The receptor for advanced glycation end products (RAGE) is a cellular binding site for amphoterin. Mediation of neurite outgrowth and co-expression of rage and amphoterin in the developing nervous system

The receptor for advanced glycation end products (RAGE), a newly-identified member of the immunoglobulin superfamily, mediates interactions of advanced glycation end product (AGE)-modified proteins with endothelium and other cell types. Survey of normal tissues demonstrated RAGE expression in situations in which accumulation of AGEs would be unexpected, leading to the hypothesis that under physiologic circumstances, RAGE might mediate interaction with ligands distinct from AGEs. Sequential chromatography of bovine lung extract identified polypeptides with M(r) values of approximately 12,000 (p12) and approximately 23,000 (p23) which bound RAGE. NH2-terminal and internal protein sequence data for p23 matched that reported previously for amphoterin. Amphoterin purified from rat brain or recombinant rat amphoterin bound to purified sRAGE in a saturable and dose-dependent manner, blocked by anti-RAGE IgG or a soluble form of RAGE (sRAGE). Cultured embryonic rat neurons, which express RAGE, displayed dose-dependent binding of 125I-amphoterin which was prevented by blockade of RAGE using antibody to the receptor or excess soluble receptor (sRAGE). A functional correlate of RAGE-amphoterin interaction was inhibition by anti-RAGE F(ab')2 and sRAGE of neurite formation by cortical neurons specifically on amphoterin-coated substrates. Consistent with a potential role for RAGE-amphoterin interaction in development, amphoterin and RAGE mRNA/antigen were co-localized in developing rat brain. These data indicate that RAGE has physiologically relevant ligands distinct from AGEs which are likely, via their interaction with the receptor, to participate in physiologic processes outside of the context of diabetes and accumulation of AGEs.

Advanced glycation endproducts interacting with their endothelial receptor induce expression of vascular cell adhesion molecule-1 (VCAM-1) in cultured human endothelial cells and in mice. A potential mechanism for the accelerated vasculopathy of diabetes

Vascular cell adhesion molecule-1 (VCAM-1), an inducible cell-cell recognition protein on the endothelial cell surface (EC), has been associated with early stages of atherosclerosis. In view of the accelerated vascular disease observed in patients with diabetes, and the enhanced expression of VCAM-1 in diabetic rabbits, we examined whether irreversible advanced glycation endproducts (AGEs), could mediate VCAM-1 expression by interacting with their endothelial cell receptor (receptor for AGE, RAGE). Exposure of cultured human ECs to AGEs induced expression of VCAM-1, increased adhesivity of the monolayer for Molt-4 cells, and was associated with increased levels of VCAM-1 transcripts. The inhibitory effect of anti-RAGE IgG, a truncated form of the receptor (soluble RAGE) or N-acetylcysteine on VCAM-1 expression indicated that AGE-RAGE-induced oxidant stress was central to VCAM-1 induction. Electrophoretic mobility shift assays on nuclear extracts from AGE-treated ECs showed induction of specific DNA binding activity for NF-kB in the VCAM-1 promoter, which was blocked by anti-RAGE IgG or N-acetylcysteine. Soluble VCAM-1 antigen was elevated in human diabetic plasma. These data are consistent with the hypothesis that AGE-RAGE interaction induces expression of VCAM-1 which can prime diabetic vasculature for enhanced interaction with circulating monocytes.

Impaired endochondral ossification and angiogenesis in mice deficient in membrane-type matrix metalloproteinase I

Membrane-type matrix metalloproteinase I (MT1-MMP)-deficient mice were found to have severe defects in skeletal development and angiogenesis. The craniofacial, axial, and appendicular skeletons were severely affected, leading to a short and domed skull, marked deceleration of postnatal growth, and death by 3 wk of age. Shortening of bones is a consequence of decreased chondrocyte proliferation in the proliferative zone of the growth plates. Defective vascular invasion of cartilage leads to enlargement of hypertrophic zones of growth plates and delayed formation of secondary ossification centers in long bones. In an in vivo corneal angiogenesis assay, null mice did not have angiogenic response to implanted FGF-2, suggesting that the defect in angiogenesis is not restricted to cartilage alone. In tissues from null mice, activation of latent matrix metalloproteinase 2 was deficient, suggesting that MT1-MMP is essential for its activation in vivo.

Inhibitory PAS domain protein is a negative regulator of hypoxia-inducible gene expression

Alteration of gene expression is a crucial component of adaptive responses to hypoxia. These responses are mediated by hypoxia-inducible transcription factors (HIFs). Here we describe an inhibitory PAS (Per/Arnt/Sim) domain protein, IPAS, which is a basic helix-loop-helix (bHLH)/PAS protein structurally related to HIFs. IPAS contains no endogenous transactivation function but demonstrates dominant negative regulation of HIF-mediated control of gene expression. Ectopic expression of IPAS in hepatoma cells selectively impairs induction of genes involved in adaptation to a hypoxic environment, notably the vascular endothelial growth factor (VEGF) gene, and results in retarded tumour growth and tumour vascular density in vivo. In mice, IPAS was predominantly expressed in Purkinje cells of the cerebellum and in corneal epithelium of the eye. Expression of IPAS in the cornea correlates with low levels of expression of the VEGF gene under hypoxic conditions. Application of an IPAS antisense oligonucleotide to the mouse cornea induced angiogenesis under normal oxygen conditions, and demonstrated hypoxia-dependent induction of VEGF gene expression in hypoxic corneal cells. These results indicate a previously unknown mechanism for negative regulation of angiogenesis and maintenance of an avascular phenotype.

Vascular endothelial growth factor C induces angiogenesis in vivo

Vascular endothelial growth factor C (VEGF-C) recently has been described to be a relatively specific growth factor for the lymphatic vascular system. Here we report that ectopic application of recombinant VEGF-C also has potent angiogenic effects in vivo. VEGF-C is sufficiently potent to stimulate neovascularization from limbal vessels in the mouse cornea. Similar to VEGF, the angiogenic response of corneas induced by VEGF-C is intensive, with a high density of new capillaries. However, the outgrowth of microvessels stimulated by VEGF-C was significantly longer than that induced by VEGF. In the developing embryo, VEGF-C was able to induce branch sprouts from the established blood vessels. VEGF-C also induced an elongated, spindle-like cell shape change and actin reorganization in both VEGF receptor (VEGFR)-2 and VEGFR-3-overexpressing endothelial cells, but not in VEGFR-1-expressing cells. Further, both VEGFR-2 and VEGFR-3 could mediate proliferative and chemotactic responses in endothelial cells on VEGF-C stimulation. Thus, VEGF-C may regulate physiological angiogenesis and participate in the development and progression of angiogenic diseases in addition to lymphangiogenesis.

Purification and functional characterization of a histone H3-lysine 4-specific methyltransferase

Methylation of histone H3 at lysine 9 by SUV39H1 and subsequent recruitment of the heterochromatin protein HP1 has recently been linked to gene silencing. In addition to lysine 9, histone H3 methylation also occurs at lysines 4, 27, and 36. Here, we report the purification, molecular identification, and functional characterization of an H3-lysine 4-specific methyltransferase (H3-K4-HMTase), SET7. We demonstrate that SET7 methylates H3-K4 in vitro and in vivo. In addition, we found that methylation of H3-K4 and H3-K9 inhibit each other. Furthermore, H3-K4 and H3-K9 methylation by SET7 and SUV39H1, respectively, have differential effects on subsequent histone acetylation by p300. Thus, our study provides a molecular explanation to the differential effects of H3-K4 and H3-K9 methylation on transcription.

Receptor-mediated endothelial cell dysfunction in diabetic vasculopathy. Soluble receptor for advanced glycation end products blocks hyperpermeability in diabetic rats

Dysfunctional endothelium is associated with and, likely, predates clinical complications of diabetes mellitus, by promoting increased vascular permeability and thrombogenicity. Irreversible advanced glycation end products (AGEs), resulting from nonenzymatic glycation and oxidation of proteins or lipids, are found in plasma, vessel wall, and tissues and have been linked to the development of diabetic complications. The principal means through which AGEs exert their cellular effects is via specific cellular receptors, one of which, receptor for AGE (RAGE), is expressed by endothelium. We report that blockade of RAGE inhibits AGE-induced impairment of endothelial barrier function, and reverse, in large part, the early vascular hyperpermeability observed in diabetic rats. Inhibition of AGE- and diabetes-mediated hyperpermeability by antioxidants, both in vitro and in vivo, suggested the central role of AGE-RAGE-induced oxidant stress in the development of hyperpermeability. Taken together, these data support the concept that ligation of AGEs by endothelial RAGE induces cellular dysfunction, at least in part by an oxidant-sensitive mechanism, contributing to vascular hyperpermeability in diabetes, and that RAGE is central to this pathologic process.

Leptin induces vascular permeability and synergistically stimulates angiogenesis with FGF-2 and VEGF

Most endocrine hormones are produced in tissues and organs with permeable microvessels that may provide an excess of hormones to be transported by the blood circulation to the distal target organ. Here, we investigate whether leptin, an endocrine hormone, induces the formation of vascular fenestrations and permeability, and we characterize its angiogenic property in the presence of other angiogenic factors. We provide evidence that leptin-induced new blood vessels are fenestrated. Under physiological conditions, capillary fenestrations are found in the leptin-producing adipose tissue in lean mice. In contrast, no vascular fenestrations were detected in the adipose tissue of leptin-deficient ob/ob mice. Thus, leptin plays a critical role in the maintenance and regulation of vascular fenestrations in the adipose tissue. Leptin induces a rapid vascular permeability response when administrated intradermally. Further, leptin synergistically stimulates angiogenesis with fibroblast growth factor (FGF)-2 and vascular endothelial growth factor (VEGF), the two most potent and commonly expressed angiogenic factors. These findings demonstrate that leptin has another new function-the increase of vascular permeability.

Receptor for advanced glycation end products (AGEs) has a central role in vessel wall interactions and gene activation in response to circulating AGE proteins

The extended interaction of aldoses with proteins or lipids results in nonenzymatic glycation and oxidation, ultimately forming AGEs, the presence of which in the plasma and vessel wall is associated with diabetic vascular complications. We show here that AGE albumin in the intravascular space interacts with the vessel wall via binding to an integral membrane protein, receptor for AGE (RAGE), a member of the immunoglobulin superfamily, resulting in clearance from the plasma and induction of interleukin 6 mRNA. Intravenously infused 125I-AGE albumin showed a rapid phase of plasma clearance with deposition in several organs. Rapid removal of 125I-AGE albumin from the plasma was prevented by administration of a soluble, truncated form of RAGE, which blocked binding of 125I-labeled AGE albumin to cultured endothelial cells and mononuclear phagocytes, as well as by pretreatment with anti-RAGE IgG. Ultrastructural studies with AGE albumin-colloidal gold conjugates perfused in situ showed that in murine coronary vasculature this probe was taken up by endothelial plasmalemmal vesicles followed by transport either to the abluminal surface or by accumulation in intracellular vesicular structures reminiscent of endosomes and lysosomes. Consequences of AGE-RAGE interaction included induction of interleukin 6 mRNA expression in mice. These data indicate that RAGE mediates the interaction of AGEs with the vessel wall, both for removal of these glycated proteins from the plasma and for changes in gene expression.

RAGE: a novel cellular receptor for advanced glycation end products

Exposure of proteins to reducing sugars results in nonenzymatic glycation with the ultimate formation of advanced glycation end products (AGEs). One means through which AGEs modulate cellular functions is through binding to specific cell surface acceptor molecules. The receptor for AGEs (RAGE) is such a receptor and is a newly identified member of the immunoglobulin superfamily expressed on endothelial cells (ECs), mononuclear phagocytes (MPs), and vascular smooth muscle cells (SMCs) in both vivo and in vitro. Binding of AGEs to RAGE results in induction of cellular oxidant stress, as exemplified by the generation of thiobarbituric acid-reactive substances, expression of heme oxygenase type I, and activation of the transcription factor NF-kB, with consequences for a range of cellular functions. AGEs on the surface of diabetic red cells enhance binding to endothelial RAGE and result in enhanced oxidant stress in the vessel wall. By using reagents to selectively block access to RAGE, the role of this receptor in AGE-mediated perturbation of cellular properties can be dissected in detail.

Advanced glycation endproducts (AGEs) induce oxidant stress in the gingiva: a potential mechanism underlying accelerated periodontal disease associated with diabetes

We hypothesized that one mechanism underlying advanced periodontal disease in diabetes may involve oxidant stress in the gingiva, induced by the effects of Advanced Glycation Endproducts (AGEs), the irreversible products of non-enzymatic glycation and oxidation of proteins and lipids which accumulate in diabetic plasma and tissue. Infusion of AGE albumin, a prototypic ligand, into mice resulted in increased generation of thiobarbituric acid reactive substances (TBARS) compared with infusion of non-glycated albumin in the gingiva, as well as in the lung, kidney and brain. Pretreatment of the animals with the antioxidants probucol or N-acetylcysteine (NAC) prevented the generation of TBARS in the gingiva. Affinity-purified antibody to AGEs demonstrated increased immunoreactivity for AGEs in the vasculature and connective tissues of the gingiva in streptozotocin-induced diabetic mice compared to non-diabetic controls. Increased immunoreactivity for AGEs was also demonstrated in the gingiva of diabetic humans compared with non-diabetic individuals via immunohistochemistry and ELISA. Consistent with these data, immunohistochemistry for heme oxygenase-1, a marker of enhanced oxidant stress, was increased in the gingival vasculature of diabetic mice and humans compared with non-diabetic controls. These data suggest that AGEs present in diabetic gingiva may be associated with a state of enhanced oxidant stress, a potential mechanism for accelerated tissue injury.

The metastasis-associated Mts1(S100A4) protein could act as an angiogenic factor

The involvement of Mts1(S100A4), a small Ca(2+)-binding protein in tumor progression and metastasis had been demonstrated. However, the mechanism by which mts1(S100A4) promoted metastasis had not been identified. Here we demonstrated that Mts1(S100A4) had significant stimulatory effect on the angiogenesis. We detected high incidence of hemangiomas--benign tumors of vascular origin in aged transgenic mice ubiquitously expressing the mts1(S100A4) gene. Furthermore, the serum level of the Mts1(S100A4) protein increased with ageing. Tumors developed in Mts1-transgenic mice revealed an enhanced vascular density. We showed that an oligomeric, but not a dimeric form of the Mts1(S100A4) protein was capable of enhancing the endothelial cell motility in vitro and stimulate the corneal neovascularization in vivo. An oligomeric fraction of the protein was detected in the conditioned media as well as in human serum. The data obtained allowed us to conclude that mts1(S100A4) might induce tumor progression via stimulation of angiogenesis.

Interleukin-18 acts as an angiogenesis and tumor suppressor

Interleukin-18 (IL-18), also called interferon-gamma (IFN-gamma)-inducing factor, has recently been characterized as a potent IFN-gamma-inducing cytokine. We now report that IL-18 is a novel antiangiogenic and antitumor cytokine. In vitro, IL-18 specifically inhibits fibroblast growth factor-2-stimulated proliferation of capillary endothelial cells. In vivo, IL-18 is sufficiently potent to suppress the fibroblast growth factor-induced corneal neovascularization by systemic administration in mice. This cytokine also inhibits embryonic angiogenesis in the chick chorioallantoic membrane assay. Systemic and intralesional administrations of IL-18 produce a significant suppression of the growth of murine T241 fibrosarcoma in syngeneic C57Bl6/J and immunodeficient SCID mice. The antitumor effect appears to be potent because an average of >75% inhibition of primary tumor growth was observed at a dose of 50 microg/kg/day. In cell culture, murine T241 fibrosarcoma cells are insensitive to recombinant IL-18 at concentrations that significantly inhibit endothelial cell proliferation. Immunohistochemical studies of tumor tissues reveal hypovascularization of the IL-18-treated tumors. These results suggest that IL-18 may participate in the regulation of a switch of tumor angiogenesis.-Cao, R., Farnebo, J., Kurimoto, M., Cao, Y. Interleukin-18 acts as an angiogenesis and tumor suppressor.

Suppression of angiogenesis and tumor growth by the inhibitor K1-5 generated by plasmin-mediated proteolysis

Proteolytic enzymes are involved in generation of a number of endogenous angiogenesis inhibitors. Previously, we reported that angiostatin, a potent angiogenesis inhibitor, is a proteolytic fragment containing the first four kringle modules of plasminogen. In this report, we demonstrate that urokinase-activated plasmin can process plasminogen to release an angiogenesis inhibitor, K1-5 (protease-activated kringles 1-5). K1-5 inhibits endothelial-cell proliferation with a half-maximal concentration of approximately 50 pM. This inhibitory effect is endothelial-cell-specific and appears to be at least approximately 50-fold greater than that of angiostatin. A synergistic efficacy of endothelial inhibition was observed when angiostatin and kringle 5 (K5) were coincubated with capillary endothelial cells. The synergistic effect is comparable to that produced by K1-5 alone. Systemic treatment of mice with K1-5 at a low dose significantly blocked the fibroblast growth factor-induced corneal neovascularization, whereas angiostatin had no effect at the same dose. K1-5 also suppressed angiogenesis in chicken embryos. Systemic administration of K1-5 at a low dose at which angiostatin was ineffective significantly suppressed the growth of a murine T241 fibrosarcoma in mice. The antitumor effect correlates with the reduced neovascularization. These findings suggest that the plasmin-mediated proteolysis may be involved in the negative switch of angiogenesis.

Preparations, structures, and magnetic properties of a series of novel copper(II)-lanthanide(III) coordination polymers via hydrothermal reaction

The hydrothermal reaction of Ln2O3 (Ln = Er, Gd, and Sm), pyridine-2,5-dicarboxylic acid (H2pydc), and Cu(II) reagents (CuO, Cu(OAc)2-2H2O, or CuCl2-2H2O) with a mole ratio of 1:2:4 resulted in the formation of six polymeric Cu(II)-Ln(III) complexes, [(Ln2Cu3(pydc)6(H2O)12)-4H2O]n (Ln = Er (1); Ln = Gd (2)), [(Ln4Cu2(pydc)8(H2O)12)-4H2O]n (Ln = Sm (3); Ln = Gd (4); Ln = Er (5)), and [(Gd2Cu2(pydc)4(H2O)8)-Cu(pydc)2-12H2O]n (6). 1 and 2 are isomorphous and crystallize in triclinic space group Ponebar. Compounds 3-5 are isomorphous and crystallize in monoclinic space group P2(1)/c. Compound 6 crystallizes in triclinic space group Ponebar. Complexes 1 and 2 have one-dimensional zigzag chain structures and compounds 3-5 display three-dimensional wavelike polymeric structures, while 6 has an infinite sandwich-type structure. The different structures of the complexes are induced by the different forms of Cu(II) reagents; the reactions of Cu(OAc)2-2H2O yield high Cu/Ln ratio products 1, 2, and 6, while the reactions of CuO or CuCl2-2H2O/2,2'-bipyridine results in low Cu/Ln ratio compounds 3-5. Temperature-dependent magnetic susceptibilities for 2, 4, and 5 were studied, and the thermal stabilities of complexes 2 and 4 were examined.

Assembly of silver(I) polymers with helical and lamellar structures

The new versatile multidentate nonchelating ligand 1,2-bis[(2-pyr-imidinyl)-sulfanylmethyl]benzene (bpsb) was designed and prepared for supramolecular syntheses. Self-assembly between silver nitrate and the bpsb ligand resulted in the polymer [Ag4(bpsb)2-(NO3)4]n (1) with a single-stranded helical chain structure. Each bpsb ligand in 1 acts as a tetradentate ligand, in which two sulfur atoms and two nitrogen atoms from different pyrimidine groups coordinate to four Ag atoms in four different directions. The nitrate anions serve as a template for the formation of the helix and are either embedded in the interior of the helix or located in the flank of the helix. Self-assembly between silver perchlorate and the bpsb ligand under the same conditions gave rise to the polymer [Ag2(bpsb)3(ClO4)2]n (2) comprising a two-dimensional lamellar network containing crownlike cavities. The silver atoms in two adjacent layers are arranged staggered in 2. The two-dimensional lamellar network comprising isolated cavities of [Ag6(bpsb)6] is very different from that of usual honeycomb structures.

Vascular endothelial growth factor-B-deficient mice display an atrial conduction defect

BACKGROUND

Vascular endothelial growth factors (VEGFs) and their receptors are essential regulators of vasculogenesis and angiogenesis in both embryos and adults. One of the factors with a still unknown physiological function is VEGF-B, which is expressed in many tissues, including the heart.

METHODS AND RESULTS

Mice carrying a targeted deletion in the VEGF-B gene were developed. In VEGF-B(-/-) animals, no gross abnormalities were observed in organs that normally show high expression of VEGF-B, such as the heart, muscle, and kidney. Analysis of heart function by ECG showed that adult VEGF-B(-/-) mice have an atrial conduction abnormality characterized by a prolonged PQ interval. VEGF- or basic fibroblast growth factor-induced corneal angiogenesis was similar in normal and VEGF-B(-/-) mice.

CONCLUSIONS

VEGF-B seems to be required for normal heart function in adult animals but is not required for proper development of the cardiovascular system either during development or for angiogenesis in adults.

Nestin-containing cells express glial fibrillary acidic protein in the proliferative regions of central nervous system of postnatal developing and adult mice

We are interested in the expression patterns of nestin, an embryonic intermediate filament that represent a neural precursor marker, in the mammalian central nervous system. With an immunohistochemical approach, distribution of nestin-containing cells and their colocalization with glial fibrillary acidic protein (GFAP) or neuronal nuclear specific protein (NeuN) were studied in adult and postnatal days 2-30 (P2-30) mice. Nestin-immunoreactivity was predominately distributed in certain proliferative regions, such as cerebral cortex, hippocampus, hypothalamus, subfornical organ, cerebellar cortex, area postrema, midline raphe glial structures, as well as ependymal and subependymal zones of the brain and spinal cord. The majority of nestin-immunoreactive cells, characterized by astroglial profiles of multiple and radial processes, showed a partial overlapping distribution with that of GFAP-immunoreactive astroglial cells. Double immunofluorescence confirmed that about 77% of these nestin-immunoreactive cells exhibited GFAP-immunoreactivity, indicating that a large percentage of nestin-expressing cells may have committed to astroglial cells. In developing mice, down-regulation of nestin expression was observed between P7 and P14. Although co-expression of nestin and NeuN occurred in cortical neurons of P2-7 mice, nestin-containing cells showing NeuN-immunoreactivity disappeared in CNS in older animals. Our results reveal the distribution pattern of nestin-containing neural precursors in the postnatal CNS and provide evidence on their differentiation fate to neurons and astrocytes, suggesting that nestin-containing glial cells may play an important role in remodeling and repairing in the postnatal and adult central nervous system.

Design, synthesis and in vitro and in vivo antitumor activities of novel β-carboline derivatives

To further our SAR study on the chemistry and antitumor activity/neurotoxicity of beta-carboline alkaloids, several series of beta-carboline derivatives with various substituents were designed and synthesized from the starting material l-tryptophan on the basis of harmine chemical structure. Cytotoxic activities of these compounds were investigated in vitro. The results showed that some beta-carboline derivatives had significant cytotoxic activities against human tumor cell lines. Among all the synthesized beta-carboline derivatives, the compounds 27, 28 and 32, having a benzyl substituent at both position-2 and 9, respectively, were found to be the most potent compounds with IC50 value lower than 50 microM against all human tumor cell lines examined. Acute toxicities and antitumor activities of the selected beta-carboline derivatives in mice were also evaluated. The results demonstrated that a benzyl substituent at position-2 increased the antitumor activity as well as acute toxicity significantly. However an (ethoxycarbonyl)amino substituent at position-3 reduced the acute toxicity as well as antitumor activity remarkedly. These data suggested that (1) the antitumor potencies of beta-carboline derivatives were enhanced by the introduction of benzyl substituent into the position-2; (2) the acute toxicity of beta-carboline derivatives reduced dramatically by the introduction of an appropriate substituent into the position-3 and 9; (3) the beta-carboline structure might be an important basis for the design and synthesis of new antitumor drugs with significant antitumor activity and low toxicity.

Elevated plasma levels of vascular cell adhesion molecule-1 (VCAM-1) in diabetic patients with microalbuminuria: a marker of vascular dysfunction and progressive vascular disease

Advanced glycation endproducts (AGEs), which accumulate in diabetic vasculature, result in enhanced expression of endothelial cell-associated vascular cell adhesion molecule-1 (VCAM-1) as well release of a soluble form of VCAM-1 (sVCAM-1) into culture supernatants. We hypothesized that sVCAM-1 in diabetic plasma might reflect early vascular perturbation in diabetic vasculopathy. Diabetic patients with microalbuminuria, a group with a high incidence of vascular complications, had increased plasma levels of sVCAM-1, approximately 1.5-fold greater than diabetic patients without microalbuminuria; P < 0.05. sVCAM-1 may be an indicator of ongoing cellular dysfunction in diabetes, as well as a dynamic surrogate marker for the effectiveness of therapeutic interventions.