Neonatal jaundice is a common symptom that occurs in neonates during the first month of their life and is generally divided into physiological and pathological subtypes. In serious cases, pathological neonatal jaundice frequently shows complications including seizures, cerebral palsy, and kernicterus. However, due to the unclear pathogenesis of pathological neonatal jaundice, effective drugs for this disease remain unsatisfied. In the present study, we first estimated the protective effects of folic acid (FA) on phenylhydrazine (PHA) or homocysteine (Hcy)-injected neonatal rats (2–3 days aged). Intriguingly, we found that FA significantly decreased the elevated total bilirubin (TBIL) and direct bilirubin (DBIL) concentration, alanine aminotransferase (ALT), aspartate aminotransferase (AST), and alkaline phosphatase (ALP) activity in PHA- or Hcy-injected rats, indicating that FA improves liver functions. Meanwhile, our results also showed that the plasma Hcy level and N-homocysteinylation (N-Hcy) modification of albumin were significantly elevated in the jaundice rats, which were obviously reversed after FA administration. Furthermore, we identified a novel N-Hcy modification site K⁵⁴⁵ of human serum albumin (HSA) using LC-MS/MS, and the mutagenesis assay in HEK293 further validated these observations. Besides, we demonstrated that the N-Hcy modification of albumin functionally inhibits the bilirubin-binding ability of albumin without altering its protein level both in vitro and in vivo. Altogether, we highlight a mechanism that FA reduces the plasma Hcy level and thereby enhance the bilirubin-binding ability of albumin, which may provide a novel therapeutic strategy for the treatment of pathological neonatal jaundice.

Graphical abstract

中文翻译：

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叶酸通过降低白蛋白的赖氨酸同型半胱氨酸化减轻苯肼（PHA）诱导的新生大鼠黄疸

新生儿黄疸是新生儿出生后第一个月出现的常见症状，一般分为生理性和病理性亚型。在严重的情况下，病理性新生儿黄疸经常出现癫痫发作、脑瘫和核黄疸等并发症。然而，由于新生儿病理性黄疸的发病机制尚不明确，治疗该病的有效药物仍不尽人意。在本研究中，我们首先评估了叶酸 (FA) 对注射苯肼 (PHA) 或同型半胱氨酸 (Hcy) 的新生大鼠（2-3 天龄）的保护作用。有趣的是，我们发现 FA 显着降低升高的总胆红素 (TBIL) 和直接胆红素 (DBIL) 浓度、丙氨酸氨基转移酶 (ALT)、天冬氨酸氨基转移酶 (AST)、PHA 或 Hcy 注射大鼠的碱性磷酸酶 (ALP) 活性，表明 FA 可改善肝功能。同时，我们的研究结果还表明，黄疸大鼠的血浆 Hcy 水平和白蛋白的 N-同型半胱氨酸化 (N-Hcy) 修饰显着升高，FA 给药后明显逆转。此外，我们发现了一个新的 N-Hcy 修饰位点 K⁵⁴⁵人血清白蛋白 (HSA) 使用 LC-MS/MS 和 HEK293 中的诱变试验进一步验证了这些观察结果。此外，我们证明了白蛋白的 N-Hcy 修饰在功能上抑制了白蛋白的胆红素结合能力，而不改变其体外和体内的蛋白质水平。总之，我们强调了FA降低血浆Hcy水平从而增强白蛋白的胆红素结合能力的机制，这可能为治疗新生儿病理性黄疸提供新的治疗策略。

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