Contribution of growth hormone and IGF-I to early diabetic nephropathy in type 1 diabetes

A cohort study found a high risk of end-stage kidney disease associated with acromegaly

Acromegaly is a chronic systemic disease caused by excess levels of growth hormone and insulin-like growth factor-1 and is associated with numerous complications. Significantly, there is a lack of longitudinal data on kidney complications in patients with acromegaly. As such, we investigated the risk of end-stage kidney disease (ESKD) (stage 5D, 5T) in these patients with nationwide data obtained from the National Health Information Database of the National Health Insurance Service in Republic of Korea. A retrospective cohort study was conducted of 2.187 patients with acromegaly and 10,935 age- and sex-matched (1:5) control subjects without acromegaly over a mean follow-up period of 6.51 years. The study outcomes were analyzed using Cox proportional hazards regression analysis controlling for age, sex, household income, residential area, type 2 diabetes, hypertension, dyslipidemia, urolithiasis, congestive heart failure, myocardial infarction, stroke, and atrial fibrillation. The incidence (per 1,000 person-years) ESKD was 2.00 among patients with acromegaly but only 0.46 among controls, (hazard ratio 4.35 (95% confidence interval 2.63-7.20)) implicating a significantly higher risk. After adjustment for covariates, the risk of ESKD (2.36 (1.36-4.12)) was still significantly higher in patients with acromegaly than that in controls. Among the covariates, diabetes and hypertension were significant facilitators between acromegaly and ESKD in mediation analysis. Pituitary surgery and somatostatin analogues did not significantly change these associations. Thus, acromegaly may be linked with a higher risk for ESKD both independently and through mediators such as diabetes and hypertension.

Youth versus adult-onset type 2 diabetic kidney disease: Insights into currently known structural differences and the potential underlying mechanisms

Type 2 diabetes (T2D) is a global health pandemic with significant humanitarian, economic, and societal implications, particularly for youth and young adults who are experiencing an exponential rise in incident disease. Youth-onset T2D has a more aggressive phenotype than adult-onset T2D, and this translates to important differences in rates of progression of diabetic kidney disease (DKD). We hypothesize that youth-onset DKD due to T2D may exhibit morphometric, metabolic, and molecular characteristics that are distinct from adult-onset T2D and develop secondary to inherent differences in renal energy expenditure and substrate metabolism, resulting in a central metabolic imbalance. Kidney structural changes that are evident at the onset of puberty also serve to exacerbate the organ’s baseline high rates of energy expenditure. Additionally, the physiologic state of insulin resistance seen during puberty increases the risk for kidney disease and is exacerbated by both concurrent diabetes and obesity. A metabolic mismatch in renal energetics may represent a novel target for pharmacologic intervention, both for prevention and treatment of DKD. Further investigation into the underlying molecular mechanisms resulting in DKD in youth-onset T2D using metabolomics and RNA sequencing of kidney tissue obtained at biopsy is necessary to expand our understanding of early DKD and potential targets for therapeutic intervention. Furthermore, large-scale clinical trials evaluating the duration of kidney protective effects of pharmacologic interventions that target a metabolic mismatch in kidney energy expenditure are needed to help mitigate the risk of DKD in youth-onset T2D.

Renal effects of growth hormone in health and in kidney disease

Growth hormone (GH) and its mediator insulin-like growth factor-1 (IGF-1) have manifold effects on the kidneys. GH and IGF receptors are abundantly expressed in the kidney, including the glomerular and tubular cells. GH can act either directly on the kidneys or via circulating or paracrine-synthesized IGF-1. The GH/IGF-1 system regulates glomerular hemodynamics, renal gluconeogenesis, tubular sodium and water, phosphate, and calcium handling, as well as renal synthesis of 1,25 (OH)2 vitamin D3 and the antiaging hormone Klotho. The latter also acts as a coreceptor of the phosphaturic hormone fibroblast-growth factor 23 in the proximal tubule. Recombinant human GH (rhGH) is widely used in the treatment of short stature in children, including those with chronic kidney disease (CKD). Animal studies and observations in acromegalic patients demonstrate that GH-excess can have deleterious effects on kidney health, including glomerular hyperfiltration, renal hypertrophy, and glomerulosclerosis. In addition, elevated GH in patients with poorly controlled type 1 diabetes mellitus was thought to induce podocyte injury and thereby contribute to the development of diabetic nephropathy. This manuscript gives an overview of the physiological actions of GH/IGF-1 on the kidneys and the multiple alterations of the GH/IGF-1 system and its consequences in patients with acromegaly, CKD, nephrotic syndrome, and type 1 diabetes mellitus. Finally, the impact of short- and long-term treatment with rhGH/rhIGF-1 on kidney function in patients with kidney diseases will be discussed.

A review of renal GH/IGF1 family gene expression in chronic kidney diseases

Despite decades of study on the contribution of growth hormone (GH) to the development of kidney disease, there remains the question of the relative contribution of elevated levels of GH to kidney damage in humans, particularly in diabetic nephropathy occurring in type 1 patients. In this study, we reviewed several publicly available datasets to examine transcription of twelve genes associated with the GH/IGF1 axis in several types of human and rodent kidney diseases. Our analyses revealed downregulation of renal GHR and IGF1 gene expression in several different chronic human kidney diseases, including diabetic nephropathy, with general upregulation of IGFBP6 in the same tissues and diseases. These findings were generally supported by a review of studies in rodent models. In healthy and diseased human kidneys, increased GHR gene expression was associated with increases in glomerular filtration rate (GFR) and decreases in serum creatinine. IGFBP6 gene expression demonstrated the opposite clinical correlation. Our results suggest the kidney may exhibit GH insensitivity due to low GHR gene expression during most chronic kidney diseases.

Future glycemic control of children diagnosed with type 1 diabetes mellitus at toddler and preschool/school age

Background The main objective of this study was to compare future glycemic control in children diagnosed with type 1 diabetes mellitus (T1DM) at toddler age and preschool/school age. In addition, we aimed to examine risk factors known to be associated with future glycated hemoglobin A1c (HbA1c) levels in children diagnosed with T1DM. Methods This is a retrospective cohort study of 85 patients diagnosed with T1DM at toddler age (group 1; 0-2.9 years; n = 36) or preschool/school age (group 2; 5-6.9 years; n = 49) who were followed up at the University Children's Hospital in Zurich for at least 10 consecutive years or until the age of 15 years. Results The mean HbA1c level in the first year after diagnosis had a highly predictive value about glycemic control in the following 6 years. In addition, a longer duration of T1DM was associated with higher HbA1c values. HbA1c values did not differ significantly within 11 years after diagnosis between children in the two age groups. Neither was a difference found when comparing the two groups in respect to their chronological age, although a trend was noted (p = 0.09). This trend is very likely due to a longer duration of diabetes in group 1. Conclusions HbA1c level in the first year predicts glycemic control for the next 6 years and deterioration of HbA1c values can be noted with longer duration of T1DM. Moreover, our study demonstrated similar future glycemic control in patients diagnosed with T1DM at toddler age and preschool/school age.

Focal segmental glomerulosclerosis in which urinary protein improved after surgical treatment for acromegaly: a case report

Background

Focal segmental glomerulosclerosis is characterized by partial (segmental) sclerotic lesions in some glomeruli (focal). Primary focal segmental glomerulosclerosis is generally considered resistant to steroid therapy. However, acromegaly is a disease that causes peculiar facial features, body types, and metabolic abnormalities due to the excessive secretion of growth hormone by a pituitary adenoma. Growth hormone has been reported to be involved in glomerular cell growth, mesangial proliferation, and glomerulosclerosis in the kidney.

Case presentation

We report a case of a Japanese patient with focal segmental glomerulosclerosis in whom decreased urinary protein was observed after surgical treatment for acromegaly.

Conclusion

The patient’s urinary protein improved as the concentration of growth hormone/insulin-like growth factor 1 decreased.

The effects of growth hormone on therapy resistance in cancer

Pituitary derived and peripherally produced growth hormone (GH) is a crucial mediator of longitudinal growth, organ development, metabolic regulation with tissue specific, sex specific, and age-dependent effects. GH and its cognate receptor (GHR) are expressed in several forms of cancer and have been validated as an anti-cancer target through a large body of in vitro, in vivo and epidemiological analyses. However, the underlying molecular mechanisms of GH action in cancer prognosis and therapeutic response had been sparse until recently. This review assimilates the critical details of GH-GHR mediated therapy resistance across different cancer types, distilling the therapeutic implications based on our current understanding of these effects.

Cumulative Kidney Complication Risk by 50 Years of Type 1 Diabetes: The Effects of Sex, Age, and Calendar Year at Onset

OBJECTIVE

A common belief is that only a minority of patients with type 1 diabetes (T1D) develop advanced kidney disease and that incidence is higher among men and lower in those diagnosed at a younger age. However, because few patients with T1D survived to older ages until recently, long-term risks have been unclear.

RESEARCH DESIGN AND METHODS

We examined the 50-year cumulative kidney complication risk in a childhood-onset T1D cohort diagnosed during 1950-80 (n = 932; mean baseline age 29 years, duration 19 years). Participants comprised 144 who died prior to baseline, 130 followed with periodic surveys, and 658 followed with biennial surveys and a maximum of nine examinations for 25 years. Micro- and macroalbuminuria were defined as an albumin excretion rate of 20-199 and ≥200 μg/min, respectively, and end-stage renal disease (ESRD) was defined as dialysis or kidney transplantation. Cumulative incidence was estimated at 10-year intervals between 20 and 50 years^, duration and compared by calendar year of diabetes onset.

RESULTS

By 50 years^, T1D duration, ESRD affected 60% of the cohort; macroalbuminuria, 72%; and microalbuminuria, 88%. Little evidence existed for declines in cumulative incidence in recent cohorts, except for ESRD (microalbuminuria 3% increase, macroalbuminuria no change; ESRD 45% decrease by 40 years of T1D duration). Onset before age 6 years was associated with the lowest risk; incidence generally did not differ by sex.

CONCLUSIONS

Some degree of kidney disease in T1D is virtually universal at long durations and not declining, which has major implications for formulating health care and research strategies. ESRD has declined, but continues to affect >25% of the population by 40 years^, duration.

[Importance of diabetic nephropathy in childhood. Clinical findings and basic research in recent decades]

Over the past decades diabetes mellitus is becoming a global pandemic affecting more than 371 million people worldwide. Parallel with the increasing prevalence of type 1 diabetes, there is a growing number of type 2 diabetes cases among children and adolescents that poses new challenges to pediatricians. Diabetic nephropathy is one of the major causes of end stage renal disease, developing in approximately 30% of diabetic patients. However, overt nephropathy is rare in childhood; screening and ongoing assessment for the earliest manifestation of renal injury is extremely important in this young population, as well. Although in the past decades intensive research activity focused on understanding of the pathomechanism of diabetic nephropathy and invention of new therapeutic approaches, prevention and definitive care are still urgently needed. The clinical section of the article summarizes the present state of epidemiology, diagnosis and current therapies of childhood diabetic nephropathy. Then, the authors discuss the state of basic research and show a few promising targets for drug development.

Growth hormone, insulin-like growth factor-1, and the kidney: pathophysiological and clinical implications

Besides their growth-promoting properties, GH and IGF-1 regulate a broad spectrum of biological functions in several organs, including the kidney. This review focuses on the renal actions of GH and IGF-1, taking into account major advances in renal physiology and hormone biology made over the last 20 years, allowing us to move our understanding of GH/IGF-1 regulation of renal functions from a cellular to a molecular level. The main purpose of this review was to analyze how GH and IGF-1 regulate renal development, glomerular functions, and tubular handling of sodium, calcium, phosphate, and glucose. Whenever possible, the relative contributions, the nephronic topology, and the underlying molecular mechanisms of GH and IGF-1 actions were addressed. Beyond the physiological aspects of GH/IGF-1 action on the kidney, the review describes the impact of GH excess and deficiency on renal architecture and functions. It reports in particular new insights into the pathophysiological mechanism of body fluid retention and of changes in phospho-calcium metabolism in acromegaly as well as of the reciprocal changes in sodium, calcium, and phosphate homeostasis observed in GH deficiency. The second aim of this review was to analyze how the GH/IGF-1 axis contributes to major renal diseases such as diabetic nephropathy, renal failure, renal carcinoma, and polycystic renal disease. It summarizes the consequences of chronic renal failure and glucocorticoid therapy after renal transplantation on GH secretion and action and questions the interest of GH therapy in these conditions.

The insulin-like growth factor system in chronic kidney disease: Pathophysiology and therapeutic opportunities

The growth hormone-insulin-like growth factor-insulin-like growth factor binding protein (GH-IGF-IGFBP) axis plays a critical role in the maintenance of normal renal function and the pathogenesis and progression of chronic kidney disease (CKD). Serum IGF-I and IGFBPs are altered with different stages of CKD, the speed of onset, the amount of proteinuria, and the potential of remission. Recent studies demonstrate that growth failure in children with CKD is due to a relative GH insensitivity and functional IGF deficiency. The functional IGF deficiency in CKD results from either IGF resistance due to increased circulating levels of IGFBPs or IGF deficiency due to increased urinary excretion of serum IGF-IGFBP complexes. In addition, not only GH and IGFs in circulation, but locally produced IGFs, the high-affinity IGFBPs, and low-affinity insulin-like growth factor binding protein-related proteins (IGFBP-rPs) may also affect the kidney. With respect to diabetic kidney disease, there is growing evidence suggesting that GH, IGF-I, and IGFBPs are involved in the pathogenesis of diabetic nephropathy (DN). Thus, prevention of GH action by blockade either at the receptor level or along its signal transduction pathway offers the potential for effective therapeutic opportunities. Similarly, interrupting IGF-I and IGFBP actions also may offer a way to inhibit the development or progression of DN. Furthermore, it is well accepted that the systemic inflammatory response is a key player for progression of CKD, and how to prevent and treat this response is currently of great interest. Recent studies demonstrate existence of IGF-independent actions of high-affinity and low-affinity-IGFBPs, in particular, antiinflammatory action of IGFBP-3 and profibrotic action of IGFBP-rP2/CTGF. These findings reinforce the concept in support of the clinical significance of the IGF-independent action of IGFBPs in the assessment of pathophysiology of kidney disease and its therapeutic potential for CKD. Further understanding of GH-IGF-IGFBP etiopathophysiology in CKD may lead to the development of therapeutic strategies for this devastating disease. It would hold promise to use of GH, somatostatin analogs, IGFs, IGF agonists, GHR and insulin-like growth factor-I receptor (IGF-IR) antagonists, IGFBP displacer, and IGFBP antagonists as well as a combination treatment as therapeutic agents for CKD.

The effects of type 1 IGF receptor inhibition in a mouse model of diabetic kidney disease

OBJECTIVE

We have recently shown increased sensitivity to IGF-I induced signal transduction in kidneys of diabetic mice. Accordingly we investigated the effects of PQ401, a novel diarylurea compound that inhibits IGF1R autophosphorylation in type I diabetes.

METHODS

Control (C) and Diabetic (D) mice were administered PQ401 (CP, DP) or vehicle (C, D) for 3weeks.

RESULTS

CP animals showed a decrease in renal phosphorylated (p-)AKT and p-IGF1R. However, PQ401 had no effect on diabetic state (hyperglycemia, weight loss) or renal disease parameters (hypertrophy, hyperfiltration and albuminuria). Type IV collagen as well as TGF-β mRNA increased in DP and D compared to C. In the CP group renal hypertrophy with fat accumulation in proximal tubuli and increased renal IGF-I, collagen IV and TGF-β mRNA were seen.

CONCLUSIONS

IGF1R inhibition by PQ401 exerted no significant effects on diabetic kidney disease parameters, arguing against a role for IGF-I in the pathogenesis of diabetic kidney disease. However, PQ401 affects normal kidneys, inducing renal hypertrophy as well as collagen and fat accumulation, with increased renal IGF-I mRNA, suggestive of a damage-regeneration process. Therefore, this diarylurea compound is not beneficial in early diabetic kidney disease. Its potential deleterious effects on kidney tissue need to be further investigated.

Sex-related differences in the long-term risk of microvascular complications by age at onset of type 1 diabetes

AIMS/HYPOTHESIS

This study examined sex-related differences in the cumulative risk of proliferative retinopathy (PR) and end-stage renal disease (ESRD) over 40 years of duration of type 1 diabetes according to age at diabetes onset.

METHODS

We assessed 4,416 patients from the Finnish Diabetic Nephropathy Study population. Kaplan-Meier analysis was used to provide cumulative incidence rates and Cox regression analyses for HRs.

RESULTS

There were no sex-related differences in the cumulative incidence of ESRD in patients diagnosed with type 1 diabetes between 0 to 4 and 5 to 9 years. Thereafter the risk started to diverge. The cumulative incidence of ESRD in patients diagnosed between 10 to 14 and ≥15 years was 17.4% (95% CI 13.4-21.2) and 13.0% (9.6-16.2) respectively in women, while in men it was 32.2% (28.0-36.1) and 24.6% (20.8-28.1) respectively. The respective HRs were (onset at 10 to 14 years) 1.9 (p < 0.0001) and (onset at ≥15 years) 1.8 (p < 0.001), respectively. There was no difference in the risk of PR between men and women diagnosed between 0 and 4 years of age, but progressive sex-related differences in the cumulative incidence of PR were observed with increasing age at onset. The HRs for men in the age-at-onset groups 5 to 9, 10 to 14 and ≥15 years of age were 1.3 (95% CI 1.0-1.6), 1.3 (1.1-1.6) and 2.1 (1.6-2.6) compared with women in these groups, respectively.

CONCLUSIONS/INTERPRETATION

The difference between the sexes with regard to risk of diabetic microvascular complications is highly dependent on the age at onset of diabetes. The risk of ESRD and PR risk doubled in men compared with women when age at onset was ≥15 years.

Podocytopathy in diabetes: a metabolic and endocrine disorder

Diabetic nephropathy (DN) represents a major public health cost. Tight glycemic and blood pressure control can dramatically slow, but not stop, the progression of the disease, and a large number of patients progress toward end-stage renal disease despite currently available interventions. An early and key event in the development of DN is loss of podocyte function (or glomerular visceral epithelial cells) from the kidney glomerulus, where they contribute to the integrity of the glomerular filtration barrier. Recent evidence suggests that podocytes can be the direct target of circulating hormones, lipids, and adipokines that are affected in diabetes. We review the clinical and experimental evidence implicating novel endocrine and metabolic pathways in the pathogenesis of podocyte dysfunction and the development of DN.

Correlation of serum insulin like growth factor-I with retinopathy in Malaysian pregnant diabetics

AIM

To study the association of serum insulin-like growth factor-I (IGF-I) with diabetic retinopathy.

METHODS

Serum IGF-1 levels were measured in 25 pregnant diabetic patients and 25 pregnant non-diabetic patients who were matched for age, ethnicity, parity and period of gestation. Fundus examination was performed in both groups at 28, 32 and 36 weeks of gestation.

RESULTS

The serum IGF-I level was significantly elevated in pregnant diabetics compared to pregnant non-diabetics (366±199μg/L vs 184±89μg/L, (P=0.0001) at 24 weeks, 535±251μg/L vs 356±89μg/L, (P=0.007) at 32 weeks and 404±166μg/L vs 264±113μg/L, (P=0.003) at 36 weeks of gestation). The pregnant diabetics with established diabetes had significantly higher IGF-1 level than gestational diabetes at 28, 32 and 36 weeks of gestation. The serum IGF-I level in pregnant diabetics with retinopathy was significantly higher than that in those without retinopathy at all periods of gestation.

CONCLUSION

Increased serum IGF-1 in pregnancy may increase the risks for retinopathy.

The glomerular podocyte as a target of growth hormone action: implications for the pathogenesis of diabetic nephropathy

Involvement of the growth hormone (GH) / insulin-like growth factor 1 (IGF-I) axis in the pathogenesis of diabetic nephropathy (DN) is strongly suggested by studies investigating the impact of GH excess and deficiency on renal structure and function. GH excess in both the human (acromegaly) and in transgenic animal models is characterized by significant structural and functional changes in the kidney. In the human a direct relationship has been noted between the activity of the GH/IGF-1 axis and renal hypertrophy, microalbuminuria, and glomerulosclerosis. Conversely, states of GH deficiency or deficiency or inhibition of GH receptor (GHR) activity confer a protective effect against DN. The glomerular podocyte plays a central and critical role in the structural and functional integrity of the glomerular filtration barrier and maintenance of normal renal function. Recent studies have revealed that the glomerular podocyte is a target of GH action and that GH's actions on the podocyte could be detrimental to the structure and function of the podocyte. These results provide a novel mechanism for GH's role in the pathogenesis of DN and offer the possibility of targeting the GH/IGF-1 axis for the prevention and treatment of DN.

Growth hormone (GH)-dependent expression of a natural antisense transcript induces zinc finger E-box-binding homeobox 2 (ZEB2) in the glomerular podocyte: a novel action of gh with implications for the pathogenesis of diabetic nephropathy

Growth hormone (GH) excess results in structural and functional changes in the kidney and is implicated as a causative factor in the development of diabetic nephropathy (DN). Glomerular podocytes are the major barrier to the filtration of serum proteins, and altered podocyte function and/or reduced podocyte number is a key event in the pathogenesis of DN. We have previously shown that podocytes are a target for GH action. To elucidate the molecular basis for the effects of GH on the podocyte, we conducted microarray and RT-quantitative PCR analyses of immortalized human podocytes and identified zinc finger E-box-binding homeobox 2 (ZEB2) to be up-regulated in a GH dose- and time-dependent manner. We established that the GH-dependent increase in ZEB2 levels is associated with increased transcription of a ZEB2 natural antisense transcript required for efficient translation of the ZEB2 transcript. GH down-regulated expression of E- and P-cadherins, targets of ZEB2, and inhibited E-cadherin promoter activity. Mutation of ZEB2 binding sites on the E-cadherin promoter abolished this effect of GH on the E-cadherin promoter. Whereas GH increased podocyte permeability to albumin in a paracellular albumin influx assay, shRNA-mediated knockdown of ZEB2 expression abrogated this effect. We conclude that GH increases expression of ZEB2 in part by increasing expression of a ZEB2 natural antisense transcript. GH-dependent increase in ZEB2 expression results in loss of P- and E-cadherins in podocytes and increased podocyte permeability to albumin. Decreased expression of P- and E-cadherins is implicated in podocyte dysfunction and epithelial-mesenchymal transition observed in DN. We speculate that the actions of GH on ZEB2 and P- and E-cadherin expression play a role in the pathogenesis of microalbuminuria of DN.

Identification of differentially expressed genes in the kidneys of growth hormone transgenic mice

OBJECTIVE

Bovine growth hormone (bGH) transgenic mice develop severe kidney damage. This damage may be due, at least in part, to changes in gene expression. Identification of genes with altered expression in the bGH kidney may identify mechanisms leading to damage in this system that may also be relevant to other models of kidney damage.

DESIGN

cDNA subtraction libraries, northern blot analyses, microarray analyses and real-time reverse transcription polymerase chain reaction (RT/PCR) assays were used to identify and verify specific genes exhibiting differential RNA expression between kidneys of bGH mice and their non-transgenic (NT) littermates.

RESULTS

Immunoglobulins were the vast majority of genes identified by the cDNA subtractions and the microarray analyses as being up-regulated in bGH. Several glycoprotein genes and inflammation-related genes also showed increased RNA expression in the bGH kidney. In contrast, only a few genes were identified as being significantly down-regulated in the bGH kidney. The most notable decrease in RNA expression was for the gene encoding kidney androgen-regulated protein.

CONCLUSIONS

A number of genes were identified as being differentially expressed in the bGH kidney. Inclusion of two groups, immunoglobulins and inflammation-related genes, suggests a role of the immune system in bGH kidney damage.

Cumulative risk, age at onset, and sex-specific differences for developing end-stage renal disease in young patients with type 1 diabetes: a nationwide population-based cohort study

OBJECTIVE

This study aimed to estimate the current cumulative risk of end-stage renal disease (ESRD) due to diabetic nephropathy in a large, nationwide, population-based prospective type 1 diabetes cohort and specifically study the effects of sex and age at onset.

RESEARCH DESIGN AND METHODS

In Sweden, all incident cases of type 1 diabetes aged 0-14 years and 15-34 years are recorded in validated research registers since 1977 and 1983, respectively. These registers were linked to the Swedish Renal Registry, which, since 1991, collects data on patients who receive active uremia treatment. Patients with > or =13 years duration of type 1 diabetes were included (n = 11,681).

RESULTS

During a median time of follow-up of 20 years, 127 patients had developed ESRD due to diabetic nephropathy. The cumulative incidence at 30 years of type 1 diabetes duration was low, with a male predominance (4.1% [95% CI 3.1-5.3] vs. 2.5% [1.7-3.5]). In both male and female subjects, onset of type 1 diabetes before 10 years of age was associated with the lowest risk of developing ESRD. The highest risk of ESRD was found in male subjects diagnosed at age 20-34 years (hazard ratio 3.0 [95% CI 1.5-5.7]). In female subjects with onset at age 20-34 years, the risk was similar to patients' diagnosed before age 10 years.

CONCLUSIONS

The cumulative incidence of ESRD is exceptionally low in young type 1 diabetic patients in Sweden. There is a striking difference in risk for male compared with female patients. The different patterns of risk by age at onset and sex suggest a role for puberty and sex hormones.

Pegvisomant: current and potential novel therapeutic applications

BACKGROUND

Pegvisomant is a genetically engineered molecule, which exhibits specific growth hormone (GH) antagonism by directly interacting with the GH receptor. It is currently licensed for the treatment of acromegaly where surgery and medical therapy with somatostatin analogues have failed.

OBJECTIVE

To delineate the role of pegvisomant in the treatment of acromegaly and its novel application in other areas of clinical medicine where suppression of GH action may be of therapeutic benefit.

METHODS

A literature review from PubMed- and EMBASE-listed publications and the web-sites of licensing organisations for medicinal products.

CONCLUSION

Pegvisomant is currently used as a second line therapy in the management of acromegaly. It is highly effective in suppressing the metabolic effects of elevated GH levels when used alone or in combination with somatostatin analogues. However, its long term efficacy and safety for this indication has yet to be established. Preliminary data indicate that pegvisomant may have a role in management of type 1 diabetes with beneficial effects on insulin sensitivity and in preventing the progression of microvascular complications. Additional roles as an adjunct to cancer chemotherapy regimens and for the diagnosis of GH deficiency have been proposed, but have yet to be confirmed.

IGF-1 increases laminin, cyclin D1, and p21Cip1 expression in glomerular mesangial cells: an investigation of the intracellular signaling pathway and cell-cycle progression

Insulin-like growth factor (IGF)-1 is accumulated in the diabetic kidney and is considered to be involved in the development of glomerular sclerosis. Here, we investigate IGF-1 regulation of laminin, an extracellular matrix (ECM) component, and cyclin D1 and p21Cip1, cell-cycle progression factor, expressions in glomerular mesangial cells. We show that IGF-1 increases the level of laminin gamma1 and beta1 subunits approximately 1.5- and 2.5-fold, respectively, in a time-dependent manner. IGF-1 also stimulates protein kinase Akt/PKB phosphorylation at Thr 308, which correlates with its activity, up to 24 h. The Akt activation is coupled with Ser 9 phosphorylation of its downstream target, glycogen synthase kinase-3beta (GSK-3beta), which inhibits its kinase activity. Laminin beta1 is reduced significantly (P < 0.03) by inhibitors of Akt and p38MAPK whereas laminin gamma1 is not affected. Surprisingly, IGF-1 activates the expression of both cyclin D1 and cell-cycle arrest factor, p21Cip1 parallely. Pharmacological inhibition of calcineurin by cyclosporin A blocks IGF-1-induced cyclin D1 and p21Cip1expression significantly (P < 0.05). IGF-1 enhances cellular metabolic activity and viability of rat mesangial cells; however, they are arrested at the G1 phase of cell cycle as revealed by the FACS analysis. These results indicate that IGF-1 mediates mesangial cell-cycle progression, hypertrophy, and ECM protein synthesis. The Akt/GSK-3beta, p38MAPK, and calcineurin pathways may play an important role in IGF-1 signaling, cell-cycle regulation, and matrix gene expression in mesangial cells leading to the development of diabetic glomerulopathy.

The podocyte and diabetes mellitus: is the podocyte the key to the origins of diabetic nephropathy?

PURPOSE OF REVIEW

Podocyte injury plays a key role in the development of diabetic nephropathy. This review discusses recent advances in our understanding of mechanisms of podocyte injury in diabetes mellitus and the associated alterations in the function of the glomerular filtration barrier.

RECENT FINDINGS

The effects of hyperglycemia on critical podocyte parameters including cell-cell interactions, attachment to the glomerular basement membrane, and podocyte apoptosis have been determined in both cell culture and in-vivo models of diabetes mellitus. The podocyte has also been identified as a target of action for insulin and growth hormone, hormones with significant roles in the altered homeostasis of diabetes mellitus.

SUMMARY

Understanding the cellular and molecular basis for changes in podocyte structure and function in diabetes mellitus may lead to novel diagnostic tools and treatment strategies for diabetic nephropathy.

Hexosamine induction of oxidative stress, hypertrophy and laminin expression in renal mesangial cells: effect of the anti-oxidant alpha-lipoic acid

We have previously shown that one of the potential mediators of the deleterious effects of high glucose on extracellular matrix protein (ECM) expression in renal mesangial cells is its metabolic flux through the hexosamine biosynthesis pathway (HBP). Here, we investigate further whether the hexosamines induce oxidative stress, cell-cycle arrest and ECM expression using SV-40-transformed rat mesangial (MES) cells and whether the anti-oxidant alpha-lipoic acid will reverse some of these effects. Culturing renal MES cells with high glucose (HG, 25 mM) or glucosamine (GlcN, 1.5 mM) for 48 h stimulates laminin gamma1 subunit expression significantly approximately 1.5 +/- 0.2- and 1.9 +/- 0.3-fold, respectively, when compared to low glucose (LG, 5 mM). Similarly, HG and GlcN increase the level of G0/G1 cell-cycle progression factor cyclin D1 significantly approximately 1.7 +/- 0.2- and 1.4 +/- 0.04-fold, respectively, versus LG (p < 0.01 for both). Azaserine, an inhibitor of glutamine:fruc-6-PO(4) amidotransferase (GFAT) in the HBP, blocks the HG-induced expression of laminin gamma1 and cyclin D1, but not GlcN's effect because it exerts its metabolic function distal to GFAT. HG and GlcN also elevate reactive oxygen species (ROS) generation, pro-apoptotic caspase-3 activity, and lead to mesangial cell death as revealed by TUNEL and Live/Dead assays. FACS analysis of cell-cycle progression shows that the cells are arrested at G1 phase; however, they undergo cell growth and hypertrophy as the RNA/DNA ratio is significantly (p < 0.05) increased in HG or GlcN-treated cells relative to LG. The anti-oxidant alpha-lipoic acid (150 microM) reverses ROS generation and mesangial cell death induced by HG and GlcN. Alpha-lipoic acid also reduces HG and GlcN-induced laminin gamma1 and cyclin D1 expression in MES cells. In addition, induction of diabetes in rats by streptozotocin (STZ) increases both laminin gamma1 and cyclin D1 expression in the renal cortex and treatment of the diabetic rats with alpha-lipoic acid (400 mg kg(-1) body weight) reduces the level of both proteins significantly (p < 0.05) when compared to untreated diabetic rats. These results support the hypothesis that the hexosamine pathway mediates mesangial cell oxidative stress, ECM expression and apoptosis. Anti-oxidant alpha-lipoic acid reverses the effects of high glucose, hexosamine and diabetes on oxidative stress and ECM expression in mesangial cells and rat kidney.

Identification of the glomerular podocyte as a target for growth hormone action

GH excess in both the human and transgenic animal models is characterized by significant changes in blood pressure and renal function. The GH/GH receptor (GHR) axis is also implicated in the development of diabetic nephropathy. However, it is not clear whether GH's actions on renal function are due to indirect actions mediated via changes in blood pressure and vascular tone or due to direct action of GH on the kidney. We hypothesized that functional GHRs are expressed on the glomerular podocyte enabling direct actions of GH on glomerular function. Real-time PCR, immunohistochemistry, and Western blot analysis of murine podocyte cells (MPC-5) and kidney glomeruli demonstrated expression of GHR mRNA and protein. Exposure of both murine and human podocytes to GH (50-500 ng/ml) resulted in an increase in abundance of phosphorylated signal transducer and activator of transcription-5, Janus kinase-2, and ERK1/2 proteins. Exposure of podocytes to GH also caused changes in the intracellular distribution of the Janus kinase-2 adapter protein Src homology 2-Bbeta, stimulation of focal adhesion kinase, increase in reactive oxygen species, and GH-dependent changes in the actin cytoskeleton. We conclude that glomerular podocytes express functional GHRs and that GH increases levels of reactive oxygen species and induces reorganization of the actin cytoskeleton in these cells. These results provide a novel mechanistic link between GH's actions and glomerular dysfunction in disorders such as acromegaly and diabetic glomerulosclerosis.

Alteration of the gene and protein levels of insulin-like growth factors in streptozotocin-induced diabetic male rats

Insulin-like growth factor (IGFs: IGF-I and IGF-II) systems have been reported to be associated with the onset of diabetic mellitus. Therefore, we investigated the effect of diabetes on regulation of the IGF system in the liver, kidneys and heart, which are important organs in the pathogenesis of diabetes. The experimental groups were subdivided into three groups: 1) controls, 2) streptozotocin (STZ)-induced untreated diabetic group, and 3) an insulin-treated group (plus diabetic rats). In the present study, starting on the second day after STZ treatment, the diabetic group exhibited hyperglycemia, polyuria, and polydipsia, which are characteristic of diabetes melittus. Serum levels of IGF-I were decreased, but those of IGF-II were increased in the diabetic group compared with the controls. The expression levels of IGF-I and IGF-II protein in the livers of the diabetic group had a similar pattern to the serum. In addition, the expression levels of liver IGF-I mRNA and IGF-II mRNA were decreased in the diabetic groups. In the heart, IGF-I levels were decreased, but IGF-II levels were increased in the untreated diabetic groups, which was consistent with the expression levels of their mRNA. However, both the IGF-I and IGF-II levels in the kidneys were increased in the untreated diabetic groups, but the mRNA levels were decreased. Insulin treatment ameliorated the changes of IGF system in the serum, liver, kidneys, and heart. In conclusion, diabetes induced alteration of the IGF system tissue-specifically, and this was blocked by insulin treatment.

Proteomic identification of 14-3-3zeta as an adapter for IGF-1 and Akt/GSK-3beta signaling and survival of renal mesangial cells

Recently we demonstrated that IGF-1 expression is increased in the diabetic kidney and that it may involve in renal hypertrophy and extracellular matrix protein (ECM) accumulation in mesangial cells as seen in diabetic glomerulopathy. The present study investigates the molecular mechanism(s) of IGF-1 and Akt/glycogen synthase kinase-3beta (GSK-3beta) signaling pathway in the regulation of fibronectin and cyclin D1 expression and survival of renal mesangial cells. A proteomic approach is also employed to identify protein targets of IGF-1 signaling via GSK-3beta inhibition in mesangial cells. We show that IGF-1 (100 ng/ml) significantly increases the protein kinase Akt/PKB activity (1.5-2-fold, p<0.05) within 1-5 minutes, which is completely blocked by the presence of 100 nM Wortmannin (phosphatidyl-inositol 3-kinase inhibitor). Akt activation is coupled with Ser9 phosphorylation and inactivation of its down-stream target GSK-3beta. IGF-1 increases the cyclic AMP-responsive element (CRE) binding transcription factor CREB phosphorylation at Ser 133 and CRE-binding activity in mesangial cells, which parallels cyclin D1 and fibronectin expressions. Both proteins are known to have CRE-sequences in their promoter regions upstream of the transcription start site. Suppression of GSK-3beta by SB216763 (100 nM) increases CREB phosphorylation, cyclin D1 and fibronectin levels. Two dimensional gel electrophoresis followed by MALDI-TOF mass spectrometric analysis of mesangial proteins reveals that IGF-1 treatment or an inhibition of GSK-3beta increases the expression of the phosphorylated Ser/Thr binding signal adapter protein 14-3-3zeta. Immuno-precipitation of 14-3-3zeta followed by Western blotting validates the association of phosphorylated GSK-3beta with 14-3-3zeta in renal mesangial cells. Stable expression of a constitutively active GSK-3beta(Ser9Ala) induces cell death while overexpression of HA-tagged 14-3-3zeta increases cell viability as measured by MTT assays. These results indicate that the Akt/GSK-3beta pathway and the adapter protein 14-3-3zeta may play an important role in IGF-1 signaling and survival of mesangial cells in diabetic nephropathy.

Short-term suppression of elevated growth hormone concentrations following insulin-like growth factor 1 administration in young adults with type 1 diabetes does not alter glomerular filtration or albumin excretion rates

OBJECTIVE

Young adults with type 1 diabetes mellitus (T1DM) have increased glomerular filtration rate (GFR), which may mediate progressive renal disease and microalbuminuria. This may be secondary to low concentrations of insulin-like growth factor (IGF)-I and GH hypersecretion. We tested the hypothesis that restoration of circulating IGF-I concentrations in young adults with T1DM might suppress GH secretion, GFR and urinary albumin excretion.

DESIGN

In a randomized double blind crossover study six young adults with T1DM (three men, 19-24 years) received 7 days treatment with rhIGF-I/insulin-like growth factor binding protein (IGFBP)-3 complex (SomatoKine) 0.4 mg/kg/day and placebo. Subjects underwent overnight insulin infusion for euglycaemia, followed by determination of GFR and albumin excretion rate.

RESULTS

Following IGF-I/IGFBP-3 complex, overnight insulin requirements (0.15 vs placebo 0.21 mU/kg/min, P < 0.04), plasma insulin (77 vs placebo 152 pmol/l, P < 0.01) and mean overnight GH (2.6 vs placebo 4.8 mU/l, P < 0.04) fell. IGF-I (492 vs placebo 218 ng/ml, P < 0.01) and IGFBP-3 (4.5 vs placebo 3.9 microg/ml, P < 0.05) increased. GFR did not change (145.5 (23.9) ml/min/1.73 m(2) post-IGF-I/IGFBP-3 complex vs 152.2 (19.8) post placebo). Albumin excretion rate did not change 9.5 (5.5-16.6)mg/24 h pre- vs 11.5 (9.9-20.2) post-IGF-I/IGFBP-3 complex and 10.7 (8.1-21.2) pre- vs 11.5 (8.7-29.9) post placebo. Plasma creatinine levels were lower following IGF-I/IGFBP-3 complex (mean +/- SD, 56.2 +/- 16.8 micromol/l) vs placebo (61.5, 45.0, P < 0.02).

CONCLUSIONS

Seven days treatment with IGF-I/IGFBP-3 complex enhanced overnight insulin sensitivity and reduced GH levels, but there was no effect on glomerular hyperfiltration or albumin excretion rates.

Diabetic microangiopathy: IGFBP control endothelial cell growth by a common mechanism in spite of their species specificity and tissue peculiarity

Endothelial cells (EC) play a role in many diseases including diabetes mellitus. EC share common functions, such as angiogenesis and vascular remodeling both regulated by proliferation and apoptosis, anti-thrombotic properties, regulation of vascular tone, control in the passage of nutrients and secretion of peptides and growth factors. However, EC are characterized by site-specificity so their characteristics depend on the organs and tissues where they are. The IGF system induces important growth factors that control cell growth in different microvascular EC (mEC). This family includes IGF-I and IGF-II peptides, their receptors and regulatory proteins IGF-binding proteins (IGFBP-1 to IGFBP-6). The IGFBP modulate their interaction with the IGF membrane receptors and might be regulated at a transcriptional and post-transcriptional level, thus determining the biological IGF-dependent effects on target cells. The IGF system is also a mediator of vascular diseases, and its altered balance might contribute to endothelial dysfunction with the development and evolution of diabetic microangiopathy. We reported here the reviewed literature of IGFBP production from various sources of mEC, showing that they predominantly express IGFBP-2 through IGFBP-5 mRNA. The different pattern of IGFBP secretion depends on the anatomical district and on the species of the tissues. Nevertheless, based on our and other experimental observations, we suggested that a common mechanism of IGFBP regulation in mEC could be hypothized. In retinal and glomerular EC the IGFBP4/IGFBP5 ratio controls the response of these cells to IGF-I and high levels of glucose, in terms of cellular growth.

Growth hormone hypothesis and development of diabetic nephropathy in Type 1 diabetes

In Type 1 diabetes, poor glycemic control is the key predictor for the development of microalbuminuria, an established early marker of overt nephropathy. However, the role of other pathways in the development of diabetic nephropathy may also be important. The growth hormone (GH) hypothesis suggests that the GH-insulin-like growth factor (IGF)-1 axis may play an important role in this disease process. In Type 1 diabetes, the characteristic pattern of GH hypersecretion and low circulating IGF-1 levels results from hepatic GH resistance owing to the lack of portal insulin. Clinical data indicate that high GH and low IGF-1 levels reduce insulin sensitivity and worsen glycemic control. Furthermore, despite hepatic GH resistance, GH receptors at the kidney remain intact. Experimental data show that excess GH stimulates renal GH receptors and, through paracrine IGF-1 production, results in pathophysiological changes consistent with diabetic nephropathy, namely nephromegaly, glomerular hyperfiltration and eventual proteinuria. These abnormalities are reversed by intervention to block or normalize the local effects of GH and IGF-1. Although such data in humans are limited, preliminary trials show that interventions to increase IGF-1 levels and reduce GH hypersecretion improve glycemic control and insulin sensitivity in the short term. However, their effects on early nephropathy and end points, such as the prevalence of end stage renal disease, have yet to be determined.

Prevalence and risk factors for microalbuminuria in a population-based sample of children and adolescents with T1DM in Western Australia

OBJECTIVE

To define the prevalence and describe the natural history of microalbuminuria (MA) in a population-based sample of children with type 1 diabetes mellitus (T1DM).

METHODS

Children with T1DM diagnosed <or=16 yrs and screened for MA were identified through the Western Australia diabetes register. Three-monthly hemoglobin (HbA1c) was performed from diagnosis. MA screening (albumin excretion rate in three timed overnight samples) was performed yearly after 10 yrs of age or after 5 yrs from diagnosis. Cox proportional model assessed the risk of different variables on the occurrence of MA. Kaplan-Meier survival analyses (log-rank test) estimated the probability of developing MA.

RESULTS

Nine hundred and fifty-five T1DM children (462 male), mean diabetes duration of 7.6 yrs and mean age at onset of diabetes of 8.5 yrs were selected for the study. MA, mean albumin excretion rate >or=20 and <200 microg/min, developed in 128 subjects (13.4%) at mean diabetes duration of 7.6 yrs. Cumulative probability for MA was 16% after 10 yrs. Determinants for MA were HbA1c [hazard ratio (HR) 1.21; 95% confidence interval (CI) 1.05-1.38; p = 0.007], onset of puberty (HR 8.01; 95% CI 3.18-20.16; p < 0.001) and age at diagnosis (HR 1.25; 95% CI 1.18-1.33; p < 0.001). Females had a higher probability for MA during puberty than males (p = 0.03). The total incidence of MA (subjects with MA/100 person-years) was 1.26, 1.85 and 2.44 for those who developed diabetes at ages <5 yrs, 5-11 yrs and >11 yrs, respectively.

CONCLUSIONS

Onset of puberty, diabetes duration and metabolic control are major factors predisposing the development of MA. Children diagnosed with T1DM at younger ages have a prolonged time for developing MA.

Age at onset of childhood-onset type 1 diabetes and the development of end-stage renal disease: a nationwide population-based study

OBJECTIVE

To analyze the impact of age at onset on the development of end-stage renal disease (ESRD) due to diabetic nephropathy in a nationwide population-based cohort with childhood-onset type 1 diabetes.

RESEARCH DESIGN AND METHODS

A record linkage between two nationwide registers, the Swedish Childhood Diabetes Registry, including 12,032 cases with childhood-onset diabetes, and the Swedish Registry for Active Treatment of Uraemia was performed. Log-rank test was used to test differences between cumulative risk curves of developing ESRD due to diabetic nephropathy in three different strata of age at onset (0-4, 5-9, and 10-14 years).

RESULTS

At a maximum follow-up of 27 years, 33 patients had developed ESRD due to diabetic nephropathy and all had a diabetes duration >15 years. In total, 4,414 patients had diabetes duration >15 years, and thus the risk in this cohort to develop ESRD was 33 of 4,414 (0.7%). A significant difference in risk of developing ESRD was found between the youngest (0-4 years) and the two older (5-9 and 10-14 years) age-at-onset strata (P = 0.03 and P = 0.001, respectively). A significant difference in the risk of developing ESRD was also found between children with prepubertal (0-4 and 5-9 years, n = 2,424) and pubertal (10-14 years, n = 2000) onset of diabetes (P = 0.002). No patient with onset of diabetes before 5 years of age had developed ESRD.

CONCLUSIONS

With a median duration of 21 years in this population-based Swedish cohort with childhood-onset diabetes, <1% of the patients had developed ESRD due to diabetic nephropathy, and a prepubertal onset of diabetes seems to prolong the time to development of ESRD.

The IGF-I system and the renal and haemodynamic effects of losartan in normotensive patients with type 2 diabetes mellitus: a randomized clinical trial

OBJECTIVE

Losartan has been shown to protect the diabetic kidney, at least partly independent of changes in blood pressure. Imbalances in the IGF-I system are associated with the development of diabetic nephropathy. We investigated whether renal as well as haemodynamic effects of losartan are associated with changes in the IGF-I system in normotensive patients with type 2 diabetes mellitus (T2DM).

DESIGN AND PATIENTS

This randomized, double-blind placebo-controlled clinical trial involved 74 normotensive patients with T2DM and microalbuminuria. Thirty-eight patients were assigned to receive losartan and 36 patients were assigned to receive placebo for 10 weeks.

MEASUREMENTS

Serum levels of total and free IGF-I, IGFBP-3, creatinine and haemoglobin A(1c) (HbA(1c)), as well as urinary albumin excretion rate, creatinine clearance and blood pressure, were measured prior to the start of treatment and after 10 weeks of treatment.

RESULTS

At baseline, serum levels of IGFBP-3 were elevated and serum levels of free IGF-I were reduced. Losartan tended to reduce IGFBP-3 levels and to increase free IGF-I levels, although neither effect was statistically significant. These effects were more pronounced in a subanalysis of 18 losartan-treated patients with stable metabolic parameters, with a decrease in IGFBP-3 from 133.2 to 122.6 nmol/l (P=0.006) and an increase in free IGF-I levels by 8% (ns). Serum levels of total IGF-I were unaffected. The change in IGFBP-3 was inversely correlated to the change in creatinine clearance (r=-0.4; P=0.02). Total and free IGF-I inversely correlated to systolic blood pressure (r= -0.46; P=0.007 and r=0.26; P=0.14 respectively). Furthermore, changes in total IGF-I and IGFBP-3 correlated to changes in serum creatinine levels in the metabolically stable patients (r=0.58, P=0.02 and r=0.6, P=0.01, respectively). Changes in the IGF-I system were unrelated to a reduction in microalbuminuria associated with losartan.

CONCLUSIONS

Losartan lowered the elevated levels of IGFBP-3, although only significantly in the metabolically stable patients. A tendency towards an increase in free IGF-I levels was also observed, but this change was small and not statistically significant. These changes were not related to reduction in microalbuminuria, but might contribute to effects of losartan on creatinine clearance and blood pressure of losartan in normotensive patients with T2DM.

Gender differences in renal responses to hyperglycemia and angiotensin-converting enzyme inhibition in diabetes

BACKGROUND

Diabetes mellitus reduces female gender-mediated protection against progression of renal disease but the mechanisms responsible for this loss of protection are unknown. The impact of gender on the diabetic hyperfiltration state has not previously been studied. Since hyperfiltration is a factor in the development of diabetic renal disease, and is influenced by hyperglycemia and renin-angiotensin system (RAS) blockade, we examined gender differences in the renal response to hyperglycemia and angiotensin-converting enzyme (ACE) inhibition in young males and females with uncomplicated type 1 diabetes mellitus.

METHODS

Ten male and 12 female normoalbuminuric, normotensive, adolescents with type 1 diabetes mellitus were studied before ACE inhibition during clamped euglycemia and hyperglycemia, and then after 21 days treatment with enalapril (0.1 mg/kg daily x 1 week and then 0.1 mg/kg twice a day x 2 weeks).

RESULTS

During clamped euglycemia, males exhibited significantly higher effective renal plasma flow (ERPF) and renal blood flow (RBF) and a lower renal vascular resistance (RVR). During clamped hyperglycemia, females exhibited reductions in ERPF and RBF, and increased RVR and filtration fraction (FF). Males exhibited no significant renal hemodynamic changes during hyperglycemia. After ACE inhibition treatment, both genders exhibited significant declines in arterial pressure, but only females displayed a reduction in glomerular filtration rate (GFR) and FF.

CONCLUSION

The renal responses to hyperglycemia and ACE inhibition appear to differ between male and female adolescents with uncomplicated type 1 diabetes mellitus. Hyperglycemia-induced changes in RVR and FF in women may account, at least in part, for the loss of gender-based protection in diabetic renal disease.

Assessment of 115 candidate genes for diabetic nephropathy by transmission/disequilibrium test

Several lines of evidence, including familial aggregation, suggest that allelic variation contributes to risk of diabetic nephropathy. To assess the evidence for specific susceptibility genes, we used the transmission/disequilibrium test (TDT) to analyze 115 candidate genes for linkage and association with diabetic nephropathy. A comprehensive survey of this sort has not been undertaken before. Single nucleotide polymorphisms and simple tandem repeat polymorphisms located within 10 kb of the candidate genes were genotyped in a total of 72 type 1 diabetic families of European descent. All families had at least one offspring with diabetes and end-stage renal disease or proteinuria. As a consequence of the large number of statistical tests and modest P values, findings for some genes may be false-positives. Furthermore, the small sample size resulted in limited power, so the effects of some tested genes may not be detectable, even if they contribute to susceptibility. Nevertheless, nominally significant TDT results (P < 0.05) were obtained with polymorphisms in 20 genes, including 12 that have not been studied previously: aquaporin 1; B-cell leukemia/lymphoma 2 (bcl-2) proto-oncogene; catalase; glutathione peroxidase 1; IGF1; laminin alpha 4; laminin, gamma 1; SMAD, mothers against DPP homolog 3; transforming growth factor, beta receptor II; transforming growth factor, beta receptor III; tissue inhibitor of metalloproteinase 3; and upstream transcription factor 1. In addition, our results provide modest support for a number of candidate genes previously studied by others.

Insulin-Like Growth Factor-1 and Its Binding Proteins, IGFBP-1 and IGFBP-3, in Adolescents with Type-1 Diabetes mellitus and Microalbuminuria

BACKGROUND/AIMS

Numerous clinical and experimental studies suggest that growth factors may contribute to the development of diabetic microvascular complications. The aim of the study was to test the hypothesis that in adolescents with type-1 diabetes mellitus and microalbuminuria (MA) there are specific disorders of serum insulin-like growth factor-1 (IGF-1) and concentrations of its binding proteins, IGFBP-1 and IGFBP-3, that could be of importance in the pathogenesis of microvascular diabetic complications.

METHODS

25 adolescents with MA, 24 adolescents with diabetes without complications, and 17 controls were examined. There were no differences with regard to age, puberty stage, HbA1c and body mass index between the groups examined. Two of the patients in the first group also had diabetic retinopathy. Serum fasting concentrations of IGF-1 and overnight urine albumin concentrations were measured by radioimmunoassay, IGFBP-1 and IGFBP-3 concentrations by immunoradiometric assay and HbA1c by high-performance liquid chromatography methods. Diabetic patients were examined by an experienced ophthalmologist and neurologist. The data were analyzed using Kruskal-Wallis ANOVA and multiple regression analysis.

RESULTS

Significantly lower IGF-1 concentrations were found in adolescents with diabetes and MA compared to diabetic patients without complications and healthy contemporaries. IGFBP-1 concentrations were significantly higher and IGFBP-3 concentrations were statistically lower in diabetic patients with MA than in patients without complications.

CONCLUSIONS

The IGF-IGFBP system is deranged in adolescents with type-1 diabetes mellitus and MA. Our results suggest the participation of circulating IGFBP-1 in the origin of diabetic complications. It could be also possible that IGFBP-3 takes part in the protection from them.

Early Diabetes-Related Complications in Adolescents

Micro- and macrovascular complications account for the major part of the morbidity and mortality associated with diabetes developing in childhood. Although advanced complications are exceptionally rare in the adolescent age group, it is during this phase that the progression of risk may accelerate. A number of potentially important factors have been identified which might contribute to risk of complication development: some provide insights into the genetics of these complications, while others are potentially modifiable, such as metabolic control, hypertension, smoking, obesity and hyperlipidemia. Recently, both consensus and evidence-based guidelines have been developed to guide those involved in the care of adolescents with diabetes in the prevention, screening and management of early diabetes-related complications in this vulnerable population. This article reviews the literature that underpins the available guidelines and stresses the pivotal role of excellent metabolic control in complication prevention.

Increasing urine albumin excretion is associated with growth hormone hypersecretion and reduced clearance of insulin in adolescents and young adults with type 1 diabetes: the Oxford Regional Prospective Study

HYPOTHESIS

We previously described lower insulin-like growth factor I (IGF-I) levels in association with increased microalbuminuria (MA) risk in type 1 diabetic subjects followed from diabetes diagnosis through puberty into adulthood. By inference lower IGF-I levels may be associated with higher GH levels and changes in insulin sensitivity.

METHODS

To test this hypothesis, microalbuminuric subjects (MA+, n = 14) from the same cohort had overnight GH levels measured during euglycaemia (5 mmol/l, 01:00-07:30 h) maintained by a variable rate insulin infusion followed by a 2-step hyperinsulinaemic, euglycaemic clamp study using [6.6 2H2] glucose, and were compared to MA- controls (MA-, n = 14), matched for age (median 19.3 years, range 15.8-30.5), sex, duration of diabetes (11.1 years, range 5.1-16.4).

RESULTS

In MA+ cases GH levels, measured by the Pulsar programme, were higher (baseline; 1.8 +/- 1.4 vs. 0.7 +/- 0.5 ng/ml, P = 0.02, mean; 3.8 +/- 1.3 vs. 2.6 +/- 1.6 ng/ml, P = 0.03, maximum; 16.7 +/- 7.0 vs. 12.3 +/- 5.4, P = 0.02), despite similar HbA1(c) levels (9.8%vs. 9.6%, P = 0.6) and body or truncal fat mass. Fourier transform revealed increased GH pulse amplitude at all periodicities and overnight insulin clearance was reduced (11.7 +/- 6.9 vs. 20.1 +/- 6.5 ml/kg/min, P < 0.02). In multiple regression analysis, urine albumin excretion was associated with higher GH levels and reduced insulin clearance, independent of HbA1(c) and body composition. In female cases (n = 9), dextrose requirements were reduced during the first step of the euglycaemic clamp (1.7 +/- 0.8 vs. 2.7 +/- 1.4, P < 0.05) but no such differences existed in males or in the rate of glucose production or disposal.

CONCLUSION

The development of MA during puberty and young adulthood is associated with higher GH levels and abnormalities in insulin metabolism, particularly in females. These data extend support for our previous findings indicating a role for the GH/IGF-I axis in the pathogenesis of MA.

From hyperglycemia to diabetic kidney disease: the role of metabolic, hemodynamic, intracellular factors and growth factors/cytokines

At present, diabetic kidney disease affects about 15-25% of type 1 and 30-40% of type 2 diabetic patients. Several decades of extensive research has elucidated various pathways to be implicated in the development of diabetic kidney disease. This review focuses on the metabolic factors beyond blood glucose that are involved in the pathogenesis of diabetic kidney disease, i.e., advanced glycation end-products and the aldose reductase system. Furthermore, the contribution of hemodynamic factors, the renin-angiotensin system, the endothelin system, and the nitric oxide system, as well as the prominent role of the intracellular signaling molecule protein kinase C are discussed. Finally, the respective roles of TGF-beta, GH and IGFs, vascular endothelial growth factor, and platelet-derived growth factor are covered. The complex interplay between these different pathways will be highlighted. A brief introduction to each system and description of its expression in the normal kidney is followed by in vitro, experimental, and clinical evidence addressing the role of the system in diabetic kidney disease. Finally, well-known and potential therapeutic strategies targeting each system are discussed, ending with an overall conclusion.

Early glycemic control, age at onset, and development of microvascular complications in childhood-onset type 1 diabetes: a population-based study in northern Sweden

OBJECTIVE

The aim of this work was to study the impact of glycemic control (HbA(1c)) early in disease and age at onset on the occurrence of incipient diabetic nephropathy (MA) and background retinopathy (RP) in childhood-onset type 1 diabetes.

RESEARCH DESIGN AND METHODS

All children, diagnosed at 0-14 years in a geographically defined area in northern Sweden between 1981 and 1992, were identified using the Swedish Childhood Diabetes Registry. From 1981, a nationwide childhood diabetes care program was implemented recommending intensified insulin treatment. HbA(1c) and urinary albumin excretion were analyzed, and fundus photography was performed regularly. Retrospective data on all 94 patients were retrieved from medical records and laboratory reports.

RESULTS

During the follow-up period, with a mean duration of 12 +/- 4 years (range 5-19), 17 patients (18%) developed MA, 45 patients (48%) developed RP, and 52% had either or both complications. A Cox proportional hazard regression, modeling duration to occurrence of MA or RP, showed that glycemic control (reflected by mean HbA(1c)) during the follow-up was significantly associated with both MA and RP when adjusted for sex, birth weight, age at onset, and tobacco use as potential confounders. Mean HbA(1c) during the first 5 years of diabetes was a near-significant determinant for development of MA (hazard ratio 1.41, P = 0.083) and a significant determinant of RP (1.32, P = 0.036). The age at onset of diabetes significantly influenced the risk of developing RP (1.11, P = 0.021). Thus, in a Kaplan-Meier analysis, onset of diabetes before the age of 5 years, compared with the age-groups 5-11 and >11 years, showed a longer time to occurrence of RP (P = 0.015), but no clear tendency was seen for MA, perhaps due to lower statistical power.

CONCLUSIONS

Despite modern insulin treatment, >50% of patients with childhood-onset type 1 diabetes developed detectable diabetes complications after approximately 12 years of diabetes. Inadequate glycemic control, also during the first 5 years of diabetes, seems to accelerate time to occurrence, whereas a young age at onset of diabetes seems to prolong the time to development of microvascular complications.

Microalbuminuria as a marker of cardiovascular and renal risk in type 2 diabetes mellitus: a temporal perspective

Microalbuminuria is a marker for diabetic nephropathy. It also signifies cardiovascular disease, as well as nephropathy, in type 2 diabetes (DM2). Microalbuminuria may precede DM2, occurring with the insulin resistance syndrome and its components, including obesity and hypertension. Other indicators of cardiovascular risk, such as markers of inflammation, are associated with microalbuminuria in populations of patients with and without diabetes. With the rising prevalence of DM2 in minority youth, especially in Native Americans, a marker for future disease risk would allow earlier prevention strategies to be tested. Before microalbuminuria can be used in a prevention strategy, more needs to be known about the mechanism(s) of the association between elevated excretion, its relationship to glucose intolerance, and its relative contribution to cardiovascular and renal disease. These questions are especially applicable as we begin to observe the long-term complications of diabetes in youth.

Growth factors and the development of diabetic nephropathy

Growth factors play an important role in the development of functional and structural changes associated with diabetic nephropathy. Although it has been known for years that these factors are important for early renal hypertrophy and subsequent development of glomerulosclerosis and tubulointerstitial fibrosis, the exact molecular mechanism of many of these factors has only recently been more elucidated. Furthermore, growth factors also link the metabolic theory of diabetic complications with renal hemodynamic changes in diabetic nephropathy because some growth factors could directly influence glomerular hemodynamics and tubular transport in diabetic nephropathy. The high glucose environment with stimulated cellular uptake of glucose and accelerated nonenzymatic reactions resulting in Amadori-modified proteins and the later-developing advanced glycation end products are the main stimulators for intrarenal induction of growth factors. Intracellular generation of reactive species is an important signal intermediate in these stimulated expressions of growth factors. Taking into consideration the pivotal role of growth factors in the development of diabetic nephropathy, a therapeutic strategy to antagonize growth factor effects appears to be straightforward. However, the pleiotropic function of many of these factors and their physiologic role in normal renal homeostasis may make this approach difficult.

Effects of duration and age at onset of type 1 diabetes on preclinical manifestations of nephropathy

Several studies have reported that the effect of type 1 diabetes disease duration on nephropathy may be greater during or after puberty than an equivalent number of years before puberty. The International Diabetic Nephropathy Study examined the effects of disease duration and age at onset on glomerular morphometry obtained from kidney biopsy in 243 young type 1 diabetic subjects with albumin excretion rates <100 micro g/min: 184 with prepubertal onset, 35 with pubertal onset, and 24 with postpuberty onset. Outcomes included the volume fraction of the glomerulus occupied by the mesangium [Vv(Mes/glom)], glomerular basement membrane (GBM) width, and the surface density of peripheral glomerular capillary basement membrane per glomerulus Sv(PGBM/glom). Vv(Mes/glom) progressed slowly in the first 14 or 15 years after disease onset but more rapidly thereafter. GBM width increased, while Sv(PGBM/glom) decreased with increasing disease duration. No statistically significant differences in the effect of duration were observed among the three age-at-onset subgroups, even with multivariate adjustment for sex, center, baseline HbA(1c) concentration, diastolic blood pressure, height, and BMI. Our results may explain the conflicting results of previous studies regarding the effects of pre-versus postpuberty disease duration.

Low IGF-I and elevated testosterone during puberty in subjects with type 1 diabetes developing microalbuminuria in comparison to normoalbuminuric control subjects: the Oxford Regional Prospective Study

OBJECTIVE

To describe longitudinal variations in pubertal hormonal variables in subjects with and without microalbuminuria (MA).

RESEARCH DESIGN AND METHODS

Blood samples collected annually from subjects recruited at diagnosis of type 1 diabetes and followed prospectively through puberty (median follow-up 9.3 years, range 4.7-12.8) were analyzed for total and free IGF-I, IGF binding protein-1, testosterone, sex hormone-binding globulin, and HbA(1c). A total of 55 subjects who developed MA (MA(+) group) were compared with 55 age-, sex-, and duration-matched control subjects who did not develop MA (MA(-) group).

RESULTS

For female subjects, total IGF-I (MA(+) 1.2 mU/l vs. MA(-) 1.4 mU/l, P = 0.03) and free IGF-I levels (MA(+) 1,767 ng/l vs. MA(-) 2010 ng/l, P = 0.002) were lower, whereas the free androgen index (MA(+) 2.4 vs. MA(-) 2.0, P = 0.03) was higher in those with MA. These changes were less pronounced in male subjects. For both sexes, in a Cox model after adjusting for puberty, the presence of MA was associated with lower free IGF-I levels, higher testosterone standard deviation score (SDS), and poor glycemic control. We found that 22 of 55 case subjects (40%) developed persistent MA, whereas 33 (60%) had transient MA. In the persistent MA group compared with the transient and control groups, total IGF-I levels were lower (1.1 vs. 1.3 vs. 1.4 mU/l, P = 0.002) as were free IGF-I levels (1,370.9 vs. 1,907.3 vs. 1,886.7 ng/l, P < 0.001), whereas HbA(1c) levels were higher (11.8 vs. 10.3 vs. 9.9%, P < 0.001).

CONCLUSIONS

Poor glycemic control and differences in IGF-I levels and androgens, particularly in female subjects, accompany development of MA at puberty. These differences may in part account for the sexual dimorphism in MA risk during puberty and could relate to disease progression.

Diabetic kidney disease: impact of puberty

Puberty accelerates microvascular complications of diabetes mellitus, including nephropathy. Animal studies confirm a different renal hypertrophic response to diabetes before and after puberty, probably due to differences in the production of transforming growth factor-beta (TGF-beta). Many of the complex physiological changes during puberty could affect potentially pathogenic mechanisms of diabetic kidney disease. Increased blood pressure, activation of the growth hormone-insulin-like growth factor I axis, and production of sex steroids could all play a role in pubertal susceptibility to diabetic renal hypertrophy and nephropathy. These factors may influence the effects of hyperglycemia and several systems that ultimately control TGF-beta production, including the renin-angiotensin system, cellular redox systems, the polyol pathway, and protein kinase C. These phenomena may also explain gender differences in kidney function and incidence of end-stage renal disease. Normal changes during puberty, when coupled with diabetes and superimposed on a genetically susceptible milieu, are capable of accelerating diabetic hypertrophy and microvascular lesions. A better understanding of these processes may lead to new treatments to prevent renal failure in diabetes mellitus.

Treatment of hypertension and microalbuminuria in children and adolescents with type 1 diabetes mellitus

Nephropathy is the main cause of morbidity and mortality in patients with type 1 diabetes and, in adults, persistent microalbuminuria is the best marker of the consequent risk for its development. In the pediatric population, puberty represents the most important risk factor for the development of microangiopathic complications, although it is not necessarily associated with the progression to frank proteinuria. As many as 50% of subjects may revert to normoalbuminuria. Hypertension is a further risk factor and may accelerate the progression of micro- and macrovascular complications. There is evidence that angiotensin-converting enzyme (ACE) inhibitors reduce renal damage by one or more mechanisms independent of their antihypertensive effects--hence they represent the drug of choice for the treatment of diabetic nephropathy. However, as angiotensin II receptor antagonists are more specific, they may become the obvious treatment choice in the near future. There is no consensus as to who should be treated and when treatment with renoprotective drugs should begin in the pediatric population, due to the lack of a clear definition of the natural history of microalbuminuria in this age group. In this review some models and controversial aspects of this issue are presented and discussed.