PL01 H2S: Controversies and conundrums

Research into the biological effects of hydrogen sulfide (H2S) have at times outpaced an understanding of the physical and chemical properties of this signaling molecule. In this talk some of the more outstanding “controversies and conundrums” of H2S will be examined. Perhaps the most pressing issue is what are “physiological” concentrations of H2S in blood and tissues? Can many of the values reported in the literature, especially those in blood in excess of 20 μmol/l be realistic, even when they can’t be detected by the nose, or when they should be theoretically fatal? A brief overview of the more commonly used methods for these analyses such as methylene blue, ion selective electrodes, monobromobimane, headspace gas, fluorescent dyes and polarographic electrodes will be examined along with their advantages and shortcomings. A number of these methods especially the methylene blue and ion selective methods are associated with obvious artifacts and these will be described. Strong support will be given to the polarographic electrode as to date this is the only method available for analyzing H2S concentration in unadulterated, living tissues and in real time. Tissue concentrations of H2S, often reported in nmoles or μmoles per mg protein often lead to excessive intracellular concentrations when expressed per volume of cytosol and these calculations will be examined critically. Volatility of H2S is another problem, the extent of which is seldom appreciated. In tissue culture wells the half-life may be less than 5 min, it is even shorter in preparations that are aerated with either oxygen or nitrogen and in the Langendorff heart preparation little H2S makes a single complete circuit through the system. How these problems affect long-range studies will be examined. Diffusion of H2S into and within tissues will be examined from a theoretical perspective and these studies will illustrate potential mechanisms for regulating H2S concentration as well as provide some perspective regarding potential pitfalls associated with exogenous H2S applications. Other problems that will be addressed include persulfides as contaminants of commonly used sulfide salts, H2S as a contaminant of other sulfides, notably dithiothreitol (DTT) and whether or not we should be concerned about chemical interactions of H2S with O2, H2O2. Other analytic compounds that are often used to modify protein sulfhydryl groups or inhibit unrelated enzyme pathways such as N-methylmalemide, phenyl arsine and zinc protoporphyrin IX also may react with H2S and these will be examined. Recently there has been an increased interest and emphasis on correlating plasma H2S concentrations with a broad spectrum of pathophysiological conditions including cancer, obesity, diabetes, hypertension, coronary heart disease, COPD, asthma and even survival probability in patients in septic shock in intensive care units. The utility of such endeavors will be examined from a variety of perspectives including methods and procedures used to measure H2S, the validity of values obtained and statistical approaches regarding trends and differences and the probability of making false positive and false negative errors. Hopefully this talk will initiate constructive dialogue and positively impact the field. Supported: National Science Foundation, IOS 1051627.