to its recovery. There is no evidence that the purine nucleotide cycle operates in liver. Deficiency of muscle AMP deaminase is an apparently frequent disorder, which might affect approximately 2% of the general population. The observation that it can be found in clinically asymptomatic individuals suggests, paradoxically, that the ATP-regenerating function which has been attributed to the purine nucleotide cycle is not essential for muscle function. Further work should be aimed at identifying the conditions under which AMP deaminase deficiency becomes symptomatic. Adenylosuccinate lyase deficiency provokes psychomotor retardation, often accompanied by autistic features. Its clinical heterogeneity justifies systematic screening in patients with unexplained mental deficiency. Additional studies are required to determine the mechanisms whereby this enzyme defect results in psychomotor retardation.

Effects of ribose on exercise-induced ischaemia in stable coronary artery disease

There is no established treatment specifically aimed at protecting or restoring cardiac energy metabolism, which is greatly impaired by ischaemia. Even after reperfusion, myocardial content of ATP remains low for more than 72 h. Long-term post-ischaemic dysfunction and irreversibility of ischaemic damage have been associated with low ATP content. Evidence that the pentose sugar ribose stimulates ATP synthesis and improves cardiac function led us to test the possibility that ribose increases tolerance to myocardial ischaemia in patients with coronary artery disease (CAD). 20 men with documented severe CAD underwent two symptom-limited treadmill exercise tests on 2 consecutive days; we postulated that the ischaemia induced might bring about changes in ATP metabolism lasting for several days. Patients whose baseline tests showed reproducibility were randomly allocated 3 days of treatment with placebo or ribose 60 g daily in four doses by mouth. Exercise testing was repeated after treatment on day 5. At that time mean (95% confidence interval) treadmill walking time until 1 mm ST-segment depression was significantly greater in the ribose than in the placebo group (276 [220-331] vs 223 [188-259] s; p = 0.002). The groups did not differ significantly in time to moderate angina. In the ribose-treated group the changes from baseline to day 5 in both time to ST depression and time to moderate angina were significant (p less than 0.005), but these changes were not significant in the placebo group. In patients with CAD, administration of ribose by mouth for 3 days improved the heart's tolerance to ischaemia. The presumed effects on cardiac energy metabolism offer new possibilities for adjunctive medical treatment of myocardial ischaemia.

The oxidative pentose phosphate pathway in the heart: regulation, physiological significance, and clinical implications

The capacity of the oxidative pentose phosphate pathway (PPP) in the heart is small, since the activity of glucose-6-phosphate dehydrogenase (G-6-PD), the first and rate-limiting enzyme, is very low. Basically, two mechanisms are involved in the regulation of this pathway. Under normal conditions, G-6-PD is inhibited by NADPH. This can immediately be overcome in the isolated perfused rat heart by increasing the oxidized glutathione and by elevating the NADP+/NADPH ratio. Apart from this rapid control mechanism, there exists a long-term regulation which involves the synthesis of G-6-PD. All catecholamines that were administered stimulated the activity of myocardial G-6-PD in a time- and dose-dependent manner. This stimulation was due to increased new synthesis of enzyme protein, since the G-6-PDmRNA was specifically enhanced. As a consequence of the stimulation of the oxidative PPP, the available pool of 5-phosphoribosyl-1-pyrophosphate (PRPP) was elevated which serves as an important precursor substrate for purine and pyrimidine nucleotide synthesis. The limiting step in the oxidative PPP can be bypassed by ribose which leads to an elevation of the cardiac PRPP pool. The decline in the ATP that is induced in many pathophysiological conditions can be attenuated or even entirely prevented by i.v. infusion of ribose. In some experimental in vivo rat models such as in the overloaded and catecholamine-stimulated heart and in the non-ischemic region of the infarcted heart, the normalization of the metabolic situation was accompanied by an improvement of global heart function. Ribose application has been shown to be beneficial in several clinical disease states such as myoadenylate deaminase deficiency and McArdle's disease. Moreover, ribose facilitated thallium-201 redistribution and markedly improved the detection of reversible ischemic injury of the pig and human heart.

Nucleotide precursors modify the effects of isoproterenol. Studies on heart function and cardiac adenine nucleotide content in intact rats

In closed-chest rats, isoproterenol (ISO, 25 mg/kg), 5 hours after subcutaneous administration, increased heart rate by 53%, left ventricular (LV) dP/dtmax by 80%, and cardiac output by 37%. LV systolic pressure (LVSP, -10%), mean arterial pressure (MAP, -12%), and total peripheral resistance (TPR, -36%) were diminished. In separate experiments, continuous intravenous infusion of adenine (50 mg/kg/hr) for 5 hours reduced heart rate (-11%), LVSP (-16%), MAP (-20%), TPR (-33%), and LV dP/dtmax (-20%). Cardiac output was increased (+20%). Inosine has been shown to have similar effects, except for a decline in cardiac output. Adenine (50 mg/kg/hr) attenuated the ISO-induced increase in heart rate and LV dP/dtmax and aggravated the decline in LVSP, MAP, and TPR. The increase in cardiac output was not changed. Inosine (200 mg/kg/hr) modified the ISO effects to a similar extent. Ribose (200 mg/kg/hr) added to the adenine infusion did not have functional effects. However, it aggravated the modifying influence of inosine on LVSP, LV dP/dtmax, and MAP. ISO reduced the cardiac ATP content (mumol/g) from a control value of 5.02 +/- 0.06 (n = 12) to 3.51 +/- 0.13 (n = 10). Adenine (3.56 +/- 0.21, n = 7) and ribose (3.64 +/- 0.11, n = 9) alone did not affect it, but inosine attenuated it (4.33 +/- 0.08, n = 8). Adenine and inosine in combination with ribose abolished the ISO-induced ATP decline (5.18 +/- 0.23, n = 7, and 4.76 +/- 0.10, n = 8, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Muscle metabolism and red cell ATP/ADP concentration during bicycle ergometer in patients with AMPD-deficiency

6 patients with AMPD-deficiency and 6 control subjects performed exercise on a bicycle ergometer until heart rate was 200 minus age. During exercise the increase of ammonia plasma concentrations was reduced in AMPD-deficient patients compared with that of control subjects. Plasma concentrations of lactate, pyruvate, inosine, hypoxanthine and xanthine increased during exercise in both groups. The concentrations of lactate, inosine and hypoxanthine were lower in AMPD-deficient patients during exercise, the difference was not significant. In AMPD-deficient patients the ATP-concentrations of red blood cells increased during exercise in contrast to control subjects, whereas the ADP amount did not change significantly. Our data suggest that in AMPD-deficient-patients AMP is mainly reduced to adenosine during exercise resulting in decreased ammonia concentrations. The increased concentrations of ATP in red blood cells may be the consequence of increased phosphorylation.

Ribose administration during exercise: effects on substrates and products of energy metabolism in healthy subjects and a patient with myoadenylate deaminase deficiency

Nine healthy men and a patient with myoadenylate deaminase deficiency were exercised on a bicycle ergometer (30 minutes, 125 Watts) with and without oral ribose administration at a dose of 2 g every 5 minutes of exercise. Plasma or serum levels of glucose, free fatty acids, lactate, ammonia and hypoxanthine and the urinary hypoxanthine excretion were determined. After 30 minutes of exercise without ribose intake the healthy subjects showed significant increases in plasma lactate (p less than 0.05), ammonia (p less than 0.01) and hypoxanthine (p less than 0.05) concentrations and a decrease in serum glucose concentration (p less than 0.05). When ribose was administered, the plasma lactate concentration increased significantly higher (p less than 0.05) and the increase in plasma hypoxanthine concentration was no longer significant. The patient showed the same pattern of changes in serum or plasma concentrations with exercise with the exception of hypoxanthine in plasma which increased higher when ribose was administered.

Type 2a fibre rhabdomyolysis in myoadenylate deaminase deficiency

A 31-year-old woman developed an acute, potentially fatal rhabdomyolysis of undetermined origin. Muscle biopsy revealed selective lysis involving exclusively type 2a fibers. Myoadenylate-deaminase (MAD) deficiency was proven by a negative histochemical reaction as well as by an enzymatic biochemical determination. The significantly greater energetic dependence of type 2a fibres on MAD explains their selective damage. The patient's mother also suffers from a similar muscle disease of still unclarified origin.

Serum levels of glucose, insulin, and C-peptide during long-term D-ribose administration in man

D-ribose was given orally and/or intravenously to nine healthy subjects at doses ranging from 83.3 to 222.2 mg/kg per hour for at least four hours. The serum ribose level increased in a dose-dependent manner to maximum concentrations of 75 to 85 mg/dl. The serum glucose level decreased after the beginning of continuous ribose administration and was reduced as long as ribose was being administered. The oral or intravenous administration of 166.7 mg/kg per hour of ribose resulted in a 25% decrease in serum glucose. Higher intravenous doses of ribose did not provoke a further decrease in serum glucose concentration. Oral administration of 166.7 mg/kg per hour led to an increase in serum insulin concentrations from a mean of 8.4 (range 6.4-11.5) to 10.4 (range 6.3-15.4) microU/ml (p less than 0.05). In contrast, intravenous administration did not change serum insulin concentrations significantly. The serum c-peptide concentration remained unchanged regardless of treatment. We conclude that the variations in plasma insulin concentrations do not account for the observed decrease in mean serum glucose concentrations accompanying D-ribose administration.

Metabolism of D-ribose administered continuously to healthy persons and to patients with myoadenylate deaminase deficiency

D-ribose was administered orally or intravenously over at least 5 h to eight healthy volunteers and five patients with myoadenylate deaminase deficiency. Intravenous administration rates were 83, 167, and 222 mg/kg/h, which were well tolerated but oral administration of more than 200 mg/kg/h caused diarrhea. The average steady state serum ribose level ranged between 4.8 mg/100 ml (83 mg/kg/h, oral administration) and 81.7 mg/100 ml (222 mg/kg/h, intravenous administration). Serum glucose level decreased during ribose administration. The intestinal absorption rate of orally administered ribose was 87.8%-99.8% of the intake at doses up to 200 mg/kg/h without first pass effect. Urinary losses were 23% of the intravenously administered dose at 222 mg/kg/h. Ribose appeared to be excreted by glomerular filtration without active reabsorption; a renal threshold could not be demonstrated. The amount of ribose transported back from the tubular lumen depended on the serum ribose level. There was no difference in ribose turnover in healthy subjects and patients with MAD deficiency.

Uricosuric effect of irtemazole in healthy subjects

Following a single dose of 50 mg irtemazole per os, plasma uric acid levels decreased after 1 h and fell to 53.5% of the original value within 6-12 h. Renal uric acid excretion increased up to 66 mg/h 30 min after drug application and reached its maximum of 151 mg/h 30 min later. Uric acid clearance also increased after 30 min and reached its maximum of 56 ml/min after 60 min. The response of the kidney to irtemazole is faster than to benzbromarone or probenecid. Lowering of plasma uric acid has a shorter-lasting effect than benzbromarone or probenecid. At 24 h after the application of 50 mg irtemazole the decrease of the plasma uric acid was between 15.4% and 30.0%, or 24.7% on average. Three days after the application the basic plasma uric acid levels were reached again.

Myoadenylate deaminase deficiency

Myoadenylate deaminase (MAD) is the rate-limiting enzyme in the purine nucleotide cycle which is biochemically linked to glycolysis and the citric cycle and thereby providing energy during intense muscular activity. In muscle fibers, myoadenylate deaminase operates at considerably higher activity levels than in other organs. First detected using enzyme-histochemical methods, it now appears that deficiency of myoadenylate deaminase is one of the most frequent enzyme defects in muscle. The primary defect may occur as an isolated nosological entity or not infrequently it is also associated with a large spectrum of different neuromuscular conditions. It seems to be the primary unassociated MAD deficiency that has recently become amenable to successful treatment with D-ribose in high doses. Secondary MAD deficiency may occur in muscle fibers and muscles that have undergone structural damage as seen, for instance, in polymyositis, muscular dystrophy, and denervation. The wealth of biochemical, morphological, and clinical data that has accumulated since the discovery of MAD deficiency during the past decade provides nosological significance of MAD deficiency as a real entity.