N-Carbamoyl-α-Amino Acids Rather than Free α-Amino Acids Formation in the Primitive Hydrosphere: A Novel Proposal for the Emergence of Prebiotic Peptides

Our previous kinetic and thermodynamic studies upon the reactional system HCHO/HCN/ NH₃ in aqueous solutions are completed. In the assumed prebiotic conditions of the primitive earth ([HCHO] and [HCN] near 1 g L^–1, T = 25 °C, pH = 8, [NH₃] very low), this system leads to 99.9% of -hydroxyacetonitrile and 0.1% of -aminoacetonitrile (precursor of the -amino acid). The classical base-catalyzed hydration of nitriles, slow and not selective, can not modify significantly this proportion. On the contrary, we found two specific and efficient reactions of -aminonitriles which shift the initial equilibrium in favor of the -aminonitrile pathway. The first reaction catalyzed by formaldehyde generates -aminoamides, precursors of -aminoacids. The second reaction catalyzed by carbon dioxide affords hydantoins, precursors of N-carbamoyl--aminoacids. In the primitive hydrosphere, where the concentration in carbon dioxide was estimated to be higher than that of formaldehyde, the formation of hydantoins was consequently more efficient. The rates of hydrolysis of the -aminoacetamide and of the hydantoin at pH 8 being very similar, the synthesis of the N-carbamoyl--amino acid seems then to be the fatal issue of the HCHO/HCN/NH₃ system that nature used to perform its evolution. These N-protected -amino acids offer new perspectives in prebiotic chemistry, in particular for the emergence of peptides on the prebiotic earth.     

Place des troubles de la spermatogenèse dans l’hypofertilité masculine

According to Thonneauet al., (1991), 14% of couples are subfertile. In at least 59% of the cases, a male factor was involved. This indicates that 8% (14% × 59%) of men are hypofertile. Since several causes can induce male infertility and because of the heterogeneous criteria and classifications used in the literature, the percentage of each etiologic factor has not been very precisely established. In a population of 2072 consecutive patients we identified an alteration of spermatogenesis in 52% of the cases. This indicates that about 4% of men might have a spermatogenic problem. The spermatogenic insufficiency was isolated in 43% of the cases (i.e. 23% of the total population) or associated with post-testicular causes of male infertility (infectious/inflammatory; autoimmune; obstructive) in 57% of the cases (i.e. 30% of the total population studied). An etiologic factor is clinically identified for 64% of the patients presenting with a spermatogenic insufficiency. The most relevant risk factors linked to spermatogenic alteration were history of mumps orchitis (OR [IC95%]=14,6 [3,4–62,3]), history of radiotherapy-chemotherapy (OR=14,7 [3,4–63,2]). These situations were found with a low frequency (1,4% and 1,3% of the cases respectively) but provoked a spermatogenic alteration in a large majority of cases (92,9% and 92,3% respectively). On the other hand, varicoceles (OR=3,7 [2,9–4,8]) and troubles in testicular descend (OR=2,9 [2,3–3,7]), were more frequent (20,6% and 20,1% of the cases respectively), but less frequently associated with spermatogenic insufficiency (in 73,7 and 69,6% of the cases).     

Inséminations intra-utérines avec sperme du conjoint dans les indications masculines: Influence de l'âge de l'homme

This paper presents the analysis of 492 cycles of Intra Uterine Artificial Insemination Homologous (IU AIH) in 152 couples with male infertility; 36 pregnancies were achevied. We used the life table method and the Cox model to analyse the results and to determine prognosis factors. Univariate analysis did not disclose any prognostic factor. Multivariate analysis revealed 3 negative prognostic factors: husband's age ≥ 35 years (p: 0.04), dysovulation, secondary infertility in man. On the contrary, secondary infertility in woman and oligozoospermia were found to be of good prognosis. Surprisingly, the wife's age ≥ 35 years did not appear to be of poor prognosis in the multivariate analysis. The husband's age has been shown to play a role in fertility by others authors using the Cox method.