"Insulin-like" effects of palmitate compromise insulin signalling in hypothalamic neurons

Marine n-3 polyunsaturated fatty acids slow sleep impairment progression by regulating central circadian rhythms in type 2 diabetes

The role of marine n-3 polyunsaturated fatty acids (PUFAs) in promoting sleep has been proposed, yet their benefits for patients with type 2 diabetes (T2D) and the underlying molecular mechanisms remain poorly understood. In this study, we identify a significant association between habitual fish oil use and improved sleep quality in a cohort of 27,549 patients with T2D. A subsequent randomized controlled trial demonstrates that fish oil supplementation enhances sleep parameters in patients with T2D, accompanied by the upregulation of core circadian clock genes, including Clock, Bmal1, and Per2. In vitro, DHA and EPA restore the rhythmic oscillations of key clock genes in hypothalamic neurons disrupted by palmitic acid. Notably, n-3 PUFAs target RORα to regulate circadian clock oscillations and facilitate BMAL1 nuclear translocation. Collectively, our findings highlight the potential of marine n-3 PUFAs as a dietary intervention to improve sleep health in patients with T2D. This study was registered at ClinicalTrials.gov (NCT03708887).

Hypoglycaemic activity of Smilax canellifolia Mill. rhizomes: a bioassay-guided isolation and identification of synergistic compounds

Background

Smilax canellifolia Mill. is a native shrub used in commercial root tonics as an aphrodisiac, stimulant, and pain reliever. Traditional medicine incorporates the rhizomes of S. canellifolia for the treatment of anaemia, rheumatoid arthritis, and diabetes in Jamaica and its diaspora. In particular, the use of this plant in the management of diabetes has yet to receive any scientific evaluation. In this study, the hexane crude extract of S. canellifolia rhizomes (SCH) was investigated to determine its hypoglycaemic activity in normal Sprague-Dawley rats and to identify the compounds contributing to this activity.

Methods

The hypoglycaemic compounds were isolated using bioactivity-guided purification which involved hypoglycaemic screening using an Oral Glucose Tolerance Test (via intravenous administration of SCH and its fractions). Purification was performed using column chromatography, and the bioactive fractions were elucidated using spectroscopic techniques (IR; GC-MS; 1H NMR and 13C NMR).

Results

Administration of SCH at 50 mg/kg body weight (BW) to normal S-D rats produced a reduced glycaemic response, notably from the 90 to the 150-min intervals when compared with the control, dimethyl sulfoxide (p < 0.05). Purification of this extract yielded four main fractions, SCH1 – SCH4, of which SCH3 and SCH4 displayed significant hypoglycaemia. Further purification of both SCH3 and SCH4 led to the isolation of sub-fractions SCH3.6 and SCH4.2, respectively. Using spectroscopic techniques stigmasterol (1) and β-sitosterol (2) from SCH3.6; and the fatty acids palmitic acid (3), oleic acid (4), and stearic acid (5) from SCH4.2 were identified as the major compounds with significant hypoglycaemic activities comparable to that of glibenclamide.

Conclusion

This study demonstrates that the rhizomes of Smilax canellifolia contain several bioactive constituents that are responsible for its hypoglycaemic activity and may be beneficial in the management of hyperglycaemia and complications associated with diabetes.

Interplay of Dietary Fatty Acids and Cholesterol Impacts Brain Mitochondria and Insulin Action

Overconsumption of high-fat and cholesterol-containing diets is detrimental for metabolism and mitochondrial function, causes inflammatory responses and impairs insulin action in peripheral tissues. Dietary fatty acids can enter the brain to mediate the nutritional status, but also to influence neuronal homeostasis. Yet, it is unclear whether cholesterol-containing high-fat diets (HFDs) with different combinations of fatty acids exert metabolic stress and impact mitochondrial function in the brain. To investigate whether cholesterol in combination with different fatty acids impacts neuronal metabolism and mitochondrial function, C57BL/6J mice received different cholesterol-containing diets with either high concentrations of long-chain saturated fatty acids or soybean oil-derived poly-unsaturated fatty acids. In addition, CLU183 neurons were stimulated with combinations of palmitate, linoleic acid and cholesterol to assess their effects on metabolic stress, mitochondrial function and insulin action. The dietary interventions resulted in a molecular signature of metabolic stress in the hypothalamus with decreased expression of occludin and subunits of mitochondrial electron chain complexes, elevated protein carbonylation, as well as c-Jun N-terminal kinase (JNK) activation. Palmitate caused mitochondrial dysfunction, oxidative stress, insulin and insulin-like growth factor-1 (IGF-1) resistance, while cholesterol and linoleic acid did not cause functional alterations. Finally, we defined insulin receptor as a novel negative regulator of metabolically stress-induced JNK activation.

Docosahexaenoic acid prevents palmitate-induced insulin-dependent impairments of neuronal health

The importance of fatty acids (FAs) for healthy brain development and function has become more evident in the past decades. However, most studies focus on the hypothalamus as an important FA-sensing brain region involved in energy homeostasis. Less work has been done to evaluate the effects of FAs on brain regions such as the hippocampus or cortex, two important centres of learning, memory formation, and cognition. Furthermore, the mechanisms of how FAs modulate the neuronal development and function are incompletely understood. Therefore, this study examined the effects of the saturated FA palmitic acid (PA) and the polyunsaturated FA docosahexaenoic acid (DHA) on primary hippocampal and cortical cultures isolated from P0/P1 Sprague Dawley rat pups. Exposure to PA, but not DHA, resulted in severe morphological changes in primary neurons such as cell body swelling, axonal and dendritic blebbing, and a reduction in synaptic innervation, compromising healthy cell function and excitability. Pharmacological assessment revealed that the PA-mediated alterations were caused by overactivation of neuronal insulin signaling, demonstrated by insulin stimulation and phosphoinositide 3-kinase inhibition. Remarkably, co-exposure to DHA prevented all PA-induced morphological changes. This work provides new insights into how FAs can affect the cytoskeletal rearrangements and neuronal function via modulation of insulin signaling.

Nonesterified fatty acids, cognitive decline, and dementia

PURPOSE OF REVIEW

Dementia is rapidly growing as sources of morbidity and mortality as the US population ages, but its pathophysiology remains poorly understood. As a result, no disease-modifying treatments currently exist. We review the evidence that nonesterified fatty acids may play a key role in this condition.

RECENT FINDINGS

Nonesterified fatty acids appear to influence several pathways leading to dementia. In addition to their vascular effects, these moieties cross the blood-brain barrier, where they are toxic to several cell types. They may also influence insulin metabolism in the brain directly and indirectly, and some drugs that lower circulating levels appear to slow cognitive decline and brain atrophy in diabetes.

SUMMARY

Nonesterified fatty acids may contribute to dementia, much as they do to diabetes and cardiovascular disease. Several therapeutic agents lower circulating levels of nonesterified fatty acids and should be tested for their potential preventive effects on cognitive decline in healthy populations before irreversible neuronal attrition occurs.

Maternal Obesity during Pregnancy Alters Daily Activity and Feeding Cycles, and Hypothalamic Clock Gene Expression in Adult Male Mouse Offspring

An obesogenic diet adversely affects the endogenous mammalian circadian clock, altering daily activity and metabolism, and resulting in obesity. We investigated whether an obese pregnancy can alter the molecular clock in the offspring hypothalamus, resulting in changes to their activity and feeding rhythms. Female mice were fed a control (C, 7% kcal fat) or high fat diet (HF, 45% kcal fat) before mating and throughout pregnancy. Male offspring were fed the C or HF diet postweaning, resulting in four offspring groups: C/C, C/HF, HF/C, and HF/HF. Daily activity and food intake were monitored, and at 15 weeks of age were killed at six time-points over 24 h. The clock genes Clock, Bmal1, Per2, and Cry2 in the suprachiasmatic nucleus (SCN) and appetite genes Npy and Pomc in the arcuate nucleus (ARC) were measured. Daily activity and feeding cycles in the HF/C, C/HF, and HF/HF offspring were altered, with increased feeding bouts and activity during the day and increased food intake but reduced activity at night. Gene expression patterns and levels of Clock, Bmal1, Per2, and Cry2 in the SCN and Npy and Pomc in the ARC were altered in HF diet-exposed offspring. The altered expression of hypothalamic molecular clock components and appetite genes, together with changes in activity and feeding rhythms, could be contributing to offspring obesity.