Anick De Vos

Metabolic fate of glucose in purified islet cells. Glucose-regulated anaplerosis in beta cells.

Previous studies in rat islets have suggested that anaplerosis plays an important role in the regulation of pancreatic β cell function and growth. However, the relative contribution of islet β cells versus non-β cells to glucose-regulated anaplerosis is not known. Furthermore, the fate of glucose carbon entering the Krebs cycle of islet cells remains to be determined. The present study has examined the anaplerosis of glucose carbon in purified rat β cells using specific 14C-labeled glucose tracers. Between 5 and 20 mm glucose, the oxidative production of CO2 from [3,4-14C]glucose represented close to 100% of the total glucose utilization by the cells. Anaplerosis, quantified as the difference between14CO2 production from [3,4-14C]glucose and [6-14C]glucose, was strongly influenced by glucose, particularly between 5 and 10 mm. The dose dependence of glucose-induced insulin secretion correlated with the accumulation of citrate and malate in β(INS-1) cells. All glucose carbon that was not oxidized to CO2 was recovered from the cells after extraction in trichloroacetic acid. This indirectly indicates that lactate output is minimal in β cells. From the effect of cycloheximide upon the incorporation of 14C-glucose into the acid-precipitable fraction, it could be calculated that 25% of glucose carbon entering the Krebs cycle via anaplerosis is channeled into protein synthesis. In contrast, non-β cells (approximately 80% glucagon-producing α cells) exhibited rates of glucose oxidation that were 1 3 to 1 6 those of the total glucose utilization and no detectable anaplerosis from glucose carbon. This difference between the two cell types was associated with a 7-fold higher expression of the anaplerotic enzyme pyruvate carboxylase in β cells, as well as a 4-fold lower ratio of lactate dehydrogenase to FAD-linked glycerol phosphate dehydrogenase in β cells versus α cells. Finally, glucose caused a dose-dependent suppression of the activity of the pentose phosphate pathway in β cells. In conclusion, rat β cells metabolize glucose essentially via aerobic glycolysis, whereas glycolysis in α cells is largely anaerobic. The results support the view that anaplerosis is an essential pathway implicated in β cell activation by glucose.

Influence of individual sperm morphology on fertilization, embryo morphology, and pregnancy outcome of intracytoplasmic sperm injection

OBJECTIVE To evaluate the influence of morphology of individual spermatozoa on fertilization and pregnancy outcome. DESIGN Retrospective analysis. SETTING An IVF center in an institutional research environment. PATIENT(S) Fertilization and embryo quality according to individual sperm morphology were analyzed in 662 consecutive ICSI cycles. Pregnancy outcome was evaluated for these cycles and an additional 1005 consecutive ICSI cycles. INTERVENTION(S) ICSI was performed using sperm cells of ejaculated, epididymal, or testicular origin. Observation through an inverted microscope was used to prospectively classify injected sperm cells as normal or morphologically abnormal. MAIN OUTCOME MEASURE(S) Oocyte fertilization, embryo morphology, and pregnancy outcome of unmixed embryo transfers. RESULT(S) Injection of morphologically abnormal spermatozoa (irrespective of origin) resulted in a lower fertilization rate (60.7%) than did injection of morphologically normal spermatozoa (71.7%). Embryo cleavage quality did not differ between groups. Higher pregnancy and implantation rates were obtained in patients with normal sperm morphology (36.7% and 18.7%, respectively) than in those with abnormal sperm morphology (20.2% and 9.6%). CONCLUSION(S) Individual sperm morphology assessed at the moment of ICSI correlated well with fertilization outcome but did not affect embryo development. The implantation rate was lower when only embryos resulting from injection of an abnormal spermatozoon were available.

Aspects of biopsy procedures prior to preimplantation genetic diagnosis

Today, preimplantation genetic diagnosis (PGD) is offered in over 40 centres worldwide for an expanded range of genetic defects causing disease. This very early form of prenatal diagnosis involves the detection of affected embryos by fluorescent in situ hybridization (FISH) (sex determination or chromosomal defects) or by polymerase chain reaction (PCR) (monogenic diseases) prior to implantation. Genetic analysis of the embryos involves the removal of some cellular mass from the embryos (one or two blastomeres at cleavage‐stage or some extra‐embryonic trophectoderm cells at the blastocyst stage) by means of an embryo biopsy procedure. Genetic analysis can also be performed preconceptionally by removal of the first polar body. However, additional information is then often gained by removal of the second polar body and/or a blastomere from the embryo. Removal of polar bodies or cellular material from embryos requires an opening in the zona pellucida, which can be created in a mechanical way (partial zona dissection) or chemical way (acidic Tyrodes solution). However, the more recent introduction of laser technology has facilitated this step enormously. Different biopsy procedures at different preimplantation stages are reviewed here, including their pros and cons and their clinical applications. The following aspects will also be discussed: safety of zona drilling by laser, use of Ca2+/Mg2+‐free medium for decompaction, and removal of one or two cells from cleavage‐stage embryos. Copyright

Embryo implantation after biopsy of one or two cells from cleavage-stage embryos with a view to preimplantation genetic diagnosis

Preimplantation genetic diagnosis (PGD) can be offered as an alternative to prenatal diagnosis (PND) to couples at risk of having a child with a genetic disease. The affected embryos are detected before implantation by fluorescent in situ hybridisation (FISH) for sexing (X‐linked diseases) and chromosomal disorders (numerical and structural) or by polymerase chain reaction (PCR) for monogenic disorders (including some X‐linked diseases). The accuracy and reliability of the diagnosis is increased by analysing two blastomeres of the embryo. However, the removal of two blastomeres might have an effect on the implantation capacity of the embryo. We have evaluated the implantation of embryos after the removal of one, two or three cells in 188 PGD cycles where a transfer was done. The patients were divided into five groups: a first group which received only embryos from which one cell had been removed, a second group which received only embryos from which two cells had been removed, a third group which received a mixture of embryos from which one and two cells had been taken, a fourth group where two and three cells had been removed, and a fifth group where three cells had been removed. The overall ongoing pregnancy rate per transfer was 26.1%, the overall implantation rate per transfer was 15.2% and the overall birth rate was 14.2%. Although pregnancy rates between the groups cannot be compared because the second group (two cells removed) contains more rapidly developing and therefore ‘better quality’ embryos, an ongoing pregnancy rate of 29.1% and an implantation rate of 18.6% per transferred embryo in this group is acceptable, and we therefore advise analysing two cells from a ≥7‐cell stage embryo in order to render the diagnosis more accurate and reliable. Copyright

Prospectively randomized controlled trial of PGS in IVF/ICSI patients with poor implantation.

This randomized, controlled trial verifies whether patients with recurrent failed implantation benefit from preimplantation genetic diagnosis for aneuploidy, as compared with conventional assisted reproduction treatment procedures. Two hundred patients with recurrent failed implantation were randomized into two groups. A total of 139 patients underwent ovarian stimulation, and preimplantation genetic screening was performed in 72 patients. Analysis of chromosomes X, Y, 13, 16, 18, 21 and 22 was carried out using fluorescence in-situ hybridization in blastomeres of day-3 cleavage-stage embryos in the study group. The primary endpoint was implantation rate. Secondary endpoints were embryonic morphology and chromosomal status, number of transferred embryos and clinical pregnancy rate. With regard to the implantation rate, there was no significant difference between the study group (21.4%) and the control group (25.3%). The number of embryos transferred was significantly lower in the study group, namely 1.4 (SD 1.0) versus 2.1 (SD 1.0) in the control group (P < 0.05). The clinical pregnancy rate was not significantly different between the groups (25.0% in the study group versus 40.3% in the control group). It can be concluded that preimplantation genetic screening does not increase the implantation rates after IVF-intracytoplasmic sperm injection in women with repeated implantation failure.

PGD in the lab for triplet repeat diseases — myotonic dystrophy, Huntington's disease and Fragile-X syndrome

Myotonic dystrophy (DM), Huntingtons disease (HD) and Fragile X syndrome (FRAXA) are three monogenic disease which are caused by so-called dynamic mutations. These mutations are caused by triplet repeats inside or in the vicinity of the gene which have the tendency to expand beyond the normal range thus disrupting the normal functioning of the gene. We describe here our experiences from 1995 to May 2000 with PGD for these three triplet repeat diseases.

Preimplantation genetic diagnosis for Huntington's disease with exclusion testing

Huntingtons disease is an autosomal dominant, late-onset disorder, for which the gene and the causative mutation have been known since 1993. Some at-risk patients choose for presymptomatic testing and can make reproductive choices accordingly. Others however, prefer not to know their carrier status, but may still wish to prevent the birth of a carrier child. For these patients, exclusion testing after prenatal sampling has been an option for many years. A disadvantage of this test is that unaffected pregnancies may be terminated if the parent at risk (50%) has not inherited the grandparental Huntington gene, leading to serious moral and ethical objections. As an alternative, preimplantation genetic diagnosis (PGD) on embryos obtained in vitro may be proposed, after which only embryos free of risk are replaced. Embryos can then be selected, either by the amplification of the CAG repeat in the embryos without communicating results to the patients (ie non-disclosure testing), which brings its own practical and moral problems, or exclusion testing. We describe here the first PGD cycles for exclusion testing for Huntingtons disease in five couples. Three couples have had at least one PGD cycle so far. One pregnancy ensued and a healthy female baby was delivered.

Preimplantation genetic diagnosis for spinal and bulbar muscular atrophy (SBMA)

Abstract. X-linked spinal and bulbar muscular atrophy is characterized by adult onset motor neuron disease and results from a defect in the androgen receptor. The disease is caused by a dynamic mutation in the first exon of the androgen receptor gene, involving a CAG trinucleotide repeat. We have developed a single-cell polymerase chain reaction assay for the androgen receptor gene and describe the application of this assay for preimlantation genetic diagnosis (PGD) in a couple at risk, where the female partner is a carrier of 47 repeats. Diagnosis was based on the detection of both normal and expanded alleles. Allele dropout of the expanded allele was observed in only 1 of 25 lymphoblasts of the carrier and of a non-expanded allele in 1 of 20 research blastomeres tested before the actual PGD. One contraction of four repeats was also found in the carriers lymphoblasts. Neither expansions nor contractions were observed in the blastomeres biopsied from 11 embryos. Two embryos were unaffected, eight were female carriers and one was an affected male embryo.

Two pregnancies after preimplantation genetic diagnosis for osteogenesis imperfecta type I and type IV

Abstract. Osteogenesis imperfecta (OI) is an autosomal dominant genetic disorder characterized by the presence of brittle bones and decreased bone mass (osteopenia), as a result of mutations in the genes that encode the chains of type I collagen, the major protein of bone. The clinical features of the disease range from death in the perinatal period to normal life span with minimal increase in fractures. The present report describes two polymerase chain reaction (PCR)-based assays allowing preimplantation genetic diagnosis (PGD) on the one hand for OI type I, the mildest form, and on the other hand for OI type IV, which is intermediate in severity between OI type I and OI type III. In the couple referred for PGD for OI type I, the female partner carried a 1-bp deletion in exon 43 of the COL1A1 gene, resulting in a premature stop codon in exon 46. The synthesis of too little type I procollagen results from such a non-functional or COL1A1 null allele. In the other couple, referred for PGD for OI type IV, the male partner carried a G to A substitution in exon 19 of the COL1A2 gene, which results in an abnormal gene product due to an αGly247 (GGT) to Ser (AGT) substitution (G247S). Both mutations result in the loss of a specific restriction enzyme recognition site and can therefore be detected by PCR amplification followed by restriction fragment analysis. PCR amplification of genomic DNA of the parents-to-be with one of the two primers fluorescently labelled, followed by automated laser fluorescence (ALF) gel electrophoresis of the amplified and restricted fragments, allowed a distinction between the healthy and affected genotypes. PCR on single Epstein-Barr-virus (EBV)-transformed lymphoblasts resulted in acceptable amplification efficiencies (87% and 85% for OI type I and OI type IV respectively) and the allele drop-out (ADO) rate was assessed at 11.5% and 11.1% for OI type I and OI type IV respectively. With research blastomeres, 100% amplification rates were obtained and no contamination was observed in the blank controls, which validated the tests for clinical application. Embryos obtained after intracytoplasmic sperm injection (ICSI) were evaluated for the presence of the normal genotype of the non-affected parent. For OI type I, two frozen-thawed ICSI-PGD cycles and two fresh ICSI-PGD cycles were carried out for the same couple. The transfer of two unaffected embryos in the last cycle resulted in a twin pregnancy. A twin pregnancy was also achieved in one clinical ICSI-PGD cycle for OI type IV.

Comparison of transfers to Fallopian tubes or uterus after ICSI

The aim of this study was to compare the implantation rate of tubal-replaced microinjected oocytes (MIFT) versus conventional day 2 intrauterine embryo transfer in patients undergoing intracytoplasmic sperm injection (ICSI). Sixty-three patients in need of ICSI, between 18 and 37 years of age with normal menstrual cycles and fewer than four previous ICSI attempts, were randomized between April 1999 and December 2001. In the MIFT group, up to three micro-injected oocytes were transferred laparoscopically 4 h after microinjection. In the ICSI-embryo transfer group, up to three cleaving embryos were replaced into the uterine cavity 48 h after insemination. Fifty-nine patients reached the stage of oocyte retrieval; 31 patients had a day 2 embryo transfer and 28 patients had MIFT. The ongoing clinical pregnancy and implantation rate (i.e. the total number of gestational sacs with fetal heartbeat divided by the total number of transferred embryos or micro-injected oocytes) was 35 and 24% in the ICSI-embryo transfer group and 29 and 11% in the MIFT group respectively. In conclusion, this study shows a significant decrease in implantation rate in the MIFT group (P < 0.05). In this group of patients there seems to be no advantage to tubal replacement of micro-injected oocytes.