Cardiac function, substrate utilization, and myocardial energy metabolism studied with 31-P NMR spectroscopy during acute hypoglycemia and hyperketonemia

Anti-remodeling and anti-fibrotic effects of the neuregulin-1β glial growth factor 2 in a large animal model of heart failure

BACKGROUND

Neuregulin-1β (NRG-1β) is a growth factor critical for cardiac development and repair with therapeutic potential for heart failure. We previously showed that the glial growth factor 2 (GGF2) isoform of NRG-1β improves cardiac function in rodents after myocardial infarction (MI), but its efficacy in a large animal model of cardiac injury has not been examined. We therefore sought to examine the effects of GGF2 on ventricular remodeling, cardiac function, and global transcription in post-MI swine, as well as potential mechanisms for anti-remodeling effects.

METHODS AND RESULTS

MI was induced in anesthetized swine (n=23) by intracoronary balloon occlusion. At 1 week post-MI, survivors (n=13) received GGF2 treatment (intravenous, biweekly for 4 weeks; n=8) or were untreated (n=5). At 5 weeks post-MI, fractional shortening was higher (32.8% versus 25.3%, P=0.019), and left ventricular (LV) end-diastolic dimension lower (4.5 versus 5.3 cm, P=0.003) in GGF2-treated animals. Treatment altered expression of 528 genes, as measured by microarrays, including collagens, basal lamina components, and matricellular proteins. GGF2-treated pigs exhibited improvements in LV cardiomyocyte mitochondria and intercalated disk structures and showed less fibrosis, altered matrix structure, and fewer myofibroblasts (myoFbs), based on trichrome staining, electron microscopy, and immunostaining. In vitro experiments with isolated murine and rat cardiac fibroblasts demonstrate that NRG-1β reduces myoFbs, and suppresses TGFβ-induced phospho-SMAD3 as well as αSMA expression.

CONCLUSIONS

These results suggest that GGF2/NRG-1β prevents adverse remodeling after injury in part via anti-fibrotic effects in the heart.

Duration and severity of hypoglycemia needed to induce neuropathy

The duration and severity of hypoglycemia needed to induce neuropathy is not known. To test these variables, the percentage of teased fibers of peroneal and tibial nerves showing graded pathologic abnormalities was estimated in groups of rats that had been made hypoglycemic for various times and severities one week earlier. The techniques used maintained core temperature, pO2, pCO2, and hematocrit within physiologic limits. A control group was anesthetized and mechanically ventilated but insulin was not given. A second control group underwent no experimental manipulation. Life could not be sustained with hypoglycemia below 1 mmol/l. In 23 rats that were hypoglycemic (1.4 +/- 0.2 mmol/l, mean +/- S.E.M.) for various times less than 11 h, the frequency of axonal degeneration of teased myelinated fibers (0%-1%) was not different than in controls. In 9 young rats that were hypoglycemic (1.4 +/- 0.0 mmol/l) for various times of 12 or more hours, the frequency of fiber degeneration was significantly higher than in controls (P less than 0.01) and increased to as high as 26%. By contrast, in 5 older rats that were hypoglycemic (1.5 +/- 0.1 mmol/l) for various times of 12 or more hours, the frequency of degeneration was not different from that of controls. Both duration and severity of hypoglycemia are risk factors for fiber degeneration. The peripheral nerves are more vulnerable to prolonged severe hypoglycemia in younger rats than in older rats.