Analytical measurement of discrete hydrogen sulfide pools in biological specimens

Hydrogen sulfide (H2S) is a ubiquitous gaseous signaling molecule that plays a vital role in numerous cellular functions and has become the focus of many research endeavors, including pharmacotherapeutic manipulation. Among the challenges facing the field is the accurate measurement of biologically active H2S. We have recently reported that the typically used methylene blue method and its associated results are invalid and do not measure bona fide H2S. The complexity of analytical H2S measurement reflects the fact that hydrogen sulfide is a volatile gas and exists in the body in various forms, including a free form, an acid-labile pool, and bound as sulfane sulfur. Here we describe a new protocol to discretely measure specific H2S pools using the monobromobimane method coupled with RP-HPLC. This new protocol involves selective liberation, trapping, and derivatization of H2S. Acid-labile H2S is released by incubating the sample in an acidic solution (pH 2.6) of 100 mM phosphate buffer with 0.1 mM diethylenetriaminepentaacetic acid (DTPA), in an enclosed system to contain volatilized H2S. Volatilized H2S is then trapped in 100 mM Tris–HCl (pH 9.5, 0.1 mM DTPA) and then reacted with excess monobromobimane. In a separate aliquot, the contribution of the bound sulfane sulfur pool was measured by incubating the sample with 1 mM TCEP (tris(2-carboxyethyl)phosphine hydrochloride), a reducing agent, to reduce disulfide bonds, in 100 mM phosphate buffer (pH 2.6, 0.1 mM DTPA), and H2S measurement was performed in a manner analogous to the one described above. The acid-labile pool was determined by subtracting the free hydrogen sulfide value from the value obtained by the acid-liberation protocol. The bound sulfane sulfur pool was determined by subtracting the H2S measurement from the acid-liberation protocol alone compared to that of TCEP plus acidic conditions. In summary, our new method allows very sensitive and accurate measurement of the three primary biological pools of H2S, including free, acid-labile, and bound sulfane sulfur, in various biological specimens.

Graphical AbstractFigure optionsDownload high-quality image (78 K)Download as PowerPoint slideHighlights
► We report a novel analytical method to measure all bioavailable pools of H2S.
► We report that tris(2-carboxyethyl)phosphine hydrochloride is an ideal reductant to liberate bound persulfides.
► CSE genetic deficiency decreases free and acid-labile H2S pools.
► Human plasma contains nanomolar levels of free H2S and low-millimolar levels of acid-labile H2S.