Metabolic consequences of modern immunosuppressive agents in solid organ transplantation

Abstract

Among other factors, sophistication of immunosuppressive (IS) regimen accounts for the remarkable success attained in the short- and medium-term solid organ transplant (SOT) survival. The use of steroids, mycophenolate mofetil and calcineurin inhibitors (CNI) have led to annual renal graft survival rates exceeding 90% in the last six decades. On the other hand, attrition rates of the allograft beyond the first year have remained unchanged. In addition, there is a persistent high cardiovascular (CV) mortality rate among transplant recipients with functioning grafts. These shortcomings are in part due to the metabolic effects of steroids, CNI and sirolimus (SRL), all of which are implicated in hypertension, new onset diabetes after transplant (NODAT), and dyslipidemia. In a bid to reduce the required amount of harmful maintenance agents, T-cell-depleting antibodies are increasingly used for induction therapy. The downsides to their use are greater incidence of opportunistic viral infections and malignancy. On the other hand, inadequate immunosuppression causes recurrent rejection episodes and therefore early-onset chronic allograft dysfunction. In addition to the adverse metabolic effects of the steroid rescue needed in these settings, the generated proinflammatory milieu may promote accelerated atherosclerotic disorders, thus setting up a vicious cycle. The recent availability of newer agent, belatacept holds a promise in reducing the incidence of metabolic disorders and hopefully its long-term CV consequences. Although therapeutic drug monitoring as applied to CNI may be helpful, pharmacodynamic tools are needed to promote a customized selection of IS agents that offer the most benefit to an individual without jeopardizing the allograft survival.

Keywords: Immunosuppressive therapy; Metabolic adverse effects; Solid organ transplants.

Conflict of interest statement

Conflict of interest statement: The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Figures

Figure 1.

Mechanisms of calcineurin-inhibitor induction of pancreatic beta cell toxicity in new onset diabetes mellitus after transplant. Ca2+, calcium ions; NFATc, cytoplasmic nuclear factor of activated T cells Calcineurin-inhibitor (CNI) causes new onset diabetes after transplant (NODAT) by producing pancreatic beta cells toxicity with reduction in insulin secretion and a cellular resistance to the effect of insulin. It causes hypomagnesemia which impairs beta cell insulin secretion by increasing cytosolic calcium ion concentration. CNI prevents dephosphorylation of NFATc, a transcription factor for genes that promotes islet cell proliferation. It also reduces efficient insulin secretion by causing functional alteration of glucokinase enzyme. Finally, a high dose of CNI causes apoptosis of pancreatic beta cells.

Figure 2.

Biphasic effect of sirolimus: acute treatment enhances insulin sensitivity while chronic dosing causes insulin resistance. Acute sirolimus treatment enhances insulin sensitivity by inhibition of mechanistic target of rapamycin complex 1 (mTORC1). It decreases serine phosphorylation of insulin receptor substrate-1, which in turn activates phosphatidyl inositol 3-kinase, and thereby sensitizes the cell to insulin action. Paradoxically, chronic administration of sirolimus produces hyperglycemia by overriding the inhibitory effect of insulin on the transcription of hepatic gluconeogenic enzymes.