Exenatide administration time determines the effects on blood pressure dipping in db/db mice via modulation of food intake and sympathetic activity.

Type 2 diabetics have an increased prevalence of hypertension and nondipping blood pressure (BP), which worsen cardiovascular outcomes. Exenatide, a short acting glucagon-like peptide-1 receptor agonist (GLP-1RA) used to treat type 2 diabetes, also demonstrates blood pressure (BP)-lowering effects. However, the mechanisms behind this and the impact of administration timing on BP dipping remain unclear. We investigated the effects of exenatide intraperitoneal injected at light onset (ZT0) or dark onset (ZT12) in diabetic (db/db) mice and nondiabetic controls. Using radio-telemetry and BioDAQ cages, we continuously monitored BP and food intake. Db/db mice exhibited non-dipping BP and increased food intake. ZT0 exenatide administration restored BP dipping by specifically lowering light-phase BP, while ZT12 exenatide reversed dipping by lowering dark-phase BP. These effects correlated with altered food intake patterns, and importantly, were abolished when food access was removed. Additionally, urinary norepinephrine excretion, measured by HPLC, was significantly reduced 6 hours post-exenatide at both ZT0 and ZT12, suggesting sympathetic nervous system involvement. Notably, combining exenatide with either ganglionic blocker mecamylamine or α-blocker prazosin did not enhance BP reduction beyond the individual effects of each blocker. These findings reveal that exenatide, when administered at light onset, restores BP dipping in db/db mice by suppressing light-phase food intake and sympathetic activity. Importantly, the efficacy of exenatide is dependent on food availability and its timing relative to circadian rhythms, highlighting the potential for chronotherapy in optimizing GLP-1RA- based treatments for type 2 diabetes and hypertension. Article Highlights: Maintaining a normal blood pressure (BP) circadian rhythm is vital for cardiovascular health, but diabetes often disrupts this rhythm. The effect of exenatide, a GLP-1 receptor agonist (GLP-1RA), on BP rhythm in diabetes is uncertain.This study investigates the impact of exenatide administration timing on BP patterns in diabetic db/db mice.Findings indicate that exenatide given at the onset of rest restores normal BP dipping, while at the start of the active phase worsens BP rhythm by modulating food intake and sympathetic activity.Timing GLP-1 RA administration may optimize BP control and provide cardiovascular benefits for type 2 diabetes patients.

Role of sympathetic pathway in light-phase time-restricted feeding-induced blood pressure circadian rhythm alteration.

Disruption of blood pressure (BP) circadian rhythm, independent of hypertension, is emerging as an index for future target organ damage and is associated with a higher risk of cardiovascular events. Previous studies showed that changing food availability time alters BP rhythm in several mammalian species. However, the underlying mechanisms remain largely unknown. To address this, the current study specifically investigates (1) the relationship between rhythms of food intake and BP in wild-type mice; (2) effects of light-phase time-restricted feeding (TRF, food only available during light-phase) on BP circadian rhythm in wild-type and diabetic db/db mice; (3) the roles of the autonomic system and clock gene in light-phase TRF induced changes in BP circadian rhythm. Food intake and BP of C57BL/6J and db/db mice were simultaneously and continuously recorded using BioDAQ and telemetry systems under ad libitum or light-phase TRF. Per2 protein daily oscillation was recorded in vivo by IVIS spectrum in mPer2 Luc mice. Autonomic nerve activity was evaluated by heart rate variability, baroreflex, urinary norepinephrine (NE) and epinephrine (Epi) excretion, and mRNA expressions of catecholamines biosynthetic and catabolic enzymes, and alpha-adrenergic receptors in mesenteric resistance arteries. We found that in wild-type mice, the BP level was correlated with the food intake temporally across the 24 h. Reversing the feeding time by imposing light-phase TRF resulted in reverse or inverted BP dipping. Interestingly, the net changes in food intake were correlated with the net alteration in BP temporally under light-phase TRF. In db/db mice, light-phase TRF worsened the existing non-dipping BP. The food intake and BP circadian rhythm changes were associated with alterations in Per2 protein daily oscillation and the time-of-day variations in heart rate variability, baroreflex, and urinary excretion of NE and Epi, and increased mRNA expression of Slc6a2 (encoding NE transporter) and Adra1d (encoding alpha-adrenergic receptor 1d) in the mesenteric resistance arteries, indicating the sympathetic nervous system (SNS) was modulated after light-phase TRF. Collectively, our results demonstrated that light-phase TRF results in reverse dipping of BP in wild-type and diabetic db/db mice and revealed the potential role of the sympathetic pathway in light-phase TRF-induced BP circadian rhythm alteration.

Time-restricted feeding protects the blood pressure circadian rhythm in diabetic mice.

The quantity and quality of food intake have been considered crucial for peoples' wellness. Only recently has it become appreciated that the timing of food intake is also critical. Nondipping blood pressure (BP) is prevalent in diabetic patients and is associated with increased cardiovascular events. However, the causes and mechanisms of nondipping BP in diabetes are not fully understood. Here, we report that food intake and BP were arrhythmic in diabetic db/db mice fed a normal chow diet ad libitum. Imposing a food intake diurnal rhythm by time-restricted feeding (TRF; food was only available for 8 h during the active phase) prevented db/db mice from developing nondipping BP and effectively restored the already disrupted BP circadian rhythm in db/db mice. Interestingly, increasing the time of food availability from 8 h to 12 h during the active dark phase in db/db mice prompted isocaloric feeding and still provided robust protection of the BP circadian rhythm in db/db mice. In contrast, neither 8-h nor 12-h TRF affected BP dipping in wild-type mice. Mechanistically, we demonstrate that TRF protects the BP circadian rhythm in db/db mice via suppressing the sympathetic activity during the light phase when they are inactive and fasting. Collectively, these data reveal a potentially pivotal role of the timing of food intake in the prevention and treatment of nondipping BP in diabetes.

Circadian variations of vasoconstriction and blood pressure in physiology and diabetes.

The intrinsic vascular smooth muscle contraction and vasoconstriction show time-of-day variations, contributing to the blood pressure circadian rhythm, which is essential for cardiovascular health. This brief review provides an overview of our current understanding of the mechanisms underlying the time-of-day variations of vascular smooth muscle contraction. We discuss the potential contribution of the time-of-day variations of vasoconstriction to the physiological blood pressure circadian rhythm. Finally, we survey the data obtained in the type 2 diabetic db/db mouse model that demonstrate the alterations of the time-of-day variations of vasoconstriction and the nondipping blood pressure in diabetes.

Active Time-Restricted Feeding Improved Sleep-Wake Cycle in db/db Mice.

People with diabetes are more likely to experience sleep disturbance than those without. Sleep disturbance can cause daytime sleepiness in diabetic patients, which may impair their daytime performance or even lead to workplace injuries. Therefore, restoring the normal sleep-wake cycle is critical for diabetic patients who experience daytime sleepiness. Previous data on a diabetic mouse model, the db/db mice, have demonstrated that the total sleep time and sleep fragmentation are increased and the daily rhythm of the sleep-wake cycle is attenuated. Accumulating evidence has shown that active time-restricted feeding (ATRF), in which the timing of food availability is restricted to the active-phase, is beneficial to metabolic health. However, it is unknown whether ATRF restores the normal sleep-wake cycle in diabetes. To test that, we used a non-invasive piezoelectric system to monitor the sleep-wake profile in the db/db mice with ad libitum feeding (ALF) as a baseline and then followed with ATRF. The results showed that at baseline, db/db mice exhibited abnormal sleep-wake patterns: the sleep time percent during the light-phase was decreased, while during the dark-phase it was increased with unusual cycling compared to control mice. In addition, the sleep bout length during both the light-phase and the full 24-h period was shortened in db/db mice. Analysis of the sleep-wake circadian rhythm showed that ATRF effectively restored the circadian but suppressed the ultradian oscillations of the sleep-wake cycle in the db/db mice. In conclusion, ATRF may serve as a novel strategy for treating diabetes-induced irregularity of the sleep-wake cycle.

Transcriptional Suppression of CPI-17 Gene Expression in Vascular Smooth Muscle Cells by Tumor Necrosis Factor, Krüppel-Like Factor 4, and Sp1 Is Associated with Lipopolysaccharide-Induced Vascular Hypocontractility, Hypotension, and Mortality.

Vasodilatory shock in sepsis is caused by the failure of the vasculature to respond to vasopressors, which results in hypotension, multiorgan failure, and ultimately patient death. Recently, it was reported that CPI-17, a key player in the regulation of smooth muscle contraction, was downregulated by lipopolysaccharide (LPS) in mesenteric arteries concordant with vascular hypocontractilty. While Sp1 has been shown to activate CPI-17 transcription, it is unknown whether Sp1 is involved in LPS-induced smooth muscle CPI-17 downregulation. Here we report that tumor necrosis factor (TNF) was critical for LPS-induced smooth muscle CPI-17 downregulation. Mechanistically, we identified two GC boxes as a key TNF response element in the CPI-17 promoter and demonstrated that KLF4 was upregulated by TNF, competed with Sp1 for the binding to the GC boxes in the CPI-17 promoter, and repressed CPI-17 transcription through histone deacetylases (HDACs). Moreover, genetic deletion of TNF or pharmacological inhibition of HDACs protected mice from LPS-induced smooth muscle CPI-17 downregulation, vascular hypocontractility, hypotension, and mortality. In summary, these data provide a novel mechanism of the transcriptional control of CPI-17 in vascular smooth muscle cells under inflammatory conditions and suggest a new potential therapeutic strategy for the treatment of vasodilatory shock in sepsis.

A Novel Diabetic Mouse Model for Real-Time Monitoring of Clock Gene Oscillation and Blood Pressure Circadian Rhythm.

Diabetic patients have an increased prevalence of blood pressure (BP) circadian rhythm disruption, which is associated with an increased risk of target organ damage and detrimental cardiovascular events. Limited information is available regarding the role of clock genes in the disruption of BP circadian rhythm in diabetes due to the lack of a diabetic animal model that allows real-time monitoring of clock gene oscillation. Here, we generated a novel diabetic db/db-mPer2Luc mouse model by crossing type 2 diabetic db/db mice with mPer2Luc knock-in mice. The daily rhythms of BP, heart rate, locomotor activity, and food and water intake were acquired by radiotelemetry or using metabolic chambers. The daily oscillation of mPer2 bioluminescence was recorded by LumiCycle in real-time in tissue explants and using the IVIS system in vivo. Our results show that db/db-mPer2Luc mice are obese, diabetic, and glucose intolerant. The db/db-mPer2Luc mice displayed a compromised BP daily rhythm, which was associated with disrupted daily rhythms in baroreflex sensitivity, locomotor activity, and metabolism, but not heart rate or food and water intake. The phase of the mPer2 daily oscillation was advanced to different extents in the explanted peripheral tissues from db/db-mPer2Luc mice relative to control mice. In contrast, no phase shift was detected in mPer2 daily oscillations in the explanted SCN. Moreover, advanced phase shift of the mPer2 daily oscillation was detected in the liver, kidney and submandibular gland in vivo of db/db-mPer2Luc mice. In conclusion, the diabetic db/db-mPer2Luc mouse is a novel animal model that allows real-time monitoring of mPer2 circadian rhythms ex vivo and in vivo. The results from db/db-mPer2Luc mice suggest that the desynchrony of mPer2 daily oscillation in peripheral tissues contributes to the loss of BP daily oscillation in diabetes.

Deletion of BMAL1 in Smooth Muscle Cells Protects Mice From Abdominal Aortic Aneurysms.

OBJECTIVE: Abdominal aortic aneurysm (AAA) has high mortality rate when ruptured, but currently, there is no proven pharmacological therapy for AAA because of our poor understanding of its pathogenesis. The current study explored a novel role of smooth muscle cell (SMC) BMAL1 (brain and muscle Arnt-like protein-1)-a transcription factor known to regulate circadian rhythm-in AAA development. APPROACH AND RESULTS: SMC-selective deletion of BMAL1 potently protected mice from AAA induced by (1) MR (mineralocorticoid receptor) agonist deoxycorticosterone acetate or aldosterone plus high salt intake and (2) angiotensin II infusion in hypercholesterolemia mice. Aortic BMAL1 was upregulated by deoxycorticosterone acetate-salt, and deletion of BMAL1 in SMCs selectively upregulated TIMP4 (tissue inhibitor of metalloproteinase 4) and suppressed deoxycorticosterone acetate-salt-induced MMP (matrix metalloproteinase) activation and elastin breakages. Moreover, BMAL1 bound to the Timp4 promoter and suppressed Timp4 transcription. CONCLUSIONS: These results reveal an important, but previously unexplored, role of SMC BMAL1 in AAA. Moreover, these results identify TIMP4 as a novel target of BMAL1, which may mediate the AAA protective effect of SMC BMAL1 deletion.

Serum amyloid A is found on ApoB-containing lipoproteins in obese humans with diabetes.

OBJECTIVE: In murine models of obesity/diabetes, there is an increase in plasma serum amyloid A (SAA) levels along with redistribution of SAA from high-density lipoprotein (HDL) to apolipoprotein B (apoB)-containing lipoprotein particles, namely, low-density lipoprotein and very low-density lipoprotein. The goal of this study was to determine if obesity is associated with similar SAA lipoprotein redistribution in humans. DESIGN AND METHODS: Three groups of obese individuals were recruited from a weight loss clinic: healthy obese (n = 14), metabolic syndrome (MetS) obese (n = 8), and obese with type 2 diabetes (n = 6). Plasma was separated into lipoprotein fractions by fast protein liquid chromatography, and SAA was measured in lipid fractions using enzyme-linked immunosorbent assay and Western blotting. RESULTS: Only the obese diabetic group had SAA detectable in apoB-containing lipoproteins, and SAA reverted back to HDL with active weight loss. CONCLUSIONS: In human subjects, SAA is found in apoB-containing lipoprotein particles only in obese subjects with type 2 diabetes, but not in healthy obese or obese subjects with MetS.