Hypercalcemia and bone resorption in malignancy

Hypercalcemia is the most common paraneoplastic syndrome associated with cancer. This paper addresses the etiology and pathogenesis of hypercalcemia of malignancy and discusses the relative contributions of local and humoral effects on bone and renal calcium homeostasis. The roles of parathyroid hormone-related protein and other osteolytic cytokines are outlined. New biochemical markers that enable more specific monitoring of the response of bone metastases to treatment are introduced, including urinary excretion of the collagen crosslinks pyridinoline and deoxypyridinoline. The clinical management and prevention of hypercalcemia is systemically outlined, including indications for bisphosphonate, glucocorticoid, and calcitonin therapy. The results of recent trials of bisphosphonate therapy for the prevention of tumor progression and its subsequent problems such as bone pain, fracture, and hypercalcemia also are discussed.

High incidence of end-stage renal disease in Indo-Asians in the UK

In a retrospective survey, we show that the incidence of end-stage renal disease (ESRD) is significantly raised among immigrant Indo-Asians referred to two UK renal units (p < 0.001). In addition to the expected increase in diabetic nephropathy, glomerulonephritis and chronic pyelonephritis are also seen more frequently in Indo-Asians. The most striking finding was a five-fold increase in ESRD of uncertain cause (p < 0.001) presenting with small smooth kidneys, which was strongly associated with active, mostly non-renal tuberculosis. The causes of this generalized increased susceptibility to renal disease are unknown. These findings have important implications both for primary health care screening and for planning the provision of renal replacement therapy.

Renal failure due to cholesterol embolisation

Five cases of cholesterol crystal embolisation resulting in impaired renal function are reported and their investigation and management discussed.

Haemoglobin--is more better?

Recombinant human erythropoietin (r-HuEPO) treatment reduces cardiac output and increases left ventricular mass: beneficial effects that might be expected to be maximized at near-normal haemoglobin values. Quality of life in dialysis patients treated with r-HuEPO has been shown to be related to haemoglobin, up to a haematocrit of 35%. The potential benefits of increasing the target haemoglobin must, however, be seen in the context of the haemodynamic changes that occur during r-HuEPO treatment, in particular, increased peripheral resistance (leading to hypertension), and possible adverse effects on the coagulation system and microcirculation. Pending further trials with a target haemoglobin of 14 g/dl or a haematocrit of 40%, a target haematocrit of 34-37% seems reasonable; it might also be appropriate to adjust the target haematocrit according to the individual's symptoms and lifestyle.

Parathyroid hormone-related protein (PTHrP) in breast cancer and benign breast tissue

Parathyroid hormone-related protein (PTHrP) 1-86 was quantified by immunoassay in extracts of 132 breast cancers, 27 samples of normal breast tissue and four fibroadenomas. PTHrP 1-86, was detected in 68% of primary tumours (range 40-302,000 fmol/g), 33% of normal breast tissues (range 100-1800 fmol/g), and all four fibroadenomas (range 110-11,600 fmol/g). PTHrP displayed molecular heterogeneity on gel filtration chromatography, and 1-86, 1-34 and 37-67 immunoreactivity eluted as 25-27 kDa together with a peak of 19-21 kDA containing only 37-67 activity. Tumour PTHrP 1-86 levels correlated inversely with age (P < 0.05) and were higher in premenopausal women (P = 0.05). The proportion of tumours containing PTHrP was higher in axillary node positive premenopausal women (P < 0.05). These data suggest that oestrogen may regulate expression of PTHrP in breast cancer and that production of PTHrP may be linked to development of axillary node metastases.

Growth of proximal tubular cells in the presence of albumin and proteinuric urine

The degree of interstitial scarring and proteinuria both correlate with renal function in progressive renal disease. Cellular hypertrophy and hyperplasia have been shown to occur under different experimental conditions. This study investigated the effect of protein on the growth of OK cells. Bovine serum albumin (BSA)- and fatty-acid-free BSA (FFBSA)-stimulated proliferation of OK cells and hypertrophy occurred when the cells were incubated with 10 mg/ml of BSA or FFBSA. Incubation with proteinuric urine from nephrotic rats resulted in much greater proliferation. Hence protein can alter proximal tubular cell growth in culture and the mixture of proteins in proteinuric urine has a greater effect than can be explained by albumin alone. These findings may be of significance in the progression of renal disease and indicate the potential importance of urinary proteins other than albumin in modulating tubular cell growth.

Parathyroid hormone and parathyroid hormone-related protein in the investigation of hypercalcaemia in two hospital populations

BACKGROUND AND OBJECTIVE

Parathyroid hormone-related protein (PTHrP) produced by cancers has a central role as a humoral mediator of hypercalcaemia in patients with malignancy. Since the prevalences of hypercalcaemia of malignancy and parathyroid disease reflect the population studied, hypercalcaemic patients from a district general hospital (DGH) and an oncology centre (OC) were studied in order to assess the diagnostic role of assays for serum PTH and plasma PTHrP in different clinical settings.

DESIGN

A prospective study of consecutive patients presenting with their first episode of hypercalcaemia during an 18-month period.

PATIENTS

A total of 123 patients (DGH, n = 69; OC, n = 54) had corrected serum calcium concentrations > 2.65 mmol/l.

MEASUREMENTS

PTH, PTHrP, calcium and albumin were measured together with urine calcium and creatinine, enabling fractional calcium excretion to be assessed. Urine cyclic adenosine monophosphate was also measured.

RESULTS

Hypercalcaemia was attributed to malignancy alone in 72 patients (DGH, n = 20; OC, n = 52), benign causes in 42 (DGH, n = 42) and parathyroid disease coexisting with malignancy in 9 (DGH, n = 7; OC, n = 2). Plasma PTHrP levels were increased in 59/72 (82%) patients with hypercalcaemia due to malignancy. Measurements of both analytes contributed to a change in the final diagnosis in 12 patients (10%). Thus serum PTH was increased in seven patients with parathyroid disease coexisting with malignancy, and plasma PTHrP was increased in five patients with previous undiagnosed malignancy. Median survival for patients with parathyroid disease and coexisting malignancy was 13 months compared with 3 months for those with hypercalcaemia due to malignancy alone (P < 0.02).

CONCLUSIONS

Since hypercalcaemia was attributable to parathyroid disease in 10% of all patients with malignancy we advise measurement of serum PTH at the initial presentation of hypercalcaemia in all patients, while plasma PTHrP may be useful to identify those patients in whom malignancy may not be clinically apparent, or coexist with primary hyperparathyroidism.

Continuing clinically severe vitamin D deficiency in Asians in the UK (Leicester)

Deprivational vitamin D deficiency began to be noted in immigrant Asians in the early 1960s. Although there have been suggestions that the level of this problem may be declining, we describe a number of clinical cases seen over a consecutive 3 1/2 year period. Musculoskeletal symptoms were the commonest though there were a variety of medical presentations requiring hospital referral. Most of the cases were Hindu vegetarians. There is likely to be significant underdiagnosis of this condition. In spite of the extensive medical, social and political attention this condition has received, our study shows that vitamin D deficiency continues to persist in certain Asians in a clinically florid fashion. An effective preventative policy is long overdue.

Influence of nifedipine on interstitial fibrosis in renal transplant allografts treated with cyclosporin A

AIMS

To compare the degree of interstitial fibrosis in renal transplant biopsy specimens from immunosuppressed patients using conventional doses of cyclosporin with and without calcium channel blockade with a combination of low dose cyclosporin and azathioprine; to correlate the degree of interstitial fibrosis with the glomerular filtration rate.

METHODS

A single blind histomorphometric assessment was done of cortical interstitial volume fraction from biopsy specimens taken intraoperatively and at one, six, and 12 months after transplantation from three prospectively randomised groups of patients: (A) conventional dose cyclosporin; (B) conventional dose cyclosporin plus nifedipine; (C) low dose cyclosporin plus azathioprine.

RESULTS

Interstitial volume increased with time in all groups. No differences in interstitial volume were present at operation or at one month, but at six months interstitial volume was significantly less in group B than group A (p < 0.001) or group C (p < 0.05). More grafts failed in group A than group B leaving only small numbers for comparison at 12 months. At 12 months the differences persisted but did not reach significance. These results strongly reflected the clinical findings, where glomerular filtration rate was significantly lower in group A than groups B or C at six and 12 months; no differences in glomerular filtration rate were found at one month. In a direct comparison glomerular filtration rate showed a significant negative correlation with interstitial volume fraction.

CONCLUSIONS

These findings suggest that calcium channel blockade with nifedipine slows the development of interstitial fibrosis in renal transplant recipients treated with cyclosporin. When clinical data are considered, it is suggested that calcium channel blockade may have a mitigating effect on the long term nephrotoxic effects of cyclosporin and should be considered as adjunctive treatment in patients requiring this immunosuppressant following renal transplantation.

Hypertrophy of proximal tubular epithelial cells induced by low pH in vitro is independent of ammoniagenesis

Metabolic acidosis can lead to tubular hypertrophy in vivo. This is thought to arise from stimulation of renal production of ammonia, a known hypertrophic agent. To examine this effect in vitro, confluent opossum (OK) proximal tubular epithelial cells were cultured at acidic pH (7.21 +/- 0.02) or at control pH (7.37 +/- 0.01) for 4 days. Protein content was 9% higher at acidic pH whereas DNA content was unaffected. The resulting increase in mean cell size (protein/DNA ratio) was 10% but correlated inversely with the mass of cells in control wells, varying from +48% at low cell mass to -14% at high cell mass. In contrast, low pH decreased 3H-thymidine incorporation by 9%. However, ammonia production was unaffected. These changes in protein/DNA ratio and 3H-thymidine incorporation cannot therefore be attributed to acid-induced ammoniagenesis and imply that low pH exerts a more direct effect on tubular cell growth than previously envisaged.

Response to intravenous bisphosphonate therapy in hypercalcaemic patients with and without bone metastases: the role of parathyroid hormone-related protein

Plasma parathyroid hormone related-protein (PTHrP) may inhibit the calcium-lowering effect of bisphosphonate therapy. In this prospective study we examined the relationship between plasma PTHrP levels, renal tubular markers of calcium reabsorption, and the effectiveness of intravenous bisphosphonate therapy (IVBPT) in lowering serum calcium in patients with hypercalcaemia of malignancy (HM), with and without bone metastases. Thirty-five symptomatic hypercalcaemic patients (17 without and 18 with bone metastases) were treated with IVBPT (pamidronate 30-60 mg or BM21.0955 2-6 mg). Normocalcaemia was achieved in 24/35 (71%) patients with a mean fall in serum calcium of 0.85 mmol l-1 (range 0.11-1.93, P < 0.001). In the 35 patients studied, serum calcium levels reached a nadir between days 3 and 7, and this was accompanied by a small but significant reduction in plasma PTHrP levels (median reduction 0.77 pmol l-1, P = 0.007). Patients who responded to bisphosphonate therapy by becoming normocalcaemic had significantly lower basal plasma PTHrP levels, mean 4.06 vs 8.2 pmol l-1 (P < 0.04). A significant reduction in urinary calcium excretion was seen (mean 106 mumol l-1, P < 0.02) in patients with bone metastases, and urinary cAMP (mean 170 mmol l-1, P < 0.01) fell in all patients. Patients without demonstrable bone metastases had significantly higher plasma PTHrP levels (P < 0.002), required more doses of IVBPT, and had a poorer reduction in serum calcium compared with patients with bone metastases, only one of whom required more than one dose. We conclude that circulating PTHrP has an important role in increasing renal tubular reabsorption of calcium in HM, thus reducing the effectiveness of bisphosphonate therapy, particularly in patients with humoral HM and no bone metastases.

Regulation of intracellular creatine in erythrocytes and myoblasts: influence of uraemia and inhibition of Na,K-ATPase

The regulation of intracellular creatine concentration in mammalian cells is poorly understood, but is thought to depend upon active sodium-linked uptake of creatine from extracellular fluid. In normal human erythrocytes, creatine influx into washed cells was inhibited by 40 per cent in the absence of extracellular sodium. In washed cells from uraemic patients, sodium-independent creatine influx was normal, whereas the sodium-dependent component of creatine influx was 3.3 times higher than normal, possibly reflecting the reduced mean age of uraemic erythrocytes. In spite of this, the intracellular creatine concentration was no higher than normal in uraemic erythrocytes, implying that some factor in uraemic plasma in vivo inhibits sodium-dependent creatine influx. Both in normal and uraemic erythrocytes, the creatine concentration was 10 times that in plasma, and the concentration in the cells showed no detectable dependence on that in plasma, suggesting that the intracellular creatine concentration is controlled by an active saturable process. Active sodium-dependent accumulation of creatine was also demonstrated in L6 rat myoblasts and was inhibited when transport was measured in the presence of 10(-4) M ouabain or digoxin, implying that uptake was driven by the transmembrane sodium gradient. However, when creatine influx was measured immediately after ouabain or digoxin had been washed away, it was higher than in control cells, suggesting that Na,K-ATPase and/or sodium-linked creatine transport are up-regulated when treated with inhibitors of Na,K-ATPase.

Glomerular disease as a cause of isolated microscopic haematuria

Microscopic haematuria is a common clinical finding, with reported prevalences of up to 22%. The role of renal biopsy in the investigation of this condition is still debated. Currently urological investigation including cystourethroscopy is often regarded as adequate. We investigated 165 patients (94 male, 71 female; mean age 37.5 years, range 10-71) referred with isolated microscopic haematuria, using renal biopsy and cystourethroscopy. All patients were normotensive with normal serum creatinine, no proteinuria, sterile urine and a normal IVU. Renal biopsy abnormalities were found in 77/165 (46.6%): IgA nephropathy (49), global or segmental mesangial proliferative glomerulonephritis without IgA deposits (16), thin membrane nephropathy (7), vascular changes suggestive of hypertension (3), interstitial nephritis (1), and membranous nephropathy (1). Only five abnormalities were found on cystourethroscopy (cystitis 3, urethral stricture 1, bladder stone 1). Two patients with cystitis also had IgA nephropathy. Biopsy abnormalities were commonest under the age of 20 (69.2%), but 40% of biopsies were abnormal even in the seventh decade of life. Because renal biopsy abnormalities are very frequent in patients with isolated haematuria, renal biopsy is indicated in patients over 45 years of age if renal imaging and cystoscopy are normal. In those under 45 years, renal biopsy should replace cystoscopy as the investigation to follow normal renal imaging.

Plasma amino acid profile in the elderly with increasing uraemia

Abnormalities in plasma amino acid profiles have been reported in severe uraemia and dialysis patients and may be a consequence of altered protein metabolism in the presence of metabolic acidosis. We studied plasma amino acid profiles in 7 control subjects [GFR 92.7 +/- (SEM) 14.5 ml/min/1.73 m2] and 7 elderly patients with renal failure (GFR 16.5 +/- 1.3 ml/min/1.73 m2). Uraemic patients had significantly reduced plasma levels of valine, tyrosine, phenylalanine, tryptophan and elevated histidine compared to controls. There was no correlation between arterial pH or bicarbonate and plasma amino acid levels.

Simvastatin therapy for hypercholesterolemic patients with nephrotic syndrome or significant proteinuria

Experimental evidence suggests that lipid lowering therapy could slow the progression of renal disease in humans. We have conducted a double-blind, placebo controlled trial of the HMG CoA reductase inhibitor simvastatin in patients with the nephrotic syndrome or significant proteinuria (> 1 g/day) and hypercholesterolemia (> or = 6.5 mmol/liter). Patients were placed on a lipid lowering diet for at least 10 weeks before randomization. After a four-week placebo run-in, 30 adults were randomized to simvastatin or placebo therapy (10 mg/day, increasing to 20 to 40 mg/day as required) for 24 weeks. There were seven dropouts, none of whom were "definitely" related to drug therapy. Total and LDL cholesterol levels fell by a mean of 33 and 31%, respectively, in simvastatin treated patients, compared with only 5 and 1% in patients on placebo (P < 0.001, P = 0.002, respectively). Apolipoprotein B100 levels fell by a mean of 31% in the simvastatin group but rose 0.3% in the placebo group (P = 0.014). There were no significant changes in HDL levels. There were no significant differences between the groups in their urine protein levels, their rise in plasma creatinine, or decline in plasma inulin clearance. Simvastatin is a safe, effective therapy for hypercholesterolemia in proteinuric states. A much larger trial is needed to show if potent lipid-lowering therapy slows progression of hypercholesterolemic proteinuric diseases.

Effects of acid loading on serum amino acid profiles and muscle composition in normal fed rats

1. Impaired body growth, loss of lean body mass and negative nitrogen balance are common findings in chronic renal failure. Enhanced endogenous protein catabolism in skeletal muscle induced by co-existent metabolic acidosis seems to be an important aetiological factor. 2. In uraemic patients abnormalities in blood amino acid profiles are present after a protein meal, suggesting impaired metabolism of ingested proteins. 3. This study demonstrates that acidosis induces changes in arterial amino acid profiles in fed non-uraemic rats. These included increased levels of threonine, histidine, proline, serine and glycine, and decreased levels of tryptophan. These changes are similar to those found in uraemic patients after a protein meal, suggesting a pathogenic role of acidosis in the impairment of exogenous protein metabolism. 4. Intracellular amino acid levels in the muscle tissue partly reflect the changes in the extracellular level. 5. Acidotic animals had a decreased body weight gain and a reduced alkali-soluble protein/DNA ratio in muscle cells compared with controls. 6. In conclusion, the results show that acidosis per se modifies the circulating amino acid profile in fed rats, resulting in a pattern similar to the post-prandial amino acid changes described in uraemic patients. These abnormalities occur together with impaired growth of skeletal muscle cells.