Short-Term Endogenous Hydrogen Sulfide Upregulation For Vein Graft Disease

Peripheral arterial disease (PAD) remains a major health issue in the United States, especially with the metabolic syndrome and aging population. Surgical bypass using autogenous vein remains the most effective and durable choice for patients with advanced PAD. However, these vascular interventions suffer from high failure rates due to the development of significant occlusive lesions (intimal hyperplasia [IH]). Similar failure mechanisms plague coronary artery bypass grafts and endovascular interventions. Despite decades of vein graft research, our understanding of the biologic mechanisms of vein graft failure remains obscure.

Hydrogen sulfide (H2S) has emerged as a critical gaseous signaling molecule in multiple processes including ischemia/reperfusion (IR) injury, angiogenesis, intimal hyperplasia, and anti-inflammatory mechanisms. It even appears to hold anti-atherosclerotic properties. However, the gas is toxic with a half-life of minutes, and it can be rapidly oxidized. Furthermore, clinically useful pharmacologic H2S donors have not been developed to date. In our 2015 Cell paper the investigators link substantial upregulation of endogenous H2S via short-term manipulation of mammalian dietary intake: simple dietary restriction. Our first pilot study had aims to determine the feasibility and safety of a PCR diet in vascular patients, concluding with no significant serious adverse events in any of the patients receiving the diet. The investigators learned that patients do not like having to stay in the hospital research unit pre-operatively. Long term the investigators aim to substantively impact the vascular patient at several levels: protection from IR, intimal hyperplasia, peri-procedural events such as stroke, cardiac dysfunction and myocardial infarction, and promotion of angiogenesis. For the current effort, the investigators will focus on potential biologic mechanisms of PCR and feasibility of eventual larger initiatives to accomplish this long-term aim.

A powerful method to upregulate H2S is PCR. Defined as reduced food intake without malnutrition, PCR is best known for extending lifespan in model organisms from yeast to non-human primates. The efficacy of PCR against acute stress, including surgical stress, in preclinical models is also well established. Pilot studies suggest that humans respond to PCR in beneficial ways with respect to metabolic fitness (including improved glucose homeostasis, lipid profiles, and cardiovascular performance). But humans also have great difficulty complying with long-term voluntary food restriction, which is a prime reason that PCR has not been previously exploited in the clinical setting despite promising efficacy. However, recent data in model organisms point to a rapid onset of PCR benefits and challenges the notion that long-term PCR is required for benefits to accrue. In fruit flies, the maximal benefit of PCR on mortality risk occurs within 2-3 days. In rodents, the investigators have shown that surgical stress resistance also occurs within days, and the benefits center on upregulation of endogenous H2S. Nonetheless, except for pre-operative overnight fasting (which serves a different purpose) dietary recommendations are largely absent from peri-op management.

Pilot data suggest that adverse post-operative outcomes linked to oxidative stress, inflammation and stress hormones may be modified by brief PCR in humans as well. In subjects who undertook food restriction for 12 hours per day for a month, markers of inflammation decreased significantly. PCR has been shown to reduce oxidative stress in both chronic and acute settings. Similarly, PCR may decrease stress hormone release. PCR also appears to work rapidly even in obese individuals or ill individuals. In gastric bypass surgery, two weeks of PCR reduced the risk of complications and procedure difficulty. With respect to patient compliance, brief (4 days to 2 weeks) pre-operative dietary interventions have been shown to be feasible and safe in selected patients, ranging from obese candidates for laparoscopic surgery to living organ donors. In our own human pilot research, vascular surgery patients have safely completed 3 days of pre-operative PCR diet without serious adverse events or reactions.

For the current project the investigators propose a randomized, controlled trial to evaluate patient compliance and biologic effects of a short-term pre-operative PCR diet in comparison to a normal ad libitum diet for 4 days before elective vascular surgery involving an open major operation. This mechanistic clinical study is structured as a prospective, multi-year study of 226 vascular surgery patients undergoing non-emergency lower-extremity arterial vein bypass surgery randomized into two pre-operative dietary groups: observational group (n=90) and PCR (commercially available ScandiShake x 4 days, n=136). This specific dietary intervention to upregulate endogenous H2S is based on our preliminary data balanced with economic and clinical feasibility considerations. The event rate for the control group is assumed to be 33% based on the literature and data largely from our institutions. Our goal is to find a suitable (total) sample size for power 1 - β=0.8 at 5% level of significance. It has been assumed that Relative Risk Reduction (RRR) is 50% or Absolute Risk Reduction (ARR) is 16.5%. Projected total sample size, for treatment group to control group ratio of 1.5 (60% to 40%), is 225.55 which approximate to 226. For the structure of our dietary intervention this means 90 for the control group and 136 for the treatment group. However, it must be emphasized that the primary goal of this project is to decipher mechanisms in humans rather than evaluate clinical efficacy.