Fibroblast growth factor-23 and parathyroid hormone suppress small intestinal magnesium absorption

Inquiry of the Metabolic Traits in Relationship with Daily Magnesium Intake: Focus on Type 2 Diabetic Population

Magnesium (Mg), an essential nutrient with a wide area of physiological roles, stands as a cofactor in over 600 enzymatic reactions involved in the synthesis of proteins and nucleic acids, DNA repair, neuromuscular functions, neuronal transmission, cardiac rhythm regulation, and the modulation of metabolic pathways, as well as acting as a natural blocker for the calcium channels. Our objective was to highlight the most recent clinical data with respect to daily Mg intake (DMI) and metabolic traits, particularly type 2 diabetes mellitus (DM). This was a PubMed-based review of the English-language medical papers across different key terms of search; the time frame was from January 2019 until April 2024. We included (clinically relevant) original studies and excluded cases reports, series, reviews, editorials, opinion, experimental studies, and non-human data as well as studies that did not specifically assessed DMI and only provided assays of serum Mg, studies on patients diagnosed with type 1 or secondary DM. A total of 30 studies were included and we organized the key findings into several sections as follows. Studies investigating DMI in relationship with the adherence to local recommendations in diabetic subjects (n = 2, one transversal and another retrospective cohort; N = 2823) found that most of them had lower DMI. Deficient DMI was correlated with the risk of developing/having DM across five studies (n = 5, one prospective and four of cross-sectional design; N = 47,166). An inverse correlation between DMI and DM prevalence was identified, but these data are presented amid a rather heterogeneous spectrum. Four novel studies (N = 7279) analysed the relationship between DMI and DM control according to various methods (HbA1c, fasting and postprandial glycaemia, and insulin); the association may be linear in diabetic subjects only at certain levels of DMI; additionally, the multifactorial influence on HBA1c should take into consideration this dietary determinant, as well, but there are no homogenous results. Three studies concerning DMI and diabetic complications (one cross-sectional, one prospective, and another case-control study) in terms of retinopathy (n = 1, N = 3794) and nephropathy (n = 2, N = 4805) suggested a lower DMI was associated with a higher risk of such complications. Additionally, two other studies (one prospective and one retrospective cohort) focused on mortality (N = 6744), which, taking only certain mortality indicators into consideration, might be decreased in the subgroups with a higher DMI. Seven studies (N = 30,610) analysed the perspective of DMI in the general population with the endpoint of different features amid glucose profile, particularly, insulin resistance. Concerning HOMA-IR, there were three confirmatory studies and one non-confirmatory, while fasting plasma glucose was highlighted as inversely correlated with a DMI (n = 1). The highest level of evidence regarding Mg supplementation effects on glucose metabolism stands on seven randomised controlled trials (N = 350). However, the sample size was reduced (from 14 to 86 individuals per study, either diabetic or pre-diabetic) and outcomes were rather discordant. These clinical aspects are essential from a multidisciplinary perspective and further trials are mandatory to address the current areas of discordant results.

Contribution of thick ascending limb and distal convoluted tubule to glucose-induced hypercalciuria in healthy controls

Carbohydrates increase kidney stone risk and increase urine calcium and magnesium. We hypothesize that the effects of glucose as an allosteric modulator of calcium-sensing receptors may mediate this effect. Six healthy subjects were on a low-sodium diet before consuming 100 g of glucose beverage. Timed fasting (3) and postglucose (6) urine and blood samples were collected every 30 min. Urine composition and serum markers were measured and microvesicular abundance of tubular transport proteins (NHE3, NKCC2, NCC, and TRPV5) were quantified. Postglucose, serum glucose, and insulin rose rapidly with a parallel increase in calcium and magnesium excretion and no change in fractional excretion of sodium. Both serum parathyroid hormone (PTH) and urine TRPV5 fell in the postglucose periods. The rise in the calcium and magnesium excretion likely occurred primarily in the thick ascending limb where they are both under control of the calcium-sensing receptor. The fall in PTH and TRPV5 support the role of glucose as an allosteric modulator of calcium-sensing receptor.NEW & NOTEWORTHY Sugar increases urine calcium and magnesium as well as kidney stone and bone disease risk. Our study provided new insights into the underlying mechanism as we gave healthy subjects an oral glucose load and used newer tools such as fractional excretion of lithium, serum parathyroid hormone, and microvesicular abundance of tubular transport proteins to characterize the mechanism and identify the thick ascending limb with possible calcium-sensing receptor mediation as a likely contributor to this mechanism.

Clinical and histological evaluation of the effect of magnesium oxide administration on relapse after orthodontic teeth movement (Rabbit Model Study)

OBJECTIVE

This study aimed to evaluate the clinical and histological administration of magnesium oxide (MgO) supplementation on orthodontic relapse and bone remodeling.

MATERIALS AND METHODS

Twenty male albino rabbits were classified into four groups (five animals for each as two control (positive and negative), plus two experimental (low dose 40 mg/kg) and (high dose 80 mg/kg)/b.w. daily). An orthodontic force was applied (40 gm) to the lower incisors using modified orthodontic appliance adapted on the lower central incisors. During the period of retention, MgO was given orally. Relapse was estimated after appliance removal. A digital Calliper was used to compete the space between incisors' mesial tips of rabbits at six successive time points (0, 3, 7, 10, 15, and 21 days). Histologically, osteoblast, osteoclast, and osteocyte account were assessed. Data analyses were performed by SPSS using ANOVA and Tukay HSD (P ≤ 0.05) for statistically significant differences between groups.

RESULTS

The high dose group had a lower relapse rate than the low dose and control groups. Histologically, the high dose group had more osteoblasts and osteocytes than low dose and control groups. While osteoclasts were significantly lower than the control group in low and high dose groups.

CONCLUSIONS

MgO supplementation during an orthodontic retention phase, particularly at a level of high dose, clinically decreased orthodontic relapse in a rabbit model. Histologically, MgO has a significant effect on alveolar bone after the orthodontic retention period.

Current opinion on the regulation of small intestinal magnesium absorption

Magnesium (Mg²⁺) has an important role in numerous biological functions, and Mg²⁺ deficiency is associated with several diseases. Therefore, adequate intestinal absorption of Mg²⁺ is vital for health. The small intestine was previously thought to absorb digested Mg²⁺ exclusively through an unregulated paracellular mechanism, which is responsible for approximately 90% of total Mg²⁺ absorption. Recent studies, however, have revealed that the duodenum, jejunum, and ileum absorb Mg²⁺ through both transcellular and paracellular routes. Several regulatory factors of small intestinal Mg²⁺ uptake also have been explored, e.g., parathyroid hormone, fibroblast growth factor-23, apical acidity, proton pump inhibitor, and pH-sensing channel and receptors. The mechanistic factors underlying proton pump inhibitor suppression of small intestinal Mg²⁺, such as magnesiotropic protein dysfunction, higher mucosal bicarbonate secretion, Paneth cell dysfunction, and intestinal inflammation, are currently being explored. The potential role of small intestinal microbiomes in Mg²⁺ absorption has also been proposed. In this article, we reviewed the current knowledge on the mechanisms and regulatory factors of small intestinal Mg²⁺ absorption.

Mass spectrometric analysis of TRPM6 and TRPM7 from small intestine of omeprazole-induced hypomagnesemic rats

Disruption of small intestinal Mg²⁺ absorption has been reported as the underlying mechanism of proton pump inhibitor-induced hypomagnesemia (PPIH); hence, this study evaluated the expression, localization, phosphorylation, and oxidation of transient receptor potential melastatin 6 (TRPM6) and TRPM7 in the small intestine of rats subjected to PPIH. The expression and localization of cyclin M4 (CNNM4) was also analyzed. We show that, compared to control rats, membrane expression of the TRPM6/7 heterodimer and TRPM7 was markedly lower in the duodenum and the jejunum of PPIH rats; in contrast, expression of membrane TRPM6 and CNNM4 was higher in these organs. Mass spectrometric analysis of TRPM6 demonstrated hyper-phosphorylation, especially T1851, and hyper-oxidation at M1755, both of which can suppress its channel permeability. Further, hypo-phosphorylation of S141 and the dimerization motif domain of TRPM6 in PPIH rats might be involved in lower TRPM6/7 heterodimer expression. Hypo-phosphorylation, especially at S138 and S1360 in TRPM7 from PPIH rats disrupted stability of TRPM7 at the cell membrane; hyper-oxidation of TRPM7 was also observed. These results help explain the mechanism underlying the disruption of small intestinal Mg²⁺ absorption in PPIH.