Chen et al. Medical Gas Research 2012, 2:3 http://www.medicalgasresearch.com/content/2/1/3 MEDICAL GAS RESEARCH LETTERTOTHEEDITOR Open Access Lactulose: an effective preventive and therapeutic option for ischemic stroke by production of hydrogen Xiao Chen1, Xiao Zhai2, Zhimin Kang3 and Xuejun Sun3* Abstract Lactulose, a synthetic sugar not able to be digested and absorbed by human beings, is widely used to treat constipation and hepatic encephalopathy clinically. Through fermentation by the bacteria in the gastrointestinal tract, lactulose can produce considerable amount of hydrogen, which is protective for ischemic stroke as a unique antioxidant. We propose that lactulose can induce the production of endogenous hydrogen that in turn reduces oxidative stress and ameliorate the stroke damage in human beings. Keywords: lactulose, hydrogen, ischemia/reperfusion, antioxidant, stroke Introduction (H2O2) [5]. ROS are known to be able to result in Currently stroke is the second leading cause of death in macromolecular damages including lipid peroxidation, the Western world, ranking after heart diseases and protein oxidation, and DNA oxidation, which result in before cancer [1], causing 10% of deaths worldwide [2]. ischemic brain injury [6]. Clinically, a number of recent It is estimated that stroke could soon be the most com- studies have revealed that stroke and oxidative stress are mon cause of death worldwide [3]. An ischemic stroke closely related and excess oxidative stress may have can be due to ischemia (lack of blood flow) caused by deleterious effects on clinical outcome in acute ischemic blockage (thrombosis, arterial embolism), which may stroke [7,8]. Therefore, antioxidants have been consid- lead to rapidly developing loss of brain functions as a ered in prevention and treatment of stroke and certain result of disturbance in the blood supply to the brain agents with antioxidative effects did have neuroprotec- [4]. Stroke can affect patients physically, mentally, emo- tive effects [9]. tionally, or a combination of the three and bring heavy burdens to society. Molecular hydrogen (H2) serves as a novel inflammation Ischemia induces production of reactive oxygen spe- suppressor cies (ROS), which can react with and damage a number In recent years, experimental evidences have documen- of cellular and extracellular elements. Evidence has ted that without influencing other less potent ROS, accumulated showing that ROS are involved in cerebral important in intracellular signaling, molecular hydrogen ischemia and reperfusion. During cerebral ischemia, cer- possesses the ability to selectively neutralize ONOO- ebral blood flow was partially or completely cut off in and •OH, the most cytotoxic ROS, which can damage brain regions supplied by the occluded vessels. Reoxy- cellular macromolecules aggressively and indiscrimi- genation due to spontaneous or thrombolytic reperfu- nately. Thus, hydrogen can protect cells from oxidative sion offers oxygen as a substrate for a number of stress injuries [10]. Therapeutic effects of hydrogen gas enzymatic oxidation, constantly generating ROS like and hydrogen-rich saline have been experimentally con- superoxide anion radicals(O2·-) and hydrogen peroxide firmed in a number of studies, including hypoxia [11,12], ischemia-reperfusioninjuriesinvarioustissues and organs [13-18], and other injuries related to oxida- * Correspondence: [email protected] 3Department of Diving Medicine, Faculty of Naval Medicine, Second Military tive stress. Especially in brain ischemia, our previous Medical University, Shanghai 200433, PR China research has demonstrated that hydrogen administration Full list of author information is available at the end of the article © 2012 Chen et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Chen et al. Medical Gas Research 2012, 2:3 Page 2 of 4 http://www.medicalgasresearch.com/content/2/1/3 after hypoxia appeared to provide brain protection via Some of the recent findings further imply the potential inhibition of neuronal apoptosis in neonatal hypoxia- therapeutic effects of endogenous hydrogen. Acarbose, ischemia rat model [19]. Another study reported that which inhibits glucose absorption and often causes 2.1% hydrogen-supplemented room air ventilation abdominal distention in diabetes mellitus treatment, would preserve cerebrovascular reactivity (CR) and brain shows an amazing cardiac protective effect. One of the morphology after asphyxia/reventilation (A/R) in new- main gases generated, which cause the abdominal dis- born pigs [20]. For transient cerebral ischemia, hydrogen tention, is hydrogen [29]. Oral administration of curcu- also showed significant protective effects [21]. Several min could also promote the production of endogenous studies have demonstrated the neuroprotective effects of hydrogen, which may be one of the mechanisms for cur- molecular hydrogen. Interestingly enough, even for cumin treatment of some diseases [30]. Moreover, it is some chronic neurodegenerative diseases, like the Alz- reported that oral administration of bacteria producing heimer’s disease [22] and Parkinson disease [23,24], hydrogen gas can prevent Con A-induced hepatitis. And hydrogen showed certain protective effects. after antibiotic treatment, the protective effect amazingly As a novel antioxidant, hydrogen possesses a number disappeared, indicating that hydrogen produced by of advantages. (1) Due to its high permeability, hydrogen intestinal bacteria was the key for therapeutic effects can easily penetrate biomembranes and diffuse into the [31]. cytosol, mitochondria and nucleus. (2) It is nontoxic to Since hydrogen production in man is primarily depen- the organisms, which has been proven by hyperbaric dent on the delivery of ingested, fermentable substrates diving study for decades. (3) Due to its selectivity as an to an abundant intestinal flora normally present only in antioxidant, hydrogen has less impact on other less the colon, identifying an ideal endogenous hydrogen active but very important ROS within the cells. inducer seems strikingly attractive. Lactulose is a good option worth considering. Endogenous hydrogen is effective for alleviating oxidative stress Lactulose mediates hydrogen production and is an ideal For therapeutic purposes, whether inhalation of hydro- endogenous hydrogen inducer gen gas or injection or drinking of hydrogen-rich saline Lactulose is a synthetic sugar used in the treatment of have unavoidable inconvenience. Hydrogen gas is highly constipation [32] and hepatic encephalopathy. It is a dis- flammable and explosive, thus being very dangerous. accharide formed from one molecule fructose and one The effects of hydrogen-rich saline are not so ideally molecule of galactose and cannot be absorbed by maintained. Therefore, frequent administration is human bodies but can be digested by bacteria colonizing required. Couldn’t it be better if there is a way leading within the gastrointestinal tract, especially in the colon. to persistent hydrogen generation under control? Endo- One of the main byproducts is hydrogen. Oral adminis- genous hydrogen may give a perfect answer. tration of lactulose significantly increases hydrogen pro- Early in 1969, a study published in the New England duction [33], which can be detected by hydrogen breath Journal of Medicine showed that endogenous hydrogen test, introduced several decades ago as a diagnostic test existed within human beings [25]. Studies have revealed for small bowel bacterial overgrowth [34]. that bacteria in the large intestine could generate endo- In 2004, it was observed that lactulose had some pro- genous hydrogen through anaerobic metabolism in tective effects on DSS-induced colitis [35]. Interestingly human beings and animals [26]. Previously, the biologic enough,itdemonstratedthatlactulosereducedthe effects of this little amount of hydrogen were often severity of colonic lesions induced by DSS treatment in neglected, because studies have shown that the hydro- a dose-dependent manner, the effect at 100 mg/kg being gen level in normal terminal breath is about 5-10 ppm. more potent than that of 5-ASA. Lactulose also pre- However, in patients with lactose intolerance and bac- vented the colon shortening and ameliorated the histo- terial disorders, the level may reach more than 90 ppm logical inflammation, together with significant [27]. Hydrogen concentration has been measured in dif- attenuation of the increase in MPO activity as well as ferent organs of normal mice. The results showed that lipid peroxidation following DSS treatment. Lactulose hydrogen level was very high in the large intestine, lowered oxidative stress state. Hydrogen may be the key. spleen, liver and gastric mucosa [28]. In the liver it A study showed that 20 g lactulose administration reached to 42 μM, and in the large intestine and spleen could increase the exhaled hydrogen nearly to the same it was even higher. A research on PC12 cells showed level of exhaled hydrogen as compared to the consump- that a concentration of 25 μMofhydrogeninthemed- tion of 300 ml hydrogen-rich saline and had a longer ium would display a significant anti-oxidation effect maintenance time of hydrogen concentration [32]. [10]. These results indicated that endogenous hydrogen Therefore, oral administration