Differences in bone microarchitecture between genetic and secondary iron-overload mouse models suggest a role for hepcidin deficiency in iron-related osteoporosis.

Iron overload is one of the secondary osteoporosis etiologies. Cellular and molecular mechanisms involved in iron-related osteoporosis are not fully understood. AIM: The aim of the study was to investigate the respective roles of iron excess and hepcidin, the systemic iron regulator, in the development of iron-related osteoporosis. MATERIAL AND METHODS: We used mice models with genetic iron overload (GIO) related to hepcidin deficiency (Hfe-/- and Bmp6-/- ) and secondary iron overload (SIO) exhibiting a hepcidin increase secondary to iron excess. Iron concentration and transferrin saturation levels were evaluated in serum and hepatic, spleen, and bone iron concentrations were assessed by ICP-MS and Perl's staining. Gene expression was evaluated by quantitative RT-PCR. Bone micro-architecture was evaluated by micro-CT. The osteoblastic MC3T3 murine cells that are able to mineralize were exposed to iron and/or hepcidin. RESULTS: Despite an increase of bone iron concentration in all overloaded mice models, bone volume/total volume (BV/TV) and trabecular thickness (Tb.Th) only decreased significantly in GIO, at 12 months for Hfe-/- and from 6 months for Bmp6-/- . Alterations in bone microarchitecture in the Bmp6-/- model were positively correlated with hepcidin levels (BV/TV (ρ = +.481, p < .05) and Tb.Th (ρ = +.690, p < .05). Iron deposits were detected in the bone trabeculae of Hfe-/- and Bmp6-/- mice, while iron deposits were mainly visible in bone marrow macrophages in secondary iron overload. In cell cultures, ferric ammonium citrate exposure abolished the mineralization process for concentrations above 5 µM, with a parallel decrease in osteocalcin, collagen 1, and alkaline phosphatase mRNA levels. Hepcidin supplementation of cells had a rescue effect on the collagen 1 and alkaline phosphatase expression level decrease. CONCLUSION: Together, these data suggest that iron in excess alone is not sufficient to induce osteoporosis and that low hepcidin levels also contribute to the development of osteoporosis.

Drivers for primary producers' dynamics: New insights on annual benthos pelagos monitoring in anthropised freshwater marshes (Charente-Maritime, France).

Wetlands, especially marshes, support many services such as carbon catchment control or water purification led by primary producers such as phytoplankton and microphytobenthos (PB). The impact of the sedimentary compartment, as source and sink of essential nutrients for the water column, is often neglected in the study of their dynamics and water purification capacity of the systems. This work compared monthly (between February 2020 and April 2021) the benthic and pelagic primary producers' dynamics in two anthropised freshwater marshes (Marans and Genouillé), with the simultaneous follow-up of physico-chemical parameters of the water column and nutrient fluxes at the sediment-water (SWI) interface. It was suggested a strong contribution of phytoplankton (pumping) and the benthic compartment (denitrification) to the water purification of these two nitrates (NO3-)-rich marshes. Total phytoplankton production fluctuated between ∼5 (winter) and 1500 mg C m-3 d-1 (fall) at Marans and between 40 (winter) and ∼750 mg C m-3 d-1 (spring) at Genouillé. At Marans, soluble reactive phosphorus (SRP) benthic effluxes (-2.101 to -6.102 µmol m-2 d-1 in fall and summer, respectively) coincided with phytoplankton bloom periods. These effluxes were inhibited by NO3- penetration in the sediment (0 to 5.104 µmol m-2 d-1), by inhibiting iron respiration. At Genouillé, inhibition of SRP effluxes depended on denitrification rate and on P stocks in the sediment, where slight SRP effluxes (-101 µmol m-2 d-1) could have co-occurred with slight NO3- influxes (5.102 µmol m-2 d-1) in spring. The presence of PB (between 10-60 and 40-120 mg gsed-1 at Marans and Genouillé, respectively), suggested a strong contribution of the benthic compartment to the total primary production (benthic and pelagic through resuspension processes) in these environments. This work encourages to consider the benthos and the pelagos as a unicum to provide better sustainable management of such systems and limit eutrophication risks in coastal areas.

Oxidative and glycolytic skeletal muscles deploy protective mechanisms to avoid atrophy under pathophysiological iron overload.

BACKGROUND: Iron excess has been proposed as an essential factor in skeletal muscle wasting. Studies have reported correlations between muscle iron accumulation and atrophy, either through ageing or by using experimental models of secondary iron overload. However, iron treatments performed in most of these studies induced an extra-pathophysiological iron overload, more representative of intoxication or poisoning. The main objective of this study was to determine the impact of iron excess closer to pathophysiological conditions on structural and metabolic adaptations (i) in differentiated myotubes and (ii) in skeletal muscle exhibiting oxidative (i.e. the soleus) or glycolytic (i.e. the gastrocnemius) metabolic phenotypes. METHODS: The impact of iron excess was assessed in both in vitro and in vivo models. Murine differentiated myotubes were exposed to ferric ammonium citrate (FAC) (i.e. 10 and 50 µM) for the in vitro component. The in vivo model was achieved by a single iron dextran subcutaneous injection (1 g/kg) in mice. Four months after the injection, soleus and gastrocnemius muscles were harvested for analysis. RESULTS: In vitro, iron exposure caused dose-dependent increases of iron storage protein ferritin (P < 0.01) and dose-dependent decreases of mRNA TfR1 levels (P < 0.001), which support cellular adaptations to iron excess. Extra-physiological iron treatment (50 µM FAC) promoted myotube atrophy (P = 0.018), whereas myotube size remained unchanged under pathophysiological treatment (10 µM FAC). FAC treatments, whatever the doses tested, did not affect the expression of proteolytic markers (i.e. NF-κB, MurF1, and ubiquitinated proteins). In vivo, basal iron content and mRNA TfR1 levels were significantly higher in the soleus compared with the gastrocnemius (+130% and +127%; P < 0.001, respectively), supporting higher iron needs in oxidative skeletal muscle. Iron supplementation induced muscle iron accumulation in the soleus and gastrocnemius muscles (+79%, P < 0.001 and +34%, P = 0.002, respectively), but ferritin protein expression only increased in the gastrocnemius (+36%, P = 0.06). Despite iron accumulation, muscle weight, fibre diameter, and myosin heavy chain distribution remained unchanged in either skeletal muscle. CONCLUSIONS: Together, these data support that under pathophysiological conditions, skeletal muscle can protect itself from the related deleterious effects of excess iron.

Calcium pyrophosphate deposition (CPPD) in a liver transplant patient: are hypomagnesemia, tacrolimus or both guilty? A case-based literature review.

Calcium pyrophosphate deposition (CPPD) can be induced by a persistent hypomagnesemia. Tacrolimus is an immunosuppressive treatment especially used in organ transplant, potentially inducer of hypomagnesemia by renal loss. A 53-year-old man, liver transplant 10 months earlier, developed an acute peripheral oligoarthritis of wrist, hip and elbow with fever, associated with acute low back pain. Synovial fluid was sterile, and revealed calcium pyrophosphate crystals. Spinal imaging showed inflammatory changes. Magnesium blood level was low at 0.51 mmol/l, with high fractional excretion in favor of renal loss. Tacrolimus was changed for everolimus, proton pump inhibitor was stopped, and magnesium oral supplementation was started. After 8 months follow-up and slow prednisone tapering, he did not relapse pain. Persistent hypomagnesemia is a rare secondary cause of CPPD. In this entity, drug liability should be investigated such as tacrolimus in organ transplant patient.

Coupling between sediment biogeochemistry and phytoplankton development in a temperate freshwater marsh (Charente-Maritime, France): Evidence of temporal pattern.

In freshwater systems, sediment can be an important source for the internal loading of PO4. The limiting character of this element in such system leads to consider this phenomenon in terms of eutrophication risks and water quality stakes. A four-months follow-up (January, March, April and May 2019) was carried out in a strong phosphate (PO4) limited secondary channel from an artificial irrigation system of Charente Maritime (France) to link the mobilization of remineralization products in the upper 6 cm layer of sediment (conventional core slicing/centrifugation and DET probes) and the phytoplankton biomass dynamics in the water column. Results showed congruent patterns between the temporal succession of the organic matter mineralization processes in the sediment and the primary biomass dynamics in the water column. In January and March (considered in winter), PO4 proved to be retained by adsorption onto iron oxides in anoxic sediment since pore water nitrate inhibited for about a month the respiration of metal oxides in the first cm of sediment, thus limiting PO4 availability and the phytoplankton growth. In April and May (early spring), after exhaustion of pore water nitrate, the dissolutive reduction of iron oxides released PO4 into pore water generated a significant diffusive outgoing flux from the sediment to the water column with a maximum in April (-1.10E-04±2.81E-05 nmol cm-2 s-1). This release coincided with the nanophytoplankton bloom (5.50 µg Chla L-1) and a potential increase of PO4 concentration in the water column. This work provides some insight on the importance of benthic-pelagic coupling in anthropogenic systems. This conceptual model has to be deployed on other sites of interest where internal loading of P takes precedence over external inputs and nitrate mitigation drives its benthic recycling and ultimately its bioavailability. This is to be essential to characterize the aquatic environment quality in order to limit eutrophication risks.