Sperma Saklanmasında Düşük Yoğunluklu Lipoproteinlerin Rolü

Öz

The discovery that egg yolk has a beneficial effect on fertility in semen extenders led to its widespread use in semen extenders. Egg yolk is commonly found in semen extenders to preserve mammalian spermatozoa against cold shock during freeze-thaw process. Protective action of yolk is largely presumed to be due to low density lipoproteins (LDL). In recent years, there have been increasing demands to replace whole yolk in semen extenders because of presence of substances in yolk that inhibit respiration of spermatozoa or diminish their motility. Consequently, it could be of great benefit to remove these detrimental substances in yolk rather than complete egg yolk. Recent studies have confirmed that LDL extracted from egg yolk is successful for cryopreservation of semen from various species. Density gradient ultracentrifugation has been generally used for purification of egg yolk LDL. LDL are composed of 84-89% lipids and 11-17% proteins. Lipids of LDL are composed of approximately 69% triglycerides, 26% phospholipids and 5% cholesterol. Phospholipids play an essential role in the stability of LDL structure because association forces are essentially hydrophobic. LDL presents a density of 0.982 g/ml. They are spherical molecules of 1760 nm diameters. The interactions of lipid and protein are disrupted and under freezing, but interactions between proteins are increased and adhere to cell membranes, thus preserving spermatozoa membranes. In conclusion, researches are still carried out needed to evaluate and understand the respective roles of lipids and apoproteins from LDL and to isolate the antagonistic agent contained in egg yolk. ●●●

Anahtar Kelimeler

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Role of Low Density Lipoproteins in Semen Preservation

Öz

Sperma Saklanmasında Düşük Yoğunluklu Lipoproteinlerin Rolü Fertilite üzerine olumlu etkisinin keşfinden sonra yumurta sarısı, sperma sulandırıcılarında yaygın olarak kullanılmaktadır. Yumurta sarısının kullanılmasındaki temel amaç; dondurma çözdürme sonrasındaki soğuk şokuna karşı spermatozoanın korunmasıdır. Bu koruyucu etkisini, içerdiği düşük yoğunluklu lipoproteinler (LDL) ile gerçekleştirdiği düşünülmektedir. Son yıllarda yumurta sarısının tamamının kullanılması yerine, spermatozoon motilitesini olumsuz etkileyen içeriğinin uzaklaştırılarak, faydalı kısımlarının sulandırıcıya ilave edilmesi tercih edilmeye başlanmıştır. Çeşitli çalışmalarda yumurta sarısından elde edilen düşük yoğunluklu lipoproteinlerin farklı türlere ait spermaların dondurularak saklanmasında başarıyla kullanıldığı bildirilmektedir. Yumurta sarısından LDL elde etmek için genellikle ultrafaz santrifüj ile yoğunluk farkına göre ayırma yöntemi kullanılır. LDL, %84-89 lipid, %11-17 oranında proteinlerden oluşmaktadır. Lipid içeriğin yaklaşık olarak %69’unu trigliseridler, %26’sını fosfolipidler ve %5’ini de kolesterol oluşturmaktadır. Fosfolipidler özellikle hidrofobik karakterleri ile LDL yapısının korunmasında etkilidirler. LDL 0,982 g/ml yoğunluğa sahip bir moleküldür. 17-60 nm çapında olan ve küresel biçime sahip bu moleküllerin, dondurma sırasında spermatozoon membranına bağlanarak ve seminal plazma proteinleri ile birleşerek koruyucu etkilerini gösterdikleri düşünülmesine rağmen koruma mekanizması henüz tam olarak aydınlatılamamıştır. Çeşitli çalışmalarda bildirildiği üzere; sulandırıcılarda standart olarak kullanılan %20 yumurta sarısı yerine %8 LDL kullanımı, sperma parametrelerine olumlu katkı sağlamakta ve antioksidan enzim aktivitesini önemli ölçüde arttırmaktadır. Buna karşın sulandırıcıda %10’un üzerindeki oranlarda kullanılan LDL ise spermatozoa kalitesini azaltmaktadır. Sonuç olarak hem LDL yapısındaki lipid ve apoproteinlerin etki mekanizmalarının aydınlatılmasına yönelik hem de yumurta sarısındaki zararlı bileşenlerin izole edilmesine yönelik araştırmalar halen devam etmektedir

Anahtar Kelimeler

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Kaynakça

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