Clinical And Basic Researches In Relationships Between Hydrogen Sulfide And Resistant Hypertension Among Hemodialysis Patients

Hydrogen sulfide (H2S) has long been thought as a colorless and toxic gas with the smell of rotten eggs. Recent studies have shown that H2S is not only a chemical hazard, but also be produced endogenously in ammalian tissues from L-cysteine decomposition mainly by3enzymes:cystathionine β-synthetase (CBS), cystathionine γ-lyase (CSE), and3-mercaptosulfurtransferase. During the past twenty years, H2S has been considered as a important regulator and plays important roles, both in normal physiology conditions and in the process of a variety of diseases. Now H2S has now been konwn to be the third gaseous transmitter, as well as nitric oxide (NO) and carbon monoxide (CO),2gaseous transmitters in mammals.A great number of researches have confirmed its functions in preventing the development of hypertension through different pathways, including relaxing vascular smooth muscles by the activation of KATP channels, inhibiting smooth muscle cell proliferation via the mitogen-activated protein kinase signaling pathway. An animal experiment shows that in the spontaneously hypertensive rats (SHR), plasma levels of H2S and CSE gene expression were significantly lower than that of normal rats (WKY), while exogenous H2S can reduce blood pressure in rats. Besides, CSE inhibitors can promote the development of hypertension. In CSE knockout rats, plasma and tissue H2S levels are significantly lower than that in wild type rats. An observational study has also shown that plasma H2S is much lower in coronary heart disease patients, hypertensives, and smokers, compared to normal subjects.Hypertension is one of the most common cardiovascular diseases in hemodialysis(HD) patients, and is very important to the development of other cardiovascular diseases. It is now be recognized as an independent risk factor for HD patients morbidity and mortality. As a result, the importance of H2S in hypertension and other cardiovascular diseases has provide nephrologists with a new research direction and possible therapeutic targets.Objective This study was designed to investigate:1) distribution characteristics of H2S in HD patients, and some influence factors;2) functions of H2S in HD patients with resistant hypertension and its clinical mechanisms;3) exact relationships of H2S, NO and indoxyl sulfate in basic researches.Methods This study was composed of two parts, clinical researches and basic experiments.1) clinical researches. Based on screening and exclusion criteria, patients who conformed to the demands were enrolled. Then according to predialysis blood pressure(BP) and antihypertensive medications,50patients with normal blood pressure (defined as90/60-140/90mmHg with no antihypertensive medications),48patients with controlled hypertension (defined as90/60-140/90mmHg with≤3antihypertensive agents),52patients with resistant hypertension (defined as BP uncontrolled despite the use of≥3antihypertensive agents, or controlled with≥4antihypertensive agents) were selected. Laboratory parameters were obtained from routine monthly mid-week, pre-and post-dialysis, venous blood samples blood specimens, and included plasma H2S, NO, sulfuredhemoglobin, indoxyl sulfate;2) basic experiment.On the basis of the clinical findings, we further investigated the effects of Sodium hydrosulfide (NaHS) on high IS-induced NO production decreasing in human umbilical vein endothelium cells (HUVECs), and clarify its mechanisms by the application of ATP dependent potassium channels (KATP) antagonist glibenclamide and P13K/Akt antagonist LY294002. ELISA was used to observe the generations of NO and H2S, while western blot to distinguish the mechanisms.Results Clinical studies showed that:1) Compared with healthy controls, predialytic plasma H2S, NO, NO/ET-1and Sulphhaemoglobin decreased significantly in HD patients (P<0.05); Predialytic plasma H2S levels were positively related with predialytic NO (r, p:0.546,0.000), NO/ET-1(r, p:0.527,0.000), Sulphhaemoglobin (r, p:0.553,0.000) and eGFR (r, p:0.399,0.001), while negatively linked to serum Cr(r, p:-0.439,,0000), IS (r, p:-0.426,0.000), predialytic SBP (r, p:-0.258,0.027) and PP (r, p:-0.231,0.048); Plasma H2S levels increased obviously, while NO, NO/ET-1decreased significantly after dialysis; Monocyte CSE gene expression increased after dialysis.2) patients with resistant hypertension were characterized as younger, with lower levels of prediaytic plasma H2S, NO, NO/ET-1and Sulphhaemoglobin, while higher levels of serum (32-MG and NT-proBNP; In multivariate multinomial logistic regression, the inverse association between H2S and resistant hypertension disappeared after adjustment for NO, age and other factors(P>0.10), and only NO was left in the Statistical model (P<0.10);7) The relationship with plasma NO levels in resistant hypertension was attenuated after additional adjustment for albumin and BMI, and abolished after adjustment for IS((P>0.10)).Basic research shows:1) IS induced a dose dependent reduction in HUVEC in NO, H2S production and eNOS activity;2) NO production increased greatly in IS-incubated HUVEC with pretreatment of low concentrations of Sodium hydrosulfide (NaHS);3) Wesern blot showed that IS stimulation inhibited Akt phosphorylation levels and eNOS expression significantly, while giving low concentrations of HoS can upregulate Akt phosphorylation and eNOS expression. Both KAtp antagonist glibenclamide and P13K/Akt blocking agent LY294002can supress such protection.Conclusions Predialytic plasma H2S and NO levels were significantly lower in HD patients, Compared with healthy population. Both the two markers were inversely related to serum IS; Plasma H2S levels increased obviously after dialysis, independent of ultrafiltration. Relationship between H2S and refractory hypertension may depend on factors such as age, NO; nutrition metabolism and uremic toxins, especially IS, may play a significant role in the inverse association between NO and resistant hypertension; IS can dose-dependently reduced the production of NO, and H2S; Low concentrations of H2S can be primarily through KATP-P13K/Akt-eNOS pathway, to protect HUVEC from high-IS induced damage, and improve NO production.