Iron-carbohydrate complexes treating iron anaemia: Understanding the nano-structure and interactions with proteins through orthogonal characterisation

Intravenous (IV) iron-carbohydrate complexes are widely used nanoparticles (NPs) to treat iron deficiency anaemia, often associated with medical conditions such as chronic kidney disease, heart failure and various inflammatory conditions. Even though a plethora of physicochemical characterisation data and clinical studies are available for these products, evidence-based correlation between physicochemical properties of iron-carbohydrate complexes and clinical outcome has not fully been elucidated yet. Studies on other metal oxide NPs suggest that early interactions between NPs and blood upon IV injection are key to understanding how differences in physicochemical characteristics of iron-carbohydrate complexes cause variance in clinical outcomes. We therefore investigated the core-ligand structure of two clinically relevant iron-carbohydrate complexes, iron sucrose (IS) and ferric carboxymaltose (FCM), and their interactions with two structurally different human plasma proteins, human serum albumin (HSA) and fibrinogen, using a combination of cryo-scanning transmission electron microscopy (cryo-STEM), x-ray diffraction (XRD), small-angle x-ray scattering (SAXS) and small-angle neutron scattering (SANS). Using this orthogonal approach, we defined the nano-structure, individual building blocks and surface morphology for IS and FCM. Importantly, we revealed significant differences in the surface morphology of the iron-carbohydrate complexes. FCM shows a localised carbohydrate shell around its core, in contrast to IS, which is characterised by a diffuse and dynamic layer of carbohydrate ligand surrounding its core. We hypothesised that such differences in carbohydrate morphology determine the interaction between iron-carbohydrate complexes and proteins and therefore investigated the NPs in the presence of HSA and fibrinogen. Intriguingly, IS showed significant interaction with HSA and fibrinogen, forming NP-protein clusters, while FCM only showed significant interaction with fibrinogen. We postulate that these differences could influence bio-response of the two formulations and their clinical outcome. In conclusion, our study provides orthogonal characterisation of two clinically relevant iron-carbohydrate complexes and first hints at their interaction behaviour with proteins in the human bloodstream, setting a prerequisite towards complete understanding of the correlation between physicochemical properties and clinical outcome.

Uncovering the dynamics of cellular responses induced by iron-carbohydrate complexes in human macrophages using quantitative proteomics and phosphoproteomics

Iron-carbohydrate complexes are widely used to treat iron deficiencies. Macrophages play a crucial role in the uptake and fate of these nanomedicines, however, how complexed iron carbohydrates are taken up and metabolized by macrophages is still not fully understood. Using a (phospho-)proteomics approach, we assessed differences in protein expression and phosphorylation in M2 macrophages triggered by iron sucrose (IS). Our results show that IS alters the expression of multiple receptors, indicative of a complex entry mechanism. Besides, IS induced an increase in intracellular ferritin, the loss of M2 polarization, protective mechanisms against ferroptosis, and an autophagic response. These data indicate that macrophages can use IS as a source of iron for its storage and later release, however, the excess of iron can cause oxidative stress, which can be successfully regulated by the cells. When comparing IS with ferric carboxymaltose (FCM) and iron isomaltoside-1000 (IIM), complexes with a higher carbohydrate ligand stability, we observed that FCM and IIM are metabolized at a slower rate, and trigger M2 polarization loss to a lower extent. These results indicate that the surface characteristics of the iron-carbohydrate complexes may influence the cell responses. Our data show that the application of (phospho-)proteomics can lead to a better understanding of metabolic processes, including the uptake, biodegradation and bioavailability of nanomedicines.

Critical nanomaterial attributes of iron-carbohydrate nanoparticles: Leveraging orthogonal methods to resolve the 3-dimensional structure

Intravenous iron-carbohydrate nanomedicines are widely used to treat iron deficiency and iron deficiency anemia across a wide breadth of patient populations. These colloidal solutions of nanoparticles are complex drugs which inherently makes physicochemical characterization more challenging than small molecule drugs. There have been advancements in physicochemical characterization techniques such as dynamic light scattering and zeta potential measurement, that have provided a better understanding of the physical structure of these drug products in vitro. However, establishment and validation of complementary and orthogonal approaches are necessary to better understand the 3-dimensional physical structure of the iron-carbohydrate complexes, particularly with regard to their physical state in the context of the nanoparticle interaction with biological components such as whole blood (i.e. the nano-bio interface).

Putting square pegs in round holes: why traditional pharmacokinetic principles cannot universally be applied to iron-carbohydrate complexes

Intravenous iron-carbohydrate complexes are nanomedicines that are commonly used to treat iron deficiency and iron deficiency anemia of various etiologies. Many challenges remain regarding these complex drugs in the context of fully understanding their pharmacokinetic parameters. Firstly, the measurement of the intact iron nanoparticles versus endogenous iron concentration fundamentally limits the availability of data for computational modeling. Secondly, the models need to include several parameters to describe the iron metabolism which is not completely defined and those identified (e.g. ferritin) exhibit considerable interpatient variability. Additionally, modeling is further complicated by the lack of traditional receptor/enzyme interactions. The known parameters of bioavailability, distribution, metabolism, and excretion for iron-carbohydrate nanomedicines will be reviewed and future challenges that currently prevent the direct application of physiologically-based pharmacokinetic or other computational modeling techniques will be discussed.

Probing Subcellular Iron Availability with Genetically Encoded Nitric Oxide Biosensors

Cellular iron supply is required for various biochemical processes. Measuring bioavailable iron in cells aids in obtaining a better understanding of its biochemical activities but is technically challenging. Existing techniques have several constraints that make precise localization difficult, and the lack of a functional readout makes it unclear whether the tested labile iron is available for metalloproteins. Here, we use geNOps; a ferrous iron-dependent genetically encoded fluorescent nitric oxide (NO) biosensor, to measure available iron in cellular locales. We exploited the nitrosylation-dependent fluorescence quenching of geNOps as a direct readout for cellular iron absorption, distribution, and availability. Our findings show that, in addition to ferrous iron salts, the complex of iron (III) with N,N'-bis (2-hydroxybenzyl)ethylenediamine-N,N'-diacetic acid (HBED) can activate the iron (II)-dependent NO probe within intact cells. Cell treatment for only 20 min with iron sucrose was also sufficient to activate the biosensor in the cytosol and mitochondria significantly; however, ferric carboxymaltose failed to functionalize the probe, even after 2 h of cell treatment. Our findings show that the geNOps approach detects available iron (II) in cultured cells and can be applied to assay functional iron (II) at the (sub)cellular level.

Correction: Funk et al. Criticality of Surface Characteristics of Intravenous Iron-Carbohydrate Nanoparticle Complexes: Implications for Pharmacokinetics and Pharmacodynamics. Int. J. Mol. Sci. 2022, 23, 2140

The authors wish to make the following corrections to this paper [...]

Need for Expansion of Pharmacy Education Globally for the Growing Field of Nanomedicine

The emerging landscape of nanomedicine includes a wide variety of active pharmaceutical ingredients and drug formulations. Their design provides nanomedicines with unique features leading to improved pharmacokinetics and pharmacodynamics. They are manufactured using conventional or biotechnological manufacturing processes. Their physical characteristics are vastly different from traditional small-molecule drugs. Pharmacists are important members of the multi-disciplinary team of scientists involved in their development and clinical application. Consequently, their training should lead to an understanding of the complexities associated with the production and evaluation of nanomedicines. Therefore, student pharmacists, post-doctoral researchers, and trainees should be given more exposure to this rapidly evolving class of therapeutics. This commentary will provide an overview of nanomedicine education within the selection of pharmacy programs globally, discuss the current regulatory challenges, and describe different approaches to incorporate nanomedicine science in pharmacy programs around the world.

The Growing Field of Nanomedicine and Its Relevance to Pharmacy Curricula

The field of nanomedicine is a rapidly growing scientific domain. Nanomedicine encompasses a diverse number of active pharmaceutical ingredients. Submissions of Investigational New Drugs and New Drug Applications have risen dramatically over the last decade. There are over 50 nanomedicines approved for use by the US Food and Drug Administration (FDA). Because of the fundamental role pharmacists will play in therapeutic and administrative decisions regarding nanomedicines, it is imperative for future pharmacists to gain exposure early in their training to this rapidly evolving class of drugs. This commentary describes nanomedicines, discusses current regulatory challenges, and provides recommendations for judicious incorporation of nanomedicine topics into the Doctor of Pharmacy curriculum based on emerging pharmaceutical and clinical science applications.

A pragmatic regulatory approach for complex generics through the U.S. FDA 505(j) or 505(b)(2) approval pathways

The diverse nature of complex drug products poses challenges for the development of regulatory guidelines for generic versions. While complexity is not new in medicines, the technical capacity to measure and analyze data has increased. This requires a determination of which measurements and studies are relevant to demonstrate therapeutic equivalence. This paper describes the views of the NBCD Working Group and provides pragmatic solutions for approving complex generics by making best use of existing U.S. Food and Drug Administration's abbreviated approval pathways 505(j) and 505(b)(2). We argue that decisions on the appropriateness of submitting a 505(j) or 505(b)(2) application can build on the FDA's complex drug product classification as well as the FDA's much applauded guidance document for determining whether to submit an ANDA or a 505(b)(2) application. We hope that this paper contributes to the discussions to increase the clarity of regulatory approaches for complex generics, as well as the predictability for complex generic drug developers, to facilitate access to much‐needed complex generics and to promote the sustainability of the healthcare system.

Tackling the challenges of nanomedicines: are we ready?

PURPOSE

This review provides an overview of the proceedings of the symposium "Tackling the Challenges of Nanomedicines: Are We Ready?" organized by the International Pharmaceutical Federation (FIP) Hospital Pharmacy Section and Non-Biological Complex Drugs (NBCDs) Working Group at the 2019 FIP World Congress of Pharmacy and Pharmaceutical Sciences. Debate centered on reasons underlying the current complex regulatory landscape for nanomedicines and their follow-on products (referred to as nanosimilars) and the pivotal role of hospital pharmacists in selecting, handling, and guiding usage of nanomedicines and nanosimilars.

SUMMARY

The evaluation and use of nanomedicines are recognized among scientific, pharmaceutical, and regulatory bodies as complex. Interchangeability and substitutability of nanomedicines and nanosimilars are confounded by a lack of pharmaceutical and pharmacological equivalence, reflecting the inherent complex nature of these drug products and manufacturing processes. Consequences include implications for clinical safety and efficacy and, ultimately, comparability. Local regulatory approvals of some nanomedicines have occurred, but there is no standard to ensure streamlined evaluation and use of consistent measures of therapeutic equivalence of reference products and their nanosimilars. Hospital pharmacists are expected to be experts in the selection, handling, and substitution of nanomedicines and familiarize themselves with the limitations of current methods of assessing pharmaceutical and clinical equivalence of nanosimilars in order to ensure informed formulary decision-making and eventual patient benefit.

CONCLUSION

Supportive guidance for pharmacists focusing on the substitutability and/or interchangeability of nanomedicines and their nanosimilars is needed. Current FIP guidance for pharmacists on therapeutic interchange and substitution should be extended to include nanomedicines and nanosimilars.

Factors influencing safety and efficacy of intravenous iron-carbohydrate nanomedicines: From production to clinical practice

Iron deficiency is an important subclinical disease affecting over one billion people worldwide. A growing body of clinical records supports the use of intravenous iron-carbohydrate complexes for patients where iron replenishment is necessary and oral iron supplements are either ineffective or cannot be tolerated by the gastrointestinal tract. A critical characteristic of iron-carbohydrate drugs is the complexity of their core-shell structure, which has led to differences in the efficacy and safety of various iron formulations. This review describes parameters influencing the safety and effectiveness of iron-carbohydrate complexes during production, storage, handling, and clinical application. We summarized the physicochemical and biological assessments of commercially available iron carbohydrate nanomedicines to provide an overview of publicly available data. Further, we reviewed studies that described how subtle differences in the manufacturing process of iron-carbohydrate complexes can impact on the physicochemical, biological, and clinical outcomes of original product versus their intended copies or so-called iron "similar" products.

Differences between intravenous iron products: focus on treatment of iron deficiency in chronic heart failure patients

Iron deficiency is the leading cause of anaemia and is highly prevalent in patients with chronic heart failure (CHF). Iron deficiency, with or without anaemia, can be corrected with intravenous (i.v.) iron therapy. In heart failure patients, iron status screening, diagnosis, and treatment of iron deficiency with ferric carboxymaltose are recommended by the 2016 European Society of Cardiology guidelines, based on results of two randomized controlled trials in CHF patients with iron deficiency. All i.v. iron complexes consist of a polynuclear Fe(III)‐oxyhydroxide/oxide core that is stabilized with a compound‐specific carbohydrate, which strongly influences their physico‐chemical properties (e.g. molecular weight distribution, complex stability, and labile iron content). Thus, the carbohydrate determines the metabolic fate of the complex, affecting its pharmacokinetic/pharmacodynamic profile and interactions with the innate immune system. Accordingly, i.v. iron products belong to the new class of non‐biological complex drugs for which regulatory authorities recognized the need for more detailed characterization by orthogonal methods, particularly when assessing generic/follow‐on products. Evaluation of published clinical and non‐clinical studies with different i.v. iron products in this review suggests that study results obtained with one i.v. iron product should not be assumed to be equivalent to other i.v. iron products that lack comparable study data in CHF. Without head‐to‐head clinical studies proving the therapeutic equivalence of other i.v. iron products with ferric carboxymaltose, in the highly vulnerable population of heart failure patients, extrapolation of results and substitution with a different i.v. iron product is not recommended.

How to select a nanosimilar

Nanomedicines in the class of nonbiological complex drugs (NBCDs) are becoming increasingly available. Up to 23 nanomedicines have been approved, and approximately 50 are in clinical development. Meanwhile, the first nanosimilars have entered the market through the generic approval pathway, but clinical differences have been observed. Many healthcare professionals may be unaware of this issue and must be informed of these clinically relevant variances. This article provides a tool for rational decision making for the inclusion of nanomedicines into the hospital formulary, including defined criteria for evaluation of substitutability or interchangeability. The tool was generated by conducting a roundtable with an international panel of experts and follows the same thought process that was developed and published earlier for the selection of biologicals/biosimilars. In addition to the existing criteria for biosimilars, a set of seven criteria was identified that specifically apply to nanosimilars. These include (1) particle size and size distribution, (2) particle surface characteristics, (3) fraction of uncaptured bioactive moiety, (4) stability on storage, (5) bioactive moiety uptake and (6) distribution, and (7) stability for ready-to-use preparation. Pharmacists should utilize their pharmaceutical expertise to use the appropriate criteria to evaluate the comparability of the drug to decide on interchangeability or substitutability.

Equivalence of complex drug products: advances in and challenges for current regulatory frameworks

Biotechnology and nanotechnology provide a growing number of innovator-driven complex drug products and their copy versions. Biologics exemplify one category of complex drugs, but there are also nonbiological complex drug products, including many nanomedicines, such as iron-carbohydrate complexes, drug-carrying liposomes or emulsions, and glatiramoids. In this white paper, which stems from a 1-day conference at the New York Academy of Sciences, we discuss regulatory frameworks in use worldwide (e.g., the U.S. Food and Drug Administration, the European Medicines Agency, the World Health Organization) to approve these complex drug products and their follow-on versions. One of the key questions remains how to assess equivalence of these complex products. We identify a number of points for which consensus was found among the stakeholders who were present: scientists from innovator and generic/follow-on companies, academia, and regulatory bodies from different parts of the world. A number of topics requiring follow-up were identified: (1) assessment of critical attributes to establish equivalence for follow-on versions, (2) the need to publish scientific findings in the public domain to further progress in the field, (3) the necessity to develop worldwide consensus regarding nomenclature and labeling of these complex products, and (4) regulatory actions when substandard complex drug products are identified.

Medication practice in hospitals: are nanosimilars evaluated and substituted correctly?

Introduction

This study investigates the drug selection and dispensing behaviour of hospital pharmacists of intravenous iron products including iron sucrose and iron sucrose similar, with special emphasis on substitution and interchangeability in France and Spain. Iron-carbohydrate complex drugs represent different available intravenous iron drugs and are part of the non-biological complex drug (NBCD) class, an expanding drug class with up to 30 brands available in intravenous pharmacotherapy and over 50 in clinical development. Follow-on versions of iron sucrose have appeared in some markets such as France and Spain, which were authorised by the generic approval pathway. However, differences in clinical efficacy and safety of iron sucrose similars compared with the reference originator drug Venofer have been observed, putting a question mark on their equivalence as assessed for authorisation and consequently their substitutability and interchangeability.

Method

70 French and 70 Spanish hospital pharmacists were surveyed via an online questionnaire on their formulary selection and dispensing behaviour of intravenous iron medicines.

Results

There is little awareness about the characteristics of this class of drugs and the reported differences in safety and efficacy between iron sucrose and iron sucrose similars. In approximately 85% of cases the intravenous iron is chosen according to the hospital formulary. In 30% (France) and 34% (Spain) of cases an iron sucrose similar was dispensed because the formulary requires dispensing an alternative lower cost drug when available. In 26% (France) and 52% (Spain) of cases the physician is not informed on such a medication change using a similar product.

Conclusions

Evaluation of NBCD similars for substitution and interchange by hospital pharmacists is rarely based on scientific and clinical criteria but rather on cost aspects only, which does not ensure safe, efficacious and cost-effective use of such drugs.

How to regulate nonbiological complex drugs (NBCD) and their follow-on versions: points to consider

The aim of this critical review is to reach a global consensus regarding the introduction of follow-on versions of nonbiological complex drugs (NBCD). A nonbiological complex drug is a medicinal product, not being a biological medicine, where the active substance is not a homo-molecular structure, but consists of different (closely related and often nanoparticulate) structures that cannot be isolated and fully quantitated, characterized and/or described by state of the art physicochemical analytical means and where the clinical meaning of the differences is not known. The composition, quality and in vivo performance of NBCD are highly dependent on manufacturing processes of both the active ingredient as well as in most cases the formulation. The challenges posed by the development of follow-on versions of NBCD are illustrated in this paper by discussing the 'families' of liposomes, iron-carbohydrate ('iron-sugar') drugs and glatiramoids. It is proposed that the same principles for the marketing authorization of copies of NBCD as for biosimilars be used: the need for animal and/or clinical data and the need to show similarity in quality, safety and efficacy. The regulatory approach of NBCD will have to take into consideration the specific characteristics of the drugs, their formulation and manufacturing process and the resulting critical attributes to achieve their desired quality, safety and efficacy. As with the biosimilars, for the NBCD product, family-specific methods should be evaluated and applied where scientifically proven, including sophisticated quality methods, pharmacodynamic markers and animal models. Concerning substitution and interchangeability of NBCD, it is also advisable to take biosimilars as an example, i.e. (1) substitution without the involvement of a healthcare professional should be discouraged to ensure traceability of the treatment of individual patients, (2) keep an individual patient on a specific treatment if the patient is doing well and only switch if unavoidable and (3) monitor the safety and efficacy of the new product if switching occurs.

Nanoparticle iron medicinal products - Requirements for approval of intended copies of non-biological complex drugs (NBCD) and the importance of clinical comparative studies

Currently, most countries apply the standard generic approach for the approval of intended copies of originator nanoparticle iron medicinal products, requiring only demonstration of bioequivalence to a reference medicinal product by bioavailability studies. However, growing evidence suggests that this regulatory approach is not appropriate. Clinical and non-clinical studies have shown that intended copy preparations of nanoparticle iron medicinal products can differ substantially from the originator product in their efficacy and potentially in their safety profile. An adapted regulatory pathway (separate from the standard generic approach) with defined data requirements is needed for approval of intended copies of iron medicinal products. Here, we discuss the difficulties involved in assessing therapeutic equivalence of nanoparticle iron medicinal products and suggest key concepts of a regulatory approach. Standardized non-clinical comparative studies are necessary but, as demonstrated in the reported clinical data, they may not be sufficient to demonstrate a comparable efficacy and safety profile. Validated, prospective, comparative clinical studies might be needed, in addition to non-clinical studies, in order to enable appropriate assessment of therapeutic equivalence. Furthermore, including brand names in addition to the International Non-proprietary Names (INNs) in safety reports could enable effective safety monitoring of intended copies and originator products.

Development of bioactive substances for functional foods--scientific and other aspects

The discovery and development of bioactive substances and their use in the manufacture of food products has the potential to contribute to the optimal health of populations and in reducing the risk of chronic disease. In assessing the efficacy of these substances in man, the concept of biomarkers could play a key role. However, it is the validation of such biomarkers which is crucial to the eventual availability of foods containing bioactive substances. Determining the safety and efficacy of these substances, and in particular in establishing claims, requires close cooperation between industry, regulatory authorities and the scientific community.

Bonistein (synthetic genistein), a food component in development for a bone health nutraceutical

In the discussion of the risk-benefit relation of the hormone replacement therapy (HRT) for elder women phytochemicals with estrogenic activity received a great deal of attention. Phytoestrogens are naturally occurring compounds with structural similarity to 17beta-estradiol. Especially genistein, an isoflavone most abundant in soy, possess a high and selective binding-affinity to the mammalian estrogen receptors. It has been found, that genistein exert in humans both: weak estrogenic and anti-estrogenic effects, similar to the SERMs. Consequently, it was concluded, that genistein might provide an alternative to prevent postmenopausal bone-loss and ameliorate menopausal symptoms without side-effects similar to HRT. Pre-clinical experiments and results from clinical pilot studies with pure genistein confirmed its efficacy in these indications. Nevertheless, currently some open issues still exist to recommend its intake thoughtlessly. Bonistein, pure synthetic genistein developed by DSM Nutritional Products, was tested extensively in appropriate models for bone health. A battery of toxicological studies was conducted to determine safe intake levels. In the early clinical development pharmacokinetic studies were performed in healthy volunteers and in postmenopausal women. Now large-scale studies are in preparation to investigate Bonistein's efficacy in postmenopausal bone-loss and climacteric syndrome.

The extreme N-terminus of the calcitonin-like receptor contributes to the selective interaction with adrenomedullin or calcitonin gene-related peptide

The calcitonin (CT)-like (CL) receptor is a CT gene-related peptide (CGRP) receptor or an adrenomedullin (AM) receptor when co-expressed with receptor-activity-modifying proteins (RAMP) 1 or 2, respectively. The CL receptor shows 57% overall sequence identity with the CT receptor, but the homology is much lower in the extreme N-terminus. An N-terminal deletion mutant of the human (h) CL receptor (Delta18-hCL) and a chimeric receptor consisting of the N-terminal amino acids of the porcine (p) CT receptor fused to the Delta18-hCL receptor (pCT-hCL) were therefore analyzed. The Delta18-hCL receptor function was abolished when co-expressed with RAMP1 or -2. The pCT-hCL receptor was a fully functional CGRP receptor when co-expressed with RAMP1, but the RAMP2-dependent AM receptor function was impaired. Limited sequence similarities in the N-terminus of the pCT and the hCL receptors rescue CGRP but not AM receptor binding and signalling.

Paracrine/autocrine function of adrenomedullin in peripheral nerves of rats

The presence of adrenomedullin (AM) and of an AM receptor were investigated in highly enriched primary cultures of Schwann cells and perineural fibroblasts of newborn and adult rats. AM was released into the conditioned medium of adult perineural fibroblasts (1749+/-629 pgeq/10(5) cells per 24 h). mRNA encoding AM was also predominantly expressed in adult perineural fibroblasts. mRNA encoding the calcitonin receptor-like receptor (CRLR) and the receptor-activity-modifying proteins (RAMP) 1, -2 and -3 were demonstrated in all the primary cells, but the levels of RAMP1 mRNA relative to 18s rRNA were 10-fold lower than those of CRLR and RAMP2 and -3 encoding mRNA. The results are consistent with the expression of CRLR/RAMP2 and CRLR/RAMP3 heterodimeric AM receptors in all the primary cells examined. AM stimulated cAMP accumulation in newborn (EC(50) 0.62+/-0.29 nM) and adult (EC(50) 0.45+/-0.03 nM) rat Schwann cells and in newborn (EC(50) 0.79+/-0.50 nM) and adult (EC(50) 1.06+/-0.72 nM) rat perineural fibroblasts. The EC(50) of calcitonin gene-related peptide stimulated cAMP production was 93- to 100-fold higher than those of AM in the four types of primary cells studied. The co-expression of AM and its receptor in perineural fibroblasts and the expression of an AM receptor in Schwann cells suggest autocrine and/or paracrine modes of action of AM in peripheral nerves.

Critical roles of PPAR beta/delta in keratinocyte response to inflammation

The immediate response to skin injury is the release of inflammatory signals. It is shown here, by use of cultures of primary keratinocytes from wild-type and PPAR beta/delta(-/-) mice, that such signals including TNF-alpha and IFN-gamma, induce keratinocyte differentiation. This cytokine-dependent cell differentiation pathway requires up-regulation of the PPAR beta/delta gene via the stress-associated kinase cascade, which targets an AP-1 site in the PPAR beta/delta promoter. In addition, the pro-inflammatory cytokines also initiate the production of endogenous PPAR beta/delta ligands, which are essential for PPAR beta/delta activation and action. Activated PPAR beta/delta regulates the expression of genes associated with apoptosis resulting in an increased resistance of cultured keratinocytes to cell death. This effect is also observed in vivo during wound healing after an injury, as shown in dorsal skin of PPAR beta/delta(+/+) and PPAR beta/delta(+/-) mice.

Parathyroid hormone responses of cyclic AMP-, serum- and phorbol ester-responsive reporter genes in osteoblast-like UMR-106 cells

Parathyroid hormone (PTH) and PTH-related protein interact with a G protein-coupled receptor linked to the activation of adenylyl cyclase and phospholipase C signaling pathways. Regulation by PTH of the expression of three distinct, stably transfected luciferase reporter genes responsive to cAMP (CRE-luc), serum (SRE-luc) and phorbol ester (TRE-luc) has been studied in rat osteoblast-like UMR-106 cells. Maximal 43-fold induction of CRE-luc expression occurred in response to 100 nM rat (r)PTH(1-34) (EC50=0.44 nM), but SRE-luc and TRE-luc remained unaffected. Maximal 2.8- and 3.4-fold inductions of SRE-luc by 10 ng/ml EGF and 100 nM phorbol ester (PMA) were suppressed with 100 nM rPTH(1-34) (IC50=0.04 and 0.15 nM, respectively). Similarly, 7.3-fold induction of TRE-luc by 100 nM PMA was inhibited to 50% with 100 nM rPTH(1-34) (IC50=0.5 nM). Activation of mitogen-activated protein kinase by EGF and PMA was also suppressed by rPTH(1-34). 1 mM 8-Br-cAMP and 0.1 mM forskolin mimicked all the effects of rPTH(1-34). In conclusion, the regulation of target genes by PTH in osteoblast-like UMR-106 cells is mediated by the activation of the cAMP/protein kinase A signaling pathway.

Tissue-specific mRNA expression of a calcitonin receptor-like receptor during fetal and postnatal development

The distribution of calcitonin receptor-like receptor (CRLR) mRNA in developing rats was investigated by in situ hybridization. Signals were found in the piriform cortex, the central and basolateral amygdala and the amygdalostriatal transition area. Among peripheral organs, the CRLR was predominantly expressed in the lung. mRNA expression in blood vessels, liver, midgut, rectum and urethra was restricted to gestational days 16 and/or 20. The CRLR was thought to be a calcitonin gene-related peptide (CGRP) type 1 receptor (Aiyar et al., J. Biol. Chem., 271 (1996) 11325-11329). This contrasts with previously reported evidence that the CRLR is an orphan receptor with no identifiable interactions with CGRP and other related ligands (Flühmann et al., Biochem. Biophys. Res. Commun., 206 (1995) 341-347). In situ hybridization signals have not been detected in the cerebellum and the spleen known to present a high density of CGRP binding sites. The different regional distribution of CGRP receptor binding sites and CRLR mRNA implies the latter encoding a different CGRP receptor subtype.

Structure of a parathyroid hormone/parathyroid hormone-related peptide receptor of the human cerebellum and functional expression in human neuroblastoma SK-N-MC cells

Cloning and functional expression of a cDNA from the human cerebellum revealed a parathyroid hormone/parathyroid hormone-related peptide (PTH/PTHrP) receptor protein of 593 amino acids, identical in sequence to the PTH/PTHrP receptor of the human kidney and an osteoblast-like cell line (Schipani et al., Endocrinology, 132 (1993) 2157-2165). Expression of mRNA hybridizing with the cloned cDNA, indistinguishable in size on Northern blots from a 2.3 kb transcript in kidney and liver, was detected in eight brain areas. In situ hybridization histochemistry in rat brain tissue sections revealed predominant signals in the Purkinje cell layer of the cerebellum and in the mesencephalic nucleus of the trigeminal nerve. In human neuroblastoma (SK-N-MC) cells, stably transfected with the cloned cDNA, hPTH(1-84) and hPTH(1-34) displaced binding of 125 pM [125I][Tyr36]chPTHrP(1-36) to the PTH/PTHrP receptor with IC50 values of 4.0 +/- 0.6 nM and 2.00 +/- 0.08 nM, and stimulated cyclic AMP accumulation with EC50 values of 0.19 +/- 0.06 nM and 0.09 +/- 0.01 nM, respectively. 16 out of 48 cells responded to 100 nM hPTH(1-34) with a 2-10-fold transient increase of cytosolic free calcium concentrations. In conclusion, a PTH/PTHrP receptor, identified in the human cerebellum, has the primary structure of the corresponding receptors of kidney and bone. Expression in human neuroblastoma SK-N-MC cells revealed functional properties indistinguishable from those of non-neuronal tissues. The widespread distribution of PTHrP and its receptor in brain implies biological functions remaining to be elucidated.

A human orphan calcitonin receptor-like structure

A novel calcitonin receptor-like protein of 461 amino acids with seven putative transmembrane domains has been identified through molecular cloning in a cDNA library of the human cerebellum. 91% and 56% of the amino acids are identical in a rat orphan calcitonin receptor-like sequence and the human calcitonin receptor, respectively. 5.2 kb mRNA is predominantly expressed in the lung, heart and kidney. Specific binding of 125I-labeled salmon calcitonin and human calcitonin gene-related peptide-I to COS-7 cells transiently transfected with the receptor cDNA was less then 0.5%. Cellular cAMP accumulation was indistinguishable in cDNA transfected and non-transfected control COS-7 and renal tubular cells from the American opossum stimulated with human and salmon calcitonin, human calcitonin gene-related peptide-I and -II, human amylin, human adrenomedullin, lizard helodermin, salmon stanniocalcin and chicken parathyroid hormone-related protein. The receptor-like protein whose ligand remains to be discovered belongs to the family of receptors of calcitonin, parathyroid hormone, secretin, vasointestinal peptide and pituitary adenylate cyclase-activating polypeptide.