Early alteration in glomerular reserve in humans at genetic risk of essential hypertension: mechanisms and consequences

The BDNF Val66Met Polymorphism is a Relevant, But not Determinant, Risk Factor in the Etiology of Neuropsychiatric Disorders - Current Advances in Human Studies: A Systematic Review

Brain-derived neurotrophic factor (BDNF) is the brain's most-produced neurotrophin during the lifespan, essentially involved in multiple mechanisms of nervous system development and function. The production/release of BDNF requires multi-stage processing that appears to be regulated at various stages in which the presence of a polymorphism "Val66Met" can exert a critical influence.

Aim

To synthesize the knowledge on the BDNF Val66Met polymorphism on intracellular processing and function of BDNF.

Methods

We performed a systematic review and collected all available studies on the post-translation processes of BDNF, regarding the Val66Met polymorphism. Searches were performed up to 21st March 2021.

Results

Out of 129 eligible papers, 18 studies addressed or had findings relating to BDNF post-translation processes and were included in this review.

Discussion

Compilation of experimental findings reveals that the Val66Met polymorphism affects BDNF function by slightly altering the processing, distribution, and regulated release of BDNF. Regarding the critical role of pro-BDNF as a pro-apoptotic factor, such alteration might represent a risk for the development of neuropsychiatric disorders.

Functional Reserve of the Kidney

An exploration of the normal limits of physiologic responses and how these responses are lost when the kidney is injured rarely occurs in clinical practice. However, the differences between "resting" and "stressed" responses identify an adaptive reactiveness that is diminished before baseline function is impaired. This functional reserve is important in the evaluation of prognosis and progression of kidney disease. Here, we discuss stress tests that examine protein-induced hyperfiltration, proximal tubular secretion, urea-selective concentration defects, and acid retention. We discuss diseases in which these tests have been used to diagnose subclinical injury. The study and follow-up of abnormal functional reserve may add considerable understanding to the natural history of CKD.

Assessing Microvascular Function in Humans from a Chronic Disease Perspective

Microvascular dysfunction (MVD) is considered a crucial pathway in the development and progression of cardiometabolic and renal disease and is associated with increased cardiovascular mortality. MVD often coexists with or even precedes macrovascular disease, possibly due to shared mechanisms of vascular damage, such as inflammatory processes and oxidative stress. One of the first events in MVD is endothelial dysfunction. With the use of different physiologic or pharmacologic stimuli, endothelium-dependent (micro)vascular reactivity can be studied. This reactivity depends on the balance between various mediators, including nitric oxide, endothelin, and prostanoids, among others. The measurement of microvascular (endothelial) function is important to understand the pathophysiologic mechanisms that contribute to MVD and the role of MVD in the development and progression of cardiometabolic/renal disease. Here, we review a selection of direct, noninvasive techniques for measuring human microcirculation, with a focus on methods, interpretation, and limitations from the perspective of chronic cardiometabolic and renal disease.

Renal Haemodynamics are not Related to Genotypes in Offspring of Parents with Essential Hypertension

Introduction. The pathogenesis of essential hypertension (EH) has a major genetic component and is associated with renal abnormalities. Normotensive offspring of hypertensive parents are likely to develop EH and are a suitable population for identifying possible relations between genetic and renal abnormalities.

Methods. We investigated if renin-angiotensin-aldosterone system associated genotypes (angiotensinogen [M235T] and ACE [I/D]) are related to blood pressure (BP), renal haemodynamics and sodium excretion in sex and age-matched (18—35 years) healthy Caucasian offspring of either two parents with EH (n=101, EH-offspring) or two normotensive parents (n=50, controls). The alpha-adducin polymorphism (G460W) was also investigated.

Results. Compared to controls, BP, heart rate, renal vascular resistance (RVR) and urinary sodium excretion were, respectively, 5%, 7%, 15% and 20% higher in EH-offspring. In controls, the TT-genotype of the M235T angiotensinogen polymorphism was associated with higher BP and higher plasma angiotensinogen. By contrast, in EHoffspring the TT-genotype was associated with lower BP and unchanged plasma angiotensinogen. Plasma angiotensinogen correlated positively with BP in EH-offspring, with a similar tendency (p=0.08) in controls. The distributions of the three candidate polymorphisms were similar in EH-offspring and controls. There were no associations between any of the polymorphisms and any of the renal parameters measured.

Conclusion. The markedly greater RVR, proportionally larger than the greater BP, supports a role for RVR in the pathogenesis of EH. The lack of association between the candidate polymorphisms and the investigated parameters, even in this homogenous and for hypertension strongly predisposed group, suggests that the polymorphisms investigated do not play important roles in the pathogenesis of hypertension.

Nitric oxide and the cardiovascular system

Nitric oxide (NO) generated by endothelial cells to relax vascular smooth muscle is one of the most intensely studied molecules in the past 25 years. Much of what is known about NO regulation of NO is based on blockade of its generation and analysis of changes in vascular regulation. This approach has been useful to demonstrate the importance of NO in large scale forms of regulation but provides less information on the nuances of NO regulation. However, there is a growing body of studies on multiple types of in vivo measurement of NO in normal and pathological conditions. This discussion will focus on in vivo studies and how they are reshaping the understanding of NO's role in vascular resistance regulation and the pathologies of hypertension and diabetes mellitus. The role of microelectrode measurements in the measurement of [NO] will be considered because much of the controversy about what NO does and at what concentration depends upon the measurement methodology. For those studies where the technology has been tested and found to be well founded, the concept evolving is that the stresses imposed on the vasculature in the form of flow-mediated stimulation, chemicals within the tissue, and oxygen tension can cause rapid and large changes in the NO concentration to affect vascular regulation. All these functions are compromised in both animal and human forms of hypertension and diabetes mellitus due to altered regulation of endothelial cells and formation of oxidants that both damage endothelial cells and change the regulation of endothelial nitric oxide synthase.

Progression of chronic kidney disease: Adrenergic genetic influence on glomerular filtration rate decline in hypertensive nephrosclerosis

BACKGROUND

African-Americans are likely to develop hypertension and hypertensive nephrosclerosis. This grave prognosis, coupled with familial aggregation of end-stage renal disease (ESRD) in Blacks, prompts a search for genetic risk factors for ESRD. Recent evidence implicates a crucial role for the sympathetic nervous system in progressive renal disease.

METHODS

We used the African-American Study of Kidney Disease to probe whether beta2-adrenergic receptor (ADRB2) predicts glomerular filtration rate (GFR) decline rate. A total of 580 participants were included. Baseline GFR was 51.2 +/- 0.5 ml/min/1.73 m2. Subjects were randomized in a 2 x 3 block design: to intensively lowered (MAP < or = 92 mm Hg) versus 'usual' (MAP = 102-107 mm Hg) blood pressure goal groups, and also divided by three randomized antihypertensive drugs (ramipril, metoprolol, or amlodipine). We scored 4 SNPs at the ADRB2 locus.

RESULTS

Haplotypes at ADRB2 predicted chronic GFR decline rate, GFR declined more slowly in individuals with haplotype-1 (-804G-->173T-->16Gly-->27GIn), and faster in those who carried haplotype-3 (-804G-->173T-->16Arg-->27Gln). ADRB2 genotype interacted with antihypertensive drug class to influence GFR slope (p = 0.001-0.037). We extended our findings to an independent case/control sample of Black hypertensive ESRD, in which we found that variant Gly16Arg that tagged the GFR slope-determining ADRB2 haplotype also conferred risk for the ESRD trait in Blacks.

CONCLUSIONS

The GFR decline/progression rate in hypertensive renal disease is controlled in part by genetic variation within the adrenergic pathway.

Adrenergic beta-1 receptor genetic variation predicts longitudinal rate of GFR decline in hypertensive nephrosclerosis

BACKGROUND

End-stage renal disease (ESRD) due to hypertension is common and displays familial aggregation in African Americans, suggesting genetic risk factors, including adrenergic activity alterations which are noted in both hypertension and ESRD.

METHODS

We analysed 554 hypertensive nephrosclerosis participants (without clinically significant proteinuria) from the longitudinal National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) African American Study of Kidney Disease and Hypertension (AASK) cohort to determine whether decline in glomerular filtration rate (GFR) over approximately 3.8 years was predicted by common genetic variation within the adrenergic beta-1 (ADRB1) receptor at non-synonymous positions Ser49Gly and Arg389Gly.

RESULTS

The polymorphism at Ser49Gly (though not Arg389Gly, in only partial linkage disequilibrium at r(2) = 0.18) predicted the chronic rate of GFR decline, with minimal decline in Gly(49)/Gly(49) (minor allele) homozygotes compared to Ser(49) carriers; concordant results were observed for haplotypes and diploid haplotype pairs at the locus. An independent replication study in 1244 subjects from the San Diego Veterans Affairs Hypertension Cohort confirmed that Gly(49)/Gly(49) homozygotes displayed the least rapid decline of eGFR over approximately 3.6 years.

CONCLUSION

We conclude that GFR decline rate in hypertensive renal disease is controlled in part by genetic variation within the adrenergic pathway, particularly at ADRB1. The results suggest novel strategies to approach the role of the adrenergic system in the risk and treatment of progressive renal disease.

Endothelial dysfunction in patients with noncomplicated and complicated hypertension

Endothelial dysfunction plays an important role in the pathogenesis of hypertension. Other risk factors of atherosclerosis also affect its development. The aim of the study was to assess nitric oxide metabolites concentration (nitrites and nitrates No(x)) and endothelin (ET-1) in plasma and cyclic 3,5-guanosine monophosphate (cGMP) in 24 h-urine collection in patients with noncomplicated hypertension without risk factors of atherosclerosis and in hypertensive patients with coronary artery disease (CAD). Sixty-eight subjects were included in the study (44 men, 24 women), aged 47 +/- 76 years, allotted into four groups: I - controls (18 clinically healthy subjects); II - 12 subjects with hypertension without risk factors of atherosclerosis; III - 16 subjects with hypertension and risk factors of atherosclerosis; and IV - 22 subjects with hypertension and CAD. Plasma NO(x) concentration was determined using the Greiss method, plasma ET-1 by ELISA, and urine cGMP using the immunoenzymatic method. Plasma NO(x) concentration was 14.00 +/- 6.88 micromol/L in group I, in group II - 18.62 +/- 5.84 micromol, in group III - 9.96 +/- 4.72 micromol/L, and in group IV - 8.78 +/- 3.72 micromol/L. Statistically significant differences were between groups I and III (p < 0.05) and I and IV (p < 0.04) and groups II and III (p < 0.01) and II and IV (p < 0.01). The concentration of cGMP in 24 h urine collection was in group I - 40 +/- 24 pmol/L; in group II - 54 +/- 41 pmol/L; in group III - 38 +/- 32 pmol/L; and in group IV - 42 +/- 36 pmol/L. There were no significant differences between the groups. Plasma ET-1 concentration was 3.86 +/- 0.52 pg/mL in group I, in group II - 4.05 +/- 0.71 pg/mL, in group III - 4.22 +/- 0.79 pg/mL and in group IV - 4.38 +/- 0.75 pg/mL. Statistically significant differences were between group I and III (p < 0.05), I and IV (p < 0.03), and between group II and IV (p < 0.04). Endothelial dysfunction was not found in hypertensive patients without a family history of cardiovascular diseases and without other risk factors of atherosclerosis. Deterioration of endothelial function was observed in patients with hypertension with risk factors of atherosclerosis. It was most pronounced in those with CAD.

L-arginine-induced glomerular hyperfiltration response: the roles of insulin and ANG II

Infusion of L-arginine produces an increase in glomerular filtration via kidney vasodilation, correlating with increased kidney excretion of nitric oxide (NO) metabolites, but the specific underlying mechanisms are unknown. We utilized clearance and micropuncture techniques to examine the whole kidney glomerular filtration rate (GFR) and single nephron GFR (SNGFR) responses to 1) L-arginine (ARG), 2) ARG+octreotide (OCT) to block insulin release, 3) ARG+OCT+insulin (INS) infusion to duplicate ARG-induced insulin levels, and 4) losartan (LOS), an angiotensin AT-1 receptor blocker, +ARG+OCT. ARG infusion increased GFR, while increasing insulin levels. OCT coinfusion prevented this increase in GFR, but with insulin infusion to duplicate ARG induced rise in insulin, the GFR response was restored. Identical insulin levels in the absence of ARG had no effect on GFR. In contrast to ARG infusion alone, coinfusion of OCT with ARG reduced proximal tubular fractional and absolute reabsorption potentially activating tubuloglomerular feedback. Losartan infusion, in addition to ARG and OCT (LOS+ARG+OCT), restored the increase in both SNGFR and proximal tubular reabsorption, without increasing insulin levels. In conclusion, 1) hyperfiltration responses to ARG require the concurrent, modest, permissive increase in insulin; 2) inhibition of insulin release after ARG reduces proximal reabsorption and prevents the hyperfiltration response; and 3) inhibition of ANG II activity restores the hyperfiltration response, maintains parallel increases in proximal reabsorption, and overrides the arginine/octreotide actions.

Impaired renal haemodynamic response to L-arginine in essential hypertension: role of buffering anion and tubuloglomerular feedback

OBJECTIVE

To investigate whether changes in tubuloglomerular feedback (TGF) dependent upon the tubular effects of buffering anions affect the renal haemodynamic response to L-arginine in healthy (control) individuals and patients with essential hypertension.

METHODS

Mean arterial pressure (MAP), glomerular filtration rate (GFR), renal blood flow (RBF) and fractional excretion of sodium (FENa), chloride (FECl) and lithium (FELi) were measured in 10 control individuals and 10 hypertensive patients during two 3-h infusions of 0.012 mmol/kg per min L-arginine buffered with either HCl or citric acid.

RESULTS

FELi, FECl and FENa increased (P < 0.001) comparably in controls and hypertensive individuals with arginine-HCl and decreased with arginine-citrate (P < 0.001). MAP was unchanged in controls with arginine-HCl and decreased by 3% with arginine-citrate (P < 0.001), and decreased in hypertensive individuals with both arginine-HCl and arginine-citrate (by 3 and 7%, respectively; P < 0.001). GFR increased with arginine-citrate in controls and hypertensive individuals (by 6.1 and 5.4%, respectively; P < 0.001), but did not change with arginine-HCl in controls and declined by 4.6% in hypertensive individuals (P < 0.05). RBF increased equally after arginine-citrate in controls and hypertensive individuals (by 34 and 33%, respectively; P < 0.001); it also increased after arginine-HCl (22 and 13%, respectively; P < 0.001), but less than after arginine-citrate (P < 0.001), and 41% less in hypertensive individuals than in controls (P < 0.001).

DISCUSSION

Because arginine-HCl, unlike arginine-citrate, inhibits tubular reabsorption and elicits much less renal vasodilatation than does arginine-citrate, renal haemodynamics in response to L-arginine are modulated by changes in reabsorption and TGF according to the tubular effects of the attendant anion. As renal vasodilatation in hypertensive individuals was reduced only with arginine-HCl, which activates TGF, the blunted vasodilatation of the hypertensive kidney in response to arginine-HCl reflects an exaggerated response to an activated TGF.

Renal functional reserve in obesity hypertension

The capacity to increase glomerular filtration rate in response to an acute oral protein load is known as the renal functional reserve; the loss of such capacity is used as a marker of hyperfiltration. This physiological response in obese hypertensives is not yet fully understood. We aimed to study the interdependent effects of obesity and hypertension on renal reserve, taking into account renal kallikrein and nitric oxide in the modulation of that parameter. Fourteen obese hypertensives (mean age, 50.5 +/- 0.9 years) and nine lean hypertensives (mean age, 50.6 +/- 2.7 years) were evaluated. Renal haemodynamics and the levels of serum nitric oxide and urinary kallikrein were assessed at baseline and after a protein load (1 g/kg of body weight). An increase in the following parameters was observed when comparing obese and lean hypertensives: basal glomerular filtration rate; renal plasma flow; and urinary kallikrein and nitric oxide levels (129.2 +/- 2.9 vs. 101.4 +/- 3.4 ml/min/1.73 m2; 587.5 +/- 18.2 vs. 502.8 +/- 16.7 ml/min/1.73 m2; 0.120 +/- 0.02 vs. 0.113 +/- 0.02 mU/ml; 23.2 +/- 0.8 vs. 19.5 +/- 1.2 mmol/ml, respectively). The renal reserve was lower in obese hypertensives when compared with that of lean hypertensives (4.1 +/- 0.5 vs. 11.8 +/- 0.8 ml/min, p < 0.005). After a protein load, contrasting with the lean group, inability to elevate the nitric oxide serum levels and a lower increase in urinary kallikrein were observed in the obese group. These data suggest that obese hypertensives lose renal reserve earlier in the evolution to renal dysfunction. This may be due to the defective modulation of renal vasodilatation mechanisms by renal kallikrein and nitric oxide production.

Reduced renal reserve and increased cardiac output in adult female sheep uninephrectomized as fetuses

BACKGROUND

Removal of one kidney during the period of nephrogenesis in the sheep leads to offspring with elevated blood pressure and reduced glomerular filtration rate (GFR) at 6 and 12 months of age. The mechanisms underlying the hypertension and the degree of renal impairment are not known.

METHODS

Changes in GFR were measured in response to an infusion of amino acids and cardiac output was measured by thermal dilution in female offspring at 2 years of age in eight control (sham-operated) and seven animals that had been unilaterally nephrectomized at 100 days of gestation.

RESULTS

Animals uninephrectomized as fetuses had significantly higher blood pressure (91 +/- 2 mm Hg) compared to control animals (86 +/- 2 mm Hg) (P < 0.05). Cardiac output was significantly higher in the uninephrectomized group (148 +/- 10 mL/kg/min) compared to the control group (124 +/- 6 mL/kg/min) (P < 0.05). Heart rate and stroke volume were similar in the two groups although both parameters tended to be higher in the uninephrectomized group. Uninephrectomized animals had a lower basal GFR (P < 0.05). An infusion of amino acids caused a significantly different response in GFR in the two groups (P < 0.01 between the groups) with the uninephrectomized animals having significantly lower GFRs during the infusion period.

CONCLUSION

The increased blood pressure observed after fetal uninephrectomy is due to an increase in cardiac output. Thus, formation of a low number of nephrons in utero may predispose an individual to later renal failure and elevated blood pressure.

Cardiovascular haemodynamic response to repeated mental stress in normotensive subjects at genetic risk of hypertension: evidence of enhanced reactivity, blunted adaptation, and delayed recovery

To identify unique cardiovascular responses to stressors in a population at genetic risk of hypertension, we studied haemodynamic responses in initial reactivity to, subsequent adaptation to, and final recovery from repeated active mental stress in young, normotensive individuals stratified by hypertension parental history (PH). Two groups (n=21/group) of normotensive white males underwent stress testing. One group (N+PH) had a hypertensive parent, while the other group (N-PH) did not. Cardiovascular response was measured before, during, and after repeated serial-subtraction math. Initial reactivity was measured as the difference between baseline and initial stress response, subsequent adaptation as the difference in response to repeated trials, and final recovery was assessed by the difference between baseline and postbaseline levels. The influence of PH on reactivity, adaptation, and recovery was assessed by repeated measures ANOVA for stroke volume, cardiac output, pre-ejection period, total peripheral resistance, mean successive heartbeat time difference, blood pressure, and heart rate. Multivariate analysis of variance (MANOVA) determined the effect of PH on overall reactivity, adaptation, and recovery. As compared to the N-PH group, initial reactivity was higher in the N+PH group for cardiac index (P<0.05) and pre-ejection period (P<0.05). Subsequent adaptation in the N+PH group was significantly slower for pre-ejection period (P=0.03). Finally, the N+PH group showed delayed recovery in heart rate (P=0.03), diastolic blood pressure (P<0.05), and pre-ejection period (P=0.007). In conclusion, the heightened reactivity, lack of adaptation, and delayed recovery occur in the sympathetic system of normotensive subjects at genetic risk of hypertension, specifically in beta-adrenergic responses (pre-ejection period). The parasympathetic response (mean successive heartbeat time difference) was not different. Increased cardiac output reactivity in the N+PH group (P<0.05) thus precedes any difference in blood pressure reactivity (P<0.99). Delayed recovery of diastolic blood pressure is also found in the N+PH group (P<0.05), which suggests lower baroreceptor sensitivity. Since delayed recovery in heart rate (P=0.03), and diastolic blood pressure (P<0.05) occur in N+PH subjects even before the corresponding changes in reactivity (P>0.10) or adaptation (P>0.07) are seen, these recovery impairments may be among the earliest precursors to the development of essential hypertension in this population. Finally, PH group haemodynamic differences suggest that these traits (reactivity, adaptation, and recovery) may constitute early 'intermediate' phenotypes in the pathogenesis of hypertension.

Prenatal exposure to glucocorticoids and adult disease

There is evidence to suggest that an individual's susceptibility to cardiovascular disease cannot be entirely explained by differences in life style factors (i.e., low physical activity, high fat/salt diet), or genetic causes, but may also be influenced by factors encountered during intrauterine life. Epidemiological studies found the link between low birth weight for gestational age (a broad index of sub-optimal intrauterine environment) and increased incidence of cardiovascular and metabolic diseases in adulthood. Many animal models in which the intrauterine environment was altered during early/late or throughout gestation demonstrated long-term effects on adult health. In general stress in early gestation is more likely to be associated with adult cardiovascular disease including hypertension, whereas late gestation stress may also be associated with adult hypotension in addition to metabolic/endocrine abnormalities. Two systems have been widely hypothesised to serve as mechanisms via which adverse prenatal influences impinge on adult cardiovascular and metabolic disease; hippocampal-hypothalamo-pituitary-adrenal axis (HHPA) and renin-angiotensin system (RAS). Interestingly, at least in our animal model of adult hypertension after brief/early prenatal glucocorticoid exposure, HHPA axis is not altered when studied either in late gestation or at several stages during adulthood. However, our more recent results, using the same animal model, suggest a major role for the central and renal RAS. This review will mainly focus on animal models and potential mechanisms via which a perturbed intrauterine environment (undernutrition or steroid exposure) lead to adult cardiovascular and/or metabolic disease.

Effects of amino acids and glucagon on renal hemodynamics in type 1 diabetes

Increased dietary protein and circulating amino acids raise glomerular filtration rate (GFR) and pressure. In diabetes, this glomerular hyperfiltration response is augmented. The purpose of this study was to determine whether glucagon mediates the augmented GFR response to amino acids in diabetes and whether the responses to amino acids and glucagon depend on prostaglandins. Patients with type 1 diabetes mellitus (n = 12) and normal control subjects (n = 12) were studied in a series of six experiments, each on different occasions. Baseline GFR was not significantly increased, but filtration fraction was higher in diabetes. In response to amino acid infusion, GFR increased more and filtration fraction was greater among those with diabetes. Their augmented GFR response to amino acids was not inhibited by octreotide or indomethacin. Participants with diabetes also had enhanced GFR and renal plasma flow responses to glucagon infusion, both of which were inhibited by indomethacin. Glomerular hyperfiltration responses induced by amino acids or glucagon occur by divergent pathways in diabetes; only the response to glucagon is prostaglandin dependent.