Adiponectin: good, bad, or just plain ugly?

Sterile inflammation of peritoneal membrane caused by peritoneal dialysis: focus on the communication between immune cells and peritoneal stroma

Peritoneal dialysis is a widely used method for treating kidney failure. However, over time, the peritoneal structure and function can deteriorate, leading to the failure of this therapy. This deterioration is primarily caused by infectious and sterile inflammation. Sterile inflammation, which is inflammation without infection, is particularly concerning as it can be subtle and often goes unnoticed. The onset of sterile inflammation involves various pathological processes. Peritoneal cells detect signals that promote inflammation and release substances that attract immune cells from the bloodstream. These immune cells contribute to the initiation and escalation of the inflammatory response. The existing literature extensively covers the involvement of different cell types in the sterile inflammation, including mesothelial cells, fibroblasts, endothelial cells, and adipocytes, as well as immune cells such as macrophages, lymphocytes, and mast cells. These cells work together to promote the occurrence and progression of sterile inflammation, although the exact mechanisms are not fully understood. This review aims to provide a comprehensive overview of the signals from both stromal cells and components of immune system, as well as the reciprocal interactions between cellular components, during the initiation of sterile inflammation. By understanding the cellular and molecular mechanisms underlying sterile inflammation, we may potentially develop therapeutic interventions to counteract peritoneal membrane damage and restore normal function.

Adipocyte-Derived Paracrine Factors Regulate the In Vitro Development of Bovine Mammary Epithelial Cells

The mammary gland is composed of epithelial tissue forming ducts and lobules, and the stroma, composed of adipocytes, connective tissue, and other cell types. The stromal microenvironment regulates mammary gland development by paracrine and cell-cell interactions. In the present study, primary cultures of bovine mammary epithelial cells (bMEC) and bovine adipose-derived stem cells (bASC) subjected to adipogenic differentiation were used to investigate the influence of paracrine factors secreted by preadipocytes and adipocytes on bMEC development. Four types of conditioned media (CM) were collected from undifferentiated preadipocytes (preA) and adipocytes on days: 8, 12, 14 of differentiation. Next, bMEC were cultured for 24 h in CM and cell viability, apoptosis, migratory activity, ability to form spheroids on Matrigel, and secretory activity (alpha S1-casein concentration) were evaluated. CM derived from fully differentiated adipocytes (12 d and 14 d) significantly decreased the number of apoptotic cells in bMEC population and increased the size of spheroids formed by bMEC on Matrigel. CM collected from preadipocytes significantly enhanced bMEC's migration, and stimulated bMEC to produce alpha S1-casein, but only in the presence of prolactin. These results confirm that preadipocytes and adipocytes are important components of the stroma, providing paracrine factors that actively regulate the development of bovine mammary epithelium.

Adiponectin: a pleiotropic hormone with multifaceted roles

Adipose tissue mostly composed of different types of fat is one of the largest endocrine organs in the body playing multiple intricate roles including but not limited to energy storage, metabolic homeostasis, generation of heat, participation in immune functions and secretion of a number of biologically active factors known as adipokines. The most abundant of them is adiponectin. This adipocite-derived hormone exerts pleiotropic actions and exhibits insulin-sensitizing, antidiabetic, anti-obesogenic, anti-inflammatory, antiatherogenic, cardio- and neuroprotective properties. Contrariwise to its protective effects against various pathological events in different cell types, adiponectin may have links to several systemic diseases and malignances. Reduction in adiponectin levels has an implication in COVID-19-associated respiratory failure, which is attributed mainly to a phenomenon called 'adiponectin paradox'. Ample evidence about multiple functions of adiponectin in the body was obtained from animal, mostly rodent studies. Our succinct review is entirely about multifaceted roles of adiponectin and mechanisms of its action in different physiological and pathological states.

Serum Adiponectin Levels Are Positively Associated With Diabetic Peripheral Neuropathy in Chinese Patients With Type 2 Diabetes

OBJECTIVE

To investigate the association between serum adiponectin levels and diabetic peripheral neuropathy (DPN) in Chinese type 2 diabetes (T2D) patients.

DESIGN AND METHODS

Two hundred nineteen T2D patients aged 40-79 years were divided into two groups according to whether they had DPN. The systemic levels of five biomarkers were measured using a human adipokine multiplexed bead-based immunoassay. Diabetic peripheral neuropathy diagnostic criteria included both common DPN symptoms and neurological screening tests.

RESULTS

Most features of DPN (n=98) and non-DPN patients (n=121) are similar, but the DPN patients were slightly older, had longer diabetes duration, higher hemoglobin (Hb) A1c, lower estimated glomerular filtration rates (eGFR), less exercise, and used lipid-lowering drugs more often. Serum adiponectin levels of DPN patients were higher than that of non-DPN patients (8.13 vs. 9.63 mg/ml, P = 0.004). Serum adiponectin levels were positively associated with DPN after adjusting for age, gender, body mass index, hypertension, HbA1c, alcohol intake, smoking status, physical activity, log-transformed low density lipoprotein cholesterol, lipid-lowering drug usage, eGFR, and diabetes duration {odds ratio (OR) 1.72 [95% confidence interval (CI) 1.02-2.89], P = 0.041}. The OR refers to a doubling in biomarkers.

CONCLUSIONS

Serum adiponectin levels were higher in DPN patients compared to non‑DPN patients in this Chinese T2D population. Serum adiponectin levels were positively associated with DPN presence, independent of multiple confounders.

High molecular weight adiponectin inhibits vascular calcification in renal allograft recipients

BACKGROUND

Adiponectin (ADPN) prevents the development/recurrence of cardiovascular events via its anti-atherogenic effects. However, few long-term studies have examined the changes in serum ADPN levels and arterial calcification seen in renal allograft recipients.

SUBJECTS AND METHODS

The effects of the serum ADPN level on arterial calcification were examined in 51 Japanese renal allograft recipients. Abdominal aorta calcification was evaluated on computed tomography using the aortic calcification area index (ACAI). The change in the ACAI and serum high-molecular-weight (HMW)-ADPN fractions were studied over an 8-year period. The arterial expression of ADPN, ADPN receptors (AdipoR)1 and 2, and T-cadherin (cadherin-13) were also examined by immunohistochemistry.

RESULTS

The change in the ACAI were grouped into quartiles and compared with the alterations in the serum levels of each ADPN fraction over an 8-year period. The change in the ACAI was much lower in the patients with highly elevated HMW-ADPN levels.Multiple regression analysis demonstrated that an advanced age at transplant and a history of cardiovascular complications were associated with an increased change in the ACAI, while higher HMW-ADPN concentrations were associated with improvements in the ACAI. Serum HDL-C level was also identified as a positive factor to increase serum HMW-ADPN level.In immunohistochemical examinations, ADPN was detected on CD31-positive arterial endothelial cells from renal allograft biopsy samples. ADPN co-localized with T-cadherin and AdipoR1, but only partially co-localized with AdipoR2.

CONCLUSION

Both HMW-ADPN and HDL-C might inhibit the progression of vascular calcification by promoting ADPN binding to vascular endothelial cells via T-cadherin and AdipoR in Japanese renal allograft recipients.

Angiogenesis and Inflammation in Peritoneal Dialysis: The Role of Adipocytes

Chronic inflammation and angiogenesis are the most common complications in patients undergoing maintenance peritoneal dialysis (PD), resulting in progressive peritoneum remolding and, eventually, utrafiltration failure. Contributing to the deeper tissue under the peritoneal membrane, adipocytes play a neglected role in this process. Some adipokines act as inflammatory and angiogenic promoters, while others have the opposite effects. Adipokines, together with inflammatory factors and other cytokines, modulate inflammation and neovascularization in a coordinated fashion. This review will also emphasize cellular regulators and their crosstalk in long-term PD. Understanding the molecular mechanism, targeting changes in adipocytes and regulating adipokine secretion will help extend therapeutic methods for preventing inflammation and angiogenesis in PD.

Adiponectin is associated with early diabetic kidney disease in adults with type 1 diabetes: A Coronary Artery Calcification in Type 1 Diabetes (CACTI) Study

OBJECTIVE

The associations between elevated adiponectin and end-stage renal disease are well recognized and thought to be at least partially explained by reduced renal clearance. Conversely, the relationship between adiponectin and early diabetic kidney disease (DKD) with preserved glomerular filtration rate (GFR), including rapid GFR decline and incident chronic kidney disease (CKD) is unclear. We hypothesized that elevated adiponectin would be associated with early DKD in adults with type 1 diabetes.

METHODS

Adults with type 1 diabetes (n=646 at baseline, n=525 at 6years) had adiponectin and renal function by estimated GFR (eGFR) by CKD-EPI creatinine and albumin-excretion rate (AER) evaluated at baseline and 6years. Linear and logistic models evaluated the associations of baseline adiponectin with AER, macroalbuminuria (AER ≥200μg/min), eGFR, CKD (<60mL/min/1.73m²) and rapid GFR decline (>3mL/min/1.73m²/year). Models adjusted for age, sex, duration, HbA1c, SBP, LDL-C and current smoking.

RESULTS

Compared to non-diabetics, adults with type 1 diabetes had significantly higher adiponectin, and the difference remained significant after adjusting for AER and/or eGFR (p<0.0001). Adiponectin at baseline was positively associated with rapid GFR decline (OR: 1.24, 95% CI 1.00-1.53), incident CKD (OR: 1.75, 1.14-2.70), and persistent macroalbuminuria and CKD (OR: 1.61, 1.10-2.36) over 6years in adjusted models. The associations also remained significant after further adjustments for CRP, estimated insulin sensitivity and ACEi/ARB therapy.

CONCLUSIONS

Adults with type 1 diabetes have higher adiponectin than their non-diabetic peers, and elevated adiponectin at baseline is independently associated with greater odds of developing early DKD over 6years.

Adiponectin Fractions Influence the Development of Posttransplant Diabetes Mellitus and Cardiovascular Disease in Japanese Renal Transplant Recipients

Background

A few studies have investigated the role of adiponectin fraction for cardiovascular disease (CVD) in RTx recipients.

Subjects and Methods

We studied 57 adult subjects (39 males, 18 females; 10 cadaveric donors) with at least three years of allograft survival (median 251 months). We examined clinical backgrounds such as treated drugs, blood pressure (BP, mmHg), body mass index (BMI), and blood chemistry including cholesterol (total, LDL-C, HDL-C), glucose, glycated hemoglobin (HbA1c), and serum high and low-molecular-weight (HMW/LMW) ADPN fractions with regard to the associations of the visceral and subcutaneous fat areas on CT scan. We also analyzed the associations of CVD and post-transplant diabetes (PTDM) with ADPN fractions and the fat areas.

Results

The visceral fat area was inversely correlated with serum HMW and LMW ADPN levels and HMW ADPN ratio (r = -0.400, p = 0.002 and r = -0.296, p = 0.025 and r = -0.444, p<0.001, respectively). Furthermore, the visceral fat area was positively with the LMW ADPN ratio (r = 0.467, p<0.001), but no significant correlation was noted between the subcutaneous fat area and the ADPN ratio. On multiple regression analysis, eGFR and the visceral fat area were significant reducing factors of HMW ADPN levels, and the alteration of eGFR was identified as an increasing factor of HMW ADPN levels. Patients with CVD had larger visceral fat area (p = 0.004), lower HMW ADPN ratio (p = 0.022) and higher LMW ADPN ratio (p = 0.049). In addition, the higher HMW ADPN ratio and statin treatment were identified as reducing factors of the development of CVD, but the LDL-C level was an aggravating factor. Moreover, the higher LMW ADPN ratio and the visceral fat area were aggravating factors of PTDM.

Conclusion

Even in Japanese renal transplant recipients, visceral fat area and ADPN fractions were significant factors for the development of both CVD and PTDM.

Association between circulating adipocytokine concentrations and microvascular complications in patients with type 2 diabetes mellitus: A systematic review and meta-analysis of controlled cross-sectional studies

BACKGROUND

The adipocytokines leptin and adiponectin have been variously associated with diabetic microvascular complications. No comprehensive clinical data exist examining the association between adipocytokines and the presence of these complications.

METHODS

This is a systematic review of cross-sectional studies comparing circulating adipocytokines in patients with type 2 diabetes mellitus (T2DM), with and without microvascular complications. Studies were retrieved from MEDLINE, EMBASE, Scopus and Cochrane databases. Study quality was evaluated using a modified Newcastle-Ottawa Scale. Meta-analysis was performed using an inverse-variance model, providing standardised mean differences (SMD) and 95% confidence intervals (CI). Heterogeneity was determined by I(2) statistic.

RESULTS

Amongst 554 identified studies, 28 were included in the review. Study quality range was 3.5-9 (maximum 11). Higher leptin levels were associated with microalbuminuria (SMD=0.41; 95% CI=0.14-0.67; n=901; p=0.0003), macroalbuminuria (SMD=0.68; 95% CI=0.30-1.06; n=406; p=0.0004), and neuropathy (SMD=0.26; 95% CI=0.07-0.44; n=609; p=0.008). Higher adiponectin levels were associated with microalbuminuria (SMD=0.55; 95% CI=0.29-0.81, n=274; p<0.001), macroalbuminuria (SMD=1.37; 95% CI=0.78-1.97, n=246; p<0.00001), neuropathy (SMD=0.25; 95% CI=0.14-0.36; n=1516; p<0.00001), and retinopathy (SMD=0.38; 95% CI=0.25-0.51; n=1306; p<0.00001). Meta-regression suggested no influence of body mass index and duration of diabetes on effect size, and a weak trend in terms of age on effect size.

DISCUSSION

Our meta-analysis suggests leptin and adiponectin levels are higher in T2DM patients with microvascular complications. Studies were limited by cross-sectional design. Large prospective analyses are required to validate these findings.

Adiponectin gene expression in human primary adipocyte culture treated with uremic serum

End-stage renal disease (ESRD) is accompanied by an increased rate of morbidity and mortality due to cardiovascular disease (CVD). Although renal replacement therapy is required at this stage, it is associated with additional complications such as inflammation and dyslipidemia. It has been suggested that adiponectin has anti-inflammatory properties. We studied the potential role of uremic mileu on the adiponectin expression in human primary adipocyte culture. A cohort of 18 patients with ESRD (hemo-and peritoneal dialysis) and nine healthy controls were analyzed in a prospective cross-sectional study. Single blood samples were taken pre-and post-hemodialysis and in peritoneal dialysis patients. Serum concentrations of total adiponectin (7.95 ± 1.44 μg/mL; 6.73 ± 1.2 μg/mL; 13.7 ± 3.04 μg/mL, respectively) and high molecular weight adiponectin (3.03 ± 1.95 μg/mL; 3.57 ± 2.44 14 μg/mL; 8.02 ± 5 μg/mL respectively) were measured. Other biochemical parameters (cholesterol, low-density lipoprotein cholesterol and triglycerides) were assessed in all groups of patients. Adiponectin gene expression was determined using real-time polymerase chain reaction, and was found to be lower in ESRD patients compared with healthy controls with low dose but not with high-dose treatments. Serum concentrations of total adiponectin and high molecular weight adiponectin were significantly higher in the ESRD versus control group. These results provide an initial insight into understanding the putative role of adipose tissue in contributing to the association of CVD risk in patients with chronic kidney disease.

Oxidative stress and response in relation to coronary artery disease in type 1 diabetes

OBJECTIVE

Although oxidative stress (OxS) is thought to contribute to atherosclerosis and coronary artery disease (CAD), little is known about the variability in an individual's ability to respond to OxS. Therefore, we assessed potential indices of response to OxS and evaluated whether they modify the association between OxS and CAD.

RESEARCH DESIGN AND METHODS

We evaluated plasma α- and γ-tocopherol per unit cholesterol (potential response markers); urinary 15-isoprostane F2t per milligram creatinine (isoprostane [IsoP], a potential stress marker); and the α-tocopherol-to-IsoP ratio (as a measure of response to stress), measured three times during 20 years of follow-up, in relation to CAD incidence in a cohort with childhood-onset type 1 diabetes (n = 658; mean age at baseline, 28 years; duration of diabetes, 19 years). Participants with three samples (blood and either 24-h or overnight urine) available before the onset of CAD or the end of follow-up (n = 356) were selected for study.

RESULTS

In multivariable mixed models, α-tocopherol over time was inversely associated with CAD (β = -0.27; P = 0.02), whereas a direct association was observed for IsoP (β = 0.0008; P = 0.06). Moreover, the α-tocopherol-to-IsoP ratio was strongly and inversely related to CAD incidence (β = -0.72; P = 0.003), whereas in a separate model including α-tocopherol and IsoP, both biomarkers maintained statistical significance. No association was observed for γ-tocopherol (β = -0.22; P = 0.54).

CONCLUSIONS

These data suggest that a greater potential capability (α-tocopherol) to respond to OxS (urinary IsoP) relates to CAD incidence.

Urinary adiponectin excretion rises with increasing albuminuria in type 1 diabetes

AIM

Urinary adiponectin (u-adiponectin) excretion has been suggested to reflect early glomerular damage. Inspired by this, we studied the levels of u-adiponectin in type 1 diabetic patients with different levels of urinary albumin excretion (UAE).

METHODS

U-adiponectin was analysed by ELISA in type 1 diabetic patients: Fifty-eight with normoalbuminuria (<30mg albumin/24h), 43 with persistent microalbuminuria (30-300mg/24h) and 44 with persistent macroalbuminuria (>300mg/24h). For comparison, a control group of 55 healthy individuals was included.

RESULTS

U-adiponectin increased with increasing levels of UAE (p<0.01). U-adiponectin median (interquartile range): Normoalbuminuria 0.38 (0.14-1.31), microalbuminuria 1.12 (0.20-2.68), macroalbuminuria 9.20 (1.10-23.35) and controls 0.09 (0.06-0.24) μg/g creatinine. Levels were unrelated to sex, age, cholesterol, diastolic BP and BMI. U-adiponectin was weakly associated with increasing systolic BP and HbA1c (r(2)<0.1, p<0.05), but strongly related to increasing UAE (r(2)=0.57, p<0.001) and decreasing eGFR (r(2)=0.26, p<0.001). The relationship between UAE and u-adiponectin was significant in all groups and independent of eGFR, BMI, BP and HbA1c. Furthermore, u-adiponectin was associated with markers of tubular damage (p<0.01).

CONCLUSION

U-adiponectin rises with increasing levels of UAE in patients with type 1 diabetes. This is in accordance with the hypothesis that loss of adiponectin may reflect glomerular and/or tubular damage.

Differential effect of baseline adiponectin on all-cause mortality in hemodialysis patients depending on initial body mass index. Long-term follow-up data of 4.5 years

OBJECTIVES

We sought to investigate the interaction of adiponectin levels and body mass index (BMI) for predicting all-cause mortality in a cohort of hemodialysis (HD) patients.

DESIGN

Longitudinal, observational cohort study.

SETTING

HD unit.

SUBJECTS

Sixty patients (mean age: 64 ± 13 years, 39 men) with end-stage renal disease on maintenance HD followed up for 4.5 years represented the prospective study cohort.

INTERVENTION

Associations between baseline plasma adiponectin levels and initial BMI with all-cause mortality were assessed taking into account the assumption of nonlinear correlations. The association between adiponectin, BMI, and serum levels of interleukin-10 (IL-10) and interleukin-6 (IL-6) with survival was determined cross-sectionally.

MAIN OUTCOME MEASURE

All-cause mortality.

RESULTS

Nonlinear survival modeling showed that there was a U-shaped association of BMI with all-cause mortality, whereas there was an inverse U-shaped association for plasma adiponectin levels. Using a BMI of 24 kg/m(2) as a cutoff, an interaction effect of BMI on the association between adiponectin and mortality was observed (P = .045). In participants with BMI ≥ 24 kg/m(2), each 15 μg/mL increase in plasma adiponectin levels was associated with a decreased hazard of death (hazard ratio: 0.57, 95% CI: 0.32 to 0.99) in unadjusted analysis. In HD patients with BMI < 24 kg/m(2), no significant association was observed between adiponectin and mortality (P = .989). Cross-sectional analysis showed that in the subgroup of patients in whom the protective effect of adiponectin was observed (BMI ≥ 24 kg/m(2)), a positive linear association existed between adiponectin and IL-10 levels (r = 0.345, P = .027) as well as a negative association with IL-6 levels (r = -0.322, P = .040). No association was observed in patients with BMI < 24 kg/m(2), neither with IL-10 nor with IL-6.

CONCLUSIONS

Obesity possibly modifies the effect of adiponectin on all-cause mortality in HD patients, thus explaining the published conflicting results in recent literature regarding the association of plasma adiponectin levels and mortality in chronic kidney disease patients.

Is adiponectin a marker of preclinical atherosclerosis in kidney transplantation?

The aim of this study was to analyze the relationship between pre-transplant adiponectin (pre-ADP), abnormalities in glucose homeostasis (AGH) at three months post-transplantation, and preclinical atherosclerosis in non-diabetic patients prior to kidney transplantation (KT).

METHODS

We carried out a multicenter study in 157 non-diabetic KT patients (66.5% men; age: 50±13 yr). Pre-ADP levels were analyzed using radioimmunoassay. Carotid ultrasound was performed to determine carotid intima-media thickness (c-IMT). Oral glucose tolerance test was carried out to classify patients according ADA criteria.

RESULTS

Of the patients, 52.8% had AGH. Median pre-ADP was 19.5 (14-27) μg/mL. An inverse correlation was found between ADP and HOMA index (r=-0.432; p<0.001). Median c-IMT was 0.6 (0.48-0.71) mm. Significant inverse correlation existed between ADP and c-IMT on both sides (p<0.05). Patients with c-IMT >0.6 mm had more AGH (p=0.012) and lower ADP levels (p=0.02). We performed a logistic regression analysis using preclinical atherosclerosis (c-IMT ≥0.6 mm) as dependent variable and sex, age, BMI, ADP, AGH, and HOMA index as independent variables of altered c-IMT. Age, pre-ADP, and AGH were independent risk factors for elevated c-IMT.

CONCLUSIONS

Patients with AGH have a greater presence of preclinical atherosclerosis. ADP has an inverse relationship with AGH and is an independent marker of preclinical atherosclerosis.

Tumor necrosis factor (TNF-alpha) and C-reactive protein (CRP) are positively associated with the risk of chronic kidney disease in patients with type 2 diabetes

PURPOSE

Chronic low-grade inflammation may induce chronic kidney disease in patients with type 2 diabetes. This study investigated the relation between inflammatory biomarkers and chronic kidney disease in patients with type 2 diabetes, which has not yet been reported in Asian populations.

MATERIALS AND METHODS

A cross-sectional study was performed in 543 patients recruited from diabetic clinics for an ongoing, prospective study. Multivariate logistic regression was used to evaluate the association between inflammatory biomarkers and the presence of chronic kidney disease (estimated glomerular filtration rate < 60 mL/min per 1.73 m(2) by the simplified Modification of Diet in Renal Disease equation using plasma creatinine).

RESULTS

The risk of chronic kidney disease increased in the highest quartiles of C-reactive protein (CRP) [multivariate odds ratio (OR) = 3.73; 95% CI = 1.19-1.70] and tumor necrosis factor-alpha (multivariate OR = 4.45; 95% CI = 1.63-12.11) compared to the lowest quartiles after adjustments for age, sex, zinc intake, and other putative risk factors for chronic kidney disease.

CONCLUSION

Our results suggest that CRP and tumor necrosis factor-alpha may be independent risk factors for chronic kidney disease in patients with type 2 diabetes. A causal mechanism of this association should be evaluated in a followup study of Korean patients with type 2 diabetes.