Calcitonin gene-related peptide-mediated ischemic preconditioning in the rat heart: influence of age

Influence of strain, age, origin, and anesthesia on the cardioprotective efficacy by local and remote ischemic conditioning in an ex vivo rat model

Background

Local ischemic preconditioning (IPC) and remote ischemic conditioning (RIC) induced by brief periods of ischemia and reperfusion protect against ischemia‐reperfusion injury.

Methods

We studied the sensitivity to IR‐injury and the influence of strain, age, supplier, and anesthesia upon the efficacy of IPC and RIC in 7‐ and 16‐weeks‐old Sprague‐Dawley and Wistar rats from three different suppliers. The influence of sedation with a hypnorm and midazolam mixture (rodent mixture) and pentobarbiturate was compared.

Results

IPC attenuated infarct size in both 7‐weeks‐old Sprague–Dawley (48.4 ± 17.7% vs. 20.3 ± 6.9, p < 0.001) and 7‐weeks‐old Wistar (55.6 ± 10.9% vs. 26.8 ± 5.0%, p < 0.001) rats. Infarct size was larger in 16‐weeks‐old Sprague–Dawley rats, however, IPC still lowered infarct size (78.8 ± 9.2% vs. 58.3 ± 12.3%, p < 0.01). RIC reduced infarct sizes in 7‐weeks‐old Sprague–Dawley (75.3 ± 11.8% vs. 58.6 ± 8.9%, p < 0.05), but not in 7‐weeks‐old Wistar rats (31.7 ± 17.6% and 24.0 ± 12.6%, p = 0.2). In 16‐weeks‐old Sprague–Dawley rats, RIC did not induce protection (76.4 ± 5.5% and 73.2 ± 14.7%, p = 0.6). However, RIC induced protection in 16‐weeks‐old Wistar rats (45.2 ± 8.5% vs. 14.7 ± 10.8%, p < 0.001). RIC did not reduce infarct size in 7‐weeks‐old Sprague–Dawley rats from Charles River (62.0 ± 13.5% and 69.4 ± 10.4% p = 0.3) or 16‐weeks‐old Wistar rats from Janvier (50.7 ± 11.3 and 49.2 ± 16.2, p = 0.8). There was no difference between sedation with rodent mixture or pentobarbiturate.

Conclusion

The cardioprotective effect of IPC is consistent across rat strains independent of age, strain, and supplier. RIC seems to be less reproducible, but still yields protection across different rat strains. However, age, animal supplier, and anesthetics may modulate the sensitivity of IR‐injury and the response to RIC.

Myocardial susceptibility to ischaemia/reperfusion in obesity: a re-evaluation of the effects of age

Background

Reports on the effect of age and obesity on myocardial ischaemia/reperfusion (I/R) injury and ischaemic preconditioning are contradictory. The aim of this study was to re-evaluate the effects of age and diet-induced obesity (DIO) on myocardial I/R injury and preconditioning potential.

Methods

Four groups of Wistar male rats were used: age-matched controls (AMC) receiving standard rat chow for (i) 16 weeks and (ii) 16 months respectively; DIO rats receiving a sucrose-supplemented diet for (iii) 16 weeks and (iv) 16 months respectively. The ages of groups (i) and (iii) were 22 weeks (“young”) and groups (ii) and (iv) 17 months (“middle-aged”) at time of experimentation. Isolated perfused working hearts were subjected to 35 min regional ischaemia/1 h reperfusion. Endpoints were infarct size (tetrazolium staining) and functional recovery. Hearts were preconditioned by 3 × 5 min ischaemia/5 min reperfusion. Results were processed using GraphPad Prism statistical software.

Results

Age did not affect baseline heart function before induction of ischaemia and I/R damage as indicated by infarct size and similar values were obtained in hearts from both age groups. Age also had no effect on functional recovery of hearts during reperfusion after regional ischaemia in AMC rats, but cardiac output during reperfusion was better in hearts from middle-aged than young DIO rats.

The diet reduced infarct size in hearts from young rats (% of area at risk: AMC: 32.4 ± 3.6; DIO: 20.7 ± 2.9, p < 0.05), with no differences in hearts from middle-aged rats (AMC: 24.6 ± 4.6; DIO: 28.3 ± 13.5, p = NS). Compared to their respective AMC, diet-induced obesity had no significant effect on functional recovery of hearts from both age groups after exposure to regional ischaemia.

When exposed to the more severe stress of global ischaemia, the functional recovery potential of middle-aged DIO rats appeared to be impeded compared to hearts of young DIO rats, while age had no effect on the functional recovery of AMC hearts.

Preconditioning reduced infarct size in hearts from young control rats and both middle-aged groups, but not from young DIO rats. Age had a significant effect on functional recovery in preconditioning: it was improved in hearts from young control and DIO rats, but depressed in both middle-aged groups.

Conclusions

The data showed that middle-age and obesity had no effect on baseline myocardial function and did not increase susceptibility to I/R damage upon exposure to regional ischaemia. On the contrary, obesity reduced I/R damage in young rats. Preconditioned aging hearts showed a decreased infarct size, but a reduction in functional recovery.

What is hormesis and its relevance to healthy aging and longevity?

This paper provides a broad overview of hormesis, a specific type of biphasic dose response, its historical and scientific foundations as well as its biomedical applications, especially with respect to aging. Hormesis is a fundamental component of adaptability, neutralizing many endogenous and environmental challenges by toxic agents, thereby enhancing survival. Hormesis is highly conserved, broadly generalizable, and pleiotrophic, being independent of biological model, endpoint measured, inducing agent, level of biological organization and mechanism. The low dose stimulatory hormetic response has specific characteristics which defines both the quantitative features of biological plasticity and the potential for maximum biological performance, thereby estimating the limits to which numerous medical and pharmacological interventions may affect humans. The substantial degrading of some hormetic processes in the aged may profoundly reduce the capacity to respond effectively to numerous environmental/ischemic and other stressors leading to compromised health, disease and, ultimately, defining the bounds of longevity.

Calcitonin gene-related peptide: physiology and pathophysiology

Calcitonin gene-related peptide (CGRP) is a 37-amino acid neuropeptide. Discovered 30 years ago, it is produced as a consequence of alternative RNA processing of the calcitonin gene. CGRP has two major forms (α and β). It belongs to a group of peptides that all act on an unusual receptor family. These receptors consist of calcitonin receptor-like receptor (CLR) linked to an essential receptor activity modifying protein (RAMP) that is necessary for full functionality. CGRP is a highly potent vasodilator and, partly as a consequence, possesses protective mechanisms that are important for physiological and pathological conditions involving the cardiovascular system and wound healing. CGRP is primarily released from sensory nerves and thus is implicated in pain pathways. The proven ability of CGRP antagonists to alleviate migraine has been of most interest in terms of drug development, and knowledge to date concerning this potential therapeutic area is discussed. Other areas covered, where there is less information known on CGRP, include arthritis, skin conditions, diabetes, and obesity. It is concluded that CGRP is an important peptide in mammalian biology, but it is too early at present to know if new medicines for disease treatment will emerge from our knowledge concerning this molecule.

Age-related differences in cardiac ischemia-reperfusion injury: effects of estrogen deficiency

Despite conflicting evidence for the efficacy of hormone replacement therapy in cardioprotection of postmenopausal women, numerous studies have demonstrated reductions in ischemia/reperfusion (I/R) injury following chronic or acute exogenous estradiol (E2) administration in adult male and female, gonad-intact and gonadectomized animals. It has become clear that ovariectomized adult animals may not accurately represent the combined effects of age and E2 deficiency on reductions in ischemic tolerance seen in the postmenopausal female. E2 is known to regulate the transcription of several cardioprotective genes. Acute, non-genomic E2 signaling can also activate many of the same signaling pathways recruited in cardioprotection. Alterations in cardioprotective gene expression or cardioprotective signal transduction are therefore likely to result within the context of aging and E2 deficiency and may help explain the reduced ischemic tolerance and loss of cardioprotection in the senescent female heart. Quantification of the mitochondrial proteome as it adapts to advancing age and E2 deficiency may also represent a key experimental approach to uncover proteins associated with disruptions in cardiac signaling contributing to age-associated declines in ischemic tolerance. These alterations have important ramifications for understanding the increased morbidity and mortality due to ischemic cardiovascular disease seen in postmenopausal females. Functional perturbations that occur in mitochondrial respiration and Ca(2+) sensitivity with age-associated E2 deficiency may also allow for the identification of alternative therapeutic targets for reducing I/R injury and treatment of the leading cause of death in postmenopausal women.

Ischemic preconditioning in the aging heart: from bench to bedside

Coronary artery disease is the leading cause of death in industrialized countries for people older than 65 years of age. The reasons are still unclear. A reduction of endogenous mechanisms against ischemic insults has been proposed to explain this phenomenon. Cardiac ischemic preconditioning represents the most powerful endogenous protective mechanism against ischemia. Brief episodes of ischemia are able to protect the heart against a following more prolonged ischemic period. This protective mechanism seems to be reduced with aging both in experimental and clinical studies. Alterations of mediators release and/or intracellular pathways may be responsible for age-related ischemic preconditioning reduction. Opposite studies are questionable for the experimental model used, the timing of ischemic preconditioning, and the selection of elderly patients. Several pharmacological stimuli failed to mimic ischemic preconditioning in the aging heart but exercise training and caloric restriction separately, and more powerfully taken together, are able to completely preserve and/or restore the age-related reduction of ischemic preconditioning.

Clinical cardioprotection and the value of conditioning responses

Adjunctive cardioprotective strategies for ameliorating the reversible and irreversible injuries with ischemia-reperfusion (I/R) are highly desirable. However, after decades of research, the promise of clinical cardioprotection from I/R injury remains poorly realized. This may arise from the challenges of trialing and effectively translating experimental findings from laboratory models to patients. One can additionally consider whether features of the more heavily focused upon candidates could limit or preclude therapeutic utility and thus whether we might shift attention to alternate strategies. The phenomena of preconditioning and postconditioning have proven fertile in identification of experimental means of cardioprotection and are the most intensely interrogated responses in the field. However, there is evidence these processes, which share common molecular signaling elements and end effectors, may be poor choices for clinical exploitation. This includes evidence of age dependence, limiting efficacy in target aged or senescent hearts; refractoriness to conditioning stimuli in diseased myocardium; interference from a variety of relevant pharmaceuticals; inadvertent induction of these responses by prior ischemia or commonly used drugs, precluding further benefit; and sex dependence of protective signaling. This review focuses on these features, raising questions about current research strategies, and the suitability of these widely studied phenomena as rational candidates for clinical translation.

TRPV1 Gene Knockout Impairs Postischemic Recovery in Isolated Perfused Heart in Mice

BACKGROUND

Although pharmacological studies suggest that the transient receptor potential vanilloid type 1 (TRPV1) channels expressed in sensory nerve fibers innervating the heart may exert a cardioprotective effect, definitive evidence supporting such a notion is lacking. In addition, function and regulation of sensory neuropeptides, namely, calcitonin gene-related peptide (CGRP) and substance P (SP), in the face of challenges induced by cardiac injury in the presence or absence of the TRPV1 are largely unknown.

METHODS AND RESULTS

The hearts of gene-targeted TRPV1-null mutant (TRPV1(-/-)) mice or wild-type (WT) mice were perfused in a Langendorff apparatus in the presence or absence of capsazepine (a TRPV1 receptor antagonist), CGRP, CGRP(8-37) (a CGRP receptor antagonist), SP, or RP67580 (a neurokinin-1 [NK1] receptor antagonist) when hearts were subjected to 40 minutes of ischemia and 30 minutes of reperfusion. Hemodynamic alterations and SP release measured by radioimmunoassay were assessed before and after ischemia/reperfusion injury of the heart. Expression of the NK1 receptor in the hearts of TRPV1(-/-) and WT mice were determined with the use of Western blot analyses. Impairment of postischemic recovery, defined by increased left ventricular end-diastolic pressure (LVEDP) and decreased left ventricular developed pressure (LVDP) and coronary flow (CF), was more severe in TRPV1(-/-) hearts than in WT hearts. Although it had no effect on postischemic recovery of TRPV1(-/-) hearts, blockade of the TRPV1 with capsazepine caused a most severe impairment of postischemic recovery in WT hearts compared with untreated WT and TRPV1(-/-) hearts. Exogenous CGRP and SP produced a significant improvement in postischemic recovery in both TRPV1(-/-) and WT hearts, and the maximal functional improvement in TRPV1(-/-) hearts was not different from that of WT hearts except that SP-induced increases in LVDP were larger in the former than in the latter. Blockade of the NK1 receptor with RP67580, but not blockade of the CGRP receptor with CGRP(8-37), caused more severe impairment in postischemic recovery in both TRPV1(-/-) and WT hearts than in untreated hearts in both genotypes. The release of SP after ischemia/reperfusion injury was increased in both WT and TRPV1(-/-) hearts, albeit with a smaller magnitude of the increase in the latter. Capsazepine attenuated injury-induced SP release in WT but not TRPV1(-/-) hearts. There was no difference in the expression of the NK1 receptor between the 2 genotype hearts.

CONCLUSIONS

Thus, our data show that (1) TRPV1 gene deletion decreases injury-induced SP release and impairs cardiac recovery function after ischemia/reperfusion injury; (2) TRPV1 gene deletion leads to reconditioning of the heart with improved postischemic recovery compared with that induced by acute TRPV1 blockade and in terms of cardiac response to exogenous SP; and (3) blockade of the NK1 but not CGRP receptors worsens postischemic recovery of hearts in both genotypes. Taken together, these data indicate that TRPV1 plays a role in protecting the heart from injury possibly via increasing SP release and that deletion of this receptor reconditions the heart for escaping, at least in part, from injury possibly via enhancing NK1 receptor function.

Effect of estrogen replacement treatment on ischemic preconditioning in isolated rat hearts

In the present study, we tested the effects of long-term estrogen replacement treatment on myocardial ischemia-reperfusion injury and on the cardioprotection of ischemic preconditioning in isolated hearts from ovariectomized rats. Ovariectomized rats were treated with 17β-estradiol (30 µg/kg/d, s.c.) for 12 weeks. Isolated rat hearts were perfused in the Langendorff mode. Heart rate, coronary flow, left ventricular pressure and its first derivative (±LVdp/dtmax) were recorded. Fifteen-min global ischemia and 30-min reperfusion caused a significant decrease of cardiac mechanical function, which were not affected by ovariectomy or estrogen replacement treatment. The isolated hearts in all groups could be preconditioned, and the cardioprotection afforded by preconditioning in the sham-operated rats was greater compared with ovariectomized rats with or without estrogen treatment. These results suggest that long-term estrogen replacement treatment exerts no effect on the inhibition of mechanical function after ischemia-reperfusion, and this study also suggests that estrogen does not affect ischemic preconditioning in isolated hearts of ovariectomized rats.Key words: ERT (estrogen replacement treatment), ischemia-reperfusion, ischemic preconditioning, heart, rat.

Exercise improves postischemic function in aging hearts

Exercise improves cardioprotection against ischemia-reperfusion in young animals but has not been investigated in older animals, which represent the population most likely to suffer an ischemic event. Therefore, we sought to determine the effects of aging on exercise-induced cardioprotection. Young, middle-aged, and old (4, 12, and 21 mo old) male Fischer 344 rats ran 60 min at 70-75% of maximum oxygen consumption. Twenty-four hours postexercise, isolated perfused working hearts underwent 22.5 min of global ischemia and then 30 min of recovery (reperfusion). Compared with sedentary rats (n = 8-9 rats/group), recovery of function (cardiac output x systolic pressure) improved after exercise (n = 9 rats/group) by 40% at 4 mo, 78% at 12 mo, and 59% at 21 mo. Exercise increased inducible heat shock protein 70 expression 105% at 4 mo but only 27% at 12 mo and 24% at 21 mo. Catalase activity progressively increased with age (P < 0.05) and was increased by exercise at 4 mo (26%) and 21 mo (19%). Manganese superoxide dismutase activity was increased by exercise only at 21 mo (45%). No exercise-related change in any antioxidant enzyme was observed at 12 mo. We conclude that exercise can enhance cardioprotection regardless of age, but the cardioprotective protein phenotype changes with age.

Different effects of acute clenbuterol on vasomotor response in mesenteric arteries from young and old spontaneously hypertensive rats

We analysed the influence of aging on the acute effect of clenbuterol, a beta(2)-adrenoceptor agonist, on the vasoconstrictor response induced by electrical field stimulation in mesenteric arteries from young and old spontaneously hypertensive rats (SHRs). Clenbuterol increased the contraction elicited by electrical field stimulation in arteries from both groups, and this was prevented by propranolol. N(G)-nitro-L-arginine methyl ester (L-NAME) also increased the electrical field stimulation-elicited contractions in arteries from both age groups. However, pretreatment with capsaicin increased the electrical field stimulation-induced contractions in young SHRs, but did not modify it in old SHRs. In segments from young SHRs, the treatment with the calcitonin gene-related peptide (CGRP) receptor antagonist, CGRP-(8-37), induced an increase in the electrical field stimulation-induced vasoconstrictor response that was not modified by the subsequent addition of capsaicin. Addition of clenbuterol to L-NAME-treated segments from both groups further increased the response to electrical field stimulation. In segments from young SHRs, clenbuterol failed to increase the electrical field stimulation-induced response in the capsaicin-treated segments, but the response was increased by the subsequent addition of L-NAME. The addition of L-NAME to the clenbuterol-treated segments from old SHRs did not modify the enhanced electrical field stimulation response. Electrical field stimulation induced a similar tritium release in arteries from young and old SHRs preincubated with [3H]noradrenaline. In arteries from young SHRs, isoproterenol increased this release and the increase was abolished by propranolol. Clenbuterol increased the stimulated tritium overflow and exogenous noradrenaline response only in segments from old SHRs, and both effects were abolished by propranolol. To summarize and conclude, clenbuterol increased the electrical field stimulation-induced contraction in segments from both age groups. In young SHRs, clenbuterol seems to inhibit CGRP release, while in old SHRs, it increases the release of and response to noradrenaline and decreases neuronal nitric oxide (NO) release.

Effect of age on alpha-calcitonin gene-related peptide-mediated delayed cardioprotection induced by intestinal preconditioning in rats

In the present study, we examined whether age-related reduction in cardioprotection of intestinal ischemic preconditioning is related to stimulation of the release and synthesis of calcitonin gene-related peptide (CGRP) in rats. Ischemia-reperfusion injury was induced by a 45-min coronary artery occlusion and 180-min reperfusion, and ischemic preconditioning was induced by six cycles of 4-min ischemia and 4-min reperfusion of the small intestine. The serum concentration of creatine kinase, infarct size, the expression of CGRP isoforms (alpha- and beta-CGRP) mRNA in lumbar dorsal root ganglia and CGRP concentration in plasma were measured. Pretreatment with intestinal ischemic preconditioning for 24 h significantly reduced infarct size and creatine kinase release concomitantly with a significant increase in the expression of alpha-CGRP mRNA, but not beta-CGRP mRNA, and plasma concentrations of CGRP at 6 months of age but not at 24 months of age. These results suggest that the delayed cardioprotective effect of intestinal ischemic preconditioning is decreased in senescent rats, and the age-related change is related to reduction of the synthesis and release of alpha-CGRP.

Cardioprotective effect of ischemic preconditioning is preserved in food-restricted senescent rats

Ischemic preconditioning (PC) has been proposed as an endogenous form of protection against-ischemia reperfusion injury. We have shown that PC does not prevent postischemic dysfunction in the aging heart. This phenomenon could be due to the reduction of cardiac norepinephrine release, and it has also been previously demonstrated that age-related decrease of norepinephrine release from cardiac adrenergic nerves may be restored by caloric restriction. We investigated the effects on mechanical parameters of PC against 20 min of global ischemia followed by 40 min of reperfusion in isolated hearts from adult (6 mo) and "ad libitum"-fed and food-restricted senescent (24 mo) rats. Norepinephrine release in coronary effluent was determined by high-performance liquid chromatography. Final recovery of percent developed pressure was significantly improved after PC in adult hearts versus unconditioned controls (85.2 +/- 19% vs. 51.5 +/- 10%, P < 0.01). The effect of PC on developed pressure recovery was absent in ad libitum-fed rats, but it was restored in food-restricted senescent hearts (66.6 +/- 13% vs. 38.3 +/- 11%, P < 0.05). Accordingly, norepinephrine release significantly increased after PC in both adult and in food-restricted senescent hearts, and depletion of myocardial norepinephrine stores by reserpine abolished the PC effect in both adult and in food-restricted senescent hearts. We conclude that PC reduces postischemic dysfunction in the hearts from adult and food-restricted but not in ad libitum-fed senescent rats. Despite the possibility of multiple age-related mechanisms, the protection afforded by PC was correlated with increased norepinephrine release, and it was blocked by reserpine in both adult and food-restricted senescent hearts. Thus caloric restriction may restore PC in the aging heart probably via increased norepinephrine release.