Bariatric surgery, osteoarthritis and arthroplasty of the hip and knee in Swedish Obese Subjects - up to 31 years follow-up of a controlled intervention study.

OBJECTIVE: To study the long-term effect of obesity and bariatric surgery on incidences of osteoarthritis and arthroplasty of hip and knee. DESIGN: Hazard ratios (HR) and incidence rates (IR) of osteoarthritis and arthroplasty of hip and knee were studied in the prospective, controlled, non-randomized Swedish Obese Subjects (SOS) study (bariatric surgery group, n = 2007; matched controls given usual obesity care, n = 2040) and the SOS reference cohort (n = 1135, general population). Osteoarthritis diagnosis and arthroplasty for osteoarthritis were captured from the National Swedish Patient Register. Median follow-up time was 21.2 (IQR 16.4-24.8), 22.9 (IQR 19.1-25.7), and 20.1 years (IQR 18.7-20.9) for the control group, surgery group and reference cohort, respectively. RESULTS: The surgery group displayed lower incidence of hip osteoarthritis (IR 5.3, 95% CI 4.7-6.1) compared to controls (IR 6.6, 95% CI 5.9-7.5, adjHR 0.83, 95% CI 0.69-1.00) but similar incidence of hip arthroplasty. Similar incidence of knee osteoarthritis was observed in the surgery group and controls, but knee arthroplasty was more common in the surgery group (IR 7.4, 95% CI 6.6-8.2 and 5.6, 95% CI 4.9-6.4, adjHR 1.45, 95% CI 1.22-1.74). The reference cohort displayed lower incidences of osteoarthritis and arthroplasty of hip and knee compared with the surgery group and controls. CONCLUSION: Bariatric surgery did not normalize the increased risk of knee and hip osteoarthritis in patients with obesity but was associated with an increased incidence of knee arthroplasty compared to the control group. With the limitations inherent to the present data, additional studies are needed to confirm these results. TRIAL REGISTRATION: clinicaltrials.gov Identifier: NCT01479452.

Remission and progression of pre-existing micro- and macroalbuminuria over 15 years after bariatric surgery in Swedish Obese Subjects study.

BACKGROUND: Bariatric surgery reduces incidence of albuminuria and end-stage renal disease in patients with obesity. Effects of bariatric surgery on long-term remission and progression of pre-existing obesity-related renal damage are mainly unexplored. Here we investigate the long-term effects of bariatric surgery compared with conventional obesity care on remission and progression of albuminuria. METHODS: 4047 patients were included in the Swedish Obese Subjects study. Inclusion criteria were age 37-60 years, BMI ≥ 34 kg/m2 in men and BMI ≥ 38 kg/m2 in women. Our analysis comprised 803 patients (19.8% of total population, 357 control, 446 surgery) with pre-existing albuminuria including 693 patients (312 control, 381 surgery) with microalbuminuria, and 110 patients (45 control, 65 surgery) with macroalbuminuria. Surgery patients were treated with banding, vertical banded gastroplasty, or gastric bypass. Control patients received conventional obesity care. RESULTS: Total urinary albumin excretion was 36.5% lower in all patients with albuminuria after 15 years, 44.5% lower in patients with microalbuminuria after 15 years, and 27.8% lower in patients with macroalbuminuria after 2 years following bariatric surgery compared with conventional care. In surgery patients with microalbuminuria, remission to normoalbuminuria was higher (OR, 5.9, 2.2, 3.2, p < 0.001) and progression to macroalbuminuria was lower (OR, 0.28, 0.26, 0.25, p ≤ 0.02) at 2, 10, and 15 years, respectively, compared with control patients. In surgery patients with macroalbuminuria remission to normo- or microalbuminuria was higher (OR, 3.67, p = 0.003) after 2 years. No differences between surgery and control patients with macroalbuminuria were observed after 10 and 15 years. Surgery slowed progression of eGFR decline after 2 years in patients with microalbuminuria and macroalbuminuria (treatment effect: 1.0 ml/min/1.73 m2/year, p = 0.001 and 1.4 ml/min/1.73 m2/year, p = 0.047, respectively). CONCLUSION: Bariatric surgery had better effects than conventional obesity care on remission of albuminuria and prevention of eGFR decline, indicating that patients with obesity-related renal damage benefit from bariatric surgery.

Fracture risk after three bariatric surgery procedures in Swedish obese subjects: up to 26 years follow-up of a controlled intervention study.

BACKGROUND: Previous studies have reported an increased fracture risk after bariatric surgery. OBJECTIVE: To investigate the association between different bariatric surgery procedures and fracture risk. METHODS: Incidence rates and hazard ratios for fracture events were analysed in the Swedish Obese Subjects study; an ongoing, nonrandomized, prospective, controlled intervention study. Hazard ratios were adjusted for risk factors for osteoporosis and year of inclusion. Information on fracture events were captured from the Swedish National Patient Register. The current analysis includes 2007 patients treated with bariatric surgery (13.3% gastric bypass, 18.7% gastric banding, and 68.0% vertical banded gastroplasty) and 2040 control patients with obesity matched on group level based on 18 variables. Median follow-up was between 15.1 and 17.9 years for the different treatment groups. RESULTS: During follow-up, the highest incidence rate for first-time fracture was observed in the gastric bypass group (22.9 per 1000 person-years). The corresponding incidence rates were 10.4, 10.7 and 9.3 per 1000 person-years for the vertical banded gastroplasty, gastric banding and control groups, respectively. The risk of fracture was increased in the gastric bypass group compared with the control group (adjusted hazard ratio [adjHR] 2.58; 95% confidence interval [CI] 2.02-3.31; P < 0.001), the gastric banding group (adjHR 1.99; 95%CI 1.41-2.82; P < 0.001), and the vertical banded gastroplasty group (adjHR 2.15; 95% CI 1.66-2.79; P < 0.001). CONCLUSIONS: The risk of fracture is increased after gastric bypass surgery. Our findings highlight the need for long-term follow-up of bone health for patients undergoing this treatment.

Incidence of end-stage renal disease following bariatric surgery in the Swedish Obese Subjects Study.

BACKGROUND: Obesity is a major public health problem leading to co-morbidities such as diabetes, hypertension and kidney failure. Bariatric surgery results in pronounced and maintained weight loss and prevention of obesity-related diseases and their complications. Most studies of bariatric surgery on kidney disease show improvements after surgery. However, long-term studies analyzing hard end-points are lacking. Here we report on the long-term effects of bariatric surgery compared to usual obesity care on incidence of end-stage renal disease (ESRD) alone and in combination with chronic kidney disease stage 4 (CKD4/ESRD). METHODS: 4047 patients were included in the Swedish Obese Subjects (SOS) study. Inclusion criteria were age 37-60 years and BMI ≥ 34 in men and BMI ≥ 38 in women. Patients in the bariatric surgery group (N = 2010) underwent banding (18%), vertical banded gastroplasty (69%), or gastric bypass (13%); controls (N = 2037) received usual obesity care. In this analysis, patients were followed up for a median time of 18 years. The incidence of ESRD and CKD4 was obtained by crosschecking the SOS database with the Swedish National Patient Register. RESULTS: During follow-up, ESRD occurred in 13 patients in the surgery group and in 26 patients in the control group (adjusted hazard ratio (HR) = 0.27; 95% CI 0.12-0.60; p = 0.001). The number of CKD4/ESRD events was 23 in the surgery group and 39 in the control group (adjusted HR = 0.33; 95% CI 0.18-0.62; p < 0.001). In both analyses, bariatric surgery had a more favorable effect in patients with baseline serum insulin levels above median compared to those with lower insulin levels (interaction p = 0.010). Treatment benefit of bariatric surgery was also greater in patients with macroalbuminuria at baseline compared to those without macroalbuminuria (interaction p < 0.001). CONCLUSIONS: Our study showed for the first time that bariatric surgery is associated with a long-term protection against ESRD and CKD4/ESRD.

Causal relationship of hepatic fat with liver damage and insulin resistance in nonalcoholic fatty liver.

BACKGROUND AND AIMS: Nonalcoholic fatty liver disease is epidemiologically associated with hepatic and metabolic disorders. The aim of this study was to examine whether hepatic fat accumulation has a causal role in determining liver damage and insulin resistance. METHODS: We performed a Mendelian randomization analysis using risk alleles in PNPLA3, TM6SF2, GCKR and MBOAT7, and a polygenic risk score for hepatic fat, as instruments. We evaluated complementary cohorts of at-risk individuals and individuals from the general population: 1515 from the liver biopsy cohort (LBC), 3329 from the Swedish Obese Subjects Study (SOS) and 4570 from the population-based Dallas Heart Study (DHS). RESULTS: Hepatic fat was epidemiologically associated with liver damage, insulin resistance, dyslipidemia and hypertension. The impact of genetic variants on liver damage was proportional to their effect on hepatic fat accumulation. Genetically determined hepatic fat was associated with aminotransferases, and with inflammation, ballooning and fibrosis in the LBC. Furthermore, in the LBC, the causal association between hepatic fat and fibrosis was independent of disease activity, suggesting that a causal effect of long-term liver fat accumulation on liver disease is independent of inflammation. Genetically determined hepatic steatosis was associated with insulin resistance in the LBC and SOS. However, this association was dependent on liver damage severity. Genetically determined hepatic steatosis was associated with liver fibrosis/cirrhosis and with a small increase in risk of type 2 diabetes in publicly available databases. CONCLUSION: These data suggest that long-term hepatic fat accumulation plays a causal role in the development of chronic liver disease.

Body composition through adult life: Swedish reference data on body composition.

BACKGROUND/OBJECTIVES: The prevalence of obesity, defined as body mass index (BMI) ⩾30 kg/m(2), differs between populations; however, there is a need for data on description on body composition in reference populations of different ages and from different countries. The objective of this study was to pool dual-energy X-ray absorptiometry (DXA) body composition reference data from population-based Swedish cohorts. SUBJECTS/METHODS: Four population-based cross-sectional cohort studies including 1424 adult Swedes were divided into five age groups (20-29, 30-39, 40-49, 50-61 and 75 years of age); BMI 24.6±3.9 kg/m(2) were pooled. Body composition was measured with DXA. RESULTS: The difference in BMI from the youngest to the oldest age group was 3.2 and 4.3 kg/m(2) in men and women, respectively (P<0.001, both sexes), and fat mass (FM) was 9.9 and 9.1% higher in the oldest compared with the youngest men and women (P<0.001, both sexes). Fat-free mass (FFM) remained stable up to 60 years of age in men (P=0.83) and was lower at 75 years of age compared with the younger ages. In women, FFM was lower from age 60. From youngest to oldest age groups, height-adjusted FM differed from 4.6 to 7.8 kg/m(2) in men and from 6.8 to 10.8 kg/m(2) in women (P<0.001, both sexes). CONCLUSIONS: Our results provide reference data on body composition in Swedish populations. BMI and FM were higher among older age groups compared with the younger ones. FFM remained stable up to 60 years of age and was lower first among the 75 years of age.

The incidence of albuminuria after bariatric surgery and usual care in Swedish Obese Subjects (SOS): a prospective controlled intervention trial.

BACKGROUND: Obesity is associated with increased risk of chronic kidney disease and albuminuria is a predictor of renal impairment. Bariatric surgery reduces body weight in obese subjects, but it is not known whether surgery can prevent development of albuminuria. This study aims to determine the long-term effect of bariatric surgery on the incidence of albuminuria. SUBJECTS: The Swedish Obese Subjects study is a non-randomized, prospective, controlled study conducted at 25 public surgical departments and 480 primary health care centers in Sweden. Between 1 September 1987 and 31 January 2001, 2010 participants who underwent bariatric surgery and 2037 controls were recruited. Inclusion criteria were age 37-60 years and BMI ⩾ 34 in men and BMI ⩾ 38 in women. In this analysis, we included 1498 patients in the surgery group and 1610 controls without albuminuria at baseline. Patients in the bariatric surgery group underwent banding (18%), vertical banded gastroplasty (69%) or gastric bypass (13%); controls received usual obesity care. Date of analysis was 1 January 2011. Median follow-up was 10 years, and the rates of follow-up were 87%, 74 and 52% at 2, 10 and 15 years, respectively. The main outcome of this report is incidence of albuminuria (defined as urinary albumin excretion >30 mg per 24 h) over up to 15 years. RESULTS: During the follow-up, albuminuria developed in 246 participants in the control group and in 126 in the bariatric surgery group, corresponding to incidence rates of 20.4 and 9.4 per 1000 person years, respectively (adjusted hazard ratio, 0.37; 95% confidence interval, 0.30-0.47; P < 0.001). The expected number of surgeries needed to prevent the development of albuminuria in one patient at 10 years was nine. CONCLUSIONS: Bariatric surgery is associated with reduced incidence of albuminuria compared with usual obesity care.

Macrophage gene expression in adipose tissue is associated with insulin sensitivity and serum lipid levels independent of obesity.

OBJECTIVE: Obesity is linked to both increased metabolic disturbances and increased adipose tissue macrophage infiltration. However, whether macrophage infiltration directly influences human metabolism is unclear. The aim of this study was to investigate if there are obesity-independent links between adipose tissue macrophages and metabolic disturbances. DESIGN AND METHODS: Expression of macrophage markers in adipose tissue was analyzed by DNA microarrays in the SOS Sib Pair study and in patients with type 2 diabetes and a BMI-matched healthy control group. RESULTS: The expression of macrophage markers in adipose tissue was increased in obesity and associated with several metabolic and anthropometric measurements. After adjustment for BMI, the expression remained associated with insulin sensitivity, serum levels of insulin, C-peptide, high density lipoprotein cholesterol (HDL-cholesterol) and triglycerides. In addition, the expression of most macrophage markers was significantly increased in patients with type 2 diabetes compared to the control group. CONCLUSION: Our study shows that infiltration of macrophages in human adipose tissue, estimated by the expression of macrophage markers, is increased in subjects with obesity and diabetes and associated with insulin sensitivity and serum lipid levels independent of BMI. This indicates that adipose tissue macrophages may contribute to the development of insulin resistance and dyslipidemia.

Alcohol and macronutrient intake patterns are related to general and central adiposity.

BACKGROUND/OBJECTIVES: Alcohol and dietary fat have high energy densities and may therefore be related to body weight and fat deposition. We studied associations between alcohol and macronutrient intake patterns and general and central adiposity. SUBJECTS/METHODS: A population-based cross-sectional study of 524 men and 611 women. The participants answered a dietary questionnaire describing habitual food consumption including intake of alcoholic beverages. Macronutrient intake was analysed in relation to anthropometric measures and dual energy X-ray absorptiometry determined body fat. RESULTS: In women, total alcohol intake was negatively associated with body fat percentage (ß:-0.67, P<0.01). In men, total alcohol intake was positively associated with sagittal abdominal diameter (SAD) (ß: 0.28, P=0.01). In addition, positive associations were found between intake of alcohol from spirits and body fat percentage (ß: 1.17, P<0.05), SAD (ß: 0.52, P<0.05) and waist circumference (ß: 2.29, P=0.01). In men, protein intake was positively associated with body mass index (BMI) (ß: 0.03, P=0.001), body fat percentage (ß: 0.04, P<0.05), SAD (ß: 0.02, P=0.01) and waist circumference (ß: 0.09, P<0.01). Also in men only, negative associations between fat intake and BMI (ß: -0.03, P<0.01), SAD (ß: -0.02, P<0.05) and waist circumference (ß: -0.05, P<0.05) were found. CONCLUSIONS: Alcohol intake was inversely associated to relative body fat in women whereas spirits consumption was positively related to central and general obesity in men. Macronutrient intakes, particularly protein and fat, were differently associated with obesity indicators in men versus women. This may reflect a differential effect by gender, or differential obesity related reporting errors in men and women.

Differential coexpression analysis of obesity-associated networks in human subcutaneous adipose tissue.

OBJECTIVE: To use a unique obesity-discordant sib-pair study design to combine differential expression analysis, expression quantitative trait loci (eQTLs) mapping and a coexpression regulatory network approach in subcutaneous human adipose tissue to identify genes relevant to the obese state. STUDY DESIGN: Genome-wide transcript expression in subcutaneous human adipose tissue was measured using Affymetrix U133 Plus 2.0 microarrays (Affymetrix, Santa Clara, CA, USA), and genome-wide genotyping data was obtained using an Applied Biosystems (Applied Biosystems; Life Technologies, Carlsbad, CA, USA) SNPlex linkage panel. SUBJECTS: A total of 154 Swedish families ascertained through an obese proband (body mass index (BMI) >30 kg m(-2)) with a discordant sibling (BMI>10 kg m(-2) less than proband). RESULTS: Approximately one-third of the transcripts were differentially expressed between lean and obese siblings. The cellular adhesion molecules (CAMs) KEGG grouping contained the largest number of differentially expressed genes under cis-acting genetic control. By using a novel approach to contrast CAMs coexpression networks between lean and obese siblings, a subset of differentially regulated genes was identified, with the previously GWAS obesity-associated neuronal growth regulator 1 (NEGR1) as a central hub. Independent analysis using mouse data demonstrated that this finding of NEGR1 is conserved across species. CONCLUSION: Our data suggest that in addition to its reported role in the brain, NEGR1 is also expressed in subcutaneous adipose tissue and acts as a central 'hub' in an obesity-related transcript network.

Self-reported sleep apnoea and mortality in patients from the Swedish Obese Subjects study.

Sleep apnoea is associated with increased mortality in sleep clinic and community population groups. It is unclear whether a clinical report of sleep apnoea results in additional mortality risk in patients with severe obesity. The Swedish Obese Subjects (SOS) study is a nonrandomised controlled trial of bariatric surgery versus conventional treatment for the treatment of severe obesity and its complications (mean ± SD body mass index 41 ± 5 kg · m(-2)). The presence or absence of sleep apnoea (witnessed pauses in breathing) was determined by self-reporting at baseline in 3,953 patients who were observed for 54,236 person-yrs (mean 13.5 maximum 21.0 yrs). Sleep apnoea was reported by 934 (23.6%) patients at baseline and was a significant univariate predictor of mortality (hazard ratio (95% CI) 1.74 (1.40-2.18)). In a range of multivariate models of mortality risk, controlling for ≤ 16 other potential confounders and established mortality risk factors, sleep apnoea remained a significant prognostic factor (fully adjusted model 1.29 (1.01-1.65)). Self-reported sleep apnoea is an independent prognostic marker of all-cause mortality in obese patients.

Associations of markers in 11 obesity candidate genes with maximal weight loss and weight regain in the SOS bariatric surgery cases.

PURPOSE: To test whether DNA sequence variation in 11 obesity genes is associated with maximum weight loss and weight regain over 6 years of follow-up in bariatric surgery patients of the Swedish obese subjects (SOS) intervention study. METHODS: A total of 1443 subjects were available for analysis (vertical banded gastroplasty: n = 966, banding: n = 293 and gastric bypass: n = 184). Single-nucleotide polymorphisms (SNPs) from the following 11 genes were included: ADIPOQ, BDNF, FTO, GNB3, LEP, LEPR, MC4R, NR3C1, PPARG, PPARGC1A and TNF. General linear models were used to analyze associations between the SNPs and maximum weight loss and weight regain. RESULTS: The average maximum weight loss was 33.7 kg (s.d. 13.3; min -95.5 kg, max +2.0 kg), which was reached 2.2 (s.d. 1.6) years after the surgery. Subjects regained approximately 12 kg (range 0.0-51.4 kg) by year 6. After correcting for multiple testing, the FTO SNP rs16945088 remained significantly associated with maximum weight loss (P = 0.0002), as minor allele carriers lost approximately 3 kg less compared with common allele homozygotes. This association was particularly evident in the banding surgery patients (P < 0.0001), whereas no significant association was found in the gastric bypass subjects. No other SNPs were associated with maximum weight loss. Furthermore, no SNPs were significantly associated with weight regain. CONCLUSION: The FTO SNP rs16945088 was associated with maximum weight loss after banding surgery. We found no evidence that obesity-risk SNPs in FTO or other obesity candidate genes derived from genome-wide association studies are associated with maximum weight loss or weight regain over 6 years of follow-up in bariatric surgery patients. The potential role of other obesity genes remains to be investigated.

Decrease in adiponectin levels correlates to growth response in growth hormone-treated children.

BACKGROUND/AIMS: Adiponectin is secreted by adipose tissue and circulates in human plasma at high levels. Decreased adiponectin levels are associated with insulin resistance and obesity. The aim of this study was to investigate whether changes in serum adiponectin levels are related to the growth response, insulin levels and insulin resistance during growth hormone (GH) treatment. METHODS: The study included 94 short prepubertal children (19 girls and 75 boys). The mean age at the start of daily GH injections was 9.04 +/- 2.38 years. Adiponectin levels in serum were measured using an ELISA. RESULTS: At baseline, adiponectin correlated with the first-year growth response (r = 0.26, p = 0.012). Adiponectin decreased significantly after 1 week, 3 months and 1 year from 14.5 +/- 5.71 to 13.1 +/- 5.22 (p < 0.0001), 10.3 +/- 4.82 (p < 0.0001) and 12.5 +/- 5.34 microg/ml (p < 0.0001), respectively. There were significant correlations between the first-year growth response and the decrease in adiponectin levels after 3 months and 1 year (r = -0.38, p < 0.0001 and r = -0.47, p < 0.0001, respectively). No correlations between adiponectin, insulin and the homeostasis model assessment of insulin resistance were seen. CONCLUSIONS: GH treatment in prepubertal children decreases serum adiponectin levels, and the decrease is correlated to the growth response. No correlations between adiponectin and insulin levels or insulin resistance were found.

Increased levels of acylation-stimulating protein in interleukin-6-deficient (IL-6(-/-)) mice.

IL-6-deficient (IL-6(-/-)) mice develop obesity at 6-7 months of age. To elucidate the mechanisms of this mature-onset obesity, global gene expression profiles of 3-month-old preobese IL-6(-/-) were compared with those of IL-6(+/+) mice using DNA arrays. Genes that were up-regulated in IL-6(-/-) mice included the factors transthyretin and properdin in white adipose tissue and adipsin in muscle. These factors have been shown to influence the formation of acylation-stimulating protein (ASP), a cleavage product of complement C3. ASP stimulates the synthesis of triacylglycerol in adipocytes, and ASP-deficient mice are resistant to diet-induced obesity. In line with the increases in transthyretin, properdin, and adipsin, ASP levels in serum were increased by 31-54% in IL-6(-/-) compared with IL-6(+/+) mice. Furthermore, IL-6 replacement treatment in IL-6(-/-) mice decreased ASP levels significantly by 25-60%. In conclusion, ASP levels are increased in preobese IL-6(-/-) mice. This increase may result in increased triacylglycerol formation and uptake in IL-6(-/-) adipocytes and thereby contribute to the development of obesity in IL-6(-/-) mice.

Circulating non-22 kDa growth hormone isoforms after a repeated GHRH stimulus in normal subjects.

The aim of this study was to evaluate the proportion of non-22 kDa GH isoforms in relation to total GH concentration after a repeated GHRH stimulus in healthy subjects. We studied 25 normal volunteers (12 males and 13 females, mean age 13.1 years, range 6-35), who received two GHRH bolus (1.5 mug/kg body weight, i.v.) administered separately by an interval of 120 minutes. The proportion of non-22 kDa GH was determined by the 22 kDa GH exclusion assay (GHEA), which is based on immunomagnetic extraction of monomeric and dimeric 22 kDa GH from serum, and quantitation of non-22 kDa GH isoforms using a polyclonal GH assay. Samples were collected at baseline and at 15-30 min intervals up to 240 min for total GH concentration. Non-22 kDa GH isoforms were measured in samples where peak GH after GHRH was observed. Total GH peaked after the first GHRH bolus in all subjects (median 37.2 ng/ml; range: 10.4-94.6). According to GH response to the second GHRH stimulus, the study group was divided in "non-responders" (n=7; 28%), with GH peak levels lower than 10 ng/ml (median GH: 8.7 ng/ml; range 7.3-9.6) and "responders" (n=18; 72%), who showed a GH response greater than 10 ng/ml (median 17 ng/ml; range 10.1-47.0). The median proportion of non-22 kDa GH on the peak of GH secretion after the first GHRH administration was similar in both groups ("responders" median: 8.6%, range 7-10.9%; "non-responders" median: 8.7%, range 6.7-10.3%), independently of the type of response after the second GHRH. In contrast, the median proportion of non-22 kDa GH was greater at time of GH peak after the second GHRH bolus in the "non-responders" (median 11.4%; range 9.1-14.3%) in comparison with the "responders" (median 9.1%; range 6.7-11.9%; p=0.003). A significant negative correlation between the total GH secreted and the percentage of non-22 kDa isoforms was seen in the "non-responders" (p=0.003). These differences in GH response to repeated GHRH stimulation and in the pattern of GH isoforms at GH peak among subjects might be due to distinct recovery patterns of somatrotrophic function and/or differences in metabolic clearance of GH isoforms.

Cartilage oligomeric matrix protein increases in serum after the start of growth hormone treatment in prepubertal children.

Both GH and IGF-I stimulate bone growth, but the molecular mechanisms mediating their effects on the growth plate are not fully understood. We measured gene expression by microarray analysis in primary cultured human chondrocytes treated with either GH or IGF-I. One of the genes found to be up-regulated by both GH and IGF-I was that encoding cartilage oligomeric matrix protein (COMP). This protein is predominantly found in the extracellular matrix of cartilage. Mutations in the COMP gene have been associated with syndromes of short stature. To verify that COMP is regulated by GH in vivo, we measured COMP levels in serum in short children treated with GH. The study included 113 short prepubertal children (14 girls and 99 boys) with a mean (+/- sd) age of 8.84 +/- 2.76 yr, height sd score of -2.74 +/- 0.67, and IGF-I sd score of -1.21 +/- 1.07 at the start of GH administration. Serum levels of COMP were 1.58 +/- 0.28, 1.83 +/- 0.28 (P < 0.0001), 1.91 +/- 0.28 (P < 0.0001), 1.78 +/- 0.28 (P < 0.001), and 1.70 +/- 0.24 (P < 0.05) microg/ml at baseline and after 1 wk and 1, 3, and 12 months, respectively. In conclusion, we have demonstrated that COMP expression is up-regulated by both GH and IGF-I in primary cultured human chondrocytes. Furthermore, serum levels of COMP increase after the start of GH treatment in short children.

Construction of a soluble human GH-receptor/EGF-receptor hybrid and its activation by GH.

To develop a cell-free system that can be used to measure cytokine bioactivity we have designed a soluble hybrid molecule consisting of the extracellular domain of the GH-receptor (GHR) and the intracellular domain of the epidermal growth factor receptor (EGFR). A DNA construct encoding this hybrid-receptor was inserted into a baculoviral expression vector and expressed in Sf9-cells. Activation of the hybrid-receptor by ligand-induced dimerization can be measured as the incorporation of radiolabeled phosphate into a biotinylated tyrosine kinase peptide substrate. The kinase activity in samples stimulated with GH (10 ng/ml) increased 5-fold compared to samples without addition of GH. This is the first example of a functional hybrid-receptor where the transmembrane domain has been deleted. Our results suggest that such hybrid-receptors may be used for detection of GH and other cytokine-receptor activating substances in biological fluids.

The effect of treatment with the oral growth hormone (GH) secretagogue MK-677 on GH isoforms.

Growth hormone (GH) consists of several isoforms. We have studied the proportion, expressed as percentage of total GH concentration, of non-22kDa (non-22K) GH isoforms and 20K GH during 8-week oral treatment with MK-677 25mg daily in 12 obese males. The proportion of non-22K GH isoforms in peak total GH samples after the initial MK-677 administration was higher than that after 2 and 8 weeks (p<0.01 and p<0.05, respectively). In selected non-peak total GH samples after the initial MK-677 administration, however, the proportion of non-22K GH isoforms was similar to that in the peak total GH samples after 2 and 8 weeks. The proportion of 20K GH in 2-h samples after the initial MK-677 administration was lower than that after 2 and 8 weeks (p<0.01 and p<0.05, respectively). We concluded that the proportion of non-22K GH isoforms was higher in peak, but not in non-peak, total GH samples after the initial MK-677 administration than that observed after multiple doses. The proportion of 20K GH in 2-h samples after the initial MK-677 administration was lower than that after 2 and 8 weeks. These moderate changes in the proportion non-22K GH isoforms are likely of small importance for the clinical response to MK-677 treatment.

Growth hormone receptor interaction with Jak proteins differs between tissues.

Janus kinases (Jak) play an important role in the initial steps of cytokine receptor signaling. The specificity of the four members of the Jak family (Jak1, Jak2, Jak3, and Tyk2) for different cytokine receptors is not fully understood. Recent studies have indicated that a specific cytokine receptor can activate several Jak and that this may differ between tissues. The growth hormone receptor (GHR) is believed to interact predominantly with Jak2, but studies on cell lines have shown that it may also induce phosphorylation of Jak1 and Jak3. Little is known about the interaction between the GHR and Jak in tissues. Our aim, therefore, was to elucidate which Jak interact with the GHR in two target tissues for GH, liver and adipose tissue. Western blot analysis showed that all four members of the Jak family are present in both rat liver and adipose tissue. However, coprecipitation using an anti-GHR antibody revealed that only Jak1 and Jak2 were associated with the GHR in these tissues. The relative amount of Jak1 and Jak2 that coprecipitated with the GHR differed markedly between tissues. In the liver, Jak2 dominated, and only a small amount of Jak1 was detected. In adipose tissue, at least one third of the coprecipitated Jak was Jak1. This is the first study to show that both Jak1 and Jak2 are associated with the GHR in rat tissues. The difference in the ratio between GHR-associated Jak1 and Jak2 in liver and adipose tissue may indicate that GHR signaling in different tissues could differ in terms of Jak specificity.

Leptin receptor 5'untranslated regions in the rat: relative abundance, genomic organization and relation to putative response elements.

Hypothalamic sensitivity to leptin has been suggested to be important for regulation of body fat mass. Mice heterozygous for a mutation in the leptin receptor (leptin-R) have an increased body fat mass suggesting that the abundance of leptin-R may be an important determinator of leptin sensitivity. Leptin-R cDNAs from several species contain alternative 5'untranslated regions (5'UTRs), suggesting that several distinct regulatory regions may exist. To investigate possible mechanisms by which leptin-R expression may be regulated, we searched for possible alternative 5'UTRs of the leptin-R in the rat and determined their location in relation to putative response elements. Four leptin-R 5'UTRs (exons 1A-1D), which diverged 23 bp upstream of the start codon, were identified by 5'Rapid Amplification of cDNA Ends (5'RACE) and sequencing. Exons 1B and 1C were present in 31 and 61%, respectively, of all leptin-R transcripts in the hypothalamus as determined by a ribonuclease protection assay. Analysis of the 5' flanking genomic sequences revealed an imperfect estrogen response element (ERE), two Spl-sites, three CCAAT-boxes and one octamer. Exons 1A and 1D corresponded to a putative second gene, encoding the OB-Receptor Gene Related Protein (OB-RGRP), which is transcribed from a promoter shared with the leptin-R. DNA sequencing revealed that the rat OB-RGRP had 98 and 97% homology with the mouse and human sequence, respectively. We report here that transcription of the rat leptin-R gene may generate transcripts with four alternative 5'UTRs. The presence of a putative ERE, close to the most frequently used transcriptional start sites of the leptin-R gene in the hypothalamus, provides a possible mechanism by which estrogen may exert its effects on food intake.