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Biomedical subjects

D J Kok

Publications and source records attributed to D J Kok.

At least 19 recordsLinked to original sources

Abnormal urine flow in boys with distal hypospadias before and after correction.

PURPOSE: We established the urine flow rate and the effect of surgical correction on that rate in patients with hypospadias. MATERIALS AND METHODS: The urine flow rate, voided volume and residual urine were measured using an ultrasound flow probe and bladder scan in boys with distal hypospadias before operative correction in 42 with a mean age of 16 months, 3 and 9 months after operative correction in 28 and 11, respectively, and in a control group of 51 boys 0 to 3 years old (mean age 11 months). Long-term flow data were obtained retrospectively from the records of 63 patients with hypospadias 1 to 10 years after operation. RESULTS: Of the controls 37% had mainly intermittent and sometimes fractionated flows, 4% had a plateau phase flow and 59% had mainly bell-shaped flow curves. The average maximum flow rate +/- SD was 6.8 +/- 4.1 ml per second and maximum flow rate/voided volume was 0.26 +/- 0.11 l per second. Of the boys with distal hypospadias 76% produced intermittent flows (fractionated in the majority) before correction. After correction this percent decreased to 50%. The average maximum flow rate was 7.5 +/- 2.5 ml per second before correction, and 6.6 +/- 2.8 and 7.2 +/- 1.8 ml per second 3 and 9 months after operation, respectively. Average maximum flow rate/voided volume was 0.22 +/- 0.12 l per second before, and 0.16 +/- 0.09 and 0.16 +/- 0.09 l per second 3 and 9 months after operation, respectively. In the long-term group maximum flow rate/voided volume was 0.13 +/- 0.11 l per second. The number of patients voiding with a plateau phase increased from 6% before to 13% and 17% after correction, respectively. An obstructive pattern was also observed in 41% of the long-term followup group. CONCLUSIONS: An intermittent flow pattern is common in 0 to 3-year-old boys. It appears to be more common and more pronounced or fractionated in boys with distal hypospadias at the same ages. In relation to voided volume patients with hypospadias already produce an abnormally low urine flow rate before correction and even more so thereafter in the short and intermediate term. The corrective procedure increases the occurrence of flows with an obstructive pattern.

Adolescent↗

Evaluation of the efficacy of emodepside+praziquantel topical solution against cestode (Dipylidium caninum, Taenia taeniaeformis, and Echinococcus multilocularis) infections in cats.

Emodepside+praziquantel topical solution was developed to provide broad-spectrum anthelmintic activity against gastrointestinal parasites in cats. Eight controlled studies were conducted to evaluate the efficacy of a topical solution of emodepside (3 mg/kg) and praziquantel (12 mg/kg) (Profender, BayerAG, Leverkusen, Germany) against feline infections with three species of cestodes. Studies featured naturally acquired infections of Dipylidium caninum or Taenia taeniaeformis, or experimental infections with Echinococcus multilocularis that were placebo-controlled, randomized and blinded. Cats were euthanatized and necropsied between 2 and 11 days after treatment, depending on the target parasite. The efficacy of emodepside+praziquantel topical solution was 100% against D. caninum and T. taeniaeformis, and 98.5- 100% against E. multilocularis. No significant systemic or local adverse reactions to treatment were noted in cats that received the combination. Topical treatment of cats with emodepside+praziquantel topical solution was safe and highly effective against cestode infections.

Administration, Topical↗

Raman spectroscopic analysis identifies testicular microlithiasis as intratubular hydroxyapatite.

PURPOSE: As diagnosed by ultrasonography, testicular microlithiasis is associated with various benign and malignant conditions. The molecular constitution of these microliths is largely unknown. Raman spectroscopy provides detailed in situ information about the molecular composition of tissues and to our knowledge it has not been applied to gonadal microliths. We analyzed the molecular composition of gonadal microlithiasis and its surrounding region using Raman spectroscopy in malignant and benign conditions. MATERIALS AND METHODS: Multiple microliths from 6 independent samples diagnosed with gonadal microlithiasis by ultrasound and histologically confirmed were investigated by Raman spectroscopy. The samples included 4 testicular parenchyma samples adjacent to a germ cell tumor (4 seminomas), a gonadoblastoma of a dysgenetic gonad and testicular biopsy of a subfertile male without malignancy. RESULTS: Raman spectroscopic mapping demonstrated that testicular microliths were located within the seminiferous tubule. Glycogen surrounded all microliths in the samples associated with germ cell neoplasm but not in the benign case. The molecular composition of the 26 microliths in all 6 conditions was pure hydroxyapatite. CONCLUSIONS: Microliths in the testis are located in the seminiferous tubules and composed of hydroxyapatite. In cases of germ cell neoplasm they co-localize with glycogen deposits.

Calculi↗

The interaction between Sillence type and BMD in osteogenesis imperfecta.

Clinical studies with bisphosphonates in children with osteogenesis imperfecta (OI) show an increase in BMD and a decrease in fracture rate. Bone strength in children with OI is not only influenced by changes in BMD but also by changes in collagen I structure of the organic bone matrix. Therefore, we studied the interaction between these two factors in a cross-sectional, single center study including 54 children. We assumed that vertebral deformities in OI represent an unbalance between load and bone strength. Body weight was considered to be a well quantifiable load on vertebral bodies. BMD served as a marker, representing the amount of bone tissue available for vertebral load bearing, and the Sillence classification, either type I or III/IV, as a marker representing the quality of the organic bone matrix. Independent associations were observed between the prevalence of vertebral deformities and (1) Sillence type (OR: 5.7, 95%Cl:1.2-26.8), (2) BMD (OR: 0.003, 95%Cl: 0-0.25) and (3) body weight (OR: 1.15, 95%Cl: 1.05-1.25). Regarding the anthropometrical differences among the different types of OI, the BMD/body weight ratio was introduced to evaluate the BMD in relation to body size. Prevalent vertebral deformities were associated with low BMD/body weight ratios (OR: 0.04, 95%Cl: 0.008-0.2) in OI type I, but no association was found in type III/IV. It was concluded that BMD and Sillence type have independent relationships with vertebral deformities. The BMD/body weight ratio correlates with vertebral deformities in children with OI type I. Its meaning in types III/IV needs further research with larger samples because of the relatively high prevalence of vertebral deformities in this group.

Absorptiometry, Photon↗

Is enalapril adequate for the prevention of renal tissue damage caused by unilateral ureteral obstruction and/or hyperoxaluria?

Unilateral ureteral obstruction (UUO) and hyperoxaluria (HOX) can lead to end-stage renal disease with tubulointerstitial fibrosis. We investigated the effects of enalapril (E), an ACE-inhibitor, on rat kidneys with either UUO or HOX. Sham-operated, UUO, HOX, UUO+HOX, UUO+E and HOX+E rats were killed 14 days after UUO and/or HOX was initiated. Rat kidney sections were histologically scored for tissue damage and monocyte/macrophage infiltration was demonstrated with ED1 antibody and measured by computer image analysis software. Serious glomerular and tubulointerstitial damage was found for UUO and HOX, consisting of glomerular basement membrane thickening, tubular dilatation/collapse, tubular basement membrane thickening and the infiltration of mononuclear leucocytes (mainly macrophages). For HOX, calcium oxalate crystals were visible. Neither the scored histological parameters nor monocyte/macrophage infiltration was significantly decreased when E-treated were compared with untreated groups. We conclude that E did not ameliorate the parameters scored in either UUO or HOX. This being contrary to findings by other research groups, we hypothesize that E may be effective only in short-term UUO/HOX, with transforming growth factor, TGF-beta1, formation becoming partly independent of Ang II in late-stage UUO/HOX, or other fibrogenic cytokines than TGF-beta1 becoming predominant.

Angiotensin-Converting Enzyme Inhibitors↗

The growth of sheep scab lesions in relation to sheep breed and time of the year.

Numerically equal groups of between five and ten young Merino and Dorper sheep were artificially infested with sheep scab mites, Psoroptes ovis. Separate groups of sheep were infested during the early winter of two successive years as well as during the early summer of the second year. Lesion growth was measured at two-weekly intervals for a period of six weeks during the first winter and for eight weeks during the second winter and in the summer. The rate of lesion growth and mean lesion size on Merino sheep was significantly greater than that on Dorper sheep at each two-weekly recording during the winter of both years. The rate of growth of the lesions did not differ significantly between the two sheep breeds during summer, although, with the exception of eight weeks post-infestation, the mean lesion size on Merino sheep was significantly larger than that on Dorper sheep at each assessment.

Animals↗

Identification of bladder wall layers by Raman spectroscopy.

PURPOSE: We explored the applicability of Raman spectroscopy to in situ investigation of bladder wall tissue. MATERIALS AND METHODS: Bladder wall tissue was obtained from a guinea pig model and frozen sections were used for Raman spectroscopic investigations. From each section 500 to 700 spectra were obtained in a 2-dimensional grid spanning the urothelium, lamina propria and muscle layer. The data set of spectra was subdivided into groups of similar spectra by a cluster analysis algorithm. With each group assigned a different color Raman maps of frozen sections were constructed based on group membership of measured spectra. These maps were then compared with histological and histochemical data obtained from hematoxylin and eosin and immunohistochemical staining for collagen I and III and for smooth muscle actin to correlate Raman spectral features with bladder wall structure and molecular composition. RESULTS: Urothelium, lamina propria and muscle layers could be clearly distinguished based on Raman spectra. Lamina propria spectra were dominated by signal contributions of collagen and the smooth muscle layer showed strong signal contributions of actin. The urothelium had a relatively strong lipid signal contribution. CONCLUSIONS: These results and the fact that Raman spectroscopy is rapidly evolving into a technology that can be applied in vivo by thin, flexible fiberoptic catheters indicate that prospects are good for in vivo analysis of the molecular composition of the normal and pathological bladder without biopsies.

Actins↗

Hosts, seasonal occurrence and life cycle of Rhipicentor nuttalli (Acari: Ixodidae).

There are only two species worldwide within the genus Rhipicentor, namely Rhipicentor bicornis and Rhipicentor nuttalli and both occur only in Africa. Rhipicentor nuttali has a widespread distribution in South Africa and the present investigation was initiated to elucidate its host preference, seasonality and life cycle. Rock elephant shrews, Elephantulus myurus were examined for ticks at four localities in the Free State Province, one in Gauteng Province and two in Limpopo Province, South Africa. Cape elephant shrews, Elephantulus edwardii were examined at two places in the Western Cape Province, and a single specimen of the bushveld elephant shrew, Elephantulus intufi was examined in central Namibia. Small mammals of other species were also examined at two of these localities. The majority of E. myurus at two sites in the Free State, at the locality in Gauteng and both sites in Limpopo Province were infested with larvae and/or nymphs of R. nuttalli, while the single E. edwardii examined at one site in the Western Cape Province and the single E. intufi examined in Namibia were infested with nymphs of this tick. Not one of the other small animals was infested. Although larvae and nymphs of R. nuttalli were present on E. myurus throughout the year, the former were generally most numerous during the period March to September, and the latter during May to October. The preferred hosts of the adults are domestic dogs, leopards, Panthera pardus and South African hedgehogs, Atelerix frontalis. Adult females engorged on Atelerix frontalis in 16-32 days and, after a preoviposition period of 2-4 days, produced approximately 170,00 eggs during the following 60-70 days. The average incubation period of the eggs was 59 days. Larvae engorged on E. myurus in 4-10 days and moulted to nymphs 12-20 days later. Nymphs required 11-15 days to engorge on E. myurus and moulted to adults 32-47 days later. Allowing 14 days for the exoskeletons and mouthparts of each of the three parasitic stages to harden before they can attach to a host, the life cycle took approximately 214 days to complete in the laboratory. The length of this period, considered in conjunction with the times of maximum seasonal occurrence of the immature stages, indicates that the life cycle probably takes a year to complete in the field.

Animals↗

Indinavir crystallization around the loop of Henle: experimental evidence.

OBJECTIVE: To determine the probable site of the nephron and the plasma indinavir (IDV) concentration at which intrarenal IDV crystallization occurs. DESIGN: We performed in vitro crystallization experiments in IDV solutions simulating conditions found in the nephron. METHODS: To determine intrarenal IDV concentrations at which conditions in the nephron allow crystallization, several concentrations of IDV basic solutions (0-800 mM) were titrated from pH 4.0 to higher pH values until crystals formed within 1 minute. Based on the combination of pH and ionic strength at which crystals formed, we determined the site of the nephron at which this combination was first attained. Based on the capacity for concentration at that site, we were able to measure the corresponding plasma IDV concentration. RESULTS: Under conditions normally found at the proximal tubule (i.e., pH 6.7 and ionic strength of 200 mM), IDV crystallized at 200 mg/L. Under conditions applying to the loop of Henle, pH 7.4 and ionic strength of 200 mM, IDV crystallized at 125 mg/L, which would correspond to a plasma IDV concentration of 8 mg/L. CONCLUSIONS: IDV crystallization is most likely in the loop of Henle and may already start at plasma IDV concentrations as low as 8 mg/L. Increasing hydration does not reduce the risk of IDV crystallization in the loop of Henle but instead prevents IDV crystallization and aggregation in the lower urinary tract. It remains to be confirmed whether prevention of high IDV plasma concentrations will reduce the risk of IDV crystallization in the loop of Henle.

Crystallization↗

Urodynamic follow-up of experimental urethral obstruction in individual guinea pigs.

It is unknown whether changes in bladder function due to urethral obstruction follow a specific sequence. To answer this, we adapted a small animal model to allow repeated complete pressure-flow studies, enabling individual follow-up of changes in bladder function on urethral obstruction. Obstruction was induced in guinea pigs by placing a silver ring around the urethra. Urodynamic studies were repeated under anesthesia with ketamine/xylazine. Bladders were filled and bladder pressure measured through a single suprapubic catheter. Urine flow rate was measured using an ultrasound probe around the penis. Accurate measurements of bladder pressure and urine flow rates were obtained at 1-week intervals for 11 weeks in individual guinea pigs. In the control animals, the urodynamic parameters did not show significant changes. In the obstructed group, urethral resistance (P(low,ave)) increased from 20 to 35 cm H(2)O after 4 weeks and remained at that level. The maximum flow rate (Q(max)) increased from 0.17 to 0.24 mL/s after 2 to 3 weeks. After this peak, it gradually decreased to lower than the starting value after 10 to 11 weeks. The pressure at maximum flow rate (p(Qmax)) increased from 24 to 47 cm H(2)O after 6 to 7 weeks and thereafter declined. During weeks 1 through 4 of obstruction, unstable contractions were seen. All animals followed a similar sequence of patterns but at variable rates. Our animal model allows complete urodynamic follow-up of individual animals with urethral obstruction. We observed a specific sequence of changes in urodynamic patterns and parameters of bladder function.

Animals↗

Cytokine production induced by binding and processing of calcium oxalate crystals in cultured macrophages.

Deposition of calcium oxalate (CaOx) crystals in the renal interstitium is common in humans with primary oxalosis and secondary hyperoxaluria, as well as in kidneys of rats with CaOx nephrolithiasis. In vivo, macrophages and multinucleated giant cells mostly encapsulate these crystals. To investigate whether macrophages are able to dispose of CaOx crystals after phagocytosis, we used a nontransformed macrophage cell line derived from mouse spleen progenitors. Cytokine assays showed that in response to crystal binding and phagocytosis, these macrophages release tumor necrosis factor-alpha. This release was evident at 8 hours, maximal at 24 hours, and decreased to control values after 48 hours of incubation with crystals. A very low but significant release of interleukin-6 into the culture medium was only noticed after 32 hours. Radiochemical experiments showed that these cells bind 38.8% of the CaOx crystals added. After 4 days, all internalized crystals had been dissolved and their molecular constituents released into the extracellular environment. Confocal laser scanning microscopy followed by morphometrical analyses confirmed these results. Long-term (survival) analyses showed that in the interval under study and at the crystal doses used, cell viability was not significantly affected. These findings support the view that properly functioning macrophages are able to remove CaOx deposits from the renal interstitium and that these cells produce inflammatory cytokines before crystal dissolution.

Animals↗

Modulation of calcium oxalate monohydrate crystallization kinetics by urine of preterm neonates.

Preterm neonates frequently develop nephrocalcinosis (NC). However, the cause has not yet been elucidated. This study focuses on the effects of urine from preterm neonates on crystallization kinetics. Urine samples were collected and renal ultrasound examinations of preterm neonates (gestational age < 32 weeks) were performed during the first weeks of life, at term, and ages 6, 12, and 24 months. The effect of urine on crystallization was determined using a seeded crystal growth system, which measures the square root of solubility product ( radicalLc), percentage of growth inhibition (GI), and agglomeration inhibition ([tm]) of calcium oxalate crystals. Data for preterm neonates in the first weeks of life (n = 19) were compared with those for full-term neonates (n = 17) and healthy adults. Moreover, the correlation between [tm] and urinary (U)citrate level was studied. Mean radicalLc (0.27 +/- 0.1 versus 0.36 +/- 0.08 mmol/L) and mean [tm] (81 +/- 32 versus 143 +/- 97 minutes) were lower and mean Ucalcium-creatinine (2.20 +/- 1.74 versus 0.46 +/- 0.73 mol/mol) and Uoxalate-creatinine ratios (0.39 +/- 0.21 versus 0.16 +/- 0.09 mol/mol) were greater in preterm neonates in the first weeks of life compared with full-term neonates (p < 0.05). Furthermore, [tm] was less than the lower limit for healthy adults for all but one preterm neonate; [tm] increased and Ucalcium-creatinine and Uoxalate-creatinine ratios decreased with age (p < 0.005). There was a correlation between [tm] and citrate excretion (coefficient of 38; P < 0.001). Patients with and without NC at term did not differ statistically in mean radicalLc, percentage of GI, or [tm]. In conclusion, urine from preterm neonates in the first weeks of life is highly supersaturated and has a defective ability to inhibit calcium oxalate crystal agglomeration. This ability improves with age and is citrate mediated. We suggest that both the high level of supersaturation and defective ability to inhibit calcium oxalate crystal agglomeration contribute to the high incidence of NC.

Adult↗

Methods for measuring crystallization in urolithiasis research: why, how and when?

Whereas crystalluria does not distinguish between kidney stone formers and healthy people and thus can be considered a physiologic event, kidney stone formation is a pathologic incident and reflects a specific form of biomineralization. Both single urinary crystals as well as whole kidney stones form under exquisite control of organic macromolecules. Simple crystal formation in the urinary tract is distinguished from stone formation in the kidney by the process of particle retention. The latter occurs either because nucleated crystals strongly aggregate to particles too large to pass freely through the tubules ('free particle' theory), or because crystals become abnormally adherent to tubular cell surfaces ('fixed particle' theory). Since it is impossible to mimic all the processes involved in stone formation in vitro, it is highly important to carefully chose a specific crystallization process for in vitro studies, and to select the most appropriate experimental conditions for measuring the chosen process as reliably as possible. This overview aims at critically reviewing the principles of currently available assay systems for studying crystallization processes involved in stone formation. Consensus is reached by the experts that no in vitro system really mimics what happens in renal stone formation, but that carefully designed in vitro studies will always play an important part in urolithiasis research. For such studies, it is highly important to exactly control the appropriate experimental conditions that are relevant to a specific crystallization process under investigation. Practical guidelines for researchers working with crystallization systems are provided, and it is concluded that international efforts should be made to standardize the terminology, to agree on a set of basic experimental parameters (temperature, pH, artificial urine composition), and to adopt simple tests or conditions are reference points for quality and comparative control.

Calcium Oxalate↗

Influence of sheep breed and application site on the efficacy of a flumethrin pour-on formulation against ticks.

The objectives of this study were to determine the influence of application site and sheep breed on the efficacy of a flumethrin (1% m/v) solution for the control of 'bont'-legged (Hyalomma spp.) and red-legged ticks (Rhipicephalus evertsi evertsi). This study was conducted from November 1996 to February 1997 on 3 farms in the southwestern Free State Province. Two trials were conducted on Dorper sheep and 2 on Merino sheep. For each specific application 30 sheep were selected and allocated to 3 groups of 10 animals each using randomisation through minimisation, with pre-treatment total tick count as only criterion. Groups consisted of an untreated control group, a group treated with 3 ml of a flumethrin (1% m/v) solution applied only to the anogenital region, and a group treated at a dose rate of 1 mf flumethrin (1% m/v)/5 kg host body mass. The total dose volume for animals in the last group was divided into 3 equal parts and applied to the brisket/axillae, groin and anogenital regions respectively. Animals grazed under extensive farming conditions and were infested by ticks that occurred naturally in the environment. Ticks were counted and removed weekly over a 6-week period. In all 4 trials, Rhipicephalus e. evertsi was the dominant tick species, followed, in 3 of the trials, by Hyalomma spp. Efficacy (%) of control against ticks for Dorper sheep, treated only on the anogenital region, was variable, ranging between 29.5 and 97%. In Merino sheep the efficacy values ranged between 23.1 and 90 %. The site-spcific (anogenital region) efficacy of control against ticks infesting Merino sheep was in general 100% or almost 100%. In Dorper sheep the efficacy values were >80 % for 3-5 weeks. The efficacy (%) of control against ticks for sheep treated on the brisket/axillae, groin and anogenital regions was always higher compared to sheep treated only on the anogenital region. In Dorper sheep, efficacy of control was >80 % for up to 4 weeks and in Merino sheep >80 % for 6 weeks.

Administration, Topical↗

Measurement of urinary flow rate using ultrasound in young boys and infants.

PURPOSE: We present a technique for measuring urinary flow rates with ultrasound in male infants and children. MATERIALS AND METHODS: Urinary flow rate was measured simultaneously by an ultrasound probe placed around the base of the penis and by a funnel with a rotating disk at the bottom in 30 boys with a mean age of 6.7 years (range 4.5 to 10.5), and by ultrasound in 8 infants with a mean age of 10 months (range 1 to 28). Voided volume was measured with a graded cylinder or calculated from the weight change of diapers in infants. Ultrasound and rotating disk maximum flow rates were calculated. The ultrasound signal was calibrated by comparing the collected voided volume to the area under the curve for that void. The volume calculated from the rotating disk flow rate curve was also compared with the collected volume. RESULTS: Both methods yielded similar flow curves. However, ultrasound maximum flow rate significantly exceeded rotating disk maximum flow rate (13 +/- 6 ml. per second, range 5 to 22 versus 10 +/- 4 ml. per second, range 4 to 21, t test p <0.001). The underestimation of the flow rate by the rotating disk method may have been due to adherence of urine to the funnel wall. Rotating disk maximum flow rate was lower and voided volume was underestimated by up to 50% (average 15 +/- 2%) in 21 cases. Ultrasound maximum flow rate averaged 6 +/- 3 ml. per second (range 3 to 11.6 [oldest infant]) in the 8 infants. CONCLUSIONS: Urinary flow rates can be measured accurately using ultrasound in boys who produce small volumes and/or who are not toilet trained and also in infants. In future studies ultrasound will be applied to subsets of male infants with bladder dysfunction.

Child↗

Cellular membrane associated mucins in artificial urine as mediators of crystal adhesion: an in vitro enterocystoplasty model.

PURPOSE: Cells are a major component of mucus in enterocystoplasties. We evaluate the role of secreted mucins on cells and cellular membranes as crystal adhesion and agglomeration mediators in artificial urine infected with Proteus mirabilis. MATERIALS AND METHODS: Five human intestinal cell lines, HT29, HT29-18N2, HT29-FU, HT29-MTX, Caco-2 and 1 ureter cell line, SV-HUC-1, were incubated for 3 hours in artificial urine with P. mirabilis (ATCC49565) in monolayer and scraped conditions. We isolated Triton X-100 soluble membrane proteins from cells to evaluate the effect of MUC2 and MUC 5AC as membrane associated proteins on crystal formation and crystal adherence. Scanning electron microscopy, light microscopy, Coulter Counter measurements and x-ray microanalysis were used to evaluate crystal formation. RESULTS: Brushite crystals were adhered to cellular surface sites rich in sulfur as crystal agglomerates. Smaller and more numerous crystals were observed in the presence of scraped cells. Crystal growth and agglomeration was inhibited by the presence of MUC 5AC, whereas MUC2 had the opposite effect. Both are present on cellular membranes and are rich in sulfur. Cellular invasion by bacteria occurred in all cell lines. CONCLUSIONS: Membrane associated cellular secretions such as MUC2 and 5AC are important crystal adhesion molecules on cells and have a clear effect on urease induced crystallization in vitro. MUC2 and MUC 5AC induce crystal adhesion and mucin type dependent effects on crystal agglomeration. The effects of MUC2 and MUC 5AC may explain the high incidence of bladder calculi in enterocystoplasties and emphasize the role of cellular surfaces in urine.

Cell Adhesion↗