Cloning and sequence analysis of a highly polymorphic Cryptosporidium parvum gene encoding a 60-kilodalton glycoprotein and characterization of its 15- and 45-kilodalton zoite surface antigen products

The apicomplexan parasite Cryptosporidium parvum is a major cause of serious diarrheal disease in both humans and animals. No efficacious chemo- or immunotherapies have been identified for cryptosporidiosis, but certain antibodies directed against zoite surface antigens and/or proteins shed by gliding zoites have been shown to neutralize infectivity in vitro and/or to passively protect against, or ameliorate, disease in vivo. We previously used monoclonal antibody 11A5 to identify a 15-kDa surface glycoprotein that was shed behind motile sporozoites and was recognized by several lectins that neutralized parasite infectivity for cultured epithelial cells. Here we report the cloning and sequence analysis of the gene encoding this 11A5 antigen. Surprisingly, the gene encoded a 330-amino-acid, mucin-like glycoprotein that was predicted to contain an N-terminal signal peptide, a homopolymeric tract of serine residues, 36 sites of O-linked glycosylation, and a hydrophobic C-terminal peptide specifying attachment of a glycosylphosphatidylinositol anchor. The single-copy gene lacked introns and was expressed during merogony to produce a 60-kDa precursor which was proteolytically cleaved to 15- and 45-kDa glycoprotein products that both localized to the surface of sporozoites and merozoites. The gp15/45/60 gene displayed a very high degree of sequence diversity among C. parvum isolates, and the numerous single-nucleotide and single-amino-acid polymorphisms defined five to six allelic classes, each characterized by additional intra-allelic sequence variation. The gp15/45/60 single-nucleotide polymorphisms will prove useful for haplotyping and fingerprinting isolates and for establishing meaningful relationships between C. parvum genotype and phenotype.

Do foot examinations reduce the risk of diabetic amputation?

BACKGROUND

Foot examinations are widely recommended as a means to reduce amputation risk, but no investigators have studied their independent effect on this outcome.

METHODS

We conducted a population-based case-control study of primary care provided to Pima Indians from the Gila River Indian Community. Sixty-one Pima Indians with type 2 diabetes and a first lower-extremity amputation between January 1, 1985, and December 31, 1992, were compared with 183 people who had no amputation by December 31, 1992. The type of foot examination conducted, comorbid conditions, and foot risk factors present in the 36 months before the pivotal event were abstracted from medical records. All ulcer care was excluded. The independent effect of foot examinations on the risk of amputation was assessed by logistic regression.

RESULTS

During the 36 study months, 1857 foot examinations were performed on 244 subjects. The median number of preventive foot examinations was 7 for case patients and 3 for control patients. After controlling for differences in comorbid conditions and foot risk conditions, the risk of amputation for persons with 1 or more foot examinations was an odds ratio (OR) of 0.55 (95% confidence interval [CI], 0.2-1.7; P=.31). The risk of amputation associated with written comments of nonadherence with therapeutic foot care recommendations or diabetic medication was an OR of 1.9 (95% CI, 0.9-4.3; P=.10).

CONCLUSIONS

Our study failed to demonstrate that foot examinations decrease the risk of amputation in Pima Indians with type 2 diabetes. However, foot examinations detect high-risk conditions for which specific interventions have been shown to be effective in reducing amputation risk.

Identification of Cryptosporidium parvum dihydrofolate reductase inhibitors by complementation in Saccharomyces cerevisiae

There is a pressing need for drugs effective against the opportunistic protozoan pathogen Cryptosporidium parvum. Folate metabolic enzymes and enzymes of the thymidylate cycle, particularly dihydrofolate reductase (DHFR), have been widely exploited as chemotherapeutic targets. Although many DHFR inhibitors have been synthesized, only a few have been tested against C. parvum. To expedite and facilitate the discovery of effective anti-Cryptosporidium antifolates, we have developed a rapid and facile method to screen potential inhibitors of C. parvum DHFR using the model eukaryote, Saccharomyces cerevisiae. We expressed the DHFR genes of C. parvum, Plasmodium falciparum, Toxoplasma gondii, Pneumocystis carinii, and humans in the same DHFR-deficient yeast strain and observed that each heterologous enzyme complemented the yeast DHFR deficiency. In this work we describe our use of the complementation system to screen known DHFR inhibitors and our discovery of several compounds that inhibited the growth of yeast reliant on the C. parvum enzyme. These same compounds were also potent or selective inhibitors of the purified recombinant C. parvum DHFR enzyme. Six novel lipophilic DHFR inhibitors potently inhibited the growth of yeast expressing C. parvum DHFR. However, the inhibition was nonselective, as these compounds also strongly inhibited the growth of yeast dependent on the human enzyme. Conversely, the antibacterial DHFR inhibitor trimethoprim and two close structural analogs were highly selective, but weak, inhibitors of yeast complemented by the C. parvum enzyme. Future chemical refinement of the potent and selective lead compounds identified in this study may allow the design of an efficacious antifolate drug for the treatment of cryptosporidiosis.

Preliminary profile of the Cryptosporidium parvum genome: an expressed sequence tag and genome survey sequence analysis

Cryptosporidium parvum is a protozoan enteropathogen that infects humans and animals and causes a pronounced diarrheal disease that can be life-threatening in immunocompromised hosts. No specific chemo- or immunotherapies exist to treat cryptosporidiosis and little molecular information is available to guide development of such therapies. To accelerate gene discovery and identify genes encoding potential drug and vaccine targets we constructed sporozoite cDNA and genomic DNA sequencing libraries from the Iowa isolate of C. parvum and determined approximately 2000 sequence tags by single-pass sequencing of random clones. Together, the 567 expressed sequence tags (ESTs) and 1507 genome survey sequences (GSSs) totaled one megabase (1 mb) of unique genomic sequence indicating that approximately 10% of the 10.4 mb C. parvum genome has been sequence tagged in this gene discovery expedition. The tags were used to search the public nucleic acid and protein databases via BLAST analyses, and 180 ESTs (32%) and 277 GSSs (18%) exhibited similarity with database sequences at smallest sum probabilities P(N)< or =10(-8). Some tags encoded proteins with clear therapeutic potential including S-adenosylhomocysteine hydrolase, histone deacetylase, polyketide/fatty-acid synthases, various cyclophilins, thrombospondin-related cysteine-rich protein and ATP-binding-cassette transporters. Several anonymous ESTs encoded proteins predicted to contain signal peptides or multiple transmembrane spanning segments suggesting they were destined for membrane-bound compartments, the cell surface or extracellular secretion. One-hundred four simple sequence repeats were identified within the nonredundant sequence tag collection with (TAA)(> or =6)/(TTA)(> or =6) and (TA)(> or = 10)/(AT)(> or =10 ) being the most prevalent, occurring 40 and 15 times, respectively. Various cellular RNAs and their genes were also identified including the small and large ribosomal RNAs, five tRNAs, the U2 small nuclear RNA, and the small and large virus-like, double-stranded RNAs. This investigation has demonstrated that survey sequencing is an efficient procedure for gene discovery and genome characterization and has identified and sequence tagged many C. parvum genes encoding potential therapeutic targets.

Podocyte number predicts long-term urinary albumin excretion in Pima Indians with Type II diabetes and microalbuminuria

AIMS/HYPOTHESIS

The predictive value of glomerular structure on progression of renal disease was examined in patients with Type II (non-insulin-dependent) diabetes and microalbuminuria (urinary albumin-to-creatinine ratio = 30-299 mg/g).

METHODS

Kidney biopsy specimens were obtained from 16 diabetic Pima Indians (6 men, 10 women). Progression of renal disease was assessed by measuring urinary albumin excretion 4 years after the biopsy (UAE(4 years)) and by computing the change in urinary albumin excretion during the study (Delta UAE).

RESULTS

At baseline, the duration of diabetes averaged 13.3 years (range = 4.0-23.8 years) and the mean glomerular filtration rate was 159 ml x min(-1) x 1.73 m(-2) (range = 98 - 239 ml x min(-1) x 1.73 m(-2)). Median urinary albumin excretion was 67 mg/g (range = 25-136 mg/g) and it increased to 625 mg/g (range = 9-13471 mg/g) after 4 years; 10 subjects (63 %; 4 men, 6 women) developed macroalbuminuria (urinary albumin-to-creatinine ratio >/= 300 mg/g). Neither mean arterial pressure nor HbA(1 c) changed substantially during follow-up. Among the glomerular morphologic characteristics, the number of visceral epithelial cells, or podocytes, per glomerulus was the strongest predictor of renal disease progression (UAE(4 years), r = -0.49, p = 0.05; DeltaUAE, r = -0.57, p = 0.02), with fewer cells predicting more rapid progression. Glomerular basement membrane thickness did not predict progression (UAE(4 years), r = 0.11, p = 0.67; DeltaUAE, r = 0.09, p = 0.73) and mesangial volume fraction had only a modest effect (UAE(4 years,) r = 0.42, p = 0.11; DeltaUAE, r = 0.48, p = 0.06).

CONCLUSION/INTERPRETATION

Whether lower epithelial cell number per glomerulus among those that progressed was due to cellular destruction, a reduced complement of epithelial cells, or both is uncertain. Nevertheless, these findings suggest that podocytes play an important part in the development and progression of diabetic renal disease. [Diabetologia (1999) 42: 1341-1344]

Effect of hypertension on mortality in Pima Indians

BACKGROUND

The effect of hypertension on mortality was examined in 5284 Pima Indians, 1698 of whom had type 2 diabetes at baseline or developed it during follow-up.

METHODS AND RESULTS

During a median follow-up of 12.2 years (range, 0.01 to 24.8 years), 470 nondiabetic subjects and 488 diabetic subjects died. In the nondiabetic subjects, 45 of the deaths were due to cardiovascular disease, 208 to other natural causes, and 217 to external causes; in the diabetic subjects, 106 of the deaths were due to cardiovascular disease, 85 to diabetic nephropathy, 226 to other natural causes, and 71 to external causes. In the nondiabetic subjects, after adjusting for age, sex, body mass index, and serum cholesterol concentration in a proportional hazards model, hypertension predicted death from cardiovascular disease (death rate ratio [DRR]=2.8; 95% CI, 1.4 to 5. 6; P=0.003). In the diabetic subjects, after additional adjustment for duration of diabetes, plasma glucose concentration, and proteinuria, hypertension strongly predicted deaths from diabetic nephropathy (DRR=3.5; 95% CI, 1.7 to 7.2; P<0.001), but it had little effect on deaths from cardiovascular disease (DRR=1.4; 95% CI, 0.88 to 2.3; P=0.15).

CONCLUSIONS

We propose that the weak relationship between hypertension and cardiovascular disease in diabetic Pima Indians is not because of a diminished effect of hypertension on cardiovascular disease in diabetes, but because of a relatively greater effect of hypertension on the progression of diabetic nephropathy. Factors that may account for this finding in Pima Indians include a younger age at onset of type 2 diabetes, a low frequency of heavy smoking, favorable lipoprotein profiles and, possibly, enhanced susceptibility to renal disease.

Effect of glycemia on mortality in Pima Indians with type 2 diabetes

The effect of plasma glucose concentration on overall and cause-specific mortality was examined in 1,745 Pima Indians (725 men, 1,020 women) > or = 15 years old with type 2 diabetes. During a median follow-up of 10.6 years (range 0.1-24.8), 533 subjects (275 men, 258 women) died; 113 of the deaths were attributable to cardiovascular disease, 96 to diabetes-related diseases (diabetic nephropathy for 92 of these), 249 to other natural causes, and 75 to external causes. After adjusting for age, sex, duration of diabetes, and BMI in a generalized additive proportional hazards model, higher baseline 2-h postload plasma glucose concentration predicted deaths from cardiovascular disease (P = 0.007) and diabetes-related diseases (P = 0.003), but not from other natural causes (P = 0.73). An increment of 5.6 mmol/l (100 mg/dl) in the 2-h plasma glucose concentration was associated with 1.2 times (95% CI 1.1-1.4) the death rate from cardiovascular disease, 1.3 times (95% CI 1.1-1.5) the death rate from diabetes-related diseases, and almost no change in the death rate from other natural causes (rate ratio = 1.0; 95% CI 0.94-1.1). In Pima Indians with type 2 diabetes, higher plasma glucose concentration predicts deaths from cardiovascular and diabetes-related diseases but has little or no effect on deaths from other natural or external causes.

Changing glomerular filtration with progression from impaired glucose tolerance to Type II diabetes mellitus

Glomerular filtration rate (iothalamate clearance) was measured serially for 48 months in 26 Pima Indians with impaired glucose tolerance and 27 with normal glucose tolerance. At baseline, the mean glomerular filtration rate (SEM) was 133+/-8 ml/min in subjects with impaired glucose tolerance and 123+/-5 ml/min in those with normal glucose tolerance (p = 0.12). In the 12 subjects with impaired glucose tolerance who progressed to Type II (non-insulin-dependent) diabetes during follow-up, mean glomerular filtration rate increased by 30% (p = 0.011). Among the remaining 14 subjects with impaired glucose tolerance, 12 reverted to normoglycaemia. The glomerular filtration rate both at baseline and after 48 months in this subgroup exceeded the values of subjects with normal glucose tolerance by 20 % (p = 0.008) and 14% (p=0.013), respectively. A pronounced rise in the glomerular filtration rate occurs at the onset of Type II diabetes but a trend to hyperfiltration is also present in those with impaired glucose tolerance.

An epidemic of proteinuria in Pima Indians with type 2 diabetes mellitus

BACKGROUND

The risk of proteinuria in Type 1 diabetes declined > or = 30% over the past 50 years, and improvements in metabolic control are believed to be largely responsible. Little is known about secular changes in the risk of proteinuria in Type 2 diabetes.

METHODS

We examined trends in the incidence rate of proteinuria in Pima Indians > or = 20 years of age with diabetes diagnosed between January 1, 1955 and December 31, 1994.

RESULTS

Among 1305 initially non-proteinuric diabetic subjects, 433 developed proteinuria during a median follow-up of 8.0 years (range 0.8 to 30.2 years). With subjects with diabetes diagnosed between 1955 and 1964 serving as the reference group, the rate of proteinuria was similar (rate ratio 1.0; 95% confidence interval, 0.79 to 1.3) in the cohort diagnosed between 1965 and 1974, 1.5 times as high (95% confidence interval, 1.1 to 2.0) in the cohort diagnosed between 1975 and 1984, and 1.9 times as high (95% confidence interval, 1.1 to 3.0) in the cohort diagnosed between 1985 and 1994, after adjusting for potential confounders in a generalized additive proportional hazards model. Between the first and last cohorts, plasma glucose concentration declined, on average, by 17% (P = 0.0001) and the mean arterial pressure declined by 11% (P = 0.0001).

CONCLUSIONS

The incidence rate of proteinuria in Pima Indians with Type 2 diabetes increased nearly twofold in the last 40 years, despite improvements in plasma glucose and blood pressure. Rapidly changing environmental or behavioral factors must play an important role in the pathogenesis of diabetic renal disease in this population.

Birth weight and renal disease in Pima Indians with type 2 diabetes mellitus

Congenital retardation of renal development may increase the risk of renal disease, and this risk may be enhanced by diseases, such as diabetes, that damage the kidney. In this study, the prevalence of urinary albumin excretion, determined in 308 Pima Indians with type 2 diabetes, was 63% in subjects with low birth weight (<2,500 g), 41% in those with normal birth weight (2,500-4,499 g), and 64% in those with high birth weight (> or =4,500 g). When examined as a continuous variable by generalized additive logistic regression, birth weight had a U-shaped association with the prevalence of elevated urinary albuminuria (p = 0.04) after adjustment for age, sex, duration of diabetes, glycosylated hemoglobin, and blood pressure. The odds of elevated albuminuria in subjects of low birth weight was 2.3 times (95% confidence interval 0.72-7.2) that in subjects of normal birth weight, and the odds in subjects of high birth weight was 3.2 times (95% confidence interval 0.75-13.4) as high. Sixty-four percent of the subjects with high birth weight and none of those with low birth weight were offspring of diabetic mothers. After maternal diabetes during pregnancy was controlled for, the odds of elevated albuminuria in subjects of high birth weight was no longer higher (odds ratio = 1.0, 95% confidence interval 0.22-4.9). The higher prevalence of elevated albuminuria in diabetic Pima Indians with high birth weight may be due to intrauterine diabetes exposure, whereas the higher prevalence in those with low birth weight may be due to the effects of intrauterine growth retardation.

Plasma lipoproteins and the incidence of abnormal excretion of albumin in diabetic American Indians: the Strong Heart Study

Animal studies suggest that lipids are risk factors for kidney diseases. Some prospective studies and clinical trials have reported predictive effects of lipoproteins on different stages of diabetic nephropathy in humans. We examined lipoprotein abnormalities to determine if they predict abnormal urinary excretion of albumin (> or = 30 mg albumin/g creatinine), using logistic regression. We followed 671 American Indians (211 men, 460 women) with Type II diabetes for a mean of 3.9 years (range 1.7-6.2). Participants were aged 45-74 years. They had normal excretion of albumin and normal serum creatinine at baseline. 67 men and 144 women developed abnormal excretion of albumin. In models controlled for age, treatment with oral hypoglycaemic agents or insulin, HbA1c, study site, degree of Indian heritage, mean arterial blood pressure, albumin excretion at baseline and duration of diabetes, a high HDL cholesterol was a protector for abnormal excretion of albumin in women [odds ratio (OR) comparing the 90th with the 10th percentile = 0.56, 95% confidence interval (CI) = 0.32-0.98], but not in men (OR = 1.5, 95% CI = 0.66-3.4). Further adjustment for obesity, insulin concentration, alcohol consumption or physical activity did not change the results. There was a tendency for high values of VLDL and total triglyceride and small LDL size to predict abnormal excretion of albumin in women only. We conclude that low HDL cholesterol was a risk factor for abnormal excretion of albumin in women, but not in men. Sex hormones may be responsible for sex differences in the association between HDL cholesterol and abnormal excretion of albumin.

Intrauterine diabetes exposure and the risk of renal disease in diabetic Pima Indians

The association between the diabetic intrauterine environment and renal disease was examined cross-sectionally in 503 Pima Indians with type 2 diabetes. Subjects were selected from participants in an ongoing study of diabetes and its complications in the Gila River Indian Community of Arizona. Subjects' exposure to diabetes in utero was established from periodic examinations conducted as part of the study. The prevalence of elevated urinary albumin excretion (UAE) (albumin-to-creatinine ratio > or = 30 mg/g) was 40% (83 of 207) in the offspring of nondiabetic mothers, 43% (105 of 246) in the offspring of prediabetic mothers (i.e., women who were not diabetic at the time of the pregnancy but who developed diabetes after the pregnancy), and 58% (29 of 50) in the offspring of mothers who had diabetes during pregnancy. After controlling for age, sex, duration of diabetes, HbA1c, and mean arterial pressure in the offspring in a logistic regression analysis using generalized estimating equations, maternal diabetes during pregnancy was strongly associated with elevated UAE. The odds of elevated UAE in the offspring of mothers who had diabetes during pregnancy was 3.8 times (95% CI 1.7-8.4) that of the offspring of prediabetic mothers; the odds of elevated UAE in the offspring of nondiabetic and prediabetic mothers were similar (odds ratio of 0.94; 95% CI 0.59-1.5). We concluded that exposure to a diabetic intrauterine environment increases the risk of elevated UAE in diabetic Pima Indians. The effect of this exposure appears to be independent of other susceptibility factors that lead to nephropathy in diabetes.

Dietary calcium and blood pressure in a Native American population

OBJECTIVE

To assess the relationship between dietary calcium and blood pressure.

METHODS

Cross-sectional study of 404 adult Pima Indians of Arizona. Dietary variables were assessed by the 24-hour recall. Hypertension (HTN) was defined as systolic blood pressure (SBP) > or = mmHg or diastolic blood pressure (DBP) > or = 90 mmHg or drug treatment.

RESULTS

Controlled for age and sex, dietary calcium intake was higher in subjects with HTN than in those without (p < 0.01), and higher dietary calcium was associated with a higher prevalence of HTN (odds ratio comparing highest with lowest tertile group of calcium = 2.6, 95% CI 1.4-4.8). Age-sex-adjusted men DBP in low, middle and high tertiles of calcium was 74, 76, and 79 mmHg, respectively (p < 0.001). SBP was not significantly different in the three tertiles (p = 0.07). Multiple regression analyses that controlled for age, sex, body mass index, sodium, potassium and alcohol also suggested a positive association between DBP and dietary calcium (p < 0.01), an association which was stronger at higher glucose concentrations (p < 0.01 for the calcium-glucose interaction).

CONCLUSION

In Pima Indians, a population with a high incidence of diabetes, the inverse association between dietary calcium and blood pressure reported in other populations was not found.

Course of renal disease in Pima Indians with non-insulin-dependent diabetes mellitus

The course of renal disease attributable to non-insulin-dependent diabetes mellitus (NIDDM) has been characterized extensively in the Pima Indians of Arizona. Studies in this population indicate that the glomerular filtration rate often increases at the onset of NIDDM and remains elevated as long as normal urinary albumin excretion (< 30 mg albumin/g creatinine) or microalbuminuria (30-299 mg albumin/g creatinine) persist. After the development of macroalbuminuria (> or = 300 mg albumin/g creatinine), the glomerular filtration rate declines at least as rapidly as reported in subjects with insulin-dependent diabetes. Morphologic examination of kidney tissue reveals extensive glomerular sclerosis, mesangial expansion, and widening of epithelial cell foot processes and the glomerular basement membrane in the subjects with macroalbuminuria, but not in those with normo- or microalbuminuria. These findings suggest that substantial structural damage to the kidney occurs at or about the time that macroalbuminuria develops, and the decline in glomerular function in those with macroalbuminuria is due to a loss of ultrafiltration surface area and a reduction in glomerular hydraulic permeability.

Serum cholesterol and mortality rates in a Native American population with low cholesterol concentrations: a U-shaped association

BACKGROUND

Low serum cholesterol concentrations are associated with high death rates from cancer, trauma, and infectious diseases, but the meaning of these associations remains controversial. The present report evaluates whether low cholesterol is likely to be a causal factor for mortality from all causes or from specific causes.

METHODS AND RESULTS

Among 4553 Pima Indians > or =20 years old, a population with low serum cholesterol (median, 4.50 mmol/L), 1077 deaths occurred during a mean follow-up of 12.8 years. Trauma was the most common cause. The relationship between serum cholesterol measured at 2-year intervals and age- and sex-standardized mortality rates was U-shaped. Cholesterol was related positively to mortality from cardiovascular diseases and diabetes (including nephropathy) and negatively to mortality from cancer and alcohol-related diseases. The relationship was U-shaped for mortality from infectious diseases, and cholesterol was not related to mortality from trauma. Change in cholesterol from one examination to the next was positively related to mortality from diabetes. In proportional-hazards models adjusted for potential confounders, the relationship between baseline cholesterol and mortality was U-shaped for all causes and diabetes and positive for cardiovascular diseases. Other relationships were nonsignificant. Among 3358 subjects followed > or =5 years, the relationship was significant and positive only for mortality from cardiovascular diseases.

CONCLUSIONS

Despite a high exposure risk for Pima Indians, if low cholesterol level is a causal factor, the relationships between low serum cholesterol and high mortality rates probably result from diseases lowering cholesterol rather than from a low cholesterol causing the diseases.

Clinical and pathological course of renal disease in non-insulin-dependent diabetes mellitus: the Pima Indian experience

Non-insulin-dependent diabetes mellitus (NIDDM) and the renal disease attributable to it have been characterized extensively in the Pima Indians, a group of American Indians who form the Gila River Indian Community in Arizona. Both of these diseases are common in this community, and their onset and duration are known with greater certainty than in other populations because research examinations, which include oral glucose tolerance tests and measures of urinary protein excretion, have been performed frequently on most members of the population for the past 30 years. Studies of glomerular structure and hemodynamic function in diabetic Pima Indians indicate that glomerular hyperfiltration often develops at the onset of NIDDM and remains elevated until after overt nephropathy appears. Structurally, the glomeruli in subjects with microalbuminuria are not clearly distinguishable from those in subjects with normoalbuminuria, but macroalbuminuria is characterized by extensive glomerular sclerosis, mesangial expansion, and widening of epithelial cell foot processes that together lead to a rapid decline in the glomerular filtration rate. The decline in glomerular function in subjects with macroalbuminuria is due both to a loss of ultrafiltration surface area and to reduction in glomerular hydraulic permeability.

Podocyte loss and progressive glomerular injury in type II diabetes

Kidney biopsies from Pima Indians with type II diabetes were analyzed. Subjects were classified clinically as having early diabetes (n = 10), microalbuminuria (n = 17), normoalbuminuria, despite a duration of diabetes equal to that of the subjects with microalbuminuria (n = 12), or clinical nephropathy (n = 12). Subjects with microalbuminuria exhibited moderate increases in glomerular and mesangial volume when compared with those with early diabetes, but could not be distinguished from subjects who remained normoalbuminuric after an equal duration of diabetes. Subjects with clinical nephropathy exhibited global glomerular sclerosis and more prominent structural abnormalities in nonsclerosed glomeruli. Marked mesangial expansion was accompanied by a further increase in total glomerular volume. Glomerular capillary surface area remained stable, but the glomerular basement membrane thickness was increased and podocyte foot processes were broadened. Broadening of podocyte foot processes was associated with a reduction in the number of podocytes per glomerulus and an increase in the surface area covered by remaining podocytes. These findings suggest that podocyte loss contributes to the progression of diabetic nephropathy.

Plasma lipoproteins and incidence of non-insulin-dependent diabetes mellitus in Pima Indians: protective effect of HDL cholesterol in women

The role of plasma lipoproteins in the development of non-insulin-dependent diabetes mellitus (NIDDM) was studied in 787 non-diabetic (2-h glucose < 11.1 mmol/l) Pima Indians (265 men and 522 women). Subjects were followed for a mean of 9.8 (range: 1.8-16.4) years, during which 261 (76 men and 185 women) developed NIDDM. In men and women, very-low-density lipoprotein (VLDL) cholesterol, VLDL triglyceride, low-density lipoprotein triglyceride and total triglyceride, controlled for age, predicted NIDDM (P < 0.01 for each). These effects diminished when controlled for age, sex, body mass index, systolic blood pressure and 2-h glucose. However, high-density lipoprotein (HDL) cholesterol, controlled for age, body mass index, systolic blood pressure and 2-h glucose, was a significant protective factor for NIDDM in women (hazard rate ratio (HRR) = 0.35, 95% CI (0.23-0.54), P < 0.001, 90th compared with 10th percentile) but not in men (HRR = 1.04, 95% CI (0.53-2.05), P = 0.915). This association remained significant in women when controlled for fasting or 2-h plasma insulin concentrations, other estimates of insulin resistance or alcohol consumption. The protective effect of HDL cholesterol was similar among women with normal (2-h glucose < 7.8 mmol/1) or impaired (7.8 mmol/l < or = 2-h glucose < 11.1 mmol/l) glucose tolerance at baseline. These results indicate that lipoprotein disorders are an early accompaniment of the abnormalities that lead to NIDDM.

Survival during renal replacement therapy for diabetic end-stage renal disease in Pima Indians

OBJECTIVE

To examine survival in Pima Indians receiving renal replacement therapy for end-stage renal disease attributed to NIDDM.

RESEARCH DESIGN AND METHODS

Vital status through 1994 was determined for 136 diabetic Pima Indians from the Gila River Indian Community who began renal replacement therapy between 1973 and 1990.

RESULTS

Median survival from the onset of renal replacement therapy was 39 months (95% Ci, 31-54), 31 months (95% Ci, 11-48) in those who began treatment between 1973 and 1981, and 44 months (95% Ci, 32-56) in those who began treatment between 1982 and 1990 (P = 0.020). During these periods, mean age at onset of treatment increased from 53.3 to 56.1 years (P = 0.166), and mean duration of diabetes at the onset of treatment increased from 16.5 to 20.2 years (P = 0.003). After adjustment for sex, duration of diabetes, initial dialysis type, and kidney transplantation by an age-stratified proportional-hazards analysis, the death rate after starting renal replacement therapy in the second half of the study was 0.54 times (95% CI, 0.33-0.88) that in the first half. If this analysis was restricted to those who survived at least 90 days of therapy, the difference between the time periods was diminished (death rate ratio = 0.76; 95% CI, 0.43-1.32).

CONCLUSIONS

Survival in Pima Indians receiving renal replacement therapy improved significantly over the study despite an increase in the average age and diabetes duration of those beginning dialysis. Much of the improvement in survival is attributable to a reduction in the number of deaths within the first 90 days of therapy. The median survival of 47 months in Pima Indians < 65 years old at the initiation of therapy is substantially longer than the 30 months reported in blacks and 16 months reported in whites of similar age with NIDDM.

Development and progression of renal disease in Pima Indians with non-insulin-dependent diabetes mellitus. Diabetic Renal Disease Study Group

BACKGROUND

Non-insulin-dependent diabetes mellitus (NIDDM) is a major cause of end-stage renal disease. However, the course and determinants of renal failure in this type of diabetes have not been clearly defined.

METHODS

We studied glomerular function at intervals of 6 to 12 months for 4 years in 194 Pima Indians selected to represent different stages in the development and progression of diabetic renal disease. Initially, 31 subjects had normal glucose tolerance, 29 had impaired glucose tolerance, 30 had newly diagnosed diabetes, and 104 had had diabetes for five years or more; of these 104, 20 had normal albumin excretion, 50 had microalbuminuria, and 34 had macroalbuminuria. The glomerular filtration rate, renal plasma flow, urinary albumin excretion, and blood pressure were measured at each examination.

RESULTS

Initially, the mean (+/-SE) glomerular filtration rate was 143+/-7 ml per minute in subjects with newly diagnosed diabetes, 155+/-7 ml per minute in those with microalbuminuria, and 124+/-7 ml per minute in those with macroalbuminuria; these values were 16 percent, 26 percent, and 1 percent higher, respectively, than in the subjects with normal glucose tolerance (123+/-4 ml per minute). During four years of follow-up, the glomerular filtration rate increased by 18 percent in the subjects who initially had newly diagnosed diabetes (P=0.008); the rate declined by 3 percent in those with microalbuminuria at base line (P=0.29) and by 35 percent in those with macroalbuminuria (P<0.001). Higher base-line blood pressure predicted increasing urinary albumin excretion (P=0.006), and higher base-line urinary albumin excretion predicted a decline in the glomerular filtration rate (P<0.001). The initial glomerular filtration rate did not predict worsening albuminuria.

CONCLUSIONS

The glomerular filtration rate is elevated at the onset of NIDDM and remains so while normal albumin excretion or microalbuminuria persists. It declines progressively after the development of macroalbuminuria.

Potential antifolate resistance determinants and genotypic variation in the bifunctional dihydrofolate reductase-thymidylate synthase gene from human and bovine isolates of Cryptosporidium parvum

We have determined the nucleic acid sequences of a gene encoding the bifunctional enzyme dihydrofolate reductase-thymidylate synthase (DHFR-TS) from bovine and human AIDS isolates of Cryptosporidium parvum. THe DHFR-TS gene was isolated from genomic DNA libraries by hybridization with a probe amplified from C. parvum genomic DNA using generic TS primers in the polymerase chain reaction. Genomic Southern and electrophoretic karyotype analyses reveal C. parvum DHFR-TS is a single-copy gene on a 1200-kb chromosome. The DHFR-TS nucleic acid sequence contains no introns and the single 1563-bp open reading frame encodes a 179 residue N-terminal DHFR domain connected by a 55 amino acid junction peptide to a 287 residue C-terminal TS domain. The sequences of the DHFR-TS gene from the bovine and human C. parvum isolates differ at two positions in the 5'-flanking sequence and at 38 positions in the encoding sequence. These DNA sequence polymorphisms will provide a powerful probe to examine the genotypic diversity and genetic population structure of C. parvum. The two sequences encode identical TS domains which share all except one of the phylogenetically conserved amino acid residues identified among reported TS sequences. The predicted DHFR domain sequences contain nine amino acid differences; these polymorphisms all map to non-active site, surface locations in known DHFR structures. The C. parvum DHFR active site contains novel residues at several positions analogous to those at which point mutations have been shown to produce antifolate resistance in other DHFRs. Thus C. parvum DHFR may be intrinsically resistant ti inhibition by some antifolate DHFR inhibitors which may explain why cryptosporidiosis is refractory to treatment with the clinically common antibacterial and antiprotozoal antifolates.

Survey of the diet of Pima Indians using quantitative food frequency assessment and 24-hour recall. Diabetic Renal Disease Study

OBJECTIVE

A dietary survey was conducted in the Gila River Indian Community in Arizona using two methods of dietary assessment--24-hour recall and quantitative food frequency (QFF) assessment--to determine the usual intake of the population.

DESIGN

Interviews were conducted by Pima women who were trained and monitored by a research dietitian. Energy and nutrient intake were calculated using a computerized dietary database that included specific Pima foods.

SUBJECTS

An age- and sex-stratified sample of 575 Pima Indians (273 men, 302 women) aged 18 to 74 years participated in the study.

STATISTICAL ANALYSES

Spearman correlations were used to compare the results of the two survey methods for energy and each nutrient. Intraclass correlations were used to measure reproducibility.

RESULTS

According to the 24-hour recall, mean reported energy intakes within decades of age were 95% to 112% of those in the US population for Pima women, and 76% to 94% of those in the US population for Pima men. Total energy intake assessed using QFF was 30% higher in men and 33% higher in women than the intake assessed using the 24-hour recall method.

CONCLUSIONS

A large dietary survey conducted using lay interviewers in a Native-American community was as reproducible as studies conducted in the general US population. The Pima diet was distributed among the major nutrients in a proportion similar to the US diet.