The NRF2 stimulating agent, tin protoporphyrin, activates protective cytokine pathways in healthy human subjects and in patients with chronic kidney disease

Oxidant- induced preconditioning: A pharmacologic approach for triggering renal 'self defense'

Acute kidney injury (AKI) is a common event, occurring in ~5% and ~35% of hospitalized and ICU patients, respectively. The development of AKI portends an increased risk of morbidity, mortality, prolonged hospitalization, and subsequent development of chronic kidney disease (CKD). Given these facts, a multitude of experimental studies have addressed potential methods for inducing AKI prevention in high-risk patients. However, successful clinical translation of promising experimental data has remained elusive. Over the past decade, our laboratory has focused on developing a method for safely triggering AKI protection by inducing "kidney preconditioning" in mice by the intravenous administration of a combination of Fe sucrose (FeS) + tin protoporphyrin (SnPP). These agents induce mild, but short lived, 'oxidant stress' which synergistically activate a number of kidney 'self-defense' pathways (e.g., Nrf2, ferritin, IL-10). Within 18-24 h of Fe/SnPP administration, marked protection against diverse forms of experimental toxic and ischemic AKI results. FeS/SnPP-mediated reductions in kidney injury can also indirectly decrease injury in other organs by mitigating the so called "organ cross talk" phenomenon. Given these promising experimental data, three phase 1b clinical trials were undertaken in healthy subjects and patients with stage 3 or 4 CKD. These studies demonstrated that FeS/SnPP were well tolerated and that they up-regulated the cytoprotective Nrf2, ferritin, and IL-10 pathways. Two subsequent phase 2 trials, conducted in patients undergoing 'on-pump' cardiovascular surgery or in patients hospitalized with COVID 19, confirmed FeS/SnPP safety. Furthermore, interim data analyses revealed statistically significant improvements in several clinical parameters. The goals of this review are to: (i) briefly discuss the historical background of renal "preconditioning"; (ii) present the experimental data that support the concept of FeS/SnPP- induced organ protection; and (iii) discuss the initial results of clinical trials that suggest the potential clinical utility of an 'oxidant preconditioning' strategy.

The Effects of Nuclear Factor Erythroid 2 (NFE2)-Related Factor 2 (Nrf2) Activation in Preclinical Models of Peripheral Neuropathic Pain

Oxidative stress, resulting from an imbalance between the formation of damaging free radicals and availability of protective antioxidants, can contribute to peripheral neuropathic pain conditions. Reactive oxygen and nitrogen species, as well as products of the mitochondrial metabolism such as superoxide anions, hydrogen peroxide, and hydroxyl radicals, are common free radicals. Nuclear factor erythroid 2 (NFE2)-related factor 2 (Nrf2) is a transcription factor encoded by the NFE2L2 gene and is a member of the cap 'n' collar subfamily of basic region leucine zipper transcription factors. Under normal physiological conditions, Nrf2 remains bound to Kelch-like ECH-associated protein 1 in the cytoplasm that ultimately leads to proteasomal degradation. During peripheral neuropathy, Nrf2 can translocate to the nucleus, where it heterodimerizes with muscle aponeurosis fibromatosis proteins and binds to antioxidant response elements (AREs). It is becoming increasingly clear that the Nrf2 interaction with ARE leads to the transcription of several antioxidative enzymes that can ameliorate neuropathy and neuropathic pain in rodent models. Current evidence indicates that the antinociceptive effects of Nrf2 occur via reducing oxidative stress, neuroinflammation, and mitochondrial dysfunction. Here, we will summarize the preclinical evidence supporting the role of Nrf2 signaling pathways and Nrf2 inducers in alleviating peripheral neuropathic pain.

Catalytic iron mediated renal stress responses during experimental cardiorenal syndrome 1 ("CRS-1")

Cardiorenal syndrome I (CRS-1) denotes a state in which acute kidney injury occurs in the setting of acute heart failure (AHF). Isoproterenol (Iso) administration is widly used as an AHF model by transiently inducing extreme tachycardia, hypotension, and myocyte apoptosis and/or necrosis. To gain potential insights into renal manifestations of CRS-1, mice were subjected to the Iso-AHF model (50 mg Iso/kg), followed by renal functional and renal cortical assessments over 4 hours Iso induced acute azotemia (doubling of BUN, plasma creatinine) and significantly reduced renal plasma flow (prolonged plasma para-amino-hippurate clearance). Although no morphologic tubular injury was identified, marked increases in renal cortical 'stress markers' (NGAL, HO-1, IL-6, MCP-1 mRNAs) and oxidant stress (decreased glutathione, increased malondialdehyde) were observed. These changes were catalytic Fe dependent, given that the iron chelator desferrioxamine (DFO) significantly blunted, or completely reversed, these renal cortical abnormalities. Despite these acute changes, no lasting renal injury was observed (assessed over 3 days). To determine whether Iso directly impacts tubular cell integrity, cultured proximal tubule (HK-2) cells were exposed to Iso. Substantial Fe dependent cell injury (decreased MTT uptake), and Fe independent increases in HO-1/IL-6 mRNA expression were observed. We conclude that Iso-induced AHF is a useful reversible model of CRS-1. Despite its largely hemodynamic ('pre-renal') nature, Fe-mediated oxidative stress and pro-inflammatory reactions are induced. These arise, at least in part, from direct Iso- induced tubular cell toxicity, rather than simply being secondary to Iso-mediated hemodynamic events. Finally, Iso-triggered renal cytokine production can potentially contribute to 'organ cross talk' and a systemic pro-inflammatory state.

The NRF2 stimulating agent, tin protoporphyrin, activates protective cytokine pathways in healthy human subjects and in patients with chronic kidney disease

BACKGROUND

Tin protoporphyrin (SnPP), a heme oxygenase 1 (HO-1) inhibitor, triggers adaptive tissue responses that confer potent protection against acute renal- and extra-renal tissue injuries. This effect is mediated, in part, via SnPP-induced activation of the cytoprotective Nrf2 pathway. However, it remains unclear as to whether SnPP can also upregulate humoral cytokine defenses, either in healthy human subjects or in patients with CKD. If so, then systemically derived cytokines could contribute SnPP-induced tissue protection.

METHODS

SnPP (90 mg IV) was administered over 2 hr to six healthy human volunteers (HVs) and 12 subjects with stage 3-4 CKD. Plasma samples were obtained from baseline upto 72 hr post injection. Two representative anti-inflammatory cytokines (IL-10, TGFβ1), and a pro-inflammatory cytokine (TNF-α), were assayed. Because IL-6 has been shown to induce tissue preconditioning, its plasma concentrations were also assessed. In complementary mouse experiments, SnPP effects on renal, splenic, and hepatic IL-10, IL-6, TGFβ1, and TNF-α production (as gauged by their mRNAs) were tested. Tissue HO-1 mRNA served as an Nrf2 activation marker.

RESULTS

SnPP induced marked (~5-7x) increases in plasma IL-10 and IL-6 concentrations within 24-48 hr, and to equal degrees in HVs and CKD patients. SnPP modestly raised plasma TGFβ1 without impacting plasma TNF-α levels. In mouse experiments, SnPP did not affect IL-6, IL-10, TNF-α, or TGFβ1 mRNAs in kidney despite marked renal Nrf2 activation. Conversely, SnPP increased splenic IL-10 and hepatic IL-6/TGFβ1 mRNA levels, suggesting these organs as sites of extra-renal cytokine generation.

CONCLUSIONS

SnPP can trigger cytoprotective cytokine production, most likely in extra-renal tissues. With ready glomerular cytokine filtration, extra-renal/renal "organ cross talk" can result. Thus, humoral factors seemingly can contribute to SnPP's cytoprotective effects.