Evidence against the involvement of the nucleus tractus solitarii in the sympatholytic effect of 8-hydroxy-2-(di-n-propylamino)tetralin in the cat

Reaffirmation of Mechanistic Proteomic Signatures Accompanying SGLT2 Inhibition in Patients With Heart Failure: A Validation Cohort of the EMPEROR Program

BACKGROUND

Sodium-glucose cotransporter 2 (SGLT2) inhibitors exert a distinctive pattern of direct biological effects on the heart and kidney under experimental conditions, but the meaningfulness of these signatures for patients with heart failure has not been fully defined.

OBJECTIVES

We performed the first mechanistic validation study of large-scale proteomics in a double-blind randomized trial of any treatment in patients with heart failure.

METHODS

In a discovery cohort from the EMPEROR (Empagliflozin Outcome Trial in Patients With Chronic Heart Failure and Reduced Ejection Fraction) program, we studied the effect of randomized treatment with placebo or empagliflozin on 1,283 circulating proteins in 1,134 patients with heart failure with a reduced or preserved ejection fraction. In a validation cohort, we expanded the number to 2,155 assessed proteins, which were measured in 1,120 EMPEROR participants who had not been studied previously.

RESULTS

In the validation cohort, 25 proteins were the most differentially enriched by empagliflozin (ie, ≥15% between-group difference and false discovery rate <1% at 12 weeks with known effects on the heart or kidney): 1) 13 proteins promote autophagy and other cellular quality-control functions (IGFBP1, OTUB1, DNAJB1, DNAJC9, RBP2, IST1, HSPA8, H-FABP, FABP6, ATPIFI, TfR1, EPO, IGBP1); 2) 12 proteins enhance mitochondrial health and ATP production (UMtCK, TBCA, L-FABP, H-FABP, FABP5, FABP6, RBP2, IST1, HSPA8, ATPIFI, TfR1, EPO); 3) 7 proteins augment cellular iron mobilization or erythropoiesis (TfR1, EPO, IGBP1, ERMAP, UROD, ATPIF1, SNCA); 4) 3 proteins influence renal tubular sodium handling; and 5) 9 proteins have restorative effects in the heart or kidneys, with many proteins exerting effects in >1 domain. These biological signatures replicated those observed in our discovery cohort. When the threshold for a meaningful between-group difference was lowered to ≥10%, there were 58 additional differentially enriched proteins with actions on the heart and kidney, but the biological signatures remained the same.

CONCLUSIONS

The replication of mechanistic signatures across discovery and validation cohorts closely aligns with the experimental effects of SGLT2 inhibitors. Thus, the actions of SGLT2 inhibitors-to promote autophagy, restore mitochondrial health and production of ATP, promote iron mobilization and erythropoiesis, influence renal tubular ion reabsorption, and normalize cardiac and renal structure and function-are likely to be relevant to patients with heart failure. (EMPagliflozin outcomE tRial in Patients With chrOnic heaRt Failure With Preserved Ejection Fraction [EMPEROR-Preserved], NCT03057951; EMPagliflozin outcomE tRial in Patients With chrOnic heaRt Failure With Reduced Ejection Fraction [EMPEROR-Reduced], NCT03057977).

Systemic 8-OH-DPAT challenge causes hyperventilation largely via activating pre-botzinger complex 5-HT1A receptors

Systemic 8-OH-DPAT (a 5-HT_1A receptor agonist) challenge evokes hyperventilation independent of peripheral 5-HT_1A receptors. Though the pre-Botzinger Complex (PBC) is critical in generating respiratory rhythm and activation of local 5-HT_1A receptors induces tachypnea via disinhibition of local GABA_A neurons, its role in the respiratory response to systemic 8-OH-DPAT challenge is still unclear. In anesthetized rats, 8-OH-DPAT (100 μg/kg, iv) was injected twice to confirm the reproducibility of the evoked responses. The same challenges were performed after bilateral microinjections of (S)-WAY-100135 (a 5-HT_1A receptor antagonist) or gabazine (a GABA_A receptor antagonist) into the PBC. Our results showed that: 1) 8-OH-DPAT caused reproducible hyperventilation associated with hypotension and bradycardia; 2) microinjections of (S)-WAY-100135 into the PBC attenuated the hyperventilation by ˜60 % without effect on the evoked hypotension and bradycardia; and 3) the same hyperventilatory attenuation was also observed after microinjections of gabazine into the PBC. Our data suggest that PBC 5-HT_1A receptors play a key role in the respiratory response to systemic 8-OH-DPAT challenge likely via disinhibiting local GABAergic neurons.

Effects of medullary alpha2-adrenoceptor blockade in the rat

The effect of alpha2-adrenoceptor blockade in the medulla was studied in pentobarbital anesthetized rats in which arterial blood pressure, heart rate and renal sympathetic nerve activity were analysed. Three series of experiments were performed: (1) i.c. administration of alpha2-adrenoceptor antagonists with different subtype affinities; (2) i.v. administration of methoxy-idazoxan to study its effects on neuronal activity into the rostral ventral medulla; (3) microinjections of methoxy-idazoxan in rostral ventral medulla and nucleus tractus solitarii. Methoxy-idazoxan (0.1-3 microg x kg(-1) i.c., n=5), but not saline, rauwolscine, BRL 44408 (2-[2H-(1,3,dihydroisoindol)methyl]-4,5dihydroimidazol) or ARC 239 (2-[2-(4-(2-methoxyphenyl)piperazin-1-yl)ethyl]-4,4-dimethyl-1,3-(2H,4H)-isoquilindione) (each at 10-100 microg x kg(-1) i.c., n=5-5-6-5, respectively), increased mean arterial blood pressure, heart rate and renal nerve activity (+19+/-6 mm Hg, +72+/-22 beats x min(-1), +43+/-9%) and blocked the sympatho-inhibitory action of clonidine (10 microg x kg(-1) i.v.). In further experiments, methoxy-idazoxan, BRL 44408 and the highest dose of rauwolscine i.c., reversed the clonidine-induced sympatho-inhibition (order of potency: methoxy-idazoxan>BRL4440>rauwolscine, n=6 each), whereas ARC 239 (n=5) or saline (n=7) did not. Methoxy-idazoxan i.v. (n=7, 10-100 microg x kg(-1)) increased the renal sympathetic nerve and rostral ventral medulla neuronal activity and the heart rate (+36+/-7%, +66+/-29% and +18+/-9 beats x min(-1)) without a significant effect on mean arterial blood pressure. Microinjection of methoxy-idazoxan (1 nmol/40 nl) into the rostral ventral medulla reversed the effect of clonidine microinjected into the same site (2 nmol/40 nl, n=5). In another group of rats (n=8), methoxy-idazoxan increased mean arterial blood pressure, heart rate and renal nerve activity (+16+/-2 mm Hg, +42+/-7 beats x min(-1), +24+/-5%) and blocked the effect of clonidine i.v. (10 microg x kg(-1)). Bilateral microinjections into the nucleus tractus solitarii (n=5) did not alter mean arterial blood pressure but decreased heart rate and sympathetic nerve activity (-30+/-16 beats x min(-1), -20+/-14%). Our results offer direct in vivo evidence for the main role of the alpha2A/D-adrenoceptors located in the ventral pressor area. The data show that the sympathy-excitatory effect of alpha2-adrenoceptor antagonists is due to the blockade of a tonic activation of these alpha2A/D-adrenoceptors present in the rostral ventral pressor area.

Central integration of the Bezold-Jarish reflex in the cat

The medullary structures involved in the central Bezold-Jarisch reflex pathway were studied by recording unit activity of sympatho-excitatory (SE) or inhibitory (SI) cardiovascular neurons in pentobarbital-anesthetized cats. The neurons were selected based upon their spontaneous activity and upon their sensitivity to baroreceptor reflex activation by L-phenylephrine. The Bezold-Jarisch reflex was induced by i.v. injection of chlorophenylbiguanide 10 micrograms/kg which produced a short-lasting decrease in blood pressure, heart rate and renal nerve activity. 76 neurons were studied. In 10 out of 12 SE neurons of the rostral ventrolateral medulla the activity was inhibited by chlorophenylbiguanide whereas in 10 out of 11 SI neurons and 6 out of 6 baroreflex-insensitive cells of the caudal ventrolateral medulla it was activated. The others cells were insensitive. Three types of neurons: excitatory, inhibitory or non-barosensitive, were recorded in the lateral tegmental field (27 cells) and the medullary raphe (20 cells). These neurons were either activated, inhibited or insensitive to Bezold-Jarisch reflex activation. Microinjection of the glutamate receptor antagonist kynurenic acid (2.5 nmol/site) or the GABAergic agonist muscimol (1 nmol/site) into the nucleus tractus solitarii abolished the effects of both L-phenylephrine and chlorophenyl-biguanide on heart rate and renal nerve activity. These results indicate that the cardiovascular neurons (sympatho-excitatory and sympatho-inhibitory) located in the medullary areas, involved in cardiovascular and baroreflex mechanisms, are implicated in the central Bezold-Jarish reflex pathway.