Ilkka Mononen

Enzyme replacement therapy in a mouse model of aspartylglycosaminuria

Aspartylglycosaminuria (AGU), the most common lysosomal disorder of glycoprotein degradation, is caused by deficient activity of glycosylasparaginase (AGA). AGA‐deficient mice share most of the clinical, biochemical and histopathologic characteristics of human AGU disease. In the current study, recombinant human AGA administered i.v. to adult AGU mice disappeared from the systemic circulation of the animals in two phases predominantly into non‐neuronal tissues, which were rapidly cleared from storage compound aspartylglucosamine. Even a single AGA injection reduced the amount of aspartylglucosamine in the liver and spleen of AGU mice by 90% and 80%, respectively. Quantitative biochemical analyses along with histological and immunohistochemical studies demonstrated that the pathophysiologic characteristics of AGU were effectively corrected in non‐neuronal tissues of AGU mice during 2 wk of AGA therapy. At the same time, AGA activity increased to 10% of that in normal brain tissue and the accumulation of aspartylglucosamine was reduced by 20% in total brain of the treated animals. Immunohistochemical studies suggested that the corrective enzyme was widely distributed within the brain tissue. These findings suggest that AGU may be correctable by enzyme therapy.—Dunder, U., Kaartinen, V., Valtonen, P., Väänänen, E., Kosma, V.‐M., Heisterkamp, N., Groffen, J., Mononen, I. Enzyme replacement therapy in a mouse model of aspartylglycosaminuria. FASEB J. 14, 361–367 (2000)

Twenty-four-month α-galactosidase A replacement therapy in Fabry disease has only minimal effects on symptoms and cardiovascular parameters

SummaryFabry disease is an X-linked lysosomal storage disease caused by deficiency of α-galactosidase A enzyme activity. Decreased enzyme activity leads to accumulation of glycosphingolipids in different tissues including endothelial cells and smooth-muscle cells and cardiomyocytes, and cardiovascular complications are common in the disease. Since 2001, specific enzyme replacement therapy (ERT) with α-galactosidase A has been available. It has been reported to improve clinical symptoms and quality of life. However, limited and controversial data on its efficacy to cardiac involvement have been published. Nine patients (5 male) with Fabry disease were included in an open-label prospective follow-up study of 24-month ERT. Comprehensive cardiovascular evaluation was performed by MRI, stress echocardiography and quality of life assessment. Plasma globotriaosylceramide decreased from 6.2 to 1.4xa0μg/ml during ERT (p<0.05). The only other measured parameters that changed significantly were resting heart rate that decreased from 79 to 67xa0bpm (p<0.01) and end-systolic volume that decreased by 12.4xa0ml (p<0.05). The other parameters consisting of quality of life, self-estimated cardiovascular condition, diastolic function, exercise capacity, ECG parameters, ejection fraction and ventricular mass did not change. ERT has only minimal effect on symptoms and cardiovascular morphology and function in Fabry disease. Therefore, effective conventional medical therapy is still of major importance in Fabry disease. Larger ERT studies are warranted, especially in women, to solve current open questions, such as the age at which ERT should be started, optimal dosage and intervals between infusions. Furthermore, longer follow-up studies are needed to assess the effects of ERT on prognosis.

β-Aspartylpeptides as substrates of L-asparaginases from Escherichia coli and Erwinia chrysanthemi

L‐Asparaginase is known to catalyze the hydrolysis of L‐asparagine to L‐aspartic and ammonia, but little is known about its action on peptides. When we incubated L‐asparaginases purified either from Escherichia coli or Erwinia chrysanthemi – commonly used as chemotherapeutic agents because of their antitumour activity – with eight small β‐aspartylpeptides such as β‐aspartylserineamide, β‐aspartylalanineamide, β‐aspartylglycineamide and β‐aspartylglycine, we found that both L‐asparaginases could catalyze the hydrolysis of five of them yielding L‐aspartic acid and amino acids or peptides. Our data show that L‐asparaginases can hydrolyze β‐aspartylpeptides and suggest that L‐asparaginase therapy may affect the metabolism of β‐aspartylpeptides present in human body.

Myocardial blood flow and its transit time, oxygen utilization, and efficiency of highly endurance-trained human heart

Highly endurance-trained athlete’s heart represents the most extreme form of cardiac adaptation to physical stress, but its circulatory alterations remain obscure. In the present study, myocardial blood flow (MBF), blood mean transit time (MTT), oxygen extraction fraction (OEF) and consumption (MVO2), and efficiency of cardiac work were quantified in highly trained male endurance athletes and control subjects at rest and during supine cycling exercise using [15O]-labeled radiotracers and positron emission tomography. Heart rate and MBF were lower in athletes both at rest and during exercise. OEF increased in response to exercise in both groups, but was higher in athletes (70xa0±xa021 vs. 63xa0±xa011xa0% at rest and 86xa0±xa013 vs. 73xa0±xa010xa0% during exercise). MTT was longer and vascular resistance higher in athletes both at rest and during exercise, but arterial content of 2,3-diphosphoglycerate (oxygen affinity) was unchanged. MVO2 per gram of myocardium trended (pxa0=xa00.08) lower in athletes both at rest and during exercise, while myocardial efficiency of work and MVO2 per beat were not different between groups. Arterial levels of free fatty acids were ~twofold higher in athletes likely leading to higher myocardial fatty acid oxidation and hence oxygen cost, which may have blunted the bradycardia-induced decrease in MVO2. Finally, the observed group differences in MBF, OEF, MTT and vascular resistance remained significant also after they were controlled for differences in MVO2. In conclusion, in highly endurance-trained human heart, increased myocardial blood transition time enables higher oxygen extraction levels with a lower myocardial blood flow and higher vascular resistance. These physiological adaptations to exercise training occur independently of the level of oxygen consumption and together with training-induced bradycardia may serve as mechanisms to increase functional reserve of the human heart.

Echocardiography in Fabry disease: diagnostic value of endocardial border binary appearance

Background and Aim:u2002 It has been reported that the endocardium in Fabry disease has a binary appearance on transthoracic echocardiography. It has been suggested that this sign could be used with good accuracy to differentiate Fabry disease from hypertrophic cardiomyopathy and even as a first filter to screen for suspected Fabry disease.

Cardiopulmonary involvement in Fabry's disease

Background — Fabry’s disease is an X-linked lysosomal storage disease caused by deficiency of alpha-galactosidase A enzyme activity. Decreased enzyme activity leads to accumulation of glycosphingolipid in different tissues, including endothelial and smooth-muscle cells and cardiomyocytes. Objectives — There is controversial data on cardiopulmonary involvement in Fabry’s disease, because many reports are based on small and selected populations with Fabry’s disease. Furthermore, the aetiology of cardiopulmonary symptoms in Fabry’s disease is poorly understood. Methods — We studied cardiopulmonary involvement in seventeen patients with Fabry’s disease (20-65 years, 6 men) using ECG, bicycle stress, cardiac magnetic resonance imaging, spirometry, diffusing capacity and pulmonary high-resolution computed tomography (HRCT) tests. Cardiopulmonary symptoms were compared to observed parameters in cardiopulmonary tests. Results — Left ventricular hypertrophy (LVH) and reduced exercise capacity are the most apparent cardiac changes in both genders with Fabry’s disease. ECG parameters were normal when excluding changes related to LVH. Spirometry showed mild reduction in vital capacity and forced expiratory volume in one second (FEV1), and mean values in diffusing capacity tests were within normal limits. Generally, only slight morphological pulmonary changes were detected using pulmonary HRCT, and they were not associated with changes in pulmonary function. The self-reported amount of pulmonary symptoms associated only with lower ejection fraction (P < 0.001) and longer QRS-duration (P = 0.04) of all measured cardiopulmonary parameters, whereas cardiac symptoms have no statistically significant association with any of these parameters. Conclusion — LVH and reduced exercise capacity are the most apparent cardiopulmonary changes in Fabry’s disease but they have only a minor association to cardiopulmonary symptoms.Therefore, routine cardiopulmonary evaluation in Fabry’s disease using echocardiography is maybe enough when integrated to counselling for aerobic exercise training.

Human leukocyte glycosylasparaginase: cell-to-cell transfer and properties in correction of aspartylglycosaminuria

Aspartylglycosaminuria (AGU), a severe lysosomal storage disease, is caused by the deficiency of the lysosomal enzyme, glycosylasparaginase (GA), and accumulation of aspartylglucosamine (GlcNAc‐Asn) in tissues. Here we show that human leukocyte glycosylasparaginase can correct the metabolic defect in Epstein–Barr virus (EBV)‐transformed AGU lymphocytes rapidly and effectively by mannose‐6‐phosphate receptor‐mediated endocytosis or by contact‐mediated cell‐to‐cell transfer from normal EBV‐transformed lymphocytes, and that 2–7% of normal activity is sufficient to correct the GlcNAc‐Asn metabolism in the cells. Cell‐to‐cell contact is obligatory for the transfer of GA since normal transformed lymphocytes do not excrete GA into extracellular medium. The combined evidence indicates that cell‐to‐cell transfer of GA plays a main role in enzyme replacement therapy of AGU by normal lymphocytes.