Participation and risk-taking behaviour in sports in children with haemophilia.

The aim of this study was to investigate participation in sports activities and risk-taking behaviour in children with haemophilia and the relationship to personal and health related factors. Ninety-nine children (mean age 12.6 years) completed questionnaires regarding participation in sports and physical education, medication, health related quality of life, and perceived motor competence. Furthermore, weight, height, active range of motion, pain, and muscle strength were assessed. Based on a risk exposure factor (REF) we defined subgroups with low, medium, and high risk when participating in sport. Most children participate in sport five times a week (mean 140 min per week), and little absence during school sports was reported. In general, prophylaxis was not tailored to sport activities. Boys with haemophilia preferred other sports than their Dutch contemporaries. The top-5 being soccer, swimming, tennis, gymnastics, and cardio-fitness for the former; soccer, gymnastics, tennis, hockey, and swimming for the latter. Significant differences between the low risk group and both other groups were found for sport intensity, total energy expenditure (EE) and average risk factor (ARF), however the medium and high-risk groups did not differ in ARF. REF and sport participation increased associated with increasing interest in athletic and motor activities. No significant differences were found between REF groups regarding age, Z-BMI, Z-AROM, Z-Muscle force, and the presence of painful joints. As in normal peers motivation to participate in sport depends upon the enthusiasm and interest, in children with haemophilia choice of sports differs, probably related to sport advice.

Targeting of captopril to the kidney reduces renal angiotensin-converting enzyme activity without affecting systemic blood pressure.

We have synthesized a prodrug of the angiotensin-converting enzyme (ACE) inhibitor captopril by coupling this drug covalently to the low molecular weight protein (LMWP) lysozyme. Such drug-LMWP conjugates can be used for renal drug delivery, since LMWPs accumulate specifically in the proximal tubular cells of the kidney. In the present study, we compared the effects of captopril-lysozyme and free captopril in male Wistar rats. ACE activity in plasma and the kidney was measured after intravenous bolus injection of either the captopril-lysozyme conjugate (33 mg. kg(-1), corresponding to 0.2 mg. kg(-1) captopril) or equivalent dosages of free captopril and lysozyme. The administration of the captopril-lysozyme conjugate resulted in less plasma ACE inhibition and a longer-lasting renal ACE inhibition compared with the free drug. Effects on blood pressure and natriuresis were studied during intravenous infusion of captopril-lysozyme (275 mg. kg(-1). 6 h(-1) conjugate, corresponding to 5 mg. kg(-1). 6 h(-1) captopril) or an equimolar dosage of free captopril. Captopril-lysozyme did not affect systemic blood pressure, whereas free captopril lowered blood pressure significantly (-23 +/- 32% versus control after 6 h). Captopril-lysozyme increased natriuresis about 3-fold compared with control levels (260 +/- 32% after 6 h), whereas free captopril treatment resulted in a reduced sodium excretion (26 +/- 12%). Furthermore, captopril at a lower dose, which only moderately lowered blood pressure, showed an increased sodium excretion. We conclude that renal delivery of captopril using captopril-lysozyme results in reduced systemic activity and increased kidney-specific activity of the targeted drug.

Sample dilution: a methodological pitfall in the measurement of tissue but not serum ace-activity.

Many tissue ACE-assays suffer from underestimation of the ACE-activity at low sample dilutions. However, measurement of ACE-activity as the amount of hippuric acid produced by cleavage of the commonly used substrate hippuryl-histidyl-leucine might circumvent this problem. In this study, we investigated whether sample dilution affects the measurement of ACE-activity in rat tissue and serum. We found that serum ACE-activity was not affected by sample dilution. In homogenates of aorta, kidney, left ventricle, and lung, however, ACE-activity increased 1.6-2.8 times with increasing sample dilution until, ultimately, a plateau was reached at dilution factor 100, 50, 20, and 100, respectively. In addition, tissue homogenates inhibited the activity of exogenous ACE, whereas serum did not. These data suggest that the dilution effect probably results from interactions of inhibitory substances from the homogenates with ACE. The implications of these findings are that tissue ACE-activity measurements by any assay should be performed using sample dilution at the plateau. In many studies in the literature, specifications of sample dilution are lacking. Our findings demonstrate that caution is warranted in the interpretation of these studies.

Low molecular weight proteins as carriers for renal drug targeting. Preparation of drug-protein conjugates and drug-spacer derivatives and their catabolism in renal cortex homogenates and lysosomal lysates.

Low molecular weight proteins (LMWPs) are known to be reabsorbed and catabolized primarily by the proximal tubular cells of the kidneys. As such, LMWPs might serve as drug carriers that release drugs site-specifically in the kidney. We tested this concept in vitro by coupling different drugs to the LMWP lysozyme both directly (amide bond) and via different spacers: oligopeptides (amide bond), (poly-)alpha-hydroxy acids (ester bond), and a pH sensitive cis-aconityl spacer (amide bond). The capability of the kidney to release the parent drug from such drug-spacer derivatives and drug-LMWP conjugates by enzymatic or chemical hydrolysis of the bond was tested by incubation experiments in renal cortex homogenates and lysosomal lysates. Directly coupled conjugates of terminal carboxyl group containing drugs and lysozyme were catabolized to single amino acids, but did not result in release of the parent drug. The amide bond between the drug and the final amino acid (lysine) appeared to be stable in the incubation milieu. Different oligopeptide spacers coupled to the drugs showed similar results: the oligopeptide itself was cleaved but the amide bond between the drug and different single amino acids remained untouched. Only amide bonds of derivatives of carboxylic drugs with peptide structures themselves were cleaved. Some of the directly coupled conjugates of terminal amino drugs and oligopeptides showed clear release of the parent drug whereas others were stable. Terminal amino drugs were rapidly released from an acid-sensitive cis-aconityl spacer. Terminal carboxyl group containing drugs were enzymatically released from their glycolic and lactic ester spacers at different rates. These kinds of drugs were also released as parent drug from LMWP conjugates with ester spacers like L-lactic acid. Increasing spacer length by intercalating a tetra(L-lactic acid) molecular between the drug and the protein further increased the extent and rate of drug release, indicating increased accessibility of the bond to the enzymes. Terminal amino group containing drugs were rapidly generated as parent drug from LMWP conjugates using an acid-sensitive spacer. In addition the conjugates were found to be adequately stable in plasma, considering their rapid clearance from the bloodstream. It is concluded that LMWPs may indeed be of use as carriers for specific renal delivery of drugs, since renal cortex homogenates and lysosomal lysates are able to catabolize the protein and generate the parent drug from drug-LMWP conjugates bearing suitable spacers. The option of enzymatic release is limited by the narrow specificity of the lysosomal enzymes.(ABSTRACT TRUNCATED AT 400 WORDS)