In Memoriam: Charles (Chuck) Crawford Sweeley, Jr. (1930–2012)

Chuck Sweeley died in Lansing, Michigan, on September 21, 2012, at the age of 82 after a long battle with a rare form of bladder cancer. He was born in Williamsport, Pennsylvania on April 15, 1930, where he grew up and attended primary and secondary school. He received a B.S. in Chemistry from the University of Pennsylvania in 1952 and a Ph.D. in Biochemistry in 1955 at the University of Illinois, Urbana-Champaign, working under the direction of Professor Herbert Carter. After further training with Evan Horning at the National Institutes of Health, Chuck took a position in the Department of Biochemistry and Nutrition at the University of Pittsburgh in 1960. He was promoted to Professor in 1966. He moved to the Department of Biochemistry at Michigan State University in 1968 and spent the rest of his career there. He served as Chairperson of the department at MSU from 1979 to 1985 and was a University Distinguished Professor at Michigan State University when he retired in 1992.(1)

Dr. John Law with Dr. Sweeley at the Herbert Carter Symposium held at the University of Arizona in Tucson in October, 2007.

Dr. William Lands with Dr. Sweeley at the Herbert Carter Symposium held at the University of Arizona in Tucson in October, 2007. Drs. Law, Lands, and Sweeley were all Ph.D. students in the Carter laboratory at the University of Illinois, Urbana-Champaign from 1952 to 1955.

During his career, he made major scientific contributions to the fields of sphingolipids and biomedical mass spectrometry. Here, we summarize and highlight some of his accomplishments, which are described in greater detail in a recent review (2). Chuck's illustrious research career began during his Ph.D. training. His Ph.D. thesis was on the chemistry of antibiotics, one of the major interests of the Carter laboratory. After graduation, Chuck switched his interest to the chemistry and biochemistry of sphingolipids and glycosphingolipids, stating that “It might seem odd to some that I would devote much of my professional career studying the biochemistry of sphingolipids… because …my doctoral thesis was entitled “Studies on Streptolidine, a Degradation Product of Streptothricin”….Carter had two laboratories, one for students working on antibiotics and one for students working on sphingosine and sphingolipids. Little did I know that the research being done in the “sphingolipids lab” would stick to me and that I would turn to that field soon after I began postdoctoral work.” (2).

Chuck was the first to develop a sensitive method for determining the sphingoid bases using periodate oxidation and analysis of the resultant long-chain fatty aldehydes by gas-liquid chromatography (GLC), then a novel technology for which he was pivotal in its development. Chuck commented, “An unexpected, career-altering opportunity came to me when Horning ordered the first gas chromatograph at the National Institutes of Health and I was given the task of setting up this machine…Later, I set out independently to apply gas-liquid chromatography (GC) to other lipids. We reported a new method to analyze sphingolipid bases in sphingomyelin and glycosphingolipids by conversion of these long-chain bases to aldehydes with periodate and separation by GC … [and]…Human plasma sphingomyelin was found to contain sphingosine, dihydrosphingosine, and two unknown bases which were later shown to be sphinga-4,14-dienine and hexadecasphing-4-enine.” (2). His method to hydrolyze sphingolipids is still in use today when laboratories need to analyze the de novo biosynthesis of sphingolipids by following labeling of the sphingoid base backbone or to quantify sphingolipids on the basis of the amount of the sphingoid bases released.

He was the first to characterize a novel unsaturated sphingoid base, sphinga-4,14-dienine, in the sphingomyelin fraction of human plasma. The presence of substantial amounts of this backbone in intact complex sphingolipids has been confirmed by subsequent mass spectrometric analyses of human plasma.

With the characterization of sphingoid bases as a background, he further investigated the biosynthesis of sphingosine as a condensation product of palmitoyl CoA and serine, and employing elegant biochemical tools, he elucidated the stereochemistry of the reaction intermediates and products. These elegant studies led to a proposed mechanism for how the first sphingolipid intermediate, 3-ketosphinganine, is formed by removal of the α-proton from serine as the Schiff base with pyridoxal 5-phosphate, displacement of the CoA moiety from palmitoyl-CoA to form the carbon-carbon bond, then decarboxylation. This mechanism has been borne out by subsequent spectroscopic and X-ray crystallographic studies. His lab also demonstrated that double bonds in the sphingoid base and the 4-hydroxyl- of phytosphingosine are added after 3-ketosphinganine has been made.

Chuck was also the first to introduce derivatization of complex and simple sugars by the trimethylsilyl (TMS) hydroxyl protecting group. This chemical maneuver rendered these and related compounds sufficiently volatile and thermally stable that they could pass through a gas chromatograph. Conversion to TMS derivatives greatly facilitated analysis of nonvolatile compounds owing to the ease in sample preparation and predicable elution profiles. Previously, these natural products were converted to volatile peracetyl or permethyl derivatives for GLC analysis. Chuck's 1963 paper on TMS derivatization of carbohydrates (3) was one of the 500 most cited papers of the 1960s. The success of his strategy to derivatize sugars was also made possible by his introduction of the stationary phase, SE-30, for GLC.

He was one of the early investigators to utilize stable isotopes, especially deuterium, to assist in elucidating the metabolism of glycosphingolipids and carbohydrates, with Dennis Vance, who was one of his doctoral students.

Chuck first recognized Fabry's disease as a lysosomal glycolipid storage disease and went on to isolate and partially characterize one of the major accumulated glycosphingolipids as trihexosyl globoside. As described by Sweeley: “I was fortunate at about this time to be introduced to a University of Pittsburgh colleague in the Pathology Department, Bernard Klionsky….[who]… told me about a rare genetic disorder called Fabry's disease, supposedly a sphingomyelin disorder…I was pleased that he was willing to give me a piece of formalin-fixed kidney from a Fabry patient…. It did not take long to find that this kidney contained abnormal amounts of two novel glycosphingolipids….” (2)

Although the glycosidic linkage of the terminal galactosyl residue was wrongly assigned the β configuration, Chuck always acknowledged at scientific meetings and in publications the contributions from other investigators who showed it was actually of the α configuration, a true reflection of his graciousness and generosity. His work on the lysosomal glycosphingolipid storage disorders further led to the characterization of many serum neutral glycosphingolipids and to the study of a variety of glycosidases in animal and plant sources. These studies provided insights into the nature of lysosomal glycolipid storage disorders and paved the way for the development of enzyme replacement therapy for lysosomal lipid storage disorders.

Chuck undertook an investigation on the biosynthesis of gangliosides, in particular, GM3 or hematoside, and purified a sialyltransferase from rat liver to homogeneity, employing classical biochemical techniques and affinity column chromatography. This was a remarkable feat as glycosyltransferases in general are of very low abundance in tissue. He further elucidated the biological function of the interconversion of GM3 and lactosylceramide in human fibroblasts in relation to cellular proliferation.

He made important contributions to the emerging technique of biochemical mass spectrometry in terms of analytical instrumention, applications to the analysis of complex lipids, and the use of stable isotope labeled precursors as a strategy to study lipid biochemistry. By the late 1960s, he was using combined GC-MS in the studies of sphingolipid bases and publishing on the extraordinary power of this approach. His interest in using stable isotope labeling in biochemical studies directly led him to observe a problem due to a separation of deuterium labeled molecules from the corresponding protium species by gas chromatography. This feature, resulting from an isotope-effect, complicated analysis of the isotope ratios of peaks eluting from the gas chromatograph. At this time, Sweeley was on sabbatical in Ragnar Ryhage's laboratory at the Karolinska Institute, and Ryhage's lab was developing one of the first specifically designed GC-MS instruments, the LKB 9000. To address the isotope-effect problem, a method was developed to switch the ion source acceleration potential in a rapid fashion to alternatively focus the appropriate isotope-labeled ions at the detector, thus enabling specific ions to be rapidly sampled at an appropriate time scale for elution from the gas chromatography. This voltage alternation approach was published in 1966, and the concept of selected ion recording remains a mainstay of GC-MS and LC-MS techniques.

Sweeley was before his time in promoting the power of time-of-flight (TOF) mass spectrometry. Using a fast TOF detector, he showed that it was possible to obtain 10 complete mass spectra/second during a GC separation of extracts of biological fluids using a time array detection strategy. While the true speed potential for TOF would have to wait for the development of fast timing circuits and faster data acquisition systems, he used this concept of rapid mass-to-charge scanning to reveal the wealth of molecules present in urine and other biological fluids, a type of study he would call metabolic profiling. This was a prototype experiment for an approach that we now call metabolomics. His metabolic profiling was decades ahead of his time. As Chuck describes (2): “Our first paper was on the development of an on-line computer system for single focusing mass spectrometry (1970). This was followed by a report on computer-controlled multiple ion detection in combined gas chromatography-mass spectrometry (GC-MS) (1973) and development of a computer system for selected ion monitoring of multi-component mixtures by computer control of accelerating voltage and magnetic field strength (1975). This allowed investigators to determine several substances in mixtures at the very high sensitivity obtained by selected ion monitoring. The next step was to develop methods for the automated determination of many substances in a mixture and this led to the development of MSSMET, a computer system for metabolic profiling (1974-1986). We utilized metabolic profiling to examine the urinary organic acid fraction in natural early-onset insulin-dependent diabetic dogs (1988) and in studies of the turnover of [U-¹⁴C]glucose into various metabolites in lactic acidemias (1988). This technique was utilized not only in studies of urinary organic acids but also in the analysis of urinary steroids…” “Metabolic profiling was also extended to a new and novel detection system using musical sounds instead of graphs or tables to analyze normal and abnormal samples of urine (1987). Intensities at the apex of each GC peak were converted to frequencies and played on a digital keyboard, higher notes reflecting greater concentrations of metabolites. This was one of the first reports on the use of sound as a sense of perception in the field of analytical chemistry and became known whimsically in the press world-wide as “musical urines.”

In the closing comments in Chuck's “Reflections….” article he noted that “By now the work I have described is ancient history. Such progress has been made over the past 15 years that my studies are but faint memories in the dusty archives of science. But I lived in exciting times, times that marked the beginnings in most of the areas of my research. It was the beginning of gas chromatography, nearly the beginning of mass spectrometry in the biomedical sciences, the beginning of chemistry and metabolism of sphingolipids, and certainly the beginning of what we now know about intermediary metabolism in man. Our generation provided a foundation upon which modern investigation in these fields has grown and prospered. It was indeed exciting, and I am fortunate to have known and considered as my friends some of the giants in chromatography and sphingolipid research.” (2)

Chuck Sweeley mentored 20 PhD. graduate students and 33 postdoctoral fellows. His abundant enthusiasm for science and research was clear to his trainees. Chuck instilled the need for originality, precision, and quality in research. He was readily available for consultation about problems and approaches. Trainees were encouraged to develop hypotheses and devise experimental approaches to test these hypotheses. His approach to mentoring was collaborative, but he did not hesitate to tell trainees they needed to get the work done. Chuck was very articulate and was more than willing to help his trainees improve their written English. He also stressed the need to deliver high quality presentations at meetings, seminars, and to colleagues. He had a great sense of humor that he conveyed to his trainees and this was very helpful on those many days where the experiments had not gone well.

Many researchers have stepped forward to share their personal remembrances of Chuck Sweeley. Dennis Vance of the University of Alberta said of Sweeley's contributions to lipid research, “His direct legacy is in the many fundamental contributions he made to biomedical research. Equally important, his dedication to training future researchers is reflected by the large number of his trainees that went on to have productive careers in academia and industry. The important contributions of these scientists are based on the excellent training they received from Chuck Sweeley, a model mentor.” Robert K. Yu of Georgia Health Sciences University recalled his interactions with Sweeley: “My first contact with Chuck was in the early 1960s, when I was a graduate student in Herb Carter's lab. Employing the then state-of-the art gas-liquid chromatographic technique developed in his laboratory for analyzing long-chain bases, I discovered the first branched-chain phytosphingosine bases from Crithidia fasiculata and that formed the basis of my thesis dissertation. In subsequent years, the Sweeley Laboratory was a constant source of new knowledge and technology, and his seminal discoveries have greatly influenced the science of today. Chuck and I also attended many conferences on sphingolipids and glycolipids, and I had the opportunity of knowing him well, both scientifically and personally. He was like a patriarchal figure to me and had greatly influenced my career through his scientific and professional wisdom. I have had many fond memories of him in the years past.”

Alfred H. Merrill, Jr. of Georgia Institute of Technology said of Sweeley, “I always had the feeling that Chuck Sweeley adopted me into his scientific family; likewise, he seemed to take delight in the growing field of sphingolipid signaling that helped explain why nature had selected these particular backbones to build this category of lipids. Chuck Sweeley could see the big picture and knew that his job was to develop technologies to define and quantify its elements, so his and future generations could understand nature at the level we now call systems biology.” Robert C. Murphy of University of Colorado Health Sciences Center described Sweeley's ability to be an all-around person: “While Chuck Sweeley was a pioneer in analytical biochemistry and lipid biochemistry, he remained throughout his life and career a generous and caring individual. He was concerned about his faculty while Chairman of Biochemistry at Michigan State University, but also was always willing to help and advise many as they were beginning their careers in the biomedical sciences.”

John E. Wilson remembers working with Sweeley at Michigan State University: ”Chuck Sweeley came to MSU as a highly recruited Professor just a year after I joined the faculty as a newly minted Assistant Professor. He was a great colleague, always enthusiastic, congenial (though not shy about speaking his mind), and a great example for a guy like me, just starting his academic career. Chuck's devotion to research was so evident, and his stature in the field so eminent, that I figured he’d never retire. Thus, it was a shocker when Chuck told me (I happened to be Chair of our department at the time) that he was going to take advantage of an early retirement option offered by MSU. In hindsight (and maybe Chuck had the foresight), I am glad he did so that he and Marilyn could enjoy some years of retirement before her progressing Alzheimer's made things so difficult. After I retired in 2004, Chuck and I became regular golfing partners, and I got to see a side of Chuck that was quite different from our interactions while we were active faculty members. “Inspirational” is the word I would use to describe this new (to me) Chuck Sweeley. His devotion to Marilyn's care and his undying love for “Momma” were so evident, and despite all his concerns for her and, in more recent years, his own well-being, he still maintained that cheery demeanor that always defined Chuck. Even just a few weeks before his death, Chuck wanted to come out on Timber Ridge with me and “maybe I’ll play a few holes,” he would say. And struggle though it was, play a few holes he did. Inspirational.”

William L. Smith from the University of Michigan reflected that “Chuck Sweeley was my lab neighbor when I started my independent career at Michigan State University and became a good personal friend, golf partner, and advocate. In thinking of adjectives to describe him, “exuberant” is one that captures his nature. Others are “lively”, “fun”, “driven”, “fearless”, “energetic”, “talented”, “brilliant”, “confident”, “dedicated”, and “principled”. It is “dedicated” and “principled” and “driven” that led Chuck to provide home care for Marilyn, his high school sweetheart and wife of almost 65 years, who had suffered from Alzheimer's disease for the past ten years. Toward the end, they entered hospice care together, and they died within 48 hours of one another. It is a remarkable story. We were all privileged to have known him.”