Effects of carnosine supplementation on glucose metabolism: Pilot clinical trial

OBJECTIVE

Carnosine is a naturally present dipeptide in humans and an over-the counter food additive. Evidence from animal studies supports the role for carnosine in the prevention and treatment of diabetes and cardiovascular disease, yet there is limited human data. This study investigated whether carnosine supplementation in individuals with overweight or obesity improves diabetes and cardiovascular risk factors.

METHODS

In a double-blind randomized pilot trial in nondiabetic individuals with overweight and obesity (age 43 ± 8 years; body mass index 31 ± 4 kg/m(2) ), 15 individuals were randomly assigned to 2 g carnosine daily and 15 individuals to placebo for 12 weeks. Insulin sensitivity and secretion, glucose tolerance (oral glucose tolerance test), blood pressure, plasma lipid profile, skeletal muscle ((1) H-MRS), and urinary carnosine levels were measured.

RESULTS

Carnosine concentrations increased in urine after supplementation (P < 0.05). An increase in fasting insulin and insulin resistance was hampered in individuals receiving carnosine compared to placebo, and this remained significant after adjustment for age, sex, and change in body weight (P = 0.02, P = 0.04, respectively). Two-hour glucose and insulin were both lower after carnosine supplementation compared to placebo in individuals with impaired glucose tolerance (P < 0.05).

CONCLUSIONS

These pilot intervention data suggest that carnosine supplementation may be an effective strategy for prevention of type 2 diabetes.

No evidence of ectopic lipid accumulation in the pathophysiology of the acromegalic cardiomyopathy

CONTEXT

PATIENTS with acromegaly frequently display disturbances of glucose and lipid metabolism, which might contribute to their increased cardiovascular risk. Because insulin resistance and increased lipolysis have been linked to ectopic lipid deposition, altered lipid accumulation in the liver and the myocardium might contribute to metabolic and cardiac complications in these patients.

OBJECTIVE

The aim of this study was to investigate myocardial (MYCL) and hepatic lipid content (HCL), insulin sensitivity, and cardiac function in active acromegaly and after control of GH excess through transsphenoidal surgery.

PATIENTS

Ten patients with newly diagnosed acromegaly (ACRO_active) were compared with 12 healthy controls (CON), matched for age, body mass index, and gender. In seven patients GH excess was controlled, and they were compared with their active state.

METHODS

MYCL and HCL were assessed by (1)H-magnetic resonance spectroscopy, pericardial fat and cardiac function by (1)H-magnetic resonance imaging, and insulin sensitivity and secretion by an oral glucose tolerance test.

RESULTS

Although MYCL tended to be lower, HCL was significantly lower in ACRO_active compared with CON (HCL: 1.2% ± 1.2% vs 4.3% ± 3.5% of (1)H-magnetic resonance spectroscopy signal, P < .02). Parameters of systolic function and hypertrophy were significantly increased in ACRO_active compared with CON, as were insulin secretion and resistance. After the control of GH excess, HCL and MYCL remained unchanged, but pericardial fat was increased in the patients in whom GH excess was controlled (from 11.6 ± 5.5 to 14.7 ± 6.2 cm(2), P = .02).

CONCLUSION

Acromegaly represents a unique condition characterized by low myocardial and hepatic lipid content despite decreased insulin sensitivity, hyperinsulinemia, and hyperglycemia. Hence, ectopic lipid accumulation does not appear to contribute to cardiac morbidity, and increased lipid oxidation might counteract ectopic lipid accumulation in GH excess.

Two-dimensional spectroscopic imaging with combined free induction decay and long-TE acquisition (FID echo spectroscopic imaging, FIDESI) for the detection of intramyocellular lipids in calf muscle at 7 T

The aim of this study was to introduce a two-dimensional chemical shift imaging (2D CSI) sequence, with simultaneous acquisition of free induction decay (FID) and long TEs, for the detection and quantification of intramyocellular lipids (IMCLs) in the calf at 7 T. The feasibility of the new 2D CSI sequence, which acquires FID (acquisition delay, 1.3 ms) and an echo (long TE) in one measurement, was evaluated in phantoms and volunteers (n = 5): TR/TE*/TE = 800/1.3/156 ms; 48 × 48 matrix; field of view, 200 × 200 × 20 mm(3) ; Hamming filter; no water suppression; measurement time, 22 min 2 s. The IMCL concentration and subcutaneous lipid contamination were assessed. Spectra in the tibialis anterior (TA), gastrocnemius (GM) and soleus (SOL) muscles were analyzed. The water signal from the FID acquisition was used as an internal concentration reference. In the spectra from subcutaneous adipose tissue (SUB) and bone marrow (BM), an unsaturation index (UI) of the vinyl-H (5.3 ppm) to methyl-CH3 ratio, and a polyunsaturation index (pUI) of the diallylic-H (2.77 ppm) to -CH3 ratio, were calculated. Long-TE spectra from muscles showed a simplified spectral pattern with well-separated IMCL for several muscle groups in the same scan. The IMCL to water ratio was largest in SOL (0.66% ± 0.23%), and lower in GM (0.37% ± 0.14%) and TA (0.36% ± 0.12%). UI and pUI for SUB were 0.65 ± 0.06 and 0.18 ± 0.04, respectively, and for BM were 0.60 ± 0.16 and 0.18 ± 0.08, respectively. The new sequence, with the proposed name 'free induction decay echo spectroscopic imaging' (FIDESI), provides information on both specific lipid resonances and water signal from different tissues in the calf, with high spectral and spatial resolution, as well as minimal voxel bleeding and subcutaneous lipid contamination, in clinically acceptable measurement times.

Time-resolved phosphorous magnetization transfer of the human calf muscle at 3 T and 7 T: a feasibility study

Phosphorous ((31)P) magnetization transfer (MT) experiments enable the non-invasive investigation of human muscle metabolism in various physiological and pathological conditions. The purpose of our study was to investigate the feasibility of time-resolved MT, and to compare the results of MT experiments at 3 T and 7 T. Six healthy volunteers were examined on a 3T and a 7 T MR scanner using the same setup and identical measurement protocols. In the calf muscle of all volunteers, four separate MT experiments (each ∼10 min duration) were performed in one session. The forward rate constant of the ATP synthesis reaction (kATP) and creatine kinase reaction (kCK), as well as corresponding metabolic fluxes (FATP, FCK), were estimated. A comparison of these exchange parameters, apparent T₁s, data quality, quantification precision, and reproducibility was performed. The data quality and reproducibility of the same MT experiments at 7 T was significantly higher (i.e., kATP 2.7 times higher and kCK 3.4 times higher) than at 3 T (p<0.05). The values for kATP (p=0.35) and kCK (p=0.09) at both field strengths were indistinguishable. Even a single MT experiment at 7 T provided better data quality than did a 4 times-longer MT experiment at 3T. The minimal time-resolution to reliably quantify both FATP and FCK at 7 T was ∼6 min. Our results show that MT experiments at 7 T can be at least 4 times faster than 3 T MT experiments and still provide significantly better quantification. This enables time-resolved MT experiments for the observation of slow metabolic changes in the human calf muscle at 7 T.