Abstract：
Bumetanide is used widely as a tool and off-label treatment to inhibit the Na-K-2Cl cotransporter NKCC1 in the brain and thereby to normalize intra-neuronal chloride levels in several brain disorders. However, following systemic administration, bumetanide only poorly penetrates into the brain parenchyma and does not reach levels sufficient to inhibit NKCC1. The low brain penetration is a consequence of both the high ionization rate and plasma protein binding, which restrict brain entry by passive diffusion, and of brain efflux transport. In previous studies, bumetanide was determined in the whole brain or a few brain regions, such as the hippocampus. However, the blood-brain barrier and its efflux transporters are heterogeneous across brain regions, so it cannot be excluded that bumetanide reaches sufficiently high brain levels for NKCC1 inhibition in some discrete brain areas. Here, bumetanide was determined in 14 brain regions following i.v. administration of 10 mg/kg in rats. Because bumetanide is much more rapidly eliminated by rats than humans, its metabolism was reduced by pretreatment with piperonyl butoxide. Significant, up to 5-fold differences in regional bumetanide levels were determined with the highest levels in the midbrain and olfactory bulb and the lowest levels in the striatum and amygdala. Brain:plasma ratios ranged between 0.004 (amygdala) and 0.022 (olfactory bulb). Regional brain levels were significantly correlated with local cerebral blood flow. However, regional bumetanide levels were far below the IC50 (2.4 μM) determined previously for rat NKCC1. Thus, these data further substantiate that the reported effects of bumetanide in rodent models of brain disorders are not related to NKCC1 inhibition in the brain.
摘要：
布美他尼被广泛用作工具和标记外治疗，以抑制脑中的Na-K-2Cl协同转运蛋白NKCC1，从而使几种脑疾病中的神经元内氯化物水平正常化。然而,全身给药后，布美他尼仅很少渗透到脑实质中，并且没有达到足以抑制NKCC1的水平。低脑穿透率是高电离率和血浆蛋白结合的结果，通过被动扩散限制大脑进入，和脑外排运输。在以往的研究中,布美他尼被确定在整个大脑或一些大脑区域，比如海马。然而,血脑屏障及其外排转运蛋白在大脑区域是异质的，因此，不能排除布美他尼在某些离散的大脑区域达到足够高的大脑水平，从而抑制NKCC1。这里,在大鼠中静脉内施用10mg/kg后,在14个脑区中测定布美他尼。因为布美他尼被大鼠比人类更快地消除，用胡椒基丁醚预处理可降低其代谢。重要的,确定了区域布美他尼水平的5倍差异，中脑和嗅球中的水平最高，纹状体和杏仁核中的水平最低。脑:血浆比率介于0.004(杏仁核)和0.022(嗅球)之间。局部脑水平与局部脑血流量显着相关。然而,区域布美他尼水平远低于先前测定的大鼠NKCC1的IC50(2.4μM).因此，这些数据进一步证实,报道的布美他尼在脑部疾病啮齿动物模型中的作用与脑中NKCC1抑制无关.
