SGLT‐2 inhibitors and the risk of lower‐limb amputation: Is this a class effect?

Inhibitors of the sodium‐glucose co‐transporter‐2 (SGLT‐2) are a novel class of glucose‐lowering agents that show promising results. However, the use of canagliflozin has been associated with an increased risk of lower‐limb amputation. Whether this risk concerns other SGLT‐2 inhibitors is unclear, and our objective was to address this issue. We performed a disproportionality analysis using the WHO global database of individual case safety reports (VigiBase). Among the 8 293 886 reports available between January 2013 and December 2017, we identified 79 reports of lower‐limb amputation that were associated with SGLT‐2 inhibitors. Among all blood glucose lowering drugs, the proportional reporting ratio (PRR) was increased only for SGLT‐2 inhibitors (5.55 [4.23, 7.29]). While we observed an expected signal for canagliflozin (7.09 [5.25, 9.57]), the PRR was also high for empagliflozin (4.96 [2.89, 8.50]) and, for toe amputations only, for dapagliflozin (2.62 [1.33, 5.14]). In conclusion, our results reveal a positive disproportionality signal for canagliflozin, and also for empagliflozin, and, for toe amputations only, for dapagliflozin. However, our analysis relies on a limited number of cases and is exposed to the biases inherent to pharmacovigilance studies. Further prospective data are therefore needed to better characterize the risk of amputations with different SGLT‐2 inhibitors.     

Tryptophanemia is controlled by a tryptophan-sensing mechanism ubiquitinating tryptophan 2,3-dioxygenase

Maintaining stable tryptophan levels is required to control neuronal and immune activity. We report that tryptophan homeostasis is largely controlled by the stability of tryptophan 2,3-dioxygenase (TDO), the hepatic enzyme responsible for tryptophan catabolism. High tryptophan levels stabilize the active tetrameric conformation of TDO through binding noncatalytic exosites, resulting in rapid catabolism of tryptophan. In low tryptophan, the lack of tryptophan binding in the exosites destabilizes the tetramer into inactive monomers and dimers and unmasks a four–amino acid degron that triggers TDO polyubiquitination by SKP1-CUL1-F-box complexes, resulting in proteasome-mediated degradation of TDO and rapid interruption of tryptophan catabolism. The nonmetabolizable analog alpha-methyl-tryptophan stabilizes tetrameric TDO and thereby stably reduces tryptophanemia. Our results uncover a mechanism allowing a rapid adaptation of tryptophan catabolism to ensure quick degradation of excess tryptophan while preventing further catabolism below physiological levels. This ensures a tight control of tryptophanemia as required for both neurological and immune homeostasis.

Blood levels of essential amino acids are remarkably constant despite large variations in diet supply, but the mechanisms ensuring amino acid homeostasis remain poorly understood (1). Systemic homeostasis is particularly important for tryptophan given its key roles as a neurotransmitter precursor and a regulator of immune responses (2–5). In humans, tryptophanemia is stably maintained around 60 ± 15 µM (mean ± SD) (6). Tryptophan catabolism involves dioxygenation leading to the production of kynurenine and derivatives (7, 8). This first and rate-limiting step can be catalyzed by two enzymes: TDO and indoleamine 2,3-dioxygenase (IDO1). Despite functional homology, these two enzymes differ in sequence, structure, expression, and physiological role. TDO (gene name TDO2) is a tetrameric enzyme expressed in the liver and responsible for degradation of excess dietary tryptophan (7, 9, 10). IDO1 is monomeric, only expressed in immune and inflammatory sites and mostly involved in immunoregulation (7, 11–13). Tryptophan catabolism by IDO1 can locally suppress T lymphocyte responses by depleting tryptophan and producing kynurenine. This immunosuppressive effect is exploited by tumors to resist immune rejection, and IDO1 inhibitors have been developed for cancer immunotherapy (3, 14). While IDO1 activity produces detectable levels of kynurenine in the blood, TDO does not as the kynurenine produced by TDO undergoes further degradation in the liver along the kynurenine pathway, leading to NAD and/or quinolinic acid (8). However, TDO activity is needed to control tryptophanemia. TDO-knockout (TDO-KO) mice and TDO-deficient humans have plasmatic tryptophan concentrations eight- to ninefold higher than wild-type mice or healthy humans (9, 15). As a result, TDO-KO mice better reject tumors and have higher levels of serotonin and other tryptophan metabolites in the brain, resulting in anxiolytic modulation and increased neurogenesis (9, 16). TDO is also expressed in some human tumors and may contribute to tumoral immune resistance (10, 16–18).     

Lipotoxicity plays a key role in the development of both insulin resistance and muscle atrophy in patients with type 2 diabetes

Insulin resistance and muscle mass loss often coincide in individuals with type 2 diabetes. Most patients with type 2 diabetes are overweight, and it is well established that obesity and derangements in lipid metabolism play an important role in the development of insulin resistance in these individuals. Specifically, increased adipose tissue mass and dysfunctional adipose tissue lead to systemic lipid overflow and to low‐grade inflammation via altered secretion of adipokines and cytokines. Furthermore, an increased flux of fatty acids from the adipose tissue may contribute to increased fat storage in the liver and in skeletal muscle, resulting in an altered secretion of hepatokines, mitochondrial dysfunction, and impaired insulin signalling in skeletal muscle. Recent studies suggest that obesity and lipid derangements in adipose tissue can also lead to the development of muscle atrophy, which would make insulin resistance and muscle atrophy two sides of the same coin. Unfortunately, the exact relationship between lipid accumulation, type 2 diabetes, and muscle atrophy remains largely unexplored. The aim of this review is to discuss the relationship between type 2 diabetes and muscle loss and to discuss some of the joint pathways through which lipid accumulation in organs may affect peripheral insulin sensitivity and muscle mass.     

Detection of recombinant and endogenous mouse melatonin receptors by monoclonal antibodies targeting the C‐terminal domain

Melatonin receptors play important roles in the regulation of circadian and seasonal rhythms, sleep, retinal functions, the immune system, depression, and type 2 diabetes development. Melatonin receptors are approved drug targets for insomnia, non‐24‐hour sleep‐wake disorders, and major depressive disorders. In mammals, two melatonin receptors (MTRs) exist, MT₁ and MT₂, belonging to the G protein‐coupled receptor (GPCR) superfamily. Similar to most other GPCRs, reliable antibodies recognizing melatonin receptors proved to be difficult to obtain. Here, we describe the development of the first monoclonal antibodies (mABs) for mouse MT₁ and MT₂. Purified antibodies were extensively characterized for specific reactivity with mouse, rat, and human MT₁ and MT₂ by Western blot, immunoprecipitation, immunofluorescence, and proximity ligation assay. Several mABs were specific for either mouse MT₁ or MT₂. None of the mABs cross‐reacted with rat MTRs, and some were able to react with human MTRs. The specificity of the selected mABs was validated by immunofluorescence microscopy in three established locations (retina, suprachiasmatic nuclei, pituitary gland) for MTR expression in mice using MTR‐KO mice as control. MT₂ expression was not detected in mouse insulinoma MIN6 cells or pancreatic beta‐cells. Collectively, we report the first monoclonal antibodies recognizing recombinant and native mouse melatonin receptors that will be valuable tools for future studies.     

Measuring social participation: reliability of the LIFE-H in older adults with disabilities

Purpose: Much more attention should be paid to instruments documenting social participation as this area is increasingly considered a pivotal outcome of a successful rehabilitation. The purpose of this study was to document the reliability of a participation measure, the Assessment of Life Habits (LIFE-H), in older adults with functional limitations.

Methods: Eighty-four individuals with physical disabilities living in three different environments were assessed twice with the LIFE-H, an instrument that documents the quality of social participation by assessing a person's performance in daily activities and social roles (life habits).

Results: The intraclass correlation coefficients (ICC) computed for intrarater reliability exceeded 0.75 for seven out of the 10 life habits categories. For interrater reliability, the total score and daily activities subscore are highly reliable (ICC ??0.89), and the social roles subscore is moderately reliable (ICC?=?0.64). ‘Personal care’ is the category with the highest ICC, and for five other categories ICCs are moderate to high (<?0.60).

Conclusion: LIFE-H is a valuable addition to instruments that mostly emphasize the concepts of function or functional independence. It is particularly meaningful to evaluate the participation of older adults in significant social role domains such as recreation and community life. It may be considered among the instruments having the best fit with the ICF definition of participation (the person's involvement in a life situation) and a majority of its related domains.     

Can personal and environmental factors explain participation of older adults?

Purpose. This study explores the extent to which personal and environmental factors explain participation in daily activities and social roles of older adults with chronic conditions.

Method. Two hundred older adults with chronic conditions completed the following assessments: Assessment of Life Habits (participation); Interpersonal Support Evaluation List (social support); Activities Specific Balance Confidence Scale (balance confidence); Timed Up and Go Test (mobility capacity); and Centre for Epidemiological Studies Depression Scale (depression symptomatology).

Results. Mobility and balance confidence explained 30% of the level of participation in daily activities and 24% of participation in social roles, whereas social support and depression did not contribute to the explanation of participation. When explaining participation in daily activities, sex had a significant contribution to the model.

Conclusions. Participation accomplishment is explained by personal factors related to an elder's physical and mental ability while sex differences had an important role for explaining accomplishment of daily activities. Additional aspects of participation, environmental barriers, and level of disability, are key factors identified for further inquiry.     

Human induced pluripotent stem cells can reach complete terminal maturation: in vivo and in vitro evidence in the erythropoietic differentiation model

Background

Human induced pluripotent stem cells offer perspectives for cell therapy and research models for diseases. We applied this approach to the normal and pathological erythroid differentiation model by establishing induced pluripotent stem cells from normal and homozygous sickle cell disease donors.

Design and Methods

We addressed the question as to whether these cells can reach complete erythroid terminal maturation notably with a complete switch from fetal to adult hemoglobin. Sickle cell disease induced pluripotent stem cells were differentiated in vitro into red blood cells and characterized for their terminal maturation in terms of hemoglobin content, oxygen transport capacity, deformability, sickling and adherence. Nucleated erythroblast populations generated from normal and pathological induced pluripotent stem cells were then injected into non-obese diabetic severe combined immunodeficiency mice to follow the in vivo hemoglobin maturation.

Results

We observed that in vitro erythroid differentiation results in predominance of fetal hemoglobin which rescues the functionality of red blood cells in the pathological model of sickle cell disease. We observed, in vivo, the switch from fetal to adult hemoglobin after infusion of nucleated erythroid precursors derived from either normal or pathological induced pluripotent stem cells into mice.

Conclusions

These results demonstrate that human induced pluripotent stem cells: i) can achieve complete terminal erythroid maturation, in vitro in terms of nucleus expulsion and in vivo in terms of hemoglobin maturation; and ii) open the way to generation of functionally corrected red blood cells from sickle cell disease induced pluripotent stem cells, without any genetic modification or drug treatment.Key words: human induced pluripotent stem cells, terminal maturation, erythropoietic differentiation     

Ultrasonographic hand features in systemic sclerosis and correlates with clinical,biologic, and radiographic findings

Objective

To investigate ultrasonographic (US) hand features in systemic sclerosis (SSc) patients and their relationship with clinical, biologic, and radiographic data.

Methods

Fifty‐two consecutive SSc patients were included in a cross‐sectional observational study together with 24 rheumatoid arthritis (RA) patients enrolled as controls. All patients underwent clinical examination, including tender and swollen joint counts, measurement of disability indices, and hand/wrist radiographs. US was performed on the hand and wrist joints and was aimed at the detection of synovitis, tenosynovitis, and calcinosis.

Results

Synovitis and tenosynovitis were more frequently detected with US in SSc patients (46% and 27%, respectively) than with clinical examination (15% and 6%, respectively; P < 0.01 for both comparisons). Fifty‐seven percent of patients had inflammatory synovitis (mostly Doppler grade 1), and tenosynovitis was either inflammatory or fibrotic. Calcifications were observed using US and radiographs in 40% and 36% of SSc patients, respectively (P = 0.8). As compared to RA, US features specific to SSc were sclerosing tenosynovitis (P < 0.01) and soft tissue calcifications (P = 0.01).

Conclusion

Our study confirms that articular involvement in SSc is underestimated by a single clinical examination. It is characterized by mild inflammatory changes and the specific findings include sclerotic US aspects together with calcinosis. Further prospective studies are warranted to evaluate the predictive value of these findings and determine whether they should be considered for adapting a therapeutic strategy.