Impact of Hydroxyurea and Vaso-Occlusive Crisis on Ovarian Follicle Density in Girls and Young Females with Sickle Cell Disease

Introduction: Over the last four decades, multiple advancements have led to a growing number of sickle cell disease patients. One of the major advances in care for sickle cell disease (SCD) is the introduction of hydroxyurea (HU) in the middle of the 1980s to prevent vaso-occlusive crisis. Despite the proven benefit of HU, there are concerns about side effects. In male mice application of HU impacts spermatogenesis resulting in a hypogonadism. In young boys, it is been shown that HU didn't affect the spermatogonial pool. In adult men a reduction of sperm count was observed. Little is known about gonadotoxicity in women with SCD who are taking HU. The purpose of the study was to assess the impact of HU exposure and vaso-occlusive crisis on ovarian follicle density in young females with SCD who had an ovarian tissue cryopreservation (OTC) before hematological stem cell transplantation (HSCT), as fertility preservation measure.

Material and Methods: Included were female sickle cells patients who underwent an OTC before HSCT at our institution between April 1998 and November 2020. After written informed consent from patient or their parents at time-point of OTC, a fragment of ovarian tissue was evaluated histologically. Each histological slide was revised from two independent investigators with a digital system (Hewell, Paris, France). All follicles were counted and classified according to their growing stage. Surface of each fragment was measured. The follicular density was calculated as number of primordial follicles divided by the surface of the sample and expressed in mm². For the comparison of the follicle density values two non-paired Wilcoxon Rank-sum test were performed and for the concordance test between the two investigators, the Cronbach's alpha was used. Medical data concerning presence of vaso-occlusive crisis (VOC), applied transfusion units, applied HU dosage, total exposure of HU in months and pubertal development were collected from each patient from medical records. This study was approved by ethical committee of Avicenne Hospital, France (CLEA-2021-195).

Results: Population of this cross-sectional study consisted of 88 sickle cell females with HbSS. Their median age at OTC was 9.92 years (IQR 6.18-12.85). Fifty-seven (65%) were prepubertal at time point of OTC. Forty patients (45%) were under HU treatment at the time of OTC with a median daily dosage of 23mg/kg (IQR 20-25mg/kg) and a median exposure time of 43.5 months (IQR 21-54months). VOC were reported in 78% (69/88) of the cohort, 49% (34/69) were under HU treatment. Blood transfusion were administered in 94% (83/88). The median applied units were 22 (IQR 11.50-47.50). Concordance test showed an accordance of 97% between the two investigators for histological evaluation. Follicle density was similar in the HU group compared to those without HU exposure (median 5.97 follicle/mm² (IQR 1.19-13.70 follicles/mm2) versus 5.59 follicle/mm2 (1.65-12.79/mm2), p=0.614. Follicle density was significantly higher in patients without VOC (median 12.307 (IQR 7.440-21.886; p = 0.015)) compared to those with VOC (median 5.019 (IQR 1.500-12.016)). There was no correlation between applied transfusion units and follicle density (p = 0.45).

Conclusion: Hydroxyurea exposure does not appear to reduce cortical follicle density in females with SCD. For the first time our study could show an influence of VOC on ovarian follicle density possibly related to reduced blood flow.

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