Ischemic preconditioning reduces endoplasmic reticulum stress and upregulates hypoxia inducible factor-1α in ischemic kidney: the role of nitric oxide

Remote preconditioning reduces oxidative stress, downregulates cyclo-oxygenase-2 expression and attenuates ischaemia-reperfusion-induced acute kidney injury

Remote preconditioning (rPeC) is a phenomenon by which short-time intermittent ischaemia-reperfusion (I/R) of a remote organ during ischaemia protects other organs from I/R injury (IRI). The aim of the present study was to investigate the protective effect of rPeC on renal IRI in rats. Rats were subjected to right nephrectomy and randomized as into a sham group (no additional intervention), an I/R group (subjected to 45 min left renal pedicle occlusion) and an rPeC group (subjected to four cycles of 5 min I/R of the left femoral artery administered at the beginning of renal ischaemia). After 24 h, blood, urine and tissue samples were collected. Compared with the sham group, I/R resulted in renal dysfunction, as evidenced by significantly lower creatinine clearance (CCr; 0.52 ± 0.06 vs 0.11 ± 0.02 mL/min, respectively) and higher fractional excretion of sodium (FE(Na) ; 0.80 ± 0.07% vs 2.46 ± 0.20%, respectively). This was accompanied by decreased superoxide dismutase (SOD; 6.9 ± 1.7 vs 26.7 ± 2.7 U/g tissue) and catalase (CAT; 20.2 ± 8.8 vs 32.2 ± 8.7 K/g tissue) activity in the I/R group, as well as decreased levels of reduced glutathione (GSH; 21.7 ± 8.1 vs 81.2 ± 20.2 μmol/g tissue) and increased malondialdehyde levels (MDA; 1.2 to 0.1 vs 0.5 ± 0.2 μmol/100 mg), cyclo-oxygenase (COX)-2 expression and histological damage. In the rPeC group, renal histology and function were significantly improved (CCr 0.32 ± 0.02 mL/min; FE(Na) 1.33 ± 0.12%) compared with the I/R group. Furthermore, compared with the I/R group, the rPeC group exhibited increases in SOD and CAT activity (22.8 ± 3.8 U/g tissue and 21.7 ± 8.6 K/g tissue, respectively), increased GSH levels (74.0 ± 4.9) and decreased MDA levels (1.1 ± 0.3 μmol/100 mg) and COX-2 expression. In conclusion, rPeC appears to exert protective effects against renal IRI. This protection may be a consequence of reductions in lipid peroxidation, intensification of anti-oxidant systems and downregulation of COX-2 expression. A simple approach, rPeC may be a promising strategy for protection against IRI in clinical practice.

Priming adult stem cells by hypoxic pretreatments for applications in regenerative medicine

The efficiency of regenerative medicine can be ameliorated by improving the biological performances of stem cells before their transplantation. Several ex-vivo protocols of non-damaging cell hypoxia have been demonstrated to significantly increase survival, proliferation and post-engraftment differentiation potential of stem cells. The best results for priming cultured stem cells against a following, otherwise lethal, ischemic stress have been obtained with brief intermittent episodes of hypoxia, or anoxia, and reoxygenation in accordance with the extraordinary protection afforded by the conventional maneuver of ischemic preconditioning in severely ischemic organs. These protocols of hypoxic preconditioning can be rather easily reproduced in a laboratory; however, more suitable pharmacological interventions inducing stem cell responses similar to those activated in hypoxia are considered among the most promising solutions for future applications in cell therapy. Here we want to offer an up-to-date review of the molecular mechanisms translating hypoxia into beneficial events for regenerative medicine. To this aim the involvement of epigenetic modifications, microRNAs, and oxidative stress, mainly activated by hypoxia inducible factors, will be discussed. Stem cell adaptation to their natural hypoxic microenvironments (niche) in healthy and neoplastic tissues will be also considered.

Effect of ischemia preconditioning on renal ischemia/reperfusion injury in rats

OBJECTIVE

To study the effect of ischemia preconditioning (IP) on renal ischemia/reperfusion (I/R)-associated functional injury and expression of renal adhesion molecules in rats.

MATERIALS AND METHODS

The ischemia preconditioning plan adopted in this experiment involved renal warm ischemia for 6 min. and blood flow for 4 min., repeated four times. The Wistar rat kidneys used for warm ischemia preconditioning were subjected to 60 min of renal warm ischemia followed by reperfusion. The rat kidneys with ischemia/reperfusion were compared with the ischemia preconditioning group to observe rat renal function and changes in the expression of renal adhesion molecules ICAM-1, P-Selectin, and E-Selectin.

RESULTS

The expression of rat renal adhesion molecules (ICAM-1, P-Selectin, and E-Selectin) with ischemia preconditioning was significantly lower than that of the ischemia/reperfusion group. Serum creatinine was significantly lower than that in the ischemia/reperfusion group after 48 hours.

CONCLUSIONS

Ischemia preconditioning has a protective effect on renal function. Reduced expression of renal adhesion molecules is likely a mechanism involved in the observed protection.

The effect of hyperbaric oxygen on nitric oxide synthase activity and expression in ischemia-reperfusion injury

BACKGROUND

Hyperbaric oxygen (HBO) mitigates ischemia-reperfusion (IR) injury via a nitric oxide mechanism that is nitric oxide synthase (NOS) dependent. The purpose of this study was to investigate this NOS-dependent mechanism by examining isoform-specific, tissue-specific, and time-specific upregulation of NOS mRNA, protein, and enzymatic activity.

METHODS

We raised a gracilis flap in Wistar rats that were separated into early and late phases. Treatment groups included nonischemic control, IR, HBO-treated ischemia-reperfusion (IR-HBO), and nonischemic HBO control. We harvested tissue-specific samples from gracilis, rectus femoris, aorta, and pulmonary tissues and processed them by reverse transcription polymerase chain reaction and Western blot to determine upregulation of isoform-specific NOS mRNA and protein. We also harvested tissue for NOS activity to investigate upregulation of enzymatic activity. Data are presented as mean ± standard error of the mean with statistics performed by analysis of variance. P ≤ 0.05 was considered significant.

RESULTS

There was no increase in NOS mRNA in the early phase. In the late phase, there was a significant increase in endothelial-derived NOS (eNOS) mRNA in IR-HBO compared with IR in gracilis muscle (79.4 ± 22.3 versus 36.1 ± 4.5; P < 0.05) and pulmonary tissues (91.0 ± 31.2 versus 30.2 ± 3.1; P < 0.01). There was a significant increase in the late-phase eNOS pulmonary protein IR-HBO group compared with IR (235.5 ± 46.8 versus 125.2 ± 14.7; P < 0.05). Early-phase NOS activity was significantly increased in IR-HBO compared with IR in pulmonary tissue only (0.049 ± 0.009 versus 0.023 ± 0.003; P < 0.05).

CONCLUSIONS

The NOS-dependent effects of HBO on IR injury may result from a systemic effect involving an early increase in eNOS enzymatic activity followed by a late-phase increase in eNOS protein expression within the pulmonary tissues.

Remote ischemic preconditioning regulates HIF-1α levels, apoptosis and inflammation in heart tissue of cardiosurgical patients: a pilot experimental study

Transient episodes of ischemia in a remote organ (remote ischemic preconditioning, RIPC) bears the potential to attenuate myocardial injury, but the underlying mechanisms are only poorly understood. In the pilot experimental study presented we investigated cellular and molecular effects of RIPC in heart tissue of cardiosurgical patients with cardiopulmonary bypass (CPB) and focussed on apoptotic events, local and systemic inflammation as well as the regulation of the hypoxia induced factor-1α (HIF-1α). RIPC was induced by four 5-min cycles of transient upper limb ischemia/reperfusion using a blood-pressure cuff. Right atrial tissue and serum were obtained from patients receiving RIPC (N = 32) and control patients (N = 29) before and after CPB. RIPC patients showed reduced troponin T serum concentrations in the first 48 h after surgery (P < 0.05 vs. control) indicating cardioprotective effects of RIPC. Samples from RIPC patients that were collected before CPB contained significantly increased amounts of HIF-1α and procaspase-3 (HIF-1α: P < 0.05 vs. control, procaspase-3: P < 0.05 vs. control), whereas activities of caspases 3 and 7 were by trend reduced. Samples from RIPC patients that were taken after CPB showed an increased activity of myeloperoxidase (P < 0.05 vs. control; P < 0.05 vs. RIPC before CPB) as well as elevated tissue concentrations of the interleukin (IL)-1β (P < 0.05 vs. RIPC before CPB). Serum levels of IL-8, IL-1β and TNFα were significantly increased in RIPC patients before CPB (P < 0.05 vs. control before CPB). In summary, RIPC regulates HIF-1α levels, apoptosis and inflammation in the myocardium of cardiosurgical patients and leads to increased concentrations of circulating cytokines.

Neurophysiologic responses of peripheral nerve to repeated episodes of anoxia

OBJECTIVE

Determine the effects of serial episodes of anoxia in an in vitro peripheral nerve preparation.

METHODS

The nerve action potential (NAP) from rat sciatic nerve was recorded during 5 cycles of anoxia and reperfusion. Multiple NAP parameters were analyzed as well as stimulus response curves.

RESULTS

The amplitude of the NAP declined to half baseline in 865 s on the first cycle of anoxia and recovered to half baseline during recovery in 470 s. These times increased with successive cycles of anoxia. The current required to produce a half maximal NAP showed a variable initial decrease before increasing with anoxia. The paired-pulse response showed a decline at 2-3 ms interstimulus interval during anoxia but was less dependent of interstimulus interval during recovery. NAP amplitude and velocity decrease over successive cycles of anoxia at a rate greater than in the absence of anoxia.

CONCLUSIONS

The NAP declines slowly when peripheral nerve is exposed to anoxia but returns at least twice as quickly when re-exposed to oxygen. Short periods of anoxia produce long lasting changes in the nerve suggesting greater resistance to anoxia. With serial episodes of anoxia there is gradual NAP amplitude reduction and increase in duration and latency.

SIGNIFICANCE

Anoxic-preconditioning appears in isolated peripheral nerve.