Acrosome-reacted human sperm in insemination medium do not bind to the zona pellucida of human oocytes

In the literature there is still confusion whether acrosome-reacted sperm in medium can initiate primary binding to human zona pellucida (ZP). The ability of acrosome-reacted sperm to bind to ZP in vitro can be deduced by measuring the acrosome reaction (AR) of ZP-bound sperm compared with sperm in medium after incubation under different conditions inhibiting the ZP-induced AR. Motile sperm from fertile men, normospermic men and infertile men diagnosed with disordered ZP-induced AR (DZPIAR) were selected by swim-up (2 x 10(6) in 1 mL medium) and incubated for 1-2 h with four oocytes from failed in vitro fertilization (IVF). The acrosome status of sperm was assessed using pisum sativum agglutinin labelled with fluorescein. The ZP-induced AR was inhibited in experiments using sperm from DZPIAR patients, hyper-osmotic medium (400 mOsm/kg) and medium containing soybean trypsin inhibitor (SBTI; 4 mg/mL). Pre-treatment with calcium ionophore was used to create a sperm population with elevated AR. In all experiments with factors inhibiting the ZP-induced AR, the AR was significantly lower for ZP-bound sperm compared with sperm in medium: DZPIAR patients 4% vs. 15%, hyper-osmotic medium 3% vs. 12%, SBTI 2% vs. 12% and SBTI 3% vs. 23% after treatment with calcium ionophore. In conclusion, acrosome-reacted sperm in vitro have significantly reduced, in fact probably zero ability to bind to the ZP.

Tyrosine phosphorylation on capacitated human sperm tail detected by immunofluorescence correlates strongly with sperm-zona pellucida (ZP) binding but not with the ZP-induced acrosome reaction

BACKGROUND

Protein tyrosine phosphorylation (TP) of human sperm is related to sperm capacitation and zona pellucida (ZP) binding. The aim of this study was to determine whether the TP of capacitated sperm is a useful marker for the ability of sperm to bind to the ZP and undergo the ZP-induced acrosome reaction (AR).

METHODS

Semen samples were obtained from 115 subfertile men with sperm count > or =20 x 10(6)/ml, motility > or =25% and variable morphology. Motile sperm (2 x 10(6)/ml) selected by swim-up were incubated with four oocytes for 2 h, and the number of sperm bound to the ZP and the ZP-induced AR was examined. TP of sperm tail was assessed by immunofluorescence (IF) with anti-phosphotyrosine monoclonal antibody. The time course and effects of dibutyryl cyclic adenosine monophosphate (dbcAMP) and phorbol myristate acetate (PMA) on TP were also studied.

RESULTS

TP was stimulated more by dbcAMP (P < 0.001) and less by PMA (P < 0.05). TP increased significantly with time of incubation of sperm. TP was not detectable on the surface of unfixed live sperm by either Dynabeads or IF. Sperm TP at 2, 4 and 20 h incubation was all significantly correlated with sperm-ZP binding but not with the ZP-induced AR.

CONCLUSION

Sperm TP detected by IF correlates strongly with sperm-ZP binding capacity but not with the ZP-induced AR. This simple IF assay of TP may be a clinically useful test of sperm function that is predictive of normal sperm ZP-binding capacity.

Hyper-osmotic condition enhances protein tyrosine phosphorylation and zona pellucida binding capacity of human sperm

BACKGROUND

The aim of this study was to determine the effect of culture medium osmolality, in the range known to occur in the male and female reproductive tracts, on human sperm tyrosine phosphorylation and sperm-zona pellucida (ZP) interaction in vitro.

METHODS

Motile sperm (2x10(6)), selected by swim-up from semen of normozoospermic men with normal sperm-ZP binding, were incubated with or without four oocytes in 1 ml human tubal fluid (HTF) medium with different osmolalities (150, 200, 280, 350, 400 mOsm/kg) adjusted by variation of the NaCl concentration. After 2 h incubation, the number of sperm bound to the four ZP was examined, sperm motility and velocities were assessed by Hamilton-Thorn Motility Analyzer (IVOS 10) and sperm tyrosine phosphorylation was assessed by both western immunoblotting and immunofluorescence with an anti-phosphotyrosine monoclonal antibody (PY20). The effect of hyper-osmolality (400 mOsm/kg) on the ZP-induced acrosome reaction (AR) was also determined.

RESULTS

Incubation of human sperm in hyper-osmotic medium significantly increased tyrosine phosphorylation and the number of sperm bound to the ZP. In contrast, hypo-osmotic medium significantly decreased both tyrosine phosphorylation and sperm-ZP binding. Medium with high osmolality (400 mOsm/kg) significantly reduced the ZP-induced AR. Both hypo- and hyper-osmotic media significantly decreased average sperm percentage progressive motility and velocities.

CONCLUSION

Incubation of human sperm in hyper-osmotic media was associated with significantly increased tyrosine phosphorylation and ZP-binding ability but severely reduced the ZP-induced AR.

Time course of changes in sperm morphometry and semen variables during testosterone-induced suppression of human spermatogenesis

BACKGROUND

Quantification of changes in semen may give insight into the testosterone (T)-induced disruption of spermatogenesis in man.

METHODS

A model analogous to flushing of sperm from the genital tract after vasectomy was used to quantify the time course of semen changes in subjects participating in male contraceptive trials using 800 mg T-implant (n = 25) or 200 mg weekly intramuscular injection (IM-T; n = 33). A modified exponential decay model allowed for delayed onset and incomplete disruption to spermatogenesis. Semen variables measured weekly during a 91-day period after initial treatment were fitted to the model.

RESULTS AND CONCLUSIONS

Sperm concentration, total count, motility and morphometry exhibited similar average decay rates (5 day half-life). The mean delay to onset of decline in concentration was 15 (IM-T) and 18 (T-implant) days. The significantly longer (P < 0.005) delays deduced for the commencement of fall in normal morphology (41 days), normal morphometry (40 days) and sperm viability (43 and 55 days), and the change of morphometry to smaller more compact sperm heads are consistent with sperm being progressively cleared from the genital tract rather than continued shedding of immature or abnormal sperm by the seminiferous epithelium. A significant negative relationship was found between lag time and baseline sperm concentration, consistent with longer sperm-epididymal transit times associated with lower daily production rates.

Exposure of actin on the surface of the human sperm head during in vitro culture relates to sperm morphology, capacitation and zona binding

BACKGROUND

The aim of this study was to determine the relationship between the proportion of motile sperm with actin exposed on the surface of the head and sperm function.

METHODS

Semen samples were obtained from normozoospermic men and sperm function tests were performed. Motile sperm selected by swim-up were incubated with actin monoclonal antibody (A-mAb, 1:100) for 2 h, then anti-mouse IgG Dynabeads were used to detect sperm-bound A-mAb. Sperm capacitation was increased by phorbol myristate acetate (PMA) and decreased by bicarbonate-free medium.

RESULTS

The proportion of sperm with exposed actin increased with time for up to 2 h incubation. Bicarbonate-free medium significantly decreased the proportion of sperm with exposed actin. PMA significantly enhanced this phenomenon. Sperm bound to zona pellucida (ZP) had a significantly higher proportion with exposed actin than did sperm remaining in medium. Of the 79 samples studied, an average of 9.4% (range 1-27%) of motile sperm had exposed actin after 2 h incubation and this was significantly correlated with sperm normal morphology and ZP binding.

CONCLUSION

Exposure of actin on the surface of the sperm head during in vitro culture may be related to membrane modification during sperm capacitation and hence may be a useful marker for this subpopulation of sperm.

Low proportions of sperm can bind to the zona pellucida of human oocytes

BACKGROUND

Sperm binding to the zona pellucida (ZP) is required for human fertilization. Under experimental conditions not limited by ZP binding sites, the cumulative numbers of sperm binding tightly to the ZP will asymptote with time to the total number of sperm in the insemination medium capable of binding.

METHODS

Numbers of ZP-bound sperm were counted after groups of 10 oocytes were incubated with 2x10(4) motile sperm in 20 micro l droplets. The time-course of sperm binding was measured in three consecutive 2 h incubation periods using fresh oocytes for each period (n = 12). Using the kinetic theory of gases to model sperm-oocyte collision rates, the time-course results were extrapolated to give the total proportion of motile sperm capable of binding to the ZP. ZP binding of sperm after 4 h incubation was studied in 20 fertile and 20 normozoospermic subfertile men.

RESULTS

The percentage of motile sperm capable of binding was for fertile men: mean 14% (range 8-25) and for the subfertile: 4.3% (range 0.1-13, P < 0.001). Sperm morphology correlated with the proportion of ZP-bound sperm.

CONCLUSIONS

More than 75% of motile sperm from fertile men have no ability to bind to the ZP. This finding has important implications for improvement of semen analysis.

[Application of dot immunogold filtration assay for detecting serum antibodies in clonorchiasis patients]

OBJECTIVE

To establish a new, fast, sensitive and specific assay for detecting antibodies in clonorchiasis.

METHODS

Using Clonorchis sinensis adult worm antigen and SPA labelled with colloidal gold as color developing agent, a dot immunogold filtration assay (DIGFA) for detecting clonorchiasis antibodies was tested. Dot-ELISA was used as the parallel control.

RESULTS

The positive rate of DIGFA and dot-ELISA in testing the sera from 119 proved cases were 96.4% (115/119) and 92.4% (110/119), respectively, the difference between the two assays being in significant (P > 0.05). The negative rate of DIGFA in healthy people was 100% (40/40). The cross reaction rate in 20 cysticercosis cases and 25 schistosomiasis cases were 5% (1/20) and 4% (1/25), respectively. Both coincidence rates comparing DIGFA with dot-ELISA were 90.9% (50/55).

CONCLUSION

DIGFA is as sensitive and specific as the dot-ELISA, and has the advantages of simplicity and without specific equipment.

Automated semen analysis: 'zona pellucida preferred' sperm morphometry and straight-line velocity are related to pregnancy rate in subfertile couples

BACKGROUND

Standard semen analysis has low objectivity and reproducibility and is not closely related to fertility. We assess the prognostic value of automated measurements of sperm motility and morphology.

METHODS

During 1997-1999, 1191 infertile couples with no known absolute barrier to conception were assessed by conventional semen analysis, and automated measurements of average straight-line velocity (VSL) and the percentage of sperm with characteristics that conform to those of sperm which bind to the zona pellucida of the human oocyte (%Z). During follow-up to 2001, there were 336 natural pregnancies.

RESULTS

Only %Z, VSL and female age were independently significantly related to pregnancy rate by Cox regression analysis. Pregnancy rate was higher with above average %Z and VSL, indicating a continuous rather than a threshold relationship. The likelihood of pregnancy within 12 cycles can be evaluated for specific values of %Z, VSL and female age using the Cox regression model.

CONCLUSIONS

The automated semen measures of sperm morphometry (%Z) and velocity (VSL) are related to pregnancy rates in subfertile couples and should assist clinicians in counselling subfertile patients about their prognosis for a natural pregnancy. Objective automated methods should replace the traditional manual assessments of semen quality.

Improved sperm cryopreservation using cold cryoprotectant

It has generally been assumed that very rapid cooling above freezing point would be deleterious to human sperm because it would result in cold shock. Consequently, most routine cryopreservation protocols involve the use of warm (20–30°C) cryoprotectant and slow cooling above the freezing point in order to minimise the risk of cold shock. In order to test this assumption, we added an equal volume of cold (4°C) cryoprotectant in a single aliquot to warm (20, 30 or 37°C) semen to induce rapid cooling. The results of this procedure were compared with those obtained using warm cryoprotectant or with the routine cryopreservation protocol used in this laboratory. The use of cold cryoprotectant resulted in a significant (P = 0.016) improvement (mean 63%, range 42%–79%) in post-thaw motility recovery compared with a standard procedure(mean 47%, range 35%–67%) and a significant (P = 0.016) improvement in post-thaw sperm velocity. A cold glycerol/egg yolk/citrate (GEYC) mixture also gave significantly higher motility recovery than GEYC equilibrated to either room temperature (20°C) or body temperature (37°C). Sperm frozen using the cold cryoprotectant protocol were as efficient at binding to and penetrating the human zona pellucida as sperm frozen with a standard protocol.The modified cryopreservation procedure may lead to improved pregnancy rates in donor insemination and in vitro fertilisation. Further investigation is required to determine how the cold cryoprotectant improves the cryopreservation outcome.

Evaluation and assessment of semen for IVF/ICSI

Evaluation and assessment of semen is very important for both diagnosis of male infertility and selection of patients for treatment with IVF or ICSI. In standard IVF, sperm function is essential for normal fertilization: sperm must be able to bind to zona pellucida (ZP), undergo the acrosome reaction and penetrate the ZP and fuse with the oolemma before fertilization takes place. In contrast, most sperm functions are not required for fertilization in ICSI since sperm bypass the ZP and oolemma by injection of a single sperm directly into cytoplasm of oocyte. Therefore, the clinical decision on treatment of patients with either IVF or ICSI is mostly dependent on results of sperm tests. However, conventional semen analyses do not provide accurate information about sperm fertilizing ability since many patients with subtle sperm defects can not be detected. More advanced sperm function tests are required to detect sperm defects that may lead to failure of fertilization in standard IVF. In the last 15 years we performed extensive studies on relationship between sperm functions and fertilization rates by logistic regression analysis in large numbers of IVF patients including 370 patients with zero fertilization rate by IVF. We confirmed sperm morphology assessed strictly was strongly related to fertilisation rate with standard IVF. Thus sperm morphology assessment is very useful for selection of patients for ICSI. We also developed a number of new tests including sperm-ZP binding, sperm-ZP penetration and the ZP-induced AR and evaluated the clinical value of these tests. Sperm-ZP binding and sperm-ZP penetration tests are the most powerful indicators for sperm fertilizing ability in vitro. The ZP-induced AR is highly correlated with sperm-ZP penetration. We discovered a condition we call disordered ZP-induced AR which causes serve infertility in up to 25% men with otherwise idiopathic infertility In conclusion, the combination of semen analysis with advanced sperm function tests provide important diagnostic and prognostic information for male infertility and is crucial for selection of patients for treatment with IVF or ICSI.

Characterization of two isomeric beta-d-glucosiduronic acids derived from 1,2-diethyl-3-hydroxypyridin-4-one (CP94) in rat liver homogenate incubates

1,2-Diethyl-3-hydroxypyridin-4-one (CP94) is an orally active iron chelator with potential for use in photodynamictherapy. This investigation reports the formation and characterization of two isomeric glucuronides of CP94 in rat liver homogenate incubates. To assign the glucuronidation sites in the CP94 molecule, two O-methylated derivatives of CP94 have been synthesized. By comparing the spectral characteristics of the CP94 3-O- and 4-O-methyl derivatives with CP94 and the CP94 glucuronides formed during incubation, evidence was obtained which enabled the assignment of these two isomeric glucuronides to the 3-O-glucuronide and 4-O-glucuronide of CP94. It was found that the 3-O-glucuronide was the dominant CP94 metabolite under in-vitro conditions. In an attempt to understand the potential influence of structural variation on the glucuronidation of CP94 analogues, the 1-and 2-monoethyl derivatives of CP94 were investigated. The 2-monoethyl derivative of CP94 yielded only the 3-O-glucuronide in rat liver homogenate incubate, while no glucuronide was formed from the 1-monoethyl derivative. In addition, no glucuronide from the 3-O-methyl or 4-O-methyl derivatives of CP94 could be detected. The relevance of these findings to the development of new 3-hydroxypyridin-4-one iron chelators is discussed.

An anti-actin monoclonal antibody inhibits the zona pellucida-induced acrosome reaction and hyperactivated motility of human sperm

We report an inhibitory effect of an anti-actin monoclonal antibody (mAb) on the human zona pellucida (ZP)-induced acrosome reaction (AR). Motile sperm were incubated with native human ZP for 2 h in medium containing either the anti-actin mAb, an irrelevant control mAb or cytochalasins B or D (40 micromol/l). Sperm bound to the ZP were recovered and the AR was determined by fluorescein-labelled Pisum Sativum agglutinin. Anti-mouse immunoglobulin G (mIgG) Dynabeads, immunofluorescence and immunogold were used to detect the location of the anti-actin mAb in sperm. The anti-actin mAb significantly inhibited the ZP-induced AR (equivalent to cytochalasins), the ionophore A23187-induced AR and hyperactivation of sperm in medium. After incubation with anti-actin mAb, anti-mIgG beads bound to the head of >50% of sperm recovered after binding to the ZP and 10% of sperm remaining in the medium. The proportion of sperm that bound anti-mIgG beads after recovery from binding to the ZP in the presence of the anti-actin mAb was significantly correlated with the ZP-induced AR in the absence of the antibody. Immunofluorescence and immunogold demonstrated entry of the anti-actin mAb into sperm. This study suggests that the sperm plasma membrane becomes permeable to the anti-actin mAb during capacitation and initiation of the AR.

Inhibition of the mitogen activated protein kinase, p38 alpha, prevents proinflammatory cytokine induction by human adherent mononuclear leukocytes in response to lipid loading

Macrophage infiltration, inflammatory processes and oxidatively modified low density lipoprotein (LDL) are known contributing factors in the formation of the atherosclerotic plaque. To determine whether a direct link might exist between these factors, we examined the effect of oxidized LDL upon proinflammatory cytokine production in adherent human peripheral blood mononuclear leukocytes. Oxidized LDL, as well as a combination of cholesterol and 25-hydroxycholesterol, induced tumor necrosis factor-alpha (TNFalpha) and interleukin-1 beta (IL-1 beta) mRNA as measured by quantitative real time PCR, by a maximum of two- to fourfold following a 24-h incubation. Analysis of cell culture supernatants revealed a concomitant stimulation of TNFalpha and IL-1 beta secreted protein as determined by ELISA. Treatment of human peripheral blood mononuclear leukocytes with oxidized LDL or the combination of cholesterol and 25-hydroxycholesterol caused activation of p38 alpha as determined by the ability of immunoprecipitated p38 to phosphorylate an ATF-2 fusion protein, a surrogate substrate of p38 alpha. VK-19911 (Pyridine, 4-[4-(4-fluorophenyl)-1-(4-piperidinyl)-1H-imidazol-5-yl]-dihydrochloride), a specific inhibitor of p38 alpha, prevented the induction of TNFalpha and IL-1 beta by oxidized LDL in a dose-dependent manner. Activated p38 alpha is known to be involved in the stabilization of cyclooxygenase-2 mRNA in response to stimuli such as lipopolysaccharide; however, in the setting of oxidized LDL-induced p38 alpha activation, COX-2 mRNA levels were not affected. Taken together, the data imply a potential role for p38 alpha activation in lipid-associated inflammatory processes.

Frequency of disordered zona pellucida (ZP)-induced acrosome reaction in infertile men with normal semen analysis and normal spermatozoa-ZP binding

Results of zona pellucida (ZP)-induced acrosome reaction (AR) are reported for 186 normospermic men with unexplained infertility and compared with 34 normal fertile men and 54 patients with disordered ZP-induced AR (DZPIAR) diagnosed after failure of standard IVF. For each ZP-induced AR test, four oocytes that failed to fertilize in IVF were incubated for 2 h with 2x10(6)/ml motile spermatozoa. Spermatozoa tightly bound to the ZP were recovered by aspirating the oocytes with a pipette and the AR assessed using pisum sativum agglutinin labelled with fluorescein. The standard deviation of the difference was 5.2% for repeated tests for ZP-induced AR on different ejaculates from 54 men. The ranges for the ZP-induced AR were 3-98% for normospermic infertile men, 24-95% for fertile men and 0-16% for DZPIAR patients. In the normospermic group, there was a significant correlation between ZP-induced AR and sperm concentration (Spearman r = 0.238, P < 0.001). Using ZP-induced AR < or =16% as the threshold for diagnosis of DZPIAR, the frequency of this condition in normospermic infertile men would be 25%. Thus DZPIAR is common with normospermic idiopathic infertility and this condition should be diagnosed before assisted reproductive technology since it requires intracytoplasmic sperm injection.

Synthesis of 2-amido-3-hydroxypyridin-4(1H)-ones: novel iron chelators with enhanced pFe3+ values

The synthesis of a range of 2-amido-3-hydroxypyridin-4-ones as bidentate iron(III) chelators with potential for oral administration is described. The pKa values of the ligands together with the stability constants of their iron(III) complexes have been determined. Results indicate that the introduction of an amido substituent at the 2-position leads to an appreciable enhancement of the pFe3+ values. The ability of these novel 3-hydroxypyridin-4-ones to facilitate the iron excretion in bile was investigated using a 59Fe-ferritin loaded rat model. The optimal effect was observed with the N-methyl amido derivative 15b, which has an associated pFe3+ value of 21.7, more than two orders of magnitude higher than that of deferiprone (1,2-dimethyl-3-hydroxypyridin-4-one) 1a (pFe3+ = 19.4). Dose response studies suggest that chelators with high pFe3+ values scavenge iron more effectively at lower doses when compared with simple dialkyl substituted hydroxypyridinones.

[The treatment of hypopharyngoesophageal stenosis]

OBJECTIVE

To improve the curative effects of hypopharyngoesophageal stenosis.

METHOD

35 patients treated for hypopharyngoesophageal stenosis were retrospectively reviewed. The curative methods were selected on the stage of stenosis, including drug, dilatation, reconstruction of hypopharynx and oesophagus.

RESULT

33 patients resumed a normal oral diet, no stenosis of anastomosis occurred.

CONCLUSION

For the early mild lesions, using of steroids, antibacterial and dilatation is considered to be the procedure of choice, for those severe lesions, reconstruction of hypopharynx and oesophagus with selected appropriate materials can obtain good results.

The human acrosome reaction

We developed tests of sperm-oocyte interaction: sperm-zona binding, zona-induced acrosome reaction, spermzona penetration and sperm-oolemma binding, using oocytes which failed to fertilise in clinical in vitro fertilization (IVF). Although oocyte defects contribute to failure of sperm oocyte interaction, rarely are all oocytes from one woman affected. Low or zero fertilization in standard IVF was usually caused by sperm abnormalities. Poor sperm-zona pellucida binding was frequently associated with failure of standard IVF and obvious defects of sperm motility or morphology. The size and shape of the acrosome is particularly important for sperm binding to the oocyte. The proportion of acrosome intact sperm in the insemination medium was related to the IVF rate. Inducing the acrosome reaction with a calcium ionophore reduced sperm-zona binding. Blocking acrosome dispersal with an acrosin inhibitor prevented spermzona penetration. Sperm-zona penetration was even more highly related to IVF rates than was sperm-zona binding. Some patients had low or zero fertilization rates with standard IVF but normal sperm by conventional tests and normal sperm-zona binding. Few of their sperm underwent the acrosome reaction on the surface of the zona and none penetrated the zona. In contrast, fertilization and pregnancy rates were high with intracytoplasmic sperm injection. We call this condition defective zona pellucida induced acrosome reaction. Discovery of the nature of the abnormalities in the signal transduction and effector pathways of the human zona pellucida induced acrosome reaction should result in simpler tests and treatments for the patients and also provide new leads for contraceptive development.

Biliary and urinary metabolic profiles of 1,2-diethyl-3-hydroxypyridin-4-one (CP94) in the rat

This study compares the biliary and urinary metabolic profiles of 1,2-diethyl-3-hydroxypyridin-4-one (CP94), an orally active iron chelator, in the normal rat. Surprisingly, CP94 was found to form two phase II metabolites, the 3-O- and 4-O-glucuronides. These glucuronides accounted for 38 and 28% of the administered CP94 dose, in bile and urine, respectively. Unchanged CP94 accounted for 5% of the CP94 dose in both bile and urine. The 2-(1'-hydroxy) metabolite of CP94 was found to be the dominant metabolite in urine. In addition, an unstable metabolite was detected in the bile although its structure remains unknown at the present stage. The excretion of iron in bile, after administration of CP94, was found to parallel the biliary elimination of CP94 together with its hydroxylated derivatives, indicating the importance of metabolites in iron excretion.

Comparison of metabolic rates of some 9-aralkyladenines obtained using hamster hepatic microsomes

Previous investigations have revealed that N1-oxidation is a major metabolic pathway in vitro for some 9-aralkyladenines (AAs) such as 9-benzyladenine (BA). However, dealkylation and other metabolic pathways are also involved. In addition, various substituents on the benzyl moiety of BA seem to have a marked effect on the metabolic rate. In order to establish the potential structure-metabolism relationship of this class of compounds, the enzyme kinetics of the substrates, which possess 2'-nitro (2NBA), 3'-nitro (3NBA), 4'nitro (4NBA), 2'-chloro (2CBA), 2'-methyl (2MBA), or 2-methoxy (2MOBA) substitution of the benzyl moiety of BA, were compared using hamster hepatic microsomes. The results show that the formation rates of the N1-oxides are in the order 2NBA > 2CBA > BA > 3NBA and 4NBA > 2MBA and 2MOBA; the formation rates of the total metabolites except N1-oxides are in the order 2MOBA and 2MBA > 2CBA > BA > 4NBA > 3NBA > 2NBA; however, the total biotransformation rates of the substrates are in the order 2MBA and 2MOBA > 2CBA > BA and 2NBA > 4NBA > 3NBA. The results strongly imply that the electronic, steric and other physicochemical properties are potential controlling factors for AA metabolism.

Hydrolytic and metabolic characteristics of the esters of 1-(3'-hydroxypropyl)-2-methyl-3-hydroxypyridin-4-one (CP41), potentially useful iron chelators

1-(3'-Hydroxypropyl)-2-methyl-3-hydroxypyridin-4-one (CP41) has been extensively investigated as an orally effective iron chelator. In order to improve the pharmacokinetic and metabolic properties of CP41, eleven aromatic esters have been synthesised and tested as potential prodrugs. In the present study, the hydrolytic rates of these CP41 esters in phosphate buffer (pH2.0 and pH 7.4), rat blood and rat liver homogenate have been determined and found to cover a wide range. Generally, they possessed relatively slow hydrolytic rates in phosphate buffer (0-50 nmol/ml/hr at pH 2.0 and 0-140 nmol/ml/hr at pH 7.4). The hydrolytic rates in rat blood fell in the range of 9-5766 nmol/ml blood/hr and in rat liver homogenate 1-800 micromol/g liver tissue/hr. All esters possess a higher lipophilicity than that of the parent compound CP41. Although no apparent relationship was observed between the lipophilicities and hydrolytic rates, the esters with relatively higher hydrolytic rates in liver homogenate tend to possess higher iron scavenging efficacies. Further investigation of the metabolism of selected CP41 esters indicates that metabolism is a key factor influencing the efficacy of CP41 esters, as some esters can be metabolically inactivated in the liver in preference to undergoing ester hydrolysis. Ester design, combined with a knowledge of the prodrug metabolism, is a useful strategy for the production of 3-hydroxypyridin-4-ones with enhanced iron scavenging efficacy.

Design, synthesis, and biological evaluation of aromatic ester prodrugs of 1-(3'-hydroxypropyl)-2-methyl-3-hydroxypyridin-4-one (CP41) as orally active iron chelators

In order to improve chelation efficacy and to minimise toxicity, eleven aromatic ester prodrugs of 1-(3'-hydroxypropyl)-2-methyl-3-hydroxypyridin-4-one (CP41) have been synthesised. The distribution coefficients of these ester prodrugs between 1-octanol and MOPS buffer pH 7.4 were measured together with their rates of hydrolysis at pH 2 and pH 7.4, in rat blood and liver homogenate. The biliary metabolic profiles of selected ester prodrugs were investigated in rats. The in vivo iron mobilisation efficacy of these ester prodrugs has been compared with that of the parent drug using a 59Fe-ferritin loaded rat model. The hydrolytic rates of these esters vary appreciably, esters with heteroaromatic acid moieties being less stable than the corresponding benzoyl analogues. Many prodrugs were found to enhance the ability of the parent hydroxypyridinone to facilitate 59Fe excretion, the optimal effect being observed with the 4-methylbenzoyl ester derivative 8d. However, not all prodrugs provide an increased efficacy, indicating that lipophilicity is not the only factor which influences drug efficacy. Furthermore no clear correlation between lipophilicity, susceptibility towards hydrolysis and efficacy was detected.

Effects of cAMP-dependent protein kinase and ATP on N1-oxidation of 9-benzyladenine by animal hepatic microsomes

N1-Oxidation is a major metabolic pathway for 9-benzyladenine (BA) catalyzed by the cytochrome P450 system in animal hepatic microsomes. After normal hamster hepatic microsomes or phenobarbital induced rabbit hepatic microsomes were preincubated in the presence of cyclic AMP-dependent protein kinase catalytic subunit (PKA), MgCl2 and ATP, BA-N1-oxidation was significantly decreased. However, further investigation indicated that the decrease of BA-N1-oxidation seemed to be a combination of the effects of PKA and ATP, as ATP alone showed a biphasic regulatory effect on BA-N1-oxidation when microsomes were preincubated in the presence of various concentrations of ATP. In the lower ATP concentration range (0.5-2.5mM), BA-N1-oxidation increased along with the increase of ATP concentration; whereas BA-N1-oxidation decreased when the ATP concentration was higher (>5mM). The biphasic regulatory effects of ATP on BA-N1-oxidation seem dependent on the incubation process, as preincubation markedly strengthened the effects. When microsomes were incubated at 37 degrees C for different time lengths in the absence or presence of ATP (2.5 or 20mM), the activity of BA-N1-oxidase decreased at similar rates in all groups, but the activity levels of BA-N1-oxidase were different among the groups. The cytochrome P450 content was not changed parallel to the variation of BA-N1-oxidation when microsomes were incubated in the presence of ATP, indicating that the effects of ATP on BA-N1-oxidation were not mediated by affecting CYP stability. In addition, the activity of NADPH-cytochrome P450 reductase was not markedly affected by ATP without incubation. The result implied that ATP did not inhibit the reductase directly. After microsomes were incubated in the presence of low ATP concentration (2.5mM), the reductase was slightly inhibited, whilst high ATP concentration (20mM) showed marked inhibition (83% of control). This may partially contribute to the down-regulatory effect of ATP on BA-N1-oxidation. Furthermore, it was found that the presence of magnesium ions during preincubation weakened the up-regulatory effect of ATP (2.5mM) on BA-N1-oxidation, but showed no effect on the down-regulatory effect of ATP (20mM). Since these observed phenomena are not readily explained, a possible mechanism, i.e. phosphorylation and dephosphorylation of cytochrome P450, is suggested.

Defective sperm-zona pellucida interaction: a major cause of failure of fertilization in clinical in-vitro fertilization

Sperm-zona pellucida binding and penetration were assessed on the oocytes that failed to fertilize from couples with >/=3 oocytes treated by standard in-vitro fertilization (IVF). There were four groups: fertilization rate 0% (n = 369), 1-25% (n = 194), 26-50% (n = 81) and 51-95% (n = 100). Of the couples with zero fertilization rate 70% had </=5 spermatozoa bound per zona pellucida and 42% had no spermatozoa penetrating the zona pellucida of any oocyte. In contrast, in the 51-95% fertilization rate group, only 17% had </= 5 spermatozoa bound per zona pellucida and 6% had no spermatozoa penetrating the zona pellucida. There was a significantly higher frequency of poor sperm morphology (</= 5% normal) in couples with zero fertilization rate (36%) than in the fertilization rate group 51-95% (7%). Incubation of oocytes from 68 couples with zero fertilization rate and low sperm-zonae pellucidae binding with fertile donor spermatozoa resulted in normal sperm-zona pellucida binding and most zonae pellucidae being penetrated. In conclusion, defective sperm-zona pellucida interaction was the major cause for low fertilization rates in standard IVF. This was usually because of defects of the spermatozoa rather than defects of the oocytes. Sperm defects likely to cause failure of fertilization should be diagnosed before commencing IVF and the patients directed to intracytoplasmic sperm injection.

Liquid extraction and ion-pair HPLC for determination of hydrophilic 3-hydroxypyridin-4-one iron chelators

Hydrophilic 3-hydroxypyridin-4-ones (HPOs), such as 1-(2'-carboxyethyl)-2-methyl-3-hydroxypyridin-4-one (CP38), 1-(3'-hydroxypropyl)-2-methyl-3-hydroxypyridin-4-one (CP41) and 1-(2'-hydroxyethyl)-2-ethyl-3-hydroxypyridin-4-one (CP102), are orally active iron chelators and ester prodrugs of these molecules are currently under investigation. A liquid extraction method using acetonitrile and 2-propanol (80:20 v/v) under acidic and NaCl-saturated conditions has been developed in order to efficiently extract these HPOs from various matrices. The extracted HPOs were determined using a reversed phase polymer HPLC column (PLRP-S 100 A) and the gradient ion-pair mobile phase containing tetrabutylammonium chloride (5 mM) and EDTA (0.5 mM). The extraction recovery of these chelators in phosphate buffer, rat blood and liver homogenate varied from 85 to 94%. The coefficients of variation (C.V.) for within-day determination were in the range of 1.4-3.3% at 1 mM and 2.0-4.7% at 0.1 mM. High accuracy of determination was also achieved.