DIVERSIFICACIÓN DE LA EVALUACIÓN

Cytokines are inflammatory molecules that orchestrate communication amongst different cell types.

They may have autocrine and paracrine functions. These encompass previously named groups of cytokines with specific functions such as interleukins, inducing the effects of lymphocytes and chemokines that have chemoattractant properties.

Chemokines are usually 8kDa molecules and are mainly soluble factors which mediate intercellular communication and cell migration (Gunther, Zimmermann et al. 2011). Chemokines have more than 50 ligands with approximately 17 identified receptors. The chemokine families use the prefix C, CC, CXC or C’C to represent the residue at the amino terminus of the protein. CXC is the largest of these families, and has two amino-terminal cysteines that are separated by a nonconserved amino acid. CC chemokines are where the two amino-terminal cysteines are juxtaposed. All chemokine receptors (CCR 1-10 and CXCR 1-5) have been found in glomerular mRNA; however, this includes many cell types including infiltrating cells (Huber, Reinhardt et al. 2002). Human podocyte culture has shown expression of CXCR subtypes 1, 3, 4, 5 and CCR types 4, 8, 9, 10. Monocyte chemoattractant protein-1 (MCP-1), also known as CCL2; and CCL18 also known as PARC are CC chemokines.

The role of chemokines in DN and progression are increasingly being described. MCP-1, fractalkine and cytokine TNF-α, are all associated with progression of DN (Navarro-Gonzalez, Mora-Fernandez et al. 2011). Chemokines and cytokines are able to attract a number of immune cells including macrophages. Macrophages have been found in the interstitium of DN biopsies in those who had disease progression or advanced DN (Lewis, Steadman et al. 2008) hence these molecules may play an important role in orchestrating the progression of DN. In addition, coronary atherectomy specimens from diabetics have larger areas of monocyte-macrophage infiltration compared to those without diabetes (Moreno, Murcia et al. 2000). Chemokines have been found in atherosclerotic tissue and DM. MCP-1 has been shown to attract monocytes to vascular smooth muscle cells, contributing to the progression of atherosclerosis (Isoda, Folco et al. 2008). Recent clinical RCTs have looked into the benefit of TNF-α as a therapeutic target with Pentoxifylline, see section 1.11

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(Navarro-Gonzalez, Jarque et al. 2009). An initial study has shown a decrease in proteinuria and a slowing of disease progression with ACEi and ARBs (Navarro, Mora et al. 2003; Navarro, Mora et al. 2005).

Tubular epithelial cells are known to produce/overexpress MCP-1 and on activation regulate normal T cell expressed and secreted (RANTES or CCL5), when proteinuria occurs (Abbate, Zoja et al.

2006). Albumin upregulates IL-6 expression in tubular cells and is chemoattactant for lymphocytes and neutrophils. The proximal tubule has the receptor for megalin thereby facilitating internalisation and intracellular trafficking of cubulin. Cubulin binds albumin and transfers immunoglobulin G light chains. It has no transmembrane domain. Endocytosis may induce activation of transcription factors and gene expression that affect the haemodynamic and metabolic pathways identified in DN (Abbate, Zoja et al. 2006). Table 1.1 below shows the chemokines causing macrophage accumulation associated with tubulointerstitial injury that have been described since 2006 (Chow, Nikolic-Paterson et al. 2006).

Table 1.1 Cytokine effects in DN Cytokine Effects

IL-1 Alters expression of chemotactic factors, adhesion molecules, intraglomerular haemodynamics via prostaglandin synthesis. May increase vascular endothelial cell permeability and increase hyaluron production by renal tubular epithelial cells that increase glomerular cellularity (Jones and Phillips 2001).

Polymorphisms in IL-1R and IL-1β reported increased risk of ESRD in T2DM (Lee, Ihm et al. 2004) that was not seen in T1DM (Tarnow, Pociot et al. 1997).

IL-6 Has been seen to be involved in the development of thickening of GBM.

Possible effect on endothelial permeability and mesangial expansion (Navarro-Gonzalez and Mora-Fernandez 2008).

IL-18 Induces production of IL-1, interferon gamma (IFN-γ), TNFα and may be associated with endothelial cell apoptosis (Navarro-Gonzalez, Mora-Fernandez et al. 2011). Increases TGF-β via MAPK in tubuloepithelial cells (Miyauchi, Takiyama et al. 2009).

TNFα Causes direct renal injury, cellular apoptosis, endothelial permeability, glomerular haemodynamics and cell-cell adhesion. Contributes to early hypertrophy and hyperfiltration in DN (DiPetrillo, Coutermarsh et al. 2003).

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1.12.1 Monocyte Chemoattractant protein – 1/CCL2 (MCP-1)

MCP-1 is a CC chemokine attracting monocytes/macrophages and T cells (Yoshimura and Leonard 1992). MCP-1 is localised on chromosome 17q11-21 with a molecular weight between 9-17kDa and a mature peptide of 76 amino acids with its signal precursor of 23 amino acids (Yoshimura, Yuhki et al. 1989). Mesangial cells, podocytes and tubular epithelial cells have been found to produce MCP-1 when exposed to high glucose concentrations and AGEPs (Ha, Yu et al. 2002; Zhang, Nguyen et al.

2006). MCP-1 has previously been found in the urine of humans with DN (Banba, Nakamura et al.

2000). MCP-1 knockout mice were found to be protected from STZ induced DN (Chow, Nikolic-Paterson et al. 2006). In high glucose, MCP-1 can be induced in cultured mesangial cells without mechanical strain (Ihm, Park et al. 1998).

In a prospective study of patients with renal biopsies for CKD, high levels of proteinuria correlated with MCP-1 induced interstitial damage indicating a common pathway in the presence of proteinuria (Eardley, Zehnder et al. 2006). NF-κB activation and MCP-1 upregulation in the proximal tubular cells has been reported in DM (Mezzano, Aros et al. 2004).

Urinary MCP-1 has previously been reported to be significantly raised in macroalbuminuric diabetic patients (Tam, Riser et al. 2009). In microalbuminuric diabetic patients this relationship is reversed with low urinary levels of MCP-1 in DM. Urinary MCP-1 levels are not raised in proteinuric renal diseases such as nephrotic syndrome secondary to minimal change (Wada, Yokoyama et al. 1996).

Urinary MCP-1 has been seen to correlate with DN tubulointerstitial lesions and fibrosis (Wada, Furuichi et al. 2000) and with glomerular injury (Banba, Nakamura et al. 2000); thus the literature of MCP-1 in DN is well established.

1.12.2 Macrophage Migration Inhibitory Factor (MIF)

MIF is a pleiotropic cytokine that has been previously described in the recruitment of macrophages and T-cell activation (Metz and Bucala 1997). MIF is known to be produced by mesangial, glomerular epithelial, glomerular endothelial and tubular cells (Tesch, Nikolic-Paterson et al. 1998;

Matsumoto, Maruyama et al. 2005). MIF receptor CD74 has been found on podocytes in DN (Sanchez-Nino, Sanz et al. 2009). Recent phase 1 clinical trials are underway with anti-MIF antibodies in the treatment of prostate cancer following tumour regression in a mouse model using

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these antibodies (Hussain, Freissmuth et al. 2013). Previous studies with MIF knockout mice and MIF transgenic animals have demonstrated that MIF is an essential mediator in the development of renal disease (Leung, Chan et al. 2004; Sasaki, Nishihira et al. 2004). Recently MIF has been described as a candidate for inducing microalbuminuria in diabetic mice; however, db/db mice that do not develop microalbuminuria had higher urinary MIF levels than ob/ob mice that have microalbuminuria (Watanabe, Tomioka et al. 2013). Both diabetic mice strains had significantly increased MIF protein with significantly higher MIF gene expression in the db/db strain. The study suggests that MIF could be responsible for initiating microalbuminuria in DN.

MIF is preformed and stored within the cytoplasm of macrophages, pancreatic islet cells, myocytes, cardiomyocytes and intrinsic renal cells – glomerular/tubular epithelial cells and rat mesangial cells (Tesch, Nikolic-Paterson et al. 1998; Toso, Emamaullee et al. 2008). MIF has also been described in rejecting kidney allografts (Lan, Yang et al. 1998). Inhibition of MIF does not ameliorate acute renal allograft rejection in mice (Jose, David et al. 2003). MIF is known to prevent inhibition of NF-κB activation induced by glucocorticoids. In addition, MIF inhibits glucocorticoid induction of the mitogen activated protein kinase (MAPK) pathway (Lan 2008).

MIF receptor CD74 is found in podocytes and tubular cells in human DN. Receptor CD74 recruits CD44 to form a receptor complex activating the extracellular signal regulated kinase 1/2 (ERK1/2) pathways and MAPK p38 that promotes cell proliferation and the synthesis of prostaglandin E in leukocytes and fibroblasts (Leng, Metz et al. 2003). This is thought to be another pathway by which MIF induces its effects. MAPK p38 is a pathway involved in regulating proinflammatory cytokines, cell survival together with apoptosis, and maintaining the cytoskeleton (Adams, Badger et al. 2001).

ERK1/2 pathways are involved in transmitting signals from extracellular factors to regulate cellular processes (Koshikawa, Mukoyama et al. 2005). MAPK p38 and ERK1/2 pathways are reported to be needed for MIF induction of TNF related apoptosis inducing ligand (TRAIL) and MCP-1 in both podocytes and tubular epithelial cells (Benito-Martin, Ucero et al. 2009).

Ang2 has been reported to increase the synthesis of MIF from tubular epithelial cells whilst recruiting and activating leukocytes (Rice, Nikolic-Paterson et al. 2003). MIF receptor was found to be increased in podocytes stimulated with high glucose, TNFα and MCP-1 (Sanchez-Nino, Sanz et

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al. 2009). Urinary MIF is elevated in proliferative glomerulonephritis (GN) with no change detected in serum MIF levels of healthy controls or those with GN (Brown, Nikolic-Paterson et al. 2002).

The levels of urinary and serum MIF in the DN population are currently unknown.

MIF serum levels were found to be high in those with DN (Herder, Kolb et al. 2006). MIF was not found to increase apoptotic cell death, but to activate MAP kinases and increase TRAIL expression (Sanchez-Nino, Benito-Martin et al. 2010). TRAIL expression has previously been reported to be increased in patients with DN (Schneider, Thome et al. 1997). An increase in TRAIL has also been correlated with interstitial fibrosis, cell death, tubular atrophy and interstitial inflammation; hence activation of this cytokine by MIF could lead to progression in DN (Lorz, Benito-Martin et al. 2008).

The ESTHER study recently reported an increased risk of cardiovascular outcomes in DM with or without DN, proinflammatory cytokines and adiponectin. The study looked at serum MIF, 6, IL-18, adiponectin and leptin. In those with high MIF and IL-6 levels that had DN, an association was found with higher cardiovascular morbidity that was not seen in the absence of renal dysfunction.

High adiponectin levels were associated with higher risk of a primary cardiovascular event.

1.12.3 CC-Chemokine Ligand 18 (CCL18)

Cytokine CCL18 also known as PARC/MIP-4/AMAC-1/DCCK1/SYCA-18 is an 89 amino acid polypeptide on chromosome 17q11.2. No CCL18 is found in rodents. CCL18 is chemotactic for naïve T lymphocytes, CD38 mantle zone B lymphocytes and immature dendritic cells (van der Voort, Kramer et al. 2005). CCL18 has been described in a number of diseases such as Idiopathic pulmonary fibrosis, Systemic sclerosis, Rheumatoid arthritis, Gaucher’s disease, Atopic dermatitis, Bullous pemphigoid, Childhood acute lymphoblastic leukaemia and in particular ovarian and gastric malignancies (Atamas, Yurovsky et al. 1999; Struyf, Schutyser et al. 2003; Vulcano, Struyf et al.

2003; Leung, Yuen et al. 2004; Schutyser, Richmond et al. 2005; Boot, Verhoek et al. 2006; Luzina, Papadimitriou et al. 2006; Auer, Blass et al. 2007; Babu, Kumaraswami et al. 2009; Gunther, Carballido-Perrig et al. 2009). Expression of CCL18 is known to increase in antigen presenting cells exposed to IL-4/IL-10/IL-13 and vitamin D (Babu, Kumaraswami et al. 2009) Th2 lymphocyte cytokines. Expression of CCL18 in antigen presenting cells is decreased with Th1 lymphocyte cytokines, IFN-γ and with Lipopolysaccharide (LPS) (Gunther, Carballido-Perrig et al. 2009). The role of CCL18 in DN is unknown. More recently CCL18 has been found in adipocytes in people

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with non-alcoholic steatotic hepatitis (NASH). Those with fibrosis and NASH had a higher level of CCL18 messenger RNA (mRNA) in their adipocytes compared with those with NASH without fibrosis (Estep, Baranova et al. 2009). The role of CCL18 in insulin resistance and DN is unknown.

There is increasing evidence that insulin resistance has been linked with obesity and the metabolic syndrome and these are known risk factors for the development of T2DM. The finding of CCL18 in adipocytes together with its link to fibrosis makes CCL18 in DN an interesting area to examine.

CCL18 has previously been described to have a T-lymphocyte TGF-β dependent fibrotic pathway producing Col1 in resident fibroblasts, together with a TGF-β independent pathway where CCL18 directly acts on resident fibroblasts to produce Col4 (Luzina, Papadimitriou et al. 2006; Prasse, Pechkovsky et al. 2006; Pochetuhen, Luzina et al. 2007). Production of Col1 has been directly seen in response to stimulation of fibroblasts with CCL18 independent of TGF-β1 (Atamas, Luzina et al.

2003).

In Dr Tam and Dr Frankel’s research laboratory, (Ahmad, North et al. 2010) high levels of CCL18 were found in the peritoneal fluid of renal patients on peritoneal dialysis who developed encapsulating peritoneal sclerosis (EPS), a fibrotic condition affecting the peritoneum. Multivariate analysis showed that the amount of peritoneal CCL18 correlated significantly with the amount of glucose exposure in the patient’s dialysis regimen.

A prospective cohort study examining diabetic urine in Dr Tam and Dr Frankel’s research group (Qureshi A 2007 ASN abstract #551921) showed urinary CCL18 in T2DM with macroalbuminuria correlated positively with urinary ACR (Spearman’s correlation r =-0.36 p<0.0005) and negatively with estimated glomerular filtration rate (eGFR), Spearman’s correlation r =-0.36, p =0.0003).

Urinary CCL18 was raised and correlated with the severity of DN. These results were taken from 107 diabetic participants and 121 non-diabetic participants with other proteinuric renal diseases.

There was no significant difference in plasma CCL18 among three groups of diabetic participants with different severity of albuminuria. There was no correlation between urinary and plasma CCL18 suggesting CCL18 may be locally produced in the kidney.

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Recently a receptor for CCL18 has been described in tumour associated macrophages (TAM) that promote breast cancer metastasis (Bonecchi, Locati et al. 2011). It is a phosphatidyl-inosytol transfer protein that has an acidic region with a calcium binding domain and a 6 transmembrane domain with a C-terminal that interacts with PYK2 that is downstream from PKC pathways. The functional G-protein receptor is known as PITPNM3. It is unknown whether this receptor is required for CCL18 to exert all its effects or whether it uses a paracrine or autocrine method to exert its effects in addition to the use of this receptor. PITPNM3 has not been found on gastric invasive cancer tissue margin TAMs and may be tissue/organ specific. A role for serum CCL18 as a predictor for worsening lung fibrosis seen in systemic sclerosis has been proposed (Tiev, Hua-Huy et al.

2011).