Ischemia-reperfusion injury in transplantation: novel mechanisms and protective strategies

Hydrogen Sulfide-Releasing Fibrous Membranes: Potential Patches for Stimulating Human Stem Cells Proliferation and Viability under Oxidative Stress

The design of biomaterial platforms able to release bioactive molecules is mandatory in tissue repair and regenerative medicine. In this context, electrospinning is a user-friendly, versatile and low-cost technique, able to process different kinds of materials in micro- and nano-fibers with a large surface area-to-volume ratio for an optimal release of gaseous signaling molecules. Recently, the antioxidant and anti-inflammatory properties of the endogenous gasotramsmitter hydrogen sulfide (H₂S), as well as its ability to stimulate relevant biochemical processes on the growth of mesenchymal stem cells (MSC), have been investigated. Therefore, in this work, new poly(lactic) acid fibrous membranes (PFM), doped and functionalized with H₂S slow-releasing donors extracted from garlic, were synthetized. These innovative H₂S-releasing mats were characterized for their morphological, thermal, mechanical, and biological properties. Their antimicrobial activity and effects on the in vitro human cardiac MSC growth, either in the presence or in the absence of oxidative stress, were here assessed. On the basis of the results here presented, these new H₂S-releasing PFM could represent promising and low-cost scaffolds or patches for biomedical applications in tissue repair.

Hydrogen, a potential safeguard for graft-versus-host disease and graft ischemia-reperfusion injury?

Post-transplant complications such as graft-versus-host disease and graft ischemia-reperfusion injury are crucial challenges in transplantation. Hydrogen can act as a potential antioxidant, playing a preventive role against post-transplant complications in animal models of multiple organ transplantation. Herein, the authors review the current literature regarding the effects of hydrogen on graft ischemia-reperfusion injury and graft-versus-host disease. Existing data on the effects of hydrogen on ischemia-reperfusion injury related to organ transplantation are specifically reviewed and coupled with further suggestions for future work. The reviewed studies showed that hydrogen (inhaled or dissolved in saline) improved the outcomes of organ transplantation by decreasing oxidative stress and inflammation at both the transplanted organ and the systemic levels. In conclusion, a substantial body of experimental evidence suggests that hydrogen can significantly alleviate transplantation-related ischemia-reperfusion injury and have a therapeutic effect on graft-versus-host disease, mainly via inhibition of inflammatory cytokine secretion and reduction of oxidative stress through several underlying mechanisms. Further animal experiments and preliminary human clinical trials will lay the foundation for hydrogen use as a drug in the clinic.

Biological thiols-triggered hydrogen sulfide releasing microfibers for tissue engineering applications

By electrospinning of polycaprolactone (PCL) solutions containing N-(benzoylthio)benzamide (NSHD1), a H2S donor, fibrous scaffolds with hydrogen sulfide (H2S) releasing capability (H2S-fibers) are fabricated. The resultant microfibers are capable of releasing H2S upon immersion in aqueous solution containing biological thiols under physiological conditions. The H2S release peaks of H2S-fibers appeared at 2-4h, while the peak of donor alone showed at 45 min. H2S release half-lives of H2S-fibers were 10-20 times longer than that of donor alone. Furthermore, H2S-fibers can protect cells from H2O2 induced oxidative damage by significantly decreasing the production of intracellular reactive oxygen species (ROS). Finally, we investigated the H2S-fibers application as a wound dressing in vitro. Given that H2S has a broad range of physiological functions, H2S-fibers hold great potential for various biomedical applications.

STATEMENT OF SIGNIFICANCE

Hydrogen sulfide, as a gaseous messenger, plays a crucial role in many physiological and pathological conditions. Recent studies about functions of H2S suggests H2S-based therapy could be promising therapeutic strategy for many diseases, such as cardiovascular disease, arthritis, and inflammatory bowel disease. Although many H2S donors have been developed and applied for biomedical studies, most of H2S donors have the shortage that the H2S release is either too fast or uncontrollable, which poorly mimic the biological generation of H2S. By simply combining electrospinning technique with our designed biological thiols activated H2S donor, NSHD1, we fabricated H2S releasing microfibers (H2S-fibers). This H2S-fibers significantly prolonged the releasing time compared to H2S donor alone. By adjusting the electrospinning parameters, tunable releasing profiles can be achieved. Moreover, the H2S fibers can protect cardiac myoblasts H9c2 and fibroblast NIH 3T3 from oxidative damage and support their proliferation as cellular scaffolds. To our knowledge, this is the first report of electrospun fibers with H2S releasing capacity. We anticipate this H2S-releasing scaffold will have great potential for biomedical applications.

Mathematical Modeling of Early Cellular Innate and Adaptive Immune Responses to Ischemia/Reperfusion Injury and Solid Organ Allotransplantation

A mathematical model of the early inflammatory response in transplantation is formulated with ordinary differential equations. We first consider the inflammatory events associated only with the initial surgical procedure and the subsequent ischemia/reperfusion (I/R) events that cause tissue damage to the host as well as the donor graft. These events release damage-associated molecular pattern molecules (DAMPs), thereby initiating an acute inflammatory response. In simulations of this model, resolution of inflammation depends on the severity of the tissue damage caused by these events and the patient's (co)-morbidities. We augment a portion of a previously published mathematical model of acute inflammation with the inflammatory effects of T cells in the absence of antigenic allograft mismatch (but with DAMP release proportional to the degree of graft damage prior to transplant). Finally, we include the antigenic mismatch of the graft, which leads to the stimulation of potent memory T cell responses, leading to further DAMP release from the graft and concomitant increase in allograft damage. Regulatory mechanisms are also included at the final stage. Our simulations suggest that surgical injury and I/R-induced graft damage can be well-tolerated by the recipient when each is present alone, but that their combination (along with antigenic mismatch) may lead to acute rejection, as seen clinically in a subset of patients. An emergent phenomenon from our simulations is that low-level DAMP release can tolerize the recipient to a mismatched allograft, whereas different restimulation regimens resulted in an exaggerated rejection response, in agreement with published studies. We suggest that mechanistic mathematical models might serve as an adjunct for patient- or sub-group-specific predictions, simulated clinical studies, and rational design of immunosuppression.

Neuroprotective effect of tadalafil, a PDE-5 inhibitor, and its modulation by L-NAME in mouse model of ischemia-reperfusion injury

BACKGROUND

The present study investigates the neuroprotective effect of tadalafil, a selective phosphodiesterase-5 inhibitor, in a mouse model of ischemia-reperfusion injury.

MATERIALS AND METHODS

Bilateral carotid artery occlusion for 12 min followed by reperfusion for 24 h was employed to produce ischemia-reperfusion-induced cerebral injury in male Swiss mice. Cerebral infarct size was measured using triphenyltetrazolium chloride staining. Memory was assessed using Morris water maze test. Degree of motor incoordination was evaluated using inclined beam walk test, rota-rod test, and lateral push test. Brain nitrite/nitrate, brain acetylcholinesterase activity, brain thiobarbituric acid reactive species, and glutathione levels were also estimated.

RESULTS

Bilateral carotid artery occlusion, followed by reperfusion, produced a significant rise in cerebral infarct size, brain nitrite/nitrate levels, acetylcholinesterase activity, and thiobarbituric acid reactive species level along with a fall in glutathione. A significant impairment of memory and motor coordination was also noted. Pretreatment of tadalafil significantly attenuated the above effects of ischemia-reperfusion injury. Tadalafil-induced neuroprotective effects were significantly attenuated by administration of L-NAME, a nonselective nitric oxide synthase inhibitor.

CONCLUSIONS

Results indicate that tadalafil exerts neuroprotective effects, probably through nitric oxide-dependent pathways. Therefore, phosphodiesterase-5 can be explored as an important target to contain ischemia-reperfusion injury.

Effect of sildenafil in renal ischemia/reperfusion injury in rats

PURPOSE

To evaluate the effect of sildenafil, administered prior to renal ischemia/reperfusion (I/R), by scintigraphy and histopathological evaluation in rats.

METHODS

Twenty-four rats were divided randomly into two groups. They received 0.1 ml of 99mTechnetium-etilenodicisteine intravenous, and a baseline (initial) renal scintigraphy was performed. The rats underwent 60 minutes of ischemia by left renal artery clamping. The right kidney was not manipulated. The sildenafil group (n=12) received orally 1 mg/kg of sildenafil suspension 60 minutes before ischemia. Treatment with saline 0.9% in the control group (n=12). Half of the rats was assessed after 24 hours and half after seven days I/R, with new renal scintigraphy to study differential function. After euthanasia, kidneys were removed and subjected to histopathological examination. For statistical evaluation, Student t and Mann-Whitney tests were used.

RESULTS

In the control group rats, the left kidneys had significant functional deficit, seven days after I/R, whose scintigraphic pattern was consistent with acute tubular necrosis, compared with the initial scintigraphy (p<0.05). Sildenafil treatment resulted in better differential function of the left kidneys 24h after reperfusion, compared with controls. Histopathologically, the left kidney of control rats (24 hours after I/R) showed a higher degree of cellular necrosis when compared with the sildenafil treated rats (p<0.05).

CONCLUSION

Sildenafil had a protective effect in rat kidneys subjected to normothermic I/R, demonstrated by scintigraphy and histomorphometry.

Renal ischemia in rats: mitochondria function and laser autofluorescence

Ischemia-reperfusion injury is the major cause of organ dysfunction or even nonfunction following transplantation. It can attenuate the long-term survival of transplanted organs. To evaluate the severity of renal ischemia injury determined by histology, we applied laser- (442 nm and 532 nm) induced fluorescence (LIF), mitochondria respiration, and membrane swelling to evaluate 28 Wistar rats that underwent left kidney warm ischemia for 20, 40, 60, or 80 minutes. LIF performed before ischemia (control) was repeated at 20, 40, 60, and 80 minutes thereafter. We harvested left kidney tissue samples immediately after LIF determination for histology and mitochondrial analyses: state 3 and 4 respiration, respiration control rate (RCR), and membrane swelling. The association of optic spectroscopy with histological damage showed: LIF, 442 nm (r2 = 0.39, P < .001) and 532 nm, (r2 = 0.18, P = .003); reflecting laser/fluorescence-induced, 442 nm (r2 = 0.20, P = .002) and 532 nm (r2 = 0.004, P = .67). The associations between mitochondria function and tissue damage were: state 3 respiration (r2 = 0.43, P = .0004), state 4 respiration (r2 = 0.03, P = 0.38), RCR (r2 = 0.28, P = .007), and membrane swelling (r2 = 0.02, P = .43). The intensity of fluorescence emitted by tissue excited by laser, especially at a wave length of 442 nm, was determined in real time. Mitochondrial state 3 respiration and respiratory control ratio also exhibited good correlations with the grade of ischemic tissue damage.